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The severe capacity fade of lithium-ion cells with silicon-dominant anodes has hindered their widescale commercialization. In this work, we link cell capacity fade to the heterogeneous physicochemical evolution of silicon anodes during battery cycling. Through a multilength scale characterization approach, we demonstrate that silicon particles near the anode surface react differently from those near the copper current collector. In particular, near the anode surface we find an amorphized wispy silicon encased in a highly fluorinated matrix of electrolyte-reduction products. In contrast, closer to the current collector, the silicon retains more of its initial morphology and structure, suggesting the presence of isolated particles. The results show that the accessibility of active silicon to lithium ions varies across the anode matrix. Material and cell designs, which minimize electrode expansion resulting from the in-filling of pores with the solid electrolyte interphase (SEI), are needed to enhance anode homogeneity during the electrochemical cycling.

High-energy batteries for automotive applications require cells to endure well over a decade of constant use, making their long-term stability paramount. This is particularly challenging for emerging cell chemistries containing silicon, for which extended testing information is scarce. While much of the research on silicon anodes has focused on mitigating the consequences of volume changes during cycling, comparatively little is known about the time-dependent degradation of silicon-containing batteries. Here we discuss a series of studies on the reactivity of silicon that, collectively, paint a picture of how the chemistry of silicon exacerbates the calendar aging of lithium-ion cells. Assessing and mitigating this shortcoming should be the focus of future research to fully realize the benefits of this battery technology. Silicon-containing batteries are increasingly becoming a reality in the mass market, but their calendar aging behaviours have received comparatively little attention. Researchers from the Silicon Consortium Project discuss the issues surrounding the calendar lifetime of silicon anodes for lithium-ion batteries.

Simply mixing several lithium salts in one electrolyte to obtain blended salt electrolytes has been demonstrated as a promising strategy to formulate advanced electrolytes for lithium metal batteries (LMBs) and lithium-ion batteries (LIBs). In this study, we report the use of dual-salt electrolytes containing lithium hexafluorophosphate (LiPF6) and lithium difluorophosphate (LiDFP) in ethylene carbonate/ethyl methyl carbonate (EC/EMC) mixture and tested them in layered high-nickel LIB cells. LiNi0.94Co0.06O2 was synthesized through a coprecipitation method and was used as a representative high-nickel cathode for the U.S. DOE realizing next-generation cathode (RNGC) deep dive program. The ionic conductivity of dual-salt electrolytes can be maintained by controlling the amount of LiDFP. Techniques including 1H Nuclear Magnetic Resonance (NMR), X-ray photoelectron spectroscopy (XPS), inductively coupled plasma-mass spectrometry (ICP-MS), and differential voltage analysis (DVA) were used to understand the improved performance. The multifaceted benefits of using the dual-salt electrolytes include (1) reduced transesterification, (2) formation of a stable cathode electrolyte interface, and (3) mitigation of cathode degradation at high voltages, especially stabilization of oxide particles during the H2 ↔ H3 transformation.

Coin cells are used extensively as test devices in battery research for evaluation of new materials and optimization of cycling protocols. In this study, in situ X-ray diffraction profilometry is used to characterize spatial distribution of the active materials, lithiation, and phase distribution in electrodes of NCM523/graphite coin cells. The X-ray data indicate uneven areal compression of the electrode assembly in such cells, which we trace to a specific design feature that leads to elastic deformation of a metal spacer. Steep lithiation gradients observed in the electrodes imply radially-dependent resistivity, for which uneven compression of the separator is a likely cause. Electrochemical model calculations suggest that variable porosity of the polymer separator would account for the salient features of spatial profiles observed in these coin cells.

Instability of nickel-rich layered oxides at high voltages is an impediment to their wider use in Li-ion batteries. HF generated via LiPF6 hydrolysis accelerates corrosion, further destabilizing th...

Increasing the energy densities of Li-ion batteries necessitates operation of layered lithiated oxide cathodes at potentials exceeding 4 V vs Li/Li+. When continually exposed to such high potential...

Safe, fast, and energy efficient cycling of lithium ion batteries is desired in many practical applications. However, modeling studies predict steep Li+ ion gradients in the electrodes during cycling at the higher currents. Such gradients introduce heterogeneities in the electrodes, which make it difficult to predict cell lifetimes as different portions of the cell age at different rates. There is a dearth of experimental methods to probe these concentration gradients across the depth of the electrode. Here we use spatially resolved energy dispersive X-ray diffraction to obtain a “movie” of lithiation and delithiation in different sections of the cell and quantify lithium gradients that develop in a porous graphite electrode during cycling at a 1C rate. Inhomogeneity in the total Li content, and in the individual ordered LixC6 phases formed during lithium insertion into (and extraction from) the graphite, has been observed in an operando fashion. The complex dynamics of lithium-staging in graphite with the distinct front propagation of phase changes have been characterized and new features of these dynamics are highlighted here. As large Li+ ion gradients contribute to cell polarization, our results suggest that Li plating conditions can be met near the graphite electrode surface, even when the cell is charged at a moderate (1C) rate.

Fast charging of Li-ion batteries would ease consumer concerns regarding refueling time of electric vehicles. In this series of articles, we are systematically examining the effects of high currents flowing through the cell. Here we consider open-circuit relaxation dynamics for cell voltage and individual electrode potentials after abrupt termination of steady-state charging currents (1-6C) or short current pulses (< 30 s) of either polarity (to 16C). We demonstrate that dispersive kinetics observed after these current perturbations become faster for higher currents applied before the rest period. Our observations indicate that the voltage relaxation behaviors (i) depend on the current during charge, and less so on the state of charge, (ii) display universal stretched-exponential kinetics, (iii) can be induced by a short current pulse, (iv) require a minimum amount of charge transfer during the pulse, and (v) originate mainly from the oxide cathode. Trap controlled Li+ ion transport through a partially disordered oxygen-depleted subsurface layer in the cathode is suggested as a possible origin for the relaxation behavior. The slow multidecadal responses to high currents can cause the nonlinearities observed during rapid charging of the electrochemical cells, reported in Part 2 of this series.

The high capacity of silicon motivates its use as anode material for Li-ion batteries. While such Si-based electrodes are typically processed from aqueous slurries, elemental silicon is highly susceptible to hydrolysis, yielding flammable hydrogen gas as a byproduct. This gassing can present numerous safety and quality concerns for scaling up of the production. In this study we describe a method to quantify the volume of gases generated using the Archimedes principle. We show that the gas volumes are affected by various factors, which include the characteristics of the electrode slurry and attributes (particle size, surface coatings) of the silicon powders. A catalytic effect on gas evolution is observed when a lithiated polycarboxylate binder is present in the solution. On the other hand, negligible gas generation is observed in electrode slurries containing the N-methyl-2-pyrrolidone (NMP) solvent, which could be considered as an alternative to the water-based processes presently under consideration. Our study can be used as a guide for the development of slurry mixtures that can mitigate the safety concerns associated with the silicon-electrode fabrication process.

Electrolyte additives are known to improve the performance of lithium-ion cells. In this work we examine the performance of Li 1.03 Ni 0.5 Mn 0.3 Co 0.3 O 2 -graphite (NMC532/Gr) cells containing combinations of lithium bis(oxalate)borate (LiBOB), vinylene carbonate (VC), trivinylcyclotriboroxane (tVCBO), prop-1-ene-1,3-sultone (PES), phenyl boronic acid ethylene glycol ester (PBE), tris(trimethylsilyl) phosphite (TMSPi), triethyl phosphite (TEPi), and lithium difluoro(oxalate)borate (LiDFOB) added to our baseline (1.2 M LiPF 6 in EC:EMC, 3:7 w/w) electrolyte. In order to rank performance of the various electrolytes, we developed two separate figures of merit (FOM), which are based on the energy retention and power retention of the cells. Using these two metrics in conjunction, we show that only one of the fifteen electrolyte formulations tested significantly outperforms the baseline electrolyte: this electrolyte contains the 0.25 wt% tVCBO + 1 wt% TMSPi additive mix. Little correlation was observed between the FOMs for energy retention and power retention, which indicates that the mechanisms that govern these performance parameters are likely independent of each other. Our FOM approach has general applicability and can be used to develop electrolyte and electrode formulations that prolong the life of lithium-ion batteries.

Li 1.03 (Ni 0.5 Mn 0.3 Co 0.2 ) 0.97 O 2 (NMC)-based coin cells containing the electrolyte additives vinylene carbonate (VC) and tris(trimethylsilyl)phosphite (TMSPi) in the range of 0–2 wt% were cycled between 3.0 and 4.4 V. The changes in capacity at rates of C/10 and C/1 and resistance at 60% state of charge were found to follow linear-with-time kinetic rate laws. Further, the C/10 capacity and resistance data were amenable to modeling by a statistics of mixtures approach. Applying physical meaning to the terms in the empirical models indicated that the interactions between the electrolyte and additives were not simple. For example, there were strong, synergistic interactions between VC and TMSPi affecting C/10 capacity loss, as expected, but there were other, more subtle interactions between the electrolyte components. The interactions between these components controlled the C/10 capacity decline and resistance increase.

Prolonged decomposition of electrolytes forming a thick and unstable solid-electrolyte interphase (SEI) continues to be a major bottleneck in designing sodium-ion batteries (SIBs). We have carried out quantum chemistry simulations to investigate the fundamental mechanisms of reduction-induced decomposition of electrolyte solvents in the vicinity of a sodium ion. Kinetics and thermodynamics of several reaction pathways for one- and two-electron reduction of ethylene carbonate (EC) have been examined. Our calculations indicate that the high reduction potential and low barrier for the ring opening of EC is the main cause for the continuous growth of SEI observed in SIBs. The impact of two well-known electrolyte additives, vinyl carbonate (VC) and fluoroethylene carbonate (FEC), on SEI composition was evaluated by studying decomposition pathways of (1) VC and FEC molecules in the bulk EC solvent and (2) an EC molecule in a supermolecular cluster comprising an EC and the additive molecule. The additive molecul...

Coin-cells are often the test format of choice for laboratories engaged in battery research and development as they provide a convenient platform for rapid testing of new materials on a small scale. However, reliable, reproducible data via the coin-cell format is inherently difficult, particularly in the full-cell configuration. In addition, statistical evaluation to prove the consistency and reliability of such data is often neglected. Herein we report on several studies aimed at formalizing physical process parameters and coin-cell construction related to full cells. Statistical analysis and performance benchmarking approaches are advocated as a means to more confidently track changes in cell performance. We show that trends in the electrochemical data obtained from coin-cells can be reliable and informative when standardized approaches are implemented in a consistent manner.

The impedance of a lithium- and manganese-rich layered transition-metal oxide (LMR-NMC) positive electrode, specifically Li1.2Ni0.15Mn0.55Co0.1O2, is compared to two other transition-metal layered oxide materials, specifically LiNi0.8Co0.15Al0.05O2 (NCA) and Li1.05(Ni1/3Co1/3Mn1/3)0.95O2 (NMC). A more detailed electrochemical impedance spectroscopy (EIS) study is conducted on the LMR-NMC electrode, which includes a range of states-of-charge (SOCs) for both current directions (i.e. charge and discharge) and two relaxation times (i.e. hours and one hundred hours) before the EIS sweep. The LMR-NMC electrode EIS studies are supported by half-cell constant current and galvanostatic intermittent titration technique (GITT) studies. Two types of electrochemical models are utilized to examine the results. The first type is a lithium ion cell electrochemical model for intercalation active material electrodes that includes a complex active material/electrolyte interfacial structure. The other is a lithium ion half-cell electrochemical model that focuses on the unique composite structure of the bulk LMR-NMC materials. The LMR-NMC electrode impedance is much higher than the impedance of the NCA and NMC electrodes. The higher impedance of the LMR-NMC electrode suggests that it would be better utilized in a high energy battery rather than a high power battery. The intercalation active material electrochemical model and supporting studies indicate the source of the higher impedance can be associated with a much higher electronic contact resistance between the oxide active material and the conducting carbon additive, as well as the material’s interfacial and bulk transport and kinetic characteristics being significantly worse than the other oxides, as typified by the active material lithium diffusion coefficients for the surface layer and bulk material (DSi and DSb) and the kinetic exchange current density (io). As typical of layered oxide active materials the LMR-NMC electrode impedance increases at low and high SOCs, corresponding to DSi, DSb, and io all decreasing. Further, the rate of decrease in the parameters with SOC (i.e increase in impedance) is higher than observed for the other layered oxides. When the LMR-NMC electrode is allowed to relax for a very long time (i.e. approximately 100 hours) the impedance is observed to be significantly higher. Also, the resulting DSi, DSb, and io parameters determined by the intercalation electrochemical model from the EIS studies during charge and discharge where found to correlate with electrode voltage. This unique behavior for the LMR-NMC electrode is explained by the LMR-NMC bulk reaction and transport electrochemical model, which accounts for the individual domains in the active material. Specifically, the Li2MnO3 domains when allowed to relax are either nearly full or empty depending on the SOC. Because of the large characteristic time constant for the Li2MnO3 domains’ transition, when the LMR-NMC material is used in transportation applications the Li2MnO3 domains typically never relax and the electrode exhibits a lower impedance. The LMR-NMC bulk reaction and transport electrochemical model describes much of the observed behavior that cannot be accounted for using a standard intercalation active material electrochemical model. This includes the voltage hysteresis as shown in Figure 1, as well as the slow relaxation phenomena. However, the complexity of this model makes determining the parameters for the individual domains quite a challenge. ACKNOWLEDGMENT Support from the Vehicle Technologies Program, Hybrid and Electric Systems, David Howell (Team Lead) and Peter Faguy, at the U.S. Department of Energy, Office of Energy Efficiency and Renewable Energy, is gratefully acknowledged. The submitted manuscript has been created by UChicago Argonne, LLC, Operator of Argonne National Laboratory (“Argonne”). Argonne, a U.S. Department of Energy Office of Science laboratory, is operated under Contract No. DE-AC02-06CH11357. The U.S. Government retains for itself, and others acting on its behalf, a paid-up nonexclusive, irrevocable worldwide license in said article to reproduce, prepare derivative works, distribute copies to the public, and perform publicly and display publicly, by or on behalf of the Government. Figure 1. Electrochemical model simulation of LMR-NMC standard electrode half-cell charge and discharge curves at a C/300 rate. Figure 1

Lithium- and manganese-rich (LMR) transition metal oxide cathodes are of interest for lithium-ion battery applications due to their increased energy density and decreased cost. However, the advantages in energy density and cost are offset, in part, due to the phenomena of voltage fade. Specifically, the voltage profiles (voltage as a function of capacity) of LMR cathodes transform from a high energy configuration to a lower energy configuration as they are repeatedly charged (Li removed) and discharged (Li inserted). We propose a physical model of voltage fade that accounts for the emergence of a low voltage Li phase due to the introduction of transition metal ion defects within a parent Li phase. The phenomenological model was re-cast in a general form and experimental LMR charge profiles were de-convoluted to extract the evolutionary behavior of various components of LMR capacitance profiles. Evolution of the voltage fade component was found to follow a universal growth curve with a maximal voltage fade capacity of ≈20% of the initial total capacity. © The Author(s) 2015. Published by ECS. This is an open access article distributed under the terms of the Creative Commons Attribution 4.0 License (CC BY, http://creativecommons.org/licenses/by/4.0/), which permits unrestricted reuse of the work in any

In the last decade, many studies applied surface analysis techniques (SEM, XPS and SIMS) to understand the formation of SEI layers on Li-ion battery electrodes. This work was meant as a comparative model study of the SEI layer formation, which combined in situ SEM imaging with TOF SIMS depth profiling of four samples of the same graphite electrode material, which was subjected to different charge–discharge cycling schemes in a Li-ion battery. Besides comparing compositions of sub-surface regions of these differently processed electrodes, we wanted to know whether these compositions depend on after-cycling sample preparation, in particular if a brief exposure of these samples to air would affect the compositions measured by TOF SIMS. We found that the exposure to air (1) increases secondary ion yield for all species, and (2) changes shapes of SIMS depth profiles for some key species. For selected samples, we also conducted a comparison between the conventional single beam TOF-SIMS depth profiling and a high resolution dual beam depth profiling and found that the former approach can detect the same features in depth profiles as the latter one. We interpreted this as an indication that the sample surface morphology (high roughness) could be a limiting factor in this SEI study, suggesting that specially designed model samples with smooth surfaces are a better choice for future studies.

In this article we describe efforts to improve performance and cycle life of cells containing Li1.2Ni0.15Mn0.55Co0.1O2-based positive and graphite-based negative electrodes. Initial work to identify high-performing materials, compositions, fabrication variables, and cycling conditions is conducted in coin cells. The resulting information is then used for the preparation of double-sided electrodes, assembly of pouch cells, and electrochemical testing. We report the cycling performance of cells with electrodes prepared under various conditions. Our data indicate that cells with positive electrodes containing 92 wt.% Li1.2Ni0.15Mn0.55Co0.1O2, 4 wt.% carbons (no graphite), and 4 wt.% PVdF (92–4–4) show ∼20% capacity fade after 1000 cycles in the 2.5–4.4 V range, significantly better than our baseline cells that show the same fade after only 450 cycles. Our analyses indicate that the major contributors to cell energy fade are capacity loss and impedance rise. Therefore incorporating approaches that minimize capacity fade and impedance rise, such as electrode coatings and electrolyte additives, can significantly enhance calendar and cycle life of this promising cell chemistry.

High-capacity x Li 2 MnO 3 ·(1 − x )LiMO 2 (M = Ni, Mn, Co) oxides show relatively rapid performance degradation when cycled at voltages >4.5 V vs. Li/Li + . Previous research has indicated that modifying the oxide surfaces with coatings, such as alumina, reduces cell impedance rise and improves capacity retention. In this article, we demonstrate pulsed-sonication as a rapid and effective approach for coating alumina on Li 1.2 Ni 0.175 Mn 0.525 Co 0.1 O 2 (0.5Li 2 MnO 3 ·0.5LiNi 0.44 Mn 0.31 Co 0.25 O 2 ) particles. Oxide integrity and morphology is maintained after the sonochemical process and subsequent heat-treatment. Energy dispersive spectroscopy (EDS) X-ray elemental maps show uniform coating of all secondary particles. 27 Al Magic Angle Spinning (MAS) NMR data confirm the presence of alumina and mainly indicate octahedral aluminum occupancy in a six-coordinate environment with oxygen. Full cells containing electrodes with the alumina-coated particles demonstrate lower initial impedance rise and better capacity retention during extended cycling to high voltages. However, the coating has a negligible effect on the voltage hysteresis and voltage fade behavior displayed by these oxides. The various data indicate that the pulsed sonochemical technique is a viable approach for coating oxide particles. The methodology described herein can easily be extended beyond alumina to include coatings such as AlF 3 , MgO, and MgF 2 .

The effects of the coatings Al 2 O 3 , LiAlO x , ZrO 2 , TiO 2 , AlPO 4 , and LiPON and of the electrolyte additives 3-hexylthiophene and lithium difluoro (oxalato)borate (LiDFOB) on the voltage fade phenomenon in 0.5Li 2 MnO 3 ·0.5LiNi 0.375 Mn 0.375 Co 0.25 O 2 cathodes were investigated. Cells containing these materials or additives were cycled according to a standard protocol at room temperature between 2.0 and 4.7 V vs. Li + /Li. As expected, the cells containing either an additive or a coated cathode displayed less capacity loss than cells containing an uncoated cathode and no additive. The voltage fade phenomenon was quantified in terms of changes in the average cell voltage (Wh/Ah). The results indicate that, within experimental error, all of the coatings and additives produced little-to-no effect on voltage fade.

Boronate-based electrolyte additives are tested in high-capacity lithium-ion cells containing graphite-based negative and Li1.2Ni0.15Mn0.55Co0.1O2-based positive electrodes. Cells containing small amounts (0.25 wt%) of phenyl boronic acid ethylene glycol ester (PBE) in an EC:EMC (3:7 by wt) + 1.2M LiPF6 (Gen2) electrolyte show improved capacity retention and reduced impedance rise compared to cells without the additive. Adding a perfluorooctyl chain to PBE creates the phenyl boronic acid perfluorooctyl ethylene glycol ester (PFO-PBE) compound. Cells with 0.25 wt% PFO-PBE additive display the lowest capacity fade (21%) compared to the PBE (34%) and Gen2 (65%) cells after more than 200, 2.2–4.6 V cycles, at 30◦C. These data validate our modular-electrolyte additive concept (PBE head and perfluoroalkyl tail) for high-capacity lithium-ion cells. Impedance rise is reduced further by addition of 2 wt% LiDFOB (LiF2BC2O4) to cells with 0.25 wt% PFO-PBE, thus demonstrating that additive combinations can enhance performance during extended cycling. © 2014 The Electrochemical Society. [DOI: 10.1149/2.0081410jes] All rights reserved.

A new family of polyfluoroalkyl-substituted ethylene carbonates is synthesized and tested as additives in lithium-ion cells containing EC:EMC + LiPF 6 -based electrolyte. The influence of these compounds is investigated in Li 1.2 Ni 0.15 Mn 0.55 Co 0.1 O 2 //graphite cells via a combination of galvanostatic cycling and electrochemical impedance spectroscopy (EIS) tests. Among the four additives studied in this work (4-(trifluoromethyl)-1,3-dioxolan-2-one (TFM-EC), 4-(perfluorobutyl)-1,3-dioxolan-2-one (PFB-EC), 4-(perfluorohexyl)-1,3-dioxolan-2-one (PFH-EC), and 4-(perfluorooctyl)-1,3-dioxolan-2-one (PFO-EC)), small amounts (0.5 wt%) of PFO-EC is found to be most effective in lessening cell performance degradation during extended cycling. Linear sweep voltammetry (LSV), X-ray photoelectron spectroscopy (XPS) and Raman spectroscopy are used to further characterize the effects of PFO-EC on the positive and negative electrodes. LSV data from the electrolyte, and XPS analyses of electrodes harvested after cycling, suggest that PFO-EC is oxidized on the cathode forming surface films that slow electrode/cell impedance rise. Differential capacity (dQ/dV) plots from graphite//Li cells suggest that PFO-EC is involved in solid electrolyte interphase (SEI) formation. Raman data from anodes after cycling suggest that structural disordering of graphite is reduced by the addition of PFO-EC, which may explain the improved cell capacity retention.

The synergistic effects of LiB(C 2 O 4 ) 2 (LiBOB), LiF 2 B(C 2 O 4 ) (LiDFOB), triphenylamine (Ph 3 N), and 1,4-benzodiozane-6,7-diol (BDOD) as functional electrolyte additives in high-energy electrochemical cells is examined. The influence of these additives, individually, and in different combinations, is evaluated using galvanostatic cycling of cells containing Li 1.2 Ni 0.15 Mn 0.55 Co 0.1 O 2 (0.5Li 2 MnO 3 ·0.5LiMn 0.375 Ni 0.375 Co 0.25 O 2 )-based positive electrodes, graphite-based negative electrodes, and a LiPF 6 -based electrolyte. Electrochemical impedance spectroscopy (EIS), linear sweep voltammetry (LSV), and voltage-hold tests are also used. By itself, LiBOB is a good additive for reducing cell capacity loss, but cell impedance rise is still significant after extended cycling. Similarly, neither Ph 3 N nor BDOD alone provide desired improvements in cell performance. However, cells containing LiBOB in combination with LiDFOB, Ph 3 N, or BDOD exhibit enhanced capacity retention, rate capability, and cyclability; probable reaction mechanisms are highlighted here. Combining electrolyte additives that act synergestically is a practical and versatile strategy to improve performance and life of lithium-ion cells.

Practical high-capacity Li-ion cells containing Li1.2Ni0.15Mn0.55Co0.1O2-based positive and graphite-based negative electrodes show substantial capacity loss and impedance rise when repeatedly cycled to, or held for extended periods, at voltages exceeding 4.5 V. Their performance can be effectively improved by modifying the positive electrode. The positive composite electrodes are modified here in two different ways: by (i) alumina coatings of up to ∼4 nm applied via atomic layer deposition (ALD), and (ii) addition of nanoscale alumina powder. Thicknesses of the ALD coatings are estimated via X-ray photoelectron spectroscopy (XPS). Electrochemical cycling reveals that capacity retention is better, and impedance rise is smaller for cells containing ALD-coated electrodes. Cells with alumina-powder modified electrodes show also improved capacity retention, but without improvements in impedance. Improved capacity retention is primarily due to reduced Li trapping on the negative electrode. Lower impedance growth, in ALD modified cells, is attributed to improved electro-mechanical integrity and altered surface films inside the positive electrode. The alumina coating inhibits, but does not prevent, transition metal dissolution. The coating also reduces electrolyte oxidation. Significant accumulation of Al on the negative electrode indicates electrochemical crosstalk between the electrodes and chemical instability of the ALD coatings during extended cycling.

We developed a simple approach to carry out in situ electron microscopy of single Li-ion battery cathode particles during electrochemical cycling. We focused on Li(Ni0.8Co0.15Al0.05)O2-based cathode materials because life-cycle tests suggest a strong contribution of the cathode material to changes in cell impedance. In situ scanning electron microscopy was carried out operando during cycling and at various stages by interrupted cycling. Our work revealed several important aspects of cathode oxide particle dynamics: significant separations develop between grains even during the very first charge (oxide delithiation) and electrolyte penetration through that crack network all the way into the particle interior. Comparing these results to post-test microstructural characterization of oxide particles subjected to extensive cycling confirms the occurrence of these processes in practical cells and suggests that the physical separation and isolation of grains may contribute to performance degradation of lithium-ion cells.

Athree-dimensionalelectrochemicalmodelwasdevelopedtoexaminetheperformance(i.e.impedancedeterminedbyapulsechangeinpotential)ofalithium-ionintercalationpositiveelectrodesingleparticle.Acomprehensiveparameterstudywasconducted,basedona layered nickel oxide parameter set previously developed. The dominance of the interfacial impedance on the particle performanceaccentuates the impact of the secondary particle porosity and electrolyte wetting of the porosity. Electronic distribution effects,includingconductivityandparticlecontacts,alsobecomesignificantwhenthesecondaryparticle’seffectiveconductivityislessthanabout 10

We report real-time average stress measurements on composite silicon electrodes made with two different binders [Carboxymethyl cellulose (CMC), and polyvinylidene fluoride (PVDF)] during electrochemical lithiation and delithiation. During galvanostatic lithiation at very slow rates, the stress in a CMC-based electrode becomes compressive and increases to 70 MPa, where it reaches a plateau and increases slowly thereafter with capacity. The PVDF-based electrode exhibits similar behavior, although with lower peak compressive stress of about 12 MPa. These initial experiments indicate that the stress evolution in a Si composite electrode depends strongly on the mechanical properties of the binder. Stress data obtained from a series of lithiation/delithiation cycles suggests plasticity induced irreversible shape changes in contacting Si particles, and as a result, the stress response of the system during any given lithiation/delithiation cycle depends on the cycling history of the electrode. While these results constitute the first in-situ stress measurements on composite Si electrodes during electrochemical cycling, the diagnostic technique described herein can be used to assess the mechanical response of a composite electrode made with other active material/binder combinations., 22 pages, 8 figures

Hierarchical surface morphologies form when thin films are deposited onto preexisting templates of vertically aligned wires using a line-of-sight deposition method, providing a facile path to experimental battery electrodes with high surface-to-volume ratios. To demonstrate this, we fabricate and electrochemically cycle highly textured thin film electrodes of Li x Mn 2− y O 4 with large surface-to-volume ratios and low impedance. The active surface area of the electrodes exceeds the area of the substrate by at least a factor of five. This factor is due in part to the textured template, and in part to the effects of local shadowing during line-of-sight film deposition, resulting in a hierarchical surface morphology. The textured electrodes maintain their structural integrity for at least 30 cycles, as shown through microstructural characterization and reversible cycling against metallic lithium over the range of 2.0–4.4 V. In comparison to planar thin film electrodes of equal mass, they also offer a lasting reduction in internal impedance. Overall, textured thin film electrodes of any material are readily fabricated through this templating technique and can be used to improve three-dimensional battery architectures or to simply probe electrochemical surface effects.

An approach for the volume averaged numerical modeling of phase-transition intercalation electrodes is presented for lithiated graphite, LixC6, in lithium-ion batteries. The proposed method directly treats phase formation and growth through a modified form of the Avrami equation enabling the physics-based mathematical model to capture the additional time constant observed in the two phase regions of lithiated graphite as well as a portion of the hysteresis commonly observed between charge and discharge voltage. The graphite phase diagram was taken to be composed of three stages, or phases, each with a Nernstian or ideal solution based equilibrium potential function. The behavior of the potential rise from a current pulse in the two-phase region is matched well with this methodology resulting in higher valued diffusion coefficients than found when only a single-phase approach is used. Simulated results for mesocarbon microbeads show the co-existence of all three phases within the electrode during higher rate discharges. Concentration dependent diffusion coefficients are found to be necessary to match experimental results at rates significantly higher than 1C. The model is shown to be capable of exhibiting core-shell behavior when fitted phase-transformation rate constants are sufficiently high in value, although not observed for MCMB.

A rich research history exists for crystalline growth by vapor–liquid–solid (VLS) methods, but not for amorphous growth. Yet VLS growth in the absence of crystallographic influences provides an ideal laboratory for exploring surface energy effects, including the role of line tension. We discuss the growth of amorphous silica nanowires from indium droplets by a modified VLS method. Multiple strands issue from each droplet, each strand having

The layered oxides being considered as intercalation compounds for lithium batteries display significant differences between the long-range crystal structure and local arrangements around individual atoms. These differences are important, because the local atomic environments affect Li-ion transport and, hence, the oxide’s rate capability, by determining activation barrier energies, by blocking or opening Li-diffusion pathways, etc. Traditional diffraction methods provide key information on the average crystal structure. However, no single experimental technique can unequivocally determine the average long-range crystal structure and the distribution of local environments over crystallographic distances while retaining atomic-scale resolution. Therefore, in this study, we have employed a combination of diffraction, microscopy, and spectroscopy techniques to investigate the long-range (∼1 μm) and local structure (≤1 nm) of Li1.2Co0.4Mn0.4O2, which is a model compound for layered oxides being considered for...

The structure of as-prepared Li1.2Co0.4Mn0.4O2 is studied using a combination of techniques that includes high-resolution electron microscopy (HREM), high-angle annular dark-field imaging in scanning transmission electron microscopy (HAADF-STEM), selected-area electron diffraction (SAED) and electron energy loss spectroscopy (EELS). Electron diffraction and imaging revealed Li ordering in the transition metal planes consistent with the presence of locally monoclinic (Li2MnO3-like) regions with three different topotaxial orientations with respect to a parent rhombohedral (LiCoO2-like) structure. EELS analyses revealed compositional variations too small to be compatible with perfect, or close to perfect, segregation into pure LiCoO2 and Li2MnO3 over length scales longer than the sample thickness. We propose a structural model in which Mn and Co segregate within TM planes to form LiMn6 and Co clusters, which overlap within EELS sampling volumes causing the observed Co/Mn homogeneity.

Electrolytes containing LiB(C2O4)2 (LiBOB) salts are of increasing interest for lithium-ion cells for several reasons that include their ability to form a stable solid electrolyte interphase on graphite electrodes. However, cells containing these electrolytes often show inconsistent performance because of impurities in the LiBOB salt. In this work we compare cycling and impedance data from cells containing electrolytes with LiBOB that was obtained commercially and LiBOB purified by a rigorous recrystallization procedure. We relate the difference in performance to a lithium oxalate impurity that may be a residual from the salt manufacturing process. We also examine the reaction of LiBOB with water to determine the effect of salt storage in high-humidity environments. Although LiBOB electrolytes containing trace amounts (∼100 ppm) of moisture appear relatively stable, higher moisture contents (∼1 wt%) lead to observable salt decomposition resulting in the generation of B(C2O4)(OH) and LiB(C2O4)(OH)2 compounds that do not dissolve in typical carbonate solutions and impair lithium-ion cell performance.

Cells with and without a LiC2O4BF2 electrolyte additive and that contained Li1.05(Mn1/3Co1/3Ni1/3)0.95O2 (NMC) positive electrodes were tested for calendar and cycle life at 60% state of charge. The temperatures used in these tests were 25 and 45 °C (cycle life) and 45 and 55 °C (calendar life). An analysis of the C/25 capacity data shows that the C/25 capacity decreases with the square root of time. The additive slowed down the rate of capacity decline. The C/25 data were subjected to differential voltage analysis to determine the possible cause of the capacity decrease and at which electrode the capacity decrease was occurring. Data from full cells and half-cells were compared to elucidate individual electrode contributions. This analysis indicated that lithium-capacity-consuming side reactions were occurring primarily at the negative electrode.

Galvanostatic Intermittent Titration Technique (GITT) experiments were conducted to determine the lithium diffusion coefficient of LiNi 0.8 Co 0.15 Al 0.05 O 2 , used as the active material in a lithium-ion battery porous composite positive electrode. An electrochemical model, based on concentrated solution porous electrode theory, was developed to analyze the GITT experimental results and compare to the original GITT analytical theory. The GITT experimental studies on the oxide active material were conducted between 3.5 and 4.5 V vs. lithium, with the maximum lithium diffusion coefficient value being 10 −10 cm 2 s −1 at 3.85 V. The lithium diffusion coefficient values obtained from this study agree favorably with the values obtained from an earlier electrochemical impedance spectroscopy study.

The first-cycle irreversibility of Li1.048(Ni1/3Co1/3Mn1/3)0.952O2 (LiMO2) cathode material in lithium and lithium-ion cells has been studied using galvanostatic cycling and in situ synchrotron X-ray diffraction. The so-called “lost capacity” of a Li/LiMO2 cell observed during initial cycle in conventional voltage ranges (e.g., 3.0–4.3 V) could be completely recovered by discharging the cell to low voltages (

Layered lithium metal oxide cathodes typically exhibit irreversibility during the first cycle in lithium cells when cycled in conventional voltage ranges (e.g., 3–4.3 V vs. Li+/Li). In this work, we have studied the first-cycle irreversibility of lithium cells containing various layered cathode materials using galvanostatic cycling and in situ synchrotron X-ray diffraction. When cycled between 3.0 and 4.3 V vs. Li+/Li, the cells containing LiCoO2, LiNi0.8Co0.15Al0.05O2, and Li1.048(Ni1/3Co1/3Mn1/3)0.952O2 as cathodes showed initial coulombic efficiencies of 98.0, 87.0, and 88.6%, respectively, at relatively slow current (8 mA/g). However, the “lost capacity” could be completely recovered by discharging the cells to low voltages (