Recent Progress and Remaining Challenges in Solid-State Design for Safe Energy Storage

ABSTRACT The transition from conventional lithium-ion batteries using liquid electrolytes to solid-state batteries represents a critical advancement in electrochemical energy storage. Solid-state electrolytes offer inherent safety benefits by reducing risks of thermal runaway, leakage, and flammability, while also exhibiting resistance to dendrite formation and improved long-term stability. These attributes position solid-state systems as promising candidates for next-generation energy storage applications. Recent progress in both lithium and sodium-based solid-state technologies has driven innovation across the field. Lithium solid-state batteries provide high theoretical energy density, fast-charging capability, and extended cycle life. However, their large-scale deployment is constrained by the limited availability and rising cost of lithium resources. Moreover, environmental concerns are associated with their extraction. In contrast, sodium-based solid-state batteries present a more sustainable and cost-effective pathway due to sodium's natural abundance and wide geographic distribution. Despite these advantages, current sodium systems suffer from lower energy densities, slower ionic transport, and reduced rate performance compared to lithium-based systems. Both lithium and sodium solid-state batteries continue to face critical challenges, including high interfacial impedance, mechanical brittleness, and unstable cyclability at ambient conditions. Addressing these issues requires advances in the design of composite electrolytes that combine the mechanical flexibility of polymers with the high ionic conductivity of ceramics. At Dartmouth, ongoing research focuses on developing solid composite electrolytes optimized for sodium-ion transport and stability at low temperatures. This work integrates research in improving interfacial contact, mechanical integrity, and overall electrochemical performance. These efforts contribute to establishing a foundation for scalable, safe, and high-performance solid-state sodium batteries suitable for grid-scale applications.