McColl, K;
Corà, F;
(2019)
Mg²⁺ storage and mobility in anatase TiO₂: the role of frustrated coordination.
Journal of Materials Chemistry A
, 7
(8)
pp. 3704-3713.
10.1039/c8ta09939a.
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Abstract
Anatase TiO₂ is a candidate high-power electrode material in Li-ion and Na-ion batteries and has been explored as a Mg battery cathode material, although Mg capacity in undoped anatase is limited. Here we use hybrid-exchange density functional theory calculations to investigate the underlying factors affecting Mg intercalation and mobility in anatase. We find that at the dilute limit, Mg ions have 5-fold coordinated insertion sites, and activation barriers for migration are a surprisingly low 537 meV. As the concentration of Mg inserted into the structure is increased, a cooperative distortion of the lattice occurs, contracting the c lattice parameter. The distortion results in stable orderings of Mg ions in sites which are 6-fold coordinated, but also results in migration barriers that exceed 1500 meV in Mg₀.₅ TiO₂ due to a collective relaxation of the host lattice. The total increase in barrier is predominantly a result of the stabilisation of the insertion sites, as opposed to a destabilisation of the activated sites along the migration pathway. The insertion sites in the dilute limit can be described as frustrated, and it is this unfavourable insertion geometry under dilute conditions that allows the Mg ions to migrate with low activation barriers. The limited performance for Mg²⁺ storage can therefore be attributed to the loss of frustrated coordination at high Mg concentration, which restricts Mg mobility and therefore capacity. Strategies to enhance the capacity of Mg in anatase should therefore aim to inhibit the c lattice parameter contraction or otherwise destabilise stable orderings of Mg in Mg₀.₅ TiO₂ to retain the frustrated coordination of Mg ions at high Mg concentrations.
| Type: | Article |
|---|---|
| Title: | Mg²⁺ storage and mobility in anatase TiO₂: the role of frustrated coordination |
| Open access status: | An open access version is available from UCL Discovery |
| DOI: | 10.1039/c8ta09939a |
| Publisher version: | http://doi.org/10.1039/c8ta09939a |
| Language: | English |
| Additional information: | © The Royal Society of Chemistry 2019. This article is licensed under a Creative Commons Attribution 3.0 Unported Licence (https://creativecommons.org/licenses/by/3.0/). |
| 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/10069325 |
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