C. Delmas

Optimization of the composition of the Li{sub 1{minus}z}Ni{sub 1+z}O{sub 2} electrode materials: Structural, magnetic, and electrochemical studies

Lithium nickel oxide, used as the positive electrode in lithium batteries, crystallizes in the rhombohedral system (SG :R3m) with a layered structure. In fact, stoichiometric LiNiO 2 has never been reported. The true formula is Li 1-z Ni 1+z O 2 (0.00 < z < 0.20) ; z is dependent on the experimental conditions. This nonstoichiometry leads to a strong decrease of the battery performance. Therefore, several methods of preparation were investigated to synthesize stoichiometric LiNiO 2 . The Li 0.98 Ni 1.02 O 2 composition, which is very close to the ideal one, was obtained from a mixture of Li 2 O and NiO heated at 700°C. This quasi-2D LiNiO 2 was submitted to several thermal treatments, in order to determine the influence of the temperature on the composition. Purposely lithium deficient phases were also prepared. Correlations between the composition of each material (deduced from the Rietveld refinement of the x-ray diffraction pattern) and the magnetic and electrochemical behavior are discussed

Synthesis and characterization of new LiNi1-yMgyO2 positive electrode materials for lithium-ion batteries

New LiNi 1-y Mg y O 2 (0 ≤ y ≤ 0.20) layered oxides were synthesized by a coprecipitation method followed by a high-temperature thermal treatment. Rietveld refinements of their X-ray diffraction patterns showed that they exhibit a quasi-two-dimensional structure, isostructural to LiNiO 2 . for small substitution amounts (y ≤ 0.10). For larger amounts (y = 0.15, 0.20), the Li/(Ni + Mg) ratio is significantly lower than unity. In all cases, the extra ions located in the inter-slab space for lithium deficiency compensation are preferentially Mg 2+ ions. A magnetic study confirmed the cationic distributions which result from the size difference between Ni 3+ and Mg 2+ ions. An electrochemical study showed reversible behavior for all materials. A high capacity (≥ 150 Ah kg -1 ) was found for LiNi 1-y Mg y O 2 phases (y ≤ 0.02), which decreased when y increased. The presence of Mg 2+ cations in the inter-slab space, which cannot be oxidized and have a size close to Li + , prevents the local collapses of the structure which occurs for the Li 1-zNi1+zO2 system; therefore good cycling stability is observed.

Electrochemical Behavior of Iron‐Substituted Lithium Nickelate

Lamellar phases with nominal composition Li(Ni 1-y Fe y )O 2 (y ≤ 0.30) were synthesized and characterized by Rietveld refinement of their X-ray diffraction (XRD) patterns. These materials exhibited the formula Li 1-z (Ni 1-y Fe y ) 1+z O 2 with 0.06 ≤ z ≤ 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 Mossbauer spectroscopy. A solid solution appeared in the entire deintercalation domain 0.28 ≤ x ≤ 0.94, and Rietveld refinement of the XRD patterns allowed us to characterize the variation of structural parameters upon lithium deintercalation. 57 Fe Mossbauer spectroscopy showed that nickel and iron ions were oxidized simultaneously. The fraction of high-spin Fe 4+ was related to the strong ligand field resulting from the presence of the prevailing Ni 3+ and Ni 4+ 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 .

Magnetism of Li1−zNi1+zO2: A powerful tool for structure determination

Abstract Magnetic properties of the Li1−zNi1+zO2 family have been studied as a function of stoichiometry. It is shown that the magnetic structure evolves from a 2D fully frustrated antiferromagnet (z = 0) to a 3D ferrimagnet (z > 0.22).

Raman and infrared spectra of some chromium Nasicon-type materials: Short-range disorder characterization

Abstract The infrared and Raman spectra of the Nasicon-type chromium systems are found to be very sensitive to the composition and to the nature of the metallic ions. The frequency shift of the infrared active modes involving the metallic ions is correlated to the modification of the crystal field around these ions. The static short-range disorder, particularly characterized from the Raman spectra, is essentially interpreted in terms of Na+ ion site occupation change vs the composition and the temperature.

O3–NaxMn1/3Fe2/3O2 as a positive electrode material for Na-ion batteries: structural evolutions and redox mechanisms upon Na+ (de)intercalation

The electrochemical properties of the O3-type NaxMn1/3Fe2/3O2 (x = 0.77) phase used as positive electrode material in Na batteries were investigated in the 1.5–3.8 V, 1.5–4.0 V and 1.5–4.3 V ranges. We show that cycling the Na cells in a wider voltage range do not induce a significant gain on long term cycling as the discharge capacities reached for the three experiments are identical after the 14th cycle. The structural changes the material undergoes from 1.5 V (fully intercalated state) to 4.3 V were investigated by operando in situ X-ray powder diffraction (XRPD) and were further characterized by ex situ synchrotron XRPD. We show that the low amount of Mn3+ ions (≈33% of total Mn+ ions) is enough to induce a cooperative Jahn–Teller effect for all MO6 octahedra in the fully intercalated state. Upon deintercalation the material exhibits several structural transitions: O′3 → O3 → P3. Furthermore, several residual phases are observed during the experiment. In particular, a small part of the O3 type is not transformed to P3 but is always involved in the electrochemical process. To explain this behaviour the hypothesis of an inhomogeneity, which is not detected by XRD, is suggested. All phases converge into a poorly crystallized phase for x ≈ 0.15. The short interslab distance of the resulting phase strongly suggests an octahedral environment for the Na+ ions. X-ray absorption spectroscopy and 57Fe Mossbauer spectroscopy were used to confirm the activity of the Mn4+/Mn3+ and Fe4+/Fe3+ redox couples in the low and high voltage regions, respectively. 57Fe Mossbauer spectroscopy also showed an increase of the disorder into the material upon deintercalation.

Structure and reversible lithium intercalation in a new P′3-phase: Na2/3Mn1−yFeyO2 (y = 0, 1/3, 2/3)

In this contribution, new data on the reversible Li+ intercalation in iron substituted sodium manganates are provided. Novel Na2/3Mn1−yFeyO2 (y = 0, 1/3 and 2/3) compounds with a P′3-type structure are prepared from freeze-dried citrate precursors at 500 °C. A new structural element is the development of three-layer oxygen stacking contrary to the well-known P2-type Na2/3MnO2 with a two-layer sequence. The effect of Fe additives on the structure of Na2/3MnO2 was examined by XRD powder diffraction and TEM analysis. The oxidation state and the distribution of transition metal ions in Na2/3Mn1−yFeyO2 were analysed using electron paramagnetic resonance spectroscopy. The lithium intercalation in Na2/3Mn1−yFeyO2 was investigated in two-electrode lithium cells of the type Li|LiPF6 (EC:DMC)|Na2/3Mn1−yFeyO2. The stability of the layered phases during lithium intercalation was studied by ex situ Raman spectroscopy. It was found that the intermediate Na2/3Mn2/3Fe1/3O2 composition is able to intercalate Li+ reversibly in high amounts. Details of the structure and its stability during the Li+ intercalation are discussed.

Synthesis of Li1.1(Ni0.425Mn0.425Co0,15)0.9O1.8F0.2 Materials by Different Routes : Is There Fluorine Substitution for Oxygen?

A one-step synthesis method was used, with LiF or NiF 2 as fluorine precursor, to prepare Li 1.1 (Ni 0.425 Mn 0.425 Co 0.15 ) 0.9 O 1.8 F 0.2 materials. 7 Li and 19 F magic angle spinning NMR analyses revealed the presence of fluorine as LiF at the surface of the Li(Ni 0.425 Mn 0.425 Co 0.15 )O 2 particles, rejecting the formation of fluorine-substituted Li 1.1 (Ni 0.425 Mn 0.425 Co 0.15 ) 0.9 O 8 F 0.2 materials. These results highlighted that change in cell parameters with increasing fluorine content is not by itself proof for effective fluorine substitution for oxygen in layered oxides and that heterogeneity in the transition metal and fluoride-ion distribution at the crystallite scale can be at the origin of these modifications. LiF was shown to be present as small particles in some grain boundaries but not as a continuous layer covering the particles surface. Improved cycling stability was observed for these LiF-coated materials, showing that effective fluorine substitution for oxygen is not required for improvement of the cyclability of these layered oxides; a surface modification can be sufficient and can also have a huge impact.

Lithium intercalation in Ln/sub 1/3NbO/sub 3/ perovskite-type phases (Ln = La, Nd)

Abstract Lithium can be intercalated either chemically or electrochemically in Ln 1 3 NbO 3 perovskite-type phases (Ln = La,Nd). In the starting material the electrostatic repulsion between rare earth ions leads to relative ordering within the NbO3 network. Every other plane of perovskite cavities contains rare earths. The related formula is □ 1 2 (Ln 1 3 □′ 1 6 ) NbO 3 . In both systems, solid solutions are observed in the first part of the intercalation reaction. While almost all perovskite cavities are filled in the neodymium phases, the higher ionic character of the LaO bonds prevents practically the □′ sites from Li intercalation. For the highest intercalation rates which attain 0.80, a new site is involved. The physical properties of the intercalated materials have been described in connection with the electrochemical behavior. Whatever the intercalation rate, the d electrons remain localized and the electronic behavior is characterized by a hopping mechanism.

Chemical, structural and magnetic studie of Mn0.50Ti2(PO4)3 and its solid solution with NaTi2(PO4)3

Summary Na (1−2x) Mn x Ti 2 (PO 4 ) 3 (0 ≤ x ≤ 0.5) phosphates have been prepared by solid state reaction and by sol-gel method. The X-ray diffraction study shows that these materials belong to the Nasicon-type structure. The structure of Mn 0.5 Ti 2 (PO 4 ) 3 has been solved in the R — space group. Mn 2+ ions are ordered in half of M(1) sites. The magnetic study undertaken on Mn 0.5 Ti 2 (PO 4 ) 3 shows a paramagnetic behaviour with absence of Mn 2+ -Mn 2+ interactions even at low temperature.