A corrosion study of lithium-ion batteries during NaCl electrochemical discharge: mechanistic origins and Zn-based mitigation strategies

Abstract

As lithium-ion battery (LIB) demand increases, there is growing interest in their recycling to reduce the environmental impact of mining. The safe handling of end-of-life batteries during transportation, storage and mechanical treatment requires development of environmentally sustainable and industrially scalable discharging processes. In this context, electrochemical discharge shows promise due to its simplicity, robustness, and potentially low cost. NaCl solution has been extensively studied as a promising discharge medium because of its availability and reportedly fast discharge potential. However, the use of NaCl aqueous electrolyte solutions has resulted in casing corrosion, which is associated with inefficient discharge and losses of critical raw materials. To overcome these issues, the present study offers for the first time an in-depth exploration of the potential mechanisms responsible for LIB corrosion in NaCl solutions. It is found that corrosion is a consequence of multiple parallel reactions driven by the presence of dissolved oxygen produced during electrochemical water splitting. As the corrosion pathways are identified, a novel approach is proposed to prevent it, namely, the use of Zn-salts as corrosion inhibitors. The experimental results suggest that Zn²⁺ ions aid in corrosion prevention in three main ways: (i) by forming non-soluble Zn(OH)₂ with OH⁻ ions produced on the metal surfaces; (ii) by forming mixed Fe–Zn oxide in corrosion pits; and (iii) by consuming electrons from the battery during discharge and forming a sacrificial anode of metallic Zn. The present work thus proposes an economical and reliable approach to discharge LIBs efficiently using aqueous electrolyte media.