Chemical Vapor Deposition of Lithium Phosphate Thin-Films for 3D All-Solid-State Li-Ion Batteries

High quality Lithium phosphate (Li 3 PO 4 ) thin films have been deposited by metal-organic chemical vapor deposition (MOCVD), using tert-butyllithium and trimethyl phosphate as precursors. The Li 3 PO 4 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 Li 3 PO 4 deposition is a diffusion-controlled process in the temperature range of 300 to 500°C. Li 3 PO 4 films have also been deposited on highly structured substrates to investigate, for the first time, the feasibility of 3D deposition of Li 3 PO 4 by MOCVD. Furthermore, very thin films of Li 3 PO 4 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.