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.
Original language | English |
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Pages (from-to) | 484-495 |
Number of pages | 12 |
Journal | ACS Applied Energy Materials |
Volume | 6 |
Issue number | 1 |
Early online date | 16 Dec 2022 |
DOIs | |
Publication status | Published - 9 Jan 2023 |
Bibliographical note
Funding Information:N.T-.R. and D.O.S. are indebted to the Faraday Institution NEXGENNA project (FIRG018) for financial support. N.T-.R. would like to acknowledge Lancaster University for financial support. Y.-S.C. and D.O.S. are grateful to the Faraday Institution for funding the Michael (FIRG030) computing cluster hosted at University College London (UCL). The calculations have been also carried out on the Myriad (Myriad@UCL), Young (Young@UCL), and Kathleen (Kathleen@UCL) High Performance Computing Facility provisioned by UCL. Via our membership of the UK’s HEC Materials Chemistry Consortium, which is funded by EPSRC (EP/L000202, EP/R029431), this work used the ARCHER2 UK National Supercomputing Service. We are also grateful to the UK Materials and Molecular Modelling Hub for computational resources, which were partially funded by EPSRC (EP/P020194/1 and EP/T022213/1).
Publisher Copyright:
© 2022 The Authors. Published by American Chemical Society.
Keywords
- density functional theory
- electrical conductivity
- intrinsic defect chemistry
- phase transition
- Schottky pair
- sodium-ion battery
- titanate anodes
ASJC Scopus subject areas
- Chemical Engineering (miscellaneous)
- Energy Engineering and Power Technology
- Electrochemistry
- Materials Chemistry
- Electrical and Electronic Engineering