When a graphite anode is fully lithiated, it becomes LiC₆. Which value is closest to the theoretical capacity of graphite (per mass of graphite)? Take the atomic mass of carbon as 12.01, the Faraday constant as 96485 C/mol and 1 mAh = 3.6 C.

Answer: C. About 372 mAh/g

One mole of C₆ (72.06 g) takes up one mole of Li⁺ and one mole of electrons, so the stored charge is 96485 C. The capacity per mass is Q = nF/(3.6M) = 1 × 96485 / (3.6 × 72.06) ≈ 372 mAh/g. About 339 mAh/g uses the mass of LiC₆ including Li (78.99 g/mol) in the denominator; anode capacity is normally expressed per mass of lithium-free graphite. About 2230 mAh/g is the mistake of assuming one lithium per carbon atom. Real graphite anodes are used at about 350–360 mAh/g, close to the theoretical value, and materials such as silicon are being researched to achieve higher capacity.