High electrochemical performance is important to achieve practical application of energy storage devices. It has been found recently that it is hard to achieve high capacity and high stability simultaneously using a single electrode material. Thus, constructing composite electrode materials which can combine the advantages of different materials together is an efficient approach to improve the electrochemical properties. In this work, we have built a vacancy‐rich MnO_2−x/reduced graphene oxide (rGO) composite film through a facile one‐step route. In the synthesis process, GO nanosheets were reduced into rGO to improve the electronic conductivity, while Mn²⁺ was oxidized to MnO₂ with vacancies. The obtained vacancy‐rich MnO_2−x/rGO composite showed a superior electrochemical performance: The specific capacitance reached 675.5 F/g at a current density of 0.5 A/g and the material demonstrated high capacitance retention (96.1 % after 10000 cycles). Besides, the symmetric electrochemical capacitor based on the vacancy‐rich MnO_2−x/rGO composite electrode can achieve a high energy density (8.42 mWh/cm³) and power density (3.78 W/cm³) as well as excellent stability.

中文翻译：

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高电化学性能的空位丰富的MnO2-x /还原氧化石墨烯复合膜的一步合成

高电化学性能对于实现储能装置的实际应用很重要。最近发现，使用单一电极材料难以同时实现高容量和高稳定性。因此，构建可以将不同材料的优点结合在一起的复合电极材料是提高电化学性能的有效方法。在这项工作中，我们通过一条简便的单步路线构建了一个空位丰富的MnO ₂ - _x /还原氧化石墨烯（rGO）复合膜。在合成过程中，GO纳米片被还原为rGO以提高电子电导率，而Mn ²⁺被空位氧化为MnO ₂。获得的富空位MnO _2−x / rGO复合材料显示出优异的电化学性能：在0.5 A / g的电流密度下，比电容达到675.5 F / g，并且该材料显示出高的电容保持率（10000次循环后为96.1％）。此外，基于富空位MnO _{2− x} / rGO复合电极的对称电化学电容器可实现高能量密度（8.42 mWh / cm ³）和功率密度（3.78 W / cm ³）以及出色的稳定性。