CNT Interwoven Nitrogen and Oxygen Dual-Doped Porous Carbon Nanosheets as Free-Standing Electrodes for High-Performance Na-Se and K-Se Flexible Batteries

Na-Se and K-Se batteries are attractive as a stationary energy storage system because of much abundant resources of Na and K in the Earth's crust. As the alloy-type Se has a severe pulverization issue, one critical challenge to develop advanced Na-Se and K-Se batteries is to explore a highly efficient and stable Se-based cathode. Herein, a flexible free-standing Se/carbon composite film is prepared by encapsulation of Se into a carbon nanotube (CNT) interwoven N,O dual-doped porous carbon nanosheet (Se@NOPC-CNT). The 3D interconnected CNT uniformly wrapped on the N, O dual-doped porous carbon skeletons improves the flexibility and offers an interconnected conductive pathway for rapid ionic/electronic transport. In addition, the N, O dual-doping significantly enhances the chemical affinity and adhesion between NaxSe/KxSe (0 < x <= 2) and porous carbon, which is confirmed by density functional theory calculation. When used as the cathode in Na-Se batteries, the Se@NOPC-CNT delivers a remarkable reversible capacity of 400 mA h g(-1) at 1 A g(-1) after 2000 cycles with a 0.008% capacity decay per cycle. For K-Se batteries, it also exhibits an excellent cycling stability (335 mA h g(-1) after 700 cycles at 0.8 A g(-1)). This unique design may open an avenue for practical application of flexible Na-Se and K-Se batteries.