Effect Of Additives On Microstructure And Properties Of Pulse Deposited Electrolytic Copper Foil

The prosperity of new energy industry has greatly promoted the development of electrolytic copper foil industry.As a negative collector,electrolytic copper foil is an indispensable raw material for lithium-ion batteries.Lithium-ion batteries require electrolytic copper foil to have the characteristics of fine grain,low surface roughness,ultra-thin and high hardness,so as to ensure the close contact between the negative active material of the battery and the collector,maintaining the battery capacity and improving the safety of the battery.Therefore,it is of great significance to study the preparation and properties of high-strength ultra-thin electrolytic copper foil.Electrolyte is the basis for the preparation of electrolytic copper foil.Deposition process and organic additives are important factors to regulate the properties of electrolyte,which significantly affect the microstructure and properties ofcopper foil.In this paper,the basic electrolyte is acidic copper sulfate solution,which is widely employed in the production of electrolytic copper foil.The stable,efficient and suitable process parameters of pulse electrodeposition were explored.The addition amount and action mechanism of four organic additives and their corresponding composite additives in the process of copper foil electrodeposition were clarified,in order to optimize the copper foil production process and improve the quality of copper foil.The main research contents and conclusions are as follows:（1）Through single factor experiment,stable basic electrolyte(Cu²⁺:40 g/L、concentrated H₂SO₄:110 g/L)was selected to study the effects of pulse electrodeposition time,temperature and voltage on the thickness,Vickers microhardness,surface roughness and microstructure morphologies of copper foil.Results revealed that when the electroplating time was 3 min,electrolyte temperature was 50℃ and pulse voltage was 2.5 V,the surface of copper foil was bright and flat,and the particle size was small.At present,the thickness of copper foil was less than 6 μm,the microhardness was the highest,and the surface roughness was small,which were 5.89 μm,251.66 HV_0.05 and 2.199 μm,respectively.The average grain size of copper foil prepared by basic electrolyte was 116.7 nm,and the copper foil showed the preferred orientation of（111）crystal plane.（2）The effects of four organic additives such as SPS,HEC,gelatin and collagen on the microstructure and properties of electrolytic copper foil were studied,and the mechanism on copper foil electrodeposition was explored.The results showed that SPS,gelatin and collagen had the effect of grain refinement and leveling.Among them,collagen had a stronger effect on grain refinement.and the average surface particle size and grain size of copper foil with the addition concentration of 0.08 g/L were 83.8%and 45.5%lower than that of the basic electrolyte,respectively.Meanwhile,the thickness of copper foil,Vickers microhardness and surface roughness reached the optimal values,which were 5.12 μm、279.63 HV_0.05 and 1.885μm.The HEC electrolytic liquid system had no grain refining ability,but the lowest surface roughness of copper foil was 1.828 μm at the concentration of 0.12 g/L.The study found that the high microhardness of electrolytic copper foil was the result of the combined effect of grain refinement and preferred orientation of（220）crystal surface.It is preliminarily concluded that the mechanism of SPS inhibiting copper ion deposition was that the complex produced by SPS and Cu⁺ was adsorbed and desorbed,which increased the cathodic polarization and made the grains smaller.（3）The effects of two-component and three-component composite additives formed by SPS,HEC and collagen on the microstructure and properties of copper foil were investigated,and the electrochemical behavior of two-component composite additives on copper ion deposition was analyzed.The results demonstrated that the system of SPS and collagen formation（SC）was superior to the system of SPS and HEC formation（SH）.SH had the effect of depolarization,and the cathode electrodeposition of copper required a smaller barrier,which can promote the deposition of copper ions.Therefore,the microstructure was not uniform and the particle size was large.This indicated that there was antagonism between SPS and HEC,and the addition of HEC weakened the effect of SPS grain refinement.Three component composite additive（SHC）for SPS,HEC and collagen formation was studied by orthogonal experiment.It was found that the addition of SPS had the greatest influence on the microhardness of copper foil,and the surface roughness of copper foil was mainly controlled by concentration of HEC.The two-component（SH,SC）and three-component composite additive（SHC）formed by SPS,HEC and collagen did not form a new preferred orientation for the growth of grain plane,and TC（111）was still the largest and the preferred orientation of（111）crystal plane as before.