Electric cars and sustainable batteries — a decidedly topical subject. From a technological standpoint, there has been remarkable progress in recent years; the work now under way aims to make them completely sustainable. Two main aspects must be taken into account. The first is linked to the origin of the energy used to charge the batteries, with an ever-growing share of electricity coming from renewable sources. The second is connected to the method used to produce batteries and to the technology chosen to store energy. Audi, which with e-tron (and e-tron Sportback) is already on the market with a battery-powered model, is engaged in sustainability on every front: including that of battery sustainability, starting from the extraction of the materials needed to build them.

Reusing valuable elements from end-of-life batteries

If it is true that the best money earned is money not spent, it is equally true that the best resource not wasted is one that is recycled. That is why Audi is investing heavily in extracting and reusing the valuable elements contained in batteries at the end of their lifecycle. According to the results of an internal test, more than 90 per cent of the cobalt and nickel present in Audi e-tron batteries can be recycled for use in new cells. Moreover, it is sometimes possible to reuse entire batteries: no longer in an electric car, whose performance requirements are very high, but for less demanding applications. An example? Powering transport vehicles inside factories.

Lithium, the state of the art

The valuable materials mentioned above: lithium is the most well-known and most widely used among them, as well as representing the state of the art in batteries, starting from computing and consumer electronics. The reason? Superior efficiency and energy density compared to alkaline batteries. It is no coincidence that the cost of lithium doubled between 2016 and 2018. And not because there is little of it on Earth, in fact: an estimated 43 million tonnes. The problem is that only one third of the total can be extracted, 87 per cent of which is found in the salt waters of South America.

How is lithium obtained?

And if Audi is investing so heavily in the search for a faster and more sustainable process for battery production, it is not because the lithium extraction process is complex — quite the opposite. To obtain lithium carbonate, it is in fact sufficient to drill into the salt flats and pump the mineral-rich brine to the surface. The brine is then evaporated and the resulting salts are filtered to extract the lithium carbonate. From a technical standpoint, then, the process is fairly straightforward. The critical issues, rather, concern the large quantity of water required and the overall duration: 18 to 24 months. When discussing lithium extraction, the humanitarian dimension cannot be ignored: Audi collaborates in various initiatives with partners whose focus is human rights and the environmental sustainability of the supply chain, and is a member of the Global battery alliance, which is committed to protecting human rights in the process of extracting noble materials for batteries.

New technologies for lithium batteries

Recycling the valuable materials contained in lithium batteries is not the only avenue being pursued. The entire scientific community is also paying very close attention, for example, to reducing the size of batteries and the quantity of lithium and rare components (such as cobalt) used. Or, returning to extraction, there is the solution developed by Tsuyoshi Hoshino of the Rokkasho fusion institute at the Japan atomic energy agency: extracting lithium from seawater through electrodialysis. In practice, this involves using a membrane that can be crossed — by osmosis — only by lithium ions. While waiting for this technology to reach the market, Hoshino says he is convinced of its energy efficiency and scalability.

Graphene supercapacitors

Finding a more sustainable way to extract lithium is just one part of the work facing engineers and scientists. Equally crucial is ensuring that the batteries of the future deliver greater efficiency. Graphene supercapacitors are being studied, for instance: instead of storing electricity as chemical potential — as happens in lithium and alkaline batteries — this solution makes it possible to store energy in an electric field. The challenge to overcome is the low capacity of these supercapacitors to retain a charge for a long time and the fact that they are subject to sudden charge loss.

Electricity from water and in water

Another technology under investigation is the Blue battery, which stores energy in water. In essence, an electric current passes through salt water and divides it into concentrated saline solution and fresh water (electrolysis); in this way it is possible to store energy. The energy-release phase involves reversing the process, whereby the two types of water (fresh and salt) are combined, releasing the stored energy, which is then reconverted into electric current by means of special membranes.