Low-crystalline FeOx@PPy hybridized with (Ni0.25Mn0.75)3O4@PPy to constructed high-voltage aqueous hybrid capacitor with 2.4 V

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The operating voltage of aqueous hybrid capacitors are generally limited to 2 V due to the decomposition of water, which significantly impede the progress of energy density. Herein, the porous low-crystalline FeOx nanorod array on carbon cloth is prepared by the novel electrochemical Li+ pre-insertion method, and a 2.4 V high-voltage aqueous hybrid capacitor device is successfully obtained after matching with the nickel doped (Ni0.25Mn0.75)3O4@PPy nanoprisms array. The low-crystalline structure of FeOx preserved during the first Li+ insertion and space created via the elimination of low-crystalline Li2O dramatically provides sufficient electronic and ionic transfer channels. In addition, surface polypyrrole (PPy) stabilization is employed to further enhance electron conductivity and electrode stabilization. Benefitting from increasing active sites, fast ion diffusion and electron transfer the obtained low-crystalline FeOx@PPy electrode exhibits improved electrochemical performance, especially for capacitance and stability. Moreover, the aqueous hybrid capacitors (Ni0.25Mn0.75)3O4@PPy//FeOx@PPy device delivers a high energy density of 72.4 Wh kg−1 with the ultra-high voltage, and admirable cycling stability (94.7% retention after 4000 cycles). Our work highlights the novel electrochemical Li+ pre-insertion method to achieve superior low-crystalline electrodes materials and designs the high-voltage aqueous hybrid energy storage devices.