JP3552377B2 - Rechargeable battery - Google Patents

Description

【００８１】
表１において、「４．２Ｖ充電後の電池厚み」は、実施例１〜４については、凸部の頂上を含む最大厚みを測定した値である。
【００８２】
また、「９０℃一日保存後電池厚み増加分」は、電池を９０℃で一日保存した後に測定した電池厚みの値から、「４．２Ｖ充電後電池厚み」の値を引いたものである。
【００８３】
表から明らかなように、比較例１および２では電池厚み増加分がそれぞれ０．６３ｍｍおよび０．５５ｍｍであるのに対して、実施例１〜４では０．２３〜０．４３ｍｍと非常に小さい値を示している。
【００８４】
電池を９０℃で１日間保存すると、電解液中の溶媒の蒸気圧が上昇することにより電池内部の圧力が上昇する。また、電解液中の溶質が分解しガス化することによりさらに電池内部の圧力が上昇することになる。
【００８５】
この結果、凸部を持っていない比較例１および２の電池では、電池厚みの増加分が比較的大きな値となる。これに対して、実施例１〜４においては、電池ケースの側面に凸部があるので電池内部の圧力が上昇しても電池ケースの変形を抑えることになる。
【００８６】
このように、本発明の電池ケースを用いた扁平角形非水電解液二次電池は９０℃に保存した場合、電池ケースの厚み増加が小さく、高温保存時において高い信頼性が得られることがわかった。
【００８７】
なお、本発明は上述の実施例に限らず本発明の要旨を逸脱することなくその他種々の構成を採り得ることはもちろんである。
【００８８】
【発明の効果】
以上の説明からも明らかなように、本発明は角形などの扁平な形状の電池において、最も面積の大きい面（広幅面）に外部方向に向いた凸部を一つ以上設け強度を与えることにより、電池を高温に曝しても電池内圧の上昇に対して電池厚みの膨張を抑え機器の破損を防止することが可能となり、高い信頼性と高エネルギー密度を有する非水電解液二次電池を提供することができる。
【図面の簡単な説明】
【図１】本発明二次電池の一実施例を示す断面図である。
【図２】本発明二次電池に用いる負極、正極、およびセパレータを示す平面図である。
【符号の説明】
１ 負極
２ 正極
３ セパレータ
４ 負極リード
５ 正極リード
６ サブリード
７ ガスケット
８ 正極端子
９ 電池フタ
１０ 接着テープ
１１ 絶縁シート
１２ 電池ケース
１３，１４ 凸部[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a secondary battery, and more particularly to a battery case and a secondary battery using the same.
[0002]
[Prior art]
In recent years, new portable electronic devices such as a camera-integrated VTR, a mobile phone, and a laptop computer have been appearing one after another, and their size and weight have been reduced more and more. In order to obtain higher energy density, active research and development are being carried out.
[0003]
Under such circumstances, a lithium ion secondary battery using a non-aqueous electrolyte has been proposed 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, and commercialization has begun. Was.
[0004]
Lithium ion secondary batteries include a cylindrical battery in which spirally wound electrodes are inserted into a cylindrical case, a folded electrode, a rectangular laminated electrode, and an elliptically wound electrode in a rectangular shape. There is a prismatic battery inserted in the case. The latter has higher space efficiency than cylindrical batteries, and has been increasingly required in recent years as devices have become thinner.
[0005]
[Problems to be solved by the invention]
By the way, the above-mentioned small secondary battery is used not only in normal use but also in a car in the middle of summer, and high reliability is required. In particular, a rectangular battery case is weaker in strength than a cylindrical battery case, and thus easily deforms as the battery internal pressure increases. Therefore, in the case of a battery that can be housed inside a device, if the battery is exposed to a high temperature, it may not be able to be taken out due to the 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.
[0006]
Therefore, the present invention has been proposed in view of such a conventional situation, and has a high reliability and a high energy density without suppressing the expansion of the battery case even when exposed to a high temperature without damaging the device. It is an object of the present invention to provide a non-aqueous electrolyte secondary battery having:
[0007]
[Means for Solving the Problems]
In order to achieve the above object, the present inventors have conducted intensive studies, and found that, by providing a convex portion on the side surface of the battery, it is possible to suppress expansion of the battery thickness even when exposed to high temperatures and prevent damage to the device. .
[0008]
The present invention provides a flat battery such as a prismatic battery, which has one or more protrusions on a surface having the largest area (hereinafter, abbreviated as a wide surface), thereby giving strength to the wide surface and increasing the internal pressure of the battery. On the other hand, it is intended to prevent swelling.
[0009]
Although the present invention is applicable to any secondary battery, a nonaqueous electrolyte secondary battery will be described below as an example.
[0010]
Any positive / negative electrode material that can constitute a non-aqueous electrolyte secondary battery can be used.However, considering the degree of expansion of the active material due to charge and discharge and the boiling point of the non-aqueous solvent used in the electrolyte, the shape of the convex portion is considered. , Dimensions, and the number thereof can be appropriately selected.
[0011]
Further, the material of the battery case used in the present invention can be appropriately selected in consideration of strength and workability thereof. Available materials include iron, nickel, stainless steel, aluminum, and the like. If corrosion occurs with a non-aqueous electrolytic solution or the like, plating or the like can be used.
[0012]
The battery case having a flat shape of the present invention can be manufactured by any method. For example, it can be manufactured by squeezing a steel plate or the like made of the above-mentioned various materials into several stages using a mold made of at least one set of male and female. Then, before or after the squeezing molding, the can is subjected to embossing using another mold to obtain the convex-shaped can of the present invention.
[0013]
However, since the ratio of the effective volume that can be filled with the positive electrode and the negative electrode to the total volume of the battery is reduced by providing the convex portion, and the energy density is lost, the dimensions need to be determined in consideration of this point.
[0014]
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 a positive electrode and a negative electrode are insulated by a resinous porous separator, is made by injecting a non-aqueous electrolyte, and has one or more convex portions on a wide surface of a battery case. It is characterized by having.
[0015]
As the secondary battery of the present invention, a stacked electrode element formed by stacking a plurality of combinations of flat positive and negative electrodes and an elliptical electrode element obtained by winding a strip-shaped positive and negative electrodes in an elliptical shape can be used.
[0016]
Materials that can be used as the negative electrode material of the present invention include oxides having relatively low potential, such as iron oxide, ruthenium oxide, molybdenum oxide, tungsten oxide, and titanium oxide, and other oxides and carbon materials.
[0017]
As the carbon material used for the negative electrode, any of the carbon materials used for this type of secondary battery can be used, but the carbon materials listed below are particularly preferable.
[0018]
First, a carbonaceous material obtained by carbonizing an organic material by a method such as firing.
[0019]
Organic materials used as starting materials include phenolic resins, acrylic resins, vinyl halide resins, polyimide resins, polyamideimide resins, polyamide resins, conjugated resins such as polyacetylene and poly (p-phenylene), cellulose and derivatives thereof, and Can be used.
[0020]
Others, condensed polycyclic hydrocarbon compounds such as naphthalene, phenanthrene, anthracene, triphenylene, pyrene, perylene, pentaphene, pentacene, and other derivatives (for example, carboxylic acids, carboxylic anhydrides, carboxylic imides, etc.), Various types of pitches containing a mixture as a main component, acenaphthylene, indole, isoindole, quinoline, isoquinoline, quinoxaline, condensed heterocyclic compounds such as phthalazine, carbazole, acridine, phenazine, phenanthridine, and derivatives thereof can also be used.
[0021]
Further, a furan resin composed of a homopolymer or copolymer of furfuryl alcohol or furfural is also particularly suitable. The carbonaceous material obtained by carbonizing this furan resin has a (002) plane spacing of 0.370 nm or more, a true density of 1.7 g / cc or less, has no oxidative heat generation peak at 700 ° C. or more in DTA, and has a negative electrode of a battery. It shows very good properties as a material.
[0022]
The temperature at which these organic materials are fired varies depending on the starting materials, and is usually 500 to 2000 ° C.
Alternatively, a petroleum pitch having a specific H / C atomic ratio into which a functional group containing oxygen is introduced (so-called oxygen cross-linking) also exhibits excellent properties when carbonized, similar to the furan resin. It can be used as an organic material.
[0023]
The petroleum pitch is distilled (vacuum distillation, normal pressure distillation, steam distillation) from coal tar, ethylene bottom oil, tar obtained by high-temperature pyrolysis of crude oil, asphalt, etc., thermal polycondensation, extraction, chemical polycondensation, etc. Obtained by the following operation.
[0024]
At this time, the H / C atomic ratio of the petroleum pitch is important, and in order to obtain non-graphitizable carbon, the H / C primitive ratio needs to be 0.6 to 0.8.
The specific means for introducing a functional group containing oxygen into these petroleum pitches is not limited. For example, a wet method using an aqueous solution of nitric acid, mixed acid, sulfuric acid, hypochlorous acid or the like, or an oxidizing gas (air, oxygen) A dry method, and a reaction with a solid reagent such as sulfur, ammonium nitrate, ammonium persulfate, and ferric chloride are used.
[0025]
For example, when oxygen is introduced into petroleum pitch by the above-described method, the final carbonaceous material is obtained in a solid state without melting in the carbonization process (400 ° C. or higher). Similar to
[0026]
The negative electrode material is obtained by carbonizing the petroleum pitch into which the functional group containing oxygen is introduced by the above-described method, regardless of the conditions at the time of carbonization, where the (002) plane spacing is 0.370 nm or more and the true density is 1 If the carbonaceous material is set so as to satisfy the property of not more than 0.7 g / cc and having no oxidative heat generation peak at 700 ° C. or more in DTA, a large lithium doping amount per unit weight can be obtained. This is because, for example, by setting the oxygen content of the precursor obtained by subjecting petroleum pitch to oxygen cross-linking to 10% by weight or more, the spacing between the (002) planes can be made 0.370 nm or more. Therefore, the oxygen content of the precursor is preferably set to 10% by weight or more, and is practically in the range of 10 to 20% by weight.
[0027]
When a carbonaceous material is obtained using the above raw material organic materials, for example, after carbonizing at 300 to 700 ° C. in a nitrogen stream, the temperature is increased at a rate of 1 to 20 ° C. per minute in a nitrogen stream, and an ultimate temperature of 900 to 1300 ° C. The baking may be performed under the condition that the holding time at the ultimate temperature is about 0 to 5 hours. Of course, the carbonization operation may be omitted in some cases.
[0028]
Further, a special negative electrode compound having a large lithium doping amount can be used by adding a phosphorus compound or a boron compound when carbonizing the furan resin or petroleum pitch.
[0029]
Examples of the phosphorus compound include oxides of phosphorus such as phosphorus pentoxide, oxo acids such as orthophosphoric acid, and salts thereof. Phosphorus oxide and phosphoric acid are preferable from the viewpoint of ease of handling.
[0030]
The amount of the phosphorus compound to be 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 ratio of phosphorus remaining in the negative electrode material is 0%. 0.2 to 9.0% by weight, preferably 0.3 to 5% by weight.
[0031]
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 to be 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 ratio of boron remaining in the negative electrode material is 0%. 0.2 to 9.0% by weight, preferably 0.3 to 5% by weight.
[0032]
In addition, graphite has a higher true density than low-temperature-treated carbonaceous materials such as coke and glassy carbon, and thus has a high electrode filling property as an active material, and therefore has a high energy density secondary battery in design. Becomes possible.
[0033]
As a material having a large true density that gives high electrode filling properties, a carbon material such as graphite is preferable. Among them, in order to obtain a higher electrode filling property, the true density is 2.1 g / cm. ³ More preferably, 2.18 g / cm ³ The above is more preferred. In order to obtain such a true density, the (002) plane spacing obtained by the X-ray diffraction method preferably satisfies less than 0.339 nm, more preferably 0.335 nm or more and 0.337 nm or less, and the C-axis of the 002 plane. It is necessary that the crystallite thickness be 16.0 nm or more, more preferably 300 nm or more.
[0034]
A typical example of the carbon material having the above-mentioned properties is natural graphite. Further, artificial graphite obtained by carbonizing an organic material and further performing high-temperature treatment also shows the crystal structure parameters.
[0035]
Coal and pitch are typical examples of the organic material used as a starting material in producing the artificial graphite.
Examples of pitch include distillation (vacuum distillation, normal pressure distillation, steam distillation) from coal tar, ethylene bottom oil, tar obtained from high-temperature pyrolysis of crude oil, asphalt, etc., hot polycondensation, extraction, chemical polycondensation, etc. There are also those obtained by the operation, and other pitches generated during wood carbonization.
[0036]
Further, starting materials for forming the pitch include polyvinyl chloride resin, polyvinyl acetate, polyvinyl butyrate, and 3,5-dimethylphenol resin.
[0037]
These coals and pitches exist in a liquid state at a maximum of about 400 ° C. during the carbonization, and by holding at that temperature, the aromatic rings are condensed and polycyclic to form a laminated orientation, and thereafter, a temperature of about 500 ° C. or more , A solid carbon precursor or semi-coke is formed. Such a process is called a liquid phase carbonization process, and is a typical production process of graphitizable carbon.
[0038]
In addition, condensed polycyclic hydrocarbon compounds such as naphthalene, phenanthrene, anthracene, triphenylene, pyrene, perylene, pentaphene, and pentacene, other derivatives (for example, carboxylic acids, carboxylic anhydrides, and carboxylic imides), or mixtures thereof, and acenaphthylene , Indole, isoindole, quinoline, isoquinoline, quinoxaline, phthalazine, carbazole, acridine, phenazine, phenanthridine and the like, and also derivatives thereof can be used as raw materials.
[0039]
In order to produce a desired artificial graphite using the above organic material as a starting material, for example, the above organic material is carbonized at 300 to 700 ° C. in an inert gas stream such as nitrogen and then heated in an inert gas stream. It is obtained by calcining at a rate of 1 to 100 ° C. per minute, a reaching temperature of 900 to 1500 ° C., a holding time at the reaching temperature of about 0 to 30 hours, and a heat treatment at 2000 ° C. or higher, preferably 2500 ° C. or higher Can be Of course, in some cases, the carbonization or calcination operation may be omitted.
[0040]
The carbon material or graphite material that has been heat-treated at a high temperature is pulverized and classified for use as a negative electrode material. This pulverization may be performed before or after carbonization, calcination, high-temperature heat treatment, or during the temperature raising process.
[0041]
Further, in order to obtain a graphite material having more practical performance, it is preferable to use a material satisfying the following physical properties.
[0042]
True density 2.1 g / cm as graphite material ³ And the bulk specific gravity is 0.4 g / cm ³ It is preferable to use the above graphite materials. Since the graphite material has a high true density, forming a negative electrode with the graphite material enhances the electrode filling property and improves the energy density of the battery. In particular, the bulk specific gravity of the graphite material is 0.4 g / cm. ³ When the above graphite material is used, such a graphite material having a large bulk specific gravity can be dispersed relatively uniformly in the negative electrode mixture layer. The characteristics are improved.
[0043]
Furthermore, the bulk specific gravity is 0.4 g / cm ³ When a material having a low flatness and having the average shape parameter xave of 125 or less is used, the electrode structure is further improved, and the cycle characteristics are further improved.
[0044]
In order to obtain the above graphite material, a method of performing a heat treatment for graphitization in a state where carbon is formed into a molded body is preferable. By grinding this graphitized molded body, the bulk specific gravity is higher, and the average shape parameter is increased. A graphite material having a small xave can be obtained.
[0045]
Further, the bulk specific gravity and the average shape parameter xave of the graphite material are in the above ranges, and the specific surface area is 9 m. ² / G or less, the amount of submicron fine particles adhering to the graphite particles is small, the bulk specific gravity is high, the electrode structure is good, and the cycle characteristics are further improved.
[0046]
In the particle size distribution determined by the laser diffraction method, graphite powder having a cumulative 10% particle size of 3 μm or more, a cumulative 50% particle size of 10 μm or more, and a cumulative 90% particle size of 70 μm or less is used. Thus, a non-aqueous electrolyte secondary battery with high safety and reliability can be obtained. Small particles have a large specific surface area, but by limiting this content, it is possible to suppress abnormal heat generation such as overcharging due to particles having a large specific surface area and to limit the content of large particles. Thereby, an internal short circuit due to the expansion of the particles at the time of the initial charge can be suppressed, and a practical non-aqueous electrolyte secondary battery having high safety and reliability can be realized.
[0047]
Further, the average value of the breaking strength of the particles is 6.0 kgf / mm. ² By using the graphite powder described above, a large number of pores for allowing the electrolyte to be contained in the electrode can be present, and a nonaqueous electrolyte secondary battery having good load characteristics can be obtained.
[0048]
On the other hand, the cathode material used in combination with the anode made of the above-mentioned anode material is not particularly limited, but preferably contains a sufficient amount of Li, for example, a general formula LiMO ₂ (Where M represents at least one of Co, Ni, Mn, Fe, Al, V, and Ti), a composite metal oxide composed of lithium and a transition metal, an intercalation compound containing Li, or the like is preferable. is there.
[0049]
In the non-aqueous electrolyte used in the non-aqueous electrolyte secondary battery of the present invention, a non-aqueous electrolyte obtained by dissolving an electrolyte in a non-aqueous solvent is used as the electrolyte.
[0050]
As a non-aqueous solvent for dissolving the electrolyte, it is premised that a solvent having a relatively high dielectric constant such as EC is used as a main solvent, but it is necessary to further add a low viscosity solvent of a plurality of components to complete the present invention. There is.
[0051]
As the high dielectric constant solvent, PC, butylene carbonate, vinylene carbonate, sulfolane, butyrolactone, valerolactone, and the like are preferable. As the low-viscosity solvent, symmetric or asymmetric chain carbonates such as diethyl carbonate, dimethyl carbonate, methyl ethyl carbonate, and methyl propyl carbonate are preferable, and furthermore, two or more low-viscosity solvents may be used in combination. The result is obtained.
[0052]
In particular, when a graphite material is used for the negative electrode, EC is first preferred as the main solvent of the non-aqueous solvent, but a compound having a structure in which a hydrogen atom of EC is replaced by a halogen element is also suitable.
[0053]
In addition, although it is reactive with a graphite material like PC, a very small amount of the second component solvent is used for EC or a compound having a structure in which a hydrogen atom of EC is replaced with a halogen element as a main 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-dioxolan, 4- Methyl-1,3-dioxolan, sulfolane, methylsulfolane and the like can be used, and the addition amount thereof is preferably less than 10 Vol%.
[0054]
Further, to 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 conductivity, suppress EC decomposition, and improve low-temperature characteristics. In addition, the reactivity with lithium metal may be reduced to improve safety.
[0055]
As the solvent of the third component, a chain carbonate such as DEC (diethyl carbonate) or DMC (dimethyl carbonate) is preferable. Further, an asymmetric chain carbonate such as MEC (methyl ethyl carbonate) and MPC (methyl propyl carbonate) is preferable. 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 (main solvent or the mixed solvent of the main solvent and the second component solvent: the third component solvent) is a volume. The ratio is preferably from 15:85 to 40:60, and more preferably from 18:82 to 35:65.
[0056]
Further, the solvent of the third component may be a mixed solvent of MEC and DMC. The MEC-DMC mixing ratio is preferably in the range represented by 1/9 ≦ d / m ≦ 8/2, where the MEC capacity is m and the DMC capacity is d. The mixing ratio of the main solvent or the mixed solvent of the main solvent and the second component solvent and the MEC-DMC serving as the solvent of the third component is as follows: when the MEC capacity is m, the DMC capacity is d, and the total amount of the solvent is T, The range is preferably represented by 3/10 ≦ (m + d) / T ≦ 9/10, and more preferably the range represented by 5/10 ≦ (m + d) / T ≦ 8/10.
[0057]
As the electrolyte dissolved in such a non-aqueous solvent, any electrolyte used in this main battery can be used by mixing one or more kinds. For example, LiPF ₆ Is preferred, but other LiClO ₄ , LiAsF ₆ , LiBF ₄ , LiB (C ₆ H ₅ ) ₄ , CH ₃ SO ₃ Li, CF ₃ SO ₃ Li, LiN (CF ₃ SO ₂ ) ₂ , LiC (CF ₃ SO ₂ ) ₃ , LiCl, LiBr and the like can also be used.
[0058]
The present invention provides a battery having a flat shape such as a rectangular shape, in which one or more convex portions are provided on the widest surface having the largest area to provide strength. It is intended to provide a non-aqueous electrolyte secondary battery having high reliability and high energy density, which can suppress expansion of the battery and prevent breakage of equipment.
[0059]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, an embodiment of the secondary battery of the present invention will be described with reference to FIGS.
[0060]
Example 1
FIG. 1 shows the configuration of the nonaqueous electrolyte secondary battery manufactured in this example.
First, the negative electrode 1 was produced as follows.
A petroleum pitch appropriately selected from the H / C atomic ratio range of 0.6 to 0.8 was pulverized and oxidized 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 (by organic element analysis) was 15.4% by weight.
[0061]
The carbon precursor was heated to 1000 ° C. in a nitrogen stream and heat-treated, and then pulverized to obtain a carbon material powder having an average particle diameter of 10 μm. As a result of X-ray diffraction measurement of the non-graphitizable carbon material obtained at this time, the (002) plane spacing was 0.381 nm and the true specific gravity was 1.54.
[0062]
90 parts by weight of the carbon material powder is mixed with 10 parts by weight of polyvinylidene fluoride as a binder to prepare a negative electrode mixture, and the negative electrode mixture is dispersed in a solvent N-methyl-2-pyrrolidone to form a slurry, and the negative electrode slurry is prepared. Prepared.
[0063]
Then, the negative electrode slurry thus obtained is uniformly applied to both sides of a 10 μm-thick strip-shaped copper foil serving as a negative electrode current collector, dried, and then compression-molded by a roll press to produce a strip-shaped electrode. did. This strip electrode was cut into a rectangular shape as shown in FIG.
[0064]
Next, the positive electrode 2 was produced as follows.
Lithium carbonate and cobalt carbonate were mixed at a ratio of 0.5 mol: 1.0 mol and calcined in air at 900 ° C. for 5 h to obtain LiCoO 2.
[0065]
LiCoO thus obtained ₂ , 91 parts by weight were 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 this positive electrode mixture was dispersed in a solvent N-methyl-2-pyrrolidone to prepare a slurry. And a positive electrode slurry was prepared.
[0066]
Then, the positive electrode slurry thus obtained is uniformly applied to both sides of a 20 μm-thick strip-shaped aluminum foil serving as a positive electrode current collector, dried, and then compression-molded by a roll press to produce a strip-shaped electrode. did. This strip-shaped electrode was cut into a rectangular shape shown by a dotted line in FIG.
[0067]
Then, the negative electrode 1 and the positive electrode 2 were sandwiched by a separator 3 made of a microporous polypropylene film, and fixed with an adhesive tape 10 to obtain a laminated electrode element.
[0068]
Next, as shown in FIG. 1, an insulating sheet 11 is laid on the bottom of a flat iron battery case 12 made of nickel and having a thickness of 450 μm and having two convex portions 13 and 14 facing outward, and is placed in the nickel sheet. The laminated electrode element was inserted.
Note that, when viewed from the left and right directions in FIG. 1, the projections 13 and 14 have a circular shape around them.
[0069]
Next, the sub-lead 6 was welded to the positive electrode terminal 8 attached to the battery lid 9 via the gasket 7 in advance. Here, the positive electrode leads of the laminated electrode element were bundled and welded to the sub-leads 6. The negative electrode lead was also bundled and welded to the battery case 12.
[0070]
LiPF in a mixed solvent of 50% by volume of PC and 50% by volume of DMC ₆ Was dissolved into the battery case 12 at a rate of 1 mol / l, and the battery lid 9 was fixed to the battery case 12 by laser welding to produce a flat rectangular lithium ion secondary battery. .
[0071]
Example 2
A flat rectangular lithium ion secondary battery was manufactured in the same manner as in Example 1, except that a battery case having one convex portion was used.
[0072]
Example 3
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.
[0073]
First, 30 parts by weight of coal tar pitch as a binder is added to 100 parts by weight of coal-based coke as a filler, mixed at about 100 ° C., and then compression-molded by a press to obtain a precursor of a carbon molded body. Obtained. The carbon material molded body obtained by heat-treating the precursor at a temperature of 1000 ° C. or less is further impregnated with a binder pitch melted at a temperature of 200 ° C. or less, and heat-treated at a temperature of 1000 ° C. or less. Was. Thereafter, this carbon molded body was heat-treated at 2600 ° C. in an inert atmosphere to obtain a graphitized molded body, and then pulverized and classified to prepare a graphite material powder as a sample.
[0074]
The graphite material powder obtained at this time had a true density of 2.23 g / cm. ³ , Bulk specific gravity = 0.83 g / cm ³ , Average shape parameter Xave. = 10, specific surface area = 4.4m ² / G, average particle size = 31.2 μm, cumulative 10% particle size = 12.3 μm, cumulative 50% particle size = 29.5 μm, cumulative 90% particle size = 53.7 μm.
[0075]
This graphite material powder was used as a negative electrode material, and LiPF was used as a mixed solvent of EC 50% by volume and DEC 50% by volume. ₆ Was prepared in the same manner as in Example 1 except that an electrolytic solution prepared by dissolving the compound at a ratio of 1 mol / l was used.
[0076]
Example 4
The same negative electrode material as in Example 3 was used. The battery case used had one convex portion. Except for these, a flat rectangular lithium ion secondary battery was manufactured in the same manner as in Example 1.
[0077]
Comparative Example 1
A flat prismatic lithium ion secondary battery was produced in the same manner as in Example 1, except that a flat prismatic battery case having no convex portion was used.
[0078]
Comparative Example 2
A flat prismatic lithium ion secondary battery was produced in the same manner as in Example 3, except that a flat prismatic battery case having no convex portion was used.
[0079]
For each of Examples 1-4 and Comparative Examples 1-2 produced as described above, the battery was charged to a constant current of 400 mA, 4.2 V, and 5 hours, and then discharged to 2.75 V at a constant current of 400 mA. Was measured. After charging at 4.2 V, the battery was stored at 90 ° C., and the thickness of the battery case was measured. The results are shown in Table 1.
[0080]
[Table 1]

[0081]
In Table 1, “Battery thickness after 4.2 V charge” is a value obtained by measuring the maximum thickness including the top of the convex portion in Examples 1 to 4.
[0082]
The “increase in battery thickness after storage at 90 ° C. for one day” is obtained by subtracting the value of “battery thickness after charging 4.2 V” from the value of the battery thickness measured after storing the battery at 90 ° C. for one day. is there.
[0083]
As is clear from the table, in Comparative Examples 1 and 2, the increase in the battery thickness was 0.63 mm and 0.55 mm, respectively, whereas in Examples 1 to 4, it was very small, 0.23 to 0.43 mm. Indicates the value.
[0084]
When the battery is stored at 90 ° C. for one day, the internal pressure of the battery increases due to an increase in the vapor pressure of the solvent in the electrolyte. Further, the pressure inside the battery further increases due to the decomposition and gasification of the solute in the electrolytic solution.
[0085]
As a result, in the batteries of Comparative Examples 1 and 2 having no protrusion, the increase in the battery thickness becomes a relatively large value. On the other hand, in Examples 1 to 4, since the battery case has the convex portion on the side surface, the deformation of the battery case is suppressed even when the pressure inside the battery increases.
[0086]
Thus, when the flat non-aqueous electrolyte secondary battery using the battery case of the present invention is stored at 90 ° C., the increase in thickness of the battery case is small, and high reliability can be obtained during high-temperature storage. Was.
[0087]
The present invention is not limited to the above-described embodiment, but may adopt various other configurations without departing from the gist of the present invention.
[0088]
【The invention's effect】
As is clear from the above description, the present invention provides a battery having a flat shape such as a prismatic shape by providing one or more convex portions facing the outer direction on a surface having the largest area (wide surface) to give strength. Provides a non-aqueous electrolyte secondary battery with high reliability and high energy density by suppressing the expansion of the battery thickness against the rise in battery internal pressure even when the battery is exposed to high temperatures and preventing damage to equipment. can do.
[Brief description of the drawings]
FIG. 1 is a sectional view showing an embodiment of the secondary battery of the present invention.
FIG. 2 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 terminal
9 Battery cover
10 Adhesive tape
11 Insulation sheet
12 Battery case
13,14 convex part

Claims (7)

A negative electrode mixture containing a negative electrode material capable of doping and undoping lithium ions is applied to both sides of a strip-shaped foil, and a shaped strip negative electrode,
Li _x A positive electrode mixture containing a positive electrode material composed of MO _y (where M represents at least one of Co, Ni, Mn, Fe, Al, V, and Ti) is applied to both sides of a strip-shaped foil and molded. Strip-shaped positive electrode,
Having an electrode element in which the positive electrode and the negative electrode are insulated by the separator,
In a secondary battery in which the battery element is housed in a flat battery can and an electrolyte is injected,
A secondary battery characterized in that the battery case has one or more convex portions having a substantially circular shape facing the outside on a wide surface of the battery case. The secondary battery according to claim 1, further comprising an electrode element in which a positive electrode and a negative electrode are insulated by a resin porous separator, and wherein a non-aqueous electrolyte is injected. A negative electrode made of a carbon material capable of doping and undoping lithium ions; and a positive electrode made of Li _x MO _y (where M represents at least one of Co, Ni, Mn, Fe, Al, V, and Ti). 2. The secondary battery according to claim 1, comprising a non-aqueous electrolyte. A negative electrode made of a graphite material capable of doping / dedoping lithium ions; and a positive electrode made of Li _x MO _y (where M represents at least one of Co, Ni, Mn, Fe, Al, V, and Ti). 2. The secondary battery according to claim 1, comprising a non-aqueous electrolyte. In a secondary battery having an electrode element in which a positive electrode and a negative electrode are insulated by a separator, and injecting an electrolytic solution,
A secondary battery having at least one convex portion facing outward in a wide surface of a battery case. In a secondary battery having an electrode element in which a positive electrode and a negative electrode are insulated by a separator, and injecting an electrolytic solution,
A secondary battery having at least one convex portion facing outward on a wide surface of a rectangular battery case. In a secondary battery having an electrode element in which a positive electrode and a negative electrode are insulated by a separator, and injecting an electrolytic solution,
A secondary battery having at least one convex portion facing outward on a wide surface of a flat rectangular battery case.

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