Recent experimental results suggest that silicon suboxides (SiOx, x < 2) can be a promising anode material for high performance lithium-ion batteries (LIBs), especially when the oxygen content is relatively low. Very recently, Mullins and coworkers reported that nanostructured Si thin films with homogeneous O incorporation (< 18 at. % O) were able to deliver an excellent capacity (about 2200 mAh/g) and maintain 80 % of the initial reversible capacity even after 300 cycles. Despite the encouraging improvements, the atomistic mechanisms underlying the lithiation of Si-rich oxides remain a puzzling question. In this talk we will present the lithiation behavior in partially oxidized Si at the atomistic level based on density functional theory calculations of the structure, mechanical property, bonding mechanism and energetics of lithiated a-SiO1/3. Our results show that Li atoms can be favorably accommodated by both Si and O atoms. Interestingly, with lithiation, the Si-Li coordination number (CN) is found to monotonically increase up to CNSi-Li ~ 10 in a-Li4SiO1/3, whereas CNO-Li tends to saturate at 6 far before full lithiation, resulting in the formation of Li6O complexes with a unique Oh symmetry. The formation of intriguing Li6O complexes is a new and interesting finding, unlike commonly observed Li2O or other Li-silicates in lithiated SiO or SiO2. The interplay between Li-Si and Li-O interactions facilitates favorable Li incorporation with competitive capacity relative to pure Si. The lithiation voltage for a-SiO1/3 is predicted to be around 0.2-0.8 V, which is within the desirable range for LIB anode application but slightly higher than that of pure Si, the up-shift in voltage profile reflects the more energetically favorable incorporation of Li in a-SiO1/3. Our study highlights the importance of tuning O concentration and spatial distribution in order to maximize the performance of Si suboxide-based anodes.

Intriguing lithiation behavior of Si-rich oxides: A first principles study

247th National Meeting (2014)

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