Fabrication and Performance Evaluation of Dry Spray-Coated Graphite Electrodes for Lithium-Ion Batteries for Electric Vehicle Applications
Authors: Barreras Uruchurtu Jesus Alberto , Besnard Nicolas , Paul Clément , Marchal Lauréline , Devisme Samuel , Lestriez Bernard 
Published: December 2024

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.

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Figure 1