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Intrinsic Defects and Their Role in the Phase Transition of Na-Ion Anode Na<sub>2</sub>Ti<sub>3</sub>O<sub>7</sub>

Choi, Yong-Seok; Costa, Sara IR; Tapia-Ruiz, Nuria; Scanlon, David O; (2022) Intrinsic Defects and Their Role in the Phase Transition of Na-Ion Anode Na<sub>2</sub>Ti<sub>3</sub>O<sub>7</sub>. ACS Applied Energy Materials 10.1021/acsaem.2c03466. (In press). Green open access

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Abstract

The development of high-power anode materials for Na-ion batteries is one of the primary obstacles due to the growing demands for their use in the smart grid. Despite the appealingly low cost and non-toxicity, Na2Ti3O7 suffers from low electrical conductivity and poor structural stability, which restricts its use in high-power applications. Viable approaches for overcoming these drawbacks reported to date are aliovalent doping and hydrogenation/hydrothermal treatments, both of which are closely intertwined with native defects. There is still a lack of knowledge, however, of the intrinsic defect chemistry of Na2Ti3O7, which impairs the rational design of high-power titanate anodes. Here, we report hybrid density functional theory calculations of the native defect chemistry of Na2Ti3O7. The defect calculations show that the insulating properties of Na2Ti3O7 arise from the Na and O Schottky disorder that act as major charge compensators. Under high-temperature hydrogenation treatment, these Schottky pairs of Na and O vacancies become dominant defects in Na2Ti3O7, triggering the spontaneous partial phase transition to Na2Ti6O13 and improving the electrical conductivity of the composite anode. Our findings provide an explanation on the interplay between intrinsic defects, structural phase transitions, and electrical conductivity, which can aid understanding of the properties of composite materials obtained from phase transitions.

Type: Article
Title: Intrinsic Defects and Their Role in the Phase Transition of Na-Ion Anode Na<sub>2</sub>Ti<sub>3</sub>O<sub>7</sub>
Open access status: An open access version is available from UCL Discovery
DOI: 10.1021/acsaem.2c03466
Publisher version: https://doi.org/10.1021/acsaem.2c03466
Language: English
Additional information: This work is licensed under a Creative Commons Attribution 4.0 International License. The images or other third-party material in this article are included in the Creative Commons license, unless indicated otherwise in the credit line; if the material is not included under the Creative Commons license, users will need to obtain permission from the license holder to reproduce the material. To view a copy of this license, visit http://creativecommons.org/licenses/by/4.0/
UCL classification: UCL
UCL > Provost and Vice Provost Offices > UCL BEAMS
UCL > Provost and Vice Provost Offices > UCL BEAMS > Faculty of Maths and Physical Sciences
UCL > Provost and Vice Provost Offices > UCL BEAMS > Faculty of Maths and Physical Sciences > Dept of Chemistry
URI: https://discovery.ucl.ac.uk/id/eprint/10162146
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