Preparation And Study Of Copper-based Porous Current Collector For Lithium Ion Battery

At present,graphite is usually used as the negative electrode material for lithium ion batteries.It has the advantages of high electronic conductivity,large lithium ion diffusion coefficient,small volume change of the layered structure before and after lithium insertion,and low lithium insertion potential.However,due to the theoretical specific capacity?372mAh/g?is limited,it has been increasingly unable to meet the energy supply needs of electrochemical devices.Therefore,lithium metal with a theoretical capacity of 3860mAh/g has returned to people's attention.Researchers have proposed a variety of solutions to the problems of easily forming dead lithium and dendrite lithium during the cycle,causing puncture of the diaphragm,and the huge volume change when lithium is deintercalated.Among them,constructing a three-dimensional porous current collector as lithium intercalation has become a hot topic in recent years.The large specific surface area provided by the three-dimensional porous current collector can effectively reduce the current density during charge and discharge,so that the deposition of lithium ions can proceed relatively slowly,and more nucleation sites are provided,thereby alleviating the formation of dendritic lithium,dead lithium and the huge volume change during deintercalation of lithium.In this paper,electroplating,hydrothermal and ultrasonic methods are mainly used to prepare three-dimensional porous current collector materials.The specific research work of this paper is as follows:By means of electroplating,a layer of copper dendrite was grown on the foam copper skeleton,which greatly expanded the specific surface area of the material through the large number of pores existing between the dendrite itself and dendrite,and was applied to the lithium ion battery to test its electrochemical performance.The results show that after 70 cycles under the current density of 1mA/cm²,the coulomb efficiency of the three-dimensional porous collector is still stable at 90%,while the peak coulomb efficiency of flat copper foil and bare foam copper is only about 80%.In the cycle test of symmetrical battery,the cycle life of electroplated copper foam electrode is over 1000h,and the polarization voltage is small,which greatly exceeds the performance of flat copper foil.When applied to the full battery,it still produces 102mAh/g capacity after 350 cycles,with a retention rate of 67%.Using hydrothermal technology,the smooth planar copper foil was subjected to surface corrosion under high temperature and high pressure to obtain a three-dimensional porous copper material with tiny holes,which was used as a negative electrode current collector of a lithium-ion battery to study the relief of lithium dendrites and the role of volume expansion.The experimental results show that when using NH₄Cl as the hydrothermal solution,as the concentration of NH₄Cl increases,the more severe the corrosion of the copper foil surface,the more obvious holes and fissures are generated,and the higher the porosity,the result is significantly better than KCl solution and both Effect of mixed solution.Cyclic tests were performed at a current density of 1 mA/cm².The three-dimensional porous material's coulomb efficiency was up to 99.9%,and it began to slowly decrease after 300 cycles.In the symmetrical battery test,the overpotential was significantly reduced,and the curve did not appear to fluctuate significantly,and the cycle performance was significantly improved.In the ultrasonic environment,a porous copper material with a three-dimensional structure was prepared through the corrosion of ammonia on metals.The effect of ammonia concentration on the corrosion results was studied.The material was used as a lithium ion battery current collector to test and compare its electrochemical performance.The results show that with the increase of the ammonia concentration,the surface roughness of the copper foil continues to increase,and the diameter and depth of the pores are significantly improved.When the ammonia concentration increases to 75%,the surface morphology reaches the best.In the lithium-copper battery test,the Coulomb efficiency is still 90%after 270 cycles.In the symmetric battery test,the battery polarization and impedance are significantly reduced,and the cycle life exceeds 1000h.