Determination of the Volume Changes Occurring for Conversion/Alloying-Type Li-Ion Anodes upon Lithiation/Delithiation

High-capacity lithium-ion anodes such as alloying-, conversion-, and conversion/alloying-type materials are subjected to extensive volume variation upon lithiation/delithiation. However, a careful examination of these processes at the particle and electrode level as well as the impact of the kind of lithium-ion uptake mechanism is still missing. Herein, we investigated the volume variation upon lithiation/delithiation for a series of conversion/alloying materials with a varying relative contribution of the alloying and conversion reaction, i.e., carbon-coated ZnFe₂O₄, Zn_0.9Fe_0.1O, and Sn_0.9Fe_0.1O₂ by operando dilatometry and ex situ scanning electron microscopy of the electrode cross section. While the theoretical estimation at the particle level indicates a rather large volume expansion of 113% (ZnFe₂O₄) and more, the true volume variation on the electrode level reveals very limited changes of only around 11% (ZnFe₂O₄). Combining the experimental findings with some theoretical considerations highlights the (to a certain extent unexpected) impact of the initial electrode porosity.