JPH0935748A - Secondary battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a lithium secondary battery with high weight energy density by using a power generating element comprising a whole solid type stacked structure containing a solid electrolyte and forming an outer jacket with a very thin metal plate. SOLUTION: A lithium secondary battery has a power generating element comprising a stacked structure of at least a positive current collector layer, a positive active material layer, an electrolyte layer, a negative active material layer capable of absorbing/releasing lithium, and a negative current collector layer. A solid electrolyte is used as the electrolyte, and the power generating element of the whole solid type and generating no gas in charge/discharge is used. The power generating element is housed in an outer jacket container made of a 200μm or less metal plate. A terminal part of the secondary battery is preferable to be formed with a hermetic member of the inside of a battery container, especially with a glass hermetic member formed by burring work to the inside. A safety valve of one way breaking type is preferably formed in the battery container by metal brazing, and the battery container can be assembled by metal brazing.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a secondary battery.

[0002]

2. Description of the Related Art Recent advances in miniaturization, thinning, and weight reduction of electronic devices have been remarkable, and in the OA field, in particular, desktop devices have been reduced in size and weight to laptop types and notebook types. In addition, the field of new small electronic devices such as electronic notebooks and electronic still cameras has also appeared, and in addition to the miniaturization of conventional hard disks and floppy disks, the development of new memory media, memory cards, is underway. In the wave of miniaturization, thinning, and weight reduction of such electronic devices, high performance is also required for secondary batteries that support these electric powers. In response to such demands, development of lithium secondary batteries as high energy density batteries replacing lead-acid batteries and NiCd batteries has been rapidly advanced. In a lithium secondary battery, in order to widen the electrode area and improve the battery characteristics during current discharge, the positive electrode plate and the negative electrode plate are often wound spirally with a separator interposed between them to form a battery. . Most of the batteries formed in such a case have a cylindrical shape. However, in recent years, there have been many requests from designers of devices that use batteries to make the shape of the battery match the shape of the device. Various types have been developed and many have come to be marketed. When using a prismatic battery case, that is, a rectangular parallelepiped battery case, many efforts have been made to reduce the weight of the case. Nickel cadmium battery,
When a nickel-metal hydride battery or a lithium secondary battery is configured in a prismatic battery case, it is possible to avoid an increase in the internal pressure of the battery due to the gas generation accompanying the battery reaction and an increase in the pressure applied to the side surface of the battery case due to the swelling of the electrodes. Absent. If the plate thickness of the rectangular case was reduced to reduce the weight, the internal pressure increased and the case was deformed. Therefore, Japanese Patent Application Laid-Open
-52842 discloses a rectangular case with less deformation due to the thickness of a pair of opposing wide sides being thicker than the thickness of a pair of opposing narrow sides.
The thickness of the narrow side of mm is the thinnest and the weight has not yet been reduced. Further, in Japanese Patent Laid-Open No. 6-124692, the water vapor transmission rate 2
Disclosed is a lithium secondary battery in which a power generation element is packaged by a multilayer plastic film having a plastic protective layer of 0 g / m ² · 24H or less and an electrically insulating inorganic coating layer formed thereon. Is excellent, but from the viewpoint of completely shutting off humidity, it is important in a lithium secondary battery to seal it with a metal container.

[0003]

[Objective] The present invention basically aims to develop a lithium secondary battery having a high weight energy density by using a power generation element that does not generate gas during charge and discharge.

[0004]

[Structure] The present inventors have arrived at the present invention as a result of extensive studies to solve the above problems. That is, the present invention is a secondary battery comprising a laminated structure of at least a positive electrode current collector layer, a positive electrode active material layer, an electrolyte layer, a negative electrode active material layer capable of inserting and extracting lithium, and a negative electrode current collector layer, wherein the electrolyte is By using an all-solid-state power generating element that is a solid electrolyte, it is possible to make the plate thickness of the battery outer container 200 μm or less. In the secondary battery of the present invention, it is possible to suppress gas generation due to charge and discharge by using an all-solid-state power generation element in which the electrolyte is a solid electrolyte, and to use a thin plate thickness that was difficult to use in the conventional battery system. It has become possible to use a battery case. Therefore, in the secondary battery of the present invention, by reducing the plate thickness of the members constituting the battery case, the weight of the battery case, which occupies a large part of the battery weight, can be reduced, thereby improving the safety of the battery. , The energy density per weight, which represents the performance of the battery, was significantly improved without impairing the stability.

On the other hand, when the terminals of the power generating element of the battery are led to the outside, a member called a hermetic, which has a role of measuring the insulation between the positive and negative electrodes while maintaining the sealing property with the outside air, is particularly important. When the plate thickness of the battery case is 200 μm or less, the hermeticity and stability of the battery case are significantly deteriorated, and it is very difficult to equip the battery case with the terminals. The present inventors have found that the above technical problem can be solved by providing a terminal portion made of a hermetic material provided inside the battery container. That is, by providing the hermetic portion inside the battery case having a thin plate thickness, it is possible to provide a container having both hermeticity and stability without the protrusion of the hermetic portion outside. As described above, the hermeticity of the hermetic part is an important factor, but it is necessary to completely bond the hermetic part to the terminal part when the hermetic part is provided inside the battery case. At that time, a hermetic material formed of a material such as metal, glass, and ceramics is usually used. In the present invention, a glass hermetic material is particularly preferable, and by providing the hermetic material inside the battery by burring, labor saving of the manufacturing process in the hermetic part could be achieved. As the hermetic material in the present invention, an amorphous glass material or a crystallized glass material (pyroceram or the like) is used. As the crystallized glass material, a material that melts at 500 ° C. or lower and has a good affinity with glass, metal and ceramics is generally used. The characteristic of the seal in the case of using the crystallized glass material is that it has a high sealing reliability because it serves to prevent the generation of large cracks in the fine glass crystals grown by heating above the melting point. On the other hand, amorphous low-melting-point glass materials also have many achievements in sealing not only between metal and glass but also between ceramics, but in any case, glass and metal are required for sealing between glass and metal. It is necessary to fully consider the affinity with and the coefficient of thermal expansion.

As the solid electrolyte, for example, in an inorganic system,
Examples thereof include metal halides such as AgCl, AgBr, AgI and LiI, and RbAg ₄ I ₅ and RbAg ₄ I ₄ CN ion conductors. In organic systems, polyethylene oxide, polypropylene oxide, polyvinylidene fluoride, polyacrylonitrile, etc. are used as a polymer matrix to dissolve an electrolyte salt, or a cross-linked product, low molecular weight polyethylene oxide, polyethyleneimine, crown ether, etc. The polymer solid electrolyte in which the ion dissociative group of is grafted to the polymer main chain can be mentioned. The gelled polymer solid electrolyte used in the present invention is one in which a polymerizable compound is added to an ordinary electrolytic solution, and polymerization is performed by heat or light to solidify the electrolytic solution.
More specifically, those described in WO91 / 14294 are used. As a polymerizable compound, an acrylate (eg, methoxydiethyl glycol methacrylate, methoxydiethylene glycol diacrylate) -based compound is polymerized using a polymerization initiator such as benzoyl peroxide, azobisisobutyronitrile, methylbenzoyl formate, or benzoin isopropyl ether. It solidifies the electrolytic solution. It has been found that the ionic conductivity and flexibility are remarkably improved by using a gel-like polymer solid electrolyte among such solid electrolytes. Examples of the electrolyte salt used for the gel solid electrolyte in the present invention include L
_{iCF 3 SO 3, LiN (CF} 3 SO 2) 2, LiC (CF 3
Examples thereof include lithium salts having a sulfonic acid anion such as SO ₂ ) ₃ and LiCH ₃ (CF ₃ SO ₂ ) ₂ and LiBF _4. Among them, LiN (CF ₃ SO ₂ ) ₂ and LiBF _{4 are included.}
It has been found that it is possible to provide a lithium secondary battery that not only suppresses the deposition of lithium on the negative electrode but also has high energy density and high cycle characteristics. At present, deep drawing of a metal rectangular container is usually performed with a thickness of about 8 mm, but when attempting to produce a thinner battery to meet the demand accompanying the thinning of personal devices, it is thinner. Forming a container by deep drawing is very difficult. In particular, it is still necessary to form a container member having a thin plate thickness.
Therefore, as a result of diligent studies, the present inventors first drawn a metal plate, preferably a metal plate having a thickness of 200 μm or less, as shown in FIG.
A battery container obtained by forming three flanges of the same width corresponding to the narrow side faces of a set, and joining the upper surface of the flange of the metal plate and the metal plate having the same area as the metal plate with a metal solder. By packaging the power generation element, we have succeeded in producing a thin battery container that has both productivity and hermeticity like deep drawing.

A carbon material is used as the negative electrode material used in the battery of the present invention. Examples of the carbonaceous negative electrode active material include graphite, pitch coke, synthetic polymer, and fired body of natural polymer. In the present invention, (1) synthetic polymer such as phenol or polyimide, or natural polymer is used.
Obtained by firing insulating or semiconducting carbon, (2) coal, pitch, synthetic polymer, or natural polymer obtained by firing in a reducing atmosphere at 800 to 1300 ° C. in a reducing atmosphere at 800 to 1300 ° C. A carbon body obtained by firing a conductive carbon body, (3) coke, pitch, synthetic polymer, natural polymer in a reducing atmosphere at a temperature of 2000 ° C. or higher, and a graphite-based carbon body such as natural graphite are used. , The carbon body of (3) is preferable,
Among them, a carbon body obtained by firing natural graphite, mesophase pitch, and coke in a reducing atmosphere at 2500 ° C. or higher has excellent potential flatness and has preferable electrode characteristics. The carbon body is formed into a sheet by a wet papermaking method using the carbon body and a binder, or by a coating method using a coating material in which a suitable binder is mixed with a carbon material. The electrode can be manufactured by supporting the electrode on a current collector as required by a method such as application, adhesion, or pressure bonding.

In the present battery system, by using an all-solid-state power generating element in which the electrolyte is a solid electrolyte, it is possible to suppress gas generation due to charge and discharge, and a thin battery case which is difficult to use in the conventional battery system. However, it is inevitable to install a safety valve because the danger of gas generation due to the mixing of water cannot be ruled out. However, since the plate thickness of this battery case is as thin as that of conventional batteries, it is a very difficult task to equip the battery case with a safety valve, and the productivity is extremely low. However, in a separate process, a one-way destructive safety valve with a notch is made by metal brazing so that it can operate accurately and stably at the desired pressure in a separate container. A container with high productivity can be manufactured. An organic non-aqueous polar solvent is used as the electrolytic solution used in the present invention, and an organic non-aqueous polar solvent having an aprotic property and a high dielectric constant is preferable. Specific examples thereof include, but are not limited to, propylene carbonate, ethylene carbonate, γ-butyl lactone, dimethylsulfoxide, dimethylformamide, dimethoxyethane, dimethoxycarbonate and diethoxycarbonate. The organic non-aqueous polar solvent may be used alone or in combination of two or more, but according to the present invention, by using a mixed solvent of propylene carbonate, ethylene carbonate and dimethoxy carbonate,
It is possible to suppress self-discharge of the positive and negative electrodes and suppress cycle characteristics. Further, although the low temperature coagulation of ethylene carbonate has conventionally determined the low temperature characteristics of the battery, by mixing propylene carbonate, which is a carbonate-based material similar to ethylene carbonate, and dimethoxycarbonate, coagulation at low temperature is prevented, It is possible to improve the low temperature characteristics of. The electrolyte concentration is the positive electrode used,
It cannot be unconditionally specified because it depends on the type of electrolyte and organic non-aqueous polar solvent, etc.
The range is preferably from 10 mol / l.

Examples of the positive electrode current collector used in this battery include stainless steel, gold, platinum, nickel, aluminum,
Examples thereof include metal sheets such as molybdenum and titanium, metal foils, metal nets, punching metals, expanded metals, and nets and non-woven fabrics made of metal-plated fibers, metal vapor-deposited wires, metal-containing synthetic fibers and the like. Of these, aluminum and stainless steel are particularly preferable in view of electrical conductivity, chemical stability, electrochemical stability, economic efficiency and workability. Aluminum is more preferable because of its light weight. Furthermore, the surfaces of the positive electrode current collector layer and the negative electrode current collector layer used in the present invention are preferably roughened. By roughening the surface, the contact surface of the active material layer is increased and the adhesion is improved, which has the effect of lowering the impedance of the battery. Further, in the preparation of an electrode using a coating solution, the adhesion between the active material and the current collector can be greatly improved by performing a surface roughening treatment. Examples of the surface roughening treatment include polishing with an emery paper, blasting, and chemical or electrochemical etching, whereby the current collector can be roughened. In particular, in the case of stainless steel, it is preferable to use blasted aluminum, and in the case of aluminum, it is preferable to use etched aluminum. Since aluminum is a soft metal, it is difficult to effectively roughen it by blasting, which causes deformation of aluminum itself. On the other hand, the etching treatment can effectively roughen the surface on the order of micrometer without reducing the deformation of aluminum and its strength itself, and is the most preferable method for roughening aluminum. is there.

Usually, the battery container is often made of stainless steel, nickel-plated carbon steel or the like, but it is not particularly limited as long as it does not affect the corrosion resistance and the like, but it is heated and heated in a vacuum furnace. It is necessary that the material be capable of thermocompression bonding by pressing. That is, stainless steel, iron, nickel, or alloys thereof can be used. A separator can be used in the battery of the present invention. As the separator, it is preferable to use a separator having a low resistance to the ion transfer of the electrolyte solution and having an excellent solution retention. Examples of such a separator include a glass fiber, a filter, a non-woven fabric filter made of polymer fibers such as polyester, Teflon, polyflon, and polypropylene, and a non-woven fabric filter made by mixing glass fibers and these polymer fibers.

[0011]

EXAMPLES The details will be described below with reference to examples.

Embodiment 1 FIG. 1 is a structural view of a battery case in an embodiment of the present invention. In Figure 1, stainless steel 304 thickness 1
The plate member 1 of 50 μm and the plate member are subjected to erection processing, and the plate member 2 having three flanges of the same width corresponding to the bottom surface of the battery container and one set of narrow side surfaces is welded with nickel solder. 86 × 47 × 2.8m shown in 2
A battery case with a thickness of m was manufactured. The member 1 was provided with a safety valve 3 provided with an opening having a size of 10 × 5 mm and opening a 50-micron-thick aluminum foil with nickel braze at a predetermined pressure. Further, the battery power generation element was inserted into the battery case and the terminal surface was sealed.
The figure which sealed the terminal surface is shown in FIG. In FIG. 3, reference numeral 31 denotes a positive electrode plate, which is a PAN in which polyaniline powder (hereinafter referred to as PANI) obtained by chemically polymerizing N-methylpyrrolidone is dissolved.
V ₂ of an average particle 5μm in N- methylpyrrolidone solution of I
A coating solution obtained by homogeneously mixing O ₅ powder with PANI: V ₂ O ₅ = 3: 7 in weight ratio with respect to PANI and having a thickness of 20 μm.
The thickness of the active material layer is 1 after coating and drying on both sides of SUS foil of m
It was set to 20 μm. Next, the positive electrode was cut into a predetermined size and the size of the electrode was 44 × 77 mm. 32 is a negative electrode, and 25 is coke as a negative electrode active material.
A coating solution consisting of 47.4 parts by weight of a negative electrode active material fired at 00 ° C., 5.2 parts by weight of polyvinylidene fluoride and 47.4 parts by weight of n-methylpyrrolidone was used as an electrolytic copper foil 20.
It is applied onto both surfaces of a μm current collector and dried at 80 ° C. so that the thickness of the active material layer is 160 μm. Next, the negative electrode was cut into a predetermined size and the size of the electrode was 45 × 78.
mm. Reference numeral 33 is a separator in which a negative electrode is wrapped in a bag using a porous polypropylene film (trade name Celgard). This separator has 1.8M concentration of L
iN (CF ₃ SO ₂ ) ₂ + 0.2M concentration LiBF ₄ / (propylene carbonate + dimethoxyethane) (volume ratio 7:
A solid polymer electrolyte composition prepared by mixing 80% of the electrolytic solution of 3), 19.2% of ethoxydiethylene glycol acrylate, and 0.8% of benzoin isopropyl ether is permeated, irradiated with a high-pressure mercury lamp, and gelled. I was there. A stack of these electrode groups so that they face each other is inserted into a battery case. Next, the lead 35 made of stainless steel taken out from each positive electrode and stacked is spot-welded to the positive electrode terminal 36. Further, the nickel lead 37 taken out from each negative electrode and stacked is spot-welded to the negative electrode terminal 38. Then, the terminal surface 39 was covered with the case 34, and the periphery was sealed by laser welding to complete the battery. FIG. 4 shows a sectional view of the terminal surface of the battery case. In this sectional view, a glass hermetic portion 43 is provided by burring to form a terminal portion. Battery capacity per unit weight is 53m
Ah / g. In the figure, 41 is a terminal pin, and 42
Is a burring portion, and 44 is a terminal surface.

COMPARATIVE EXAMPLE 1 LiN (CF ₃ S having a concentration of 1.8M was prepared without solidifying the electrolytic solution.
O ₂ ) ₂ + 0.2M concentration LiBF ₄ / (propylene carbonate + dimethoxyethane) (volume ratio 7: 3) was used in the same manner as in Example 1 except that an electrolytic solution was used. The battery capacity per unit weight was 51 mAh / g, but deformation of the container was observed due to internal gas generation.

Comparative Example 2 The procedure of Example 1 was repeated except that the battery case was made of 304 steel having a thickness of 450 μm.
The battery capacity per unit weight was 39 mAh / g.

Specific embodiments of the present invention will be described below. 1. In a secondary battery having at least a positive electrode current collector layer, a positive electrode active material layer, an electrolyte layer, a negative electrode active material layer capable of inserting and extracting lithium, and a power generation element composed of a laminated structure of a negative electrode current collector layer, the electrolyte is solid. A secondary battery using an all-solid-state power generating element that is an electrolyte, and an outer container of the power generating element is a metal plate having a plate thickness of 200 microns or less. 2. The secondary battery according to the above-mentioned item 1, wherein the terminal portion is provided by a hermetic member inside the battery container. 3. The secondary battery according to any one of 1 and 2 above, wherein the hermetic member is a glass hermetic member, and the hermetic member is provided inside the battery by burring. 4. The secondary battery according to any one of 1 to 3 above, wherein the electrolyte layer is a gel-like solid electrolyte. 5. In the secondary battery of 4, the electrolyte layer is LiCF _{3
SO 3, LiN (CF 3 SO} 2) 2, LiC (CF 3 SO 2)
_A secondary battery containing at least one electrolyte salt selected from the group consisting of ₃ , LiCH ₃ (CF ₃ SO ₂ ) ₂ and LiBF ₄ . 6. In the secondary battery of 5, the electrolyte salt is LiN (C
A secondary battery comprising a combination of F ₃ SO ₂ ) ₂ and LiBF ₄ .

[7] In the rechargeable batteries 1 to 6,
A secondary battery characterized in that the battery container is provided with a one-way destruction type safety valve by metal brazing. 8. A metal plate, preferably a metal plate having a thickness of 200 μm or less, is drawn to form the bottom surface or the top surface of the battery container and 1
A battery container obtained by forming three flanges of the same width corresponding to the narrow side faces of a set, and joining the upper surface of the flange of the metal plate and the metal plate having the same area as the metal plate with a metal solder. The method for manufacturing a secondary battery according to any one of 1 to 7 above, wherein the power generating element is packaged.

[0017]

【effect】

1. Claim 1 By using an all-solid-state power generating element in which the electrolyte is a solid electrolyte, it is possible to suppress gas generation due to charge and discharge, and it is possible to use a battery case with a thin plate thickness that was difficult to use in conventional battery systems. it can. In addition, by reducing the plate thickness of the members that make up the battery case, we succeeded in reducing the weight of the battery case, which occupies most of the battery weight, and thereby, without compromising the safety and stability of the battery, A secondary battery having a markedly improved energy density per weight, which represents performance, was obtained. 2. According to a second aspect of the present invention, there is provided a secondary battery having an outer container that has both hermeticity and stability without protrusion of a hermetic portion. 3. According to a third aspect of the present invention, there is provided a secondary battery, which does not require a separate member in the hermetic portion and succeeds in achieving labor saving in the process. 4. [Claim 4] By using a gelled polymer solid electrolyte among the solid electrolytes, the ionic conductivity and flexibility are significantly improved. Further, the use of the gel solid electrolyte not only suppresses the deposition of lithium on the negative electrode, but also provided a lithium secondary battery having both high energy density and high cycle characteristics. 5. [Claim 5] Safe, hermeticity and production can be achieved by using a one-way destructive safety valve with a notch in one part so as to operate accurately and stably at a desired pressure by metal brazing as a container. A secondary battery provided with a highly reliable container is provided. 6. Claim 6 A thin battery container having both productivity and hermeticity can be produced.

[Brief description of drawings]

FIG. 1 is a perspective view of constituent members of a battery outer container.

FIG. 2 is a perspective view of a thin battery outer container formed by metal brazing the constituent members of FIG.

FIG. 3 is a partial cross-sectional view of a secondary battery.

4 is a sectional view of a terminal portion and a terminal surface of the secondary battery of FIG.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Stainless steel member 2 Vertical stainless steel member 3 Safety valve 4 Nickel braze welding part 5 Thin container 31 Positive electrode plate 32 Negative electrode 33 Separator 34 Battery case 35 Positive electrode lead 36 Positive electrode terminal 37 Negative electrode lead 38 Negative electrode terminal 39 Terminal surface 41 Terminal pin 42 Burring part 43 Glass hermetic part 44 Terminal surface

 ─────────────────────────────────────────────────── ─── Continuation of front page (72) Inventor Hiroki Uemoto 1-3-6 Nakamagome, Ota-ku, Tokyo Inside Ricoh Co., Ltd.

Claims (6)

[Claims] 1. A secondary battery having a power generation element including at least a positive electrode current collector layer, a positive electrode active material layer, an electrolyte layer, a negative electrode active material layer capable of inserting and extracting lithium, and a laminated structure of a negative electrode current collector layer. 2. A prismatic battery, wherein an all-solid-state power generation element in which the electrolyte is a solid electrolyte is used, and an outer container of the power generation element is a metal plate having a plate thickness of 200 microns or less. 2. The secondary battery according to claim 1, wherein the terminal portion is provided by a hermetic member inside the battery container. 3. The secondary battery according to claim 1, wherein the hermetic member is a glass hermetic member, and the hermetic member is provided inside the battery by a burring process. battery. 4. The secondary battery according to claim 1, 2 or 3, wherein the electrolyte layer is a gel-like solid electrolyte. 5. The secondary battery according to claim 1, 2, 3 or 4, wherein the battery container is provided with a one-way destruction type safety valve by metal brazing. 6. The secondary battery according to claim 1, 2, 3, 4 or 5, wherein a metal solder is used for assembling and joining the battery container.