A Novel High Capacity, Environmental Benign Energy Storage System: Super-iron Boride Battery
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1041-R04-01
A Novel High Capacity, Environmental Benign Energy Storage System: Super-iron Boride Battery Xingwen Yu1, and Stuart Licht2 1 Department of Chemical and Biological Engineering, The University of British Columbia, 2360 East Mall, Vancouver, V6T 1Z3, Canada 2 Department of Chemistry, University of Massachusetts, 100 Morrissey Blvd, Boston, MA, 02125 ABSTRACT High electrochemical capacity of alkaline boride anodes is presented. The alkaline anodes based on transition metal borides can deliver exceptionally high discharge capacity. Over 3800 mAh/g discharge capacity is obtained for the commercial available vanadium diboride (VB2), much higher than the theoretical capacity of commonly used zinc metal (820 mAh/g) alkaline anode. Coupling with the super-iron cathodes, the novel Fe6+/B2- battery chemistry generates a matched electrochemical potential to the pervasive, conventional MnO2-Zn battery, but sustains a much higher electrochemical capacity. INTRODUCTION Alkaline Zn-MnO2 redox charge storage has been established for over a century, and is still playing the dominant share in primary alkaline battery market. However, this battery chemistry is increasingly limited in meeting the growing energy and power demands of contemporary optical, electromechanical, electronic, and medical consumer devices. Therefore, the search for new energy storage chemistry systems with higher capacity and energy density has been increasingly emphasized. A number of new materials, such as metal hydride and intercalation compounds have been successfully applied to the high performance Ni-MH and Li-ion batteries [1,2]. We introduced a new battery type, super-iron battery based on the high Fe(VI) cathodic charge storage in 1999 [3]. Followed the primary alkaline super-iron battery, recently, rechargable thin layer super iron cathode has been reported [4,5], and a high performance composite Fe(VI)/AgO composite cathode stabilized by a 1% zirconia coating has also been successfully developed [6]. In 2004 it was reported that metal borides could be used as anodic alkaline charge storage materials [7,8]. Representative transition metal borides include TiB2 and VB2 which can store several folds more charge than a zinc anode through multi-electron charge transfer: [7] TiB2 + 12OHVB2 + 20OH-
→ Ti(amorphous) + 2BO + 6H O + 6e → VO + 2BO + 10H O + 11e 3-
4
3-
3
3-
3
2
2 -
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(1) (2)
However, one obstacle was evident towards implementation of this alkaline boride (MB2, M = Ti or V) anodic chemistry. The electrochemical potential of the boride anodes was more positive than that of zinc. Therefore the voltage of a boride MnO2 cell was low compared to the voltage of the pervasive Zn–MnO2 battery. In our recent communication, we introduced a novel Fe6+/B2- battery chemistry in which the super-iron (Fe6+) cathode provides the requisite additional electrochemical potential for the boride (B2-) anode. Therefore, the Fe(VI)–MB2
couple generates a similar potential to the Zn–MnO2 battery. In addition, the obstacles of the boride anode decom
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