Vapor phase infiltration (VPI) derived from atomic layer
deposition
(ALD) enables inorganic materials to nucleate and grow within the
free volume of polymers, which has shown promising prospects in the
field of composite solid polymer electrolytes (CSPEs). However, there
are only a few types of metal oxides that can be incorporated into
the polymer matrix by VPI, let alone binary metal oxides, due to the
limited knowledge of the VPI synthesis process. To combine the merits
of different metal oxides, we investigate the VPI method to prepare
ZnO-Al2O3 composites in poly(ethylene oxide)
(PEO). When the introducing order is Al2O3/ZnO
(AZO), due to the extremely high reactivity of trimethyl aluminum
(TMA) with PEO, VPI-Al2O3 will accumulate near
the surface of PEO. The surface Al2O3 layer
inhibits the further diffusion of the diethyl zinc (DEZ) into the
PEO matrix, leading to weak polymer–filler interactions and
limited improvement of the Li+ conduction. In the incorporation
order of ZnO/Al2O3 (ZAO), the moderate reactivity
of DEZ renders the uniform distribution of VPI-ZnO within PEO, and
the following TMA can both react with PEO and VPI-ZnO particles near
the surface of PEO, which not only preserves the interactions between
VPI-ZnO and PEO but also better inhibits the growth of lithium dendrites.
The incorporation order plays a crucial role in the morphology and
composition of binary metal oxides synthesized by VPI.