| The advantages of sodium-ion hybrid capacitors combined with batteries and supercapacitors have attracted extensive attention in the field of high-energy and high-power storage.The key difficulty in the construction of high-performance sodium-ion hybrid capacitor is the dynamic difference between the slow Faraday reaction in the balanced anode and the fast non-faraday adsorption/desorption process in the cathode.Effective measures include the design of nano-electrode structures and pseudocapacitive materials with larger lattice spacings.Transition metal oxides have attracted much attention as anode materials for sodium ion batteries and hybrid capacitors.In this thesis,two kinds of transition metal oxides,Nb2O5 and TiO2,are discussed,and the properties of their respective electrochemical properties as anode of sodium ion hybrid capacitors are systematically studied.The main research contents and results encompass:(1)Sodium-ion hybrid capacitors based on Nb2O5 and activated carbon:Orthorhombic Nb2O5 nanowire(T-Nb2O5 NWs)was prepared by hydrothermal and ion exchange.At 0.25 C,the charging capacity can reach 273 mAh g-1,and the coulomb efficiency is 34.2%.When reaching 10 C,the charging capacity of 125 mAh g-1 can still be reached.In addition,the T-Nb2O5 NWs electrode was subjected to 10 C,1,000-turn deep cycle.It is worth noting that in the cyclic process,the stable capacity of 95.2-98.6 mAh g-1can still be maintained without obvious capacity attenuation.The sodium-ion hybrid capacitors with T-Nb2O5 NWs negative electrode and activated carbon positive electrode showed high energy/power density(106.2 Wh kg-1/78.3 W kg-1 and 47 Wh kg-1/4976 W kg-1)and stable cycle life in the voltage range of 1.0-4.3 V.Moreover,the obtained T-Nb2O5 NWs as a negative electrode assembled into a flexible sodium-ion hybrid capacitor,in the deformation conditions showed satisfactory performance.More encouragingly,we have designed a self-powered wearable sensor composite device by combining our flexible sodium-ion hybrid capacitor with a pressure sensor.(2)Sodium-ion hybrid capacitors based on Gr-Nb2O5 and activated carbon:Based on the previous studies in the field of CVD design of graphene materials in the research group,ultra-thin graphene was in-situ coated on the T-Nb2O5 NWs surface by PECVD(Gr-Nb2O5),and defect regulation was carried out at the same time to ensure the high electronic conductivity of graphene-coated layer and the efficient transmission of ions.The Gr-Nb2O5 electrode was thoroughly circulated at 10 C and 20 C.At 10 C,the capacity is stable at 153-171 mAh g-1,and at 20 C,the capacity is maintained at 133-147 mAh g-1,and there is no obvious attenuation in the cycle.The maximum energy density of our Gr-Nb2O5//AC hybrid capacitor is 112.9 Wh kg-1,and the power density is 80.1W kg-1.When the maximum power density is 5330 W kg-1,the capacitor can obtain a high energy density of 62.2 Wh kg-1.The negative electrode of Gr-Nb2O5 and the positive electrode of commercial activated carbon formed a sample of flexible sodium-ion hybrid capacitor,which showed stable and lasting electrochemical properties over a long lifespan under different deformation conditions and different bending release cycles.(3)Sodium-ion hybrid capacitors based on Gr-TiO2 and activated carbon:Ultra-long TiO2 nanotubes were prepared by oil bath method and ion exchange.Ultrathin graphene was coated on the surface of TiO2 in situ with PECVD(Gr-TiO2).At 5 C and 20 C,Gr-TiO2 electrode has good cyclic stability,and the capacity is stable at 110-125 mAh g-1 at 5 C and 95-100 mAh g-1 at 20 C.The maximum energy density of the Gr-TiO2 negative electrode and the activated carbon positive electrode of the sodium-ion hybrid capacitor is 71.59 Wh kg-1,and the power density is 72.2 W kg-1.The highest power density is 2216 W kg-1,at which time the hybrid capacitor enables an energy density of 31.39 Wh kg-1. |
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