JP4479236B2 - Non-aqueous electrolyte secondary battery - Google Patents

Description

  The present invention relates to a non-aqueous electrolyte secondary battery such as a lithium ion secondary battery, and more particularly to a non-aqueous electrolyte secondary battery having an improved negative electrode plate and separator.

  In a non-aqueous electrolyte secondary battery represented by a lithium ion secondary battery, a generally well-known structure includes a positive electrode plate in which an active material is coated on a strip-shaped current collector, and a strip-shaped current collector. A strip-shaped separator is arranged between a negative electrode plate coated with an active material on the body, and an electrode plate group wound in a spiral shape is provided. The electrode plate group is housed in a metal container together with an electrolytic solution.

  In some conventional non-aqueous electrolyte secondary batteries, the separator is made of two or more materials having different melting points. Specifically, among the two separators facing the negative electrode plate, one is composed of a microporous thin film separator and the other is composed of a nonwoven fabric separator. A device that prevents thermal runaway has been proposed (Patent Document 1).

  Apart from this, in the alkaline storage battery, among the two separators facing the negative electrode plate, one separator is composed of a microporous thin film separator and the other one is a non-woven separator. It has been proposed that the quick charge characteristics are improved by being disposed on a surface having a low capacity density or a surface having a high capacity density of the negative electrode plate.

However, such an alkaline storage battery is generally a battery that does not require special consideration for overcharging due to the function of the battery, and therefore the configuration described above, that is, the nonwoven fabric separator has a capacity density of the positive electrode plate. Even when the configuration is arranged on a low surface or a surface having a high capacity density of the negative electrode plate, it is different from the overcharge countermeasure of the nonaqueous electrolyte secondary battery of the present invention. (Patent Document 2).
JP 2002-025526 A Japanese Patent No. 3436058

  As described above, the separator in the conventional lithium ion secondary battery is composed of two or more materials having different melting points. Specifically, one of the two separators facing the negative electrode plate is fine. Another porous thin film separator was composed of a nonwoven fabric separator. Therefore, during overcharge, as the temperature rises, the pores that are the ion conduction path of the microporous thin film separator melt and collapse, and ions can propagate between the positive electrode plate and the negative electrode plate that sandwich the microporous thin film separator. It becomes so-called shutdown that does not function as a battery. However, in the nonwoven fabric separator having a high melting point, pores that are ion conduction paths are still retained. In this portion, discharge occurs between the positive electrode plate and the negative electrode plate, and the overcharged state of the positive electrode plate and the negative electrode plate does not proceed. This can prevent abnormal temperature rise and thermal runaway. However, in the overcharge cycle in which the end-of-charge voltage is 4.23 to 4.25 V, there is a problem that a voltage failure occurs.

  The present invention solves such a conventional problem, and even when overcharged, it is possible to prevent overcharge without falling into an overcharged state by a mechanism different from the conventional one. An object of the present invention is to provide a highly reliable non-aqueous electrolyte secondary battery capable of preventing the occurrence of voltage failure even when the cycle is repeated.

In order to solve the above problems, a non-aqueous electrolyte secondary battery according to the present invention includes a positive electrode plate in which an active material is applied to a strip-shaped current collector, and an active material applied to the strip-shaped current collector. A non-aqueous electrolyte secondary battery comprising a group of electrode plates wound in a spiral shape with a strip-shaped separator disposed between and a negative electrode plate, the electrode plate group being housed in a metal container together with an electrolyte. The separator has a configuration in which the nonwoven fabric part is connected to a part of the microporous thin film part along the long or short direction, and the negative electrode plate per unit area facing the microporous thin film part of the separator. When the weight of the active material is 100, the active material weight per unit area facing the nonwoven fabric portion is 105 to 120, and the area of the nonwoven fabric portion of the separator is 1 of the total area of the separator used in the electrode plate group configuration. It was 50%, the microporous membrane unit, polypropylene Or consists of polyethylene alone or a polyolefin polymer of a combination of these, nonwoven portion, polybutylene terephthalate nonwoven or those that are non-woven fabric made of glass fibers or cellulose fibers.

  As a result, in the case of overcharging, an electronic conduction path is formed by lithium metal deposited on the surface of the negative electrode plate in the non-woven fabric portion of the separator between the positive electrode plate and the negative electrode plate. Since the overcharge state stops, overcharge can be prevented.

  Furthermore, even when the overcharge cycle is repeated, the weight of the negative electrode active material per unit area of the negative electrode plate in the portion facing the nonwoven fabric portion of the separator is increased by 5 to 20% of that facing the microporous thin film portion. Thereby, since the charging load of the negative electrode plate in the portion facing the nonwoven fabric portion can be reduced, the occurrence of voltage failure can be prevented and high reliability can be obtained.

  The non-aqueous electrolyte secondary battery of the present invention can prevent overcharge without falling into an overcharge state even in the case of overcharge, and further, even when the overcharge cycle is repeated, Generation | occurrence | production can be prevented and a highly reliable non-aqueous-electrolyte secondary battery can be obtained.

In the non-aqueous electrolyte secondary battery of the present invention, the strip separator has a configuration in which a nonwoven fabric part is connected to a part of a microporous thin film part along the long or short direction, and the negative electrode plate is When the weight of the active material per unit area facing the microporous thin film portion of the separator is 100, the weight of the active material per unit area facing the nonwoven fabric portion is 105 to 120. Furthermore, the area of the nonwoven fabric portion is 1 to 50% of the total area of the separator used for the electrode plate group structure. Thereby, even when the overcharge cycle is repeated, the occurrence of voltage failure can be prevented, high reliability can be obtained, and a high capacity non-aqueous electrolyte secondary battery can be obtained. The microporous thin film portion is made of a polyolefin polymer obtained by combining polypropylene or polyethylene alone or a combination thereof, and the non-woven fabric portion is a non-woven fabric made of polybutylene terephthalate, or a non-woven fabric made of glass fiber or cellulose fiber.

  Therefore, by configuring the nonaqueous electrolyte secondary battery of this embodiment, in the case of overcharging, an electronic conduction path is formed by lithium metal deposited on the surface of the negative electrode plate at the nonwoven fabric portion of the separator between the positive and negative electrodes. When the charging current flows through this path, the overcharge state is substantially stopped, so that overcharge can be prevented.

  Further, when a failure or malfunction of the charging protection circuit of the charger occurs, the charging end voltage becomes 4.25 V at the maximum (normal charging end voltage 4.20 V), and the overcharge cycle is repeated. When the end-of-charge voltage increases from 4.20 V to 4.25 V, the amount of charge electricity increases by 5% or more. Even in such a case, by increasing the weight of the negative electrode active material per unit area of the portion of the negative electrode plate facing the nonwoven fabric portion by 5% or more, the charging load on the negative electrode plate of the portion facing the nonwoven fabric portion can be reduced. it can. As a result, even when the overcharge cycle is repeated, the occurrence of voltage failure can be prevented and the reliability can be improved.

  Further, in this non-aqueous electrolyte secondary battery, the microporous thin film portion and the non-woven fabric portion of the separator are configured in a horizontal stripe shape or a vertical stripe shape, and even when the overcharge cycle is repeated, the occurrence of voltage failure Can be prevented, and the reliability can be improved.

  Examples of the present invention will be described in detail below.

  FIG. 1 shows a longitudinal sectional view of a cylindrical 17500 size lithium ion secondary battery which is an example of an embodiment of the present invention.

  As shown in detail in FIG. 1 and partly in FIG. 2, a positive electrode plate 1 in which a positive electrode active material 1b is applied to a strip-shaped positive electrode current collector 1a, and a negative electrode active material 2b, 2c to a strip-shaped negative electrode current collector 2a. The electrode plate group 4 is formed by spirally winding the electrode plate 2 and the negative electrode plate 2 coated with each other with the separator 3 therebetween, and the electrode plate group 4 is stored in the battery container 5 together with the electrolyte. Has been placed. A positive electrode lead 6 is drawn from the positive electrode plate 1 and welded to a sealing plate 7 provided with a safety valve, and a negative electrode lead 8 is drawn from the negative electrode plate 2 and welded to the bottom of the battery container 5. . Insulating rings 9 are provided at the upper and lower portions of the electrode plate group 4, respectively.

  Below, the structure relevant to the separator 3, the positive electrode plate 1, and the negative electrode plate 2 is demonstrated.

  In the drawings used for the following description, the thickness direction is shown enlarged for easy understanding.

(Example 1)
FIG. 2 shows a schematic cross-sectional view of the laminated state of the separator 3 and the positive and negative electrode plates in Example 1.

As shown in FIG. 2, the strip-shaped negative electrode plate 2 has a length of 420 mm, and negative electrode active materials 2b and 2c are applied to both surfaces of the strip-shaped negative electrode current collector 2a. The strip-shaped positive electrode plate 1 has a length of 390 mm, and the positive electrode active material 1b is applied to both surfaces of the strip-shaped positive electrode current collector 1a.
The length of the separator 3 is 500 mm, and the main thickness is 0. 200 mm corresponding to 40% of the length of the 020 mm polyethylene microporous thin film separator 3 a has a thickness of 0. It is composed of a 040 mm polybutylene terephthalate nonwoven fabric separator 3b.
When the weight per unit area of the negative electrode active material 2b facing the polyethylene microporous thin film separator 3a is 100, the negative electrode plate 2 is made of the negative electrode active material 2c facing the polybutylene terephthalate nonwoven fabric separator 3b. It is applied so that the weight per unit area is 105 and rolled to a certain thickness.

(Example 2)
FIG. 3 shows a schematic cross-sectional view of the laminated state of the separator, the negative electrode plate, and the positive electrode plate in Example 2.

Using the strip-like positive and negative electrode plates described in Example 1,
The length of the separator 3 is 500 mm, and the main thickness is 0. 5 mm corresponding to 1% of the length of the polyethylene microporous thin film separator 3a having a thickness of 0. It is composed of a 040 mm polybutylene terephthalate nonwoven fabric separator 3b.
In the same manner as in Example 1, the negative electrode plate 2 had the weight per unit area of the negative electrode active materials 2b and 2c facing the separators 3a and 3b set to 100/105.

(Example 3)
FIG. 4 shows a schematic cross-sectional view of the laminated state of the separator, the negative electrode plate, and the positive electrode plate in Example 3.

This also uses the strip-like positive and negative electrode plates described in Example 1,
The length of the separator 3 is 500 mm, and the main thickness is 0. 350 mm corresponding to 70% of the length of the polyethylene microporous thin film separator 3a having a thickness of 0. It is composed of a 040 mm polybutylene terephthalate nonwoven fabric separator 3b.
In the same manner as in Example 1, the negative electrode plate 2 had the weight per unit area of the negative electrode active materials 2b and 2c facing the separators 3a and 3b set to 100/105.

(Example 4)
FIG. 5 is a schematic cross-sectional view of the laminated state of the separator, the negative electrode plate, and the positive electrode plate in Example 4.

This also uses the strip-like positive and negative electrode plates described in Example 1,
The length of the separator 3 is 500 mm, and the main thickness is 0. A thickness of 0.2 mm corresponding to 0.5% of the length of the polyethylene microporous thin film separator 3a of 020 mm is 0.5%. It is composed of a 040 mm polybutylene terephthalate nonwoven fabric separator 3b.
In the same manner as in Example 1, the negative electrode plate 2 had the weight per unit area of the negative electrode active materials 2b and 2c facing the separators 3a and 3b set to 100/105.

  Here, the thickness difference between the polybutylene terephthalate nonwoven fabric separator 3b and the polyethylene microporous thin film separator 3a is 0.020 mm, but the strip separator, the negative electrode plate, and the positive electrode plate are alternately stacked and wound in a spiral shape. In some cases, pressure is applied and the difference in thickness between the separators 3a and 3b is negligible. Therefore, as shown in FIGS. 2 to 5, both separators 3 a and 3 b are shown as schematic diagrams having no step.

  In addition, as a method for producing the separator 3, a non-woven separator 3b made of polybutylene terephthalate and a microporous thin film separator 3a made of polyethylene were heated to 150 ° C. along the short direction of the strip-like separator 3, that is, in the form of vertical stripes. And bonded together by heat welding. Apart from this, as a pattern for replacing a part of the polyethylene microporous thin film separator 3a, which is a main component, with the non-woven fabric separator 3b made of polybutylene terephthalate, the same effect can be obtained even in the longitudinal direction of the strip-shaped separator 3, that is, in the form of horizontal stripes. Is obtained. From the viewpoint of mass productivity of the separator 3, it is desirable to bond the microporous thin film separator 3a made of polyethylene and the nonwoven fabric separator 3b made of polybutylene terephthalate in a horizontal stripe shape.

  In the above-described example, the separator 3 facing both sides of the negative electrode plate 2 has been described with respect to the case where a part of the main polyethylene microporous thin film separator 3a is replaced with the polybutylene terephthalate nonwoven fabric separator 3b. Only the separator 3 facing one side of this can obtain substantially the same effect even when a part of the polyethylene microporous thin film separator 3a is replaced with the polybutylene terephthalate nonwoven fabric separator 3b.

  By configuring the lithium ion secondary battery using the configuration of the separator 3 and the positive and negative electrode plates of Examples 1 to 4 above, in the case of overcharging, the positive and negative electrodes sandwiching the polybutylene terephthalate nonwoven fabric separator 3b of the separator 3 Between them, an electronic conduction path is formed by lithium metal deposited in dendritic form on the negative electrode plate surface, and the overcurrent state is effectively stopped by the charging current flowing through this path, preventing overcharge. can do.

  Further, when a failure or malfunction of the charging protection circuit of the charger occurs, the charging end voltage becomes 4.25 V at the maximum (normal charging end voltage 4.20 V), and the overcharge cycle is repeated. When the end-of-charge voltage is increased from 4.20V to 4.25V, the charge electric capacity is increased by 5% or more. In such a case, by increasing the weight of the negative electrode active material per unit area of the negative electrode plate of the portion facing the non-woven fabric separator 3b made of polybutylene terephthalate by 5% or more, the portion facing the non-woven fabric separator 3b made of polybutylene terephthalate The load on the negative electrode plate can be reduced. As a result, even when the overcharge cycle is repeated, the overcharge is not continued, the battery voltage does not rise abnormally, the occurrence of voltage failure can be prevented, and high reliability can be obtained.

  As in Examples 1 to 4 above, 30 lithium ion secondary batteries each comprising a separator and a positive and negative electrode plate were produced.

(Comparative example)
FIG. 6 shows a schematic cross-sectional view of a laminated state of a separator and positive and negative electrode plates used as a comparative example.

As shown in FIG. 6, the strip-shaped negative electrode plate 2 has a negative electrode active material 2c applied to both surfaces of a strip-shaped negative electrode current collector 2a, and all the separators 3 have a length of 500 mm, a thickness of 0. This is a 020 mm polyethylene microporous thin film separator 3a.
The negative electrode active material weight 2c of the negative electrode plate 2 was 105 per unit area. The other components were the same as in Example 1, and 30 were produced.

<Battery evaluation>
The overcharge test and the overcharge cycle test were performed on 30 batteries each of Examples 1 to 4 and Comparative Example described above.

  In the overcharge test, 20 cells were overcharged at an environmental temperature of 20 ° C. and a current value of 0.8 A corresponding to the 1C rate from the charged state, and it was confirmed whether or not the battery generated abnormal heat.

The overcharge cycle test assumes that only the charging control circuit of the charger has failed, uses 10 cells each, charges at a current value of 0.8 A at an environmental temperature of 20 ° C., and the battery voltage reaches 4.25 V. Once reached, charging was continued at a constant voltage until the current value reached 0.04 A, which was 0.05 C. Next, the battery in a charged state is continuously discharged at 20 ° C. at a current value of 0.8 A until the battery voltage reaches 3 V. This charging and discharging is continued as one cycle up to 500 cycles, and then the ambient temperature is 20 ° C. Saved for hours. Subsequent voltage failure was confirmed.

The results are shown in Table 1. In the overcharge test, the batteries of Examples 1 to 3 did not generate abnormal heat. This is because an electron conduction path is formed by lithium metal deposited on the surface of the negative electrode plate between the positive and negative electrodes sandwiching the non-woven fabric separator 3b made of polybutylene terephthalate, and the charge current flows through this path. This is because it stopped.

  However, in the overcharge cycle test, the negative electrode plates of Examples 1 to 4 have an active material weight per unit area facing the polybutylene terephthalate nonwoven fabric separator 3b per unit area facing the polyethylene microporous thin film separator 3a. By making the weight 5% heavier than the active material weight, the voltage failure was drastically reduced. This is because when the end-of-charge voltage increases from 4.20 V to 4.25 V, the charging electric capacity increases by 5% or more, but the negative electrode active material weight per unit area of the negative electrode plate facing the polybutylene terephthalate nonwoven fabric separator 3b is reduced. This is considered to be because by increasing 5% or more, the load on the negative electrode plate in that portion can be reduced.

  From the result of Example 4, when the occupation ratio of the non-woven fabric separator 3b made of polybutylene terephthalate with respect to the total area of the separator 3 used for the electrode plate group structure is smaller than 1%, the non-woven plate separator 3b made of polybutylene terephthalate is sandwiched between the positive and negative electrode plates. A sufficient electron conduction path is not formed, and charging current does not flow through this path, causing abnormal heat generation. Therefore, the occupation ratio of the polybutylene terephthalate nonwoven fabric separator 3b is desirably 1% or more. Further, in the example, the case where the occupation ratio of the polybutylene terephthalate nonwoven fabric separator 3b is 40% has been described. However, even if the occupation ratio is increased up to 50%, substantially the same effect was obtained, so the polybutylene terephthalate nonwoven fabric separator 3b. It can be said that the occupancy of 50% or less is sufficient. From this point of view, it is desirable that the non-woven separator 3b made of polybutylene terephthalate is 1 to 50% of the total area of the separator 3 used in the electrode plate group configuration from both viewpoints of high reliability and high capacity.

Moreover, although the negative electrode plate 2 demonstrated the case where the active material weight 2c per unit area which opposes the nonwoven fabric part of the separator 3 was 105, in the range where the negative electrode active material weight 2c is smaller than 105, at the time of an overcharge The effect of preventing the abnormal rise in temperature and the occurrence of voltage failure during the overcharge cycle cannot be obtained. The negative electrode active material weight 2c can be increased without limitation, but if it is too large, it becomes difficult to roll the negative electrode plate 2 at a constant thickness, and the negative electrode plate 2, the positive electrode plate 1, and the separator 3 are spirally formed. The electrode plate group 4 formed by winding the electrode plate has a problem that the diameter increases and the electrode plate group 4 cannot be inserted into the battery container 5. Therefore, in order to roll the thickness of the negative electrode plate 2 constant, the negative electrode active material weight 2c needs to be 120 or less.
Therefore, the range of the negative electrode active material weight 2c is 105 to 120, and the range of 105 to 110 was desired by the inventors' investigation.

Further, here, the case where the polyethylene microporous thin film separator 3a is used as the microporous thin film separator has been described. However, in addition to the polyethylene microporous thin film separator 3a, it has a large ion permeability and has a predetermined mechanical property. Any material having strength and insulating properties may be used. Moreover, you may have a function which obstruct | occludes a hole at 80 degreeC or more and raises resistance. As the physical properties of the separator 3, the maximum pore diameter is 0.5 μm or less, preferably 0.1 to 0.2 μm, and the Gurley number is 200 to 600 seconds / 100 cm ³ , preferably 250 to 300 seconds / 100 cm ^3. . From the viewpoint of organic solvent resistance and hydrophobicity, it is preferable to use a polyolefin polymer such as polypropylene or polyethylene alone or in combination thereof.

Moreover, although the non-woven fabric separator 3b made of polybutylene terephthalate has been described here as the non-woven fabric separator, other than the non-woven fabric separator 3b made of polybutylene terephthalate, a non-woven fabric made of glass fiber or cellulose fiber may be used. As physical properties of the separator, the fiber diameter is preferably 0.5 to 5.0 μm, preferably 1 to 2 μm, the maximum pore diameter is 2 μm or less, preferably 0.5 to 1 μm, and the Gurley number is preferably ³ to 50 seconds / 100 cm ³ . Is 8 to 10 seconds / 100 cm ³ , and the aspect ratio is 50 or more, preferably 100.

  Moreover, although the case where electrolyte solution was used was demonstrated here, the gel electrolyte which made the polymer material contain electrolyte solution can also be used as electrolyte other than a solution. As the polymer material, for example, a polymer matrix material such as polyethylene oxide, polypropylene oxide, polyvinylidene fluoride and the like, derivatives, mixtures and composites thereof are effective. In particular, a copolymer of vinylidene fluoride and hexafluoropropylene or a mixture of polyvinylidene fluoride and polyethylene oxide is preferable.

  Although the cylindrical 17500 size has been described here as the form of the lithium ion secondary battery, the same effect can be obtained without being restricted by the shape and the battery size.

  Moreover, although the lithium ion secondary battery was demonstrated as a nonaqueous electrolyte secondary battery, the same effect is acquired also in nonaqueous electrolyte secondary batteries, such as magnesium secondary batteries other than a lithium ion secondary battery. Is.

  INDUSTRIAL APPLICABILITY The present invention can be used for a non-aqueous electrolyte secondary battery such as a lithium ion secondary battery in which a positive electrode plate and a negative electrode plate are spirally wound via a separator. By improving the structure, a highly reliable non-aqueous electrolyte secondary battery can be provided.

The longitudinal cross-sectional view of the lithium ion secondary battery in an example which implemented this invention Schematic sectional view of the laminated state of the separator and positive and negative electrode plates in Example 1 of the present invention Schematic sectional view of the laminated state of the separator and positive and negative electrode plates in Example 2 of the present invention Schematic sectional view of the laminated state of the separator and positive and negative electrode plates in Example 3 of the present invention Schematic sectional view of the laminated state of the separator and positive and negative electrode plates in Example 4 of the present invention Schematic sectional view of the laminated state of the separator and positive and negative electrode plates in the comparative example

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Positive electrode plate 1a Positive electrode current collector 1b Positive electrode active material 2 Negative electrode plate 2a Negative electrode current collector 2b Negative electrode active material 2c Negative electrode active material 3 Separator 3a Polyethylene microporous thin film separator 3b Polybutylene terephthalate nonwoven fabric separator 4 Electrode plate group 5 Container 6 Positive electrode lead 7 Sealing plate 8 Negative electrode lead 9 Insulating ring

Claims (1)

An electrode plate in which a strip-shaped separator is disposed between a positive electrode plate in which an active material is applied to a strip-shaped current collector and a negative electrode plate in which the active material is coated to a strip-shaped current collector, and is wound in a spiral shape A non-aqueous electrolyte secondary battery in which the electrode plate group is housed in a metal container together with an electrolyte, and a strip-shaped separator is formed along the long or short direction of the microporous thin film portion. Active material per unit area facing the non-woven fabric part when the weight of the active material per unit area facing the microporous thin film part of the separator is 100 The weight is 105 to 120, the area of the nonwoven fabric portion of the separator is 1 to 50% of the total area of the separator used in the electrode plate group configuration, and the microporous thin film portion is made of polypropylene or polyethylene alone. Or a combination of these Made of a polyolefin polymer, wherein the nonwoven section, polybutylene terephthalate nonwoven fabric or a non-aqueous electrolyte secondary battery which is a nonwoven fabric made of glass fibers or cellulose fibers.