Positive electrode active material/graphene composite particles, positive electrode material for lithium ion cell, and method for manufacturing positive electrode active material/graphene composite particles

Positive electrode active material and graphene composite particles which comprise:

• positive electrode active material particles and
• a matrix containing partially functionalized graphene,
• wherein
• the partially functionalized graphene comprises graphene modified with a hydroxyl, carboxyl, ketone or epoxy group, and
• the composite particles have a ratio of functionalization that is not less than 0.15 and not more than 0.80, the ratio of functionalization being determined, based on measurements by X-ray photoelectron spectroscopic measurement of the composite particles, from the following equation:
• Ratio of functionalization=[(peak area based on C—O single bond)+(peak area based on C═O double bond)+(peak area based on COO bond)]/(peak area based on C—C, C═C and C—H bonds).