Preparation And Lithium Ion Storage Property Of Ge/Cu Composite Porous Microspheres Via Chemical Etching

With the rapid development of new energy electric vehicles and portable electronic devices,there is an increasing demand for energy storage devices with high power density and high energy density.Secondary batteries that are safe,environmentally friendly,and efficient have attracted much attention.Lithium-ion（Li⁺）batteries are considered the preferred power supply because of their advantages such as high specific capacity,high cycle performance,and high discharge efficiency.As the key component of lithium battery,negative electrode material directly determines the performance of battery.As the next generation negative electrode material,germanium（Ge）stands out among all kinds of materials because of its high theoretical capacity and excellent multiplier performance.However,as the negative electrode material,Ge also has the problem of volume expansion during the process of Li⁺embedding and removal.The internal stress and deformation of the battery are caused,which affects the performance and life of the battery.In this paper,a new method for the fabrication of germanium-copper composite porous microspheres（Ge/Cu@PMS）with low cost and high efficiency has been proposed.Firstly,germanium-copper（Ge/Cu）composite microspheres（Ge/Cu@MS）were prepared by pulse discharge method using Ge/Cu target as workpiece electrode and Cu as tool electrode to improve the electrical conductivity of the materials.Secondly,finite element method was used to analyze the formation mechanism of Ge/Cu@PMS,and Ge/Cu@MS was used as the raw material to quantitatively remove Ge material inside the microsphere through chemical etching,to construct a Ge/Cu@PMS with uniform distribution of holes,which could improve the electrical conductivity of Ge material and alleviate the volume expansion during Li⁺charging and discharging.Finally,electrochemical tests were carried out on the prepared Ge/Cu@MS and Ge/Cu@PMS to explore their influence on lithium storage performance as anode materials.The main research contents are as follows:（1）Preparation method of Ge/Cu@MS and study on its electrochemical properties.The Ge/Cu@MS materials with uniform particle size distribution and controllable element proportion were prepared by pulse discharge method with Cu as tool electrode and Ge/Cu target as workpiece electrode by controlling discharge processing parameters.The prepared Ge/Cu@MS was used as the negative electrode material to prepare button battery,and its electrochemical performance was tested.The results showed that Ge/Cu@MS as the negative electrode material had a current density of 800 mA g^-1,and after 200 cycles,the capacity was reduced to 119 mAh g^-1,and the battery capacity was low.It is proved that Cu composite of Ge material can not meet the performance requirements of anode material.（2）The formation mechanism of Ge/Cu@PMS.By using the finite element method and COMSOL Multiphysics software,the cube space around a single microsphere particle was taken as the calculation domain,and the general rule of the change of etching depth with reaction temperature and reaction time was obtained.According to the simulation results,the concentration and temperature of the reaction solution were prepared,and the microsphere particles were put into the etching solution for corrosion.The experimental parameters were optimized through orthogonal experiment.The research showed that when the reaction temperature was 20℃and the reaction time was20 min,the microsphere morphology was most close to the theoretical model.（3）Electrochemical performance of Ge/Cu@PMS.Using Ge/Cu@MS prepared above as raw material,H₂O₂ and NaOH as etching solutions,HCl as cleaning agent,Ge/Cu@PMS was prepared by chemical etching method by controlling reaction temperature and reaction time,and its electrochemical performance was tested.The results are as follows:Ge/Cu@PMS,when the current density is 800 mA g^-1,the initial charge-discharge capacity is 603 mAh g^-1.After 200 constant-current charge-discharge cycles,the capacity retention rate is as high as 466 mAh g^-1 and the capacity retention rate is as high as 79.1%.This is mainly attributed to the full fusion of Ge and Cu,which will increase the overall conductivity of the material.Meanwhile,the porous structure of the etched material will increase the contact between the active material and the electrolyte,which is conducive to the transmission of ions.The abundant pore structure can also effectively accommodate the volume expansion,preventing the material from fast powder in the process of charge and discharge.