JP2002367588A - Battery - Google Patents

Abstract

(57) [Summary] (Modified) [PROBLEMS] To provide a battery excellent in cycle life performance and storage performance under a high temperature environment by improving the liquid retention of a separator. A positive electrode (3) and a negative electrode (4) shown in an electrode group (2) in a rectangular nonaqueous secondary battery (1) having a safety valve (8) on a battery lid (7).
The separator 5 is characterized by using a polyolefin containing a plasticizer of 600 ppm or less, and the plasticizer is liquid paraffin at 25 ° C.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a battery provided with a polyolefin separator.

[0002]

2. Description of the Related Art In recent years, as electronic devices such as mobile phones and portable personal computers have become smaller, lighter, and more sophisticated, lightweight batteries having a high energy density have been adopted as built-in batteries. I have. A typical battery that satisfies such requirements is an active material such as lithium metal or lithium alloy, or a carbon material that uses lithium ions as a host material (here, a host material refers to a material that can absorb and release lithium ions). The lithium intercalation compound occluded in the anode is used as a negative electrode, an aprotic organic solvent in which a lithium salt such as LiClO ₄ or LiPF ₆ is dissolved is used as an electrolyte, and an organic separator is provided between the positive electrode and the negative electrode. A non-aqueous electrolyte secondary battery using a polyolefin-based material which is insoluble in a solvent and stable to an electrolyte or an electrode active material and is processed into a microporous film or nonwoven fabric.

In particular, lithium cobalt composite oxide, lithium nickel composite oxide, and spinel type lithium manganese oxide can be charged and discharged at an extremely noble potential of 4 V (vs. Li ^/ Li ⁺ ) or more. By using a positive electrode as a positive electrode active material, a battery having a high discharge voltage can be realized.

[0004] As an aqueous solution type battery, nickel-
Hydrogen batteries and the like are widely used as power sources for portable electronic devices.

[0005]

Recently, various batteries have been increasingly used in electronic devices used not only in a normal temperature environment but also in various environments from a low temperature to a high temperature. Particularly, in a notebook personal computer, the internal temperature of the personal computer increases as the speed of the central processing unit increases, and the built-in battery is used for a long time in a high-temperature environment.
For this reason, among the characteristics of the battery, characteristics under a high-temperature environment are becoming important.

[0006] However, although the conventional non-aqueous electrolyte secondary battery shows very excellent performance in a normal temperature environment, it is apparent that the cycle life performance at high temperature or the leaving performance is not always sufficient. It has become. Also, for nickel-hydrogen batteries, etc.
There is a need for improved characteristics at high temperatures.

The present invention has been made to solve the above-mentioned problems, and an object of the present invention is to provide a battery having excellent cycle life performance at high temperature and excellent storage performance.

As a result of intensive studies to solve the above-mentioned problems, the present inventor has found that the content of the plasticizer in the polyolefin membrane separator has a great effect on high-temperature cycle life performance and high-temperature storage performance. The present invention has been accomplished.

[0009]

The invention according to claim 1 relates to a battery provided with a separator, wherein the separator has a thickness of 60%.
It is characterized by comprising a polyolefin containing 0 ppm or less of a plasticizer.

According to the first aspect of the present invention, by suppressing the amount of the plasticizer in the polyolefin to a certain amount or less, the affinity between the separator and the electrolytic solution is not reduced, and the electrolytic solution holding capacity of the separator is maintained. Even when the charge / discharge cycle is repeated or left at a high temperature, liquid leakage between the electrodes can be prevented, and a battery having excellent cycle life performance and high temperature performance at a high temperature can be obtained.

According to a second aspect of the present invention, in the separator, the plasticizer is liquid paraffin at 25 ° C.

According to the second aspect of the present invention, a uniform film can be easily obtained in the film forming process.

[0013]

BEST MODE FOR CARRYING OUT THE INVENTION The separator provided in the battery of the present invention is characterized by comprising a polyolefin containing 600 ppm or less of a plasticizer, and characterized in that the plasticizer is paraffin which is liquid at 25 ° C. Things.

When the content of the plasticizer contained in the polyolefin exceeds the above range, the affinity between the separator and the electrolyte decreases, so that the separator's ability to retain the electrolyte (hereinafter referred to as liquid retention) decreases. I do. This is because the affinity between the plasticizer and the polyolefin is higher than the affinity between the plasticizer and the electrolyte.

Therefore, in a battery using a separator having a large plasticizer content, when the charge / discharge cycle is repeated or left at a high temperature, the liquid retaining property of the separator is low. There has been a problem that peeling occurs early and sufficient performance cannot be obtained. Therefore, it is important to use a separator having a plasticizer content of 600 ppm or less in the polyolefin.

Next, a method for producing the separator of the present invention will be described. The separator used in the present invention can be formed by performing three steps of film formation, stretching, and extraction.

In the first film forming step, a polyolefin solution is prepared by heating and dissolving the polyolefin in a plasticizer. The plasticizer is not particularly limited as long as it is a liquid at room temperature and can sufficiently dissolve the polyolefin. Can be used.

In the film forming process, paraffin which is liquid at 25 ° C. is used because it is easy to handle, has excellent workability, is chemically stable, and does not adversely affect the characteristics of the battery. Is preferred. Examples of the paraffin liquid at 25 ° C. include a linear saturated hydrocarbon represented by the general formula C _n H _{2n + 2.}
-Pentane, n-hexane, n-heptane, n-octane, n-nonane, n-decane, n-undecane, n-dodecane, n-tridecane, n-tetradecane, n-pentadecane, n-hexadecane, n-heptadecane , N-
Octadecane is mentioned.

A mixed solution in which a gas or solid saturated hydrocarbon is dissolved at 25 ° C. in a mixture of these linear saturated hydrocarbons, or a linear saturated hydrocarbon or a mixture thereof, and is liquid at 25 ° C. May be used.

In addition, spilled oil obtained by vacuum distillation of depressurized oil (dewaxed oil) in a filter press dewaxing method,
It is also possible to use paraffin oil which is refined and used as a raw material for light lubricating oil, liquid paraffin which is highly purified from dewaxed oil having low viscosity, and the like.

In the second stretching step, the polyolefin solution is extruded from a die to form a gel-like sheet.
The stretching method is not particularly limited. For example, the stretching is performed at a predetermined magnification by a tenter method, a roll method, an inflation method, a rolling method, or a combination of these methods. The stretching direction is preferably biaxial stretching.
Axial stretching is preferred.

In the third extraction step, a plasticizer is extracted from the obtained stretched film to obtain a microporous film. The extraction solvent is not particularly limited, but can be well dissolved according to the plasticizer used, for example, hydrocarbons such as pentane, hexane, heptane, chlorinated methylene chloride, carbon tetrachloride, etc. Hydrocarbons, fluorinated hydrocarbons such as ethane trifluoride, diethyl ether,
Ethers such as dioxane, methanol, ethanol,
Easily volatile solvents such as alcohols such as propanol can be used. After the stretched film is immersed in an extraction solvent to extract the plasticizer, the stretched film is heated and air-dried to remove the extraction solvent.

The content of the plasticizer can be adjusted by variously changing the time and the number of times of the plasticizer extraction step.

The amount of the plasticizer contained in the polyolefin separator may be 600 ppm or less, as shown in the results of the following examples. The smaller the value, the more preferable.

As the polyolefin material, polyethylene, polypropylene, polybutene and the like can be used, and among these, polyethylene is preferably used. In this case, as the polyethylene, any polyethylene such as various types of high-density, medium-density and low-density branched polyethylenes, linear polyethylenes, high-molecular weight and ultra-high-molecular-weight polyethylenes can be used. Further, those containing appropriate amounts of additives such as various antioxidants and flame retardants may be used. The polyolefin used in the present invention preferably has a weight average molecular weight in the range of 500,000 to 2,000,000.

When the non-secondary battery of the present invention is manufactured, the battery may be manufactured by a usual method using the separator manufactured as described above.

The battery of the present invention is used for a non-aqueous electrolyte secondary battery.
Can absorb and release lithium as its positive electrode active material
Compound Li_xMO₂Or Li_yM
₂O ₄(Where M is a transition metal, 0 ≦ x ≦ 1, 0 ≦ y ≦
Complex oxide represented by 2), having tunnel-like vacancies
Oxide, layered metal chalcogenide, etc.
Can be. As a specific example, LiCoO₂ , L
iNiO₂, LiMn ₂O₄ , Li₂Mn₂O₄ , M
nO₂, FeO₂, V₂O₅, V₆O₁₃, TiO₂,
TiS₂Etc. In addition, conductive polymers such as polyaniline
It is also possible to use organic compounds such as
These may be used as a mixture. Also, using a granular active material
For example, when the active material particles, the conductive auxiliary agent, and the binder are used,
Formed on a metal current collector such as aluminum
Can be produced by

As the negative electrode active material, for example, A
Alloys of lithium with l, Si, Pb, Sn, Zn, Cd, etc., transition metal oxides such as LiFe ₂ O ₃ , WO ₂ , MoO ₂ , carbonaceous materials such as graphite, carbon, and Li ₅
Lithium nitride such as (Li ₃ N) or metallic lithium foil, or a mixture thereof may be used. When a granular carbonaceous material is used, for example, an inorganic solid electrolyte can be prepared by forming a mixture of active material particles and a binder on a metal current collector such as copper. Although, a polymer solid electrolyte, an electrolytic solution and the like can be used, when producing a non-aqueous electrolytic solution secondary battery, as an electrolytic solution solvent, for example, ethylene carbonate, propylene carbonate, dimethyl carbonate, diethyl carbonate, γ-butyrolactone, Sulfolane, dimethyl sulfoxide, acetonitrile, dimethylformamide, dimethylacetamide,
A polar solvent such as 1,2-dimethoxyethane, 1,2-diethoxyethane, tetrahydrofuran, 2-methyltetrahydrofuran, dioxolan, methyl acetate, or a mixture thereof can be used.

Lithium salts dissolved in these electrolyte solvents include LiPF ₆ , LiClO ₄ , LiBF
_{4, LiAsF 6, LiCF 3 CO} 2, LiCF 3 SO
₃ , LiN (SO ₂ CF ₃ ) ₂ , LiN (SO ₂ CF ₂₎
CF ₃ ) ₂ , LiN (COCF ₃ ) ₂ and LiN (C
OCF ₂ CF ₃₎ salt, or mixtures thereof, such as ₂ may be used. The shape of the battery is not particularly limited, and the present invention is applicable to non-aqueous electrolyte secondary batteries of various shapes such as a square, a cylinder, a long cylinder, a coin, a button, and a sheet battery. Applicable.

Further, the separator of the present invention can be used for various alkaline batteries such as nickel-hydrogen batteries and nickel-cadmium batteries, and other aqueous batteries.

[0031]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, a non-aqueous electrolyte secondary battery will be described as an example to which the present invention is applied. However, the present invention is not limited to the present embodiment at all, and the scope of the present invention is not changed. It can be carried out with appropriate changes.

The test method of the separator in the present embodiment is as follows. The film thickness was measured on a cross section with a scanning electron microscope. The porosity was measured by a gravimetric method. The air permeability was measured according to JIS P8117. The extraction of the plasticizer contained in the separator was performed using a Soxhlet extractor, and n-hexane (nC ₆ H ₁₄ ) was used as an extraction solvent.
, And 3 g of the separator was continuously extracted for 12 hours. The quantitative analysis of the plasticizer contained in the separator was measured using gas chromatography.

The parts common to all test batteries are as follows. A rectangular non-aqueous electrolyte secondary battery was used as a test battery. FIG. 1 is a diagram showing a cross-sectional structure of a prismatic nonaqueous electrolyte secondary battery of the present embodiment. In FIG. 1, 1 is a prismatic nonaqueous electrolyte secondary battery, 2 is a flat electrode group, 3 is a positive electrode, 4 is a negative electrode, 5 is a separator, 6 is a battery case, 7 is a battery lid, 8
Is a safety valve, 9 is a positive electrode terminal, and 10 is a positive electrode lead wire.

The prismatic nonaqueous electrolyte secondary battery 1 of the first embodiment
Are composed of a positive electrode 3 formed by applying a positive electrode mixture containing a substance capable of absorbing and releasing lithium ions to an aluminum current collector, and a substance capable of absorbing and releasing lithium ions to a copper current collector. A flat electrode group 2 in which a negative electrode 4 coated with a negative electrode mixture is wound via a separator 5 and a non-aqueous electrolyte containing an electrolyte salt are housed in a battery case 6. . The design capacity of the battery was 600 mA.
h.

A battery cover 6 provided with a safety valve 8 is attached to the battery case 6 by laser welding.
Is connected to the positive electrode 3 via the positive electrode lead 10, and the negative electrode 4 is electrically connected to the inner wall of the battery case 6 by contact.

The positive electrode mixture is obtained by mixing 90 parts by weight of LiCoO _{2 as} an active material, 5 parts by weight of acetylene black as a conductive material, and 5 parts by weight of polyvinylidene fluoride as a binder, and mixing N-methyl-2-pyrrolidone. Was added and dispersed to prepare a slurry. This slurry was uniformly applied to a 20 μm-thick aluminum current collector, dried, and then compression-molded with a roll press to produce a positive electrode 3.

The negative electrode mixture was prepared as a slurry by mixing 90 parts by weight of a carbon material capable of inserting and extracting lithium ions and 10 parts by weight of polyvinylidene fluoride, adding N-methyl-2-pyrrolidone as needed, and dispersing the slurry. . The slurry was uniformly applied to a 10 μm-thick copper current collector, dried, and then compression-molded by a roll press to produce a negative electrode 4.

The electrolyte is ethylene carbonate (EC)
1 mol / l of LiPF ₆ dissolved in a mixed solvent of 1: 1 by volume and diethyl carbonate (DEC).

The test conditions for the battery were as follows. In the high-temperature storage test, the battery was first charged at room temperature with a constant current and constant voltage of 1 CmA to 4.2 V for 3 hours, and then discharged at a constant current of 1 CmA to 2.75 V, and the discharge capacity at that time was measured. The initial discharge capacity was used. Next, at room temperature,
3 constant current / constant voltage charging up to 4.2 V with 1 CmA current
It was left for 60 days in a charged state for 30 days. Thereafter, the battery was discharged to 2.75 V at a constant current of 1 CmA, and the discharge capacity at that time was defined as the capacity after being left at high temperature. Then, the ratio (%) of the capacity after high-temperature storage to the initial discharge capacity was determined, and this value was defined as the high-temperature storage capacity retention. Batteries with a high-temperature capacity retention of 80% or more were rated good, and batteries with a high-temperature capacity retention of less than 80% were rated poor.

In the high temperature cycle life test, the above battery was
At 45 ° C., constant-voltage / constant-current charging was performed for 3 hours at a current of 1 CmA to 4.2 V, and then discharging was performed to 2.75 V at a constant current of 1 CmA. The ratio (%) of the discharge capacity at the 300th cycle to the discharge capacity was determined, and this value was defined as the high-temperature cycle capacity retention. Batteries with a high-temperature cycle capacity retention of 80% or more were rated good, and batteries with less than 80% were rated poor.

In the following examples, batteries under the same conditions were manufactured for each 10 cells, and the obtained data were all represented by the average value of 10 cells.

[Example 1] Six kinds of polyolefins were used, in which polyethylene was used and paraffin oil (manufactured by Witco, trade name: carnation) was used as a plasticizer, and the paraffin oil content was varied between 100 and 1000 ppm. A battery using the separator was manufactured. The paraffin oil content in the separator was adjusted by the time and the number of times of extraction and washing with methylene chloride. The obtained separator had a thickness of 25 μm, a porosity of 40%, and an air permeability of 500 sec / 100.
cc. Table 1 shows the results of the high-temperature storage test and the high-temperature cycle life test of each battery.

[0043]

[Table 1]

From Table 1, it was found that as the amount of the plasticizer (paraffin oil) contained in the polyethylene separator decreases, the high-temperature storage capacity retention rate and the high-temperature cycle capacity retention rate increase. It is considered that the reason for this is that the smaller the amount of the plasticizer contained in the separator, the more excellent the liquid retaining property of the separator, and thus the more the amount of plasticizer contained in the separator was, so that the liquid leakage between the electrodes was suppressed.

As shown in Examples A, B, C and D in Table 1, a non-aqueous electrolyte secondary battery using a polyethylene separator having a plasticizer (paraffin oil) content of 600 ppm or less in the separator was used. The batteries E and F having a plasticizer (paraffin oil) content of 800 ppm or 1000 ppm, while exhibiting good characteristics, with both the high-temperature storage capacity retention rate and the high-temperature cycle capacity retention rate exceeding 80%.
Showed that both the high-temperature storage capacity retention rate and the high-temperature cycle capacity retention rate sharply decreased.

Example 2 Three types of batteries were manufactured in the same manner as the battery C of Example 1 except that the content of the plasticizer in polyethylene was 400 ppm and the type of the plasticizer was changed. Table 2 shows the results of the high-temperature storage test and the high-temperature cycle life test of each battery.

[0047]

[Table 2]

As can be seen from Table 2, even when the type of the plasticizer was changed, both the high-temperature storage capacity retention rate and the high-temperature cycle capacity retention rate exceeded 80%, indicating good characteristics.
However, when the liquid paraffin at 25 ° C. is used as in the battery C in Table 1, the battery G and the battery H in Table 2,
Both the high-temperature storage capacity retention rate and the high-temperature cycle capacity retention rate were superior to the battery I in Table 2 using other plasticizers.

Example 3 A battery J was made in the same manner as the battery C of Example 1 except that the type of polyolefin was changed from polyethylene to polypropylene. Battery J had a high-temperature storage capacity retention of 84% and a high-temperature cycle capacity retention of 8%.
4%, and even when polypropylene is used, both the high-temperature storage capacity retention rate and the high-temperature cycle capacity retention rate are 80%.
And good characteristics were exhibited.

[0050]

The separator provided in the battery of the present invention has the following properties.
It is characterized by being composed of a polyolefin containing 00 ppm or less of a plasticizer.
It is characterized by being paraffin which is a liquid at a temperature of ° C.

According to the present invention, by suppressing the amount of plasticizer in the polyolefin to a certain level or less, the affinity between the separator and the electrolyte does not decrease, the ability of the separator to retain the electrolyte is maintained, Even if the charge / discharge cycle is repeated or left, the liquid can be prevented from leaking between the electrodes, and a secondary battery with excellent cycle life performance and storage performance at high temperatures can be obtained. It is possible to improve the performance of electronic devices to be used.

[Brief description of the drawings]

FIG. 1 is a diagram showing a cross-sectional structure of a prismatic nonaqueous electrolyte secondary battery of the present embodiment.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Non-aqueous electrolyte secondary battery 2 Flat electrode group 3 Positive electrode 4 Negative electrode 5 Separator

Claims (2)

[Claims] 1. A battery, wherein the separator is made of a polyolefin containing 600 ppm or less of a plasticizer. 2. The battery according to claim 1, wherein the plasticizer is liquid paraffin at 25 ° C.