Solid-state Li-ion batteries (SS-LIBs) have been widely demonstrated and represent a safer, more stable alternative to wet batteries in several applications. Specifically, thin-film SS-LIBs allow integration with microelectronics and, in general, can be prepared over a wide range of substrates and shapes such as flexible metal sheets or coaxially deposited on wires. One of the best performing chemistries for thin-film SS-LIBs, based on its energy density, long-term stability and very-low self-discharge, has a LiCoO₂ cathode, LiPON solid electrolyte, and Si anode. Preparation of the efficient 'high-temperature' LiCoO₂ phase typically requires substrate annealing during deposition (300-500 C) and post-annealing of the sputter-deposited films (500-800 C in oxygen) to increase crystallinity. The process is incompatible with most flexible polymer substrates and other inexpensive organic materials that cannot be heated much beyond room temperature.

Here we demonstrate solid-state thin-film Li-ion batteries based on LiCoO₂/LiPON/Si chemistry over a variety of flexible organic substrates using an all-room temperature preparation. The batteries show good overall performance and have a long cycle life. We compare several metrics of performance with state-of-the-art annealed LiCoO₂ batteries on silicon substrates. Finally, we explore the cases when room temperature batteries show a larger initial capacity than high-temperature LiCoO₂ SS-LIBs.