Layered lithium transition metal oxides are promising high-capacity cathode materials for Li-ion batteries. However, capacity fading has restricted the practical capacity to less than 70% of the theoretical capacity. Higher initial capacity can be achieved by charging to a higher voltage, yet this initial gain in capacity is quickly offset by the rapid fade in capacity. Understanding the capacity fading mechanism will help develop strategies to mitigate this problem. We used operando X-ray powder diffraction to follow the reactions of the layered LiNi_0.8Co_0.15Al_0.05O₂ over extended charge-discharge cycles at a slow current rate. The operando result shows that the capacity loss can be explained by the heterogeneity developed in the electrode after extended charge-discharge cycles.