JP2000173580A - Thin secondary battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a thin secondary battery capable of being equipped with a protection circuit board having a function to shut off the current in the event of failure such as over-charging or over-discharging without reducing the volume-energy density to a great extent. SOLUTION: A thin secondary battery is composed of a power generating element, an outer material 2 to store the power generating element and with the opening sealed by hot melting, a positive and a negative lead connected electrically with the power generating element and with the forefront parts extending out from the outer material 2, and a protection circuit board 3 installed on the hot melt attaching part of the outer material 2 in the condition connected with the leads, having a function to shut off the current in the event of failure, and including an FET element 16.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a thin secondary battery provided with a protection circuit board having a function of interrupting current when an abnormality occurs.

[0002]

2. Description of the Related Art A polymer lithium secondary battery, which is an example of a thin secondary battery, can be reduced in thickness to about 0.5 mm, and is being developed as a power source for thin electronic devices. I have.

[0003] In order to put a polymer lithium secondary battery into practical use, in addition to the selection of positive and negative electrode active substances and battery construction technology, sealing technology for power generation elements with an exterior material and reliable and easy installation of equipment are required. Packaging technology is important.

As the exterior material, the use of a laminate film in which a heat-fusible resin film is disposed on the inner surface and a metal foil such as an aluminum foil is interposed in an intermediate layer has been studied. In addition, if a structure in which a power generation element is housed in the laminate film is incorporated into an electronic device as a polymer lithium secondary battery, it becomes difficult to easily insert and remove the device from the device. Attempts have been made to further house the package in a package having external terminals.

On the other hand, from the viewpoint of enhancing safety, a protection circuit board (PCB) having a function of interrupting a current when an abnormality such as overcharge or overdischarge is frequently used in a lithium ion secondary battery is replaced with a polymer lithium secondary battery. It is considered to be attached to the next battery.

[0006]

An object of the present invention is to provide a protection circuit board having a function of interrupting a current in the event of an abnormality such as overcharging or overdischarging without significantly reducing the volume energy density. It is an object of the present invention to provide a secondary battery.

[0007]

According to the present invention, there is provided a thin secondary battery comprising: a power generating element; an exterior material in which the power generating element is housed and whose opening is sealed by heat sealing; A positive and negative electrode lead that is electrically connected and whose tip is extended from the exterior material is disposed on the heat-sealed portion of the exterior material while being electrically connected to the positive and negative electrode lead. And a protection circuit board including an FET element.

[0008]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A thin secondary battery according to the present invention will be described below with reference to FIGS. 1 to 6 by taking a polymer lithium secondary battery as an example.

FIG. 1 is a sectional view showing a state in which a thin secondary battery according to the present invention is housed in a pack, FIG. 2 is a sectional view showing a power generating element of the thin secondary battery in FIG. 1, and FIG. FIG. 4 is a top view showing the exterior material of the thin secondary battery of FIG. 4, FIG. 4 is a cross-sectional view of the exterior material of FIG.
5 is a top view showing a thin secondary battery, FIG. 6 is an enlarged side view showing a protection circuit board of the thin secondary battery of FIG. 1, and FIG. 7 is a plan view of the protection circuit board of FIG.

As shown in FIG. 1, a rectangular pack 1 made of a synthetic resin such as polyethylene terephthalate (PET) contains an exterior material 2 containing a power generation element. The pack 1 houses a protection circuit board 3 having a function of interrupting a current when an abnormality such as overcharge or overdischarge occurs.

First, the power generating element will be described. As shown in FIG. 2, separators 5 are bonded to both surfaces of the negative electrode 4. The two positive electrodes 6 are bonded to the separator 5 respectively. The negative electrode 4 has a structure in which a negative electrode layer is supported on both surfaces of a negative electrode current collector having a porous structure. Each of the positive electrodes 6 has a structure in which a positive electrode layer is supported on both surfaces of a positive electrode current collector having a porous structure. The negative electrode terminal 7 is formed by extending the negative electrode current collector in a belt shape. The positive electrode terminal 8 is formed by extending the positive electrode current collector in a belt shape. Positive and negative leads (not shown) are connected to the positive and negative terminals 7, 8, respectively.

The exterior member 2 will be described. The exterior material 2
As shown in FIG. 3 and FIG. 4, a box-shaped container 9 having an opening is bordered, and a lid plate 10 formed by extending one end of the opening. A heat-fusible resin is disposed on the inner surface and opening edge of the box-shaped container 9 and the inner surface of the lid 10.

As shown in FIG. 5, the power generating element includes the positive electrode lead 11 and the negative electrode lead 1 in the exterior material 2.
2 is stored so as to extend from between the container 9 and the lid 10. The opening edge 13 of the container 9 and the lid 10
Are bonded by heat fusion, and the power generating element
Sealed inside.

The protection circuit board 3 will be described. Figure 6
As shown in FIG. 7, the substrate 14 includes electronic elements 15a, 1
5b and the FET element 16 are arranged. The radiating fins 17a and 17b as radiating means are provided in the FET element 1 described above.
6 are mounted upward on both sides. Positive electrode lead connection part 1 to which positive electrode lead 11 of the thin type secondary battery is connected
The negative electrode lead connection portion 19 to which the negative electrode lead 8 and the negative electrode lead 12 of the secondary battery are connected extends from an end of the substrate 14. The external positive terminal 20 and the external negative terminal 21 are connected to ends opposite to the ends where the connecting portions 18 and 19 extend, respectively.

In the thin type secondary battery, as shown in FIG. 1 described above, the positive and negative electrode leads 11 and 12 are folded back on the upper surface in the closed container 1 and the heat-sealed portion 13 along the longitudinal direction is downward. It is stored in a folded state on the side. The protection circuit board 3 is provided with the exterior material 2 with the FET element 16 side facing upward.
The positive and negative electrode leads 11 and 12 of the heat-sealed portion 13 are disposed on the sides where the positive and negative leads 11 and 12 are fixed. The positive electrode lead connecting portion 18 of the protection circuit board 3 is connected to the positive electrode lead 11 of the thin type secondary battery.
The negative electrode lead connection portion 19 of the circuit board 3 is connected to the negative electrode lead 12 of the secondary battery.

According to such a thin secondary battery, since the protection circuit board 3 is disposed on the heat-sealed portion 13 which is recessed from the portion where the power generating element is stored, the volume energy density is reduced. Thus, the safety at the time of abnormality such as overcharging or overdischarging can be improved. In particular, the heat-sealed portion 13
By arranging the protection circuit board 3 on the side to which the positive and negative electrode leads 11 and 12 are fixed, the allowable occupation volume of the protection circuit board 3 can be increased, and two sides orthogonal to this side are placed on the lower side. Since it can be bent, the volume energy density can be improved.

The positive and negative electrode leads 1 of the heat-sealed portion 13
By using the box-shaped exterior member 2 when arranging the protection circuit board 3 on the side to which 1 and 12 are fixed, it is possible to reduce a decrease in volume energy density as compared with a film-shaped exterior member. That is, when the power generation element is sealed in the film-like exterior material, the positive and negative electrode leads extend from between the films, so that the positive and negative electrode leads are positioned at a height of about half the height of the battery. For this reason, when the circuit board is placed on the heat-sealed portion where the positive and negative electrode leads are fixed, if the occupied height of the circuit board exceeds half the height of the battery, the volume energy density may be significantly reduced. is there. on the other hand,
When the power generating element is sealed in the box-shaped exterior material 2, the positive and negative electrode leads are located at the bottom of the battery. As a result, the allowable value of the occupied height of the circuit board 3 becomes substantially equal to the height of the battery, and can be made larger than that of the film-like exterior material, so that a decrease in the volume energy density can be largely suppressed.

Further, by arranging the protection circuit board 3 with the FET element 16 side facing upward, the heat generated by the FET element 16 during operation of the protection circuit board 3 is prevented from being heated by the heat-fused portion. Therefore, softening or melting of the heat-sealed portion can be avoided, and the airtightness of the exterior material 2 in which the power generation element is stored can be sufficiently maintained. Further, when the protection circuit board 3 is arranged in this way, the FET
By attaching the radiating fins 17a and 17b as radiating means to the element 16, the heat radiation efficiency of the FET element 16 can be increased, so that the thermal effect on the heat fusion portion 13 can be further reduced, and the power generation element can be housed. It is possible to further enhance the airtightness of the provided exterior material 2.

Hereinafter, the positive electrode, the negative electrode, the separator, and the exterior material will be described. 1) Positive electrode This positive electrode has a structure in which a positive electrode layer containing a positive electrode active material, a non-aqueous electrolyte, and a polymer having a function of holding the non-aqueous electrolyte is supported on a current collector.

[0020] As the positive electrode active material, various oxides (e.g., lithium manganese composite oxides such as LiMn ₂ O _4, manganese dioxide, for example, lithium-containing nickel oxides such as LiNiO _2, for example, lithium-containing cobalt such as LiCoO ₂ Oxide, lithium-containing nickel cobalt oxide, amorphous vanadium pentoxide containing lithium, and the like, and chalcogen compounds (for example, titanium disulfide, molybdenum disulfide, and the like). Among them, it is preferable to use a lithium manganese composite oxide, a lithium-containing cobalt oxide, and a lithium-containing nickel oxide.

The non-aqueous electrolyte is prepared by dissolving an electrolyte in a non-aqueous solvent. As the non-aqueous solvent,
Ethylene carbonate (EC), propylene carbonate (PC), butylene carbonate (BC), dimethyl carbonate (DMC), diethyl carbonate (DE
C), ethyl methyl carbonate (EMC), γ-butyrolactone (γ-BL), sulfolane, acetonitrile, 1,2-dimethoxyethane, 1,3-dimethoxypropane, dimethyl ether, tetrahydrofuran (TH
F) and 2-methyltetrahydrofuran. The non-aqueous solvents may be used alone or as a mixture of two or more.

Examples of the electrolyte include lithium perchlorate (LiClO ₄ ) and lithium hexafluorophosphate (L
iPF _6), boric tetrafluoride lithium (LiBF _4), lithium hexafluoroarsenate (LiAsF _6), lithium salts such as lithium trifluoromethane sulfonate (LiCF ₃ SO ₃₎ may be mentioned.

The amount of the electrolyte dissolved in the non-aqueous solvent is desirably 0.2 mol / l to 2 mol / l.

It is desirable that the polymer having the function of retaining the non-aqueous electrolyte further has a binding function. Examples of the polymer having a function of retaining a non-aqueous electrolyte and a binding function include, for example, polyethylene oxide derivatives,
Examples thereof include a polypropylene oxide derivative, a polymer containing the derivative, and a copolymer of vinylidene fluoride (VdF) and hexafluoropropylene (HFP). Among them, a VdF-HFP copolymer is preferable.

The positive electrode may include a conductive material from the viewpoint of improving conductivity. Examples of the conductive material include artificial graphite, carbon black (eg, acetylene black), nickel powder, and the like.

As the current collector, for example, those having a porous structure such as aluminum mesh, aluminum expanded metal or aluminum punched metal, or metal foil such as aluminum foil can be used. . When a metal foil is used as the current collector, it is preferable that the positive electrode layer be supported on only one surface of the current collector. Further, in FIG. 2 described above, a part of the current collector is used as the positive electrode terminal. However, the positive electrode terminal may be separated from the current collector and fixed to the current collector by welding or the like.

The positive electrode lead can be formed of, for example, an aluminum foil.

2) Negative Electrode The negative electrode has a structure in which a negative electrode layer containing a negative electrode active material, a non-aqueous electrolyte, and a polymer having a function of holding the electrolyte is supported on a current collector.

Examples of the negative electrode active material include a carbonaceous material that stores and releases lithium ions. As such a carbonaceous material, for example, an organic polymer compound (for example,
Phenolic resin, polyacrylonitrile, cellulose, etc.) by firing, coke,
Examples thereof include those obtained by firing pitch, and carbonaceous materials represented by artificial graphite, natural graphite, and the like. Among them, in an atmosphere of an inert gas such as an argon gas and a nitrogen gas, 500 ° C. to 3000 ° C.
It is preferable to use a carbonaceous material obtained by firing the organic polymer compound at a temperature of ° C. under normal pressure or reduced pressure.

As the non-aqueous electrolyte and the polymer having a function of holding the non-aqueous electrolyte, the same ones as those described for the positive electrode described above are used.

As the current collector, for example, those having a porous structure such as copper mesh, copper expanded metal or copper punched metal, or metal foil such as copper foil can be used. When a metal foil is used as the current collector, it is desirable that the negative electrode layer be supported on only one surface of the current collector. Further, in FIG. 2 described above, a part of the current collector is used as the negative electrode terminal. However, the negative electrode terminal may be separated from the current collector and fixed to the current collector by welding or the like.

3) Separator The separator is a sheet containing a non-aqueous electrolyte and a polymer having a function of holding the electrolyte. As the non-aqueous electrolyte and the polymer having a function of holding the non-aqueous electrolyte, those similar to those described for the positive electrode described above are used. From the viewpoint of further improving the strength, the separator may include an inorganic filler such as silicon oxide powder.

4) Exterior material This exterior material is preferably made of, for example, a laminate film in which a heat-fusible resin is disposed on the sealing surface and a thin metal film such as aluminum (Al) is interposed therebetween.
Specifically, a laminated film of acid-modified polypropylene (PP) / polyethylene terephthalate (PET) / Al foil / PET laminated from the sealing surface side to the outer surface;
Acid-modified PE / nylon / Al foil / PET laminated film; Ionomer / Ni foil / PE / PET laminated film; Ethylene vinyl acetate (EVA) /
A laminated film of PE / Al foil / PET; a laminated film of ionomer / PET / Al foil / PET can be used. Here, the film other than PE, ionomer, and EVA on the sealing surface has moisture resistance, air resistance, and chemical resistance.

The thickness of the thin metal film in the laminate film is preferably 30 μm or more. If the thickness of the metal thin film is less than 30 μm, it may be difficult to form a container having the above-described shape from a laminate film, and the shape retention of the exterior material may be reduced. However, the thickness of the metal thin film is 100 μm
When the pressure exceeds the above, the pressing force required for sheet forming becomes considerably high, so that capital investment such as press is increased, but shape retention as an exterior material becomes more than necessary. For this reason, it is more preferable that the thickness of the metal thin film is 30 μm to 80 μm.

In FIG. 1 described above, an example is described in which an exterior material is used in which the container and the cover plate are integrated, but the container and the cover plate may be separate. In addition, as the exterior material, a film material can be used in addition to the above-described box-shaped material. As the film material, the above-described laminated film can be used.

As described in detail above, the thin secondary battery according to the present invention comprises a power generating element, an exterior material in which the power generating element is housed and whose opening is sealed by heat sealing, A positive and negative electrode lead that is electrically connected and whose tip is extended from the exterior material is disposed on the heat-sealed portion of the exterior material while being electrically connected to the positive and negative electrode lead. And a protection circuit board including an FET element. According to such a secondary battery, since the protection circuit board is disposed in the heat-sealed portion that is recessed from the portion in which the power generation element is stored, overcharge or overdischarge can be performed without lowering the volume energy density. It is possible to improve the safety at the time of abnormality such as. In particular, by arranging the protection circuit board on the side of the heat-fused portion where the positive and negative electrode leads are fixed, the allowable occupation volume of the protection circuit board can be increased, and two sides orthogonal to this side are placed on the lower side. Can be bent, so that the volume energy density can be improved.

Further, by arranging the protection circuit board with the FET element side facing upward, it is possible to prevent the heat generated from the FET element from being heated by the heat generated by the FET element during operation of the protection circuit board. Therefore, melting of the heat-sealed portion can be avoided, and the airtightness of the exterior material in which the power generation element is stored can be sufficiently maintained. When the protection circuit board is disposed as described above, the heat generated from the FET element can be efficiently released by the FET element having the heat radiating means, so that the heat influence on the heat-sealed portion is further reduced. The airtightness of the exterior material in which the power generation element is stored can be further improved.

[0038]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments according to the present invention will be described below in detail with reference to the drawings.

(Example 1) <Preparation of positive electrode not impregnated with non-aqueous electrolytic solution> Vinylidene fluoride-hexafluoropropylene (VdF-H) was added to acetone.
After dissolving the copolymer powder of FP), dibutyl phthalate (DBP) and a lithium-containing cobalt oxide represented by a composition formula of LiCoO ₂ as an active material are added to the acetone solution, mixed, and then mixed. Was prepared. The obtained paste was applied to a porous current collector made of an aluminum lath metal except for a portion to be a positive electrode terminal, dried, and then cut to produce a non-aqueous electrolyte-unimpregnated positive electrode.

<Preparation of Negative Electrode Not Impregnated with Nonaqueous Electrolyte> After dissolving vinylidene fluoride-hexafluoropropylene (VdF-HFP) copolymer powder in acetone, dibutyl phthalate (DBP) was added to the acetone solution. Was added, and mesophase pitch carbon fibers were added and mixed to prepare a paste. The obtained paste was applied to a porous current collector made of a copper lath metal except for a portion to be a negative electrode terminal, dried, and then cut to prepare a non-aqueous electrolyte-unimpregnated negative electrode.

<Preparation of Separator> Vinylidene fluoride-hexafluoropropylene (VdF-H) was added to acetone.
After dissolving the copolymer powder of FP), dibutyl phthalate (DBP) was added to the acetone solution and mixed to prepare a paste. The obtained paste was applied on a smooth glass plate, formed into a sheet, and cut to prepare a non-aqueous electrolyte-unimpregnated separator.

<Preparation of Nonaqueous Electrolyte> A nonaqueous solvent in which ethylene carbonate (EC) and dimethyl carbonate (DMC) were mixed at a volume ratio of 1: 1 was mixed with LiPF ₆ as an electrolyte at a concentration of 1 mol / mol. 1 to prepare a non-aqueous electrolyte.

<Battery assembly> The obtained non-aqueous electrolyte-unimpregnated positive electrode, negative electrode and separator were laminated in the order of (positive electrode / separator / negative electrode / separator / positive electrode), and heated and pressed with a heated rigid roll to obtain a thickness. A laminate having a thickness of 0.65 mm was produced. By immersing such a laminate in methanol, DBP was removed from the laminate.

A positive electrode lead made of strip-shaped aluminum foil was connected to the positive electrode terminal of the positive electrode. Further, a negative electrode lead made of a strip-shaped copper foil was connected to the negative electrode terminal of the negative electrode.

On the other hand, a laminate film having a thickness of 0.15 mm consisting of an acid-modified polypropylene (PP) film / PET film / Al film / PET film was preformed into a box shape, and the structure shown in FIGS. An exterior material was produced. The preforming was performed so that the acid-modified polypropylene (PP) film would be the inner surfaces of the box-shaped container and the lid.

The obtained non-aqueous electrolyte-unimpregnated power generating element was housed in the package so that the positive and negative electrode leads extended from the end perpendicular to the longitudinal direction. The outer edge of the box-shaped container of the exterior material and the lid were heat-sealed except for a part, and a non-aqueous electrolyte was injected from the unsealed part. Thereby, a 3.6-mm-thick polymer lithium secondary battery having the structure shown in FIG. 5 described above was manufactured. The heat-sealed portion along the longitudinal direction of the obtained secondary battery was folded inward, and the external dimensions excluding the extended positive and negative electrode leads were 33 mm.
× 70 mm. The width of the heat-sealed portion was 5 mm on the side where the positive and negative electrode leads were fixed, and 3 mm on the other side.

A protection circuit board (having a height of 2.5 mm, a width of 5 mm, and a length of 29 m) having the structure shown in FIGS.
m) was prepared. After welding the positive and negative electrode leads of the secondary battery and the positive and negative electrode lead connection portions of the protection circuit board, respectively, the protection circuit board is placed on the heat-sealed portion where the positive and negative electrode leads of the secondary battery are extended. The protection circuit board was attached to the polymer lithium secondary battery with the side on which the FET element was arranged facing upward.

Comparative Example A polymer lithium secondary battery similar to that of Example 1 described above was used, except that the protection circuit board was placed on the power generation element of the secondary battery with the side on which the FET element was placed facing up. Manufactured.

The occupied volumes of the obtained secondary batteries of Example 1 and Comparative Example were measured, and the results are shown in Table 1 below. Table 1 below shows the battery thickness, width and length in the occupied volume.

[0050]

[Table 1]

As is clear from Table 1, Example 1 in which the protection circuit board was disposed on the heat-sealed portion where the positive and negative electrode leads extended.
It can be seen that the secondary battery has a smaller occupied volume and a larger volume energy density than the secondary battery of the comparative example in which the protection circuit board is disposed on the power generating element.

(Example 2) A polymer lithium secondary battery was manufactured in the same manner as in Example 1, except that the heat radiation fins were removed from the FET element of the protection circuit board.

(Example 3) As shown in FIG. 8, except that the protection circuit board 3 is placed on the heat-sealed portion where the positive and negative leads of the exterior material 2 are extended with the FET element 16 side down. , Example 1
In the same manner as in the above, a polymer lithium secondary battery was manufactured.

30 obtained secondary batteries of Examples 1 to 3 were prepared, and each secondary battery was charged at 1 C in a thermostat at 25 ° C. and discharged at 1 C in a charge / discharge cycle of 300.
The cycle was repeated, and the weight loss rate and discharge capacity after 300 cycles were measured. The results are shown in Table 2 below. However,
The weight change is based on the weight at the first cycle. In addition, the discharge capacity at the 300th cycle was expressed assuming that the discharge capacity of the secondary battery of Example 1 was 100%.

[0055]

[Table 2]

As is clear from Table 2, the secondary battery of Example 1 in which the protection circuit board is arranged with the FET element side facing upward and the FET element has a radiation fin has a weight reduction rate after 300 cycles. No discharge occurs, and it can be seen that the discharge capacity after 300 cycles is higher than the secondary batteries of Examples 2 and 3.

[0057]

As described in detail above, according to the present invention, there is provided a thin secondary battery capable of improving safety during overcharge or overdischarge without impairing volume energy density. Can be.

[Brief description of the drawings]

FIG. 1 is a sectional view showing a state in which a thin secondary battery according to the present invention is housed in a pack.

FIG. 2 is a sectional view showing a power generating element of the thin secondary battery of FIG.

FIG. 3 is a top view showing an exterior material of the thin secondary battery of FIG. 1;

FIG. 4 is a sectional view of the exterior material of FIG. 3;

FIG. 5 is a top view showing a thin secondary battery.

FIG. 6 is an enlarged side view showing a protection circuit board of the thin secondary battery of FIG. 1;

FIG. 7 is a plan view of the protection circuit board of FIG. 6;

FIG. 8 is a side view showing a polymer lithium secondary battery of Example 3.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Pack, 2 ... Exterior material, 3 ... Protection circuit board, 11 ... Positive electrode lead, 14 ... Substrate, 15a, 15b ... Electronic element, 16 ... FET element, 17a, 17b ... Heat radiation fin, 18 ... Positive electrode connection part .

 ──────────────────────────────────────────────────続 き Continued on the front page F term (reference) 5H011 AA07 AA13 BB03 CC02 CC06 CC10 DD13 EE04 FF02 GG09 HH02 5H022 AA09 BB12 BB19 KK01 5H029 AJ12 AK02 AK05 AL06 AM01 AM02 AM03 AM04 AM05 AM06 AM07 AM16 BJ05 DJ03 DJ08 EJ01 EJ12

Claims (4)

[Claims] 1. A power generating element, and said power generating element is housed therein.
An exterior material whose opening is sealed by heat fusion, a positive / negative lead electrically connected to the power generation element, and a tip extending from the exterior material, and a heat-sealed portion of the exterior material A thin secondary battery which is disposed in a state of being electrically connected to the positive and negative electrode leads, has a function of interrupting current when an abnormality occurs, and includes a protection circuit board including an FET element. 2. The thin secondary battery according to claim 1, wherein the protection circuit board is disposed on a side of the heat-sealed portion to which the positive and negative electrode leads are fixed. 3. The thin secondary battery according to claim 1, wherein the protection circuit board is disposed on the heat-sealed portion of the exterior material with the FET element side facing upward. 4. The thin secondary battery according to claim 1, wherein the FET element has a heat radiating unit.