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Lithium anode primary batteries display numerous outstanding characteristics including high energy density, long shelf life, low self-discharge, and ability to function under a broad temperature operating range. This has led to the design and implementation of lithium primary cells for a variety of applications in the commercial, military, space, and medical fields. The development of these primary batteries has required understanding and resolution of complex reaction mechanisms as well as optimized electrode and cell designs to meet the needs of the target applications. Notably, a variety of cathode materials have been paired with lithium metal anodes including carbon monofluoride (CFx), manganese oxide (MnO2), thionyl chloride (SOCl2), and sulfur dioxide (SO2). A specific application of primary lithium battery systems is to power implantable medical devices. These primary systems utilize lithium metal anodes with cathodes such as iodine, manganese oxide, carbon monofluoride, silver vanadium oxide, and hybrid cathodes. While the specific performance requirements of applications vary, lithium batteries can provide the solutions for single use power source needs.

Over the past decade, conversion-type anodes have been viewed as an attractive alternative for use in the next-generation of high capacity battery materials. However, many technological limitations exist in the stability and long-term reliability of these anodes for the commercialization of these electrodes. Here, we explore the complex interfacial interactions between the components of composite electrodes along with the impact of the chemical/electrochemical environment on performance. Fundamental insight into the factors that influence ion and electron transport within the composite systems are expected to help elucidate the key physical and chemical properties needed for the development of high-capacity materials for battery applications.

As batteries revolutionize all technological areas – from miniaturized electronic devices to electric vehicles and to large-scale energy storage, understanding the complex morphological, chemical and structural evolution and their interplays has been at the forefront of the research. Synchrotron X-ray characterization techniques provide insights into the electrochemical reactions and multiscale, multiphysics environments to address the fundamental mechanisms in these systems. The presentation will highlight the application of synchrotron X-ray analysis in two Li-ion battery systems, including both aqueous and non-aqueous systems. X-ray nano-tomography via transmission X-ray microscopy and spectroscopic imaging, complemented by other diffraction, spectroscopy and microscopy techniques, will be discussed. We will present how synchrotron X-ray nano-tomography and quantitative 3D morphological analysis were instrumental in revealing the dimensionality effect of conductive carbon fillers in LiNi 1/3Mn1/3Co1/3O2 (NMC111) cathode [1]. Additionally, we will discuss how a multimodal characterization approach offered insights when probing kinetics of water-in-salt aqueous batteries with thick, porous LiV3O8-LiMn2O4 electrodes [2, 3]. Through the morphological and chemical analyses, the work aims to facilitate the design of future advanced energy storage materials, as well as provide a novel characterization framework for studying a wider range of electrochemical systems. References: [1] "Dimensionality effect of conductive carbon fillers in LiNi 1/3Mn 1/3Co 1/3O 2 cathode", Cheng-Hung Lin, Zhengyu Ju, Xiaoyin Zheng, Xiao Zhang, Nicole Zmich, Xiaoyang Liu, Kenneth J. Takeuchi, Amy C.Marschilok, Esther S.Takeuchi, Mingyuan Ge, Guihua Yu, Yu-chen Karen Chen-Wiegart, Carbon (2021), DOI: https://doi.org/10.1016/j.carbon.2021.11.014 [2] "Probing Kinetics of Water-in-Salt Aqueous Batteries with Thick Porous Electrodes", Cheng-Hung Lin, Lei Wang, Steven T. King, Jianming Bai, Lisa M. Housel, Alison H. McCarthy, Mallory N. Vila, Hengwei Zhu, Chonghang Zhao, Lijie Zou, Sanjit Ghose, Xianghui Xiao, Wah-Keat Lee, Kenneth J. Takeuchi, Amy C. Marschilok, Esther S. Takeuchi, Mingyuan Ge, and Yu-chen Karen Chen-Wiegart, ACS Central Science (2021), DOI: 10.1021/acscentsci.1c00878 [3] "Systems-Level Investigation of Aqueous Batteries for Understanding the Benefit of Water-In-Salt Electrolyte by Synchrotron Nano-Imaging", Cheng-Hung Lin, Ke Sun, Mingyuan Ge, Lisa Housel, Alison McCarthy, Mallory Vila, Chonghang Zhao, Xianghui Xiao, Wah-Keat Lee, Kenneth J. Takeuchi, Esther S. Takeuchi, Amy C. Marschilok, Yu-chen Karen Chen-Wiegart, Science Advances (2020), DOI: 10.1126/sciadv.aay7129

Lithium-ion batteries have become ubiquitous in a variety of energy storage applications ranging from grid storage to consumer electronics to electric vehicles. However, their continued usage in a vastly dynamic world predicates on their ability to be not only safe, sustainable, and reliable, but also contain high capacity under a variety of fast charge/discharge conditions. Multiple studies have shown that increased performance at fast charge/discharge rates can be achieved through systematic manipulation of key interfaces at various nano-, micro- and mesoscales of the electrode. Through careful tuning of the processing and chemical modification of polymeric binders, capping agents, and conductive additives, rational design of battery electrodes with specific performance characteristics can be achieved. Careful manipulation of interfacial chemistries can help push the boundaries of electrochemical performance in a wide variety of cell components. This presentation will focus on the chemical manipulation of polymers within a composite electrode to gain fundamental insights needed for the realization of next-generation battery systems.

Mixed transition metal oxides, such as Ni0.8Mn0.1Co0.1O2 (NMC811), are intended to combine the high capacity of nickel oxides, the rate capability of cobalt oxides, and the structural stability of manganese oxides to meet the capacity and power demands of electric vehicles and commercial portable electronics. However, the capacity fade mechanisms in Ni-rich chemistries (x >y+z in NixMnyCozO2) can be elusive due to factors at the crystallographic, particle, or electrode level. In this study, bulk and surface x-ray spectroscopy characterization of NMC cathodes was used to explore cathode degradation mechanisms as influenced by cycling protocol, namely current rate and upper voltage limits. Soft x-ray absorption spectroscopy (sXAS) was used to probe the surface of recovered NMC electrodes via transition metal L-edge and O K-edge spectroscopy. The effect of rate and upper voltage potential under charge will be discussed to illustrate the versatility of sXAS for NMC cathode electrode characterization.

Vanadium dioxides exist as different polymorphs, each with unique electrochemical properties. Herein, we investigate the monoclinic to rutile transition of vanadium dioxide using different temperatures. The transition from monoclinic to rutile is characterized using synchrotron-based X-ray diffraction and electrochemical performance is performed using electrochemical impedance spectroscopy and intermittent pulsatile galvanostatic discharge tests in a lithium-ion environment. The experimental results indicate a decrease in ohmic resistance when lithium-ion cells are tested at higher temperatures. Density functional theory calculations also identified a possible LixVO2(M) to LixVO2(R) phase transition during the discharging process. Since the monoclinic to rutile transition corresponds to an increase of electrical conductivity by 2 orders of magnitude this can favorably impact the function of a lithium-based electrochemical cell.

Newer, more demanding energy storage systems require high energy density along with high power and fast charge rates. Conventional battery electrode fabrication techniques are often limited by how much active material they can hold in the case of slurry-cast electrodes and how much of the electrode can be utilized in the case of dense pelletized electrodes. Thick porous electrode fabrication techniques have been developed as a way to obtain a higher active mass loading and an architecture which enables ionic and electronic transport. The homogeneity of the phase distribution of lithiated LVO in thick (∼500 μm) porous electrodes (TPEs) designed to facilitate both ion and electron transport was determined using synchrotron-based operando energy dispersive X-ray diffraction (EDXRD). Probing 3 positions in the TPE while cycling at a fast rate of 1C revealed a homogeneous phase transition across the thickness of the electrode at the 1st and 95th cycles. Continuum modelling indicated homogenous lithiation across the electrode upon discharge at 1C consistent with the EDXRD results and ascribed decreasing accessible active material to be the cause of loss in delivered capacity between the 1st and 95th cycles. The model was supported by the observation of significant particle fracture by SEM consistent with loss of electrical contact. The absence of the beta phase peaks in the EDXRD over extended cycling are consistent with electrochemical accessibility of only part of the active material. Overall, the combination of operando EDXRD, continuum modeling, and ex situ measurements enabled a deeper understanding of lithium vanadium oxide transport properties under high rate extended cycling within a thick highly porous electrode architecture.

In order to overcome the limitations of static and destructive characterizations of Li-ion battery materials and components, comprehensive investigation peering into batteries over various length and time scales is essential. In this regard, emerging in situ and operando characterization methodologies focusing on multiple size domains become a powerful approach to resolve current challenges and navigate future directions. This perspective provides a series of illustrative examples of in situ and operando characterizations over atomic, crystallite/particle, electrode, and battery system length scales with a focus on two electrode material classes: insertion and conversion materials. The operating principles, features, analysis methods, and information gained from each characterization method are discussed. Herein, we present the necessity and opportunity for in situ and operando characterization of electrochemical energy storage materials and systems. Further, we suggest future directions to gain the insight needed to tackle currently intractable issues on Li-ion battery application, failure, and emerging design concepts.

LiNi0.6Mn0.2Co0.2O2 (NMC622) is a highly promising Li-ion battery cathode due to its high energy density and excellent reversibility. However high potential charging which can lead to much greater energy density comes at the cost of compromised reversibility. It has been suggested that this loss of reversibility is a result of particle disintegration caused by the anisotropic lattice changes and elevated microstrain at high potentials. Operando X-ray diffraction was utilized to probe the influence of these factors on capacity fade in Li/NMC622 cells both before and after 100 cycles at 3-4.3 or 4.7 V. In addition, scanning electron microscopy (SEM) was performed to observe potential particle disintegration. This study allowed for the collection of structural information about the battery system in real time over the time frame in which capacity fade was observed. Initially, charging to 4.7 V led to increased lattice distortions when compared to 4.3 V; however, after cycling, the lattice distortions were identical independent of charging potential but charging to 4.7 V led to a substantial buildup of microstrain. Additionally, SEM showed that significant damage was done to the particle morphology at 4.7 V, while there were minimal changes at 4.3 V; showing that high potential elevated microstrain is likely a major factor in particle disintegration and capacity fade in this system. This study demonstrates important findings on the mechanisms of capacity fade in NMC622 batteries, which is crucial for the design of next generation NMC battery systems that can maximize both energy density and reversibility.

Advances in electrochemical energy storage are key for the integration of intermittent wind and solar energy sources into the grid, widespread adoption of electric vehicles, and development of new safe and reliable consumer devices. For grid, transportation, and electronic energy storage markets, each application has distinct needs. Therefore, developing battery technology for emerging and wide-spread applications demands greater understanding of the complex chemical and electrochemical processes that occur within rechargeable batteries. Electron transfer and ion transport are the foundation of battery function where the capacity, loaded voltage and current define the practical energy and power delivery of the system. During operation, repetitive addition and removal of electrons and ions can lead to structural change within the electrode and interfacial formation that can dramatically impact electrochemical outcomes. Thus, structural, chemical, and electrochemical characterization during operation is critically important for next generation electrochemical energy storage technologies. The research efforts highlighted in this talk use multiple advanced characterization techniques, including operando methods, to probe charge transport properties, structural changes, and interfacial evolution in multiple rechargeable battery systems. Specifically, spatiotemporal x-ray fluorescence mapping was used to quantify elemental composition near the electrode and in the electrolyte of operando cells. Isothermal microcalorimetry was used to determine heat evolution due to parasitic or decomposition reactions operando. X-ray absorption spectroscopy enabled structure and oxidation state elucidation in the absence of long-range order. X-ray diffraction was employed to track phase changes of distinct electroactive materials. Using advanced characterization, these research efforts provide insight into electron transfer and ion transport properties and their impact on application relevant outcomes (resistance, cycle life, delivered capacity) of electrochemical energy storage technologies.

The electrochemical charge storage of sodium vanadate (NaV3O8 or NVO) cathodes in aqueous Zn-ion batteries has been hypothesized to be influenced by the inclusion of structural water for facilitating ion transfer in the material. Materials properties considered important (morphology, crystallite and particle size, surface area) are systematically studied herein through investigation of two NVO materials, NaV3O8· 0.34H2O [NVO(300)] and NaV3O8·0.05H2O [NVO(500)], with different water content, acicular morphologies with different size and surface area achieved via post-synthesis heat treatment. The electrochemistry of the two materials was evaluated in aqueous Zn-ion cells with 2 M ZnSO4 electrolyte using cyclic voltammetry, galvanostatic cycling, and rate capability testing. The thinner NVO(300) nanobelts (0.13 mm) demonstrate greater specific capacities and higher effective diffusion coefficients relative to the thicker NVO(500) nanorods. Notably however, while cells containing NVO(500) deliver lower specific capacity, they demonstrate enhanced capacity retention with cycling. The structural changes accompanying oxidation and reduction are elucidated via ex situ X-ray diffraction, transmission electron microscopy, and operando V K-edge X-ray absorption spectroscopy (XAS), where NVO material properties are shown to influence the ion insertion. Operando XAS verified that electron transfer corresponds directly to change in vanadium oxidation state, affirming vanadium redox as the governing electrochemical process.

There is critical need for advances in electrochemical energy storage as the technologies are often pivotal for the success of an application. For example, transportation, personal electronics and biomedical applications have ever increasing demands for portable power. Further, stationary energy storage may be a key factor in the ability to broadly integrate intermittent renewable energy sources such as wind and solar. Despite remarkable advances in electrochemically active materials over the last several decades, there remains an urgent need to enhance utilization efficiencies and to develop materials that can safely deliver both high power and energy density. An existing challenge for each specific system of electric energy storage is understanding the basic science associated with the gap between the usable output of the energy storage system and its theoretical energy content. The goal of overcoming this inefficiency is to achieve more useful work (w) and minimize the generation of waste heat (q). Optimization can be approached at the macro level, where bulk parameters are identified and manipulated. However, such a strategy may not provide insight toward the complexities of electric energy storage, especially the inherent heterogeneity of ion and electron flux contributing to the local resistances at numerous interfaces found over several scale lengths within a battery. We are pursuing the investigation of factors that affect ion and electron transport including properties of electroactive materials, interfaces, and electrode structures. Recent advances in the use of in-situ and operando characterization techniques with spatio-temporal resolution of electrochemical activity have enabled us to gain significant mechanistic insight. The ability to understand and ultimately tune these complex electrochemical systems to specific applications, both current and future, depends on specific experimentation and understanding over multiple length scales.

Advances in electrochemical energy storage are key for the integration of intermittent wind and solar energy sources into the grid, widespread adoption of electric vehicles, and development of new safe and reliable consumer devices. For grid, transportation, and electronic energy storage markets, each application has distinct needs. Therefore, developing battery technology for emerging and wide-spread applications demands greater understanding of the complex chemical and electrochemical processes that occur within rechargeable batteries. Electron transfer and ion transport are the foundation of battery function where the capacity, loaded voltage and current define the practical energy and power delivery of the system. During operation, repetitive addition and removal of electrons and ions can lead to structural change within the electrode and interfacial formation that can dramatically impact electrochemical outcomes. Thus, structural, chemical, and electrochemical characterization during operation is critically important for next generation electrochemical energy storage technologies. The research efforts highlighted in this talk use multiple advanced characterization techniques, including operando based methods, to probe charge transport properties, structural changes, and interfacial evolution in multiple rechargeable battery systems. Specifically, X-ray absorption spectroscopy enabled structure and oxidation state elucidation in the absence of long-range order. Isothermal microcalorimetry was used to determine heat evolution due to parasitic or decomposition reactions operando. X-ray diffraction was employed to track temperature-induced and lithiation-induced phase changes of distinct electroactive materials. Using advanced characterization, these research efforts provide insight into electron transfer and ion transport properties and their impact on application relevant outcomes (resistance, cycle life, delivered capacity) of electrochemical energy storage technologies.

The 2D structured dichalcogenide molybdenum(IV) sulfide (MoS2) has generated significant interest for Li ion batteries due to its high theoretical capacity, good rate capability, and minimal volume changes during cycling. To enable full realization of MoS2 as an electroactive material, an important and continuing challenge is to understand the many polymorphs of MoS2 that can be (de)stabilized by electrochemical lithiation and nanosizing. Characteriation of bulk MoS2 and nanosheet-type MoS2 as solids, both structurally (X-ray diffraction (XRD), X-ray absorption spectroscopy (XAS)) and compositionally (X-ray photoelectron spectroscopy (XPS), inductively coupled plasma-optical emission spectroscopy (ICP-OES)) will be described to rationalize observed differences in capacity and efficiency in lithium based cells. X-ray analysis compatible lithium cells (in situ XRD and ex situ XAS) measurements of the specific phase changes to rationalize the significant difference in electrochemistry between the nanosheet and bulk materials upon (de)lithiation will also be discussed. The application of 2D MoS2 nanosheets for lithium sulfur batteries (Li−S) will also be described. Significantly improved Li−S electrochemistry in an environmentally friendly electrolyte solvent is demonstrated through implementation of MoS2 nanosheet materials as cathode additives, leading to improved capacity retention upon extended cycling in lithium sulfur cells. The findings will be discussed in light of the unique attributes of the MoS2 atomic level (2D) and mesoscale (3D) heterostructure.

Manganese is desirable due to its high environmental abundance and low cost. Some manganese oxides (α-MnO2, Mn8O16) possess a tunneled structure comprised of one-dimensional 2 × 2 tunnels formed by corner and edge sharing manganese octahedral [MnO6] units which can be substituted in the central tunnel by a variety of cations of varying size, providing a robust framework for ion insertion and (de)insertion. Control of composition, crystallite size, and defect through scalable synthesis approaches will be described in this presentation. Impact of nanostructure and mesoscale electrode structure on capacity, rate capability, and capacity retention in lithium and beyond lithium batteries will be discussed. Specific improvements in capacity retention realized through targeted elemental substitution will be highlighted. Mechanistic differences in aqueous and non-aqueous battery systems will be described. The use of x-ray absorption spectroscopy to gain insight into mechanism and the evolution of local coordination environment in these systems will be reviewed.

Conceptually, there are two related electrochemical storage redox mechanisms for materials: insertion where the host structure is largely maintained, and conversion there is a chemical transformation leading to a formation of one or more new phases. For some materials, each of these mechanisms may participate at different stages of the electrochemical redox process, where the kinetics for ion and electron transport can play a determinstic role regarding which process dominates at a particular state of (dis)charge. Parasitic side reactions can also make significant contributions to the function of the energy storage system, through formation of resistive interfaces and consumption of redox active material/s. Progress towards distinguishing insertion and conversion processes, and decovoluting productive and parasitic processes within batteries will be discussed. Specifically, insight gained from complementary ex situ, in situ, and operando spectroscopy, diffraction and electrochemistry studies will be highlighted in this presentation.

Solid state batteries are receiving attention due to the possibility of the incorporation of the high energy density of lithium metal coupled with increased safety due to the elimination of flammable organic electrolytes. The lithium/iodine (Li/I2) solid electrolyte battery system has been used successfully for decades as a primary battery to power implantable cardiac pacemakers and has demonstrated an exceptional record of predictability and reliability with high energy density (1536 Wh/L, 560 Wh/kg). This presentation describes the demonstration of a lithium/iodine rechargeable battery based on the use of LiI rich lithium iodide-(3-hydroxyproprionitrile)2 solid state electrolyte. The battery is first assembled fully discharged using only the solid state electrolyte. The LiI is transformed into the active material where, on charge, lithium metal forms at the negative side of the battery and iodine forms at the positive side. To our knowledge, this is the first demonstration of a rechargeable self-forming solid state lithium battery with electrolyte including LiI(HPN)2. Results on cell formation, cycling, Coulombic efficiency as well as electrochemical impedance spectroscopy will be presented. The results show promise for this conceptual approach for achieving high energy density solid state rechargeable batteries.

Batteries for implantable medical devices have requirements specific to each device. However, some characteristics are demanded by all implantable applications including high energy density both volumetrically and gravimetrically, exceptional reliability, predictable behavior, and ability to determine state of charge. The lithium/iodine (Li/I2) solid electrolyte battery system has been used successfully for decades as a high energy density primary battery to power implantable cardiac pacemakers delivering microampere level currents with an exceptional record of predictability and reliability. In contrast, high power cells capable of delivering ampere level pulses based on the lithium/silver vanadium oxide chemistry power implantable cardiac defibrillators. Case studies will be provided to illustrate that understanding the batteries systems used under the rigorous requirements demanded by implantable medical devices can provide inspiration for addressing issues in battery systems intended for a wide variety of applications. Strategies to extend the life time of lithium batteries comparing cathode materials based on transition metal oxides with transition metal phosphates will be described. Known failure modes are explored along with their impact on interfacial phenomena. The lithium/iodine pacemaker battery is used as inspiration for demonstration of a rechargeable solid state battery based on the use of LiI rich lithium iodide-(3-hydroxyproprionitrile)2 solid state electrolyte. The battery is assembled fully discharged using only the solid state electrolyte. On charge, lithium metal forms at the negative side of the battery and iodine forms at the positive side. Finally, strategies to successfully increase power of high energy density batteries will be described.

Electrochemistry of lithium trivanadate (LiV3O8, LVO) has been extensively studied due to its large capacity and high rate capability. The material undergoes both insertion/extraction and phase transform reactions during discharge and charge in a Li-ion battery. However, the rate limiting factors of the material are unclear over the cycling window of 2.0 -3.8 V. In this work, LVO thin films are fabricated from RF magnetron sputtering and annealed at different temperatures of 260, 350, 400 and 500°C. Crystallinity, crystallite size and preferred orientation of the thin films are analyzed by x-ray diffraction. All solid-state thin film batteries are fabricated with LVO cathodes annealed at different temperatures of 260, 350 and 400°C. The electrochemical properties are investigated at two different test temperatures to compare the rate limiting process for discharge and charge. AC impedance is applied on the 260 and 350°C cells to characterize the voltage dependence of the diffusion coefficient during both discharge and charge. Our work correlates the cell polarization with both the diffusion coefficient and the Li+ concentration, showing that these parameters play different roles in the insertion and phase transform reactions, and shows the structural dependence of these parameters. Figure 1

Conversion-type materials for next generation lithium ion systems are of particular interest due to the opportunity for high delivered capacity. However, implementation of conversion materials has been hindered by the phase transformations and large volume changes occurring during cycling. An associated factor is that liquid electrolytes are often not thermodynamically stable at the potentials of the active electrodes while the battery is functioning. This results in the decomposition of electrolyte leading to organic and inorganic interphases formed at the electrode surface. The influence of the interphases can be particularly profound for conversion materials where phase change takes place during (de)lithiation. Notably, the interfaces are critical factors in determining the transport of electrons and ions, the resultant polarization, and associated heat generation. The use of isothermal microcalorimetry (IMC) will be described as an operando tool to determine the heat evolved due to parasitic or decomposition reactions during lithiation. The total heat measured is assessed in light of the contributions from cell polarization, entropic contributions and the parasitic reactions. This study will describe the use of complementary ex-situ and operando characterization techniques to provide insight into decomposition reactions taking place within energy storage systems.

Building upon a previously validated crystal-scale model, a coupled electrode/crystal-scale mathematical model is used to compare phase-change behavior and electrochemical performance of lithium trivanadate (LiV3O8). The agreement between simulated and observed electrochemical performance is compelling. Observations about the phase-change dynamics of the material were gathered using time and space-resolved operando EDXRD measurements. These observations were compared with simulated concentration and phase profiles. Both simulation and experiment reveal that during lithiation, phase transformations preferentially occur near the separator, while during delithiation the disappearance of the lithium-rich β-phase occurs uniformly across the electrode.

Magnesium-ion (Mg2+) batteries (MIB) can be desirable relative to lithium ion batteries (LIB) as they offer the opportunity for high volumetric capacity due to the divalent nature of Mg2+ (3832 mAh/cm3 of Mg) and enhanced safety due to unlikely dendrite formation on Mg anodes. Spinel magnesium manganese oxide (MgMn2O4) has a tetragonal structure different from the typical cubic structure of spinels, due to distortion induced by the strong Jahn-Teller effect of Mn3+. In this work we present the first systematic study of MgMn2O4 as a cathode material in MIB. The materials were synthesized by a modified Pechini method, and annealing temperature was used to control the crystallite size of the products. The electrochemistry of two different sized samples was studied in magnesium based electrolyte with and without added water in the electrolyte. The MgMn2O4 samples were characterized by synchrotron X-ray powder diffraction (XPD), Transmission electron microscopy (TEM) data was collected and the BET surface area was determined. Capacity retention and rate capability was determined in the presence and absence of water in the electrolyte for both samples. Results with respect to crystallite size and water content will be discussed.

Electroactive materials are typically incorporated into batteries through the fabrication of composite electrodes including additives to enhance conductivity and to mechanically bind the components. These structures provide an opportunity to decrease inert material content if multifunctional materials can be designed and employed. For example, redox active materials that incorporate silver cation (Ag+) demonstrate the possibility for in-situ generation of an electrically conductive percolation network of Ag0 metallic nanoparticles through a reduction displacement reaction. This paradigm has been demonstrated with silver vanadium phosphorous oxide (Ag2VO2PO4) where the electrical conductivity increased 15,000-fold upon lithiation. This presentation provides new strategies for the deliberate design of composite materials taking advantage of the opportunity for in-situ reduction displacement to form conductive networks. Several new approaches will be described. These include a one pot synthetic approach for the direct formation of a composite where one component is silver ion containing and the second is not. Additionally, surface modification approaches to generate conductive surface coatings will be introduced. These methods can significantly benefit the electrochemistry compared to composites formed by mechanical mixing alone, as will be illustrated in this presentation.

In recent years, binary transition metal oxides such as magnetite, Fe3O4, zinc ferrite, ZnFe2O4, magnesium ferrite, MgFe2O4 and copper ferrite, CuFe­2O4, have gained significant attention as prospective electrodes for lithium based batteries. These materials hold interest due to the low cost iron center, their low environmental impact, and in particular for their high theoretical capacities. Through a combined insertion and conversion mechanism theoretical capacities of up to 1000 mAh/g would be possible, thus, storing more energy than typical insertion materials. Interestingly, along with the commonality of the iron metal center, the materials often have spinel or inverse spinel structures. The densely packed structure of these spinel materials has led to the demonstration that smaller crystallite size samples can provide higher practical energy density than larger size samples. This presentation will provide insight into the role of crystallite size as well as the lithiation/delithiation mechanisms of this class of bimetallic iron oxide structures.

This report describes a synthetic approach to control the crystallite size of silver vanadium phosphorous oxide, Ag0.50VOPO4·1.9H2O, and the impact on electrochemistry in lithium based batteries. Ag0.50VOPO4·1.9H2O was synthesized over a range of temperatures. X-ray diffraction (XRD) was used to confirm the crystalline phase and the crystallite size sizes. Particle size and morphology were characterized using scanning electron microscopy and surface area measurements. Galvanostatic reduction and intermittent discharge were used to evaluate functional capacity and resistance. This systematic study of electrochemistry and material properties shows that deliverable capacity and cell resistance are impacted by both interparticle and intraparticle transport properties.

Inverse spinel magnetite, Fe3O4, has been studied as an electrode material for lithium-ion batteries due to its low cost, high abundance, and low environmental impact.1 Experimental discharge profiles of Fe3O4 initially show a concentration dependent voltage profile. The lithium concentration range of that profile varies as a function of nanoparticle size, with smaller particles exhibiting a larger intercalation regime.2,3 Thackeray et al. proposed initial lithium intercalation into magnetite on 16c sites, where the lattice accommodates a critical concentration of lithium without significant structural rearrangements. Above a critical concentration of lithium, Thackeray et al. proposed that with further discharge, lithium insertion to 16c sites leads to Fe8a displacement to vacant 16c sites in the material.4 It is also known that magnetite is iron deficient, Fe3-δO4 in the bulk and in the nanoparticulate forms with vacancies on the octahedral 16d sites.5–7 The most drastic manifestation of this oxidation process is maghemite, with δ=1/3, the topotactic oxidative product written as (Fe1 3+)8a[Fe1.66 3+♦0.33]16dO4 with ♦ as a 16d iron defect, or γ-Fe2O3. Menard et al. showed that the defects in nanoparticulate magnetite increase with decreasing nanoparticle size, but a thorough investigation of how defects affect the electrochemistry is yet to be presented.2 Using DFT+U calculations, we have investigated lithium intercalation in Fe3O4 magnetite. Our results show that stoichiometric Fe3O4 is not an intercalation material, with no stable phases for the LixFe3O4 03O4 to rock-salt LiFe3O4with Li and Fe occupying 16c sites. This rules out the original hypothesis for a critical concentration of lithium hosted on the 16c sites resulting in a concentration dependent voltage at low concentrations of lithium in magnetite. We have performed DFT+U calculations on lithiated Fe3-δO4 with δ=0,1/8, and 1/3 to understand how 16d iron defects affect the open circuit potential of magnetite and therefore the discharge behaviour. In the presence of 16d iron defects, we have found that even at low concentrations of lithium, insertion on vacant 16c sites causes significant Fe8a rearrangements. When lithium is inserted on 16c positions, its proximity to Fe8a induces Coulombic repulsion between the Li16c and the Fe8a, and the resultant material is thermodynamically unstable against phase segregation. On the other hand, when lithium is inserted on vacant 16d sites available in the δ=1/8 and 1/3 cases, a structurally stable intercalated material results and DFT+U predicted voltages align with experimental observation. We further hypothesize that the concentration of defects is a function of nanoparticle size. Then we are able to explain the experimentally observed size-dependent open circuit potential and the variation of discharge capacity with particle size in a natural way. Finally, with DFT+U calculations we are able to provide a mechanism for intercalation and phase-segregation that is consistent with the nanoparticle size dependence observed in the electrochemical experiments. This work was supported as part of the Center for Mesoscale Transport Properties, an Energy Frontier Research Center supported by the U. S. Department of Energy, Office of Science, Basic Energy Sciences, under award #DE-SC0012673. This research used resources of the Center for Functional Nanomaterials, a U.S. DOE Office of Science User Facility, at Brookhaven National Laboratory, Contract No. DE-SC0012704. The Extreme Science and Engineering Discovery Environment (XSEDE) was used, supported by National Science Foundation grant number ACI-1548562. The Yeti Shared HPC Cluster at Columbia University was used, which includes support from Empire State Development's Division of Science, Technology, and Innovation, contract number C090171. C. N. L. acknowledges the support of the National Science Foundation Graduate Research Fellowship under Grant No. DGE-11-44155. Any opinions, findings, and conclusions or recommendations expressed in this material are those of the authors and do not necessarily reflect the views of the National Science Foundation. (1) Ito, S.; Nakaoka, K.; Kawamura, M.; Ui, K.; Fujimoto, K.; Koura, N. J. Power Sources 2005, 146, 319–322. (2) Menard, M. C.; Marschilok, A. C.; Takeuchi, K. J.; Takeuchi, E. S. Electrochim. Acta 2013, 94, 320–326. (3) Menard, M. C.; Takeuchi, K. J.; Marschilok, C.; Takeuchi, E. S. 2013, 15, 18539–18548. (4) Thackeray, M. M.; David, W. I. F.; Goodenough, J. B. Mater. Res. Bull. 1982, 17, 785–793. (5) Daniels, J. M.; Rosencwaig, a. J. Phys. Chem. Solids 1969, 30, 1561–1571. (6) Dieckmann, R. Berichte der Bunsen-Gesellschaft fur Phys. Chemie 1982, 86, 112–118. (7) Johnson, C. E.; Johnson, J. A.; Hah, H. Y.; Cole, M.; Gray, S.; Kolesnichenko, V.; Kucheryavy, P.; Goloverda, G. Hyperfine Interact. 2016, 237, 1–10.

Manganese oxide materials are desirable cathode materials due to their low cost and environmentally benign character. Specifically, 2-D layered birnessite (RyMnO2·xH2O, R = monovalent or divalent metal ions) materials are conceptually appealing because of their excellent ion-exchange properties. Edge-sharing MnO6 octahedra constitute the MnO2 layers where the interlayer spacing of 7 Å is occupied by metal ions and water molecules. Herein, we designed a study of a Mg cation containing birnessite with different crystallite sizes synthesized through a room temperature precipitation and ion exchange reaction, and characterized to determine structure and magnesium content. Electrochemical behavior was tested in lithium ion, sodium ion and magnesium ion based electrolytes, where the influence of crystallite size on electrochemical activity of Mg-birnessite was evaluated. Results and implications for future materials design will be discussed.

Ag0. 50VOPO4·1.8H2O (silver vanadium phosphate, SVOP) demonstrates a counterintuitive higher initial loaded voltage under higher discharge current. Energy dispersive X-ray diffraction (EDXRD) from synchrotron radiation was used to create tomographic profiles of thick cathodes at various depths of discharge for two discharge rates. SVOP displays two reduction mechanisms, reduction of a vanadium center accompanied by lithiation of the structure, or reduction-displacement of a silver cation to form silver metal. In-situ EDXRD provides the opportunity to observe spatially resolved changes to the parent SVOP crystal and formation of Ag0 during reduction. Discharge rate can influence the preferred initial reaction either V5+ reduction or reduction of Ag+ with formation of conductive Ag0. Discharge rate also affects the spatial location of reduction products. This study highlights the importance of mesoscopic analysis and illuminates the roles of electronic and ionic conductivity limitations within a cathode and how they impact the course of reduction processes and loaded voltage.

Energy storage materials remain important due to their ability to store electricity for many applications including aerospace, transportation, portable electronics, and biomedical devices. Full utilization of materials requires fast transport of both ions and electrons to all regions of the electrode. Several approaches have been utilized to facilitate ion diffusion including dimension reduction, morphology control, and synthesis of layered and tunneled structures, however, electron access must also be considered. Low electrical conductivity can limit active material utilization, especially at high rates, and may be a cause of capacity fade. One approach to address the low electrical conductivity of cathode materials is to utilize composite electrodes that contain conductive media, most often carbon. While commonly employed, this strategy is imperfect, as inhomogeneous dispersion of the active material in the conductive additive results in incomplete electrical contact to all particles in the electrode. Encapsulation of individual active material particles with a carbon coating can be more effective for providing electrical contact to each particle, however have the disadvantages of additional synthesis steps and increased production cost. An alternative strategy to approach an ideal electrode that we have been exploring is the use of bimetallic material systems. In this approach, the active material particles are electrically connected as they generate a conductive network in-situ on initiation of reduction. Bimetallic cathode materials offer the opportunity for conductive matrix formation via reduction displacement reactions that result in the formation of metal nanoparticles providing the electrical connections. The investigation of bimetallic materials and the formation of electrically conductive pathways has included exploration of metal oxide and metal polyanion type structures including phosphate and diphosphate moieties. Additionally, composites containing bimetallic materials have been explored. The impact of this strategy on delivered capacity and capacity retention will be discussed.

Overcoming the difference between the usable output of any energy storage systems and its theoretical energy content remains a critical challenge. The inefficiency typically results in the production of waste heat (q) rather than useful work (w). Minimization of inefficiency can be approached through optimization at the macro level, where bulk parameters are identified and varied. One approach to analyze multivariate systems is through optimization, often involving statistical methods such as design of experiments. This is an effective tool when the needed information regarding the parameters affecting the system is known. However, the diversity and intricacies of new and modified battery materials inherently reduce the probability of optimization experiments resulting in marketable products because the detailed operation mechanisms are unknown. Further, optimization will likely not yield insight into the complexities of electric energy storage systems, especially when considering any heterogeneity of ion and electron flux at the numerous interfaces over several scale lengths within a battery. This would require multiple characterization approaches used in concert, to assemble information gathered at the local or atomic level and link it to mesoscale characterization and finally system level performance. Thus, the ability to control and ultimately predict the behavior of complex systems demands not just parameterization at the bulk scale, but rather specific experimentation and understanding over multiple length scales within the same battery system, from the molecular- to the meso-scale through understanding the associated basic science. This presentation will examine insights and implications from multiscale investigations of energy storage related materials.

Layered materials are desirable for energy storage as they offer opportunity for facile ion transport in two dimensions. In some cases, interlayer spacing can change significantly upon ion insertion and deinsertion, while in others the material structure can be largely maintained during the discharge and charge process. Progress involving synthesis, characterization and electrochemical investigation of select examples from the families of vanadium, iron, and manganese oxide systems will be discussed.

Silver vanadium phosphorous oxide, Ag2VO2PO4, was used as a bimetallic cathode system to systematically study the impact of the constituents of a composite electrode, including polymeric and conductive additives, on the electrochemical polarization and the bimetallic discharge progression of the battery. Ag2VO2PO4 has been developed as a cathode material intended for use in batteries that power implantable cardiac defibrillators (ICDs). This application demands primary battery systems that are reliable over long periods of implantation and are able to deliver high current pulses to charge the capacitors of the device. With these requirements in mind, primary Li/ Ag2VO2PO4 batteries are particularly promising because of their high capacity (270 mAh/g), excellent rate capability with pulses >30 mA sq. 1/cm, and lower cathode dissolution compared to the commercially used Li/Ag2V4O11system. Ag2VO2PO4 is especially well suited for studies of discharge progression in bimetallic cathode systems. Notably, it can be discharged as a pure electroactive material in the absence of a conductive additive as it generates an in situ conductive matrix via a reduction displacement reaction resulting in the formation of Ag0 nanoparticles. The electrochemical reduction of Ag+ and V5+ in Ag2VO2PO4 has previously been determined to take place sequentially at low rates, with reduction of Ag+ to Ag0 through a reduction-displacement reaction occurring first but with a small level of V5+ reduction occurring concurrently. The Ag0nanoparticles formed can be detected by diffraction based techniques and can be spatially resolved by in situ Energy Dispersive X-ray Diffraction (EDXRD) to assess the homogeneity of discharge. EDXRD provides unique insight into the state of the electrode by enabling evaluation of discharged phases as a function of spatial location. Furthermore, the white beam energy of the synchrotron light source can penetrate the steel casing of the battery, providing in situ measurements of coin type cells without the need for specially designed X-ray windows. Three different electrode compositions were investigated: Ag2VO2PO4 only, Ag2VO2PO4 with binder, and Ag2VO2PO4 with binder and carbon. Constant current discharge, pulse testing and impedance spectroscopy measurements were used to characterize the electrochemical properties of the electrodes as a function of depth of discharge. In situ EDXRD was used to spatially resolve the discharge progression within the cathode by following the formation of Ag0. Ex situ X-ray Diffraction (XRD) and Extended X-ray Absorption Fine Structure (EXAFS) modeling were used to quantify the amount of Ag0 formed. Results indicated that the metal center reduced (V5+ or Ag+) were highly dependent on composite composition (presence of PTFE, carbon), depth of discharge (Ag0 nanoparticle formation), and spatial location within the cathode.

Numerical simulations are an important tool used to improve overall performance in lithium ion batteries. Often numerical methods are utilized for system optimization, however, coupling traditional electrochemical measurements and characterization techniques with numerical simulations allows for insights into the basic science that dictate battery performance. The focus of the presentation is on the analysis of current interrupt experiments and materials characterization, coupled with numerical simulations to gain insights into mass and charge-transport, electron-transfer, and phase change. Understanding how to interpret and apply these insights can directly inform the synthesis of new nanomaterial constructs, resulting in systems with improved performance. Previous research used numerical methods in conjunction with electrochemical measurements and characterization techniques to understand mass-transport and electron-transfer processes in a model cathode material, and included effects across different lengths scales (1-3). These previous studies focused on the processes occurring during lithiation and voltage recovery, and the implications from these studies have been used to inform electrode synthesis and positively impact performance. However, there remained significant challenges to overcome, namely understanding delithiation and phase change. Validating the model with a different chemistry not only demonstrated the broad applicability of model, but also allowed us to study phase change (4). Integrating phase change built upon our understanding of mass-transport and charge-transfer effects. Using the advantages of numerical simulations allowed us to decouple the losses associated with each process and thereby better understand how these governing processes influence battery performance. Extending the model to envelope both lithiation and delithiation is important for the battery field in general because asymmetries are commonly observed between charge and discharge for a variety of battery chemistries. Understanding the physics of mass-transfer, charge-transfer, and phase change as well as charge/discharge asymmetries informs electrode fabrication and battery operation and lends itself to improving the overall performance of these systems. 1. N. W. Brady, K. W. Knehr, C. A. Cama, C. N. Lininger, Z. Lin, A. C. Marschilok, K. J. Takeuchi, E. S. Takeuchi and A. C. West, Journal of Power Sources, 321, 106 (2016). 2. K. W. Knehr, N. W. Brady, C. A. Cama, D. C. Bock, Z. Lin, C. N. Lininger, A. C. Marschilok, K. J. Takeuchi, E. S. Takeuchi and A. C. West, Journal of The Electrochemical Society, 162, A2817 (2015). 3. K. W. Knehr, N. W. Brady, C. N. Lininger, C. A. Cama, D. C. Bock, Z. Lin, A. C. Marschilok, K. J. Takeuchi, E. S. Takeuchi and A. C. West, ECS Transactions, 69, 7 (2015). 4. N. W. Brady, Q. Zhang, K. W. Knehr, P. Liu, A. C. Marschilok, K. Takeuchi, E. S. Takeuchi and A. C. West, Journal of the Electrochemical Society, 163, 2890 (2016). Figure 1

Future device applications will dictate increases in the energy density of batteries, which may be accomplished by incorporating high capacity electroactive materials into composite electrodes where all the electroactive material is electrochemically accessible and the mass and volume contributions of passive components are minimized. Electroactive materials are incorporated into batteries through the fabrication of composite electrodes, where several additives may be used to enhance conductivity and to mechanically bind the components. Typically, an electrically conductive carbon additive (e.g. acetylene black or graphite) and a polymer binder (e.g. PVDF and PTFE) are mixed with the electroactive material to form a composite electrode. Electrically conducting polymers are intriguing as composite electrode additives since conceptually they can fulfill the roles of both carbon and binder. Magnetite is a naturally occurring mineral found in the earth’s crust; therefore, it is abundant, environmentally friendly, cheap, and non-toxic. Magnetite is also easy to synthesize and can be prepared through simple, non-hazardous techniques such as through a facile aqueous co-precipitation method. Complete reduction of magnetite involves the transfer of 8 electrons, providing opportunity for an impressive capacity of 925 mAh/g. Notably, the initial reactions are insertion reactions where the lithium ion can insert into the Fe3O4 structure with minimal structural distortion, while upon further reduction, a conversion reaction occurs generating Fe metal and Li2O as products of full discharge. To further probe the role of the electrically conductive polymer in the mesoscale (bulk) properties of composite electrodes, this study focuses on the Fe3O4 conversion reaction and its relationship to the electrically conductive polymer binder, PPy, including a detailed study of composite electrodes with nanoscale Fe3O4 and PPy. Magnetite, Fe3O4, with 6% and 20% polypyrrole (PPy) was used to prepare composite electrodes with and without added carbon. Galvanostatic cycling and Electrochemical Impedance Spectroscopy (EIS) measurements were used in tandem to determine delivered capacity, capacity retention, and the related impedance at various stages of discharge and charge. Further, the reversibility of Fe3O4 to iron metal conversion observed during discharge was quantitatively assessed, ex situ, using X-ray Absorption Spectroscopy (XAS). The Fe3O4 composite containing the largest weight fraction of PPy (20 wt%) with added carbon demonstrated reduced irreversible capacity on initial cycles and improved cycling stability over 50 cycles. This study illustrated the beneficial role of PPy addition to Fe3O4 based electrodes partially related to improved electrical conductivity and also to improved ion transport related to the formation of a more favorable surface electrolyte interphase (SEI).

Fundamental studies involving the impact of physical and chemical properties of materials on their electrochemical properties are critical to the rational development of battery materials which may address the present and future requirements for stationary and portable power. For large scale batteries, the use of environmentally benign and low cost energy storage materials is desired. Manganese-based materials are desirable in this regard as they are environmentally friendly, inexpensive, and can be prepared using scalable, aqueous based synthesis methods. Preparation, characterization, and battery electrochemistry of two promising structural motifs of manganese oxides will be described, specifically tunneled (hollandite) and layered (birnessite) crystallographic structures. The use of complimentary bulk (synchrotron based diffraction, thermogravimetric analysis, optical emission spectroscopy) and local (transmission electron microscopy based atomic imaging, nanodiffraction and electron energy loss spectroscopy) to elucidate structures of as-prepared, electrochemically reduced and oxidized materials will be highlighted. The impact of crystallite size will also be discussed. Hollandites (Mx’Mn8O16) are one-dimensionally (1D) structured materials consisting of octahedral units of edge-sharing manganese oxide octahedra which interlink to form tunnels of 2 x 2 dimensions. Bimetallic hollandite type materials have been prepared where cations with 1+ or 2+ charge partially occupy locations within the manganese oxide tunnels, and the Mn cations possess mixed 3+ and 4+ oxidation states. Typically, the ion located within the tunnel (M’) is electrochemically inert (i.e. K+); however, silver hollandite is an interesting case as the Ag+ cationic center is potentially electrochemically active. The electrochemistry of potassium and silver based hollandites in lithium-ion and beyond lithium-ion battery systems will be described. The impact of the structural M’ cation and the role of oxygen vacancies on ion transport will be discussed. A novel recyclable battery electrode will also be described, which provides full restoration of initial capacity after a facile regeneration process. Birnessite (Mx’MnO2), a layered manganese oxide, exists as a monoclinic crystal comprised of layers of edge-sharing manganese-oxygen octahedra (MnO6) with cations positioned between the layers. Although birnessite can be formed without any interlayer cations, monovalent (i.e. Na+, K+, Li+, Cs+) or divalent (Mg2+ or Cu2+) cations can also be incorporated between the layers. The impact of an electrochemically active interlayer cation, copper (Cu2+), on capacity and structural integrity of the birnessite structure upon discharge-charge cycling will be described, including a detailed view of the Mn and Cu oxidation state changes along with variations of the local neighboring atom environments around the Mn and Cu centers.

Conventionally, battery electrodes are prepared from physical mixtures of conductive additives, polymeric binders, and electroactive active material particles which are usually coated onto metal foil current collectors. The three passive components serve distinct functions, where the current collector provides structural support, the binder maintains physical adhesion throughout the composite, and the conductive additives establish an interconnected conduction network. Minimizing the mass of passive material in the electrode is desirable to maximize functional gravimetric capacity. To maximize energy density and rate capability, obtaining a continuous conductive pathway with open pores for fast ion transport is critical. Electrodeposition is presented here as a design strategy for lightweight, high performing, high energy density battery electrodes. Opportunity for removal or reduction of passive components will be discussed. Examples of direct deposition of electroactive particles onto a three-dimensional, lightweight, conductive substrate will be described, along with functional testing of the resulting composite electrodes for beyond lithium-ion batteries (i.e. magnesium-ion batteries and metal air batteries). Benefits of the electrodeposition based fabrication strategy, including quantitative control over active material loading, and opportunity to realize continuous electrical contact by design, will be highlighted.

Energy dispersive x-ray diffraction (EDXRD) presents a special opportunity to achieve spatial resolution of an electrochemical process within the electrode inside a functioning electrochemical cell, providing the opportunity for tomographic-like data analysis. White beam radiation coupled with a synchrotron “wiggler” insertion device emits high energy radiation which can penetrate bulk engineering materials such as steel, enabling in-situ measurement of conventionally designed prototype and production level batteries. Unlike other in-situ methods, EDXRD does not require the use of a modified or special cell design. Rather, the method enables a direct probe of electrode reactions in cells fully encased in their steel housings. These studies used a family of AgxVOy(PO4)z materials as model systems to provide insights into the electrochemical reduction process for inherently poorly conducting phosphate and diphosphate based cathode materials. The systems proved to be particularly well suited for EDXRD in-situ studies as the Ag0metal product formed on reduction could be detected in small amounts. In-situ EDXRD was measured at several x-direction locations in several stainless steel coin cells with AgxVOy(PO4)z cathodes discharged to different depths of discharge under several rates. At each location spectra were collected in increments through the thickness of the electrode. The presence of Ag0 as a reduction product in silver vanadium phosphate cathodes had been verified ex situ using x-ray diffraction and scanning electron microscopy experiments. However, in situ measurements of the Ag0 provided the opportunity for further insight into the electrochemical reduction mechanism, regarding the location and distribution of the reduction products.

Characterization of electrochemical properties determines the energy content for new materials and possible viability for a potential application. Equally critical yet more challenging is determining the non-Faradaic parasitic reactions of the active materials in a battery environment and their relationship to useful battery life. In order to be successful in long calendar life battery applications, only very low levels of parasitic reactions can be tolerated. For example, calendar life is a particularly important consideration for implantable medical batteries, especially for devices powering essential life functions such as cardiac rhythm management devices. Determining stability by direct systems level testing is slow and expensive as it can require many years and many batteries to affirm. The dissolution of cathode materials including manganese, cobalt and vanadium oxides in battery systems has been identified as a specific battery failure mechanism. However, dissolution studies including kinetic analysis of the dissolution of active battery materials in non-aqueous electrolytes are largely absent from the literature. We developed a quantitative approach to assess battery materials for their solubility and then validated the approach with battery testing. In this study, a series of vanadium oxide and vanadium phosphate based cathode materials were studied relative to their dissolution in battery electrolyte. Kinetic analysis of the results provided a quantitative approach for understanding the impact of structure and composition on the dissolution of active materials. Negative electrode surfaces from cells using cathodes displaying different levels of solubility were analyzed. A conceptual model of the negative electrode surface electrolyte interphase was developed to rationalize the observed cell impedance and performance. Implications for lifetime prediction for these and other battery systems will be discussed.

Capacity fade mechanisms can be difficult to pinpoint in conventional composite cathodes for Li-ion batteries. Capacity fade associated with the cathode can be caused by: (1) irreversible reactions involving the active material, possibly with the electrolyte, (2) degraded integrity of the composite structure, or (3) anode contamination by cathode dissolution products. Post-cycling characterization can be difficult, because these potential capacity fade mechanisms would occur in a complicated cathode structure with: porosity, possible microcracks, irregular surfaces, and multiple particulate phases (active material, binder, and conducting additive). Thin film cathodes were used to study how LiV3O8 (LVO) microstructure affects cycling performance without the added complications associated with a conventional composite cathode structure. Thin film cathodes were produced by magnetron sputtering a Pt current collector layer and an LVO layer onto alumina disks. The thin film geometry with its uniform layered structure was well suited for analysis of pristine and cycled LVO cathodes by several characterization techniques, including transmission electron microscopy, energy dispersive x-ray spectroscopy, and x-ray photoelectron spectroscopy. The cycling performance of heat-treated thin film cathodes was directly compared to that of conventional composite cathodes with heat-treated sol-gel derived LVO powder. Thin film and sol-gel derived LVO cathodes showed excellent microstructural and electrochemical agreement as a function of heat-treatment temperature. Depending on heat-treatment temperature, the microstructure ranged from amorphous (as-deposited or low temperature heat-treatment) to coarse-grained crystalline material (higher temperature). The maximum specific capacity and the maximum capacity fade were both observed for LVO nanocrystalline material fired at intermediate temperature, where reduced capacity and reduced capacity fade were observed for higher and lower firing temperatures. Capacity fade was linked to vanadium dissolution, where amorphous LVO cathodes showed much lower vanadium dissolution than nanocrystalline LVO material. This work was supported as part of the Center for Mesoscale Transport Properties, an Energy Frontier Research Center funded by the U.S. Department of Energy, Office of Science, Basic Energy Sciences under Award # DE-SC0012673.

Understanding electrochemical behavior requires inquiry of the material fundamental properties as well as the behavior of the material when configured into a fully functioning device. Thus, the ability to use local electrochemical probes and integrate the results with system level behavior is needed. In this work, quantitative electrochemistry was conducted on individual particles of vanadium phosphorous oxides, (specifically SVPO, AgwVxPyOz) cathode materials. Silver ions incorporated into the layered vanadium phosphorous oxide structure facilitated monitoring of the reaction progress through the formation of silver metal. The results obtained from the single particle were related to the systems level through in-situ examination of the reduction progress in fully assembled cells probed through energy dispersive x-ray diffraction, EDXRD. At the particle level, individual particles of active material, Ag2VO2PO4, were electrochemically reduced to various depths of discharge. After the material was reduced, the conductivity of the individual particles was determined using a nanoprobe integrated with a scanning electron microscope, Fig. 1. The individual particles showed a drastic reduction in local resistance when discharged. At the system level, in situ energy dispersive X-ray spectroscopy (EDXRD) was used to probe Li/ Ag2VP2O8 cells at several stages of reduction, allowing depth profile analysis of the discharge process. This technique enables micron scale spatial resolution of reduced Ag2VP2O8 and Ag0 discharge products in the bulk electrode. Results suggest the formation of a 3-dimensional Ag0 percolation network that increases conductivity throughout the entire electrode, occurs concurrently with a substantial decrease in the charge transfer resistance. The resistance of the reduced cathode is dependent upon discharge rate even in the presence of conductive additives. Development of the next generation of battery systems with improved energy utilization requires accessing all of the active material in an electrode. The multiscale inquiry methodology described provides a template for future investigations of both particle level and system level properties of electrochemically discharged materials highlighting the importance of advanced instrumental techniques to gain insight into complex discharge processes. Figure 1

As the demand for large scale batteries has grown, considerations such as earth abundance, cost, and toxicity have assumed a greater significance. Metal oxides such as magnetite (Fe3O4) are worthy of evaluation as active materials for electrochemical energy storage due to its earth abundance, low cost, environmentally benign iron metal centers and high theoretical capacity, 926 mAh/g. Implementation in the future will require understanding of the fundamental electrochemical reduction-oxidation mechanisms of the electroactive materials is required, coupled with characterization at the mesoscale to understand the underlying contributors to localized resistance which must be addressed in order to achieve significant improvements to current capability and reversibility. An emerging paradigm for the implementation of close-packed materials in higher current applications is the tuning of the materials crystallite dimensions, where the reduction of crystallite size should minimize the path length for ion transport upon discharge, resulting in a reduction of both internal cell resistance and the resultant structural strain associated with lithium insertion. The electrochemical impact of controlled crystallite size of magnetite will be described. In addition to the crystallite size of the electroactive material, a complete study of an electroactive nanomaterial in the complex mesoscale environment of a composite battery electrode should also consider the level of electroactive particle agglomeration, and agglomerate distribution within the battery electrode. Nanocrystalline magnetite (Fe3O4) powders and composite electrodes with different crystallite sizes were prepared, characterized, and electrochemically evaluated. Transmission electron microscopy (TEM) examination of cross-sectioned electrodes was used to quantify the aggregate size of the Fe3O4 active material. Notably, although the crystallite sizes of two magnetite samples Fe3O4 are different (28 and 9 nm), the observed sizes of the aggregates and aggregate distribution within the electrodes were similar, see TEM images of sectioned electrodes fabricated with the 28 nm (A,B) and 9 nm (C,D) sized Fe3O4 in the Figure. Transmission x-ray microscopy (TXM) combined with x-ray absorption near edge spectroscopy (XANES) at the National Synchrotron Light Source (NSLS) were used to determine the distribution of the iron oxidation states within the electrodes before and after electrochemical testing. The impact of both crystallite size and agglomeration on electrochemical performance were assessed. Figure 1

The Lithium-Sulfur (Li-S) battery has been a subject of intensive research in recent years due to its potential to provide much higher energy density and lower cost than the current state-of-the-art lithium-ion battery technology. However, both cell reaction active materials, sulfur and Li2S, are electronically non-conductive, which leads to the low electrode utilization and fast capacity fade during cell cycling. Large amounts of non-active carbon host materials must be added to boost sulfur electrode electronic conductivity for high rate discharge, which lowers the sulfur electrode specific energy density. Transition metal sulfides have been utilized as cathode material with high energy density and have been demonstrated to be rechargeable in lithium batteries. Many of these sulfides are electronic conductive with conductivity comparable to that of graphite and carbon black. Since they are also electrochemically active and can be cycled within the voltage window of sulfur battery, transition metal sulfides could be used as capacity contributing conductive cathode additive for sulfur batteries. We have investigated Titanium Disulfide (TiS2), Pyrite (FeS2) and Cupric Sulfide (CuS) as capacity-contributing conductive cathode additives to the sulfur electrodes in Li-S battery. Sulfur electrodes containing the metal sulfide additives showed improved power capability under high rate discharge. While the cyclability of the hybrid electrodes vary widely depending on the type of conductive additive, different and unique electrochemical behaviors were observed for hybrid electrodes with TiS2, FeS2 and CuS respectively. Improved coin cell cycling performance was observed with TiS2 as the cathode additive at 1C discharge rate. The TiS2 distribution within the hybrid electrode showed significant impact on cell cycling capacity fade. The mechanisms associated with the electrochemical performance of each chemical system are discussed.

Hollandites(OMS-2) are an intriguing class of energy storage materials with a tunnel structure permitting one-dimensional insertion and deinsertion of ions and small molecules along the c direction. Previous research demonstrated the ability to control crystal size of AgxMn8O16 by manipulation of Ag content over a range of 1.0 ≤ x ≤ 1.8 where lower Ag content was accompanied by small crystallite size and higher silver content demonstrated large crystallite size (Figure 1a-c) Notably, we recently observed a seven-fold increase in delivered capacity for Li/AgxMn8O16 electrochemical cells (160 versus 23 mAh/g) upon a seemingly small change in silver content (x ~1.1(L-Ag-OMS-2) and 1.6(H-Ag-OMS-2)) (Figure 1f). This led us to characterize the structure and defects of the silver hollandite nanorods through the combined use of local (atomic imaging, nanodiffraction, electron energy-loss spectroscopy) and bulk (synchrotron based x-ray diffraction, thermogravimetric analysis) techniques. Selected area diffraction and high resolution transmission electron microscopy show a structure consistent with that refined by synchrotron based XRD (NSLS II), however the Ag occupancy varies significantly even within neighboring channels. Both local (EELS) and bulk measurements (TGA) indicate a greater quantity of oxygen vacancies in L-Ag-OMS-2, resulting in lower average Mn valence relative to H-Ag-OMS-2. Electron energy loss spectroscopy shows a lower Mn oxidation state on the surface relative to the interior of the nanorods (Figure 1d, e). Considering Ag occupancy and oxygen vacancies, the average Mn valence can be estimated to be about Mn3.7+ for H-Ag-OMS-2 and Mn3.5+ for L-Ag-OMS-2 nanorods, respectively. The significance of the oxygen vacancies can be best understood through consideration of the crystallographic structure of silver hollandite. Silver hollandite has a body-centered tetragonal structure where the Ag is surrounded by eight MnO6 octahedra, forming a tunnel with a dimension of ~0.51 nm in the ab plane which extends along the [001] direction. Though there is a small gap (less than 0.06 nm) in the a or b direction, in the ab plane all directions are basically closed by MnO6 octahedra. Therefore, if the nanorod has no defects, the diffusion of Li ions in ab plane would be limited. The oxygen vacancies and MnO6 octahedra distortion may open the MnO6 octahedra walls, facilitating Li ion diffusion in the ab plane (Figure 1g, h). Thus, the higher capacity of the L-Ag-OMS-2 samples may be due to not only to the smaller crystallite size but also to the presence of more oxygen vacancies as compared to the H-Ag-OMS-2 samples. Thus the oxygen vacancies and MnO6 octahedra distortion are assumed to open the MnO6 octahedra walls, facilitating Li diffusion in the ab plane. In-situ transmission electron microscopy was used to probe lithium transport and phase evolution in silver hollandite, Ag1.63Mn8O16, nanowires by nanoscale imaging, diffraction and EELS spectroscopy. Additionally, the findings were further rationalized through density functional theory (DFT). These results indicate both crystallite size and surface defects are significant factors affecting battery performance. Figure 1 caption: Typical TEM bright field images from (a) H-Ag-OMS-2 and (b) L-Ag-OMS-2. (c) HRTEM image of L-Ag-OMS-2 nanorod. (d) Relative composition map calculated from EELS spectrum across L-Ag-OMS-2 nanorod. (e) HAADF of H-Ag-OMS-2 along [001], Ag (red) and Mn (green) indicated. (f) Discharge curves of Li/AgxMn8O16 (L-Ag-OMS-2, H-Ag-OMS-2) batteries. (g) Conceptual perspective along [001], with Ag (red), Mn (green), O (yellow), (h) with oxygen vacancy facilitating ab plane diffusion. Figure 1

Lithium-Sulfur (Li-S) battery has been a hot research topic currently due to its potential of combining high energy density and low cost together. In this work, we have investigated various transition metal sulfides (CuS, FeS2, TiS2, CoS2) as conductive additive to sulfur electrode in lithium-sulfur (Li-S) battery. We found that all metal sulfides additives enhanced the utilization of sulfur cathode at high rate discharge when compared with a sulfur-carbon composite electrode with equivalent sulfur volumetric loading. Systematic study suggests the reason for the enhancement is the activation of the polysulfide to Li2S2/Li2S conversion process that constitutes the second plateau in Li-S battery discharge. Besides, the results also indicate that the high electronic conductivity of transition metal sulfides could not fully account for the second plateau activation. Instead, it is found that the interaction between polysulfide and metal sulfides is actually helping the nucleation process of Li2S2/Li2S nucleation and deposition, and the level of this interaction also has profound influence on the cycle life and columbic efficiency of sulfur electrodes with transition metal sulfide additives. The results of this study will help to direct the design of non-carbon based conductive fillers for sulfur electrodes and enable the development of high power Li-S batteries.

With the state-of-art synchrotron-based X-ray and modern electron microscopy, the spatial resolution and measurement sensitivity have been significantly improved in analyzing materials’ nanostructure, by taking advantages of the high beam flux density or the source brightness. Associated with the ever brighter beam, it also brings the opportunity to investigate the beam effect to material structure modification, which is of significant interests in view of understanding the underlying physics, and it is also important to develop proper methodologies to use these state-of-the art probes to accurately characterize the intrinsic and extrinsic properties of materials. In our work, we performed x-ray imaging experiment on single crystalline Ag2VO2PO4 battery material sample with a 15 nm resolution using the recently commissioned x-ray imaging capability at the Hard X-ray Nanoprobe Beamline at the National Synchrotron Light Source II. Probe-induced electrochemical reaction was observed, which was revealed by the Ag reduction as well as diffusion and re-distribution of Ag. In order to better understand the probe-induced electrochemical reactions, we also performed imaging experiments with other imaging methods: white-beam microdiffraction, transmission x-ray microscopy (TXM), and transmission electron microscopy (TEM). These probes deliver different levels of radiation does and provides different pathways for probe-induced structural modification. This presentation will elaborate and quantify the probe-specific structural modifications.

The electrochemistry of an active material in a composite battery electrode may vary significantly depending on the selection of the type and amount of binder and conductive additives, as well as the preparation method used for the electrode. Only a few studies on the electrochemistry of individual particles have been reported where the lithiation or delithiation of individual particles of the pure active material in the absence of any additives was conducted. These types of studies provide the ability to interrogate the intrinsic properties of an active material directly without the complications of a composite electrode. Here we report the electrochemistry, conductivity, and visual changes associated with the electrochemical reduction of small individual particles of electrochemically active material. Our examination of individual small particles involves aggregates of several crystallites where the influence of grain boundaries must be considered. In addition to quantitative electrochemistry, the particles were characterized as a function of state of charge. For example, a nanoprobe system was utilized to determine the resistance of the particle. Different locations within an individual particle were measured and probed the local resistance changes as a function of particle reduction. Finally, correlation of the behavior of the individual particle was reconciled relative to bulk material electrochemical performance. This study will help elucidate the behavior of mesoscale energy storage systems.

The mission of the m2m EFRC is to understand and to ultimately control transport properties in complex battery systems with respect to multiple length scales, from molecular to mesoscale (m 2 m); to minimize heat and maximize work of electrical energy storage devices. In the context of energy storage the focus is on battery polarization (i.e. thermodynamic voltage - loaded voltage) under use conditions. The determination of the factors that contribute to and control polarization at the material, electrode, and cell level will be explored under the program. The organization of the center has been developed to facilitate investigation of the processes taking place over multiple length scales. Additionally, as electroactive materials in the battery system are in complex environments, including multiple solid as well as liquid interfaces, the behavior of the materials in complex environments will be probed in detail. Lastly, the impact of time and extended electrochemical activity (electron and ion flux) on the material and energy storage system behavior will be determined. The efforts of the Center are unified through the investigation of model materials where the initial focus includes examples of 1D, 2D and densely packed materials. Understanding the function of model materials from the atomic scale to the mesoscale to the systems level will reveal insight into the phenomena that control battery behavior, establishing the paradigms by which to explore and control other storage systems. Examples of the research results from the Center will be described.