| By combining the characteristics of lithium-ion batteries and supercapacitors,lithium-ion capacitor is a new type energy storage device,which has high energy density,power density,long cycle performance and low self-discharge rate.The rapid development of new energy systems and electronic equipment put forward higher requirements on the performance of lithium-ion capacitors.The thesis reported optimizing the interface characteristics to improve overall performance of lithium-ion capacitors through surface modification of the current collector.The effect of surface modification on the electrochemical performance was studied by using the conductive carbon coating fabricated by chemical vapor deposition,using the perforated foil processed by laser treatment,and using the Dexmet's porous metal mesh arrays as a current collector.Meanwhile,we also developed a class of asymmetric lithium-ion capacitor operating under the electrolyte consumption mechanism,which provides direction for the further development of lithium-ion capacitor.The main contents of the thesis are as follows:(1)The interfacial properties of Cu current collector have been improved by the monolayer graphene coating,which is prepared by a low pressure chemical vapor deposition method.The graphene not only reduces the contact resistance,improves the electronic conductivity,but also optimizes the interfacial electrochemical kinetics,suppresses the oxidation of the copper foil in the electrolyte,improves the electron collecting ability and suppresses the Li+ interface diffusion.Therefore,the utilization rate of commercial Li4Ti5O12 anode electrode has been improved by this new type current collector.The discharge capacities of the modified and unmodified copper foils were 101.7 and 83.7 mAh g-1 at 10 A g-1,and the capacity retention rates were 96.9% and 85.1%,respectively.The results show that the lithium ion capacitor has better electrochemical performance by using the graphenemodified current collector.We also fabricated highly graphitized carbon and nano-sized Pt co-modified stainless steel collectors(SS@C@Pt)by chemical vapor deposition and chemical impregnation.Highly graphitized carbon and nano-Pt particles can provide a good electron transport network,reduce contact resistance and polarization,enhancing the adhesion strength between the active material and the current collector,greatly improving the rate performance of Li4Ti5O12 anode(2)The effect on the electrochemical performance were investigated by using conventional Cu current collector(CCC)and prepunched Cu current collector(PCC),respectively.Although using CCC has slightly higher pre-lithiation level with a higher energy density in CLIC,it suffered from considerable decrease at higher charge-discharge rates.In addition,90.0% of the initial capacity in PLIC was maintained,while the value of CLIC was only 73.2% over 1000 cycles in the voltage range of 2~3.8 V.A thin and stable SEI on the surface of graphite can be obtained after pre-lithiated by using the PCC.Therefore,the PLIC show better rate performance and cycle performance with the smaller selfdischarge rate,voltage drop,and interfacial resistance.(3)The nitrogen-doped polyimide derived carbon microspheres as new dual electrodes for lithiumion capacitor was obtained by solvothermal and subsequent high temperature carbonization.Lithiumion capacitor assembled in a class of asymmetrical configuration with the two carbon materials delivered an energy density up to 90.0 Wh kg-1 at a power density of 300 W kg-1,especially at a power density of 15000 W kg-1,45.8 Wh kg-1 still can maintained.In addition,a porous metal mesh kindly provide by Dexmet company instead of the traditional current collector has been studied,the results show that lithium-ion capacitors using porous metal mesh as current collectors have a capacity retention rate of 80% after cycling 5000 times,which is higher than the traditional current collectors with a value of 71.1%. |
PDF Full Text Request