First-Principles Studies of the Lithiation and Delithiation Paths in Si Anodes in Li-Ion Batteries

Kwai S. Chan, Wu Wei Liang, Candace K. Chan

Research output: Contribution to journalArticle

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 languageEnglish (US)
Pages (from-to)22775-22786
Number of pages12
JournalJournal of Physical Chemistry C
Volume123
Issue number37
DOIs
StatePublished - Sep 19 2019

Fingerprint

electric batteries
Anodes
anodes
Amorphization
tensile stress
Tensile stress
cells
Crystalline materials
ledges
Silicides
ions
Lithium batteries
silicides
lithium batteries
Silicon
energy of formation
hydrostatics
Lithium
Crystal lattices
phase transformations

ASJC Scopus subject areas

  • Electronic, Optical and Magnetic Materials
  • Energy(all)
  • Physical and Theoretical Chemistry
  • Surfaces, Coatings and Films

Cite this

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 journalArticle

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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.

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