University of Leicester scientists have developed a technique for sustainably extracting valuable metals from a waste product of used batteries with a mix of water and cooking oil.

The technology allows lithium-ion battery ‘black mass,’ a low-value mixture of anode and cathode and other materials, to be purified directly within minutes of operation at room temperature.

Oil and water do not mix, but using ultrasound nano-droplets of oil can be created that are stable for weeks. Crucially, oil nano-droplets are found to purify battery waste commonly known as ‘black mass’ as it contains a mixture of carbon (graphite) and valuable lithium, nickel and cobalt metal oxides (NMC). The oil nano-droplets stick to the surface of the carbon, acting as a ‘glue’ to bind hydrophobic graphite particles together to form large oil-graphite conglomerates which float on water, leaving the valuable and hydrophilic lithium metal oxides untouched. The oil-graphite conglomerate can simply be skimmed off leaving pure metal oxides.

Current recycling techniques use a combination of furnace heat treatment to burn off the undesired graphite, thereby increasing the CO2 footprint of the EV value chain, as well as concentrated corrosive acids which take valuable battery-grade metal oxides all the way back to the lower-valued battery precursor materials from which the battery was first made.

The Leicester-developed emulsion technique allows short-loop recycling of lithium-ion batteries. The battery-grade crystalline structure of the recovered material is not destroyed in this process and allows the remanufacturing of the recovered material directly back into new battery cells, unlike pyro/hydrometallurgical methods. This could potentially make the battery supply chain more sustainable and cheaper.

Dr Jake Yang from the University of Leicester School of Chemistry said: “This quick, simple and inexpensive method could revolutionise how batteries are recycled at scale. We now hope to work with a variety of stakeholders to scale up this technology and create a circular economy for lithium-ion batteries.”

---