Probing the roles of polymeric separators in lithium-ion battery capacity fade at elevated temperatures

Jianchao Chen, Yongda Yan, Tao Sun, Yue Qi, Xiaodong Li

Research output: Contribution to journalArticle

  • 10 Citations

Abstract

The high temperature mechanical property of separators is very important for safety of lithium-ion batteries. However, the mechanical integrity of polymeric separators in lithium-ion batteries at elevated temperatures is still not well characterized. In this paper, the temperature dependent micro-scale morphology change of PP (polypropylene)-PE (polyethylene)-PP sandwiched separators (Celgard 2325) was studied by in-situ high temperature surface imaging using an atomic force microscope (AFM) coupled with power spectral density (PSD) analysis and digital image correlation (DIC) technique. Both PSD and DIC analysis results show that the PP phase significantly closes its pores by means of dilation of the nanofibrils surrounding the pores in the transverse direction and shrinkage in the machine direction, when cycled at 90°C, even below the separator's shutdown temperature (∼120°C) and its own melting temperature (165°C). This is presumably due to surface melting effect in nanostructures and should be size dependent-the surface melting temperature may decrease with the diameter of nanofibrils. Therefore, some pore closing might happen even at operating temperatures, it will lead to capacity fade that is undesired for battery performance.

LanguageEnglish (US)
JournalJournal of the Electrochemical Society
Volume161
Issue number9
DOIs
StatePublished - 2014

Profile

separators
Separators
electric batteries
lithium
polypropylene
Polypropylenes
melting
ions
porosity
Power spectral density
Temperature
temperature
Melting point
shutdowns
closing
operating temperature
shrinkage
Plant shutdowns
integrity
Polyethylene

ASJC Scopus subject areas

  • Materials Chemistry
  • Surfaces, Coatings and Films
  • Renewable Energy, Sustainability and the Environment
  • Condensed Matter Physics
  • Electrochemistry
  • Electronic, Optical and Magnetic Materials

Cite this

Probing the roles of polymeric separators in lithium-ion battery capacity fade at elevated temperatures. / Chen, Jianchao; Yan, Yongda; Sun, Tao; Qi, Yue; Li, Xiaodong.

In: Journal of the Electrochemical Society, Vol. 161, No. 9, 2014.

Research output: Contribution to journalArticle

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N2 - The high temperature mechanical property of separators is very important for safety of lithium-ion batteries. However, the mechanical integrity of polymeric separators in lithium-ion batteries at elevated temperatures is still not well characterized. In this paper, the temperature dependent micro-scale morphology change of PP (polypropylene)-PE (polyethylene)-PP sandwiched separators (Celgard 2325) was studied by in-situ high temperature surface imaging using an atomic force microscope (AFM) coupled with power spectral density (PSD) analysis and digital image correlation (DIC) technique. Both PSD and DIC analysis results show that the PP phase significantly closes its pores by means of dilation of the nanofibrils surrounding the pores in the transverse direction and shrinkage in the machine direction, when cycled at 90°C, even below the separator's shutdown temperature (∼120°C) and its own melting temperature (165°C). This is presumably due to surface melting effect in nanostructures and should be size dependent-the surface melting temperature may decrease with the diameter of nanofibrils. Therefore, some pore closing might happen even at operating temperatures, it will lead to capacity fade that is undesired for battery performance.

AB - The high temperature mechanical property of separators is very important for safety of lithium-ion batteries. However, the mechanical integrity of polymeric separators in lithium-ion batteries at elevated temperatures is still not well characterized. In this paper, the temperature dependent micro-scale morphology change of PP (polypropylene)-PE (polyethylene)-PP sandwiched separators (Celgard 2325) was studied by in-situ high temperature surface imaging using an atomic force microscope (AFM) coupled with power spectral density (PSD) analysis and digital image correlation (DIC) technique. Both PSD and DIC analysis results show that the PP phase significantly closes its pores by means of dilation of the nanofibrils surrounding the pores in the transverse direction and shrinkage in the machine direction, when cycled at 90°C, even below the separator's shutdown temperature (∼120°C) and its own melting temperature (165°C). This is presumably due to surface melting effect in nanostructures and should be size dependent-the surface melting temperature may decrease with the diameter of nanofibrils. Therefore, some pore closing might happen even at operating temperatures, it will lead to capacity fade that is undesired for battery performance.

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