WO2015132842A1 - Flame retardant for lithium ion secondary batteries, electrolyte solution for lithium ion secondary batteries, lithium ion secondary battery, and power supply or device system utilizing lithium ion secondary battery - Google Patents

Abstract

To improve the safety of a lithium ion secondary battery. A flame retardant for lithium ion secondary batteries, which contains a compound that has phosphorus as a ligand, and wherein one or more elements selected from among Cu, Ag, Fe, Ru and Pt and a halogen element are contained in the compound and the halogen element is, for example, fluorine. In cases where an electrolyte solution for lithium ion secondary batteries contains this flame retardant for lithium ion secondary batteries, the amount of the compound added is 10% by weight or more relative to the weight of the electrolyte solution for lithium ion secondary batteries.

Description

Flame retardant for lithium ion secondary battery, electrolyte solution for lithium ion secondary battery, lithium ion secondary battery, power supply or equipment system using lithium ion secondary battery

The present invention relates to a flame retardant for a lithium ion secondary battery, an electrolyte for a lithium ion secondary battery, a lithium ion secondary battery, and a power source or an equipment system using the lithium ion secondary battery.

Lithium ion secondary batteries (or called lithium secondary batteries) have high energy density and are attracting attention as batteries for electric vehicles and power storage. In particular, as electric vehicles, there are zero-emission electric vehicles that are not equipped with an engine, hybrid electric vehicles that are equipped with both an engine and a secondary battery, and plug-in hybrid electric vehicles that are directly charged from system power. In addition, it is expected to be used as a stationary power storage system that stores power and supplies power in an emergency when the power system is cut off.

For such various uses, lithium ion batteries having high energy density are expected. On the other hand, with the increase in energy density, the safety design of batteries becomes more and more difficult, and more advanced technology is required. One of them is the electrolyte combustion suppression technology. The electrolyte used in the lithium ion battery does not completely determine the safety of the battery, but because it is flammable, it suppresses the combustion reaction of the electrolyte and improves the safety of the battery. There is a desire to want.

There is trimethyl phosphite as an additive for making the electrolyte solution flame-retardant, and the following technologies are disclosed. Patent Document 1 and Patent Document 2 disclose a technique for making a battery safe with an electrolytic solution to which a phosphite is added.

JP 2010-282906 A JP 2011-165606 A

Since the electrolyte contained in the lithium ion secondary battery contains a combustible component, the electrolyte may burn. Although there is trimethyl phosphite described in Patent Documents 1 and 2 as a flame retardant for the electrolytic solution, trimethyl phosphite causes a transfer reaction in the electrolytic solution, so that the safety of the lithium ion secondary battery can be ensured. difficult. This invention is improving the safety | security of a lithium ion secondary battery.

A flame retardant for a lithium ion secondary battery containing a compound having phosphorus as a ligand, wherein the compound contains one or more of Cu, Ag, Fe, Ru, Pt and a halogen element Flame retardant.

According to the present invention, the safety of the lithium ion secondary battery can be improved. Problems, configurations, and effects other than those described above will be clarified by the following description of embodiments.

The cross-sectional structure of the lithium ion secondary battery of this invention is shown. 1 shows a battery system of the present invention.

Hereinafter, embodiments of the present invention will be described with reference to the drawings. The following description shows specific examples of the contents of the present invention, and the present invention is not limited to these descriptions. Various modifications by those skilled in the art are within the scope of the technical idea disclosed in this specification. Changes and modifications are possible. In all the drawings for explaining the present invention, components having the same function are denoted by the same reference numerals, and repeated description thereof may be omitted.

<Structure of lithium ion secondary battery>
FIG. 1 schematically shows the internal structure of the lithium ion secondary battery 101. The lithium ion secondary battery 101 is a general term for an electrochemical device that can store and use electrical energy by occluding and releasing ions to and from an electrode in a non-aqueous electrolyte. In this example, a lithium ion secondary battery will be described as a representative example.

In the lithium ion secondary battery 101 of FIG. 1, an electrode group including a positive electrode 107, a negative electrode 108, and a separator 109 inserted between both electrodes is housed in a battery container 102 in a sealed state. A lid 103 is provided on the upper part of the battery container 102, and the lid 103 has a positive external terminal 104, a negative external terminal 105, and a liquid inlet 106. After the electrode group is stored in the battery container 102, the lid 103 is put on the battery container 102, and the outer periphery of the lid 103 is welded to be integrated with the battery container 102. For attachment of the lid 103 to the battery container 102, other methods such as caulking and bonding can be employed in addition to welding.

<Preparation of Positive Electrode 107>
The positive electrode 107 includes a positive electrode mixture layer and a positive electrode current collector. The positive electrode mixture layer is composed of a positive electrode active material, and if necessary, a conductive agent and a binder. Illustrative examples of the positive electrode active material include LiCoO ₂ , LiNiO ₂ , and LiMn ₂ O ₄ . In addition, LiMnO ₃ , LiMn ₂ O ₃ , LiMnO ₂ , Li ₄ Mn ₅ O ₁₂ , LiMn _2−x M _x O ₂ (where M = Co, Ni, Fe, Cr, Zn, Ta, = 0.01-0.2), Li ₂ Mn ₃ MO ₈ (where M = Fe, Co, Ni, Cu, Zn), Li _1-x AxMn ₂ O ₄ (where A = Mg, Ba, B) , Al, Fe, Co, Ni, Cr, Zn, Ca, where x = 0.01 to 0.1), LiNi _1-x MxO ₂ (where M = Co, Fe, Ga, x = 0. 01 to 0.2), LiFeO ₂ , Fe ₂ (SO ₄ ) ₃ , LiCo _1-x M _x O ₂ (where M = Ni, Fe, Mn, and x = 0.01 to 0.2) , LiNi _1-x M _x O ₂ (where M = Mn, Fe, Co, Al, Ga, Ca, Mg, x = 0.01 to 0.2), Fe ( MoO ₄ ) ₃ , FeF ₃ , LiFePO ₄ , LiMnPO _{4 and the} like can be listed. Since the present invention is not limited to the positive electrode material, it is not limited to these materials.

The particle size of the positive electrode active material is specified to be equal to or less than the thickness of the positive electrode mixture layer. When there are coarse particles having a size equal to or larger than the thickness of the positive electrode mixture layer in the positive electrode active material powder, the coarse particles are removed in advance by sieving classification, wind classification or the like, and particles having a thickness of the positive electrode mixture layer or less are prepared.

Since the positive electrode active material is a powder, a binder for bonding the particles of the powder is necessary to form a positive electrode. In addition, when the positive electrode active material is an oxide, the conductivity of the oxide is generally low, so carbon powder is added to increase the conductivity between the oxide particles.

The positive electrode active material, the conductive agent and the binder are blended so that the mixing ratio (weight percentage display) of the positive electrode active material is 80 to 95% by weight, the conductive agent is 3 to 15% by weight, and the binder is 1 to 10% by weight. . In order to sufficiently exhibit electrical conductivity and enable charging / discharging of a large current, it is desirable that the mixing ratio of the conductive agent is 5% by weight or more. This is because the resistance of the entire positive electrode is reduced and the ohmic loss is reduced even when a large current is passed. Conversely, when increasing the energy density of the battery, the mixing ratio of the positive electrode active material is desirably in the high range of 85 to 95% by weight.

As the conductive agent, known materials such as carbon black such as graphite, amorphous carbon, graphitizable carbon, and Denka black, activated carbon, carbon fiber, and carbon nanotube can be used. Examples of the conductive fiber include vapor-grown carbon, fiber produced by carbonizing pitch (by-products such as petroleum, coal, coal tar, etc.) as a raw material at high temperature, carbon fiber produced from acrylic fiber (polyacrylonitrile), and the like. . In addition, it is a material that does not oxidize and dissolve at the charge / discharge potential of the positive electrode (usually 2.5 to 4.3 V), and has a lower electrical resistance than the positive electrode active material, such as a corrosion-resistant metal such as titanium or gold. Alternatively, a fiber made of carbide such as SiC or WC, or a nitride such as Si ₃ N ₄ or BN may be used. As a manufacturing method, an existing manufacturing method such as a melting method or a chemical vapor deposition method can be used.

For the positive electrode current collector, an aluminum foil having a thickness of 10 to 100 μm, an aluminum perforated foil having a thickness of 10 to 100 μm and a hole diameter of 0.1 to 10 mm, an expanded metal, a foam metal plate, etc. are used. In addition, stainless steel, titanium and the like are also applicable. In the present invention, any current collector can be used without being limited by the material, shape, manufacturing method and the like.

For the application of the positive electrode 107, a known production method such as a doctor blade method, a dipping method, or a spray method can be adopted, and there is no limitation on the means. In addition, after the slurry is attached to the current collector, the organic solvent is dried, and the positive electrode is pressure-formed by a roll press, whereby the positive electrode 107 can be manufactured. Moreover, it is also possible to laminate a plurality of mixture layers on a current collector by performing a plurality of times from application to drying.

<Preparation of negative electrode 108>
The negative electrode 108 includes a negative electrode mixture layer and a negative electrode current collector. The negative electrode mixture layer is mainly composed of a negative electrode active material and a binder, and a conductive agent may be added as necessary. A method for manufacturing the negative electrode will be described.

The negative electrode active material is, for example, a carbon material having a graphene structure. That is, natural graphite, artificial graphite, mesophase carbon, expanded graphite, carbon fiber, vapor grown carbon fiber, pitch-based carbonaceous material, needle coke, petroleum coke that can occlude and release lithium ions electrochemically, Uses carbonaceous materials such as polyacrylonitrile-based carbon fiber and carbon black, or amorphous carbon materials synthesized by thermal decomposition of 5-membered or 6-membered cyclic hydrocarbons or cyclic oxygen-containing organic compounds. Is possible. Even if it is a mixed negative electrode of a material such as graphite, graphitizable carbon, non-graphitizable carbon, or a mixed negative electrode or a composite negative electrode of the metal or the alloy as the carbon material, there is no obstacle to carrying out the present invention. In this invention, there is no restriction | limiting in particular in a negative electrode active material, It can utilize other than the above-mentioned material.

A conductive polymer material made of polyacene, polyparaphenylene, polyaniline, or polyacetylene can also be used for the negative electrode 108. These materials can be combined with a carbon material having a graphene structure such as graphite, graphitizable carbon, and non-graphitizable carbon.

Examples of the negative electrode active material that can be used in an embodiment of the present invention include aluminum, silicon, and tin that are alloyed with lithium, and further, from graphite or amorphous carbon that can electrochemically occlude and release lithium ions. There are also carbonaceous materials. In this invention, there is no restriction | limiting in particular in a negative electrode active material, It can utilize other than the above-mentioned material.

A slurry is prepared by adding a solvent to a mixture composed of the negative electrode active material prepared above and the binder according to one embodiment of the present invention, and sufficiently kneading or dispersing the mixture. The solvent can be arbitrarily selected as long as it is an organic solvent, water or the like and does not alter the binder of the present invention.

The mixing ratio of the negative electrode active material and the binder is preferably in the range of 80:20 to 99: 1 by weight. In order to sufficiently exhibit electrical conductivity and enable charging / discharging of a large current, it is desirable that the weight composition has a value of a negative electrode active material ratio smaller than 99: 1. On the contrary, in order to increase the energy density of the battery, it is preferable to blend so as to have a negative electrode active material ratio larger than 90:10.

Conductive agent is added to the negative electrode as necessary. For example, when charging or discharging a large current, it is desirable to add a small amount of a conductive agent to reduce the resistance of the negative electrode. As the conductive agent, known materials such as graphite, amorphous carbon, graphitizable carbon, carbon black, activated carbon, carbon fiber, and carbon nanotube can be used. Examples of the conductive fiber include vapor-grown carbon, fiber produced by carbonizing pitch (by-products such as petroleum, coal, coal tar, etc.) as a raw material at high temperature, carbon fiber produced from acrylic fiber (polyacrylonitrile), and the like. .

The above slurry is applied to the negative electrode current collector, and the negative electrode 108 is manufactured by evaporating the solvent and drying. For the negative electrode current collector, a copper foil having a thickness of 10 to 100 μm, a copper perforated foil having a thickness of 10 to 100 μm and a hole diameter of 0.1 to 10 mm, an expanded metal, a foam metal plate, etc. are used. In addition, stainless steel, titanium, and the like are also applicable. In the present invention, any current collector can be used without being limited by the material, shape, manufacturing method and the like.

For the application of the negative electrode 108, a known production method such as a doctor blade method, a dipping method, or a spray method can be adopted, and there is no limitation on the means. In addition, after the negative electrode slurry is attached to the current collector, the solvent is dried, and the negative electrode is pressure-formed by a roll press, whereby the negative electrode 108 can be manufactured. Moreover, it is also possible to laminate | stack a several negative mix layer on a collector by performing from application | coating to drying in multiple times.

<Production of battery>
At least one of the positive electrode 107 and the negative electrode 108 is alternately stacked, and a separator 109 is inserted between the positive electrode 107 and the negative electrode 108 to prevent a short circuit between the positive electrode 107 and the negative electrode 108. The positive electrode 107, the negative electrode 108, and the separator 109 constitute an electrode group. It is possible to use a polyolefin polymer sheet made of polyethylene, polypropylene, or the like, or a separator 109 having a multilayer structure in which a polyolefin polymer and a fluorine polymer sheet typified by tetrafluoropolyethylene are welded. A mixture of ceramics and a binder may be formed in a thin layer on the surface of the separator 109 so that the separator 109 does not contract when the battery temperature increases. Since these separators 109 need to allow lithium ions to pass therethrough during charge and discharge of the battery, they are generally used for the lithium ion secondary battery 101 if the pore diameter is 0.01 to 10 μm and the porosity is 20 to 90%. Is possible.

The separator 109 is also inserted between the electrode disposed at the end of the electrode group and the battery container 102 so that the positive electrode 107 and the negative electrode 108 are not short-circuited through the battery container 102. Electrolytic solution 113 is held on the surfaces of separator 109, positive electrode 107, and negative electrode 108 and inside the pores.

The upper part of the electrode group is electrically connected to an external terminal via a lead wire. The positive electrode 107 is connected to the positive electrode external terminal 104 via the positive electrode lead wire 110. The negative electrode 108 is connected to the negative electrode external terminal 105 through the negative electrode lead wire 111. The positive electrode lead wire 110 and the negative electrode lead wire 111 can take any shape such as a wire shape or a plate shape. Any material can be used for the positive electrode lead 110 and the negative electrode lead 111 as long as it has a structure capable of reducing ohmic loss when a current is passed and does not react with the electrolytic solution 113.

Further, an insulating sealing material 112 is inserted between the positive electrode external terminal 104 or the negative electrode external terminal 105 and the battery container 102 so that both terminals are not short-circuited. The insulating sealing material 112 can be selected from a fluororesin, a thermosetting resin, a glass hermetic seal, and the like, and any material that does not react with the electrolytic solution 113 and has excellent airtightness can be used.

A positive temperature coefficient (PTC) is provided in the middle of the positive electrode lead wire 110 or the negative electrode lead wire 111, or at the connection portion between the positive electrode lead wire 110 and the positive electrode external terminal 104, or at the connection portion between the negative electrode lead wire 111 and the negative electrode external terminal 105. ) When a current interruption mechanism using a resistance element is provided, when the temperature inside the battery becomes high, charging / discharging of the lithium ion battery 101 can be stopped to protect the battery. Note that the positive electrode lead wire 110 and the negative electrode lead wire 111 can have any shape such as a foil shape or a plate shape.

The structure of the electrode group can be various shapes such as a stack of strip-shaped electrodes shown in FIG. 1, or a wound shape in an arbitrary shape such as a cylindrical shape or a flat shape. The shape of the battery container may be selected from shapes such as a cylindrical shape, a flat oval shape, and a square shape according to the shape of the electrode group.

The material of the battery container 102 is selected from materials that are corrosion resistant to the non-aqueous electrolyte, such as aluminum, stainless steel, and nickel-plated steel. When the battery container 102 is electrically connected to the positive electrode lead wire 110 or the negative electrode lead wire 111, the material is altered by corrosion of the battery container or alloying with lithium ions in the portion in contact with the nonaqueous electrolyte. Select the lead wire material to prevent this from occurring.

Thereafter, the lid 103 is brought into close contact with the battery container 102 and the whole battery is sealed. There are known techniques for sealing the battery, such as welding and caulking.

<Preparation of Electrolytic Solution 113>
As a typical example of the electrolytic solution 113 that can be used in the present invention, a solvent in which dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, and the like are mixed in ethylene carbonate, lithium hexafluorophosphate (LiPF ₆ ), or lithium borofluoride as an electrolyte is used. There is a solution in which (LiBF ₄ ) is dissolved. In the present invention, other types of electrolytes can be used without being limited by the type of solvent or electrolyte and the mixing ratio of the solvents. The electrolyte can also be used in a state of being contained in an ion conductive polymer such as polyvinylidene fluoride and polyethylene oxide. In this case, the separator becomes unnecessary.

Solvents that can be used for the electrolytic solution 113 are propylene carbonate, ethylene carbonate, butylene carbonate, vinylene carbonate, γ-butyrolactone, dimethyl carbonate, diethyl carbonate, methyl ethyl carbonate, 1,2-dimethoxyethane, 2-methyltetrahydrofuran, Dimethyl sulfoxide, 1,3-dioxolane, formamide, dimethylformamide, methyl propionate, ethyl propionate, phosphoric acid triester, trimethoxymethane, dioxolane, diethyl ether, sulfolane, 3-methyl-2-oxazolidinone, tetrahydrofuran, There are non-aqueous solvents such as 1,2-diethoxyethane, chloroethylene carbonate, chloropropylene carbonate and the like. Other solvents may be used as long as they do not decompose on the positive electrode 107 or the negative electrode 108 incorporated in the battery of the present invention.

Further, the _{electrolyte, LiPF 6, LiBF 4, LiClO} 4, LiCF 3 SO 3, LiCF 3 CO 2, LiAsF 6, LiSbF 6 or imide lithium salts represented by lithium trifluoromethane sulfonimide in Formula, LiNSO ₂ F There are many types of lithium salts such as Li (NSO ₂ ) ₂ . Furthermore, LiB (CN) ₄ can also be used. A non-aqueous electrolytic solution obtained by dissolving these salts in the above-described solvent can be used as a battery electrolytic solution. Other electrolytes may be used as long as they do not decompose on the positive electrode 107 or the negative electrode 108 incorporated in the battery of the present invention.

As the above-mentioned electrolyte solution 113, an ionic liquid is selected and electrolyzed on the condition that it does not react with the flame retardant of the present invention (formula 1 described later) or does not react with the phosphorus compound contained in the flame retardant. It can be used instead of liquid. For example, 1-ethyl-3-methylimidazole tetrafluoroborate (EMI-BF ₄ ), lithium salt LiN (SO ₂ CF ₃ ) ₂ (LiTFSI), triglyme and tetraglyme) mixed complex, cyclic quaternary ammonium cation (N— A combination that does not decompose at the positive electrode and the negative electrode is selected from the methyl-N-propylpyrrolidinium and imide anions (exemplified by bis (fluorsulfonyl) imide) and used for the lithium ion battery of the present invention. be able to. The flame retardant of the present invention is dissolved in these ionic liquids.

When a solid polymer electrolyte (polymer electrolyte) is used, an ion conductive polymer such as ethylene oxide, acrylonitrile, polyvinylidene fluoride, methyl methacrylate, or hexafluoropropylene polyethylene oxide can be used as the electrolyte. These can be impregnated with the flame retardant or electrolytic solution of the present invention and used as a gel electrolyte. When these solid polymer electrolytes are used, there is an advantage that the separator 109 can be omitted.

There are two methods for injecting the electrolytic solution 113: a method in which the lid 103 is removed from the battery container 102 and added directly to the electrode group, or a method in which the electrolytic solution 113 is added from the liquid injection port 106 installed in the lid 103. The liquid injection port 106 of the lithium ion battery shown in FIG. 1 is installed on the upper surface of the lid 103. It is also possible to add a safety mechanism to the liquid injection port 106. As a safety mechanism, a pressure valve for releasing the pressure inside the battery container may be provided.

<How to use flame retardant>
The flame retardant for lithium ion secondary battery in one embodiment of the present invention is a flame retardant for lithium ion secondary battery containing a compound having phosphorus as a ligand, and any of Cu, Ag, Fe, Ru, and Pt A flame retardant for a lithium ion secondary battery containing at least one of them and a halogen element. As one embodiment of the present invention, a flame retardant for a lithium ion secondary battery containing a compound of (formula 1) or a compound of (formula 2) having the following phosphorus as a ligand is held or added to the battery. By including the following compound in the lithium ion secondary battery, it is possible to suppress the transfer reaction of the phosphorus compound and maintain the flame retardancy of the electrolyte over a long period of time.
R ¹ R ² R ³ PMX (Formula 1)
(R ¹ R ² R ³ P) ₅ —Fe—X (Formula 2)

R ¹ , R ² and R ³ in (Formula 1) and (Formula 2) are each directly bonded to a P atom and may be the same or different from each other, and may be the same or different from each other, a linear or branched alkyl group or alkoxy group It is. X in the corners (Formula 1) and (Formula 2) is a halogen element. M in (Formula 1) is at least one of Cu, Ag, Fe, Ru, and Pt.

As a flame retardant for a lithium ion battery, it may be composed of only the above compound (Formula 1) or (Formula 2), but may contain other materials. Only one of the compound of (Formula 1) or the compound of (Formula 2) may be included in the flame retardant for lithium ion batteries, and the compound of (Formula 1) and (Formula 2) may be included in the flame retardant for lithium ion batteries. ) May be included. The flame retardant for a lithium ion battery may contain one or more compounds of (Formula 1), or may contain one or more compounds of (Formula 2).

In (Formula 1) and (Formula 2), R ¹ , R ² , and R ³ are preferably CH ₃ O. The molecular weight of the flame-retardant gas R ¹ R ² R ³ P generated after decomposition of (Formula 1) is minimized, that is, trimethyl phosphite, (CH ₃ O) ₃ P is generated, so the P content Is the maximum. Therefore, oxygen in the vicinity of the electrolytic solution 113 can be captured and the oxygen concentration can be effectively reduced. Furthermore, when the flame retardant captures oxygen, the amount of heat generated by the combustion of R ¹ , R ² , and R ³ can be minimized, so that the combustion heat of the electrolytic solution 113 can be reduced.

When the electrolytic solution 113 is used for the lithium ion secondary battery and the flame retardant for the lithium ion secondary battery is added to the electrolytic solution 113, the amount of the flame retardant for the lithium ion secondary battery is 10 with respect to the weight of the electrolytic solution. If it is set to not less than 100% by weight, particularly not less than 20% by weight, oxygen desorption from the positive electrode 107 (generally 200 to 300 ° C.) is effectively suppressed and thermal runaway of the battery is avoided. It becomes possible. Since the weight energy density of the battery decreases as the amount of the flame retardant added increases, the weight energy density of the battery does not significantly decrease if the amount added is 20 wt% or more and 40 wt% or less with respect to the weight of the electrolyte. In addition, the purpose of suppressing thermal runaway of the battery can be achieved. If the addition amount is 40 wt% or more and 100 wt% or less, the battery temperature becomes close to the shutdown temperature (130 to 135 ° C.) of the polyolefin separator, and the temperature rise of the battery can be suppressed more effectively. Become.

By holding the flame retardant for lithium ion secondary battery that releases trimethyl phosphite in the battery, when the temperature of the lithium ion secondary battery rises or when oxygen is desorbed from the positive electrode 107, The safety of the lithium ion secondary battery can be improved.

As a method for retaining the flame retardant for lithium ion secondary battery in the lithium ion secondary battery, in addition to the method for adding the flame retardant for lithium ion battery to the electrolytic solution 113, a porous material containing the flame retardant for lithium ion secondary battery In this form, it is possible to install a flame retardant on the electrode group.

As an example, polyfluorinated ethylene particles and (CH ₃ O) ₃ PCuI powder were mixed, and a pellet-shaped porous plate containing a flame retardant was prepared using a tablet molding machine. Before attaching the battery lid to the can, it was placed on the electrode group and the battery lid was attached to the can. No difference was found in the maximum battery temperature (Table 1) described later. Since this method prevents the (CH ₃ O) ₃ PCul powder from being unevenly distributed due to gravity by tilting the battery, it is effective when the battery is placed horizontally. If an insulating sheet is laid on the electrode, an electron conductive material such as porous carbon or porous metal (foamed nickel) can be used.

The flame retardant in one embodiment of the present invention may be applied to the separator surface or held in a part of the pores.

In this example, LiNi _1/3 Mn _1/3 Co _1/3 O ₂ was used as the positive electrode active material, polyvinylidene fluoride (PVDF) was used as the binder, and carbon black was used as the conductive agent. A binder previously dissolved in 1-methyl-2-pyrrolidone (hereinafter referred to as NMP) was used. The weight composition of the positive electrode active material was 85%, the weight composition of the binder was 8%, and the weight composition of the conductive agent was 7%. While stirring and mixing the mixture of the positive electrode active material, the binder NMP solution and the conductive agent, NMP was added to prepare a slurry having smooth fluidity. The slurry was applied to a positive electrode current collector made of an aluminum foil having a thickness of 10 μm, and the solvent was evaporated and dried to manufacture the positive electrode 107. A blade coater was used to apply the positive electrode 107.

As a negative electrode active material, graphite powder having an average particle diameter of 10 μm in which the graphite layer interval d ₀₀₂ obtained from the (002) plane X-ray diffraction peak is in the range of 0.35 to 0.36 nm, carbon black as a conductive agent, and as a binder Polyvinylidene fluoride was used. As the binder, 1-methyl-2-pyrrolidone was used as a polyvinylidene fluoride solvent. The weight composition of the negative electrode active material, the conductive agent, and the binder was 93: 2: 5. The slurry was applied to a negative electrode current collector made of a copper foil having a thickness of 10 μm, and the solvent was evaporated to dry the negative electrode 108. A blade coater was used for coating the negative electrode 108.

An electrolytic solution 113 in which LiPF ₆ was dissolved in a 1: 1: 1 volume mixed solvent of ethylene carbonate, dimethyl carbonate, and ethyl methyl carbonate to a concentration of 1 mol / liter was used. After the electrode group was housed in the battery container 102 and sealed, an electrolytic solution 113 composed of an electrolyte and a non-aqueous solvent was dropped from the liquid inlet 106 and filled with 70 ml of the electrolytic solution 113. When the amount of the electrolyte is equivalent to 50 to 100% of the total volume of the positive electrode, negative electrode, and separator, the surface of the electrode and separator and the pores are sufficiently distributed, resulting in good battery characteristics. Can be obtained.

The compound in the flame retardant for lithium ion batteries used in this example is (CH ₃ O) ₃ PCuI described in the column of Example 1 in Table 1. In the structure of (Formula 1), halogen X was iodine. The purity of the compound was 98% or more, and (CH ₃ O) ₃ PCuI powder was passed through a sieve in an argon glove box so that the particle size range was 1 μm to 50 μm. These powders were filled above the electrode group from the liquid injection port 106 after being filled with the electrolytic solution.

The addition amount of the flame retardant for lithium ion battery of the present invention was a weight ratio with respect to the weight of the electrolyte described later, and the values are shown in Table 1. In this example, six types of batteries having different addition amounts with respect to the weight of the electrolytic solution were manufactured using the compounds shown in Table 1 (Formula 1). Respective batteries are designated as B11, B12, B13, B14, B15, and B16.

<Initial battery aging>
The rated capacity is 10 Ah. Initial aging was performed to obtain the rated capacity. The condition is that charging is first performed at a charging current of 5 A until the battery voltage reaches 4.2 V, and after reaching 4.2 V, charging is performed until the current decreases to 0.1 A while maintaining 4.2 V. Continued. Next, after 30 minutes of rest, discharging was performed at a discharge current of 5 A until the battery voltage reached 2.5V. This was repeated three times to obtain a capacity of 9.97-9.98 Ah.

<Battery safety test>
After obtaining the initial capacity, each battery was recharged to the same capacity to a charge depth of 100%. From that state, a φ3 mm iron nail was pierced on the side of the battery. The moving speed of the nail was 1 mm / second. Using a thermocouple affixed to the side of the battery, the nail started to pierce the battery container, and the time change of the side temperature of the battery was measured. The maximum value of the battery temperature in the course of this test is shown in the “maximum temperature” column of Table 1. Regarding the batteries of this example, none of the batteries burst or ignited. The maximum temperature of the battery of this example tended to decrease as the amount of (CH ₃ O) ₃ PCuI increased. That is, it was shown that the amount of trimethyl phosphite released increases, and has an effect of suppressing the temperature rise of the battery.

Comparative Example 1

In the battery of Example 1, a battery B51 that does not use the flame retardant for lithium ion secondary battery of the present invention was produced. Initial aging was performed under the same conditions as in Example 1. Thereafter, a nail penetration test was performed under the same conditions. When the flame retardant for lithium ion secondary battery of the present invention was not used, the maximum temperature of the battery increased.

The flame retardant for lithium ion secondary batteries of the present invention is considered to function by the following mechanism. By inserting a nail into a charged battery, the positive electrode 107 and the negative electrode 108 are short-circuited, and the temperature rises locally. At that time, oxygen is desorbed from the positive electrode 107. When (CH ₃ O) ₃ PCuI is used as a flame retardant for lithium ion batteries, (CH ₃ O) ₃ PCuI decomposes into trimethyl phosphite and CuI depending on the temperature. Trimethyl phosphite reacts with oxygen desorbed from the positive electrode 107 to capture oxygen. Alternatively, as another reaction route, trimethyl phosphite is directly oxidized by oxygen desorbed from the positive electrode 107. Therefore, by any reaction route, oxygen desorbed from the positive electrode 107 is removed from the inside of the battery, so that it is possible to prevent the combustion reaction of the flammable carbonate.

As can be seen from the results of the maximum temperatures of B11, B12, B13, B14, B15, and B16, by adding the amount of the flame retardant for the lithium ion secondary battery to 10% by weight or more with respect to the electrolyte weight, The amount of trimethyl acid released is sufficient, and the maximum temperature can be kept low.

In this example, the compound of (Formula 1) in Example 1 was changed to the compound of (Formula 2) to produce 5 types of batteries. The compound is [(CH ₃ O) ₅ ] PFeI. Compared with the compound of Example 1, a material having a higher ratio of trimethyl phosphite per unit weight is used.

The initial aging was performed under the same conditions as in Example 1. Thereafter, the battery was charged to 4.2 V and a nail penetration test was conducted. The maximum battery temperature during the nail penetration test is shown in Table 1.

As in Example 1, the maximum temperature of the battery decreased as the amount of the flame retardant for the lithium ion secondary battery increased. Compared with Example 1, even in the same addition amount, a lower temperature was obtained in this Example. This is probably because the ratio of trimethyl phosphite contained per unit weight of [(CH ₃ O) ₃ P] ₅ FeI is high.

In this example, compounds in which the iodine of the compound of Example 1 was changed to fluorine, chlorine or bromine were synthesized. These were added to the battery by 40% by weight to produce three types of batteries. Initial aging was performed under the same conditions as in Example 1. Thereafter, the battery was charged to 4.2 V and a nail penetration test was conducted. The maximum battery temperature during the nail penetration test is shown in Table 1.

Compared with Example 1, the maximum temperature of the battery tended to decrease when bromine was replaced by iodine, chlorine by bromine, and chlorine by fluorine. This is presumably because the proportion of trimethyl phosphite contained in the compound per unit weight increases as the halogen atomic weight decreases.

In this example, compounds in which the iodine of the compound of Example 2 was changed to fluorine, chlorine or bromine were synthesized. These were added to the battery by 20% by weight to produce three types of batteries. Initial aging was performed under the same conditions as in Example 2. Thereafter, the battery was charged to 4.2 V and a nail penetration test was conducted. The maximum battery temperature during the nail penetration test is shown in Table 1.

Compared with Example 2, the maximum temperature of the battery tended to decrease when bromine was replaced by iodine, chlorine by bromine, and fluorine by chlorine. This is presumably because the proportion of trimethyl phosphite contained in the compound per unit weight increases as the halogen atomic weight decreases. Moreover, compared with Example 3, since the compound of the present Example contained trimethyl phosphite at a higher ratio, the temperature was lower. This result is similar to the difference between Example 1 and Example 2.

The size of the battery B23 of Example 2 was increased by a factor of 5 to produce two 50Ah prismatic lithium ion secondary batteries. FIG. 2 shows the battery system of the present invention in which the lithium ion secondary batteries 201a and 201b are connected in series.

Each of the lithium ion secondary batteries 201 a and 201 b has an electrode group having the same specifications including a positive electrode 207, a negative electrode 208, and a separator 209, and is housed in a battery container 202. A battery lid 203 having a positive external terminal 204 and a negative external terminal 205 is provided on the upper part of the battery container 202. An insulating seal member 212 is inserted between each external terminal and the battery lid 203 so that the external terminals are not short-circuited. In FIG. 2, components corresponding to the positive electrode lead wire 110 and the negative electrode lead wire 111 in FIG. 1 are omitted, but the internal structure of the lithium ion secondary batteries 201a and 201b is the same as that in FIG.

The negative external terminal 205 of the lithium ion secondary battery 201 a is connected to the negative input terminal of the charging controller 216 by the power cable 213. The positive external terminal 204 of the lithium ion secondary battery 201a is connected to the negative external terminal 205 of the lithium ion secondary battery 201b via the power cable 214. The positive external terminal 204 of the lithium ion secondary battery 201 b is connected to the positive input terminal of the charging controller 216 by the power cable 215. With such a wiring configuration, the two lithium ion secondary batteries 201a and 201b can be charged or discharged. The lithium ion secondary batteries are connected in series as shown in FIG. 2, but they may be connected in parallel. Moreover, the number of batteries is arbitrary.

The charge / discharge controller 216 exchanges power with an externally installed device (hereinafter referred to as an external device) 219 via the power cable 217 and the power cable 218. The external device 219 includes various electric devices such as an external power source and a regenerative motor for supplying power to the charge / discharge controller 216, and an inverter, a converter, and a load that supply power from the system. An inverter or the like may be provided in accordance with the type of AC or DC that the external device 219 supports. As these devices, known devices can be arbitrarily applied.

Also, a power generator 222 that simulates the operating conditions of a wind power generator was installed as a device that generates renewable energy, and was connected to the charge / discharge controller 216 via the power cable 220 and the power cable 221. When the power generation device 222 generates power, the charge / discharge controller 216 shifts to the charge mode, supplies power to the external device 219, and charges surplus power to the lithium ion secondary battery 201a and the lithium ion battery secondary 201b. Further, when the power generation amount simulating the wind power generator is smaller than the required power of the external device 219, the charge / discharge controller 216 operates to discharge the lithium ion secondary battery 201a and the lithium ion secondary battery 201b. The power generation device 222 can be replaced with another power generation device, that is, any device such as a solar cell, a geothermal power generation device, a fuel cell, or a gas turbine generator. The charge / discharge controller 216 stores a program that can be automatically operated so as to perform the above-described operation.

The lithium ion secondary battery 201a and the lithium ion secondary battery 201b are normally charged so that a rated capacity can be obtained. For example, constant voltage charging with the voltage of each battery held at 4.2 V can be performed for 0.5 to 2 hours at a charging current of 1 hour rate. Since the charging conditions are determined by the design of the material and amount of use of the lithium ion battery, the conditions are optimal for each battery specification.

After charging the lithium ion secondary battery 201a and the lithium ion secondary battery 201b, the charge / discharge controller 216 is switched to the discharge mode to discharge each battery. Normally, the discharge was stopped when the battery voltage reached a certain lower limit, and the lower limit was set to 2.5 V in this example.

With the system configuration described above, the external device 219 supplies power during charging and consumes power during discharging. In this embodiment, charging is performed at a 2-hour rate, and discharging is performed at a 1-hour rate. The initial discharge capacity was determined. As a result, a capacity of 99.5 to 100% of the designed capacity 50Ah of each lithium ion secondary battery 201a, 201b was obtained.

Thereafter, the charge / discharge cycle test described below was conducted under the condition of the environmental temperature of 20 to 30 ° C. First, charging is performed at a current of 2 hours (25 A), and when the depth of charge reaches 50% (25 Ah charged state), a 5 second pulse is charged in the charging direction and a 5 second pulse is discharged in the discharging direction. A pulse test was performed to simulate the acceptance of power from the power generation device 222 and the supply of power to the external device 219. The magnitude of the current pulse was 150A for both. Subsequently, the remaining capacity 25Ah was charged with a current (25A) at a rate of 2 hours until the voltage of each battery reached 4.2V, and after constant voltage charging for 1 hour at that voltage, the charging was terminated. . Thereafter, the voltage of each battery was discharged to 2.5 V at a current of 1 hour rate (50 A).

Such a series of charge / discharge cycle tests was repeated 500 times, and a capacity of 97 to 98% of the initial discharge capacity was obtained. It was found that the performance of the system was hardly degraded when the battery was given a current pulse of power acceptance and power supply.

Next, only the lithium ion secondary battery 201a was charged in advance to the rated capacity, and the system was assembled with the lithium ion secondary battery 201b discharged. In this state, when the lithium ion secondary battery 201b was charged to the rated capacity, the lithium ion secondary battery 201a was overcharged, but the battery temperature remained at 140 ° C. or lower and the separator shutdown mechanism worked. , Charging stopped. During this process, the lithium ion secondary battery 201a did not rupture or ignite.

101, 201a, 201b Lithium ion secondary battery 102, 202 Battery container 103 Lid 104, 204 Positive external terminal 105, 205 Negative external terminal 106, 206 Injection port 107, 207 Positive electrode 108, 208 Negative electrode 109, 209 Separator 110 Positive electrode lead Wire 111 Negative electrode lead wire 112, 212 Insulating sealing material 113 Electrolytic solution 213, 214, 215, 217, 218, 220, 221 Power cable 216 Charge / discharge controller 219 External device 222 Power generation device

Claims (6)

1. A flame retardant for a lithium ion secondary battery containing a compound having phosphorus as a ligand,
   A flame retardant for a lithium ion secondary battery, wherein the compound contains one or more of Cu, Ag, Fe, Ru, Pt and a halogen element.
2. In claim 1,
   The said compound is a flame retardant for lithium ion secondary batteries represented by the following (Formula 1) or (Formula 2).
   (R ¹ R ² R ³ ) PMX (Formula 1)
   [(R ¹ R ² R ³ ) P] ₅ —Fe—X (Formula 2)
   R ¹ , R ² and R ³ in (Formula 1) and (Formula 2) represent a linear or branched alkyl group or alkoxy group which may be the same or different from each other.
   In (Formula 1) and (Formula 2), X is a halogen element.
   In (Formula 1), M is one or more of Cu, Ag, Fe, Ru, and Pt.
3. In any one of Claims 1 thru | or 2.
   The flame retardant for a lithium ion secondary battery, wherein the halogen element is fluorine.
4. An electrolyte solution for a lithium ion secondary battery comprising the flame retardant for a lithium ion secondary battery according to claim 1,
   The amount of the compound added is 10% by weight or more based on the weight of the electrolyte solution for lithium ion secondary batteries.
5. A lithium ion secondary battery comprising the flame retardant for a lithium ion secondary battery according to any one of claims 1 to 3,
   The lithium ion secondary battery has a porous material,
   The flame retardant for a lithium ion secondary battery is a lithium ion secondary battery held in the porous material.
6. A battery system having the lithium ion secondary battery according to claim 5.

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