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

Abstract

Abstract 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.