Atomistics of the lithiation of oxidized silicon (SiOx) nanowires in reactive molecular dynamics simulations.
Although silicon oxide (SiOx) nanowires (NWs) are recognized as a promising anode material for lithium-ion batteries (LIBs), a clear understanding of their lithiation mechanism has not been reported yet. We elucidate the lithiation mechanism of SiOxNWs at the atomic scale based on molecular dynamics (MD) simulations employing the ReaxFF reactive force field developed through first-principles calculations. SiOxNWs with crystalline Si (c-Si) core and amorphous SiO2(a-SiO2) shell structures of ∼1 nm in thickness show smaller volume expansion than pristine Si NWs, as found in previous experiments. Lithiation into SiOxNWs creates two interfaces: c-Si/a-LixSi and a-LixSi/a-LiySiO2. The mobility of the latter, which is located farther toward the outside of the NW, is slower than that of the former, which is one of the reasons why the thin SiO2layer can suppress the volume expansion of SiOxNWs during lithiation. Another reason can be found from the stress distribution, as the SiOxNWs show stress distribution different from the pristine case. Moreover, the lithiation of SiOxNWs leads to the formation of Li2O and Li4SiO4compounds in the oxide layer, where several Li atoms (not a majority) in Li4SiO4can escape from the compound and diffuse into the c-Si, in contrast to the Li2O case. However, Li atoms that pass through the SiO2layer penetrate into the c-Si preferentially along the 〈110〉 or 〈112〉 direction, similar to the mechanism observed in pristine Si NWs. We expect that our comprehensive understanding of the lithiation mechanism of SiOxNWs will provide helpful guidance for the design of SiOxanodes to obtain better performing LIBs.
Center for Computational Science, Korea Institute of Science and Technology (KIST), Hwarangno 14-gil 5, Seongbuk-gu, Seoul 136-791, Republic of Korea. sangsoo@kist.re.kr and Department of Physics, Hanyang University, 222 Wangsimni-ro, Seongdong-gu, Seoul 133-791, Republic of Korea.
Hyun
H
Jung
Center for Computational Science, Korea Institute of Science and Technology (KIST), Hwarangno 14-gil 5, Seongbuk-gu, Seoul 136-791, Republic of Korea. sangsoo@kist.re.kr.
Byung Chul
BC
Yeo
Center for Computational Science, Korea Institute of Science and Technology (KIST), Hwarangno 14-gil 5, Seongbuk-gu, Seoul 136-791, Republic of Korea. sangsoo@kist.re.kr.
Kwang-Ryeol
KR
Lee
Center for Computational Science, Korea Institute of Science and Technology (KIST), Hwarangno 14-gil 5, Seongbuk-gu, Seoul 136-791, Republic of Korea. sangsoo@kist.re.kr.
Sang Soo
SS
Han