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

Abstract

CoTe2 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 CoTe2 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, CoSe1.33Te0.67@C with a 〈111〉 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 Na3V2(PO4)3 cathode and a CoSe0.67Te0.33@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.