Electrochemical Performance of Lithium-Ion Batteries Using Si-Based Alloys as Anode Materials

Silicon (Si) is a promising element as an anode material for lithium-ion batteries (LIBs) due to its exceptionally high theoretical capacity (~3579 mAh/g). However, in practical applications, Si anodes face significant challenges due to substantial volume expansion (~300 %) during lithiation, which leads to structural degradation and rapid capacity fading. We present here an innovative approach to the development of Si-based alloys as anode materials synthesized by a melt spinning process. Finally, we propose a unique approach to significantly enhance electrochemical performance.<br/>In this study, we introduced a copper (Cu) as an alloying element into the silicon matrix for the purpose of enhancing electrical conductivity and structural stability, and reducing the volumetric change that occurs during cycling. The melt spinning (MS) process ensures the uniform distribution of Cu within the silicon matrix by rapid quenching of molten Si alloys. We optimized the size of inclusions affecting enhanced structural stability of the Si alloys by mitigating volumetric changes during charge-discharge cycles. Furthermore, we anticipate that the addition of Cu will improve electric conductivity, as the melt spinning process can yield a homogeneous Cu dispersion with fine microstructures. This should suppress the capacity fading typically observed in traditional silicon anodes due to their volume expansion during the cycling.<br/>Following the MS synthesis of the Si-based alloys, ball milling was employed to produce small and uniform particles with an optimized particle size of 5.6 µm (D50). Structural characterization using scanning electron microscopy (SEM) and X-ray diffraction (XRD) revealed the formation of fine intermetallic particles, which will provide enhanced mechanical stability to the silicon matrix. The electrochemical characterization was performed using galvanostatic charge-discharge tests with the Si alloy-graphite composite electrode in a 2023 coin-type cell. The Si alloy demonstrated an initial reversible capacity of 505.6 mAh/g at a current density of 0.2C, with a coulombic efficiency of 92.75%. The cell demonstrated high cycling stability, retaining over 88% of its initial capacity after 30 cycles. The addition of Cu to the alloy matrix has resulted in enhanced charge transport and reduced volume expansion, thereby enhancing the overall structural integrity of the anode materials as expected.<br/>This study demonstrates that Cu-containing Si alloys produced by the MS technique enhance the electrochemical performance of LIBs. The incorporation of Cu has proved beneficial in improving both electrical conductivity and structural stability, particularly by alleviating volume expansion issues of the anode. This has resulted in enhanced cycling stability and capacity retention. The present work demonstrates that Cu-containing Si alloys are well-suited for high-performance LIB applications. Further work is underway, with a focus on the further development of Si alloys and the scale-up of the melt spinning process for commercial production.