JP2010225539A - Electrode for lithium ion secondary battery, and lithium ion secondary battery - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an electrode for a lithium ion secondary battery for forming the lithium ion secondary battery which is superior in safety in temperature rise, superior in rate characteristics, and sufficiently suppressed of increase in impedance in repeated use. <P>SOLUTION: The electrode for the lithium ion secondary battery includes a current collector 16, an active material layer 18 formed on the current collector 16, and a protection layer 30 formed on the active material layer 18. The protection layer 30 contains low-melting point organic particles with a melting temperature of 100-200°C and high-melting point organic particles with a melting temperature of 300°C or more. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to an electrode for a lithium ion secondary battery and a lithium ion secondary battery.

  As a safety measure for lithium ion secondary batteries, a method of forming a protective layer on the electrode (negative electrode) surface has been proposed (see, for example, Patent Documents 1 to 3). Conventional protective layers are mainly formed by depositing inorganic particles. However, inorganic particles have a wide particle size distribution, and those having a small particle size are selected to make the protective layer uniform in thickness.

Japanese Patent Laid-Open No. 7-220759 International Publication WO97 / 01870 Pamphlet Japanese Patent Laid-Open No. 11-54147

  However, when particles having a small particle size are used for the protective layer, there is a problem that the electrolytic solution is less likely to penetrate into the protective layer, and battery characteristics such as rate characteristics are deteriorated. Moreover, since the protective layer using inorganic particles does not have a shutdown function, safety at the time of temperature rise is not sufficient.

  On the other hand, even with a protective layer using organic particles, it is difficult to achieve both of providing a shutdown function and suppressing the occurrence of an internal short circuit due to shrinkage (shrinkage) of the protective layer during temperature rise. In addition, when the protective layer is provided with a shutdown function using organic particles, there is a possibility that the impedance is increased by repeatedly using the lithium ion secondary battery.

  The present invention has been made in view of the above-described problems of the prior art, and is excellent in safety at the time of temperature rise, excellent in rate characteristics, and sufficiently reduced in impedance increase during repeated use. It aims at providing the electrode for lithium ion secondary batteries which can form a secondary battery, and a lithium ion secondary battery using the same.

  In order to achieve the above object, the present invention comprises a current collector, an active material layer formed on the current collector, and a protective layer formed on the active material layer. An electrode for a lithium ion secondary battery comprising low melting point organic particles having a melting temperature of 100 to 200 ° C. and high melting point organic particles having a melting temperature of 300 ° C. or higher is provided.

  The protective layer contains two kinds of organic particles having different melting temperatures, so that a sufficient shutdown function can be obtained without deteriorating battery characteristics such as impedance and rate characteristics, and shrinkage at the time of temperature rise can be achieved. It can be sufficiently suppressed. That is, when the temperature rises, the low melting point organic particles are first melted and shut down, and the high melting point organic particles are maintained without being melted to maintain the shape of the protective layer and prevent internal short circuit. It becomes possible to do. Therefore, according to the electrode for a lithium ion secondary battery of the present invention having this protective layer on the surface, it has excellent safety at the time of temperature rise, excellent rate characteristics, and sufficiently suppresses an increase in impedance during repeated use. A lithium ion secondary battery can be formed.

  In the electrode for a lithium ion secondary battery of the present invention, the low-melting-point organic particles are preferably particles made of at least one material selected from the group consisting of polyethylene, polypropylene, and polymethyl methacrylate. As a result, the protective layer can provide a better shutdown function, and can form a lithium ion secondary battery in which the safety at the time of temperature rise is better and the increase in impedance at the time of repeated use is more sufficiently suppressed. Can do.

  In the lithium ion secondary battery electrode of the present invention, the high-melting-point organic particles are preferably particles made of at least one material selected from the group consisting of polyimide and polytetrafluoroethylene. Thereby, the protective layer can suppress the shrink at the time of temperature rise more fully, and can form the lithium ion secondary battery which the safety | security at the time of temperature rise improved more.

  In the electrode for a lithium ion secondary battery of the present invention, the ratio of the content of the low-melting organic particles and the content of the high-melting organic particles in the protective layer is 1: 1 to 1: 4 in mass ratio. Is preferred. When the protective layer contains the low melting point organic particles and the high melting point organic particles in the above ratio, the protective layer has a shutdown function and suppresses the occurrence of an internal short circuit due to the shrinking of the protective layer at the time of temperature rise. Can be achieved at a high level.

  The present invention also provides a lithium ion secondary battery having a positive electrode and a negative electrode, wherein at least one of the positive electrode and the negative electrode includes a current collector, an active material layer formed on the current collector, and the active material. An electrode comprising a protective layer formed on a material layer, the protective layer comprising low melting point organic particles having a melting temperature of 100 to 200 ° C and high melting point organic particles having a melting temperature of 300 ° C or higher. A lithium ion secondary battery is provided.

  The protective layer contains two kinds of organic particles having different melting temperatures, so that a sufficient shutdown function can be obtained without deteriorating battery characteristics such as impedance and rate characteristics, and shrinkage at the time of temperature rise can be achieved. It can be sufficiently suppressed. That is, when the temperature rises, the low melting point organic particles are first melted and shut down, and the high melting point organic particles are maintained without being melted to maintain the shape of the protective layer and prevent internal short circuit. It becomes possible to do. Therefore, according to the lithium ion secondary battery of the present invention having the negative electrode and / or positive electrode having this protective layer on the surface, excellent safety at the time of temperature rise is obtained, and excellent rate characteristics are obtained, Furthermore, an increase in impedance during repeated use can be sufficiently suppressed.

  In the lithium ion secondary battery of the present invention, the low-melting-point organic particles are preferably particles made of at least one material selected from the group consisting of polyethylene, polypropylene, and polymethyl methacrylate. As a result, the protective layer has a better shutdown function, and the lithium ion secondary battery can further improve the safety at the time of temperature rise and more sufficiently suppress the increase in impedance at the time of repeated use. be able to.

  In the lithium ion secondary battery of the present invention, the high melting point organic particles are preferably particles made of at least one material selected from the group consisting of polyimide and polytetrafluoroethylene. As a result, the protective layer can sufficiently suppress shrinkage at the time of temperature rise, and can further improve the safety at the time of temperature rise of the lithium ion secondary battery.

  In the lithium ion secondary battery of the present invention, the ratio of the content of the low-melting organic particles and the content of the high-melting organic particles in the protective layer is preferably 1: 1 to 1: 4 by mass ratio. . When the protective layer contains the low melting point organic particles and the high melting point organic particles in the above ratio, the protective layer has a shutdown function and suppresses the occurrence of an internal short circuit due to the shrinking of the protective layer at the time of temperature rise. Can be achieved at a high level. Therefore, the safety at the time of temperature rising of the lithium ion secondary battery can be further improved.

  In the lithium ion secondary battery of the present invention, it is preferable that at least the negative electrode is an electrode including the current collector, the active material layer, and the protective layer.

  If the protective layer is provided on the negative electrode rather than the positive electrode, the safety at the time of temperature rise can be further improved. This is because dendrite growth on the active material surface of the negative electrode can be suppressed.

  ADVANTAGE OF THE INVENTION According to this invention, while being excellent in the safety | security at the time of temperature rising, it is excellent in a rate characteristic, and the electrode for lithium ion secondary batteries which can form the lithium ion secondary battery by which the raise of the impedance at the time of repeated use was fully suppressed And a lithium ion secondary battery using the same can be provided.

It is a front view which shows suitable one Embodiment of the lithium ion secondary battery of this invention. It is the schematic cross section which cut | disconnected the lithium ion secondary battery shown in FIG. 1 along the XX line of FIG. It is a schematic cross section which shows one Embodiment of the basic composition of the negative electrode of a lithium ion secondary battery. It is a schematic cross section which shows one Embodiment of the basic composition of the positive electrode of a lithium ion secondary battery. It is a partially broken perspective view which shows other suitable one Embodiment of the lithium ion secondary battery of this invention. FIG. 6 is a schematic cross-sectional view along the YZ plane of the lithium ion secondary battery shown in FIG. 5.

  Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the drawings. In the drawings, the same or corresponding parts are denoted by the same reference numerals, and redundant description is omitted. Further, the positional relationship such as up, down, left and right is based on the positional relationship shown in the drawings unless otherwise specified. Further, the dimensional ratios in the drawings are not limited to the illustrated ratios.

  FIG. 1 is a front view showing a preferred embodiment of the lithium ion secondary battery of the present invention. FIG. 2 is a schematic cross-sectional view of the lithium ion secondary battery 1 of FIG. 1 cut along the line XX.

  As shown in FIGS. 1 and 2, the lithium ion secondary battery 1 is mainly disposed adjacent to each other between the plate-like negative electrode 10 and the plate-like positive electrode 20 facing each other, and the negative electrode 10 and the positive electrode 20. A power generation element 60 having a plate-like separator 40, an electrolyte solution containing lithium ions (in this embodiment, a nonaqueous electrolyte solution), a case 50 containing these in a sealed state, and one end of the negative electrode 10 Are electrically connected and the other end is protruded to the outside of the case 50, and one end is electrically connected to the positive electrode 20 and the other end is the case 50. It is comprised from the lead | read | reed 22 for positive electrodes protruded outside.

  In the present specification, the “negative electrode” is an electrode based on the polarity at the time of discharge of the battery and emits electrons by an oxidation reaction at the time of discharge. Further, the “positive electrode” is an electrode based on the polarity at the time of discharging of the battery and accepts electrons by a reduction reaction at the time of discharging.

  3 and 4 are schematic cross-sectional views showing a preferred embodiment of the electrode for a lithium ion secondary battery of the present invention. Here, FIG. 3 is a schematic cross-sectional view showing an embodiment of the basic configuration of the negative electrode 10 of the lithium ion secondary battery 1. FIG. 4 is a schematic cross-sectional view showing an embodiment of the basic configuration of the positive electrode 20 of the lithium ion secondary battery 1.

  As shown in FIG. 3, the negative electrode 10 includes a current collector 16, a negative electrode active material layer 18 formed on the current collector 16, and a protective layer 30 formed on the negative electrode active material layer 18. Become. As shown in FIG. 4, the positive electrode 20 includes a current collector 26, a positive electrode active material layer 28 formed on the current collector 26, and a protective layer 30 formed on the positive electrode active material layer 28. It consists of. The protective layer 30 is a layer containing low melting point organic particles having a melting temperature of 100 to 200 ° C. and high melting point organic particles having a melting temperature of 300 ° C. or higher.

  The current collector 16 and the current collector 26 are not particularly limited as long as they are good conductors that can sufficiently transfer charges to the negative electrode active material layer 18 and the positive electrode active material layer 28, and are known lithium ion secondary batteries. The current collector used in the above can be used. For example, examples of the current collector 16 and the current collector 26 include metal foils such as copper and aluminum.

  The negative electrode active material layer 18 of the negative electrode 10 is mainly composed of a negative electrode active material and a binder. In addition, it is preferable that the negative electrode active material layer 18 further contains a conductive additive.

The negative electrode active material is not particularly limited as long as it is capable of reversibly proceeding with lithium ion insertion and extraction, lithium ion desorption and insertion (intercalation), or lithium ion doping and dedoping. Instead, a known negative electrode active material can be used. As such a negative electrode active material, for example, it can be combined with a carbon material such as natural graphite, artificial graphite, non-graphitizable carbon, graphitizable carbon, low-temperature calcined carbon, or lithium such as Al, Si, or Sn. Examples thereof include amorphous compounds mainly composed of oxides such as metals, SiO, SiO ₂ , SiO _x , and SnO ₂ , lithium titanate (Li ₄ Ti ₅ O ₁₂ ), and TiO ₂ .

  As the binder used for the negative electrode 10, known binders can be used without particular limitation. For example, polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), tetrafluoroethylene-hexafluoropropylene copolymer ( FEP), tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer (PFA), ethylene-tetrafluoroethylene copolymer (ETFE), polychlorotrifluoroethylene (PCTFE), ethylene-chlorotrifluoroethylene copolymer (ECTFE) ), A fluororesin such as polyvinyl fluoride (PVF). In order to more fully bind the constituent materials such as the active material particles and the conductive auxiliary agent added as necessary to the binder, and to bind the constituent materials and the current collector more sufficiently. In addition, a functional group such as carboxylic acid may be introduced.

  In addition to the above, as the binder, for example, vinylidene fluoride-based fluororubber such as vinylidene fluoride-hexafluoropropylene-based fluororubber (VDF-HFP-based fluororubber) may be used.

  In addition to the above, for example, polyethylene, polypropylene, polyethylene terephthalate, aromatic polyamide, cellulose and derivatives thereof, styrene / butadiene rubber, isoprene rubber, butadiene rubber, ethylene / propylene rubber, and the like may be used as the binder. . Examples of the cellulose derivative include sodium carboxymethyl cellulose, hydroxyethyl cellulose, cellulose acetate, cellulose nitrate, and cellulose sulfate. Also, thermoplastic elastomeric polymers such as styrene / butadiene / styrene block copolymers, hydrogenated products thereof, styrene / ethylene / butadiene / styrene copolymers, styrene / isoprene / styrene block copolymers, and hydrogenated products thereof. May be used. Further, syndiotactic 1,2-polybutadiene, ethylene / vinyl acetate copolymer, propylene / α-olefin (carbon number 2 to 12) copolymer and the like may be used. Further, a conductive polymer may be used.

  It does not specifically limit as a conductive support agent used as needed, A well-known conductive support agent can be used. Examples of the conductive assistant include carbon blacks, carbon materials, metal powders such as copper, nickel, stainless steel, and iron, a mixture of carbon materials and metal powders, and conductive oxides such as ITO.

  The content of the negative electrode active material in the negative electrode active material layer 18 is preferably 80 to 98% by mass, and more preferably 85 to 97% by mass based on the total amount of the negative electrode active material layer 18. When the content of the active material is less than 80% by mass, the energy density tends to be lower than when the content is within the above range. When the content exceeds 98% by mass, the content is within the above range. Compared with the case where it is, there exists a tendency for an adhesive force to be insufficient and for cycling characteristics to fall.

  The positive electrode active material layer 28 of the positive electrode 20 is mainly composed of a positive electrode active material and a binder. In addition, it is preferable that the positive electrode active material layer 28 further contains a conductive additive.

The positive electrode active material is not particularly limited as long as it can occlude and release lithium ions, desorption and insertion (intercalation) of lithium ions, or reversibly proceed with doping and dedoping of lithium ions. A known positive electrode active material can be used. Examples of such a positive electrode active material include lithium cobaltate (LiCoO ₂ ), lithium nickelate (LiNiO ₂ ), lithium manganese spinel (LiMn ₂ O ₄ ), and a general formula: LiNi _x Co _y Mn _z M _a O ₂ (x + y + z + a = 1, 0 ≦ x ≦ 1, 0 ≦ y ≦ 1, 0 ≦ z ≦ 1, 0 ≦ a ≦ 1, M is selected from Al, Mg, Nb, Ti, Cu, Zn, Cr 1 Mixed metal oxides represented by at least one kind of element), lithium vanadium compound (LiV ₂ O ₅ ), olivine type LiMPO ₄ (where M is Co, Ni, Mn, Fe, Mg, Nb, Ti, Al, A composite metal oxide such as lithium titanate (Li ₄ Ti ₅ O ₁₂ ), or one or more elements selected from Zr).

  As the binder used for the positive electrode 20, the same binder as that used for the negative electrode 10 can be used. Moreover, as a conductive support agent used for the positive electrode 20 as needed, the same conductive support agent used for the negative electrode 10 can be used.

  The content of the positive electrode active material in the positive electrode active material layer 28 is preferably 80 to 98% by mass, and more preferably 85 to 97% by mass based on the total amount of the positive electrode active material layer 28. When the content of the active material is less than 80% by mass, the energy density tends to be lower than when the content is within the above range. When the content exceeds 98% by mass, the content is within the above range. Compared with the case where it is, there exists a tendency for an adhesive force to be insufficient and for cycling characteristics to fall.

  The protective layer 30 in each of the negative electrode 10 and the positive electrode 20 is a layer containing low melting point organic particles having a melting temperature of 100 to 200 ° C. and high melting point organic particles having a melting temperature of 300 ° C. or higher. The protective layer 30 may be a layer composed only of low melting point organic particles and high melting point organic particles, or a layer containing low melting point organic particles and high melting point organic particles and another material such as a binder. It may be.

  The low melting point organic particles are not particularly limited as long as the melting temperature is 100 to 200 ° C. Examples of the material of the low melting point organic particles include polyethylene (PE), polypropylene (PP), polymethyl methacrylate (PMMA), ethylene / acrylic acid copolymer (EA), polyvinyl chloride (PVC), and the like. Among these, the low melting point organic particles are preferably particles made of at least one material selected from the group consisting of polyethylene, polypropylene, and polymethyl methacrylate from the viewpoint of obtaining the effects of the present invention more sufficiently.

  The melting temperature of the low-melting organic particles is 100 to 200 ° C, preferably 102 to 190 ° C, and more preferably 105 to 180 ° C. If the melting temperature of the low melting point organic particles is less than 100 ° C., the temperature at which the protective layer 30 shuts down becomes too low, causing an unintended shutdown when the lithium ion secondary battery is used repeatedly, increasing the impedance. Problem arises. On the other hand, when the melting temperature of the melting point organic particles exceeds 200 ° C., the protective layer 30 cannot obtain a sufficient shutdown function, and there arises a problem that thermal runaway progresses when the temperature rises.

  The average particle diameter D50 of the low melting point organic particles is preferably 0.10 to 6.0 μm, more preferably 0.30 to 5.0 μm, and 0.50 to 4.0 μm. Is particularly preferred. When the average particle diameter D50 is less than 0.10 μm, the penetration of the electrolytic solution into the protective layer 30 and the active material layer is hindered, and battery characteristics such as rate characteristics tend to deteriorate. On the other hand, when the average particle diameter D50 exceeds 6.0 μm, the impedance tends to increase.

  The high melting point organic particles are not particularly limited as long as the melting temperature is 300 ° C. or higher. Examples of the material of the high melting point organic particles include polybenzimidazole (PBI), polyimide (PI), polytetrafluoroethylene (PTFE), polytetrafluoroethylene-perfluoroalkyl vinyl ether copolymer (PFA), and polyether ketone. (PEK), polyether ether ketone (PEEK), polyether sulfone (PES), polyamideimide (PAI), polyetherimide (PEI) and the like. Among these, the high melting point organic particles are preferably particles made of at least one material selected from the group consisting of polyamideimide, polyimide and polytetrafluoroethylene from the viewpoint of obtaining the effects of the present invention more sufficiently. .

  The polyimide (PI) particles used in Example 5 to be described later can be prepared by, for example, an isocyanate method which is a known production method from JP-A-59-108030 and JP-A-60-221425. it can.

  Although the melting temperature of the high melting point organic particles is 300 ° C. or higher, it is preferably 300 to 350 ° C., more preferably 350 to 400 ° C. When the melting temperature of the high-melting-point organic particles is less than 300 ° C., the protective layer 30 is shrunk when the temperature is raised, causing a problem that an internal short circuit is likely to occur.

  The average particle diameter D50 of the high melting point organic particles is preferably 0.30 to 6.0 μm, more preferably 0.50 to 5.0 μm, and 1.0 to 4.0 μm. Is particularly preferred. When the average particle diameter D50 is less than 0.30 μm, the penetration of the electrolytic solution into the protective layer 30 and the active material layer is hindered, and battery characteristics such as rate characteristics tend to deteriorate. On the other hand, when the average particle diameter D50 exceeds 6.0 μm, the impedance tends to increase.

  The average particle diameter D50 of the low-melting-point organic particles and the high-melting-point organic particles is measured by a particle size distribution measuring device (manufactured by Microtrack, device name: HRA) by a laser diffraction / scattering method.

  The ratio of the average particle diameter D50 of the low-melting organic particles to the average particle diameter D50 of the high-melting organic particles (average particle diameter D50 of the low-melting organic particles: average particle diameter D50 of the high-melting organic particles) is 1: 1. 5 to 1: 8 is preferable, and 1: 2 to 1: 6 is more preferable. If the average particle diameter D50 of the low-melting organic particles relative to the average particle diameter D50 of the high-melting organic particles is smaller than the above range, the low-melting organic particles tend to melt quickly when the temperature rises, so that the internal impedance tends to increase. is there. On the other hand, when the average particle diameter D50 of the low melting point organic particles relative to the average particle diameter D50 of the high melting point organic particles is larger than the above range, the specific surface area of the particles decreases and the shutdown reaction is delayed, resulting in the result of the overcharge test. Tend to get worse.

  In the protective layer 30, the ratio of the content of the low-melting-point organic particles to the content of the high-melting-point organic particles (the content of the low-melting-point organic particles: the content of the high-melting-point organic particles) is 1: 1 to 1 in mass ratio. It is preferably 1: 4, preferably 1: 1.3 to 1: 3.2, and particularly preferably 1: 1.5 to 1: 3.0. If the content of the low-melting-point organic particles relative to the content of the high-melting-point organic particles is less than the above range, the shutdown function of the protective layer 30 is lowered, and the safety at the time of temperature rise tends to be lowered. On the other hand, when the content of the low-melting-point organic particles with respect to the content of the high-melting-point organic particles is larger than the above range, the protective layer 30 tends to shrink when the temperature rises, and the effect of suppressing the occurrence of internal short circuit tends to decrease. is there.

  Examples of the binder used as necessary for the protective layer 30 include styrene-butadiene rubber, sodium carboxymethyl cellulose, polyvinyl alcohol, PVDF, PTFE, and the like. Among these, styrene-butadiene rubber and sodium carboxymethyl cellulose are preferable from the viewpoint of adhesion to the active material layer and viscosity adjustment of the coating solution.

  Other materials that can be used for the protective layer 30 other than the low-melting-point organic particles, the high-melting-point organic particles, and the binder include, for example, inorganic materials such as ceramics. Any material that does not desorb lithium ions may be used as needed.

  When the protective layer 30 contains a binder in addition to the low-melting organic particles and the high-melting organic particles, the content of the binder is 10 based on the total amount of the protective layer 30 from the viewpoint of not impairing the shutdown effect in the overcharge test. It is preferable that it is mass% or less, and it is more preferable that it is 8 mass% or less.

  The thickness of the protective layer 30 is preferably 0.3 to 6.0 μm, and more preferably 0.5 to 5.0 μm. When the thickness of the protective layer 30 is less than 0.3 μm, the effect of suppressing the occurrence of internal short circuit by the protective layer 30 tends to be insufficient, and when it exceeds 6.0 μm, the rate characteristics are deteriorated. Impedance tends to increase.

  The protective layer 30 of the negative electrode 10 and the protective layer 30 of the positive electrode 20 may have the same configuration or may be different.

  The current collector 26 of the positive electrode 20 is electrically connected to one end of a positive electrode lead 22 made of, for example, aluminum, and the other end of the positive electrode lead 22 extends to the outside of the case 50. On the other hand, the current collector 16 of the negative electrode 10 is also electrically connected to one end of the negative electrode lead 12 made of, for example, copper or nickel, and the other end of the negative electrode lead 12 extends to the outside of the case 50.

  The separator 40 disposed between the negative electrode 10 and the positive electrode 20 is not particularly limited as long as it is formed of a porous body having ion permeability and electronic insulation properties, and is a known lithium ion secondary. The separator used for a battery can be used. For example, a laminate of a film made of polyethylene, polypropylene or polyolefin, a stretched film of a mixture of the above polymers, or a fiber nonwoven fabric made of at least one constituent material selected from the group consisting of cellulose, polyester and polypropylene, etc. It is done.

An electrolytic solution (not shown) is filled in the internal space of the case 50, and a part of the electrolytic solution is contained in the negative electrode 10, the positive electrode 20, and the separator 40. As the electrolytic solution, a non-aqueous electrolyte solution in which a lithium salt is dissolved in an organic solvent is used. Examples of the lithium salt include LiPF ₆ , LiClO ₄ , LiBF ₄ , LiAsF ₆ , LiCF ₃ SO ₃ , LiCF ₃ CF ₂ SO ₃ , LiC (CF ₃ SO ₂ ) ₃ , LiN (CF ₃ SO ₂ ) ₂ , LiN Salts such as (CF ₃ CF ₂ SO ₂ ) ₂ , LiN (CF ₃ SO ₂ ) (C ₄ F ₉ SO ₂ ), LiN (CF ₃ CF ₂ CO) ₂ are used. In addition, these salts may be used individually by 1 type, and may use 2 or more types together. The electrolytic solution may be gelled by adding a polymer or the like.

  Moreover, the solvent currently used for the well-known lithium ion secondary battery can be used for an organic solvent. For example, propylene carbonate, ethylene carbonate, diethyl carbonate and the like are preferable. These may be used alone or in combination of two or more at any ratio.

  As shown in FIG. 2, the case 50 is formed using a pair of films (a first film 51 and a second film 52) facing each other. The edges of the opposing and overlapping films are sealed with an adhesive or heat seal to form a seal portion 50A.

  The film which comprises the 1st film 51 and the 2nd film 52 is a film which has a flexibility. These films are not particularly limited as long as they are flexible films. However, while ensuring sufficient mechanical strength and light weight of the case, moisture and air intrusion into the case 50 from the outside of the case 50 and From the viewpoint of effectively preventing the electrolyte component from escaping from the inside of the case 50 to the outside of the case 50, a polymer innermost layer in contact with the power generation element 60 and an innermost layer on the side in contact with the power generation element. It is preferable to have at least a metal layer disposed on the opposite side.

  The portion of the negative electrode lead 12 that contacts the seal portion 50A is covered with an insulator 14 for preventing contact between the negative electrode lead 12 and the metal layer of the case 50, and the positive electrode lead 22 that contacts the seal portion 50A. This portion is covered with an insulator 24 for preventing contact between the positive lead 22 and the metal layer of the case 50. Another role of the insulators 14 and 24 is to improve the adhesion between the innermost layer of the case 50 and the leads 12 and 22.

  Next, the manufacturing method of the lithium ion secondary battery 1 mentioned above is demonstrated.

  First, the negative electrode 10 and the positive electrode 20 are produced. In the production of the negative electrode 10, the method for forming the negative electrode active material layer 18 is not particularly limited. For example, the components of the negative electrode 10 described above are mixed and dispersed in a solvent in which the binder can be dissolved to prepare a negative electrode active material layer forming coating solution (slurry or paste). The solvent is not particularly limited as long as the binder can be dissolved. For example, N-methyl-2-pyrrolidone, N, N-dimethylformamide, water or the like may be used depending on the type of the binder. Can do.

  Next, the negative electrode active material layer forming coating liquid is applied onto the surface of the current collector 16, dried, and subjected to rolling or the like as necessary to form the negative electrode active material layer 18 on the current collector 16. . The method for applying the coating liquid for forming the negative electrode active material layer on the surface of the current collector 16 is not particularly limited, and may be appropriately determined according to the material, shape, and the like of the current collector 16. Examples of the coating method include a metal mask printing method, an electrostatic coating method, a dip coating method, a spray coating method, a roll coating method, a doctor blade method, a gravure coating method, and a screen printing method.

  Next, the protective layer 30 is formed on the negative electrode active material layer 18.

  When the protective layer 30 is a layer containing low-melting-point organic particles, high-melting-point organic particles, a binder, and other materials as necessary, first, the constituent components of the protective layer 30 described above are mixed, and the binder can be dissolved. A protective layer-forming coating solution (slurry or paste) is prepared by dispersing in a solvent. The solvent is not particularly limited as long as the binder can be dissolved and the low-melting organic particles and the high-melting organic particles do not dissolve. For example, water, methanol, ethanol, isopropyl alcohol, amyl Compounds having hydroxyl groups such as alcohol, ethylene glycol, glycerin and cyclohexanol, ketones such as acetone, methyl ethyl ketone, methyl isobutyl ketone and cyclohexanone, esters such as ethyl acetate, propyl acetate, butyl propionate, butyl butyrate and ethyl lactate , Hydrocarbons such as toluene, xylene, n-butane, cyclohexane and cyclopentane, ethers such as ethyl ether, butyl ether, ethyl propyl ether, allyl ether, tetrahydrofuran and phenyl ether It can be used depending on the type of binder used.

  Next, the protective layer-forming coating solution is applied onto the surface of the negative electrode active material layer 18 and dried to form the protective layer 30 on the negative electrode active material layer 18. At this time, from the viewpoint of maintaining the shape of the low-melting organic particles and the high-melting organic particles, it is preferable not to perform a treatment such as rolling on the protective layer 30, but if the shape of the organic particles is not affected, rolling is performed. Processing may be performed. The method for applying the coating liquid for forming the protective layer on the surface of the negative electrode active material layer 18 is not particularly limited, and may be appropriately determined according to the material, shape, etc. of the negative electrode active material layer 18. As a coating method, the same method as the coating method of the coating liquid for forming the negative electrode active material layer can be mentioned.

  When the protective layer 30 is composed of only low-melting-point organic particles and high-melting-point organic particles, first, a dispersion liquid (coating liquid) is prepared by dispersing the organic particles in a solvent. The protective layer 30 can be formed by performing pressing or the like accordingly.

  Also, the positive electrode 20 can be manufactured in the same procedure as the negative electrode 10.

  After producing the negative electrode 10 and the positive electrode 20 as described above, the negative electrode lead 12 and the positive electrode lead 22 are electrically connected to the negative electrode 10 and the positive electrode 20, respectively.

  Next, the separator 40 is disposed between the negative electrode 10 and the positive electrode 20 in a contacted state (preferably in a non-adhered state), and the power generation element 60 (the negative electrode 10, the separator 40, and the positive electrode 20 are sequentially laminated in this order). (Laminate) is completed. At this time, it arrange | positions so that the surface F2 by the side of the protective layer 30 of the negative electrode 10 and the surface F2 by the side of the protective layer 30 of the positive electrode 20 may contact the separator 40. FIG.

  Next, the edges of the superimposed first film 51 and second film 52 are sealed (sealed) with an adhesive or heat sealing to produce the case 50. At this time, in order to secure an opening for introducing the power generation element 60 into the case 50 in a later step, a part that is not partially sealed is provided. As a result, the case 50 having an opening is obtained.

  The power generation element 60 to which the negative electrode lead 12 and the positive electrode lead 22 are electrically connected is inserted into the case 50 having an opening, and an electrolyte solution is further injected. Subsequently, the lithium ion secondary battery 1 is completed by sealing the opening of the case 50 in a state where a part of the negative electrode lead 12 and the positive electrode lead 22 are respectively inserted into the case 50.

  As mentioned above, although one suitable embodiment of the present invention was described in detail, the present invention is not limited to the above-mentioned embodiment.

  For example, in the description of the above embodiment, the case where both the negative electrode 10 and the positive electrode 20 have the protective layer 30 has been described. However, only one of the negative electrode 10 and the positive electrode 20 may have the protective layer 30. . From the viewpoint of obtaining the effects of the present invention more sufficiently, it is preferable that at least the negative electrode 10 has the protective layer 30.

  In the description of the above embodiment, the lithium ion secondary battery 1 having one negative electrode 10 and one positive electrode 20 has been described. However, the negative electrode 10 and the positive electrode 20 are each provided with two or more negative electrodes 10 and 20. One separator 40 may be always arranged between the two. Moreover, the lithium ion secondary battery 1 is not limited to the shape as shown in FIG. 1, and may be, for example, a cylindrical shape.

  The lithium ion secondary battery of the present invention can also be used for a power source of a self-propelled micromachine, an IC card, or a distributed power source disposed on or in a printed board.

  Hereinafter, other preferred embodiments of the lithium ion secondary battery of the present invention will be described.

  FIG. 5 is a partially broken perspective view showing a lithium ion secondary battery 100 according to another preferred embodiment of the present invention. 6 is a cross-sectional view taken along the YZ plane of FIG. As shown in FIGS. 5 and 6, the lithium ion secondary battery 100 according to the present embodiment mainly includes a laminated structure 85 and a case (exterior body) 50 that houses the laminated structure 85 in a sealed state, It is composed of a negative electrode lead 12 and a positive electrode lead 22 for connecting the laminated structure 85 and the outside of the case 50.

  As shown in FIG. 6, the laminated structure 85 includes a double-sided negative electrode 130, a separator 40, a double-sided positive electrode 140, a separator 40, a double-sided negative electrode 130, a separator 40, a double-sided positive electrode 140, a separator 40, and double-sided. The coated negative electrode 130 is laminated.

  The double-sided coated negative electrode 130 includes a current collector (negative electrode current collector) 16, two negative electrode active material layers 18 formed on both surfaces of the current collector 16, and 2 formed on each negative electrode active material layer 18. Two protective layers 30. The double-sided coated negative electrode 130 is laminated so that the protective layer 30 is in contact with the separator 40.

  The double-sided coated positive electrode 140 includes a current collector (positive electrode current collector) 26 and two positive electrode active material layers 28 formed on both surfaces of the current collector 26. The double-sided coated positive electrode 140 is laminated so that the positive electrode active material layer 28 is in contact with the separator 40.

  An electrolytic solution (not shown) is filled in the internal space of the case 50, and a part thereof is contained in the negative electrode active material layer 18, the positive electrode active material layer 28, the protective layer 30, and the separator 40.

  As shown in FIG. 5, tongues 16a and 26a are formed at the ends of the current collectors 16 and 26, respectively. Each of the current collectors extends outward. Further, as shown in FIG. 5, the negative electrode lead 12 and the positive electrode lead 22 protrude from the case 50 to the outside through the seal portion 50b. The ends of the leads 12 in the case 50 are welded to the tongues 16 a of the three current collectors 16, and the leads 12 are electrically connected to the negative electrode active material layers 18 through the current collectors 16. Connected. On the other hand, the ends of the leads 22 in the case 50 are welded to the tongues 26 a of the two current collectors 26, and the leads 22 are electrically connected to the positive electrode active material layers 28 via the current collectors 26. Connected.

  Further, as shown in FIG. 5, the portions of the leads 12 and 22 that are sandwiched between the seal portions 50b of the case 50 are covered with insulators 14 and 24 such as resin in order to improve the sealing performance. Further, the lead 12 and the lead 22 are separated from each other in a direction orthogonal to the stacking direction of the stacked structure 85.

  As shown in FIG. 5, the case 50 is formed by folding a rectangular flexible sheet 51 </ b> C at a substantially central portion in the longitudinal direction, and the laminated structure 85 is stacked in the stacking direction (vertical direction). It is sandwiched from both sides. Of the end portion of the folded sheet 51C, the seal portions 50b on the three sides excluding the folded portion 50a are adhered by heat sealing or an adhesive, and the laminated structure 85 is sealed inside. Further, the case 50 seals the leads 12 and 22 by being bonded to the insulators 14 and 24 at the seal portion 50b.

  The current collectors 16 and 26, the active material layers 18 and 28, the protective layer 30, the separator 40, the electrolytic solution, the leads 12 and 22 in the lithium ion secondary battery 100 shown in FIGS. 24 and the case 50 are made of the same material as that of the lithium ion secondary battery 1 shown in FIGS.

  In the lithium ion secondary battery 100 shown in FIGS. 5 and 6, the laminated structure 85 has four secondary battery elements as a single cell, that is, four combinations of negative electrode / separator / positive electrode. You may have more than four and may be three or less.

  Moreover, in the said embodiment, although the form which made the two outermost layers each the double-sided coating negative electrode 130 is illustrated as a preferable form, it is possible to implement even one or both of the two outermost layers as a two-layer negative electrode. It is.

  Moreover, in the said embodiment, although the form which used two outermost layers as a negative electrode as a preferable form is illustrated respectively, what used two outermost layers as the positive electrode and the negative electrode, and what used the positive electrode and the positive electrode Even so, the present invention can be implemented.

  Moreover, although the form which provided the protective layer 30 only in the negative electrode was illustrated in the said embodiment, you may provide the protective layer 30 also in a positive electrode. Moreover, you may provide the protective layer 30 only in a positive electrode, without providing the protective layer 30 in a negative electrode. Furthermore, in the said embodiment, although the form which provided the protective layer 30 on both surfaces of the double-sided coating negative electrode was illustrated, you may provide the protective layer 30 only on one negative electrode active material layer.

  EXAMPLES Hereinafter, although this invention is demonstrated more concretely based on an Example and a comparative example, this invention is not limited to a following example.

[Example 1]
(Preparation of negative electrode)
1.5 parts by mass of sodium carboxymethylcellulose (Daiichi Kogyo Seiyaku Co., Ltd., trade name: Serogen WS-C) is dissolved in pure water (obtained by purifying with an ion exchange membrane and distilled), and the solution 93.5 parts by mass of natural graphite (manufactured by Hitachi Chemical Co., Ltd., trade name: HG-702), 2.0 parts by mass of acetylene black (manufactured by Denki Kagaku Kogyo Co., Ltd., trade name: Denka Black), and styrene-butadiene rubber ( Nippon A & L Co., Ltd., trade name: SN-307R) and 3.0 parts by mass were mixed and dispersed with a planetary mixer to obtain a slurry-like coating liquid for forming a negative electrode active material layer. This coating solution was applied to both sides of a 15 μm thick copper foil by a doctor blade method, dried, and then pressed with a calender roll to form a negative electrode active material layer having a thickness of 80 μm (per one side).

  Next, polyethylene particles as low melting point organic particles (manufactured by Sumitomo Seika Co., Ltd., trade name: Flow beads HE series classified, melting temperature: 130 ° C., average particle diameter D50: 2.0 μm) 31.8 63.7 parts by mass of polytetrafluoroethylene particles (manufactured by SHAMROCK TECHNOLOGIES, trade name: SST series, melting temperature: 327 ° C., average particle size D50: 2.0 μm) as high melting point organic particles, and styrene 3.0 parts by mass of butadiene rubber (manufactured by Nippon A & L Co., Ltd., trade name: SN-307R) and 1.5 parts by mass of sodium carboxymethylcellulose (Daiichi Kogyo Seiyaku Co., Ltd., trade name: Serogen WS-C) are mixed. Then, it was dissolved in pure water (purified with an ion exchange membrane and obtained by distillation) to obtain a slurry-like coating solution for forming a protective layer. This coating solution was applied onto each negative electrode active material layer by a doctor blade method and dried to form a protective layer having a thickness of 3.0 μm (per one side). This obtained the negative electrode (double-sided coating negative electrode) by which the negative electrode active material layer and the protective layer were formed on both surfaces of the electrical power collector.

(Preparation of positive electrode)
44.5 parts by mass of lithium nickel cobalt manganate (trade name: NCM-01ST-5, manufactured by Toda Kogyo Co., Ltd.) and 44.5 parts by mass of lithium manganese spinel (trade name: HPM-6050, manufactured by Toda Kogyo Co., Ltd.) 3.0 parts by mass of acetylene black (trade name: Denka Black, manufactured by Denki Kagaku Kogyo Co., Ltd.), 3.0 parts by mass of graphite (trade name: KS-6, manufactured by Timcal), and polyvinylidene fluoride (PVdF) (Arkema) (Trade name: KYNAR-761), 5.0 parts by mass, was mixed with N-methylpyrrolidone (NMP) to obtain a slurry-like coating liquid for forming a positive electrode active material layer. This coating solution was applied to both surfaces of an aluminum foil having a thickness of 20 μm by a doctor blade method, dried, and then pressed with a calender roll, thereby forming a positive electrode active material layer having a thickness of 95 μm (per one surface). This obtained the positive electrode (double-sided coating positive electrode) in which the positive electrode active material layer was formed on both surfaces of the electrical power collector.

(Preparation of electrolyte)
20 parts by volume of propylene carbonate (PC), 10 parts by volume of ethylene carbonate (EC), and 70 parts by volume of diethyl carbonate were mixed to obtain a mixed solvent. In this mixed solvent, lithium hexafluorophosphate (LiPF ₆ ) was dissolved to a concentration of 1.5 mol · dm ⁻³ to obtain an electrolytic solution.

(Production of lithium ion secondary battery)
The double-coated negative electrode has a size of 31.0 mm × 41.5 mm and has a tongue-shaped portion, and the double-coated negative electrode has a size of 30.5 mm × 41.0 mm and has a tongue-shaped portion. I punched each one. In addition, a polyethylene separator having a size of 32.0 mm × 43.0 mm was prepared. Six double-coated negative electrodes and five double-coated positive electrodes are alternately stacked with a separator interposed therebetween, and double-coated negative electrode / separator / double-coated positive electrode / separator / double-coated negative electrode / separator / double-coated positive electrode. / Separator / Double coated negative electrode / Separator / Double coated positive electrode / Separator / Double coated negative electrode / Separator / Double coated positive electrode / Separator / Double coated negative electrode / Separator / Double coated positive electrode / Separator / Double coated negative electrode Formed. The obtained laminated structure was put into an aluminum laminate film, an electrolytic solution was injected, and the mixture was vacuum-sealed. Thereby, a lithium ion secondary battery having the same structure as that shown in FIGS. 5 and 6 was produced except that the number of laminated layers of the double-coated negative electrode and the double-coated positive electrode was different.

[Example 2]
As the low-melting-point organic particles of the protective layer, polyethylene particles (manufactured by Sumitomo Seika Co., Ltd., trade name: those obtained by classifying flow beads LE series, melting temperature: 105 ° C., average particle diameter D50: 2.0 μm) are used. A lithium ion secondary battery was produced in the same manner as in Example 1 except that.

[Example 3]
As the low-melting-point organic particles of the protective layer, polypropylene particles (manufactured by Trial Co., Ltd., trade name: polypropylene particles [TRL-PP-101 series] classified) are used, melting temperature: 170 ° C., average particle diameter D50: 2. A lithium ion secondary battery was produced in the same manner as in Example 1 except that 0 μm) was used.

[Example 4]
As the high melting point organic particles of the protective layer, polymethyl methacrylate particles (manufactured by Negami Kogyo Co., Ltd., product name: Hyperl series (acrylic beads) classified) are used, melting temperature: 195 ° C., average particle size D50: 2. A lithium ion secondary battery was produced in the same manner as in Example 1 except that 0 μm) was used.

[Example 5]
Example 1 except that polyimide particles (synthesized by isocyanate method, melting temperature: 300 ° C. or higher (not softened below 300 ° C.), average particle diameter D50: 2.0 μm) were used as the high melting point organic particles of the protective layer. Similarly, a lithium ion secondary battery was produced.

  In addition, the said polyimide particle was produced with the following isocyanate methods. A solution was prepared by dissolving 0.1 mol of 3,3 ', 4,4'-benzophenonetetracarboxylic dianhydride (BTDA) in 224 g of N-methyl-2-pyrrolidone (NMP). While heating and stirring this solution at 140 ° C., 0.05 mol of triethylenediamine (TEDA) as a catalyst was added and dispersed well, and then 0.1 mol of 2,4-tolylene diisocyanate (TDI) was added and mixed. The polyimide precursor fine particles were deposited by stirring for 24 hours. Thereafter, the polyimide precursor fine particles collected using a centrifuge were washed with acetone. Centrifugation and washing were repeated to purify the polyimide precursor fine particles, then dispersed with N-methyl-2-pyrrolidone (NMP) and refluxed at 190 ° C. for 5 hours to continue the polymerization reaction. After the reaction, the reaction mixture was cooled and the polyimide was filtered, washed with acetone and dried to obtain polyimide particles. The obtained polyimide particles were classified and collected so that the average particle diameter D50 was 2.0 μm, and used as the high-melting-point organic particles of this example.

[Example 6]
In the protective layer, the lithium ion secondary is the same as in Example 1 except that the amount of the low-melting organic particles is 47.7 parts by mass and the amount of the high-melting organic particles is 47.8 parts by mass. A battery was produced.

[Example 7]
In the protective layer, a lithium ion secondary was prepared in the same manner as in Example 1 except that the blending amount of the low melting point organic particles was 53.0 parts by mass and the blending amount of the high melting point organic particles was 42.5 parts by mass. A battery was produced.

[Example 8]
In the protective layer, a lithium ion secondary was prepared in the same manner as in Example 1 except that the blending amount of the low melting point organic particles was 19.1 parts by mass and the blending amount of the high melting point organic particles was 76.4 parts by mass. A battery was produced.

[Example 9]
In the protective layer, a lithium ion secondary was prepared in the same manner as in Example 1 except that the amount of the low-melting organic particles was 17.4 parts by mass and the amount of the high-melting organic particles was 78.1 parts by mass. A battery was produced.

[Comparative Example 1]
As the low-melting-point organic particles of the protective layer, ethylene-vinyl acetate copolymer (EVA) particles (manufactured by Chuo Rika Kogyo Co., Ltd., trade name: Aqua-Tech EC-1700 solution is extracted from ethylene-vinyl acetate copolymer particles and classified. A lithium ion secondary battery was produced in the same manner as in Example 1 except that the melt temperature was 80 ° C. and the average particle diameter D50 was 2.0 μm.

[Comparative Example 2]
As the low-melting-point organic particles of the protective layer, benzoguanamine (BG) particles (product name: Eposter (registered trademark) MS grade classified by this catalyst company are used, melting temperature: 228 ° C., average particle diameter D50: 2 0.0 μm) was used in the same manner as in Example 1 to produce a lithium ion secondary battery.

[Comparative Example 3]
As the high melting point organic particles of the protective layer, polyphenylene sulfide (PPS) particles (manufactured by Polyplastics, trade name: [Fortron 0220A9 grade], finely pulverized and classified, melting temperature: 282 ° C., average A lithium ion secondary battery was produced in the same manner as in Example 1 except that the particle size D50: 2.0 μm) was used.

[Comparative Example 4]
In the protective layer, a lithium ion secondary battery was produced in the same manner as in Example 1 except that the blending amount of the low melting point organic particles was 95.5 parts by mass and the high melting point organic particles were not blended.

[Comparative Example 5]
A lithium ion secondary battery was produced in the same manner as in Example 1 except that the protective layer did not contain the low melting point organic particles and the amount of the high melting point organic particles was 95.5 parts by mass.

[Comparative Example 6]
In the protective layer, low melting point organic particles and high melting point organic particles are not blended, and instead alumina particles (manufactured by Sumitomo Chemical Co., Ltd., trade name: AL series, average particle size D50: 2.0 μm) 95.5 mass as inorganic particles A lithium ion secondary battery was produced in the same manner as in Example 1 except that the parts were blended.

[Comparative Example 7]
In the protective layer, the low melting point organic particles are not blended, and instead of the inorganic particles, 31.8 parts by mass of alumina particles (manufactured by Sumitomo Chemical Co., Ltd., trade name: AL series, average particle size D50: 2.0 μm) are blended, And the lithium ion secondary battery was produced like Example 1 except the compounding quantity of the high melting point organic particle having been 63.7 mass parts.

[Comparative Example 8]
A lithium ion secondary battery was produced in the same manner as in Example 1 except that the protective layer was not provided.

<Measurement of rate characteristics>
About the lithium ion secondary battery obtained by the Example and the comparative example, the discharge capacity in 1C (current value which complete | finishes discharge in 1 hour when a constant current discharge is performed at 25 degreeC), and 5C (25 degreeC) The discharge capacity at a constant current discharge at a current value at which discharge is completed in 0.2 hours is measured, and the ratio of the discharge capacity at 5C when the discharge capacity at 1C is 100% ( %) As a rate characteristic. The results are shown in Tables 1-2.

<Measurement of impedance rise rate>
About the lithium ion secondary battery obtained by the Example and the comparative example, the alternating current impedance (m (ohm)) of 1kHz was measured using the impedance analyzer (SI1287, SI1260) by a Toyo technica company, and this was made into initial impedance. did. Next, about the lithium ion secondary battery, after performing 0.05C low rate charge / discharge at 25 degreeC beforehand, CC charge and CV charge were performed to 4.2V by 1C charge in the environment of 50 degreeC. Thereafter, discharging to 3.0 V at 1 C was taken as one cycle, and was repeated up to 100 cycles in the same manner. Thereafter, the 1 kHz AC impedance (mΩ) of the lithium ion secondary battery was measured using an impedance analyzer (SI 1287, SI 1260) manufactured by Toyo Technica Co., Ltd., and this was taken as the impedance after the cycle test. The impedance was measured at a measurement environment temperature of 25 ° C. and a relative humidity of 60%. The initial impedance was R1, the impedance after the cycle test was R2, and the rate of increase in impedance was determined by the following formula (A). The results are shown in Tables 1-2.
Impedance increase rate (%) = {(R2-R1) / R1} × 100 (A)

<Overcharge test>
About the lithium ion secondary battery obtained by the Example and the comparative example, after performing the low rate charge / discharge of 0.05C at 25 degreeC beforehand, it was made to CC charge until it became 10V at 3C, and cell temperature was set after that. The CV charge was kept until it decreased. The measurement result was obtained by observing the maximum surface temperature of the cell surface and the state of the cell. The results are shown in Tables 1-2. The lithium ion secondary battery in which no cell rupture occurred in this overcharge test has a protective layer having a sufficient shutdown function, and can be judged to be excellent in safety at the time of temperature rise. . Further, among those in which no rupture occurred, the lower the cell temperature, the more the temperature inside the battery is suppressed and the higher the safety. The cell temperature is preferably 80 ° C. or lower.

<Temperature test>
About the lithium ion secondary battery obtained by the Example and the comparative example, after performing 0.05 C low-rate charge / discharge in advance at 25 ° C., the thickness of the cell after being charged to 4.2 V at 1 C (Before storage) was measured. Thereafter, the lithium ion secondary battery was put in an oven, heated up to 150 ° C. at a heating rate of 5 ° C./min, and then the state of the cell after being stored at 150 ° C. for 1 hour was observed. For cells that did not rupture, the thickness of the cells was measured (after storage), and the difference in thickness before and after storage was determined as swelling (mm). The results are shown in Tables 1-2. It should be noted that the lithium ion secondary battery in which no rupture occurred in this temperature rise test is judged to be excellent in safety at the time of temperature rise because the shrinkage of the protective layer at the time of temperature rise is sufficiently suppressed. it can.

  DESCRIPTION OF SYMBOLS 1,100 ... Lithium ion secondary battery, 10 ... Negative electrode, 12 ... Negative electrode lead, 14 ... Insulator, 16 ... Current collector, 18 ... Negative electrode active material layer, 20 ... Positive electrode, 22 ... Positive electrode lead, 24 ... Insulator, 26 ... current collector, 28 ... positive electrode active material layer, 30 ... protective layer, 40 ... separator, 50 ... case, 60 ... power generation element.

Claims (9)

A current collector, an active material layer formed on the current collector, and a protective layer formed on the active material layer,
The said protective layer is an electrode for lithium ion secondary batteries containing the low melting point organic particle whose melting temperature is 100-200 degreeC, and the high melting point organic particle whose melting temperature is 300 degreeC or more.   2. The electrode for a lithium ion secondary battery according to claim 1, wherein the low-melting-point organic particles are particles made of at least one material selected from the group consisting of polyethylene, polypropylene, and polymethyl methacrylate.   The electrode for a lithium ion secondary battery according to claim 1 or 2, wherein the high-melting-point organic particles are particles made of at least one material selected from the group consisting of polyimide and polytetrafluoroethylene.   The ratio of the content of the low-melting-point organic particles and the content of the high-melting-point organic particles in the protective layer is 1: 1 to 1: 4 in a mass ratio. The electrode for lithium ion secondary batteries as described. A lithium ion secondary battery having a positive electrode and a negative electrode,
At least one of the positive electrode and the negative electrode is an electrode comprising a current collector, an active material layer formed on the current collector, and a protective layer formed on the active material layer,
The said protective layer is a lithium ion secondary battery containing the low melting point organic particle whose melting temperature is 100-200 degreeC, and the high melting point organic particle whose melting temperature is 300 degreeC or more.   The lithium ion secondary battery according to claim 5, wherein the low melting point organic particles are particles made of at least one material selected from the group consisting of polyethylene, polypropylene, and polymethyl methacrylate.   The lithium ion secondary battery according to claim 5 or 6, wherein the high melting point organic particles are particles made of at least one material selected from the group consisting of polyimide and polytetrafluoroethylene.   In the said protective layer, ratio of content of the said low melting point organic particle and content of the said high melting point organic particle is 1: 1-1: 4 by mass ratio, It is any one of Claims 5-7. The lithium ion secondary battery as described.   The lithium ion secondary battery according to any one of claims 5 to 8, wherein at least the negative electrode is an electrode including the current collector, the active material layer, and the protective layer.

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