电池之死
为什么电池会死?并且，为什么它们一生只能被充电有限的次数?
My young son asked me about that years ago when his battery-powered toy car stopped moving, wondering about what he called an "everlasting battery".
几年前，当装有电池的玩具车停止移动时，我的小儿子问我，他想知道为什么不买一块 “永恒的电池”。
And this same question has probably crossed the mind of every cellphone user trying to send one last text before the screen blinks off.
同样的问题可能经常闪过那些赶在手机屏幕变黑前发出最后一条信息的用户的脑海里。
Research, like mine, continues around the world to make batteries that charge faster, last longer, and can be recharged and discharged many more times than today's.
在世界各地，都有像我这样的人从事着类似的研究，目的是使电池充电更快，使用寿命更长，充电和放电的次数比现在多很多倍。
But as much as you and I would like, it's impossible to make a truly everlasting battery. I have taught thermodynamics for more than 30 years. So far, there is nothing that suggests we can break the fundamental laws of science to get that elusive battery.
但是，就像你和我所知道的那样，制造一块真正永恒的电池是不可能的。我在课堂上讲授热力学的时间已有30多年，到目前为止，没有任何迹象表明我们能够打破最基本的科学定律制造出神奇的电池。
Battery scientists and engineers call the main problem "capacity fade".
电池科学家和工程师将主要问题称之为“容量衰减”。
Regular people wonder about it with questions like "Why won't my battery hold a charge?" and complaints like "I just recharged this thing and it's already out again!"
普通人或许会对这个问题感到疑惑，发出这样的疑问：“为什么我的电池不能充电了?”或者投诉：“我刚刚充好，它就又用光了!”
It's a result of the second law of thermodynamics, which states that whenever some real process happens, it creates a certain amount of wasted energy along the way that can never be recovered.
这是热力学第二定律的结果，该定律支配着事件万物，无论何时发生的现实过程，都会浪费掉一定量的能量，而这些能量是绝无可能被回收利用的。
Any time a battery is charged or discharged, there's a little bit of wasted energy – a little bit of wasted capacity in the battery that cannot be recovered.
电池充电或放电，都会浪费一点能量，而这一点点浪费对于电池而言，是无法恢复的。
To envision how this works, think about battery use like transferring water between two cups. Using a battery is like emptying the water from one cup into the other, and charging the battery involves pouring the water back into the first cup.
为了设想它们的工作机理，考虑一下电池的使用情景，类似于在两个杯子之间转移水。使用电池就像将水从一个杯子倒入另一个杯子中，给电池充电就是将水倒回到第一杯子里。
Even if you do it one or two times without spilling a drop, there's always just a little tiny bit left in each cup that you can't pour out.
即使你连续好几次都没有在杯子外掉落一滴水，但是每个杯子里总会残留下你无法倒出来的一点点水。
Now imagine pouring back and forth hundreds or even thousands of times over a period of two or three years (for a cellphone battery) or 10 to 20 years (for an electric car).
现在想象一下，在2、3年(手机电池)或10到20年(电动汽车)中来回倾倒数百次甚至数千次。
Over time, all the thousands of little and big things that go wrong add up to quite a bit of water going missing.
随着时间的推移，所有的阴差阳错都会导致相当多的水流失到杯子外面。
Even spilling a barely visible drop – say one-tenth of a milliliter – adds up to an entire liter if it happens 10,000 times. That doesn't even include the possibility of one cup failing in some way that loses even more water – like springing a leak or heating up and causing evaporation.
即使只是溢出几乎不可见的水滴——比如十分之一毫升——如果发生了10000次，就会变成一升。这甚至还没有计算进蒸发之类的影响。
Just as water inevitably goes missing when pouring from one cup to another, more energy is required to charge the battery than it actually stores, and less energy comes out than is stored in it. The proportion of wasted energy to stored energy grows over time.
就像把水从一个杯子倒到另一个杯子时，水不可避免地会有损失一样，为电池充电所需的能量比实际存储的更多，并且电池可用的能量比储存在其中的更少。浪费掉的能量与储存能量的比例随着时间的推移而增长。
The ConversationIn fact, the more you use a battery, the more energy gets wasted, and the sooner the battery will reach a point where it's dead and can't usefully be recharged.
换句话说，你使用电池的次数越多，浪费的能量就越多，电池就会越早进入僵死状态，无法进行充电。
I and others are studying ways to have those discharging-recharging cycles run more smoothly to reduce the amount of waste, but the second law of thermodynamics will always make sure that there's no way to get rid of it entirely.
我和其他人正在研究如何让电池放电—充电循环得更为顺畅地以减少浪费，但热力学第二定律确保了没有人能够一劳永逸地解决这一问题。
