Interface Engineering V₂O₅ Nanofibers for High‐Energy and Durable Supercapacitors

Abstract

been made on elaborating the electrode materials with higher energy density for supercapacitors to meeting ever-increasing requirements. The energy density (E) of a supercapacitor is mainly dependent on the specific capacitance (C) and cell potential window (V) of electrode materials according to the equation E = 1/2CV 2 . [3] Thus, developing electrode materials with enhanced specific capacitance is crucial for high-energy supercapacitors. Carbonaceous material based electric double-layer capacitors appear with a low capacitance due to the physical absorption/desorption at the electrode surface. [4] Comparatively, transition metal oxides (TMOs) and conductive polymers (CPs) based pseudocapacitors exhibit higher theoretical storage capacitance because of the reversible faradic reactions on or near the electrode surface. [5] Vanadium pentoxide (V 2 O 5 ), a layer-structured TMO, has prospective applications in electrochemical energy storage due to its high theoretical capacitance (2020 F g −1 ), a broader operating voltage( up to ≈2.8 V), as well as low cost and abundance in nature. [6] However, the poor electrical conductivity of V 2 O 5 (10 −3 to 10 −2 S cm −1 ) limits the electron transfer kinetics for redox reactions. As a result, the pseudocapacitive reactions mainly occur on the surface or near-surface region of V 2 O 5 electrode materials, leading to a low utilization of V 2 O 5 and unsatisfactory specific capacitance. [7] In addition, the vanadium dissolution and structural instability reduces its cycling life. [8] To address these problems, many synthetic methods have been proposed. First, nanostructured V 2 O 5 materials with a large specific surface area are fabricated to provide sufficient contact area for fast Faradic reactions, such nanoribbons, [9] and nanobelts. [10] Second, tailoring the materials with multiple physicochemical properties can effectively enhance the electrochemical performance of V 2 O 5 with diverse functions from components. For instance, layered V 2 O 5 /poly(3,4-ethylenedioxythiophene) (PEDOT)/MnO 2 nanosheets show enhanced energy density (39.2 W h kg −1 ) and cycling stability (93.5% capacitance retention after 3000 cycles) due to the synergistic combination of PEDOT, MnO 2 , and V 2 O 5 . [11] However, V 2 O 5 electrode materials with enhanced electrochemical performance, fabricated in an uncomplicated and low-cost process are still necessary for practical applications. Based on the previous study, both polyaniline (PANI) and PEDOT improve the electrical conductivity as well as the stability of V 2 O 5 by forming a conductive coating, [8,11] A local electric field is induced to engineer the interface of vanadium pentoxide nanofibers (V 2 O 5 -NF) to manipulate the charge transport behavior and obtain high-energy and durable supercapacitors. The interface of V 2 O 5 -NF is modified with oxygen vacancies (Vö) in a one-step polymerization process of polyaniline (PANI). In the charge storage process, the local electric field deriving from the lopsided charge distribution arou...

Interphases, Interfaces, and Surfaces of Active Materials in Rechargeable Batteries and Perovskite Solar Cells

“…Beyond the atmospheric treatment and doping, surface coatings such as conductive polymers can also introduce gradient oxygen vacancies in V 2 O 5 through in-situ polymerization. [185][186][187][188] The concentration of oxygen vacancies gradually decrease from the highest concentration at the surface, i.e., the interface between V 2 O 5 and poly (3, 4-ethylenedioxythiophene) (PEDOT), to near zero inside. [186] During cycling, a local electric field develops, which is derived from lopsided charge distribution around oxygen vacancies.…”

“…coating synergistically enhances charge transfer kinetics by shortening the charge transport distance. [185,188] After long-term cycling, the oxygen vacancy concentration profile is redistributed as individual vacancies migrate inward under the applied voltage. The result is more V 5+ are available for redox reactions and the specific capacitance increased.…”

“…Adapted with permission. [185] Copyright 2009, RSC. The reduced band gap implies the reduction of V 5+ when the V 2 O 5 film is annealed in nitrogen.…”

“…During cycling, a local electric field develops, which is derived from lopsided charge distribution around oxygen vacancies. The vacancies induce a Coulombic driving force that promotes ionic transport, and the conductive PEDOT (or polyaniline or polypyrrole) coating synergistically enhances charge transfer kinetics by shortening the charge transport distance 185,188. After long‐term cycling, the oxygen vacancy concentration profile is redistributed as individual vacancies migrate inward under the applied voltage.…”

“…The inset shows the films after annealing in air (left) and nitrogen (right). Adapted with permission [185]. Copyright 2009, RSC.…”