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Probing Lithium Germanide Phase Evolution and Structural Change in a Germanium-in-Carbon Nanotube Energy Storage System

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journal contribution
posted on 25.02.2015, 00:00 by Wei Tang, Yanpeng Liu, Chengxin Peng, Mary Y. Hu, Xuchu Deng, Ming Lin, Jian Zhi Hu, Kian Ping Loh
Lithium alloys of group IV elements such as silicon and germanium are attractive candidates for use as anodes in high-energy-density lithium-ion batteries. However, the poor capacity retention arising from volume swing during lithium cycling restricts their widespread application. Herein, we report high reversible capacity and superior rate capability from core–shell structure consisting of germanium nanorods embedded in multiwall carbon nanotubes. To understand how the core–shell structure helps to mitigate volume swings and buffer against mechanical instability, transmission electron microscopy, X-ray diffraction, and in situ 7Li nuclear magnetic resonance were used to probe the structural rearrangements and phase evolution of various Li–Ge alloy phases during (de)­alloying reactions with lithium. The results provide insights into amorphous-to-crystalline transition and lithium germanide alloy phase transformation, which are important reactions controlling performance in this system.