Solid Electrolyte Interphase Evolution Research Articles

Solid Electrolyte Interphase Formation and Failure Mechanisms in Lithium–Ion Batteries: In-Situ AFM Imaging

The lifetime and performance of lithium-ion batteries depend significantly on the formation and evolution of the solid electrolyte interphase (SEI) layer. Si has almost 10 times theoretical specific capacity compared to current state-of-the-art graphite anode materials in Li-ion batteries, which is highly attractive for electric vehicle applications. However, this energy advantage comes with a ~300% volume change during voltage cycling, which causes substantial deformations to SEI. The mechanical integrity of SEI on Si electrodes is highly important in developing commercial Si-based batteries. For R&D, directly probing the SEI evolution is challenging due to 1) SEI thickness is from 10 to 100s of nm; 2) SEI is fragile, which requires a gentle probing force; 3) in situ and operando measurements in electrolyte and under ambient control are needed; 4) multimodal information to clarify the convoluted topographical, mechanical, electrical and electrochemical properties is desired; and 5) a well-defined specimen configuration is needed to interpret the deformation. We have addressed these issues by applying controlled strains to the SEI layer using patterned Si island electrodes and by monitoring these electrodes during voltage cycling on a PeakForce electrochemical AFM system housed inside an Ar-filled glove box (< 1ppm O2 and H2O contents). From this study, we verified that 1) SEI crack formation occured during lithiation, which has been predicted but not directly observed previously; 2) additional SEI formation at low potentials did not fill these cracks, which directly contradicts some prior speculation; 3) SEI had a layered structure, the individual layer of which could be differentiated by the quantitative nanomechanical probing. We are also using Scanning electrochemical microscopy (SECM) to detect local electrochemical differences at stable and unstable SEI sites. Our comprehensive studies not only provide a new in-depth understanding of the in operando SEI formation, evolution and its mechanical response, but also offer guidance to tailor passivation layers for optimal battery performance. Figure 1.(A)-(D) AFM images of surface topographic evolution of the SEI layer during lithiation-dethiation cycles. (E) SEM image of a PeakForce SECM nanoelectrode probe. The probe is fully insulated with only the Pt-coated tip apex exposed. Reference: [1] Tokranov et al., ACS Appl. Mater. Interfaces, 2014, 6, 6672 [2] Tokranov et al., Adv. Energy Mater., 2016, 6, 1502302 [3] Kumar et al., ACS Energy Lett., 2016, 1, 689 Figure 1

Layer Number Dependence of Li+ Intercalation on Few-Layer Graphene and Electrochemical Imaging of Its Solid-Electrolyte Interphase Evolution

Bulk and surface electrochemical reactivity converge on ultrathin electrochemical interfaces such as few-layer graphene (FLG). In spite of the many recent works regarding the use of exfoliated graphene materials for charge storage, we still lack a detailed mechanistic understanding of how Li+ intercalates in FLG. Li+ intercalation in graphitic carbon is known to proceed through a staging mechanism, where intercalation occurs at selected interlayers at a time, rather than randomly on any available empty interlayer galleries, until reaching the nominal composition LiC6. Thus, on graphite this process is strongly dependent on the number of neighboring empty galleries at any given time. FLG naturally displays a limited number of galleries, therefore, we hypothesize that this process will also necessarily be distributed unevenly. In this study, we applied FLG (1-10 layers) to explore the alkaline ion uptake mechanisms. Chemical vapor deposition methods with varies recipes were applied to grow double and multilayer graphene. By multicycle wet transfer of bilayer graphene, 2-8 layer graphene with well-defined area and low defect density. Direct growth of multilayer graphene (>10 layers) serves as control group. Photolithography method was used to generate micro patterns on graphene as “point of entry” for Li+intercalation. Lithium ion intercalation on FLG, as measured via cyclic voltammetry, shows a staging-type process, which has strong dependence on the number of layers of graphene sheets that compose the electrode. On a graphene electrode with less than five layers, the numbers of intercalation/de-intercalation peaks were limited due to the lack of graphene interlayer galleries to stabilize Li ions. Those peaks broaden and increase in number as the layer number increases to six. Despite these mechanistic differences on ion intercalation, the formation of a solid-electrolyte interphase (SEI) was observed on all electrodes. Scanning electrochemical microscopy (SECM) in the feedback mode was used to demonstrate spatial resolved changes in the surface conductivity of FLG during SEI evolution. The fabrication of “ionic channels” on the FLG electrode provided preferential positions for Li ion insertion. The role of these channels can be evidenced using a Li-ion sensitive SECM imaging technique through localized flux measurements. This work highlights the impact of nano-structure and micro-structure on macroscopic electrochemical behavior and provides guidance to the mechanistic control of ion intercalation using atomically thin graphene interface. Figure 1

Direct Visualization of the Solid Electrolyte Interphase and Its Effects on Silicon Electrochemical Performance

Fluoroethylene carbonate (FEC) as an electrolyte additive can considerably improve the cycling performance of silicon (Si) electrodes in Li‐ion batteries. However, the fundamental mechanism for how FEC contributes to solid electrolyte interphase (SEI) morphological changes and chemical composition is not well understood. Here, scanning transmission electron microscopy coupled with electron energy loss spectroscopy gives a comprehensive insight as to how FEC affects the SEI evolution in terms of composition and morphology throughout electrochemical cycling. In the first lithiation cycle, the electrode cycled in ethylene carbonate (EC): diethylene carbonate (DEC) forms a porous uneven SEI composed of mostly Li2CO3. However, the electrode cycled in EC/DEC/FEC is covered in a dense and uniform SEI containing mostly LiF. Interestingly, the intrinsic oxide layer (Li x SiO y ) is not observed at the interface of electrode cycled in EC/DEC/FEC after 1 cycle. This is consistent with fluoride anion formation from the reduction of FEC, which leads to the chemical attack of any silicon‐oxide surface passivation layer. Furthermore, surface sensitive helium ion microscopy and X‐ray photoelectron spectroscopy techniques give further insights to the SEI composition and morphology in both electrodes cycled with different electrolytes.

An electrochemical surface‐enhanced Raman spectroscopic study on nanorod‐structured lithium prepared by electrodeposition

Lithium is an s‐electron metal which is expected to support surface‐enhanced Raman scattering (SERS) effect. But the experimental investigation of the SERS effect of Li was reported once under high vacuum condition because of its extremely active surface chemistry. However, such investigations become increasingly important with stimulation by the active researches in lithium‐based batteries. In this paper, we present an electrochemical Raman spectroscopic study of electrochemically prepared Li surface combined with a simulation on the enhancement factor. Electrochemical roughening of Li foil surface and electrodeposition of Li on copper substrates are employed to prepare Li nanostructures. Only the nanorod arrays prepared by the electrodeposition on Cu in the electrolyte of LiPF6–PC–H2O or LiPF6–EC–DMC–H2O appear to be effective for obtaining the SERS effect. The spectra show two broad yet dominant bands at 720 and 1020 cm−1, which are considered to arise mainly from combined contribution by LiOH and LiF (720 cm−1) and LiF and Li2CO3 (1020 cm−1) contained in the solid‐electrolyte interphase (SEI) layer on the nanorod‐structured Li surface. The enhancement factor is calculated for coupled nanorods of ca. 240 nm in diameter, which is about 30 and 7 times for 638 and 532‐nm excitations, respectively. Experimentally, the signals with 638‐nm laser excitation are two to three times stronger than those with 532‐nm laser excitation. The SERS effect of Li may provide a useful and convenient in‐situ method to follow the SEI evolution process in lithium‐based batteries without introducing extra SPR active metals that may have impact on the performance of the Li anode. Copyright © 2016 John Wiley &amp; Sons, Ltd.

Understanding Failure Mechanisms of Solid Electrolyte Interphase on Silicon Anodes: An in-Situ AFM Approach

The formation and evolution of solid electrolyte interphase (SEI) directly governs the lifetime and performance of rechargeable Lithium-ion batteries. There are lots of studies dealing with chemistry of the SEI layer but very little information is available in terms of its mechanical behavior for example fracture behavior, strength etc. To enable utilization of high capacity anode materials such as Silicon which goes through large volume changes (~300%) during cycling, a mechanistic understanding of SEI layer is of critical importance. In this study we have used in-situ atomic force microscopy (AFM) to monitor the formation, evolution and failure of the SEI layer on patterned Si island electrodes. The unique PeakForce tapping mode was used to image the extremely fragile SEI layer, which is very challenging for conventional AFM modes in organic solvent. Our in situ studies show for the first time the in operando cracking of SEI layer and its evolution during cycling. Based on a succession of AFM images showing failure of SEI layer, we were able to calculate the critical strain at which this failure starts. A classical energy release rate approach was used to get a bound of fracture energy values of SEI layer for a range of elastic moduli of SEI layer. This study not only provides an in-depth understanding of failure modes of SEI layer but also offer guidance towards tailoring passivation layers for optimal battery performance.

In Situ Measurement of Solid Electrolyte Interphase Evolution on Silicon Anodes Using Atomic Force Microscopy

In situ measurements of the growth of solid electrolyte interphase (SEI) layer on silicon and the lithiation‐induced volume changes in silicon in lithium ion half‐cells are reported. Thin film amorphous silicon electrodes are fabricated in a configuration that allows unambiguous separation of the total thickness change into contribution from SEI thickness and silicon volume change. Electrodes are assembled into a custom‐designed electrochemical cell, which is integrated with an atomic force microscope. The electrodes are subjected to constant potential lithiation/delithiation at a sequence of potential values and the thickness measurements are made at each potential after equilibrium is reached. Experiments are carried out with two electrolytes—1.2 m lithium hexafluoro‐phosphate (LiPF6) in ethylene carbonate (EC) and 1.2 m LiPF6 in propylene carbonate (PC)—to investigate the influence of electrolyte composition on SEI evolution. It is observed that SEI formation occurs predominantly during the first lithiation and the maximum SEI thickness is ≈17 and 10 nm respectively for EC and PC electrolytes. This study also presents the measured Si expansion ratio versus equilibrium potential and charge capacity versus equilibrium potential; both relationships display hysteresis, which is explained in terms of the stress–potential coupling in silicon.

SEI Formation and Evolution in Graphite and ZFO-C Electrodes Probed by X-ray Absorption Spectroscopy

Li-ion batteries (LIBs) are considered to be one of the most reliable, and hazard free energy storage devices known by today’s conventional technology. However, they face several limitation in energy storage due to their dependence on the solid state electrolyte-electrode reactions. The efficiency and durability of cells are also significantly altered by SEI (Solid Electrolyte Interphase) medium that is built within electrode-electrolyte admix with various celerities during the first cell full cycle. The study and hence control of the SEI formation process remains one of the challenges in cell design. Recent efforts have been dedicated to investigate the SEI phase evolution mechanism and explore new active materials to enhance the durability and energy storage capability of the cells [1-3]. Natural graphite occupies a considerable share of the market in the anode materials in lithium-ion batteries by virtue of its low and flat potential, low cost, relatively high reversible capacity of 370 mAh/g and high columbic efficiency in proper electrolytes. On the other hand Zinc iron oxide (ZnFe2O4, ZFO) encapsulated by a carbonaceous matrix (ZFOC) is recently explored to be a high capacity anode replacement [2]. In these systems the exchange of Li+ and e− via the alloy generation and conversion. Thus, metaphases such as Li, Zn, Li2O, LiC6 are formed upon lithiation, which are dispersed in the host matrix. While the lithiation kinetics have already been probed by electrochemical impedance spectroscopy (EIS) and x-ray diffraction (XRD) analysis, clear understanding of the evolution of passivation layer evolution and properties on ZFO-C and graphite is still lacking. In this work, performed within a European FP7 project (SIRBATT) collaboration effort, we present a study of the evolution of the SEI in these innovative anode material at selected charging steps by using the x-ray absorption fine structure (XAFS) technique. The local probe chosen for the SEI evolution are the As atoms embedded in the solid interphase as an effect of the reaction of the electrolyte (LiAsF6) at the electrode surface. The SEI evolution is thus monitored collecting As K-edge XAFS spectra thus the experiments require synchrotron radiation, used for the first time for such a purpose. The aim is to provide detailed and precise fine structural analysis of the SEI of these innovative electrodes. As K-edge XAFS experiments on ZFO-C and graphite based anodes at different Li charge uptakes were thus carefully performed at the LISA BM08 beamline in fluorescence mode. XAFS spectra were used to analyze the sub monolayer structure of the electrolyte related phase evolution within the thin (typically 2-20 nm) SEI layer. Graphite electrodes showed a much faster SEI formation procedure. Typical reactions leading to changes in As valence and coordination are of the type: AsF6 +2xLi+2xe- → LixAsF3-x +xLiF Combined data-analysis of near-edge and extended XAFS spectra has shown the occurrence of transformations from As5+ valence state (typical of the pure electrolyte) to a combination of As3+ and As2+ valences with increasing As2+ ratio by the charging steps. Quantitative XAFS analysis [4] also confirms the transitions between the polyhedral structures of As-F formed on the SEI and a corresponding reduction of the first-neighbor coordination number of As atoms. [1] E. Peled, Journal of the Electrochemical Society 1998, 145, 3482. [2] D. Bresser, E. Paillard, R. Kloepsch, S. Krueger, M. Fiedler, R. Schmitz, D. Baither, M. Winter, S. Passerini, Advanced Energy Materials 2013, 3, 513–523. [3] P. Verma, P. Maire, P. Novk, Electrochimica Acta 2010, 55, 6332– 6341. [4] A. Filipponi, A. Di Cicco, and C. R. Natoli, Phys. Rev. B 1995, 52 15122-15134.

Stability of Solid Electrolyte Interphase Components on Lithium Metal and Reactive Anode Material Surfaces

Lithium ion batteries (LIB) can feature reactive anodes that operate at low potentials, such as lithium metal or silicon, passivated by solid electrolyte interphase (SEI) films. SEI is known to evolve over time as cycling proceeds. In this modeling work, we focus on the stability of two main SEI components, lithium carbonate (Li2CO3) and lithium ethylene dicarbonate (LEDC). Both components are electrochemically stable but thermodynamically unstable near the equilibrium Li+/Li(s) potential. Interfacial reactions represent one way to trigger the intrinsic thermodynamic instability. Both Li(2)CO(3) and LEDC are predicted to exhibit exothermic reactions on lithium metal surfaces, and the barriers are sufficiently low to permit reactions on battery operation time scales. LEDC also readily decomposes on high Li-content Li(x)Si surfaces. Our studies suggest that the innermost SEI layer on lithium metal surfaces should be a thin layer of Li(2)O -- the only thermodynamically and kinetically stable component (in the absence of a fluoride source). This work should also be relevant to inadvertant lithium plating during battery cycling, and SEI evolution on Li(x)Si surfaces.

Layer Number Dependence of Li(+) Intercalation on Few-Layer Graphene and Electrochemical Imaging of Its Solid-Electrolyte Interphase Evolution.

A fundamental question facing electrodes made out of few layers of graphene (FLG) is if they display chemical properties that are different to their bulk graphite counterpart. Here, we show evidence that suggests that lithium ion intercalation on FLG, as measured via stationary voltammetry, shows a strong dependence on the number of layers of graphene that compose the electrode. Despite its extreme thinness and turbostratic structure, Li ion intercalation into FLG still proceeds through a staging process, albeit with different signatures than bulk graphite or multilayer graphene. Single-layer graphene does not show any evidence of ion intercalation, while FLG with four graphene layers displays limited staging peaks, which broaden and increase in number as the layer number increases to six. Despite these mechanistic differences on ion intercalation, the formation of a solid-electrolyte interphase (SEI) was observed on all electrodes. Scanning electrochemical microscopy (SECM) in the feedback mode was used to demonstrate changes in the surface conductivity of FLG during SEI evolution. Observation of ion intercalation on large area FLG was conditioned to the fabrication of "ionic channels" on the electrode. SECM measurements using a recently developed Li-ion sensitive imaging technique evidenced the role of these channels in enabling Li-ion intercalation through localized flux measurements. This work highlights the impact of nanostructure and microstructure on macroscopic electrochemical behavior and provides guidance to the mechanistic control of ion intercalation using graphene, an atomically thin interface where surface and bulk reactivity converge.

In‐Situ Spectro–electrochemical Insight Revealing Distinctive Silicon Anode Solid Electrolyte Interphase Formation in a Lithium–ion Battery

AbstractThe formation and evolution of solid electrolyte interphase (SEI) layer on a silicon electrode in 1 m LiPF6 in EC/DMC electrolyte is investigated by in‐situ FTIR spectroscopy. The results point that lithium alkyl carbonates formation is initiated during a lithiation process via a one‐electron reduction of EC/DMC, followed by a free radical reaction. Interesting enough, the studies indicate that most of the SEI material is actually formed in the delithiation process. Carbon dioxide (CO2) generated at low potentials during the shallow lithiation process is consumed during a deeper lithiation process and also during subsequent delithiation processes, resulting in the formation of lithium carbonate.

Local Structure and Stability of SEI in Graphite and ZFO Electrodes Probed by As K-Edge Absorption Spectroscopy

The evolution of the solid electrolyte interphase (SEI) during the first Li uptake in advanced Li-ion electrodes is studied by X-ray absorption spectroscopy (XAS). The As atoms present in the electrolyte solution were used as a local probe for monitoring the SEI growth on different electrodes. High-quality As K-edge spectra were collected in fluorescence mode for a set of graphite and carbon-coated ZnFe2O4 electrodes. XAS measurements have been preceded and corroborated by electrochemical characterizations. SEI phase evolution was analyzed by distinct As valence states in the subsequent stages of SEI formation, while X-ray fluorescence (XRF) was used to estimate the As content. Detailed structural results are presented for different Li contents in different electrodes including the estimated thickness of the SEI layer, contribution of different As oxidation states, and As local structure. The formation of AsFN complexes with different local coordination N is clearly observed and measured at various SEI evolution stages. Evidence of a partially reversed redox process, taking place within the SEI by charge–discharge cycling, was also obtained.

Free-standing Ni–NiO nanofiber cloth anode for high capacity and high rate Li-ion batteries

Here we present a low cost, free-standing, high capacity, stable, and environmentally benign nickel–nickel oxide (Ni–NiO) nanofiber cloth anode for Li-ion batteries. Ni–NiO nanofibers are fabricated by simple electrospinning and thermal oxidation processes which create a free-standing, core–shell nanofiber structure. The nickel backbone mitigates poor conductivity issues observed in Li-ion anodes due to repeated volume change during lithiation/delithiation. The Ni–NiO nanofiber anode possesses a high surface area compared to that of a slurry cast electrode which helps facilitate Li-ion diffusion into the active material. Electrochemical impedance spectroscopy indicates improved capability of current collecting metal (nickel in this case) to withstand volume change in our free-standing structure. Furthermore, scanning electron microscopy indicates the stability of the Ni–NiO nanofiber cloth anode in excess of 400 charge/discharge cycles, partly evidenced by the stable evolution of solid-electrolyte interphase. As an anode, the Ni–NiO nanofiber cloth shows impressive results with a gravimetric capacity of 1054mAhg−1 at a current density of 2154mAg−1 or 3C (1C=718mAg−1), a long cycle life of more than 1500 cycles, and exceptional stability throughout its cycle life with a Coulombic efficiency >99%. Performance evaluation enables the Ni–NiO cloth material for next-generation high capacity, high rate, stable, and environmentally benign Li-ion batteries.

Binary iron-chromium oxide as negative electrode for lithium-ion micro-batteries – spectroscopic and microscopic characterization

(Fe,Cr)-binary oxide thin film electrodes were prepared as negative electrode material for lithium-ion micro-batteries by thermal growth on a stainless steel (AISI 410, FeCr12.5) current collector. The mechanisms of lithiation/delithiation were investigated by means of electrochemical (CV, galvanostatic cycling), spectroscopic (XPS, ToF-SIMS) and microscopic (SEM, AFM) analytical techniques. The as-prepared (Fe, Cr)-binary oxide electrodes exhibit a good cycling performance except the first discharge/charge cycle where a high irreversible capacity is observed due to formation of a solid electrolyte interphase (SEI) layer. The influence of substituting an oxidized iron by an oxidized chromium (CrxFe2−xO3 phase) was evaluated. The data show that the inferior electrochemical conversion activity of substituted oxidized chromium results in hindering lithium transport in the bulk thin film electrode. It was observed that the irreversible morphology modifications together with SEI evolution are critical to capacity degradation while retaining good coulombic efficiency.

Cover Picture: Solid–Electrolyte Interphase Evolution of Carbon‐Coated Silicon Nanoparticles for Lithium‐Ion Batteries Monitored by Transmission Electron Microscopy and Impedance Spectroscopy (Energy Technol. 7/2015)

Cover Picture: Solid–Electrolyte Interphase Evolution of Carbon‐Coated Silicon Nanoparticles for Lithium‐Ion Batteries Monitored by Transmission Electron Microscopy and Impedance Spectroscopy (Energy Technol. 7/2015)

Solid–Electrolyte Interphase Evolution of Carbon‐Coated Silicon Nanoparticles for Lithium‐Ion Batteries Monitored by Transmission Electron Microscopy and Impedance Spectroscopy

AbstractThe main drawbacks of silicon as the most promising anode material for lithium‐ion batteries (theoretical capacity=3572 mAh g−1) are lithiation‐induced volume changes and the continuous formation of a solid–electrolyte interphase (SEI) upon cycling. A recent strategy is to focus on the influence of coatings and composite materials. To this end, the evolution of the SEI, as well as an applied carbon coating, on nanosilicon electrodes during the first electrochemical cycles is monitored. Two specific techniques are combined: Transmission Electron Microscopy (TEM) is used to study the surface evolution of the nanoparticles on a very local scale, whereas electrochemical impedance spectroscopy (EIS) provides information on the electrode level. A TEM–EELS fingerprint signal of carbonate structures from the SEI is discovered, which can be used to differentiate between the SEI and a graphitic carbon matrix. Furthermore, the shielding effect of the carbon coating and the thickness evolution of the SEI are described.

Single nanowire electrode electrochemistry of silicon anode by in situ atomic force microscopy: solid electrolyte interphase growth and mechanical properties.

Silicon nanowires (SiNWs) have attracted great attention as promising anode materials for lithium ion batteries (LIBs) on account of their high capacity and improved cyclability compared with bulk silicon. The interface behavior, especially the solid electrolyte interphase (SEI), plays a significant role in the performance and stability of the electrodes. We report herein an in situ single nanowire atomic force microscopy (AFM) method to investigate the interface electrochemistry of silicon nanowire (SiNW) electrode. The morphology and Young's modulus of the individual SiNW anode surface during the SEI growth were quantitatively tracked. Three distinct stages of the SEI formation on the SiNW anode were observed. On the basis of the potential-dependent morphology and Young's modulus evolution of SEI, a mixture-packing structural model was proposed for the SEI film on SiNW anode.

Evolution of Solid Electrolyte Interphase during Cycling and Its Effect on Electrochemical Properties of LiMn2O4

Thickness variation of the solid electrolyte interphase (SEI) produced during charge-discharge cycling is investigated to analyze the effect of SEI on the electrochemical properties of LiMn2O4. Atomic force microscopy (AFM) is used to measure the SEI thickness and elastic modulus on the LiMn2O4 surface. The SEI shows a broad thickness distribution due to the random nature of the LiMn2O4 electrode surfaces, while the average SEI thickness increases with cycling and stabilizes after the 20th cycle. Formation of a relatively thin SEI on the LiMn2O4 surface accompanies low Coulombic efficiency at early cycling stages. The SEI produced in the early stages of cycling is vulnerable to capacity fading due to inefficient surface protection against possible side reactions. A fully-grown stable SEI after 20 cycles shields the cathode surface from the electrolyte, minimizing capacity fading.

Molecular Structure and Ion Transport Near Electrode-Electrolyte Interfaces in Lithium-Ion Batteries

The performance of lithium-ion secondary batteries (LIBs) is strongly tied to ionic transport through electrode-electrolyte interfaces. Solvation structure strongly affects ion mobility, and differences in ion solvation near the interface compared to the bulk may affect conductivity. Furthermore, the formation and evolution of solid-electrolyte interphase (SEI) layers, which impede transport between electrode and electrolyte while passivating the interface, are related to molecular interactions at the interface involving solvent molecules, ions, and the electrode surface. In addition, the chemistry of the electrode surface, in particular the edge termination of graphite electrodes, can impact Li ion transport into the electrode and formation of SEI. Understanding these effects is critical to optimizing battery performance.Here we present molecular dynamics (MD) simulations of typical organic liquid LIB electrolytes in contact with graphite electrodes to understand the relationship between ion solvation structure and transport near the interface. Results for different graphite terminations are presented and the effect of an electric field is explored. Different prototypical organic liquids, including ethylene carbonate and ethyl methyl carbonate, are compared. We observe that anion mobility in an electric field is much greater than that for Li ions, a phenomenon due to the very different solvation structures. In addition, we observe a barrier to Li insertion into graphite when its surface is hydroxyl terminated. Furthermore, we compare the results of ab initio MD with the empirical reactive forcefield ReaxFF and the non-reactive, non-polarizable COMPASS forcefield and note differences in the predictive power of each technique. Prepared by LLNL under Contract DE-AC52-07NA27344.

Solid Electrolyte Interphase Evolution in the Presence of Vinylene Carbonate and Vinyl Ethylene Carbonate Electrolyte Additives in Li-Ion Battery Anodes

not Available.

NUMERICAL IMPLEMENTATION OF POROUS COMPOSITE ELECTRODE–DEGRADATION MODEL TO STUDY THE CYCLE LIFE OF LI-ION CELL

A numerical study is performed on the cyclic capacity degradation of a lithium manganese oxide (LMO) cell, under 21 different combinations of temperature and state of charge (SOC), based on the phenomenological model developed earlier. Out of the 21 sets, six are used for fitting in order to establish the degradation parameters of the model and the rest could be predicted with an average accuracy of about 90%. Two optimization algorithms (Genetic and Nelder Mead) are used and the consistency of the convergence is verified. The discussion includes sensitivity analysis of a selected set of degradation parameters. In addition, an analysis of the evolution of solid electrolyte interphase (SEI) and isolation (islanding) mechanisms under varying conditions of SOC and temperatures is performed which brings out the relative contribution of each mechanism to the overall capacity fade.