Additionally, these quantitative results show that the arrangement of primary particles within secondary particles results in notable heterogeneity in the extent of oxygen loss among the primary particles. This observed heterogeneity in oxygen deficiency aligns with the predicted inhomogeneous distribution of plastic shear-induced oxygen loss within the secondary particle, as shown in the middle of Fig. . Despite the spatial variation in oxygen deficiency, both experiments and predictions depicted in Fig. consistently indicate that, on average, primary particles located near the exterior of the agglomerate are more susceptible to oxygen loss compared to those in the interior. Fig. shows the effect of the secondary particle size and discharge rate on the fraction of the oxygen-deficient phase within the secondary particle. The results demonstrate that significant bulk structural degradation occurs in secondary particles larger than approximately 8 µm when subjected to discharge rates exceeding 1 C, leading to a loss of over 10% of active materials. This emphasizes the critical impact of both cathode microstructure and operating conditions on the overall quantity and distribution of the oxygen-deficient phase, a factor that can significantly affect the electrochemical performance of composite cathodes. Fig. shows the predicted capacity loss of composite cathodes after accounting for the irreversible oxygen-deficient phase transition in cathodes, as a function of secondary particle size and discharge rate. A noticeable difference in behaviour is observed: particles exceeding 8 µm in diameter exhibit a significant normalised capacity loss, ranging from 0.2 to 0.4, as the discharge rate increases from 1 C to 5 C, while this effect is less pronounced for smaller particles. This phase transition-induced capacity loss is attributed to a combination of factors, 1 including the loss of active materials (thermodynamic effect) and the impediment of 2 Li-ion intercalation pathways within the cathodes (kinetic effect). Furthermore, Fig. 5f shows that secondary particles exceeding 8 µm in diameter and subjected to dis-4 charge rates greater than 1 C experience a kinetically-induced capacity loss of over 5 0.1, which is primarily attributed to the accumulation of crystal defects and associated 6 structural degradation at the particle's periphery.