Long-term cycling behavior of Mg-doped LiCoO2 materials investigated with the help of laboratory scale X-ray absorption near-edge spectroscopy

Lahtinen, Katja; Labmayr, Maximillain; Mäkelä, Ville.; Jiang, Hua; Lahtinen, Jouko; Yao, Lide; Fedorovskaya, Ekaterina O.; Räsänen, Samuli; Huotari, Simo; Kallio, Tanja

doi:10.1016/j.mtener.2022.101040

Cited by 7 publications

(7 citation statements)

References 59 publications

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“…This site may be prone to Co(II) sorption, thereby maintaining the oxidative activity of the MnO 2 layer. Results of this study will help understanding the oxidation of Co(II) to Co(III) in MnO 2 -based batteries and catalysts. − Experimental studies are needed to test the effect of oxygen vacancies , on Co(II) oxidation and to allow consider this effect in DFT modeling.…”

Section: Discussionmentioning

confidence: 99%

Density Functional Theory Modeling of the Oxidation Mechanism of Co(II) by Birnessite

Manceau

Steinmann

2022

ACS Earth Space Chem.

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Phyllomanganates of the birnessite family are the most abundant manganese oxides on Earth and the strongest inorganic oxidants in the environment. Birnessite controls the oxidative scavenging of cobalt in soils, lake and marine sediments, and ferromanganese crusts and nodules, leading to enrichments of the order of one billion times the concentration in solution. However, a detailed mechanistic understanding of the enrichment processes is lacking. Here, we perform density functional theory (DFT) calculations to explore the mechanisms of Co(II) to Co(III) oxidation on the layer edge and surface of birnessite nanoparticles. We show that Co(II) sorption on a layer edge is an unlikely oxidation pathway. In contrast, Co(II) sorbed on a Mn(IV) vacancy site exposed on the layer surface as an octahedral triple-corner sharing (TCS) complex enters the vacancy where it is oxidized to Co(III) by a layer Mn(IV) cation, which is reduced to Mn(III). The stepwise reaction proceeds as follows. The octahedral TCS complex is transformed to a smaller tetrahedral TCS complex, allowing Co(II) to cross the surface oxygen layer and to fill the empty octahedral Mn(IV) site. When in the octahedral vacancy, Co(II) is converted from the high-spin (t2g 5 eg 2 ) to the low-spin (t2g 6 eg 1 ) state and the Co(II) octahedron becomes strongly distorted by the Jahn-Teller effect. Afterward, the electron exchange reaction between Mn(IV) (t2g 3 eg 0 ) and Co(II) (t2g 6 eg 1 ) takes place, resulting in the formation of a regular lowspin Co(III) (t2g 6 eg 0 ) octahedron and a Jahn-Teller distorted high-spin Mn(III) (t2g 3 eg 1 ) octahedron.These findings refine previously proposed mechanisms of Co(II) oxidation by birnessite and fill gaps in our understanding of global Co sequestration in natural systems.

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Section: Discussionmentioning

confidence: 99%

Density Functional Theory Modeling of the Oxidation Mechanism of Co(II) by Birnessite

Manceau

Steinmann

2022

ACS Earth Space Chem.

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“…On the other hand, over-discharging LiMn 2 O 4 was shown to significantly degrade performance, as the M 3 O 4 spinel structure does not easily accommodate excess metal ions 22 . In particular, the battery performance of Li- and Mg-doped LiCoO 2 was shown to be resilient to over-discharge compared to native LiCoO 2 23 , however the location of the excess Li in LiCoO 2 was not determined. These findings make it evident that detailed probes of electrode local structures are needed to elucidate the process of over-discharge.…”

Section: Introductionmentioning

confidence: 99%

Surface chemical heterogeneous distribution in over-lithiated Li1+xCoO2 electrodes

Sun

et al. 2022

Nat Commun

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In commercial Li-ion batteries, the internal short circuits or over-lithiation often cause structural transformation in electrodes and may lead to safety risks. Herein, we investigate the over-discharged mechanism of LiCoO2/graphite pouch cells, especially spatially resolving the morphological, surface phase, and local electronic structure of LiCoO2 electrode. With synchrotron-based X-ray techniques and Raman mapping, together with spectroscopy simulations, we demonstrate that over-lithiation reaction is a surface effect, accompanied by Co reduction and surface structure transformation to Li2CoO2/Co3O4/CoO/Li2O-like phases. This surface chemical distribution variation is relevant to the depth and exposed crystalline planes of LiCoO2 particles, and the distribution of binder/conductive additives. Theoretical calculations confirm that Li2CoO2-phase has lower electronic/ionic conductivity than LiCoO2-phase, further revealing the critical effect of distribution of conductive additives on the surface chemical heterogeneity evolution. Our findings on such surface phenomena are non-trivial and highlight the capability of synchrotron-based X-ray techniques for studying the spatial chemical phase heterogeneity.

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“…However, low Zr solubility and small size of (Co, Zr)O x inclusions were observed in the crystals . Besides, Mg doping at Co 3+ sites in LiCoO 2 polycrystalline materials has shown several degrees of success in achieving high capacity and long cycle life at high operating voltage. ,,− Previous studies showed that the Mg-doped LiCoO 2 cathode material offered high capacity at cycling above 4.5 V and exhibited less capacity fading in the long-cycle performance compared to the pure LiCoO 2 polycrystalline cathodes. − These results may have happened due to the prevention of structural collapse by Mg doping at the cobalt sites. It has also been reported that Mg doping enhanced the electrical conductivity of polycrystalline LiCoO 2 by generating holes due to the partial oxidation of Co 3+ ions to Co 4+ to compensate for charge imbalance. ,, Moreover, during the intercalation and deintercalation process, Mg-doped LiCoO 2 retains its single phase compared to other dopants. , However, to date, all of the reported articles are based on polycrystalline Mg-doped cathode materials, so the actual effect of the Mg dopant into LiCoO 2 is hindered owing to the presence of defects in the samples.…”

Section: Introductionmentioning

confidence: 99%

TSFZ Growth and Anisotropic Ionic Conductivity of Mg-Doped LiCoO₂ Single Crystals

Khandaker

Maruyama

Nagao

et al. 2023

Crystal Growth & Design

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We have successfully grown LiCo1–x Mg x O2 (x = 0.01 ∼ 0.04) single crystals using the traveling solvent floating zone (TSFZ) technique for the first time. Inclusion-free single crystals were obtained from 1.0 atom % Mg-doped feeds, whereas (Co, Mg)O x inclusions segregated in the crystals were grown using feeds more than 2.0–4.0 atom % Mg. The Mg concentration of the LiCoO2 phase in the crystal grown with 1.0 atom % Mg-doped feed was determined to be 0.87 ± 0.02 atom % Mg, which suggests that the distribution coefficient of Mg into LiCoO2 is slightly lower than unity. However, the Mg concentration in the LiCoO2 phase was saturated toward about 2.1 atom % due to the solubility limit of Mg into LiCoO2, even though the Mg concentration in feeds increased up to 4.0 atom % Mg. The room temperature ionic conductivities of 1.0 atom % Mg-doped LiCoO2 single crystals along [100] and [001] were 7.2 × 10–5 and 1.1 × 10–8 S·cm–1, respectively, indicating significantly high anisotropy of about 6545. The ionic conductivity along [100] is about 18 times higher than that of undoped LiCoO2 single crystals, whereas the ionic conductivity along [001] is slightly lower than that of undoped LiCoO2 crystals. Mg doping into LiCoO2 is significantly effective in the enhancement of ionic conductivity along [100] rather than along [001]. Thus, high ionic conductivity and proper orientation of crystallographic planes may assist in increasing capacity as well as upper cutoff voltage in the next-generation solid-state Li-ion batteries.

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Long-term cycling behavior of Mg-doped LiCoO2 materials investigated with the help of laboratory scale X-ray absorption near-edge spectroscopy

Cited by 7 publications

References 59 publications

Density Functional Theory Modeling of the Oxidation Mechanism of Co(II) by Birnessite

Density Functional Theory Modeling of the Oxidation Mechanism of Co(II) by Birnessite

Surface chemical heterogeneous distribution in over-lithiated Li1+xCoO2 electrodes

TSFZ Growth and Anisotropic Ionic Conductivity of Mg-Doped LiCoO₂ Single Crystals

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Long-term cycling behavior of Mg-doped LiCoO2 materials investigated with the help of laboratory scale X-ray absorption near-edge spectroscopy

Cited by 7 publications

References 59 publications

Density Functional Theory Modeling of the Oxidation Mechanism of Co(II) by Birnessite

Density Functional Theory Modeling of the Oxidation Mechanism of Co(II) by Birnessite

Surface chemical heterogeneous distribution in over-lithiated Li1+xCoO2 electrodes

TSFZ Growth and Anisotropic Ionic Conductivity of Mg-Doped LiCoO2 Single Crystals

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TSFZ Growth and Anisotropic Ionic Conductivity of Mg-Doped LiCoO₂ Single Crystals