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The effect of mechanical grinding on the electrochemical properties of Li2Ti3O7 regarding lithium insertion is studied. X-ray diffraction experiments of milling compounds showed a progressively amorphization of the crystalline material due to both crystalline size decreasing and internal strain increasing. These structural modifications are reflected in the electrochemical behavior of Li2Ti3O7, when it is used as the positive electrode in lithium cells. As a function of milling time a higher specific capacity is obtained during the first discharge of the cell, but when charging an increasing in the irreversible capacity is observed. The most promising Li2Ti3O7 based electrode has been achieved, under our experimental conditions, for 13 hours milling that produces a compound with crystallite size of approximately 20 nm. [ABSTRACT FROM AUTHOR]

Abstract: Li2Ti6O13 has been prepared from Na2Ti6O13 by Li ion exchange in molten LiNO3 at 325°C. Chemical analysis and powder X-ray diffraction study of the reaction product respectively indicate that total Na/Li exchange takes place and the Ti–O framework of the Na2Ti6O13 parent structure is kept under those experimental conditions. Therefore, Li2Ti6O13 has been obtained with the mentioned parent structure. An important change is that particle size is decreased significantly which is favoring lithium insertion. Electrochemical study shows that Li2Ti6O13 inserts ca. 5 Li per formula unit in the voltage range 1.5–1.0V vs. Li+/Li, yielding a specific discharge capacity of 250mAhg−1 under equilibrium conditions. Insertion occurs at an average equilibrium voltage of 1.5V which is observed for oxides and titanates where Ti(IV)/Ti(III) is the active redox couple. However, a capacity loss of ca. 30% is observed due to a phase transformation occurring during the first discharge. After the first redox cycle a high reversible capacity is obtained (ca. 160mAhg−1 at C/12) and retained upon cycling. Taking into consideration these results, we propose Li2Ti6O13 as an interesting material to be further investigated as the anode of lithium ion batteries. [ABSTRACT FROM AUTHOR]

Abstract: Materials of the series La2−x Sr x NiTiO6−δ (0 ≤ x ≤ 0.5) have been characterized by both structural and electrochemical methods in order to assess their possible use as electrodes for SOFCs. Neutron and X-ray powder diffraction experiments have shown that they are stable under both oxidizing and reducing conditions while chemically compatible with YSZ at SOFC operating temperatures. Moreover, the thermal expansion has been determined to be isotropic with α L = 10.0(3) × 10−6 K−1. This value is similar to that found for other perovskite materials used in SOFCs. However, polarization resistances reveal modest values of electrochemical response under oxygen (1.5 Ω cm2 at 900 °C) and are quite poor in 5%H2/N2 mixtures (15 Ω cm2) at the same temperature. Nevertheless, microstructure has not been optimized fully enough to discard the material as a potential SOFC cathode. [Copyright &y& Elsevier]

The effect of mechanical grinding (MG) on the electrochemical properties of Si3N4 is studied as the processing produces different particle size. The evolution of the amorphisation stage has been monitored by X-ray diffraction (XRD), although particle size has also been studied through transmission electron microscopy experiments. Processed Si3N4 has been used as the positive electrode in electrochemical cells, where the negative electrode is lithium. We do not expect an intercalation process during the discharge step of such a type of cell, but a behaviour similar to that named as “convertible compounds”. As the main result, the specific capacity of these lithium cells is increased up to 34% in relation to the starting, non-milled material. However, even though the size of the Si3N4 particles has been reduced, from micrometer to nanometer scale, no appreciable changes in the cycling behaviour is observed when compared with the pristine material. [Copyright &y& Elsevier]