Preparation And Electrochemical Performance Of Silicon Dioxide/carbon Negative Electrode Composite Material

The proliferation of various electric vehicles and portable electronic devices has stimulated the demand for high-power-density energy storage devices.Among various energy storage devices,lithium-ion batteries are widely used worldwide due to their high energy density,safety,portability and environmental friendliness.Compared with conventional graphite anode,SiO material has higher charge/discharge specific capacity and lower operating potential,making it more suitable for high energy density devices.However,the further development of SiO materials is severely limited by the poor conductivity of SiO and the drastic volume change during the cycle.In this paper,SiO（mSiO）was modified by Na₂CO₃ to improve its initial coulomb efficiency.On this basis,modified SiO/graphite（mSiO/G）composites and two carbon-coated mSiO/G@C_PDA and mSiO@C_PANi composites were developed.The detailed contents and results are shown as follows:（1）A simple high-temperature solid-phase method was used to induce disproportionation of SiO using Na₂CO₃,and the effects of different levels of Na₂CO₃ on the initial charge/discharge specific capacity as well as the initial coulomb efficiency of SiO were investigated.In addition,the electrochemical performances of SiO materials and SiO/graphite composites before and after modification were compared.The electrochemical test results showed that the addition of Na₂CO₃ had a positive effect on the disproportionation reaction of SiO,which can improve the initial coulomb efficiency of SiO.Secondly,the introduction of graphite can slow down the bulk effect of SiO and improve the cycling performance of the electrode.Among them,the mSiO-2 material obtained by the addition of Na₂CO₃ at 5wt%has the largest improvement in the initial coulomb efficiency,which is 14%higher compared with the unmodified SiO.The mSiO/G-2 composite compounded with graphite also exhibited the best electrochemical performance with an initial coulomb efficiency of 77.6%,a reversible specific capacity of nearly 400 mAh g^-1 for 300 cycles at a current density of 0.5 A g^-1,and a capacity retention rate of 75.8%.（2）In order to further improve the electrochemical performance of mSiO,mSiO/G@C_PDAcomposites were synthesized by introducing polydopamine（PDA）as a carbon source.By using in situ self-polymerization at room temperature,a polydopamine layer was grown on the surface of the material,and the mSiO/G@C_PDA composites could be obtained after high-temperature heat treatment.At the same time,the influence of mass ratio of mSiO/G to dopamine monomer on the morphology and electrochemical performance of mSiO/G@C_PDA composite was investigated by different characterization methods and electrochemical tests.The results showed that the mSiO/G@C_PDAcomposites exhibited better cycling and rating properties compared to the mSiO/G materials without added polydopamine.This is attributed to the synergistic effect of graphite and the polydopamine carbon layer:the graphite mitigated volume changes during the cycle,and the presence of the polydopamine carbon layer stabilized the electrode and electrolyte interface,reducing the consumption of active lithium.When the mass ratio of mSiO/G to dopamine monomer was 1:2,the mSiO/G@C_PDA-3 composite showed the best electrochemical performance,and the capacity retention rate reached 86.2%after 300cycles,which was 11%higher than that of mSiO/G.It is worth noting that 78%of the capacity can still be retained after 500 cycles,which fully demonstrates that the addition of polydopamine carbon layer can effectively improve the electrochemical performance of mSiO/G.（3）Polyaniline based coated modified SiO composites were successfully synthesized using conductive polymers as carbon source.The mSiO@C_PANi composites were obtained by oxidative self-polymerization of ammonium persulfate as initiator and phosphoric acid solution as reaction medium on the mSiO surface under low temperature conditions,and finally heat treated at 900℃.The effects of N doping and N and P co-doping on the morphological structure as well as electrochemical properties of the composites were investigated comparatively.Compared with mSiO@C_PANi-4 composites,N and P co-doped carbon in mSiO@C_PANicomposites is beneficial to improve the electronic conductivity of mSiO materials and thus the electrochemical properties.Meanwhile,the effects of the morphology and content of the polyaniline carbon layer on the electrochemical properties of the mSiO@C_PANi composites were investigated by varying the addition of aniline monomer.The experimental results showed that the addition of polyaniline carbon layer could substantially improve the cyclic stability of mSiO materials.Among the three mSiO@C_PANi composites with different carbon contents,the mSiO@C_PANi-2 composite with 0.4g of aniline monomer addition exhibited the best electrochemical performance with a specific capacity retention of 80.7%after 200 cycles at a current density of 0.5 A g^-1.The discharge specific capacity and capacity retention after 300cycles at a current density of 1 A g^-1 were 585 mAh g^-1 and 86.4%,respectively.