WO2018230058A1

WO2018230058A1 - Secondary battery

Info

Publication number: WO2018230058A1
Application number: PCT/JP2018/009663
Authority: WO
Inventors: 高光鎌田; 八木　陽心; 貴宏相馬
Original assignee: 日立オートモティブシステムズ株式会社
Priority date: 2017-06-13
Filing date: 2018-03-13
Publication date: 2018-12-20
Also published as: JP2020129432A

Abstract

The present invention addresses the problem of providing a secondary battery which has improved safety against overcharging. A secondary battery according to the present invention is a cylindrical secondary battery (1) that comprises a positive electrode (174), a negative electrode (175) and a current interrupting mechanism (181), said cylindrical secondary battery (1) being characterized in that: the positive electrode mixture contains from 1% by weight to 4% by weight (inclusive) of lithium carbonate; the NP ratio, which is the ratio of the negative electrode capacity to the positive electrode capacity, is from 1.4 to 2.0 (inclusive); and the coating amount of the positive electrode mixture is from 110 g/m2 to 140 g/m2 (inclusive).

Description

Secondary battery

The present invention relates to a secondary battery used as a power source for an electric vehicle or a hybrid vehicle, for example.

In recent years, lithium ion secondary batteries have been used as power sources for electric vehicles and hybrid vehicles. A lithium ion secondary battery for automobiles is required to have high output, high energy density, and high safety.

Also, with lithium ion secondary batteries, it is important to ensure that the safety of the battery system is not compromised even during overcharging due to misoperation. In order to improve safety during overcharge, it is required to appropriately control the current interruption mechanism and heat generation of the secondary battery.

In Patent Document 1, lithium carbonate is used as a compound that generates a decomposition gas during overcharge and activates a current interruption mechanism, and numerically limits the lithium carbonate content in a specific positive electrode mixture.

JP 2013-138014 A

However, in the method of Patent Document 1, when the content of lithium carbonate cannot be increased, the configuration content of the positive electrode and the negative electrode of the secondary battery is changed to improve safety against overcharging. I can't let you.

The present invention aims to solve the above problems. Specifically, it is to provide a secondary battery that can improve safety against overcharge.

In order to solve the above problems, the secondary battery according to the present invention includes a positive electrode coated with a positive electrode mixture, a negative electrode coated with a negative electrode mixture, and a battery containing the positive electrode and the negative electrode. A secondary battery having a container and a current interrupting mechanism that interrupts current when the internal pressure of the battery container reaches a predetermined operating pressure, wherein the positive electrode mixture contains 1 wt% or more and 4 wt% or less. NP ratio, which is the ratio of the capacity of the positive electrode to the capacity of the negative electrode, is 1.4 or more and 2.0 or less, and the coating amount of the positive electrode mixture is 110 g / m ² or more. 140 g / m ² or less.

The NP ratio is preferably 1.4 or more and 1.6 or less, and the coating amount of the positive electrode mixture is preferably 120 g / m ² or more and 140 g / m ² or less. Moreover, NP ratio is 1.5, it is preferable coating amount of the positive electrode mixture is 130 g / ^{m 2} or more 140 g / ^{m 2} or less. Moreover, it is preferable that the coating amount of a positive mix is 130 g / m < ² >.

ADVANTAGE OF THE INVENTION According to this invention, the secondary battery excellent in the safety | security with respect to an overcharge can be provided.
Further features related to the present invention will become apparent from the description of the present specification and the accompanying drawings. Further, problems, configurations, and effects other than those described above will be clarified by the following description of embodiments.

Sectional drawing of the cylindrical secondary battery as one Embodiment of this invention. FIG. 2 is an exploded perspective view of the cylindrical secondary battery shown in FIG. 1. The perspective view of the state which cut | disconnected a part for showing the detail of the electrode group of FIG. 1 is an external perspective view of a prismatic secondary battery as one embodiment of the present invention. FIG. 5 is an exploded perspective view of the prismatic secondary battery shown in FIG. 4. The perspective view which shows the winding electrode group. The table | surface which shows the structure of positive electrode mixture coating amount and NP ratio. The table | surface which shows the test result of an overcharge test.

FIG. 1 is a longitudinal sectional view showing an embodiment of a cylindrical secondary battery of the present invention. The cylindrical secondary battery 1 has dimensions of, for example, an outer diameter of 40 mmφ and a height of 100 mm. The cylindrical secondary battery 1 is configured by housing the power generation unit 20 in a bottomed cylindrical battery can 60 whose opening is sealed with a sealing lid 50. First, the battery can 60 and the power generation unit 20 will be described, and then the sealing lid 50 will be described.

In the bottomed cylindrical battery can 60, a caulking portion 61 is formed at a can opening end portion (upper side in the figure). By caulking and fixing the sealing lid 50 to the battery can 60 with the caulking portion 61, the opening portion is hermetically sealed and the sealing performance of the sealed cylindrical secondary battery 1 using a non-aqueous electrolyte is ensured. The caulking portion 61 includes an annular protrusion, a bent portion 62 formed by bending the end portion of the can opening inward, and a grooving portion 63 protruding inward at a predetermined distance from the battery bottom surface. As will be described later, the sealing lid 50 is caulked and fixed with the gasket 43 interposed between the bent portion 62 and the grooving portion 63, and the battery is sealed.

The power generation unit 20 is configured by integrally uniting the electrode group 10, the positive electrode current collecting member 31, and the negative electrode current collecting member 21 as described below. The electrode group 10 has a shaft core 15 at the center, and a positive electrode, a negative electrode, and a separator are wound around the shaft core 15. A hollow cylindrical shaft core 15 is formed with a large-diameter recess 15a on the inner surface of the upper end in the axial direction (vertical direction in the drawing), and the positive electrode current collector 31 is press-fitted into the recess 15a. The positive electrode current collecting member 31 is formed of, for example, aluminum, and has a disk-like base portion 31a, a lower cylindrical portion 31b that protrudes toward the shaft core 15 side at the inner peripheral portion of the base portion 31a and is press-fitted into the inner surface of the shaft core 15. And an upper cylindrical portion 31c protruding toward the sealing lid 50 at the outer peripheral edge. An opening 31d for releasing gas generated inside the battery is formed in the base 31a of the positive electrode current collecting member 31.

All the positive leads 16 of the positive electrode sheet 11 a are welded to the upper cylindrical portion 31 c of the positive current collecting member 31. In this case, the positive electrode lead 16 is overlapped and bonded onto the upper cylindrical portion 31 c of the positive electrode current collecting member 31. Since each positive electrode lead 16 is very thin, a large current cannot be taken out by one. Therefore, a large number of positive leads 16 are formed at predetermined intervals over the entire length from the start to the end of winding around the shaft core 15.

The positive electrode lead 16 of the positive electrode sheet 11a and the ring-shaped pressing member 32 are welded to the outer periphery of the upper cylindrical portion 31c of the positive electrode current collecting member 31. A number of the positive leads 16 are brought into close contact with the outer periphery of the upper cylindrical portion 31 c of the positive current collecting member 31, and the pressing member 32 is wound around the outer periphery of the positive lead 16 and temporarily fixed, and is welded in this state.

Since the positive electrode current collecting member 31 is oxidized by the electrolytic solution, the reliability can be improved by forming it with aluminum. When the surface of aluminum is exposed by some processing, an aluminum oxide film is immediately formed on the surface, and this aluminum oxide film can prevent oxidation by the electrolytic solution. Moreover, by forming the positive electrode current collecting member 31 from aluminum, the positive electrode lead 16 of the positive electrode sheet 11a can be welded by ultrasonic welding, spot welding, or the like.

A step portion 15b having a small outer diameter is formed on the outer periphery of the lower end portion of the shaft core 15, and the negative electrode current collecting member 21 is press-fitted and fixed to the step portion 15b. The negative electrode current collecting member 21 is formed of, for example, copper, and an opening 21b that is press-fitted into the step portion 15b of the shaft core 15 is formed in a disc-shaped base portion 21a. An outer peripheral cylindrical portion 21c that protrudes out is formed.

The negative electrode lead 17 of the negative electrode sheet 12a is all welded to the outer peripheral cylindrical portion 21c of the negative electrode current collecting member 21 by ultrasonic welding or the like. Since each negative electrode lead 17 is very thin, a large number of negative leads 17 are formed at predetermined intervals over the entire length from the start of winding to the shaft core 15 to take out a large current.

The negative electrode lead 17 and the ring-shaped pressing member 22 of the negative electrode sheet 12a are welded to the outer periphery of the outer peripheral cylindrical portion 21c of the negative electrode current collecting member 21. A number of the negative electrode leads 17 are brought into close contact with the outer periphery of the outer peripheral cylindrical portion 21c of the negative electrode current collecting member 21, and the holding member 22 is wound around the outer periphery of the negative electrode lead 17 to be temporarily fixed, and are welded in this state.

A negative electrode conducting lead 23 made of copper is welded to the lower surface of the negative electrode current collecting member 21. The negative electrode conducting lead 23 is welded to the battery can 60 at the bottom of the battery can 60. The battery can 60 is made of carbon steel having a thickness of 0.5 mm, for example, and has a nickel plating on the surface. By using such a material, the negative electrode conducting lead 23 can be welded to the battery can 60 by resistance welding or the like.

A flexible positive electrode conductive lead 33 formed by laminating a plurality of aluminum foils is joined to the upper surface of the base portion 31a of the positive electrode current collecting member 31 by welding one end thereof. The positive electrode conductive lead 33 can flow a large current by laminating and integrating a plurality of aluminum foils, and is provided with flexibility. In other words, it is necessary to increase the thickness of the connecting member in order to pass a large current, but if it is formed of a single metal plate, the rigidity increases and the flexibility is impaired. Therefore, a large number of aluminum foils having a small thickness are laminated to give flexibility. The thickness of the positive electrode conductive lead 33 is, for example, about 0.5 mm, and is formed by stacking five aluminum foils having a thickness of 0.1 mm.

FIG. 2 is an exploded perspective view of the cylindrical secondary battery shown in FIG.
The electrode group 10 has a shaft core 15 at the center, and a positive electrode, a negative electrode, and a separator are wound around the shaft core 15. Then, the outermost first separator 13 is fixed with an adhesive tape 19.

The sealing lid 50 includes a cap 3 having an exhaust port 3 c, a cap case 37 attached to the cap 3 and having a cleavage groove 37 a, a positive electrode connection plate 35 spot-welded to the back of the central portion of the cap case 37, and a positive electrode connection plate An insulating ring 41 sandwiched between the upper surface of the peripheral edge of 35 and the back surface of the cap case 37 is provided and assembled in advance as a subassembly.

The cap 3 is formed by applying nickel plating to iron such as carbon steel. The cap 3 has a disc-shaped peripheral edge portion 3a and a headless and bottomless cylindrical portion 3b protruding upward from the peripheral edge portion 3a, and has a hat shape as a whole. An exhaust port 3c is formed at the center of the cylindrical portion 3b. The cylinder part 3b functions as a positive electrode external terminal and is connected to a bus bar or the like.

The peripheral edge of the cap 3 is integrated with a folded flange 37b of a cap case 37 formed of an aluminum alloy. In other words, the cap 3 is caulked and fixed by folding the periphery of the cap case 37 along the upper surface of the cap 3. The ring that is folded back on the upper surface of the cap 3, that is, the flange 37 b and the cap 3 are friction-welded. That is, the cap case 37 and the cap 3 are integrated by caulking and welding by the flange 37b. As described above, the sealing lid 50 includes the flange 37b in which the cap case 37 and the cap 3 are integrated.

In the central circular region of the cap case 37, a circular cleavage groove 37a and a cleavage groove 37a extending radially from the cleavage groove 37a are formed. The cleaving groove 37a is formed by crushing the upper surface side of the cap case 37 into a V shape by pressing and thinning the remaining portion. The cleavage groove 37a is cleaved when the internal pressure in the battery container 60 rises to a predetermined value or more, and releases the internal gas.

The sealing lid 50 constitutes an explosion-proof mechanism. When the internal pressure exceeds the reference value due to the gas generated in the battery can 60, a crack occurs in the cap case 37 in the cleavage groove, and the internal gas is discharged from the exhaust port 3c of the cap 3 to be inside the battery can 60. The pressure of is reduced. Further, the cap case 37 bulges outward from the container due to the internal pressure of the battery can 60, and the electrical connection with the positive electrode connection plate 35 is cut off, thereby suppressing overcurrent. The cylindrical secondary battery 1 is overcharged, and a positive electrode gas generating compound such as lithium carbonate contained in the positive electrode mixture is decomposed by the positive electrode potential to generate gas, and a battery can (battery container) When the internal pressure of 60 rises to a predetermined operating pressure, for example, a pressure in the range of 0.4 MPa or more and 1.0 MPa or less, the cap case 37 bulges outward from the container to interrupt the current (current) Blocking mechanism).

The sealing lid 50 is placed on the upper cylindrical portion 31c of the positive electrode current collecting member 31 in an insulated state. That is, the cap case 37 in which the cap 3 is integrated is placed on the upper end surface of the positive electrode current collecting member 31 in an insulated state via the insulating ring 41. However, the cap case 37 is electrically connected to the positive electrode current collector 31 by the positive electrode conductive lead 33, and the cap 3 of the sealing lid 50 becomes the positive electrode of the cylindrical secondary battery 1. Here, the insulating ring 41 has an opening 41a and a side portion 41b protruding downward. A connection plate 35 is fitted in the opening 41 a of the insulating ring 41.

The connection plate 35 is formed of an aluminum alloy, and has a substantially dish shape in which almost the whole except the central portion is uniform and the central side is bent to a slightly lower position. The thickness of the connection plate 35 is, for example, about 1 mm. A projection 35a that is thin and formed in a dome shape is formed at the center of the connection plate 35, and a plurality of openings 35b are formed around the projection 35a. The opening 35b has a function of releasing gas generated inside the battery. The protrusion 35a of the connection plate 35 is joined to the bottom surface of the central portion of the cap case 37 by resistance welding or friction diffusion bonding.

Then, the electrode group 10 is accommodated in the battery can 60, and the sealing lid 50 previously prepared as a partial assembly is electrically connected by the positive electrode current collecting member 31 and the positive electrode conductive lead 33 and placed on the upper part of the cylinder. Then, the outer peripheral wall portion 43b of the gasket 43 is bent by pressing or the like, and the sealing lid 50 is crimped by the base portion 43a and the outer peripheral wall portion 43b so as to be pressed in the axial direction. Thereby, the sealing lid 50 is fixed to the battery can 60 via the gasket 43.

The gasket 43 includes an outer peripheral wall portion 43b that is formed to stand substantially vertically toward the upper direction on the peripheral edge of the ring-shaped base portion 43a, and an inner peripheral side substantially downward from the base portion 43a. It has the shape which has the cylinder part 43c formed by dripping vertically. By caulking the battery can 60, the sealing lid 50 is sandwiched by the battery can 60 via the outer peripheral wall 43b.

A predetermined amount of non-aqueous electrolyte is injected into the battery can 60. As an example of the non-aqueous electrolyte, it is preferable to use a solution in which a lithium salt is dissolved in a carbonate solvent. Examples of the lithium salt include lithium fluorophosphate (LiPF ₆ ), lithium fluoroborate (LiBF ₆ ), and the like. Examples of carbonate solvents include ethylene carbonate (EC), dimethyl carbonate (DMC), propylene carbonate (PC), methyl ethyl carbonate (MEC), or a mixture of solvents selected from one or more of the above solvents, Is mentioned.

FIG. 3 is a diagram for explaining the power generation unit, showing the details of the structure of the electrode group 10 and is a perspective view in a state where a part thereof is cut. As shown in FIG. 3, the electrode group 10 has a configuration in which the positive electrode 11, the negative electrode 12, and the first and

second separators

13 and 14 are wound around the outer periphery of the shaft core 15.

In this electrode group 10, the first separator 13 is wound on the innermost periphery that is in contact with the outer periphery of the shaft core 15, and the negative electrode 12, the second separator 14, and the positive electrode 11 are laminated in this order on the outer side. Has been wound up. A first separator 13 and a second separator 14 are wound several times inside the innermost negative electrode 12. The outermost periphery is the negative electrode 12 and the first separator 13 wound around the outer periphery.

The positive electrode 11 is formed of an aluminum foil and has a strip shape. The positive electrode 11 includes a positive electrode sheet 11a and a positive electrode processing portion (positive electrode mixture layer) in which the positive electrode mixture 11b is applied to both surfaces of the positive electrode sheet 11a. The upper side edge along the longitudinal direction of the positive electrode sheet 11a is a positive electrode mixture untreated portion 11c where the positive electrode mixture 11b is not applied and the aluminum foil is exposed. In the positive electrode mixture untreated portion 11 c, a large number of positive electrode leads 16 protruding upward in parallel with the shaft core 15 are integrally formed at equal intervals.

The positive electrode mixture 11b includes a positive electrode active material, a positive electrode conductive material, a positive electrode binder, and a positive electrode gas generating compound. The positive electrode active material is preferably lithium oxide. Examples include lithium cobaltate, lithium manganate, lithium nickelate, lithium composite oxide (lithium oxide containing two or more selected from cobalt, nickel, and manganese).

The positive electrode conductive material is not limited as long as it can assist the transmission of electrons generated by the occlusion / release reaction of lithium in the positive electrode mixture to the positive electrode. Examples of the positive electrode conductive material include graphite and acetylene black.

The positive electrode binder can bind the positive electrode active material and the positive electrode conductive material, and can bind the positive electrode mixture and the positive electrode current collector, and should not deteriorate significantly due to contact with the non-aqueous electrolyte. There is no particular limitation. Examples of the positive electrode binder include polyvinylidene fluoride (PVDF) and fluororubber.

As the positive electrode gas generating compound, an inorganic carbonate compound, an oxalic acid inorganic compound, or a nitric acid inorganic compound that generates gas at a positive electrode potential in an overcharged state can be mentioned. Among these, a carbonic acid inorganic compound is preferable, for example, lithium carbonate. The content of lithium carbonate in the positive electrode mixture is preferably 1 wt% or more and 4 wt% or less, but in Example 1, it was 1.8 wt%.

The method for forming the positive electrode mixture layer is not limited as long as the positive electrode mixture is formed on the positive electrode. As an example of a method for forming the positive electrode mixture 11b, a method in which a dispersion solution of constituent materials of the positive electrode mixture 11b is applied on the positive electrode sheet 11a.

Examples of the method for applying the positive electrode mixture 11b to the positive electrode sheet 11a include a roll coating method and a slit die coating method. After adding N-methylpyrrolidone (NMP) or water as an example of a solvent for the dispersion solution to the positive electrode mixture 11b and uniformly kneading the slurry on both sides of an aluminum foil having a thickness of 20 μm, and drying it. , Press and cut. An example of the coating thickness of the positive electrode mixture 11b is about 40 μm on one side. When cutting the positive electrode sheet 11a, the positive electrode lead 16 is integrally formed. In Example 1, the coating amount of the positive electrode mixture on one surface of the positive electrode is 140 g / m ² .

The negative electrode 12 is formed of a copper foil and has a strip shape. The negative electrode 12 includes a negative electrode sheet 12a and a negative electrode treatment portion (negative electrode mixture layer) in which a negative electrode mixture 12b is applied to both surfaces of the negative electrode sheet 12a. The lower side edge along the longitudinal direction of the negative electrode sheet 12a is a negative electrode mixture untreated portion 12c in which the negative electrode mixture 12b is not applied and the copper foil is exposed. In the negative electrode mixture untreated portion 12c, a large number of negative electrode leads 17 extending in the direction opposite to the positive electrode lead 16 are integrally formed at equal intervals.

The negative electrode mixture 12b is composed of a negative electrode active material, a negative electrode binder, and a thickener. The negative electrode mixture 12b may have a negative electrode conductive material such as acetylene black. Graphite carbon is preferably used as the negative electrode active material. By using graphite carbon, a lithium ion secondary battery for a plug-in hybrid vehicle or an electric vehicle requiring a large capacity can be manufactured. The formation method of the negative electrode mixture 12b is not limited as long as the negative electrode mixture 12b is formed on the negative electrode sheet 12a. As an example of a method of applying the negative electrode mixture 12b to the negative electrode sheet 12a, a method of applying a dispersion solution of the constituent material of the negative electrode mixture 12b onto the negative electrode sheet 12a can be mentioned. Examples of the coating method include a roll coating method and a slit die coating method.

As an example of a method of coating the negative electrode mixture 12b on the negative electrode sheet 12a, N-methyl-2-pyrrolidone or water as a dispersion solvent is added to the negative electrode mixture 12b, and the kneaded slurry is rolled into a 10 μm thick rolled copper foil. After coating uniformly on both sides, press and cut. An example of the coating thickness of the negative electrode mixture 12b is about 40 μm on one side. When the negative electrode sheet 12a is cut, the negative electrode lead 17 is integrally formed.

The width of the first separator 13 and the second separator 14 is W _S , the width of the negative electrode mixture 12b formed on the negative electrode sheet 12a is W _C , and the width of the positive electrode mixture 11b formed on the positive electrode sheet 11a is W _A. In this case, it is formed so as to satisfy the following formula.
W _S > W _C > W _A

That is, the width W _{C of the} negative electrode mixture 12b is always larger than the width W _{A of the} positive electrode mixture 11b. This is because in the case of a lithium ion secondary battery, lithium as the positive electrode active material is ionized and penetrates the separator, but the negative electrode sheet is not formed on the negative electrode side and the negative electrode sheet 12a is exposed. This is because lithium is deposited on 12a and causes an internal short circuit.

The negative electrode capacity / positive electrode capacity, which is the ratio of the respective capacities of the formed positive electrode and negative electrode, was defined as the NP ratio. The NP ratio is preferably 1.1 or more, but in Example 1, it was set to 1.4.

(Example 1)
As described above, in the secondary battery of Example 1, the lithium carbonate content in the positive electrode mixture was 1.8 wt%, the NP ratio was 1.4, and the coating amount of the positive electrode mixture on one surface of the positive electrode was 140 g / m ² .

(Example 2)
A secondary battery of Example 2 was produced in the same manner as in Example 1 except that the coating amount of the positive electrode mixture was 130 g / m ² .

(Example 3)
A secondary battery of Example 3 was produced in the same manner as in Example 1 except that the coating amount of the positive electrode mixture was 120 g / m ² .

Example 4
A secondary battery of Example 4 was produced in the same manner as in Example 1, except that the coating amount of the positive electrode mixture was 110 g / m ² .

(Example 5)
A secondary battery of Example 5 was made in the same manner as in Example 1 except that NP was made to be 1.5.

(Comparative Example 1)
A secondary battery of Comparative Example 1 was fabricated in the same manner as in Example 1 except that the coating amount of the positive electrode mixture was 110 g / m ² and the NP ratio was 1.1.

(Comparative Example 2)
A secondary battery of Comparative Example 2 was fabricated in the same manner as in Example 1 except that the coating amount of the positive electrode mixture was 110 g / m ² and the NP ratio was 1.2.

(Comparative Example 3)
A secondary battery of Comparative Example 2 was fabricated in the same manner as in Example 1 except that the coating amount of the positive electrode mixture was 90 g / m ² and the NP ratio was 1.2.

(Comparative Example 4)
A secondary battery of Comparative Example 2 was produced in the same manner as in Example 1 except that the NP ratio was made to be 1.3.

(Comparative Example 5)
A secondary battery of Comparative Example 5 was fabricated in the same manner as in Example 1 except that the coating amount of the positive electrode mixture was 130 g / m ² and the NP ratio was 1.3.

(Comparative Example 6)
A secondary battery of Comparative Example 6 was fabricated in the same manner as in Example 1 except that the coating amount of the positive electrode mixture was 120 g / m ² and the NP ratio was 1.3.

The present invention is not limited to a cylindrical secondary battery but can also be applied to a prismatic secondary battery. FIG. 4 is an external perspective view of a prismatic secondary battery 100 as an embodiment of the electricity storage device, and FIG. 5 is an exploded perspective view showing the configuration of the prismatic secondary battery 100.

As shown in FIG. 4, the square secondary battery 100 includes a battery container including a battery can 101 and a battery lid 102. The material of the battery can 101 and the battery lid 102 is aluminum or an aluminum alloy. The battery can 101 is formed in a flat rectangular box shape with one end opened by performing deep drawing. The battery can 101 includes a rectangular plate-like bottom plate 101c, a pair of wide side plates 101a rising from each of a pair of long sides of the bottom plate 101c, and a pair of narrow side plates 101b rising from each of a pair of short sides of the bottom plate 101c. And have.

As shown in FIG. 5, the battery can 101 accommodates a wound electrode group 170 (see FIG. 6). The positive electrode current collector 180 joined to the positive electrode 174 of the wound electrode group 170 and the negative electrode 175 of the wound electrode group 170 are joined. The negative electrode current collector 190 and the wound electrode group 170 are composed of an insulating sheet 108a covering the center of the wound electrode group, an insulating sheet 108b covering the positive electrode uncoated part of the wound electrode group, and a negative electrode uncoated of the wound electrode group. It is accommodated in the battery can 101 in a state covered with an insulating sheet 108c covering the construction part. The material of the insulating

sheets

108a, 108b, 108c is an insulating resin such as polypropylene, and the battery can 101 and the wound electrode group 170 are electrically insulated.

4 and 5, the battery lid 102 has a rectangular flat plate shape and is laser-welded so as to close the opening of the battery can 101. That is, the battery lid 102 seals the opening of the battery can 101. As shown in FIG. 1, a positive electrode external terminal 104 and a negative electrode external terminal 105 that are electrically connected to the positive electrode 174 and the negative electrode 175 of the wound electrode group 170 are disposed on the battery lid 102.

As shown in FIG. 5, the positive external terminal 104 is electrically connected to the positive electrode 174 (see FIG. 3) of the wound electrode group 170 via the current interrupt mechanism 181 and the positive current collector 180, and the negative external terminal 105. Is electrically connected to the negative electrode 175 of the wound electrode group 170 via the negative electrode current collector 190. Therefore, electric power is supplied to the external device via the positive external terminal 104 and the negative external terminal 105, or external generated power is supplied to the wound electrode group 170 via the positive external terminal 104 and the negative external terminal 105. Charged.

As shown in FIG. 5, the battery lid 102 is provided with a liquid injection hole 106 a for injecting an electrolytic solution into the battery container. The liquid injection hole 106a is sealed by a liquid injection plug 106b after the electrolytic solution is injected. As the electrolytic solution, for example, a non-aqueous electrolytic solution in which a lithium salt such as lithium hexafluorophosphate (LiPF ₆ ) is dissolved in a carbonate-based organic solvent such as ethylene carbonate can be used.

The battery cover 102 is provided with a gas discharge valve 103. The gas discharge valve 103 is formed by partially thinning the battery lid 102 by press working. The thin-walled member may be attached to the opening of the battery lid 102 by laser welding or the like, and the thin portion may be used as a gas discharge valve. The gas discharge valve 103 is heated when the rectangular secondary battery 100 generates heat due to an abnormality such as an internal short circuit, and gas is generated. By discharging, the pressure in the battery container is reduced.

The current interruption mechanism 181 operates when the square secondary battery 100 is overcharged, the positive electrode gas generating compound is decomposed by the positive electrode potential at that time, gas is generated, and the internal pressure is increased. The current interruption mechanism 181 has, for example, a diaphragm, and when the inside of the battery container reaches a predetermined operating pressure, for example, a pressure in a range of 0.4 MPa to 1.0 MPa, the diaphragm is deformed to interrupt the contact. It has a configuration.

The wound electrode group 170 will be described with reference to FIG. FIG. 6 is a perspective view showing the wound electrode group 170 and shows a state where the winding end side of the wound electrode group 170 is developed. The wound electrode group 170, which is a power generation element, has a laminated structure by winding a belt-like positive electrode 174 and a negative electrode 175 in a flat shape around the wound central axis W with

separators

173a and 173b interposed. .

The positive electrode 174 has a positive electrode mixture layer 176 formed on both surfaces of the positive electrode foil 171. The positive electrode mixture is a mixture of a positive electrode active material and a binder (binder) and a positive gas generating compound. Examples of the positive electrode gas generating compound include a carbonic acid inorganic compound, an oxalic acid inorganic compound, or a nitric acid inorganic compound that generates gas at a positive electrode potential in an overcharged state. Among these, a carbonic acid inorganic compound is preferable, for example, lithium carbonate.
The negative electrode 175 has a negative electrode mixture layer 177 formed on both surfaces of a negative electrode foil 172. The negative electrode mixture is a mixture of a negative electrode active material and a binder.

The positive foil 171 is an aluminum foil having a thickness of about 20 to 30 μm, and the negative foil 172 is a copper foil having a thickness of about 15 to 20 μm. The material of the

separators

173a and 173b is a microporous polyethylene resin through which lithium ions can pass. The positive electrode active material is a lithium-containing transition metal double oxide such as lithium manganate, and the negative electrode active material is a carbon material such as graphite capable of reversibly occluding and releasing lithium ions.

One of the end portions of the winding electrode group 170 in the width direction, that is, the direction of the winding central axis W perpendicular to the winding direction is a laminated portion of the positive electrode 174 and the other is a laminated portion of the negative electrode 175. Yes. The laminated portion of the positive electrode 174 provided at one end is obtained by laminating an uncoated positive electrode portion where the positive electrode mixture layer 176 is not formed, that is, an exposed portion of the positive foil 171. The laminated portion of the negative electrode 175 provided at the other end is obtained by laminating the negative electrode uncoated portion where the negative electrode mixture layer 177 is not formed, that is, the exposed portion of the negative electrode foil 172. The laminated portion of the positive electrode uncoated portion and the laminated portion of the negative electrode uncoated portion are respectively crushed in advance and connected to the positive electrode current collector 180 and the negative electrode current collector 190 by ultrasonic bonding, respectively.

Subsequently, FIG. 7 is a table showing the composition of the coating amount and the NP ratio of the positive electrode mixture of the cylindrical secondary batteries of Examples 1 to 5 and Comparative Examples 1 to 6. In Examples 1 to 5 and Comparative Examples 1 to 6, the lithium carbonate content is 1.8 wt% (wt%).

FIG. 8 is a table showing test results of overcharge tests of Examples 1 to 5 and Comparative Examples 1 to 6.
All the batteries were put into the end-of-charge state by constant current and constant voltage charging for 10 hours, 10 A, 4.2 V, and 3 hours before the test. At a temperature of 25 ° C., a direct current of 8.4 V and 10 A was applied to each battery using a direct current power source capable of knowing the accumulated amount of electricity supplied. The test was terminated when the current interruption mechanism was activated and the battery temperature was around 20 ° C.

Also, as a result of each overcharge test, the charge depth of each battery at the end of the test was indicated in SOC% based on the accumulated amount of electricity supplied. Note that SOC 100% corresponds to the state before the overcharge test.

The overcharge test results shown in FIG. 8 are the battery heat generation maximum temperature (° C.), the current interruption mechanism operation SOC (%), and the overcharge capacity (Ah) during the test.

As shown in the test results of Comparative Examples 1 and 3, when the coating amount of the positive electrode mixture is decreased in order to reduce the overcharge capacity and the battery internal resistance due to the battery heat generation, It has been found that the absolute amount of lithium carbonate decreases and the operating SOC (%) of the current interrupt mechanism tends to increase. Furthermore, an event was confirmed in which safety against overcharging was reduced and an excessively high temperature state (overtemperature) was reached.

Next, as shown in the test results of Comparative Example 1 and Comparative Example 2 and Example 1 and Example 5, as the NP ratio increases, the ability of the negative electrode to receive lithium from the positive electrode increases and excessively increases. The charge capacity was reduced and the battery heat generation was reduced. Moreover, it led to suppression of lithium dendrite precipitation during overcharging, and safety against overcharging was improved. However, if the NP ratio is increased too much, it is estimated that the battery internal resistance (DCR) increases, the battery temperature rises, and the safety during overcharge decreases. Furthermore, in FIG. 8, the range which the safety | security at the time of the overcharge shown by the claim improves is each shown.

The boundary line of the coating amount 110 g / m ² of the positive electrode mixture in the range of claim 1 is a boundary where the absolute amount of lithium carbonate in the battery is not less than the content of the coating amount 110 g / m ² of the positive electrode mixture. Moreover, the boundary line of NP ratio 1.4 is a boundary with high safety | security at the time of an overcharge whose overcharge capacity will be 14 Ah or less, and battery heat generation maximum temperature is 120 degrees C or less. The boundary line of the coating amount of the positive electrode mixture of 140 g / m ² is the result of the NP ratio of 1.4 or more, the overcharge capacity of 14 Ah or less, and the maximum battery heat generation temperature of 120 ° C. or less. Is set because a high boundary was confirmed. The boundary of the NP ratio 2.0 is set because an internal resistance increase of 1.3 times or more is expected compared to the NP ratio 1.4, and battery heat generation is expected to become remarkable.

The range of claim 2 shows the range where safety improvement at the time of overcharge can be expected with respect to claim 1.

The range of claim 3 shows the range in which the safety improvement at the time of overcharge can be expected with respect to claim 2.

The point of Claim 4 has shown the structure of the coating amount and NP ratio of the positive mix which can anticipate the safety | security improvement at the time of an overcharge most.

Although the embodiments of the present invention have been described in detail above, the present invention is not limited to the above-described embodiments, and various designs can be made without departing from the spirit of the present invention described in the claims. It can be changed. 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. Furthermore, it is possible to add, delete, and replace other configurations for a part of the configuration of each embodiment.

DESCRIPTION OF SYMBOLS 1 Cylindrical secondary battery 10 Electrode group 50 Sealing lid 60 Battery can 61 Caulking part 63 Grooving part 100 Rectangular secondary battery 101c Bottom plate 101a Wide side plate 101b Narrow side plate 101 Battery can 102 Battery lid 107 Lid assembly 170 Winding electrode group 174 Positive electrode 175 Negative electrode 176 Positive electrode mixture layer 177 Negative electrode mixture layer 180 Positive electrode current collector 181 Current interruption mechanism

Claims

A positive electrode coated with a positive electrode mixture, a negative electrode coated with a negative electrode mixture, a battery container containing the positive electrode and the negative electrode, and the internal pressure of the battery container becomes a predetermined operating pressure A secondary battery having a current interruption mechanism for interrupting current when
The positive electrode mixture includes 1 to 4% by weight of lithium carbonate,
The NP ratio, which is the ratio between the capacity of the positive electrode and the capacity of the negative electrode, is 1.4 or more and 2.0 or less, and the coating amount of the positive electrode mixture is 110 g / m 2 or more and 140 g / m 2 or less. A secondary battery characterized by being.
2. The secondary battery according to claim 1, wherein the NP ratio is 1.4 or more and 1.6 or less, and the coating amount of the positive electrode mixture is 120 g / m 2 or more and 140 g / m 2 or less. .
The secondary battery according to claim 2, wherein the NP ratio is 1.5, and the coating amount of the positive electrode mixture is 130 g / m 2 or more and 140 g / m 2 or less.
The secondary battery according to claim 3, wherein a coating amount of the positive electrode mixture is 130 g / m 2 .
The secondary battery according to claim 1, wherein the operating pressure of the current interrupt mechanism is 0.4 MPa or more and 1.0 MPa or less.