A CRITICAL REVIEW ON THERMAL PRE-TREATMENT OF SPENT LITHIUM-ION BATTERIES TOWARD GRAPHITE, LITHIUM AND VALUABLE METALS RECOVERIES

ABSTRACT There is a pressing need for sustainable end-of-life management techniques due to the rapid deployment of lithium-ion batteries (LIBs) in portable gadgets, grid-scale energy storage, and electric vehicles. In order to safely handle old batteries and improve the recovery efficiency of graphite, lithium, and precious transition metals like cobalt, nickel, and manganese, thermal pre-treatment has become an essential upstream step in LIB recycling. The concepts, technological methods, and performance results of thermal pre-treatment procedures are assessed in this critical analysis, with an emphasis on how they affect material selectivity, recovery effectiveness, and environmental sustainability. In order to eliminate electrolytes, break down polymeric binders such as polyvinylidene fluoride (PVDF), neutralize potentially dangerous organic components, and encourage phase changes in cathode materials, thermal pre-treatment usually entails carefully regulated heating in inert, oxidative, vacuum, or reducing atmospheres. The main benefits of low-temperature pyrolysis (300–600°C) are the elimination of binder and improved mechanical liberation of electrode materials, which promote the preservation of graphite and improved hydrometallurgical leaching downstream. High-temperature pyrometallurgical processes (>800°C), on the other hand, promote the creation of metal alloys and the concentration of transition metals, but they also frequently cause graphite oxidation and lithium partitioning into slag phases, which may lower recovery selectivity. Although scalability and process optimization are still issues, emerging techniques, including vacuum thermal treatment, microwave heating, and hybrid thermal–mechanical systems show promise for increased energy efficiency and material preservation. The paper highlights the trade-offs between activating lithium for leaching and loss through vaporization or slag entrapment by closely analyzing the behaviour of lithium speciation and volatilization during heating. Given that maintaining anode integrity is becoming more and more important for accomplishing the goals of the circular economy, special emphasis is paid to graphite structural stability under various atmospheres. Techno-economic aspects impacting industrial adoption are assessed in conjunction with environmental factors, such as energy intensity, fluorinated gas release, and greenhouse gas emissions. In general, thermal pre-treatment is essential for improving material release and recovery performance; yet, process parameters need to be carefully adjusted to strike a balance between the concentration of precious metals, lithium retention, and graphite preservation. One key road to environmentally friendly and financially feasible LIB recycling systems is the combination of sophisticated atmospheric control, energy-efficient reactor designs, and hybrid processing methods. KEYWORDS: lithium-ion batteries; thermal pre-treatment; graphite recovery; lithium recovery; cobalt; nickel; pyrometallurgy; pyrolysis; battery recycling; black mass; circular economy.