Black phosphorus hybrid films enabled by a covalently chemical and spatial hierarchical-locking effect for flexible supercapacitors with 100% cycling stability

Abstract

Black phosphorus (BP) has attracted rapidly growing attention for potential applications in next-generation flexible supercapacitors (FSCs) owing to its exceptional properties such as large specific surface area, unique lamellar structure, and excellent flexibility. However, one intractable problem is that BP-based FSCs suffer from poor cycling stability due to the high reactivity toward O₂ and inherent structural instability of BP. Herein, a “chemical and spatial hierarchical-locking” strategy is developed to successfully construct ultra-stable BP hybrids. Three-dimensional encapsulation of a covalently bonded BP/conductive carbon nitride (BP/c-CN) domain with electrolyte-infiltrated SCNT networks yields a spatial solid-electrolyte interphase that can effectively shield against O₂, slowing down the degradation of BP. Besides, the solid-electrolyte interphase can shorten the transfer distance of electrolyte ions to the electrode, thus achieving rapid charge-transfer kinetics. Meanwhile, the covalent P–C bonds between BP and c-CN contribute to building a “robust skeleton”, concurrently preventing the structural distortion of BP. Significantly, the BP/c-CN@SCNT-based FSC delivers a remarkable cycling ability with 100% capacitance retention after 50 000 cycles, less than 10% capacitive decay after 6 months under ambient conditions, and a high energy density of 15.1 mW h cm⁻³, making it promising for practical applications. This work provides a new insight for designing high-performance and stable BP-based electrodes for FSCs.