This study presents a novel approach to enhance the performance and biocompatibility of aqueous Zn-MnO₂ batteries by integrating biomass-derived carbon with γ-MnO₂. The research focuses on synthesizing a composite cathode using γ-MnO₂ loaded on N-doped biomass carbon (CP) derived from grapefruit peel. The composite cathode, with a carbon carrier quality percentage of 20 wt%, demonstrates exceptional electrochemical performance, including a specific capacity of 391.2 mAh g⁻¹ at 0.1 A g⁻¹, a cyclic stability of 92.17% after 3000 cycles at 5 A g⁻¹, and an energy density of 553.12 Wh kg⁻¹. The cathode also exhibits a high coulombic efficiency of ~100%, indicating its potential for practical applications. The study also investigates the biocompatibility of the composite cathode through in vitro cell toxicity experiments, which show that the composite material is non-toxic and has clinical potential. The enhanced performance is attributed to the regulation of Mn–O bond distances, Mn valence, and Mn domains, which are supported by theoretical calculations and experimental data. The composite strategy not only improves the structural stability of MnO₂ but also enhances the electrochemical properties of the cathode. The research highlights the potential of using renewable biomass resources to develop sustainable and high-performance cathode materials for aqueous zinc-ion batteries. The integration of biomass-derived carbon with γ-MnO₂ offers a promising strategy for improving the safety, efficiency, and biocompatibility of Zn-MnO₂ batteries, making them suitable for both large-scale energy storage and biomedical applications. The findings contribute to the development of environmentally friendly and efficient energy storage systems.This study presents a novel approach to enhance the performance and biocompatibility of aqueous Zn-MnO₂ batteries by integrating biomass-derived carbon with γ-MnO₂. The research focuses on synthesizing a composite cathode using γ-MnO₂ loaded on N-doped biomass carbon (CP) derived from grapefruit peel. The composite cathode, with a carbon carrier quality percentage of 20 wt%, demonstrates exceptional electrochemical performance, including a specific capacity of 391.2 mAh g⁻¹ at 0.1 A g⁻¹, a cyclic stability of 92.17% after 3000 cycles at 5 A g⁻¹, and an energy density of 553.12 Wh kg⁻¹. The cathode also exhibits a high coulombic efficiency of ~100%, indicating its potential for practical applications. The study also investigates the biocompatibility of the composite cathode through in vitro cell toxicity experiments, which show that the composite material is non-toxic and has clinical potential. The enhanced performance is attributed to the regulation of Mn–O bond distances, Mn valence, and Mn domains, which are supported by theoretical calculations and experimental data. The composite strategy not only improves the structural stability of MnO₂ but also enhances the electrochemical properties of the cathode. The research highlights the potential of using renewable biomass resources to develop sustainable and high-performance cathode materials for aqueous zinc-ion batteries. The integration of biomass-derived carbon with γ-MnO₂ offers a promising strategy for improving the safety, efficiency, and biocompatibility of Zn-MnO₂ batteries, making them suitable for both large-scale energy storage and biomedical applications. The findings contribute to the development of environmentally friendly and efficient energy storage systems.