NOVELTY - The electrode material comprises a core containing a lithium silicon oxide compound (Li2MSiO4), where M is iron, cobalt, manganese and nickel as a main component, a covering layer containing a lithium phosphate compound (LiMPO4) and covering the core, a carbon coat layer that covers the covering layer, and a solid solution material between the core and the covering layer. The LiMPO4 compound has high conductivity as compared to the Li2MSiO4 compound. The LiMPO4 compound (10%) is dissolved in the Li2MSiO4 compound in the solid solution material. The carbon coat layer has a thickness.    USE - The electrode material is useful in a power storage device (claimed) such as lithium-ion secondary battery, which is useful in: a portable electronic device such as cameras including digital cameras or video cameras, digital photo frames, mobile phones including cellular phones or cellular phone devices, portable game machines, portable information terminals, personal computers or audio reproducing devices; and electric propulsion vehicles such as electric vehicles, hybrid vehicles, train vehicles, maintenance vehicles, carts, wheelchairs and bicycles.    ADVANTAGE - The electrode material exhibits high electrical conductivity and capacity, and improves discharge capacity and energy density and reduces the size and weight of the power storage device.    DETAILED DESCRIPTION - The electrode material comprises a core containing a lithium silicon oxide compound (Li2MSiO4), where M is iron, cobalt, manganese and nickel as a main component, a covering layer containing a lithium phosphate compound (LiMPO4) and covering the core, a carbon coat layer that covers the covering layer, and a solid solution material between the core and the covering layer. The LiMPO4 compound has high conductivity as compared to the Li2MSiO4 compound. The LiMPO4 compound (10%) is dissolved in the Li2MSiO4 compound in the solid solution material. The carbon coat layer has a thickness of 0-100 nm. INDEPENDENT CLAIMS are included for:    (1) a power storage device; and    (2) a method for forming an electrode material.    DESCRIPTION OF DRAWING(S) - The diagram shows a schematic cross-sectional view of a power storage device.    Positive electrode (202)    Negative electrode (207)    Separator (210)    Electrolyte solution (211)    Housing. (220)