  Solid-state electrolytes for Li-ion batteries are attracting growing interest
as they allow building safer batteries, also using lithium metal anodes. Here
we studied a compound in the lithium superionic conductor (LISICON) family,
i.e. Li4-xGe1-xPxO4 (LGPO). Thin films were deposited via pulsed laser
deposition and their electrical properties were compared with ceramic pellets.
A detailed characterization of the micro structure shows that thin films can be
deposited fully crystalline at higher temperatures but also partially amorphous
at room temperature. The conductivity is not strongly influenced by the
presence of grain boundaries, exposure to air or lithium deficiencies.
First-principles molecular dynamics simulations were employed to calculate the
lithium ion diffusion profile and the conductivity at various temperatures of
the ideal LGPO crystal. Simulations gives the upper limit of conductivity for a
defect free crystal, which is in the range of 10-2 S cm-1 at 300 deg. The ease
of thin film fabrication, the room-temperature Li-ion conductivity in the range
of a few microS cm-1 make LGPO a very appealing electrolyte material for thin
film all-solid-state all-oxide microbatteries.
