JP2008041504A - Nonaqueous electrolyte battery - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To prevent contact between a positive electrode and a negative electrode caused by contraction of a separator in temperature rise in a battery. <P>SOLUTION: For the separator, a surface layer containing polymer particles having a melting point lower than that of a separator material is formed on a surface thereof. The surface layer is formed by applying slurry comprising, for instance, a binder, a solvent and polymer particles to the separator, phase-separating it by making it pass through a poor solvent of the binder and a solvent affinity bath of the solvent, and thereafter drying it. A material high in affinity to the separator material is preferable for the polymer particles used in this case, and the average particle diameter thereof is preferably set not larger than 5.0 μm in order to prevent the degradation of volume efficiency and a load characteristic of the battery caused by excessive increase of thickness of the surface layer. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a nonaqueous electrolyte battery in which a positive electrode and a negative electrode are arranged to face each other with a separator interposed therebetween.

  In recent years, with the remarkable development of portable electronic technology, electronic devices such as mobile phones, notebook personal computers, and PDAs (Personal Digital Assistants) have been recognized as fundamental technologies that support an advanced information society. It was. Furthermore, research and development related to the enhancement of the functionality of these devices is being pursued energetically, and the power consumption of electronic devices is steadily increasing in proportion thereto. On the other hand, these electronic devices are required to be driven for a long time, and it has been desired to increase the energy density of the secondary battery, which is a driving power source.

  From the viewpoint of the occupied volume and weight of the battery built in the electronic device, the higher the energy density of the battery, the better. Therefore, in order to meet this demand, batteries using lithium (Li) as an electrode reactant, for example, lithium / manganese dioxide batteries, lithium / iron sulfide batteries, and lithium ion batteries have been proposed. These batteries have a winding structure in which a positive electrode and a negative electrode are stacked via a separator and wound in a spiral shape, thereby exhibiting high storage characteristics, low temperature characteristics, load characteristics, and the like.

  On the other hand, the temperature in the battery rises when a large current flows due to overcharging or misuse. Since these batteries use a non-aqueous solvent as an electrolytic solution, there is a risk of thermal runaway when the temperature in the battery rises. For this reason, in order to ensure the safety of these batteries, a mechanism for interrupting the current when the batteries generate heat is incorporated.

  Therefore, in order to deal with such a problem, as in Patent Document 1 below, when the temperature in the battery rises or when a large current flows, a current interruption mechanism that physically interrupts the circuit in the battery is provided. Provided batteries have been proposed.

JP 2004-031165 A

  In such a battery, the current is cut off by a current cut-off mechanism, and when the internal temperature of the battery becomes high, for example, a polyolefin resin material disposed between the positive electrode and the negative electrode is stretched. The separator has a so-called shutdown function in which the current is interrupted by melting the separator and closing the holes produced by stretching.

  However, when the separator shuts down, the separator contracts, which may cause secondary problems such as a direct contact between the positive electrode and the negative electrode, which may cause a short circuit.

  Accordingly, an object of the present invention is to solve the above problems and provide a non-aqueous electrolyte battery that can stably ensure the safety of the battery even when the temperature inside the battery becomes high.

  In order to solve the above problems, the present invention is a nonaqueous electrolyte battery in which a positive electrode and a negative electrode are arranged to face each other with a separator interposed therebetween, and a surface layer is provided on at least one main surface of the separator. A nonaqueous electrolyte battery comprising polymer particles having a melting point lower than that of a separator.

  The average particle size of the polymer particles is preferably 5.0 μm or less, and the microporous membrane is preferably made of polypropylene.

  The surface layer preferably includes polymer particles and a binder, and the binder is preferably a copolymer of vinylidene fluoride and hexafluoropropylene.

  In this invention, when the temperature inside the battery becomes high, the polymer particles having a melting point lower than that of the separator are melted before the separator and form a film on the separator surface. Membrane vacancies can be blocked.

  According to the present invention, the current can be interrupted without contracting the separator when the temperature inside the battery becomes high.

(1) First Embodiment (1-1) Configuration of Lithium Iron Disulfide Primary Battery Hereinafter, embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a cross-sectional perspective view of a lithium iron disulfide primary battery, which is an example of a nonaqueous electrolyte battery according to the first embodiment of the present invention.

The lithium iron disulfide primary battery using iron disulfide (FeS ₂ ) as the positive electrode, for example, in the case of the AAA type, has an initial open circuit voltage (OCV) of 1.7 V to 1.8 V and an average discharge. Since the voltage is about 1.3 V to 1.6 V and has an average discharge voltage that is 0.2 V higher than that of the alkaline dry battery, it is possible to discharge longer than the alkaline dry battery in the constant output discharge. The practical value is also high in terms of compatibility with other 1.5V class primary batteries, such as manganese batteries, alkaline manganese batteries, silver oxide batteries, air batteries, and nickel / zinc batteries using an aqueous solution as an electrolyte.

  In addition, the positive electrode active material iron disulfide is about 894 mAh / g, and the negative electrode active material lithium is about 3863 mAh / g, which is composed of a positive electrode material and a negative electrode material showing very high theoretical capacity, and has a high capacity and light weight. From the viewpoint of battery characteristics such as load characteristics and low temperature characteristics, the battery is extremely excellent.

  Hereinafter, the configuration of the lithium iron disulfide primary battery will be described in detail.

  A lithium iron disulfide primary battery 10 shown in FIG. 1 is a so-called cylindrical type, and has a wound electrode body 20 inside a substantially hollow cylindrical battery can 1. The wound electrode body 20 is formed by winding a strip-shaped positive electrode 11 having a positive electrode active material and a strip-shaped negative electrode 12 having a negative electrode active material many times through a separator 13 having ion permeability.

  The battery can 1 is made of, for example, iron plated with nickel, and has one end closed and the other end open. Inside the battery can 1, a pair of insulating plates 8 and 9 are arranged perpendicular to the peripheral surface so as to sandwich the wound electrode body 20.

  At the open end of the battery can 1, there is a battery lid 2, a thermal resistance element (Positive Temperature Coefficient; PTC element) 4 provided inside the battery lid 2, and a safety valve 3 through an insulating sealing gasket 5. The battery can 1 is attached by being caulked, and the inside of the battery can 1 is sealed. Further, between the wound electrode body 20 and the safety valve 3, a shut-off disk 6 and an insulating ring 7 for insulating the safety valve 3 and the shut-off disk 6 are arranged.

  The battery lid 2 is made of, for example, the same material as the battery can 1. The safety valve 3 is electrically connected to the battery lid 2 via the heat sensitive resistance element 4 and deforms in the direction of the battery lid 2 when the internal pressure of the battery becomes a certain level or more due to an internal short circuit or external heating. To do. The positive terminal 14 led out from the wound electrode body 20 is connected to the safety valve 3 through a hole portion of the shut-off disk 6. The mechanism mainly composed of the safety valve 3 and the shutoff disk 6 is such that the positive electrode terminal 14 is caught by the shutoff disk 6 when the safety valve 3 is deformed and the connection is released, so that the battery lid 2 and the wound electrode body 20 are electrically connected. It has a function as a so-called current interruption mechanism.

  When the temperature rises, the heat sensitive resistance element 4 limits the current by increasing the resistance value and prevents abnormal heat generation due to a large current, and is made of, for example, barium titanate semiconductor ceramics. The insulating sealing gasket 5 is made of, for example, an insulating material, and the surface is coated with, for example, asphalt.

  Hereinafter, the wound electrode body 20 will be described.

[Wound electrode body]
The wound electrode body 20 is produced by winding a laminated electrode body 16 in which the positive electrode 11 and the negative electrode 12 are laminated via the separator 13.

[Positive electrode]
The positive electrode 11 includes a positive electrode current collector 11b having a strip shape and a positive electrode mixture layer 11a formed on both surfaces of the positive electrode current collector 11b. The positive electrode current collector 11b is a metal foil such as an aluminum (Al) foil, a nickel (Ni) foil, or a stainless (SUS) foil.

The positive electrode mixture layer 11a includes, for example, iron disulfide (FeS ₂ ) that is a positive electrode active material, a conductive agent, and a binder. Iron disulfide, which is a positive electrode active material, is obtained by pulverizing pyrite (Pyrite) that exists mainly in nature. Chemical synthesis, for example, ferrous chloride (FeCl ₂ ) is converted to hydrogen sulfide (H ₂ S). Iron disulfide obtained by firing inside can also be used.

  As the binder, for example, polyvinylidene fluoride (PVdF), polytetrafluoroethylene (PTFE) or the like is used. Further, as the conductive agent, a material that can be mixed with an appropriate amount of the positive electrode active material to impart conductivity, for example, carbon powder such as graphite and carbon black can be used.

[Negative electrode]
The negative electrode 12 is made of a metal foil having a strip shape. Examples of the metal foil material that is also the negative electrode active material include lithium metal or lithium alloy obtained by adding an alloy element such as aluminum to lithium.

[Electrolyte]
The electrolytic solution is a solution in which an electrolyte salt is dissolved in a non-aqueous solvent, and generally used materials can be used.

  Examples of the non-aqueous solvent include propylene carbonate, ethylene carbonate, diethyl carbonate, dimethyl carbonate, methyl ethyl carbonate, γ-butyrolactone, tetrahydrofuran, 2-dimethoxyethane, 1,3-dioxolane, 4-methyl-1,3-dioxolane. , Diethyl ether, sulfolane, methyl sulfolane, acetonitrile or propionitrile, anisole, acetic acid ester, tangled acid ester or propionic acid ester, etc. are preferred, and any one of these or a mixture of two or more may be used. it can.

As the electrolyte salt, one that dissolves in the non-aqueous solvent is used, and a combination of a cation and an anion is used. Alkali metal or alkaline earth metal is used as the cation, and Cl ⁻ , Br ⁻ , I ⁻ , SCN ⁻ , ClO ₄ ⁻ , BF ₄ ⁻ , PF ₆ ⁻ , CF ₃ SO ₃ ⁻ or the like is used as the anion. It is done. Specifically, for example, LiCl, LiClO ₄ , LiAsF ₆ , LiPF ₆ , LiBF ₄ , LiB (C ₆ H ₅ ) ₄ , LiBr, CH ₃ SO ₃ Li, CF ₃ SO ₃ Li, N (CnF _{2n + 1} SO ₂ ) ₂ Li and the like, and any one of these or a mixture of two or more thereof is used. Among them, it is preferable to mainly use LiPF ₆ . The electrolyte salt concentration is not a problem as long as it can be dissolved in the non-aqueous solvent, but the lithium ion concentration is 0.4 mol / kg or more and 2.0 mol / kg or less with respect to the non-aqueous solvent. A range is preferable.

[Separator]
The separator 13 is made of, for example, a microporous film made of a resin material having a large number of minute holes produced by uniaxial stretching or biaxial stretching of a resin material, and has a lower melting point than the resin material of the separator 13 on the surface thereof. A surface layer containing polymer particles is provided. Here, the microporous membrane has a large number of micropores having an average pore diameter of about 5.0 μm or less, for example.

  As the separator 13, it is possible to use polypropylene (PP), polytetrafluoroethylene (PTFE), or a resin material produced by melt-kneading polypropylene (PP) and polyethylene (PE).

  For example, the separator 13 has a thickness in the range of 5.0 μm or more and 50 μm or less, and a porosity representing a ratio of the void volume in the entire volume thereof in a range of 20% or more and 60% or less. Is preferred. With the separator 13 meeting such conditions, it becomes possible to obtain the lithium iron disulfide primary battery 10 excellent in manufacturing yield, output characteristics, cycle characteristics, and safety.

  The surface layer provided on the surface of the separator 13 is made of a binder carrying polymer particles. The surface layer in which polymer particles having a melting point lower than that of the resin material of the separator 13 are supported on the binder is formed on the surface of the separator 13 so that the shutdown of the separator 13 can be performed when the temperature inside the battery becomes high. The polymer particles melt before they occur. As a result, a film is formed on the surface of the separator 13 and the pores of the separator 13 are closed. For this reason, at the temperature lower than the melting point of the separator 13, it is possible to obtain almost the same effect as when the microporous membrane itself shuts down, and the current is blocked by preventing ions from passing through the separator 13. Can do.

  In the present invention, the current interruption includes not only complete interruption but also a state where the interruption is caused by a small amount of current.

  Examples of the binder include polyvinylidene fluoride (PVdF), hexafluoropropylene (HFP), polytetrafluoroethylene (PTFE), polyvinyl alcohol (PVA), styrene-butadiene rubber (SBR), and carboxymethyl cellulose (CMC). It is also possible to use a copolymer of vinylidene fluoride (VDF) and hexafluoropropylene (HFP) or a copolymer of vinylidene fluoride (VDF) and monomethylmaleic acid (MMM). It is.

  As the polymer particles, polyethylene (PE), a copolymer of polypropylene (PP) and polyethylene (PE), polyvinyl chloride (PVC), a copolymer of polyethylene (PE) and vinyl acetate, and the like can be used. Yes, polyethylene (PE) is preferably low density polyethylene (LDPE).

  In addition, it is preferable to use a material having high compatibility with the resin material of the separator 13 for the polymer particles. This is because when a material having low compatibility is used, the polymer particles are not adhered to the separator 13 when forming a film, and the current blocking effect may be weakened.

  These polymer particles have a melting point of about 100 ° C. to 130 ° C., which is lower than that of polypropylene (PP) or the like used as a separator material, and melt before the separator when the temperature in the battery rises.

  The average particle diameter (median diameter) of the polymer particles is preferably 5.0 μm or less. This is because when the polymer particles exceeding 5.0 μm are used, the surface layer becomes thick, the volume efficiency is lowered, the battery capacity is lowered, and the load characteristics are lowered.

  The surface layer can be provided on one side or both sides of the separator 13, but is preferably provided on one side. Since the thinner the surface layer is, the more difficult it is to control, it is preferable to form a surface layer having a necessary thickness on one surface. The surface layer may be on either the positive electrode 11 side or the negative electrode 12 side.

  Such a separator 13 is impregnated with, for example, a nonaqueous electrolytic solution, and has a function of preventing physical contact between the positive electrode 11 and the negative electrode 12 by being disposed between the positive electrode 11 and the negative electrode 12. Further, the separator 13 absorbs the non-aqueous electrolyte so as to hold the non-aqueous electrolyte in the pores and allows lithium ions to pass during discharge.

[Positive terminal]
A positive electrode terminal 14 made of aluminum (Al) or the like is connected to the positive electrode current collector 11b. The positive electrode terminal 14 is preferably connected to one surface of the positive electrode current collector 11b where the positive electrode mixture layer 11a is not provided. The positive electrode terminal 14 is electrically connected to the battery lid 2 by being welded to the safety valve 3.

[Negative terminal]
A negative electrode terminal 15 made of nickel (Ni) or the like is connected to the negative electrode 12. Such a negative electrode terminal 15 is fixed and electrically connected to the battery can 1.

(1-2) Method for Producing Lithium Iron Disulfide Primary Battery Hereinafter, a method for producing the lithium iron disulfide primary battery 10 will be described.

[Production of positive electrode]
First, for example, a positive electrode active material, a binder, and a conductive agent are mixed to prepare a positive electrode mixture, and this positive electrode mixture is dispersed in a solvent such as N-methyl-2-pyrrolidone (NMP) to form a paste A positive electrode mixture slurry is obtained. The positive electrode mixture slurry is applied on the positive electrode current collector 11b and dried, and then compression molded by a roller press or the like to form the positive electrode mixture layer 11a. Furthermore, the positive electrode 11 is fabricated by connecting the positive electrode terminal 14 to one end of the positive electrode current collector 11b by resistance welding or ultrasonic welding.

  The positive electrode terminal 14 is preferably a metal foil or a mesh-like one, but there is no problem even if it is not a metal as long as it is electrochemically and chemically stable and can conduct electricity. Examples of the material of the positive electrode terminal 14 include aluminum (Al).

[Production of negative electrode]
The negative electrode 12 is produced by fixing the negative electrode terminal 15 to lithium metal or a lithium alloy by pressure bonding or the like.

[Production of surface layer]
The surface layer provided on the surface of the separator 13 is formed by, for example, applying a slurry composed of a binder, a solvent, and polymer particles on the microporous film, and in a poor solvent of the binder and a solvate bath of this solvent. Through a phase separation and then dried.

[Production of wound electrode body]
The positive electrode 11 having the strip shape obtained as described above, the negative electrode 12, and the separator 13 are laminated in the order of the positive electrode 11, the separator 13, the negative electrode 12, and the separator 13, for example, to obtain a laminated electrode body 16. Subsequently, the laminated electrode body 16 is wound many times in the longitudinal direction to produce a wound electrode body 20.

  Next, the lithium iron disulfide primary battery 10 is manufactured using such a wound electrode body 20.

[Production of lithium iron disulfide primary battery]
First, the wound electrode body 20 is accommodated in the battery can 1 in which the insulating plate 8 is inserted in advance at the bottom and nickel plating is applied in advance on the inside. Then, the insulating plate 9 is disposed on the upper surface of the wound electrode body 20. Thereafter, in order to collect current from the negative electrode 12, one end of the negative electrode terminal 15 led out from the wound electrode body 20 is welded to the battery can 1 by resistance welding or ultrasonic welding.

  As a result, the battery can 1 is electrically connected to the negative electrode 12 and becomes an external negative electrode. Further, in order to collect the current of the positive electrode 11, one end of the positive electrode terminal 14 led out from the wound electrode body 20 is connected to the safety valve 3 to be electrically connected to the battery lid 2. As a result, the battery lid 2 is electrically connected to the positive electrode 11 and becomes an external positive electrode.

  Subsequently, after injecting the electrolyte into the battery can 1, the blocking disc 6 and the insulating ring 7 are inserted, and the battery lid 2 is caulked through the insulating sealing gasket 5 coated with asphalt to thereby remove the battery can 1. Seal. Thereby, a cylindrical lithium iron disulfide primary battery is manufactured.

(2) Second Embodiment (2-1) Configuration of Lithium Ion Secondary Battery FIG. 2 shows a configuration of a lithium ion secondary battery 30 which is an example of a nonaqueous electrolyte battery according to the second embodiment of the present invention. It is a schematic diagram which shows. FIG. 3 is a cross-sectional view showing the laminated structure of the electrodes of the lithium ion secondary battery 30.

  The lithium ion secondary battery 30 uses a lithium-containing transition metal compound for the positive electrode and a carbon material for the negative electrode. For example, an open circuit voltage in a fully charged state (hereinafter appropriately referred to as a fully charged state) per pair of positive electrode and negative electrode. Is in the range of 4.20V to 4.60V, or 4.25V to 4.60V. By increasing the charging voltage to 4.25 V or higher as compared with the conventional 4.20 V, the capacity of the positive electrode active material that has not been used so far can be utilized. That is, the amount of lithium released per unit mass of the positive electrode active material is increased and occluded in the negative electrode active material, so that the capacity and energy density can be increased. Hereinafter, a lithium ion secondary battery used in a high charge voltage state where the open circuit voltage in the fully charged state is 4.25 V or more will be described.

  The lithium ion secondary battery 30 is sealed by housing the wound electrode body 40 in an exterior material 38 made of a moisture-proof laminate film and welding the periphery of the wound electrode body 40 as shown in FIG. It becomes. The wound electrode body 40 is provided with a positive electrode terminal 35 and a negative electrode terminal 36, and these terminals are sandwiched between outer packaging materials 38 and pulled out to the outside. Both surfaces of the positive electrode terminal 35 and the negative electrode terminal 36 are covered with sealants 37a and 37b made of resin pieces in order to improve the adhesion to the exterior material 38.

  In addition, in the wound electrode body 40, since the same material as 1st Embodiment can be used except the positive electrode active material used for the positive electrode 31, the negative electrode 32, and the gel electrolyte 34, description is abbreviate | omitted.

[Exterior material]
The exterior material 38 has, for example, a laminated structure in which an adhesive layer, a metal layer, and a surface protective layer are sequentially laminated, and is provided with a housing portion 38a that houses the wound electrode body 40, for example. The adhesive layer is made of a polymer film. Examples of the material constituting the polymer film include polypropylene (PP), polyethylene (PE), unstretched polypropylene (CPP), linear low density polyethylene (LLDPE), and low density. A polyethylene (LDPE) is mentioned. The metal layer is made of a metal foil, and an example of a material constituting the metal foil is aluminum (Al). Moreover, it is also possible to use metals other than aluminum as a material which comprises metal foil. Examples of the material constituting the surface protective layer include nylon (Ny) and polyethylene terephthalate (PET). The surface on the adhesive layer side is a storage surface on the side where the battery element 30 is stored.

[Positive electrode]
As the positive electrode 11, the same configuration as that of the first embodiment can be used. Moreover, the following materials can be used as a positive electrode active material.

As the positive electrode active material, for example, one or more positive electrode active materials capable of inserting and extracting lithium can be used. As the positive electrode active material capable of inserting and extracting lithium, for example, lithium-containing transition metal compounds such as lithium oxide, lithium phosphorus oxide, and lithium sulfide are suitable. In order to increase the energy density, a lithium-containing transition metal oxide containing lithium, a transition metal element, and oxygen (O) is preferable. Among them, as the transition metal element, cobalt (Co), Ni, manganese (Mn), and iron It is more preferable if it contains at least one of the group consisting of (Fe). Examples of such a lithium-containing transition metal compound include a lithium-containing transition metal oxide having a layered rock-salt structure shown in Chemical Formula 1 below and a lithium composite phosphate having an olivine-type structure shown in Chemical Formula 2 below. Specific examples include LiNi _0.50 Co _0.20 Mn _0.30 O ₂ , LiCoO ₂ , LiNiO ₂ , LiNi _c Co _1-c O ₂ (0 <c <1), LiMn ₂ O _4, LiFePO _{4, and the} like. is there.

Formula _{1] Li p Ni (1-} qr) Mn q M1 r O (2-y) X z
In the formula, M1 represents at least one element selected from Groups 2 to 15 excluding Ni and Mn, and X represents at least one element selected from Group 16 elements and Group 17 elements other than oxygen (O). p, q, y and z are 0 ≦ p ≦ 1.5, 0 ≦ q ≦ 1.0, 0 ≦ r ≦ 1.0, −0.10 ≦ y ≦ 0.20, 0 ≦ z ≦ 0.2 It is a value within the range.

[Formula 2] Li _a M2 _b PO ₄
In the formula, M2 represents at least one element selected from Groups 2 to 15. a and b are values within the range of 0 ≦ a ≦ 2.0 and 0.5 ≦ b ≦ 2.0.

[Negative electrode]
In the negative electrode 32, a negative electrode mixture layer 32a containing a negative electrode active material is formed on both surfaces of a negative electrode current collector 32b. The negative electrode current collector 32b is made of a metal foil such as a copper (Cu) foil, a nickel (Ni) foil, or a stainless steel (SUS) foil.

  The negative electrode mixture layer 32a includes, for example, a negative electrode active material, a conductive agent if necessary, and a binder. Here, the mixing ratio of the negative electrode active material, the conductive agent, and the binder is not limited as in the positive electrode active material.

As the negative electrode active material, lithium metal, a lithium alloy, a carbon material that can be doped / undoped with lithium, or a composite material of a metal material and a carbon material is used. Specific examples of the carbon material that can be doped / undoped with lithium include graphite, non-graphitizable carbon, and graphitizable carbon. More specifically, pyrolytic carbons, cokes (pitch coke, needle coke, petroleum coke), graphites, glassy carbons, organic polymer compound fired bodies (phenolic resin, furan resin, etc.) at an appropriate temperature. Carbon materials such as those obtained by firing and carbonization), carbon fibers, activated carbon, and the like can be used. Furthermore, as a material that can be doped / undoped with lithium, polymers such as polyacetylene and polypyrrole, and oxides such as SnO ₂ can be used.

  In addition, various kinds of metals can be used as materials capable of alloying lithium, and lithium metals and alloys thereof are often used. When lithium metal is used, it is not always necessary to use powder as a coating film with a binder, and as with the negative electrode 12 in the first embodiment, a method of press-bonding lithium metal to a current collector may be used.

  As the binder, for example, polyvinylidene fluoride (PVdF), styrene butadiene rubber (SBR) or the like is used. As the solvent, for example, N-methyl-2-pyrrolidone (NMP), methyl ethyl ketone, or the like is used.

[Gel electrolyte]
The gel electrolyte is used by gelling the electrolyte used in the first embodiment with a matrix polymer. The matrix polymer is not particularly limited as long as it is compatible with a nonaqueous electrolytic solution obtained by dissolving an electrolyte salt in a nonaqueous solvent and can be gelled. Examples of such a matrix polymer include polymers containing repeating units of polyvinylidene fluoride (PVdF), polyethylene oxide (PEO), polypropylene oxide (PPO), polyacrylonitrile (PAN), and polymethacrylonitrile (PMAN). Such a polymer may be used individually by 1 type, and may mix and use 2 or more types.

Among them, a copolymer in which hexafluoropropylene is introduced into polyvinylidene fluoride (PVdF) or polyvinylidene fluoride at a ratio of 7.5% or less is particularly preferable as the matrix polymer. Such polymers have a number average molecular weight in the range of 5.0 × 10 ⁵ to 7.0 × 10 ⁵ (500,000 to 700,000) or a weight average molecular weight of 2.1 × 10 ⁵ to 3. The range is 1 × 10 ⁵ (210,000 to 310,000), and the intrinsic viscosity is 1.7 to 2.1.

(2-2) Manufacturing Method of Lithium Ion Secondary Battery Hereinafter, a manufacturing method of the lithium ion secondary battery 30 will be described.

[Production of positive electrode]
The positive electrode 31 can be produced in the same manner as in the first embodiment.

[Production of negative electrode]
For example, a negative electrode active material, a binder, and a conductive agent are mixed to prepare a negative electrode mixture, and the negative electrode mixture is dispersed in a solvent such as N-methyl-2-pyrrolidone (NMP) to form a paste-like negative electrode mixture. A slurry is obtained. The negative electrode mixture slurry is applied onto the negative electrode current collector 32b and dried, and then compression molded by a roller press or the like to form the negative electrode mixture layer 32a. Further, the negative electrode 11 is fabricated by connecting the negative electrode terminal 36 to one end of the negative electrode current collector 31b by resistance welding or ultrasonic welding.

  Although the positive electrode terminal 35 and the negative electrode terminal 36 are preferably derived from the same direction, there is no problem even if they are derived from any direction as long as no short circuit or the like occurs and there is no problem in battery performance. Moreover, the positive electrode terminal 35 and the negative electrode terminal 36 are not limited to the above example as long as the positive electrode terminal 35 and the negative electrode terminal 36 are attached as long as they are in electrical contact.

[Production of wound electrode body]
The gel electrolyte solution prepared as described above is uniformly applied to the positive electrode 31 and the negative electrode 32, impregnated in the positive electrode mixture layer 31a and the negative electrode mixture layer 32a, and then stored at room temperature or a drying step. Then, the gel electrolyte layer 34 is formed. Next, the positive electrode 31 formed with the gel electrolyte layer 34, the negative electrode 32, and the separator 33 provided with the surface layer are laminated in the order of the positive electrode 31, the separator 33, the negative electrode 32, and the separator 33, and then wound many times in the longitudinal direction. A flat wound electrode body 40 is produced.

[Production of lithium ion secondary battery]
After the spirally wound electrode body 40 as described above is accommodated in the accommodating portion 38a of the exterior member 38, the periphery of the spirally wound electrode body 40 is welded and sealed, whereby the lithium ion secondary battery 30 is manufactured.

  The nonaqueous electrolyte batteries of the first embodiment and the second embodiment manufactured as described above are high at a temperature lower than the microporous membrane itself shuts down when the temperature inside the battery becomes high. The molecular particles melt and form a film on the surface of the microporous film to interrupt the current. Thereby, since a current can be interrupted without the separator contracting, high safety can be realized.

  EXAMPLES Hereinafter, the present invention will be specifically described with reference to examples. However, the present invention is not limited to these examples.

  In the following examples, lithium iron disulfide primary batteries were produced by changing the material and average particle size of the surface layer formed on the separator surface, and the material of the binder. The separator shrinkage ratio and load characteristics were measured.

<Example 1>
[Production of positive electrode]
Lithium iron phosphate (LiFePO ₄ ) as a positive electrode active material, graphite as a conductive agent, polyvinylidene fluoride (PVdF) as a binder, 92% by weight of lithium iron phosphate, 3.0% by weight of graphite, Polyvinylidene fluoride (5.0% by weight) was mixed and sufficiently dispersed in N-methyl-2-pyrrolidone (NMP) as a solvent to obtain a positive electrode mixture slurry.

  Next, the positive electrode mixture slurry was applied to one surface of a positive electrode current collector made of an aluminum foil, dried under reduced pressure at a temperature of 120 ° C. for 24 hours to volatilize N-methyl-2-pyrrolidone, and then rolled using a roll press. Compression molding was performed at a constant pressure. Next, the positive electrode current collector on which the positive electrode mixture layer was formed was punched into a diameter of 16 mm to obtain a positive electrode.

[Production of negative electrode]
Artificial graphite is used as a negative electrode active material, polyvinylidene fluoride (PVdF) is used as a binder, 91% by weight of artificial graphite and 9.0% by weight of polyvinylidene fluoride are mixed, and N-methyl-2-2 which is a solvent is mixed. A negative electrode mixture slurry was obtained by sufficiently dispersing in pyrrolidone (NMP).

  Next, the negative electrode mixture slurry was applied to one side of a negative electrode current collector made of copper foil, dried under reduced pressure at a temperature of 120 ° C. for 24 hours to volatilize N-methyl-2-pyrrolidone, and then in a roll press machine. Compression molding was performed at a constant pressure. Next, the negative electrode current collector on which the negative electrode mixture layer was formed was punched into a diameter of 16 mm to obtain a negative electrode.

[Non-aqueous electrolyte]
Lithium hexafluorophosphate (LiPF ₆ ) is added to a mixed solvent of polycarbonate (PC) and polyethylene (PE) in a volume ratio of 1: 1, and the molar concentration of lithium hexafluorophosphate is 0.6 mol. A nonaqueous electrolytic solution was prepared by adjusting to 1 / l.

[Preparation of separator]
A single layer film (manufactured by Celgard Inc., # 2500) made of polypropylene was used as the microporous membrane, and a surface layer was formed on one side of the separator. For the surface layer, polyvinylidene fluoride (PVdF) is used as a binder, low-density polyethylene (LDPE) having an average particle size of 5.0 μm is used as polymer particles, and the binder and polymer particles are mixed with N-methyl-2. -Dispersed and mixed in a solvent composed of pyrrolidone (NMP) and applied to the surface of the microporous membrane.

[Preparation of non-aqueous electrolyte battery]
The produced positive electrode was accommodated in a positive electrode can made of stainless steel so that the positive electrode current collector was on the positive electrode can side. Next, the separator in which the surface layer was formed was accommodated, and a nonaqueous electrolytic solution was dropped. Subsequently, the negative electrode current collector is accommodated in a negative electrode can made of stainless steel so that the negative electrode current collector is located on the negative electrode can side, and this is fixed to the positive electrode can through an insulating gasket, whereby R2016 type (diameter 20 mm, thickness 1. 6 mm) coin-type non-aqueous electrolyte battery was produced.

<Example 2>
A nonaqueous electrolyte battery was produced in the same manner as in Example 1 except that a copolymer of vinylidene fluoride (VDF) and hexafluoropropylene (HFP) was used as a binder for the surface layer.

<Example 3>
A nonaqueous electrolyte battery was produced in the same manner as in Example 1 except that a copolymer of vinylidene fluoride (VDF) and monomethylmaleic acid (MMM) was used as a binder for the surface layer.

<Example 4>
A nonaqueous electrolyte battery was produced in the same manner as in Example 1 except that polyvinyl alcohol (PVA) was used as the binder for the surface layer, and 10% N-methyl-2-pyrrolidone was mixed with water as the solvent. did.

<Example 5>
A non-aqueous electrolyte battery in the same manner as in Example 1 except that styrene-butadiene rubber (SBR) was used as the binder for the surface layer and 10% N-methyl-2-pyrrolidone was mixed with water as the solvent. Was made.

<Example 6>
A non-aqueous electrolyte battery was produced in the same manner as in Example 1 except that carboxymethyl cellulose (CMC) was used as the binder for the surface layer and 10% N-methyl-2-pyrrolidone was mixed with water as the solvent. did.

<Comparative Example 1>
A nonaqueous electrolyte battery was produced in the same manner as in Example 1 except that a separator without a surface layer was used.

<Comparative example 2>
A nonaqueous electrolyte battery was produced in the same manner as in Example 1 except that the average particle diameter of the polymer particles was 75 μm.

<Comparative Example 3>
A nonaqueous electrolyte battery was produced in the same manner as in Example 1 except that the average particle diameter of the polymer particles was 10 μm.

<Comparative Example 4>
A nonaqueous electrolyte battery was produced in the same manner as in Example 1 except that the polymer particles were polypropylene (PP) having an average particle diameter of 10 μm.

[Evaluation]
The non-aqueous electrolyte batteries of Examples and Comparative Examples produced as described above were evaluated for (a) current interruption temperature, (b) separator shrinkage rate at current interruption, and (c) load characteristics.

(A) Current interruption temperature A nonaqueous electrolyte battery is placed in a thermostatic chamber, and the temperature is gradually increased while measuring the impedance at a frequency of 1 kHz using an LCR meter (manufactured by Hioki Electric Co., Ltd., LCR Hitester 3511-50). The temperature at which the temperature rapidly increased was measured, and the current interruption occurred at this temperature.

(B) Separator shrinkage rate The separator shrinkage rate is not measured by disassembling an actual battery, but (a) how much shrinkage occurs at the current interruption temperature obtained by measuring the current interruption temperature. The measurement was performed under an atmosphere having the same temperature and environment conditions. In the measurement, a separator provided with a surface layer prepared in each Example and Comparative Example (a separator without a surface layer only in Comparative Example 1) was placed under the cutoff temperature condition in each Example and Comparative Example, and thermomechanical analysis was performed. Measurement was performed with a constant load using an apparatus (TMA; Thermo Mechanical Analysis).

(C) Load characteristics For the obtained non-aqueous electrolyte batteries of Examples and Comparative Examples, discharge was performed at a current of 10 mA, and the discharge capacity (10 mA discharge until the discharge was terminated when the battery voltage reached 1.0 V). Capacity). Next, the discharge capacity (1 mA discharge capacity) of the obtained nonaqueous electrolyte batteries of each of the examples and comparative examples was discharged at a current of 1 mA until the discharge was finished when the battery voltage reached 1.0 V. The load characteristics were evaluated from (10 mA discharge capacity / 1 mA discharge capacity).

  Table 1 below shows the results of the evaluation. In the table, the copolymer of vinylidene fluoride (VDF) and hexafluoropropylene (HFP) is P (VDF-HFP), and the copolymer of vinylidene fluoride (VDF) and monomethylmaleic acid (MMM) is P ( VDF-MMM).

  As can be seen from Table 1, in Examples 1 to 6 and Comparative Examples 2 to 4 using the separator provided with the surface layer, the impedance is abrupt near the melting point of the polymer material contained in the surface layer. An increase was observed.

  In particular, in Examples 1 to 6 using low-density polyethylene (LDPE) as the polymer material, current interruption occurs when the temperature in the battery is about 130 ° C., and the separator has high safety without contraction. I understand. In particular, when a copolymer of vinylidene fluoride (VDF) and hexafluoropropylene (HFP) is used as a binder for the surface layer, very excellent load characteristics can be obtained.

  On the other hand, in Comparative Example 2 and Comparative Example 3 using low density polyethylene (LDPE) having an average particle size of 10 μm or more, high safety is obtained, but load characteristics are remarkably lowered. This is thought to be because the thickness of the surface layer is increased, preventing the permeation of ions.

  In Comparative Example 4 using polypropylene (PP) as polymer particles and Comparative Example 1 using a separator without a surface layer, high load characteristics can be obtained, but the separator shrinks when current is interrupted. This is because in Comparative Example 1, current interruption occurred due to the shutdown of the separator itself. In Comparative Example 4, although the surface layer was provided, the melting point of the polymer particles was the same as the melting point of the separator. This is probably because the separator shuts down almost simultaneously with the melting of.

  As mentioned above, although embodiment of this invention was described concretely, this invention is not limited to the above-mentioned embodiment, The various deformation | transformation based on the technical idea of this invention is possible.

  For example, the numerical values and materials listed in the above-described embodiments are merely examples, and different numerical values and materials may be used as necessary.

  Further, the separator according to the present invention can be used not only in the first and second embodiments described above, but also in any battery as long as the positive electrode and the negative electrode are opposed to each other through the separator.

1 is a cross-sectional perspective view showing an example of a nonaqueous electrolyte battery according to a first embodiment of the present invention. It is a schematic diagram which shows an example of the nonaqueous electrolyte battery by 2nd Embodiment of this invention. It is sectional drawing which shows the laminated structure of the electrode of the nonaqueous electrolyte battery by 2nd Embodiment of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Battery can 2 ... Battery cover 3 ... Safety valve 4 ... Heat sensitive resistance element 5 ... Insulation sealing gasket 6 ... Shut-off disk 7 ... Insulation ring 8, 9 ... Insulating plate 10 ... Lithium iron disulfide primary battery 11, 31 ... Positive electrode 12, 32 ... Negative electrode 13, 33 ... Separator 14, 35 ... Positive electrode terminal 15, 36 ... Negative electrode terminal 20 ... Winding electrode body 30, 40 ... Lithium ion secondary battery 31a ... Positive electrode mixture layer 31b ... Positive electrode current collector 32a ... Negative electrode mixture layer 32b ... Negative electrode current collector 34 ... Gel electrolyte layer 37a, 37b ... Sealant 38 ... Exterior material 38a ... Housing

Claims (4)

A non-aqueous electrolyte battery in which a positive electrode and a negative electrode are arranged to face each other with a separator interposed therebetween,
A surface layer is provided on at least one main surface of the separator,
The non-aqueous electrolyte battery, wherein the surface layer includes polymer particles having a melting point lower than that of the separator. The nonaqueous electrolyte battery according to claim 1, wherein the polymer particles have an average particle size of 5 μm or less. The nonaqueous electrolyte battery according to claim 1, wherein the microporous membrane includes polypropylene. The surface layer includes the polymer particles and a binder,
The non-aqueous electrolyte battery according to claim 1, wherein the binder is a copolymer of vinylidene fluoride and hexafluoropropylene.

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