Molecularly Tailored Dual-Function Deep Eutectic Solvent Enhances Spent Lithium-Ion Battery Cathode Delamination and...

Deep eutectic solvents (DES) are efficient for separating cathode materials and current collectors from spent lithium-ion batteries due to their high solubility and tunable properties. However, they suffer from slow reaction kinetics (>30 min) and high-temperature requirement (>120°C). Herein, a dual-function DES composed of diethyl (hydroxymethyl) phosphonate (DHP) and malonic acid (MA) with low temperature and faster kinetics was designed. The nucleophilic groups (─OH and alkoxy) on DHP and MA created extensive negative electrostatic potential regions, facilitating the degradation of polyvinylidene fluoride (PVDF) binder at low temperatures. Concurrently, the formed hydrogen-bonding network weakened intermolecular interactions, reducing viscosity and enhancing mass transfer. For LiCoO₂, a separation efficiency of >99% was achieved within 15 min at 60°C. Separation mechanism confirmed that PVDF degradation was triggered by the reaction of DHP-MA molecules with H-atoms, forming solvent channels. Furthermore, with the penetration of H⁺ and MA towards channels, the activation of the corrosion-passivation reaction brought about the accelerated cathode material detachment. The separated material exhibited low impurity content (<0.026 wt%), minimal metal loss (<2 wt%), and a well-preserved crystal structure, conducing to the repair of high-performance materials. Similar results were achieved for LiFePO₄ and LiNi_0.3Co_0.3Mn_0.3O₂, offering a universal strategy for high-quality cathode materials recycling.