From LiNiO2 to Li2NiO3: Synthesis, Structures and Electrochemical Mechanisms in Li-Rich Nickel Oxides

Abstract

The Li−Ni−O phase diagram contains a variety of compounds, most of which are electrochemically active in Li-ion batteries [1-2]. LiNiO2 (LNO) is particularly well-known due to its behavior as cathode active material, potentially excellent but in practice plagued by several instability issues, which ultimately led to elemental substitutions of Ni with Co, Mn and Al towards NCM and NCA materials. A significant amount of understanding on LNO and on the elemental substitution it can allow were developed in the group of Claude Delmas [3]. In this contribution, I will briefly review the Li−Ni−O phase diagram, its history and the special role LNO occupies in it, with a focus on its synthesis, structure and decomposition [4-6]. Additionally, Li-rich phases of composition nearing Li2NiO3 will be discussed [7-9]. I will report a facile solid-state method to prepare Li2NiO3 and other Li-rich Ni oxides of composition Li1+xNi1−xO2 (0 ≤ x ≤ 0.33) [10]. I will also detail their crystal and electronic structure, exhibiting a highly oxidized Ni state and defects of various nature (Li−Ni disorder, stacking faults, oxygen vacancies). Moreover, the use of Li2NiO3 as a cathode active material has been investigated. It shows remarkably high specific capacity, which however fades quickly. While we demonstrate that the initial capacity is due to irreversible O2 release, such process stops quickly in favor of more classical reversible redox mechanisms that allow cycling the material for >100 cycles. After the severe oxygen loss (∼15−20%) and prolonged cycling, the Bragg reflections of Li2NiO3 disappear. Analysis of the diffracted intensities suggests the resulting phase is a disordered rock salt-type material with high Li content, close to Li0.5Ni0.5O, never reported to date and capable of Li diffusion. Our findings demonstrate that the Li−Ni−O phase diagram has not been fully investigated yet, especially concerning the preparation of new promising materials by out-of-equilibrium methods.Bibliography[1] Dahn, J., Vonsacken, U., Michal, C. A., Structure and Electrochemistry of Li1+-yNiO2 and a New Li2NiO2 Phase with the Ni(OH)2 Structure, Solid State Ionics, 1991, 44, (1-2), 87-97[2] Goodenough, J. B.; Wickham, D. G.; Croft, W. J. Some Magnetic and Crystallographic Properties of the System Lix +Ni1−2x +2Nix +++O. J.Phys. Chem. Solids 1958, 5 (1−2), 107−116.[3] Delmas, C., Menetrier, M., Croguennec, L., Saadoune, I., Rougier, A., Pouillerie, C., Prado, G., Grune, M., Fournes, L., An overview of the Li(Ni,M)O2 systems: syntheses, structures and properties, Electrochimica Acta, 1999, 45, (1-2), 243-253[4] Bianchini, M.; Roca-Ayats, M.; Hartmann, P.; Brezesinski, T.; Janek, J. There and Back Again-The Journey of LiNiO2 as a Cathode Active Material. Angew. Chem., Int. Ed. 2019, 58, 10434−10458.[5] Delmas, C., Croguennec, L., Layered Li(Ni,M)O2 Systems as the Cathode Material in Lithium-Ion Batteries, MRS Bullettin, 2002, 27 (8), 608-612[6] Bianchini, M.; Fauth, F.; Hartmann, P.; Brezesinski, T.; Janek, J, An in situ structural study on the synthesis and decomposition of LiNiO2, J. Mat. Chem. A, 2020, 8 (4), 1808-1820.[7] Migeon, H.; Courtois, A.; Zanne, M.; Gleitzer, C. Preparation and Study of Li2NiO3−y (y less-than-or-equal-to 0.135). Rev. Chim. Minér. 1976, 13 (1), 1−8.[8] Stoyanova, R.; Zhecheva, E.; Alcántara, R.; Tirado, J. L.; Bromiley, G.; Bromiley, F.; Boffa Ballaran, T. Lithium/nickel mixing in the transition metal layers of lithium nickelate: high-pressure synthesis of layered Li[LixNi1−x]O2 oxides as cathode materials for lithium-ion batteries. Solid State Ionics 2003, 161 (3), 197−204[9] Tabuchi, M.; Kuriyama, N.; Takamori, K.; Imanari, Y.; Nakane, K. Appearance of Lithium-Excess LiNiO2 with High Cyclability Synthesized by Thermal Decomposition Route from LiNiO2 - Li2NiO3 Solid Solution. J. Electrochem. Soc. 2016, 163 (10), A2312−A2317.[10] Bianchini M.; Schiele, A.; Schweidler S.; Sicolo, S.; Fauth, F.; Suard, E.; Indris, S.; Mazilkin, A.; Nagel, P.; Schuppler, S.; Merz, M.; Hartmann, P.; Brezesinski, T.; Janek, J.; From LiNiO2 to Li2NiO3: Synthesis, Structures and Electrochemical Mechanisms in Li-Rich Nickel Oxides, Chem. Mater. 2020, 32, 9211−9227 Figure 1