Dendrite-structured FeF2 consisting of closely linked nanoparticles as cathode for high-performance lithium-ion capacitors

Lithium-ion capacitors (LICs) are regarded as a good choice for next-generation energy storage devices, which are expected to exhibit high energy densities, high power densities, and ultra-long cycling stability. Nevertheless, only a few battery-type cathode materials with limited kinetic properties can be employed in LICs, and their electrochemical properties need to be optimized urgently. Here, we exploit a new dendrite-structured FeF2 consisting of closely linked primary nanoparticles using a facile solvothermal method combined with the subsequent annealing treatment. This particular architecture has favorable transport pathways for both lithium ions and electrons and exhibits an ultrafast charge-discharge capability with high reversible capacities. Furthermore, a well-designed LIC employing the prepared dendrite-structured FeF2 as the battery-type cathode and commercialized activated carbon (AC) as supercapacitor-type anode was constructed in an organic electrolyte containing Li ions. The LIC operates at an optimal voltage range of 1.1-3.8 V and shows a maximum high energy density of 152 W h kg(1) and a high power density of 4900 W kg(1) based on the total mass of cathode and anode. Long-term cycling stability (85% capacity retention after 2000 cycles) was achieved at 1 A g(1) . This work suggests that the dendrite-structured FeF2 is a prime candidate for high-performance LICs and accelerates the development of hybrid ion capacitor devices. (C) 2020 Science Press and Dalian Institute of Chemical Physics, Chinese Academy of Sciences. Published by ELSEVIER B.V. and Science Press. All rights reserved.

Automated summary

In this study, a new dendrite-structured FeF2 was utilized to construct a high-performance LIC with high energy density, high power density, and ultra-long cycling stability. The LIC demonstrated excellent charge-discharge capability and cycling stability, making it a promising candidate for next-generation energy storage devices.