New tech allows lithium batteries to charge faster, and hold charge longer
By Bryan Clark
November 20, 2011
For those of us using smart phones, an all-too-familiar problem is that of a dead battery. The computing power, as well as the multi-purpose abilities of modern-day phones is nothing short of amazing. However, until battery life catches up with the functionality, we're still forced to carry multiple devices. For example, what good is 32GB of memory to store music and movies if it leaves me with a dead phone after an hour or two of my favorite tunes? Even though my phone can easily handle the music and movie abilities of my iPod, I still carry the iPod. I still have a GPS in my car, even though my phone is more than capable. New technology from Northwestern University is aiming to change all that. Engineers there have created an electrode for lithium-ion batteries - the rechargeables commonly found in our devices - that allows them to run ten times longer, while only taking only one-tenth of the time to charge.
"We have found a way to extend a new lithium-ion battery's charge life by 10 times," said Harold H. Kung, in a paper published in the journal Advanced Energy Materials. Kung is professor of chemical and biological engineering at the McCormick School of Engineering and Applied Science. "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."
Close your eyes for a moment and imagine a week - or more - of battery life. If that doesn't bring a smile to your face, the next statement will: imagine your phone running for a week after charging for only 15 minutes.
Currently, lithium-ion batteries charge by a chemical reaction that occurs when lithium ions are sent back and forth between the two ends of the battery; the anode and the cathode. When the battery is fully charged and in use, the ions travel from the anode through the electrolyte and ultimately make their way to the cathode. When all the ions make their way to the cathode, the battery is dead.
When you charge the battery, you are reversing the process and sending the ions from the cathode to the anode.
The electrode combines two chemical engineering processes to eliminate the two major flaws in lithium-ion battery technology; their limited energy capacity and relatively slow recharge rate. The electrode virtually eliminates these problems and promises super batteries for the next generation of devices.
The first problem is limited energy capacity, which is why your current battery can't maintain a charge for long periods of time. The culprit here is called charge density. Charge density is basically how many lithium ions you can pack into one battery between the anode and cathode. The second problem is charge rate. This problem stems from the speed at which the lithium ions can travel from the cathode to the anode. In essence, speed them up and you have a faster charge.
In its current state, the anode - made up of thin layers of graphene sheets - can only accommodate one lithium atom for every six carbon atoms. Scientists have experimented with replacing the carbon with silicon, as silicon can accommodate much more lithium (four lithium atoms for every silicon atom) than the carbon. The problem is, silicon expands and contracts rapidly during the charging process. This causes the battery to lose its recharge capabilities relatively quickly.
Kung's team fixed the energy capacity problem by stabilizing the silicon. This involved sandwiching silicon between the graphene sheets. This maximizes the amount of ions that can travel through the sheets, while maintaining flexibility so that the battery isn't compromised while charging.
The second problem fixed by Kung's team was the recharge rate. This was accomplished by creating microscopic (10 to 20 nanometers) holes in the graphene sheets. This process was named "in-plane defects" and it allowed the ions a shorter, secondary route to the anode. This reduced the charge time to one-tenth of the previous time it took to charge the battery.
Looking past the implications of longer battery life for your personal devices, the electrode could also make batteries for electric cars smaller, and longer-lasting.
The Northwestern University technology is expected to hit the marketplace in the next three to five years.