Enhancing Lithium Recycling Efficiency in Pyrometallurgical Processing through Thermodynamic-Based Optimization and Design of Spent Lithium-Ion Battery Slag Compositions

The increasing demand for lithium in lithium-ion battery (LIB) applications necessitates innovative recycling strategies. Combined pyrometallurgical–hydrometallurgical recycling has gained increased attention for lithium recovery from slags. One challenge in the technological advancement of recycling lithium from spent LIBs with lithium-nickel-manganese-cobalt-oxide cathodes (NMC), characterized by a Li–Al–Si–Ca–Mn–O slag system, lies in the distribution of lithium across multiple silicate and oxide phases. Hence, the goal of this work is to significantly enrich the lithium in the single target phase γ-LiAlO2 with thermodynamic-based optimization for tailored slag designs. This is achieved by coupling a sophisticated thermodynamic database and model reassessment related to practical NMC-type LIB slag system composition fields with Pareto optimization. Extensive experimental investigations are performed for model and design validations, and procedures for selecting the best phase candidates with individual lithium content are systematically presented. A strong nonlinear influence of CaO on the formation of the target product γ-LiAlO2 could be revealed, where the addition of SiO2 for lithium slagging needs to be limited to enrich lithium in the target phase. Higher amounts of added CaO and SiO2, such as both at 30 wt %, result in the undesired transfer of lithium into other Li-containing phases. Based on this approach, an artificial slag is computationally designed for the first time, where theoretically 100% of the lithium is trapped in γ-LiAlO2. After production of this slag and experimental analysis, it was found that 96% of lithium was transferred into γ-LiAlO2. This demonstrates the great potential of thermodynamics-based artificial slag design for enhancing lithium recycling efficiency in LIB recycling processes.