Direct Calculation of Li-Ion Transport in the Solid Electrolyte Interphase
Shi, S, P Lu, Z Liu, Y Qi, LG Hector Jr., H Li, and SJ Harris
Journal of the American Chemical Society 134, no. 37: 15476–15487.
The mechanism of Li⁺ transport through the solid electrolyte interphase (SEI), a passivating film on electrode surfaces, has never been clearly elucidated despite its overwhelming importance to Li-ion battery operation and lifetime. The present paper develops a multiscale theoretical methodology to reveal the mechanism of Li⁺ transport in a SEI film. The methodology incorporates the boundary conditions of the first direct diffusion measurements on a model SEI consisting of porous (outer) organic and dense (inner) inorganic layers (similar to typical SEI films).
New experimental evidence confirms that the inner layer in the ∼20 nm thick model SEI is primarily crystalline Li₂CO₃. Using density functional theory, we first determined that the dominant diffusion carrier in Li₂CO₃ below the voltage range of SEI formation is excess interstitial Li⁺. This diffuses via a knock-off mechanism to maintain higher O-coordination, rather than direct-hopping through empty spaces in the Li₂CO₃ lattice.