Pore formation and evolution mechanism during biaxial stretching of β-iPP used for lithium-ion batteries separator

Ding, Lei; Xu, Ruizhang; Pu, Lian; Yang, Feng; Wu, Tong; Xiang, Ming

doi:10.1016/j.matdes.2019.107880

Cited by 39 publications

(36 citation statements)

References 41 publications

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“…The size and distribution of these cavities determine the porosity and pore size distribution in the finished membrane after the transverse stretching. In our previous studies, we found that at the initial stage of deformation, the inter‐spherulitic deformation occured when the strain rate was low (Figure a), while the intra‐spherulitic deformation was prone to be activated at high strain rate (Figure b) which would lead to the non‐uniform distribution of cavities in the film.…”

Section: Manufacturing Technique Optimization Of Dry Process Separatomentioning

confidence: 92%

“…However, in our previous studies, we found that the β‐α phase transformation is not the primary origin of pore formation in stretching β‐iPP, the micropores are directly initiated from the weak interfaces between β‐lamellae. Furthermore, in the case of “bundle‐like” β‐crystals or β‐hedrites which are the most common β‐crystals (Figure ), the β‐lamellae epitaxially grow on the surface of β‐NA in the form of “flat‐on” and the bond between β‐lamellae in the spherulites is relative weak, resulting in the lamellar separation under tensile loading. Furthermore, the β‐lamellae with different angles to the loading direction have various deformation modes.…”

Section: Manufacturing Technique Optimization Of Dry Process Separatomentioning

confidence: 99%

“…In order to improve the pore size distribution of the separator produced by biaxial stretching β‐iPP, we devoted to preparing the β‐crystals with geometry symmetrical morphology. In our previous studies, we found that the highly effective and selective β‐NAs, such as TMB‐5 and WBG‐II, are soluble in the iPP melt and in the subsequential cooling course will self‐assemble into precursors prior to the occurrence of iPP bulk crystallization. Since the β‐NA precursors act as template for guiding iPP crystallization behavior, their profiles dominate the resultant β‐crystalline morphologies.…”

Section: Manufacturing Technique Optimization Of Dry Process Separatomentioning

confidence: 99%

“…Based on the CN‐ T f phase diagram, we controlled the β‐NA self‐assembly behavior and produced β‐spherulites . In the β‐spherulites, the β‐lamellae formed by means of “edge‐on” around the β‐NA and the bond between the β‐lamellae is strong, which leads to the initiation of inter‐spherulitic deformation at low strains during longitudinal stretching (Figure ) and substantial cavities originate from the boundaries β‐spherulites.…”

Section: Manufacturing Technique Optimization Of Dry Process Separatomentioning

confidence: 99%

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Progresses in Manufacturing Techniques of Lithium‐Ion Battery Separators in China

Wang

Xiang

et al. 2019

Chin. J. Chem.

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The lithium‐ion batteries (LIBs) have been widely used in the world since the first introduction in 1991. The microporous polyolefin separator is the key component to determine the electrical properties and safety of LIBs. In China, the LIBs separators were completely imported and expensive before 2008. We have realized the industrialization of LIBs separators by either dry or wet process successfully. Nowadays, China has become the biggest manufacturing country of LIBs separators in the world and the price is very much reduced. Among the separator processing techniques, the dry process based on biaxial stretching β nucleated polypropylene (β‐iPP) was originated from China and has the lowest manufacturing cost. However, the separator produced by this method has non‐uniform pore size distribution which limits its wider application. In this article, based on the better understanding of original crystal morphology on the pore formation during stretching, we present our recent works to improve the performance of dry process separator through the preparation of β‐spherulites, casting technique optimization, improved annealing treatment and multi‐stages longitudinal stretching. As a result, we produced the dry process separator with much more uniform pore size distribution than that made from the traditional dry process.

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Section: Manufacturing Technique Optimization Of Dry Process Separatomentioning

confidence: 92%

Section: Manufacturing Technique Optimization Of Dry Process Separatomentioning

confidence: 99%

Section: Manufacturing Technique Optimization Of Dry Process Separatomentioning

confidence: 99%

Section: Manufacturing Technique Optimization Of Dry Process Separatomentioning

confidence: 99%

See 2 more Smart Citations

Progresses in Manufacturing Techniques of Lithium‐Ion Battery Separators in China

Wang

Xiang

et al. 2019

Chin. J. Chem.

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“…At present, the most commonly used commercial separators are made from polyolefin due to the low cost. Three classical industrial processes used to produce LIB separators are the dry process with uniaxial stretching, 21,22 the dry process with biaxial stretching 23–25 and the wet process 26,27 . All these processes include an extrusion step to make cast films and employ one or more orientation steps to impart porosity.…”

Section: Introductionmentioning

confidence: 99%

The unusual delamination phenomenon of three kinds of lithium‐ion battery separators

Ding

Zhang

et al. 2020

Polymer International

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An unusual delamination phenomenon on three kinds of lithium‐ion battery separators was investigated in this study, which is closely associated with the compression resistance of the separator. The delamination trends of three kinds of polymer separators were analyzed systematically. Scanning electron microscopy, two‐dimensional wide‐angle X‐ray diffraction, compression and delamination tests show that a separator prepared by the dry process with uniaxial stretching delaminate hardest due to abundant connection or support structure along the thickness direction. However, the multilayer structure stacked along the thickness direction can be seen clearly for separators experiencing biaxial stretching, both for the dry process and wet process. In particular, a separator prepared by the wet process has the poorest connection or support structure along the thickness direction, leading to the strongest delamination trend and the worst compression resistance. Based on this, we control the delamination trend of the separator by adjusting the condensed structure of the precursor film. Besides, the delamination test can quantify the delamination trend of different kinds of separators accurately and further supplement the evaluation criteria of lithium‐ion battery separators, which can help us to better understand and design a separator with optimal microporous structure. © 2020 Society of Industrial Chemistry

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Structural evolution and properties of polyamide‐6/poly(ether block amide) films during the simultaneous biaxial stretching

Lin

Fan

et al. 2022

J of Applied Polymer Sci

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The purpose of this study was to investigate the structural evolution and properties of simultaneously biaxially stretched polyamide-6/poly(ether block amide) copolymer (PA6/PEBA) films. The results showed the melting temperature of PA6 increased from 220.02 C to 225.56 C when the stretching ratios increased from 1 Â 1 to 3.5 Â 3.5, suggesting the occurrence of β ! α crystal transformation. Meanwhile, the increase of stretching ratios increased the crystallinity of the films due to the molecular orientation, which could create a more tortuous path for the diffusion of oxygen molecules through the films. As a result, the oxygen barrier performance of the stretched PA6/PEBA film was increased after biaxial stretching. The morphological observation showed that spherical or slightly ellipsoidal PEBA particles were dispersed in the PA6 matrix. The thermal shrinkage of the stretched film increased as the stretching ratios increased, and no significant difference of the shrinkage between machine direction (MD) and transition direction (TD) was observed in the stretched films. It was also found that the tensile strength of the stretched films in MD and TD exhibited the highest value at a stretching ratio of 3.5 Â 3.5, which was about 1.7 times and 2.1 times higher than that of the unstretched PA6/PEBA film, respectively.

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Pore formation and evolution mechanism during biaxial stretching of β-iPP used for lithium-ion batteries separator

Cited by 39 publications

References 41 publications

Progresses in Manufacturing Techniques of Lithium‐Ion Battery Separators in China

Progresses in Manufacturing Techniques of Lithium‐Ion Battery Separators in China

The unusual delamination phenomenon of three kinds of lithium‐ion battery separators

Structural evolution and properties of polyamide‐6/poly(ether block amide) films during the simultaneous biaxial stretching

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