JP2000251890A - Negative electrode for nonaqueous electrolyte secondary battery, and secondary battery using the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an electrode of high capacity, capable of easily enhancing a density without crashing an active material particle, prevented from decomposition of an electrolyte to exhibit superior potential smoothness, and provide a secondary battery using the electrode. SOLUTION: In this negative electrode, a carbon material prepared by mixing at least one kind selected from among a group of artificial graphite and natural graphite, and a carbon material having a volatile component in its surface or its inside, and by firing a mixture provided therein is used as an active material particle, resin is used as a binder, metal is used as a current collecting material, and the electrode has 20-35% of porosity, 1.20-1.60 g/cm3 of electrode density and 400 mAh/cm3 or more of electrode capacity.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a secondary battery using a non-aqueous electrolyte, and more particularly to a novel negative electrode which significantly improves the performance of a lithium secondary battery.

[0002]

2. Description of the Related Art In recent years, portable or cordless consumer electronic devices have been rapidly advanced. With this,
There is also a growing demand for improvements in functions / performance such as miniaturization, weight reduction, and high energy density of secondary batteries as power supplies for driving electronic devices. From such a viewpoint, there is great expectation for non-aqueous secondary batteries, particularly lithium secondary batteries having basically a high voltage / high energy density, and their practical use has been rushed.

That is, in a nonaqueous electrolyte secondary battery provided with a positive electrode made of a lithium ion-containing composite oxide, a nonaqueous electrolyte, and a rechargeable negative electrode, lithium ions are charged at the negative electrode during charging. It is doped between the layers, and is dedoped from the carbon layer during discharge. For this reason, even if the charge / discharge cycle proceeds, precipitation of dendrite-like crystals does not occur at the time of charging in the negative electrode, so that an internal short circuit hardly occurs and good charge / discharge cycle characteristics are exhibited. In addition, since the energy density is high and the weight is low, development is proceeding toward practical use.

JP-A-57-208079 and JP-A-63-24
Japanese Patent Publication No. 555 proposes the use of graphite as a negative electrode material which is excellent in flexibility and does not cause moss-like lithium to be deposited due to repeated charge / discharge cycles. Graphite has a unique layer structure and has the property of forming an interlayer compound, and therefore has been put to practical use as an electrode material for secondary batteries utilizing this property. When used in an electrolytic solution, it is known that a carbon material having low crystallinity, for example, a carbon material having a turbostratic structure obtained by thermally decomposing a hydrocarbon in a gas phase and a selective orientation is preferable. (Japanese
No. 63-24555). However, when a carbon material having low crystallinity is used as the negative electrode material, the potential change accompanying the release of lithium ions becomes large, so that the capacity that can be used as a battery is reduced, and it is difficult to manufacture a high-capacity battery. is there.

On the other hand, when a highly crystalline carbon material having graphite as its apex is used as a negative electrode material, the change in potential accompanying the release of lithium ions is theoretically small, and the capacity that can be used as a battery is reduced. Is known to grow. However, as the crystallinity of the carbon material increases, the charging efficiency is reduced, which is considered to be caused by the decomposition of the electrolytic solution. Further, the carbon material is destroyed by expansion / contraction of the interplanar spacing of the crystal due to repeated charge and discharge. Leads to.

Japanese Patent Application Laid-Open No. 4-368778 discloses that the formation of a double structure in which carbon particles having high crystallinity are coated with carbon having low crystallinity can prevent the destruction of the carbon material due to repeated charge and discharge. ing. When using a carbon material prepared by this method as an active material, theoretically,
A high-capacity electrode with excellent potential smoothness can be obtained by preventing decomposition of the electrolyte solution. However, when an attempt was made to produce a practical electrode using the double-structured active material particles,
For example, for a cylindrical battery, when an active material was applied on a copper foil to produce an electrode having a thickness of 50 to 500 μm, the electrode density was hard to increase, and the capacity per electrode volume did not increase. More specifically, it is difficult to increase the electrode density.
If the g / cm ³ or more is to be used, the double-structured active material particles are destroyed, so that a high capacity of 400 mA / cm ³ or more cannot be obtained.

[0007]

Therefore, according to the present invention, the density can be easily increased without destroying the active material particles, and the decomposition of the electrolytic solution can be prevented, so that the excellent electric potential smoothness can be obtained. It is a main object of the present invention to provide a high-capacity electrode exhibiting the above characteristics and a secondary battery using the same.

[0008]

Means for Solving the Problems The inventors of the present invention have conducted various studies while paying attention to the state of the art as described above, and as a result, have found that at least one of artificial graphite and natural graphite and volatile components on the surface and / or inside thereof. When a carbon material produced by mixing and then firing is used as active material particles, a high capacity and high density negative electrode for a non-aqueous electrolyte secondary battery can be obtained. Was found.

That is, the present invention provides the following negative electrode for a non-aqueous electrolyte secondary battery and a non-aqueous electrolyte secondary battery using the same. 1. A carbon material produced by mixing at least one kind of artificial graphite and natural graphite with a carbon material having a volatile component on the surface and / or inside thereof and firing the mixture is used as active material particles, and a resin is used as a binder. Used, formed using metal as current collector, porosity 20-35%,
A negative electrode for a non-aqueous electrolyte secondary battery, having an electrode density of 1.20 to 1.60 g / cm ³ and an electrode capacity of 400 mAh / cm ³ or more. 2. Item 2. The negative electrode for a non-aqueous electrolyte secondary battery according to Item 1, wherein the electrode density is 1.35 to 1.60 g / cm ³ . 3. A non-aqueous electrolyte secondary battery using the negative electrode for a non-aqueous electrolyte secondary battery described in the above item 1 or 2.

[0010]

BEST MODE FOR CARRYING OUT THE INVENTION The active material used in the present invention comprises at least one of artificial graphite and natural graphite and a carbon material having a volatile component on its surface and / or inside (hereinafter referred to as a "volatile component-containing carbon material"). Is a carbon material (hereinafter, referred to as a “coated graphite material”) produced by mixing and firing. In the coated graphite material obtained in this way, the volatile component derived from the volatile component-containing carbon material adheres to at least a part of artificial graphite and / or natural graphite by firing the mixed raw material, or the artificial graphite and / or Alternatively, it has a structure in which at least a part of natural graphite is covered. Such an attachment structure or coating structure
Once the volatile components of the volatile component-containing carbon material are vaporized, they adhere to part or all of artificial graphite and / or natural graphite, or by coating part or all of artificial graphite and / or natural graphite, It is considered formed. In other words, it is considered that part or all of artificial graphite and / or natural graphite has been coated in the gas phase.

In general, artificial graphite and natural graphite as negative electrode materials have a large capacity that can be used as a battery as compared with other graphite-based carbon materials, but have a large specific surface area, which impairs the stability of the electrolytic solution. The problem arises. However, when artificial graphite or natural graphite is coated in the gas phase, the coating thickness is assumed to be extremely thin and uniform. As a result, the specific surface area of artificial graphite or natural graphite can be reduced without substantially lowering the high capacity of artificial graphite or natural graphite, so that a high-capacity coated graphite material can be obtained. Conceivable.

Incidentally, the formation of the coated graphite material is possible even in the liquid phase. That is, the graphite material used as the core material is made into a liquid phase state, and “the carbon material for forming the coating”
It is possible to obtain a coated graphite material by immersion in a graphite. Also in this case, the volatile component for forming the coating / (core material +
By reducing the coating forming volatile component (hereinafter, this ratio is referred to as “coating ratio”), it is expected that a higher capacity carbon material may be obtained as in the case of the gas phase method. However, in practice, when a thin coating layer is formed in the liquid phase, there is a problem that the coating layer is peeled off from the core material or the coating layer lacks uniformity. Is unsuitable because it becomes large.

The volatile component-containing carbon material used in the present invention includes a carbon material (a volatile component-containing carbon material) in which a part or all of the core carbon material is coated with a coating-forming volatile component (such as coal tar pitch). Materials), mesocarbon microbeads, carbon fiber, mesophase pitch, isotropic pitch, resin, and mixtures thereof. Among them, the volatile component-containing carbon material is preferable in terms of cost. The coating ratio of the volatile component-containing carbon material is preferably 0.01 or more, more preferably 0.05 or more, and further preferably 0.05 or more and 0.3 or less.

If the coating ratio of the volatile component-containing carbon material is too low, the amount of volatile components that evaporates during firing in a mixed state with artificial graphite and / or natural graphite is small, so that artificial graphite and / or natural graphite are used. Is not sufficiently adhered or coated on some or all of them. In contrast,
If the covering ratio is too large, the capacity in the low potential portion depending on the core material decreases, so that it is difficult to obtain a sufficient capacity when a battery is manufactured. It should be noted that the amount of the “volatile component” referred to in the present specification is based on the JI value of the carbon component derived from heavy oil covering the periphery of the carbon material as the core material before firing.
Solvent analysis was carried out according to the method specified in SK2423. First, quinoline-insoluble matter (%) was measured, and then [100- (quinoline-insoluble matter)] was determined as quinoline-soluble matter (%). This quinoline-soluble content is the above-mentioned “volume of volatile component for coating formation”,
Using this amount and the carbon material as the core material, the above-mentioned “coverage ratio” can be calculated.

A volatile component-containing carbon material in which a part or the whole of a carbon material as a core material is coated with a volatile component is produced as follows. That is, carbon material particles serving as a core material are preferably immersed in coal or petroleum heavy oil such as tar or pitch at about 10 to 300 ° C., and then the carbon material is separated from the heavy oil and then separated. An organic solvent is added to the carbon material, and washing is preferably performed at 10 to 300 ° C. By appropriately adjusting the mixing ratio between the carbon material particles and the heavy oil, the above-described washing step can be omitted, but the washing step is preferably performed. In a case where the washing step is omitted, in particular, there may be a problem that particles of the volatile component-containing carbon material adhere to each other at the time of firing, agglomerate, or the volatile component is not uniformly attached or coated on the core material. . Further, the same problem may occur when a carbon material is immersed in heavy oil at a high temperature exceeding 300 ° C. to promote the polycondensation reaction of the heavy oil and produce a volatile component-containing carbon material. . Alternatively, 300-600 ° C instead of the above washing step
Although it is possible to carry out the calcination step at a degree, in this case, although the particles do not often adhere or aggregate, it becomes difficult for the volatile component-containing carbon material to uniformly adhere or coat the core material. .

In producing the volatile component-containing carbon material,
Examples of a method for mixing the carbon material particles serving as the core material and the heavy oil include a mechanical stirring method using a Nauta mixer, a ribbon mixer, a screw-type kneader, a universal mixer, or the like.

The mixing ratio of the artificial graphite and / or natural graphite to the volatile component-containing carbon material mainly depends on the amount of the volatile component, but usually 100 parts by weight of the volatile component-containing carbon material, And / or about 10 to 1000 parts by weight of natural graphite, more preferably about 10 to 300 parts by weight of artificial graphite and / or natural graphite, and still more preferably about 30 to 100 parts by weight of artificial graphite and / or natural graphite. . If the amount of artificial graphite and / or natural graphite is too small, the proportion of the coated graphite component that should become a higher capacity portion in the carbon material for a battery is reduced, and the capacity is not sufficiently increased. On the other hand, if the amount of artificial graphite and / or natural graphite is too large, the amount of volatiles vaporized during firing of the mixture is relatively small, and thus the coating of artificial graphite and / or natural graphite is not sufficiently performed, The specific surface area of the desired carbon material increases.

The mixture of artificial graphite and / or natural graphite and a volatile component-containing carbon material is calcined in a non-oxidizing atmosphere such as a reducing atmosphere, an inert gas stream, a closed state in the presence of an inert gas, or a vacuum. Do with. The firing of this mixture
Since the volatile component in the multilayer carbon material is vaporized in the gas phase to cover part or all of the artificial graphite and / or natural graphite, the volatile components of the volatile component-containing carbon material are likely to stay. It is more preferable to carry out the reaction in an atmosphere, that is, in a reducing atmosphere or in a closed state of an inert gas. Carbonization in a vacuum state has the effect of removing the surface functional groups of the carbon material and has the advantage of reducing retention, but has the disadvantage that volatile components from the volatile component-containing carbon material are easily lost. .

When carbonizing the above mixture, usually 600
~ 2000 ℃, more preferably 900 ℃ -1300 ℃
Bake at a temperature of about. When the same mixture is graphitized, it is usually fired at a temperature of about 2000 to 3000 ° C, more preferably at a temperature of about 2500 to 3000 ° C. Note that, depending on the firing conditions of the mixture, an ungraphitized portion may remain in the fired product, which may slightly affect the characteristics as a negative electrode material, but does not substantially cause a problem. However, in order to further improve the negative electrode characteristics, it is necessary to use a graphite material as the core material of the volatile component-containing carbon material or to increase the degree of graphitization of the fired product as much as possible by increasing the firing temperature. More preferred.

The rate of temperature rise during firing of the mixture can be appropriately selected from the range of about 1 to 300 ° C./hr at any firing temperature. The firing time is about 6 hours to 1 month.

The particle size of the coated graphite material obtained as described above and used as an active material in the present invention is usually 1 to 50
It is about μm, more preferably about 3 to 40 μm, and still more preferably about 5 to 35 μm. If the particle size of the coated graphite material is too small, the electrode density cannot be increased. On the other hand, if the electrode is too large, when producing a thin electrode having a thickness of about 100 μm, if press working is performed to increase the electrode density, the coated graphite material particles will be broken, and a high capacity cannot be achieved.

The resin used as a binder in the present invention has a function of binding the coated graphite material particles and binding and fixing the active material particles on the metal foil. The type of the resin as the binder is not particularly limited, but specifically, a fluororesin such as polyvinylidene fluoride and polytetrafluoroethylene; a polyolefin such as polyethylene and polypropylene; a fluororubber; And acrylic resin. Among these, polyvinylidene fluoride, which is soluble in general-purpose organic solvents (N-methylpyrrolidone, toluene, styrene, etc.), and is excellent in electrolyte resistance and withstand voltage, is particularly preferable.

The amount of the binder in the negative electrode according to the present invention is as follows:
The type, the particle size, and the shape of the coated graphite material particles, the thickness and strength of the target electrode, the strength, and the type of the binder may be appropriately determined, and are not particularly limited. About 1 to 30% (more preferably about 5 to 25%).

In the negative electrode according to the present invention, the metal used as the current collector is not particularly limited.
Examples include copper foil, stainless steel foil, and titanium foil. Further, a material on which an electrode can be formed on a metal foil or in a gap between metals, for example, an expanded metal, a steel material, or the like can also be used. Among these, a copper foil having a thickness of about 1 to 50 μm is more preferable because it is easy to manufacture a negative electrode by a coating method described later and is excellent in strength, electric resistance, and the like.

As an example of a specific method for producing a negative electrode for a non-aqueous secondary battery according to the present invention, a method using polyvinylidene fluoride as a binder resin and a copper foil as a current collector will be described below. The production of the negative electrode according to the present invention is not limited by this method.

First, a coated graphite material particle is uniformly dissolved in a binder resin solution in which polyvinylidene fluoride is dissolved in N-methylpyrrolidone to prepare a slurry. At this time, if necessary, a conductive material such as acetylene black,
A molding aid such as polyvinylpyrrolidone may be added. Next, the obtained slurry was coated using a coater,
A negative electrode for a non-aqueous secondary battery having a thickness of about 50 μm to 500 μm can be obtained by coating on a copper foil, drying and forming an electrode layer on the copper foil, and then pressing. The electrode layers are formed on both sides or one side of the copper foil as required.

The thus obtained negative electrode for a non-aqueous electrolyte secondary battery according to the present invention has a density of about 1.20 to 1.60 g / cm ³ , more preferably about 1.35 to 1.60 g / cm ³ , and a porosity of 20 to 35%. Yes, and the electrode capacity is 400 mAh / cm ³ or more. These densities and porosity are values for the electrode layer itself formed on the metal foil, and the porosity is calculated from the particle diameter of the coated graphite material in the electrode layer, the true density of the binder resin, and the electrode density. be able to. The electrode capacity is also a capacity based on the volume of the electrode layer.

When the density of the negative electrode for a non-aqueous electrolyte secondary battery is too low, sufficient electrode capacity cannot be obtained. On the other hand, when the density is too high, the capacity decreases due to the destruction of the coated graphite material. Is not preferred. If the porosity is too low, sufficient rate characteristics cannot be obtained, while if it is too high, sufficient electrode capacity cannot be obtained.

The negative electrode for a non-aqueous electrolyte secondary battery according to the present invention is a high-density electrode having an electrode capacity of 400 mAh / cm ³ or more and no capacity reduction.

The electrode capacity in the present invention is the electrode capacity when lithium is sufficiently doped and then undoped. For example, an electrochemical cell using lithium metal as a counter electrode and a reference electrode is assembled, and in a non-aqueous electrolyte described below, a constant voltage is applied at a potential of 1 mV with respect to the lithium metal potential, and the current value is sufficiently small (for example, After doping lithium to 0.01 mA / cm ² ), the undoping capacity is measured by undoping up to ² V with respect to the lithium metal potential at a sufficiently slow rate (for example, 0.25 mA / cm ² ). By dividing the undoped capacity by the electrode volume, the electrode capacity according to the present invention can be obtained.

With respect to the negative electrode for a non-aqueous electrolyte secondary battery of the present invention, the battery to be used is not limited. For example, lithium is properly combined with a known positive electrode and a non-aqueous electrolyte to form a lithium battery. A secondary battery can be manufactured. In this case, in order to obtain a high voltage and a high capacity, it is preferable to use a lithium composite oxide such as LiCoO ₂ , LiMnO ₂ , LiMn ₂ O ₄ , and LiNiO ₂ as the positive electrode. As the non-aqueous electrolyte, a non-aqueous electrolyte containing a lithium salt is used. The type of the electrolytic solution is appropriately determined depending on the type of the positive electrode material, the properties of the dual-structure active material particles, the use conditions such as the charging voltage, and the like.

Examples of the electrolyte include LiPF ₆ , LiBF ₄ ,
Dissolve lithium salt such as LIClO ₄ in one or more organic solvents such as propylene carbonate, ethylene carbonate, diethyl carbonate, dimethyl carbonate, methyl ethyl carbonate, dimethoxyethane, γ-butyl lactone, methyl acetate, methyl formate Are preferred.

[0033]

EXAMPLES Examples and comparative examples are shown below to further clarify the features of the present invention. Examples 1 to 3 Artificial graphite (“KS-44” manufactured by Lonza, center particle size D50 = 20.1 μm)
m, particle size distribution 0.1-150 μm, d002 = 0.336 nm, Lc = 110 nm, La
= 105 nm, specific surface area = 8.2 m ² / g, R value = 0.23, true specific gravity 2.25 g / cm
³ ) 50 g of coal tar pitch with a softening point of 80 ° C from which primary QI has been removed in advance (quinoline-insoluble matter = trace, toluene-insoluble matter =
30%) and 5 g of tar medium oil were placed in a 500 ml separate flask and distilled at 200 ° C. and 10 torr. After recovering the oil in the tar, the distillation was stopped to obtain pitch-coated graphite.

Since the measured value of the quinoline-soluble component of the obtained pitch-coated graphite is 6.8%, the coating ratio of the coating-forming carbon material (carbon material containing volatile components) is 0.068. For 100 parts by weight of this pitch-coated graphite, artificial graphite ("KS-44" manufactured by Lonza, with the same properties as above)
The parts by weight were mixed and fired in a nitrogen atmosphere at 1200 ° C. for 1 hour (heating rate 50 ° C./hr) to carbonize the coating layer. The specific surface area of the obtained coated graphite particles was 2.5 m ² / g, and the average particle size was 20.3 μm. The coated graphite particles are used as a negative electrode active material, acetylene plaque ("Denka Black", manufactured by Denki Kagaku Kogyo Co., Ltd.) is used as a conductive material, and polyvinylidene fluoride (Kureha Chemical Industry Co., Ltd.) is used as a binder.
(KF # 1100) was dissolved in N-methylpyrrolidone to prepare an electrode.

The mixing ratio was 87: 3: 10 (weight ratio): coated graphite particles: acetylene black: polyvinylidene fluoride.

The above mixed solution was applied to a copper foil having a thickness of 14 μm at a different thickness, and then dried at 80 ° C. for 15 minutes to obtain a radius of curvature of 30 cm.
Were continuously pressed by a roll press to produce three types of negative electrodes having an electrode thickness of 100 μm.

Using these negative electrodes, a capacity test was performed by the method described above. As the electrolytic solution, ethylene carbonate: dimethyl carbonate: methyl ethyl carbonate
A solution in which LiPF ₆ was dissolved in a mixed solvent of 7: 6: 6 (weight ratio) at a concentration of 1 mol / kg was used.

The obtained electrode density, initial capacity and initial efficiency are shown in Table 1 together with the results of Comparative Examples 1 to 3 below. Comparative Example 1 50 g of artificial graphite (manufactured by Lonza “KS-44”, the same as in Example 1), and a coal tar pitch having a softening point of 80 ° C. from which primary QI had been previously removed (quinoline insoluble matter = trace, toluene insoluble matter = Three
5 g of 0%) and 50 g of tar medium oil were placed in a 500 ml separate flask and distilled at 200 ° C. and 10 torr. After recovering the oil in the tar, the distillation was stopped to obtain pitch-coated graphite.

Since the measured value of the quinoline-soluble component of the obtained pitch-coated graphite is 6.8%, the coating ratio of the coating-forming carbon material (multilayer carbon material) is 0.068. This pitch coated graphite was fired in a nitrogen atmosphere at 1200 ° C. for 1 hour (heating rate 50 ° C./hr) to carbonize the coating layer. The specific surface area of the obtained coated graphite particles was 2.1 m ² / g, and the particle size was 20.5 μm.

Thereafter, in the same manner as in Example 1, an electrode was formed and the capacity was evaluated. Table 1 shows the obtained electrode densities, initial capacities, and initial efficiencies. Comparative Examples 2 to 4 Graphitized MCMB (manufactured by Osaka Gas Co., Ltd., product number 6-28, particle size 6.3 μm)
m, and a specific surface area of 3.2 m ² / g), three types of electrodes were prepared in the same manner as in Examples 1 to 3, and the capacities were evaluated. Table 1 shows the obtained electrode densities, initial capacities, and initial efficiencies. The difference in electrode density is due to the difference in coating thickness (coating amount) on the copper foil. Comparative Example 5 Using artificial graphite (“KS-44” manufactured by Lonza, the same properties as in Example 1), an electrode was formed in the same manner as in Example 1, and the capacity was evaluated. Table 1 shows the obtained electrode densities, initial capacities, and initial efficiencies.

[0041]

[Table 1]

As is clear from the results shown in Table 1, when the negative electrode according to the present invention is used, high density, high efficiency and high discharge capacity are obtained.

[0043]

According to the present invention, an inexpensive coated graphite material produced by mixing artificial graphite and / or natural graphite with a carbon material having a volatile component on the surface or in the interior and firing the mixture is used as an active material. Since it is used, it is possible to contribute to cost reduction of the negative electrode and the non-aqueous electrolyte secondary battery using the same.

Further, the particle diameter of the active material, the porosity of the electrode,
By optimizing the electrode density and the like, a negative electrode having a higher density and a higher capacity than a conventional negative electrode material can be obtained. As a result, a high performance non-aqueous electrolyte secondary battery can be obtained.

 ────────────────────────────────────────────────── ─── Continued on the front page (72) Haruo Kikuta, Inventor 4-1-2, Hirano-cho, Chuo-ku, Osaka-shi, Osaka F-term in Osaka Gas Co., Ltd. (reference) 5H003 AA01 AA02 BA01 BA03 BB01 BC01 BD00 BD03 BD05 5H014 AA01 BB01 BB06 EE08 HH00 HH01 HH02 HH04 HH08 5H029 AJ02 AJ03 AK03 AL06 AM03 AM04 AM05 AM07 CJ02 CJ08 DJ16 HJ01 HJ08 HJ09 HJ19

Claims (3)

[Claims] A carbon material produced by mixing at least one kind of artificial graphite and natural graphite with a carbon material having a volatile component on its surface and / or inside and firing the mixture, and using the carbon material as active material particles. Using a resin as an adhesive,
It is formed using metal as a current collector and has a porosity of 20
~ 35%, electrode density 1.20 ~ 1.60g / cm ³ , electrode capacity 400mAh / cm
^A negative electrode for a non-aqueous electrolyte secondary battery, wherein the number is ³ or more. 2. The negative electrode for a non-aqueous electrolyte secondary battery according to claim 1, wherein the electrode density is 1.35 to 1.60 g / cm ³ . 3. A non-aqueous electrolyte secondary battery using the negative electrode for a non-aqueous electrolyte secondary battery according to claim 1.