JP2013073794A - Nonaqueous electrolyte secondary battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To suppress locally generated heat originated from a winding end part of a positive electrode of an outermost periphery of a battery and suppress breakage of a portion of case near the winding end part of the positive electrode when heat is rapidly applied to the battery from outside.SOLUTION: The outermost of the electrode grope is arranged so as to be a negative electrode collector exposed part in which a negative electrode active material is not formed, a belt like positive electrode is arranged so that a winding end part in longitudinal direction has active material layer formed on both face of the collector and furthermore, a surface of the winding end part is coated with heat-resistant insulating tape having a softening temperature of 200°C or more.

Description

  The present invention relates to a non-aqueous electrolyte secondary battery, and particularly to a battery having a particularly suitable electrode group structure.

  Conventionally, in a lithium ion secondary battery using a non-aqueous electrolyte, a lithium composite oxide is generally applied to an aluminum foil as a positive electrode active material to form a positive electrode, and a carbonaceous material is applied to a copper foil as a negative electrode active material. The wound body formed by interposing a separator made of a polyethylene microporous membrane or the like between the obtained sheet-like electrodes and winding and laminating them is an external electrode, for example, an external negative electrode It is stored in an iron can.

  Since such lithium ion secondary batteries have characteristics such as high capacity, high voltage, and high output, abnormalities such as a short circuit between the positive electrode and the negative electrode of the battery due to an abnormality in the circuit, etc. Sometimes, in order to prevent the temperature rise of the battery, various protection means such as a temperature fuse, a current fuse, and a PTC element are provided, and a safety valve for preventing an increase in the internal pressure of the battery is provided.

  In Patent Document 1, a positive electrode in which a positive electrode active material layer is formed on both surfaces of a strip-shaped positive electrode current collector and a negative electrode in which a negative electrode active material layer is formed on both surfaces of a strip-shaped negative electrode current collector, A wound body is described that is wound through a separator. Further, the positive electrode has a positive electrode current collector exposed portion where the positive electrode current collector is exposed on both surfaces at one end portion in the length direction, and the negative electrode has a negative electrode current collector on both ends on the length direction. A negative electrode current collector exposed portion exposed from the body, and the positive electrode current collector exposed portion and the negative electrode current collector exposed portion cover at least one circumference of the wound body via a separator. It is described. With this configuration, since the outer periphery of the wound body is covered with the positive electrode current collector exposed portion and the negative electrode current collector exposed portion, when the battery is short-circuited by an external impact, the positive electrode current collector is first The body exposed portion and the negative electrode current collector exposed portion are short-circuited first. In the non-aqueous electrolyte battery having such a structure, the generated heat is diffused due to a short circuit between the exposed portion of the positive electrode current collector and the exposed portion of the negative electrode current collector, so that there is almost no influence on the electrode active material layer. There are few, and it is hard to reach thermal runaway of the whole battery.

  On the other hand, Patent Document 2 describes that safety is significantly improved by disposing a heat-resistant porous layer on the positive electrode sheet side using a separator composed of a heat-resistant porous layer and a shutdown layer. This is because the heat-resistant porous layer suppresses the shrinkage of the separator at the time of a short circuit, so that the current flowing through the short circuit point is minimized and heat generation is suppressed.

  Further, in order to increase heat dissipation to the outside of the battery against heat generation inside the battery, the outermost periphery of the electrode group is a negative electrode current collector, and the negative electrode current collector has a structure in contact with the outer case. Safety is also improved by adopting a structure that easily dissipates heat generated inside the battery.

JP 62-256371 A JP 2000-100408 A

However, various abnormal situations are assumed other than a short circuit between the positive electrode and the negative electrode of the battery due to a circuit abnormality or an external impact. For example, in an unforeseen situation where the battery is dropped into a fire or heated on a hot plate, heat is generated due to an internal short circuit along with a sudden rise due to heat applied from the outside. Increased risk of breakage.

  The reason why the case is damaged will be further described.

  As described above, when the battery is rapidly heated from the outside, the outer separator near the case of the electrode group is first softened by the heat applied from the outside. When the separator on the outer peripheral side was softened, it was found that the separator facing the winding end of the positive electrode, which is under stress, in the electrode group is most susceptible to damage. It was found that when the separator facing the winding end of the positive electrode is damaged, the negative electrode facing the winding end of the positive electrode and the separator is short-circuited, and the battery suddenly generates heat due to Joule heating due to the short circuit. .

  When sudden heat generation occurs locally due to a short circuit starting from the end of winding of the positive electrode, the thermal damage of the case is greatest due to Joule heat generation due to the short circuit near the short circuit, so the end of winding of the positive electrode It was found that the case was prone to breakage starting from a location close to the part.

  The present invention has been proposed in view of the above-described conventional situation, and an object thereof is to provide a non-aqueous electrolyte battery that does not damage the battery case even when the battery is heated.

The non-aqueous electrolyte battery of the present invention includes a positive electrode in which a positive electrode active material layer is formed on a part of both surfaces of a strip-shaped positive electrode current collector, and a negative electrode active material layer on a part of both surfaces of the strip-shaped negative electrode current collector A negative electrode formed with a negative electrode current collector exposed portion in which the negative electrode active material layer is not formed. The belt-like positive electrode has an end portion in the longitudinal direction where an active material layer is formed on both sides of the current collector, and the surface of the end portion in the winding is 18 in accordance with JIS K 7207. It is coated with a heat resistant insulating layer made of a resin having a deflection temperature under load of 200 ° C. or higher in the measurement at a load of 0.6 kg / cm ² .

  The outermost periphery indicates the relationship between the positive electrode and the negative electrode, and a separator or an insulating tape may exist between the negative electrode current collector exposed portion and the battery case.

  In the non-aqueous electrolyte battery according to the present invention, the winding end of the belt-like positive electrode in the longitudinal direction in the wound body is covered with a heat-resistant insulating layer made of a resin having a load deflection temperature of 200 ° C. or higher. Heat generation can be prevented from the winding end end of the positive electrode at the outer periphery as a starting point. As a result, unlike the concentrated short circuit at the winding end end of the positive electrode, a short circuit occurs due to the contraction of the separator over a wider range. Joule heat is distributed over a wide range, and local case thermal damage can be mitigated, and damage to the case can be prevented.

As a material of the heat-resistant insulating layer, from polyimide, polyamideimide, aramid, polyethersulfone, polyetherimide, which is a resin having a deflection temperature under load of 200 ° C. or higher in the measurement under 18.6 kg / cm ² load according to JIS K 7207 It is preferable to use at least one selected from the group consisting of

In the non-aqueous electrolyte battery of the present invention, when a sudden heat is applied to the battery from the outside, damage is caused when the separator facing the winding end of the positive electrode, which is under stress in the outer periphery of the electrode group, is softened. Can suppress local heat generation starting from the winding end of the positive electrode at the outermost periphery of the battery, and can prevent damage to the case near the winding end of the positive electrode. it can.

  Therefore, in the present invention, damage to the battery and influence on the surroundings can be minimized, and a non-aqueous electrolyte battery excellent in safety and reliability can be realized.

The longitudinal cross-sectional view which shows one structural example of the nonaqueous electrolyte battery which concerns on this invention The cross-sectional view which shows the form of the rolling end of the electrode group of the nonaqueous electrolyte battery of this invention

  Embodiments of the present invention will be described below.

  FIG. 1 is a longitudinal sectional view showing a configuration example of a nonaqueous electrolyte battery according to the invention.

  FIG. 2 is a cross-sectional view showing the form of the end of the electrode group of the nonaqueous electrolyte battery of the present invention.

  In this non-aqueous electrolyte battery, an electrode group 30 in which a belt-like positive electrode 10 and a belt-like negative electrode 20 are wound in close contact via a heat-resistant insulating layer 15 as a separator is a cylindrical battery case 40. It is inserted inside.

  As the positive electrode, as shown in FIG. 2, a positive electrode mixture layer 12 containing a positive electrode active material, a conductive material and a binder is carried on a positive electrode current collector 11. Specifically, as the positive electrode active material, a material containing a material that can be doped / undoped with lithium ions, a carbonaceous material as a conductive material, and a thermoplastic resin as a binder can be used.

  In addition, at the end of winding end of the positive electrode 10 forming the electrode group 30, the positive electrode mixture layer 12 is formed on both surfaces of the positive electrode current collector 11. Since the positive electrode mixture layer 12 is formed at the end of the positive electrode winding, the positive electrode current collector portion unnecessary for the structure is eliminated, a space is secured in the battery case 40, and the capacity can be increased.

  Further, the nonaqueous electrolyte secondary battery of the present invention is coated with a heat resistant insulating tape 50 which is a heat resistant insulating layer having a deflection temperature under load of 200 ° C. or more on the surface of the active material layer formed on both surfaces of the current collector of the positive electrode termination portion. Has been.

  The heat-resistant insulating tape 50 is preferably coated at least 0.5 mm or more and 2 mm or less in the longitudinal direction of the positive electrode 10. If it is 0.5 mm or less, there is a possibility of peeling off. On the other hand, since the area of the positive electrode which does not contribute to charging / discharging will increase when the length covered is too long, it is preferably 2 mm or less.

  The heat-resistant insulating tape 50 is preferably entirely covered in the width direction of the positive electrode 10. If there is an exposed portion of the active material layer at the end of winding of the positive electrode, there is a risk that a short circuit occurs at the exposed portion of the positive electrode mixture layer 12. From the above viewpoint, the width of the heat resistant insulating tape 50 is preferably equal to or greater than the width of the positive electrode 10.

The material of the heat-resistant insulating tape 50 is preferably at least one heat-resistant resin selected from resins having a deflection temperature under load of 200 ° C. or higher in the measurement under 18.6 kg / cm ² load according to JIS K 7207. Examples of the resin having a deflection temperature under load of 200 ° C. or higher include polyimide, polyamideimide, aramid, polyethersulfone, and polyetherimide. Furthermore, it is particularly preferable that the material excellent in electrochemical and chemical resistance is selected from the group consisting of polyimide, polyamideimide and aramid.

Examples of the positive electrode active material that can be doped / undoped with lithium ions include lithium composite oxides containing at least one transition metal such as V, Mn, Fe, Co, and Ni. Among these, a layered lithium composite oxide based on an α-NaFeO ₂ type structure such as lithium nickelate or lithium cobaltate, or a spinel type structure such as lithium manganese spinel is preferable based on a high average discharge potential. Examples include lithium composite oxides.

  The thermoplastic resin used as the binder for the positive electrode includes polyvinylidene fluoride, vinylidene fluoride copolymer, polytetrafluoroethylene, tetrafluoroethylene-hexafluoropropylene copolymer, tetrafluoroethylene-per Fluoroalkyl vinyl ether copolymer, ethylene-tetrafluoroethylene copolymer, thermoplastic polyimide, polyethylene, polypropylene and the like.

  Examples of the carbonaceous material as the conductive agent include natural graphite, artificial graphite, cokes, and carbon black.

  As shown in FIG. 2, the negative electrode 20 is formed by forming a negative electrode mixture layer 22 on both surfaces of a negative electrode current collector 21. As the negative electrode active material, for example, a carbon material that can be doped / dedoped with lithium ions can be used. Examples of materials that can be doped / undoped with lithium ions include carbonaceous materials such as natural graphite, artificial graphite, cokes, carbon black, pyrolytic carbons, carbon fibers, and fired organic polymer compounds. As a carbonaceous material, a carbonaceous material mainly composed of graphite materials such as natural graphite and artificial graphite, because it has a high potential flatness and a low average discharge potential, so that a large energy density can be obtained when combined with a positive electrode. Is preferred.

  The negative electrode mixture layer 22 can be added with a binder or a thickener as necessary.

  In addition, the end of winding of the negative electrode 20 forming the electrode group is a negative electrode so that the negative electrode current collector 21 is exposed at least around the outer circumference of the negative electrode mixture layer 22 formed on both surfaces of the negative electrode current collector 21. It has a portion where the mixture layer is not formed.

  Thus, the negative electrode current collector 21 is exposed around the outer circumference of the electrode group 30, so that when the battery is manufactured, heat generated by a short circuit between the positive electrode and the negative electrode inside the battery is easily released to the outside. Therefore, improvement in safety is expected.

  As the negative electrode current collector 21 used in the non-aqueous electrolyte secondary battery of the present invention, Cu, Ni, stainless steel and the like can be used. In particular, in a lithium secondary battery, it is difficult to form an alloy with lithium, and a thin film is used. Cu is preferable because it is easy to process.

  As a method for supporting the negative electrode mixture layer 22 containing the negative electrode active material on the negative electrode current collector 21, a method of pressure molding, or pasting using a solvent or the like, applying the coating to the current collector, pressing the current collector, etc. The method of crimping is mentioned.

  The electrode group 30 is formed by winding a laminated body in which the positive electrode 10, the heat-resistant insulating layer 15, the negative electrode 20, and the heat-resistant insulating layer 15 are laminated in this order. Furthermore, the end position of the porous insulating layer is adjusted so that the negative electrode current collector 21 is exposed around the outer circumference of the electrode group 30.

  Here, an insulating separator or the like can be used for the heat-resistant insulating layer 15.

  The non-aqueous electrolyte battery includes the electrode group 30 as described above housed in a battery case 40.

  In order to house the electrode group 30 in the battery case 40 to make a non-aqueous electrolyte battery, first, an insulating plate 45 is inserted into the bottom of the battery case 40 made of, for example, iron and pre-plated with nickel, to form the electrode group 30. And an insulating plate 44 is also inserted into the upper part.

  In order to collect the negative electrode, for example, one end of a negative electrode lead 46 made of nickel, for example, is welded to the negative electrode, and the other end is welded to the battery case 40. As a result, the battery case 40 is electrically connected to the negative electrode, and becomes an external negative electrode of the nonaqueous electrolyte battery. In order to collect the positive electrode, for example, one end of a positive electrode lead 41 made of, for example, aluminum is attached to the positive electrode, and the other end is electrically connected to the sealing plate 42 through a thin plate for current interruption. This thin plate for current interruption interrupts current according to the battery internal pressure. As a result, the battery lid is electrically connected to the positive electrode, and becomes the external positive electrode of the nonaqueous electrolyte battery.

  Next, a non-aqueous electrolyte is injected into the battery case 40.

  As the non-aqueous electrolyte solution used in the lithium secondary battery, for example, a non-aqueous electrolyte solution in which a lithium salt is dissolved in an organic solvent can be used. As the organic solvent furnace, a mixed solvent containing carbonates is preferable, and a mixed solvent of cyclic carbonate and acyclic carbonate or cyclic carbonate and ether is more preferable. In addition, a mixed solvent containing ethylene carbonate, dimethyl carbonate and ethyl methyl carbonate is preferable in that it is hardly decomposable even when a graphite material such as natural graphite or artificial graphite is used as the active material of the negative electrode.

  A sealing plate 42 is caulked to the opening via a gasket 43, and the opening is sealed by caulking the sealing plate 42. A cylindrical nonaqueous electrolyte battery is produced.

  In this nonaqueous electrolyte battery, a center pin connected to the positive electrode lead 41 and the negative electrode lead 46 is provided, and the internal gas is extracted when the internal pressure of the battery becomes higher than a predetermined value. A safety valve device and a PTC element for preventing temperature rise inside the battery are provided.

  EXAMPLES Hereinafter, although this invention is demonstrated concretely based on an Example, this invention is not limited to a following example.

-Battery manufacturing method-
(Preparation of positive electrode)
First, LiNi _0.82 Co _0.15 Al _0.03 O ₂ having an average particle diameter of 13 μm was used as the positive electrode active material. An N-methyl-2-pyrrolidone (NMP) solution of 1.0 part by mass of acetylene black (conductive agent) and polyvinylidene fluoride (PVDF, binder) with respect to 100 parts by mass of the positive electrode active material (manufactured by Solvay Co., Ltd.) No. 5130) was mixed to obtain a positive electrode mixture slurry. The amount of PVDF added was 0.9 parts by mass per 100 parts by mass of the positive electrode active material.

  Next, the obtained positive electrode mixture slurry was applied to both surfaces of a 15 μm thick iron-containing aluminum foil (8021 made by Sumigar Co., Ltd.) as a positive electrode current collector. Then, an uncoated portion with a width of 6 mm was given as a position to be welded.After drying the positive electrode mixture slurry, the positive electrode current collector provided with the positive electrode active material or the like on the surface was rolled to obtain a positive electrode active material density of 3 A positive electrode plate having a thickness of .65 g / cc and a thickness of 0.166 mm was obtained.

Subsequently, the obtained positive electrode plate was cut into a width of 58.5 mm and a length of 560 mm to obtain a positive electrode.
During the cutting of the positive electrode, the cutting was performed so that the uncoated portion of the positive electrode mixture layer was located at the center in the length direction of the belt-shaped positive electrode.

  Then, the obtained positive electrode was subjected to heat treatment by bringing it into contact with a hot roll at 195 ° C. for 7 seconds.

Next, a polyimide tape made of Nitto Denko with a length of 3 mm and a width of 59.5 mm (a deflection temperature under load of 18.6 kg / cm ^{2 in} accordance with JIS K 7207 is 200 ° C.) is prepared, and serves as a terminal portion of the positive electrode. The aforementioned polyimide tape was applied to both surfaces of the mixture layer at the positive electrode end on the side so as to cover the surface of the mixture layer in the length direction by 2 mm and in the width direction by 58.5 mm.

(Preparation of negative electrode)
First, graphite having an average particle size of about 20 μm was used as a negative electrode active material (manufactured by Hitachi Chemical). 1 part by mass of styrene butadiene rubber (binder) and 100 parts by mass of an aqueous solution containing 1% by weight of carboxymethylcellulose were mixed with respect to 100 parts by mass of the negative electrode active material to obtain a negative electrode mixture slurry.

  Next, the obtained negative electrode mixture slurry was applied to both sides of an electrolytic copper foil (manufactured by Nippon Electrolytic Co., Ltd.) having a thickness of 8 μm. After drying the negative electrode mixture slurry, the negative electrode current collector provided with the negative electrode active material on the surface is rolled to obtain a negative electrode plate having a negative electrode active material density of 1.60 g / cc and a thickness of 0.195 μm. It was.

  Subsequently, the obtained negative electrode plate was cut into a width of 59.5 mm and a length of 640 mm to obtain a negative electrode.

  In the strip-shaped negative electrode, an uncoated portion in which the negative electrode mixture layer was not formed on the inner side of the end portion of the electrode group at the end of 25 mm and the outer side of the 60 mm negative electrode mixture layer was given.

  Then, the obtained negative electrode was heat-treated in a nitrogen atmosphere with hot air at 190 ° C. for 10 hours.

(Preparation of non-aqueous electrolyte)
Vinylene carbonate was added at a concentration of 5 wt% to a mixed solvent containing ethylene carbonate and dimethyl carbonate in a volume ratio of 1: 3, and LiPF ₆ was dissolved at a concentration of 1.4 mol / L.

(Assembly of cylindrical battery)
First, the positive electrode lead made of aluminum was attached to the exposed portion of the current collector where the positive electrode mixture layer was not formed, and the negative electrode lead made of nickel was similarly attached to the negative electrode current collector at a portion 5 mm from the end of winding. . Thereafter, the positive electrode and the negative electrode were opposed to each other so that the positive electrode lead and the negative electrode lead extended in opposite directions, and a polyethylene separator (porous insulating layer) was disposed between the positive electrode and the negative electrode. Subsequently, the positive electrode and negative electrode which were arrange | positioned through the separator around the winding core were wound. Thereby, a wound-type electrode group was produced. The electrode group was prepared on the outermost periphery of the electrode group such that the exposed portion of the negative electrode current collector was exposed for one week.

  Next, an upper insulating plate was disposed on the upper surface of the electrode group, and a lower insulating plate was disposed under the electrode group. Thereafter, the negative electrode lead was welded to the battery case and the positive electrode lead was welded to the sealing plate, and the electrode group was housed in the battery case. Thereafter, a non-aqueous electrolyte was injected into the battery case by a decompression method, and the sealing plate was caulked to the opening of the battery case via a gasket. Thereby, the battery of Example 1 was produced.

(Comparative Example 1)
A battery was produced in Comparative Example 1 in the same manner as in Example 1 except that no polyimide tape was attached to the end of the positive electrode.

(Combustion test)
Ten nonaqueous electrolyte batteries of Example 1 and Comparative Example 1 obtained as described above were prepared, and the batteries were charged. Specifically, charging was performed at a constant current by passing a current of 1.45 A until the voltage reached 4.20 V, and charging was performed at a constant voltage until the current reached 50 mA after reaching 4.25 V.

  Subsequently, the battery which carried out the above-mentioned charge was subjected to a combustion test using a propane gas burner. The number of batteries in which damage was confirmed in the battery outer case after the test is shown in the table.

  As is clear from Table 1, the case was not damaged in the battery of Example 1 in which the heat-resistant insulating tape was installed at the positive electrode terminal portion. On the other hand, for the nonaqueous electrolyte battery of Comparative Example 1 in which no heat-resistant insulating tape was installed at the end of the positive electrode winding, the case was damaged.

  From this result, it was clarified that damage to the exterior case is suppressed by suppressing the short circuit at the positive terminal.

  Since the nonaqueous electrolyte secondary battery of the present invention is excellent in safety, it is useful as a power source for portable electronic devices such as personal computers.

DESCRIPTION OF SYMBOLS 10 Positive electrode 11 Positive electrode collector 12 Positive electrode mixture layer 15 Heat-resistant insulating layer 20 Negative electrode 21 Negative electrode collector 22 Negative electrode mixture layer 30 Electrode group 40 Battery case 41 Positive electrode lead 42 Sealing plate 43 Gasket 44, 45 Insulating plate 46 Negative electrode lead 50 heat resistant insulating tape 100 non-aqueous electrolyte secondary battery

Claims (2)

A positive electrode in which a positive electrode active material layer is formed on a part of both surfaces of a strip-shaped positive electrode current collector and a negative electrode in which a negative electrode active material layer is formed on a part of both surfaces of a strip-shaped negative electrode current collector are separators. The outermost periphery of the electrode group is configured to be a negative electrode current collector exposed portion in which the negative electrode active material layer is not formed, and the belt-like positive electrode is An active material layer is formed on both sides of the current collector at the winding end in the longitudinal direction, and the surface of the winding end is covered with a heat-resistant insulating layer made of a resin having a load deflection temperature of 200 ° C. or higher. A non-aqueous electrolyte secondary battery characterized by comprising: 2. The nonaqueous electrolyte secondary battery according to claim 1, wherein the heat-resistant insulating layer is at least one selected from the group consisting of polyimide, polyamideimide, aramid, polyethersulfone, and polyetherimide.