Discovering a Dual-Buffer Effect for Lithium Storage: Durable Nanostructured Ordered Mesoporous Co-Sn Intermetallic Electrodes

Lithiation-delithiation reactions in Li-ion batteries do exhibit a huge electrochemically driven volume change of the anode material between the lithium-free and lithiated-host states, which results in a gradually fading capacity. Minimizing this volume change of the electrode during cycling is essential to achieve stable electrochemical behavior and thus for innovating design of electrode materials for Li storage. Here, ordered mesoporous CoSn intermetallic anode materials with various Co/Sn atomic ratios are developed. A dual-buffer effect is discovered that accommodates the volume changes in the electrode material by not only repeatedly generating void nanospaces but also by incorporating electrochemically inactive elements. Novel insights into the nanostructural changes of electrode materials during the lithiation-delithiation process are obtained by in operando small angle X-ray scattering. The degrees of volume change and nanoscopic order are found to be highly dependent on the Co contents in the mesoporous CoSn intermetallic anode materials, being possible to achieve a durable nanostructured electrode upon prolonged cycling. Ordered mesoporous intermetallic Co_xSn_y electrode materials with various Co/Sn ratios are successfully constructed. In operando small angle X-ray scattering relveals the nanostructural changes of electrode materials during the lithiation-delithiation process. A dual-buffer effect accomodating the volume changes in the mesoporous intermetallic electrodes is discovered.