The Application Of Ni-Based Compounds And Porous Carbon-Based Materials In Aqueous Supercapacitors

The energy crisis and environment crisis have promoted the research and development of new energy storage devices.Aqueous supercapacitors（ASC）,as a new kind of energy storage devices,are environmentally friendly,and have fast charging/discharging speed,long cycle life and other advantages.But,the energy density of ASC is not high,which is closely related to the electrochemical performance of positive and negative electrode materials.To improve the energy density of ASC,several positive and negative electrode materials with high specific capacity were prepared.The positive electrode materials are studied on Ni-based transition metal compounds.In view of the actually low specific capacity and poor rate capability of Ni-based transition metal compounds,the first half of this paper focuses on the construction of metal-rich phosphides,the construction of composites,and metal ion doping.Ni-based positive electrode materials with high specific capacity were obtained.The studied positive materials include ZnNi-Co-P quaternary metal phosphide（ZNCP-NF）,Ni-Mo-S@Ni-P composite material（NMPS）,Zn2+-doped NiSe₂@Ni（OH）₂ composite material.The negative electrode materials are based on porous carbon.Aiming at the problem that porous carbon has a low specific capacitance,the second half of this paper focuses on oxygen atom doping,building hierarchically porous structures,and constructing new composite material.The porous carbon-based negative electrode materials with high electrochemical performance were obtained.The studied negative electrode materials include oxygen doped hierarchically porous carbon（HPC）,antimonene nanosheet@oxygen doped hierarchically porous carbon（Sb@HPC）composite material.Finally,commercial activated carbon（AC）was replaced by optimized negative electrode,and the optimized positive and negative electrodes were assembled into aqueous asymmetric supercapacitors（AASC）to achieve a high energy density,which provides a strategy reference for developing ASC with high energy density.The specific chapters are as follows:The first chapter mainly introduces the development history,the overview of supercapacitors,the research progress of Ni-based transition metal compounds and porous carbon-based electrode materials in ASC,as well as the research background and content of this paper.In Chapter 2,ZNCP-NF nanowires binder-free electrode composed of Ni₂P,Co₂P and Zn4（PO4）2（OH）2·3H2O were grown on a nickel foam by a simple two-step method.The unique chemical composition of ZNCP-NF makes ZNCP-NF has a higher electrochemical reaction reactivity and conductivity.Thus the specific capacity of ZNCP-NF is much higher than that of ZNCO-NF at 10 A g^-1(1111 C g^-1).The assembled ZNCP-NF//AC AASC exhibits a specific capacity of 181.6 C g^-1 and an energy density of 37.59 Wh kg^-1 at 0.2 A g^-1.After 10000 charge/discharge tests at 2 A g^-1,the initial specific capacity of 92.68%is retained.The excellent electrochemical properties prove that ZNCP-NF is a good positive material for AASC.In Chapter 3,Ni-Mo-O materials were prepared on a nickel foam by hydrothermal method and converted into NMPS and Ni-Mo-S（NMS）by heat treatment.NMPS has a unique morphology and mesoporous structure of nanoflowers covered on nanowires,and the introduction of Ni-P significantly improves the conductivity and enriches redox reaction of NMS,so that the specific capacity of NMPS is much higher than that of NMS(1 A g^-1,1062 C g^-1).The assembled NMPS//AC AASC at 0.2 A g^-1 shows a specific capacity of 179.2 C g^-1 and an energy density of 31.57 Wh kg^-1,and a good cyclic stability,which proves the practical application potential of NMPS as AASC positive material.This work also provides a reference for improving the electrochemical performance of other related electrode materials.In Chapter 4,the oxygen-doped HPC was prepared by a simple heat treatment and activation treatment derived from ethylenediaminetetraacetic acid tetrasodium salt.When the mass ratio of the precursor to activator is 1:6,the obtained HPC-1:6 sample has a hierarchically porous network structure,and a high specific surface area of 3043.3 m2 g^-1.which makes HPC-1:6 shows a high specific capacitance,low resistance and good rate performance in the electrochemical test at a three-electrode system.It is proved that HPC-1:6 is a good negetive material for ASC.In addition,the electrochemical performance of the HPC-1:6-based ASC in alkaline and neutral electrolyte was investigated,which proves a good practical application potential of HPC-1:6 and prepares a way for the research in Chapter 6.In Chapter 5,the Sb nanosheets were mixed with oxygen-doped HPC with an abundant pore structure,and a new type of composite negative electrode Sb@HPC was obtained.The layered porous structure of HPC help to effectively adsorb Sb nanosheets.Sb nanosheets could provide a large number of two-dimensional surface and edge active sites for HPC.Thus,the specific capacitance and cycle performance of HPC can be improved without reducing the rate performance of HPC.This work provides a reference for improving the specific capacitance and cycle life of other electrode materials.In Chapter 6,the Zn2+-doped NiSe₂@Ni（OH）₂ composite material was successfully prepared on nickel foam by a two-step hydrothermal method.And the effect of Zn resourse dosage in the reactants on the specific capacity of the ZnNiSe₂@Ni（OH）₂ was investigated.When the molar ratio of Zn:Ni in the reactants is 1:2,the Zn-NiSe₂@Ni（OH）₂ material has the highest specific capacity(6 A g^-1,1525.8 C g^-1),which is due to Zn2+ doping to optimize the electronic structure and morphology of NiSe₂@Ni（OH）₂.Zn-NiSe₂@Ni（OH）₂//HPC AASC was assembled with optimized Zn-NiSe₂@Ni（OH）₂ as the positive electrode and the optimized HPC-1:6 in Chapter 4 as the negative electrode.The electrochemical performance of ZnNiSe₂@Ni（OH）₂//HPC AASC is significantly higher than that of the ASC devices prepared in the previous chapters,showing that the use of optimized positive electrode and optimized negative electrode to assemble AASC can effectively improve the overall electrochemical performance of ASC.This provides a strategy reference for the development of high energy density of ASC.Chapter 7 provides a summary of the thesis and an outlook.