Mechanisms of Lithium-Ion Transport in Solid-State Electrolyte and Cathode Materials Prepared By PVD

Abstract

Conventional liquid-state lithium-ion batteries are currently limited in their energy density, lifetime, thermal stability, and safety. The design of viable solid-state batteries shows promise to improve upon the shortcomings of liquid cells. Removal of organic electrolytes increases the lifetime while making these batteries more environmentally friendly and safe. Solid-state batteries also have the potential to demonstrate higher energy density and provide ultrafast charging. However, these desirable properties require significant efforts to uncover and utilize the chemical, morphological, and electrochemical properties of solid-state electrolytes and cathode nanocomposites. This study addresses physical vapor deposition (PVD) technology for design of solid-state material architectures with the properties needed to create high-performance electrochemical cells. The PVD process allows cathodes and electrolytes to be deposited as dense films, thereby increasing their energy density and electrochemical performance. Furthermore, this process results in excellent adhesion between dissimilar materials allowing for increased electrical and ionic conductivity. This work uses lithium oxyhalide electrolytes and eco-friendly lithium iron phosphate cathodes, which were both deposited in vacuum using radio frequency power and magnetron sputtering sources. A co-deposition technique was used to successfully deposit thin film layers of cathode, electrolyte, cathode/electrolyte mixture, and carbon thin films in a single process. Electrochemical cells with different functional layers deposited by PVD (~7 mm) were compared to the cells with commercial LFP cathodes (~32 mm thick). The electrochemical cells created by PVD showed lower charge transfer resistances and high electrochemical stability at ultra-high (10C) charging rates. Significant improvements in performance are expected to continue as the process is improved in terms of ionic and electronic transport at cathode-electrolyte interfaces. The authors acknowledge financial support from the DOD Navy SBIR Phase II project (N68335-18-C-0021), the NSF IUCRC program for supporting the “Center for solid-state electric power storage” (#2052631), and the South Dakota “Governor’s Research Center for electrochemical energy storage”. Figure 1