Universal and efficient extraction of lithium for lithium-ion battery recycling using mechanochemistry

The escalating production of lithium-ion batteries (LIBs), driven by the electric vehicle and energy storage markets, necessitates the development of cost-effective and environmentally friendly recycling technologies. Current methods, including pyrometallurgy and hydrometallurgy, suffer from high energy consumption, the use of corrosive reagents, and significant environmental risks. Pyrometallurgy, while requiring no pretreatment, involves high temperatures (above 1000 °C), substantial energy expenditure, and significant pollution. Hydrometallurgy, despite offering lower emissions and milder reaction conditions, presents challenges in process complexity, dependence on electrode chemistry, and the generation of hazardous waste. Specifically, lithium loss during co-extraction with other metals is a significant problem. Biohydrometallurgy, though environmentally friendlier, is still in its early stages of development. This research investigates mechanochemistry (MC), an emerging technology that uses mechanical forces to induce chemical reactions, as a promising alternative. MC offers advantages of low cost, scalability, unique reaction mechanisms, and reduced environmental impact, making it an attractive option for LIB recycling. While MC has previously been used as a pretreatment step in hydrometallurgical processes, this study focuses on a direct mechanochemical reaction between battery materials and additives, aiming for efficient lithium recovery at ambient conditions without the need for corrosive solvents. Previous work by the authors demonstrated solvent-free processing to convert LiCoO₂ into metallic cobalt and lithium derivatives. This paper builds on that research by systematically studying lithium recovery from various commercially used cathode materials, with the objective of developing a universal and sustainable lithium recycling method.

Existing LIB recycling technologies have significant limitations. Pyrometallurgical processes, while simple, generate high emissions and consume considerable energy. Hydrometallurgical methods, though more environmentally benign, are complex and generate substantial waste, often leading to lithium loss through co-extraction with other metals. Biohydrometallurgical approaches, which avoid toxic chemicals, are still under development. Mechanochemical approaches offer a potential solution, leveraging mechanical forces for efficient and environmentally friendly reactions. Previous studies have explored mechanochemistry for pre-treatment or selective extraction of specific metals from spent LIBs, but a comprehensive method for universal lithium recovery across diverse cathode chemistries remains elusive. This paper addresses this gap by investigating the feasibility and efficiency of a mechanochemical approach for universal lithium recovery from common LIB cathode materials.

Two lithium extraction processes were developed and compared. Both processes begin with a reactive milling step where cathode material (LiCoO₂, LiMn₂O₄, Li(CoNiMn)O₂, LiFePO₄, or a mixture) is ball-milled with aluminum foil (acting as the reducing agent) for 0.5-3 hours in a hardened-steel vial. **Process 1:** After milling, the sample undergoes aqueous leaching at room temperature. The soluble filtrate (containing lithium) is then purified by heating to 350°C for 3 hours, followed by water dissolution and filtration to isolate pure Li₂CO₃. **Process 2:** Following milling, the sample undergoes a carbonization step where it's mixed with deionized water and heated to 90°C for 1 hour, then dried at 70°C. This step aims to convert any insoluble lithium compounds into Li₂CO₃. Aqueous leaching at room temperature is then performed, followed by filtration and recrystallization to isolate pure Li₂CO₃. The molar ratios of cathode material to aluminum were optimized for each cathode type to maximize lithium recovery. The reactions involved include the reduction of transition metal oxides by aluminum, formation of intermediate compounds like LiAlO₂, and subsequent transformation into Li₂CO₃ during the aqueous leaching and/or carbonization steps. Different reaction pathways were observed for different cathode chemistries, leading to the formation of various intermediate and by-product phases. The characterization methods included X-ray powder diffraction (XRD) to identify phases and scanning electron microscopy (SEM) to investigate the morphology of the samples before and after each step. The purity of the final Li₂CO₃ product was determined using inductively coupled plasma optical emission spectroscopy (ICP-OES). Lithium yield was calculated by comparing the weight of the recovered Li₂CO₃ to the theoretical amount of lithium in the initial mixture.

Process 1, involving room-temperature aqueous leaching and subsequent purification, yielded 29.8-39.6% lithium recovery depending on the cathode material. This lower yield was attributed to the formation of insoluble lithium aluminum oxide (LiAlO₂), which remained in the solid residue after leaching. Process 2, which incorporated a carbonization step to convert any insoluble lithium compounds to Li₂CO₃, significantly improved lithium recovery (55.6-75.9%). The carbonization step proved crucial in transforming a larger fraction of the lithium into a water-soluble form. XRD analysis revealed different reaction pathways and intermediate products for different cathode chemistries. For LCO, NMC, and LMO, the reduction reaction with Al led to the formation of metallic composites and LiAlO₂, while for LFP, Fe₂P and Al₂O₃ were formed, along with LiAlO₂. Process 2 simplified the flowsheet and increased efficiency. The ICP-OES analysis showed that Li₂CO₃ with purity above 99 wt% could be obtained from LCO, NMC, LMO, and mixtures of these materials. LFP yielded lower purity due to the presence of phosphorus- and aluminum-containing impurities. The study successfully demonstrated the universal applicability of the mechanochemical method to various cathode chemistries, including mixtures, thereby eliminating the need for pre-sorting of battery waste materials.

The results confirm the high efficiency and versatility of the mechanochemically induced lithium recovery method. Process 2, with the carbonization step, significantly outperforms process 1 in terms of lithium yield, demonstrating its superiority for industrial applications. The universal applicability to different cathode chemistries and their mixtures is a major advancement, simplifying the recycling process and eliminating the need for battery pre-sorting—a significant cost and time saver. The high purity of the recovered Li₂CO₃ (above 99% for most cathode materials) further validates the method's potential for commercial viability. While the LFP system showed lower purity due to phosphorus and aluminum impurities, further optimization of the process could potentially address this limitation. The findings presented in this study contribute significantly to the development of sustainable and economically feasible lithium-ion battery recycling technologies.

This research successfully developed a universal and efficient mechanochemical method for lithium recovery from various lithium-ion battery cathode materials. Process 2, incorporating a carbonization step, significantly enhanced lithium yield compared to Process 1. The method's ability to handle various cathode types and their mixtures eliminates the need for pre-sorting, simplifying the recycling process. The high purity of the recovered Li₂CO₃ highlights its potential for industrial application. Future work should focus on optimizing the LFP recycling process and investigating the method's scalability and applicability to real-world battery waste streams containing additional components.

The study focused on relatively pure cathode materials. The presence of other components (binders, conductive additives, electrolyte salts) in actual battery waste might affect the efficiency of the mechanochemical process and the purity of the recovered Li₂CO₃. Further research is needed to address this and to optimize the method for industrial-scale recycling of complex waste streams. The LFP system presented challenges regarding phosphorus and aluminum impurities which requires further investigation and optimization.