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Redesigned lithium ion battery charges faster, holds charge longer

Researchers at Northwestern University redesign the lithium ion battery to charge faster and increase energy capacity, paving the way for better battery performance on our gadgets.

HTC Droid Incredible
Battery life on smartphones, such as the HTC Droid Incredible, has never been stellar, but longer-lasting cells might be on the way.
Josh Miller/CNET

Battery life is always an issue with today's gadgets, from smartphones to tablets to electric cars, but researchers at Northwestern University have come up with a new technology that might lead to longer-lasting devices in the next few years.

Engineers from Northwestern's McCormick School of Engineering and Applied Science discovered a way to redesign today's lithium ion cells, which are used in a number of consumer electronics, to address two major problems with today's batteries: energy capacity and charging time.

"We have found a way to extend a new lithium ion battery's charge life by 10 times," explained Harold H. Kung, professor of chemical and biological engineering at McCormick and lead author of the research paper. "Even after 150 charges, which would be one year or more of operation, the battery is still five times more effective than lithium ion batteries on the market today."

The team was able to do this by making changes to the material used in a battery and the way ions travel within a cell.

Understanding how lithium ion batteries work
To better understand the technology, it's helpful to know how lithium ion batteries work in the first place. As soon as you engage your smartphone, tablet, or some other device, a chemical reaction takes place where the lithium ions move from one end of the battery (called the anode) to the other end (called the cathode) of the battery. During this process, the ions are traveling through the electrolyte and giving off an electrical charge to the device. When you recharge the battery, the ions travel in the opposite direction, going from the cathode back to the anode.

The problem with today's batteries
The current design of lithium ion batteries presents two big problems, however. The first is that the number of ions that can be packed into the anode or cathode is limited, which affects how long a battery can maintain its charge. The second issue is that there can be a delay in how fast the ions travel from the electrolyte back to the anode, thus affecting the recharge time. The culprit of both these predicaments? The material used to make the anode.

By creating miniscule holes in the graphene sheets, lithium ions can travel faster back to the anode and speed of charging time. Advanced Energy Materials

The anode consists of layers of carbon-based graphene sheets. As it currently stands, the anode can only accommodate one lithium atom for every six carbon atoms, which isn't very much, so scientists have tried replacing carbon with silicon, which handle four lithium atoms for every silicon atom. That said, problem with silicon is that it expands and contracts dramatically during the charging process and causes fragmentation.

On the charging issue, the shape of the graphene sheets slows down the whole process. The sheets are thin but very long, and the lithium ions need to travel to the outer edges first before entering and settling between the sheets. However, as researchers explain, since it takes so long for the ions to make their way back to the middle, an "ionic traffic jam" occurs and slows down the charging rate.

A fix
The engineers at Northwestern came up with a solution for these problems by recreating the anode using a graphene-silicon design. By sandwiching silicon clusters between the graphene sheets, the anode can accommodate more lithium atoms, while the flexibility of the graphene can combat the silicon's fragmentation.

In addition, the team used a chemical oxidation process to create miniscule holes in the sheets, so the lithium ions could travel faster back to the anode. The result of all this was a 10x increase in speed in recharge time.

What's next?
Though all the focus was on the anode this time around, the group from Northwestern say it will work on the cathode next to increase the effectiveness of batteries and aim to improve the electrolyte system so the battery will automatically shut down at higher temperatures. The latter pertains more to electric cars and is viewed as a safety mechanism.

Researchers say that we could see the new battery technology hit the marketplace in the next three to five years. I'm sure more than a few mobile device users will agree with me when I say, that day can't come soon enough.

(Source: Popular Science)