Properties Of Solid Electrolyte Interphase Research Articles

Tuning the Formation and Structure of the Silicon Electrode/Ionic Liquid Electrolyte Interphase in Superconcentrated Ionic Liquids.

The latest advances in the stabilization of Li/Na metal battery and Li-ion battery cycling have highlighted the importance of electrode/electrolyte interface [solid electrolyte interphase (SEI)] and its direct link to cycling behavior. To understand the structure and properties of the SEI, we used combined experimental and computational studies to unveil how the ionic liquid (IL) cation nature and salt concentration impact the silicon/IL electrolyte interfacial structure and the formed SEI. The nature of the IL cation is found to be important to control the electrolyte reductive decomposition that influences the SEI composition and properties and the reversibility of the Li-Si alloying process. Also, increasing the Li salt concentration changes the interface structure for a favorable and less resistive SEI. The most promising interface for the Si-based battery was found to be in P1222FSI with 3.2 m LiFSI, which leads to an optimal SEI after 100 cycles in which LiF and trapped LiFSI are the only distinguishable lithiated and fluorinated products detected. This study shows a clear link between the nanostructure of the IL electrolyte near the electrode surface, the resulting SEI, and the Si negative electrode cycling performance. More importantly, this work will aid the rational design of Si-based Li-ion batteries using IL electrolytes in an area that has so far been neglected, reinforcing the benefits of superconcentrated electrolyte systems.

Solid Electrolyte Interphase on Li/Na Anodes in Contact with Liquid Electrolytes

Electrolyte consumption and continuous solid electrolyte interphase (SEI) growth are some of the crucial issues preventing the commercialization of battery systems depending on implementation of Li/Na metal anodes.1 In this work, recent study of SEI growth on Li metal in contact with glyme-based liquid/solid electrolyte under galvanostatic and OCV conditions by electrochemical impedance spectroscopy (EIS), ex situ X-ray photoelectron spectroscopy (XPS), and focused ion beam scanning electron microscopy (FIB-SEM) is presented.2,3 Under OCV conditions, reaction-controlled mechanism is substituted by diffusion-controlled mechanism at longer growth times. Upon galvanostatic cycling, both the SEI thickness and its room temperature ionic conductivity increase. Additionally, the transport properties of SEI are strongly influenced by the type of lithium salt and the concentration used. In the last part, a comparison of SEI growth in Li vs. Na cells in contact with glymes, carbonates, and water-containing electrolytes is given.4 Zhang, Zuo, Popovic, Lim, Yin, Maier, Guo, Towards better Li metal anodes: Challenges and strategies, Materials Today, 33, 56 (2020)Nojabaee, Popovic, Maier, Glyme-based liquid-solid electrolytes for lithium metal batteries, J. Mater. Chem. A, 7, 13331 (2019)Nojabaee, Küster, Starke, Popovic, Maier, Solid electrolyte interphase evolution on lithium metal in contact with glyme-based electrolytes, Small, 16(23), 2000756 (2020)Lim, Popovic, Maier, in preparation

Unraveling the mechanical origin of stable solid electrolyte interphase

Summary The capability of a solid electrolyte interphase (SEI) in accommodating deformation is critical to the electrode integrity. However, the nanoscale thickness and environmental sensitivity of SEI make it challenging to characterize multiple mechanical parameters and identify an appropriate predictor for such capability. Here, we develop a feasible atomic force microscopy (AFM)-based nanoindentation test that circumvents the interference of the anode substrate and allows accurate probing of Young's modulus and elastic strain limit of SEI. The "maximum elastic deformation energy" (U) that an SEI can absorb is proposed to predict the stability of the SEI, as successfully demonstrated in Li/K metal anodes. We show that another asset of U is to provide a rapid and effective means to screen proper electrolytes for the stabilization of Sn and Sb microparticle anodes through building high-U SEIs. Overall, this new indicator, U, offers future directions toward rational design of robust SEIs for advanced anodes.

Synergistic Effect of Temperature and Electrolyte Concentration on Solid‐State Interphase for High‐Performance Lithium Metal Batteries

Lithium metal batteries (LMBs) are considered as the development direction of next‐generation rechargeable lithium batteries owing to their high energy densities. The electrochemical and safety performances of LMBs are significantly influenced by the solid electrolyte interphase (SEI) formed on the surface of lithium anode. Herein, the effects of both salt concentration and temperature on the SEI composition and properties are systematically investigated. The results reveal that either reducing the salt concentration to ultralow levels or elevating the temperature can lead to a more complete decomposition of the LiFSI salt. Meanwhile, the LiNO3‐rich SEI formed in the most dilute electrolyte (0.1 m) exhibits a better protective effect on lithium metal than the Li3N‐rich SEI formed in other electrolytes with higher salt concentrations. Benefiting from the compact and stable SEI, Li|Li4Ti5O12 batteries using the 0.1 m electrolyte possess the most superior cycling and rate performance at high temperature. This work generates a holistic understanding of the synergistic effects of salt concentration and temperature on SEI. Moreover, the utilization of dilute electrolytes not only renders a superior electrochemical performance of batteries at high temperature, but can also lower the production cost of electrolytes, showing a promising application potential in LMBs.

Influence of Mn2+ on mechanical, dynamical, and structural properties of solid electrolyte interphase in Li-ion batteries: A molecular dynamics simulation study

The influence of different amounts of Mn2+ contaminants on mechanical, dynamical, and structural properties of a solid electrolyte interphase (SEI) has been studied using atomistic molecular dynamics and Monte-Carlo simulations employing the many-body polarizable APPLE&P force field. Bulk SEI systems comprised of amorphous Li2CO3 with some fraction of cations replaced with Mn2+ ions have been investigated over a wide temperature range. Replacement of 5, 10, or 20% of positive charges with Mn2+ ions resulted in 3, 6, or 11% increase in density and leading to approximately a 20, 50, or 100 K increase in the glass transition temperature (Tg), respectively. Cations and anions showed similar dynamics at high temperatures, however at temperatures approaching Tg the CO32− and Mn2+ ions showed an expected divergent slowing down in dynamics therefore forming a glassy matrix in which Li+ ions continued to show significant movements, i.e. Li+ dynamics showed a decoupling from the dynamics of other ions. The Li+ conductivity values on the order of 10−6 S/cm have been observed for all concentrations at room temperature. Addition of Mn2+ ions also resulted in an increase of the shear modulus leading to values higher than 8 GPa at room temperature, which is high enough to potentially suppress the Li metal dendrite growth.

Recent Progress in Understanding Solid Electrolyte Interphase on Lithium Metal Anodes

AbstractLithium metal batteries (LMBs) are one of the most promising candidates for next‐generation high‐energy‐density rechargeable batteries. Solid electrolyte interphase (SEI) on Li metal anodes plays a significant role in influencing the Li deposition morphology and the cycle life of LMBs. However, a thorough understanding on the mechanisms of SEI formation and evolution is still inadequate. In this review, the progress in understanding structures, properties, and influencing factors of SEI, as well as efficient strategies of tailoring SEI are focused upon. First, the compositions, models, and recent progress in characterizing atomic structures of SEI are summarized. Second, the properties of SEI, including electronic conduction, ionic conduction, stability, and mechanical properties are elucidated. Structures and properties of SEI are greatly affected by multiple factors, thus interactions between these factors and SEI are systematically discussed. Correlations of SEI with Li deposition morphology, rate capability, and cycle life are further summarized. Moreover, efficient strategies of tailoring SEI with desired properties, including in situ SEI and ex situ SEI, are also reviewed. Finally, future directions, including in‐operando techniques, multi‐modality approaches for characterization of SEI, and artificial intelligence assisted understanding of correlations between electrolyte components and SEI properties are proposed.

Polysulfide reduction and Li2S phase formation in the presence of lithium metal and solid electrolyte interphase layer

Lithium sulfur battery is an attractive next generation technology that can meet many demands of modern society. Unfortunately, the lithium sulfur battery faces unique issues related to the polysulfide shuttle effect, that is due to reduction products dissolving in the electrolyte and their subsequent reduction on the lithium metal electrode. This adds further problems to the already challenging needs of understanding and engineering a solid electrolyte interphase (SEI) layer with desired properties. One of the most important SEI properties is its passivation of lithium metal which is critically important to the overall battery performance. Passivation is difficult to measure experimentally without the influence of many factors. This study reports an investigation of the reduction of the intermediate Li2S8 over lithium already passivated with Li2O, Li2CO3, LiOH, LiF and Li2S along with exploration of Li2S8 reduction over pristine lithium nanoclusters using first principles computational models. Significant formation of Li2S phase nucleation is found to stabilize the reduction products of the Li2S8. The formation of Li2S is explored in-depth with lithium nanocluster-based models determining a 2 V potential increase for the reduction of polysulfides due to the formation of Li2S. This investigation demonstrates passivation effects of important SEI components including Li2S.

Nucleation, Growth, and Properties of the Solid Electrolyte Interphase – a Multimodal Approach Using a Model System

Due to the low potentials on anode materials in lithium-ion batteries, the electrolyte decomposes on the anode forming a passivation layer, termed solid electrolyte interphase (SEI). The SEI plays an essential role in battery performance since it is a major source of capacity loss and dictates cell kinetics. Nevertheless, the properties of the SEI are not yet well-understood.Here, we present the utilization of a simple and well-defined model system to understand the atomic level SEI nucleation and growth, as well as structural and chemical properties. Experiments were performed in a half-cell configuration with N-doped silicon carbide (N-SiC) wafer working electrode, Li metal counter/reference electrode, and LP30 electrolyte (1M LiPF6 in 1:1 wt% ethylene carbonate:dimethyl carbonate). N-SiC has the advantage of being electrically conductive but electrochemically inactive, allowing for a straightforward interpretation of electrochemical and structural measurements, and provides information on the intrinsic electrolyte reactivity.We used a multimodal approach combining in-situ X-ray reflectivity (XRR), precision electrochemistry at slow rates (e.g. 0.16 mV/s cyclic voltammetry), X-ray photoelectron spectroscopy (XPS), and X-ray diffraction (XRD). We obtained the evolution of the SEI’s thickness, electron density, and roughness through quantitative operando XRR measurements during the first two cyclic voltammetry (CV) cycles. Further, we found via complementary XPS experiment that the SEI was mainly composed of LiF, and we tracked the crystalline LiF growth with in-situ XRD. LiF can be formed via two reaction pathways. One is the direct reduction of PF6 -, the other is the electrocatalytic hydrogen evolution reaction of the trace amount of HF in the electrolyte, forming LiF and H2. In order to elucidate the formation mechanism of LiF, we combined the electrochemical and structural/chemical results for LP30 with precise electrochemistry using several baseline LiPF6 and/or HF containing electrolytes. The results indicate that the direct reduction of PF6 - contributes to LiF formed at ~ 1.5 V versus Li/Li+, consistent with our quantum chemistry calculations. Finally, we revealed that the ratio between organic and inorganic compounds in SEI could be tuned by changing the cycling rate.We envision that this methodology and the use of well-defined model systems can be applied to other electrolyte-electrode systems. Our results are essential in understanding the formation mechanism and properties of SEI and can aid future experimental and computational works.

(Invited) Visualizing Live-Formation of Interphase at Atomic Scale

The solid-electrolyte-interphase (SEI) in Li-ion battery has been considered one of the most important but least understood and elusive component. In this work, its live-formation was visualized quantitatively at atomistic level with unique combination of in-situ/operando techniques. For the first time, the precise weighing of graphitic anode during its initial lithiation process was realized with electrochemical quartz crystal microbalance, which unequivocally identifies lithium fluoride (LiF) and lithium alkylcarbonates as the main chemical components of the interphase at different potentials. In-situ gas analysis confirmed the preferential reduction of cyclic over acyclic carbonate molecules, making lithium ethylene dicarbonate (LEDC) the major product contributed from solvent. This lithium alkylcarbonate, at least in its nascent form, was revealed to be re-oxidizable, despite general belief that interphase is electrochemically inert and its formation irreversible. Meanwhile, atomic force microscope found that the presence of LEDC on graphitic surface started at edge sites, which does not seem to occur in an obvious staging manner as the intercalation of Li+ does. These atomistic and quantitative observations shed new light on the formation chemistry, mechanism and properties of SEI. Such in-depth understanding will serve as guiding principles for the tailor-design of ideal interphases in future battery chemistries.

Effect of Artificial SEI Content on Lithium Metal Anode Morphology and Performance

Lithium metal is often deemed the “Holy Grail” of rechargeable battery technology, due to its high theoretical capacity and low electrochemical potential. However, the cascading heterogeneity from the formation of the solid-electrolyte interphase (SEI) up to the non-uniform current distribution leads to both poor efficiency via rapid consumption of active materials as well as safety issues from treacherous dendrite growth. An SEI that is ionically conductive while electrically resistive, viscoelastic, electrochemically stable, and possesses good mechanical properties is paramount for hindering these failure mechanisms. The discovery of novel approaches to producing an ideal SEI is a crucial piece to solving the lithium metal anode puzzle.One route of controlling the SEI is through interface engineering by producing a stable artificial SEI. In this work, a mixed artificial SEI was produced with aim toward improving ionic conductivity while retaining electrochemical stability and mechanical properties. This mixed SEI embraces the unavoidable surface heterogeneity, all the while preventing dendrite growth that plagues lithium metal batteries. A mixed artificial SEI, as well as a single-component artificial SEI, were produced through a simple and rapid deposition method and tested to observe their failure mechanisms compared to bare lithium.Symmetric cells (i.e., Li||Li) were utilized to isolate the failure mechanisms of these different anode treatments. The failure mechanism of the single-component artificial SEI cells shifted to failure via electrolyte consumption rather than short circuiting seen with bare lithium. This revealed that artificial interphases led to reduced dendrite propagation. Additionally, a reduction in cell potential range was observed with the mixed artificial SEI when compared to the single-component artificial SEI, as well as improved cyclability. Upon further investigation, it appears that the added component of the mixed artificial SEI, which was meant to improve the ionic conductivity, dissolved into the electrolyte upon initial exposure. This dissolution left behind a new SEI structure, theoretically producing easier ionic pathways and thus resulting in decreased cell overpotential. Dissolution was confirmed with high-resolution surface characterization techniques. Additionally, symmetric cell electrodes rinsed with solvent prior to testing retained superior cell performance. Though this dissolution should lead to increased available “hot spots”, the growth of dendrites was hindered. This work discusses the effect an artificial SEI has on failure mechanisms, as well as provides insight into the methods of producing stable, long-life lithium metal batteries. This includes a focus on how nanoscale heterogeneity effects cell-scale performance via high-resolution characterization and computational simulations.Different surface to sub-surface characterization techniques were utilized to measure properties of artificial SEIs and bare lithium. Scanning electron microscopy with energy dispersive X-ray spectroscopy (SEM/EDS) provided elemental make-up and distribution, as well as morphological characteristics. X-ray photoelectron spectroscopy (XPS) provided the chemical state of surfaces, as well as sub-surfaces with the use of depth profiling. Different atomic force microscopy (AFM) techniques were used to spatially measure nanoscale properties such as work functions with the Kelvin probe technique (SKPFM) and quantifiable nanomechanical properties (QNM), as well as observe kinetic mechanisms with in-situ electrochemical methods (EC-AFM). Lastly, computational simulations from the atomistic scale via density functional theory (DFT) up to molecular dynamics (MD) were utilized to support assumptions on the reaction mechanisms derived from experimental observations. Figure 1

A review on the failure and regulation of solid electrolyte interphase in lithium batteries

SEI failure mechanisms, involving thermal failure, chemical failure, and mechanical failure and effective regulation strategies are summarized in this review. Solid electrolyte interphase (SEI) has been widely recognized as the most important and the least understood component in lithium batteries. Considering the intrinsic instability in both chemical and mechanical, the failure of SEI is inevitable and strongly associated with the performance decay of practical working batteries. In this Review, the failure mechanisms and the corresponding regulation strategies of SEI are focused. Firstly, the fundamental properties of SEI, including the formation principles, and the typical composition and structures are briefly introduced. Moreover, the common SEI failure modes involving thermal failure, chemical failure, and mechanical failure are classified and discussed, respectively. Beyond that, the regulation strategies of SEI with respect to different failure modes are further concluded. Finally, the future endeavor in further disclosing the mysteries of SEI is prospected.

Structures of Solid‐Electrolyte Interphases and Impacts on Initial‐Stage Lithium Deposition in Pyrrolidinium‐Based Ionic Liquids

AbstractElectrodeposition of lithium is of both fundamental significance and practical importance. However, Li deposition has to proceed beneath a solid‐electrolyte interphase (SEI). Herein, we present a fundamental study on the formation of SEIs and their influences on Li initial‐stage deposition on Cu in Py14 cation‐based ionic liquids (ILs) combined with different ratios of TFSI and FSI anions. Different SEIs are pre‐formed on Cu by using cyclic voltammetry, followed by detailed characterizations by XPS and AFM, which elucidate that all the SEIs bear mosaic‐like I−O structures but with different compositions and structures and varying thicknesses of approximately 60–150 nm. The Li initial‐stage depositions are studied by using cyclic voltammetric and potential stepping techniques, and current‐time transients are analyzed with the aid of the Scharifker‐Hills model. Discrepancies in nucleation density and diffusion coefficients and their relationships with overpotentials are investigated in correlation with the SEI structures. The present work demonstrates that interfacial and bulk properties of SEI strongly affect the Li deposition processes, which provides opportunities for uniform Li deposition.

Effect of Water Concentration in LiPF6-Based Electrolytes on the Formation, Evolution, and Properties of the Solid Electrolyte Interphase on Si Anodes.

A trace amount of water in an electrolyte is one of the factors detrimental to the electrochemical performance of silicon (Si)-based lithium-ion batteries that adversely affect the formation and evolution of the solid electrolyte interphase (SEI) on Si-based anodes and change its properties. Thus far, a lack of fundamental and mechanistic understanding of SEI formation, evolution, and properties in the presence of water has inhibited efforts to stabilize the SEI for improved electrochemical performance. Thus, we investigated the SEI formed in a Gen2 electrolyte (1.2 M LiPF6 in ethylene carbonate/ethyl methyl carbonate, 3:7 wt %, water content: <10 ppm) with and without additional water (50 ppm) at varying potentials (1.0, 0.5, 0.2, and 0.01 V vs Li/Li+). The impact of additional water on the morphological, (electro)chemical, and structural properties of SEI was studied using microscopic (atomic force microscopy and scanning spreading resistance microscopy) and spectroscopic (X-ray photoelectron spectroscopy, attenuated total reflection Fourier-transform infrared spectroscopy, and time-of-flight secondary ion mass spectrometry) techniques. The SEI exhibits both potential- and water concentration-dependent trends in its morphology and chemical composition. The presence of additional water in the electrolyte causes parasitic reactions, which onset at ∼1.0 V, resulting in a reduction of electrolyte components and result in the formation of an insulating, fluorophosphate-rich SEI. In addition, hydrolysis of LiPF6 creates hydrofluoric acid, which reacts with the surface oxide layer on the Si electrode, leading to a pitted and inhomogeneous SEI structure.

Not All Fluorination Is the Same: Unique Effects of Fluorine Functionalization of Ethylene Carbonate for Tuning Solid-Electrolyte Interphase in Li Metal Batteries.

Li metal batteries (LMBs) are crucial for electrifying transportation and aviation. Engineering electrolytes to form desired solid-electrolyte interphase (SEI) is one of the most promising approaches to enable stable long-lasting LMBs. Among the liquid electrolytes explored, fluoroethylene carbonate (FEC) has seen great success in leading to desirable SEI properties for enabling stable cycling of LMBs. Given the many facets to desirable SEI properties, numerous descriptors and mechanisms have been proposed. To build a detailed mechanistic understanding, we analyze varying degrees of fluorination of the same prototype molecule, chosen to be ethylene carbonate (EC) to tease out the interfacial reactivity at the Li metal/electrolyte. Using density functional theory (DFT) calculations, we study the effect of mono-, di-, tri-, and tetra-fluorine substitutions of EC on its reactivity with Li surface facets in the presence and absence of Li salt. We find that the formation of LiF at the early stage of SEI formation, posited as a desirable SEI component, depends on the F-abstraction mechanism rather than the number of fluorine substitution. The best illustrations of this are cis- and trans-difluoro ECs, where F-abstraction is spontaneous with the trans case, while the cis case needs to overcome a nonzero energy barrier. Using a Pearson correlation map, we find that the extent of initial chemical decomposition quantified by the associated reaction free energy is linearly correlated with the charge transferred from the Li surface and the number of covalent-like bonds formed at the surface. The effect of salt and the surface facet have a much weaker role in determining the decompositions at the immediate electrolyte/electrode interfaces. Putting all of this together, we find that tetra-FEC could act as a high-performing SEI modifier as it leads to a more homogeneous, denser LiF-containing SEI. Using this methodology, future investigations will explore -CF3 functionalization and other backbone molecules (linear carbonates).

Evaluating Solid-Electrolyte Interphases for Lithium and Lithium-free Anodes from Nanoindentation Features

Summary The morphology and mechanical property of SEIs for lithium anodes crucially affect the electrochemical cycling performance of Li-metal batteries such as Li-S and Li-O2 batteries. Herein, we establish the standards for rapidly assessing SEIs for Li and Li-free type of anodes by AFM nanoindentation features toward prediction of corresponding electrochemical performances. A series of single-layered and multi-layered SEIs with known composition and structures are purposely constructed. A set of unique nanoindentation features representative of mechanical properties of the basic SEIs are formed, serving as the standards for rapidly assessing the mechanical properties and electrochemical performances of unknown SEIs together with their Young’s modulus, smoothness, and thickness. To validate the applicability of the method, SEIs formed by electrochemical aging and formed on Cu substrates are further evaluated. Our work not only contributes to understanding the influence of SEIs on cycling performances but also provides a rapid way for screening SEIs.

Origins of irreversible capacity loss in hard carbon negative electrodes for potassium-ion batteries.

Hard carbon (HC) is considered as a negative electrode material for potassium-ion batteries, but it suffers from significant irreversible capacity loss at the first discharge cycle. Here, we investigated the possible reasons of this capacity loss with a combination of in situ AFM and various ex situ TEM techniques (high resolution TEM and high angle annular dark field scanning TEM imaging, and STEM-EELS and STEM-EDX spectroscopic mapping) targeting the electrode/electrolyte interphase formation process in the carbonate-based electrolyte with and without vinylene carbonate (VC) as an additive. The studied HC consists of curved graphitic layers arranged into short packets and round cages, the latter acting as traps for K+ ions causing low Coulombic efficiency between cycling. Our comparative study of solid electrolyte interphase (SEI) formation in the carbonate-based electrolyte with and without the VC additive revealed that in the pristine electrolyte, the SEI consists mostly of inorganic components, whereas adding VC introduces a polymeric organic component to the SEI, increasing its elasticity and stability against fracturing upon HC expansion/contraction during electrochemical cycling. Additionally, significant K+ loss occurs due to Na+ for K+ exchange in Na-carboxymethyl cellulose used as a binder. These findings reflect the cumulative impact of the internal HC structure, SEI properties, and binder nature into the electrochemical functional properties of the HC-based anodes for K-ion batteries.

Methods of Composite Electrode Imaging

Lithium intercalation electrodes are composite devices that consist of typically at least four different constituents that provide separately charge storage, electronic conduction, ionic conduction and mechanical integrity. Consequently, the microstructure of these composites has an important role to play in intercalation electrode performance. An inhomogeneous electrode microstructure affects battery performance by increasing peak local current densities and resistances during the operation. This reduces accessible capacity, compromises safety, as it facilitates localized overcharging, and impacts ion transport and consequently power performance.1 Origins for inhomogeneity in electrode microstructure can lie in the casting procedure, slow carbon agglomeration over cycling as well as in binder adhesive failure due to active material volume changes, which causes a connectivity loss between active material and the matrix.Given this impact of the electrode microstructure, an improved understanding of microstructure and microscopic performance variations is of great importance to optimizing overall battery performance. As such, we need tools that allow us to measure microscopic performance, and correlate to microstructure, interfaces and their development over cycling. Thus a variety of spatial imaging techniques can be used to characterize the processes ex situ, in situ, and operando. Each technique gives a unique and specific information about certain process.2 , 1 We are highlighting herein X-ray tomography and scanning electrochemical microscopy (SECM) as tools for the investigation of disconnection mechanisms.X-ray Tomography (XRT) is a 3D imaging technique used to visualize complex mechanical interactions in batteries during operation. This nondestructive technique can provide a spatial resolution down to the nanometer scale. X-ray tomography can provide information of the material porosity and tortuosity, chemical composition and crystals and the reactions inside the battery.4 , 2 We are using this technique in the imaging, analysis and tracking of electrode microstructure with cycling.Scanning electrochemical microscopy (SECM) is a scanning probe technique that uses a microscopic electrochemical electrode as probe. This allows the measurement of local electrochemical activity on a substrate surface. It has previously been used to investigate the properties of solid electrolyte interphase (SEI) of the negative electrode as well as exploring the lithium ion activity at micro and nano scales resolution.3 We are employing this method to correlate microstructure and performance inhomogeneity.This presentation summarizes first results from both techniques and contrasts structural with performance inhomogeneity. We will be using these tools as we are developing new binders and microstructures for intercalation electrodes to improve the synergy between electrode constituents and optimize overall electrode performance.References(1) Müller, S.; Eller, J.; Ebner, M.; Burns, C.; Dahn, J.; Wood, V. Quantifying Inhomogeneity of Lithium Ion Battery Electrodes and Its Influence on Electrochemical Performance. J. Electrochem. Soc. 2018, 165 (2), A339–A344. https://doi.org/10.1149/2.0311802jes.(2) Schröder, D.; Bender, C. L.; Arlt, T.; Osenberg, M.; Hilger, A.; Risse, S.; Ballauff, M.; Manke, I.; Janek, J. In Operando X-Ray Tomography for next-Generation Batteries: A Systematic Approach to Monitor Reaction Product Distribution and Transport Processes. J. Phys. D. Appl. Phys. 2016, 49 (40), 404001. https://doi.org/10.1088/0022-3727/49/40/404001.(3) Ventosa, E.; Schuhmann, W. Scanning Electrochemical Microscopy of Li-Ion Batteries. Phys. Chem. Chem. Phys. 2015, 17 (43), 28441–28450. https://doi.org/10.1039/c5cp02268a.(4) Pietsch, P.; Wood, V. X-Ray Tomography for Lithium Ion Battery Research: A Practical Guide. Annu. Rev. Mater. Res. 2017, 47 (1), 451–479. https://doi.org/10.1146/annurev-matsci-070616-123957.

(Invited) Stability and Evolution of Solid Electrolyte Interphase on Silicon Anodes

Solid electrolyte interphase (SEI), which forms at the interface between the electrolyte and the electrode, can passivate the surface of graphite anodes and finally facilitate the intercalation of lithium ions into graphite electrodes. However, the concept of only using SEI protects the electrode surface from the reductive electrolyte may be not applicable for silicon (Si) anodes. Different from the intercalation chemistry in graphite anodes, Si anodes experience alloying/dealloying reactions during electrochemical process, leading to phase transformation, morphology and volumetric changes. It generates great complexity in understanding the formation and the structural/composition evolution of the SEI layer during electrochemical process. Considering the high theoretical capacity Si anodes can offer, the investigation of SEI behavior on Si anodes is critical for developing next-generation anode materials. This presentation, which is based on recent results from advanced electrochemical and spectroscopy characterization, systematically elaborates the chemical and physical properties of SEI toward mitigation strategies for stabilizing SEI on Si anodes.

(Invited) Multiscale Modeling of Formation and Properties of Solid-Electrolyte Interphases in Li-Ion Batteries

In this talk we will discuss recent efforts on multiscale modeling of solid-electrolyte interphase (SEI) and cathode-electrolyte interphases(CEI). The complexity and multiscale phenomena operating at electrode/electrolyte interfaces do not allow to access all necessary length and time scales using a single modeling approach. Combining information from high-level ab initio and DFT calculations, polarizable atomistic molecular dynamics simulations, coarse-grained implicit solvent simulations and continuum level modeling, we focus on understanding the mechanisms of formation of SEI/CEI layers, mechanisms of Li-ion transport, and mechanical and failure properties of SEI during charging/discharging processes.

Electrode roughness dependent electrodeposition of sodium at the nanoscale

Na metal is an attractive anode material for rechargeable Na ion batteries, however, the dendritic growth of Na can cause serious safety issues. Along with modifications of solid-electrolyte interphase (SEI), engineering the electrode has been reported to be effective in suppressing Na dendritic growth, likely by reducing localized current density accumulation. However, fundamental understanding of Na growth at the nanoscale is still limited. Here, we report an in-situ study of Na electrodeposition in electrochemical liquid cells with the electrodes in different surface roughness, e.g., flat or sharp curvature. Real time observation using transmission electron microscopy (TEM) reveals the Na electrodeposition with remarkable details. Relatively large Na grains (in the micrometer scale) are achieved on the flat electrode surface. The local SEI thickness variations impact the growth rate, thus the morphology of individual grains. In contrast, small Na grains (in tens of nanometers) grow explosively on the electrode at the point with sharp curvature. The newly formed Na grains preferentially deposit at the base of existing grains close to the electrode. Further studies using continuum-based computational modeling suggest that the growth mode of an alkali metal (e.g. Na) is strongly influenced by the transport properties of SEI. Our direct observation of Na deposition in combination with the theoretical modeling provides insights for comprehensive understanding of electrode roughness and SEI effects on Na electrochemical deposition. Electrode engineering has been explored to direct the deposition of Na in battery applications. However, the fundamental understanding of Na electrodeposition at the nanoscale is still lacking. By developing electrochemical liquid TEM cells with patterned electrodes, we have directly observed Na deposition on the electrodes with flat or sharp curvature. It shows different growth mode and grain morphology depending on the electrode roughness. “Base growth” and smaller grains are found on the sharp nodules of an electrode, in contrast to the occurrence on an electrode with flat curvature. The individual Na grain growth and morphology are also influenced by the local variations of solid-electrolyte interphase (SEI). • In-situ TEM observation unveils Na growth at the nanoscale on patterned electrodes. • Different electrode roughness results in different growth mode and grain sizes. • SEI thickness variations on Na grains impact local growth rate and grain morphology. • Na shows “base growth” at a sharp nodule on the rough electrode. • Continuum-based modeling suggests Na growth is strongly influenced by the transport properties of SEI.