Unveiling the impact of inherent LiFePO4 powder properties for dry-processed electrodes

Raffenberg, Simon; Rodehorst, Uta; Junghans, Katrin; Winter, Martin; Börner, Markus

Abstract

This study provides a comprehensive analysis of five lithium iron phosphate (LFP) grades, examining the inherent material properties in dry battery electrodes (DBE). The study demonstrated that both particle size and particle stability/breakage under shear force drastically influences granulate processability and electrode film formation during calendering. Smaller particles were found to hinder binder fibrillation, due to extensive surface coverage of the binder. Additionally, particle breakage during electrode processing was identified as contributor to accelerated material aging for DBE, whereby particles with a high specific surface area proved to be particularly stable against shear force. Furthermore, a correlation between LFP crystallite size and electrochemical electrode properties was observed, with intermediate crystallite sizes showing a favourable influence on the specific discharge capacity. Contrary to prevailing assumptions derived from wet processed electrodes, the rate capability and specific discharge capacity of DBE were found to be less associated with tortuosity or porosity. Instead, a necessity of enhancing electronic conductivity within DBE through stable carbon-binder networks was identified. Furthermore, the study introduced rheological granulate metrics to quantify PTFE-based granulate processability for calendering. These findings contribute valuable insights for the design of not only DBE and their processing strategies, but also for general advanced LFP processing.