The Insertion Mechanism of Lithium into Mg2Si Anode Material for Li‐Ion Batteries

Abstract

The reaction mechanism of lithium insertion into Mg 2 Si was studied using various analytic techniques including electrochemical measurements, X-ray diffraction (XRD), and Auger electron spectroscopy (AES). Electrochemical tests demonstrated that 1 mol Mg 2 Si reacted with 3.9 mol Li from which the initial capacity obtained was approximately 1370 mAh/g. Ex situ XRD and AES data showed that lithium intercalated into the Mg 2 Si lattice first followed by alloying with Si and Mg. The degradation mechanism of Mg 2 Si during cycling was investigated because the Mg 2 Si materials degraded rapidly within ten cycles. The electrode material disintegrated and Li remained within the active material after ten cycles. The XRD and scanning electron microscope data suggested that the degradation mechanism of Mg 2 Si was due to the volume change during the alloying/dealloying reaction, and the volume expansion/contraction made the Mg 2 Si electrode materials electrically isolated.

Nanostructured magnesium silicide Mg2Si and its electrochemical performance as an anode of a lithium ion battery

“…Based on the reference data, we suggest that the cathodic peak at 0.02 V is related to the lithiation of Mg [27], while the peaks at 0.16 and 0.20 V are associated with lithium insertion into Mg 2 Si [13]. Finally, the peaks at 0.09, 0.13 and 0.25 V are due to the formation of Li-Si alloys [14,28,29].…”

“…At the same time, the deintercalation of lithium from Li 2 MgSi is associated with the peak at 0.6 V [14]. An extra anodic peak at 0.4 V develops at the second cycle, which corresponds to the further de-alloying of Si.…”

“…Kim et al [14] proposed a three-step mechanism of the electrochemical lithium intercalation into Mg 2 Si. After the initial lithium intercalation limit (1 atom of Li/Mg 2 Si [14]) was reached, the formed Li critical Mg 2 Si decomposed into Li saturated Mg 2 Si, Mg and Li-Si alloys.…”

“…After the initial lithium intercalation limit (1 atom of Li/Mg 2 Si [14]) was reached, the formed Li critical Mg 2 Si decomposed into Li saturated Mg 2 Si, Mg and Li-Si alloys. At the final stage of the lithiation, the formed Mg reacted with Li to form binary Li-Mg intermetallics.…”

Amorphous and nanocrystalline Mg2Si thin-film electrodes

“…[1][2][3] This is due to large volume and particle morphology changes that occur during lithiation and delithiation. Also it is partly due to a relatively low conductivity, such that the electrode performance depends on particle size, morphology and current density.…”