High‐Performance Supercapacitors Based on Intertwined CNT/V₂O₅ Nanowire Nanocomposites

Abstract

packaging, account for a large fraction of the total weight of the device, the use of thin electrodes results in a signifi cantly lower energy density than what could be attained using thicker electrodes. [ 3 ] Therefore, the development of thick electrodes for supercapacitors represents an important direction for making high-energy supercapacitors for practical applications.We recently developed a class of pseudocapacitive anode materials for asymmetric supercapacitors composed of interpenetrating networks of carbon nanotubes (CNTs) and V 2 O 5 nanowires. [ 16 ] The CNTs and nanowires were intimately intertwined into a hierarchically porous structure, enabling effective electrolyte access to the electrochemically active materials without limiting charge transport. Such composites exhibited high specifi c capacitance ( > 300 F g − 1 ) at high current density (1 A g − 1 ) in aqueous electrolyte. In this paper we report the fabrication of high energy density asymmetric supercapacitors containing thick-fi lm electrodes (over 100 μ m thick) of the CNT/V 2 O 5 nanowire composite in combination with an organic electrolyte, which allows for a higher initial cell potential. The excellent conductivity, high specifi c capacitance, and large voltage window of the CNT/V 2 O 5 nanocomposite enable the fabrication of devices with an energy density as high as 40 Wh kg − 1 at a power density of 210 W kg − 1 . Even at a high power density of 6 300 W kg − 1 , the device possesses an energy density of nearly 7.0 Wh kg − 1 . Moreover, the resulting devices exhibit excellent cycling stability. This work demonstrates that the nanowire composite approach is an effective strategy towards high-energy and high power density supercapacitors. Figure 1 A shows a representative scanning electron microscopy (SEM) image of a nanocomposite with 18 wt% of CNTs, demonstrating a continuous fi brous structure (Figure 1 A). The intertwined networks of the CNTs and nanowires exhibit an electrical conductivity of ≈ 3.0 S cm − 1 , which is 80 times higher than that of V 2 O 5 nanowires (0.037 S cm − 1 ). Figure 1 B is a transmission electron microscopy (TEM) image of a V 2 O 5 nanowire with a diameter of around 50 nm. The high-resolution TEM (HRTEM) image (inset) suggests the nanowire contains a layered crystalline structure; the small nanowire dimension allows effective Li + diffusion. Moreover, nitrogen sorption isotherms ( Figure S1, Supporting Information) and higher resolution SEM images of the etched composite fi lm (Figure 1 A, inset) show that the composite possesses a hierarchically porous structure; the presence of large pores enables rapid electrolyte transport while the small pores effectively increase the surface area available for electrochemical reactions. These small pores are responsible for the surface area of 125 m 2 g − 1 determined for the composite.An ideal electrical energy storage device provides both high energy and power density. [ 1 , 2 ] Supercapacitors exhibit signifi cantly higher power densities compared to batteries and ...

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