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Simon Fleischmann1 2 Desirée Leistenschneider3 Lars Borchardt3 Volker Presser1 2

1, INM - Leibniz Institute for New Materials, Saarbrucken, , Germany
2, Saarland University, Saarbrücken, , Germany
3, Technische Universität Dresden, Dresden, , Germany

The development of novel electrode materials that exhibit both high specific power and energy is at the focal point of current research activities.1 Synergistically combining supercapacitor and battery materials yields hybrid electrodes with improved performance metrics.2 To enable high charging and discharging rates, limitations posed by both electron and ion mobility need to be overcome. Consequently, advanced electrode materials have to offer high electrical conductivity and nanostructured surfaces yielding large electrode/electrolyte interfaces. For that purpose, a nanoscopic decoration of high surface area carbons with metal oxides is explored.
In this study, we synthesized hybrid electrodes of carbon and vanadium oxide by atomic layer deposition (ALD). The carbon substrate was obtained by hard templating using SiO2 nanospheres that were removed by hydrofluoric acid. The obtained spherical pores were especially tailored to offer high internal surface area (1000 m2/g) and mesopore volume (1.18 cm3/g) and ensured a homogenous adsorption of ALD precursors during synthesis.3 Up to 65 mass% vanadium pentoxide was deposited inside the carbon mesopores without an obstruction of internal surface area or pore blocking. This ensured a high accessibility of electrolyte during electrochemical cycling. The hybrid materials were benchmarked as lithium and sodium intercalation hosts, resulting in specific capacities of 310 and 250 mAh/g per V2O5 at a rate of 0.5C, respectively, and retained about 50 % of the capacity at a high rate of 100C. Charge storage behavior was predominantly pseudocapacitive, that is, showing constant voltage profiles like a capacitor. The materials also showed a remarkable cycling stability, with an increase in capacity to 116 % of the initial value (lithium) and a retention of 75 % (sodium) after 2,000 cycles. The homogenous distribution and local confinement of nanoscopic V2O5 domains inside the tailored carbon matrix were identified as the reason for enhanced rate handling and cyclability of the material.
(1) Augustyn, V.; Simon, P.; Dunn, B., Pseudocapacitive Oxide Materials for High-Rate Electrochemical Energy Storage. Energy Environ. Sci. 2014, 7, 1597-1614.
(2) Dubal, D.; Ayyad, O.; Ruiz, V.; Gómez-Romero, P., Hybrid energy storage: the merging of battery and supercapacitor chemistries. Chem. Soc. Rev. 2015, 44, 1777-1790.
(3) Fleischmann, S.; Leistenschneider, D.; Lemkova, V.; Krüner, B.; Zeiger, M.; Borchardt, L.; Presser, V., Tailored Mesoporous Carbon/Vanadium Pentoxide Hybrid Electrodes for High Power Pseudocapacitive Lithium and Sodium Intercalation. Chem. Mater. 2017, 29, 8653-8662.

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