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Most of today’s cars derive energy from burning petrol or diesel. In 2021 fossil fueled powertrains accounted for 92% of all light-duty vehicle sales at a global level. However, there is a growing number of vehicles which get power directly from a stack of batteries. These batteries are similar to lithium-ion (Li-ion) batteries in mobile phones, but form a pack which is comprised of several individual Li-ion cells working together. During charging, electricity is used to make chemical changes inside its batteries, whereas during motion of the vehicle these changes are reversed to produce electricity. The remaining challenge is to modify these battery packs that they can power vehicles for more than a thousand miles on a single charge.

Now (2023), researchers at the Illinois Institute of Technology (IIT) and Argonne National Laboratory have developed a lithium-air battery which might achieve just that. Moreover, the new battery design could someday be used to power domestic airplanes and long-haul trucks.

The battery’s main and also new component is a solid electrolyte instead of the common liquid one. Batteries with solid electrolytes do not have the usual safety issues witnessed in batteries with liquid electrolytes relating to overheating and catching fire.

Formerly, lithium-air battery designs used to have a lithium metal anode which moved through a liquid electrolyte to combine with oxygen during the discharge. This yielded lithium peroxide (Li₂O₂) or superoxide (LiO₂) at the cathode. Then the lithium peroxide or superoxide was then reduced to its lithium and oxygen components during the charge.

The new solid electrolyte incorporates a ceramic polymer material made from fairly inexpensive elements in nanoparticle form. The solids can initiate chemical reactions that produce lithium oxide (Li₂O) on discharge. The reaction can store more electrons which also causes greater energy density. The new design is the first which has achieved a four-electron reaction at room temperature. Moreover, it works with oxygen supplied by air from the surrounding environment, which makes large oxygen tanks superfluous.

To prove that a four-electron reaction was actually taking place, the team used transmission electron microscopy (TEM) of the discharge products on the cathode surface. This provided valuable insight into the four-electron discharge mechanism. They also found that a shortcoming of former lithium-air designs, short life cycles, could not be detected in their new battery design. This characteristic was detected by means of operating a test cell for 1000 cycles, which demonstrated its stability over repeated charge and discharge.

Scientists have long tried to develop an effective lithium-air battery. In 2014, scientists demonstrated how water-stable, solid electrolyte-protected lithium electrodes can solve many of these issues related to common lithium batteries and form the beginning of aqueous and nonaqueous Li-Air batteries with unprecedented energy densities. The scientists also provided data for fully packaged Li-Air cells that achieve more than 800 Wh/kg. The use of a protected lithium electrode (PLE) was found to be a basic requirement for both nonaqueous and aqueous Li-Air technologies. In all scenarios tested, the using a PLE was responsible for to a self-discharge rate of effectively zero. It also became apparent that for nonaqueous Li-Air the use of a PLE could be necessary to enable a stable performance of electrolytes when used with lithium peroxide and superoxide and to protect the negative electrode from reaction with moisture in the ambient air.

Image: Schematics of Li-Air cells employing PLE. a With nonaqueous electrolyte. b With aqueous electrolyte



Source: Steven J. Visco, Vitaliy Y. Nimon, Alexei Petrov, Kirill Pridatko/ Aqueous and nonaqueous lithium-air batteries enabled by water-stable lithium metal electrodes/ Journal of Solid State Electrochemistry 18(5), May 2014/ DOI:10.1007/s10008-014-2427-x/ Open Source This is an Open Access article is distributed under the terms of the Creative Commons Attribution 4.0 International (CC BY 4.0)

In 2023, in a study a closed lithium–oxygen battery model based on the conversion of lithium superoxide and lithium peroxide (LiO₂ + e− + Li+ ↔ Li₂O₂) was designed. In the experiment, palladium with reduced graphene oxide was used as a catalyst and produced LiO₂ in the pre-discharge process. The closed battery was able to cycle over 57 cycles stably. Apart from in situ Raman spectra chemical analysis, electrochemical quartz crystal microbalance (EQCM) and differential electrochemical mass spectrometry (DEMS) were used to observe the conversion between LiO₂ and Li₂O₂ during the charge–discharge process. The study was aimed at advancing the development of a new closed “lithium–oxygen” battery system for developing large-capacity green energy.

Image: Batteries have two different stages of discharge products: LiO₂ and Li₂O₂. The conversion from LiO₂ to Li₂O₂ does not require O₂. This can realize the reversible cycle of a closed battery with a capacity of 480 mAh g⁻¹



Source: Junkai Wang, Rui Gao, Xiangfeng Liu/ Reversible Conversion between Lithium Superoxide and Lithium Peroxide: A Closed “Lithium–Oxygen” Battery/ Inorganics 11(2):69, February 2023/ DOI:10.3390/inorganics11020069/ Open Source This is an Open Access article is distributed under the terms of the Creative Commons Attribution 4.0 International (CC BY 4.0)

There are many advantages involved in the new solid-electrolyte lithium-air battery design: Batteries with solid electrolytes do not display the typical safety issues with the liquid electrolytes used in lithium-ion and other batteries, which can overheat and catch fire. Also, the new battery chemistry with the solid electrolyte is able to boost the energy density by as much as four times above lithium-ion batteries, thus achieving a longer driving range.
The scientists expect that with appropriate research the new design for the lithium-air battery will also reach a record energy density of 1200 watt-hours per kilogram. This is almost four times better than current lithium-ion batteries and enables more reliable powering of vehicles.

By the Editorial Board