Li_1.4Al_0.4Ge_0.1Ti_1.5(PO₄)₃: A stable solid electrolyte for Li-CO₂ batteries

In this study, a solid electrolyte, Li_1.4Al_0.4Ge_0.1Ti_1.5(PO₄)₃ (LAGTP), with a sodium superionic conductor-type crystal structure, was prepared using a facile solution-based method. LAGTP exhibited exceptional ionic conductivity (1.05 × 10⁻³ S cm⁻¹) and a low activation energy (0.237 eV). The LAGTP pellet was employed as a solid-state electrolyte in a Li-CO₂ battery, showcasing charge-discharge characteristics via a reversible electrochemical reaction (4Li⁺ + 3CO₂ ↔ 2Li₂CO₃ + C). As-synthesized multi-walled carbon nanotubes, drop-cast on carbon cloth, were used as the cathode. The battery underwent 60 cycles with a cut-off capacity of 1000 mAh g⁻¹ at various current densities, and a full-depth charge and discharge test was conducted at 100 mA g⁻¹. During the charge/discharge process, the particle size of the dead lithium increased on the cathode surface, leading to the blockage of active sites for conversion. Post-cycling analyses were performed to elucidate the cathode degradation mechanism. The incorporation of LAGTP significantly enhanced battery cycle life and safety, making it a suitable candidate for use in next-generation, high-performance Li-CO₂ batteries.