Electric cars and other mobile uses could use fast-charging batteries that pack a lot of energy in a small space. Now, a team devised a way to create electrodes for such batteries. Their new synthesis technique produces electrode sheets made from nanostructured selenium (Se) - carbon composites. The new positive electrodes (that is, cathodes) have the electrical and mechanical properties needed for use in rechargeable batteries. The approach represents a new paradigm in high energy density battery design.
The team’s new electrodes enable battery designs with three big benefits. The battery stores a significant amount of energy in a small space. It’s durable. And it charges quickly. These are important factors for mobile battery applications, such as electrically powered vehicles.
Despite the intense focus in current scientific literature on batteries’ specific energy (energy per weight), it is the energy density (energy per volume) that is the primary consideration for automotive and other mobile applications. A novel approach to battery materials design presented in this work addresses this underappreciated but key design consideration and radically departs from prior state-of-the-art approaches. Rather than seeking to fabricate conventional nanostructured high surface area porous electrodes, this work takes the opposite approach by creating a dense, non-porous monolithic electrode-grade sheet. The sheet is mechanically self-supporting, potentially eliminating the need for a cathode current collector entirely, further reducing battery volume. Se-metal batteries are emerging as high-energy alternatives to conventional ion batteries used in automotive and grid applications. By volume, the cathodes in these batteries (dense structures made from Se and carbon) are twice as energetic as porous Se materials. Because the Se-carbon electrodes remain internally nanostructured, the rate at which the electrodes charge and the number of times the battery can be recharged before the electrode breaks down (cyclability) is good. The Se-carbon electrode has a relatively high volumetric density of 2.37 g/cc, which enables a theoretical amount of charge stored (volumetric capacity) of 1121 mAh/cc. For lithium (Li) storage, the cathode delivers a reversible capacity of 1028 mAh/cc and 82 percent capacity retention over 300 charge-discharge cycles. The new electrodes yield unparalleled volumetric energy densities, being 1,727 Wh/L for Li-Se (compared to 770 Wh/L for commercial Li-ion cells) and 980 Wh/L for sodium (Na) - Se that has a comparable total composite volume. With both Li and Na, over 60 percent of the capacity is maintained as the current density is increased across a wide range of charging rates, which makes it a good candidate for high-power battery systems and for automotive rapid charging applications.
The Department of Energy, Office of Science, Basic Energy Sciences, Materials Sciences and Engineering Division funded this research.
J. Ding, H. Zhou, H. Zhang, L. Tong, and D. Mitlin, “Selenium impregnated monolithic carbons as free‐standing cathodes for high volumetric energy lithium and sodium metal batteries.” Advanced Energy Materials 8, 1701918 (2018). [DOI: 10.1002/aenm.201701918]
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Advanced Energy Materials 8, 1701918 (2018). [DOI: 10.1002/aenm.201701918]