Redox aspects of lithium-ion batteries. Is graphite an anode?

Abstract

Graphite is the most commonly used negative electrode in lithium-ion batteries. This perspective article reviews the charge transfer aspects of the graphite electrode, presenting the different mechanisms of the graphite electrode involved during its charging from an electrochemical standpoint. Different reaction mechanisms can be distinguished: (1) adsorption of solvated lithium ions on negatively charged graphite, (2) intercalation of de-solvated lithium ions in graphite as a solid solution, (3) biphasic (liquid–solid) formation of solid LiC₃₆ and LiC₁₂ phases, (4) biphasic (solid–solid) formation of a LiC₆ phase and (5) under potential deposition of lithium atoms on the LiC₆ phase, which may be followed by classical electroplating of Li⁺ on Li. Only the last electrodeposition reactions are truly a redox process. The other reaction mechanisms represent the potentiometric titration of carbon sites for lithium ion adsorption and intercalation.