Modification Of Graphite Anode Materials For Li-ion Battery

Facing the severe energy shortage,contemporary society has paid extensive attention to the development of renewable energy sources and the related research on energy storage equipment.Lithium-ion batteries are small size,light weight,long life,environment friendly,and no memory effect.As the most commercially available negative electrode material,graphite shows long life,low cost,environment friendly,low charge and discharge voltage,and high stability.However,there are still some problems,such as the low specific capacity,the peeling of the graphite sheet occurs during the cycle to shorten the life,poor rate performance and low temperature performance,make it impossibly meet the demand of the high energy density power system of the new generation of electric vehicles.To obtain the graphite anode material with better electrochemical performance,this paper has prepared different compound modified graphite materials,then the microscopic morphology,chemical composition and reaction mechanism have been analyzed:(1)As a promising lithium-conducting solid electrolyte,LiAlO2 has not gained deserved attention in the modification of lithium ion batteries anode material.In this paper,the LiAlO2/C nano-composites have been prepared by simply mixing with the appropriate proportion of Al(NO3)3,LiNO3 and graphite homogeneously and subsequent sintering.The successfully prepared LiAlO2 nano-particles are investigated by X-ray photoelectron spectra(XPS)and X-ray diffraction(XRD).The electrochemical tests indicate that the LiAlO2/C composite exhibits outstanding circulation property at a current density of 0.1 C and excellent rate performance.Both the Scanning Electron Microscope(SEM)test and the Raman spectra shows that sintering induces the increase of the disordered degree of the surface and the uniform distribution of the LiAlO2 nano-particles,both of which are valuable for improvement of the battery performance.First-principles calculations are used to confirm the transfer pathway of the Li-ion which indicates a possibility of using inorganic compounds to improve the electrochemical performance of graphite.It is concluded that Li-ion can pass through the lattice via vacancies and the interstitial Li in the lattice.(2)Severe mechanical strains and rapid capacity decay during Li+insertion/extraction processes restrict the potential application of copper oxides as lithium-ion battery anode material and electrode modified material.Herein,a new method to obtain nano-copper-oxides by decomposing Cu(CH3COO)2-H2O at high temperatures has been put forward to improve the electrochemical properties of graphite.Moreover,the positive effect of the LiAlO2 and Al2O3 on the electrochemical properties of natural graphite has been proved by our laboratory.Then the modified-graphite containing these nano-metallic-oxides is fabricated by solution mixing and high temperature sintering and their discharge capacity is 493.3 mAh/g at 0.5 C after 120 cycles and raise significantly from 522.8 to 675.9 mAh/g after 155 cycles at 0.1 C.Microstructural analysis shows that the thickness of the graphite layers and the disordered degree are caused by the chemical reactions.First principles calculations are performed to investigate the structure,conductivity and lithium storage properties of the graphite that is intercalated by different metal ions.The results prove that metal insertion can efficiently improve the performance of the material.(3)Electrochemical performance of a graphite negative electrode of lithium-ion batteries has been enhanced by treating raw graphite with alkali molten salt.Here,the KCl-modified graphite is fabricated via a simple and low-cost technique that graphite powders are simply dispersed in the potassium chloride aqueous solutions and sintered.Compared to the raw material,the rate capability of the graphite modified by potassium is enhanced significantly to 269.7 mAh/g at 1 C after 200 cycles which effectively solves the main problem to limit the application of the graphite anode for Li-ion batteries in the field of hybrid vehicles.First-principle calculations have been done to analyze the effect of K-ions on the lithium storage capacity of the graphite.This study provides a scientific basis for adopting the K-modified technique to improve the electrochemical properties of the negative electrode materials.