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We describe the synthesis, crystal structure and lithium deinsertion-insertion electrochemistry of two new lithium-rich layered oxides, Li3MRuO5 (M = Mn, Fe), related to rock salt based Li2MnO3 and LiCoO2. The Li3MnRuO5 oxide adopts a structure related to Li2MnO3 (C2/m) where Li and (Li0.2Mn0.4Ru0.4) layers alternate along the c-axis, while the Li3FeRuO5 oxide adopts a near-perfect LiCoO2 (R3[combining macron]m) structure where Li and (Li0.2Fe0.4Ru0.4) layers are stacked alternately. Magnetic measurements indicate for Li3MnRuO5 the presence of Mn(3+) and low spin configuration for Ru(4+) where the itinerant electrons occupy a π*-band. The onset of a net maximum in the χ vs. T plot at 9.5 K and the negative value of the Weiss constant (θ) of -31.4 K indicate the presence of antiferromagnetic superexchange interactions according to different pathways. Lithium electrochemistry shows a similar behaviour for both oxides and related to the typical behaviour of Li-rich layered oxides where participation of oxide ions in the electrochemical processes is usually found. A long first charge process with capacities of 240 mA h g(-1) (2.3 Li per f.u.) and 144 mA h g(-1) (1.38 Li per f.u.) is observed for Li3MnRuO5 and Li3FeRuO5, respectively. An initial sloping region (OCV to ca. 4.1 V) is followed by a long plateau (ca. 4.3 V). Further discharge-charge cycling points to partial reversibility (ca. 160 mA h g(-1) and 45 mA h g(-1) for Mn and Fe, respectively). Nevertheless, just after a few cycles, cell failure is observed. X-ray photoelectron spectroscopy (XPS) characterisation of both pristine and electrochemically oxidized Li3MRuO5 reveals that in the Li3MnRuO5 oxide, Mn(3+) and Ru(4+) are partially oxidized to Mn(4+) and Ru(5+) in the sloping region at low voltage, while in the long plateau, O(2-) is also oxidized. Oxygen release likely occurs which may be the cause for failure of cells upon cycling. Interestingly, some other Li-rich layered oxides have been reported to cycle acceptably even with the participation of the O(2-) ligand in the reversible redox processes. In the Li3FeRuO5 oxide, the oxidation process appears to affect only Ru (4+ to 5+ in the sloping region) and O(2-) (plateau) while Fe seems to retain its 3+ state.

The structural features of intercalated Li3AlxTi2-x(PO4)3 compounds, with x = 0 and 0.2, have been deduced by Rietveld analysis of neutron diffraction (ND) patterns recorded between 100 and 500 K. The Li insertion decreases the symmetry from R3̄c to R3̄ in analyzed compounds. In pristine Li1+xAlxTi2-x(PO4)3 samples, Li occupies mainly six-fold M1 sites at ternary axes; but in lithiated Li3AlxTi2-x(PO4)3 samples, Li is located near M2 positions at M3/M3' four-fold coordinated sites. In both cases, Li arrangement minimizes electrostatic Li-Li repulsions. The insertion of lithium resulted in the reduction of Ti(4+) to Ti(3+) that shifts (7)Li, (27)Al and (31)P MAS-NMR resonances towards more positive chemical shifts, improving the resolution of different sites. The detection of twelve components in (7)Li MAS-NMR spectra recorded at room temperature suggests the location of Li(+) ions at three-oxygen faces that define M2 cavities. From (7)Li MAS-NMR spectra, the occupancy of sites and mobility of lithium were investigated in the temperature range 100-500 K. The correlation between structural information, deduced by neutron diffraction, and lithium mobility, deduced by NMR spectroscopy, provides new insights into structural factors that affect lithium mobility in materials with NASICON structure.

Structural features responsible for lithium conductivity in Li(1+x)Ti(2-x)Al(x)(PO4)3 (x = 0, 0.2, and 0.4) samples have been investigated by Rietveld analysis of high-resolution neutron diffraction (ND) patterns. From structural analysis, variation of the Li site occupancies and atomic thermal factors have been deduced as a function of aluminum doping in the temperature range 100-500 K. Fourier map differences deduced from ND patterns revealed that Li ions occupy M1 sites and, to a lower extent, M3 sites, disposed around ternary axes. The occupation of M1 sites by Li ions is responsible for the preferential expansion of the rhombohedral R3c unit cell along the c axis with temperature. The occupation of less symmetric M3 sites decreases electrostatic repulsions among Li cations, favoring ion conductivity in Li(1+x)Ti(2-x)Al(x)(PO4)3 compounds. The variations detected on long-range lithium motions have been related to variations of the oxygen thermal factors with temperature. The information deduced by ND explains two lithium motion regimes deduced previously by (7)Li NMR and impedance spectroscopy.

Two materials in the Li-Fe-F system, monoclinic (α)- and orthorhombic (β)-Li3FeF6, have been investigated as hosts for lithium insertion reactions. Both of them are related to the cryolite-type structure. Although the as-prepared materials do no insert lithium reversibly, decreasing the particle size by mechanical milling in the presence of carbon activates them. In α-Li3FeF6, the synthesis procedure yields particles with a smaller size and, hence, processing time can be decreased. After milling α-Li3FeF6 for 5 h, a fully reversible behavior involving ca. 0.45 Li/formula is observed at ca. 3.0 V, whereas for β-Li3FeF6 the same processing time produces a material that exhibits a capacity corresponding to 0. 12 Li/formula. Capacity increases notably after 12 h of milling, reaching 100 mAh g-1 (0.7 Li/formula) in the α-polymorph. For the β-polymorph, capacity also increases, getting closer to the one obtained for the α-polymorph in as much as particle sizes are becoming more similar after prolonged milling. The characteristics of the insertion reaction make these two cryolites interesting as cathode materials for batteries. Because the a-polymorph can be prepared at room temperature from an aqueous solution, this polymorph seems to be more adequate to develop a cathode material. [ABSTRACT FROM AUTHOR]

Abstract: Structural evolution during topotactical electrochemical lithium insertion and deinsertion reactions in ramsdellite-like Li x Ti2O4 has been followed by means of in situ X-ray diffraction techniques. The starting Li x Ti2O4 (x =1) exists as a single phase with variable composition which extends in the range 0.50≤ x ≤1.33. However, beyond the lower and upper compositional limits, two other single phases, with ramsdellite-like structure, are detected. The composition of these single phases are: TiO2 upon lithium deinsertion and Li2Ti2O4 upon lithium insertion. Both TiO2 and Li2Ti2O4 are characterized by narrow compositional ranges. The close structural relationship between pristine LiTi2O4 and the inserted and deinserted compounds together with the relative small volume change over the whole insertion–deinsertion range (not more than 1.1% upon reduction) is a guaranty for the high capacity retention after long cycling in lithium batteries. The small changes in cell parameters well reflect the remarkable flexibility of the ramsdellite framework against lithiation and delithiation reactions. [Copyright &y& Elsevier]

Abstract: The layered nitrides LiWN2 and Li0.84W1.16N2 are investigated related to their electrochemical performances as possible electrodes for rechargeable lithium batteries. In the case of LiWN2, for which Li and W atoms are ideally ordered in alternating Li and W layers, de-intercalation of lithium proceeds up to 50%. The de-intercalated lithium can be intercalated again subsequently. The reversible reaction is the origin of the high cyclability observed in the corresponding lithium cells. On the other hand, in Li0.84W1.16N2 the Li layers are statistically occupied by tungsten (16%) and lithium (84%). A clear effect of the disordered cationic occupation on the electrochemical behaviour has been found, since for Li0.84W1.16N2 a very low extraction rate is obtained during the first oxidation (0.03 Li per formula unit). In addition, cyclability is rather poor. The very different electrochemical behaviour is explained by the structural differences between both layered nitrides. [Copyright &y& Elsevier]

Abstract: New olivines LiMAsO4 (M=Mn, Fe, Co, and Ni) have been tested as positive electrode in lithium cells. Under the used experimental conditions we did not succeed to remove lithium ions from LiFeAsO4, LiMnAsO4 or LiNiAsO4. More work is needed in order to verify whether the lack of electrochemical activity is intrinsic to these materials, or it is due to kinetical limitations such as particle size and poor conductivity. On the contrary lithium ions could be reversibly deinserted/inserted from/into LiCoAsO4 at average voltages of 4.8 and 4.6V respectively; the delithiated compound maintaining the olivine structural framework. The high pressure polymorph of LiMAsO4 (M=Fe, Co, Ni) crystallizing with the spinel structure did not show any electrochemical activity potentially useful in rechargeable lithium batteries. [Copyright &y& Elsevier]

Abstract: Electron energy loss spectroscopy has been used to investigate the average oxidation state of Cr in both electrochemically and chemically delithiathed Li5/3−x Ti7/3CrO7. The O K edge, Ti L2,3 and Cr L2,3 edge were monitored. Upon removal of Li ions, the oxygen K edge shows a continuous change while the Cr L edges remain almost unchanged. The Cr 2p multiplet was compared with reference samples (Cr2O3, CrO2 and K2Cr2O7) in order to assess on the sensitivity of the Cr L-edge to the oxidation state of chromium ion. The similarity between the Cr L spectra of Cr2O3 and CrO2 makes the valence analysis difficult in Li5/3−x Ti7/3CrO7 but the presence of CrVI is excluded in oxidized samples. However, evolution of the low energy loss spectra observed in the 10–15eV region confirms the modification of the electronic structure and partial oxidation of CrIII to CrIV. [Copyright &y& Elsevier]