Fig. 2. Half-cell electrochemical performances of the (Mg_0.2Ti_0.2Zn_0.2Cu_0.2Fe_0.2)₃O₄ electrode for LIBs. (a) Representative cyclic voltammetry (CV) curves at a scanning rate of 0.2 mV s⁻¹ in the voltage range of 0.01–3.00 V versus Li⁺/Li; (b) cycling performances and the corresponding coulombic efficiencies at 100 mA g⁻¹ for 300 cycles; (c) discharge–charge voltage profiles for the 1st, 2nd, 10th, 100th, 200th and 300th cycles in the voltage range of 0.01–3.00 V at a current rate of 100 mA g⁻¹; (d) rate performance at different current densities ranging from 100 to 2000 mA g⁻¹; (e) the discharge–charge curves under different current densities; (f) Nyquist plots of the (Mg_0.2Ti_0.2Zn_0.2Cu_0.2Fe_0.2)₃O₄ electrode: before cycling (at the open circuit voltage, 3.0 V) and after 300 cycles (at the specific charge voltage, 3.0 V) at a current density of 100 mA g⁻¹; (g) cycling performances and the corresponding coulombic efficiencies at 2000 mA g⁻¹ for 800 cycles.