Development of Na-ion battery electrolyte with high-performance electrochemical properties and high safety is still challenging to achieve. In this study, we report on a NASICON (Na 3 Zr 2 Si 2 PO 12 )-based composite hybrid solid electrolyte (HSE) designed for use in a high safety solid-state sodium battery for the first time. The composite HSE design yields the required solid-state electrolyte properties for this application, including high ionic conductivity, a wide electrochemical window, and high thermal stability.The solid-state batteries of half-cell type exhibit an initial discharge capacity of 330 and 131 mA h g À1 for a hard carbon anode and a NaFePO 4 cathode at a 0.2C-rate of room temperature, respectively.Moreover, a pouch-type flexible solid-state full-cell comprising hard carbon/HSE/NaFePO 4 exhibits a highly reversible electrochemical reaction, high specific capacity, and a good, stable cycle life with high flexibility.
Broader contextThe considerable interest in Na-ion batteries has continued to increase as a result of their applicability to large-scale energy storage systems, and also because of the high abundance and uniform worldwide distribution of Na and its corresponding low cost compared to Li. However, safety issues related to the use of conventional combustible organic electrolytes in large-scale batteries for vehicle or grid applications are of great concern. It is anticipated that such safety issues can be fully addressed through the use of non-flammable solid electrolytes in solid-state batteries. However, the application of solid ceramic and polymer electrolytes in batteries has led to poor electrochemical performance, which is primarily due to the resultant high solid-solid interface resistance. Thus, a new electrolyte strategy is urgently required in order to overcome this problem. In this work, a NASICON (Na 3 Zr 2 Si 2 PO 12 ) ceramic-based hybrid solid electrolyte (HSE) is proposed and shown to exhibit high electrochemical performances as a result of its decreased interface resistance, high thermal stability, and high electrochemical stability. Using the HSE, a flexible pouch-type full cell of hard carbon/HSE/NaFePO 4 is assembled for the first time, exhibiting good and stable cycle performance with a high capacity. † Electronic supplementary information (ESI) available: XRD, FT-IR, SEM-EDX, DSC, FT-Raman, Arrhenius plots, bond length of CF 3 SO 3 , shrinkage test, chargedischarge curves, photographs of a flexible solid-state Na battery, short-term cycling of flexible solid-state batteries with conducting and non-conducting ceramic. See
