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In situ Raman spectroscopy is a powerful technique for probing the structure and phase composition of the electrode materials that are undergoing charge-discharge process. Herein, the charge storage mechanism of as-prepared Ni(HCO3)2 nanomaterial is successfully studied by using the in situ Raman spectroscopy. The charge storage can be attributed to the deep oxidation of Ni2+ into Ni3+, and the irreversible phase transformation of γ-NiOOH into disordered β-Ni(OH)2 damages the crystal structure of Ni(HCO3)2, arousing the capacity loss of the electrode during the long-term cycling process. Under the guidance of the experimental investigations, a porous Ni(HCO3)2/reduced graphene oxide (rGO) nanocomposite is designed and synthesized, exhibiting ultrahigh specific capacity (846 C g−1) and excellent rate capability (618 C g−1 at 20 A g−1). When coupled with an negative electrode based on rGO, the resulting hybrid supercapacitor shows an ultrahigh energy density of 66 Wh kg−1 at power density of 1.9 kW kg−1 and good cycling stability. These findings provide important insight into the mechanism of charge storage, and scientific basis for design of high-performance energy storage materials.
A porous Ni(HCO3)2/rGO nanocomposite used as a positive electrode for hybrid supercapacitor delivers high energy density, superior rate capability and good cycling stability. The energy storage behavior and structural evolution of the Ni(HCO3)2 nanomaterial are carefully investigated using in situ Raman spectroscopy. [Display omitted]
•The Ni(HCO3)2/rGO nanocomposite was successfully prepared, demonstrating high capacity and excellent rate performance.•The energy storage mechanism of the Ni(HCO3)2 is investigated by using in situ Raman spectroscopy.•The hybrid supercapacitor demonstrates ultrafast energy storage capability.