Classification of Graphite Carbon Anode Materials and Their Advantages and Disadvantages
Graphite carbon anode materials can be divided into three categories: natural graphite, artificial graphite, double graphite.
1. Natural Graphite
Natural graphite is purified from natural graphite ore and has two layered crystal structures, hexagonal and rhomboidal.
Advantages of natural graphite: large reserves, low cost, safe and non-toxic.
Disadvantages of natural graphite: In lithium-ion batteries, the outer surface of the particles of natural graphite powder is not uniform in
reactivity, the crystal size is large, the surface crystal structure is easy to be destroyed during the charge and discharge process, and the
surface SEI film (solid electrolyte interface film, which can allow lithium ions to pass through, but not allow electrons to pass through the
film) is not uniform, resulting in low initial coulomb efficiency (according to the data: That is, the first coulomb efficiency, which can be
regarded as the maximum value of the ratio of discharge capacity and charging capacity of lithium-ion batteries, and the magnification
performance is insufficient. Modification technology for the shortcomings of natural graphite: particle spherification, surface oxidation,
surface fluorination, surface carbon coating, etc. From the comprehensive consideration of cost and performance, at present, the industry
mainly uses carbon coating process for graphite modification.
Through the carbon coating process, the battery using natural graphite as the negative material can basically meet the performance
requirements of consumer products for small batteries.
2. Artificial Graphite
Artificial graphite is generally obtained from easily graphitized carbon by high temperature graphitization. Easy graphitized carbon
includes petroleum coke, needle coke, asphalt coke, metallurgical coke and other coke materials.
The advantages of artificial graphite: similar to the advantages of natural graphite (large energy storage, safety and non-toxic), and the
cycle performance, large rate charge and discharge performance, and the compatibility with the electrolyte are better than natural
graphite.
Disadvantages of artificial graphite: the process is more complex, the cost is relatively high compared with natural graphite, and the
energy density is lower than that of natural graphite.
With the explosive growth of the global power battery market, the comprehensive requirements of power batteries for materials such as
cost, processing performance, energy density, cycle life, fast charge rate and other factors have increased, and artificial graphite has
become the mainstream negative material for power batteries and high-end consumer batteries.
Artificial graphite can be subdivided into three categories: mesophase carbon microsphere artificial graphite, needle coke artificial
graphite, graphite general coke artificial graphite. Among them, synthetic graphite with mesophase carbon microspheres is an
important kind of synthetic graphite.
In the 1960s, researchers studying coal-coking asphalt found some small spheres of optical anisotropy (a substance with different
properties in different directions), and these small spheres of anisotropy are the prototype of mesophase carbon microspheres.
In 1973, Japanese scientists separated mesophase pellets from the asphalt matrix and named them mesophase carbon microspheres.
In the 1990s, graphitized mesophase carbon microspheres were gradually applied to the negative electrode of lithium-ion batteries and
realized industrialization, and gradually replaced the needle coke in the first generation of lithium-ion batteries developed by Sony.
Because the outer surface of the meso-phase carbon microspheres is the edge surface of the graphite structure, the reactivity is uniform,
and it is easy to form a stable SEI film, which is more conducive to the embedding and removal of lithium ions. Therefore, the mesophase
carbon microspheres have high first cycle efficiency (similar to the first coulomb efficiency and initial coulomb efficiency) and excellent
magnification performance. But the mesophase carbon microspheres have the disadvantage of high production cost.
3. Composite Graphite
Composite graphite is a graphite material containing a combination of natural graphite and artificial graphite.