Leaching of lithium-ion battery materials in sulfate and chloride media for hydrometallurgical recycling

As a result of the worldwide attempt to phase out fossil fuels and implement cleaner technologies, batteries are becoming increasingly important. One of the most obvious effects of this green transition in everyday life has been the rapid increase in the number of electric vehicles (EVs) over the past few years. Li-ion batteries used in EVs contain high concentrations of valuable materials, many of which are classified as critical. To ensure the circulation of these materials back to reuse after End-of-Life (EoL), efficient recycling is necessary. The most commonly used battery recycling processes are hydrometallurgical and pyrohydrometallurgical. This thesis studies the leaching step of the hydrometallurgical recycling route. Leaching experiments were performed in sulfate and chloride media, using both pure commercial battery cathode chemicals and industrially processed battery waste – black mass – originating from EoL batteries. This allowed for the investigation of both fundamental phenomena associated with cathode materials leaching as well as holistic process considerations related to the presence of other battery components. During the leaching of pure cathode chemicals, Mn was observed to precipitate out of sulfate media at temperatures T ≥ 70 °C in the absence of external reductants. This precipitation was inhibited in chloride-containing lixiviants, where Cl2 gas was formed instead. Moreover, a system utilizing the reductive properties of soluble cuprous chloride complex species was found to be efficient for battery cathode materials leaching, reaching over 90% Co and Li yields under relatively mild conditions (1 M H2SO4, 0.2 M NaCl, 30 °C, 2 h). Nonetheless, observations on the use of real industrial black mass in a similar system raised questions about the compatibility of chloridecontaining lixiviants, as the reactor overflowed due to rapid gas evolution. In studies involving industrial black mass, the reductive properties of Cu were found to be improved in response to an increased solution iron concentration – up to 0.4 g/L Fe – whereas Al reductive properties were only improved as the temperature was increased. Furthermore, Cu was found to be overall a more efficient reductant in terms of electron efficiency when compared with Al. In the presence of both Cu and Al, copper was also found to temporarily cement on Al particle surfaces and redissolve as leaching progressed. Furthermore, Design of Experiments (DoE) methodology was used in combination with regression modeling to derive equations that can predict leaching yields based on input parameters – temperature, solution Fe concentration, Cu amount, and H2O2 amount. This analysis revealed solution Fe concentration and feed Cu amount as more impactful variables in terms of cathode material reduction when compared with the commonly used hydrogen peroxide. This finding was attributed to the various side-reactions associated with H2O2. Existing literature on LIB cathode material and industrial black mass leaching has largely focused on the development of novel leaching systems by the investigation of alternative reductants to H2O2 while often neglecting the role of various metallic components found within industrial black masses. This thesis contributes to the field by providing a detailed comparison of sulfate and chloride media leaching efficiencies, elucidating the capability of soluble cuprous complexes to catalyze the leaching system, and investigating the reductive efficiencies of current collector metals Cu and Al and the role of soluble Fe as an electron transporter between these metals and battery cathode materials. The research presented in this thesis will help future researchers and industrial operators by providing detailed information about the performance of various leaching media and the reductive efficiency of metallic fractions found within industrial black mass.