Study On Lithium-ion Capacitors Based On Pre-lithiated Carbon-based Anode

Lithium powder is easily corroded by the electrolyte,so the negative electrode cannot effectively supplement lithium.During the cycle,too much lithium will form dendrites,piercing the surface of the separator and the electrode sheet to damage the battery.The formation of the SEI film will cause ions in the electrolyte,and the ions will hardly migrate into the negative electrode sheet,thereby reducing the energy storage and rate performance of the lithium ion capacitor.Porous cathode materials are beneficial to improve the electrochemical performance of lithium ion capacitors.The stable lithium metal powder with a fluorinated surface can be stably stored in the air for a long time.When applied to electrode materials,the corrosion effect of organic electrolyte on lithium powder and the formation of lithium metal dendrites are prevented,and the formation of SEI film is suppressed,and the surface resistance of the negative electrode is reduced,thereby adding the reversible circulating capacitance of the negative electrode It not only brings convenience to the storage of lithium powder,but also brings convenience to the pre-lithiation process of LIC and improves the performance of LIC.HAC enables the retention of the special characteristics of AC,as well as the retention of the unique colloidal properties and adsorption properties of the concave-convex rod-shaped clay.When be used to the positive electrode,it will enforce the electrochemical capacity of lithium ion capacitors.In this paper,chemical vapor deposition(CVD)method is applied to synthesize acidified activated carbon(HAC),lithium fluoride(LiF),and polytetramethylethylene lithium powder(TME-Li).Intermediate carbon microspheres are used as the negative electrode of lithium ion capacitors.The internal short-circuit method and the stable metal lithium powder intercalation method were used to pre-lithiate the intermediate carbon microsphere anode.The scanning electron microscope(SEM)and transmission electron microscope(TEM)were used to characterize the material and electrode pads.Current charge and discharge(GCD)and alternating current impedance spectroscopy(EIS)study the performance of lithium-ion capacitors.The main research results are as follows:1.By using perfluororesin(CYTOP)as the source of fluorine,through the action of nitrogen(N2),the lithium powder(Li)can be fluorinated under a high temperature environment to obtain lithium powder(LiF)after fluorination.LiF can be combined behind the plate of the previously embedded LIC anode to form the LIC.Next,through the use of scanning electron microscope(SEM)and X-ray diffraction(XRD)method to analyze and test the material and electrode sheet.The electrochemical characteristics of LIC were studied through constant current charging and discharging(GCD)and alternating current impedance(EIS).The test results show that the lithium powder was successfully fluorinated,and the lithium fluoride pre-embedded in the negative electrode can change the electrochemical characteristics of the device that can store charge.If the current density is 50 mA g-1,the capacitance of the concrete can reach 51.92 F g-1.If the continuous current density ranges between 50 mA g-1 and 700 mA g-1,the minimum power density can reach 68.51 Wh kg-1 and the maximum energy density can reach 1.02 kW kg-1.After repeated charging and discharging through 2,000 continuous constant currents,the capacitance maintain at around 96%.2 Using tetramethylethylene(2,3-dimethyl-2-butene-TME)as the material of the polymer,the lithium powder(Li)is immersed in water to gain the coated poly 2,3-Lithium powder of dimethyl-2-butene(TME-Li).The composite material of the middle carbon microspheres(MCMB)/multi-walled carbon nanotubes(MWCNTs)/super carbon black(SP)is used as the negative electrode,which is embedded in the electrode sheet and assembled together to form a lithium ion capacitor(LIC).Then the data analysis of lithium powder and electrode sheet was carried out using scanning electron microscope(SEM)and intelligent Fourier transform infrared spectroscopy(FTIR).In addition,the electrochemical performance of LIC was obtained by using continuous current to charge and discharge(GCD)and electrochemical impedance spectroscopy(EIS).The test results show that TME-Li can improve the electrochemical performance of the capacitor.When the current density reaches 50ma/g,the specific capacitance can reach 69.09f/g.Within the current density range of 50-700ma/g,the maximum power density reaches 1.02kw/kg,and the energy density reaches 91.14wh/kg..Through 4000 cycles of constant current charging and discharging,the capacitance retention rate is still above 83%,reflecting good electrochemical performance.3.We used dilute sulfuric acid(H2SO4)as an acidizing reagent to acidify the activated carbon(AC).After obtaining the acidified activated carbon(HAC),the activated carbon(HAC)was together with the conductive agent(SP)and polyvinylidene fluoride(PVDF)to make a positive electrode,and then the capacitor(LIC)of lithium ions was formed.Next,TEM and SEM were used to characterize the material and the pole.And using intelligent Fourier transform infrared spectrometer(FTIR)and the voidage tester(BET)on the surface of a than being acidification of activated carbon to the analysis of above elements and chemical bonds of analysis and the analysis of the specific surface area and using the constant current charge and discharge and electrochemical ac impedance test of the electrochemical performance of lithium ions capacitor.The end result of the experiment showed that the activated carbon was acidified and the specific surface area increased by about 60%of AC.We used the charge and discharge current density of 50 mA/g,the mass specific capacitance of the capacitor reached 40.17 F/g,the maximum power density was 0.98 kW/kg(700 mA/g),the maximum energy density was 52.34wh/kg(50 mA/g).Therefore,it has low impedance characteristics;After the detection of 2 000 charging and discharge cycles,the retention efficiency of capacity is more than 60%,which indicates that the activated carbon after acidification increases the electrochemical efficiency of lithium ion capacitors after using activated carbon as positive electrode.