Electrochemical properties of LiFe5O8-Li4Ti5O12 solid solution

The electrochemical properties of LiFe5O8-Li4Ti5O12 solid solutions, Li4/3- 5y/3(3-y)Fe5y/(3-y)Ti5(1-y)/(3-y)O4, 0 less than or equal to y less than or equal to 1, are investigated. In a low level of Fe doping, y < 0.5, the si ze of the unit cell is only slightly influenced and gives good discharge/ch arge properties with a specific capacity nearly to the theoretical values f or Fe2+/Fe3+ redox couple. However, the solid solution with y <greater than or equal to> 0.5 mainly features an inverse spinel structure with the exte nsive occupation of Fe in 8a sites and the decrease of O-O distance, which impede the diffusion of Li+ ions through 8a-16c-8a channels. The crystallog raphic characteristics would result in a poor Li+ insertion/extraction elec trochemistry. From ac impedance analysis, the D-Li(+) decreased with the in crease in Fe doping level. It is considered that the impeded Li diffusion c aused the electrode polarization that is observed in the highly Fe-doped sa mples. (C) 2001 The Electrochemical Society.