Synergistic Effects of Ge and Si on the Performances and Mechanism of the Ge_xSi_1–x Electrodes for Li Ion Batteries

Abstract

While silicon is attractive due to its high capacity, germanium possesses a superior electronic and ionic conductivity, and is able to support much higher cycle rates. In the present paper, we investigate the electrochemical performances of Ge x Si 1−x -based electrodes with x = 0, 0.25, 0.5, 0.75, and 1. The Ge x Si 1−x samples are easily prepared by short ball milling. X-ray diffraction (XRD), Raman spectroscopy, and scanning electron microscopy−energy-dispersive X-ray spectrometry confirm that Si/Ge solid solutions are obtained with different ratios. We show that appropriate formulations of Ge x Si 1−x electrodes can produce excellent cycling performances, with an increased capacity retention compared to that of Sibased electrodes only, and with higher capacity than that of Ge-based electrodes cycled in the same conditions. For Ge 0.1 Si 0.9 , a capacity of 1138 (mA h)/g is retained after 50 cycles, and is stabilized around 1020 (mA h)/g after 100 cycles. Moreover, a limited irreversible capacity is lost on the first discharge. The electrochemical data suggest that the copresence of Si and Ge in the same phase creates a synergistic beneficial effect on the Ge x Si 1−x electrochemical performances. The electrochemical behavior of Ge x Si 1−x is investigated for the first time by in situ XRD, and an original mechanism is highlighted with the reversible formation of a new Li 15 (Si x /Ge y ) 4 ternary phase at the end of discharge. Interestingly, a decrease of the cell parameter of this ternary phase is observed continuously from the end of discharge to the beginning of charge, which might be correlated to a loss of germanium of the lithiated Li 15 (Si x /Ge y ) 4 phase.

Electrolytic Formation of Crystalline Silicon/Germanium Alloy Nanotubes and Hollow Particles with Enhanced Lithium‐Storage Properties

“…[13] Recently,i t has been demonstrated that the combination of Si and Ge (Si/ Ge) either by alloying Si with Ge (SiGe) or by employing SiGe heterostructures can take full advantages of the merits from these two materials with modified physicochemical properties and enhanced lithium-storage performance. [14][15][16][17][18][19] However,d ramatic volume changes associated with the lithium insertion and extraction reactions (up to 400 %) lead to pulverization of the Si/Ge based materials and thus poor cycling life of electrodes. [20] One typical approach to overcome this problem is the design and synthesis of complex micro-/nanostructured electrodes that can maintain their structural integration after many cycles.…”

Microscale Alloy Type Lithium Ion Battery Anodes

“…[1][2][3] Silicon (Si), germanium (Ge), tin (Sn), and aluminum (Al) all can alloy with Li at low electrochemical potentials relative to Li/Li+. 4,5 At the high end, Si can store more than 10 times the amount of Li than the state-of-the-art anode material, graphite, can store. 1 Unfortunately, these materials also undergo an approximately 300% volume expansion during the alloy process.…”

“…Researchers have taken several approaches to studying the material, including making powders of varying composition, growing thin films, in situ transmission electron microscopy (TEM) testing of single particles, computational simulation, and in situ atomic force microscopy (AFM) testing. 1,5,[7][8][9] The in situ AFM testing confers the benefits of visualizing nano-and microscale particles in conventional electrolytes with the ability to use conventional electrochemical testing.…”

Magnesiothermic Reduction‐Enabled Synthesis of Si−Ge Alloy Nanoparticles with a Canyon‐Like Surface Structure for Li−Ion Battery

“…[5] For example, the low capacity of Ge is improved by alloying with Si, whereas the inferior Li-ion diffusivity (6.25 10 À12 cm 2 s À1 for Ge; 1.9 10 À14 cm 2 s À1 for Si) and poor electrical conductivity (2.1 S m À1 for Ge; 1.6 10 À3 S m À1 for Si) of Si are enhanced when alloyed with Ge. [8] In particular, extensive studies demonstrated that alloying Si with Ge provides an effective means to improve the capacity, cycling performance, and rate performance. [8] In particular, extensive studies demonstrated that alloying Si with Ge provides an effective means to improve the capacity, cycling performance, and rate performance.…”