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Multi-scale simulation study for high entropy materials as electrode


Department of Chemistry

About the Project

This project is part of a 4-year Dual PhD degree programme between the National Tsing Hua University (Taiwan) and the University of Liverpool (England). As part of the NTHU-UoL Dual PhD Award students are in the unique position of being able to gain 2 PhD awards at the end of their degree from two internationally recognised world-leading Universities. As well as benefiting from a rich cultural experience, students can draw on large-scale national facilities of both countries and create a worldwide network of contacts across two continents.
The latest set of projects targeted goal #11 from the UN Sustainable Development Goals: Sustainable Cities and Communities.
High entropy materials is first proposed in 2004[1], receiving much interest from many materials field and application. In 2018 and 2019, Sarkar’s group[2] and Qiu’s group[3] both use high entropy oxide (HEO) (Mg Co Ni Cu Zn) O as anode materials of lithium ion battery (LIB). They found that the materials are conversion-type anodes. Conversion-type anodes can demonstrate a very high specific capacity, but usually also show a low cycle life relative to commercialized intercalation-type anodes such as graphite. This drawback makes conversion-type anodes hard to commercialize. However, the most prominent performance of (Mg Co Ni Cu Zn) O anodes is extremely high cyclic stability during charge / discharge process. The specific capacity of HEO anode is ~600 mAh/g. Comparing with the commercialized graphite anode (specific capacity[4] ~372 mAh/g), we believe that HEOs may be potential candidate as anode in next-generation lithium ion battery.
However, the internal phase transformation and electrochemical reaction mechanisms underlying HEO operation as anodes are still in debate. Sarkar’s group and Qiu’s group provides two different mechanisms to explain their result. Sarkar’s group believed that nano-scale Li2O and metal particles are formed and trapped in HEO matrix, and there is no other secondary phase formation. This mechanism makes the constituent elements of nano-scale Li2O and metal particles easily diffuse back to the HEO phase. That’s the reason why high cyclic stability of HEO.
In this project, we plan to use multi-scale materials simulation method to calculate and determine the phase evolution mechanism of HEO. Providing some alternative aspects can make researchers better understand the internal mechanism of HEO electrode. And based on this understanding, we may optimize the performance of HEO anodes or even re-design new kinds of HEO anode with excellence performance.
In Angstrom-scale simulations, we plan to use DFT (Density Functional Theory) calculations to understanding Li+- anode interaction and crystal structure evolution during charge / discharge. We can use ATAT (Alloy Theoretic Automated Toolkit) and SQS theory to construct high-disorder crystal model and use VASP (Vienna Ab initio Simulation Package) to calculate phase evolution and voltage evolution of HEO during charge / discharge cycle. In nanometer-scale simulations, we can use AIMD (Ab Initio Molecular Dynamic) calculation (small scale) and classic MD (Molecular Dynamic) calculation to understand the interaction between metal particles, Li2O particles and the HEO matrix or the MgO phase effect. In larger-scale simulations, we can understand the influence of defect mechanism and SEI (Solid Electrolyte Interface) layer interaction[5] on performance of HEO anode materials.
HEOs not only have potential applications as anode materials of LIB, but also as cathodes of LIB[6], cathodes of NIB[7] (Na-ion battery), and solid-electrolyte materials[8]. Their highly tailorable ability to host many constituent elements give HEO many different potential applications and are worth detail research and discussion.
Applicants should apply via the University of Liverpool application form, for a PhD in the subject area listed above.

Funding Notes

Both the University of Liverpool and NTHU have agreed to waive the tuition fees for the duration of the project and stipend of TWD 11,000/month will be provided as a contribution to living costs (the equivalent of £280 per month when in Liverpool).
When applying please ensure you Quote the supervisor & project title you wish to apply for and note ‘NTHU-UoL Dual Scholarship’ when asked for details of how plan to finance your studies.

References

1. Yeh, J.-W., et al., Nanostructured High-Entropy Alloys with Multiple Principal Elements: Novel Alloy Design Concepts and Outcomes. Advanced Engineering Materials, 2004. 6(5): p. 299-303.
2. Sarkar, A., et al., High entropy oxides for reversible energy storage. Nat Commun, 2018. 9(1): p. 3400.
3. Qiu, N., et al., A high entropy oxide (Mg0.2Co0.2Ni0.2Cu0.2Zn0.2O) with superior lithium storage performance. Journal of Alloys and Compounds, 2019. 777: p. 767-774.
4. Cao, K., et al., Recent progress in conversion reaction metal oxide anodes for Li-ion batteries. Materials Chemistry Frontiers, 2017. 1(11): p. 2213-2242.
5. Wang, A., et al., Review on modeling of the anode solid electrolyte interphase (SEI) for lithium-ion batteries. npj Computational Materials, 2018. 4(1).
6. Wang, Q., et al., Multi-anionic and -cationic compounds: new high entropy materials for advanced Li-ion batteries. Energy & Environmental Science, 2019.
7. Yue, J.L., et al., A quinary layer transition metal oxide of NaNi1/4Co1/4Fe1/4Mn1/8Ti1/8O2 as a high-rate-capability and long-cycle-life cathode material for rechargeable sodium ion batteries. Chem Commun (Camb), 2015. 51(86): p. 15712-5.
8. Bérardan, D., et al., Room temperature lithium superionic conductivity in high entropy oxides. Journal of Materials Chemistry A, 2016. 4(24): p. 9536-9541.

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