Preparation And Properties Of LiMn₂O₄ Cathode Materials For Li-ion Batteries

In this paper,LiMn2O4 cathode materials have been synthesized by a high temperature solid-state reaction method.The structure,morphology and electrochemical properties of LiMn2O4 were investigated by XRD,SEM,galvanostatic charge/discharge testing and electrochemical impedance spectroscopy,respectively.This article focuses on the second phase in the LiMn2O4 cathode material and explores the optimum sintering conditions and lithium doping of LiMn2O4 cathode materials.In the LixMn2O4 cathode material doped with different Li content(x=1,1.02,1.04,1.06),the XPS test found that with the increase of lithium content,the Mn4+content decreased from 84.80%to 82.62%and then increased to 88.98%.Subsequently,we tested the electrochemical properties of the samples.It was found that with the increase of lithium content,the rate performance of samples increased continuously,and the values of Rct and Rsf first increased and then decreased.Through experimental analysis,we believe that with the increase of lithium content,these changes in Mn4+ content,rate performance,Rct and Rsf values are related to the change in the second phase in LiMn2O4 cathode material.In addition,we also studied the effects of different sintering time(5 h,10 h,15 h and 20 h)on the LiMn2O4 cathode materials.It was found that the sample showed the best electrochemical performance when the sintering time was 10h.We performed XRD data refinement of samples and found that there was the second phase in four samples,and XPS test showed that with the increase of sintering time,the content of Mn4+in the sample is decreased,and the rate performance is also getting worse.We believe that with the increase of sintering time,changes in Mn4+content and rate performance are related to the change in the second phase in LiMn2O4 cathode material.In order to further explore the best synthetic conditions for the synthesis of LiMn2O4 cathode materials,we synthesized LiMn2O4 cathode materials at different sintering temperatures(750?,850?,950?).In order to improve the cycle performance of the sample,we doped the same amount of Al2O3 in the sample.The experimental results show that the second phase of the sample increases as the sintering temperature rises from 750? to 950?,and the intensity ratio of the(311)/(400)peaks increases.We tested the samples by SEM.It is found that when the sintering temperature is 950?,the crystallinity of the sample is the highest and the size of the primary particle is the largest,which indicates that the increase of sintering temperature will promote the improvement of the crystallinity of the samples.In the electrochemical performance test,the most excellent electrochemical performance was shown at the sintering temperature of 850?.