Research Progress on the Solid Electrolyte of Solid-State Sodium-Ion Batteries

Because sodium-ion batteries are relatively inexpensive, they have gained significant traction as large-scale energy storage devices instead of lithium-ion batteries in recent years. However, sodium-ion batteries have a lower energy density than lithium-ion batteries because sodium-ion batteries have not been as well developed as lithium-ion batteries. Solid-state batteries using solid electrolytes have a higher energy density than liquid batteries in regard to applications with sodium-ion batteries, making them more suitable for energy storage systems than liquid batteries. Due to their low ionic conductivity, solid electrolytes are currently unable to achieve comparable performance to liquid electrolytes at room temperature. In this review, we discuss the advancements in SSEs applied to sodium-ion batteries in recent years, including inorganic solid electrolytes, such as Na–β-Al₂O₃, NASICON and Na₃PS₄, polymer solid electrolytes based on PEO, PVDF-HFP and PAN, and plastic crystal solid electrolytes mainly composed of succinonitrile. Additionally, appropriate solutions for low ionic conductivity, a narrow electrochemical stability window and poor contact with electrodes, which are the significant flaws in current SSEs, are discussed in this review. Graphical Abstract: [Figure not available: see fulltext.]