Solvent exchange-induced facile recrystallisation and particle size control of sulphide solid electrolytes for all-solid-state Li-ion batteries

Practical All-Solid-State Li-Ion Batteries (ASSLBs) require small-sized sulphide solid electrolyte (SSE) particles (SSE membranes (few microns) and composite electrodes (sub-microns)). However, particle-size reduction via mechanical crushing and classification significantly reduces the crystallinity and Li-ion conductivity of SSEs. Here, we introduce a novel facile polar-to-nonpolar solvent exchange technique, wherein an SSE-dissolved polar solvent (e.g., Li6PS5Cl in ethanol) is injected into a heated nonpolar solvent (e.g., n-decane at 100 degrees C), leading to instantaneous volume-confined recrystallisation. Using this method, the particle size can be easily controlled by adjusting the process parameters. The average particle size of the solvent-exchanged commercial Li6PS5Cl SSE decreases from 8 to 0.88 mu m, while a Li-ion conductivity of 1.54 mS cm(-1) (similar to 85% vs. pristine Li6PS5Cl) is retained after annealing at 550 degrees C. The sub-micron SSE particles, incorporated into a composite cathode with Li(Ni0.8Co0.1Mn0.1)O-2, improve the utilisation and interfacial robustness of the active material. The initial discharge capacity of the ASSLB increases from 179 to 197 mA h g(-1) at 0.05C, and the capacity retention improves from 79% to 85% after 50 cycles at 0.1C and 55 degrees C. Thus, the solvent exchange approach may open new pathways for the synthesis of size-controlled high-quality SSEs for ASSLBs.

Automated summary

This study introduces a novel solvent exchange technique to prepare small-sized high-quality sulphide solid electrolyte (SSE) for lithium-ion batteries. By adjusting the process parameters, the particle size can be easily controlled, resulting in improved battery performance and cycle life.