A Study Of Surface Metal Modification Technology Of Silicon Monoxide Anode Materials For Lithium Ion Batteries

Lithium ion battery is an energy storage device with high energy density,long cycle life and environmental protection.At present,graphite has been promoted as the anode material for commercial lithium-ion batteries.Despite its excellent cycling stability,its theoretical specific capacity is only 372 m Ah g^-1,unable to meet the demand for high energy density lithium-ion batteries for electric vehicles and consumer electronics.Due to the high theoretical specific capacity(2100 m Ah g^-1)and good cycling stability of silicon monoxide（Si O_x,0<x<2）materials have attracted much attention.However,the Si O_x anode material will generate a huge volume expansion effect（～200%）in the process of lithiation/delithiation.The Si O_x material conductivity is very poor and close to that of an insulator.In order to solve these problems,the solutions proposed in this paper and the main results of the study are summarized as follows:（1）Submicron particles were obtained by ball-milling the raw Si O_x.The milled Si O_x particles were reacted in the mixed solution of HF and Ag NO₃.The optimal concentration of HF and Ag NO₃ was 2 M and 10 m M,respectively,and the reaction time was 5 min to prepare Si O_x/Ag composites that were uniformly attached to the Si O_xparticle surface by Ag nanoparticles.Then,Si O_x/Ag/C composite particles were prepared by carbon-coated of Si O_x/Ag composites using high temperature pyrolysis carbon source method.Ag nanoparticles provide a good conductive network,the constructed carbon coating can enhance the conductivity and relieve the volume expansion stress,so Si O_x/Ag/C particles show excellent electrochemical performance.It is shown in the cycling performance and rate performance test,the discharge specific capacity of the obtained Si O_x/Ag/C composite particle was maintained at 1102.7 m Ah g^-1 under a current density of 0.5 C(1C=2.1 A g^-1)after 150 cycles,which was 345.1m Ah g^-1 higher than that of Si O_x/C.The discharge specific capacity of Si O_x/Ag/C was946.7 m Ah g^-1at 2 C,which was 403.2 m Ah g^-1 higher than that of Si O_x particle.At the same time,it also showed a rapid capacity recovery when it returned to 0.1 C.（2）The milled Si O_x particles were performed Cu-deposition by self-selective electroless deposition.The optimal concentration was 2 M HF and 15 m M Cu SO₄·5H₂O,and the reaction time was 5 min to prepare Si O_x/Cu composite particles that Cu nanoparticles uniformly adhering to the surface of the Si O_x particles.The optimum sintering temperature and time were 600℃and 90 s respectively after optimizing the parameters of the alloying.The composite particles with Si O_x/Cu₃Si/Cu structure were obtained by alloying treatment.Due to the extra electron transport channel provided by Cu nanoparticles,the formed Cu₃Si alloy can maintain the stability of the structure,making the synthesized Si O_x/Cu₃Si/Cu composite particles exhibit excellent electrochemical performance.The test results of cycling performance and rate performance show that the discharge specific capacity of the obtained Si O_x/Cu₃Si/Cu composite material was found to be 1091.9 m Ah g^-1 under a current density of 0.5 C after 150 cycles,which was 439.2 m Ah g^-1 higher than that of Si O_x.The discharge specific capacity of Si O_x/Cu₃Si/Cu was 872.4 m Ah g^-1at 2 C,which was 361.2 m Ah g^-1 high than that of Si O_x.（3）The work of these two parts shows that Ag and Cu particles improve the electrical conductivity of Si O_x particles,in combination with the SEM morphology of the pole film before and after cycling,it can be proved that carbon layer and the formed Cu₃Si alloy can alleviate the volume expansion effect of Si O_x particles to a certain extent.This further demonstrates that the prepared Si O_x/Ag/C and Si O_x/Cu₃Si/Cu composite particles have excellent electrochemical performance.