JP4550367B2 - Nonaqueous electrolyte secondary battery - Google Patents

Description

【００４６】
表１から明らかなように、ガス抜き孔とは異なる形状でガス抜き孔の開口面積以上の面積の封止断面部を有する弾性体を用いる実施例１〜３の二次電池は、充電高温貯蔵時の膨れが比較例１〜２に比較して小さいことがわかる。特に、封止断面部の最小差し渡し長さがガス抜き孔の最大差し渡し長さよりも大きい実施例１〜２の二次電池は、膨れ度合いのばらつきを示す膨れの変動係数が１０％台と小さかった。
【００４７】
これに対し、封止断面部の形状がガス抜き孔と同じである比較例１の二次電池と、ガス抜き孔に平板状ゴムを圧着させた構成の比較例２の二次電池は、膨れ量が大きく、そのばらつきも大きかった。
【００４８】
【発明の効果】
以上詳述したように本発明によれば、高温貯蔵時の外装缶の膨れが抑制された非水電解質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】 本発明に係る非水電解質二次電池の一実施形態である角形非水電解質二次電池を示す部分分解斜視図。
【図２】 図１の二次電池の要部を示す断面図。
【図３】 図２におけるIII−III線に沿う断面図。
【符号の説明】
１…外装缶、２…電極群、４…封口板、５…負極端子、６…絶縁部材、９…窪み部、１０…ガス抜き孔、１１…弾性体、１２ａ…大径面、１２ｂ…小径面、１３…背板。[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a non-aqueous electrolyte secondary battery.
[0002]
[Prior art]
Nonaqueous electrolyte secondary batteries, such as lithium ion secondary batteries, have a higher operating voltage than conventional alkaline storage batteries and lead storage batteries, and are practically used for both energy density by weight and energy density by volume. Since it is the largest, demand has increased greatly in recent years.
[0003]
However, as a reverse of the fact that a high operating voltage can be obtained, when the electrode in the charged state is placed in a remarkably abnormal high temperature environment, the electrolyte and the oxidized positive electrode or the electrolyte and the reduced negative electrode are slightly However, since the reaction occurs, the internal pressure of the outer can rises due to the generated gas, causing the problem that the outer can expands and deforms. Usually, since a battery is stored in a plastic case or the like and incorporated in a portable device as a battery pack, if the outer can is deformed, the outer shape of the portable device is distorted, resulting in a problem that the appearance of the device is impaired.
[0004]
Japanese Patent Application Laid-Open No. 2000-268811 has a support member fixed as a sealing plug for a liquid filling hole of a sealing lid of a sealed battery in a state of covering the liquid filling hole on the surface of the sealing lid, and has elasticity. It is described that a material made of a material and composed of a press-fitting member supported by the support member in a state of being press-fitted into the liquid injection hole is described.
[0005]
[Patent Document 1]
JP 2000-268811 A (Claims)
[0006]
[Problems to be solved by the invention]
An object of the present invention is to provide a nonaqueous electrolyte secondary battery in which swelling of an outer can in a high temperature environment is suppressed.
[0007]
[Means for Solving the Problems]
Nonaqueous electrolyte secondary battery according to the present invention, an outer can,
An electrode group housed in the outer can and including a positive electrode and a negative electrode;
A non-aqueous electrolyte held in the electrode group;
A sealing plate disposed at the opening of the outer can;
A vent hole opened in the outer can or the sealing plate;
An elastic body having a sealing cross-section having a shape different from the vent hole and having an area larger than the opening area of the vent hole;
The elastic body is inserted into the gas vent hole, and the entire peripheral surface of the sealing cross section of the elastic body is in contact with the inner surface of the gas vent hole in a compressed state.
[0008]
DETAILED DESCRIPTION OF THE INVENTION
A non-aqueous electrolyte secondary battery according to the present invention includes an outer can, an electrode group that is housed in the outer can and includes a positive electrode and a negative electrode, a non-aqueous electrolyte that is held in the electrode group, and an opening of the outer can. A sealing cross section having a shape different from that of the gas vent hole and a size larger than the opening area of the gas vent hole. An elastic body having
The elastic body is inserted into the gas vent hole, and the sealing cross section of the elastic body is in contact with the inner surface of the gas vent hole in a compressed state.
[0009]
In a non-aqueous electrolyte secondary battery, particularly a secondary battery using a non-aqueous electrolyte containing a cyclic carbonate or a chain carbonate, when placed in a high temperature environment (for example, about 90 ° C.) in a fully charged state or nearly full charged state, The carbonates in the nonaqueous electrolyte react with the positive electrode in a highly oxidized state to produce decomposition products such as carbon dioxide. In order to suppress an increase in internal pressure and battery swelling due to the generated gas, it is necessary to provide a mechanism for releasing the generated gas to the outside.
[0010]
On the other hand, since the nonaqueous electrolyte and the negative electrode included in the secondary battery have reactivity with moisture, it is necessary to suppress moisture in the air from entering the cell as much as possible.
[0011]
In order to achieve both of these, a gas vent hole is opened in the sealing plate, and the gas vent hole is sealed with a rubber stopper to prevent moisture from entering from the outside and A mechanism has been proposed in which the sealed state is released only when the pressure in the can rises, and the gas is released to the outside through the vent hole. However, elastic materials such as rubber-like polymers generally expand in volume as the temperature rises. Therefore, if the stopper is used for the purpose of improving the sealing performance under normal use conditions, that is, near room temperature, the stopper will further open at high temperatures. There is a problem that the desired pressure relief mechanism may not work when the pressure in the outer can rises, and the operation becomes unstable.
[0012]
In the present invention, the elastic body inserted into the gas vent hole opened in the outer can or the sealing plate has a shape different from that of the gas vent hole and has a sealing cross section larger than the opening area of the gas vent hole. use. Since this sealing cross section is in contact with the inner surface of the gas vent hole in a compressed state, a sufficient repulsive elastic force can be generated between the elastic body and the inner surface of the gas vent hole. Sealing can be performed. For this reason, the penetration | invasion of the moisture from the outside at the time of normal use can fully be suppressed. In addition, when gas is generated under high temperature conditions, the elastic body thermally expands. However, because the shapes of the gas vent hole and the sealing cross section are different, the compression state of the sealing cross section is not uniform and is relatively weak. Since the portion can be secured, the pressure relief when the internal pressure increases in a high temperature state can be performed with good reproducibility.
[0013]
In addition, by making the minimum passing length in the free state of the sealing cross section longer than the maximum passing length of the gas vent hole, it is possible to prevent the elastic body from falling out of the gas vent hole, Variations in battery swelling can be reduced.
[0014]
Hereinafter, an example of the non-aqueous electrolyte secondary battery according to the present invention will be described with reference to FIGS.
[0015]
FIG. 1 is a partially exploded perspective view showing a prismatic nonaqueous electrolyte secondary battery which is an embodiment of a nonaqueous electrolyte secondary battery according to the present invention, and FIG. 2 shows a main part of the secondary battery of FIG. FIG. 3 is a cross-sectional view taken along line III-III in FIG.
[0016]
The rectangular tubular outer can 1 also serves as a positive electrode terminal and is made of a metal such as aluminum or an aluminum alloy. Housed in the outer can 1 is an electrode group 2 in which a positive electrode and a negative electrode are wound in a flat shape with a separator interposed therebetween.
The nonaqueous electrolytic solution is accommodated in the outer can 1. The insulating plate 3 is disposed on the electrode group 2. A metal (for example, aluminum or aluminum alloy) sealing plate 4 also serving as a positive electrode terminal is attached to the opening of the outer can 1 by, for example, laser welding. The hat-shaped negative electrode terminal 5 is attached to the sealing plate 4 via an insulating material 6.
[0017]
The positive electrode current collecting tab 7 has one end connected to the positive electrode of the electrode group 2 and the other end connected to the lower surface of the sealing plate 4. The negative electrode current collecting tab 8 has one end connected to the negative electrode of the electrode group 2 and the other end connected to the negative electrode terminal 5.
[0018]
A part of the sealing plate 4 is recessed in a circular shape, and a circular gas vent hole 10 is opened in the recessed portion 9. The elastic body 11 has a truncated cone structure in which a part of the peripheral surface is provided with a flat region 11a by cutting out a part of the peripheral surface (curved surface). The large diameter surface 12 a of the elastic body 11 has an area larger than the opening area of the gas vent hole 10. On the other hand, the small diameter surface 12 b has an area smaller than the opening area of the gas vent hole 10. When such an elastic body 11 is inserted into the gas vent hole 10 so that the large-diameter surface 12a is positioned in the recess 9 of the sealing plate 4 and the small-diameter surface 12b is positioned on the inner surface side of the sealing plate 4, A sealing cross section having a size larger than the opening area of the vent hole 10 contacts the inner surface of the gas vent hole 10 in a compressed state, and as a result, the gas vent hole 10 is sealed. It is desirable that the sealing section has a minimum passing length D in a free state (a state in which it is not inserted into the gas vent hole 10) longer than the diameter of the gas vent hole 10. As a result, variations in battery swelling can be suppressed, and it is possible to prevent the elastic body 11 from falling out of the vent hole 10 into the outer can 1, particularly when the recess 9 is provided in the sealing plate 4. become. As the elastic material forming the elastic body 11, it is desirable to use a material having high resistance to swelling with respect to the non-aqueous electrolyte. Examples of such an elastic material include ethylene-polyethylene-diene copolymer (EPDM) rubber.
[0019]
After the elastic body 11 is inserted into the vent hole 10, it is fixed to the sealing plate 4 with the back plate 13 so as not to be pushed out when the pressure inside the outer can 1 rises. The back plate 13 can be made of, for example, an aluminum thin plate, and a gas diffusion path can be secured by performing multi-point welding with a shape leaving a gap between the back plate 13 and the sealing plate 4.
[0020]
In addition, although the example which provided the hollow part 9 in the sealing board 4 was demonstrated in FIGS. 1-3 mentioned above, the flat plate in which the hollow part 9 is not provided may be used for the sealing board 4. FIG.
[0021]
According to the non-aqueous electrolyte secondary battery shown in FIG. 1 to FIG. 3 described above, the sealing cross section having an area equal to or larger than the opening area of the gas vent hole 10 is normally compressed on the inner surface of the gas vent hole 10. Since they are in contact with each other, the intrusion of moisture from the vent hole 10 can be sufficiently suppressed. When the secondary battery is stored in a high temperature environment in a charged state, gas is generated due to oxidative decomposition of the nonaqueous electrolyte, and thermal expansion occurs in the elastic body 11, but there is a variation in the compression state of the sealed cross section. In addition, since there is a relatively weak spot, the gas can escape from the weak spot so as to leak to the outside, and swelling of the outer can 1 can be suppressed.
[0022]
Hereinafter, the positive electrode, the negative electrode, the separator, and the nonaqueous electrolyte will be described.
[0023]
1) Positive electrode The positive electrode active material contained in this positive electrode includes various oxides such as manganese dioxide, lithium manganese composite oxide, lithium-containing nickel oxide, lithium-containing cobalt oxide, lithium-containing nickel cobalt oxide, and lithium-containing materials. Examples thereof include iron oxide, vanadium oxide containing lithium, and chalcogen compounds such as titanium disulfide and molybdenum disulfide.
[0024]
2) Negative electrode Examples of the active material contained in the negative electrode include those containing carbonaceous materials or chalcogen compounds that absorb and release lithium ions, and those made of light metals.
[0025]
Examples of the carbonaceous material that occludes / releases lithium ions include coke, carbon fiber, pyrolytic vapor phase carbonaceous material, graphite, resin fired body, mesophase pitch carbon fiber, and mesophase spherical carbon fired body. . Among these, mesophase pitch-based carbon fiber or mesophase spherical carbon graphitized at 2500 ° C. or higher is preferable because the electrode capacity increases.
[0026]
Examples of chalcogen compounds that occlude and release lithium ions include titanium disulfide (TiS ₂ ), molybdenum disulfide (MoS ₂ ), and niobium selenide (NbSe).
[0027]
Examples of the light metal include aluminum, aluminum alloy, lithium metal, and lithium alloy.
[0028]
3) As the separator separator, for example, a nonwoven fabric, a polypropylene microporous film, a polyethylene microporous film, a polyethylene-polypropylene microporous laminated film, or the like can be used.
[0029]
4) Nonaqueous electrolyte As the nonaqueous electrolyte, a liquid nonaqueous electrolyte (so-called nonaqueous electrolyte), a gel nonaqueous electrolyte, a solid nonaqueous electrolyte, or the like can be used. The nonaqueous electrolytic solution includes a nonaqueous solvent and an electrolyte (for example, lithium salt) dissolved in the nonaqueous solvent.
[0030]
Examples of the non-aqueous solvent include cyclic carbonates such as propylene carbonate (PC) and ethylene carbonate (EC), chain carbonates such as dimethyl carbonate (DMC), methyl ethyl carbonate (MEC), and diethyl carbonate (DEC), Chain ethers such as 2-dimethoxyethane (DME) and diethoxyethane (DEE), cyclic ethers and crown ethers such as tetrahydrofuran (THF) and 2-methyltetrahydrofuran (2-MeTHF), γ-butyrolactone (γ-BL) And fatty acid esters such as acetonitrile, nitrogen compounds such as acetonitrile (AN), sulfur compounds such as sulfolane (SL) and dimethyl sulfoxide (DMSO), and the like. The type of the non-aqueous solvent can be one type or two or more types.
[0031]
Among these, at least one selected from EC, PC and γ-BL, at least one selected from EC, PC and γ-BL, and DMC, MEC, DEC, DME, DEE, THF, 2-MeTHF, and It is desirable to use a mixed solvent consisting of at least one selected from AN. In particular, when a negative electrode containing a carbonaceous material that occludes / releases lithium ions is used, EC and PC and γ-BL, EC and PC and MEC, and EC and PC from the viewpoint of improving the cycle life of the secondary battery. And DEC, EC and PC and DEE, EC and AN, EC and MEC, PC and DMC, PC and DEC or EC and DEC are preferably used.
[0032]
As the electrolyte, for example, lithium perchlorate (LiClO _4), lithium hexafluorophosphate (LIPF _6), tetrafluoride lithium borate (LiBF _4), hexafluoro arsenate lithium (LiAsF _6), trifluoroacetic meta sulfonic Examples include lithium salts such as lithium acid lithium (LiCF ₃ SO ₃ ), lithium aluminum tetrachloride (LiAlCl ₄ ), and lithium bistrifluoromethylsulfonylimide [LiN (CF ₃ SO ₂ ) ₂ ]. Among these, LIPF ₆ , LiBF ₄ , and LiN (CF ₃ SO ₂ ) ₂ are preferable because conductivity and safety are improved.
[0033]
The amount of electrolyte dissolved in the non-aqueous solvent is preferably in the range of 0.5 mol / L to 2 mol / L.
[0034]
【Example】
Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings described above.
[0035]
Example 1
<Preparation of electrode group and preparation of non-aqueous electrolyte>
A slurry containing lithium cobaltate as an active material was applied to an aluminum foil as a current collector, dried and pressed to produce a positive electrode. On the other hand, a slurry containing a graphite-based carbon material as an active material was applied to a copper foil as a current collector, dried, and pressed to prepare a negative electrode. The electrode group 2 was produced by winding the positive electrode and the negative electrode in a flat shape with a separator interposed therebetween. Further, a nonaqueous electrolyte was prepared by dissolving LiPF ₆ at a concentration of 1 mol / L in a nonaqueous solvent in which ethylene carbonate (EC) and methyl ethyl carbonate (MEC) were mixed at a volume ratio of 1: 2.
[0036]
<Assembly of sealing member>
A circular depression 9 is formed in a part of a rectangular aluminum plate (thickness: 1.0 mm) by pressing, and a circular (diameter 1.0 mm) gas vent hole 10 is opened in the depression 9. Thus, a sealing plate 4 was obtained. Prepare a frustoconical EPDM rubber with a diameter of the large diameter surface 12a of 1.4 mm, a diameter of the small diameter surface 12b of 0.8 mm and a height of 2.0 mm, and cut out a part of this curved surface. The elastic body 11 was prepared by providing the planar region 11a having a width of 9.0 mm on the large diameter surface side. The area of the large diameter surface 12 a of the elastic body 11 is larger than the opening area of the gas vent hole 10, and the area of the small diameter surface 12 b is smaller than the opening area of the gas vent hole 10. When the elastic body 11 is inserted into the gas vent hole 10 with the large-diameter surface 12a facing up, a portion (sealed cross section) having a cross-sectional area larger than the opening area of the gas vent hole 10 is formed on the inner surface of the gas vent hole 10. The gas vent hole 10 was sealed with the elastic body 11 in contact with each other in a compressed state. The minimum passing length D in the free state of the sealed cross section was 1.1 mm to 1.4 mm, which was larger than the diameter (maximum passing length) of the gas vent hole 10.
[0037]
A back plate 13 made of a rectangular aluminum plate was prepared, and the recess 9 of the sealing plate 4 was covered with the back plate 13 and fixed by spot welding. The non-welded portion between the sealing plate 4 and the back plate 13 can function as a gas vent passage.
[0038]
<Battery assembly>
After the electrode group 2 was housed in an aluminum square can (exterior can) 1 serving also as a positive electrode terminal, 2 g of a nonaqueous electrolyte was injected. The positive current collecting tab 7 was welded to the sealing plate 4, and the negative current collecting tab 8 was welded to the negative electrode terminal 5. The sealing plate 4 is laser welded to the outer can 1 so that the outer dimensions (height 40 mm, width 30 mm), the battery thickness after charging with 4.2 V constant current / constant voltage is 5.2 mm, and the discharge is 0.2 C. A prismatic nonaqueous electrolyte secondary battery with a capacity of 630 mAh was assembled.
[0039]
Ten such batteries were prepared, charged with 4.2 V constant current / constant voltage (constant current value 630 mA, charging time 3 hours), then stored in a thermostat at 90 ° C. for 5 days, and the swelling amount immediately after the end of storage ( The value obtained by subtracting the battery thickness before storage from the battery thickness after storage) was measured, the average of 10 batteries was determined, and the results are shown in Table 1 below. Further, the coefficient of variation (%) of swelling is obtained from the following equation (1), and the result is also shown in Table 1 below.
[0040]
Coefficient of variation of swelling (%) = (σ / Ave.) × 100 (1)
Where σ is the standard deviation of the bulge amount variation, and Ave. is the average value of the bulge amount.
[0041]
(Example 2)
The shape of the vent hole was changed to an ellipse (the major axis was 1.1 mm and the minor axis was 1.0 mm). Further, an EPDM truncated cone having a large diameter surface of 1.4 mm, a small diameter surface of 0.8 mm, and a height of 2.0 mm was prepared as an elastic body. The minimum passing length D in the free state of the sealed cross section was 1.15 mm to 1.4 mm, which was larger than the major diameter (maximum passing length) of the gas vent hole. As for other configurations, a rectangular nonaqueous electrolyte secondary battery similar to that in Example 1 described above was assembled, and the average value of the amount of swelling and the coefficient of variation of swelling were obtained in the same manner as described in Example 1, and the results are shown below. Table 1 shows.
[0042]
(Example 3)
By enlarging the width of the cutout portion (planar region 11a) of the elastic body 11 on the large-diameter surface side to 10 mm, the minimum passing length D in the free state of the sealing cross section is 0.9 mm to 0.99 mm. A rectangular nonaqueous electrolyte secondary battery having the same configuration as that described in Example 1 was assembled except that the diameter of the gas vent hole 10 was smaller than the diameter (maximum passing length). In the same manner as above, the average value of the amount of swelling and the coefficient of variation of swelling are obtained, and the results are shown in Table 1 below.
[0043]
(Comparative Example 1)
A rectangular nonaqueous electrolyte secondary battery having the same configuration as that described in Example 1 was assembled except that the cutout portion (planar region 11a) was not provided in the elastic body 11, and was described in Example 1. In the same manner as above, the average value of the amount of swelling and the coefficient of variation of swelling are obtained, and the results are shown in Table 1 below.
[0044]
(Comparative Example 2)
Using a flat rubber as an elastic body, except that this flat rubber is pressure-bonded to the sealing plate with a back plate, a rectangular non-aqueous electrolyte secondary battery having the same configuration as described in Example 1 is assembled. The average value of the amount of swelling and the coefficient of variation of swelling are determined in the same manner as described in Example 1, and the results are shown in Table 1 below.
[0045]
[Table 1]

[0046]
As is clear from Table 1, the secondary batteries of Examples 1 to 3 using an elastic body having a sealing cross-section having a shape different from that of the vent hole and having an area larger than the opening area of the vent hole are charged and stored at high temperature. It turns out that the swelling of time is small compared with Comparative Examples 1-2. In particular, in the secondary batteries of Examples 1 and 2 in which the minimum passing length of the sealing cross section is larger than the maximum passing length of the gas vent hole, the fluctuation coefficient of the swelling indicating the degree of swelling is as small as 10%. .
[0047]
On the other hand, the secondary battery of Comparative Example 1 in which the shape of the sealing cross section is the same as that of the gas vent hole and the secondary battery of Comparative Example 2 having a configuration in which a flat rubber is pressure-bonded to the gas vent hole are swollen. The amount was large and the variation was large.
[0048]
【The invention's effect】
As described above in detail, according to the present invention, it is possible to provide a non-aqueous electrolyte secondary battery in which swelling of the outer can at the time of high-temperature storage is suppressed.
[Brief description of the drawings]
FIG. 1 is a partially exploded perspective view showing a prismatic nonaqueous electrolyte secondary battery which is an embodiment of a nonaqueous electrolyte secondary battery according to the present invention.
2 is a cross-sectional view showing a main part of the secondary battery of FIG. 1;
3 is a cross-sectional view taken along line III-III in FIG.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 ... Exterior can, 2 ... Electrode group, 4 ... Sealing plate, 5 ... Negative electrode terminal, 6 ... Insulating member, 9 ... Depression part, 10 ... Degassing hole, 11 ... Elastic body, 12a ... Large diameter surface, 12b ... Small diameter Surface, 13 ... back plate.

Claims (3)

An outer can,
An electrode group housed in the outer can and including a positive electrode and a negative electrode;
A non-aqueous electrolyte held in the electrode group;
A sealing plate disposed in the opening of the outer can;
A vent hole opened in the outer can or the sealing plate;
An elastic body having a sealing cross-section having an area larger than the opening area of the gas vent hole in a shape different from the gas vent hole;
The non-aqueous electrolyte secondary battery, wherein the elastic body is inserted into the gas vent hole, and the entire peripheral surface of the sealing cross section of the elastic body is in contact with the inner surface of the gas vent hole in a compressed state. .   The nonaqueous electrolyte secondary battery according to claim 1, wherein a minimum passing length of the sealing cross section is longer than a maximum passing length of the gas vent hole. The elastic body has a truncated cone structure in which a part of the peripheral surface is provided with a planar region by cutting out a part of the peripheral surface, and one end surface of the elastic body has the opening area of the gas vent hole 3. The large-diameter surface having a larger area, and the other end surface of the elastic body is a small-diameter surface having an area smaller than the opening area of the vent hole . Non-aqueous electrolyte secondary battery.

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