<p>Micro-/mesopore structures in carbon anode are highly desirable for increasing active sites and accelerating ion migration, favoring high capacity and rate performance. However, some structure–performance relationships still need to be clarified, and an in-depth understanding of how pore size and volume affect capacity and rate performance has rarely been mentioned. Herein, a series of carbon nanosheets with different micro-/mesopore sizes and volumes are precisely prepared. Detailed experimental analyses demonstrate that micropore volume rather than size is tightly responsible for capacity, resulting from its “accommodation effect” for ions. Conversely, mesopore size instead of volume is closely related to rate performance, which can be ascribed to its “channels effect” for ions. Capacity and rate performance first increase and then decrease with increasing micropore volume and mesopore size. In this work, the sample featured with the optimal micropore volume (1.6&#xa0;cm³·g⁻¹) and mesopore size (2.55&#xa0;nm) delivers the highest capacity (453&#xa0;mAh·g⁻¹ at 0.5&#xa0;A·g⁻¹) and excellent rate performance (235.1&#xa0;mAh·g⁻¹ at 2&#xa0;A·g⁻¹). This work provides a new insight into the understanding of micro-/mesopore parameters and their effect on capacity and rate performance.</p> Graphical Abstract <p></p>