Electrodes For Lithium-ion Batteries Research Articles

Fabrication and Performance Evaluation of Dry Spray-Coated Graphite Electrodes for Lithium-Ion Batteries for Electric Vehicle Applications

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.

Investigating Non-Solvent Induced Phase Separation as a Fabrication Method for Lithium-Ion Battery Electrodes

Lithium-ion batteries (LIBs) are considered a key technology in the ongoing sustainable energy transition due to their importance in decarbonizing the transportation and electric power sectors. However, present embodiments cannot fully address the stringent, and often incongruous, performance, cost, and scale requirements associated with current and emerging applications, hindering widespread adoption.1 A critical barrier lies in electrode architectures capable of accommodating the high mass loadings of charge-storage materials needed to increase system-level energy densities and reduce system costs. A direct approach to maximizing electrode areal capacity and, consequently, enhancing energy densities is the use of thicker electrodes (>150 μm). While techniques such as particle alignment via magnetic fields2 and directional ice templating3 have shown promise in producing robust, thick electrodes beyond what is achievable with conventional slurry casting, these methods result in a constrained set of attainable microstructures, thus limiting design flexibility and complicating the understanding of structure-property relationships.Non-solvent induced phase separation (NIPS), a well-established membrane fabrication approach, holds potential for thick electrode production. Unlike many other processes, NIPS enables greater control over the electrode microstructure through systematic adjustment of reaction precursors and synthesis conditions, supporting the development of complex electrode designs tailored for a diversity of applications.4 Despite its promise, to date only a few studies of NIPS for LIB electrode production exist,5,6 which hampers our understanding of how design parameters impact the resulting electrode structure and performance.In this presentation, we describe how various process parameters in the NIPS fabrication procedure impact the final LIB electrode morphology, including the loading and distribution of charge-storage materials. Employing a combination of imaging and analytical techniques such as SEM-EDS, XTM, and thermogravimetric analysis, we offer insights into the critical design parameters governing the integration of active materials into the polymer matrix. Electrochemical methods including voltammetry, impedance spectroscopy, and durational cycling are utilized to evaluate performance characteristics and establish connections to the physical structure. We close with a discussion of the implementation of such electrodes into novel cell architectures and the opportunities this may enable for deploying thick electrodes. Overall, this work provides a basis for future optimization of the NIPS methodology, facilitating the advancement of thick electrodes for electrochemical energy storage and conversion.

Mapping Li Concentration Gradients across Battery Cathodes

Lithium-ion batteries (LIBs) are playing an increasingly important role in enabling the transition to a low-carbon global economy, in electric vehicle and grid storage applications. Despite increasing LIB ubiquity, there remains gaps in our understanding of how to optimize further LIB electrode design and structure, and how to achieve such designs in practice and at scale without excessive trial-and-error experimentation. For example, thicker electrodes are desirable for improved volumetric capacity but particularly during rapid charging and discharging cycles, a significant through-electrode thickness Li ion concentration gradient in the electrolyte builds up. This leads to a spatially varying concentration overpotential that in turns leads to uneven utilization of the active material, resulting in diminished capacity and accelerated degradation. Although models of electrode dynamics can help qualitatively to understand concentration polarization effects as a function of electrode design, there are few practical experimental tools to visualize or resolve Li-ion concentration gradients in practice. For example, the widely-used energy dispersive X-ray spectroscopy (EDS) in a scanning electron microscopy cannot resolve elements with very low atomic number such as Li.In this presentation we describe the development of a methodology to visualize Li-ion concentration gradients across a range of electrodes based on secondary ion mass spectroscopy (SIMS). We combine SIMS with EDS to collect elemental maps of all principle LIB electrode elements in a single workflow, which is also extended to 3D by further combining with a plasma field ion microscope (P-FIB) capability. We apply the new methodology for LIB cathodes based on LiFePO4 (LFP) and LiMn2O4 (LMO) that are at different state of overall charge, achieved at a range charging rates. The electrodes also span a range of thicknesses from 100 to 700 µm. We show how the approach can operate over cross-sections large enough to encompass all the electrode thickness while maintaining sufficient spatial resolution to capture key features of the local Li concentration. While EDS elemental maps, with appropriate calibration, can be correlated to local element concentration with good accuracy, SIMS spectra and specifically the intensity of the 7Li+ peaks cannot be readily related to local Li concentration since the yield of 7Li+ ion relates to additional factors, such as the local atomic environment, surface topology and more. We describe how we inter-relate the EDS and SIMS maps for non-Li elements to account for some of these features, and show how these reveals the underlying Li distributions. We consider how these measurements of the Li concentration in the solid particles of the electrode relate to the local state of charge, and the conditions in the electrolyte when charge/discharge was halted and the sample was retrieved from the cell for examination. Fine-scale variations in local 7Li+ ion intensity are also revealed and explained in terms of local microstructural features such as particle size, any particle cracking, the growth of secondary electrolyte interphase, etc.

(Invited) Digital Twin for Inverse Design of Battery Manufacturing Processes

The manufacturing process of lithium ion battery (LIB) electrodes impacts their architecture and the practical properties of the cells, such as their energy and power densities, their durability and safety. Therefore, it is crucial to optimize this manufacturing process in a proper manner. Such an optimization is highly complex because of the very significant amount of parameters and numerous interdependencies between the process steps, such as the slurry mixing, the casting, the drying, the calendering, the assembly, the electrolyte filling and the solid electrolyte interphase formation. As a consequence, traditional trial and error approaches can lead to high scrap rates in LIB cell manufacturing.ARTISTIC is a digital twin for inverse design of LIB manufacturing process that we keep developing since several years.[1] ARTISTIC is supported on a combination of physics-based models and machine learning. The physics-based models simulate the dynamics, with 3D resolution, of the slurry mixing, the slurry coating and its drying, the resulting electrode calendering, the cell infiltration by the liquid electrolyte, the formation step and the resulting electrochemical performance of the virtually produced electrodes and cells. These physics-based models are linked with each other in a sequential manner, and they are supported on a combination of methods, such as Coarse Grained Particle Dynamics, Discrete Element Method, Lattice Boltzmann Method and Finite Element Method. Deep learning is used to derive time-dependent 3D surrogate models mimicking the behavior of the physics-based models with much less computational cost. Furthermore, a wide diversity of machine learning techniques are used to accelerate the calibration of the physics-based models with experimental observables (e.g. slurry viscosity and density, electrode porosity, tortuosity factor and conductivity) and to unravel correlations between manufacturing parameters and electrode and cell properties. All these pieces are integrated in a single computational infrastructure performing the inverse design. For that purpose, the deep learning surrogates and the machine learning models are coupled to a multi-objective Bayesian Optimizer. The latter allows predicting which manufacturing parameters to adopt (e.g. slurry formulation, drying rate, calendering degree) in order to reach desired properties for the electrodes (e.g. loading, porosity, conductivity) and for the cells (energy and power densities). We have demonstrated this pionneering digital twin for multiple manufacturing steps and electrode chemistries (e.g. NMC111, NMC622, LFP, graphite, silicon-graphite blends), with the strong support of experimental databases acquired in our LIB manufacturing pilot line.[2] We have also demonstrated the transferability of our approach to Sodium Ion and Solid State Batteries, and we start to adapt it for dry processing methods. In my talk, I will present the latest updates of this research and development effort. Furthermore, I will also present the latest updates of the ARTISTIC Online Calculator, a free service to perform battery manufacturing simulations from an internet browser, as well as of our Virtual and Mixed Reality tools to train students, researchers and operators in the battery manufacturing field. These updates will include the presentation of the first "battery manufacturing metaverse", a multi-user battery manufacturing pilot line in Virtual Reality designed to perform practices with the MSc. students of the i-MESC Erasmus+ programme (Interdisciplinarity in Materials for Energy Storage and Coversion).[3]References[1] https://www.erc-artistic.eu/[2] https://www.modeling-electrochemistry.com/publications[3] https://i-mesc.eu/

Effect of Polyvinylidene Fluoride Binder Distribution on Dry Spray-Coated Graphite Electrodes for Lithium-Ion Batteries for Electric Vehicle Applications

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.

New Insights into the Electrochemical Reactions of Fluoride Ions in Carbon-Based Positive Electrodes

The reversible and electrochemical reactions for the formation of graphite intercalation compounds (GICs) are fundamental to their use as electrode reactions in rechargeable batteries. A common practical application is the electrochemical intercalation and de-intercalation of Li+ ions within graphite electrodes of lithium-ion batteries (LIBs). Similarly, dual-graphite batteries (DGBs) employ GIC formation reactions and operate through the intercalation and de-intercalation of both cations and anions at the negative and positive electrodes, respectively, during charging/discharging processes. DGBs are gaining recognition as a viable alternative to LIBs because of their affordability, high operational potentials, reduced resource constraints, and environmental benefits.This study presents the first observation of the electrochemical formation of F-GICs within LiF-containing organic liquid electrolytes. Despite attempts spanning nearly a century, the reversible intercalation of fluoride ions (F−) and their direct detection in electrochemical systems have remained elusive. Fluoride ions, known for their small ionic radius and high electronegativity, are theorized to provide high specific capacity and reaction potential, potentially leading to high energy densities in rechargeable batteries if they can be reversibly intercalated into graphite electrodes. Our findings were substantiated through operando Raman spectroscopy, which revealed changes in the G band peaks (i.e., in-plane mode of sp2 bonded carbon with a planar configuration) in highly oriented pyrolytic graphite (HOPG) during electrochemical oxidation. This indicates the formation of F-GICs. Moreover, the introduction of a LiF-based surface layer on the HOPG electrodes significantly improved the kinetics and reversibility of the electrochemical intercalation and de-intercalation processes of F−.Consequently, based on these results, the present study suggests that the electrochemical formation of F-GICs can occur in organic electrolytes without the need for additional acceptors or additives. Furthermore, this study provides insights into the operando Raman spectra for the electrochemical formation of F-GICs, elucidating the mechanisms of the electrochemical F− reactions in HOPG electrodes. Moreover, enhancing the contact between LiF and the graphite surface can significantly accelerate the rate of F− intercalation, offering a new perspective on the design of graphite positive electrodes for rechargeable batteries. Figure 1

Revealing the Impact of Graphite Reaction and Binder Structural Changes on the Degradation of Silicon-Graphite Composite Electrodes via Differential Capacity and Stress Analysis

Silicon-graphite (Si-Gr) composite electrodes, which are based on high-capacity silicon mixed with conductive graphite with low volume expansion, have garnered significant interest due to their excellent electrochemical performance and stability. However, increasing the silicon content in the composite electrodes accelerates degradation, leading to a limitation in achieving higher energy density. In addition, Si-Gr composite electrodes undergo multi-stage reactions of silicon and graphite, resulting in complex reaction kinetics and intricate volume change behaviors. Therefore, it is challenging to analyze the impact of each active material's reaction on the electrode degradation. Furthermore, as the degradation of composite electrodes has primarily been understood and studied in the context of silicon's significant volume expansion and degradation, there is a lack of research evaluating the influence of graphite reactions. Despite having a low volume expansion upon lithiation, graphite occupies a significant volume fraction in the composite electrode and exhibits a relatively consistent arrangement. Therefore, it is anticipated that graphite would also influence electrode structural changes and the consequent electrode defect formation.In this study, we observe the average stress corresponding to the electrochemical reactions of the charge/discharge processes of Si-Gr composite electrodes in situ. The average stress can be understood as the internal pressure build-up within the electrode due to the volume expansion of the reactions. The stress and the reaction capacity were differentiated with respect to potential to analyze the contributions of each reaction on the volume change and the internal force evolution. Interestingly, graphite reactions generally induced higher stress than those of silicon during the lithiation process, and their stress per capacity increased as the State of Charge (SoC) increased. These results indicate that graphite can significantly contribute to the stress inside the electrode even though it exhibits a much lower expansion rate than silicon. Moreover, stress behavior that contradicts the silicon volume contraction was also observed during silicon delithiation. This result can be attributed to the stress-relieving phenomenon of the binder, highlighting the importance of the interaction between the active materials and binders. To observe the initial degradation of the composite electrode, repeated charge-discharge cycles were conducted, revealing intervals of unstable stress variation. Subsequent examination using ex-situ SEM showed that debonding and fracture at the interface between graphite and silicon/binder were the primary causes. Furthermore, EDS, XPS, and indentation analysis showed that such structural defects were caused by changes in the silicon-binder structure due to SEI formation. As confirmed by the micro indentation test, the viscoelastic binder and silicon were transformed into a brittle silicon-binder structure. Consequently, it failed to sufficiently dampen the forces generated by the active materials’ volume change resulting in the defects. These research findings contribute to a fundamental understanding of the stability of Si-Gr composite electrodes and our method can be expanded to various energy electrodes of different materials and compositions to enhance understanding of their behavior and contribute to their stability improvement. Choi, J., G. Kim, and S.Y. Kim, Silicon Graphite Composite Anode Degradation: Effects of Silicon Ratio, Current Density, and Temperature. Energy Technology, 2023. Ghamlouche, A., M. Müller, F. Jeschull, and J. Maibach, Degradation Phenomena in Silicon/Graphite Electrodes with Varying Silicon Content. Journal of The Electrochemical Society, 2022. 169(2). Wetjen, M., et al., Differentiating the Degradation Phenomena in Silicon-Graphite Electrodes for Lithium-Ion Batteries. Journal of The Electrochemical Society, 2017. 164(12): p. A2840-A2852. Berhaut, C.L., et al., Multiscale Multiphase Lithiation and Delithiation Mechanisms in a Composite Electrode Unraveled by Simultaneous Operando Small-Angle and Wide-Angle X-Ray Scattering. ACS Nano, 2019. 13(10): p. 11538-11551. Yao, K.P.C., et al., Operando Quantification of (De)Lithiation Behavior of Silicon–Graphite Blended Electrodes for Lithium ‐Ion Batteries. Advanced Energy Materials, 2019. 9(8). Sethuraman, V.A., et al., Real-time stress measurements in lithium-ion battery negative-electrodes. Journal of Power Sources, 2012. 206: p. 334-342. Schweidler, S., et al., Volume Changes of Graphite Anodes Revisited: A Combined Operando X-ray Diffraction and In Situ Pressure Analysis Study. The Journal of Physical Chemistry C, 2018. 122(16): p. 8829-8835. Liu, X.H., et al., Size-dependent fracture of silicon nanoparticles during lithiation. ACS Nano, 2012. 6(2): p. 1522-31. Lee, H.-J., et al., Lithiation Pathway Mechanism of Si-C Composite Anode Revealed by the Role of Nanopore using In Situ Lithiation. ACS Energy Letters, 2022. 7(8): p. 2469-2476. Ogata, K., et al., Revealing lithium–silicide phase transformations in nano-structured silicon-based lithium ion batteries via in situ NMR spectroscopy. Nature Communications, 2014. 5(1).

Do Binders Form Surface Films on Active Particles in Li-Ion Electrodes? Revealing Nanoscopic Surface Binder Morphology in Graphitic Electrodes Using Chemical Staining and High-Resolution Energy-Selective Backscattered Electron Imaging

Although polymeric binders constitute only a small fraction (< 5% volume) of Li-ion electrodes, they are an essential component of Li-ion batteries, binding otherwise loose active particles to each other and to the current collector. Yet, despite more than 30 years of development of Li-ion batteries, the exact morphology that binders adopt on and around the active particle surfaces in the electrodes remains extremely difficult to assess, similarly to the fraction of active particle surface covered by the binder. It is already well established that binder chemistry strongly influences key battery surface reactions, such as Li insertion/deinsertion or formation of solid electrolyte interface (SEI).1,2 Also, binder chemistry can be a decisive factor in reaching long cycle stability over rapid failure of, for example, silicon-based electrodes.3 Therefore, quantifying surface coverage of the binders on active particles remains the missing piece for fully understanding binder roles in batteries, and can open new avenues for improving lifetime and rate performance of current and next generation electrodes.In this work, we present a newly established method for large-scale, high-resolution imaging and quantification of carboxymethyl cellulose (CMC) and styrene butadiene rubber (SBR) binders in graphitic Li-ion electrodes. The imaging was enabled using highly selective chemical staining of the binders with high atomic number elements that act as excellent contrast agents during backscattered electron (BSE) imaging. Following staining of the binders, we imaged them using a variant of BSE known as energy-selective backscattered electron imaging (EsB), which operates at low beam voltage and can provide nanometer-level resolution by selective energy filtering of backscattered electrons. By acquiring images at different beam voltages, we selectively captured different fine-scale morphological details of the binder on and around the graphite particles. We revealed binder/carbon additive agglomerates, islands of non-dispersed SBR nanoparticles and, for the first time, details of a continuous thin layer formed by CMC and SBR on the graphite surface that spans across the entire graphitic electrode. Using a combination of Monte Carlo simulations and high resolution cross-sectional EsB imaging, we estimated the thickness of this surface film to be only 10 nanometers. Because of such small thickness, the film adopts the morphology of the underlying graphite surface, which is why it cannot be observed using conventional secondary electron imaging, even at very low beam voltages. Using quantitative image analysis, we also characterized electrodes before and after calendering, finding that calendering shatters the previously-continuous binder film, leaving only 30% of graphitic surfaces covered by irregular patches of the binder layer. We also verified our results by analyzing commercial graphitic electrodes used in electric vehicle batteries, finding identical binder morphologies inside these electrodes.Considering the likely impact of binder coverage on e.g. active particle stability, SEI formation or distribution of local current density during electrochemical cycling, we suggest that this new ability to rapidly image and quantify binder coverage on active particle surfaces will open new avenues to optimize Li-ion electrodes, bridging the gaps between the chemistry, processing and performance of binder-active particle interfaces.(1) Fedorova, A. A.; Levin, O. V.; Eliseeva, S. N.; Katrašnik, T.; Anishchenko, D. V. Investigating the Coating Effect on Charge Transfer Mechanisms in Composite Electrodes for Lithium-Ion Batteries. Int. J. Mol. Sci. 2023, 24.(2) Young, B. T.; Nguyen, C. C.; Lobach, A.; Heskett, D. R.; Woicik, J. C.; Lucht, B. L. Role of Binders in Solid Electrolyte Interphase Formation in Lithium Ion Batteries Studied with Hard X-Ray Photoelectron Spectroscopy. J. Mater. Res. 2019, 34, 97–106.(3) Jung, C. H.; Kim, K. H.; Hong, S. H. Stable Silicon Anode for Lithium-Ion Batteries through Covalent Bond Formation with a Binder via Esterification. ACS Appl. Mater. Interfaces 2019, 11, 26753–26763.Figure 1. Combined secondary electron image (left) and color-enhanced EsB image (right) of an internal part of uncalendered graphitic electrode with chemically stained CMC binder (colored green in the EsB image). Figure 1

Bi-Dimensional PTFE Fibrillation Process Implemented in Solvent-Free Manufacturing of Ultra Thick Electrodes for Lithium-Ion Batteries

A method for manufacturing electrodes via a solvent-free dry process can dramatically increase the energy density of lithium-ion batteries (LIBs) without the use of toxic organic solvents. This innovative approach is a strong candidate for advanced battery technologies due to its environmental benefits and cost savings. However, ultra thick electrode required to achieve high energy density significantly intensifies the migration resistance (Rion) and charge transfer resistance (Rct) by longer diffusion length of lithium ions and electrons.The fundamental solution proposed to solve this problem is to increase the conductive additives content to form the enhanced electronic conductivity networks. However, the higher the content of conductive additives in the electrode composition, the more binder is required. If the binder content is insufficient, the increased contact area and excessive agglomeration due to the high specific surface area of the conductive additives will result in reduced interparticle cohesion and uneven packing density. This hinders the formation of a continuous fiber matrix in the PTFE fibrillation process and consequently weakens the mechanical properties of the electrode.In this study, the proposed bi-dimensional PTFE fibrillation process can be effectively utilized to form a uniform and efficient fiber matrix within electrodes, even at high conductive additives content (≥5 wt%) and low binder content (≤1 wt%). This process enables the electrodes to be stored and transported in roll form and preserves the structural integrity of the electrodes during mass production. Moreover, the high and uniform conductivity of the manufactured electrodes prevents significant increases in resistance, even with increased electrode thickness, thus enhancing the electrochemical performance of high energy density LIBs.

Insights into Crystallography and Electrochemical Performance of Doped Li-Rich Layered Oxides for Lithium-Ion Batteries

The development of new materials is imperative to meet the growing demand for systems delivering higher capacity, energy density, cycle life stability, and safety. Lithium-Rich Layered Oxides (LRLOs) are at the forefront of enabling high-capacity and high energy density positive electrodes for Lithium-Ion Batteries, addressing the challenges of green and safe transportation and sustainable stationary energy storage from renewable sources [1]. LRLOs, with the general formula Li1+xTM1-xO2 (where TM represents a blend of transition metals such as Mn, Co, Ni...), belong to the layered material family but their crystal structure remains elusive [2]. On the other hand, they exhibit excellent reversible performance in aprotic lithium-metal and lithium-ion batteries over numerous charge/discharge cycles. Their higher specific capacity compared to commercial cathodes can be attributed to cumulative cationic and anionic redox processes, wherein anionic redox reactions involve lattice oxygen, balancing lithium extraction with the activation of the O2-/O- redox couple. However, inadequate cycle life stability and capacity retention hinder their commercial adoption, owing to structural rearrangements and phase transitions upon cycling. Moreover, reducing costs and toxicity of raw materials such as cobalt is crucial for large-scale production [3].In this communication, we elucidate the significant influence of extensive defectivity on the description of LRLOs crystal structure. Specifically, we illustrate how the utilization of supercells or defects (antisite defects, stacking faults ...) contribute to a more accurate structural description. Additionally, doping strategies were used to enhance the electrochemical behavior and mitigate the structural rearrangements. Our findings showcase optimized layered materials boasting exceptional electrochemical performance, enhanced environmental compatibility, and reduced manufacturing costs relative to the current state-of-the-art.

Simultaneous Analysis of Reaction Distribution at LiFePO4 and LiCoO2 Electrodes of Lithium-Ion Batteries

The electrode reaction distribution of lithium-ion batteries is a noteworthy issue for the construction of safe and sustainable storage battery systems. Electrode reactions at composite electrodes are inhomogeneous on the micrometer to millimeter scale due to local differences in electronic and ionic conductivity. There are many reports on the reaction distribution of single electrodes. How the inhomogeneous chemical state distribution generated in the electrode affects the subsequent charge-discharge reaction has not been systematically studied. The purpose of this study is to clarify how the inhomogeneous reaction distribution affects the other electrode. Synchrotron radiation X-rays can be used to observe inhomogeneous states without disassembling the battery. However, because common negative electrode materials are composed of light elements, X-ray absorption fine structure (XAFS) is usually not applicable for in situ observation of the negative electrode of practical batteries. Therefore, in this study, we fabricated a battery by combining a LiFePO4 electrode and a LiCoO2 electrode, which are normally used as positive electrodes, and analyzed the heterogeneous electrode reactions inside the battery for both electrodes simultaneously. Although the battery is not a combination of positive and negative electrodes as used in practice, the distribution of the chemical states of both electrodes can be visualized using X-rays. XAFS experiments using a two-dimensional detector were performed at SPring-8 BL01B1. The chemical state of the LiFePO4 electrode was determined from the Fe K-edge XAFS spectrum, and that of the LiCoO2 electrode was determined from the Co K-edge to create a chemical state map in the electrode. The battery was equipped with a graphite electrode in addition to LiFePO4 and LiCoO2 electrodes for the initial delithiation process. Charging and discharging were repeated with a combination of LiFePO4 and LiCoO2 electrodes to examine the behavior of the reaction distribution and the positional relationship between the reaction distributions of both electrodes. The result that the reaction progressed in the region of the LiCoO2 electrode that overlapped the region where the reaction was progressing at the LiFePO4 electrode clearly indicates that the inhomogeneous reaction at the electrode propagated to the opposite electrode.

An SEI-Forming Fluorophosphate Solvent for High-Temperature Lithium-Ion Batteries

Introduction Recently, there has been an increasing demand for high-energy-density lithium-ion batteries (LIBs) that operate under broad temperature conditions (–40 to 70°C). As an electrolyte solvent, ethylene carbonate (EC) has been essential to form a solid electrolyte interphase (SEI), which effectively suppresses side reactions such as graphite exfoliation and continuous electrolyte decomposition on negative electrodes(1). However, EC is not only flammable but also susceptible to severe oxidative and reductive decomposition at high temperatures, thereby limiting the operational temperature of LIBs to around 55°C(2). There has been no alternative solvent that has (i) SEI-forming ability, (ii) nonflammability, and (iii) high-temperature stability. Hence, it has been challenging to realize the high-temperature and safe operation of LIBs.In this study, we designed and synthesized a novel phosphate solvent, FDPO, which is nonflammable and can form stable SEI on graphite. FDPO has a structural feature similar to LiPO2F2, which can improve SEI properties and high-temperature performance of batteries(3-4). We investigated the charge-discharge performances of negative and positive electrodes for LIBs with FDPO-based electrolytes at high temperature. Experimental methods Electrolytes were prepared by mixing LiPF6, FDPO, and methyl 2,2,2-trifluoroethyl carbonate (FEMC), which is known as a low viscous and flame-retardant solvent. Charge-discharge tests were conducted using coin cells with the natural graphite|Li cell configuration. The current density of 186 mA g-1 (2C) was applied from the 4th cycle after pre-conditioning three cycles at a current density of 37.2 mA g-1 (10C). The cut-off voltage range was set to 2.5 V – 0.01 V. Results and discussion Figure 1 shows the charge-discharge performances of natural graphite|Li coin cells at 70°C. The cell with the commercial electrolyte exhibited severe capacity decay to ca. 142 mAh g-1 after 50th cycles. On the other hand, the cell with FDPO-based electrolyte retained a high reversible capacity of ca. 343 mAh g-1. In addition, the charge-discharge efficiency was over 99.6% in the FDPO-based electrolyte, indicating suppressed electrolyte decomposition even at 70°C. Based on these results, the FDPO itself is thermally stable and also forms a thermally stable SEI on graphite, thereby suppressing capacity degradation under high-temperature conditions. In the presentation, the results of X-ray photoelectron spectroscopy and time-of-flight secondary ion mass spectrometry analyses for the SEI derived from FDPO-based electrolytes, along with the charge-discharge performances of positive electrodes, will be discussed. References (1) Wang, A. et al., npj Computational Materials, 2018, 4, 15.(2) Lu, L. et al., J. Power Sources, 2013, 226, 272.(3) Yang, G. et al., RSC Adv, 2017, 7, 26052.(4) Kuang, S. et al., ACS Appl. Mater. Interfaces, 2022, 14, 19056-19066. Acknowledgment A part of this work was supported by JST GteX (JPMJGX23S3). Figure 1

Dry Battery Electrode Manufacturing for Graphite Anodes: Implications on Electrochemical Properties and Cell Manufacturing

Dry Coating of Lithium-Ion Battery electrodes is widely considered as a gamechanger technology to reduce the cost, energy demand and footprint of battery Gigafactories. By now, industrialization has primarily focused on the negative electrode using graphite and as active material, notably by Tesla.[1] Yet, the full scope of the implications and advancements brought by a dry coating process for graphite anodes on cell properties and downstream manufacturing processes remains unexplored.Current dry coating technologies necessitate using a fibrillizable PTFE binder. While PTFE is very stable towards oxidation when used as a binder in Lithium-Ion Battery cathodes, a reduction of the fluoropolymer in battery anodes at low potentials < 1 V vs. Li/Li+ is reported.[2] We discuss the decomposition reaction of PTFE in graphite anodes during the formation process and the resulting irreversible consumption of Li. Our interest focuses on the decomposition mechanism of PTFE, examining the nature of the decomposition products through XPS analysis. We assess whether the reduction is quantitative and if the decomposition persists beyond the initial lithiation of graphite into subsequent cycles. We contemplate strategies to reduce the irreversible capacity loss and show that reducing the PTFE binder content while maintaining the mechanical integrity of the electrode is a promising approach to enhance the coulombic efficiency during formation.Beyond the electrochemical implications, differences in microstructural properties and the processing conditions during electrode manufacturing between a wet and a dry coated graphite anode offer opportunities for adaptions in the downstream process of Lithium-Ion Battery manufacturing. We demonstrate that the electrolyte filling time of cylindrical cells in a 4695-format is strongly influenced by the coating method and the arising differences in pore size distribution and electrode tortuosity. Also, we show that a vacuum drying of the anodes might not be needed if the electrode is dry coated instead of using water as the solvent for a slurry-based coating.[1] https://www.youtube.com/watch?v=8WPPBhqeekw[2] Y. Suh, J. K. Koo, H. Im, Y.-J. Kim, Chemical Engineering Journal 2023, 476, 146299.

Impact of Sodium Carboxymethylcellulose Binder on the Performance of Lithium-Ion-Batteries for Industrially Relevant Anode Formulations

To change the solvent in LIB electrodes to water, a water-based polymer binder has to replace the current PVdF binder. This led to Sodium Carboxymethylcellulose (NaCMC) being introduced as a water-soluble binder for LIBs. Due to NaCMC creating a weak connection with the current collector, usually, another additive like SBR rubber is usually added to increase adhesion. Nevertheless, NaCMC dominates the properties of the slurry and influences the structure of the final electrode decisively. Combining the multitude of functionalities of the NaCMC with it being produced from the most abundant polymer in the world, it creates a highly attractive binder, also from an industrial point of view. However, despite widespread use, there is only limited knowledge on how the NaCMC influences key battery properties and battery performance.The objective of this research is to provide valuable insights into optimizing the composition of lithium-ion battery electrodes for enhanced energy storage and cycling stability, based on a better understanding of the influence of NaCMC. Especially, the influence of varying properties of the NaCMC, like degree of substitution and molecular weight are explained in more detail, which were analysed via adhesion strength testing, Karl-Fischer titration, electrical resistance and potentiostatic cycling. Finally, the influence of the varying NaCMC properties on the battery performance and SEI formation was investigated with post-mortem liquid NMR.

Time-Dependent Deep Learning Manufacturing Process Model for Battery Electrode Microstructure Prediction

Manufacturing process of Lithium-ion battery electrode has a direct impact on the resulting practical properties of the cell such as durability, safety and overall performance. In this scenario, together with experimental efforts to understand the correlation between manufacturing process parameters and final overall electrode performance, computational tools have shown the potential to produce insights on the manufacturing properties interdependencies. The ARTISTIC initiative [1] pioneered the development of a series of computational 3D-resolved physics-based models describing each step of the manufacturing process following a sequential pattern, going from the slurry phase, through the drying phase, to produce a calendered electrode. Such physics-based models have the capability to predict how manufacturing parameters impact the electrode microstructure. At the end of each phase the output microstructure is carefully validated with experimental data, assuring that the model is in good agreement with real properties. For the calendering phase, the Discrete Element Method (DEM) is used for the model simulation.One of the main limitations of the DEM simulations is their high computational cost, preventing their direct application in electrode optimization loops. In this matter, and given the great amount of already validated data that was produced in our previous works by using the ARTISTIC model, we take one step forward in the development of a new generation model employing machine learning (ML) techniques to accelerate the physics-based simulations but keeping their accuracy. In this presentation we report a novel time-dependent deep learning (DL) model of the battery electrodes manufacturing process. The DL model is demonstrated for calendering of nickel manganese cobalt (NMC111) electrodes, and trained with time-series data arising from physics-based DEM simulations coming from the ARTISTIC physics-based modeling pipeline [2]. The innovative DL model presented in this work can predict an electrode microstructure evolution over time at a given compression degree during calendering and provide the associated final relaxed electrode microstructure. Here we used the formulation of 96% AM and 4% CBD as a proof of concept.The DL model predictions are validated by comparing data evaluation metrics (e.g., mean square error (MSE) and R2 score) and electrode functional metrics (contact surface area, porosity, diffusivity, and tortuosity factor), showing very good accuracy with respect to the DEM simulations (all the properties are above 90% accurate when compared to target data). Regarding transport properties and given the high accuracy of the DL model to predict tortuosity factor and porosity values we can conclude that the model correctly predicts the effect of the calendering on the transport properties since tortuosity factor and porosity has a high impact on the effective transport properties of Li-ions in the electrolyte. The DL model can remarkably capture the elastic recovery of the electrode upon compression (spring-back phenomenon) and the main 3D electrode microstructure features without using the functional descriptors during its training. In terms of computational cost, the DL model performs a timestep in 15 seconds (wall time) while the DEM model performs an equivalent time step in ∼47 minutes (wall time). Given the DL model significant lower computational cost than the DEM simulations, it paves the way toward quasi-real-time optimization loops of the 3D electrode architecture predicting the calendering conditions to adopt in order to obtain the desired electrode performance. Moreover, we consider that our model has tremendous potential to grow in several aspects such as accuracy and predictability. Therefore, our incoming efforts will be focused on continuing the development of the model and testing it for other formulations and in other manufacturing stages.[1] ARTISTIC Project website. https://www.erc-artistic.eu.[2] D. E. Galvez-Aranda, T. L. Dinh, U. Vijay, F. M. Zanotto, A. A. Franco, Time-Dependent Deep Learning Manufacturing Process Model for Battery Electrode Microstructure Prediction. Adv. Energy Mater. 2024, 2400376. https://doi.org/10.1002/aenm.202400376 Figure 1

Enhancing the Cycle Life of Silicon Microparticle Anodes for High-Energy Density Lithium-Ion Batteries through a Reinforced Conductive Matrix

Silicon (Si) is increasingly regarded as a promising candidate for anode materials in lithium-ion batteries (LIBs) owing to its exceptional theoretical specific capacity and abundant material resources. However, widespread commercial adoption faces hurdles due to inherent challenges such as significant volume expansion and the uncontrolled growth of the solid-electrolyte interphase (SEI) during cycling. To address these obstacles, numerous strategies have been proposed, including the fabrication of nano-sized silicon structures to enhance structural stability and long cyclability. Nonetheless, reducing silicon to the nanoscale diminishes the initial coulombic efficiency (ICE) and tap density of Si nanomaterials, thereby hindering the commercialization of Si anodes. Si microparticles (SiMPs) exhibit higher ICE and volumetric capacity compared to Si nanoparticles (SiNPs), making them better suited to meet the requirements of high energy density. However, their larger particle size also increases susceptibility to pulverization during cycling. Despite numerous efforts to enhance the performance of SiMP anodes, the conventional anode structure typically comprises active materials, conductive additives, and a polymeric binder. This traditional structure is prone to damage caused by the substantial volume expansion and shrinkage of SiMPs, resulting in the isolation of electrical network. To overcome these limitations, we propose a novel electrode architecture consisting of active materials, reinforcing materials, and a conductive matrix. The reinforcing materials act as a bridge between the active materials and the conductive matrix, enhancing the electrode's elasticity. The conductive matrix integrates the functionalities of both binder and conductive additive, eliminating the need for nonconductive binders. Consequently, the issue of electrical connectivity in the SiMP electrode during repeated cycling is addressed. The conductive matrix is synthesized using a simple method involving the cyclization of polymers at a specific temperature, thereby enhancing the electrical conductivity of the polymer. Through the examination of mechanical and electrical characteristics, our proposed electrode structure demonstrates improved electrical conductivity while preserving electrode integrity when compared to the conventional SiMP electrode structure. In conclusion, our novel electrode structure presents a promising solution for enhancing the applicability of SiMPs in LIB electrode materials. This advancement holds potential for overcoming challenges associated with SiMPs, thus facilitating their broader utilization in next-generation lithium-ion batteries.

Importance of Selecting an Appropriate Li+ Concentration in Prolonging the Cyclability of a Solid-State Si Anode with an Organic Ionic Plastic Crystal

To address the ever-growing demands for battery-driven electrification, successful solid-state batteries (SSBs) are expected to deliver a higher energy density than lithium-ion batteries (LIBs). One of the drastic pathways to realize this is utilizing a high-capacity anode active material such as silicon and lithium metal. In particular, silicon electrodes can be made via a roll-to-roll process that has been used in producing LIB electrodes without worrying about the ambient moisture level and, therefore, their use in SSBs will be more cost-competitive and safer than those using lithium metal if the incorporation of solid electrolytes into the electrode layer can be achieved easily. In this respect, we previously developed an incorporation method of emergent soft solid electrolytes, i.e., Li+-containing organic ionic plastic crystals (OIPCs), into a silicon electrode and demonstrated their excellent applicability to doctor-blade coating, which can be scaled up to the roll-to-roll process.1 OIPCs, which are composed of organic cations and organic/inorganic anions, are unique ion-conduction media and have been actively employed in research of SSBs, especially since the discovery of a significant improvement of ionic conductivity by the addition of a Li+ salt to OIPCs.2 Incorporating additional components into OIPC structures alters their ion-conduction behaviors and the resulting ionic conductivities of the composites depend on various factors such as the chemical nature,3 particle size,4 and concentration of dopants.5 In the case of Li+ addition, it has been known that the physical states (i.e., softness) of Li+-containing OIPCs also depend on Li+ concentration.1 Therefore, both the electrochemical and mechanical properties of Li+-containing OIPCs need to be tailored to achieve the long-term cyclability of OIPC-containing electrodes for SSBs, but this has yet to be fully explored.In the present study, we made solid-state silicon composite electrodes with Li+- containing triethylmethylphosphonium bis(fluorosulfonyl)imide (Li x [P1222]1−x [FSI]) of various Li+ concentrations (x = 0.05, 0.10, 0.30, 0.50, 0.70, or 0.90) via the “all-in-one” method1 and evaluated their electrochemical performances in CR2032 half cells with Li0.50[P1222]0.50[FSI]-containing poly(diallyl dimethylammonium) bis(fluorosulfonyl)imide (PDADMA-FSI) interlayers at 50 °C, where the silicon electrode’s composition was 70 : 15 : 15 wt% and the weight ratio of the electrode to Li x [P1222]1−x [FSI] was 85 : 15 wt%. The mechanical properties of Li x [P1222]1−x [FSI] were evaluated by rheometry. We also performed cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS), and galvanostatic intermittent titration technique (GITT) to decipher the electrochemical properties of the electrodes with different Li+ concentrations. These results allowed a discussion about how the properties of Li x [P1222]1−x [FSI] influenced the half-cell cyclability.Fig. 1 shows the delithiation capacities of silicon–OIPC composite electrodes with different Li+ concentrations over the first ten cycles. From the first cycle, the delithiation capacity of the electrode with a relatively low or high Li+ concentration (i.e., 5, 70, or 90 mol%) was lower than those of the other electrodes with middle Li+ concentrations. As the cycle number increased, the dependence of the delithiation capacity on the Li+ concentration became obvious and, at the 10th cycle, the electrode with 50 mol% Li+ showed the highest delithiation capacity. The potential difference (ΔE) between dQ/dV peaks for the redox couple involving amorphous silicon (a-Si) also showed the same trend (Fig. 2), i.e., the 50 mol% sample provided the prolonged observation of the redox couple over the cycle test as well as the lowest ΔE value among various Li+ concentrations. This highlights the importance of controlling the interfacial Li+ concentration at a silicon surface to a middle range. In the presentation, we will show the results of other electrochemical and mechanical analyses to clarify the benefit of using the middle concentration further. Acknowledgment The authors acknowledge the Australian Research Council (ARC) for the financial support under the Linkage Project scheme [grant number: LP180100674]. H. Ueda would like to thank Deakin University for providing an Alfred Deakin Postdoctoral Research Fellowship. References H. Ueda, F. Mizuno, M. Forsyth and P. C. Howlett, J. Electrochem. Soc., 171, 020556 (2024).D. R. Macfarlane, J. Huang and M. Forsyth, Nature, 402, 792 (1999).J. M. Pringle, Y. Shekibi, D. R. MacFarlane and M. Forsyth, Electrochim. Acta, 55, 8847 (2010).Y. Zhou, X. Wang, H. Zhu, M. Armand, M. Forsyth, G. W. Greene, J. M. Pringle and P. C. Howlett, Energy Storage Mater., 15, 407 (2018).H. Ueda, N. Saito, A. Nakanishi, H. Zhu, R. Kerr, F. Mizuno, P. C. Howlett and M. Forsyth, Mater. Today Phys., 43, 101395 (2024). Figure 1

Surface Engineering of LiNi0.8Co0.1Mn0.1O2 By Ultrathin Al2O3 Via Atomic Layer Deposition

Nickel-rich Li(NixCoyMn1-x-y)O2 (NCM) is considered one of the most promising cathode materials for next-generation high-energy lithium-ion batteries (LIBs). However, nickel-rich NCM suffers from short battery lifespan, poor rate performance, and structural instability during cycling due to side reactions between the cathode material and the electrolyte. To overcome the aforementioned problems, coating the surface of nickel-rich NCM powders is an efficient and straightforward strategy. In recent years, atomic layer deposition (ALD) has been gaining attention for its utility in preparing LIB electrode materials. Compared to traditional coating methods, ALD can form uniform and ultrathin coating layers, which protect the cathode from reactions with the electrolyte while maintaining electrical conductivity and fast electron transport. More importantly, this process is energy-efficient, rapid (taking only a few minutes), and does not damage the electrode. Nevertheless, attempts to directly deposit ALD coatings onto nickel-rich NCM composite electrodes to enhance the electrochemical performance of NCM have not been widely reported.This study provides an efficient technique based on ALD to enhance the electrochemical performance of Ni-rich NCM cathode materials. The surface of the Li(Ni0.8Co0.1Mn0.1)O2 (NCM811) composite electrode was directly coated with a high-quality ultrathin layer of aluminum oxide (Al2O3). The thickness of the coating layer was precisely controlled at the sub-nanometer scale by the number of ALD cycles. It could protect the surface of the active NCM811 powder and maintain interparticle electron pathways, thereby enhancing electrochemical performance. The optimal thickness of the Al2O3 coating for maximizing the electrochemical performance of NCM811 was grown via 10 ALD cycles. The ALD-based ultrathin Al2O3 coating on the NCM811 was performed using a rotary ALD system. The morphology of the samples was confirmed using scanning electron microscopy (SEM) and transmission electron microscopy (TEM). Energy-dispersive X-ray spectroscopy (EDS) elemental mapping was collected in scanning transmission electron microscopy (STEM) mode. X-ray diffraction (XRD) patterns were collected using X-ray powder diffraction equipment. The chemical composition of the coating was analyzed using X-ray photoelectron spectroscopy (XPS) with Al Kα radiation. Cell testing was conducted using a coin-type half-cell with lithium metal as the anode.

Electrochemical synthesis and carbon doping of nanostructured iron fluorides from the selection of metal current collectors in lithium-ion batteries

The use of materials that rely on conversion reactions as electrodes in lithium-ion batteries is extensively investigated due to their potential for enhanced capacity compared to traditional electrode materials. Iron fluorides, in particular, present a promising alternative in terms of specific capacity. However, these materials often face challenges related to low intrinsic conductivity. This issue is typically addressed in the literature by doping the active material with carbon particles and reducing the particle size of the active material. This study explores the feasibility of directly integrating conductive carbon from the substrate into the fluoride-based active material during the synthesis process. The synthesis employs a simple anodic method conducted directly on the chosen metallic substrate, which then functions as the current collector in the devices. This approach simplifies the synthesis process, reduces processing time, and eliminates the need for additives and binders at the conventional active material-current collector interface. Two FeF3 layers were electrochemically synthesized on steel substrates with different carbon contents. These layers were evaluated as cathode-active materials for rechargeable lithium-ion batteries. The influence of carbon on the conductivity of the conversion layer was assessed using Electrochemical Impedance Spectroscopy (EIS) with a model based on conductive porous electrodes. Morphological and thickness analyses of the layers showed a strong correlation between increased pore size and layer thickness and the carbon content in the metallic substrate. The optimal performance was observed with the layer on the substrate with higher carbon content. The electrochemical performance of the active material was further evaluated using electrochemical impedance spectroscopy and galvanostatic tests in pouch cells. The conversion layers derived from carbon steel exhibited reduced resistivity and enhanced specific capacitance and cyclability compared to layers formed on pure iron.

Facile preparation of Co3O4/Super P/multi-walled carbon nanotube films for high-performance Li-ion battery anodes

This study prepared Co3O4/Super P/Multi-walled carbon nanotube (MWCNT) free-standing films through a simple vacuum filtration method. The free-standing films showed that Co3O4 particles were well dispersed within the Super P and MWCNT network backbone without deforming oxide materials, confirmed by scanning electron microscopy (SEM) images and X-ray diffraction (XRD) patterns. Employing Co3O4/Super P/MWCNT free-standing films as an anode electrode in lithium-ion batteries is superior to conventional electrode procedures because a binder is not required, and the current collector and laminate process are required. Moreover, the Co3O4/Super P/MWCNT electrodes showed remarkable capacity and rate capability compared to that of conventional laminated Co3O4/carbon composites. The enhanced electrochemical performance of Co3O4/Super P/MWCNT electrodes could be attributed to the extraordinary electrical conduction of MWCNT in nature and its stable connection between the conductive substrate and active materials. Furthermore, this connection offers the integrity of the electrode despite volume variation during Lithium (Li)-ion intercalation and deintercalation.