Research On Preparation Of Cu/Si Composite Material And Its Application In Lithium-ion Batteries

Lithium-ion batteries are considered to be one of the most promising energy storage devices due to their high energy density,excellent cycling performance and environmental friendliness.However,with the increasing demand of energy storage technology development,the theoretical specific capacity of graphite anode lithium ion battery is low,about 372 mAh g^-1,which is far from meeting the huge demand brought by the rapid growth of the market.Therefore,efforts have been made to develop the next generation of lithium ion batteries with low cost and high energy storage anode materials.Silicon-based anode materials have the highest weight capacity and volume capacity,but their huge volume changes and low electronic and ionic conductivity still hinder their wide application in the field of energy storage,and the introduction of appropriate buffer phase can better solve these problems.The focus of this study is to improve the conductivity of the entire electrode by preparing silicon/copper materials with high conductivity using different preparation processes,such as mechanical ball milling,vacuum melting,and supersonic cold spraying.At the same time,conductive lithium and inert compound Cu₃Si also play a role of buffer silicon volume drastic change as the matrix,so that its electrochemical cycling performance is more excellent.（1）Using a combination of mechanical ball milling and high-temperature carbonization,a layer of copper silicide Cu₃Si intermetallic compound is modified on the surface of micron silicon to form a Si-Cu₃Si structured silicon-based composite material.The presence of Cu₃Si not only improves conductivity,but also effectively buffers the volume expansion of silicon materials,thereby improving the electrochemical stability of silicon materials.Then it is compounded with graphite（G）ball milling,so that the silicon material is embedded in the graphite conductive matrix as a whole.In order to enhance the transmission rate of electrons,the relatively small volume change of graphite is used to buffer the volume effect of silicon.Finally,10 wt%of polyvinylpyrrolidone（PVP）was added as a carbon source,and the（Si-Cu-G）/C composite material obtained under high temperature carbonization had the highest coulombic efficiency and good cycle stability for the first time.The first charge-discharge specific capacity is 1343.3 mAh g^-1,1634.2 mAh g^-1,the first coulombic efficiency（ICE）is 82.2%,and the capacity is still 582.5 mAh g^-1 after 90 cycles at 100mA g^-1 current density.（2）It is different from the preparation of silicon/copper alloy by mechanical ball milling.Here,pure copper particles and industrial grade silicon material are selected as the experimental raw materials,and different quality silicon/copper samples are weighed,and the Cu/Si alloy is prepared by a two-step vacuum melting-mechanical ball milling method.The phase structure is Si phase and Cu₃Si phase.After the electrochemical performance test,when the mass ratio of Si:Cu is 8:2,the electrochemical performance of the alloy material marked as Si80Cu20 is the best.Under the current of 100 mA g^-1,the first lithium insertion/delithiation capacity is respectively 2789.8 mAh g^-1,2284.4 mAh g^-1,ICE is 81.9%.After 50 cycles,the capacity of the Si80Cu20 alloy sample is still 860 mAh g^-1,and the cycle stability is better than that of other samples.By controlling the Cu₃Si content,the silicon-based material can obtain higher coulombic efficiency and excellent cycleability.（3）Using supersonic cold spray technology to prepare electrode sheets with different silicon-based composite coatings on copper sheets,explore the impact of different silicon-based composite materials on the spray coating structure and electrochemical performance under cold spray technology,and compare the results with traditional use The adhesive coating process of silicon coating is compared.Compare with the bonding agent silicon coating.After electrochemical performance test,analysis and comparison,it is concluded that the first charge-discharge specific capacity of conventional binder silicon-coated（CB-Si）anode is 2241.8 mAh g^-1,3495.5 mAh g^-1,and ICE is 65.2%,and 93.5 mAh g^-1 is left when the cycle reaches the 100th circle.It can be seen that the pure silicon anode prepared with the binder has a rapid capacity decay and poor cycle performance.The first charge-discharge specific capacity of the cold sprayed silicon-coated（CS-Si）anode is 2860.1 mAh g^-1 and 3344.9 mAh g^-1,respectively,ICE is 85.5%,and the discharge specific capacity after the 100th cycle is2418.2 mAh g^-1.The capacity retention rate is 84.5%,and the capacity decay rate per cycle is only 0.193%.As the copper content in the initial composite material increases,the first discharge capacity decreases,but the ICE is increased.The advantage of using cold spray technology is that the technology deposits silicon on the copper sheet,and the deposition form of silicon particles is shown as being covered by continuously distributed copper around to form a special three-dimensional structure composite material.This mosaic structure can effectively overcome the heat caused by heat.The large-scale separation and even shedding of silicon-copper composite materials caused by stress also strengthens the conduction of Li⁺and electrons,and improves the cycle stability of the silicon-based coating.