title: High-Performance Supercapacitors from Niobium Nanowire Yarns.
abstract: The large-ion-accessible surface area of carbon nanotubes (CNTs) and graphene sheets formed as yarns, forests, and films enables miniature high-performance supercapacitors with power densities exceeding those of electrolytics while achieving energy densities equaling those of batteries. Capacitance and energy density can be enhanced by depositing highly pseudocapacitive materials such as conductive polymers on them. Yarns formed from carbon nanotubes are proposed for use in wearable supercapacitors. In this work, we show that high power, energy density, and capacitance in yarn form are not unique to carbon materials, and we introduce niobium nanowires as an alternative. These yarns show higher capacitance and energy per volume and are stronger and 100 times more conductive than similarly spun carbon multiwalled nanotube (MWNT) and graphene yarns. The long niobium nanowires, formed by repeated extrusion and drawing, achieve device volumetric peak power and energy densities of 55 MW·m(-3) (55 W·cm(-3)) and 25 MJ·m(-3) (7 mWh·cm(-3)), 2 and 5 times higher than that for state-of-the-art CNT yarns, respectively. The capacitance per volume of Nb nanowire yarn is lower than the 158 MF·m(-3) (158 F·cm(-3)) reported for carbon-based materials such as reduced graphene oxide (RGO) and CNT wet-spun yarns, but the peak power and energy densities are 200 and 2 times higher, respectively. Achieving high power in long yarns is made possible by the high conductivity of the metal, and achievement of high energy density is possible thanks to the high internal surface area. No additional metal backing is needed, unlike for CNT yarns and supercapacitors in general, saving substantial space. As the yarn is infiltrated with pseudocapacitive materials such as poly(3,4-ethylenedioxythiophene) (PEDOT), the energy density is further increased to 10 MJ·m(-3) (2.8 mWh·cm(-3)). Similar to CNT yarns, niobium nanowire yarns are highly flexible and show potential for weaving into textiles and use in wearable devices.
authors.affiliation: †Department of Mechanical Engineering, BioInstrumentation Laboratory, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, United States.
authors.forename: Seyed M
authors.initials: SM
authors.lastname: Mirvakili
authors.affiliation: ‡Department of Chemical and Biological Engineering, University of British Columbia, Vancouver, BC V6T 1Z3, Canada.
authors.forename: Mehr Negar
authors.initials: MN
authors.lastname: Mirvakili
authors.affiliation: ‡Department of Chemical and Biological Engineering, University of British Columbia, Vancouver, BC V6T 1Z3, Canada.
authors.forename: Peter
authors.initials: P
authors.lastname: Englezos
authors.affiliation: §Department of Electrical and Computer Engineering, Advanced Materials and Process Engineering Laboratory, University of British Columbia, Vancouver, BC V6T 1Z4, Canada.
authors.forename: John D W
authors.initials: JD
authors.lastname: Madden
authors.affiliation: †Department of Mechanical Engineering, BioInstrumentation Laboratory, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, United States.
authors.forename: Ian W
authors.initials: IW
authors.lastname: Hunter
mesh_terms: D019086:Bridged Bicyclo Compounds, Heterocyclic / Q000737:chemistry; D002482:Cellulose / Q000737:chemistry; D025802:Electric Capacitance; D055615:Electrical Equipment and Supplies; D053770:Nanowires / Q000737:chemistry*; D009556:Niobium / Q000737:chemistry*; D011108:Polymers / Q000737:chemistry
chemical_list: D019086:Bridged Bicyclo Compounds, Heterocyclic; D011108:Polymers; C121383:poly(3,4-ethylene dioxythiophene); D009556:Niobium; D002482:Cellulose
keywords: PEDOT; cellulosic separators; energy storage; flexible capacitors; metal nanowires; niobium nanowires; supercapacitors; yarn nanowires