Impact of the Morphology of V2O5 Electrodes on the Electrochemical Na+-Ion Intercalation. Issue 11 (1st January 2018)

• Record Type: Journal Article
• Authors: Si, Huinan; Seidl, Lukas; Chu, Eileen Miao Ling; Martens, Slađana; Ma, Jiwei; Qiu, Xinping; Stimming, Ulrich; Schneider, Oliver
• Is Part Of: Journal of the Electrochemical Society. Volume 165:Issue 11(2018)
• Page Start: A2709
• Page End: A2717
• Publication Date: 2018-01-01
• Subjects: Na-Ion Battery -- V2O5 electrode; Electrochemistry -- Periodicals; 541.3705
• DOI: 10.1149/2.0621811jes
• Languages: English
• ISSNs: 0013-4651

Abstract

Abstract : The development of high performance electrodes for Na-ion batteries requires a fundamental understanding of the electrode electrochemistry. In this work, the effect of the morphology of vanadium oxide on battery performance is investigated. First, the phase transitions upon sodiation/de-sodiation of Nax V2 O5 cathodes in standard battery solvents are explored by cyclic voltammetry and X-Ray diffraction. At potentials 1.5 V positive of Na/Na + the insertion of the first Na + into pristine V2 O5 is completed and α'-NaV2 O5 is formed. A discharge to 1.0 V results in the introduction of a second Na + and after a deep discharge to 0 V a third Na + is intercalated. When cycled as an intercalation electrode, the Na-content x in Nax V2 O5 varies between x = 1 (charged) and x = 2 (discharged). For studying the effect of electrode morphology on the battery performance, several types of V2 O5 (hollow V2 O5 microspheres, V2 O5 nanobundles and V2 O5 nanobundles blended with 10%wt TiO2 ) were prepared and compared to a commercially available V2 O5 -micropowder. The nanobundles were prepared by a facile sonochemical process. In comparison to the microsized V2 O5 morphologies, the potential plateaus in the charge/discharge curves of the V2 O5 nanobundles are at more positive potentials and the capacity loss in the first cycle is suppressed. The V2 O5 nanobundles showed the best battery performance with a reversible capacity of 209.2 mAh g −1 and an energy density of 571.2 mWh kg −1 (2 nd cycle). After an initial capacity fading, which can be slightly suppressed by blending the V2 O5 with TiO2, the pure V2 O5 nanobundles have a practical capacity of 85 mAh g −1, an operation potential of 2.4 V, an energy density of 266.5 mWh kg −1 and a capacity retention of 83% after 100 cycles. The best battery performance of the nanomaterial is ascribed in this study to the amorphous character of the electrode, favoring faster electrode kinetics due to a (pseudo-) capacity dominated charging/discharging, reducing diffusion lengths and preventing further amorphization, which all is beneficial in terms of lifetime, capacity, operation voltage, energy density and energy efficiency.