TECHNICAL FIELD

The present disclosure relates to packaging materials for power storage devices and power storage devices using the same.

BACKGROUND ART

Known power storage devices include secondary batteries such as lithium ion batteries, nickel hydride batteries, and lead batteries, and electrochemical capacitors such as electric double layer capacitors. As mobile devices have been downsized or limited in installation space, there have been demands for further downsized power storage devices. Accordingly, lithium ion batteries having high energy density have been attracting attention. The conventional packaging materials for lithium ion batteries have been metal cans. However, multilayer films have been increasingly used due to their light weight, high heat dissipation, and low production cost.

In a configuration of lithium ion batteries using such a multilayer film as a packaging material, battery contents (e.g., cathode, separator, anode, electrolyte solution) are covered with packaging materials that include an aluminum foil layer to thereby prevent moisture from penetrating into the battery. Lithium ion batteries using such a configuration are referred to as aluminum laminated lithium ion batteries.

Known examples of aluminum laminated lithium ion batteries include embossed lithium ion batteries. An embossed lithium ion battery is produced by forming a recess for accommodate the battery contents in a portion of the packaging material by cold forming, folding the remaining part of the packaging material, and sealing the edge portions by heat sealing (see, for example, PTL 1). In such lithium ion batteries, more battery contents can be stored by increasing the depth of the recess formed by cold forming, and thus higher energy density can be achieved.

[Citation List] [Patent Literature] PTL 1: JP 2013-101765 A

SUMMARY OF THE INVENTION

Technical Problem

The packaging materials for power storage devices described in PTL 1 have room for improvement in deep drawing properties. The present disclosure has been made to provide a packaging material for power storage devices with improved deep-drawing properties, and a power storage device using the same.

Solution to Problem

A power storage device packaging material according to the first aspect of the present disclosure includes a structure including at least a substrate layer, an adhesive layer, a metal foil layer, a sealant adhesive layer, and a sealant layer, which are laminated in this order.

In the power storage device packaging material according to the first aspect, the adhesive layer has a yield stress in the range of 3500 to 6500 N/cm2and breaking elongation of 45 to 200% in a stress-strain curve determined by a tensile test at a tension rate of 6 mm/min. The substrate layer has conventionally played a role of protecting the metal foil layer during deep drawing, and the adhesive layer has been mainly required to provide adhesion between the substrate layer and the metal foil layer. According to the packaging material of this aspect, however, the adhesive layer has the yield stress and breaking elongation of the above ranges to thereby ensure improved deep drawing properties that could not have been achieved only by improvement of the substrate layer. Although the reason that the deep drawing properties are improved by providing the adhesive layer with the yield stress and breaking elongation of the above ranges has not been fully elucidated, the present inventors consider it to be as follows: Since the above physical properties of the adhesive layer are close to those of the metal foil layer compared with the conventional art, the behavior of the adhesive layer when a stress is applied by deep drawing becomes more like that of the metal foil layer, and thus the adhesive layer is more likely to follow the metal foil layer after deep drawing.

The above power storage device packaging material preferably further includes anticorrosion treatment layers respectively provided on both surfaces of the metal foil layer. With this configuration, adhesion between the substrate layer and the metal foil layer can be further improved. The anticorrosion treatment layers preferably include a rare earth element oxide, and phosphoric acid or phosphate. With this configuration, adhesion between the substrate layer and the metal foil layer can be further improved.

In the above power storage device packaging material, the rare earth element oxide is preferably a cerium oxide. With this configuration, adhesion between the substrate layer and the metal foil layer can be further improved.

A power storage device packaging material according to the second aspect includes a structure including at least a substrate layer, an adhesive layer, a metal foil layer, a first anticorrosion treatment layer, a sealant adhesive layer, and a sealant layer, which are laminated in this order, wherein the adhesive layer has a glass transition temperature in a range of 140° C. or more and 160° C. or less.

The substrate layer has conventionally played a role of protecting the metal foil layer during deep drawing, and the adhesive layer has been mainly required to provide adhesion between the substrate layer and the metal foil layer. According to the packaging material of this aspect, however, the adhesive layer has the glass transition temperature of the above ranges to thereby ensure improved deep drawing properties that could not have been achieved only by improvement of the substrate layer. That is, the packaging material of this aspect has been achieved focusing on the hardness of the adhesive layer. By virtue of the sufficient hardness of the adhesive layer, the packaging material can withstand shear stress applied to the adhesive layer when it is stretched by deep drawing, and ensure good deep drawing properties. On the other hand, due to the adhesive layer being not too hard, the adhesive layer is prevented from being rigid and fragile, and can follow the stretching of the substrate layer or the metal foil layer to thereby reduce occurrence of fine breakage in the adhesive layer and ensure good deep drawing properties. The present inventors have found that such an appropriate hardness of the adhesive layer can be achieved by preparing an adhesive layer having a glass transition temperature in the range of 140° C. or more and 160° C. or less.

In the power storage device packaging material according to the present disclosure, the adhesive layer preferably includes a reaction product of a polyester polyol and isocyanate compound. Furthermore, the isocyanate compound is preferably an aromatic isocyanate compound. Still furthermore, the aromatic isocyanate compound is preferably a diisocyanate adduct. With this configuration, the glass transition temperature of the adhesive layer can be easily controlled within the above range.

The power storage device packaging material according to the present disclosure preferably further includes a second anticorrosion treatment layer provided between the adhesive layer and the metal foil layer. With this configuration, adhesion between the substrate layer and the metal foil layer can be further improved, and deep drawing properties can be further improved.

The power storage device packaging material according to the present disclosure preferably further includes an adhesion-enhancing treatment layer provided between the substrate layer and the adhesive layer. With this configuration, adhesion between the substrate layer and the adhesive layer can be further improved, and deep drawing properties can be further improved. From the viewpoint of improving these properties, the adhesion-enhancing treatment layer preferably includes at least one resin selected from the group consisting of a polyester resin, an acrylic resin, a polyurethane resin, an epoxy resin, and an acrylic grafted polyester resin.

The present disclosure further provides a power storage device including: a battery element including electrodes; leads respectively extending from the electrodes; and a container accommodating the battery element, wherein the container is formed of the power storage device packaging material with the sealant layer being located on the inside. Since such a power storage device uses the power storage device packaging material according to the present disclosure (first aspect or second aspect) as a container for accommodating the battery element, a deep recess can be formed in the container without causing breakage.

Advantageous Effects of Invention

According to the present disclosure, a power storage device packaging material having improved deep-drawing properties, and a power storage device using the same can be provided.

