Evolution of solid electrolyte interphase during cycling and its effect on electrochemical properties of LiMn₂O₄

Thickness variation of the solid electrolyte interphase (SEI) produced during charge-discharge cycling is investigated to analyze the effect of SEI on the electrochemical properties of LiMn₂O₄. Atomic force microscopy (AFM) is used to measure the SEI thickness and elastic modulus on the LiMn₂O₄ surface. The SEI shows a broad thickness distribution due to the random nature of the LiMn2O4 electrode surfaces, while the average SEI thickness increases with cycling and stabilizes after the 20^th cycle. Formation of a relatively thin SEI on the LiMn₂O₄ surface accompanies low Coulombic efficiency at early cycling stages. The SEI produced in the early stages of cycling is vulnerable to capacity fading due to inefficient surface protection against possible side reactions. A fully-grown stable SEI after 20 cycles shields the cathode surface from the electrolyte, minimizing capacity fading.