Synthesis And Electrochemical Characterization Of Layered LiNi_1-x-yCo_xMn_yO₂Cathode Material

At present, the main commercialized cathode material is LiCoO₂. Also, Co isexpensive and toxic, plus the defects of its electrochemical performance. Thesedrawbacks have generated enormous interest in the development of alternative cathodes.Layered Li-Ni-Co-Mn oxide electrode materials have been found to exhibit good cyclestability performance, high specific capacity, higher safety and lower cost characteristics,It is considered to be the most likely alternative cathodes of LiCoO₂.On the base of LiNi_0.33Co_0.33Mn_0.33O₂, first the effect of different synthesis methodon structure, lattice parameter, particle distribution and electrochemical performancewere studied of the dissertation．Co-precipitation method is chosen as the optimalsynthetic method for layered lithium nickel cobalt manganese oxide. Then, thedissertation emphasized on optimization research of synthesis process conditions. Suchas types of precipitating agent, addition manner of precipitation agent, pH value ofprecipitation reaction, concentration of reactant, process mode of precursors and molarration of Li/M（M=Ni, Co, Mn）. The effect of those synthesis conditions on structurecharacteristic, particle distribution, specific surface area and electrochemicalperformance were studied．The optimum conditions for co-precipitation were obtainedthrough the investigations of LPSA, XRD, TG-DTA, galvanostatic charge-discharge andcycle voltammetry were introduced to characterize the structure and electrochemicalproperties of the layered Li-Ni-Co-Mn oxide. The optimized flowsheet were selected asfollows: Sodium hydroxide solution（2mol/L） with ammonia water as precipitating agent,parallel addition manner of precipitation agent, pH=11, Mixed metal ion concentrationof2mol/L, precursors process mode of low temperature drying with biodiesel,Li/M（M=Ni, Co, Mn） ration of1.0, the ratio for transition metal ions Ni: Co: Mn is4:2:4.LiNi_0.4Co_0.2Mn_0.4O₂with excellent electrochemical performance was synthesizedunder the above optimized flowsheet. Its initial discharge capacity was197.4mAh/g andinitial discharge efficiency is85.49%in2.5-4.6V at0.1C rate, the specific dischargecapacity retention is90.13%after50cycles. Meanwhile, Li_1.2Ni_0.1Co_0.2Mn_0.5O₂andLi_1.2Ni_0.13Co_0.13Mn_0.54O₂were also synthesized under the optimized flowsheet, Its initialdischarge capacity were195.8mAh/g and206.95mAh/g respectively in2.5-4.6V at0.1C rate, the specific discharge capacity were224.6mAh/g and221.6mAh/g after30 cycles respectively. Its show high specific charge-discharge capacity and good cyclestability.