Dielectric relaxation and charge transport mechanisms in LiCoO2-incorporated P2O5 glasses

Following the successful vitrification and characterization of LiCoO 2 –P 2 O 5 glasses containing 20–40 mol% LiCoO 2 (5 mol% increments), the present study reports X-ray photoelectron spectroscopy (XPS) results and then focuses on their dielectric properties, ac/dc conductivity, and the examination of their suitability for solid-state batteries. XPS O 1 s results indicated that the amount of non-bridging oxygens increased with LiCoO 2 content in the glasses, consistent with a network depolymerization effect. The presence of Co 2+ and Co 3+ was also verified by XPS; estimates based on the Co 2p 3/2 satellites region indicated an increase in Co 3+ concentration within ∼26–30% of total cobalt with increasing LiCoO 2 content. The dielectric parameters, ac conductivity (measured from 4 Hz to 8 MHz and temperatures from 306 to 633 K) and dc conductivity in the same temperature range were found to increase, while the electrical impedance decreased with LiCoO 2 content. Electrical modulus analysis and Cole-Cole plots revealed dipolar relaxation, with activation energy decreasing as LiCoO 2 increased. This relaxation is ascribed to complexes of octahedrally coordinated Co 2+ ions and surrounding oxygen ions. At higher LiCoO 2 levels the conductivity (both ac and dc) is dominated by ionic contribution, whereas at lower concentrations, a polaronic contribution via electron hopping among Co 2+ and Co 3+ ions seemed to be significant. Overall, the results identify the higher-LiCoO 2 glasses as promising candidates for further investigation as glassy solid-electrolyte materials, while the lower-LiCoO 2 compositions may warrant investigation for electrode-related applications. Direct electrochemical measurements, including ionic transference, electrochemical stability, and cell-level cycling, are required to establish practical suitability for solid-state battery applications.