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Effect of Phosphorus-Doping on Electrochemical Performance of Silicon Negative Electrodes in Lithium-Ion Batteries

Domi, Yasuhiro, Usui, Hiroyuki, Shimizu, Masahiro, Kakimoto, Yuta, Sakaguchi, Hiroki
ACS Applied Materials & Interfaces 2016 v.8 no.11 pp. 7125-7132
Raman spectroscopy, X-ray diffraction, crystal structure, electrochemistry, electrodes, energy, lithium batteries, phase transition, phosphorus, scanning electron microscopy, silicon
The effect of phosphorus (P)-doping on the electrochemical performance of Si negative electrodes in lithium-ion batteries was investigated. Field-emission scanning electron microscopy was used to observe changes in surface morphology. Surface crystallinity and the phase transition of Si negative electrodes before and after a charge–discharge cycle were investigated by Raman spectroscopy and X-ray diffraction. Li insertion energy into Si was also calculated based on computational chemistry. The results showed that a low P concentration of 124 ppm has a meaningful influence on the electrochemical properties of a Si negative electrode; the cycle performance is improved by P-doping of Si. P-doping suppresses the changes in the surface morphology of a Si negative electrode and the phase transition during a charge–discharge cycle. Li insertion energy increases with an increase in the P concentration; Li insertion into P-doped Si is energetically unfavorable, which indicates that the crystal lattice of Si shrinks as a result of the replacement of some Si atoms with smaller P atoms, and therefore, it is more difficult to insert Li into P-doped Si. These results reveal that suppression of the phase transition reduces the large change in the volume of Si and prevents a Si negative electrode from disintegrating, which helps to improve the otherwise poor cycle performance of a Si electrode.