Lithium-ion batteries (LIBs) are the core technology for addressing the formidable and ever-increasing needs for portable energy storage, benefiting from their safety, versatility, and excellent electrochemical properties. (1,2) With continuous marketing expansion, the estimated global market demand for LIBs is projected to reach $95 billion and 439.32 GWh by 2025. (3,4) The rapid growth of LIBs has led to a proliferative demand for critical metal resources, including lithium (Li), manganese (Mn), cobalt (Co), and nickel (Ni). (5) In this regard, recovering critical metals from spent LIBs is of great urgency to address the metal resource shortage and achieve a circular economy.

Cathodes with high-density critical metals are the most valuable component in spent LIBs. (6) To recycle critical metals from the spent cathode, pyrometallurgy and hydrometallurgy methods are extensively employed for the recycling of spent LIBs. (7) Meanwhile, the pyrometallurgy approach requires a pyrolysis treatment at high temperatures, resulting in higher energy consumption, severe CO₂ emissions, and secondary pollution. (8) In contrast, the hydrometallurgical process, which involves massive amounts of hazardous acid or potent redox agents shipped long distances and then used in wet-chemistry leaching, has been extensively employed in spent cathode recycling. (9−11) Despite the high leaching efficiency, the hazardous nature of acid or oxidizing agents may cause substantial adverse environmental and health effects, resulting in excess wastewater or air pollution and leading to severe health and safety issues (Figure 1a). (12−14) In this regard, developing green and environmentally friendly solvents for the universal and sustainable leaching of critical metals from LIBs is urgently needed. Under these circumstances, mild and green extraction solvents such as hydrogen peroxide (H₂O₂), sodium sulfite (Na₂SO₃), persulfate, and deep-eutectic solvents (DES) have been recognized as greener reagents, recently being explored for cathode leaching. (15,16) For instance, a deep eutectic solvent composed of chloroacetic acid and ethanol, with oxygen as the oxidant, has been applied for the recovery of lithium from spent LiFePO₄ (LFP) powder. (17) In addition, sulfites and sodium persulfate have been employed as oxidants to selectively extract lithium from spent LiCoO₂ (LCO) and LiMn₂O₄ (LMO), respectively. (18,19) Unfortunately, their high cost and low universality hinder their broad application for recycling diverse types of spent LIB cathodes.

Herein, to develop a green and universal agent for critical metal recycling from multiple types of LIBs cathodes, we employed a multifunctional peracetic acid (PAA) for highly efficient critical metal extraction from different spent cathodes (Figure 1a). Benefiting from the high redox potentials, (20) acidic proton attacking, and coordination function (denoted as three-in-one driven forces) from the carboxyl group, PAA undergoes a self-sacrifice process and delivers a highly efficient critical metal recovery from multiple types of cathodes, including LFP, LCO, LMO, and LiNi_xCo_yMn_1–x–yO[sub[2 (NCM). Furthermore, acetic acid (HAc) could be recovered from wastewater after critical metal precipitation, thereby enabling solvent recycling and contributing to a closed-loop wastewater treatment process. Employing PAA as the green critical metal extraction reagent here demonstrates a novel, integrated three-in-one self-sacrifice mechanism for universal critical metal leaching, which is technically important for the circular economy and closed-loop resource utilization of urban mines.

Figure 1. Three-in-one self-sacrifice mechanism in PAA for critical metal leaching from spent LIBs cathodes. (a) Schematic comparison between the traditional recycling methods and the green PAA leaching method. (b) Redox potentials of PAA refer to the metal ion redox pair frequently present in typical spent LIBs cathodes. (c) Volume concentration-dependent pH values of PAA aqueous solution. (d) Stability constants of typical transition metal-acetate complexes.

Figure 2. Critical metals leaching behaviors of spent NCM622 reacting with PAA. (a) Schematic representation of the leaching experiments setup. Effects of (b) initial pH value, (c) PAA concentration, (d) S/L ratio, (e) reaction temperature, and (f) reaction time on critical metal leaching. (g) Comparison of metals leaching behaviors with HAc, H₂O₂, HAc + H₂O₂, and PAA. Error bars: mean ± standard deviation of three replicates.

Figure 4. Universality of the three-in-one self-sacrifice leaching mechanism in PAA. (a) Schematic diagram of ion migration at the solid–liquid interface in PAA (left) and illustration of the three-in-one self-sacrificial leaching mechanism (right). High universality of employing PAA for multiple spent cathodes: (b) Optical images of leaching experiments. (c) Leaching efficiency of multiple LIBs cathodes under the previous optimal condition. (d) Effect of the S/L ratio of PAA for LCO leaching. Error bars: mean ± standard deviation of three replicates.

Figure 5. Recycling of critical metals from leachate. (a) A heating-condensation reflux apparatus for HAc recovery. (b) 1H NMR spectrum of the obtained liquid by heating-condensation reflux. (c) Effect of heating temperature on HAc recovery for 12 h. Solubility-pH diagrams of (d) Ni, (e) Co, and (f) Mn in leachate. Influence of initial pH on (g) reaction solution color change and (h) precipitation ratio of critical metals in leachate at 25 °C. Error bars: mean ± standard deviation of three replicates.

Figure 6. Techno-economic and environmental benefits analysis of recycling valuable metals from spent LIBs with PAA. (a) Economic analysis. Proportions of (b) inputs and (c) outputs. (d) Environmental benefits assessment.

PAA aqueous solution, a commercial environmentally sustainable green chemical reagent, was first reported as a potent agent for recycling critical metals from spent NCM622 cathodes. Effective recovery of all critical metals was achieved under the optimized conditions. A comprehensive in situ structural evolution and spectroscopy characterization unveils the synergistic mechanism of proton attack, redox reactions, and complex interactions that collectively facilitate critical metal leaching and result in PAA self-sacrifice. Simultaneously, PAA has also effectively facilitated the recovery of critical metals from multiple types of spent cathodes, further underscoring the universal applicability of the reagent. Additionally, the effective recovery of HAc from the residue solution by the evaporation–condensation reflux system establishes a closed-loop process that significantly reduces the level of generation of secondary hazardous wastewater. Moreover, compared with traditional mineral acids such as H2SO4, HCl, and HNO3 that are often associated with severe corrosion, secondary pollution, and downstream waste management, PAA decomposes into environmentally benign byproducts (HAc and oxygen), generates minimal hazardous emissions, and thus significantly reduces environmental risks. This highlights PAA as a greener, safer, and more sustainable alternative for the recovery of critical metals. Furthermore, this economically viable and environmentally benign approach provides a robust theoretical foundation and practical framework for the recovery and recycling of critical metals from various types of spent LIB cathodes, with the potential to enhance the sustainable resource recycling from urban mines and beyond.