Direct observation of layered-to-spinel phase transformation in Li<sub>2</sub>MnO<sub>3</sub> and the spinel structure stabilised after the activation process

Shimoda, Kei; Oishi, Masatsugu; Matsunaga, Toshiyuki; Murakami, Miwa; Yamanaka, Kazushi; Arai, Hajime; Ukyo, Yoshio; Uchimoto, Yoshiharu; Ohta, Toshiaki; Matsubara, Eiichiro; Ogumi, Zempachi

doi:10.1039/c6ta11151c

Cited by 78 publications

(76 citation statements)

References 58 publications

(79 reference statements)

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“…Among these drawbacks, voltage decay phenomenon, which is not observed in other layered oxides, is an unique and delicate issue for researchers. Previous studies with cation-focused analysis interpreted this phenomenon as ‘layered-to-spinel’ phase transition and suggested ‘surface doping’ as a solution for the voltage decay 12–25 . Furthermore, 4 d and 5 d transition-metal (TM) oxides having a pure C2/m monoclinic structure, such as Li 2 Ru 1− y M y O 3 (M = Ti, Mn, Sn), were introduced to reveal origin of the voltage decay 26 .…”

Section: Introductionmentioning

confidence: 95%

Understanding voltage decay in lithium-excess layered cathode materials through oxygen-centred structural arrangement

et al. 2018

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Lithium-excess 3d-transition-metal layered oxides (Li1+xNiyCozMn1−x−y−zO2, >250 mAh g−1) suffer from severe voltage decay upon cycling, which decreases energy density and hinders further research and development. Nevertheless, the lack of understanding on chemical and structural uniqueness of the material prevents the interpretation of internal degradation chemistry. Here, we discover a fundamental reason of the voltage decay phenomenon by comparing ordered and cation-disordered materials with a combination of X-ray absorption spectroscopy and transmission electron microscopy studies. The cation arrangement determines the transition metal-oxygen covalency and structural reversibility related to voltage decay. The identification of structural arrangement with de-lithiated oxygen-centred octahedron and interactions between octahedrons affecting the oxygen stability and transition metal mobility of layered oxide provides the insight into the degradation chemistry of cathode materials and a way to develop high-energy density electrodes.

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Section: Introductionmentioning

confidence: 95%

Understanding voltage decay in lithium-excess layered cathode materials through oxygen-centred structural arrangement

et al. 2018

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“…We used HAADF‐STEM to directly observe and verify the above‐mentioned spectroscopic results regarding bulk and surface crystalline structures ( Figure ). According to some previous reports, [ 21,22 ] layered‐to‐spinel phase transitions are generally known to occur in LMR lattice systems, depending on the degree of oxygen deficiency (layered, Li x TMO 2 → I4 1 , Li x TM 1.33 O 2 → spinel, Li x TM 3 O 4 ). In their pristine states, L‐LMR and D‐LMR show similar crystalline structures to those of layered bulk phases with very thin I4 1 phases on their surfaces.…”

Section: Figurementioning

confidence: 99%

Excess‐Li Localization Triggers Chemical Irreversibility in Li‐ and Mn‐Rich Layered Oxides

et al. 2020

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Li‐ and Mn‐rich layered oxides (LMRs) have emerged as practically feasible cathode materials for high‐energy‐density Li‐ion batteries due to their extra anionic redox behavior and market competitiveness. However, sluggish kinetics regions (<3.5 V vs Li/Li+) associated with anionic redox chemistry engender LMRs with chemical irreversibility (first‐cycle irreversibility, poor rate properties, voltage fading), which limits their practical use. Herein, the structural origin of this chemical irreversibility is revealed through a comparative study involving Li1.15Mn0.51Co0.17Ni0.17O2 with relatively localized and delocalized excess‐Li in its lattice system. Operando fine‐interval X‐ray absorption spectroscopy is used to simultaneously observe the interplay between transition‐metal–oxygen (TM‐O) redox chemistry and TM migration behavior in real time. Density functional theory calculations show that excess‐Li localization in the LMR structure attenuates TM‐O covalency and stability, leading to overall chemical irreversibility. Hence, the delocalized excess‐Li system is proposed as an alternative design for practically feasible LMR cathodes with restrained TM migration and sustainable O‐redox chemistry.

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“…In the past two decades, LiCoO 2 has dominated the LIB market as the predominant commercial cathode material. [14,19,20] Nevertheless, the initiation mechanisms for oxygen evolution and oxide phase transitions have not been well understood, yet. [6,9,10,15] At the surface of layered oxides, carbonaceous molecular species and fluorine-based Li salts in the electrolyte can react with the cathode powder surface, which can induce undesirable interface phase formation or accelerate the oxide phase transition at surface.…”

Section: Introductionmentioning

confidence: 99%

Kinetic Stability of Bulk LiNiO₂ and Surface Degradation by Oxygen Evolution in LiNiO₂‐Based Cathode Materials

Kong

Liang

Wang

et al. 2018

Advanced Energy Materials

194

187

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Capacity degradation by phase changes and oxygen evolution has been the largest obstacle for the ultimate commercialization of high‐capacity LiNiO2‐based cathode materials. The ultimate thermodynamic and kinetic reasons of these limitations are not yet systematically studied, and the fundamental mechanisms are still poorly understood. In this work, both phenomena are studied by density functional theory simulations and validation experiments. It is found that during delithiation of LiNiO2, decreased oxygen reduction induces a strong thermodynamic driving force for oxygen evolution in bulk. However, oxygen evolution is kinetically prohibited in the bulk phase due to a large oxygen migration kinetic barrier (2.4 eV). In contrast, surface regions provide a larger space for oxygen migration leading to facile oxygen evolution. These theoretical results are validated by experimental studies, and the kinetic stability of bulk LiNiO2 is clearly confirmed. Based on these findings, a rational design strategy for protective surface coating is proposed.

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Direct observation of layered-to-spinel phase transformation in Li₂MnO₃ and the spinel structure stabilised after the activation process

Abstract: The layered-to-spinel phase transformation in Li2MnO3 during the initial charge process occurs by a two-phase reaction process within a single particle.

Cited by 78 publications

References 58 publications

Understanding voltage decay in lithium-excess layered cathode materials through oxygen-centred structural arrangement

Understanding voltage decay in lithium-excess layered cathode materials through oxygen-centred structural arrangement

Excess‐Li Localization Triggers Chemical Irreversibility in Li‐ and Mn‐Rich Layered Oxides

Kinetic Stability of Bulk LiNiO₂ and Surface Degradation by Oxygen Evolution in LiNiO₂‐Based Cathode Materials

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Direct observation of layered-to-spinel phase transformation in Li2MnO3 and the spinel structure stabilised after the activation process

Abstract: The layered-to-spinel phase transformation in Li2MnO3 during the initial charge process occurs by a two-phase reaction process within a single particle.

Cited by 78 publications

References 58 publications

Understanding voltage decay in lithium-excess layered cathode materials through oxygen-centred structural arrangement

Understanding voltage decay in lithium-excess layered cathode materials through oxygen-centred structural arrangement

Excess‐Li Localization Triggers Chemical Irreversibility in Li‐ and Mn‐Rich Layered Oxides

Kinetic Stability of Bulk LiNiO2 and Surface Degradation by Oxygen Evolution in LiNiO2‐Based Cathode Materials

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Direct observation of layered-to-spinel phase transformation in Li₂MnO₃ and the spinel structure stabilised after the activation process

Kinetic Stability of Bulk LiNiO₂ and Surface Degradation by Oxygen Evolution in LiNiO₂‐Based Cathode Materials