Direct Recycling of Spent Lithium-Ion Batteries at Room Temperature and Pressure in Aqueous Media

Abstract

Listen

Translate article

Lithium-ion batteries (LIBs) have emerged as an indispensable power source, driving innovations across a range of sectors, including consumer electronics, electric vehicles, and renewable energy deployment. However, the exponential growth in LIB demand has paralleled concerns regarding their end-of-life management. Key characteristics of spent LIBs include capacity fading due to repeated charge and discharge processes, loss of lithium inventory, and chemo-mechanical degradation of crystalline lattice in cathode active material. Pyrometallurgy and hydrometallurgy, the most prominent methods of LIB recycling, indirectly extract only critical metals from spent batteries but require significant energy inputs, use of harsh chemicals, and suboptimal operating conditions only to recover metal salts and require future resynthesis of the cathode active material. Direct recycling, an alternative to these process-intensive methods, allows for the regeneration of cathode active material with its structure and morphology intact, thereby conserving valuable resources directly from spent batteries and minimizing the need for extensive processing of recycled material and waste product. Solid-state sintering and thermal relithiation have recently gained traction as direct recycling alternatives, but they operate at relatively high temperature and pressure, which translates to high process intensity at scale.This presentation will discuss the effectiveness of a novel direct recycling method for LiNi0.5Mn0.3Co0.2O2 (NMC 532), a common cathode active material widely used in electric vehicles and energy storage systems. The process restores the structure and capacity of spent NMC 532 via a reduction and relithiation mechanism at standard temperature and pressure using an inorganic solution in aqueous media. The solution effectively reduces transition metals in the cathode to their original oxidation states, restores lithium vacancies that have accumulated through battery cycling, and reverses degradation of the crystalline lattice. Unlike typical solution-based direct recycling methods, this process does not require input of energy for the reaction to proceed and can be carried out in ambient operating conditions with minimal waste byproducts. Carrying out this one-step process on spent NMC 532 produces cathode active material that is identical in crystalline structure to its pristine counterpart, as validated by x-ray diffraction (XRD) characterization while galvanostatic cycling of regenerated cathode further demonstrates the restoration of peak performance capacity. The effects of water on the cathode material surface are studied to gain an understanding of electrode recycling efficiency in aqueous conditions. This study is the first to successfully implement direct recycling of NMC 532 at room temperature and pressure in aqueous media. The ambient reaction conditions and use of water as primary solvent eliminates the need for energy input and minimizes the extensive use of harmful solvents that result in toxic waste. The efficacy of this approach renders it scalable and more sustainable as a long-term solution to the management of end-of-life batteries.