Study On Preparation And Modification Of LiNi_xCo_yMn_zAl_1-x-y-zO₂ Cathode Materials For Lithium-ion Battery

In this paper,the series of electrode materials LiNi_xCo_yMn_zAl_1-x-y-zO₂ were synthesized via the modified hydroxide co-precipitation method and high temperature solid state method.During the process of precursor preparation,a small amount of cobalt were partially replaced with aluminum to achieve the lower cost,the better environment friendship and the more excellent electrochemical properties.Eventually XRD,SEM,particle size,CV and EIS tests were combined to make a further mechanism research and validation.In this paper,firstly different feeding ways,feeding speeds and solution pH values were considered during the preparing of Ni_0.5Co_0.15Mn_0.3Al_0.05?OH?₂ precursor,which had different influences on the charge-discharge properties of materials.As a result,the sample exhibited the best electrochemical performances which was synthesized under the following processes:mixing Al?OH?3 precipitate with ammonia as mother liquor,feeding sodium hydroxide solution and the ternary salt solution by flow and feeding manner,controlling pH value was 11 and the feeding speed of the ternary salt solution was 0.15mL·min^-1 as well.In the best preparation process of co-crystallization reaction,originally formed Al?OH?₃ precipitates are regarded as seeds to be introduced?act as crystal nucleus?.The transition metal co-precipitation crystals form by the subsequent reaction which can grow up on the surfaces of Al?OH?₃ precipitates evenly.And ultimately the precursor product is obtained which is the closest to the theory of stoichiometric ratio.And then the different calcination regulations were investigated in detail.The results show that the LiNi_0.5Co_0.13Mn_0.3Al_0.07O₂ sample which calcined at 850°C has the highest layered structure growing degree,best morphology,the higher lithium ionic activity and better cyclic discharge properties.In addition,the series of the electrode materials LiNi_0.6Co_0.2-xMn_0.2Al_xO₂ exhibit the best performance synthesized under oxygen atmosphere,and calcining temperature at 800°C.It is attributed to that the oxygen deficiency during high temperature calcination can be offset by oxygen passing into,which also can decrease the reaction activation energy and the calcining temperature accordingly.Then the doping aluminum content was changed to obtain a series of cathode electrode materials LiNi_xCo_yMn_zAl_1-x-y-zO₂ under the optimal condition.Afterwards their electrochemical performances were compared to determine the best doping content.Eventually XRD,SEM,particle size,CV and EIS tests were combined to make a further mechanism research and validation.Experimental results show that doping aluminum will not change the layer structure of ternary material.And the cathode material LiNi_0.5Co_0.13Mn_0.3Al_0.07O₂ in its system shows the best electrochemistry properties,with an initial discharge specific capacity of 159.7 mAh·g^-1 at 0.2C,and a capacity retention rate of92.84%after 50 cycles at 0.5C.Simultaneously LiNi_0.6Co_0.14Mn_0.2Al_0.06O₂ in its system also shows the most excellent electrochemistry performances,with an initial discharge specific capacity of 172.3 mAh·g^-1 at 0.2C,and a capacity retention rate of 71.26%after 50cycles at 0.5C.It is closely related to their smaller impedances and weaker polarization.