Due to the chemical and thermal stability, lithium iron phosphate is a popular cathode material, the properties of which can be improved by doping. This work presents a study of the charge/discharge mechanisms for the LiFe1-XMnXPO4/C cathodes using synchrotron operando Mössbauer measurements. Both an increase in the cycling rate and Mn-substitution in the LiFePO4 structure lead to a gradual switch of lithium intercalation mechanisms between the two-phase transformation and the formation of an extended solid solution domain at the Fe1-XMnXPO4/LiFe1-XMnXPO4 interface. The role of doping in improving the cycling of LiFe1-XMXPO4/C cathodes during both charge and discharge and their cycling mechanism are discussed.