Lithium ion conduction in lithium metaphosphate based systems

A comparative investigation on Li+ ion transport has been carried out in various phases of lithium metaphosphate such as (i) crystalline LiPO3, (ii) glassy form as mol % 50Li(2)O50P(2)O(5), synthesized by melt-quenching process, (iii) single phase glass-ceramic LiPO3 obtained through controlled heat treatment of mol% 50Li(2)O-50P(2)O(5) and (iv) newly identified polymer-metal salt complex (PEO)(6): LiPO3. All of the above materials have been characterized through XRD, DSC, optical microscopy and impedance spectroscopy techniques. The Li+ ions, migrating with an activation energy value of 1.4 eV through " interstitial mechanism" in polycrystalline LiPO3, exhibited a dc conductivity value of 2.5 x 10(-8) Scm(-1) at 280 degrees C. The above conductivity value was enhanced by four orders of magnitude in Li2O-P2O5 glass, with an activation energy value of 0.72 eV. The glass subjected to controlled heat treatment devitrified into single phase glass-ceramic, as revealed by XRD and optical microscopy studies. The glass-ceramic exhibited better conduction characteristics compared to polycrystalline LiPO3. Polycrystalline LiPO3, complexed with polymer PEO has exhibited a conductivity value of 3.1 x 10(-7) Scm(-1) at 78 degrees C with activation energies of 0.21 and 0.88 eV for Li+ ion migration above and below the softening point of the polymer, respectively.