Encasing Si particles within a versatile TiO 2−x F x layer as an extremely reversible anode for high energy-density lithium-ion battery

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Abstract

The chemical phenomena occurring at the electrode-electrolyte interfaces profoundly determine the cycle behavior of a lithium ion battery. In this work, we report that silicon-based anodes can attain enhanced levels of capacity retention, rate performance and lifespan when a versatile protective layer of, F-doped anatase (TiO 2−x F x ), is applied towards taming the interfacial chemistry of the silicon particles. With careful choice of titanium fluoride as a precursor, internal voids can be generated upon in-situ fluoride etching of the native oxide layer and are used to alleviate the mechanical stress caused by volume expansion of silicon during cycling. In the course of F-doping, part of the Ti 4+ (d 0 ) ions in anatase are reduced to Ti 3+ (d 1 ), thereby increasing charge carriers in the crystal structure. Hence, the multifunctional F-doped TiO 2−x coating, not only minimizes the direct exposure of the Si surface to the electrolyte, but also improves the electronic conductivity via inter-valence electron hopping. The best-performing composite electrode, Si@TiO 2−x F x -3 , delivered a satisfactory performance in both half-cell and full-cell configurations. Furthermore, we present a study of 1) the Si valence change at the buried interface using synchrotron based hard X-ray photoelectron spectroscopy, and 2) the phase transformation of the electrode monitored in operando using X-ray diffraction. Based on these characterizations, we observe that the Li + conducting intermediate phase (Li x TiO 2−x F x ) formed inside the surface coating enables deep lithiation and delithiation of the silicon during battery operation, and thus increase the capacity that can be accessed from the electrodes.

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Ma, Y., Desta Asfaw, H., Liu, C., Wei, B., & Edström, K. (2016). Encasing Si particles within a versatile TiO 2−x F x layer as an extremely reversible anode for high energy-density lithium-ion battery. Nano Energy, 30, 745–755. https://doi.org/10.1016/j.nanoen.2016.09.026

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