Solvated Ions in Solid Electrodes: Alternative routes toward rechargeable batteries based on abundant elements

Project Information

SEED

Grant agreement ID: 864698

DOI

10.3030/864698

Project closed

EC signature date 18 February 2020

Start date 1 June 2020

End date 31 May 2025

Funded under

• EXCELLENT SCIENCE - European Research Council (ERC)

Total cost

€ 1 997 811,00

EU contribution

€ 1 997 811,00

Coordinated by

HUMBOLDT-UNIVERSITAET ZU BERLIN
Germany

Periodic Reporting for period 4 - SEED (Solvated Ions in Solid Electrodes: Alternative routes toward rechargeable batteries based on abundant elements)

Reporting period: 2024-12-01 to 2025-05-31

Summary of the context and overall objectives of the project

The transition from fossil to renewable energies is one of the largest and most urgent challenges humanity faces. The energy transition will be only successful if energy can be stored in a safe, efficient and sustainable way. This especially relates to electrifying the mobility sector (EVs) and storing renwable energy. Rechargeable batteries are the key towards this.
Since its commercialization in 1991, the lithium-ion battery technology is a real success story. Costs have been dramatically reduced and the energy density increased from less than 100 Wh/kg to almost 300 Wh/kg today. On the other hand, the technology is expected to reach its physical limits within the next years. At the same time, the demand for LIBs is projected to increase manifold times in the near future. Concerns have been raised whether this demand will create issues related to element resources, market access and supply chains on the long-term. The global distribution of lithium and cobalt resources are highly unequal with Europe being in an inferior situation. Numerous (sometimes controversial) reports on the availability of “battery materials” were published recently. Although long-term predictions are naturally difficult, there is broad consensus that the development of alternative batteries based on abundant elements is an important strategy to minimize the risk of resource depletion or of restricted access. This has recently resurged a lot of interest in alternatives to LIBs. A major approach is to adopt the LIB rocking chair concept to other working ions, i.e. replacing Li+ by more abundant ions such as Na+, K+, Mg2+, Ca2+ or Al3+, while at the same time also avoiding other critical elements. An additional argument for multivalent ions is that their use is one of the very few options to theoretically surpass the charge/energy density of LIBs.
On the other hand, the electrochemistry of alternative ions can be an extreme challenge, especially considering multivalent ions. Unconventional approaches are therefore needed to overcome unfavourable ion size and/or polarization effects.
The SEED project is such an unconventional approach, breaking with what has been common sense in the design of electrode materials so far: Instead of intercalating ions into solid electrodes, the SEED project aims at intercalating solvated ions into solid electrodes.

Overall objectives are:
- Understand the intercalation of solvated ions into solid electrodes
- Starting from graphite, explore the concept for other materials
- Starting with abundant Na+, explore the concept for multivalent ions
- Combine experiment with theory.

Work performed from the beginning of the project to the end of the period covered by the report and main results achieved so far

From the start of the project to the end of the period, the action successfully established solvent co-intercalation as a viable electrochemical storage mechanism for rechargeable batteries, with a particular focus on sodium-ion systems. The work addressed electrolyte formulation, electrode material development, structural understanding, and advanced characterization.
Key efforts were dedicated to the discovery of new solvent formulations capable of reversible co-intercalation in graphite electrodes while maintaining electrochemical stability, resulting in several peer-reviewed publications (Energy Technol., 9, 2000880; Batteries & Supercaps, 2024, 7, e202300506). In parallel, suitable host materials were identified and validated, including sustainable graphite derived from spheroidization waste (J. Phys. Energy, 5, 014011), TiS2 with the first proof-of-concept solvent co-intercalation battery (Adv. Energy Mater., 2022, 12, 2202377), sodium layered sulfides enabling co-intercalation in cathodes (Nature Materials, 24, 1441–1449, 2025), and Prussian Blue Analogues (Batteries & Supercaps, 2022, 5, e202200043).
Fundamental understanding of the co-intercalation mechanism was achieved through a comprehensive multi-technique approach that led to a new mechanistic model and improved experimental methodologies (Adv. Energy Mater., 2023, 13, 2301944; Batteries & Supercaps, 2023, 6, e202200421; Batteries & Supercaps, 2024, 7, e202400006). Finally, a comprehensive review summarizing the key results of the project was recently published, discussing the main characteristics, advantages, and challenges of co-intercalation reactions, together with experimental and theoretical approaches for their detection and characterization, and a critical assessment (Chem. Rev. 2025, 125, 6, 3401–3439).
The project also explored solvent co-intercalation beyond sodium demonstrating the broader applicability of the concept. The results provide transferable design principles and descriptors for future electrode and electrolyte development, supporting exploitation in sustainable and large-scale energy storage technologies.
Dissemination was extensive, with numerous high-impact publications, two PhD theses in preparation, and wide presentation of results at international conferences. The project team organized the “Sodium Battery Symposium SBS-5” (Berlin, September 2024). The scientific impact of the project was further recognized to the PI by the 2024 Berlin Science Award for his groundbreaking and internationally pioneering contributions in battery research, especially in sustainable and sodium-ion batteries.

Progress beyond the state of the art and expected potential impact (including the socio-economic impact and the wider societal implications of the project so far)

Prior to this project, solvent co-intercalation in rechargeable batteries was restricted to a limited set of ether-based electrolytes, graphite anodes, and predominantly sodium ions, with large electrode expansion, incomplete structural understanding, and little demonstration at the full-cell level. This action has clearly advanced the state of the art by broadening the range of materials, improving performance metrics, and establishing solvent co-intercalation as a viable battery concept.
A key advancement beyond the state of the art was the significant reduction of electrode expansion during the intercalation of solvated ions by the rational combination of different solvents. This result directly addresses one of the main limitations of co-intercalation systems and demonstrates the feasibility of controlling volume changes through electrolyte design. In addition, the project delivered the first demonstration of a co-intercalation battery (CoIB), providing a proof of principle that the concept can operate in a complete electrochemical cell (Adv. Energy Mater., 2022, 12, 2202377; doi:10.1002/aenm.202202377).
The project also went beyond the state of the art by establishing a comprehensive understanding of solvent co-intercalation through the combined use of operando and in situ techniques together with theoretical simulations.
By the end of the project, the expected results have been achieved and, in several aspects, exceeded. Despite the substantial progress achieved, some work remains ongoing. Further investigations using complementary techniques, particularly electrochemical impedance spectroscopy (EIS), have also been conducted to gain deeper insight into charge-transfer processes, interfacial phenomena, and kinetic limitations in solvent co-intercalation systems. In parallel, studies on alternative electrode materials, with a focus on transition metal dichalcogenides, are underway to explore the generality of the co-intercalation concept and optimize performance. These ongoing studies are being prepared for future publications and will form the basis of the upcoming PhD theses, which will ensure the results contribute to both scientific dissemination and doctoral training.

Classical ion storage vs. SEED project