Seminar in Rovira i Virgili University
Date: 4 pm on 25th Sept. 2014
Place: Sala de Graus (Conference Room).
Title: Novel rechargeable batteries using molecular clusters ascathode active materials
Hirofumi Yoshikawa
Department of Chemistry, Nagoya University, Furo-cho, Chikusa, Nagoya
Email: yoshikawah@chem.nagoya-u.ac.jp
Solid-state electrochemistry is a wide research area covering various topics from fundamental
sciences to applications. At present, one of the most important goals is to develop high-performance
rechargeable batteries due to the ever-increasing energy demands and pressing environmental
concerns. We have recently proposed a new type of lithium battery, “the molecular cluster battery(MCB)”, in which the cathode active materials are polynuclear metal complexes (molecular clusters)such as Mn12 clusters ([Mn12O12(RCOO)16(H2O)4], R = CH3, C6H5, etc.) and polyoxometalates (POMs),
in order to achieve both high battery capacity and fast charging/discharging. It is expected that MCBs
would show a high capacity and a rapid charging/discharging due to multi-electron redox reactions ofthe molecular clusters and quick lithium-ion diffusion, respectively (the left of Fig. 1).
In this seminar, I talk about the performance of the MCBs based on “solid-state electrochemistry
3of molecular clusters”. Actually, using a Keggin-type POM, [PMo12O40] (KPOM), which is well known
as catalysts, as a cathode-active material, we achieved a higher battery capacity of ca. 270 Ah/kg,
which was larger than those of the lithium ion batteries (ca. 148Ah/kg), and a more rapid charging.
Operando Mo K-edge X-ray absorption fine structure (XAFS) analyses on the KPOM-MCBs
demonstrated that KPOM underwent twenty four electrons reduction in the discharging process, which
6+4+indicated that all of Mo ions in KPOM changed into Mo . This means the formation of a
27super-reduced state, [PMo12O40] , and the super-reduction electron number of twenty four can explain
the large capacity of the KPOM-MCBs. This electron sponge behaviour indicates that molecularclusters are promising cathode active materials for high-performance rechargeable batteries.
Furthermore, we exhibited nano-hybrid materials between KPOMs and single-walled carbon nanotubes(SWNTs), in which KPOMs are individually adsorbed on the SWNT surfaces for application to thecathode active materials of MCBs (the right of Fig. 1). The charging/discharging measurements for theKPOM-SWNT hybrid MCBs indicated a higher battery capacity and a faster charging/discharging
compared with those of the initial KPOM MCBs.

Fig.1. Schematic View of MCBs (Left) and TEM Images of Nanohybrid Materials (Right).
References
1) H. Yoshikawa et al., Chem. Commun. 2007, 3169-3170. 2) H. Yoshikawa et al., Inorg. Chem. 2009, 48,9057-9059. 3) H. Yoshikawa et al., Chem. Asian J. 2011, 6, 1074-1079. 4) H. Yoshikawa et al., J. Am. Chem. Soc.
2012, 134, 4918-4924. 5) H. Yoshikawa et al., Angew. Chem. Int. Ed. 2011, 50, 3471-3474. 6) H. Yoshikawa et al.,Dalton Trans. 2012, 4, 9863-9866. 7) H. Yoshikawa et al., Chem. Eur. J. 2013, 19, 11235-11240. 8) H. Yoshikawaet al., J. Mater. Chem. A 2014, 2, 3801-3807. 9) H. Yoshikawa et al., Chem. Lett, in press. 10) H. Yoshikawa, S. Irleet al., J. Am. Chem. Soc. in press.