Study On The Modification Of Graphite Surface With Water-soluble Asphalt Coated To Enhance The Electrochemical Properties Of The Material

Among so many lithium battery negative electrode,artificial graphite has become the focus of attention in the industry due to its large interplanar spacing,which helps to reduce the volume effect caused by embedding/deintercalation.However,it has the large specific surface area,and the surface of artificial graphite is rough and porous,sensitive to the solvent in the electrolyte limits its superior performance.The modification of graphite surface to improve the electrochemical negative electrode performance as a material for lithium ion batteries has become the main research direction.In this paper,artificial graphite is coated with water-soluble asphalt to enhance the electrochemical properties of the material.The medium-temperature asphalt is used as a raw material,and the mixed acid is oxidized to prepare water-soluble asphalt.The response surface methodology is used to optimize the process of coating artificial graphite modified with water-soluble asphalt.The factors considered are the mass ratio of water-soluble asphalt to graphite,coating time,carbonization time and carbonization final temperature.The optimized results is obtained by using the particle size distribution of coated graphite and the charge-discharge capacity of the battery negative electrode as the indicator:?1?The best coating process is obtained by using the charge specific capacity as an indicator:the mass ratio of water-soluble asphalt to graphite is 1:6,coating time is61 min,carbonization time is 90 min and carbonization final temperature is 786?.The predicted value of the model is that the charge specific capacity of 145 m Ah/g,the discharge specific capacity of 150 m Ah/g,the efficiency of 97.34%,and the cycle retention rate of 93.66%.?2?The best coating process is obtained by using the particle size as an indicator:the mass ratio of water-soluble asphalt to graphite is 1:6,coating time is 50 min,carbonization time is 60 min and carbonization final temperature is675?.Under this condition,the median diameter D50 of the carbon composite is expected to be 23.21 ?m,the yield is 93.37%,the true density is 2.324g/ml,the median diameter is 23.21 ?m,the volume average diameter is 24.68 ?m,the area average diameter is 19.25 ?m,and the specific surface area is 116.2 m²/kg.?3?The samples after multiple coatings were superior to the graphite materials in electrochemical performance.As the number of coatings increased,the charge specific capacity increased first and then decreased,and the fourth coating reached a maximum of 217.6 m Ah/g.Scanning electron microscopy,infrared spectroscopy,Raman spectroscopy,X-ray single crystal diffraction,particle size distribution and thermogravimetric analysis of the microstructure of graphite and coated graphite show that: The surface and concave surface of the coated graphite can clearly see that the small dew-like adhesion,and the concave defect is reduced compared with graphite;Coated graphitehas more lattice defects,marginal disorder and “amorphous carbon” than natural graphite;The thermal conversion occurs only in the asphalt layer of the shell,and the graphite core remains unchanged.In summary,it can be seen that the water-soluble asphalt is coated on the graphite surface and the modification is successful.The charge specific capacity of coated graphite is positively correlated with material structure disorder R₁,amorphous carbon R₃,average stack height Lc,number of microcrystalline structure layers n and specific surface area.It's negatively correlated with the microcrystalline layer spacing d₀₀₂,the degree of graphitization g,and the median diameter D50.It has little correlation with the grain size La.Through the test of the materials microstructure by XRD,Raman and laser particle size test,calculate the microstructure parameters of the material,and discusse the influence of fitting micro parameters on the storage properties to give the structure-activity relationship provides the theoretical guidance for material's design.