Solid‐State Electrolytes for Sodium Metal Batteries: Recent Status and Future Opportunities

Abstract

Solid‐state sodium metal batteries (SSMBs) possess superior safety and high energy density over liquid counterparts, and therefore hold great promise for large‐scale energy storage application. In this review, the recent development of the advanced sodium‐based solid‐state electrolytes (SSEs) for high‐performance SSMBs is systematically summarized. First, the fundamental mechanisms and key parameters of SSEs, including ionic conductivity, electrochemical stability and Na+ transference number, are introduced in details, and then various inorganic (Na‐β‐alumina, Na superionic conductors, and sulfides), polymer SSEs (solid polymer SSEs and gel polymer SSEs), and inorganic‐polymer hybrid SSEs are elaborately discussed, emphasizing the unique roles of structure optimization and interface engineering of SSEs for boosting electrochemical performance in SSMBs. Finally, the key challenges and promising prospects of advanced SSEs in terms of interface optimization of inorganic SSEs, molecular design and screening of polymer SSEs, objective evaluation, and multiscale characterizations of SSEs are briefly proposed.

Wide-temperature-range sodium-metal batteries: from fundamentals and obstacles to optimization

“…156,239 Unfortunately, the terrible interfacial compatibility between Na metal and ISEs hinders the Na + transfer number, inevitably increasing the interfacial resistance. 244,245 Therefore, a highly promising ISE should simultaneously have excellent ionic conductivity, good interfacial compatibility and stable cycling performance. 239,240,246…”

Reinvestigation of Na5GdSi4O12: A Potentially Better Solid Electrolyte than Sodium β Alumina for Solid-State Sodium Batteries

“…Grounded on these facts, solid-state sodium batteries (SSSBs) have emerged as a promising alternate system, where flammable liquid electrolytes are replaced with solid electrolytes, offering higher thermal stability and overall system stability against Na-metal. , Solid electrolytes play an important role in deciding the overall performance of SSSBs. High ionic conductivity and chemical and electrochemical stability are essential criteria that solid electrolytes should be endowed with for solid-state battery applications . Among various classes of solid electrolytes (SEs), ceramic-based SEs exhibit most of these properties and, thus, are widely investigated for SSSBs.…”

“…Among various classes of solid electrolytes (SEs), ceramic-based SEs exhibit most of these properties and, thus, are widely investigated for SSSBs. When sodium-ion (Na + ) conducting SEs are considered, Na-β″-alumina (BASE) and NASICON-based Na 3 Zr 2 PSi 2 O 12 (NZPS and doped) are highly regarded for solid electrolyte applications. , BASE exhibits ionic conductivity of 10 –2 –10 –3 S cm –1 at room temperature (RT). It is highly stable against Na-metal and has long been used in commercial Na–NiCl 2 and Na–S cells that operate between 300 and 350 °C .…”

“…However, the synthesis of BASE involves several processing steps. Temperatures higher than 1500 °C are required to sinter, and additives are needed to stabilize higher conducting polymorph of BASE. , It is also highly sensitive to water or water vapors. , On the other hand, the ionic conductivity of NZPS-based compounds ranges from 10 –3 to 10 –4 S cm –1 at RT . Similar to BASE, they exhibit high stability against Na-metal and impressive stability against moisture .…”

“…However, synthesizing NZPS compounds on a large scale is a matter of concern . They also suffer from high interfacial resistance . Consequently, research and development efforts to identify, design, and formulate suitable Na + conducting solid electrolytes gain prominence.…”