Lithium Ion Secondary Battery
Analysis of the Separator Before and After Life Test

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Summary

The surface and cross section of the separator for the lithium ion secondary battery whose performance had declined due to life test were observed with the scanning electron microscope (SEM) and subjected to EDS element analysis. A comparison of the separator between before and after life test makes it possible to determine the cause of a decline in the performance of the lithium ion secondary battery.
Equipment: SEM(scanning electron microscope); analysis function: EDS(Energy Dispersive Spectroscopy)

Morphological observation and element analysis of surface of the separator of the negative electrode material

(SEM) Before life test After life test

Before life test, the porous structure of the separator was observed. After life test, however, deposits were observed on the surface of the separator.

(EDS) Before life test After life test

A comparison of the results of the element analysis conducted before and after life test revealed that Co and P were detected from the separator surface after life test. These are presumed to be an elute from the positive electrode and the decomposition products of the electrolytic solution.

Morphological observation and element analysis of a cross section of the negative-electrode-side separator after life test

Results of EDS element analysis of the area having changed in quality in the vicinity of the negative-electrode-side separator surface

  • Deposits of solid matter were observed near the surface of the negative electrode side.
  • O, Co, P and F were detected from EDS element analysis of the deposits.
  • From these results, it was presumed that the P and F which were assumed to have derived from an elute of the positive electrode Co and the electrolytic solution clogged the separator on the negative electrode side, thus causing a decline in the performance of the battery.

Search Number 4016

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