In situ synthesis of core-shell structured Ge@NC hybrids as high performance anode material for lithium-ion batteries

Abstract

Core-shell structured germanium@nitrogen-doped carbon (Ge@NC) hybrids with well-encapsulated Ge particles within a conductive coating is an ideal anode material for high energy and power density lithium-ion batteries (LIBs). Here, we propose a novel route to synthesize core-shell structured Ge@NC hybrids by the modified in situ spray pyrolysis technique using a mixed spray solution consisting of a Ge precursor as an active material source and polyvinylpyrrolidone (PVP) as a carbon source. It is found that in situ formed submicron Ge (200–800 nm) crystals encapsulated in a N-doped carbon coating, allows the increase of electrical conductivity for Ge with enhanced structural stability. For lithium storage, the Ge@NC hybrids exhibit superior properties compared to that of pure Ge such as excellent long-term cycling stability (917 mAh g−1 with a capacity decay of 0.018% per cycle for 1000 cycles at 1 C) and outstanding rate capability (806 mAh g−1 at 5 C after 400 cycles). The full cell assembled with Ge@NC anode and LiNi0.5Co0.2Mn0.3O2 cathode presents high energy density. Moreover, the spray pyrolysis method allows a yield of ∼4.8 g h−1 with a lab-scale equipment, demonstrating that established industrial processes can be applied to produce Ge-based anodes with sophisticated structures.