All-solid-state sodium batteries enabled by flexible composite electrolytes and plastic-crystal interphase

Solid electrolytes with satisfactory ionic conductivity, good flexibility, and ideal interface compatibility are the key to developing next-generation solid-state rechargeable sodium metal batteries. Herein, nano-sized NASICON-type Na3Zr2Si2PO12 (NZSP) powders were firstly prepared by sol–gel method. After that, two kinds of high-performance polyethylene oxide/NZSP composite solid electrolytes were fabricated by solution-casting method, which exhibit high ionic conductivities (>10−4 S cm−1 at 55 °C), wide electrochemical window (>4.7 V vs. Na+/Na), and good capability to impede sodium dendrites. In order to build better transfer channels for sodium ions in cathode and relieve the volume change of cathode particles during cycling, succinonitrile interphase was introduced by a simple dispersing method. The all-solid-state Na0.67Ni0.33Mn0.67O2|Na batteries based on the two kinds of electrolytes both exhibit excellent electrochemical performances with high discharge capacity of 73.2 mA h g−1 (68.2 mA h g−1) and high capacity retention of 98.4% (97.6%) after 100 cycles at 0.5C and 55 °C. These results promise a splendid strategy for designing high performance all-solid-state sodium batteries.