储能科学与技术 ›› 2021, Vol. 10 ›› Issue (1): 156-162.doi: 10.19799/j.cnki.2095-4239.2020.0322

• 储能材料与器件 • 上一篇    下一篇

锂离子电池内隔膜褶皱的原因及消除

闫晓清1(), 胡志宇1, 刘凤泉1, 李林1, 谷传明2, 戴熙瀛3, 肖雨3, 邢照亮3, 周建军1()   

  1. 1.北京师范大学，北京 100088
    2.沧州明珠塑料股份有限公司，河北 沧州 061014
    3.全球能源互联网研究院先进输电技术国家重点实验室，北京 102200
  • 收稿日期:2020-09-18 修回日期:2020-10-01 出版日期:2021-01-05 发布日期:2021-01-08
  • 作者简介:闫晓清（1995—），女，研究方向为锂离子电池隔膜，E-mail：201821150092@mail.bnu.edu.cn|周建军，副教授，研究方向为聚合物隔膜和电解质，E-mail：11112010101@bnu.edu.cn。
  • 基金资助:
    国家自然科学基金(21973008);先进输电技术国家重点实验室开放基金项目(GEIRI-SKL-2020-009)

The origin and elimination of separator wrinkles in lithium-ion batteries

Xiaoqing YAN1(), Zhiyu HU1, Fengquan LIU1, Lin LI1, Chuanming GU2, Xiying DAI3, Yu XIAO3, Zhaoliang XING3, Jianjun ZHOU1()   

  1. 1.Beijing Normal University, Beijing 100088, China
    2.Cangzhou Mingzhu Plastic Co. Ltd. , Cangzhou 061014, Hebei, China
    3.State Key Laboratory of Advanced Transmission Technology, Global Energy Internet Research Institute, Beijing 102200, China
  • Received:2020-09-18 Revised:2020-10-01 Online:2021-01-05 Published:2021-01-08

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摘要：

在锂离子电池制造过程中，电芯注入电解液时，隔膜局部区域出现褶皱并在隔膜和极片间残留有气泡是一个常见的现象。隔膜上的褶皱和隔膜/极片间界面的缺陷会造成电池内阻分布不均匀，内阻低的地方电池循环过程中可能会局部过充或过放，进而影响电池的一致性及循环性能。针对这一现象，对不同种类的隔膜进行了研究，发现溶剂碳酸二甲酯(DMC)在流动浸润隔膜过程中，各种隔膜均会产生褶皱，且褶皱间距随隔膜厚度的增加略有增大。通过对DMC流动浸润隔膜的前端进行分析，发现隔膜产生褶皱主要有两个原因：DMC局部浸润隔膜过程中，毛细作用导致隔膜在液体流动前端出现隆起，在隔膜和极片间出现间隙。同时，DMC扩散到隔膜和极片的内部孔隙所排出的气体在极片/隔膜界面处积累形成气泡，导致隔膜出现局部的变形和皱褶。为解决上述问题，本文提出在电池加工过程中把涂布有聚偏氟乙烯(PVDF)的复合隔膜与正负极片热压黏合，粘合力抵消DMC浸润隔膜时所产生的毛细作用，能够减少或完全消除隔膜的褶皱。实验表明，当隔膜和正极极片热压后的剥离强度小于10 mN/cm时，黏结力尚不足以完全平衡毛细作用，隔膜仍会出现局部的皱缩，但褶皱数量明显减少。当剥离强度大于15 mN/cm时，隔膜的褶皱现象才被完全消除，说明提高隔膜与极片间的黏结强度，是一个解决隔膜/极片界面处缺陷的有效方法，隔膜褶皱等宏观缺陷的消除也有利于提高锂离子电池的一致性及循环稳定性，具有明确的实际应用价值。

关键词: 隔膜褶皱, 毛细作用, PVDF复合隔膜, 黏结力

Abstract:

In the manufacturing of lithium-ion batteries (LIBs), a common phenomenon occurs where wrinkles containing residual air bubbles are formed between the separator and electrodes, usually observed on local areas of the separator when the liquid electrolyte is added. Wrinkles on the separator and defects at the interface between the separator and electrodes will result in a non-uniform internal resistance distribution in the batteries. In the low internal resistance area, over-discharge or overcharge may occur during cycling, which might affect the cycle performance of the batteries. In this manuscript, various kinds of separators were investigated to address this issue. When dimethyl carbonate (DMC) is used to wet the separator surface, wrinkles form on all types of separators, and the wrinkle spacing increases with the thickness of the separator. The wetting frontier of the separator by DMC was investigated, and the resulting separator wrinkle can be attributed to two factors. When DMC is flowing on and wetting the separator, capillary action leads to the uplift of the separator, and a small gap can form between the separator and electrode. The air driven out of micropores in the separator and electrode after wetting with DMC aggregates at the interface to form air bubbles, resulting in local deformation and wrinkles. To address the wrinkle problem in LIB manufacturing, adhering polyvinylidene difluoride (PVDF) coated composite separators to electrodes under a hot press can counteract the capillary action and mitigate the formation of wrinkles. It was found that when the peeling strength is smaller than 10 mN/cm, the adhesion force cannot counteract the capillary action. Although local wrinkles may still be present, the number of wrinkles was significantly decreased. When the peeling strength is larger than 15 mN/cm, separator wrinkles are completely eliminated, suggesting that an increase in the adhesion force between the separator and electrodes reduces the defects at the interface. Reducing defects such as separator wrinkles is a valuable strategy to promote the consistency and cycle stability of LIBs.

Key words: separator wrinkle, capillary force, PVDF composite separator, adhesion force

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