High separation of positive electrode powder from aluminum foil and reduction leaching of positive electrode powder of waste lithium-ion batteries

Considering the strong binding force provided by polyvinylidene fluoride (PVDF), it is challenging to separate the positive electrode material from the aluminum foil. In this study, the positive electrode sheet was placed in heated ethylene glycol. As the temperature of ethylene glycol reached the melting point of the PVDF binder, PVDF gradually changed from a solid to a liquid state. At this point, its adhesive force on both the positive electrode material and aluminum foil decreased, allowing separation through the action of stirring forces. A detailed analysis of the forces acting on the positive electrode material was conducted during stirring in ethylene glycol, and the boundary layer theory was employed, proposing the Blasius solution for describing the boundary layer. The theoretical stirring linear velocity required for separating the aluminum foil from the positive electrode material was calculated. Fluid dynamics calculations demonstrated that the theoretical stirring linear velocity for separating positive electrode material in ethylene glycol was 5.08 m/s, corresponding to a rotational speed exceeding 441 r/min. When the rotational speed reached this value, the positive electrode material generated a net force greater than zero in ethylene glycol, enabling its separation from the aluminum foil. Experimental results showed that under conditions of heating at 180 ℃, stirring at 550 r/min, and a stirring time of 120 min, the delamination rate exceeded 93.00%, consistent with the theoretical rotational speed. The separated positive electrode powder was subjected to a sulfuric acid-catechol system for reduction and leaching. Ultimately, under the optimal conditions of a sulfuric acid concentration of 1.25 mol/L, catechol content of 5 g/L, a leaching temperature of 65 ℃, and a leaching time of 90 min, the leaching rates for lithium, nickel, cobalt, and manganese all surpassed 95.00%.