Redox chemistry of ternary graphite intercalation compounds

The proposed research project focuses on the systematic investigation of ternary graphite intercalation compounds (t-GICs), which are formed via the electrochemical co-intercalation of solvated cations (Li?, Na?, Mg??) and organic solvent molecules into graphite. Based on prior work by the applicants, it has been demonstrated that especially solvated Na? ions can be reversibly intercalated into graphite – a behavior that markedly differs from classical binary GICs. This process is characterized by substantial volume changes, the absence of a solid electrolyte interphase (SEI), and pronounced temperature-dependent effects.
The goal of this project is to elucidate the structural, thermodynamic, and kinetic properties of such t-GICs and to extend the concept to multivalent ions and mixed-cation systems. The work program is divided into three closely interlinked work packages:
WP1: Investigation of the structure, dynamics, and diffusion of solvated Li? and Na? complexes in t-GICs, as a function of temperature, solvent type (glyme derivatives), and state of charge. Techniques include operando dilatometry, galvanostatic cycling, GITT, solid-state NMR, and advanced modeling using DFT and AIMD.
WP2: Extension of the t-GIC concept to divalent cations (in particular Mg??), which typically suffer from poor mobility in solid-state host structures – a major challenge for multivalent ion battery development. Co-intercalation may screen the strong electrostatic interactions and enable new storage mechanisms. Experimental investigations are complemented by operando Raman, XRD, and DEMS measurements.
WP3: Exploratory development of quaternary GICs (q-GICs) through the combined intercalation of different cations (e.g., Li?/Na?, Na?/Mg??) along with solvent co-intercalation. The aim is to synthesize novel, structurally complex GICs with enhanced functionality and potentially higher specific capacity.
The project strongly integrates experimental (HU Berlin, Adelhelm group) and theoretical (JLU Giessen, Mollenhauer group) approaches. In addition to electrochemical methods, the project utilizes advanced simulation techniques (DFT-D3, AIMD, ML-trained force fields) and state-of-the-art in situ/operando characterization tools.
Overall, the project will make a substantial contribution to the fundamental understanding of redox-active, structurally adaptive intercalation systems based on graphite. It will also open new perspectives for the development of alternative anode materials for post-lithium energy storage technologies, particularly sodium- and magnesium-ion batteries.