JP2014035858A - Secondary battery - Google Patents

Abstract

[PROBLEMS] To prevent a reduction in frictional force between a separator sheet and a positive and negative electrode sheet when a separator sheet having a porous heat-resistant layer is used.
A secondary battery provided by the present invention includes a wound electrode body (80) formed by winding a positive electrode sheet (10) and a negative electrode sheet (20) together with separator sheets (40A, 40B). A porous heat-resistant layer (44A, 44B) is formed on at least one surface of the base material (42A, 42B) of the separator sheet, and the separator base material that does not have a porous heat-resistant layer at both ends in the width direction is exposed. Separator substrate exposed portions arranged at positions that can contact the positive electrode active material layer non-formation portion (16) or the negative electrode active material layer non-formation portion (26) that face each other (46A, 46B). It is formed in the direction.
[Selection] Figure 3

Description

  The present invention relates to a secondary battery. Specifically, the present invention relates to a secondary battery including a separator having a porous heat-resistant layer.

In recent years, secondary batteries such as lithium secondary batteries and nickel metal hydride batteries have been used as so-called portable power sources such as personal computers and portable terminals and power sources for driving vehicles. In particular, a lithium secondary battery that is lightweight and obtains a high energy density is preferably used as a high-output power source for driving vehicles such as electric vehicles and hybrid vehicles.
As one typical structure of such a secondary battery, a long sheet-like positive electrode and a negative electrode are similarly wound on a long sheet-like separator (typically two separator sheets). A wound electrode body is constructed, and the constructed wound electrode body is housed in a battery case together with a predetermined electrolyte (typically a non-aqueous electrolyte) so that the contents of the case do not leak out. A secondary battery having a hermetically sealed structure (hereinafter, a secondary battery having such a structure is also referred to as a “sealed secondary battery”).

The separator used for this type of battery is usually a porous sheet made of a synthetic resin such as polyolefin as having a function of electrically insulating the positive electrode and the negative electrode and a function of holding a non-aqueous electrolyte. Is used. Furthermore, the separator used in this type of battery has a certain temperature range because the inside of the battery is overheated for the purpose of ensuring the safety of the battery and the device in which the battery is mounted, in addition to the insulating function and the electrolyte holding function. It softens when it reaches (typically the softening point of the resin) and has a function of shutting down (shutdown) the conduction path of the charge carrier.
Moreover, while providing the said shutdown function, a predetermined level heat resistance is desired for a separator. That is, in this type of battery, it is necessary to prevent an internal short circuit due to melting of the separator even when the inside of the battery is heated to a temperature higher than the softening point of the separator.
As one means for meeting such demands, the use of a separator in which a porous heat-resistant layer is formed on the surface of a separator substrate made of a synthetic resin such as polyolefin has been proposed. Such a porous heat-resistant layer is typically composed of a metal oxide or other inorganic filler having heat resistance, and a binder for binding the inorganic fillers together and fixing them to the separator substrate. For example, Patent Documents 1 and 2 describe a nonaqueous electrolyte secondary battery including a separator having such a porous heat-resistant layer formed on the surface of a substrate.

JP2011-253684A JP 2008-300362 A

  By the way, as a problem in the case of constructing a secondary battery using a separator having a porous heat-resistant layer as described above, it is necessary to distinguish the separator from a positive electrode or a negative electrode (hereinafter, positive and negative electrodes). In the case where there is no electrode, it is generally called “electrode”). Specifically, the electrode active material layer (also referred to as an electrode mixture layer) formed on the surface of the current collector constituting the electrode and the porous heat-resistant layer of the opposing separator are both porous layers. Therefore, the frictional force at the contact surface where both or at least one of these layers is involved is caused by the surface of the separator substrate made of a synthetic resin such as polyolefin and the current collector (for example, the positive electrode current collector) constituting the electrode. Compared with the case where the surface of the aluminum foil or the copper foil that constitutes the negative electrode current collector is in direct contact with the surface, it is significantly reduced.

Such a decrease in frictional force is a problem particularly when the wound electrode body as described above is configured. That is, in a wound electrode body obtained by winding such a separator sheet with a porous heat-resistant layer together with positive and negative electrode sheets with an active material layer, the reduction in frictional force between the electrode sheet and the separator sheet is caused by the wound electrode body itself. Shape retention performance can be reduced. Specifically, the positional relationship between the separate sheet and each electrode sheet constituting the wound electrode body is likely to be displaced, or a part of the wound electrode body is likely to be buckled. In particular, a separator sheet with a porous heat-resistant layer has high hardness due to the presence of the porous heat-resistant layer, and thus the flexibility is reduced, and the occurrence of such deviation and buckling can be promoted.
Therefore, such a decrease in the frictional force is caused by an increase in the frequency of occurrence of defective products due to misalignment or buckling, or by the careful insertion of the electrode body into the case (that is, a decrease in insertability). In addition to reducing the production efficiency of the wound electrode body, expansion and contraction of the wound electrode body due to repeated charge and discharge in a secondary battery constructed using the electrode body in order to reduce the rigidity of the wound electrode body Sometimes the above-mentioned deviation or buckling occurs, which may be a factor of deteriorating battery performance (cycle characteristics).

  Therefore, the present invention was created as a problem to be solved for the above-described reduction in frictional force, and the object of the present invention is to achieve the above-mentioned frictional force even when a separator sheet having a porous heat-resistant layer is used. It is an object of the present invention to provide a wound electrode body that realizes prevention of deviation and buckling due to a decrease, and a secondary battery including the wound electrode body.

In order to achieve the above object, the secondary battery disclosed herein is a positive electrode in which a positive electrode active material layer and a negative electrode active material layer are formed on each surface of a long sheet-like positive electrode current collector and a negative electrode current collector, respectively. And a negative electrode including a wound electrode body formed by winding a negative electrode together with a long sheet-shaped separator, and a case containing the wound electrode body and an electrolyte.
Further, in the secondary battery disclosed herein, one end portion of the winding electrode body in the winding axis direction has a positive electrode active material layer non-formed portion where the positive electrode active material layer is not formed. The negative electrode active material layer non-formed portion where the negative electrode active material layer is not formed is stacked with the other end portion of the two layers being stacked in a state protruding from the negative electrode. Configured.
In the secondary battery disclosed herein, the long sheet-shaped separator is a separator base material made of synthetic resin (typically made of polyolefin resin) and a porous heat-resistant layer mainly composed of inorganic filler. And a porous heat-resistant layer formed in the sheet longitudinal direction of the separator on at least one surface of the substrate.
The secondary battery disclosed herein has a width in which the porous heat-resistant layer of the separator can include the whole of the positive electrode active material layer or the negative electrode active material layer facing each other in the winding axis direction. It is formed in a dimension (that is, a dimension in the direction perpendicular to the longitudinal direction of the long sheet (winding axis direction)), and does not have the porous heat-resistant layer at both ends in the winding axis direction of the separator. Separator substrate exposed portions, which are disposed in positions that can contact the positive electrode active material layer non-forming portion or the negative electrode active material layer non-forming portion facing each other, are formed in the sheet longitudinal direction. It is characterized by that.

As described above, in the secondary battery disclosed herein, the long sheet-shaped separator constituting the wound electrode body is provided with the porous heat-resistant layer facing either the positive or negative active material layer, Separator substrate exposed portions that do not have a porous heat-resistant layer are provided at both ends in the rotational axis direction. Then, a positive or negative active material layer non-formed part (that is, the surface of the electrode current collector) is disposed at a position facing the separator base material exposed part.
In the wound electrode body having such a configuration, the separator base material exposed portion and the opposing positive or negative active material layer non-forming portion (current collector) can be brought into direct contact at both ends in the winding axis direction of the separator. it can. As a result, a high frictional force can be exhibited at the contact portion, and the adhesion between the electrode (current collector) and the separator can be improved.
Therefore, according to the wound electrode body of this configuration, the provision of the porous heat-resistant layer prevents an internal short circuit due to separator melting in the case where the inside of the battery is overheated above the separator softening point, and the separator and the electrode. It is possible to prevent the occurrence of deviation and buckling due to the lowering of the frictional force, and to maintain the rigidity of the wound electrode body, thereby preventing the productivity from being lowered.
In addition, according to the secondary battery including the wound electrode body of this configuration, the above-described misalignment and buckling at the time of expansion and contraction of the wound electrode body due to repeated charging and discharging are prevented in advance. High battery characteristics (for example, cycle characteristics) can be maintained.

In a preferred embodiment of the secondary battery disclosed herein, the separator base material exposed portions are formed on both ends of the separator in the winding axis direction so that the dimension in the winding axis direction is 1 mm or more. Features.
By providing the separator substrate exposed portions with such width dimensions on both sides of the porous heat-resistant layer in the winding axis direction (hereinafter also simply referred to as “width direction”), the separator (base material) and the electrode (current collector) are provided. The frictional force with the body) can be further improved.

Moreover, in another preferable aspect of the secondary battery disclosed herein, the separator includes a positive electrode active material layer non-formation part or a negative electrode active material in which separator base exposed parts at both ends in the winding axis direction face each other. It is formed so as to be disposed in a portion closer to the active material layer than half of the dimension in the same direction of the layer non-forming portion.
Thus, the active material layer of the width direction in the said electrode active material layer non-formation part is made into the opposing part (a contact part is included) of the separator base-material exposed part and the electrode active material layer non-formation part of either the positive or negative which opposes. By prescribing to the near part, the frictional force can be improved without obstructing the connection of the external connection terminal in the electrode active material layer non-forming part.

In the secondary battery disclosed herein, the separator may have a porous heat-resistant layer and a separator substrate exposed portion formed on one surface, or a porous heat-resistant layer and a separator substrate exposed on both surfaces. A part may be formed. In a wound electrode body that employs a separator having a porous heat-resistant layer formed on both sides, the frictional force tends to decrease particularly. However, the implementation of the present invention can prevent the reduction of the frictional force.
Further, as a wound electrode body to which the present invention is preferably applied, a flat-shaped wound electrode body formed by winding a long sheet-like positive electrode, a negative electrode, and a separator together and further crushing them into a flat shape. Such a wound electrode body is a wound electrode body having a shape suitable as an application target of the present invention because it is particularly necessary to prevent the occurrence of displacement and buckling.

According to another aspect of the present invention, there is provided an assembled battery comprising any one of the secondary batteries disclosed herein as a unit cell, and a plurality of unit cells electrically connected to each other.
The assembled battery having such a configuration is suitable as a power source for driving a vehicle such as an electric vehicle or a hybrid vehicle because it maintains high rigidity of the wound electrode body in the unit cell constituting the battery and is excellent in cycle characteristics and other battery characteristics. It is.
Therefore, the present invention also provides a vehicle such as a plug-in hybrid vehicle (PHV), a hybrid vehicle (HV), or an electric vehicle (EV) that includes any of the secondary batteries or assembled batteries disclosed herein as a driving power source. provide.

It is a perspective view which shows typically the external shape of the secondary battery (lithium secondary battery) which concerns on one Embodiment. It is a figure which shows typically the cross-sectional structure in the II-II line of the secondary battery of FIG. It is a schematic diagram which shows the structure of the winding electrode body of the secondary battery which concerns on one Embodiment. It is a schematic diagram which expands and shows a part (main part) of the wound electrode body shown in FIG. It is a perspective view which shows typically the assembled battery which combined multiple secondary batteries (single battery) which concern on one Embodiment. It is a side view which shows typically the vehicle (automobile) provided with the assembled battery which concerns on one Embodiment.

Hereinafter, preferred embodiments of the present invention will be described. Note that matters other than matters specifically mentioned in the present specification and necessary for the implementation of the present invention can be grasped as design matters of those skilled in the art based on the prior art in this field. The present invention can be carried out based on the contents disclosed in this specification and common technical knowledge in the field.
In this specification, the “secondary battery” generally refers to a rechargeable power storage device in general, a so-called storage battery such as a lithium secondary battery (typically a lithium ion battery), a nickel hydrogen battery, a nickel cadmium battery, and the like. It is a term that encompasses power storage elements (physical batteries) such as electric double layer capacitors. In the present specification, the “electrode active material” refers to a material capable of reversibly occluding and releasing (typically inserting and detaching) chemical species serving as a charge carrier in a secondary battery. The “lithium secondary battery” refers to a secondary battery that uses lithium ions as electrolyte ions and is charged and discharged by movement of charges accompanying the lithium ions between the positive and negative electrodes. A secondary battery generally called a lithium ion battery (or a lithium ion secondary battery) is a typical example included in the lithium secondary battery in this specification.

As described above, the secondary battery of the present invention has a long positive electrode and a negative electrode in which a positive electrode active material layer and a negative electrode active material layer are formed on each surface of a long sheet-like positive electrode current collector and a negative electrode current collector, respectively. A secondary battery comprising a wound electrode body wound together with a sheet-like separator, and a case for accommodating the wound electrode body and an electrolyte, wherein the above structural features, that is, a porous heat-resistant layer and a separator base Other battery components are not particularly limited as long as they have the structural characteristics of the separator having the exposed material portion.
For example, typical secondary batteries that can be provided by the present invention include lithium secondary batteries (such as lithium ion batteries), nickel hydride batteries, lithium ion capacitors, and other electric double layer capacitors.
Hereinafter, a preferred embodiment relating to a lithium secondary battery (lithium ion battery) as an example of the secondary battery disclosed herein will be described with reference to the drawings. Although not intended to be particularly limited, a lithium secondary battery in a form in which a wound electrode body and a nonaqueous electrolyte (nonaqueous electrolyte solution) are accommodated in a rectangular (that is, a rectangular box shape) case will be described below. This will be described as an example. The dimensions (length, width, thickness, etc.) in each figure do not reflect actual dimensional relationships. Further, members / parts having the same action are denoted by the same reference numerals, and redundant description is omitted or simplified.

FIG. 1 is a perspective view schematically showing an outer shape of a sealed nonaqueous electrolyte secondary battery 100 according to the present embodiment. FIG. 2 is a diagram schematically showing a cross-sectional structure taken along line II-II of the sealed secondary battery shown in FIG. FIG. 3 is a partially broken perspective view schematically showing the configuration of the wound electrode body 80.
As shown in FIGS. 1 and 2, the secondary battery 100 according to this embodiment includes a wound electrode body 80 and a battery case (outer container) 50. The battery case 50 includes a flat rectangular parallelepiped (square) battery case main body 52 having an open upper end, and a lid 54 that closes the opening. On the upper surface of the battery case 50 (that is, the lid 54), a positive terminal 70 for external connection that is electrically connected to the positive electrode of the wound electrode body 80 and a negative electrode terminal 72 that is electrically connected to the negative electrode of the electrode body 80. Is provided. In addition, the lid 54 is provided with a safety valve 55 for discharging gas generated inside the battery case 50 to the outside of the case 50, similarly to the battery case of the conventional nonaqueous electrolyte secondary battery.

Inside the battery case 50, a long sheet-like positive electrode (positive electrode sheet) 10 and a long sheet-like negative electrode (negative electrode sheet) 20 are flattened via two long sheet-like separators 40A and 40B. A wound electrode body (winding electrode body) 80 is accommodated together with a non-aqueous electrolyte (not shown). In addition, the material itself of each member constituting the wound electrode body 80 may be the same as the electrode body provided in the conventional lithium secondary battery, and there is no particular limitation.
For example, the positive electrode current collector 12 of the positive electrode sheet 10 is made of a metal foil such as an aluminum foil. The negative electrode current collector 22 of the negative electrode sheet 20 is made of a metal such as copper foil. Although the thickness of these foil-shaped current collectors is not particularly limited, those having a thickness of about 5 μm to 50 μm (more preferably 8 μm to 30 μm) can be used in consideration of the capacity density of the battery and the strength of the current collector.

As the positive electrode active material used for forming the positive electrode active material layer 14, one or two or more materials conventionally used in lithium secondary batteries can be used without any particular limitation. As a preferred example, an oxide containing lithium and a transition metal element as constituent metal elements such as lithium nickel oxide (for example, LiNiO ₂ ), lithium cobalt oxide (for example, LiCoO ₂ ), and lithium manganese oxide (for example, LiMn ₂ O ₄ ). And a phosphate containing lithium and a transition metal element as constituent metal elements, such as lithium oxide (lithium transition metal oxide), lithium manganese phosphate (LiMnPO ₄ ), and lithium iron phosphate (LiFePO ₄ ). The positive electrode active material layer 14 may be in the form of a slurry (paste or ink) by mixing a powdery positive electrode active material with an appropriate conductive material and a binder (binder) in an appropriate solvent. )), The slurry is applied on the positive electrode current collector 12 in the longitudinal direction of the sheet, dried, and pressed as necessary. Although it does not specifically limit, the ratio of the positive electrode active material to the whole positive electrode active material layer 14 is 50 mass% or more (typically 70 mass% or more and less than 100 mass%, for example, 80 mass% or more and 99 mass% or less). It is preferable that The density of the positive electrode active material layer is, for example, 2.0 g / cm ³ or more (typically 2.5 g / cm ³ or more) and 4.5 g / cm ³ or less (typically 4.2 g / cm ^3). Below).

  As the conductive material used, one or more kinds of substances conventionally used for secondary batteries can be used without any particular limitation. For example, carbon black (acetylene black, furnace black, ketjen black, channel black, lamp black, thermal black, etc.), coke, graphite (natural graphite and its modified products, artificial graphite), carbon fiber (PAN-based carbon fiber, Pitch-based carbon fiber) or one or more selected from carbon materials such as nanocarbon. The proportion of the conductive material in the entire positive electrode active material layer 14 is not particularly limited, but is, for example, 0.1% by mass or more and 15% by mass or less (typically 1% by mass or more and 10% by mass or less, for example, 2% by mass). % To 6% by mass).

  As the binder, one kind or two or more kinds of substances conventionally used in non-aqueous electrolyte secondary batteries can be used without any particular limitation. For example, when the positive electrode active material layer is formed using an organic solvent-based slurry (a solvent-based slurry in which the main component of the dispersion medium is an organic solvent), a polymer material that is dispersed or dissolved in the organic solvent can be preferably used. . Examples of such a polymer material include polyvinylidene fluoride (PVdF), polyvinylidene chloride (PVdC), and polyethylene oxide. Alternatively, when the positive electrode active material layer is formed using an aqueous slurry, a polymer material that is dissolved or dispersed in water can be preferably used. Examples of water-soluble (water-soluble) polymer materials include cellulose polymers such as carboxymethyl cellulose (CMC), methyl cellulose (MC), cellulose acetate phthalate (CAP), and hydroxypropyl methyl cellulose (HPMC); polyvinyl alcohol (PVA) ); Acrylic polymers such as polymethyl methacrylate (PMMA), urethane polymers such as polyurethane; and the like. Examples of the polymer material that is dispersed in water (water dispersible) include vinyl polymers such as polyethylene (PE) and polypropylene (PP); polyethylene oxide (PEO), polyethylene oxide, polytetrafluoroethylene (PTFE), and the like. Fluoropolymers such as ethylene polymer, tetrafluoroethylene-hexafluoropropylene copolymer (FEP), tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer (PFA); vinyl acetate copolymer; styrene butadiene rubber ( SBR) and rubbers such as acrylic acid-modified SBR resin (SBR latex). Although it does not specifically limit, the ratio of the binder to the whole positive electrode active material layer 14 can be 0.1 mass% or more and 10 mass% or less (preferably 1 mass% or more and 5 mass% or less), for example.

The solvents used for preparing the slurry are roughly classified into aqueous and organic solvents. Examples of organic solvents include amides, alcohols, ketones, esters, amines, ethers, nitriles, cyclic ethers, aromatics. Group hydrocarbons and the like. More specifically, N-methyl-2-pyrrolidone (NMP), N, N-dimethylformamide, N, N-dimethylacetamide, 2-propanol, ethanol, methanol, acetone, methyl ethyl ketone, methyl propenoate, cyclohexanone, acetic acid Methyl, ethyl acetate, methyl acrylate, diethyltriamine, N, N-dimethylaminopropylamine, acetonitrile, ethylene oxide, tetrahydrofuran, dioxane, benzene, toluene, ethylbenzene, xylene dimethyl sulfoxide, dichloromethane, trichloromethane, dichloroethane, etc. Typically, NMP can be used. In addition, the aqueous solvent is preferably water or a mixed solvent mainly composed of water. As the solvent other than water constituting the mixed solvent, one or more organic solvents (lower alcohol, lower ketone, etc.) that can be uniformly mixed with water can be appropriately selected and used.
The solid content concentration (NV) of the positive electrode active material layer forming slurry can be about 50% by mass to 80% by mass (for example, 55% by mass to 70% by mass).

On the other hand, as the negative electrode active material used for forming the negative electrode active material layer 24, one or more kinds of materials conventionally used in lithium secondary batteries can be used without particular limitation. Preferable examples include carbon-based materials such as graphite carbon and amorphous carbon, lithium transition metal oxides, lithium transition metal nitrides, and the like. The negative electrode active material layer 24 is prepared by mixing a powdered negative electrode active material and a suitable binder in a suitable solvent as described above to prepare a slurry-like composition. It can be formed in the same manner as the positive electrode active material layer 14 by being applied onto 22, dried, and pressed as necessary. Although not particularly limited, the proportion of the negative electrode active material in the entire negative electrode active material layer 24 is usually about 50% by mass or more, preferably about 90% by mass to 99% by mass (for example, about 95 mass% to 99 mass%). The density of the negative electrode active material layer 24 is, for example, 1.0 g / cm ³ or more (typically 1.2 g / cm ³ or more, for example, 1.3 g / cm ³ or more), and 1.5 g / cm ³ or less. It can be.

  As the binder, an appropriate material can be selected from the polymer materials exemplified as the binder for forming the positive electrode active material layer. For example, styrene butadiene rubber (SBR), polyvinylidene fluoride (PVdF), polytetrafluoroethylene (PTFE) and the like are exemplified. The proportion of the binder in the entire negative electrode active material layer 24 is not particularly limited, but may be, for example, 1% by mass to 10% by mass (preferably 2% by mass to 5% by mass).

  Moreover, as the base materials 42A and 42B of the separator sheets 40A and 40B, various synthetic resin porous sheets similar to those conventionally used for secondary batteries can be used. For example, a porous resin sheet (film) made of a synthetic resin such as polyethylene (PE), polypropylene (PP), polyester, cellulose, polyamide and the like can be mentioned. In particular, a polyolefin-based porous resin sheet is preferable. Separator sheets 40A and 40B (base materials 42A and 42B) may have a single-layer structure, or a multilayer structure of two or more layers (for example, PP-PE- in which polypropylene layers are laminated on both sides of a polyethylene layer in the thickness direction). PP three-layer structure). Details of the configuration of the separator sheets 40A and 40B according to the present embodiment will be described later.

As shown in the figure, the positive electrode sheet 10 has a positive electrode active material layer in which a positive electrode active material layer (positive electrode mixture layer) 14 is not formed at one end of both ends in the winding axis direction (width direction). A forming portion 16 is formed in the longitudinal direction of the sheet. That is, the positive electrode active material non-forming portion 16 is formed so that the positive electrode current collector 12 is exposed on the surface.
Similarly, in the negative electrode sheet 20, the negative electrode active material non-formation part 26 in which the negative electrode active material layer (negative electrode mixture layer) 24 is not formed at the other end of both ends in the winding axis direction (width direction). Are formed in the longitudinal direction of the sheet. That is, the negative electrode active material non-forming portion 26 is formed so that the negative electrode current collector 22 is exposed on the surface.
The positive electrode sheet 10 and the negative electrode sheet 20 are formed so that the positive electrode active material layer non-forming portion 16 protrudes from the negative electrode sheet 20 and the negative electrode active material layer non-forming portion 26 protrudes from the positive electrode sheet 10. The wound electrode body 80 according to the present embodiment is formed by winding the separator sheets 40A and 40B into a flat shape while overlapping them.
In the wound electrode body 80 accommodated in the battery case 50, the positive electrode current collector plate 74 is formed on the positive electrode active material layer non-formation part 16 of the positive electrode current collector 12, and the negative electrode active material layer non-formation part of the negative electrode current collector 22 is formed. 26 are respectively attached to the negative electrode current collector plates 76 and are electrically connected to the positive electrode terminal 70 and the negative electrode terminal 72, respectively.

Inside the battery case 50, a current interrupting mechanism 30 that is activated by an increase in the internal pressure of the battery case is provided. The current interruption mechanism 30 only needs to be configured to cut a conductive path (for example, a charging path) from at least one electrode terminal to the electrode body 80 when the internal pressure of the battery case 50 increases, and has a specific shape. It is not limited to. For example, in the embodiment shown in FIG. 2, the current interruption mechanism 30 is provided between the positive electrode terminal 70 fixed to the lid body 54 and the electrode body 80, and when the internal pressure of the battery case 50 rises, the electrode body from the positive electrode terminal 70. The conductive path reaching 80 is cut.
Specifically, the current interrupt mechanism 30 can include, for example, a first member 32 and a second member 34. When the internal pressure of the battery case 50 rises, at least one of the first member 32 and the second member 34 is deformed and separated from the other, thereby cutting the conductive path. In this embodiment, the first member 32 is a deformed metal plate, and the second member 34 is a connection metal plate joined to the deformed metal plate 32. The deformed metal plate (first member) 32 has an arch shape in which a central portion is curved downward, and a peripheral portion thereof is connected to the lower surface of the positive electrode terminal 70 via a current collecting lead terminal 35. Further, the tip of the curved portion 33 of the deformed metal plate 32 is joined to the upper surface of the connection metal plate 34. A positive current collector plate 74 is joined to the lower surface (back surface) of the connection metal plate 34, and the positive current collector plate 74 is connected to the positive electrode 10 of the electrode body 80. In this way, a conductive path from the positive electrode terminal 70 to the electrode body 80 is formed.

The current interrupt mechanism 30 includes an insulating case 38 made of plastic or the like. The insulating case 38 is provided so as to surround the deformed metal plate 32 and hermetically seals the upper surface of the deformed metal plate 32. The internal pressure of the battery case 50 does not act on the upper surface of the hermetically sealed curved portion 33. The insulating case 38 has an opening into which the curved portion 33 of the deformed metal plate 32 is fitted, and the lower surface of the curved portion 33 is exposed from the opening to the inside of the battery case 50. The internal pressure of the battery case 50 acts on the lower surface of the curved portion 33 exposed inside the battery case 50. In the current interrupt mechanism 30 having such a configuration, when the internal pressure of the battery case 50 increases, the internal pressure acts on the lower surface of the curved portion 33 of the deformed metal plate 32, and the curved portion 33 curved downward is pushed upward. The upward push of the curved portion 33 increases as the internal pressure of the battery case 50 increases. When the internal pressure of the battery case 50 exceeds the set pressure, the curved portion 33 is inverted so as to be bent up and down. Due to the deformation of the curved portion 33, the joint point 36 between the deformed metal plate 32 and the connection metal plate 34 is cut. As a result, the conductive path from the positive electrode terminal 70 to the electrode body 80 is cut, and the overcharge current is cut off.
The current interrupt mechanism 30 is not limited to the positive terminal 70 side, and may be provided on the negative terminal 72 side. Further, the current interrupt mechanism 30 is not limited to the mechanical cutting accompanied by the deformation of the deformed metal plate 32 described above. For example, the internal pressure of the battery case 50 is detected by a sensor, and the internal pressure detected by the sensor sets the set pressure. An external circuit that cuts off the charging current when exceeded can be provided as a current cut-off mechanism.

As the electrolyte (electrolyte solution) used, one kind or two or more kinds similar to those conventionally used for lithium secondary batteries can be used without any particular limitation. Such an electrolyte typically has a composition in which a supporting salt (typically a lithium salt) is contained in a suitable non-aqueous solvent, but a polymer is added to the liquid electrolyte to form a solid (typically It may be a so-called gel.
As the non-aqueous solvent, aprotic solvents such as carbonates, esters, ethers, nitriles, sulfones, and lactones can be used. For example, ethylene carbonate (EC), propylene carbonate (PC), diethyl carbonate (DEC), dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), 1,2-dimethoxyethane, 1,2-diethoxyethane, tetrahydrofuran, Examples include 2-methyltetrahydrofuran, dioxane, 1,3-dioxolane, diethylene glycol, dimethyl ether, ethylene glycol, dimethyl ether, acetonitrile, propionitrile, nitromethane, N, N-dimethylformamide, dimethyl sulfoxide, sulfolane, and γ-butyrolactone. Among them, ECs having a high relative dielectric constant and carbonates such as DMC and EMC having a high standard oxidation potential (that is, having a wide potential window) can be preferably used. For example, the nonaqueous solvent contains one or more carbonates, and the total volume of these carbonates is 60% by volume or more (more preferably 75% by volume or more, and further preferably 90% by volume) of the total volume of the nonaqueous solvent. That is, it may be substantially 100% by volume.) A non-aqueous solvent can be preferably used.

As the supporting salt, various materials known to function as a supporting electrolyte for the secondary battery can be appropriately employed. For example, LiPF ₆ , LiBF ₄ , LiClO ₄ , LiN (SO ₂ CF ₃ ) ₂ , LiN (SO ₂ C ₂ F ₅ ) ₂ , LiCF ₃ SO ₃ , LiC ₄ F ₉ SO ₃ , LiC (SO ₂ CF ₃ ) ₃ One or two or more selected from various lithium salts known to be capable of functioning as a supporting electrolyte for lithium secondary batteries such as LiClO ₄ can be used, and LiPF ₆ is preferably used among them. it can. The concentration of the supporting salt is not particularly limited, but if it is too low, the amount of lithium ions contained in the electrolyte is insufficient and the ionic conductivity tends to be lowered. On the other hand, if the concentration is extremely high, the viscosity of the electrolyte becomes too high, and the ionic conductivity tends to decrease. Therefore, the concentration of the supporting salt is preferably about 0.1 mol / L to 2 mol / L (preferably about 0.8 mol / L to 1.5 mol / L).

Various additives can be contained in the electrolyte. For example, as an overcharge preventive agent, the oxidation potential is higher than the operating voltage of the lithium secondary battery (for example, 4.2 V or higher in the case of a lithium secondary battery that is fully charged at 4.2 V) and is oxidized. A compound that generates a large amount of gas can be used without particular limitation. For example, a lithium secondary battery that is fully charged at 4.2 V preferably has an oxidation reaction potential in the range of 4.6 V to 4.9 V. For example, a biphenyl compound, a cycloalkylbenzene compound, an alkylbenzene compound, an organic phosphorus compound, a fluorine atom-substituted aromatic compound, a carbonate compound, a cyclic carbamate compound, an alicyclic hydrocarbon, and the like can be given. More specifically, biphenyl (BP), alkylbiphenyl, terphenyl, 2-fluorobiphenyl, 3-fluorobiphenyl, 4-fluorobiphenyl, 4,4′-difluorobiphenyl, cyclohexylbenzene (CHB), trans-butylcyclohexyl Benzene, cyclopentylbenzene, t-butylbenzene, t-aminobenzene, o-cyclohexylfluorobenzene, p-cyclohexylfluorobenzene, tris- (t-butylphenyl) phosphate, phenyl fluoride, 4-fluorophenyl acetate, diphenyl carbonate, Examples thereof include methyl phenyl carbonate, bicterary butyl phenyl carbonate, diphenyl ether, dibenzofuran, and the like. In particular, cyclohexylbenzene (CHB) and a cyclohexylbenzene derivative are preferably used. The amount of the overcharge inhibitor used relative to 100% by mass of the electrolytic solution used is, for example, about 0.01 to 10% by mass, preferably about 0.1 to 5% by mass.
Furthermore, various additives (for example, additives that can improve battery performance. Specifically, vinylene carbonate (VC), fluoroethylene carbonate (FEC), and the like) can be appropriately added to the electrolyte.

Hereinafter, the separator sheets 40A and 40B constituting the wound electrode body 80 according to the present embodiment will be described in more detail.
As shown in FIGS. 3 and 4, two long sheet separators (separator sheets) 40 </ b> A and 40 </ b> B are used for the wound electrode body 80 of the secondary battery 100 according to the present embodiment. As described above, the base materials 42A and 42B of the separator sheets 40A and 40B are made of a polyolefin-based synthetic resin (for example, a three-layer structure of PP-PE-PP).
In the secondary battery 100 disclosed herein, the porous heat-resistant material including the inorganic filler with a predetermined width in the winding axis direction (width direction) on one surface of the base materials 42A and 42B of the separator sheets 40A and 40B. Layers (Heat Resistance Layer: also referred to as “HRL”) 44A and 44B are formed. Specifically, as shown in FIG. 3, in the separator sheets 40A and 40B according to the present embodiment, the porous heat-resistant layer 44A is formed on the surface facing the winding center (that is, the inner surface when wound). , 44B are formed.

The method of forming the porous heat-resistant layers 44A and 44B may be the same as the conventional method, and no special treatment is required for the implementation of the present invention. For example, a method of applying a slurry composition obtained by mixing an inorganic filler and a binder in an appropriate solvent onto the base materials 42A and 42B can be employed.
As the inorganic filler, particles of various inorganic compounds can be employed. For example, it may be one or more selected from oxides, carbides, silicides, nitrides, and the like of metal elements or nonmetal elements. More specifically, aluminum oxide (alumina: Al ₂ O ₃ ), zirconium dioxide (zirconia: ZrO ₂ ), magnesium oxide (magnesia: MgO), silicon oxide (silica: SiO ₂ ), titanium oxide (titania: TiO _2). ), Cerium oxide (ceria: CeO ₂ ), yttrium oxide (yttria: Y ₂ O ₃ ), barium titanate (BaTiO ₃ ) and other oxide materials; cordierite (2MgO · 2Al ₂ O ₃ · 5SiO ₂ ) , mullite _{(3Al 2 O 3 · 2SiO 2} ), forsterite (2MgO · _SiO 2), steatite (MgO · _SiO 2), sialon _{(Si 3 N 4 · Al 2} O 3), zirconium _{(ZrO 2} · SiO 2 ), complex oxide material such as ferrite _{(M 2 O · Fe 2 O} 3); silicon nitride (Silicon _nitride: Si _{3 N} 4), aluminum nitride hydroxide-based material hydroxyapatite and the like;::; (SiC silicon carbide) carbide-based material such as (aluminum nitride AlN) nitride material such as silicon carbide Elemental materials such as carbon (C), silicon (Si), aluminum (Al), and iron (Fe); or a composite material containing one or more of these materials. Among these, it is preferable that at least one of alumina, magnesia, zirconia, silica, boehmite, and titania is included. The above compound has a high melting point and is excellent in heat resistance and chemical stability. Moreover, since it is comparatively cheap, raw material cost can be suppressed. The D ₅₀ particle size of the inorganic filler can be, for example, from 0.1 μm to 15 μm (typically from 0.2 μm to 1.5 μm). The ratio of the inorganic filler contained in the porous heat-resistant layer is not particularly limited, but is 50% by mass or more (typically 85% by mass or more, for example, 90% by mass or more), and 99.9% by mass or less (for example, 99% Mass% or less).

  The porous heat-resistant layers 44A and 44B typically include a binder (polymer component) in addition to the inorganic filler. Examples of the binder include a binder that can be blended in the above-described slurry for forming an electrode active material layer, acrylonitrile-butadiene copolymer rubber (NBR), acrylonitrile-isoprene copolymer rubber (NIR), and acrylonitrile-butadiene-isoprene copolymer. Rubbers containing acrylonitrile as a copolymerization component such as polymer rubber (NBIR); suitably from acrylic polymers having acrylic acid, methacrylic acid, acrylic acid ester or methacrylic acid ester (eg alkyl ester) as the main copolymerization component Can be selected and used. Among these polymers, an acrylic polymer based on an acrylic resin has a strong binding force and is electrochemically stable, and can be preferably used. In addition, even if this acrylic polymer consists of one type of homopolymer (for example, polymethyl methacrylate), it is a copolymer of two or more types of methacrylic acid or acrylic acid (for example, methyl methacrylate-butyl acrylate). Copolymer), or a copolymer of methacrylic acid or acrylic acid and other monomers (for example, methyl acrylate-ethylene copolymer), or a mixture of a plurality of homopolymers or copolymers. Good.

  The total thickness of the separator sheets 40A and 40B (total thickness of the base materials 42A and 42B and the porous heat-resistant layers 44A and 44B) is not particularly limited, but is, for example, 10 μm to 50 μm (typically 10 μm to 40 μm). can do. The thickness of the porous heat-resistant layers 44A and 44B can be set to, for example, 2 μm to 20 μm (typically 3 μm to 15 μm). Further, the porosity (porosity) of the separator sheets 40A and 40B as a whole is not particularly limited. For example, 20% to 90% by volume (typically 30% to 80% by volume, for example, 35% to 70% by volume). Volume% or less).

As shown in FIGS. 3 and 4 (for convenience of explanation, the outer separator 40B is not shown), the separator sheets 40A and 40B according to the present embodiment are arranged at both ends in the winding axis direction (width direction). Separator substrate exposed portions 46A and 46B in which the porous heat-resistant layers 44A and 44B are not formed are formed in the sheet longitudinal direction.
Specifically, in the winding axis direction, the porous heat-resistant layers 44A and 44B are formed in a width dimension that can include the entire positive electrode active material layer 14 or the negative electrode active material layer 24 facing each other, and both ends thereof are formed. The separator substrate exposed portions 46A and 46B are formed in the sheet longitudinal direction with a predetermined width dimension (L).
Here, the separator base material exposed portions 46A and 46B do not overlap the positive electrode active material layer 14 and the negative electrode active material layer 24, and are always out of the positive electrode active material layer non-formation portion 16 and the negative electrode active material layer non-formation portion 26. It is formed at a position facing either one. In other words, the width dimension of the separator sheets 40A and 40B as a whole is such that both ends in the width direction (that is, the edge portions of the separator base material exposed portions 46A and 46B) are the positive electrode active material layer non-forming portion 16 or the negative electrode active material layer non-forming portion. 26 can be contacted. Thus, by defining the width dimension of separator sheet 40A, 40B and providing separator base-material exposed part 46A, 46B at both ends, either positive or negative facing the separator base-material exposed part 46A, 46B in the wound electrode body 80 The active material layer non-forming portions 16 and 26 (that is, the current collectors 12 and 22) can be brought into direct contact so that a high frictional force can be exerted at the contact portion. Thereby, it is possible to prevent the winding electrode body 80 from being displaced or buckled when the wound electrode body 80 is constructed or after the battery is used.

  Preferably, as shown in the drawing, the separator base material exposed portions 46A and 46B are formed so that the active material layer 14 and the positive electrode active material layer non-formed portion 16 or the negative electrode active material layer non-formed portion 26 are more than half of the width dimension. It is formed so as to be arranged at a position close to 24. By disposing the separator substrate exposed portions 46A and 46B so as to be able to come into contact with a relatively central portion (ie, close to the active material layers 14 and 24) of the active material layer non-forming portions 16 and 26, the active material layer non-forming is formed. The frictional force can be improved without obstructing the connection of the external connection terminals 70 and 72 (specifically, current collector plates 74 and 76 connected to the terminals) in the portions 16 and 26.

  Although it does not specifically limit because it depends on the size of the wound electrode body 80, the width dimension (L) of the separator base material exposed portions 46A and 46B is preferably 1 mm or more (for example, about 1 to 3 mm). By providing the separator base material exposed portions 46A and 46B at both ends of the separator sheets 40A and 40B with such dimensions, the frictional force between the separator sheets 40A and 40B and the electrode sheets 10 and 20 can be further increased. In addition, the width dimension (L) of the separator base material exposed portions 46A and 46B is less than or equal to half the width dimension of the opposed electrode active material layer non-forming portions 16 and 26 (more preferably one third or less, particularly Is preferably about 1/4 or less). If the width dimension (L) is too large, the connection of the external connection terminals 70 and 72 (specifically, current collector plates 74 and 76 connected to the terminals) in the opposing electrode active material layer non-forming portions 16 and 26 is hindered. This is not preferable.

In the separator sheets 40A and 40B according to the present embodiment, separator base material exposed portions 46A and 46B having substantially the same width dimension are formed at both ends in the width direction, but as long as the above-described improvement in frictional force can be realized, The separator substrate exposed portions 46A and 46B at both ends need not have the same width dimension, and may have different width dimensions.
Further, the separator sheets 40A and 40B according to the present embodiment have the porous heat-resistant layers 44A and 44B formed on one surface (the wound inner surface side), but the porous heat-resistant layers 44A and 44B are formed on both surfaces. It may be.

As described above, the secondary battery 100 disclosed herein prevents the winding electrode body 80 from being displaced or buckled when the wound electrode body 80 is constructed or after the battery is used. Since the body 80 maintains high rigidity and is excellent in cycle characteristics and other battery characteristics, it is suitable as a driving power source for the vehicle 1 (FIG. 6) such as an electric vehicle or a hybrid vehicle.
FIG. 5 is an example of an assembled battery 200 that can be used as a power source for driving a vehicle 1 (FIG. 6) in which such secondary batteries (unit cells) 100 are connected in series and / or in parallel. A secondary battery (typically a sealed nonaqueous electrolyte secondary battery) 100 disclosed herein is suitable as an assembled battery in which a plurality of the batteries (single cells) are connected in series and / or in parallel. Can be used. In the form shown in FIG. 5, the assembled battery 200 includes a plurality of (typically 10 or more, preferably about 10 to 30, for example, 20) secondary batteries (unit cells) 100, each positive terminal 70. In addition, the wide surfaces of the battery case 50 are arranged in the facing direction (stacking direction) while being inverted one by one so that the negative terminals 72 are alternately arranged. A cooling plate 110 having a predetermined shape is sandwiched between the arranged unit cells 100. The cooling plate 110 functions as a heat dissipating member for efficiently dissipating heat generated in each unit cell 100 during use, and preferably a cooling fluid (typically between the unit cells 100). Air) (for example, a shape in which a plurality of parallel grooves extending vertically from one side of the rectangular cooling plate to the opposite side are provided on the surface). A cooling plate made of metal having good thermal conductivity or lightweight and hard polypropylene or other synthetic resin is suitable.

  A pair of end plates (restraint plates) 120 are arranged at both ends of the unit cells 100 and the cooling plate 110 arranged as described above. One or a plurality of sheet-like spacer members 150 as length adjusting means may be sandwiched between the cooling plate 110 and the end plate 120. The unit cell 100, the cooling plate 110, and the spacer member 150 arranged in the above manner are applied with a predetermined restraining pressure in the stacking direction by a fastening restraint band 130 attached so as to bridge between both end plates. It is restrained. More specifically, by tightening and fixing the end portion of the restraining band 130 to the end plate 120 with screws 155, the unit cells and the like are restrained so that a predetermined restraining pressure is applied in the arrangement direction. Thereby, restraint pressure is also applied to the wound electrode body 80 housed in the battery case 50 of each unit cell 100. Then, between the adjacent unit cells 100, one positive terminal 70 and the other negative terminal 72 are electrically connected by a connecting member (bus bar) 140. Thus, the assembled battery 200 of the desired voltage is constructed | assembled by connecting each cell 100 in series.

  EXAMPLES Hereinafter, the present invention will be specifically described with reference to examples. However, the present invention is not intended to be limited to those shown in the specific examples.

As a lithium secondary battery for evaluation tests, a sealed lithium secondary battery (lithium ion battery) having a structure in which a wound electrode body was housed in a rectangular battery case as shown in FIGS.
<Separator>
First, a heat-resistant layer forming slurry for forming a porous heat-resistant layer in the separator was prepared. Specifically, alumina (D ₅₀ : 0.9 μm, BET specific surface area: 18 m ² / g) as an inorganic filler, styrene butadiene rubber (SBR) as a binder, and carboxymethyl cellulose CMC as a thickener. The slurry for heat-resistant layer formation was prepared by mixing with ion exchange water so that mass ratio of these materials might be 97: 2: 1 as an alumina: binder: thickening material. For the preparation of such a slurry, mixing and kneading were carried out using an ultrasonic disperser (manufactured by M Technique, CLEARMIX) under conditions of 15,000 rpm for 5 minutes as preliminary dispersion and 15 minutes at 20000 rpm as main dispersion.

As the separator substrate, a porous sheet having a three-layer structure of PP / PE / PP made of polypropylene (PP) and polyethylene (PE) was used. The substrate had a width-wise dimension of 112 mm, a sheet length of about 5000 mm, a thickness of 20 μm, and a shutdown temperature (PE layer softening point) of 128 ° C.
And the said slurry for heat-resistant layer formation was apply | coated to the single side | surface of a separator base material with the general gravure coating method. As coating conditions, a gravure roll having a line number: # 100 lines / inch and an ink holding amount: 19.5 ml / cm ² was used, the coating speed was 3 m / min, the gravure roll speed was 3.8 m / min, and the gravure The coating was performed under the condition of a speed / coating speed ratio of 1.27. Then, the porous heat-resistant layer was formed in the single side | surface of a base material by drying the separator after coating. In addition, the thickness of the whole separator which combined the base material and the porous heat-resistant layer was about 25 μm.
Thus, a porous heat-resistant layer having various width dimensions was formed on one side of the separator substrate in the longitudinal direction of the sheet by the coating method. Here, a separator having the following configuration was prepared for testing.
(Example 1) Width dimension of porous heat-resistant layer: 106 mm
Width dimension (L) of the separator substrate exposed part at both ends: 3.0 mm each
(Example 2) Width dimension of porous heat-resistant layer: 107 mm
Width dimension (L) of separator substrate exposed part at both ends: 2.5 mm each
(Example 3) Width dimension of porous heat-resistant layer: 108 mm
Width dimension (L) of the separator substrate exposed part at both ends: 2.0 mm each
(Example 4) Width dimension of porous heat-resistant layer: 109 mm
Width dimension (L) of separator substrate exposed part at both ends: 1.5 mm each
(Example 5) Width dimension of porous heat-resistant layer: 110 mm
The width dimension (L) of the separator substrate exposed part at both ends: 1.0 mm each
(Comparative example 1) The width dimension of a porous heat-resistant layer: 112 mm
That is, a porous heat-resistant layer was formed on the entire surface of the substrate (no exposed part)
(Comparative example 2) The width dimension of a porous heat-resistant layer: 104 mm
Width dimension (L) of separator substrate exposed portions at both ends: 4.0 mm each
(Comparative example 3) The width dimension of a porous heat-resistant layer: 112 mm
That is, a porous heat-resistant layer was formed on the entire surface of the substrate (no exposed part)

<Negative electrode>
Graphite (negative electrode active material), styrene butadiene block copolymer (SBR) as a binder, and carboxymethyl cellulose (CMC) as a thickener have a mass ratio of 100: 1: 1. Thus, the slurry for negative electrode active material layer formation was prepared by mixing with ion-exchange water. In addition, a copper foil having a width-direction dimension of 119 mm, a sheet length of 4700 mm, and a thickness of 14 μm was prepared as the negative electrode current collector.
Thus, the slurry has a negative electrode active material coverage (unit weight) on both sides while leaving an uncoated part (that is, a negative electrode active material layer non-formed part) along one end of the copper foil. Both sides were applied and dried so as to be 7.3 mg / cm ² . After drying, rolling was performed with a rolling press so that the density of the negative electrode active material layer was approximately 1.0 to 1.2 g / cm ³ and the thickness of the negative electrode sheet was 150 μm. As a result, a negative electrode sheet in which the width dimension of the negative electrode active material layer was 106 mm and the width dimension of the negative electrode active material layer non-forming portion was 13 mm was produced.

<Positive electrode>
A lithium transition metal composite oxide having a composition represented by the general formula Li _1.14 Ni _0.34 Co _0.33 Mn _0.33 O ₂ is used as a positive electrode active material, and the positive electrode active material and a conductive material Formation of positive electrode active material layer by mixing acetylene black (AB) and polyvinylidene fluoride (PVDF) as a binder with NMP (solvent) so that the mass ratio of these materials is 90: 8: 2. A slurry was prepared. Further, an aluminum foil having a width-direction dimension of 116 mm, a sheet length of 4500 mm, and a thickness of 15 μm was prepared as a positive electrode current collector.
Thus, the coating amount (weight per unit area) of the positive electrode active material per unit area is kept on both sides while leaving the uncoated part (that is, the positive electrode active material layer non-formed part) along one end of the aluminum foil. Both surfaces were applied and dried so as to be 11.2 mg / cm ² . After drying, rolling was performed with a rolling press so that the density of the positive electrode active material layer was approximately 1.9 to 2.3 g / cm ³ and the thickness of the positive electrode sheet was 170 μm. Thus, a positive electrode sheet in which the positive electrode active material layer had a width dimension of 100 mm and the positive electrode active material layer non-formed portion had a width dimension of 16 mm was produced.

<Construction of evaluation test battery>
A lithium secondary battery for an evaluation test was constructed by using two separator sheets of any one of Examples 1 to 5 and Comparative Examples 1 to 3, and one positive electrode sheet and one negative electrode sheet.
That is, as shown in FIG. 3, the positive electrode and the negative electrode are arranged with the separator interposed therebetween, so that the active material layer non-forming portion is located on the opposite side, and the negative electrode active material layer is the positive electrode active material layer. Except when laminated in a width direction and wound into an ellipsoidal shape so that both ends of the separator in the width direction do not cover the negative electrode active material layer and the positive electrode active material layer, and then the separator of Comparative Example 3 was used. A wound electrode body was produced by applying a pressure of about 4 minutes at a pressure of 4 kN / cm ² using a flat plate or the like at room temperature (25 ° C.) and causing it to be flattened.
On the other hand, in the case of using the separator of Comparative Example 3 (i.e., the separator having no separator substrate exposed portion), the flat shape is obtained by heating the wound electrode body to 80 ° C. in order to maintain the shape of the wound electrode body. I was kidnapped.

The wound electrode body formed as described above was accommodated in an aluminum prismatic battery case together with a non-aqueous electrolyte and sealed to construct a lithium secondary battery for evaluation test.
The nonaqueous electrolytic solution was prepared by mixing 1 mol / liter of LiPF ₆ as a lithium salt in a mixed solvent obtained by mixing ethylene carbonate (EC), ethyl methyl carbonate (EMC), and dimethyl carbonate (DMC) at 3: 3: 4 (volume ratio). It added so that it might become L, and also added CHB and BP so that it might become 1 mass% of each. About 125 g of this electrolyte was injected into the case. The battery capacity of the evaluation lithium secondary battery was about 24.0 Ah.
In the following evaluation tests, the type of separator used (Examples 1 to 5 and Comparative Examples 1 to 3) is directly referred to as the battery of Examples 1 to 5 or Comparative Examples 1 to 3.

<Evaluation Test 1: Measurement of Battery Resistance>
After measuring the battery capacity, the battery resistance (internal resistance: IV resistance value) of each battery was measured. Specifically, each battery was discharged at a constant current to 3.0 V under a temperature condition of 25 ° C., and then charged at a constant current and a constant voltage to adjust to SOC (state of charge) 60%. Thereafter, a discharge pulse current of 10 seconds was applied at 25 ° C. and 1 C, and the voltage V1 at the 10 seconds was measured. Then, for the battery adjusted to SOC 60% again, the pulse current is increased stepwise in the order of 2C, 5C, and 10C to alternately discharge and charge, and measure the voltage 10 seconds after the start of each discharge. An IV characteristic graph of each battery was prepared. The IV resistance value (mΩ) at 25 ° C. was calculated from the slope of this IV characteristic graph. Measurement was performed with 10 samples (N), and the average value was obtained. The results are shown in the corresponding column of Table 1.

<Evaluation Test 2: Confirmation of Battery Capacity and Measurement of Cycle Capacity Maintenance Ratio>
The battery capacity of each example and comparative example was measured. That is, first, under a temperature condition of room temperature (25 ° C.), the battery was charged to 4.1 V at a current density equivalent to 1 C by a constant current-constant voltage (CCCV) method and rested for 5 minutes. Thereafter, the battery was discharged at a constant current to 3.0 V at the same current density and rested for 5 minutes. Thereafter, the initial capacity was confirmed by performing CCCV charging (up to 4.1 V, rate is 1 C, 0.1 C cut) and CCCV discharge (up to 3.0 V, rate is 1 C, 0.1 C cut).
After confirming the initial capacity, 1000 cycles of 2C CC cycle charge / discharge were performed in a constant temperature bath at 50 ° C., and then the capacity was confirmed. Thus, the cycle capacity retention rate was determined from the capacity after 1000 cycles / initial capacity. The number of samples (N) was 5, and the average value was obtained. The results are shown in the corresponding column of Table 1.

<Evaluation Test 3: Storage Durability Test>
The batteries of each Example and Comparative Example were adjusted to SOC 100% under a room temperature (25 ° C.) temperature condition and stored for 100 days under a 60 ° C. condition.
Thereafter, the battery capacity was confirmed and the cycle capacity retention rate was measured in the same manner as in the evaluation test 2 described above. The number of samples (N) was 50, and the average value was obtained. The results are shown in the corresponding column of Table 1.

As shown in Table 1, when the separator substrate exposed portions at both ends are 1 to 3 mm, the battery resistance (internal resistance) is relatively low, and the cycle capacity retention rate is good and the capacity is maintained after storage. Showed the rate.
On the other hand, in the battery of Comparative Example 1 that does not have the separator substrate exposed portion, displacement or buckling occurs in the wound electrode body due to expansion and contraction during the cycle, and as a result, the unreacted portion increases in the electrode body and the capacity is maintained. A decrease in rate was observed. In addition, as described above, in the battery of Comparative Example 3 in which the wound electrode body was constructed while performing the heat treatment at 80 ° C., although the deviation or buckling due to expansion / contraction during the cycle did not occur, A decrease in porosity (that is, clogging) was observed, an increase in battery resistance, and a decrease in high-rate characteristics was observed.
Further, in the battery of Comparative Example 2 in which the separator base exposed portions at both ends are each 4 mm, although the shape of the wound electrode body is maintained, a part of the separator base exposed portion faces the negative electrode active material layer. In other words, a portion where the porous heat-resistant layer does not exist is formed in the facing portion of the negative electrode active material layer. As a result, the space between the positive and negative electrodes is narrowed and an undesirable portion is formed at the end in the width direction, leading to a decrease in capacity.

  As is clear from the above examples, according to the secondary battery (rolled electrode body) disclosed herein, when the inside of the battery is overheated to the separator softening point or more due to the provision of the porous heat-resistant layer, etc. In addition to preventing an internal short circuit due to the melting of the separator, it is possible to prevent the occurrence of displacement and buckling due to a decrease in the frictional force between the separator and the electrode. In addition, it is possible to prevent the battery performance from being deteriorated due to deviation or buckling during expansion and contraction of the wound electrode body due to repeated charge and discharge, and to maintain high battery characteristics (for example, cycle characteristics).

  Specific examples of the present invention have been described in detail above, but these are merely examples and do not limit the scope of the claims. The technology described in the claims includes various modifications and changes of the specific examples illustrated above.

DESCRIPTION OF SYMBOLS 1 Vehicle 10 Positive electrode sheet 12 Positive electrode collector 14 Positive electrode active material layer 16 Positive electrode active material layer non-formation part 20 Negative electrode sheet 22 Negative electrode collector 24 Negative electrode active material layer 26 Negative electrode active material layer non-formation part 40A, 40B Separator sheet 42A , 42B Base material 44A, 44B Porous heat resistant layer (HRL)
46A, 46B Separator substrate exposed portion 50 Battery case 52 Case body 70 Positive electrode terminal 72 Negative electrode terminal 74 Positive electrode current collector plate 76 Negative electrode current collector plate 80 Winding electrode body 100 Secondary battery (lithium secondary battery)
200 batteries

Claims (5)

A wound electrode obtained by winding a positive electrode and a negative electrode each having a positive electrode active material layer and a negative electrode active material layer formed on each surface of a long sheet-like positive electrode current collector and a negative electrode current collector together with a long sheet-like separator. Body,
A case for accommodating the wound electrode body and the electrolyte;
A secondary battery comprising:
One end of both ends in the winding axis direction of the wound electrode body is configured by being laminated in a state where the positive electrode active material layer non-formed portion where the positive electrode active material layer is not formed protrudes from the negative electrode, In addition, the other end of the both ends is configured by being laminated in a state where the negative electrode active material layer non-formed portion where the negative electrode active material layer is not formed protrudes from the positive electrode,
The long sheet separator is a separator base material made of a synthetic resin and a porous heat-resistant layer mainly composed of an inorganic filler, and is formed on at least one surface of the base material in the longitudinal direction of the separator sheet. A heat-resistant layer, and
Here, the porous heat-resistant layer of the separator is formed in a width dimension in which the whole of the positive electrode active material layer or the negative electrode active material layer facing each other in the winding axis direction can be included in the heat-resistant layer, and
At both ends in the winding axis direction of the separator, the separator base material exposed portion that does not have the porous heat-resistant layer, and can be in contact with the opposing positive electrode active material layer non-forming portion or negative electrode active material layer non-forming portion. The secondary battery in which the separator base material exposed part arranged at various positions is formed in the sheet longitudinal direction.   The secondary battery according to claim 1, wherein the separator base material exposed portions are respectively formed at both ends of the separator in the winding axis direction so that a dimension in the winding axis direction is 1 mm or more.   In the separator, the active material is more than half the dimension in the same direction of the positive electrode active material layer non-formed part or negative electrode active material layer non-formed part facing the separator base material exposed parts at both ends in the winding axis direction. The secondary battery according to claim 1, wherein the secondary battery is formed so as to be disposed at a portion closer to the layer.   A secondary battery according to any one of claims 1 to 3 is a single battery, and a plurality of the single batteries are electrically connected to each other to provide a battery pack.   A vehicle comprising the secondary battery according to any one of claims 1 to 3 or the assembled battery according to claim 4 as a driving power source.

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