Neutron Diffraction and Electrochemical Study of Fe­Nb₁₁­O₂₉/Li₁₁­Fe­Nb₁₁­O₂₉ for Lithium Battery Anode Applications

Lithium was found to be inserted into FeNb₁₁O₂₉ by reaction with <i>n</i>-butyllithium, producing Li₁₁­Fe­Nb₁₁­O₂₉ samples with good crystallinity, and the <i>Amma</i> crystallographic-shear structures of both compounds (<i>a</i> = 28.7093(6)/28.4036(4), <i>b</i> = 3.8256(1)/4.08447(9), <i>c</i> = 20.6241(4)/20.7067(2) Å, respectively) were Rietveld-refined by high-resolution neutron powder diffraction. Lithium atoms of Li₁₁­Fe­Nb₁₁­O₂₉ were located both in 4-fold- and in 5-fold-coordinated positions, lying respectively inside and between the 4 × 3 perovskite blocks of Nb­(Fe)­O₆ octahedra. Electrochemical measurements on a Fe­Nb₁₁­O₂₉/ Li_<i>x</i>­Fe­Nb₁₁­O₂₉ electrode vs metallic Li showed that lithium can be intercalated/deintercalated reversibly in the 1.1–2.5 V range with a stable capacity of 185 mAh/g, which roughly corresponds to 11 Li atoms per f.u. as obtained by chemical lithiation. The rather uniform structural distribution found for Li atoms is consistent with the good electrode reversibility, which makes this material promising as anode in rechargeable lithium batteries

LiBH₄−Mg(BH₄)₂: A Physical Mixture of Metal Borohydrides as Hydrogen Storage Material

The LiBH4−Mg(BH4)2 system has been investigated as a possible hydrogen storage material. Several composites were synthesized by ball milling, namely, xLiBH4−(1−x)Mg(BH4)2 with x = 0, 0.10, 0.25, 0.33, 0.40, 0.50, 0.60, 0.66, 0.75, 0.80, 0.90, 1. The physical mixture was investigated by using X- ray powder diffraction and thermal analysis. Interestingly, already a small amount of LiBH4 makes the α to β transition of Mg(BH4)2 reversible, which has not been reported before. The eutectic composition was found to exist at 0.50 x x = 0.50 composite releases about 7.0 wt % of hydrogen