Solid Electrolyte Interphase Layer Research Articles

A Data-Driven Approach for Predicting the Lifetime of Lithium-Metal Batteries

Lithium-metal batteries (LMBs) are promising candidates for accelerating the implementation of electric vehicles in our society. LMBs comprise of a lithium-metal anode that possesses the highest theoretical specific capacity (3860 mAh/g) and the lowest redox potential (-3.04V vs standard hydrogen electrode).1 LMBs undergo repeated plating and stripping of lithium ions on the anode surface. The non-homogenous stripping process leads to the isolation of metallic lithium from the anode surface, forming dead-lithium.2 The parasitic reaction between the lithium-metal anode and the electrolyte leads to the formation of the solid electrolyte interphase (SEI) layer. These phenomena lead to the reduction of available lithium and a rise in cell impedance, causing a rapid reduction of lifetime for these batteries.3 , 4 In this talk, we present a diverse dataset collected from different LMBs of different capacities and voltage ranges, that includes features from the initial formation cycle, rest voltages and CV charging during cycling. A data-driven model from the LMB cycling data is presented to predict the remaining useful lifetime (RUL) of these cells. Insights from the model can be used to determine the bad cells in a batch, improve the designs of the cells and derive optimal charging protocols for their implementation in the BMS. References Lin, D., Liu, Y. & Cui, Y. Reviving the lithium metal anode for high-energy batteries. Nat. Nanotechnol. 12, 194 (2017).Xu, S., Chen, K.-H., Dasgupta, N. P., Siegel, J. B. & Stefanopoulou, A. G. Evolution of Dead Lithium Growth in Lithium Metal Batteries: Experimentally Validated Model of the Apparent Capacity Loss. J. Electrochem. Soc. 166, A3456–A3463 (2019).Liu, G. & Lu, W. A Model of Concurrent Lithium Dendrite Growth, SEI Growth, SEI Penetration and Regrowth. J. Electrochem. Soc. 164, A1826–A1833 (2017).Gao, N. et al. Fast Diagnosis of Failure Mechanisms and Lifetime Prediction of Li Metal Batteries. Small Methods 5, 1–11 (2021).

(Invited) A Facile Three-Dimensional Lightweight Current Collector Strategy for High Energy Density Lithium Metal Batteries

Despite the great achievement in the development of rechargeable lithium (Li) metal batteries (LMBs) with high energy densities, their practical application is still facing difficulties due to the intrinsic issues of Li metal anode (LMA) including high reactivity and dendritic Li formation which cause low Coulombic efficiency, constant loss of Li and electrolyte, and unstable solid electrolyte interphase (SEI) layer, etc. Additionally, from the structural point of view, LMA which consists of Li foil on the two-dimensional copper (Cu) current collector brings the formidable loss of the areal capacity that leads to less specific energy density since Cu is non-faradaic and one of the heavy metals. Further, the “hostless” feature of LMA induces more issues like volume expansion and limited utilization of Li. To address such issues, a metal-coated polymeric three-dimensional (3D) scaffold is designed here. In this study, Cu is selected as an electronic conductivity provider, and electrospun polyimide (PI) is chosen as a 3D scaffold because of its high thermal stability and good mechanical properties. Cu-coated PI (Cu@PI) was produced via a facile electroless process. Driven by the structural/material uniqueness, the developed 3D Cu@PI current collector enables a uniform/continuous Li-ion conduction pathway thus leading to dense Li deposition and enhancing the electrochemical performance of LMBs containing the electrochemically deposited Li on Cu@PI and the specific energy density due to the great reduction in substrate weight. We anticipate the suggested new strategy of 3D structured LMAs would lead to a facile route toward the high energy density LMBs beyond the conventional technologies.

(Invited) Model-Based BMS for Current and Next-Generation Batteries

Fast charging is researched heavily for the widespread implementation of lithium-ion batteries for electric vehicles. However, charging at high currents accelerates several parasitic reactions that lead to the degradation of the cell, affecting its lifetime. These reactions lead to loss of lithium inventory, loss of active material, and increased impedance in the cell. Examples of these side reactions include the growth of the solid-electrolyte interphase (SEI) layer, transition metal dissolution and deposition, lithium plating, solvent oxidation, etc. These mechanisms degrade the cell and reduce its cycle life.Physics-based multi-scale battery models solve for equations that govern the charge and mass balances within the cell. Using these detailed mathematical models, it is possible to study material degradation mechanisms and predict their impact on capacity loss under several operating conditions. These models can be used to design new batteries with appropriate materials and design parameters suited for any given purpose.More critically, these models can be integrated with battery management systems (BMS) to control the cell’s performance. These models can further be used to design novel charging protocols that enable safe and optimal cell performance and suppress cell material degradation. The BMS monitors and maintains the voltage, current, and temperature and estimates the internal states of the cell. Model-based BMS algorithms require fast codes that can predict and estimate battery parameters in real-time and control the battery’s performance under different loads.Currently, the BMS implements equivalent circuit models that inadequately predict the cell’s performance for various conditions and design parameters. This talk presents the current efforts to move the models for BMS for current and next-generation batteries for single-cell to pack-level simulations. Figure 1

Designing High Stability Fluorinated Materials to Replace Carbonate Additives in Li-Ion Batteries Under Extreme Test Conditions

Graphite-based Li-ion batteries require the formation of a solid electrolyte interphase (SEI) on the surface of the anode to prevent solvent co-intercalation and graphite exfoliation. Materials such as vinylene carbonate (VC) and fluoroethylene carbonate (FEC) that have been successfully deployed as SEI layer forming additives show limited utility under high voltage and high temperature conditions due to low electrochemical and/or thermal stability.1-3 Development of Li-ion batteries that meet the needs of automotive and other electrification applications require advanced electrolyte additives that can support operation under extreme conditions.Koura has developed fluorinated additives that demonstrate improved stability and performance over conventional SEI layer forming additives under the high temperature and high voltage conditions relevant to the automotive industry. In this study, the performance of Koura’s fluorinated additives was compared to common commercial additives in the multiple cell designs, including 4.3V Gr/NMC811, to identify candidates to replace VC and FEC. Testing included 45°C cycling and 60°C storage. It has been found that these materials reduce gassing and increase capacity retention during high-temperature battery operation.To gain a fundamental understanding of how these molecules function in the battery, including mechanisms of solvation, interfacial behavior, and bulk reactivity; and how the structure of the molecule contributes to its properties and behavior, comprehensive post-test analysis was conducted, including gas composition analysis and quantification via gas chromatography, bulk electrolyte composition analysis via NMR spectroscopy, and surface layer characterization via XPS and SEM. Also, performance of multiple structural variants was examined to develop a structure-property relationship to guide rational design of additives for advanced Li-ion batteries.This presentation will summarize Koura’s efforts to supply advanced fluorinated materials for Li-ion batteries that satisfy the arduous demands of current and future applications. Specifically, we will present data showing the capability of fluorinated Koura materials to replace and/or enable existing Li-ion additives under extreme operating conditions, specifically high temperature and/or voltage. Multiple structures will be compared, where appropriate, to highlight our fundamental understanding of the structure-property relationships critical to designing next generation materials.

Operando Electrochemical Liquid Cell STEM Investigation of the Growth and Evolution of the Mosaic Solid Electrolyte Interphase for Lithium-Ion Batteries

The solid electrolyte interphase (SEI) is a key component of a lithium-ion battery forming during the first few dis-/charge cycles at the interface between the anode and the electrolyte. The SEI passivates the anode-electrolyte interface by inhibiting further electrolyte decomposition extending the battery's cycle life. Insights into SEI growth and evolution in terms of structure and composition remain difficult to access. To unravel the formation of the SEI layer during the first cycles, operando electrochemical liquid cell scanning transmission electron microscopy (ec-LC-STEM) is employed to monitor in real time the nanoscale processes that occur at the anode-electrolyte interface in their native electrolyte environment [1]. The results show that the formation of the SEI layer is not a one-step process, but comprises multiple steps. The growth of the SEI is initiated at low potential during the first charge by decomposition of electrolyte leading to the nucleation of inorganic nanoparticles. Thereafter, the growth continues during subsequent cycles by forming an island-like layer. Eventually, a thick dense layer is formed with a mosaic structure composed of larger inorganic patches embedded in a matrix of organic compounds. While the mosaic model for the structure of the SEI is generally accepted, our observations document for the first time how the complex structure of the SEI is built up during dis-/charge cycling.[1] W. Dachraoui, R. Pauer, C. Battaglia, R. Erni, ACS Nano 2023, 17, 20434

Effect of Water–Soluble Polyimide (w-PI) Type Binders on the Performance of High-Capacity Silicon Anodes of Lithium-Ion Batteries

In order to enhance rapid charging and driving range for electric vehicles, the high-capacity of lithium-ion batteries (LIBs) is imperative. Commercially available graphite as an anode material has long cycle life, abundance, and low cost. However, it has a limitation in its theoretical specific capacity (372 mAh g−1).To overcome this limitation, much attention has been paid to silicon (Si), which offers a high theoretical specific capacity of 4,200 mAh g−1. Nevertheless, silicon suffers from excessive volume expansion, resulting in issues such as pulverization of active alloy particles, delamination, and the formation of an unstable Solid Electrolyte Interphase layer. This lead to a limitation to use the silicon in large amount in an electrode. A polymeric binder has a critical role in improving the high-capacity Si anode. Conventional polyimide (PI), one of various super-engineering plastics, was applied to the Si anodes, but it is still challenged to water-insolublity and high temperature imidization process around 300 oC. In this study, a water-soluble PI (w-PI) is designed by the polycondensation between dianhydrides and diamine in water environment. In addition, a relatviely low-temperature imidization temperature below 200 oC will be appled by the introduction of dimethylimidazole. This study will briefly outline the direction for implementing a w-PI binder and improving electrochemical performance of high-capacity anode compared to conventional binders such as PVdF and CMC/SBR. Keyword: high-capacity Si anode; dianhydrides and diamine; Polyimide (PI); and water-soluble PI Figure 1

Salt-Assisted Recovery of Sodium Metal Anodes for High-Rate Capability Sodium Batteries.

Rechargeable sodium metal batteries are considered to be one of the most promising high energy density and cost-effective electrochemical energy storage systems. However, their practicality is constrained by the high reactivity of sodium metal anodes that readily brings about excessive accumulation of inactive Na species on the surface, either by chemical reactions with oxygen and moisture during electrode handling or through electrochemical processes with electrolytes during battery operation. Herein, this paper reports on an alkali, salt-assisted, assembly-polymerization strategy to recover Na activity and to reinforce the solid-electrolyte interphase (SEI) of sodium metal anodes. To achieve this, an alkali-reactive coupling agent 3-glycidoxypropyltrimethoxysilane (GPTMS) is applied to convert inactive Na species into Si-O-Na coordination with a self-assembly GPTMS layer that consists of inner O-Si-O networks and outer hydrophobic epoxides. As a result, the electrochemical activity of Na metal anodes can be fully recovered and the robust GPTMS-derived SEI layer ensures high capacity and long-term cycling under an ultrahigh rate of 30 C (93.1 mAh g-1, 94.8% after 3000 cycles). This novel process provides surface engineering clues on designing high power density and cost-effective alkaline metal batteries.

Impact of Electrolyte on Direct-Contact Prelithiation of Silicon-Graphite Anodes in Lithium-Ion Cells with High-Nickel Cathodes.

Silicon-based anodes offer high specific capacities to enhance the energy density of lithium-ion batteries, but are severely hindered by the immense volume expansion and subsequent breakage of the solid-electrolyte-interphase (SEI) during cycling. Herein, we utilize an effective strategy, known as direct-contact prelithiation, to mitigate the challenges associated with expansion and surface instability in SiOx/graphite (SG) anodes. It involves introducing lithium into the anode via physical contact with lithium metal and electrolyte before cycling. Prelithiation of SG anodes with an advanced localized high-concentration electrolyte is shown to develop a mechanically robust artificial SEI that tolerates better the electrode volume expansion. The modified SG anode paired with the high-Ni cathode LiNi0.90Mn0.05Co0.05O2 delivers a high initial capacity of 191 mA h g-1 with 80% capacity retention over 150 cycles, compared to 46% retention with a conventional electrolyte. The bolstered SEI layer with reduced surface reactivity is due to the reduced electrolyte consumption and regulated SEI formation during cycling. Furthermore, the advanced electrolyte and fortified SG anode help reduce cathode degradation, transition-metal dissolution, and loss of active lithium. This study highlights viable prelithiation strategies to stabilize Si-based anodes for high-energy-density batteries through electrolyte design.

Nucleation, growth and dissolution of Li metal dendrites and the formation of dead Li in Li-ion batteries investigated by operando electrochemical liquid cell scanning transmission electron microscopy

Li metal dendrites, which can form on the anode of Li-ion batteries during charging, not only accelerate their aging but may also pose a safety hazard when causing a short-circuit within the battery. Therefore, a fundamental understanding of the mechanisms governing the early stages of Li plating, the progression into dendrites, and the formation of dead Li, is imperative. Here, we employ operando electrochemical liquid cell scanning transmission electron microscopy (ec-LC-STEM) to monitor, in real-time, nanoscale processes occurring at the anode-electrolyte interface of a Li-ion battery during charge/discharge. Our results indicate that Li metal dendrites nucleate as spherical Li nanoparticles beneath the solid electrolyte interphase (SEI) and subsequently grow until dendritic Li metal is formed. During discharge, Li dendrites undergo incomplete dissolution, leading to the formation of dead Li. Interestingly, the SEI layers play a pivotal role in both the growth and the dissolution processes. Our findings reveal that the growth of Li dendrites is a multi-step process: (i) nucleation, (ii) root growth, and (iii) tip growth. We elucidate that the formation of dead Li is associated with the morphology of the initially developed dendrites and the structure of the SEI layer. The thinning of the inhomogeneously thick Li whiskers leads to the contraction of the root before the tip, ultimately resulting in the creation of electrically isolated Li metal. This work sheds light on dendritic Li growth as well as on the formation of dead Li and provides significant insights for future electrode designs.

Electrolyte Design for NMC811||SiOx-Gr Lithium-Ion Batteries with Excellent Low-Temperature and High-Rate Performance

The use of high-nickel NMC811 cathode and SiOx-Gr anode can greatly improve the overall energy densities of lithium-ion batteries. However, the unfavorable solid electrolyte interphase (SEI) layer generated from the decomposition of EC-based electrolytes lead to the poor cycling stability of NMC811||SiOx-Gr cells. Here we report an electrolyte design of 1.5 M LiPF6 dissolved in FEC/MA/BN 2:2:6 by volume, which can form thin, robust, and homogeneous SEI layer to greatly improve the charge transfer at the electrode-electrolyte interface. Importantly, the designed electrolyte shows an outstanding low temperature performance that it can deliver a capacity of 123.3 mAh g–1 after 50 cycles at −20 °C with a current density of 0.5 C, overwhelming the standard EC-based electrolyte (1.2 M LiPF6 EC/EMC 3:7 by volume) with a capacity of 35.7 mAh g–1. The electrolyte also has a superior rate performance that it achieves a capacity of 122.5 mAh g−1 at a high current density of 10 C. Moreover, the LTE electrolyte holds the great potential of extreme fast-charging ability because of the large part of CC contribution in the CCCV charging model at high charging current densities.

Reactive Solid Polymer Layer: From a Single Fluoropolymer to Divergent Fluorinated Interface

AbstractControlling the structure and chemistry of solid electrolyte interphase (SEI) underpins the stability of electrolyte‐electrode interface, and is crucial for advancing rechargeable lithium metal batteries (LMBs). Here, we utilized photo‐controlled copolymerization to achieve the on‐demand synthesis of fluorosulfonyl fluoropolymers as unprecedented artificial SEI layers on Li metal anodes. This work not only enables instant formation of a hybrid polymer‐inorganic interphase that consists of a polymer‐enriched top layer and a LiF‐fortified bottom layer, originating from a single polymeric component, but also imparts various desirable physical properties (e.g., good mechanical strength and flexibility, high ion conductivity, low overpotential) to SEI via a single‐to‐divergent strategy. Model reactions and structural characterizations supported the formation of a divergent fluorinated interphase, which furnished prolonged stabilization of Li deposition, high coulombic efficiency and improved cycling behavior in electrochemical experiments. This work highlights the great potential of exploring reactive polymers as versatile coatings to stabilize Li metal anodes, providing a promising avenue to solve electrode‐electrolyte interfacial problems for LMBs.

Application of artificial SEI layers for lithium metal battery anodes

Unpredictable lithium dendrite growth on the metal anode and repeated destruction and creation of the solid electrolyte interphase (SEI) layer result in hidden risks and low Coulombic efficiencies (CEs). Researchers have found that designing a high-quality SEI layer can prevent the growth of dendrite. However, designing and forming a high-quality SEI layer is still a problem. Making trade-off between capacity reduction caused by the SEI layer and better cycle stability significantly limits the general performance of lithium metal batteries. In this research, characteristics of SEI layers and some significant advancements made in SEI formation are outlined. Some designs for the SEI layers on the lithium metal anodes include designing hybrid polymer SEI layers, producing synthetic SEI layers. By controlling the behaviours of Li ions throughout the stripping and depositing processes, the capacity and stability of Li metal anodes may be improved. Finally, some case studies of the applying of SEI in lithium metal battery systems are introduced.

Influence of Vinylene Carbonate and Fluoroethylene Carbonate on Open Circuit and Floating SoC Calendar Aging of Lithium-Ion Batteries

The purpose of this study was to investigate the calendar aging of lithium-ion batteries by using both open circuit and floating current measurements. Existing degradation studies usually focus on commercial cells. The initial electrolyte composition and formation protocol for these cells is often unknown. This study investigates the role of electrolyte additives, specifically, vinylene carbonate (VC) and fluoroethylene carbonate (FEC), in the aging process of lithium-ion batteries. The results showed that self-discharge plays a significant role in determining the severity of aging for cells without additives. Interestingly, the aging was less severe for the cells without additives as they deviated more from their original storage state of charge. It was also observed that the addition of VC and FEC had an effect on the formation and stability of the solid electrolyte interphase (SEI) layer on the surface of the carbonaceous anode. By gaining a better understanding of the aging processes and the effects of different electrolyte additives, we can improve the safety and durability of lithium-ion batteries, which is critical for their widespread adoption in various applications.

Heterogeneous Solid Electrolyte Interphase Interactions Dictate Interface Instability in Sodium Metal Electrodes.

Sodium (Na) metal batteries have attracted recent attention due to their low cost and high abundance of Na. However, the advancement of Na metal batteries is impeded due to key challenges such as dendrite growth, solid electrolyte interphase (SEI) fracture, and low Coulombic efficiency. This study examines the coupled electro-chemo-mechanical interactions governing the electrodeposition stability and morphological evolution at the Na/electrolyte interface. The SEI heterogeneities influence transport and reaction kinetics leading to the formation of current and stress hotspots during Na plating. Further, it is demonstrated that the heterogeneity-induced Na metal evolution and its influence on the stress distribution critically affect the mechanical overpotential, contributing to a faster SEI failure. The analysis reveals three distinct failure mechanisms-mechanical, transport, and kinetic-that govern the onset of instabilities at the interface. Finally, a comprehensive comparative study of SEI failure in Na and lithium (Li) metal anodes illustrates that the electrochemical and mechanical characteristics of the SEI are crucial in tailoring the anode morphology and interface stability. This work delineates mechanistic stability regimes cognizant of the SEI attributes and underlying failure modes and offers important guidelines for the design of artificial SEI layers for stable Na metal electrodes.

Long-life and high-power Sodium-Selenium Batteries realized by Vanadium single atom catalyzed cathodes and tailored carbonate-based electrolytes

The practical implementation of resources-abundant sodium-selenium batteries (SSBs) has been retarded by the low-capacity utilization and poor reversibility from the sluggish conversion kinetics of selenides, the notorious polyselenides shuttling effect and the dendritic deposition of sodium metal. This work presents a rational design of vanadium single atom catalyst on nitrogen-doped carbon sheets (V-N-C) as selenium host to address the instability of cathodes. Density function theory calculations reveal the superiority of V-N4 in V-N-C over other transition metal and nitrogen atoms in facilitating the adsorption-diffusion-conversion of polyselenides. Se@V-N-C cathodes deliver a high capacity utilization (603 mAh g−1 at 0.1 C, over 89 % of theoretical capacity), excellent reversibility (470 mAh g-1 at 0.1 C after 500 cycles), and remarkably high-power cyclability (260 mAh g−1 at 5 C over 1000 cycles). The prolong cycle life can also be originated from our tailored NaPF6 carbonate electrolyte with 1 wt% LiDFBOP additive. The new electrolyte is illustrated to generate inorganic-rich solid electrolyte interphase layers to protect sodium metal anodes from polyselenides corrosion and dendritic deposition at high rates. Fundamental findings in this work present a two-pronged approach to the prevailing challenges in the nascent metal-selenium battery chemistry.

Acetonitrile-Based Local High-Concentration Electrolytes for Advanced Lithium Metal Batteries.

Acetonitrile (AN) is a compelling electrolyte solvent for high-voltage and fast-charging batteries, but its reductive instability makes it incompatible with lithium metal anodes (LMAs). Herein, 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether (TTE) is used as the diluent to build an AN-based local high-concentration electrolyte (LHCE) to realize dense, dendrite-free, and stable LMAs. Such LHCE exhibits an exceptional electrochemical stability window close to 6V (vs Li+/Li), excellent wettability, and promising flame retardancy. Compared to a baseline carbonate-based electrolyte, its electrochemical performance is prominent: the overpotential of lithium nucleation is minimal (only 24mV), the average half-cell coulombic efficiency (CE) reaches 99.5% at 0.5mAcm-2, and its practicality in full cells with LiFePO4 (LFP) and LiNi0.8Co0.1Mn0.1O2 (NCM811) cathodes is also demonstrated. Compounding factors are identified to decipher the superiority of the AN-based LHCE. From the respect of solvation structures, both the elimination of free AN molecule and the diluent separation would contribute to prevention of anodic AN decomposition. Based on cryogenic electron microscopy (Cryo-EM) characterization and theoretical simulations results, the produced solid-electrolyte interphase (SEI) layer is uniform and compact. Thus, this work demonstrates a successful application of AN-based electrolytes in LMAs-traditionally deemed impractical-via the combined regulation of solvation and SEI structures.

LiF modified hard carbon from date seeds as an anode material for enhanced low-temperature lithium-ion batteries

The performance of traditional Li-ion batteries deteriorates when operating at sub-zero temperatures mainly due to the slow diffusion of Li-ions in commercial negative electrode materials. Various alternative anodes have been explored, but complex fabrication methods hinder practical implementation. This work proposes a cost-effective anode material, a porous structured nitrogen-doped hard carbon synthesized from date seeds with further LiF modification to achieve an artificial LiF-rich solid electrolyte interphase (SEI) layer. The resulting anode material showcases promising characteristics, achieving a specific capacity of 525 mAh g−1 after 50 cycles at room temperature. Furthermore, it maintains a substantial capacity of 280 mAh g−1 after 100 cycles at −20 °C. Notably, even when subjected to a high current of 2C at −20 °C, the electrode still provides a remarkable capacity of 72 mAh g−1 after 500 cycles. The outstanding charge storage performance at low temperatures is attributed to the predominance of capacitance-controlled charge storage mechanisms in the prepared anode. Post-mortem analysis confirms structural stability and formation of a uniform LiF-rich SEI layer. This novel approach presents a practical solution to the difficulties encountered by LIBs in cold environments, paving the way for improved battery performance and longevity.

Rationally Designed Li-Ag Alloy with In-Situ-Formed Solid Electrolyte Interphase for All-Solid-State Lithium Batteries.

All-solid-state lithium batteries (ASSLBs) with sulfide-based solid electrolytes have attracted significant attention as promising energy storage devices, owing to their high energy density and enhanced safety. However, the combination of a lithium metal anode and a sulfide solid electrolyte results in performance degradation, owing to lithium dendrite growth and the side reactions of lithium metal with the solid electrolyte. To address these issues, a Ag-based Li alloy with a favorable solid electrolyte interphase (SEI) was prepared using electrodeposition and applied to the ASSLB as an anode. The electrochemically formed SEI layer on the Li-Ag alloy primarily comprised LiF and Li2O with high mechanical strength and Li3N with high ionic conductivity, which suppressed the formation of lithium dendrites and short-circuiting of the cell. The symmetric cell with the Li-Ag alloy achieved a critical current density of 1.6 mA cm-2 and maintained stable cycling for over 2000 h at a current density of 0.6 mA cm-2. Consequently, the all-solid-state lithium cell assembled with the Li-Ag alloy anode with SEI, Li6PS5Cl solid electrolyte, and LiNi0.78Co0.10Mn0.12O2 cathode delivered a high discharge capacity of 185 mAh g-1 and exhibited good cycling performance in terms of cycling stability and rate capability at 25 °C.

Deciphering the structural and kinetic factors in lithium titanate for enhanced performance in Li+/Na+ dual-cation electrolyte

The widespread application of Li4Ti5O12 (LTO) anode in lithium-ion batteries has been hindered by its relatively low energy density. In this study, we investigated the capacity enhancement mechanism of LTO anode through the incorporation of Na+ cations in an Li+-based electrolyte (dual-cation electrolyte). LTO thin film electrodes were prepared as conductive additive-free and binder-free model electrodes. Electrochemical performance assessments revealed that the dual-cation electrolyte boosts the reversible capacity of the LTO thin film electrode, attributable to the additional pseudocapacitance and intercalation of Na+ into the LTO lattice. Operando Raman spectroscopy validated the insertion of Li+/Na+ cations into the LTO thin film electrode, and the cation migration kinetics were confirmed by ab initio molecular dynamic (AIMD) simulation and electrochemical impedance spectroscopy, which revealed that the incorporation of Na+ reduces the activation energy of cation diffusion within the LTO lattice and improves the rate performance of LTO thin film electrodes in the dual-cation electrolyte. Furthermore, the interfacial charge transfer resistance in the dual-cation electrolyte, associated with ion de-solvation processes and traversal of the cations in the solid-electrolyte interphase (SEI) layer, are evaluated using the distribution of relaxation time, Fourier transform infrared spectroscopy and X-ray photoelectron spectroscopy. Our approach of performance enhancement using dual-cation electrolytes can be extrapolated to other battery electrodes with sodium/lithium storage capabilities, presenting a novel avenue for the performance enhancement of lithium/sodium-ion batteries.

Deciphering the degradation mechanisms of nano-Si and micro-SiO anodes in lithium-ion battery full-cells using distribution relaxation times analysis

Silicon (Si) and silicon monoxide (SiO) have attracted great interest as next-generation anode materials for lithium-ion batteries (LiBs) due to their high energy density. However, their commercialization has been hindered by rapid capacity fading, which stems from mechanical degradation (e.g., cracking and delamination) and the aggressive formation of solid electrolyte interphase (SEI) layer. While understanding these degradation mechanisms in batteries necessitates in-operando measurement techniques, very few non-destructive analytical methods have been documented in literature. This paper highlights the effectiveness of combined electrochemical impedance spectroscopy (EIS) and distribution of relaxation times (DRT) techniques in performing systematic characterization of LiNi0.6Mn0.2Co0.2O2 (NMC)/nano-Si and NMC/micro-SiO full-cells. The systematic design of experiments enabled the separate deconvolution of anode and cathode aging using symmetrical cells. This approach offered a clear understanding of the overall degradation mechanisms in the full-cells. The major impedance sources in the NMC/nano-Si full-cell were anode contact impedance, resulting from mechanical degradation of Si, and cathode charge transfer impedance, due to significant lithium loss and consequently deeper extraction of lithium ions in NMC. In contrast, micro-SiO anodes exhibited less electrode-level degradation, as evidenced by SEM images and relatively stable impedance behaviors during extended cycling, which strongly corroborate its superior capacity retention (66 % at 300th cycle) compared to that of nano-Si anode in full-cells (26.5 % at 300th cycle).