Metastable layered lithium-rich niobium and tantalum oxides via nearly instantaneous cation exchange

Abstract

Lithium-rich early transition metal oxides are the source of excess removeable lithium that affords high energy density to lithium-rich battery cathodes. They are also candidates for solid electrolytes in all-solid-state batteries. These highly ionic compounds are sparse on phase diagrams of thermodynamically stable oxides, but soft chemical routes offer an alternative to explore new alkali-rich crystal chemistries. In this work, a new layered polymorph of Li3NbO4 with coplanar [Nb4O16]12− clusters is discovered through ion exchange chemistry. A more detailed study of the ion exchange reaction reveals that it takes place almost instantaneously, changing the crystal volume by more than 22% within seconds. The transformation of coplanar [Nb4O16]12− in L-Li3NbO4 into the supertetrahedral [Nb4O16]12− clusters found in the stable cubic c-Li3NbO4 is also explored. Furthermore, this synthetic pathway is extended to access a new layered polymorph of Li3TaO4. NMR crystallography with 6,7Li, 23Na, and 93Nb NMR, X-ray diffraction, neutron diffraction, and first-principles calculations is applied to A3MO4 (A = Li, Na; M = Nb, Ta) to identify local and long-range atomic structure, to monitor the unusually rapid reaction progression, and to track the phase transitions from the metastable layered phases to the known compounds found using high-temperature synthesis. A mechanism is proposed whereby some sodium is retained at short reaction times, which then undergoes proton exchange during water washing, forming a phase with hydrogen bonds bridging the coplanar [Nb4O16]12− clusters. This study has implications for lithium-rich transition metal oxides and associated battery materials and for ion exchange chemistry in non-framework structures. The role of techniques that can detect light elements, local structure, and subtle structural changes in soft-chemical synthesis is emphasized.

Graphical abstract: Metastable layered lithium-rich niobium and tantalum oxides via nearly instantaneous cation exchange

Supplementary files

Article information

Article type
Paper
Submitted
16 mei 2024
Accepted
23 jul 2024
First published
20 sep 2024

Faraday Discuss., 2024, Advance Article

Metastable layered lithium-rich niobium and tantalum oxides via nearly instantaneous cation exchange

S. L. Ko, J. A. Dorrell, A. J. Morris and K. J. Griffith, Faraday Discuss., 2024, Advance Article , DOI: 10.1039/D4FD00103F

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