Constructing non-hierarchical heterostructure Fe2O3/Fe2F5 porous spheres via precursor self-adsorbed fluoride ions for enhanced lithium- ion storage

Transition metal oxides have been considered as the next lithium-ion batteries (LIBs) anode materials because of their ultrahigh specific capacity, tunable redox reaction, high stability, and low cost. However, their shortcomings of inherent large volume expansion (except titanium dioxide and vanadium pentoxide), low conductivity, and poor reaction kinetics seriously hinder the practical applications in LIBs. To overcome these problems, non-hierarchical heterostructure Fe2O3/Fe2F5 porous spheres (NHFs) are designed and successfully prepared by the simultaneously adsorption of fluoride ions during the formation of the precursor with a facile one-pot self-assembly approach. Compared with traditional counterparts, the NHF exhibits high structural stability and improved reaction dynamics upon repeated electrochemical lithiation/delithiation. Furthermore, NHF exhibits an outstanding reversible capacity of 765 mA h g−1 at the current density of 0.2 A g−1, an excellent rate capability of 265 mA h g−1 at 10 A g−1, and an eminent cyclability with a capacity retention of 87.4% after 3000 cycles. The non-hierarchical heterostructure Fe2O3/Fe2F5 porous spheres (NHFs) provide plenty of space to buffer the volume expansion and improve the stability of the structure during the lithiation/delithiation. In addition, the Fe2F5 pyrochlore phase does not contain Fe–F octahedral chains, and the corner-sharing of FeF6 octahedral units are linked in a more random way to form a meandering ion channel, which provides enough space for electrolyte access and alleviates the volume expansion during cycling process. More importantly, with the introduction of F ions and oxygen vacancies, the pseudocapacitive effect and conductivity of the NHF can be effectively improved, so as to effectively improve the reaction kinetics of the material in the process of charging/discharging. [Display omitted] •Fluorine doping is realized by the self-adsorption of precursor.•Non-hierarchical heterostructure of Fe2O3/Fe2F5 spheres can greatly improve the cycling stability.•Excellent capacity retention of 87.4% is maintained after 3000 cycles at 10 A g−1.•The pseudocapacitance effect enhances the reaction kinetics of NHF.