Comprehensive understanding of the Na1+xZr2SixP3−xO12 solid-state electrolyte in advanced sodium metal batteries: a critical review

Abstract

All solid-state sodium metal batteries (ASSSMBs) have emerged as promising candidates to be a key technology in large-scale energy storage systems relative to mature Li/Na-ion batteries using flammable liquid electrolytes, owing to their abundant sodium resources, robust safety performance, desirable energy density, and favorable reliability and stability. A series of solid-state electrolytes (SSEs), regarded as an essential component of ASSSMBs, have been extensively developed in recent years. Among them, the Na superionic conductor (NASICON)-structure Na_1+xZr₂Si_xP_3−xO₁₂ (0 ≤ x ≤ 3, defined as NZSP) materials have attracted overwhelming attention as the most appropriate SSEs for the next-generation high energy density ASSSMBs. Herein, this review seeks to provide a comprehensive and in-depth understanding of NZSP SSEs, by first investigating their fundamentals, including composition, crystal structure, Na⁺-ion conduction mechanism, synthetic methods, and the key challenges associated with the NZSP-based ASSSMBs. Subsequently, comprehensive constructive modification strategies are proposed to optimize integrated NZSP SSE-based ASSSMBs. Finally, informed and strategic perspectives from various angles are summarized, providing potential guidance and possible avenues for further research aimed at achieving exceptional NZSP SSE-based ASSSMBs for practical applications.