Lithium Ion Capacitor Based On AC/LiNi_0.5Co_0.2Mn_0.3O₂ Composite Positive Electrode And Its Electrochemical Performance The Study

Lithium ion capacitor?LIC?as a new type of electrochemical energy storage device has attracted widespread attention,because it has higher energy density than the electric double layer capacitor?EDLC?and superior power density and cycle performance than lithium ion batteries?LIB?.Its application in hybrid cars and large boot device can simultaneously satisfy the demand for energy and power equipment.The use of carbon materials such as graphite for the anode of the traditional carbon-based LIC needs to be pre-embedded with lithium to some extent in the fabrication process,which largely increases the fabrication cost of the device.In addition,LIC should have long cycle stability and be able to operate in a wide range of temperature during the working process,which puts forward high requirements for electrolytes.Based on the above problems,the preparation of high performance electrode and the development of functional electrolyte were studied in this paper.In the production of high-performance electrode,Li Ni_0.5Co_0.2Mn_0.3O₂,a lithium ion battery cathode material,was introduced into the active carbon cathode to prepare AC/Li Ni_0.5Co_0.2Mn_0.3O₂composite cathode.The addition of Li Ni_0.5Co_0.2Mn_0.3O₂ not only improves the specific capacity of the cathode,but also can supplement the lithium ion concentration in the system during the first charging process.At the same time,activated carbon can improve the conductivity of the composite cathode so that it possesses better rate performance.The LAC composite cathode and hard carbon anode were matched to assemble the LIC.The results show that the energy and power characteristics of LIC can be adjusted by changing the mass ratio of Li Ni_0.5Co_0.2Mn_0.3O₂ in the composite cathode.The use of LAC cathode improves the cycling stability of the capacitor while increasing the energy density of LIC.The LAC40/HC capacitor has an energy density of 28 Wh kg^-1 at the maximum power density of 3645 W kg^-1,the capacity retention rate is 80.74%after 1000 cycles at 0.5C.It has a high energy density under the precondition of maintaining a high power density.In the research of functional electrolyte,a novel lithium salt lithium difluoroxalate borate?Li DFOB?was used as electrolyte additive in LIC.The results show that the discharge specific capacity of LIC in the electrolyte with 5%Li DFOB has been improved to some extent under high rate.The capacity retention ratio is88.43%after 1000 cycles under 0.5C.The addition of Li DFOB also improves the high-temperature cycling performance of LIC being attributed to the decomposition of Li DFOB forms a thin and dense electrode protective layer,which prevents the further decomposition of electrolyte,thus improving the stability of LIC in the charge and discharge process.