Topic 01-23 : Novel (poly)anionic structures for highly Li-ion conductive solid polymer electrolytes : A combined theoretical and experimental study

We propose to combine theoretical and experimental techniques to identify and synthetise new types of anionic structures for being applied in solid-state lithium batteries, aiming at improving,  among other properties, ionic conductivity and Li-ion transference number. Based on our previous works, we know that anionic structure flexibility and negative charge delocalization are key aspects to effectively screen good candidate Li salts for SPEs. So, based on these two criteria and considering archetype perfluorinated anions as reference, we will first employ densitiy funtional theory (DFT) calculations and classical molecular dynamics simulations to computationally identify new salts. And then, for the most promising and practically suitable cantidates, we will proceed to their actual synthesis and electrochemical testing taking advantage of our ample know-how on polymer electrolyte synthesis and characterization at CIC energiGUNE. Additionally, we will explore the possibility of chemically grafting some of the identified anions to different polymer backbones, with the aim of obtaining SLICs. To this end, anion and polymer functionalizations that can maximize the interactions between the two components will be sought; again, with theoretical guidance first, followed by experimental validation. This project offers therefore the possibility of carrying out a highly multidisciplinary PhD on a highly relevant domain in battery research, exposing the student to advanced modelling and experimental approaches.

The aim of the secondment is to enhance the predictive capabilities of the proposed theoretical studies be accurately accounting for the electronic structure of SPEs. The presence of the salt in the polymer matrix can lead to a significant decrease of the system's band gap, which might have a strong impact on the leakage currents in SPEs. This is therefore a relevant topic, but often overlooked in theoretical studies due to the large simulation boxes needed to accuartely model these materials. Brandell's group has recently applied the linear scaling DFT method to overcome this issue and assessed the electronic properties of LiTFSI in PEO.

[1]. We therefore propose a secondment of 6 months in his group to apply this technique in the project.
[1] Unge, M. et al. Phys. Chem. Chem. Phys., 2020,22, 7680-7684.