Enhancing electrochemo-mechanical properties of graphite-silicon anode in all-solid-state batteries via solvent-induced polar interactions in nitrile binders

Abstract

All-solid-state batteries (ASSBs) with sulfide-type solid electrolytes (SEs) are gaining significant attention due to their potential for the enhanced safety and energy density. In the slurry-coating process for ASSBs, nitrile rubber (NBR) is primarily used as a binder due to its moderate solubility in non-polar solvents, which exhibites minimal chemical reactivity with sulfide SEs. However, the NBR binder, composed of butadiene and acrylonitrile units with differing polarities, exhibits different chemical compatibility depending on the subtle differences in polarity of solvents. Herein, we systematically demonstrate how the chemical compatibility of solvents with the NBR binder influences the performance of ASSBs. Anisole is found to activate the acrylonitrile units, inducing an elongated polymer chain configuration in the binder solution, which gives an opportunity to strongly interact with the solid components of the electrode and the current collector. Consequently, selecting anisole as a solvent for the NBR binder enables the fabrication of a mechanically robust graphite-silicon anode, allowing ASSBs to operate at a lower stacking pressure of 16 MPa. This approach achieves an initial capacity of 480 mAh g⁻¹, significantly higher than the 390 mAh g⁻¹ achieved with the NBR/toluene binder that has less chemical compatibility. Furthermore, internal stress variations during battery operation are monitored, revealing that the enhanced mechanical properties, achieved through acrylonitrile activation, effectively mitigate internal stress in the graphite/silicon composite anode.