Capacity loss in different charge/discharge cycles of Lithium ion batteries

Lithium iron phosphate batteries, as the most promising candidate for EV/HEV power unit, are now under intensive R&D all over the world. Cycle performance experiments of a commercial LiFePO ₄ conducted in Electric Vehicle Laboratory at Tsinghua University show that different charge/discharge cycles would lead to different capacity loss, this phenomenon is believed to be of considerable relevance with the mechanism of insertion/extraction in the cathode material. This paper, based on the shrinking core model, firstly explores the behaviour of the LiFePO ₄/FePO ₄ phase change in Lithium iron phosphate during charge/discharge schematically. Secondly, for improving the charge performance, a charge-discharge-charge profile is introduced to re-evaluate the shrinking core model for explain the capacity loss. Finally, based on the microscopic analysis, a schematic stochastic mosaic model is proposed, through which one can both learn how the battery really works and get valuable information for battery applications.