A green and efficient strategy for leaching critical metals from spent LiNixCoyMnzO2 cathodes: modulating the dielectric SiO2 contact-electro-catalytic activity

Owing to the global transition toward carbon neutrality, lithium-ion batteries (LIBs) are experiencing unprecedented demand growth as key energy storage components. A contact-electro-catalysis (CEC) method has been utilized in recycling spent LIBs for some time due to the process economy, efficiency and environmental sustainability. However, systematic investigations into the effects of the microstructure and surface chemical environment of dielectric materials on their catalytic activity in the CEC process remain scarce. Here, we demonstrated that the metal leaching efficiency simultaneously depended on the size and porous structure of SiO2 microspheres. Appropriate size and narrow distribution could dominantly diminish the scattering intensity of ultrasonic waves to gather energy and then facilitate the formation of cavitation bubbles to generate abundant electrons and radicals. Similarly, the porous structure also promoted the generation of electrons and radicals by enhancing aqueous-phase contact interfaces. Moreover, we manipulated the surface chemical environment of porous SiO2 microspheres by incorporating sodium alginate (SA) and polyethyleneimine (PEI). Hydroxyl, carboxyl and amino groups and –COO−/–NH3+-microstructures not only accelerated electron transfer from water molecules to SiO2 microspheres, inducing hydroxyl radicals, but also boosted electron transfer from SiO2 microspheres to O2, generating superoxide radicals. Consequently, under the experimental conditions established in this study, approximately 100% leaching efficiency of metals in the spent ternary cathode was achieved in 8 h at 80 °C due to the synergistic effect of hydroxyl and superoxide radicals. We anticipate this innovative strategy will significantly expand the applicability of CEC in LIB recycling, thereby addressing the growing global demand for sustainable LIBs.