Hierarchical Nanosheets/Walls Structured Carbon-Coated Porous Vanadium Nitride Anodes Enable Wide-Voltage-Window Aqueous Asymmetric Supercapacitors with High Energy Density.

Jun Huang,Yazhou Xu,Licheng Tan,Yiwang Chen,Zhongyou Peng,Yingbo Xiao,Yushuai Xiong,Kai Yuan,Lingfang Chen

doi:10.1002/advs.201900550

Jun Huang, Yazhou Xu + Show 7 more

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https://doi.org/10.1002/advs.201900550

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Abstract

The energy density of aqueous asymmetric supercapacitors (ASCs) is usually limited by low potential windows and capacitances of both anode and cathode. Herein, a facile strategy to fabricate hierarchical carbon‐coated porous vanadium nitride nanosheet arrays on vertically aligned carbon walls (CC/CW/p‐VN@C) as anode for aqueous ASCs is reported. The potential window of CC/CW/p‐VN@C electrode can be stably extended to –1.3 to 0 V (vs Ag/AgCl) with greatly improved specific capacitance (604.8 F g−1 at 1 A g−1), excellent rate capability (368 F g−1 at 60 A g−1), and remarkable electrochemical stability. To construct ASCs, a Birnessite Na0.5MnO2 nanosheet arrays (CC/CW/Na0.5MnO2) cathode is similarly built. Benefiting from the matchable potential windows and high specific capacitances of the rationally designed anode and cathode, aqueous CC/CW/p‐VN@C||CC/CW/Na0.5MnO2 ASCs with a wide voltage window of 2.6 V are fabricated. Moreover, the ASCs showcase an ultrahigh energy density up to 96.7 W h kg−1 at a high power density of 1294 W kg−1, and excellent cycling stability (92.5% retention after 10 000 cycles), outperforming most of previously reported ASCs and even comparable to that of organic electrolyte supercapacitors (SCs). This efficient strategy for fabricating 2.6 V aqueous ASCs suggests a promising research system for high energy density SCs.

Highlights

Benefiting from the ultrathin carbon layer coating, the carbon cloth (CC)/CW/p-vanadium nitride (VN)@C electrode exhibits excellent rate capability (368 F g−1 at 60 A g−1) and remarkable cycling stability (90.5% retention after 10 000 cycles)
Due to the matchable potential windows and high specific capacitances of both anode and cathode, a 2.6 V aqueous CC/CW/p-VN@ C||CC/CW/Na0.5MnO2 asymmetric supercapacitors (ASCs) has been fabricated with an ultrahigh energy density up to 96.7 W h kg−1 and excellent cycling stability (92.5% retention after 10 000 cycles), outperforming most of previously reported ASC devices and even comparable to that of organic electrolyte SCs
The carbon wall arrays were growth on the surface of CC (CC/CW), which severed as secondary substrate for further growth of carboncoated porous VN and Na0.5MnO2 nanosheet arrays, detailed synthesis procedures are given in the Experimental Section

Summary

Morphology and Structure Characterization

The low-magnification SEM images of CC/CW reveal that the carbon wall arrays can be uniformly prepared on CC in a large scale (Figure S1, Supporting Information). The ultrafine cross-linked Mn3O4 nanosheets with smooth surface were uniformly deposited on the carbon walls (Figure S6, Supporting Information). In the absence of carbon walls, the low mass loading of Mn3O4 nanosheets was coated on CC (Figure S7, Supporting Information). From the XRD patterns of the CC/CW/Mn3O4 and in situ formed CC/CW/Na0.5MnO2 after electrochemical oxidation (Figure S10, Supporting Information), all diffraction peaks of Mn3O4 can be well indexed to the tetrahedral hausmannite Mn3O4. The newly emerged diffraction peaks can be indexed to monoclinic Birnessite These results were further confirmed by XPS analysis (Figure S11, Supporting Information), which are consistent with previously reported results.[34]

Electrochemical Properties

Conclusion

Experimental Section

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