Effect of lithiation/delithiation rate on the interface of LiFe0.5Mn0.5PO4/Fe0.5Mn0.5PO4: Tracking through structure, surface chemistry and impedance

Abstract

LiFe_0.5Mn_0.5PO₄ (LFMP) is regarded as a promising cathode that can combine the advantages of LiFePO₄ and LiMnPO₄, providing higher energy density, cycle life and good thermal stability. In this work, we report the electrochemical performance of LFMP cathode prepared using a microwave-assisted solvothermal process and subsequent carbon coating. Apart from comprehensive materials analysis, the electrochemical analysis has been conducted; the best sample delivered a discharge capacity of 134 mAh/g at 25 mA/g and 112 mAh/g at a higher current density of 300 mA/g. To understand the lithiation rate or delithiation rate, which plays a major impact on the performance, asymmetric charge–discharge rates between 25 and 300 mA/g were investigated. It is realized that the asymmetric condition of fast charging and practical discharge rate is suitable for LFMP to retain the benefit of higher Mn-redox voltage, in spite of a slight compromise on the capacity. The operando-X-ray diffraction studies were conducted to examine structural changes that occur during 1st charge/discharge cycle. Also, impedance analysis, ex situ XRD and surface chemical studies with different charge/discharge rates have been investigated and correlated. Two different high-temperature cycling tests were carried out for a correlation with the room temperature performance.