In this paper we propose a new way for Mössbauer data treatment when numerous experimental spectra are recorded in operando conditions depending on a perturbation. In our example, the perturbation is the Li amount extracted from a positive electrode material LiFe0.75Mn0.25PO4. In other cases perturbation could be the recording temperature, the pressure or kinetic parameter or even time for isothermal experiments. From analysis of both synchronous and asynchronous 2D-correlation spectra, we can focus our attention on the intensity variations at some specific positions deduced from cross-peaks. This analytical method is very powerful when overlap between absorption lines is observed. This is typically the case when Fe2+/Fe3+ contributions are simultaneously present in a Mössbauer spectrum at lower velocities.