Synthesis Arid Electrochemical Performance Of Nickel Manganese Based Li-excess Layered Cathode Materials For Lithium-ion Batteries

Great efforts have been done on Li-excess layered cathod materials forlithium-ion batteries since J.R. Dahn introduced the high capacitiy material in2001.Nowadays, more and more peple are desired to develop this material. Recently,international study of Li-excess cathod material gradully in-depth, and the source ofthis kind of material high capacity have a more clear understanding. In view of thelarge scale synthesis of battery materials is the key links of lithium ion battery actualapplication. How to develop low cost, large scale preparation of uniform quality andmorphology of battery materials, green preparatio is the key to the lithium ion batteryneeded to solve in the study of scientfic and technical problems. For rich lithiumlayered cathode material, the different synthesis methods can have differernt effects.And the selection of process parameters is still on the material performance has agreat influece, so different synthetic methods for optimizing the rich lithium layerdepositive electrode materials of electrochemical performance is particularly important.In view of the above problems, the main research objebct is Li1.13Ni0.3Mn0.57O2, andwe hope to throgh modulation of experiment parameters improve the electrochemicalperformance of lithium rich layered cathode materal.In this chapter, we used solid-state method to synthesis Li1.13Ni0.3Mn0.57O2materials. We chose the synthesis temperature is850°C、900°C、950°C, andcalcination time is6h、12h、18h, respectively, via thermal gravimetric analysis forLi1.13Ni0.3Mn0.57O2. The cycling performance of the cathode shows that the materialsof synthesis temperature is900°C and calcination time is12h presented a excellent cycleability，its capacity retention ratio is99%after100cyclies. But the materials ofsynthesis temperature is850°C and950°C were77%and85%. The electrochemicalimpedance spectra(EIS) of these showed that the materials of synthesis temperature is900°C and calcination time is12h whether the resistance of solid electeolyteinterphase or the resistance of charge-transfer presented a best value.Secondly, we successfully prepared Li1.13Ni0.3Mn0.57O2using the co-precipitationmethod. We controled pH=11、12、13when synthesis of precursor(M(OH)2). Due tothe Ni(OH)2and Mn(OH)2have different solubility product constant, pH=12ofmaterials have a best dispersibility. The particle size of pH=11、12、13were565nm,489nm,493nm via particle size analysis, hence the material of pH=12have a shorterlithium ion diffusion path. The cycling performance of the cathode show that thematerial of pH=12presented a best cycle stability，its capacity retention ratio is92.4%after100cyclies.Then, Li-excess layered materials Li1.13Ni0.3Mn0.57O2was synthesized viasucrose combustion (SC) and glycine combustion (GC) methods. SEM images of SCand GC show that the particles are different. Due to sucrose and glycine havedifferent melting point and inflammable point, the strong chemical reactions willdifferent. Lattiee parameters of the SC and GC samples show that the two materialshave good Li-excess layered structure. The c/a ratio of SC material is the bigger andthis behavior indicates that the SC material easier to transfer for Li+, so the materialshowed excellent cycleability.Finally, we compared the electrochemical properties Li1.13Ni0.3Mn0.57O2ofsolid-state method、co-precipitation method and combustion method, The SEMimages of solid-state method material have serious very serious reunionphenomenon, and the lengthen Li+diffusion path will lead to the discharge capacitydecreased. The combustion method of material is uniform. Then we studied theelectrochemical properties of this material, our experiments showed it obtainedexcellent cycleabillity, the material showed s high dischage capacity of210mAh g-1 after80cycles. Because of the different transition metal elements of nickel andmanganese in the electrochemical. So we fuuther researched the structure propertiesof Li(1-2x)/3NixMn(2-x)/3O2using XRD, CV and EIS. X-ray diffraction based onwhich we determined the materials of x=0.2and x=0.3obtained excellent order oflayered structure. Then, we compared the electrochemical performances ofLi(1-2x)/3NixMn(2-x)/3O2via cyclic voltammetry,due to the oxygen loss a strength peakappeared. We know that the charge capacity is related to the integral under the peak,so the material of Li1.13Ni0.3Mn0.57O2have excellent discharge capacity is294.3mAhg-1.