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Achieving high voltage and safety simultaneously in energy storage devices can greatly advance the development of flexible and wearable electronics. Thus, flexible aqueous asymmetric lithium‐ion supercapacitors with a high voltage attract the interest of many researchers. Herein, a new flexible aqueous asymmetric lithium‐ion supercapacitor with a high voltage and superior safety is fabricated using manganese oxide and iron hydroxide, which are electrodeposited on carbon cloths as electrodes and a super‐concentrated gel polymer as the electrolyte. Impressively, the flexible asymmetric lithium‐ion supercapacitor delivers a high voltage of 3.2 V, which is a high value in aqueous asymmetric supercapacitors. Moreover, the asymmetric supercapacitor exhibits a specific capacitance of 227.6 F g−1, a maximum energy density of 49.3 Wh kg−1, and a maximum power density of 11.5 kW kg−1, together with a capacitance retention of 82% after 1000 cycles at a current density of 2 A g−1. Importantly, the supercapacitor can keep good electrochemical performance under extremely harsh conditions, such as compressing, hammering, punching, and tailoring, which demonstrates superior safety. [ABSTRACT FROM AUTHOR]

Tris(2,2,2-trifluoroethyl) phosphite (TTFEP) is investigated as an electrolyte additive to improve the electrochemical performance of LiNi 1/3 Co 1/3 Mn 1/3 O 2 cathode at high operating voltage (4.6 V). Charge/discharge measurements demonstrate that TTFEP is effective to improve the cycling stability and rate capability of LiNi 1/3 Co 1/3 Mn 1/3 O 2 cathode. The capacity retention of LiNi 1/3 Co 1/3 Mn 1/3 O 2 /Li cell with 1% TTFEP-containing electrolyte reaches up to 85.4% after 100 cycles at 0.5C (1C = 160 mA g −1 ), while that of the cell with the baseline electrolyte (1 M LiPF 6 in EC/DMC electrolyte) only remains 74.2%. Moreover, the discharge capacity of the cathode with 1% TTFEP-containing electrolyte could maintain around 112.0 mAh g −1 at 4C. Based on the characterization of electrochemical impedance spectroscopy (EIS), scanning electron microscopy (SEM), X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS), a protective interphase film formed on the cathode surface can be found due to the preferential oxidation of TTFEP, which inhibits the electrolyte decomposition and mitigates the cathode structural destruction, leading to the improved electrochemical performance of LiNi 1/3 Co 1/3 Mn 1/3 O 2 cathode at high voltage. [ABSTRACT FROM AUTHOR]