Maximum Current Density in Polymer-Ceramic Composite Electrolytes Based on Interconnected Ceramic Scaffold

Significant efforts have been made to develop composite electrolytes, combining a polymer matrix with Li-ion conducting inorganic solids, for feasible construction of solid-state batteries. It’s been found that there is a relatively large interfacial resistance for ion transport crossing the polymer-ceramic interface in common polymer and ceramic combinations such as poly(ethylene oxide) (PEO) based polymer electrolytes (PE) and lithium aluminum titanium phosphate (LATP) ceramic. The development of a three-dimensionally interconnected composite can potentially alleviate this issue as the interconnected ceramic and polymer phases provide ion transport pathways through individual phases by bypassing the high-resistance interface. However, in such an interconnected design, it is unclear 1) what the concentration gradient is like in an interconnected composite, and 2) what determines the rate capability and dendrite resistance.

In this work, we compare the concentration gradient, maximum current density and dendrite resistance in interconnected composites made with two types of PEs and two types of ceramic scaffolds. The two types of PEs are crosslinked PEO based PE with a low Li⁺ transference number (t₊) of 0.05 and a single-ion-conducting PE with a high t₊ of 0.75. The two ceramic scaffolds are a doped LATP ceramic (Li_1+x+yAl_xTi_2-xSi_yP_3-yO₁₂) and Al-doped La₃Li₇O₁₂Zr₂. Our results reveal that changing the polymer phase from a low t₊ polymer to a high t₊ polymer results in a 6-fold increase in the limiting current density, although the interfacial resistance between the polymer and LATP ceramic remains high. The concentration gradient of the composite is largely determined by that of the polymer phase, which in turn, dictates the limiting current density of the composite. The dendrite resistance of the composites prepared using LATP scaffold and LLZO scaffold reveals the detrimental effect from the reactivity between LATP and lithium anode. Through these investigations, we shed light on how to design composite electrolytes to maximize favorable ion transport paths and minimize barriers.

Acknowledgements: This research was sponsored by the U.S. Department of Energy (DOE), Office of Energy Efficiency and Renewable Energy for the Vehicle Technologies Office’s Advanced Battery Materials Research Program (Simon Thompson, Program Manager).