The combination of Li+-conducting ceramics and polymers offers a new pathway to create better electrolytes for solid state batteries with both high ionic conductivity and good (electro)mechanical interfacial properties. The total Li-ion conductivity of the composite polymer electrolytes is still governed by the polymer matrix due to high interfacial resistance between the garnet particles and the PEO/LiTFSI matrix. We modeled our composite electrolytes with two Li⁺-conductive phases (PEO and LLZO) and two interphases. The conductive interphase is attributed to the LLZO nanofiller’s disruption of PEO crystallization, essentially acting as a plasticizer. The resistive interphase is attributed to the adsorption of PEO on LLZO and the limited segmental motion of the polymer chains when near the LLZO surface. To disrupt this resistive interphase at ceramic/polymer interface we synthetically modified the surface of LLZO nanoparticles with functional silane chemistries (Figure 1). This simultaneously added surface moieties that interact with the polymer matrix and protected the LLZO surface from continual Li₂CO3 formation. The incorporation of functionalized nanoparticles into the composite polymer membrane resulted in lower interfacial impedance, improved conductivity and transference numbers and the cycling characteristics against the lithium anode in addition to significantly improved handleability and processability. Li solid-state NMR shed the light on the mechanism of enhanced Li-transport and the nature of the resistive interphase. This work revealed a new design strategy for a composite polymer electrolyte with enhanced Li⁺- transport properties for high-performance Li metal batteries.

<b>Figure 1.</b> a) Schematic of functionalized LLZO nanoparticles b) Photograph of reflux surface modification set-up c) FT-IR spectrum of LLZO nanoparticles and APTES-modified LLZO nanoparticles showing surface functional groups.

Figure 1. a) Schematic of functionalized LLZO nanoparticles b) Photograph of reflux surface modification set-up c) FT-IR spectrum of LLZO nanoparticles and APTES-modified LLZO nanoparticles showing surface functional groups.

Michael Counihan

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