Thermodynamics and kinetics of lithium intercalation into Nb2O5 electrodes for a 2 V rechargeable lithium battery

Niobium pentoxide was synthesized by heating niobium hydroxide in the temperature range of 600-1100 degrees C. The crystal system of Nb2O5 compounds depended on the heating temperatures, i.e., hexagonal, orthorhombic, and monoclinic Nb2O5 compounds were obtained at ca. 600, 800, and >1000 degrees C, respectively. Electrochemical lithium intercalation into the three Nb2O5 compounds was investigated in a cell with a LiClO4-propylene carbonate electrolytic solution for application as lithium battery cathodes. As a result, they displayed good charge-discharge performance as the cathode of a 2 V lithium battery, which will play an important role in power supply for integrated circuit memory backup developed recently. The thermodynamics and kinetics of lithium intercalation into the Nb2O5 cathode and their characteristics have been investigated. The thermodynamic parameters, such as standard free energies, lithium partial molar entropy, interaction energies between ions, crystal lattice parameters, and kinetic parameters, such as chemical and self diffusion constants, have been obtained as a function of x value in LixNb2O5. These results were compared to those of a Nb2O5 thin-film electrode prepared by a radio frequency sputtering method, which has high potential for fabricating thin microbatteries. (C) 1999 The Electrochemical Society. S0013-4651(99)01-034-4. All rights reserved.