▎ 摘　　要

Organic cathodes, especially conjugated carbonyl polymers, have been developed as promising alternatives to inorganic cathodes for rechargeable lithium and sodium batteries due to their high theoretical capacities, fast reaction kinetics, mechanical flexibility, environmental sustainability, and structural diversity. However, because of the intrinsic electrical insulation of conjugated carbonyl polymers, it is a great challenge to simultaneously achieve high capacity, high rate capability, and long cycle life. In this paper we report, for the first time, the preparation of monolithic 3D graphene/ polyimide composites (GF-PI) through a one-step solvothermal strategy with simultaneous in situ polymerization of PI on the graphene surface and self-assembly of graphene into a 3D network structure. The mechanically strong GF-PI can be used directly as highly flexible lithium-ion-battery (LIB) cathodes without adding any other binder or conductive carbon and deliver a very high reversible capacity (240 mA h g(-1) at 40 mA g(-1)), excellent rate capability (102 mA h g(-1) at 4000 mA g(-1)) and remarkable cycling stability (81.2% capacity retention after 600 cycles at 100 mA g(-1)). The flexible GF-PI electrode also delivers an ultrahigh Na storage capacity of 213 mA h g(-1) at 50 mA g(-1), and outstanding capacity retention of 80.4% after 1000 cycles at 1000 mA g(-1) when used as a sodium-ion-battery (SIB) cathode. The comprehensive electrochemical performances of GF-PI are superior to those of the state-of-art PI-based LIB and SIB cathodes that have been reported thus far.