Determination of optimal parameters for the application of hydrogen peroxide as reducing agent in the leaching process

Abstract

TheuseofsecondaryLi-ionbatterieshasgrownsignificantlyinrecentyearsbecause of their high energy density and are currently used in a wide range of applications suchaselectronicappliances, energystorageapplications, andelectricvehicles. Due to the limited resources and environmental problems after end-of-use, the recycling4 of valuable metals from spent batteries is substantially essential. In this work, sulfuricacid(H2SO4)leachingwiththehelpofareducingagent(hydrogenperoxide) of four different cathode materials was studied. The cathode materials that were investigatedareLCO,NMC111,NMC622,andNMC811. The aim wast odetermine the optimal leaching conditions including leaching temperature, acid concentration, solid-to-liquid ratio, amount (%v/v), and addition strategy of the reducing agent. The optimal leaching temperature and acid concentration, without the addition of hydrogen peroxide and current collectors, were 50◦C and 2 M H2SO4, respectively. A solid-to-liquid ratio of 1:20 g/mL was selected for further leaching experiments carried out when hydrogen peroxide was added as a reducing agent. In addition, a better mixing was found to promote the leaching performance. Both metals’ leaching efficiencies for cobalt, lithium, nickel, and manganese and the hydrogen peroxide consumption were determined in order to determine the optimal hydrogen peroxide concentration in the leaching solution and the best way to add hydrogen peroxide. Differentamountsofhydrogenperoxidewereneededtoefficientlyleachthe four different cathode materials studied. Addition of hydrogen peroxide once at the beginning of leaching yielded 100% leaching efficiency faster than adding hydrogen peroxide at several occasions (same total hydrogen peroxide charge). Moreover, an addition of copper and aluminum foils, which represent the current collectors that also can act as reducing agents, can improve all metal leaching efficiencies except for lithium because lithium doesn’t need to change oxidation state. It was thus shown that the proposed leaching conditions can effectively leach valuable metals out from pure cathode materials. Crushed spent cathode material ("black mass") with the composition of Li1.087Ni0.308Mn0.300Co0.392O2 was then leached with the optimum conditions for pure cathode material (NMC111). The outcome was a leaching efficiency of almost 100% for cobalt, nickel, and manganese and with low amounts of residual hydrogen peroxide in the leachate