We fabricated an all-solid-state lithium ion battery with magnesium hydride (MgH
2) anode which was catalyzed by doping 5mol% Nb
2O
5 (95MgH
2-5Nb
2O
5) to increase low first-coulombic-efficiency of MgH
2 anode. The catalyzed MgH
2 (99MgH
2-1Nb
2O
5, 95MgH
2-5Nb
2O
5) and solid electrolyte were independently synthesized by mechanical ball milling. In order to investigate the hydrogen desorption temperature of pristine MgH
2, 99MgH
2-1Nb
2O
5 and 95MgH
2-5Nb
2O
5, thermal desorption mass spectroscopy was carried out. In addition, the charge and discharge measurement for 95MgH
2-5Nb
2O
5 was carried out at 100 ℃ and at current density of 0.05 mA cm
-2 and 0.15 mA cm
-2. As a result, the following results were revealed. (1) The hydrogen desorption temperature decreases with increasing Nb
2O
5 contents and columbic efficiency increases with increasing Nb
2O
5 contents. Therefore, the columbic efficiency increases with decreasing hydrogen desorption temperature. (2) Rate properties of MgH
2 are also improved with increasing Nb
2O
5 contents. (3) Effect of Nb
2O
5 additives on anode properties of MgH
2 is clearer upon the Li extraction reaction than that upon the Li insertion reaction due to thermodynamically and electrochemically reasons. (4) Upon the Li insertion reaction, effect of Nb
2O
5 additives become clearer at current density of 0.15 mA cm
-2 than that of 0.05 mA cm
-2. Thus, the anode properties of MgH
2 are improved by adding Nb
2O
5.
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