| Supercapacitor-battery (SCB) is a kind of combination of secondary battery and supercapacitor, and has high energy density as the secondary battery and high power density as the supercapacitor. It storages energy mainly through electric double layer and lithium ion intercalate/deintercalate. It is significant to exploit "dual-functional" anode for (SCB). In this thesis, the LiMn2O4/actived carbon and the AG/actived carbon composite materials with different mass ratio were prepared. Electrochemical performances of composites materials were investigated. The possible electrochemical reactions of activated carbon in lithium-ion battery electrolyte 1M LiPF6-EC/EMC/DMC were investigated. The main conclusions are as follows:(1) The physical and electrochemical performances of AC between different voltage ranges were investigated, Between 0.01-2.0V,2.0-3.5V, 3.0-4.3V, the first reversible capacity of activated carbon are respectively 210.7mAh/g,25.3mAh/g and 50.2mAh/g. between 0.01-2.0V, the first discharge process include the forming of SEI and double layer storage. The charge and discharge curves after the first time showed obvious beeline which didn't show the plateau of lithium ion intercalate/deintercalate, this demonstrated that AC showed capacitance storage in battery electrolyte 1M LiPF6-EC/EMC/DMCC, not lithium ions intercalate-deintercalate energy storage, on the other hand, between 3.0-4.3V, AC also showed classic double layer performances.(2) The composite materials based on activated carbon and LiMn2O4 and AG were investigated. It demonstrated that the composite materials have advantages of both the high rate capability from the supercapacitor and the high capacity from the secondary battery; and the increase of the content of activated carbon in the composite materials caused a more obvious capacitive property. Between 3.0-4.3V, the charge and discharge curves of the composite materials indicated that the energy storage occured not only in the lithium ions intercalate/deintercalate process but also in the double-layer adsorption process. The composite materials of AG/AC with a mass ratio of 4:1 showed excellent electrochemical performance. The first charge capacity and the first charge and discharge efficiency were respectively 339.5mAh/g and 49%. The performance of high current on composite materials was improved compared with the pure AG. The charge time of the composite materials is two times as long as the pure AG at 2 A/g. The charge capacity increased by 30 mAh/g and the potential of charge plateau decreases 0.2V.(3) The relationship between the content of activated carbon and the capacitance was studied. The results showed that between the 3.0-3.8V the capacitance was provided by the activated carbon, and the Faraday capacitances provided by the activated carbon were respectively 23.4, 64.4,99.0 and 141.3 F/g; between the 3.8-4.3V, the Faraday capacitances provided by the activated carbon(AC) were respectively 27.1,67.7,80.6 and 135.4 F/g; between the 0.25-2V, the Faraday capacitances provided by the activated carbon were respectively 57.7,129.9 and 204.0 F/g. Faraday capacitance caused by activated carbon was typical linear growth, and has the same characteristics of the double-layer capacity. It proved that:composite materials have intercalate/deintercalate characteristics and capacitance characteristics, are dual-function electrode materals.(4) The lithiumion diffusion coefficient in composite cathode materials was studied by chronoamperometry measurements. The results indicated that the diffusion speed of ion deintercalating from AG decreased as the quantity of lithium ion intercalated decreased. The lithium ion diffusion coefficient in electrode materials increased as the AC increased, the lithium ion diffusion coefficient of composite materials is larger than that of pure AG. The high rate performance of composite materials added AC was better. |
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