Lithium-ion batteries have become the backbone of electric mobility with their ability to store more energy in smaller, lighter-weight cells than any other materials. These properties — high energy density and light weight — have made lithium the material of choice not only for electric vehicles but also for smartphones, laptops, and other battery-powered devices. When they reach the end of their useful life and are discarded, however, lithium batteries become an environmental liability. To address this issue, research groups worldwide are exploring methods to recycle and repurpose the metal content in batteries, including cobalt, lithium, copper, graphite, and aluminum. In Brazil, one of the most advanced projects in this field is hosted at the Center for Advanced and Sustainable Technologies (CAST), at São Paulo State University’s (UNESP) School of Engineering in São João da Boa Vista (SP).
“Our techniques can be used to recover and repurpose potentially toxic materials, helping to advance a circular economy. This can reduce the environmental impact that would otherwise result from mining fresh metals,” says José Augusto de Oliveira, an environmental engineer at CAST. The methods being developed employ a hydrometallurgical process involving leaching, which separates the metals contained in the batteries by incrementally dissolving them in an aqueous solution.
A lithium-ion battery consists of a number of small cells that are joined to form a larger “pack” in engineering parlance (see Pesquisa FAPESP issue nº 261). The first step in any battery recycling operation is disassembling the pack. This typically involves identifying cells that are still viable to be refurbished into a new pack, creating a second-life battery. Cells that have reached the end of their useful life are designated for disposal. These end-of-life cells are the primary focus of the CAST team’s research.
The process developed at UNESP, as described by Oliveira, begins with separating all the components of the cells, such as the plastics in the casing used as a barrier between the metal structure and the material inside. The internal structure consists of a cathode (the battery’s positive electrode), an aluminum sheet containing lithium and cobalt oxides, an anode (the negative electrode), a copper sheet lined with graphite, and a plastic membrane that separates the two electrodes. Because it is in contact with both electrodes, this membrane may contain graphite and metal oxides.
The cell is dismantled manually using cutting machines. The metal sheets are placed in an aqueous chemical solution designed to remove copper and aluminum, which are ready for reuse at the end of the process. Graphite and high-purity lithium and cobalt oxides are extracted by filtering their respective solutions. Processing the membrane also requires filtration and a subsequent separation step to purify the metal oxides it contains.
“Organic chemical reagents are used to minimize environmental impacts and maximize economic benefits and workplace safety,” explains chemist Mirian Paula dos Santos, the researcher in charge of the metal oxide leaching process. “We’re constantly refining the technology, and will assess the environmental impacts and economic feasibility once our research is complete,” she says. So far, she notes, the technique has been validated on a laboratory scale.
LFREEDOM_WANTED / Alamy / FotoarenaA lithium mining field in the Atacama Desert, ChileLFREEDOM_WANTED / Alamy / Fotoarena
The economic potential of their method, according to Oliveira, is promising. “Preliminary studies suggest that sales of lithium oxide would generate sufficient revenue to cover recycling expenses,” he says. At its current stage of development, the new method — for which a patent application was filed at the National Institute of Industrial Property (INPI) in 2020 — provides a recovery rate of 90% for lithium oxide with 98% purity; when contaminated with graphite, the purity rate is reduced to 50%. The remaining components of the battery are fully recoverable, as reported in a 2021 article in Resources, Conservation and Recycling.
These early results convinced a Brazilian company with global operations to sign a technological development and licensing agreement with UNESP to replicate the recycling process using new reagents. In the first phase of the collaboration, the technology will be used to recycle spent batteries from the vehicles the company manufactures. Looking ahead, Oliveira says the company (which cannot be named due to nondisclosure agreements) is exploring a commercial strategy with UNESP to offer the recycling process to other companies as a service on a broader scale. UNESP’s collaboration has received funding from FAPESP through the Research Partnership for Technological Innovation (PITE) program.
Another lithium-ion battery recycling technique currently under development at CAST is taking an unconventional approach that uses water in a supercritical state as a solvent to recover the metal oxides. “To achieve this, the water must be heated to temperatures exceeding 374 degrees Celsius [°C] and pressures as high as 240 atmospheres [atm]. Under these conditions, the distinction between the liquid and gaseous states of water disappears,” says chemical engineer Lúcio Cardozo Filho, who is leading the research project. “Supercritical water, under extreme temperatures and pressures, has the reactivity required for processing, treating, and extracting inorganic compounds, such as the metal oxides contained in lithium batteries.”
While bringing water to a supercritical state is no small feat, according to Cardozo, the fluid used does not need to be high quality and can be reused water. In addition, the process does not require any additional chemical reagents to extract the metal oxides. “The success rate in metal separation is higher than 98%,” he says. The result is a blend of metal oxides, commonly referred to as “black mass,” which still needs to undergo a separation and purification step as in conventional hydrometallurgy. Cardozo Filho adds: “Our next challenge is to secure additional funding to scale up the process.”
Recycling lithium-ion batteries is more sustainable and cost-effective than mining raw minerals. In the case of lithium, it takes 100 kilograms (kg) of ore to produce 1.6 kg of lithium. In contrast, 7 kg of lithium oxide can be recovered from every 100 kg of batteries. Mining ore has a significant environmental impact as a water-intensive operation, while refining the ore requires it to be heated to temperatures exceeding 1,000 °C, an energy-intensive process.
According to a McKinsey report, global demand for lithium battery storage is projected to surge from 700 gigawatt-hours (GWh) in 2022 to 4,700 GWh in 2030. This, say experts, is also driving up demand for recovery of the metals contained in used batteries.
Markus Scholz / Picture Alliance via Getty ImagesUsed lithium batteries disassembled and ready for recycling at a company in Hamburg, GermanyMarkus Scholz / Picture Alliance via Getty Images
The automotive industry is the primary destination for lithium batteries, with approximately 80% of production output going to automakers. A typical electric vehicle battery weighs over 200 kg and has a lifespan of 8 to 10 years. The International Energy Agency (IEA) predicts that lithium production will need to increase nearly tenfold by 2050 to meet the rising global demand for the product.
“Raw material production is at risk of falling behind the escalating global demand. Consequently, we could face a battery shortage by 2030,” warns Hudson Zanin from the School of Electrical Engineering and Computing at the University of Campinas (FEEC-UNICAMP), who is leading a research project to develop a sodium-based battery (see Pesquisa FAPESP issue nº 329). “Recycling and the gradual incorporation of recovered materials into new batteries offer advantages from both an environmental and economic standpoint, ensuring a reliable supply of raw materials,” he explains.
Zanin notes that the recycling processes most widely used are pyrometallurgical and hydrometallurgical, which achieve efficiency levels higher than 80%. In pyrometallurgy, incinerating the material releases undesirable toxic gases.
Hydrometallurgical processes, despite being water-intensive, are less polluting and require less energy. “Water consumption is still much lower compared to lithium mining. In hydrometallurgical recycling processes, about 5 liters [L] of water are used to produce 100 grams [g] of lithium salt. In mining, water consumption can range from 50 to 90 L for every 100 g of lithium carbonate,” says Oliveira.
Refurbishing lithium batteries into new packs — using cells that have lost performance but have not yet reached their end of life — is the focus of a project at the CPQD innovation center in Campinas, São Paulo, in collaboration with CPFL Energia and BYD, a Chinese manufacturer of batteries and electric vehicles.
Aristides Ferreira, an engineer and energy systems manager at the CPQD, explains that the batteries used in electric vehicles are traction batteries, which means they are designed for vehicle drivetrains and rigorous running conditions. After a period of 8 to 10 years, depending on usage, they start to lose their ability to hold a sufficient charge for vehicle propulsion. However, these batteries can still be valuable in less demanding applications, such as stationary batteries, backup systems, and energy storage modules for solar and wind power, which are intermittent in nature. They could be used, for instance, to store electricity generated during the day by a solar panel for nighttime use, or to store wind power for use when there is no wind.
The CPQD project developed special algorithms to assess the quality of cells salvaged from lithium-ion vehicle batteries and determine their remaining lifespan without the need for extended laboratory tests. This streamlines the selection of the best cells for second-life stationary batteries. The CPQD has also developed a prototype second-life battery, which is currently undergoing testing at a laboratory equipped with a photovoltaic panel array at UNICAMP.
Project
Technology for recycling lithium-ion batteries: Lifecycle engineering applications for the circular economy (nº 20/11874-5); Grant Mechanism Research Partnership for Technological Innovation (PITE); Principal Investigator José Augusto de Oliveira (UNESP); Investment R$198,854.94.
Scientific article
SANTOS, M. P. et al.A technology for recycling lithium-ion batteries promoting the circular economy: The RecycLib. Resources Conservation and Recycling. dec. 2021.
