Effects Of Shell Composition And Thickness On Properties Of Core-shell NCM Material

The life and safety of lithium-ion batteries largely depends on the performance of cathode materials, so the research of cathode materials is a top priority at present. LiNixCoyMn1-x-yO2 with ternary layered structure and the advantages of LiNiO2, LiCoO2 and LiMnO2, has low cost, high reversible capacity and stable cycle performance, so it is considered as a very promising material. Y.K. Sun group and Argonne laboratory have successfully redesigned and synthesized a series of Li NixCoyMn1-x-yO2 with core-shell structure or concentration-gradient structure by co-precipitation method and high-temperature solid-phase process. However, Y.K.Sun group and Argonne laboratory have not researched the effect of the shell component and shell thickness on the properties of core-shell structure materials in detail. Therefore, based on the LiNi O2-LiCoO2-Li MnO2 ternary phase diagram, Li Ni0.5Co0.2Mn0.3O2 and LiNi1/3Co1/3Mn1/3O2 which have been commercially used were designed respectively to double core shell structure and single core shell structure with the same components. By comparing the difference of shell composition in double shell structure, the effect of shell composition on properties of core-shell NCM material was analyzed.LiNi0.8Co0.1Mn0.1O2 with high capacity was chose as core, LiNi1/3Co1/3Mn1/3O2 which could be easily synthesized and had been commercially used was chose as transition layer material,and LiNi0.4Co0.2Mn0.4O2, Li Ni0.45Co0.1Mn0.45O2, LiNi0.475Co0.05Mn0.475O2, LiNi0.5Mn0.5O2 with high stability were chose as shell. Therefore, LiNi0.5Co0.2Mn0.3O2 was redesigned as double core-shell structure Li[(Ni0.8Co0.1Mn0.1)core(Ni1/3Co1/3Mn1/3)inter shell(Ni(1-x)/2CoxMn(1-x)/2)shell]O2(x=0?0.05?0.1?0.2). Firstly, double core-shell structure precursors were synthesized by co-precipitation route, then the mixtures of the precursors and a certain amount of Li2CO3(Li/M = 1.05:1) were calcined at 850 °C for 16 h to prepared lithium oxide preparation of double core-shell structure. Then the composition, structure, morphology and electrochemical properties of the lithium oxide were studied and the effect of shell composition on properties of core-shell NCM material was analyzed.LiNi1/3Co1/3Mn1/3O2 was designed into a single core-shell structure Li{[NiyCo1-2yMny](1-x)}core{[Ni1/2Mn1/2]x}shell O2(0 ? x ? 0.5; 6y+3x-6xy=2),{[NiyCo1-2yMny](1-x)}core{[Ni1/2Mn1/2]x}shell(OH)2 precursor was successfully synthesized by co-precipitation route. After washing, drying and sieving, the mixtures of the precursors and a certain amount of Li OH(Li/M = 1.05) were calcined at 800 °C for 16 h to prepare lithium oxide with single core-shell structure. Then the composition, structure, morphology and electrochemical properties of the lithium oxide were studied and the effect of shell thicknesson properties of core-shell NCM material was analyzed.By comparing core-shell structure Li Ni0.5Co0.2Mn0.3O2 and Li Ni1/3Co1/3Mn1/3O2 and with non-core-shell structure material with the same composition, it is found as follows,(a) the core-shell structure can improve the cycle performance and thermal stability performance of the material;(b) in the core-shell structure materials, the cycle performance and thermal stability performance improve with the increasing Mn element content in the shell;(c) the cycle performance and thermal stability performance also improve with the increasing shell thickness.