Recycling of NMC from Lithium-ion batteries as potential catalysts for Oxygen Evolution Reaction

초록

Recycling of lithium-ion batteries (LIB) has gained traction in the recent years due to their high demand and the scarcity of lithium reserves. However, in most cases, only lithium is recovered and used for re-lithiation of LIBs. Other materials from the cathode active material, such as nickel, manganese, and cobalt (NMC) are considered byproducts from the recycling process. In this study, the NMC-rich byproducts from a universal lithium-recovery process are utilized as a precursor for synthesizing electrocatalysts for oxygen evolution reaction (OER). The NMC-rich byproduct was treated with 25% ethylene glycol in 0.5M HCl with heating to extract the Ni, Mn, and Co as ions. To the extract, a mixture of NaOH and Na2CO3 was added to synthesize NixMnyCoz layered double hydroxides (LDH) as a precipitate. At the same time, adding the basic mixture can also separate the Al and small amounts of Li from the treated NMC-rich byproduct, which are not active materials for OER. X-ray diffraction (XRD) patterns of the synthesized NixMnyCoz LDHs match the characteristic diffraction pattern of a rhombohedral α-Ni(OH)2. XRD peaks at 2θ 11.78°, 23.58°, 34.70°, and 61.58° correspond to (003), (006), (012), and (113) phases of α-Ni(OH)2, respectively. The NixMnyCoz LDH products were also calcined to check if their activity for OER will increase. For the electrochemical testing, catalyst inks were made with synthesized LDHs and were drop-casted on a glassy carbon electrode with a catalyst loading of 0.1 mg cm-2. Linear sweep voltammetry in 1.0 M KOH as electrolyte was done with a three-electrode set-up with Ag/AgCl and Pt sheet as reference and counter electrodes, respectively. Results show that the calcined NixMnyCoz LDH has the highest activity for OER with an overpotential of 367 mV at 10 mA cm-2 and a Tafel slope of 45.75 mV dec-1. The synthesis of NixMnyCoz LDH as an OER catalyst from the byproducts of LIB recycling increases the salvage value of battery recycling methods.