Achieving ultra-high cycle stability of ZnCo2O4/SrF2-0.2 as positive electrode materials for supercapacitors: Realization and investigation of underlying mechanisms

The snowflake ZCO/SF-0.2 formed by SrF 2 modification of ZnCo 2 O 4 has excellent electrochemical properties . • The stable cathode materials of ZCO/SF-X supercapacitor with different morphologies were synthesized by modifying ZnCo 2 O 4 with SrF 2 . • The possibility of successful composite of SrF 2 and ZnCo 2 O 4 is confirmed by DFT theory, which proves that the composite has more stable structure and higher electrical conductivity. • The snowflake ZCO/SF-0.2 maintained 100% capacitance retention and Coulomb efficiency after 21,000 cycles of three electrodes, and 91.67% capacitance retention and 100% Coulomb efficiency after 40,000 cycles of two electrodes. • The ZCO/SF-0.2 and AC assembled HSC has an energy density of 63.28 Wh/kg at a power density of 850.03 W/kg and an impressive energy density of 40.85 Wh/kg at a power density of 8500.58 W/kg. Electron/ion transport dynamics and cyclic stability are the keys to research supercapacitor devices. In this paper, we designed the snowflake ZnCo 2 O 4 /SrF 2 -0.2 composite by a simple one-step hydrothermal process. By changing the number of metal sources, adjusting the core–shell, adjusting the interaction, and exerting the synergistic effect between materials, ZCO/SF-X composites with different morphologies were synthesized. The feasibility of the composite between the two materials is discussed by DFT theory. The overall energy of the successful composite of ZnCo 2 O 4 and SrF 2 is lower, and a more stable structure is formed. When ZnCo 2 O 4 is combined with SrF 2 , the carrier density near the Fermi level is enhanced, and the electrical conductivity is enhanced, thus facilitating charge transport. Specifically, the snowflake ZCO/SF-0.2 active electrode has a specific capacitance of 1086C/g at a specific current of 1 A/g. After more than 21,000 cycles, the specific capacitance is maintained at 100 %, and the coulomb efficiency is maintained at 100 %, showing excellent cycle stability. The assembled HSC has an energy density of 63.28 Wh/kg at a power density of 850.03 W/kg and an impressive energy density of 40.85 Wh/kg at a power density of 8500.58 W/kg. Importantly, after 40,000 cycles, the specific capacitance is maintained at 91.67 %, which is further confirmed by the density universal function calculation. The snowflake ZCO/SF-0.2 electrode synthesized by a simple method overcomes the inherent volume expansion problem of the material, forms a more stable structure, and shows unprecedented cyclic stability. This strategy provides a new method and idea for improving the performance of electrode materials, and opens up a new road for efficient electrode materials. Guidance is provided for designing devices for energy conversion and storage.