Ionic conductivity and diffusion coefficients of lithium salt polymer electrolytes measured with dielectric spectroscopy

Ionic conductivity, diffusion coefficients, mobility and ionic concentration for lithium salts dissolved in polymer electrolytes are determined by the modeling of the dielectric loss and spectra. Cation and anion diffusion coefficients are quantified using the Trukhan model depending on the assumed ratio of the cation to anion diffusion coefficients. Measurements are performed for polymer electrolytes consisting of polyethylene oxide (PEO) with dissolved LiClO4 salts for different sample thicknesses and temperatures ranging from 5 to 105 °C, which comprises both the crystalline and amorphous phases of the composite electrolyte. A good phenomenological description of the dielectric loss spectra is obtained for both the semi-crystalline and amorphous phases. The fraction of mobile ions is estimated to vary from 0.002% at 25 °C (semi-crystalline phase) up to 0.05% at 80 °C (amorphous phase).

Research highlights
► Ionic conductivity of PEO electrolytes with LiClO4 salts is measured for different thickness and temperatures from 5 to 105 C.
► The dielectric spectra have been successfully modeled for temperatures below and above the PEO fusion point.
► The model correctly accounts for the effects of macroscopic electrode polarization and ionic.
► With the Trukhan model, salt diffusion coefficients, dissociation degree and conductivity can be measured only by impedance.
► This could be a new approach with some value for the ion-lithium batteries polymer electrolytes community.