Solid-State Electrolytes for Lithium Metal Batteries: State-of-the-Art and Perspectives

The use of all-solid-state lithium metal batteries (ASSLMBs) has garnered significant attention as a promising solution for advanced energy storage systems. By employing non-flammable solid electrolytes in ASSLMBs, their safety profile is enhanced, and the use of lithium metal as the anode allows for higher energy density compared to traditional lithium-ion batteries. To fully realize the potential of ASSLMBs, solid-state electrolytes (SSEs) must meet several requirements. These include high ionic conductivity and Li⁺ transference number, smooth interfacial contact between SSEs and electrodes, low manufacturing cost, excellent electrochemical stability, and effective suppression of dendrite formation. This paper delves into the essential requirements of SSEs to enable the successful implementation of ASSLMBs. Additionally, the representative state-of-the-art examples of SSEs developed in the past 5 years, showcasing the latest advancements in SSE materials and highlighting their unique properties are discussed. Finally, the paper provides an outlook on achieving balanced and improved SSEs for ASSLMBs, addressing failure mechanisms and solutions, highlighting critical challenges such as the reversibility of Li plating/stripping and thermal runaway, advanced characterization techniques, composite SSEs, computational studies, and potential and challenges of ASS lithium–sulfur and lithium–oxygen batteries. With this consideration, balanced and improved SSEs for ASSLMBs can be realized.