A high-energy-density aqueous zinc–manganese battery with a La–Ca co-doped ε-MnO2 cathode†
Aqueous zinc–manganese dioxide batteries (Zn//MnO2) are gaining considerable research attention for energy storage taking advantage of their low cost and high safety. However, the capacity and cycling stability of the state-of-the-art devices are still utterly disappointing because of the inevitable MnO2 dissolution and its low conductivity. In this work, to elevate the energy density of Zn//MnO2, a La–Ca co-doping strategy is proposed to boost the electrochemical performance of the ε-MnO2 cathode. Specifically, the introduction of heteroatoms, La3+ and Ca2+, is achieved via a facile one-step liquid coprecipitation method. Our experimental results reveal that Ca2+ significantly improves the stability of ε-MnO2 while Ca2+ and La3+ both contribute to the capacity and reversibility enhancement. Therefore, the overall performance of the La–Ca co-doped ε-MnO2 cathode exceeds the pristine sample, as demonstrated by its commendable capacity of 297.3 mA h g−1 at 0.2 A g−1, superior cycle stability (up to 76.8% capacity retention after 200 cycles) and excellent rate capability (161 mA h g−1 when the current density increased to 1.6 A g−1). Besides, the assembled Zn//ε-MnO2 device delivers a maximum energy and power density of 401.22 W h kg−1 and 5.2 kW kg−1 respectively, outperforming most of the recently reported Zn//MnO2 counterparts.