Defect Thermodynamics and Diffusion Mechanisms in Li2CO3 and Implications for the Solid Electrolyte Interphase in Li-Ion Batteries

Abstract

Understanding and improving Li transport through crystalline Li2CO3, a stable component of the solid electrolyte interphase (SEI) films in Li-ion batteries, is critical to battery rate performance, capacity drop, and power loss. Identification of the dominant diffusion carriers and their diffusion pathways in SEI films coated on anode and cathode surfaces is a necessary step toward the development of methods to increase Li conductivity. In this paper, we identify the dominant Li diffusion carriers in Li2CO3 over a voltage range (0–4.4 V) that includes typical anode and cathode materials by computing and comparing thermodynamics of all seven Li-associated point defects with density functional theory (DFT). The main diffusion carriers in Li2CO3 below 0.98 V are excess Li-ion interstitials; however, above 3.98 V, Li-ion vacancies become the dominant diffusion carrier type, and they have the same concentration in the voltage range of 0.98–3.98 V. Diffusion mechanisms of the main diffusion carriers were comput...