Batteries of the future: How cotton and seawater might power our devices

Mining the lithium and other minerals we need for batteries is taking an increasing toll on the environment. There are alternative materials all around us though.

Zip. The power's out. But on a street in India, there's a cash machine still happily dispensing banknotes. Thanks, in part, to burnt cotton. For this cash machine has a backup battery inside it – a battery that contains carbon from carefully combusted cotton.

"The exact process is secret, to be honest with you," says Inketsu Okina, chief intelligence officer at PJP Eye, the Japanese firm that made the battery. He's not joking, either. "The temperature is secret and atmosphere is secret. Pressure is secret," he continues, cagily.

Okina does say that a high temperature is required, above 3,000C (5,432F). And that 1kg (2.2lbs) of cotton yields 200g (7oz) of carbon – with just 2g (0.07oz) needed for each battery cell. The firm bought a shipment of cotton in 2017 and still hasn't used all of it, says Okina.

In the batteries developed by the company, together with researchers at Kyushu University in Fukuoka, Japan, carbon is used for the anode – one of the two electrodes between which flow ions, the charged particles in batteries. Ions move in one direction when the battery is charging and in the other direction when it releases energy to a device. The majority of batteries use graphite as an anode but PJP Eye argues their approach is more sustainable, since they can make anodes using waste cotton from the textile industry.

With huge demand for batteries expected in the coming years, propelled by the rise of electric vehicles and large energy storage systems, some researchers and businesses are frantically developing possible alternatives to the lithium ion and graphite batteries that are commonplace today. Like PJP Eye, they argue we could be using much more sustainable and widely available materials for battery production.

Lithium mining can have a considerable impact on the environment. Extracting the metal requires large amounts of water and energy, and the process can leave huge scars in the landscape. The recovered lithium is often shipped long distances from where it is mined to be refined in countries such as China. Graphite, too, is mined or made from fossil fuels, both of which also have negative environmental impacts.

"It's very easy to imagine, as a battery material goes through mining and transportation, how that carbon footprint can really add up," says Sam Wilkinson, an analyst at S&P Global Commodity Insights.

To take another example: cobalt, which is used in many lithium-ion batteries, is predominantly extracted in the Democratic Republic of Congo. But there have been reports of dangerous working conditions there.

From seawater to biowaste and natural pigments, there is a long list of potential alternatives in nature that would be much more widely available – the hard part is proving that any of them can realistically compete with the kinds of batteries already on the market, which are seemingly so indispensable in our gadget-strewn world.

PJP Eye also touts the possibility of improving battery performance as well as making batteries greener. "Our carbon has a bigger surface area than graphite," says Okina, describing how the chemistry of the anode in their Cambrian single carbon battery allows for a battery that charges very quickly, up to 10 times faster than existing lithium ion batteries, he claims.

The battery's cathode is made from a "base metal" oxide. Although Okina won't disclose exactly which one, these metals include copper, lead, nickel and zinc, which are more readily and less reactive than alkaline metals such as lithium. The company claims to be working on a dual carbon electrode battery, where both electrodes are made from plant-based carbon. The technology is based on research conducted by researchers at Kyushu University, although the battery is not expected to be available until 2025.

Being able to charge a battery quickly doesn't matter too much for a cash machine, but it does for an electric vehicle when you just want to juice it up and go. He mentions that the Chinese firm Goccia, in partnership with Hitachi, has developed an e-bike that uses PJP Eye's battery and will put it on sale in Japan early in 2023. The bike's maximum speed is 50km/h (31mph) and you can travel a distance of 70km (44 miles) on one charge, he says.

It's far from the only battery that uses carbon from waste biomaterials. Stora Enso in Finland has developed a battery anode that uses carbon from lignin, a binding polymer found in trees.

Cotton could also be used in place of the electrolyte that facilitates the flow of ions between the cathode and anode, potentially creating more stable, solid-state batteries than those currently available, according to some researchers.

But some see even bigger, potentially inexhaustible, sources of energy out there in nature. The world's vast oceans represent a "practically unlimited" store of material for batteries, argues Stefano Passerini, deputy director of the Helmholtz Institute Ulm in Germany.

He and colleagues described their design for a battery that transfers sodium ions out of seawater, in order to build up a store of the metal sodium, in a paper published in May 2022. To do this, the team designed a special polymer electrolyte through which sodium ions may pass.

The seawater acts as the cathode here, or the positively charged electrode. But there is no anode because the sodium does not become negatively charged, it just piles up in a neutral form. Passerini says surplus wind or solar energy could be used to accumulate the sodium, which can just sit there until required.

"When you need the energy, you can reverse the process and generate the electricity," he explains, describing how the metal would simply be returned to the ocean.

There are challenges with this, though. To put it mildly, sodium – much like lithium – reacts energetically when it comes into contact with water. As Passerini puts it: "You will get an explosion." It's therefore vital to ensure that no seawater leaks through to the sodium store – otherwise, disaster could ensue.

So, some researchers are looking to a material found naturally in our bones and teeth, among many other places, as a safer alternative for cathodes – calcium. It could, for example, be combined with silicon, which would assist the transport of calcium ions, in a future battery.

The list of materials that could give future batteries their oomph only gets weirder. George John at the City College of New York-CUNY and colleagues have long investigated the potential for quinones, biological pigments found in plants and other organisms, to act as electrodes in batteries. They have even had promising results with a molecule derived from henna – the tattooing dye that comes from Lawsonia inermis, the henna tree.

"This is our dream," says John. "We want to make a sustainable battery."

One of the hurdles, he notes, is that the natural henna molecule is very soluble. When used as a cathode, it gradually dissolves away into a liquid electrolyte. But by combining four henna molecules together and adding in lithium, John explains they were able to make a recyclable material with a crystal structure that is much more robust.

"Because the crystallinity increases, the solubility decreases," he explains.

John adds that the battery designs he and his colleagues are working on may not have high enough capacities to power electric vehicles but they could one day be used in small, wearable devices. Perhaps gadgets that measure blood sugar levels in people with diabetes, or other biomarkers, for instance.

Other researchers are looking at using materials as diverse as corn waste and melon seed shells to generate new types of electrodes for use in batteries. The challenge, however, may be in producing these on a scale that can meet the growing demand of the battery industry.

And the challenge overall, for any alternative battery materials, is always in terms of meeting extraordinary expected demand. Take the lithium and graphite-based battery technology of today. If we continue using that, the world will need about two megatonnes of graphite annually by 2030 in order to satisfy the booming battery industry, estimates Max Reid, an analyst at Wood Mackenzie. That's compared to 700 kilotonnes now.

"A tripling in demand, really," he says. This is partly why graphite alternatives have to meet such a high bar. "Reaching these scales is going to be incredibly difficult for any new material."

Shifting manufacturing processes away from graphite would be very expensive, and potentially a big commercial risk, notes Jill Pestana, a California-based battery scientist and engineer currently working as an independent consultant.

She is sceptical about using biowaste for carbon anodes because the sources of such waste might not always be very environmentally friendly. A tree plantation that is poorly managed for biodiversity, for example.

On the flipside, in markets where consumers appear to really care about the sustainability of the products they buy, appropriately sourced alternative battery materials might have more of a chance – whether batteries are made with biowaste-derived carbon or any other potentially more sustainable substance. "The public could play a big role in really pushing that effort forward," suggests Pestana.

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