Aluminum-ion batteries could be a breakthrough in battery technology, especially considering the scarcity and complicated recycling process of lithium batteries. Not only is aluminum one of the most abundant elements on Earth, but it also has an easier and less expensive recycling process, making it a more sustainable option. Despite this, the development of aluminum-ion batteries has been limited due to a lack of suitable electrode materials with enough storage capacity.
A team of researchers led by Prof. Dr. Birgit Esser of the University of Ulm and Prof. Dr. Ingo Krossing as well as Prof. Dr. Anna Fischer of the University of Freiburg has made progress on this issue by developing a positive electrode material from an organic redox polymer built on phenothiazine. During the experiment, the aluminum-ion batteries using this electrode material achieved a previously unattained capacity of 167 milliampere hours per gram (mAh/g). This organic redox polymer provides more capacity than graphite, which has been the most commonly used electrode material in batteries so far. The findings of the experiment are published in the Energy & Environmental Science journal.
Phenothiazine-based polymer for more storage capacity
The positive electrode material gets oxidized upon charging, absorbing complex aluminate anions in return. Therefore, the organic redox polymer called poly(3-vinyl-N-methylphenothiazine) has the ability to insert two [AlCl4]− anions reversibly upon charging. The researchers used the ionic liquid ethylmethylimidazolium chloride with added aluminum chloride as the electrolyte in their experiments.
“The study of aluminum-ion batteries is an exciting field of research with great potential for future energy storage systems,” says Gauthier Studer, a member of the research team. “Our focus is on developing new organic redox-active materials that exhibit high performance and reversible properties. By studying the redox properties of poly(3-vinyl-N-methylphenothiazine) in chloroaluminate-based ionic liquid, we have made a significant breakthrough by demonstrating for the first time a reversible two-electron redox process for a phenothiazine-based electrode material.”
Poly(3-vinyl-N-methylphenothiazine) shows [AlCl4]− anions deposition at 0.81 and 1.65 volts and achieves specific capacities of up to 167 mAh/g. By comparison, graphite used as electrode material for aluminum-ion batteries shows a discharge capacity of 120 mAh/g. The battery presented by the researchers retained 88% of its capacity after 5,000 charge cycles at 10 C, which translates to a charge and discharge rate of six minutes. By implementing a lower C rate, the battery returned to its original capacities without any changes.
“With its high discharge voltage and specific capacity, as well as its excellent capacity retention at fast C rates, the electrode material suggests a major advancement in rechargeable aluminum-ion batteries and thus in advanced and affordable energy storage solutions,” says Birgit Esser.
More information:
Gauthier Studer et al, On a high-capacity aluminium battery with a two-electron phenothiazine redox polymer as positive electrode, Energy & Environmental Science (2023). DOI: 10.1039/D3EE00235G
Citation:
Team develops organic redox polymer for aluminum-ion batteries with improved storage capacity (2023, June 12)
retrieved 13 June 2023
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