Combining silicon and graphite in electrode materials leverages the high energy density of silicon while using graphite to mitigate the significant volumetric expansion of silicon based electrodes during cycling. Such combination will impact the formation and evolution of the solid electrolyte interphase (SEI). In this study, we compare silicon (Si) and silicon/graphite blend Si/Gr (50:50) electrodes and investigated their electrochemical performance in a highly concentrated triethyl(methyl)phosphonium bis(fluorosulfonyl)imide (P1222FSI) ionic liquid electrolyte in both half-cells and full-cells. Through a combination of transmission electron microscopy (STEM-EDX), X-ray photoelectron spectroscopy (XPS), and magic angle spinning nuclear magnetic resonance (MAS-NMR), we monitored the evolution of the SEI and silicon particles morphology. Although displaying similar capacity fading profile, failure mechanisms for Si and Si/Gr electrodes cycled in full-cell configuration are completely different. For Si/Gr blend full-cells, nano-porosification of silicon particles occurs, leading to SEI accumulation and the capacity fade is largely attributed to the loss of cyclable lithium. Contrarily, the absence of nano-porosification and an extremely stable and blocking SEI characterize Si electrodes in full-cell. This study provides new insights into how SEI evolution and silicon morphology impact the electrochemical performance of Si and Si/Gr blend electrodes across different cell configurations in non-carbonated electrolytes.

Even though oxide solid electrolytes (SEs) have several advantages such as high chemical/thermal stability over conventional liquid electrolytes, their low ionic conductivity and difficult integration during cell fabrication hinder practical application. Here, the Li ionic conductivity of the LISICON (lithium super ionic conductor)-type SE is enhanced by substitution of Ge, achieving conductivity approximately 5 times higher than that of the unsubstituted. The Ge substitution can not only increase the concentration of Li but also enhance partial occupancies of Li at specific sites, enabling additional Li diffusion pathways and thereby leading to high ionic conductivity. Surprisingly, unlike other Ge-based solid electrolytes, the Ge-substituted LISICON-type SE exhibits excellent wetting behavior with Li metal and co-sintering capability with high-capacity cathodes even at temperatures above 700 degrees C. The increased Li ionic conductivity and excellent co-sintering capability enable the fabrication of an all-solid-state battery (ASSB) with an ultra-thick composite electrode (similar to 140 & micro;m), which delivers high electrochemical activity/reversibility at room temperature without external pressure. These findings clearly demonstrate that the LISICON-type SE with enhanced Li ionic conductivity provides a completely novel strategy for achieving high energy density in ASSBs and offers a promising route toward practical application of oxide-based SEs in high-energy density ASSBs.

This study investigates a strategy to simultaneously enhance oxygen and cationic (Ni) redox reactions in Li2MnO3-based Li-rich cathode materials composed of LiNi0.5Mn0.5O2 (LNMO) and Li2MnO3 phases. It is demonstrated that high-temperature synthesis, particularly at 900 degrees C, promotes stabilization of the LNMO-like phase over the Li2MnO3-like phase, enabling concurrent activation of both redox reactions. The increased fraction of the LNMO-like phase significantly enhances the Ni redox reaction and raises the average discharge voltage. At the same time, the LNMO-like phase stabilization increases Ni incorporation into the Li2MnO3-like phase, which is crucial for activating the oxygen redox reaction. As a result, the material synthesized at 900 degrees C can achieve both high capacity and elevated discharge voltage. Additionally, the ratio of Li2MnO3 to NiO at 900 degrees C strongly influences redox reactions through its effect on the LNMO-like phase stabilization. While increasing NiO amount almost linearly enhances the Ni redox reaction, the oxygen redox reaction depends primarily on the Ni content incorporated into the Li2MnO3-like phase rather than its quantity. Therefore, simultaneous optimization of both redox reactions is achieved only within a specific compositional range, which can achieve certain amount of the Ni into the Li2MnO3-like phase. These findings demonstrate the phase stabilization control as an effective design strategy for high-energy-density Li2MnO3-based Li-rich layered materials.

Polyacrylic acid (PAA) is an emerging binder for silicon-graphite (Si-Gr) composite anodes due to its strong affinity for the native SiOx layer that covers Si particles and its ability to act as an artificial solid-electrolyte interphase (SEI). Here, PAA with a high molecular weight (Mw = 845 kg mol(-1)) is synthesized using a green, aqueous route. The effect of varying PAA content (from similar to 3 to 15wt%) on electrode processing, physical properties, and cycling stability is systematically investigated. Increasing PAA concentration improves slurry stability and dispersion, widening the electrode processability window. X-ray photoelectron spectroscopy (XPS) confirms that PAA preferentially localizes on the silicon surface, with evidence of agglomeration at higher concentrations. An optimal PAA content of 10.6 wt% delivers the highest reversible specific capacity and good cycling stability (1270 mAh gelectrode(-1) at the 50th cycle in half cell and 860 mAh g(electrode)(-1) in full cell). Lower PAA content results in deficient binder networks and increased irreversible capacity, while excessive binder content leads to binder agglomeration and increased resistivity. Post-mortem solid-state NMR analysis further supports the role of PAA as an artificial SEI, mitigating uncontrolled electrolyte decomposition and lithium loss.

MnP4 has already been identified as a promising negative electrode for Li-ion batteries. Despite its interesting theoretical capacity, well above that of graphite, this material was not studied further due to its poor cyclability. MnP4 was here prepared by ball milling and used as an active negative electrode material in optimised electrode formulation. This ball milled MnP4 optimised electrode shows improving cycling performance, with a stable specific capacity of 600 mAh g-1 over 60 cycles. The combination of operando X-ray diffraction, Mn K-edge X-ray absorption spectroscopy, and 31P and 7Li NMR analyses reveals a two-step reversible mechanism: Li insertion in MnP4 forming amorphous "LixMnP4" which is converted into Li3P and Mn metal at low potential. Unlike in previous studies related to MnP4, the MnP4 CMC-based electrode shows neither crystalline Li7MnP4 formation at mid discharge, nor MnP4 reformation upon charge. This modified reaction pathway appears to be beneficial for long-term capacity retention.

The design flexibility of organic materials has enabled numerous applications for energy storage systems. However, few examples of low-potential p-type materials for the negative electrode are known in the field of organic batteries, particularly relevant for anion-rocking-chair full-cells. Herein, we present a synthetic design to incorporate bridged 2,2'-bipyridinium units, which in their reduced form are known as super-electron-donors, into a polymer structure. By adapting their synthesis, we obtain a hydroxy-functionalized bridged bipyridinium salt with interesting structural features that are determined by molecular symmetry and environmental effects. Incorporation into a linear and cross-linked poly(methacrylate) reduces its electrolyte solubility, enabling its initial electrochemical evaluation in lithium battery half-cells. After testing electrodes with different compositions and screening electrolytes, we demonstrate that these polymers have the potential to function as electrode-active materials, operating at an attractively low potential of 1.8 V vs. Li/Li+. This work highlights the opportunities of low-potential 2,2'-bipyridinium-based polymers and demonstrates how synthetic design strategies can guide the development of novel organic electrode materials, providing a foundation for future research in this field.

One promising way for enhancing Li-ion battery performance is the use of silicon-graphite-composite anodes. Even though this complex system has been extensively studied, the lithium dynamics in silicon/graphitecomposite electrode material, as well as at the interfaces, are still not well understood. To investigate lithium mobility and trapping effects in the solid electrolyte interphase (SEI) during lithiation and at rest state in Si-C/Gr composites, we use here a methodology based on combined MAS NMR and FIB-SIMS, both sensitive to lithium isotopic labeling. Labeling electrolyte and Li metal counter electrode with 6Li and SEI with 7Li allows distinguishing the origin of lithium ions within graphite and silicon active materials. Following electrochemical lithiation, the SEI shows the lowest 7Li fraction while it is higher in both Si and graphite, providing a direct observation of the so-called knock-off mechanism for the movement of lithium ions through the SEI. However, the lower 7Li fraction of silicides points out that another mechanism of Li transport, possibly through vehicular mechanism (solvated or desolvated Li), is also at play, enabling a more direct transfer of lithium ions from the electrolyte to silicon particles. In addition, in Open Circuit Voltage (OCV) experiments, Li movement seems to be different in Li-rich and Li-poor silicides, as the Li-rich phase exchanges faster with 6Li enriched electrolyte. The innovative 6/7Li isotope tracing approach described here paves the way for further understanding of the transport properties between electrodes and electrolyte, controlling these phenomena and developing knowledge for the development of high-performance battery technology.

Recent pioneering research has identified halide electrolytes, particularly Li₂ZrCl₆, as a novel and promising class of Solid-State Electrolytes (SSEs). These electrolytes exhibit exceptional oxidative stability, achieving potentials up to 4 V vs Li⁺/Li 1 , with notable partial reversibility of their oxidation reactions 2 . Despite these impressive attributes, the broader capabilities of halide-based catholytes to boost All Solid-State Batteries (ASSB) performance beyond mere ionic conductivity have remained largely unexplored. We demonstrate that diverse compositions within the Li x ZrCl 4+x (LxZC) family effectively function as secondary redox-active materials alongside primary electroactive species within composite cathodes ( Figure 1a ). This results in substantial enhancements in overall cell-specific capacity — by several tens of percent—even under demanding, industrially relevant high cathode mass loadings (>4 mAh/cm²) 3,4 . Furthermore, we innovatively exploit the irreversible (sacrificial) capacity of the LxZC catholyte for in-situ prelithiation of micro-Si anodes and the deposition of thin lithium films in anode-less configurations. We believe this novel " self-healing " approach represents a significant advancement towards implementation of both micro-Si and anode-less ASSB architectures. Elucidating the redox mechanism that allows such an outstanding performance of this SSE family will be explained by coupling the data from several operando techniques, including attenuation and diffraction based Synchrotron X-ray Computed Tomography (SXCT) ( Figure 1b ), powder X-ray diffraction, Mechanical Pressure Measurements (MCP) and Online Electrochemical Mass Spectroscopy (OEMS). K. Wang et al., Nat. Commun., 12, 4410 (2021). H. Kwak et al., Nat. Commun., 14, 2459 (2023). B. Stamenkovic, Y. S. Meng, P. Moreau, and J. Gaubicher, J. Electrochem. Soc., 171, 050554 (2024). 4. B. Stamenkovic et al., ACS Materials Lett., 4873–4880 (2024). Figure 1a. Impact of the halide catholyte composition on the electrochemistry of LFP based cathodes Figure 1b. Experimental setup and acquired data of operando SXRD CT experimen Figure 1

Silicon is a promising active material for Li-ion battery negative electrodes because of its high theoretical specific capacity as compared to the standard graphite materials (3579 mAh/g vs 372 mAh/g). However, the capacity retention of Si-based anodes is negatively impacted by the Si expansion during lithiation (up to ~300% for Li 15 Si 4 compared to ~10% for LiC 6 ) and subsequent contraction during delithiation. The primary sources of this capacity fade are the delamination of the anode material from the current collector, the isolation of active material, and uncontrolled solid electrolyte interphase (SEI) formation. A resilient polymer binder network can help mitigate the effects of the expansion and contraction of silicon particles and prolong the cycle life of Si-based electrodes. Polyacrylic acid (PAA) is a prevalent binder material for Si-based and Si-Graphite composite electrodes that features carboxylic acid functional groups, which can bind to the native silanol layer on silicon particles. It is known to increase the adhesion of the electrode to the current collector and the cohesion strength of the bulk electrode, as well as act as an artificial SEI layer. The present study aims to optimize the PAA binder formulation in respect to several key parameters, namely its neutralisation degree, substituting cation, polymer molecular weight, and coverage ratio. Previous work from our group on silicon-graphite composite electrodes with a partially neutralized PAA binder yielded promising results. In fact, the simple addition of metal hydroxide has the double effect of increasing the slurry pH and forming carboxylate groups along the polymer chains. The former brings the active materials further away from their isoelectric points (pH ≈ 2.35 for silicon and pH ≈ 4 for graphite), preventing flocculation, while the latter increases interactions between the polymer chains through carboxylate-cation attractive interactions. The strength of these interactions depends on their nature. Monovalent metal cations (Na + , Li + ) promote weaker dipole interactions while polyvalent cations (Mg 2+ , Zn 2+ , Ca 2+ ) create stronger coordination bonds. These interactions have been shown to improve the mechanical properties of the dried electrodes, as well as their capacity retention over cycling in previous studies. Furthermore, the predominant trend in literature is to use a commercially available, high-molecular weight PAA for electrochemical studies. However, these long polymer chains require a more intensive synthesis process and run the risk of folding in on themselves due to intramolecular interactions, especially after the addition of polyvalent cations. Shorter chains are easier to synthesize but are typically thought to be less effective as binders due to their small size compared to the active material particles. High-, intermediate- and low-molecular weight PAA binders are compared in this study to verify these hypotheses. In a final step, an ideal polymer coverage ratio – a compromise between capacity retention and energy density – is determined for each binder formulations. The impact of each of these binder parameters is explored through a variety of characterisation techniques carried out at each electrode processing and testing step. The relative adsorption of each polymer formulation during the slurry dispersion step is studied by gel permeation chromatography. Next, the rheological properties of each slurry under shearing are compared, namely the viscosity, which relates to slurry milling and tape-casting conditions, and the storage and loss moduli, which affect the slurry stability and the electrode coating homogeneity. Next, the mechanical properties of the electrodes are determined by nanoindentation and the coating resistivities are measured with a 4-point probe. The electrochemical performances are ultimately compared to identify optimal binder characteristics for increased capacity retention. In sum, the impacts of the PAA chain length and partial neutralisation through the addition of various metal hydroxides are elucidated. Ideal coverage ratios are also determined for each formulation and an optimized, PAA-based binder for silicon-graphite composite electrodes is highlighted. References: Obrovac, M. N. Si-Alloy Negative Electrodes for Li-Ion Batteries. Curr. Opin. Electrochem. 2018 , 9 , 8–17. https://doi.org/10.1016/j.coelec.2018.02.002. Meyssonnier, C.; Merabet, A.; Dupré, N.; Paireau, C.; Lestriez, B. Critical Binder‐to‐Powders Coverage Ratio for Faster Graphite/SiOx Electrode Formulation Optimization. Small Methods 2024 , 8 (8), 2301370. https://doi.org/10.1002/smtd.202301370. Vanpeene, V.; Huet, L.; Villanova, J.; Olbinado, M.; Marone, F.; Maire, E.; Roué, L.; Devic, T.; Lestriez, B. Deciphering the Benefits of Coordinated Binders in Si‐Based Anodes by Combined Operando/In Situ and Ex Situ X‐Ray Micro‐ and Nano‐Tomographies. Adv. Energy Mater. 2024 , 2403741. https://doi.org/10.1002/aenm.202403741. Jiang, H.; Wei, C.; Yasmin, S.; Obrovac, M. N. Deconvoluting Slurry Rheology from Binder Performance in Si-Based Anodes. J. Electrochem. Soc. 2023 , 170 (12), 120522. https://doi.org/10.1149/1945-7111/ad136f.

Organic host electrode materials offer a promising route for the development of sustainable secondary batteries, with reduced resource dependency and eco-friendly synthesis. However, the understanding of insertion mechanisms remains complex, primarily due to the challenges associated with resolving the crystal structures of these materials especially with lithiated structures. This study investigates the phase transformation pathways occurring in magnesium (2,5-dilithium-oxy)-terephthalate during the electrochemical reversible extraction/uptake of lithium. A combination of advanced techniques, including electron diffraction tomography, powder X-ray diffraction, and density functional theory calculations, was successfully employed to elucidate the crystal structure of this electrode material. The structure exhibits a compact layered arrangement (2.189 g cm-3) and a distinctive coordination environment surrounding the phenolate group, which involves both Li+ and Mg2+ ions. The Mg2+ ion, exhibiting a high ionic potential, mitigates the donor inductive effect of the conjugated CO-/CO2groups, resulting in a high working potential for this n-type redox-active organic skeleton, comparable to that of LiFePO4. The electrochemical solid-state process, studied using operando synchrotron X-ray diffraction, revealed an asymmetric delithiation/lithiation mechanism, linked to Peierls-distorted it-stacks of radicals, confirmed by DFT calculations and electron spin resonance experiments. Finally, analysis of the electronic structure of the semiquinone Mg(Li1)-p-DHT center dot phase, with spin-coupled diamagnetic dimers, showed that removal of the second electron (resulting in the quinone form) is unfavorable due to the weakening or destruction of the carboxylate C=O bond. This observation sheds light on the limited capacity of p-DHT-based compounds, which typically reach only half of their theoretical capacity due to the occurrence of the Kolbe electrolysis reaction.

Design of tailored materials using innovative approaches that allow faster charging/discharging processes could be the key for improvement of electric mobility. In this work, a strategy is developed to modify KNbO3 perovskite structure by partially substituting K+ with La3+ at the A-site of the structure, creating two cation vacancies per substitution in the lattice. Materials with the general formula K1-3x La x square 2x NbO3 (with 0 <= x <= 0.15; square is an A-site vacancy) have been synthesized by the sol-gel method. With La substitution and creation of artificial vacancies in the structure, KNbO3 became activated for Li+ insertion. The highly substituted K0.55La0.15 square 0.30NbO3 (30% atomic A-site vacancies) exhibited 164 mAh g-1 at 0.02 A g-1 in the 0.05-3.0 V vs Li+/Li potential window. Ex situ 7Li and 93Nb MAS NMR confirmed an increased Li+ insertion in relation to vacancies and corresponding changes in Nb5+ local environment, respectively. In situ X-ray diffraction (XRD) analysis revealed a solid-solution-type storage mechanism with a maximum volume change of only 1.3% upon Li+ insertion for highly substituted material. This accounts for the remarkable capacity retention obtained after 900 cycles at 0.1 Ag-1. Diverged from the classical design of insertion materials, this study presents an alternative approach of creating vacancies without sacrificing the pristine phase, with a possibility to use the not so common class of ABO3-type perovskites as the battery electrode.

Lithium-ion batteries are ubiquitous in many amenities of daily life, from portable electronics to electric vehicles and stationary energy storage, all thanks to major improvements in their performance. However, the need for higher energy density, longer lifespans and safer units is relentless. A wide variety of cathode and anode materials are currently being developed and tested to meet these needs. Therefore, the detailed description of the solid electrolyte interface (SEI) formation, lithium transport mechanisms within cell components, electrochemical activity, loss of lithium and/or active materials, and their evolution during the battery life are pivotal in pinpointing the origin of battery performance loss. Hence, there is a demand for improved characterization methodologies to better understand the physical, chemical, and electrochemical processes taking place during cycling. Isotopic labeling is a robust method for studying chemical reactions, interactions, and transport phenomena. The technique involves "labeling" a specific component of the system with a distinct isotopic composition and allowing it to participate in the reaction. By analyzing the final isotopic distribution within the system, the movement and transformation of the labeled reactant can be precisely tracked. Moreover, lithium isotopic tracing has been successfully applied to study lithium dynamics in anodes and cathode materials, as well as diffusion in solid electrolytes and to investigate Li-ion transport and pathways in the SEI of anodes 1–3 . Nonetheless, new materials with complex architectures bring new challenges to understand in deeper detail the specific transport mechanism at interfaces and bulk of active materials 4 . Secondary Ion Mass Spectrometry (SIMS) is a powerful surface analysis technique that detects all elements and their isotopes (e.g. 6 Li, 7 Li) with high sensitivity. Focused Ion Beam (FIB)-SIMS platforms with a magnetic sector SIMS system have emerged as high-resolution high-sensitivity multi-task tools, standing out from conventional equipment as in situ correlative analysis can be performed 5 . Thus, highly sensitive and high spatial resolution chemical mapping down to 15 nm complemented with high resolution secondary electron imaging is routinely obtained. A fully integrated sample transfer system (e.g. to a glove box) allows the analysis of air-sensitive materials which makes the FIB-SIMS platforms very suitable for battery research. In this work, we first introduce the FIB-SIMS equipment and the specific in situ sample preparation used to have access to interfaces and the bulk active material for post mortem analysis of Si-carbon/graphite negative electrodes 6 . Then the isotopic tracing methodology used to study the Li-ion transport in these composite electrodes is described. The capability to correlate the morphology with the isotopic enrichment maps permits to locally describe and/or distinguish the Li-ion exchange at electrode and particle size scale. The capacity fade observed after several cycles may be caused by the lithium trapping in the active material and the SEI build-up at the electrolyte/active material interfaces. Thanks to the synergy of FIB-SIMS with analytical tools such as ssNMR to investigate the entire electrode, we suggest possible Li-ion pathways for lithiation. We believe these results can shed light on the development of future optimized active materials and/or improved interface engineering. This work is co-funded by the Luxembourg National Research Fund and the Agence Nationale de la Recherche through the grant INTER/ANR/21/NANOLIT. Ho, J. S. et al. Quantifying Lithium Ion Exchange in Solid Electrolyte Interphase (SEI) on Graphite Anode Surfaces. Inorganics (Basel) 10 , (2022). Berthault, M. et al. Lithium isotope tracing in silicon-based electrodes using solid-state MAS NMR: a powerful comprehensive tool for the characterization of lithium batteries. Physical Chemistry Chemical Physics 25 , 22145–22154 (2023). Meyer, T., Gutel, T., Manzanarez, H., Bardet, M. & De Vito, E. Lithium Self-Diffusion in a Polymer Electrolyte for Solid-State Batteries: ToF-SIMS/ssNMR Correlative Characterization and Modeling Based on Lithium Isotopic Labeling. ACS Appl Mater Interfaces 15 , 44268–44279 (2023). Lombardo, T. et al. ToF-SIMS in battery research: Advantages, limitations, and best practices. Journal of Vacuum Science & Technology A 41 , 053207 (2023). De Castro, O. et al. Magnetic Sector Secondary Ion Mass Spectrometry on FIB-SEM Instruments for Nanoscale Chemical Imaging. Anal Chem 94 , 10754–10763 (2022). Delfino, P. M. et al. Lift-Out Specimen Preparation and Multiscale Correlative Investigation of Li-Ion Battery Electrodes Using Focused Ion Beam-Secondary Ion Mass Spectrometry Platforms. ACS Appl Mater Interfaces (2024) doi:10.1021/acsami.4c12915.

Ionogel electrolytes offer a promising alternative to conventional liquid electrolytes, combining the thermal stability of solid-state electrolytes with the high ionic conductivity of liquid electrolytes. Phosphonium-based ionic liquids (ILs) exhibit superior electrochemical properties especially at high lithium salt concentrations. Although acrylic acid (AA)-based ionogels demonstrate favorable lithium-ion diffusion, their mechanical limitations hinder practical application. To address this, a novel ionogel electrolyte is developed through copolymerization of AA with 1,6-hexanediol diacrylate (HDDA). This in-situ phase separation process yields a tough, flexible, and self-standing ionogel capable of confining a high amount (85 wt%) of ionic liquid. The resulting material exhibits excellent ionic conductivity (similar to 2.5 mS cm(-1) at 30 degrees C) and thermo-mechanical properties while maintaining the safety standards of solid electrolytes. Furthermore, the ionogel demonstrated promising cycling stability in a LiFePO4|ionogel|Li metal battery configuration, retaining 97 % of its initial capacity after 60 cycles at 50 degrees C and 0.2C C-rate. The scalability of this ionogel electrolyte is demonstrated through the successful fabrication of lab-scale single-layer pouch cells. These findings position ionogel electrolytes as a promising technology for next-generation lithium batteries.

In the quest for sustainable and metal-free energy storage systems, viologen-based materials offer exciting prospects as they are synthetically well accessible and show two reversible electrochemical processes with anion insertion. This study introduces and compares two pi-extended viologen-carboxylate materials bearing double zwitterionic backbones as model compounds based on 1,1 '-bis(4-carboxyphenyl)-4,4 '-bipyridinium ([bcbp]): the neutral [bcbp] as a double zwitterionic molecule ( 1 ) and its corresponding (Li)2[bcbp](ClO4)2 disalt ( 2 ). The choice of these two materials for our electrochemical studies is motivated by the literature available on their synthesis routes and solid-state properties. Electrochemical tests in lithium half-cells revealed that compound ( 1 ) is initially inactive but gradually converts into the electroactive disalt ( 2 ) via spontaneous chemical insertion of LiClO4 from the electrolyte. Compound ( 2 ) directly displays the expected reversible two-electron p-type mechanism involving perchlorate anion (de)insertion, while lithium ions act as spectator species. The system delivers stable cycling performance and high coulombic efficiency, supporting the interest of viologen-based zwitterionic salts as host material for negative electrode application in anionic rocking-chair organic batteries. The bipyridinium-bis(carboxylate) radical ((Li)[bcbp]center dot ( 3 )) formed during our synthesis optimizations is likewise electrochemically assessed. This fundamental work highlights the tunability of double zwitterionic viologens as molecular platforms to promote optimized p-type negative electrode materials.

Local structure model and corresponding Na + conduction network of Na 1/2− x La 1/2− x Ba 2 x ZrO 3 , x = 6/32, obtained from analysis of X-ray spectroscopy and neutron total-scattering data.

Slurry solid fraction is often treated as an innocuous battery electrode processing parameter at the laboratory scale. In fact, articles that put a number to the water content of their slurries are few and far between. However, recent studies from our group have shown that the slurry solid fraction can have a significant impact on the electrochemical performances of the resulting electrodes. The present research aims to highlight the importance of optimising this parameter by demonstrating its impact throughout the electrode preparation and testing processes of Si-graphite electrodes for Li-ion batteries. Silicon, graphite, a conductive additive of graphene nanoplatelet (GnP) and a partially neutralized PAA-based binder (PAH 0.8 Na 0.2 , pH ≈ 4, M w = 1084k, 393k or 7.6k g/mol) were dispersed in a variable amount of deionized water, yielding slurries of different solid fractions according to equation 1: Eq. 1 SF = (m Si + m Gr + m GnP ) / m Slurry An initial impact of the slurry solid fraction can be seen in the adsorption of the binder onto the active material and conductive additive in aqueous conditions. Gel permeation chromatography of the polymer remaining in the liquid phase after slurry dispersion reveals a strong preferential adsorption of high-molecular weight PAA, mainly on the silicon particles, that is even more pronounced at higher solid fraction. This localized polymer distribution affects its ability to fulfill its functions as a binder and an artificial solid-electrolyte interphase (SEI), which can later be seen in the irreversible capacity loss that arises from both electrical disconnections and SEI formation during cycling. The solid fraction is also a principal determinant of the rheological properties of the slurry, namely its viscosity under shearing and storage and loss moduli. Shear-thinning behavior is favourable to ensure homogeneous dispersion of matter in the electrode slurry and avoid creating surface defects during the coating process. Increasing the solid fraction leads to shear-thickening behavior in slurries with high-molecular weight binders. As such, large agglomerates of silicon and multiple surface defects are observed in these electrodes. On the other hand, the storage and loss moduli of the slurry will determine its stability during the drying process where there is a risk of sedimentation. The effects of the slurry solid fraction can also be seen in the dried electrodes. For example, the mechanical properties (hardness, elasticity) of the electrodes made with low-solid fraction slurries are comparatively poor, as measured by nanoindentation. Conversely, 4-point probe testing shows that electrodes made with high-solid fraction slurries are more resistive due to the presence of large silicon particles covered in a high concentration of polymer. The numerous impacts of the slurry solid fraction across the electrode preparation and testing processes culminate in a strong dependence of the resulting electrochemical performances on this often-neglected parameter. An optimal solid fraction is determined for the given materials. Formulations with different binder molecular weights are also compared at different solid fractions to illustrate the importance of this optimization step in drawing accurate and meaningful conclusions on the materials at study. References: Ligneel, E.; Lestriez, B.; Hudhomme, A.; Guyomard, D. Effects of the Solvent Concentration (Solid Loading) on the Processing and Properties of the Composite Electrode. J. Electrochem. Soc. 2007 , 154 (3), A235. https://doi.org/10.1149/1.2431316. Porcher, W.; Lestriez, B.; Jouanneau, S.; Guyomard, D. Design of Aqueous Processed Thick LiFePO 4 Composite Electrodes for High-Energy Lithium Battery. J. Electrochem. Soc. 2009 , 156 (3), A133. https://doi.org/10.1149/1.3046129. Xiong, J.; Dupré, N.; Mazouzi, D.; Guyomard, D.; Roué, L.; Lestriez, B. Influence of the Polyacrylic Acid Binder Neutralization Degree on the Initial Electrochemical Behavior of a Silicon/Graphite Electrode. ACS Appl. Mater. Interfaces 2021 , 13 (24), 28304–28323. https://doi.org/10.1021/acsami.1c06683.

The use of key parameters of the SiO x /graphite electrode formulation, and their critical values, makes it possible, without any trial-and-error type experimentation, to identify optimal electrode formulations for different SiO x /graphite mass ratios ranging up to 40:60. From the first attempt, electrodes presenting good cyclability at high surface capacity of 5.2 mA h cm −2 were formulated, reaching for example more than 93% capacity retention after 60 cycles in a full cell, with an electrolyte rich in FEC and EC-free, however with a prelithiation strategy. With a positive electrode based on NMC 811 , the gains in volumetric energy and power density are + 18 and + 28% compared to graphite, considering only the electrode volumes. The principle of using the key electrode formulation parameters introduced here is expected to accelerate and facilitate the optimization of electrode formulations.

Ternary alloys such as TiSnSb and NbSnNb have been proposed as suitable negative electrode materials for lithium-ion batteries due to their large capacities and rate capability over many cycles. During lithiation, TiSnSb undergoes a conversion reaction, leading to the formation of multiple, highly reactive species. Previous in situ 119Sn Mössbauer and 7Li magic-angle spinning (MAS) NMR spectroscopic studies suggested the phases Li3Sb, Li7Sn2, Li7Sn3 and Li2−xSb are formed at the end of lithiation alongside Ti or Nb nanoparticles. However, their stability and overall contribution to the conversion reaction is not yet fully understood. A series of model Sn- and Sb-based mixtures and alloys (both binary and ternary) have been investigated at the end of lithiation using 7Li MAS NMR spectroscopy to determine both the phases formed and their contribution to the conversion reaction. In all cases, a mixture of reactive lithiated phases and metallic nanoparticles are formed at the end of lithiation. Changing the nature of the inactive element in binary and ternary alloys changes the local Li environment and the observed chemical shifts. Considerable differences in chemical shift are observed for alloys relative to less intimate mixtures. The synthetic conditions used, particularly the intimacy of mixing achieved during synthesis, is key in determining both the phases formed and how the reaction proceeds, i.e., via a conversion or alloying reaction. The data presented show that the so-called "inactive" element and its nature in fact plays a key role in the conversion mechanism and therefore influences the ability for this class of materials to be commercialised in the future.

The search for safer next‐generation lithium‐ion batteries (LIBs) has driven significant research on non‐toxic, non‐flammable solid electrolytes. However, their electrochemical performance often falls short. This work presents a simple, one‐step photopolymerization process for synthesizing biphasic liquid–solid ionogel electrolytes using acrylic acid monomer and P111i4FSI ionic liquid. We investigated the impact of lithium salt concentration and temperature on ion diffusion, particularly lithium‐ion (Li+) mobility, within these ionogels. Pulsed‐field gradient nuclear magnetic resonance (PFG‐NMR) revealed enhanced Li+ diffusion in the acrylic acid (AA)‐based ionogels compared to their non‐confined ionic liquid counterparts. Remarkably, Li+ diffusion remained favorable in the ionogels regardless of salt concentration. These AA‐based ionogels demonstrate very good ionic conductivity (>1 mS cm−1 at room temperature) and a wide electrochemical window (up to 5.3 V vs Li+/Li0). These findings suggest significant promise for AA‐based ionogels as polymer solid electrolytes in future solid‐state battery applications.