JP2003297424A - Nonaqueous electrolyte battery and method for manufacturing the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To suppress battery performance degradation caused by high temperature preservation. <P>SOLUTION: The battery comprises a positive electrode 2 having a positive active material capable of doping/dedoping lithium and containing lithium carbonate, a negative electrode 3 having a negative active material capable of doping/ dedoping lithium, and a solid electrolyte 4 containing a nonaqueous solvent to which N-methyl-2-pyrrolydone (NMP) is added and an electrolyte salt. The lithium carbonate suppresses decomposition of the solid electrolyte 4 caused by heating and the NMP prevents gas generation caused by heating, thus suppressing the battery performance degradation caused by high temperature preservation. <P>COPYRIGHT: (C)2004,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a non-aqueous electrolyte battery having a positive electrode, a negative electrode and a non-aqueous electrolyte and having greatly improved battery characteristics, and a method for producing the same.

[0002]

2. Description of the Related Art In recent years, for example, a notebook type portable computer, a mobile phone, a camera-integrated VTR (vide)
o tape recorders) and other portable electronic equipment power supplies,
Development of lightweight secondary batteries with high energy density is underway. As a secondary battery having this high energy density, for example, it has a larger energy density than a lead battery or a nickel-cadmium battery, and the charge / discharge reaction of the battery causes lithium or a lithium alloy or lithium ion between the positive electrode and the negative electrode. A lithium ion secondary battery is known which is carried out by moving it.

This lithium ion secondary battery uses a non-aqueous electrolytic solution in which an electrolyte salt is dissolved in a non-aqueous solvent, unlike the above-mentioned lead battery, nickel cadmium battery and the like. Therefore, in this lithium ion secondary battery, it is necessary to use a metal container having high airtightness as the exterior material to prevent leakage of the nonaqueous electrolytic solution. When such an exterior material is used, in a lithium ion secondary battery, for example, a sheet type,
It is difficult to manufacture it into a thin shape such as a card type or to give it flexibility.

As a means for solving such a problem, for example, a battery using a solid electrolyte made of an inorganic or organic substance, a gel electrolyte having a polymer substance, or the like has been proposed. Specifically, for example, a solid electrolyte battery using a polymer solid electrolyte having a polymer material and an electrolyte salt, a gel electrolyte in which a non-aqueous electrolyte is held in a matrix polymer, or the like has been proposed.

In this solid electrolyte battery, since the electrolyte is solid or gel, it is possible to prevent liquid leakage and control the thickness of the electrolyte. In addition, this solid electrolyte battery,
Since the electrolyte has adhesiveness to the electrode, the contact between the electrolyte and the electrode and the distance between the positive electrode and the negative electrode can be improved. For this reason, in this solid electrolyte battery, it is not necessary to use a metal container to prevent leakage of the electrolytic solution or pressurize the electrode in the thickness direction. be able to. Specifically, in the solid electrolyte battery, for example, a moisture-proof laminated film made of a heat-fusible polymer film and a metal foil is used as the film-shaped exterior material.

As a result, in the solid electrolyte battery, by sealing the moisture-proof laminated film with a hot seal or the like, the airtightness is high and the overall thickness can be reduced. Further, in this solid electrolyte battery, since the moisture-proof laminated film is lighter and cheaper than the metal container, it is possible to reduce the weight and cost.

[0007]

However, since the lithium ion secondary battery is used as a power source for portable electronic equipment as described above, in the case of a notebook type portable computer or the like, a CPU ( cent
The temperature may rise due to heat generated by the ral processing unit) and the battery characteristics such as cycle characteristics may deteriorate. Further, the portable electronic device may be exposed to a high temperature state in which the ambient temperature becomes about 100 ° C. when left in the car interior or the like in the summer. In this case, especially in solid electrolyte batteries, a thin moisture-proof laminated film is used for the exterior material and is easily affected by the ambient temperature. Deteriorates.

Therefore, the present invention has been proposed in view of such conventional circumstances, and a non-aqueous electrolyte battery excellent in high-temperature storage characteristics in which deterioration of the battery characteristics is suppressed even when stored at high temperatures, and the same. It is intended to provide a manufacturing method.

[0009]

[Means for Solving the Problems] In order to achieve this object, as a result of intensive studies by the present inventors, it was found that lithium carbonate was contained in the positive electrode active material and N-methyl was contained in the non-aqueous solvent of the non-aqueous electrolyte. It was found that by adding 2-pyrrolidone, it is possible to suppress deterioration of battery characteristics after storage at high temperature.

That is, the non-aqueous electrolyte battery according to the present invention is capable of lithium doping / dedoping and a positive electrode having a positive electrode active material containing lithium carbonate, and a lithium doping / dedoping negative electrode. It is provided with a negative electrode having an active material and a non-aqueous electrolyte containing a non-aqueous solvent added with N-methyl-2-pyrrolidone represented by Chemical Formula 1 and an electrolyte salt.

[0011]

[Chemical 3]

As a result, in this non-aqueous electrolyte battery, lithium carbonate contained in the positive electrode active material and N-methyl-2-pyrrolidone added to the non-aqueous solvent decompose the non-aqueous electrolyte and generate gas during high temperature storage. Therefore, the deterioration of the battery characteristics due to the high temperature storage is suppressed.

Further, the method for producing a non-aqueous electrolyte battery according to the present invention comprises a positive electrode having a positive electrode active material capable of lithium doping / dedoping and a negative electrode having a negative electrode active material capable of lithium doping / dedoping. And a non-aqueous electrolyte containing a non-aqueous solvent and an electrolyte salt, wherein the positive electrode active material contains lithium carbonate and the non-aqueous solvent is represented by Chemical Formula 1. It is characterized by adding N-methyl-2-pyrrolidone.

[0014]

[Chemical 4]

In this method for producing a non-aqueous electrolyte battery, a positive electrode having a positive electrode active material containing lithium carbonate,
A non-aqueous electrolyte battery using a non-aqueous electrolyte obtained by adding N-methyl-2-pyrrolidone to a non-aqueous solvent is obtained. Therefore, in this method for manufacturing a non-aqueous electrolyte battery, lithium carbonate contained in the positive electrode active material or N-methyl-2-pyrrolidone added to the non-aqueous solvent of the non-aqueous electrolyte is used to remove the non-aqueous electrolyte during high-temperature storage. Since decomposition and gas generation are suppressed, it is possible to obtain a non-aqueous electrolyte battery in which deterioration of battery characteristics due to high temperature storage is suppressed.

[0016]

BEST MODE FOR CARRYING OUT THE INVENTION A non-aqueous electrolyte battery to which the present invention is applied will be described below. FIG. 1 shows a configuration example of a lithium ion secondary battery (hereinafter referred to as a battery) as the non-aqueous electrolyte battery. This battery 1 includes a positive electrode 2 formed in a long shape, a negative electrode 3 formed in a long shape, and a solid electrolyte 4 such as a gel electrolyte in which a polymer matrix is impregnated with a nonaqueous solvent together with an electrolyte salt. I have it. In this battery 1, the solid electrolyte 4 is formed on the main surfaces of the positive electrode 2 and the negative electrode 3, and the positive electrode 2 and the negative electrode 3 are wound in a state of being laminated with the solid electrolyte 4 interposed therebetween to form a power generating element. Battery element 5
And has a structure in which the battery element 5 is enclosed in an exterior material 6.

The positive electrode 2 is coated on the positive electrode current collector 7 with a positive electrode mixture coating liquid containing a positive electrode active material and a binder, dried, and pressed to form a positive electrode current collector 7 on the positive electrode current collector 7. It has a structure in which the positive electrode mixture layer 8 is formed by compression. In the positive electrode 2, the positive electrode terminal 9 is provided at a predetermined position of the positive electrode current collector 7, and the positive electrode current collector 7 is provided.
Are connected so as to project in the width direction. For the positive electrode terminal 9, for example, a strip-shaped metal piece made of aluminum is used.

The positive electrode active material includes TiS ₂ , MoS ₂ and N.
A metal sulfide or oxide such as bSe ₂ or V ₂ O ₅ can be used. In addition, LiM _x O ₂ (wherein M is C
It represents one or more transition metals such as o, Ni, Mn, Fe, Al, V, and Ti, and x varies depending on the charge / discharge state of the battery and is usually 0.05 or more and 1.10 or less. It is possible to use a lithium composite oxide mainly containing). As the transition metal M constituting the lithium composite oxide, Co, Ni, Mn and the like are preferable. Specific examples of such a lithium composite oxide include LiCoO ₂ and Li.
NiO ₂ , LiNi _y Co _1-y O ₂ (wherein 0 <y <
It is 1. ), LiMn ₂ O _{4 and the} like.

The positive electrode active material contains lithium carbonate. As a result, in the battery 1, when stored in a high temperature state, lithium carbonate is prevented from decomposing the electrolyte salt or the like in the solid electrolyte 4 due to, for example, heat, so that deterioration of battery characteristics due to high temperature storage is suppressed. To be done.

In the positive electrode 2, the content of lithium carbonate in the positive electrode active material is in the range of 0.05% by weight or more and 0.2% by weight or less. For example, when the content of lithium carbonate is less than 0.05 wt% with respect to the positive electrode active material, in the battery 1, it is possible to suppress decomposition of the electrolyte salt or the like in the solid electrolyte 4 during high temperature storage. It will be difficult. On the other hand, when the content of lithium carbonate is more than 0.2 wt% with respect to the positive electrode active material, in the battery 1, too much lithium carbonate is decomposed during high temperature storage to generate carbon dioxide gas in the battery element 5. Therefore, carbon dioxide gas is stored between the positive electrode 2 and the negative electrode 3 to improve the battery resistance. Therefore, in the positive electrode 2, the content of lithium carbonate in the positive electrode active material is 0.05% by weight or more,
By setting the content in the range of 0.2% by weight or less, it becomes possible to appropriately suppress the decomposition of the solid electrolyte 4 at high temperature.

As a method of incorporating lithium carbonate into the positive electrode active material, for example, when LiCoO ₂ is obtained as the positive electrode active material, lithium carbonate as a starting material and cobalt carbonate are mixed and the mixture is fired to produce the positive electrode active material. The material contains lithium carbonate. That is, in this case, a positive electrode active material in which the content of lithium carbonate is controlled can be obtained by adjusting the mixing ratio when mixing lithium carbonate and cobalt carbonate.

In the positive electrode 2, a binder such as polyvinylidene fluoride or styrene butadiene rubber which is used in a positive electrode mixture of a non-aqueous electrolyte battery can be used as the binder of the positive electrode mixture layer 8 in addition to the above. For example, a carbonaceous material as a conductive material or a known additive can be added to the positive electrode mixture layer 8. In the positive electrode 2, a foil-shaped metal or a net-shaped metal made of, for example, aluminum is used as the positive electrode current collector 9.

The negative electrode 3 is coated on the long negative electrode current collector 10 with a negative electrode mixture coating liquid containing a negative electrode active material and a binder, dried, and pressed to form a negative electrode current collector 10 on the negative electrode current collector 10. It has a structure in which the negative electrode mixture layer 11 is formed by compression. A negative electrode terminal 12 is connected to the negative electrode 3 at a predetermined position of the negative electrode current collector 10 so as to project in the width direction of the negative electrode current collector 10. For the negative electrode terminal 12, for example, a strip-shaped metal piece made of copper or nickel is used.

As the negative electrode active material, lithium, a lithium alloy, or a carbon material capable of doping / dedoping lithium is used. Examples of the carbon material capable of doping / dedoping lithium include a low crystalline carbon material obtained by firing at a relatively low temperature of 2000 ° C. or lower, and artificial graphite obtained by firing a raw material that is easily crystallized at a high temperature of around 3000 ° C. A highly crystalline carbon material or the like can be used. Specifically, use carbonaceous materials such as non-graphitizable carbon, pyrolytic carbons, cokes, graphites, glassy carbon fibers, organic polymer compound fired bodies, carbon fibers, activated carbon and carbon blacks. You can The cokes include pitch coke, needle coke, petroleum coke, and the like. Also,
The organic polymer compound fired body is obtained by firing a phenol resin, a furan resin, or the like at an appropriate temperature to carbonize.
In addition to the carbonaceous materials described above, examples of materials that can be doped / dedoped with lithium include polymers such as polyacetylene and polypyrrole, and oxides such as iron oxide, ruthenium oxide, molybdenum oxide, tungsten oxide, titanium oxide, and tin oxide. Alternatively, a nitride in which oxygen of these oxides is replaced with nitrogen can be used.

In the negative electrode 3, as the binder for the negative electrode mixture layer 11, a binder such as polyvinylidene fluoride or styrene butadiene rubber, which is used in the negative electrode mixture for non-aqueous electrolyte batteries, can be used. For example, known additives can be added to the negative electrode mixture layer 11. In the negative electrode 3, as the negative electrode current collector 10, for example, a foil-shaped metal or a net-shaped metal made of copper or the like is used.

As the solid electrolyte 4, a gel electrolyte in which an organic polymer such as a polymer matrix is impregnated with a nonaqueous electrolytic solution containing a nonaqueous solvent and an electrolyte salt is used.

As the polymer matrix, various polymers can be used as long as they absorb a non-aqueous electrolyte and gelate. Specifically, for example, fluorine-based polymers such as poly (vinylidene fluoride) and poly (vinylidene fluoride-co-hexafluoropropylene), ether-based polymers such as poly (ethylene oxide) and cross-linked products thereof, poly (Acrylonitrile) and the like, and any one or a plurality of these may be mixed and used.

A solvent having a relatively high dielectric constant is used as the non-aqueous solvent. Specifically, for example, cyclic carbonic acid esters such as propylene carbonate and ethylene carbonate, chain carbonic acid esters such as diethyl carbonate and dimethyl carbonate, solvents in which hydrogen of these carbonic acid esters is replaced with halogen, methyl propionate, and the like. Carboxylic acid esters such as methyl butyrate, ethers such as 2-methyltetrahydrofuran and dimethoxyethane, butyl lactones such as γ-butyl lactone, γ-
Examples thereof include valerolactones such as valerolactone, sulfolanes and the like. Then, one or more of these non-aqueous solvents are mixed and used.

As the electrolyte salt, the electrolyte salt used in the non-aqueous electrolytic solution of the non-aqueous electrolyte battery can be used.
Specifically, for example, LiPF ₆ , LiBF ₄ , LiAs
_{F 6, LiClO 4, LiB (} C 6 H 5) 4, CH 3 S
O ₃ Li, CF ₃ SO ₃ Li, LiN (SO ₂ CF ₃ )
₂ , LiN (SO ₂ C ₂ F ₅ ) ₂ , LiC (SO ₂ CF
₃ ) ₃ , LiAlCl ₄ , LiSiF ₆ , LiCl, L
An electrolyte salt such as iBr may be used. Then, one or more of these are mixed and used. Particularly, as the electrolyte salt, LiPF ₆ , L which is excellent in oxidation stability is used.
iBF ₄ is used. The concentration of the electrolyte salt in the non-aqueous solvent is not particularly limited, but the ionic conductivity of the non-aqueous electrolyte is increased by setting the concentration in the range of 0.4 mol / liter or more and 1.5 mol / liter or less. You can

In the solid electrolyte 4, N-methyl-2-pyrrolidone (hereinafter referred to as NMP) is added to the non-aqueous solvent. As a result, in the battery 1, when stored in a high temperature state, NMP, for example, the solid electrolyte 4
Is prevented from being decomposed by heat, and the positive electrode 2 reacts with the solid electrolyte 4 to generate a gas.

Further, in the solid electrolyte 4, the amount of NMP added is 0.1% by weight or more and 3% with respect to the nonaqueous solvent of the nonaqueous electrolytic solution.
It is in the range of not more than wt%. For example, when the amount of NMP added is less than 0.1% by weight with respect to the non-aqueous solvent, it is difficult for the battery 1 to obtain the function and effect of NMP during high temperature storage, and the solid electrolyte 4 is decomposed and gas is generated. Will happen. On the other hand, when the addition amount of NMP is more than 3% by weight with respect to the non-aqueous solvent, in the battery 1, the NMP swells with the binder in the positive electrode mixture layer 8 and the negative electrode mixture layer 11, and the mixture layer. Peeling and collapse of the will occur. Therefore, in the positive electrode 2, the amount of NMP added to the non-aqueous solvent of the non-aqueous electrolytic solution is in the range of 0.1% by weight or more and 3% by weight or less, whereby the solid electrolyte 4 when stored in a high temperature state It suppresses decomposition and gas generation, and suppresses peeling and collapse of the mixture layer due to NMP.

The exterior material 6 is formed by laminating, for example, two or more insulating layers, metal layers, etc., and laminating them together so that the inner surface of the battery serves as an insulating layer. The material of the insulating layer is not particularly limited as long as it has adhesiveness to the positive electrode terminal 9 and the negative electrode terminal 12, but polyethylene, polypropylene, modified polyethylene, modified polypropylene, copolymers thereof, and the like are selected from polyolefin resins. The following is used because it has low permeability and is excellent in airtightness. As the metal layer, for example, aluminum, stainless steel, nickel, iron or the like formed in a foil shape, a plate shape or the like is used. Further, in the exterior material 6, by using an insulating layer made of nylon or the like for the outer peripheral layer of the battery 1, it is possible to improve the strength against breakage or puncture.

The battery 1 having the above structure is manufactured as follows. First, the positive electrode 2 is manufactured. When manufacturing the positive electrode 2, a positive electrode mixture coating liquid containing a positive electrode active material containing a predetermined amount of the above-mentioned lithium carbonate, a conductive material, and a binder is prepared. The positive electrode mixture layer 8 is formed by uniformly coating and drying on the positive electrode current collector 7 made of foil or the like, and cut into a predetermined size. Next, the positive electrode terminal 9 is connected to a predetermined position of the positive electrode current collector 7 by, for example, ultrasonic welding or spot welding. In this way, the elongated positive electrode 2 is manufactured.

Next, the negative electrode 3 is prepared. When producing the negative electrode 3, a negative electrode mixture coating liquid containing the above-mentioned negative electrode active material and a binder is prepared, and this negative electrode mixture coating liquid is applied onto the negative electrode current collector 10 made of, for example, a copper foil or the like. The negative electrode mixture layer 11 is formed by uniformly applying and drying, and cut into a predetermined size. Next, the negative electrode terminal 12 is connected to a predetermined position of the negative electrode current collector 10 by, for example, ultrasonic welding or spot welding. In this way, the elongated negative electrode 3 is manufactured.

Next, the solid electrolytes 4 are formed in layers on the main surface of the positive electrode mixture layer 8 of the positive electrode 3 and the main surface of the negative electrode mixture layer 11 of the negative electrode 3 manufactured as described above. Solid electrolyte 4
When forming, the non-aqueous electrolytic solution is prepared by dissolving the electrolyte salt in the above-mentioned non-aqueous solvent. At this time, in the non-aqueous electrolyte, a predetermined amount of NMP is added to the non-aqueous solvent.

Next, the non-aqueous electrolytic solution, the above-mentioned matrix polymer, and, if necessary, the non-aqueous solvent as a diluting solvent are mixed and stirred to prepare an electrolyte solution in a sol state, and this electrolytic solution is prepared. Main surface of the polarizable electrode mixture layer 8 and the negative electrode mixture layer 11
By coating each of them on the main surfaces of the positive electrode 2 and the negative electrode 3, an electrolyte membrane made of a gel electrolyte is formed. When a diluting solvent is used, the non-aqueous solvent is volatilized to form a gel electrolyte. In this way, the solid electrolyte 4 is formed on the positive electrode 2 and the negative electrode 3, respectively.

Next, as shown in FIG. 2, the positive electrode 2 and the negative electrode 3 on which the solid electrolyte 4 is formed on the main surface as described above are laminated so that the solid electrolyte 4 faces each other, and the electrode is elongated. Then, the battery element 5 is manufactured by flatly winding. At this time, the positive electrode terminal 9 and the negative electrode terminal 12 are made to project from one end surface of the battery element 5.

Next, as shown in FIG.
The positive electrode terminal 9 and the negative electrode terminal 12 provided in the above are led out and housed inside the exterior material 6. At this time, the battery element 5
The resin piece 13 made of propylene or the like having an adhesive property is applied between the positive electrode terminal 9 and the negative electrode terminal 12 and the exterior material 6, and is housed in the exterior material 6. As a result, in the battery 1, it is possible to prevent the positive electrode terminal 9 and the negative electrode terminal 12 from being short-circuited with the metal layer of the exterior material 6, and to prevent the airtightness from decreasing.

Next, as shown in FIG. 4, the battery element 5 is sealed in the exterior material 6 by bonding the peripheral edge of the exterior material 6 containing the battery element 5 inside by, for example, heat sealing. In this way, the battery 1 is manufactured.

In the battery 1 manufactured as described above, the lithium carbonate contained in the positive electrode active material suppresses the decomposition of the solid electrolyte 4, particularly the decomposition of the electrolyte salt, which occurs during high temperature storage. In addition, in this battery 1, the NMP added to the non-aqueous solvent suppresses decomposition of the non-aqueous electrolyte and gas generation that occur during high-temperature storage.

Therefore, in this battery 1, by adding NMP to the non-aqueous solvent of the solid electrolyte 4 while adding lithium carbonate to the positive electrode active material, decomposition of the solid electrolyte 4 which occurs during high temperature storage and solid electrolyte 4 Since the generation of gas accompanying the decomposition of No. 4 is appropriately suppressed, deterioration of battery characteristics due to high temperature storage is suppressed.

The non-aqueous electrolyte battery to which the present invention is applied is not particularly limited in its shape such as a cylindrical shape, a square shape, a coin shape and a button shape using a metal container as an exterior material. It is also possible to make various sizes such as thin and large. Further, in the non-aqueous electrolyte battery to which the present invention is applied, the battery element 5 of the battery 1 in the above-described embodiment is used.
Is wound, but is not limited to this, for example, a structure in which a negative electrode and a positive electrode are laminated via a separator and wound, or a long negative electrode and a positive electrode are separated. The present invention is also applicable to the case where a battery element having a structure in which a zigzag is folded in a state of being interposed, that is, a so-called bellows-like configuration is used.

[0043]

[Examples] Hereinafter, a sample in which a lithium-ion secondary battery using a gel electrolyte as a non-aqueous electrolyte battery to which the present invention is applied is actually manufactured will be described.

<Sample 1> To manufacture a lithium ion secondary battery as Sample 1, first, a positive electrode active material was synthesized. In order to obtain a positive electrode active material, a mixture of predetermined amounts of lithium carbonate and cobalt carbonate as starting materials is fired in air at 900 ° C. for about 5 hours and pulverized to obtain LiCoO 2 having an average particle diameter of 8 μm. ₂ was obtained. At this time, when the content of lithium carbonate in the obtained LiCoO ₂ was measured by the neutralization titration method, it was found to be 0.05.
% By weight.

Next, 91 parts by weight of the obtained LiCoO 2, 6 parts by weight of scaly graphite as a conductive material, 3 parts by weight of polyvinylidene fluoride (hereinafter referred to as PVdF) as a binder, and a solvent. And N-methyl-2-pyrrolidone (hereinafter referred to as NMP) were added, and the mixture was kneaded and dispersed by a planetary mixer to prepare a positive electrode mixture coating liquid. Next, using a die coater as a coating device, the positive electrode current collector was uniformly coated on both sides of a strip-shaped aluminum foil having a thickness of 20 μm, dried at 100 ° C. under reduced pressure for 24 hours, and then compressed by a roll press. Molded, width 118m
m and a length of 640 mm. A long positive electrode was produced as described above.

Next, a negative electrode was prepared. When making a negative electrode
Is a negative electrode active material having a (002) plane spacing of 0.33.
7 nm, C-axis crystallite thickness of (002) plane is 50 nm,
True density of 2.23 g / cc by the knometer method, BET
Specific surface area by the method is 1.6m ^Two/ G, average particle size is 33μ
m, bulk density 0.98 g / cm^Three90% by weight of graphite
And 10% by weight of PVdF as a binder and NM as a solvent.
Add P and knead with a planetary mixer
Dispersion was performed to prepare a negative electrode mixture coating liquid. Next, this negative electrode
Negative electrode current collection using a mixture coating liquid as a coating device using a die coater
Uniformly on both sides of the strip-shaped copper foil with a thickness of 10 μm
Applied and dried at 120 ° C. under reduced pressure for 24 hours
Later, compression molding with a roll press machine, width 120 mm, length
It was cut to 800 mm. As described above, the long negative
The pole was made.

Next, a gel electrolyte was formed as an electrolyte layer on both main surfaces of the positive electrode and the negative electrode produced as described above.
When forming the electrolyte layer made of a gel electrolyte, a mixture of ethylene carbonate (EC) of 39.6 wt%, propylene carbonate (PC) of 59.4 wt% and NMP of 1 wt% was used. L for water solvent to solvent weight
A non-aqueous electrolytic solution in which 0.8 mol / kg of iPF ₆ was dissolved was prepared.

Next, this non-aqueous electrolyte, PVdF in which hexafluoropropylene was copolymerized at a ratio of 7%, and dimethyl carbonate were mixed and stirred to prepare a gel electrolyte solution in a sol state. Next, the gel electrolyte solution was applied on both main surfaces of the positive electrode and the negative electrode to volatilize dimethyl carbonate. In this way, an electrolyte layer made of a gel electrolyte was formed on both main surfaces of the positive electrode and the negative electrode.

Next, the positive electrode and the negative electrode having the electrolyte layer formed on the main surface as described above were bonded so that the gel electrolyte faces each other, and the positive electrode was flatly wound in the longitudinal direction of the positive electrode to produce a battery element. . At this time, a strip-shaped positive electrode terminal made of aluminum was attached to an arbitrary position of the positive electrode, and a strip-shaped negative electrode terminal made of nickel was attached to an arbitrary position of the negative electrode.

Next, the positive electrode terminal and the negative electrode terminal provided in this battery element were led out to the outside, and were housed inside a three-layer exterior material in which an aluminum foil having a thickness of 50 μm was sandwiched between polyolefin films having a thickness of 30 μm. At this time, the battery element was housed in the exterior material such that a propylene resin piece having adhesiveness was applied between the positive electrode terminal and the negative electrode terminal and the exterior material. As a result, in the battery element, short circuit between the positive electrode terminal and the negative electrode terminal via the aluminum foil of the exterior material, deterioration of airtightness, etc. are prevented. Next, the battery element was enclosed in the exterior material by sticking together the peripheral edge portions of the exterior material containing the battery element inside. As described above, the lithium ion secondary battery of Sample 1 was manufactured. In the following description, the lithium-ion secondary battery is simply referred to as a battery for convenience.

<Sample 2> In Sample 2, EC was 40% by weight and PC was 59.% on both main surfaces of the positive electrode and the negative electrode.
In a non-aqueous solvent prepared by mixing 9% by weight and 0.1% by weight of NMP, 0.8 mol / k of LiPF ₆ with respect to the solvent weight.
A battery was manufactured in the same manner as in Sample 1, except that a gel electrolyte using a dissolved non-aqueous electrolytic solution was formed as the electrolyte layer.

<Sample 3> In Sample 3, EC was 38.8 wt% and PC was 5 on both the main surfaces of the positive electrode and the negative electrode.
In a non-aqueous solvent in which 8.2 wt% and 3 wt% NMP are mixed, LiPF ₆ is 0.8 mol / k with respect to the solvent weight.
A battery was manufactured in the same manner as in Sample 1, except that a gel electrolyte using a dissolved non-aqueous electrolytic solution was formed as the electrolyte layer.

<Sample 4> In Sample 4, as the positive electrode active material, L containing 0.2% by weight of lithium carbonate was prepared by adjusting the mixing ratio of lithium carbonate and cobalt carbonate.
A battery was manufactured in the same manner as in Sample 2 except that iCoO ₂ was synthesized and LiCoO ₂ was used.

<Sample 5> In Sample 5, as the positive electrode active material, L containing 0.2% by weight of lithium carbonate was prepared by adjusting the mixing ratio of lithium carbonate and cobalt carbonate.
A battery was manufactured in the same manner as in Sample 3 except that iCoO ₂ was synthesized and LiCoO ₂ was used.

<Sample 6> In Sample 6, a non-aqueous solvent in which 40% by weight of EC and 60% by weight of PC were mixed on both the main surfaces of the positive electrode and the negative electrode, and LiP was added to the solvent weight.
A battery was manufactured in the same manner as in Sample 1, except that a gel electrolyte using a nonaqueous electrolytic solution in which F ₆ was dissolved at 0.8 mol / kg was formed as the electrolyte layer.

<Sample 7> In Sample 7, a non-aqueous solvent prepared by mixing 38% by weight of EC, 57% by weight of PC and 5% by weight of NMP on both main surfaces of the positive electrode and the negative electrode was used as a solvent. A battery was manufactured in the same manner as in Sample 1, except that a gel electrolyte using a nonaqueous electrolytic solution in which 0.8 mol / kg of LiPF ₆ was dissolved was formed as the electrolyte layer with respect to the weight.

<Sample 8> In Sample 8, as the positive electrode active material, LiCo to which lithium carbonate was not added by adjusting the mixing ratio of lithium carbonate and cobalt carbonate.
O ₂ was synthesized and LiCoO ₂ was used, except that
A battery was manufactured in the same manner as in Sample 2.

<Sample 9> In Sample 9, as the positive electrode active material, LiCo to which lithium carbonate was not added by adjusting the mixing ratio of lithium carbonate and cobalt carbonate.
O ₂ was synthesized and LiCoO ₂ was used, except that
A battery was manufactured in the same manner as in Sample 3.

<Sample 10> In Sample 10, LiCoO ₂ containing 0.25 wt% of lithium carbonate was synthesized as the positive electrode active material by adjusting the mixing ratio of lithium carbonate and cobalt carbonate, and this LiCoO ₂ was synthesized. A battery was manufactured in the same manner as in Sample 2 except that

[0060] <Sample 11> In sample 11, as a positive electrode active material, lithium carbonate to synthesize LiCoO ₂ which contained 0.25 wt% by adjusting the mixing ratio of lithium carbonate and cobalt carbonate, this LiCoO ₂ A battery was manufactured in the same manner as in Sample 3 except that

Next, Samples 1 to 1 produced as described above
For the battery of Sample 11, the cycle characteristics after high temperature storage, specifically, the discharge capacity retention rate after 250 cycles of charge / discharge after high temperature storage were measured.

Table 1 shows the evaluation results of the discharge capacity retention rate after 250 cycles in the battery stored at high temperature in each sample.

[0063]

[Table 1]

The cycle characteristics of each sample after high temperature storage were evaluated as follows. First, as initial charge / discharge, each sample was subjected to constant current / constant voltage charging in a 23 ° C. atmosphere at a current of 0.2 C, an upper limit voltage of 4.2 V, and a charging time of 10 hours, and then in a 23 ° C. atmosphere at 0. 5C
A constant current discharge of up to 3 V was performed with the current value of. Next, each sample was subjected to constant current constant voltage charging in a 23 ° C. atmosphere with a current of 0.5 C, an upper limit voltage of 4.2 V, and a charging time of 5 hours, and then stored in a 60 ° C. atmosphere for 30 days at a high temperature. After storage, constant current discharge of up to 3 V was performed at a current value of 1 C in an atmosphere of 23 ° C. Next, for each sample, a constant current constant voltage charge with a current of 1 C, an upper limit voltage of 4.2 V, and a charging time of 3 hours was performed in an atmosphere of 23 ° C., and a current value of 1 C was 3 V in an atmosphere of 23 ° C.
Charge and discharge up to 250 with constant current discharge up to 250
Repeated several times. The cycle characteristic after high temperature storage is the ratio of the discharge capacity at the 250th cycle to the discharge capacity at the 3rd cycle when charging and discharging are repeated as described above.

From the evaluation results shown in Table 1, Sample 1 to Sample 5 in which NMP is added in the range of 0.1% by weight or more and 3% by weight or less with respect to the non-aqueous solvent in the gel electrolyte.
It can be seen that, in comparison with Sample 6 in which NMP is not added to the non-aqueous solvent in the gel electrolyte, the cycle characteristics after high temperature storage are good.

In Sample 6, since NMP was not added to the non-aqueous solvent in the gel electrolyte, it was difficult to suppress decomposition of the gel electrolyte and gas generation from the positive electrode due to heat during high temperature storage. It deteriorates the battery characteristics after high temperature storage.

From the evaluation results shown in Table 1, NMP is 0.1% by weight or more with respect to the non-aqueous solvent in the gel electrolyte,
In samples 1 to 5 added in the range of 3% by weight or less, NMP was added to the non-aqueous solvent in the gel electrolyte.
It can be seen that the cycle characteristics after storage at high temperature are better than those of Sample 7 in which 5 wt% was added.

In Sample 7, since the amount of NMP added to the non-aqueous solvent in the gel electrolyte was too large, excess NMP swelled with PVdF in the mixture layer during storage at high temperature and the mixture layer was peeled off. Disintegration occurs and deteriorates the battery characteristics after storage at high temperature.

On the other hand, in Samples 1 to 5, NMP was 0.1 with respect to the non-aqueous solvent in the gel electrolyte.
It is added in the range of more than 3% by weight, and the amount of NMP added to the non-aqueous solvent is appropriate. Therefore, decomposition of gel electrolyte, gas generation, and peeling of the mixture layer that occur during high temperature storage. The deterioration of the cycle characteristics after storage at high temperature is suppressed by suppressing the deterioration and the like.

From the above, the addition of NMP in the range of 0.1% by weight or more and 3% by weight or less with respect to the non-aqueous solvent in the gel electrolyte is a battery having excellent cycle characteristics after high temperature storage. It is very effective for manufacturing.

From the evaluation results shown in Table 1, the lithium carbonate content of the positive electrode active material is 0.05% by weight or more and 0.2% by weight or more.
It can be seen that Samples 1 to 5, which are contained in the following ranges, have better cycle characteristics after high temperature storage than Samples 8 and 9 in which lithium carbonate is not added to the positive electrode active material.

In Samples 8 and 9, since the positive electrode active material does not contain lithium carbonate, LiPF ₆ which is the electrolyte salt of the gel electrolyte is decomposed during storage at high temperature to generate hydrofluoric acid (HF). This HF deteriorates the battery element, gel electrolyte and the like.

From the evaluation results shown in Table 1, the lithium carbonate content was 0.05% by weight or more, 0.2% or more, based on the positive electrode active material.
In Samples 1 to 5 which are contained in the range of less than or equal to 5% by weight, 0.25% by weight of lithium carbonate is contained in the positive electrode active material.
It can be seen that the cycle characteristics after high-temperature storage are better than those of Samples 10 and 11 that contain the same.

In Samples 10 and 11, since the content of lithium carbonate in the positive electrode active material was too large, excess lithium carbonate was decomposed during high temperature storage and gas such as carbon dioxide was generated in the battery element. This gas is stored between the positive electrode and the negative electrode to increase the battery resistance and deteriorate the battery characteristics.

On the other hand, in Samples 1 to 5, 0.05 wt% or more of lithium carbonate was added to the positive electrode active material,
Since it is contained in the range of 0.2% by weight or less and the amount of lithium carbonate added to the positive electrode active material is appropriate, the cycle after high temperature storage is suppressed by suppressing the generation of HF and gas generated during high temperature storage. Deterioration of characteristics is suppressed.

From the above, the fact that lithium carbonate is contained in the range of 0.05 wt% to 0.2 wt% with respect to the positive electrode active material means that the battery has excellent cycle characteristics after high temperature storage. It is very effective for manufacturing.

[0077]

As is apparent from the above description, according to the present invention, N-methyl-2-pyrrolidone is added to the non-aqueous solvent of the non-aqueous electrolyte while the positive electrode active material contains lithium carbonate. As a result, the decomposition of the non-aqueous electrolyte and the generation of gas that occur during high-temperature storage are suppressed, so that a non-aqueous electrolyte battery having excellent high-temperature storage characteristics in which deterioration of the battery characteristics due to high-temperature storage is suppressed can be obtained.

[Brief description of drawings]

FIG. 1 shows an internal structure of a lithium-ion secondary battery according to the present invention, (a) is a perspective plan view showing a part of it, and (b) is a schematic sectional view.

FIG. 2 is a diagram for explaining a manufacturing process of the lithium-ion secondary battery and is a schematic perspective view showing a battery element.

FIG. 3 is a diagram for explaining a manufacturing process of the lithium-ion secondary battery, and is a schematic perspective view showing a state in which the battery element is housed in an exterior material.

FIG. 4 is a view for explaining the manufacturing process of the lithium-ion secondary battery and is a schematic perspective view showing a completed lithium-ion secondary battery.

[Explanation of symbols]

1 lithium-ion secondary battery, 2 positive electrode, 3 negative electrode, 4
Solid electrolyte, 5 Battery element, 6 Exterior material, 7 Positive electrode current collector, 8 Positive electrode mixture layer, 9 Positive electrode terminal, 10 Negative electrode current collector, 11 Negative electrode mixture layer, 12 Negative electrode terminal, 13 Resin piece

   ─────────────────────────────────────────────────── ─── Continued front page    (72) Inventor Akira Yamaguchi             1 Shimo-Sugishita, Takakura, Hiwada-cho, Koriyama City, Fukushima Prefecture             1 Sony Fukushima Co., Ltd. (72) Inventor Takeshi Okawa             1 Shimo-Sugishita, Takakura, Hiwada-cho, Koriyama City, Fukushima Prefecture             1 Sony Fukushima Co., Ltd. F-term (reference) 5H029 AJ00 AK02 AK03 AK05 AL06                       AL07 AL08 AL12 AM03 AM04                       AM05 AM07 AM16 BJ04 DJ08                       DJ09 EJ03 EJ11 HJ01                 5H050 AA10 BA16 BA17 BA18 CA07                       CA08 CA09 CA10 CA11 CB07                       CB08 CB09 CB12 DA09 DA13                       EA01 EA22 HA01

Claims (6)

[Claims] 1. A positive electrode having a positive electrode active material capable of lithium doping / dedoping and containing lithium carbonate, a negative electrode having a negative electrode active material capable of lithium doping / dedoping, and a chemical formula 1 A non-aqueous electrolyte battery comprising a non-aqueous solvent to which N-methyl-2-pyrrolidone is added and a non-aqueous electrolyte containing an electrolyte salt. [Chemical 1] 2. The non-aqueous electrolyte battery according to claim 1, wherein the content of the lithium carbonate is in the range of 0.05% by weight or more and 0.2% by weight or less with respect to the positive electrode active material. 3. The non-aqueous electrolyte battery according to claim 1, wherein the addition amount of the N-methyl-2-pyrrolidone is in the range of 0.1% by weight or more and 3% by weight or less with respect to the non-aqueous solvent. 4. A positive electrode having a positive electrode active material capable of lithium doping / dedoping, a negative electrode having a negative electrode active material capable of lithium doping / dedoping, and a non-aqueous solvent and an electrolyte salt-containing non-aqueous solvent. In a method for manufacturing a non-aqueous electrolyte battery including a water electrolyte, lithium carbonate is contained in the positive electrode active material,
A method for producing a non-aqueous electrolyte battery, comprising adding N-methyl-2-pyrrolidone represented by Chemical Formula 1 to the non-aqueous solvent. [Chemical 2] 5. The non-aqueous electrolyte according to claim 4, wherein the lithium carbonate is contained in the range of 0.05% by weight or more and 0.2% by weight or less with respect to the positive electrode active material. Battery manufacturing method. 6. The non-aqueous solution according to claim 4, wherein the N-methyl-2-pyrrolidone is added to the non-aqueous solvent in a range of 0.1% by weight or more and 3% by weight or less. Method for manufacturing electrolyte battery.