| Lithium-ion batteries have high energy density,while supercapacitors have high power density and excellent cycle performance.In order to combine the advantages of them,lithium-ion capacitors constructed from battery-type anode,capacitor-type cathode materials,and organic electrolytes have been emerged.Lithium-ion capacitors are more promising for achieving the above-mentioned excellent performance.Metal sulfides have attracted much attention because they own high theoretical capacity and can be used as electrode materials for constructing high-performance lithium ion capacitors.Graphene nanosheets/Fe S2(GNS/Fe S2)composites were prepared by thermal decomposition and solvothermal methods.It can be seen from scanning electron microscopy and transmission electron microscopy that Fe S2 nanoparticles are uniformly attached to graphene nanosheets.Electrochemical tests have shown that when the graphene content is24%(GNS/Fe S2-24),it has the best electrochemical performance in the half-cell.Lithium-ion capacitors were assembled by matching GNS/Fe S2-24 with activated carbon,and show the best performance when the mass ratio of positive and negative active materials is 2:1.The maximum energy density and power density are 104 Wh·kg-1 and 17589 W·kg-1,respectively.Moreover,the cycle performance is excellent,which shows 92.5%capacity retention after circulating 5000 cycles at a current density of 1000 m A·g-1.Graphene nanosheets/Ni-5-Sn S2(GNS/Ni-5-Sn S2)composites were prepared by hydrothermal method.The Ni-5-Sn S2 nanoparticles of about 27 nm are uniformly dispersed on graphene.In the electrochemical performance test,the composite material with a graphene content of 10%(GNS/Ni-5-Sn S2-10)shows the highest electrochemical performance.The GNS/Ni-5-Sn S2-10//AC lithium ion capacitor was assembled by matching it with commercial activated carbon.Lithium-ion capacitors fabricated with positive and negative mass ratios of3:1 exhibits the best electrochemical performance.Its maximum energy density and power density are 133 Wh·kg-1 and 21270 W·kg-1,respectively.Additionally,it shows excellent cycle stability(92.2%retention after 5000 cycles at 1000 m A·g-1).The graphene nanosheets/Co-Sn-S-Se(GNS/Co-Sn-S-Se)composites were prepared by solvothermal method.The hollow Co-Sn-S-Se cubes are uniformly dispersed on graphene.Electrochemical test results show that the composite material(GNS/Co-Sn-S-Se-10)with10%graphene content has the best electrochemical performance.By matching GNS/Co-Sn-S-Se-10 with activated carbon,a lithium-ion capacitor with excellent performance and a mass ratio of positive and negative active materials of 2:1 was obtained.Its maximum energy density and power density are 124 Wh·kg-1 and 20672 W·kg-1,respectively.In addition,GNS/Co-Sn-S-Se-10//AC has good cycle stability,and the capacity retention rate is as high as 79.1%after 5000 cycles at the current density of 1000 m A·g-1. |
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