Study On Microstructure And Mechanical Properties Of Ultra-thin Electrolytic Copper Foil And Surface Treatment Technology

According to actual production demand and high performance copper foil enterprise development request,focusing on the low tensile strength and elongation of copper foil for lithium ion battery,high roughness value and poor peel strength of high-frequency copper foil,the experiment has carried out the effects of single additive,sodium tungstate,rare earth and CNTs on the microstructure and properties of copper foil deposition.The codeposition technology of CuZn alloy foil was analyzed,and the new preparation method of ultra-thin copper foil and the structure-activity relationship between microstructure and mechanical properties were studied.It was found that pinholes appeared in copper foils prepared by adding Cl^-,SPS and HEC respectively in the experiment.The copper foils showed pinholes when added Cl^-,SPS and HEC respectively,but Cl^-showed the effect of brightening,and HEC increased the current efficiency,up to 98.75%.SPS enhanced the（220） plane orientation of copper foil,refined the grain and improved the tensile strength,but reduced the current efficiency due to its severe hydrogen evolution.PEG reduced the roughness value and pinhole of copper foil,and improved tensile strength and elongation.Collagen refined the grain size,but excessive collagen caused abnormal growth of local grain and reduced the overall organizational performance.The experimental result shows that 6-8μm double-smooth electrolytic copper foil was prepared by using 15mg/L Cl^-,3 mg/L SPS,10 mg/L collagen,5mg/L PEG and 8 mg/L HEC as combined additives.And the current efficiencyη=92%,roughness Rz=1.47μm,tensile strengthσ_b=518MPa,and elongationε=4.2%.The shape of nodules was changed from spherical to vertical rice grains by micro-coarsening with sodium tungstate.The nodules on smooth surface of copper foil increased with the concentration of sodium tungstate.The actual addition of sodium tungstate was less than 0.05 g/L.With the addition of rare earth,Cu deposition was promoted,the limiting current density was increased,the micro-coarsening ability was enhanced,the crystal structure was refined,and the nodules was more uniform and compact.The vertical and horizontal size ratio of nodules increased,and the ratio was≥1.9.Compared with the original surface area,the surface area micro-coarsened by sodium tungstate was increased by 20.6%,and the peel strength was increased from 0.33N/mm to 1.29N/mm.After adding 0.05-0.15 g/L terbium sulfate,the roughness value Ra decreased to 0.304μm.The surface area was increased by 42.33%,and the peel strength was increased to 1.43 N/mm.The optimum conditions of micro-coarsening was as follows:100g/L H₂SO₄,10g/L Cu²⁺,0.05g/L sodium tungstate and 0.10 g/L terbium sulfate as micro-coarsening solution.At the current density of 20～25A·dm^-2 with micro-coarsening time of 3 seconds at room temperature,the smooth roughness value of copper foil was increased slightly and the peeling strength was greatly improved.After the mixed acid treatment with volume content of sulfuric acid:nitric acid=3:1,oxygen-containing groups were successfully introduced on the surface of CNTs to eliminate agglomeration.The surface charges of CNTs was transformed from negative to positive by adding the cationic surfactant of PDDA,and the Cu/CNTs copper foil was produced by codeposition of CNTs and Cu²⁺.According to the microstructure analysis,the distribution of CNTs in Cu/CNTs copper foil was staggered like grid.Because of CNTs presence,there were nano-twins with（111） as the coherent plane in the crystal,the size of which is less than 10nm.At the same time,micro-nano structure was formed in the crystal.And the synergistic effect of the three factors improved the mechanical properties of copper foil significantly.The surface roughness of monolayer Cu/CNTs copper foil is high.By adding 6 mg/L MPS,10 mg/L Cl^-and 4 mg/L PDDA as combined additives,the Cu-Cu/CNTs-Cu composite copper foil was prepared like a sandwich layer,which could reduce the roughness of copper foil with R_z≤1.5μm.In this experiment,the resistivity of the composite copper foil prepared by adding 0.1g/L CNTs was only 2% higher than that of pure copper foil,the elongation was 3.27%,which was only 8% lower,and the tensile strength was significantly increased to 582MPa,which was increased by 62%.In addition,CNTs can reduce the internal stress of copper foil and stabilize the microstructure and properties.Cyclic voltammetry showed that the potassium sodium tartrate complex system could effectively reduce the reduction potential range of Cu²⁺ and Zn²⁺ metal ion,and the lowest potential range was reduced to 0.13V,which was conducive to the electrodeposition of Zn²⁺ ions.At the same time,the codeposition of CuZn alloy was greatly affected by cathode potential,which belongs to non-regular codeposition.And it is also an irreversible reduction reaction,showing continuous nucleation.Trace Bi could reduce the content of Zn,released the internal stress,and effectively alleviated the microstructure cracking of CuZn alloy.The experiment shows that sodium dodecyl sulfate（SDS）was affected by the increase of cathode potential.The adsorption of organic layer depended on cathode potential,which inhibited the deposition of CuZn alloy.Sodium dodecylbenzene sulfonate（SDBS）reduced the overpotential of CuZn codeposition and caused cathodic depolarization.Benzotriazole（BTA）increased the overpotential of CuZn codeposition,which shows cathodic polarization.Polyethylene glycol（PEG）was not suitable for the complex system of potassium sodium tartrate.The effect of SDBS on the inhibition of CuZn codeposition was greater than that of BTA on the promotion of ZuZn codeposition,so the depolarization effect of electrodeposition was dominant.In addition,CuZn alloy could form double electric layer structure in the deposition process,which induced the nucleation complete in 2s and crystallize into alloy crystal.The CuZn alloy was still crystal structure of Cu,Zn deposited into Cu matrix.The Cu（311）crystal plane orientation was caused by the increase of internal stress,and the content of Zn increased with the increase of current density.