JP4395071B2 - Nonaqueous electrolyte for nonaqueous electrolyte secondary battery and nonaqueous electrolyte secondary battery - Google Patents

Description

The present invention relates to a non-aqueous electrolyte for a non-aqueous electrolyte secondary battery and a non-aqueous electrolyte secondary battery including the non-aqueous electrolyte.

  In recent years, electronic devices such as mobile communication devices, notebook computers, palmtop computers, integrated video cameras, portable CD (MD) players, cordless telephones, etc. have been reduced in size and weight. As a power source, a battery having a small size and a large capacity is required.

  Examples of batteries that are widely used as power sources for these electronic devices include primary batteries such as alkaline manganese batteries, and secondary batteries such as nickel cadmium batteries and lead storage batteries. Among these, non-aqueous electrolyte secondary batteries that use lithium composite oxide for the positive electrode and carbonaceous materials that can occlude and release lithium ions for the negative electrode are small and light, have high unit cell voltage, and have high energy density. Is attracting attention.

  In recent years, as a container for storing an electrode group including a positive electrode and a negative electrode as described above, a laminate film obtained by bonding a metal foil such as aluminum and a resin and molded into a bag shape or a cup shape is used. As a result, the weight and size of the nonaqueous electrolyte secondary battery can be further reduced.

  In a non-aqueous electrolyte secondary battery using a container made of this laminate film, it is desirable that the non-aqueous electrolyte used satisfies the following conditions. First of all, because of the high flexibility of the container, if gas is generated due to a decomposition reaction or the like inside the battery, the container may be greatly deformed, and as a non-aqueous electrolyte, the charged state, that is, the state where the potential of the positive electrode is high However, it must be such that no electrochemical decomposition occurs. Secondly, when a container made of a laminate film is used, it is difficult to provide a mechanism such as a shutoff valve or safety valve. As a non-aqueous electrolyte, an exothermic reaction occurs even in abnormal usage conditions such as overcharging. It is desirable that it is difficult.

For this reason, γ-butyrolactone (GBL), which does not easily cause a gas generation reaction due to decomposition and does not easily generate an exothermic reaction even in an overcharged state, has high conductivity and a high boiling point. It has been studied to use a mixture of cyclic carbonates such as lithium tetrafluoroborate (LiBF ₄ ) which does not easily cause an exothermic reaction as a non-aqueous solvent. For example, Japanese Laid-Open Patent Publication No. 11-31525 (Patent Document 1) discloses a lithium secondary battery in which a lithium transition metal oxide is used for a positive electrode, a graphite-based material is used for a negative electrode, and an electrolytic solution is an organic electrolytic solution in which a lithium salt is dissolved. It is described that a solvent having a composition containing γ-butyrolactone as a main component and at least ethylene carbonate as a subcomponent is used as a solvent of an organic electrolyte.

  However, the secondary battery having such a configuration is not sufficiently safe at the time of abnormal overcharging due to a failure of the charger or the like. That is, when the positive electrode potential becomes 4.7 V or more with respect to metallic lithium due to overcharge, the decomposition reaction of GBL occurs at the positive electrode, and the exothermic reaction accompanying this reaction gradually proceeds. When overcharge progresses and the positive electrode potential (potential with respect to metallic lithium) exceeds 5.0 V, the decomposition reaction proceeds rapidly, and the temperature of the secondary battery rises due to the heat generated by this reaction. As a result, the decomposition reaction is further accelerated, so that a thermal runaway state occurs and there is a risk of ignition in severe cases.

Incidentally, JP-A-7-302614 (Patent Document 2) relates to an overcharge prevention technique using a redox shuttle. Table 5 of Example 3 in paragraph (0053) shows a redox potential of 4.8. A benzene derivative of about ~ 4.9V is described.

  Although these benzene derivatives can suppress the decomposition reaction of GBL because the overcharge current is consumed by the redox shuttle reaction, it does not stop the function of the battery, and the exothermic reaction accompanying the decomposition reaction continuously occurs. Risk of thermal runaway.

Japanese Patent Laid-Open No. 9-50822 (Patent Document 3) is an invention aimed at promptly interrupting current during overcharge by utilizing an exothermic reaction accompanying an oxidation reaction of a benzene compound. In the examples of this publication, a benzene compound having a heat generation start voltage in the range of 4.45 V to 4.75 V is described. It has been shown that

  However, since the heat generation due to the oxidation reaction of the benzene compound is almost completed before the heat generation due to the decomposition reaction of GBL starts, current interruption cannot be performed quickly when GBL is used.

On the other hand, JP 2000-156243 A (Patent Document 4) discloses a reversible oxidation-reduction potential in a non-aqueous electrolyte solution to a battery potential nobler than a positive electrode potential at the time of full charge of the non-aqueous electrolyte battery. It is described that by adding an organic compound having an organic compound, an oxidative decomposition reaction of a solvent generated in an overcharged state is promoted by the organic compound, and an overcharge current is cut off using heat generated by the chemical reaction. .

  However, since the calorific value obtained when the decomposition reaction of GBL is promoted by the organic compound is not sufficient to cut off the overcharge current, the current is not cut off quickly, and thermal runaway occurs due to the decomposition reaction of GBL. High risk.

JP-A-11-329496 (Patent Document 5) discloses fluorinated benzene, fluorine atoms and fluorine as described in paragraph 0026 as fluorine-containing aromatic compounds having a fluorine atom and an aromatic ring. Examples include those having a substituted alkyl group, those containing a fluorine atom and a carbonyl group, ether fluorides, fluorides of aromatic amines, those having a fluorine atom and a cyano group, and fluorine-containing phosphate esters. These fluorine-containing aromatic compounds are physically safe, difficult to be pyrolyzed, flame retardant, and not susceptible to electrochemical oxidation / reduction (described in paragraph 0028). By using a non-aqueous electrolyte consisting of a non-aqueous solvent containing an aromatic compound and an electrolyte, the reaction rate between the positive electrode and the non-aqueous electrolyte is suppressed, and an exothermic reaction occurs. It has been described to suppress.

  Use of the fluorine-containing aromatic compound reduces the amount of heat generated during overcharging, but delays the operation of the current interrupting mechanism by the separator, which increases the time during which the overcharge current flows and may lead to thermal runaway. There is.

Furthermore, JP 2001-256996 A (Patent Document 6) includes 20 to 60% by volume of ethylene carbonate, 20 to 70% by volume of dialkyl carbonate, and 5 to 30% by volume of a fluorinated toluene compound. It is described that by using an organic electrolyte solution containing an organic solvent, an increase in the internal pressure of the battery when left at a high temperature for a long time is suppressed.

  Since the oxidative decomposition potential of each of ethylene carbonate and dialkyl carbonate contained in the organic electrolyte is higher than the oxidative decomposition potential of the fluorinated toluene compound, the secondary battery including the organic electrolyte is overcharged. Then, only the fluorinated toluene compound is oxidatively decomposed first. The amount of heat generated by this oxidative decomposition is insufficient to operate the separator's current interrupt mechanism, so the overcharge current continues to flow without the current interrupt mechanism being activated, leading to the risk of thermal runaway. There is sex.

Japanese Patent Laid-Open No. 11-31525 JP-A-7-302614 Japanese Laid-Open Patent Publication No. 9-50822 JP 2000-156243 A Japanese Patent Laid-Open No. 11-329496 JP 2001-256996 A

The present invention provides a non-aqueous electrolyte for a non-aqueous electrolyte secondary battery that is excellent in both high temperature storage characteristics and overcharge safety, and a non-aqueous electrolyte secondary battery that satisfies both high temperature storage characteristics and overcharge safety. An object is to provide a battery.

A nonaqueous electrolyte for a nonaqueous electrolyte secondary battery according to the present invention is a nonaqueous electrolyte for a nonaqueous electrolyte secondary battery containing a nonaqueous solvent and an electrolyte dissolved in the nonaqueous solvent,
The non-aqueous solvent includes at least one kind of halogenated toluene selected from the group consisting of chlorotoluene (CT) and orthofluorotoluene (o-FT), γ-butyrolactone (GBL), and cyclic carbonate, the GBL of the non-aqueous solvent, the halogenated toluene and the cyclic ratio of carbonate respectively x (mass%), y (mass%), the upon the z (mass%) x, wherein y And z satisfies 40 ≦ x ≦ 80, 0.1 ≦ y ≦ 15, 19.9 ≦ z ≦ 59.9, and x + y + z ≦ 100,
The electrolyte is characterized in that it contains 50 mass% or more as a percentage of the total mass of the LiBF ₄ the electrolyte.

A non-aqueous electrolyte secondary battery according to the present invention is a non-aqueous electrolyte secondary battery comprising a positive electrode, a negative electrode, and a non-aqueous electrolyte containing a non-aqueous solvent and an electrolyte dissolved in the non-aqueous solvent. ,
The non-aqueous solvent includes at least one kind of halogenated toluene selected from the group consisting of chlorotoluene (CT) and orthofluorotoluene (o-FT), γ-butyrolactone (GBL), and cyclic carbonate, the GBL of the non-aqueous solvent, the halogenated toluene and the cyclic ratio of carbonate respectively x (mass%), y (mass%), the upon the z (mass%) x, wherein y And z satisfies 40 ≦ x ≦ 80, 0.1 ≦ y ≦ 15, 19.9 ≦ z ≦ 59.9, and x + y + z ≦ 100,
The electrolyte is characterized in that it contains 50 mass% or more as a percentage of the total mass of the LiBF ₄ the electrolyte.

A non-aqueous electrolyte secondary battery according to the present invention includes a positive electrode, a negative electrode, a separator interposed between the positive electrode and the negative electrode, a non-aqueous solvent and an electrolyte dissolved in the non-aqueous solvent. It comprises. The non-aqueous solvent includes at least one kind of halogenated toluene selected from the group consisting of toluene chloride {chlorotoluene (CT)} and orthofluorinated toluene {orthofluorotoluene (o-FT)}, and γ-butyrolactone (GBL). ) and, and a cyclic carbonate, the GBL of the non-aqueous solvent, the halogenated toluene and the cyclic carbonate fraction each x (mass%), y (mass%), z (mass%) In this case, x, y, and z satisfy 40 ≦ x ≦ 80, 0.1 ≦ y ≦ 15, 19.9 ≦ z ≦ 59.9, and x + y + z ≦ 100, respectively. The content of LiBF ₄ in the electrolyte is 50 mass% or more. Incidentally, mass ratio (mass%) x, more preferably in the range of mass ratio (mass%) y and Weight Ratio (mass%) Total amount of z is at 60 ≦ x + y + z ≦ 100, more preferably ranges Is 90 ≦ x + y + z ≦ 100.

  According to such a secondary battery, when the potential of the positive electrode rises due to an overcharged state due to a failure of a charger of a portable device incorporating the secondary battery, the separator can be reliably shut down. The overcharge state can be safely terminated. That is, in an overcharged state, the battery temperature can be quickly raised to the shutdown temperature of the separator by causing an exothermic reaction due to oxidation of halogenated toluene at the same time as the exothermic reaction due to the reaction between GBL and the positive electrode. The overcharge current can be cut off early. In addition, since the non-aqueous electrolyte having the above-described composition has a relatively low reactivity with the positive electrode during overcharge, the reaction between the positive electrode and the non-aqueous electrolyte is quickly terminated after the current interruption. Therefore, it is possible to avoid the non-aqueous electrolyte secondary battery from causing a thermal runaway.

  Moreover, according to the secondary battery which concerns on this invention, the capacity | capacitance fall at the time of storing a secondary battery in a high temperature environment in a discharge state can be decreased, and the outstanding high temperature leaving property can be acquired.

  Hereinafter, the positive electrode, the negative electrode, the separator, and the nonaqueous electrolyte will be described.

1) Positive electrode The positive electrode includes a current collector and a positive electrode layer that is supported on one or both surfaces of the current collector and includes an active material.

  The positive electrode layer includes a positive electrode active material, a binder, and a conductive agent.

Examples of the positive electrode active material include various oxides such as manganese dioxide, lithium manganese composite oxide, lithium-containing nickel oxide, lithium-containing cobalt oxide, lithium-containing nickel cobalt oxide, lithium-containing iron oxide, and lithium. Examples thereof include vanadium oxide and chalcogen compounds such as titanium disulfide and molybdenum disulfide. Among them, when a lithium-containing cobalt oxide (for example, LiCoO ₂ ), a lithium-containing nickel cobalt oxide (for example, LiNi _0.8 Co _0.2 O ₂ ), or a lithium manganese composite oxide (for example, LiMn ₂ O ₄ , LiMnO ₂ ) is used. This is preferable because a high voltage can be obtained. As the positive electrode active material, one kind of oxide may be used alone, or two or more kinds of oxides may be mixed and used.

  Examples of the conductive agent include acetylene black, carbon black, and graphite.

  Examples of the binder include polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVdF), polyether sulfone, ethylene-propylene-diene copolymer (EPDM), and styrene-butadiene rubber (SBR). Can be used.

The positive active material, the mixing ratio of the conductive agent, and the binder, the cathode active material of 80 to 95 mass%, the conductive agent 3 to 20 mass%, be in the range of the binder 2 to 7 mass% preferable.

  As the current collector, a conductive substrate having a porous structure or a non-porous conductive substrate can be used. These conductive substrates can be formed from, for example, aluminum, stainless steel, or nickel.

  The positive electrode is produced, for example, by suspending a conductive agent and a binder in an appropriate solvent in a positive electrode active material, applying the suspension to a current collector, and drying to form a thin plate.

2) Negative electrode The negative electrode includes a current collector and a negative electrode layer supported on one side or both sides of the current collector.

  The negative electrode layer includes a negative electrode active material that absorbs and releases lithium ions and a binder.

Examples of the negative electrode active material include graphite materials, carbonaceous materials such as graphite, coke, carbon fiber, spherical carbon, pyrolytic gas phase carbonaceous material, and resin fired body; thermosetting resin, isotropic pitch, mesophase Graphite material obtained by subjecting pitch-based carbon, mesophase pitch-based carbon fiber, mesophase microspheres, etc. (especially mesophase pitch-based carbon fiber is preferable because of its high capacity and charge / discharge cycle characteristics) to 500-3000 ° C. Or a carbonaceous material; a chalcogen compound such as titanium disulfide, molybdenum disulfide, or niobium selenide; a light metal such as aluminum, an aluminum alloy, a magnesium alloy, lithium, or a lithium alloy; Among them, it is preferable to use a graphite material having a graphite crystal having a (002) plane spacing _d002 of 0.34 nm or less. A nonaqueous electrolyte secondary battery provided with a negative electrode containing such a graphite material as a negative electrode active material can greatly improve battery capacity and large current discharge characteristics. More preferably, the surface interval _d002 is 0.337 nm or less.

  Examples of the binder include polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVdF), ethylene-propylene-diene copolymer (EPDM), styrene-butadiene rubber (SBR), carboxymethyl cellulose (CMC), and the like. Can be used.

The mixing ratio of the negative electrode active material and the binder, carbonaceous material 90-98 mass%, is preferably in the range of the binder 2-20 mass%.

  As the current collector, a conductive substrate having a porous structure or a non-porous conductive substrate can be used. These conductive substrates can be formed from, for example, copper, stainless steel, or nickel.

  The negative electrode is prepared by, for example, kneading a negative electrode active material and a binder in the presence of a solvent, applying the obtained suspension to a current collector, drying it, and then pressing it once at a desired pressure or 2 It is produced by multi-stage pressing ˜5 times.

3) Separator As this separator, a microporous film, a woven fabric, a non-woven fabric, a laminate of the same material or different materials among these can be used. In particular, the microporous membrane causes a so-called shutdown phenomenon in which the resin constituting the separator plastically deforms and closes the fine pores when the temperature of the electrode group rises abnormally due to heat generated by overcharging, etc., and the flow of lithium ions Is prevented, and further overheating is prevented, and the overcharge state can be safely terminated, which is preferable. Examples of the material for forming the separator include polyethylene, polypropylene, ethylene-propylene copolymer, and ethylene-butene copolymer. As a material for forming the separator, one type or two or more types selected from the types described above can be used.

The separator preferably has an air permeability of 200 to 600 seconds / 100 cm ³ . The air permeability means the time (seconds) required for 100 cm ³ of air to pass through the separator, and it is measured by the air permeability test method for paper and paperboard specified in P8117 of JIS (Japanese Industrial Standard). Can do. The reason why the air permeability is defined within the above range will be described. When the air permeability is less than 200 seconds / 100 cm ^3, the pores of the separator are large and rough, and there is a possibility that the shutdown phenomenon as described above does not occur promptly and a thermal runaway occurs. On the other hand, when the air permeability exceeds 600 seconds / 100 cm ³ , the pores of the separator are extremely small, and a portion where the nonaqueous electrolyte is not completely held in the pores of the separator is generated. May occur only partially, that is, the lithium ion flow may not be completely blocked. Further, when the air permeability exceeds 600 seconds / 100 cm ³ , the resistance of ion movement during normal charge / discharge increases, and thus the internal resistance of the battery may increase. The range of the air permeability is more preferably 250 to 500 seconds / 100 cm ³ , and further preferably 300 to 450 seconds / 100 cm ³ .

The temperature at which the separator causes a shutdown phenomenon, the so-called shutdown temperature, is preferably in the range of 100 ° C to 160 ° C. This shutdown temperature can be measured as the separator temperature at which the separator is heated and the air permeability value becomes 100,000 seconds / 100 cm ³ or more. The reason for defining the shutdown temperature within the above range will be described. When the shutdown temperature exceeds 160 ° C., there is a high possibility that the separator will not be shut down rapidly in an overcharged state, resulting in thermal runaway. On the other hand, when the shutdown temperature is less than 100 ° C., the air permeability of the separator increases when placed in a high temperature state such as in a car under the hot sun in the normal use state of the nonaqueous electrolyte secondary battery, There is a possibility that problems such as deterioration of the large current discharge characteristics of the battery may occur. The shutdown temperature of the separator is more preferably 110 ° C to 150 ° C. A more preferable range is 130 ° C to 140 ° C.

  The temperature at which the separator melts to form a film breakage, so-called melting temperature, is preferably 160 ° C. or higher and 15 ° C. or higher than the shutdown temperature. When the melting temperature is less than 160 ° C. or the difference from the shutdown temperature is less than 15 ° C., even if the shutdown phenomenon occurs once due to the rise in battery temperature, the separator melts and breaks the film afterwards. There is a risk that a so-called short-circuit state may occur, in which the electrode and the negative electrode are in direct contact. When the short circuit is reached, the electrical resistance of the shorted part is extremely small, so a large current continues to flow in the shorted part, and the temperature of the shorted part rises locally by generating Joule heat, and the surrounding separator May melt or cause thermal runaway.

  The separator preferably has a porosity in the range of 30 to 60%. A more preferable range of the porosity is 35 to 50%.

  The thickness of the separator is preferably 30 μm or less, and more preferably 25 μm or less. Moreover, it is preferable that the lower limit of thickness is 5 micrometers, and a more preferable lower limit is 8 micrometers.

  The width of the separator is desirably wider than the width of the positive electrode and the negative electrode. By adopting such a configuration, it is possible to prevent the positive electrode and the negative electrode from coming into direct contact without a separator.

  An electrode group is formed by combining the positive electrode, the negative electrode, and the separator. For example, (i) the positive electrode and the negative electrode are wound in a flat shape or a spiral shape with a separator interposed therebetween, or (ii) the positive electrode and the negative electrode are wound in a spiral shape with a separator interposed therebetween. Rotating and then compressing in the radial direction, (iii) bending the positive electrode and the negative electrode one or more times with a separator interposed therebetween, or (iv) laminating the positive electrode and the negative electrode with a separator interposed therebetween It is produced by.

  The electrode group need not be pressed, but may be pressed to increase the integrated strength of the positive electrode, the negative electrode, and the separator. It is also possible to heat at the time of pressing.

  The electrode group can contain an adhesive polymer in order to increase the integrated strength of the positive electrode, the negative electrode, and the separator. It is desirable that the polymer having adhesiveness can maintain high adhesiveness while holding the nonaqueous electrolyte. Furthermore, it is more preferable that such a polymer has high lithium ion conductivity. Specific examples include polyacrylonitrile (PAN), polyacrylate (PMMA), polyvinylidene fluoride (PVdF), polyvinyl chloride (PVC), and polyethylene oxide (PEO).

4) Non-aqueous electrolyte The non-aqueous electrolyte includes a non-aqueous solvent and an electrolyte (for example, lithium salt) dissolved in the non-aqueous solvent. The form of the non-aqueous electrolyte can be liquid (non-aqueous electrolyte) or gel.

  First, the nonaqueous solvent will be described.

a. γ-butyrolactone (GBL)
GBL has a relatively low reactivity with the positive electrode in the charged state, that is, in the state where the positive electrode has a high potential, compared to the cyclic carbonate. Therefore, the decomposition reaction of the non-aqueous solvent in the overcharged state and the accompanying exothermic reaction are relatively It is difficult to occur, and after the overcharge current is cut off by the separator, the decomposition reaction of the non-aqueous electrolyte can be quickly terminated. Ratio nonaqueous solvent total mass of GBL (x) is preferably in the range of 40 mass% to 80 mass%. This is due to the following reason. When GBL ratio of the (x) is less than 40 mass%, the solvent (e.g., ethylene carbonate (EC)) having high reactivity with the positive electrode than GBL ratio of increases, degradation of the non-aqueous solvent in the overcharged state Reaction and exothermic reaction are likely to occur, and the risk of falling into a so-called thermal runaway state in which the temperature of the battery rises and the decomposition reaction of the nonaqueous solvent is further promoted increases. On the other hand, when the GBL ratio of (x) exceeds 80 mass%, particularly since the reactivity with the negative electrode surface and the GBL is high at high temperatures, low capacity recovery rate after storage under a high temperature environment in a discharged state Or the charge / discharge cycle life may be shortened.

More preferred ratios of GBL (x) is a 50 mass% to 80 mass%, more preferably the ratio (x) is a 55 mass% to 75 mass%.

b. Cyclic carbonates Cyclic carbonates react with GBL and lithium ions occluded in the negative electrode active material without losing the advantages of GBL, ie, the low freezing point, high lithium ion conductivity, and excellent safety. Can be suppressed. Examples of the cyclic carbonate include ethylene carbonate (EC) and propylene carbonate (PC). In particular, EC is preferable because it has a large effect of suppressing the reaction between lithium ions and GBL. In addition, the kind of cyclic carbonate may be one, or two or more kinds.

Ratio nonaqueous solvent total mass of the cyclic carbonate is preferably in the range of 19.9 to 59.9 mass%. This is due to the following reason. When the ratio non-aqueous solvent total volume of cyclic carbonate to less than 19.9 mass%, there is a risk that especially not be suppressed reaction between the lithium ions and GBL in a high-temperature environment. Moreover, the cyclic carbonate (especially EC) has higher than GBL reactivity with the positive electrode in a charged state, the ratio of cyclic carbonate exceeds 59.9 mass%, decomposition of the nonaqueous solvent during overcharge Reaction is likely to occur, and there is a high risk that the decomposition reaction will continue even after the current is cut off by the separator, leading to thermal runaway. Also, cyclic carbonate has a high freezing point, the ratio of cyclic carbonate exceeds 59.9 mass%, there is a possibility that the low-temperature discharge characteristics is significantly reduced. Further, the ratio of cyclic carbonate exceeds 59.9 mass%, the ion conductivity of the viscosity of the nonaqueous electrolyte becomes higher is lowered, there is a possibility that the large current discharge characteristics decrease. A more preferable range of the ratio of the cyclic carbonate in the range of 25 to 50 mass%, further preferred ratio is in the range of 25 to 45 mass%.

c. Halogenated toluene The halogenated toluene is composed of at least one selected from the group consisting of toluene chloride {chlorotoluene (CT)} and orthofluorinated toluene {orthofluorotoluene (o-FT)}.

In the non-aqueous solvent containing a 40 mass% to 80 mass% of GBL and 19.9 to 59.9 mass% of a cyclic carbonate, more than 4.7V at a potential positive potential with respect to lithium metal by overcharge When it reaches, the decomposition reaction of GBL and the exothermic reaction accompanying this decomposition reaction begin to occur gradually in the positive electrode, and when the overcharge further proceeds and the positive electrode potential exceeds 5.0 V in terms of the metal lithium, these reactions rapidly proceed. At this time, if the separator causes a shutdown phenomenon as described above due to an increase in battery temperature, the flow of lithium ions is blocked, and the overcharged state can be safely terminated. However, in order for this shutdown phenomenon to occur completely, the temperature at which the resin constituting the separator undergoes plastic deformation uniformly and in a short time in all areas in contact with the positive electrode and negative electrode of the separator (shutdown) Temperature). The time until the temperature of the separator reaches the shutdown temperature is shorter as the flowing current is larger, and the time is longer as the flowing current is smaller. In addition, the time until the shutdown temperature is reached is longer as the so-called heat dissipation efficiency, in which heat escapes from the secondary battery, and becomes shorter as the heat dissipation efficiency is lower. The efficiency of this heat dissipation varies depending on the material and shape of the members constituting the secondary battery.

  In the present invention, the non-aqueous solvent containing GBL and cyclic carbonate in a predetermined ratio is selected from the group consisting of toluene chloride {chlorotoluene (CT)} and orthofluorinated toluene {orthofluorotoluene (o-FT)}. At least one toluene halide is added. The oxidation potential of orthofluorinated toluene {orthofluorotoluene (o-FT)} (potential with respect to metallic lithium) is 4.9 V. Orthochlorinated toluene {orthochlorotoluene (o-CT)} and parachlorinated toluene {parachlorotoluene ( p-CT)} and metachlorinated toluene {metachlorotoluene (m-CT)} have an oxidation potential (potential with respect to metallic lithium) of 4.8V.

  The exothermic reaction accompanying the oxidation reaction of the halogenated toluene occurs at the same time as the exothermic reaction due to the reaction between the positive electrode and the GBL, and the calorific value due to the oxidation reaction is large. Thus, the shutdown temperature can reach the shutdown temperature, and the shutdown phenomenon can surely occur during overcharge. Moreover, since these halogenated toluenes do not react with any of the positive electrode, the negative electrode, and the nonaqueous electrolyte (particularly GBL) when the positive electrode potential is less than 4.7 V, the charge / discharge characteristics of the secondary battery are It will not be damaged. Furthermore, when the composition of the nonaqueous electrolyte is defined as in the present invention, the decomposition reaction of the nonaqueous electrolyte can be stopped quickly after the overcharge current is interrupted. As a result, thermal runaway can be suppressed without impairing the charge / discharge characteristics of the secondary battery.

  Furthermore, as halogenated toluene, it consists of orthochlorinated toluene {orthochlorotoluene (o-CT)}, parachlorinated toluene {parachlorotoluene (p-CT)}, and orthofluorinated toluene {orthofluorotoluene (o-FT)}. Use of at least one kind of halogenated toluene selected from the group is preferable because safety during overcharging can be further improved. In these halogenated toluenes, not only the timing at which the oxidation reaction occurs is optimal and a sufficient calorific value is obtained, but also a polymer of halogenated toluene is produced by the oxidation reaction, and the produced polymer is fixed to the separator. This is because the hole can be blocked and the current shielding effect of the separator can be further enhanced. In particular, orthofluorinated toluene {orthofluorotoluene (o-FT)} is more preferably used from the viewpoint of obtaining excellent high-temperature storage characteristics.

  When a substance that causes an oxidation reaction at a potential of less than 4.7 V (to lithium metal) is added to the non-aqueous solvent, the reaction of the added substance is completed before the exothermic heat generated by the GBL reaction occurs. The temperature of the separator cannot reach the shutdown temperature within a short time. On the other hand, when a substance that causes an oxidation reaction at a potential exceeding 5.0 V (with respect to lithium metal) is added to the nonaqueous solvent, heat is generated by the reaction between the positive electrode and the GBL before the added substance causes an oxidation reaction. Therefore, when the added substance causes an oxidation reaction, the temperature of the secondary battery has already risen, and there is a risk of promoting thermal runaway if heat is generated by the oxidation reaction in that state.

Ratio nonaqueous solvent total mass of the halogenated toluene (y) is preferably in the range of 0.1 to 15 mass%. This is due to the following reason. When the ratio of halogenated toluene (y) less than 0.1 mass%, the amount of heat generated by the oxidation reaction of the halogenated toluene is reduced, the effect of shutting down the separator is reduced. Conversely, if the ratio of halogenated toluene (y) exceeds 15 mass%, the amount of heat generated by the oxidation reaction of the halogenated toluene becomes too large, the risk that the temperature of the secondary battery reaches the rapidly rises to thermal runaway Increases sex. The ratio of halogenated toluene (y) is more than 15 mass%, high temperature storage characteristics decreases.

More preferred ratios of halogenated toluene (y) is in the range of 0.5 to 10 mass%, more preferably the ratio (y) is in the range of 1-8 mass%.

d. Subcomponent In the non-aqueous solvent, a solvent other than GBL, cyclic carbonate and halogenated toluene can be contained as a subcomponent.

  The non-aqueous solvent preferably contains a surfactant such as trioctyl phosphate (TOP) in order to improve the wettability with the separator. The addition amount of the surfactant is preferably 3% or less, and more preferably in the range of 0.1 to 1%.

  As an auxiliary component, for example, vinylene carbonate, vinyl ethylene carbonate, phenyl ethylene carbonate, diethyl carbonate, dimethyl carbonate, ethyl methyl carbonate, γ-valerolactone, methyl propionate, ethyl propionate, 2-methylfuran, furan, thiophene, Examples thereof include catechol carbonate, ethylene sulfite, 12-crown-4, and tetraethylene glycol dimethyl ether. The kind of subcomponent can be made into one kind or two kinds or more.

Among them, the secondary component containing vinylene carbonate (VC) produces a dense protective film on the negative electrode surface, so that the reactivity between lithium ions occluded in the negative electrode active material and GBL can be further reduced. The neglected discharge characteristics can be improved. Mass ratio of the secondary components of the nonaqueous solvent is preferably in the range of 10 mass% or less. This is because when the mass ratio of the secondary components to more than 10 mass%, low-temperature discharge characteristics of lithium ion permeability of the protective film on the negative electrode surface is reduced there is a possibility that impaired significantly. A more preferable range of the mass ratio of subcomponents is 0.01 to 5 mass%, still more preferably in the range of from 0.1 to 3 mass%.

e. Electrolyte Examples of the electrolyte dissolved in the non-aqueous solvent include lithium perchlorate (LiClO ₄ ), lithium hexafluorophosphate (LiPF ₆ ), lithium tetrafluoroborate (LiBF ₄ ), and arsenic hexafluoride. Lithium (LiAsF ₆ ), lithium trifluorometasulfonate (LiCF ₃ SO ₃ ), lithium bistrifluoromethylsulfonylimide (LiN (CF ₃ SO ₂ ) ₂ ), lithium bispentafluoroethylsulfonylimide (LiN (C ₂ F ₅₎ There may be mentioned lithium salts such as SO ₂ ) ₂ ). The type of electrolyte used can be one type or two or more types.

Among them, LiBF ₄ is preferable because it has a low reactivity with the positive electrode when the temperature of the secondary battery rises, and thus can quickly terminate the decomposition reaction of the nonaqueous electrolyte after the current interruption. Also, a lithium salt of at least one of LiN (CF ₃ SO _{2) 2} and _{LiN (C 2 F 5 SO 2} ) 2, or a mixed salt containing a lithium salt comprising LiBF _4, or LiBF ₄ and LiPF _When a mixed salt containing ₆ is used, the cycle life at a high temperature can be further improved.

The mass ratio of LiBF ₄ relative to the total mass of the electrolyte, it is desirable to more than 50 mass%. This is because when the mass ratio of LiBF ₄ in less than 50 mass%, the proportion of highly reactive electrolyte between the positive electrode than LiBF ₄ (e.g. LiPF ₆₎ is increased, easily occurs exothermic reactions in the overcharged state This is because the risk of falling into a thermal runaway state increases.

More preferred ratios of LiBF ₄ is a 70 mass% or more, more preferred ratio is 80 mass% or more.

  The amount of the electrolyte dissolved in the non-aqueous solvent is preferably 0.5 to 2.5 mol / L. A more preferable range is 1 to 2.5 mol / L.

  The amount of the nonaqueous electrolyte is preferably 0.2 to 0.6 g per 100 mAh of battery unit capacity. A more preferable range of the nonaqueous electrolytic mass is 0.25 to 0.55 g / 100 mAh.

  A thin lithium ion secondary battery, which is an example of a nonaqueous electrolyte secondary battery according to the present invention, will be described in detail with reference to FIGS.

  FIG. 1 is a perspective view showing a thin lithium ion secondary battery which is an example of a nonaqueous electrolyte secondary battery according to the present invention, and FIG. 2 is a cross-sectional view of the thin lithium ion secondary battery of FIG. It is a fragmentary sectional view.

  As shown in FIG. 1, an electrode group 2 is accommodated in a container body 1 having a rectangular cup shape. The electrode group 2 has a structure in which a laminate including a positive electrode 3, a negative electrode 4, and a separator 5 disposed between the positive electrode 3 and the negative electrode 4 is wound into a flat shape. The nonaqueous electrolyte is held in the electrode group 2. A part of the edge of the container body 1 is wide and functions as the lid plate 6. The container body 1 and the cover plate 6 are each composed of a laminate film. The laminate film includes an external protective layer 7, an internal protective layer 8 containing a thermoplastic resin, and a metal layer 9 disposed between the external protective layer 7 and the internal protective layer 8. A lid 6 is fixed to the container body 1 by heat sealing using a thermoplastic resin of the inner protective layer 8, whereby the electrode group 2 is sealed in the container. A positive electrode tab 10 is connected to the positive electrode 3, and a negative electrode tab 11 is connected to the negative electrode 4, and each is pulled out of the container and serves as a positive electrode terminal and a negative electrode terminal.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

Example 1
<Preparation of positive electrode>
First, lithium cobalt oxides; in (Li _x CoO ₂ where, X is 0 <X ≦ 1 a is) powder 90 mass%, and 5 mass% of acetylene black, polyvinylidene fluoride (PVdF) 5 mass% of Dimethylformamide (DMF) solution was added and mixed to prepare a slurry. The slurry was applied to both sides of a current collector made of an aluminum foil having a thickness of 15 μm, then dried and pressed to produce a positive electrode having a structure in which the positive electrode layer was supported on both sides of the current collector. The thickness of the positive electrode layer was 60 μm per side.

<Production of negative electrode>
And 95 mass% of powder of mesophase pitch-based carbon fibers heat-treated (determined by powder X-ray diffraction (002) plane interval of (d ₀₀₂₎ is 0.336 nm) at 3000 ° C. As the carbonaceous material, polyvinylidene fluoride (PVdF) 5 mass% of a mixture of dimethyl formamide (DMF) solution to prepare a slurry. The slurry was applied to both surfaces of a current collector made of a copper foil having a thickness of 12 μm, dried, and pressed to prepare a negative electrode having a structure in which the negative electrode layer was supported on the current collector. The thickness of the negative electrode layer was 55 μm per side.

The surface spacing d ₀₀₂ of (002) plane of the carbonaceous material were respectively determined by the powder X-ray diffraction spectrum half width midpoint method. At this time, scattering correction such as Lorentz scattering was not performed.

<Separator>
A separator made of a microporous polyethylene film having a thickness of 25 μm, a porosity of 45%, a shutdown temperature of 135 ° C., an air permeability of 300 seconds / 100 cm ³ and a melting temperature of 170 ° C. was prepared.

<Production of electrode group>
After the positive electrode lead made of a strip-shaped aluminum foil (thickness 100 μm) is ultrasonically welded to the positive electrode current collector, and the negative electrode lead made of a strip-shaped nickel foil (thickness 100 μm) is ultrasonically welded to the negative electrode current collector The positive electrode and the negative electrode were spirally wound through the separator between them to prepare an electrode group. The electrode group was formed into a flat shape by applying pressure with a press while heating.

  A laminate film having a thickness of 100 μm in which both surfaces of an aluminum foil were covered with polyethylene was formed into a rectangular cup shape by a press machine, and the electrode group was housed in the obtained container.

  Next, the electrode group in the container was vacuum dried at 80 ° C. for 12 hours to remove moisture contained in the electrode group and the laminate film.

<Preparation of liquid nonaqueous electrolyte>
Ethylene carbonate (EC), .gamma.-butyrolactone (GBL) and ortho-toluene chloride; the mass ratio {orthochlorotoluene (o-CT) versus oxidation potential 4.8V at the metal lithium} (EC: GBL: o- CT) To 35: 60: 5 to prepare a non-aqueous solvent. A liquid non-aqueous electrolyte was prepared by dissolving lithium tetrafluoroborate (LiBF ₄ ) in the obtained non-aqueous solvent so that its concentration was 1.5 mol / L.

  After injecting the liquid non-aqueous electrolyte into the electrode group in the container so that the amount per battery capacity 1Ah is 4.8 g and sealing by heat sealing, the structure shown in FIGS. A nonaqueous electrolyte secondary battery having a thickness of 3.6 mm, a width of 35 mm, a height of 62 mm, and a nominal capacity of 0.65 Ah was assembled.

  The following treatment was applied to the non-aqueous electrolyte secondary battery as an initial charge / discharge process. First, constant current / constant voltage charging was performed for 15 hours at room temperature to 4.2 V at 0.2C. Then, it discharged to 3.0V at 0.2C at room temperature, and manufactured the nonaqueous electrolyte secondary battery.

  Here, 1C is a current value necessary for discharging the nominal capacity (Ah) in one hour. Therefore, 0.2 C is a current value necessary for discharging the nominal capacity (Ah) in 5 hours.

(Examples 2 to 4)
A nonaqueous electrolyte secondary battery was produced in the same manner as in Example 1 except that the type of halogenated toluene in the nonaqueous solvent was changed as shown in Table 1 below. In Table 1 below, p-CT is parachlorotoluene (parachlorotoluene; oxidation potential with lithium metal 4.8 V), o-FT is orthofluorinated toluene (orthofluorotoluene; oxidation potential 4 with lithium metal) .9V), m-CT represents metachlorotoluene (metachlorotoluene; oxidation potential of 4.8 V with lithium metal).

(Examples 5-7)
EC, GBL, except for changing the mass ratio of the o-CT as shown in the following Table 1, were prepared non-aqueous electrolyte secondary battery in the same manner as in Example 1 described above.

(Example 8)
A nonaqueous electrolyte secondary battery was manufactured in the same manner as in Example 1 except that propylene carbonate (PC) was used instead of EC.

Example 9
Ethylene carbonate (EC), .gamma.-butyrolactone (GBL), ortho-toluene chloride {orthochlorotoluene (o-CT)} a mass ratio (EC: GBL: o-CT ) is 35: 60: mixed at a 5 Thus, a non-aqueous solvent was prepared. The resulting non-aqueous solvents, was mixed with equal mass of lithium tetrafluoroborate (LiBF ₄₎ and lithium hexafluorophosphate (LiPF _6), the concentration of the total of 1.5 mol / L Thus, a liquid non-aqueous electrolyte was prepared.

  A nonaqueous electrolyte secondary battery was manufactured in the same manner as in Example 1 described above except that this liquid nonaqueous electrolyte was used.

(Examples 10 to 11)
A nonaqueous electrolyte secondary battery was produced in the same manner as in Example 1 except that a nonaqueous solvent having the composition shown in Table 1 below was used.

(Comparative Example 1)
A nonaqueous electrolyte secondary battery was produced in the same manner as in Example 1 except that no halogenated toluene was added to the nonaqueous solvent.

(Comparative Example 2)
A nonaqueous electrolyte secondary battery was manufactured in the same manner as in Example 1 described above, except that biphenyl (BP; oxidation potential of 4.5 V with respect to metallic lithium) was added to the nonaqueous solvent instead of o-CT.

(Comparative Examples 3-5)
EC, GBL, except for changing the mass ratio of the o-CT as shown in the following Table 1, were prepared non-aqueous electrolyte secondary battery in the same manner as in Example 1 described above.

(Comparative Example 6)
Ethylene carbonate (EC), .gamma.-butyrolactone (GBL), ortho-toluene chloride {orthochlorotoluene (o-CT)} a mass ratio (EC: GBL: o-CT ) is 35: 60: mixed at a 5 Thus, a non-aqueous solvent was prepared. The resulting non-aqueous solvent, lithium tetrafluoroborate (LiBF ₄₎ and lithium hexafluorophosphate (LiPF ₆₎ the mass ratio (LiBF _4: LiPF ₆₎ were mixed such that the 40:60 The liquid non-aqueous electrolyte was prepared by dissolving so that the total concentration was 1.5 mol / L.

  A nonaqueous electrolyte secondary battery was manufactured in the same manner as in Example 1 described above except that this liquid nonaqueous electrolyte was used.

(Comparative Example 7)
A nonaqueous electrolyte secondary battery was prepared in the same manner as in Example 1 except that 2,4-dichlorotoluene (oxidation potential 4.5 V with respect to metallic lithium) was added to the nonaqueous solvent instead of o-CT. Manufactured.

(Comparative Example 8)
Except for adding 2,4-dimethylanisole described in JP-A-7-302614 (oxidation potential of 4.35 V with respect to metallic lithium) instead of o-CT to a non-aqueous solvent, the same as in Example 1 described above. Thus, a non-aqueous electrolyte secondary battery was manufactured.

(Comparative Example 9)
Except for adding 2,3,5,6-tetrafluoro-4-methylanisole described in JP-A-9-50822 (oxidation potential of 4.75 V with respect to metallic lithium) instead of o-CT to a non-aqueous solvent. A non-aqueous electrolyte secondary battery was manufactured in the same manner as in Example 1 described above.

(Comparative Example 10)
A nonaqueous electrolyte secondary battery was produced in the same manner as in Example 1 except that p-fluorotoluene (oxidation potential with respect to metallic lithium of 4.9 V) was added to the nonaqueous solvent instead of o-CT. .

(Comparative Example 11)
EC, GBL, the o-CT in mass ratio of 10: 85: except changing to 5, to prepare a non-aqueous electrolyte secondary battery in the same manner as in Example 1 described above.

(Comparative Example 12)
A nonaqueous electrolyte secondary battery was produced in the same manner as in Example 1 except that a nonaqueous solvent having the composition shown in Table 2 below was used. In addition, EMC in Table 2 shows ethyl methyl carbonate.

  An overcharge test was performed on each of the ten nonaqueous electrolyte secondary batteries of Examples 1 to 11 and Comparative Examples 1 to 12. In the overcharge test method, charging is continued at a current value of 3 C, and the number of nonaqueous electrolyte secondary batteries that have generated abnormal heat generation or ignition at that time is recorded. Tables 1 and 2 below show the percentage (%) of the total number of batteries that generate abnormal heat generation and ignition.

Further, the nonaqueous electrolyte secondary batteries of Examples 1 to 11 and Comparative Examples 1 to 12 were discharged for 1 month in an environment at a temperature of 65 ° C. after being discharged under the conditions of a discharge current of 1 C and a discharge end voltage of 3.0 V. Then, the capacity retention rate after storage (the discharge capacity before storage is 100%) is determined, and the results are also shown in Tables 1 and 2 below.

As apparent from Table 1-2, mass ratio (mass%) of GBL x is 40 ≦ x ≦ 80, mass ratio of the cyclic carbonate (mass%) z is 19.9 ≦ z ≦ 59.9 and mass ratio (mass%) of halogenated toluene y is 0.1 ≦ y ≦ 15 is used non-aqueous solvents are, and mass ratio of LiBF ₄ to the total mass of the electrolyte 50 mass% or more As for the secondary batteries of Examples 1-11, the abnormal heat generation out of the 10 batteries subjected to the overcharge test is at most 2 (20% or less), and the effect of safely terminating the overcharge state is achieved. Can be said to be large. In particular, the secondary batteries of Examples 1 to 3 to which o-CT, p-CT, and o-FT were added as halogenated toluene were compared with the secondary battery of Example 4 to which m-CT was added as a halogenated toluene. Thus, it can be said that the effect of safely terminating the overcharge state with the same addition amount is great.

  It can be understood that the secondary batteries of Examples 1 to 11 have a capacity retention rate of 80% or more when stored in a high temperature environment of 65 ° C. in a discharged state, and are excellent in high temperature storage characteristics. Regarding the influence of the capacity retention rate when left at high temperature due to the difference in the type of halogenated toluene, the capacity is maintained in the order of o-FT (Example 3)> o-CT (Example 1)> p-CT (Example 2). It can be seen that the rate is high. Moreover, the secondary battery of Example 10 using the non-aqueous solvent containing EC, GBL, o-FT, and VC has the highest capacity retention ratio among Examples 1-11.

On the other hand, all of the nonaqueous electrolyte secondary batteries of Comparative Example 1 made of EC and GBL and using a nonaqueous solvent to which no halogenated toluene was added generated abnormal heat. The portable device used as a power source is not suitable because it is likely to overheat in the worst case when it is continuously charged with a large current due to a failure of the charging device, etc. It is clear that The same applies to the secondary battery of Comparative Example 2 using a non-aqueous solvent composed of EC, GBL, and BP. Moreover, in the secondary battery of the comparative example 7 using the nonaqueous solvent which consists of dichlorotoluene described in EC, GBL, and Unexamined-Japanese-Patent No. 2000-156243 (patent document 4) , out of 10 which performed the overcharge test Five of them generated abnormal heat, and the capacity retention rate when left at high temperature was low.

  In the secondary battery of Comparative Example 3 in which 0.01% of o-CT was added to the non-aqueous solvent, 5 out of 10 batteries subjected to the overcharge test generated abnormal heat generation. It can be said that the effect of safely terminating charging is insufficient. In the secondary battery of Comparative Example 4 in which 20% o-CT was added to the non-aqueous solvent, not only the capacity maintenance rate when left at high temperature was low, but also 4 out of 10 batteries that were subjected to the overcharge test generated abnormal heat. Has occurred. This is presumably because the amount of o-CT added is large, so the amount of heat generated by the oxidation reaction of o-CT itself is large, and the temperature of the battery has risen.

In the secondary battery of Comparative Example 5 mass ratio of GBL to the total mass of the nonaqueous solvent is 30%, four ten of which were overcharging test occurs abnormal heat. This is because the amount of GBL is small, so that the effect of oxidizing the GBL in the overcharged state to form a resistance film on the positive electrode is small, and heat generation is likely to occur due to the reaction between the positive electrode and the liquid nonaqueous electrolyte in the overcharged state. Therefore, it is considered that the temperature of the battery has increased.

In the secondary battery of Comparative Example 6 mass ratio of LiBF ₄ and LiPF ₆ to the total mass is 40:60 of the electrolyte to be dissolved in the nonaqueous solvent, four of the ten which were overcharge test An abnormal fever is generated. This, LiPF ₆ is lacking in stability at high temperature, since the LiPF ₆ itself tends to generate heat in response, presumably because the temperature of the battery had risen.

Mass ratio of 10 percent each of the EC and GBL in the total mass of the nonaqueous solvent, in the secondary battery of Comparative Example 11 is 85%, the discharge capacity after storage is reduced to 10% of the discharge capacity before storage Was. This is presumably because the reaction between the negative electrode surface and GBL tends to proceed at a high temperature because the proportion of GBL in the non-aqueous solvent is high, and the negative electrode deteriorated during storage at 65 ° C.

  The secondary battery of Comparative Example 12 comprising a non-aqueous solvent consisting of a dialkyl carbonate such as EMC, EC, and a halogenated toluene has a small capacity drop when left at a high temperature in a discharged state. Abnormal heat generation rate was inferior at 100%. This is because during the overcharge, the halogenated toluene was oxidatively decomposed before the carbonates, and the heat generation amount caused the thermal shutdown because the separator shutdown mechanism did not operate.

(Method of detecting halogenated toluene)
For the secondary batteries of Examples 1 to 3, after the initial charge / discharge step, the circuit was opened for 5 hours or more to sufficiently settle the potential, and then the Ar concentration was 99.9% or more and the dew point was − It decomposed | disassembled in the glove box below 50 degreeC, and took out the electrode group. The electrode group was put in a centrifuge tube, dimethyl sulfoxide (DMSO) -d ₆ was added and sealed, removed from the glove box, and centrifuged. Thereafter, a mixed solution of the electrolytic solution and the DMSO-d ₆ was collected from the centrifuge tube in the glove box. About 0.5 ml of the mixed solvent was put into a 5 mmφ NMR sample tube and subjected to NMR measurement. The apparatus used for the NMR measurement is JNM-LA400WB manufactured by JEOL Ltd., the observation nucleus is ¹ H, the observation frequency is 400 MHz, and the residual proton signal slightly contained in dimethyl sulfoxide (DMSO) -d ₆ is used as an internal reference. (2.5 ppm). The measurement temperature was 25 ° C. ^{In the 1} HNMR spectrum, a peak corresponding to EC was observed around 4.5 ppm, and a peak corresponding to GBL was observed around 2.1 ppm, around 2.4 ppm, and around 4.2 ppm. Furthermore, in the secondary battery of Example 1, peaks corresponding to o-CT were observed around 2.3 ppm and around 7.2 to 7.4 ppm. In the secondary battery of Example 2, peaks corresponding to p-CT were observed around 2.2 ppm and around 7.1 to 7.3 ppm. In the secondary battery of Example 3, peaks corresponding to o-FT were observed around 2.2 ppm and around 7.1 to 7.3 ppm. From these results, it was confirmed that o-CT, p-CT, and o-FT were respectively contained in the nonaqueous solvent present in the secondary batteries of Examples 1 to 3 after the initial charge / discharge step. .

Further, when ¹³ CNMR measurement was performed with an observation frequency of 100 MHz and dimethyl sulfoxide (DMSO) -d ₆ (39.5 ppm) as an internal reference substance, peaks corresponding to EC were observed around 66 ppm and 156 ppm. Peaks corresponding to are observed around 22 ppm, 27 ppm, 68 ppm, and 178 ppm. Furthermore, in the secondary battery of Example 1, peaks corresponding to o-CT were observed around 19 ppm, around 127 ppm, around 128 ppm, around 129 ppm, around 131 ppm, around 133 ppm, and around 136 ppm. In the secondary battery of Example 2, peaks corresponding to p-CT were observed in the range of around 20 ppm, around 128 ppm, around 131 ppm, around 133 ppm, and 137 ppm. In the secondary battery of Example 3, peaks corresponding to o-FT were observed at around 14 ppm, around 115 ppm, around 124 ppm, around 128 ppm, around 132 ppm, around 160 ppm, and around 162 ppm. Also from this result, it was confirmed that o-CT, p-CT, and o-FT were respectively contained in the nonaqueous solvent present in the secondary batteries of Examples 1 to 3 after the initial charge / discharge step. .

Furthermore, in the ¹ H NMR spectrum, the ratio of the NMR integrated intensity of the o-CT to the EC integrated intensity of the EC is obtained, and compared with the value of the integrated intensity ratio of the electrolytic solution whose ratio of EC and o-CT is known. The ratio of o-CT to the whole non-aqueous solvent could be obtained.

Further, when the ¹ HNMR measurement was performed on the secondary battery of Example 10 in the same manner as described for the secondary batteries of Examples 1 to 3, the peak corresponding to EC was around 4.5 ppm and the VC was Corresponding peaks were observed in the vicinity of 7.7 ppm, and peaks corresponding to GBL were observed in the vicinity of 2.1 ppm, 2.4 ppm, and 4.2 ppm. Furthermore, peaks corresponding to o-FT were observed around 2.2 ppm and around 7.1-7.3 ppm. From these results, it was confirmed that VC and o-FT were contained in the nonaqueous solvent present in the secondary battery of Example 10 after the initial charge / discharge step.

On the other hand, in the ¹³ C NMR measurement for the secondary battery of Example 10, peaks corresponding to EC were observed near 66 ppm and 156 ppm, peaks corresponding to VC were observed near 133 ppm, and peaks corresponding to GBL were 22 ppm, 27 ppm, It was observed around 68 ppm and 178 ppm. Furthermore, peaks corresponding to o-CT were observed around 14 ppm, around 115 ppm, around 124 ppm, around 128 ppm, around 132 ppm, around 160 ppm, and around 162 ppm. Also from this result, it was confirmed that VC and o-FT were contained in the non-aqueous solvent present in the secondary battery of Example 10 after the initial charge / discharge step.

Further, in the ¹ H NMR spectrum, the ratio of the NMR integrated intensity of GBL, VC, and o-FT to the NMR integrated intensity of EC was obtained, respectively, and this was calculated as a liquid non-aqueous solution having a known ratio of EC, GBL, VC, and o-FT. By comparing with the value of the integral intensity ratio of the electrolyte (the ratio of the NMR integral intensity of GBL, VC and o-FT to the NMR integral intensity of EC), the four components (GBL, EC, VC) constituting the non-aqueous solvent are compared. , it is possible to obtain the o-FT) composition ratio of, it was possible to determine the proportion of o-FT in the non-aqueous solvent total mass of the composition ratio.

  The present invention is not limited to the above-described embodiments, and can be similarly applied to other types of combinations of positive electrode, negative electrode, separator, and container. In addition to the non-aqueous electrolyte secondary battery in which the container is formed from the laminated film as in the above-described embodiment, the present invention can be applied to a secondary battery having a cylindrical or rectangular container.

As described above in detail, according to the present invention, both the non-aqueous electrolyte for a non-aqueous electrolyte secondary battery excellent in both high temperature storage characteristics and overcharge safety, and both high temperature storage characteristics and overcharge safety. It is possible to provide a non-aqueous electrolyte secondary battery that satisfies the above.

FIG. 1 is a perspective view showing a thin nonaqueous electrolyte secondary battery which is an example of a nonaqueous electrolyte secondary battery according to the present invention. 2 is a partial cross-sectional view of the thin non-aqueous electrolyte secondary battery of FIG. 1 cut along the line II-II.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Container body, 2 ... Electrode group, 3 ... Positive electrode, 4 ... Negative electrode, 5 ... Separator, 6 ... Cover plate, 7 ... External protective layer, 8 ... Internal protective layer, 9 ... Metal layer, 10 ... Positive electrode tab, 11 ... negative electrode tab.

Claims (16)

A nonaqueous electrolyte for a nonaqueous electrolyte secondary battery comprising a nonaqueous solvent and an electrolyte dissolved in the nonaqueous solvent,
The non-aqueous solvent includes at least one kind of halogenated toluene selected from the group consisting of chlorotoluene (CT) and orthofluorotoluene (o-FT), γ-butyrolactone (GBL), and cyclic carbonate, the GBL of the non-aqueous solvent, the halogenated toluene and the cyclic ratio of carbonate respectively x (mass%), y (mass%), the upon the z (mass%) x, wherein y And z satisfies 40 ≦ x ≦ 80, 0.1 ≦ y ≦ 15, 19.9 ≦ z ≦ 59.9, and x + y + z ≦ 100,
The electrolyte contains 50 mass% or more as a percentage of the total mass of the LiBF ₄ the electrolyte. 2. The non-aqueous electrolyte secondary battery according to claim 1, wherein the chlorotoluene (CT) is at least one selected from the group consisting of orthochlorotoluene (o-CT) and parachlorotoluene (p-CT). Water electrolyte. The nonaqueous electrolyte for a nonaqueous electrolyte secondary battery according to claim 1, wherein the GBL ratio x satisfies 55 ≦ x ≦ 75. The nonaqueous electrolyte for a nonaqueous electrolyte secondary battery according to claim 1, wherein the proportion y of the halogenated toluene satisfies 1 ≦ y ≦ 8. The nonaqueous electrolyte for a nonaqueous electrolyte secondary battery according to claim 1, wherein the ratio z of the cyclic carbonate satisfies 25 ≦ z ≦ 45. The non-aqueous solvent is vinylene carbonate, vinyl ethylene carbonate, phenyl ethylene carbonate, diethyl carbonate, dimethyl carbonate, ethyl methyl carbonate, γ-valerolactone, methyl propionate, ethyl propionate, 2-methylfuran, furan, thiophene, catechol. The nonaqueous electrolyte for a nonaqueous electrolyte secondary battery according to claim 1, further comprising at least one solvent selected from the group consisting of carbonate, ethylene sulfite, 12-crown-4, and tetraethylene glycol dimethyl ether. The electrolyte total mass non-aqueous electrolyte secondary battery nonaqueous electrolyte according to claim 1, wherein mass ratio of LiBF ₄ is 80 mass% or more with respect to the. A non-aqueous electrolyte secondary battery comprising a positive electrode, a negative electrode, and a non-aqueous electrolyte containing a non-aqueous solvent and an electrolyte dissolved in the non-aqueous solvent,
The non-aqueous solvent includes at least one kind of halogenated toluene selected from the group consisting of chlorotoluene (CT) and orthofluorotoluene (o-FT), γ-butyrolactone (GBL), and cyclic carbonate, the GBL of the non-aqueous solvent, the halogenated toluene and the cyclic ratio of carbonate respectively x (mass%), y (mass%), the upon the z (mass%) x, wherein y And z satisfies 40 ≦ x ≦ 80, 0.1 ≦ y ≦ 15, 19.9 ≦ z ≦ 59.9, and x + y + z ≦ 100,
The electrolyte contains 50 mass% or more as a percentage of the total mass of the LiBF ₄ the electrolyte.   The non-aqueous electrolyte secondary battery according to claim 8, wherein the chlorotoluene (CT) is at least one selected from the group consisting of orthochlorotoluene (o-CT) and parachlorotoluene (p-CT).   The nonaqueous electrolyte secondary battery according to claim 8, wherein the GBL ratio x satisfies 55 ≦ x ≦ 75.   The nonaqueous electrolyte secondary battery according to claim 8, wherein the proportion y of the halogenated toluene satisfies 1 ≦ y ≦ 8.   The non-aqueous electrolyte secondary battery according to claim 8, wherein the ratio z of the cyclic carbonate satisfies 25 ≦ z ≦ 45.   The non-aqueous solvent is vinylene carbonate, vinyl ethylene carbonate, phenyl ethylene carbonate, diethyl carbonate, dimethyl carbonate, ethyl methyl carbonate, γ-valerolactone, methyl propionate, ethyl propionate, 2-methylfuran, furan, thiophene, catechol. The nonaqueous electrolyte secondary battery according to claim 8, further comprising at least one solvent selected from the group consisting of carbonate, ethylene sulfite, 12-crown-4, and tetraethylene glycol dimethyl ether. The non-aqueous electrolyte secondary battery according to claim 8, wherein the mass ratio of LiBF ₄ is 80 mass% or more to the total mass of the electrolyte.   The nonaqueous electrolyte secondary battery according to claim 8, further comprising a separator having a shutdown temperature in a range of 100 ° C. to 160 ° C. The non-aqueous electrolyte secondary battery according to claim 15, wherein the air permeability of the separator is in a range of 200 seconds / 100 cm ³ to 600 seconds / 100 cm ³ .

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