Electrochemical Reduction and Oxidation of Ruddlesden–Popper-Type La₂NiO₃F₂ within Fluoride-Ion Batteries

Abstract

Within this article, it is shown that an electrochemical defluorination and additional fluorination of Ruddlesden−Poppertype La 2 NiO 3 F 2 is possible within all-solid-state fluoride-ion batteries. Structural changes within the reduced and oxidized phases have been examined by X-ray diffraction studies at different states of charging and discharging. The synthesis of the oxidized phase La 2 NiO 3 F 2+x proved to be successful by structural analysis using both X-ray powder diffraction and automated electron diffraction tomography techniques. The structural reversibility on re-fluorinating and re-defluorinating is also demonstrated. Moreover, the influence of different sequences of consecutive reduction and oxidation steps on the formed phases has been investigated. The observed structural changes have been compared to changes in phases obtained via other topochemical modification approaches such as hydride-based reduction and oxidative fluorination using F 2 gas, highlighting the potential of such electrochemical reactions as alternative synthesis routes. Furthermore, the electrochemical routes represent safe and controllable synthesis approaches for novel phases, which cannot be synthesized via other topochemical methods. Additionally, side reactions, occurring alongside the desired electrochemical reactions, have been addressed and the cycling performance has been studied.

Structure, Magnetism, and Thermal Stability of La2NiO2.5F3: A Ruddlesden–Popper Oxyfluoride Crystallizing in Space Group P42/nnm

“…In a subsequent study Wissel et al reported on topochemical defluorination of La 2 NiO 3 F 2 , leading to the first Ni-containing T′ Ruddlesden–Popper oxyfluoride La 2 NiO 3 F . Additionally, it was found that during the electrochemical oxidation of La 2 NiO 3 F 2 a monoclinic La 2 NiO 3 F 3 is formed. These impressive results demonstrate the wide chemical and structural flexibility of the La 2 Ni­(O,F) 4+ x system.…”

“…This arrangement leads to a pronounced tilting of the NiO 4 F 2 octahedra accompanied by the formation of alternating narrow and wide channels in the interlayers with the wide channel containing interstitial oxygen ions. In a subsequent study Wissel et al reported on topochemical defluorination of La 2 NiO 3 F 2 , leading to the first Ni-containing T′ Ruddlesden−Popper oxyfluoride La 2 NiO 3 F. 37 Additionally, it was found that during the electrochemical oxidation of La 2 NiO 3 F 2 a monoclinic La 2 NiO 3 F 3 38 is formed. These impressive results demonstrate the wide chemical and structural flexibility of the La 2 Ni(O,F) 4+x system.…”

Single-Layer T′ Nickelates: Synthesis of the La and Pr Members and Electronic Properties across the Rare-Earth Series

“…Thus, it will be interesting to further explore the synthesis of single-layer T′ nickelates by means of alternative methods also. These include topotactic reactions with different fluorinating/reducing agents and electrochemical methods . In addition, the thin-film route also remains as another possible direction because the Ruddlesden–Popper precursors can be readily obtained in this way (see, e.g., ref ).…”

“…These include topotactic reactions with different fluorinating/ reducing agents and electrochemical methods. 33 In addition, the thin-film route also remains as another possible direction because the Ruddlesden−Popper precursors can be readily obtained in this way (see, e.g., ref 34). Thus, our findings are expected to motivate further investigations of these fundamental questions in materials science and condensed matter physics.…”

Improvement of electric insulation in dielectric layered perovskite nickelate films via fluorination

“…This can be rationalized by assuming that the reaction kinetics at the surface dominate the topotactic fluorination of (La,Sr) 2 NiO 4 thin films. 38 It is known that the total anion content in bulk nickel oxyfluorides with a K 2 NiF 4 -type structure, such as Sr 2 NiO 3 F and La 2 NiO 3 F 2 , varies in the range of 4-5, 17,39,40 where the latter has one additional anion in the rock-salt layer. Sr 2 NiO 3 F consists of [ANi(O,F) 3 ] perovskite and [A(O,F) 1 ] block layers whereas La 2 NiO 3 F 2 is a stacking of [ANi(O,F) 3 ] perovskite and [A(O,F) 2 ] rock-salt layers.…”