Operando Raman Spectroscopy Measurements of a High-Voltage Cathode Material for Lithium-Ion Batteries

Jehnichen, Philipp; Korte, Carsten

doi:10.1021/acs.analchem.8b05819

Cited by 25 publications

(17 citation statements)

References 26 publications

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“…In the midwavenumber region (680–1300 cm –1 ), the Raman bands undergo similar evolution in both pristine LNCM and NFO3 (Figure c,f). Our results are consistent with Raman spectra of the LiPF 6 -salt electrolyte. , …”

Section: Resultssupporting

confidence: 90%

Phase Compatible NiFe₂O₄ Coating Tunes Oxygen Redox in Li-Rich Layered Oxide

et al. 2021

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Li-rich layered oxides have attracted intense attention for lithium-ion batteries, as provide substantial capacity from transition metal cation redox simultaneous with reversible oxygen-anion redox. However, unregulated irreversible oxygen-anion redox leads to critical issues such as voltage fade and oxygen release. Here, we report a feasible NiFe2O4 (NFO) surface-coating strategy to turn the nonbonding coordination of surface oxygen into metal–oxygen decoordination. In particular, the surface simplex M–O (M = Ni, Co, Mn from MO6 octahedra) and N–O (N = Ni, Fe from NO6 octahedra) bonds are reconstructed in the form of M–O–N bonds. By applying both in operando and ex situ technologies, we found this heterostructural interface traps surface lattice oxygen, as well as restrains cation migration in Li-rich layered oxide during electrochemical cycling. Therefore, surface lattice oxygen behavior is significantly sustained. More interestingly, we directly observe the surface oxygen redox decouple with cation migration. In addition, the NFO-coating blocks HF produced from electrolyte decomposition, resulting in reducing the dissolution of Mn. With this strategy, higher cycle stability (91.8% at 1 C after 200 cycles) and higher rate capability (109.4 mA g–1 at 1 C) were achieved in this work, compared with pristine Li-rich layered oxide. Our work offers potential for designing electrode materials utilizing oxygen redox chemistry.

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Section: Resultssupporting

confidence: 90%

Phase Compatible NiFe₂O₄ Coating Tunes Oxygen Redox in Li-Rich Layered Oxide

et al. 2021

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“…Four different characteristic types of Raman spectra were observed; two in S1 (Figure d), four in S2 (Figure e), and three in S3 (Figure f). The red-colored spectra all exhibit a sharp peak at ∼638 cm –1 , a smaller peak at ∼407 cm –1 , and smaller peaks around 590–610 cm –1 , which are characteristics of the P4 3 32 LNMO (i.e., the ordered phase) according to previous studies. , In the green-colored spectra, by contrast, the peaks at ∼638 cm –1 are weaker and broader, which indicates the presence of the Fd 3̅ m LNMO (i.e., the disordered phase). , To the best of our knowledge, the blue- and black-colored Raman spectra have never been reported for LNMO samples in the literature. They are clearly different from those reported for P4 3 32 and Fd 3̅ m LNMOs (red and green-colored spectra).…”

Section: Results and Discussionsupporting

confidence: 70%

Controlling Particle Size and Phase Purity of “Single-Crystal” LiNi_0.5Mn_1.5O₄ in Molten-Salt-Assisted Synthesis

et al. 2020

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Spinel-structured lithium nickel manganese oxide (LiNi0.5Mn1.5O4, LNMO) is a low-cost battery cathode material with a high operating voltage (∼4.7 V vs Li+/Li), relatively high capacity (∼147 mA h g–1), and good rate performance. Previous studies have suggested that large particle size, single-crystal-like morphology, and high phase purity are favorable for achieving good electrochemical performance. However, simultaneous control over these properties is difficult for conventional solid-state synthesis at high temperatures. Here, we report a molten-salt-assisted method to prepare large-size (median grain size D50 = 16.8 μm) single-crystal LNMO with molten lithium molybdate (Li2MoO4) serving as the medium of ion diffusion and crystal growth. In situ X-ray diffraction (XRD) studies of the material preparation process reveal structural disorder and formation of the rock-salt impurity phase at high temperatures, which are reverted upon cooling. The correlations between the cooling rate and structural ordering/phase purity at the single-particle level are further studied using correlative scanning electron microscopy and Raman spectroscopy (SEM-Raman) techniques. SEM-Raman studies for the first time reveal that the Ni-rich rock-salt impurity phase actually exists at the interior of the large-size LNMO particles, which is difficult to be detected by conventional XRD or Raman spectroscopy because of limitations in probing depth. We further confirm that slow cooling is the key to increasing structural ordering and enhancing electrochemical performance of LNMO. The optimized LNMO sample shows excellent cycle performance by retaining ∼85% initial capacity after 300 charge–discharge cycles and acceptable level of rate capability despite its large particle size. Our results highlight the importance of mechanistic studies into material synthesis, which provide the basis for designing better materials and more efficient preparation methods.

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“…Samples 2 and 3 (d-LNMO-48 and d-LNMO-44) show very similar spectra, which are fully consistent with the commonly specified properties of disordered LNMO. [36,37] The Raman spectra of sample 4 (o-LNMO-43) in contrast, provides typical features of ordered LNMO. In comparison to the disordered phases, T 2g and E g modes at 160 and 410 cm −1 exhibit higher intensities, and the A 1g modes of Mn 4+ and Ni 2+ at 590 and 610 cm −1 can clearly be distinguished.…”

Section: Samplementioning

confidence: 99%

On the Composition of LiNi_0.5Mn_1.5O₄ Cathode Active Materials

Stüble

Mereacre

Geßwein

et al. 2023

Advanced Energy Materials

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A characteristic advantage over state-of-the-art Ni-rich cathode active materials such as LiNi 0.6 Co 0.2 Mn 0.2 O 2 (NCM-622) or LiNi 0.8 Co 0.1 Mn 0.1 O 2 (NCM-811) is that LNMO is cobalt free and the redox capacity of nickel is used in its entirety. The latter could become more important considering rising nickel prices. Based on realistic full cell capacities of 120 mAh g −1 for LNMO and 170 mAh g −1 for the NCM materials, 43.8 Ah per mol Ni is obtained for LNMO, whereas NCM-622 and NCM-811 only yield 27.5 and 20.7 Ah mol −1 , respectively. The specific energy density of LNMO vs. graphite full cells is likewise highly competitive. For LNMO, up to 464 Wh kg −1 are expected, which exceeds the energy densities of corresponding NCM-622 and NCM-811 cells, yielding 416 and 448 Wh kg −1 , respectively. [2] Despite these favorable features, commercialization of LNMO cathode materials never succeeded. Up to date, it was not possible to build competitive cells with graphite anodes, as the degradation of these full cells has not been brought under control. [3,4] The problem, however, is not the stability of LNMO itself, but the dissolution and disproportionation of Mn(III) from LNMO, which leads to continuous decomposition reactions on the anode side and ongoing loss of cyclable lithium. [3,5,6] LNMO is nevertheless a very stable cathode material, which does not tend to decompose or release oxygen during cycling. [7] There is scientific consensus that LNMO crystallizes as an ordered or disordered spinel phase in the space groups P4 3 32 or Fd3m, respectively, or as intermediate, partial ordered phases. The term "order" refers to the distribution of transition metal cations on the octahedral sites of the spinel structure. In the ordered structure, Mn and Ni predominantly occupy the Wyckoff positions 12d and 4a, while in the disordered structure, they are statistically distributed over the 16c octahedral site. [8,9] Whether an LNMO material is predominantly ordered or disordered is commonly associated with the calcination temperature. Temperatures below 730 °C are reported to favor the formation of the ordered phase, whereas at higher temperatures disordered crystal structures are reported to occur. [10] LNMO phases with the composition LiNi 0.5 Mn 1.5 O 4 , where Mn is Mn(IV) exclusively, are reported to be obtained by calcining LNMO materials at 700 °C. [11] Increasing calcination temperatures however, lead to a partial reduction of Mn(IV) to Mn(III), which becomes obvious from an increasing Mn 3+ /Mn 4+ LiNi 0.5 Mn 1.5 O 4 (LNMO) cathode active materials for lithium-ion batteries have been investigated for over 20 years. Despite all this effort, it has not been possible to transfer their favorable properties into applicable, stable battery cells. To make further progress, the research perspective on these spinel type materials needs to be updated and a number of persisting misconceptions on LNMO have to be overcome. Therefore, the current knowledge on LNMO is summarized and controversial points are addressed by detaile...

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Operando Raman Spectroscopy Measurements of a High-Voltage Cathode Material for Lithium-Ion Batteries

Cited by 25 publications

References 26 publications

Phase Compatible NiFe₂O₄ Coating Tunes Oxygen Redox in Li-Rich Layered Oxide

Phase Compatible NiFe₂O₄ Coating Tunes Oxygen Redox in Li-Rich Layered Oxide

Controlling Particle Size and Phase Purity of “Single-Crystal” LiNi_0.5Mn_1.5O₄ in Molten-Salt-Assisted Synthesis

On the Composition of LiNi_0.5Mn_1.5O₄ Cathode Active Materials

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Operando Raman Spectroscopy Measurements of a High-Voltage Cathode Material for Lithium-Ion Batteries

Cited by 25 publications

References 26 publications

Phase Compatible NiFe2O4 Coating Tunes Oxygen Redox in Li-Rich Layered Oxide

Phase Compatible NiFe2O4 Coating Tunes Oxygen Redox in Li-Rich Layered Oxide

Controlling Particle Size and Phase Purity of “Single-Crystal” LiNi0.5Mn1.5O4 in Molten-Salt-Assisted Synthesis

On the Composition of LiNi0.5Mn1.5O4 Cathode Active Materials

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Phase Compatible NiFe₂O₄ Coating Tunes Oxygen Redox in Li-Rich Layered Oxide

Phase Compatible NiFe₂O₄ Coating Tunes Oxygen Redox in Li-Rich Layered Oxide

Controlling Particle Size and Phase Purity of “Single-Crystal” LiNi_0.5Mn_1.5O₄ in Molten-Salt-Assisted Synthesis

On the Composition of LiNi_0.5Mn_1.5O₄ Cathode Active Materials