Homogeneous nanocomposites of nanocrystalline Li2MnSiO4 and carbon as well as a carbon nanotubes-embedded nanocomposite are synthesized directly by a novel method using organic-inorganic hybrid polymers which consist of covalently bonded phenolic oligomer and siloxane parts. The nanocomposites show superior charge-discharge performance at room temperature in spite of low carbon contents.