Modification of Natural Graphite and Artificial Graphite
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Update time : 2022-10-10 11:47:53
According to the difference of raw materials and processing technology, graphite powder is divided into natural graphite and artificial graphite. Because of its low lithium potential, high initial efficiency, good cycle stability and low cost, graphite has become an ideal anode material for lithium ion batteries.
Analysis of natural graphite
Natural graphite is generally made of natural flake graphite as raw material and modified to make spherical natural graphite. Although natural graphite is widely used, it has several disadvantages:
The natural graphite has many surface defects, large specific surface area and low first efficiency.
Using PC-based electrolyte, there is a serious phenomenon of solvated lithium ion co-embedding, which leads to the expansion and peeling of graphite layer and the failure of battery performance.
Natural graphite has strong anisotropy, lithium ion can only be embedded from the end face, and the rate performance is poor and easy to precipitate lithium. Artificial graphite is generally made of dense petroleum coke or needle coke as precursors, which avoids the surface defects of natural graphite, but there are still some problems, such as poor magnification performance, poor low temperature performance, easy to separate lithium and so on.
Modification of natural graphite
In order to solve the problems of many surface defects of natural graphite and poor tolerance of electrolyte, different surfactants were used to modify it.
The first method is to change the pore structure surface and increase the micropores and lithium intercalation path on the graphite surface to improve the magnification performance of natural graphite by high temperature oxygen-free atmosphere sintering after etching in strong alkali (KOH) aqueous solution.
The second method is to use different strong oxidant solutions for oxidation treatment to passivate the surface active potential and reductive functional groups to improve the first efficiency of natural graphite.
The third method is to fluorinate the natural graphite with ClF3. It is found that the charge and discharge ratio and cycle life are effectively improved.
Another treatment method is to coat the amorphous carbon of natural graphite to construct "core-shell" structure particles. the carbon source of amorphous carbon is usually pitch, phenolic resin and other low temperature pyrolytic carbon materials. the existence of carbon layer can not only isolate the direct contact of electrolyte, reduce the surface active points of particles, reduce the specific surface area, but also reduce the interfacial impedance because of the large distance between carbon layers. Improve the intercalation and diffusion ability of lithium ion.
In order to solve the problem of strong anisotropy of natural graphite, mechanical treatment is often used to spheroidize the particle morphology in industrial production, and the air flow 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 introduce doping impurities and has high spheroidizing efficiency, but it will lead to the pulverization of a large number of particles and low yield.
The mechanical fusion machine uses the material to rotate at high speed in the rotor, clings to the wall under the action of centrifugal force, and passes through at high speed between the rotor and the stator extrusion head. At this moment, the material is subjected to both extrusion pressure and shear force. Under the action of friction between particles and particles and between particles and equipment, the surface presents a state of mechanical melting to achieve the purpose of spheroidization.
After spheroidization treatment, the particle size of natural graphite is in the range of 15-20 μ m, the first efficiency and cycle performance are obviously improved, and the magnification performance is greatly improved.
Modification of artificial graphite
Modification of artificial graphite: the modification mode of artificial graphite is different from that of natural graphite. Generally, the position degree (OI value) of graphite grains can be reduced through the reorganization of particle structure. Usually, the needle coke precursor with a diameter of 8-10 μ m is selected, and the easily graphitized materials such as asphalt are used as the carbon source of the binder. Several needle coke particles are bonded through drum furnace treatment, and the secondary particles with a particle size of 14-18 μ m are made to complete graphitization, which can effectively reduce the Oi value of the material.
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