Silicon sponge is considered as a promising anode material for lithium battery because of the preformed meso/macro porous structures in silicon sponge that can accommodate large volume expansion during the lithiation process. It has been proved to have higher electrochemical performances. Temperature dependent HP 129Xe NMR has been applied to investigate the structure and porosity of four silicon sponge materials with varying pore and particle sizes: 20n 50u, 20n 5u, 50n 50u, and 50n 5u. Temperature dependent chemical shifts and the line-widths of the HP 129Xe NMR spectra provide the information not only on pore sizes and structures, but also the homogeneity of the pore surface and interconnectivity of the pores. The 129Xe NMR data reveal non-uniform porosity and irregular micropore structures in all silicon sponge materials whereas nitrogen adsorption data only show contrasting pore size distributions for 20 nm and 50 nm pores regardless of particle sizes. At low temperature, Xe principally occupies the micropores and at high temperature, Xe starts to percolate into a larger mesopores. Relative narrow peaks observed for all four samples at low temperature suggest the presence of uniform micropores inside the larger meso/macropore channels. The broader Xe NMR peaks observed at higher temperature is due to the exchanges of Xe among several different types of pore environments. The HP 129Xe NMR data provided detailed information on the structure and connectivity of the pores for each material. Such information is useful for a better understanding of the relationship between porous structures and their corresponding electrochemical properties in order to have a better design of novel electrodes. This study has demonstrated that HP 129Xe NMR is a unique tool for probing structures, uniformity and connectivity of the pores, complementary to other characterization techniques.

Probing structures and porosity in novel nanostructured electrode materials

251st National Meeting (2016)

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