Chemical vapor deposition of lithium phosphate thin-films for 3D all-solid-state Li-Ion Batteries.

High quality Lithium phosphate (Li3PO4) thin films have been deposited by metal-organic chemical vapor deposition (MOCVD), using tert-butyllithium and trimethyl phosphate as precursors. The Li3PO4 films deposited at 300°C yielded the highest ionic conductivity (3.9 × 10-8 S·cm-1). Increasing the deposition temperature led to crystallization of the deposited films and, consequently, to lower ionic conductivities. Kinetic studies on planar substrates showed that Li3PO4 deposition is a diffusion-controlled process in the temperature range of 300 to 500°C. Li3PO4 films have also been deposited on highly structured substrates to investigate, for the first time, the feasibility of 3D deposition of Li3PO4 by MOCVD. Furthermore, very thin films of Li3PO4 have been deposited onto thin film Si anodes and it was found that these layers effectively suppress the SEI formation and dramatically improve the cycle performance of Si film anodes.