Abstract
Understanding the lithiation of Si and the resulting formation of amorphous lithium silicides (a-LixSi) has been the subject of numerous studies due to the importance of silicon anodes for next-generation, high-energy-density lithium batteries. Experimental studies have shown that a-LixSi with 2 ≤ x ≤ 3.75 appears as a prominent phase in the phase transformations of Si during lithiation and delithiation, but computational studies have yet to elucidate why. In this work, first-principles molecular dynamics computations were performed to simulate the various immediate steps associated with lithiation and delithiation of Si anodes in a Li-ion half-cell battery. The energy of formation and unit cell volume for relevant LixSi phases and Si have been computed for both crystalline and amorphous states. The first-principles results are utilized to construct lithiation and delithiation pathways and compute the corresponding changes in the voltage, capacity, and cell volume of the anode. These results indicate that multiple pathways are possible during delithiation of c-Li15/4Si and a two-phase delithiation field is energetically favored to occur between a-Li15/4Si and a-Li9/4Si due to a large amorphization energy for Li3Si and a site-dependent amorphization energy for Li9/4Si. In addition, large tensile stresses are generated during the removal of Li atoms from the 48e sites in the Li15/4Si crystalline lattice. These hydrostatic tensile stresses can cause changes to the open-circuit potential, can lead to the fracture of Si or Li15Si4, and may be responsible for the change in the lithiation process from a ledge mechanism to a two-phase mechanism at x ≈ 2.25.
| Original language | English (US) |
|---|---|
| Pages (from-to) | 22775-22786 |
| Number of pages | 12 |
| Journal | Journal of Physical Chemistry C |
| Volume | 123 |
| Issue number | 37 |
| DOIs | |
| State | Published - Sep 19 2019 |
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ASJC Scopus subject areas
- Electronic, Optical and Magnetic Materials
- Energy(all)
- Physical and Theoretical Chemistry
- Surfaces, Coatings and Films
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First-Principles Studies of the Lithiation and Delithiation Paths in Si Anodes in Li-Ion Batteries. / Chan, Kwai S.; Liang, Wu Wei; Chan, Candace K.
In: Journal of Physical Chemistry C, Vol. 123, No. 37, 19.09.2019, p. 22775-22786.Research output: Contribution to journal › Article
}
TY - JOUR
T1 - First-Principles Studies of the Lithiation and Delithiation Paths in Si Anodes in Li-Ion Batteries
AU - Chan, Kwai S.
AU - Liang, Wu Wei
AU - Chan, Candace K.
PY - 2019/9/19
Y1 - 2019/9/19
N2 - Understanding the lithiation of Si and the resulting formation of amorphous lithium silicides (a-LixSi) has been the subject of numerous studies due to the importance of silicon anodes for next-generation, high-energy-density lithium batteries. Experimental studies have shown that a-LixSi with 2 ≤ x ≤ 3.75 appears as a prominent phase in the phase transformations of Si during lithiation and delithiation, but computational studies have yet to elucidate why. In this work, first-principles molecular dynamics computations were performed to simulate the various immediate steps associated with lithiation and delithiation of Si anodes in a Li-ion half-cell battery. The energy of formation and unit cell volume for relevant LixSi phases and Si have been computed for both crystalline and amorphous states. The first-principles results are utilized to construct lithiation and delithiation pathways and compute the corresponding changes in the voltage, capacity, and cell volume of the anode. These results indicate that multiple pathways are possible during delithiation of c-Li15/4Si and a two-phase delithiation field is energetically favored to occur between a-Li15/4Si and a-Li9/4Si due to a large amorphization energy for Li3Si and a site-dependent amorphization energy for Li9/4Si. In addition, large tensile stresses are generated during the removal of Li atoms from the 48e sites in the Li15/4Si crystalline lattice. These hydrostatic tensile stresses can cause changes to the open-circuit potential, can lead to the fracture of Si or Li15Si4, and may be responsible for the change in the lithiation process from a ledge mechanism to a two-phase mechanism at x ≈ 2.25.
AB - Understanding the lithiation of Si and the resulting formation of amorphous lithium silicides (a-LixSi) has been the subject of numerous studies due to the importance of silicon anodes for next-generation, high-energy-density lithium batteries. Experimental studies have shown that a-LixSi with 2 ≤ x ≤ 3.75 appears as a prominent phase in the phase transformations of Si during lithiation and delithiation, but computational studies have yet to elucidate why. In this work, first-principles molecular dynamics computations were performed to simulate the various immediate steps associated with lithiation and delithiation of Si anodes in a Li-ion half-cell battery. The energy of formation and unit cell volume for relevant LixSi phases and Si have been computed for both crystalline and amorphous states. The first-principles results are utilized to construct lithiation and delithiation pathways and compute the corresponding changes in the voltage, capacity, and cell volume of the anode. These results indicate that multiple pathways are possible during delithiation of c-Li15/4Si and a two-phase delithiation field is energetically favored to occur between a-Li15/4Si and a-Li9/4Si due to a large amorphization energy for Li3Si and a site-dependent amorphization energy for Li9/4Si. In addition, large tensile stresses are generated during the removal of Li atoms from the 48e sites in the Li15/4Si crystalline lattice. These hydrostatic tensile stresses can cause changes to the open-circuit potential, can lead to the fracture of Si or Li15Si4, and may be responsible for the change in the lithiation process from a ledge mechanism to a two-phase mechanism at x ≈ 2.25.
UR - http://www.scopus.com/inward/record.url?scp=85073122296&partnerID=8YFLogxK
UR - http://www.scopus.com/inward/citedby.url?scp=85073122296&partnerID=8YFLogxK
U2 - 10.1021/acs.jpcc.9b05933
DO - 10.1021/acs.jpcc.9b05933
M3 - Article
AN - SCOPUS:85073122296
VL - 123
SP - 22775
EP - 22786
JO - Journal of Physical Chemistry C
JF - Journal of Physical Chemistry C
SN - 1932-7447
IS - 37
ER -