Polyatomic anion insertion electrodes present compositional and morphological variety, as well as the ability to tune operational voltages by influencing the nature of metal-oxygen bonding. Realizing the application of these compounds as electrodes in Li- and Na-ion batteries requires a detailed understanding of ion dynamics in these systems. Here is presented the microscopic Li-ion and Na-ion diffusion properties in LiFeSO4F and Na2FePO4F, respectively, using muon spin relaxation (μ +SR) spectroscopy for the first time. Li-ion diffusion processes in the tavorite LiFeSO4F phase are found to proceed with an activation energy (E a) of 48(4) meV and a diffusion coefficient of 1.71 × 10−9 cm2 s−1, while Na-ion mobility in Na2FePO4F has a calculated diffusion coefficient of 3.47 × 10−10cm2 s−1 and a higher energy barrier to ion diffusion at 96(8) meV. This is the first such examination of fluoride-containing polyatomic cathodes using μ +SR, where the presence of the highly electronegative fluoride species was thought to preclude activation energy and diffusion coefficient determination due to strong μ +-F− interactions. These insights open up the possibility of studying a myriad of fluoride-containing electrode materials using the μ +SR technique.