Kim Chaewon, Hwang Useul, Lee Sangjin, Han Young-Kyu
Department of Energy and Materials Engineering, Dongguk University-Seoul, Seoul 04620, Republic of Korea.
Nanomaterials (Basel). 2023 Oct 30;13(21):2868. doi: 10.3390/nano13212868.
Germanium, a promising electrode material for high-capacity lithium ion batteries (LIBs) anodes, attracted much attention because of its large capacity and remarkably fast charge/discharge kinetics. Multivalent-ion batteries are of interest as potential alternatives to LIBs because they have a higher energy density and are less prone to safety hazards. In this study, we probed the potential of amorphous Ge anodes for use in multivalent-ion batteries. Although alloying Al and Zn in Ge anodes is thermodynamically unstable, Mg and Ca alloys with Ge form stable compounds, MgGe and CaGe that exhibit higher capacities than those obtained by alloying Li, Na, or K with Ge, corresponding to 1697 and 1771 mA·h·g, respectively. Despite having a slightly lower capacity than Ca-Ge, Mg-Ge shows an approximately 150% smaller volume expansion ratio (231% vs. 389%) and three orders of magnitude higher ion diffusivity (3.0 × 10 vs. 1.1 × 10 cm s) than Ca-Ge. Furthermore, ion diffusion in Mg-Ge occurs at a rate comparable to that of monovalent ions, such as Li, Na, and K. The outstanding performance of the Mg-Ge system may originate from the coordination number of the Ge host atoms and the smaller atomic size of Mg. Therefore, Ge anodes could be applied in multivalent-ion batteries using Mg as the carrier ion because its properties can compete with or surpass monovalent ions. Here, we report that the maximum capacity, volume expansion ratio, and ion diffusivities of the alloying electrode materials can be understood using atomic-scale structural properties, such as the host-host and host-ion coordination numbers, as valuable indicators.
锗作为一种用于高容量锂离子电池（LIBs）负极的有前景的电极材料，因其大容量和极快的充放电动力学而备受关注。多价离子电池作为LIBs的潜在替代品受到关注，因为它们具有更高的能量密度且更不易发生安全隐患。在本研究中，我们探究了非晶态锗负极用于多价离子电池的潜力。尽管在锗负极中合金化铝和锌在热力学上是不稳定的，但镁和钙与锗形成稳定的化合物MgGe和CaGe，它们表现出比锂、钠或钾与锗合金化时更高的容量，分别对应1697和1771 mA·h·g。尽管Mg-Ge的容量略低于Ca-Ge，但Mg-Ge的体积膨胀率比Ca-Ge小约150%（231%对389%），离子扩散率比Ca-Ge高三个数量级（3.0×10对1.1×10 cm²/s）。此外，Mg-Ge中的离子扩散速率与锂、钠和钾等单价离子相当。Mg-Ge体系的优异性能可能源于锗主体原子的配位数和镁较小的原子尺寸。因此，锗负极可应用于以镁作为载流子离子的多价离子电池，因为其性能可与单价离子竞争或超越单价离子。在此，我们报告合金化电极材料的最大容量、体积膨胀率和离子扩散率可以用原子尺度的结构性质来理解，例如主体-主体和主体-离子配位数，这些是有价值的指标。
