MNS In Sunday Tele, page-6

Why purity is important

Purity heightens critical performance factors for lithium-ion batteries, including resistance to thermal shock, a low coefficient of thermal expansion, high electrical conductivity, high structural integrity, and low reactivity.
The quality of a deposit is determined by flake size, grade, purity, and purification costs. The higher the grade, the less processing it may need; thus, a higher purity provides a better cost-value for investors. The preferred purity level for flake graphite is 94 to 96 percent in order to be considered for batteries.
The process to qualify graphite for the high quality lithium ion batteries used in electric vehicles has many steps. But the general consensus is that if using raw material, flake and spherical graphite is the way to go if you want high quality.
Flake graphite takes purity and size into consideration, but spherical graphite considers purity and shape. Spherical graphite is flake graphite that has been through an expensive secondary process to turn its flat shape into a spherical shape. This requires a lot of fine grinding, spheroidization, and chemical purification that ultimately produces a desirable and pure product that is very fine. Spheridization improves density and reduces particle size, which is ideal when improving the quality of a li-ion battery.
After ore is mined from the deposit, it is crushed and ground and put through a floatation process to separate graphite and create a concentrate. Afterwards, producers use processing techniques to upgrade the graphite concentrate to an ideal 99.9 percent in purity.