Li3V2(PO4)3-Based Cathode Materials for Li-Ion Batteries: Time Evolution of the Vanadium Valence State

• Published in: Bulletin of the Russian Academy of Sciences. Physics 2024-07, Vol.88 (7), p.1115-1121
• Main Authors: Yagfarova, A. R., Yatsyk, I. V., Mamedov, D. V., Deeva, Y. A., Uporova, A. M., Chupakhina, T. I., Khantimerov, S. M., Gavrilova, T. P.
• Format: Article
• Language: English
• Subjects: Cathodes; Chemical synthesis; Degradation; Electrode materials; Electron paramagnetic resonance; Electron spin; Electrons; Hadrons; Heavy Ions; Identification methods; Lithium; Lithium-ion batteries; Nuclear Physics; Physics; Physics and Astronomy; Spin resonance; Time measurement; Valence; Vanadium
• ISSN: 1062-8738; 1934-9432
• DOI: 10.1134/S1062873824707177

Li 3 V 2 (PO 4 ) 3 -based composites as a lithium-ion battery cathode material were synthesized by the hydrothermal method with subsequent annealing in an Ar atmosphere. The as-prepared samples were characterized by X-ray diffraction analysis and electron spin resonance (ESR) methods. Based on ESR, data the quantitative estimation of V 4+ content was performed. The tetravalent vanadium ions arised instead of trivalent vanadium ions due to lithium nonstoichiometry in Li 3 V 2 (PO 4 ) 3 structure. This method of identifying nonstoichiometry via ESR detection of V 4+ ions is very simple and demonstrative and can be used to characterize not only as-prepared samples but also samples after multiple electrochemical cycling. This technique of the lithium nonstoichiometry detection in Li 3 V 2 (PO 4 ) 3 can be used if the valence state of vanadium ions is stable and investigated samples are not degraded during a long time. To clarify the question, the additional ESR measurements were performed for Li 3 V 2 (PO 4 ) 3 samples which were air-stored over a long period (up to 2 years). The obtained data proved the sample degradation in the form of increasing in V 4+ content. It was found that in the presence of LiPO 3 salt in the composite the number of magnetic centers increased significantly, so it contributed to sample degradation, while the pure Li 3 V 2 (PO 4 ) 3 sample Li 3 V 2 (PO 4 ) 3 /C were most stable.