Sulfur-doped carbon nanosheet anode with superior rate performance of sodium-ion storage in ether-based electrolyte

Heteroatom doping is a universal approach to improve rate capability for various carbon anodes of sodium-ion batteries (SIBs) owing to the interlayer spacing expansion and pseudocapacitive enhancement. However, there is still a limitation for ion adsorption of internal voids and dopants in the bulk phase of carbon materials due to the sluggish intercalation kinetics of large-size sodium ions. In this work, the highly sulfur-doped carbon nanosheets are synthesized and investigated as the anode of SIBs. It shows that the electrochemical performance in ether-based electrolytes significantly outperforms that in ester-based electrolytes. The carbon anodes exhibit a specific capacity of 617 mAh·g⁻¹ at 100 mA·g⁻¹ after 300 cycles, especially an outstanding rate performance of delivering specific capacities of 305 and 191 mAh·g⁻¹ at current densities of 10 and 50 A·g⁻¹, respectively. It is speculated that the ion-storage kinetics was greatly enhanced in ether-based electrolytes owing to the better accessibility of sodium-ion diffusion from electrode interfaces to internal hosts. As a result, the carbon nanovoids and sulfur dopants in the bulk phase are efficiently activated for ion storage. This work provides a new insight into the ion-storage mechanism optimization of carbon materials for SIBs.