New Li Ion Conductors and Solid State Hydrogen Storage Materials: LiM(BH4)3Cl, M = La, Gd

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• 作者：Morten B. Ley ; Sylvain Boulineau ; Rapha毛l Janot ; Yaroslav Filinchuk ; Torben R. Jensen
• 刊名：The Journal of Physical Chemistry C
• 出版年：2012
• 出版时间：October 11, 2012
• 年：2012
• 卷：116
• 期：40
• 页码：21267-21276
• 全文大小：579K
• 年卷期：v.116,no.40(October 11, 2012)
• ISSN：1932-7455

文摘

Multiple reaction mixtures with different composition ratios of MCl₃鈥揕iBH₄ (M = La, Gd) were studied by mechano-chemical synthesis, yielding two new bimetallic borohydride chlorides, LiM(BH₄)₃Cl (M = La, Gd). The Gd-containing phase was obtained only after annealing the ball-milled mixture. Additionally, a solvent extracted sample of Gd(BH₄)₃ was studied to gain insight into the transformation from Gd(BH₄)₃ to LiGd(BH₄)₃Cl. The novel compounds were investigated using in situ synchrotron radiation powder X-ray diffraction, thermal analysis combined with mass spectroscopy, Sieverts measurements, Fourier transform infrared spectroscopy, and electrochemical impedance spectroscopy. The two new compounds, LiLa(BH₄)₃Cl and LiGd(BH₄)₃Cl, have high lithium ion conductivities of 2.3 脳 10p>鈥?p> and 3.5 脳 10p>鈥?p> S路cmp>鈥?p> (T = 20 掳C) and high hydrogen densities of 蟻_m = 5.36 and 4.95 wt % H₂, and both compounds crystallize in the cubic crystal system (space group I-43m) with unit cell parameter a = 11.7955(1) and a = 11.5627(1) 脜, respectively. The structures contain isolated tetranuclear anionic clusters [M₄Cl₄(BH₄)₁₂]p>4鈥?/sup> with distorted cubane M₄Cl₄ cores M = La or Gd. Each lanthanide atom coordinates three chloride ions and three borohydride groups, thus completing the coordination environment to an octahedron. The Lip>+p> ions are disordered on 2/3 of the 12d Wyckoff site, which agrees well with the very high lithium ion conductivities. The conductivity is purely ionic, as electronic conductivities were measured to only 1.4 脳 10p>鈥?p> and 9 脳 10p>鈥?p> S路cmp>鈥?p> at T = 20 掳C for LiLa(BH₄)₃Cl and LiGd(BH₄)₃Cl, respectively. In situ synchrotron radiation powder X-ray diffraction (SR-PXD) reveals that the decomposition products at 300 掳C consist of LaB₆/LaH₂ or GdB₄/GdH₂ and LiCl. The size of the rare-earth metal atom is shown to be crucial for the formation and stability of the borohydride phases in MCl₃鈥揕iBH₄ systems.