Key Takeaways & Executive Findings
- •• • Achieved 99.4% Li leaching efficiency and 97.8% Co recovery as CoC2O4·2H2O under optimal conditions (ChCl:OA:H2O molar ratio 1:1:8, solid-liquid ratio 100 g/L, 90 °C, 6.5 h), demonstrating near-complete metal extraction from spent LiCoO2. • • Lithium recovery via evaporation crystallization as Li2C2O4 reached 88.3%, enabling selective separation without additional precipitants, simplifying the process and reducing chemical consumption. • • The DES solvent exhibited excellent reusability: after six regeneration cycles, Li and Co recoveries remained at 78.1% and 92.8%, respectively, underscoring process sustainability and cost-effectiveness for industrial scale-up. • • The water-regulated strategy allows precise control of metal speciation, providing a mechanistic basis for selective recovery and offering a green alternative to conventional acid leaching methods.
Abstract
The proliferation of lithium-ion batteries (LIBs) in portable electronics and electric vehicles has generated a pressing need for sustainable recycling of spent batteries. Conventional pyrometallurgical and hydrometallurgical routes suffer from low metal recovery efficiencies or require additional precipitants. This study introduces a clean and efficient process for recovering lithium (Li) and cobalt (Co) from spent LiCoO2 cathode materials using a choline chloride-oxalic acid-water (ChCl-OA-H2O) deep eutectic solvent (DES). The method exploits selective precipitation of Co as cobalt oxalate dihydrate (CoC2O4·2H2O) followed by water-content-regulated recovery of Li as lithium oxalate (Li2C2O4) via evaporation crystallization, eliminating the need for external precipitants. Under optimized conditions (molar ratio 1:1:8, solid-liquid ratio 100 g/L, 90 °C, 6.5 h), the leaching efficiency of Li reached 99.4%, with recovery efficiencies of 88.3% for Li and 97.8% for Co. The DES system demonstrated robust cycling stability, maintaining Li and Co recoveries of 78.1% and 92.8% after six regeneration cycles. This work provides a low-pollution, economically viable pathway for LIB recycling, contributing to resource sustainability and offering significant industrial potential.
1. Introduction
The exponential growth of lithium-ion battery (LIB) deployment in consumer electronics and electric vehicles has created an urgent environmental and economic imperative to recycle spent batteries. Global LIB waste surpassed 500,000 tonnes in 2022, increasing at an annual rate of 20%. Conventional recycling technologies, primarily pyrometallurgical and hydrometallurgical processes, have reached relative maturity but exhibit critical bottlenecks: pyrometallurgy suffers from low metal recovery efficiencies and high energy consumption, while hydrometallurgical acid/alkali leaching often requires additional precipitants to selectively recover metals, generating secondary waste streams. These limitations hinder the development of a truly circular economy for critical battery materials.
This study addresses these bottlenecks by introducing a deep eutectic solvent (DES) system based on choline chloride, oxalic acid, and water (ChCl-OA-H2O) that enables simultaneous leaching and selective recovery of lithium and cobalt from spent LiCoO2 cathodes. The key innovation lies in the water-content-regulated precipitation: cobalt is selectively precipitated as cobalt oxalate dihydrate, while lithium is subsequently recovered as lithium oxalate by adjusting water content, eliminating the need for external precipitants. The process operates at a high solid-liquid ratio (100 g/L) and moderate temperature (90 °C), achieving high recovery efficiencies (Li: 88.3%, Co: 97.8%) with excellent solvent recyclability (six cycles). This approach offers a low-pollution, economically viable alternative to conventional methods, with direct implications for industrial battery recycling.
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Libin TANG, Mingqiang CHENG, Zhipeng ZHOU, Juanjian RU, Cunying XU, Yixin HUA, Ding WANG (2026). Efficient Recovery of Lithium and Cobalt from Spent Lithium-Ion Batteries Using a ChCl-OA-H2O Deep Eutectic Solvent. The Chinese Journal of Process Engineering. https://doi.org/10.12034/j.issn.1009-606X.225221
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Frequently Asked Questions
What is the maximum solid-liquid ratio that can be processed without compromising leaching efficiency, and how does this compare to conventional acid leaching?
The optimized solid-liquid ratio is 100 g/L, achieving 99.4% Li leaching efficiency. This is comparable to or higher than conventional acid leaching processes, which typically operate at lower solid-liquid ratios (e.g., 20-50 g/L) to avoid pulp viscosity issues. The high solid-liquid ratio reduces reactor volume and waste generation, enhancing process economics.
How does the water content in the ChCl-OA-H2O DES influence the selective precipitation of cobalt and lithium, and what is the underlying mechanism?
Water content modulates the solubility of metal oxalates. At low water content (molar ratio 1:1:8), cobalt oxalate (CoC2O4·2H2O) precipitates selectively due to its low solubility, while lithium remains in solution. Increasing water content later facilitates lithium oxalate (Li2C2O4) precipitation during evaporation. This water-regulated strategy enables stepwise recovery without additional reagents.
What are the long-term stability and recyclability of the DES solvent under repeated use, and what regeneration steps are required?
The DES solvent can be regenerated by replenishing oxalate ions (C2O4^2-) and water. After six regeneration cycles, Li and Co recovery efficiencies remain at 78.1% and 92.8%, respectively, indicating good stability. The slight decline is likely due to accumulation of impurities or changes in solvent composition, but the process remains economically viable.
How does the energy consumption and environmental footprint of this DES-based process compare to conventional pyrometallurgical and hydrometallurgical routes?
The process operates at 90 °C, significantly lower than pyrometallurgical temperatures (>1000 °C), reducing energy consumption. It avoids the use of strong acids and bases, and eliminates the need for additional precipitants, minimizing chemical waste. The DES is recyclable, further reducing environmental impact. These factors contribute to a lower overall carbon footprint and improved sustainability.
What are the purity levels of the recovered cobalt oxalate and lithium oxalate products, and are they suitable for direct reuse in battery manufacturing?
The paper reports recovery efficiencies of 97.8% for Co and 88.3% for Li, but does not specify product purity. Typically, oxalate precipitation yields high-purity products (>99%) that can be converted to battery-grade oxides (e.g., Co3O4, Li2CO3) via calcination. Further purification steps may be required to meet stringent battery-grade specifications, but the process provides a promising precursor route.
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