Modification of Graphite Anode Materials and Their Lithium Storage Properties

Graphite is divided into natural graphite and artificial graphite according to the difference of its raw materials and processing technology. Because of its low potential to lithium, high initial efficiency, good cycle stability, and low cost, graphite has become an ideal lithium-ion battery application. negative electrode material.

Natural and artificial graphite

Natural graphite generally uses natural flake graphite as raw material, and is modified into spherical natural graphite for use. Although natural graphite is widely used, it has several disadvantages:

①Natural graphite has many surface defects, large specific surface area, and low initial efficiency;

② Using PC-based electrolyte, there is a serious co-intercalation phenomenon of solvated lithium ions, which leads to the expansion and peeling of the graphite layer, and the battery performance fails;

③Natural graphite has strong anisotropy, lithium ions can only be embedded from the end face, and the rate performance is poor and lithium is easily precipitated. Artificial graphite is generally made of dense petroleum coke or needle coke as a precursor, which avoids the surface defects of natural graphite, but there are still problems such as poor rate performance, poor low temperature performance, and easy lithium precipitation due to crystal anisotropy.

Modification of Graphite Anode Materials

Modification of natural graphite:

①In view of the problems of many surface defects and poor electrolyte tolerance of natural graphite, different surfactants are used for modification. CHENG et al. improved the rate performance of natural graphite by sintering in a high-temperature oxygen-free atmosphere after etching with a strong alkali (KOH) aqueous solution, changing the surface of the pore structure, increasing the micropores on the graphite surface and the path of lithium intercalation. WU et al. used different strong oxidant solutions for oxidation treatment to passivate the surface active potential and reducing functional groups, and improve the initial efficiency of natural graphite. MATSUMOTU et al. used ClF3 to fluoride natural graphite, and found that the charge-discharge rate and cycle life were effectively improved. Another treatment method is to carry out coating modification, coating natural graphite amorphous carbon to build “core-shell” structure particles. Usually, the carbon source of amorphous carbon is low-temperature pyrolysis carbon materials such as pitch and phenolic resin. The existence of the layer can not only isolate the direct contact of the electrolyte, reduce the active points on the surface of the particles, and reduce the specific surface area, in addition, due to the large interlayer spacing of the carbon layer, it can also reduce the interface impedance and improve the intercalation and diffusion capacity of lithium ions;

② In view of the strong anisotropy of natural graphite, mechanical treatment is often used in industrial production to spheroidize the particle morphology. The airflow shaping machine uses wind impact to make the particles rub against each other and cut the edges and corners of the particles. This method does not Doping impurities will be introduced, and the spheroidization efficiency is high, but a large number of particles will be pulverized and the yield will be low. The mechanical fusion machine uses the material to rotate at high speed in the rotor, adheres to the wall of the device under the action of centrifugal force, and passes through the extrusion head of the rotor and the stator at high speed. At this moment, the material is under the action of extrusion force and shear force at the same time. Under the action of friction between particles and between particles and equipment, the surface presents a mechanical melting state to achieve the purpose of spheroidization. After spheroidization of natural graphite, the particle size D50 range is 15-20μm, the initial efficiency and cycle performance are significantly improved, and the rate performance is greatly improved.

Artificial graphite modification: The modification method of artificial graphite is different from that of natural graphite. Generally, the purpose of reducing the degree of graphite grain orientation (OI value) is achieved through the reorganization of the particle structure. Usually, needle coke precursors with a diameter of 8-10 μm are selected, and easily graphitized materials such as pitch are used as the carbon source of the binder. After being treated in a drum furnace, several needle coke particles are bonded together, and the particle size D50 range is 14. -18μm secondary particles complete graphitization, effectively reducing the OI value of the material.

In view of the industrialization technology of anode materials and the market conditions at home and abroad, China Powder Network will hold the 2022 Advanced Anode Material Technology and Industry Summit Forum in Qingdao on October 18-19, aiming to build a platform for upstream, mid- and downstream enterprises in the anode material industry chain. A platform for in-depth exchanges, carry out cooperation in production, academia and research, and promote the sustainable and healthy development of the anode material industry. At that time, Professor Song Huaihe from Beijing University of Chemical Technology will give a report entitled “Modification of Graphite Anode Materials and Their Lithium Storage Properties”. On the basis of summarizing the relationship between the current carbon anode material structure and its electrochemical lithium storage performance, the report will introduce the research group’s work on graphite anode modification based on different performance requirements of lithium-ion batteries, mainly including surface coating, secondary fabrication. Research progress in granules, synthesis of artificial graphite with special structure, and structural design of silicon-carbon materials.

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