Discharging of Spent Cylindrical Lithium-Ion Batteries in Sodium Hydroxide and Sodium Chloride for a Safe Recycling Process

Abstract

Battery discharging prior to size reduction is an essential treatment in spent lithium-ion battery recycling to avoid the risk of fire and explosion. The main challenge for discharging the residual charges by immersion in an electrolyte solution is corrosion because of electrolysis reactions occurring at the battery terminals. This study investigated the discharging process of 18650 cylindrical lithium-ion batteries (LiBs) in NaCl and NaOH solutions and the generation of corrosion products, with the aim of developing a safe and clean discharging system for practical applications. The results show that water electrolysis is the primary reaction during battery immersion in either NaCl or NaOH solutions. Different forms of corrosion occur in each solution. Unlike the NaCl solution, which severely corroded the positive terminal of the battery, resulting in significant amount of solid residue, build-up of fluoride ions, and chlorine gas evolution, in the NaOH solution, a darkened surface of the negative terminal was the only obvious solid product, with no solid residue in the bulk solution, while oxygen gas was evolved. The NaOH solution was found to reduce battery capacity to a residual capacity range of 0–25 mAH after immersing batteries in the solution for 20 h. This value puts the battery in a safe condition for subsequent mechanical treatment. The results indicated that NaOH creates a clean discharging system and can potentially be reused.