What is Graphite Anode Material?

Among various anode materials, graphite, due to its outstanding comprehensive advantages, occupies more than 90% of the market share. And it is the core component of graphite batteries and graphite anode lithium batteries, which performance directly determines the capacity, lifespan, fast-charging capability and safety of the battery.

Definition and Structure of Graphite Anode Materials

Definitie

The graphite anode material is a core material composed of carbon and possesses a graphite crystal structure, used as graphite anode lithium ion battery. It is the carrier of lithium ions and electrons during the charging process of the battery. And it plays a role in energy storage and release through the “lithium ion insertion – extraction” mechanism. With the high reversibility and stability, it has become the core reason for the high safety of graphite battery. And it is also the key support for the large-scale commercial application of graphite batteries. 

Key Structures

Due to its unique microstructure – a hexagonal crystal lattice layered structure, it has two core advantages.

Appropriate interlayer clearance

Its interlayer gap is approximately 0.335 nm, which is compatible with the size of lithium ions. This provides a stable storage space for lithium ions, making the structure less prone to damage during insertion and extraction.

Goede elektrische geleidbaarheid

The carbon atoms form a conductive network through strong covalent bonds, which resistivity is approximately 10^-5Ω·m. This enables it to conduct electricity quickly and reduces the battery’s internal consumption.

Main Classifications

Natural Graphite Anode

It uses natuurlijk grafiet in vlokken as the raw material, which is processed through purification, sphericalization, and coating techniques. It has high crystallinity, complete layered structure, and which raw material cost is low and easy to process. However, because it is mostly in the form of thin sheets and has an irregular shape, it has some disadvantages. During charging and discharging, the electrolyte is not evenly distributed, resulting in poor cycle stability and affecting the battery’s lifespan. So you can mostly use it in graphite batteries that are cost-sensitive and have low requirements for cycle life.

Artificial Graphite Anode

Its raw materials usually use petroleumcoke, needle coke, etc. as raw materials, and its preparation process is controllable. You can adjust parameters to optimize the performance such as processing it into spherical shapes. It has high packing density and uniform crystal structure, which improves the volumetric energy density of the battery. So its rate performance is superior to natural graphite, and the spherical structure reduces side reactions. But its raw material costs is high, which the price is 10% – 20% higher than that of natural graphite. It is used in the new energy vehicle batteries field, which accounts for most negative electrode market of batteries.

Composite Graphite Anode

It is composed by combining natural graphite, artificial graphite, silicon-based materials, hard carbon and other functional materials. It breaks through the performance bottleneck of a single type of graphite, providing a path for the performance upgrade. When combined with graphite, the graphite buffers the expansion, and silicon enhances the specific capacity. It is mainly used in graphite anode lithium batteries with high energy density requirements, such as high-end new energy vehicles.

Core Properties of Graphite Anode Material

Stable lithium storage capacity and strong adaptability

It has a hexagonal crystal lattice layered structure, which interlayer gap is 0.335nm, perfectly matching the size of lithium ions. This provides a naturally stable storage space for lithium ions,  which makes the theoretical specific capacity reach 372mAh/g. And the actual specific capacity of commercial products can also reach 340-360mAh/g, meeting the basic storage requirements of graphite battery.

Long cycle life

With its unique mechanism, the volume change rate of the layered structure during charging and discharging is only about 10%. And the crystal structure is not easily damaged, especially for artificial graphite, its capacity retention rate remaining ≥85% after 2000 cycles. So it can meet the long-term usage requirements of 5-8 years and 100,000-200,000 kilometers for new energy vehicles.

Excellent fast-charging potential

The layered structure provides a fast migration channel for lithium ions, and the high crystallinity ensures good electronic conductivity. And artificial graphite can further shorten the ion and electron conduction paths through spherical processing. So it can meet the scenario requirements of half-hour fast charging to 80% capacity for graphite anode lithium-ion batteries.

High safety

Because its lithiumization potential is approximately 0.15V, and it has a low volume expansion rate. It is close to that of metallic lithium but without forming dendrites, avoiding puncturing the separator and causing short circuits. At the same time, it can reduce the risk of material pulverization and active substance detachment. After optimization through coating and other processes, it can meet the safety standards for scenarios such as consumer electronics.

Key Preparation Processes

Raw Material Treatment

This step is impurity removal and adjustment of particle morphology, which lays the foundation for the subsequent processes.

Natuurlijk grafiet

It uses flake graphite as the raw material, which is first purified through flotation using the difference in hydrophobicity to remove impurities. And then undergoes spherification treatment which through grinding and collision to form spherical shapes, enhancing the bulk density.

Artificial graphite

It uses petroleum coke and other materials as the raw material, which is first calcined at 1000 – 1300℃. This removes volatile components and impurities and stabilizing the carbon structure.  Then ground and granulated, adding binders to form spherical particles to avoid any impact on the conductivity, stability and consistency.

Grafitisatie

This is to convert low-crystallinity carbon into high-crystallinity graphite, which determines the crystal structure and conductivity of the material. Usually, heat the material at a temperature of 2000 – 3000°C for 10 – 20 hours to reduce the layer spacing. This rearranges the carbon atoms into a hexagonal layered structure, and impurities escape as gases. For artificial graphite, this process consumes a lot of energy, accounting for more than 30% of the cost. So it usually use the continuous graphitization furnaces to reduce costs and improve efficiency, enhancing the cost-effectiveness of graphite batteries.

Modification and Optimization

This step aims to address the shortcomings of graphite, providing support for the upgrade of battery performance. There are three main methods:

Coating modification

This coats the surface of particles with amorphous carbon, etc., which enhances the cycle stability of natural graphite.

Doping modification

It introduce nitrogen, boron, etc. as impurities during graphiteification to improve the rate performance.

Pore formation modification

It creates micro pores to increase the storage sites for lithium and shorten the migration path.

Electrode Formation

It is process the graphite material into directly assembly table negative electrode sheets, which involves four steps.

Pulping

Mix graphite, binder, conductive agent and solvent in proportion to form a uniform slurry.

Coating

Apply the slurry onto copper foil to form a dry film coating of 50 – 100μm.

Rolling

Apply pressure to densify the coating to increase the volumetric energy density of the battery.

Cutting

Cut it into shapes suitable for the batterij to avoid battery performance variations due to process deviations.

Conclusie

With the graphite’s unique layered structure, graphite anode material as a main material used in the field of lithium batteries. It has stable lithium storage mechanism, excellent cycle performance and safety, becoming the core support for the large-scale commercial application. And it supports the development of industries such as consumer electronics, new energy vehicles and energy storage.