Preparation Of Lini_1/3Co_1/3Mn_1/3O₂and Cr Or F Doped LiNi_1/3Co_1/3Mn_1/3O₂Powders Via Quasi-coprecipitation Method, And Their Electrochemical Properties

LiNi_1/3Co_1/3Mn_1/3O₂is now widely studied as a cathode material to replace LiCoO₂for use in the next generation of lithium ion batteries for high specific capacitance, longcycle life, good thermal stability and low cost. In this paper, a one-stepquasi-coprecipitation method has been used to synthesize LiNi_1/3Co_1/3Mn_1/3O₂and itsDoped powders （Cr or F） directly. Through TG-DTA, XRD, SEM, EDS, XPS, CV andEIS, the processing conditions and electrochemical properties of LiNi_1/3Co_1/3Mn_1/3O₂powders were studied in detail. And the influence of the Cr and F doping on thestructure, morphology and electrochemical performance of the LiNi_1/3Co_1/3Mn_1/3O₂powders were discussed especially. The obtained main results are as follows:（1） A mixing precipitation precursors were prepared by one-stepquasi-coprecipitation method in mixed solution contained Li⁺, Co²⁺, Ni²⁺and Mn²⁺ionsusing （NH4）2CO3as precipitant. After being dried and ground, the precursors weresintered under different sintering temperatures （700¹000℃） and different sinteringtimes （6²4h）, and then LiNi_1/3Co_1/3Mn_1/3O₂powders were obtained. Test resultsindicate that:①The sintering parameters have important influence on the crystal structure,morphology and electrochemical performance of the LiNi_1/3Co_1/3Mn_1/3O₂powders. Theoptimal calcining temperature is900℃and the optimal calcining time is12h. The as-prepared LiNi_1/3Co_1/3Mn_1/3O₂powders calcined at under the optimal calciningconditions exhibit a perfect layered structure and a good morphology. And the dischargecapacitance of the as-prepared LiNi_1/3Co_1/3Mn_1/3O₂powders is419.37F g-1, exhibiting aexcellent electrochemical properties.②Stoicheiometric LiNi_1/3Co_1/3Mn_1/3O₂can be achieved by thisquasi-coprecipitation method and the oxidation states of Ni, Co, Mn are+2,+3and+4respectively.（2） LiNi_1/3Co_1/3-xMn_1/3CrxO₂and Li[Ni_1/3-x/3Co_1/3-x/3Mn_1/3-x/3]CrxO₂powders weresynthesized through two doping methods for Cr element under the optimal processingconditions. The obtained results are as follows:①Through the one-step quasi-coprecipitation method, the stoicheiometric Crdoped electrode materials can be achieved.②The doping amount of Cr has significant influence on the structure andmorphology of the product.③A small amount of the doping Cr can enhance the discharge capacitance, but anexcessive Cr can weaken it. The proper doping amount of Cr is0.03.（3） LiF is mixed into the solution directly to prepare F-dopedLiNi_1/3Co_1/3Mn_1/3O₂-xFxpowders through the quasi-coprecipitation method. The resultsillustrate:①LiF can promote sintering, the optimal calcining temperature can be reduced to800℃.②A small amount of doped F-have little influence on the structure of the product,and the oxidation states of the transition metal ions are not changed. But the doping ofF-can affect the morphology.③The electrochemical performance can be modified by the doping of F-. A smallamount of doped F-can enhance the discharge capacitance, but an excessive F-canweaken it. The feasible doping amount of F-is0.05.