Electrochemical Synthesis of Germanium-Polypyrrole Composite Nanomaterials in Ionic Liquids for the Fabrication of Lithium-Ion Batteries

Abstract

Herein, we report the coating of nanostructured germanium using a polypyrrole (PPy) polymer coat as a composite anode material for the fabrication of lithium-ion batteries. The Ge/PPy composites were synthesized following the direct electrochemical deposition method in an ionic liquid (IL). The results revealed that the coating of PPy on Ge helped realize stable battery cycling and reversible capacities, which were not observed in uncoated Ge. The PPy layers could effectively inhibit side reactions between the electrode and electrolyte. The composition of the solid electrolyte interphase (SEI) formed after lithiation/delithiation cycles were analyzed using the X-ray photoelectron spectroscopy (XPS). Compact SEI layers consisted of decomposed TFSI− anion products such as LiF, Li2S, Li2NS2O4, and Li2CO3 at the Ge-PPy/IL interphase. In contrast, thick SEI layers consisted of not only decomposed TFSI− anion and [Py1,4]+ cation products but also chemically or physically adsorbed IL compounds at the Ge/IL interphase. In addition, the PPy coating could effectively inhibit Ge oxidation, resulting in improved battery capacity.