Synthesis and Characterisation of Lithium Silicides

Thermal batteries are primary (non-rechargeable) batteries. To activate the battery, a pyrotechnic heat source melts the solid electrolyte to a molten salt at high temperature (typically around 500°C). The battery activation starts by a pyrotechnic source such as Fe/KClO4. Thermal batteries are made from a positive electrode material such as FeS2, a molten salt electrolyte such as LiCl:KCl and a negative electrode material. Li13Si4 is the preferred anode material for thermal batteries. The electrolyte is mixed with a binder material. MgO is a typical binder. The positive electrode material attracted attention with the aim of having a high capacity, a high voltage and good thermal stability. Previous work focused on new cathode materials and investigated battery discharge mechanisms. The negative electrode material is of interest because the high temperature structures and phase transitions have not been studied in the current literature. In this work, lithium-silicon phases were synthesised by a solid-state reaction between lithium metal and silicon powder inside evacuated quartz ampoules. The phases were characterised by powder neutron diffraction, carried out on the Polaris diffractometer at ISIS facility, Rutherford Appleton Laboratory, UK, differential scanning calorimetry (DSC) and magnetic measurements on the superconducting quantum interference device (SQUID). The lithium-silicon phases are remarkably stable at high temperature and remains crystalline, with phase transitions only occurring below room temperature.