Limited Content of Fe in Solid Solution Li(Ni, Mn, Co, Fe)O 2 : Polyhedron Homogeneity and Specific Capacity
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Limited Content of Fe in Solid Solution Li(Ni, Mn, Co, Fe)O2: Polyhedron Homogeneity and Specific Capacity G. D. Nipan1 • M. N. Smirnova1 • D. Yu. Kornilov2 • M. A. Kop’eva1 G. E. Nikiforova1 • S. P. Gubin1
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Submitted: 27 February 2020 / in revised form: 22 April 2020 ASM International 2020
Abstract The samples with nominal compositions Li1.1(Ni0.33Mn0.33Co0.33)xFe1-xO2 (0 B x B 1) were synthesized by the starch-based gel combustion. The obtained samples had homogeneity composition Li1?yNi0.27Mn0.27Co0.27Fe0.20O2 in the solid solution with a-NaFeO2 structure based on the results of the x-ray phase analysis. The structure of stable homogeneity Li(Ni,Mn,Co,Fe)O2 can be represented as a pentahedron having the base Li1?yNiO2Li1?yNi0.5Mn0.5O2-Li1?yCoO2 with Fe content limit * 15% of the total cation number. It is observed within the concentrations of tetrahedron consisting the pseudo-fourcomponent system (Li1?yNiO2-Li1?yMnO2-Li1?yCoO2Li1?yFeO2) upon set isobaric-isothermal conditions (T = 800 C, PO2 = 21 kPa). The electrochemical testing of homogeneous samples such as Li1?yNi0.23Mn0.23Co0.30Fe0.23O2, Li1?yNi0.27Mn0.27Co0.20Fe0.27O2 and Li1?yNi0.30Mn0.23Co0.23Fe0.23O2 was carried out with almost the equimolar ratio of transition metals. Keywords gel combustion Li-ion battery materials phase diagram solid solution Li(Ni, Mn, Co,Fe)O2 x-ray diffraction
& G. D. Nipan [email protected]; [email protected] 1
Kurnakov Institute of General and Inorganic Chemistry of RAS, Moscow, Russia 119991
2
AkKo Lab Ltd, Moscow, Russia 129110
1 Introduction By the intentional content reducing of the expensive and toxic Co cation in layer modified LiCoO2 (R-3m) structure[1] of principal functional components for Li-ion battery (LIB) cathodes, there has been initially obtained the continuous solid solution Li(Ni, Co)O2[2] and then the limited solid solution Li(Ni, Mn, Co)O2.[3] Despite the significant sophistication of the chemical composition, the concept of the further cation replacement, preserving the R-3m structure is still relevant. Fe is considered the most appealing alternate owing low cost and ecological safety. However, until recently all the attempts to obtain Li(Ni, Mn, Co, Fe)O2 (R-3m) leaded to a replacement one of the cations in triad Ni, Mn and Co and the obtaining next compositions of the solid solution. Among them LiNi0.33Mn0.33Co0.33-xFexO2 (x = 0.017,[4] 0.04,[5] 0.08,[5,6] 0.10,[7] 0.11[8] and 0.17[9]), LiNi0.6Mn0.2Co0.15Fe0.05O2,[10] LiNi0.4Mn0.4Co0.15Fe0.05O2,[11] Li1.2Ni0.16Mn0.56Co0.04Fe0.04O2,[12] LiNi0.317Mn0.33Co0.33Fe0.017O2,[4,13] LiNi0.33Mn0.317Co0.33Fe0.017O2[4] as well as replacement of all the cations up to [7,14,15] LiNi0.3Mn0.3Co0.3Fe0.1O2. During our initial studies the single phase samples Li1?yNi0.2Mn0.2Co0.2Fe0.4O2 and Li1?yNi0.42Mn0.14Co0.14Fe0.3O2 were synthezed by the gel combustion method with reference value y = 0.05.[16] However, the multiple synthesis replication undermined the homogeneity, which defines the stability of electrochemical characteristics of the material. It has
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