Researchers at the Southern University of Science and Technology in China have proposed a single way to address two waste problems: PET plastics and lithium-ion batteries, widely used in electronic products and electric vehicles (EV).
The team used a lab scale pyrolysis process involving spent lithium-ion battery cathodes containing Nickel-Cobalt-Manganese (NCM) and waste PET.
The method leverages the chemical reactions between the two materials at 550 C for 30 minutes, without added chemicals, to recover 99% of valuable metals (lithium, nickel, cobalt, and manganese). The high environmental and ethical impact of extracting these metals makes their efficient recovery an ever more pressing need for a sustainable energy transition.
The scientists’ choice to pyrolyse PET may seem counterproductive to the plastics industry. After all, it is well known that PET tends to degrade and undergo thermal cracking at relatively low temperatures, causing instability and uncontrollability in the pyrolysis process. PET pyrolysis also produces gases and by-products that affect yield, quality, and shorten the life of refining equipment.
However, the academics used exactly those properties to lower the temperature of the PET-NCM pyrolysis process to recover valuable metals, as well as to increase the efficiency of the process.
“It is hypothesised that PET and its intermediate pyrolysis products could react with and deconstruct the crystal lattice of NCM materials, therefore converting target metals into separated and easy-collected phases,” the scientists explained.
They found that the degradation of PET during pyrolysis released active free radicals and reductive gases that captured oxygen, destroying the stable crystal lattice structure of Li, Ni, Co, and Mn metal ions. In turn, that enabled the separation of lithium and transition metals, resulting in a recovery rate of 99% for lithium, nickel, cobalt, and manganese.
The addition of PET to NCM also reduced both the temperature and duration of the synergetic pyrolysis process.
The scientists said their method provides a chemical-free, energy-saving, and scalable lithium-ion recovery strategy while addressing PET waste minimisation. They shared their findings in ‘Synergetic pyrolysis of lithium-ion battery cathodes with polyethylene terephthalate for efficient metal recovery and battery regeneration’, recently published in communications engineering, a nature journal.