Towards a Greener and Scalable Synthesis of Sodium Titanate Nanorods and Its Application as Anode in Sodium Ion Batteries

Abstract

Sodium ion batteries are accepted as LIB (lithium ion batteries) alternative to large scale energy storage, but its wide application is currently limited by both the synthesis and electrode materials. Thus, simple and scalable synthesis of electrode materials is desirable to lower the cost of synthesis. In this study, we report a surfactant-free, energy-efficient solid state synthesis to mass-produce uniform, single crystalline 1D metal oxide nanorods with tunable composition. To demonstrate the methodology, a series of single-crystalline Na2Ti3O7/Na2Ti6O13 nanorods with tunable composition are synthesized and applied in sodium ion batteries. By control of synthesis parameter, it provides an alternative low-temperature route to transform Na2Ti3O7 into Na2Ti6O13. The high theoretical capacity of Na2Ti3O7 and the low volume expansion of Na2Ti6O13 upon charge/discharge are synergistically exploited to achieve high electrochemical performance and stability. This synthesis method opens up a scalable, energy-saving route to mass-produce uniform 1D nanostructured electrode materials and fine-tune the composition and morphology according to performance demands. The electrochemical performance of Na2Ti3O7 and Na2Ti3O7/Na2Ti6O13 nanorods are compared to conventionally synthesized Na2Ti3O7 irregular particles. Na2Ti3O7 nanorods outperform Na2Ti3O7irregular particles at all current rates in the range of 0.1 to 5C. Without surface modification, the nanorods can still manifest a reversible discharge capacity of 70 mAh/g at a high current rate of 5C. The enhanced electrochemical performance can be attributed to the high surface area of the nanorods as well as efficient ion transport induced in highly uniform one-dimensional nanostructure.