Porous W2N fibrous nanograins and TiN nanopyramid framework for high-energy density flexible asymmetric supercapacitors

Abstract

Enhancing the energy density of flexible asymmetric supercapacitors (ASCs) necessitates developing and implementing high-performance anode materials for technological developments in wearable energy storage systems. Tungsten nitride (W2N) offers enormous potential as an anode material for ASCs, ascribed to its substantial specific capacitance, massive electrical conductivity, and extended negative potential window. In this work, we fabricated a durable coin cell and flexible ASC utilizing W2N/SSM fibrous nanograins for the anode and TiN/SSM nanopyramids for the cathode, both deposited over flexible stainless steel mesh (SSM) substrate using the DC magnetron sputtering technique. The W2N/SSM//TiN/SSM ASC device demonstrates a high areal capacitance of 21.3 mF cm−2, operating across a wide and stable electrochemical voltage window of 1.3 V, with outstanding cycling robustness, demonstrating 89.09% retention over 8000 charge–discharge cycles. Notably, the ASC achieved a high energy density of 34.33 mWh.cm−3 and a high power density of 17.32 W.cm−3. The persistent electrochemical performance of ASC is mainly attributed to the dominance of surface-controlled capacitive and pseudocapacitive charge storage kinetics of W2N/SSM for Na+ ions, as comprehensively examined employing 3D Bode and Dunn's techniques. The flexible ASC shows remarkable mechanical stability of 92.36% over 500 bending cycles. This study establishes the potential of W2N nanograins as a high-energy anode material, revealing its capability to increase the effectiveness of ASC for portable and miniaturized energy storage devices.