Porosity and phase fraction evolution with aging in lithium iron phosphate battery cathodes

Rechargeable Lithium-ion batteries designed for electric vehicles operate under different charge and discharge rates, state of charge and temperature. However, aging of these batteries due to disruption of ionic or electronic conductivity while operating under these different cycling conditions has been a concern. In this research, we measured statistical distribution of porosity in the cathode as a function of aging and location within the cylindrical battery, using X-Ray micro-computed tomography. A change in porosity (similar to 20%) of the sample is noticed between aged and unaged samples. Concurrent X-Ray diffraction studies in these samples showed an increase (similar to 34%) in FePO4 phase fraction. Structural breakdown of the composite cathode material during charge and discharge cycling is proposed as a possible mechanism to rationalize the above results. (C) 2013 Elsevier B.V. All rights reserved.