This study explores the development of a high-performance aqueous Zn-ion battery using γ-MnO₂ loaded on N-doped biomass carbon derived from grapefruit peel. The composite cathode, with a carbon carrier quality percentage of 20 wt%, exhibits excellent electrochemical performance, including a specific capacity of 391.2 mAh g⁻¹ at 0.1 A g⁻¹, a remarkable energy density of 553.12 Wh kg⁻¹, and a coulombic efficiency of ~100%. The in vitro cytotoxicity tests show that the material is biocompatible, making it potentially useful in clinical applications. The enhanced Zn-ion storage efficiency is attributed to the regulation of Mn–O bond distance, Mn valence, and Mn domains, which are further supported by theoretical calculations and experimental data. This work provides a novel approach to converting biomass waste into biocompatible Mn-based cathodes for high-performance energy storage.This study explores the development of a high-performance aqueous Zn-ion battery using γ-MnO₂ loaded on N-doped biomass carbon derived from grapefruit peel. The composite cathode, with a carbon carrier quality percentage of 20 wt%, exhibits excellent electrochemical performance, including a specific capacity of 391.2 mAh g⁻¹ at 0.1 A g⁻¹, a remarkable energy density of 553.12 Wh kg⁻¹, and a coulombic efficiency of ~100%. The in vitro cytotoxicity tests show that the material is biocompatible, making it potentially useful in clinical applications. The enhanced Zn-ion storage efficiency is attributed to the regulation of Mn–O bond distance, Mn valence, and Mn domains, which are further supported by theoretical calculations and experimental data. This work provides a novel approach to converting biomass waste into biocompatible Mn-based cathodes for high-performance energy storage.