Dataset Information

Surface chemical heterogeneous distribution in over-lithiated Li_1+xCoO₂ electrodes.

ABSTRACT: 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.

SUBMITTER: Sun G

PROVIDER: S-EPMC9617898 | biostudies-literature | 2022 Oct

REPOSITORIES: biostudies-literature

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

Sun Gang G Yu Fu-Da FD Lu Mi M Zhu Qingjun Q Jiang Yunshan Y Mao Yongzhi Y McLeod John A JA Maley Jason J Wang Jian J Zhou Jigang J Wang Zhenbo Z

Nature communications 20221029 1

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 t ...[more]

PMID: 36309496

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Project description:Li3(Li,Ti5)O12 (LTO) is a stable and safe negative electrode material for Li-ion batteries, and its Na substitute Na3(Li,Ti5)O12 (NTO) is a counterpart for the Na-ion battery. In LTO and NTO, a sixth of the Ti-sites (16d) in the spinel framework are replaced by Li: Li mixing in the 16d sites. For conducting theoretical studies on these materials, e.g., density functional theory (DFT) calculations, one has to confront the astronomical number of combinations of Li distribution in 16d sites to construct model structures, of which the size is sufficiently large to represent the bulk material properties. Only a limited number of models, whose structures are a priori specified by "researcher intuition," have been examined thus far, and how Li-mixing determines the material stability has yet to be clarified. Herein, we statistically analyzed the DFT total energy of more than 2 × 104 model structures of LTO and NTO that were extracted from the 4 × 108 possible combinations of Li-mixing with computer-aided symmetry analysis and an automated model building system. The local energy analysis further revealed the local stability/instability of each structure. We found that LTO and NTO stability can be well explained by the apparent coulombic repulsion between Li+ in the 16d sites as if they were placed in a matrix of dielectric constants of 1.92 and 2.04 for LTO and NTO, respectively. That is, the sum of the inverse of the Li-Li distance (S) serves as a good descriptor in predicting the stability of these materials. The extent to which the O2- anions are displaced from the Wyckoff position (32e) is considered to differentiate NTO from LTO. However, the electronic structure of NTO does not significantly differ from that of LTO unless S exceeds a certain limit. These results suggest that the spinel framework tolerates the structural instability and variety to some extent, which is important in constructing a spinel structure with the mixing of other cations, thereby replacing the rare element Li.

Dataset Information

Surface chemical heterogeneous distribution in over-lithiated Li_1+xCoO₂ electrodes.

Publications

Surface chemical heterogeneous distribution in over-lithiated Li<sub>1+x</sub>CoO<sub>2</sub> electrodes.

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