JP2002158037A - Polymer secondary battery and its manufacturing method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent that as the interface of the polymer electrolyte layer and the electrode is formed by contact of a solid-solid, contact of the interface of an active substance and an electrolyte is likely to become unstable and the battery property deteriorates such as deterioration of charge and discharge characteristics and increase of internal resistance. SOLUTION: The polymer battery uses for jointing of the interface of the positive and negative electrodes a polymer having an average molecular weight of 5,000 to 1,000,000 that has a cyanic group or ester group having a large electron suctioning performance and an oligomer having an average molecular weight of 500 to 3,000 that has compatibility with the above polymer and has an unsaturated double bond of more than two functional groups, and comprises a process of laminating the electrode painted with the polymer and the electrolyte layer containing the thermal polymerization initiator and the oligomer and making thermal polymerization.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a lithium secondary battery,
In particular, the present invention relates to a secondary battery using a solid polymer electrolyte and a method for manufacturing the same.

[0002]

2. Description of the Related Art In recent years, notebook computers, mobile phones, PDAs
And other electronic devices are actively used.
Thinner and lighter are being promoted. Secondary batteries are mainly used as power sources for these devices, and among them, lithium ion secondary batteries having high energy density are often used.

At present, the most widespread secondary battery is a so-called lithium ion secondary battery using a carbon material for the negative electrode and a lithium oxide for the positive electrode. Although the electric capacity is lower than when lithium metal is used for the negative electrode, it has excellent cycle characteristics and the like, and is currently mounted on various devices, especially mobile devices that require light weight and high capacity.

[0004] However, these lithium ion batteries use a non-aqueous electrolyte and may cause leakage of the electrolyte.

[0005] For this reason, studies on solid secondary batteries using a solid electrolyte free from the risk of liquid leakage have been actively conducted, and particularly studies on a polymer solid electrolyte using polyethylene oxide (PEO) have been actively conducted. Was done. For example, in 1975, Wright et al. Discovered that PEO and an alkali metal form a complex, and found that it has a conductivity of 10 ⁻⁴ [S / cm] or more at 60 ° C. (Br. Polym.
J. , 7, 319). Armand also described the ion conduction mechanism of PEO, polypropylene oxide (PPO) and various alkali metal salts in 1988 (Electroresponsive Mol).
ecological and polymericSystem
ms Vol 1, Marcel Dekker I
nc Publisher,). However, they have sufficient conductivity at high temperatures but have low conductivity at room temperature.

For this purpose, a large amount of an organic solvent is added as a plasticizer to a polymer solid electrolyte to form a gel, thereby improving the ionic conductivity, and improving the ion conductivity of a polymer such as polyethylene oxide or polyvinylidene fluoride (PVDF). In general, a so-called gel polymer containing an organic electrolyte solution is used for a battery as a solid electrolyte. For example, B
The company discloses a patent for a polymer battery using a polyvinylidene fluoride-based polymer (for example, US Pat. No. 5,296,318, US Pat. No. 5,545,6000).

In order to improve mechanical strength, two or more kinds of polymers are mixed. For example, JP-A-8-165395 discloses a semiconductive solid composition comprising polyvinylidene fluoride (polyvinylidene fluoride), a polyalkylene oxide, and an ion dissociable salt. Also, JP-A-8-1
No. 76389 discloses a thermoplastic resin such as polyvinylidene fluoride, a combination of an acrylate-substituted polyalkylene oxide and a copolymer of an alkyl acrylate,
Further, a semiconductive solid composition further containing an ion dissociable salt is disclosed. JP-A-9-97618 discloses a battery in which a polymer alloy film is prepared by mixing a poorly soluble polyvinylidene fluoride and a soluble polyethylene oxide or polymethyl methacrylate in an organic electrolytic solution, and impregnated with the organic electrolytic solution and cured. A disclosed polymer electrolyte is disclosed. Also, JP-A-11-1498
No. 22, JP-A-11-35765 and the like also disclose a polymer electrolyte in which a mixture of a polyvinylidene fluoride polymer and a polyethylene oxide polymer contains an ion dissociable salt.

[0008]

However, as disclosed in these publications, the combination of polyvinylidene fluoride and polyethylene oxide improves mechanical strength but is not a compatible system, so that it is difficult to obtain a homogeneous gel electrolyte, and moreover, Complicated steps are required to produce a homogeneous gel. That is, a gel electrolyte that is strictly homogeneous and has high mechanical strength cannot be obtained by this method. Further, even if the mechanical strength of the electrolyte is improved, the problem of stabilizing the interface bonding between the electrolyte and the electrode remains.

As a measure for improving the stability of interfacial contact, an attempt has been made to improve the bonding at the interface between the electrode plate and the electrolyte layer by applying an adhesive to the interface between the electrode plate and the electrolyte layer. For example, Japanese Patent Application Laid-Open No. H11-40201 proposes that a polyvinylidene fluoride or an ethylene-vinyl acetate copolymer or the like be applied to an electrode plate as an adhesive for an electrolyte layer to improve the adhesion, The interface has not reached stable contact.

In the case of a polymer battery, the interface between the polymer electrolyte layer and the electrode is formed by a solid-solid contact, not by a reaction system formed at a solid-liquid interface as in a conventional battery using only an electrolytic solution. Therefore, the interface contact between the active material and the electrolyte tends to be unstable. As a result, battery characteristics such as deterioration of charge / discharge characteristics and increase in internal resistance are deteriorated. That is, when a transition metal oxide such as lithium cobaltate or cobalt nickelate is used for the positive electrode, and a layered negative electrode active material such as graphite is used for the negative electrode, these compounds undergo expansion and contraction of crystals due to charge / discharge reaction. Interfacial contact between the active material and the electrolyte becomes unstable and deteriorates.

Various attempts have been made to improve such a problem. For the purpose of interfacial bonding, conventional polyvinylidene fluoride-based polymers are joined by heat-welding an electrode and an electrolyte layer to integrate them. Although the above-mentioned problems have been solved, there is a drawback that mass production is inferior because the construction method is complicated and difficult.

On the other hand, in the case of a chemically crosslinked polymer electrolyte, if the polymer concentration is high, the conductivity is low, and the polymer does not operate as a battery or a high-viscosity liquid is used. Use lower. When the polymer concentration is lowered, the physical properties of the electrolyte become closer to the state of the electrolyte and the permeability to the electrodes is improved, but the low polymer concentration causes the crosslink density to decrease, and the mechanical strength of the gel polymer is low. Disadvantages. As a result, the probability of inducing an internal short circuit increases, leading to deterioration of the battery.

The present invention has been made to solve such a problem, and an object of the present invention is to provide a polymer secondary battery using a polymer electrolyte having good cycle characteristics by strengthening the bonding between an electrode and an electrolyte layer.

[0014]

As a result of research for solving the above problems, the present invention has been made as follows. That is, a polymer having an average molecular weight of 5,000 to 1,000,000 having a cyano group or an ester group having a high electron-withdrawing property is used for bonding the interface between the positive electrode and the negative electrode and the electrolyte. By using a cyano group or an ester group, the ability to adhere to a positive electrode active material such as lithium cobalt oxide or a negative electrode active material such as a carbon material or an alloy can be increased.

Further, the use of an oligomer having an average molecular weight of from 500 to 3,000 having an unsaturated double bond having two or more functional groups in the electrolyte is compatible with the polymer, and is therefore compatible with the polymer. It has become possible to form a homogeneous and stable interface between the electrode and the polymer electrolyte.

In addition, since it is compatible at room temperature, there is no need for a process such as heat welding, and the electrode coated with an adhesive polymer is laminated with an electrolyte layer containing a thermal polymerization initiator and an oligomer, and is simply subjected to thermal polymerization. An object of the present invention is to provide a method for producing a polymer secondary battery capable of producing a battery in a process.

[0017]

FIG. 1 shows an example of a polymer secondary battery according to the present invention. One negative electrode 5 is sandwiched between two positive electrodes 3. A polymer layer is applied to the surfaces of the negative electrode 5 and the positive electrode 3, and an electrolyte layer in which the oligomer is impregnated in the separator 4 is interposed between the polymer layers. The basic stack formed here is sealed in the battery case 1 under reduced pressure. In this figure, the number of basic stacks is one, but actually a plurality of sheets are stacked. The basic stack is not limited to this configuration, but may be a configuration in which one positive electrode and one negative electrode are provided with an electrolyte layer facing each other, or a configuration of a wound electrode group.

The constituent of the polymer in the present invention must be a polymer containing a cyano group or an ester group. The molecular weight is from 5,000 to 1,000.
Those in the range of 000 are preferred. Here, the reason for containing a cyano group or an ester group is to make use of its strong electron-withdrawing property so that the polymer has a function as an adhesive and has a role as an adhesive polymer. When the average molecular weight is less than 5000, the main chain of the polymer becomes shorter,
Since the tackiness is reduced, the role of the polymer as a binder is reduced. Conversely, if the average molecular weight is 1,
If it is more than 1,000,000, the main chain of the polymer becomes too long, and the compatibility with the oligomer becomes poor.

Further, since the oligomer forms a matrix polymer, it is necessary that at least two of an acrylate group and a methacrylate group which are cross-linking points during polymerization are provided. In addition, an alkylene oxide group having a branched structure must be provided. If this side chain is present, the polymer is likely to be entangled with a polymer having a cyano group and an ester group, and when the polymer and the oligomer form an electrolyte layer, the polymer is easily dissolved in a polymer matrix formed from the oligomer, and compatibility appears. is there.

The average molecular weight of the oligomer is from 500 to 3,0
A range of 00 is preferred. If the average molecular weight is 500 or less, the network of the matrix when cured becomes small, and sufficient electrolyte retention cannot be obtained. On the other hand, if the average molecular weight is 3,000 or more, if the molecular weight between cross-linking points is too large, sufficient electrolyte retention property cannot be obtained, and the charge / discharge characteristics deteriorate.

It is preferable that the battery is formed by using a laminated type and applying a polymer to an electrode plate, but a wound type may be used. The reason why the polymer is impregnated in vacuum at this time is to increase the impregnation property of the electrode plate.

The positive electrode to be used is not particularly limited as long as the active material is a lithium-containing metal oxide. Examples thereof include lithium cobaltate, lithium nickelate and lithium manganate. The negative electrode may be made of a negative electrode active material selected from a carbon material, an alloy, and a nitrogen compound capable of inserting and extracting lithium metal or lithium ions. Natural graphite, artificial graphite, lithium cobalt nitride, and the like are preferable. The separator is not limited as long as it is porous.

The battery case 1 to be used is not particularly limited, but it is preferable to use an aluminum laminate. This is because aluminum laminate has a greater degree of freedom in shape, is thinner and lighter, and is therefore suitable for a polymer battery case. Another advantage is that the battery manufacturing process is easy.

The solvent used for the electrolytic solution is preferably a non-aqueous solvent in order to use lithium for charging and discharging. Further, those having high ionic conductivity when a lithium salt is mixed are more preferable. For example, ethylene carbonate (EC), propylene carbonate (PC), γ-butylactone (GBL), ethyl methyl carbonate (E
MC), diethyl carbonate (DEC) and the like. The non-aqueous solution used in the present invention is preferably used as a mixture of at least one kind or two or more kinds, and more preferably EC, which is a high dielectric constant solvent, is used as one of the mixed elements. .

The lithium salt is not particularly limited as long as it can be mixed with the above-mentioned non-aqueous solution and can be used as an electrolyte of a lithium battery. For example, LiPF6,
LiClO4, LiBF4, LiN (C2F5SO2)
2 and the like. These lithium salts can be used alone or in combination of two or more. Especially L
Since iBF4 and the like have a lower ionic conductivity when dissolved in a solvent such as a non-aqueous solution than LiPF6 and LiClO4, it is preferable to use a mixed system of two or more types.

It is preferable that the lithium salt concentration of the non-aqueous electrolyte obtained by mixing the non-aqueous solution and the lithium salt is in the range of 0.5 mol / L to 2 mol / L.
Generally, as the concentration of the non-aqueous electrolyte decreases, the ionic conductivity decreases, and as the concentration increases, the dissociation of ions becomes difficult, and in any case, the ionic conductivity tends to decrease.

The method of polymerizing the oligomer depends on the type of polymerization initiator used. In this case, a thermal polymerization initiator is preferred in view of the constitution method. Specific examples include azo-based polymerization initiators such as azobis (isobutyronitrile) and azobis (dimethylvaleronitrile) and organic peroxide-based compounds such as benzoyl peroxide. Although only the case of thermal polymerization is described here, electron beam polymerization in which an oligomer is polymerized by irradiating an electron beam from the battery surface can also be employed.

After laminating the positive electrode, the negative electrode, and the separator layer, the oligomer is polymerized to form a gel electrolyte layer, but it is preferable to polymerize after a certain period of time, not immediately after the lamination. . This is for the purpose of allowing the oligomer and the polymer to blend in and the electrode layer to be blended with these solutions.

It is desirable that the water content of the combined solution of the polymer and the oligomer and the electrolytic solution and the polymerization initiator be 20 ppm or less. If the water content is too high, it causes coloration or decomposition of the electrolyte layer after polymerization.

As described in detail above, the polymer secondary battery according to the present invention has a positive electrode, a negative electrode, and a polymer electrolyte layer, arranges a polymer at the interface between the electrolyte layer and the electrode, and forms an oligomer compatible with the polymer. This is a battery in which a solution obtained by mixing an electrolytic solution and a polymerization initiator is crosslinked to form an electrolyte.

Since the polymer has a cyano group or an ester group, it has an adhesive property to the electrode plate. Further, since the polymer is formed by using an oligomer compatible with the polymer, the adhesive property between the polymer and the electrolyte layer is increased. As a result, the interfacial contact between the active material and the electrolyte layer becomes stable, maintaining the junction between the electrode plate (active material) and the electrolyte even after repeated charge / discharge, and a polymer secondary with excellent charge / discharge cycle characteristics. A battery is obtained.

According to the present invention, a battery is also prepared by simply impregnating a separator with a solution obtained by mixing an electrolytic solution, an oligomer and a polymerization initiator into a battery, and thermally polymerizing the battery to form an electrolyte layer. Therefore, an extra step such as heat welding for stabilizing the interface contact between the active material and the electrolyte layer is not required, so that a polymer secondary battery with high productivity can be provided.

[0033]

EXAMPLES Hereinafter, the solid electrolyte secondary battery of the present invention and the method for producing the same will be described in detail with reference to examples, but the present invention is not limited to these examples.

Example 1 First, LiClO4 was prepared.
An electrolytic solution is prepared by dissolving in a mixed solution of ethylene carbonate (EC) and diethyl carbonate (DEC).
At this time, EC and DEC are mixed at a volume ratio of 1: 1.
The concentration of the electrolytic solution of ClO4 was 1 mol / liter.

Next, a positive electrode using lithium cobalt oxide as an active material, a positive electrode using artificial graphite as a negative electrode active material, and a negative electrode
Was coated with an NMP solution of a polymer having an average molecular weight of 85,000 and impregnated in a vacuum, followed by drying at 80 ° C. under reduced pressure. Positive electrode / separator / negative electrode / separator /
An electrode group laminated with the positive electrode was produced. Separator thickness 2
7 μm, porosity 50% was used. This electrode group is inserted into an aluminum laminate. Then, the oligomer represented by the structure of Chemical Formula 2 and azobisisobutyronitrile (AI
BN) and the prepared electrolytic solution were mixed at a weight ratio of 25: 0.125: 100.

[0036]

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[0037]

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A mixed solution of the oligomer and the electrolytic solution was injected into the electrode group in the aluminum laminate case, and after performing vacuum impregnation, the opening was sealed. After that, the battery is kept at 80 ° C for 1 hour.
The oligomer was cross-linked while holding for a time.

Example 2 A polymer battery was manufactured in the same manner as in Example 1 except that the molecular weight of the polymer of Chemical Formula 1 was changed to 5,000.

Example 3 A polymer battery was manufactured in the same manner as in Example 1, except that the molecular weight of the polymer of Chemical Formula 1 was changed to 1,000,000.

Example 4 A polymer battery was manufactured in the same manner as in Example 1 except that the molecular weight of the oligomer of Chemical Formula 2 was changed to 500.

Example 5 A polymer battery was manufactured in the same manner as in Example 1 except that the molecular weight of the oligomer of Chemical Formula 2 was changed to 3,000.

Example 6 A polymer battery was manufactured in the same manner as in Example 1 except that the molecular weight of the polymer of Chemical Formula 1 was changed to 4,000.

Example 7 A polymer battery was manufactured in the same manner as in Example 1 except that the molecular weight of the polymer of Chemical Formula 1 was changed to 2,000,000.

Example 8 A polymer battery was manufactured in the same manner as in Example 1 except that the molecular weight of the oligomer of Chemical Formula 2 was changed to 400.

Example 9 A polymer battery was manufactured in the same manner as in Example 1 except that the molecular weight of the oligomer of Chemical Formula 2 was changed to 4,000.

Comparative Example 1 A polymer battery was manufactured in the same manner as in Example 1, except that polyvinylidene fluoride having an average molecular weight of 300,000 was used instead of the polymer of Chemical Formula 1.

Comparative Example 2 Example 1 was repeated except that polyethylene dimethacrylate having an average molecular weight of 1,000 was used in place of the oligomer of polyvinylidene fluoride and (formula 2).
The same operation as described above was performed to produce a polymer battery.

(Sample Evaluation Method and Results) Examples 1 to 9
And the polymer batteries prepared in Comparative Examples 1 and 2 were subjected to a charge / discharge test. In the charge / discharge test, the battery was charged to 4.2 V at a 10-hour rate current, and then discharged to 3.0 V. The downtime between charge and discharge is 30 minutes. The charging / discharging operation was performed up to 100 cycles, and the capacity retention rate at this time is shown in (Table 1). After the cycle test, the state of the electrolyte membrane of the batteries prepared in each of the examples and comparative examples was also observed.

[0050]

[Table 1]

From Table 1, it was found that the capacity retention ratio after 100 cycles was the largest in Example 1. From the comparison of Examples 1, 2, 3, 6, and 7, the molecular weight of the polymer is preferably in the range of 5,000 to 1,000,000, and the molecular weights of the oligomers of Examples 1, 4, 5, 6, 8,
9, it is understood that the range of 500 to 3,000 is preferable.

[0052]

According to the polymer secondary battery of the present invention, a polymer having a high interfacial adhesion ability between an electrode and an electrolyte is used, and an oligomer compatible with the polymer is used as a polymer electrolyte to repeatedly charge and discharge. Accordingly, a polymer secondary battery that maintains the connection between the electrode and the electrolyte and has excellent charge / discharge cycle characteristics can be provided.

[Brief description of the drawings]

FIG. 1 is a schematic sectional view of one embodiment of a polymer secondary battery of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Battery case 2 Positive electrode core material 3 Positive electrode active material 4 Separator 5 Negative electrode active material 6 Negative electrode core material

 ────────────────────────────────────────────────── ─── Continuing on the front page (72) Inventor Kenichi Morigaki 1006 Kadoma Kadoma, Osaka Prefecture Inside Matsushita Electric Industrial Co., Ltd. F-term (reference) 4J011 HA04 HA06 HB06 PA69 PA90 PC02 PC08 4J027 AC02 AC03 CA10 CB09 CC02 5H029 AJ05 AK03 AL01 AL06 AL07 AL12 AM03 AM05 AM07 AM16 BJ02 BJ12 CJ02 CJ08 CJ22 CJ23 CJ28 DJ02 DJ04

Claims (2)

[Claims] 1. A negative electrode comprising a negative electrode active material selected from a carbon material, an alloy, and a nitrogen compound capable of inserting and extracting lithium metal or lithium ions using a positive electrode comprising a positive electrode active material comprising a lithium-containing metal oxide, and a polymer electrolyte. A secondary battery containing a polymer having a cyano group or an ester group and having an average molecular weight of 5,000 to 1,000,000 at an interface between an electrode plate and a polymer electrolyte layer, comprising an acrylate group, a methacrylate Having at least two or more of one or both of the groups and having an average molecular weight of 5 including an alkylene oxide group having a branched structure.
A polymer secondary battery which is used as a polymer electrolyte in which an oligomer having a molecular weight of from 00 to 3,000, which is compatible with the polymer, is crosslinked in the presence of an electrolytic solution. 2. A step of applying the polymer to at least one of a positive electrode and a negative electrode and performing vacuum impregnation, and a step of impregnating a separator with a solution obtained by mixing an oligomer, a polymerization initiator, and an electrolytic solution into a separator; And then inserting the battery into a battery case, sealing under reduced pressure, cross-linking and heating, to produce a polymer secondary battery.