Calendering is a crucial manufacturing process in the optimization of battery performance and lifetime due to its significant effect on the 3D electrode microstructure. By conducting an in situ calendering experiment on lithium-ion battery cathodes using X-ray nano-computed tomography, here we show that the electrodes composed of large particles with a broad size distribution experience heterogeneous microstructural self-arrangement. At high C-rates, the performance is predominantly restricted by sluggish solid-state diffusion, which is exacerbated by calendering due to the increased microstructural and lithiation heterogeneity, leading to active material underutilization. In contrast, electrodes consisting of small particles are structurally stable with more homogeneous deformation and a lower tortuosity, showing a much higher rated capacity that is less sensitive to calendering densification. Finally, the dependence of performance on the dual variation of both porosity and electrode thickness is investigated to provide new insights into the microstructural optimization for different applications in electrode manufacturing. Display omitted •Electrode with coarse architecture is prone to self-arrangement under calendering•Solid-state diffusion determines the performance of a large-particle electrode•Small-particle electrode maintains high power performance under calendering•Calendering exacerbates reaction heterogeneity and underutilization of capacity The rapid evolution of electric vehicles market has inspired a major effort in the fundamental research of lithium-ion batteries (LiBs). A rationalized electrode-processing philosophy is critical to improve the rate capability, capacity, cycle life, and safety of LiBs. Calendering is one of the key production steps that tunes the energy and power performance for different applications by tailoring the 3D microstructure of the electrodes. Here, we conduct an in situ compression experiment to replicate the calendering process on LiB electrodes. Using X-ray nano-computed tomography, we track the electrode’s microstructural evolution and correlate it with the battery performance. The critical porosity and electrode thickness are suggested, beyond which a catastrophic drop is expected in battery performance. Knowledge gained from this study is anticipated to suggest a route to maximise the energy and power density of batteries via electrode design and manufacturing for demanding applications. Calendering is a critical step in the production of the lithium-ion battery, as it reduces the electrode thickness compressively to achieve high energy density, which significantly determines the driving range of electric vehicles. This study conducts an in situ calendering experiment on lithium-ion battery cathodes using X-ray nano-computed tomography to correlate the microstructural evolution with the electrochemical performance so as to rationalize the manufacturing process. Distinct susceptibility of microstructure and performance is found for electrodes composed of large and small particles.