Cl^-/SO₃^2--Codoped Poly(3,4-ethylenedioxythiophene) That Interpenetrates and Encapsulates Porous Fe₂O₃ to Form Composite Nanoframeworks for Stable Lithium-Ion Batteries

Penetrating into the inner surface of porous metal-oxide nanostructures to encapsulate the conductive layer is an efficient but challenging route to exploit high-performance lithium-ion battery electrodes. Furthermore, if the bonding force on the interface between the core and shell was enhanced, the structure and cyclic performance of the electrodes will be greatly improved. Here, vertically aligned interpenetrating encapsulation composite nanoframeworks were assembled from Cl^-/SO₃^2--codoped poly(3,4-ethylenedioxythiophene) (PEDOT) that interpenetrated and coated on porous Fe₂O₃ nanoframeworks (PEDOT-IE-Fe₂O₃) via a one-step Fe³⁺-induced in situ growth strategy. Compared with conventional wrapped structures and methods, the special PEDOT-IE-Fe₂O₃ encapsulation structure has many advantages. First, the codoped PEDOT shell ensures a high conductive network in the composites (100.6 S cm^-1) and provides interpenetrating fast ion/electron transport pathways on the inner and outer surface of a single composite unit. Additionally, the pores inside offer void space to buffer the volume expansion of the nanoscale frameworks in cycling processes. In particular, the formation of Fe-S bonds on the organic-inorganic interface (between PEDOT shell and Fe₂O₃ core) enhances the structural stability and further extends the cell cycle life. The PEDOT-IE-Fe₂O₃ was applied as lithium-ion battery anodes, which exhibit excellent lithium storage capability and cycling stability. The capacity was as high as 1096 mA h g^-1 at 0.05 A g^-1, excellent rate capability, and a long and stable cycle process with a capacity retention of 89% (791 mA h g^-1) after 1000 cycles (2 A g^-1). We demonstrate a novel interpenetrating encapsulation structure to highly enhance the electrochemical performance of metal-oxide nanostructures, especially the cycling stability, and provide new insights for designing electrochemical energy storage materials.