A Novel Na-β″-Al<sub>2</sub>O<sub>3</sub> Nanosheet Enhanced Environmentally Friendly\nSolid Electrolyte for\na Highly Stable Na–Metal Battery

The use of low-cost and easy-to-prepare solid electrolytes\nis expected\nto yield sodium-ion batteries with good chemical and thermal stability.\nHowever, the current solid electrolytes generally suffer from the\ndefects of poor electrochemical performances, high fabrication cost,\ndemanding fabrication environment, and serious pollution caused by\nthe release of a large amount of organic solvents during the preparation\nprocess. Herein, an environmentally friendly polymer-based solid electrolyte\nwas prepared by using a water-soluble triblock copolymer (Pluronic\nF127), sodium perchlorate as sodium salt, and water as solvent. The\nwhole preparation process contains no organic pollutants and is accomplished\nunder an air atmosphere. In addition, the introduction of Na-β″-Al<sub>2</sub>O<sub>3</sub> nanosheet-like fillers not only improves the\nionic conductivity of the solid electrolyte by lowering the glass\ntransition temperature (<i>T</i><sub>g</sub>) and releasing\nmore free sodium ions, but also improves the stability of the electrolyte/sodium\nanode interface through the reaction of Na-β″-Al<sub>2</sub>O<sub>3</sub> with the sodium anode to form a stable solid\nelectrolyte interphase (SEI). The ionic conductivity and electrochemical\nwindow of the electrolyte were as high as 5.33 × 10<sup>–4</sup> S cm<sup>–1</sup> and 4.8 V, respectively. The assembled\nNa<sub>3</sub>V<sub>2</sub>(PO<sub>4</sub>)<sub>3</sub>/Na battery\nalso exhibited good rate and cycling performance, which could be charged\nand discharged at 1 C and stably cycled more than 500 times at 0.3\nC with a capacity retention rate of 95%. This low-cost environmentally\nfriendly and easy-to-manufacture sodium-ion solid electrolyte provides\na new idea and technology for the practical application of highly\nstable sodium-ion batteries.