Realization of highly deformable freestanding borophene hybrid film for flexible energy storage device

As a unique elemental metallic Dirac material, borophene, which is predicted to have ever-increasing mechanical and electronic characters, attracts fast-grown attention in electronics. In fact, it is theoretically addressed and experimentally confirmed that borophene works well for energy storage. However, limited by the current synthesis techniques, until now, there is no attempt that has been made to explore borophene's application in the prospective flexible electrodes. This fact keeps us pondering. In this work, we offers a reliable way to overcome the adversity by randomly stacking MXene and borophene flakes to form macroscopic flexible film. It is proved that the insertion of borophene into the hybrid film can remarkably enhance the energy storage capability and energy output. The optimized hybrid film electrode shows an outstanding specific areal capacitance of 1328 mF cm⁻² at a current density of 0.5 mA cm⁻² in 1 M LiCl aqueous electrolyte, which is highly comparable with, or in most cases much higher than previously reported MXene-based flexible electrodes tested in neutral electrolyte. Additionally, the high specific capacitance can be well preserved with a capacitance retention of more than 98.5% even after charging-discharging for 10,000 cycles. Besides, the borophene hybrid film based flexible supercapacitor maintains stable capacitive performance when subjected to bending of up to 180° for 100 cycles, suggesting great feasibility for applying borophene in future flexible and portable electronics.