One of the most demanding challenges for Na-ion batteries is finding a suitable anode material that will provide high capacity, while at the same time its structure will not degrade during repeated sodiation and desodiation (processes that occur during the operation of cells). A group of researchers from the AGH University of Science and Technology and the Paul Scherrer Institute in Switzerland, conducting research on the ASTRA line, undertook an attempt to find a suitable material, and their studies were published in the journal “Energy Storage Materials”.
Among the many proposed anode materials, antimony attracts the attention of scientists because of its high theoretical capacity and good electrical conductivity. However, at the same time, its significant volume changes during operation can lead to the destruction of the material’s microstructure. A solution to the problem of volume changes can be the application of composite materials, where the matrix alleviates stresses. A research team has obtained a composite material Sb/Sb4O5Cl2/C in which the Sb grains are characterized by a unique shape, branches. This morphology is advantageous for materials characterized by large volume changes when voids between branches are filled during operation. Electrochemical characterization results indicate that the composite material works in a more stable manner than individual phases that work separately.
Through measurements by multiple techniques, it was possible to determine the exact mechanism of sodiation and desodiation of this composite material. Unique operando XAS measurements during cell operation with the proposed anode material and metallic sodium were carried out on the ASTRA line. Measurements at the SOLARIS synchrotron made it possible to observe and understand the incomplete reversibility of the reaction in the first cycle of the material and to identify the source of the additional capacitance observed in sodiation below 0.4 V and in desodiation above 1.0 V.
The activity of three phases was observed in the proposed composite material: Sb, Sb4O5Cl2, and C, and demonstrated high mechanical integrity of the electrode by providing space for volume changes in the branch-like shape. At the same time, the presence of an amorphous matrix (originating from the products of the sodiated Sb4O5Cl2 phase) allowed for buffer expansion and contraction of the material during operation.
Read more on SOLARIS website
Image: SEM picture of examined material.