Molecular Dynamics modelling transport processes and interfacial structure in Li-metal/polymer systems

Dnr:

SNIC 2017/1-258

Type:

SNAC Medium

Principal Investigator:

Daniel Brandell

Affiliation:

Uppsala universitet

Start Date:

2017-06-01

End Date:

2018-06-01

Primary Classification:

10403: Materialkemi

Secondary Classification:

10404: Oorganisk kemi

Tertiary Classification:

10304: Den kondenserade materiens fysik

Webpage:

Allocation

Abstract

Using Li-metal as anode material in rechargeable Li-batteries has the possibility to revolutionize energy storage in terms of energy and power density – the material has an extremely low electrochemical potential, extremely high capacity, and can fast and reversibly liberate and absorb Li ions from the battery electrolyte [1]. But due to that the material is prone to side reactions, most notably Li-dendrite formation during battery cycling, it is not yet realized in most commercial devices. Recent advancements in the area have, however, shown that Li-metal can be stabilized by using solid-state polymer electrolytes instead of the common liquid counterparts. It is therefore of fundamental importance to understand how polymer composition, structure and dynamics are influences by the presence of a Li-metal surface, and how this is associated with the ionic transport properties. We have previously pioneered the structure-dynamic properties of bulk polymer electrolytes using Molecular Dynamics (MD) simulations [2-4], thereby exploring the critical polymer properties for enhanced ionic transportation. Recently, we have also used DFT calculations to model surface decomposition of electrolytes on Li-metal [5]. We are therefore in a position where we would now like to take a significant step forward by analyzing the Li-metal/polymer interface by MD techniques, which is an area not yet explored in scientific literature. The presence of a Li-metal surface is likely to affect the polymer stability, structure and dynamics as compared to the bulk. This will, in turn, affect ionic transport in a way which is critical for battery performance. We seek polymers with a good stability towards Li-metal, a good affinity to its surface, and with a flexibility and coordination properties to Li ions to promote ion conduction. By selecting polymers with a good affinity and a good stability to Li-metal (work which is carried out experimentally within our group), a better electrode/electrolyte interface can be created. It is, however, yet unknown how this will influence the ionic transport. Hence these proposed MD studies. Since MD simulations are beneficial to perform at heavily parallelized sources, we prefer to have run them at such centres. [1] X.-B. Cheng, et al., A Review of Solid Electrolyte Interphases on Lithium Metal Anode, Adv. Sci., 2015 [2] D. Brandell, H. Kasemägi, T. Tamm, A. Aabloo, Molecular Dynamics Modeling the Li-PolystyreneTFSI/PEO blend, Solid State Ionics, 262 (2014) 769. [3] H. Kasemägi, M. Ollikainen, D. Brandell, A. Aabloo, Molecular Dynamics Modelling Block-Copolymer Electrolytes with High t+ Values, Electrochimica Acta, 175 (2015) 47. [4] L.T. Costa, B. Sun, F. Jeschull, D. Brandell, Polymer-Ionic liquids ternary systems for Li-battery electrolytes: Molecular Dynamics studies of LiTFSI in a EMIm-TFSI and PEO blend, Journal of Chemical Physics, 143 (2015) 024924. [5] M. Ebadi, D. Brandell, C. Moyses Araujo, Electrolyte decomposition on Li-metal surfaces from first-principles theory, Journal of Chemical Physics, 145 (2016) 204701