Electrochemical Characterization of Degradation Modes of High-Voltage Li_xNi_0.33Mn_0.33Co_0.33O₂ Electrodes

While deeply charged high-voltage cathodes can improve battery energy density, understanding and preventing any accelerated cell degradation is crucial to practical success. To analyze the degradation of LiNi_xMn_yCo_1-x-yO₂ (NMC) type material charged to 4.3 and 4.5 V, a physics-based model is applied to cycling data to obtain parameter estimates indicative of degradation modes, which are validated by simple electrochemical measurements and further interpreted by materials characterization. Growth rates of interfacial impedance and active material loss are greater at 4.5 V, as might be expected. However, when charged to 4.5 V, degradation rates are initially lower at a cycling C-rate of 1.0 C than at 0.5 C. Once degradation mode changes are quantified, simulations evaluate the contribution of individual degradation mode to performance losses and provide estimates of the energy-power correlation (Ragone plots) of cells after cycling.