Study On Asymmetric Capacitor Matching And Capacitance Behavior Based On Lithium Battery Materials

The electrochemical hybrid capacitors(EHC)is a novel storage device between supercapacitor and battery, having higher energy density compared with supercapacitor and higher power density compared with battery, it can overcome the defect of supercapacitor and battery, it's one of the optimum choices for hybrid electrochemical vehicles and power sources. This device can well satisfy the requirement of the load for the energy density and power density of the power sources. The research focused on the electrode materials of hybrid capacitor based on Lithium battery material and activated carbon, and it was investigated by means of mass match, electrolyte match, constant charge/discharge, cyclic voltammetry and electrochemical impedance spectroscopy measurements.The olivine phase LiFePO4 was prepared by high temperature solid-phase and hydrothermal methods, and the product prepared had phase purity and good crystallite. The value of the products capacity was almost same, and the performance of the cycling exhibited well.The LiFePO4/AC hybrid capacitor, consisted of a LiFePO4 cathode synthesized by high temperature solid-phase method, hydrothermal method, commercialization and a high specific surface area AC anode in 1M TEA/PC and LiFP6/(EC+EMC+DC), was assembled, respectively. The result showed the mass specific capacitance reached 34.1mAh/g (based on the total weight of the electrodes) at 250mA/g current when the ratio of anode mass to cathode mass equaled 1:2, and the cycle efficiency is 99%. The best operating voltage range was 2.5-4.1V, and it exhibited a good cycling profile and desirable high rate capability. The CV curves showed that simultaneous with nonfaradic reaction in AC anode, a faradic reaction occurred on LiFePO4 cathode.The LiFePO4/AC hybrid capacitor, consisted of a commercialization LiFePO4 cathode and a high specific surface area AC anode in 1M Li2SO4, was assembled. The electrochemical performance was investigated. The special capacitance can reached 24.6mAh/g, almost same as the special capacitance in organic system. It also exhibited good cycling profile with the cycle efficiency above 90% within 100cycles, but it had low energy density duo to its low voltage platform.The AC/Li4Ti5O12 hybrid capacitor was assembled with activated carbon as the cathode, lithium-ion battery materials Li4Ti5O12 as the anode, respectively,1M TEA/PC and LiFP6/ (EC+EMC+DC) as the electrolyte. The result showed the mass specific capacitance reached 12.4mAh/g (based on the total weight of the electrodes) at 160mA/g current when the ratio of anode mass to cathode mass equaled 3:1, and the cycle efficiency was 95%.