Study on Morphology Control of Germanium-based Anode Materials for Lithium-ion Batteries

Abstract

Lithium-ion batteries (LIBs) have been used to power portable electronic devices and electric vehicles. However, current LIBs consisting of graphite anode and LiCoO2 cathode do not meet increasing requirements of more advanced applications with higher energy density and higher power density. Thus, it is important to develop new promising alternative electrode materials with higher gravimetric and volumetric capacity than conventional ones. Silicon (Si) and germanium (Ge) have attracted great attention as promising anode materials due to their high capacity (>1000 mAh g-1) and relative low reaction potential (vs. Li/Li+). Even though Ge has attracted less attention than Si owing to its higher cost, the increased interest in Ge-based materials might bring about a decrease in its cost as a result of the abundance of Ge as much as tin in the Earth’s crust. Compared to Si, Ge has several advantages including high electrical conductivity (104 times higher than in Si) and exceptional lithium ion diffusivity (400 times greater than in Si at room temperature) allowing high rate capability. Similar to Si, however, one critical issue of Ge anode is its drastic volume change of >230% which may lead to the cracking and pulverization of particles, resulting in a poor cycle life. To solve this problem, synthesis of nanostructured Ge is important. Yet, synthetic routes that can satisfy cost-effective large-scale production remain significant challenges. One of the most effective methods producing macro- and/or nano-porous materials and pure materials is metallothermic reduction process, and is simple, cost-effective and scalable approach. Herein, we report a facile, cost-effective and large-scale zincothermic reduction route for the synthesis of mesoporous germanium from cost-effective germanium oxide particles ranging from 420 to 600 oC. This zincothermic reactions have several advantages including (i) a successful synthesis of germanium particles at low temperature (~450 oC), (ii) accommodation of a large volume change due to a mesoporous structure, and (iii) a cost-effective scalable synthesis (staring from inexpensive metal oxides). An optimized mesoporous germanium anode exhibits a reversible capacity of ~1400 mAh g-1 after 300 cycles at 0.5 C rate and stable cycling in full-cell consisting LiCoO2 cathode having high energy density.