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

摘要

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 (～20%) of the sample is noticed between aged and unaged samples. Concurrent X-Ray diffraction studies in these samples showed an increase (～34%) in FePO_4 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.