Electrochemical Studies of Vanadium-Based Polyoxometalate Molecular-Cluster Batteries

Monday, 27 July 2015
Hall 2 (Scottish Exhibition and Conference Centre)
H. Y. Chen, J. Friedl (TUM CREATE, Technische Universität München), R. Al-Oweini (Jacobs University), C. J. Pan, B. J. Hwang (National Taiwan University of Science and Technology), U. Kortz (Jacobs University), M. Srinivasan (Nanyang Technological University, TUM CREATE), and U. Stimming (Technische Universität München, Newcastle University)
The lithium ion battery (LIB) is a promising energy storage technology for electric vehicles [1]. The most commonly used cathode material in LIBs is LiCoO2. Lithium ion intercalation/de-intercalation into the layer-structured LixCoO2 can result in fast capacity fading. Besides, the kinetic rate of lithium ion intercalation/de-intercalation in the lattice structure is slow which causes low power density.[2] Polyoxometalates (POMs) are transition metal oxide molecular clusters with various structures and have been reported as promising cathode active material for energy storage applications. Due to their multiple redox centers they can undergo fast and reversible redox reactions.[3-5] POMs are expected to undergo redox process as a molecular cluster, thus the stability of the POMs is not depended on the recoverability of its long-term crystal structure. The most commonly used POMs in Li ion Molecular-Cluster Batteries (MCBs) are Mo-based POMs which can achieve a capacity of 270 mAh g-1. However, the cycling stability of Mo-based POMs is poor because of the instability of molecular cluster ions [PMo12O40]3- in the reduced state and high solubility in the electrolytes. Vanadium based POMs have been reported to possess a high capacity of up to 200 mAh g-1, and higher cycling stability than Mo-based POMs. However, the valence and fine structural changes of V-based POMs MBCs during charging/discharging have not yet been investigated. Thus, we performed in-situ V K-edge XAFS measurements for V-based POM molecular cluster batteries, and determined the oxidation states and inner structure changes of V-based POM during charging/discharging. Furthermore, the kinetic studies of V-based POM MCBs were also performed by chronoamperometry experiments in this research.

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