Electric cars

电动汽车

Million-mile car batteries are coming

百万英里电池

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

它们更多是为提高汽车的可靠性而非使用寿命

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.

有手机的人都知道，新机使用大概一年后，电池就开始老化，需要更频繁地充电。这挺烦人的，但更换手机电池并不太贵，或者还可以干脆把整部手机以旧换新成最新款。相比之下，电动汽车可是一项大得多的投资，而电池又是其中最昂贵的组件，大概占一辆普通中型车成本的30％。电池持续老化不但会增加汽车半路没电抛锚的风险，还会导致一辆车在二手市场上快速贬值。

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.

为让买家多少安心些，汽车公司通常会为电池提供八年或20万公里左右的保修。但现在有些生产商计划推出保修“百万英里”（160万公里）的电池，大大超越之前的标准。为多家汽车制造商生产电池的中国大型企业宁德时代的老板曾毓群在6月表示，其公司已准备就绪，即将生产寿命长达16年或200万公里的电池。加州电动汽车制造商特斯拉的老板马斯克暗示，公司正在开发一款百万英里寿命的电池。传闻它可能在9月面世。而在底特律，通用汽车也在研发一款据称寿命差不多长的先进电池，已进入最后阶段。

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 fast-charging 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.

往返月球两次

“百万英里电池，这真是个好口号。” 芝加哥附近的美国阿贡国家实验室（Argonne National Laboratory）能源存储联合研究中心（JCESR）的主管乔治·克拉布特里（George Crabtree）表示。“但能续航一百万英里可能不是最应该关注的参数。”激烈驾驶会让电池老化得更快。常规快速充电、过度充电和深度放电也会缩短电池的寿命。在极热或极寒天气下驾驶也会损害电池。就算把车停在车库不用，电池寿命也在缩减。百万英里电池的真正意义在于它背后的技术进步也能解决上述问题。

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.

电动汽车使用的锂离子电池有两种老化方式：时间老化和使用老化。电池制造商将随时间推移发生的老化称为“日历老化”，是构成电池的某些材料逐渐损耗的结果。这种退化会降低电池的蓄电能力，但这个问题在一定程度上是可以改善的。例如，汽车如果充满电停着，电池的日历老化速度会比没充满电时更快。

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.

使用老化是电池经过多次充放电循环的结果。这是由电池运作时发生的复杂化学反应引起的。其中一部分反应对于电池存储和释放能量必不可少。“但也会产生不可抑制的副反应，有些是有害的。”克拉布特里解释道。

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.

电池放电时，阳极产生锂离子（即失去一个电子的锂原子）。然后这些锂离子会通过液体电解质转移到阴极。同时，在阳极失去的电子会沿着外部电路向阴极移动，从而为汽车供电。锂离子和电子在阴极重新结合，并停留在那里，直到电池接入充电器使上述过程反向进行。

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 this, charging up faster than ions can be absorbed by the anode may result in a layer of lithium “plating” building up on the anode’s surface, reducing its storage capacity.

每一次充放电循环都会损耗电池。锂具有很高的反应活性，很难在使用电池时阻止它与其他化合物结合。即便每次充放电只有少量损失，加起来也会导致用于储能的锂减少。此外，充电速度快于锂离子被阳极吸收的速度可能导致阳极表面积聚一层锂“镀层”，降低蓄电容量。

Plating becomes yet more of a problem if it leads to the development of structures called dendrites. These are small, finger-like fibres which project into the electrolyte from points on the anode where plating is especially elevated. If a dendrite reaches the cathode the battery will short-circuit, causing it to heat up rapidly and possibly catch fire. Other side reactions can have similarly adverse consequences.

假如这样的镀层再进一步形成“枝晶”，问题就更大了。枝晶是一种细小的指状纤维，从阳极上镀层特别厚的地方探伸至电解质中。当枝晶接触到阴极，电池就会短路，导致其迅速发热并可能自燃。其他副反应也可能产生类似的不良后果。

It is difficult to generalise about the extent to which these processes reduce a battery’s lifetime. Not only does it depend on how that battery is used, but also how it is made. Li-ion cells come in different forms and a variety of chemistries, some of which have not been around long enough in cars for people to know for sure how long they will last. Nor is there any independent testing, says Dr Crabtree.

这些过程会在多大程度上缩短电池的寿命很难一概而论。这不仅取决于电池的使用方式，也取决于其制造方式。锂离子电池各式各样，化学原理也各异，其中一些被应用到汽车上的时间还不长，让人难以确切知道电池的寿命如何。而且也没有任何独立测试，克拉布特里表示。

Nevertheless, the industry has a few rules of thumb. Once a battery’s capacity falls below 80% of its starting value, it is generally thought no longer suitable for use in vehicles. Some reckon that, on average, Li-ion batteries lose 2% of their capacity a year. This may not seem much, but by the time a vehicle is six years old it could mean it is halfway through its useful life.

但业内有几条经验法则。一旦电池容量下降到初始值的80％以下，通常认为这块电池已不再适用于汽车。据称，锂离子电池每年平均损耗2％的容量。听上去好像不多，但这意味着在新车落地的第六年电池的使用寿命就已过半了。

The long road ahead

Battery technology is improving all the time. As a consequence, so are calendar and use-dependent lifetimes. Getting direct experience of how electric cars are used is helping researchers come up with ways to mitigate some of the side reactions, says Tim Grewe, the head of GM’s electrification strategy. The company employs remote, “telematic” monitoring to keep track of how batteries are performing in its cars, and also takes back some batteries from high-mileage drivers and those living in extreme environments, such as deserts and mountainous regions, for analysis.

前路漫漫

电池技术一直在提升。电池的时间寿命和使用寿命也随之延长。通用汽车的电气化战略负责人蒂姆·格雷威（Tim Grewe）表示，了解电动汽车如何被使用的直接数据有助于研究人员找到减轻某些副反应的方法。该公司采用远程“车载通讯”功能追踪车内电池的使用情况，还取回了一些高行驶里程以及在沙漠和山区等极端环境下使用的电池做分析。

Dealing with impurities which get into batteries helps to extend their lives. Water, for example, reacts with salts in the electrolyte to form an acid, which attacks the electrodes. To prevent this, GM has developed an additive made from a type of material called a zeolite. Zeolites are molecular sponges. GM’s version serves to mop up any moisture which enters a battery cell.

去除混入电池内的杂质有助延长其寿命。例如，水与电解质内的盐反应形成的一种酸会腐蚀电极。为防止这种情况，通用汽车开发了一种由名为沸石的物质制成的添加剂。沸石堪称分子“海绵”。通用汽车的这款添加剂可以吸走进入电池内的任何水分。

Adding a little aluminium to a nickel-cobalt-manganese cathode, a type that is widely used in Li-ion batteries, saves on cobalt, the most expensive ingredient in a battery. But the aluminium delivers other benefits as well, adds Mr Grewe. It boosts the battery’s energy density, meaning a car can travel farther on a single charge. It also makes the battery last longer.

往镍钴锰型阴极（在锂离子电池中广泛使用）上添加少量铝可以节省钴这种电池中最昂贵的成分。但铝还会带来其他好处，格雷威补充道。它能提高电池的能量密度，意味着汽车充一次电可以跑更远。它还能延长电池的寿命。

GM will be using these cathodes in a new battery, called Ultium, that it has developed in partnership with LG Chem, a South Korean firm. Ultium batteries, production of which is planned to start next year at a factory in Ohio, should provide electric cars with single-charge ranges of 650km or more. That compares with the 400km range which might these days reasonably be expected from a mid-size electric car. Asked if the Ultium is a million-mile battery, Mr Grewe replied, “Many customers could get that.”

通用汽车将在与韩国公司LG化学合作开发的新型电池Ultium中使用这种阴极。这款电池计划明年在俄亥俄州的一家工厂启动生产，应该能为电动汽车提供650公里或以上的单次充电续航里程。相比之下，目前一般中型电动汽车能指望的续航里程为400公里。当被问及Ultium是不是一款百万英里电池时，格雷威回答：“许多客户能得到。”

On to two million!

As a marketing device, the million-mile battery will give electric-car buyers—even those never likely to put a million miles on the clock—more confidence that their batteries are robust. But some users might truly desire a lifetime range that great.

向两百万进发！

作为一种营销手段，百万英里电池将使电动汽车的购买者（甚至那些根本不会用一辆车跑上百万英里的人）更确信其电池坚固耐用。但的确可能有一些用户希望拥有如此耐用的电动汽车。

Jeff Dahn, who leads a group of battery researchers at Dalhousie University in Halifax, Canada, who are sponsored by Tesla, points out that autonomous electric vehicles like “robo taxis” could clock up vast mileages by operating around the clock. So, too, would long-haul lorries and electric buses. And some cars may end up being more than just means of transport. Plans are afoot to let electric-vehicle owners connect their jalopies to the grid in a way that will store surplus electricity generated in times of plenty by wind and sunshine and release it during hours of peak demand, with the owner collecting a fee for doing so. That means these grid-buffering vehicles will be racking up lots of charging cycles even when they are not moving.

位于加拿大哈利法克斯（Halifax）的戴尔豪西大学（Dalhousie University）的电池研究小组获得了特斯拉的赞助，小组负责人杰夫·戴恩（Jeff Dahn）指出，诸如“机器人出租车”之类的无人驾驶电动汽车全天候运行，将会达到超长的行驶里程。长途卡车和电动巴士也一样。而且有些汽车最终可能不会只充当交通工具。有的项目正在研究让电动汽车车主把自己的旧车接入电网，将风力和日照充足时生成的多余电力存储起来，然后在用电高峰时段释放，车主可以就此收费。这意味着，这些旧的电动汽车即便上不了路，也能作为“电网缓冲站”再做很多次充放电。

Nor are million-mile batteries the limit of engineers’ aspirations. The next objective is to replace Li-ions’ liquid electrolytes with solid ones. That would keep the ions under stricter control and allow even longer driving ranges. This could make a two-million-mile battery a feasible objective. If that day comes, the tables would have been turned. From being the first part of a car to fail, its battery will have become the last.■

工程师的追求也不止于百万英里电池。下一个目标是以固态电解质代替锂离子电池中的液体电解质。这将能更严格地控制锂离子，进一步延长电池的续航里程。“两百万英里”电池因而可成为切实可行的目标。等到它实现的那一天，局面将完全扭转，电池将从汽车中最先报废的部分变成最耐用的。