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%～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.