What is phase separation in the positive electrode of high voltage spinel lithium ion batteries?

Represented by spinel lithium nickel manganese acid of high voltage anode lithium ion batteries have high capacity, low cost, small environmental hazards and safety of strong advantages, such as obtaining battery industry recognition. Think in terms of basic theory, the deep understanding of solid phase separation of electrode to fundamentally solve this material is of great significance to the stability of the intrinsic defects. From a practical point of view, the phase separation in the actual behavior of porous composite electrode and the size effect of nickel and manganese acid lithium, regulation and control of crystal and surface passivation membrane correlation matching is the fundamental research and practical application of combining the ideal method. However, the idea must be advanced characterization methods can achieve.

Canadian light source energy storage group Zhou Ji Gang Dr. Wang and Xiamen, chemical imaging line stand way close associate professor of technology and Harbin industrial university professor Haitao Fang close cooperation, innovative with element and selectivity, chemical and electronic structure sensitivity of transmission X-ray scanning microscopy (STXM) used to study the phase separation behavior in the porous electrode. Researchers for the first time by the work cycle of the complex composite electrode and after long time storage of a variety of the correlation of phase separation phenomenon of nanoscale visualization. After phase separation electrode is not uniformity than predicted. This is not uniformity and spinel size, crystal structure, surface passivation has close correlation.

The study found that for the first time, traditionally thought that only exists in the fast charging and discharging of phase separation is not uniformity can be achieved under the condition of the approximate steady-state response. The findings for further understand important electrode process of phase separation is of great significance. This method can be extended to other electrode system, used to study the reaction mechanism, the attenuation mechanism, etc.

Phase separation imaging is for each pixel element absorption spectra using a single phase spectral decomposition of the fitting. The work is based on principal component analysis (PCA) for each single phase (Ni4 corresponding fully charged facies, Ni3 + + counterpart, Ni2 + reduction phase corresponds to completely restore phase).Using PCA can avoid the human error, introduced external standard spectrum, thus get the phase separation of imaging is more accurate and reliable. Figure c is to use PCA to obtain three kinds of corresponding Ni absorption spectra, the height of the phase separation inhomogeneity in figure b well, it can be seen that the phase separation in the first place in the electrode thickness direction is uneven. Second, the phase separation exists within a single electrode particle. The distribution is different between different electrode particles, and the particle morphology, size, all have influence on phase separation.

The author found that the vast majority of completely restore phase (Ni2 +) exist in the surface of the electrode particles, only a complete electrode Ni2 + phase particles exist, but its spectrum and form different in Ni2 + phase on the surface of the electrode particles. The result indicates the surface of the Ni2 + should be with high voltage anode during the charging and discharging cycle of the generated surface passivation layer. They found through further observation, larger particles can well protect the surface of the electrode passivation electrode particles within the full charge. Again, this separation is not uniformity is achieved under the experimental condition of slow, thus the reaction thermodynamics behavior should be to the intrinsic properties of electrode particles, including surface defects, element segregation, etc. Relevant work published in Chemical Communications.

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