JP5444781B2 - Electrode for lithium ion secondary battery and lithium ion secondary battery - Google Patents

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). The protective layer is mainly formed by particle deposition. In this case, the particle size and particle size distribution affect battery characteristics such as rate characteristics and charge / discharge cycle characteristics, and safety such as internal short circuit due to dendrite formation. . Inorganic particles are mainly used in conventional protective layers, but inorganic particles have a small particle size in order to make the protective layer uniform in thickness because it is difficult to control the particle size and particle size distribution. Is selected.

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 diameter are used for the protective layer, dendrite growth is likely to occur, and it is difficult to obtain good characteristics in rate characteristics, charge / discharge cycle characteristics, and safety.

  The present invention has been made in view of the above-described problems of the prior art, and it is possible to form a lithium ion secondary battery in which the occurrence of an internal short circuit due to dendrite growth is sufficiently suppressed and which has excellent rate characteristics and charge / discharge cycle characteristics It is an object to provide an electrode for a lithium ion 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. , containing organic particles made of polymethylmethacrylate having a crosslinked structure, an average particle diameter D50 of the organic particles Ri 0.5~4.0μm der, durometer hardness of the organic particles is in the range of 70 to 130 there, a lithium ion secondary battery electrode.

  According to such an electrode for a lithium ion secondary battery, a protective layer using organic particles made of polymethyl methacrylate having a crosslinked structure and having an average particle diameter D50 of 0.5 to 4.0 μm is provided on the electrode surface. Therefore, compared to the case where a protective layer using organic particles other than conventional inorganic particles or organic particles specific to the present application is provided, the occurrence of internal short circuit due to dendrite growth is sufficiently suppressed, rate characteristics and charge / discharge cycle A lithium ion secondary battery having excellent characteristics can be formed. Further, by using the specific organic particles, the protective layer has an excellent shutdown function at high temperatures, and the safety at high temperatures can be improved as compared with the case of using inorganic particles.

In the electrode for a lithium ion secondary battery of the present invention, the organic particles preferably have a shape that satisfies a condition represented by the following formula (1).
1.00 ≦ (major axis length / minor axis length) ≦ 1.30 (1)

  When the organic particles satisfy the condition of the above formula (1), it becomes easy to arrange the organic particles uniformly in the protective layer without gaps, so that dendrite growth in the thickness direction of the protective layer is inhibited and internal short circuit occurs. Can be more sufficiently suppressed, and the rate characteristics and charge / discharge cycle characteristics of the lithium ion secondary battery can be further improved.

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 the material layer, wherein the protective layer contains organic particles made of polymethyl methacrylate having a crosslinked structure, and the average particle diameter D50 of the organic particles is 0.5 to 4 .0μm der is, durometer hardness of the organic particles is in the range of 70 to 130, to provide a lithium ion secondary battery.

  According to such a lithium ion secondary battery, a negative electrode having a protective layer on the surface, which is made of polymethyl methacrylate having a cross-linked structure and using organic particles having an average particle diameter D50 of 0.5 to 4.0 μm, and / or Or, by providing a positive electrode, compared with the case where a protective layer using organic particles other than conventional inorganic particles and organic particles specific to the present application is provided, the occurrence of internal short circuit due to dendrite growth is sufficiently suppressed, and excellent Rate characteristics and excellent charge / discharge cycle characteristics can be obtained. Further, by using the specific organic particles, the protective layer has an excellent shutdown function at high temperatures, and the safety at high temperatures can be improved as compared with the case of using inorganic particles.

In the lithium ion secondary battery of the present invention, the organic particles preferably have a shape that satisfies the condition represented by the following formula (1).
1.00 ≦ (major axis length / minor axis length) ≦ 1.30 (1)

  When the organic particles satisfy the condition of the above formula (1), it becomes easy to arrange the organic particles uniformly in the protective layer without gaps, so that dendrite growth in the thickness direction of the protective layer is inhibited and internal short circuit occurs. Can be more sufficiently suppressed, and the rate characteristics and charge / discharge cycle characteristics 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 occurrence of an internal short circuit due to dendrite growth can be more sufficiently suppressed. This is because dendrite growth is likely to occur particularly when graphite having a low potential is used as the negative electrode active material.

  According to the present invention, the occurrence of an internal short circuit due to dendrite growth is sufficiently suppressed, and an electrode for a lithium ion secondary battery capable of forming a lithium ion secondary battery excellent in rate characteristics and charge / discharge cycle characteristics, and The used lithium ion secondary battery 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. And the protective layer 30 is a layer which consists of polymethylmethacrylate (PMMA) which has a crosslinked structure, and contains the organic particle whose average particle diameter D50 is 0.5-4.0 micrometers.

  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 the negative electrode 10 and the positive electrode 20 is a layer made of polymethyl methacrylate having a crosslinked structure and containing organic particles having an average particle diameter D50 of 0.5 to 4.0 μm. The protective layer 30 may be a layer made of only the organic particles or a layer containing organic particles and other materials such as a binder.

  The average particle diameter D50 of the organic particles made of polymethyl methacrylate having a crosslinked structure is 0.5 to 4.0 μm, preferably 0.8 to 3.5 μm, and 1.0 to 3.0 μm. It is more preferable. If the average particle diameter D50 is less than 0.5 μm, it becomes difficult to sufficiently suppress dendrite growth, and sufficient charge / discharge cycle characteristics and safety cannot be obtained. On the other hand, if the average particle diameter D50 exceeds 4.0 μm, sufficient rate characteristics cannot be obtained. The average particle diameter D50 of the organic particles is measured by a particle size distribution measuring device (manufactured by Microtrack, device name: HRA) by a laser diffraction / scattering method.

Moreover, it is preferable that an organic particle has a shape which satisfy | fills the conditions represented by following formula (1).
1.00 ≦ (major axis length / minor axis length) ≦ 1.30 (1)

  The value of the major axis length / minor axis length of the organic particles is preferably 1.00 to 1.30, more preferably 1.00 to 1.20, and 1.00 to 1.10. It is particularly preferred. The organic particles preferably have a shape close to a true sphere. When the value of the major axis length / minor axis length exceeds 1.30, the rate characteristics and the charge / discharge cycle characteristics tend to deteriorate.

  The value of the major axis length / minor axis length can be measured using an electron microscope. In the present invention, the value of the major axis length / minor axis length is specifically calculated as an average value obtained by calculating the major axis length / minor axis length value for any 10 organic particles with an electron microscope. It is.

  Characteristics such as weight average molecular weight, hardness, and degree of crosslinking of the organic particles made of polymethyl methacrylate having a crosslinked structure affect the characteristics of the protective layer 30. The weight average molecular weight of the organic particles is preferably in the range of 100,000 to 1,000,000. When the weight average molecular weight is smaller than 100,000, the electrolytic solution is not sufficiently penetrated into the protective layer 30, and the amount of electrolytic solution retained in the negative electrode active material layer 18 and the positive electrode active material layer 28 is decreased, so that the impedance is increased. Tend. When the weight average molecular weight is larger than 1,000,000, the particle size of the organic particles becomes too large due to swelling, so that the distance between the positive electrode 20 and the negative electrode 10 becomes large, and the impedance tends to increase.

  The hardness of the organic particles can be evaluated by durometer hardness measurement (JIS K7215 test method). The durometer hardness is preferably in the range of 70 to 130, and more preferably in the range of 90 to 130. When the durometer hardness is less than 70, the mechanical strength of the protective layer 30 is lowered, and the protective layer 30 tends to be easily broken by dendrite generated on the electrode surface. When the durometer hardness is larger than 130, the electrode surface tends to be damaged during the expansion / contraction of the electrode in the charge / discharge cycle, and the charge / discharge characteristics tend to be impaired.

  The degree of crosslinking of polymethyl methacrylate constituting the organic particles can be estimated by measuring the gel fraction. The gel fraction is preferably in the range of 98.0 to 100% as a value determined from a mass decrease when the organic particles are immersed in a solvent at 25 ° C. for 24 hours. When the gel fraction is less than 98.0%, the mechanical strength of the protective layer 30 decreases, and the protective layer 30 tends to be easily broken by dendrites generated on the electrode surface.

  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 carboxymethylcellulose are preferable from the viewpoint of adhesion to the electrode and viscosity adjustment of the coating solution.

  Examples of other materials that can be used for the protective layer 30 other than the organic particles and the binder include inorganic materials such as ceramics. From the viewpoint of dendrite suppression, lithium ion desorption is performed during charging and discharging with high resistance. If it is a material that does not, it may be used as necessary.

  When the protective layer 30 contains a binder in addition to the organic particles, the content of the binder is 1% by mass or more based on the total amount of the protective layer 30 from the viewpoint of particle dropout from the protective layer 30 and the electrolyte permeability. Is preferable, and it is more preferable that it is 1.5-30 mass%.

  The thickness of the protective layer 30 is preferably 0.5 to 4.0 μm, and more preferably 1.0 to 4.0 μm. When the thickness of the protective layer 30 is less than 0.5 μm, the effect of suppressing dendrite growth tends to decrease, and when it exceeds 4.0 μm, the rate characteristics tend to decrease.

  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 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 organic particles, a binder, and other materials as necessary, first, the constituent components of the protective layer 30 described above are mixed and dispersed in a solvent in which the binder can be dissolved. A forming coating solution (slurry or paste or the like) is prepared. The solvent is not particularly limited as long as the binder can be dissolved and the organic particles do not dissolve. For example, water, methanol, ethanol, isopropyl alcohol, amyl alcohol, ethylene glycol, glycerin, Compounds having a hydroxyl group such as 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, toluene, xylene, n- Species of binders using hydrocarbons such as 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.

  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, you may process a press etc. with respect to the protective layer 30 as needed.

  The press can be performed by, for example, a roll press such as a calender roll or a flat plate press. In the present invention, it is desirable to use a roll press that is advantageous for increasing the density of the negative electrode active material layer 18. If processing is performed at a high pressure and there is an influence such as deformation of the negative electrode 10, it may be hot pressed at a low pressure. When performing hot pressing, it is desirable to perform appropriately considering heat resistance. In addition, it is preferable that the temperature in that case shall be 80-180 degreeC normally. The pressing pressure is preferably adjusted so that the porosity of the protective layer 30 ([1- (density of the protective layer 30 / true density of the protective layer 30)] × 100) is 20 to 40%. It is more preferable to adjust so that it may become 25 to 35%. 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.

  Moreover, when the protective layer 30 consists only of organic particles, the organic particles are dispersed in a solvent to prepare a dispersion liquid (coating liquid), and coating, drying, and pressing as necessary as described above. The protective layer 30 can be formed.

  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 coated negative electrode 130, a separator 40, a double-sided coated positive electrode 140, a separator 40, a double-sided coated negative electrode 130, a separator 40, a double-sided coated 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 structural body 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) 3.0 parts by mass was added and 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, polymethylmethacrylate particles having a crosslinked structure as organic particles (manufactured by Negami Kogyo Co., Ltd., trade name: Art Pearl series (crosslinked acrylic beads), classifying and collecting beads having an average particle diameter D50: 2.0 μm, long axis length / Short axis length: 1.03) 95.5 parts by mass, 3.0 parts by mass of styrene butadiene rubber (manufactured by Nippon A & L Co., Ltd., trade name: SN-307R), sodium carboxymethylcellulose (Daiichi Kogyo Seiyaku Co., Ltd., The product name: Serogen WS-C) is mixed with 1.5 parts by mass and dissolved in pure water (obtained by purifying with an ion exchange membrane and distilled) to form a slurry-like coating solution for forming a protective layer. Obtained. 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 2.0 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 (made by Toda Kogyo Co., Ltd., trade name: NCM-01ST-5), 44.5 parts by mass of lithium manganese spinel (made by Toda Kogyo Co., Ltd., trade name: HPM-6050), 3.0 parts by mass of acetylene black (manufactured by Denki Kagaku Kogyo Co., Ltd., trade name: Denka Black), 3.0 parts by mass of graphite (trade name: KS-6, produced 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-sided coated negative electrodes and five double-sided coated positive electrodes are alternately laminated with a separator interposed therebetween, and double-sided coated negative electrode / separator / double-sided coated positive electrode / separator / double-sided coated negative electrode / separator / double-sided 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 protective layer organic particles, polymethylmethacrylate particles having a crosslinked structure (manufactured by Negami Kogyo Co., Ltd., trade name: Art Pearl series (crosslinked acrylic beads), classifying beads with an average particle diameter D50: 0.5 μm, long axis length / Minor axis length: 1.03) A lithium ion secondary battery was produced in the same manner as in Example 1, except that 1.03) was used.

[Example 3]
As protective layer organic particles, polymethylmethacrylate particles having a crosslinked structure (manufactured by Negami Kogyo Co., Ltd., trade name: Art Pearl series (crosslinked acrylic beads) are classified and collected with beads having an average particle diameter D50: 4.0 μm, long axis length / Minor axis length: 1.03), and a lithium ion secondary battery was fabricated in the same manner as in Example 1 except that the thickness of the protective layer was 4.0 μm.

[Example 4]
As protective layer organic particles, polymethylmethacrylate particles having a crosslinked structure (manufactured by Negami Kogyo Co., Ltd., trade name: Art Pearl series (crosslinked acrylic beads), classifying beads having an average particle diameter D50: 2.0 μm, taking a long axis length / Minor axis length: 1.30) A lithium ion secondary battery was fabricated in the same manner as in Example 1 except that the above was used.

[Example 5]
As protective layer organic particles, polymethylmethacrylate particles having a crosslinked structure (manufactured by Negami Kogyo Co., Ltd., trade name: Art Pearl series (crosslinked acrylic beads), classifying beads having an average particle diameter D50: 2.0 μm, taking a long axis length / Minor axis length: 2.00) was used in the same manner as in Example 1 to produce a lithium ion secondary battery.

[Comparative Example 1]
Lithium ions were obtained in the same manner as in Example 1 except that non-crosslinked polymethyl methacrylate powder (average particle diameter D50: 2.0 μm, long axis length / short axis length: 1.03) was used as the organic particles of the protective layer. A secondary battery was produced.

[Comparative Example 2]
As organic particles of the protective layer, polyethylene (PE) particles (manufactured by Sumitomo Seika Co., Ltd., trade name: Fluxen classifies beads with an average particle size D50: 2.0 μm, major axis length / minor axis length: 1.03 ) Was used in the same manner as in Example 1 except that lithium ion secondary battery was manufactured.

[Comparative Example 3]
As organic particles of the protective layer, polytetrafluoroethylene (PTFE) particles (manufactured by SHAMROCK TECHNOLOGIES, trade name: classified from SST series, beads having an average particle diameter D50: 2.0 μm are collected, major axis length / minor axis length: 1 0.03) was used in the same manner as in Example 1 to produce a lithium ion secondary battery.

[Comparative Example 4]
Example 1 with the exception that alumina particles (manufactured by Sumitomo Chemical Co., Ltd., trade name: AKP, classifying beads having an average particle diameter D50: 0.20 μm) are used instead of organic particles in the protective layer. Similarly, a lithium ion secondary battery was produced.

[Comparative Example 5]
In the protective layer, Example 1 was used except that alumina particles (manufactured by Sumitomo Chemical Co., Ltd., trade name: AL and beads having an average particle diameter D50: 2.0 μm were classified and collected) were used instead of organic particles in the protective layer. Similarly, a lithium ion secondary battery was produced. The protective layer varied in thickness between 2.0 and 4.0 μm.

[Comparative Example 6]
As organic particles for the protective layer, polymethylmethacrylate particles having a crosslinked structure (manufactured by Negami Kogyo Co., Ltd., trade name: Art Pearl series (crosslinked acrylic beads), classifying beads with an average particle diameter D50: 0.3 μm, taking a long axis length / Minor axis length: 1.03) A lithium ion secondary battery was produced in the same manner as in Example 1, except that 1.03) was used.

[Comparative Example 7]
As protective layer organic particles, polymethylmethacrylate particles having a cross-linked structure (manufactured by Negami Kogyo Co., Ltd., trade name: Art Pearl series (cross-linked acrylic beads), classifying and collecting beads having an average particle diameter D50: 6.0 μm, long axis length / Minor axis length: 1.03), and a lithium ion secondary battery was fabricated in the same manner as in Example 1 except that the thickness of the protective layer was 6.0 μm.

<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 Table 1.

<Charge / discharge cycle test>
About the lithium ion secondary battery obtained by the Example and the comparative example, it charged by the rate of 1C by CCCV charge of 4.2V. Thereafter, constant current discharge was performed at a rate of 1 C up to 2.5V. These charging / discharging was performed in the temperature environment of 45 degreeC. This is performed as 500 cycles, and the difference between the thickness of the lithium ion secondary battery after 500 cycles and the thickness of the initial lithium ion secondary battery (thickness after 500 cycles−initial thickness) is expanded. As sought. The results are shown in Table 1. The initial thickness of the lithium ion secondary battery is about 2.80 mm, although it depends on the thickness of the protective layer. It can be said that the smaller the value of the cell swelling, the more the dendrite growth is suppressed, and the better the charge / discharge cycle characteristics and safety.

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 (5)

A current collector, an active material layer formed on the current collector, and a protective layer formed on the active material layer,
The protective layer contains organic particles made of polymethyl methacrylate having a crosslinked structure,
The average particle size D50 of the organic particles Ri 0.5~4.0μm der,
The electrode for lithium ion secondary batteries whose durometer hardness of the said organic particle is the range of 70-130 . The electrode for a lithium ion secondary battery according to claim 1, wherein the organic particles have a shape satisfying a condition represented by the following formula (1).
1.00 ≦ (major axis length / minor axis length) ≦ 1.30 (1) 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 protective layer contains organic particles made of polymethyl methacrylate having a crosslinked structure,
The average particle size D50 of the organic particles Ri 0.5~4.0μm der,
The lithium ion secondary battery whose durometer hardness of the said organic particle is the range of 70-130 . The lithium ion secondary battery according to claim 3, wherein the organic particles have a shape that satisfies a condition represented by the following formula (1).
1.00 ≦ (major axis length / minor axis length) ≦ 1.30 (1)   The lithium ion secondary battery according to claim 3 or 4, 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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