Preparation And Study In Electrode Materials Of Electric Double Layer Capacitor And Lithium Ion Capacitor

The electric double layer capacitor(EDLC)is a new type of energy storage devices.It is widely used in the fields of aerospace,defense technology,electric vehicles,and mobile communication because of its higher power density,faster charge-discharge rates,wider temperature range,longer cycle life and friendliness to environment.It has been attracted great attention in the field of hybrid electric vehicles particularly.With the enlargement of the applying fields,it is pretty necessary to improve its performance for electric double layer capacitor.That is to say,the major direction for future research is to obtain higher specific capacity and specific energy under the condition of high power density for EDLC.It is well known that the partial micropores of the activated carbon materials can not be infiltrated by the electrolyte ions in the electric double layer capacitor.As a result,it is difficult to form effective electrical double layer and reduces the effective specific surface area,which leads to the lower specific capacity for activated carbon materials.However,the structure of mesoporous can reduce the migration resistance of electrolyte ion in the pore and increase the surface utilization rate of the activated carbon materials.Therefore,it is the key to obtain the activated carbon materials with high specific surface area and mesoporous structure.Similarly,in order to improve the specific energy of capacitor,it is performed to add the lithium transition metal oxides to activated carbon electrode materials.It is called lithium ion capacitor(LIC).It is major applied to the electric vehicles field because of the characteristics with high energy density and high power density.In order to better meet the needs of electric vehicles,it is the key to research and develop the lithium transition metal oxides electrode materials with high performance and low cost.Aiming at these problems above,some researches were carried out as followed:1.A series of micro-mesoporous activated carbon materials were prepared by template method.The magnesium citrate was selected as raw materials due to template agent and carbon source are gathered in integral whole.The different carbonization temperatures were identified by using thermo gravimetric analysis(TG-DTG)for raw material and obtained a series of micro-mesoporous activated carbon electrode materials(MCx);they were MC1,MC2 and MC3 respectively.The activated carbon materials were characterized by X ray powder diffraction(XRD),N2 adsorption-desorption measurement,transmission electron microscopy(TEM)and galvanostatic charge-discharge measurement.And it would seem logical to draw the following conclusions:(1)The MC1 has the most prominent structure among all the activated carbon materials.for instance,the specific surface area is 1913.474 m g-1 and the pore size distribution of micro-mesoporous is centered at about 1.4 nm and 2.75 nm-3.6 nm.That is to say,the MC1 activated carbon material possesses high specific surface area and wide pore size distribution.(2)The MCI activated carbon electrode material exhibit excellent electrochemical performance in 1 mol L-1 Et3MeNBF4/PC electrolyte.It not only displays the high specific capacitance of 145.5 F g-1 at a current density of 60 mA g-1,but also shows superior rate capability.Such as,when the current density increase to 1000 mA g-1,the MC1 display specific capacitance as high as 140.1 F g-1 and the capacity retention rate of 96.29%compared to the specific capacitance at current density of 60 mA g-1.Moreover,the MCI has a good cycling stability with capacity retention rate of 93.53%over 1000 cycles.In addition,the average specific energy of MCI could reach up to 35.72 Wh kg-1.And it should be attributed to the high specific surface area and wide pore size distribution.Therefore,the MC1 micro-mesoporous activated carbon material has perfect electrochemical performance.2.The Nano-LiFePO4/C(Nano-LFP)composite electrode material was synthesized by applying high temperature solid-phase reaction method.The composite was characterized by X ray powder diffraction(XRD),scanning electron microscopy(SEM)and transmission electron microscopy(TEM).And confirm it is nano material with high conductivity.The Nano-LFP-AC(Nano-LAC)and S-LFP-AC(S-LAC)cathode materials for LIC were prepared by selecting Nano-LFP and commercial lithium iron phosphate(S-LFP)to mix with the MCl activated carbon material at ratio of 3:7,respectively.The electrochemical properties of Nano-LAC,S-LAC,Nano-LFP and MCI were characterized by galvanostatic charge-discharge measurement in 1 mol L-1 LiPF6/(EC+DMC)electrolyte.As the conclusions follow:The specific capacitances of Nano-LAC cathode composite were 95.8mAh g-1 and 58.6 mAh g-1 corresponds to the rate of 0.1 C and 10C,respectively.And it possesses better capacity and rate capability compared with S-LAC and MCl.Furthermore,the Nano-LAC has a good cycling stability with capacity retention rate of 87.5%over 1000 cycles.Most importantly,it own higher specific energy-specific power than the others and the energy density could reach up to 179.9 Wh kg-1 at the power density of 5222.9 W kg-1.And the excellent electrochemical performance of Nano-LAC is owing to the synergy between pseudo capacitance and double layer capacitance.Thus,it not only has high power density,but also higher energy density.And which make up for the lacks of EDLC and lithium ion battery(LIB).Therefore,the Nano-LAC cathode composite material has excellent electrochemical performance.