Electrochemical Behavior of Iron-Substituted Lithium Nickelate

Abstract

Lamellar phases with nominal composition Li(Ni 1Ϫy Fe y )O 2 (y Յ 0.30) were synthesized and characterized by Rietveld refinement of their X-ray diffraction (XRD) patterns. These materials exhibited the formula Li 1Ϫz (Ni 1Ϫy Fe y ) 1ϩz O 2 with 0.06 Յ z Յ 0.08 and were used as positive electrodes in lithium batteries. Their electrochemical performances decreased with increasing iron content. The Li x (Ni 0.90 Fe 0.10 ) 1.06 O 2 phases were characterized by XRD and Mössbauer spectroscopy. A solid solution appeared in the entire deintercalation domain 0.28 Յ x Յ 0.94, and Rietveld refinement of the XRD patterns allowed us to characterize the variation of structural parameters upon lithium deintercalation. 57 Fe Mössbauer spectroscopy showed that nickel and iron ions were oxidized simultaneously. The fraction of high-spin Fe 4ϩ was related to the strong ligand field resulting from the presence of the prevailing Ni 3ϩ and Ni 4ϩ ions which lead to a lattice contraction. The behavior upon deintercalation of the Li(Ni 0.90 Fe 0.10 )O 2 phase was compared to that of two-dimensional LiFeO 2 .

On The LixNi0.70Fe0.15Co0.15O2 System: An X-Ray Diffraction and Mössbauer Study

“…Figure 9 shows the variations of the populations of the various iron oxidation states for the Li V (Ni Fe Co ) O system compared to that obtained for the Li V (Ni Fe ) O system reported in a previous study (9). In the two systems, the general evolutions of the populations are quite similar in that they occur in several steps.…”

“…Conversely, the presence of the larger iron ions in the vicinity of the nickel ions leads to an expansion of the [NiO ] octahedra, making the nickel ion's oxidation more di$cult than in the Li V NiO system. As a result, a simultaneous oxidation of nickel and iron ions is experimentally observed (9,37,38 Fe ) O system for compositions with x'0.50. This observation proves that, in the "rst part of the charge, cobalt substitution favors in the same proportion the oxidation of both iron and nickel ions.…”

“…It should be noted that for some compositions the values are quite high; this e!ect is certainly due to a low signal/noise ratio resulting from the counting statistic. Nevertheless, this has no e!ect on the population ratio found in the "t. Three di!erent iron species are evidenced and characterized by three isomer shifts at 0.33, 0.20, and !0.11 mm/s: (9), in iron-substituted nickel hydroxide (31}33), and in many materials with perovskiterelated structure (34,35).…”

Electrochemical properties of Li1−z (Ni1−y Fe y )1+z O2 synthesized by the combustion method in an air atmosphere

“…ions from entering the Li sites and leads to the formation of Li 1-z (Ni 1-y Co y ) 1?z O 2 with z = nearly zero, resulting in better electrochemical properties. Prado et al [47] reported that the substitution of Fe for Ni in LiNiO 2 degrades the electrochemical properties, by making the lattice size larger and thus making the Ni 2? ions more stable than Ni 3?…”

Preparation and Characterization of LiNi0.8Co0.2O2 Synthesized by an Emulsion Drying Method

“…However, it has some disadvantages such as nonstoichiometry (called cation mixing), degradation of the retention capacity due to a structural change during the cycling [1], and thermal instability at a highly oxidized state. Partial substitution of other elements (Co, Mn, Fe, Al, Zr, and Ti) for Ni sites has been studied to improve the electrochemical performance of LiNiO 2 [2][3][4][5][6][7][8]. Of these elements, cobalt has attracted much attention because only cobalt substitution can form a complete solid solution, and the solid solution shows better thermal stability than pristine LiNiO 2 .…”