JP5031453B2 - Lithium secondary battery - Google Patents

Description

The present invention relates to a lithium secondary battery excellent in cycle characteristics and high-temperature discharge characteristics, for example, a thin and light lithium secondary battery capable of discharging even in a high-temperature environment of 140 ° C. or higher. By the way, according to the Japan Lighting Equipment Manufacturers Association JIL5501 “Emergency Lighting Equipment Technical Standards” established by the Ordinance for Enforcement of Fire Service Act and Building Standard Law, the lighting equipment for guide lights and emergency lights has an atmosphere of 140 ° C. A continuous light of 20 minutes or more is required for a guide light, and 30 minutes or more for an emergency light.
In this specification, the lithium ion secondary battery and the lithium polymer secondary battery may be collectively referred to as a lithium secondary battery.

In recent years, as electronic devices have become smaller and lighter, batteries having a high degree of freedom in shape have been demanded. Especially, the lithium ion secondary battery using a non-aqueous electrolyte is regarded as promising from the market as a battery having a high capacity and a low environmental load.
Lithium-ion secondary batteries consist of a positive electrode in which lithium cobaltate that can be occluded and released electrochemically is applied to an aluminum foil, and a negative electrode in which graphite that is capable of electrochemically occluded and released lithium ions is applied to a copper foil. Is made up of a separator made of porous polyolefin, a nonaqueous electrolytic solution in which a lithium salt is dissolved in an organic solvent, and a case for housing these.

In recent years, lithium polymer batteries in which the electrolyte of a lithium ion secondary battery is replaced from a liquid state to a solid state or a gel state have been increasing in order to increase safety.
By making the electrolyte into a gel, there is an advantage that no leakage occurs when there is an accident in the battery case.
The electrolyte of the lithium polymer battery is a mixture of the above-described organic electrolyte and polymer compound, which is solidified in a gel form. In general, two types of manufacturing methods have been put to practical use. .

The first production method (pre-impregnation) is, for example, ethylene carbonate in which a lithium salt having a high temperature is dissolved as described in Patent Document 1 [boiling point 248 ° C., flash point 143 ° C., viscosity 1.86 cP (40 ° C. )], A non-aqueous electrolyte composed of propylene carbonate (boiling point 241.7 ° C., flash point 132 ° C., 2.53 cP) and chain carbonate, polyvinylidene fluoride-hexafluoropropylene copolymer (hereinafter abbreviated as PVdF-HFP) There is a method in which after the solution is applied to the positive electrode and the negative electrode, the solution is gelled by cooling to room temperature, an electrode group is produced through a separator made of porous polyolefin, and then stored in a battery case.
In the second production method (post-impregnation), for example, as described in Patent Document 2, a positive electrode and a negative electrode are produced through a separator made of porous polyolefin, and are stored in a battery case. After injecting a monomer and a polymerization initiator dissolved in a non-aqueous electrolyte consisting of ethylene carbonate and chain carbonate at high temperature into the battery case, sealing the battery case, and then heating the monomer There is a method of polymerizing.

  In these production methods, chain carbonates have been mixed for the purpose of improving separator wettability and the like. This chain carbonate is a solvent having a low boiling point and flash point, such as diethyl carbonate (boiling point 126.8 ° C., flash point 25 ° C., viscosity 0.748 cP), dimethyl carbonate (boiling point 91 ° C., flash point 16 ° C.). , A viscosity of 0.59 cP) has been used.

JP 11-31536 A Japanese Patent Laid-Open No. 2001-110446

As one of the disaster prevention equipment in public facilities, it is obliged to install lighting equipment such as emergency lights and guide lights. This kind of lighting equipment is equipped with a secondary battery because it needs to be operated even during a power failure. Conventionally, a nickel cadmium secondary battery has been used for this secondary battery.
Recently, replacement of nickel metal hydride secondary batteries has been started for the purpose of environmental protection and miniaturization.

  Replacement with lithium secondary batteries has been attempted for further miniaturization, but conventional lithium ion secondary batteries and lithium polymer secondary batteries cannot be discharged at 120 ° C. Adoption was difficult. There are two main reasons why discharge at 120 ° C. is impossible. One is the shutdown of the separator, and the other is the boiling point of the electrolyte.

As for the separator, a conventional separator made of porous polyolefin uses polyethylene having a shutdown function at about 110 to 120 ° C. in order to increase safety at high temperatures. The shutdown function is a function that prevents the battery from being discharged at a certain temperature or higher.
However, in order to use it as a disaster prevention instrument, the temperature at which the shutdown function works needs to be higher than before. For this reason, the adoption of polypropylene having a shutdown function at about 160 to 170 ° C. has been studied, but when polypropylene is used as a separator, a non-aqueous solvent for the electrolyte that can wet the polypropylene requires a chain carbonate. It becomes.
However, chain carbonates that can be used as a non-aqueous solvent for a lithium secondary battery have a boiling point of 130 ° C. or less such as dimethyl carbonate, diethyl carbonate, and ethyl methyl carbonate. The electrode distance of the negative electrode is increased. As a result, in an environment of 140 ° C. or higher, there is a problem that the internal resistance increases and discharge cannot be performed.

In addition, in lithium ion secondary batteries, when the battery case is damaged or the electrolyte leaks, the electrolyte contains a corrosive component for the metal. However, there is a problem that the electronic device becomes unusable.
Even in the case of a lithium polymer secondary battery, when the battery case is damaged, external moisture reacts with the electrolyte little by little to generate corrosive gas, so the circuit of the electronic device is corroded by the corrosive gas and the electronic device is used. There was a problem of becoming impossible.

  An object of the present invention is to solve the above-mentioned problems and to provide a lithium secondary battery excellent in cycle characteristics and high-temperature discharge characteristics.

The inventor considered that the separator is made of polypropylene whose shutdown function operates at 160 to 170 ° C., but when made of polypropylene, the surface is very hydrophobic and the wettability of the non-aqueous electrolyte is poor. Faced a problem. Therefore, as a result of various studies to solve such problems, it is contained in an electrolytic solution mainly composed of ethylene carbonate and propylene carbonate in which an ester compound represented by the general formula [I] and a lithium salt are dissolved. As a result, the inventors have found that it is possible to wet a polypropylene separator. That is, by selecting a specific number of n in the carboxylic acid residue C _n H _{2n + 1} chain of the ester compound represented by the general formula [I], the wettability with polypropylene is improved, and the ester compound When a specific m number of the alcohol residue C _m H _{2m + 1} was selected, it was possible to arbitrarily mix with a non-aqueous solvent.
In addition, since the ester compound represented by the general formula [I] has a characteristic fragrance that can be used in a fragrance, it has been found that it can emit a scent and give an alarm when the battery case is broken. It was.

That is, the present invention is a lithium secondary battery comprising a positive electrode, a separator, a negative electrode, and an electrolyte layer, wherein the electrolyte layer is an ester compound of a fragrance component that can be aromad when the battery is broken, preferably under atmospheric pressure. A lithium secondary battery characterized by containing an ester compound having a boiling point of 140 ° C. or higher, more specifically an ester compound represented by the following general formula [I], preferably in a high temperature environment of 140 ° C. or higher The gist is a lithium secondary battery that can be discharged for 30 minutes or more.
(In the formula, n is an integer of 5 to 12, and m is an integer of 1 to 3.)

  The electrolyte layer is composed of a non-aqueous electrolyte solution, and the ester compound is contained in the non-aqueous electrolyte solution in an amount of 5% by weight or less. Preferably, a cyclic alkylene carbonate having 3 to 5 carbon atoms is used with the non-aqueous electrolyte solution as a solvent. That is, the present invention is a lithium secondary battery comprising a positive electrode, a separator, a negative electrode and an electrolyte layer, wherein the electrolyte layer is composed of a non-aqueous electrolyte solution, preferably a non-aqueous electrolyte solution. An ester compound of a fragrance component, which is composed of a cyclic alkylene carbonate having 3 to 5 carbon atoms as a solvent and can be fragrant when the battery is broken, preferably an ester compound having a boiling point of 140 ° C. or higher under atmospheric pressure More specifically, it is characterized in that the ester compound represented by the above general formula [I] is contained in the nonaqueous electrolytic solution in an amount of 5% by weight or less. Lithium secondary battery, preferably gist lithium secondary battery can be discharged under 140 ° C. to temperatures higher than 30 minutes or more.

  The electrolyte layer is composed of a non-aqueous gel electrolyte, and the ester compound is contained in the non-aqueous gel electrolyte in an amount of 10% by weight or less. That is, the present invention includes a positive electrode, a separator, a negative electrode, and an electrolyte layer. A lithium secondary battery, wherein the electrolyte layer is composed of a non-aqueous gel electrolyte, and is an ester compound of a fragrance component that can be aromad when the battery is broken, preferably 140 ° C. or higher under atmospheric pressure A lithium secondary battery, preferably 140, containing an ester compound having a boiling point of 10% by weight or less, more specifically, an ester compound represented by the above general formula [I] in a non-aqueous electrolyte solution. The gist of the present invention is a lithium secondary battery that can be discharged for 30 minutes or more in a high temperature environment of at least ° C.

  The separator is a porous polyolefin resin having a melting point of 140 ° C. or higher, preferably porous polypropylene, that is, the present invention is a lithium secondary battery comprising a positive electrode, a separator, a negative electrode and an electrolyte layer. , An ester compound of a fragrance component that allows the electrolyte layer to be fragranced when the battery is broken, preferably an ester compound having a boiling point of 140 ° C. or higher under atmospheric pressure, more specifically in the above general formula [I] A lithium secondary battery, preferably a high temperature environment of 140 ° C. or higher, characterized by containing the ester compound represented, and the separator is a porous polyolefin resin having a melting point of 140 ° C. or higher, preferably porous polypropylene The gist of the present invention is a lithium secondary battery that can be discharged for 30 minutes or more. Also in the present invention, the electrolyte layer is composed of a non-aqueous electrolyte solution, and the ester compound is contained in the non-aqueous electrolyte solution in an amount of 5% by weight or less, preferably having 3 to 5 carbon atoms using the non-aqueous electrolyte solution as a solvent. It includes an embodiment in which a cyclic alkylene carbonate is used, or an embodiment in which the electrolyte layer is composed of a non-aqueous gel electrolyte and the ester compound is contained in the non-aqueous gel electrolyte by 10% by weight or less.

ADVANTAGE OF THE INVENTION According to this invention, the lithium secondary battery which can be discharged at high temperature can be provided, without reducing a battery characteristic.
Moreover, it is possible to issue an alarm when the electrolyte layer contains an ester compound of a fragrance component that can be fragrant when the battery is broken.

  In the following, the best mode of the present invention will be described using an example of a non-aqueous electrolyte secondary battery. The best mode of the present invention is a non-aqueous electrolyte secondary battery using a positive electrode active material and a negative electrode material doped or dedoped with lithium, and an electrolyte layer (non-aqueous electrolyte or non-aqueous gel electrolyte). The nonaqueous electrolyte secondary battery is characterized in that an ester compound represented by the following general formula [I] is blended in the nonaqueous electrolytic solution.

(In the formula, n is an integer of 5 to 12, and m is an integer of 1 to 3.)

The ester compound represented by the general formula [I] has a unique fragrance as it is used as a perfume. Further, it is a compound having a boiling point of 140 ° C. or higher under atmospheric pressure (ethyl octoate: boiling point 208 ° C.). Furthermore, a polypropylene separator can be wetted by being contained in an electrolytic solution mainly composed of ethylene carbonate or propylene carbonate in which a lithium salt is dissolved. Further, by selecting a specific to m number of C m _H 2m _{+ 1,} it is possible to mix a non-aqueous solvent and optionally.

  The ester compound represented by the general formula [I] is methyl hexanoate, ethyl hexanoate, hexanoate (methyl ester, ethyl ester, propyl ester), methyl heptanoate, ethyl heptanoate, methyl octanoate, ethyl octanoate, Examples include methyl nonanoate, ethyl nonanoate, methyl decanoate, ethyl undecanoate, ethyl undecanoate, methyl dodecanoate, ethyl dodecanoate, methyl tridecanoate, and ethyl tridecanoate.

The ester compound represented by the general formula [I] is added in an amount of 0.5 to 5% by weight, preferably 1 to 3% by weight in the total amount of the electrolyte layer (non-aqueous electrolyte or non-aqueous gel electrolyte). From the point of view of the fragrance, the function is exhibited even in the presence of a trace amount, but it is preferably 0.5% by weight or more from the viewpoint of wetting of the polypropylene separator with respect to the non-aqueous electrolyte or non-aqueous gel electrolyte. Beyond%, it is not economically advantageous.

[Separator]
A separator for a non-aqueous electrolyte secondary battery will be described as an example of a known separator for a non-aqueous electrolyte secondary battery.
The thermoplastic resin as the base resin of the thermoplastic resin composition constituting the separator is particularly preferably a polyolefin resin because of its excellent balance of heat resistance, solvent resistance and flexibility. In the present invention, it is preferable to use polypropylene among the polyolefin resins. As a filler contained in the thermoplastic resin composition constituting the separator, an inorganic filler having a property of not decomposing a non-aqueous electrolyte used in a lithium secondary battery is selected. The blending amount of the filler is preferably 20 to 30% by volume in the thermoplastic resin composition containing the thermoplastic resin and the filler. If the blending amount of the filler is extremely small, for example, less than 10% by volume, it is difficult to form a communication hole, and it becomes difficult to develop a function as a separator. Further, if the amount is extremely large, for example, exceeding 50% by volume, the viscosity at the time of film forming becomes high and the processability is inferior, and the film may be broken at the time of stretching for porous formation. If necessary, the thermoplastic resin composition may further contain other additives such as a low molecular weight compound and a heat stabilizer. The additive is not particularly limited as long as it is a known additive.

The microporous membrane made of polypropylene is a known one and contains polypropylene as an essential component, and it is preferable that polypropylene is the main matrix.
As the polypropylene, one type or a plurality of polypropylenes can be used. Examples of the polypropylene to be used include homopolymers, random copolymers, and block copolymers, but the comonomer (usually ethylene) content in all the polypropylenes used is preferably 1 mol% or less, and is a homopolymer polypropylene. preferable. There are no particular limitations on the polypropylene polymerization catalyst used, and examples include Ziegler-Natta catalysts and metallocene catalysts.

The pore clogging temperature of the polypropylene microporous membrane is preferably 140 ° C. or higher from the viewpoint of preventing heat clogging in the heat drying step during battery assembly and in the normal use state of the battery, and 170 from the viewpoint of pore clogging properties during abnormal battery reaction. C. or lower is preferable. More preferably, it is 145-165 degreeC. The membrane breaking temperature of the polypropylene microporous membrane is improved to 190 ° C. to 300 ° C. even under a high temperature heating condition of 20 ° C./min. By having a high membrane breaking temperature, the possibility of thermal runaway can be significantly reduced in a battery incorporating a polypropylene microporous membrane.
The polypropylene microporous membrane is kept in an oven at 150 ° C. for 1 hour with MD (longitudinal direction of the microporous membrane, ie, machine direction) fixed and TD (direction perpendicular to the machine direction) fixed. It is characterized by not rupturing even after having been. As a result, the oven safety of a battery incorporating a polypropylene microporous membrane is significantly improved over conventional products such as polyethylene.

[Non-aqueous electrolyte secondary battery]
The non-aqueous electrolyte secondary battery of the present invention includes a positive electrode capable of occluding and releasing lithium ions, a negative electrode capable of occluding and releasing lithium ions, a non-aqueous electrolyte containing a non-aqueous solvent and a lithium salt, and And a non-aqueous electrolyte secondary battery separator made of polypropylene.

(1) Non-aqueous electrolyte a) Non-aqueous solvent As the non-aqueous solvent of the electrolyte used in the non-aqueous electrolyte secondary battery of the present invention, a known cyclic alkylene carbonate as a solvent for the non-aqueous electrolyte secondary battery. Is used. Examples of the cyclic alkylene carbonate include ethylene carbonate, propylene carbonate, 1,2-butylene carbonate, 2,3-butylene carbonate, 1,3-propylene carbonate, 1,3-butylene carbonate, etc., but ethylene carbonate (boiling point 248). C), cyclic alkylene carbonates (alkylene carbonates having 3 to 5 carbon atoms) such as alkylene carbonates such as propylene carbonate (boiling point 242 ° C.) and butylene carbonate (boiling point 240 ° C.).
These may be used alone or in combination of two or more. A non-aqueous solvent using a cyclic carbonate is preferable from the viewpoint of improving overall battery performance such as charge / discharge characteristics and battery life. Moreover, it is preferable to mix | blend this non-aqueous solvent so that a cyclic carbonate may become 70 volume% or more of the whole non-aqueous solvent. Furthermore, the non-aqueous solvent may contain a solvent other than the cyclic carbonate as long as the battery performance of the manufactured lithium battery is not deteriorated. The proportion of the solvent other than the cyclic carbonate in the non-aqueous solvent is usually 30% by volume or less, preferably 10% by volume or less.

B) Lithium salt Any lithium salt that is a solute of the non-aqueous electrolyte can be used. For example, inorganic lithium salts such as LiClO ₄ , LiPF ₆ , LiBF ₄ ; LiCF ₃ SO ₃ , LiN (CF ₃ SO ₂ ) ₂ , LiN (C ₂ F ₅ SO ₂ ) ₂ , LiN (CF ₃ SO ₂ ) (C _{4 F9SO 2), LiC (CF} 3 SO 2) 3, LiPF 4 (CF 3) 2, LiPF 4 (C 2 F 5) 2, LiPF 4 (CF 3 SO 2) 2, LiPF 4 (C 2 F 5 SO _{2) 2, LiBF 2 (CF} 3) 2, LiBF 2 (C 2 F 5) 2, LiBF 2 (CF 3 SO 2) 2, LiBF 2 (C 2 F 5 SO 2) 2 fluorine-containing organic lithium salt such as Etc. Of these, fluorine-containing organic lithium salts such as LiPF ₆ , LiBF ₄ , LiCF ₃ SO ₃ , LiN (CF ₃ SO ₂ ) ₂ , and LiN (C ₂ F ₅ SO ₂ ) ₂ , particularly LiPF ₆ and LiBF ₄ are preferable. . In addition, about lithium salt, 1 type may be used independently and 2 or more types may be used together.

  The lower limit of the concentration of these lithium salts in the non-aqueous electrolyte is usually 0.5 mol / l or more, especially 0.75 mol / l or more, and the upper limit is usually 2 mol / l or less, especially 1.5 mol / l. l or less. If the concentration of the lithium salt exceeds this upper limit, the viscosity of the non-aqueous electrolyte increases and the lithium ion conductivity decreases. Moreover, since lithium ion conductivity will become low if less than a lower limit, it is preferable to prepare a non-aqueous electrolyte within the said concentration range.

  In addition to the non-aqueous solvent and the lithium salt, the non-aqueous electrolyte includes various other useful components as necessary, such as conventionally known overcharge inhibitors, dehydrating agents, deoxidizing agents, positive electrode protecting agents, and the like. An agent may be included.

(2) Positive electrode As a positive electrode, what formed the active material layer containing a positive electrode active material and a binder on a collector normally is used. The positive electrode active material is not particularly limited as long as it can electrochemically occlude and release lithium ions. Preferable examples include lithium transition metal composite oxides.

Specific examples of lithium transition metal composite oxides include lithium / cobalt composite oxides such as LiCoO ₂ , lithium / nickel composite oxides such as LiNiO _2, and lithium / manganese composite oxides such as LiMnO ₂ and LiMn ₂ O _4. Is mentioned. In these lithium transition metal composite oxides, some of the main transition metal atoms are Al, Ti, V, Cr, Mn, Fe, Co, Li, Ni, Cu, Zn, Mg, Ga, Zr, Si, etc. Replacing with other metals is preferable because it can be stabilized. Any one of these positive electrode active materials may be used alone, or two or more thereof may be used in any combination and ratio.

  The binder is not particularly limited as long as it is a material that is stable with respect to the solvent and electrolyte used during electrode production and other materials used during battery use. Specific examples thereof include polyvinylidene fluoride, polytetrafluoroethylene, fluorinated polyvinylidene fluoride, EPDM (ethylene-propylene-diene terpolymer), SBR (styrene-butadiene rubber), NBR (acrylonitrile-butadiene rubber), Examples thereof include fluororubber, polyvinyl acetate, polymethyl methacrylate, polyethylene, and nitrocellulose. These may be used individually by 1 type, or may use multiple types together.

  As for the ratio of the binder in the positive electrode active material layer, the lower limit is usually 0.1% by weight or more, preferably 1% by weight or more, more preferably 5% by weight or more, and the upper limit is usually 80% by weight or less, preferably 60% by weight or less, more preferably 40% by weight or less, and still more preferably 10% by weight or less. If the proportion of the binder is small, the active material cannot be sufficiently retained, so that the mechanical strength of the positive electrode is insufficient, and the battery performance such as cycle characteristics may be deteriorated. On the contrary, if the amount is too large, the battery capacity and conductivity are lowered. It will be.

  The positive electrode active material layer usually contains a conductive agent in order to increase conductivity. Examples of the conductive agent include carbonaceous materials such as graphite fine particles such as natural graphite and artificial graphite, carbon black such as acetylene black, and amorphous carbon fine particles such as needle coke. These may be used individually by 1 type, or may use multiple types together.

  The ratio of the conductive agent in the positive electrode active material layer is such that the lower limit is usually 0.01% by weight or more, preferably 0.1% by weight or more, more preferably 1% by weight or more, and the upper limit is usually 50% by weight or less. , Preferably 30% by weight or less, more preferably 15% by weight or less. If the proportion of the conductive agent is small, the conductivity may be insufficient, and conversely if too large, the battery capacity may be reduced.

  In addition, the positive electrode active material layer can contain additives for a normal active material layer such as a thickener. The thickener is not particularly limited as long as it is a material that is stable with respect to the solvent and electrolyte used during electrode production and other materials used during battery use.

  Aluminum, stainless steel, nickel-plated steel or the like is used for the current collector of the positive electrode.

  The positive electrode can be formed by applying a slurry obtained by slurrying the above-described positive electrode active material, a binder, a conductive agent, and other additives added as necessary with a solvent onto a current collector, and drying the positive electrode active material. . As the solvent used for slurrying, an organic solvent that dissolves the binder is usually used. For example, N-methylpyrrolidone, dimethylformamide, dimethylacetamide, methyl ethyl ketone, cyclohexanone, methyl acetate, methyl acrylate, diethyltriamine, N, N-dimethylaminopropylamine, ethylene oxide, tetrahydrofuran and the like are used, but not limited thereto. These may be used individually by 1 type, or may use multiple types together.

  Thus, the thickness of the positive electrode active material layer formed is about 10-200 micrometers normally. The active material layer obtained by coating and drying is preferably consolidated by a roller press or the like in order to increase the packing density of the active material.

(3) Negative electrode As the negative electrode, a material in which an active material layer containing a negative electrode active material and a binder is usually formed on a current collector is used.

  As a negative electrode active material, a carbonaceous material capable of occluding / releasing lithium such as organic pyrolysate, artificial graphite and natural graphite under various pyrolysis conditions; capable of occluding / releasing lithium such as tin oxide and silicon oxide Metal oxide material; lithium metal; various lithium alloys can be used. These negative electrode active materials may be used individually by 1 type, and may mix and use 2 or more types.

  The binder is not particularly limited as long as it is a material that is stable with respect to the solvent and electrolyte used during electrode production and other materials used during battery use. Specific examples thereof include polyvinylidene fluoride, polytetrafluoroethylene, styrene-butadiene rubber, isoprene rubber, butadiene rubber and the like. These may be used individually by 1 type, or may use multiple types together.

  The ratio of the binder in the negative electrode active material layer is such that the lower limit is usually 0.1% by weight or more, preferably 1% by weight or more, more preferably 5% by weight or more, and the upper limit is usually 80% by weight or less. Preferably it is 60 weight% or less, More preferably, it is 40 weight% or less, More preferably, it is 10 weight% or less. If the ratio of the binder is small, the active material cannot be sufficiently retained, so that the negative electrode mechanical strength may be insufficient, and the battery performance such as cycle characteristics may be deteriorated. become.

  In addition, the negative electrode active material layer may contain additives for a normal active material layer such as a thickener. The thickener is not particularly limited as long as it is a material that is stable with respect to the solvent and electrolyte used during electrode production and other materials used during battery use. Specific examples thereof include carboxymethyl cellulose, methyl cellulose, hydroxymethyl cellulose, ethyl cellulose, polyvinyl alcohol, oxidized starch, phosphorylated starch, and casein. These may be used individually by 1 type, or may use multiple types together.

  Copper, nickel, stainless steel, nickel-plated steel, or the like is used for the negative electrode current collector.

  The negative electrode can be formed by applying a slurry obtained by slurrying the above-described negative electrode active material, a binder, and other additives added as necessary with a solvent, and then drying the current collector. As the solvent used for slurrying, an organic solvent that dissolves the binder is usually used. For example, N-methylpyrrolidone, dimethylformamide, dimethylacetamide, methyl ethyl ketone, cyclohexanone, methyl acetate, methyl acrylate, diethyltriamine, N, N-dimethylaminopropylamine, ethylene oxide, tetrahydrofuran and the like are used, but not limited thereto. These may be used individually by 1 type, or may use multiple types together. Moreover, a dispersing agent, a thickener, etc. can be added to water, and an active material can also be slurried with latex, such as SBR.

  Thus, the thickness of the negative electrode active material layer formed is about 10-200 micrometers normally. The active material layer obtained by coating and drying is preferably consolidated by a roller press or the like in order to increase the packing density of the active material.

(4) Battery configuration The non-aqueous electrolyte secondary battery of the present invention is manufactured by assembling the above-described positive electrode, negative electrode, non-aqueous electrolyte, and separator into an appropriate shape. Furthermore, other components such as an outer case can be used as necessary.

  The battery shape is not particularly limited, and can be appropriately selected from various commonly used shapes according to the application. Examples of commonly used shapes include a cylinder type with a sheet electrode and separator spiral, an inside-out cylinder type with a combination of pellet electrode and separator, a coin type with a stack of pellet electrode and separator, and a sheet Examples include a laminate type in which electrodes and separators are laminated. The method for assembling the battery is not particularly limited, and can be appropriately selected from various commonly used methods according to the shape of the target battery.

As one embodiment of the battery of the present invention, a single cell made of a positive electrode, a negative electrode, and a separator, which is a plate-shaped unit battery element, is laminated and enclosed in a polymer-metal composite laminate film bag. FIG. 1 shows an example of the structure of a single cell. A current collector is an aluminum foil, and a positive electrode made by impregnating a transition metal lithium oxide (LiCoO ₂ or the like) with a gel electrolyte on the lower side. A separator made of a porous polymer film under the gel electrolyte solution, a negative electrode made of graphite impregnated with a gel electrolyte solution underneath, and a copper collector as the bottom Has a foil. Although the positive electrode is positioned as a battery element on the upper side in the drawing, the negative electrode may be positioned.
In addition, this invention can be applied also to the winding type battery which wound the electrode group on a thin plate in the shape of a spiral, and can also be applied to the lithium secondary battery which does not gelatinize electrolyte solution.

  The battery of the present invention is configured by stacking a plurality of single cells in a housing. The housing is a container in which a container (for example, a pouch) is constituted by a laminate film in which a polymer and a metal are combined, and a battery laminated inside can be vacuum-sealed. Encapsulation is performed mainly by heat-sealing polyolefin films. By using the laminate container, the external potential becomes neutral, and the safety at the time of crash can be further increased.

In the present invention, the unit battery element in which the positive electrode plate, the separator, and the negative electrode plate are laminated is configured in the same manner as the conventional unit battery element. For example, the positive electrode plate is formed by applying and drying the above-described positive electrode active material on one side of the reaction part of the positive electrode current collector, and the negative electrode plate is formed by applying and drying the negative electrode active material as described above on both sides of the reaction part of the negative electrode current collector. Thus, the separator can be exemplified by a polyolefin porous film. Further, a positive electrode current collector is formed on the positive electrode plate, and a negative electrode current collector is formed on the negative electrode plate, and these are joined to the positive electrode terminal lead and the negative electrode terminal lead by ultrasonic welding or the like. This joining may be performed by resistance welding. However, the unit cell element of the present invention is not limited to these.
The general embodiment of the non-aqueous electrolyte secondary battery of the present invention has been described above, but the non-aqueous electrolyte secondary battery of the present invention is not limited to the above-described embodiment and does not exceed the gist thereof. As long as it is possible, various modifications can be made.

  Hereinafter, details of the present invention will be described with reference to examples, but the present invention is not limited to the examples.

[Example 1]
(Preparation of pre-curing electrolyte composition)
In a polyethylene container, 500 g of tetraethylene glycol diacrylate and 50 g of molecular sieve 4A (manufactured by Wako Pure Chemical Industries, Ltd.) were placed and allowed to stand at 5 ° C. for 14 days. Tetraethylene glycol diacrylate thus dehydrated 7% by weight, Sollite (Mitsubishi Chemical Co., Ltd., LiPF ₆ dissolved in an equal weight mixed solution of propylene carbonate and ethylene carbonate to a concentration of 1.3 mol / L) 93 Weight percent, Trigonox 23-C70 (manufactured by Kayaku Akzo) 0.2 weight percent was weighed into an Erlenmeyer flask and mixed in an inert atmosphere. This is referred to as a base electrolyte.
To this base electrolyte, ethyl hexanoate, ethyl heptanoate, and ethyl octanoate, which are chain esters, were added at the composition ratio shown in Table 1.

(Separator impregnation test)
In the lithium ion secondary battery and the lithium polymer secondary battery, it is essential that the separator is an electrolytic solution that gets wet.
This time, the impregnation test was performed for the wettability test of the separator with the pre-curing electrolyte containing the chain ester prepared in Table 1.
The test method was evaluated by the transparency of the separator when a polyethylene separator and a polypropylene separator were immersed in the electrolyte before curing shown in Table 1 for 30 seconds and pulled up.
It was found that the polyethylene ester-containing pre-curing electrolyte shown in Table 1 can wet the polyethylene separator.
From Table 1, only the pre-curing electrolyte containing ethyl octoate was able to wet the polypropylene separator.
With the pre-curing electrolyte (No. D) having no chain ester, neither polyethylene nor polypropylene separator could be wetted.

(Manufacture of positive electrode)
92% by weight of LiCoO ₂ (produced by Honjo Chemical Co., Ltd.) as the positive electrode active material, 4% by weight of acetylene black (produced by Denki Kagaku Kogyo) as the conductive material, and 4% of polyvinylidene fluoride (produced by Kureha Chemical) as the binder. % By weight and further 80% by weight of N-methylpyrrolidone as a solvent were mixed, and kneaded and dispersed in a sand mill for 0.5 hours. This mixture was applied onto an aluminum foil having a thickness of 15 μm using a doctor blade, dried at 120 ° C. to remove the solvent, and then a calendar process was added to produce a positive electrode having a thickness of about 80 μm.

(Manufacture of negative electrode)
A sand mill was mixed with 92% by weight of graphite (made by Osaka Gas Co., Ltd.), 8% by weight of polyvinylidene fluoride (made by Kureha Chemical), and 80% by weight of N-methylpyrrolidone as a solvent. The mixture was kneaded and dispersed for 0.5 hour. This mixture was applied onto a copper foil having a thickness of 10 μm using a doctor blade, dried at 120 ° C. to remove the solvent, and then a calendar process was added to produce a negative electrode having a thickness of about 80 μm.

(Production of battery 1: B-1)
Pre-curing electrolyte composition (A) in Table 1 on positive electrode (vertical 60 mm × horizontal 63 mm single-sided electrode), polypropylene separator (vertical 64 × horizontal 68, Celgard 2500, manufactured by Celgard), negative electrode (vertical 61 mm × horizontal 64 mm single-sided electrode) -5) is applied and impregnated in the active material layer, and then sandwiched between the positive electrode and the negative electrode, and cured by heating at 90 ° C. for 5 minutes to form a positive electrode / polymer gel electrolyte / porous membrane / polymer gel electrolyte / A unit cell having a negative electrode as one unit was produced. After stacking 26 sets of these, a lead for current extraction was attached and housed in an aluminum laminate case to produce a 2200 mAh battery.

(Initial charge / discharge)
i) Charging The battery was constant current charged to 4.2 V at 440 mA, which is 1/5 of the battery capacity (hereinafter referred to as 1/5 C), and constant voltage charged at 4.2 V. The charge termination condition was 8 hours from the start of charging.
ii) Discharge A constant current was discharged to 3.0V at 1 / 5C. A battery for which a capacity of 2100 mAh or more was confirmed in this initial charge / discharge test was regarded as a non-defective battery and subsequently a test evaluation battery.

(Cycle test)
The battery was charged at a constant current up to 4.2 V at 2200 mA, which is a current of 2200 mAh (hereinafter referred to as 1C), and was charged at a constant voltage at 4.2 V. The charge termination condition was 2.5 hours from the start of charging. The discharge was a constant current discharge to 3.0V at 1C. This operation was repeated 400 times. The capacity retention rate was obtained by dividing the capacity after 400 times by the theoretical capacity (2200 mAh). The atmospheric temperature of the cycle test was tested at 25 ° C. ± 3 ° C.
The test results are shown in Table 2. From Table 2, the capacity retention rate after 400 times of the battery of Example 1 was 85%.

(High temperature discharge test)
The battery was constant-current charged to 4.2 V at 440 mA, which is a current of 1/5 of the battery capacity (hereinafter referred to as 1/5 C), and constant voltage charged at 4.2 V. The charge termination condition was 8 hours from the start of charging.
The charged battery was heated and reached 140 ° C., and then discharged at 1 C while being maintained at 140 ° C.
The test results are shown in Table 2. From Table 2, the capacity retention rate at 140 ° C. of the battery of Example 1 was 70%.

[Example 2]

(Production of battery 2: B-2)
A battery was prepared and evaluated in the same manner except that the pre-curing electrolyte composition (A-5) of battery preparation 1 was changed to A-6.
The test results are shown in Table 2. From Table 2, the capacity retention rate after 400 times of the battery of Example 2 was 88%. Further, the capacity retention rate at 140 ° C. was 75%.
[Comparative Example 1]

(Production of battery 3: B-3)
A battery was prepared and evaluated in the same manner except that the separator of battery preparation 1 was polyethylene (length 64 × width 68, manufactured by Asahi Kasei Corporation).
The test results are shown in Table 2. From Table 2, the capacity retention rate after 400 times of the battery of Comparative Example 1 was 88%. Moreover, discharge at 140 ° C. was impossible. The reason is that the separator shut down at a high temperature.
[Comparative Example 2]

(Production of battery 4: B-4)
A battery was prepared and evaluated in the same manner except that the separator of battery preparation 2 was polyethylene (length 64 × width 68, manufactured by Asahi Kasei Corporation).
The test results are shown in Table 2. From Table 2, the capacity retention rate after 400 times of the battery of Comparative Example 2 was 89%. Moreover, discharge at 140 ° C. was impossible. The reason is that the separator has shut down at a high temperature.
[Example 3]

(Odor test when battery case is damaged)
A hole was made in the aluminum laminate of discharged batteries B-1, B-2, B-3, and B-4, and it was confirmed whether or not there was an odor. As a result, all of these batteries smelled and it was clear from the smell that there was a hole. On the other hand, the batteries without holes did not smell.

  According to the present invention, not only can the battery be miniaturized, but also the damage can be grasped by the scent and can be discharged at 140 ° C. or higher for 30 minutes or more. It is expected that their installation will be promoted by using them for guide lights.

It is the figure which showed an example of the single cell structure of the battery which concerns on this invention.

Explanation of symbols

1 Positive electrode 2 Negative electrode 3 Aluminum foil (current collector)
4 transition metal lithium oxide (LiCoO ₂ ) + gel electrolyte 5 porous polymer film (separator) + gel electrolyte 6 graphite + gel electrolyte 7 copper foil (current collector)

Claims (4)

A lithium secondary battery comprising a positive electrode, a separator, a negative electrode and an electrolyte layer and capable of discharging for 30 minutes or more in a high temperature environment of 140 ° C. or higher , wherein the separator is a porous polyolefin resin having a melting point of 140 ° C. or higher; In addition, the electrolyte layer is composed of a non-aqueous electrolyte solution or a non-aqueous gel electrolyte, and an ester compound represented by the following general formula [I] as a fragrance component that can be fragranced when the battery is broken is used as a non-aqueous electrolyte solution. A lithium secondary battery comprising 5% by weight or less or 10% by weight or less in a non-aqueous gel electrolyte .



(In the formula, n is an integer of 5 to 12, and m is an integer of 1 to 3.)   The lithium secondary battery according to claim 1, wherein the ester compound is a compound having a boiling point of 140 ° C. or higher under atmospheric pressure. The lithium secondary battery according to claim 1 or 2 , wherein a cyclic alkylene carbonate having 3 to 5 carbon atoms is used as a solvent of the non-aqueous electrolyte solution. The lithium secondary battery according to claim 1, 2 or 3 wherein the porous polyolefin resin is a porous polypropylene.