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Lithium was found to be inserted into FeNb 11 O 29 by reaction with n-butyllithium, producing Li 11 Fe-Nb 11 O 29 samples with good crystallinity, and the Amma crystallographic-shear structures of both compounds (a = 28.7093(6)/28.4036(4), b = 3.8256(1)/4.08447(9), c = 20.6241(4)/20.7067(2) Å, respectively) were Rietveld-refined by high-resolution neutron powder diffraction. Lithium atoms of Li 11 FeNb 11 O 29 were located both in 4-fold-and in 5-foldcoordinated positions, lying respectively inside and between the 4 × 3 perovskite blocks of Nb(Fe)O 6 octahedra. Electrochemical measurements on a FeNb 11 O 29 / Li x FeNb 11 -O 29 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.

Conduction properties and intermolecular interactions in systems based on high mole cular weight sulfonic acids (poly(4 styrenesulfonic), poly(2 acrylamidomethylpropane sulfonic), and perfluorosulfonic (MF 4SC)) and polyaniline were studied by impedance and IR spectroscopy. In all systems, an interpolyelectrolyte complex is formed due to strong hydrogen bonding. In two former cases, the interpolyelectrolyte complexes form nanodispersed powders with ionic and electronic conductivity. MF 4SC-polyaniline solu tions were used for the membranes preparation with high ionic conductivity.

The rates of the irreversibile LiBH4 +Mg2FeH6  LiH +2MgH2 + FeB + 5/2H2 and reversible (with significant sorption/desorption hysteresis) LiBH4 + 1/2Mg  LiH + 1/2MgB2 + 3/2H2 reactions were measured by isothermal-isobaric experiments in a Sievert-type apparatus. Measurements were done at several temperature T and overpressure p/p values, deriving the rate constants k(T,p/p) by Avrami's fitting of reaction advancement vs. time. The results could be rationalized on the basis of the k = Aexp(-Ea/RT) = A0exp[-/RT+a(p/p)] kinetic formula, which couples the standard Arrhenius approach for thermal effects with an exponential dependence of the rate constant on overpressure. The empirical a coefficient varies with temperature in a way that requires the activation energy and entropy to depend linearly on p/p. For the first of the above reactions, Ea =-151(p/p) + 118 kJ mol-1 and ln(A/min-1) =-34(p/p) + 16; similar values are obtained for the second one. Relations of this kinetic model with the thermodynamic driving force G and with equations of electrochemical kinetics, where overpressure is replaced by overvoltage, are discussed.

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