Ultrasmall Iron Fluoride Nanoparticles Embedded in Graphitized Porous Carbon Derived from Fe‐Based Metal Organic Frameworks as High‐Performance Cathode Materials for Li Batteries

Abstract

Iron‐based metal organic framework (MOF) MIL‐53 is used as a precursor and self‐template to synthesize a 3D porous carbon/FeF3 ⋅ 0.33 H2O composite in situ. We find that the organic ligands in iron‐containing MOFs can convert into highly graphitized carbon with the catalysis of central Fe atoms. The FeF3 ⋅ 0.33 H2O nanoparticles formed after fluorination and dehydration are surrounded by highly graphitized carbon. In the composite, the graphitized 3D porous carbon can provide passageways for electron transport and ultrasmall FeF3 ⋅ 0.33 H2O nanoparticles facilitate the diffusion of Li ions. The composite shows excellent performance for the Li storage. A capacity of 86 mAh g−1 can be reached at an ultra‐high rate of 20 C. Even after 300 charge−discharge cycles at 5 C, the capacity remains at 113 mAh g−1.

Improved Electrochemical Performance of FeF3 by Inlaying in a Nitrogen‐Doped Carbon Matrix

“…[6,27,28,79] Meanwhile, the surplus carbon between distant particle also promoted the transfer of charges over wide range, greatly reducing the charge transfer resistance. [69] The above description also explains the reasons why FeF 3 @N doped carbon composites exhibited a superior performance at high current. [32,69,92] The more important is that the N atoms were doped into the carbon structure, and binding to C atoms in the form of pyrrole nitrogen (Figure 7c).…”

“…[93][94][95] This not only contributed to further reduce the charge transfer resistance, but also facilitated rapid electrochemical reaction of Li + with the adjacent FeF 3 . [69] The above description also explains the reasons why FeF 3 @N doped carbon composites exhibited a superior performance at high current.…”

“…The pores increased the contact area between the particles and the electrolyte, which facilitates the large exchange of Li + (porous carbon skeleton in Figure 7a). [32,69,92] The more important is that the N atoms were doped into the carbon structure, and binding to C atoms in the form of pyrrole nitrogen (Figure 7c). [6,27,28,79] Meanwhile, the surplus carbon between distant particle also promoted the transfer of charges over wide range, greatly reducing the charge transfer resistance.…”

“…The discharge specific capacity of FeF 3 /carbon hybrids were greatly improved due to the advantage effects of carbon. The carbon not only enhance the conductive of FeF 3 grains, [28,69] but also to facilitate the rapid transmission of electrons between particles. [70] Meanwhile, the addition of carbon increased the surface area of composites and significantly enhanced the contact area between the electrolyte and the FeF 3 particles.…”

“…[70] Furthermore, carbon structure provided buffer space for the volume changes caused by insertion and extraction of Li + . [32,69,92] The more important is that the N atoms were doped into the carbon structure, and binding to C atoms in the form of pyrrole nitrogen (Figure 7c). The unbound electron around N nucleus contributed to further increase conductivity, while the positions doped N atoms were act as active sites to adsorb lithium ions.…”