具有高倍率性能的还原氧化石墨烯包覆MnO微球负极用于锂离子电容器

Reduced graphene oxide encapsulated MnO microspheres as an anode for high-rate lithium ion capacitors

发展一种具有优异脱/嵌锂能力且存在稳定放电平台的负极材料是解决锂离子电容器(LICs)负极动力学性能较差以及提升循环稳定性的关键。本文通过溶剂热和热处理制备了一种还原氧化石墨烯(rGO)包覆MnO微球(~2μm)的复合材料(MnO/rGO)。电化学测试表明,MnO/rGO材料表现出较好的循环稳定性(在0.1 A g~(-1)的电流密度下循环110圈后比容量为846 mAh g~(-1))和良好的倍率性能(在6.2 A g~(-1)时比容量为207 mAh g~(-1))。通过对锂离子存储的动力学行为进行分析,表明赝电容性贡献对容量存储起主要作用。以MnO/rGO为阳极,活性炭(AC)为阴极组装的MnO/rGO//AC LICs,在10 350 W kg~(-1)的功率密度下,具有98 Wh kg~(-1)的高能量密度,并且在1.6 A g~(-1)的电流密度下循环5 000圈后容量保持率为71%。

Developing an anode material with high-rate Li+intercalation and stable charge/discharge platform is important for achieving high performance lithium ion capacitors(LICs).Reduced graphene oxide(rGO)-encapsulated MnO microspheres(~2μm)are obtained by a simple process including solvothermal and calcination techniques.The material contains a large number of mesopores(~2.8 nm diameter).The MnO/rGO has a favorable cycling stability(846 mAh g-1 at 0.1 A g-1 after 110 cycles)and an outstanding rate performance(207 mAh g-1 at 6.4 A g-1).Kinetic analysis reveals that a pseudocapacitive contribution plays a dominant role for the energy storage.The improvement in the pseudocapacitive behavior is ascribed to the fact that the uniform rGO coating on the MnO provides continuous pathways for electron transport,and the mesoporous structure provides numerous migration paths for Li-ions.Furthermore,MnO/rGO//activated carbon(AC)LICs have a high energy density of 98 Wh kg-1 at a relatively high power density of 10350 W kg-1,and have a capacity retention of 71%after 5000 cycles at 1.6 A g-1.These outstanding results indicate that the enhanced Li+intercalation of the anode offsets the kinetic imbalance between the two electrodes.