Synergistic thermal treatment of mixed lithium iron phosphate and lithium nickel manganese cobalt oxide black mass for improved recycling operations

Various approaches are being investigated to recover valuable materials from end-of-life lithium-ion batteries, particularly for lithium nickel manganese cobalt oxide (NMC) and lithium iron phosphate (LFP) cathode chemistries. Graphite recovery has gained increasing interest due to its classification as a critical raw material, with Flotation being a promising process for its recovery from black mass. A requirement for successfully realizing this process is the removal of binders from the anode and cathode surfaces, which is usually achieved through thermal treatment. This paper investigates the thermal decomposition behavior of pure and mixed NMC/LFP materials under oxidative and inert atmospheres and examines how these differences affect subsequent flotation performance. Macro thermobalance analysis, combined with differential thermal analysis (DTA) and mass spectrometry for multidimensional thermal analysis, was used to understand possible reactions and obtain thermally treated samples for flotation. The thermally pretreated samples were then subjected to flotation to assess the influence of the mixing ratio and evaluate the thermal treatment's quality. Differences between roasting and pyrolysis were identified, with roasting exhibiting higher net exothermicity, which increased with rising NMC content. Fluorine behavior also differed: in LFP, it was released as hydrogen fluoride (HF) gas, whereas in NMC, it remained in the residue and could continue to react during thermal treatment and subsequent processes. The findings demonstrate that cathode composition significantly influences behavior in thermal treatment and has to be considered to optimise pretreatment strategies for effective graphite recovery.