The paper presents and discusses a method to achieve beneficial electrochemical effects mediated by interfaces in an ionic conducting polymer matrix. The beneficial effects include enhanced ionic transport, catalysis of anodic oxidation reaction, and stabilization of the lithium-electrolyte interface in lithium-based electrochemical cells. Polyethylene oxide (PEO) doped with LiN(SO2CF2CF3)2 (LiBETI) was chosen as the ion conducting polymer matrix. The polymer-ceramic (PC) composite electrolytes from the PEO:LiBETI-BN and PEO:LiBETI-Li2O systems were optimized to achieve high conductivity, reduce charge-transfer resistance, and stabilize the solid electrolyte interface (SEI) layer at the lithium anode. Both BN and Li2O were effective in enhancing interface-mediated lithium ion transport. The charge-transfer resistance was reduced by orders of magnitude and the long-term stability of the cells was improved remarkably due to the addition of BN and Li2O in the PEO:LiBETI polymer matrix. AC impedance spectroscopy was used to investigate the phenomenon by measuring the time- and temperature-dependent electrical behavior of the aforementioned materials and cells. The interface-mediated effects due to the addition of BN and Li2O dielectrics contributed to the improved cell properties.