Modelling of Solvent-free Manufacturing of Lithium-ion Batteries

With the rapid development of industries such as new energy vehicles, the demand for lithium-ion batteries (LIBs) has been increasing steadily year by year. The conventional slurry coating process involves the use of N-methyl-2-pyrrolidone (NMP), which requires an expensive and resource-intensive solvent evaporation and recovery system. Consequently, solvent-free (a.k.a dry) electrode manufacturing has demonstrated substantial advantages and has become a focal point of extensive research.
This study employs relatively large-scale Discrete Element Method (DEM) simulations to conduct a mesoscopic-scale computational investigation of the twin-screw extrusion process in solvent-free (SF) filament fabrication for LIB electrode manufacturing. Through appropriate model simplifications, the study achieves efficient simulation of molten polymer extrusion, thereby enabling quantitative analysis of extruded filaments.
The research focusses on examining the effects of different screw rotation speeds, feeding strategies, and levels of inter-particle contact forces (used to emulate particle states under varying heating temperatures) in a twin-screw extruder (TSE) on the microstructural parameters of LIB filaments. The key microstructural parameters considered include porosity (ε), effective diffusion coefficient (Deff), effective electrical conductivity (σeff), and tortuosity (τ).
The computations were implemented in Python by voxelising the filament structure and solving the three-dimensional Poisson equation, together with applying the Bruggeman relation, among others. Porosity exhibits a slight increase with rising screw rotation speed, which can be attributed to the reduction in carbon agglomerates. Compared with the premixed feeding strategy, the side-by-side method produces denser filament structures with lower porosity; however, due to incomplete mixing of LFP and BC particles, a minor decline in transport efficiency is observed.
In addition, filament expansion was investigated. Higher screw speeds were found to suppress swelling, enhance structural stability, and reduce filament porosity. As a further novel approach to exploring SF electrode manufacturing, this study introduced the Augmented Dickey Fuller (ADF) test to assess the dynamic stability of extruded filaments.
While this work contributes to the advancement of the understanding of extrusion processes in dry electrode manufacturing, certain limitations remain in terms of model simplification, which may serve as important directions for future research.