Lithium-ion intercalation by coupled ion-electron transfer

The underlying reaction mechanism in lithium-ion batteries remains poorly understood. We provide experimental and theoretical evidence that lithium intercalation occurs by coupled ion-electron transfer, where ion transfer across the electrode-electrolyte interface is facilitated by electron transfer to a neighboring redox site. Electrochemical measurements for a variety of common electrode and electrolyte materials reveal a universal dependence of the (de-)intercalation rate on Li + vacancy fraction, as well as temperature and electrolyte effects consistent with the theory, which could be used to guide the molecular design of lithium-ion battery interfaces.