Nanostructured germanium is a promising material for high-performance energy storage devices. However, synthesizing it in a cost-effective and simple manner on a large scale remains a significant challenge. Herein, we report a redox-transmetalation reaction-based route for the large-scale synthesis of mesoporous germanium particles from germanium oxide at temperatures of 420-600 °C. We could confirm that a unique redox-transmetalation reaction occurs between Zn(0) and Ge(4+) at approximately 420 °C using temperature-dependent in situ X-ray absorption fine structure analysis. This reaction has several advantages, which include (i) the successful synthesis of germanium particles at a low temperature (∼450 °C), (ii) the accommodation of large volume changes, owing to the mesoporous structure of the germanium particles, and (iii) the ability to synthesize the particles in a cost-effective and scalable manner, as inexpensive metal oxides are used as the starting materials. The optimized mesoporous germanium anode exhibits a reversible capacity of ∼1400 mA h g(-1) after 300 cycles at a rate of 0.5 C (corresponding to the capacity retention of 99.5%), as well as stable cycling in a full cell containing a LiCoO2 cathode with a high energy density (charge capacity = 286.62 mA h cm(-3)).
Keywords: energy storage devices; germanium anode; mesoporous germanium; redox-transmetalation; zincothermic reduction.