JPH09161734A - Secondary battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To attain high reliability and high energy density without damaging an apparatus by restraining expansion of a battery case even when it is exposed to a high temperature. SOLUTION: This battery is provided with an electrode element where a positive electrode 2 and a negative electrode 1 are insulated from each other by a separator 3 and a battery case 12 into which this electrode element is inserted, and electrolyte is injected into it. In this case, the battery case 12 is formed of a thin plate material, and an edge formed of adjacent two planes among plural planes formed of this thin plate material, is composed of a curved surface. The positive electrode 2 and the negative electrode 1 are insulated from each other by the resinous porous separator 3. Electrolyte is composed of nonaqueous electrolyte. The negative electrode 1 is composed of a carbon material or a graphite material capable of doping-dedoping a lithium ion, and the positive electrode 2 is composed of Lix and MOy (herein, M represents at least one kind of Co, Ni, Mn, Fe, Al, V and Ti).

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a secondary battery,
In particular, it relates to a battery case and a secondary battery using the same.

[0002]

2. Description of the Related Art In recent years, camera-integrated VTRs, mobile phones,
With the emergence of new portable electronic devices such as laptop computers, which are becoming smaller and lighter, secondary batteries have come into the limelight as portable portable power sources, resulting in higher energy density. Active research and development is being done.

Under such circumstances, a lithium ion secondary battery using a non-aqueous electrolyte has been proposed and put into practical use as a secondary battery having a higher energy density than an aqueous electrolyte secondary battery such as a lead battery and a nickel-cadmium battery. The transformation has begun.

The battery type of the lithium ion secondary battery includes a cylindrical battery in which spirally wound electrodes are inserted in a cylindrical case, folded electrodes, rectangular laminated electrodes, and elliptical wound electrodes. There is a prismatic battery in which is inserted into a prismatic case. The latter prismatic battery has higher space efficiency than the cylindrical battery, and the demand for it is increasing with the recent thinning of the device.

[0005]

By the way, the above-mentioned small secondary battery is used not only in normal use but also in a vehicle in the midsummer, and high reliability is required. In particular, the prismatic battery case is weaker in strength than the cylindrical battery case, and is therefore easily deformed as the battery internal pressure increases. Therefore, in the case of a type of battery that is stored inside the device, if it is exposed to a high temperature, it may not be taken out due to expansion of the battery or the device may be damaged. If an attempt was made to give a margin to the dimensions in advance, the energy density was lowered and a sufficient operating time could not be obtained.

Therefore, the present invention has been proposed in view of such a conventional situation, and suppresses the expansion of the battery case even when it is exposed to a high temperature without damaging the device,
An object is to provide a secondary battery using a non-aqueous electrolyte having high reliability and high energy density.

[0007]

In order to achieve the above-mentioned object, the inventors of the present invention have made diligent studies and found that, as shown in FIG. 1, all ridges are curved except for an opening for inserting an electrode element. By doing so, that is, by forming the ridge formed by two adjacent flat surfaces among the plurality of flat surfaces formed by the thin plate material of the battery case into a curved surface, the internal pressure is partially concentrated even when exposed to high temperature. It has been found that the above can be suppressed, the increase in battery thickness can be suppressed, and the equipment can be prevented from being damaged.

Although the present invention is applicable to any secondary battery, a non-aqueous electrolyte secondary battery will be described below as an example.

Any positive and negative electrode materials that can form a non-aqueous electrolyte secondary battery can be used, but the degree of expansion of the active material due to charge and discharge, the boiling point of the non-aqueous solvent used in the electrolyte, the shape of the electrode element, etc. The radius of curvature of each curved surface can be appropriately selected by considering it.

However, when the radius of curvature of the curved surface is large,
The effective volume that can be filled with the positive and negative electrodes decreases, which may result in a loss of energy density per volume. Therefore, it is necessary to determine the radius of curvature in consideration of this point.

The material of the battery case used in the present invention can be appropriately selected in consideration of strength and workability thereof. Examples of usable materials include iron, nickel, stainless steel, aluminum, etc. When corrosion occurs in a nonaqueous electrolytic solution, it can be used by plating or the like.

The flat battery case of the present invention is
It can be manufactured by any method. For example, a steel plate or the like made of the above-mentioned various materials can be manufactured by using at least one set of male and female dies and performing the squeezing process in several stages.

Further, the secondary battery of the present invention will be described in detail. The secondary battery of the present invention has an electrode element in which the positive electrode and the negative electrode are insulated by a resin porous separator, is made by injecting a non-aqueous electrolytic solution, and has an opening for inserting the electrode element of the battery case. It is characterized in that all edges except for are curved surfaces.

For the secondary battery of the present invention, use is made of a laminated electrode element formed by stacking a plurality of combinations of flat positive and negative electrodes, or an elliptical electrode element formed by winding strip-shaped positive and negative electrodes in an elliptical shape. You can

Materials usable as the negative electrode material of the present invention include oxides having a relatively low potential such as iron oxide, ruthenium oxide, molybdenum oxide, tungsten oxide, and titanium oxide, and other oxides and carbon materials. .

As the carbon material used for the negative electrode, any of those used for this type of secondary battery can be used, but the carbon materials listed below are particularly preferable.

First, there is a carbon material obtained by carbonizing an organic material by a method such as firing.

As the organic material as a starting material, phenol resin, acrylic resin, vinyl halide resin, polyimide resin, polyamideimide resin, polyamide resin,
Conjugated resins such as polyacetylene and poly (p-phenylene), cellulose and its derivatives, and any organic polymer compounds can be used.

In addition, condensed polycyclic hydrocarbon compounds such as naphthalene, phenanthrene, anthracene, triphenylene, pyrene, perylene, pentaphene and pentacene, other derivatives (for example, carboxylic acid, carboxylic acid anhydride, carboxylic acid imide, etc.) thereof, the above Various pitches containing a mixture of each compound as a main component, acenaphthylene, indole, isoindole, quinoline, isoquinoline, quinoxaline, phthalazine, carbazole, acridine, phenazine, phenanthridine and the like, and their derivatives can also be used. .

Furan resins which are homopolymers or copolymers of furfuryl alcohol or furfural are also particularly suitable. The carbonaceous material obtained by carbonizing the furan resin has a (002) plane spacing of 0.370 nm or more, a true density of 1.7 g / cc or less, and has no oxidation exothermic peak at DTA of 700 ° C. or more, and thus has a negative electrode of a battery. It has very good properties as a material.

The temperature for firing these organic materials is as follows:
Depends on the starting material, usually 500-2000 ° C
It is said.

Alternatively, a petroleum pitch having a specific H / C atomic ratio to which a functional group containing oxygen is introduced (so-called oxygen cross-linking) exhibits excellent characteristics when carbonized, like the furan resin. Therefore, it can be used as the organic material.

The petroleum pitch is tars obtained by high temperature thermal decomposition of coal tar, ethylene bottom oil, crude oil, etc.,
It is obtained from asphalt and the like by operations such as distillation (vacuum distillation, atmospheric distillation, steam distillation), thermal polycondensation, extraction, chemical polycondensation and the like.

At this time, the H / C atomic ratio of petroleum pitch is important, and it is necessary to set the H / C primitive ratio to 0.6 to 0.8 in order to obtain non-graphitizable carbon.

The specific means for introducing a functional group containing oxygen into these petroleum pitches is not limited, but for example nitric acid,
Wet method using an aqueous solution of mixed acid, sulfuric acid, hypochlorous acid, etc., or dry method using oxidizing gas (air, oxygen), and reaction with solid reagents such as sulfur, ammonium nitrate, ammonium persulfate, ferric chloride, etc. Used.

For example, when oxygen is introduced into petroleum pitch by the above-mentioned method, the final carbonaceous material is obtained in the solid phase without melting during the carbonization process (400 ° C. or higher),
It is similar to the formation process of non-graphitizable carbon.

The petroleum pitch having oxygen-containing functional groups introduced therein is carbonized by the above-mentioned method to form a negative electrode material. The carbonaceous condition does not matter, and the (002) plane spacing is 0.370.
nm or more, true density of 1.7 g / cc or less and DTA of 70
When a carbonaceous material satisfying the characteristic of not having an oxidation exothermic peak at 0 ° C. or higher is obtained, a large lithium doping amount per unit weight can be obtained. For example, when the oxygen content of the precursor obtained by oxygen-crosslinking petroleum pitch is 10% by weight or more, the interplanar spacing of the (002) plane can be 0.370 nm or more. Therefore, the oxygen content of the precursor is preferably 10% by weight or more, and practically in the range of 10 to 20% by weight.

When a carbonaceous material is obtained by using the above raw material organic material, for example, after carbonizing at 300 to 700 ° C. in a nitrogen stream, the temperature rising rate is 1 to 20 ° C. per minute in the nitrogen stream, and the reached temperature is 900. ~ 1300 ℃, holding time at ultimate temperature 0-5
It suffices to bake under conditions of time. Of course, in some cases, the carbonization operation may be omitted.

Further, by adding a phosphorus compound or a boron compound when carbonizing the furan resin or petroleum pitch, a special negative electrode compound having a large lithium doping amount can be used.

Examples of the phosphorus compound include phosphorus oxides such as phosphorus pentoxide and oxo acids such as orthophosphoric acid and salts thereof. Among them, phosphorus oxide and phosphoric acid are preferable from the viewpoint of easy handling. is there.

The amount of the phosphorus compound added is 0.2 to 30% by weight, preferably 0.5 to 15% by weight, in terms of phosphorus, based on the organic material or the carbonaceous material, and the amount of phosphorus remaining in the negative electrode material. The proportion is 0.2 to 9.0% by weight, preferably 0.3 to 5% by weight.

As the boron compound, boron oxide or boric acid can be added in the form of an aqueous solution. The amount of the boron compound added is 0.2 to 30% by weight, preferably 0.5 to 15% by weight, in terms of boron based on the organic material or the carbonaceous material, and the proportion of boron remaining in the negative electrode material is 0. 0.2 to 9.0% by weight, preferably 0.3 to 5
% By weight.

Further, since graphites have a higher true density as compared with low-temperature treated carbon materials such as coke and glassy carbon, they have a high electrode packing property as an active material, and therefore have a high energy density in terms of design. The next battery becomes possible.

A carbon material such as graphite is suitable as a material having a high true density and a high electrode filling property. Among them, the true density is 2.1 in order to obtain a higher electrode filling property.
g / cm ³ or more is preferable, and 2.18 g / cm ³ or more is more preferable. In order to obtain such a true density, the (002) plane spacing obtained by the X-ray diffraction method is preferably 0.33.
Less than 9 nm, more preferably 0.335 nm or more,
It is necessary that the thickness is 0.337 nm or less and the C-axis crystallite thickness on the 002 plane is 16.0 nm or more, and more preferably 300 nm or more.

Typical carbon materials exhibiting the above physical properties are:
Examples include natural graphite. Further, artificial graphite obtained by carbonizing an organic material and further treated at high temperature also exhibits the above-mentioned crystal structure parameter.

Coal and pitch are typical examples of the organic material used as a starting material for producing the artificial graphite.

As pitch, distillation (vacuum distillation, atmospheric distillation, steam distillation), thermal polycondensation, extraction, chemical polycondensation from coal tar, ethylene bottom oil, tars obtained by high temperature thermal decomposition of crude oil, asphalt, etc. There are those obtained by operations such as condensation, and other pitches produced during carbonization of wood.

Further, as the starting material for the pitch, there are polyvinyl chloride resin, polyvinyl acetate, polyvinyl butyrate, 3,5-dimethylphenol resin and the like.

These coals and pitches exist in a liquid state at a maximum temperature of about 400 ° C. during carbonization, and when kept at that temperature, aromatic rings are condensed with each other to form a polycycle and become laminated orientation, and then about 500 ° C. At the above temperature, a solid carbon precursor, that is, semi-coke is formed. Such a process is called a liquid-phase carbonization process and is a typical formation process of graphitizable carbon.

In addition, condensed polycyclic hydrocarbon compounds such as naphthalene, phenanthrene, anthracene, triphenylene, pyrene, perylene, pentaphene and pentacene, other derivatives (for example, carboxylic acid, carboxylic acid anhydride, carboxylic acid imide, etc.) thereof, or Mixtures, condensed heterocyclic compounds such as acenaphthylene, indole, isoindole, quinoline, isoquinoline, quinoxaline, phthalazine, carbazole, acridine, phenazine, phenanthridine, and their derivatives can also be used as raw materials.

In order to produce desired artificial graphite using the above organic materials as starting materials, for example, after carbonizing the above organic materials at 300 to 700 ° C. in a stream of an inert gas such as nitrogen,
In an inert gas stream, the temperature rising rate is 1 to 100 ° C. per minute, the reached temperature is 900 to 1500 ° C., and the holding time at the reached temperature is 0 to 30.
It can be obtained by calcination under the condition of about time and further heat treatment at 2000 ° C. or higher, preferably 2500 ° C. or higher. Of course, in some cases, the carbonization and calcination operations may be omitted.

The carbon material or graphite material heat-treated at a high temperature is crushed and classified to be used as a negative electrode material. This crushing may be performed before or after carbonization, calcination, high-temperature heat treatment, or during the temperature rising process. good.

Further, in order to obtain a graphite material having more practical performance, it is preferable to use a material satisfying the following physical property values.

As the graphite material, it is preferable to use a graphite material having a true density of 2.1 g / cm ³ or more and a bulk specific gravity of 0.4 g / cm ³ or more. Since the graphite material has a high true density, if the negative electrode is composed of this, the electrode filling property will be improved,
The energy density of the battery is improved. When a graphite material having a bulk specific gravity of 0.4 g / cm ³ or more is used among the graphite materials, the graphite material having such a large bulk specific gravity can be relatively uniformly dispersed in the negative electrode mixture layer. For the above reasons, the electrode structure becomes good and the cycle characteristics are improved.

Furthermore, if a material having a low specificity of 0.4 g / cm ³ or more in bulk specific gravity and 125 or less in average shape parameter xave is used, the electrode structure is further improved and the cycle characteristics are further improved. Be improved.

In order to obtain the above-mentioned graphite material, it is preferable to carry out a heat treatment for graphitization in a state where carbon is formed into a molded body. By crushing this graphitized molded body, the bulk specific gravity becomes higher, A graphite material having a small average shape parameter xave becomes possible.

The graphite material has a bulk specific gravity, an average shape parameter xave within the above range, and a specific surface area of 9
When the graphite powder of m ² / g or less is used, the number of submicron fine particles attached to the graphite particles is small, the bulk specific gravity is high, the electrode structure is good, and the cycle characteristics are further improved.

In the particle size distribution obtained by the laser diffraction method, the cumulative 10% particle size is 3 μm or more, the cumulative 50% particle size is 10 μm or more, and the cumulative 90%.
By using graphite powder having a% particle size of 70 μm or less, a safe and reliable non-aqueous electrolyte secondary battery can be obtained. Particles with a small particle size have a large specific surface area, but by limiting this content rate, it is possible to suppress abnormal heat generation such as overcharging due to particles with a large specific surface area, and to limit the content rate of particles with a large particle size. As a result, it is possible to suppress an internal short circuit due to the expansion of particles at the time of initial charging, and it is possible to provide a practical non-aqueous electrolyte secondary battery having high safety and reliability.

The average value of the breaking strength of the particles is 6.0 k.
By using a graphite powder having a gf / mm ² or more,
A large number of holes for containing the electrolytic solution can be present in the electrode, and a non-aqueous electrolytic solution secondary battery having good load characteristics can be obtained.

On the other hand, the positive electrode material used in combination with the negative electrode composed of the above negative electrode material is not particularly limited, but preferably contains a sufficient amount of Li, for example, the general formula LiMO ₂ (where M is Co, Ni. , Mn, Fe, A
represents at least one of l, V, and Ti. ), A composite metal oxide composed of lithium and a transition metal, an intercalation compound containing Li, and the like are preferable.

In the non-aqueous electrolytic solution used in the non-aqueous electrolytic solution secondary battery of the present invention, a non-aqueous electrolytic solution in which an electrolyte is dissolved in a non-aqueous solvent is used as the electrolytic solution.

As the non-aqueous solvent for dissolving the electrolyte, EC
It is premised that a solvent having a relatively high dielectric constant such as (ethylene carbonate) is used as the main solvent, but it is necessary to further add a low-viscosity solvent having a plurality of components to complete the present invention.

As the high dielectric constant solvent, PC (propylene carbonate), butylene carbonate, vinylene carbonate, sulfolanes, butyrolactones, valerolactones and the like are preferable. As the low-viscosity solvent, symmetrical or asymmetrical chain carbonic acid esters such as diethyl carbonate, dimethyl carbonate, methyl ethyl carbonate, and methyl propyl carbonate are preferable, and two or more low-viscosity solvents may be mixed and used. The result is obtained.

Especially when a graphite material is used for the negative electrode, EC is the most suitable as the main solvent of the non-aqueous solvent.
A compound having a structure in which a hydrogen atom of EC is replaced with a halogen element is also suitable.

Although it is reactive with a graphite material such as PC, a small amount of a small portion of EC as a main solvent or a compound having a structure in which a hydrogen atom of EC is replaced by a halogen element is used. By substituting with a two-component solvent, good characteristics can be obtained. As the second component solvent, PC, butylene carbonate, 1,2-dimethoxyethane, 1,
2-diethoxymethane, γ-butyrolactone, valerolactone, tetrahydrofuran, 2-methyltetrahydrofuran, 1,3-dioxolane, 4-methyl-1,3-
Dioxolane, sulfolane, methylsulfolane, etc. can be used, and the addition amount thereof is preferably less than 10 Vol%.

In order to further complete the present invention, a third solvent is added to the main solvent or a mixed solvent of the main solvent and the second component solvent to improve the conductivity, suppress the decomposition of EC, and reduce the temperature. It is also possible to improve the characteristics and reduce the reactivity with lithium metal to improve the safety.

As the solvent for the third component, a chain ester carbonate such as DEC (diethyl carbonate) or DMC (dimethyl carbonate) is preferable. Also, MEC
Asymmetric chain ester carbonate such as (methyl ethyl carbonate) or MPC (methyl propyl carbonate) is suitable. The mixing ratio of the chain carbonate as the third component to the main solvent or the mixed solvent of the main solvent and the second component solvent (the main solvent or the mixed solvent of the main solvent and the second component solvent: the third component solvent) is the volume. The ratio is preferably 15:85 to 40:60, more preferably 18:82 to 35:65.

Further, the solvent of the third component may be a mixed solvent of MEC and DMC. The MEC-DMC mixing ratio is preferably in a range represented by 1/9 ≦ d / m ≦ 8/2, where MEC capacity is m and DMC capacity is d. Further, the mixing ratio of the main solvent or the mixed solvent of the main solvent and the second component solvent and the solvent of the third component MEC-DMC, when the MEC capacity is m, the DMC capacity is d, and the total amount of the solvent is T, 3/10 ≦ (m + d) / T ≦ 9 /
The range shown by 10 is preferable, and 5/10 ≦
It is more preferable to set the range to be (m + d) / T ≦ 8/10.

As an electrolyte soluble in such a non-aqueous solvent
As long as it is used for this main battery,
One or more kinds can be mixed and used. For example LiPF₆Is good
Suitable but other LiClO_Four, LiAsF₆, Li
BF_Four, LiB (C₆H_Five) _Four, CH_ThreeSO_ThreeLi, C
F_ThreeSO_ThreeLi, LiN (CF_ThreeSO_Two)_Two, LiC
(CF_ThreeSO_Two)_Three, LiCl, LiBr, etc. can also be used
It is.

According to the present invention, in a battery having a flat shape such as a prism, by making all the ridges except the opening for inserting the electrode element of the battery case a curved surface, the internal pressure is kept even when exposed to high temperature. Concentration on a part is suppressed,
A non-aqueous electrolyte secondary battery having high reliability and high energy density capable of suppressing an increase in battery thickness and preventing damage to equipment.

[0061]

BEST MODE FOR CARRYING OUT THE INVENTION An embodiment of the secondary battery of the present invention will be described below with reference to FIGS.

Example 1 The structure of the non-aqueous electrolyte secondary battery produced in this example is shown in FIG. First, the negative electrode 1 was manufactured as follows. H / C
A petroleum pitch appropriately selected from the atomic ratio range of 0.6 to 0.8 was crushed and subjected to oxidation treatment in an air stream to obtain a carbon precursor. The quinoline insoluble matter (JIS centrifugal method: K2425-1983) of this carbon precursor was 80%, and the oxygen content rate (by organic elemental analysis method) was 15.4% by weight.

This carbon precursor was heated at 1000 ° C. in a nitrogen stream.
The temperature was raised to 1, and heat treatment was performed, followed by pulverization to obtain a carbon material powder having an average particle size of 10 μm. The non-graphitizable carbon material obtained at this time was subjected to X-ray diffraction measurement. As a result, the (002) plane spacing was 0.381 nm and the true specific gravity was 1.54.

90 parts by weight of this carbon material powder was mixed with 10 parts by weight of polyvinylidene fluoride as a binder to prepare a negative electrode mixture, and this negative electrode mixture was dispersed in a solvent N-methyl-2-pyrrolidone to form a slurry, A negative electrode slurry was prepared.

The negative electrode slurry thus obtained was evenly applied to both sides of a strip-shaped copper foil having a thickness of 10 μm to serve as a negative electrode current collector, dried, and then compression-molded by a roll press machine to form a strip. An electrode was prepared. This strip electrode was cut into a rectangular shape shown in FIG. 3A to obtain a negative electrode 1.

Next, the positive electrode 2 was produced as follows. 0.5 mol of lithium carbonate and cobalt carbonate: 1.0
LiCoO ₂ was obtained by mixing in a molar ratio and baking in air at 900 ° C. for 5 hours.

LiCoO ₂ , 9 thus obtained
1 part by weight is mixed with 6 parts by weight of graphite as a conductive material and 3 parts by weight of polyvinylidene fluoride as a binder to prepare a positive electrode mixture, and the positive electrode mixture is dispersed in a solvent N-methyl-2-pyrrolidone to form a slurry. Then, a positive electrode slurry was prepared.

The positive electrode slurry thus obtained was evenly applied to both sides of a strip-shaped aluminum foil having a thickness of 20 μm to be a positive electrode collector, dried and then compression-molded by a roll press machine to form a strip. An electrode was prepared. This strip electrode is shown in FIG.
B was cut into a rectangular shape indicated by a dotted line to obtain a positive electrode 2.

Then, the negative electrode 1 and the positive electrode 2 were sandwiched by the separator 3 made of a microporous polypropylene film and fixed with the adhesive tape 10 to obtain a laminated electrode element.

Then, as shown in FIG. 2, the thickness is 450 μm.
Iron flat prismatic battery case with nickel plating 1
(R1 = 7.5 mm, R2 = 7.5 mm, R3 = 7.5
mm, R4 = 7.5 mm, R5 = 3 mm, R6 = 3 m
m, R7 = 3 mm, R8 = 3 mm (see FIG. 1)), an insulating sheet 11 was laid on the bottom, and the laminated electrode element was inserted therein.

Then, the sub-lead 6 is attached to the gasket 7 in advance.
It was welded to the positive electrode terminal 8 attached to the container lid 9 via. Here, the positive electrode leads of the laminated electrode element were bundled and welded to the sub lead 6. The negative electrode leads were also bundled and welded to the battery case 12.

An electrolytic solution prepared by dissolving LiPF _{6 in} a mixed solvent of 50% by volume of PC and 50% by volume of DMC at a ratio of 1 mol / l was poured into a battery case 12, and the container lid 9 was laser-welded to cover the container lid 9. It fixed to 12, and produced the flat type lithium ion secondary battery.

Example 2 A method for producing a graphite sample powder obtained from the graphitized molded body used in this example as a negative electrode material will be described.

First, coal-based coke 10 serving as a filler
To 0 parts by weight, 30 parts by weight of coal tar pitch serving as a binder was added, mixed at about 100 ° C., and compression-molded by a press to obtain a precursor of a carbon molded body. The pitch impregnation / firing process of impregnating the carbon material molded body obtained by heat-treating this precursor at 1000 ° C or lower with the binder pitch melted at 200 ° C or lower and heat-treating at 1000 ° C or lower is repeated several times. It was Thereafter, this carbon molded body was heat-treated at 2600 ° C. in an inert atmosphere to obtain a graphitized molded body, which was then pulverized and classified to prepare a sample graphite material powder.

The graphite material powder obtained at this time had a true density of 2.23 g / cm ³ and a bulk specific gravity of 0.83 g / cm ³ .
³ , average shape parameter Xave. = 10, specific surface area =
4.4 m ² / g, average particle size = 31.2 μm, cumulative 10%
Particle size = 12.3 μm, cumulative 50% particle size = 29.5 μm,
The cumulative 90% particle size was 53.7 μm.

Using this graphite material powder as a negative electrode material, EC5
A flat type lithium ion secondary battery was produced in the same manner as in Example 1 except that an electrolytic solution prepared by dissolving LiPF ₆ at a ratio of 1 mol / l in a mixed solvent of 0% by volume and 50% by volume of DEC was used. .

Comparative Example 1 A flat prismatic battery case (R1 = 0.
6 mm, R2 = 0.6 mm, R3 = 0.6 mm, R4 =
0.6 mm, R5 = 1 mm, R6 = 1 mm, R7 = 1 m
m, R8 = 1 mm) was used, and a flat prismatic lithium ion secondary battery was produced in the same manner as in Example 1.

Comparative Example 2 A flat prismatic battery case (R1 = 0.
6 mm, R2 = 0.6 mm, R3 = 0.6 mm, R4 =
0.6 mm, R5 = 1 mm, R6 = 1 mm, R7 = 1 m
m, R8 = 1 mm), but a flat prismatic lithium ion secondary battery was prepared in the same manner as in Example 2.

Comparative Example 3 A flat prismatic battery case (R1 = 7.
5 mm, R2 = 7.5 mm, R3 = 7.5 mm, R4 =
7.5 mm, R5 = 1 mm, R6 = 1 mm, R7 = 1 m
m, R8 = 1 mm) was used, and a flat prismatic lithium ion secondary battery was produced in the same manner as in Example 1.

Comparative Example 4 A flat prismatic battery case (R1 = 7.
5 mm, R2 = 7.5 mm, R3 = 7.5 mm, R4 =
7.5 mm, R5 = 1 mm, R6 = 1 mm, R7 = 1 m
m, R8 = 1 mm), but a flat prismatic lithium ion secondary battery was prepared in the same manner as in Example 2.

A constant current of 400 mA was applied to each of Examples 1 and 2 and Comparative Examples 1 to 4 produced as described above.
After charging at a constant voltage of 4.2 V for 5 hours, the battery case was stored at 90 ° C. and the thickness of the battery case was measured. The results are shown in Table 1.

[0082]

[Table 1]

The "4.2V battery thickness after charging (mm)" shown in Table 1 is a value obtained by measuring the battery thickness after charging for 5 hours under the conditions of 400 mA and 4.2V. In addition, "9
"Battery thickness increase after storage at 0 ° C for 1 day (mm)" is the thickness of the battery after being stored for 1 day at 90 ° C after being charged, and the value of the above-mentioned "4.2V battery after charging was measured". The value of "thickness (mm)" is subtracted.

As can be seen from Table 1, "Increase in battery thickness after storage at 90 ° C. for 1 day (mm)" indicates Comparative Examples 1 to 4.
Shows a large value of 0.45 to 0.63 mm, while in Examples 1 and 2, 0.31 mm and 0.3
It shows a small value of 3 mm. This is because the battery cases of Examples 1 and 2 have more ridges with a larger radius of curvature than the battery cases of Comparative Examples 1 to 4, and thus the portion with a large radius of curvature has a battery thickness It is considered to have the effect of suppressing the deformation of the.

As described above, when the flat non-aqueous electrolyte secondary battery using the battery case of the present invention is stored at 90 ° C., the increase in the thickness of the battery case is small, and high reliability can be obtained during high temperature storage. I understood.

The present invention is not limited to the above-mentioned embodiments, and it goes without saying that various other configurations can be adopted without departing from the gist of the present invention.

[0087]

As is apparent from the above description, in the present invention, in a flat battery such as a prism, all the edges except the opening for inserting the electrode element of the battery case have curved surfaces. As a result, the internal pressure can be prevented from concentrating on a part even when it is exposed to high temperatures, and it is possible to prevent an increase in battery thickness and prevent damage to equipment, and to provide a highly reliable and high energy density non-aqueous electrolyte solution. A secondary battery can be provided.

[Brief description of the drawings]

FIG. 1 is a conceptual diagram for explaining an embodiment of a secondary battery of the present invention.

FIG. 2 is a cross-sectional view showing an embodiment of the secondary battery of the present invention.

FIG. 3 is a plan view showing a negative electrode, a positive electrode, and a separator used in the secondary battery of the present invention.

[Explanation of symbols]

 1 Negative electrode 2 Positive electrode 3 Separator 4 Negative electrode lead 5 Positive electrode lead 6 Sub lead 7 Gasket 8 Positive electrode terminal 9 Battery lid 10 Adhesive tape 11 Insulating sheet 12 Battery case 13 Electrode element 14 Opening

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Masayuki Nagamine Inventor Masayuki Nagamine 1 of Shimosugishita, Takakura, Hiwada-cho, Koriyama-shi, Fukushima Prefecture Sony Energy Tech Co., Ltd.

Claims (4)

[Claims] 1. A secondary battery having an electrode element in which a positive electrode and a negative electrode are insulated by a separator and a battery case into which the electrode element is inserted, wherein an electrolytic solution is injected, wherein the battery case is a thin plate material. And a ridge formed by two adjacent flat surfaces among a plurality of flat surfaces formed by the thin plate material is a curved surface. 2. The secondary battery according to claim 1, further comprising an electrode element in which a positive electrode and a negative electrode are insulated from each other by a resin porous separator, and a nonaqueous electrolytic solution is injected. 3. A negative electrode made of a carbon material capable of being doped / dedoped with lithium ions, and Li _x MO _y (wherein M represents at least one of Co, Ni, Mn, Fe, Al, V and Ti). 2. The secondary battery according to claim 1, wherein the secondary battery is composed of a positive electrode made of (4) and a non-aqueous electrolyte. 4. A negative electrode made of a graphite material capable of being doped / dedoped with lithium ions, and Li _x MO _y (wherein M represents at least one of Co, Ni, Mn, Fe, Al, V and Ti). 2. The secondary battery according to claim 1, wherein the secondary battery is composed of a positive electrode made of (4) and a non-aqueous electrolyte.