JP7506506B2 - Non-aqueous electrolyte secondary battery - Google Patents

Description

This disclosure relates to a non-aqueous electrolyte secondary battery.

In a secondary battery, the opening of the exterior body that contains the electrode body and electrolyte is sealed with a sealing body. In order to give the sealing body functions such as explosion prevention, the sealing body may be composed of multiple parts. In this case, multiple parts may be crimped and fixed inside the sealing body via an insulating member, and electrical continuity may be ensured by contacting the metal parts with each other. Patent Document 1 discloses a sealing body in which the surface of the spacer is metal-plated and the contact surface between the spacer and the metal foil is welded to reduce internal resistance.

JP 2007-27020 A

In recent years, the applications of secondary batteries have expanded, and they are sometimes used not only indoors but also outdoors. Compared to indoors, the outdoor environment is harsher, with large changes in temperature and humidity, and the insulating material may deteriorate, causing a decrease in the contact pressure of the conductive part of the sealing body that is crimped and fixed, resulting in an increase in the internal resistance of the battery. Patent Document 1 does not take into account the deterioration of the insulating material, and there is still room for improvement regarding the decrease in contact pressure of the conductive part.

The objective of this disclosure is to provide a non-aqueous electrolyte secondary battery that can suppress an increase in internal resistance even in harsh environments.

The nonaqueous electrolyte secondary battery according to one aspect of the present disclosure includes an electrode assembly including a positive electrode, a negative electrode, and a separator, a cylindrical exterior body with a bottom that houses the electrode assembly, and a sealing body that seals the opening of the exterior body. The sealing body includes a first valve cap that is a positive electrode terminal, an explosion-proof valve, an intermediate member sandwiched between the first valve cap and the explosion-proof valve, and a second valve cap that is in contact with the bottom of the explosion-proof valve and that crimps and fixes the first valve cap, the intermediate member, and the explosion-proof valve via an insulating member at the bent peripheral portion, and is characterized in that the contact pressure between the first valve cap and the intermediate member is nonuniform.

The nonaqueous electrolyte secondary battery according to the present disclosure can suppress an increase in internal resistance even after long-term use.

1 is an axial cross-sectional view of a cylindrical secondary battery according to an embodiment of the present invention; 2 is a cross-sectional view of a sealing body provided in the secondary battery shown in FIG. 1 . 3A to 3C are front and side views of an intermediate member constituting the sealing body shown in FIG. 2, and FIG. 3D is a front and side view of an intermediate member used in a conventional secondary battery.

In the following, an example of an embodiment of a cylindrical secondary battery according to the present disclosure will be described in detail with reference to the drawings. In the following description, the specific shapes, materials, values, directions, etc. are examples for facilitating understanding of the present invention, and can be appropriately changed according to the specifications of the cylindrical secondary battery. In addition, the exterior body is not limited to a cylindrical shape, and may be, for example, a rectangular shape. In addition, in the following description, when multiple embodiments and modified examples are included, it is assumed from the beginning that the characteristic parts of these will be used in appropriate combination.

Figure 1 is an axial cross-sectional view of a cylindrical secondary battery 10, which is an example of an embodiment. The secondary battery 10 includes an electrode body 14, an exterior body 15 that houses the electrode body 14, and a sealing body 16 that seals the opening of the exterior body 15. The electrode body 14 has a wound structure in which a positive electrode 11 and a negative electrode 12 are wound with a separator 13 interposed therebetween. The outermost periphery of the electrode body 14 is the separator 13 in Figure 1, but it may also be the negative electrode 12. In addition, the electrode body 14 is not limited to a wound type, and may be a laminated type. In the following, for convenience of explanation, the sealing body 16 side will be described as the "top" and the bottom side of the exterior body 15 as the "bottom".

The positive electrode 11 may have a strip-shaped positive electrode collector and a positive electrode mixture layer formed on both sides of the positive electrode collector. For example, a metal foil such as aluminum or a film with the metal disposed on the surface layer is used for the positive electrode collector. The positive electrode mixture layer contains at least a positive electrode active material, and may also contain a conductive agent, a binder, etc. An example of the positive electrode active material is a lithium-containing transition metal oxide containing a transition metal element such as Co. The positive electrode 11 can be produced by applying a positive electrode mixture slurry in which the positive electrode active material and the like are dispersed in a solvent to both sides of the positive electrode collector, and then drying and compressing the positive electrode mixture layer.

The negative electrode 12 may have a strip-shaped negative electrode collector and a negative electrode mixture layer formed on both sides of the negative electrode collector. For example, a metal foil such as copper or a film with the metal disposed on the surface layer is used for the negative electrode collector. The negative electrode mixture layer contains at least a negative electrode active material and may contain a binder, etc. Examples of the negative electrode active material include carbon materials such as natural graphite and artificial graphite. The negative electrode 12 can be produced by applying a negative electrode mixture slurry, in which the negative electrode active material, etc. is dispersed in a solvent, to both sides of the negative electrode collector, and then drying and compressing the negative electrode mixture layer.

The exterior body 15 contains a non-aqueous electrolyte (not shown) in addition to the electrode body 14. As a non-aqueous solvent (organic solvent) for the non-aqueous electrolyte, carbonates, lactones, ethers, ketones, esters, etc. can be used, and two or more of these solvents can be mixed. As an electrolyte salt for the non-aqueous electrolyte, LiPF ₆ , LiBF ₄ , LiCF ₃ SO ₃ , etc., and mixtures thereof can be used. The amount of electrolyte salt dissolved in the non-aqueous solvent can be, for example, 0.5 to 2.0 mol/L.

The opening of the exterior body 15 is closed with the sealing body 16, so that the inside of the secondary battery 10 is sealed. Insulating plates 17, 18 are provided above and below the electrode body 14. A positive electrode lead 19 attached to the inner peripheral end of the positive electrode 11 extends upward through a through hole in the insulating plate 17 and is welded to the sealing body 16. In the secondary battery 10, the sealing body 16 serves as the positive electrode terminal. On the other hand, a negative electrode lead 20 attached to the outer peripheral end of the negative electrode 12 passes outside the insulating plate 18, extends to the bottom side of the exterior body 15, and is welded to the inner surface of the bottom of the exterior body 15. In the secondary battery 10, the exterior body 15 serves as the negative electrode terminal.

The exterior body 15 is a cylindrical metal exterior can with a bottom. A gasket 21 is provided between the exterior body 15 and the sealing body 16 to ensure the internal sealing of the secondary battery 10. The exterior body 15 has a grooved portion 22 that supports the sealing body 16, formed, for example, by pressing the side portion from the outside. The grooved portion 22 is preferably formed in an annular shape along the circumferential direction of the exterior body 15, and its upper surface supports the sealing body 16 via the gasket 21.

Next, the sealing body 16 will be described in detail with reference to the cross-sectional view of the sealing body 16 shown in FIG. 2. The sealing body 16 includes a first valve cap 30, which is a positive terminal, an explosion-proof valve 32, an intermediate member 34 sandwiched between the first valve cap 30 and the explosion-proof valve 32, and a second valve cap 38 that is in contact with the bottom of the explosion-proof valve 32 and that crimps and fixes the first valve cap 30, the intermediate member 34, and the explosion-proof valve 32 via an insulating member 36 at the bent peripheral portion.

Each member constituting the sealing body 16 has, for example, a disk shape or a ring shape, and each member except for the insulating member 36 is electrically connected to each other. The explosion-proof valve 32 and the second valve cap 38 are connected to each other at their respective centers, and are fixed to each other, for example, by ultrasonic welding or the like. The explosion-proof valve 32 and the first valve cap 30 are electrically connected to each other at their respective peripheral edges via the intermediate member 34.

The sealing body 16 has an explosion-proof function. When the internal pressure of the secondary battery 10 rises due to abnormal heat generation, the explosion-proof valve 32 swells toward the first valve cap 30 and separates from the second valve cap 38, cutting off the electrical connection between them. If the internal pressure rises further, the explosion-proof valve 32 breaks and gas is discharged from the opening 30a of the first valve cap 30.

The shape of the first valve cap 30 is not particularly limited, but since the first valve cap 30 of the sealing body 16 serves as the positive terminal, it may protrude upward as shown in FIG. 2. This makes it easier to connect the first valve cap 30 to external devices, etc. The material of the first valve cap 30 is not particularly limited as long as it is conductive, and may be, for example, nickel-plated iron, aluminum, or an aluminum alloy.

The explosion-proof valve 32 is, for example, a thin plate-shaped metal member. As described above, when the internal pressure of the secondary battery 10 increases, the ring-shaped intermediate member 34 is inverted upward about the inner circumference of the ring-shaped intermediate member 34 as a fulcrum, and moves away from the second valve cap 38. The explosion-proof valve 32 may have a notch 40 as shown in FIG. 2. The notch 40 becomes the starting point for rupture when the internal pressure of the secondary battery 10 increases further.

The second valve cap 38 is a disk-shaped member larger than the first valve cap 30, the intermediate member 34, and the explosion-proof valve 32, as described above, and has a through hole to transmit the internal pressure of the secondary battery 10 to the explosion-proof valve 32. The material of the second valve cap 38 is not particularly limited as long as it is conductive, and may be, for example, aluminum or an aluminum alloy.

The insulating member 36 electrically isolates the second valve cap 38 from the first valve cap 30, the intermediate member 34, and the explosion-proof valve 32 at the periphery. The insulating member 36 is elastic, and is compressed in the vertical direction to ensure airtightness between the first valve cap 30, the intermediate member 34, and the explosion-proof valve 32. In other words, by covering the periphery of the first valve cap 30, the intermediate member 34, and the explosion-proof valve 32 with the insulating member 36 and the second valve cap 38 and applying a load in the vertical direction to crimp and fix them, the repulsive force from the compressed insulating member 36 is applied to the first valve cap 30, the intermediate member 34, and the explosion-proof valve 32 from the vertical direction, and a certain level of contact pressure can be ensured. The material of the insulating member 36 is not particularly limited as long as it fulfills the above-mentioned functions, and examples that can be used include polypropylene (PP), polyphenylene sulfide (PPS), polyethylene (PE), polybutylene terephthalate (PBT), perfluoroalkoxyalkane (PFA), polytetrafluoroethylene (PTFE), polyamide (PA), etc.

Next, the intermediate member 34 will be described with reference to FIG. 3. FIGS. 3(a) to 3(c) are front and side views of the intermediate member 34 constituting the sealing body 16 according to the present disclosure, and FIG. 3(d) is a front and side view of the intermediate member 34 used in a conventional secondary battery 10.

3A is ring-shaped and has an uneven thickness. The thickness of the left half is t1, and the thickness of the right half is t2, which is thicker than t1. By forming the sealing body 16 using the intermediate member 34a having parts of different thicknesses, the contact pressure between the first valve cap 30 and the intermediate member 34a becomes uneven, resulting in a so-called one-sided contact state. As a result, even if the elastic force of the insulating member 36 decreases with long-term use, the contact pressure between the intermediate member 34a and the first valve cap 30 can be maintained at least in the part that is in contact with the intermediate member 34a at a stronger pressure than other parts due to the one-sided contact, so that an increase in internal resistance can be suppressed. Similarly, it is preferable that the contact pressure between the explosion-proof valve 32 and the intermediate member 34a is uneven.

In FIG. 3(a), thickness t1 is, for example, 0.05 mm to 1.0 mm, and preferably 0.1 mm to 0.5 mm. Thickness t2 is, for example, 0.1 mm to 1.5 mm, and preferably 0.2 mm to 0.6 mm, and the difference between thickness t2 and thickness t1 is, for example, 0.05 mm to 0.5 mm, and preferably 0.05 mm to 0.2 mm. Note that in intermediate member 34a, the area ratio of the thicker portion to the thinner portion is not limited to 1:1, and is preferably 1:3 to 3:1.

The intermediate member 34b in FIG. 3(b) has a spiral shape, and has a so-called spring washer shape. The height difference t3 between the upper surface of one end and the upper surface of the other end is, for example, 0.3 mm to 1.0 mm, and preferably 0.5 mm to 0.9 mm. The thickness of the intermediate member 34b is, for example, 0.05 mm to 1.0 mm, and preferably 0.1 mm to 0.5 mm, and may be constant. By forming the sealing body 16 using the intermediate member 34b having a spiral shape, an elastic force acts locally on the intermediate member 34b, so that the contact pressure between the first valve cap 30 and the intermediate member 34b becomes uneven, resulting in a so-called one-sided contact state. As a result, even if the elastic force of the insulating member 36 decreases with long-term use, a certain level of contact pressure can be maintained at least in the part between the intermediate member 34b and the first valve cap 30 that is in contact with the intermediate member 34b at a stronger pressure than other parts due to the one-sided contact, so that an increase in internal resistance can be suppressed.

The intermediate member 34c in FIG. 3(c) is ring-shaped and has a slope from the outer periphery to the inner periphery. The height difference t4 between the upper surface of the outer periphery and the upper surface of the inner periphery is, for example, 0.1 mm to 0.7 mm, preferably 0.3 mm to 0.5 mm. The thickness of the intermediate member 34c is, for example, 0.05 mm to 1.0 mm, preferably 0.1 mm to 0.5 mm, and may be constant. By forming the sealing body 16 using the intermediate member 34c having a slope from the outer periphery to the inner periphery, an elastic force acts locally on the intermediate member 34c, so that the contact pressure between the first valve cap 30 and the intermediate member 34c becomes uneven, resulting in a so-called one-sided contact state. As a result, even if the elastic force of the insulating member 36 decreases with long-term use, the contact pressure between the intermediate member 34c and the first valve cap 30 can be maintained at least in the part that is in contact with the intermediate member 34c at a higher pressure than other parts due to the one-sided contact, so that an increase in internal resistance can be suppressed.

The intermediate member 34d in FIG. 3(d) has a ring shape and has the shape of a normal washer. The thickness of the intermediate member 34d is constant at about 0.3 mm. By forming the sealing body 16 using the intermediate member 34d, the intermediate member 34d is crimped between the first valve cap 30 and the explosion-proof valve 32 in a nearly parallel state, so that the contact pressure between the first valve cap 30 and the intermediate member 34d becomes uniform. If the elastic force of the insulating member 36 decreases due to long-term use, the contact pressure between the intermediate member 34b and the first valve cap 30 decreases uniformly on the contact surface, which may increase the internal resistance of the secondary battery 10.

The present disclosure will be further explained below with reference to examples, but the present disclosure is not limited to these examples.

Example 1
[Preparation of positive electrode]
Lithium cobalt oxide represented by _LiCoO2 was used as the positive electrode active material. 100 parts by mass of this positive electrode active material, 1 part by mass of acetylene black (AB) as a conductive agent, and 1 part by mass of polyvinylidene fluoride (PVDF) as a binder were mixed, and an appropriate amount of N-methyl-2-pyrrolidone (NMP) was added to prepare a positive electrode mixture slurry. Next, this positive electrode mixture slurry was applied to both sides of a positive electrode collector made of aluminum foil, dried in a dryer, cut into a predetermined electrode size, and rolled using a roller to obtain a band-shaped positive electrode. In addition, a plain part where no active material was formed was formed at one end in the longitudinal direction of the positive electrode, and an aluminum positive electrode lead was fixed to the plain part by ultrasonic welding.

[Preparation of negative electrode]
As the negative electrode active material, powder of natural graphite was used. 100 parts by mass of this negative electrode active material, 1 part by mass of styrene-butadiene rubber (SBR) as a binder, and 1 part by mass of carboxymethyl cellulose (CMC) as a thickener were mixed, and an appropriate amount of water was added to prepare a negative electrode mixture slurry. Next, this negative electrode mixture slurry was applied to both sides of a negative electrode current collector made of copper foil, dried in a dryer, cut into a predetermined electrode size, and rolled using a roller to obtain a band-shaped positive electrode. In addition, a plain part where no active material was formed was formed at one end in the length direction of the negative electrode, and a nickel negative electrode lead was fixed to the plain part by ultrasonic welding.

[Preparation of electrode body]
The prepared positive and negative electrodes were spirally wound with a separator between them to prepare a wound electrode body. At this time, one end of the positive electrode connected to the positive electrode lead was located on the inner periphery side (the start of winding side), and one end of the negative electrode connected to the negative electrode lead was located on the outer periphery side (the end of winding side). The separator used was a polyethylene microporous film with a heat-resistant layer formed on one side in which polyamide and alumina fillers were dispersed.

[Preparation of non-aqueous electrolyte]
_{LiPF6 was} added to a mixed solvent obtained by mixing ethylene carbonate (EC), ethyl methyl carbonate (EMC), and diethyl carbonate (DEC) in a volume ratio of EC:EMC:DMC=3:3:4 to give a concentration of 1 mol/L to prepare a nonaqueous electrolyte solution.

[Preparation of intermediate member]
A three-layer clad plate of Ni-Fe-Ni was pressed so that the thickness of one side was 0.3 mm and the thickness of the other side was 0.4 mm, with the center line as the boundary. A ring shape was punched out so that the diameter passed through the center line of the clad plate, and an intermediate part was produced. The outer shape of the intermediate part was the same as that shown in Figure 3(a), with an outer diameter of φ15 mm and an inner diameter of φ6.3 mm.

[Preparation of sealing body]
The insulating member and the explosion-proof valve were laminated on the second valve cap, and the bottom of the explosion-proof valve and the second valve cap were ultrasonically welded. Furthermore, the intermediate member and the first valve cap were laminated on the explosion-proof valve, and then the peripheral portion of the second valve cap was bent, and the first valve cap, the intermediate member, and the explosion-proof valve were crimped and fixed via the insulating member to produce a sealing body.

[Preparation of secondary battery]
A cylindrical exterior body with a diameter of φ18 mm and a height of 65 mm was prepared. Insulating plates were placed on the top and bottom of the electrode body, respectively, the negative electrode lead was welded to the bottom of the exterior body, and the positive electrode lead was welded to the sealing body, and then the electrode body was housed in the exterior body. Then, a nonaqueous electrolyte was injected into the interior of the exterior body. Furthermore, the opening of the exterior body was sealed with a sealing body via a gasket to prepare a cylindrical nonaqueous electrolyte secondary battery. The secondary battery prepared had a nominal voltage of 4.2 V and a rated capacity of 1500 mAh. In this manner, five secondary batteries were prepared.

[Evaluation of durability]
The following heat shock cycle test was performed on all of the five secondary batteries. The internal resistance of the secondary batteries was measured before and after the heat shock cycle test using a low resistance meter (AC four-terminal method set at a measurement frequency of 1 kHz). The average value of the internal resistance of the five secondary batteries was calculated to evaluate the durability.
<Heat shock cycle test>
The secondary battery was held at -30°C for 30 minutes and then held at 70°C for 30 minutes, which constituted one cycle of the heat shock test. After this cycle test was performed 500 times, the secondary battery was returned to room temperature, and the internal resistance after 500 cycles was measured. After that, this cycle was performed another 500 times, and the secondary battery was returned to room temperature, and the internal resistance after 1000 cycles was measured.

Example 2
In the preparation of the intermediate member, a ring-shaped sample with an outer diameter of φ15 mm and an inner diameter of φ6.3 mm was prepared by punching using a pressed Ni-Fe-Ni three-layer clad plate with a thickness of 0.3 mm, and then this ring-shaped sample was cut in one place with a width of 2 mm, and then bent so that the difference in height between the upper surface of one end and the upper surface of the other end was 0.7 mm to prepare the intermediate member. Except for this, a secondary battery was prepared and evaluated in the same manner as in Example 1. The crimping load when preparing the sealing body was the same as in Example 1. The outer shape of the intermediate member was the same as that shown in FIG. 3(b).

Example 3
In the preparation of the intermediate member, a ring-shaped sample with an outer diameter of φ15 mm and an inner diameter of φ6.3 mm was prepared by punching out a pressed Ni-Fe-Ni three-layer clad plate with a thickness of 0.3 mm, and the center of the ring-shaped sample was pressed with a spherical punch with a tip diameter of φ10 mm to prepare an intermediate member in a bowl shape with a height difference of 0.4 mm between the upper surface of the outer periphery and the upper surface of the inner periphery. Except for this, a secondary battery was prepared and evaluated in the same manner as in Example 1. The crimping load during the preparation of the sealing body was the same as in Example 1. The outer shape of the intermediate member was the same as that shown in FIG. 3(c).

Comparative Example
A secondary battery was produced and evaluated in the same manner as in Example 1, except that the intermediate member was produced by punching a pressed Ni-Fe-Ni three-layer clad plate having a thickness of 0.3 mm into a ring shape having an outer diameter of φ15 mm and an inner diameter of φ6.3 mm. The crimping load during the production of the sealing body was the same as in Example 1. The outer shape of the intermediate member was the same as that shown in FIG. 3(d).

Table 1 shows the measurement results of the internal resistance of the batteries after the heat shock cycle test in the examples and comparative examples. For each of the batteries in the examples and comparative examples, the average internal resistance of the battery before the heat shock cycle test was set to 100, and the average internal resistance after 500 cycles and 1000 cycles was shown as a relative value. The crimping load when making the sealing body was the same as in Example 1. The initial internal resistance of the batteries in Examples 1 to 3 and the comparative example was the same.

In Examples 1 to 3, the increase in the internal resistance of the battery was significantly suppressed compared to the Comparative Example. It is believed that the elasticity of the insulating member is reduced to the same extent in both the Example and Comparative Example batteries, but in the Example battery, the effect of the shape of the intermediate member allows the contact pressure between the metal parts to be maintained at a high level, which is presumably why the increase in the internal resistance of the battery was suppressed.

10 Secondary battery, 11 Positive electrode, 12 Negative electrode, 13 Separator, 14 Electrode body, 15 Exterior body, 16 Sealing body, 17, 18 Insulating plate, 19 Positive electrode lead, 20 Negative electrode lead, 21 Gasket, 22 Grooved portion, 30 First valve cap, 32 Explosion-proof valve, 34 Intermediate member, 36 Insulating member, 38 Second valve cap

Claims (4)

A nonaqueous electrolyte secondary battery comprising: an electrode assembly including a positive electrode, a negative electrode, and a separator; a cylindrical exterior body having a bottom and configured to house the electrode assembly; and a sealing body that seals an opening of the exterior body,
The sealing body is
A first valve cap which is a positive terminal;
Explosion-proof valve;
an intermediate member sandwiched between the first valve cap and the explosion-proof valve;
a second valve cap that is in contact with the bottom of the explosion-proof valve and that is crimped and fixed to the first valve cap, the intermediate member, and the explosion-proof valve via an insulating member at a bent peripheral portion;
the intermediate member has a ring shape and a non-uniform thickness;
a contact pressure between the first valve cap and the intermediate member being non-uniform; The nonaqueous electrolyte secondary battery according to claim 1, wherein the contact pressure between the explosion-proof valve and the intermediate member is non-uniform. A nonaqueous electrolyte secondary battery comprising: an electrode assembly including a positive electrode, a negative electrode, and a separator; a cylindrical exterior body having a bottom and configured to house the electrode assembly; and a sealing body that seals an opening of the exterior body,
The sealing body is
A first valve cap which is a positive terminal;
Explosion-proof valve;
an intermediate member sandwiched between the first valve cap and the explosion-proof valve;
a second valve cap that is in contact with the bottom of the explosion-proof valve and that is crimped and fixed to the first valve cap, the intermediate member, and the explosion-proof valve via an insulating member at a bent peripheral portion;
the intermediate member has a helical shape;
a contact pressure between the first valve cap and the intermediate member being non-uniform; A nonaqueous electrolyte secondary battery comprising: an electrode assembly including a positive electrode, a negative electrode, and a separator; a cylindrical exterior body having a bottom and configured to house the electrode assembly; and a sealing body that seals an opening of the exterior body,
The sealing body is
A first valve cap which is a positive terminal;
Explosion-proof valve;
an intermediate member sandwiched between the first valve cap and the explosion-proof valve;
a second valve cap that is in contact with the bottom of the explosion-proof valve and that is crimped and fixed to the first valve cap, the intermediate member, and the explosion-proof valve via an insulating member at a bent peripheral portion;
the intermediate member has a ring shape and is inclined from an outer circumferential edge toward an inner circumferential edge,
a contact pressure between the first valve cap and the intermediate member being non-uniform;

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