<i>In Situ</i> Dealloying of Bulk Mg₂Sn in Mg-Ion Half Cell as an Effective Route to Nanostructured Sn for High Performance Mg-Ion Battery Anodes

Abstract

Nanostructured Sn as negative electrode material in Mg-ion batteries suffers from very slow magnesiation kinetics when its nanoscale feature sizes are not in the sub-100 nm range. Herein, we use electrochemical experiments in combination finite element modeling (FEM) to demonstrate a cost-effective route to nanostructured Sn for high performance Mg-ion battery anodes. Using FEM we found that antagonistic stresses developed during dealloying of Mg2Sn induce pulverization of the dealloyed material and formation of nanostructured Sn with the characteristic feature size in the sub-100 nm range. These results were further confirmed through electrochemical experiments using a Mg half-cell consisting of bulk Mg2Sn particles with an average characteristic size larger than 10 μm as the working electrode, cycled versus Mg metal as counter and reference electrodes, and all-phenyl complex (APC) electrolyte. Ex situ electron microscopy and diffraction techniques were used to study the working electrode material in the pristine, demagnesiated, and remagnesiated forms. The results suggest that the starting micrometer-sized Mg2Sn particles are converted into nanostructured β-Sn with characteristic sizes ranging from 10 to 50 nm during the first demagnesiation. Electrochemical performance of the in situ formed nanostructured Sn was further investigated during subsequent (de)magnesiation cycles in combination with electrochemical impedance spectroscopy (EIS). EIS studies suggest the formation of passive films on the Mg2Sn electrode. A reversible capacity of 300 mAh/g was demonstrated over 150 cycles at the rate of C/5 after application of a combined sequence of regular galvanostatic cycling with an oxidative pulse to control the passive film formation. This work is expected to open new avenues for cost-effective routes to high performance alloy-type Mg-ion battery anodes without complex nanosynthesis steps.