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• A high-performance low-cost energy storage halogenated polymer material is developed. • Increased permittivity caused by fluorophenyl leads to high energy storage density. • High charge trap density caused by halogen groups leads to high cycling efficiency. • Moderate crosslinking structure further deepen the charge traps in dielectrics. Capacitor dielectric films exhibiting high energy storage density and efficiency within a wide operating temperature range are crucial for advancing electrical and electronic devices. The low energy storage density and working temperature as well as the high manufacturing costs of the state-of-the-art BOPP films limit their use as an energy storage unit for developing smart grids or the internet of things, while most of the polymer-based dielectric films reported currently are facing the issues of the rapid efficiency deterioration with the increasing of temperature. In this work, the high energy storage density and efficiency are achieved in the low-cost flexible epoxy films innovatively modified by trifluoro-phenyl group functionalization. Introducing strongly electronegative fluorinated phenyl groups greatly improves the energy storage density due to the increase of the total molecular dipole moment of the polymer film. Meanwhile, achieving the high energy storage efficiency is accomplished via gradually increasing the charge trapping site density of epoxy resins functionalized with different densities of fluorinated phenyl groups, which can be demonstrated through both thermally stimulated current (TSC) spectroscopy and the first-principles calculations results. Finally, it is experimentally demonstrated that deeper charge traps can be obtained in slightly crosslinked trifluoro-phenyl functionalized epoxy films, resulting in an energy storage density of 3.31 J/cm3 and a high energy storage efficiency of 95% at 100 °C. [ABSTRACT FROM AUTHOR]

[Display omitted] • The high-stable ionogel electrolyte (PAAm/IL-X) was prepared. • The PAAm/IL-X can be operated in a wide temperature range from 0 °C to 90 °C. • The conductivity of the prepared ionogel was up to 23 mS cm−1 at 90 °C. • The PEDOT/CC electrode displayed excellent electrochemical performance. • The capacitance performance of the device ASSC-X was increased by 5% at 90 °C. Supercapacitors (SCs), a type of energy storage devices, have dragged an attention worldwide due to its high electrochemical performance for various applications. However, the use of liquid electrolyte in SCs spresents several drawbacks on packaging and security. Therefore, the preparation of SCs using solid electrolytes is a feasible method. Here, we report an ionogel electrolyte (PAAm/IL-X) which composed of polyacrylamide (PAAm) network and ionic liquid 1-vinyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide ([VMIM][TFSI]). The introduction of ionic liquid ([VMIM][TFSI]) improves the thermal stability and conductivity of the electrolyte. The conductivity of the prepared ionogel is up to 23 mS cm−1 at 90 °C, which still retained 71% even after 20 days at room temperature. It is noted that the thermal decomposition temperature of PAAm/IL-X was above 220 °C. In addition, the poly(3,4-ethylenedioxythiophene/carbon cloth (PEDOT/CC) electrode prepared by electroplating method exhibits excellent electrochemical performance. The specific capacitance can reach 157.8 F g−1, and the capacitance retention rate is 93% after 3000 GCD. All-solid-state supercapacitor (ASSC-X) is assembled using PAAm/IL-X electrolyte and PEDOT/CC electrodes. The energy density of ASSC-X can reach 14.22 Wh kg−1 satisfying the require of energy density for commercial devices. Interestingly, its capacitance performance of the device ASSC-X was increased by 5% at 90 °C. These high electrochemical properties indicate the potential of PAAm/IL-X as an electrolyte/separator for safe SCs. [ABSTRACT FROM AUTHOR]