FEATURES OF PHASE TRANSFORMATIONS IN THE SYNTHESIS OF COMPLEX LITHIUM-CONDUCTING OXIDE MATERIALS

Abstract

Lithium-ion batteries (LIB`s) are widely used in consumer electronics, mobile phones, personal computers, as well as in hybrid and electric vehicles. Liquid electrolytes, which mainly consist of aprotic organic solvents and lithium-conductive salts, are used for the transfer of lithium ions in LIB`s. However, the application of liquid electrolytes in LIB`s leads to a number of problems, the most significant of which are the risk of battery ignition during operation due to the presence of flammable organic solvents and loss of capacity due to the interaction of liquid electrolyte with electrode materials during cycling. An alternative that can ensure the safety and reliability of lithium batteries is the development of completely so­lid state batteries (SSB`s). SSB`s are not only inherently safer due to the absence of flammable organic components, but also have the potential to increase significantly the energy density. Instead of a porous separator based on polypropylene saturated with a liquid electrolyte, the SSB`s use a solid electrolyte that acts as an electrical insulator and an ionic conductor at the same time. The use of a compact solid electrolyte, which acts as a physical barrier that prevents the growth of lithium dendrites, also allows using lithium metal as the anode material.
 It is desirable to use oxide systems as the so­lid electrolytes for SSB`s, as they are resistant to moisture and atmospheric air. Among the lithi­um-conducting oxide materials, which exhibit relatively high lithium conductivity at a room temperature and can be used as a solid electrolyte in the completely solid-state batteries, lithium-air batteries and other electrochemical devices, the most promising materials are ones with NASICON, perovskite and garnet-type structures.
 The phase transformations that occur during the synthesis of complex lithium-conductive oxides, namely Li1.3Al0.3Ti1.7(PO4)3 with the NASICON-type structure, Li0.34La0.56TiO3 with the perovskite-type structure and Li6.5La3Zr1.5Nb0.5O12 with the garnet-type structure by the solid-state reactions method in an air were investigated. The optimal conditions for the synthesis of each of the above-mentioned compounds were determined.