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Different ceramic synthesis conditions of ramsdellite LiTiO have been investigated in order to determine the influence on the electrochemical performances as the negative electrode of lithium-ion batteries. Lithium source, thermal pretreatment, synthesis temperature, and time of reactions were the analyzed conditions. A convenient and cheap reagent like LiCO treated with TiO at high temperature (1250 °C) for very short time (2 h) provides a reliable active material. When tested versus lithium, the initial specific capacity (150 mAh g) is lower than that of ceramic samples prepared at lower temperature or for longer treatment times (ca. 170 mAh g). The lower initial capacity is attributed to the large particle size obtained at high temperature. However, advantageously the capacity retention of the former is superior. Thus, 115 mAh g at C/20 rate is fairly kept (77 % retention) after 100 cycles. The better cyclability of samples prepared at high temperature (with large particle size) is likely due to lower surface reactivity that compensates the lower initial discharge capacity when cycling. A compromise between high initial capacity and capacity retention must be reached when using LiTiO as a battery electrode. The good behavior of the optimized material is shown by testing it against commercial LiCoO as the positive electrode. The high capacity (ca. 135 mAh g) and outstanding cyclability observed prove that optimized ramsdellite may be effectively used as a long-life negative electrode material. [ABSTRACT FROM AUTHOR]

Aliovalent substitution of Nb5+ by Ti4+ in Sr2LuNbO6 is limited to 10% of Nb atoms. A full structural determination by NPD confirms this and reveals that the structure is better described as a superstructure of the simple cubic perovskite (as previously reported) with the monoclinic cell 21/2ap × 21/2ap × ²ap and ß ≈ 90° (S.G. P21/n). The substituted materials present both oxygen-vacancies induced by charge compensation and Sr-deficiency. Therefore, their formula should be given as Sr2-yLuNb1-xTixO6-δ. Electrical properties can be fully understood considering these compositional defects. The parent compound Sr2LuNbO6 presents low electrical conductivity in air, which improves by more than one order of magnitude upon Ti substitution. In any case, the title oxides show low electrical conductivity in a wide oxygen partial pressure (pO2) range (10-25 atm = pO2 = 10-1 atm). At high pO2 the conductivity increases with pO2 due to oxygen-vacancy annihilation and hole creation, according to a general p-type semiconducting mechanism; A-site substoichiometry and Tisubstitution are the origin of this behaviour. In the low pO2 region, the conductivity increases as the oxygen partial pressure decreases. Reduction of cations, Nb5+ or Ti4+, supports n-type conduction by electrons and oxygen vacancy creation. For the intermediate pO2 range a low ionic conduction contribution is observed. Although the estimated ionic conductivity is not high in the substituted compounds, the strategy seems to be valid since a significant enhancement of ionic conduction is observed upon aliovalent substitution. [ABSTRACT FROM AUTHOR]