Sodiation and Delithiation of Li4Ti5O12 for the Synthesis of Spinel-Type Sodium Titanium Oxide as an Anode Material for Sodium-Ion Batteries

Abstract

Spinel-type sodium titanium oxide, Na3LiTi5O12 (NTO) has a structure analogous to that of Li4Ti5O12 (LTO) and is a promising anode material for sodium-ion batteries exhibiting good cyclability. However, the synthesis of NTO using LTO is a tedious process and requires more than nine iterated procedures, which involves the reductive insertion of Na+ in a glovebox, followed by oxidation using water, and subsequent extraction of Li+. Therefore, in this study, a efficient method was developed for the conversion of LTO to NTO. The conversion ratio of sodiated LTO to NTO during water oxidation was determined from the quantity of Li+ released into water, which was evaluated using ion chromatography. The results revealed that the conversion ratio was approximately 53 mol% at 273 K but decreased to 45 mol% at 303 K confirming its temperature dependence. Moreover, the sodiation of LTO could be accelerated via stirring, ultrasonication, and heating to 323 K. NTO was successfully produced via five treatment cycles using a method without using the glovebox. The half-cell employing the obtained NTO afforded a capacity of 125 mA h g−1, and stable cyclability for up to 200 cycles, with a retention ratio of 97.6% and a coulombic efficiency of 99.8%.