Novel Complex Stacking of Fully-Ordered Transition Metal Layers in Li₄FeSbO₆ Materials

Abstract

As part of a broad project to explore Li4MM′O6 materials (with M and M′ being selected from a wide variety of metals) as positive electrode materials for Li-ion batteries, the structures of Li4FeSbO6 materials with both stoichiometric and slightly deficient lithium contents are studied here. For lithium content varying from 3.8 to 4.0, the color changes from yellow to black and extra superstructure peaks are seen in the XRD patterns. These extra peaks appear as satellites around the four superstructure peaks affected by the stacking of the transition metal atoms. Refinements of both XRD and neutron scattering patterns show a nearly perfect ordering of Li, Fe, and Sb in the transition metal layers of all samples, although these refinements must take the stacking faults into account in order to extract information about the structure of the TM layers. The structure of the most lithium rich sample, where the satellite superstructure peaks are seen, was determined with the help of HRTEM, XRD, and neutron scattering. The satellites arise due to a new stacking sequence where not all transition metal layers are identical but instead two slightly different compositions stack in an AABB sequence giving a unit cell that is four times larger than normal for such monoclinic layered materials. The more lithium deficient samples are found to contain metal site vacancies based on elemental analysis and Mössbauer spectroscopy results. The significant changes in physical properties are attributed to the presence of these vacancies. This study illustrates the great importance of carefully determining the final compositions in these materials, as very small differences in compositions may have large impacts on structures and properties.

A Cobalt‐Free Li(Li0.16Ni0.19Fe0.18Mn0.46)O2 Cathode for Lithium‐Ion Batteries with Anionic Redox Reactions

“…demonstrated that the reversible capacity of Li 1+ x Fe y Mn 1− x − y O 2 is generated from the Fe 3+ /Fe 4+ redox couple at approximately 4 V, which was further confirmed by the 57 Fe Mössbauer spectrum . Tarascon and co‐workers also found that in Li 4 FeSbO 6 and Li 2 Ru 1‐ x Fe x O 3 , Fe 3+ can be oxidized to Fe 4+ , which was accompanied by the oxidation of O 2− to O 2 2− during delithiation. Although most observations verify the oxidation of Fe 3+ , a clear explanation of the redox mechanism for either Fe or O in the Ni‐, Fe‐, and Mn‐containing Li‐rich materials is still lacking.…”

Anionic Redox in Rechargeable Lithium Batteries

“…A solid solution of Li 4 FeSbO 6 was investigated as a new cathode material, with oxygen‐release and oxygen‐redox occurring during charging and discharging. The limited reversibility of the oxygen redox was first presented and discussed in these investigations.…”

“…Li 2 Ru 0.75 Sn 0.25 O 3 was found to display highly reversible anionic redox, though 0.2 Li ions per formula still cannot be reinserted into the host due to partial oxygen loss in the first cycle. The lithium‐excess oxides Li 2 MoO 3 , Li 4 FeSbO 6 , and Y‐doped Li 6 ZrO 8 all display low Coulombic efficiency and involve anionic redox …”

Origin of stabilization and destabilization in solid-state redox reaction of oxide ions for lithium-ion batteries

“…Manganese-substituted Li 3 NbO 4 , Li 1.3 Nb 0.3 Mn 0.4 O 2 (0.43Li 3 NbO 4 –0.57LiMnO 2 ), delivers large reversible capacity (approximately 300 mAh g −1 ) with reversible solid-state redox reaction of oxide ions20. Similar to pentavalent niobium, a material with pentavalent antimony, Li 4 FeSbO 6 , has been recently reported25. Solid-state redox reaction of oxide ions is also activated in Li 4 FeSbO 6 , and a reductive coupling mechanism as an irreversible process has been evidenced in this system.…”