Nano-Level Homogeneity of SiGe-Cu Composite Anodes
Authors: Alvi Sajid Ali , Fazi Andrea , Bäcke Olof , Jozami Ignacio , Colliander Magnus , Akhtar Farid , Thuvander Mattias , Johansson Patrik 
Published: December 2024

Employing alloy anodes based on Si, Ge, Sn, etc. can increase the energy density of lithium-ion batteries (LIBs) by their high gravimetric capacity.1 Their large volumetric expansion during lithiation, however, leads to cracks and solid electrolyte interphase (SEI) breakdown, followed by pulverization.2 Alloy engineering, creating composite alloys via ball milling of e.g. an active Si-phase embedded in an inactive matrix to buffer volume expansion, is one alternative approach/remedy.3-6 But the homogeneity of the alloy created varies with the processing conditions, such as the ball milling material (steel/WC/ZrO2), speed and duration, as well as the diameter and number of balls.
As proof-of-concept and to learn more about the dependency on high-energy ball milling conditions, we have here synthesized SiGeCu (SGC) composite alloy anodes. Cu forms in situ Cu3Ge, which enhances electrical conductivity and acts as the buffer phase for SiGe. Atom probe tomography (APT) is used to quantify the nano-level homogeneity, and this is correlated vs. the electrochemical performance in LIB half-cells of Li/1 M LP57 + 10% FEC/SGC, with the composite anode subject to different ball milling durations. The shorter duration (40 h) leads to formation of an isolated Si-phase (Figure 1a) and this half-cell has quite different characteristics as compared to the half-cell when only SiGe and Cu3Ge phases are formed (longer duration, 60 h) (Figure 1b) – especially w r t the reproducibility of the capacity, proving the role and importance of nano-level homogeneity.
Figure 1: a) the isolated Si-phase as revealed by APT, and b) cycling data for the Li/1 M LP57 + 10% FEC/SGC half-cells – two for each ball-milling duration produced SGC.

References

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Figure 1