The Economist - USA (2020-08-01)

62 TheEconomistAugust 1st 2020

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A

s every mobile-phoneowner 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, how-

ever, is a much bigger investment. And bat-

teries are its priciest component, repre-

senting 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.

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 ki-

lometre) batteries. Zeng Yuqun, the boss of

Contemporary Amperex Technology, a

giant Chinese firm which produces batter-

ies for a number of carmakers, said in June

that his company was ready to start manu-

facturing 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. Ru-

mours suggest this could be unveiled in

September. And over in Detroit, General

Motors (gm) is in the final stages of devel-

oping an advanced battery which it says

has similar longevity.

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 Re-

search 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. Driv-

ing in extremely hot or cold weather does

not help either. And battery life will dimin-

ish even if you just leave the car in the ga-

rage. The real point of a million-mile bat-

tery is that the technological advances

required to make it possible will deal with

these things as well.

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 age-

ing”. It is a consequence of the gradual deg-

radation of some of the materials em-

ployed in battery construction. This

degradation reduces a battery’s ability to

hold a charge—though even here it is pos-

sible 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.

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 re-

actions that you can’t stop and some of

those are harmful,” explains Dr Crabtree.

Electric cars

Million-mile car batteries are coming

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

Science & technology

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