Thermoelectric (TE) materials directly convert thermal into electrical energy and vice versa, making them promising for a plethora of applications in refrigeration or power generation. However, state-of-theart semiconductors in the focus of current research did not make the leap into broad applications due to their low power density and poor mechanical properties. Metallic systems would be superior in this regard, but remained largely neglected so far due to their small Seebeck coefficient S. Here we realize high TE performance in metals via controlled tuning of electronic scattering. Strikingly, we discover record-high power factors in binary NixAu1-x alloys, exceeding previous benchmark values by several times [1,2]. The unusually high S in this metallic system results from strongly electron-hole asymmetric charge transport in a highly conductive s-band, where we selectively reduce the mobility of holes by interband scattering from localized Ni d-electron states placed right below EF. Through our new paradigm of enhancing S in metals by scattering – cardinally different from tuning the density of states of the conduction electrons in semiconductors – we implement high-throughput computational materials screening and discover ultrahigh power factors also in Ni-based systems without Au [3]. [1] Sci. Adv. 9, eadj1611, (2023) [2] Phys. Rev. Materials 8, 095403 (2024) [3] arXiv:2404.08067