An international team of scientists has discovered a material that could allow lithium-ion batteries to have more energy without sacrificing battery life, according to foreign media reports. The team found that antimony crystals spontaneously and reversibly hollow out during charge and discharge cycles, a highly anticipated property that could increase energy density without compromising safety.
Lithium-ion batteries generate electricity by transferring ions back and forth between positive and negative electrodes. But in their current state, they have reached their limits. Efforts to increase the flow of lithium ions are hampered by the aging of the anode material, which expands and contracts during charging and discharging, creating more stress and thus reducing battery life.
Scientists see a solution in "yolk-shear" particles, as the hollow space can accommodate volume changes during charge and discharge of the battery while providing a stable outer surface, thereby increasing cycling capacity. Replacing metal alloy anode materials with these particles has long been thought to be a promising approach, but manufacturing them in a cost-effective manner has proven problematic.
Intentional engineering of hollow nanomaterials has emerged as a promising avenue for improving the lifetime and stability of high-energy density batteries," said study author Matthew McDowell of the Georgia Institute of technology. " The problem has always been that direct synthesis of these hollow nanostructures on the scale required for commercial applications is challenging and costly. Our findings could provide a simpler, streamlined process to improve performance in a similar way to intentionally designed hollow structures."
McDowell and his colleagues from Georgia Tech, ETH Zurich and Oak Ridge National Laboratory set out to study tiny particles with diameters of one thousandth of a hair. The team found that these oxide encrusted antimony nanocrystals spontaneously hollow out during the cell cycle, rather than expanding and contracting as expected.
This hollowing behavior was confirmed by observing the nanoparticles in a small test cell using high-resolution electron microscopy, which found that only particles smaller than 30 nm in diameter were present. It works by causing the material to swell as ions pass through the elastic oxide layer into the anode, while creating a gap as the ions are removed, rather than causing the typical shrinking behavior.
McDowell said, "When we first observed this unique hollow behavior, it was very exciting, and we knew right away that it could have an important impact on battery performance." .
While these hollow nanoparticles were an exciting discovery, the team faced a challenge. Antimony itself is expensive, so it hasn't been used to produce battery electrodes. However, the scientists suspect that other, cheaper materials, such as tin, may exhibit the same hollow behavior. They now hope to explore these possibilities and work on larger batteries for commercial applications.
McDowell said, "It will be interesting to test other materials to see if they will transform based on a similar hollow mechanism." This could expand the range of materials available for batteries. Our small test cells showed promising charge and discharge performance, so we hope to evaluate these materials in larger cells."
The study was published in the journal Nature Nanotechnology.
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