電池之死

為什么電池會(huì)死?并且，為什么它們一生只能被充電有限的次數(shù)?

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".

幾年前，當(dāng)裝有電池的玩具車(chē)停止移動(dòng)時(shí)，我的小兒子問(wèn)我，他想知道為什么不買(mǎi)一塊 “永恒的電池”。

And this same question has probably crossed the mind of every cellphone user trying to send one last text before the screen blinks off.

同樣的問(wèn)題可能經(jīng)常閃過(guò)那些趕在手機(jī)屏幕變黑前發(fā)出最后一條信息的用戶(hù)的腦海里。

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，都有像我這樣的人從事著類(lèi)似的研究，目的是使電池充電更快，使用壽命更長(zhǎng)，充電和放電的次數(shù)比現(xiàn)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樣，制造一塊真正永恒的電池是不可能的。我在課堂上講授熱力學(xué)的時(shí)間已有30多年，到目前為止，沒(méi)有任何跡象表明我們能夠打破最基本的科學(xué)定律制造出神奇的電池。

Battery scientists and engineers call the main problem "capacity fade".

電池科學(xué)家和工程師將主要問(wèn)題稱(chēng)之為“容量衰減”。

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!"

普通人或許會(huì)對(duì)這個(gè)問(wèn)題感到疑惑，發(fā)出這樣的疑問(wèn)：“為什么我的電池不能充電了?”或者投訴：“我剛剛充好，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.

這是熱力學(xué)第二定律的結(jié)果，該定律支配著事件萬(wàn)物，無(wú)論何時(shí)發(fā)生的現(xiàn)實(shí)過(guò)程，都會(huì)浪費(fèi)掉一定量的能量，而這些能量是絕無(wú)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.

電池充電或放電，都會(huì)浪費(fèi)一點(diǎn)能量，而這一點(diǎn)點(diǎn)浪費(fèi)對(duì)于電池而言，是無(wú)法恢復(fù)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.

為了設(shè)想它們的工作機(jī)理，考慮一下電池的使用情景，類(lèi)似于在兩個(gè)杯子之間轉(zhuǎn)移水。使用電池就像將水從一個(gè)杯子倒入另一個(gè)杯子中，給電池充電就是將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.

即使你連續(xù)好幾次都沒(méi)有在杯子外掉落一滴水，但是每個(gè)杯子里總會(huì)殘留下你無(wú)法倒出來(lái)的一點(diǎn)點(diǎn)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).

現(xiàn)在想象一下，在2、3年(手機(jī)電池)或10到20年(電動(dòng)汽車(chē))中來(lái)回傾倒數(shù)百次甚至數(shù)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.

隨著時(shí)間的推移，所有的陰差陽(yáng)錯(cuò)都會(huì)導(dǎo)致相當(dāng)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.

即使只是溢出幾乎不可見(jiàn)的水滴——比如十分之一毫升——如果發(fā)生了10000次，就會(huì)變成一升。這甚至還沒(méi)有計(jì)算進(jìn)蒸發(fā)之類(lèi)的影響。

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.

就像把水從一個(gè)杯子倒到另一個(gè)杯子時(shí)，水不可避免地會(huì)有損失一樣，為電池充電所需的能量比實(shí)際存儲(chǔ)的更多，并且電池可用的能量比儲(chǔ)存在其中的更少。浪費(fèi)掉的能量與儲(chǔ)存能量的比例隨著時(shí)間的推移而增長(zhǎng)。

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.

換句話(huà)說(shuō)，你使用電池的次數(shù)越多，浪費(fèi)的能量就越多，電池就會(huì)越早進(jìn)入僵死狀態(tài)，無(wú)法進(jìn)行充電。

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讓電池放電—充電循環(huán)得更為順暢地以減少浪費(fèi)，但熱力學(xué)第二定律確保了沒(méi)有人能夠一勞永逸地解決這一問(wèn)題。