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. 2024 Sep 17;16(18):2627.
doi: 10.3390/polym16182627.

Effect of a Polypropylene Separator with a Thin Electrospun Ceramic/Polymer Coating on the Thermal and Electrochemical Properties of Lithium-Ion Batteries

Yeongsu Hwang  1 , Minjae Kim  1
Affiliations

Effect of a Polypropylene Separator with a Thin Electrospun Ceramic/Polymer Coating on the Thermal and Electrochemical Properties of Lithium-Ion Batteries

Yeongsu Hwang et al. Polymers (Basel). .

Abstract

Lithium-ion batteries (LIBs) are well known for their energy efficiency and environmental benefits. However, increasing their energy density compromises their safety. This study introduces a novel ceramic-coated separator to enhance the performance and safety of LIBs. Electrospinning was used to apply a coating consisting of an alumina (Al2O3) ceramic and polyacrylic acid (PAA) binder to a polypropylene (PP) separator to significantly improve the mechanical properties of the PP separator and, ultimately, the electrochemical properties of the battery cell. Tests with 2032-coin cells showed that the efficiency of cells containing separators coated with 0.5 g PAA/Al2O3 was approximately 10.2% higher at high current rates (C-rates) compared to cells with the bare PP separator. Open circuit voltage (OCV) tests revealed superior thermal safety, with bare PP separators maintaining stability for 453 s, whereas the cells equipped with PP separators coated with 4 g PAA/Al2O3 remained stable for 937 s. The elongation increased from 88.3% (bare PP separator) to 129.1% (PP separator coated with 4 g PAA/Al2O3), and thermal shrinkage decreased from 58.2% to 34.9%. These findings suggest that ceramic/PAA-coated separators significantly contribute to enhancing the thermal safety and capacity retention of high-energy-density LIBs.

Keywords: ceramic coated separator; electrospinning; ionic conductivity; lithium-ion battery safety; polymer binder; thermal stability; wettability.

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Conflict of interest statement

The authors declare no conflicts of interest.

Figures

Figure 1
Figure 1
Schematic illustration of the fabrication of the ceramic/polymer coated separator with a simple electrospinning process.
Figure 2
Figure 2
FE-SEM images of (a) bare PP separator, (b) 0.5g-PAA/Al2O3, (c) 1g-PAA/Al2O3, (d) 2g-PAA/Al2O3, (e) 3g-PAA/Al2O3, and (f) 4g-PAA/Al2O3 ceramic coated separators.
Figure 3
Figure 3
(a) Variation in the OCV of the NCM 811/graphite cells employing the bare PP separator and ceramic/binder-coated separators measured at 150 °C. (b) Tensile strength: stress-elongation curve for bare PP separator and CCSs with different PAA contents. (c) Thermal shrinkage: photographs of the bare PP separator and PAA/Al2O3-coated separators after heat treatment at 150 °C for 0.5 h.
Figure 4
Figure 4
(a) First charge/discharge profiles of graphite half-cells prepared with separators with different compositions. Cycling performance of the coin cells with the PP separator and ceramic/binder separators at (b) 0.5 C and (c) 1 C. The arrow represents Coulomb efficiency.
Figure 5
Figure 5
AC impedance measurements of lithium-ion cells assembled with different separators.
Figure 6
Figure 6
(a) Rate performance of cells with separators coated with xg-PAA/Al2O3 (x = 0, 0.5, 1, 2, 3, and 4) and (b) ionic conductivities of cells with separators coated with xg-PAA/Al2O3 (x = 0, 0.5, 1, 2, 3, and 4) and soaked in liquid electrolyte.
Figure 7
Figure 7
Photographs to demonstrate the wettability and contact angle with the liquid electrolyte (EC:DEC = 1:1 v/v containing 1 M LiPF6 + 5% FEC) of separators coated with xg-PAA/Al2O3 (x = 0, 0.5, 1, 2, 3, and 4).
See this image and copyright information in PMC

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