H‐TiO₂@MnO₂//H‐TiO₂@C Core–Shell Nanowires for High Performance and Flexible Asymmetric Supercapacitors

Abstract

A flexible solid-state asymmetric supercapacitor device with H-TiO(2) @MnO(2) core-shell NWs as the positive electrode and H-TiO(2) @C core-shell NWs as the negative electrode is developed. This device operates in a 1.8 V voltage window and is able to deliver a high specific capacitance of 139.6 F g(-1) and maximum volumetric energy density of 0.30 mWh cm(-3) with excellent cycling performance and good flexibility.

Ultrahigh‐Power Pseudocapacitors Based on Ordered Porous Heterostructures of Electron‐Correlated Oxides

“…Considering that the electrical property and electrochemical performance of TMOs can be improved by the introduction of heteroatoms or intrinsic defects,6, 44 the as‐prepared NP V 2 O 3 /MnO 2 films are subsequently exposed in H 2 /Ar at 400 °C. This process maintains the chemical states of V 2 O 3 scaffold and hydrogenates the MnO 2 layer,44 which are verified by X‐ray photoelectron spectroscopy (XPS) survey (Figure S5a–c, Supporting Information).…”

“…With fast‐growing demands for energy storage devices that can store/deliver high‐density energy at rapid charge/discharge rates,1, 2 enormous research interest has recently been stimulated in exploring pseudocapacitive materials as electrodes in electrochemical capacitors for achieving much higher levels of energy storage than carbon electrode materials 1, 3, 4, 5, 6, 7. Unlike electrochemical double‐layer capacitors (EDLCs),8, 9, 10, 11, 12 in which charge storage is achieved by nonfaradaic electrostatic adsorption in nanostructured carbons with low intrinsic capacitance (≈20 μF cm −2 carbon ),1, 13, 14 pseudocapacitors store high‐density energy on pseudocapacitive materials by fast and reversible surface redox reactions at or near the electrode/electrolyte interface 1, 2, 3, 4, 5, 6, 7, 15, 16, 17.…”

“…Unlike electrochemical double‐layer capacitors (EDLCs),8, 9, 10, 11, 12 in which charge storage is achieved by nonfaradaic electrostatic adsorption in nanostructured carbons with low intrinsic capacitance (≈20 μF cm −2 carbon ),1, 13, 14 pseudocapacitors store high‐density energy on pseudocapacitive materials by fast and reversible surface redox reactions at or near the electrode/electrolyte interface 1, 2, 3, 4, 5, 6, 7, 15, 16, 17. The surface mechanisms are fundamentally distinguished from rate‐limited volumetric reactions in batteries by short charge/discharge time, high power density and long‐term cycling stability 1, 2, 3, 18.…”

“…These advantageous features enlist pseudocapacitors to be attractive alternatives or complements to batteries for many high‐power applications in hybrid electric vehicles, portable electronic devices and renewable energy 1, 2, 3, 4, 8, 9, 13. However, conventional pseudocapacitors made from state‐of‐the‐art electrode materials, typically transition‐metal oxides (TMOs) such as MnO 2 ,5, 15, 19, 20 TiO 2 ,6, 16 and Co 3 O 4 ,19, 21 often exhibit much lower power capability than EDLCs due to their intrinsically poor conductivity 15, 21. It thus remains a primarily challenge in realizing high‐power and high‐energy densities in pseudocapacitors, which requires pseudocapacitive electrode materials simultaneously providing large specific surface area and ultrahigh transports of ions and electrons 22, 23, 24.…”

“…It thus remains a primarily challenge in realizing high‐power and high‐energy densities in pseudocapacitors, which requires pseudocapacitive electrode materials simultaneously providing large specific surface area and ultrahigh transports of ions and electrons 22, 23, 24. In this regard, controlling nanostructures and exploring novel materials have become critical processes to meet these requirements in developing TMO‐based composite electrodes,1, 6, 17, 23, 25 wherein various conductive materials, including nanostructured carbons (such as porous carbon,14, 26 carbon nanotubes,27, 28, 29, 30 and graphene 31, 32) and conducting polymers, are extensively employed to serve as electron pathways. Although the large specific surface area in these low‐dimensional composite nanostructures allows ion transports,1, 17, 23, 26, 27, 28, 29, 30, 31, 32 their assembled bulk electrodes usually exhibit high electrical resistance as a result of the short electron transport distance within these low‐dimensional conductive materials, the undesirably high contact resistances produced by the coating of electrically insulating active TMOs and polymer binders, as well as the weak and noncoherent TMO/conductor interfaces 24, 33, 34, 35.…”