WO2004001878A1

WO2004001878A1 - Lithium polymer secondary battery and process for producing the same

Info

Publication number: WO2004001878A1
Application number: PCT/JP2003/003120
Authority: WO
Inventors: Naoto Nishimura; Naoto Torata; Kouichi Ui; Motoaki Nishijima
Original assignee: Sharp Kabushiki Kaisha
Priority date: 2002-06-19
Filing date: 2003-03-14
Publication date: 2003-12-31
Also published as: TWI222232B; CN1643712A; CN100454610C; TW200404377A

Abstract

Lithium polymer secondary batteries employing a solid polymer electrolyte layer obtained through crosslinking with energy such as heat or light have a low discharge capacity at temperatures as low as, e.g., -20°C. It is hence desired to improve the low-temperature characteristics without causing capacity deterioration even when charge-discharge cycling is repeated. The lithium polymer secondary battery comprises: a solid polymer electrolyte layer comprising a separator (excluding nonwoven fabrics) and an organic electrolytic solution united therewith through crosslinking; and a positive electrode and a negative electrode each obtained by uniting the organic electrolytic solution with an active material through crosslinking. This lithium polymer secondary battery has a constitution in which the organic electrolytic solution contains Ϝ-butyrolactone and the solid polymer electrolyte layer has a light transmittance of 50% or higher.

Description

Description Lithium polymer secondary battery and its manufacturing method

The present invention relates to a lithium polymer secondary battery and a method for manufacturing the same. More specifically, the present invention relates to a lithium polymer secondary battery having more excellent charge / discharge cycle characteristics and low-temperature characteristics than before and a method for producing the same. Background art

With the advancement of I τ technology, many lithium-ion secondary batteries have been used as power sources for mobile phones, personal digital assistants, and notebook computers. In recent years, the development of lithium polymer secondary batteries using a solid electrolyte layer instead of the organic electrolyte solution of a lithium ion secondary battery has been actively carried out. Bell-core type lithium polymer secondary batteries using an electrolyte layer have come to the market.

However, lithium polymer secondary batteries using physical cross-linking are highly likely to undergo phase separation in the matrix of the solid electrolyte layer and ooze out of the organic electrolyte when the battery is in a high temperature environment or when the battery is abnormally heated. There still remains a problem in the reliability of the system. In addition, a lithium polymer secondary battery that has undergone phase separation may suddenly undergo a sudden decrease in capacity when repeated charge / discharge cycles are repeated. In contrast, a lithium polymer that uses a polymer solid electrolyte layer in which an organic electrolyte is Secondary batteries have been developed. This polymer solid electrolyte layer is formed by using a solution obtained by mixing a precursor before crosslinking having at least one unsaturated double bond or more and an organic electrolyte solution containing a lithium salt with energy such as heat or light. Polymerization). 'Therefore, once the polymer solid electrolyte layer has been crosslinked, Matritus rarely causes phase separation even in a high-temperature environment or abnormal heat generation of a battery. Therefore, it is considered promising as a lithium polymer secondary battery with high reliability and excellent charge / discharge cycle characteristics. Lithium polymer secondary batteries using a polymer solid electrolyte layer obtained by cross-linking with energy such as heat or light are unlikely to cause liquid leakage etc. due to liquid seepage even in a high-temperature environment or when the battery is abnormally heated. However, there is an advantage that a rapid decrease in capacity does not occur when the charge / discharge cycle is repeated. However, since the solid polymer electrolyte layer has a robust network structure formed by chemical crosslinking, the ion mobility is lower than that of a lithium polymer secondary battery using physical crosslinking, especially at −20 ° C. At such a low temperature, the problem remains that the discharge capacity is reduced.

In addition, a lithium polymer secondary battery has a polymer solid electrolyte layer interposed between the positive and negative electrodes as an electrolyte layer. This electrolyte layer is a matrix containing an organic electrolyte and prevents short circuits inside the battery. Is insufficient in strength. Therefore, it is common to integrate the separator with the organic electrolyte and use it as a polymer solid electrolyte layer. However, if a separator is used, when the polymer solid electrolyte layer is cross-linked by, for example, irradiation with ultraviolet light, the light is blocked by the separator, and the cross-linking is insufficient, and the reliability of the battery is reduced. There still remains the issue of impairing the performance. For example, Japanese Patent Application Laid-Open No. 9-77577 discloses a technique for measuring the degree of phase change of a polymer electrolyte in a battery by utilizing light transmittance. Is applied to the technology of determining the preparation standard of the raw material when producing the carbon material of the negative electrode for the lithium secondary battery by using the light transmittance. However, there has not been disclosed any application in which the light transmittance is applied to improve the performance of a polymer solid electrolyte layer of a lithium polymer secondary battery. Disclosure of the invention

The present invention has been made in view of the above problems, and has as its object to provide a lithium polymer secondary battery excellent in low-temperature characteristics without impairing charge-discharge cycle characteristics, and a method for manufacturing the same.

Thus, according to the present invention, a positive electrode and a negative electrode containing a polymer cross-linked in the presence of an organic electrolyte and an active material are located between the two electrodes, and the organic electrolyte and a separator (not including a nonwoven fabric) A polymer solid electrolyte layer containing a polymer cross-linked in the presence of a polymer, the organic electrolyte solution contains Y-petit mouth rataton, and the polymer solid electrolyte layer has a light transmission of 50% or more. The present invention provides a lithium polymer secondary battery characterized by having a high efficiency.

Further, according to the present invention, there is provided the method for producing a lithium polymer secondary battery, wherein the light transmittance of the separator in the presence of the organic electrolyte and the polymer before crosslinking is 50% or more. The method for producing a lithium polymer secondary battery further comprises a step of obtaining a polymer solid electrolyte layer by crosslinking the polymer before crosslinking after the above adjustment. BRIEF DESCRIPTION OF THE FIGURES FIG. 1 is a schematic sectional view of a lithium polymer secondary battery of the present invention. Embodiment of the Invention

One of the features of the present invention is to adjust the light transmittance of the separator in the presence of the organic electrolyte solution and the polymer before the bridge to be 50% or more in the production of the polymer solid electrolyte layer. And By measuring the light transmittance, it is determined whether or not a solution obtained by mixing the precursor before crosslinking (hereinafter simply referred to as “precursor”) and the organic electrolyte containing a lithium salt has sufficiently penetrated the separator. Can be confirmed.

In the present invention, a simple and high-performance lithium polymer secondary battery can be manufactured by adjusting the transmittance to 50% or more.

The light transmittance can be calculated, for example, by irradiating an object with ultraviolet rays having a wavelength of 365 nm and measuring the illuminance through a separator, and calculating by the following formula. Transmittance = (illuminance through a separator) / ( Illuminance without separator) XI 0 0 (%)

The separator is white before being impregnated with the solution, and has almost zero light transmittance. /. However, it becomes translucent to transparent when impregnated with the solution. Therefore, the degree of impregnation of the solution into the separator can be determined by the light transmittance according to the above equation. At this time, if the transmittance is less than 50%, the impregnation of the solution into the separator is insufficient, so that not only the internal resistance of the battery is increased but also the crosslinking reaction when bridging with light is insufficient. It is not preferable because it becomes. More preferably, the transmittance is 60% or more, further preferably 70% or more, particularly preferably 80% or more, and most preferably 90% or more (the upper limit is 100%). ). In addition, the light transmittance of the polymer solid electrolyte layer after cross-linking is almost the same as the light transmittance of the separator before cross-linking or is about 1 to 2% lower, so it can be measured after cross-linking. It is. In addition, if measurement is performed after crosslinking, only a solid polymer electrolyte layer having excellent characteristics can be selected in advance. FIG. 1 shows a schematic cross-sectional view of one example of the lithium polymer secondary battery of the present invention. In FIG. 1, 1 is a separator, 2 is a solid polymer electrolyte layer, 3 is a positive electrode active material, 4 is a negative electrode active material, and 5 is a current collector.

The separator in the polymer solid electrolyte layer of the present invention is not particularly limited as long as it is other than a nonwoven fabric, and a known separator can be used.

The thickness of the separator is preferably 5 to 30 μm, and particularly preferably 8 to 25 m. If the thickness is less than 5 μπι, the mechanical strength becomes low, and the positive and negative electrodes of the battery may be short-circuited, which is not preferable. When the thickness is more than 30 μπι, not only the distance between the electrodes becomes longer and the impedance inside the battery becomes higher, but also a precursor having at least one unsaturated double bond and an organic electrolyte containing a lithium salt are mixed. It is not preferable because the light transmittance when the solution is impregnated may decrease.

Also, examples of the separator include a microporous membrane. As a separator, there is a nonwoven fabric, which has a larger pore diameter than the microporous membrane, and the positive electrode and / or the negative electrode active material penetrates the nonwoven fabric, which is likely to cause a short circuit of the battery. Therefore, it is preferable to use a microporous membrane. In particular, a polyolefin-based microporous membrane composed of polyethylene, polypropylene, or a composite of polyethylene and polypropylene is preferable in terms of strength and cost. Here, the microporous membrane, 0. 0 1~1 0 μ πι of holes refers to 1 0 ^2-1 0 ¹² Z cm ² existing film. Furthermore, when using a solvent that is difficult to penetrate into a polyolefin-based membrane such as “y-butyrolataton (GBL)”, a membrane with improved solvent affinity is preferred. A method of treating the surface, a method of coating the film with a surfactant, and the like are exemplified, but not limited thereto.

As the organic electrolyte for the polymer solid electrolyte layer in the present invention, a solution in which a lithium salt is dissolved at a predetermined concentration in an organic solvent containing GBL is used. The amount of water in the organic electrolyte is preferably 50 ppm or less, particularly preferably 20 ppm or less. A large amount of water is not preferable because when the battery is charged, the electrolysis of water occurs and the charge / discharge efficiency decreases.

The lithium salt concentration is preferably 0.5 to 2.5mo 1/1. 0.5mo

If the concentration is lower than 1Z1, the charge concentration of the polymer solid electrolyte layer becomes low, and the impedance inside the battery may increase, which is not preferable. If the concentration is higher than 2.5 mo 1/1, lithium ions and anions recombine, which may lower the ionic conductivity and increase the impedance inside the battery, which is not preferable.

The type of the lithium salt is not particularly limited, but Li PF ₆ , Li BF ₄ , Li N (CF ₃ S 0 ₂ ) _{2 and the} like can be used.

GBL, which is an essential component in the organic solvent, is preferably contained in a volume ratio of at least 60% with respect to other solvents. If the GBL is less than 60%, the ionic conductivity decreases at a low temperature such as 20 ° C, and the low-temperature characteristics of the battery deteriorate, which is not preferable. Other solvents include, for example, cyclic carbonates such as propylene carbonate (PC) and ethylene carbonate (EC), dimethyl carbonate (DMC), and dimethyl carbonate (DMC). Chain car such as, ethyl methyl carbonate (EMC) Cyclic ethers such as ponates, tetrahydrofuran and 2-methyltetrahydrofuran; chain ethers such as getyl ether, dimethoxetane, diethoxyethane and ethoxymethoxetane; methyl acetate; ethyl acetate; methyl propionate; ethyl propionate; And acetonitrile, sulfolane, N-methyl-1-pyrrolidone and the like. These other solvents may be used in plural types.

More specifically, for example, when a graphite-based material is used as the negative electrode active material, a solvent in which GBL and EC are mixed is preferable because the low-temperature characteristics can be improved without lowering the charge / discharge efficiency. In particular, it is preferable that the volume ratio of GBL: EC is 60:40 to 80:20. 60: If the GBL is less than 40, the ion conductivity at a low temperature of 120 ° C. is lowered, and the battery performance may be lowered, which is not preferable. If the GBL is more than 80:20, the charge / discharge efficiency of the battery decreases, and if the charge / discharge cycle is repeated, the battery capacity may deteriorate, which is not preferable.

The polymer (precursor) before crosslinking (polymerization) of the polymer solid electrolyte layer is a random copolymer or block copolymer containing an ethylenoxide unit and a propylene oxide unit in the molecule. A polyfunctional compound having an unsaturated bond, such as an acrylyl group or a methacryloyl group, is preferred. This is because the terminal group can be crosslinked even in the presence of a solvent having high solubility such as a polymer such as GBL. Further, by mixing a precursor having a monofunctional group and a precursor having a polyfunctional group, solid electrolyte layers having various cross-linked structures can be produced.

The amount of the precursor relative to the organic electrolyte containing a lithium salt is preferably such that the weight ratio of the precursor to the organic electrolyzed solution is 7: 93-3: 97. When the amount of the precursor exceeds 7:93, the ionic conductivity of the polymer solid electrolyte layer decreases. Unfavorable because there are cases. If the amount of the precursor is less than 3:97, the crosslinking reaction may not be sufficient, which is not preferable.

An initiator may be used to accelerate the crosslinking (polymerization) reaction. Initiators that initiate the reaction due to photoenergy include phosphinoxides, acetophenones, benzophenones, _α -hydroxyketones, Michler's ketones, benzinoles, benzoins, benzoinates / resins, and benzylmethylketals. And the like. These initiators may be used alone or in combination of two or more.

The reaction is started by thermal energy. As the S initiator, an organic peroxide compound is preferable. Specific examples thereof include isobutyryl peroxide, α, α′-bis (neodecanylperoxy) diisopropylbenzene, cumylperoxyneodecanoate, di-η-propylperoxy dicarbonate, Disopropyl peroxydicarbonate, 1,1,3,3-tetramethylbutylperoxyneodecanoate, bis (41 t-butoxyresin hexoxy) peroxydicarbonate, 1-cyclohexyl Λ ^ — 1-Methylethoxy peroxy neodecanoate, G 2-ethoxy xyshelboxy dicarbonate, di (2-ethylhexyl peroxy) dicarbonate, t-hexyl peroxy neodecanoate, Toxyl butyl carbonate, dixy carbonate, di (3-methyl-3-methoxybutyl peroxy) dicarbonate, t-butyl peroxy neodecanoate, t-butyl peroxybivalate and the like. These initiators may be used alone or as a mixture of two or more.

These initiators are preferably added at a rate of 100 to 500 ppm based on the total weight of the solution obtained by mixing the precursor and the organic electrolyte containing a lithium salt. As a specific method for producing a polymer solid electrolyte layer, first, a solution in which a precursor is mixed with a lithium salt and an organic electrolyte solution (in some cases, an initiator is added) is impregnated in a separator in advance. . Then, when the case of crosslinking by light, the wavelength is 1 irradiated 1200 seconds in the range of the illuminance of the 5~ 500 mW / cm ² light 300 to 800n m, crosslinking with heat,. 30 to 80 ° C Then, heat treatment is performed for 0 • 5-100 hours to produce a polymer solid electrolyte layer.

When the wavelength is shorter than 30 Onm when cross-linking by light, the decomposition of the precursor itself and the decomposition of the lithium salt may occur, which is not preferable. If it is longer than 800 nm, the crosslinking reaction may be insufficient, which is undesirable. If the temperature is lower than 30 ° C. when cross-linking by heat, the cross-linking reaction may be insufficient, which is not preferable. If the temperature is higher than 80 ° C, the organic solvent contained in the solution may be volatilized or the lithium salt may be decomposed, which is not preferable.

The polymer solid electrolyte layer in the present invention is impregnated or held with an organic electrolyte containing a lithium salt. Such a layer is a macroscopic solid state, but microscopically, a lithium salt solution forms a continuous phase, and has a higher ionic conductivity than a polymer solid electrolyte layer without using a solvent.

The cathode active material is not particularly limited, and any of those known in the art can be used. For example, in the present invention, a metal oxide containing lithium can be used as the positive electrode active material. In particular, in _{_{L i a (A) h (}} B) c 0 2 ( where, A is one or more elements of transition metal elements. B periodic table IIIB, I VB and Group VB non of One or more elements selected from metal elements such as metal elements and metalloid elements, alkaline earth metals, Zn, Cu, Ti, etc. a, b, c are each 0 <a ≤ 1.15, 0.85≤b + c≤l. 30, 0 and c. It is preferable to select from at least one of the composite oxide having a layered structure or the composite oxide having a spinel structure represented by Further, these metal oxides are preferable because they also have an effect of accelerating the reaction of the thermal polymerization initiator of the organic peroxide. Exemplary complex _{oxide, L i C o 0 2,} L i N i 0 2, L i C o x

N ih〇 ₂ (0 <x <1). These composite oxides, when using a carbonaceous material as the negative electrode active material,

(1) Voltage change due to charging and discharging of carbonaceous material itself (about 1 V vs.

L i / L i ⁺ ) shows a sufficiently practical working voltage even if

(2) lithium ions required to charge-discharge reaction of the battery, and before that assembled battery, for example, are already containing chromatic into battery _{L i C o 0 2, L} i N i 0 2 such forms of

Has the benefit that

The negative electrode active material is not particularly limited, and any of those known in the art can be used. For example, a carbonaceous material can be used as the negative electrode active material. The carbonaceous material is preferably a material capable of electrochemically inserting / desorbing lithium. Since the potential for inserting and removing Z is close to the potential for dissolving and dissolving metallic lithium, a high energy density battery can be constructed. A typical example is natural or artificial graphite in the form of particles (scale, lump, fibrous, whiskers, spheres, ground particles, etc.). It is also possible to use artificial graphite obtained by graphitizing mesocarbon micro beads, mesophase pitch powder, isotropic pitch powder, and the like.

More preferred carbonaceous materials include graphite particles having amorphous carbon adhered to the surface. As a method of adhesion, graphite particles are dipped in coal-based heavy oil such as tar or pitch, or petroleum-based heavy oil such as heavy oil, and then lifted. It can be obtained by decomposing heavy oil by heating to a degree or higher. Also, the obtained carbonaceous material may be pulverized as necessary. Such treatment significantly suppresses the decomposition reaction of the organic solvent and lithium salt that occurs at the negative electrode during charging, thus improving the charge-discharge cycle life and suppressing gas generation due to the decomposition reaction. Becomes possible.

In the carbonaceous material, pores related to the specific surface area measured by the BET method are blocked to some extent by the adhesion of amorphous carbon. The specific specific surface area is preferably in the range of 1 to 5 m ² / g. If the specific surface area is larger than this range, the contact area with an organic electrolyte solution in which a lithium salt is dissolved in an organic solvent also becomes large, and the decomposition reaction thereof easily occurs, which is not preferable.

. In addition, the amount of the initiator adsorbed to form the polymer solid electrolyte layer on the negative electrode increases, which is not preferable because the crosslinking of the precursor is hindered. If the specific surface area is smaller than this range, the contact area with the electrolyte is also reduced, so that the electrochemical reaction rate is slowed down and the load characteristics of the battery are sometimes undesirably reduced.

The positive electrode and the negative electrode are basically formed by forming respective active material layers in which a positive electrode and a negative electrode active material are fixed with a binder, on a metal foil serving as a current collector. Examples of the material of the metal foil serving as the current collector include aluminum, stainless steel, titanium, copper, and nickel. Of these, aluminum foil is preferable for the positive electrode and copper foil is preferable for the negative electrode in consideration of electrochemical stability, stretchability and economy.

Examples of the form of the positive and negative electrode current collectors other than the foil include a mesh, an expanded metal, a lath, a porous body, and a resin film coated with an electron conductive material, but are not limited thereto. Not something. Graphite and car if necessary for the production of positive and negative electrodes;

By using a chemically stable conductive material such as acetylene black, Ketjen black, carbon fiber, or a conductive metal oxide in combination with an active material, electron conductivity can be improved.

In preparing the positive and negative electrodes, it is preferable to select a binder from resins that are chemically stable and are soluble in an appropriate solvent but are not affected by an organic electrolyte. Many resins are known. For example, polyvinylidene fluoride (PVDF), which dissolves selectively in the organic solvent N-methyl-1-pyrrolidone (NMP) but is stable in organic electrolytes, is preferred. used. The binder that does not dissolve in the solvent may be used as a dispersion. Other resins that can be used include, for example, acrylonitrile, methacrylonitrile, bifluoride, chloroprene, vinylinpyridine, styrene butadiene rubber (SBR), carboxymethyl cellulose (CMC) and its derivatives, chlorovinylidene, ethylene, propylene, cyclic gen (eg, Pentagen, 1,3-cyclohexadiene, etc.) and copolymers.

For the electrode, the active material and, if necessary, the conductive material are kneaded into a binder resin solution to form a paste, which is applied to a metal foil using a suitable coater to a uniform thickness, dried and pressed. It can be manufactured by the following. It is preferable that the ratio of the binder in the electrode is the minimum necessary. Generally, 1 to 15 parts by weight of the electrode is 100 parts by weight. The conductive material is generally used in an amount of 2 to 15 parts by weight, with the electrode being 100 parts by weight.

The lithium polymer secondary battery of the present invention can be manufactured, for example, by the following method. (1) Each of the positive electrode, the negative electrode, and the separator is previously impregnated with a solution in which a precursor having at least one unsaturated double bond and an organic electrolyte containing a lithium salt are mixed, and heat or light is applied to each. Alternatively, a battery is produced by irradiating and irradiating both of the energies and bonding them together to form a battery.

(2) to that carrying the separator in advance on either one of the electrodes, on the other hand the electrode, and an organic electrolyte containing precursor and Lithium salt having at least one unsaturated double bond A method of producing a battery by impregnating a solution obtained by mixing the two, irradiating both with heat and / or light energy, and then bonding together to obtain a battery.

(3) A separator is previously sandwiched between the positive electrode and the negative electrode, and impregnated with a mixed solution of a precursor having at least one unsaturated double bond and an organic electrolyte containing a lithium salt, and then heat or A method for producing a battery by irradiating light or both energy and crosslinking.

According to the present invention, it is possible to provide a lithium polymer secondary battery having excellent low-temperature characteristics without impairing charge-discharge cycle characteristics.

The unit composed of the positive electrode, the separator and the negative electrode can be stacked or wound to form a laminated or wound lithium polymer secondary battery.

The battery produced can be made of nickel-plated iron, aluminum cylindrical cans, square cans, or films of aluminum foil laminated with resin as the exterior material, but is not limited to these is not.

These battery manufacturing steps are preferably performed in an inert gas atmosphere such as argon gas / nitrogen gas or in dry air in order to prevent ingress of moisture. Example

Hereinafter, the present invention will be described in detail with reference to examples, but the present invention is not limited thereto. The capacity of the battery to be manufactured was set to be 2 OmAh.

(Example 1)

• The battery of Example 1 was manufactured by the following steps.

a) Preparation of positive electrode

And L i C o 0 ₂ 1 00 parts by weight of the average particle diameter of 7 m, the PVDF of Asechire down black 5 parts by weight and the binder of the conductive material was mixed with 5 parts by weight, and an appropriate amount was added kneaded NMP as Solvent Thus, a positive electrode material paste was obtained. This was applied on a 20 μm A1 foil, dried and pressed to obtain a positive electrode sheet. This positive electrode sheet was cut into 30 X 3 Omm, and an A1 current collecting tab was welded to obtain a positive electrode. b) Preparation of negative electrode

Carbon material powder in which amorphous carbon is attached to the surface of graphite particles (average particle size: 12 μΐΐί, specific surface area: 2 m ² / g) 100 parts by weight and binder PVD F by weight ratio of 100 : 9 to obtain a negative electrode material paste by adding an appropriate amount of NMP as a solvent and kneading. This was applied on a 18 m Cu foil, dried and pressed to obtain a negative electrode sheet. This negative electrode was cut into a size of 30 × 30 mm, and a Ni current collecting tab was welded to obtain a negative electrode.

c) Preparation of precursor solution for polymer solid electrolyte layer

Li iBF ₄ was dissolved in a mixed solvent of GB L and EC at a volume ratio of 80:20 to a concentration of 2 mo 1/1 to obtain an organic electrolyte.

This organic electrolyte 9 5 weight ^_0/0, the molecular weight 7 5 0 0-9 0 00 3 functional Po Li polyether polyols § acrylic acid ester of 3.5 weight ^_0/0 and molecular weight 2 8 0 A monofunctional polyether polyol acrylate of 0 to 3000 was mixed with 1.5% by weight, and 2,4,6-trimethylbenzoinolephenyl phosphinoxide, a photopolymerization initiator, was added at 2000 pm to the above solution. To obtain a precursor solution.

d) Align the battery

On the positive electrode obtained above, a polypropylene separator (24 μπι in thickness) surface-treated with polyoxypropylene glycol was applied, and a precursor solution was injected. This was sandwiched between two quartz glass plates (thickness: 500 πι) and irradiated with ultraviolet light having a wavelength of 365 nm at an illuminance of 20 mW / cm ² for 2 minutes. Next, the precursor solution was injected into the negative electrode, and irradiated with ultraviolet light similarly to the positive electrode. They were attached so that the positive and negative electrodes faced each other, inserted into a bag made of A1 laminate resin film as an exterior material, and sealed with a heat sealer. It was heated at 60 ° C for 24 hours to complete the battery. The light transmittance of the polymer solid electrolyte layer alone at a wavelength of 365 nm was 87% (89% before ultraviolet irradiation).

(Example 2)

The battery of Example 2 was manufactured by the following steps.

a) Preparation of positive electrode

The same operation as in Example 1 was repeated to obtain a positive electrode.

b) Preparation of negative electrode

The same operation as in Example 1 was repeated to obtain a negative electrode.

c) Preparation of precursor solution for polymer solid electrolyte layer

Li BF ₄ was dissolved in a mixed solvent of GBL and EC at a volume ratio of 60:40 to a concentration of lmo 1/1 to obtain an organic electrolyte. This organic electrolyte solution 80 weight ^_0/0, the molecular weight 7500 to 9000 of trifunctional Po Li polyether polyols § acrylic acid ester 1 2 wt ^_0/0 and a monofunctional polyether polyol acrylic acid ester with a molecular weight of from 220 to 300 8 Weight ⁰ / ₀ and are mixed. Further, 300 (ppm) of bis (2,6-dimethoxybenzoinole) -1,2,4,4-trimethyl-pentylphosphinoxide, a photopolymerization initiator, is added to the above solution. Thus, a precursor solution was obtained.

d) Battery assembly

On the positive electrode obtained above, a polyethylene separator (9 ^ πι thick) surface-treated with polyoxyethylene dalicol was applied, and a precursor solution was injected. This was sandwiched between two quartz glass plates (thickness 500 πι), and irradiated with ultraviolet light having a wavelength of 365 nm at an illuminance of 20 mW / cm ² for 2 minutes. Next, the precursor solution was injected into the negative electrode, and irradiated with ultraviolet rays similarly to the positive electrode. They were bonded so that the positive and negative electrodes faced each other, inserted into a bag made of A1 laminated resin film as an exterior material, and sealed with a heat sealer. It was heated at 80 ° C for 2 hours to complete the battery. The light transmittance of the polymer solid electrolyte layer alone at a wavelength of 365 nm was 92% (93% before UV irradiation).

(Example 3)

The battery of Example 3 was manufactured by the following steps.

a) Preparation of positive electrode

The same operation as in Example 1 was repeated to obtain a positive electrode.

b) Preparation of negative electrode

Artificial graphite powder (average particle diameter 1 2 m, a specific surface area of 5 ² / g) 1 00 1 and PVDF parts by weight and the binder at a weight ratio of 00: 9 were mixed so that, an appropriate amount of added kneaded NMP as solvent Thus, a negative electrode material paste was obtained. this It was applied on an 18 m Cu foil, dried and pressed to obtain a negative electrode sheet. This negative electrode was cut into 30 X 3 Omm, and a Ni current collecting tab was welded to obtain a negative electrode.

c) Preparation of precursor solution for polymer solid electrolyte layer

An organic electrolyte was obtained by dissolving Li BF ₄ in a mixed solvent of 75:25 by volume of GBL and EC to a concentration of 0.8 mo 1/1.

This organic electrolyte solution 97 wt%, a molecular weight from 7,500 to 3 functional Po Li polyether polyols § acrylic acid ester 2.4 wt ^_0/0 and a monofunctional polyether polyols § acrylic acid ester having a molecular weight of from 220 to 300 0.6 fold 9000 %, And t-butyl peroxyneode.canoate l OOOppm, which is a thermal polymerization initiator, was added to the above solution to obtain a precursor solution.

d) Battery assembly

A separator made of polyethylene (thickness 13 / m) surface-treated with oxygen plasma is sandwiched between the negative electrode and positive electrode obtained above, and inserted into a bag made of A1 laminating resin film, which is an exterior material. Then, the precursor solution obtained in c) was injected, and the bag was sealed. It was heated at 60 for 72 hours to complete the battery. The light transmittance at a wavelength of 760 nm of only the polymer solid electrolyte layer was measured. The light transmittance was 59% (before heating it was 60%).

(Comparative Example 1)

The battery of Comparative Example 1 was manufactured in the following steps.

a) Preparation of positive electrode

The same operation as in Example 1 was repeated to obtain a positive electrode.

b) Preparation of negative electrode

The same operation as in Example 1 was repeated to obtain a positive electrode. C) Preparation of precursor solution for polymer solid electrolyte layer

Li BF ₄ was dissolved in a mixed solvent of EC and DMC at a volume ratio of 30:70 to 'concentration of 1.5 mo 1/1' to obtain an organic electrolyte.

Otherwise, the same operation as in Example 1 was repeated to obtain a precursor solution. d) Battery assembly

A polypropylene separator (24 m thick) was placed on the positive electrode obtained above, and a precursor solution was injected. This was sandwiched between two quartz glass plates (thickness: 500 μτη), and irradiated with ultraviolet light having a wavelength of 365 nm at an intensity of 20 mW / cm ² for 2 minutes. Next, the precursor solution was injected into the negative electrode, and irradiated with ultraviolet light similarly to the positive electrode. They were attached so that the positive and negative electrodes faced each other, inserted into an A1 laminated resin film bag as an exterior material, and sealed with a heat sealer. It was heated at 60 ° C for 24 hours to complete the battery. The light transmittance of the polymer solid electrolyte layer alone at a wavelength of 365 nm was 80% (before heating, it was 82%).

(Comparative Example 2)

A battery of Comparative Example 2 was manufactured in the following steps.

a) Preparation of positive electrode

The same operation as in Example 1 was repeated to obtain a positive electrode.

b) Preparation of negative electrode

The same operation as in Example 1 was repeated to obtain a positive electrode.

c) Preparation of precursor solution for polymer solid electrolyte layer

The same operation as in Example 1 was repeated to obtain a precursor solution.

d) Battery assembly

A polypropylene separator (thickness: 30 m) was placed on the positive electrode obtained above, and a precursor solution was injected. Other operations are the same as those in the first embodiment. The battery was completed repeatedly. The light transmittance of the polymer solid electrolyte layer alone at a wavelength of 365 nm was 48% (49% before ultraviolet irradiation).

) C

(Comparative Example 3)

A battery of Comparative Example 3 was manufactured through the following steps.

a) Preparation of positive electrode

The same operation as in Example 1 was repeated to obtain a positive electrode.

b) Preparation of negative electrode

The same operation as in Example 1 was repeated to obtain a positive electrode.

c) Preparation of precursor solution for polymer solid electrolyte layer

The same operation as in Example 1 was repeated to obtain a precursor solution.

d) Battery assembly

A polyester nonwoven fabric (thickness: 40 μπι) was placed on the positive electrode obtained above, and a precursor solution was injected. Otherwise, the same operation as in Example 1 was repeated to complete the battery. The light transmittance of the polymer solid electrolyte layer alone at a wavelength of 365 ηm was 73% (75% before ultraviolet irradiation). Each of the batteries prepared above was charged to 4.2 V at a constant current of 4 mA, and after reaching 4.2 V, charged at a constant voltage until the current attenuated to 1 mA (hereinafter referred to as 0.2 C charging). Low-temperature capacity retention rate when discharging to 3 V at 25 ° C and 120 ° C at constant current of 2 OmA, and repeating 0.2 C charging and discharging to 3 V at constant current of 20 mA up to 500 times at 25 ° C The cycle maintenance rate at the time of heating was measured. These definitions are represented by the following equations.

Low temperature capacity maintenance rate (%)

= (-20. C discharge capacity) / (25. C discharge capacity) x 100

Cycle maintenance rate (%) = (500th discharge capacity) / (initial discharge capacity) X100 The results of the above Examples and Comparative Examples are shown in Table 1 below. table 1

As shown in Table 1, from the results of Example 1 and Comparative Example 1, in order to improve the low-temperature characteristics while maintaining the cycle characteristics of the battery, the light transmittance of the polymer solid electrolyte layer must be 50% or more. Even so, it was found that it was necessary to use a polymer solid electrolyte layer containing GBL.

Further, from the results of Example 1 and Comparative Example 2, it was found that when the light transmittance of the polymer solid electrolyte layer was less than 50%, both the low-temperature characteristics and the cycle characteristics of the battery deteriorated.

Furthermore, from the results of Example 1 and Comparative Example 3, it was found that even if the light transmittance was 50% or more, the nonwoven fabric instead of the separator caused a short circuit inside the battery, and the cycle characteristics could not be maintained. According to the present invention, it is possible to provide a lithium polymer secondary battery which maintains excellent cycle characteristics and does not cause performance degradation even at a low temperature such as 120 ° C.

In addition, the production method of measuring the permeability of the polymer before cross-linking of the polymer solid electrolyte layer and the τ / —petit mouth rataton into the separator by light transmittance is a simple and high-performance lithium polymer secondary battery. It turns out that this is a manufacturing method.

Claims

The scope of the claims

1. In the presence of a positive electrode and a negative electrode containing a polymer crosslinked in the presence of an organic electrolyte and an active material, between the two electrodes, and in the presence of an organic electrolyte and a separator (not including nonwoven fabric) Lithium comprising a polymer solid electrolyte layer containing a crosslinked polymer, wherein the organic electrolyte contains y_petit mouth rataton, and the polymer solid electrolyte layer has a light transmittance of 50% or more. Polymer secondary battery

2. The lithium polymer secondary battery according to claim 1, wherein the separator is a microporous membrane made of polyethylene, polypropylene, or a composite of polyethylene and polypropylene.

3. The lithium polymer secondary battery according to claim 1, wherein the organic electrolyte further contains ethylene carbonate, and the volume ratio of petit-mouthed ratatone: ethylene power, -carbonate is 60:40 to 80:20.

4. The polymer contained in the polymer solid electrolyte layer is a random copolymer or a block copolymer containing an ethylene oxide unit and a propylene oxide unit in the molecule, and has an acryloyl group or a methacryloyl group as a terminal group. 2. The lithium polymer secondary battery according to claim 1, wherein a precursor comprising a polyfunctional compound having an unsaturated bond of a methyl group is polymerized.

5. The lithium polymer secondary battery according to claim 2, wherein the microporous membrane is a membrane in which 0.01 to: L 0 μπι pores are present in 10 ² to: L 0 ¹² Zcm ² .

6. The lithium polymer secondary battery according to claim 1, wherein the separator has a thickness of 5 to 30.

7. A method for producing a lithium polymer secondary battery according to any one of claims 1 to 6, wherein the separation is performed in the presence of an organic electrolyte solution and a polymer before crosslinking. A step of obtaining a solid polymer electrolyte layer by cross-linking the polymer before cross-linking after adjusting the light transmittance of the polymer to 50% or more. Production method.

8. The method for producing a lithium polymer secondary battery according to claim 7, wherein the light transmittance is measured with light having a wavelength in a range of 300 to 800 nm.