Impact of Surface Structure on SEI for Carbon Materials in Alkali Ion Batteries: A Review

Due to their low cost, suitable working potential and high stability, carbon materials have become an irreplaceable anode material for alkali ion batteries, such as lithium ion batteries, sodium ion batteries and potassium ion batteries. During the initial charge, electrolyte is reduced to form a solid electrolyte interphase (SEI) on the carbon anode surface, which is an electron insulator but a good ion conductor. Thus, a stable surface passivation is obtained, preventing the decomposition of electrolyte in the following cycles. It has been widely accepted that SEI is essential for the long-term performance of batteries, such as calendar life and cycle life. Additionally, the initial coulombic efficiency, rate capability as well as safety of the batteries are dramatically influenced by the SEI. Extensive research efforts have been made to develop advanced SEI on carbon materials via optimization of electrolytes, including solutes, solvents and additives, etc. However, SEI is produced via the catalytic decomposition of electrolyte by the surface of electrode materials. The surface structure of the carbon material is another important aspect that determines the structure and property of SEI, which little attention has been paid to in previous years. Hence, this review is dedicated to summarizing the impact of the surface structure of carbon materials on the composition, structure and electrochemical performance of the SEI in terms of surface atoms exposed, surface functionalization, specific surface area and pore structure. Some insights into the future development of SEI from the perspective of carbon surface are also offered.