JP2000306607A - Nonaqueous electrolyte battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce generation of defectives when manufacturing a nonaqueous electrolyte battery having a battery capacity not less than 100 Ah. SOLUTION: This nonaqueous electrolyte battery uses a separator 5 being composed of a polyethylene microporous film and polypropylene nonwoven fabric and having a thickness not less than 50 μm. Lithium cobaltate is used as a positive electrode active material, a graphitic carbon material is used as a negative electrode active material, and applying weight of a positive electrode active material mix is set to 4 g/100 cm2. A positive electrode plate 4 and a negative electrode plate 3 are laminated via the separator 5.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to the structure of a large non-aqueous electrolyte battery.

[0002]

2. Description of the Related Art In non-aqueous electrolyte batteries represented by lithium secondary batteries, it is difficult to obtain a large current compared to batteries using an aqueous electrolyte because of the high resistance of the electrolyte. For this reason, the electrode area is made as large as possible and the thickness of the active material layer of the electrode plate is made as thin as possible. By winding these through a separator, a battery with low internal resistance and capable of extracting a large current is realized. are doing. For this reason,
An electrode plate having an active material layer thickness of less than 100 μm on one side is used, and a separator having a thickness of 40 μm or less is usually used. In particular, the separator is required to have high performance such as good electrolyte ion permeability and low electric resistance, and high density filling in a battery container for high capacity. . The wound lithium secondary battery manufactured in this manner is used as a power source for, for example, a notebook computer or a mobile phone, and has a large external capacity of about 35 cc and a capacity of about 3 Ah. In addition, a current extraction of about 2 C is possible by reducing the internal resistance.

[0003]

Although small lithium secondary batteries have been put to practical use, electric vehicles and large batteries that store nighttime electric power and are used for load leveling have not been developed yet. It has not yet been fully commercialized and is currently being vigorously developed.

In order to increase the size of the battery, the size of the battery container is increased, the amount of the positive electrode active material and the amount of the negative electrode active material filled therein are increased, and the energy density is increased as much as possible.
Battery element members other than active materials that are not directly involved in the accumulation of electrochemical energy, such as current collectors and separators, should be as thin as possible. On the other hand, by increasing the size of the battery, it is possible to take out a large current as the whole battery without increasing the current density per unit area of the electrode so much. In some cases, the thickness of the active material layer should be as large as possible.

The inventor of the present invention has conducted various studies to put a non-aqueous electrolyte battery having a battery capacity of 100 Ah or more into practical use. As a result, from the viewpoint of battery safety and energy density, the positive electrode active material layer It has been found that it is preferable that the thickness be somewhat thicker than the conventional one, and accordingly, the thickness of the negative electrode active material layer also needs to be increased in accordance with the amount of the positive electrode active material. I found that it was necessary to make it somewhat thick. However, it was found that when the active material layer was thickened, a new problem which did not become a problem when the electrode area was small occurred. That is, when the battery has a large battery capacity of 100 Ah or more, there is an upper limit to the coating thickness, so that the area of the entire electrode plate needs to be larger than in the past. This causes a problem that the yield rate of non-defective products increases.

[0006] It is an object of the present invention to reduce the occurrence of defective products in the production of a non-aqueous electrolyte battery having a battery capacity of 100 Ah or more.

[0007]

The non-aqueous electrolyte battery of the present invention has a battery capacity of 100 Ah or more and a thickness of 50 μm.
It is characterized by having the above separator.

Although there are various types of non-aqueous electrolyte batteries having a battery capacity of 100 Ah or more, such batteries having a common feature that the total amount of charge / discharge current is large, the thickness of the separator is large. Is set to 50 μm or more, the occurrence of defective products not only during manufacturing but also during use can be significantly reduced.

It is more preferable to use a separator having a thickness of 90 μm or more. Further, as its material and structure, various materials can be used, but at least two or more kinds of separators including a microporous membrane are laminated, and the thickness of the microporous membrane is 40 μm or more. It is preferable to use a suitable separator.

The non-aqueous electrolyte battery of the present invention is applicable to non-aqueous electrolyte batteries having various structures.
Applicable to non-aqueous electrolyte batteries comprising a negative electrode using a carbon material that reversibly absorbs and releases lithium ions as an active material, a positive electrode using a lithium-containing metal oxide as an active material, and a non-aqueous electrolyte. In this case, the coating amount per area of the active material layer of the positive electrode is preferably 3 g / 100 cm ² or more. When the positive electrode active material layer is formed on the metal foil current collector, the thickness of the active material layer on one side should be 100 μm.
As described above, the thickness is preferably 150 μm or more, and the coating amount per area is preferably 3 g / 100 cm ² or more.

[0011]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, the present invention will be described in detail while describing embodiments of the present invention. The non-aqueous electrolyte battery of the present invention is a battery having a capacity of 100 Ah or more. However, in the case of a battery having such a large capacity, even if the active material layer is thickened, there is a limit in the coating thickness thereof, so that the electrode plate is limited. Is considerably larger than the conventional one. This means that the internal resistance is further reduced, and that a current having a higher density can be flown, which is very convenient.

However, on the other hand, as the volume of the battery is increased in order to increase the capacity of the battery, the dissipation of heat generated inside the battery becomes worse. It has been found that there is a problem that excessive current flows and heat that cannot be completely dissipated from the outer surface of the battery occurs, causing the battery to generate abnormal heat. This is because as the size of the battery increases, the surface area per volume decreases and the heat radiation efficiency decreases, while the internal resistance of the battery decreases and the heat generation increases rapidly.

In consideration of such problems, the present inventor has found that when increasing the capacity of the battery, it is necessary to suppress the internal resistance of the battery from decreasing to some extent. Therefore, as a result of examining the battery structure from such a viewpoint, it was found that it is better to increase the resistance value of the positive electrode active material layer, which easily affects the internal resistance of the battery, to some extent, and to make the layer thickness thicker than before. Came to the conclusion that it was better. Also, from the viewpoint of increasing the energy density of the battery, it is preferable to increase the thickness of the active material layer.

However, when the thickness of the active material layer is increased, the difference in thickness between locations within the electrode surface also increases, and there is a problem that the conventionally used separator is more likely to cause a local short circuit during manufacturing. In addition, as the capacity of the battery increases, the non-uniformity of the electrode reaction becomes more prominent due to the flow of a large amount of current, and in the conventional separator, the probability of occurrence of a local short circuit during repeated use increases. It turned out that there was a problem of getting it.

[0015] Such a problem has been clarified in promoting the practical use of a large capacity battery of 100 Ah or more. To solve these problems, it is effective to use a separator having a thickness of 50 µm or more. It works. In particular,
If the thickness is 90 μm or more, the above problem can be solved even more reliably.

The structure of the separator may be a single-layer structure or a laminated structure. However, since it is difficult to produce a thick single-layer separator, it is easier to produce a laminated structure. In the case of laminating, it is preferable to use two or more types, whereby each layer can be assigned a different function, and a high-performance separator can be realized.
Furthermore, using two or more types of separators including a microporous membrane, and forming a separator by stacking these,
It is preferable to use a microporous membrane having a thickness of 40 μm or more. This is because the air permeability is mainly controlled by a microporous membrane, and by setting the air permeability to 40 μm or more, a separator having a somewhat large resistance can be obtained. The reason why the resistance is increased is that in a battery having a capacity of 100 Ah or more, it is necessary to intentionally increase the internal resistance, and it is difficult to sufficiently control the resistance only by controlling the positive electrode active material layer. is there.

With respect to the internal resistance value, in the case of a battery having an external volume of 1000 cc or more, it is preferable that the internal resistance value be 0.5 mΩ or more. If it cannot be set to a value, the resistance value of the battery is set to 0.5 mΩ by providing a resistance member or the like.
It is better to do above. In the case of a battery of 100 Ah or more, the external volume of the battery body is usually 1000 cc or more.

When two or more separators are stacked to form a separator, for example, it is preferable to use a polyethylene film and a polypropylene film. Performs the function, and the polypropylene film performs the function of maintaining strength and shape during shutdown. And in this case,
The polyethylene film preferably has a thickness of 40 μm or more, and particularly preferably has a thickness of 40 μm or more when the total thickness is 90 μm or more. This is mainly due to the increased resistance and the good functioning of the shutdown.

In this case, when the polyethylene film and the polypropylene film are combined, it is preferable that the thickness of the polyethylene microporous film is larger than the thickness of the polypropylene nonwoven fabric. This is because controlling the thickness with a polyethylene microporous membrane can reduce the variation in thickness, increasing the reliability of the battery and improving the life performance, and increasing the thickness of the polyethylene microporous membrane. This is because the film resistance can be increased.

Further, when a polyethylene film and a polypropylene film are combined, it is preferable to combine a polyethylene microporous film and a polypropylene microporous film from the viewpoint of reducing the occurrence of defective batteries. This is because the variation in the film thickness of the polypropylene microporous membrane is smaller than that of the polypropylene nonwoven fabric. For example, a polyethylene microporous membrane having a thickness of 40 μm and 50-80
In the case of a laminated film with a non-woven fabric made of polypropylene having a thickness of μm, while the variation in the film thickness is ± 20 to 30 μm,
In the case of a laminated film of an m-thick polyethylene microporous film and a 50 μm-thick polypropylene microporous film, the variation in film thickness falls within ± 3 μm.

As described above, in a non-aqueous electrolyte battery having a capacity of 100 Ah or more, by providing a separator with a thickness of 50 μm or more, a local short circuit can be prevented. Since increasing the thickness alone decreases the capacity density, it is preferable to use an appropriately thick active material layer in order to prevent this, and this means that in a battery having a large capacity, the thickness of the active material layer is reduced. This is consistent with the requirement that the thickness be better.

The present invention also includes a negative electrode using a carbon material capable of reversibly occluding and releasing lithium ions as an active material, a positive electrode using a lithium-containing metal oxide as an active material, and a non-aqueous electrolyte. In this case, the coating amount per area of the active material layer of the positive electrode is 3 g / kg because of a request to increase the thickness of the positive electrode active material layer.
May preferably be 100 cm ² or more, in the case of forming the positive electrode active material layer on a metal foil current collector, or 100μm thickness of one side of the active material layer, preferably better to the above 150 [mu] m, further, 3 g / 100 application amount per area
cm ² or more. Such a limitation on the positive electrode active material layer has a large effect on the internal resistance of the positive electrode active material layer, and the internal heat should be uniformly generated. This is because, when adjusting, it is effective to adjust the active material layer of the positive electrode.

In the case where the positive electrode active material layer is formed in this manner, it is difficult to wind the electrode when the electrode is thick. Therefore, the electrode structure is preferably a stacked type rather than a wound type. In this case, 5
The present invention is more effective for a battery having a large structure in which zero or more positive plates and 50 or more negative plates are stacked with a separator interposed therebetween. For example, such a stacked battery has a very high rate. This is particularly suitable for a battery that does not require the above discharge characteristics, for example, a battery that only discharges at a maximum of 1C. In the case of such a stacked battery, it is preferable that the outer shape of the battery is rectangular, and by adopting such a shape, the energy density can be further increased.

[0024] Of the batteries having the above-described structure, L
It is effective to apply the present invention to a battery using lithium cobaltate or lithium manganate as a positive electrode active material such as iCoO ₂ or LiMn ₂ O ₄ or a battery using a carbonate-based organic solvent as an electrolyte. It is.

Further, according to the present invention, the outer volume of the battery body is 10
The true value is further exhibited by applying the present invention to a battery having a battery resistance value of not less than 00 cc and a battery resistance value of not less than 0.5 mΩ. This structure is suitable for non-aqueous electrolyte batteries with terminal voltage.By adopting these structures, there is little occurrence of defective products during manufacturing and excellent safety that does not cause abnormal temperature rise even when external short circuit occurs. Battery. The resistance of the battery means the resistance between the positive terminal and the negative terminal of the battery, and is the impedance at 1 KHZ and 25 ° C.
It is a resistance value by a dance measurement method.

A non-aqueous electrolyte battery comprising a negative electrode using a carbon material capable of reversibly occluding and releasing lithium ions as an active material, a positive electrode using a lithium-containing metal oxide as an active material, and a non-aqueous electrolyte solution. In the case of manufacturing, for example, in the case of a lamination type, the required number of positive electrode plates and negative electrode plates are stacked in this order with a separator interposed therebetween, which is stored in a battery container, filled with an electrolytic solution, and sealed. I can do things.
Each member can be manufactured, for example, as follows.

The positive electrode plate is made of LiCoO ₂ , LiMn ₂ O ₄
An active material mixture is prepared by mixing lithium-containing metal oxide particles such as acetylene black or graphite with a conductive agent such as acetylene black or graphite and a binder such as polyvinylidene fluoride or polytetrafluoroethylene. It can be prepared by applying the composition to an electrode substrate such as an aluminum foil and drying.

As the negative electrode plate, various materials such as metallic lithium, lithium alloy, graphite capable of inserting and extracting lithium, artificial graphite, low-crystalline carbon material, and metal oxide can be used as the active material. For example, it can be produced by applying and drying a graphite powder on an electrode substrate such as a copper foil using a binder similarly to the above positive electrode.

As the non-aqueous electrolyte, either a solid or liquid electrolyte may be used, and a gel may be used. In the case of the non-aqueous electrolyte, the solvent may be, for example, propylene carbonate, ethylene carbonate, γ -Butyrolactone, a mixture of a high-viscosity solvent such as dimethyl sulfoxide and a low-viscosity solvent such as dimethoxyethane, dimethyl carbonate, ethyl methyl carbonate, and diethyl carbonate, and LiCl as an electrolyte salt.
O ₄ , LiBF ₄ , LiPF ₆ , LiCF ₃ SO ₃ , L
iN (CF ₃ SO ₂ ) ₂ , LiN (Cn F _{2n + 1} SO ₂ )
₂ (where n is 1, 2, 3 or 4 each independently). In particular, L
iPF ₆ and LiN (CF ₃ SO ₂ ) ₂ are particularly preferred in that they are highly safe and the ionic conductivity of the dissolved electrolyte is high.

The separator is as described above.

[0031]

The present invention will be described in more detail with reference to the following examples. Embodiment 1 FIG. 1 is a perspective view showing an external shape of a lithium ion secondary battery according to an embodiment of the present invention. This battery has a rectangular box shape, and is formed by welding a stainless steel plate lid plate 9 to a cylindrical battery body container 8 made of stainless steel plate by welding. And 2 from the opposite surface
It has a structure in which a positive electrode terminal 1 and a negative electrode terminal 2 are drawn out. The external volume of the battery body is about 4000 cc.

FIG. 2 is a schematic sectional view showing a laminated structure of power generating elements inside the battery of this embodiment, and FIG. 3 is a schematic sectional view showing a current collecting structure of the battery. The battery of the present embodiment is a laminated structure battery in which a positive electrode plate 4 and a negative electrode plate 3 are alternately laminated with a separator 5 interposed therebetween, and the electrode plates are both rectangular plates.
The current collector metal is exposed without forming an active material layer on one side of the end, and the same polarity electrode plates are overlapped with each other at the current collector where the current collector metal is exposed. After that, this portion is sandwiched, then welded, and further caulked with rivets 7 to have a current collecting structure firmly fixed. With such a structure, the present battery has improved vibration / shock performance. The upper ends of the positive electrode terminal 1 and the negative electrode terminal 2 are inserted in advance into opening holes of the cover plate 9 and screwed with nuts (omitted in FIG. 1) via a sealing material. It is designed to be insulated and sealed.

In the battery, two power generating elements as shown in FIG. 2 are housed. In one power generating element, 60 positive electrode plates 4 and 61 negative electrode plates 3 are laminated. A separator is interposed between the plate and the negative electrode plate. The battery of this embodiment has the advantage that such a stack-type power generation element is housed in a rectangular box-shaped battery container, so that the gap can be reduced and the energy density of the battery can be increased. Have

Next, the internal structure will be further described.
The positive electrode plate 4 is composed of 94 parts by weight of LiCoO ₂ particles, 1 part by weight of Ketjen black, and polyvinylidene fluoride (PVdF).
5 parts by weight, and N-methyl-2-pyrrolidone (NMP) was added as a solvent to obtain an active material mixture paste.
This is uniformly applied to an aluminum foil having a thickness of 40 μm,
It is manufactured by roll pressing after drying. The size of the active material layer formed on the positive electrode plate is 117 mm × 380 mm, and the thickness of the active material layer is 35 mm.
0 μm, and the applied weight of the active material mixture was 4 g / 100 cm ² .

It should be noted that, as in the present embodiment, lithium cobalt oxide
Graphite-based carbon material as shown below
When the battery capacity is 100 Ah or more,
The discharge rate during normal use is 1C or less.
In the case of a battery, the applied weight of the active material mixture is 3 g / 100 cm.
^Two~ 5g / 100cm^TwoIs to change the energy density
Preferred for increasing the size, especially 3.5 g / 100 cm^Two
~ 4.5g / 100cm ^TwoEspecially 4g / 100cm^Two
From the viewpoint of increasing the production yield.
preferable. Furthermore, the application weight of such an active material mixture and
If so, the thickness of the aluminum foil is 35 μm or more,
More preferably, the thickness is 40 μm or more. this is,
If the aluminum foil is thin, the electrode plate will break.
You. However, aluminum foil improves energy density
From the viewpoint that
No.

The negative electrode plate 3 was prepared by mixing 94 parts by weight of flaky artificial graphite particles and 6 parts by weight of PVdF, and using N-
Methyl-2-pyrrolidone (NMP) is added to form an active material mixture paste, which is uniformly applied to a copper foil having a thickness of 40 μm, dried, and roll-pressed to produce a negative electrode plate. The size of the portion where the active material layer is formed is 117 mm × 380 mm, and the thickness of the active material layer is 3 mm.
50 μm, application weight of active material mixture is 2 g / 100 cm ²
It is.

The separator 5 is composed of a laminate in which a 15 μm-thick polypropylene nonwoven fabric is sandwiched between two 40 μm-thick polyethylene microporous membranes. The non-aqueous electrolyte is obtained by dissolving 1 mol / l of LiPF ₆ in a mixed solvent of ethylene carbonate and diethyl carbonate at a volume ratio of 1: 1.

The capacity of the battery of this embodiment having the above-mentioned structure was 400 Ah, and the internal resistance was measured by an impedance measuring method (1 kHz, temperature 25 ° C.) and found to be 0.8 mΩ. The internal resistance was measured by connecting two positive terminals 1 and two negative terminals 2 so as to be one terminal each, and then measuring the distance between these terminals.

An external short circuit test was performed using this battery.
The test was performed at a temperature of 25 ° C. and a constant current of 200 A / 4.1.
After repeating constant-current constant-voltage charging of V constant voltage × 4 h and constant-current discharging at 200 A (3 V end voltage), the test was performed in a fully charged state. As a result, the battery temperature was 110 ° C. or lower, and the safety valve was not opened. In addition, the above charging and 200
The cycle life at a DOD of 50% obtained by repeating the constant current discharge at A was 800 times or more. The production yield of this battery was 5/5.

(Example 2, Comparative Examples 1 and 2) Separator 5
Was manufactured in the same manner as in Example 1 except that a microporous polyethylene membrane having a thickness of 50 μm was prepared. A laminated battery B was produced in the same manner as in Example 1 except that the separator 5 was a 25 μm-thick polyethylene microporous film. A laminated battery C was produced in the same manner as in Example 1 except that the separator 5 was a polyethylene microporous film having a thickness of 40 μm. These batteries were subjected to an external short-circuit test and a life test under the same conditions as in Example 1. Table 1 shows the results. The battery temperature is a temperature 10 minutes after the short circuit, and was measured by inserting a thermistor inside the battery.

[0041]

[Table 1] Further, the yield of the stacked battery C was 1/2, and the yield of the stacked battery A was 1/2.

(Examples 3, 4, 5 and Comparative Example 3) A polyethylene microporous membrane having a thickness of 40 μm
A laminated structure battery prepared in the same manner as in Example 1 except that a laminated film of a non-woven fabric made of polypropylene and a non-woven fabric of polypropylene having a thickness of 40 μm and a non-woven fabric made of polypropylene having a thickness of 58 μm was used. A laminated battery prepared in the same manner as in Example 1 except that a laminated film was used as E, and a laminated film of a microporous polyethylene film of 40 μm thickness and a nonwoven fabric of polypropylene of 98 μm thickness was used as the separator 5. Except for the difference, the laminated battery prepared in the same manner as in Example 1 was used in Example F, except that a laminated film of a 25 μm-thick polyethylene microporous film and a 13 μm-thick polypropylene nonwoven fabric was used as the separator 5. G is a laminated battery manufactured in the same manner as in Example 1. These batteries were subjected to an external short-circuit test and a life test under the same conditions as in Example 1. Table 2 shows the results. The battery temperature is a temperature 10 minutes after the short circuit, and was measured by inserting a thermistor inside the battery.

[0043]

[Table 2]

As shown in the above examples, the battery of the present invention has a rectangular box type in which a carbonate-based organic solvent is used as an electrolyte and lithium cobaltate is used as a positive electrode active material. Particularly suitable for lithium ion secondary batteries.

[0045]

According to the present invention, a battery of 100 Ah or more with less occurrence of defective products during manufacturing can be realized.

[Brief description of the drawings]

FIG. 1 is a perspective view showing an external shape of a lithium ion secondary battery according to an embodiment of the present invention.

FIG. 2 is a schematic sectional view showing a laminated structure of a power generating element inside a battery according to an embodiment of the present invention.

FIG. 3 is a schematic sectional view showing a current collecting structure of a battery according to an embodiment of the present invention.

[Explanation of symbols]

 Reference Signs List 1 positive electrode terminal 2 negative electrode terminal 3 negative electrode plate 4 positive electrode plate 5 separator

 ──────────────────────────────────────────────────続 き Continued on the front page F term (reference) 5H029 AJ14 AK03 AL02 AL06 AL07 AL12 AM00 AM03 AM04 AM05 AM07 BJ02 BJ12 CJ22 DJ04 DJ13 EJ12 HJ00 HJ04 HJ07 HJ19 HJ20

Claims (6)

[Claims] 1. A non-aqueous electrolyte battery having a battery capacity of 100 Ah or more and a separator having a thickness of 50 μm or more. 2. The separator according to claim 1, wherein at least two types of separators including at least a microporous membrane are stacked, and the thickness of the microporous membrane is 40 μm or more. The nonaqueous electrolyte battery according to any one of the preceding claims. 3. The non-aqueous electrolyte battery according to claim 2, wherein the separator is a laminated film of a polyethylene film and a polypropylene film. 4. A positive electrode comprising a negative electrode using a carbon material that reversibly stores and releases lithium ions as an active material, a positive electrode using a lithium-containing metal oxide as an active material, and a non-aqueous electrolyte. The coating amount per area of the active material layer is 3 g / 10
^{3. The device according} to claim 1, wherein the size is 0 cm ² or more.
The nonaqueous electrolyte battery according to any one of the preceding claims. 5. The non-aqueous electrolyte battery according to claim 1, wherein 50 or more positive plates and 50 or more negative plates are laminated with a separator interposed therebetween. 6. The non-aqueous electrolyte battery according to claim 1, wherein the external volume of the battery body is 1000 cc or more, and the resistance value of the battery is 0.5 mΩ or more.