If electric power is the future of travel, we've got to engineer a better battery. Although batteries have been improving markedly in recent years, they need to store more energy in a smaller package if they are going to compete with gasoline for
As reported in MIT Technology Review, there is hope for the future. New materials are allowing increased capability through improved reliability. Researchers at Stanford University have shown that mixing silicon microparticles with self-healing polymers may extend both the performance and useful life of lithium-based batteries.
Why mix these materials? To start, the silicon - similar to that in computer chips - is a promising battery material when paired with lithium. It can store about 10 times more lithium than current, carbon-based technology.
The problem occurs when the battery is charged and discharged. When charged, the silicon anodes take in large amounts of lithium. Even though lithium is a small atom, its absorption (known as lithiation) causes the silicon to expand significantly.
When the battery is used (discharged), the lithium is released and the silicon contracts. This cycling can damage the anode and cause the battery to fail quickly.
That is why the silicon is mixed with a polymer. As described in previous work from Lawrence Berkeley National Lab, “The secret is a tailored polymer that conducts electricity and binds closely to lithium-storing silicon particles, even as they expand to more than three times their volume during charging and then shrink again during discharge.”
Self-healing polymers act like “chemical zippers” and close cracks that form when the battery is used and recharged. When the polymer cracks, it flows back together. The Stanford group mixed carbon particles with the polymer to enhance electrical conductivity. This “gooey” mixture was combined with silicon microparticles to make an anode.
So far these self-healing anodes have been paired successfully with a pure Li cathode. The new, silicon-based anode material is capable of eight times more storage than the conventional carbon anode used in lithium-ion batteries. If paired with a high-capacity cathode, the energy storage may be doubled or tripled.
There are some other promising methods of extending battery capability using nanostructured silicon. Other materials are being developed as well, such as tin, graphene, germanium and others. As the demand for long-life, high-capacity batteries increases, so will the innovative solutions.
Images courtesy of MIT Technology Review (top) and Lawrence Berkeley National Laboratory (bottom)