The present invention relates to composite bodies that include at least one layer having the following composition: (a) between 1 and 99 wt % of a solid (I) having a primary particle size of 5 nm to 100 νm or a mixture of at least two solids; (b) between 99 and 1 wt % of a polymer binder (II). This polymer binder comprises: between 1 and 100 wt % of a polymer (IIa) or a copolymer (IIa) having reactive groups (RG) located on the chain, at the ends and/or on the sides and capable of cross-linking reactions thermally and/or under the action of UV; and between 0 and 99 % of at least one polymer or copolymer (IIb) free from reactive groups. The at least one layer is applied on at least a second layer comprising at least one traditional separator.