The electrode properties of todorokite-type tunnel-structured manganese oxides (TodMO) were examined for their potential use as cathode materials in calcium batteries. TodMO with a chemical composition of Mg0.19Na0.07MnO2·0.37H2O was prepared through hydrothermal treatment of layer-structured manganese oxide using magnesium ions as interlayer guest ions. The TodMO exhibited a dis-charge and charge capacity of 100 and 80 mAh g−1, respectively, at a relatively large current density of 100 mA g−1. The reaction mecha-nism was studied in detail using X-ray absorption spectroscopy measurements. Consequently, it became clear that the newly formed Mn3+-compound converted from TodMO is responsible for the reversible capacity.
todorokite-type manganese oxide, cathodes, Ca batteries, X-ray absorption spectroscopy
 P.G. Bruce, S. A. Freunberger, L. J. Hardwick, J.-M. Tarascon, Nat. Mat., 11, 19 (2012).
 F. Cheng, J. Chen, Chem. Soc. Rev., 41, 2172 (2012).
 J. Muldoon, C. B. Bucur, T. Gregory, Chem. Rev., 114, 11683 (2014).
 D. Aurbach, Z. Lu, A. Schechter, Y. Gofer, H. Gizbar, R. Turgeman, Y. Cohen, M. Moshkovich, E. Levi, Nature, 407, 724 (2000).
 E. Levi, Y. Gofer, D. Aurbach, Chem. Mater., 22, 860 (2010).
 A. Ponrouch, C. Frontera, F. Bardé, M. R. Palacin, Nat. Mater., 15, 169 (2016).
 M.-C. Lin, M. G. Gong, B. Lu, Y. Wu, D.-Y. Wang, M. Guan, M. Angell, C. Chen, J. Yang, B.-J. Hwang, H. Dai, Nature, 520, 324 (2015).
 R. Mohtadi, F. Mizuno, J. Nanotechnol., 5, 1291 (2014).
 I. Kim, K. Yamabuki, M. Morita, H. Tsutsumi, N. Yoshimoto, J. Power Sources, 278, 340 (2015).
E. Levi, A. Mitelman, D. Aurbach, M. Brunelli, Chem. Mater., 19, 5131 (2007).
S. Rasul, S. Suzuki, S. Yamaguchi, M. Miyayama, Solid State Ionics, 225, 542 (2012).
S. Rasul, S. Suzuki, S. Yamaguchi, M. Miyayama, Electro-chem. Acta, 82, 243 (2012).
S. Rasul, S. Suzuki, S. Yamaguchi, M. Miyayama, Electro-chim. Acta, 110, 247 (2013).
N. Kumagai, S. Komaba, H. Sakai, H. Sakai, J. Power Sources, 97–98, 515 (2001).
D. Aurbach, R. Skaletsky, Y. Gofer, J. Electrochem. Soc., 138, 3536 (1991).
M. Hayashi, H. Arai, H. Ohtsuka, Y. Sakurai, J. Power Sources, 119–121, 617 (2003).
Z.-H. Liu, L. Kang, K. Ooi, Y. Makita, Q. Feng, J. Colloid Interface Sci., 285, 239 (2005).
N. M. Brown, J. B. McMonegle, G. N. Greves, J. Chem. Soc. Faraday Trans., 80, 589 (1984).
T. S. Arthur, R. Zhang, C. Ling, P.-A. Glans, X. Fan, J. Guo, F. Mizuno, ACS Appl. Mater. Interfaces, 6, 7004 (2014).