LiFe1−yMnyPO4/C (y = 0–0.3) nanocomposites are prepared by the sol–gel method, and their properties are characterized with the use of the XRD analysis, SEM, impedance spectroscopy, charge/discharge tests, and Mössbauer spectroscopy. The samples with a low manganese content, LiFe1−yMnyPO4 (y = 0.1, 0.2) are characterized by an increased conductivity. In LiFe1−yMnyPO4 (x = 0.1–0.3), electrochemical lithium deintercalation/intercalation proceeds in two stages which due to the subsequent oxidation/reduction of iron and manganese ions. The LiFe1−yMnyPO4/С (y = 0.1, 0.2) samples show enhanced charge/discharge capacity, especially, at high current density (for LiFe0.9Mn0.1PO4/C, the discharge capacity is equal to 142 and 55 mAh g−1 at a current density of 20 and 1600 mA g−1, respectively). Mn2+ ↔ Mn3+ transition in LiFe1−yMnyPO4 proceeds via the solid solutions formation under gradual changes in the potential. For LiFe0.7Mn0.3PO4, oxidation and reduction of iron ions follow the same scenario. According to the Mössbauer spectroscopy data, manganese is orderly distributed in LixFeIII 1−yMnyPO4: iron contains not more than one manganese cation in its nearest neighborhood. Moreover, combination of the Mössbauer spectroscopy and X-ray analysis data indicates that, in the interval where solid solutions exist in LixFe0.7Mn0.3PO4, the regions with an inhomogeneous distribution of divalent and trivalent manganese ions are formed.