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LiNi0.8Co0.16Mg0.04O2 layered oxide samples were synthesized by a chemical route that led to a crystalline phase at a relatively low temperature and allowed the control of the homogeneity and the microstructural properties of the final compounds. The structural properties of the synthesized sample were investigated by performing XRD Rietveld refinement. The role of the doping metal (Mg²⁺) on the electrochemical characteristics of this layered oxide was investigated via its use as cathode material in a lithium cell and observation of its structural evolution upon cycling by in-situ energy dispersive X-ray diffraction (EDXD). The thermal stability of the delithiated LixNi0.8Co0.16Mg0.04O2 cathodes was evaluated using differential scanning calorimetry (DSC). The results demonstrate that the Mg²⁺ doping greatly reduces the unit cell volume change during cycling, because of a very limited variation of the c lattice parameter. This improved structural retention also reflects an improvement of the stability of the doped cathode in its fully charged state.

Iron-substituted lithium titanium spinels with stoichiometry Li4/3-y/3FeyTi5/3-2y/3O4, were synthesized by a sol gel process. The attention was focused on two compositions, namely Li1.3Fe0.1Ti1.6O4 and Li1.25Fe0.25Ti1.5O4. The first spinel crystallizes in the typical Fd&thremacr;m space group while the second adopts the P4332 symmetry. The two spinels were tested as electrodes in lithium cells. It was observed that these electrodes are capable of inserting up to 1.4−1.6 lithium ion equivalents per formula unit and to cycle reversibly 160−180mAh/g at C/5 in the 2.9−0.2 V potential range. The electrochemical responses are quite different from that of pure Li4/3Ti5/3O4, since the lithium insertion (deinsertion) processes evolve through several one-phase and two-phase steps, clearly involving the reduction (oxidation) of both titanium (IV) and iron (III) which occupy different framework positions. The electrochemical discharge mechanism of the two spinel electrodes was investigated by combining electrochemical tests with in situ diffraction measurements carried out using high-energy synchrotron radiation.

In-situ X-ray diffraction studies have been performed on a Li4/3Ti5/3O4 electrode upon cycling in a Li cell, by using a very high energy (87.5 keV) synchrotron beam. The real time structural changes of its crystalline lattice were observed over two complete cycles of the cell. The high-resolution measurements allowed us to precisely monitor the extremely small breathing movement of the structure and to plot the curve of the lattice parameter as a function of the lithiation degree. The investigation revealed an unexpected behavior in the structural evolution upon cycling, which was attributed to the reversible passage from a monophasic to a biphasic domain upon insertion. Furthermore, the structural evolution turned out to be slightly different in the first and in the second cycle. This suggests that irreversible rearrangements, like the ones observed for every other insertion compound, occur also in this case, although on an extremely smaller scale.

Layered compounds, such as LiNiO₂ and LiCoO₂ , have been extensively studied as active cathodic materials in lithium-ion batteries. Mixed oxides having general formula LiNi_yCo_1−yO₂ represent a good compromise between the limited cyclability of LiNiO₂ and the high cost of LiCoO₂. However, recent studies have demonstrated that LiNi_yCo_1−yO₂ compounds are thermally unstable in their charged state, undergoing exothermic reactions that might cause thermal runaway and safety concern. The stability of the compounds may be greatly controlled by doping with a suitable metal, M = Al, Mg. In this work we further investigate the role of the doping metal on the thermal, electrochemical and structural characteristics of the LiNi_yCo_1−y−zM_zO₂ electrode materials. These materials were prepared using a soft chemistry route, to achieve the proper control of the chemical homogeneity and of the microstructural properties of the final samples. The thermal behavior of the doped LiNi_y Co_1−y−zM_z O₂, where M = Al, was studied using differential scanning calorimetry. The structural properties upon cycling were investigated by a recently, in-house developed, in situ energy dispersive X-ray diffraction (EDXD) technique. The reversibility and rate capabilities of the cathodes in lithium cells were characterized using electrochemical equipment.

The in situ observation of the structural changes induced in electrodic active materials upon cycling is commonly performed by angular dispersive X-ray diffraction (ADXD). Here an alternative approach based on the energy dispersive X-ray diffraction (EDXD) is described, together with its application to the study of the well-known LiNi0.8Co0.2O2 cathode material. In the first part, we briefly describe the technique and its application to the in situ study of electrode materials. In the second part, we discuss how the experimental data have to be processed in order to separate the signal produced by the active material only from that of the other parts of the cell. In the third part, a dense sampling of the changing structure of LiNi0.8Co0.2O2 during the first three charge−discharge cycles is shown in terms of the lattice parameters time evolution. The results confirm what was already reported in the literature on the behavior of similar materials, providing, at the same time, detailed information on the evolving structure. In fact, although the resolution of EDXD is lower than that of ADXD, the measurements have a good accuracy, which guarantees a small statistical scattering of the lattice parameters experimental points. This, together with the high sampling density, gives the points the aspect of almost continuous curves, whose features can be of interest in the study of electrodic materials.

The investigation of structural changes of intercalation materials during cycling is of primary importance to understand the factors that limit their cyclability. In particular in-situ measurements, allowing the simultaneous acquisition of structural and electrochemical data, consent to directly correlate the cycling performance of the material under test to its structure evolution and vice versa.The energy dispersive X-ray diffraction (EDXD) technique has been applied to the study of the structural evolution of LiNi0.8Co0.2O2 during several charge−discharge cycles performed with increasing anodic limits. This way of monitoring the effect of Li ions intercalation−deintercalation process on the host materials lattice parameters proved to be a valid alternative to the traditional angle dispersive X-ray diffraction (ADXD) method, solving some of its problems, first of all the question of the X-ray absorption.The results described in this paper confirm what reported in previous literature works based on in-situ ADXD and deepen the study of the LiNi0.8Co0.2O2 structural changes, with large oversampling and good statistical accuracy, extending the investigation to the first 7 cycles with increased anodic limits approaching full delithiation.

The physical and chemical properties of a new class of lithium conducting polymer electrolytes formed by dispersing ceramic powders at the nanoscale particle size into a poly(ethylenoxide) (PEO)− lithium salt, LiX complexes, are reported and discussed. These true solid-state PEO−LiX nanocomposite polymer electrolytes have in the 30−80 °C range an excellent mechanical stability (due to the network of the ceramic fillers into the polymer bulk) and high ionic conductivity (promoted by the high surface area of the dispersed fillers). These important and unique properties are accompanied by a wide electrochemical stability and by a good compatibility with the lithium electrode (assured by the absence of any liquids and by the interfacial stabilizing action of the dispersed filler), all this making these nanocomposite electrolytes of definite interest for the development of advanced rechargeable lithium batteries.

An in-situ energy dispersive X-ray diffraction (EDXD) analysis has been run on the Li[Li_1/3Ti_5/3]O₄ compound upon Li intercalation–deintercalation process. The results confirm that this process is accompanied by a very small variation of the host lattice parameter, i.e., confined between 1 over the entire cycle. This value, which agrees with previous literature information, concurs to demonstrate that Li[Li_1/3Ti_5/3]O₄ may indeed be considered as a zero-strain intercalation compound, this being a characteristic of key technological importance since lattice strains upon cycling are among the main causes of capacity decays in lithium battery electrodes. In addition, this work confirms that EDXD is a quite convenient technique for electrochemical measurements since, allowing in-situ lattice parameter determinations, may lead to a complete evaluation of the intermediate stages of the intercalation process and, possibly, to detect differences among the various cycles.

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For Abstract see ChemInform Abstract in Full Text.