为什么手机电池会在低温下罢工？

如果你在户外遭遇了极地涡旋，即让北美瑟瑟发抖的北极气团——但愿不要如此！——你的手机可能会有奇怪的表现。没错，你会发现手机的续航时间受到了影响。一不小心，电量就可能在不发出警报的情况下从30%猛然跌到……好吧，0%。

是的，寒冷天气会降低手机电池的性能。尽管这一点似乎不可思议，不过耗电飞快的原因很简单。以下是这一现象背后的科学道理，以及让你的设备持续工作的一些小建议，它们大多都是常识。

又冷又酷的科学知识

简单来说，低温天气下手机电池续航降低是由于化学原因。

包括手机、笔记本电脑、电动汽车在内的大部分现代消费品，它们的可充电电池都采用了锂离子技术。在这些电池系统里，电流会从通常由石墨制成的阳极流向金属氧化物制成的阴极。而两极之间的电解质，通常是含盐液体或胶体，则用于导电。

一般情况下，带电粒子会在两极之间无缝流动，产生电流和能量。不过低温会让情况变得更加复杂。将液体放在冷冻库中，它会结冻，电池芯中的情况也是类似。

加拿大滑铁卢大学（University of Waterloo）的化学教授琳达·纳扎尔表示，低温会导致电解质变浓，粘性增加。材质的导电性会随之减弱，降低了推动电池中化学引擎的带电粒子的移动性。

纳扎尔说道：“电池是根据电化学的规律工作的，气温降低，反应就会变慢。这只是自然规律导致的结果。”

科技公司怎么说

大部分大型手机厂商都向消费者发出了警告，称严寒天气可能会影响公司的产品性能。

iPhone的制造商苹果（Apple）表示，寒冷气温下电池续航时间会有所减少，不过也指出“这种情况是暂时的”。公司在官网上保证：“一旦电池的温度回到正常工作温度，性能也会回归正常。”

按照苹果所述，“理想的舒适区”是62华氏度至72华氏度。不过根据苹果提供的下图显示，只要气温在水的冰点之上，iPhone的性能应该就不会受到影响。

If you’re caught outside—heaven forbid!—in polar vortex, an Arctic air spillover numbing North America, your phone might act peculiar. Indeed, you may notice the battery life of your handset take a hit. If you’re not careful, the charge could drop precipitously, without warning, from 30% to…well, zero.

It’s true: Cold weather worsens the performance of phone batteries. While this may seem mysterious, there’s a simple reason for the juice-sapping affliction. Here’s what’s behind the phenomenon and a few tips, mostly common sense, for keeping your devices alive.

Cool science

Put simply, phone batteries worsen in the cold because of chemistry.

The rechargeable batteries in most modern consumer products, including cellphones, laptops, and electric vehicles, use Lithium ion technology. In these systems, an electrical current flows from a positively charged anode, typically made of graphite, to a negatively charged cathode, a metal oxide. In between, an electrolyte, usually a salty liquid or gel, conducts electricity.

Under normal conditions, charged particles flow seamlessly between opposing nodes, creating an electric current and source of power. But cold temperatures complicate the situation. Put a liquid in a freezer and it will freeze; a similar principle is at work inside a battery cell.

Cooling causes the electrolytic medium to thicken and become more viscous, explains Linda Nazar, a chemistry professor at the University of Waterloo in Canada. This makes the material a poorer conductor, reducing the mobility of the charged particles that drive the battery’s chemical engine.

“Batteries work on electrochemistry and those processes get slow when the temperature drops,” Nazar says. “That’s just a consequence of the laws of nature.”

What tech companies say

Most major phone-makers alert customers that frigid environments will affect their products’ performance.

Apple, maker of the iPhone, says that battery life decreases in colder temperatures, but notes that “this condition is temporary.” As the company’s website reassures, “Once the battery’s temperature returns to its normal operating range, its performance will return to normal as well,”

The “ideal comfort zone,” as Apple puts it, ranges from 62° Fahrenheit to 72°F. But iPhones should remain unaffected as long as they’re kept above the freezing point of water, as the Apple graphic below advises.

另一方面，苹果警告称，高温可能“对电池容量造成永久损害”。换句话说，把手机放到高温下炙烤，电池的蓄电量将永久减少。

与此同时，三星公司（Samsung）在设法打消某些消费者坚信的“常见谣言”：电池在冷冻冰箱中储存，能够工作更长时间。公司特别指出不建议这样做，并警告称这是“错误的做法，可能损坏你的电池”。

永远做好准备

现在你知道了气温和电池性能背后的科学道理，接下来我们提供了一些建议。这里重申，没错，它们大多都是常识。

——让你的手机在合适温度下工作。（例如，三星公司就建议在酷暑或酷寒天气把手机放在汽车的储物箱中。）

——带上便携式充电宝。它们既便宜，又能在关键时刻派上用场。

现在在那里穿暖一点吧！（财富中文网）

译者：严匡正

Screenshot from Apple’s website

On the other end of the spectrum, hot temperatures can “permanently damage battery capacity,” Apple warns. In other words, cook your phone and a charge will forever carry less juice.

Samsung seeks, meanwhile, to dispel what it calls a “common myth” persisting among some consumers: that batteries last longer if stored in a freezer. The company specifically advises against this practice, warning that it “is not correct and can damage your battery.”

Always be prepared

Now that you understand the science behind temperature and battery performance, here are our tips for you. To reiterate, yes, they’re mostly common sense.

—Keep your phone within the right temperature range. (Samsung, for instance, advises against stashing phones in the glove compartments of cars on very hot or cold days.)

—Bring a portable, external battery pack with you. They’re cheap, and they can come in handy in a pinch.

Now bundle up out there!