image: As the battery is gradually fully charged, the color of the electrochromic electrode is gradually darkened and tends to become opaque, while discharging process is the opposite. The essence of electrochromism is valance change in the electrode material, which is related to electricity change. view more
Recently, SCIENCE CHINA Materials published online a research paper on functionalization of flexible electrochromic batteries, which cooperatively led by the School of Physics, East China University of Science and the School of Physics and Electronic Science, East China Normal University. NiCo bimetallic hydroxide (NiCo BH) benefiting from its rich accessible active sites and excellent redox reversibility, was widely used as cathode material for Ni//Zn battery. Significantly, as an electrochromic material, the transparency of the NiCo BH reversibly varies with ion valence during the electrochemical process. Therefore, this study designs a Ni//Zn battery cathode by combining NiCo BH with the transparency flexible ITO electrode to endow a new feature of electricity visual alerting function for flexible battery.
Design of Flexible Electrochromic Electrode
NiCo BH active materials usually require an alkaline electrolyte to achieve a reversibly electrochemical cycles, while the flexible ITO electrode is not stable and easily falls off the flexible substrate in strong alkaline solvent. In order to overcome this technological bottleneck, an ultrathin non-continuous nanometer-thick Ni buffer layer was employed to protect the ITO films from falling off the PET substrate in an alkaline solution during electrodeposition process, which enables the operation of flexible electrochromic electrode in alkaline solutions. Ni is relative stable in alkaline environments. This strategy electrodepositing an ultrathin non-continuous Ni buffer layer on ITO surface to protect the ITO from falling off the substrate, maintains the transparency of the ITO, and optimizes the interfacial contact between the flexible ITO and NiCo BH.
The essence of electrochromism is valance change in material. NiCo BH is a faraday-redox type battery material, and its electrochemical detailed reactions can be described by a redox pair of Ni(II)/Ni(III). During the charging process, the electrode material is oxidized and the Ni ion valence state increases (residual electricity of battery increasing). At the same time, the color of the material gradually deepens and changes to an opaque state. While during the discharging process, the Ni ion valence decreases (the residual electricity of battery releasing) and the electrodes return to a faded transparent state. Therefore, the electrochromic characteristics of nickel-ion redox can be correlated with the residual electricity of battery.
PhD student Xiaoyang Xuan (East China University of Science and Technology) is the first author. Professor Likun Pan (East China Normal University), Professor Shangqing Gong (East China University of Science and Technology), and Associate Professor Min Qian (East China University of Science and Technology) are the co-corresponding authors of the paper.
A NiCo Bimetallic Hydroxide Electrode Based Flexible Ni//Zn Battery with Smart Electrochromic Function for Visually Monitoring Battery Residual Electricity
https://doi.org/10.1007/s40843-022-2174-y
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Bei Yan Science China Press yanbei@scichina.org
Copyright © 2022 by the American Association for the Advancement of Science (AAAS)
Copyright © 2022 by the American Association for the Advancement of Science (AAAS)