Direct regeneration of NMC811 cathode materials from spent lithium-ion batteries : technical performance and circular raw material impact

Abstract

Spent NMC 811 cathode material loses lithium and structural order during cycling, and conventional recycling routes destroy this structure to recover only metal salts, so this thesis investigated direct solid-state regeneration as a structure-preserving alternative, aiming to identify the optimal LiOH supplementation level and determine the effect of sintering atmosphere on regeneration quality. The spent black mass was subsequently re-lithiated with 0, 4, 10, and 15 wt% LiOH and was calcined in two stages (450°C/4h, 750°C/8h), first in a passive atmosphere (Phase I) and then in a continuous oxygen supply (Phase II) with all other conditions kept constant, and the regenerated material was analysed using XRD analysis, SEM, and coin-cell cycling. Oxygen-assisted sintering significantly improved capacity under all conditions in Phase II (highest capacity with 4 wt% LiOH at 186.9 mAh/g, or approximately 89% of the typical commercial NMC 811 benchmark, but reversed the capacity trend for LiOH in Phase I) while maintaining the best structure. Based on these results, it was found that the quality of regeneration was primarily controlled by the sintering atmosphere and not by the amount of lithium, and that oxygen-assisted direct regeneration can return spent NMC 811 to an almost commercial standard with a low-reagent sintering process in line with the EU battery recycling targets.