Applications of secondary lithium-ion batteries are greatly hindered by their low energy (<300 Wh kg−1) and power density (<400 W kg−1) due to the use of low-capacity graphite anodes possessing sluggish Li-ion diffusion kinetics. Herein, we report a high energy (451 Wh kg−1) and power density (980 W kg−1) lithium-ion full-cell enabled by nanograin-boundary induced pseudocapacitance of hierarchical Co3O4 nanorods. This highly pseudocapacitive (∼81 %) anode exhibited high reversible capacity (1593 mAh g−1 @ 50 mA g−1), rate-performance (800 mAh g−1@ 30 A g−1), cycling stability (∼60 % after 1000 cycles @ 1 A g−1), coulombic efficiency (∼100 %) and ultrafast-charging (∼35 s @ 30 A g−1). These Li-ion storage performances are significantly better than the previously reported conversion type anodes. Li-ion full-cell composed of Co3O4 nanorod anode and LiNiMnCoO2 cathode demonstrated excellent stability (∼85 % after 200 cycles @ 1 A g−1). Mechanistic studies including in-situ XRD and EELS mapping illustrated unique Li-ion storage at nanograin boundaries. Outstanding performance of Co3O4 nanorods anode is credited to the synergy between conversion reaction and pseudocapacitive Li-ion storage at numerous Li2O/Co/Li1.47Co3O3.72 nanointerfaces. This strategy of nanograin-boundary induced pseudocapacitance can be extended for various transition metal-oxide anodes for next-generation high energy/ power density rechargeable batteries.