An electrode material and a Lithium-ion energy storage device are provided. The electrode material includes at least one material selected from the following structures: a Keplerate-type structure polyoxometalates containing molybdenum and iron; a Keplerate-type structure polyoxometalates containing molybdenum and vanadium; a bi-capped Keggin-type structure polyoxometalates containing vanadium; and polyoxometalates containing vanadium and a transition metal, wherein the transition metal is nickel, cobalt, iron, or manganese. The Lithium-ion energy storage device having above electrode materials can maintain a relatively high electric capacity at a relatively high current density, and can maintain original electric capacity after long cycling. |