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Correlating the influence of porosity, tortuosity, and mass loading on the energy density of LiNi0.6Mn0.2Co0.2O2 cathodes under extreme fast charging (XFC) conditions

by Dhrupadkumar P Parikh, Tommiejean Christensen, Jianlin Li
Publication Type
Journal
Journal Name
Journal of Power Sources
Publication Date
Page Number
228601
Volume
474

Extreme fast charging capabilities along with high energy density of Li-ion batteries are the key factors to increase the adoption of electric vehicles while eliminating the problem of range anxiety. In order to achieve the U.S DOE goal of less than 15 minutes charging time with energy density >200 Wh/kg, a combined improvement in the electrode architecture, electrolyte properties, and separator membrane is necessary. Cells with state-of-the art electrodes are to achieve extreme fast charging from 4C to 6C using thin electrode. However, its drawback is low energy density and high manufacturing cost. LiMn0.6Ni0.2Co0.2O2 (NMC622) is a promising cathode material having high energy density and cycle life. In the present study, the influence of porosity, tortuosity, and areal loading on the electrochemical rate performance and electrode kinetics are investigated under extreme fast charging conditions. Increasing the mass loading from 11.5 mg/cm2 to 25 mg/cm2 reduces the rate performance of the cells due to the mass transport limitation and underutilization of thick electrodes. Reducing the electrode porosity from 50% to 35% helps in improving the rate performance of the cell. The impedance results verify that the performance of the cathodes was improved when electrode porosity was lowered due to reduction in the tortuous pathways which created shorter Li-ion diffusion pathlength. Symmetric cells are cycled to verify the results of the half cells, suggesting that cell over potential is not the limiting condition.