3) Continuous consumption of Li by SEI layer and dead Li
Li is a very strong reducing agent because of the lowest redox potential (-3.04 V vs. SHE). Thus, Li reacts intensely with the electrolytes, forming the SEI layer, which passivates the Li surface to prevent further consumption of Li and electrolytes.[51]However, the SEI layer is usually cracked owing to the large volume change during the charge/discharge process,[70] so that fresh Li is inevitably exposed to the electrolytes, leading to the repetitive loss of Li and electrolytes. A thick and non-uniform SEI layer formed by the repeated formation of SEI interferes with Li ion conduction and induces uneven and dendritic Li deposition. This unfavorable morphology of Li is susceptible to the formation of electrically isolated dead Li,[35] which accelerates active Li loss.[71]