AbstractGlasses with compositions of stoichiometric and nonstoichiometric (with an excess of lithium oxide) Li-aegirine (LiFeSi2O6), as well as nonstoichiometric Li-aegirine with the addition of carbon and copper, are synthesized. The processes of the formation of crystalline phases and their evolution during the heat treatment of initial quenched glasses in the temperature range of 600–1100°C are studied by X-ray diffraction analysis. The phase composition of the initial glasses is different: the stoichiometric Li-aegirine glass contains cubic nanocrystals of magnetite, Fe3O4, ~ 21 nm in size, formed during the casting and quenching of the initial glass. An increase in the quenching rate leads to diminishing the magnetite crystal size to ~ 8 nm and to a decrease in their number. Glasses of nonstoichiometric composition are X-ray amorphous. The X-ray diffraction analysis of the crystals formed during the heat treatment of quenched glasses in a gradient furnace showed that, in all glasses at temperatures of 700 to 1040°C, crystals of monoclinic Li-aegirine (space group С2/c) are formed. At heat treatment temperatures above 1040°C, incongruent melting of Li-aegirine occurs with the formation of cristobalite and/or magnetite. The obtained results will form the base for the development of an electrode material for lithium-ion batteries (LIBs).