JPH10302748A - Non-aqueous electrolytic battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a non-aqueous electrolytic battery having a wound electrode so produced as to retain safety by a separator even in the case forcible inner short-circuiting is caused by, for example, a nail. SOLUTION: A wound electrode body comprises a separator 3 having fine pores with 0.01-0.2 μm average pore diameter in a first face which is to be brought into contact with a cathode 1 and fine pores with 0.02-0.5 μm average pore diameter in a second face which is to be brought into contact with an anode 2. A ratio (R1 /R2 ) of the average pore diameter R2 of the second face to the average pore diameter R1 of the first face is set to be 0.04-0.95.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a non-aqueous electrolyte battery such as a lithium battery.
The present invention relates to a non-aqueous electrolyte secondary battery having characteristics of a separator and further improving safety.

[0002]

2. Description of the Related Art Non-aqueous electrolyte batteries using a light metal such as lithium as a negative electrode have a high energy density and low self-discharge. . As an electrode of such a non-aqueous electrolyte battery, a spiral wound body having a wide effective electrode area has been used by laminating and winding a strip-shaped positive electrode, a negative electrode, and a separator. Is coming. The separator basically prevents both electrodes from short-circuiting, and allows the battery to react by allowing its ions to pass through its microporous structure. As the temperature rises, the resin melts and deforms, closing the micropores and stopping the battery reaction,
Devices having a so-called shutdown function (SD function) have been adopted from the viewpoint of improving safety.

A separator having such an SD function is, for example, a multilayered combination of a microporous polyethylene film having a low melting temperature and a microporous polypropylene film having a closing temperature of 20 ° C. or more higher than that of the membrane. A configuration is known. This separator maintains the entire shape even if the low melting point portion is melted, and prevents the separator from shrinking, exposing the electrodes and causing an internal short circuit. Such a separator and a non-aqueous electrolyte battery provided with the separator are disclosed in, for example, JP-A-63-9455.
No. 6, JP-A-6-20671, JP-A-8-2
No. 27705.

[0004]

However, a non-aqueous electrolyte battery using the above-mentioned conventional separator does not always provide sufficient safety when a forced internal short circuit occurs, which may cause the battery outer can to be destroyed. Could not be secured. When a forced and almost instantaneous internal short circuit occurs due to nail penetration or the like, a sharp temperature rise in a short time and an internal pressure rise due to the generation of internal gas occur, so that shrinkage and flow due to melting of the low melting point film become remarkable. Alternatively, the microporous clogging due to melting may be insufficient, and the SD function of the separator may not be sufficiently exhibited.

[0005] In view of the circumstances, an object of the present invention is to provide a non-aqueous electrolyte battery that can ensure safety even if a forced internal short circuit occurs.

[0006]

In order to achieve the above object, a nonaqueous electrolyte battery according to the present invention comprises a strip-shaped positive electrode, a negative electrode, and a separator laminated such that the separator is interposed between the positive electrode and the negative electrode. In a non-aqueous electrolyte battery provided with a wound electrode, the separator has a microporous average pore size of 0.01 to 0.2 μm on a first surface in contact with the positive electrode,
The average pore size is 0.02 to 0.5 μm on the second surface in contact with the negative electrode.
m, and the ratio (R ₁ / R ₂ ) of the average pore size (R ₁ ) of the first surface to the average pore size (R ₂ ) of the _second surface is 0.04 to 0.5 μm. 95.

In general, the positive electrode material has a higher heat generation than the negative electrode material. Non-aqueous electrolyte battery of the present invention, when a forced internal short circuit occurs, in order to reliably suppress the temperature rise inside the battery that occurs almost instantaneously, contact the separator surface having a small average pore diameter with the cathode material In this aspect, one of the features is to deal with dangers such as smoke and ignition by closing the micropores early due to heat generation of the positive electrode.

In the nonaqueous electrolyte battery according to the present invention, the average pore diameter of the first surface facing the positive electrode is set to 0.01 to 0.2 μm. This is because the movement of the separator is hindered and the battery reaction is hindered. If the thickness exceeds 0.2 μm, the micropores of the separator are not quickly closed when a forced internal short circuit occurs. The average pore diameter of the first surface is preferably 0.02 to 0.15 μm. Further, the reason why the average pore diameter is set to 0.02 to 0.5 μm on the second surface in contact with the negative electrode is that if the average pore diameter is less than 0.02 μm, the polarization in the battery becomes large and lithium in the negative electrode is easily precipitated. If the thickness exceeds 0.5 μm, pores are hardly formed, and dendritic lithium inside the pores is also easily deposited.

Further, the average pore diameter (R_Two)
Mean diameter of the first surface (R ₁) Ratio (R₁/
R_Two) Of 0.04 to 0.95 is less than 0.04
Since the hole diameter of the first surface substantially decreases when
When it exceeds 0.95, the dendritic lithium
The side with the smaller pore diameter directly inside the separator when grown
Easy to reach, the polarization is increased and the precipitation is easy
It is because it becomes a state.

Here, the average pore diameter of the separator means the geometric mean of the average major axis and the average minor axis of the pore diameter measured by observing at a magnification of about 10,000 to 25,000 times with a scanning electron microscope. I do.

[0011] Further, in the above configuration, it is preferable to provide a separator having different components on the first surface and the second surface. With such a configuration,
Easily control the average pore size of the separator for each surface
Will be able to

[0012]

FIG. 1 illustrates the structure of a nonaqueous electrolyte battery according to an embodiment of the present invention. In this non-aqueous electrolyte battery, a wound electrode body obtained by laminating and winding a strip-shaped negative electrode 1, a positive electrode 2 and a separator 3 is housed in a battery can 5, an electrolytic solution is injected into the battery can 5, and an upper and lower battery It has a structure in which necessary members such as an insulating plate are appropriately arranged according to a commercially available battery.

The material of the separator 3 is not particularly limited as long as it is conventionally used, and polyolefin resins such as polyethylene, polypropylene and polybutylene, nylon, cellulose acetate, polyacrylonitrile and the like can be used. However, polyethylene and polypropylene are preferred. More specifically, as the polypropylene, isotactic polypropylene, syndiotactic polypropylene, or the like is preferable. Among them, isotactic polypropylene having high crystallinity is preferable because a porous structure is easily formed.
Further, as polyethylene, high-density polyethylene, ultra-high-molecular-weight polyethylene, medium-density polyethylene, low-density polyethylene, linear low-density polyethylene and the like are preferable,
Particularly, high-density polyethylene and ultra-high-molecular-weight polyethylene are preferable from the viewpoint of porosity and film strength.

The separator 3 may be a single-layer film or a multi-layer film.
It is preferable to use a two-layer film or a three-layer film, for example, a two-layer film composed of a polyethylene layer and a polypropylene layer, a two-layer film composed of a polypropylene layer and a mixture layer of polypropylene and polyethylene, and a polypropylene layer. A three-layer film in which a mixture layer of polypropylene and polyethylene is disposed on both sides, a three-layer film in which a polypropylene layer is disposed on both sides of a polyethylene layer, and the like can be used. The thickness of the separator 1 is preferably 20 to 30 μm in consideration of the characteristics of the secondary battery and the like.

Next, an example of a method for manufacturing the separator 3 will be described. The separator 3 can be manufactured by melt-coextruding the above-mentioned material such as a polyolefin resin so as to have a predetermined layer structure, stretching and making it porous, and aging it.

At the time of melt extrusion, an appropriate amount of a lubricant, an antioxidant, an antistatic agent and the like may be added in advance, if necessary. The thickness of the film to be extruded can be appropriately set.
It is preferably set to 00 μm.

The film is preferably subjected to a heat treatment prior to stretching. The method of this heat treatment may be any method, for example, a method of contacting the film with a heated roll or metal plate, a method of heating the film in air or an inert gas, and a method of winding the film in a roll around a core. Then, a method of heating this in the gas phase can be adopted. The temperature and time of this heat treatment may be appropriately set according to the method of heat treatment and the like, but usually, the temperature is 120 to 170 ° C. and the time is 2 seconds to
About 50 hours is appropriate. By performing such a heat treatment, the degree of crystallinity of the film is increased, the formation of fine pores by stretching performed later is facilitated, and a porous film having a higher porosity can be obtained.

The stretching for making porous is not particularly limited, but in order to increase the porosity and lower the electric resistance, a multistage stretching method in which high-temperature stretching is performed after low-temperature stretching is adopted. Is preferred. In the multi-stage stretching method, low-temperature stretching is
It is preferable to carry out at -20 ° C to 60 ° C. If the stretching temperature is lower than this, the film may be broken during the work, and if the stretching temperature is higher than this, it is difficult to make the film porous. In addition, as a method of low-temperature stretching, a conventionally known roll stretching method, tenter stretching method, or the like can be employed. In low-temperature stretching, the stretching ratio is 20 to 2
It is preferably set to 00%. This low temperature stretching ratio (E ₁ )
Is calculated by the following equation.

E ₁ (%) = (L ₁ −L ₀ ) / L ₀ × 100 (1) Here, L ₀ is a dimension before low-temperature stretching, and L ₁ is a dimension after low-temperature stretching.

The high-temperature stretching is performed at a temperature of 90.degree.
It is preferably performed at 130 ° C. This temperature range is preferred for the same reason as the temperature range for low-temperature stretching. As the stretching method, similarly to the low-temperature stretching, a conventionally known stretching method can be adopted. In high temperature stretching, the stretching ratio is 1
It is preferably set to 0 to 500%. This high-temperature stretching ratio (E ₂ ) is calculated by the following equation.

E ₂ (%) = (L ₂ −L ₁ ) / L ₀ × 100 (2) Here, L ₀ and L ₁ are the same as above, and L ₂ is a dimension after high-temperature stretching.

In the porous film obtained in this manner, the stress acting during low-temperature stretching and high-temperature stretching remains, and the film tends to shrink in the stretching direction and change its dimension. , The dimensional stability can be increased. This shrinkage can be performed, for example, under a heating condition similar to the stretching temperature. Although the degree of shrinkage may be arbitrarily determined, it is usually set to such an extent that the film size after stretching is reduced by about 10 to 40%. Also, by controlling so that the dimension of the porous membrane in the stretching direction does not change, and by performing a so-called “heat set” in which the porous membrane is heated at or above the stretching temperature, it is dimensionally stable similarly to the above-described shrinkage treatment. Properties can be improved. Of course, both the heat setting and the shrinkage may be performed.

The average pore size on each surface of the separator 3 is as follows:
The components on each surface are individually formed by forming the separator into a multilayer film as described above, or by changing the blend ratio of the same or different resin in the film thickness direction even in the case of a single layer film. If you adjust it, you can control it arbitrarily. In addition, the average pore size can be individually controlled by using a cover film on only one of the surfaces during stretching, or by using a different cover film on both surfaces. Here, as the cover film, a film made of a film made of the same material and the same manufacturing method as that of the separator 3 and capable of being made porous by stretching can be used.

As described above, the separator 3 can be manufactured by a series of steps including a step of manufacturing a film so that the components on both sides are different, and a step of stretching the film to make it porous.

As the electrolytic solution, for example, a solution obtained by dissolving a lithium salt in an organic solvent can be used. The organic solvent is not particularly limited, for example, propylene carbonate, ethylene carbonate, butylene carbonate, γ-butyrolactone, γ-valerolactone, dimethyl carbonate, esters such as methyl propionate and butyl acetate, acetonitrile and the like. Ethers such as 1,2-dimethoxymethane, 1,2-dimethoxyethane, dimethoxypropane, 1,3-dioxolane, tetrahydrofuran, 2-methyltetrahydrofuran, and 4-methyl-1,3-dioxolane; Sulfolane or the like can be used alone or in combination of two or more.

As the negative electrode 1, a material obtained by integrating an alkali metal or a compound containing an alkali metal with a current collecting material such as a stainless steel net can be used. Here, examples of the alkali metal include lithium, sodium, and potassium.Examples of the compound containing the alkali metal include an alkali metal and an alloy of aluminum, lead, indium, potassium, cadmium, tin, and magnesium; Further, a compound of an alkali metal and a carbon material, a metal oxide of a low potential alkali metal, a compound of a sulfide, and the like can be given. When a carbon material is used for the negative electrode, the carbon material may be any material capable of doping and undoping lithium ions, for example, graphite,
Pyrolytic carbons, cokes, glassy carbons, fired bodies of organic polymer compounds, mesocarbon microbeads, carbon fibers, activated carbon, and the like can be used.

For the positive electrode 2, for example, metal oxides such as lithium cobalt oxide, lithium nickel oxide, lithium manganese oxide, manganese dioxide, vanadium pentoxide, and chromium oxide, and metal nitrides such as molybdenum disulfide are used. It can be used as an active material. A mixture obtained by appropriately adding a conductive auxiliary agent or a binder to polytetrafluoroethylene or the like to these positive electrode active materials, and finishing a molded body using a current collector material such as a stainless steel net as a core material. Used as positive electrode 2.

[0028]

【Example】

(Example 1) Lithium cobalt oxide (LiCoO ₂ )
Was added and mixed as a conductive aid in a weight ratio of 90: 5, and the mixture was mixed with a solution of polyvinylidene fluoride dissolved in N-methylpyrrolidone to form a slurry. After passing the positive electrode mixture slurry through a 70-mesh net to remove large ones, the slurry was uniformly applied to both sides of a positive electrode current collector made of aluminum foil having a thickness of 20 μm, dried, and then roll-pressed. After compression molding, it was cut and the lead body was welded to produce a strip-shaped positive electrode. Next, a carbon material having an average pore diameter of 10 μm was mixed with a solution of vinylidene fluoride dissolved in N-methylpyrrolidone to form a slurry. The negative electrode mixture slurry was passed through a 70-mesh net to remove large ones, and then uniformly applied to both surfaces of a negative electrode current collector made of a strip-shaped copper foil having a thickness of 18 μm, dried, and then roll-pressed. After compression molding and cutting, the lead body was welded to produce a strip-shaped negative electrode.

As a separator, polypropylene is provided on one side.
Ren layer, polyethylene and polypropylene on the other side
Prepare 26μm thick microporous film with mixed layer
did. This separator is manufactured by the method described above,
The average pore diameter of the microporous is 0.0% on the polypropylene layer side.
2μm, on the side of the mixed layer of polyethylene and polypropylene
Was 0.07 μm. These positive electrode, negative electrode and cell
Parator so that both poles overlap each other via the separator
And the polypropylene layer having a small average pore size is
They were laminated so as to be in contact with each other and wound to form an electrode body. This electrode
The body is housed in a cylindrical battery case with an outer diameter of 18 mm and a bottom.
Then, the lead body was welded to each of the positive electrode and the negative electrode.
Next, ethylene carbonate was used as an electrolytic solution in an amount of 1 part by weight.
And methyl ethyl carbonate in 2 parts by weight of the mixed solvent
Lithium lithium fluoride (LiPF) ₆Is dissolved in 1.4
M electrolyte solution. Inject this electrolyte into the battery can and seal
Perform pre-charging and aging, and have a wound electrode
A non-aqueous electrolyte secondary battery was used.

(Example 2) As a separator, a mixed layer of polyethylene and polypropylene (first layer), a polypropylene layer (second layer), and a mixed layer of polyethylene and polypropylene (first layer) which were more polyethylene-rich than the first layer. 3
Layers) were sequentially laminated to prepare a three-layer microporous film. This separator is manufactured by the method described above, and the average pore diameter of the microporous is 0.06 μm on the surface of the first layer,
The side of the third layer was 0.3 μm. This separator,
The same positive electrode and negative electrode as those used in Example 1 were laminated so that both electrodes overlap each other with a separator interposed therebetween, and the first layer having a smaller average pore diameter was in contact with the positive electrode, and the electrode was wound and wound. And With respect to this electrode body, a non-aqueous electrolyte secondary battery was produced in the same manner as in Example 1.

(Comparative Examples 1 and 2) Non-aqueous electrolyte secondary batteries were produced in the same manner as in Examples 1 and 2, except that the side having the smaller average pore diameter was used as the negative electrode side.

Comparative Example 3 As a separator, a polyethylene single-layer microporous film having an average pore diameter of 0.2 μm on both surfaces was prepared. With respect to this separator, a non-aqueous electrolyte secondary battery was produced in the same manner as in Example 1.

Each of the non-aqueous electrolyte secondary batteries prepared above was charged at a constant current of 0.2 C at an upper limit voltage of 4.2 V,
After leaving the battery in the charged state at 40 ° C. for 2 hours, it was fixed on a holder, and a round nail having a diameter of 3 mm and a length of 5 cm was pierced into the center of the side surface to a depth of の of the battery diameter. The condition was observed. Table 1 shows the results.

(Table 1) Average pore diameter on the positive electrode side Average negative electrode diameter on the positive electrode side ------------------------------------------ pore size R ₁ / R ₂ nail after penetration of _{(R 1: μm) (R} 2: μm) × 100 observations ------------------------ −−−−−−−−−−−− Example 1 0.02 0.07 28.6 No change Example 2 0.06 0.3 20.0 No change Comparative example 1 0.07 0.02 350 0.0 Smoke Comparative Example 2 0.3 0.06 500.0 Outer Can Expansion Comparative Example 3 0.2 0.2 100.0 Smoke----------------- −−−−−−−−−−−−−−−−−−−−

From Table 1, it was confirmed that the nonaqueous electrolyte batteries of Examples 1 and 2 did not generate smoke even when a forced internal short circuit was caused by nail penetration.

The separator has an average pore diameter of 0.5 μm.
After a non-aqueous electrolyte battery was prepared in the same manner as in the above example using the polypropylene single-layer microporous membrane, a safer nail puncture was performed than described above, and the separator was observed with a scanning electron microscope after the test. The results are shown in FIGS. FIG.
According to FIG. 3 and FIG. 3, it can be seen that the pores on the positive electrode side are more closed than those on the negative electrode side.

[0037]

According to the non-aqueous electrolyte battery of the present invention, when a forced internal short circuit occurs, such as when a nail is pierced, the temperature rise inside the battery and gas generation that occur in a short time are reduced. Thus, the safety of the battery can be further improved.

[Brief description of the drawings]

FIG. 1 is a cross-sectional perspective view of one embodiment of a non-aqueous electrolyte battery of the present invention.

FIG. 2 is a photograph of a positive electrode side surface of a separator observed by a scanning electron microscope in Examples.

FIG. 3 is a photograph of a negative electrode side surface of a separator observed by a scanning electron microscope in Examples.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Negative electrode 2 Positive electrode 3 Separator 5 Battery can

Claims (2)

[Claims] 1. A non-aqueous electrolyte battery including a strip-shaped positive electrode, a negative electrode, and an electrode wound by laminating a separator such that the separator is interposed between the positive electrode and the negative electrode, wherein the separator contacts the positive electrode. The first surface has an average pore size of 0.0
A second layer having a microporosity of 1 to 0.2 μm and in contact with the negative electrode;
Has micropores having an average pore size of 0.02 to 0.5 μm on the surface of the first surface, and the ratio (R) of the average pore size (R ₁ ) of the first surface to the average pore size (R ₂ ) of the _second surface. ₁ / R ₂ ) is 0.04
Non-aqueous electrolyte battery, characterized by being 0.95 to 0.95. 2. The non-aqueous electrolyte battery according to claim 1, further comprising a separator having a different component on the first surface and a different component on the second surface.