Stable Long Cycling of Small Molecular Organic Acid Electrode Materials Enabled by Nonflammable Eutectic Electrolyte.

Abstract

Small molecule organic acids as electrode materials possess the advantages of high theoretical capacity, low cost, and good processability. However, these electrode materials suffer from poor cycling stability due to the inevitable dissolution of organic molecules in the electrolytes. Here, a eutectic mixture of lithium bis(trifluoromethanesulfonyl)imide and N-methylamine is employed as a eutectic electrolyte in Li-ion batteries with small molecule organic acids as electrodes. To enhance the cycling stability of the electrolyte, fluoroethylene carbonate is used as an additive. The electrolyte exhibits nonflammability, high ionic conductivity, and good electrochemical stability. Molecular dynamics simulations and density functional theory are performed to further investigate the solvation chemistry of the eutectic electrolyte. The well-designed eutectic electrolyte inhibits the dissolution of terephthalic acid effectively and displays superior performance with a capacity retention of ≈84% after 2000 cycles at a high current density of 1 A g-1 . It also enables stable cycling of more than 900 cycles at a high current density of 2 A g-1 at 60°C. This study provides a strategy to enhance the cycling stability and safety of Li-ion batteries with organic electrode materials.