White lines and<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mrow><mml:mi>d</mml:mi></mml:mrow></mml:math>-band occupancy for the<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mrow><mml:mn>3</mml:mn><mml:mi>d</mml:mi></mml:mrow></mml:math>transition-metal oxides and lithium transition-metal oxides

Graetz, Jason; Ahn, Channing C.; Ouyang, Hao; Rez, Peter; Fultz, B.

doi:10.1103/physrevb.69.235103

Cited by 106 publications

(71 citation statements)

References 36 publications

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“…3e-h). The variation of the Mn oxidation state along the scanning direction is evident by the blue shift of the absolute energy onset and the reduced L3/L2 ratio 33 . A calculation based on the linear combination of Mn 2 þ and Mn 4 þ was performed and the corresponding concentration profiles are presented in Fig.…”

Section: Resultsmentioning

confidence: 99%

“…Depth profiling of the electronic structure was carried out using XAS and STEM-EELS. Transition metal L-edge XAS and EELS measure the dipole allowed transitions from metal 2p orbitals to unoccupied metal 3d orbitals [31][32][33] and indirectly probe the local hybridization states for metal-oxygen octahedral units 34 in an NMC material. Transition metal L-edge XAS is superior to K-edge XAS in terms of resolving local hybridization states, as the former directly probes the unoccupied 3d states in the metal 3d-oxygen 2p hybridized octahedral crystal field.…”

Section: Resultsmentioning

confidence: 99%

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Surface reconstruction and chemical evolution of stoichiometric layered cathode materials for lithium-ion batteries

et al. 2014

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The present study sheds light on the long-standing challenges associated with high-voltage operation of LiNi x Mn x Co 1 À 2x O 2 cathode materials for lithium-ion batteries. Using correlated ensemble-averaged high-throughput X-ray absorption spectroscopy and spatially resolved electron microscopy and spectroscopy, here we report structural reconstruction (formation of a surface reduced layer, R 3m to Fm 3m transition) and chemical evolution (formation of a surface reaction layer) at the surface of LiNi x Mn x Co 1 À 2x O 2 particles. These are primarily responsible for the prevailing capacity fading and impedance buildup under high-voltage cycling conditions, as well as the first-cycle coulombic inefficiency. It was found that the surface reconstruction exhibits a strong anisotropic characteristic, which predominantly occurs along lithium diffusion channels. Furthermore, the surface reaction layer is composed of lithium fluoride embedded in a complex organic matrix. This work sets a refined example for the study of surface reconstruction and chemical evolution in battery materials using combined diagnostic tools at complementary length scales. C hemical evolution and structural transformations at the surface of a material directly influence characteristics relevant to a wide range of prominent applications including heterogeneous catalysis 1-3 and energy storage 4,5 . Structural and/or chemical rearrangements at surfaces determine the way a material interacts with its surrounding environment, thus controlling the functionalities of the material [6][7][8][9][10] . Specifically, the surfaces of lithium-ion battery electrodes evolve simultaneously with charge-discharge cycling (that is, in situ surface reconstruction and formation of a surface reaction layer (SRL)) that can lead to deterioration of performance 4,5,11 . An improved understanding of in situ surface reconstruction phenomena imparts knowledge not only for understanding degradation mechanisms for battery electrodes but also to provide insights into the surface functionalization for enhanced cyclability 12,13 .The investigation of in situ surface reconstruction of layered cathode materials, such as stoichiometric LiNi x Mn x Co 1 À 2x O 2 (that is, NMC), lithium-rich Li(Li y Ni x À y Mn x Co 1 À 2x )O 2 , lithium-rich/ manganese-rich (composite layered-layered) xLi 2 MnO 3 Á (1 À x) LiMO 2 (M ¼ Mn, Ni, Co, and so on) materials, is technologically significant as they represent a group of materials with the potential to improve energy densities and reduce costs for plug-in hybrid electric vehicles and electric vehicles [14][15][16][17] . Practical implementation of some of these materials is thwarted by their high first-cycle coulombic inefficiencies [17][18][19][20] , capacity fading 18,21 and voltage instability [20][21][22] , especially during high-voltage operation. Specifically, high-voltage charge capacities achieved in lithiumrich/manganese-rich layered cathodes are directly associated with various irreversible electrochemical processes including o...

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Section: Resultsmentioning

confidence: 99%

Section: Resultsmentioning

confidence: 99%

Surface reconstruction and chemical evolution of stoichiometric layered cathode materials for lithium-ion batteries

et al. 2014

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“…Previous studies of transition metals 19,20 and their oxides 21 have revealed a linear relationship between the intensity of the energy-loss features associated with these transitions ͑called "white lines"͒ and the 3d-band occupancy. This can be used to quantitatively determine the occupancy of the d states.…”

Section: Introductionmentioning

confidence: 99%

Transition metald-band occupancy in skutterudites studied by electron energy-loss spectroscopy

et al. 2007

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The transition-metal 3d occupancy of a series of thermoelectric skutterudites is investigated using electron energy-loss spectroscopy. We find that bonding causes an emptying of the 3d states in the binary skutterudites CoP 3 , CoAs 3 , CoSb 3 , and NiP 3 , while compared to the pure Fe the 3d occupancy in LaFe 4 P 12 is significantly increased, consistent with the idea that each interstitial La atom ͑rattler͒ donates three electrons to compensate for missing valence electron of Fe as compared to Co. These experimental results are in agreement with previous models suggesting a predominantly covalent bonding between transition metal and pnictogen atoms in skutterudites, and provide evidence of charge transfer from La to the Fe-P complex in LaFe 4 P 12 .

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“…The Ti and O ELNES contain key information about octahedral distortions within the crystal structure as electron energy loss spectra reflect the density of unoccupied states of the material and can thus be used to identify changes in valence and atomic bonding. [27][28][29] Figure 4(a) is a high resolution high-angle annular dark-field (HAADF) image containing the grain boundary shown in Fig. 3, where EEL spectra have been extracted from 25 positions.…”

Section: -6mentioning

confidence: 99%

Mapping grain boundary heterogeneity at the nanoscale in a positive temperature coefficient of resistivity ceramic

et al. 2017

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White lines andd-band occupancy for the3dtransition-metal oxides and lithium transition-metal oxides

Cited by 106 publications

References 36 publications

Surface reconstruction and chemical evolution of stoichiometric layered cathode materials for lithium-ion batteries

Surface reconstruction and chemical evolution of stoichiometric layered cathode materials for lithium-ion batteries

Transition metald-band occupancy in skutterudites studied by electron energy-loss spectroscopy

Mapping grain boundary heterogeneity at the nanoscale in a positive temperature coefficient of resistivity ceramic

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