JP2002245994A - Accommodation member for lithium secondary battery and secondary battery pack using it - Google Patents

Abstract

PROBLEM TO BE SOLVED: To enhance a safety at the time of excess charging. SOLUTION: When the lithium secondary battery in which a battery element having a positive electrode and a negative electrode is accommodated in a flat plate-like case comprising an outer packaging material is accommodated in an accommodation member, a vertical strength of the accommodation member against a flat plate surface of the case is made to a strength withstanding a pressure of 0.5 kg/cm2 or more.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a secondary battery, and more particularly, to a secondary battery with improved safety during overcharge.

[0002]

2. Description of the Related Art Due to the high energy density of recently developed lithium secondary batteries with high energy density, there is an increased danger of ignition, smoking, etc. due to misuse of batteries or failure of equipment used. . From such a background, ensuring the safety of the secondary battery is one of the essential issues in the current battery design with a higher energy density.

One of the important issues in ensuring the safety of a battery is to ensure safety, especially against overcharging. this is,
If a certain amount of electricity flows for some reason when charging a secondary battery, the battery will be overcharged, resulting in an internal short circuit, etc. This is because the danger is relatively high. For example, generally, when a lithium secondary battery is in an overcharged state, first, gas is generated due to decomposition of an electrolytic solution or the like. The generation of gas not only leads to the rupture of the battery, leakage of liquid, and the like, but also the continuation of this state may eventually raise the battery temperature, which may even lead to accidents such as smoking and ignition. From such a viewpoint, various methods for preventing overcharge have been proposed.

[0004]

As a specific method for preventing overcharge, a control method using an electronic circuit attached to the outside of the battery and a safety valve utilizing gas generated by decomposition of an electrolyte or the like at the time of overcharge are used. A mechanical current interruption method and the like are known as general methods. However, in such a method, there is a problem in that an electronic circuit and a safety valve must be mounted on the battery, so that the battery cost is increased and the design of the battery is restricted.

[0005] In recent years, a flat case is formed by using a lightweight exterior material such as a laminate film in which resin layers are provided on both surfaces of a gas barrier layer, and a battery element having a positive electrode and a negative electrode is sealed therein. Types of batteries have been developed. Since such a battery can use a lightweight film as an exterior material, it has several advantages over a conventional case made of metal. That is, not only can the battery be reduced in weight and size, but also the case configuration is simpler than when a case made of a metal can including an electronic circuit and a safety valve is used. You. On the other hand, in such a battery, there is a problem that the control method using the electronic circuit and the mechanical current interrupting method using the safety valve are particularly difficult due to the configuration of the battery case.

On the other hand, as a specific method for preventing overcharge, a method of shutting down using the melting of a separator due to a rise in battery temperature, or a method of preventing overcharge having an oxidation potential higher than the positive electrode potential at full charge. There is also known a method of adding an agent to an electrolytic solution to cause an oxidation reaction of an organic additive when a positive electrode potential increases in an overcharged state, thereby suppressing a runaway reaction in a battery at the time of overcharge. However, in the former shutdown method using the separator, the runaway reaction at the time of overcharge is rapid, so that it may be difficult to sufficiently function as overcharge protection. In addition, in the latter method, the battery performance is adversely affected because an overcharge inhibitor that is not directly involved in the charge and discharge of the battery is added to the electrolyte, or the overcharge inhibitor is oxidized during overcharge. As a result of the reaction, gas is generated, and there is a concern that the generated gas may corrode equipment to be used or leak toxic gas such as organic gas.

[0007]

Means for Solving the Problems As a result of intensive studies to achieve the above object, the present inventors have found that the generation of gas in the battery during overcharging is more than a certain amount between the electrodes during overcharging. In addition to being able to suppress when the pressure of the battery is added, and suppressing the generation of gas in the battery at the time of overcharging, it is possible to not only prevent damage to the used equipment due to swelling of the battery and leakage of corrosive gas and toxic gas from the battery The present inventors have found that since the rise in battery temperature can be suppressed, the risk of smoke and ignition of the battery can be further reduced, and the present invention has been completed.

That is, the gist of the present invention resides in the following. (1) In a housing member for housing a lithium secondary battery in which a battery element having a positive electrode, a negative electrode, and an electrolyte is housed in a flat case made of an exterior material, the strength in a direction perpendicular to the flat surface of the case is zero. An accommodating member for a lithium secondary battery, having a strength capable of withstanding a pressure of 0.5 kg / cm ² or more. (2) The housing member for a lithium secondary battery according to (1), wherein the height of the housing portion of the housing member is 101 to 120% of the total thickness of the lithium secondary battery. (3) A secondary battery including a lithium secondary battery in which a battery element having a positive electrode, a negative electrode, and an electrolyte is housed in a flat case made of an exterior material inside the housing member of (1) or (2). pack. (4) The secondary battery pack according to (3), wherein the thickness of the exterior material is 0.2 mm or less. (5) The secondary battery pack according to (3) or (4), wherein the thickness of the lithium secondary battery is 2 mm or more. (6) The nominal capacity of the battery is 100 mAh or more (3)
The secondary battery pack according to (5). (7) The secondary battery pack according to any one of (3) to (6), wherein the exterior material is a laminated film in which a synthetic resin layer and a gas barrier layer are laminated. (8) The secondary battery pack according to any one of (3) to (7), wherein the battery element has a non-fluid electrolyte between the positive electrode and the negative electrode.

[0009]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, embodiments of the present invention will be described. FIG. 18 is a schematic exploded perspective view of a housing member according to an embodiment of the present invention, and FIG. 19 is a cross-sectional view taken along line AA of FIG. 18, showing a state where the battery element is housed in the housing member. is there. In the drawings, a direction indicated by x may be referred to as a left-right direction, a direction indicated by y may be referred to as a front-rear direction, and a direction indicated by z may be referred to as a thickness direction for convenience.

[0010] The housing member 181 comprises a cylindrical body 181a and two lids 181b and 181c. Cylindrical body 181a
Is an open-cylindrical body having an upper surface portion, a lower surface portion, a front surface portion, and a back surface portion, and has a flat rectangular parallelepiped shape spreading on an xy plane as a whole. The cylindrical body 181a is a resin member integrally molded. Further, the cylindrical body 181a has a housing part (space part) that opens to the outside in the left-right direction in the figure. Lid 181
Reference numerals b and 181c denote plate-shaped resin members spreading in the yz directions, respectively.
81a, and separates the housing from the outside. Cylinder 18
1a and lids 181b and 181c are screwed with screws 182, respectively. The lid 181c is provided with a terminal 182 connected to the positive and negative electrodes of the battery element.

[0011] The battery element is housed in the housing section. The battery element is formed by stacking a plurality (three in this case) of unit battery elements in which the positive electrode 192a and the negative electrode 192b are stacked via an electrolyte layer (spacer) 193c. The battery element has a flat plate shape extending in the xy directions as a whole. The battery element is vacuum-sealed in a case composed of two exterior materials 191a and 191b.

In the present invention, the above-mentioned structure which spreads in the xy directions
The direction perpendicular to the flat surface of the case (thickness
The strength of the housing member 181 in the vertical direction z) is 0.5 kg /
cm ^TwoAbove, preferably 0.6 kg / cm^TwoAbove.
If the housing member having such strength is used, the housing portion is overcharged.
The material presses the electrode with an appropriate pressure.
As a result, the battery that triggers a runaway
Significantly reduces the amount of gas generated by the decomposition reaction of the lysate
be able to. The load between the electrodes is under normal operating conditions.
In the following, it may lead to adverse effects such as short-circuit of the battery.
Housing member so that pressure is applied between electrodes only when charging
Is preferably designed. That is, at the time of overcharge,
Depth of lithium ion from cathode in particular
Increases remarkably from the vicinity of the charging depth at which the charging ends. Therefore,
By taking advantage of this phenomenon, pressing the electrode during normal use
Make sure that the thickness of the housing member is not
When the housing member comes into close contact with the battery to suppress swelling,
It is preferable that the thickness of the storage member be such that the battery is compressed.
No. Specifically, charge the battery even under normal use conditions.
Considering that there is a slight swelling of the battery when
The height of the storage section (L in FIG. 19)_Two),
Thickness of the secondary battery (L in FIG. 19).₁)
It is preferably set to 101 to 120%.

The strength of the housing member is usually 100 kg / cm, since it is difficult to obtain a material having an excessively high strength.
² or less, preferably 50 kg / cm ² or less. The strength of the housing member can be controlled by the material of the housing member, the strength of its assembly, and the like. In the above example, the housing member 1
Although 81 is made of a resin, the material is not particularly limited, and various materials such as a metal and a hybrid of a resin and a metal can be used. In the above example, the cylinder 181a and the lids 181b and 181b are assembled with screws, but are not particularly limited. For example, the cylinder 181a may be fixed with an adhesive or an adhesive tape, or fixed with a nail. Can be.

Further, in the above example, the housing member 1
As for 81, the one composed of the cylindrical body 181a and the lids 181b and 181b is used. In addition, as shown in FIG. 20, for example, as shown in FIG.
21b, and a bottomed cylindrical body 181a and a lid 1 opening upward (in the thickness direction) as shown in FIG.
An accommodation member composed of a pair of upper and lower flat members 184a supported by a plurality of (in this case, four) legs 185 as shown in FIG. 22 can be used. Also in these cases, the cylinder 181a and the lid 181b are assembled with screws, nails, an adhesive, an adhesive tape, or the like.

The secondary battery pack in which the battery element is housed in the housing member 181 is usually used by being connected to another battery-using device. Such devices using batteries include mobile phones, portable terminals, portable audio devices, cordless phone handsets, battery book players, pagers, handy terminals, portable faxes, portable copies, portable printers, headphone stereos, video movies, and LCDs. Televisions, handy cleaners, portable CDs, electric shavers, electronic translators, car phones, transceivers, power tools, electronic organizers, calculators, memory cards, tape recorders, radios, backup power supplies, cameras, medical equipment such as pacemakers and hearing aids, etc. Devices. In addition, various functions (circuits,
(A driving device, etc.), and the battery pack itself can be used as a battery-using device.

Next, the lithium secondary battery housed in the housing member will be described. The lithium secondary battery used in the present invention is a battery in which a battery element having a positive electrode and a negative electrode is housed in a flat case made of an exterior material. Since the amount is relatively small, the effect of the present invention is particularly remarkable when it is 1 mm or more, particularly 2 mm or more. On the other hand, if the thickness is too large, it is difficult to reduce the size and weight of the battery, so it is usually 5 mm or less, preferably 4.5 mm or less, and more preferably 4 m or less.
m or less.

Since a battery having a small capacity has a relatively small amount of gas generated during overcharge, a lithium secondary battery having a nominal capacity of usually 100 mAh or more, preferably 200 mAh or more is used. The battery element has a positive electrode and a negative electrode. The shape of the battery element is not particularly limited, and various shapes that can be stored in the flat case can be adopted. For example, as a battery element, as shown in FIG.
The positive electrode 192a and the negative electrode 192b are connected to an electrolyte layer (spacer).
It is possible to adopt a flat plate stacking shape in which a plurality (three in this case) of flat unit battery elements formed by stacking via the 193c are stacked in the stacking direction. Further, it is also possible to adopt a wound shape in which a belt-like laminate in which a positive electrode and a negative electrode are laminated with an electrolyte layer interposed therebetween is wound.

Hereinafter, a battery element formed by stacking a plurality of flat unit battery elements each having a positive electrode, a negative electrode, and a non-fluid electrolyte layer in a thickness direction is hermetically sealed by a film-like outer material. An embodiment of a lithium secondary battery will be described in detail using a secondary battery as an example. 1 is an exploded perspective view of a battery according to an embodiment, FIG. 2 is a sectional view of a main part of the battery, FIG. 3 is a schematic perspective view of a battery element, and FIGS. 4 and 5 are perspective views of the battery. 6 is a cross-sectional view of the case ((a) is an entire cross-sectional view, (b) is an enlarged cross-sectional view of a B portion of (a)), and FIG. 7 is a schematic cross-sectional view showing a state where the battery swells. For convenience of description, the battery shown in FIG. 1 is shown upside down in FIGS. 4 and 5.

In this battery, after the battery element 1 is accommodated in the concave portion of the exterior material 3, the terminal portions (tabs 4a, 4b) of the battery element 1 are provided.
An insulating material 5 such as an epoxy resin or an acrylic resin is injected into the vicinity, and then the exterior material 2 is put on the exterior material 3, and the peripheral parts 2a and 3a of the exterior materials 2 and 3 are joined by vacuum sealing. As shown in FIG. 1, the exterior material 2 is in a flat plate shape. The exterior material 3 includes a housing portion 3b formed of a rectangular box-shaped recess, and the housing portion 3b
And a peripheral portion 3a that protrudes outward from the four peripheral edges in a flange shape.

As shown in FIG. 3, the battery element 1 is formed by stacking a plurality of unit battery elements in the thickness direction. The tab 4a or 4b is extended from the unit battery element. The tabs 4a from the positive electrode are bundled (that is, overlapped with each other), and the positive electrode lead 21 is joined to form a positive electrode terminal portion. The tabs 4b from the negative electrode are also bundled together, and the negative electrode lead 21 is joined to form a negative electrode terminal.

The battery element 1 is accommodated in the accommodating portion 3b of the exterior material 3, and the insulating material 5 is injected near the tabs 4a and 4b.
After the sides of the battery element near the positive electrode terminal portion and the negative electrode terminal portion are covered with an insulating material, the exterior material 2 is covered. Battery element 1
Are extended from the exterior material 2, respectively.
3 is drawn out to the outside through the mating surfaces of the peripheral edges 2a, 3a on one side. Then, pressure reduction (preferably vacuum)
Under the atmosphere, the four peripheral edges 2a, 3a of the outer packaging materials 2, 3 are hermetically joined to each other by a method such as thermocompression bonding or ultrasonic welding, and the battery element 1 is sealed in the outer packaging materials 2, 3. Thereafter, the insulating material 5 is subjected to a hardening treatment by heating or the like, and the insulating material 5 is completely fixed near the terminal portion. Since the exterior material is sealed before completely fixed, the shape of the battery hardly changes during fixing.

By joining the peripheral portions 2a, 3a to each other, a case composed of the exterior materials 2, 3 is formed. FIG.
As shown in the figure, this case is composed of a side wall 4B ₁ , an upper bottom 4
B ₂ and lower bottom and the encapsulation portion 4B substantially rectangular parallelepiped formed by encapsulating battery element 1 (not shown), the peripheral edge portion 2a of the outer member, the bonding piece 4A of 3a with each other is formed by bonding, 4
F, 4G.

[0023] In the state according to Figure 4, the joint pieces 4A, 4F, 4G is flared outwardly from the side wall portion 4B ₁ of the encapsulating portion 4B that encapsulating battery element 1. Therefore, as shown in FIG. 5, of these joint piece, joining pieces 4A, bent along the 4G on the sidewall portion 4B ₁ of the encapsulation portion 4B, the side wall of the encapsulation section 4B by an adhesive sticking to parts 4B ₁ (fixed) it can be. That is, for example, as shown in FIG. 6, the junction piece 4A, while bent along the side wall portion 4B ₁ of the needle cover 4B, is adhered by adhesive 51 to these mutually. Various adhesives such as an epoxy adhesive, an acrylic adhesive, a urethane adhesive, a hot melt adhesive, and a synthetic rubber adhesive can be used as the adhesive 51. Of course, a plurality of adhesives can be used in combination. In order to control the bonding strength between the joining piece and the side wall, it is necessary to consider the material of the surface of the joining piece and the side wall, the environment (humidity, temperature, etc.) at the time of the fixing work when selecting the adhesive. However, it is preferable to use a hot melt adhesive which has a short curing time and is easily cured even in an environment having a low dew point used in the production of a non-aqueous battery.

As described above, at least a part of the joining piece portion
(Joint pieces 4A, 4G) to side wall 4B ₁Sticking to
However, at this time, these joint pieces have the specified bonding strength.
It is preferred to be fixed with. That is, the following adhesion strength test
When performed, the joining piece portion is
45 degrees or less, preferably 30 degrees or less, more preferably
Maintain an angle of less than 20 degrees, most preferably less than 10 degrees
It is fixed with enough strength. Fixing strength test A battery having a battery voltage of 3 V was set to an upper limit voltage of 10 V.
Continue charging at a current of 1.8 C for 200 minutes in the range. Was
However, 1C is a constant voltage from 2.7V to 4.2V battery voltage.
The capacity obtained by charging until the current value becomes 0 in one hour
This is the current value for discharging. In addition, in the fixed part
The angle between the joining piece and the encapsulating part is determined by the bonding surface of the joining piece.
Angle between the plane containing
(In FIG. 6, the angle between S1 and S2. In this case,
(0 degree due to parallelism).

In general, a battery tends to swell in an overcharged state. That is, the battery tends to expand in the direction P as shown in FIG. In the present invention, the battery element is housed in the housing member having the predetermined strength so as to prevent the expansion in the direction P. As a result, a safer battery can be provided in the overcharged state. this is,
It is presumed that swelling occurring at the beginning of overcharging is effectively prevented, and that a runaway reaction of the battery thereafter is suppressed.

In the above example, the joining pieces 4A, 4G
Has been fixed by adhesive to the side wall portion 4B _1,
The method of fixing is not limited to using an adhesive. For example, the joining piece can be fixed to the envelope using an adhesive tape.

In the above example, the joining piece 4
A, 4G is being bent once along the sidewall portion 4B _1, for example, as shown in FIG. 8, and further another diffraction song junction piece 4A in the middle, the joint piece 4A it may be interposed between the tip and the junction piece 4A and the side wall portion 4B _1. In this way, by bending the joint piece a plurality of times, it is possible to prevent air or the like from entering from the side surface of the joint piece, and to further improve the mechanical strength at the side wall.

In FIG. 1, the exterior materials 2 and 3 are separate bodies. However, in the present invention, the exterior materials 2 and 3 may be integrally formed as shown in FIG. In FIG. 9, one side of the exterior material 3 and one side of the exterior material 2 are connected, and the exterior material 2 has a lid shape that is connected to the exterior material 3 so as to be bent. A concave portion of the housing portion 3b is formed from one side where the exterior materials 2 and 3 are continuous,
This one side has the same configuration as the joining piece except that no joining piece is formed. Even in the case of FIG. 9, the junction piece 4A, 4G is secured by adhesive to the side wall portion 4B _1.

FIGS. 1 and 9 show the exterior material 3 having the accommodation portion 3b and the flat exterior material 2, but in the present invention, as shown in FIG. , 7b
And a peripheral portion 6 projecting from four peripheral edges of the housing portions 6b and 7b.
The battery element 1 may be encapsulated by the exterior materials 6 and 7 having the components a and 7a. In FIG. 10, the exterior materials 6 and 7 are formed as a series, but they may be formed separately as in FIG. 1.

In the configurations shown in FIGS. 1, 9 and 10, since the accommodating portion of the battery element is formed in advance, the battery element can be accommodated more compactly and the accommodation itself is easy. In the above description, after housing the battery element in the housing section,
Insulation material is injected near the terminal part. In this case,
An insulating material may adhere to and flow into the mating surface of the peripheral portion or between the battery element and the exterior material, thereby hindering the joining of the peripheral portion or failing to achieve the designed battery shape. Therefore,
The above problem can be avoided by housing the battery element in the housing section after supplying the insulating material near the terminal portion of the battery element. In particular, in the case of FIG. 10, even if the insulating material is supplied after the battery element is accommodated, the insulating material cannot be supplied to substantially the upper half of the battery element, so this manufacturing method is preferable. On the other hand, in this method, it is necessary to transport the battery element which is difficult to handle in a state where the insulating material is supplied, and arrange the battery element on the exterior material, so that care is required in handling during manufacture. In this respect, it can be said that the former method is preferable.

In the present invention, as shown in FIG. 11, one flat sheet-like exterior material 8 is folded in two along the central side 8a to form two pieces, a first piece 8A and a second piece 8B. Forming
The battery element 1 is interposed between the first piece 8A and the second piece 8B, and as shown in FIG. 12, the peripheral parts 8b of the first piece 8A and the second piece 8B are joined to encapsulate the battery element 1. You may. Again, joint piece 4A, 4G is secured by adhesive to the side wall portion 4B ₁ of the encapsulation portion formed by encapsulating battery element 1. Even in the battery configured as described above, since the joint piece is bent along the encased portion and further fixed with an adhesive or an adhesive tape, the battery element in the initial stage of overcharging also in this case. Swelling can be effectively prevented, and the strength and rigidity of the side of the battery are high. Of course, the bent joint piece is also prevented from separating from the envelope. Also, since the strength and rigidity of the side of the battery are high, even if the side receives an impact,
Peeling of the active material is prevented.

In the above example, the joining piece 4
A and 4G are side wall portions 4B of the enclosing portion 4B. ₁Is stuck to
However, it can be fixed to a portion other than the side wall. An example
For example, as shown in FIG.
With the lead 21 pulled out so as to wind around the
Enclose and join the edges of the exterior material and pull the leads
The joining piece 4F provided on the protruding portion and the opposite side thereof
The joining piece portion 4G and the joining portion provided along the upper surface 4I of the enclosing portion.
When the joining piece 4H is formed, the joining piece 4H
The upper surface 4I can be fixed with an adhesive or an adhesive tape.
Wear.

In the above example, the insulating material 5 is filled near the terminals (tabs 4a, 4b). As a result, swelling of the battery element in the early stage of overcharging can be effectively prevented, and furthermore a short circuit is more effectively prevented. As the insulating material 5, a synthetic resin is preferable, and an epoxy resin, an acrylic resin, a silicone resin, and the like are exemplified. Among them, an epoxy resin or an acrylic resin is preferable because the curing time is short. In particular, an acrylic resin is most preferable because it has a low possibility of adversely affecting battery performance. The insulating material is supplied near the terminal portion in an uncured and fluid state, and is completely fixed near the terminal portion by curing. Further, in FIG. 1, the insulating material 5 is separately supplied to the positive electrode terminal portion and the negative electrode terminal portion. However, in order to further enhance the safety at the time of overcharging, the insulating material 5 extends from the positive electrode terminal portion to the negative electrode terminal portion. More preferably, the entire side surface of the battery element is covered. In covering the side of the battery element near the terminal,
In particular, it is preferable that a larger spacer is provided between the positive electrode and the negative electrode, and the protruding portions of the spacer are fixed to each other.

That is, for the battery element, for example, FIG.
As shown in the figure, the spacer 13 is composed of the positive electrode 11 and the negative electrode 1.
3, a protruding portion 13a is formed so as to protrude slightly, thereby preventing a short circuit between the positive electrode 11 and the negative electrode 13. Since the protruding portions 13a are fixed to each other with an insulating material, the battery elements are restrained in the stacking direction. Therefore, even when overcharged, the battery elements are prevented from swelling, and the battery is prevented from running away from heat. Of course, the insulating material can be provided over the entire side of the battery element and is preferred.

It is preferable that the exterior material for accommodating the battery element has shape changeability. As a result, not only can batteries of various shapes be easily formed, but also when the exterior material is sealed under a vacuum state, a function of strengthening the bonding between the electrodes of the battery element can be provided. In addition, battery characteristics such as cycle characteristics can be improved. The thickness of the outer packaging material is not only preferable because the volume energy density and the weight energy density of the battery become larger as the thickness becomes smaller, but also the effect of the present invention becomes particularly remarkable because the strength itself is relatively low. The thickness of the exterior material is usually 0.2 mm or less, preferably 0.15 mm or less. However, if the thickness is too thin, the strength becomes insufficient, and moisture and the like easily pass therethrough. Therefore, the thickness is usually 0.01 mm or more, preferably 0.02 m.
m or more.

As the material of the exterior material, metals such as aluminum, nickel-plated iron and copper, and synthetic resins can be used. Preferably, it is a laminated film provided with a gas barrier layer and a resin layer, particularly a laminated film provided with a resin layer on both sides of the gas barrier layer.
Such a laminated film has high gas barrier properties, high shape variability, and thinness. As a result, the thickness and weight of the exterior material can be reduced, and the capacity of the entire battery can be improved.

As the material of the gas barrier layer used for the laminate film, aluminum, iron, copper, nickel,
Metals such as titanium, molybdenum and gold, alloys such as stainless steel and Hastelloy, and metal oxides such as silicon oxide and aluminum oxide can be used. Preferably, aluminum is lightweight and excellent in workability. As the resin used for the resin layer, various synthetic resins such as thermoplastics, thermoplastic elastomers, thermosetting resins, and plastic alloys can be used. These resins include those in which a filler such as a filler is mixed.

As a specific structure of the laminated film, a laminated film of a gas barrier layer 40 and a resin layer 41 can be used as shown in FIG. Further, a more preferred laminate film is shown in FIG.
As shown in (B), a synthetic resin layer 41 for functioning as an outer protective layer is provided on the outer surface of the gas barrier layer 40, and corrosion by the electrolyte and contact between the gas barrier layer and the battery element are prevented on the inner surface. This is a three-layer structure in which synthetic resin layers 42 functioning as inner protective layers for protecting the layers are laminated.

In this case, the resin used for the outer protective layer is
Preferably, resins excellent in chemical resistance and mechanical strength, such as polyethylene, polypropylene, modified polyolefin, ionomer, amorphous polyolefin, polyethylene terephthalate, and polyamide are desirable. As the inner protective layer,
Chemical-resistant synthetic resin is used, for example, polyethylene,
Polypropylene, modified polyolefin, ionomer,
An ethylene-vinyl acetate copolymer or the like can be used.

As shown in FIG. 14, the laminated film is composed of a gas barrier layer 40 and a synthetic resin layer 4 for forming a protective layer.
1. Adhesive layers 43 can be provided between the synthetic resin layers 42 for forming the corrosion resistant layer, which is also preferable. Furthermore,
In order to bond the exterior materials, an adhesive layer made of a resin such as polyethylene or polypropylene that can be welded can be provided on the innermost surface of the composite material. A case is formed using these metals, synthetic resins or composite materials. The case may be formed by fusing the periphery of the film-like body, or the sheet-like body may be drawn by vacuum forming, pressure forming, press forming or the like. Further, it can be molded by injection molding a synthetic resin. When injection molding is used, the gas barrier layer is usually formed by sputtering or the like.

In order to previously provide an accommodating portion formed of a concave portion in the exterior material, drawing can be performed. The exterior material is
It is preferable to use a film-like material in view of easy processing. A battery element having a positive electrode, a negative electrode and an electrolyte,
It is stored in the case. As described above, the battery element is a laminate (unit battery element) including the positive electrode, the negative electrode, and the electrolyte layer.
Can be wound into a wound shape, which can be stored in a case, or the laminate (unit battery element) can be stored in a case in a flat plate shape as it is. Further, as shown in FIGS. 2 and 3, a plurality of unit battery elements may be stacked in the thickness direction to form a battery element. Hereinafter, a preferred configuration of the unit battery element will be described.

FIG. 15 shows a preferred example of a unit battery element comprising this lithium secondary battery. This unit battery element is obtained by laminating a positive electrode comprising a positive electrode current collector 22 and a positive electrode active material layer 23, a spacer (electrolyte layer) 24, and a negative electrode comprising a negative electrode active material layer 25 and a negative electrode current collector 26. . The negative electrode is made larger than the positive electrode in order to suppress the precipitation of lithium dendrite. In order to prevent a short circuit, the spacer 24 is made larger than the positive electrode and the negative electrode. By making the spacer larger than the positive and negative electrodes, the protruding portions of the spacer of the unit cell element can be fixed to each other as described above.

A plurality of these unit battery elements are stacked to form a battery element. In this stacking, a unit battery element in a forward posture (FIG. 15) with the positive electrode on the upper side and the negative electrode on the lower side is used. On the other hand, unit battery elements in an inverted posture (not shown) with the positive electrode on the lower side and the negative electrode on the upper side are alternately stacked. That is, the unit battery elements adjacent in the stacking direction are stacked such that the same electrodes face each other (that is, the positive electrodes and the negative electrodes face each other).

A positive electrode tab 4a extends from the positive electrode current collector 22 of the unit battery element, and a negative electrode tab 4b extends from the negative electrode current collector 26. In FIG. 15, it is described that the positive electrode active material layer and the negative electrode active material layer are formed on one surface of the positive electrode current collector and one surface of the negative electrode current collector, respectively. Active material layers can be formed on both sides of the body. In this case, the active material layers formed on the opposite surfaces of the same current collector can be mutually different components of the unit battery element.

The planar shape of the electrode is arbitrary, and may be square, circular, polygonal, or the like. As shown in FIG. 15, the current collectors 22 and 26 usually have tabs 4a and 4
b is continuously provided. When the electrode is rectangular,
A tab 4a protruding from the positive electrode current collector is formed near one side of the electrode as shown in FIG.
b is formed near the other side.

Laminating a plurality of unit battery elements is effective in increasing the capacity of the battery. At this time, each of the tabs 4a and 4b from each of the unit battery elements usually has a thickness. Directions to form positive and negative terminal portions. As a result, a large-capacity battery element 1 can be obtained. As shown in FIG. 2, leads 21 made of a flaky metal are connected to the tabs 4a and 4b. as a result,
The lead 21 and the positive and negative electrodes of the battery element are electrically coupled. Tabs 4a are connected to each other,
The connection between the lead 4b and the lead 21 can be performed by resistance welding such as spot welding, ultrasonic welding or laser welding.

It is preferable to use an annealed metal for at least one of the positive electrode lead and the negative electrode lead 21 and preferably for both of the leads. As a result, a battery having excellent bending durability as well as strength can be obtained. Generally, aluminum, copper, nickel, SUS, or the like can be used as the type of metal used for the lead. The preferred material for the positive electrode lead is aluminum. A preferable material for the lead of the negative electrode is copper.

The thickness of the lead 21 is usually at least 1 μm, preferably at least 10 μm, more preferably at least 20 μm.
Most preferably, it is 40 μm or more. If the thickness is too small, the mechanical strength of the lead such as tensile strength tends to be insufficient. The thickness of the lead is usually 1000 μm or less, preferably 500 μm or less, and more preferably 100 μm or less. If the thickness is too large, the bending durability tends to deteriorate, and the case tends to be difficult to seal the battery element. The advantage of using the later-described annealed metal for the lead is more remarkable as the thickness of the lead is larger.

The length of the lead exposed to the outside is usually about 1 mm or more and 50 mm or less. As described above, the battery element may be a wound type battery in which a stacked body (unit battery element) in which a positive electrode and a negative electrode are laminated with an electrolyte layer interposed therebetween is wound. It is preferable that a spacer is interposed between the positive electrode and the negative electrode, and the spacer is larger than the positive and negative electrodes.

Hereinafter, the materials used for the lithium secondary battery will be described. A battery element usually has a positive electrode, a negative electrode, and an electrolyte layer interposed therebetween. The positive and negative electrodes are
Usually, it includes a current collector and an active material layer provided thereon.
Aluminum, nickel, SUS
Although various metals can be used, aluminum is preferred. The thickness of the current collector is usually 1 μm or more,
It is preferably at least 3 μm, more preferably at least 5 μm, and usually at most 30 μm, preferably at most 25 μm, more preferably at most 20 μm. The thinner the better, the better from the viewpoint of volume energy density and weight energy density, but too thin tends to be difficult to handle in terms of strength and the like. The current collector may be in the form of a plate such as a normal metal foil or a mesh such as a punched metal. The surface of the current collector can be subjected to a roughening treatment as necessary.

The active materials that can be used for the positive electrode include:
Inorganic compounds as compounds capable of storing and releasing lithium ions
And organic compounds can be used. As inorganic compounds
Oxides of transition metals such as Fe, Co, Ni, Mn,
Oxides of transition metals and transition metals, transition metal sulfides, etc.
I can do it. Specifically, Mn is used as a transition metal oxide.
O _Two, V_TwoO_Five, V₆O₁₃, TiO_TwoEtc. can be exemplified.
Lithium Nickelate as Complex Oxide of Metal and Transition Metal
, Lithium cobaltate, lithium manganate, etc.
TiS as transition metal sulfide_Two, FeS, etc.
it can. As organic compounds, for example, polyaniline
Examples include a conductive polymer. Also, any of these
Positive electrode active material by mixing inorganic compound and organic compound in optional amounts
The method used as is also preferably used. Preferably,
Complex oxides of titanium and transition metals, especially manganese and nickel
At least one selected from the group consisting of
Complex oxidation containing one kind of transition metal oxide and lithium
Things. Above all, a complex acid containing cobalt and lithium
Oxides and composite oxides containing nickel and lithium are preferred.
No. The particle size of the positive electrode active material depends on the rate characteristics, cycle characteristics, etc.
In terms of the battery characteristics of 1 to 30 μm, preferably 1 to 30 μm
10 μm.

As the negative electrode current collector, copper, nickel, SU
Although various metals such as S can be used, copper is preferable. The thickness of the current collector is usually at least 1 μm, preferably at least 3 μm, more preferably at least 5 μm, and is usually at most 30 μm, preferably at most 25 μm, more preferably at most 20 μm. The thinner, the thinner
It is preferable from the viewpoint of volume energy density and weight energy density, but if it is too thin, handling tends to be difficult in terms of strength and the like. The current collector may be in the form of a plate such as a normal metal foil or a mesh such as a punched metal. The surface of the current collector can be subjected to a roughening treatment as necessary.

As the active material usable for the negative electrode, various compounds capable of inserting and extracting lithium can be used in addition to lithium metal. Specific examples include lithium metal; lithium alloys such as lithium-aluminum alloy, lithium-bismuth-cadmium alloy, and lithium-tin-cadmium alloy; and carbon materials such as graphite and coke. In addition, oxides such as silicon, tin, zinc, manganese, iron, and nickel, and lead sulfate can also be used. When lithium metal or lithium alloy is used, dendrite is likely to be generated at the time of charging, and the safety particularly at the time of overcharging tends to decrease. Therefore, carbon materials such as graphite and coke are preferable. The particle size of the negative electrode active material is usually 1 to 50 μm, preferably 15 to 30 μm in terms of battery characteristics such as initial efficiency, rate characteristics, and cycle characteristics.

The active material layers of the positive electrode and the negative electrode usually contain a binder in addition to the above active materials. The binder to be used must be stable with respect to an electrolytic solution or the like, and is desired to have weather resistance, chemical resistance, heat resistance, flame retardancy, and the like. Inorganic compounds such as silicate and glass as binders,
Various resins mainly composed of polymers can be used. Examples of the resin include alkane-based polymers such as polyethylene, polypropylene, and poly-1,1-dimethylethylene; unsaturated polymers such as polybutadiene and polyisoprene; and polystyrene, polymethylstyrene, polyvinylpyridine, and poly-N-vinylpyrrolidone. Polymers having a ring; Acrylic derivative polymers such as polymethyl methacrylate, polyethyl methacrylate, polybutyl methacrylate, polymethyl acrylate, polyethyl acrylate, polyacrylic acid, polymethacrylic acid, and polyacrylamide; polyvinyl fluoride , Fluorine-based resins such as polyvinylidene fluoride and polytetrafluoroethylene; C such as polyacrylonitrile and polyvinylidene cyanide
N-group-containing polymers; polyvinyl alcohol-based polymers such as polyvinyl acetate and polyvinyl alcohol; halogen-containing polymers such as polyvinyl chloride and polyvinylidene chloride; conductive polymers such as polyaniline; Further, a mixture of the above-mentioned polymers, a modified product, a derivative, a random copolymer, an alternating copolymer, a graft copolymer, a block copolymer, or the like can also be used. The molecular weight of these resins is preferably 10,000-3000
000, more preferably 100,000-100,000
0. If it is too low, the strength of the active material layer will decrease, and if it is too high, the viscosity tends to be high, and it tends to be difficult to form an electrode.

The blending amount of the binder with respect to 100 parts of the active material is preferably 0.1 to 30 parts, more preferably 1 to 20 parts. If the amount of the binder is too small, the strength of the electrode may decrease, and if it is too large, the ion conductivity tends to decrease. The active material layer may contain a powder that exhibits various functions such as a conductive material and a reinforcing material, a filler, and the like, if necessary. The conductive material is not particularly limited as long as it is capable of imparting conductivity by being mixed in an appropriate amount with the above active material, but is usually carbon powder such as acetylene black, carbon black, graphite, and various metal fibers and foils. And the like. The DBP oil absorption of the carbon powder conductive material is preferably 120 cc / 100 g or more,
In particular, 150 cc / 100 g or more is preferable because it holds the electrolytic solution. As the reinforcing material, various inorganic or organic spherical or fibrous fillers can be used.

The electrode can be manufactured by applying a coating containing the material constituting the active material layer on the current collector and drying. After that, the active material layer can be subjected to a consolidation treatment. The volume fraction of the binder in the active material layer can be controlled by controlling the composition of the paint, drying conditions, consolidation conditions, and the like. If necessary, an undercoat primer layer can be provided between the active material layer and the current collector to improve the adhesiveness between them.

When the undercoat primer layer is used, examples of the composition thereof include a resin to which conductive particles such as carbon black, graphite, and metal powder are added, and a conductive organic conjugated resin. Preferably, carbon black or graphite, which can also function as an active material, is used for the conductive particles. As the resin, it is preferable to use polyaniline, polypyrrole, polyacene, a disulfide-based compound, a polysulfide-based compound, or the like, which can function as an active material, because the capacity is not reduced.
In the case of a composition containing a resin to which conductive particles are added as a main component,
The ratio of the resin to the conductive particles is preferably 1 to 300% by weight. If it is too low, the coating strength will decrease,
At the time of using a battery, peeling may occur in the process.
If it is too high, the conductivity tends to decrease and the battery characteristics tend to decrease. Particularly preferably, the content is in the range of 5 to 100% by weight. The thickness of the undercoat primer layer is usually 0.05 to 10 μm, preferably 0.1 to 1 μm.
m. If it is too thin, application becomes difficult, and it becomes difficult to ensure uniformity. If it is too thick, the volume capacity of the battery may be unnecessarily damaged.

The electrolyte exists as a constituent of the electrolyte layer between the positive electrode and the negative electrode. The electrolyte is also usually present in the active material of the electrode as an ion mobile phase. As the electrolyte, for example, those having various properties such as an electrolyte solution, a polymer solid electrolyte, a gel electrolyte, and an inorganic solid electrolyte can be used. In general, when a non-fluid electrolyte such as a polymer solid electrolyte, a gel electrolyte, and an inorganic solid electrolyte is used, it is possible to more effectively prevent the electrolyte from leaking out of the case. In particular, in the present invention, the use of a non-fluid electrolyte is particularly remarkable when using a case having shape deformability as the electrolyte tends to leak out of the case.

On the other hand, an electrolytic solution obtained by dissolving a lithium salt in a non-aqueous solvent has a high fluidity and generally tends to have excellent ionic conductivity as compared with a non-fluid electrolyte. Therefore, it is preferable to use an electrolyte containing an electrolytic solution from the viewpoint of improving ionic conductivity. The electrolytic solution used as the electrolyte is usually obtained by dissolving a lithium salt as a supporting electrolyte in a non-aqueous solvent. As the non-aqueous solvent, a solvent having a relatively high dielectric constant is preferably used. Specifically, cyclic carbonates such as ethylene carbonate and propylene carbonate, acyclic carbonates such as dimethyl carbonate, diethyl carbonate and ethyl methyl carbonate, ethers such as tetrahydrofuran, 2-methyltetrahydrofuran, dimethoxyethane and diphenyl ether, and γ-butyl Lactones such as lactone, sulfur compounds such as sulfolane, nitriles such as acetonitrile, and the like can be mentioned. From the viewpoint of battery characteristics such as cycle characteristics, rate characteristics, and safety, cyclic carbonates and / or lactones are preferred.

In the present invention, the solvent for the electrolytic solution is
Preferably, a non-aqueous solvent having a boiling point of 150 ° C. or higher at normal pressure (hereinafter sometimes referred to as “high boiling point solvent”) is used. Here, “boiling point is not lower than X ° C.” means pressure 1a
Even when heating from room temperature to X ° C under tm, the vapor pressure is 1a
tm. That is, when heating from room temperature to 150 ° C. under a pressure of 1 atm, it is preferable to always use a non-aqueous solvent having a vapor pressure of 1 atm or less. As a result, higher cycle characteristics can be obtained and the safety of the battery can be improved. For example, when a low-boiling solvent composed of a solvent such as dimethyl carbonate, diethyl carbonate, or dimethoxyethane is used, bubbles are generated between the active material and the solvent due to the vaporization of the solvent, and the impregnation state of the electrolytic solution is reduced. And the cycle characteristics tend to deteriorate.
In addition, by using a high-boiling solvent, even when the battery element is housed in a shape-variable case, it is possible to suppress a change in shape (deformation) of the battery at high temperatures or the like, volatilization and leakage of the electrolyte, and the like. . Examples of such a high-boiling solvent include propylene carbonate, ethylene carbonate, butylene carbonate, and γ-butyrolactone.

The non-aqueous solvent has a viscosity of 1 mPa · s
It is preferable that it is above. Examples of the lithium salt as a supporting electrolyte used for the electrolyte include LiPF ₆ , LiAs
F ₆ , LiSbF ₆ , LiBF ₄ , LiClO ₄ , LiI,
LiBr, LiCl, LiAlCl, LiHF ₂ , Li
SCN, LiSO ₃ CF _{2 and the} like can be mentioned. Of these, LiPF ₆ and LiClO ₄ are particularly preferred. The content of these supporting electrolytes in the electrolytic solution is usually 0.5 to 2.5 mol / l.

A gel electrolyte can be formed from the above-mentioned electrolytic solution and a gel-forming polymer. The gel electrolyte usually comprises the above electrolyte solution held by a polymer. The gel electrolyte is a particularly preferred electrolyte in the present invention because it can impart the same degree of ionic conductivity as the electrolyte and makes the electrolyte non-fluidized. The concentration of the polymer in the gel electrolyte with respect to the electrolytic solution depends on the molecular weight of the polymer used, but is usually 0.1 to 30% by weight. If the concentration is too low, it is difficult to form a gel,
In some cases, the retention of the electrolyte is reduced, causing problems of flow and liquid leakage. On the other hand, if the concentration is too high, the viscosity becomes too high to cause difficulty in the process, and the proportion of the electrolyte solution tends to decrease, the ionic conductivity decreases, and the battery characteristics such as rate characteristics tend to deteriorate. Examples of the polymer holding the electrolyte include poly (meth) acrylate polymers, alkylene oxide polymers having alkylene oxide units, and fluorine polymers such as polyvinylidene fluoride and vinylidene fluoride-hexafluoropropylene copolymer. And various polymers having a function of gelling an electrolytic solution.

Examples of the method for forming a gel electrolyte include a method for non-fluidizing an electrolyte paint in which a polymer is dissolved in an electrolyte in advance, and a method for crosslinking an electrolyte paint containing a polymerizable gelling agent in the electrolyte. A material and a manufacturing method as required can be adopted, such as a method of forming a non-fluid electrolyte by making the non-fluid electrolyte. When the gel electrolyte is formed by a method of causing a cross-linking reaction of a paint containing a polymerizable gelling agent in the electrolyte, a monomer that forms a polymer by performing a polymerization treatment such as ultraviolet curing or heat curing. Is added to the electrolytic solution as a polymerizable gelling agent to prepare a coating.

Examples of the polymerizable gelling agent include those having an unsaturated double bond such as an acryloyl group, a methacryloyl group, a vinyl group and an allyl group. In particular,
For example, acrylic acid, methyl acrylate, ethyl acrylate, ethoxyethyl acrylate, methoxyethyl acrylate, ethoxyethoxyethyl acrylate, polyethylene glycol monoacrylate, ethoxyethyl methacrylate, methoxyethyl methacrylate, ethoxyethoxyethyl methacrylate, polyethylene glycol monomethacrylate, N , N-diethylaminoethyl acrylate, N, N-dimethylaminoethyl acrylate, glycidyl acrylate, allyl acrylate, acrylonitrile, N-vinylpyrrolidone, diethylene glycol diacrylate, triethylene glycol diacrylate, tetraethylene glycol diacrylate, polyethylene glycol diacrylate, Diethylene glycol Dimethacrylate, triethylene glycol dimethacrylate, tetraethylene glycol dimethacrylate, polyethylene glycol dimethacrylate, polyalkylene glycol diacrylates, polyalkylene glycol dimethacrylate, trimethylol propane alkoxylate triacrylate, pentaerythritol alkoxylate triacrylate,
Examples thereof include pentaerythritol alkoxylate tetraacrylate and ditrimethylolpropane alkoxylate tetraacrylate. These may be used in combination of two or more. Of these, diacrylates and triacrylates containing a plurality of ethylene oxide groups are particularly preferred. The content of the polymerizable gelling agent in the electrolyte is not particularly limited, but is preferably 1% by weight or more. When the content is low, the formation efficiency of the polymer is reduced, and the electrolyte is hardly non-fluidized. On the other hand, if the amount is too large, unreacted monomers remain and the operability as an electrolyte paint deteriorates.

In the case where the gel electrolyte is formed by a method of defluidizing an electrolyte paint containing a polymer in advance, a polymer which is dissolved in an electrolyte at a high temperature and forms a gel electrolyte at a normal temperature is used as the polymer. It is preferred to use. That is, a polymer dissolved in an electrolytic solution at a high temperature is brought to a normal temperature to obtain a gel electrolyte. The temperature at the time of high temperature is usually 50 to 200 ° C., preferably 100
１６０160 ° C. If it seems to dissolve at too low a temperature, the stability of the gel electrolyte is reduced. If the dissolution temperature is too high, decomposition of the electrolyte component, the polymer and the like may be caused. As a method of non-fluidization, it is preferable to leave the electrolytic solution at room temperature, but it is also possible to forcibly cool the electrolytic solution. Examples of the polymer that can be used include a polymer having a ring such as polyvinylpyridine and poly-N-vinylpyrrolidone; polymethyl methacrylate, polyethyl methacrylate, polybutyl methacrylate, polymethyl acrylate, polyethyl acrylate, and polyethyl acrylate. Acrylic derivative polymers such as acrylic acid, polymethacrylic acid, and polyacrylamide; fluorine resins such as polyvinyl fluoride and polyvinylidene fluoride; CN group-containing polymers such as polyacrylonitrile and polyvinylidene cyanide; polyvinyl acetate, polyvinyl alcohol, and the like And halogen-containing polymers such as polyvinyl chloride and polyvinylidene chloride. Among these, polymethyl methacrylate, polyacrylonitrile, polyethylene oxide, or a modified product thereof is preferably used. Mixtures, denatured forms, derivatives of the above polymers,
Random copolymer, alternating copolymer, graft copolymer,
Block copolymers and the like can also be used.

The weight average molecular weight of these polymers is preferably in the range from 10,000 to 5,000,000. If the molecular weight is low, it is difficult to form a gel, while if the molecular weight is too high, the viscosity becomes too high and handling becomes difficult. Among these methods of forming a gel electrolyte, a method of forming a non-fluid electrolyte by performing a cross-linking reaction of an electrolyte paint containing a polymerizable gelling agent in an electrolyte improves the adhesion between electrodes, It is preferable because the effects of the present invention become particularly remarkable.

Various additives can be added to the electrolyte as needed to improve the performance of the battery. Additives that exhibit such a function are not particularly limited, but include trifluoropropylene carbonate,
Examples thereof include 1,6-dioxaspiro [4,4] nonane-2,7-dione, 12-crown-4-ether, vinylene carbonate, catechol carbonate, and succinic anhydride.

The electrolyte layer is usually formed by impregnating a spacer made of a porous sheet with an electrolyte. The spacer is a porous film provided between the positive electrode and the negative electrode, isolates them, and supports the electrolyte layer. Examples of the material of the spacer include polyolefins such as polyethylene and polypropylene, and polyolefins in which some or all of these hydrogen atoms have been substituted with fluorine atoms, and polymers such as polyacrylonitrile and polyaramid. Preferred are polyolefins and fluorine-substituted polyolefins. Specific examples include polyethylene, polypropylene, polytetrafluoroethylene, and polyvinylidene fluoride. Needless to say, a copolymer containing a monomer unit of the above polymer or a mixture of polymers may be used. The spacer may be a stretched film formed by uniaxial stretching or biaxial stretching,
Further, it may be a non-woven fabric. The thickness of the spacer is usually 100 μm or less, preferably 50 μm or less, more preferably 30 μm or less, and most preferably 20 μm or less. If the film thickness is too large, the rate characteristics and volume energy density of the battery tend to decrease. If it is too thin, it tends to be difficult to cut due to insufficient rigidity, and short-circuit is likely to occur. Therefore, it is usually at least 5 μm, preferably at least 7 μm, more preferably at least 8 μm. The porosity of the spacer is usually 45-90%, preferably 45-90%.
75%. If the porosity is too large, the mechanical strength tends to be insufficient. If the porosity is too small, the rate characteristics and the like of the battery tend to deteriorate.

[0069]

EXAMPLES Hereinafter, the present invention will be described in more detail with reference to examples. However, the present invention is not limited to the following examples, and may be appropriately modified and practiced without departing from the gist thereof. it can. In the following description, “parts” means “parts by weight” unless otherwise specified. Positive electrode manufacturing example 1 90 parts of lithium cobaltate, 5 parts of acetylene black,
5 parts of polyvinylidene fluoride and 80 parts of N-methyl-2-pyrrolidone were kneaded with a kneader for 2 hours to obtain a positive electrode coating material 1.

Next, the positive electrode coating material 1 was applied on an aluminum current collector base material having a thickness of 20 μm by extrusion die coating, dried, and a porous material in which the active material was bound on the current collector with a binder was used. An active material layer composed of a film was formed. Then, after consolidation using a roll press (calender), it was cut to obtain a positive electrode 1. Production Example of Negative Electrode 90 parts of graphite (particle size: 15 μm), 10 parts of polyvinylidene fluoride and 100 parts of N-methyl-2-pyrrolidone were kneaded by a kneader for 2 hours to obtain negative electrode paint 1.

Next, the negative electrode paint 1 was applied on a 20 μm thick copper current collector substrate by extrusion die coating and dried, and a porous film in which the active material was bound on the current collector by a binder was used. Was formed. Then, after compaction using a roll press (calender), the compact was cut to obtain a negative electrode 1. Electrolyte paint preparation example 1 A mixed solution of ethylene carbonate, propylene carbonate and phenyl ether containing 1M concentration of LiPF ₆ (volume ratio; ethylene carbonate: propylene carbonate: phenyl ether = 7.3: 7.3: 1)
925 parts, tetraethylene glycol diacrylate 4
4 parts, polyethylene oxide triacrylate 22 parts,
2 parts of a polymerization initiator and 9 parts of an additive (succinic anhydride) were mixed with stirring and dissolved to obtain an electrolyte paint 1. Example 1 An electrolyte paint 1 was applied to the positive electrode 1 and the negative electrode 1, and a polyethylene porous film immersed in the electrolyte paint 1 was interposed therebetween and laminated, and then heated at 90 ° C. for 10 minutes to make the electrolyte non-flowable. As shown in FIG. 9, a flat unit battery element having a positive electrode, a negative electrode, and a non-fluidizing electrolyte was prepared.

After stacking the obtained unit battery elements, the terminals of the positive electrode and the negative electrode were bundled, and a lead for extracting a current was connected to each terminal. Thereafter, a laminate film having a thickness of about 100 μm having a resin layer on both sides of the aluminum layer was accommodated in a facing material as shown in FIG. Then, after enclosing the laminate film with a vacuum seal, the joining piece portion (corresponding to the joining piece portion 4A in FIG. 5) except for the side from which the lead was taken out was bent along the envelope portion. The battery capacity of the thus prepared flat battery A is 65
It was 0 mAh.

The flat battery A produced as described above is
At a constant current of 0.65 A, charging / discharging between nominal working voltages was performed for 3 cycles. The battery was sandwiched between assembled metal receiving members as shown in FIG. 22 in which the height of the gap was adjusted to 110% of the total thickness of the battery with screws, and an overcharge test was performed. That is, the upper limit voltage is set to 10 V, and the battery is discharged from a discharged state at 1.8 C (1.
The battery was continuously charged at a constant current of 17 A) for 200 minutes. The thickness of the battery in the discharged state is 3.9 mm (the thickness of the electrode is 3.7 mm)
Met. No gas leakage during overcharge was observed, and the maximum temperature on the battery surface was 94 ° C. Further, in the battery after overcharge, swelling of the battery due to gas was hardly observed, and the battery was slightly loosened. The thickness of the battery after overcharging was 4.2 mm (the thickness of the electrode was 4.0 mm). In such a battery, even if pressure was applied to the battery after overcharging, leakage of gas due to breakage of the exterior material was not observed.

In the same manner as described above, the flat battery A was sandwiched between the accommodating members, the upper limit voltage was set to 10 V, and the battery was continuously charged from the discharged state at a constant current of 1.95 A for 120 minutes. No gas leakage was observed during charging, and the maximum temperature on the battery surface was 132 ° C. Further, in the battery after overcharge, swelling of the battery due to gas was hardly observed, and the battery was slightly loosened. The thickness of the battery after overcharging was 4.3 mm (the thickness of the electrode was 3.8 mm). In such a battery, even if pressure was applied to the battery after overcharging, no gas leakage due to a break in the exterior material was observed. Reference Example The flat battery A (plate surface area 15c) prepared as described above
m ² ), charging and discharging between the nominal working voltages were performed for 3 cycles at a constant current of 0.65 A. The thickness of the battery in the discharged state is 3.
9 mm (thickness of the electrode was 3.7 mm). Next, the upper limit voltage was set to 10 V, and the battery was continuously charged at a constant current of 1.8 C (1.17 A) for 200 minutes from the discharged state by applying a load in accordance with the swelling of the battery. As a result, no swelling of the battery due to gas was observed in the overcharged battery, and the thickness of the overcharged battery was 4.6 mm (the thickness of the electrode was 4.3 m).
m). At this time, the maximum load applied to the battery was 8.3.
kg (8.3 / 15 = 0.55 kg / cm ² ). The maximum temperature of the battery surface at this time was 85 ° C. Comparative Example 1 An overcharge test of the battery A was performed in the same manner as in Example 1 except that the flat battery A was not housed in the housing member.

As a result, the battery swelled during overcharging, smoked after 72 minutes, and leakage of gas during overcharging was observed. The maximum temperature of the battery surface at that time was 140 ° C. Under the same conditions, the upper limit voltage was set to 10 V, and the battery was continuously charged at a constant current of 1.95 A from the discharged state. As a result, the battery fired after 38 minutes. From the reference example, it can be seen that by applying a specific (0.5 kg / cm ² or more) pressure to the battery at the time of overcharging, the safety of the battery at the time of overcharging can be improved.
That is, it can be seen that if the housing member is designed so that a force corresponding to this load is applied during overcharging, the safety during overcharging is improved. In fact, when comparing Example 1 and Comparative Example 1, the safety at the time of overcharging is improved by storing the battery in the housing member so that pressure is applied at the time of overcharging.

[0076]

According to the present invention, the problems inherent in safety during overcharging are clarified, and the swelling of the battery during overcharging is suppressed, thereby damaging equipment used during overcharging and generating gas. Thus, it is possible to provide a secondary battery that prevents corrosion of used equipment and leakage of toxic gas such as organic gas, and improves battery safety. Therefore, a secondary battery having an intrinsic safety function is realized, and a relatively safe secondary battery can be obtained without taking other measures for overcharging. Further, a safer lithium secondary battery can be obtained by using it together with other measures for overcharging.

[Brief description of the drawings]

FIG. 1 is an exploded perspective view of a battery according to an embodiment.

FIG. 2 is a sectional view of a main part of the battery according to the embodiment.

FIG. 3 is a perspective view showing a battery element of the battery according to the embodiment.

FIG. 4 is a perspective view of the battery according to the embodiment (before the bonding piece is fixed).

FIG. 5 is a perspective view of the battery according to the embodiment (after the joining piece is fixed).

FIG. 6 is a cross-sectional view of the case according to the embodiment.

FIG. 7 is a schematic cross-sectional view showing how a battery swells.

FIG. 8 is a cross-sectional view of a case according to another embodiment.

FIG. 9 is a perspective view of a battery according to another embodiment in the process of being manufactured.

FIG. 10 is a perspective view of a battery according to still another embodiment in the process of being manufactured.

FIG. 11 is a perspective view of a battery according to still another embodiment in the process of being manufactured.

12 is a plan view of FIG. 11 in the process of being manufactured.

FIGS. 13A and 13B are longitudinal cross-sectional views each showing an example of a composite material constituting an exterior material.

FIG. 14 is a longitudinal sectional view showing another example of the composite material constituting the exterior material.

FIG. 15 is a schematic sectional view of an example of a unit battery element.

FIG. 16 is an enlarged sectional view of a tab portion of a battery element.

FIG. 17 is a perspective view of a battery according to another embodiment.

FIG. 18 is a schematic exploded perspective view of a housing member according to an embodiment of the present invention.

FIG. 19 is a cross-sectional view taken along the line AA of FIG. 18, showing a state where the battery element is housed in the housing member.

FIG. 20 is a schematic exploded perspective view of a housing member according to another embodiment of the present invention.

FIG. 21 is a schematic exploded perspective view of a housing member according to still another embodiment of the present invention.

FIG. 22 is a schematic exploded perspective view of a housing member according to still another embodiment of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Battery element 2, 3, 6, 7, 8 Exterior material 4a, 4b Tab 4A, 4F, 4G Joint piece part 4B Enclosure part 5 Insulating material 11 Positive electrode 11a Positive electrode active material 12 Negative electrode 12b Negative electrode active material 13 Non-fluid electrolyte Layer 15a Positive electrode current collector 15b Negative electrode current collector 21 Lead 22 Positive electrode current collector 23 Positive electrode active material 24 Spacer (electrolyte layer) 25 Negative electrode active material 26 Negative electrode collector 40 Metal layer 41, 42 Synthetic resin layer 43 Adhesive layer 181 accommodation member

Continued on the front page (72) Inventor Kiichi Hashimoto 1000 Kamoshita-cho, Aoba-ku, Yokohama-shi, Kanagawa Prefecture Inside Mitsubishi Chemical Research Laboratory (72) Inventor Tomohiro Kawai 1000 Kamoshita-cho, Aoba-ku, Yokohama-shi, Kanagawa Mitsubishi Chemical Corporation F-term in Yokohama Research Institute (reference) AS23 AS24 AS25 AS26 AS27 AS28 AT04 AY05 AY08 CC05 CC20 LL01 LL06 LL10 NN01 NN05

Claims (8)

[Claims] 1. A housing member for housing a lithium secondary battery in which a battery element having a positive electrode, a negative electrode, and an electrolyte is housed in a flat case made of an exterior material, the strength in a direction perpendicular to the flat surface of the case. Is a strength capable of withstanding a pressure of 0.5 kg / cm ² or more. 2. The housing member for a lithium secondary battery according to claim 1, wherein the height of the housing portion of the housing member is 101 to 120% of the total thickness of the lithium secondary battery. 3. A lithium secondary battery containing a battery element having a positive electrode, a negative electrode and an electrolyte housed in a flat case made of an exterior material inside the housing member according to claim 1 or 2. Next battery pack. 4. The secondary battery pack according to claim 3, wherein the thickness of the exterior material is 0.2 mm or less. 5. The secondary battery pack according to claim 3, wherein the thickness of the lithium secondary battery is 2 mm or more. 6. The secondary battery pack according to claim 3, wherein a nominal capacity of the battery is 100 mAh or more. 7. An exterior material comprising a laminated film in which a synthetic resin layer and a gas barrier layer are laminated.
The secondary battery pack according to any one of the above. 8. The secondary battery pack according to claim 3, wherein the battery element has a non-fluid electrolyte between the positive electrode and the negative electrode.