T 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. The revolutionary boat powered by the ocean How sustainable are electric scooters? Norway’s plan for a fleet of electric planes 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.  The demand for longer-lasting batteries capable of holding more charge is likely to rise as more electric vehicles appear on our roads (Credit: Alamy) 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. Over the years, tweaks to the materials used in the cathode and anode have helped to improve the capacity and energy density of lithium-ion batteries, but the most dramatic improvements have been in the falling cost of the batteries. Our thirst for battery power is only likely to grow in the coming years as the range of portable electronic paraphernalia in our lives increases “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?  Much of the world's lithium is mined from the huge salt flats in South America but the process uses huge amounts of water (Credit: Reuters) 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 research into 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. Everyone is carrying around a lithium-ion battery mined by children – Jodie Lutkenhaus 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.