Graphite is a crystalline allotrope of carbon, made of carbon atoms bound hexagonally in sheets.
- Hexagonal Layers: graphite consists of carbon atoms arranged in a hexagonal lattice, forming flat, two-dimensional sheets.
- Bonding Structure: within each layer, every carbon atom is strongly covalently bonded to three other carbon atoms.
- Layered Structure: these hexagonal sheets are stacked on top of each other.
- Weak Interlayer Bonding: the layers are held together by weak van der Waals forces, not strong covalent bonds. Because of this, the layers can easily slide over one another, which makes graphite soft, slippery, and an excellent lubricant.
Outside of batteries it is used in electrodes and electrical contacts, as a moderator in nuclear reactors and as a dry lubricant.
In lithium ion batteries it is used as the anode. In battery cells we see the use of natural and synthetic graphite (see Graphite Anode for how it is processed and used at electrode level).
Choosing between the two is a trade-off. Natural graphite is usually the cheaper option, offers high capacity and needs less energy to produce, whereas synthetic graphite generally copes better with the electrolyte, tolerates fast charging better and delivers longer cycle life. [1]
Natural versus Synthetic Graphite
A comparison of the material properties and then a look at the advantages / disadvantages at cell level.
Isotropic Graphite
Isotropic graphite is designed to reduce the stress from Li+ insertion and extraction. Making it more stable and thus improving lifetime.
Graphite Development
Developing new graphite anodes to diversify the supply chain remains challenging due to proprietary formation protocols and inconsistent test formats. In this study between WMG, University of Warwick and James Durrans & Sons Limited we report on the development of industry-grade graphite as a case study to examine what is required from materials requirements to align with up adoption in Li-ion batteries – including “apples for apples” pouch cell studies with commercial benchmarks.
References
See also: Anode Manufacturing, Challenges of Adding Silicon to Graphite Anodes