Electrolyte and Interface Engineering for Solid-State Sodium Batteries

Abstract

Sodium batteries are considered as promising candidates for large-scale energy-storage systems owing to the abundant and low-cost sodium resources. However, many reported sodium batteries are based on conventional organic liquid electrolyte, which would lead to potential safety issues. Developing solid-state electrolyte (SSE) for sodium batteries is an effective way to solve such problems. Nevertheless, how to develop high-performance SSE and compatible interface for constructing solid-state sodium batteries is still challenging. In this review, we mainly focus on the development and recent advances of SSE (including all-solid-state and quasi-solid-state electrolyte) and interface engineering for sodium batteries. The structure-property correlations and design principles of different inorganic and organic SSE are discussed in depth. The comprehensive performance of SSE depends on the structural characteristics such as defects, crystallinity, and stability of bonds. The design principles mainly include increasing the density of mobile Na+ ions, reducing the energy barrier, immobilizing anions, adjusting the stability of bonds, adding specific buffer layers, and increasing interfacial contact area. Moreover, we discuss the interface between SSE and electrode because a suitable interface is the key prerequisite for high-performance solid-state sodium batteries. This review provides fundamental insights and future perspectives to design advanced SSE and concomitant interface for next-generation rechargeable solid-state sodium batteries. The recent boom in electronics and electric vehicles has raised the demand for rechargeable batteries. However, safety issues of rechargeable batteries based on liquid electrolyte such as ethers and carbonate esters are common due to the flammability of organic solvent and hazards of electrolyte leakage. In recent years, solid-state sodium batteries have attracted extensive attention because of their improved safety, considerable energy density, and low cost. Nevertheless, high-performance solid-state electrolyte and compatible interface are still absent and need to be further developed for constructing solid-state sodium batteries. The development and recent advances of solid-state electrolyte and concomitant interface issues for sodium batteries are systematically summarized in this review. We discuss the fundamental principles in the design of solid-state electrolyte with high ionic conductivity, high transference number, and high chemical/electrochemical stability. Furthermore, we highlight the design of interface between electrolyte and electrode, which is the key challenge in developing high-performance solid-state sodium batteries. Thus, future investigations of solid-state sodium batteries should focus on anode/electrolyte/cathode interface through the combination of theoretical calculations and experimental studies. Meanwhile, large-scale production of high-performance solid-state electrolyte via a facile and scalable method with low cost is also necessary. This review introduces the development and recent progress of different types of solid-state electrolyte for sodium batteries, including β-alumina, NASICON, sulfide-based electrolyte, complex hydrides, and organic electrolyte. In particular, the transport mechanism, ionic conductivity, ionic transference number, chemical/electrochemical stability, and mechanical properties of solid-state electrolyte for sodium batteries are summarized. Meanwhile, the interface issues of anode/electrolyte/cathode (interfacial contact and chemical compatibility) are discussed in depth with the aim of constructing high-performance solid-state sodium batteries.