Characterization of Lithium Phosphate Deposit by Atmospheric Plasma Spraying

Plasma spraying was used to deposit Li₃PO₄ to the applications to all-solid-state lithium battery (ASS-LB) electrode. The agglomerated Li₃PO₄ powders were used as starting material. The commercial agglomerated powder and sintered dense powder were used for plasma spraying in three different size ranges. The effects of powder structure and powder particle size, and spray distance were investigated on deposit composition and microstructure. The microstructure, crystal structure and composition of the Li₃PO₄ deposit were characterized by using SEM, XRD and ICP-MS. The result shows that the sintered dense Li₃PO₄ powders present high temperature orthorhombic phase γ-Li₃PO₄, being different from β-Li₃PO₄ of agglomerated Li3PO4. Plasma-sprayed Li₃PO₄ presents a dense microstructure with a similar fractured surface morphology to that of sintered bulk. The coating retains the phase structure of the sintered powder. The atom ratios Li/P of plasma-sprayed Li₃PO₄ deposits are a little higher than stoichimetry of 3, and increased with the increase of spray distance in a range of 3.015-3.156, being a little larger than the stoichiometric ratio of Li₃PO₄. The deposit by the smaller powders than 30 μm exhibits a hhigh Li/P ratio of 3.156. The dominant factors controlling the deposit composition during plasma spraying of Li₃PO₄ will be examined.