Investigation of crack patterns and cyclic performance of Ti–Si nanocomposite thin film anodes for lithium ion batteries

Three different Ti–Si nanocomposite thin films are prepared by the co-sputtering method with Si target and Ti target. The film thickness ranges between 250 and 480 nm. X-ray diffraction (XRD), high resolution transmission electron miscopy (HRTEM) and X-ray photoelectron spectroscopy (XPS) reveal significant charge transfer between Ti and Si and uniform dispersion of Ti–Si alloy nanograins in the amorphous Si thin films. It is found that decreasing the grain size of the TixSiy alloy below 2 nm, can improve the cyclic performance over pure Si thin film electrodes and those containing larger Ti–Si grains. This is mainly related to the improved mechanical properties that result from dispersing small grains of Ti–Si. The throughout thin film cracks formed after 10 electrochemical cycles are finer and more curved compared to the other thin films with the same film thickness. Furthermore, the width of the cracks, as well as, the area and junction angles of the remained fractured particle size of all electrode films considered, is compared and analyzed, after 10 cycles.

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► Ti-Si nanocomposite thin films with smaller TixSiy alloy grain dispersed within an amorphous silicon matrix results in better cyclic performance than an amorphous pure silicon thin film, which is directly related to its enhanced crack resistance.
► A theoretical model is applied to predict the smallest size of the fractured particles in all thin films.
► The cracks are described in statistical nature.