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At present, lithium ion batteries have shown a very wide range of applications, and the anode material is one of the key factors determining the electrochemical performance of lithium ion batteries such as energy storage and conversion. Through surface modification of carbon anode materials, the performance of lithium ion batteries can be effectively improved. Such as improving the specific capacity, the first coulomb efficiency, charge and discharge efficiency, rate performance, cycle stability, safety, prolong the service life. The methods and mechanisms of surface modification mainly include surface coating, chemical treatment and element doping:
(1) Surface coating: a "protective film" is constructed to cover the graphite surface to form a "core-shell structure", which can avoid the peeling of graphite lamellae caused by solvation and improve the cycle stability of electrode materials. The coating of metal and its oxide can also reduce the resistance of lithium ion transfer and charge migration and improve the electrochemical performance of graphite materials.
(2) Chemical treatment: surface oxidation introduces oxygen-containing functional groups, increases the active site, forms a stable SEI film at the interface between anode material and electrolyte, and improves the cycle stability of carbon anode. Surface halogenation can form a passivation film with high intermolecular force on the surface of the material, which can improve the stability of the microcrystalline structure.
(3) Element doping: metal or non-metallic elements are incorporated into carbon anode materials to change the structure and electron arrangement of carbon microcrystals, so as to improve the electrochemical behavior of lithium ion removal and insertion in the anode materials.
The electrochemical performance of carbon anode materials can be greatly improved after surface modification, but the actual operation and regulation of each modification method will still affect the final modification effect. For example, the thickness of the coating layer, the degree of chemical treatment and the uniformity of heteroatom doping dosage, distribution and dispersion will affect the final performance of the material. If the control is not good, the performance of the lithium ion battery will not be improved, but the electrochemical performance will be degraded.