Performance and Interface Properties of Vapor-Phase Deposited Electrode and Electrolyte Materials for Conformal Solid State Batteries

Abstract

All-solid-state batteries exhibit distinct advantages over existing liquid-electrolyte lithium-ion cells, including greater chemical and thermal stability, a wider voltage window, and a reduced need for packaging. Thin film solid state batteries, generally made via physical vapor deposition (PVD), are also capable of supporting high power densities due to their short diffusion pathways for transported species and high quality interfaces, but they are generally limited to planar substrates and can only store on the order of 0.1 mAhr/cm2 as a result. One route to dramatically increasing the energy density would be to develop conformal deposition processes for the electrodes and electrolyte, allowing for the deposition of solid state batteries on arbitrary 3D structures, including high aspect-ratio trenches for use in microelectronics, or conductive fabrics for use in energy-storing textiles. Multiple groups have explored atomic layer deposition (ALD) as a precisely controllable, highly conformal, and relatively low-temperature (≤ 250C) technique for synthesizing thin film battery components. Anodes and cathodes made using ALD have so far been tested almost exclusively in half cells due to the lack of an adequate ALD-grown solid electrolyte, as well as challenges relating to patterning and contacting multiple layers of conformally-deposited materials. Our group previously demonstrated1 atomic layer deposition of the solid electrolyte LiPON, which is the material used currently in PVD-based batteries and exhibits a conductivity of better than 10-6 S/cm. In this presentation, we will discuss the fabrication and testing of true solid state batteries made with ALD-deposited materials. We will present data from operating planar solid-state cells utilizing a mix of ALD and PVD deposited materials, as well as thin film stacks fabricated on both planar and 3D flexible substrates. Electrochemical characterization, secondary ion mass spectroscopy (SIMS), and x-ray photoelectron spectroscopy (XPS) are utilized to understand the processes occurring within the cells. In particular, we highlight in-situ XPS data demonstrating that undesirable interface reactions during the ALD of battery components present an additional challenge over existing PVD processes, illustrated by the deposition of LiPON on LiCoO2. 1 A.C. Kozen, A.J. Pearse, C. Lin, M. Noked, and G.W. Rubloff, Chem. Mater. 27, 150730080053001 (2015).