Zeolitic Imidazolate Framework-67-Derived Co3O4/α-MnO2 Composite as an Efficient Cathode for Aqueous Zinc-Ion Batteries

Co3O4/alpha-MnO2 composite was prepared as an efficient cathode host for zinc-ion battery (ZIB) application by utilizing a cobalt-based zeolitic imidazolate framework (ZIF-67) template. alpha-MnO2 nanorods with an open end served as foreign particles that introduced structural inhomogeneity, thereby facilitating the process of heterogeneous nucleation of ZIF-67 crystals to form Co3O4/alpha-MnO2 composite. CR-2032 coin cell configuration was used to evaluate the electrochemical performance of the Zn//Co3O4/alpha-MnO2 battery in an electrolyte mixture containing 2 M ZnSO4 and 0.1 M MnSO4 aqueous solution. The battery delivered 243.51 and 140.2 mAh<middle dot>g(-1) of initial discharge capacities at C-rates of 0.4 and 4 C, respectively (1 C = 248.67 mA<middle dot>g(-1)). The cycling performance tests for 300 cycles were performed at different values of C-rate, namely, 0.4, 1.2, 2, and 4 C, with discharge capacity retentions of 88.88, 86.16, 90.78, and 100.39%, respectively. Moreover, the long-term cycling test at 4 C for the assembled Zn//Co3O4/alpha-MnO2 battery showed a high discharge capacity retention of 90.59% after 2000 galvanostatic charge-discharge cycles with nearly 100% Coulombic efficiency. The present work also provided the calculation of the Zn2+ diffusion coefficient using the cyclic voltammetry technique, with the calculated values of Zn2+ diffusivity in the order of 10(-9) cm(2)<middle dot>s(-1). Furthermore, the viability of the Zn//Co3O4/alpha-MnO2 battery for practical implementation was also examined by self-discharge test, which showed similar to 86.9% of open-circuit voltage retention over a period of 60 days. The present work paves the way for practical implementation of aqueous ZIBs using Co-Mn-based cathodes.