INTERFACE DESIGN FOR ALL-SOLID-STATE LITHIUM METAL BATTERIES

Abstract

Lithium-ion batteries (LIBs) have expanded their application from electronics to electric vehicles (EVs). To ease the safety concerns and the “range anxiety”, solid-state lithium batteries (SSLBs) become a more attractive choice. The replacement of flammable and toxic liquid electrolytes with solid-state electrolytes (SSEs) makes it a safer option. The utilization and compatibility of high specific capacity materials such as sulfur cathode and lithium-metal anode increase the cell energy density. However, SSLBs still face challenges towards practical application, which mainly from the solid-solid contact nature on the interfaces. On the anode side, lithium dendrite growth and high interface resistance both hindered the longevity of the cells. On the cathode side, low initial Coulombic efficiency (CE) and low capacity utilization of sulfur obstructed the realization of high loading cathodes.In this dissertation, I addressed both challenges of dendrite and contact on the anode side by adding strontium into lithium anodes. Different from all previous metal/metal oxide coating on garnet or Li alloy anodes that form lithiophilic interlayer, a lithiophilic/lithiophobic bifunctional layer is formed to reduce the interfacial resistance and to suppress the growth of lithium dendrite, which is confirmed by comprehensive material characterizations, electrochemical evaluations, and simulations. The optimum Li-Sr | garnet | Li-Sr symmetric cells achieve a high critical current density (CCD) of 1.3 mA/cm2 and can be cycled for 1,000 cycles under 0.5 mA/cm2 at room temperature, providing a new strategy for high-performance garnet SSLB. Furthermore, I (1) verified the importance of lithiophobic on dendrite suppression by discovering and successfully constructing the highest interface energy (γ, against lithium) material ever reported among all lithium compounds that can be formed on the electrolyte | anode interface; (2) revealed the impact of anode properties on the interface by enhancing the Li self-diffusivity by a co-doping method, achieved an outperformed critical loading of 4.1 mAh/cm2 at 1.0 mA∙cm-2 at room temperature. On the cathode side, I tackled both low CE and low capacity utilization issues by promoting both Li+ and e- transportation across the cathode | SSE interface, resulting in high capacity utilization of 96.5% and high capacity retention of 88.8% after 145 cycles at a high loading of 4.0 mAh cm-2 under room temperature in Li6PS5Cl based SSLB.