JP2003007280A - Nonaqueous electrolyte secondary battery and manufacturing method thereof - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a manufacturing method for a nonaqueous electrolyte secondary battery, having a porous polymer electrolyte with improvel high rate discharge performance and cycle performance. SOLUTION: This nonaqueous electrolyte secondary battery has the porous polymer electrolyte between a positive electrode and a negative electrode, the porous polymer electrolyte contains a first polymer electrolyte and a second polymer electrolyte, having different melting points, and satisfies the relation T1<T2, when the melting point of the first polymer electrolyte is represented by T1( deg.C) and that of the second polymer electrolyte is represented by T2( deg.C).

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a non-aqueous electrolyte secondary battery provided with a porous polymer electrolyte and a method for producing the same.

[0002]

2. Description of the Related Art Currently available lithium secondary batteries include a positive electrode made of a transition metal composite oxide such as lithium cobalt oxide, a negative electrode made of a carbonaceous material such as graphite, a separator made of polyethylene, polypropylene, etc., and an ethylene carbonate. LiP in a mixed solvent such as carbonate ester
An organic electrolyte in which a lithium salt such as F ₆ is dissolved is used, but in order to make the battery more stable,
Attempts have been made to use solid polymer electrolytes with poor chemical reactivity instead of flammable organic electrolytes.

Recently, it has been attempted to use a polymer electrolyte obtained by wetting or swelling a polymer with an organic electrolytic solution in order to improve conductivity, and further, for improving the diffusion rate of lithium ions, for example, JP-A-8
As described in JP-A-195220 and JP-A-9-259923, by using a porous polymer electrolyte as a separator or by holding it in electrode pores, high rate charge / discharge characteristics and safety are excellent. It has been proposed to manufacture batteries.

[0004]

The purpose of utilizing a porous polymer electrolyte is to form a large number of pores in a conductive polymer electrolyte and hold an electrolytic solution in the pores to diffuse lithium ions. To improve speed.

Since the porous polymer electrolyte is provided inside the electrode, uneven distribution of the electrolytic solution due to repeated charging / discharging reaction is suppressed, so that it is possible to suppress a decrease in discharge capacity due to cycles. Become. This is because the porous polymer electrolyte provided inside the electrode holds the electrolytic solution inside the electrode and also functions as a binder, so that the active material particles are prevented from falling off.

Further, by using this electrolyte as a separator, the amount of electrolytic solution retained in the battery can be reduced. Then, the diffusion rate of lithium ions equivalent to that of the electrolytic solution can be maintained, and high rate charge / discharge characteristics can be secured. further,
Since the porous polymer electrolyte swollen or moistened with the electrolytic solution is soft, its shape changes according to the irregularities of the positive and negative electrodes. Therefore, by using the porous polymer electrolyte as the separator, it is possible to narrow the gap between the separator and the positive and negative electrodes.

However, even when the porous polymer electrolyte is used as the separator, there is still a gap at the boundary between the porous polymer electrolyte and the electrode, and this portion becomes a space in which no ionic medium exists and reacts. Is hindered. Therefore, there is a new problem that the discharge capacity is significantly reduced when high-rate discharge is performed.

Therefore, for the purpose of improving the high rate discharge characteristics, a porous polymer electrolyte layer is provided between at least one of the electrodes and between the positive electrode and the negative electrode, and the positive electrode, the negative electrode and the porous polymer electrolyte layer are fixed to each other. Is being considered. Further, in this case, since it is possible to suppress an increase in battery thickness due to cycling, it is possible to dramatically improve cycle performance as compared with the case where the porous polymer electrolyte is provided only inside the electrodes.

However, a battery in which the porous polymer electrolyte layer provided between the positive electrode and the positive electrode and the negative electrode and the porous polymer electrolyte layer provided between the negative electrode and the positive electrode and the negative electrode are fixed by heating has a sufficiently high discharge rate. May not show performance.
As a cause of this, as a result of heating, the porous polymer electrolyte provided between the positive electrode and the negative electrode is melted too much, and as a result, a part of the pores is blocked, and the ionic conductivity of the polymer electrolyte and the lithium ion during charge / discharge reaction It is thought that the reason is that the diffusion performance of was decreased. Further, in this case, if the charging is performed at a high rate, metallic lithium is likely to be deposited and the cycle performance is significantly reduced.

The present invention has been made to solve these problems, and provides a method for producing a non-aqueous electrolyte secondary battery having a porous polymer electrolyte with improved high rate discharge performance and cycle performance. The purpose is to

[0011]

According to a first aspect of the invention, in a non-aqueous electrolyte secondary battery having a porous polymer electrolyte between a positive electrode and a negative electrode, the porous polymer electrolyte has a different melting point. A second polymer electrolyte is included, and when the melting point of the first polymer electrolyte is T1 (° C.) and the melting point of the second polymer electrolyte is T2 (° C.), the relationship of T1 <T2 is satisfied. .

According to the invention of claim 1, when the battery is heated to fix the polymer electrolyte provided between the positive electrode and the negative electrode and the positive electrode and the negative electrode, the first polymer electrolyte having a low melting point is melted. Acts as an adhesive layer to fix the polymer electrolyte and the respective electrodes to each other, while maintaining the porosity of the second polymer electrolyte having a high melting point and maintaining the diffusion performance of lithium ions in the porous polymer electrolyte. As a result, the high rate discharge performance of the battery can be improved.

According to a second aspect of the present invention, in the above non-aqueous electrolyte secondary battery, the mass ratio of the first polymer and the second polymer constituting the porous polymer electrolyte provided between the positive electrode and the negative electrode is defined. Yes, the mass of the first polymer is W1,
When the mass of the second polymer is W2, 0.05 ≦ W
It is characterized in that the relationship of 1 / (W1 + W2) ≦ 0.95 is satisfied.

According to the invention of claim 2, sufficient adhesive strength between the porous polymer electrolyte provided between the positive electrode and the negative electrode and the positive electrode and the negative electrode is obtained, and the porous property of the polymer electrolyte is maintained. .

The invention of claim 3 relates to a method for producing the above non-aqueous electrolyte secondary battery, wherein the porous polymer electrolyte provided between the positive electrode and the negative electrode and the positive electrode and the negative electrode are fixed by heating, and the heating temperature is increased. Is T3 (° C.), T1 ≦
It is characterized in that the relationship of T3 ≦ (T1 + 5) and T3 ≦ (T2-3) is satisfied.

According to the third aspect of the present invention, the battery is heated so that the surface of the first polymer electrolyte having a low melting point is slightly melted, thereby fixing the respective electrodes. In this case, even when the pores of the first polymer electrolyte are closed, the porosity of the second polymer electrolyte having a high melting point is maintained. As a result, it is possible to suppress the deterioration of the diffusion performance of lithium ions in the porous polymer electrolyte provided between the positive electrode and the negative electrode, and improve the high rate discharge performance. Further, since electrolytic deposition of metallic lithium caused by an increase in polarization of the negative electrode due to non-uniform diffusion distribution of lithium ions can be suppressed, excellent cycle performance can be expected.

[0017]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the battery of the present invention will be described below. The non-aqueous electrolyte secondary battery of the present invention is provided with a porous polymer electrolyte between the positive electrode and the negative electrode, and the porous polymer electrolyte includes first and second polymer electrolytes having different melting points, The melting point of the first polymer electrolyte is T1.
(C) and the melting point of the second polymer electrolyte is T2 (° C), the relationship of T1 <T2 is satisfied.

The battery is heated at a temperature of T1 or higher to produce a positive electrode
When the polymer electrolyte provided between the negative electrodes and the positive electrode and the negative electrode are fixed to each other, the first polymer electrolyte having a low melting point melts to act as an adhesive layer, and the polymer electrolyte and each electrode are fixed to each other, which is sufficient. Oneness can be expected. On the other hand, the porosity of the second polymer electrolyte having a high melting point is maintained, the diffusion performance of lithium ions in the porous polymer electrolyte is maintained, and the high rate discharge performance of the battery can be improved.

Further, in the present invention, the mass of the first polymer having a low melting point which constitutes the porous polymer electrolyte provided between the positive electrode and the negative electrode is W1, and the mass of the second polymer having a high melting point is W2. In case of 0.05 ≦ W1 / (W1 + W
2) It is characterized in that the relationship of ≦ 0.95 is satisfied.

When the amount of the first polymer having a low melting point is less than 5% by weight, sufficient adhesive strength between the electrode and the porous polymer electrolyte provided between the positive electrode and the negative electrode cannot be obtained. Further, when the amount of the second polymer having a high melting point is less than 5 wt%, the ratio of maintaining the porosity of the polymer electrolyte decreases, and it becomes difficult to suppress the deterioration of the diffusion performance of lithium ions.

Further, in the present invention, as the polymer electrolyte provided between the positive electrode and the negative electrode, the second polymer electrolyte having a higher melting point than that of the first polymer electrolyte is provided at the same time. When the heating temperature is expressed as T3 (° C.), T1 ≦ T3
It is characterized in that ≦ (T1 + 5) and T2 ≧ (T3-3). This is because when T3> (T1 + 5), the pores of the first polymer electrolyte may be completely blocked. Further, in order to maintain the porosity of the second porous polymer electrolyte, T3 ≦ (T2-3) is preferably satisfied. It was clarified in the experiments described later that the problem can be solved by setting the temperature conditions as described above.

In the present invention, "a porous polymer electrolyte provided between the positive electrode and the negative electrode" means that the porous polymer electrolyte is used as a separator for preventing a short circuit between the positive electrode and the negative electrode. Alternatively, it means that a membrane having fine pores such as polyolefin is used as a separator, and a porous polymer electrolyte is provided between the separator and the positive electrode plate and between the separator and the negative electrode plate.

In any case, the first polymer electrolyte having a low melting point may be present on at least a part of the surface of the porous polymer electrolyte provided between the positive electrode and the negative electrode. More preferably, an amount sufficient to obtain sufficient adhesive strength between the porous polymer electrolyte and the electrode should be present on the surface.

The term "membrane having fine pores such as polyolefin" refers to, for example, an insulating film such as polypropylene or polyethylene provided with numerous fine pores, or a nonwoven fabric. The major difference from the porous polymer electrolyte membrane is that the insulating film portion has no ionic conductivity.

A porous polymer electrolyte may be provided in the pores of the separator. In this case, since the porous polymer electrolyte is continuously present, the lithium ion diffusion performance is improved.

Further, in the present invention, it is preferable that the porous polymer electrolyte is provided inside at least one of the positive electrode and the negative electrode. Here, “inside the electrode” means a gap existing in the outermost layer between the electrode mixture layers and a gap existing between particles of the electrode mixture layer inside the electrode. The porous polymer electrolyte provided inside the electrode preferably has a melting point higher than that of the first polymer electrolyte, and more preferably the melting point of the second polymer electrolyte or higher. By providing the porous polymer electrolyte inside the electrode, the amount of the electrolytic solution can be made smaller than that of the conventional lithium ion secondary battery, so that the safety of the battery is improved.

Further, since the porous polymer electrolyte provided inside the electrode also functions as a binder for the active material particles to each other, it is possible to remarkably suppress a decrease in discharge capacity due to the cycle.

In the present invention, the melting point of the porous polymer electrolyte means the differential scanning calorimetry (DSC) in the state where all the pores of the porous polymer are filled with the electrolytic solution, and the polymer observed in this measurement The temperature is the temperature at which the endothermic peak associated with melting of is obtained. However, when the endothermic peak is sharp, it is the temperature at the maximum value of the peak, and when the endothermic peak is broad, it is the temperature at the start of rising of the peak. In addition, some polymers such as polyvinyl chloride decompose instead of melting, so the melting point of these porous polymer electrolytes was set to the decomposition initiation temperature. Even if the type of the electrolyte solution filling the pores of the porous polymer was changed, the temperature at which the maximum value of the endothermic peak measured by DSC did not change much.

An example of the manufacturing process of the battery according to the present invention will be given below. The first step of assembling a battery provided with a porous polymer between the inside of at least one of the positive electrode and the negative electrode and between the positive electrode and the negative electrode, and injecting an electrolytic solution into this battery, The electrolytic solution is retained, and at the same time, the polymer portion is swollen or moistened with the electrolytic solution, and the polymer is provided with ionic conductivity. After the second step of forming an electrolyte, heating is performed in the third step. And the porous polymer electrolyte provided between the positive electrode and the negative electrode, and the porous polymer electrolyte provided between the negative electrode and the positive electrode-negative electrode are fixed. Note that the battery may be sealed before or after the third step.

When heating is performed after injecting the electrolytic solution, immediately after the injection, the electrolytic solution is often not evenly distributed in the pores of the battery constituent elements. It is better to heat after dispersing in. When graphite is used as the negative electrode and a metal such as copper is used as the negative electrode current collector, the potential of graphite may be higher than the dissolution and deposition potential of the negative electrode current collector. When the heat treatment is performed without performing the preliminary charging, the dissolution of the negative electrode current collector is promoted and the battery may be short-circuited. In this case, pre-charging is always performed so that the potential of graphite is lower than that of the current collector, and then heat treatment is performed.

Furthermore, when graphite or the like is used as the negative electrode material, it is preferable to perform heating in a discharged state (a state in which lithium ions are not inserted between graphite layers as much as possible).

When gas is further generated by heating and the case swells or is distorted, the battery case may be replaced, or the sealing part may be opened once, and the gas inside may be released and then the case may be sealed again.

Means for heating the battery include placing the battery in a constant temperature bath, heat pressing the battery, and immersing the battery in a water bath or oil bath. Further, infrared rays or ultraviolet rays may be irradiated. By the way, the heating temperature T3 refers to the actual measurement value inside the constant temperature layer when a constant temperature layer is used, and the actual measurement temperature of the solvent in the bath when a water bath or oil bath is used. When a heat press or the like is used, T3 is set as the set temperature. When irradiating with infrared rays or the like, the battery surface temperature is set to T3. Further, since the electrode current collector and the electrode terminal outside the battery case are joined by metal without heating the entire battery, only this portion may be heated.

Although the heating time is an important factor in addition to the heating temperature, the heating time depends on the size of the battery, the type of polymer used, the heating method, etc.
Just select the optimal time.

In the present invention, as a method for obtaining a porous polymer, a through-hole forming method by ultraviolet irradiation, a phase transition method and the like can be used, and among them, a wet method which is one of the phase transition methods described above is used. The method is preferred.

The wet method is a method for obtaining a porous polymer by extracting a first solvent from a polymer solution prepared by dissolving a polymer in a first solvent using a second solvent for extraction. , A portion in which the first solvent is extracted by immersing the polymer solution in a second solvent that is insoluble in the polymer and is compatible with the first solvent, and the first solvent is removed. Becomes pores and a porous polymer is formed. Then, in this solvent extraction method, a through hole having a circular opening can be formed in the polymer.

As the first solvent for dissolving the polymer,
Depending on the polymer, for example, dimethylformamide,
Carbonic acid esters such as propylene carbonate, ethylene carbonate, dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, dimethyl ether,
Ethers such as diethyl ether, ethyl methyl ether and tetrahydrofuran, dimethylacetamide, 1-methyl-pyrrolidinone, n-methyl-2-pyrrolidone and mixtures thereof can be used.

As the second solvent for extracting the first solvent in the polymer solution, one which is compatible with the first solvent is selected and, for example, water, alcohol, acetone, or a mixed solution thereof is used. it can.

By the way, when the porous polymer electrolyte is formed in the small pores inside the electrode, when only a part of the polymer electrolyte is formed, the filamentous polymer is spread in the pores. Various shapes may be shown depending on the place where the hole is formed and the method of forming the hole. Also, if functionally expressed, it has a large number of pores or voids for allowing the polymer to hold an electrolytic solution for facilitating the movement of ions (for example, by having such a structure, electrolytic It can be said that it is a polymer electrolyte in which lithium ions can move in a liquid and lithium ions can also move in a matrix forming a polymer.

In the present invention, the porous polymer electrolyte provided between the positive electrode and the negative electrode may be prepared separately from the electrode and may be sandwiched between the positive electrode and the negative electrode during battery assembly, or A porous polymer electrolyte layer may be integrally formed on the electrode surface. Further, a porous polymer electrolyte may be formed on both surfaces of a separator made of polyolefin or the like.

Further, for example, a porous polymer layer is directly formed on the surface of the negative electrode, and the positive electrode and the negative electrode are laminated in a state of being electrically insulated by the porous polymer layer and wound to form a prismatic or cylindrical shape. Alternatively, the battery may be arranged in a battery case such as a resin-processed aluminum sheet, and the electrolytic solution for a lithium secondary battery may be injected into the battery.

The material of the polymer that constitutes the porous polymer electrolyte provided inside the electrode or between the positive electrode and the negative electrode is
For example, polyvinylidene fluoride (PVdF), polyvinyl chloride, polyacrylonitrile, polyvinylidene chloride, polymethyl methacrylate, polymethyl acrylate, polyvinyl alcohol, polymethacrylonitrile, polyvinyl acetate, polyvinylpyrrolidone, or a derivative thereof is used alone. Or a mixture thereof can be used. Further, a polymer obtained by copolymerizing various monomers constituting the above polymer, for example, vinylidene fluoride / hexafluoropropylene copolymer (P (VdF / HFP)) and the like can also be used. In addition, it is preferable that the active material has flexibility capable of changing its shape following the volume expansion and contraction of the active material.

The materials of these polymers are positive electrode
It is necessary to select the relationship between the melting points of the materials of the two kinds of porous polymer electrolytes provided between the negative electrodes so as to satisfy the relationship of claim 1. Then, as an example of the combination of the porous polymer electrolyte provided between the positive electrode and the negative electrode, when PVdF is selected as the material of the first polymer, polyvinylidene chloride, polyvinyl chloride, polymethacryl is used as the second material. Examples thereof include methyl acidate and polyvinyl fluoride. However, the melting point of the polymer changes depending on factors such as the molecular weight, the crystallinity, and the copolymerization composition ratio when the polymer is copolymerized, and is not limited to the above examples.

Other combinations include, for example, P (VdF /
When a copolymer such as HFP) is selected, the material of the porous polymer provided inside the electrode is P (VdF / HFP) with a reduced HFP copolymerization composition ratio and P (VdF / Hd) with an increased average molecular weight. It is also possible to use HFP), P (VdF / HFP) or the like in which the copolymer composition is decreased and the average molecular weight is increased, or PVdF.

As the positive electrode active material in the non-aqueous electrolyte secondary battery of the present invention, for example, a compound capable of inserting and extracting lithium can be used. For example, LiCoO ₂ or Li
NiO ₂ , LiMn ₂ O ₄ , Li ₂ Mn ₂ O ₄ , MnO ₂ , F
_{eO 2, V 2 O 5,} V 6 O 13, such as TiO _2, TiS _2, etc., the composition formula Li _x MO ₂ or Li _y M ₂ O _4, (provided that
M can be a transition metal, a complex oxide represented by 0 ≦ x ≦ 1, 0 ≦ y ≦ 2), an oxide having tunnel holes, or a metal chalcogenide having a layered structure.

In addition, LiNi _0.80 Co _0.20 O ₂ , LiN
It is also possible to use an inorganic compound in which a part of the transition metal M is replaced with another element, such as i _0.80 Co _0.17 Al _0.03 O ₂ . Furthermore, an organic compound such as a conductive polymer such as polyaniline can be used. In addition, regardless of whether it is an inorganic compound or an organic compound, the above various active materials can be mixed and used.

Examples of the negative electrode active material in the non-aqueous electrolyte secondary battery of the present invention include Al, Si, Pb, Sn and Z.
n, Cd, etc. and lithium alloys, transition metal composite oxides such as LiFe ₂ O ₃ , transition metal oxides such as WO ₂ , MoO ₂ , coke, mesocarbon microbeads (MCMB), mesophase pitch carbon fibers, heat Heat-treated product of graphitizable carbon such as decomposed vapor grown carbon fiber, phenol resin fired body, polyacrylonitrile-based carbon fiber, pseudo-isotropic carbon,
Heat-treated non-graphitizable carbon such as fired furfuryl alcohol resin, natural graphite, artificial graphite, graphitized MCMB, graphitized mesophase pitch-based carbon fiber, graphite material such as graphite whiskers, or carbon composed of a mixture thereof material,
Lithium nitride, lithium metal, or a mixture thereof can be used, and a carbon material is particularly preferable.

As the electrolytic solution, as its solvent, ethylene carbonate, dimethyl carbonate, diethyl carbonate, ethylmethyl carbonate, γ-butyrolactone, sulfolane, dimethyl sulfoxide, acetonitrile, dimethylformamide, dimethylacetamide,
A polar solvent such as 1,2-dimethoxyethane, 1,2-diethoxyethane, tetrahydrofuran, 2-methyltetrahydrofuran, dioxolane or methyl acetate, or a mixture thereof can be used.

The salt contained in the electrolytic solution is L
_{iPF 6, LiBF 4, LiAsF 6} , LiClO 4, Li
SCN, LiI, LiCF ₃ SO ₃ , LiCl, LiB
r, a lithium salt such as LiCF ₃ CO ₂ or a mixture thereof can be used.

The amount of electrolyte injected is preferably 130% or less and 10% or more of the total pore volume of the positive electrode, the negative electrode and the porous polymer film, and at least in accordance with the electrode material. It is preferable that the amount is sufficient to follow the expansion and contraction of the electrode volume. Since the gap between the battery constituent elements leads to deterioration of the high rate discharge characteristic, the present invention becomes more effective when the amount of liquid injected into the battery is small.

[0051]

EXAMPLES The present invention will be further described below with reference to examples.

[Example 1] LiNi was used as the positive electrode active material.
P (VdF / HFP) in which _0.85 Co _0.15 O ₂ was used, graphite was used as the negative electrode active material, and 13 wt% of hexafluoropropylene (HFP) was copolymerized as the material of the porous polymer electrolyte provided between the positive electrode and the negative electrode. ) (Molecular weight of about 300,000) and 6 wt% of HFP are copolymerized P (V
The following battery was manufactured using dF / HFP) (molecular weight of about 300,000).

The electrolyte solution (1 m
A mixed electrolyte solution of ethylene carbonate and diethyl carbonate in which ol / l of LiClO ₄ was dissolved (volume ratio 1:
1)) was included and the melting point was measured by differential scanning calorimetry (DSC). The results are shown in FIG. In FIG.
P (VdF / HFP) copolymerized with 13 wt% HFP
The result is shown by the symbol ◯, and the result of P (VdF / HFP) copolymerized with 6 wt% HFP is shown by the symbol Δ. In this case, the melting point of the former was determined to be 96 ° C and that of the latter was determined to be 104 ° C.

First, LiNi _0.85 Co _0.15 O ₂ particles 4
8.7 wt%, acetylene black 2.7 wt%, PV
A paste in which dF 3.3 wt% and NMP 45.3 wt% were mixed was applied on both surfaces of the aluminum foil, dried at 90 ° C. to evaporate NMP, and a positive electrode main body was prepared.

Next, P co-polymerized with 6 wt% of HFP was used.
(VdF / HFP) (molecular weight about 300,000) is added to NMP
A polymer solution dissolved in wt% was prepared, and the above electrode body was immersed in this to impregnate the electrode body with the polymer solution. Then, after the polymer solution excessively attached to the electrode surface was removed by passing it through a roller, the electrode body was immersed in ion-exchanged water (25 ° C.) to extract NMP.

This electrode was taken out, dried at 130 ° C., and then pressed. The thickness of the positive electrode after pressing is 1
It was 60 μm. The mass of the active material charged per unit area of the positive electrode was 20 mg / cm ² .

Next, using graphite as the negative electrode active material, a negative electrode was prepared as follows. A paste in which 81 wt% of graphite, 9 wt% of PVdF, and 10 wt% of NMP are mixed is applied on both sides of a copper foil having a thickness of 14 μm,
A negative electrode body was prepared by drying at 90 ° C. and evaporating NMP.

Next, P which was copolymerized with 6 wt% of HFP was used.
(VdF / HFP) (molecular weight about 300,000) was added to NMP 6
A polymer solution dissolved in wt% was prepared, and the above electrode body was immersed in this to carry the polymer solution on the electrode body. Then, after the polymer solution excessively attached to the electrode surface was removed by passing it through a roller, the electrode body was immersed in ion-exchanged water (25 ° C.) to extract NMP.

This electrode was taken out, dried at 100 ° C. and then pressed. The thickness of the negative electrode after pressing is 2
It was 08 μm. The mass of the active material charged per unit area of the negative electrode was 15 mg / cm ² .

Next, a porous polymer electrolyte provided between the positive electrode and the negative electrode was manufactured by a wet method. 13 wt% HFP
Copolymerized P (VdF / HFP) 10wt%, 6w
P (VdF / HFP) 10 copolymerized with t% HFP
A solution consisting of wt% and NMP 80 wt% was prepared. This polymer solution was cast on a glass plate using a doctor blade method and immersed in ion-exchanged water containing 75 wt% of ethanol to prepare a porous polymer film. The film thickness was 25 μm and the porosity was 58%.

The porous polymer film was interposed between the positive electrode and the negative electrode, and the wound type electrode plate group was formed by winding the film in a stacked manner, and the wound electrode plate group was inserted into an aluminum case to assemble a battery. Then, a mixed electrolyte solution of ethylene carbonate and diethyl carbonate (volume ratio 1: 1) containing 1 mol / l of LiPF ₆ was added and sealed. The amount of electrolyte injected is 1 of the total pore volume of the positive electrode, the negative electrode, and the porous polymer film.
It was set to 20%. After that, immediately with a current of 120 mA, 2
Charged for hours. Furthermore, it was charged up to 4.2V with a current of 120 mA, and then charged for 2 hours at a constant voltage of 4.2V. Next, it was discharged to 2.75 V with a current of 120 mA. This was carried out at room temperature for 3 cycles.

After that, the battery was inserted into a nylon bag, sandwiched between iron plates, and placed in an oil bath set at 101 ° C.
Immersion was carried out for 0 minutes to fix the positive electrode plate, the negative electrode plate, and the porous polymer electrolyte provided between the positive electrode and the negative electrode. Thus, a battery (A) according to the present invention having a nominal capacity of 600 mAh was obtained.

Example 2 A battery was manufactured by the same procedure as in Example 1 except that a water bath was used in place of the oil bath and the temperature was set to 96 ° C. when the battery was heat-treated. This was designated as Battery (B) according to the present invention.

Example 3 As a material for the porous polymer electrolyte provided between the positive electrode and the negative electrode, 13% by weight of hexafluoropropylene (HFP) was copolymerized with P (VdF /
HFP) (molecular weight: about 300,000) and PVdF (molecular weight: about 250,000) in which HFP was not copolymerized at all were used to manufacture a battery by the same procedure as in Example 1, which was used as a battery according to the present invention. (C).

PVdF was mixed with an electrolytic solution (a mixed electrolytic solution of ethylene carbonate and diethyl carbonate (volume ratio 1: 1) in which 1 mol / l of LiClO ₄ was dissolved), and the differential scanning calorimetry (DSC) was performed. The melting point was measured by using, and it was 120 ° C.

Example 4 As a material for the porous polymer electrolyte provided between the positive electrode and the negative electrode, P (VdF / 13% by weight of hexafluoropropylene (HFP) was copolymerized.
HFP) (molecular weight: about 300,000) and polyacrylonitrile (PAN) (molecular weight: about 200,000) were used to manufacture a battery by the same procedure as in Example 1, and to manufacture the battery as a battery (D) according to the present invention. did.

The electrolyte solution (1 mol / l of L was added to the PAN).
When a differential scanning calorimetry (DSC) was carried out by including a mixed electrolytic solution of ethylene carbonate and diethyl carbonate (volume ratio 1: 1) in which iClO ₄ was dissolved, it was decomposed (melted) at 50 to 120 ° C. The peak due to was not able to be confirmed.

Example 5 A porous polymer electrolyte provided between the positive electrode and the negative electrode was manufactured as follows. 13 wt%
HFP copolymerized P (VdF / HFP) 1wt
%, 6 wt% HFP copolymerized P (VdF / HF
A solution consisting of P) 19 wt% and NMP 80 wt% was prepared. This polymer solution was cast on a glass plate using a doctor blade method and immersed in ion-exchanged water containing 75 wt% of ethanol to prepare a porous polymer film. The film thickness was 25 μm and the porosity was 60%. A battery was manufactured through the same procedure as in Example 1 except that this electrolyte was provided between the positive electrode and the negative electrode, and this was designated as battery (E).

[Example 6] A porous polymer electrolyte provided between the positive electrode and the negative electrode was produced as follows. 13 wt% H
19% by weight of P (VdF / HFP) copolymerized with FP,
P (VdF / HFP) copolymerized with 6 wt% HFP
A solution consisting of 1 wt% and NMP 80 wt% was prepared.
This polymer solution was cast on a glass plate using a doctor blade method and immersed in ion-exchanged water containing 75 wt% of ethanol to prepare a porous polymer film.
The film thickness was 25 μm and the porosity was 59%. Example 3 except that this electrolyte was provided between the positive electrode and the negative electrode.
A battery was manufactured through the same procedure as above, and this was designated as battery (F).

Comparative Example 1 Example 1 was repeated except that the temperature of the water bath was set to 90 ° C. when the battery was heat-treated.
A battery was manufactured by the same procedure as above, and this was used as a battery (G).

Comparative Example 2 A battery was manufactured by the same procedure as in Example 1 except that the temperature of the oil bath was set to 105 ° C. when the battery was heat-treated, and this was designated as battery (H).

Comparative Example 3 A porous polymer electrolyte provided between the positive electrode and the negative electrode was manufactured as follows. 13 wt% H
0.4 wt% P (VdF / HFP) copolymerized with FP
%, 6 wt% HFP copolymerized P (VdF / HF
P) A solution consisting of 19.6 wt% and NMP 80 wt% was prepared. This polymer solution was cast on a glass plate using the doctor blade method, and 75 wt% of ethanol was used.
% Of ion-exchanged water to prepare a porous polymer membrane. The film thickness is 25 μm and the porosity is 59
%Met. A battery was manufactured through the same procedure as in Example 1 except that this electrolyte was provided between the positive electrode and the negative electrode, and this was designated as battery (I). [Comparative Example 4] As the material of the porous polymer electrolyte provided between the positive electrode and the negative electrode, only P (VdF / HFP) (molecular weight of about 300,000) copolymerized with 6 wt% of HFP was used. P (Vd that is copolymerized with 6 wt% HFP
F / HFP) 20 wt% and NMP 80 wt% were prepared. This polymer solution was cast on a glass plate using the doctor blade method, and ethanol was added to
A porous polymer membrane was manufactured by immersing it in ion exchange water containing wt%. The manufactured film had a thickness of 25 μm and a porosity of 58%. A battery was manufactured by the same procedure as in Example 1 except for the above, and was used as a battery (J).

Comparative Example 5 A porous polymer electrolyte provided between the positive electrode and the negative electrode was prepared as follows. 13 wt% H
P (VdF / HFP) copolymerized with FP 19.6 wt
%, 6 wt% HFP copolymerized P (VdF / HF
A solution consisting of P) 0.4 wt% and NMP 80 wt% was prepared. This polymer solution was cast on a glass plate using a doctor blade method, and ethanol was added at 75 wt%
The porous polymer membrane was manufactured by immersing it in the contained ion-exchanged water. The film thickness is 25 μm and the porosity is 59%
Met. A battery was manufactured through the same procedure as in Example 1 except that this electrolyte was provided between the positive electrode and the negative electrode, and this was designated as battery (K).

Comparative Example 6 As the material for the porous polymer electrolyte provided between the positive electrode and the negative electrode, only P (VdF / HFP) (molecular weight of about 300,000) copolymerized with 13 wt% of HFP was used. P (V
A solution consisting of 20 wt% of dF / HFP) and 80 wt% of NMP was prepared. This polymer solution was cast on a glass plate using the doctor blade method, and ethanol was added to
A porous polymer membrane was manufactured by immersing in ion-exchanged water containing 5 wt%. The thickness of the manufactured film is 25 μm,
The porosity was 58%. A battery was manufactured by the same procedure as in Example 1 except for the above, and this was used as a battery (L).

[Comparative Example 7] A battery was manufactured through the same procedure as in Example 1 except that the battery was not subjected to heat treatment.
This was used as a battery (M).

[Comparative Example 8] A battery which is not heat-treated by using a microporous polypropylene membrane in the separator portion without any polymer electrolyte inside the electrode and between the positive electrode and the negative electrode was prepared. (N).

First, for each battery, the integrity of the battery element was investigated. First, the batteries (A) to (L) manufactured here were disassembled, and the integrity of the positive electrode plate, the negative electrode plate, and the porous polymer electrolyte membrane was investigated. As a result, although the battery (G) of the comparative example was confirmed to have integrity, its strength was low. From this, in order to sufficiently fix the porous polymer electrolyte provided between the positive electrode and the positive electrode-negative electrode and the porous polymer electrolyte provided between the negative electrode and the positive electrode-negative electrode,
When the melting point of the first polymer electrolyte is expressed as T1 and the heating temperature is expressed as T3, it has been shown that it is preferable to satisfy the relationship of T3 ≧ T1.

Further, regarding the batteries (I) and (J) of the comparative example, the integrity of the element was confirmed, but the strength was low. On the other hand, in the battery (E), sufficient integrity was confirmed. In order to sufficiently fix the porous polymer electrolyte provided between the positive electrode and the positive electrode-negative electrode and the porous polymer electrolyte provided between the negative electrode and the positive electrode-negative electrode, the porous polymer electrolyte provided between the positive electrode and the negative electrode is provided. W1 / (W1 + W2) ≧ 0.05, where W1 is the mass of the first polymer and W2 is the mass of the second polymer constituting
It was shown that it is preferable to satisfy the relationship of

Next, the high rate discharge capacity of each battery was investigated. The manufactured batteries (A) to (F) according to the present invention,
Using the batteries (H), (K), (L), and (M) for comparison, the discharge capacities of 2C rate (1200 mA constant current) were compared. Ten of each battery was prepared, charged to a constant current of 600 mA to 4.2 V, and then charged to a constant voltage of 4.2 V for 3 hours. Then, it was discharged to 2.75 V at a constant current of 1200 mA, and the discharge capacity at that time was measured.
The discharge capacity of each battery is shown in Table 1.

[0080]

[Table 1]

1200 mA of comparative battery (M) not subjected to heat treatment and batteries (A) to (L) performed.
Comparing the constant current discharge capacities, it was found that the latter capacity was high. This is because the gap between the positive electrode and the porous polymer electrolyte provided between the positive electrode and the negative electrode and the gap between the negative electrode and the porous polymer electrolyte provided between the positive electrode and the negative electrode were eliminated, so that the electrolyte solution was uniformly distributed. Is believed to be the cause. In other words, in order to improve the high rate discharge performance, it is important to fix the porous polymer electrolyte provided between the positive electrode and the positive electrode and the negative electrode and the porous polymer electrolyte provided between the negative electrode and the positive electrode and the negative electrode. I can say. Next, when the discharge capacities of the batteries (A) to (D) according to the present invention and the comparative battery (H) were compared, it was found that the former showed clearly superior results. The relationship between the heating temperature (T3) and the melting point (T2) of the second polymer electrolyte is T3> (T2-3).
Then, it is considered that not only the pores of the first polymer electrolyte but also the pores of the second polymer electrolyte are likely to be clogged. As a result, it is considered that the diffusion of lithium ions between the positive electrode and the negative electrode was significantly hindered, and the 1200 mA constant current discharge capacity was significantly reduced. From this, T3
It was shown that it is preferable to satisfy the relationship of ≦ (T2-3).

Next, the battery (A) according to the present invention,
Comparing the discharge capacities of (E) and (F) and the batteries (K) and (L) for comparison, it was found that the former showed clearly superior results. Even when the second polymer electrolyte provided between the positive electrode and the negative electrode maintains the porosity, if the proportion of the first polymer electrolyte increases, the porosity of the electrolyte as a whole becomes significantly low. It is considered that the diffusion of lithium ions during the discharge reaction is significantly hindered. To sufficiently bond the porous polymer electrolyte provided between the positive electrode and the positive electrode-negative electrode and the porous polymer electrolyte provided between the negative electrode and the positive electrode-negative electrode, W
It was shown that it is preferable to satisfy the relationship of 1 / (W1 + W2) ≦ 0.95.

Further, the cycle performance of each battery was compared. The batteries (A) to (D) according to the present invention and the batteries (G), (H), (M), and (N) for comparison were used to compare their cycle performances. Each battery was first charged to a voltage of 4.2 mA at a current value of 300 mA, and then 4.
It was charged for 3 hours at a constant voltage of 2V. Then, it was discharged to 2.75 V at a current value of 600 mA. This was carried out for 300 cycles.

Here, the ratio of the discharge capacity of each cycle to the discharge capacity of the first cycle was taken as the discharge capacity maintenance rate of each cycle, and FIG. 2 shows the transition of the discharge capacity maintenance rate depending on the number of cycles. In FIG. 2, batteries (A), (B),
The results of (C), (D), (G), (H), (M), and (N) are represented by the symbols (Δ), (▽),
(□), (○), (■), (●), (▲), (▼).

Batteries (M) and (N) are batteries that have not been heat-treated. In these batteries, the discharge capacity retention rate decreased with the passage of cycles. This is because the volume expansion and contraction of the electrode plate due to the charge / discharge reaction is repeated, so that the pressure between the electrode and the short-circuit preventive agent provided between the positive electrode and the negative electrode becomes loose, and the gap increases and the distribution of the electrolyte solution becomes uneven. It is considered that the cause is.

On the other hand, in the battery to which the porous polymer electrolyte provided between each electrode plate and the positive electrode and the negative electrode is fixed, the increase in the distance between the electrodes due to the cycle is suppressed, so that the battery is more than the untreated battery. It showed excellent cycle performance.

Next, when the cycle performances of the batteries (A) to (D) according to the present invention and the comparative batteries (G) and (H) were compared, the former showed clearly superior cycle performance. The battery (G) has low adhesion strength between the porous polymer electrolyte provided between the positive electrode and the positive electrode and the negative electrode and the porous polymer electrolyte provided between the negative electrode and the positive electrode-negative electrode, and the battery thickness increases with the cycle. Was larger than the batteries (A) to (D). It is considered that the performance deteriorated because the electrolyte solution was non-uniformly distributed with the cycle.

Further, since the heating temperature of the battery (H) was high, most of the pores of the porous polymer electrolyte provided between the positive electrode and the negative electrode were blocked from the results of the high rate discharge performance. In other words, it is considered that metallic lithium was likely to be electrolytically deposited on the negative electrode plate during the charging reaction, and the decrease in capacity with the cycle became remarkable.

From the above results, the melting point (T1) of the first polymer electrolyte, the melting point (T2) of the second polymer electrolyte,
And the heating temperature (T3) is T1 ≦ T3 ≦ (T1 +
It has been clarified that a battery having excellent high rate discharge performance and cycle performance can be manufactured by satisfying the relationship of 5) and T3 ≦ (T2-3).

When the mass of the first polymer forming the polymer electrolyte provided between the positive electrode and the negative electrode is W1 and the mass of the second polymer is W2, 0.05 ≦ W1 / (W1 +
It has been clarified that the effect of the present invention becomes remarkable by satisfying the relationship of W2) ≦ 0.95.

[0091]

In the method for producing a non-aqueous electrolyte secondary battery of the present invention, the porous polymer electrolyte provided inside the electrode and the porous polymer electrolyte layer provided between the positive electrode and the negative electrode are fixed, It will be arranged continuously. As a result, it becomes possible to disperse the electrolyte solution continuously and uniformly,
Dispersion distribution of lithium ions becomes uniform, and discharge characteristics are improved.

Further, according to the method for producing a non-aqueous electrolyte secondary battery of the present invention, the melting of the polymer electrolyte provided between the positive electrode and the negative electrode can be suppressed as much as possible, and the clogging of the pores of the polymer electrolyte can be suppressed. High rate discharge performance and cycle performance can be improved.

[Brief description of drawings]

FIG. 1 is a diagram showing a DSC measurement result of a polymer electrolyte.

FIG. 2 is a diagram showing battery cycle performance.

Continued front page    F-term (reference) 5H021 AA06 BB01 BB11 CC04 EE02                       EE23 EE27 HH01 HH06                 5H029 AJ02 AJ05 AK02 AK03 AK05                       AK16 AL02 AL03 AL06 AL07                       AL08 AL12 AM02 AM03 AM04                       AM05 AM07 CJ02 CJ05 DJ04                       DJ06 EJ12 EJ14 HJ01 HJ14

Claims (2)

[Claims] 1. A porous polymer electrolyte is provided between a positive electrode and a negative electrode, the porous polymer electrolyte includes first and second polymer electrolytes having different melting points, and the melting point of the first polymer electrolyte is T1 ( ℃), the melting point of the second polymer electrolyte is T
A non-aqueous electrolyte secondary battery characterized by satisfying the relationship of T1 <T2 when 2 (° C.). Example 2 When the mass of the first polymer is W1 and the mass of the second polymer is W2, 0.05 ≦ W1 / (W
The non-aqueous electrolyte secondary battery according to claim 1, wherein the relationship of 1 + W2) ≦ 0.95 is satisfied. 2. The porous polymer electrolyte provided between the positive electrode and the negative electrode and the positive electrode and the negative electrode are fixed by heating, and when the heating temperature is T3 (° C.), T1 ≦ T3 ≦ (T1 +
5) And the relationship of T3 <(T2-3) is satisfied, The manufacturing method of the non-aqueous electrolyte secondary battery of Claim 1 or 2 characterized by the above-mentioned.