How the world’s smelliest fruit could power your phone - iWONDER

  27 July 2020    Read: 1361
  How the world’s smelliest fruit could power your phone -   iWONDER

The lithium-ion batteries in our devices degrade over time and come with a large environmental cost. Are there better ways to store and carry energy that are kinder to the planet?

They are the beating heart of our modern portable technology – packets of energy that we can charge from a plug in the wall and slowly drain through the course of a day. Lithium-ion batteries have transformed our ability to store and carry energy around with us, and so, in turn, revolutionised the devices we use.

First commercialised by Sony in 1991 as the company sought a solution to the limited battery life of its handheld camcorders, they power many of the gadgets we use today – from smartphones and laptops to electric toothbrushes and handheld vacuum cleaners. At the end of last year, the three scientists behind its invention won the Nobel Prize in Chemistry for enabling this technical revolution.

And our need for them is only likely to grow. Electric vehicles are reliant upon lithium-ion batteries as a substitute for the fossil fuels we currently pour into our cars. As renewable energy sources make up more of the electricity supply around the world, huge battery banks are likely to be needed to store excess energy for times when the wind doesn’t blow or the Sun isn’t shining. Worldwide more than seven billion lithium-ion batteries are sold each year and that is expected to grow to more than 15 billion by 2027.

But as we know from our phones that hold less and less juice the older they are, lithium-ion batteries have their limitations. Over time their capacity to hold a charge decreases, meaning they store less energy. In extremely hot or cold weather, their performance also falls. And there are also concerns around the safety and sustainability of lithium-ion batteries – they can catch fire and explode under certain conditions, while mining the metals needed for them comes with a high social and environmental cost.

This has spurred scientists around the world to try and develop new types of battery that can overcome these problems. By harnessing a range of materials, from diamonds to super-stinky fruit, they hope to find new ways of powering the technologies of the future.

Lithium-ion batteries work by allowing charged lithium particles (ions) to move electricity from one end to the other, passing through a liquid electrolyte in the middle. One of the things that makes lithium-ion batteries so attractive is their “energy density” – the maximum energy a battery can hold for its volume – which is one of the highest of any commercially available battery on the market. They can also deliver higher voltages than other battery technologies.

Batteries are essentially made of three key components – a negative electrode, a positive electrode, and an electrolyte between them. The roles of the electrodes switch between cathode and anode depending on whether the battery is charging or discharging. In lithium-ion batteries, the cathode is typically made from a metal oxide that includes and another metal. When charging, lithium ions and electrons move from the cathode to the anode where they “stored” as electrochemical potential. This occurs through a series of chemical reactions in the electrolyte that are driven by the electrical energy flowing from the charging circuit. When a battery is in use, lithium ions flow in the opposite direction from the anode to the cathode through the electrolyte, while electrons flow through the electrical circuit of the device the battery is installed in, providing it with power.

“It’s got to a point where the chemistry developed 35 years ago has plateaued,” says Mauro Pasta, a materials scientist at the University of Oxford and project leader at The Faraday Institution, who is working on the next phase of lithium-ion batteries. His aim is to boost the energy density of lithium-ion batteries while also increasing their efficiency so they don’t lose power over repeated charges and discharges.

To do this, Pasta is focused on replacing the highly flammable electrolyte fluid found in modern lithium-ion batteries with a solid made from ceramic. Using a solid reduces the risk of electrolytes combusting in the event of a short or unstable cell, which was behind Samsung’s 2017 recall of 2.5 million Galaxy Note 7s after a series of battery fault fires. It’s important for future safety, as even the polymer-gel electrolyte found in most of our portable electronics is still flammable.

This solid state battery also makes it possible to use dense lithium metal instead of the graphite anode, which significantly increases the amount of energy it can store in the process. It could have huge implications on the future of driving.

Right now, every electric vehicle contains the equivalent of thousands of iPhone batteries. As electric vehicles look set to replace those run on fossil fuels in many countries in the coming years, the shift towards solid state batteries would mean longer journeys and more time between recharges.

Our thirst for battery power is only likely to grow in the coming years as other modes of transport attempt to go electric and the range of portable electronic paraphernalia in our lives increases, so should we be looking for alternatives to lithium that could ease the impact it has on the environment?

The “Lithium Triangle” region of the Andes – which includes parts of Argentina, Bolivia and Chile – contains a little over half of the world’s natural resources of the metal. But extracting it from the salty flats requires water – lots of water. In Chile’s Salar de Atacama region, around one million litres of water are used in the mining process to produce just 900kg of lithium. The process involves purifying the metal-rich salts by progressively dissolving them in water, filtering and then evaporating the brine until pure lithium salt is obtained. Environmental bodies run by the Chilean government, however, have warned that metal mining – mainly of lithium and copper – in the region is using more water than is replaced by snow and rainfall.

To overcome this researchers at the Karlsruhe Institute of Technology are working on batteries that use different metals in the anode, like calcium or magnesium. Calcium is the fifth-most-abundant element in the earth’s crust and is unlikely to suffer from the same supply concerns as lithium, but research to improve the performance of batteries using it is still in its infancy. Magnesium is also showing promising initial results, especially in terms of its energy density, and there are plans to commercialise in the future.

But there are some who are looking at even more readily available materials, including wood. Liangbing Hu, director of the Center for Materials Innovation at University of Maryland, recently constructed a battery using porous, holey pieces of wood as the electrodes, within which metal ions react to generate an electrical charge. Wood is plentiful, low cost and lightweight, and is showing high performance potential in batteries. The latest batteries follow years of researchinto wood’s capabilities to store energy, including coating wood cellulose fibres in tin. As wood has naturally evolved to be permeable to nutrients as they are transported around the plant, the material makes electrodes with the ability to store metal ions without the risk of swelling or shrinking dangerously, as can occur with lithium ion battery electrodes.

While Hu’s team anticipate wood-based batteries could be used in our portable electronics as well as large-scale energy storage someday, we won’t be able to charge our laptops from them just yet, as they’re still being tested in labs. The batteries lose their ability to hold a charge relatively quickly at the moment – one prototype could only hold 61% of its initial capacity after 100 recharge cycles. Right now, the amount of wood used is several centimetres in width and length, and the batteries can be stacked or wired together for larger-scale applications, which could eventually be useful for storing energy in homes or other buildings.

Lithium is not the only metal found in most modern batteries – most also use a cobalt in combination with lithium at the cathode. Mining cobalt comes with a toxic legacy that harms the health of the communities living near the mines and damages the environment. Cobalt mining is also blighted by the use of child labour, particularly in the Democratic Republic of the Congo, the country home to over half the world’s cobalt mines. Top tech firms including Apple, Tesla and Microsoft were recently sued over cobalt mining deaths.

“Everyone is carrying around a lithium-ion battery mined by children,” says Jodie Lutkenhaus, a chemical engineer at Texas A&M University.

This has inspired her to develop alternatives to these “blood batteries” using proteins, the complex molecules created and used by living organisms. Batteries’ anodes tend to be made of graphite and cathodes are made of metal oxides that contain elements such as cobalt. If these can be replaced with organic materials for both the active electrodes it means cobalt will no longer have to be mined.

Not only does this overcome the need for toxic metals that have to be mined from the ground, it also tackles another environmental legacy of lithium-ion batteries. If discarded after use into landfill, the metals and electrolytes from lithium ion can leak out into the surrounding environment, causing further damage. Only about 5% of the lithium-ion batteries used in the 1.5 billion smartphones sold each year currently go on to be recycled.

Developed in collaboration with her colleague Karen Wooley, at Texas A&M University, Lutkenhaus’ protein battery is the world’s first power cell that degrades on-demand by dissolving it in an acid, meaning it can be easily broken down and used again.

Although their proof-of-concept can’t yet compete with lithium-ion – it can only deliver up to 1.5V for around 50 recharge cycles before it loses capacity – it is part of an exciting wave of development in which sustainability is being engineered into battery design.

Super fruit

One innovative group are not only trying to find new ways to power our devices, but also tackle the issue of food waste at the same time. Vincent Gomes, a chemical engineer at the University of Sydney, and his team, including Labna Shabnam, are turning waste from the world’s smelliest fruit, durian, and the world’s largest fruit, jackfruit, into a supercapacitor that can charge mobile phones, tablets and laptops within minutes.

Supercapacitors are an alternative way of storing energy. They act like reservoirs, able to quickly charge and then discharge energy in bursts. They tend to be made out of expensive materials like graphene, but Gomes’ team has turned inedible parts of durian and jackfruit into carbon aerogels – porous super-light solids – with “exceptional” natural energy storage properties. They heated, freeze-dried and then baked the inedible spongey core of each fruit in an oven at temperatures of more than 1,500C (2732F). The black, highly porous, ultralight structures they were left with could then be fashioned into electrodes of a low-cost supercapacitor.

The supercapacitors can be charged in 30 seconds, and could be used to power a range of devices.“To be able to charge a mobile phone in a minute is incredible,” says Shabnam. The researchers’ dream is to use these sustainable supercapacitors to store electricity from renewable energy sources for use in vehicles and houses.

And that’s before considering the benefits of finding a green use for durian’s headline-making, stomach-turning waste, as over 70% of the fruit tends to be thrown away. In 2018, the smell temporarily grounded a plane in Indonesia, and leftover fruit prompted a mass evacuation of a University of Canberra library last year. In the initial stages of his research, the stench got too much Gomes’ wife, who removed all remnants of the foul-smelling fruit from the freezer after just one night – the pong was too potent.

Other types of plant waste could also be used to power the devices of the future. Mikhail Astakhov, a physical chemist at the National University of Science and Technology (MISiS) in Moscow, Russia, has turned hogweed, a weed with a toxic sap that can blister human skin, into a raw material for a supercapacitor technically able to charge a phone.

Batteries are forever

While overcoming the environmental problems of lithium-ion batteries is a challenge that could eventually be surmounted, there are others who are trying to tackle their other limitations. While Tom Scott, a materials scientist at the University of Bristol, doesn’t believe lithium-ion batteries are likely to be supplanted for most mainstream uses over the next century, there are opportunities when it comes to storing energy in more extreme environments.

Together with his team, Scott has been developing batteries made from diamonds. By growing man-made diamonds that contain radioactive carbon-14, they can create “betavoltaic batteries” that produce a constant current and could last thousands of years. Locked inside the diamond lattice, the radioactive isotopes fire out super-high energy electrons as they undergo nuclear decay. This in turn creates a shower of electrons through the diamond structure that can be harnessed to produce an electrical current. On the outside the radioactivity would remain at safe levels, the researchers say.

The team have already created a prototype “diamond battery” using man-made diamonds placed inside a radioactive field produced by the isotope Nickel-63, which triggers a flow of electrons through the diamond. But they are now working on a version that uses carbon-14 extracted from graphite blocks used in nuclear power stations. By turning this nuclear waste into a long-lived battery, Scott and his colleagues hope to find new ways of using a problematic waste from nuclear power stations as they are decommissioned.

“It’s completely game-changing,” says Sophie Osbourne, one of the team working on the project with Scott. “For so long we’ve collected nuclear waste, and now we’re no longer talking about long-term storage but actually repurposing it to make electricity.”

While chemical batteries like lithium-ion don’t fare well in high temperatures, these durable diamond batteries have the ability to work in the most challenging environments where it is hard to slip in a replacement, such as in space, at the bottom of the ocean, or perhaps at the top of a volcano. They would be perfect for keeping satellites and computerised sensors running, for example.

“The batteries are absolutely tiny,” says Scott. So far, the researchers have been able to generate diamond batteries that produce 1.8 volts – similar to an AA battery – although it has a much lower current. They are technically rechargeable too, but would require a few hours inside a reactor core to reach their original output, says Scott. Although the steady trickle of current created as the radioactive material decays means they will emit electricity for an incredibly long time –  carbon has a half-life of 5,730 years.

Despite being made from diamond, they are unlikely to be that expensive either. “You’d be surprised how little man-made diamonds can cost,” Scott says.

In the next decade or two, Scott believes we could even start to see ultra-long-lasting diamond batteries appear in our homes, perhaps in smoke alarms or TV remotes, or in medical applications like hearing aids or pacemakers.

We may never have to struggle to replace the failing battery in a smoke alarm at the dead of night again.

BBC


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