Experiments on and Modeling of Positive Electrodes with Multiple Active Materials for Lithium-Ion Batteries

Abstract

We adapt a previously developed lithium-ion mathematical model to treat multiple types of active materials in a single electrode; our model treats both direct (galvanostatic) and alternating (impedance) currents. We compare our simulations to experimental data from coin cells built with two positive-electrode materials (compositions based on LiyNi0.80Co0.15Al0.05O2 and LiyMn2O4 ) mixed in five different molar ratios and develop a model parameter set that qualitatively matches both the galvanostatic and impedance data. We found that to match the behavior of the high rate discharge curves and the impedance data (which showed a similar width of the positive-electrode kinetic arc for any composition containing LiyMn2O4 ), multiple types of electronic connections between the active material and the conductive matrix were required. Our experiments showed that at high powers the specific energy from an electrode with pure LiyMn2O4 exceeded that from an electrode with pure LiyNi0.80Co0.15Al0.05O2 , while at low specific powers the LiyNi0.80Co0.15Al0.05O2 electrode had a higher specific energy. Mixing these active materials combined power and energy characteristics. We discuss other applications in which a mixed active-material electrode may be beneficial. For example, combining a sloped-potential system with a flat-potential system may assist in electrode state-of-charge determination.