Molten-salt synthesis of crystalline C3N4/C nanosheet with high sodium storage capability

[Display omitted] •Crystalline C3N4/C was constructed through a molten-salt method for the first time.•Carbon addition can direct the growth of C3N4.•A 2D structure with abundant edges/pores and high pyridinic N contents is formed.•As SIB anode, C3N4/C presented a high capacity with excellent cycling stability. Due to high theoretical capacity and chemical stability, graphitic carbon nitride (g-C3N4) is viewed as a promising electrode candidate for energy storage devices. Nevertheless, constrained by crystallinity destruction during metal ion intercalation and large aggregation, the actual capacity of g-C3N4 is very low. Unlike amorphous or semi-crystalline C3N4 fabricated via conventional methods, here we propose a molten-salt synthesis protocol of crystalline C3N4 based carbonaceous composite. Interestingly, we find carbon addition under the molten salt environment can greatly alleviate aggregation of C3N4, leading to formation of nanosheet-like structure with abundant edges/pores and high pyridinic N contents. As a proof of concept, with glucose used as the prototype carbon source, as-prepared crystalline C3N4/C delivered a record-high reversible capacity of 286 mA h/g at 0.05 A/g while maintaining outstanding full-cell performances when assembled with a commercial-grade cathode. This work highlights an effective approach to advancing energy storage use of C3N4.