Researchers achieve long cycle life of button cell battery cr2025 through innovation

The great challenge of improving energy storage and extending battery life while ensuring safe operation is becoming increasingly important as we rely more and more on this energy source, from portable devices to electric vehicles. A Columbia Engineering team led by Yuan Yang, assistant professor of materials science and engineering, announced on April 22, 2019 that they have developed a new method to safely extend the battery life by implanting boron nitride nanocoatings to stabilize the solid electrolyte in lithium metal batteries. Their research findings were published in Joule. Conventional lithium-ion batteries are currently widely used in daily life, but their low energy density leads to short battery life.

And because the batteries contain highly flammable liquid electrolytes inside, they may short-circuit or even catch fire. Replacing the graphite anode used in lithium-ion batteries with lithium metal can improve energy density: the theoretical charge capacity of lithium metal is nearly 10 times higher than that of graphite. But during the lithium plating process, dendrites tend to form, and if they penetrate the separator in the middle of the battery, they will cause a short circuit, raising concerns about battery safety. The research team decided to focus on solid ceramic electrolytes, which show great potential for improving safety and energy density compared to the flammable electrolytes in traditional lithium-ion batteries. Rechargeable solid-state lithium batteries are of particular interest because they are promising candidates for next-generation energy storage. Most solid electrolytes are ceramic and therefore non-flammable, eliminating safety concerns.

An artificial boron nitride (BN) film that is chemically and mechanically resistant to lithium electronically isolates lithium aluminum titanium phosphate (LATP) from lithium, but still provides a stable ion channel when infiltrated by polyethylene oxide (PEO), allowing for stable cycling. Image: Qian Cheng/Columbia Engineering In addition, solid ceramic electrolytes have high mechanical strength and can actually inhibit the growth of lithium dendrites, making lithium metal a coating of choice for battery anodes. However, most solid electrolytes are unstable to lithium ions and are easily corroded by metallic lithium, making them unusable in batteries. "Lithium metal is indispensable for improving energy density, so it is crucial that we can use it as the anode of a solid electrolyte," said Qian Cheng, a postdoctoral scientist in the Department of Applied Physics and Applied Mathematics and the paper's first author. To adapt these unstable solid electrolytes for practical applications, a chemically and mechanically stable interface needs to be developed to protect these solid electrolytes from the lithium anode.

To transport lithium ions, it is crucial that the interface is not only highly electronically insulating but also ionically conductive. In addition, the interface must be ultrathin to avoid reducing the energy density of the battery. To address these challenges, the team collaborated with colleagues at Brookhaven National Lab and City University of New York. A 5-10 nm boron nitride (BN) nanofilm was deposited as a protective layer to isolate the electrical contact between metallic lithium and the ion conductor (solid electrolyte), and a small amount of polymer or liquid electrolyte was added to penetrate the electrode/electrolyte interface. BN was chosen as a protective layer because it is chemically and mechanically stable with metallic lithium and provides a high degree of electronic insulation. The boron nitride layer is designed to have intrinsic defects through which lithium ions can pass, making it an excellent separator.

Lithium aluminum titanium phosphate (LATP) particles that come into contact with lithium metal are immediately reduced, and severe side reactions between lithium and the solid electrolyte can cause the battery to fail within a few cycles. Shown on the right is an artificial boron nitride film that is chemically and mechanically resistant to lithium. It electronically isolates LATP from lithium, but still provides a stable ion channel when penetrated by polyethylene oxide (PEO), allowing stable cycling.

In addition, boron nitride prepared by chemical vapor deposition easily forms large-scale (~dm level), atomically thin (~nm level), and continuous films. While earlier studies used polymer protective layers as thin as 200 microns, the new study's BN protective film is only 5-10 nanometers thick, which is still thin at this protective layer limit without reducing the battery's energy density. This is a perfect material that can act as a barrier to prevent metallic lithium from invading solid electrolytes. Just like a bulletproof vest, a lithium metal bulletproof vest for unstable solid electrolytes has been developed, and through this innovation, a button cell battery cr2025 with a long cycle life has been achieved. The researchers are currently expanding the new method to a wide range of unstable solid electrolytes and further optimizing the interface in the hope of making high-performance, long-cycle-life solid-state batteries.

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