Critical Role of Mixing for Dry Processing Sodium Ion Cathodes

Abstract Due to the elimination of solvent removal and recovery, dry electrode processing has enabled significant reductions in energy consumption and cost for lithium-ion battery (LIB) manufacturing. However, transferring this promising manufacturing approach to sodium-ion batteries (SIBs), of which cost is the primary driver for technological development, has been surprisingly rare, with clear knowledge gaps in understanding the process–structure–performance relationship. Here, we investigate the effects of each step (mixing, calendaring, and laminating) during dry processing of an O3-type NaNi0.33Fe0.33Mn0.33O2 (NFM) cathode on the microstructure and electrochemical performance. We highlight the critical role of appropriate mixing for fabricating a high-performance dry-processed electrode. Insufficient mixing may lead to nonuniform distribution of the polytetrafluoroethylene (PTFE) in the electrode composite, which, upon laminating, can migrate to the electrode surface, leading to poor wetting between the liquid electrolyte and the cathode, while excessive mixing can lead to surface degradation of the cathode active materials due to the reduction of Ni. As the wetting ability of liquid electrolyte on the electrode is not a serious concern for LIBs, our work provides novel insights that are specific to sodium cathodes for the development of scalable, low-cost, sustainable dry processes for SIB manufacturing.