Study On Preparation Process And Properties Of Electrolytic Copper Foil For Lithium Ion Batteries

As the anode current collector,electrolytic copper foil is an important part of lithium-ion batteries.The prosperity of the new energy industry has greatly promoted the development of the electrolytic copper foil industry.The copper foil for lithium-ion batteries need to have many advantages,such as fine grains,low roughness,few defects,high tensile strength,high elongation and ultra-thin.Among them,good mechanical properties can ensure close contact between active materials and current collector,maintain capacity and improve safety,so it is of great significance to research the preparation and performance of electrolytic copper foil with high performance.In this paper,the effects of collagen,hydroxyethyl cellulose（HEC）,sodium polydithiodipropane sulfonate（SPS）and additive D on the performance of electrolytic copper foil were systematically studied.On this basis,the appropriate combined additives were determined by orthogonal experiment.The effects of current density and temperature were studied.Electrolytic copper foil with thickness of 8μm and tensile strength of 387MPa was prepared under optimized process.In order to further improve the tensile strength and other properties,the combined additives are further optimized.The best bath is:4mg·L^-1 thiourea,0.01g·L^-1SPS,0.05g·L^-1HEC,0.08g·L^-1 additive D,under the condition of j=25A·dm^-2,T=298K,the roughness of the obtained electrolytic copper foil is 2.19μm,the tensile strength is 519MPa,and the elongation is 5.1%.It was found that the enhancement of the mechanical properties was due to cumulative effects of the smaller grain size and the preferential orientation of（220）plane.Two new technologies for preparing electrolytic copper foils were discussed:copper/graphene composite electrodeposition and superimposed pulse current electrodeposition.It has been found that the addition of a suitable concentration of graphene oxide to the plating solution without additives results in a slight improvement in the mechanical properties of the electrolytic copper foil,but in the bath containing the additives,the graphene oxide plays the opposite role.When superimposed pulse current is used for electrodeposition,as the pulse current increased,the roughness of the copper foil decreased,the degree of warpage decreased,the tensile strength and elongation increased.However,compared with direct current electrodeposition,the experimental results obtained under the same experimental conditions are quite different,and the reasons cannot be determined at present,and further research is needed.Electrochemical analysis such as linear potential sweep voltammetry（LSV）,cyclic voltammetry（CV）,and chronoamperometry（CA）showed that collagen,HEC,and thiourea increased cathodic polarization,SPS and D show the effect of depolarization.Electrodeposition of copper in the plating solution without additive,pre-optimized and optimized plating solutions containing combined additives all belong to the irreversible process controlled by the diffusion process,and the nucleation modes of copper all are three-dimensional instantaneous nucleation.It is found that the electrochemical behavior of copper/graphene composite electrodeposition and the performance of electrolytic copper foil are affected by the quality of graphene oxide,the competitive adsorption between additives and graphene oxide.In the superimposed pulse current electrodeposition process,nano-sized copper crystal grains are obtained under high current,which is beneficial to increase the tensile strength of the electrolytic copper foil,micro-sized copper crystal grains are obtained at a low current,which is advantageous for increase the elongation of the electrolytic copper foil.