Selective lithium Pre-Leaching from spent NMC black mass via pyrolysis (Carbothermal thermal Treatment) and controlled leaching

Abstract

The rapid expansion of lithium-ion battery usage has intensified the need for efficient and economically viable recycling processes capable of selectively recovering lithium from spent cathode materials. Here, we develop and mechanistically evaluate a simplified, reductant-free pyrolysis–leaching route for lithium pre-extraction from NMC-type black mass. Carbothermal reduction (pyrolysis) was conducted at 550–630 °C for 60 min under nitrogen using only the inherent carbon content of the black mass as the reducing agent. Comprehensive characterization, including XRD, Raman spectroscopy, SEM-EDX, ToF-SIMS, and TC/TOC, revealed that carbothermal reduction induces a sequence of phase transformations: (i) decomposition of PVDF and organics to form reactive pyrolytic carbon; (ii) collapse of the NMC layered structure; (iii) carbothermal reduction of Ni and Co oxides; and (iv) formation of water-leachable Li₂CO₃/Li₂O. These modifications increase lithium accessibility while stabilizing transition metals as Ni⁰, Co⁰/CoO, and MnO, enabling selective lithium dissolution at near-neutral pH. Leaching experiments showed that untreated black mass achieves only 21 % Li recovery at pH around 7, whereas pyrolyzed material yields ∼ 63 % Li recovery at the same pH, with < 1–6 % dissolution of Ni, Co, and Mn. This high selectivity eliminates the need for strong acids, reduces impurity load, and preserves transition-metal phases for downstream hydrometallurgical or regeneration processes. A technoeconomic comparison with two representative literature routes demonstrates that the proposed process offers the lowest energy consumption, reagent use, and purification burden, owing to its low-temperature operation, reductant-free design, and minimal chemical inputs.