Li₃PO₄ electrolyte of high conductivity for all-solid-state lithium battery prepared by plasma spray

Li₃PO₄ (LPO) deposits were prepared for the electrolytes of all-solid-state lithium batteries (ASS-LBs) by atmospheric plasma-spraying (APS) with sintered powders of three different sizes. The effect of LPO particle size on the microstructure, chemical composition, lattice structure, and ion conductivity of LPO deposits was systematically investigated. Results showed that instead of the conventional lamellar-structured splats with limited inter-splat bonding, columnar-structured grains with chemical inter-splat bonding were formed in APS LPO due to its low melting point. The porosity of the deposits decreases with the decrease in feedstock particle size and deposits with porosity less than 1% can be deposited by using powders smaller than 50 µm. The XRD presented that all deposits have the same phase compositions as that of the sintered powders. Due to more intensively vaporization of P than Li from the molten droplets during APS, the Li/P atomic ratio in the deposits was higher than the stoichiometric ratio of 3 and ranges from 3.02 to 3.17. Owning to the high-quality inter- splat bonding and the slightly deviated Li/P atomic ratio, a high room-temperature ionic conductivity of 4.65 × 10⁻⁸ S.cm⁻¹ was achieved for APS LPO deposit by using the LPO particles with sizes of less than 30 µm.