Mechanistic Insight into the Effects of A-site Doping in Perovskite Nanorods on Interfacial Li-Ion and Na-ion Transport in Polymer-Perovskite Composite Electrolytes

Composite polymer electrolytes (CPEs) offer a promising pathway to safer and higher energy density electrochemical energy storage yet optimizing interfacial ion transport remains a critical challenge due to high resistances and a lack of understanding of the complex interfacial electrostatic interactions. This work investigates the mechanistic origins of the interfacial ion transport enhancement in single-ion conducting (SIC) polymer electrolytes filled with A-site disordered perovskite LaxMyTiOz (LMTO) (M = Li, Na, K) nanorods. By integrating Density Functional Theory (DFT) with broadband dielectric spectroscopy (BDS) and pulsed-field-gradient NMR (PFG-NMR), we analyze the ion transport behavior in Li-based and Na-based SIC systems containing compositionally distinct LMTO fillers (LMTO800 and LMTO900). Specifically, we introduce the site-to-site energy difference (∆E) descriptor, which extends beyond single-site descriptors such as adsorption energy and ion binding energies. We demonstrate that ∆E together with ion binding energies provide a more comprehensive picture of the energy landscape at the polymer-ceramic interface. The combined DFT and experimental results show that that A-site doping in the ceramic filler can effectively modulates ∆E and ion binding energies, creating a favorable potential energy landscape that promotes enhanced ion transport along the interface. This comprehensive study illustrates the impact of ceramic compositional tuning on interfacial ion transport and provides materials design rules towards real-world applications.