Li+-solvation/desolvation dictates interphasial processes on graphitic anode in Li ion cells

In any electrochemical device, the interface between electrolyte and electrode should be the only "legitimate" location where redox reactions happen. Particularly in Li ion batteries, these interfaces become "interphases" due to the reactivity of the electrode materials used, and they mainly consist of chemical species from the sacrificial decomposition of electrolyte components. Since the emergence of Li ion technology, it has been recognized that interphase on graphitic anodes, usually referred as SEI (solid electrolyte interphase) after its electrolyte attributes, is the key component supporting the reversibility of Li+-intercalation chemistry. Research attention focused on this component during the past two decades has led to substantial understanding about both its chemistry and mechanism. This article summarizes these progresses, and elaborates on the relatively recent insights, including the effect of Li+-solvation sheath structure on the interphasial processes at graphitic anode. A new strategy of forming a more desirable interphase is also discussed.