Efficient and sustainable recycling of lithium-ion batteries is a crucial element in electrifying transportation. Black mass is a mixture of cathode and anode materials remaining after disassembly and shredding of end-of-life lithium-ion batteries (LIBs). Many valuable materials, including lithium and nickel, manganese and cobalt (NMC) metal oxides, can be recovered from black mass, but current recycling practices require temperatures in excess of 1,000°C and highly corrosive acids. A new recycling method effectively separates the cathode and anode materials from black mass using ultrasound waves and oil nanodroplets in water.
“The industry standard for black-mass recycling uses a combination of pyro- and hydro-metallurgy processes. This recycling pathway is referred to as ‘long-loop’ recycling, as it takes the precious battery materials all the way back to their precursors. Our process utilizes emulsions formed by cooking oil to facilitate ‘short-loop’ recycling by directly purifying LIB black mass into pure cathode and anode components. The purified components could either go directly back into manufacturing of new battery cells, with or without further treatment steps, to regain the performance of pristine materials,” explains Jake Yang, lecturer of physical chemistry at the University of Leicester (www.le.ac.uk), who led the research along with professor Andy Abbott at the university’s Centre for Sustainable Materials Processing.
Typically, colloidal suspensions are not stable without added surfactants, but the application of ultrasound was key to creating the inexpensive nanoemulsion with only water and vegetable oil. “In our everyday experience, we know cooking oil and water don’t mix. However, intense shockwaves generated by high-power ultrasound caused the macro-sized oil droplets to break up into nanodroplets that were found to be stable for weeks,” says Yang.
First, LIB black mass must be pre-treated to remove binder materials. Then, cathode and anode metals are separated in the nanoemulsion, where the oil nanodroplets bind to the surface of hydrophobic graphite particles and form “oil-graphite conglomerates” that float on the surface of the water. “This leaves the hydrophilic lithium metal oxides essentially untouched. A simple sieving process allows for separation of the graphite, leaving pure metal oxides,” adds Yang.
The team has purified batches of 40 g of black mass using the oil emulsion technology. Plans are underway to create a pilot unit capable of processing black mass at the tens-of-kilograms scale with the ultimate aim of processing black mass on a ton-per-hour scale. Details of this work were recently published in RSC Sustainability.