Lithium Diffusion in Cation-Mixing-Free LiMn1-xFexPO₄Synthesized by Hydrothermal Process

Lithium diffusion properties of LiMn 1-x Fe x PO 4 synthesized by hydrothermal methods were characterized from electrochemical and structural analysis. Structural defects such as cation mixing in LiMn 1-x Fe x PO 4 impede the lithium-ion diffusion. Therefore, it is important to understand effects of cation mixing in LiMn 1-x Fe x PO 4 on lithium diffusivity of LiMn 1-x Fe x PO 4 . The amount of cation mixing of lithium and Mn/Fe in LiMn 1-x Fe x PO 4 was obtained by means of neutron diffraction measurements. Rietveld refinements indicated that cation mixing in the prepared LiMn 1-x Fe x PO 4 was negligible. Apparent chemical diffusion coefficients ( D app ) of lithium of LiMn 1-x Fe x PO 4 dependent on the Mn/Fe ratio were obtained by potential-step chronoamperometry (PSCA) measurements of thin composite electrodes. D app of lithium insertion or extraction reaction of LiMn 1-x Fe x PO 4 for Mn 2+ /Mn 3+ increased with Fe content. D app for Fe 2+ /Fe 3+ slightly increased with decreasing Fe content. The difference of D app value was attributed to the activation energies ( E a ) of lithium diffusion process of LiMn 1-x Fe x PO 4 . The E a of LiMn 1-x Fe x PO 4 for Mn 2+ /Mn 3+ and Fe 2+ /Fe 3+ was determined by the energy barrier of lithium hopping at the interphase between Li-rich and Li-poor phase under electrochemical kinetic conditions.