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The Secret To Improving Lithium-Ion Battery Life

2007-7-15 0:00:30 Category:Professional News

Poor battery life and the need to recharge smart phones often remain a huge pain for consumers. Help could be on the way. Researchers at the Washington State University said Wednesday they have figured out how pack more energy into a lithium-ion battery and boost the rate of charging it.

The trick is to replace graphite with tin for the anode, which is one of the two main components in a battery cell, said Grant Norton, who headed the research and is a professor of mechanical and materials engineering at the university. Using tin can increase the energy storage capacity of a battery cell by nearly three times, he said.

When you charge a battery, lithium ions travel from the cathode to the anode, where the anode holds onto the lithium ions to store the energy. When you use a battery, the lithium ions then move from the anode to the cathode and let loose of electrons in the process.

Battery cells, by the way, refer to products such as the conventional AA batteries inside a flash light. A battery pack or system, on the other hand, usually refers to a bunch of battery cells that have been encased and come with electronic devices to manage their charging and discharging and monitor their temperatures and performance. An electric car, for example, has a sophisticated battery system.

The research at Washington State focuses on the anode, which typically is made with graphite. Graphite is inexpensive and stable, and the process of using graphite to build the anode is well understood. Scientists have known that other materials can hold more lithium ions and increase the amount of energy that can be packed into a cell. But there are several key obstacles for using these alternative materials: figuring out the right nanostructures to best grab those lithium ions, trouble-shooting potential problems that could compromise a cell’s performance, and coming up with an inexpensive manufacturing process to build these materials into cells.

Silicon, for example, can hold a lot more lithium ions than graphite, but it’s quite unstable in that battery cell environment and can cut short a battery’s life. The promise of using silicon to significantly boost a battery cell’s energy density has attracted a lot of research and investment dollars,however.

Tin is better than graphite but not as good as silicon at holding onto the lithium ions. But using tin may prove a faster way to improve a battery cell’s performance. At least that was what Norton set out to prove.Sony,for example,uses a blend of tin and other materials for some of its lithium-ion batteries. After some experimenting, Norton settled on growing tin in the form of needles (about 50 nanometers in length) and adding textures to the material to create more surface area. A larger surface area means a greater ability to hold onto more lithium ions.

“It’s like when water gets absorbed into the cellular structure of a sponge. You want a lot of surface area to absorb a lot of water,” Norton said.

For an inexpensive manufacturing process, Norton has turned to electroplating,which has been around for more than a century for coating a variety of materials. The idea is to coat the tin material onto the copper component that conducts electricity. Right now, graphite has to be mixed with a binding material before being attached to this copper current collector. Putting tin directly onto the copper piece would reduce the manufacturing steps and costs, Norton said.

Of course, turning an idea from the lab to a commercial product is typically a long and expensive process. And companies often have to make many modifications along the way. Norton is hoping to catch the attention of battery makers or investors to give his idea a try.