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.

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.

Operando synchrotron techniques provide unique insights into the internal processes of lithium-ion batteries, but radiation-induced effects can alter cell behavior and compromise data interpretation. To better understand these phenomena, we developed an operando cell specifically designed for controlled irradiation studies, replicating synchrotron-like conditions, but at the laboratory scale. The electrolyte was selectively irradiated with an electron beam at doses of 5 and 10 kGy, and the resulting impacts on the electrochemical performance of a silicon-based electrode, gas evolution, and solid electrolyte interphase (SEI) composition were investigated. Irradiation led to immediate and dose-dependent degradation of cycling performance, with the 10 kGy-irradiated cells failing within four cycles. Gas analysis revealed increased formation of H2, CO2, CO, and CH4, the latter two gases being not produced in the nonirradiated cells, as well as the generation of specific compounds such as C2H6 and CH3CHO, absent in nonirradiated cells. While most gases showed dose-dependent production, H2 remained relatively insensitive to irradiation levels, likely due to residual water content. After irradiation followed by cycling of the cell, microscopic and electrochemical impedance spectroscopy analyses indicated significant modifications of the electrode surface and SEI morphology, with the formation of porous or inhomogeneous layers that promote further electrolyte degradation and gas release. These findings underscore the importance of accounting for beam-induced effects in operando studies, with a focus on the effect of the irradiation of the electrolyte, and provide a framework for understanding radiation-accelerated aging mechanisms in lithium-ion batteries.

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.

This study explores the fabrication of graphite/PVdF electrodes using electrostatic dry spray-coating, a solvent-free and energy-saving process. We analyzed the effects of different PVdF concentrations (1.5%, 3.0%, and 4.0% in weight) on the morphology, mechanical properties, and electrochemical performance of the electrodes fabricated. We found that increasing PVdF binder concentration enhances mechanical properties such as peel strength, elastic modulus, and hardness due to improved particle cohesion and mechanical interlocking. However, it also increases electrical resistivity and tortuosity, as the insulating binder disrupts electronic conduction pathways and obstructs ion diffusion. These properties were quantitatively linked to several morphological parameters: the fraction of PVdF covering graphite particles, the volume and contact surface area of PVdF agglomerates. An optimal PVdF concentration is crucial for balancing these properties. The electrode with 3.0% stands out, delivering superior performance with a delithiation capacity of 193 mAh g-1 and a capacity retention of 97% at the 100th cycle in 4 mAh cm-2 pouch-cell format full cells.

Lithium-ion batteries (LIBs) have emerged as the main energy storage solution for consumer electronics and electric vehicles (EVs). Traditional LIB electrodes are prepared through a wet process, which involves coating solvent-based mixtures onto metallic current collectors. These mixtures, often referred to as slurries, typically contain at least one electrochemically active material, a conductive carbon, a polymer binder, and a solvent for binder dissolution. For positive electrodes, polyvinylidene fluoride (PVdF) dissolved in N-methyl-2-pyrrolidone (NMP) is commonly used, while for negative electrodes, a mix of sodium carboxymethyl cellulose (CMC) and styrene-butadiene rubber (SBR) dissolved in water is preferred. Recently, there has been a surge in interest in developing new manufacturing processes for electrodes that prioritize environmental sustainability and remain economically viable. One such approach involves fabricating electrodes without the use of solvents, directly depositing active materials onto current collectors, and eliminating the need for a drying step. In this work, our objective was to manufacture graphite negative electrodes using PVdF as a binder through an electrostatic dry-spraying coating process. In this process, a high voltage is applied to a previously dry-mixed electrode powder, which then gets electrically charged, forming a cloud of charged particles. The charged particles are then accelerated towards the grounded current collector, where they form a uniform and continuous coating layer, which is then hot calendered to thermally activate the binder and control the coating thickness and density. This change in the manufacturing process can affect the electrode characteristics such as homogeneity of binder distribution, porosity, adhesion, and cohesion between active material and carbon black (CB) conducting agent particles and the current collector, electrical properties, and therefore the battery performance. Using the electrostatic spraying method, we were able to manufacture graphite/PVdF and graphite/PVdF/CB negative electrodes with high mass loadings, suitable for electric vehicle applications. We studied two different PVdF binders with different physicochemical properties such as primary particle size, crystallinity, melting temperature and viscosity, and varied the PVdF concentration in the electrode. The influence of the mixing times of the dry electrode components and of the calendering pressure were also studied. After optimization we have obtained well performing graphite electrodes of 5 mAh cm -2 surface capacity (density 1.5 g cm -3 ), showing a capacity retention of 97% at the 100th cycle as NMC811/Graphite full cells in pouch-cell format. Our findings therefore indicate that this dry fabrication technique offer viable alternative, yielding high-quality electrodes with short production time, good electrochemical and mechanical properties, comparable to those produced through conventional wet-slurry based methods. At a more fundamental level, this work opens up a deeper understanding of the binder influence. Indeed, very interestingly, the PVdF distribution in the dry mixed electrode powder, which also determine the PVdF distribution in the calendered electrode, could be visualized and precisely quantified. This one exists as discrete nanometric particles at the surface of the graphite particles and as micrometric agglomerates. The quantification of both fractions, as a function of the PVdF grade, concentration, and of the mixing times of the dry electrode powder, allowed to establish quantitative and novel relationships between the PVdF distribution and the electrode properties, which are likely also valid for wet-processed electrodes. J. A. Barreras-Uruchurtu, N. Besnard, C. Paul, L. Marchal, S. Devisme, B. Lestriez, “Effect of PVdF distribution on properties and performance of dry spray-coated graphite electrodes for lithium-ion batteries for electric vehicle applications”, J. Electrochem. Soc. , 2024 , 171, 080511 [DOI 10.1149/1945-7111/ad6936] J. A. Barreras-Uruchurtu, N. Besnard, C. Paul, L. Marchal, S. Devisme, B. Lestriez, "Erratum: Effect of PVdF distribution on properties and performance of dry spray-coated graphite electrodes for lithium-ion batteries for electric vehicle applications”, J. Electrochem. Soc. , 2024 , 171, 109002 J. A. Barreras-Uruchurtu, N. Besnard, C. Paul, L. Marchal, S. Devisme, B. Lestriez, “Effect of the physicochemical properties of PVdF on dry-sprayed graphite electrodes for lithium-ion batteries for electric vehicle applications”, submitted to J. Electrochem. Soc. Figure 1

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.

This study explores the optimization of graphite/PVdF electrodes for lithium-ion batteries using a dry electrostatic spray-coating method, with the addition of carbon black (CB) as a conductive additive. We investigate the effects of different mixing sequences, CB content, and mixing times on the processability, mechanical, electrical, and electrochemical properties of highly loaded electrodes. Our results show that mixing graphite and PVdF before adding CB ensures a more even distribution of PVdF and CB across the graphite particles, enabling effective electrostatic coating of high areal capacity electrodes (similar to 4.6 mAh cm-2). Extended mixing times further improve CB distribution, enhancing electrode performance. In contrast, introducing CB too early leads to the agglomeration of PVdF and CB, resulting in poor distribution on the graphite surface and making the powder unsuitable for electrostatic coating. At the specific binder content tested in this study (4.0% in weight), optimized electrodes with CB retain 95.2% of their initial capacity after 150 cycles, outperforming reference electrodes without CB, which retained only 60.2%.

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.

We investigated the fabrication of graphite/PVdF anodes using electrostatic dry spray-coating, employing two different PVdF binders with different physicochemical properties such as primary particle size, crystallinity, melting temperature, and viscosity. We examine and compare the morphological, mechanical, electrical, and electrochemical properties of the dry-sprayed electrodes (DSEs). Significant differences were observed, particularly in terms of adhesion/cohesion, electrical resistivity, tortuosity, and electrochemical performance, with the PVdF binder characterized by a smaller particle size (178 nm) and a slightly higher melting temperature range (165 degrees C-172 degrees C), demonstrating superior long-term cycling stability. Specifically, the best electrode made with this binder achieved 188.3 mAh g-1 with over 94.9% capacity retention after 200 cycles. In contrast, the best electrode made with the PVdF binder with a larger particle size (270 nm) and a lower melting temperature range (155 degrees C-172 degrees C), showed a performance of 173.9 mAh g-1 with 88.3% capacity retention under the same conditions. Our findings highlight the necessity of adjusting fabrication conditions according to the specific characteristics of each PVdF binder to optimize the overall performance of the DSEs.

We used electrostatic dry spray-coating to fabricate graphite/PVdF anodes. We compared the morphological, mechanical, electrical, and electrochemical properties of electrodes fabricated with three different mixing times of dry electrode components. Quantitative and novel relationships between the PVdF distribution and the electrode properties were obtained. Our investigations suggest that our fabrication methods are viable alternatives for producing electrodes with comparable properties to those fabricated using traditional wet solvent-based methods. Overall, our work provides insights into new and promising methods for fabricating high-quality dry-sprayed electrodes (DSEs) with high mass loadings for use in a variety of electrochemical applications such as electric vehicles.

Lithium-ion batteries (LIBs) have emerged as the main energy storage solution for consumer electronics and electric vehicles (EVs). Traditional LIB electrodes are prepared through a wet process, which involves coating solvent-based mixtures onto metallic current collectors. These mixtures, often referred to as slurries, typically contain at least one electrochemically active material, a conductive additive, a polymer binder, and a solvent for binder dissolution. For cathodes, polyvinylidene fluoride (PVdF) dissolved in N-methyl-2-pyrrolidone (NMP) is commonly used, while for anodes, a mix of sodium carboxymethyl cellulose (CMC) and styrene-butadiene rubber (SBR) dissolved in water is preferred.1 Recently, there has been a surge in interest in developing new manufacturing processes for electrodes that prioritize environmental sustainability and remain economically viable. One such approach involves fabricating electrodes without the use of solvents, directly depositing electrode materials onto current collectors, and eliminating the need for a drying step.2 In this work, our objective is to manufacture graphite negative electrodes using PVdF as a binder through an electrostatic dry-spraying coating process (see Fig. 1). In this process, a high voltage is applied to a previously dry-mixed electrode powder, which then gets electrically charged, forming a cloud of charged particles. The charged particles are then accelerated towards the grounded current collector, where they form a uniform and continuous coating layer, which is then hot pressed to thermally activate the binder and control the coating thickness and density. This way, both positive (LiCoO2,4 LiNi0.33Mn0.33Co0.33O2 3, LiNi0.5Mn0.3Co0.2O2,3 LiNi0.8Mn0.1Co0.1O2/LiMn2O4 4)and negative (Li4Ti5O12,5,6 graphite4)electrodes have been prepared, in most cases with PVdF binder. This change in the manufacturing process can affect the electrode characteristics such as homogeneity of binder distribution, porosity, adhesion, and cohesion between active material and carbon black (CB) conducting agent particles and the current collector, electrical properties, and therefore the battery performance7–10. The uniform mixing distribution of the binder and CB additive materials throughout the active material is crucial for manufacturing dry-processed LIB electrodes 11,12. Using the electrostatic spraying method, we were able to manufacture graphite/PVdF and graphite/PVdF/CB negative electrodes with high mass loadings, suitable for electric vehicle applications. Characterization of the electrodes include morphology assessment using Scanning Electron Microscopy (SEM) and Energy Dispersive X-ray Spectroscopy (EDS), as well as surface resistivity measurements. Mechanical properties were evaluated through peel strength tests to measure electrode-current collector adhesion force and nanoindentation tests for hardness, elastic modulus, and plasticity. Electrochemical evaluations were conducted focusing on rate capability to determine the delithiation capacity at various delithiation rates, as well as through long-term cycling measurements. Our research includes a series of studies focusing on various factors influencing dry spray-coated electrode fabrication and performance. Specifically, we examined PVdF distribution within the electrode structure, compared two different PVdF grades, analyzed the influence of different PVdF concentrations, studied the addition of CB to the mixture, and investigated the sequence of component addition during the dry mixing process. Additionally, we explored and optimized the conditions of electrostatic spraying and calendering, including potential, air flow and temperature settings employed. Through these studies, we aimed to better understand the complexities of dry electrode fabrication and improve battery technology. Our findings indicate that these fabrication techniques offer viable alternatives, yielding high-quality electrodes with short production time, good electrochemical and mechanical properties, comparable to those produced through conventional wet-slurry based methods. References: M. Armand et al., Journal of Power Sources, 479, 228708 (2020). B. Ludwig, Z. Zheng, W. Shou, Y. Wang, and H. Pan, Sci Rep, 6, 23150 (2016). E. Zhen et al., Journal of Power Sources, 515, 230644 (2021). M. Wang et al., J. Electrochem. Soc., 170, 010541 (2023). D.-W. Park, N. A. Cañas, N. Wagner, and K. A. Friedrich, Journal of Power Sources, 306, 758–763 (2016). C. Lv et al., Journal of Power Sources, 556, 232487 (2023). D. Mohanty et al., Journal of Power Sources, 312, 70–79 (2016). A. Kraytsberg and Y. Ein-Eli, Adv. Energy Mater., 6, 1600655 (2016). W. B. Hawley and J. Li, Journal of Energy Storage, 25, 100862 (2019). G. Lenze et al., J. Electrochem. Soc., 165, A314–A322 (2018). B. Ludwig et al., Adv Materials Inter, 4, 1700570 (2017). A. Yonaga et al., Journal of Power Sources, 581, 233466 (2023). Figure 1

The simple addition of a Zn(II) precursor to a preoptimized poly(carboxylic acid) binder solution enhances the electrochemical performance and cycle life of silicon-based electrodes. The binder/cation couple forms a cross-linked coordinated binder that plays a key role in enhancing the mechanical and chemical stability of the electrode microstructure. The impact of the addition of the Zn precursor on the microstructural evolution of the electrode during cycling is investigated at different scales (from cell/electrode to silicon particle scale) using complementary operando, in situ, and ex situ X-ray tomography techniques. Comparative analyses conducted on the reference and with Zn electrode formulations using operando and in situ X-ray micro-tomography allow for monitoring of the electrode morphological deformations along with the crack pattern formation and evolution during cycling. The benefits of the precursor addition include enhancing the mechanical stability of the electrode through a strengthened microstructure more apt to maintaining its integrity, as well as a better anchoring to the current collector leading to decreased electrical disconnections and capacity fade. Moreover, complementary ex situ X-ray nano-tomography measurements highlight the benefits of the precursor addition in terms of chemical stability with mitigated solid electrolyte interface (SEI) formation over the electrode cycling. The benefits of a simple, yet efficient, method to boost the mechanical and chemical stability of Si-based electrode microstructure through the addition of a Zn(II) precursor to a carboxylic binder is demonstrated thanks to a cross-correlated multiscale workflow based on operando/in situ and ex situ X-ray tomography analyses. image

Abstract We used electrostatic dry spray-coating to fabricate graphite/PVdF anodes. We compared the morphological, mechanical, electrical, and electrochemical properties of electrodes fabricated with three different mixing times of dry electrode components. Quantitative and novel relationships between the PVdF distribution and the electrode properties were obtained. Our investigations suggest that our fabrication methods are viable alternatives for producing electrodes with comparable properties to those fabricated using traditional wet solvent-based methods. Overall, our work provides insights into new and promising methods for fabricating high-quality dry-sprayed electrodes (DSEs) with high mass loadings for use in a variety of electrochemical applications such as electric vehicles.

Dry process manufacturing techniques, which involve fabricating electrodes without the use of solvents and directly depositing electrode materials onto current collectors, have emerged as an alternative to traditional lithium-ion battery (LIB) electrode preparation methods1. In the conventional wet process, solvent-based mixtures, known as slurries, are coated onto metallic current collectors. These slurries typically contain electrochemically active material, conductive additive, polymer binder, and solvent for binder dissolution. For cathodes, polyvinylidene fluoride (PVdF) dissolved in N-methyl-2-pyrrolidone (NMP) is commonly used.2 The growing interest in solvent-free techniques is due to their numerous advantages over traditional methods. For instance, eliminating the use of NMP during cathode production reduces energy consumption by almost 47% during the manufacturing process and decreases total costs by around 15%.3,4 This approach is also relevant for anodes, where a mix of sodium carboxymethyl cellulose (CMC) and styrene-butadiene rubber (SBR) dissolved in water is used. The uniform mixing distribution of the binder and CB additive materials throughout the active material is crucial for manufacturing dry-processed LIB electrodes because it can affect the electrode characteristics such as homogeneity of binder distribution, porosity, adhesion, and cohesion between active material and carbon black (CB) conducting agent particles and the current collector, electrical properties, and therefore the battery performance5–10. For our study, we prepared negative electrode powder mixtures consisting of graphite and a low-content of PVdF through a dry-mixing process at room temperature, varying the mixing time. Then, these powder electrode mixtures were subjected to a high-voltage electrostatic dry coating-spray process and applied onto a carbon-coated copper current collector. Afterwards, the electrodes were calendered at high temperature with a determined applied force. Our objective was to characterize the mixing quality in the electrode powder mixtures and explore its correlation with electrode quality. To accomplish this, we employed various methods, including notably Scanning Electron Microscopy (SEM) imaging and powder resistivity tests conducted via impedance measurements with precise pressure control. Additionally, image analysis tools were utilized to quantify the fraction of binder distributed on the surface of the graphite particles and differentiate it from the binder fraction forming agglomerates. An example of this quantification can be observed in Fig. 1a-b, where a graphite particle covered by PVdF nanoparticles is depicted, showcasing how the image analysis tool accurately distinguishes between both materials. This allowed for a better understanding and rationalization of the influence of PVdF binder distribution on the properties of the electrodes. Characterizing the electrodes produced from these powder mixtures was equally important and included a wide range of analyses such as morphology assessment using SEM and Energy Dispersive X-ray Spectroscopy (EDS), as well as surface resistivity measurements. Mechanical properties were evaluated through peel strength tests to measure electrode-current collector adhesion force and nanoindentation tests for hardness, elastic modulus, and plasticity. Electrochemical evaluations were conducted focusing on rate capability to determine the delithiation capacity at various delithiation rates, as well as through long-term cycling measurements. Our research findings suggest that mixing time, particularly the binder distribution, significantly impacts the morphology, electrical, and electrochemical properties of our electrodes. This exploration enabled us to identify optimal parameters for electrode fabrication, resulting in high-quality electrodes with relatively short production times and favorable electrochemical and mechanical properties. These electrodes exhibit performance comparable to those produced through conventional wet-slurry based methods. References: Y. Lu et al., Matter, 5, 876–898 (2022). M. Armand et al., Journal of Power Sources, 479, 228708 (2020). D. L. Wood, J. Li, and C. Daniel, Journal of Power Sources, 275, 234–242 (2015). Y. Liu, R. Zhang, J. Wang, and Y. Wang, iScience, 24, 102332 (2021). D. Mohanty et al., Journal of Power Sources, 312, 70–79 (2016). A. Kraytsberg and Y. Ein-Eli, Adv. Energy Mater., 6, 1600655 (2016). W. B. Hawley and J. Li, Journal of Energy Storage, 25, 100862 (2019). G. Lenze et al., J. Electrochem. Soc., 165, A314–A322 (2018). B. Ludwig et al., Adv Materials Inter, 4, 1700570 (2017). A. Yonaga et al., Journal of Power Sources, 581, 233466 (2023). Figure 1

Mastering electrodes' formulations is a complex and tedious task, because for each composition of electroactive material(s) it is necessary to adjust the inactive additives nature and content to optimize battery performance. In this direction, the amount of binder is proposed to be adjusted to the surface developed by all of the powders involved in the composition of the electrode, i.e., the electroactive materials and electronic conductive additives. This concept, introduces here as binder-to-powders coverage ratio, relies upon the micromechanical models developed in the field of polymer-based composite materials. The validity of this new electrode formulation parameter is shown here for two different SiOx/Graphite blends, which differ in the type of graphite, and for blends of two different binders, polyacrylic acid and styrene-butadiene rubber. At the optimal coverage ratio, a satisfactory capacity retention is obtained in full cell with an ethylene carbonate free and fluoroethylene carbonate rich electrolyte.

The optimization of composite electrodes based on a silicon/graphite mixture is essential for battery performance, but is complex due to the multiplicity of parameters that come into play. In this direction, we propose to adjust the amount of surface area developed by all the graphitic carbons, including the conductive additive to that of the silicon phase. This concept, introduced here as graphite and carbon-to-silicon contact ratio, is based on the importance of contacts on the mechanical, electrical and electrochemical properties of composite electrodes. The validity of this new formulation parameter is studied here for SiOx/Graphite composite electrodes, which differ in the proportions of two types of graphite (spherical or platelet form) and for different types of conductive additives (carbon black and carbon nanotubes). An optimal contact ratio is determined, allowing at the same time the best gravimetric and volumetric capacities, the best cyclability, and the best power performance.

This work aims at better understanding the interactions existing between the liquid electrolyte and the solid composite electrode in a Li-ion battery. We substituted the common active material (e.g. LiNi1/3Mn1/3Co1/3O2 or LiFePO4) by an insulating (inactive) gamma-Al2O3 compound in order to detect and evidence the interaction between the carbon black electronic additive and the liquid electrolyte. Our study presents the characterization of charge (electrons and ions) transport at different scales by combining a high-frequency analysis performed by broadband dielectric spectroscopy (BDS, up to 10(10) Hz), along with a low-frequency analysis performed by electrochemical impedance spectroscopy (EIS, down to 10(-3) Hz). Two carbon black materials with two different specific surface areas (80 m(2).g(-1) and 65 m(2).g(-1), respectively) were studied. The electronic percolation threshold and the kinetics of impregnation of the hierarchical composite electrode by the liquid electrolyte have been determined with respect to the carbon black content. The significant influence of the adsorbtion of ions at the carbon black surface on the electrons transport is particularly highlighted and explained.