Direct observation of reversible oxygen anion redox reaction in Li-rich manganese oxide, Li<sub>2</sub>MnO<sub>3</sub>, studied by soft X-ray absorption spectroscopy

Oishi, Masatsugu; Yamanaka, Kazushi; Watanabe, Ichiro; Shimoda, Kei; Matsunaga, Toshiyuki; Arai, Hajime; Ukyo, Yoshio; Uchimoto, Yoshiharu; Ogumi, Zempachi; Ohta, Toshiaki

doi:10.1039/c6ta00174b

Cited by 188 publications

(192 citation statements)

References 79 publications

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“…[45][46][47] It has also been reported that oxygen anions are involved in charge compensation through reversible charge redistribution between transition metal and oxygen in spinel 48 and layered oxides (e.g., NMC-333). 49 However, for the NMC-333 material, only the TEY mode was used to investigate the oxygen K-edge in that study, which only provided information about surface oxygen.…”

Section: Resultsmentioning

confidence: 99%

Depth-Dependent Redox Behavior of LiNi_0.6Mn_0.2Co_0.2O₂

Tian

Nordlund

Xin

et al. 2018

J. Electrochem. Soc.

128

125

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Nickel-rich layered materials are emerging as cathodes of choice for next-generation high energy density lithium ion batteries intended for electric vehicles. This is because of their higher practical capacities compared to compositions with lower Ni content, as well as the potential for lower raw materials cost. The higher practical capacity of these materials comes at the expense of shorter cycle life, however, due to undesirable structure and chemical transformations, especially at particle surfaces. To understand these changes more fully, the charge compensation mechanism and bulk and surface structural changes of LiNi 0.6 Mn 0.2 Co 0.2 O 2 were probed using synchrotron techniques and electron energy loss spectroscopy in this study. In the bulk, both the crystal and electronic structure changes are reversible upon cycling to high voltages, whereas particle surfaces undergo significant reduction and structural reconstruction. While Ni is the major contributor to charge compensation, Co and O (through transition metal-oxygen hybridization) are also redox active. An important finding from depth-dependent transition metal L-edge and O K-edge X-ray spectroscopy is that oxygen redox activity exhibits depth-dependent characteristics. This likely drives the structural and chemical transformations observed at particle surfaces in Ni-rich materials. The need for lithium-ion batteries with higher energy density and lower cost than currently available, particularly for transport applications, has led to intensified interest in Ni-rich NMC (LiNi x Mn y Co z O 2 ; x+y+z≈1, where x>y) cathode materials.1-5 These materials deliver higher practical capacities in a typically used voltage range than NMCs with lower Ni content (e.g., LiNi 1/3 Mn 1/3 Co 1/3 O 2 or NMC-333), and most formulations contain less of the expensive Co component, reducing raw material costs. The increase in practical capacity roughly scales with the Ni content, but comes at the expense of cycle life and thermal stability at high states-of-charge (SOC). 6 To circumvent these problems, several different strategies have been utilized to improve cycling, particularly to higher potentials. These include partial substitution with Ti 7-9 or Zr, 10 engineering the micro-or nano-structure to reduce surface Ni content using metal segregation, 11 surface pillared structures, 12 and concentration gradients, 13 coating particle surfaces, 14 and development of electrolyte additives. 15,16 While all of these approaches have resulted in improvements, further understanding of the factors that lead to capacity fading is clearly needed in order to meet the stringent performance requirements of traction applications.The formation of a resistive cathode/electrolyte interphase (CEI), such as an electrolyte decomposition layer, has been observed during cycling of LiNi 0. 20 In the study of NMC-532, it was found that surface reconstruction to a rock salt phase dominates when high voltage (4.8 V) cutoffs are used due to oxygen loss under the highly oxidizing conditions, while ...

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Section: Resultsmentioning

confidence: 99%

Depth-Dependent Redox Behavior of LiNi_0.6Mn_0.2Co_0.2O₂

Tian

Nordlund

Xin

et al. 2018

J. Electrochem. Soc.

128

125

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“…2,48-52 Involvement of oxide in reversible redox activity is supported by XANES O k-edge spectra, 46,47 EXAFS describing Mn-O bond changes, 14 HAADF STEM images showing peroxo dimer formation 48 and by ab-initio molecular orbital calculations. 2,48 The involvement of O 2− anionic redox is thought to have slower kinetics than cationic redox, as well as enhances the materials' voltage hysteresis and fade.…”

Section: Redox Designations Of Li-rich Materialsmentioning

confidence: 99%

“…46,47 One drawback of XANES is that the oxidation states measured are not absolute, since endpoints are given by standards such as NiOOH for Ni 3+ , which will have a different band structure than LiNiO 2 , though have average 3+ oxidation states. During the first charging step described in the voltage profile in Figure 2, Ni 2+ and Co 3+ are oxidized as with standard, LiNi x Co y Mn z O 2 layered materials.…”

Section: Redox Designations Of Li-rich Materialsmentioning

confidence: 99%

Review—Recent Advances and Remaining Challenges for Lithium Ion Battery Cathodes

Erickson

Schipper

Penki

et al. 2017

J. Electrochem. Soc.

152

102

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Electrodes prepared from lithium-rich (Li-rich) xLi 2 MnO 3 ·(1-x)LiNi a Co b Mn c O 2 materials (a + b + c = 1) show extremely high discharge capacities, arising from excess Li + present in their Li 2 MnO 3 component, and the ability to reversibly store charge with O 2− anions. These electrodes suffer serious voltage and capacity fading however, due to the migration of transition metals to the Li-layer at advanced states of charging, partial structural layered-to-spinel transformation and other reasons. In this focus paper, the current understanding of the above materials is summarized, briefly concluding with attempts by our groups to mitigate the voltage and capacity fade of these electrodes.

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“…Tarascon and coworkers have suggested that oxidation of oxygen generally results in the pairing of O ions, resulting in an effective 2O 2– /O 2 n– redox couple 5,9–14,21 , which is stabilized against evolution as oxygen gas in the presence of 4 d and 5 d TMs due to the increased TM–O hybridization and improved band alignment over 3 d TMs 22 . Ceder and coworkers, meanwhile, have predicted that O–O dimerization should only occur in the presence of d 0 and d 10 cations due to the rotational freedom of the O 2p orbitals, with a localized hole O 2– /O – mechanism prevailing elsewhere 23 .…”

Section: Introductionmentioning

confidence: 99%

“…For example, Li-rich surface and near-surface regions often exhibit oxygen evolution and reconstruction during delithiation 24–28 , yet surface-sensitive X-ray photoelectron spectroscopy (XPS) is often used to infer the nature of bulk anion redox 5,9,11,29 . Likewise, correlations between spatially averaged X-ray absorption spectra (XAS) are often used to assess hybridization 6,7,10,12–14,30–32 , which assumes that redox chemistry occurs uniformly. The relatively subtle evolution in the spectra during anion redox, combined with their sensitivity to probing depth (a few nm for quantitative XPS and total-electron-yield (TEY) XAS) and detection mode (e.g., self-absorption distortions in fluorescence-yield (FY) XAS) has contributed to the conflicting proposed mechanisms for oxygen redox in certain materials and, consequently, explanations for its role in determining capacity and electrochemical stability 15,21,22,32,33 .…”

Section: Introductionmentioning

confidence: 99%

Coupling between oxygen redox and cation migration explains unusual electrochemistry in lithium-rich layered oxides

et al. 2017

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Lithium-rich layered transition metal oxide positive electrodes offer access to anion redox at high potentials, thereby promising high energy densities for lithium-ion batteries. However, anion redox is also associated with several unfavorable electrochemical properties, such as open-circuit voltage hysteresis. Here we reveal that in Li1.17–xNi0.21Co0.08Mn0.54O2, these properties arise from a strong coupling between anion redox and cation migration. We combine various X-ray spectroscopic, microscopic, and structural probes to show that partially reversible transition metal migration decreases the potential of the bulk oxygen redox couple by > 1 V, leading to a reordering in the anionic and cationic redox potentials during cycling. First principles calculations show that this is due to the drastic change in the local oxygen coordination environments associated with the transition metal migration. We propose that this mechanism is involved in stabilizing the oxygen redox couple, which we observe spectroscopically to persist for 500 charge/discharge cycles.

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Direct observation of reversible oxygen anion redox reaction in Li-rich manganese oxide, Li₂MnO₃, studied by soft X-ray absorption spectroscopy

Abstract: We investigated the reversible charge compensation mechanism of an Li2MnO3 electrode using soft XAS analysis. We concluded that both the Mn and O ions participated in the charge compensation reactions during the reversible redox cycles.

Cited by 188 publications

References 79 publications

Depth-Dependent Redox Behavior of LiNi_0.6Mn_0.2Co_0.2O₂

Depth-Dependent Redox Behavior of LiNi_0.6Mn_0.2Co_0.2O₂

Review—Recent Advances and Remaining Challenges for Lithium Ion Battery Cathodes

Coupling between oxygen redox and cation migration explains unusual electrochemistry in lithium-rich layered oxides

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Direct observation of reversible oxygen anion redox reaction in Li-rich manganese oxide, Li2MnO3, studied by soft X-ray absorption spectroscopy

Abstract: We investigated the reversible charge compensation mechanism of an Li2MnO3 electrode using soft XAS analysis. We concluded that both the Mn and O ions participated in the charge compensation reactions during the reversible redox cycles.

Cited by 188 publications

References 79 publications

Depth-Dependent Redox Behavior of LiNi0.6Mn0.2Co0.2O2

Depth-Dependent Redox Behavior of LiNi0.6Mn0.2Co0.2O2

Review—Recent Advances and Remaining Challenges for Lithium Ion Battery Cathodes

Coupling between oxygen redox and cation migration explains unusual electrochemistry in lithium-rich layered oxides

Contact Info

Product

Resources

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Direct observation of reversible oxygen anion redox reaction in Li-rich manganese oxide, Li₂MnO₃, studied by soft X-ray absorption spectroscopy

Depth-Dependent Redox Behavior of LiNi_0.6Mn_0.2Co_0.2O₂

Depth-Dependent Redox Behavior of LiNi_0.6Mn_0.2Co_0.2O₂