Nanochemical imaging reveals phase separation in the positive electrode of high voltage spinel charging lithium battery

Nanochemical imaging reveals phase separation in the positive electrode of high voltage spinel charging lithium battery

High-voltage positive lithium ion batteries represented by lithium spinel nickel manganese acid have the advantages of high capacity, low cost, environmental harm and strong safety, and thus recognition of battery industry. From the perspective of basic theory, in-depth understanding of phase separation in the solid-state electrode has important significance to fundamentally solve the stability defects of the material intrinsicity..

From the perspective of practical analysis, the behavior of the study phase is separated in the actual porous composite electrode, and the size effect of the lithium nickel-manganese acid, the correlation of the crystal surface regulation, and the surface passivation film is used, which is based on the basic research and practical. Ideal for use in combination. However, this idea must be implemented under advanced characterization means.

Dr. Zhou Wei, the Canadian Light Source Storage Group, Dr. Wang Jian, a chemical imaging line station, deputy professor, deputy professor of Xiamen Institute of Technology, and Professor Harbin Institute of Technology, and innovatively will have elements and orbit selectivity, chemical and electronic structures.

Transmission X-ray scanning micro technology (STXM) is used to study the behavior of the phase separation in the porous electrode. The researchers have enabled nanometric visualization by the work through this work..

The electrode after phase separation exhibits unpredictable unevenness. This non-uniform and spine size, crystal surface structure, surface passivation have closely correlation. The study was first discovered that the phase separation unevenness that only existed during rapid charge and discharge can be obtained under approximate steady state.

. This findings have significant significance on further deepening understanding of phase separation..

This method can be extended to other electrode systems for studying reactive mechanism, attenuation mechanism, etc.. Phase separation imaging is a spectral decomposition fitting of each pixel unit using a single phase.

This work is based on PrincipalComponentanAlysis (PCA) to obtain individual single phase (Ni4 + corresponding to full charge phase, Ni3 + correspondence, Ni2 + corresponds to full reduction). Using PCA prevents people introduced by external standard spectrum, thus obtaining phase separation imaging more accurate and reliable. Figure C is the three corresponding Ni absorption spectroscopy obtained using PCA, and the high degree of unevenness of phase separation is well reflected in Fig.

B, it can be seen that this phase separation first is uneven in the electrode thickness direction.. Secondly, this phase separation is present in a single electrode particle, and the distribution between different electrode particles is different, and the morphology of particles, the size is affecting phase separation.

. Most of the complete reduction phase (Ni2 +) is present in the surface of the electrode particles, only one of the integrated electrode particles are Ni2 + phase, but the spectrum is different from the Ni2 + formed in the surface of the electrode particles..

This result indicates that the surface of Ni2 + should be associated with a surface passivation layer generated during charge and discharge cycle with a high voltage positive electrode.. They found that the surface passivation layer of large particle electrodes can be intact fully charged phase inside the electrode particles.

. It is necessary to emphasize that this phase separation unevenness is obtained under slow experimental conditions, and thus the thermodynamic behavior of its reaction should be related to the intrinsic properties of electrode particles, including surface defects, elementary segregation, and the like..

Related Work Posted in ChemicalCommunications. .

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