| As one of the new energy storage devices,supercapacitors have excellent energy storage performance.Transition metal oxides/hydroxides have become candidate materials for supercapacitors due to their high theoretical specific capacitance.However,low conductivity and small specific surface area limit their practical applications.As a member of carbon-based materials,hollow carbon spheres（HCS）have the advantages of high conductivity,large specific surface area and good mechanical strength.At the same time,the cavity in the HCS structure is conducive to the penetration and storage of electrolyte ions.Therefore,we prepared two transition metal compounds（manganese dioxide and nickel hydroxide）and used them to integrate with HCS as electrode materials for supercapacitors.At the same time,the electrochemical performances of the composites were tested.The main contents of this work are as follows:（1）Mn O2 nanoflakes anchored on the inner and outer surface of hollow carbon spheres（Mn O2/HCS）were obtained via the first synthesis of HCS and subsequent hydrothermal deposition of Mn O2.The as-prepared Mn O2/HCS nanostructures were investigated as electrode materials of asymmetric supercapacitors.It was found that the large specific surface area of HCS effectively promoted the dispersion and electroactive sites of Mn O2.The close contact between HCS and Mn O2 enhanced the stability of the composite and subsequently boosted the electrochemical performance of Mn O2/HCS.Mn O2/HCS-30 possessed the best performance with a specific capacity of 209 F g-1 at the current density of 0.2 A g-1.The asymmetric supercapacitors（ASC）device consisting of Mn O2/HCS-30 as a positive electrode and HCS as a negative electrode in 1 M Na2SO4 electrolyte displayed a high energy density of26.8 W h kg-1 at the power density of 170.0 W kg-1.（2）Nitrogen-doped hollow carbon spheres（NHCS）were prepared by the modified St?ber method using silica as the sacrificial template and polydopamine as the carbon source,and hierarchical Ni（OH）2/NHCS were prepared via a simple chemical precipitation method.It was found that NHCS effectively inhibited the accumulation of Ni（OH）2and improved the utilization of active materials during the electrochemical reaction.The hollow structure of the composite facilitated the penetration of electrolyte ions,and shortened the transport path of electrolyte ions,and subsequently effectively enhanced the electrochemical performance of Ni（OH）2/NHCS.Ni（OH）2/NHCS exhibited a high specific capacitance of 1276 F g-1 at the current density of 0.5 A g-1,which was better than Ni（OH）2(967 F g-1).In addition,an asymmetric supercapacitor assembled with Ni（OH）2/NHCS as the positive electrode and activated carbon（AC）as the negative electrode could provide a high energy density of 25.4W h kg-1 at a power density of 374.9 W kg-1,and the capacity retention was 86.1%after 1000charge-discharge cycles. |
