Cold sintering process of Li_1.5Al_0.5Ge_1.5(PO₄)₃ solid electrolyte

The recently developed technique of cold sintering process (CSP) enables densification of ceramics at low temperatures, i.e., <300°C. CSP employs a transient aqueous solvent to enable liquid phase-assisted densification through mediating the dissolution-precipitation process under a uniaxial applied pressure. Using CSP in this study, 80% dense Li_1.5Al_0.5Ge_1.5(PO₄)₃ (LAGP) electrolytes were obtained at 120°C in 20 minutes. After a 5 minute belt furnace treatment at 650°C, 50°C above the crystallization onset, Li-ion conductivity was 5.4 × 10⁻⁵S/cm at 25°C. Another route to high ionic conductivities ~10⁻⁴ S/cm at 25°C is through a composite LAGP - (PVDF-HFP) co-sintered system that was soaked in a liquid electrolyte. After soaking 95, 90, 80, 70, and 60 vol% LAGP in 1 M LiPF₆ EC-DMC (50:50 vol%) at 25°C, Li-ion conductivities were 1.0 × 10⁻⁴ S/cm at 25°C with 5 to 10 wt% liquid electrolyte. This paper focuses on the microstructural development and impedance contributions within solid electrolytes processed by (i) Crystallization of bulk glasses, (ii) CSP of ceramics, and (iii) CSP of ceramic-polymer composites. CSP may offer a new route to enable multilayer battery technology by avoiding the detrimental effects of high temperature heat treatments.