Patent Publication Number: US-2023163388-A1

Title: Adhesive film for metal terminal, method for producing adhesive film for metal terminal, metal terminal with adhesive film for metal terminal attached thereto, power storage device, and method for producing power storage device

Description:
TECHNICAL FIELD 
     The present disclosure relates to an adhesive film for a metal terminal, a method for producing the adhesive film for a metal terminal, a metal terminal with the adhesive film for a metal terminal attached thereto, a power storage device, and a method for producing the power storage device. 
     BACKGROUND ART 
     Various types of power storage devices have been heretofore developed, and in every power storage device, a power storage device packaging material is an essential member for sealing a power storage device element including electrodes and an electrolyte. Metallic power storage device packaging materials have been heretofore widely used as power storage device packaging materials. In recent years, however, along with improvements in the performance of electric cars, hybrid electric cars, personal computers, cameras, mobile phones, and the like, power storage devices have been required to be diversified in shape, and to be thinner and lighter weight. However, the widely used metallic power storage device packaging materials are disadvantageous in that they have difficulty in keeping up with the diversification of shapes, and are limited in weight reduction. 
     Thus, a laminated sheet in which a base material layer/an adhesive layer/a barrier layer/a heat-sealable resin layer are sequentially laminated has been recently proposed as a power storage device packaging material that can be readily processed into various shapes, and can achieve a thickness reduction and a weight reduction. When such a laminated film-shaped power storage device packaging material is used, a power storage device element is sealed with the power storage device packaging material by heat-sealing a peripheral region of the power storage device packaging material in a state wherein the heat-sealable resin layers, positioned as the innermost layers of the power storage device packaging material, are opposed to each other. 
     Metal terminals protrude from the heat-sealed region of the power storage device packaging material, and the power storage device element sealed with the power storage device packaging material is electrically connected to the outside via the metal terminals electrically connected to the electrodes of the power storage device element. That is, in the heat-sealed region of the power storage device packaging material, the region where each of the metal terminals is present is heat-sealed with the metal terminal being held between the heat-sealable resin layers. Because the metal terminal and the heat-sealable resin layer are formed of different types of materials, the adhesion is likely to decrease at the interface between the metal terminal and the heat-sealable resin layer. 
     Thus, an adhesive film may be disposed between the metal terminal and the heat-sealable resin layer, for the purpose of improving the adhesion between these layers, for example. An example of this adhesive film is disclosed in, for example, Patent Literature 1. 
     CITATION LIST 
     Patent Literature 
     
         
         Patent Literature 1: JP-A-2015-79638 
         Patent Literature 2: JP-A-2002-8616 
       
    
     SUMMARY OF INVENTION 
     Technical Problem 
     In recent years, as smartphones have enabled faster and larger volumes of data communication, the amount of electricity consumed has also increased, and thus, research to increase the capacity of power storage devices has been conducted. However, increasing the battery capacity increases the container size and the amount of reactive substances, and also increases the amount of gas generated in the event of thermal runaway of the power storage device (i.e., in the event of a temperature rise in the power storage device), leading to an increased risk of explosion due to an increase in internal pressure of the power storage device. Power storage devices (for example, metal can batteries) produced using metallic packaging materials may be provided with a safety valve to ensure safety in the event of gas generation (see Patent Literature 2). 
     However, it is difficult to provide this safety valve in power storage devices produced using laminated film-shaped packaging materials. Thus, there is an issue of avoiding expansion of such a power storage device due to gas generated inside the power storage device when heated to a high temperature. 
     Under such circumstances, it is a main object of the present disclosure to provide an adhesive film for a metal terminal, which is to be interposed between a metal terminal electrically connected to an electrode of a power storage device element and a power storage device packaging material for sealing the power storage device element, which adhesive film for a metal terminal allows the metal terminal of the power storage device and a heat-sealable resin layer of the power storage device packaging material to adhere to each other until the power storage device is heated to a high temperature (for example, 100 to 130° C., preferably 110 to 130° C., particularly preferably 120 to 130° C.), and allows the power storage device to open at the position of the adhesive film for a metal terminal to release a gas generated inside the power storage device to the outside when the power storage device is heated to the high temperature (for example, 100 to 130° C., preferably 110 to 130° C., particularly preferably 120 to 130° C.). It is also an object of the present disclosure to provide a method for producing the adhesive film for a metal terminal, a metal terminal with the adhesive film for a metal terminal attached thereto, a power storage device, and a method for producing the power storage device. 
     Solution to Problem 
     The inventors of the present disclosure have conducted extensive research to solve the aforementioned problem. As a result, they have found that an adhesive film for a metal terminal, which is to be interposed between a metal terminal electrically connected to an electrode of a power storage device element and a power storage device packaging material for sealing the power storage device element, wherein the adhesive film for a metal terminal comprises a laminate sequentially including a first polyolefin layer disposed on the metal terminal side, a base material, and a second polyolefin layer disposed on the power storage device packaging material side, the laminate has a first adhesive layer between the first polyolefin layer and the base material, has a second adhesive layer between the second polyolefin layer and the base material, or has both the first adhesive layer and the second adhesive layer (that is, has the first adhesive layer between the first polyolefin layer and the base material, and has the second adhesive layer between the second polyolefin layer and the base material), the base material has a melting peak temperature of 135° C. or more, and at least one of the first adhesive layer and the second adhesive layer has a melting peak temperature of 100° C. or less, allows the metal terminal of the power storage device and a heat-sealable resin layer of the packaging material to adhere to each other until the power storage device is heated to a high temperature (for example, 100 to 130° C.), and allows the power storage device to open at the position of the adhesive film for a metal terminal (specifically, the position of the first adhesive layer or the second adhesive layer having a melting peak temperature of 100° C. or less) to release a gas generated inside the power storage device to the outside when the power storage device is heated to the high temperature. The present disclosure has been completed as a result of further research based on this finding. 
     In summary, the present disclosure provides an embodiment of the invention as set forth below: 
     An adhesive film for a metal terminal, which is to be interposed between a metal terminal electrically connected to an electrode of a power storage device element and a power storage device packaging material for sealing the power storage device element, 
     wherein the adhesive film for a metal terminal comprises a laminate sequentially including a first polyolefin layer disposed on the metal terminal side, a base material, and a second polyolefin layer disposed on the power storage device packaging material side, 
     the laminate has a first adhesive layer between the first polyolefin layer and the base material, has a second adhesive layer between the second polyolefin layer and the base material, or has both the first adhesive layer and the second adhesive layer, 
     the base material has a melting peak temperature of 135° C. or more, and 
     at least one of the first adhesive layer and the second adhesive layer has a melting peak temperature of 100° C. or less. 
     Advantageous Effects of Invention 
     The present disclosure can provide an adhesive film for a metal terminal, which is to be interposed between a metal terminal electrically connected to an electrode of a power storage device element and a power storage device packaging material for sealing the power storage device element, which adhesive film for a metal terminal allows the metal terminal of the power storage device and a heat-sealable resin layer of the power storage device packaging material to adhere to each other until the power storage device is heated to a high temperature (for example, 100 to 130° C., preferably 110 to 130° C., particularly preferably 120 to 130° C.), and allows the power storage device to open at the position of the adhesive film for a metal terminal to release a gas generated inside the power storage device to the outside when the power storage device is heated to the high temperature. It is also an object of the present disclosure to provide a method for producing the adhesive film for a metal terminal, a metal terminal with the adhesive film for a metal terminal attached thereto, a power storage device, and a method for producing the power storage device. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG.  1    is a schematic plan view of a power storage device according to the present disclosure. 
         FIG.  2    is a schematic cross-sectional view taken along line A-A′ in  FIG.  1   . 
         FIG.  3    is a schematic cross-sectional view taken along line B-B′ in  FIG.  1   . 
         FIG.  4    is a schematic cross-sectional view of an adhesive film for a metal terminal according to the present disclosure. 
         FIG.  5    is a schematic diagram for explaining a method of an opening test in the examples. 
         FIG.  6    is a schematic cross-sectional view of a power storage device packaging material according to the present disclosure. 
     
    
    
     DESCRIPTION OF EMBODIMENTS 
     An adhesive film for a metal terminal of the present disclosure is an adhesive film for a metal terminal, which is to be interposed between a metal terminal electrically connected to an electrode of a power storage device element and a power storage device packaging material for sealing the power storage device element, wherein the adhesive film for a metal terminal comprises a laminate sequentially including a first polyolefin layer disposed on the metal terminal side, a base material, and a second polyolefin layer disposed on the power storage device packaging material side, the laminate has a first adhesive layer between the first polyolefin layer and the base material, has a second adhesive layer between the second polyolefin layer and the base material, or has both the first adhesive layer and the second adhesive layer, the base material has a melting peak temperature of 135° C. or more, and at least one of the first adhesive layer and the second adhesive layer has a melting peak temperature of 100° C. or less. 
     Because of these features, the adhesive film for a metal terminal of the present disclosure allows the metal terminal of the power storage device and a heat-sealable resin layer of the power storage device packaging material to adhere to each other until the power storage device is heated to a high temperature (for example, 100 to 130° C., preferably 110 to 130° C., particularly preferably 120 to 130° C.), and allows the power storage device to open at the position of the adhesive film for a metal terminal to release a gas generated inside the power storage device to the outside when the power storage device is heated to the high temperature (for example, 100 to 130° C., preferably 110 to 130° C., particularly preferably 120 to 130° C.). 
     A power storage device of the present disclosure is a power storage device comprising a power storage device element comprising at least a positive electrode, a negative electrode, and an electrolyte, a power storage device packaging material for sealing the power storage device element, and a metal terminal electrically connected to each of the positive electrode and the negative electrode and protruding outside the power storage device packaging material, wherein the adhesive film for a metal terminal of the present disclosure is interposed between the metal terminal and the power storage device packaging material. 
     The present disclosure also provides a power storage device comprising a power storage device element comprising at least a positive electrode, a negative electrode, and an electrolyte, a power storage device packaging material for sealing the power storage device element, and a metal terminal electrically connected to each of the positive electrode and the negative electrode and protruding outside the power storage device packaging material, wherein an adhesive film for a metal terminal is interposed between the metal terminal and the power storage device packaging material, the adhesive film for a metal terminal comprises a laminate sequentially including a first polyolefin layer disposed on the metal terminal side, a base material, and a second polyolefin layer disposed on the power storage device packaging material side, the laminate has a first adhesive layer between the first polyolefin layer and the base material, has a second adhesive layer between the second polyolefin layer and the base material, or has both the first adhesive layer and the second adhesive layer, and the power storage device opens from a position where the first adhesive layer or the second adhesive layer of the adhesive film for a metal terminal is laminated, in an environment at a temperature of 100° C. or more and 130° C. or less (that is, the power storage device opens from a position where the first adhesive layer or the second adhesive layer of the adhesive film for a metal terminal is laminated, in any of temperature environments in the range of temperatures of 100° C. or more and 130° C. or less). 
     The following describes in detail the adhesive film for a metal terminal of the present disclosure and a method for producing the adhesive film for a metal terminal, and a power storage device and a method for producing the power storage device. 
     In the present specification, any numerical range indicated by “ . . . to . . . ” is intended to mean “ . . . or more” and “ . . . or less”. For example, the recitation “2 to 15 mm” is intended to mean 2 mm or more and 15 mm or less. 
     1. Adhesive Film for Metal Terminal 
     The adhesive film for a metal terminal of the present disclosure is interposed between a metal terminal electrically connected to an electrode of a power storage device element and a power storage device packaging material for sealing the power storage device element. Specifically, as shown in  FIGS.  1  to  3   , for example, an adhesive film  1  for a metal terminal according to the present disclosure is interposed between a metal terminal  2 , which is electrically connected to an electrode of a power storage device element  4 , and a power storage device packaging material  3  for sealing the power storage device element  4 . The metal terminal  2  protrudes outside the power storage device packaging material  3 , and is held between the power storage device packaging materials  3  with the adhesive film  1  for a metal terminal interposed therebetween, in a peripheral region  3   a  of the power storage device packaging materials  3  that have been heat-sealed. 
     In the present disclosure, a temporary bonding step of the adhesive film for a metal terminal to the metal terminal is performed, for example, about three to six times, at a temperature of about 140 to 160° C., and a pressure of about 0.01 to 1.0 MPa, for a time of about 3 to 15 seconds; and a permanent bonding step of the adhesive film for a metal terminal to the metal terminal is performed, for example, about one to three times, at a temperature of about 160 to 240° C., and a pressure of about 0.01 to 1.0 MPa, for a time of about 3 to 15 seconds. Heating for heat-sealing the power storage device packaging materials with the metal terminal with the adhesive film for a metal terminal attached thereto interposed therebetween is typically performed about once, at a temperature in the range of about 180 to 210° C., and a pressure of about 1.0 to 2.0 MPa, for a time of about 3 to 5 seconds. 
     The adhesive film  1  for a metal terminal of the present disclosure is provided to increase the adhesion between the metal terminal  2  and the power storage device packaging material  3 . The hermeticity of the power storage device element  4  is improved by increasing the adhesion between the metal terminal  2  and the power storage device packaging material  3 . As described above, during heat-sealing of the power storage device element  4 , the power storage device element is sealed in such a manner that the metal terminal  2  electrically connected to an electrode of the power storage device element  4  protrudes outside the power storage device packaging material  3 . At this time, because the metal terminal  2  formed of metal and a heat-sealable resin layer  35  (layer formed of a heat-sealable resin, such as a polyolefin) positioned as the innermost layer of the power storage device packaging material  3  are formed of different types of materials, the hermeticity of the power storage device element is likely to decrease at the interface between the metal terminal  2  and the heat-sealable resin layer  35 , if the adhesive film is not used. 
     As shown in  FIG.  4   , the adhesive film  1  for a metal terminal of the present disclosure includes a structure in which at least a first polyolefin layer  12   a , a base material  11 , and a second polyolefin layer  12   b  are sequentially laminated, and has a first adhesive layer  13   a  between the first polyolefin layer  12   a  and the base material  11 , has a second adhesive layer  13   b  between the second polyolefin layer  12   b  and the base material  11 , or has both the first adhesive layer  13   a  and the second adhesive layer  13   b  (that is, has the first adhesive layer  13   a  between the first polyolefin layer  12   a  and the base material  11 , and has the second adhesive layer  13   b  between the second polyolefin layer  12   b  and the base material  11 ). Examples of laminated structures of the adhesive film  1  for a metal terminal of the present disclosure include a laminated structure sequentially including the first polyolefin layer  12   a  disposed on the metal terminal  2  side, the first adhesive layer  13   a , the base material  11 , and the second polyolefin layer  12   b  disposed on the power storage device packaging material  3  side; a laminated structure sequentially including the first polyolefin layer  12   a  disposed on the metal terminal  2  side, the base material  11 , the second adhesive layer  13   b , and the second polyolefin layer  12   b  disposed on the power storage device packaging material  3  side; and a laminated structure sequentially including the first polyolefin layer  12   a  disposed on the metal terminal  2  side, the first adhesive layer  13   a , the base material  11 , the second adhesive layer  13   b , and the second polyolefin layer  12   b  disposed on the power storage device packaging material  3  side.  FIG.  4    schematically shows the laminated structure having both the first adhesive layer  13   a  and the second adhesive layer  13   b . The first polyolefin layer  12   a  is disposed on the metal terminal  2  side. The second polyolefin layer  12   b  is disposed on the power storage device packaging material  3  side. In the adhesive film  1  for a metal terminal of the present disclosure, the first polyolefin layer  12   a  and the second polyolefin layer  12   b  are positioned on both surfaces. 
     In the adhesive film  1  for a metal terminal of the present disclosure, each of the first polyolefin layer  12   a  and the second polyolefin layer  12   b  is a layer containing a polyolefin resin. Examples of polyolefin resins include polyolefins and acid-modified polyolefins. Of these polyolefin resins, the first polyolefin layer  12   a  preferably contains an acid-modified polyolefin, and is more preferably a layer formed of an acid-modified polyolefin. Of these polyolefin resins, the second polyolefin layer  12   b  preferably contains a polyolefin or an acid-modified polyolefin, more preferably contains a polyolefin, and is still more preferably a layer formed of a polyolefin. 
     The base material  11  preferably contains a polyolefin resin (i.e., has a polyolefin backbone), more preferably contains a polyolefin, and is still more preferably a layer formed of a polyolefin. 
     Each of the first adhesive layer  13   a  and the second adhesive layer  13   b  is preferably a cured product of a resin composition containing an acid-modified polyolefin and a curing agent. 
     In each of the first polyolefin layer  12   a , the second polyolefin layer  12   b , the first adhesive layer  13   a , the second adhesive layer  13   b , and the base material  11 , the polyolefin resin is preferably a polypropylene resin. The polyolefin is preferably polypropylene, and the acid-modified polyolefin is preferably acid-modified polypropylene. The polyolefin resin such as a polyolefin or an acid-modified polyolefin may contain known additives, the below-described fillers and pigments, and the like. 
     Specific examples of preferred laminated structures of the adhesive film  1  for a metal terminal of the present disclosure include a five-layer structure (laminated structure  1 ) in which the first polyolefin layer formed of acid-modified polypropylene/the first adhesive layer formed of a cured product of a resin composition containing acid-modified polypropylene and a curing agent/the base material formed of polypropylene/the second adhesive layer formed of a cured product of a resin composition containing acid-modified polypropylene and a curing agent/the second polyolefin layer formed of acid-modified polypropylene are sequentially laminated; a four-layer structure (laminated structure  2 ) in which the first polyolefin layer formed of acid-modified polypropylene/the first adhesive layer formed of a cured product of a resin composition containing acid-modified polypropylene and a curing agent/the base material formed of polypropylene/the second polyolefin layer formed of acid-modified polypropylene are sequentially laminated; a four-layer structure (laminated structure  3 ) in which the first polyolefin layer formed of acid-modified polypropylene/the base material formed of polypropylene/the second adhesive layer formed of a cured product of a resin composition containing acid-modified polypropylene and a curing agent/the second polyolefin layer formed of acid-modified polypropylene are sequentially laminated; a five-layer structure (laminated structure  4 ) in which the first polyolefin layer formed of acid-modified polypropylene/the first adhesive layer formed of a cured product of a resin composition containing acid-modified polypropylene and a curing agent/the base material formed of polypropylene/the second adhesive layer formed of a cured product of a resin composition containing acid-modified polypropylene and a curing agent/the second polyolefin layer formed of polypropylene are sequentially laminated; a four-layer structure (laminated structure  5 ) in which the first polyolefin layer formed of acid-modified polypropylene/the first adhesive layer formed of a cured product of a resin composition containing acid-modified polypropylene and a curing agent/the base material formed of polypropylene/the second polyolefin layer formed of polypropylene are sequentially laminated; and a four-layer structure (laminated structure  6 ) in which the first polyolefin layer formed of acid-modified polypropylene/the base material formed of polypropylene/the second adhesive layer formed of a cured product of a resin composition containing acid-modified polypropylene and a curing agent/the second polyolefin layer formed of polypropylene are sequentially laminated. Of these, the laminated structures  1  to  3  are particularly preferred in view of the adhesiveness between the second polyolefin layer  12   b  and the heat-sealable resin layer  35  of the power storage device packaging material  3 . 
     Materials constituting the first polyolefin layer  12   a , the second polyolefin layer  12   b , the first adhesive layer  13   a , the second adhesive layer  13   b , and the base material  11  are described in detail later. 
     When the adhesive film  1  for a metal terminal of the present disclosure is disposed between the power storage device packaging material  3  and the metal terminal  2  of a power storage device  10 , the surface of the metal terminal  2  formed of metal and the heat-sealable resin layer  35  (layer formed of a heat-sealable resin, such as a polyolefin) of the power storage device packaging material  3  are bonded to each other, with the adhesive film  1  for a metal terminal interposed therebetween. The first polyolefin layer  12   a  of the adhesive film  1  for a metal terminal is disposed on the metal terminal  2  side, and the second polyolefin layer  12   b  is disposed on the power storage device packaging material  3  side, such that the first polyolefin layer  12   a  adheres to the metal terminal  2 , and the second polyolefin layer  12   b  adheres to the heat-sealable resin layer  35  of the power storage device packaging material  3 . 
     In the adhesive film  1  for a metal terminal of the present disclosure, the base material  11  has a melting peak temperature of 135° C. or more, and at least one of the first adhesive layer  13   a  and the second adhesive layer  13   b  has a melting peak temperature of 100° C. or less. That is, when the adhesive film  1  for a metal terminal of the present disclosure has only the first adhesive layer  13   a  of the first adhesive layer  13   a  and the second adhesive layer  13   b , the first adhesive layer  13   a  has a melting peak temperature of 100° C. or less; when the adhesive film  1  for a metal terminal of the present disclosure has only the second adhesive layer  13   b , the second adhesive layer  13   b  has a melting peak temperature of 100° C. or less; or when the adhesive film  1  for a metal terminal of the present disclosure has both the first adhesive layer  13   a  and the second adhesive layer  13   b , at least one of the first adhesive layer  13   a  and the second adhesive layer  13   b  has a melting peak temperature of 100° C. or less. In the adhesive film for a metal terminal of the present disclosure, from the viewpoint of allowing the metal terminal of the power storage device and the heat-sealable resin layer of the power storage device packaging material to adhere to each other, and allowing the power storage device to open at the position of the adhesive film for a metal terminal to release a gas generated inside the power storage device to the outside when the power storage device is heated to a high temperature (for example, 100 to 130° C., preferably 110 to 130° C., particularly preferably 120 to 130° C.), at least one of the first adhesive layer  13   a  and the second adhesive layer  13   b  has a melting peak temperature of 100° C. or less to allow the power storage device to open from the first adhesive layer  13   a  or the second adhesive layer  13   b  having a melting peak temperature of 100° C. or less. As described below, if the melting peak temperature of the base material  11  is below 135° C., even if the melting peak temperature of at least one of the first adhesive layer  13   a  and the second adhesive layer  13   b  has a melting peak temperature of 100° C. or less, it is difficult for the power storage device to open at the position of the adhesive film for a metal terminal when the power storage device is heated to the high temperature. This is believed to be due to the following reason: If the melting peak temperature of the base material  11  is low, not only the first polyolefin layer  12   a  and the second polyolefin layer  12   b  of the adhesive film for a metal terminal, but also the base material  11  is melted, and the base material layer  11  is mixed into the first polyolefin layer  12   a  and the second polyolefin layer  12   b , in the step of heat-sealing the power storage device packaging materials and the metal terminal with the adhesive film for a metal terminal attached thereto, in the peripheral region  3   a . As a result, the heat resistance of the sealed region is increased, making it difficult for the power storage device to open. In the present disclosure, the method of measuring the melting peak temperature is as given below. 
     &lt;Measurement of Melting Peak Temperature&gt; 
     The melting peak temperature of each measurement sample is measured in accordance with JIS K 7121: 2012 (Testing Methods for Transition Temperatures of Plastics) (Supplement 1 to JIS K 7121: 1987)). The measurement is performed using a differential scanning calorimeter (DSC, for example, the differential scanning calorimeter Q200 from TA Instruments Inc.). The measurement sample is held at −50° C. for 15 minutes and then heated from −50° C. to 210° C. at a heating rate of 10° C./min to measure the first melting peak temperature P (° C.), and thereafter held at 210° C. for 10 minutes. Next, the measurement sample is cooled from 210° C. to −50° C. at a cooling rate of 10° C./min and held for 15 minutes. The measurement sample is further heated from −50° C. to 210° C. at a heating rate of 10° C./min to measure the second melting peak temperature Q (° C.). The flow rate of nitrogen gas is 50 ml/min. Using the above procedure, the first measured melting peak temperature P (° C.) and the second measured melting peak temperature Q (° C.) are obtained. Using the above procedure, the value of the first measured melting peak temperature P (° C.) is adopted as the melting peak temperature. 
     From the viewpoint of achieving the effects of the present disclosure more favorably, the melting peak temperature of the base material  11  is preferably about 150° C. or more, more preferably about 155° C. or more, still more preferably about 160° C. or more, and even more preferably about 163° C. or more. From the same viewpoint, the melting peak temperature of the base material  11  is preferably about 180° C. or less, more preferably about 175° C. or less, and still more preferably about 170° C. or less. Preferred ranges of the melting peak temperature include from about 135 to 180° C., from about 135 to 175° C., from about 135 to 170° C., from about 150 to 180° C., from about 150 to 175° C., from about 150 to 170° C., from about 155 to 180° C., from about 155 to 175° C., from about 155 to 170° C., from about 160 to 180° C., from about 160 to 175° C., from about 160 to 170° C., from about 163 to 180° C., from about 163 to 175° C., and from about 163 to 170° C. 
     From the viewpoint of achieving the effects of the present disclosure more favorably, the melting peak temperature of each of the first adhesive layer  13   a  and the second adhesive layer  13   b  is preferably about 99° C. or less, and more preferably about 97° C. or less. From the same viewpoint, the melting peak temperature of each of the first adhesive layer  13   a  and the second adhesive layer  13   b  is preferably about 80° C. or more, more preferably about 83° C. or more, and still more preferably about 85° C. or more. Preferred ranges of the melting peak temperature include from about 80 to 100° C., from about 80 to 99° C., from about 80 to 97° C., from about 83 to 100° C., from about 83 to 99° C., from about 83 to 97° C., from about 85 to 100° C., from about 85 to 99° C., and from about 85 to 97° C. It should be noted that as long as the melting peak temperature of at least one of the first adhesive layer  13   a  and the second adhesive layer  13   b  is 100° C. or less as described above, the melting peak temperature of either the first adhesive layer  13   a  or the second adhesive layer  13   b  may be above 100° C. and 130° C. or less. 
     From the viewpoint of achieving the effects of the present disclosure more favorably, the melting peak temperature of the first polyolefin layer  12   a  disposed on the metal terminal  2  side is preferably about 130° C. or more, and more preferably about 135° C. or more. From the same viewpoint, the melting peak temperature is preferably about 160° C. or less, and more preferably about 150° C. or less. Preferred ranges of the melting peak temperature include from about 130 to 160° C., from about 130 to 150° C., from about 135 to 160° C., and from about 135 to 150° C. 
     As described below, when the melting peak temperature of the base material of the adhesive film for a metal terminal is 135° C. or more, and the melting peak temperature of the second polyolefin layer  12   b  disposed on the power storage device packaging material  3  side and the melting peak temperature of the heat-sealable resin layer  35  of the power storage device packaging material  3  are both 130° C. or more, the metal terminal of the power storage device and the heat-sealable resin layer of the power storage device packaging material can adhere to each other until the power storage device is heated to a high temperature (for example, 100 to 130° C., preferably 110 to 130° C., particularly preferably 120 to 130° C.), and the power storage device can open at the position of the adhesive film for a metal terminal to release a gas generated inside the power storage device to the outside when the power storage device is heated to the high temperature (for example, 100 to 130° C., preferably 110 to 130° C., particularly preferably 120 to 130° C.). 
     From the same viewpoint, the melting peak temperature of the second polyolefin layer  12   b  disposed on the power storage device packaging material  3  side is preferably about 130° C. or more, and more preferably about 135° C. or more. From the same viewpoint, the melting peak temperature is preferably about 160° C. or less, and more preferably about 150° C. or less. Preferred ranges of the melting peak temperature include from about 130 to 160° C., from about 130 to 150° C., from about 135 to 160° C., and from about 135 to 150° C. 
     From the same viewpoint, the absolute value of the difference between the melting peak temperature of the second polyolefin layer  12   b  of the adhesive film  1  for a metal terminal and the melting peak temperature of the heat-sealable resin layer  35  of the power storage device packaging material  3  to which the adhesive film  1  for a metal terminal is applied is preferably about 0 to 5° C. or about 0 to 3° C. The smaller the absolute value of the difference between the melting peak temperatures is (that is, the closer the absolute value of the difference is to 0° C.), the more easily the adhesion between the second polyolefin layer  12   b  and the heat-sealable resin layer  35  can be increased because the second polyolefin layer  12   b  and the heat-sealable resin layer  35  of the power storage device packaging material  3  melt together during heat-sealing of the power storage device packaging materials with the metal terminal with the adhesive film for a metal terminal attached thereto interposed therebetween. 
     From the viewpoint of achieving the effects of the present disclosure more favorably, the surface hardness of the base material  11  in an environment at a temperature of 110° C. is preferably about 15 N/mm 2  or more, more preferably about 20 N/mm 2  or more, still more preferably about 25 N/mm 2  or more, and even more preferably about 30 N/mm 2  or more. From the same viewpoint, the surface hardness is preferably about 60 N/mm 2  or less, more preferably about 50 N/mm 2  or less, and still more preferably about 45 N/mm 2  or less. Preferred ranges of the surface hardness include from about 15 to 60 N/mm 2 , from about 15 to 50 N/mm 2 , from about 15 to 45 N/mm 2 , from about 20 to 60 N/mm 2 , from about 20 to 50 N/mm 2 , from about 20 to 45 N/mm 2 , from about 25 to 60 N/mm 2 , from about 25 to 50 N/mm 2 , from about 25 to 45 N/mm 2 , from about 30 to 60 N/mm 2 , from about 30 to 50 N/mm 2 , and from about 30 to 45 N/mm 2 . The method of measuring the surface hardness of the base material  11  at 110° C. is as given below. 
     &lt;Measurement of Surface Hardness of Base Material&gt; 
     The base material is bonded to one side of a glass slide (76 mm×26 mm×1 mm) with a double-faced adhesive tape attached thereto to provide a measurement sample. Next, a hot stage is mounted on an ultra-microhardness tester (for example, HM2000 from Fischer Instruments) equipped with a Vickers indenter, and the sample is heated by the hot stage set at a stage temperature of 110° C. for 5 minutes. Next, the surface hardness of the base material-side surface of the measurement sample is measured. 
     From the viewpoint of achieving the effects of the present disclosure more favorably, the entire thickness of the adhesive film  1  for a metal terminal is, for example, about 60 μm or more, preferably about 70 μm or more, and still more preferably about 80 μm or more. On the other hand, the entire thickness of the adhesive film  1  for a metal terminal of the present disclosure is preferably about 150 μm or less, more preferably about 130 μm or less, and still more preferably about 100 μm or less. Preferred ranges of the entire thickness of the adhesive film  1  for a metal terminal of the present disclosure include from about 60 to 150 μm, from about 60 to 130 μm, from about 60 to 100 μm, from about 70 to 150 μm, from about 70 to 130 μm, from about 70 to 100 μm, from about 80 to 150 μm, from about 80 to 130 μm, and from about 80 to 100 μm. 
     The materials, thicknesses, and the like of the first polyolefin layer  12   a , the second polyolefin layer  12   b , the first adhesive layer  13   a , the second adhesive layer  13   b , and the base material  11  are hereinafter described in detail. 
     [First Polyolefin Layer  12   a  and Second Polyolefin Layer  12   b ] 
     As shown in  FIG.  4   , the adhesive film  1  for a metal terminal of the present disclosure includes the first polyolefin layer  12   a  on one surface of the base material  11  and the second polyolefin layer  12   b  on the other surface. The first polyolefin layer  12   a  is disposed on the metal terminal  2  side. The second polyolefin layer  12   b  is disposed on the power storage device packaging material  3  side. In the adhesive film  1  for a metal terminal of the present disclosure, the first polyolefin layer  12   a  and the second polyolefin layer  12   b  are positioned on both surfaces. 
     From the viewpoint of achieving the effects of the present disclosure more favorably, each of the first polyolefin layer  12   a  and the second polyolefin layer  12   b  preferably has the melting peak temperature as defined above. 
     In the adhesive film  1  for a metal terminal of the present disclosure, each of the first polyolefin layer  12   a  and the second polyolefin layer  12   b  is a layer containing a polyolefin resin. Examples of polyolefin resins include polyolefins and acid-modified polyolefins. Of these polyolefin resins, the first polyolefin layer  12   a  preferably contains an acid-modified polyolefin, and is more preferably a layer formed of an acid-modified polyolefin. Of these polyolefin resins, the second polyolefin layer  12   b  preferably contains a polyolefin or an acid-modified polyolefin, more preferably contains a polyolefin, and is still more preferably a layer formed of a polyolefin or an acid-modified polyolefin. The acid-modified polyolefin has high affinity for metals. Furthermore, each of the polyolefin and the acid-modified polyolefin has high affinity for heat-sealable resins, such as a polyolefin. In the adhesive film  1  for a metal terminal of the present disclosure, therefore, the first polyolefin layer  12   a  formed of the acid-modified polyolefin is disposed on the metal terminal  2  side, such that higher adhesion can be achieved at the interface between the adhesive film  1  for a metal terminal and the metal terminal  2 . Furthermore, the second polyolefin layer  12   b  formed of the polyolefin or the acid-modified polyolefin is disposed on the heat-sealable resin layer  35  side of the power storage device packaging material  3 , such that higher adhesion can be achieved at the interface between the adhesive film  1  for a metal terminal and the heat-sealable resin layer  35 . 
     As described above, specific examples of preferred laminated structures of the adhesive film  1  for a metal terminal of the present disclosure include a five-layer structure (laminated structure  1 ) in which the first polyolefin layer formed of acid-modified polypropylene/the first adhesive layer formed of a cured product of a resin composition containing acid-modified polypropylene and a curing agent/the base material formed of polypropylene/the second adhesive layer formed of a cured product of a resin composition containing acid-modified polypropylene and a curing agent/the second polyolefin layer formed of acid-modified polypropylene are sequentially laminated; a four-layer structure (laminated structure  2 ) in which the first polyolefin layer formed of acid-modified polypropylene/the first adhesive layer formed of a cured product of a resin composition containing acid-modified polypropylene and a curing agent/the base material formed of polypropylene/the second polyolefin layer formed of acid-modified polypropylene are sequentially laminated; a four-layer structure (laminated structure  3 ) in which the first polyolefin layer formed of acid-modified polypropylene/the base material formed of polypropylene/the second adhesive layer formed of a cured product of a resin composition containing acid-modified polypropylene and a curing agent/the second polyolefin layer formed of acid-modified polypropylene are sequentially laminated; a five-layer structure (laminated structure  4 ) in which the first polyolefin layer formed of acid-modified polypropylene/the first adhesive layer formed of a cured product of a resin composition containing acid-modified polypropylene and a curing agent/the base material formed of polypropylene/the second adhesive layer formed of a cured product of a resin composition containing acid-modified polypropylene and a curing agent/the second polyolefin layer formed of polypropylene are sequentially laminated; a four-layer structure (laminated structure  5 ) in which the first polyolefin layer formed of acid-modified polypropylene/the first adhesive layer formed of a cured product of a resin composition containing acid-modified polypropylene and a curing agent/the base material formed of polypropylene/the second polyolefin layer formed of polypropylene are sequentially laminated; and a four-layer structure (laminated structure  6 ) in which the first polyolefin layer formed of acid-modified polypropylene/the base material formed of polypropylene/the second adhesive layer formed of a cured product of a resin composition containing acid-modified polypropylene and a curing agent/the second polyolefin layer formed of polypropylene are sequentially laminated. Of these, the laminated structures  1  to  3  are particularly preferred. 
     While the acid-modified polyolefin is not limited as long as it is a polyolefin modified with an acid, it is preferably a polyolefin grafted with an unsaturated carboxylic acid or an anhydride thereof. 
     Specific examples of the polyolefin to be modified with an acid include polyethylene, such as low-density polyethylene, medium-density polyethylene, high-density polyethylene, and linear low-density polyethylene; crystalline or amorphous polypropylene, such as homopolypropylene, block copolymers of polypropylene (for example, block copolymers of propylene and ethylene and block copolymers of propylene and butene), and random copolymers of polypropylene (for example, random copolymers of propylene and ethylene and random copolymers of propylene and butene); and terpolymers of ethylene-butene-propylene. Preferred among these polyolefins are polyethylene and polypropylene, with polypropylene being particularly preferred. 
     The polyolefin to be modified with an acid may also be a cyclic polyolefin. For example, a carboxylic acid-modified cyclic polyolefin is a polymer obtained by replacing a portion of the monomers that constitute the cyclic polyolefin with an α,β-unsaturated carboxylic acid or an anhydride thereof, and copolymerizing them, or by block-polymerizing or graft-polymerizing an α,β-unsaturated carboxylic acid or an anhydride thereof onto the cyclic polyolefin. 
     The cyclic polyolefin to be modified with an acid is a copolymer of an olefin and a cyclic monomer. Examples of the olefin as a constituent monomer of the cyclic polyolefin include ethylene, propylene, 4-methyl-1-pentene, butadiene, and isoprene. Examples of the cyclic monomer as a constituent monomer of the cyclic polyolefin include cyclic alkenes, such as norbornene; specifically, cyclic dienes, such as cyclopentadiene, dicyclopentadiene, cyclohexadiene, and norbornadiene. Preferred among these polyolefins are cyclic alkenes, and more preferred is norbornene. Examples of constituent monomers also include styrene. 
     Examples of the carboxylic acid or anhydride thereof to be used for the acid modification include maleic acid, acrylic acid, itaconic acid, crotonic acid, maleic anhydride, and itaconic anhydride. Preferably, when the first polyolefin layer  12   a  is analyzed by infrared spectroscopy, peaks derived from maleic anhydride are detected. For example, when a maleic anhydride-modified polyolefin is measured by infrared spectroscopy, peaks derived from maleic anhydride are detected at a wavelength near 1760 cm′ and a wavelength near 1780 cm′. When the first polyolefin layer  12   a  or the second polyolefin layer  12   b  is a layer composed of a maleic anhydride-modified polyolefin, the peaks derived from maleic anhydride are detected, as measured by infrared spectroscopy. However, if the degree of acid modification is low, the peaks may be so small that they cannot be detected. In that case, the analysis can be performed by nuclear magnetic resonance spectroscopy. 
     Each of the first polyolefin layer  12   a  and the second polyolefin layer  12   b  may be formed using one resin component alone, or may be formed using a blend polymer obtained by combining two or more resin components. Furthermore, each of the first polyolefin layer  12   a  and the second polyolefin layer  12   b  may be formed of only one layer, or may be formed of two or more layers using the same resin component or different resin components. In view of the film formability of the first polyolefin layer  12   a  and the second polyolefin layer  12   b , each of these layers is preferably formed using a blend polymer obtained by combining two or more resin components. When each of these layers is formed using a blend polymer, the blend polymer of the first polyolefin layer  12   a  preferably contains acid-modified polypropylene as a main component (component content: 50% by mass or more) and 50% by mass or less of another resin (preferably polyethylene, from the viewpoint of improving the flexibility); and the blend polymer of the second polyolefin layer  12   b  preferably contains polypropylene as a main component (component content: 50% by mass or more) and 50% by mass or less of another resin (preferably polyethylene, from the viewpoint of improving the flexibility). On the other hand, in view of the electrolytic solution resistance of the first polyolefin layer  12   a  and the second polyolefin layer  12   b , the first polyolefin layer  12   a  preferably contains acid-modified polypropylene alone as the resin, and the second polyolefin layer  12   b  preferably contains acid-modified polypropylene or polypropylene alone as the resin. 
     Each of the first polyolefin layer  12   a  and the second polyolefin layer  12   b  may further optionally contain a filler. When the first polyolefin layer  12   a  and the second polyolefin layer  12   b  contain a filler, the filler functions as a spacer, which can effectively inhibit a short circuit between the metal terminal  2  and a barrier layer  33  of the power storage device packaging material  3 . The filler has a particle diameter of about 0.1 to 35 μm, preferably about 5.0 to 30 μm, more preferably about 10 to 25 μm. The amount of the filler contained per 100 parts by mass of the resin component that forms each of the first polyolefin layer  12   a  and the second polyolefin layer  12   b  is about 5 to 30 parts by mass, and preferably about 10 to 20 parts by mass. 
     The filler may be either inorganic or organic. Examples of inorganic fillers include carbon (carbon and graphite), silica, aluminum oxide, barium titanate, iron oxide, silicon carbide, zirconium oxide, zirconium silicate, magnesium oxide, titanium oxide, calcium aluminate, calcium hydroxide, aluminum hydroxide, magnesium hydroxide, and calcium carbonate. Examples of organic fillers include fluororesins, phenol resins, urea resins, epoxy resins, acrylic resins, benzoguanamine-formaldehyde condensate, melamine-formaldehyde condensate, crosslinked polymethyl methacrylate, and crosslinked polyethylene. From the viewpoint of shape stability, rigidity, and contents resistance, aluminum oxide, silica, fluororesins, acrylic resins, and benzoguanamine-formaldehyde condensate are preferred; in particular, spherical aluminum oxide and silica are more preferred. As a method of mixing the filler into the resin component that forms each of the first polyolefin layer  12   a  and the second polyolefin layer  12   b , the following methods may be adopted, for example: a method in which both components are melt-blended beforehand in a Banbury mixer or the like to form a masterbatch, which is then adjusted to a predetermined mixture ratio; and a method in which the filler is directly mixed into the resin component. 
     Each of the first polyolefin layer  12   a  and the second polyolefin layer  12   b  may also optionally contain a pigment. Various inorganic pigments may be used as the pigment. Specific examples of preferred pigments include carbon (carbon and graphite) mentioned above as the filler. Carbon (carbon and graphite), which is a material generally used inside a power storage device, does not have the possibility of dissolving into an electrolytic solution. Moreover, carbon (carbon and graphite) has a high coloring effect and thus can achieve a sufficient coloring effect when added only in an amount that does not impair adhesiveness, and also does not melt by heat and thus, can increase the apparent melt viscosity of the added resin. Furthermore, carbon (carbon and graphite) can prevent, during thermal bonding (heat sealing), thinning of the region to which pressure is applied, thereby imparting high hermeticity between the power storage device packaging material and the metal terminal. 
     When a pigment is to be added to the first polyolefin layer  12   a  and the second polyolefin layer  12   b , in the case of using, for example, carbon black having a particle diameter of about 0.03 μm, the amount of the pigment to be added is about 0.05 to 0.3 part by mass, and preferably about 0.1 to 0.2 part by mass, per 100 parts by mass of the resin component that forms each of the first polyolefin layer  12   a  and the second polyolefin layer  12   b . By adding a pigment to the first polyolefin layer  12   a  and the second polyolefin layer  12   b , the presence or absence of the adhesive film  1  for a metal terminal can be detected with a sensor, or can be visually inspected. When a filler and a pigment are to be added to the first polyolefin layer  12   a  and the second polyolefin layer  12   b , the filler and the pigment may be added to the identical first polyolefin layer  12   a  and second polyolefin layer  12   b ; however, from the viewpoint of avoiding impairment of the heat sealability of the adhesive film  1  for a metal terminal, it is preferred to add the filler and the pigment to each of the first polyolefin layer  12   a  and the second polyolefin layer  12   b  separately. 
     From the viewpoint of achieving the effects of the present disclosure more favorably, the thickness of each of the first polyolefin layer  12   a  and the second polyolefin layer  12   b  is preferably about 10 μm or more, more preferably about 15 μm or more, and still more preferably about 20 μm or more, while it is preferably about 60 μm or less, more preferably about 55 μm or less, still more preferably about 50 μm or less, and even more preferably about 40 μm or less. Preferred ranges of the thickness of each of the first polyolefin layer  12   a  and the second polyolefin layer  12   b  include from about 10 to 60 μm, from about 10 to 55 μm, from about 10 to 50 μm, from about 10 to 40 μm, from about 15 to 60 μm, from about 15 to 55 μm, from about 15 to 50 μm, from about 15 to 40 μm, from about 20 to 60 μm, from about 20 to 55 μm, from about 20 to 50 μm, and from about 20 to 40 μm. 
     From the same viewpoint, the ratio of the thickness of the base material  11  to the total thickness of the first polyolefin layer  12   a  and the second polyolefin layer  12   b  is preferably about 0.3 or more, and more preferably about 0.4 or more, while it is preferably about 1.0 or less, and more preferably about 0.8 or less. Preferred ranges include from about 0.3 to 1.0, from about 0.3 to 0.8, from about 0.4 to 1.0, and from about 0.4 to 0.8. 
     When the entire thickness of the adhesive film  1  for a metal terminal is taken as 100%, the ratio of the total thickness of the first polyolefin layer  12   a  and the second polyolefin layer  12   b  is preferably about 30 to 80%, and more preferably about 50 to 
     [Base Material  11 ] 
     In the adhesive film  1  for a metal terminal, the base material  11  is a layer that functions as a support of the adhesive film  1  for a metal terminal. 
     The base material  11  has the melting peak temperature as defined above. From the viewpoint of achieving the effects of the present disclosure more favorably, the base material  11  preferably also has the surface hardness as defined above. 
     The material that forms the base material  11  is not limited. Examples of the material that forms the base material  11  include polyolefin resins, polyamide resins, polyester resins, epoxy resins, acrylic resins, fluororesins, silicone resins, phenol resins, polyetherimides, polyimides, polycarbonates, and mixtures or copolymers thereof, with polyolefin resins being particularly preferred among these. That is, the material that forms the base material  11  is preferably a resin containing a polyolefin backbone, such as a polyolefin or an acid-modified polyolefin. The inclusion of a polyolefin backbone in the resin that forms the base material  11  can be analyzed by, for example, infrared spectroscopy or gas chromatography-mass spectrometry. 
     As described above, the base material  11  preferably contains a polyolefin resin, more preferably contains a polyolefin, and is still more preferably a layer formed of a polyolefin. The layer formed of a polyolefin may be a stretched polyolefin film or an unstretched polyolefin film, preferably an unstretched polyolefin film. Specific examples of polyolefins include polyethylene, such as low-density polyethylene, medium-density polyethylene, high-density polyethylene, and linear low-density polyethylene; crystalline or amorphous polypropylene, such as homopolypropylene, block copolymers of polypropylene (for example, block copolymers of propylene and ethylene), and random copolymers of polypropylene (for example, random copolymers of propylene and ethylene); and terpolymers of ethylene-butene-propylene. Preferred among these polyolefins are polyethylene and polypropylene, with polypropylene being more preferred. Because of its excellent electrolytic solution resistance, the base material  11  preferably contains homopolypropylene, is more preferably formed of homopolypropylene, and is still more preferably an unstretched homopolypropylene film. 
     Specific examples of polyamides include aliphatic polyamides, such as nylon 6, nylon 66, nylon 610, nylon 12, nylon 46, and copolymers of nylon 6 and nylon 66; polyamides containing aromatics, such as hexamethylenediamine-isophthalic acid-terephthalic acid copolyamides containing structural units derived from terephthalic acid and/or isophthalic acid, for example, nylon 61, nylon 6T, nylon 61T, and nylon 616T (I denotes isophthalic acid, and T denotes terephthalic acid), and polymethaxylylene adipamide (MXD6); cycloaliphatic polyamides, such as polyaminomethyl cyclohexyl adipamide (PACM6); polyamides copolymerized with a lactam component or an isocyanate component such as 4,4′-diphenylmethane-diisocyanate, and polyester amide copolymers or polyether ester amide copolymers that are copolymers of copolyamides with polyesters or polyalkylene ether glycols; and copolymers thereof. These polyamides may be used alone or in combination. 
     Specific examples of polyesters include polyethylene terephthalate, polybutylene terephthalate, polyethylene naphthalate, polybutylene naphthalate, polyethylene isophthalate, copolyesters containing ethylene terephthalate as a main repeating unit, and copolyesters containing butylene terephthalate as a main repeating unit. Specific examples of copolyesters containing ethylene terephthalate as a main repeating unit include copolyesters obtained by polymerizing ethylene terephthalate as a main repeating unit with ethylene isophthalate (abbreviated as polyethylene (terephthalate/isophthalate); hereinafter abbreviations are made in the same manner), polyethylene (terephthalate/isophthalate), polyethylene (terephthalate/adipate), polyethylene (terephthalate/sodium sulfoisophthalate), polyethylene (terephthalate/sodium isophthalate), polyethylene (terephthalate/phenyl-dicarboxylate), and polyethylene (terephthalate/decane dicarboxylate). Specific examples of copolyesters containing butylene terephthalate as a main repeating unit include copolyesters obtained by polymerizing butylene terephthalate as a main repeating unit with butylene isophthalate (abbreviated as polybutylene (terephthalate/isophthalate); hereinafter abbreviations are made in the same manner), polybutylene (terephthalate/adipate), polybutylene (terephthalate/sebacate), polybutylene (terephthalate/decane dicarboxylate), and polybutylene naphthalate. These polyesters may be used alone or in combination. 
     Alternatively, the base material  11  may be formed of a nonwoven fabric formed of the above-described resin. When the base material  11  is a nonwoven fabric, the base material  11  is preferably formed of a polyolefin resin, a polyamide resin, or the like as described above. 
     The base material  11  may be composed of a single layer or a plurality of layers. When the base material  11  is composed of a plurality of layers, at least one of the layers may contain a layer having a melting peak temperature of 135° C. or more as described above. A specific example of the plurality of layers is a three-layer structure in which block polypropylene/homopolypropylene/block polypropylene are sequentially laminated or random propylene/block propylene/random propylene are sequentially laminated. 
     The base material  11  may be blended with a colorant to form a layer containing the colorant. Alternatively, a resin with low transparency may be selected to adjust the light transmittance. When the base material  11  is a film, the film may be a colored film or a film with low transparency. When the base material  11  is a nonwoven fabric, the nonwoven fabric may be a nonwoven fabric formed using a binder or fibers containing a colorant, or may be a nonwoven fabric with low transparency. 
     When the base material  11  is formed of a resin film, the surface of the base material  11  may be optionally subjected to a known easy-adhesion means, such as corona discharge treatment, ozone treatment, or plasma treatment. 
     From the viewpoint of achieving the effects of the present disclosure more favorably, the thickness of the base material  11  is preferably 120 μm or less, more preferably 110 μm or less, still more preferably about 100 μm or less, and even more preferably about 90 μm or less. On the other hand, the thickness of the base material  11  is preferably about 20 μm or more, more preferably about 30 μm or more, and still more preferably about 40 μm or more. Preferred ranges of the thickness of the base material  11  include from about 20 to 120 μm, from about 20 to 110 μm, from about 20 to 100 μm, from about 20 to 90 μm, from about 30 to 120 μm, from about 30 to 110 μm, from about 30 to 100 μm, from about 30 to 90 μm, from about 40 to 120 μm, from about 40 to 110 μm, from about 40 to 100 μm, and from about 40 to 90 μm. 
     [First Adhesive Layer  13   a  and Second Adhesive Layer  13   b ] As shown in  FIG.  4   , the first adhesive layer  13   a  is a layer disposed between the first polyolefin layer  12   a  and the base material  11 . The second adhesive layer  13   b  is a layer disposed between the second polyolefin layer  12   b  and the base material  11 . In the present disclosure, at least one of the first adhesive layer  13   a  and the second adhesive layer  13   b  has a melting peak temperature of 100° C. or less. In the adhesive film for a metal terminal of the present disclosure, from the viewpoint of allowing the metal terminal  2  of the power storage device and the heat-sealable resin layer  35  of the power storage device packaging material to adhere to each other, and allowing the power storage device to open at the position of the adhesive film for a metal terminal to release a gas generated inside the power storage device to the outside when the power storage device is heated to a high temperature (for example, 100 to 130° C., preferably 110 to 130° C., or even 120 to 130° C.), the melting peak temperature of at least one of the first adhesive layer  13   a  and the second adhesive layer  13   b  is 100° C. or less to allow the power storage device to open from the first adhesive layer  13   a  or the second adhesive layer  13   b  having a melting peak temperature of 100° C. or less. That is, when the adhesive film  1  for a metal terminal of the present disclosure has only the first adhesive layer  13   a  of the first adhesive layer  13   a  and the second adhesive layer  13   b , the first adhesive layer  13   a  has a melting peak temperature of 100° C. or less, such that the power storage device opens from the first adhesive layer  13   a . Alternatively, when the adhesive film  1  for a metal terminal of the present disclosure has only the second adhesive layer  13   b , the second adhesive layer  13   b  has a melting peak temperature of 100° C. or less, such that the power storage device opens from the second adhesive layer  13   b . Still alternatively, when the adhesive film  1  for a metal terminal of the present disclosure has both the first adhesive layer  13   a  and the second adhesive layer  13   b , at least one of the first adhesive layer  13   a  and the second adhesive layer  13   b  has a melting peak temperature of 100° C. or less, such that the power storage device opens from the layer having a melting peak temperature of 100° C. or less. 
     Each of the first adhesive layer  13   a  and the second adhesive layer  13   b  is preferably a cured product of a resin composition containing an acid-modified polyolefin and a curing agent. 
     While the acid-modified polyolefin is not limited as long as it is a polyolefin modified with an acid having a molecular weight such that it dissolves in a hydrocarbon-based solvent, it is preferably a polyolefin grafted with an unsaturated carboxylic acid or an anhydride thereof. Examples of each of the polyolefin to be modified with an acid and the carboxylic acid or anhydride thereof to be used for the acid modification include the same as those mentioned in the [First Polyolefin Layer  12   a  and Second Polyolefin Layer  12   b ] section above. The acid-modified polyolefin can be synthesized using the method as disclosed in WO 2015/033703. 
     Each of the first adhesive layer  13   a  and the second adhesive layer  13   b  is preferably a cured product of a resin composition containing an acid-modified polyolefin and at least one selected from the group consisting of a compound having an isocyanate group, a compound having an oxazoline group, and a compound having an epoxy group, and particularly preferably a cured product of a resin composition containing an acid-modified polyolefin and at least one selected from the group consisting of a compound having an isocyanate group and a compound having an epoxy group. 
     While the compound having an isocyanate group is not limited, it is preferably a polyfunctional isocyanate compound. The polyfunctional isocyanate compound is not limited as long as it is a compound having two or more isocyanate groups. Specific examples of the polyfunctional isocyanate-based curing agent include pentane diisocyanate (PDI), isophorone diisocyanate (IPDI), hexamethylene diisocyanate (HDI), tolylene diisocyanate (TDI), diphenylmethane diisocyanate (MDI), polymer or isocyanurate form thereof, mixtures thereof, and copolymers thereof with other polymers. Examples also include adducts, biurets, isocyanurates, and other forms thereof. 
     The content of the compound having an isocyanate group in each of the first adhesive layer  13   a  and the second adhesive layer  13   b  is preferably in the range of 0.1 to 50% by mass, and more preferably in the range of 0.5 to 40% by mass, in the resin composition constituting each of the first adhesive layer  13   a  and the second adhesive layer  13   b.    
     The compound having an oxazoline group is not limited as long as it is a compound having an oxazoline backbone. Specific examples of the compound having an oxazoline group include those having a polystyrene main chain and those having an acrylic main chain. Commercial products include, for example, the Epocros series from Nippon Shokubai Co., Ltd. 
     The content of the compound having an oxazoline group in each of the first adhesive layer  13   a  and the second adhesive layer  13   b  is preferably in the range of 0.1 to 50% by mass, and more preferably in the range of 0.5 to 40% by mass, in the resin composition constituting each of the first adhesive layer  13   a  and the second adhesive layer  13   b.    
     Examples of the compound having an epoxy group include an epoxy resin. The epoxy resin is not limited as long as it is a resin capable of forming a crosslinked structure with an epoxy group present in the molecule, and a known epoxy resin may be used. The weight average molecular weight of the epoxy resin is preferably about 50 to 2,000, more preferably about 100 to 1,000, and still more preferably about 200 to 800. In the present disclosure, the weight average molecular weight of the epoxy resin is the value as measured by gel permeation chromatography (GPC) using polystyrene as standard samples. 
     Specific examples of the epoxy resin include glycidyl ether derivative of trimethylolpropane, bisphenol A diglycidyl ether, modified bisphenol A diglycidyl ether, bisphenol F glycidyl ether, novolac glycidyl ether, glycerol polyglycidyl ether, and polyglycerol polyglycidyl ether. These epoxy resins may be used alone or in combination. 
     The content of the epoxy resin in each of the first adhesive layer  13   a  and the second adhesive layer  13   b  is preferably in the range of 0.1 to 50% by mass, and more preferably in the range of 0.5 to 40% by mass, in the resin composition constituting each of the first adhesive layer  13   a  and the second adhesive layer  13   b.    
     From the viewpoint of achieving the effects of the present disclosure more favorably, the thickness of each of the first adhesive layer  13   a  and the second adhesive layer  13   b  is preferably about 0.1 μm or more, more preferably about 1 μm or more, and still more preferably about 2 μm or more, while it is preferably about 5 μm or less, and more preferably about 3 μm or less. Preferred ranges of the thickness of each of the first adhesive layer  13   a  and the second adhesive layer  13   b  include from about 0.1 to 5 μm, from about 0.1 to 3 μm, from about 1 to 5 μm, from about 1 to 3 μm, from about 2 to 5 μm, and from about 2 to 3 μm. 
     Each of the first adhesive layer  13   a  and the second adhesive layer  13   b  can be formed by applying the adhesive using a known coating method, such as a dry lamination method, a bar coating method, a roll coating method, or a gravure coating method, and drying. The amount of the adhesive (mixture of a resin, a curing agent, and a solvent) for forming each of the first adhesive layer  13   a  and the second adhesive layer  13   b  to be applied may be adjusted appropriately to achieve the thickness as defined above, and may be, for example, about 0.05 to 3.0 mg/m 2 , and preferably about 0.1 to 2.0 mg/m 2 . 
     The adhesive film  1  for a metal terminal of the present disclosure may be produced by laminating the first polyolefin layer  12   a  and the second polyolefin layer  12   b  onto both surfaces of the base material  11  with the first adhesive layer  13   a  and the second adhesive layer  13   b , respectively, interposed therebetween. Lamination between the base material  11 , and the first polyolefin layer  12   a  and the second polyolefin layer  12   b  with the first adhesive layer  13   a  and the second adhesive layer  13   b  interposed therebetween may be accomplished using a known method such as a dry lamination method. 
     The method of interposing the adhesive film  1  for a metal terminal between the metal terminal  2  and the power storage device packaging material  3  is not limited; for example, as shown in  FIGS.  1  to  3   , the adhesive film  1  for a metal terminal may be wound around the metal terminal  2  in the region where the metal terminal  2  is held between the power storage device packaging materials  3 . Alternatively, although this is not illustrated, the adhesive film  1  for a metal terminal may be disposed on both surfaces of each of the metal terminals  2  as to as cross the two metal terminals  2 , in the region where each metal terminal  2  is held between the power storage device packaging materials  3 . 
     [Metal Terminal  2 ] 
     The adhesive film  1  for a metal terminal of the present disclosure is used by being interposed between the metal terminal  2  and the power storage device packaging material  3 . The metal terminal  2  (tab) is a conductive member electrically connected to an electrode (the positive electrode or the negative electrode) of the power storage device element  4 , and is formed of a metal material. Examples of the metal material constituting the metal terminal  2  include, but are not limited to, aluminum, nickel, and copper. For example, the metal terminal  2  connected to the positive electrode of a lithium ion power storage device is typically formed of aluminum or the like. The metal terminal  2  connected to the negative electrode of a lithium ion power storage device is typically formed of copper, nickel, or the like. 
     Preferably, the surface of the metal terminal  2  is subjected to a chemical conversion treatment, from the viewpoint of improving the electrolytic solution resistance. For example, when the metal terminal  2  is formed of aluminum, specific examples of the chemical conversion treatment include a known method in which a corrosion-resistant film composed of a phosphate, a chromate, a fluoride, a triazine-thiol compound, or the like is formed. Preferred among methods of forming a corrosion-resistant film is a phosphoric acid chromate treatment that uses a material composed of three components, i.e., a phenol resin, a chromium(III) fluoride compound, and phosphoric acid. 
     The dimensions of the metal terminal  2  may be adjusted appropriately according to the dimensions of the power storage device to be used, for example. The thickness of the metal terminal  2  is preferably about 50 to 1,000 μm, and more preferably about 70 to 800 μm. The length of the metal terminal  2  is preferably about 1 to 200 mm, and more preferably about 3 to 150 mm. The width of the metal terminal  2  is preferably about 1 to 200 mm, and more preferably about 3 to 150 mm. 
     [Power Storage Device Packaging Material  3 ] 
     The power storage device packaging material  3  is, for example, a power storage device packaging material having a laminated structure formed of a laminate sequentially having at least a base material layer  31 , the barrier layer  33 , and the heat-sealable resin layer  35 .  FIG.  6    shows one embodiment of the cross-sectional structure of the power storage device packaging material  3 , in which the base material layer  31 , an optional adhesive agent layer  32 , the barrier layer  33 , an optional adhesive layer  34 , and the heat-sealable resin layer  35  are sequentially laminated. In the power storage device packaging material  3 , the base material layer  31  is the outermost layer, and the heat-sealable resin layer  35  is the innermost layer. During the assembly of a power storage device, the heat-sealable resin layers  35  positioned on the periphery of the power storage device element  4  are brought into surface contact and heat-sealed with each other to hermetically seal the power storage device element  4 , such that the power storage device element  4  is sealed. While  FIGS.  1  to  3    illustrate the power storage device  10  that uses the embossed-type power storage device packaging material  3  molded by embossing molding, for example, the power storage device packaging material  3  may also be of a pouched type that is not molded. The pouched type includes a three-side seal type, a four-side seal type, and a pillow type, and any of these types may be used. 
     While the thickness of the laminate constituting the power storage device packaging material  3  is not limited, the upper limit is preferably about 180 μm or less, about 160 μm or less, about 155 μm or less, about 140 μm or less, about 130 μm or less, or about 120 μm or less, from the viewpoint of reducing costs, improving the energy density, and the like. On the other hand, the lower limit is preferably about 35 μm or more, about 45 μm or more, about 60 μm or more, or about 80 μm or more, from the viewpoint of maintaining the function of the power storage device packaging material  3  to protect the power storage device element  4 . Preferred ranges include from about 35 to 180 μm, from about 35 to 160 μm, from about 35 to 155 μm, from about 35 to 140 μm, from about 35 to 130 μm, from about 35 to 120 μm, from about 45 to 180 μm, from about 45 to 160 μm, from about 45 to 155 μm, from about 45 to 140 μm, from about 45 to 130 μm, from about 45 to 120 μm, from about 60 to 180 μm, from about 60 to 160 μm, from about 60 to 155 μm, from about 60 to 140 μm, from about 60 to 130 μm, from about 60 to 120 μm, from about 80 to 180 μm, from about 80 to 160 μm, from about 80 to 155 μm, from about 80 to 140 μm, from about 80 to 130 μm, and from about 80 to 120 μm. 
     (Base Material Layer  31 ) 
     In the power storage device packaging material  3 , the base material layer  31  is a layer that functions as the base material of the power storage device packaging material, and forms the outermost layer side. 
     The material that forms the base material layer  31  is not limited as long as it has insulation properties. Examples of the material that forms the base material layer  31  include polyesters, polyamides, epoxy, acrylic resins, fluororesins, polyurethanes, silicone resins, phenol, polyetherimides, polyimides, and mixtures or copolymers thereof. A polyester, such as polyethylene terephthalate or polybutylene terephthalate, which has the advantage of having excellent electrolytic solution resistance, and being unlikely to cause whitening or the like due to attachment of the electrolytic solution, is suitably used as the material that forms the base material layer  31 . Moreover, a polyamide film, which has excellent stretchability, and can prevent whitening due to cracking of the resin in the base material layer  31  during molding, is suitably used as the material that forms the base material layer  31 . 
     The base material layer  31  may be formed of a uniaxially or biaxially stretched resin film, or may be formed of an unstretched resin film. Among the above, a uniaxially or biaxially stretched resin film, particularly a biaxially stretched resin film, which has improved heat resistance through oriented crystallization, is suitably used as the base material layer  31 . 
     Preferred among the above as the resin film that forms the base material layer  31  are nylons and polyesters, and more preferred are biaxially stretched nylons and biaxially stretched polyesters. 
     The base material layer  31  can also be laminated with a resin film made of a different material, in order to improve the pinhole resistance, and the insulation properties when used as a packaging material for a power storage device. Specific examples include a multilayer structure in which a polyester film and a nylon film are laminated, and a multilayer structure in which a biaxially stretched polyester and a biaxially stretched nylon are laminated. When the base material layer  31  has a multilayer structure, the resin films may be bonded with an adhesive, or may be directly laminated without an adhesive. Examples of methods of bonding the resin films without an adhesive include methods in which the resin films are bonded in a heat-melted state, such as a co-extrusion method, a sandwich lamination method, and a thermal lamination method. 
     The base material layer  31  may be subjected to a friction-reducing treatment beforehand to improve moldability. When the base material layer  31  is subjected to a friction-reducing treatment, the coefficient of friction of the surface of the base material layer  31  is 1.0 or less, for example, although not limited thereto. Examples of the friction-reducing treatment of the base material layer  31  include matting treatment, formation of a thin film layer of a slipping agent, and a combination thereof. 
     The thickness of the base material layer  31  is, for example, about 10 to 50 μm, and preferably about 15 to 30 μm. 
     (Adhesive Agent Layer  32 ) 
     In the power storage device packaging material  3 , the adhesive agent layer  32  is a layer that is optionally disposed on the base material layer  31  to impart adhesion to the base material layer  31 . That is, the adhesive agent layer  32  is provided between the base material layer  31  and the barrier layer  33 . 
     The adhesive agent layer  32  is formed of an adhesive capable of bonding the base material layer  31  and the barrier layer  33 . The adhesive to be used for forming the adhesive agent layer  32  may be a two-liquid curable adhesive or a one-liquid curable adhesive. The adhesion mechanism of the adhesive used for forming the adhesive agent layer  32  is not limited, and may be any of a chemical reaction type, a solvent volatilization type, a heat melting type, a heat pressing type, and the like. 
     Preferred examples of the resin component of the adhesive that can be used to form the adhesive agent layer  32  include a polyurethane-based two-liquid curable adhesive; and a polyamide, a polyester, or a blend resin of any of these resins and a modified polyolefin, from the viewpoint of having excellent extensibility, excellent durability and yellowing-inhibiting action under high-humidity conditions, excellent thermal degradation-inhibiting action during heat-sealing, and the like, and effectively inhibiting delamination by preventing a decrease in the lamination strength between the base material layer  31  and the barrier layer  33 . 
     The adhesive agent layer  32  may be multilayered with different adhesive components. When the adhesive agent layer  32  is to be multilayered with different adhesive components, from the viewpoint of improving the lamination strength between the base material layer  31  and the barrier layer  33 , it is preferred to select a resin having excellent adhesion to the base material layer  31  as the adhesive component to be disposed on the base material layer  31  side, and select an adhesive component having excellent adhesion to the barrier layer  33  as the adhesive component to be disposed on the barrier layer  33  side. When the adhesive agent layer  32  is to be multilayered with different adhesive components, specific examples of preferred adhesive components to be disposed on the barrier layer  33  side include acid-modified polyolefins, metal-modified polyolefins, mixed resins of polyesters and acid-modified polyolefins, and resins containing copolyesters. 
     The thickness of the adhesive agent layer  32  is, for example, about 0.5 to 50 μm, and preferably about 1 to 25 μm. 
     (Barrier Layer  33 ) 
     In the power storage device packaging material  3 , the barrier layer  33  is a layer that functions to improve the strength of the power storage device packaging material, and prevent the ingress of water vapor, oxygen, light, and the like into the power storage device. The barrier layer  33  is preferably a metal layer, that is, a layer formed of a metal. Specific examples of the metal constituting the barrier layer  33  include aluminum, stainless steel, and titanium, with aluminum being preferred. The barrier layer  33  may be formed of, for example, a metal foil or a vapor-deposited metal film, a vapor-deposited inorganic oxide film, a vapor-deposited carbon-containing inorganic oxide film, or a film provided with any of these vapor-deposited films. The barrier layer  33  is preferably formed of a metal foil, and more preferably formed of an aluminum foil. From the viewpoint of preventing the occurrence of creases and pinholes in the barrier layer  33  during the production of the power storage device packaging material, the barrier layer is still more preferably formed of a soft aluminum foil, for example, annealed aluminum (JIS H4160: 1994 A8021 H-O, JIS H4160: 1994 A8079 H-O, JIS H4000: 2014 A8021 P-O, and JIS H4000: 2014 A8079 P-O). 
     The thickness of the barrier layer  33  is preferably about 10 to 200 μm, and more preferably about 20 to 100 μm, from the viewpoint of making the occurrence of pinholes less likely during molding, while reducing the thickness of the power storage device packaging material. 
     Preferably, at least one surface, preferably both surfaces, of the barrier layer  33  is/are subjected to a chemical conversion treatment, in order to stabilize the adhesiveness, and prevent dissolution or corrosion, for example. As used herein, the chemical conversion treatment refers to a treatment for forming a corrosion-resistant film on a surface of the barrier layer. 
     [Adhesive Layer  34 ] 
     In the power storage device packaging material  3 , the adhesive layer  34  is a layer that is optionally provided between the barrier layer  33  and the heat-sealable resin layer  35 , in order to strongly bond the heat-sealable resin layer  35 . 
     The adhesive layer  34  is formed of an adhesive capable of bonding the barrier layer  33  and the heat-sealable resin layer  35 . While the composition of the adhesive used for forming the adhesive layer is not limited, it is, for example, a resin composition containing an acid-modified polyolefin. Examples of the acid-modified polyolefin include the same acid-modified polyolefins as those mentioned as the first polyolefin layer  12   a  and the second polyolefin layer  12   b.    
     The thickness of the adhesive layer  34  is, for example, about 1 to 40 μm, and preferably about 2 to 30 μm. 
     [Heat-Sealable Resin Layer  35 ] 
     In the power storage device packaging material  3 , the heat-sealable resin layer  35  is a layer that corresponds to the innermost layer, and is heat-sealed with another heat-sealable resin layer during the assembly of a power storage device to hermetically seal the power storage device element. 
     As described above, the absolute value of the difference between the melting peak temperature mp 1  of the second polyolefin layer  12   b  of the adhesive film  1  for a metal terminal and the melting peak temperature mp 3  of the heat-sealable resin layer  35  of the power storage device packaging material  3  to which the adhesive film  1  for a metal terminal of the present disclosure is applied is preferably about 0 to 5° C. or about 0 to 3° C. The smaller the absolute value of the difference between the melting peak temperatures is (that is, the closer the absolute value of the difference is to 0° C.), the more easily the adhesion between the second polyolefin layer  12   b  and the heat-sealable resin layer  35  can be increased because the second polyolefin resin layer  12   b  and the heat-sealable resin layer  35  of the power storage device packaging material  3  melt together during heat-sealing of the power storage device packaging materials with the metal terminal with the adhesive film for a metal terminal attached thereto interposed therebetween. 
     While the resin component to be used as the heat-sealable resin layer  35  is not limited as long as it can be heat-sealed, examples include a polyolefin and a cyclic polyolefin. 
     Furthermore, as described above, the absolute value of the difference between a melt mass-flow rate (MFR) T 2  of the second polyolefin layer  12   b  of the adhesive film  1  for a metal terminal and a melt mass-flow rate (MFR) T 4  of the heat-sealable resin layer  35  of the power storage device packaging material  3  to which the adhesive film  1  for a metal terminal of the present disclosure is applied is preferably about 0 to 5 g/10 min or about 0 to 3 g/10 min. The smaller the absolute value of the difference between the melt mass-flow rate (MFR) T 4  and the melt mass-flow rate (MFR) T 2  is (that is, the closer the absolute value of the difference is to 0 g/10 min), the more easily the adhesion between the second polyolefin layer  12   b  and the heat-sealable resin layer  35  can be increased because the second polyolefin resin layer  12   b  and the heat-sealable resin layer  35  of the power storage device packaging material  3  melt together during heat-sealing of the power storage device packaging materials  3  with the metal terminal with the adhesive film for a metal terminal attached thereto interposed therebetween. 
     Specific examples of the polyolefin include polyethylene, such as low-density polyethylene, medium-density polyethylene, high-density polyethylene, and linear low-density polyethylene; crystalline or amorphous polypropylene, such as homopolypropylene, block copolymers of polypropylene (for example, block copolymers of propylene and ethylene), and random copolymers of polypropylene (for example, random copolymers of propylene and ethylene); and terpolymers of ethylene-butene-propylene. Preferred among these polyolefins are polyethylene and polypropylene. 
     The cyclic polyolefin is a copolymer of an olefin and a cyclic monomer. Examples of the olefin as a constituent monomer of the cyclic polyolefin include ethylene, propylene, 4-methyl-1-pentene, butadiene, and isoprene. Examples of the cyclic monomer as a constituent monomer of the cyclic polyolefin include cyclic alkenes, such as norbornene; specifically, cyclic dienes, such as cyclopentadiene, dicyclopentadiene, cyclohexadiene, and norbornadiene. Preferred among these polyolefins are cyclic alkenes, and more preferred is norbornene. Examples of constituent monomers also include styrene. 
     Preferred among these resin components are a crystalline or amorphous polyolefin, a cyclic polyolefin, and a blend polymer thereof; and more preferred are polyethylene, polypropylene, a copolymer of ethylene and norbornene, and a blend polymer of two or more of the above. 
     The heat-sealable resin layer  35  may be formed using one resin component alone, or may be formed using a blend polymer obtained by combining two or more resin components. Furthermore, the heat-sealable resin layer  35  may be formed of only one layer, or may be formed of two or more layers using the same resin component or different resin components. It is particularly preferred that the second polyolefin layer  12   b  and the heat-sealable resin layer  35  be formed of the same resin, which improves the adhesion between these layers. 
     The melting peak temperature of the heat-sealable resin layer  35  is, for example, about 120° C. or more, preferably about 125° C. or more, still more preferably about 130° C. or more, even more preferably 130° C. or more, and still more preferably 135° C. or more, while it is preferably about 160° C. or less, and more preferably 155° C. or less. Preferred ranges of the melting peak temperature of the heat-sealable resin layer  35  include from about 120 to 160° C., from about 120 to 155° C., from about 125 to 160° C., from about 125 to 155° C., from about 130 to 160° C., from about 130 to 155° C., from about 135 to 160° C., from about 135 to 155° C., from about 140 to 160° C., and from about 140 to 155° C. As described above, when the melting peak temperature of the second polyolefin layer  12   b  disposed on the power storage device packaging material  3  side and the melting peak temperature of the heat-sealable resin layer  35  of the power storage device packaging material  3  are both 130° C. or more, the metal terminal of the power storage device and the heat-sealable resin layer of the power storage device packaging material can adhere to each other until the power storage device is heated to a high temperature (for example, 100 to 130° C., preferably 110 to 130° C., particularly preferably 120 to 130° C.), and the power storage device can open at the position of the adhesive film for a metal terminal to release a gas generated inside the power storage device to the outside when the power storage device is heated to the high temperature (for example, 100 to 130° C., preferably 110 to 130° C., particularly preferably 120 to 130° C.). 
     While the thickness of the heat-sealable resin layer  35  is not limited, it is about 2 to 2,000 μm, preferably about 5 to 1,000 μm, and more preferably about 10 to 500 μm. The thickness of the heat-sealable resin layer  35  is, for example, about 100 μm or less, preferably about 85 μm or less, and more preferably about 15 to 85 μm. For example, when the thickness of the below-described adhesive layer  5  is 10 μm or more, the thickness of the heat-sealable resin layer  4  is preferably about 85 μm or less, and more preferably about 15 to 45 μm. For example, when the thickness of the below-described adhesive layer  5  is less than 10 μm, or when the adhesive layer  5  is not provided, the thickness of the heat-sealable resin layer  4  is preferably about 20 μm or more, and more preferably about 35 to 85 μm. 
     2. Power Storage Device 
     The power storage device  10  of the present disclosure comprises the power storage device element  4  comprising at least a positive electrode, a negative electrode, and an electrolyte, the power storage device packaging material  3  for sealing the power storage device element  4 , and the metal terminal  2  electrically connected to each of the positive electrode and the negative electrode and protruding outside the power storage device packaging material  3 . In the power storage device  10  of the present disclosure, the adhesive film  1  for a metal terminal of the present disclosure is interposed between the metal terminal  2  and the power storage device packaging material  3 . That is, the power storage device  10  of the present disclosure may be produced by a method comprising the step of interposing the adhesive film  1  for a metal terminal of the present disclosure between the metal terminal  2  and the power storage device packaging material  3 . 
     Specifically, the power storage device element  4  including at least a positive electrode, a negative electrode, and an electrolyte is covered with the power storage device packaging material  3  such that, in a state wherein the metal terminal  2  connected to each of the positive electrode and the negative electrode protrudes outside, the adhesive film  1  for a metal terminal of the present disclosure is interposed between the metal terminal  2  and the heat-sealable resin layer  35 , and a flange of the power storage device packaging material (region where the heat-sealable resin layer  35  is brought into contact with the other heat-sealable resin layer  35 , i.e., the peripheral region  3   a  of the power storage device packaging material) can be formed on the periphery of the power storage device element  4 , and then the heat-sealable resin layers  35  in the flange are heat-sealed to hermetically seal the power storage device element. As a result, the power storage device  10  that uses the power storage device packaging material  3  is provided. When the power storage device packaging material  3  is used to house the power storage device element  4 , it is used such that the heat-sealable resin layer  35  of the power storage device packaging material  3  is positioned on the inner side (surface in contact with the power storage device element  4 ) thereof. 
     Moreover, the power storage device  10  of the present disclosure may be a power storage device comprising a power storage device element comprising at least a positive electrode, a negative electrode, and an electrolyte, a power storage device packaging material for sealing the power storage device element, and a metal terminal electrically connected to each of the positive electrode and the negative electrode and protruding outside the power storage device packaging material, wherein an adhesive film for a metal terminal is interposed between the metal terminal and the power storage device packaging material, the adhesive film for a metal terminal comprises a laminate sequentially including a first polyolefin layer disposed on the metal terminal side, a base material, and a second polyolefin layer disposed on the power storage device packaging material side, the laminate has a first adhesive layer between the first polyolefin layer and the base material, has a second adhesive layer between the second polyolefin layer and the base material, or has both the first adhesive layer and the second adhesive layer, and the power storage device opens from a position where the first adhesive layer or the second adhesive layer of the adhesive film for a metal terminal is laminated, in an environment at a temperature of 100° C. or more and 130° C. or less. That is, in the power storage device, as long as the power storage device opens from the position where the first adhesive layer  13   a  or the second adhesive layer  13   b  of the adhesive film  1  for a metal terminal is laminated, the melting peak temperature of the base material  11  may not necessarily be 135° C. or more, and the melting peak temperature of at least one of the first adhesive layer  12   a  and the second adhesive layer  12   b  may not necessarily be 100° C. or less. As in the adhesive film  1  for a metal terminal of the present disclosure as described above, when the melting peak temperature of the base material  11  is 135° C. or more, and the melting peak temperature of at least one of the first adhesive layer  13   a  and the second adhesive layer  13   b  is 100° C. or less, the power storage device can be opened favorably from the position where the first adhesive layer  13   a  or the second adhesive layer  13   b  of the adhesive film  1  for a metal terminal is laminated, in an environment at a temperature of 100° C. or more and 130° C. or less, preferably 120° C. or more and 130° C. or less. 
     Furthermore, the power storage device  10  of the present disclosure may be a power storage device comprising the power storage device element comprising at least a positive electrode, a negative electrode, and an electrolyte, a power storage device packaging material for sealing the power storage device element, and the metal terminal electrically connected to each of the positive electrode and the negative electrode and protruding outside the power storage device packaging material, wherein an adhesive film for a metal terminal is interposed between the metal terminal and the power storage device packaging material, the adhesive film for a metal terminal comprises a laminate sequentially including a first polyolefin layer disposed on the metal terminal side, a base material, and a second polyolefin layer disposed on the power storage device packaging material side, the laminate has a first adhesive layer between the first polyolefin layer and the base material, has a second adhesive layer between the second polyolefin layer and the base material, or has both the first adhesive layer and the second adhesive layer, the base material has a melting peak temperature of 135° C. or more, at least one of the first adhesive layer and the second adhesive layer has a melting peak temperature of 100° C. or less, the power storage device packaging material comprises a laminate including at least a base material layer, a barrier layer, and a heat-sealable resin layer, and the heat-sealable resin layer has a melting peak temperature of 130° C. or more. That is, in the power storage device, the melting peak temperature of the base material of the adhesive film for a metal terminal is 135° C. or more, and the melting peak temperature of the second polyolefin layer disposed on the power storage device packaging material side and the melting peak temperature of the heat-sealable resin layer of the power storage device packaging material are both 130° C. or more. Because of these features of the power storage device, the metal terminal of the power storage device and the heat-sealable resin layer of the power storage device packaging material can adhere to each other until the power storage device is heated to a high temperature (for example, 100 to 130° C., preferably 110 to 130° C., particularly preferably 120 to 130° C.), and the power storage device can open at the position of the adhesive film for a metal terminal to release a gas generated inside the power storage device to the outside when the power storage device is heated to the high temperature (for example, 100 to 130° C., preferably 110 to 130° C., particularly preferably 120 to 130° C.). 
     The power storage device packaging material of the present disclosure is suitable for use in power storage devices, such as batteries (including condensers and capacitors). The power storage device packaging material of the present disclosure may be used for either primary batteries or secondary batteries, preferably secondary batteries. While the type of secondary batteries to which the power storage device packaging material of the present disclosure is applied is not limited, examples include lithium ion batteries, lithium ion polymer batteries, all-solid-state batteries, lead storage batteries, nickel-hydrogen storage batteries, nickel-cadmium storage batteries, nickel-iron storage batteries, nickel-zinc storage batteries, silver oxide-zinc storage batteries, metal-air batteries, polyvalent cation batteries, condensers, and capacitors. Among these secondary batteries, preferred secondary batteries to which the power storage device packaging material of the present disclosure is applied include lithium ion batteries and lithium ion polymer batteries. 
     EXAMPLES 
     The present disclosure will be hereinafter described in detail with reference to examples and comparative examples; however, the present disclosure is not limited to the examples. 
     Example 1 
     &lt;Production of Adhesive Film for Metal Terminal&gt; 
     With reference to WO 2015/033703, a maleic anhydride-modified propylene-butene copolymer (acid value 20 mg KOH/g-resin, weight average molecular weight 70,000) as an acid-modified polyolefin was produced. Next, a 10% solution of the copolymer in methylcyclohexane was prepared, and 1.5% of a polyfunctional isocyanate compound (TAP100) from Asahi Kasei was added to give an adhesive. Next, an unstretched polypropylene film (CPP, homopolypropylene, thickness 40 μm, melting peak temperature 163° C.) was prepared as a base material. The adhesive (resin composition containing maleic anhydride-modified polypropylene and a curing agent) was applied at an amount of 2 g/m 2  to one surface of the base material, and a maleic anhydride-modified polypropylene film (PPa, thickness 20 μm, melting peak temperature 140° C.) was laminated thereon at a temperature of 120° C., using a laminator. Then, a maleic anhydride-modified polypropylene film (PPa, thickness 20 μm, melting peak temperature 140° C.) was similarly laminated to the opposite surface of the base material. The resulting laminate was aged at 80° C. for 72 hours to give an adhesive film for a metal terminal in which a first polyolefin layer (PPa layer, thickness 20 μm)/a first adhesive layer (cured PPa layer, thickness 2 μm)/a base material (CPP layer, thickness 40 μm)/a second adhesive layer (cured PPa layer, thickness 2 μm)/a second polyolefin layer (PPa layer, thickness 20 μm) were sequentially laminated. 
     &lt;Measurement of Melting Peak Temperature of Adhesive Layer&gt; 
     The adhesive was applied to a thickness of 100 μm and dried, and then cured by heating at 80° C. for 72 hours. The melting peak temperature was measured in accordance with JIS K 7121: 2012 (Testing Methods for Transition Temperatures of Plastics) (Supplement 1 to JIS K 7121: 1987)). The measurement was performed using a differential scanning calorimeter (DSC, the differential scanning calorimeter Q200 from TA Instruments Inc.). The measurement sample was held at −50° C. for 15 minutes and then heated from −50° C. to 210° C. at a heating rate of 10° C./min to measure the first melting peak temperature P (° C.), and thereafter held at 210° C. for 10 minutes. Next, the measurement sample was cooled from 210° C. to −50° C. at a cooling rate of 10° C./min and held for 15 minutes. The measurement sample was further heated from −50° C. to 210° C. at a heating rate of 10° C./min to measure the second melting peak temperature Q (° C.). The flow rate of nitrogen gas was 50 ml/min. Using the above procedure, the first measured melting peak temperature P (° C.) and the second measured melting peak temperature Q (° C.) were obtained, and the first measured melting peak temperature was adopted as the melting peak temperature. The measured result is shown in Table 1. 
     &lt;Measurement of Surface Hardness of Base Material&gt; 
     The Martens hardness was adopted as the surface hardness of the base material. The unstretched polypropylene film (CPP) used as the base material was bonded to one side of a glass slide (76 mm×26 mm×1 mm) with a double-faced adhesive tape to provide a measurement sample. Next, a hot stage was mounted on an ultra-microhardness tester (for example, HM2000 from Fischer Instruments) equipped with a Vickers indenter, and the sample was heated by the hot stage set at a stage temperature of 110° C. for 5 minutes. Next, the indenter was pressed into the base material-side surface of the measurement sample to a depth of 1 μm at an indentation rate of 0.1 μm/s to measure the surface hardness. Ten measurements were taken, and the average value was adopted. The measured result is shown in Table 1. 
     &lt;Method of Opening Test&gt; 
     An aluminum sheet with a width of 4 mm, a thickness of 70 μm, and a length of 40 mm was used as a metal terminal. The adhesive film for a metal terminal was cut into a size of 1 cm in length and 1 cm in width. Next, as shown in the schematic diagram of  FIG.  5   , the metal terminal was inserted between the two pieces of the adhesive film for a metal terminal such that the long sides of the metal terminal and the long sides of the adhesive film for a metal terminal were orthogonal to each other, and the pieces of the adhesive film for a metal terminal were heat-sealed to the metal terminal at a pressure of 0.2 MPa and a temperature of 180° C. for a time of 3 seconds to produce the metal terminal with the adhesive film for a metal terminal attached thereto. Separately, a power storage device packaging material with an entire thickness of 121 μm, composed of a laminate sequentially having a base material layer (PET (thickness 12 μm)/an adhesive (thickness 2 μm)/nylon (thickness 15 μm))/an adhesive agent layer (thickness 2 μm)/a barrier layer (aluminum alloy foil, thickness 40 μm)/an adhesive layer (maleic anhydride-modified polypropylene, thickness 25 μm)/a heat-sealable resin layer (polypropylene, melting peak temperature 150° C., thickness 25 μm), was prepared and then cut into a size of 8 cm×19 cm. Next, two metal terminals with the adhesive film for a metal terminal attached thereto were placed on a short side of the power storage device packaging material at a spacing of 2 cm therebetween, and the long sides of the power storage device packaging material were folded over. Next, the short side of the power storage device packaging material having the metal terminals with the adhesive film for a metal terminal attached thereto was heat-sealed at a pressure of 0.5 MPa, a temperature of 190° C., and a seal width of 3 mm. Then, one long side of the power storage device packaging material was similarly heat-sealed, and 1 g of water was placed in the resulting bag-shaped sample. Thereafter, the open side (long side) of the power storage device packaging material was similarly heat-sealed to give a test sample with water hermetically sealed in. A thermocouple was attached to the metal terminal region of the test sample, and the test sample was placed in an oven and heated from room temperature (25° C.) to 140° C. at a heating rate of 6° C./minute. If the test sample opened at a temperature of 120° C. or more and 130° C. or less, it was evaluated as “A”; if the test sample opened at a temperature of 100° C. or more and less than 120° C., it was evaluated as “B”; and if the test sample opened at a temperature above 130° C. and 140° C. or less, or if the test sample did not open even at a temperature above 130° C. and 140° C. or less, it was evaluated as “C”. The result is shown in Table 1. 
     &lt;Evaluation of Insulation Properties&gt; 
     The power storage device packaging material prepared in &lt;Opening Test&gt; above was cut into pieces with a size of 1 cm×4 cm. Next, the metal terminal with the adhesive film for a metal terminal attached thereto produced above was disposed between the two pieces of the power storage device packaging material such that the heat-sealable resin layers were opposed to each other. Next, each of the metal terminal and the aluminum alloy foil of the power storage device packaging material was connected to a resistivity meter. While a voltage of 100 V was being applied in this state by the resistivity meter, the metal terminal with the adhesive film for a metal terminal attached thereto and the power storage device packaging material were heat-sealed with a heat-seal bar with a width of 7 mm and at 190° C. (pressure 0.5 MPa, 10 sec). During the heat-sealing, if the value of the resistivity meter was 200 MΩ or more, the insulation properties were evaluated as A, and if the value of the resistivity meter was less than 200 MΩ, the insulation properties were evaluated as C. The result is shown in Table 1. 
     Example 2 
     A sample was produced and evaluated as in Example 1, except that the acid-modified polyolefin for use as the adhesive was a maleic anhydride-modified propylene-butene copolymer (acid value 15 mg KOH/g-resin, weight average molecular weight 40,000), and the melting peak temperature of each of the first adhesive layer and the second adhesive layer was 85° C. 
     Example 3 
     A sample was prepared and evaluated as in Example 1, except that the unstretched polypropylene film of the base material was replaced by an unstretched polypropylene film with a melting peak temperature of 140° C. and a surface hardness at 110° C. of 16 N/mm 2 . 
     Example 4 
     A sample (adhesive film for a metal terminal in which a first polyolefin layer (PPa layer, thickness 20)/a first adhesive layer (cured PPa layer, thickness 2 μm)/a base material (CPP layer, thickness 40 μm)/a second polyolefin layer (PPa layer, thickness 20 μm) were sequentially laminated) was produced and evaluated as in Example 1, except that the adhesive was used on the metal terminal side of the base material, and not used on the packaging material side of the base material, and the base material and the maleic anhydride-modified polypropylene film (PPa, thickness 20 μm, melting peak temperature 140° C.) were heat-sealed in a vacuum chamber at 190° C. for 15 seconds. 
     Example 5 
     A sample (a first polyolefin layer (PPa layer, thickness 20 μm)/a base material (CPP layer, thickness 40 μm)/a second adhesive layer (cured PPa layer, thickness 2 μm)/a second polyolefin layer (PPa layer, thickness 20 μm) was produced and evaluated as in Example 1, except that the adhesive was used on the packaging material side of the base material, and not used on the metal terminal side of the base material, and the base material and the maleic anhydride-modified polypropylene film (PPa, thickness 20 μm, melting peak temperature 140° C.) were heat-sealed in a vacuum chamber at 190° C. for 15 seconds. 
     Comparative Example 1 
     A sample (a first polyolefin layer (PPa layer, thickness 20 μm)/a base material (CPP layer, thickness 40 μm)/a second polyolefin layer (PPa layer, thickness 20 μm) was produced and evaluated as in Example 1, except that the adhesive was not used, and both surfaces of the base material were heat-sealed to maleic anhydride-modified polypropylene films (PPa, thickness 20 μm, melting peak temperature 140° C.) in a vacuum chamber at 190° C. for 15 seconds. 
     Comparative Example 2 
     A sample was produced and evaluated as in Example 1, except that the unstretched polypropylene film of the base material was replaced by an unstretched polypropylene film with a melting peak temperature of 133° C. and a surface hardness at 110° C. of 12 N/mm 2 . 
     Comparative Example 3 
     A sample was produced and evaluated as in Example 1, except that the acid-modified polyolefin for use as the adhesive was a maleic anhydride-modified propylene-butene copolymer (acid value 7 mg KOH/g-resin, weight average molecular weight 180,000), and the melting peak temperature of each of the first adhesive layer and the second adhesive layer was 105° C. 
     Comparative Example 4 
     A sample was produced and evaluated as in Example 1, except that the acid-modified polyolefin for use as the adhesive was a maleic anhydride-modified propylene-butene copolymer (acid value 7 mg KOH/g-resin, weight average molecular weight 180,000), the melting peak temperature of each of the first adhesive layer and the second adhesive layer was 105° C., and the unstretched polypropylene film of the base material was replaced by an unstretched polypropylene film with a melting peak temperature of 133° C. and a surface hardness at 110° C. of 12 N/mm 2 . 
     
       
         
           
               
               
               
             
               
                   
                 TABLE 1 
               
             
            
               
                   
                   
               
               
                   
                 Melting Peak Temperature (° C.) 
                   
               
            
           
           
               
               
               
               
               
               
               
               
               
            
               
                   
                 Metal 
                   
                   
                   
                   
                 Surface 
                   
                   
               
               
                   
                 Terminal- 
                   
                   
                   
                   
                 Hardness 
               
               
                   
                 Side 
                 Packaging- 
                   
                   
                   
                 (N/mm 2 ) 
               
               
                   
                 First 
                 Side 
                   
                 First 
                 Second 
                 at 110° C. 
                 Evaluation of 
                 Evaluation of 
               
               
                   
                 Polyolefin 
                 Second 
                 Base 
                 Adhesive 
                 Adhesive 
                 of Base 
                 Opening 
                 Insulation 
               
               
                   
                 Layer 
                 Polyolefin 
                 Material 
                 Layer 
                 Layer 
                 Material 
                 Temperature 
                 Properties 
               
               
                   
                   
               
            
           
           
               
               
               
               
               
               
               
               
               
            
               
                 Example 1 
                 140 
                 140 
                 163 
                 97 
                 97 
                 39 
                 A 
                 A 
               
               
                 Example 2 
                 140 
                 140 
                 163 
                 85 
                 85 
                 39 
                 A 
                 A 
               
               
                 Example 3 
                 140 
                 140 
                 140 
                 97 
                 97 
                 16 
                 A 
                 A 
               
               
                 Example 4 
                 140 
                 140 
                 163 
                 None 
                 97 
                 39 
                 A 
                 A 
               
               
                 Example 5 
                 140 
                 140 
                 163 
                 97 
                 None 
                 39 
                 A 
                 A 
               
               
                 Comparative 
                 140 
                 140 
                 163 
                 None 
                 None 
                 39 
                 C 
                 A 
               
               
                 Example 1 
               
               
                 Comparative 
                 140 
                 140 
                 133 
                 97 
                 97 
                 12 
                 C 
                 C 
               
               
                 Example 2 
               
               
                 Comparative 
                 140 
                 140 
                 163 
                 105  
                 105 
                 39 
                 C 
                 A 
               
               
                 Example 3 
               
               
                 Comparative 
                 140 
                 140 
                 133 
                 105  
                 105 
                 12 
                 C 
                 C 
               
               
                 Example 4 
               
               
                   
               
            
           
         
       
     
     As described above, the present disclosure provides embodiments of the invention as set forth below: 
     Item 1. An adhesive film for a metal terminal, which is to be interposed between a metal terminal electrically connected to an electrode of a power storage device element and a power storage device packaging material for sealing the power storage device element, 
     wherein the adhesive film for a metal terminal comprises a laminate sequentially including a first polyolefin layer disposed on the metal terminal side, a base material, and a second polyolefin layer disposed on the power storage device packaging material side, 
     the laminate has a first adhesive layer between the first polyolefin layer and the base material, has a second adhesive layer between the second polyolefin layer and the base material, or has both the first adhesive layer and the second adhesive layer, 
     the base material has a melting peak temperature of 135° C. or more, and 
     at least one of the first adhesive layer and the second adhesive layer has a melting peak temperature of 100° C. or less. 
     Item 2. The adhesive film for a metal terminal according to item 1, wherein the base material has a surface hardness of 15 N/mm 2  or more, as measured in an environment at a temperature of 110° C. 
     Item 3. The adhesive film for a metal terminal according to item 1 or 2, wherein each of the first adhesive layer and the second adhesive layer has a melting peak temperature of 100° C. or less. 
     Item 4. The adhesive film for a metal terminal according to any one of items 1 to 3, wherein at least one of the first polyolefin layer and the second polyolefin layer contains an acid-modified polyolefin. 
     Item 5. The adhesive film for a metal terminal according to any one of items 1 to 4, wherein each of the first adhesive layer and the second adhesive layer is a cured product of a resin composition containing an acid-modified polyolefin and a curing agent. 
     Item 6. The adhesive film for a metal terminal according to any one of items 1 to 5, wherein the base material contains a polyolefin backbone. 
     Item 7. A method for producing an adhesive film for a metal terminal, which is to be interposed between a metal terminal electrically connected to an electrode of a power storage device element and a power storage device packaging material for sealing the power storage device element, 
     wherein the adhesive film for a metal terminal comprises a laminate sequentially including a first polyolefin layer disposed on the metal terminal side, a base material, and a second polyolefin layer disposed on the power storage device packaging material side, and 
     the laminate has a first adhesive layer between the first polyolefin layer and the base material, has a second adhesive layer between the second polyolefin layer and the base material, or has both the first adhesive layer and the second adhesive layer, 
     the method comprising the step of obtaining the laminate sequentially including the first polyolefin layer, the base material, and the second polyolefin layer, 
     wherein the base material has a melting peak temperature of 135° C. or more, and 
     at least one of the first adhesive layer and the second adhesive layer has a melting peak temperature of 100° C. or less. 
     Item 8. A metal terminal with an adhesive film for a metal terminal attached thereto, comprising the adhesive film for a metal terminal according to any one of items 1 to 6, wherein the adhesive film for a metal terminal is attached to the metal terminal. 
     Item 9. A power storage device comprising the power storage device element comprising at least a positive electrode, a negative electrode, and an electrolyte, the power storage device packaging material for sealing the power storage device element, and the metal terminal electrically connected to each of the positive electrode and the negative electrode and protruding outside the power storage device packaging material, 
     wherein the adhesive film for a metal terminal according to any one of items 1 to 6 is interposed between the metal terminal and the power storage device packaging material. 
     Item 10. A power storage device comprising the power storage device element comprising at least a positive electrode, a negative electrode, and an electrolyte, the power storage device packaging material for sealing the power storage device element, and the metal terminal electrically connected to each of the positive electrode and the negative electrode and protruding outside the power storage device packaging material, 
     wherein an adhesive film for a metal terminal is interposed between the metal terminal and the power storage device packaging material, 
     the adhesive film for a metal terminal comprises a laminate sequentially including a first polyolefin layer disposed on the metal terminal side, a base material, and a second polyolefin layer disposed on the power storage device packaging material side, 
     the laminate has a first adhesive layer between the first polyolefin layer and the base material, has a second adhesive layer between the second polyolefin layer and the base material, or has both the first adhesive layer and the second adhesive layer, and 
     the power storage device opens from a position where the first adhesive layer or the second adhesive layer of the adhesive film for a metal terminal is laminated, in an environment at a temperature of 100° C. or more and 130° C. or less. 
     Item 11. A power storage device comprising a power storage device element comprising at least a positive electrode, a negative electrode, and an electrolyte, a power storage device packaging material for sealing the power storage device element, and the metal terminal electrically connected to each of the positive electrode and the negative electrode and protruding outside the power storage device packaging material, 
     wherein an adhesive film for a metal terminal is interposed between the metal terminal and the power storage device packaging material, 
     the adhesive film for a metal terminal comprises a laminate sequentially including a first polyolefin layer disposed on the metal terminal side, a base material, and a second polyolefin layer disposed on the power storage device packaging material side, 
     the laminate has a first adhesive layer between the first polyolefin layer and the base material, has a second adhesive layer between the second polyolefin layer and the base material, or has both the first adhesive layer and the second adhesive layer, 
     the base material has a melting peak temperature of 135° C. or more, 
     at least one of the first adhesive layer and the second adhesive layer has a melting peak temperature of 100° C. or less, 
     the power storage device packaging material comprises a laminate including at least a base material layer, a barrier layer, and a heat-sealable resin layer, and 
     the heat-sealable resin layer has a melting peak temperature of 130° C. or more. 
     Item 12. A power storage device packaging material for use in a power storage device, 
     wherein the power storage device comprises a power storage device element comprising at least a positive electrode, a negative electrode, and an electrolyte, the power storage device packaging material for sealing the power storage device element, and the metal terminal electrically connected to each of the positive electrode and the negative electrode and protruding outside the power storage device packaging material, and wherein an adhesive film for a metal terminal is interposed between the metal terminal and the power storage device packaging material, and 
     the adhesive film for a metal terminal comprises a laminate sequentially including a first polyolefin layer disposed on the metal terminal side, a base material, and a second polyolefin layer disposed on the power storage device packaging material side, and the adhesive film for a metal terminal has a function of opening from a position where the first adhesive layer or the second adhesive layer of the adhesive film for a metal terminal is laminated, in an environment at a temperature of 100° C. or more and 130° C. or less, 
     the power storage device packaging material comprising a laminate including at least a base material layer, a barrier layer, and a heat-sealable resin layer, wherein the heat-sealable resin layer has a melting peak temperature that is 130° C. or more and higher than a melting peak temperature of the first polyolefin layer of the adhesive film for a metal terminal. 
     Item 13. A method for producing a power storage device comprising the power storage device element comprising at least a positive electrode, a negative electrode, and an electrolyte, the power storage device packaging material for sealing the power storage device element, and the metal terminal electrically connected to each of the positive electrode and the negative electrode and protruding outside the power storage device packaging material, 
     the method comprising the step of interposing the adhesive film for a metal terminal according to any one of items 1 to 6 between the metal terminal and the power storage device packaging material, and sealing the power storage device element with the power storage device packaging material. 
     REFERENCE SIGNS LIST 
     
         
           1 : adhesive film for a metal terminal 
           2 : metal terminal 
           3 : power storage device packaging material 
           3   a : peripheral region of power storage device packaging material 
           4 : power storage device element 
           10 : power storage device 
           11 : base material 
           12   a : first polyolefin layer 
           12   b : second polyolefin layer 
           13   a : first adhesive layer 
           13   b : second adhesive layer 
           31 : base material layer 
           32 : adhesive agent layer 
           33 : barrier layer 
           34 : adhesive layer 
           35 : heat-sealable resin layer