In this work, polyoxometalates (POMs) are introduced as a new material class for Na-ion battery (NIB) anodes using the example of Na6[V10O28], which combines promising capacities with high cycling performance due to the elimination of detrimental structural processes during repeated Na+-insertion into the electrode material.
NIBs carry the potential to become an alternative to the widespread lithium-ion battery (LIB) technology due to cost advantages based on resource abundance and the option to replace the copper current collector by aluminium, but also due to kinetic advantages. However, cycling performance still remains a challenge on the route to commercial applications of NIBs. Consequently, new materials that combine high cycling performance with high capacity need to be identified and thoroughly understood to bring this technology closer to promising commercial applications. One route to decrease capacity fading is to eliminate processes that cause a decrease in capacity over the course of cycling, such as structural deterioration as a consequence of repeated Na+-insertion into a given crystal structure.
Polyoxometalates are anionic metal-oxo clusters of early transition metals in high oxidation states. They consist of isolated, discrete polyanions, such as [V10O28]6- for the material presented in this work, rather than extended crystal lattices. Thus, instead of incorporating Na+ into a crystal lattice, Na-ions can insert into the cavities between the polyanionic clusters, which reduces structural stress for the electrode material and therefore increases cycling performance.
The obtained results show that capacities above 250 mA h g-1 can be obtained with Na6[V10O28] as NIB anode while cycling performance is very promising. During cycling, Na-ions are reasoned to be inserted into and extracted from intercluster cavities between the [V10O28]6- polyanions. A successful proof of concept in a full cell set-up verified the suitability of the polyoxometalate Na6[V10O28] as NIB anode, paving the way for further exploration of this material class in NIBs.
Steffen Hartung1,2, icolas Bucher1,2, Han-Yi Chen1,2, Rami Al-Oweini4,7, Sivaramapanicker Sreejith6, Parijat Borah6, Zhao Yanli6, Ulrich Kortz4, Ulrich Stimming1, Harry E. Hoster1,2,5, Madhavi Srinivasan1,3,5Show Affiliations
- TUM CREATE, 1 CREATE Way, #10-02 CREATE Tower, Singapore 138602, Singapore
- Technische Universität München, 85748 Garching, Germany
- School of Materials Science and Engineering, Nanyang Technological University, Singapore 639798, Singapore
- School of Engineering and Science, Jacobs University, P.O. Box 750561, 28725 Bremen, Germany
- Energy Research Institute @ NTU ([email protected]), Research Techno Plaza, 50 Nanyang Drive, Singapore 637553, Singapore
- Division of Chemistry and Biological Chemistry, School of Physical and Mathematical Sciences, Nanyang Technological University, 21 Nanyang Link, Singapore 637371, Singapore
- Department of Chemistry, Faculty of Science, Beirut Arab University, P.O. Box 11 50 20, Riad El Solh 1107 2809, Beirut, Lebanon
Affordable energy storage is crucial for a variety of technologies. One option is sodium-ion batteries (NIBs) for which, however, suitable anode materials are still a problem. We report on the application of a promising new class of materials, polyoxometalates (POMs), as an anode in NIBs. Specifically, Na6[V10O28]·16H2O is being synthesized and characterized. Galvanostatic tests reveal a reversible capacity of approximately 276 mA h g−1 with an average discharge potential of 0.4 V vs. Na/Na+, as well as a high cycling stability. The underlying mechanism is rationalized to be an insertion of Na+ in between the [V10O28]6− anions rather than an intercalation into a crystal structure; the accompanying reduction of V+V to V+IV is confirmed by X-ray Photoelectron Spectroscopy. Finally, a working full-cell set-up is presented with the polyoxometalates as the anode, substantiating the claim that Na6[V10O28]·16H2O is a promising option for future high-performing sodium-ion batteries.
Go To Journal of Power Sources