Lithium-ion battery use is booming as the electric vehicle market continues to grow. These batteries have a longer life than many others on the market, but they bear drawbacks such as safety issues and using rare metals whose supplies are depleting. Scientists continuously work to build better, less environmentally damaging batteries with longer lifespans.
Lithium-sulfur batteries show promise for holding up to five times more energy than lithium-ion batteries. A University of Michigan team created an innovation that extends the number of times lithium-sulfur batteries can charge and discharge to about 1,000 times, the real-world equivalent of 10 years. The technology uses nanofibers recycled from Kevlar — the ultra-strong material in bulletproof vests.
Challenges
When developers extend the life of lithium-sulfur batteries, it usually comes at a cost. The alterations tend to decrease safety, resilience, charging rate, and capacity.
“The challenge nowadays is to make a battery that increases the cycling rate from the former 10 cycles to hundreds of cycles and satisfies multiple other requirements including cost,” Nicholas Kotov, chemical sciences and engineering professor, said in a news release.
Another problem is that lithium and sulfur form small molecules, polysulfides, that attach to the lithium side of the battery and reduce battery capacity. A membrane is needed to allow lithium ions to flow back and forth but block the lithium-sulfur particles. But the polysulfides are similar in size to the lithium ions, making it difficult to block one and not the other.
The batteries also are prone to growing dendrites, spiky structures that pierce the membrane and other internal components and decrease battery life, stability, and safety.
The technology
The University of Michigan team created a membrane out of recycled Kevlar fibers, which increased the component’s toughness. This robust design prevents dendrite damage.
They added an electrical charge to the membrane pores. Positively charged lithium ions can pass through freely while the negatively charged polysulfides are blocked.
The hardy design also allows the battery to function well in the extreme temperatures in vehicles — from the winter cold to the heat of charging in full sunlight.
“Achieving record levels for multiple parameters for multiple materials properties is what is needed now for car batteries,” Kotov said.
What’s next
The team already received a patent for the Kevlar-infused membrane. Kotov said the design already is almost perfect, and the battery capacity and efficiency are near their theoretical limits. He is creating a company to bring the product to market.
