In situ Raman study of nickel bicarbonate for high-performance energy storage device

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 asprepared 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 gamma-NiOOH into disordered beta-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 20A 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.