Issue 11, 2023

Cationic vacancies and interface engineering on crystalline–amorphous gamma-phase Ni–Co oxyhydroxides achieve ultrahigh mass/areal/volumetric energy density flexible all-solid-state asymmetric supercapacitor

Abstract

Construction of gamma-phase transition metal oxyhydroxides for electrode materials is an effective strategy for improving electrochemical properties. However, the preparation of gamma-phase transition metal oxyhydroxides with various defects remains an arduous challenge. Herein, gamma-phase Ni–Co oxyhydroxides with cationic vacancy defects and crystalline–amorphous interfaces are synthesized successfully via electrochemical reconstruction to achieve an ultrahigh mass/areal/volumetric energy density, flexible all-solid-state asymmetric supercapacitor (ASC). The Ni–Co oxyhydroxides consist of γ-NiOOH, γ-CoOOH and NiOOH phases; the γ-NiOOH and γ-CoOOH phases can effectively improve electronic conductivity and theoretical capacitance due to the abundant Ni4+/Co4+. The cationic vacancy defects and crystalline–amorphous interfaces not only endow the gamma-phase Ni–Co oxyhydroxides with abundant electrochemical active sites, but also enable fast electron transfer between the electrode and electrolyte. Therefore, the as-obtained gamma-phase Ni–Co oxyhydroxides display a high capacitance of 20.9 F cm−2 at 4 mA cm−2 and 3483 F g−1 at 0.67 A g−1, as well as excellent rate characteristics (90.5% capacitance retention at a high current density of 240 mA cm−2 and 40 A g−1). Density functional theory calculations reveal that Ni–Co oxyhydroxides with cationic vacancies can increase the adsorption energy of H2O, which is beneficial for the capture of H2O to occur for subsequent charge storage reactions. Furthermore, the assembled Ni–Co oxyhydroxides//active carbon all-solid-state ASC shows ultrahigh mass/areal/volumetric energy density of 92.6 W h kg−1/3.3 mW h cm−2/19.5 mW h cm−3 (at 1156 W kg−1/34.6 mW cm−2/204.1 mW cm−3) and possesses excellent electrochemical stability with 91% retention after 7000 cycles.

Graphical abstract: Cationic vacancies and interface engineering on crystalline–amorphous gamma-phase Ni–Co oxyhydroxides achieve ultrahigh mass/areal/volumetric energy density flexible all-solid-state asymmetric supercapacitor

Supplementary files

Article information

Article type
Paper
Submitted
19 Nov 2022
Accepted
13 Feb 2023
First published
14 Feb 2023

J. Mater. Chem. A, 2023,11, 5754-5765

Cationic vacancies and interface engineering on crystalline–amorphous gamma-phase Ni–Co oxyhydroxides achieve ultrahigh mass/areal/volumetric energy density flexible all-solid-state asymmetric supercapacitor

X. Ren, M. Li, L. Qiu, X. Guo, F. Tian, G. Han, W. Yang and Y. Yu, J. Mater. Chem. A, 2023, 11, 5754 DOI: 10.1039/D2TA09035J

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