In-situ Raman spectroscopic investigation of LiMn1.45Ni0.45M0.1O4 (M = Cr, Co) 5 V cathode materials
Résumé
In-situ Raman spectroscopy is employed to investigate the valence state variations of nickel and manganese,
as well as the local structure change of LiMn1.45Ni0.45M0.1O4 (M ¼ Cr, Co) cathodes (LMN) during
galvanostatic chargeedischarge. Raman spectra are collected between 3.5 and 4.9 V in the wave number
range of 100e800 cm1. The Raman observations showed that the pristine cathodes of Cr- and Co-doped
LMN have essentially the same spectra, and they also have similar evolution patterns during cycling
showing their reversible behaviour in the de-lithiation and lithiation processes. The Raman spectra of the
pristine cathodes have eleven bands, located at 162, 220, 378, 408, 486, 498, 528, 593, 613, 639 and
672 cm1. The bands with wave number <300 cm1 are attributed to the translation mode of molecular
vibration; the 486, 593 and 639 cm1 bands are assigned to the stretching mode of MneO bond; and the
vibration modes at 408, 498, 528 and 613 cm1 originated from the NieO bond; The band at 672 cm1 is
attributed to A1g mode of Cr3þ
eO/Co3þ
eO. During cycling, several new bands are detected near the end
of charge, among which the T2g(T) band at 170 cm1 is attributed to the translation mode of lattice vibration
in which the lithium concentration is low, and the T2g band at 538 cm1 is due to the presence of
Ni4þ
eO bond in the crystal structure. The T2g(T) and T2g(Ni4þ
eO) bands are clearly evident at V 4.78
(x ~ 0.32) and V 4.82 (x ~ 0.28) for Cr- and Co-doped LMN, respectively.