Highly Cross-Linked 3D ε-Fe2O3 Networks Organized by Ultrathin Nanosheets as High-Performance Anode Materials for Lithium-Ion Storage

The rational design and engineering of threedimensional (3D) micro-/nano-architectures still remains a technological challenge for electrochemical energy storage materials. In the current work, a facile and scalable structural engineering strategy is described for the synthesis of highly cross linked 3D epsilon-Fe2O3 networks via an in situ manipulation of the molecular framework-engaged reactions. The as-obtained epsilon-Fe2O3 with a large specific surface area and abundant mesopores possesses a 3D interlocked architecture organized by ultrathin nanosheets. The formation mechanism of this unique structure is explored, which is shown to be Fe(CN)64--mediated molecular level template action leading to the self-assembly of a 3D framework. As a conversion-type anode for LIBs, the optimized epsilon-Fe2O3 networks exhibit a high reversible specific capacity, good rate capability, as well as long-term stability, with a reversible capacity of 953.8 mAh g-1 that is retained beyond 600 cycles at 1.0 A g-1. In addition, the excellent Li storage performance can be ascribed to the microarchitectured epsilon-Fe2O3 networks, which provide multiscale dimensions, mesoporous structure, some oxygen deficiencies, as well as good structural integrity upon prolonged cycling. Furthermore, the experimental results and DFT calculations showed that epsilon-Fe2O3 was able to form a key Li5Fe5O8-x phase during the lithiation/delithiation process, in which the structural properties of epsilon-Fe2O3 inherently favor the intercalation of Li+ ions within epsilon-Fe2O3, thus leading to the experimentally observed high performance rates.