Progress toward a new generation of rechargeable batteries
Redox mediator improves performance and lifespan of Li-O2 batteries
Wiley
Lithium–air batteries have the potential to outstrip conventional lithium-ion batteries by storing significantly more energy at the same weight. However, their high-performance values have thus far remained theoretical, and their lifespan remains too short. A Chinese team has now proposed addition of a soluble catalyst to the electrolyte. It acts as a redox mediator that facilitates charge transport and counteracts passivation of the electrodes.
In contrast to lithium-ion batteries, in which lithium ions are “pushed” back and forth between two electrodes, lithium-air batteries (Li-O2) use an anode made of metallic lithium. As the battery is used, positively charged lithium ions dissolve and move over to the porous cathode, which has air flowing through it. Oxygen is oxidized and bound into lithium peroxide (Li2O2). Upon charging, the oxygen is released, and the lithium ions are reduced back to metallic lithium, which deposits back onto the anode. Unfortunately, the theoretically high performance of such batteries has not become a reality.
In practice, an effect known as overpotential slows the electrochemical reactions: the formation and decomposition of insoluble Li2O2 are slow and its conductivity is also very low. In addition, the pores of the cathode tend to become clogged, and the high potential required for the formation of oxygen decomposes the electrolyte and promotes undesirable side reactions. This causes the batteries to lose the majority of their performance after only a few charge/discharge cycles.
A team led by Zhong-Shuai Wu from the Dalian Institute of Chemical Physics of CAS, collaborating with Xiangkun Ma from the Dalian Maritime University, has now proposed the addition of a novel imidazole iodide salt (1,3-dimethylimidazolium iodide, DMII) to act as a catalyst and redox mediator to enhance the performance and lifespan.
The iodide ions (I−) in the salt can easily react to form I3− and then back again (redox pair). In this process, they transfer electrons to oxygen (discharge) and take them back up (charge). This facilitated charge transport accelerates the reactions, reduces the overpotential of the cathode, and increases the discharge capacity of the electrochemical cell. The DMI+ ions from the salt contain a ring made from three carbon and two nitrogen atoms. This ring has freely mobile electrons and can “capture” lithium ions during discharge and effectively transfer them to the oxygen at the cathode. In addition, the DMI+ ions form an ultrathin but highly stable interface film on the anode, which prevents direct contact between the electrolyte and the lithium surface, minimizing the decomposition of the electrolyte and preventing side reactions. This stabilizes the anode and increases the lifespan of the battery.
The electrochemical test cells produced by the team were highly promising, demonstrating a very low overpotential (0.52 V), high cycle stability over 960 hours, and highly reversible formation/decomposition of Li2O2 with no side reactions.
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About the Author
Dr Zhong-Shuai Wu is a Chair Professor and group leader of 2D Materials Chemistry & Energy Applications at the Dalian Institute of Chemical Physics, CAS. His research interests revolve around topics of the chemistry of graphene and 2D materials, surface and nanoelectrochemistry, microscale electrochemical energy storage devices, supercapacitors, batteries, and energy catalysis.
Journal
Angewandte Chemie International Edition
Method of Research
Experimental study
Subject of Research
Not applicable
Article Title
A Bifunctional Imidazolyl Iodide Mediator of Electrolyte Boosts Cathode Kinetics and Anode Stability Towards Low Overpotential and Long-Life Li-O2 Batteries
Article Publication Date
30-Jan-2025
New design makes aluminum batteries last longer
American Chemical Society
image:
A porous salt produces a solid-state electrolyte that facilitates the smooth movement of aluminum ions, improving this Al-ion battery’s performance and longevity.
view moreCredit: Adapted from ACS Central Science 2024, DOI: 10.1021/acscentsci.4c01615
Large batteries for long-term storage of solar and wind power are key to integrating abundant and renewable energy sources into the U.S. power grid. However, there is a lack of safe and reliable battery technologies to support the push toward sustainable, clean energy. Now, researchers reporting in ACS Central Science have designed a cost-effective and environment-friendly aluminum-ion (Al-ion) battery that could fit the bill.
Lithium-ion (Li-ion) batteries are in many common consumer electronics, including power tools and electric vehicles. These batteries are ubiquitous because of their high energy density. But lithium is cost prohibitive for the large battery systems needed for utility-scale energy storage, and Li-ion battery flammability poses a considerable safety risk. Potential substitutes for reliable long-term energy storage systems include rechargeable Al-ion batteries. However, their most common electrolyte, liquid aluminum chloride, corrodes the aluminum anode and is highly sensitive to moisture, which exacerbates the corrosion. Both factors contribute to poor stability and a decline in electrical performance over time. So, Wei Wang, Shuqiang Jiao and colleagues wanted to design an improved Al-ion battery without these limitations.
The team added an inert aluminum fluoride salt to an Al-ion-containing electrolyte, turning it into a solid-state electrolyte. The aluminum fluoride salt has a 3D porous structure, allowing aluminum ions to easily hop across the electrolyte and increase conductivity. Additionally, when the researchers constructed their Al-ion battery, they used fluoroethylene carbonate as an interface additive to create a thin solid coating on the electrodes to prevent the formation of aluminum crystals that degrade battery health.
In experiments, the battery’s moisture resistance as well as physical and thermal stability were enhanced, allowing it to withstand repeated jabs from a sharp object and temperatures as high as 392 degrees Fahrenheit. The solid-state Al-ion battery also had an exceptionally long life, lasting 10,000 charge-discharge cycles while losing less than 1% of its original capacity. Moreover, most of the aluminum fluoride could be recovered with a simple wash and then recycled into another battery with slightly diminished performance. The new battery could reduce the production cost of Al-ion batteries and extend their life, thus increasing their practicality.
“This new Al-ion battery design shows the potential for a long-lasting, cost-effective and high-safety energy storage system. The ability to recover and recycle key materials makes the technology more sustainable,” says Wang. The researchers add that further improvements in energy density and life cycle are needed before commercialization.
The authors acknowledge funding from the National Natural Science Foundation of China, the Beijing Nova Program, and the Interdisciplinary Research Project for Young Teachers of the University of Science and Technology Beijing.
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Journal
ACS Central Science
Article Title
“A Recyclable Inert Inorganic Framework Assisted Solid-State Electrolyte for Long-Life Aluminum Ion Batteries”
