Customizing solid electrolyte interphase with bilayer spatial structure to mitigate swelling towards long-term life lithium battery

Abstract

The swelling behavior and stability in solid electrolyte interphase (SEI) have been proved to determine the battery cycle life. A high swollen, unstable SEI shows a high permeability to electrolyte, which results in the rapid battery performance degradation. Here, we customize two SEIs with different spatial structures (bilayer and mosaic) by simply regulating the proportion of additive fluoroethylene carbonate. Surprisingly, due to the uniform distribution of dense inorganic nano-crystals in the inner, the bilayer SEI exhibits low-swelling and excellent mechanical properties, so the undesirable side reactions of the electrolyte are effectively suppressed. In addition, we put forward the growth rate of swelling ratio (GSR) as a key indicator to reveal the swelling change in SEI. The GSR of bilayer SEI merely increases from 1.73 to 3.16 after the 300th cycle, which enables the corresponding graphite||Li battery to achieve longer cycle stability. The capacity retention is improved by 47.5% after 300 cycles at 0.5 C. The correlation among SEI spatial structure, swelling behavior, and battery performance provides a new direction for electrolyte optimization and interphase structure design of high energy density batteries.