Oxide and sulphide solid electrolyte materials have enjoyed significant interest in the solid-state
battery community. Phosphide materials however are relatively unexplored despite the potential
for being high lithium containing systems. This work reports on the phosphidosilicate system
Li2SiP2
, one of many systems in the Li-Si-P phase diagram. The phosphidosilicates display complex structures and very large unit cells, which present challenges for ab-initio simulations. We
present the first computational report on the theoretical ionic conductivity and related diffusion
mechanisms of the material Li2SiP2
, selected due to it’s unusual supertetrahedral framework
which is a recurrent motif amongst the phosphidosilicates. Group 13 dopants have also been
introduced into Li2SiP2
showing preference for the silicon site over the lithium site, with Al0
Si doping showing extremely low defect incorporation energies of 0.05 eV, with no increase in defect
energy up to concentrations of 10% Al0
Si. Furthermore, clustering of Al0
Si has been found to be
unfavourable, in line with trends seen in oxide zeolite structures. Ab-initio molecular dynamics
(AIMD) simulations indicate high ionic conductivity in pure Li2SiP2
of up to 3.19 × 10−1 S.cm-1
at 700 K. Doping with 10% Al0
Si and associated Li•
i
compensating defects leads to higher ionic
conductivities at lower temperatures when compared to pure Li2SiP2
. The activation energies
to lithium diffusion were found to be low at 0.30 eV and 0.24 eV for pure and 10% Al0
Si doped
Li2SiP2
respectively, in line with previous experimental observations of pure Li2SiP2
. Multiple
lithium migration pathways have also been extracted, with some mechanisms displaying activation energies as low as 0.05 eV. Furthermore, our calculated intercalation voltages suggest that
these materials are stable against lithium metal and therefore could be very attractive in stabilising
the electrode/electrolyte interface.
Funding
The authors acknowledge the support of EPSRC SUPERGEN
grant, EP/N001982/1.
History
School
Science
Department
Chemistry
Published in
Journal of Materials Chemistry A
Volume
7
Issue
8
Pages
3953-3961
Citation
YEANDEL, S.R., SCANLON, D.O. and GODDARD, P., 2019. Enhanced Li-ion dynamics in trivalently doped Lithium Phosphidosilicate Li2SiP2: A candidate material as a solid li electrolyte. Journal of Materials Chemistry A, 7 (8), pp.3953-3961.
This paper was accepted for publication in the journal Journal of Materials Chemistry A and the definitive published version is available at https://doi.org/10.1039/c8ta10788b.