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

Abstract

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 °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 μm, while a Li-ion conductivity of 1.54 mS cm⁻¹ (∼85% vs. pristine Li₆PS₅Cl) is retained after annealing at 550 °C. The sub-micron SSE particles, incorporated into a composite cathode with Li(Ni_0.8Co_0.1Mn_0.1)O₂, 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 °C. Thus, the solvent exchange approach may open new pathways for the synthesis of size-controlled high-quality SSEs for ASSLBs.