In-situ synthesis TiO2 nanosheets@rGO for ultrafast sodium ion storage at both room and low temperatures

Sodium ion (Na+) storage has attracted wide attention as an advanced large-scale energy storage system for our modern society. Due to the larger radius of Na+ than lithium ion, finding a suitable anode material for sodium ion batteries (SIBs) is a big challenge especially at low temperature. Here, an in-situ method which simultaneous reduction of graphene and oxidation of Ti3+ was used to synthesize a 3 dimensional (3D) TiO2@ reduced graphene oxide (TiO2@rGO) structure. The special 3D structure built with the basic structure units of TiO2@rGO heterojunctions could offer fast ion insertion/deinsertion, short diffusion distance, and lower diffusion energy barrier as well, thus enhance the Na+ intercalation pseudocapacitive process. The enhanced pseudocapacitive process could increase the kinetic reaction of the cell especially at the high current densities. The synthesized TiO2@rGO sample exhibits an outstanding electrochemistry performance as an anode material for SIBs with superior cycling and rate performance. At a current density of 7 A g−1, it showed a high capacity retention of above 90% and with a capacity decay of 0.0003% per cycle. Most importantly, owning to the fast electron exchange rate in the system, the cell shows an outstanding electrochemical performance at an ultra-low temperature of −40 °C.