An ultrathin defect-rich Co₃O₄ nanosheet cathode for high-energy and durable aqueous zinc ion batteries

The rational design of cathodes with high capacity, rate capability and stability is intriguing but challenging to achieve state-of-the-art aqueous Zn-based batteries. Co₃O₄ has aroused intense interest as cathodes of Zn-based batteries based on its attractive merits of high theoretical capacity in alkaline electrolytes and good thermodynamic stability. Unfortunately, the poor electric conductivity and insufficient active sites of Co₃O₄ materials impede their more extensive applications. Herein, a facile solvothermal reduction strategy is demonstrated to introduce oxygen defects into the ultrathin Co₃O₄ nanosheets (R–Co₃O₄), which function as an advanced cathode for Zn//Co batteries. In comparison with pristine Co₃O₄, the solvothermal reduction process can endow the R–Co₃O₄ sample with improved electric conductivity, enhanced specific surface area and enriched active sites. As a result, the alkaline Zn//Co battery with the R–Co₃O₄ cathode presents a considerable capacity (240.8 mA h g⁻¹), good rate performance and excellent stability. Furthermore, an admirable energy density of 295.5 W h kg⁻¹ (14 mW h cm⁻³) is achieved by this Zn//Co battery, surpassing that of most reported aqueous rechargeable batteries.