High content anion (S/Se/P) doping assisted by defect engineering with fast charge transfer kinetics for...

The rate-determining process for sodium storage in TiO₂ is greatly depending on charge transfer happening in the electrode materials owing to its inferior diffusion coefficient and electronic conductivity. Apart from reducing the diffusion distance of ion/electron, the increasement of ionic/electronic mobility in the crystal lattice is also very important for charge transport. Here, an oxygen vacancy (OV) engineering assisted in high-content anion (S/Se/P) doping strategy to enhance charge transfer kinetics for ultrafast sodium-storage performance is proposed. Theoretical calculations indicate that OV-engineering evokes spontaneous S doping into the TiO₂ phase and achieves high dopant concentration to bring about impurity state electron donor and electronic delocalization over S occupied sites, which can largely reduce the migration barrier of Na⁺. To realize the speculation, high-content anion doped anatase TiO₂/C composites (9.82 at% for S in A-TiO_2-x-S/C) are elaborately designed. The optimized A-TiO_2-x-S/C anode exhibits extraordinarily high-rate capability with 209.6 mAh g^-1 at 5000 mA g^-1. The assembled sodium ion capacitors deliver an ultrahigh energy density of 150.1 Wh kg^-1 at a power density of 150 W kg^-1 when applied as anode materials. This work provides a new strategy to realize high content anion doping concentration, and enhances the charge transfer kinetics for TiO₂, which delivers an efficient approach for the design of electrode materials with fast kinetic.