Study of the Lithium-Rich Integrated Compound xLi₂MnO₃·(1-x)LiMO₂(x around 0.5; M = Mn, Ni, Co; 2:2:1) and Its Electrochemical Activity as Positive Electrode in Lithium Cells

Abstract

We investigated the structural characteristics of Li-rich xLi2MnO3·(1-x)Li[MnyNizCow]O2 cathode material (x around 0.5, y:z:w around 2:2:1) and its electrochemical performance in lithium cells at 30 and 60°C. It was established that nanoparticles of the xLi2MnO3·(1-x)Li[MnyNizCow]O2 compound are intergrown on the nano-scale and are built of thin plates of 40–50 Å. We demonstrated that xLi2MnO3·(1-x)Li[MnyNizCow]O2 electrodes exhibited at 60°C high capacities of ∼270 and ∼220 mAh/g at 1C and 2C rates, respectively. They can be cycled effectively at 30 and 60°C providing capacity ∼250 mAh/g in the initial cycles, but it fades upon prolonged cycling due, to some extent, to increasing the electrode impedance (charge-transfer resistance) especially at the elevated temperature. The effective chemical diffusion coefficient of Li+ in these electrodes measured during charge to 4.7 V by potentiostatic intermittent titration technique (PITT) was found to be ∼10−10 cm2/s. From convergent beam electron diffraction and Raman spectroscopy studies we established, for the first time, that partial structural transition from layered-type to spinel-type ordering in xLi2MnO3·(1-x)Li[MnyNizCow]O2 electrodes occurred in the initial charge to 4.7 V and even at the early stages of charging at 4.1 V–4.4 V. The thermal behavior of the xLi2MnO3·(1-x)Li[MnyNizCow]O2 material and electrodes are also discussed.

A Raman-Based Investigation of the Fate of Li2MnO3in Lithium- and Manganese-Rich Cathode Materials for Lithium Ion Batteries

“…At potentials greater than 4.0 V, their Raman band envelope structure above 550 cm −1 fades away to the point that it bears little resemblance to our 4.6 V spectrum in Fig. 6 or to the in situ spectra reported by Rao et al 7 at potentials greater than 4.0 V. This discrepancy in the ≥4.0 V Raman spectra from the two in situ studies, 7,12 from our ex situ studies, and from two other relevant ex situ studies 6,9 leaves the matter of the phase chemistry above 4.0 V for LMR-NMC compositions somewhat unresolved from a Raman spectroscopy perspective.…”

“…6-13 Amalraj et al 6 used a combination of XRD, TEM, and ex situ Raman spectroscopy to establish that a partial structural transition from a layered-type to a spinel-type of ordering occurred in the initial charge to 4.7 V when their xLi 2 MnO 3 · (1-x)LiMO 2 cathode (M = Ni-Mn-Co) was cycled * Electrochemical Society Active Member.…”

“…A number of pertinent studies, particularly some of the more recent ones, have employed Raman spectroscopy to elucidate the chemical and structural transformations that the LMR-NMC composition undergoes during electrochemical cycling in cells with lithium-based anodes. [6][7][8][9][10][11][12][13] Amalraj et al 6 used a combination of XRD, TEM, and ex situ Raman spectroscopy to establish that a partial structural transition from a layered-type to a spinel-type of ordering occurred in the initial charge to 4.7 V when their xLi 2 MnO 3 · (1-x)LiMO 2 cathode (M = Ni-Mn-Co) was cycled * Electrochemical Society Active Member.…”

Raman Microscopy of Lithium-Manganese-Rich Transition Metal Oxide Cathodes

“…18,19,24,[26][27][28][29][30][31] Raman microscopy offers high spatial resolution (< 1μm 3 ), large field of view, and chemical specificity, making it an ideal tool to investigate both the pristine material and composite battery electrodes. 32,33 Nonetheless, there are significant differences in the spectra reported for LMR-NMC oxides, as well as ambiguity in the interpretation of the vibrational modes.…”

“…32,33 Nonetheless, there are significant differences in the spectra reported for LMR-NMC oxides, as well as ambiguity in the interpretation of the vibrational modes. 18,19,24,30,31 Some of the discrepancy may arise from a failure to recognize the susceptibility of manganese oxides to laser induced phase transformations. In this contribution, we first establish the laser power dependence of the Raman spectra of LMR-NMC cathode.…”