Recently, Ma Yanwei's team from the Institute of Electrical Engineering of the Chinese Academy of Sciences and Wu Zhongshuai, a researcher at the Dalian Institute of Chemical Physics, have made progress in the preparation of high-performance graphene composite materials and the development of graphene-based lithium-ion capacitors.
As a new type of electrochemical energy storage device that effectively combines lithium-ion batteries and super capacitors, lithium-ion capacitors have high power density, high energy density, and long cycle life, effectively compensating for the performance differences between lithium-ion batteries and super-capacitors. As an important part of lithium-ion capacitors, electrode materials are the key factors affecting the performance of lithium-ion capacitors.
Fine structural design engineering is considered to be one of the effective ways to improve the electrochemical performance of electrode materials. We propose a general electrostatic self-assembly strategy to in situ grow MnO composite nanomaterials (rGO/MnO) with a cabbage structure on reduced graphene oxide. Through in-situ experimental characterization and theoretical calculations, it is confirmed that the rGO/MnO heterostructure has strong interfacial interaction and good lithium storage kinetics. Due to the high charge transfer rate, abundant reaction sites, and stable heterostructures of rGO/MnO composite nanomaterials, the electrodes prepared based on rGO/MnO composite nanomaterials have high specific capacity (the specific capacity at 0.1 A/g current density is 860 mAh/g), excellent rate performance (specific capacity of 211 mAh/g at 10 A/g), and long-cycle stability. Therefore, rGO/MnO composite nanomaterials can be used as ideal anode materials for high-performance Li-ion capacitors.
By assembling this high-performance graphene-based composite as anode and activated carbon cathode, a flexible solid-state Li-ion capacitor (AC//rGO/MnO) was prepared. After testing, the capacitor has an energy density of up to 194 Wh/kg and a power density of up to 40.7 kW/kg based on the total mass of the electrode active material. This is the highest energy density and power density reported to date for flexible solid-state Li-ion capacitors. In addition, after 10,000 charge-discharge cycles, the capacity retention rate of the AC//rGO/MnO capacitor can reach 77.8% with high safety performance.
The metal oxide/graphene composite design strategy proposed in this study has great application prospects in flexible Li-ion capacitors with high energy density and high power density.