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First principles simulations of the porous layered calcogenides
Li2+xSnO3 and Li2+xSnS3
Jason Howard
and N.A.W. Holzwarth
accepted for publication in Phys. Rev. B
(2016)
Local copy
First principles simulations of the porous layered calcogenide materials
Li2SnO3 and Li2SnS3 are used
to study their structures, Li ion
mobilities, and their interactions with excess Li. The pristine
materials are characterized by a regular pattern of voids within the
calcogenide layers which are occupied by intralayer Li ions. The
energetically most favorable Li ion migration processes for both
materials result in a net motion perpendicular to the layers and involve
intralayer Li ions and nearby interstitial sites. The ideal lattice has
8 symmetry related stable interstitial sites within the conventional
unit cell which, in addition to participating in the Li ion migration
processes, are also important for accomodating excess Li during
lithiation processes. Consistent with experimental findings, the
simulations find that the addition of Li atoms to Li2SnO3 results in a
disruption of the calcogen lattice with the breaking of Sn-O bonds. The
estimated voltage versus bcc Li for this system is in qualitative
agreement with experiment provided that Sn/Li disorder is taken into
account. By contrast, the simulations predict that the addition of Li
atoms to Li2SnS3 results in a stable metallic material up to a
stoichiometry of Li3SnS3.
This prediction has not yet been studied
experimentally. Simulations of surfaces of these materials find that it
is energetical favorable to add a small amount of excess surface Li.
However, interfaces of these materials with Li metal are found to be
reactive. Some of the findings may be relevant to other materials having
the same crystal structure such as Li2MnO3
and Li2TiO3.