In situ TEM investigation of large crystal formation in lithiated SnO2 anode assisted by electron beam irradiation

The formation of large crystals in an anode during the working cycle is harmful to the lithium-ion battery's capacity and cycling performance. However, the underlying mechanism is not clearly revealed, which significantly hinders the development of strategies to suppress the formation of large particles. Here, we studied the formation mechanism of large crystals with the assistance of electron beam irradiation. The large crystal formed after the lithiation of SnO2 was identified as Li4.4Sn. The formation of such large Li4.4Sn is significantly promoted by the high Li+ concentration in the sample, which contributes to the formation of more Li4.4Sn/Li2O interfaces. Within the Li+ supersaturation environment, a considerable number of Li4.4Sn nanocrystals with larger size are formed. Theoretical calculation results revealed that the Li4.4Sn/Li2O interface is unstable, which thus drives the aggregation of Li4.4Sn nanocrystals. Moreover, by reducing the Li+ concentration and the size of SnO2 below 15 nm, the formation of large Li4.4Sn crystals can be effectively suppressed. This work reveals the formation mechanism of large crystals in lithiated SnO2, which may supply enlightening insights into the structural engineering of tin-based anode materials.