Surface Modification Of Commercial Copper Foil In The Presence Of Ionic Liquid And Its Effect On The Battery Performance Of Graphite Material

Lithium-ion batteries have been widely used in portable electronic devices and electric vehicles due to their remarkable advantages.The main components of lithium-ion battery are positive electrode material,negative electrode material,current collector,diaphragm and electrolyte.The research on improving its performance generally starts from these aspects The collector plays an important role in loading active materials,collecting and outputting electricity,so its material composition and surface morphology will significantly affect the performance of the battery.In this paper,CuCl,CuBr,Cu2O and CuCl-Cu composite thin films have been grown on the surface of copper foil for the first time in the co-existence of ionic liquid and CuSO4 aqueous solution.The whole process takes place at room temperature.The composition and morphology of the samples were analyzed by XRD,EDS,XPS and SEM.Then the modified copper foil was used as the negative collector,and commercial graphite was used as the active material to assemble the Lithium-ion half battery.The electrochemical performance of the half battery was investigated by CV,EIS and constant current charge-discharge tests.The main contents are as follows:(1)Copper foil was immersed in CuSO4 aqueous solution containing ionic liquid 1-butyl-3-methylimidazolium chloride salt([Bmim]Cl),and a CuCl thin film was deposited on the surface of copper foil at room temperature.The successful preparation of CuCl was confirmed by XRD,EDS and XPS tests.SEM results showed that the morphology of CuCl obtained was regular and uniform cube structure.The prepared CuCl/Cu was used as a new type of negative collector,and graphite was used as the active material to assemble lithium-ion half battery.It was found that the electrochemical performance of the prepared lithium-ion half battery was significantly improved by testing,and the capacity was much higher than the theoretical capacity of graphite(372 mAh g-1).The effects on the sample performance of the amount of[Bmim]Cl and the deposition time were investigated.The sample prepared by adding 4 g[Bmim]Cl in 100 mL 0.8 M CuSO4 and depositing for 15 min had the best performance.The first specific discharge capacity of the battery reached 665 mAh g-1 at the current density of 100 mA g-1,and remained at 579 mAh g-1 after 20 cycles.In other words,a layer of CuCl with cube structure can be grown on the surface of copper foil by using the above method,and it can significantly improve the capacity of traditional graphite lithium-ion batteries.(2)Similarly,CuBr can be grown on the surface of copper foil by soaking copper foil in CuSO4 aqueous solution containing ionic liquid 1-butyl-3-methylimidazolium bromide salt([Bmim]Br)at room temperature.CuBr was confirmed by XRD,EDS and XPS,and SEM images showed that a large number of CuBr particles could be prepared on the surface of commercial copper foil after a simple soaking process.Interestingly,CuBr/Cu as negative collector can also improve the capacity of graphite cells.The effects of the amount of[Bmim]Br and the concentration of H2SO4 on the performance of the sample were investigated.The sample prepared by adding 0.5 g[Bmim]Br in 100 mL 0.8 M CuSO4 without H2SO4 had the best performance.At the current density of 100 mA g-1,the initial discharge specific capacity of the battery was 462 mAh g-1,which remained at 428 mAh g-1 after 20 cycles.The discharge specific capacity of 86 mAh g-1 was still provided at a high current density of 1 A g-1.(3)In the presence of ionic liquid 1-butyl-3-methylimidazolium trifluoroacetate([Bmim]CF3COOH),Cu2O was chemically deposited on the surface of copper foil using CuSO4 and Na2S2O3 as raw materials at room temperature.Namely,a new Cu2O/Cu collector was prepared.The composition and morphology of the samples were characterized by SEM,EDS,XRD and XPS.The effects of different concentration of solution and deposition time on the growth of Cu2O and its performance as a negative collector for graphite lithium ion batteries were investigated.The capacity of battery using Cu2O/Cu collector prepared under different conditions was significantly higher than that of the battery using original copper foil.When the initial CuSO4 and Na2S2O3 solution concentration is 2 mM and the deposition time is 15 h,the samples obtained showed the best electrochemical performance.When the current density is 100 mA g-1,the specific discharge capacity of the battery reached 535 mAh g-1 for the first time,and remained at 424 mAh g-1 after 20 cycles of charge and discharge,which is much higher than that of the battery using original copper foil.(4)On the basis of the first part,the acidic CuSO4 aqueous solution containing ionic liquid 1-butyl-3-methylimidazole chloride salt([Bmim]Cl)was used as the electrolyte,copper foil was used as the working electrode,platinum plate as the counterelectrode,and saturated mercurous sulfate electrode as the reference electrode.The electrodeposition on the surface of copper foil was carried out by using the method of constant current.XRD results showed that Cu and CuCl growed on the surface of copper foil at the same time SEM results showed that the morphology of electrochemical deposition and chemical deposition was very different.The influence of current value and electrodeposition time on the sample was investigated.The results showed that the performance of the battery was improved by using the electrochemically modified collector.The performance of the sample obtained by electrodepositing 700 s at the current density of 10 mA cm-2 was the best,and the first discharge specific capacity of the battery reached 490 mAh g-1 at the current density of 100 mA g-1.This work significantly improves the capacity of traditional graphite lithium ion batteries and provides a new idea for improving the performance of lithium ion batteries.