One-step nickel-cobalt alloy electrodeposition from spent lithium-ion battery via synergistic pH adjustment and Mn2+ supplementation

Abstract

Alloy productization of nickel (Ni) and cobalt (Co) in spent lithium-ion batteries (LIBs) is an effective way for their high-value conversion. Herein, we dynamically supplemented divalent manganese (Mn2+) ions into the LIBs leachate while synergistically adjusting the pH for rapid electrodeposition of Ni-Co alloys on the cathode. Benefiting from the suitable redox potential, Mn2+ ions can be easily oxidized to MnO2 at the anode thus providing electrons push the cathodic reaction, and without being reduced by the cathode. The electrons provided by the oxidation of Mn2+ ions occupied 51% of the required for the cathodic electrodeposition. However, the oxidation of Mn2+ gave rise to a decrease in pH (from 3 to 2 within 30 min), which caused protonation on the cathode surface, resulting in electrostatic repulsion of Ni2+ and Co2+ by the cathode. By dynamically adjusting the pH to 3 every half hour using ammonia, the protonation of the cathode can be effectively suppressed, thereby converting electrostatic repulsion into attraction. The methods of dynamic supplementation of Mn2+ ions and pH adjustment have complementary effects. Compared with the control group, the deposition rates of Ni and Co are increased by 6.59 and 11.09 times, and the obtained Ni-Co alloys with the purity of 99.80%. Concurrently, the MnO2 by-product of 99.52% purity is obtained on the anode. This strategy does not cause additional contamination of the LIBs leachate because the LIBs leachate contains Mn2+.