Li-Si Alloy Research Articles

3D self-supporting core-shell silicon-carbon nanofibers-based host enables confined Li+ deposition for lithium metal battery

Three-dimensional (3D) porous hosts play pivotal roles in realizing dendrite-free lithium metal anodes (LMAs) owing to their high specific area. However, uneven local electric field and lack of lithiophilic sites on the reactive interface cause nonuniform lithium ion (Li+) deposition, leading to Li dendrite growth and parasitic reactions. These issues will inevitably incur short cycling life and severe safety hazards of lithium metal batteries. Herein, a 3D self-supporting host composed of hollow carbon nanofibers incorporated with silicon (Si) nanoparticles inside (Si-HCF) is constructed as Li metal host by a scalable coaxial electrospinning technique. During the first cycle, the Si nanoparticles is alloyed with Li+ to form lithiophilic Li-Si alloy, contributing to deliver a low nucleation overpotential and homogeneous surface potential confirmed by Kelvin probe force microscopy, finally guiding Li+ flux homogeneously throughout the fibrous mat. As expected, the Li metal can percolate through Si-HCF host reversibly without uncontrollable Li dendrites and the Si-HCF exhibits a stable cycle life of Li plating/stripping over 1400 h. Additionally, the full cell combined with LiFePO4 cathodes presents steady cycling over 400 cycles with a high average coulombic efficiency of 99.4 %. This work provides new insights for the synthesis of 3D hosts with controllable nucleation sites to homogenize Li+ deposition in LMAs.

Stability and performance of lithium metal batteries using silicon and silver alloyed separator surfaces

Lithium metal is renowned for its exceptional theoretical capacity and the lowest electrochemical potential, making it a cornerstone for batteries that can push the boundaries of energy and power density. However, its widespread adoption has been hindered by significant drawbacks, such as an unstable solid electrolyte interface (SEI) layer, substantial volume changes during charge-discharge cycles, and the formation of lithium dendrites. In our study, we have addressed these challenges by employing an innovative alloying technique to modify the surface of the separator with silicon (Si) and silver (Ag). This approach facilitates the formation of LiSi and LiAg alloys on the separator surface, leading to the creation of a novel lithium metal-lithium alloy composite anode. Our electrochemical tests have demonstrated that batteries equipped with this surface-modified lithium alloy composite anode exhibit superior coulombic efficiency and an impressively extended cycle life. Furthermore, when utilizing an ether-based electrolyte, the LiAg and LiSi alloy composite anodes have shown remarkable capacity retention rates of 89.1 % and 86.3 %, respectively, after 200 cycles in full cell tests. These results are notably superior to those of anodes made with bare lithium metal. In conclusion, the development of the face-to-face lithium alloy composite anode holds great promise for the practical application of lithium batteries with enhanced stability and performance. This advancement is a significant step towards realizing the full potential of lithium metal batteries in a variety of applications.

Exploring silicon nanoparticles and nanographite-based anodes for lithium-ion batteries

This study investigates the performance of silicon nanoparticles (Si NPs) and silicon nanographite (SiNG) composite-based anodes for lithium-ion batteries (LiBs). Si offers a promising alternative to traditional graphite anodes due to its higher theoretical capacity, despite encountering challenges such as volume expansion, pulverization, and the formation of a solid electrolyte interface (SEI) during lithiation. SiNPs anode exhibited initial specific capacities of 1568.9 mAh/g, decreasing to 1137.6 mAh/g after 100th cycles, with stable Li–Si alloy phases and high Coulombic efficiency (100.48%). It also showed good rate capability, retaining 1191.3 mAh/g at 8400 mA g−1 (2.82C), attributed to its carbon matrix structure. EIS indicated charge transfer with RB of 3.9 Ω/cm−2 and RCT of 11.4 Ω/cm−2. Contrastingly, SiNG composite anode had an initial capacity of 1780.7 mAh/g, decreasing to 1297.5 mAh/g after 100 cycles. Its composite structure provided cycling stability, with relatively stable capacities after 50 cycles. It exhibited good rate capability (1191.3 mAh/g at 8399.9 mA g−1), attributed to its carbon matrix structure. Electrochemical impedance spectroscopy showed higher resistances for RB of 4.2 Ω/cm−2 and RCT of 15.6 Ω/cm−2 compared to SiNPs anode. These findings suggest avenues for improving energy storage devices by selecting and designing suitable anode materials.

Unveiling Electrochemical Properties of Silicon for Stable Cycling Performance of Silicon Anode Materials

Research on silicon (Si) as an anode material for Li-ion batteries has spanned two decades; however, certain electrochemical properties of Si remain unclear. Specifically, the cyclic voltammogram (CV) pattern of Li/Si cells varies from case to case, influenced not only by the material but also by the experimental conditions. In this work, slow cyclic voltammetry is employed to investigate Li/Si cells, resulting in three distinct CV patterns. It is further observed that the CV pattern, particularly during the delithiation, is contingent on the state-of-lithiation (SOL) during lithiation and correlates with the capacity fade of Li/Si cells in subsequent cycles. Additionally, it is revealed that the primary mechanism for capacity fade differs between nano-sized silicon (Si-NP) and micro-sized silicon (Si-MP). In brief, capacity fade in Li/Si-NP cells predominantly arises from parasitic reactions between the highly lithiated Li-Si alloy and electrolyte solvents, exacerbated by the large specific surface area of Si-NP materials, whereas capacity fade in Li/Si-MP cells is primarily attributed to the Li electrode rather than the Si-MP electrode due to the restricted lithiation of Si-MP materials. Finally, this work concludes that limiting the SOL of Li/Si cells offers a straightforward and effective pathway to achieving stable cycling performance.

An in-situ polymerization strategy for gel polymer electrolyte Si||Ni-rich lithium-ion batteries

Coupling the Si-based anodes with nickel-rich LiNixMnyCo1−x−yO2 cathodes (x ≥ 0.8) in the energy-dense cell prototype suffers from the mechanical instability of the Li-Si alloys, cathode collapse upon the high-voltage cycling, as well as the severe leakage current at elevated temperatures. More seriously, the cathode-to-anode cross-talk effect of transitional metal aggravates the depletion of the active Li reservoir. To reconcile the cation utilization degree, stress dissipation, and extreme temperature tolerance of the Si-based anode||NMC prototype, we propose a gel polymer electrolyte to reinforce the mechanical integrity of Si anode and chelate with the transitional cations towards the stabilized interfacial property. As coupling the conformal gel polymer electrolyte encapsulation with the spatial arranged Si anode and NMC811 cathode, the 2.7 Ah pouch-format cell could achieve the high energy density of 325.9 Wh kg−1 (based on the whole pouch cell), 88.7% capacity retention for 2000 cycles, self-extinguish property as well as a wide temperature tolerance. Therefore, this proposed polymerization strategy provides a leap toward the secured Li batteries.

Robust 3D carbon host decorated with in-situ generated Li–Si alloy and Li3N for Li metal anodes

Lithium metal batteries hold a great promise for next-generation high-energy-density energy storage devices. However, severe Li dendrite growth and low Coulombic efficiency limit the application of lithium metal as anodes in Li batteries. Herein, we report a novel N-doped carbon host decorated with in-situ generated Li–Si alloy and Li3N for Li metal anode, showing a high theoretical specific capacity of 3090.0 mAh g−1. The as-prepared lithium composite (SiO2-N-CP@Li) electrode maintains stable cycling for over 960 h at 1.0 mA cm−2/1.0 mAh cm−2 and still has excellent stability (>900 h) especially at a high current density of 5.0 mA cm−2. Furthermore, when the SiO2-N-CP@Li anode is paired with LiFePO4 (LFP) cathode, the assembled full cell manages to deliver an impressive cycling performance for 450 cycles at 1C. This work offers a new insight for the rational design and utilization of Li metal anode in the next-generation high-energy-density batteries.

Lithiophilic Li-Si alloy-solid electrolyte interface enabled by high-concentration dual salt-reinforced quasi-solid-state electrolyte

Solid polymer electrolytes (SPEs) are urgently required to achieve practical solid-state lithium metal batteries (LMBs) and lithium-ion batteries (LIBs). Herein, we proposed a mechanism for modulating interfacial conduction and anode interfaces in high-concentration SPEs by LiDFBOP. Optimized electrolyte exhibits superior ionic conductivity and remarkable interface compatibility with salt-rich clusters: (1) polymer-plastic crystal electrolyte (P-PCE, TPU-SN matrix) dissociates ion pairs to facilitate Li+ transport in the electrolyte and regulates Li+ diffusion in the SEI. The crosslinking structure of the matrix compensates for the loss of mechanical strength at high-salt concentrations; (2) dual-anion TFSI–n-DFBOP–m in the Li+ solvation sheath facilitates facile Li+ desolvation and formation of salt-rich clusters and is conducive to the formation of Li conductive segments of TPU-SN matrix; (3) theoretical calculations indicate that the decomposition products of LiDFBOP form SEI with lower binding energy with LiF in the SN system, thereby enhancing the interfacial electrochemical redox kinetics of SPE and creating a solid interface SEI layer rich in LiF. As a result, the optimized electrolyte exhibits an excellent ionic conductivity of 9.31 × 10−4 S cm−1 at 30 °C and a broadened electrochemical stability up to 4.73 V. The designed electrolyte effectively prevents the formation of Li dendrites in Li symmetric cells for over 6500 h at 0.1 mA cm−2. The specific Li-Si alloy-solid state half-cell capacity shows 711.6 mAh g−1 after 60 cycles at 0.3 A g−1. Excellent rate performance and cycling stability are achieved for these solid-state batteries with Li-Si alloy anodes and NCM 811 cathodes. NCM 811|| Prelithiated silicon-based anode solid-state cell delivers a discharge capacity of 195.55 mAh g−1 and a capacity retention of 97.8% after 120 cycles. NCM 811||Li solid-state cell also delivers capacity retention of 84.2% after 450 cycles.

Mitigating Chemo-Mechanical Degradation in Sulfide-Based All-Solid-State Batteries Comprising Sulfur Composite Cathode and Li–Si Alloy Anode

In this study, all-solid-state batteries consisting of an Li2S5–P2S5 (LPS) glass electrolyte, a sulfur/LPS glass/carbon composite cathode, and an Li–Si anode are prepared and tested under high cut-off voltage conditions (0.5–3.7 V) to elucidate the effect of LPS redox activity on the chemo-mechanical stability of LPS-based cells. The cell cycled in the voltage range 0.5–3.7 V exhibits unstable charging behaviors and voltage noise, with substantial LPS oxidative decomposition. X-ray photoelectron spectroscopy and impedance spectra analyses of a three-electrode system reveal that the cathode resistance is remarkably increased by the oxidative decomposition of LPS when the cell is charged to 3.7 V, which induces dendritic lithium growth at the anode side, resulting in a micro-short circuit through the electrolyte. Composite anodes of Li3PS4 glass+Li–Si alloy (Type 1) and Li3N+LiF+Li–Si alloy (Type 2) are also prepared for all-solid-state batteries (ASSBs) with LPS glass electrolyte and sulfur/LPS glass/carbon composite cathode. Using a three-electrode system, the anode and cathode potentials are separated, and their polarization resistances are individually traced. Even under high-cutoff-voltage conditions (3.7 V), Type 1 and 2 cells are stably cycled without voltage noise for >200 cycles. Although cathode polarization resistance drastically increases after 3.7 V charge owing to LPS oxidation, LPS redox behavior is fairly reversible upon discharge–charge unlike the non-composite alloy anode cell. Time-of-flight secondary ion mass spectrometry (TOF-SIMS) analysis reveals that the enhanced cyclability is attributed to uniform Li–Si alloying throughout the composite anode, providing more pathways for lithium ions even when these ions are over-supplied via LPS oxidation. These results imply that LPS-based cells can be reversibly cycled with LPS redox even under high-cutoff voltages, as long as non-uniform alloying (lithium dendrite growth) is prevented.

Mechanical and Electrochemical Properties of Highly-Dense Li-Si Alloy Anodes Fabricated by Arc Plasma Deposition

Silicon is one of the most promising anode materials because it has a very high theoretical capacity (4200 mAh g− 1). This capacity is about 10 times higher than that of carbon anode (372 mAh g− 1).[1] However, enormous volumetric change and mechanical stress occur in a silicon anode during electrochemical lithiation-delithiation. Consequently, the specific capacity is degraded during repetition of charge-discharge because of cutting off conductive paths caused by mechanical fracture. It is reported that pre-lithiation by sputtering and electrochemical methods suppresses fracture of silicon anodes by decrease in elastic modulus and yielding stress.[2] However, the reported Li-Si alloy anodes possesses the mechanical properties derived from both the deposited silicon and the voids generated during the synthetic processes. Therefore, a highly-dense alloy is necessary to investigate relationships between mechanical and electrochemical properties of Li-Si itself. We have already fabricated highly-dense amorphous silicon films by an arc plasma deposition (APD) method.[3] Thus, we attempted to fabricate highly-dense Li-Si alloy films by an APD method. The obtained Li-Si alloy films were investigated with focusing on relationships between mechanical properties and electrochemical properties.Li x Si (x = 0-3.56) alloy films were prepared on Al2O3(0001) single-crystal and Cu substrates by an APD method. Metallic lithium and B-doped silicon coated with carbon were used as target materials in the APD apparatus. The physical structures and chemical states of the obtained Li x Si alloy films were investigated with Raman spectroscopy, hard X-ray photoelectron spectroscopy (HAXPES), and neutron reflectometry (NR). Elastic modulus and hardness of the Li x Si alloy films were calculated from load-displacement curves gained by nanoindentation measurement. Constant-current charge-discharge tests were carried out with 2032-type coin cells assembled using the Li x Si films as the working electrodes, Li foils as counter electrodes, and 1 M LiPF6 in EC: DEC 3:7 vol% as electrolytes. The charge-discharge tests were conducted with constant current of 0.01-0.16 mA (1C rate), lower and upper voltages of 20 mV and 1.5 V vs. Li/Li+.In HAXPES spectra, Si 2p peaks derived from Si0 shifted to lower binding energy compared to the Si (x = 0) film as x increased. Therefore, Li x Si alloy films with different compositions were successfully fabricated by the APD method. The peaks because of Si-Si bonds in Raman spectra also shifted to lower wavenumber with the increase in x. The shifts suggest that the length of the Si-Si bonds extended with the increase in x. The NR analyses revealed that Li x Si alloy films possessed the smooth surface with the roughness less than 3 nm. The elastic modulus and hardness of Li x Si alloy films decreased as x increased, meaning that Li x Si alloy films were softer and more easily deformed compared to Si films. In addition, the elastic modulus and hardness of Li x Si alloy films were higher than those of Li x Si films previously reported,[2] suggesting that the APD method more densely made the Li x Si alloy films than the reported sputtering and electrochemical methods. Thus, the objective highly-dense films of Li x Si alloys were successfully obtained. The plateaus corresponding to the reactions of Li x Si ↔︎ Li x ’Si ↔︎ Li y Si (x < x’ < y) were observed in charge-discharge curves of Li x Si alloy films. The first discharge capacities of Li x Si alloy films were lower than the theoretical capacity of silicon. This is due to the existence of lithium in the structure by pre-lithiation. Cycle stabilities of Li x Si alloy films were superior to the Si film. To reveal factors of the cycle stabilizing, the charge-discharge reactions were analyzed with dQ/dV plots. The peaks around 0.5 V in the delithation process decreased about Si film. This decrease in the reaction peak is attributed to the decrease in the active species during the reaction process because of the fracture. In contrast, the peaks of Li x Si alloy films around 0.5 V hardly decreased. This result suggests that delamination and fracture by volumetric change during charge-discharge processes were suppressed in Li x Si alloy films because of their softness. Thus, the analyses of the highly-dense Li x Si alloy films fabricated by the APD method clarified that cycle stabilities of active materials were improved by controlling mechanical properties.[1] Ashuri, M.et al., Nanoscale 2016, 8, (1), 74-103.[2] Sitinamaluwa, H. et al., RSC Adv. 2017, 7, 13487-13497.[3] Asano, S. et al., Highly-dense and smooth amorphous silicon films fabricated by arc plasma deposition and electrochemical properties., ACSSI-17, 3A-06, 9.15.2022.

NMR, x-ray, and Mössbauer results for amorphous Li-Si alloys using density functional tight-binding method

NMR, x-ray, and Mössbauer results for amorphous Li-Si alloys using density functional tight-binding method

(Keynote) Parameterize Important Factors for Li Metal Batteries: Cycle Life, Calendar Life and Reactivity

The lithium (Li) metal anode is essential for next-generation high-energy-density lithium metal batteries. The calendar life and reactivity (safety) are equally important to cycle stability for the real application of Li metal anode in different devices. Our recent studies have identified that preventing Li dendrite growth by stacking pressure could improve cycle life by consuming less electrolyte and preventing inactive Li0 accumulation. A similar conclusion is obtained in the study of electrodepositing Li metal anode calendar life and reactivity (safety), in which the porosity of the deposited Li dominates the Li metal corrosion rate and reactivity. The larger the porosity of deposited Li, the faster the corrosion rate/higher reactivity will be. Moreover, all cell components must be considered when it comes to the reactivity (safety) of Li metal batteries because components may react with each other. Our results revealed that dense Li metal anode owns similar reactivity as lithiated graphite/ Li-Si alloy. All results facilitate lithium metal battery design and manufacturing.

Study of Li-Si Alloy Composition for Anode Materials in Sulfide-Based All-Solid-State-Batteries

Lithium alloys are promising anode materials with high specific capacity for all-solid-state-batteries (ASSBs). In this study, ASSBs were fabricated by consisting of Li-Si alloy anode, sulfide electrolytes and sulfur composite cathode. During discharge-charge cycles, changes in polarization resistance in the anode and cathode were separately traced using three-electrode system of an embedded Indium reference electrode in ASSBs. As de-alloying and alloying in Li-Si anode, Li distribution and phase changes were investigated using x-ray diffraction, optical microscopy and Time-of-Flight Secondary Ion Mass Spectrometry (TOF-SIMs). A half-cell was fabricated by using Indium foil as a counter electrode to study the Li ion diffusion coefficient in Galvanostatic Intermittent Titration Technique(GITT). It is observed that Li composition (22:5 ~ 1:1) in Li-Si alloy anode affected the chemo-mechanical stability and volume expansion behavior in ASSBs, which were associated with the redox behavior of sulfide solid electrolyte.

Design Strategies of Li-Si Alloy Anode for Mitigating Chemo-Mechanical Degradation in Sulfide-Based All-Solid-State Batteries.

Composite anodes of Li3 PS4 glass+Li-Si alloy (Type 1) and Li3 N+LiF+Li-Si alloy (Type 2) are prepared for all-solid-state batteries with Li3 PS4 (LPS) glass electrolyte and sulfur/LPS glass/carbon composite cathode. Using a three-electrode system, the anode and cathode potentials are separated, and their polarization resistances are individually traced. Even under high-cutoff-voltage conditions (3.7V), Type 1and 2cells are stably cycled without voltage noise for >200cycles. Although cathode polarization resistance drastically increases after 3.7V charge owing to LPS oxidation, LPS redox behavior is fairly reversible upon discharge-charge unlike the non-composite alloy anode cell. Time-of-flight secondary ion mass spectrometry analysis reveals that the enhanced cyclability is attributed to uniform Li-Si alloying throughout the composite anode, providing more pathways for lithium ions even when these ions are over-supplied via LPS oxidation. These results imply that LPS-based cells can be reversibly cycled with LPS redox even under high-cutoff voltages, as long as non-uniform alloying (lithium dendrite growth) is prevented. Type 1and 2cells exhibit similar performance and stability although reduction product is formed in Type 1. This work highlights the importance of alloy anode design to prevent chemo-mechanical failure when cycling the cell outside the electrochemical stability window.

Stainless Steel-Like Passivation Inspires Persistent Silicon Anodes for Lithium-Ion Batteries.

Passivation of stainless steel by additives forming mass-transport blocking layers is widely practiced, where Cr element is added into bulk Fe-C forming the Cr2 O3 -rich protective layer. Here we extend the long-practiced passivation concept to Si anodes for lithium-ion batteries, incorporating the passivator of LiF/Li2 CO3 into bulk Si. The passivation mechanism is studied by various ex situ characterizations, redox peak contour maps, thickness evolution tests, and finite element simulations. The results demonstrate that the passivation can enhance the (de)lithiation of Li-Si alloys, induce the formation of F-rich solid electrolyte interphase, stabilize the Si/LiF/Li2 CO3 composite, and mitigate the volume change of Si anodes upon cycling. The 3D passivated Si anode can fully retain a high capacity of 3701 mAh g-1 after 1500 cycles and tolerate high rates up to 50C. This work provides insight into how to construct durable Si anodes through effective passivation.

Lithium isotope tracing in silicon-based electrodes using solid-state MAS NMR: a powerful comprehensive tool for the characterization of lithium batteries.

The introduction of lithiated components with different 7Li/6Li isotopic ratios, also called isotopic tracing, can give access to better understanding of lithium transport and lithiation processes in lithium-ion batteries. In this work, we propose a simple methodology based on high-resolution solid-state NMR for the determination of the 7Li/6Li ratio in silicon electrodes following different strategies of isotopic tracing. The 6Li and 7Li MAS NMR experiments allow obtaining resolved spectra whose spectral components can be assigned to different moieties of the materials. In order to measure the ratio of the 6Li/7Li NMR integrals, a silicon electrode with a natural 7Li/6Li isotope abundance was used as a reference. This calibration can then be used to determine the 7Li/6Li ratio of any similar samples. This method was applied to study the phenomena occurring at the interface between a silicon electrode and a labeled electrolyte, which is an essential step for isotopic tracing experiments in systems after the formation of the solid electrolyte interphase (SEI). Beyond the isotopic exchanges between the SEI and the electrolyte already observed in the literature, our results show that isotopic exchanges also involve Li-Si alloys in the electrode bulk. Within a 52-hour contact, the electrolyte labeling disappeared: isotopic concentrations of the electrolyte and electrode become practically homogenized. However, at the electrode level, different silicides are characterized by rather different isotopic enrichment. In the present work, ToF SIMS and liquid state NMR were also used to cross-check and discuss the solid-state NMR method we have proposed.

Quantification of Lithium Inventory Loss in Micro Silicon Anode Via Titration-Gas Chromatography

Enabling silicon as an anode material for LIBs has been largely impeded by the severe volume changes it undergoes during cell operation, causing continuous Li inventory loss . Therefore, It is important to understand and quantify various sources of capacity fade in order to design effective mitigation strategies. In this work, we used a method based on Titration Gas Chromatography (TGC) to show a non-linear volume expansion in µSi anode during the electrochemical lithiation process. The severe volume expansion towards the end of lithiation leads to the accelerated SEI formation and thus leading to the conductive pathway loss, which results in a large amount of trapped Li-Si alloy accumulation. This TGC method was also applied to study μSi anodes with two different binders namely: Sodium Carboxymethyl Cellulose (CMC-Na) and Polyacrylic Acid (PAA). The main reason for capacity loss for the anode with CMC-Na binder was the trapped Li-Si alloy, which was reduced by using a more mechanically robust PAA binder. The concept of State of Charge (SoC) control was also investigated in µSi-LFP full cells with both the binders by tuning the N/P ratios from 1.5 to 3. The results showed that binder robustness is important for mitigating the trapped Li-Si alloy accumulation in µSi anode. Additionally, the effect of particle size of active material on trapped Li-Si accumulation was also investigated using the TGC method Figure: Cycle performance of µSi- CMC-Na-LFP full-cell with various N/P ratios (b) Cycle performance of µSi-PAA-LFP full-cell with various N/P ratios (c) TGC Data for Lithium inventory loss of full cell after 1st cycle for various N/P ratios (d) TGC Data for Lithium inventory loss of full cell after 10 cycles for various N/P ratios Figure 1

Electrodeposition of crystalline Si in molten alkali metal fluoride–chloride mixtures: Comparative study of Li, Na, K, and Cs systems

A comparative study was conducted on the electrodeposition of Si using molten salts of AF–ACl–A2SiF6 (A = Li, Na, K, Cs, AF–ACl = 50:50 mol%) at 1073 K. Cyclic voltammetry revealed that the electrodeposition potential of Si was negative in the order of Na > K > Cs systems with reference to Cl2/Cl−, and almost the same as with reference to F2/F−. In the Li system, no cathodic current peak was observed, owing to the formation of the Li–Si alloy. In the Na and Li systems, the cathodic peak current density decreased with time owing to the decomposition of SiF62− ions. The differences in the Si electrodeposition and thermal stability of SiF62− ions can be explained by the interactions of alkaline cations and F− ions; smaller cations interact more strongly with F−, resulting in the reduced thermal stability of SiF62−. Electrodeposited Si was confirmed to be crystalline by XRD, and its morphology was film-like in the K and Cs systems, and whisker-like in the Na system. A difference in nucleation and growth was observed between the K and Na systems, which explains the difference in the morphology of the Si deposits.

Lithium diffusion through the TiN coating layer and formation of Li-Si alloy over Si@TiN anode

• In-situ X-ray diffraction is used to detect the diffusion of lithium in TiN layer and the formation of Li-Si alloy over Si@TiN anode. • The alloying reaction is controlled by diffusion, and the Li-Si alloy formation corresponds with the shrinking core model in Si@TiN system. • The use of the non-Faradaic process prevents the formation of an unstable solid electrolyte interphase (SEI), and this avoids the interference from the SEI. • Empirical equation is established to quantify the lithium diffusion across the TiN layer. In this study, the diffusion of lithium in the TiN layer and the formation of Li-Si alloy over Si@TiN anode are experimentally evaluated with the help of in-situ X-ray diffraction. The results reveal that lithium diffuses into TiN layer and reacts with the Si core to produce Li-Si alloy once the temperature is higher than 200 °C. Raising temperature contributes to more Li-Si alloy, and the alloying reaction is controlled by diffusion. Increasing reaction time leads to the enlargement of Li-Si alloy crystal size and the mathematical fitting between Si conversion and reaction time suggests that the formation of Li-Si alloy corresponds with the shrinking core model in Si@TiN system. Empirical equation is also established to describe the diffusion of lithium in TiN layer, where the potential energy barrier is 19.4 kJ/mol and pre-exponent is 2.2 × 10 -18 m 2 /s. This work is beneficial to know deep insight into the lithium diffusion through TiN layer and the formation of Li-Si alloy over Si@TiN anode.

Redox activity of Li2S–P2S5 electrolyte inducing chemo-mechanical failure in all-solid-state batteries comprising sulfur composite cathode and Li–Si alloy anode

In this study, all-solid-state batteries consisting of an Li2S5–P2S5 (LPS) glass electrolyte, a sulfur/LPS glass/carbon composite cathode, and an Li–Si anode are prepared and tested under two different cut-off voltage conditions (0.5–2.7 V and 0.5–3.7 V) to elucidate the effect of LPS redox activity on the chemo-mechanical stability of LPS-based cells. In the voltage range 0.5–2.7 V, which is outside the theoretical stability window for LPS, the cell is stably cycled, indicating that there exists a practical stability window that fulfills each cell condition. On the other hand, the cell cycled in the voltage range 0.5–3.7 V exhibits unstable charging behaviors and voltage noise, with substantial LPS oxidative decomposition. X-ray photoelectron spectroscopy and impedance spectra analyses of a three-electrode system reveal that the cathode resistance is remarkably increased by the oxidative decomposition of LPS when the cell is charged to 3.7 V, which induces dendritic lithium growth at the anode side, resulting in a micro-short circuit through the electrolyte. When the cycles are repeated with voltage noise, the capacity loss becomes significant, which is attributed to cathode degradation (irreversible LPS decomposition) and cracks through the cell, as promoted by the micro-short circuit. This study shows that LPS redox activity outside the practical stability window can lead not only to oxidative degradation of the cathode itself, but also to chemo-mechanical failure in LPS-based cells (especially with high-capacity anode materials such as lithium alloys).

Quantification of lithium inventory loss in micro silicon anode via titration-gas chromatography

The commercialization of silicon as an anode material for lithium-ion batteries has been largely impeded by its severe volume changes during cell operation, causing continuous loss of Li inventory. As such, it is vital to understand and quantify the sources of capacity fade in order to design effective mitigation strategies. Herein, we design a method based on Titration Gas Chromatography (TGC) to reveal a non-linear volume expansion in μSi anode during the lithiation process. The severe volume expansion towards the end of lithiation leads to accelerated SEI formation and conductive pathway loss, resulting in a large amount of trapped Li–Si alloy accumulation. The TGC method is also applied to investigate μSi anodes with two different binders: Sodium Carboxymethyl Cellulose (CMC-Na) and Polyacrylic Acid (PAA). The primary reason for capacity loss for anode with CMC-Na binder is trapped Li–Si alloy, which can be mitigated by using more robust PAA binder. The Sate of Charge (SoC) control principle is also investigated in μSi-LFP full cells with both binders by tuning the N/P ratios (1.5–3). The results indicate binder robustness is crucial for mitigating the trapped Li–Si alloy accumulation in μSi anode.