Energy-dense Li metal anodes enabled by thin film electrolytes

Abstract

Next-generation, energy-dense, rechargeable lithium batteries require Li metal anodes that provide ten times the specific capacity of state-of-the-art graphite anodes. But, there are many challenges to the successful utilization of Li anodes, including high chemical reactivity and the propensity to deposit into non-dense, high surface area morphologies, which can result in dendritic growth and significant, associated safety hazards, such as short-circuiting and potential combustion of the liquid electrolyte. Solid-state thin film electrolytes have been used to address both of these challenges. In this review, we will provide an overview of thin film battery designs, highlighting the role of thin film electrolytes, lithium phosphorous oxynitride (LiPON) in particular, in enabling highly reversible, efficient cycling of Li metal anodes. We then discuss progress in thin film electrolyte compositions and vacuum deposition processing that has occurred in roughly the past 20 years. It will be shown how these novel electrolyte compositions and processing capabilities have been used to integrate thin film electrolytes with bulk Li metal anodes required for large format energy storage cells, such as those used in consumer electronics and electric vehicles. We end the review with a brief outlook on the outstanding questions and potential future research directions.