The ubiquitous implementation of integrated microelectronics requires the on-chip power sources featured with the lightweight configuration design, high areal-capacity-loadings as well as facile reaction kinetics that beyond the current available microbattery prototypes. Herein, this study constructs a mechanically flexible, nanocellulose fiber (NCF) reinforced microbattery configuration, which consists of metal–organic frameworks (ZIF-8) modified NCF as the separator (MOF@NCF), the carbonized MOF@NCF as the metallic deposition substrate (c-MOF@NCF) as well as gradient-structured LiFePO₄ particles infiltrated in the NCF matrix (LFP@NCF) as the cathode. The film-stacked, integrated NCF-based microbattery prototype not only achieves the facile reaction kinetics with homogenized, dendrite-free Li metal deposition at high-capacity-loadings (2 mAh·cm⁻²), but also eliminates the necessary use of metallic current collector to maximize the electroactive mass ratio, which therefore enables the high energy density of 6.8 mWh·cm⁻² at the power output of 1.36 mW·cm⁻² as well as the robust cyclability upon various geometric flexing states. This study presents a quantum leap towards the facile reaction kinetics and multi-scale interfacial stability for the flexible microbattery construction that based on the sustainable utilization of bio-scaffolds.