Preparation Of Bimetallic Oxide Of Spinel Type A?A=Co/Ni/Zn?Ga₂O₄ And Application Of Lithium Ion Capacitor

As a new type of energy storage device,lithium ion capacitors have the high power density and long cycle life of supercapacitors,and also combine the high energy density of lithium ion batteries,so they have received extensive attention and research in recent years.The different energy storage mechanisms of the positive and negative electrodes place higher requirements on the electrode material.The battery-based negative electrode has a slower kinetic process due to the Faraday electrochemical reaction,and it has a problem of kinetic mismatch with the capacitive positive electrode material.Therefore,the development and research of anode materials with excellent rate performance is the key to achieving high-performance lithium-ion capacitors.Transition metal oxides?TMOs?materials have been widely used in the field of energy storage due to their low cost,high chemical and thermodynamic stability,and high theoretical specific capacity.Among them,bimetal oxides are more widely used than monometal oxides.It has attracted more attention due to its higher conductivity.Spinel?AB₂O₄?transition metal oxides have aroused great interest due to their unique structure and high electrochemical activity.Among them,A is Fe,Co,Ni,Mn,Cu,and Zn,and B is Co,Mn,and Fe.There are many researches on these materials,but because the A and B-site elements have the same energy storage mechanism?transformation?,As a result,the volume change during charge and discharge process is large,which results in the collapse of the material structure and the aggregation of particles,which in turn affects the specific capacity and ion diffusion kinetics of TMOs anode materials.Based on the above considerations,a gallium element with a different energy storage mechanism is introduced at the B site,which undergoes an alloying reaction with lithium?xGa+yLi⁺=Li_y Ga_x?.In order to further study the effect of the A-site element in spinel oxide on electrochemical performance,three elements Co,Ni,and Zn with increasing atomic number in the same period were selected to prepare AB₂O₄ type bimetal oxides CoGa₂O₄?NiGa₂O₄ and ZnGa₂O₄.The research on the electrochemical properties of these three spinel-type bimetal oxide electrode materials has found that the A-site element has an important effect on the rate performance of AB₂O₄-type bimetal oxides.The specific research content is as follows:1.A simple hydrothermal method and subsequent calcination in a muffle furnace were used to successfully prepare the spinel-type bimetal oxide CoGa₂O₄ nanosheets.First,the electrochemical performance of this half-cell was tested,and the CV curve of 0.1 mV s^-1 was studied.Through analysis of the electrochemical reaction at a specific potential,it was found that the energy storage mechanism of the element at the A and B sites is different.Elemental alloying is combined with the transformational energy storage mechanism of cobalt.By the method of calculating the capacitance contribution rate by Dunn et al.,Calculating the relationship between the peak current and the sweep speed,it is obtained that b=0.93,and the electrochemical behavior is closer to the capacitance behavior.When the scan rate is 2 mV s^-1,the capacitance contribution is60.06%.The combination of nanostructure construction and energy storage mechanism makes it have excellent rate performance and cycle stability.Therefore,the assembled CoGa₂O₄//AC lithium ion capacitor exhibits excellent cycle stability?capacity retention rate after 8000 cycles is 83%?,high energy density of 111.5 Wh kg^-1(100 W kg^-1)and a high power density of 3927 W kg^-1(24 Wh kg^-1).2.Through simple hydrothermal growth and subsequent calcination in a muffle furnace,a NiGa₂O₄ material deposited into a micro flower shape by nanoplatelets was obtained.The samples were characterized by XRD and EDS.The results showed that the nanosheet-like self-assembled micro flower NiGa₂O₄ was successfully prepared.The electrochemical performance of the half-cell was also tested,and the relationship between the peak current and the sweep speed was calculated by the same method,and b=0.94 was obtained.According to the calculation method of the capacitance contribution rate,when the scanning rate is 2 mV s^-1,the capacitance contribution rate is 57.31%.Therefore,NiGa₂O₄//AC lithium ion capacitors show excellent cycle stability?capacity retention rate after 8000 cycles is 82%?,high energy density of104.89 Wh kg^-1(200 W kg^-1)and high power density of 3999 W kg^-1(25.44 Wh kg^-1).3.The corresponding salt was added to a mixed solution of water and ethylenediamine,and a solvothermal reaction was performed at 180°C.in a reaction kettle to obtain ZnGa₂O₄ materials in which nanosheets were stacked on each other into a micro flower shape.The material was successfully prepared through qualitative and quantitative test analysis.In the electrochemical performance test of the half-cell,it was found that its cycle stability was poor,which was related to the alloying reaction and transformation reaction of both Zn and Ga.The two metal ions reacted simultaneously in the same potential interval.The structure is more destructive.By calculating the relationship between the peak current and the sweep speed,it is found that b=0.85,which is lower than the above two materials.In the ZnGa₂O₄//AC lithium ion capacitor performance test,its cycle stability is also poor?capacity retention rate after 5000 cycles is 65.6%?,with an energy density of 71.51 Wh kg^-1(175 W kg^-1)and a high power density of 5600 W kg^-1(25.34 Wh kg^-1).