In this Article, we present a flexible nanogenerator (FNG) that incorporates enhanced flexoelectricity in few atomic layers-thick membranes of an inexpensive mineral, Hausmannite (Mn3O4), to produce up to 7.99 mW m -2 power density (active surface area ~2.5 cm 2 ). We exfoliated membranes with an average thickness of 2 -6 nm using a liquid exfoliation technique and characterized their structure and electronic properties. We fabricated flexible NGs with one of the electrodes being Mn3O4 membranes and observed a ~700% increment (at the highest load) in the voltage output of devices as compared to those having bulk Mn3O4 polycrystals as the electrode. Using first-principles calculations, we attribute the enhanced power output to flexoelectric effects. We show that flexoelectricity in bulk Mn3O4 is subdued due to a destructive interference between the bending and shearing modes; whereas in monolayer and bilayer Mn3O4, the contribution of the shearing mode diminishes, leading to flexoelectric coefficients that are two orders of magnitude larger than other 2D materials such as MoS2. We demonstrate generation of voltages up to 6.24 V (peak to peak) using these exfoliated Mn3O4-membrane-based FNGs from mechanical perturbations. These results open up a large family of centrosymmetric layered oxides as potential candidates for portable nanogenerators due to enhanced flexoelectricity.