Towards a scalable production of β-Li3PS4-based all-solid-state batteries: Optimizing pressing parameters of the tape-casted solid electrolyte and composite cathode films

Abstract

Pressing of all-solid-state batteries (ASSBs) components is one of the most important processes for scalable production. Henceforth, pressing parameters (pressure and temperature) for β-Li₃PS₄ (β-LPS) solid electrolyte (SE) separator films and LiNi_0.6Co_0.2Mn_0.2 (NCM622)/β-LPS composite cathode films prepared by a slurry-based process were investigated and optimized. Compression of the β-LPS film at a temperature of 100 °C led to higher ionic conductivity than cold-pressed films. Raman and X-ray photoelectron spectroscopic analyses revealed no changes in the chemical nature of β-LPS material after hot pressing. Interestingly, time-of-flight secondary ion mass spectrometric (ToF-SIMS) analyses indicated a binder enrichment in the upper layers of the hot-pressed film. In a similar trend, increasing compression and temperature resulted in higher densification of NCM622/β-LPS composite cathode films. Based on galvanostatic intermittent titration technique (GITT) and electrochemical impedance spectroscopy (EIS) measurements, hot-pressed composite cathode at 200 MPa/100 °C exhibited a higher coverage percent of catholyte on cathode active material and a greater Li⁺ diffusion coefficient (D_Li⁺) than cold-pressed one at 200 MPa/20 °C. Cycling tests of “Li–In│β-LPS│NCM/β-LPS” ASSBs with hot-pressed films displayed better cycling performance than that with cold-pressed ones, attributed to the higher concentration of electrochemically active NCM in close contact with β-LPS catholyte.