Lithium Trapping Research Articles

Investigating the Reduction of Fluoroethylene Carbonate and Vinylene Carbonate in Lithium‐Ion Cells with Silicon‐Graphite Anodes

AbstractThe electrolyte additives fluoroethylene carbonate (FEC) and vinylene carbonate (VC) improve the lifetime of lithium‐ion batteries with silicon‐containing anodes by their reduction yielding a more stable solid electrolyte interphase (SEI). However, the reductive decomposition mechanism of FEC and VC has not yet been fully clarified. For this purpose, we investigate the electrolyte decomposition in LiNi0.6Co0.2Mn0.2O2 (NCM622)/silicon‐graphite pouch cells containing either 1 M LiPF6 in FEC:dimethyl carbonate (DMC) or 1 M LiPF6 in VC:DMC using high‐performance liquid chromatography, gas chromatography, X‐ray photoelectron spectroscopy, and inductively coupled plasma optical emission spectrometry. Based on the molar consumptions of FEC and VC, and the cumulative irreversible capacities, we show that three electrons are consumed for every reduced FEC molecule, and that one electron is consumed for every reduced VC molecule. Based on the results, reactions of the FEC reduction are proposed yielding LiF, Li2CO3, Li2C2O4, HCO2Li, and a PEO‐type polymer. Furthermore, the reaction of the VC reduction is proposed yielding lithium‐containing, polymerized VC. During formation, the capacity loss of the cells is induced by lithium trapping in LixSiy/LixSiOy under the SEI and by lithium trapping in the SEI. During subsequent cycling, only lithium trapping in the SEI triggers the capacity loss.

Effect of Microstructure on Chemo-Mechanical Damage Evolution in Aluminum Foil Anodes for Lithium-Ion Batteries

Aluminum-based foil anodes could enable lithium-ion batteries with high energy density comparable to silicon and lithium metal. However, mechanical pulverization and lithium trapping within aluminum tend to cause capacity fading. The complex interplay between these damage modes is not well understood, as well as the role of microstructure on reaction front evolution. Here, we investigate aluminum foils with different compositions and processing conditions to understand how microstructure influences chemo-mechanical degradation. Backscattered electron imaging of ion-milled foil cross sections is used to visualize reaction front evolution and chemo-mechanical degradation. We find that the shape of the reaction front during lithiation is strongly affected by foil composition, defect distribution, and grain size, which, in turn, affects the evolution of chemo-mechanical damage within the foils. Furthermore, a key finding is that the extent of fracture upon delithiation is inversely related to lithium trapping, with foil compositions that exhibit uniform lithiation, and therefore, less fracturing showing greater lithium trapping. Nonreactive precipitate inclusions within alloy foils are also found to induce void formation. This work shows that material design strategies designed to overcome the inverse fracture-lithium trapping relationship could be useful for improving performance. Published by the American Physical Society 2024

Synthesis and characterization of hierarchically porous carbon anodes from furfural biorefinery residues for sustainable lithium-ion batteries

This study aims to valorize abundant lignocellulosic residues from furfural biorefineries into hierarchically porous carbon anodes for sustainable lithium-ion batteries (LIBs). Simultaneously, it addresses the growing demand for high-performance anode materials by leveraging renewable waste feedstocks. Sugarcane bagasse waste residues obtained after furfural extraction were used as the precursor. The furfural-derived bagasse residue (FDBR) underwent pyrolysis at 700 °C to produce a carbon-rich char, which was further activated using KOH and steam at 900 °C for 15–60 minutes to enhance porosity development. Comprehensive physicochemical characterizations, including proximate analysis, N2 adsorption-desorption, SEM-EDX, FTIR, and TGA/DTG, and Raman spectroscopy were performed to evaluate the properties of the synthesized activated carbons. The results demonstrated the successful generation of high surface area (405.8 m2/g) activated carbons with a hierarchical pore structure comprising micropores and mesopores. SEM and EDX analyses revealed a uniform, porous morphology enriched with 10.41 % at oxygen-containing functional groups. FTIR spectra confirmed the presence of hydroxyls, carbonyls, and carboxylic acid groups, beneficial for pseudocapacitive charge storage. The Raman analysis revealed a highly disordered and amorphous carbon structure with a significant concentration of defects, as evidenced by a high-intensity ratio (ID/IG ≈ 1.2–1.4) of the disordered carbon band to the graphitic band. The activated carbons exhibited a high initial discharge capacity of 1055 mAh/g in lithium half-cells, significantly exceeding the theoretical limit of commercial graphite anodes (372 mAh/g). This superior capacity was attributed to the high surface area, hierarchical porosity, and pseudocapacitive contributions from the oxygen functionalities. However, rapid capacity fading from 1055 to ∼250 mAh/g was observed over 100 cycles at a C/2 rate. The capacity retention stabilized at ∼88 % after 47 cycles, indicating irreversible capacity losses. These limitations were ascribed to the disordered amorphous structure, instability of the solid-electrolyte interphase, lithium trapping by oxygen groups, and structural changes during cycling. Optimizing activation conditions, incorporating conductive additives/coatings, exploring alternative binders, and surface functionalization are proposed to improve long-term cycling stability. Overall, this study demonstrates the feasibility of upcycling furfural biorefinery waste into sustainable LIB anodes while highlighting challenges and potential solutions for enhancing their electrochemical performance.

Electrochemical behavior of elemental alloy anodes in solid-state batteries.

Lithium alloy anodes in the form of dense foils offer significant potential advantages over lithium metal and particulate alloy anodes for solid-state batteries (SSBs). However, the reaction and degradation mechanisms of dense alloy anodes remain largely unexplored. Here, we investigate the electrochemical lithiation/delithiation behavior of 12 elemental alloy anodes in SSBs with Li6PS5Cl solid-state electrolyte (SSE), enabling direct behavioral comparisons. The materials show highly divergent first-cycle Coulombic efficiency, ranging from 99.3% for indium to ∼20% for antimony. Through microstructural imaging and electrochemical testing, we identify lithium trapping within the foil during delithiation as the principal reason for low Coulombic efficiency in most materials. The exceptional Coulombic efficiency of indium is found to be due to unique delithiation reaction front morphology evolution in which the high-diffusivity LiIn phase remains at the SSE interface. This study links composition to reaction behavior for alloy anodes and thus provides guidance toward better SSBs.

Lithium Trapping in Silicon Nanowire Anodes for Lithium-Ion Batteries

Silicon has long been considered a prospective anode material for lithium-ion batteries (LIBs) due to its high theoretical specific capacity and natural abundance. However, silicon is known to suffer from significant volumetric expansion (~ 400%) during lithiation and de-lithiation. The induced mechanical stress leads to pulverization of silicon as well as electrolyte consumption, which results in poor coulombic efficiency, high irreversible capacity loss and cell failure(1-3). Nanostructured silicon in the form of nanoparticles, nanowires, nanotubes, and nanoporous silicon has demonstrated high capacities, greatly improved coulomb efficiencies, and capacity compared to bulk silicon(4-6). Silicon nanowires (Si NWs) have also shown improved charge transport and capacity retention over nanoparticles. Related to this, silicon-graphite composite anodes featuring 30% Si NWs have demonstrated a capacity of almost 3x graphite(7). However, nanostructured silicon is still prone to capacity fade, primarily caused by the formation of the solid-electrolyte interphase (SEI) and lithium trapping(5, 8-11). Though SEI formation has been widely studied, there has been far less study regarding lithium trapping, despite it contributing to ~30% of the initial capacity loss and accelerating further capacity loss(11, 12). There is a noticeable gap in the literature dedicated to understanding the effect of lithium trapping in Si NWs. In this study, we aim to address this by investigating the effect of lithium trapping in Si NWs anodes for LIBs. Using electrochemical techniques such as constant current (CC), constant current constant voltage (CCCV), electrochemical impedance spectroscopy (EIS), at different rates, we have compared the effects of lithium trapping in Si NWs and the role it plays in determining the end performance of Si NW electrodes. We have also compared the morphological changes induced in Si NWs from lithium trapping. The findings of this study serve to highlight the importance of electrochemical optimisation and form a basis for the future design and testing of LIBs involving Si NWs. REFERENCE LIST D. McNulty, A. Hennessy, M. Li, E. Armstrong and K. M. Ryan, Journal of Power Sources, 545, 231943 (2022).T. Kennedy, E. Mullane, H. Geaney, M. Osiak, C. O’Dwyer and K. M. Ryan, Nano Letters, 14, 716 (2014).T. Kennedy, M. Bezuidenhout, K. Palaniappan, K. Stokes, M. Brandon and K. M. Ryan, ACS Nano, 9, 7456 (2015).M. A. Rahman, G. Song, A. I. Bhatt, Y. C. Wong and C. Wen, Advanced Functional Materials, 26, 647 (2016).X. Zhao and V.-P. Lehto, Nanotechnology, 32, 042002 (2021).T. Kennedy, M. Brandon and K. M. Ryan, Advanced Materials, 28, 5696 (2016).S. Karuppiah, C. Keller, P. Kumar, P.-H. Jouneau, D. Aldakov, J.-B. Ducros, G. Lapertot, P. Chenevier and C. Haon, ACS Nano, 14, 12006 (2020).C. Erk, T. Brezesinski, H. Sommer, R. Schneider and J. Janek, ACS Applied Materials & Interfaces, 5, 7299 (2013).M. N. Obrovac and L. J. Krause, Journal of The Electrochemical Society, 154, A103 (2007).D. Rehnlund, F. Lindgren, S. Böhme, T. Nordh, Y. Zou, J. Pettersson, U. Bexell, M. Boman, K. Edström and L. Nyholm, Energy & Environmental Science, 10, 1350 (2017).T. Kennedy, M. Brandon, F. Laffir and K. M. Ryan, Journal of Power Sources, 359, 601 (2017).B. Zhu, G. Liu, G. Lv, Y. Mu, Y. Zhao, Y. Wang, X. Li, P. Yao, Y. Deng, Y. Cui and J. Zhu, Science Advances, 5, eaax0651 (2019).

Lithium-Ion Batteries Enhancing Cycling Performance of Silicon Graphite Anodes Using Carbon Nanotubes

Silicon graphite anodes have emerged as promising candidates to replace conventional graphite anodes due to their higher theoretical capacity and ability to store more lithium ions. However, the significant volume expansion of silicon during lithiation and delithiation cycles results in severe mechanical degradation and rapid capacity fade, limiting their practical application. Additionally, the realisation of electrodes with high Si content are further limited by poor diffusion kinetics, resulting in an insufficient rate capability performance and lithium trapping.In this study carbon nanotubes (CNTs) are incorporated into the silicon graphite anode matrix as a strategy to mitigate these issues and enhance the cycling performance of LIBs. The CNTs, with their unique mechanical, electrical, and chemical properties, offer numerous benefits, including enhanced structural integrity, improved electrical conductivity, and increased lithium-ion diffusion kinetics. We investigated the effect of different ratios of CNTs on the cycling performance of silicon graphite anodes. The electrochemical performance of the composite electrodes were systematically evaluated using galvanostatic cycling, cyclic voltammetry, and electrochemical impedance spectroscopy. Preliminary results show that the addition of CNTs to silicon graphite anodes significantly improves their cycling stability and rate capability. The composites exhibit reduced capacity fade, improved coulombic efficiency, and enhanced rate performance compared to silicon graphite anodes absent of the CNTs, facilitated by faster lithium-ion diffusion kinetics, leading to improved electrochemical performance.

(Best Presentation Award - 2nd Place) Investigating Low Temperature Reaction Mechanisms of Alloy Anodes for Lithium-Ion Batteries

Lithium-ion batteries (LIBs) are the battery of choice for most energy storage applications, including personal electronic devices and electric vehicles. However, poor low temperature performance, resulting from hindered solid state diffusion, slow desolvation kinetics, and dendrite formation, limits their use in nascent applications that require operation below -20 ºC, like electric aviation and space exploration. A small number of previous studies have shown that anode materials that electrochemically alloy with lithium ions can be cycled at temperatures as low as -40 ºC with significantly improved performance compared to graphite. Despite their improved low-temperature performance, reaction mechanisms and degradation behavior for these materials at low temperatures are poorly understood. This work aims to fill this gap in understanding by investigating the structural pathways during reactions of alloy anodes at low temperatures as well as characterizing their mechanical and electrochemical degradation. Electrode cross sectioning and scanning electron microscopy reveal that rapid capacity decay in antimony anodes at -40 ºC is a result of increased lithium trapping as well as particle fracture due to mechanical damage associated with volume change. We show that rapid capacity degradation of antimony at -40 ºC can be mitigated through the use of nanoscale particles. While nanoscale particles have been studied extensively at room temperature, little is known about they behave at low temperatures. Through SEM cross-sectioning and the galvanostatic intermittent titration technique (GITT), we show that the improvement in stability is likely due to faster kinetics related to the shorter diffusion length and increased mechanical stability resulting in less lithium trapping at low temperatures. Additionally, X-ray diffraction measurements were carried out as a function of temperature on micron- and nanosized antimony particles, as well as tin and graphite, to determine the composition and structure of lithiated phases formed at low temperatures. The results show that reduced temperatures alter phase transformation behavior in certain alloy materials. Overall, this work provides improved mechanistic understanding of alloy anodes at low temperatures, setting the stage for enhanced electrochemical performance.

Boosting Solid-State Reconversion Reactivity to Mitigate Lithium Trapping for High Initial Coulombic Efficiency.

An initial Coulombic efficiency (ICE) higher than 90% is crucial for industrial lithium-ion batteries, but numerous electrode materials are not standards compliant. Lithium trapping, due to i) incomplete solid-state reaction of Li+ generation and ii) sluggish Li+ diffusion, undermines ICE in high-capacity electrodes (e.g., conversion-type electrodes). Current approaches mitigating lithium trapping emphasize ii) nanoscaling (<50nm) to minimize Li+ diffusion distance, followed by severe solid electrolyte interphase formation and inferior volumetric energy density. Herein,this work accentuates i) instead, to demonstrate that the lithium trapping can be mitigated by boosting the solid-state reaction reactivity. As a proof-of-concept, ternary LiFeO2 anodes, whose discharged products contain highly reactive vacancy-rich Fe nanoparticles, can alleviate lithium trapping and enable a remarkable average ICE of ≈92.77%, much higher than binary Fe2 O3 anodes (≈75.19%). Synchrotron-based techniques and theoretical simulations reveal that the solid-state reconversion reaction for Li+ generation between Fe and Li2 O can be effectively promoted by the Fe-vacancy-rich local chemical environment. The superior ICE is further demonstrated by assembled pouch cells. This work proposes a novel paradigm of regulating intrinsic solid-state chemistry to ameliorate electrochemical performance and facilitate industrial applications of various advanced electrode materials.

Interfacial Chemistry Effects in the Electrochemical Performance of Silicon Electrodes under Lithium-Ion Battery Conditions.

Understanding the solid electrolyte interphase (SEI) formation and (de)lithiation phenomena at silicon (Si) electrodes is key to improving the performance and lifetime of Si-based lithium-ion batteries. However, these processes remain somewhat elusive, and, in particular, the role of Si surface termination merits further consideration. Here, scanning electrochemical cell microscopy (SECCM) is used in a glovebox, followed by secondary ion mass spectrometry (SIMS) at identical locations to study the local electrochemical behavior and associated SEI formation, comparing Si (100) with a native oxide layer (SiOx /Si) and etched with hydrofluoric acid (HF-Si). HF-Si shows greater spatial electrochemical heterogeneity and inferior lithiation reversibility than SiOx /Si. This is attributed to a weakly passivating SEI and irreversible lithium trapping at the Si surface. Combinatorial screening of charge/discharge cycling by SECCM with co-located SIMS reveals SEI chemistry as a function of depth. While the SEI thickness is relatively independent of the cycle number, the chemistry - particularly in the intermediate layers - depends on the number of cycles, revealing the SEI to be dynamic during cycling. This work serves as a foundation for the use of correlative SECCM/SIMS as a powerful approach to gain fundamental insights on complex battery processes at the nano- and microscales.

Lithium Trapping and Irreversible Atomic-Scale Structure Evolution during Delithiation of Silicon Oxides as Lithium-Ion Battery Anodes

Optimizing the oxygen content of silicon oxides used as anode materials for high-performance lithium-ion batteries is critical since it has diverse effects on lithium storage properties. However, the atomic-scale understanding of the effect of the oxygen content on structural evolution of the materials, particularly during delithiation is still limited. With this aim, we employ an iterative lithium extraction-relaxation algorithm based on reactive molecular dynamics simulations to investigate the dynamic processes of various silicon oxides. Our study highlights the effect of the oxygen content on various lithium storage properties, including the energetics of the interaction, lithium diffusion behaviors, lithium entrapment, structural reversibility during cycling, and mechanical properties. In particular, the simulations show that although increasing the oxygen content can significantly reduce the percentage of volume expansion during lithiation, which is a major cause of poor cycle retention of silicon- and silicon oxide-based anodes, this leads to an increased amount of the trapped lithium and an irreversible structural change during the reverse process. As contradictory conditions are required to achieve high specific capacity, long cycle life, and high coulombic efficiency, this atomistic study could provide a fundamental understanding beneficial for optimizing the oxygen content toward the development of silicon oxide-based anodes.

Diffusional lithium trapping as a failure mechanism of aluminum foil anodes in lithium-ion batteries

Aluminum foils are an appealing anode for lithium-ion batteries due to high capacity and low-cost, but their viability has been limited due to poor cyclability arising from pulverization and solid-electrolyte interphase growth. Here, we show that significant capacity degradation of aluminum foil anodes during electrochemical cycling also occurs due to diffusional lithium trapping. Scanning electron microscopy of cross-sectioned, cycled foils in the delithiated state reveals large regions of β-LiAl that are passivated by a surface layer of ⍺-Al, which has poor Li+ diffusivity. It is found that lithium diffusion occurs preferentially along the β-LiAl grain boundaries, so the grain structure after initial lithiation significantly affects the trapping behavior. Diffusional lithium trapping is exacerbated by both higher delithiation rates and higher areal capacity, presenting a challenge towards commercialization of aluminum foil anodes. We further demonstrate that diffusional trapping in aluminum foil anodes can be mitigated through alloy design, with the addition of 2–3 wt% Li yielding improved first cycle efficiency, and the addition of 1 wt% Si yielding improved cycle life. These results provide a mechanistic understanding of diffusional lithium trapping in aluminum foil anodes and highlight compositional design of alloys as a promising strategy to overcome it.

Artificial solid electrolyte interphase coating to reduce lithium trapping in silicon anode for highly stable lithium storage

Silicon (Si) has been regarded as a commercially viable anode material because of its outstanding theoretical capacity and rich abundance. However, the poor intrinsic electric conductivity, inherent volume expansion, and lithium trapping problems impede further commercialization. Here, we proposed a dual-design strategy by introducing mesoporous carbon and LiAlO2 as an artificial solid electrolyte interphase (SEI) on Si-based anode. The combination of mesoporous carbon and LiAlO2 both improves the structural stability of the Si-based anode and provides a fast diffusion pathway for lithium ions, thus improving the utilization of lithium. Moreover, thanks to the artificial SEI, the Si anode represent a remarkable electrochemical performance, delivering a specific capacity of 1910.3 mAh g-1 at a current density of 0.2 A g-1 with capacity retention of 73.4% in 140 cycles and prominent rate capability with a discharge capacity of 795.4 mAh g-1 at 1.0 A g-1 in 500 cycles, 456.2 mAh g-1 at 5.0 A g-1 in 1000 cycles.

Lithium trapping in germanium nanopores during delithiation process

Irreversible capacity loss is a critical problem in high capacity anode materials of Li-ion batteries, such as silicon, germanium, and tin. In addition to solid electrolyte interface formation and active material loss, Li trapping in high capacity anode materials during cycling has been considered a new mechanism of capacity loss but received less attention. In this study, we used single particle battery-based in situ focused ion beam-scanning electron microscopy, transmission electron microscopy (TEM), and scanning TEM to investigate the microstructure and composition of germanium nanopores formed at the end of delithiation. Our results show that a significant amount of Li accumulates inside the nanopores.

A Simplified Model to Track Si Degradation in Various Systems

Silicon (Si) is considered one of the most promising anode materials for next generation lithium-ion batteries (LIBs), due to the extremely high specific capacity (3580mAh/g). However, it is challenging to use Si anodes for LIBs, because of the large volumetric changes and phase evaluation associated with lithiation/delithiation of Si. These intrinsic issues of Si lead to the rapid degradation in capacity during cycling, especially in full cells assembled with commercial lithium-ion battery cathodes. Efforts have been made in order to stabilize the Si anodes including developing new electrolytes to increase the surface stability, inventing new binders to enhance the mechanical integrity, and using nanoarchitecture to reduce mechanical failures. Leveraging the previous research, this work introduces a simple and effective method to fast identify the failure mechanism for Si anodes and decouple the impacts of surface instability and lithium trapping on the electrochemical behavior. Here, we will apply our model for various systems of Si half cells to discuss the effectiveness of adding the fluorinated electrolyte additive and the use of nanoparticles. Moreover, we will study the effects of surface modification via atomic/molecular layer deposition on the electrochemistry of Si anodes by using our developed method and provide the insights in designing the highly reversible Si anodes. In this study, we will investigate how these aforementioned factors may affect the stability of Si particles as well as the cycle performances. Assisted with electrochemical impedance spectroscopy (EIS), we will keep track with the SEI evolution on Si anode and connect with the capacity degradation in order to explain the importance of interface stability.

Solid Electrolyte Interphase Layer Formation during Lithiation of Single-Crystal Silicon Electrodes with a Protective Aluminum Oxide Coating.

The lithiation of crystalline silicon was studied over several cycles using operando neutron reflectometry over six cycles. A thin layer of aluminum oxide was employed as an artificial coating on the silicon to suppress the solid electrolyte interphase (SEI) layer-related aging effects. Initially, the artificial SEI prevented side effects but led to increased lithium trapping. This layer degraded after two cycles, followed by side reactions, which decrease the coulombic efficiency. No hint for electrode fracturization was found even though the lithiation depth exceeded 1 μm. Two distinct zones with high and low lithium concentrations were found, initially separated by a sharp interface, which broadens with cycling. The correlation of the reflectometry results with the electrochemical current showed the lithium fraction that is lithiated in the silicon and the lithium consumed in side reactions. Also, neutron reflectometry was used to quantify the amount of lithium that remained inside of the silicon. Additional electrochemical impedance spectroscopy was used to gain insights into the electrical properties of the sample via fitting to an equivalent circuit.

Nanostructured Sn Plating and Pre-Lithiation on Cu Current Collector for Anode-Free Lithium Batteries

The fast and growing employment of Li-ion batteries in automotive and electrical mobility is pushing research towards the development of higher energy density and safer Li-ion batteries. Regarding the anodic material, metal and semi-metals as Al, Sn, Ag and Si are known to electrochemically alloy at low potential with lithium resulting in extremely high specific capacity, up to 4200 mAh/g for Li22Si5. However, severe issues as volumetric expansion and non-reversible lithium trapping strongly limit their cyclability and performances.[1] Anode-free Li battery (AFLB) strategy is a promising alternative to find a good compromise between safety and energy and power density because of the absence of an anodic active material in assembly phase. However, these systems suffer from severe challenges, including low coulombic efficiency (CE) due to intrinsic unstable interface that rapidly leads to dendritic growth and short-circuit.[2] To overcome this problem, nano-structuring of current collector has been demonstrated to be a valid approach to stabilize Li plating and stripping without dendrites formation.[3,4,5] In this work, we address current collector nano structuring by Sn plating as an efficient route for reversible Li plating/stripping. Interface stability is correlated with morphology of Sn deposits on Cu current collector in different conditions. Sn deposits were examined by AFM, SEM and XRD analysis and electrochemical behavior by galvanostatic charging and discharging cycles as well as EIS measurements. Sn pre-lithiation is also investigated as suitable strategy to further smoothing Li plating.

Encasing Prelithiated Silicon Species in the Graphite Scaffold: An Enabling Anode Design for the Highly Reversible, Energy-Dense Cell Model.

Si anodes suffer from poor cycling efficiency because of the pulverization induced by volume expansion, lithium trapping in Li-Si alloys, and unfavorable interfacial side reactions with the electrolyte; the comprehensive consideration of the Si anode design is required for their practical deployment. In this article, we develop a cabbage-inspired graphite scaffold to accommodate the volume expansion of silicon particles in interplanar spacing. With further interfacial modification and prelithiation processing, the Si@G/C anode with an areal capacity of 4.4 mA h cm-2 delivers highly reversible cycling at 0.5 C (Coulombic efficiency of 99.9%) and a mitigated volume expansion of 23%. Furthermore, we scale up the synthetic strategy by producing 10 kg of the Si@G/C composite in the pilot line and pair this anode with a LiNi0.8Co0.1Mn0.1O2 cathode in a 1 A h pouch-type cell. The full-cell prototype realizes a robust cyclability over 500 cycles (88% capacity retention) and an energy density of 301.3 W h kg-1 at 0.5 C. Considering the scalable fabrication protocol, holistic electrode formulation design, and harmony integration of key metrics evaluated both in half-cell and full-cell tests, the reversible cycling of the prelithiated silicon species in the graphite scaffold of the composite could enable feasible use of the composite anode in high-energy density lithium batteries.

Looking for the Lost Lithium: Lithium Trapping and Its Effect on Capacity Losses in Li-Ion Batteries

Rechargeable lithium batteries are well-known to exhibit progressive capacity decays upon cycling, leading to loss of cell voltage, power and energy. However, the origins of capacity losses are still not fully understood and are largely attributed to the formation of a solid electrolyte interface layer and volume expansion. Another largely overlook capacity decay mechanism is lithium trapping 1–4. Lithium trapping, caused by incomplete delithiation, is here demonstrated to be the main source of capacity losses in high energy density anodes (e.g. Si) while SEI formation and dissolution affect the accumulated capacity loss due to decreased coulombic efficiency. In the following paper we will present our findings on capacity losses in standard and optimized Si-Li half cells and how these systems affect lithium trapping inside the active electrode material. We will discuss how the cycling protocol (e.g. full capacity cycling vs coulombic limited cycling) can mask signs of Li trapping and temporarily delay capacity decay in half-cells. We will highlight the importance of lithium-trapping induced capacity or voltage decays effect in lithium-based batteries, explain the mechanism for lithium-trapping and establish diffusion-controlled lithium-trapping models. Approaches toward identifying and circumventing lithium-trapping problem will also be discussed as well as challenges and proposed future research directions within this exciting and important research field. Figure 1. Capacity evolution for an optimized nano-Silicon composite electrode in a half-cell configuration during coulombic limited cycling (i.e. 1200 mAh/g). Critical capacity decay is observed when the accumulated trapped lithium has saturated the electrode core and counteracts the deposited Li layer 1.

Understanding and Modelling the Thermodynamics and Electrochemistry of Lithiation of Tin Sulfide Compounds As Novel Anode Materials for Lithium Ion Batteries

Due to its theoretical capacity of 960 mAh/g, which is approximately two and a half times that of graphite (372 mAh/g), as well as its natural abundance, Sn is as an interesting anode active material to replace the currently used graphite in lithium ion batteries. However, Sn-based anodes have not been commercialized because they suffer from prohibitively large volume expansions due to the formation of brittle LixSn alloys during lithiation (>185 % for full lithiation to Li17Sn4). These volume changes lead to extensive crack formation, loss of electrical contact between particles, pulverization of the electrode during cycling, lithium trapping, and the growth of an unstable SEI. One way to take advantage of the high capacity of Sn and simultaneously overcome its degradation mechanisms is to use Sn-based chalcogenide compounds such as SnS2 and SnS as anode active materials. During lithiation of these compounds, a composite electrode structure consisting of active Sn particles embedded in an inactive Li2S buffer matrix is formed, which is expected to accommodate the mechanical stress of the alloying and de-alloying reactions during cycling.Although several authors have studied the lithiation of SnS2 via in-situ electron microscopy techniques, there are still many open questions regarding 1) the amount of lithium which can be intercalated into the layered structure of SnS2, 2) the structural changes of SnS2 during lithiation, and 3) if the reaction occurs via a one-phase or a two-phase process. Additionally, there are no published phase diagrams of the Li–Sn–S system at room temperature, which could be used to explore the changes in the electrode constitution during lithiation and de-lithiation. In fact, only Hwang et al. [1] modelled the phase equilibria in the Li–Sn–S at 0 K using density functional theory (DFT) calculations, but their data are incomplete since they omitted the Sn2S3, Li7Sn3 and Li5Sn2 phases and did not take into account the electrochemically and chemically observed solubility of lithium in SnS2. Therefore, in this work, the CALPHAD (CALculation of PHAse Diagrams) and computational thermodynamics methods were combined with key experiments to 1) understand the electrochemical lithiation of SnS2, 2) model the phase development during the equilibrium and non-equilibrium lithiation of the SnxSy tin sulfide compounds, and 3) evaluate the energetics of the competing lithiation reactions for the first time.Firstly, a thermodynamic description for the ternary Li–Sn–S system was developed by combining the descriptions of the Li–Sn system from Reichmann et al. [2] with that for the Sn–S system from Lindwall et al. [3] and the Gibbs free energy function for Li2S from the Scientific Group Thermodata Europe (SGTE) [4]. The ternary database was used to calculate the Li–Sn–S phase diagram at room temperature and simulate the titration curves for the equilibrium lithiation of the tin sulfide compounds. At the same time, homogeneous and heterogeneous Sn–S powder samples were processed as slurries, coated onto copper-foil substrates and subjected to electrochemical testing vs Li+/Li. The galvanostatic intermittent titration technique was used to characterize the quasi-equilibrium open circuit potentials of the electrodes during full and partial de-/lithiation in the potential range of 0.01-2.5 V. Additionally, a full profile, Rietveld refinement of the ex-situ XRD patterns of selected electrodes was performed in order to assess the phase development and structural changes of the electrode active materials during titration. These data were used to suggest a one-phase mechanism for the equilibrium lithiation of SnS2 after voltage relaxation. Finally, the electrochemical and crystallographic data were used to develop a new thermodynamic model to describe the intercalation of lithium ions into the layered SnS2 structure and calculate the measured open circuit voltage values. Using this description, it could be shown that lithiated SnS2 is indeed a metastable phase, which forms due to the energetic feasibility of the intercalation mechanism compared to the equilibrium conversion reaction.

Prelithiation of silicon/graphite composite anodes: Benefits and mechanisms for long-lasting Li-Ion batteries

Prelithiation of silicon/graphite-based composite anodes is a promising strategy to limit Li-ion battery capacity loss over long cycling. We report on the spontaneous-corrosion-driven-lithiation (SCDL) of lithium metal on the anode surface of a-Si/c-FeSi2/graphite//LiNi0·6Mn0·2Co0·2O2 cells, and compare it to electrochemically-driven-lithiation (EDL). High cyclability performances are achieved, i.e. more than 1760 cycles at 100% depth-of-discharge with less than 11% capacity loss at C/2. To quantify the fate of the lithium supply over prolonged cycling and follow in situ the benefits of prelithiation, we perform simultaneous operando synchrotron wide-angle and small-angle X-ray scattering (WAXS/SAXS). By accessing both the graphite lithiation process (WAXS) and the nanostructural variations of the silicon phase (SAXS), we obtain a complete picture of the lithium repartition during lithiation/delithiation of the prelithiated anode. Results indicate that the additional lithium is stored in the silicon, which acts as a reservoir compensating for lithium trapping. The silicon phase therefore plays an essential role but without the detrimental effect of large volume variations. By design, SCDL leads to a more heterogeneous prelithiation compared to EDL given that only the electrode area directly in contact with the lithium metal is initially prelithiated. However, we show that during cycling the additional lithium is redistributed throughout the electrode by migrating into the silicon and, finally, the two methods yield equivalent systems, with similar electrode morphologies and a much increased cell performance over cycling. Prelithiation could therefore be used for the production of high energy density and highly stable Li-ion batteries, implementing the easily up-scalable SCDL process.