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United States Of America- As a standard, metals serve as negative electrodes in batteries but recently, redox-active organic molecules have replaced metal materials. The redox-active organic molecules, including quinone and amine-based molecules, have been utilized as negative electrodes in rechargeable metals, specifically in air batteries with oxygen-reducing positive electrodes.
In an air battery, protons and hydroxide ions participate in the redox reactions. These batteries therefore perform incredibly highly, nearing the maximum capacity that is theoretically possible.
Using metals in air batteries result in the formation of dendrites, which weaken the battery’s capability and performance, constituting a negative environmental impact. However, the rechargeable air batteries still use liquid electrolytes, like metal-based batteries, meaning the risk for high electrical resistance, leaching effects, and flammability remains high.
In a study published in Angewandte Chemie International Edition, Japanese researchers and scientists have created an all-solid-state rechargeable air battery. The capacity and durability of the air battery was investigated.
The group of researchers selected chemical 2,5-dihydroxy-1, 4-benzoquinone (DHBQ) and its polymer poly(2,5-dydroxy-1, 4-benzoquinone-3, 6-methylene) (PDBM) as the active materials for the negative electrodes. The chemical and polymer have stable and reversible redox reactions in acidic conditions. Additionally, the researchers used Nafion, a proton-conductive polymer, as the solid electrolyte in substitution of conventional liquid electrolytes.
“To the best of my knowledge, no air batteries based on organic electrodes and solid polymer electrolyte have been developed yet,” said Miyatake.
Researchers experimented with the rechargeable air battery’s charge, discharge performance, rate characteristics, and cyclability. Unlike air batteries that use a metallic negative electrode and an organic liquid electrolyte, the SSAB did not deteriorate in the presence of water and oxygen.
Replacing the redox-active molecule DHBQ with PDBM established a better negative electrode. The per gram-discharge capacity of the SSAB-DHBQ was 29.7 mAh, while the value of the SSAB-PDB< was 176.1 mAh with a constant current density of 1 mAcm ⁻².
The coulombic efficiency of SSAB-PDBM was 84% at 4 C rate which eventually decreased to 66% at 101 °C. Although the discharge capacity of SSAB-PDBM was reduced to 44% after 30 cycles, researchers increased it to 78% by increasing the proton-conductive polymer content of the negative electrode. Electron microscopic images confirmed that the addition of Nafion bettered the performance and durability of the PDBM-based electrode.
The study has succeed in the construction and operation of a SSAB comprising redox-active organic molecules as a negative electrode, a proton-conductive polymer as the solid electrolyte, and an oxygen-reducing, diffusion type positive electrode. “This technology can extend the battery life of small electronic gadgets such as smartphones and eventually contribute to realizing a carbon-free society” says Miyatake.
Researchers are hoping that further advancements can be made. Known research and development has been underway similarly from BYLT and Microsoft.