Nanostructured Ball-Milled Ni-Co-Mn Oxides from Spent Li-Ion Batteries as Electrocatalysts for Oxygen Evolution Reaction

Discovering sources of transition metals, such as Ni, Co, and Mn, has become crucial due to their broad applicability, particularly as electrocatalysts for the oxygen evolution reaction (OER). Upcycled spent batteries have emerged as alternatives for transition metal sources for the OER electrocatalysts. In this work, Ni-Co-Mn oxalates were extracted from the spent LiNi_xCo_yMn_zO₂ (NCM) cathode of lithium-ion batteries. The extracted oxalates were further processed via ball milling as a rapid and scalable mechanochemical route to engineer their structures. After calcination, Ni-Co-Mn oxides with nanosized granules on the surface that mainly consist of MnCo₂O₄ were obtained. With a correlation of morphology and trimetallic oxide formation with the OER catalytic performance, Ni-Co-Mn oxides exhibit OER overpotentials of 367 and 732 mV in alkaline and neutral media, respectively, showing OER catalytic activity in a wide pH range. The results indicate that ball milling can induce particle size reduction and bond formation between metals to facilitate mixed-metal oxide formation. Furthermore, the resulting material is also applicable as the catalyst in the air cathode of Zn-air batteries, where the battery achieved a power density of 85.42 mW cm^-2 and 100 h of cycling stability, showing comparability with a battery with a Pt/C-Ir/C catalyst.