Fig. 3. Charge and discharge curves of anatase TiO₂ (a) and TiO₂@Co₃O₄ (b) for 1, 2, 3, 10, and 100 cycles at a 0.2 C current density; (c) cyclic performance of anatase TiO₂, TiO₂@Co₃O₄, spinel Co₃O₄, and commercial graphite at a 2 C current density, with the coulombic efficiency diagram of TiO₂@Co₃O₄; (d) rate performance of anatase TiO₂, TiO₂@Co₃O₄, spinel Co₃O₄, and commercial graphite at current densities of 100 mA g⁻¹, 200 mA g⁻¹, 400 mA g⁻¹, 800 mA g⁻¹, and 1600 mA g⁻¹.