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Negative electrode material: analysis of graphitization depth



Graphite has a layered structure,with sp2 hybrid orbitals of carbon atoms in each layer forming a 120°triple coordinated planar hexagonal grid,covalently bonded,with a carbon atom spacing of 0.142nm.Hexagonal carbon atoms are stacked in a parallel grid,forming a network of hexagonal carbon atoms that translate from top to bottom until the carbon atoms are located at the center of the hexagon and are staggered.The configuration of the third layer of carbon atoms is the same as that of the first layer.Due to its high temperature resistance and conductivity,it is widely used in:

1)Conductive materials such as blast furnace electrodes,lithium negative electrodes,and other fields;

2)Refractory materials such as metallurgical crucibles and refractory bricks;

3)Wear resistant and lubricating materials,such as plug rings,sealing rings,and bearings.

Graphitization refers to the process of heating a product to over 2000℃in a high-temperature electric furnace using non graphite carbon as a protective medium or isolated from air.Physical changes improve the development of hexagonal carbon atom planar network layer stacking structure and transform it into graphite carbon with three-dimensional regular and ordered structure.Graphitization enhances the bulk density,conductivity,thermal conductivity,corrosion resistance,and machining performance of products.Graphitization is a key process in the production of artificial graphite negative electrodes.

Graphitization is mainly applied in the fields of lithium battery negative electrode artificial graphite,blast furnace/electrolytic aluminum electrode,etc.According to the prospectus of Xiangfenghua,some natural graphite will also undergo high-temperature treatment to further enhance the degree of graphitization,thereby increasing energy density.

The main factors affecting graphitization are raw materials,temperature,time,pressure,and catalysts.

1)Raw material:Amorphous carbon that is easily converted into graphite at high temperatures is called easily graphitized carbon(or graphitized carbon).Petroleum coke,needle coke,etc.belong to easily graphitized carbon.During the carbonization preparation process,easily graphitized carbon generally undergoes a melting state,with carbon molecular clusters arranged in close parallel to each other in its structure.

2)Temperature determines the degree of graphitization:different carbon materials have different temperatures at which graphitization begins.Petroleum coke generally enters the graphitization stage at 1700℃,while needle coke can only enter the graphitization conversion stage at around 2000℃.The higher the heating temperature,the lower the resistivity,and the closer the distance between adjacent crystal layers to the 0.3354nm ideal graphite crystal,indicating a higher degree of graphitization.

3)Time:There is also a certain relationship between the degree of graphitization and the residence time at high temperatures.The higher the graphitization temperature,the shorter the time required to enter a stable state of graphitization.The longer the insulation time,the lower the resistivity,and the higher the degree of graphitization.In addition,pressure has a significant promoting effect on graphitization;The addition of catalysts under certain conditions can promote graphitization,such as boron,iron,vanadium,titanium,bonds,magnesium,and certain compounds.

Continuous method refers to the process where raw materials are continuously fed into a heating furnace without power outage during production. The graphitized product needs to pass through a series of temperature zones and be moved and heated in the furnace to achieve continuous graphitization. The crucible furnace charging method and the box furnace charging method require intermittent production, with a fixed amount of raw materials placed in the furnace each time and discharged after high-temperature heating is completed. Taking the Acheson method of crucible charging as an example, a graphitization furnace has a production cycle of day 12-14 from the start of furnace cleaning to the loading, heating, cooling, and unloading of products. Among them, electric heating only takes day 2-3. Although each furnace group has 6-8 graphitization furnaces, each graphitization furnace can only rotate 2-2.5 hours within a month, resulting in lower efficiency.