Single Ion Conducting Two-Dimensional Anionic Covalent Organic Framework Electrolytes for Next Generation Solid State Batteries

• Applicant: Professor Dr. Thomas Heine
• Subject Area: Theoretical Chemistry: Electronic Structure, Dynamics, Simulation
• Term: since 2024
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 551217520

With the growing demand for clean, sustainable, and affordable energy, the next-generation batteries based on solid-state electrolytes (SSEs) offer significant advantages, such as enhanced safety, wide voltage windows and high working temperatures, etc., over conventional batteries. Natural resource concerns have also prompted the investigation of batteries based on more abundant metals such as Na, and K. In this regard, anionic covalent organic frameworks (COFs) are suitable as potential solid conductors with well-defined directional channels, tunable functional groups, and, superior thermal and electrochemical stabilities, however, their ionic conduction mechanisms are not well understood. We propose to study Li+, Na+, and K+ conduction in two-dimensional (2D) anionic COFs as suitable SSEs for the next generation of solid-state batteries. We will exploite three different concepts, each of them related to an Objective: (1) anionic framework functionality, (2) pore size and pore wall decoration, and (3) ionic liquids (IL) as guest molecules. We will employ state-of-the-art methodology of computational materials science. Structural and electronic characterization (for either insulator or wide band gap semiconductors) will be followed by evaluation of ion transport mechanism using the combination of climbing-image nudged elastic band (CI-NEB) method and well-tempered metadynamics (WTMetaD) simulations. The ion conduction mechanism of Li+, Na+, and K+ in IL-mediated anionic COFs (IL@COFs) will be studied using ab-initio molecular dynamics (AIMD) simulations and analysis of the ion conductivity variation from solvent-free SSEs. For geometry optimization and electronic properties, we will use the already benchmarked D3(BJ)-dispersion corrected density functional theory (DFT) method implemented in the Vienna ab-initio simulation package (VASP). Calculations of ion transport will be performed using the CP2K software package. Analyzing the diffusion mechanism and interstitial crystallographic sites of the individual diffusion paths will give an accurate understanding. The dynamics and microstructural evolution during ion diffusion in the constructed IL@SSEs will be investigated to provide molecular-level insight into the facile Li, Na, and K ion traffic, which will pave the way for the improved design of 2D-COF-based electrolytes regarding the optimal combination between the COF skeleton, metal ion, and the IL. Promising candidates for anionic COF-based SSEs will be shared with our experimental collaborators and aimed for synthesis.

• DFG Programme: Research Grants