Provided is a lithium-ion battery or lithium-ion capacitor electrode material that can compensate for the drawbacks of a hydrophobic active material, that can impart hydrophilicity to the hydrophobic active material, and that can exhibit excellent dispersibility without deteriorating electrode characteristics. Specifically provided is an electrode material for a lithium-ion battery or a lithium-ion capacitor, the electrode material comprising a composite powder in which a B component is supported or coated on a surface of an A component, the A component comprising a material capable of electrochemically occluding and releasing lithium ions, the B component being sulfur-modified cellulose, and the B component being contained in an amount of 0.01 mass % or more based on 100 mass % of the total amount of the A component and the B component.