Real-time in situ TEM studying the fading mechanism of tin dioxide nanowire electrodes in lithium ion batteries

Fading mechanism of tin dioxide (SnO2) electrodes in lithium ion batteries has attracted much attentions, which is of great importance for the battery applications. In this paper, electrochemical lithiation-delithiation cycles of individual SnO2 nanowires were conducted in situ in a high-resolution transmission electron microscopy (TEM). Major changes in volume with expansions of 170%similar to 300% on SnO2 nanowire electrodes were observed during the first lithiation process in electrochemical cycling, including conversion reaction of SnO2 precursor to Li2O matrix and active lithium host Sn, and alloying of Sn with Li to form brittle Li-Sn alloy. SnO2 nanowire electrodes were inclined to suffer from thermal runaway condition in the first two cycles. During cycling, morphology and composition evolution of SnO2 nanowire electrodes were recorded. Cyclic lithiation and delithiation of the electrode demonstrated the phase transition between Li13Sn5 and Sn. Metallic Sn clusters were formed and their sizes enlarged with increasing cycle times. Detrimental aggregation of Sn clusters caused pulverization in SnO2 nanowire electrodes, which broke the conduction and transport path for electrons and lithium ions. The real-time in situ TEM revealed fading mechanism provides important guidelines for the viable design of the SnO2 nanowire electrodes in lithium ion batteries.