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    Altered Microstructure Improves Organic-Based, Solid State Lithium EV Battery

    Only 2% of vehicles are electrified to date, but that is projected to reach 30% in 2030. A key toward improving the commercialization of electric vehicles (EVs) is to heighten their gravimetric energy density—measured in watt-hours per kilogram—using safer, easily recyclable materials that are abundant. Lithium-metal in anodes is considered the “holy grail” for improving energy density in EV batteries compared to incumbent options like graphite at 240 Wh/kg in the race to reach more competitive energy density at 500 Wh/kg.

    Researchers at the University of Houston are taking on this challenge with Rice University colleagues. The team demonstrate a two-fold improvement in energy density for organic-based, solid-state lithium batteries by using a solvent-assisted process to alter the electrode microstructure.

    We are developing low-cost, earth-abundant, cobalt-free organic-based cathode materials for a solid-state battery that will no longer require scarce transition metals found in mines,” said the team. “This research is a step forward in increasing EV battery energy density using this more sustainable alternative.

    Any battery includes an anode, also known as the negative electrode, and a cathode, also known as the positive electrode, that are separated in a battery by a porous membrane. Lithium ions flow through an ionic conductor—an electrolyte, which allows for the charging and discharging of electrons that generates electricity for, say, a vehicle.

    Electrolytes are usually liquid, but that is not necessary—they can also be solid, a relatively new concept. This novelty, combined with a lithium-metal anode, can prevent short-circuiting, improve energy density and enable faster charging.

    Cathodes typically determine the capacity and voltage of a battery and are subsequently the most expensive part of batteries due to the usage of scarce materials like cobalt—set to reach a 65,000-ton deficit in 2030. Cobalt-based cathodes are almost exclusively used in solid-state batteries due to their excellent performance; only recently have organic compound-based lithium batteries (OBEM-Li) emerged as a more abundant, cleaner alternative that is more easily recycled.

    There is major concern surrounding the supply chain of lithium-ion batteries in the United States. In this work, researchers show the possibility of building high energy-density lithium batteries by replacing transition metal-based cathodes with organic materials obtained from either an oil refinery or biorefinery, both of which the U.S. has the largest capacity in the world.

    Cobalt-based cathodes generate 800 Wh/kg of material-level specific energy, or voltage multiplied by capacity, as do OBEM-Li batteries, which was first demonstrated by the team in their earlier publication, but previous OBEM-Li batteries were limited to the low mass fraction of active materials due to non-ideal cathode microstructure. This capped total energy density.

    The team uncovered how to improve electrode-level energy density in OBEM-Li batteries by optimizing the cathode microstructure for improved ion transport within the cathode. To do this the microstructure was altered using a familiar solvent—ethanol. The organic cathode used was pyrene-4,5,9,10-tetraone or PTO.

    Cobalt-based cathodes are often favored because the microstructure is naturally ideal but forming the ideal microstructure in an organic-based solid-state battery is more challenging.

    On an electrode level, the solvent-assisted microstructure increased energy density to 300 Wh/kg compared to the dry-mixed microstructure at just under 180 Wh/kg by improving the utilization rate of active material significantly. Previously, the number of active materials could be increased but the utilization percentage was still low, near 50%.

    Over the last ten years, the cost of EV batteries declined to nearly 10% of their original cost, making them commercially viable. So, a lot can happen in a decade. This research is a pivotable step in the process toward more sustainable EVs and a springboard for the next decade of research. At this rate, perhaps just as literally as euphemistically, the future looks much greener on the other side.

    ELE Times Research Desk
    ELE Times Research Desk
    ELE Times provides extensive global coverage of Electronics, Technology and the Market. In addition to providing in-depth articles, ELE Times attracts the industry’s largest, qualified and highly engaged audiences, who appreciate our timely, relevant content and popular formats. ELE Times helps you build experience, drive traffic, communicate your contributions to the right audience, generate leads and market your products favourably.

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