Challenges of Stable Ion Pathways in Cathode Electrode for All-Solid-State Lithium Batteries: A Review

For energy storage devices, high energy density, high power density, cycle stability, and safety are the development goals. Solid-state lithium metal batteries, with both safety and high performance, have become a hot topic in recent research. Although each component of these batteries has been studied for decades, and their individual performance has been improved markedly, the performance of their combination is still far less than expected. Without the aid of a liquid electrolyte, the ion pathways within and between solid elements are tortuous or even disconnected, making the cathode development in solid-state lithium metal batteries more challenging than for those in lithium-ion batteries with liquid electrolytes. This review focuses on the ion pathways in the cathode for all-solid-state lithium batteries with different dimensions, covering their types, characteristics, and challenges. The design and modification methods of the ion pathways, including element doping, coating, composite pathways, and new functional structures, are also discussed.