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Conventional cathodes for Li-ion batteries (LIBs) are reaching their theoretical capacity limits. One way to meet the growing demands for high-capacity LIBs is by developing so-called Li-rich cathode materials that greatly benefit from additional capacities from anionic moieties in the structure. Li-rich materials are intrinsically subject to higher degrees of (de)intercalation, leaving the particles more prone to fractures and thus rapid capacity fade. Alkali-rich LiNaFeS₂ reversibly cycles with capacities exceeding 300 mAh g⁻¹, but its capacity fades faster than an isostructural material Li₂FeS₂. Using synchrotron-based transmission X-ray microscopy (TXM), we demonstrate that the capacity fade of LiNaFeS₂ stems from particle fractures in the first charge cycle. We improve the cycling performance of LiNaFeS₂ by means of cryomilling, which enhances capacity retention at cycle 50 by 76%. Through crystallographic and morphological characterization techniques, we confirm that cryomilling not only decreases particle and crystallite size while increasing microstrain but also prevents particles from fracturing. Cryomilling is a powerful tool to engineer nanoscale battery materials, and TXM allows the direct observation of morphological changes of the particles, which can be leveraged to develop next-generation cathode materials for LIBs.

Lithium–sulfur (Li–S) batteries offer high theoretical gravimetric capacities at low cost relative to commercial lithium-ion batteries. However, the solubility of intermediate polysulfides in conventional electrolytes leads to irreversible capacity fade via the polysulfide shuttle effect. Highly concentrated solvate electrolytes reduce polysulfide solubility and improve the reductive stability of the electrolyte against Li metal anodes, but reactivity at the Li/solvate electrolyte interface has not been studied in detail. Here, reactivity between the Li metal anode and a solvate electrolyte (4.2 M LiTFSI in acetonitrile) is investigated as a function of temperature. Though reactivity at the Li/electrolyte interface is minimal at room temperature, we show that reactions between Li and the solvate electrolyte significantly impact the solid electrolyte interphase (SEI) impedance, cyclability, and capacity retention in Li–S cells at elevated temperatures. Addition of a fluoroether cosolvent to the solvate electrolyte results in more fluoride in the SEI which minimizes electrolyte decomposition, reduces SEI impedance, and improves cyclability. A 6 nm AlF₃ surface coating is employed at the Li anode to further improve interfacial stability at elevated temperatures. The coating enables moderate cyclability in Li–S cells at elevated temperatures but does not protect against capacity fade over time.

Despite ongoing efforts to identify high-performance electrolytes for solid-state Li-ion batteries, thousands of prospective Li-containing structures remain unexplored. Here, we employ a semi-supervised learning approach to expedite identification of ionic conductors. We screen 180 unique descriptor representations and use agglomerative clustering to cluster ~26,000 Li-containing structures. The clusters are then labeled with experimental ionic conductivity data to assess the fitness of the descriptors. By inspecting clusters containing the highest conductivity labels, we identify 212 promising structures that are further screened using bond valence site energy and nudged elastic band calculations. Li3BS3 is identified as a potential high-conductivity material and selected for experimental characterization. With sufficient defect engineering, we show that Li3BS3 is a superionic conductor with room temperature ionic conductivity greater than 1 mS cm-1. While the semi-supervised method shows promise for identification of superionic conductors, the results illustrate a continued need for descriptors that explicitly encode for defects.

Development of next-generation battery technologies is imperative in the pursuit of a clean energy future. Toward that end, battery chemistries capable of multielectron redox processes are at the forefront of studies on Li-based systems to increase the gravimetric capacity of the cathode. Multielectron processes rely either on the iterative redox of transition metal cations or redox involving both the transition metal cations and the anionic framework. Targeting coupled cation and anion redox to achieve multielectron charge storage is difficult, however, because the structure–property relationships that govern reversibility are poorly understood. In an effort to develop fundamental understanding of anion redox, we have developed a materials family that displays tunable anion redox over a range of potentials that are dependent on a systematic modification of the stoichiometry. We report anion redox in the chalcogenide solid solution Li₂FeS_(2–y)Se_y, wherein the mixing of the sulfide and selenide anions yields a controllable shift in the high voltage oxidation plateau. Electrochemical measurements indicate that reversible multielectron redox occurs across the solid solution. X-ray absorption spectroscopy supports the oxidation of both iron and selenium at high states of charge, while Raman spectroscopy indicates the formation of Se–Se dimers in Li₂FeSe₂ upon Li deintercalation, providing insight into the charge mechanism of the Li-rich iron chalcogenides. Anion substitution presents direct control over the functional properties of multielectron redox materials for next generation battery technologies.

Conventional Li-ion cathodes store charge by reversible intercalation of Li coupled to metal cation redox. There has been increasing interest in new materials capable of accommodating more than one Li per transition-metal center, thereby yielding higher charge storage capacities. We demonstrate here that the lithium-rich layered iron sulfide Li₂FeS₂ as well as a new structural analogue, LiNaFeS₂, reversibly store ≥1.5 electrons per formula unit and support extended cycling. Ex situ and operando structural and spectroscopic data indicate that delithiation results in reversible oxidation of Fe²⁺ concurrent with an increase in the covalency of the Fe–S interactions, followed by reversible anion redox: 2 S²⁻/(S₂)²⁻. S K-edge spectroscopy unequivocally proves the contribution of the anions to the redox processes. The structural response to the oxidation processes is found to be different in Li₂FeS₂ in contrast to that in LiNaFeS₂, which we suggest is the cause for capacity fade in the early cycles of LiNaFeS₂. The materials presented here have the added benefit of avoiding resource-sensitive transition metals such as Co and Ni. In contrast to Li-rich oxide materials that have been the subject of so much recent study and that suffer capacity fade and electrolyte degradation issues, the materials presented here operate within the stable potential window of the electrolyte, permitting a clearer understanding of the underlying processes.

Recent research in medicinal chemistry suggests a correlation between an increase in the fraction of sp³ carbons, those bonded to four other atoms, in drug candidates with their improved success rate in clinical trials. As such, the development of robust and selective methods for the construction of C(sp³)-C(sp³) bonds remains a critical problem in modern organic chemistry. Owing to the broad availability of alkyl halides, their direct cross coupling—commonly known as cross-electrophile-coupling (XEC)—provides a promising route toward this objective. Such transformations circumvent the preparation of carbon nucleophiles used in traditional cross-coupling reactions as well as stability and functional group tolerance issues that commonly associate with these reagents. However, achieving high selectivity in C(sp³)-C(sp³) XEC remains a largely unmet challenge. Here, we employ electrochemistry to achieve the differential activation of alkyl halides by exploiting their disparate electronic and steric properties. Specifically, the selective cathodic reduction of a more substituted alkyl halide gives rise to a carbanion, which undergoes preferential coupling with a less substituted alkyl halide via bimolecular nucleophilic substitution (S_N2) to forge a new C–C bond. This transition-metal-free protocol enables efficient XEC of a variety of functionalized and unactivated alkyl electrophiles and exhibits improved chemoselectivity versus existing methods.

Mg-based batteries are an attractive next-generation energy storage chemistry due to the high natural abundance and inexpensive cost of Mg, along with the high theoretical energy density compared to that of conventional Li-ion chemistry. The greater energy density is predicated on a Mg metal anode, and pathways to achieving reversible Mg electrodeposition and stripping are reliant on the development of Mg electrolytes. Although Mg electrolyte chemistry has advanced significantly from the reactive Grignards of the 1920s to the carboranes of this decade, there remains significant challenges in correlating the Mg metal anode electrochemistry with the composition of the electrolyte salts as a result of the complicated interface of Mg metal and the electrolyte. To probe the effect of the interface on Mg electrodeposition, we turn to an electrolyte with a known solution-phase composition: the magnesium aluminum chloride complex (MACC) electrolyte. The MACC electrolyte requires electrolytic conditioning to support reversible Mg electrodeposition and stripping. Here, we show that a small concentration (2-5 mM) of Mg(HMDS)2 with respect to the MACC electrolyte salts suppresses Al3+ deposition and promotes reversible Mg electrodeposition and stripping in the first cycle. The significant effect of a small concentration of additive is attributed to changes to the electrode interface. The impact of the Mg interface on the observed electrochemical performance is discussed.

Next-generation batteries based on divalent working ions have the potential to both reduce the cost of energy storage devices and increase performance. Examples of promising divalent systems includ...

As Li-ion battery optimization approaches theoretical limits, interest has grown in designing next-generation batteries from low-cost earth-abundant materials. Mg–S batteries are promising candidates, exhibiting widespread abundance of elemental precursors and a relatively large theoretical energy density albeit at lower cell voltage. However, Mg–S batteries exhibit poor reversibility, in part due to interactions between dissolved polysulfides and the Mg anode. Herein, we employ electrochemical experiments using Ag₂S quasi-reference electrodes to probe the interactions between Mg anodes and dissolved polysulfides. We show that Mg²⁺ reduction (charging) is impeded in the presence of polysulfides, while Mg metal oxidation (discharging) remains facile. Large reduction overpotentials arise due to the formation of a passivation layer on the anode surface, likely composed primarily of MgS. The passivation layer is removed under oxidative conditions but quickly reforms during reduction. We discover that dissolved S8 influences the rate of MgS formation by shifting the polysulfide disproportionation equilibria. Shorter-chain polysulfides react more readily than longer-chain polysulfides at the Mg electrode, and thus, film formation is mediated by the electrochemical generation of shorter-chain polysulfide species.

Mg batteries are attractive next-generation energy storage systems due to their high natural abundance, inexpensive cost, and high theoretical capacity compared to conventional Li-ion based systems. The high energy density is achieved by electrodeposition and stripping of a Mg metal anode and requires the development of effective electrolytes enabled by a mechanistic understanding of the charge-transfer mechanism. The magnesium aluminum chloride complex (MACC) electrolyte is a good model system to study the mechanism as the solution phase speciation is known. Previously, we reported that minor addition of Mg(HMDS)2 to the MACC electrolyte causes significant improvement in the Mg deposition and stripping voltammetry resulting in good Coulombic efficiency on cycle one and, therefore, negating the need for electrochemical conditioning. To determine the cause of the improved electrochemistry, here we probe the speciation of the electrolyte after Mg(HMDS)2 addition using Raman spectroscopy, 27Al nuclear magnetic resonance spectroscopy, and 1H-29Si heteronuclear multiple bond correlation spectroscopy on MACC + Mg(HMDS)2 at various Mg(HMDS)2 concentrations. Mg(HMDS)2 scavenges trace H2O, but it also reacts with MACC complexes, namely, AlCl4-, to form free Cl-. We suggest that although both the removal of H2O and the formation of free Cl- improve electrochemistry by altering the speciation at the interface, the latter has a profound effect on electrodeposition and stripping of Mg.

We report a high-yield single-step method for synthesizing nitrogen-doped graphene nanostripes (N-GNSPs) with an unprecedentedly high percentage of pyridinic-type doping (>86% of the nitrogen sites), and investigate the performance of the resulting N-GNSPs as a lithium-ion battery (LIB) anode material. The as-grown N-GNSPs are compared with undoped GNSPs using scanning electron microscopy (SEM), Raman spectroscopy, X-ray photoelectron spectroscopy (XPS), helium ion-beam microscopy (HIM), and electrochemical methods. As an anode material we find that pyridinic-type N-GNSPs perform similarly to undoped GNSPs, suggesting that pyridinic sites alone are not responsible for the enhanced performance of nitrogen-doped graphene observed in previous studies, which contradicts common conjectures. In addition, post-mortem XPS measurements of nitrogen-doped graphene cycled as a lithium-ion battery anode are conducted for the first time, which reveal direct evidence for irreversible chemical changes at the nitrogen sites during cycling. These findings therefore provide new insights into the mechanistic models of doped graphene as LIB anodes, which are important in improving the anode designs for better LIB performance.

The effects of shear planes in perovskite materials have been studied in order to identify their role in the electrochemical behavior of Li+ intercalation hosts. These planes modulate the structural stability and ionic transport pathways and therefore play an intimate role in the characteristics and performance of shear compounds. Herein, two Nb-based compounds, NbO2F and Nb3O7F, were chosen as representative perovskite and shear derivatives respectively to investigate the role of crystallographic shear. A series of operando measurements, including X-ray diffraction and X-ray absorption spectroscopy, in conjunction with structural analysis, Raman spectroscopy, and detailed electrochemical studies identified the effect of shear planes. It was found that shear planes led to increased structural stability during Li+ (de)intercalation with shear layers being maintained, while perovskite layers were seen to degrade rapidly. However, disordering in the shear plane stacking introduced during delithiation ultimately led to poor capacity retention despite structural maintenance as Li+ diffusion channels are disrupted.

While the icosahedral closo-[B12H12]2– cluster does not display reversible electrochemical behavior, perfunctionalization of this species via substitution of all twelve B–H vertices with alkoxy orbenzyloxy (OR) substituents engenders reversible redox chemistry, providing access to clusters in the dianionic,monoanionic, and neutral forms. Here, we evaluated the electrochemical behavior of the electron-rich B12(O-3-methylbutyl)12 (1) cluster and discovered that a new reversible redox event that gives rise to a fourth electronic state is accessible through one-electron oxidation of the neutral species. Chemical oxidation of 1 with [N(2,4-Br2C6H3)3]•+ afforded the isolable[1] •+ cluster, which is the first example of an open-shell cationic B12 cluster in which the unpaired electron is proposed to be delocalized throughout the boron cluster core. The oxidation of 1 is also chemically reversible, where treatment of [1]•+ with ferrocene resulted in its reduction back to 1. The identity of [1]•+ is supported by EPR, UV-vis, multinuclear NMR (1H, 11B), and X-ray photoelectron spectroscopic characterization.

We evaluate hydrofluoroether (HFE) cosolvents with varying degrees of fluorination in the acetonitrile-based solvate electrolyte to determine the effect of the HFE structure on the electrochemical performance of the Li–S battery. Solvates or sparingly solvating electrolytes are an interesting electrolyte choice for the Li–S battery due to their low polysulfide solubility. The solvate electrolyte with a stoichiometric ratio of LiTFSI salt in acetonitrile, (MeCN)2–LiTFSI, exhibits limited polysulfide solubility due to the high concentration of LiTFSI. We demonstrate that the addition of highly fluorinated HFEs to the solvate yields better capacity retention compared to that of less fluorinated HFE cosolvents. Raman and NMR spectroscopy coupled with ab initio molecular dynamics simulations show that HFEs exhibiting a higher degree of fluorination coordinate to Li+ at the expense of MeCN coordination, resulting in higher free MeCN content in solution. However, the polysulfide solubility remains low, and no cr...

Magnesium batteries offer an opportunity to use naturally abundant Mg and achieve large volumetric capacities reaching over four times that of conventional Li-based intercalation anodes. High volumetric capacity is enabled by the use of a Mg metal anode in which charge is stored via electrodeposition and stripping processes, however, electrolytes that support efficient Mg electrodeposition and stripping are few and are often prepared from highly reactive compounds. One interesting electrolyte solution that supports Mg deposition and stripping without the use of highly reactive reagents is the magnesium aluminum chloride complex (MACC) electrolyte. The MACC exhibits high Coulombic efficiencies and low deposition overpotentials following an electrolytic conditioning protocol that stabilizes species necessary for such behavior. Here, we discuss the effect of the MgCl_2 and AlCl_3 concentrations on the deposition overpotential, current density, and the conditioning process. Higher concentrations of MACC exhibit enhanced Mg electrodeposition current density and much faster conditioning. An increase in the salt concentrations causes a shift in the complex equilibria involving both cations. The conditioning process is strongly dependent on the concentration suggesting that the electrolyte is activated through a change in speciation of electrolyte complexes and is not simply due to the annihilation of electrolyte impurities. Additionally, the presence of the [Mg_2(μ-Cl)_3·6THF]^+ in the electrolyte solution is again confirmed through careful analysis of experimental Raman spectra coupled with simulation and direct observation of the complex in sonic spray ionization mass spectrometry. Importantly, we suggest that the ∼210 cm^(–1) mode commonly observed in the Raman spectra of many Mg electrolytes is indicative of the C_(3v) symmetric [Mg_2(μ-Cl)_3·6THF]^+. The 210 cm^(–1) mode is present in many electrolytes containing MgCl_2, so its assignment is of broad interest to the Mg electrolyte community.

Mg–S batteries are attractive for next-generation energy storage because of their high theoretical capacity and low cost. The foremost challenge in Mg–S batteries is designing electrolytes that support reversible electrochemistry at both electrodes. Here, we target a solution-mediated reduction pathway for the S_8 cathode by tailoring the electrolyte solvent. Varying the solvent in Mg-based systems is complicated because of the active nature of the solvent in solvating Mg^(2+) and the complex dynamics of electrolyte–Mg interfaces. To understand the effect of the solvent on the S_8 reduction processes in the Mg–S cell, the magnesium–aluminum chloride complex (MACC) electrolyte was prepared in different ethereal solvents. Reversible Mg electrodeposition is demonstrated in the MACC electrolyte in several solvent systems. The electrodeposition overpotentials and current densities are found to vary with the solvent, suggesting that the solvent plays a noninnocent role in the electrochemical processes at the Mg interface. Mg–S cells are prepared with the electrolytes to understand how the solvent affects the reduction of S_8. A reductive wave is present in all linear-sweep voltammograms, and the peak potential varies with the solvent. The peak potential is approximately 0.8 V versus Mg/Mg^(2+), lower than the expected reduction potential of 1.7 V. We rule out passivation of the Mg anode as the cause for the low voltage peak potential, making processes at the S8 cathode the likely culprit. The ability to oxidize MgS with the MACC electrolyte is also examined, and we find that the oxidation current can be attributed to side reactions at the C–electrolyte interface.

Development of next generation batteries is predicated on the design and discovery of new, functional materials. Divalent cations are promising options that go beyond the canonical Li-based systems, but the development of new materials for divalent ion batteries is hindered due to difficulties in promoting divalent ion conduction. We have developed a family of cathode materials based on the divalent cation conductor ZnPS3. Substitution of V for Zn in the lattice concomitant with vacancy introduction yields isostructural but redox-active materials that can reversibly store Zn2 + in the vacancies. A range of voltammetry and galvanostatic cycling experiments along with x-ray photoelectron spectroscopy support that redox is indeed centered on V and that capacity is dependent on the V content. The voltage of the materials is limited by the irreversible decomposition of the [ P 2 S 6 ] 4 − polyanion above 1.4 V vs. Zn/Zn2 + . The reversible capacity before anion decomposition is limited to half the vacancies and is due to the relative ratios of oxidized and reduced V centers. Such observations provide useful design rules for cathode materials for divalent cation based battery technologies, and highlight the necessity for a holistic interpretation of physical and electronic structural changes upon cycling.

Conventional positive electrode materials for Li-ion technology utilize a Li+ intercalation mechanism charge-balanced by redox on transition metals within an oxide host lattice. Moving forward, multi-electron cathodes that gain capacity by contribution to the redox from the structural anions are of interest for the hybrid intercalation- and conversion-type chemistry during cycling. One such material, Li2RuO3, first studied by Goodenough and coworkers, exhibits high capacity but also a significant capacity loss after the first charge and long-term capacity fade. We suspect the capacity loss is due to structural distortions induced as the lattice accommodates the removal of Li+. Electrolyte additives with tailored chemistry can be an efficient and cost-effective way to stabilize structural changes and promote reversible cycling. Here, in situ, irreversibleelectrooxidation of soluble electrolyte additives at the cathode-electrolyte interface was investigated as a route to stabilizing the cathode surface. Electrooxidation causes dramatically improved capacity retention and stabilizes high-voltage oxidation processes in Li2RuO3. Through understanding how to stabilize structural distortions in Li-rich layered oxide cathodes, we hope to promote reversible cycling near theoretical capacity and target design principles for active electrolyte additives that enhance battery performance.

Li-S batteries are a promising alternative to conventional Li-ion batteries as Li-S batteries enable low-cost, lightweight, and high capacity cells. However, the polysulfide shuttle effect and Li reactivity with common organic solvents have limited commercialization of Li-S batteries. Highly concentrated electrolytes known as solvate electrolytes have been shown to limit polysulfide solubility in Li-S cells by reducing the ability of solvent molecules to solvate polysulfides through coordination to Li+.1 The challenges with using solvate electrolytes in electrochemical cells are associated with the high viscosity and low ionic conductivity of solvates. Addition of 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether (TTE) significantly decreases the solvate viscosity with slight improvement in ionic conductivity.1 TTE has been shown to suppress the polysulfide shuttle effect and is suggested to act as a nonsolvent for polysulfides. Although bulk electrolyte speciation is unchanged when the solvate is exposed to Li metal,2 the reactivity of the solvate electrolyte with and without TTE with Li metal has not been studied in detail. To study the reactivity, we evaluate the behavior of Li-S cells and Li metal at various temperatures in the solvate electrolyte with and without TTE. Increasing the temperature of the solvate electrolyte affects the equilibrium between free and coordinated MeCN and results in increased electrolyte decomposition and anode passivation. We demonstrate here that reactivity between the solvate electrolyte and the Li anode significantly impacts the cyclability and capacity retention in Li-S cells. The results indicate that TTE is necessary to stabilize the electrode/electrolyte interface and mitigate Li reactivity. Introducing a protecting layer onto the Li anode enables moderate cyclability but does not protect against decomposition over time. 1. Energy Environ. Sci. 2014, 7, 2697. 2. J. Am. Chem. Soc. 2014, 136, 13, 5039.

Mg metal is a promising alternative anode material that offers higher theoretical specific capacity than conventional Li-ion batteries (LIBs), and the high natural abundance of Mg makes it more economically appealing than other post-LIB anode materials. The greater energy density hinges on a Mg-metal anode, and reversible Mg electrodeposition and stripping require an effective Mg electrolyte. Various electrolyte systems that support reversible have been introduced, but many of them contain drawbacks, such as narrow electrochemical window, reactivity with electrode materials, or poor Coulombic efficiency. In addition, challenges remain in understanding the relationship between electrochemistry at the Mg anode and the electrolyte composition due to the complicated interface of Mg metal and the electrolyte. To probe the effect of the interface on Mg electrodeposition, an electrolyte with a known solution phase composition, the magnesium aluminum chloride complex (MACC) electrolyte, is explored. The MACC electrolyte undergoes electrolytic conditioning to support reversible Mg electrodeposition and stripping. During conditioning, free Cl- is released electrolytically while Al3+ is irreversibly deposited, and the concentration of the active species [Mg2(µ−Cl)3·6(THF)]+ increases, activating the MACC electrolyte. Here, we show that a small concentration of Mg(HMDS)2 to the MACC electrolyte suppresses Al3+ deposition and promotes reversible Mg electrodeposition and stripping on the first cycle. Such a drastic change from a small concentration suggests that changes are localized at the electrode-electrolyte interface. We show spectroscopically that Mg(HMDS)2 scavenges trace water in the solution. Spectroscopic results also suggest that Mg(HMDS)2 reacts with AlCl4 - in the MACC electrolyte to form free Cl-. Based on the spectroscopic and electrochemical results, we suggest that the formation of Cl- is the primary cause for improved behavior on cycle one, highlighting the role of Cl- in Mg deposition and stripping.

The development of a Mg ion based energy storage system could provide several benefits relative to today's Li-ion batteries, such as improved energy density. The electrolytes for Mg batteries, which are typically designed to efficiently plate and strip Mg, have not yet been proven to work with high voltage cathode materials that are needed to achieve high energy density. One possibility is that these electrolytes are inherently unstable on porous electrodes. To determine if this is indeed the case, the electrochemical properties of a variety of electrolytes were tested using a porous carbon coating on graphite foil and stainless steel electrodes. It was determined that the oxidative stability limit on these porous electrodes is considerably reduced as compared to those found using polished platinum electrodes. Furthermore, the voltage stability was found to be about 3 V vs. Mg metal for the best performing electrolytes. These results imply the need for further research to improve the stability of Mg electrolytes to enable high voltage Mg batteries.

Mg batteries are an attractive alternative to Li-based energy storage due to the possibility of higher volumetric capacities with the added advantage of using sustainable materials. A promising emerging electrolyte for Mg batteries is the magnesium aluminum chloride complex (MACC) which shows high Mg electrodeposition and stripping efficiencies and relatively high anodic stabilities. As prepared, MACC is inactive with respect to Mg deposition; however, efficient Mg electrodeposition can be achieved following an electrolytic conditioning process. Through the use of Raman spectroscopy, surface enhanced Raman spectroscopy, ^(27)Al and ^(35)Cl nuclear magnetic resonance spectroscopy, and pair distribution function analysis, we explore the active vs inactive complexes in the MACC electrolyte and demonstrate the codependence of Al and Mg speciation. These techniques report on significant changes occurring in the bulk speciation of the conditioned electrolyte relative to the as-prepared solution. Analysis shows that the active Mg complex in conditioned MACC is very likely the [Mg_2(μ–Cl)_3·6THF]^+ complex that is observed in the solid state structure. Additionally, conditioning creates free Cl^– in the electrolyte solution, and we suggest the free Cl^– adsorbs at the electrode surface to enhance Mg electrodeposition.

We propose a nanostructured Mn-doped V2O5 lithium-ion battery cathode material that facilitates cathodic charge transport. The synthesis strategy uses a layered compound, vanadium(III) jarosite, as the precursor, in which the Mn2+ ions are doped uniformly between the vanadium oxide crystal layers. Through a two-step transformation, the vanadium jarosite was converted into Mn2+-doped V2O5. The resulting aliovalent doping of the larger Mn cations in the modified V2O5 structure increases the cell volume, which facilitates diffusion of Li+ ions, and introduces oxygen vacancies that improve the electronic conductivity. Comparison of the electrochemical performance in Li-ion batteries of undoped and the Mn2+-doped V2O5 hierarchical structure made from layered vanadium jarosite confirms that the Mn-doping improves ion transport to give a high cathodic columbic capacity (253 mAhg–1 at 1C, 86% of the theoretical value, 294 mAhg–1) and excellent cycling stability.

International audience; We report the use of X-ray diffraction in combination with computed tomography to provide quantitative information of a coin cell Li-ion battery and a commercial Ni/MH AAA battery for the first time. This technique allows for structural information to be garnered and opens up the possibility of tracking nanostructural changes in operandi. In the case of the cylindrically wound, standard AAA Ni/MH cell, we were able to map all the different phases in the complex geometry, including anode, cathode, current collector and casing, as well as amorphous phases such as the binder and separator. In the case of a Li-ion coin cell battery, we show how the X-ray diffraction tomography data can be used to map crystal texture of the LiCoO2 particles over the cathode film. Our results reveal that the LiCoO2. microparticles show a high degree of preferred orientation, but that this effect is not homogenous over the film, which may affect the electrochemical properties. (C) The Author(s) 2015. Published by ECS. All rights reserved

We evaluate hydrofluoroether (HFE) cosolvents with varying degrees of fluorination in the acetonitrile-based solvate electrolyte to determine the effect of the HFE structure on the electrochemical performance of the Li-S battery. Solvates or sparingly solvating electrolytes are an interesting electrolyte choice for the Li-S battery due to their low polysulfide solubility. The solvate electrolyte with a stoichiometric ratio of LiTFSI salt in acetonitrile, (MeCN)

Garnet-type electrolytes with high ionic conductivity and chemical stability against lithium metal show promise as solid-state electrolytes for lithium-ion batteries. However, a high concentration of pores and grain boundaries in air-processed polycrystalline electrolytes makes them prone to dendrite formation and reaction with atmospheric moisture, leading to electrochemical and mechanical instability. In this work, we illustrate that abnormal grain growth, an often-avoided phenomenon in conventional ceramic processing, can be employed as a unique approach to obtain extraordinarily large oligo crystals for minimal grain boundaries. Here we report a straightforward approach to develop a robust Ga-doped garnet, Li_(6.25)Ga_(0.25)La_3Zr_2O_(12) (LGLZO) electrolyte with conventional solid-state sintering in air. By preparing nanopowders without agglomeration through ball milling and freeze drying, we can control the microstructure of air-sintered electrolytes for desirable properties of a high density (98% of theoretical density) and an average grain size of 460 µm. The robust air-processed LGLZO electrolytes demonstrate high ionic conductivity, stability in air, and mechanical robustness relative to other garnet electrolytes offering promise as cost- and performance-competitive solid-state electrolytes for safe lithium-ion batteries.

Due to their significantly higher volumetric capacity, natural abundance, and decreased cost compared to Li metal, Zn, Mg, and Ca rechargeable metal batteries in nonaqueous electrolyte solutions have been the subject of extensive research and development. In this study, we employ the electrochemistry and computational simulation to examine the reversible electrodeposition processes of multivalent metals in nonaqueous electrolytes. Cyclic voltammetry (CV) obtained from Zn electroplating/stripping at an ultramicroelectrode (UME) shows that current density and scan rate are independent as predicted from a simple electron transfer process. However, CVs obtained from Mg and Ca deposition/stripping processes at an UME displays an inverse dependence between current density and scan rate. COMSOL simulations suggest that Zn deposition is governed by a one−step two−electron (E) transfer process while Mg and Ca plating requires a chemical step prior to electron transfer step, suggesting a chemical−electrochemical (CE) mechanism.

The electrochemical performance of alternative anode materials for Li-ion batteries is often measured using composite electrodes consisting of active material and conductive carbon additives. Cycling of these composite electrodes at low voltages demonstrates charge storage at the operating potentials of viable anodes, however, the conductive carbon additive is also able to store charge in the low potential regime. The contribution of the conductive carbon additives to the observed capacity is often neglected when interpreting the electrochemical performance of electrodes. To provide a reference for the contribution of the carbons to the observed capacity, we report the charge storage behavior of two common conductive carbon additives Super P and Ketjenblack as a function of voltage, rate, and electrolyte composition. Both carbons exhibit substantial capacities after 100 cycles, up to 150 mAh g^(−1), when cycled to 10 mV. The capacity is dependent on the discharge cutoff voltage and cycling rate with some dependence on electrolyte composition. The first few cycles are dominated by the formation of the SEI followed by a fade to a steady, reversible capacity thereafter. Neglecting the capacity of the carbon additive can lead to significant errors in the estimation of charge storage capabilities of the active material.

Li–S batteries are a promising next-generation battery technology. Due to the formation of soluble polysulfides during cell operation, the electrolyte composition of the cell plays an active role in directing the formation and speciation of the soluble lithium polysulfides. Recently, new classes of electrolytes termed “solvates” that contain stoichiometric quantities of salt and solvent and form a liquid at room temperature have been explored due to their sparingly solvating properties with respect to polysulfides. The viscosity of the solvate electrolytes is understandably high limiting their viability; however, hydrofluoroether cosolvents, thought to be inert to the solvate structure itself, can be introduced to reduce viscosity and enhance diffusion. Nazar and co-workers previously reported that addition of 1,1,2,2-tetrafluoroethyl 2,2,3,3-tetrafluoropropyl ether (TTE) to the LiTFSI in acetonitrile solvate, (MeCN)_2–LiTFSI, results in enhanced capacity retention compared to the neat solvate. Here, we evaluate the effect of TTE addition on both the electrochemical behavior of the Li–S cell and the solvation structure of the (MeCN)_2–LiTFSI electrolyte. Contrary to previous suggestions, Raman and NMR spectroscopy coupled with ab initio molecular dynamics simulations show that TTE coordinates to Li^+ at the expense of MeCN coordination, thereby producing a higher content of free MeCN, a good polysulfide solvent, in the electrolyte. The electrolytes containing a higher free MeCN content facilitate faster polysulfide formation kinetics during the electrochemical reduction of S in a Li–S cell likely as a result of the solvation power of the free MeCN.

Nanostructured uniformly Mn-doped V2O5 Li on battery cathode material is prepared via layered VIII jarosite as precursor, which is obtained by microwave-assisted solvothermal reaction of VOSO4, Mn(OAc)2, and glucose in a H2O/1-hexanol emulsion containing cetyltrimethylammoniumbromide (sealed vial, 195 °C, 1 h) followed by vacuum annealing (900 °C, 1 h) and firing in air (400 °C, 1 h) to convert V2O3 into V2O5.

Redox active electrode materials derived from organic precursors are of interest for use as alternative cathodes in Li batteries due to the potential for their sustainable production from renewable resources. Here, a series of organic networks that either contain triazine units or are derived from triazine-containing precursors are evaluated as cathodes versus Li metal anodes as possible active materials in Li batteries. The role of the molecular structure on the electrochemical performance is studied by comparing several materials prepared across a range of conditions allowing control over functionality and long-range order. Well-defined structures in which the triazine unit persists in the final material exhibit very low capacities at voltages relevant for cathode materials (

Next-generation batteries offer the promise of higher performance using materials that are less expensive and more abundant than those in convention Li-ion cells. From a fundamental point-of-view, the new chemistries involved in these also systems allow for exploration of the unknown and generation of new, fundamental knowledge. To that end, this talk will explore the local structure of the active cations in electrolyte solutions for Li-S and Mg batteries and the effect of this structure on the charge storage reactions and ultimately on the battery metrics. The first part of the talk will discuss the emerging solvate electrolytes as possible electrolyte solutions for Li-S batteries. The solvate electrolytes are characterized by extremely high quantities of salt resulting in interesting electrochemistry at the S cathode. Because the behavior of the electrolyte solution is governed by the complexes in the solution, we will explore the local solvation structure of the active cation, Li+, and how it is affected by the addition of what are commonly thought to be innocuous cosolvents. The addition of the cosolvents to the solvate electrolyte results in subtle but important changes in the Li+ solvation structure that affect the kinetics of the S reduction. The second part of the talk will focus on electrolytes for Mg batteries. We will explore the local structure of Mg2+ in the seemingly simple MgCl2 + AlCl3 in THF electrolyte known as the magnesium aluminum chloride complex (MACC) electrolyte. The importance of Mg speciation in active electrolytes and the effect these complexes have on the charge transfer processes at the electrode-electrolyte interface will be addressed. We will also explore the role of chloride in facilitating the electrodeposition of divalent Mg2+ and the implications of using halogenated electrolytes in full cells. Figure 1

Lithium-sulfur (Li-S) batteries are a promising next generation energy storage technology owing to their high theoretical energy density (2,500 Wh/kg) and the abundance, non-toxicity, and low cost of sulfur. However, Li-S systems face a number of challenges including degradation of the Li anode, electrolyte consumption, and dissolution of soluble polysulfide intermediates from the cathode, all of which cause fast capacity fade and poor cyclability. One approach to solving these problems is the use of sparingly solvating electrolytes, which allows for control of polysulfide solubility and thus the prevention of these degradation modes while maintaining good ionic conductivity. One promising electrolyte is a combination of bis(trifluoromethane)sulfonimide lithium salt (LiTFSI) in a mixture of acetonitrile (ACN) and 1,1,2,2-tetrafluoroethyl 2,2,3,3-tetrafluoropropyl ether (TTE). It is theorized that dilution of the solvate electrolyte with TTE improves performance by decreasing viscosity and allowing TTE to take the place of some of the ACN in the solvation shell of Li, freeing up the ACN to solubilize polysulfides and improve cathode reaction kinetics. The solvation shell of Li influences the electrolyte viscosity, which is related to Li ion mobility, and the Li ion desolvation energy, which controls the charge transfer between Li in the solvent and the sulfur electrode. However, a better understanding of the local environment of the Li ion and the role of TTE in this system is needed to tailor the electrolyte properties for optimal battery performance. Additionally, investigating the molecular interactions in this electrolyte system will provide insight into how fluorinated electrolytes minimize the reaction between the Li anode and polysulfides and limit the polysulfide shuttle between electrodes; both of which are believed to lead to capacity loss. See et al. used in situ Raman spectroscopy and nuclear magnetic resonance (NMR) spectroscopy to identify the average coordination number of Li ions, and ab initio molecular dynamics (AIMD) simulations have shed light on the solvation shell structure. However, these techniques are unable to directly measure the coordination lengths between Li and species in the first solvation shell. In this work, we perform experimental verification of the solvation shell structure using pair distribution function (PDF) measurements employing both hard X-rays (Advanced Photon Source) and neutrons (Oak Ridge National Laboratory, Spallation Neutron Source) as a probe. While X-rays interact with the electron cloud surrounding an atom, neutrons interact with atomic nuclei, thus these techniques provide complimentary information, as neutrons are more sensitive to light elements. Neat electrolyte (without TTE) is measured as a function of LiTFSI concentration to determine the concentration at which solvate complexes form. The solvate electrolyte, (ACN)2-LiTFSI, is diluted to different levels with TTE to determine how the TTE molecule interacts with the first solvation shell of Li. PDF obtained from experimental data are compared to simulated patterns generated from the results of AIMD simulations both to aid in data analysis and to contribute to the model to help improve its predictive capability for use in studying yet to be developed electrolytes.

The Li-S system offers a tantalizing battery for electric vehicles and renewable energy storage due to its high theoretical capacity of 1675 mAh g-1and its employment of abundant and available materials. One major challenge in this system stems from the formation of soluble polysulfides during the reduction of S8, the active cathode material, during discharge. The ability to deploy this system hinges on the ability to control the behavior of these polysulfides by containing them in the cathode and allowing for further redox. Here, we exploit the high surface areas and good electrical conductivity of mesoporous carbons (MC) to achieve high sulfur utilization while functionalizing the MC with sulfur (S-MC) in order to modify the surface chemistry and attract polysulfides to the carbon material. S-MC materials show enhanced capacity and cyclability trending as a function of sulfur functionality, specifically a 50% enhancement in discharge capacity is observed at high cycles (60-100 cycles). Impedance spectroscopy suggests that the S-MC materials exhibit a lower charge-transfer resistance compared with MC materials which allows for more efficient electrochemistry with species in solution at the cathode. Isothermal titration calorimetry shows that the change in surface chemistry from unfunctionalized to S-functionalized carbons results in an increased affinity of the polysulfide intermediates for the S-MC materials, which is the likely cause for enhanced cyclability. © 2014 American Chemical Society.

The lithium–sulfur (Li–S) system is an attractive candidate to replace the current state-of-the-art lithium-ion battery due to the promising theoretical charge capacity of 1675 mA h/g and energy density of 2500 Wh/kg; however, the dissolution of intermediate polysulfides into the organic liquid electrolyte during cycling hinders its practical realization. We report the synthesis of mesoporous graphene–silica composite (m-GS) as a supporting material of sulfur for Li–S batteries. The ordered porous silica structure was synthesized parallel to functionalized graphene sheets (FGSs) through the ternary cooperative assembly of the graphene, silica, and block copolymer precursors. The well-defined, unique mesoporous structure integrates the electronic conductivity of graphene and the dual functions of silica as a structure building block and in situ polysulfide ab-/ad-sorbing agent to give a Li–S battery that has both good retention ability of polysulfides and good rate capability.

Nonprecious transition metal nitrides have attracted considerable attention as an alternative catalyst to noble metals for electrochemical reactions. Titanium nitride (TiN), in particular, is an interesting material that exhibits excellent thermal, chemical, and mechanical stability, electrical conductivity, and in particular electrocatalytic activity. TiN is often prepared by the nitridation of titanium oxide using gaseous ammonia or hydrazine as a nitrogen source. This high temperature synthesis, however, gives a material with low surface area, which is unfavorable for its application in heterogeneous electrocatalysis. The shape and size of the assembly, and thus the resulting g-CN materials, can be tailored simply by using different precipitation temperatures, solvents, and comonomers. Furthermore, the assembly develops unique nanostructures during the polycondensation without losing the pristine macrostructures.

Conversion reaction cells afford the ability to explore new energy storage paradigms that transcend the dogma of small, low‐charge cations essential to intercalative processes. Here we report the use of earth‐abundant and green calcium and sulfur in unprecedented conversion reaction Ca–S primary cells. Using S‐infiltrated mesoporous carbon (abbreviated S@meso‐C) cathodes, we achieve discharge capacities as high as 600 mAh g^(−1) (S basis) within the geometry Ca|Ca(ClO_4)_2/CH_3CN|S@meso‐C, at a discharge rate of C/3.5. The electrolyte system in the Ca–S battery is of paramount importance as the solid electrolyte interface (SEI) formed on the Ca anode limits the capacity and stability of the cell. We determine that 0.5 M Ca(ClO_4)_2 in CH_3CN forms an SEI that advantageously breaks down under anodic bias to allow oxidation of the anode. This same SEI, however, exhibits high impedance which increases over time at open circuit limiting the shelf life of the cell.

We present a versatile strategy to prepare a range of nanostructured poly(styrene)-block-poly(2-vinyl pyridine) copolymer particles with tunable interior morphology and controlled size by a simple solvent exchange procedure. A key feature of this strategy is the use of functional block copolymers incorporating reactive pyridyl moieties which allow the absorption of metal salts and other inorganic precursors to be directed. Upon reduction of the metal salts, well-defined hybrid metal nanoparticle arrays could be prepared, whereas the use of oxide precursors followed by calcination permits the synthesis of silica and titania particles. In both cases, ordered morphologies templated by the original block copolymer domains were obtained.

Here, we propose thiol-based electrolyte additives (biphenyl-4,4’-dithiol (BPD)) to enhance the capacity retention of lithium-sulfur batteries. In-situ Raman and UV-Vis spectroscopy are used to investigate the effect of the additive on the sulfur reduction mechanism. Raman spectroscopy shows that long chain polysulfides (S8 2-) are formed via S8 ring opening in the first reduction process at ~2.4 V vs Li/Li+ and short chain polysulfides such as S4 2-, S4 -, S3 ․ - and S2O4 2- are observed with continued discharge at ~2.0 V vs Li/Li+ in the second reduction process. In the Kinetic study, rate constants obtained for the appearance and disappearance polysulfide species show that short chain polysulfides are directly formed from S8 decomposition. The polysulfide oxidation and reduction is quasi-reversible. With the BPD additive, an additional reduction process is observed at ~2.1 V vs Li/Li+. This reduction is associated with the formation of BPD-polysulfide complexes. The BPD-polysulfide complexes form at ~2.1 V followed by the formation of short chain polysulfides upon further discharge. The reduction of these complexes is reversible during the charge process. The BPD additive inhibits the formation rate of short chain polysulfides, suggesting that there is a strong interaction between BPD and short chain polysulfides. In-situ UV-Vis spectroscopy shows that the polysulfide solubility decreases in the presence of the BPD additive and forms thiol-polysulfide complexes during the cycling. The (-)ESI-MS shows the formation of BPD-S and BPD-S2 and BPD-S3, suggesting that BPD interacts with short chain polysulfides. The decomposition of the thiol-based additive was found during the battery cycling and resulted in a dense and smooth SEI film on the Li anode. References: (1) Zhang, S.S. et al J. Power Sources 2013, 231, 153-162. (2) Barchasz, C. et al., Anal. Chem. 2012, 84, 3973. (3) Cuisinier, M. et al., J. Phys. Chem. Lett. 2013, 4, 3227. (4) Hagen, M. et al., J. Electrochem. Soc. 2013, 160, A1205.

Magnesium batteries are theoretically capable of achieving up to five times higher volumetric energy densities compared to Li ion batteries. The enhanced volumetric capacity is enabled by the use of a Mg metal anode that undergoes Mg electrodeposition and stripping processes during battery cycling. Fortunately, Mg electrodeposition largely results in morphologically smooth surfaces that bypass the risk of battery shorts due to dendrite formation. The challenge, therefore, lies in the development of electrolyte solutions from which Mg electrodeposition and stripping readily occurs. Mg metal is highly reactive and thus precludes the use of conventional battery electrolyte components such as carbonates. Currently, most electrolyte solutions from which Mg electrodeposition and stripping occur almost always contain chloride including the traditional Grignard and organohaloaluminate electrolytes in addition to the more recently developed all-inorganic magnesium aluminum chloride complex (MACC) electrolyte. Here we describe a multimodal approach to explore the activity of chloride in Mg electrolyte solutions. The MACC electrolyte solution is taken as a model electrolyte system upon which a variety of spectroscopic techniques are applied. The benefit of MACC lies in the electrolytic conditioning process that is required to activate the electrolyte providing both an “off” state and “on” state from which relative changes can be elucidated. Raman spectroscopy, 27Al NMR, 35Cl NMR, and pair distribution function analysis reveal the change in the Mg and Al related complexes in the as-prepared (off) versus conditioned (on) electrolyte solution. The Al concentration drops as the electrolyte is conditioned due to the irreversible Al plating occurring during the initial conditioning. The drop in Al concentration is accompanied by an increase in Mg concentration due to oxidation of the Mg counter electrode. The Mg complexes in both the as-prepared and conditioned electrolyte, however, are confirmed to be the elusive Mg dimer complex [Mg2(μ-Cl)3·6THF]+ commonly implicated as the active Mg complex. The Mg dimer is a common moiety found in the solid state crystal structures of dried Mg electrolytes, however, this is the first time the Mg dimer has been characterized in solution. The fact that the dimer is present in both the inactive and active electrolyte suggests that its mere presence is not the cause for increased activity. Instead, the formation of free chloride in the MACC electrolyte is responsible for enhanced Mg electrodeposition and stripping as observed by surface enhanced Raman spectroscopy. The ability of chloride to promote Mg electrodeposition and stripping has important implications for the development of Mg battery electrolytes and cathode materials. Recently, the field has been moving away from electrolytes that contain chloride due to the inherent instability of oxide cathodes with chloride-containing electrolytes. The role of chloride in the Mg electrodeposition and stripping processes must be elucidated further to determine if alternative enhancing agents can be designed.