Lithiation Mechanism Research Articles

Sustainable Electrochemical Recycling of Spent Lithium-Ion Batteries: Selective Extraction of Lithium and Direct Regeneration of De-Lithiated Material

The recycling of spent lithium-ion batteries has become an urgent imperative. In recent years, the rising demand for lithium has sparked interest in the selective extraction of lithium from spent LIBs cathode materials. This process is of interest as it can streamline processes, improve lithium recovery efficiency, and reduce processing costs. Electrochemical methods for selectively extracting lithium from spent cathode materials have gained significant attention among various selective extraction methods due to their advantages, such as low energy consumption and environmental friendliness. Despite substantial progress in improving the efficiency of lithium recovery through electrochemical methods, the economic returns from lithium salt products, to some extent, are still insufficient to offset the processing costs of the entire process, thereby limiting the further development of this technology. Therefore, it is necessary to develop reasonable strategies for the utilization of such de-lithiated materials to further enhance product yields. One promising strategy among these approaches is direct regeneration of fresh cathode materials from the de-lithiated material. However, due to a lack of clear understanding of the structural evolution of transition metal oxides during the lithium extraction process, and the lithiation mechanisms of lithium-depleted materials, there is currently no research report on the direct regeneration of such de-lithiated materials into battery materials.Herein, an electrochemical method using LiCl aqueous as electrolyte is developed to realize the selective extraction of lithium from spent polycrystal LiNi0.55Co0.15Mn0.3O2 (NCM) cathode materials, with a maximum de-lithiation rate approaching 90%. Thorough characterizations were conducted to monitor the morphological, structural, and compositional evolution of NCM during the electrochemical de-lithiation process. These findings contribute to a profound understanding of the characteristics of the de-lithiated material and inform the rational design of regeneration pathways tailored to such materials. The results reveal that the deep de-lithiation of NCM in lithium-aqueous electrolyte triggers water-molecule intercalation, leading to an unusual phase transformation beyond H1→H2→H3. This phase transformation causes substantial lattice expansion along c-axis and introduces severe lattice distortion in de-lithiated material. The over-expanded lattice and the presence of bulk defects resulted in an unstable structure, posing huge challenge for the subsequent direct regeneration of de-lithiated material using conventional calcination methods. To address this, we employ a hydrothermal re-lithiation process, characterized by a milder, lithium-rich and water-based environment. This process is able to create a “lithium-water-balance” structure for de-lithiated materials by promoting the lithium diffusion into the lithium-deficiency structure and facilitating the exchange between lithium ions and water molecules. This process effectively enhances structural stability of the de-lithiated material. As a result, subsequent calcination successfully converts the degraded structure back into the original lithium-conductive layer structure by further eliminating the remaining lattice defects in material and promoting the cation rearrangement. The regenerated material exhibits decent electrochemical performances, which delivers a capacity of 153.2 mAh g−1 at 1C and 132.5 mAh g− 1 at 5C. This work provides insights into the electrochemical de-lithiation method and fills a gap in the utilization of de-lithiated NCM, paving the way for the sustainable recycling of spent LIBs.

Phase Field Damage Framework for Modeling Thin-Film Silicon Anodes in All-Solid-State Batteries

Recent advancements in solid electrolyte research have revived interest in the concept of silicon anodes for All-Solid-State Batteries (aSSBs). Tan et al. have recently proposed stable cyclic performance of micro-grain size pure silicon anodes paired with sulfide-based solid electrolytes [1]. This development has opened pathways toward potential aSSBs without encountering dendrite growth issues. This rediscovery of the thin-film a-silicon anodes concept has sparked computational interest in simulating the fracture-chemo-mechanical silicon lithiation mechanism. Understanding chemical reactions during lithiation and crack evolution during de-lithiation processes are intriguing topics. Especially, elastic-plastic deformation coupled with phase-field continuous fracture is crucial in comprehending the underlying physics and enhancing performance of battery cell through reverse engineering approaches.In this work, we develop a thermodynamically consistent deformation-diffusion-damage coupled framework to model the evolution of dense, thin-film-like a-silicon anodes during lithiation and delithiation. During delithiation, tensile stress develops inside the film as the lithiated film overcomes the initial stack pressure and compressive stress prevalent during lithiation. As tensile stress and strain evolve, randomly distributed weak spots lead to crack nucleation. This fracture occurs throughout the silicon film, forming sharp vertical cracks, and depending on surface conditions along the solid-state electrolyte, some interfacial cracks may emerge, leading to permanent contact loss and resulting in capacity reduction.From the model, we observed “mud crack” like phenomena, where crack distribution is not controlled by particle’s property, but entire cluster’s thickness matters. While flat model suggests that one that nucleate the crack was weak spots where they make stress concentration over entire body, whether they can evolve into big vertical crack mostly governed by connectivity of such weak spot maps. However, from our interface roughness model, what governs the crack evolution most was not the randomly distributed weak spot, but its geometric relative thickness difference between one another. Due to manufacturing process, perfect interface is hard to be achieved and such geometric irregularity always exist, thus, additive and binder studies along the silicon anode and its interface between sse would be key to achieve long and stable life span for a-silicon based aSSBs. Reference [1] Tan, Darren HS, et al. "Carbon-free high-loading silicon anodes enabled by sulfide solid electrolytes." Science 373.6562 (2021): 1494-1499.

Deciphering the Impact of Current, Composition, and Potential on the Lithiation Behavior of Graphite in Silicon-Graphite Anodes

Graphite is the most used anode material for current-generation lithium-ion batteries due to its beneficial cycle life, availability and reasonable rate capability. Still, the modest capacity of 372 mAhg-1 represents a bottleneck in the pursuit of high-energy density anodes. Enabling much higher theoretical capacities of 3600 mAhg-1 [1], silicon represents a promising candidate as anode material for next generation batteries. However, the alloying-based lithiation mechanism of silicon is accompanied by a large volumetric change of up to 300% upon cycling, leading to fast degradation due to electrode pulverization, continuous SEI formation and extensive electrolyte consumption. Even though shallow cycling of silicon anodes has been demonstrated in laboratory scale cells [2], the mixing of silicon with graphite is considered the most viable approach to lift energy density while maintaining appropriate cycle life.Due to the fundamentally different kinetics and potentials of Li insertion and extraction of both materials, the development of silicon-graphite composite electrodes is not straightforward. One of the key questions for optimization is how the incorporation of silicon impacts the (de)lithiation behavior of graphite as a function of the silicon:graphite mass ratio, operating current and electrode potential. While lithiation of graphite in composite electrodes of 15 wt% silicon has been shown to occur in a similar manner as pure graphite, higher fractions of silicon are expected to exert more stress on the graphite and represent kinetic barriers for Li diffusion. This study presents results from in-situ X-ray diffraction experiments (XRD) of silicon-graphite/Li half cells conducted at the European Synchrotron Radiation Facility (ESRF). Serving as a reference, the current-dependent (de)lithiation behavior of a pure graphite/Li half cell has been thoroughly investigated and systematically compared to the (de)lithiation behavior of two selected silicon-graphite composite anodes (silicon:graphite ratio of 30:70 and 70:30, respectively) exposed to the same formation cycle and C-rate protocol. An optimized and novel measurement setup was used, based on a perforated current collector of the anode, providing a complete picture of the graphite in-plane and interplanar structural changes as well as the evolution of semicrystalline silicon peaks which would usually be obscured by the current collector signal.By correlating the electrochemical features (voltage curve and differential capacity plot) with the in-situ diffraction data, it was possible to identify and assign the occurrence and absence of dilute-stage and ordered graphite intercalation compounds (GICs) for the respective electrodes, yielding an in-depth insight into the graphite state of charge upon (de)lithiation and how it is influenced by the silicon content and applied C-rate.As expected, the silicon is (de)lithiated within the entire potential range, whereas graphite is most electrochemically active at potentials lower than 260 mV. In both composite electrodes, graphite attains a lower lithiation degree compared to pure graphite. This is because the high theoretical capacity of silicon results in high specific currents, ultimately challenging the rate capability of graphite. Moreover, the high delithiation overpotential encountered in the composite electrodes results in a highly asymmetrical lithiation/delithiation behavior of graphite. Also, graphite lithiation is less uniform in the composite anodes, indicated by the coexistence of dilute GICs upon (de)lithiation, compared to pure graphite where dilute phases are fully consumed (formed) as (de)lithiation progresses. Surprisingly, the in-situ XRD studies did not reveal signs of structural degradation and strain of graphite as a result of mechanical interaction with silicon. Instead, the volume change of graphite is well correlated with the amorphization of crystalline, unreacted silicon and the volume evolution of silicon crystallites upon charge-discharge.To mitigate the observed effects, the work suggests nanostructuring and advanced electrode architectures towards higher utilization and more homogeneous lithiation of graphite. Overall, the study provides a demonstration of a suitable operando cell for studies of anodes for Li-based systems, and aids the rational design of silicon-graphite composite anodes.

Zirconium effect on the lithiation mechanism of LiNi0.83Mn0.05Co0.12O2 positive electrode material

Ni-rich LiNi1-x-yMnxCoyO2 (x + y ≤ 0.2) materials are employed to enhance the energy density of lithium-ion batteries, while they are still facing the stability issue. Doping is considered as an efficient approach to improve the stability of the LiNi1-x-yMnxCoyO2 materials. A considerable number of studies have concluded that Zr-doping improves the stability when undoped and doped LiNi1-x-yMnxCoyO2 materials are lithiated under the same conditions. Unfortunately, a fundamental understanding of the Zr dopants role during lithiation conditions is still lacking. This work investigates the Zr effects on lithiation mechanism of LiNi0.83Mn0.05Co0.12O2 (NMC). The main findings are: First, the NMC and Zr-doped NMC have different lattice parameter growth speeds, and the (003) & (101) lattice planes form order structures at lower temperatures during lithiation process when the dopant is included. Second, Zr is prone to locate near the surface region of NMC secondary particles. Third, when lithiation time increases from 8 h to 12 h at 800 °C, the undoped NMC electrochemical performance deteriorates whereas the doped material improves. These findings highlight that understanding the mechanism behind lithiation conditions is essential for doped LiNi1-x-yMnxCoyO2. The insights revealed in this work can guide for design of other dopants for Ni-rich positive electrode materials.

Atomistic phase transition mechanism of zero-strain electrode material: Transmission electron microscopy investigation of Li4Ti5O12 spinel lattice upon lithiation

The lithiation mechanism of electrode materials is important for understanding the basic reactions in Li-ion batteries. In particular, zero-strain materials have garnered interest owing to their stable charge–discharge performances. In this study, we investigated the atomistic phase transition mechanism of spinel Li4Ti5O12, a well-known zero-strain material, using high-resolution transmission electron microscopy. A single-crystalline Li4Ti5O12 (100) specimen was prepared and observed in situ at a lattice resolution under electron-beam-assisted lithiation. The lattice fringes originating from the Li plane of the spinel crystal were anisotropically altered during phase transition, suggesting the asymmetrical site shifting of Li atoms during lithiation. This spontaneous symmetry-breaking mechanism for the phase transition is considered essential for the lithiation of spinel lattice.

The impact of integrated circuits’ performance in low-temperature environments on charging efficiency of chargers

Abstract This paper explores the current research status of chargers and lithium-ion batteries in low-temperature environments. Based on this, it provides a detailed discussion and analysis of charger charging conditions, lithium-ion battery performance analysis, the correlation between low-temperature environments and charging, and optimization design strategies for charging in low-temperature environments. The study reveals that low-temperature environments distort charger current harmonics, disrupt the power supply capacity of the grid, and reduce fast charging conversion efficiency. The paper elucidates the lithium-ion battery lithiation mechanism, lithiation detection methods, and countermeasures for lithiation issues in low temperatures. Besides highlighting the various adverse effects of lithiation on low-temperature charging, it also points out the shortcomings of detection methods and proposes appropriate strategies to inhibit lithiation. Addressing charging issues in low-temperature environments, the paper introduces charging optimization design strategies involving temperature-modulated current charging and genetic algorithm optimization. This research offers theoretical guidance and technical support for the design and optimization of chargers and lithium-ion batteries in low-temperature environments, further advancing the development and application of low-temperature charging technology.

Enhanced reversible reaction of hexagonal SnS2@rGO as anode materials for lithium-ion batteries: Analysis of the morphological change mechanism

Tin-based materials have attracted attention as a promising anode material for lithium-ion batteries due to their high theoretical capacity and alloy metal characteristics. However, the structure tends to easily collapse with repetitive charging and discharging processes, leading to volume expansion. The conversion step in the SnS2 reaction mechanism is also sometimes considered irreversible. To address these challenges, this study synthesized layered hexagonal 2D structure-type SnS2 using the oleylamine as surfactant through a wet chemical process. Subsequently, SnS2@rGO was synthesized after compounding with reduced graphene oxide (rGO), utilizing a smaller amount of nanomaterials compared to rGO, showing optimal efficiency. The morphological changes in SnS2 and SnS2@rGO during the charging and discharging processes was revealed that pulverization occurred more slowly in SnS2@rGO compared to SnS2. We quantified the volume expansion rates of SnS2 and SnS2@rGO electrodes, demonstrating that rGO effectively reduces volume expansion. Additionally, an analysis of lithiation mechanism through a comprehensive analysis method using CV, ex-situ XRD, and ex-situ TEM demonstrated that SnS2@rGO enhanced Li+ storage characteristics compared to SnS2, resulting in more reversible chemical changes. rGO and bare SnS2 show poor capacities 307.23 mAh/g and 87.17 mAh/g after 120 cycles, respectively. However bare SnS2 anchored on the surface of rGO exhibits increased electrical conductivity and improved performance (711 mAh/g after 120 cycles), confirming that rGO plays an important role. SnS2@rGO showed enhanced cycling stability and discharge capacity as shown in the electrochemical testing.

Identification of polypyrrole-encapsulated BiSCl as a viable conversion/alloying anode material for high-performance lithium storage

Anode materials combining conversion and alloying mechanisms are increasingly valued in advanced rechargeable batteries for their exceptional theoretical capacities and advantageous working voltages. This study showcases BiSCl as a promising conversion/alloying anode material, demonstrating a high specific capacity and enhanced durability through polypyrrole encapsulation. Employing in situ X-ray diffraction, X-ray photoelectron spectroscopy, ex situ transmission electron microscopy, and field emission scanning electron microscopy, we offer a detailed analysis of the lithiation mechanism in BiSCl. The anode exhibits a low average working potential of approximately 0.6 V, supporting a theoretical specific capacity of 784 mAh/g and a volumetric capacity of 4664 mAh/cm3. The innovative BiSCl-PPy core-shell composite effectively addresses the challenges of volumetric expansion and polysulfide dissolution. This composite delivers a remarkable reversible capacity of 753 mAh/g at a current rate of 100 mA/g, maintaining 96% of its specific capacity over 400 cycles, and sustains 419 mAh/g at 500 mA/g after 800 cycles, demonstrating more superior performance than that of BiSCl. These findings establish BiSCl as a highly promising conversion/alloying anode material for lithium storage, significantly enhanced in durability by the BiSCl-PPy core-shell composite.

Controlled Growth Lateral/Vertical Heterostructure Interface for Lithium Storage.

Artificial heterostructures with structural advancements and customizable electronic interfaces are fundamental for achieving high-performance lithium-ion batteries (LIBs). Here, a design idea for a covalently bonded lateral/vertical black phosphorus (BP)-graphdiyne oxide (GDYO) heterostructure achieved through a facile ball-milling approach, is designed. Lateral heterogeneity is realized by the sp2-hybridized mode P-C bonds, which connect the phosphorus atoms at the edges of BP with the carbon atoms of the terminal acetylene in GDYO. The vertical connection of the heterojunction of BP and GDYO is connected by P-O-C bond. Experimental and theoretical studies demonstrate that BP-GDYO incorporates interfacial and structural engineering features, including built-in electric fields, chemical bond interactions, and maximized nanospace confinement effects. Therefore, BP-GDYO exhibits improved electrochemical kinetics and enhanced structural stability. Moreover, through ex- and in-situ studies, the lithiation mechanism of BP-GDYO, highlighting that the introduction of GDYO inhibits the shuttle/dissolution effect of phosphorus intermediates, hinders volume expansion, provides more reactive sites, and ultimately promotes reversible lithium storage, is clarified. The BP-GDYO anode exhibits lithium storage performance with high-rate capacity and long-cycle stability (602.6 mAh g-1 after 1000 cycles at 2.0 A g-1). The proposed interfacial and structural engineering is universal and represents a conceptual advance in building high-performance LIBs electrode.

Redox process and lithiation mechanism of amorphous vanadium-silicon materials as lithium-ion battery anode

V2O5-TeO2 (VT) is a vanadium-based amorphous lithium-ion battery (LIB) anode material that exhibits a high specific energy, but its low-capacity retention rate and low conductivity limit its widespread application. Different amounts of Si were introduced into VT anode materials to increase their initial discharge capacity and conductivity, which regulated the vanadium redox reaction. 67 V2O5-30TeO2-3Si (VTS3) exhibited the highest conductivity and V4+ content (49.8%). When the Si content was increased, the V4+ content decreased, indicating that Si successfully regulated the redox reaction. The results showed that VTS3 had a high initial discharge capacity of 1187.3 mAh g−1, while that of VT was only 906.5 mAh g−1. After 50 charge-discharge cycles, the retention rates of VT and VTS3 were 15.6% and 25.0%, respectively. After cycling, the precipitation of nanocrystals, especially LiV2O5, from the glass matrix improved the capacity retention of VTS3 by enhancing reversible lithium insertion. The synergy of this disordered-ordered transition improved the discharge capacity and reversibility. Density functional theory (DFT) calculations showed that due to the substitution of Si, the gap between Highest Occupied Molecular Orbital (HOMO) and HOMO-1 was shortened, Li-O electron aggregation was enhanced, the structure was improved, and electronic conductivity was enhanced. At the same time, sufficient Si content increased the initial specific capacity but reduced the retention rate, which was because the volume expansion during the charge-discharge cycle reduced the number of active sites. This work offers a new strategy for preparing LIB electrode materials by introducing Si to regulate redox reactions and precipitate nanocrystals.

Mechanistic Insights into the Discharge Processes of Li-CO2 Batteries.

Li-CO2 batteries facilitate renewable energy storage in a cost-effective, eco-friendly manner. However, an inadequate understanding of their reaction mechanism severely impedes their development. Here we outline recent mechanistic advances in the discharge processes of Li-CO2 batteries, particularly in terms of the theoretical aspect. First, the vital factors affecting the formation of discharge intermediates are highlighted, and a surface lithiation mechanism predominantly applicable to catalysts with weak CO2 adsorption is proposed. Subsequently, the modeling of the chemical potential of Li++e-, which is crucial for the evaluation of the theoretical limiting voltage, is detailed. Finally, challenges and future directions pertaining to the further development of Li-CO2 are discussed. In essence, this concept article seeks to inspire future experimental and theoretical studies in advancing the development of Li-CO2 electrochemical technology.

Nanocarbon-enabled mitigation of sulfur expansion in lithium–sulfur batteries

Significant lithiation-induced sulfur expansion hinders the development of commercial lithium–sulfur (Li–S) batteries, highlighting a pressing need to comprehend the sulfur lithiation mechanism. Coupled molecular dynamics (MD) and finite element analysis (FEA) simulations were used to unveil the chemo-mechanics of rate-dependent sulfur anomalous volumetric changes. The lithiation-induced sulfur transition was found to proceed in four stages, ranging from sulfur lithiation to the formation of Li2S. Lithiation induced sulfur swelling and shrinking, which were accompanied by increased and decreased lithiation stresses, respectively. Although the precipitation of Li2S4, Li2S2, and Li2S resulted in partial lithiation of the sulfur, the formation of these precipitates in turn buffered sulfur expansion by 48.64 %. A high current density was able to mitigate lithiation-induced sulfur expansion with trade-off in battery-specific capacity degradation. Nanocarbons, characterized by high porosity and outstanding mechanical properties, were robust enough to guide sulfur expansion along their open ends, thus effectively buffering sulfur volume change. Our findings provide a new mechanism for previously unexplained experimental observations, advance the understanding of sulfur expansion-caused cathode deterioration, and offer a new design guideline for high-performance Li–S batteries.

Interfacial Electrochemical Lithiation and Dissolution Mechanisms at a Sulfurized Polyacrylonitrile Cathode Surface.

Advances in sulfurized-polyacrylonitrile (SPAN)-based cathode materials promise safer and more efficient lithium-sulfur (Li-S) battery performance. To elucidate electrolyte-cathode interfacial electrochemistry and polysulfide (PS) dissolution, we emulate discharge SPAN reactions via ab initio molecular dynamics (AIMD) simulations. Plausible structures and their lithiation profiles are cross-validated via Raman/IR spectroscopy and density functional theory (DFT). Lithium bis(fluorosulfonyl)imide (LiFSI) plays versatile roles in the Li-SPAN cell electrochemistry, primarily as the major source in forming the cathode-electrolyte interphase (CEI), further verified via X-ray photoelectron spectroscopy and AIMD. Besides being a charge carrier and CEI composer, LiFSI mediates the PS generation processes in SPAN electrochemical lithiation. Analysis of AIMD trajectories during progressive lithiation reveals that, compared to carbonates, ether solvents enable stronger solvation and chemical stabilization for both salt and SPAN structures. Differentiated CEI formation and electrochemical lithiation decomposition pathways and products are profoundly associated with the intrinsic nature of lithium bonding with oxygen and sulfur.

The lithiation mechanism of ultrathin 2D ZnO systems working as anode materials for lithium-ion batteries: From Wurtzite to graphene-like structures

Several ZnO nanostructures such as nanosheets, nanotubes and quantum dots with Wurtzite structure have been prepared and studied as lithium-ion anode materials revealing that the increasing interface is a key aspect to improve their performance. To the best of our knowledge, up to now, there are no reports in the literature that deal directly with lithium-ion transport and charge transfer on ultrathin 2D ZnO exhibiting graphene-like and Wurtzite structures working as anode materials for lithium-ion batteries. Here, we present a DFT study on the lithiation of ultrathin 2D ZnO nanostructures including graphene-like (monolayer and bilayer) and Wurtzite (trilayer) structures. We focus on the ionic-electronic transport properties addressing the ionic transport through the different surfaces as well as charge transfer, equilibrium voltages, and work function variations due to lithiation for all systems. We reveal interesting features regarding how deep the reduction of Zn ions is still observed allowing more efficient charge transfer for graphene-like and Wurtzite systems working as anode material for a lithium-ion battery.

Towards an enhanced understanding of the particle size effect on conversion/alloying lithium-ion anodes

Conversion/alloying materials (CAMs) represent a potential alternative to graphite as a Li-ion anode active material, especially for high-power applications. So far, however, essentially all studies on CAMs have been dealing with nano-sized particles, leaving the question of how the performance (and the de-/lithiation mechanism in general) is affected by the particle size. Herein, we comparatively investigate four different samples of Zn0.9Co0.1O with a particle size ranging from about 30 nm to a few micrometers. The results show that electrodes made of larger particles are more susceptible to fading due to particle displacement and particle cracking. The results also show that the conversion-type reaction in particular is affected by an increasing particle size, becoming less reversible due to the formation of relatively large transition metal (TM) and alloying metal nanograins upon lithiation, thus hindering an efficient electron transport within the initial particle, while the alloying contribution remains essentially unaffected. The generality of these findings is confirmed by also investigating Sn0.9Fe0.1O2 as a second CAM with a substantially greater contribution of the alloying reaction and employing Fe instead of Co as a TM dopant.

Lithiation of phosphorus at the nanoscale: a computational study of LinPm clusters.

Systematic structure prediction of LinPm nanoclusters was performed for a wide range of compositions (0 ≤ n ≤ 10, 0 ≤ m ≤ 20) using the evolutionary global optimization algorithm USPEX coupled with density functional calculations. With increasing Li concentration, the number of P-P bonds in the cluster reduces and the phosphorus backbone undergoes the following transformations: elongated tubular → multi-fragment (with mainly P5 rings and P7 cages) → cyclic topology → branched topology → P-P dumbbells → isolated P ions. By applying several stability criteria, we determined the most favorable LinPm clusters and found that they are located in the compositional area between m ≈ n/3 and m ≈ n/3 + 6. For instance, the Li3P7 cluster has the highest stability and is known to be the structural basis of the corresponding bulk crystal. The obtained results provide valuable insights into the lithiation mechanism of nanoscale phosphorus which is of interest for development of novel phosphorus-based anode materials.

Introducing a Novel Light Scattering Technique for Visualising Operando State-of-Charge Changes Within Individual Active Particles and Across the Electrode

In our presentation we will demonstrate the application of a recently developed operando optical microscopy technique to mechanistic studies of lithium-ion battery electrodes and active material characterisation. Our technique probes state-of-charge (SoC) changes in the active particles within the electrode during battery operation, based on the intensity variation of scattered light across each active particle. This enables detailed spatially resolved data on an individual particle level to be utilised for furthering mechanistic understanding of battery capability and degradation, and it also allows global statistics to be established for the optimisation and screening of new electrode materials. The technique is agnostic to the underlying battery chemistry, so in principle can be applied to study any battery electrode.In this talk, we will demonstrate how our technique can be used in the study of two key dynamic processes, solid-state ion transport and mechanical degradation. The ability to quantify ion transport during battery operation helps to provide insights into how lithium-ion dynamics affect the (de)lithiation mechanisms and degradation mechanisms of battery electrodes, which is crucial to improving their electrochemical performance. Using lithium cobalt oxide (LCO) as a case study, we will show how ion-transport mechanisms can be deduced by observing moving phase boundaries within particles during cycling.We will then demonstrate how local SoC changes within Ni-rich nickel manganese cobalt oxide (NMC) active particles can be visualised during operation, and how the intra-particle ion gradients identified can be used to determine the mechanistic origins of first-cycle capacity losses. Building on this, we will highlight how variation in the rates of (dis)charge between a population of active particles could be used to characterise the performance of new electrode compositions.In addition, we will highlight how lithium-ion concentration gradients can also be identified in high-rate niobium tungsten oxide (NWO) anode materials during initial lithiation and under initial rapid delithiation conditions and demonstrate how this can lead to particle cracking. Expanding on this, we illustrate how the proportion of cracked particles within an electrode can be quantified and then monitored over successive cycles as a potential metric for screening the stability of new electrode materials.

Atomistic study on the origins of the anisotropic lithiation behaviors of the silicon anode using the reactive force field based molecular dynamics simulations

We employed the Reactive-Force-field (ReaxFF) based molecular dynamics simulations to investigate the lithiation mechanisms and anisotropic lithiation behaviors of the Si-based anode during the lithiation processes. In order to accurately predict the relative lithiation kinetics on different surface facets of c-Si, we have developed new ReaxFF parameters for the Li-Si system based on first-principles calculations. Our results demonstrated that the lithiation kinetics on the Si(110) and (112) surfaces manifestly outperformed those occurred on the Si(100) and (111) surfaces. The lithiation reactions on the Si(110) and (112) surfaces tend to proceed through a ledge mechanism involving the layer-by-layer peeling of the {111} atomic facets. However, the lithiation reaction on the Si(100) surface is more likely to occur via the layer-by-layer etching of the {100} atomic facets. The discrepancy in the lithiation kinetics among the c-Si(100), (110) and (112) substrates was mainly ascribed to the variation in the compressive stresses that developed within the phase boundary upon lithiation. Regarding the Si(111) surface, the significantly slower lithiation kinetics than other surface facets were primarily attributed to the presence of a considerably larger barrier for Li insertion into the subsurface region to initiate the lithiation reaction. Furthermore, the order of the energy barriers for Li insertion into different c-Si surfaces was determined as follows: Si(111)>>(100)>(110)>(112), indicating that Li atoms tend to migrate into c-Si predominantly through the (110) and (112) surfaces upon lithiation. Consequently, lithiation reactions would occur majorly on the (110) and (112) surfaces due to the much lower compressive stresses that developed within the phase boundary and smaller Li insertion barriers than other surface facets, resulting in the observed anisotropic lithiation behaviors of the c-Si nanomaterials.

Investigation of the lithiation mechanism of tin phosphite SnHPO3 as anode for Lithium-ion batteries

Phosphite-based anodes are attracting increasing attention in energy storage, especially for lithium-ion technology, due to their distinctive structures and their good electrochemical performances. Herein, the lithiation mechanism of tin phosphite SnHPO3 as lithium anode was examined for the first time. SnHPO3 has been synthesized through a soft hydrothermal route. Its structure was characterized by X-ray diffraction, Fourier Transform Infrared spectroscopy and 31P Nuclear Magnetic Resonance spectroscopy techniques. The reaction mechanisms of lithiation-delithiation of SnHPO3 anode was conducted using operando X-ray diffraction, ex-situ X-ray and ex-situ Fourier Transform Infrared spectroscopy techniques at room temperature. Both in-situ and ex-situ measurements show that SnHPO3 undergoes a conversion mechanism. The lithiation-delithiation of tin phosphite took place in a complex redox reaction sequence, and the reversible electrochemical phenomenon exclusively occurs through the alloying of tin at a low potential. The lithiation of tin phosphite begins by partial degradation of its structure, signifying the start of the conversion process. Then, the phosphite matrix becomes amorphous. The reversible capacity of the system is governed by the lithium‑tin alloying de-alloying process, produced at low potential.

Amorphous TiO2 shells: an Essential Elastic Buffer Layer for High-Performance Self-Healing Eutectic GaSn Nano-Droplet Room-Temperature Liquid Metal Battery.

Gallium-based alloy liquid metal batteries currently face limitations such as volume expansion, unstable solid electrolyte interface (SEI) film and substantial capacity decay. In this study, amorphous titanium dioxide is used to coat eutectic GaSn nanodroplets (eGaSn NDs) to construct the core-shell structure of eGaSn@TiO2 nanodroplets (eGaSn@TiO2 NDs). The amorphous TiO2 shell (~6.5 nm) formed a stable SEI film, alleviated the volume expansion, and provided electron/ion transport channels to achieve excellent cycling performance and high specific capacity. The resulting eGaSn@TiO2 NDs exhibited high capacities of 580, 540, 515, 485, 456 and 426 mAh g-1 at 0.1, 0.2, 0.5, 1, 2 and 5 C, respectively. No significant decay was observed after more than 500 cycles with a capacity of 455 mAh g-1 at 1 C. In situ X-ray diffraction (in situ XRD) was used to explore the lithiation mechanism of the eGaSn negative electrode during discharge. This study elucidates the design of advanced liquid alloy-based negative electrode materials for high-performance liquid metal batteries (LMBs).