JP5923431B2 - Lithium ion secondary battery - Google Patents

Description

  The present invention relates to a lithium ion secondary battery, for example, a lithium ion secondary battery mounted on a vehicle or the like.

  Lithium ion secondary batteries have a higher energy density than other secondary batteries, and so far have been used mainly in portable electronic devices such as digital cameras, notebook computers, and mobile phones.

  In recent years, research and development of large-sized lithium ion secondary batteries for electric vehicles and power storage have been actively promoted in order to cope with environmental problems. For example, in the automobile field, research and development of an electric vehicle using a motor driven by a lithium ion secondary battery as a power source and a hybrid electric vehicle using both an internal combustion engine and a motor are underway. Some electric vehicles have already been put into practical use.

  By the way, while the lithium ion secondary battery has a high energy density, for example, a large-sized lithium ion secondary battery mounted on a vehicle has a very large energy, and thus high reliability and safety are required. . Here, as a factor that lowers reliability and safety, for example, battery swelling may be mentioned. It is known that this battery swelling is mainly caused by the generation of gas during initial charging and cycling, and the expansion and contraction of the electrode accompanying charging and discharging, in particular, the bending of the wound electrode group due to the expansion and contraction of the negative electrode. It has been.

  As shown in FIG. 7 (a), in a conventional lithium ion secondary battery, between the electrode group P in which the positive electrode and the negative electrode are wound in a flat shape via a separator during discharge and the inner wall surface Ka of the battery can K In particular, a gap G is provided between the flat portion Pa of the electrode group P and the inner wall surface Ka of the battery can K. Therefore, the electrode group P that expands at the time of charging does not have a binding force from the outside until it contacts the battery can K, and the electrode group P, particularly the flat portion Pa of the electrode group P that is difficult to apply tension when the electrode is wound. Deflection due to expansion occurs. And after repeating charging / discharging, as shown in FIG.7 (b), bending will remain in the electrode group P, especially the plane part Pa of the electrode group P. FIG.

  If gas is generated at the time of initial charge or at the time of cycling, for example, the gas may be interposed between the electrodes, resulting in an increase in resistance or depletion of the electrolyte, which may deteriorate the cycle characteristics of the battery. In addition, when the electrode group is bent, the distance between the electrodes is increased at the bent portion, and the smooth battery reaction may be hindered, thereby reducing the cycle characteristics of the battery. Furthermore, the distance between the electrodes becomes non-uniform due to the occurrence of bending of the electrode group, and there is a possibility that metal lithium may be deposited in a part where the charge is locally excessive, which may affect the safety of the battery. There is also.

  For such problems, Patent Documents 1 to 4 disclose techniques for improving the reliability and safety of secondary batteries.

JP 2006-107742 A Japanese Patent No. 4789854 International Publication No. 2010/086911 JP 2004-259485 A

  According to the secondary batteries disclosed in Patent Documents 1 and 2, by providing a gap or a looseness between the electrodes at the corners of the electrode group, the deflection of the electrode group during expansion can be suppressed. Swelling can be suppressed and deterioration of cycle characteristics can be suppressed.

  Moreover, according to the secondary battery disclosed in Patent Document 3, the gap between the end portion in the major axis direction (corner end portion) of the electrode group and the inner side surface on the short side of the battery container is set in the major axis direction of the electrode group. By defining the relationship between the length of the electrode and the elongation at break of the positive electrode, the expanded electrode group can be prevented from coming into contact with the inner surface of the battery container, and the electrode group accompanying the expansion and contraction of the negative electrode can be suppressed. Generation | occurrence | production of buckling can be suppressed and the fall of cycling characteristics can be suppressed.

  Further, according to the secondary battery disclosed in Patent Document 4, by defining the relationship between the inner dimension of the battery container corresponding to the minor axis of the electrode group and the minor axis of the electrode group in a fully charged state, The compressive force of the separator when the electrode group is accommodated in the battery container and charged can be reduced, a short circuit between the electrodes can be suppressed, and high volume energy can be secured.

  However, in the secondary batteries disclosed in Patent Documents 1 and 2, there is a problem that it is difficult to suppress the bending at the time of expansion of the electrode group only by a gap provided between the electrodes of the corner portion, There is a problem in that it is difficult to provide a precise gap between the electrodes at the corners.

  Further, in the secondary battery disclosed in Patent Document 3, the negative electrode expansion and the electrode group deflection, particularly the negative electrode expansion and the electrode group deflection in the flat portion of the electrode group, the corner end portion of the electrode group and the battery There is a problem that it is difficult to suppress only by a gap with the inner side surface on the short side of the container.

  Furthermore, in the secondary battery disclosed in Patent Document 4, the contraction of the electrode that occurs at the time of discharge is not considered, and the bending of the electrode group when charging and discharging are repeated may not be sufficiently suppressed. There is a problem that there is.

  The present invention has been made in view of the above-mentioned problems, and the object of the present invention is to expand and contract electrodes due to charge and discharge that cause battery expansion and cycle deterioration, in particular, electrodes due to expansion and contraction of the negative electrode. An object of the present invention is to provide a lithium ion secondary battery having high reliability and safety by suppressing bending of the group, suppressing deterioration of cycle characteristics and precipitation of metallic lithium.

  In order to solve the above-described problems, a lithium ion secondary battery according to the present invention includes an electrode group in which a positive electrode and a negative electrode are wound in a flat shape through a separator, a battery container that stores the electrode group, A lithium ion secondary battery having a non-aqueous electrolyte injected into the battery container, and when the direction toward the opposing surfaces of the planar portion of the electrode group is the thickness direction of the electrode group, The ratio of the outer dimension in the thickness direction during discharge of the electrode group housed in the battery container to the inner dimension in the thickness direction of the battery container before housing the electrode group is in the range of 1.01 to 1.03, and The expansion coefficient in the thickness direction at the time of full charge with respect to the time of discharge of the electrode group accommodated in the battery container is in the range of 1.01 to 1.04.

  According to the present invention, it is possible to suppress the expansion and contraction of the electrode accompanying charging and discharging, in particular the expansion and contraction of the negative electrode, the deflection of the electrode group, it is possible to suppress the deterioration of the cycle characteristics and the deposition of metallic lithium, High reliability and safety can be ensured.

  Problems, means, and effects other than those described above will become apparent from the following description of embodiments.

1 is an overall perspective view showing the appearance of an embodiment of a lithium ion secondary battery according to the present invention. The disassembled perspective view which decomposes | disassembles and shows the lithium ion secondary battery shown in FIG. The disassembled perspective view which shows the electrode group shown in FIG. 2 in the state which expand | deployed one part. The flowchart explaining the preparation process of the lithium ion secondary battery shown in FIG. The longitudinal cross-sectional view which shows typically the internal structure of the lithium ion secondary battery shown in FIG. The figure which shows the electrode group expansion coefficient and electrode group thickness ratio of each test body. It is sectional drawing which shows typically the internal structure of the conventional lithium ion secondary battery, (a) is a figure which shows the internal structure at the time of discharge, (b) is a figure which shows the internal structure after repeating charging / discharging. .

  Hereinafter, embodiments of a lithium ion secondary battery according to the present invention will be described with reference to the drawings.

  FIG. 1 shows the appearance of an embodiment of a lithium ion secondary battery according to the present invention.

  The illustrated lithium ion secondary battery 20 includes a battery can 11 and a battery lid 9, and an electrode group 19 (see FIG. 2) that is a power generator is housed inside the battery can 11, and an upper portion of the battery can 11. The opening is sealed and sealed with a battery lid 9. The battery can 11 and the battery lid 9 are joined by laser welding, and the battery can 11 and the battery lid 9 constitute a rectangular battery container 12.

  The battery lid 9 is provided with a negative electrode external terminal 7, a positive electrode external terminal 8, and a liquid injection hole 10. The liquid injection hole 10 is sealed by joining a liquid injection stopper (not shown) by laser welding. ing.

  FIG. 2 is an exploded view of the lithium ion secondary battery shown in FIG.

  As shown in the figure, a negative electrode external terminal 7 and a positive electrode external terminal 8 are connected in advance to a battery lid 9 provided with a liquid injection hole 10, and a negative electrode current collector plate 5 is connected to each of the negative electrode external terminal 7 and the positive electrode external terminal 8. The positive electrode current collector plate 6 is connected, the negative electrode external terminal 7 and the negative electrode current collector plate 5 are electrically connected, and the positive electrode external terminal 8 and the positive electrode current collector plate 6 are electrically connected.

  Further, the electrode group 19 is formed by winding the positive electrode 1 and the negative electrode 2 in a flat shape around the winding axis L via the separators 3 and 4 (see FIG. 3), and the cross section is substantially semicircular. It has a pair of curved parts 19a and 19b which oppose each other, and a flat part 19c formed between the curved parts 19a and 19b. The electrode group 19 has a negative foil exposed portion (negative electrode uncoated portion) 2a and a positive foil exposed portion (positive electrode uncoated portion) 1a in which the metal foil is exposed at the end in the winding axis L direction, The negative electrode uncoated portion 2a is joined to the negative electrode current collector plate 5 by ultrasonic welding, and the positive electrode uncoated portion 1a is joined to the positive electrode current collector plate 6 by ultrasonic welding. Thus, the electrode group 19 to which the battery lid 9 and the like are attached via the negative electrode current collector plate 5 and the positive electrode current collector plate 6 is inserted into the battery can 11 from the one curved portion 19b side, and the other curved portion 19a. The battery can 11 is housed in the battery can 11 so that the side is the upper opening side of the battery can 11.

  A non-aqueous electrolyte in an amount capable of infiltrating the entire electrode group 19 is injected into the rectangular battery container 12 through the injection hole 10, and the injection hole 10 is sealed with an injection stopper (not shown). The battery case 12 is sealed by being stopped.

  FIG. 3 shows the electrode group shown in FIG. 2 in a partially expanded state. FIG. 3 shows a state before joining the uncoated portions of the positive electrode and the negative electrode to the negative electrode current collector plate 5 and the positive electrode current collector plate 6.

  As shown in the drawing, the electrode group 19 has a positive electrode coating portion 1b having an active material layer formed on the surface of the positive electrode foil and a positive electrode foil having a constant width exposed at one end of the positive electrode foil in the winding axis L direction. A positive electrode 1 having a positive electrode uncoated portion 1a, a negative electrode coated portion 2b having an active material layer formed on the surface of the negative electrode foil, and a negative electrode having a constant width at the other end in the winding axis L direction of the negative electrode foil A negative electrode 2 having a negative electrode uncoated portion 2a from which the foil is exposed. In the electrode group 19, the positive electrode 1 and the negative electrode 2 are wound through the separators 3 and 4 so that the positive electrode uncoated portion 1a and the negative electrode uncoated portion 2a are arranged on the opposite sides in the winding axis L direction. It is formed by winding around L in a flat shape.

  FIG. 4 illustrates a manufacturing process of the lithium ion secondary battery shown in FIG. The manufacturing process of the lithium ion secondary battery shown in the figure mainly includes an electrode manufacturing process (S1) and a battery assembly process (S2).

  The electrode manufacturing step (S1) mainly comprises a kneading step (S11), a coating step (S12), a pressing step (S13), and a slitting step (S14). In the kneading step (S11), the active material, the conductive auxiliary agent and the binder were mixed at a predetermined weight ratio, and a dispersion solvent was added thereto and kneaded to adjust to a predetermined solid content concentration and viscosity. Make a slurry. In the coating step (S12), the slurry is applied on both sides of a metal foil having a predetermined thickness by a predetermined width and a predetermined weight, and then only the solvent is removed by drying, whereby the electrode after coating is formed. Make it. In the pressing step (S13), the post-coating electrode having a predetermined electrode density is produced by compressing the post-coating electrode to a predetermined thickness by a roll press. In the slitting step (S14), the post-press electrode is cut so as to have a predetermined coated part width and a predetermined uncoated part width, thereby producing an original electrode fabric.

Specifically, in the positive electrode 1, a lithium transition metal composite oxide as a positive electrode active material, scaly graphite as a conductive additive, and polyvinylidene fluoride (PVDF) as a binder are in a weight ratio. 85: 10: 5 was mixed, and N-methylpyrrolidone (NMP) as a dispersion solvent was added thereto and kneaded to prepare a slurry. The slurry was applied to both sides of an aluminum foil having a thickness of 20 μm. Apply. Thereafter, by drying, pressing, and cutting, a positive electrode raw material having a positive electrode coating portion 1b width of 80 mm, a coating amount of 130 g / m ² , and an electrode length of 4 m is produced. Here, the positive electrode uncoated part 1a where the aluminum foil is exposed is continuously formed at one end portion in the longitudinal direction of the aluminum foil of the positive electrode original fabric, and the positive electrode uncoated part 1a is formed as the positive electrode current collector plate. The positive lead connected to 6 is used.

Further, in the negative electrode 2, graphite carbon powder as a negative electrode active material and PVDF as a binder are mixed, and NMP as a dispersion solvent is added thereto and kneaded to prepare a slurry. Apply to both sides of 10μm copper foil. Thereafter, by drying, pressing and cutting, a negative electrode raw material having a negative electrode coating portion 2b width of 84 mm, a coating amount of 70 g / m ² and an electrode length of 4.4 m is produced. Here, the negative electrode uncoated part 2a where the copper foil is exposed is continuously formed on one end in the longitudinal direction of the copper foil of the negative electrode original fabric, and the negative electrode uncoated part 2a is formed as the negative electrode current collector plate. 5 is a negative electrode lead connected to 5.

  The battery assembly process (S2) mainly includes a winding process (S21), a current collector plate welding process (S22), a can insertion process (S23), a can welding process (S24), and a liquid injection process (S25). ing. In the winding step (S21), the positive electrode raw material and the negative electrode original material manufactured in the electrode manufacturing step (S1) are used with a plate-shaped winding shaft core through a separator so that the two electrodes do not directly contact each other. To produce a flat electrode group. Here, the positive electrode uncoated portion 1a and the negative electrode uncoated portion 2a are opposite ends in the winding axis L direction of the electrode group while controlling meandering so that the end surface of the electrode and the end surface of the separator are in a predetermined position. The positive electrode raw material and the negative electrode original material are wound so as to be arranged in the part. In the current collector plate welding step (S22), each of the positive electrode uncoated portion 1a and the negative electrode uncoated portion 2a disposed at the opposite ends in the winding axis L direction of the electrode group is provided with the positive electrode current collector plate 6 And the negative electrode current collector plate 5 are joined by ultrasonic welding. Note that the positive electrode current collector plate 6 and the negative electrode current collector plate 5 are respectively connected to the positive electrode external terminal 8 and the negative electrode external terminal 7 in advance at the portion of the battery lid 9. In the can insertion step (S23) and the can welding step (S24), the electrode group 19 to which the battery lid 9 and the like are attached is inserted into the battery can 11 via the positive electrode current collector plate 6 and the negative electrode current collector plate 5, and the battery The lid 9 and the battery can 11 are joined by laser welding. In the liquid injection step (S25), a predetermined amount of non-aqueous electrolyte is injected into the battery container 12 including the battery cover 9 and the battery can 11 through the liquid injection hole 10 provided in the battery cover 9. A battery stopper 12 (not shown) is joined to the liquid injection hole 10 by laser welding to seal the battery container 12.

Specifically, a flat electrode group is produced by winding the positive electrode 1 and the negative electrode 2 through a polyethylene microporous separator 3 and 4 having a width of 90 mm and a thickness of 30 μm so that the two electrodes are not in direct contact with each other. To do. Here, the positive electrode 1, the negative electrode 2, and the separators 3, 4 are all extended by applying a load of 10 N in the longitudinal direction so that the end surfaces of the positive electrode 1, the negative electrode 2 and the end surfaces of the separators 3, 4 are in a predetermined position. The positive electrode 1 and the negative electrode 2 are wound while controlling meandering, and one or more polypropylene microporous separators 3 and 4 are disposed in the center of the electrode group. Further, the positive electrode 1 and the negative electrode 2 are wound so that the positive electrode uncoated portion 1a and the negative electrode uncoated portion 2a are arranged at opposite ends in the winding axis L direction of the electrode group. Next, the positive electrode current collector plate 6 and the negative electrode current collector plate 5 are joined to each of the positive electrode uncoated portion 1a and the negative electrode uncoated portion 2a by ultrasonic welding. The electrode group 19 to which the battery lid 9 and the like are attached is inserted into a battery can 11 made of aluminum and having a plate thickness of about 1 mm, and the battery lid 9 and the battery can 11 are joined by laser welding. Thereafter, nonaqueous electrolysis in which lithium hexafluorophosphate (LiPF ₆ ) was dissolved at a concentration of 1 mol / l in a mixed solution in which ethylene carbonate (EC) and dimethyl carbonate (DMC) were mixed at a volume ratio of 1: 2. The liquid is injected into the battery container 12 through the injection hole 10 to produce a rectangular lithium ion secondary battery.

  FIG. 5 schematically shows the internal configuration of the lithium ion secondary battery shown in FIG. In FIG. 5, a restraining jig 13 that imparts a restraining force to the side surface of the battery can 11 is also shown.

  As shown in the figure, the flat electrode group 19 housed in the rectangular battery case 12 has an outer surface 19ca, 19cb of the flat surface portion 19c when the lithium ion secondary battery 20 is discharged and charged. The direction of the inner wall surface of the can 11, more specifically, of the inner wall surface of the battery can 11 toward the outer surfaces 19 ca and 19 cb facing each other of the flat portion 19 c of the electrode group 19 (thickness direction of the electrode group 19, arrow in the figure) The inner wall surfaces 11a and 11b in the (D direction) contact. That is, the electrode group 19, particularly the planar portion 19 c of the electrode group 19, is always pressed from the outside in the thickness direction by the battery can 11 or the like and is given a restraining force. Expansion and contraction in the thickness direction of the group 19 are suppressed, and occurrence of bending of the electrode group 19 is suppressed. Further, the expansion rate in the thickness direction of the electrode group at the time of full charge with respect to the discharge of the electrode group 19 is defined within a predetermined range. The occurrence of is suppressed. Note that a gap G is provided between the outer surfaces 19aa, 19ba of the curved portions 19a, 19b of the electrode group 19 and the inner wall surface of the battery can 11, and even if the electrode expands greatly with charging, The electrode group 19 is deformed in the direction of the curved portions 19a and 19b, and the increase in stress of the electrode group 19 and the swelling in the thickness direction of the battery container 12 are alleviated.

  In the present embodiment, the case where PVDF is used as the binder in the positive electrode 1 and the negative electrode 2 has been described. For example, polytetrafluoroethylene, polyethylene, polystyrene, polybutadiene, butyl rubber, nitrile rubber, styrene / butadiene rubber, Polymers such as polysulfide rubber, nitrocellulose, cyanoethyl cellulose, various latexes, acrylonitrile, vinyl fluoride, vinylidene fluoride, propylene fluoride, chloroprene fluoride, and mixtures thereof may be used.

In the present embodiment, the case where a liquid obtained by dissolving LiPF _{6 in} a mixed solution of EC and DMC is used as a nonaqueous electrolytic solution. However, a general lithium salt is dissolved in an organic solvent as an electrolyte. A non-aqueous electrolyte may be used. Here, examples of the electrolyte include LiClO ₄ , LiAsF ₆ , LiBF ₄ , LiB (C ₆ H ₅ ) ₄ , CH ₃ SO ₃ Li, CF ₃ SO ₃ Li and the like, and mixtures thereof. Is, for example, propylene carbonate, ethylene carbonate, 1,2-dimethoxyethane, 1,2-diethoxyethane, γ-butyrolactone, tetrahydrofuran, 1,3-dioxolane, 4-methyl-1,3-dioxolane, diethyl ether, sulfolane , Methyl sulfolane, acetonitrile, propiontonyl and the like, and mixed solvents in which two or more of these are mixed at an appropriate mixing ratio.

[Experiment and results of measuring the battery swelling and cycle capacity retention rate of a lithium ion secondary battery using a test specimen]
The present inventors produced 12 types of test bodies (Examples 1 to 8 and Comparative Examples 1 to 4) in which the electrode group expansion coefficient and the electrode group thickness ratio were changed, and before and after the initial charge for each test body. The battery swelling and the cycle capacity retention rate after 1000 cycles were measured. In addition, each test body was produced based on the square lithium ion secondary battery of embodiment mentioned above.

  In addition, the battery swelling of each specimen is measured by measuring the outer dimension of the battery container in the thickness direction (in the direction of arrow D in FIG. 5) before and after the initial charging with a micrometer, and the outer dimension of the battery container in the thickness direction before the initial charging. The increase rate of the outer dimension in the thickness direction of the battery container after the initial charge was measured. When the battery container was curved and deformed in the thickness direction, the maximum value of the outer dimension in the thickness direction of the battery container was measured. In addition, the cycle capacity maintenance rate of each specimen is the ratio of the discharge capacity after 1000 cycles to the initial discharge capacity by measuring the initial discharge capacity and the discharge capacity after 1000 cycles by repeating charge and discharge in a predetermined environment for 1000 cycles. Was measured.

  Here, the electrode group expansion coefficient is an expansion coefficient in the thickness direction of the electrode group at the time of full charge with respect to the discharge time of the electrode group housed in the battery container, and the electrode group thickness ratio is before the electrode group is housed. It is the ratio of the outer dimension in the thickness direction at the time of discharge of the electrode group accommodated in the battery container with respect to the inner dimension (design value of the inner dimension) in the thickness direction of the battery container. In addition, the outer dimensions in the thickness direction at the time of discharge or full charge of the electrode group accommodated in the battery container for calculating the electrode group expansion rate and the electrode group thickness ratio are determined for each test body at the time of discharge and full charge. X-rays were transmitted and measured.

[Results of measuring the battery swelling and cycle capacity retention rate of the lithium ion secondary battery with the test specimen]
Table 1 shows the measurement results of the electrode group expansion coefficient, the electrode group thickness ratio, the battery expansion, and the cycle capacity retention ratio of each test body (Examples 1 to 8, Comparative Examples 1 to 4). Moreover, FIG. 6 shows the electrode group expansion coefficient and the electrode group thickness ratio of each test body (Examples 1 to 8, Comparative Examples 1 to 4). Here, the criterion for battery swelling is 7.5% or less due to restrictions on the binding force in the thickness direction of the secondary battery due to charge / discharge and restrictions on the outer dimension in the thickness direction of the battery container after the initial charge, etc. The criterion for rate was 90% or more from the viewpoint of reliability.

[Table 1]

  As shown in Table 1 and FIG. 6, Comparative Examples 1 and 3 (electrode group thickness ratio (thickness at the time of discharge of the electrode group housed in the battery container relative to the inner dimension in the thickness direction of the battery container before housing the electrode group) If the ratio of the outer dimensions in the direction is smaller than 1.01, the electrode group housed in the battery container, in particular, the electrode group during discharge cannot be given sufficient restraint force, and the electrode group is bent. It was confirmed that the cycle capacity retention rate decreased. In Comparative Example 2 (electrode group thickness ratio is greater than 1.03), it was confirmed that the size of the battery container relative to the electrode group during discharge was reduced, the electrode group was bent, and the battery swollen.

  Further, when the electrode density of the negative electrode is increased, the electrode group expansion coefficient (expansion coefficient in the thickness direction of the electrode group at the time of full charge with respect to the discharge of the electrode group accommodated in the battery container) increases, and Comparative Example 4 (electrode group) When the expansion coefficient is larger than 1.04), it was confirmed that the size of the battery container with respect to the electrode group at the time of full charge is reduced, the electrode group is bent, and the battery swelling is increased.

  On the other hand, in Examples 1 to 8 (the electrode group thickness ratio is in the range of 1.01 to 1.03 and the electrode group expansion coefficient is in the range of 1.01 to 1.04), the discharge is accommodated in the battery case or is fully charged. Appropriate pressing force (binding force) can be applied to the electrode group during charging, battery swelling can be suppressed, battery swelling is 7.5% or less, and cycle capacity maintenance rate is 90%. That was confirmed.

  From this experimental result, in the prismatic lithium ion secondary battery of the above-described embodiment, when the electrode group thickness ratio is in the range of 1.01 to 1.03 and the electrode group expansion coefficient is in the range of 1.01 to 1.04, It has been demonstrated that battery swelling is suppressed and a high cycle capacity maintenance rate can be secured.

[Results of measuring the electrode density of the negative electrode of the lithium ion secondary battery using the specimen]
The present inventors performed electrode density measurement of the negative electrode of each test body of Examples 1 to 8 described above. As a result, it was confirmed that the electrode density of the negative electrode of each test body of Examples 1 to 8 was in the range of 1.30 g / cm ³ to 1.45 g / cm ³ . Therefore, when the electrode density of the negative electrode is lower than 1.30 g / cm ³ , the battery capacity is reduced and the energy density is lowered, and sufficient binding force is applied to the electrode group during discharge or charge. It was confirmed that the electrode capacity could be bent and the cycle capacity retention rate could be reduced. In addition, when the electrode density of the negative electrode is higher than 1.45 g / cm ³ , the size of the battery container relative to the electrode group at the time of full charge may be reduced, and the electrode group may be bent and the battery swelling may increase. confirmed.

  In addition, the present inventors set the ratio of the outer dimension in the thickness direction at the time of electrode preparation of the electrode group to the inner dimension in the thickness direction of the battery container before housing the electrode group within the range of 0.98 to 1.00, It has been confirmed that each of the specimens of Examples 1 to 8 described above can be produced.

That is, the electrode density of the negative electrode is within the range of 1.30 g / cm ³ to 1.45 g / cm ³ , and the outer electrode in the thickness direction at the time of electrode preparation of the electrode group with respect to the inner dimension in the thickness direction of the battery container before housing the electrode group The present inventors confirmed that the electrode group expansion ratio can be in the range of 1.01 to 1.04 and the electrode group thickness ratio can be in the range of 1.01 to 1.03 by setting the size ratio in the range of 0.98 to 1.00. ing.

  In addition, this invention is not limited to above-described embodiment, Various deformation | transformation forms are included. For example, the above-described embodiment has been described in detail for easy understanding of the present invention, and is not necessarily limited to one having all the configurations described. Further, a part of the configuration of an embodiment can be replaced with the configuration of another embodiment, and the configuration of another embodiment can be added to the configuration of an embodiment. In addition, it is possible to add, delete, and replace other configurations for a part of the configuration of each embodiment.

1 Positive electrode 1a Positive electrode uncoated part (positive foil exposed part)
1b Positive electrode coated part 2 Negative electrode 2a Negative electrode uncoated part (negative foil exposed part)
2b Negative electrode coating part 3, 4 Separator 5 Negative electrode current collector plate 6 Positive electrode current collector plate 7 Negative electrode external terminal 8 Positive electrode external terminal 9 Battery lid 10 Injection hole 11 Battery can 12 Battery container 13 Restraint jig 19 Electrode group 20 Lithium ion 2 Secondary battery G Electrode group and battery can gap L Winding axis

Claims (2)

A lithium ion secondary battery having an electrode group in which a positive electrode and a negative electrode are wound in a flat shape with a separator interposed therebetween, a battery container containing the electrode group, and a non-aqueous electrolyte injected into the battery container There,
The negative electrode is composed of graphite-based carbon powder as a negative electrode active material, the electrode density of the negative electrode is in the range of 1.30 g / cm ³ to 1.45 g / cm ³ , and the opposing surfaces of the planar portion of the electrode group In the thickness direction at the time of discharge of the electrode group accommodated in the battery container with respect to the inner dimension in the thickness direction of the battery container before accommodating the electrode group when the direction toward the electrode group is the thickness direction of the electrode group The ratio of the outer dimensions is in the range of 1.01 to 1.03, and the expansion coefficient in the thickness direction at the time of full charge with respect to the discharge time of the electrode group accommodated in the battery container is in the range of 1.01 to 1.04. A featured lithium ion secondary battery.   The lithium ion secondary battery according to claim 1, wherein the electrode group is pressed in the thickness direction by the battery container during use.

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