In a challenge to improve energy storage and extend battery life, researchers developed a way to make more durable lithium-ion batteries. They sought a way to make these batteries operate safely, given their somewhat controversial nature.
A Columbia University engineering team led by Yuan Yang, an assistant professor of materials science and engineering, announced that they developed a safe way to extend battery life. Their research was published in the journal Joule, and it highlights a method of adding a nano-coating of boron nitride to stabilize the electrolytes in lithium batteries.
Lithium-ion batteries are widely used in daily life. However, their safety is still questioned. Given that they have low energy density, they don’t have a very long battery life. Moreover, their highly-flammable liquid electrolytes make them catch fire easily. Researchers used lithium metal to replace the graphite anode in Li-ion batteries to enhance the energy density. However, while this approach delivers nearly 10 times greater efficiency than graphite, the formation of dendrites can often contribute to short-circuits and raise questions about the safety of these batteries.
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“We decided to focus on solid, ceramic electrolytes. They show great promise in improving both safety and energy density, as compared with conventional, flammable electrolytes in Li-ion batteries,” Yang said in a statement. “We are particularly interested in rechargeable solid-state lithium batteries because they are promising candidates for next-generation energy storage.”
Most solid electrolytes are made of ceramic and can’t catch fire, which eliminates safety concerns. The researchers also opted for solid ceramic electrolytes because of their mechanical strength, which can prevent dendrite growth, resulting in more durable lithium-ion batteries.
“Lithium metal is indispensable for enhancing energy density and so it’s critical that we be able to use it as the anode for solid electrolytes,” lead author and postdoctoral research scientist Qian Cheng said. “To adapt these unstable solid electrolytes for real-life applications, we needed to develop a chemically and mechanically stable interface to protect these solid electrolytes against the lithium anode. It is essential that the interface not only be highly electronically insulating, but also ionically conducting in order to transport lithium ions.”
The researchers collaborated with colleagues at Brookhaven National Lab and the City University of New York to overcome the challenges with this stability. They used 5~10 nm boron nitride nano-film as a protective layer to isolate the electrical contact between the lithium metal and the solid electrolyte. The research team opted for BN as a protective layer because they needed a stable material, both in the sense of chemistry and mechanics. A more stable material also provides proficient electronic insulation, resulting in more durable lithium-ion batteries.
“While earlier studies used polymeric protection layers as thick as 200 μm, our BN protective film, at only 5~10 nm thick, is record-thin—at the limit of such protection layers—without lowering the energy density of batteries,” Cheng says. “It’s the perfect material to function as a barrier that prevents the invasion of lithium metal to solid electrolyte. Like a bullet-proof vest, we’ve developed a lithium-metal-proof ‘vest’ for unstable solid electrolytes and, with that innovation, achieved long cycling lifetime lithium metal batteries.”