JP2000082451A - Non-aqueous electrolyte secondary battery - Google Patents

Abstract

(57) [Summary] In a non-aqueous electrolyte secondary battery such as a lithium secondary battery, deterioration of a separator in a temperature range where the battery is actually used is suppressed, and battery performance is improved. A battery can includes a positive electrode, a negative electrode, a non-aqueous electrolyte, and a separator in a battery can. The separator 3 is formed by joining a polymer resin sheet (for example, a polyolefin-based sheet) having a high affinity for a non-aqueous electrolyte and an oxidation-resistant sheet (for example, a fluorine-based polymer sheet) in layers. The oxidation-resistant sheet faces the positive electrode 1. The separator has fine pores having a diameter of 0.01 to 10 μm and a porosity of 20 to 90%.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a non-aqueous electrolyte (non-aqueous electrolyte) secondary battery such as a lithium secondary battery.

[0002]

2. Description of the Related Art Non-aqueous electrolyte secondary batteries typified by lithium secondary batteries have higher energy densities than lead storage batteries and nickel-cadmium batteries, and have recently been used in video cameras, portable phones, notebook computers, and the like. Used in portable electrical equipment. Recently, lithium secondary batteries have attracted attention as batteries for electric vehicles and for power storage due to needs such as prevention of air pollution and effective use of power energy. In this case, replace the lithium secondary battery with 4
The battery may be used in a high temperature environment of 0 to 80 ° C., and the cycle life of the battery is likely to be reduced.

[0003] The causes of deterioration of the life of a lithium secondary battery under a high temperature environment include acceleration of an electrolytic solution decomposition reaction due to heat generation from the battery, accumulation of an inert substance on an electrode surface, and blocking of pores in a separator. Can be These degradation modes are:
This can be avoided to some extent by cooling the battery during charging and discharging. As an example of a method for cooling a lithium secondary battery,
A method of inserting a metal beam-shaped spacer between prismatic lithium secondary batteries (Japanese Patent Application Laid-Open No. H8-212986) is disclosed.

[0004] In addition to the above-described life degradation, there is a problem in using a lithium secondary battery at a high temperature, in addition to a safety problem such as ignition and explosion of the battery due to a large amount of heat generated during abnormal operation of the battery. When the battery temperature reaches or exceeds the melting point of the separator due to overcharging of the battery, external short circuit, or the like, the separator may be melted and a short circuit between the positive electrode and the negative electrode may occur instantaneously. Such a phenomenon is likely to occur at a battery surface temperature of 100 ° C. or higher. When the separator melts in a wide area, a large current flows instantaneously between the positive electrode and the negative electrode, and the chemical reaction accompanying the heat generation explosively proceeds, causing ignition and explosion of the battery.

In order to avoid such a danger, a high-melting point separator using a fluororesin has been developed and is already known (JP-A-5-205721, JP-A-6-205721).
76808, JP-A-6-84522, JP-A-9-2
No. 45761).

For example, Japanese Patent Application Laid-Open No. 5-205721 discloses a separator having a maximum pore diameter of 0.1 having been subjected to a hydrophilic treatment as a separator.
A porous fluororesin film of μm or less and a polyethylene or polypropylene film are used in an overlapping manner. According to this conventional technique, since the melting point of the porous fluororesin film is 250 ° C. or higher, the positive electrode and the negative electrode can be separated even at a temperature at which lithium is melted (180 ° C.). Incidentally, the melting point of polyethylene or polypropylene conventionally used as a separator is 125 ° C. and 155 ° C., respectively. Note that the fluororesin film has a property of deteriorating the lithium negative electrode, and thus is disposed with the lithium resin film facing the positive electrode side.

As another conventional technique, for example, Japanese Patent Laid-Open No.
As described in JP-173566A, in an alkaline battery using an aqueous electrolyte such as potassium hydroxide, a technique has been proposed in which at least the surface located on the positive electrode side is constituted by a grafted polyethylene film having a fluorine treatment. ing. This prior art uses a grafted polyethylene film that has been treated with fluorine because the separator becomes brittle due to the oxidizing power of the positive electrode active material (active material).

In the alkaline storage battery described in Japanese Patent Application Laid-Open No. 4-87151, oxidation resistance is achieved by using a separator using a polyolefin resin fiber which has been contacted and reacted with a reaction gas containing fluorine.

[0009]

As described in the prior art, from the viewpoint of battery safety, improvements such as the use of a separator having a high melting point have been made in order to cope with an abnormally high temperature. Further, in the field of alkaline batteries, a technique for improving the oxidation resistance of the separator during normal use has been proposed.

However, in a non-aqueous electrolyte secondary battery such as a lithium battery, the oxidation resistance of the separator under actual operating temperature conditions has not yet been sufficiently improved.

As described in the prior art, the separator used for assuring a high melting point, that is, the technique in which a porous fluororesin film and a polyethylene or polypropylene film are simply overlapped with each other, requires that the porous fluororesin film have oxidation resistance. However, there is a point to be improved in terms of the capacity retention rate of such a battery (for details, use of the separator of Comparative Example 3 in the section of the means for solving the problem and the section of the embodiment of the invention) The performance evaluation).

[0012] In the oxidation-resistant technology of a separator as seen in an alkaline battery, fluorine is chemically bonded to the surface of the separator (polyolefin resin such as a grafted polyethylene film) on the positive electrode side by gas treatment. In such a fluorine treatment, the thickness of the oxidation-resistant film and the fluorine-bonded layer of the grafted polyethylene film is 3 to 5
μm, it is not possible to sufficiently suppress the cycle deterioration of the discharge capacity under conditions where the oxidizing atmosphere of the positive electrode is more severe than that of an alkaline battery, as in a non-aqueous electrolyte secondary battery. This is described using Comparative Examples 1 and 2 in the section of the embodiment.

Here, the mechanism of the deterioration phenomenon under the actual use conditions of the lithium secondary battery will be described.

In a power storage system, an electric vehicle, a notebook personal computer, a portable information terminal, and the like, the internal temperature of the lithium secondary battery during operation is higher than room temperature, and is usually between 40 and 80 ° C. The battery is used in a typical temperature range.

When a lithium secondary battery is used in such a temperature range, the oxidation reaction of the separator by the positive electrode is likely to occur. During charging and discharging of the battery, the potential of the positive electrode is in the range of 3 to 4.5 V on the basis of lithium, and thus the separator in contact with the positive electrode is in a strong oxidizing atmosphere. When a separator made of a polyolefin-based polymer such as polyethylene or polypropylene is used, carbon-hydrogen bond cleavage may occur due to oxidation catalyst action of the positive electrode, and the separator surface may be oxidized. At this time, the strength of the separator is significantly reduced as the separator is oxidized, and clogging of the separator proceeds due to the pressure applied between the positive electrode and the negative electrode.

As a result, the diffusion of lithium ions in the separator is significantly inhibited, and the battery capacity is reduced.
Such a deterioration phenomenon is not caused by the melting of the separator due to the abnormally high temperature described above. As described above, measures to suppress high-temperature deterioration due to the positive electrode in the intermediate temperature range where lithium secondary batteries are actually used (that is, between room temperature and the high temperature at which thermal runaway is supposed to occur) are still proposed as described above. It has not been.

An object of the present invention is to improve the performance of a nonaqueous electrolyte secondary battery represented by a lithium secondary battery by suppressing the deterioration of the separator in a temperature range where the battery is actually used.

[0018]

Means for Solving the Problems To achieve the above object, the present invention is basically configured as follows.

That is, in a non-aqueous electrolyte secondary battery including a positive electrode, a negative electrode, a non-aqueous electrolyte, and a separator, the separator includes a polymer resin sheet having high affinity for the non-aqueous electrolyte, an oxidation-resistant sheet, Are bonded in a layer, and the oxidation-resistant sheet is facing the positive electrode.

Here, a lithium secondary battery is taken as a typical application example of the non-aqueous electrolyte secondary battery, and the contents of the present invention will be described in detail.

(1) Positive electrode and negative electrode of lithium secondary battery The positive electrode of the lithium secondary battery is composed of a positive electrode active material, a conductive agent, a binder, and a current collector. When the positive electrode active material usable in the present invention is represented by a chemical formula, LiCoO ₂ , LiNiO ₂ ,
LiMn ₂ O ₄ and the like. Since these positive electrode active materials have high resistance, the electric conductivity of the positive electrode active material is supplemented by mixing a small amount of carbonaceous powder as a conductive agent. Since both the positive electrode active material and the conductive agent are powders, a binder is mixed with the powders so that the powders are bonded to each other and simultaneously bonded to the current collector. The current collector may be made of any material that is difficult to dissolve in the electrolytic solution, and an aluminum foil is often used. After applying a positive electrode slurry obtained by mixing a positive electrode active material, a conductive agent, a binder, and an organic solvent to a current collector by a doctor blade method, a dipping method, or the like, drying the organic solvent, and press-forming with a roll press. By
A positive electrode is produced.

The negative electrode of the lithium secondary battery includes a negative electrode active material,
It consists of a binder and a current collector. Negative electrode active materials that can be used in the present invention include aluminum, lead, silver, and the like, which are alloyed with lithium. In addition, carbonaceous materials, such as graphite and amorphous carbon, which can electrochemically occlude and release lithium, are also available. is there. In the present invention, there is no particular limitation on the negative electrode active material, and materials other than the above-mentioned materials can be used. Since the negative electrode active material to be used is powder, a binder is mixed with the negative electrode active material so that the powders are bonded to each other and simultaneously adhered to the current collector. For the current collector, a material that is difficult to alloy with lithium can be used, and copper foil is frequently used. A negative electrode active material, a binder, and a negative electrode slurry mixed with an organic solvent, a doctor blade method, after adhering to the current collector by a dipping method, by drying the organic solvent, by press molding with a roll press, A negative electrode is produced.

(2) Separator The separator of the present invention is inserted between the above-prepared positive electrode and negative electrode to secure lithium ion exchange and electrical insulation. Hereinafter, the separator of the present invention will be described in detail.

When the lithium secondary battery is charged and discharged in an intermediate temperature range between room temperature and thermal runaway, the surface of the separator is oxidized by the oxidation catalytic action of the positive electrode, and the strength of the separator is significantly reduced. As a result, it was found that clogging of the separator progressed due to the pressure of the clamping between the positive electrode and the negative electrode. As the positive electrode active material, a composite oxide including lithium and a transition metal such as manganese, nickel, and cobalt is used. At the time of charging, lithium ions move to the electrolyte as monovalent ions, and the transition metal ions are oxidized. At this time, the positive electrode active material is in a high oxidation state, and has a strong oxidation catalytic action. For example, LiMn ₂ O ₄ becomes MnO ₂ after charging, which acts as a strong oxidant.

Therefore, in order to prevent oxidation of the separator due to the charged positive electrode active material, it is necessary to change the conventionally used polyolefin polymer constituting the separator to a material having more excellent oxidation resistance. is necessary. Conventional polyolefin polymers are mainly composed of carbon-carbon bonds,
Contains carbon-hydrogen bonds. Their binding energies are 430-460 kJ / mol (edited by The Chemical Society of Japan,
Chemical Handbook Basic Edition, 4th revised edition, pages II-301). In comparison, a carbon-fluorine bond is an example having a binding energy as high as 10 to 90 kJ / mol. In the present invention, attention has been paid to a carbon-fluorine bond, and an improvement in the oxidation resistance of a separator has been achieved by using a polymer containing the carbon-fluorine bond.

According to the present invention, a polymer layer having a carbon-fluorine bond (a sheet containing a fluorine-based substance) functions to prevent oxidation of the separator, and another polyolefin-based polymer sheet serves as an electrolyte. Demonstrate the function of holding. As a result, oxidation by the positive electrode can be prevented without impairing the electrolyte retention of the separator. Hereinafter, the reason why the oxidation-resistant layer of the separator according to the present invention is a sheet and the reason why the sheet of the oxidation-resistant layer is integrated with a polymer resin layer having a high affinity for an electrolytic solution by bonding will be described.

(2-1) The ground that the oxidation-resistant layer of the separator is a sheet The separator for a lithium secondary battery used in a small consumer battery is generally prepared by forming a sheet of polyolefin such as polyethylene or polypropylene into a sheet. Many have fine holes formed on the surface. When the non-aqueous electrolyte is held in the microporous membrane, lithium ions permeate the micropores, so that the lithium secondary battery can be charged and discharged. During charging and discharging, the active materials used for the positive electrode and the negative electrode expand and contract, so that stress is generated in the electrode group. Therefore, tension or compression pressure is applied to the separator, and the separator is elongated or compressed. Such deformation becomes more remarkable as the battery external temperature changes.

Normally, a lithium secondary battery is at -20 to 60 ° C.
It can be used in the range. Due to such an external temperature fluctuation from a low temperature to a high temperature, the deformation of the separator becomes more remarkable due to a local strain caused by a volume change of the entire electrode group. Therefore, the separator is required to have strength so that cracks and pinholes in the oxidation-resistant layer do not occur due to deformation of the entire separator.

For the above reasons, it is desirable that the oxidation resistant layer formed on the surface of the separator be a sheet having a certain thickness. In order to secure the thickness of the oxidation-resistant layer, it is not possible to secure a sufficient thickness only by forming a fluorinated layer by a plasma method, a fluorination treatment after a carbonization treatment, or the like on the very surface layer of the polyolefin-based separator. Strength of the chemical layer is insufficient. Further, when the fluorination treatment as described above is performed on the polyolefin-based separator, the thickness of the separator changes due to the chemical decomposition reaction of the polyolefin layer on the surface, and the thickness varies in the separator plane.

This problem causes local deformation of the electrode group as the electrode and the separator are wound or laminated.

In the present invention, the oxidation-resistant layer is formed in a sheet shape in advance in order to ensure the thickness accuracy of the oxidation-resistant layer and to prevent thickness variation in the plane of the separator.
According to the examination results of the present invention, it is desirable that the thickness of the oxidation-resistant layer is 7 μm or more, more preferably 10 μm or more. Further, when the separator is thickened, the distance between the positive electrode and the negative electrode increases, and the ohmic loss also increases. Therefore, the thickness of the entire separator is desirably 100 μm or less, and by doing so, a separator having high strength and low resistance required for a lithium secondary battery can be obtained.

(2-2) Grounds for integrating the oxidation-resistant sheet of the separator and the high-affinity polymer resin sheet for the electrolytic solution by bonding The lithium secondary battery separator should be used as a single sheet. However, it is desirable for handling during battery production. Fluoropolymers such as polytetrafluoroethylene generally have higher strength than polyethylene, so if they are simply overlapped and wound simultaneously, the soft polyethylene separator will be stretched or compressed, resulting in a thinner. The problem of blockage of the hole occurs (this point is described in detail in the embodiment of the present invention).

When the pores of the separator are closed, the movement of lithium ions is hindered, resulting in a significant decrease in battery capacity. Further, when a wound electrode group is manufactured using a plurality of separators, precise tension control of each separator is essential. For example, the greater the diameter of the wound electrode group, the more likely it is that a strong tension is applied. Therefore, as the battery size increases, more precise and advanced battery manufacturing technology is required. Therefore, using a plurality of separators is not suitable for manufacturing a large-sized lithium secondary battery for an electric power storage system or an electric vehicle.

In order to avoid the above-mentioned problems, it is necessary to process the separator into a single sheet so as to secure the balance of the elongation of materials having different strengths. Thus, in the present invention, a separator is constructed by bonding a sheet having excellent oxidation resistance (for example, a fluorine-based polymer sheet) to the surface of a non-fluorine-based polymer resin sheet having affinity and integrating the sheet.

As the material of the oxidation-resistant sheet of the separator of the present invention, a fluoropolymer such as polytetrafluoroethylene, tetrafluoroethylene-6-propylene copolymer is suitable. Since the wettability of the electrolytic solution with respect to the oxidation-resistant layer is low, a high-affinity polymer sheet that easily holds the electrolytic solution is welded to the oxidation-resistant sheet, and by using a sheet obtained by integrating them, It becomes possible to satisfy both the requirements of oxidation resistance and the affinity of the electrolytic solution.

Examples of materials suitable for the affinity of the electrolyte include polyolefin polymers such as polyethylene and polypropylene. Polyethylene, between the positive and negative electrodes
A two-layer separator in which a polyolefin polymer sheet made of polypropylene or the like and a fluoropolymer sheet represented by polytetrafluoroethylene are welded, or a fluoropolymer sheet is welded to the outer surface of a polyolefin polymer sheet It is possible to use a three-layer structured separator or the like.

As a typical example, FIG. 1 shows the structure of the separator of the present invention. The separator shown in FIG. 1A is formed by joining an oxidation-resistant layer (fluoropolymer sheet) to the surface of one polymer layer (non-fluorine polymer sheet) to form a two-layer separator. Is the case. As an example of this,
As the polymer layer, a polyolefin polymer sheet such as polyethylene or polypropylene can be selected, and as the oxidation-resistant layer, a fluorine polymer sheet such as polytetrafluoroethylene, tetrafluoroethylene-6-propylene copolymer or the like can be selected. Both the polyolefin-based polymer sheet and the fluorine-based polymer sheet need to have pores that penetrate to move lithium ions, and have sufficient voids in the layer to hold the electrolyte. . In general, many polyolefin-based polymers have good wettability with oxygen-containing organic solvents such as propylene carbonate, ethylene carbonate, and dimethyl carbonate contained in the electrolyte, and are suitable for holding the electrolyte.

The separator shown in FIG. 1B is an example in which a fluorine-based polymer sheet of an oxidation-resistant layer, a plurality of non-fluorine-based polymer layers A and B, and the entire separator has a three-layer structure. . A plurality of polymers, each of which is effective for improving strength such as pulling or piercing, and increasing the amount of retained electrolyte, can be used for one of the polymer layers A and B. As an example, there is a combination of polytetrafluoroethylene for the oxidation-resistant layer, polypropylene for the polymer A, and polyethylene for the polymer B. Polyethylene is excellent in the retention of the electrolytic solution, while polypropylene has higher strength than polyethylene, and thus is effective in improving the strength of the entire separator.

In the present invention, it is sufficient if the separator has a pore diameter and a pore volume sufficient to allow lithium ions to permeate, and only the surface facing the positive electrode has oxidation resistance. The material, the number of layers, the arrangement, and the like are arbitrary. For example, a separator having a pore diameter of 0.01 to 10 μm and a porosity (sometimes referred to as porosity) in a range of 20 to 90% can be used for a lithium secondary battery. The surface not facing the positive electrode must have a sufficient pore diameter and pore volume for diffusion of lithium ions and holding of the electrolyte, and is not limited to the above-mentioned polyolefin polymer material. The total thickness of the separator is preferably as thin as possible so that the lithium ion conductivity between the separators is as high as possible, but it is also necessary to have a thickness sufficient to obtain sufficient strength to prevent a short circuit between the positive electrode and the negative electrode. Separator thickness is 20-1
If it is within the range of 00 μm, the present invention can be applied.

The above-described separator of the present invention can be prepared as follows.

It is possible to join an oxidation-resistant sheet (fluororesin sheet) and a non-fluorine-based polymer sheet (polyolefin sheet) by adding an adhesive or thermocompression bonding using a roller. Alternatively, the oxidation-resistant sheet and the polyolefin sheet are made porous by stretching in advance,
It is possible to manufacture a multilayered separator by laminating those sheets and further stretching, pressing and bonding with an adhesive.

It is also possible to add an adhesive between the oxidation-resistant sheet and the polyolefin sheet, or to bond the sheet by thermocompression bonding using a roller and then stretch the sheet to make the entire separator porous. As the stretching method, a uniaxial stretching method or a biaxial stretching method can be adopted. Further, as the polyolefin sheet serving as a base of the oxidation-resistant sheet, a polymer alloy composed of a plurality of polymer materials, a plurality of polyolefins having different compositions and molecular weights, or a multilayer sheet thereof can be used. In the present invention, there is no limitation on the material and configuration of the sheet underlying the oxidation-resistant layer, and also on the method of manufacturing the separator.

By winding a separator satisfying the above requirements together with a positive electrode and a negative electrode, a cylindrical electrode group can be manufactured.
When the electrodes are biaxially wound, an elliptical electrode group can be obtained. Apart from these winding methods, it is also possible to cut a positive electrode and a negative electrode into strips, alternately laminate the positive electrode and the negative electrode, and insert a separator between the electrodes to produce a laminated electrode group. The prepared electrode group is inserted into a battery container made of aluminum, stainless steel, or nickel-plated steel. After connecting the electrode to an external terminal attached to the lid, the lid and the battery container are welded. The shape of the battery can includes a cylindrical shape, a flat oblong shape, and a square shape, and any shape of battery can be selected as long as the electrode group can be accommodated. Next, an electrolyte is injected from the electrolyte injection port of the lid, and the injection port is sealed to complete the lithium secondary battery.

As a typical example of the electrolytic solution that can be used in the present invention, lithium hexafluorophosphate (LiPF ₆ ) or HF is used as an electrolyte in a solvent obtained by mixing dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate and the like with ethylene carbonate. Lithium chloride (LiB
There is a solution in which F ₄ ) is dissolved. In the present invention, other electrolytes can be used without being limited by the type of the solvent and the electrolyte, and the mixing ratio of the solvent.

By using the separator of the present invention, it is possible to prevent the separator pores from being blocked by the oxidation reaction of the separator by the positive electrode, and to provide a long-life non-aqueous electrolyte secondary battery.

[0046]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, the contents of the present invention will be described in detail based on embodiments. However, the present invention is not limited in any way by the following examples, and can be appropriately changed without changing the gist of the present invention.

Example 1 The positive electrode active material used in this example is a LiCoO ₂ powder having an average particle size of 10 μm. This positive electrode active material and natural graphite, 1-methyl-vinylidene fluoride
A 2-pyrrolidone solution was added and kneaded sufficiently to obtain a positive electrode slurry. The mixing ratio of LiCoO ₂ , natural graphite, and polyvinylidene fluoride was 90: 6: 4 by weight. This slurry was applied to the surface of a positive electrode current collector made of an aluminum foil having a thickness of 20 μm by a doctor blade method. The positive electrode has a rectangular shape with a height of 70 mm and a width of 120 mm. The positive electrode was dried at 100 ° C. for 2 hours.

The negative electrode was manufactured by the following method. Average particle size 5
μm natural graphite powder and polyvinylidene fluoride in a weight ratio of 9
The mixture was mixed at 0:10, 1-methyl-2-pyrrolidone was added as an organic solvent, and the mixture was sufficiently kneaded to prepare a negative electrode slurry. This slurry, by the doctor blade method,
It was applied to the surface of a negative electrode current collector made of a copper foil having a thickness of 10 μm. The negative electrode has a rectangular shape with a height of 70 mm and a width of 120 mm. This negative electrode was dried at 100 ° C. for 2 hours.

FIG. 2B shows a sectional structure of the prismatic lithium secondary battery of the present invention. The outer dimensions of the battery are 100 mm high,
It is 130mm wide and 25mm deep. The separator 3 used in this example has a polytetrafluoroethylene polymer sheet having an average pore diameter of 0.1 μm, a porosity (porosity) of 70%, a thickness of 10 μm, an average pore diameter of 0.2 μm, a porosity of 40%, A 30μm-thick polyethylene sheet is heat-welded to form an integral sheet. The sheet is made of a polytetrafluoroethylene polymer sheet (oxidation-resistant layer sheet) inside and a polyethylene sheet outside. The positive electrode 1 was inserted into the bag-shaped separator 3. By laminating many such positive electrode-containing separators 3 with the negative electrode 2 interposed therebetween, the positive electrode 1 and the negative electrode 2 are alternately laminated with the separator interposed therebetween. The polytetrafluoroethylene polymer sheet of the separator 3 faces the positive electrode 1, and the polyethylene sheet faces the negative electrode 2.

The positive electrode lead 5 and the negative electrode lead 7 welded to the upper portions of the electrodes 1 and 2 were connected to the positive electrode terminal 8 and the negative electrode terminal 9, respectively. The positive electrode terminal 8 and the negative electrode terminal 9 are inserted into the battery cover 11 via a packing 10 made of polypropylene. The connection between the external cable and the battery can be made by a nut 20 attached to the positive terminal 8 and the negative terminal 9 shown in FIG. The pressure inside the battery is 3
When the pressure reached 77 atm, a safety valve for releasing gas accumulated inside the battery and an electrolyte injection port were installed. The safety valve includes a gas discharge port 12, an O-ring 13, and a sealing bolt 14. The injection port is an injection port 15, an O-ring 16,
It is composed of a sealing bolt 17. After the aluminum battery can 4 and the battery lid 11 were laser-welded, an electrolytic solution was introduced from the inlet 15 and the inlet 15 was sealed with a sealing bolt 17 to complete the battery.

The electrolyte used was a solution containing 1 mol of lithium hexafluorophosphate (LiPF ₆ ) in 1 liter of an equal volume mixed solvent of ethylene carbonate and dimethyl carbonate. Nut 2 for positive terminal 8 and negative terminal 9
At 0, a cable is connected, and the electrochemical energy of the lithium secondary battery of this embodiment can be extracted to the outside via the cable and stored by recharging. The average discharge voltage of this battery is 3.7 V, the rated capacity is 27 Ah,
100 Wh. This battery is denoted by A1.

In the above description, the electrode group is a lamination type using strip electrodes. However, the present invention can be applied to a flat and elliptical winding type.

(Example 2) A positive electrode having the same specifications as in Example 1,
A prismatic lithium secondary battery was manufactured using the negative electrode and the electrolytic solution. In this embodiment, the average pore diameter is 0.1 μm and the porosity is 70
%, A polytetrafluoroethylene polymer having a thickness of 20 μm and a polyethylene having an average pore diameter of 0.2 μm, a porosity of 40%, and a thickness of 20 μm are integrally formed by heat welding.
With the other specifications being the same, the battery shown in FIG. 2 was manufactured, and the average discharge voltage was 3.7 V, the rated capacity was 27 Ah,
Wh was obtained. This battery is referred to as A2.

Comparative Example 1 A positive electrode having the same specifications as in Example 1
A prismatic lithium secondary battery was manufactured using the negative electrode and the electrolytic solution. In this comparative example, the average pore diameter was 0.2 μm, and the porosity was 40 μm.
%, A polyethylene separator with a thickness of 40 μm (separator 1) and a polyethylene separator with a fluorinated layer with an average thickness of 5 μm, a pore size of 0.2 μm, a porosity of 40%, and a thickness of 20 μm (separator 2), average 7μm thick
Having a fluorinated layer having an average pore diameter of 0.2 μm and a porosity of 40
%, A polyethylene separator (separator 3) having a thickness of 20 μm was used. As the fluorinated layer, the polyethylene sheet was brought into contact with plasma of fluorine gas to form a fluorinated layer on the surface of the polyethylene sheet. After embedding in the resin of the formed separator, and cutting and polishing the cross section, the fluorine concentration was measured by electron probe X-ray analysis. The distance from the position where the fluorine concentration was halved from the surface concentration to the surface was defined as the average thickness of the fluorinated layer. The other specifications were the same as in Example 1. The battery shown in FIG. 2 was manufactured, and an average discharge voltage of 3.7 V, a rated capacity of 27 Ah, and 100 Wh were obtained. The batteries using the separators 1, 2, 3
1, B2 and B3.

(Regarding Charge / Discharge Cycle Test Results of Examples 1 and 2 and Comparative Example 1) First, a charge / discharge cycle test was performed on the batteries A1 and B1 of Example 1 and Comparative Example 1. The charging condition is current 27A, and the termination condition is 4.2V constant voltage 3
Time regulation. The discharge current is 27A and the battery voltage is 3.0
Discharged until V was reached. The test environment temperature was 60 ° C. FIG. 3 shows the transition of the discharge capacity during the charge / discharge cycle test. The discharge capacity of the battery B1 of the comparative example decreased as the number of cycles increased, and decreased to 70% of the initial capacity of 27 Ah after 100 cycles of charge and discharge. In the battery A1 of the present invention,
The cycle deterioration of the discharge capacity was small, and the discharge capacity of 80% of the initial capacity of 27 Ah was maintained even after the charge and discharge test of 300 cycles.

After the charge / discharge test of 300 cycles, the battery A
1 and B1 were disassembled, and the Gurley number of the separator was measured. In the battery A1 of the present invention, the Gurley seconds of the separator increase from the initial value of 800 to only 20 to 30 after the cycle test, and the separator of the present invention is chemically stable by the charge / discharge test at a high temperature. Has been demonstrated. On the other hand, the Gurley number of the battery B1 of Comparative Example 1 was remarkably increased to 2 to 3 times the initial value of 750, and the pores of the separator were blocked by the charge / discharge test. As a result of performing the surface infrared analysis of the separators of the batteries A1 and B1, oxygen species were detected on the separator surface on the positive electrode facing surface of the battery B1, and it was also revealed that the separator surface was oxidized. By using the separator of the present invention, oxidation of the separator by the positive electrode is suppressed, and the life of the battery can be prolonged.

Next, the batteries A1 of Examples 1 and 2 and Comparative Example 1
A2, B1, B2, and B3 were subjected to a charge / discharge cycle test. FIG. 4 shows the test results at that time, in which the abscissa plots the thickness of the fluorinated oxidation-resistant layer and the ordinate plots the discharge capacity after 200 cycles. The charging condition is a current of 27 A, and the termination condition is a regulation of 4.2 V constant voltage for 3 hours. The discharge current was 27 A, and the battery was discharged until the battery voltage reached 3.0 V. The test environment temperature was 60 ° C.
In the batteries A1 and A2 of the present invention having a fluorinated layer of 10 μm or more, the cycle deterioration of the discharge capacity was smaller than that of the batteries B1, B2, and B3. An 80% discharge capacity was maintained.

A positive electrode, a negative electrode, and an electrolytic solution having the same specifications as those of these three types of batteries were used.
When a separator made of polytetrafluoroethylene having a m of 0.1 μm, an average pore diameter of 0.1 μm, and a porosity of 60% was used, the internal resistance of the battery was increased, and only a discharge capacity of 18 Ah was obtained.

Example 3 A positive electrode having a length of 5000 mm and a width of 150 mm, and a length of 5100 mm and a width of 155 mm were obtained in the same manner as in Example 1.
Was produced. In this example, for the positive electrode, LiCoO ₂ used in Example 1 was changed to LiMn ₂ O ₄ , and the other conditions for producing the positive electrode were the same.

FIG. 5 shows a cross-sectional structure of the cylindrical lithium secondary battery according to this embodiment. The outer dimensions of the battery are 200m high
m, diameter 50 mm. The electrode group has a wound structure wound between a positive electrode 1 and a negative electrode 2 with a separator 3 interposed therebetween.
The separator used in this example was a polytetrafluoroethylene-based polymer sheet (oxidation-resistant layer sheet) having an average pore diameter of 0.1 μm, a porosity of 70%, and a thickness of 10 μm, and an average pore diameter of 0.07 μm and a porosity of 46%. ,
A polypropylene sheet having a thickness of 10 μm and a polyethylene sheet having an average pore diameter of 0.2 μm, a porosity of 40%, and a thickness of 10 μm are sequentially laminated, and a three-layer structure is integrally formed.

With the polytetrafluoroethylene-based polymer layer (sheet) of the separator 3 facing the positive electrode, the positive electrode and the negative electrode were wound to form an electrode group. The positive electrode lead 5 and the negative electrode lead 7 welded to the upper part of each electrode were attached in opposite directions, and ten strip-shaped leads were produced for each electrode. Next, the positive electrode lead 5 and the negative electrode lead 8 were collectively welded to the positive electrode terminal 8 and the negative electrode terminal 9, respectively.
The positive electrode terminal 8 and the negative electrode terminal 9 were attached to the battery lid 11 in a state in which they were insulated by a packing 10 made of polypropylene. After the tubular aluminum battery can 18 and the battery lid 11 were laser-welded, the safety valve 30 serving as a vent for releasing the internal pressure and sealing the injection port was removed from the battery lid 11.
Inject electrolyte into the battery. Thereafter, the safety valve 30 was attached to the battery lid 11, and the battery was sealed. The vent has a sealed structure in which an aluminum thin film is sandwiched between two tubular parts. When the internal pressure of the battery reaches 3 to 7 atm, the gas accumulated inside the battery is released when the aluminum foil ruptures. Is done. The electrolytic solution used was a solution containing 1 mol of lithium borofluoride (LiBF ₄ ) in 1 liter of an equal volume mixed solvent of ethylene carbonate and dimethyl carbonate.

The electrochemical energy of the battery can be taken out from the positive electrode terminal 8 and the negative electrode terminal 9 and can be stored by recharging. The average discharge voltage of this battery is 3.7 V, the rated capacity is 27 Ah, and 100 Wh.
The battery pack of this example is denoted by A3.

Comparative Example 2 A cylindrical lithium secondary battery having the same configuration as that of Example 3 was produced using a polyethylene separator having the same specifications as Comparative Example 1. The battery of this comparative example was designated as B2
It is expressed as

Comparative Example 3 An average pore diameter of 0.1 μm, a porosity of 70%,
30μm thick polyethylene separator and average pore size 0.2μ
m, a porosity of 40%, and a 10 μm-thick polytetrafluoroethylene separator were simply superimposed, and a positive electrode and a negative electrode having the same specifications as those of Example 3 were prepared with the former facing the negative electrode and the latter facing the positive electrode. The cylindrical type lithium secondary battery was manufactured by winding and forming a wound electrode group. The battery of this comparative example is denoted by B3.

(Regarding Charge / Discharge Cycle Test Results of Example 3 and Comparative Examples 2 and 3) Battery A of Example 3 and Comparative Examples 2 and 3
3. For B2 and B3, a cycle life test was performed at an environmental temperature of 50 ° C. The charging conditions are a current of 3.4 A, a final voltage of 4.2 V and a regulation of 3 hours. The discharge current was 27 A, and the battery was discharged until the battery voltage reached 3.0 V. The capacity retention rates of the batteries B2 and B3 of Comparative Examples 2 and 3 at the time of 100 cycles were 70% and 75%, respectively. Although the battery B3 used the oxidation-resistant polytetrafluoroethylene separator, the capacity retention ratio was slightly lower than that of the battery B2.
Only a 5% improvement. As a result of disassembling the battery B3 and observing the separator, the elongation rates of the polyethylene separator and the polytetrafluoroethylene separator are different,
The pores of the polyethylene separator were compressed by the winding pressure, causing clogging of the pores. This result is 1kH
This corresponded to the result that the AC resistance value of the battery B3 at z increased from 5 mΩ measured before the cycle test to 25 mΩ after the 100-cycle charge / discharge test. In the battery A3 using the separator of the present invention, the capacity retention rate was as high as 95% or more, and the initial capacity of 80% or more was secured even after 300 cycles of the charge / discharge test.

Example 4 The separator used in this example was a polytetrafluoroethylene-based polymer sheet having an average pore diameter of 0.1 μm, a porosity of 30%, and a thickness of 7 μm (an oxidation-resistant sheet). ) And an average pore diameter of 0.07 μm and a porosity of 46
%, A 10 μm thick polypropylene sheet and a polyethylene sheet having an average pore size of 0.2 μm, a porosity of 40%, and a thickness of 10 μm are laminated in this order, and these are joined and integrally molded to form a three-layer type. It is a sheet. The polytetrafluoroethylene-based polymer layer of this separator was opposed to the positive electrode, and the materials, configuration, and specifications other than the separator were the same as in Example 3, and a cylindrical lithium secondary battery having the same specifications as in Example 3 was manufactured. did. This battery is denoted as A4.

Example 5 The separator used in this example was a polytetrafluoroethylene-based polymer sheet having an average pore diameter of 0.1 μm, a porosity of 70%, and a thickness of 10 μm (an oxidation-resistant sheet). ) And an average pore size of 0.07 μm and a porosity of 4
This is a sheet formed by integrally laminating a 6% polypropylene sheet having a thickness of 10 μm and a polyethylene sheet having an average pore diameter of 1.1 μm, a porosity of 85% and a thickness of 20 μm in this order. The material, configuration, and specifications other than the separator were the same as in Example 3, and a cylindrical lithium secondary battery having the same specifications as in Example 3 was manufactured. This battery is denoted as A5.

(Results of Cycle Life Test of Examples 4 and 5) For the batteries A4 and A5 of Examples 4 and 5, a cycle life test at an environmental temperature of 69 ° C. was performed. The charging conditions are a current of 3.4 A, an end voltage of 4.2 V and a regulation of 3 hours. The discharge current was 27 A and the battery voltage was 3.
Discharge was performed until the voltage reached 0V. The capacity retention rates of the batteries A5 and A6 at the time of 100 cycles were 92% and 96%, respectively, which were higher than those of the batteries B2 and B3 of Comparative Examples 2 and 3. The effect of the present embodiment shows the effectiveness of the separator of the present invention, battery components other than the separator,
That is, the specifications such as the positive electrode active material, the negative electrode active material, the current collector, the electrolytic solution, the material of the battery can, and the electrode dimensions are not limited to the studied Examples 3 and 4, and similar effects can be obtained in other combinations. What you get is self-evident.

Example 6 Sixty-six lithium secondary batteries A3 having the same specifications as those of Example 3 were manufactured, and twelve assembled batteries including eight batteries A3 were manufactured. An assembled battery module 41 in which all the assembled batteries were connected in series was mounted on an electric vehicle 42. FIG. 6 shows a configuration of an electric vehicle to which the lithium secondary battery according to the present invention is applied.

The assembled battery module 41 was installed on the bottom of the body of the electric vehicle. The driver controls the control device 44 with the steering wheel.
By operating, the converter 45 can be operated to increase or decrease the output from the battery module 41. The electric vehicle 42 was driven by driving the motor 46 and the wheels 47 using the electric power supplied from the converter 45. The electric vehicle of this embodiment is denoted by E6.

(Comparative Example 4) Using the battery B3 of Comparative Example 3,
An assembled battery module 41 having the same configuration as that of the sixth embodiment was manufactured. This module was mounted on an electric vehicle 42. The electric vehicle of this comparative example is denoted by F4.

(Running Test Results of Electric Vehicles E6 and F4) Running tests of the electric vehicles E6 and F4 were performed. When the assembled battery module 41 is charged once, the maximum traveling distance of the electric vehicle 42 is 200 km. In the case of the electric vehicle E6 equipped with the assembled battery module of the present invention, the number of times of charging and discharging when the maximum traveling distance is 160 km or less is 300.
It was times. On the other hand, in the electric vehicle F4 equipped with the assembled battery module of Comparative Example 4, the traveling distance became 160 km or less by repeating charging and traveling 110 times, and the electric vehicle E6 of the present invention was superior. In addition, the same effect was obtained with the use of the battery of the present invention for a hybrid electric vehicle using both an engine and a battery.

(Embodiment 7) FIG. 7 shows an example of a wheelchair 49 for medical care provided with a power supply 48 comprising a module of the assembled battery E6 or four sets of assembled batteries manufactured in the sixth embodiment. In the medical care wheelchair 49, the controller 50 can be operated in a state where the user is in the vehicle, and the drive units provided on the backrest seat 51 and the footrest seat 52 can be operated to adjust the respective angles arbitrarily. Using this function, the footrest seat 52 is lowered when the user gets on and off the vehicle, and the backrest seat 5 is used when the user rests.
1 and the footrest sheet 52 are made horizontal. Further, since the wheelchair 49 for medical care has the wheels 53 for movement, the user can move to the target position by operating the controller 50. The wheelchair 49 for medical and nursing care of this embodiment uses a lithium secondary battery provided with the oxidation-resistant separator of the present invention, and thus has excellent durability even in a high-temperature environment.

The battery pack of the present invention is not limited to the electric vehicle and the wheelchair for medical care and care described in the sixth and seventh embodiments, but may be a device system requiring a plurality of lithium secondary batteries, for example, a large-sized computer, a power tool, a cleaning tool. Machine, air conditioner, game device with virtual reality function, electric bicycle, walking aid for medical care, mobile bed for medical care,
It can be mounted on products such as escalators, elevators, forklifts, golf carts, emergency power supplies, road conditioners, and power storage systems, and the same effects as those of the embodiments described in the present specification can be obtained.

[0075]

As described above, according to the present invention, in a non-aqueous electrolyte secondary battery represented by a lithium secondary battery, deterioration of the separator in a temperature range where the battery is actually used is suppressed. As a result, the discharge capacity maintenance performance was significantly improved.

[Brief description of the drawings]

FIG. 1 is a conceptual diagram showing a configuration example of a separator of the present invention.

FIG. 2 is a top view and a sectional structural view of the prismatic lithium secondary batteries of Examples 1 and 2.

FIG. 3 is a diagram showing discharge capacity characteristics of Example 1 and Comparative Example 1.

FIG. 4 is a diagram showing the relationship between the number of charge / discharge cycles and the discharge capacity of the lithium secondary batteries of Examples 1 and 2 and Comparative Example 1.

FIG. 5 is a diagram showing a structure of a cylindrical lithium secondary battery in Examples 3, 4, and 5.

FIG. 6 is an electric vehicle equipped with the lithium secondary battery according to Embodiment 3 according to Embodiment 6 of the present invention.

FIG. 7 relates to a wheelchair for medical care using the lithium secondary battery used in the sixth embodiment according to the seventh embodiment of the present invention.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Positive electrode, 2 ... Negative electrode, 3 ... Separator, 4 ... Battery can, 5
... positive electrode lead, 7 ... negative electrode lead, 8 ... positive electrode terminal, 9 negative electrode terminal, 10 ... packing, 11 ... battery cover.

 ──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Masanori Yoshikawa 7-1-1, Omikacho, Hitachi City, Ibaraki Prefecture Inside Hitachi, Ltd. Hitachi Research Laboratory, Ltd. (72) Inventor Toshinori Dozono 7-1, Omikamachi, Hitachi City, Ibaraki Prefecture No. 1 Inside Hitachi, Ltd.Hitachi Research Laboratory (72) Inventor Takeo Yamagata 7-1-1, Omika-cho, Hitachi City, Ibaraki Prefecture Inside Hitachi, Ltd.Hitachi Laboratory (72) Inventor Ren Muranaka Hitachi, Ibaraki Prefecture 7-1-1, Omikacho Hitachi Research Laboratories, Ltd.Hitachi, Ltd. (72) Inventor Soji Nishiyama 1-1-1, Shimohozumi, Ibaraki-shi, Osaka Nitto Denko Corporation (72) Inventor Tetsu Ishizaki Osaka 1-2-2 Shimohozumi, Ibaraki-shi Nitto Denko Corporation F-term (reference) 5H021 BB11 CC04 EE04 EE10 HH02 HH03 5H029 AJ05 AK03 AL07 AL08 AL11 AM03 AM05 AM07 BJ02 BJ14 CJ22 DJ04 DJ09 DJ13 EJ12 HJ04 HJ05 HJ09

Claims (4)

[Claims] 1. A non-aqueous electrolyte secondary battery including a positive electrode, a negative electrode, a non-aqueous electrolyte, and a separator, wherein the separator comprises a polymer resin sheet and an oxidation-resistant sheet having high affinity for the non-aqueous electrolyte. Wherein the oxidation-resistant sheet is opposed to the positive electrode. A non-aqueous electrolyte secondary battery comprising: 2. The non-aqueous electrolyte secondary battery according to claim 1, wherein the polymer resin sheet is a polyolefin-based sheet, and the oxidation-resistant sheet is a sheet containing a fluorine-based substance. 3. The thickness of the separator is 20 to 100 μm.
m, the thickness of the oxidation resistant sheet is 7 μm.
The non-aqueous electrolyte secondary battery according to claim 1 or 2, wherein the value is set to m or more. 4. The separator according to claim 1, wherein the diameter is 0.01 to 10.
2. The micropores having a diameter of μm and a porosity of 20 to 90%.
4. The non-aqueous electrolyte secondary battery according to any one of claims 1 to 3.