Study On Modification Of Copper Foil Collector/Graphite Electrode By Conductive Polymer Coating

At present,commercial lithium-ion batteries generally use graphite as negative electrode materials and copper foil as current collector.However,the surface of the copper foil is smooth and flat,and the actual contact area with the electrode material is not large enough,which will lead to low bonding strength.And the copper foil is directly exposed to the electrolyte in the electrode pores,which will be subject to the chemical and electrochemical corrosion of the electrolyte,which will affect the cycle stability of the battery.In addition,graphite electrode as an important part of lithium-ion battery also shows some disadvantages.For example,the rate performance of graphite electrodes is poor,and the SEI film generated during initial charging and discharging of the electrode is not strong enough,it is easy to break and generate repeatedly during high-rate charging and discharging of the electrode,which increases the irreversible capacity loss.Therefore,it is of great significance to modify the copper current collector and graphite electrode.The specific research content is as follows.(1)Two kinds of conductive polymer(poly-3,4-ethylenedioxythiophene(PEDOT)or polyaniline(PANi))modified copper foils were obtained by a simple anode electrochemical polymerization method.The contact area between the modified copper foil and the graphite electrode material was increased,and the corrosion resistance of the electrolyte was improved,so that the Cu-graphite electrode had higher capacity and cycle stability.The results showed that the initial discharge specific capacity of the PEDOT and PANi-coated Cu-graphite/Li halfcells obtained by electropolymerization at 1.5 V voltage for 30 s were 353.9 m Ah/g and 332.8m Ah/g,which were higher than 312.2 m Ah/g of pristine Cu-graphite/Li half-cell.After 200cycles(0.5C rate),the discharge specific capacity was 323.27 m Ah/g and 279.62 m Ah/g,respectively,and the capacity retention rate was 95.64% and 87.43%,which were higher than that of pristine Cu-graphite/Li half-cell.(The capacity and retention rate after 200 cycles were189.81 m Ah/g and 67.41% respectively).This showed that the conductive polymer-modified copper current collector provided a feasible way to improve the capacity and capacity retention rate of graphite electrodes;(2)PANI was coated by electropolymerizing on rolled graphite electrode by threeelectrode system electrochemical polymerization method,and PANi was synthesised on the surface and pores of the pole piece,which increased the conductive network of the electrode and improved the rate performance of the graphite electrode,it also stabilized the SEI film and improved the discharge specific capacity and capacity retention rate during high-current charging and discharging.The results showed that the first cycle(1C rate)discharge specific capacity of the graphite electrode obtained by electropolymerization coating at voltages of 1.0V,1.25 V and 1.5 V for 30 s increased from 203.44 m Ah/g of uncoated graphite electrode to242.05 m Ah/g of the electrode coated at 1.0 V,245.93 m Ah/g of the electrode coated at 1.25 V and 233.80 m Ah/g of the electrode coated at 1.5 V respectively.After 100 cycles,the capacity increased from 160.76 m Ah/g to 203.73,227.92 and 210.72 m Ah/g respectively,and the capacity retention rate increased from 78.6% to 84.2%,92.7% and 90.1% respectively;(3)Using tetrabutylammonium tetrafluoroborate and potassium nitrate as supporting electrolytes,PANi was coated on the surface of the graphite electrode before rolling by the electrochemical polymerization method of a three-electrode system(the electropolymerization voltage was 1.25 V,and the electropolymerization time was 50 s),and then rolled the electrode to form a lithium-ion battery.When tetrabutylammonium tetrafluoroborate was used as the supporting electrolyte,the first and 100 th cycle(1C rate)capacity of the coated electrode increased from 203.41 m Ah/g and 159.45 m Ah/g of uncoated electrode to 204.06 m Ah/g and177.62 m Ah/g respectively,and the capacity retention rate increased from 78.4% to 87.04%.When potassium nitrate was used as supporting electrolyte,the corresponding values were240.8 m Ah/g,218.7 m Ah/g and 90.8%,respectively.