Tailoring Li₂SO₄‒MgO‒P₂O₅ glasses for electrodes and electrolytes in solid ‒ state batteries with CoO doping by means of dielectric studies

Li 2 SO 4 ‒MgO‒P 2 O 5 glasses with varying cobalt oxide (CoO) concentrations (0.2 to 1.0 mol%) were synthesised. Optical absorption studies revealed that cobalt ions predominantly exist in Co 2+ state and occupied tetrahedral ( T d ) sites when the concentration of CoO is at lower levels and largely octahedral (O h ) when its concentration is >0.6 mol%. Dielectric parameters and a.c. conductivity measured over broad ranges of frequency and temperature initially decreased with increasing CoO content up to 0.6 mol% and for further increase of CoO these parameters were found to increase. This behaviour is linked to the dual role of Co 2 ⁺. At lower concentrations, it strengthens the glass network, while at higher levels it weakened the network and enhanced charge carrier transport, leading to higher conductivity. Observed dipolar relaxation is attributed to Co 2 ⁺(O h )–oxygen ion complexes. Conductivity studies indicated, ionic conduction dominates at lower CoO levels, while polaronic conduction, due to electron transfer between Co 2 ⁺ and Co 3 ⁺ states, prevails at higher concentrations. From these findings it is concluded that, glasses with lower CoO concentrations (<0.6 mol%) exhibited larger ionic conductivity, making them ideal for electrolyte applications. Conversely, those with higher CoO content show enhanced electronic conductivity, making them more appropriate for use as electrodes in solid‒state batteries.