Ultrahigh-Rate-Performance Hierarchical Structured Na2Ti2O5@RGO Sodium-Ion Batteries and Revealing the Storage Mechanism Using In Situ Raman Spectroscopy

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 (about 28 C), the capacity remained at similar to 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.