JP2000188129A - Polymer electrolyte battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a polymer electrolyte battery excellent in load characteristics, by maintaining strength of gel polymer electrolyte. SOLUTION: Electrolyte containing 4-40 wt.% of a multifunctional monomer with four or more functions is impregnated in at least either one of a positive electrode 1, a negative electrode 2 or a separator 3, an active ray is irradiated on it, the monomer in the electrolyte is polymerized and the electrolyte is gelatinized. A quantity of the monomer remained in the gel polymer electrolyte obtained by the above process is maintained at not more than 40 wt.% of the quantity of the monomer inputted and not more than 3 wt.% of the total quantity of the electrolyte.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a polymer electrolyte battery, and more particularly, to a polymer electrolyte battery particularly suitable for use in portable equipment, electric vehicles, road leveling, and the like.

[0002]

2. Description of the Related Art In a polymer electrolyte battery, the electrolyte can be made into a sheet shape, thereby making it possible to produce a large-area and thin battery such as an A4 size plate or a B5 size plate.
Application to various thin products has become possible, and the range of use of batteries has been greatly expanded. In particular, batteries using polymer electrolytes have excellent safety and storage properties including leak resistance,
In addition, because it is thin and flexible, it can be designed to match the shape of the device.

[0003] This polymer electrolyte battery usually uses a laminated film having an aluminum film as a core material as an outer package, and a laminate of a thin sheet-like electrode and a sheet-like separator holding a polymer electrolyte is formed by the outer package. By packaging, it can be made into a thin battery.

[0004]

The polymer electrolyte in this polymer electrolyte battery essentially does not contain a free liquid, but is not a complete solid electrolyte but a gel in order to improve battery characteristics.

[0005] This gel polymer electrolyte needs to fix the electrolyte and maintain good charge / discharge characteristics. However, in the case of the conventional gel polymer electrolyte, the gel softens at high temperatures and leaks. Had the problem of causing

That is, conventionally, polymers such as polyvinylidene fluoride, polyacrylonitrile, and polyethylene oxide have been used as a gelling component for gelling an electrolytic solution to form a gel polymer electrolyte (for example,
However, when gelling is performed using such a polymer, there is a problem that the gel softens and liquefies at a high temperature to cause liquid leakage.

[0007] Therefore, the present inventors use a polyfunctional monomer which polymerizes by irradiation with actinic rays as a gelling component, thereby shortening the polymerization time during gelation, increasing productivity, and improving the productivity even in a high temperature environment. We have developed a polymer electrolyte battery free from the risk of liquid leakage, and have already filed a patent application for it (Japanese Patent Application No. 10-236853).
issue).

However, when the battery is further studied, it is found that the polyfunctional monomer cannot be polymerized at 100%, and the amount of the monomer remaining in the gel polymer electrolyte has a great effect on the battery characteristics. There was found.

In other words, the role of the gel polymer electrolyte is to separate the positive electrode active material particles and the negative electrode active material particles in order to prevent a short circuit, and to impart ionic conductivity as an electrolyte to the positive electrode active material. And a negative electrode active material are required to react.

[0010] The isolation function for preventing short circuit as described above depends on the strength of the gel polymer electrolyte, and the strength of the gel polymer electrolyte depends on the amount of polymer contained in the gel polymer electrolyte. Therefore, in order to prevent a short circuit, the amount of monomer in the electrolytic solution may be increased, the amount of polymer contained in the gel polymer electrolyte may be increased, and the strength of the gel polymer electrolyte may be increased.

However, if the amount of the monomer in the electrolytic solution is increased, the strength of the gel polymer electrolyte becomes too high, and the ionic conductivity may be reduced. Further, the monomer remaining in the gel polymer electrolyte may be reduced. The amount also increases.

When the monomer remains in the gel polymer electrolyte, the monomer has a higher viscosity than that of ethylene carbonate, propylene carbonate, or the like, which is a constituent solvent of the electrolyte, and inhibits the transfer of ions. It is not preferable. Therefore, it is necessary to increase the polymerization rate of the monomer.However, in order to increase the polymerization rate, it is necessary to increase the reaction time or increase the amount of the initiator, thereby reducing the productivity. Also, there is a possibility that the characteristics of the battery may be degraded due to the incorporation of a material not involved in the electrochemical reaction.

Further, the polymerized portion is
Since it is fixed in the gel polymer electrolyte, the electrode material,
In particular, it does not come into contact with the carbon-based material of the negative electrode, etc., and stably exists in the battery, but when the monomer is present in a free state, the free monomer coordinates to lithium ions,
Inhibiting the movement of ions or attaching to the surface of the carbon-based material, preventing lithium ions from invading between carbon layers,
It has been found that load characteristics and the like are reduced.

An object of the present invention is to solve the above-mentioned problems in the prior art and to provide a polymer electrolyte battery which maintains the strength of a gel polymer electrolyte and has excellent load characteristics.

[0015]

According to the present invention, a gelling monomer for gelling an electrolytic solution is used by containing a polyfunctional monomer having four or more functional groups in a concentration of 4 to 10% by weight in the electrolytic solution. The above problem has been solved by regulating the amount of residual monomer in the gel polymer electrolyte battery later.

That is, according to the present invention, at least one of a positive electrode, a negative electrode and a separator is impregnated with an electrolytic solution containing 4 to 10% by weight of a polyfunctional monomer having four or more functional groups, and in that state, an active ray is irradiated. The amount of monomers remaining in the gel polymer electrolyte obtained by polymerizing the monomers in the electrolytic solution and gelling the electrolytic solution was adjusted to 40% by weight or less of the charged monomer amount and 30% by weight or less of the total amount of the electrolytic solution. And a polymer electrolyte battery.

[0017]

DESCRIPTION OF THE PREFERRED EMBODIMENTS In the present invention, the amount of the remaining monomer is restricted to 40% by weight or less of the amount of the charged monomer (that is, the amount of the monomer contained in the electrolytic solution). If the amount is more than 40% by weight, the decrease in load characteristics and the like becomes large,
It is more preferably at most 30% by weight, further preferably at most 10% by weight. Further, in the present invention, the amount of the remaining monomer is regulated to 3% by weight or less of the total amount of the electrolytic solution. When the amount of the remaining monomer is more than 3% by weight of the total amount of the electrolytic solution, the monomer having a large molecular weight becomes lithium ion. This is because the movement speed of lithium ions decreases, and the lithium ions hardly enter the carbon layer.

In the present invention, the tetrafunctional or higher polyfunctional monomer to be added to the electrolytic solution to form a gel polymer electrolyte is a monomer having four or more double bonds per molecule which can be polymerized by irradiation with ultraviolet rays. Such tetrafunctional or higher polyfunctional monomers include, for example, pentaerythritol tetraacrylate, ditrimethylolpropane tetraacrylate, ethoxylated pentaerythritol tetraacrylate, dipentaerythritol hydroxypentaacrylate, dipentaerythritol hexa Examples include tetrafunctional or higher acrylates such as acrylates and tetrafunctional or higher methacrylates similar to the above acrylates.

In the present invention, the content of the tetrafunctional or higher polyfunctional monomer in the electrolytic solution (the amount added to the electrolytic solution), that is, the concentration of the tetrafunctional or higher polyfunctional monomer in the electrolytic solution is 4 If the concentration of the tetrafunctional or higher polyfunctional monomer is lower than the above range, the effect of increasing the strength of the gel polymer electrolyte to prevent short circuit cannot be obtained. If the concentration of the tetrafunctional or higher polyfunctional monomer is higher than the above range, the load characteristics and the like are reduced.

In the present invention, as the actinic ray, for example, ultraviolet (UV), electron beam (EB), visible ray, far-infrared ray and the like can be used.

The electrolyte as the base of the gel polymer electrolyte is prepared by dissolving an inorganic ionic salt as a solute in an organic solvent. As the organic solvent,
Any of those that can be used in preparing the electrolyte solution of this type of battery can be used.Preferred specific examples thereof include, for example, dimethyl carbonate, diethyl carbonate, methyl ethyl carbonate, methyl propionate, and ethylene. Carbonate, propylene carbonate, butylene carbonate, gamma-butyrolactone,
Ethylene glycol sulfite, 1,2-dimethoxyethane, 1,3-dioxolan, tetrahydrofuran,
Examples thereof include 2-methyl-tetrahydrofuran and diethyl ether, which can be used alone or in combination of two or more. Further, an amine-based or imide-based organic solvent, a sulfur-containing or fluorine-containing organic solvent, and the like can also be used.

Examples of the inorganic ion salt include, for example, LiCl
O_Four, LiPF₆, LiBF_Four, LiAsF₆, LiS
bF₆, LiCF_ThreeSO_Three, LiC_FourF₉SO_Three, Li
CF _ThreeCO_Two, Li_TwoC_TwoF_Four(SO_Three)_Two, LiN
(CF_ThreeSO_Two)_Two, LiC (CF_ThreeSO_Two)_Three, Li
C_nF_{2n + 1}SO_Three(N ≧ 2), LiN (RfOSO_Two)
_Two[Where Rf is a fluoroalkyl group]
Or a mixture of two or more kinds of the inorganic ion salts.
The concentration in the solution is 0.5 to 1.5 mol / l,
About 0.9 to 1.25 mol / l is preferable.

When adding the above-mentioned tetrafunctional or higher polyfunctional monomer to the electrolyte, if necessary, a polymerization initiator such as benzoyls, benzoin alkyl ethers, benzophenones, benzoylphenylphosphine oxides, acetophenone may be used. , Thioxanthones, anthraquinones, etc., and further, alkylamines, aminoesters, etc. can be used as sensitizers for the polymerization initiator.

In the present invention, as the positive electrode active material,
Various types can be used without being limited to
Transition metal oxide with high energy density
It is preferably used because it has excellent properties, and specifically,
For example, LiCoO_TwoLithium cobalt oxide, such as
LiMn_TwoO_FourSuch as lithium manganese oxide, LiN
iO_TwoSuch as lithium nickel oxide, their mixture
Objects, and even LiNiO _TwoPart of Ni is Co or
Those substituted with Mn are preferably used.

In the present invention, as the negative electrode active material, various substances can be used without particular limitation as long as they can dope and dedope lithium ions.
In particular, carbon-based materials are preferably used, and specifically, for example, graphite, pyrolytic carbons, cokes, glassy carbons, fired bodies of organic polymer compounds, mesocarbon microbeads, carbon fibers, activated carbon, Graphite or the like is preferably used.

In the present invention, as the separator, for example, a nonwoven fabric, a microporous film or the like is used.

As a method for obtaining an electrode or a separator containing a gel polymer electrolyte, for example, a paint containing an active material and necessary additives is applied on a current collector and dried to form a mixture layer. Applying an electrolytic solution containing a tetrafunctional or higher polyfunctional monomer to the prepared electrode or separator,
Alternatively, by immersing the electrode or separator in an electrolyte containing a tetrafunctional or higher polyfunctional monomer, the electrode or separator is impregnated with an electrolyte containing a tetrafunctional or higher polyfunctional monomer, and irradiating the active ray in that state. Then, it is obtained by polymerizing the monomer and gelling the electrolytic solution.

[0028]

Next, the present invention will be described more specifically with reference to examples. However, the present invention is not limited to only these examples. In the following examples,% indicating the concentration of the solution or dispersion is% by weight.

Example 1 A coating material for forming a positive electrode mixture layer having the following composition was prepared. Composition of paint for forming positive electrode mixture layer: 89.0 parts by weight of LiCoO ₂ 5.0 parts by weight of acetylene black 6.0 parts by weight of polyvinylidene fluoride 100.0 parts by weight of N-methylpyrrolidone

The above-mentioned paint was prepared by mixing each component with a planetary mixer for 60 minutes. Then, the obtained paint is coated with a blade coater to a thickness of 30 μm.
m was applied to an aluminum foil having a thickness of 100 μm after drying, and dried to form a positive electrode mixture layer on the aluminum foil serving as a current collector, thereby producing a positive electrode.

Next, a paint for forming a negative electrode mixture layer having the following composition was prepared. Coke used as a negative electrode active material In the preparation of the paint, with its (002) between the surface of the surface distance d _{00 2} is 3.4 Å, the size Lc in the c-axis direction of the crystallite was 32 Å. Composition of paint for forming negative electrode mixture layer: 83.0 parts by weight of coke 2.0 parts by weight of acetylene black 15.0 parts by weight of polyvinylidene fluoride 90.0 parts by weight of N-methylpyrrolidone

The above coating composition was prepared by mixing the components with a planetary mixer for 60 minutes. Then, the obtained paint is coated with a blade coater to a thickness of 10 μm.
A negative electrode was prepared by applying the composition on a copper foil having a thickness of 110 μm after drying on a copper foil having a thickness of 110 μm and drying to form a negative electrode mixture layer on the copper foil serving as a current collector.

Next, LiPF was added to a mixed solvent of ethylene carbonate and propylene carbonate at a volume ratio of 1: 1.
₆ is prepared by dissolving 1.0 mol / l of ₆ in the solution, and hexafunctional dipentaerythritol hexaacrylate as a tetrafunctional or higher polyfunctional monomer in a concentration of 4 to 10% by weight (that is, 4 %, 6%, 8%, and 10% by weight) of an electrolyte containing a tetrafunctional or higher polyfunctional monomer (hereinafter referred to as “monomer-containing electrolyte”). Liquid ") was prepared.

In preparing the above-mentioned monomer-containing electrolytic solution, in any case, before the addition of dipentaerythritol hexaacrylate, 2,4,6-trimethylbenzoyldiphenylphosphine oxide [lucirin] was added to the electrolytic solution as a polymerization initiator. TPO (trade name), manufactured by BSF Japan Co., Ltd.] to a concentration of 2% by weight.

Next, this monomer-containing electrolytic solution is impregnated into a separator comprising the above-mentioned positive electrode, negative electrode and polypropylene non-woven fabric, and is irradiated with ultraviolet rays to polymerize and gel the monomer components to form a gel polymer electrolyte. The separator and the separator each contained a gel polymer electrolyte. The details will be described in the order of the positive electrode, the negative electrode, and the separator.

Impregnation of the positive electrode with the monomer-containing electrolyte and its
Curing: The positive electrode was sized 38 mm × 68 mm, immersed in the monomer-containing electrolyte for 5 minutes, and taken out.
A positive electrode impregnated with the monomer-containing electrolytic solution is coated with a 50 μm thick PET (polyethylene terephthalate) from both sides.
As shown in Table 1 below, the film was irradiated with an ultraviolet lamp having an illuminance of 60 mw / cm ² (measured by a UV checker UVR-T35 manufactured by Topcon) for 30 seconds, 10 seconds, 6 seconds, and 3 seconds to cover the monomer containing the monomer. The monomer in the electrolyte was polymerized and the electrolyte was gelled to obtain a positive electrode containing a gel polymer electrolyte.

Impregnation of the negative electrode with the monomer-containing electrolyte and its
Curing: The negative electrode was sized to 40 mm × 70 mm, immersed in the same monomer-containing electrolyte solution as in the case of the positive electrode for 5 minutes, and then irradiated with ultraviolet rays in the same manner as in the case of the positive electrode.
The monomer in the monomer-containing electrolyte was polymerized and the electrolyte was gelled to obtain a negative electrode containing a gel polymer electrolyte.

[0038]Impregnation of electrolyte containing monomer into separator
And its curing:From a 50μm thick polypropylene non-woven fabric
Is immersed in the above-mentioned monomer-containing electrolyte for 5 minutes.
After immersion, take out and impregnate the monomer-containing electrolyte.
A 50 μm thick PET cover
Illumination 60mw / cm ^Two(Topcon UV checker
(Measured value by car UVR-T35)
30 seconds, 10 seconds, 6 seconds and 3 seconds as shown in Table 1
And polymerize the monomers in the monomer-containing electrolyte solution.
While the electrolyte solution is gelled to contain a gel polymer electrolyte.
A separator was obtained.

Assembly of battery: A positive electrode, a separator and a negative electrode containing a gel polymer electrolyte as described above were stacked in this order to produce a unit cell. And
Terminals were pulled out from the positive electrode and the negative electrode, and the unit cell was covered with an exterior body composed of a laminated film having a three-layer structure of a polyester film-aluminum film-modified polyolefin film, and the periphery thereof was heat-sealed to make a battery for evaluation. In producing the unit cell, the positive electrode and the negative electrode were arranged such that the respective mixture layers faced each other with a separator interposed therebetween. Also, as the exterior of the unit cell, the laminated film was composed of the modified polyolefin film composed of the positive electrode and the negative electrode. It was arranged so as to face the electric body.

Here, the schematic structure of the battery will be described with reference to FIG. 1. A separator 3 is disposed between a positive electrode 1 and a negative electrode 2 to form a unit cell. The battery is constructed by covering the package with a package 4 made of a three-layer laminated film of a film-modified polyolefin film, and pulling out the positive terminal 5 and the negative terminal 6 from the positive electrode 1 and the negative electrode 2 to the outside of the package 4.

The remaining 12 types of batteries were examined for the amount of residual monomer, the properties of the gel, the load characteristics, and the deposition of lithium on the negative electrode surface. Table 1 shows the results. The load characteristics were as follows: the battery was charged at a constant current and constant voltage of 4.2 V and 0.2 C for 8 hours, and discharged at a current density of 1 C and 0.2 C to 2.75 V, respectively, and the discharge capacity was measured. It is expressed as a ratio [(discharge capacity at 1 C / discharge capacity at 0.2 C) × 100] obtained by dividing the discharge capacity at the time of discharge by the discharge capacity at the time of discharging at a current density of 0.2 C. Further, the amount of the residual monomer was determined by adding the negative electrode to the mixed solvent of ethylene carbonate and propylene carbonate from the negative electrode after the formation of the gel polymer electrolyte.
The remaining monomer was extracted by immersion for 4 hours, the amount was determined by ultraviolet absorbance, and the result is shown in Table 1 as a ratio to the amount of monomer charged. From the amount of the residual monomer and the concentration of dipentaerythritol hexaacrylate shown in Table 1, the amount of the residual monomer with respect to the total amount of the electrolyte can be determined.
In addition, the state of the gel of the gel polymer electrolyte was visually observed, and the observation results were symbolized according to the following evaluation criteria.
Shown in

A: No adhesion to PET cover, strong gel, no release of electrolyte. 〇: The releasability from the PET cover is lower than in the case of the above ◎, but a strong gel and no release of the electrolyte solution. Δ: Difficult to peel off from PET cover, and some release of electrolyte was also observed. X: The gel has low strength and separates from the electrolytic solution.

The deposition of lithium on the negative electrode surface was examined by disassembling the battery and using an electron micrograph of the negative electrode surface. Table 1 shows the results.

[0044]

[Table 1]

As is clear from the results shown in Table 1, when the concentration of dipentaerythritol hexaacrylate in the electrolytic solution is in the range of 4 to 10%, the amount of residual monomer is 30% (in this case, When pentaerythritol hexaacrylate is 10%, the amount of the remaining monomer is 3% or less with respect to the total amount of the electrolyte solution. When the amount is less than or equal to 10%, the gel state is good, the load characteristics are excellent, and lithium is not deposited on the negative electrode surface. However, when the amount of the remaining monomer becomes 50%,
The gel causes liquid release, and lithium deposits on the negative electrode surface. The release of liquid as described above causes liquid leakage, and the precipitation of lithium on the surface of the negative electrode lowers the load characteristics, lowers the capacity, and eventually causes a danger such as short circuit, thereby lowering safety.

Since it is possible to increase the polymerization initiator in order to increase the polymerization rate, the polymerization initiator (2,4,6-trimethylbenzoyldiphenylphosphine oxide) is used three times the usual amount. When the amount of the polymerization initiator was 3 times, the amount of the residual monomer was 35%.
When the used amount of the polymerization initiator is 10 times, the residual monomer is 20%, and the properties of the gel, the load characteristics, the precipitation state of lithium, and the like tend to be similar to those when the appropriate amount of the polymerization initiator is used. Indicated. However, when the amount of the polymerization initiator used was increased three or ten times, swelling occurred slightly during charging and discharging of the battery, and gas generation was observed.

As shown in Table 1, the amount of lithium deposited on the surface of the negative electrode increases when the amount of the remaining monomer is large, but does not always agree with the absolute amount. Polymer in gel polymer electrolyte (monomer charged into electrolyte)
When the absolute amount of is increased, the strength of the gel polymer electrolyte increases and the cross-linking structure becomes denser, so that the free monomer is prevented from coordinating with lithium ions, and the penetration of lithium ions into the carbon layer is prevented. Therefore, even if the residual monomer amount increases, the amount of lithium deposited on the negative electrode surface does not increase so much.

As described above, when the amount of the residual monomer in the gel polymer electrolyte is 40% or less of the amount of the charged monomer and 3% or less of the total amount of the electrolytic solution, there is no practical adverse effect.
In addition, the polymerization time can be shortened also in productivity.

[0049]

As described above, according to the present invention, it is possible to provide a polymer electrolyte battery which maintains the strength of the gel polymer electrolyte and has excellent load characteristics.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view showing an example of a polymer electrolyte battery according to the present invention.

[Description of Signs] 1 Positive electrode 2 Negative electrode 3 Separator

 ────────────────────────────────────────────────── ─── Continuing on the front page (72) Inventor Kuze Sada 1-88 Ushitora, Ibaraki-shi, Osaka F-term in Hitachi Maxell Co., Ltd. 5H029 AJ11 AK03 AL06 AM00 AM03 AM05 AM07 AM16 BJ04 DJ09 EJ12 HJ01

Claims (2)

[Claims] 1. A polyfunctional monomer having a tetrafunctional or higher functionality of 4 to 10
A gel-like polymer electrolyte obtained by impregnating at least one of a positive electrode, a negative electrode and a separator with an electrolytic solution containing 1% by weight and irradiating ultraviolet rays to polymerize monomers in the electrolytic solution and gel the electrolytic solution. At
The amount of the monomer remaining in the gel polymer electrolyte is 40% by weight or less of the amount of the charged monomer and 3% by weight of the total amount of the electrolyte.
A polymer electrolyte battery comprising: 2. The polymer electrolyte battery according to claim 1, wherein the tetrafunctional or higher polyfunctional monomer is dipentaerythritol hexaacrylate.