Capacity and Power Fade in Lithium-ion Batteries
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Lithium-ion batteries are known to have performance degradation as repeated use and age of the batteries increase. It is essential to qualify these batteries to meet the performance goals for their intended applications. For batteries requiring long-term use, such as transportation applications in electrified vehicles, experimental testing for extended periods is generally not viable due to high costs associated with long-term testing. To minimize qualification times, accelerated experimental testing and mathematical modeling can be combined to elucidate long-term battery performance. In this work, we have investigated the long-term performance of lithium-ion batteries using accelerated experimental tests. We found that the dissolution of transition metals cause a reduction in cell capacity and cycle stability in full cells. Reduction of transition metal species in the negative electrode facilitated the growth of the solid electrolyte interphase (SEI) by increasing the rate of solvent diffusion through the SEI and the subsequent reduction of the solvent. Capacity and power fading phenomenon in commercial cells were found to occur in two stages that were caused by: (i) lithium loss in the SEI in the negative electrode and (ii) active material dissolution and surface layer growth on the positive electrode. Simulation results on batteries consisting of nickel cobalt manganese (NCM) positive electrode and graphite negative electrode showed good agreement with experimental data. The model was extended to validate capacity fade occurring in commercial cells via lithium loss mechanism.