经济学人下载:让乌龟和兔子交配(1)

Superbatteries 

超级电池

What do you get when you cross a hare with a tortoise? 

乌龟和兔子交配产下的种

Mixing supercapacitors and batteries may give electric cars what they need to overcome customer resistance. 

将超级电容器和电池混合使用，可能会给电动汽车带来克服消费者阻力所需的东西。

When it comes to putting on pace, some electric vehicles rely not only on a battery to deliver the necessary wattage, but also on a second source of power called a supercapacitor. The battery serves as a marathon runner, providing a steady discharge over a long distance. The supercapacitor is a sprinter, unleashing a large amount of energy rapidly. 

说到加速，一些电动汽车不仅要靠电池来提供必要的功率，还要靠一种叫做“超级电容器”的第二能源。电池是马拉松运动员，能够在长途中提供足够的电量。而超级电容器是短跑运动员，能够在瞬间释放大量能量。

Speedy discharge is not the only advantage supercapacitors bring. They can be recharged more quickly, too. That makes them particularly useful in regenerative-braking systems, since they are able to absorb more of the electricity that is produced as a vehicle slows down. They can, though, store only a fraction of the amount of energy which a battery stuffs away. They therefore soon run out of puff. Because of this, engineers have been trying for a while to hybridise the best bits of a supercapacitor with the most useful features of a battery, to make a storage device with both speed and endurance. They are now having some success. Indeed, NAWATechnologies, near Aix-en-Provence, France, claims its supercapacitor-like battery could more than double the range of an electric car, allowing it to be driven for 1,000km on a single charge. This new device could also, NAWA says, be recharged to 80% of its capacity in as little as five minutes. 

快速放电并不是超级电容器的唯一特长，它还能够快速充电，这一点使得它们在生制动系统中尤其出色，因为它们能够吸收汽车减速时产生的更多电力。不过，它们能够储存的能量只有电池的一小部分，过不了多久便会气喘吁吁。于是乎，工程师们一段时间以来一直在尝试将超级电容器的最佳性能和电池最有用的特性相结合，制造一种兼具速度和持久性的存储设备。他们目前取得了一些成功。其实，位于法国艾克斯-普罗旺斯附近的NAWATechnologies公司声称，其类似于超级电容的电池可以使电动汽车的续航里程增加一倍以上，充电一次可行驶1000公里，另外这种新设备还可以在五分钟内充80%的电量。

The science bit 

科学部分

Capacitors and batteries work in different ways, so combining them is tricky. A capacitor stores energy physically, in the form of static electricity. This is easily and rapidly discharged, so capacitors have good power density (the rate at which they transfer energy, per unit of weight). A decent modern supercapacitor has a power density of several kilowatts per kilogram. 

电容器和电池的工作方式不同，所以将它们结合在一起并不容易。电容器以静电的物理形式储存能量，比较容易，也比较快速，所以电容器有着良好的功率密度（每单位重量的能量传递速率）。一个优秀的现代超级电容器的功率密度是每公斤几千瓦。

Batteries store their energy chemically, in the form of reactive substances in their two electrodes. These electrodes are held physically apart, but are connected by a material called an electrolyte through which charged atoms, known as ions, can pass from one to the other, in order to permit a reaction to proceed. That, though, happens only when the ion flow is balanced by a flow of electrons through an external circuit between the electrodes. This electron flow is the electric current which is the reason for the battery's existence. 

而电池以化学方式储存能量，即在两个电极中以活性物质的形式储存能量。这些电极在物理上是分开的，但由一种叫做电解质的材料相连接。通过电解质，带电原子（离子）可以从一个电极传递到另一个电极，从而使反应得以进行。然而，只有当离子流被通过电极之间外部回路的电子流平衡时，这种情况才会发生。这种电子流就是电流，这就是电池存在的原因。

Controlled in this way, chemical reactions take time, so batteries have low power density. A lithium-ion (Li-ion) battery of the sort used in electric cars might thus muster only a tenth of a kilowatt per kilogram. But chemicals can hold a lot of energy, so batteries have high energy density (the amount of energy they can contain, again per unit weight). A Li-ion battery can store 200-300 watt-hours per kilogram (wh/kg). Supercapacitors generally manage less than 10wh/kg. 

因为化学反应需要时间，所以用这种方法操作的话电池的功率密度会很低，而电动汽车中使用的锂离子电池每千克只能产生十分之一千瓦的电量。但是化学物质可以储存很多能量，所以电池有很高的能量密度（每单位重量可以包含的能量）。锂离子电池每千克可存储200-300瓦时能量，而超级电容器一般可以控制在10wh/kg以下。