Energy storage: Towards novel solid-state calcium-based batteries
Researchers at Aarhus University have discovered materials with record-high calcium (Ca²⁺) cationic conductivity due to a relatively open structure with weak dihydrogen bonds and weak interactions between organic apolar moieties. This new electrolyte could pave the way for next-generation solid-state batteries.
In a recent scientific paper published in Angewandte Chemie International Edition, a research team from Interdisciplinary Nanoscience Center (iNANO) and Department of Chemistry Aarhus University, presents a novel material, Ca(BH4)2×2CH3NH2, which has record-high calcium conductivity. The researchers from Aarhus University have discovered several phenomena in the solid state, which facilitate fast cationic conductivity. This has allowed the rational design, synthesis and characterisation of a novel functional battery material. This work may be an important step towards cheaper and safer solid-state batteries with higher energy densities as compared to the lithium batteries used today.
A new derivative of calcium hydriborate is discovered, Ca(BH4)2·2NH2CH3, which demonstrate the highest reported Ca2+ conductivity at near ambient conditions, σ(Ca2+) ~ 10-5 S cm-1 at T = 70 °C. The structure consists of two-dimensional ‘open’ layers where the organic moiety of methylamine ligands creates relatively open pores. The layered structure and cavities include open cation positions and three-dimensional Ca2+ conduction channels throughout the crystal structure. Weak apolar (dispersion) interactions and dihydrogen bonds contribute to structural flexibility and migration of the divalent ions. The compound has a very low electronic conductivity providing an ionic transport number close to unity (tion = 0.9916), the oxidative stability is 1.7 V vs. Ca2+/Ca and Ca plating was demonstrated. However, there is still significant room for improvement of the plating/stripping process.
Interestingly, this new compound was designed and synthesised based on recent discoveries of phenomena, which facilitate fast cationic conductivity. The authors anticipate that the results presented will inspire design and discovery of other calcium hydriborate derivatives with even higher ionic conductivity and better performance. Thus, this work is a significant step forward in the development of all-solid-state calcium batteries, with a large potential for storage of ‘green’ electricity from sun and wind.

About the research
External funding:
This work was supported by the Danish Council for Independent Research (SOS-MagBat DFF9041-00226B and CaMBat DFF0217-00327B) and the Villum Foundation as part of the Villum Experiment Programme (grant no. 40717). The Carlsberg Foundation is acknowledged for funding the Tescan Clara SEM used in this work (Grant no: CF20-0364). Affiliation with the Center for Integrated Materials Research (iMAT) at Aarhus University is also gratefully acknowledged. We acknowledge MAX IV Laboratory for time on Beamline DanMAX under Proposal 20211120. Research conducted at MAX IV is supported by the Swedish Research council under contract 2018-07152, the Swedish Governmental Agency for Innovation Systems under contract 2018-04969, and Formas under contract 2019-02496. DanMAX is funded by the NUFI grant no. 4059-00009B.
Conflicts of interest:
The researchers declare that there are no conflicts of interest in connection with this research.
Link to the scientific article:
Towards Solid-State Batteries Using a Calcium Hydridoborate Electrolyte
Lasse N. Skov, Jakob B. Grinderslev, Therese S. S. Kjær, Lasse R. Kristensen, Torben R. Jensen
To be cited as: Angew. Chem. Int. Ed. 2025, e202500613
Contact
Professor Torben René Jensen
Aarhus University
Interdisciplinary Nanoscience Center (iNANO)
Department of Chemistry
Email: trj@chem.au.dk