Electrochemical features of LiMnPO₄ olivine prepared by sol-gel pathway

LiMnPO₄ is a potential cathode for lithium-ion battery of high thermal stability, low cost, environmental sustainability and high theoretical energy density. However, this intriguing olivine material suffers from intrinsic sluggish kinetics of lithium (de-)insertion, which limits the reversible reaction in practical lithium cells. Herein we report a careful study of the impedance features of LiMnPO₄ during electrochemical reaction in lithium cell. The LiMnPO₄ material is prepared by sol-gel method and fully characterized by X-ray diffraction (XRD), thermogravimetric analysis (TGA), scanning electron microscopy (SEM), and transmission electron microscopy (TEM). The material shows suitable galvanostatic cycling with a working voltage of about 4.1 V, which is higher than the 3.5 V value expected from the most common olivine material, i.e., LiFePO₄. Hence, electrochemical impedance spectroscopy (EIS) is used to study the lithium (de-)insertion within the LiMnPO₄ structure. The results indicate an impedance behavior depending on the state of charge and a lithium diffusion coefficient trend slightly decreasing during cell operation within the 10⁻¹⁴ – 10⁻¹³ cm² s⁻¹ range. The electrochemical study in lithium cell reveals remarkable enhancement of the electrode kinetics at 70 °C, which suggests preferred application of LiMnPO₄ materials at the higher temperatures