Electrochemical Characteristics Of Lithium Ion Capacitors Based On Ternary Carbon Matrix Composites

Lithium ion capacitor is a new type of electrochemical capacitor.It combines the advantages of lithium-ion battery and double-layer supercapacitor which has high energy density and excellent power density.It has huge market application value and competitive advantages in electrochemical energy storage and high-power power supply.In order to explore the preparation of lithium ion capacitors with strong practical,simple process and excellent electrochemical performance,the high specific volume electrode material system was constructed by using materials such as Li Ni?Co Mn O?(NCM),activated carbon(AC),multi-walled carbon nanotubes(MWCNTS)and hard carbon.The composite way of physical blending was adopted and combined with the device assembly of button type devices.In this thesis,different positive and negative electrode properties and electrochemical properties of lithium ion capacitors were studied.The specific research and work contents are as follows:1.The electrochemical properties of NCM523 and AC composites with different proportions in Li-ion capacitors were studied systematically.The properties of single electrode and lithium ion capacitor with graphite anode were studied by assembling up three sets of positive electrode composites of NCM523 and AC with different proportions.It is found that when the content of NCM523 in the composite material is50%,the energy density of the whole battery composed of NCM523/AC// graphite is53.9 Wh /kg,and the highest power density can reach 967.3 W/kg.At the same time,the device shows good capacitance characteristics.The further results show that the use of appropriate types and proportions of battery materials and capacitive materials can give full play to the advantages of positive and negative material capacity matching,so that different components can play their respective advantages in the energy storage device system,so as to improve the electrochemical performance of lithium ion capacitors.2.In order to improve the conductive properties of cathode materials,multi-walled carbon nanotubes(MWCNTS)were introduced,and the effects of different proportions of MWCNTS,NCM111 and AC on the electrochemical properties of composite electrode materials and lithium ion capacitors were systematically studied.The results show that the energy density of lithium ion capacitor composed of80%NCM111+15AC+5%MWCNTS(15AC)and graphite is 146.9 Wh /kg,and the highest power density is 798.1 W /kg.Further results show that the power density and cycle stability of the whole battery can be improved by adding an appropriate proportion of MWCNTS in the cathode material system.3.In order to further improve the capacitance characteristics of the device,the graphite anode material is replaced by hard carbon and the composite material of hard carbon and AC.The effects of the composite of hard carbon and AC with different proportions on the performance of lithium ion capacitors are studied systematically.The results show that the energy density of the lithium-ion capacitor composed of 15 AC and 90% hard carbon +10%AC is maintained at 90.6 Wh /kg,and the maximum power density reaches 521.3 W/kg.At the same time,the device has good capacitance characteristics.The experimental results show that hard carbon can improve the capacitance and multiplier performance of the whole device,and the proper proportion of AC can improve the life of hard carbon.