Probing the particle size dependence of nonhomogeneous degradation in nickel-rich cathodes for high-energy lithium-ion batteries

Increasing the loading and calendering density of Ni-rich cathodes by adopting a mixture of small to large particles is a practical way to create high-energy lithium-ion batteries. However, high-energy lithium-ion batteries using this type of Ni-rich electrode still suffer from rapid capacity degradation. In this work, the nonhomogeneous degradation of a Ni-rich cathode is characterized by particle size using a commercial 320 Wh kg−1 pouch cell. The correlation between the volume change (ΔV) and state-of-charge (SOC) of the cathode particles with different diameters (D) is determined using in situ transmission X-ray diffraction and numerical simulations. At 0.2 C, minor differences occur in the SOC between the small (D = 5 μm) and large (D = 25 μm) particles. However, at 3 C, the SOC and ΔV of the small particles are 1.03 and 1.11 times higher than those of the large particles, respectively. This work demonstrates that size-dependent nonhomogeneity is undesirable because it promotes the performance decay of Ni-rich cathodes, especially at high cutoff voltages and rates.