Na_1.68H_0.32Ti₂O₃SiO₄·1.76H₂O as a Low-Potential Anode Material for Sodium-Ion\nBattery

Abstract

Sodium-ion batteries\n(SIBs) have been considered as a promising candidate for large-scale\nenergy storage applications, because of the low cost of sodium element\nand a broad choice of cathode materials which do not contain expensive\nraw materials. However, a lack of promising anode materials still\nhinders the development of SIBs technology. Herein, we for the first\ntime report a new one-dimensional tunnel-structure anode material,\nNa_1.68H_0.32Ti₂O₃SiO₄·1.76H₂O, for SIBs. This material can deliver\na reversible capacity of 110 mAh g^–1 at a current\ndensity of 20 mA g^–1 and with an average working\nvoltage of 0.4 V vs Na⁺/Na. The structure changes of this\nmaterial during discharge/charge processes were investigated by using\nin situ laboratory X-ray diffraction. The results indicated that sodium\ninsertion proceeds via a topotactic intercalation pathway. We also\nidentified predehydration as an effective avenue to further improve\nthe capacity of Na_1.68H_0.32Ti₂O₃SiO₄·1.76H₂O anode (reversible\ncapacity of 131 mAh g^–1 at a current density of\n20 mA g^–1 after the predehydration process).