Want lithium-ion batteries to last? Slow charging may not be the answer

For the first time, scientists have examined how a battery operates on the particle level

Stanford University grad student Yiyang Li tests lithium ion coin cell batteries at the Stanford Institute for Materials & Energy Sciences (SIMES).

Stanford University grad student Yiyang Li tests lithium ion coin cell batteries at the Stanford Institute for Materials & Energy Sciences (SIMES).

New research by a California-based team could change the way lithium-ion batteries are charged in consumer electronics products and electric cars, leading to longer lifetimes and more useful batteries.

The work, published on Sunday in the Nature Materials journal, challenges the commonly held notion that slowly charging a battery helps prolong its life and that it's damaging to a battery if a large amount of energy is withdrawn in a short time.

"We've always thought of a battery as a [single] device, but inside an iPhone battery there are a few trillion particles," said William Chueh, a senior author of the paper and researcher at the Stanford Institute for Materials and Energy Sciences, in an interview.

"We, as a scientific community, have been looking at the macro level, at how the entire battery behaves, but our research looks at individual particles to come up with a model for how it works," he said.

Chueh and the team used the particle accelerator at the Department of Energy's SLAC National Accelerator Laboratory in Menlo Park to observe the way individual nanoparticles behave when a battery is being charged and discharged. It's the first time such detail has been observed and recorded.

Rather than electrical current being evenly distributed so that all particles gradually get charged, it actually gets absorbed by single particles or small groups of particles for a short period of time until each is charged, then moves on to the next one. The battery is effectively charged particle-by-particle through a series of very fast charges. That surprised researchers, because rapid charging was also thought to be damaging to batteries.

"For the last 10 or 20 years, we've always been told to charge as slowly as possible, to trickle charge, so that heat is reduced in the battery and it lasts longer," said Chueh. "What we found in this paper is, that's not entirely correct."

Armed with the new knowledge, the researchers are proposing several ways to charge batteries more uniformly, a change that could take the average life of a lithium-ion battery from a couple of years to around 10 years. More uniform charging, whether fast or slow, causes less localized heating that can degrade the battery.

They're also considering ways to enable faster charging or discharging while preventing damage to the battery.

This research could benefit, among other things, electric cars, which often require a charge lasting several hours. If that time could be reduced, drivers wouldn't have to endure lengthy pit stops while making long journeys. And for the electrical grid, storage batteries that are better at handling sudden surges in demand are also in the cards.

But first, the team needs to do more experimentation. In particular, they'll be running battery electrodes through thousands of charge-discharge cycles to simulate typical use and measuring the performance. Talks have already begun with companies in the consumer electronics and automotive industries.

The team included members from the Massachusetts Institute of Technology, Sandia National Laboratories, Samsung Advanced Institute of Technology America and Lawrence Berkeley National Laboratory.

Martyn Williams covers mobile telecoms, Silicon Valley and general technology breaking news for The IDG News Service. Follow Martyn on Twitter at @martyn_williams. Martyn's e-mail address is martyn_williams@idg.com

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