Altered microstructure improves organic-based, solid state lithium EV battery

Altered microstructure improves organic-based, solid state lithium EV battery

The solvent-assisted microstructure increased electrode energy density to 300 Wh/kg compared to the dry-mixed microstructure at just under 180 Wh/kg by substantially improving the utilization rate of active material.

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 are 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.

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.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 negative electrode, and a cathode, also known as 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 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.

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 low mass fraction of active materials due to non-ideal cathode microstructure. This capped total energy density.

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 amount of active materials could be increased but the utilization percentage was still low, near 50%. With Zhang’s contribution, that utilization rate improved to 98% and resulted in higher energy density. 

Jibo Zhang et al, Microstructure engineering of solid-state composite cathode via solvent-assisted processing, Joule (2021). DOI: 10.1016/j.joule.2021.05.017

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