Electrochemical Overcharge Protection of Rechargeable Lithium Batteries: I . Kinetics of Iodide/Tri‐Iodide/Iodine Redox Reactions on Platinum in Solutions

Abstract

Recently, lithium iodide has been suggested as an additive for secondary lithium batteries to prevent the oxidation of organic electrolytes during charging operations. In this study, the charge and discharge reactions of lithium iodide in (THF) solution on platinum are investigated with the cyclic voltammetric and rotating disk electrode techniques. At the anodic potentials, lithium iodide is found to undergo a two‐step process of oxidation of iodide ion to tri‐iodide ion and further oxidation of tri‐iodide ion to iodine. The diffusion coefficients of iodide and tri‐iodide ions in the electrolyte and the kinetic parameters of the redox reactions on platinum are evaluated from the rotating disk data. It is found that iodine initiates the polymerization of THF in the presence of lithium hexafluoroarsenate. To provide overcharge protection of the lithium batteries using electrolytes, large excess of lithium iodide must be present in the cell to form stable lithium tri‐iodide with the iodine generated during the charging of lithium batteries.