Anionic chemistry regulation boosting the reversible redox in CoSexTey@C polyhedrons for sodium storage

CoTe 2 as a potential electrode material for sodium-ion batteries (SIBs) suffers severe volume expansion and rapid capacity degradation. Herein, we propose an anionic chemistry regulation strategy to enhance the redox performance of CoTe 2 by Se substitution which creates more porosity inside the structure to accommodate the volume expansion. Physical characterizations and theoretical calculations have studied the structural and dynamical influence of Se/Te ratio on the overall performance. As a result, CoSe 1.33 Te 0.67 @C with a 〈1   1   1〉 preferential growth direction exhibited the most balanced performance, which delivered a high initial specific capacity of 795 mAh/g at 0.05 A/g, a high rate performance of 5 A/g and a capacity retention of 370 mAh/g after 400 cycles at 0.5 A/g. Accordingly, a full SIB was constructed with a Na 3 V 2 (PO 4 ) 3 cathode and a CoSe 0.67 Te 0.33 @C anode, delivering a maximum energy density of 197.2 Wh kg −1 . These results have proved that anionic chemistry regulation is quite efficient to synthesize metal tellurides with high redox activity and long life-span for SIB .