The emergent magnetic phase of altermagnetism supports nonrelativistic spin currents under an external electric field, even in the absence of net magnetization—a phenomenon known as the spin-splitter effect. Traditionally, this effect has been attributed to spin-dependent anisotropies in the electronic band structure or electron group velocities. However, the role of spin-dependent anisotropies in scattering processes, particularly electron-phonon interactions, has been largely overlooked. In this study, we highlight the crucial influence of electron-phonon scattering on both the efficiency and direction of charge-to-spin conversion in altermagnetic materials. When the anisotropy of electron-phonon scattering aligns with that of the electron group velocities, the charge-spin conversion is significantly enhanced. Conversely, a mismatch in their anisotropies can suppress the conversion efficiency—or even reverse the direction of the generated spin current. Our first-principles calculations demonstrate that phonons in real materials can either enhance, suppress, or reverse the spin-splitter effect depending on their interaction anisotropies. These findings underscore the importance of understanding and engineering scattering mechanisms to optimize the performance of altermagnet-based spintronic devices.

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• Altermagnetism
• Electron-phonon coupling
• Spin current
• DFT+U