A hybrid Si@FeSi<inf>y</inf>/SiO<inf>x</inf> anode structure for high performance lithium-ion batteries via ammonia-assisted one-pot synthesis

Abstract

© The Royal Society of Chemistry 2015. Synthesised via planetary ball-milling of Si and Fe powders in an ammonia (NH3) environment, a hybrid Si@FeSiy/SiOxstructure shows exceptional electrochemical properties for lithium-ion battery anodes, exhibiting a high initial capacity of 1150 mA h g-1and a retention capacity of 880 mA h g-1after 150 cycles at 100 mA g-1; and a capacity of 560 mA h g-1at 4000 mA g-1. These are considerably high for carbon-free micro-/submicro-Si-based anodes. NH3gradually turns into N2and H2during the synthesis, which facilitates the formation of highly conductive FeSiy(y = 1, 2) phases, whereas such phases were not formed in an Ar atmosphere. Milling for 20-40 h leads to partial decomposition of NH3in the atmosphere, and a hybrid structure of a Si core of mixed nanocrystalline and amorphous Si domains, shelled by a relatively thick SiOxlayer with embedded FeSi nanocrystallites. Milling for 60-100 h results in full decomposition of NH3and a hybrid structure of a much-refined Si-rich core surrounded by a mantle of a relatively low level of SiOxand a higher level of FeSi2. The formation mechanisms of the SiOxand FeSiyphases are explored. The latter structure offers an optimum combination of the high capacity of a nanostructural Si core, relatively high electric conductivity of the FeSiyphase and high structural stability of a SiOxshell accommodating the volume change for high performance electrodes. The synthesis method is new and indispensable for the large-scale production of high-performance Si-based anode materials.