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.