JP3018482B2 - Battery and manufacturing method thereof - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to a spirally wound electrode body formed by laminating a strip-shaped electrode and a strip-shaped separator and then winding the spirally wound electrode body in a battery can. And a method for manufacturing the same.

[Summary of the Invention]

In a battery in which a spirally wound electrode body is provided in a battery can, and the outer peripheral surface of the wound electrode body is covered with a shrinkable tube, both ends of the shrinkable tube correspond to those of the positive electrode. The separator is configured to be longer than the corresponding end but shorter than the corresponding end of the separator by the same length, thereby improving battery characteristics and productivity and efficiently preventing battery damage. It was done.

[Conventional technology]

2. Description of the Related Art Due to recent remarkable progress in electronic technology, electronic devices have been successively reduced in size and weight. Along with this, batteries that are smaller, lighter and have higher energy density are increasingly demanded as mobile power supplies.

Conventionally, aqueous batteries such as lead batteries and nickel-cadmium batteries have been the mainstream as secondary batteries for general use. Although these batteries are excellent in cycle characteristics, they cannot be said to have sufficiently satisfactory characteristics in terms of battery weight and energy density.

On the other hand, according to the non-aqueous electrolyte secondary battery using a non-aqueous solvent for the electrolyte and lithium or a lithium alloy for the negative electrode, weight reduction and high energy density can be achieved. Can also be improved. However, in the case of this non-aqueous electrolyte secondary battery, lithium tends to grow in a dendrite shape at the negative electrode during charging, so that with the progress of the charge / discharge cycle, the dendrite-like crystal reaches the positive electrode and causes an internal short circuit. There is a drawback that the possibility increases, which is a major obstacle to practical application.

Therefore, recently, research and development of a non-aqueous electrolyte secondary battery using a carbon material for a negative electrode have been actively performed.

According to the non-aqueous electrolyte secondary electrons, the lithium contained in the crystal structure of the positive electrode active material and lithium previously supported on the carbon material of the negative electrode by a chemical and physical method and lithium dissolved in the electrolytic solution are used. Since each of them is doped between the carbon layers of the carbon material in the negative electrode during charge / discharge and dedoped from the carbon layer, no dendrite-like crystal precipitation is observed on the negative electrode during charge even when the charge / discharge cycle proceeds. Therefore, excellent charge / discharge cycle characteristics exceeding 1,000 times can be obtained.

Applications of the nonaqueous electrolyte secondary battery as described above include use in devices such as video cameras and laptops and personal computers. Many of such devices consume relatively large current, which imposes a heavy burden on the battery. Therefore, a spiral wound electrode body structure is effective as the electrode structure of the battery.

FIG. 4A is a perspective view of a conventional spirally wound electrode body 25, and FIG.
FIG. 4B is a schematic partial longitudinal sectional view of the wound electrode body 25, respectively.

The spirally wound electrode body 25 is configured by laminating a strip-shaped negative electrode 1 and a strip-shaped positive electrode 2 via strip-shaped integral separators 3a and 3b, and then spirally winding in the longitudinal direction. .

The negative electrode 1 is provided with a negative electrode lead 11 and the positive electrode 2 is provided with a positive electrode lead 12 for current collection. Further, the wound electrode body 25 is housed in the battery can 5 indicated by a dashed line in FIG. 4A.

According to such a structure of the spirally wound electrode body 25, the battery area can be increased, so that it can sufficiently withstand a heavy load.

Further, in the battery assembling process as described above, an adhesive tape is attached to the outermost end of the electrode so that the wound spiral wound electrode body 25 is not loosened, and then the wound electrode body 25 is Inserted in can 5. In this case, the negative electrode lead 11 is bent and welded to the bottom of the electrode can 5.

In order to facilitate the above-mentioned insertion work, a certain clearance is required between the outer diameter of the wound electrode body 25 and the inner diameter of the battery can 5.

[Problems to be solved by the invention]

However, in the wound electrode body 25 described above, the looseness in the outer diameter direction is caused by the loosening of the adhesive tape after the completion thereof, or the thickness change of each of the electrodes 1 and 2 accompanying the charge and discharge during use of the battery. Sometimes happened.

The battery characteristics tend to be better when a certain pressure is applied between the electrodes 1 and 2. However, if the above-described loosening occurs, the battery characteristics are adversely affected.

Further, if the outer diameter of the spirally wound electrode body 25 increases due to the loosening, it becomes difficult to insert the spirally wound electrode body 25 into the battery can 5, so that the defective rate increases or the productivity decreases in the battery assembly process. Such a problem occurs.

An object of the present invention is to provide a battery with improved battery characteristics by reliably preventing loosening of a wound electrode body.

[Means for solving the problem]

According to the present invention, a spirally wound electrode body 15 formed by laminating a strip-shaped negative electrode 1 and a strip-shaped positive electrode 2 via strip-shaped separators 3a and 3b and then spirally winding the wound electrode body 15 in the battery can 5 is formed. In the battery, wherein the outer peripheral surface 16 of the wound electrode body 15 is covered with a shrinkable tube 20, each of both ends of the shrinkable tube 20 is more than the corresponding end of the strip-shaped positive electrode 2. It is long but the above separators 3a and 3b
Are shorter than the corresponding end portions by the same length m.

The shrinkable tube 20 is preferably a heat-shrinkable polymer tube that shrinks with warm air.

When manufacturing the battery, the wound electrode body 15
It is preferable to sequentially perform a first step of covering the outer peripheral surface with the contractible tube 20 and a second step of contracting the contractible tube 20 by heating.

[Action]

The wound electrode body 15 is uniformly shrunk in the radial direction by the shrinkable tube 20 on the outer peripheral surface 16. This uniform contraction force (force acting in the direction of the central axis C of the wound electrode body 15) continuously applies a constant pressure to the negative electrode 1 and the positive electrode 2, so that the loosening of the electrodes 1 and 2 continues. And the battery characteristics are improved.

Further, since the outer diameter of the wound electrode body 15 can be made constant, the clearance between the wound electrode body 15 and the battery can 5 can be kept constant.

〔Example〕

Hereinafter, an embodiment according to the present invention will be described with reference to FIGS.

FIG. 1 is a schematic vertical sectional view showing the structure of a cylindrical non-aqueous electrolyte secondary battery of this embodiment. FIG. 2 is a wound electrode body covered with a heat-shrinkable tube 20 shown in FIG. 15 is a perspective view of FIG.

In the negative electrode 1 in the non-aqueous electrolyte secondary battery shown in FIG. 1, a material that is doped with an alkali metal such as lithium and de-doped with the charging reaction can be used. Examples of such a material include a conductive polymer such as polyacetylene and polypyrrole, and a carbon material such as coke, polymer charcoal, and carbon fiber.

Carbon materials are particularly preferred because of their high energy density per unit volume.

In the positive electrode 2, a transition metal oxide such as manganese dioxide or vanadium pentoxide, or a transition metal chalcogenide such as iron sulfide or titanium sulfide, or a composite compound of a transition metal and lithium can be used. .
Such a material is preferable because a high voltage and a high energy density can be obtained and the cycle characteristics are excellent.

Among the above-mentioned materials, lithium-cobalt composite oxide or lithium-cobalt-nickel composite oxide can obtain higher high voltage and high energy density,
It is particularly preferable because the cycle characteristics are further excellent.

As the non-aqueous electrolyte, for example, a non-aqueous electrolyte obtained by dissolving a lithium salt as an electrolyte in a non-aqueous solvent (organic solvent) can be used.

Here, the organic solvent is not particularly limited,
For example, propylene carbonate, ethylene carbonate, 1,2-dimethoxyethane, 1,2-diethoxyethane,
r-butyrolactone, tetrahydrofuran, 1,3-dioxolane, 4-methyl-1,3-dioxolane, diethyl ether, sulfolane, methylsulfolane, acetonitrile, propionitrile, etc. can be used alone or in combination of two or more. .

As the electrolyte, conventionally known ones can be used, for example, LiCl
O ₄ , LiAsF ₆ , LiPF ₆ , LiBF ₄ , LiB (C ₆ H ₅ ) ₄ , LiCl, LiB
r, CH ₃ SO ₃ Li, CH ₃ SO ₃ Li, and the like.

The non-aqueous electrolyte may be fixed, for example, a polymer complex solid electrolyte.

As the heat-shrinkable tube 20 that works to compress the spiral wound electrode body 15 from the outer peripheral surface 16, various materials can be used, but the heat-shrinkable tube 20 has resistance to the organic solvent of the non-aqueous electrolyte. It is desirable to select in consideration of the above, or that the heating temperature at the time of heat shrinkage does not affect the separators 3a, 3b and the like.

In particular, considering the materials of the non-aqueous electrolyte and the separator used in the non-aqueous electrolyte secondary battery, a heat-shrinkable tube made of polyolefin, cross-linked polyolefin, polyvinyl chloride, saturated polyester, or the like is preferable.

The non-aqueous electrolyte secondary battery shown in FIG. 1 as described above was manufactured as follows.

Example 1 A negative electrode 1 was produced as follows.

After using petroleum pitch as a starting material and introducing 10 to 20% by weight of an oxygen-containing functional group (so-called oxygen cross-linking) into this, it is fired at 1000 ° C in an inert gas stream to be close to glassy carbon. A carbon material with properties was obtained.

As a result of performing X-ray diffraction measurement on this carbon material,
The spacing between the (002) planes was 3.76Å. Further, the true specific gravity was measured by a pycnometer method and found to be 1.58 g / cm ³ .

The above carbon material was pulverized to obtain a carbon material powder having an average particle diameter of 10 μm, and this powdered carbon material was used as a negative electrode active material carrier.

90 parts by weight of such a carbon material was mixed with 10 parts by weight of polyvinylidene fluoride (PVDF) as a binder to prepare a negative electrode mixture. This negative electrode mixture was dispersed in N-methylpyrrolidone as a solvent to form a slurry (paste).

Using a 10 μm-thick strip-shaped copper foil as the negative electrode current collector 9,
The negative electrode mixture slurry was applied to both surfaces of the current collector 9, dried, and then compression-molded to produce a strip-shaped negative electrode 1. The thickness of the negative electrode mixture after molding was 80 μm on both sides, the same, and the width of the electrode was 41.5 mm and the length was 700 mm. In this case, a negative electrode lead 11 made of nickel is welded to the negative electrode current collector 9.

 The positive electrode 2 was produced as follows.

A mixture of 0.5 mol of lithium carbonate and 1 mol of cobalt carbonate is calcined in air at 900 ° C. for 5 hours to give LiCoO.
_2, which was the LiCoO ₂ as a positive electrode active material.

To 91 parts by weight of such LiCoO _2, 6 parts by weight of graphite as a conductive agent and 3 parts of polyvinylidene fluoride as a binder
Parts by weight were mixed to form a positive electrode mixture. This positive electrode mixture was dispersed in N-methylpyrrolidone to form a slurry (paste).

A 20 μm-thick strip-shaped aluminum foil is used as the positive electrode current collector 10, a positive electrode mixture slurry is uniformly applied to both surfaces of the current collector 10, dried, and then compression-molded to form a strip-shaped positive electrode 2.
Was prepared. The thickness of the positive electrode mixture after molding is 80 μm on both sides
The width of the electrode was 40.5 mm and the length was 650 mm.
In this case, the positive electrode current collector 10 has an aluminum positive electrode lead.
12 are welded.

The strip-shaped negative electrode 1, the strip-shaped positive electrode 2 and the thickness 25 as described above.
A pair of separators 3a and 3b made of a microporous polypropylene film having a width of 44 μm and a width of 44 mm are laminated in the order of the negative electrode 1, the separator 3a, the positive electrode 2, and the separator 3b, and then the laminate is spirally wound many times. Thus, a spirally wound electrode body 15 as shown in FIG. 1 was produced.

The inner diameter of the hollow portion at the center of the wound electrode body 15 is
The outer diameter was 3.5 mm and the outer diameter was 20 mm. The core 33 is located in this hollow portion.

This wound electrode body 15 has a thickness of 90 μm, a width of 42 mm, and a circumference of
After covering with a heat-shrinkable tube 20 made of a polyvinyl chloride material of 70 mm, the heat-shrinkable tube 20 was shrunk by heating with hot air of a dryer for 5 seconds.

The contraction of the heat-shrinkable tube 20 causes the wound electrode body
As shown in FIG. 2, a contraction force as shown by an arrow is applied to the outer peripheral surface 16 from the outer peripheral surface 16 to the central axis C uniformly. Therefore, it is possible to create a state in which the electrodes 1 and 2 are pressed from the outer peripheral surface 16 of the spirally wound electrode body 15 in the direction of the central axis C, and this state is maintained even during use of the battery. Therefore, the loosening of the electrodes 1 and 2 can be reliably prevented from the completion of the wound electrode body 15 to the use thereof.

As shown in FIGS. 1 and 2, the heat-shrinkable tube 20 covers the outer peripheral surface of the spirally wound electrode body 15, and both ends of the heat-shrinkable tube 20 are separated by separators 3a and 3b. Are slightly shorter than the corresponding end portions. For example, m shown in FIG. 2 is about 1 mm. This is because both ends of the heat-shrinkable tube 20 are separated by a separator.
When protruding from both ends of 3a and 3b, the negative electrode 1 and the positive electrode 2 (both ends of the heat-shrinkable tube 20 are longer than the corresponding ends of the positive electrode 2 as shown in FIG. 1). This is to eliminate the risk that the heat-shrinkable tube 20 is deformed when contracted and shatters to break through the separators 3a and 3b. The position of the heat-shrinkable tube 20 before the contraction is adjusted so that the above “m” is substantially the same at both the upper and lower ends of the wound electrode body 15.

Next, the wound electrode body 15 covered with the heat-shrinkable tube 20 as described above was housed in a nickel-plated iron battery can 5 as shown in FIG.

At this time, since the wound electrode body 15 is not tightly bound by an adhesive tape or the like as in the related art, but is entirely tightly bound by the heat-shrinkable tube 20, it is wound. The outer diameter of the rotating electrode body 15 is substantially constant.
Therefore, the clearance between the inner diameter of the battery can 5 and the outer diameter of the spirally wound electrode body 15 becomes constant, so that the operation of inserting the battery into the battery can 5 can be performed smoothly. As a result, defects in the conventional battery assembly process can be corrected to reduce the defective rate and improve the productivity.

Insulating plates 4a and 4b are respectively disposed on the upper and lower surfaces of the wound electrode body 15, and the negative electrode lead 11 derived from the negative electrode current collector 9 is welded to the bottom of the battery can 5 and the positive electrode current collector 10 The derived positive electrode lead 12 was welded to the projection 34a of the metal safety valve 34.

In this battery can 5, propylene carbonate and 1,2-
A non-aqueous electrolyte in which LiPF ₆ was dissolved at a ratio of 1 mol / in a mixed solvent of the same volume with dimethoxyethane was injected.

Thereafter, the battery can 5 and the safety valve whose outer periphery is in close contact with each other
The battery can 5 was sealed by caulking each of the metal cover 34 and the metal battery cover 7 through an insulating sealing gasket 6 coated with asphalt on the surface. Thereby, the battery lid 7 and the safety valve 34 were fixed, and the airtightness in the battery can 5 was maintained. At this time, the lower end of the gasket 6 in FIG. 1 contacts the outer peripheral surface of the insulating plate 4a, so that the insulating plate 4a is in close contact with the upper surface of the spirally wound electrode body 15.

As described above, a cylindrical nonaqueous electrolyte secondary battery having a diameter of 20 mm and a height of 50 mm was produced.

The cylindrical non-aqueous electrolyte secondary battery has a safety valve 34, a stripper 36, and an intermediate fitting made of an insulating material for integrating the safety valve 34 and the stripper 36 in order to constitute a double safety device. It has a coalescence 35. Although not shown, the safety valve 34 is provided with a cleaving portion which is cleaved when the safety valve 34 is deformed, and the battery cover 7 is provided with a hole.

If the internal pressure of the battery rises for some reason, the safety valve 34 is deformed upward in FIG. 1 around the projection 34a, and the connection between the positive electrode lead 12 and the projection 34a is cut off. To shut off the current or use a safety valve
Each of the 34 cleavage portions is configured to cleave and exhaust gas generated in the battery.

Example 2 In Example 2, a saturated polyester-based heat-shrinkable tube having a thickness of 75 μm, a width of 42 mm, and a circumference of 70 mm was used as the heat-shrinkable tube 20 in FIGS. 1 and 2. The heat-shrinkable tube 20 is placed over the wound electrode body 15 and then heated for 5 seconds with hot air from a dryer to shrink the wound electrode body 15.
A cylindrical non-aqueous electrolyte battery having a diameter of 20 mm and a height of 50 mm was prepared in the same manner as in Example 1 except for using.

Comparative Example As a comparative example for confirming the effect of the present invention, a cylindrical non-aqueous liquid having a diameter of 20 mm and a height of 50 mm was used in the same manner as in Example 1 except that a wound electrode body not covered with a heat-shrinkable tube was used. An electrolyte battery was manufactured.

20 batteries of each of the three types in Examples 1 and 2 and the comparative example were prepared, the upper limit voltage was set to 4.1 V, the battery was charged at a constant current of 1 A for 2.5 hours, and the final voltage was set at a constant resistance of 7.5 Ω. 2.75
The charge / discharge cycle of discharging to V was repeated.

FIG. 3 is a characteristic diagram showing a change in energy density (WH /) of each battery accompanying such a charge / discharge cycle.

Table 1 below shows the average value (the number of samples n = 20) of the energy density at the 10th cycle of these batteries (hereinafter, referred to as “initial energy density”).

As shown in Table 1, the battery of this example has a higher initial energy density than the battery of the conventional comparative example.

Table 2 shows the energy density after 200 cycles, and the average cycle deterioration rate per cycle obtained from the ratio of the initial energy density to the energy density after 200 cycles.

As shown in Tables 2 and 3, the battery of this example has a higher energy density after 200 cycles than the battery of the conventional comparative example, and has a smaller average cycle deterioration rate per cycle.

As described above, according to the non-aqueous electrolyte secondary battery of the present embodiment, since the energy density is higher than that of the conventional battery and the deterioration of the energy density due to the charge / discharge cycle is small,
Battery characteristics can be improved. Thus, a cylindrical non-aqueous electrolyte secondary battery having a high capacity and a long cycle life can be obtained.

〔The invention's effect〕

As described above, according to the present invention, the outer peripheral surface of the spirally wound spirally wound electrode body is covered with the contractible tube so that a contraction force acts on the outer peripheral surface in the radial direction. The loosening of the electrodes can be reliably prevented continuously over substantially the entire length of the electrode body, and battery characteristics such as energy density, battery capacity, and cycle life can be improved.

In addition, the outer peripheral surface of the spirally wound electrode body is covered with a contractible tube so that a contraction force acts in the radial direction from the outer peripheral surface, and both ends of the contractible tube are band-shaped. By making the shrinkable tubes symmetrically arranged in the central axis direction with respect to both ends of the strip-shaped separator by shortening the separators by the same length from the corresponding ends thereof, the wound electrode body The shrinking force of the shrinkable tube applied toward the central axis is symmetrically applied to both ends of the wound electrode body in the central axis direction. Therefore, an excessive contraction force is applied to both ends of the wound electrode body which is relatively easily deformed when the contractible tube shrinks, and both ends are excessively deformed. Since there is no possibility that the portion is distorted or swelled, the outer diameter of the spirally wound electrode body can be made constant over almost the entire length, and therefore, the clearance between the battery can and the spirally wound electrode body can be substantially the same length. Over time. Therefore, in the battery assembling process, the work of inserting the wound electrode body into the battery can can be performed smoothly, so that the defective rate can be reduced and the productivity can be improved.

Further, since each of both ends of the shrinkable tube is longer than the corresponding ends of the strip-shaped positive electrode but shorter than the corresponding ends of the strip-shaped separator by the same length, the shrinkage of the shrinkable tube is reduced. At the time, both ends of the wound electrode body, which are relatively easily deformed, are subjected to excessive contraction force and are excessively deformed, so that the band-shaped positive electrode made of a transition metal oxide or the like breaks through the band-shaped separator. There is no danger of shorting,
Battery damage can be effectively prevented.

According to the second aspect of the invention, the energy density of the battery can be increased.

According to the third aspect of the invention, the voltage and the energy density of the battery can be respectively increased, and the cycle characteristics of the battery can be excellent.

[Brief description of the drawings]

FIG. 1 is a longitudinal sectional view showing a configuration of a nonaqueous electrolyte secondary battery according to an embodiment of the present invention, FIG. 2 is a perspective view of a spirally wound electrode body shown in FIG. 1, and FIG. FIG. 4 is a characteristic diagram showing a change in energy density of each battery according to a charge / discharge cycle of FIG. FIG. 4A is a perspective view of a wound electrode body of a conventional nonaqueous electrolyte secondary battery, and FIG. 4B is a longitudinal sectional view showing a part of a longitudinal section of the wound electrode body shown in FIG. 4A. In addition, in the code | symbol used for drawing, 1 ... negative electrode 2 ... positive electrode 3a, 3b ... separator 5 ... battery can 15 ... wound electrode body 16 ... outer peripheral surface 20 ... heat-shrinkable tube (shrinkable tube) ).

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-3-245466 (JP, A) JP-A-61-197653 (JP, U) JP-B-45-16660 (JP, B1) JP-B-46 18908 (JP, Y1) (58) Fields investigated (Int. Cl. ⁷ , DB name) H01M 10 / 04,10 / 28,10 / 40 H01M 6 / 02,6 / 16

Claims (4)

(57) [Claims] 1. A battery electrode comprising a wound electrode body formed by laminating a strip-shaped negative electrode and a strip-shaped positive electrode via a strip-shaped separator and spirally winding the stacked electrode body in a battery can. In a battery in which the outer peripheral surface of the body is covered by a shrinkable tube, each of both ends of the shrinkable tube is longer than the corresponding end of the strip-shaped positive electrode, but the end corresponding to these of the strip-shaped separator. The battery is configured to be shorter by the same length than the part. 2. The battery according to claim 1, wherein a carbon material is used for the strip-shaped negative electrode. 3. The belt-shaped positive electrode according to claim 1, wherein at least one selected from the group consisting of a transition metal oxide, a transition metal chalcogen compound, and a composite compound of a transition metal and lithium is used. 3. The battery according to 1 or 2. 4. The method for manufacturing a battery according to claim 1, wherein the first step of covering an outer peripheral surface of the spirally wound electrode body with a shrinkable tube; A method for manufacturing a battery, comprising: sequentially performing a second step of shrinking by heating.