JP2003317695A - Nonaqueous electrolyte lithium ion cell and separator there for - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a separator realizing a nonaqueous electrolyte lithium ion cell having a good discharge property or cycle property, and the nonaqueous electrolyte lithium ion cell. <P>SOLUTION: The separator for a nonaqueous electrolyte lithium ion cell is structured with a porous film with a thickness of 1 to 50 μm, a porosity a from 30 to 90% and an average hole diameter from 0.01 to 1 μm supporting a nonaqueous electrolyte solution and a gel electrolyte including at least one kind of inorganic fine powders selected from silica and alumina of an average primary particle diameter from 1 to 100 nm. The separator of this kind can be obtained by dipping the porous film in a nonaqueous electrolyte solution after the inorganic fine powder is dispersed in and supported by the porous film. <P>COPYRIGHT: (C)2004,JPO

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a non-aqueous electrolyte lithium ion battery and a separator therefor.

[0002]

2. Description of the Related Art Conventionally, various types of batteries have been put to practical use, but in order to cope with the cordless use of electronic devices, etc., they are lightweight and can obtain high electromotive force and high energy.
Moreover, lithium-ion batteries, which have low self-discharge, have been attracting attention. In particular, in recent years, with the demand for further weight reduction and thinning, practical use of lithium-ion batteries using polymer electrolytes instead of conventional electrolytes There is an urgent need for conversion.

According to such a lithium ion battery,
Compared with the conventional electrolyte battery, the leakage of the electrolyte is less, so it is possible to use a laminated resin film or the like having an aluminum thin film as the exterior instead of the conventional metal can, thus providing a flexible thin type. Practical application is urgent also from the standpoint that it can be used as a battery.

A polymer electrolyte is a three-dimensional entanglement of linear polymer molecular chains, that is, a so-called physical gel in which an electrolytic solution is supported in a matrix composed of a physically crosslinked polymer and a matrix composed of a chemically crosslinked polymer molecular chain. It is divided into so-called chemical gels that carry an electrolytic solution. In order to impart an appropriate hardness to the physical gel, it is necessary to increase the polymer concentration in the electrolytic solution, and if the polymer concentration is not increased, it is necessary to use a high molecular weight polymer. In such a case, it is necessary to dissolve the polymer in the electrolytic solution under heating, and therefore, it takes a lot of time. Furthermore, problems such as deterioration of the electrolyte salt due to heating also occur.

On the other hand, the chemical gel is obtained, for example, by dissolving a monomer capable of forming a crosslinked polymer and a polymerization initiator in an electrolytic solution, and then heating the polymer to polymerize the monomer to form a crosslinked polymer. be able to. Therefore, when a battery is manufactured using such a chemical gel, for example, in a battery container, a so-called cross-linked polymer can be formed by in-situ polymerization of a monomer, so that a chemical gel can be easily obtained. Although there are advantages, unreacted monomers and polymerization initiators may remain in the electrodes and separators of the battery, which may adversely affect the battery characteristics.

Therefore, as a non-aqueous solid electrolyte which does not depend on physical or chemical crosslinking, for example, in Japanese Patent No. 3098248, an electrolytic solution and an inorganic fine powder such as finely divided silica are mixed to prepare a paste. A solid electrolyte for batteries that has been solidified or solidified has been proposed. Such a solid electrolyte has high ionic conductivity, but in terms of strength,
Since the resistance to compression is small, the positive and negative electrode agents are partially short-circuited at the compressed location in lithium ion batteries in which the positive and negative electrodes repeatedly expand and contract in response to repeated charging and discharging, and the cycle characteristics deteriorate significantly. There is a drawback that. In order to overcome this drawback, the thickness of the electrolyte layer between the positive and negative electrodes must be increased, but the limited space is required.
In a battery having a battery, if the thickness of the electrolyte layer between the positive and negative electrodes is increased, the amount of the positive and negative electrode agents must be reduced, resulting in a problem that the battery capacity is reduced.

[0007]

DISCLOSURE OF THE INVENTION The present invention has been made to solve the above-mentioned problems in a solid electrolyte for a battery in which a nonaqueous electrolytic solution is pasted or solidified with an inorganic fine powder, A separator provided with such a solid electrolyte supported on a porous membrane, which provides a non-aqueous electrolyte lithium ion battery having excellent discharge characteristics and cycle characteristics, and an object of the invention is to provide such a non-aqueous electrolyte lithium-ion battery. To do. Furthermore, the present invention relates to a method for producing such a separator for a non-aqueous electrolyte lithium ion battery.

[0008]

According to the present invention, a gel electrolyte containing a non-aqueous electrolytic solution and at least one inorganic fine powder selected from silica and alumina having an average primary particle diameter of 1 to 100 nm has a thickness of 1 to 50 μm. Provided is a separator for a non-aqueous electrolyte lithium ion battery, which is supported on a porous membrane having a porosity of 30 to 90% and an average pore diameter of 0.01 to 1 μm. Moreover, according to this invention, the non-aqueous electrolyte lithium ion battery which has the said separator is provided.

Furthermore, according to the present invention, the average primary particle size is 1
The above non-aqueous electrolyte lithium ion, which is obtained by dispersing at least one inorganic fine powder selected from silica and alumina having a particle size of ˜100 nm on a porous membrane and supporting it, and then impregnating the porous membrane with a non-aqueous electrolyte. A method for manufacturing a battery separator is provided.

[0010]

BEST MODE FOR CARRYING OUT THE INVENTION A separator for a non-aqueous electrolyte lithium ion battery according to the present invention is a gel electrolyte containing a non-aqueous electrolyte solution and at least one inorganic fine powder selected from silica and alumina having an average primary particle diameter of 1 to 100 nm. The thickness 1
50 μm, porosity 30 to 90% and average pore size 0.01 to
It is supported on a 1 μm porous film.

That is, the separator according to the present invention is previously
After dispersing and supporting the inorganic fine powder in the base material porous film, impregnating such a porous film with a non-aqueous electrolytic solution, and thus, particles of the inorganic fine powder in the porous film. The composite consisting of the inorganic fine powder and the electrolytic solution is made into a paste or a solid by the bonding force between them.

In the present invention, the base material porous film that forms the base material of the separator is required to have excellent chemical stability capable of withstanding the redox of the battery, and further, the positive and negative electrodes associated with the charge and discharge cycle of the battery. Excellent mechanical strength that can withstand compression into the separator due to swelling and contraction, and a small pore size and high porosity so that the lithium dendritic that grows on the negative electrode carbon material during overcharge does not break through the separator. Is needed.

According to the present invention, the substrate porous film satisfying such required characteristics has an average pore diameter of 0.01 to 1 μm.
A porous membrane made of a polyolefin resin such as polyethylene or polypropylene having a porosity in the range of m and a porosity of 30 to 90% is preferably used. When the average pore diameter of the porous membrane is smaller than 0.01 μm, the inorganic fine powder particles in the gel electrolyte cause the clogging of the porous membrane, which increases the internal resistance of the battery. On the other hand, when the average pore diameter of the porous membrane is larger than 1 μm, the mechanical strength of the porous membrane is low and the battery is apt to cause an internal short circuit.

When the porosity of the porous film is less than 30%, the permeation of lithium ions is not sufficient. Therefore, when the obtained separator is used as a battery, the internal resistance of the battery becomes high and the battery is sufficiently high. The discharge capacity cannot be obtained. On the other hand, when the porosity of the porous film is larger than 90%, the mechanical strength of the obtained separator is small and the battery is apt to cause an internal short circuit.

Further, according to the present invention, the substrate porous membrane comprises
It preferably has a thickness in the range of 1 to 50 μm. When the thickness is less than 1 μm, the mechanical strength of the porous film is small and the separator is not practical. But,
When the thickness is larger than 50 μm, the volume of the separator in the battery is large, and the amount of the positive and negative electrode materials has to be reduced accordingly, so that the battery capacity decreases.

In the present invention, at least one selected from silica and alumina is used as an inorganic fine powder for forming a gel by combining with a non-aqueous electrolyte.
Such an inorganic fine powder has an average primary particle diameter of 1 to 1
It is preferably in the range of 00 nm, and more preferably in the range of 5 to 50 nm. When the average primary particle size of the inorganic fine powder is smaller than 1 nm, the inorganic fine powder is difficult to be uniformly dispersed in the non-aqueous electrolytic solution, and it is difficult to form a stable gel electrolyte. However, the average primary particle size of the inorganic fine powder is 100 nm.
When it is smaller than the above, the surface area of the particles of the inorganic fine powder becomes small, the binding force between the particles becomes small, and the gel cannot be formed.

Further, according to the present invention, the solvent of the non-aqueous electrolyte is not particularly limited, but for example, ethylene carbonate, propylene carbonate, butylene carbonate, γ-butyrolactone, 1,2-dimethoxyethane. , Ethyl methyl carbonate, diethyl carbonate and the like are used. The electrolyte that forms an electrolytic solution together with such a solvent is not particularly limited as long as it can be used in a lithium ion battery. For example, LiClO ₄ , LiPF ₆ , LiBF ₆ , and the like.
₄ grade is used.

According to the present invention, the ratio of the inorganic fine powder to the non-aqueous electrolyte as described above is in the range of 3 to 50% by weight. When the ratio of the inorganic fine powder to the non-aqueous electrolyte is less than 3% by weight, the gel electrolyte is not formed, while the ratio of the inorganic fine powder to the non-aqueous electrolyte is 50% by weight.
When it is more than the above range, the inorganic fine powder is not uniformly dispersed in the electrolytic solution, so that it is difficult to obtain a stable gel electrolyte.

The nonaqueous electrolyte lithium ion battery separator according to the present invention can be obtained, for example, as follows. That is, the inorganic fine powder is mixed with an organic solvent such as isopropyl alcohol, dispersed, and the porous membrane is immersed in the dispersion liquid and then dried to remove the solvent, thereby making the inorganic fine powder porous. A porous membrane supported by being dispersed in the membrane is obtained. Then, in this way, by impregnating the porous membrane supporting the inorganic fine powder with the electrolytic solution, the inorganic fine powder, by the binding force between the particles,
A gel electrolyte is formed together with the electrolytic solution, and thus, a porous membrane supporting the gel electrolyte, that is, a separator as a membranous gel electrolyte can be obtained.

The non-aqueous electrolyte lithium ion battery provided with such a separator can be manufactured, for example, as follows. That is, as described above, after the inorganic fine powder is supported on the porous film in advance, the electrode and the electrode are laminated or wound to form an electrochemical element, which serves also as an electrode plate of the battery. Place in a can. Next, a non-aqueous electrolytic solution is injected into the battery can, and the electrolytic solution is impregnated in the porous membrane supporting the inorganic fine powder to form a separator in which a gel electrolyte is supported in the porous membrane. Thus, a non-aqueous electrolyte lithium ion battery provided with the separator according to the present invention can be obtained. However, the method for producing the non-aqueous electrolyte lithium ion battery according to the present invention is not limited to the above-exemplified one.

FIG. 1 is a vertical cross-sectional view of a coin type lithium ion secondary battery provided with a separator according to the present invention. In this lithium ion secondary battery, the positive electrode can 1 also serving as a positive electrode terminal is made of, for example, a nickel-plated stainless steel plate, and a negative electrode can also serves as a negative electrode terminal insulated from the positive electrode can via an insulator 2. Combined with 3, it forms a battery can (container). The negative electrode can is also made of, for example, a nickel-plated stainless steel plate.

Inside the battery can thus formed, the positive electrode 4 is disposed in contact with the positive electrode can via the positive electrode current collector 5. For the positive electrode 4, for example, a positive electrode active material such as lithium manganese composite oxide and a conductive material such as graphite are mixed with a binder resin such as polyethylene, polypropylene or polytetrafluoroethylene, and the mixture is pressure-molded. Can be obtained. Similarly, the negative electrode 6 is disposed in contact with the negative electrode can via the negative electrode current collector 7. The negative electrode is made of, for example, a lithium plate. Between these positive and negative electrodes,
The separator 8 according to the present invention is arranged to form a battery. Thus, according to such a battery, electric energy can be taken out using the positive electrode can and the negative electrode can as terminals.

[0023]

The present invention will be described below with reference to examples.
The present invention is not limited to these examples. In the following, the physical properties of the used porous substrate membrane and the obtained separator were evaluated as follows.

(Thickness of Porous Membrane) Measured with a 1/10000 mm thickness gauge.

(Porosity of Porous Membrane) The substrate porous membrane was punched with a punch having a diameter of 60 mm, the thickness was obtained with a thickness gauge of 1/1000 mm, and the weight was weighed with an electronic balance. Porosity was determined. In addition, the density of the resin component constituting the base material porous film was 0.940 g / mL. Porosity (%) = (pore volume / volume of base material porous membrane) × 1
00

(Electrolytic solution retention rate of separator) Ethylene carbonate / ethyl methyl carbonate (volume ratio 1 /
A porous membrane carrying inorganic fine powder was immersed in an electrolytic solution in which lithium hexafluorophosphate was dissolved in the mixed solvent of 2) at a concentration of 1.4 mol / L. After that, the porous membrane was sandwiched between filter papers and treated with a centrifuge at 1500 rpm for 3 minutes, and the electrolytic solution retention rate was calculated from the weight change before and after centrifugation.

Example 1 (Preparation of Electrode) Lithium cobalt oxide as an active material and graphite as a conductive auxiliary agent were coated on a current collector aluminum foil using a binder made of polyvinylidene fluoride resin to prepare a positive electrode. A negative electrode was prepared by coating graphite as an active material on a current collector copper foil using a binder made of polyvinylidene fluoride resin.

(Preparation of Electrolyte Solution) Ethylene carbonate /
Lithium hexafluorophosphate was dissolved at a concentration of 1.4 mol / L in a mixed solvent of ethyl methyl carbonate (volume ratio 1/2) to obtain an electrolytic solution.

(Production of fine-powder silica-supporting porous membrane and membranous gel electrolyte) Fine-powder silica (manufactured by Nippon Aerosil Co., Ltd., Aerosil 200, average primary particle diameter 12 nm) was mixed in isopropyl alcohol at a concentration of 3% by weight, A porous film made of polyethylene resin (thickness 25 μm, porosity 4
5%, average pore size 0.1 μm) was immersed. The porous membrane treated in this way was dried at 80 ° C. for 3 hours to remove isopropyl alcohol and obtain a fine powder silica-supporting porous membrane. Using this fine-powdered silica-supporting porous membrane, the electrolytic solution retention rate was measured as described above. The results are shown in Table 1.

(Production of Battery) After the above-mentioned porous silica-supporting porous membrane, the above-mentioned positive electrode and the above-mentioned negative electrode are impregnated with the above-mentioned electrolytic solution, respectively, the negative electrode, the above-mentioned porous silica-supporting porous membrane and the positive electrode are placed in this order on the positive and negative electrode plates. A coin-type lithium-ion secondary battery was manufactured by charging a dual-purpose battery can (battery can for 2016 coin battery) and forming a laminate of negative electrode / separator (membrane gel electrolyte) / positive electrode in the can.

This battery was first charged and discharged at 0.2 CmA and then charged and discharged at 1 CmA for 200 cycles. All charging and discharging of the battery was performed in a thermostat at 25 ° C. Table 1 shows the initial discharge capacity and the capacity retention rate after 200 cycles.

Example 2 Finely divided silica in isopropyl alcohol (Aerosil 380, manufactured by Nippon Aerosil Co., Ltd., average primary particle diameter 7n)
m) was mixed at a concentration of 2% by weight and the same porous membrane as in Example 1 was immersed therein to prepare a fine silica powder-supporting porous membrane in the same manner as in Example 1 and to retain the electrolytic solution. Was measured. Further, a battery was prepared and a charge / discharge test was performed in the same manner as in Example 1 except that the above-mentioned fine powder silica-supporting porous film was used to determine the initial discharge capacity and the capacity retention rate after 200 cycles. . The results are shown in Table 1.

Example 3 Finely powdered silica in isopropyl alcohol (Aerosil 50, manufactured by Nippon Aerosil Co., Ltd., average primary particle diameter 30n)
m) was mixed at a concentration of 3% by weight and the same porous membrane as in Example 1 was immersed therein to prepare a fine powder silica-supporting porous membrane in the same manner as in Example 1 and to retain the electrolytic solution. Was measured. Further, a battery was prepared and a charge / discharge test was performed in the same manner as in Example 1 except that the above-mentioned fine powder silica-supporting porous film was used to determine the initial discharge capacity and the capacity retention rate after 200 cycles. . The results are shown in Table 1.

Example 4 A fine powder silica-alumina mixture (manufactured by Nippon Aerosil Co., Ltd., MOX80, average primary particle size 30 nm) was mixed in isopropyl alcohol at a concentration of 3% by weight, and the same porous film as in Example 1 was mixed therein. A finely divided silica-alumina mixture-supporting porous membrane was prepared in the same manner as in Example 1 except that was immersed in the solution, and the electrolytic solution retention rate was measured. Further, a battery was prepared and a charge / discharge test was conducted in the same manner as in Example 1 except that the above fine powder silica-alumina mixture-supporting porous film was used, and the initial discharge capacity and the capacity retention rate after 200 cycles were obtained. I asked. The results are shown in Table 1.

Example 5 Finely divided silica in isopropyl alcohol (Aerosil 380, manufactured by Nippon Aerosil Co., Ltd., average primary particle diameter 7n)
m) was mixed at a concentration of 3% by weight, and a porous membrane made of polyethylene resin (thickness 5 μm, porosity 32%, average pore diameter 0.03 μm) was immersed in the same manner as in Example 1, A fine powder silica-supporting porous material was prepared, and the electrolyte retention rate was measured. Further, a battery was prepared and a charge / discharge test was performed in the same manner as in Example 1 except that the above-mentioned fine powder silica-supporting porous film was used to determine the initial discharge capacity and the capacity retention rate after 200 cycles. . The results are shown in Table 1.

Example 6 Finely divided silica in isopropyl alcohol (Aerosil 380, manufactured by Nippon Aerosil Co., Ltd., average primary particle diameter 7n)
m) was mixed at a concentration of 3% by weight, and a porous membrane made of polyethylene resin (thickness 25 μm, porosity 70%, average pore diameter 0.07 μm) was immersed in the same manner as in Example 1, A fine powder silica-supporting porous material was prepared, and the electrolyte retention rate was measured. Further, a battery was prepared in the same manner as in Example 1 except that the above-mentioned fine powder silica-supporting porous film was used.
A charge / discharge test was performed to determine the initial discharge capacity and the capacity retention rate after 200 cycles. The results are shown in Table 1.

Example 7 Finely divided silica in isopropyl alcohol (Aerosil 200, manufactured by Nippon Aerosil Co., Ltd., average primary particle diameter 12n)
m) was mixed at a concentration of 3% by weight, and a porous membrane made of polyethylene resin (thickness 25 μm, porosity 87%, average pore diameter 0.87 μm) was immersed in the same manner as in Example 1, A fine-powder silica-supporting porous membrane was prepared, and the electrolytic solution retention rate was measured. Further, a battery was prepared and a charge / discharge test was performed in the same manner as in Example 1 except that the above-mentioned fine powder silica-supporting porous film was used to determine the initial discharge capacity and the capacity retention rate after 200 cycles. . The results are shown in Table 1.

Example 8 Finely divided silica in isopropyl alcohol (manufactured by Nippon Aerosil Co., Ltd., Aerosil 200, average primary particle diameter 12n)
m) was mixed at a concentration of 3% by weight, and a porous film made of polyethylene resin (thickness 45 μm, porosity 89%, average pore size 0.97 μm) was immersed in the same manner as in Example 1, A fine-powder silica-supporting porous membrane was prepared, and the electrolytic solution retention rate was measured. Further, a battery was prepared and a charge / discharge test was performed in the same manner as in Example 1 except that the above-mentioned fine powder silica-supporting porous film was used to determine the initial discharge capacity and the capacity retention rate after 200 cycles. . The results are shown in Table 1.

Comparative Example 1 3 parts of finely powdered silica (I-FX, manufactured by Shin-Etsu Chemical Co., Ltd., average primary particle size 800 nm) were mixed in isopropyl alcohol.
A silica-supporting porous membrane was prepared in the same manner as in Example 1 except that the same porous membrane as in Example 1 was immersed in the mixture at a concentration of wt% and the electrolytic solution retention rate was measured. Also,
A battery was prepared and a charge / discharge test was conducted in the same manner as in Example 1 except that the above silica-supporting porous membrane was used, and the initial discharge capacity and the capacity retention rate after 200 cycles were determined. The results are shown in Table 1.

Comparative Example 2 Fine silica in isopropyl alcohol (Aerosil 200, manufactured by Nippon Aerosil Co., Ltd., average primary particle diameter 12n)
m) was mixed at a concentration of 3% by weight, and a porous membrane made of polyethylene resin (thickness 40 μm, porosity 88%, average pore size 1.3 μm) was immersed in the same manner as in Example 1, A fine-powder silica-supporting porous membrane was prepared, and the electrolytic solution retention rate was measured. Further, a battery was prepared in the same manner as in Example 1 except that the above-mentioned fine powder silica-supporting porous film was used.
A charge / discharge test was performed to determine the initial discharge capacity and the capacity retention rate after 200 cycles. The results are shown in Table 1.

Comparative Example 3 Fine powder silica (Aerosil 200, manufactured by Nippon Aerosil Co., Ltd., average primary particle diameter 12n) in isopropyl alcohol.
m) was mixed at a concentration of 3% by weight, and a porous film made of polyethylene resin (thickness 65 μm, porosity 90%, average pore diameter 0.8 μm) was immersed in the same manner as in Example 1, A fine-powder silica-supporting porous membrane was prepared, and the electrolytic solution retention rate was measured. Further, a battery was prepared in the same manner as in Example 1 except that the above-mentioned fine powder silica-supporting porous film was used.
A charge / discharge test was performed to determine the initial discharge capacity and the capacity retention rate after 200 cycles. The results are shown in Table 1.

[0042]

[Table 1]

As shown in Table 1, the separator according to the present invention has a high electrolytic solution retention rate and, when incorporated in a lithium ion battery as a separator, has a high capacity retention rate and excellent cycle characteristics. On the contrary,
According to the separator of Comparative Example 1, the average primary particle diameter of the inorganic fine powder used was large, and according to the separator of Comparative Example 2, the pores of the porous film used were large, and the separator of Comparative Example 3 was used. According to this, since the thickness of the used porous membrane is large, the retention rate of the electrolytic solution is low in each case, and when incorporated in a battery, the cycle characteristics are inferior.

[0044]

INDUSTRIAL APPLICABILITY As described above, the separator according to the present invention has a high electrolytic solution retention rate and, when incorporated into a battery, provides a battery having excellent cycle characteristics.

[Brief description of drawings]

FIG. 1 is a vertical cross-sectional view showing an example of a coin-type lithium ion secondary battery including a separator according to the present invention.

[Explanation of symbols]

1. Positive electrode can that doubles as a positive electrode terminal 2 ... Insulator 3 ... Positive electrode can that doubles as a negative electrode terminal 4 ... Positive electrode 5 ... Positive electrode current collector 6 ... Negative electrode 7 ... Negative electrode current collector 8 ... Separator

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Claims (3)

[Claims] 1. A non-aqueous electrolyte and an average primary particle size of 1 to 100 n.
m, a gel electrolyte containing at least one kind of inorganic fine powder selected from silica and alumina is supported on a porous membrane having a thickness of 1 to 50 μm, a porosity of 30 to 90% and an average pore diameter of 0.01 to 1 μm. A separator for a non-aqueous electrolyte lithium-ion battery, which is characterized by: 2. A non-aqueous electrolyte lithium ion battery having the separator according to claim 1. 3. An inorganic fine powder of at least one kind selected from silica and alumina having an average primary particle diameter of 1 to 100 nm is dispersed and supported on a porous membrane, and then this porous membrane is impregnated with a non-aqueous electrolyte solution. The method for producing a separator for a non-aqueous electrolyte lithium ion battery according to claim 1, wherein