Fluorine fixation for spent lithium-ion batteries toward closed-loop lithium recycling

Abstract

The contamination of F inhibits the recovery of pure Li from spent Li-ion batteries (LIBs). In this study, we extracted F from a cathode material of spent Li-ion batteries by dry and wet processes and investigated the effect on Li recovery. In the dry process, F was removed by calcination at a controlled temperature in the presence of an F-fixing agent. In the wet process, F⁻ ions were removed by adding Ca(OH)₂ as a F-fixing agent to F-containing aqueous Li solution. Through sequential calcination (500 °C) and water leaching cycles, we achieved high Li- and F-leaching efficiencies of 87 and 93%, respectively. When the second calcination temperature (500 °C) was higher than the first (350 °C), a high-purity Li solution was attained from water leaching after the second calcination, in which the F⁻ concentration was approximately 1/10th that of the Li⁺ concentration. Furthermore, the wet process successfully removed 98% of F from a F-containing aqueous Li solution by adding Ca(OH)₂. Thus, pure Li was successfully extracted from spent LIBs by a carbothermal process using calcium salt and water leaching treatment. The proposed acid-free process facilitates the recovery of Li from spent LIBs, which is promising for the closed-loop recycling of Li.