Solid-State Synthesis of NMC111 and Impact of Impurities on the Electrochemical Performance

The growing deployment of electric vehicles will soon generate large quantities of end-of-life Li-ion batteries, making the recovery of Ni–Mn–Co (NMC) cathode active materials critical. Recycling processes often yield individual metal salts that can be directly recombined into NMC through solid-state synthesis, a simple, water-free alternative to coprecipitation. However, recycled precursors may contain residual impurities whose impact on solid-state NMC synthesis remains poorly understood, notably in terms of electrochemical performance. Therefore, investigating the influence of controlled amounts of CuO and/or Na2SO4 (typical residues from battery wastes and hydrometallurgical steps) on the morphology, structure, and electrochemical performance of NMC111 synthesized from carbonate precursors is needed. We report that both impurities reduce particle size and increase the lattice parameters, indicating their partial incorporation into the oxide structure. Cu-containing samples exhibit Cu-rich inclusions, while Na2SO4 induces strong chemical heterogeneity within particles. These impurity-driven microstructural changes enhance high-rate capability but deteriorate cycling stability. Na2SO4-containing materials in particular show rapid capacity fading, whereas low CuO levels (1–2 wt %) maintain chemical homogeneity and deliver aging performances comparable to pristine NMC. This study demonstrates that impurities introduced during solid-state synthesis can hinder particle growth and chemical homogenization, thereby governing the performance of recycled NMC materials.