THERMAL STABILITY STUDIES OF LI-ION CELL NEGATIVE ELECTRODE MATERIALS: GRAPHITE, MCMB, HARD-CARBON AND InSb

A Li-ion cell typically consists of a carbon-based negative electrode (NE); a porous polymer membrane separator (polypropylene and/or polyethylene); and a lithiated transition metal oxide (LiMxOy, M=Co, Ni, and/or Mn) positive electrode (PE). Electrodes are made by casting slurries of PE or NE-materials, PVDF-binder and carbon-black onto metal current collectors. Mixtures of Li-salts and organic solvents provide an electrolyte medium for lithium ions to shuttle between the PE and NE. Upon cycling, passivation layers (SEI-layer) form over the surface of NE and PE-materials. Studies agree that this SEI-layer on the carbon-based NE consists of Li2O, LiOH, Li2CO3, LiCO2-R and LiF or LiCl, depending on whether LiPF6 or LiClO4 salt is used. This SEI-layer prevents excessive electrolyte reaction with the NE and thus improves cell cycle-life [1].