| Summary: | Cobalt hydroxide is a widely studied electrode material for supercapacitor and alkaline zinc ion batteries. The large interlayer spacing of Co(OH)<sub>2</sub> is also attractive to store Zn ions. However, Co(OH)<sub>2</sub> is quite unstable in the acidic ZnSO<sub>4</sub> electrolyte due to its amphoteric nature. Herein, we synthesized a mixed phase of Co(OH)<sub>2</sub>/CoOOH via a two-step electrochemical preparation. As the cathode material for an aqueous zinc ion battery (AZIB), Co(OH)<sub>2</sub>/CoOOH delivered a maximum capacity of 164 mAh g<sup>−1</sup> at 0.05 A g<sup>−1</sup> and a high energy density of 275 Wh kg<sup>−1</sup>. Benefiting from the low charge-transfer resistance, a capacity of 87 mAh g<sup>−1</sup> was maintained at 1.6 A g<sup>−1</sup>, showing a good rate performance of the mixed phase. Various spectroscopy analyses and simulations based on the density functional theory (DFT) suggested a higher thermal stability of the mixed phase than pure Co(OH)<sub>2</sub>, due to its less local structural disorder. The reduced Co-Co and Co-O shells increased the mechanical strength of the mixed phase to accommodate Zn<sup>2+</sup> ions and endure the electrostatic repulsion, resulting in an enhanced cycling stability. The mixed phased also delivered a good stability at the current density of 0.05 A g<sup>−1</sup>. After 200 cycles, a capacity retention of 78% was retained, with high Coulombic efficiencies. These results provide a new route to synthesize high-performance LDH for aqueous zinc ion batteries.
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