Graphite

Graphite is pure carbon in which the atoms form flat sheets of linked hexagons, like chicken wire, stacked one on another. Inside each sheet the bonds are very strong; between sheets they are weak, so the sheets slide apart easily. That is why graphite feels slippery and leaves a mark on paper: pencil lead is graphite mixed with clay.

Graphite is carbon alone, and comes two ways. Natural graphite is mined as flakes or lumps, mostly in China, then crushed, separated from the rock and purified. Synthetic graphite is made by heating carbon-rich materials, such as petroleum coke, to around 3,000 °C without air for a long time. At that heat the carbon atoms slowly rearrange into orderly stacked sheets. For batteries it is ground to a fine powder.

Each sheet has loose electrons that can move along it, so graphite conducts electricity, unusual for a nonmetal. In an alkaline battery, a few percent of graphite powder is mixed into the manganese dioxide cathode to carry current through it. Graphite is also the main material on the negative side of lithium-ion batteries. A single sheet on its own is graphene.