Simultaneous cation-anion regulation of sodium vanadium phosphate cathode materials for high-energy and cycle-stable sodium-ion batteries

Developing advanced Na3V2(PO4)3 (NVP) cathodes with both improved capacity and reversibility is of great importance for achieving next-generation sodium-ion batteries with high energy density and long lifespan, however, high-capacity cathode materials generally suffer from short cycle-life. In this study, a simultaneous cation-anion regulation strategy is put forward to design high-capacity and cycle-stable NVP cathode materials. Specifically, anionic silicate is introduced to substitute the phosphate and improve Na+-storage capacity, meanwhile, cationic K+ is introduced as pillar ions to stabilize the crystal structure and enhance the reversibility of the NVP cathodes. The as-achieved Na3.24K0.10V2.01(PO4)2.94(SiO4)0.14 (KSi-NVP) delivered a high capacity of 116.3 mAh g−1 at 0.5 C and an impressive structural stability with only an ultra-low capacity decay rate of 0.0056% per cycle at 20 C, outperformed pristine Na3V2(PO4)3 (109.4 mAh g−1 and 0.0290% under the same test conditions). After coupling a commercial hard carbon anode, the KSi-NVP cathode enabled an advanced full cell with high specific energy density of 348.2 Wh kg−1 and a long lifespan of 900 cycles at 5 C with a remarkable Coulomb efficiency (CE) of 99.99%.