Microwave Pyrolysis of Macadamia Shells for Efficiently Recycling Lithium from Spent Lithium-ion Batteries

To reduce harm to the environment and human health and improve economic benefits, the large number of spent lithium-ion batteries that have been produced in recent years need to be reasonably recycled. The purpose of this article is to study a new method, microwave pyrolysis of the shells of macadamia nuts, for efficient recycling of lithium from spent lithium-ion batteries. XRD, SEM, and TGA analyses were used to observe the phase change during roasting. With the help of microwave heating and biomass pyrolysis, the decomposition temperature of Li(Ni_1/3Co_1/3Mn_1/3)O₂ was reduced to 300 °C. Carbonated water-soluble Li₂CO₃ was formed under the action of biochar. Accordingly, the effects of pyrolysis temperature (Pte), biomass dose (bio%), reduction roasting temperature (Rte) and reduction roasting time (Rti) on the leaching rate of lithium were studied, and the results indicated that 93.4% lithium could be leached under the following optimum conditions: bio% = 24, Pte = 500 °C, Rte = 750 °C, and Rti = 25 min. A lattice collapse model and coupling reaction theory explained the benefit of biomass pyrolysis on the decomposition of Li(Ni_1/3Co_1/3Mn_1/3)O₂. Finally, we designed a complete process for recycling the cathode powder of spent lithium-ion batteries. This study can guide industrial production to recover lithium-ion batteries in the future.