Ultrahigh-Rate-Performance Hierarchical Structured Na<sub>2</sub>Ti<sub>2</sub>O<sub>5</sub>@RGO Sodium-Ion Batteries and Revealing the Storage Mechanism Using In Situ Raman Spectroscopy
Xiaobin Zhong, Fan Gao, Chao He, Petar M. Radjenovic, Zhong‐Qun Tian, Jian‐Feng Li
Abstract
Due to sodium’s abundance and consequent affordability, sodium-ion batteries (SIBs) have attracted widespread attention as a cost-effective energy storage technology. However, poor cyclability at high current densities limits their practical applications. Owing to low volume changes during charge/discharge and high cycling stability, various sodium titanate based compounds have attracted considerable interest as anode materials. Despite this, Na2Ti2O5 has an unsatisfactory rate performance due to its sluggish Na-diffusion rates and low electrical conductivity. Herein, we show a novel anode nanocomposite material for SIBs with ultrahigh capacity and cycling stability composed of hierarchically structured Na2Ti2O5 nanofiber with reduced graphene oxide (Na2Ti2O5@RGO). Even with current density as high as 5000 mA g–1 (about 28 C), the capacity remained at ∼84 mA h g–1 after 10000 cycles. This outstanding performance and stability can be ascribed to the unique hierarchical structure of Na2Ti2O5 combined with RGO. Na2Ti2O5@RGO also exhibits an ultrahigh capacitive contribution ratio, which is critical for the superior performance. In a full battery setup containing a Na2Ti2O5@RGO anode, 36 LEDs could be illuminated simultaneously. Furthermore, the good reversibility and cycling stability of the Na2Ti2O5@RGO structure were proven using in situ Raman monitoring. These outlined results show that Na2Ti2O5@RGO has great potential for application as an energy storage technology with ultrahigh-rate charging/discharging.