Listen and read 49 Electric cars - Million-Mile car batteries are coming - Thấm Tâm Vy

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LISTEN AND READ 49

Electric cars Million-mile car batteries are coming

But they are more about improving reliability than driving the same car for ever

AS EVERY MOBILE-PHONE owner knows, after a year or so the battery starts to fade and the beast needs recharging more frequently. That is a nuisance, but a phone’s batteries can be replaced fairly cheaply—or the whole handset traded in for the latest model. An electric car, however, is a much bigger investment. And batteries are its priciest component, representing around 30% of an average mid-size vehicle. Apart from increasing the risk of running out of juice and leaving a driver stranded, a deteriorating battery quickly destroys a car’s second-hand value. To provide buyers with some peace of mind, carmakers guarantee their batteries, typically for eight years or around 200,000km. Producers are now, though, planning to go much further than that, with the launch of “million mile” (1.6m kilometre) batteries. Zeng Yuqun, the boss of Contemporary Amperex Technology, a giant Chinese firm which produces batteries for a number of carmakers, said in June that his company was ready to start manufacturing batteries which would last for 16 years or 2m kilometres. Elon Musk has hinted that Tesla, a Californian maker of electric vehicles of which he is boss, has a million-mile battery in the works. Rumours suggest this could be unveiled in September. And over in Detroit, General Motors (GM) is in the final stages of developing an advanced battery which it says has similar longevity. To the Moon and back, twice “It’s a great catchphrase; the million-mile battery,” says George Crabtree, director of the Joint Centre for Energy Storage Research at Argonne National Laboratory, near Chicago. “But the fact you can drive a million miles may not be the most relevant parameter to look at.” Thrash a car and its battery will deteriorate faster. Regular fastcharging also reduces battery life, as do overcharging and deep discharging. Driving in extremely hot or cold weather does not help either. And battery life will diminish even if you just leave the car in the garage. The real point of a million-mile battery is that the technological advances required to make it possible will deal with these things as well. The lithium-ion (Li-ion) batteries which power electric cars age in two ways: with time and with use. Battery-makers call time-dependent ageing “calendar ageing”. It is a consequence of the gradual degradation of some of the materials employed in battery construction. This degradation reduces a battery’s ability to hold a charge—though even here it is possible to ameliorate the problem to a certain extent. Leaving a car with a fully rather than partly charged battery, for example, can increase the rate of calendar ageing. Use-dependent ageing is a consequence of the number of discharge-recharge cycles a battery goes through. It is caused by the complex chemical reactions that take place when a battery is operating. Some of these are essential to a battery’s job of storing and

releasing energy. “But there are also side reactions that you can’t stop and some of those are harmful,” explains Dr Crabtree. As a battery discharges, lithium ions (lithium atoms with an electron missing) are created at one electrode, the anode. These then shuttle through a liquid electrolyte to a second electrode, the cathode. The electrons stripped away at the anode, meanwhile, travel towards the cathode along an external electrical circuit, which powers the car. Ions and electrons are reunited at the cathode and remain there until the battery is plugged into a charger and the process is reversed. Each cycle of discharge and recharge takes its toll. Lithium is so highly reactive that stopping it getting tied up in other chemical compounds while a battery is in use is hard. Even a small amount of diversion per cycle adds up, reducing the amount of the element available to store energy. On top of …