Preparation And Modification Of LiMPO₄/C （M=Fe,Mn） As Cathode Material For Li-ion Battery

Li-ion battery has been intensively applied in many electronic portable devices due toits advantages such as high energy density, long cycling life, non-memory effect, smallself-discharge rate and environment-friendliness. It is also being studied to realize itsapplications into large electricity storage devices and electric vehicles (EVs). Toimprove the electrochemical properties and decrease the cost of lithium ion battery arethe two main goals at the moment. And to improve cathode’s electrochemical propertiesand decrease its cost are especially important because cathode is the key part of battery.In this dissertation, the preparation and modification of olivine structured LiMPO4(M=Fe, Mn) have been studied, the results are as follows.1. Well-crystallized carbon-coated LiFePO4(LFP/C) and its Mg2+-doped derivative(Mg-LFP/C) have been successfully synthesized through an improved solid-statereaction method without ballmilling. The structure and morphology analysis resultsmanifest that both magnesium ions and carbon coating layer are well distributed and thethickness of carbon layer is about5nm. The electrochemical tests show that Mg-LFP/Cdisplays better electrochemical properties than LFP/C, especially for the high rateperformance. When discharging at1C and5C, Mg-LFP/C shows specific dischargecapacity of130mAh g-1and109mAh g-1respectively. After50cycles at5C thecapacity retention rate is still above98%. The enhanced electrochemical performance ofthe composite could be attributed to a combination result of the fine particle size withnarrow particle size distribution, homogeneous carbon coating on the surface of theparticles and magnesium ion doping.2. LiFexMn1-xPO4/C nanocomposite has been prepared employing a two-step method.The as-obtained composite conbines advantages of both LiFePO4and LiMnPO4. In thisdissertation, the influence of different Fe/Mn molar ratio to the electrochemicalperformance of LiFexMn1-xPO4/C has been studied. When Fe/Mn molar ratio increasesfrom0/10to5/5, the rate performance and cycling performance of the compositeimproves correspondingly, and the specific discharge capacity at0.1C are101.67mAhg-1,110.78mAh g-1,117.87mAh g-1,124.09mAh g-1,132.70mAh g-1and138.00mAhg-1when the molar ratio equals to0/10,1/9,2/8,3/7,4/6and5/5respectively.