JP2010010042A - Sheeted battery - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a sheeted battery wherein a connection portion between an electrode collector group and an electrode terminal is stably connected thereto even when using a laminated film in the state of accumulating gas in the battery for an exterior case. <P>SOLUTION: In the sheeted battery, an electrode group having a positive electrode laminated via a separator on a negative electrode is stored in the exterior case having the laminated film, and an electrode collector or the electrode terminal mounted thereon and connected to a lead wire is delivered to the outside of the case. A spacer formed of a resin material or a metal plate covered with the resin material is inserted between the connection portion between the collector or the lead wire and the electrode terminal and the exterior case in the state of being bent. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

The present invention relates to a sheet battery having an outer case made of a laminate film applied to a lithium ion secondary battery or the like.

Due to rapid progress in the electronics field in recent years, electronic devices have become more sophisticated, smaller and more portable, and the demand for rechargeable high energy density secondary batteries used in these electronic devices has increased.
Conventionally, secondary batteries mounted on these electronic devices include lead-acid batteries, nickel-cadmium batteries, nickel-hydrogen batteries, etc. Recently, carbon materials that can occlude / release lithium ions, lithium alloys, etc. are used as active materials. A lithium ion secondary battery in which the negative electrode used and a positive electrode using a lithium-containing composite oxide or the like as an active material is researched, developed, and put into practical use. This type of battery has a high battery voltage and a higher energy density per weight and volume than the conventional battery, and is the most expected secondary battery in the future.

A small and lightweight lithium-ion secondary battery having a high energy density is a lightweight and thin film that is formed by laminating and integrating a metal sheet such as aluminum on a pair of insulating resin films, particularly in applications having a large energy density. A laminate film is often used for an outer case. In this type of sheet battery, since the case itself does not have a yield strength to maintain the shape, it is general that the inside of the cell is depressurized and constrained at atmospheric pressure in order to constrain the electrode group with uniform pressure.

In sheet batteries, resistance welding, ultrasonic welding, or the like is often used for connection between the electrode current collector portion group and the electrode terminal led out of the case, but this connection portion is the most delicate portion.

As a technique related to this connection portion, in a battery having a laminate sheet as an exterior body, at least a portion of the lead surface that passes through the sealing portion of the laminate sheet is coated with a heat-fusible resin having good adhesion to metal. There are proposed ones (Patent Document 1) and those in which acid-modified polyolefin is applied to the sealing portions of the both sides of the external connection terminals in the sheet type electrochemical element (Patent Document 2).

Further, in the plate battery, an exterior member including a sealing portion where at least a part of the electrode terminal member is located, and a seal that reinforces sealing of a region where the electrode terminal member is located in the sealing portion of the exterior member The thing provided with a reinforcement means (patent document 3) is proposed.

Further, in a polymer solid electrolyte lithium ion secondary battery, a lead extended from an electrode is welded on a lead terminal, and the welded portion is wound and protected with an insulating tape (Patent Document 4). Proposed.

JP-A-11-233133 Japanese Patent Laid-Open No. 11-345599 JP 2001-93491 A JP 2004-71438 A

The sheet-like battery using the laminate film for the outer case has no problem in basic functions even if the battery itself is healthy, even if it has a connection part between the delicate electrode current collector part and the electrode terminal. In the lithium ion secondary battery, gas is generated in the battery, although this is little by little depending on the degree of use of the battery, and this gas accumulates in the battery. This kind of gas generation in the battery can also be seen in other types of storage batteries, but in the case of alkaline storage batteries, the gas generated inside is absorbed by the electrode, and in lead storage batteries, the catalyst is released outside the battery It is equipped with a mechanism to prepare for returning to water again. On the other hand, it is currently difficult to construct such a mechanism with a lithium ion secondary battery, and gas generated in the battery accumulates in the battery.

Such accumulation of gas in the battery also occurs in a lithium ion secondary battery using a hard case such as a metal can, but in a lithium ion secondary battery using a laminate film as an outer case, the internal pressure of the battery is reduced. The contact force of the electrode current collector group and the electrode terminal is reduced, and depending on the application, the connection part may be broken in the worst case due to mechanical conditions such as vibration and impact.

In the inventions described in Patent Document 1 and Patent Document 2, the contact portion between the electrode terminal and the film is protected, and the connecting portion between the current collector and the electrode terminal is not protected.

In the invention described in Patent Document 3, since the temperature of the connecting portion between the current collector and the electrode terminal is likely to rise, if this portion is used as the sealing portion of the exterior member, the sealing effect and the insulating property are adversely affected by the heat. There is a possibility of effect. In addition, since the connecting portion between the current collector and the electrode terminal is in the sealing portion of the exterior member, there is a problem that this portion that is thin and easily bent becomes a fulcrum and is vulnerable to vibration and impact. Further, since the connecting portion is hardened, there is no degree of freedom in shape, and as a result, there is a problem that it is easily broken by vibration or impact.

Further, in the invention described in Patent Document 4, the welded portion between the lead extending from the electrode and the lead terminal is wound to prevent insulation from the counter electrode. Since this portion is floated in a flexible storage container laminated with a plastic film, it is protected against external vibrations and impacts although it is protected.

The present invention has been made in view of the above-mentioned problems of the prior art, and even in a sheet-like battery using a laminate film in a state where gas is accumulated in the battery as an outer case, the current collector group of the electrode and the electrode It aims at providing the sheet-like battery in which the connection part with a terminal was connected stably.

In order to solve the above problems, the present inventor has studied in detail the connecting portion between the current collector group of the sheet-like battery and the electrode terminal. As a result, a spacer is inserted between the connecting portion and the outer case, and is fixed. By doing so, it has been found that this connecting portion is stably connected. That is, as described in claim 1, an electrode group formed by laminating a positive electrode with a negative electrode through a separator is housed in an outer case made of a laminate film, and a current collector of each electrode or a lead wire attached thereto In a sheet-like battery in which connected electrode terminals are led out of the case, a resin material or a metal plate coated with a resin material between the current collector or the lead wire and the connection portion of the electrode terminal and the outer case The sheet-like battery is characterized in that the spacer is inserted in a bent state.

In the sheet battery, the present invention is characterized in that the resin material constituting the spacer is a polyolefin resin.

According to the present invention, in the connection portion between the current collector group of the sheet-like battery and the electrode terminal, a spacer is bent between the connection portion and the exterior case, so that the current collector group and the electrode terminal are inserted. The electrode terminal is stably connected. For this reason, the decompression inside the battery is reduced, the restraining force of the connection part between the electrode current collector group and the electrode terminal is reduced, and even when mechanical pressure is applied to the connection part due to vibration or impact, the wire breaks. Internal short circuit will not occur. Therefore, by using the technique of the present invention, high reliability can be obtained even in a sheet-like high energy density type lithium ion secondary battery in which an outer case is formed of a laminate film.

Next, embodiments of the sheet battery of the present invention will be described with reference to the drawings. FIG. 1 shows a top view of a sheet battery according to an embodiment of the present invention. FIG. 2 is a sectional view taken along line AA in FIG. Further, FIG. 3 shows an enlarged cross-sectional view of the main part of FIG. Here, the sheet-like battery is shown in which one positive / negative electrode terminal is drawn out from each of two opposing sides, but it can also be applied to one in which both the positive / negative electrode terminals are drawn out from one side. A method for manufacturing the electrode will be described later in the item of the embodiment, and here, the spacer 5 which is a feature of the present invention will be described.

The electrode group 4 formed by laminating the positive electrode plate 1 and the negative electrode plate 1 housed in the bag-like separator 3 was inserted into an outer case 6 having a predetermined size embossed in a cup shape. In this electrode group 4, a positive electrode terminal connection portion 1c and a negative electrode terminal connection portion 2c are formed by ultrasonic welding the positive electrode terminal 1b to the positive electrode current collector 1a group and the negative electrode terminal 2b to the negative electrode current collector 2a group, respectively. It is. At the same time when the electrode group 4 was inserted into the outer case 6, the spacer 5 was inserted between the ultrasonic welded portion and the embossed inclined portion of the outer case 6 while being in contact with the connecting portions 1 c and 2 c. Then, along the flat part of the outer case 6, the side including the terminal part and the other side were heat-sealed to form the heat-welded region 7, thereby producing a dry cell.

The inserted state of the spacer 5 may be fixed by bonding the spacer 5 to the connecting portion in order to enhance the stability of the connecting portions 1c and 2c between the current collector group of the electrodes and the electrode terminal. .

Further, the size of the spacer 5 is preferably at least the length of the connecting portion in the electrode terminal drawing direction in the connecting portions 1c and 2c between the current collector group of the electrodes and the electrode terminals. It is preferable that there is at least 2/3 or more of the length of the connecting portion in the direction perpendicular to the terminal drawing direction. This is because if the area covering the connection portion is too small, the effect of protection against pressure is reduced. Further, in the case where both the positive and negative terminals are drawn from one side of the sheet-like battery, there is no problem as long as at least the length of both electrode terminals is covered in the direction perpendicular to the terminal drawing direction. In this case, both the electrode terminals can be covered with a single spacer 5, which is efficient.

Here, the shape of the spacer 5 will be described. A plate made of an insulating material is bent into a C shape. Then, the bent portion is inserted into the battery in a state where the bent portion is pressed and elastically deformed in the terminal direction. By doing in this way, not only when the decompression state inside a battery falls, but even if the battery internal pressure exceeds atmospheric pressure, the pressure change can be tracked. Further, there is an advantage that the pressing force can be controlled by the type and thickness of the plate, and the elastic force can be easily selected according to the characteristics of the laminate film used for the outer case 6.

Next, the material is preferably a polyolefin-based insulating material such as polyethylene or polypropylene. It does not necessarily have to be insulative, but insulative is less likely to cause a short circuit inside the battery, and in a type of battery in which the positive and negative electrodes are arranged side by side, the terminal connection portion is constrained by a single spacer. This is preferable.

Further, the plate constituting the spacer 5 is insulative and elastic by C-shaped processing, is generally insoluble in an electrolytic solution used in a lithium ion secondary battery, and is chemically and electrochemically. As long as it is stable, it is not particularly limited. A resin material or a metal plate coated with a resin material can be used. However, a polyolefin-based material is particularly preferable because it is low in cost, light weight, easy to process, and has no short circuit when the terminal is abnormally heated.

Next, a lithium ion secondary battery is suitably used for a sheet-like battery having the laminate film of the present invention as an outer case.

Examples of the positive electrode active material of the lithium ion secondary battery include a spinel structure compound such as LiMn ₂ O ₄ and a lithium-containing transition metal composite oxide having an α-NaFeO ₂ structure generally represented by LiMO ₂ (here, M Can be used alone or two or more metal elements selected from Co, Ni, Al, Mn, Ti, Fe, etc., lithium-containing phosphoric acid compounds, and the like. Furthermore, if the battery manufacturing method is devised, metal oxides such as MnO ₂ and V ₂ O ₅ into which lithium can be inserted, metal sulfides such as TiS ₂ and ZnS _2, and polyaniline having electrochemical redox activity It is also possible to use a π-conjugated polymer such as polypyrrole or a disulfide compound utilizing the formation-cleavage of a sulfur-sulfur bond in the molecule.

On the other hand, as the negative electrode, metallic lithium or various lithium alloys, various metal oxides such as SnO ₂ , or a carbon material capable of occluding and releasing lithium can be used. As the carbon material, naturally produced graphite or baked raw material is fired at a high temperature of 2000 ° C. or higher, and a graphite-based carbon material having a flat potential characteristic with a developed graphite structure, or an organic raw material is relatively heated to 1000 ° C. or lower. A coke-based carbon material that is fired at a low temperature and can be expected to have a larger charge / discharge capacity than a graphite-based material is used.

  Regarding the current collector part of the electrode plate, when an active material is applied to the current collector, a plain part on which the active material is not applied is formed largely at the end part, and this is used as the current collector part. However, when it is desired to increase the coating area of the active material, the uncoated portion may be formed small and a lead wire may be welded to the uncoated portion so that the lead wire serves as a current collecting portion.

The positive electrode current collector is preferably an aluminum foil having a thickness of 5 to 60 μm, and the positive electrode active material, a conductive auxiliary agent such as scaly graphite and carbon black, and a binder such as polyvinylidene fluoride are provided on at least one surface of the current collector. A paste formed with a solvent can be applied and dried to form a positive electrode active material-containing coating film having a thickness of 30 to 300 μm.

As the negative electrode current collector, a copper foil having a thickness of 5 to 60 μm is preferable, and the negative electrode active material and a binder such as polyvinylidene fluoride are pasted into a paste with a solvent on at least one surface of the current collector, and then dried. And what formed the 30-300 micrometer-thick negative electrode active material containing coating film can be used.

As a solvent for the electrolytic solution, a solvent usually used in an electrolytic lithium ion secondary battery, for example, ethylene carbonate (EC), propylene carbonate (PC), γ-butyrolactone (GBL), sulfolane (SL), diethyl carbonate (DEC), dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), dimethoxyethane (DME), diethoxyethane (DEE), 2-methyl-tetrahydrofuran (2MeTHF), various glymes, etc. alone or in a mixed system Although it can be used, it is necessary to have a solvent structure capable of dissolving LiBETI up to 2.0. Also, it is desirable to avoid DMC, DME, DEE, etc. because the flash point is below room temperature.

The lithium salt used as the solute of the electrolytic solution is usually a lithium salt used in an electrolytic lithium ion secondary battery, such as lithium hexafluorophosphate (LiPF ₆ ), lithium perchlorate (LiClO ₄ ). Inorganic lithium salts such as lithium tetrafluoroborate (LiBF ₄ ), lithium trifluoromethylsulfonate (LiOSO ₂ CF ₃ ), lithium bis (trifluoromethylsulfonyl) imide (LiN (CF ₃ SO ₂ ) ₂ ), An organic lithium salt such as bis (perfluoroethylsulfonyl) imidolithium (LiN (CF ₅ SO ₂ ) ₂ ) can be appropriately selected and used in accordance with the synthesis method of the electrolyte gel.

As the separator, a nonwoven fabric or a porous sheet made of a polyolefin-based synthetic resin is suitable.

Further, as the laminate film constituting the exterior case 6, a film in which a metal sheet such as aluminum is placed inside and a sheet of heat-fusible resin is bonded to both sides or one side can be used. As this heat-fusible resin, resins such as polypropylene, modified polypropylene, polyethylene, modified polyethylene, polyethylene terephthalate, heat-fusible polyethylene terephthalate, heat-fusible polyimide, polymethyl methacrylate, or two or more of these Resin copolymers can be employed.

Next, the effects of the present invention will be described in detail by way of examples.

[Production of positive electrode]
In the dispersing machine, 91 parts by weight of LiCoO ₂ powder as the positive electrode active material, 4.0 parts by weight of polyvinylidene fluoride resin as the binder, 5.0 parts by weight of graphite powder as the conductive agent, and N-methylpyrrolidone as the dispersing agent were used. Then, a slurry for coating the positive electrode active material mixture was prepared by stirring and mixing.

Next, the positive electrode active material mixture slurry is applied on both sides of the current collector 1a made of aluminum foil using a die coater and dried in an oven to remove the dispersant, thereby removing the positive electrode active material. A mixture coating film was formed. This was pressed to a predetermined density, cut into a predetermined size, and a positive electrode plate 1 having a plain portion 1a with a predetermined width was obtained.

[Production of negative electrode]
Application of negative electrode active material mixture by mixing 90 parts by weight of artificial graphite powder, 10 parts by weight of polyvinylidene fluoride resin as a binder, and N-methylpyrrolidone as a dispersant by stirring and mixing with a disperser A slurry was prepared.

Next, the negative electrode active material mixture slurry is applied on both sides of the current collector 2a made of copper foil using a die coater and dried in an oven to remove the dispersant, thereby removing the negative electrode active material. A mixture coating film was formed. This was pressed to a predetermined density and cut to a predetermined size to obtain a negative electrode plate 2 having a plain portion 2a having a predetermined width.

[Battery assembly]
A separator 3 made of two polyethylene porous sheets is partially heat-sealed to produce an envelope-like separator bag, and the prepared positive electrode plate 1 is inserted into the separator plate 1 leaving the plain portion 1a. A separator-covered positive electrode plate was obtained.

Next, the uncoated portion 1a of the positive electrode plate 1 and the uncoated portion 2a of the negative electrode plate 2 in the order of the negative electrode plate 2, the separator-covered positive electrode plate 1, the negative electrode plate 2,. Were stacked side by side to produce an electrode group 4 of 10 positive plates and 11 negative plates. In the drawing, an example of two positive plates and three negative plates is schematically shown.

Next, the positive electrode plate uncoated portion 1a of the electrode group 4 thus produced is ultrasonically welded with a positive electrode terminal 1b made of an aluminum plate, and the negative electrode plate uncoated portion 2a with a negative electrode terminal 2b made of a nickel plate under a predetermined condition. The positive electrode terminal connection part 1c and the negative electrode terminal connection part 2c were respectively formed by attaching by a method to produce a battery element.

Next, the battery element produced in this way was inserted into an outer case 6 made of an aluminum laminate film of a predetermined size embossed in a cup shape. At this time, a spacer 5 in which a polyethylene plate was bent in a C shape was inserted between the ultrasonic welded portion and the embossed inclined portion of the outer case 6 at the same time while contacting the connecting portions 1c and 2c. Then, along the flat part of the outer case 6, the side including the terminal part and the other side were heat-sealed to form the heat-welded region 7, and the remaining side was used as an opening to produce a dry cell.

Next, the dry cell is vacuum-dried under predetermined conditions, and then lithium hexafluorophosphate is dissolved in ethylene carbonate and diethyl carbonate at a weight mixing ratio of 3: 7 from the opening so as to be 1.3 mol / l. The organic solution was injected, the inside of the cell was evacuated, the opening was heat sealed and sealed, and then subjected to a predetermined initial charge at a current of 0.1 CA, storage for a predetermined time, and then a current of 0.2 CA. Then, the battery was discharged until the cell voltage reached 2.75 V, and finally the activation process was performed to produce ten sheet-like batteries. This battery is referred to as Example 1.

Ten sheet-like batteries were produced in the same manner as in Example 1 except that the spacer 5 was made of polypropylene. This battery is referred to as Example 2.

Ten sheet-like batteries were produced in the same manner as in Example 1 except that the spacer 5 was made of a stainless steel plate coated with polypropylene. This battery is referred to as Example 3.

Ten sheet-like batteries were produced in the same manner as in Example 1 except that the spacer 5 was not included. This battery is referred to as Conventional Example 1.

[Shock test]
In order to confirm the stability of the connection portion of the battery electrode terminal, an impact test was performed under the following conditions. Each battery made in this way has 5 cells at each level, with 0.5 CA current, 4.1 V voltage regulation for 4 hours charging, 30 minute rest, 0.5 CA current with a cell voltage of 2.75 V. After repeating the discharge and 30-minute pauses 1000 times, the impact of 25G ^0-P half sin waveform 10 msec is input twice in the short terminal direction of the battery, and the internal impedance of the battery before and after that is input. Measured and compared. The results (average value of 5) are shown in Table 1.

As a result of the evaluation, the batteries of Examples 1 to 3 according to the present invention did not clearly change the internal resistance before and after the impact test, and good results were obtained. On the other hand, it was found that the internal resistance value of the battery of Conventional Example 1 increased by nearly 50% after the impact test compared to before the impact test.

[Short-circuit test]
Next, in order to confirm the thermal stability of the material used for the inserted spacer 5, a short-circuit test was performed under the following conditions. The batteries of Examples 1 to 3 and the battery of Conventional Example 1 prepared above were charged at a level of 5 CA at a current of 0.5 CA for 2 hours with a 4.2 V voltage regulation, and then 10 copper wires with a circuit resistance of 5 mΩ. Shorted for hours. At this time, the external short-circuit and the short-circuit open were repeated every 0.1 minute, and the presence or absence of a short circuit in the battery was confirmed. The results (average value of 5) are shown in Table 2.

As a result, the battery of Conventional Example 1 was short-circuited in the battery after 18.7 minutes, whereas the battery of Example 3 was not short-circuited until 552.2 minutes later. Then, even if the external short circuit was performed for 600 minutes, the short circuit did not occur inside the battery. Therefore, among the batteries of the present invention, polypropylene or polyethylene as an elastic spacer material is less likely to cause a short circuit in the battery even when the terminal is exposed to an abnormally high temperature such as an internal short circuit of the battery, and is suitable as an elastic spacer material. It turns out that.

According to the present invention, both members are stably connected by inserting the spacer in a bent state between the connection portion between the current collector group of the electrode and the electrode terminal and the outer case. For this reason, the sheet-like battery of the present invention can obtain high reliability as a high energy density type lithium ion secondary battery, and can be used as a power source for motorcycles, electric cars, hybrid electric cars, etc. Is not particularly limited.

It is a top view of the sheet-like battery which is one Example of this invention. FIG. 2 is a cross-sectional view taken along line AA in FIG. 1. FIG. 3 is an enlarged cross-sectional view of a main part of FIG. 2.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Positive electrode plate 1a Positive electrode electrical power collector (positive electrode plate plain part)
1b positive electrode terminal 1c positive electrode terminal connection part 2 negative electrode plate 2a negative electrode current collector (negative electrode plate plain part)
2b Negative electrode terminal 2c Negative electrode terminal connection part 3 Separator 4 Electrode group 5 Spacer 6 Exterior case 7 Thermal welding area

Claims (2)

An electrode group consisting of a positive electrode laminated with a negative electrode through a separator is housed in an outer case made of a laminate film, and the electrode terminal connected to the current collector of each electrode or the lead wire attached to it is led out of the case In the sheet-like battery thus formed, a spacer made of a resin material or a metal plate coated with a resin material is interposed between the current collector or lead wire and electrode terminal connection portion and the outer case, and is inserted in a bent state. A sheet battery characterized by being made. The sheet-like battery according to claim 1, wherein the resin material is made of a polyolefin-based resin.