Study on the tensile properties of PET-Cu composite current collectors for lithium-ion batteries

doi:10.19799/j.cnki.2095-4239.2024.0056

Abstract

Abstract:

With the advancement of lithium-ion battery technology, composite current collectors have garnered significant interest due to their role in enhancing battery energy density and safety. The mechanical performance of composite current collectors is crucial for ensuring their reliable operation. This study systematically investigates the mechanical properties of commercial polyethylene terephthalate-copper (PET-Cu) composite current collectors. The surface morphology, microstructure, and tensile fracture behavior of the PET-Cu composite were characterized using scanning electron microscopy, laser confocal microscopy, and X-ray diffraction. Stress distribution in dog-bone-shaped and long-strip-shaped samples during tensile testing was analyzed and compared through finite element simulation. The effects of sampling direction, strain rate, and specimen geometry on the tensile properties were assessed using tensile tests supported by digital image correlation technology. The dog-bone-shaped samples were found to be more effective in evaluating mechanical properties, as their transition arcs alleviate stress concentration. The mechanical properties along the machined direction proved superior to those along the transverse directions, attributed to the orientation structures of the matrix. Higher loading strain rates enhanced the overall mechanical properties of the current collector. While the geometric size of the samples had minimal impact on strength, it significantly affected elongation at fracture. The primary deformation mechanism during tensile testing was identified as dislocation slip, with surface defects such as holes acting as favorable sites for crack initiation. Considering these factors is essential when testing the tensile properties of PET-Cu composite current collectors. This research provides a theoretical foundation and reliability demonstration for the practical application of composite collectors and offers a reference for developing relevant testing standards. This study's findings are poised to advance the development of lithium-ion batteries with improved energy density and safety.

Key words: composite current collector, tensile properties, finite element simulation, digital image correlation technique, strain rate sensitivity, geometric size effect

CLC Number:

TM 912

Feng XIAO, Fulai CHENG, Xuemei LUO, Guangping ZHANG, Bin ZHANG. Study on the tensile properties of PET-Cu composite current collectors for lithium-ion batteries[J]. Energy Storage Science and Technology, 2024, 13(6): 1755-1766.

Figures/Tables 13

Table 1

Table 2

The sample specification and experimental parameters of PET-Cu composite current collectors tensile test"

影响因素	试样形状	取样方向	应变速率/ $s - 1$	标距长度 /mm	标距宽度 /mm
试样形状	狗骨状	纵向	$1 × 10 - 3$	50	10
试样形状	矩形	纵向	$1 × 10 - 3$	50	10

取样方向	狗骨状	纵向	$1 × 10 - 3$	50	10
取样方向	狗骨状	横向	$1 × 10 - 3$	50	10

应变速率	狗骨状	纵向	$5 × 10 - 4$	50	10
	狗骨状	纵向	$1 × 10 - 3$	50	10
	狗骨状	纵向	$5 × 10 - 3$	50	10

标距宽度	狗骨状	纵向	$1 × 10 - 3$	50	5
	狗骨状	纵向	$1 × 10 - 3$	50	10
	狗骨状	纵向	$1 × 10 - 3$	50	15
	狗骨状	纵向	$1 × 10 - 3$	50	25

标距长度	狗骨状	纵向	$1 × 10 - 3$	25	10
	狗骨状	纵向	$1 × 10 - 3$	50	10
	狗骨状	纵向	$1 × 10 - 3$	75	10
	狗骨状	纵向	$1 × 10 - 3$	100	10

Table 2

Fig. 1

Fig. 2

Fig. 3

Fig. 4

Fig. 5

Table 3

Tensile properties of PET-Cu composite current collectors at different strain rates"

应变速率	屈服强度/MPa	强度极限/MPa	断裂伸长率/%
$5 × 10 - 4 s - 1$	$126.1 ± 2.0$	$192.7 ± 1.8$	$10.9 ± 0.8$
$1 × 10 - 3 s - 1$	$131.8 ± 2.1$	$201.5 ± 1.3$	$12.5 ± 0.2$
$5 × 10 - 3 s - 1$	$137.1 ± 1.7$	$221.0 ± 5.2$	$13.9 ± 0.6$

Table 3

Fig. 6

Fig. 7

Fig. 8

Fig. 9

Table 4

Tensile properties of PET-Cu composite current collector, PET film and Cu foil current collector"

材料	屈服强度/MPa	强度极限/MPa	断裂伸长率/%
PET-Cu复合集流体	$131.8 ± 2.1$	$201.5 ± 1.3$	$12.5 ± 0.2$
PET基膜	$105.0 ± 0.2$	$288.9 ± 11.8$	$170.5 ± 11.1$
Cu箔集流体	$272.6 ± 2.2$	$301.9 ± 0.4$	$7.8 ± 0.3$

Table 4

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标准号	标准名称	试样形状	标距长度 /mm	标距宽度 /mm	拉伸速率^①/(mm/min)
GB/T 1040.3—2006	塑料拉伸性能的测定第3部分：薄膜和薄片的试验条件	Ⅰ 狗骨状 Ⅱ 矩形	Ⅰ 50 Ⅱ 50	Ⅰ 10 Ⅱ 10~25	50
GB/T 41791—2022	塑料制品薄膜和薄片无取向聚对苯二甲酸乙二醇酯(PET)片材	Ⅰ 狗骨状 Ⅱ 矩形	Ⅰ 50 Ⅱ 50	Ⅰ 10 Ⅱ 10~25	50
SJ/T11483—2014	锂离子电池用电解铜箔	矩形	50	15	50
ASTM D638—2014	Standard Test Method for Tensile Properties of Plastics	狗骨状	50	13	5/50/500
ASTM E345—2016	Standard Test Methods of Tension Testing of Metallic Foil	Ⅰ 狗骨状 Ⅱ 矩形	Ⅰ 50 Ⅱ 50	Ⅰ 12.5 Ⅱ 12.5	0.002~0.01
ASTM D882—2018	Standard Test Method for Tensile Properties of Thin Plastic Sheeting	矩形	≥50	5~25.4	12.5/50/500
ISO 527-2：2012	Plastics-Determination of tensile properties-Part 2:Test conditions for moulding and extrusion plastics	狗骨状	50/75	10	50