The Influence of Porous Structure on the Electrochemical Properties of LiFe 0.5 Mn 0.5 PO 4 Cathode Material Prepared by Mechanochemically Assisted Solid-State Synthesis

Carbon-free LiFe 0.5 Mn 0.5 PO 4 and carbon-coated LiFe 0.5 Mn 0.5 PO 4 /C cathode materials were prepared by the mechanochemically assisted solid-state synthesis. The influence of the carbon coating on the porous structure, morphology, conductivity, and electrochemical characteristics of the cathode materials was analyzed using scanning electron microscopy (SEM), standard contact porosimetry (MSCP), electrochemical impedance spectroscopy (EIS), galvanostatic cycling, and galvanostatic intermittent titration technique (GITT). It has been shown that the specific surface area of LiFe 0.5 Mn 0.5 PO 4 /C is twice as high as that of LiFe 0.5 Mn 0.5 PO 4 despite the very low content of carbon (3%). This was explained by a non-additive contribution of carbon and the active cathode material to the total specific surface area of the composite due to an introduction of carbon in the pores of the cathode material. Among the two key characteristics of a porous structure—specific surface area and volumetric porosity—specific surface area has the greatest impact on electrochemistry of LiFe 0.5 Mn 0.5 PO 4 /C. Mathematical modeling of the discharge profiles of LiFe 0.5 Mn 0.5 PO 4 /C was carried out and compared with the experiment. The cathode heating at high currents was evidenced. The temperatures and coefficients of solid-state diffusion were estimated at different currents. The calculated diffusion coefficient corresponds to the experimental one obtained by GITT at room temperature.