Parametric study of dry coating process of electrode particle with model material of sulfide solid electrolytes for all-solid-state battery

Abstract

We have reported that a dry coating is a very promising process to produce a suitable composite particle for all-solid-state lithium-ion secondary batteries. We here present a parametric study of this dry coating process for further optimization and improvement. In the dry coating process, electrode particles were coated with solid electrolyte (SE) particles. LiNi1/3Co1/3Mn1/3O2 (NCM) was used as a host particle, while sodium sulfate (Na2SO4) was selected as a model material of sulfide SEs and used as a guest particle. A dry impact-blending process known as “Hybridizer” was used. Effects of critical process parameters including tip speed of rotor, processing time, and initial weight fraction of host and guest particles were investigated. Under insufficient impact force NCM particles were not fully covered with Na2SO4 particles, while under a sufficient impact force the discrete coating of Na2SO4 particles on the surface of NCM particles were observed. With an increase in the mechanical input energy per unit mass of Na2SO4, plastic deformation and coalescence of Na2SO4 particles were promoted, resulting in the continuous coating. With further increase in the mechanical input energy, breakage of the NCM particles was caused. The continuous coating exhibited a great advantage over the discrete coating for formation of the solid-solid interfacial contacts between NCM and Na2SO4 in the compressed pellet. Finally, the optimal processing conditions, where NCM particles are able to be coated by the continuous layer of much less amount of Na2SO4 (=10wt%) without breakage of NCM particles, were determined.