JP2018156816A - Liquid absorption test method of separator for electrochemical element - Google Patents

Abstract

PROBLEM TO BE SOLVED: To take a plurality of liquid absorption test at the same time easily for a high volatility liquid in a liquid absorption test method of a separator for an electrochemical element.SOLUTION: A liquid absorption test method of a separator for an electrochemical element includes sandwiching a strip-shaped separator between two transparent laminate films having a heat-bonding surface on one side such that the separator side become a heat-bonded surface, and thermally adhering the entire surface, cutting the laminate film and the separator such that the cross section of the separator on the short side of the strip is exposed, and immersing the cut surface in liquid.SELECTED DRAWING: Figure 2

Description

  The present invention relates to a liquid absorption test method for an electrochemical element separator.

  In the separator for electrochemical elements (hereinafter, sometimes referred to as “separator”), the liquid absorption characteristics with respect to the electrolyte greatly affect the performance of the electrochemical element and the production efficiency. It is an important indicator for evaluation. When examining the liquid absorption characteristics of the separator, generally, as shown in the water absorption measurement method B of Non-Patent Document 1, the separator cut in a strip shape is vertically suspended and the lower end is immersed in the test liquid, and after a certain period of time. A method of checking the height of the sucked up test solution is taken. However, this test method has a problem that it does not reflect the liquid absorption characteristics of the separator when it is actually incorporated in an electrochemical device. Further, when a highly volatile test solution is used, the sucked-up test solution is volatilized from the surface of the separator, and there is a problem that accurate measurement cannot be performed.

  As a method for solving the above problem, a method for evaluating liquid absorption characteristics in a state close to a separator when actually incorporated in an electrochemical element has been proposed. For example, a separator is sandwiched between polyester films, the separator sandwiched between the polyester films is attached to the outer periphery of a cylindrical tube, the tube is placed in a container containing a test solution, and the test solution is impregnated into the separator. A method of confirming the state of going is performed (for example, see Patent Document 1). However, this method is suitable for a liquid absorption test with a test solution having low permeability to the separator, but the test solution having high permeability to the separator causes liquid wraparound, resulting in large variations in measurement results. There was a problem. Further, since one sample is measured per test, there is a problem that a plurality of samples cannot be tested and compared at the same time.

JIS C 2300-2: 2010 "Electric cellulose paper-Part 2: Test method"

JP 2012-195386 A

  The present invention has been made in view of the above circumstances, and in a liquid absorption test method for a separator for an electrochemical element, the test liquid from the separator surface reflects the state of the separator when incorporated in an electrochemical element. It is an object of the present invention to provide a method capable of preventing volatilization of a sample and easily evaluating a plurality of samples simultaneously.

As a result of earnest research to solve the above problems,
(1) A liquid absorption test method for a separator for an electrochemical element, in which a strip-shaped separator is sandwiched between two transparent laminate films having a heat bonding surface on one side so that the separator side becomes a heat bonding surface. After the heat bonding, the laminate film and the separator are cut so that the cross section of the separator on the short side of the strip is exposed, and the liquid absorption test method for the separator for electrochemical elements, characterized in that the cut surface is immersed in the test liquid,
I found.

  By using the liquid absorption test method for an electrochemical element separator of the present invention (hereinafter, the “liquid absorption test method for an electrochemical element separator” may be referred to as “test method”), the separator is covered with a laminate film. Therefore, it is possible to evaluate the liquid absorbency of the separator with respect to a highly volatile test liquid. Moreover, there is an effect that a plurality of separators can be measured simultaneously by arranging strip-shaped separators and thermally bonding them at the same time.

It is the schematic which shows an example of the positional relationship of the separator made into strip shape and the laminate film in the liquid absorption test method of the separator for electrochemical elements of this invention. In the liquid absorption test method of the separator for electrochemical devices of this invention, it is the schematic which shows an example of the cut part of a laminate film and a separator.

  Hereinafter, the liquid absorption test method of the separator for electrochemical devices of the present invention will be described in detail.

  The electrochemical element in the present invention is an element that stores electrochemical energy therein, and refers to a primary battery, a secondary battery, a capacitor, or the like. The electrolyte used for these electrochemical elements may be either aqueous or organic electrolyte.

  Examples of the separator for an electrochemical element to be evaluated in the present invention include a nonwoven fabric, paper, and a microporous film. Moreover, the separator which gave the layers, such as an inorganic particle, an organic particle, an organic polymer, and an inorganic polymer, using a nonwoven fabric, paper, and a microporous film as a base material can also be evaluated.

  The laminate film in the present invention is a transparent plastic film having a heat bonding surface on one side. The laminate film needs to be a transparent material in order to see the liquid suction height of the separator for electrochemical elements. Generally, two plastic films, generally called pouch films, are superposed so that the inner side becomes a heat-bonding surface, and one end is temporarily fixed.

  Examples of the material for the heat bonding surface of the laminate film in the present invention include a polyethylene film, a polypropylene film, an ethylene vinyl acetate copolymer film, and an ethylene-vinyl alcohol copolymer film.

  Examples of the material used as the base of the laminate film in the present invention include a polyethylene terephthalate film and a nylon film. Use a heat-bonding surface and base that do not dissolve in the test solution.

  FIG. 1 is a schematic view showing an example of the positional relationship between a laminate film 1 and a separator 2 in the present invention. A transparent laminate film 1 having a heat bonding surface on one side is sandwiched between separators 2 arranged so that the long side of the strip is in the liquid absorption test direction. At this time, the laminate film 1 is disposed so that the heat bonding surface is on the separator 2 side. In order to reduce the unevenness of thermal bonding for each separator 2, the laminate film 2 is passed through a laminator in the direction of the liquid absorption test, and the entire surface is thermally bonded.

  The separator 2 is thermally bonded to the entire surface with the laminate film 1 so that the separator 2 is compressed as in an actual electrochemical element. Moreover, since the laminate film 1 covers the separator 2 surface, even a highly volatile test solution can be tested without volatilizing from the separator 2 surface. The thermal bonding conditions depend on the material of the laminate film 1, but it is necessary to adjust so that no gap is formed between the separator 2 and the laminate film 1 when the liquid absorption test is actually performed. If the thermal bonding is weak, the test solution is sucked up from the gap between the separator 2 and the laminate film 1 and accurate measurement cannot be performed. On the other hand, even if thermal bonding is too strong, deformation of the laminate film 1 and penetration of the thermal bonding component into the separator 2 occur, and accurate measurement cannot be performed. In the test method of the present invention, since a plurality of separators 2 can be measured at the same time, after the determination of the thermal bonding conditions, it is possible to grasp the run-out for each test by simultaneously measuring each type of separator 2 for comparison.

  FIG. 2 is a schematic view showing an example of a cut portion of the laminate film 1 and the separator 2 in the present invention. The ends of the laminate film 1 and the separator 2 subjected to the heat bonding treatment are cut at a dotted line portion indicated by an arrow 3 so that a cross section on the short side of the separator 2 is exposed. Thereby, it becomes possible to perform a liquid absorption test by immersing the cross section of the separator 2 in the test liquid. If a part of the cut surface blocks the cross section of the separator 2, accurate measurement cannot be performed. Therefore, it is preferable to use a sharp cutter knife or the like for cutting.

  EXAMPLES Hereinafter, although an Example demonstrates this invention in more detail, this invention is not limited to an Example.

Example A separator 2 having a strip shape having a width of 15 mm and a length of 100 mm is formed on a laminate film 1 (manufactured by Meiko Shokai, trade name: MS pouch film MP10-100136, 100 mm × 146 mm, thickness 100 μm) in the form shown in FIG. It was processed using a pinch and laminator (trade name: MS Pouch, manufactured by Meiko Shokai). Thereafter, as shown in FIG. 2, the laminate film 1 and the separator 2 were cut so that the cross section of the separator 2 on the short side of the strip was exposed. The opposite side of the cut surface is sandwiched between clips, the laminate film 1 sandwiching the separator 2 is hung vertically, 5 mm of the cut side is immersed in a test solution (acetonitrile), and the test solution sucked up by the separator 2 after 10 minutes. The height (sucked height) was recorded.

Comparative Example 1
A strip-shaped separator having a width of 15 mm and a length of 100 mm was hung vertically, and the lower part 5 mm was immersed in acetonitrile, and the suction height after 30 seconds was recorded.

Comparative Example 2
A separator having a width of 30 mm and a length of 100 mm was sandwiched and fixed between two polyester films of the same size, and the lower part was immersed in acetonitrile, and the suction height after 10 seconds was recorded.

  Table 1 shows the results of the liquid absorption test according to each example and comparative example. As the separator 2, wet nonwoven fabrics having a thickness of 20, 30, and 40 μm made of cellulose and polyethylene terephthalate fibers were used, and tests were performed at N = 5, respectively, to obtain an average sucking height and a standard deviation SD.

  In the test method of the example, a strip-like separator 2 is sandwiched between two transparent laminate films 1 each having a heat-bonding surface on one side so that the separator 2 side becomes a heat-bonding surface, and then the entire surface is thermally bonded. Since the laminate film 1 and the separator 2 were cut so that the cross section of the separator 2 on the short side was exposed and the cut surface was immersed in the test solution, the liquid absorption test was possible even with highly volatile acetonitrile.

  On the other hand, in the test method of Comparative Example 1, since the separator was not covered with the laminate film and exposed, the sucked up acetonitrile volatilized from the separator surface, and an accurate liquid absorption test could not be performed. In the test method of Comparative Example 2, since the subtle difference in the gap of the polyester film that shakes every measurement greatly affects the measurement result, the variation from measurement to measurement was large.

  The present invention can be used for a liquid absorption test of a separator for an electrochemical element.

1 Laminate film 2 Separator 3 Cutting part

Claims (1)

  A liquid absorption test method for a separator for an electrochemical element, in which a strip-shaped separator is thermally bonded by sandwiching two transparent laminate films each having a heat bonding surface on one side so that the separator side becomes a heat bonding surface. Thereafter, the laminate film and the separator are cut so that the cross section of the separator on the short side of the strip is exposed, and the cut surface is immersed in a liquid.

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