Functionalized Benzo-Crown Ether-Based Additives for Sodium Ion Electrolytes: Role of Nitrile and Naphthalene Groups
Eren Temur1, Christian Wölke1, Martin Winter1, Isidora Cekic-Laskovic1
1 Forschungszentrum Jülich GmbH, Helmholtz-Institute Münster (IMD-4), Corrensstraße 48, 48149 Münster, Germany

Sodium-ion batteries represent a possible alternative to the lithium-based batteries, which are already widely used in the mobility and energy industry. Unlike lithium, sodium is available in abundance and is not subject to any significant geopolitical influences . [1] Despite decades of research, sodium-based battery research is still in its infancy, as the focus has so far been mainly on optimizing electrode materials.
Over the past few years, layer oxide-based cathode materials have proven to be a cost-effective and easy-to-manufacture alternative to polyanionic systems with sufficiently high capacity. However, these materials are characterized by low cycle stability and high interfacial reactivity, which are usually addressed by material doping or coatings . Disordered graphite materials, also known as hard carbon, have proven to be suitable anode materials for sodium-based systems. These materials are capable of storing sodium ions, but suffer from structural instability, which makes the formation of a mechanically stabilizing passivation layer essential. [2] Research at the electrolyte level often takes a back seat in this context.
These challenges can be addressed, among other things, by the use of electrolyte additives that ensure an optimized passivation layer with sufficient sodium ion conductivity. Crown ethers are considered ideal candidates for this purpose, but due to their low electrochemical stability, they have received only limited recognition to date for high voltage applications up to 4.0V vs. Na/Na+. However, they deserve increased attention due to their ion-specific coordination ability and the associated control of the ion-solvate environment. [3]
In this work, the roles of nitrile and naphthalene groups on a benzo-crown ether basic structure are evaluated to address these issues.

References:
[1] Plousia Vassilaras et al J. Electrochem. Soc. 2013, 160.
[2] D. A. Stevens and J. R. Dahn J. Electrochem. Soc. 2000, 147.
[3] H. Zhao, J. Qi, X. Tang et al Journal of Alloys and Compounds 2023, 948.