Despite a slowdown in electric-vehicle (EV) sales in some countries, demand for batteries was up by around 40% globally last year, and seems likely to continue at a similar pace. Consequently, the world’s appetite for lithium, the vital ingredient in the lithium-ion (Li-ion) batteries that dominate the EV market, is expected to exceed 2.4m tonnes in 2030, more than twice its present level.
Where all this lithium will come from is a thorny question. Although 70% of the world’s reserves of lithium carbonate (from which it is mined) are in Argentina, Australia and Chile, processing it into a form suitable for use in batteries is a business currently dominated by China. As China also commands the processing of other important battery materials, including manganese, cobalt and nearly all battery-grade graphite, there is concern about the vulnerability of supply chains should China begin restricting supplies of certain raw materials, as it has done in the past. As a result, legislators and carmakers in Europe and North America have been trying to establish local supplies for batteries.
These efforts are about to be given a big boost. Recent breakthroughs in recycling, together with a spate of technological improvements, mean that within a decade or so most of the global demand for raw materials to build new batteries could be met by recycling old ones.
Lithium, manganese and cobalt are widely used to make electrodes called cathodes, the most expensive part of a Li-ion battery. When the battery is recharging, electrons are stripped from lithium atoms on the cathode to create charged particles called ions. The ions then migrate through an electrolyte, typically a liquid medium, to a second electrode called an anode. This is made from graphite, a pure form of carbon. Meanwhile, the electrons created at the cathode travel along the wires of the charging circuit towards the anode, where they reunite with the ions and are stored there. When the battery discharges, the process reverses, with electrons in the circuit powering a device—which in the case of an EV is its electric motor. Although different chemistries can be employed, manganese and cobalt are particularly good at stabilising and boosting the performance of a Li-ion battery.
At present battery recycling is mostly confined to recovering raw materials from the scrap produced by gigafactories. A much richer vein will soon present itself, however, as the first wave of EVs reach the end of their lives. By 2040, according to PwC, a professional-services firm, up to 60% of the materials used to make batteries in Europe could come from recycling old ones, helped along by innovations in recovery processes.
Other analysts take a similar view. Globally, the mining of raw ingredients for battery manufacturing could peak by the mid 2030s, reckons RMI, an American think-tank. This will be caused by a combination of better recycling and continuing advances in battery chemistry, which boosts the energy density of cells so that batteries can be made with fewer raw materials. This, RMI believes, might see mineral extraction for batteries being avoided altogether by 2050.
The ways in which batteries are recycled today pose many problems. Some are labour-intensive, whereas others need lots of energy or are environmentally harmful. But each hurdle is a spur to innovation. Stripping cells apart by physical means to remove their components, for example, takes a lot of effort. A process called pyrometallurgy can simplify the harvesting of metals like nickel and cobalt by roasting batteries at temperatures of up to 1,600°C, but this is no good for getting at the lithium. That metal instead requires a process called hydrometallurgy in which old batteries are crushed and the resulting “black mass” is treated with harsh chemicals known as lixiviants.
Some lixiviants use concentrated acids which can carry environmental and health risks. This means they have to be treated carefully before disposal, driving up recycling costs. More benign alternatives exist, such as the deep eutectic solvents (DES) developed by researchers at Rice University in Houston, Texas, which are biodegradable and non-toxic. But these solvents come with problems of their own. Because they generally require heating for a long period at around 200°C, during which time they can degrade and lose effectiveness, DES have so far not been proved to be commercially viable.
The Rice group has found a simple solution to the problem of heat-induced degradation: popping them into a microwave oven. It turns out that choline chloride, a DES ingredient which specifically leaches out lithium, is an excellent absorber of microwaves. This means the DES can rapidly heat up to the temperatures necessary to extract lithium from a black mass, says Sohini Bhattacharyya, one of the Rice team.
In a recent study published in Advanced Functional Materials, a journal, the group reports that by using microwaves a DES was able to recover some 50% of the lithium in a spent cathode in as little as 30 seconds. Recovering 87% took 15 minutes, an improvement on the 12 hours necessary to collect the same amount using a conventional electrically powered oil-bath. This discovery promises to make lithium recovery faster, cheaper and more effective (some conventional recycling processes extract as little as 5%). It should also be possible to tune DES solutions to speedily extract other metals, too.
Other researchers are taking an interest in non-metallic compounds. The graphite in an anode, for example, can represent about half of a battery by volume. Although graphite can also be mined, most of it is currently produced in a synthetic form by roasting needle coke, a by-product of some coal-processing and petrochemical plants. As graphite must be purified to above 99.95% in order to make anodes, recovering it from contaminated battery waste is extremely difficult.
Talga, an Australian materials firm, has come up with a solution to that problem. It recently signed deals with two recyclers, Altilium, a British company, and Aurubis, a German one, to purify graphite recovered from scrap and end-of-life batteries so that it can be used again to make new anodes. Talga will use a chemical purification process, the details of which are being kept under wraps while patents are pending. It is, however, known to be based on a technique used at Europe’s first anode-production facility. This was set up by Talga in northern Sweden, where the company also operates a graphite mine.
As recycling technology continues to evolve, a circular supply chain may emerge. That should allow more localised battery production and avoid supply-chain vulnerabilities. It would also reduce the overall lifetime carbon emissions involved in the mining and refining of battery raw materials—allowing the drivers of EVs to more rightfully claim to be green.
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