Study On LiMn₂O₄/AC Electrochemical Hybrid Capacitor

The electrochemical hybrid capacitors(EHC) is a novel storage device betweensupercapacitor and battery, with more specific capacitance and energy densitycomparedwithsupercapacitorandmorepowerdensitycomparedwithbattery,it'soneof the optimum choices for hybrid electrochemical vehicles and power sources. Thisdevice can well satisfy the requirement of the load for the energy density and powerdensityofthepowersources.In this study, the spinal phase LiMn₂O₄ was prepared by the high temperaturesolid-state reaction, and the composition of the LiMn₂O₄ can be determined throughthe controlling the ratio of the Li2CO3 and MnO2 and so three products Li0.95Mn2O4,LiMn₂O₄ and Li1.1Mn2O4 were obtained, and the as-received products exhibited highphase purity and good crystallite. The capacity of the three products were 105, 115and 118mAh/g, respectively, almost at the same values, but the cycling performanceandhighcurrentratecapabilityoftheLi1.1Mn2O4exhibitedpreferredvalues.Petroleum coke were activated at the temperature of 600, 700, 800 and 900℃,respectively, and four kinds of activated carbon were obtained. The coke wereactivated at 700℃is better than others, the BET specific area was 1119m2/g, and thecapacitanceofEDLCusedpetroleumcokeascathodematerialswas32.63mAh/g.YKsamplewasmoreporousthanPetroliccoke,theBETspecificareaofYKsamplewereabove 2400m2/g and the capacitance of the EDLC used this as cathode materials was47.56mAh/g and exhibited higher specific capacitance, and the three products werealmostatthesamevaluesofthecyclingprofileandhighcurrentratecapability.The LiMn₂O₄/AC hybrid capacitor, consisted of a high specific surfance area ACcathode and spinel LiMn₂O₄ anode in organic electrolyte, were investigated.Theresults show that the the cycling performance and high current rate capability of theanode materials determined the cycling profile and high current rate capability of theEHC,andthecapacityofthecathodematerialsdeterminedcapacityoftheEHC.EHCexhibited better chemical performance and the specific capacitance can be 30.78mAh/gandthecurrent densityincreasedfrom 50to200mAh/gandtheattenuationofdischargecapacityis4.7%.The chemical performance of the EHC used LiMn₂O₄ as anode materials andYK as cathode materials and non-poisonous, high-safety and environment friendly Li2SO4 solution as electrolyte was also studied. The results show that the capacitancewas almost the same as that of the organic EHC, can be 30.1mAh/g but the cyclingperformance and high current rate capability were less than that of the organic EHC,andingeneral,dischargecapacitycanbekeptabove90%after200cycles.