Investigation of Li-Li _xv ₂O ₅ rechargeable batteries at different charged states using NMR spectroscopy

Li rechargeable cells made with structural arrangement Li/membrane/ Li _xV ₂O ₅ were examined under three states using NMR spectroscopy; these states are charged, discharged, and over-cycled. ⁷Li NMR signals at chemical shifts of 0 ppm and around -20 ppm from the resonance frequency, which corresponds to the Li ions from the residual electrolyte at the cathode surface and inside the cathode material of Li _xV ₂O ₅, respectively, were obtained from Li _xV ₂O ₅ samples in both charged and discharged cells. From nuclear spin-lattice relaxation time (T ₁) measurements, two components due to the Li ions in the electrode surface region and inside the bulk of Li _xV ₂O ₅ particles were obtained from charged cell. The ⁵¹ V NMR spectra were virtually identical for Li _xV ₂O ₅ from the charged and over-cycled cells; however, the intensity of ⁵¹ V NMR signal from the discharged cell was significantly lower due to paramagnetic V ⁺⁴ and V ⁺³ species.