Patent Publication Number: US-2021167461-A1

Title: Separator sealing apparatus and method for preventing bending of separator of secondary battery

Description:
TECHNICAL FIELD 
     The present disclosure relates to a sealing apparatus and method for a separator of a secondary battery, and more particularly, to a sealing apparatus installed on a production line of a mono cell semi-finished product or a half cell semi-finished product to seal a separator in order to prevent bending of the separator, and its method. 
     The present application claims priority to Korean Patent Application No. 10-2019-0088483 filed on Jul. 22, 2019 in the Republic of Korea, the disclosures of which are incorporated herein by reference. 
     BACKGROUND ART 
     Recently, the demand for secondary batteries as an eco-friendly energy source has rapidly increased. Among the secondary batteries, a lithium secondary battery having a high energy density, a high working potential, a long cycle life and a low self-discharge rate has been commercialized and widely used. 
     The lithium secondary battery includes an electrode assembly in which a positive electrode plate and a negative electrode plate respectively coated with a positive electrode active material and a negative electrode active material are disposed with a separator being interposed therebetween, and an exterior, namely a battery case, in which the electrode assembly is hermetically accommodated together with an electrolyte. 
     The electrode assembly having the positive electrode/separator/negative electrode structure of the lithium secondary battery may be briefly classified into a jelly-roll type (winding type), a stacking type, and a stacking/folding type that is a mixture of the winding type and the stacking type. 
     The jelly-roll type electrode assembly is prepared by coating metal foils serving as a current collector with an electrode active material or the like, drying and pressing the metal foils, then cutting the metal foils into a band form with a desired width and length, separating a negative electrode and a positive electrode using a separator, and then winding the same into a spiral form. The jelly-roll type electrode assembly is suitable for cylindrical batteries. 
     A stacking type or stacking/folding type electrode assembly has a structure in which positive and negative electrode units are sequentially stacked with a separator being interposed there between, and may easily obtain a rectangular shape. 
     The stacking type or stacking/folding type lithium secondary battery may be obtained by repeatedly stacking mono cells  110  having a structure of a positive electrode plate  104 /an upper separator  101 /a negative electrode plate  103 /a lower separator  102  as shown in  FIG. 1  or folding the mono cells  110  using a continuous separator film, or by adding a positive electrode to an upper or lower portion of half cells  120  having a structure of an upper separator  101 /a negative electrode plate  103 /a lower separator  102 . 
     Meanwhile, in the stacking type or stacking/folding type lithium secondary battery, a low voltage defective cell in which the secondary battery exhibits a voltage drop behavior higher than the self-discharge rate is sometimes found. In this case, if an edge of the separator is folded or torn during the assembly process, the positive electrode and the negative electrode may directly face each other, which is a main cause of electric short circuit. For this reason, as shown in  FIG. 2 , a method of preventing a separator folding phenomenon by bonding edges S of the upper separator  101  and the lower separator  102  in a width direction of a cell semi-finished product has been proposed as the prior art. 
     However, the external exposure of the electrode between the upper separator  101  and the lower separator  102  is not blocked fundamentally just by sealing the edge of the cell semi-finished product only in the width direction. Thus, a method to further improve the low-voltage defect rate by fundamentally blocking the exposure of the electrode by additionally bonding the edges of the separator  102  in a length direction of the cell semi-finished product is being discussed. 
     DISCLOSURE 
     Technical Problem 
     The present disclosure is designed to solve the problems of the related art, and therefore the present disclosure is directed to providing a sealing apparatus and method, which may be easily applied to an existing cell semi-finished product production line and fundamentally prevent an electrode from being exposed out of the cell semi-finished product by bonding all edge lines of an upper separator and a lower separator along a width direction and a length direction. 
     Technical Solution 
     In one aspect of the present disclosure, there is provided a separator sealing apparatus for bonding an upper separator and a lower separator with an electrode plate being interposed therebetween, the separator sealing apparatus comprising: 
     a first sealing unit configured to seal a first region specified as an outer edge along a width direction of the electrode plate, among portions where the upper separator and the lower separator face each other; and a second sealing unit configured to seal a second region specified as an outer edge along a length direction of the electrode plate, among the portions where the upper separator and the lower separator face each other. 
     The separator sealing apparatus may further comprise a transfer unit configured to continuously supply the electrode plate, the upper separator and the lower separator in one direction, and the first sealing unit and the second sealing unit may be operated in synchronization with the transfer unit at a preset speed to move vertically and configured to press and thermally fuse the first region and the second region. 
     The second sealing unit may be configured to be assembled with the first sealing unit and be reassembled with the first sealing unit according to a width of the electrode plate. 
     The first sealing unit may include a first upper heating block configured to apply pressure and heat to the first region of the upper separator; and a first lower heating block provided to be vertically symmetric to the first upper heating block and configured to apply pressure and heat to the first region of the lower separator. 
     The first upper heating block may be provided in a pair, the pair of first upper heating blocks may be spaced apart from each other at a predetermined interval to extend in one direction side by side, the first lower heating block may be provided in a pair, and the pair of first lower heating blocks may be provided to be vertically symmetric to the pair of first upper heating blocks. 
     The second sealing unit may include a plurality of second upper heating blocks respectively configured to extend in a direction intersecting with the first upper heating block and coupled to the pair of first upper heating blocks at locations spaced apart from each other at a predetermined interval along an extending direction of the pair of first upper heating blocks to apply heat and pressure to the second region of the upper separator; and a plurality of second lower heating blocks provided to be symmetric with the second upper heating blocks in one-to-one relationship and coupled to the pair of first lower heating blocks to apply heat and pressure to the second region of the lower separator. 
     The pair of first upper heating blocks may have a plurality of grooves formed at predetermined intervals along the extending direction, each of the second upper heating blocks may have a connection portion with a step formed in at least one end thereof, and the connection portion may be selectively fit into one of the plurality of grooves. 
     The connection portion may be fixed and released by a bolt in the groove of the pair of first upper heating blocks. 
     In another aspect of the present disclosure, there is also provide a separator sealing method, which uses the separator sealing apparatus described above to seal the upper separator and the lower separator, the separator sealing method comprising: 
     sealing both the first region and the second region so that the electrode plate is not exposed to the outside. 
     The separator sealing method may be used to seal a mono cell semi-finished product in which a lower separator, a negative electrode plate, an upper separator and a positive electrode plate are stacked in order or a half cell semi-finished product in which a lower separator, a negative electrode and an upper separator are stacked in order. 
     Advantageous Effects 
     According to an embodiment of the present disclosure, it is possible to significantly reduce a low voltage defect rate by preventing the electrode from being exposed out of the cell semi-finished product. 
     According to another embodiment of the present disclosure, it is possible to continuously mass-produce cell semi-finished products by speed synchronization with an existing semi-finished product production line. 
    
    
     
       DESCRIPTION OF DRAWINGS 
         FIG. 1  is a cross-sectional view of cell semi-finished products schematically showing a stacked structure of a conventional mono cell semi-finished product and a half cell semi-finished product. 
         FIG. 2  is a plan view showing a conventional cell semi-finished product. 
         FIGS. 3 and 4  are diagrams for illustrating a process of sealing a separator of a cell semi-finished product by using a separator sealing apparatus according to an embodiment of the present disclosure. 
         FIG. 5  is a plan view showing the cell semi-finished product of  FIG. 4  after final cutting. 
         FIG. 6  is a diagram schematically showing a first sealing unit and a second sealing unit according to an embodiment of the present disclosure. 
         FIG. 7  is a plan view showing a first upper heating block and a second upper heating block of  FIG. 6  assembled with each other. 
         FIG. 8  is a cross-sectioned view schematically showing a coupling portion of the first upper heating block and the second upper heating block of  FIG. 7 . 
     
    
    
     BEST MODE 
     Hereinafter, preferred embodiments of the present disclosure will be described in detail with reference to the accompanying drawings. Prior to the description, it should be understood that the terms used in the specification and the appended claims should not be construed as limited to general and dictionary meanings, but interpreted based on the meanings and concepts corresponding to technical aspects of the present disclosure on the basis of the principle that the inventor is allowed to define terms appropriately for the best explanation. Therefore, the embodiments described in the specification and the configurations illustrated in the drawings are only preferred embodiments of the present disclosure, without representing all technical features of the present disclosure. In addition, in order to help the understanding of the present disclosure, the accompanying drawings are not drawn to scale, but the dimensions of some components may be exaggerated. 
     A separator sealing apparatus according to the present disclosure includes a first sealing unit  10 , a second sealing unit  20  and a transfer unit  30 , and as shown in  FIGS. 3 and 4 , before finally cutting a semi-finished product that is continuously supplied (see  FIG. 1 ), a process of bonding an upper separator  101  and a lower separator  102  in cell units may be performed. 
     Here, the cell semi-finished product refers to a cell semi-finished product before final cutting. The cell semi-finished product before final cutting may include a lower separator  102  in the form of a continuous film, negative electrode plates  103  disposed on the lower separator  102  with a certain width to be spaced apart from each other, and an upper separator  101  provided on the negative electrode plate  103  in the form of a continuous film, or may include positive electrode plates  104  disposed on the upper separator  101  with a predetermined width to be spaced apart from each other. 
     Before the final cutting, cell semi-finished products, namely mono cell semi-finished products or half cell semi-finished products, may be continuously supplied in one direction by the transfer unit  30 , and scheduled separator parts D 1 , D 2  may be sealed by first sealing unit  10  and the second sealing unit  20 . The first sealing unit  10  and the second sealing unit  20  may be operated in synchronization with the transfer unit  30  at a preset speed. 
     For example, if some of the cell semi-finished products before cutting reach a location for the separator sealing process, the transfer unit  30  stops working for a certain period of time. At this time, the first sealing unit  10  and the second sealing unit  20  may operate (move vertically) to press and thermally fuse the separator parts D 1 , D 2 , which require sealing, for a certain period of time. Then, the cell pressing operation of the first sealing unit  10  and the second sealing unit  20  is released, and the transfer unit  30  is operated again to move the cell semi-finished products before cutting. After that, the separator is cut using a cutter (not shown) to complete a final mono cell semi-finished product or a final half cell semi-finished product. 
     Hereinafter, the configuration of the first sealing unit  10  and the second sealing unit  20  will be described in more detail with reference to  FIGS. 6 to 8 . 
     The first sealing unit  10  and the second sealing unit  20  are means for bonding two separators of the cell semi-finished product, namely the upper separator  101  and the lower separator  102 , to each other by applying heat and pressure. Here, the first sealing unit  10  may be configured to apply heat and pressure to a first region D 1 , the second sealing unit  20  may be configured to apply heat and pressure to a second region D 2 . The first sealing unit  10  and the second sealing unit  20  may be embodied using, for example, heating blocks having heating wires therein. 
     Here, the first region D 1  (see  FIG. 5 ) refers to an outer edge along a width direction of the electrode plate, among portions where the electrode plate, namely outer regions at both short sides of the electrode plate, where the upper separator  101  and the lower separator  102  face each other, and the second region D 2  refers to an outer edge along a length direction of the electrode plate, namely outer regions at both long sides of the electrode plate, among the portions where the separator  101  and the lower separator  102  face each other. 
     The first sealing unit  10  according to this embodiment may include first upper heating blocks  11 ,  12  and first lower heating blocks  13  and  14 , as shown in  FIG. 6 . 
     Two first upper heating blocks  11 ,  12  are provided in a pair, and the pair of first upper heating blocks  11 ,  12  are disposed to be spaced apart from each other by a length of the cell semi-finished product (in the Y-axis direction) and extend in one direction (in the X-axis direction) side by side. In this embodiment, the extending length of the first upper heating blocks  11 ,  12  corresponds to approximately the width of three unit cell semi-finished product before cutting. Here, the extending length may be configured to be longer or shorter than this embodiment. 
     The first lower heating blocks  13 ,  14  are provided to be vertically symmetric with the first upper heating blocks  11 ,  12 . That is, two first lower heating blocks  13 ,  14  are also provided in a pair, and the pair of first lower heating blocks  13 ,  14  may be provided to be symmetric with the pair of first upper heating blocks  11 ,  12 . 
     As described above, the first sealing unit  10  including the pair of first upper heating blocks  11 ,  12  and the pair of first lower heating blocks  13 ,  14  may come into contact with the upper and lower portions of the first regions D 1  of two separators of the plurality of cell semi-finished products and be operated to apply heat and pressure thereto. 
     That is, the first regions D 1  of the upper separators  101  of the plurality of cell semi-finished products may be pressed downward at once by the first upper heating block  11 ,  12 , and simultaneously the first regions D 1  of the lower separators  102  may also be pressed upward at once by the first lower heating blocks  13 ,  14 . At this time, the first region D 1  of the upper separator  101  and the first region D 1  of the lower separator  102  may be brought into contact with each other and be fused to each other by heat. 
     Meanwhile, the second sealing unit  20  is a means for sealing the second regions D 2  of the upper separator  101  and the lower separator  102  facing each other, which cannot be sealed by the first sealing unit  10 , and includes a plurality of second upper heating blocks  21  and a plurality of second lower heating blocks  23 . 
     The second upper heating blocks  21  respectively extend in a direction (Y-axis direction) intersecting with the pair of first upper heating block  11 ,  12 , and may be coupled to the pair of first upper heating blocks  11 ,  12  at locations spaced apart at a predetermined interval along the extending direction of the pair of first upper heating blocks  11 ,  12 . 
     The second lower heating blocks  23  are provided to be vertically symmetric with the second upper heating blocks  21 . In other words, the second lower heating blocks  23  are vertically symmetric with the second upper heating blocks  21  in one-to-one relationship, and are provided to be coupled to the pair of first lower heating blocks  13 ,  14 , respectively. 
     The second upper heating blocks  21  and the second lower heating blocks  23  are heating blocks corresponding to the second regions D 2  of the cell semi-finished products, and press the cell semi-finished products like the first sealing unit  10  to apply heat and pressure to the second regions of D 2  of two separators. 
     More specifically, the second regions D 2  of the upper separators  101  of the plurality of cell semi-finished products may be pressed downward at once by the second upper heating blocks  21 , and simultaneously the second regions D 2  of the lower separators  102  may be pressed upward at once by the second lower heating blocks  23 . At this time, the second region D 2  of the upper separator  101  and the second region D 2  of the lower separator  102  may come into contact with each other and be fused to each other by heat. 
     According to the separator sealing apparatus having the above configuration and operation, after final cutting, as the first region D 1  and the second region D 2  of the upper separator  101  and the lower separator  102 , namely the upper separator  101  and the lower separator  102  facing each other at outer regions in the width direction and the length direction of the electrode plate, are completely bonded, it is possible to produce cell semi-finished products where the electrode plate (negative electrode plate) is fundamentally prevented from being exposed to the outside. If a stacking type or stacking/folding type lithium secondary battery is assembled using the cell semi-finished products  110 , a low voltage defect rate of the lithium secondary battery may be significantly lowered in comparison to the prior art. 
     In addition, by sealing the separators of the plurality of cell semi-finished products while continuously moving the cell semi-finished products before cutting along the production direction in speed synchronization with the transfer unit  30 , it is possible to continuously mass-produce final cell semi-finished products  110 . 
     Meanwhile, the first sealing unit  10  and the second sealing unit  20  according to an embodiment of the present disclosure may be provided to be assembled and disassembled with each other. Hereinafter, the assembling and disassembling configuration of the first sealing unit  10  and the second sealing unit  20  will be described. 
     The assembling and disassembling configuration of the first upper heating block  11 ,  12  and the second upper heating blocks  21  is the same as the assembling and disassembling configuration of the first lower heating block  13 ,  14  and the second lower heating block  23 . Thus, the assembling and disassembling configuration of the first lower heating block  13 ,  14  and the second lower heating blocks  23  will not be described in detail again. 
     As shown in  FIGS. 7 and 8 , the pair of first upper heating blocks  11 ,  12  have a plurality of grooves H formed at regular intervals along the extending direction. The second upper heating blocks  21  may be coupled to the pair of first upper heating blocks  11 ,  12  by selecting one of the plurality of grooves H and fitting an end of the second upper heating block  21  into the corresponding groove H. 
     More specifically, the second upper heating blocks  21  may have connection portions  21   a  with a step formed at both ends thereof, and the connection portions  21   a  may be placed in the grooves H of the first upper heating blocks  11 ,  12  in a fitting manner and may be fixed to and released from the grooves H by a bolt B. Although not shown in the figures, a hole having a thread formed in may be provided in the groove H of the connection portion  21   a  and the first upper heating blocks  11 ,  12  so that the bolt B may be vertically fastened. 
     According to the above configuration, it is possible to adjust the interval between the second upper heating blocks  21  or to further increase or decrease the number of the second upper heating blocks  21 , which makes it possible to seal separators of various cell semi-finished products with different widths by using one separator sealing apparatus. 
     In addition, if some of the heating blocks in the separator sealing apparatus are damaged, the separator sealing apparatus may be normally used by replacing only the corresponding heating blocks. Therefore, it may be effective in terms of management and maintenance of the separator sealing apparatus. 
     Subsequently, a method of sealing the separators of the cell semi-finished products using the aforementioned separator sealing apparatus will be briefly summarized as follows. 
     Referring to  FIGS. 3 and 4  again, the cell semi-finished products before cutting may be continuously supplied along the producing direction (X-axis direction) by the transfer unit  30 . The cell semi-finished products before cutting may be a mono cell semi-finished product in which the lower separator  102 , the negative electrode plate  103 , the upper separator  101  and the positive electrode plate  104  are stacked in order, or a half cell semi-finished product in which the lower separator  102 , the negative electrode and the upper separator  101  are stacked in order. 
     The first sealing unit  10  and the second sealing unit  20  may be disposed at one side of the cell semi-finished product production line as above, and may be operated in synchronization with the transfer unit  30 . As shown in  FIG. 4 , if three cell semi-finished products reach a sealing process area by the transfer unit  30 , the first sealing unit  10  and the second sealing unit  20  operate integrally in the vertical direction to press and thermally fuse the first region D 1  and the second region D 2  of each cell semi-finished product during a preset time. If the preset time passes, the first sealing unit  10  and the second sealing unit  20  are returned to the original locations, and next three cell semi-finished products in an unsealed state are placed in the sealing process area by the transfer unit  30 . After the above sealing process, the cell semi-finished products may be cut one by one using a cutter (not-shown) while moving along the production line so as to be produced in the form of a final unit cell semi-finished product. 
     As described above, the separator folding problem may be solved by implementing the separator sealing apparatus and the separator sealing method of the present disclosure, and various kinds of mono cell or half cell semi-finished products of different widths may be mass-produced in the same production line. 
     The present disclosure has been described in detail. However, it should be understood that the detailed description and specific examples, while indicating preferred embodiments of the disclosure, are given by way of illustration only, since various changes and modifications within the scope of the disclosure will become apparent to those skilled in the art from this detailed description. 
     Meanwhile, even though the terms expressing directions such as “upper”, “lower”, “left” and “right” are used in the specification, they are just for convenience of description and can be expressed differently depending on the location of a viewer or a subject, as apparent to those skilled in the art.