A recent study published in Nature Communications investigates a new cathode material—benzyltriethylammonium tellurium iodide (BzTEA)2TeI6 perovskite—that enables 11-electron transfer in zinc-ion batteries. The material demonstrates reversible redox reactions at both its X- and B-site elements, offering improved performance in energy storage systems.
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Background
Perovskites with an ABO3 structure, where A represents divalent and B tetravalent metal cations, are widely used in fields like dielectrics, ferroelectrics, magnetics, and energy storage. Their high density of oxygen vacancies also makes them suitable as catalytic electrodes.
Halide perovskites (ABX3), with monovalent A, divalent B, and halogen X (Cl, I, or Br), have smaller bandgaps, making them effective in optoelectronic applications. However, their application in batteries is still in its early stages and has mostly focused on energy storage.
A key challenge with halide perovskite cathodes lies in the inert nature of the B-site cation during redox reactions, which limits their discharge capacity. Substituting tetravalent chalcogenide cations for noble metal cations at the B-site could address this limitation, enabling greater utilization of cathode materials and supporting consistent multi-electron transfer.
Methods
Researchers synthesized (BzTEA)2TeI6 perovskite microcrystals using a saturated recrystallization process. The synthesis involved tellurium oxide, benzyltriethylammonium chloride (BzTEACl), and Ketjenblack EC-300J as a conductive agent. An electrolyte, Ch0.4Zn0.6Cl1.6·1.5H2O, was prepared from ChCl and ZnCl2.
To analyze the perovskite, the team used techniques like ultraviolet-visible (UV-Vis) spectroscopy, Fourier-transform infrared (FTIR) spectroscopy, Raman spectroscopy, powder X-ray diffraction (XRD), and X-ray photoelectron spectroscopy (XPS). Scanning electron microscopy (SEM) and energy-dispersive spectroscopy (EDS) were used to assess morphology and elemental composition.
The cathodes were fabricated by mixing (BzTEA)2TeI6 perovskite microcrystals with Ketjenblack and polyvinylidene fluoride (PVDF) binder in 1-methyl-2-pyrrolidinone. This mixture was prepared with a mass ratio of 7:2:1 and ground for one hour to ensure uniformity. The resulting liquid slurry was evenly coated onto a carbon cloth substrate and subjected to an overnight vacuum bakeout at approximately 80 °C.
Following this, the researchers assembled Zn||ZnSO4||(BzTEA)2TeI6 Swagelock cells and Zn||(BzTEA)2TeI6 batteries using a ZnCl2-based electrolyte for electrochemical characterization.
Cyclic voltammograms (CVs) and other electrochemical data were collected using an electrochemical workstation to evaluate redox activity and performance. Additionally, the long-term stability and rate performance of the batteries were assessed using a battery testing system at room temperature.
To better understand the electrochemical mechanisms, the researchers used density functional theory (DFT) calculations. They applied the Perdew-Burke-Ernzerhof (PBE) method to study electronic exchange-correlation interactions and used the Generalized Gradient Approximation (GGA) with PBE for structural optimization.
Results and Discussion
The (BzTEA)2TeI6 microcrystals formed bulk rod-shaped structures with an average length of less than 50 µm, as seen in SEM images. Their XRD patterns matched theoretical predictions, and their black appearance, confirmed by UV-Vis absorption spectra, indicated a narrow optical bandgap. SEM-EDS mapping showed a uniform elemental distribution, with 14.5 % tellurium and 85.5 % iodine.
FTIR spectra confirmed protonation at the A-site N-H bond, while Raman spectra revealed asymmetric Eg and symmetric A1g stretching of the Te-I bond, similar to the Te-O bond in TeO2. Thermogravimetric analysis showed the perovskite’s structural stability and hydrophobic nature, with minimal weight loss below 211°C.
Electrochemical tests on Zn||ZnSO4||(BzTEA)2TeI6 cells showed two distinct redox peaks associated with I0/I- and Te4+/Te0 reactions, though the latter showed fast current decay in CV curves. By comparison, other zinc electrolytes, such as zinc trifluoromethanesulfonate, zinc acetate, and zinc chloride, did not support redox reactions involving high-valent tellurium cations.
In the battery characterizations, the TeO2 + ZnI2 cathode showed two types of redox reactions (I0/I+/I- and Cl0/Cl-) but displayed unusual attenuation and a weak Te6+/Te4+ redox reaction with increasing CV scan rate. This was attributed to the catalytic role of the iodine atom.
In contrast, the (BzTEA)2TeI6 cathode demonstrated four sharp discharge peaks corresponding to I+/I0, Cl0/Cl-, Te0/Te2-, and Te6+/Te4+ redox pairs, as well as a broad peak resulting from overlapping I0/I- and Te4+/Te0.
The galvanostatic discharge curve of the Zn||(BzTEA)2TeI6 battery at 0.5 A g-1 revealed an 11-electron transfer process. This included contributions from tellurium (eight electrons), iodine (three electrons), and chlorine (one electron).
Conclusion
The researchers developed the (BzTEA)2TeI6 perovskite to support redox reactions at both the B-site chalcogen and X-site halogen. Detailed analysis confirmed its potential as a conversion-type cathode material.
The cathode effectively stabilized active chalcogen and halogen elements, facilitating fast chloride ion transfer and maintaining high-valent tellurium cations as tellurium chloride ions. When paired with the Ch0.4Zn0.6Cl1.6·1.5H2O electrolyte, the battery achieved 11-electron transfer.
Redox pairs such as Cl0/Cl-1, I+/I0/I-, Te4+/Te0, Te6+/Te4, and Te0/Te2- resulted in an energy density exceeding 577 Wh kg-1Te/I. The battery also achieved a high capacity of 473 mAh g-1Te/I at 0.5 A g-1 and retained over 77 % capacity after 500 cycles at 1 A g-1. These results show potential for practical applications in energy storage.
Journal Reference
Wang, S., et al. (2025). A tellurium iodide perovskite structure enabling eleven-electron transfer in zinc ion batteries. Nature Communications. DOI: 10.1038/s41467-024-55385-6, https://www.nature.com/articles/s41467-024-55385-6
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