تقرير
Oxygen Hole Formation Controls Stability in LiNiO$_2$ Cathodes: DFT Studies of Oxygen Loss and Singlet Oxygen Formation in Li-Ion Batteries
| العنوان: | Oxygen Hole Formation Controls Stability in LiNiO$_2$ Cathodes: DFT Studies of Oxygen Loss and Singlet Oxygen Formation in Li-Ion Batteries |
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| المؤلفون: | Genreith-Schriever, A. R., Banerjee, H., Menon, A. S., Bassey, E. N., Piper, L. F., Grey, C. P., Morris, A. J. |
| سنة النشر: | 2022 |
| المجموعة: | Condensed Matter |
| مصطلحات موضوعية: | Condensed Matter - Materials Science |
| الوصف: | Ni-rich cathode materials achieve both high voltages and capacities in Li-ion batteries but are prone to structural instabilities and oxygen loss via the formation of singlet oxygen. Using ab initio molecular dynamics simulations, we observe spontaneous O$_2$ loss from the (012) surface of delithiated LiNiO$_2$, singlet oxygen forming in the process. We find that the origin of the instability lies in the pronounced oxidation of O during delithiation, i.e., O plays a central role in Ni O redox in LiNiO$_2$. For LiNiO$_2$, NiO$_2$, and the prototype rock salt NiO, density-functional theory and dynamical mean-field theory calculations based on maximally localised Wannier functions yield a Ni charge state of ca. +2, with O varying between -2 (NiO), -1.5 (LiNiO$_2$) and -1 (NiO$_2$). Predicted XAS Ni $K$ and O $K$-edge spectra are in excellent agreement with experimental XAS spectra, confirming the predicted charge states. The calculations also show that a high-voltage O $K$-edge feature at 531 eV previously assigned to lattice O-redox processes could alternatively arise from O-redox induced water intercalation and O-O dimer formation with lattice O at high states of charge. The O$_2$ surface loss route observed here consists of 2 surface O$^{.-}$ radicals combining to form a peroxide ion, which is oxidised to O$_2$, leaving behind 2 O vacancies and 2 O$^{2-}$ ions: effectively 4 O$^{.-}$ radicals disproportionate to O$_2$ and 2 O$^{2-}$ ions. The reaction liberates ca. 3 eV per O$_2$ molecule. Singlet oxygen formation is caused by the singlet ground state of the peroxide ion, with spin conservation dictating the preferential release of $^1$O$_2$, the strongly exergonic reaction providing the free energy required for the formation of $^1$O$_2$ in its excited state. |
| نوع الوثيقة: | Working Paper |
| DOI: | 10.1016/j.joule.2023.06.017 |
| URL الوصول: | http://arxiv.org/abs/2205.10462 |
| رقم الأكسشن: | edsarx.2205.10462 |
| قاعدة البيانات: | arXiv |
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