Facile fabrication of reticular polypyrrole-silicon core-shell nanofibers for high performance lithium storage

Silicon is the most promising anode material to replace graphite in lithium ion batteries due to its high theoretical capacity of 4200 mAh g ^-1. However, the enormous volume expansion of bulk Si during the lithiation process results in severe electrode degradation and capacity decay. Extensive research effort has been devoted to fabricating nanostructured Si-based materials to improve the capacity cycling stability. Herein, a facile two-step approach is developed for the fabrication of novel three-dimensional (3D) nanoarchitectures composed of polypyrrole-silicon (PPy-Si) core-shell nanofibers. Electropolymerized PPy nanofibers are utilized as the flexible substrate for the deposition of Si thin films via a chemical vapor deposition (CVD) procedure. In this well-designed configuration, the PPy nanofibers are favorable for facile charge delivery and gathering, while the porosity of the electrode can efficiently cushion the volume expansion of Si. The electrode delivers a high reversible capacity above 2800 mAh g ^-1 with appealing cycling stability (∼91% capacity retained after 100 cycles). The rate capability of the electrode is also remarkable with a high capacity and stability. It is revealed that the reticular nanofibers' morphology is well preserved after repeated lithium insertion and extraction, which certainly indicates the superiority of our electrode design. This fabrication approach can also be extended to other electrodes for electrochemical energy conversion and storage.