JP2002015726A - Gel electrolyte secondary battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a gel electrolyte secondary battery with excellent charge/ discharge cycle life and safety. SOLUTION: The gel electrolyte secondary battery is provided with a positive electrode 1' with a positive active material layer 1b equipped on the surface of a positive collector through a positive pole substrate layer 1c, a negative electrode 2' with a negative active material layer 2b equipped on the surface of a negative collector through a negative pole substrate layer 2b, and a gel electrolyte layer 3 pinched by the positive active material layer 1b and the negative active material layer 2b. The positive pole substrate layer 1c contains conductive particles of a smaller particle diameter than that of the particulate positive active material contained in the positive active material layer 1b. Further, the negative pole substrate layer 2c contains conductive particles of a smaller particle diameter than that of the particulate negative active material contained in the negative active material layer 2b. Furthermore, the positive active material and the negative active material have particles with average particle diameter of more than 5 μm.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a gel electrolyte secondary battery using a gel electrolyte, and more particularly, to a gel having a long charge-discharge cycle life, which is an item relating to the performance during actual use of the battery, and having excellent safety. The present invention relates to an electrolyte secondary battery.

[0002]

2. Description of the Related Art In recent years, many portable electronic devices such as camera-integrated video tape recorders, mobile phones, and portable computers have appeared, and their size and weight have been reduced.
As a battery serving as a portable power supply for these electronic devices, a secondary battery which is excellent in economy and resource saving is attracting attention, and its use is rapidly expanding. Above all, with regard to lithium ion secondary batteries having a high energy density and a high output density, it is also desired to develop a battery that is thin and can be bent and has a degree of freedom in shape.

As such a secondary battery, a gel electrolyte secondary battery using a gel electrolyte containing a swelling solvent (hereinafter, referred to as a gel electrolyte) has attracted attention. As shown in FIG. 2, the gel electrolyte secondary battery has a positive electrode 1 ′ in which a positive electrode active material layer 1b is provided on a positive electrode current collector 1a, and a negative electrode active material layer 2b provided on a negative electrode current collector 2a. A gel electrolyte layer 3 is sandwiched between the negative electrode 2 ′ and the negative electrode 2 ′, and is housed inside an exterior material (not shown). Positive electrode active material layer 1
b is obtained by mixing a particulate positive electrode active material with a binder and applying the mixture on the surface of the positive electrode current collector 1a. The negative electrode active material layer 2b is obtained by mixing a particulate negative electrode active material with a binder and applying the mixture on the surface of the negative electrode current collector 2a. The gel electrolyte layer 3 is formed by swelling a matrix polymer with a non-aqueous electrolyte in which an electrolyte salt is dissolved in a non-aqueous solvent, and is sandwiched between the positive electrode active material layer 1b and the negative electrode active material layer 2b. ing.

In the gel electrolyte secondary battery having such a configuration, since the non-aqueous electrolyte is retained in the matrix polymer in the gel electrolyte layer, the problem of leakage of the non-aqueous electrolyte is eliminated, so that the hard cell is not required. This is unnecessary, and further reduction in size, weight, thickness, and shape flexibility are realized.

[0005]

However, in a gel electrolyte secondary battery having such a structure, the reaction area is reduced by increasing the particle size of the active material in the positive electrode active material layer or the negative electrode active material layer. This causes smoke and overcharging
Safety is secured by preventing ignition. However,
By reducing the reaction area, load characteristics and low-temperature characteristics deteriorate. In addition, when the particle size of the active material is increased, peeling between the active material layer and the current collector is likely to occur, so that it is difficult to obtain desired charge / discharge cycle characteristics.

Therefore, the present invention can maintain the adhesion between the active material layer and the current collector even when using active material particles having a large particle size.
An object of the present invention is to provide a gel electrolyte secondary battery which is excellent in safety and charge / discharge cycle characteristics, and is excellent in load characteristics and low-temperature characteristics.

[0007]

Means for Solving the Problems In order to achieve the above object, the present invention provides a positive electrode and a negative electrode each having an active material layer containing a particulate active material provided on the surface of a current collector; In a gel electrolyte secondary battery including a gel electrolyte layer sandwiched between active material layers in the positive electrode and the negative electrode, between a current collector and an active material layer constituting at least one of the positive electrode and the negative electrode, It is characterized in that a conductive underlayer containing conductive particles having a smaller diameter than the particulate active material constituting the active material layer is provided.

In the gel electrolyte secondary battery having such a configuration, the particle size of the conductive particles forming the conductive underlayer provided on at least one of the positive electrode and the negative electrode is determined by the active material forming the upper active material layer. It is set smaller than the particle size of the substance. For this reason, for example, even if the particle size of the active material is set to be large (for example, a size exceeding 5 μm) for the purpose of ensuring safety, the conductive material including the conductive particles having a smaller particle size is used. The underlayer serves as an adhesion layer, and adhesion between the current collector and the active material layer is ensured. In addition, the conductive underlayer improves the electron conductivity between the active material layer and the current collector.

[0009]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, an embodiment of the gel electrolyte secondary battery of the present invention will be described in detail with reference to FIG.
The same members as those of the conventional gel electrolyte secondary battery are denoted by the same reference numerals.

The feature of the gel electrolyte secondary battery shown in FIG. 1 is that the positive electrode active material layer 1b and the positive electrode current collector 1
a, and between the negative electrode active material layer 2b and the negative electrode current collector 2a in the negative electrode 2 ′, respectively.
(Referred to as an underlayer) 1c and 2c. The underlayers 1c and 2c are formed by mixing conductive particles with a binder and coating the surfaces of the positive electrode current collector 1a and the negative electrode current collector 2a. It shall be designed as follows. That is, the particle size of the conductive particles forming the underlayer (hereinafter referred to as the positive electrode underlayer) 1c on the positive electrode 1 'side is smaller than the particle size of the positive electrode active material forming the positive electrode active material layer 1b, The particle size of the conductive particles forming the underlayer (hereinafter referred to as the negative electrode underlayer) 2c on the 'side is smaller than the particle size of the negative electrode active material forming the negative electrode active material layer 2b. Here, the particle size of each particle is an average particle size.

Next, the detailed structure of each member is described as a positive electrode 1 ',
The negative electrode 2 'and the gel electrolyte layer 3 will be described in this order.

The positive electrode 1 'has a configuration in which a positive electrode active material layer 1b is provided on a positive electrode current collector 1a made of, for example, a metal foil such as an aluminum foil, with a positive electrode underlayer 1c interposed therebetween. The positive electrode active material layer 1b is a layer formed by mixing a particulate positive electrode active material with a binder and applying the mixture on the positive electrode underlayer 1c.
The positive electrode active material constituting the positive electrode active material layer 1b is set to have an average particle size exceeding 5 μm in order to prevent smoke and ignition due to overcharge and to ensure safety. The positive electrode underlayer 1c is a layer in which conductive particles having a smaller particle size than the positive electrode active material are mixed with a binder and applied on the positive electrode current collector 1a. Therefore, the average particle size of the conductive particles constituting the positive electrode underlayer 1c is 5 μm.
Or less, preferably from 0.01 μm for ease of manufacture.
m or more.

Here, as the positive electrode active material constituting the positive electrode active material layer 1b, a metal oxide, a metal sulfide, or a specific polymer can be used depending on the type of the intended battery.

For example, when forming a lithium ion battery, TiS ₂ , MoS ₂ , NbSe may be used as the positive electrode active material.
₂ , V ₂ O ₅ or the like can be used. In addition, for example, a general formula Li _x MO ₂ (M represents one or more transition metals, x represents a composition ratio of Li. However, x differs depending on the charge / discharge state of the battery, and is usually 0.05 or more. , 1.10 or less.) Can be used. As the transition metal M constituting the lithium composite oxide, Co, Ni, Mn, or the like can be suitably used. Specific examples of such a lithium composite oxide include LiCoO ₂ , LiNiO ₂ , L
iNi _y Co _1-y O ₂ (where 0 <y <1), LiMn ₂
O _{4 and the} like can be given. The above-described lithium composite oxide can generate a high voltage and is a positive electrode active material excellent in energy density. Further, a plurality of these materials may be used as the positive electrode active material.

As the binder constituting the positive electrode active material layer 1b, a known binder can be used. Further, as a constituent element of the positive electrode active material layer 1b, a known conductive agent or additive may be added as necessary, in addition to the positive electrode active material and the binder.

The conductive particles constituting the positive electrode underlayer 1c include, for example, carbon powder such as non-graphitizable carbon-based materials, easily graphitized carbon-based materials, and graphite-based carbon-based materials, aluminum, gold, silver, and the like. Metal powder such as platinum can be used.

As the binder constituting the positive electrode underlayer 1c, the same binder as that constituting the positive electrode active material layer 1b can be used, and if necessary, additives may be added. You may.

The negative electrode 2 'has a configuration in which a negative electrode active material layer 2b is provided on a negative electrode current collector 2a made of, for example, a metal foil such as a copper foil, with a negative electrode underlayer 2c interposed therebetween. The negative electrode active material layer 2b is a layer formed by mixing a particulate negative electrode active material with a binder and applying the mixture on the negative electrode base layer 2c. The negative electrode active material constituting the negative electrode active material layer 2b emits smoke due to overcharging.
In order to prevent ignition and the like and to ensure safety, the average particle size is set to exceed 5 μm. The negative electrode underlayer 2c is a layer in which conductive particles having a smaller diameter than the negative electrode active material are mixed with a binder and formed on the negative electrode current collector 2a. Therefore, the average particle size of the conductive particles constituting the negative electrode underlayer 2c is 5 μm or less, and preferably in the range of 0.01 μm or more from the viewpoint of ease of production.

As the negative electrode active material constituting the negative electrode active material layer 2b, for example, in the case of forming a lithium ion battery, it is preferable to use a material capable of doping and undoping lithium. Examples of such a material include a non-graphitizable carbon-based material and a graphite-based carbon-based material.

Specifically, pyrolytic carbons, cokes,
Graphites, glassy carbon fibers, organic polymer compound fired bodies,
Carbon materials such as carbon fiber and activated carbon can be used. Examples of the coke include pitch coke, needle coke, and petroleum coke. The fired organic polymer compound is obtained by firing carbonized phenolic resin, furan resin or the like at an appropriate temperature.

In addition to the above-mentioned materials, as materials capable of doping and undoping lithium, polyacetylene,
A polymer such as polyvinyl or an oxide such as SnO ₂ may be used.

As the binder constituting the negative electrode active material layer 2b, a known binder can be used. Further, as a component of the negative electrode active material layer 2b, a known conductive agent or additive may be added as necessary in addition to the negative electrode active material and the binder.

The conductive particles constituting the negative electrode underlayer 2c include, for example, carbon powder such as non-graphitizable carbon-based materials, easily graphitized carbon-based materials, and graphite-based carbon materials; copper, nickel, gold, and silver. And a metal powder such as platinum.

As the binder constituting the negative electrode underlayer 2c, the same binder as that constituting the negative electrode active material layer 2b can be used, and if necessary, additives may be added. You may.

Next, the gel electrolyte layer 3 has a structure in which the matrix polymer is swollen with a non-aqueous electrolyte solution (swelling solvent) in which an electrolyte salt is dissolved in a non-aqueous solvent. The gel electrolyte layer 3 is also used as a separator for separating the positive electrode 1 'and the negative electrode 2'. However, a separator not shown here may be separately inserted into the gel electrolyte layer 3 as necessary.

As the non-aqueous solvent, for example, propylene carbonate, ethylene carbonate, dimethyl carbonate, diethyl carbonate, methyl ethyl carbonate, γ-butyrolactone, N-methylpyrrolidone, dimethoxyethane, dimethylacetamide, dimethylformamide, vinylene carbonate and the like are used alone. Alternatively, they can be used in combination.

The electrolyte salt dissolved in the non-aqueous solvent includes LiPF ₆ , LiBF ₄ , LiAsF ₆ , L
Lithium salts such as iN (CF ₃ SO ₂ ), LiSO ₂ CF ₃ and LiClO ₄ are used. Among them, LiP
F ₆ and LiBF ₄ are desirable from the viewpoint of oxidation stability. Also,
The concentration of the electrolyte salt was 0.6 mol /
It is preferable to set the amount to about 1 to 1.6 mol / l.

Further, as the matrix polymer, various polymers used for constituting a usual gel electrolyte can be used. Specifically, a fluorine-based polymer such as polyvinylidene fluoride or vinylidene fluoride-hexafluoropropylene copolymer, or polyacrylonitrile, polymethyl methacrylate, or a polyethylene oxide-based copolymer is used alone or in combination. it can.
Among them, it is particularly preferable to use a fluoropolymer, whereby the oxidation-reduction stability can be improved. Further, the matrix polymer preferably has a volume ratio of 1/6 to 1/3 of the non-aqueous electrolyte (swelling solvent),
Thereby, the ionic conductivity and mechanical strength of the gel electrolyte layer 3 can be compatible. That is, if the ratio of the matrix polymer to the swelling solvent is too small, the ionic conductivity is high but the mechanical strength cannot be maintained, and the gel electrolyte layer 3 is easily broken. On the other hand, if the ratio of the matrix polymer to the swelling solvent is too large, the mechanical strength is high, but the ionic conductivity is low.

According to the gel electrolyte secondary battery having such a configuration, the average particle diameter of the positive electrode active material forming the positive electrode active material layer 1b and the negative electrode active material forming the negative electrode active material layer 2b is 5 μm.
It is set to a relatively large particle size exceeding. For this reason, smoke and ignition due to overcharging are prevented, and safety can be ensured.

In addition, the positive electrode underlayer 1c and the negative electrode underlayer 2
The particle diameter of each conductive particle constituting c is set to a range (0.01 μm to 5 μm) smaller than the particle diameter of the active material constituting these upper active material layers 1 b and 2 b. For this reason, these underlayers 1c, 2c serve as current collectors 1a, 2a.
And an active material layer 1b, 2b containing an active material having a large particle diameter. That is, the base layers 1c and 2c serve as a buffer material, and the stress generated by the expansion and contraction of the active material layers 1b and 2b and the current collectors 1a and 2a due to charge / discharge, heat cycle, and the like is reduced. In addition, since the particle size of the active material is set to be large, even if the electrolyte from the gel electrolyte layer 3 side easily passes through these active material layers 1b and 2b, the conductive material having a smaller particle size is used. Underlayer 1 containing particles
The c and 2c prevent the electrolytic solution from reaching the interface between the current collectors 1a and 2a. For these reasons, peeling between the current collectors 1a and 2a and the active material layers 1b and 2b is less likely to occur, and adhesion can be ensured.

As described above, in this gel electrolyte secondary battery, even if an active material having a large particle size is used to ensure safety, the adhesion between the active material layers 1b and 2b and the current collectors 1a and 2a can be improved. Can be maintained, and charge-discharge cycle characteristics and safety can be ensured. Also, even if the surface area (that is, the reaction area) of the active material is reduced by using the active material having a large particle size, the active material layers 1b and 2b and the current collectors 1a and 2a are provided by providing the base layers 1c and 2c. Can be improved, so that load characteristics and low-temperature characteristics can be prevented from deteriorating.

In the above description, the positive electrode 1 'is provided with the positive electrode underlayer 1c and the negative electrode 2' is provided with the negative electrode underlayer 2c. However, in the present invention, the positive electrode 1 'and the negative electrode 2' are provided. It is sufficient that the underlayer is provided on at least one of them, and it is not always necessary to provide the underlayer on both the positive electrode 1 ′ and the negative electrode 2 ′. In the case where an underlayer is provided on at least one of the positive electrode 1 ′ and the negative electrode 2 ′, the underlayer may be provided on the positive electrode 1 ′, which has a greater effect of increasing safety by increasing the particle diameter of the active material. desirable. Further, when an underlayer is provided on at least one of the positive electrode 1 ′ and the negative electrode 2 ′, the average particle size of the active material on the electrode side on which no underlayer is provided is specified to a value exceeding 5 μm. Never.

Hereinafter, a method for manufacturing the gel electrolyte secondary battery having the above configuration will be described. Note that the present invention does not limit the manufacturing method, and the following manufacturing method is merely an example.

First, in order to form the positive electrode 1 ′, conductive particles having an average particle size of 0.01 μm to 5 μm are attached together with a binder on the surface of a positive electrode current collector 1 a made of a metal foil such as an aluminum foil. A positive electrode base layer 1c is formed by applying and drying a positive electrode base slurry dispersed in a solvent.
Thereafter, a positive electrode active material slurry obtained by dispersing a particle-shaped positive electrode active material having an average particle diameter of more than 5 μm in a solvent together with a binder is applied onto the positive electrode underlayer 1c, and dried to form the positive electrode active material layer 1b. Form. Thereby, the positive electrode current collector 1
A positive electrode 1 'obtained by providing the positive electrode active material layer 1b on the positive electrode underlayer 1c via the positive electrode underlayer 1c is obtained. When the positive electrode underlayer 1c is not required, the positive electrode active material slurry is directly applied to the surface of the positive electrode current collector 1a to form the positive electrode active material layer 1b.

On the other hand, to form the negative electrode 2 ′, conductive particles having an average particle size of 0.01 μm to 5 μm together with a binder are coated on the surface of the negative electrode current collector 2 a made of a metal foil such as a copper foil. A negative electrode base layer 2c is formed by applying a negative electrode base slurry dispersed in a solvent and drying. Thereafter, an average particle size of 5 is formed on the surface of the negative electrode current collector 2a or on the negative electrode underlayer 2c.
A negative electrode active material slurry in which a negative electrode active material having a particle size exceeding μm is dispersed in a solvent together with a binder is applied and dried to form a negative electrode active material layer 2b. Thus, the negative electrode active material layer 2 is formed on the negative electrode current collector 2a via the negative electrode underlayer 2c.
The negative electrode 2 'provided with b is obtained. When the negative electrode base layer 2c is not required, the negative electrode active material slurry is directly applied to the surface of the negative electrode current collector 2a to form the negative electrode active material layer 2b.

In order to form the gel electrolyte layer 3, first, a non-aqueous electrolyte solution (swelling solvent) in which an electrolyte salt is dissolved in a non-aqueous solvent is dispersed in a matrix polymer to prepare an electrolyte solution. . Next, the electrolyte solution is uniformly applied on the positive electrode active material layer 1b and the negative electrode active material layer 2b. Thereafter, the electrolyte solution is dried, the solvent is evaporated, and the solution is gelled, so that the positive electrode active material layer 1b and the negative electrode active material layer 2 are formed.
The gel electrolyte layer 3 is formed on b.

Next, the positive electrode 1 'on which the gel electrolyte layer 3 is formed and the negative electrode 2' are bonded together with the respective surfaces on which the gel electrolyte layer 3 is formed facing each other, thereby forming a battery element. At this time, a porous separator (not shown) may be sandwiched between the gel electrolyte layers 3.

The battery element thus obtained is housed in an exterior material, and the outer peripheral edge of the exterior material is joined by heat fusion via a hot-melt agent to form a gel electrolyte. Complete the next battery. The gel electrolyte secondary battery thus formed is not particularly limited in its shape, such as a cylindrical shape, a square shape, and a coin shape, and can be formed in various sizes such as a thin shape and a large size. .

[0039]

EXAMPLES Next, specific Examples 1 to 5 of the present invention, and Comparative Examples 1 to 5 for these Examples,
Further, these evaluation results will be described. As shown in Table 1 below, the configurations of the evaluation samples (that is, Examples and Comparative Examples) are as follows as factors for evaluating safety.
The average particle size of the positive electrode active material is 10 μm (large particle size) and 3 μm
(Small particle size), and the average particle size of the negative electrode active material was set at 25 μm (large particle size) and 4 μm (small particle size). In addition, as a factor for evaluating the charge / discharge cycle life, an underlayer was set at two levels, with and without an underlayer.

[0040]

[Table 1]

(Preparation of Evaluation Sample) The procedure for preparing each of these gel electrolyte secondary batteries is as follows. The procedure for producing a gel electrolyte secondary battery without a positive electrode underlayer or a negative electrode underlayer is a procedure in which the steps of forming the positive electrode underlayer and the negative electrode underlayer in the production procedure described below are deleted.

First, a positive electrode 1 'was prepared as follows.

Graphite (conductive particles) having an average particle size of 0.5 μm
And a vinylidene fluoride-hexafluoropropylene copolymer (binder) as conductive particles: binder = 90
The base mix mixed at a ratio of 10 wt% by weight was dispersed in N-methyl-2-pyrrolidone to prepare a positive base slurry. Then, this positive electrode base slurry was uniformly applied to one surface of an aluminum foil (positive electrode current collector) having a thickness of 20 μm and dried to form a positive electrode base layer 1c.

Further, lithium carbonate and cobalt carbonate were mixed at a ratio of 0.5 mol: 1 mol and calcined in air for 5 hours to obtain a positive electrode active material composed of LiCoO ₂ . At this time, by setting the firing temperature to 900 ° C., a positive electrode active material having an average particle diameter of 3 μm was prepared, and the firing temperature was set to 950 ° C.
The positive electrode active material having an average particle size of 10 μm was prepared. Next, the obtained positive electrode active material (LiCoO ₂ )
Graphite (conductive agent) and vinylidene fluoride-hexafluoropropylene copolymer (binder) are mixed in a ratio of positive electrode active material: conductive agent: binder = 91 wt%: 3 wt%: 6 wt%. The positive electrode mixture was prepared. Then, this positive electrode mixture was dispersed in N-methyl-2-pyrrolidone to prepare a positive electrode active material slurry.

Next, the positive electrode active material slurry is uniformly applied on the positive electrode base layer 1c (or on the positive electrode current collector 1a), and then dried to form the positive electrode active material layer 1b. The positive electrode 1 'was produced by compression molding with a machine.

Further, a negative electrode 2 'was produced as follows.

First, a negative electrode base slurry was prepared in the same procedure as the positive electrode base slurry. Then, the negative electrode base slurry was uniformly applied to one surface of a copper foil (negative electrode current collector) having a thickness of 10 μm and dried to form a negative electrode base layer 2c.

Further, graphite powder pulverized to an average particle diameter of each value shown in Table 1 was used as a negative electrode active material, and this negative electrode active material and vinylidene fluoride-hexafluoropropylene copolymer (binder) were used. Negative electrode active material: binder = 90 wt%: 1
A negative electrode mixture mixed at a ratio of 0 wt% was prepared. And
This negative electrode mixture was dispersed in N-methyl-2-pyrrolidone to prepare a negative electrode active material slurry.

Next, the negative electrode active material slurry is uniformly applied on the negative electrode base layer 2c (or on the negative electrode current collector 2a) and then dried to form the negative electrode active material layer 2b.
The negative electrode 2 'is formed by compression molding with a roll press.
Was prepared.

Further, a gel electrolyte layer 3 was prepared as follows.

First, an electrolyte solution is prepared by uniformly mixing polyvinylidene fluoride (matrix polymer) and a swelling solvent (non-aqueous electrolyte) at a ratio of matrix polymer: swelling solvent = 5 wt%: 95 wt%. did. The swelling solvent is a non-aqueous solvent in which ethylene carbonate, propylene carbonate and dimethyl carbonate are mixed, and LiP is used as an electrolyte salt.
It was used by dissolving F _6. The mixing ratio is ethylene carbonate: propylene carbonate: dimethyl carbonate: electrolyte salt = 18.5 wt%: 18.5 wt%: 60 wt
%: 3 wt%.

Next, this electrolyte solution was applied on the positive electrode active material layer 1b in the positive electrode 1 'and on the negative electrode active material layer 2b in the negative electrode 2'. At this time, coating was performed so that the thickness of the gel electrolyte layer after drying the electrolyte solution was 20 μm.
Next, the electrolyte solution was dried until the weight ratio of the swelling solvent to the matrix polymer became 8: 1, whereby the gel electrolyte layer 3 was formed.

After the above, the positive electrode 1 ′ and the negative electrode 2 ′ are pressed together with the gel electrolyte layer 3 side together, and cut as needed to obtain an area of 2.5 cm × 4.0 cm and a thickness of 2.5 cm × 4.0 cm. A 0.3 mm flat-plate gel electrolyte secondary battery was produced.

(Evaluation) The following battery characteristics were measured for each of the gel electrolyte secondary batteries produced as described above, and the results of the measurements are shown in Table 1 above. Here, as an evaluation of the charge / discharge cycle life, the discharge capacity at the time of 400 cycle charge / discharge was measured. In addition, as a safety evaluation, a 150 ° C. heating test was performed during charging at 4.35 V. Further, 75 mA discharge capacity was measured as load characteristic evaluation (load characteristic equivalent to 3 C), and -20 ° C. discharge capacity was measured as low temperature characteristic evaluation.

As shown in each evaluation result in Table 1, the positive electrode 1 ′
And at least one of the negative electrode 2 'and the gel electrolyte secondary battery in which the active material is set to have a large particle size (that is, Examples 1 to 5 and Comparative Examples 1 to 3),
There was no smoke or ignition in the heating test, and it was confirmed that safety was ensured. On the other hand, in the gel electrolyte secondary batteries (Comparative Example 4 and Comparative Example 5) in which the active material is set to have a small particle size in both the positive electrode 1 ′ and the negative electrode 2 ′, there is smoke or ignition in the 150 ° C. heating test. There was a problem with safety.

Further, among the gel electrolyte secondary batteries of which safety has been confirmed, a gel electrolyte secondary battery having an underlayer provided at least on the pole side where the active material has a large particle size (implementation) In Examples 1 to 5), it was confirmed that the discharge capacity at 400 cycles was maintained higher and the charge / discharge cycle life was better than other gel electrolyte secondary batteries (Comparative Examples 1 to 3). . In addition, it was confirmed that these gel electrolyte secondary batteries maintained a sufficiently high discharge capacity at 75 mA and a discharge capacity at −20 ° C., and also had good load characteristics and low-temperature characteristics.

As a result, the active material of at least one of the positive electrode 1 'and the negative electrode 2' was set to have a large particle size, and the underlayer was provided on the side of the electrode where the active material was set to have a large particle size. It was confirmed that a gel electrolyte secondary battery having excellent safety, good discharge cycle life, and excellent load characteristics and low-temperature characteristics was obtained.

[0058]

As described above, according to the gel electrolyte secondary battery of the present invention, the active material constituting the active material layer is provided between the active material layer and the current collector in at least one of the positive electrode and the negative electrode. By providing a conductive underlayer containing conductive particles having a particle size smaller than the particle size of the active material, even if the particle size of the active material is set large for the purpose of ensuring safety, The underlayer serves as an adhesion layer, so that the adhesion between the current collector and the active material layer can be ensured. As a result, it is possible to obtain a gel electrolyte secondary battery having excellent charge / discharge cycles and safety. In addition, even if the particle size of the active material is set large for the purpose of ensuring safety, the provision of the underlayer improves the electron conductivity between the active material layer and the current collector. Therefore, the load characteristics and low-temperature characteristics of the gel electrolyte secondary battery can be improved.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view illustrating a configuration of a gel electrolyte secondary battery according to an embodiment.

FIG. 2 is a cross-sectional view illustrating a configuration of a conventional gel electrolyte secondary battery.

[Explanation of symbols]

1 ′: positive electrode, 1a: positive electrode current collector, 1b: positive electrode active material layer,
1c: positive electrode underlayer, 2 ': negative electrode, 2a: negative electrode current collector, 2
b: negative electrode active material layer, 2c: negative electrode underlayer, 3: gel electrolyte layer

 ──────────────────────────────────────────────────続 き Continued on the front page F-term (reference) 5H029 AJ03 AJ05 AJ12 AK03 AL07 AM03 AM04 AM05 AM07 AM16 BJ04 DJ08 DJ16 EJ12 HJ05 HJ12 5H050 AA02 AA06 AA15 BA18 CA08 CB08 DA09 EA09 FA04 FA08 FA17 HA05 HA12 HA12

Claims (2)

[Claims] 1. A positive electrode and a negative electrode each having an active material layer containing a particulate active material provided on a current collector surface, and a gel sandwiched between the positive electrode active material layer and the negative electrode active material layer. In a gel electrolyte secondary battery including an electrolyte layer, between the current collector and the active material layer constituting at least one of the positive electrode and the negative electrode, a particulate active material constituting the active material layer A gel electrolyte secondary battery comprising a conductive underlayer containing conductive particles having a smaller diameter. 2. The gel electrolyte secondary battery according to claim 1, wherein the particulate active material constituting the active material layer on the conductive underlayer has an average particle size larger than 5 μm. Gel electrolyte secondary battery.