Modification And Properties Of Silicon-based Anode Materials For Lithium Ion Batteries

Si has an ultrahigh theoretical capacity as an anode material of lithium ion batteries?LIBs?,but its cycle stability and coulombic efficiency are poor which have plagued researchers for more than 30 years.And this problem has not been solved hindering the development of the LIBs with high capacity.At present,the development of advanced technologies such as electric vehicles and drones has been hindered due to the low capacity of LIBs.Tremendous endeavors have been made to overcome this problem.In this paper,the three methods of processing electrode,including the nano-silicon alloy powder compounded a certain amount of graphite as the negative active substance of LIBs,the amount of the conductive agent minimized and the stirring process altered,were adjusted.In addition,a core shell Si/C anode material was synthesized by pyrolysis of polyvinylidene fluoride?PVDF?at different temperatures for a certain period of time.The morphology and structure of the silicon alloy powder and Si/C composites were analyzed by using scanning electron microscopy?SEM?and Raman spectroscopy.The electrochemical performance of the anode electrode was tested by Wuhan blue electric test system and electrochemical workstation.The specific conclusions are as follows:?1?It is found that with the decrease of the content of the nano-silicon alloy powder in anode materials,the first cycle coulombic efficiency was gradually increased,the specific capacity corresponded to the gradual decrease,and the cycle stability was continuously improved,indicating that mixing the graphite and the nano-silicon alloy powder together could function cooperatively.When the mass ratio of the graphite was 40%,the experimental results were better.Followed by reducing the content of the conductive agent,the results showed that it was advisable to incorporate 10%of the conductive agent into the anode material.In addition,it's the new stirring process that the nano-silicon alloy powder and the CMC binder were fully stirred with distilled water before graphite and conductive agent were added played a major role to improve the electrochemical performance of the cells.The cells still had a reversible capacity of 526 m A h g^-1 up to 100cycles with a high initial coulombic efficiency of 91.04%and excellent rate performance.The first efficiency has been greatly improved up to the efficiency of the graphite compared with the current technology.The specific capacity has been also greatly improved compared with the graphite currently used(about 360m A h g^-1).?2?According to Raman spectroscopy,amorphous carbon produced by pyrolysis of polyvinylidene fluoride?PVDF?was coated on the surface of the silicon particles,which could accommodate the large volume change of silicon during lithiation-delithiation,and thus reducing capacity attenuation and improving efficiency.When the temperature attained 750?,amorphous carbon was nearly completely coated onto the silicon particles,resulting in an excellent cycle stability.Si/C-3 had a high initial reversible capacity of 624.56 m A h g^-1 at100 m Ag^-1 with an initial coulombic efficiency of 88.03%and excellent cycling performance up to 50 cycles?84.7%capacity retention?.Additionally,Si/C-3showed an excellent rate performance.The test process was often overcharged and over-discharged due to the large internal resistance of the button half-cell.If the full-cell test is adopted,the negative electrode material should exhibit more excellent electrical properties.