| Owing to the ever-increasing requirement of sustainable power source,portable energe devices with high performance have become a research hotspot.Among numerous electronics,all-solid-state asymmetric supercapacitor has been supposed as one of the most potential energy conversion-storage devices,depending on its excellent electrochemical properties such as rapid charge-discharge rate,high power denstity and long lifetime.Nevertheless,developing devices with further improving energy density and cycling life while maintain high power density is still the major challenge to solve the practical application problem of supercapacitors.Metal compounds such as metal oxides,metal hydroxides and metal selenides,delivering the properties of adjustable composition,controllable morphology,high specific surface area and high theoretical capacitance,can improve the energy density of supercapacitors.However,metal compounds are prone to expansion during the charge-discharge process,exhibiting low conductivity and poor ion diffusion performance.Therefore,it is urgent to focus on the tunable control of material composition,construction of special nanostructures,as well as reasonable matching of positive and negative electrode materials,exploring the high-performance metal compound-based supercapacitor electrode materials to develop functional devices with high rate capability and energy density,while maintaining high power density and long cycle life.In this study,four kinds of metal oxiede/selenide based electrode composites with hierarchical structure are designed and prepared.The controllable preparations of these materials are explored while the electrochemical properties of the electrode materials and the assembled asymmetric hybrid supercapacitor（ASC）are tested.Besides,we analysed the energy storage mechanism of the composites.The main researches are as follows:（1）SnO2 hollow spheres with uniform size were prepared by hydrothermal method without template,the growth process of which was in accordance with Ostwald ripening mechanism.An in-situ polymerization process of PANI was optimized to form hollow spherical SnO2/PANI 3D network structure.The unique structure SnO2 created a rapid electronic transmission path and relieved the volume change during the charge-discharge process.Simultaneously,the conducting PANI provided the composite a higher electronic conductivity and hold the whole structure stability as well.The prepared SnO2/PANI electrode exhibits excellent electrochemical performance compared with other composite with different morphologies:It shows greatly enhanced specific capacitance of 477.0 F g-1 at a current density of 1 A g-1.Significantly,there is no obvious specific capacitance loss after 3000 charge discharge cycles.These intriguing features can be attributed to the ineraction between SnO2 hollow spheres and PANI network.（2）TiO2-C nanowire arrays（NWAs）were grown vertically on the flexible carbon cloth substrate by simple hydrothermal method followed with heat treatment.PANI was coated on the surface of TiO2-C nanorods by electrochemical deposition to make a core-shell structure and form a continuous PANI conductive three-demesional network between isolated TiO2-C nanorods.The electrochemical energy storage mechanisms of PANI and TiO2-C@PANI electrodes were explored,which were surface capacitive controlled behavior and battery-type capacitor,respectively.The carbon in the TiO2-C NWAs not only brings considerable double layer capacitance to the composite,but also promotes the electrochemical deposition process of PANI.Compared with other PANI based materials,the TiO2-C@PANI40 electrode material shows superior electrochemical performance:when the current density is 1 A g-1,the electrode shows remarkable mass specific capacitance of 1818 F g-1;After 5000charge-discharge cycles,it delivers 80%capacitance retention.Besides,the assembled TiO2-C@PANI//AC ASC device obtains a high energy density of 32.4 Wh kg-1 at a power density of 850 W kg-1.（3）TiO2/C@（Ni,CO）Se2 nanorod arrays（NRAs）were fabricated on a flexible carbon cloth substrate by solvothermal reaction and hydrothermal process.The reaction kinetic of the TiO2/C@（Ni,CO）Se2 electrode material confirms the combined effect between surface capacitive process and diffusion process.Therefore,the electrode exhibits the characteristics of high specific capacitance from battery-type material and high rate performance from surface capacitive material.The area specific capacitance of the composite is 5.780 F cm-2 at 2 mA cm-2,which remains 92.2%of the initial surface capacitance at the current density of 10 mA cm-2.In addition,an excellent capacitance retention rate of 92.55%over 12000 cycles is acquired.The voltage window of the assembled TiO2/C@（Ni,CO）Se2//ZC ASC device is broadened to 1.8 V,and achieves a energy density of 43.13 Wh kg-1 when the power density is900.0 W kg-1.It is worth noting that the device shows extraordinary cycle stability of90%specific capacitance retention after 20000 charge-discharge cycles.（4）With an activated carbon cloth as electrode substrate,arranged（Ni,CO）Se2@NiCoLDH（layered double hydroxide）nanoarrays were prepared through simple hydrothermal reaction and electrodepositon process.The one-dimensional（Ni,Co）Se2 nanorod arrays can offer an efficient electronic transport channel and sustain the mechanical stability of material as a support framework.Meanwhile,the ultrathin NiCoLDH nanosheets can supply larger active surface areas as well as more hierarchical paths to improve the ionic/electric diffusion between the electrolyte and the electrode material.The hierarchical（Ni,Co）Se2@NiCoLDH nano-coral structure presents gratifying electrochemical properties,including desirable specific capacity of 5.30 C cm-2(1060 C g-1,10.59 F cm-2)at a current density of 2 mA cm-2 and remarkable rate capability of 82.5%capacity retention when the current density is increased to 30 mA cm-2.Nevertheless,the as-obtained（Ni,Co）Se2@NiCoLDH//AC ASC device exhibits a ultrahigh energy density of 54.70Wh kg-1 at the power density of 400.0 W kg-1 and an exceptional cycling stability of 84.7% after 5000 cycles. |
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