Rational synthesis of Cu7Se4-CuxCo1-xSe2 double-shell hollow nanospheres for high performance supercapacitors

Novel bimetallic copper cobalt selenide (CCS) hollow nanosphere composites are synthesized with a self-template method. Instead of making the reaction more complete, the optimized Cu7Se4−CuxCo1-xSe2 composite is obtained by hydrothermal treatment with a relatively short time (CCS-2h). Such a composite electrode not only exhibits a specific capacitance of 349.1 F g−1 at 1 A g−1, a good rate performance of 80.1% capacitance retention with current density increased to 20 A g−1, but also exhibits a superior electrochemical stability of 106.4% capacitance retention after 5000 cycles. The asymmetric supercapacitor assembled by CCS-2h and activated carbon electrodes also exhibits a good energy density of 26.84 Wh kg−1 at 700 W kg−1, and a good cycling performance of 94.1% capacitance retention after 5000 cycles. This work not only demonstrates the application potential of transition metal selenides composites in supercapacitors, but also suggests a new method for designing high-performance supercapacitor materials.