Doping of Potassium by Partial Substitution of Sodium in Sodium Trititanate for Improved Sodium-Ion Storage Properties

Layered sodium trititanate (Na2Ti3O7, NTO) is a safe and cost-effective anode material for sodium-ion batteries. However, its sluggish Na+ diffusion kinetics, poor electron conductivity, and unstable layered structure against cycling pose major barriers for practical applications. Here, we show a novel doping strategy for improving Na+ storage properties of NTO. Instead of doping transition metals in the Ti4+ site, doping of alkaline metal K+ by partial substitution of Na+ in NTO is demonstrated. The K+-doped NTO displays enhanced Na+-storage capacity and transport kinetics, as well as improved cycling stability. It delivers a reversible Na+ storage specific capacity of 162 mAh g−1 at 0.1C, a capacity retention of 75 % after 8200 cycles at 1C or after 4000 cycles at 10C. In situ X-ray diffraction characterization and density functional theory calculation results reveal that the improved performance is mainly attributed to increased exposure of the Na+ storage (100) plane, widened interlayer spacing and stabilized layered structure. A full cell assembled with the K+-doped NTO as anode and Na3V2(PO4)3@C as cathode delivers a specific energy density of 165 Wh kg−1. This work provides an alternative approach to modifying NTO for improving its Na + storage properties.