Provided is a new technique related to electrochemical devices that can sufficiently ensure adhesiveness of a functional layer and safety of an electrochemical device while, on the other hand, causing an electrochemical device to display excellent high-temperature storage characteristics. A composite particle for an electrochemical device functional layer includes a core particle containing a melamine compound and a shell polymer that at least partially covers an outer surface of the core particle and that includes at least one selected from the group consisting of a nitrile group, a carboxy group, a hydroxyl group, a sulfo group, an aldehyde group, and an amide group.