▎ 摘　　要

NOVELTY - Covalent organic nanosheet comprising covalent bond-based repeating unit (I), is new. USE - (I) is useful in thin film for secondary battery i.e. sodium ion battery (all claimed). ADVANTAGE - (I) has graphene-type conjugated two-dimensional structure through Stille cross-linking reaction between monomers; has larger mesopores and lower band gaps compared to conventional triazine-based covalently bonded organic nanosheet; increases the conductivity of the charge carrier, so that when used in secondary battery; and improves storage capacity of the secondary battery. DETAILED DESCRIPTION - Covalent organic nanosheet comprising covalent bond-based repeating unit of formula (I), is new. X1 = (1,3,5-triazine-2,4,6-triyl)tris(thiophene-5,2-diyl); Y1 = benzo(c)(1,2,5)thiadiazole-4,7-diylbis(thiophene-5,2-diyl); and n = 10-200, where asterisk is a binding site. An INDEPENDENT CLAIM is also included for preparation of (I).