Evaluation of Lithium iron phosphate batteries for electric vehicles application

Abstract

160 Ah LiFePO4 prismatic cells were tested for capacity, cycle life and realistic road test evaluation for the application of electric vehicle. The testing was done to compare the performance of LiFePO4 cells to LiCoO2 cells that were previously shown to be not suitable for use in EVs. The testing was done in the Battery Evaluation Lab at UMass, Lowell (Massachusetts), which is briefly described. A brief explanation of the various types of Lithium based secondary cells is given as background. Cycle tests and capacity measurements were done on eight cells over the course of 50 full cycles lasting several weeks. Cycles were to 100% Depth of Discharge (DOD) at 20°C. The capacity tests showed that the cells had a full 160 Ah capacity and the cycle tests showed that the cells had still had full capacity after 50 cycles. There was no degradation of terminal voltage during discharge and no heating effect. The realistic road test consisted of subjecting two sample cells to the currents that are required in an actual road trip in an EV. The profile of the realistic road test is described. The road test profile was done on both cells four times at each of four ambient temperatures: −20°C, 0°C, +20°C and +40°C. The resulting conclusion is that the LiFePO4 cells are superior to the previously tested LiCoO2 cells for use in EVs and are recommended for future designs.