Recycling lithium-ion batteries using cooking oil, water, and ultrasound

A pending ‘recipe’ developed by academics from the University of Leicester in the UK could shorten the long recycling loop associated with lithium-ion batteries, thereby making recycling these batteries more profitable.

The scientists’ method 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.

Their research has been published in the journal RSC Sustainability.

The paper pointed out that recycling lithium-ion batteries is not currently very profitable or efficient due to the complex pack design. Dismantling the battery packs can be labor intensive and dangerous. For recycling lithium-ion batteries to be profitable with current processing methods, the operational cost for recyclers needs to be within $2–6 per kilogram of the spent battery – and this is without accounting for labor costs and assuming a gate fee-free process.

Typically, recycling lithium-ion batteries begins when the cells are shredded to facilitate the extraction of inactive constituents like copper and aluminum via sieving, winnowing, magnetic separation, and other methods. This process leaves behind the active components, graphite and lithium metal oxides, known collectively as ‘black mass’.

The black mass quality, and therefore its reuse value, tends to vary depending on nickel and cobalt content. Black mass is usually sold as a low-cost commodity to hydrometallurgical downstream processes.

Recyclers aim to produce single active battery components by purification of black mass to facilitate a direct, short-loop recycling process where the components can be reused with limited further processing in the battery manufacturing process.

The University of Leicester scientists used a method of direct recycling, which is an emerging approach that recovers the valuable components of lithium-ion batteries without compromising the material’s crystal structure. It is a lower-cost and safer method than traditional methods like pyrometallurgy and hydrometallurgy.

The Leicester scientists pulverized oil droplets in water without surfactant additives to selectively capture graphite in recycled lithium-ion battery black mass powder. The oil droplets can be derived from regular mineral or vegetable oil.

Oil and water don’t mix unless soap is added, but the researchers discovered that the addition of ultrasound can create nano-droplets of oil that are stable for weeks. The oil nano-droplets have been found to purify black mass by sticking to the surface of the carbon and acting as a glue to bind hydrophobic graphite particles together to form large oil-graphite conglomerates which float on water, leaving the valuable and hydrophopic lithium metal oxides untouched. The oil-graphite mix is scraped off leaving the valuable pure metal oxides.

“This quick, simple and inexpensive method could revolutionize how batteries are recycled at scale,” claimed Dr Jake Yang from the University of Leicester School of Chemistry, one of the lead authors of the research.

“We now hope to work with a variety of stakeholders to scale up this technology and create a circular economy for lithium-ion batteries.” The scientists have filed a patent based on the research with the Leicester Innovation Hub.