Achieving efficient electron and ion transport in high-loading, densely packed electrodes remains a major challenge for high-energy-density lithium-ion batteries. Increasing mass loading extends transport pathways for both charge carriers, while electrode densification by roll pressing, essential for maximizing gravimetric and volumetric energy density and minimizing electrolyte content, further restricts ion transport in low-porosity electrodes. Here, graphene mesosponge (GMS) is introduced as a functional conductive additive that tailors electrode microstructure through its sponge-like mesoporous framework. High-loading electrodes based on Co-free, pure-Ni layered oxides containing only 1 wt.% GMS exhibit enhanced electronic and ionic conductivity, delivering high reversible capacity with reduced polarization. The deformable mesoporous framework of GMS also buffers compressive stress during roll pressing, enabling practical electrode densities above 3.5 g cm−3 without inducing cracking of the active material particles. Digital-twin analysis reveals that the porous GMS architecture forms a three-dimensional electron- and ion-transport network, with electrolyte retained within its mesopores facilitating ion transport and resulting in superior rate capability compared with electrodes containing single-walled carbon nanotubes. These results demonstrate that GMS is a transformative conductive additive for simultaneously improving energy and power densities in practical lithium-ion batteries through rational microstructural design of dense composite electrodes.