Electrochemical performance of LiFe_0.99La_0.01PO ₄ coated with different organic acids

Olivine-type LiFePO₄ is one of the most popular cathode materials for high power Li-ion batteries. However, its intrinsic properties of poor conductivity and low lithium-ion diffusion limit its practical applications. In order to improve these disadvantages, we prepared the LiFe _0.99La_0.01PO₄/C composite materials by a solid state reaction method using La-ion as a metal dopant and organic diacids as carbon coating sources. In this work, the composite materials were characterized by XRD, DSC, SEM/mapping, TEM/EDS/SAED, and total organic carbon (TOC). Further, their electrochemical performance was examined. The conductivity results of the doped composites showed a distinct enhancement from 3.97×10^-8 to 2.60×10^-5 S cm^-1. The LiFe_0.99La_0.01PO₄/C composites using malonic and sebasic acids as carbon sources displayed an initial discharge capacity of 151 and 145 mAh g^-1, respectively, between 2.8 and 4.0 V at a 0.2 C rate. This is a significant improvement compared to the initial discharge capacity of 100 mAh g^-1 of the un-doped bare LiFePO₄ sample, and it may be related to electronic conductivity enhancement by carbon coating and charge transfer kinetics improvement by La-ion doping.