Patent Publication Number: US-2022231358-A1

Title: Laminate-type power storage element

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application is based upon and claims the benefit of priority of the prior Japanese Patent Application No. 2021-007003, filed on Jan. 20, 2021, the entire contents of which are incorporated herein by reference. 
     FIELD 
     The embodiment discussed herein relates to a laminate-type power storage element. 
     BACKGROUND 
     Extremely thin electronic devices (hereinafter, referred to as thin electronic devices) having built in power supplies have been put to practical use, such as IC cards with a one-time password function and a display, and tags and tokens (one-time password generators). To implement such thin electronic devices, downsizing and thinning of power storage elements (primary batteries, secondary batteries, electric double layer capacitors) serving as power supplies are indispensable. 
     There are laminate-type power storage elements that are suitable for the downsizing and thinning. A laminate-type power storage element has a configuration in which an electrode body is encapsulated in an exterior body formed of laminated films. The laminated films are each formed by sandwiching a metal layer between a resin layer and a heat sealing layer, and the heat sealing layer is placed inside the exterior body. 
     Japanese Laid-open Patent Publication No. 2020-24877 
     Japanese Laid-open Patent Publication No. 2009-266392 
     FDK Corporation, “Thin-type lithium manganese dioxide primary battery,” online, searched on Dec. 10, 2020. 
     In a conventional laminate-type power storage element, particles such as active material particles removed from a positive or negative electrode included in an electrode body at the manufacturing stage may penetrate through the heat sealing layer of a laminated film, so that the metal layer of the laminated film may be exposed and the insulating property between the metal layer and the electrode body may thus be reduced. For example, such particles may come into contact with the metal layer, which may cause the metal layer and the positive or negative electrode to conduct each other via the particles. If this happens, an internal shortcut connecting the positive electrode and the negative electrode via the metal layer may be generated. In addition, in the case of a lithium-ion-based laminate-type power storage element, there may occur problems such as one where the potential of an exposed metal layer becomes a lithium potential and the metal layer is therefore corroded. 
     SUMMARY 
     According to one aspect, there is provided a laminate-type power storage element including: an exterior body formed of laminated films, the laminated films each being formed by sandwiching a metal layer between a resin layer and a heat sealing layer; and an electrode body including a positive electrode and a negative electrode disposed opposite to each other across a separator, the electrode body being enclosed together with a non-aqueous organic electrolyte solution inside the exterior body, wherein the positive electrode or the negative electrode includes particles having a 90% cumulative particle size less than or equal to a thickness of the heat sealing layer. 
     The object and advantages of the disclosure will be realized and attained by means of the elements and combinations particularly pointed out in the claims. 
     It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory and are not restrictive of the disclosure. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1  is a sectional view illustrating an example of a laminate-type power storage element according to a present embodiment; 
         FIG. 2  is a perspective view illustrating the example of the laminate-type power storage element according to the present embodiment; and 
         FIG. 3  is a sectional view of a laminate-type power storage element as a comparative example. 
     
    
    
     DESCRIPTION OF EMBODIMENT(S) 
     An embodiment will be described below with reference to the accompanying drawings. 
       FIG. 1  is a sectional view illustrating an example of a laminate-type power storage element according to a present embodiment.  FIG. 2  is a perspective view illustrating the example of the laminate-type power storage element according to the present embodiment. 
     In this connection,  FIG. 1  illustrates part of a cross section taken along the line I-I of  FIG. 2 . 
     The laminate-type power storage element  10  of the present embodiment includes an exterior body  11  formed of laminated films  11   a  and  11   b , and an electrode body  12  enclosed together with a non-aqueous organic electrolyte solution, not illustrated, inside the exterior body  11 . 
     The laminated films  11   a  and  11   b  are made by thermal lamination processing, for example, by an extrusion lamination method. The laminated films  11   a  and  11   b  are formed by sandwiching metal layers  11   a   2  and  11   b   2  between resin layers  11   a   1  and  11   b   1  and heat sealing layers  11   a   3  and  11   b   3 , respectively. 
     The metal layers  11   a   2  and  11   b   2  are base materials for the laminated films  11   a  and  11   b . For example, the metal layers  11   a   2  and  11   b   2  are made of an aluminum foil, a stainless steel foil, or another. 
     The resin layers  11   a   1  and  11   b   1  form the outer surface of the laminate-type power storage element  10  and are made of, for example, polyethylene terephthalate (PET). 
     The heat sealing layers  11   a   3  and  11   b   3  are placed inside the laminate-type power storage element  10  (on the side where the electrode body  12  is placed) and are made of, for example, a resin having thermal solubility, such as modified polyolefin. 
     In the exterior body  11  formed of the above laminated films  11   a  and  11   b , the heat sealing layers  11   a   3  and  11   b   3  are thermally bonded together at their outer periphery so that the exterior body  11  is formed in a bag shape to enclose the electrode body  12  and the non-aqueous organic electrolyte solution therein. 
     The electrode body  12  has a positive electrode  12   a  and a negative electrode  12   c , which are disposed opposite to each other across a separator  12   b.    
     The positive electrode  12   a  is formed by applying a positive electrode material including a positive electrode active material to one principal surface of a current collector such as a metal plate or metal foil made of stainless steel or the like, for example. 
     For the separator  12   b , a cellulose product or the like is used, for example. 
     The negative electrode  12   c  is formed by applying a negative electrode material including a negative electrode active material to one principal surface of a current collector such as a metal plate or metal foil made of stainless steel or the like, for example. 
     The electrode body  12  may be thermally bonded to the laminated films  11   a  and  11   b . In this case, the positive electrode  12   a  is thermally bonded to the laminated film  11   b  by the heat sealing layer  11   b   3 , and the negative electrode  12   c  is thermally bonded to the laminated film  11   a  by the heat sealing layer  11   a   3 . 
     With respect to the small and thin laminate-type power storage element  10 , which is used as a power supply in a card, an allowable range of displacement of the electrode body  12  and so on at the assembly step is approximately ±200 μm. Since the electrode body  12  is thermally bonded to the laminated films  11   a  and  11   b  themselves using the heat sealing layers  11   a   3  and  11   b   3 , the electrode body  12  is easily fixed, which minimizes its displacement. In addition, since the electrode body  12  is thermally bonded directly to the laminated films  11   a  and  11   b  without an insulating tape interposed therebetween, no space in the thickness direction of the laminate-type power storage element  10  is uselessly used, which achieves high energy density. 
     In the case where the laminate-type power storage element  10  is a primary lithium battery, the positive electrode  12   a  is formed by applying a slurry of a positive electrode material including a positive electrode active material such as manganese dioxide (MnO 2 ) to one principal surface of a current collector. In addition, the negative electrode  12   c  does not have a current collector but is metal lithium or a lithium alloy in a foil or flat plate form. 
     In this connection, a tab  13   a  serving as a terminal is connected to the positive electrode  12   a  and a tab  13   b  serving as a terminal is connected to the negative electrode  12   c . The tabs  13   a  and  13   b  extends to the outside from one side of the laminated films  11   a  and  11   b.    
     In the above-described electrode body  12  of the laminate-type power storage element  10  of the present embodiment, the 90% cumulative particle size (hereinafter, referred to as D90 particle size) of particles included in the positive electrode  12   a  or negative electrode  12   c  is less than or equal to the thickness of the heat sealing layers  11   a   3  and  11   b   3 . The reason why not a maximum particle size but the D90 particle size is used is because the maximum particle size may vary. 
     The above-mentioned particles included in the positive electrode  12   a  or negative electrode  12   c  are the particles of the positive electrode active material or negative electrode active material, for example. Alternatively, the particles may be the particles of another material such as a conductive assistant agent included in the slurry. Note that in the case where the laminate-type power storage element  10  is a primary lithium battery, the particles of manganese dioxide that is a positive electrode active material have the maximum particle size among the particles included in the positive electrode material, and therefore the D90 particle size of the positive electrode active material may be set less than or equal to the thickness of the heat sealing layers  11   a   3  and  11   b   3 . That is to say, a material with the maximum particle size among the materials included in the positive electrode  12   a  or negative electrode  12   c  may be set to have a D90 particle size less than or equal to the thickness of the heat sealing layers  11   a   3  and  11   b   3 . 
     In this connection, the D90 particle size of particles included in the positive electrode  12   a  and negative electrode  12   c  may be set less than or equal to the thickness of the heat sealing layers  11   a   3  and  11   b   3 . Alternatively, the D90 particle size of particles included in one of the positive electrode  12   a  and negative electrode  12   c  may be set less than or equal to the thickness of the heat sealing layers  11   a   3  and  11   b   3 . In the case where the laminate-type power storage element  10  is a primary lithium battery, for example, the negative electrode  12   c  formed using metal lithium or a lithium alloy in a foil or flat plate form has a low possibility that particles are removed therefrom at the manufacturing stage. Therefore, there only needs to satisfy the above-mentioned relationship between the D90 particle size and the thickness of the heat sealing layers  11   a   3  and  11   b   3  with respect only to the positive electrode  12   a.    
     The D90 particle size that satisfies the above-mentioned relationship is obtained by, for example, milling the particles of the positive electrode material or negative electrode material for a prescribed period of time with a mill such a jet mill. The measurement for the D90 particle size is carried out with a laser diffractometry technique, for example. 
       FIG. 3  is a sectional view of a laminate-type power storage element as a comparative example. The same reference numerals as used in  FIG. 1  are used for corresponding components in  FIG. 3 . 
     In a positive electrode  21   a  and negative electrode  21   c  of an electrode body  21  in the laminate-type power storage element  20  as a comparative example, their particles are not controlled to have a D90 particle size satisfying the above-mentioned relationship, which is different from the positive electrode  12   a  or negative electrode  12   c  of the laminate-type power storage element  10  of the present embodiment. Therefore, for example, as illustrated in  FIG. 3 , a conductive particle  21   a   1  (for example, MnO 2 ) removed from the positive electrode  21   a  may penetrate through a heat sealing layer  11   b   3  of a laminated film  11   b  and may come into contact with a metal layer  11   b   2  of the laminated film  11   b . In this case, the positive electrode  21   a  and the metal layer  11   b   2  conduct each other via the particle  21   a   1 . 
     Recently, thin electronic devices demand higher energy density of power storage elements as well as higher energy density of main power supplies because of installation of displays. However, a simple increase in the dimension and thickness of the power storage elements is not acceptable because they are used in cards. A laminate-type power storage element may be configured to have higher energy density by using an electrode body with high energy density or increasing the size of the electrode body. A simple increase in the size of the electrode body, however, reduces the insulating property between the electrode body and a laminated film and thus reduces the quality. To enhance the insulating property, there is a way to protect the electrode body with an insulating tape. However, in the case where of a laminate-type power storage element with a thickness of 0.6 mm or less, the use of the insulating tape limits a space for disposing the electrode body, which does not allow the increase in the size of the electrode body and thus causes a difficulty in achieving high energy density. For this reason, it is desirable to thermally bond the electrode body directly to the laminated film without using the insulating tape. Please note however that the problem described with reference to  FIG. 3  may occur. 
     By contrast, in the laminate-type power storage element  10  of the present embodiment, particles included in the positive electrode  12   a  or negative electrode  12   c  have a D90 particle size less than or equal to the thickness of the heat sealing layers  11   a   3  and  11   b   3 . Therefore, even if a particle  12   a   1  is removed from the positive electrode  12   a  as depicted in  FIG. 1 , conduction does not occur between the positive electrode  12   a  and the metal layer  11   b   2  via the particle  12   a   1 . Therefore, it is possible to avoid the reduction in the insulating property between the electrode body  12  and the metal layers  11   a   2  and  11   b   2  included in the laminated films  11   a  and  11   b.    
     Since the above-described laminate-type power storage element  10  is able to avoid the reduction in the insulating property without using an insulating tape, it becomes possible to increase the size of the electrode body  12  and thus to achieve high energy density. 
     Note that the thickness of a thin battery such as the laminate-type power storage element  10  is predetermined. Therefore, thin laminated films  11   a  and  11   b  are used in the laminate-type power storage element  10  to secure a battery capacity. As thinner laminated films  11   a  and  11   b  are used, there is a higher possibility that the insulating property decreases. Therefore, the above-described setting, in which the D90 particle size of particles included in the positive electrode  12   a  or negative electrode  12   c  is less than or equal to the thickness of the heat sealing layers  11   a   3  and  11   b   3 , has a high degree of effectiveness and is especially effective in the case where the laminated films  11   a  and  11   b  are 40 μm or less in thickness. 
     (Performance Evaluation) 
     Hereinafter, the results of performance evaluation will be described with respect to some examples with different manufacturing conditions. 
     Example 1 
     The positive electrode  12   a  is formed by applying an aqueous slurry of a positive electrode material to one principal surface of a stainless steel current collector. The positive electrode material has a composition containing 90.2 parts by weight of MnO 2  (D90 particle size of 24.2 μm), 5 parts by weight of acetylene black (AB), 3.7 parts by weight of styrene-butadiene rubber (SBR), and 0.8 part by weight of hydroxyethyl cellulose (HEC). Here, MnO 2  is a positive electrode active material, AB is a conductive assistant agent, SBR is a binder, and HEC is a thickening agent. The positive electrode material is applied at an application amount of 31 mg/cm 2 . After the application, drying and pressing are performed. Then, a part is cut out in a size of 20×13 mm (excluding bonding portions for terminals), so that the positive electrode  12   a  is obtained. 
     The separator  12   b  is a cellulose product with a thickness of 20 μm. 
     The negative electrode  12   c  is obtained by cutting metal lithium or a lithium alloy in a size of 19×12 mm. 
     The electrode body  12  is a stack of the positive electrode  12   a , separator  12   b , and negative electrode  12   c  in this order. 
     This electrode body  12  is formed by laminating the positive electrode  12   a  thermally bonded to the heat sealing layer  11   b   3  of the laminated film  11   b  and the negative electrode  12   c  thermally bonded to the heat sealing layer  11   a   3  of the laminated film  11   a  with the separator  12   b  interposed therebetween. 
     In addition, the laminated films  11   a  and  11   b  respectively include the metal layers  11   a   2  and  11   b   2  made of aluminum and the heat sealing layers  11   a   3  and  11   b   3  made of modified polypropylene (PPa) with a thickness of 30 μm, which is an example of modified polyolefin. 
     The laminated films  11   a  and  11   b  with the electrode body  12  interposed therebetween are bonded together at three of their four sides, so that the bag-shaped exterior body  11  with the remaining one side open is obtained. Then, a non-aqueous organic electrolyte solution is injected from the opening of the exterior body  11 , and the exterior body  11  is subjected to decompression impregnation and then is vacuum sealed (the remaining one side is sealed). 
     At this time, the sealing is performed with a sealing width of 2 mm and a heat bar of 180° C. 
     Example 2 
     The manufacturing conditions for a laminate-type power storage element  10  according to an example 2 are the same as those for the example 1, except that the D90 particle size of MnO 2  is set to 28.2 μm. 
     Example 3 
     The manufacturing conditions for a laminate-type power storage element  10  according to an example 3 are the same as those for the example 1, except that the D90 particle size of MnO 2  is set to 23.6 μm. 
     Comparative Example 1 
     Using the laminate-type power storage element  20  illustrated in  FIG. 3  as an example, a comparative example 1 is that the D90 particle size of MnO 2  included in the positive electrode  21   a  is set to 43.5 μm. The other manufacturing conditions are the same as those for the example 1. 
     Comparative Example 2 
     Using the laminate-type power storage element  20  illustrated in  FIG. 3  as an example, a comparative example 2 is that the D90 particle size of MnO 2  included in the positive electrode  21   a  is set to 56.5 μm. The other manufacturing conditions are the same as those for the example 1. 
     Example 4 
     The manufacturing conditions for a laminate-type power storage element  10  according to an example 4 are the same as those for the example 1, except that the D90 particle size of MnO 2  is set to 24.4 μm and the heat sealing layers  11   a   3  and  11   b   3  of the laminated films  11   a  and  11   b  are made of PPa with a thickness of 40 μm. 
     Example 5 
     The manufacturing conditions for a laminate-type power storage element  10  according to an example 5 are the same as those for the example 1, except that the D90 particle size of MnO 2  is set to 56.5 μm and the heat sealing layers  11   a   3  and  11   b   3  of the laminated films  11   a  and  11   b  are made of PPa with a thickness of 80 μm. 
     (Performance Evaluation Results) 
     The following table 1 represents the results of an insulation test as the performance evaluation of the laminate-type power storage elements  10 . 
     
       
         
           
               
               
               
               
               
               
               
             
               
                   
                 TABLE 1 
               
               
                   
                   
               
               
                   
                   
                   
                 THICKNESS 
                   
                   
                   
               
               
                   
                 MnO 2  D50 
                 MnO 2  D90 
                 B OF HEAT 
                   
                 INSULATION 
               
               
                   
                 PARTICLE 
                 PARTICLE 
                 SEALING 
                   
                 DEFECTIVE 
                 BATTERY 
               
               
                   
                 SIZE 
                 SIZE A 
                 LAYERS 
                   
                 RATE 
                 CAPACITY 
               
               
                   
                 (μm) 
                 (μm) 
                 (μm) 
                 A/B 
                 (%) 
                 (mAh) 
               
               
                   
                   
               
             
            
               
                   
               
            
           
           
               
               
               
               
               
               
               
            
               
                 EXAMPLE 1 
                 14.4 
                 24.4 
                 30 
                 0.81 
                 0.00 
                 15.8 
               
               
                 EXAMPLE 2 
                 15.8 
                 28.2 
                 30 
                 0.94 
                 0.00 
                 16.1 
               
               
                 EXAMPLE 3 
                 14.3 
                 23.6 
                 30 
                 0.79 
                 0.00 
                 15.5 
               
               
                 COMPARATIVE 
                 22.6 
                 43.5 
                 30 
                 1.45 
                 0.32 
                 15.6 
               
               
                 EXAMPLE 1 
               
               
                 COMPARATIVE 
                 25.7 
                 56.5 
                 30 
                 1.88 
                 0.86 
                 15.9 
               
               
                 EXAMPLE 2 
               
               
                 EXAMPLE 4 
                 14.4 
                 24.4 
                 40 
                 0.61 
                 0.00 
                 14.4 
               
               
                 EXAMPLE 5 
                 25.7 
                 56.5 
                 80 
                 0.71 
                 0.00 
                 7.6 
               
               
                   
               
            
           
         
       
     
     The table 1 represents the D50 particle size and D90 particle size (A) of MnO 2 , the thickness (B) of heat sealing layers  11   a   3  and  11   b   3 , A/B, insulation defective rate, and measured battery capacity. 
     In this connection, the insulation test is carried out by applying a direct current voltage of 5.0 V between the tab  13   a  and the laminated film  11   b  of a manufactured laminate-type power storage element  10  (laminate-type power storage element  20  for the comparative examples 1 and 2) and measuring a resistance value. At this time, a resistance value less than 100 MΩ is taken to be undesirable, and some samples are tested to calculate an insulation defective rate. 
     As seen in the table 1, in the case where the D90 particle size of MnO 2  is less than or equal to the thickness of the heat sealing layers  11   a   3  and  11   b   3 , that is, in the case where A/B is one or less, the insulation defective rates are 0.00%, which exhibits good insulating property. By contrast, in the case of the comparative examples 1 and 2 in which the D90 particle size of MnO 2  is greater than the thickness of the heat sealing layers  11   a   3  and  11   b   3 , that is, in which A/B is greater than one, the insulation defective rates are 0.32% and 0.86%, which exhibits reduced insulating property. 
     In this connection, as seen in the table 1, as the heat sealing layers  11   a   3  and  11   b   3  become thicker, the battery capacity decreases. For example, with respect to the heat sealing layers  11   a   3  and  11   b   3 , a thickness of 80 μm results in a battery capacity less than half the battery capacity obtained with a thickness of 30 μm. Therefore, the thickness of the heat sealing layers  11   a   3  and  11   b   3  is desirably 40 μm or less. 
     Heretofore, one aspect of the laminate-type power storage element according to the present embodiment has been described, and this is merely an example and is not limited to the above description. 
     According to one aspect, it is possible to avoid a reduction in the insulating property between an electrode body and a metal layer included in a laminated film. 
     All examples and conditional language provided herein are intended for the pedagogical purposes of aiding the reader in understanding the disclosure and the concepts contributed by the inventor to further the art, and are not to be construed as limitations to such specifically recited examples and conditions, nor does the organization of such examples in the specification relate to a showing of the superiority and inferiority of the disclosure. Although one or more embodiments of the present disclosure have been described in detail, it should be understood that various changes, substitutions, and alterations could be made hereto without departing from the spirit and scope of the disclosure.