Effect of high temperature LiPON electrolyte in all solid state batteries

Thin film solid state Li4Ti5O12-based batteries are developed by using amorphous Lithium Phosphorus Oxynitride (LiPON) electrolyte deposited by reactive sputtering at different substrate temperatures (T-dep). Such layers maintain their amorphous character even at higher Tdep. The stoichiometry, ionic conductivity, thermal stability and overall effect on full battery stacks were investigated. The ionic conductivity falls down by nearly three orders of magnitude for samples deposited at higher temperatures while no significant compositional variations are found, in contrast with previous reports. This is interpreted as the creation of a highly thermally stable LiPON glass with a closed-packed structure which inhibits Li-ion diffusion. The onset of the glass transition (TO and the crystallization temperature (TO of LiPON shifts to higher temperatures as Tdep increases. Galvanostatic (dis)charge measurements on fully operational thin film batteries show a decrease in capacity and a worsened C-rate performance as LiPON Tdep increases. Despite the lower ionic conduction, the improved thermal stability reported here using LiPON whose properties can be properly tuned could open interesting scenarios in future advances in solid-state battery systems and new possibilities in high temperature applications.