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Some involve heavy investment in as-yet-undeveloped solutions, while others call for the faster roll-out of existing technologies, such as wind turbines and solar panels. But, no matter what course is ultimately taken, there’s no denying that electrification will play a critical role in reaching carbon neutrality.
Some have suggested that societies should “electrify everything” – including buildings and many modes of transport. For this to happen, we’re going to need a lot of efficient, high-performance batteries. Although the lithium-ion batteries (LIBs) that power the cars and phones of today are far more advanced than their predecessors, engineers and scientists are still working to create battery formulations fit for a fully electric future.
Twice as much energy
A team from Japan’s National Institute for Materials Science (NIMS) published a paper in the journal Materials Horizons outlining their promising design for a lithium-air battery (LAB). According to the scientists, their technology can hold twice as much energy by weight as existing lithium-ion models. It’s believed that LABs could achieve energy densities between two- and five-times greater than those of LIBs – making them particularly suited to powering small devices, such as drones and unmanned aerial vehicles.
Lithium-air batteries are typically lightweight because they use an electron conductor (usually made of a porous substance like carbon) rather than the heavier metal oxides found in LIBs. LAB cells create voltage from the availability of oxygen molecules at the positive electrode. The oxygen then reacts with the positively charged lithium ions to create lithium peroxide and generate electricity. Once no more lithium peroxide can be formed, the battery is flat.
However, the new materials used in the NIMS prototype are expensive and the battery is limited to only 10 charge-discharge cycles. In other words, it has a long way to go before it’s going to power a delivery drone. Many of the LABs devised to date also have a low charging efficiency, meaning you get relatively little energy output compared to the energy put into the battery. Heat production and unintended side reactions at the electrodes can also lead to energy loss in lithium-air cells.
Elsewhere, scientists are investigating other novel battery formulations – such as lithium-sulphur – that could potentially help to electrify difficult sectors. A consortium of academics led by researchers at University College London (UCL) published a roadmap for commercialising the technology, which uses metallic lithium as the negative electrode. The positive electrode is made of sulphur, which offers the theoretical potential for a five-fold improvement in capacity over LIBs.
Reduced weight
Compared to lithium-ion batteries, cells that use sulphur boast reduced weight and a greater tolerance to extreme temperatures. This means they could be useful in electrifying heavy vehicles, such as trucks and buses, and potentially planes. But the UCL researchers noted that “a significant improvement in the cycle life” of lithium-sulphur cells is needed to facilitate their commercialisation. Viable batteries, they wrote, should be capable of achieving reliable performance over a minimum of 200 cycles with a drop in capacity no greater than 60%.
Scientists have long theorised about the disruptive implications of solid-state batteries. These cells typically use a lithium-ion-based chemical reaction to discharge and store power. However, they use a solid electrolyte (often made of ceramic materials) rather than the conventional liquid-based electrolyte. This means they’re potentially lighter, smaller and more energy dense than the LIBs of today. They also present less of a fire risk.
There are a small but growing number of companies working to produce solid-state batteries, in addition to academics and researchers studying their applications. Colorado-based Solid Power is preparing pilot production of its commercial-grade batteries, which will be sent to Ford and BMW for testing in cars.
The professed safety benefits and improved performance of solid-state cells naturally appeal to carmakers. Startup Factorial Energy – which boasts “a proprietary solid electrolyte material” – has received funding from Mercedes-Benz, while battery maker QuantumScape is backed by Volkswagen.
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Content published by Professional Engineering does not necessarily represent the views of the Institution of Mechanical Engineers.