Cu,Co-based Oxide Electrode Materials For Electrochemical Energy Storage

With the improvement of economic conditions and the increase of the overall environmental protection awareness of society,more and more clean energy has entered people's field of vision.At the same time,the development of electric vehicles and various advanced household electronic devices also puts forward higher requirements for energy conversion and storage technology.As an important part of energy storage devices,lithium-ion batteries and supercapacitors have become research hotspots due to their high energy density and power density,respectively.However,the lower power density of lithium-ion batteries cannot meet the needs of high-power output devices,and the lower energy density of supercapacitors is still a major obstacle to their development.As one of the core components of the energy storage device,the electrode material determines the overall performance of the energy storage device to a large extent.Therefore,how to use simple and effective synthesis methods to prepare electrode materials with controllable morphology and adjust their structure to enhance the performance of electrochemical energy storage is an important direction of current energy storage device research.This dissertation takes transition metal copper and cobalt oxides as the research objects,and focuses on the design of micro-nano multi-level structure materials,simple and controllable preparation technology,and high-efficiency energy storage performance,etc.,and successfully prepared nano-structures with multi-level structures.Array electrode material,and shows excellent electrochemical energy storage performance.The energy storage mechanism of electrode materials with this structure is explored and studied.The specific research content includes the following four parts:(1)Using copper foil as the conductive substrate and self-template,the CuO nanosheets array material was synthesized in Na OH/(NH₄)₂S₂O₈ solution by wet chemical method.It is directly used as a binder-free electrode in a lithium-ion battery,showing excellent rate performance and cycle stability,for example,it still maintains76 m A at a current density of 20 C(1 C=674 m A g^-1)The capacity of h g-1,under a large current of 1 A g^-1,remains at a capacity of about 320 m A h g^-1 after 800 cycles.The composite material is prepared by compounding with graphene.The large specific surface area and high conductivity of graphene further improve the cycle stability of the electrode material.After the composite material was cycled to 2000 cycles,the battery capacity remained at about 370 m A h g^-1.(2)Using nickel foam as the conductive substrate and self-template,using the solvothermal method and using the weak reducibility of the solvent glycol to directly prepare the Co₃O₄ nanosheets array material with oxygen vacancy defects.It is directly applied to supercapacitors as a binder-free electrode,showing excellent capacitor performance.At a current of 1 A g^-1,it exhibits a capacity of 800 F g_-1(400 C g^-1).After2000 cycles at a high current density of 30 A g^-1,the capacity remained at 471 F g^-1(235.5 C g^-1),and the capacity retention rate was 96%.In the study,the use of near-infrared light(NIR)-assisted irradiation to control the structure of the Co₃O₄ surface is the first time that the photothermal effect has been used in the Co₃O₄ supercapacitor system to control its surface structure.And further improve the electrode material capacitor performance.At a current of 1 A g^-1,it exhibits a capacity of 1620 F g^-1(810C g^-1).After 2000 cycles at a high current density of 30 A g^-1,its capacity gradually increases from the initial 498 F g^-1(249 C g^-1)to about 950 F g^-1(475 C g^-1),Finally stabilized at 940 F g^-1(470 C g^-1),and the capacity increased by 88%.(3)Using nickel foam as the conductive substrate and self-template,using the solvothermal method and using the weak reducibility of the solvent glycol to directly prepare the Cu Co₂O₄ nanosheets array material with oxygen vacancy defects.It is directly applied to supercapacitors as a binder-free electrode,showing excellent capacitor performance.At a current of 1 A g^-1,it exhibits a capacity of 1198 F g^-1(599C g^-1).After 2000 cycles at a high current density of 30 A g^-1,the capacity remained at765.0 F g^-1(382.5 C g^-1),and the capacity retention rate was 92%.The Cu Co₂O₄nanoarray was also irradiated with NIR,and under a current of 1 A g^-1,it showed a capacity of 2518 F g^-1(1259 C g^-1).Cycling 2000 cycles at a high current density of 30A g^-1,the capacity has increased from 828.0 F g^-1(414.0 C g^-1)to 1815 F g^-1(907.5 C g^-1).and the capacity increased by 119%.(4)Finally,use Raman spectroscopy,X-ray photoelectron spectroscopy and high-resolution transmission electron microscopy to characterize the structure of Co₃O₄ and Cu Co₂O₄ nano-array materials irradiated by NIR,and analyze the enhancement of NIR-assisted irradiation Capacitance performance mechanism.For the first time,in-situ Raman testing technology was used to detect the phase changes of Co₃O₄ and Cu Co₂O₄array electrode materials in the oxidation reaction process in real time,and in-depth exploration of the energy storage mechanism of transition metal oxides Co₃O₄ and Cu Co₂O₄ before and after NIR irradiation.The results show that after the action of NIR,the surface oxygen vacancy content of Co₃O₄ and Cu Co₂O₄ increases,and the proportion of active sites Co²⁺increases,which promotes a substantial increase in their electrochemical performance.Among them,due to the enhancement of the electron/ion transmission rate of Cu Co₂O₄ due to the bimetal doping effect,the bimetal oxide Cu Co₂O₄ exhibits better electrochemical energy storage performance than the single metal oxide Co₃O₄.In addition,Co₃O₄ and Cu Co₂O₄ have obvious battery-type behavior in the electrochemical reaction process,and after the action of NIR,the peak intensity ratio of the reaction intermediate product and the raw material of the reactant increases significantly,revealing the effect of NIR on the electrode.The regulation of material surface defects deepens the degree of electrochemical reaction,and more active materials participate in the electrochemical reaction,which effectively improves the utilization rate of electrode materials.