Researchers from Kazan Federal University in Russia report in a paper in the Journal of Power Sources that heteroatoms-co-doped oxo-triarylmethyl (B/N/P@oxTAM) can be used as a viable anode material for magnesium-ion batteries (MIBs) with extended life cycle and quick charge-discharge rates due to its low open-circuit voltage and diffusion energy barrier, as well as a high theoretical specific capacity value.

Kaviani et al.

Rechargeable batteries based on multivalent metal ions such as Mg²⁺, Ca²⁺, and Al³⁺, can provide higher volumetric energy density than monovalent ions owing to multiple electron transfers occurring within each ion. Thanks to high theoretical specific capacity (2205 mAh g⁻¹), fast mobility, high abundance, low reduction potential (−2.37 V), non-toxicity, and low cost, magnesium-ion batteries (MIBs) are regarded as the most promising rechargeable ion batteries for portable electronic devices. Despite these advantages, the main problem of using MIBs commercially is the formation of a surface blocking layer (dendrite) as a result of the instability of the electrolyte in the vicinity of Mg²⁺, which can lead to decomposing electrolyte and blocking diffusion of Mg-ion during the charge-discharge process.

… Covalent organic frameworks (COFs) belong to a category of crystalline polymers with strong covalent bonds that have been widely considered to be useful materials for rechargeable batteries owing to their large specific surface area, high thermal stability, tunable nature, sustainability, high porosity, and low density. The shape of the COFs considerably enhances metal ion intercalations, ionic diffusion, and ionic transport. However, the application of COFs is limited because of poor electronic conductivity (a large band gap). Therefore, it is urgent to design novel organic electrode materials with excellent performance.

… Recently, oxo-triarylmethyl (oxTAM), as an innovative porous–conjugated COF, has received more attention in electrochemical switches and electronic devices. It was first proposed by Alc’on et al., which oxygen atoms are linked between the adjacent aryl rings. Therefore, this study demonstrates a rational design of potential anode material consisting of B, N, and P co-doped oxTAM for MIBs using DFT calculations.

—Kaviani

The B/N/P@oxTAM has a highly porous structure and affinity for Mg-ions to attach to the vacancy sites. The team calculated partial density of states, open-circuit voltage, theoretical specific capacity, and diffusion energy barrier in the study.

Results showed a significant decrease in the HOMO-LUMO gap with no structural deformation, suggesting the high cycling performance of B/N/P@oxTAM for MIBs. Moreover, the designed anode material demonstrated full loading with six Mg-ions at different active sites, indicating a high theoretical specific capacity of 513.75 mAh g⁻¹ and a low open-circuit voltage of 0.07 V. The presence of a heterocyclic ring (borabenzene) with a diffusion energy barrier of 0.039 eV increased the diffusion of Mg-ions.

Resources

• Sadegh Kaviani, Irina Piyanzina, Oleg V. Nedopekin, Dmitrii A. Tayurskii, Rezvan Rahimi (2024) “A DFT-based design of B/N/P-co-doped oxo-triarylmethyl as a robust anode material for magnesium-ion batteries,” Journal of Power Sources, Volume 604 doi: 10.1016/j.jpowsour.2024.234425