First-cycle voltage hysteresis in Li-rich 3d cathodes associated with molecular O2 trapped in the bulk

House, Robert A.; Rees, Gregory J.; Pérez-Osorio, Miguel A.; Marie, John‐Joseph; Boivin, Édouard; Robertson, Alex W.; Nag, Abhishek; García-Fernández, Mirian; Zhou, Kejin; Bruce, Peter G.

doi:10.1038/s41560-020-00697-2

Cited by 382 publications

(562 citation statements)

References 49 publications

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“…Both phenomena have been recently linked with the irreversible loss of highly ordered honeycomb superstructures belonging to the layered cathodes. In Li 1.2 Ni 0.13 Mn 0.54 Co 0.13 O 2 , 26 all oxide ions in the honeycomb lattice will be coordinated by at least two transition metal (TM) ions (O(Li 4 TM 2 )) which, during charge, are oxidized to O n– at a high potential of 4.6 V. However, this honeycomb arrangement of O n– is highly unstable. In-plane TM migration to form vacancy clusters occurs, causing some O to become coordinated by fewer than two TM ions which then dimerize to form stable O 2 molecules.…”

Section: Results and Discussionmentioning

confidence: 99%

Redox Chemistry and the Role of Trapped Molecular O₂ in Li-Rich Disordered Rocksalt Oxyfluoride Cathodes

et al. 2020

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In the search for high energy density cathodes for next-generation lithium-ion batteries, the disordered rocksalt oxyfluorides are receiving significant attention due to their high capacity and lower voltage hysteresis compared with ordered Li-rich layered compounds. However, a deep understanding of these phenomena and their redox chemistry remains incomplete. Using the archetypal oxyfluoride, Li 2 MnO 2 F, we show that the oxygen redox process in such materials involves the formation of molecular O 2 trapped in the bulk structure of the charged cathode, which is reduced on discharge. The molecular O 2 is trapped rigidly within vacancy clusters and exhibits minimal mobility unlike free gaseous O 2 , making it more characteristic of a solid-like environment. The Mn redox process occurs between octahedral Mn 3+ and Mn 4+ with no evidence of tetrahedral Mn 5+ or Mn 7+ . We furthermore derive the relationship between local coordination environment and redox potential; this gives rise to the observed overlap in Mn and O redox couples and reveals that the onset potential of oxide ion oxidation is determined by the degree of ionicity around oxygen, which extends models based on linear Li–O–Li configurations. This study advances our fundamental understanding of redox mechanisms in disordered rocksalt oxyfluorides, highlighting their promise as high capacity cathodes.

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Section: Results and Discussionmentioning

confidence: 99%

Redox Chemistry and the Role of Trapped Molecular O₂ in Li-Rich Disordered Rocksalt Oxyfluoride Cathodes

et al. 2020

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“…As recently demonstrated using O2-type layered oxides 23,50 , the suppression of cation migration is essential to mitigate the degradation of oxygen-redox cathodes. However, although cation migration should accelerate O-O dimer formation 16,20,51 , the suppression of cation migration alone is not enough to explain nonpolarizing oxygen-redox reaction. For example, P2-and P3-Na 2/3 Mg x Mn 1-x O 2 deliver large extra oxygen-redox capacities greater than 100 mAh/g with large polarization, where O-O dimers could be formed without cation migration 15,52 .…”

Section: Discussionmentioning

confidence: 99%

Nonpolarizing oxygen-redox capacity without O-O dimerization in Na2Mn3O7

et al. 2021

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Reversibility of an electrode reaction is important for energy-efficient rechargeable batteries with a long battery life. Additional oxygen-redox reactions have become an intensive area of research to achieve a larger specific capacity of the positive electrode materials. However, most oxygen-redox electrodes exhibit a large voltage hysteresis >0.5 V upon charge/discharge, and hence possess unacceptably poor energy efficiency. The hysteresis is thought to originate from the formation of peroxide-like O22− dimers during the oxygen-redox reaction. Therefore, avoiding O-O dimer formation is an essential challenge to overcome. Here, we focus on Na2-xMn3O7, which we recently identified to exhibit a large reversible oxygen-redox capacity with an extremely small polarization of 0.04 V. Using spectroscopic and magnetic measurements, the existence of stable O−• was identified in Na2-xMn3O7. Computations reveal that O−• is thermodynamically favorable over the peroxide-like O22− dimer as a result of hole stabilization through a (σ + π) multiorbital Mn-O bond.

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“…[ 3 ] However, voltage‐related problems (i.e., hysteresis and fading), which offset the high specific energy, have been stigmatized as major obstacles to their practical use; hence, studies on LMRs have been vigorously performed in recent years, unveiling their origins and solutions. [ 4,5 ]…”

Section: Introductionmentioning

confidence: 99%

Lattice‐Oxygen‐Stabilized Li‐ and Mn‐Rich Cathodes with Sub‐Micrometer Particles by Modifying the Excess‐Li Distribution

et al. 2021

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In recent years, Li‐ and Mn‐rich layered oxides (LMRs) have been vigorously explored as promising cathodes for next‐generation, Li‐ion batteries due to their high specific energy. Nevertheless, their actual implementation is still far from a reality since the trade‐off relationship between the particle size and chemical reversibility prevents LMRs from achieving a satisfactory, industrial energy density. To solve this material dilemma, herein, a novel morphological and structural design is introduced to Li1.11Mn0.49Ni0.29Co0.11O2, reporting a sub‐micrometer‐level LMR with a relatively delocalized, excess‐Li system. This system exhibits an ultrahigh energy density of 2880 Wh L−1 and a long‐lasting cycle retention of 83.1% after the 100th cycle for 45 °C full‐cell cycling, despite its practical electrode conditions. This outstanding electrochemical performance is a result of greater lattice‐oxygen stability in the delocalized excess‐Li system because of the low amount of highly oxidized oxygen ions. Geometric dispersion of the labile oxygen ions effectively suppresses oxygen evolution from the lattice when delithiated, eradicating the rapid energy degradation in a practical cell system.

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First-cycle voltage hysteresis in Li-rich 3d cathodes associated with molecular O2 trapped in the bulk

Cited by 382 publications

References 49 publications

Redox Chemistry and the Role of Trapped Molecular O₂ in Li-Rich Disordered Rocksalt Oxyfluoride Cathodes

Redox Chemistry and the Role of Trapped Molecular O₂ in Li-Rich Disordered Rocksalt Oxyfluoride Cathodes

Nonpolarizing oxygen-redox capacity without O-O dimerization in Na2Mn3O7

Lattice‐Oxygen‐Stabilized Li‐ and Mn‐Rich Cathodes with Sub‐Micrometer Particles by Modifying the Excess‐Li Distribution

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First-cycle voltage hysteresis in Li-rich 3d cathodes associated with molecular O2 trapped in the bulk

Cited by 382 publications

References 49 publications

Redox Chemistry and the Role of Trapped Molecular O2 in Li-Rich Disordered Rocksalt Oxyfluoride Cathodes

Redox Chemistry and the Role of Trapped Molecular O2 in Li-Rich Disordered Rocksalt Oxyfluoride Cathodes

Nonpolarizing oxygen-redox capacity without O-O dimerization in Na2Mn3O7

Lattice‐Oxygen‐Stabilized Li‐ and Mn‐Rich Cathodes with Sub‐Micrometer Particles by Modifying the Excess‐Li Distribution

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Product

Resources

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Redox Chemistry and the Role of Trapped Molecular O₂ in Li-Rich Disordered Rocksalt Oxyfluoride Cathodes

Redox Chemistry and the Role of Trapped Molecular O₂ in Li-Rich Disordered Rocksalt Oxyfluoride Cathodes