A prelithiated carbon anode has been produced incorporating stabilised lithium metal powder. Electrodes have been fabricated which are partially lithiated, to compensate for the irreversible capacity of the anode material and combined with conventional Li-ion cathode materials. Fully lithiated anodes have also been fabricated and combined with non-lithiated cathode materials to produce a Li-ion cell.

A Synchrotron x-ray source was used for In Situ x-ray diffraction studies during charge on a new LiMg0.125Ti0.125Ni0.75O2 cathode material synthesized by FMC Corp. It had been demonstrated by Gao(1) that this new material has superior thermal stability than LiNiO2 and LiCo0.2Ni0.8O2 at over-charged state. In this current paper, studies on the relationship between the structural changes and thermal stability at over-charged state for these materials are presented. For the fist time, The thermal stability of these materials are related to their structural changes during charge, especially to the formation and lattice constant change of a hexagonal phase (H3). The spectral evidence support our hypothesis that the improvement of thermal stability is obtained by suppressing the formation of H3 phase and reducing the shrinkage of its lattice constant "c" when charged above 4.3 V.

Using synchrotron-based in situ X-ray diffraction, the structural changes of LiCoO2, LiCo0.5Ni0.5O2, and LiNi0.65Co0.25Mg0.05Ti0.05O2 cathode materials during charge in the voltage range of 3.5 to 5.2V have been studied. When a LiCoO2 cathode was charged above 4.5V, a new intermediate phase O1a was observed, before the terminal phase O1 was formed around 4.8V. In the X-ray diffraction spectra for LiCo0.5Ni0.5O2 and LiNi0.65Co0.25Mg0.05Ti0.05O2 cathode materials, Bragg peaks representing the O1 structure were also observed. The amounts of O1 structure formed at the end of charge (5.2V for LiNi0.65Co0.25Mg0.05Ti0.05O2 and 5.0V for LiCo0.5Ni0.5O2) were increased with increasing Co content.

A synchrotron x-ray source was used for In Situ x-ray diffraction studies on cathode materials during charge and discharge. Two new cathode materials, LiNi0.75Mg0.125Ti0.125O2 and LiNi0.65Co0.25Mg0.05Ti0.05O2, were studied in comparison with LiNiO2 and LiCo0.2Ni0.8O2. The relationship between the structural changes and thermal stability at over-charged state has been investigated. For the first time, The thermal stability of these materials are related to their structural changes during charge, especially to the formation of a hexagonal phase H3 with collapsed lattice along "c" axis. A hypothesis is proposed that through suppressing the formation of H3 phase when charged above 4.3 V, the thermal stability of the cathode materials can be improved.