Electrochemical properties of p-terphenyl based lithium solvated electron solutions

Abstract Concentrated lithium solvated electron solutions (LiSESs) consisting of p-terphenyl (TER) in tetrahydrofuran (THF) prepared using suspensions of TER in THF, exhibit a more than twelve times increase in conductivity compared to more dilute solutions. The temperature dependent conductivity of LiSES has metallic-like characteristics, i.e. linear decrease of conductivity with increasing temperature, except for the solution of higher concentration (less THF) with the ratio of lithium to TER being 2 which conductivity increases as raising temperature due to the higher contribution of ionic conductivity. From temperature dependent open circuit voltage temperature measurement, the values of changes in entropy (ΔS) and enthalpy (ΔH) were determined. Unlike lithium-intercalated graphite, the ΔS decreases linearly as the ratio of lithium to TER increases, which demonstrates fundamental differences in the lithium charging/discharging processes between solution and solid state. The TER based LiSES with higher concentrations (less THF) show deviations from the ΔS and ΔH values of solutions with lower concentrations. The ΔS values for the TER based LiSES are higher than for naphthalene and biphenyl based Li SES having the same composition, but lower than those for solid lithium ion battery anode materials. LiSES with the maximum ratio of lithium to TER is 2.4 to 1 exhibits minimum conductivity which indicates the formation of a dimeric structure under these conditions. The LiSES provides higher energy density comparing to vanadium redox batteries, which demonstrates that LiSES holds good promise as anolytes in liquid-based refuelable batteries.