JP2016189303A - battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a battery having high reliability that can increase the static friction coefficient μa between the outer side surface of an insulation film and a battery case, and suppress a defect caused by increase of a constraint load Fc.SOLUTION: A battery 1 comprises a metallic rectangular parallelepiped battery case 10, an electrode body 20 housed in the battery case 10, and an insulating member 30 which is formed of an insulating film 31 and interposed between the battery case 10 and the electrode body 20 to insulate both the battery case and the electrode body from each other. In the insulating film 31, the three-dimensional average surface roughness SRaA of the outer surface 31a in contact with the battery case 10 satisfies SRaA≥0.15, and the three-dimensional average surface roughness SRaB of the inner surface 31b in contact with the electrode body 20 satisfies SRaB≥0.03 and satisfies SRaA≥SRaB.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a battery comprising a metal, rectangular parallelepiped battery case, an electrode body accommodated in the battery case, an insulating film, and an insulating member interposed between the battery case and the electrode body to insulate the two. About.

  Conventionally, in a battery in which an electrode body is housed in a rectangular battery case made of metal, an insulating member made of an insulating film is interposed between the battery case and the electrode body in order to electrically insulate between the battery case and the electrode body. It is known to let For example, Patent Document 1 discloses a battery case in which a flat wound electrode body is housed in an insulating member made of an insulating film in a bag shape, and further housed in a metal rectangular battery case. There is disclosed a battery in which a battery and an electrode body are insulated by an insulating member (see claims of FIG. 2, FIG. 2, FIG. 8, etc.).

JP 2010-287456 A

Generally, a battery for in-vehicle use is used in a state in which a battery case and an electrode body accommodated therein are pressed and restrained in the thickness direction thereof. This is because the electrode body is held so that the electrode body does not move in the battery case when an external impact is applied to the battery.
In the battery described above, the electrode body is held in the battery case via an insulating member (insulating film). In order to hold the electrode body, the battery is restrained in accordance with the smaller one of the static friction coefficient μa between the outer surface of the insulating film and the battery case and the static friction coefficient μb between the inner surface of the insulating film and the electrode body surface. It is necessary to set the load Fc. In addition, the smaller the static friction coefficient value of the battery, the larger the restraining load Fc needs to be set.

In addition, the static friction coefficient μa between the outer surface of the insulating film and the battery case and the static friction coefficient μb between the inner surface of the insulating film and the electrode body surface are found to be always smaller. (Μa <μb). The reason is considered as follows. That is, both the insulating film and the separator that forms the surface of the electrode body are made of resin and are soft and easily deformed. On the other hand, since the battery case is made of metal, it does not adhere to the insulating film unless it is subjected to a large restraining load Fc, and is easy to slide. For this reason, it is considered that the static friction coefficient μa between the outer surface of the insulating film and the battery case is smaller than the static friction coefficient μb between the inner surface of the insulating film and the electrode body surface.
Therefore, the battery having a smaller static friction coefficient μa between the outer surface of the insulating film and the battery case needs to increase the binding load Fc of the battery.

However, when the restraint load Fc of the battery is increased, as will be described later, a “high rate discharge cycle test” in which discharging at a large current value (for example, 35 C) and charging at a smaller current value (for example, 3 C) are repeated. It was found that the battery resistance greatly increased when the test was performed.
In addition, when the battery restraint load Fc is increased, when conductive foreign matter is mixed in the battery case for some reason during the manufacture of the battery, the conductive foreign matter penetrates the insulating film, and the battery case There is a high risk that a short circuit will occur between the electrode body and the electrode body. Further, the restraining member for restraining the battery is increased in size in order to increase the restraining load Fc of the battery.

  The present invention has been made in view of the current situation, and can increase the static friction coefficient μa between the outer surface of the insulating film and the battery case, and has high reliability in which problems associated with an increase in the binding load Fc of the battery are suppressed. An object is to provide a battery.

  One aspect of the present invention for solving the above problems includes a metal rectangular parallelepiped battery case, an electrode body accommodated in the battery case, and an insulating film, and the battery case and the electrode body. An insulating member that is interposed between and insulates the battery, wherein the insulating film has a three-dimensional average surface roughness SRaA of an outer surface in contact with the battery case satisfying SRaA ≧ 0.15, The battery has a three-dimensional average surface roughness SRaB on the inner surface in contact with the electrode body that satisfies SRaB ≧ 0.03 and SRaA ≧ SRaB.

  As a result of intensive studies by the inventors, the surface roughness (three-dimensional average surface roughness SRa) of both main surfaces of the insulating film is greatly related to the static friction coefficient μa between the outer surface of the insulating film and the battery case. I found out. Specifically, the three-dimensional average surface roughness SRaA of the outer surface in contact with the battery case in the insulating film is set to SRaA ≧ 0.15, and the three-dimensional average surface roughness of the inner surface in contact with the electrode body in the insulating film. It was found that when SRaB is set to SRaB ≧ 0.03 and SRaA ≧ SRaB, the static friction coefficient μa between the outer surface of the insulating film and the battery case increases.

  The reason is considered as follows. That is, when SRaA ≧ 0.15, SRaB ≧ 0.03, and SRaA ≧ SRaB, the electrolyte enters the small gap generated between the outer surface of the insulating film and the battery case. It becomes easy for the insulating film and the battery case to be in close contact with each other. For this reason, it is considered that the static friction coefficient μa between the outer surface of the insulating film and the battery case is increased, and the insulating film and the electrode body held on the inner side thereof are less likely to slip with respect to the battery case.

  On the other hand, when SRaA is small and SRaA <0.15 as in Comparative Example 1 described later, the static friction coefficient μa between the outer surface of the insulating film and the battery case is small. The reason is that SRaA is small, so that a gap is hardly formed between the outer surface of the insulating film and the battery case, and the electrolytic solution is difficult to enter. For this reason, it is considered that the insulating film and the battery case are hardly adhered to each other through the electrolytic solution, and the static friction coefficient μa is small. Therefore, SRaA ≧ 0.15 is required to increase the static friction coefficient μa.

  In addition, as in Comparative Example 2 described later, even when SRaA <SRaB, the static friction coefficient μa between the outer surface of the insulating film and the battery case is small. The reason is that when SRaA <SRaB, the electrolytic solution easily moves to the inner surface side (electrode body side) of the insulating film, and the electrolytic solution decreases on the outer surface side (battery case side) of the insulating film. It is considered that the static friction coefficient μa between the outer surface of the battery and the battery case does not increase. Therefore, in order to increase the static friction coefficient μa, it is necessary to satisfy SRaA ≧ SRaB.

It was also found that the static friction coefficient μa between the outer surface of the insulating film and the battery case was small even when SRaB was small and SRaB <0.03 as in Comparative Example 3 described later. Therefore, SRaB ≧ 0.03 is required to increase the static friction coefficient μa. In addition, when SRaB <0.03, there is little catch by the unevenness | corrugation of the inner surface of an insulating film, and it exists in the tendency for the static friction coefficient (micro | micron | mu) b between the inner surface of an insulating film and the electrode body surface to fall.
From the above, by setting SRaA ≧ 0.15, SRaB ≧ 0.03, and SRaA ≧ SRaB, the static friction coefficient μa between the outer surface of the insulating film and the battery case can be increased.

  Further, as described above, the static friction coefficient μa between the outer surface of the insulating film and the battery case and the static friction coefficient μb between the inner surface of the insulating film and the surface of the electrode body are always smaller. (Μa <μb). Since the static friction coefficient μa is smaller, the binding load Fc of the battery is sufficient if the static friction coefficient μa is taken into consideration. Further, by increasing the static friction coefficient μa, the binding load Fc of the battery can be reduced.

Specifically, as described above, one of the purposes of restraining the battery during use is to hold the electrode body so that the electrode body does not move within the battery case even when an impact is applied to the battery. is there. The restraining load Fc required to hold the electrode body even when an impact is applied can be obtained by the following equations (1) and (2). That is, the electrode body is held by the battery case via the insulating member (insulating film) on both sides in the thickness direction. For this reason, when the force applied to the electrode body (force in the direction orthogonal to the thickness direction) is Fd, a force of Fd / 2 is applied to both sides of the electrode body in the thickness direction. Therefore, the necessary restraining load Fc can be obtained from the equation (1). Further, since the force Fd applied to the electrode body is Fd = (mass M of the electrode body) × (acceleration α applied to the battery), the necessary restraining load Fc can be obtained from the equation (2).
Fc ≧ (Fd / 2) / μa (1)
Fc ≧ (M × α / 2) / μa (2)
As is clear from the equations (1) and (2), the restraining load Fc of the battery can be reduced as the static friction coefficient μa between the outer surface of the insulating film and the battery case increases.

And by making small the restraint load Fc of a battery, it can suppress that battery resistance raises, when the "high-rate discharge cycle test" mentioned later is performed.
The reason is considered as follows. That is, when a large current is discharged, pressure is applied to the electrolytic solution held (retained) in the electrode body with the expansion of the active material and the thermal expansion of the electrode body. On the other hand, with discharge, the concentration of ions responsible for electrical conduction such as lithium ions contained in the electrolyte near the negative electrode active material layer increases, and the electrolyte having a high ion concentration is pushed out from the inside of the electrode body. Therefore, when discharging with a large current is repeated, a phenomenon occurs in which the ion concentration of the electrolyte in the electrode body gradually decreases. If so, the number of ions that can contribute to the battery reaction in the electrode body is reduced, which is considered to increase the battery resistance.
When the battery restraint load Fc is reduced, the pressure applied to the electrolyte inside the electrode body during a large current discharge is reduced, so that the amount of electrolyte having a high ion concentration pushed out from the electrode body is reduced. Thereby, since it can suppress that the ion concentration of the electrolyte solution inside an electrode body falls, it is thought that the raise of battery resistance in a "high-rate discharge cycle test" can be suppressed.

  In addition, since the battery restraint load Fc can be reduced, when conductive foreign matter is mixed in the battery case, the conductive foreign matter penetrates the insulating film and short-circuits between the battery case and the electrode body. Can be prevented. In addition, the restraining member for restraining the battery can be reduced in size. It is particularly preferable that the outer surface has a three-dimensional average surface roughness SRaA of 0.15 ≦ SRaA ≦ 0.25, and the inner surface has a three-dimensional average surface roughness SRaB of 0.03 ≦ SRaB ≦ 0.17. preferable.

  The “three-dimensional average surface roughness SRa” is measured based on “JIS B 0601-1982”. The measurement length is 2.0 mm, the cutoff wavelength is 0.25 mm, and the measurement speed is 0.3 mm / s. Moreover, as a measuring apparatus, SURFCOM 1400A-3DF-12 by Toyo Seimitsu Co., Ltd. is used, for example.

Examples of the “insulating film” include a film mainly composed of a polypropylene resin and a film composed of polyethylene.
Among them, “insulating film mainly composed of polypropylene-based resin” refers to a material in which the proportion of polypropylene-based resin exceeds 50 wt% in the material constituting the insulating film.
Examples of the “polypropylene resin” include those obtained by homopolymerizing propylene, random copolymers obtained by copolymerizing propylene with ethylene or butene, and block copolymers obtained by polymerizing and blending ethylene elastomer such as ethylene / propylene rubber during propylene polymerization. Can be mentioned.

  The “insulating film” includes a film containing an ethylene-α-olefin copolymer, specifically, a low crystalline ethylene-α-olefin copolymer and an amorphous ethylene-α-olefin copolymer. A film containing at least one of the coalesces can be used. The low crystalline ethylene-α-olefin copolymer and the amorphous ethylene-α-olefin copolymer are preferably thermoplastic elastomers. In particular, when the main component of the insulating film is a polypropylene resin, the low temperature impact property of the polypropylene resin can be improved by including a thermoplastic elastomer of an ethylene-α-olefin copolymer. Specifically, as a thermoplastic elastomer of a low crystalline ethylene-α-olefin copolymer, ethylene / butene rubber (EBR), as a thermoplastic elastomer of an amorphous ethylene-α-olefin copolymer, ethylene / propylene rubber (EPR).

  The form of the “electrode body” is not particularly limited. For example, a flat wound electrode body formed by winding a positive electrode plate and a negative electrode plate each having a band shape through a separator, or a positive electrode having a rectangular shape or the like Examples thereof include a laminated electrode body in which a plurality of plates and negative electrode plates are laminated via a separator.

  Further, another aspect is an assembled battery comprising a plurality of rectangular parallelepiped batteries and a restraining member that restrains these batteries in the thickness direction, and the battery is made of metal and a rectangular parallelepiped battery case; An electrode body accommodated in the battery case; and an insulating member that is made of an insulating film and is interposed between the battery case and the electrode body to insulate the two. The insulating film includes the restraining member. The three-dimensional average surface roughness SRaA of the outer surface in contact with the battery case satisfies SRaA ≧ 0.15 and is in contact with the electrode body. The battery pack has a side surface three-dimensional average surface roughness SRaB satisfying SRaB ≧ 0.03 and satisfying SRaA ≧ SRaB.

  As described above, the battery constituting this assembled battery is a highly reliable battery that can increase the static friction coefficient μa between the outer surface of the insulating film and the battery case, and suppresses problems associated with an increase in the binding load Fc of the battery. is there. Therefore, a highly reliable assembled battery can be obtained by using this battery.

  In another aspect, the battery case is a rectangular parallelepiped battery case, an electrode body housed in the battery case, and an insulating film, and is interposed between the battery case and the electrode body. An insulating member that insulates, the insulating film used in a battery, wherein the insulating film has a three-dimensional average surface roughness SRaA of an outer surface in contact with the battery case satisfying SRaA ≧ 0.15, and the electrode The three-dimensional average surface roughness SRaB of the inner surface that is in contact with the body satisfies SRaB ≧ 0.03 and is an insulating film satisfying SRaA ≧ SRaB.

  If an insulating member is formed using this insulating film and a battery is manufactured using the insulating member, the static friction coefficient μa between the outer surface of the insulating film and the battery case can be increased as described above, and the binding load Fc of the battery can be increased. It is possible to provide a highly reliable battery that suppresses problems associated with an increase in battery life.

It is a longitudinal cross-sectional view of the lithium ion secondary battery which concerns on embodiment. It is a perspective view of the bag-shaped insulating member concerning an embodiment. It is a side view of the assembled battery which concerns on embodiment. It is explanatory drawing which shows the measuring method of static friction coefficient (mu) a and (mu) b. It is a graph which shows the resistance increase rate of the battery resistance in a high-rate discharge cycle test about each battery which concerns on Example 1 and Comparative Example 1. FIG.

Hereinafter, embodiments of the present invention will be described with reference to the drawings. FIG. 1 shows a lithium ion secondary battery (nonaqueous electrolyte secondary battery) 1 (hereinafter also simply referred to as “battery 1”) according to the present embodiment. FIG. 2 shows a bag-like insulating member (insulating member) 30 according to this embodiment. In the present specification, the upper side in FIG. 1 is described as the upper side UW of the battery 1, and the lower side is described as the lower side DW of the battery 1.
The battery 1 is a rectangular and sealed lithium ion secondary battery mounted on a vehicle such as a hybrid vehicle or an electric vehicle. The battery 1 includes a battery case 10, an electrode body 20 accommodated therein, a bag-like insulating member 30 disposed between the battery case 10 and the electrode body 20, and a positive electrode terminal supported by the battery case 10. 40, a negative electrode terminal 41, and the like. Further, a non-aqueous electrolyte solution 17 is held in the battery case 10.

  Among these, the battery case 10 has a rectangular parallelepiped shape and is made of metal (in this embodiment, aluminum). The battery case 10 includes a rectangular parallelepiped box-shaped case main body member 11 in which only the upper UW is opened, and a rectangular plate-shaped case cover member 13 which is welded so as to close the opening 11h of the case main body member 11. The The case lid member 13 is provided with a safety valve 14 that opens when the internal pressure of the battery case 10 reaches a predetermined pressure. The case lid member 13 is formed with a liquid injection hole 13 h that communicates the inside and outside of the battery case 10 and is hermetically sealed with a rivet 15.

  The case lid member 13 is fixedly provided with a positive electrode terminal 40 and a negative electrode terminal 41 each formed of an extended terminal member 43 and a bolt 44 via an insulating resin member 47 made of resin. The positive terminal 40 is made of aluminum, and the negative terminal 41 is made of copper. In the battery case 10, the positive electrode terminal 40 is connected and connected to the positive electrode current collector 21 m of the positive electrode plate 21 in the electrode body 20 described later. Further, the negative electrode terminal 41 is connected to and electrically connected to the negative electrode current collector 25m of the negative electrode plate 25 in the electrode body 20.

  Next, the electrode body 20 will be described. The electrode body 20 has a flat shape and is accommodated in the battery case 10 in a state of being accommodated in a bag-like insulating member 30 described later. The electrode body 20 is obtained by winding a belt-like positive electrode plate 21 and a belt-like negative electrode plate 25 on each other via a pair of belt-like separators 29 and compressing them in a flat shape. A separator 29 is wound around the outermost periphery of the electrode body 20 (the separator 29 forms the surface of the electrode body 20).

  The positive electrode plate 21 is formed by providing a positive electrode active material layer 23 in a band shape on a region extending in a part of the width direction and extending in the longitudinal direction among both main surfaces of a positive electrode current collector foil 22 made of a band-shaped aluminum foil. The positive electrode active material layer 23 includes a positive electrode active material, a conductive agent, and a binder. Also, one end of the positive electrode current collector foil 22 in the width direction is a positive electrode current collector part 21 m where the positive electrode current collector foil 22 is exposed without the positive electrode active material layer 23 in the thickness direction of the positive electrode current collector foil 22. Yes. The positive electrode terminal 40 is welded to the positive electrode current collector 21m.

The negative electrode plate 25 has a negative electrode active material layer 27 formed in a band shape on a part of the width direction and extending in the longitudinal direction of both main surfaces of the negative electrode current collector foil 26 made of a strip-shaped copper foil. Become. The negative electrode active material layer 27 includes a negative electrode active material, a binder, and a thickener. Also, one end of the negative electrode current collector foil 26 in the width direction is a negative electrode current collector 25m where the negative electrode active material layer 27 is not present in the thickness direction of the negative electrode current collector foil 26 and the negative electrode current collector foil 26 is exposed. Yes. The negative electrode terminal 41 is welded to the negative electrode current collector 25m.
The separator 29 is a porous film made of resin and has a strip shape. Specifically, the separator 29 has a three-layer structure in which one porous resin film made of polyethylene (PE) is overlapped between two porous resin films made of polypropylene (PP).

  Next, the bag-like insulating member 30 will be described (see also FIG. 2). This bag-like insulating member 30 is formed in a bag shape in which an insulating film 31 cut into a predetermined shape is folded, the insulating films 31 are welded and fixed to each other at a plurality of locations, and an opening 30h is provided only on the upper UW. . The bag-shaped insulating member 30 is housed in the battery case 10 in a state of surrounding the electrode body 20 and is interposed between the battery case 10 and the electrode body 20 to electrically insulate them. .

  The insulating film 31 constituting the bag-like insulating member 30 is mainly composed of polypropylene resin. Specifically, a homopolypropylene resin obtained by homopolymerizing propylene, a random copolymer resin obtained by copolymerizing propylene with ethylene or butene, and a block copolymer resin obtained by blending propylene with an ethylene-based elastomer are used. The insulating film 31 is made of an ethylene-α-olefin copolymer thermoplastic elastomer, specifically, a non-crystalline ethylene-α-olefin copolymer thermoplastic elastomer, more specifically, ethylene Contains propylene rubber (EPR).

  In addition, in the insulating film 31 of the present embodiment, the three-dimensional average surface roughness SRaA (μm) of the outer surface 31a in contact with the battery case 10 satisfies SRaA ≧ 0.15. SRaA = 0.227 (μm). In addition, in the insulating film 31, the three-dimensional average surface roughness SRaB (μm) of the inner side surface 31b in contact with the electrode body 20 satisfies SRaB ≧ 0.03. SRaB = 0.058 (μm). Therefore, the insulating film 31 of the present embodiment satisfies SRaA ≧ SRaB.

  The insulating film 31 can be manufactured by co-extrusion of two types of polymers by a co-extrusion manufacturing method such as a T-die method or an inflation method. Each layer to be coextruded is blended with an incompatible resin such as polyethylene so that the three-dimensional average surface roughness of the outer surface 31a is SRaA = 0.227 (μm) as described above. The three-dimensional average surface roughness of the side surface 31b can be set to SRaB = 0.058 (μm).

  Next, an assembled battery 200 using the battery 1 will be described (see FIG. 3). The assembled battery 200 includes a plurality of cuboid batteries 1 arranged in a row, a plurality of spacers 210 interposed between adjacent batteries 1, and the battery 1 and the spacer 210 pressed in the battery thickness direction BH. And a restraining member 220 that restrains while restraining. In FIG. 3, the positive electrode terminal 40 and the negative electrode terminal 41 of the battery 1 are not shown.

  The plurality of batteries 1 are arranged in the battery thickness direction BH via spacers 210, respectively, and adjacent batteries 1 are electrically connected by a bus bar (not shown). The spacer 210 has a rectangular plate shape and is made of resin. The alternately arranged batteries 1 and spacers 210 are restrained in a state where they are pressed and compressed by the restraining member 220 in the battery thickness direction BH. Thereby, in the inside of the battery 1, the insulating film 31 that forms the bag-like insulating member 30 is pressed between the battery case 10 and the electrode body 20.

  The restraining member 220 has a pair of end plates 221 and four restraining rods 223. The end plate 221 has a rectangular plate shape and is disposed on both sides of the batteries 1 and the spacers 210 arranged in a row. The restraining rods 223 are respectively disposed between the pair of end plates 221 and are fixed to the end plates 221 by fastening bolts 225, respectively.

(Examples and Comparative Examples)
Subsequently, the result of the test conducted in order to verify the effect of this invention is demonstrated. As Examples 1 to 4 and Comparative Examples 1 to 3, seven types of insulating films were obtained by changing the three-dimensional average surface roughness SRaA of the outer surface and the three-dimensional average surface roughness SRaB of the inner surface as shown in Table 1. Prepared. In addition, the insulating film of Example 1 is the same as the insulating film 31 used for the battery 1 of the embodiment described above.

  Next, the same aluminum plate AB (see FIG. 4) as the battery case 10 is prepared, and the static friction coefficient μa between each of the insulating films ZF and the aluminum plate AB in Examples 1 to 5 and Comparative Examples 1 to 3 is defined as JIS K7125: Plastic-film and sheet-measured according to the friction coefficient test method. Specifically, as shown in FIG. 4, the aluminum plate AB is placed and fixed on the flat first jig TG1. Further, an insulating film ZF cut to a size of 63 mm × 63 mm is attached to one main surface of the rectangular second jig TG2 having a weight of 130 g. In addition, the insulating film ZF affixes the inner surface which contacts the electrode body 20 when used for the battery 1 to the second jig TG2. Then, the insulating film ZF and the second jig TG2 are placed on the aluminum plate AB so that the outer surface of the insulating film ZF (the surface that contacts the battery case 10 when used in the battery 1) is in contact with the aluminum plate AB. To do. Thereafter, the second jig TG2 is pulled in the horizontal direction (left side in FIG. 4), and the static friction force generated at that time is measured to calculate the static friction coefficient μa. The results are shown in “Dry state” of the static friction coefficient μa in Table 1.

  Next, the static friction coefficient μa between each insulating film ZF and the aluminum plate AB in the presence of the electrolytic solution 17 was obtained. Specifically, about 20 cc of the electrolytic solution 17 is dropped in advance between the insulating film ZF and the aluminum plate AB with a dropper in advance, and the second jig TG2 is pulled in the horizontal direction in this state, and the static friction generated at that time The static friction coefficient μa is calculated by measuring the force. The results are shown in “Electrolyte immersion state” of the static friction coefficient μa in Table 1.

  Moreover, the same resin film JF as the separator 29 which comprises the electrode body 20 was prepared, and the static friction coefficient (micro | micron | mu) b of each insulating film ZF of Examples 1-5 and Comparative Examples 1-3 and the resin film JF was calculated | required. Specifically, as shown in FIG. 4, the resin film JF is placed and fixed on the first jig TG1 described above. Further, as described above, the insulating film ZF is attached to one main surface of the second jig TG2. However, the outer surface of the insulating film ZF is attached to the second jig TG2. Then, the insulating film ZF and the second jig TG2 are placed on the resin film JF so that the inner side surface of the insulating film ZF is in contact with the resin film JF. Thereafter, as described above, the second jig TG2 is pulled in the horizontal direction, the static friction force generated at that time is measured, and the static friction coefficient μb is calculated. The results are shown in “Dry state” of the static friction coefficient μb in Table 1.

  Next, the static friction coefficient μb between each insulating film ZF and the resin film JF in the state where the electrolytic solution 17 exists was obtained. Specifically, about 20 cc of the electrolytic solution 17 is dropped in advance with a dropper between the insulating film ZF and the resin film JF, and the second jig TG2 is pulled in the horizontal direction in this state, and static friction generated at that time is generated. The static friction coefficient μb is calculated by measuring the force. The results are shown in “Electrolyte immersion state” of the static friction coefficient μb in Table 1.

  As can be seen from Table 1, in any of the insulating films ZF of Examples 1 to 4 and Comparative Examples 1 to 3, the resin film JF imitating the inner surface of the insulating film ZF and the electrode body surface in the “electrolyte immersion state” The static friction coefficient μa between the outer surface of the insulating film ZF and the metal plate AB imitating the battery case is smaller (μa <μb). Therefore, it can be seen that in order to reduce the binding load Fc of the battery, it is sufficient to consider increasing the “static friction coefficient μa” which is the smaller static friction coefficient.

Next, with respect to the static friction coefficient μa between the outer surface of the insulating film ZF and the metal plate AB simulating a battery case, when comparing Examples 1-4 and Comparative Examples 1-3, the insulating film ZF of Comparative Examples 1-3 Then, there is almost no difference in the static friction coefficient μa between the “dry state” and the “electrolyte immersion state” (the difference is only 0.02 at the maximum). On the other hand, in the insulating films ZF of Examples 1 to 4, the static friction coefficient μa is larger (0.15 to 0.20) in the “electrolyte immersion state” than in the “dry state”.
In addition, about the static friction coefficient (micro | micron | mu) b of the resin film JF imitating the inner surface of the insulating film ZF and the electrode body surface, in any insulating film ZF of Examples 1-4 and Comparative Examples 1-3, it is "dry state". There was almost no difference between the “electrolyte immersion state” (the difference was only 0.03 at the maximum).

  The reason why the static friction coefficient μa in the “electrolyte immersion state” does not become larger than that in the “dry state” in the insulating film ZF of Comparative Example 1 is considered to be as follows. That is, in Comparative Example 1, since the three-dimensional average surface roughness SRaA of the outer surface of the insulating film ZF is small and SRaA <0.15, a gap is generated between the outer surface of the insulating film ZF and the metal plate AB. It is difficult and the electrolytic solution 17 is difficult to enter. For this reason, it is difficult for the insulating film ZF and the metal plate AB to be in close contact with each other through the electrolytic solution 17, so that it is considered that the static friction coefficient μa does not increase even in the “electrolyte immersed state”.

On the other hand, in the insulating films ZF of Examples 1 to 4, since the three-dimensional average surface roughness SRaA of the outer surface of the insulating film ZF is large and SRaA ≧ 0.15, the outer surface of the insulating film ZF and the metal plate AB A small gap is generated between the insulating film ZF and the insulating film ZF and the metal plate AB are easily brought into close contact with each other through the electrolytic solution 17. For this reason, it is considered that the static friction coefficient μa is larger in the “electrolyte immersion state” than in the “dry state”.
From this result, it can be seen that SRaA ≧ 0.15 is required to increase the static friction coefficient μa in the “electrolyte immersion state”.

Next, in the insulating film ZF of Comparative Example 2, the static friction coefficient μa in the “electrolyte immersion state” does not become larger than that in the “dry state”. That is, as in Comparative Example 2, when SRaA <SRaB, the static friction coefficient μa in the “electrolyte immersion state” is small. From this, it can be seen that SRaA ≧ SRaB is required to increase the static friction coefficient μa in the “electrolyte immersion state”.
Further, in the insulating film ZF of Comparative Example 3, the static friction coefficient μa in the “electrolyte immersion state” does not become larger than that in the “dry state”. That is, as in Comparative Example 3, when SRaB <0.03, the static friction coefficient μa in the “electrolyte immersion state” is small. From this, it can be seen that SRaB ≧ 0.03 is necessary to increase the static friction coefficient μa in the “electrolyte immersion state”.
From the above, it can be seen that SRaA ≧ 0.15, SRaB ≧ 0.03, and SRaA ≧ SRaB must be satisfied in order to increase the static friction coefficient μa in the “electrolyte immersion state”.

  Next, batteries were produced in the same manner as in the embodiment except that each insulating film ZF of Example 1 and Comparative Example 1 was used. And about each battery, the "high-rate discharge cycle test" was done and "resistance increase rate (%)" of the battery resistance before and behind a test was calculated | required, respectively. First, when starting the test, each battery is restrained by being sandwiched between two rectangular plate-like restraining plates in the battery thickness direction BH, and the insulating film ZF is connected to the battery case 10 in the same manner as the assembled battery 200 described above. It is set as the state pressed between the electrode bodies 20.

The restraining load Fc necessary for restraining each battery is obtained from the above-described equation (1). The coefficient of static friction μa1 in the “electrolyte immersion state” of the insulating film ZF according to Example 1 is 0.67, and the coefficient of static friction μa2 in the “electrolyte immersion state” of the insulating film ZF according to Comparative Example 1 = 0. 32. Therefore, from the following formulas (3) to (5), if the restraining load Fc1 necessary for the battery 1 of Example 1 is based on the restraining load Fc2 necessary for the battery of Comparative Example 1 (100%), 47. It can be seen that 8% is sufficient.
Fc1 = (Fd / 2) / μa1 (3)
Fc2 = (Fd / 2) / μa2 (4)
(Fc1 / Fc2) × 100 = (μa2 / μa1) × 100 = 47.8 (%) (5)

  Next, the initial battery resistance (mΩ) was measured for each battery. Specifically, each battery adjusted to SOC 60% is charged and discharged at a specified current (for example, 60, 90, 120 A, etc.) and time (for example, 10 seconds) in a temperature environment of 25 ° C. The battery IV resistance was calculated from the voltage fluctuation amount and Ohm's law (R = V / I), and this was used as the initial battery resistance.

  Thereafter, a “high rate discharge cycle test” was performed for each battery. Specifically, each battery adjusted to SOC 60% was discharged at a constant current of about 35 C for 10 seconds in a temperature environment of 25 ° C. and then rested for 5 seconds. Thereafter, the battery was charged with a constant current of about 3 C for 125 seconds and then rested for 5 seconds. This was carried out for about 1000 cycles. Thereafter, the battery resistance (mΩ) after the test was determined as described above for each battery for which the “high-rate discharge cycle test” was completed. Then, the rate of increase in resistance (%) was calculated from the initial battery resistance and the battery resistance after the test. The result is shown in FIG.

As can be seen from FIG. 5, in the battery of Comparative Example 1, the rate of increase in resistance was large and about 133%, whereas in Battery 1 of Example 1, the rate of increase in resistance was small and about 105%.
The reason for such a result is considered as follows. That is, in the “high-rate discharge cycle test”, when a large current is discharged, pressure is applied to the electrolytic solution 17 held in the electrode body 20 with the expansion of the active material and the thermal expansion of the electrode body 20. On the other hand, along with the discharge, the concentration of lithium ions contained in the electrolyte solution 17 near the negative electrode active material layer 27 increases, and the electrolyte solution 17 having a high ion concentration is pushed out of the electrode body 20 to the outside. Therefore, when large current discharge is repeated, a phenomenon occurs in which the ion concentration of the electrolyte solution 17 inside the electrode body 20 gradually decreases. Then, since lithium ions that can contribute to the battery reaction in the electrode body 20 are reduced, it is considered that the battery resistance is increased.

  In the battery 1 of Example 1, as compared with the battery of Comparative Example 1, the binding load Fc of the battery is small as described above. When the battery restraint load Fc is reduced, the pressure applied to the electrolyte solution 17 in the electrode body 20 during a large current discharge is reduced, so that the amount of the electrolyte solution 17 having a high ion concentration pushed out from the electrode body 20 is reduced. Thereby, since it can suppress that the ion concentration of the electrolyte solution 17 in the electrode body 20 falls, it is thought that the raise of the battery resistance in a "high-rate discharge cycle test" can be suppressed.

  As described above, in the battery 1 described above, the three-dimensional average surface roughness SRaA (μm) of the outer surface 31a of the insulating film 31 in contact with the battery case 10 satisfies SRaA ≧ 0.15. In this embodiment, SRaA = 0.227 (μm). In addition, in the insulating film 31, the three-dimensional average surface roughness SRaB (μm) of the inner side surface 31b in contact with the electrode body 20 satisfies SRaB ≧ 0.03 and SRaA ≧ SRaB. In the present embodiment, SRaB = 0.058 (μm). As a result, the static friction coefficient μa between the outer surface 31a of the insulating film 31 and the battery case 10 can be increased, and defects associated with an increase in the binding load Fc of the battery 1 can be suppressed and reliability can be increased. Specifically, by reducing the binding load Fc of the battery 1, it is possible to suppress an increase in battery resistance when the “high rate discharge cycle test” is performed. Further, by reducing the restraining load Fc of the battery 1, when conductive foreign matter is mixed in the battery case 10, the conductive foreign matter penetrates the insulating film 31, and the battery case 10 and the electrode body. It is possible to prevent a short circuit from occurring with 20. Further, the restraining member 220 for restraining the battery 1 can be reduced in size.

In the above, the present invention has been described with reference to the embodiment. However, the present invention is not limited to the above-described embodiment, and it is needless to say that the present invention can be appropriately modified and applied without departing from the gist thereof.
For example, in the embodiment, the insulating films 31 are fixed to each other by welding to form the bag-shaped insulating member 30, but the present invention is not limited to this. For example, the bag-shaped insulating member 30 may be formed by fixing the insulating films 31 using an adhesive tape or an adhesive.

1 Battery (Lithium ion secondary battery)
10 battery case 20 electrode body 30 bag-like insulating member (insulating member)
31 Insulating film 31a Outer surface 31b (of insulating film) Inner surface 40 (of insulating film) 40 Positive electrode terminal 41 Negative electrode terminal 200 Battery pack 220 Restraint member

Claims (1)

A rectangular battery case made of metal,
An electrode body housed in the battery case;
An insulating film comprising an insulating film and interposed between the battery case and the electrode body to insulate the battery,
The insulating film is
Three-dimensional average surface roughness SRaA of the outer surface in contact with the battery case satisfies SRaA ≧ 0.15,
The three-dimensional average surface roughness SRaB of the inner surface in contact with the electrode body satisfies SRaB ≧ 0.03, and
A battery that satisfies SRaA ≧ SRaB.

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