JP5560870B2 - Separator, electrochemical device, and separator manufacturing method - Google Patents

Description

  The present invention relates to a separator, an electrochemical device, and a method for manufacturing the separator.

  In an electrochemical device, it is known that the adhesion between power generation elements such as a current collector, an active material layer, and a separator affects performance.

In order to improve the lifetime and cycle characteristics of the electrochemical device, for example, attempts have been made to improve the adhesion between the active material layer of the electrode and the current collector.
Patent Document 1 discloses a current collector in which a plurality of convex portions are formed on the surface of a metal sheet. Patent Document 2 discloses a binder in which polymer particles obtained from a specific monomer are added to a binder polymer.

JP 2009-16310 A Special table 2008-537841 gazette

  However, the electrochemical device obtained by the conventional method has room for improvement in performance such as cycle characteristics.

  Then, an object of this invention is to provide the electrochemical device which can improve a rate characteristic and cycling characteristics, the separator which is a component of the said electrochemical device, and the manufacturing method of the said separator.

  That is, the present invention includes an electrically insulating first porous film, and a second porous film containing a fluororesin and a potassium salt and formed on at least one of the main surfaces of the first porous film. Provide a separator.

  Moreover, this invention provides the separator which consists of a 2nd porous film containing a fluororesin and potassium salt.

  The present inventors speculate that according to the separator of the present invention, the adhesion between the separator and, for example, the electrode can be further improved. The reason why the adhesion between the electrode and the separator is improved is not necessarily clear, but the present inventors infer as follows. That is, it is considered that the surface of the separator has adhesiveness due to the presence of the fluororesin and the potassium salt in the surface layer portion of at least one of the main surfaces of the separator or in the separator itself.

  Here, the fluororesin is preferably polyvinylidene fluoride. The potassium salt is preferably potassium fluoride.

  Moreover, it is preferable that content of the potassium salt in a 2nd porous film is 0.01-20 mass parts with respect to 100 mass parts of fluororesins. When the content of the potassium salt is within the above range, the adhesion between the separator and, for example, the electrode is further improved.

  The present invention also includes a positive electrode, a negative electrode disposed so as to face the positive electrode, the separator interposed between the positive electrode and the negative electrode, and contacting each of the main surface of the positive electrode and the main surface of the negative electrode. And an electrolyte contained therein.

  According to the electrochemical device according to the present invention, the adhesion between the separator and the electrode is further improved, so that the rate characteristics and cycle characteristics of the electrochemical device can be improved.

  The separator manufacturing method according to the present invention includes a step of applying a coating containing a fluororesin, a potassium salt, and a solvent for ionizing the potassium salt on the substrate, and a solvent in the coating applied on the substrate. And obtaining a second porous film by removing the step.

  According to the method for manufacturing a separator according to the present invention, it is considered that a separator having a sticky surface can be manufactured. However, the reason is not necessarily clear, and the present inventors infer as follows. That is, it is considered that the presence of potassium ions in the coating material, which is a raw material for the separator, causes the fluororesin to crosslink in the coating step and / or the solvent removal step.

  The reason why the fluororesin crosslinks due to the presence of potassium ions in the paint is not clear, but the present inventors speculate as follows. For example, it is conceivable that hydrogen fluoride is desorbed from the fluororesin due to the presence of potassium ions in the paint, and a double bond and / or a triple bond is formed in the fluororesin. Then, it is considered that a moderate cross-linked structure is formed in the fluororesin due to the interaction between the double bonds existing in the vicinity, between the triple bonds, or between the double bond and the triple bond.

  In addition, for example, fluorine atoms in the fluororesin tend to be negatively charged, so an electrical attractive force may act between potassium ions and fluorine atoms in the fluororesin. It is done. Therefore, it is conceivable that a gentle cross-linked structure is formed in the fluororesin when the fluororesin forms a gentle bond due to electrostatic attraction via potassium ions.

  In the electrochemical device including the separator thus produced, the adhesion between the separator and, for example, the electrode is further improved, so that the rate characteristic and the cycle characteristic are improved.

  Here, in the separator manufacturing method according to the present invention, the base material is preferably an electrically insulating first porous film. Thereby, the separator by which the 2nd porous film containing a fluororesin and potassium salt was formed in at least one surface among the main surfaces of the electrically insulating 1st porous film can be obtained.

  Moreover, it is preferable to provide the process of removing a base material from a 2nd porous film further after the process of obtaining a 2nd porous film. Thereby, the separator which consists of a fluororesin and the 2nd porous film containing potassium salt can be obtained.

  The fluororesin is preferably polyvinylidene fluoride. The potassium salt is preferably potassium fluoride.

  Moreover, it is preferable that potassium salt is added to a coating material so that it may become 0.01-20 mass parts with respect to 100 mass parts of fluororesins. When the addition amount of the potassium salt is within the above range, the adhesion between the separator and, for example, the electrode is further improved.

  ADVANTAGE OF THE INVENTION According to this invention, the electrochemical device which can improve a rate characteristic and cycling characteristics, the separator which is a component of the said electrochemical device, and the manufacturing method of the said separator can be provided.

1 is a schematic cross-sectional view of an electrochemical device according to a first embodiment. It is a schematic cross section of the electrochemical device which concerns on 2nd embodiment.

  Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the drawings as the case may be. In the drawings, the same or corresponding parts are denoted by the same reference numerals, and redundant description is omitted. Further, the dimensional ratios in the drawings are not limited to the illustrated ratios.

<First embodiment>
As shown in FIG. 1, the electrochemical device according to this embodiment is interposed between the positive electrode 10, the negative electrode 20 facing the positive electrode 10, the positive electrode 10 and the negative electrode 20, and the main surface 10 </ b> S of the positive electrode 10 and the negative electrode 20. It is an electrochemical device provided with the separator 18 which each contacts the main surface 20S. The separator 18 according to the present embodiment is a separator in which the second porous films 19 and 29 are formed on the two main surfaces 15S of the first porous film 15 that is electrically insulating.

  Hereinafter, the case where the separator 18 is used for a lithium ion secondary battery will be described in detail with reference to FIG. FIG. 1 is a schematic cross-sectional view showing a lithium ion secondary battery 100 according to this embodiment.

  The lithium ion secondary battery 100 mainly includes a laminate 30, a case 50 that accommodates the laminate 30 in a sealed state, and a pair of leads 60 and 62 connected to the laminate 30.

  The laminated body 30 is configured such that a pair of a positive electrode 10 and a negative electrode 20 are disposed to face each other with a separator 18 interposed therebetween. The positive electrode 10 is obtained by providing a positive electrode active material layer 14 on a plate-like (film-like) positive electrode current collector 12. The negative electrode 20 is obtained by providing a negative electrode active material layer 24 on a plate-like (film-like) negative electrode current collector 22. The main surface of the positive electrode active material layer 14 and the main surfaces 14S and 24S of the negative electrode active material layer 24 are in contact with the main surfaces 19S and 29S of the two second porous films 19 and 29, respectively. Leads 60 and 62 are connected to the end portions of the positive electrode current collector 12 and the negative electrode current collector 22, respectively, and the end portions of the leads 60 and 62 extend to the outside of the case 50.

  Hereinafter, the positive electrode 10 and the negative electrode 20 are collectively referred to as electrodes 10 and 20, and the positive electrode current collector 12 and the negative electrode current collector 22 are collectively referred to as current collectors 12 and 22, and the positive electrode active material layer 14 and the negative electrode The active material layer 24 may be collectively referred to as the active material layers 14 and 24.

First, the electrodes 10 and 20 will be specifically described.
(Positive electrode 10)
The positive electrode current collector 12 may be a conductive plate material, and for example, a thin metal plate of aluminum, copper, or nickel foil can be used.
The positive electrode active material layer 14 is mainly composed of a positive electrode active material, a binder, and a conductive auxiliary agent in an amount as necessary. The positive electrode active material includes insertion and extraction of lithium ions, desorption and insertion of lithium ions (intercalation), or doping and dedoping of lithium ions and a counter anion (for example, ClO ₄ ⁻ ) of the lithium ions. It is not particularly limited as long as it can be reversibly advanced, and a positive electrode active material used in a known lithium ion secondary battery can be used. For example, a lithium containing metal oxide is mentioned. Examples of the lithium-containing metal oxide 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 O ₂ ( x + y + z = 1), a composite metal oxide, a lithium vanadium compound (LiV ₂ O ₅ ), an olivine-type LiMPO ₄ (wherein M represents Co, Ni, Mn or Fe), lithium titanate (Li ₄ Ti ₅ O _12), and the like.

  The binder binds the active materials to each other and binds the active material to the current collector 12. The binder is not particularly limited as long as the above-described bonding is possible. 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), polyvinyl fluoride (PVF) ) And the like.

  In addition to the above, as the binder, for example, vinylidene fluoride-hexafluoropropylene-based fluororubber (VDF-HFP-based fluororubber), vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene-based fluororubber (VDF-HFP-) TFE fluorine rubber), vinylidene fluoride-pentafluoropropylene fluorine rubber (VDF-PFP fluorine rubber), vinylidene fluoride-pentafluoropropylene-tetrafluoroethylene fluorine rubber (VDF-PFP-TFE fluorine rubber), Vinylidene fluoride-perfluoromethyl vinyl ether-tetrafluoroethylene fluoro rubber (VDF-PFMVE-TFE fluoro rubber), vinylidene fluoride-chlorotrifluoroethylene fluoro rubber The containing rubbers (VDF-CTFE-based fluorine rubber) vinylidene fluoride-based fluorine rubbers such as may be used.

  In addition to the above, for example, polyethylene, polypropylene, polyethylene terephthalate, aromatic polyamide, cellulose, styrene / butadiene rubber, isoprene rubber, butadiene rubber, ethylene / propylene rubber, and the like may be used as the binder. 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.

  Alternatively, an electron conductive conductive polymer or an ion conductive conductive polymer may be used as the binder. Examples of the electron conductive conductive polymer include polyacetylene. In this case, since the binder also exhibits the function of the conductive assistant particles, it is not necessary to add the conductive assistant.

As the ion-conductive conductive polymer, for example, those having ion conductivity such as lithium ion can be used. For example, polymer compounds (polyether-based polymer compounds such as polyethylene oxide and polypropylene oxide) A crosslinked polymer of a polyether compound, polyepichlorohydrin, polyphosphazene, polysiloxane, polyvinylpyrrolidone, polyvinylidene carbonate, polyacrylonitrile, etc.) monomers, and LiClO ₄ , LiBF ₄ , LiPF ₆ , LiAsF ₆ , LiCl, LiBr, Examples thereof include a composite of a lithium salt such as Li (CF ₃ SO ₂ ) ₂ N, LiN (C ₂ F ₅ SO ₂ ) ₂ or an alkali metal salt mainly composed of lithium. Examples of the polymerization initiator used for the combination include a photopolymerization initiator or a thermal polymerization initiator that is compatible with the above-described monomer.

  The conductive auxiliary agent is not particularly limited as long as it improves the conductivity of the positive electrode active material layer 14, and a known conductive auxiliary agent can be used. Examples thereof include carbon blacks, carbon materials, metal fine powders such as copper, nickel, stainless steel and iron, a mixture of carbon materials and metal fine powders, and conductive oxides such as ITO.

The content of the binder in the positive electrode active material layer 14 is not particularly limited, but is preferably 1% by mass to 15% by mass based on the sum of the masses of the active material, the conductive additive, and the binder, and is 3% by mass. More preferably, it is 10 mass%. By setting the content of the active material and the binder in the above range, the obtained electrode active material layer 14 can suppress the tendency that the amount of the binder is too small to form a strong active material layer. In addition, the amount of the binder that does not contribute to the electric capacity increases, and the tendency that it is difficult to obtain a sufficient volume energy density can be suppressed.
The content of the conductive additive in the positive electrode active material layer 14 is not particularly limited, but when added, it is usually preferably 0.5% by mass to 20% by mass with respect to the active material, and 1% by mass to It is more preferable to set it as 12 mass%.

(Negative electrode 20)
The negative electrode current collector 22 may be a conductive plate material, and for example, a thin metal plate of aluminum, copper, or nickel foil can be used.
The negative electrode active material layer 24 is mainly composed of a negative electrode active material, a binder, and a conductive auxiliary agent in an amount as required. The negative electrode active material reversibly advances the insertion and removal of lithium ions, the desorption and insertion of lithium ions, or the doping and dedoping of lithium ions and counter anions of the lithium ions (for example, ClO ₄ ⁻ ). If it can be made, it will not specifically limit, The negative electrode active material used for the well-known lithium ion secondary battery can be used. For example, it can be combined with natural graphite, artificial graphite, mesocarbon microbeads, mesocarbon fiber (MCF), coke, glassy carbon, carbon materials such as organic compound fired bodies, lithium such as Al, Si, Sn, etc. Examples thereof include amorphous compounds mainly composed of metal, oxides such as SiO ₂ and SnO ₂ , lithium titanate (Li ₄ Ti ₃ O ₁₂ ), and the like.

  As the binder and the conductive additive, the same materials as those used for the positive electrode 10 described above can be used. Moreover, what is necessary is just to employ | adopt content similar to content in the positive electrode 10 mentioned above also about content of a binder and a conductive support agent.

  The electrodes 10 and 20 can be produced by a commonly used method. For example, it can manufacture by apply | coating the coating material containing an active material, a binder, a solvent, and a conductive support agent on a collector, and removing the solvent in the coating material apply | coated on the collector.

  As the solvent, for example, N-methyl-2-pyrrolidone, N, N-dimethylformamide and the like can be used.

  There is no restriction | limiting in particular as an application | coating method, The method employ | adopted when producing an electrode normally can be used. Examples thereof include a slit die coating method and a doctor blade method.

  The method for removing the solvent in the paint applied on the current collectors 12 and 22 is not particularly limited, and the current collectors 12 and 22 applied with the paint are dried, for example, in an atmosphere of 80 ° C. to 150 ° C. Just do it.

  Then, the electrodes on which the active material layers 14 and 24 are formed in this way may then be pressed by a roll press device or the like as necessary. The linear pressure of the roll press can be, for example, 10 to 50 kgf / cm.

  The electrodes 10 and 20 can be manufactured through the above steps.

(Separator 18)
Next, the separator 18 will be described. The separator 18 according to the present embodiment includes a first porous film 15 that is electrically insulating, a fluororesin and a potassium salt, and is formed on the two main surfaces 15S of the first porous film 15. Porous membranes 19 and 29.

  The material constituting the first porous film 15 may be any material that is normally used as a separator in a lithium ion secondary battery. For example, the material may be an electrically insulating porous body, and the porous body may be microporous. preferable. Specifically, at least one constituent material selected from the group consisting of monolayers of films made of polyolefins such as polyethylene and polypropylene, stretched films of laminates and mixtures of the above resins, or cellulose, polyester and polypropylene The fiber nonwoven fabric which consists of is mentioned. The thickness of the first porous film 15 can be 10 μm to 25 μm.

  The second porous films 19 and 29 are electrically insulating porous bodies containing at least a fluororesin and a potassium salt. The thickness of the second porous films 19 and 29 can be 1 μm to 15 μm.

  The fluororesin is an olefin polymer containing fluorine. Examples of the fluororesin include polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), tetrafluoroethylene-hexafluoropropylene copolymer (FEP), and tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer (PFA). , Ethylene-tetrafluoroethylene copolymer (ETFE), polychlorotrifluoroethylene (PCTFE), ethylene-chlorotrifluoroethylene copolymer (ECTFE), and polyvinyl fluoride (PVF). Among these, PVDF is particularly preferable.

Examples of the potassium salt include potassium fluoride (KF), potassium chloride (KCl), potassium bromide (KBr), potassium nitrate (KNO ₃ ), and potassium sulfate (KSO ₄ ).

  The content of the potassium salt in the second porous membranes 19 and 29 is preferably 0.01 to 20 parts by mass, more preferably 0.1 to 10 parts by mass with respect to 100 parts by mass of the fluororesin. 1 to 5 parts by mass is more preferable. When the content of the potassium salt is within the above range, crosslinking of the fluororesin tends to occur, and the adhesion between the active material layers 14 and 24 and the second porous films 19 and 29 tends to be further improved. The characteristics and cycle characteristics can be further improved. If the content of the potassium salt exceeds 20 parts by mass with respect to 100 parts by mass of the fluororesin, the conductivity tends to decrease, or the discharge capacity tends to decrease and the cycle characteristics tend to decrease. If the content of the potassium salt is less than 0.01 parts by mass with respect to 100 parts by mass of the fluororesin, the adhesiveness with the active material layers 14 and 24 may decrease, or the rate characteristics and the cycle characteristics tend to decrease. .

  Moreover, the 2nd porous membranes 19 and 29 may contain the inorganic filler etc. from a viewpoint of raising the porosity of the 2nd porous membranes 19 and 29 and improving the ionic conductivity in electrolyte, for example. Examples of the inorganic filler include crystalline silica, alumina, and zirconia having various shapes such as a spherical shape, an elliptical shape, and a scale shape.

  The separator 18 according to the present embodiment can be manufactured by the following method. That is, the manufacturing method of the separator 18 according to the present embodiment is a process of applying the above-described fluororesin, potassium salt, and a paint containing a solvent for ionizing the potassium salt described later to the first porous film 15 (application process). And a step of removing the solvent in the paint applied on the first porous film 15 to obtain the second porous film (drying step).

(Coating process)
In this step, a paint containing a fluororesin, a potassium salt, and a solvent that ionizes the potassium salt is applied to the first porous film 15.

As a solvent for ionizing the potassium salt, any solvent can be used as long as it can ionize the potassium salt to generate potassium ions. In addition, it is preferable that the potassium salt is not sufficiently ionized and suspended or precipitated in a solvent, and more preferably a salt that tends to be completely dissociated.
That is, in the present invention, the “solvent that ionizes potassium salt” means a solvent in which the degree of ionization of the potassium salt is greater than 0. Among such solvents, it is preferable to use N-methyl-2-pyrrolidone (NMP) or N, N-dimethylformamide (DMF). The solvent is preferable because it has a very high polarity and the potassium salt is easily ionized. The amount of the solvent in the paint is not particularly limited, and may be adjusted as appropriate so that a viscosity suitable for application can be obtained.

In the paint, the potassium salt is preferably added so as to be 0.01 to 20 parts by mass, more preferably 0.1 to 10 parts by mass with respect to 100 parts by mass of the fluororesin, It is more preferable to add so that it may become 1-5 mass parts. When the added amount of the potassium salt is within the above range, the fluororesin is easily crosslinked, and the adhesion between the active material layers 14 and 24 and the second porous films 19 and 29 tends to be further improved. The characteristics and cycle characteristics can be further improved. If the added amount of the potassium salt exceeds 20 parts by mass with respect to 100 parts by mass of the fluororesin, there is a tendency that the rate characteristic and the cycle characteristic are deteriorated because the conductivity is lowered. If the addition amount of the potassium salt is less than 0.01 parts by mass with respect to 100 parts by mass of the fluororesin, the adhesiveness with the active material layers 14 and 24 may decrease, or the rate characteristics and the cycle characteristics tend to decrease. .
Moreover, the coating material may contain the poor solvent for space | gap formation from a viewpoint of raising the porosity of the 2nd porous films 19 and 20, and improving the ionic conductivity in electrolyte, for example. Examples of the poor solvent for forming voids include butyl cellosolve (BCS), dibutyl phthalate (DBP), hexane, xylene and the like.

  The mixing method of the components constituting the coating such as the fluororesin, the potassium salt, and the solvent for ionizing the potassium salt is not particularly limited, and the mixing order is not particularly limited.

  As a method for applying the coating material onto the first porous film 15, a closed die method is suitable. Further, from the viewpoint of preventing the paint from penetrating excessively into the voids in the first porous film 15, the content of the potassium salt in the paint is adjusted according to the average diameter of the pores of the first porous film 15. The viscosity of the paint may be adjusted. Thereby, increase of the internal resistance in an electrochemical device can be suppressed due to factors such as decreasing the porosity of the separator.

(Drying process)
As a method of removing the solvent in the coating material applied on the base material, for example, a method of applying a dry gas of about 80 ° C. to 120 ° C. to the coating surface for 10 minutes to 30 minutes, the whole base material of about 80 ° C. to 120 ° C. For example, a method of leaving it in an atmosphere for 10 to 30 minutes can be mentioned.

  When the second porous films 19 and 29 are formed on the two main surfaces 15S of the first porous film 15, first, the first porous film 15 is formed on the one main surface 15S. The coating material is applied, the coating material is dried, and then the same operation may be performed on the opposite main surface 15S. Moreover, the said coating material may be apply | coated on the two main surfaces 15S of the 1st porous film 15, and both the two main surfaces 15S may be dried.

  Through the above treatment, a first porous film 15 and second porous films 19 and 29 containing fluororesin and potassium salt and formed on two main surfaces 15S of the first porous film are provided. Separator 18 is obtained.

(Function and effect)
According to the present embodiment, since the adhesiveness is generated on the surface of the separator 18, the present inventors presume that the adhesion between the separator 18 and the electrodes 10 and 20 can be further improved. The reason why the adhesion between the separator 18 and the electrodes 10 and 20 is improved is not necessarily clear, but the present inventors speculate as follows. That is, the presence of potassium ions in the coating material that is the raw material of the second porous film formed on the surface portion of the separator 18 causes the fluororesin to be applied and / or in the step of removing the solvent. This is considered to be for crosslinking.

  The reason why the fluororesin is crosslinked due to the presence of potassium ions in the paint is not clear, but the present inventors infer as follows. For example, it is conceivable that hydrogen fluoride is desorbed from the fluororesin due to the presence of potassium ions in the paint, and a double bond and / or a triple bond is formed in the fluororesin. Then, it is considered that a moderate cross-linked structure is formed in the fluororesin due to the interaction between the double bonds existing in the vicinity, between the triple bonds, or between the double bond and the triple bond.

  In addition, for example, fluorine atoms in the fluororesin tend to be negatively charged, so an electrical attractive force may act between potassium ions and fluorine atoms in the fluororesin. It is done. Therefore, it is conceivable that a gentle cross-linked structure is formed in the fluororesin when the fluororesin forms a gentle bond due to electrostatic attraction via potassium ions.

  The electrochemical device including the separator 18 as described above has improved rate characteristics and cycle characteristics.

  Here, another component of the lithium ion secondary battery 100 using the separator manufactured as described above will be described.

The electrolyte is contained in the positive electrode active material layer 14, the negative electrode active material layer 24, and the separator 18. The electrolyte is not particularly limited, and, for example, in the present embodiment, an electrolyte solution containing a lithium salt (electrolyte aqueous solution, electrolyte solution using an organic solvent) can be used. However, the electrolyte aqueous solution is preferably an electrolyte solution (non-aqueous electrolyte solution) using an organic solvent because the electrochemical decomposition voltage is low, and the withstand voltage during charging is limited to a low level. As the electrolyte solution, a lithium salt dissolved in a non-aqueous solvent (organic solvent) is preferably 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 , LiBOB can be used. In addition, these salts may be used individually by 1 type, and may use 2 or more types together.

  Moreover, as an organic solvent, propylene carbonate, ethylene carbonate, diethyl carbonate, etc. are mentioned preferably, for example. These may be used alone or in combination of two or more at any ratio.

  The case 50 seals the laminate 30 and the electrolyte solution therein. The case 50 is not particularly limited as long as it can prevent leakage of the electrolytic solution to the outside and entry of moisture and the like into the electrochemical device 100 from the outside. For example, as the case 50, as shown in FIG. 1, a metal laminate film in which a metal foil 52 is coated with a polymer film 54 from both sides can be used. For example, an aluminum foil can be used as the metal foil 52 and a film such as polypropylene can be used as the polymer film 54. For example, the material of the outer polymer film 54 is preferably a polymer having a high melting point, such as polyethylene terephthalate (PET) or polyamide, and the material of the inner polymer film 54 is polyethylene (PE) or polypropylene (PP). Etc. are preferred.

  The leads 60 and 62 are made of a conductive material such as aluminum.

  Then, the leads 60 and 62 are welded to the positive electrode current collector 12 and the negative electrode current collector 22 by a known method, respectively, and a separator is provided between the positive electrode active material layer 14 of the positive electrode 10 and the negative electrode active material layer 24 of the negative electrode 20. 18 may be inserted into the case 50 together with the electrolytic solution with the 18 interposed therebetween, and the entrance of the case 50 may be sealed.

  In the present embodiment, the second porous films 19 and 29 are formed on the two main surfaces 15S of the first porous film 15. Of the two main surfaces 15S of the first porous film 15, If the second porous film is formed on at least one surface, the rate characteristics and cycle characteristics of the electrochemical device are improved. From the viewpoint of improving the rate characteristics and cycle characteristics of the lithium ion secondary battery, it is preferable to provide the second porous film on at least the positive electrode 10 side of the first porous film 15.

<Second embodiment>
The separator 18 according to this embodiment is a porous body in which a fluororesin and a potassium salt are included in the entire separator. Specifically, it is constituted by the second porous membrane alone of the first embodiment. FIG. 2 is a schematic cross-sectional view of the electrochemical device 100 including the separator 18 according to the present embodiment.

  The separator 18 according to the present embodiment can be manufactured by the following method. That is, in the method for manufacturing a separator according to the present invention, a step of applying a coating containing a fluororesin, a potassium salt, and a solvent for ionizing the potassium salt onto the substrate (application step) was applied to the substrate. Removing the solvent in the paint to obtain a second porous film (drying step). In the present embodiment, any substrate may be used instead of the electrically insulating first porous film in the first embodiment. For example, the substrate may be the electrodes 10 and 20. When the base material is the electrodes 10 and 20, the separator 18 is formed on the surface of the positive electrode 10 or the negative electrode 20 through the coating process and the drying process.

  In the separator manufacturing method according to the present embodiment, in the coating step and the drying step, the same processes as those in the coating step and the drying step according to the first embodiment are performed. An organic filler may be mixed in the coating material which is a raw material. As a material for the organic filler, polymethyl methacrylate (PMMA), polyvinyl alcohol (PVA), polyacrylonitrile (PAN), polymethylpentene (PMP), or the like can be used. Thereby, the obtained separator 18 can be provided with a shutdown performance that automatically cuts off the flow of current when the temperature in the electrochemical device rises.

  Moreover, the manufacturing method of the separator which concerns on this embodiment WHEREIN: When a base material is materials other than the electrodes 10 and 20, the process (base material removal process) of removing a base material from a 2nd porous film after a drying process. It is preferable to provide.

  As the substrate, a polyethylene terephthalate (PET) film can be used, and it is preferable to use a PET film or the like that has been subjected to a surface treatment for imparting light peelability.

Here, the base material removal process according to the present embodiment will be specifically described.
(Substrate removal process)
In this step, after the drying step, for example, the positive electrode active material layer 14 or the negative electrode active material layer 24 / the second porous film / the base material is formed on the base material so that the second porous film is laminated in this order. The second porous membrane side of the membrane is adhered to the positive electrode active material layer 14 or the negative electrode active material layer 24. Then, the laminate is subjected to thermocompression bonding at a predetermined temperature and pressure, and then the outermost base material is peeled off, whereby a separator 18 containing a fluororesin and a potassium salt is formed on the surface of the positive electrode 10 or the negative electrode 20. Can be formed.

  Then, an electrode serving as a counter electrode of the electrode having the separator 18 formed on the surface is laminated on the main surface of the separator 18, and the side surface of the obtained laminate is adhered with an adhesive or the like, whereby the positive electrode 10 / separator 18 / A laminate 30 of the negative electrode 20 is obtained. Since the separator 18 obtained by this embodiment contains a fluororesin and a potassium salt, it can improve the adhesion at the interface of the positive electrode 10 / separator 18, and the adhesion at the interface of the separator 18 / negative electrode 20, Rate characteristics and cycle characteristics of electrochemical devices such as ion secondary batteries are improved.

  Also in the separator 18 in this embodiment, the content of the potassium salt is preferably 0.01 to 20 parts by mass, more preferably 0.1 to 10 parts by mass with respect to 100 parts by mass of the fluororesin. 1 to 5 parts by mass is more preferable. When the content of the potassium salt is within the above range, the adhesion between the active material layers 14 and 24 and the second porous films 19 and 29 tends to be further improved, and the rate characteristics and cycle characteristics are further improved. be able to. When the content of the potassium salt exceeds 20 parts by mass with respect to 100 parts by mass of the fluororesin, there is a tendency that the rate characteristics and the cycle characteristics are deteriorated because the conductivity decreases. If the content of the potassium salt is less than 0.01 parts by mass with respect to 100 parts by mass of the fluororesin, the adhesiveness with the active material layers 14 and 24 may decrease, or the rate characteristics and the cycle characteristics tend to decrease. . The thickness of the separator 18 can be 20 μm to 25 μm.

  The separator manufacturing method, the separator obtained thereby, and a preferred embodiment of a lithium ion secondary battery including the separator have been described in detail above, but the present invention is not limited to the above embodiment. .

  For example, the separator can be used in electrochemical devices other than lithium ion secondary batteries. Electrochemical devices include secondary batteries other than lithium ion secondary batteries, such as metallic lithium secondary batteries (those that use an electrode in which an active material layer is formed on a current collector as a cathode and metallic lithium as an anode). And electrochemical capacitors such as lithium capacitors. These electrochemical elements can be used for power sources such as self-propelled micromachines and IC cards, and distributed power sources arranged on or in a printed circuit board.

  For example, when the electrochemical device is an electrochemical capacitor, a known porous material having electronic conductivity may be used as the electrode active material. For example, carbon materials such as natural graphite, artificial graphite, mesocarbon microbeads, mesocarbon fiber (MCF), cokes, glassy carbon, and fired organic compound can be preferably used.

  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
[Production of positive electrode]
85 g of LiNi _1/3 Mn _1/3 Co _1/3 O ₂ as a positive electrode active material, carbon black (manufactured by Denki Kagaku Kogyo Co., Ltd., DAB50) and graphite (manufactured by Timcal Co., Ltd., KS-6) After 5 g dry MIX of each, an NMP (N-methyl-2-pyrrolidinone) solution of PVDF (polyvinylidene fluoride (manufactured by Kureha Chemical Industry Co., Ltd., KF7305 or Tokyo Materials Co., Ltd. Kyner 761)) as a binder (50 g) , PVDF component 10% by mass) was added and mixed to prepare about 145 g of paint, which was applied to an aluminum foil (thickness 20 μm) as a current collector by the doctor blade method, dried at 90 ° C. and rolled. In order to weld the external lead terminal (lead), a portion where no paint was applied was provided.

[Production of negative electrode]
After dry-mixing 45 g of natural graphite as a negative electrode active material and 2.5 g of carbon black as a conductive auxiliary agent, 22.5 g of the PVDF solution was added as a binder to prepare a negative electrode paint. This paint was applied to a copper foil (thickness 16 μm) as a current collector by the doctor blade method so as to remove the welded portion of the external lead terminal in the same manner as the positive electrode, and then dried at 90 ° C. and rolled.

[Production of laminated separator having a porous film to which fluororesin and potassium fluoride are added]
15 g of scaly crystalline silica (manufactured by Nippon Aerogel Co., Ltd., CQ-2 (trade name)) as a filler, 5.0 g of PVDF as a binder, 27.8 g of N, N-dimethylformamide (DMF) as a solvent, 9.3 g of butyl cellosolve (BCS) as a pore-forming poor solvent and 0.15 g of potassium fluoride (KF) (manufactured by Kojundo Chemical Laboratory Co., Ltd., purity 99%) were mixed, A paint for a porous film (second porous film) to which potassium fluoride was added was prepared. This paint was applied to both surfaces of a microporous polyolefin film (thickness: 17 μm, first porous film) as a first porous film by a closed die method and then dried in a drying oven maintained at about 110 ° C.

[Production of battery]
The positive electrode, the negative electrode, and the separator formed with the second porous film on both sides were cut into predetermined dimensions. A separator was interposed between the positive electrode and the negative electrode to produce a battery element in which the positive electrode / second porous film / first porous film / second porous film / negative electrode were laminated in this order. The number of laminations was such that the capacity of the lithium ion secondary battery was 200 mAh. When laminating, a small amount of hot melt adhesive (ethylene-methacrylic acid copolymer (EMAA)) was applied and fixed so that the positive electrode, the negative electrode, and the separator did not shift.
An aluminum foil (width 4 mm, length 40 mm, thickness 100 μm) and nickel foil (width 4 mm, length 40 mm, thickness 100 μm) were ultrasonically welded to the positive electrode and the negative electrode, respectively, as external lead terminals. Polypropylene (PP) grafted with maleic anhydride was wrapped around and thermally bonded to the external lead terminal in order to improve the sealability between the external lead terminal and the exterior body.
A battery outer package enclosing a battery element in which a positive electrode, a negative electrode, and a separator are laminated is made of an aluminum laminate material, and the structure thereof is polyethylene terephthalate (PET, thickness 12 μm) / Al (thickness 40 μm) / polypropylene (PP, thickness). 50 μm) was prepared. At this time, bags were made so that PP was on the inside. A battery element is put in this outer package, and an electrolytic solution (LiPF ₆ dissolved in 1M in a mixed solvent of ethylene carbonate (EC) and diethyl carbonate (DEC) (EC: DEC = 30: 70 vol%)) Was added in an appropriate amount, and the outer package was vacuum-sealed to produce a lithium ion secondary battery. Aging was performed at 10 mA (0.05 C) for 10 hours.

[Battery evaluation]
(Measurement of rate characteristics (10C discharge capacity retention rate))
In a 25 ° C. chamber, charging and discharging were repeated several times at 100 mA (0.5 C) under conditions of an upper limit voltage of 4.2 V and a lower limit voltage of 3.0 V. It was confirmed that the average discharge capacity of the lithium ion secondary battery produced as described above was about 200 mAh. After charging under the same charging conditions, only the discharge current was changed to 2A (10C), and the discharge capacity at 10C was measured. The discharge capacity was about 170 mAh, and the discharge capacity retention rate was about 85%.
(Measurement of cycle characteristics (discharge capacity retention after 500 cycles))
In a 45 ° C. chamber, charging and discharging were repeated 500 times at 200 mA (1C) under the conditions of an upper limit voltage of 4.2 V and a lower limit voltage of 3.0 V. Thereafter, charging and discharging were repeated several times at 100 mA (0.5 C) under conditions of an upper limit voltage of 4.2 V and a lower limit voltage of 3.0 V in a 25 ° C. chamber. The average discharge capacity was about 156 mAh, and the capacity maintenance rate was about 78%.

(Example 2)
A lithium ion secondary battery was produced in the same manner as in Example 1 except that 0.05 g of KF (1% by mass with respect to PVDF) was mixed, and the rate characteristics and cycle characteristics were evaluated under the same conditions as in Example 1.

[Battery evaluation]
The initial average discharge capacity was about 200 mAh. The discharge capacity at 10 C was about 156 mAh, and the discharge capacity retention rate was about 78%. The average discharge capacity after 500 cycles was about 144 mAh, and the capacity retention rate was about 72%.

(Example 3)
A lithium ion secondary battery was produced in the same manner as in Example 1 except that 0.25 g (5% by mass with respect to PVDF) was mixed with KF, and rate characteristics and cycle characteristics were evaluated under the same conditions as in Example 1.

[Battery evaluation]
The initial average discharge capacity was about 200 mAh. The 10C discharge capacity was about 174 mAh, and the discharge capacity retention rate was about 87%. The average discharge capacity after 500 cycles was about 164 mAh, and the capacity retention rate was about 82%.

(Example 4)
A lithium ion secondary battery was prepared in the same manner as in Example 1 except that 0.15 g of KF (3% by mass with respect to PVDF) was mixed and a nanofiber nonwoven fabric was used instead of the microporous polyolefin film as a separator. Then, rate characteristics and cycle characteristics were evaluated under the same conditions as in Example 1.
[Battery evaluation]
The initial average discharge capacity was about 200 mAh. The 10C discharge capacity was about 176 mAh, and the discharge capacity retention rate was about 88%. The average discharge capacity after 500 cycles was about 1166 mAh, and the capacity retention rate was about 83%.

(Example 5)
A lithium ion secondary battery was prepared in the same manner as in Example 1 except that 0.0005 g of KF was mixed (0.01% by mass with respect to PVDF), and the rate characteristics and cycle characteristics were evaluated under the same conditions as in Example 1. did.

[Battery evaluation]
The initial average discharge capacity was about 200 mAh. The 10C discharge capacity was about 146 mAh, and the discharge capacity retention rate was about 73%. In addition, the average discharge capacity after 500 cycles was about 140 mAh, and the capacity retention rate was about 70%.

(Example 6)
A lithium ion secondary battery was produced in the same manner as in Example 1 except that 1.0 g (20% by mass with respect to PVDF) was mixed with KF, and cycle characteristics were evaluated.

[Battery evaluation]
The initial average discharge capacity was about 200 mAh. The 10C discharge capacity was about 172 mAh, and the discharge capacity retention rate was about 86%. The average discharge capacity after 500 cycles was about 166 mAh, and the capacity retention rate was about 83%.

(Example 7)
A lithium ion secondary battery was produced in the same manner as in Example 1 except that 0.00025 g (0.005 mass% with respect to PVDF) was mixed, and the cycle characteristics were evaluated.

[Battery evaluation]
The initial average discharge capacity was about 200 mAh. The 10C discharge capacity was about 140 mAh, and the discharge capacity retention rate was about 70%. The average discharge capacity after 500 cycles was about 132 mAh, and the capacity retention rate was about 66%.

(Example 8)
A lithium ion secondary battery was produced in the same manner as in Example 1 except that a single-layer separator produced as described below was used in place of the laminated separator with the gel electrolyte formed on the surface in Examples 1-7. Then, rate characteristics and cycle characteristics were evaluated under the same conditions as in Example 1.

[Preparation of separator with potassium fluoride added]
Polypropylene (PP) high molecular weight high wax (NP 055 (trade name) manufactured by Mitsui Chemicals) as an organic filler, PVDF 5 g as a binder, dimethylformamide (DMF) 27.8 g as a solvent, and pore formation A separator paint was prepared by mixing 9.3 g of butyl cellosolve (BCS) as a poor solvent and 0.15 g of potassium fluoride (KF) (manufactured by Kojundo Chemical Laboratory Co., Ltd., purity 99%). . This paint was applied onto a PET film and dried, and then peeled off from the PET film to obtain a self-supporting separator.

[Battery evaluation]
The initial average discharge capacity was about 200 mAh. The 10C discharge capacity was about 178 mAh, and the discharge capacity retention rate was about 89%. Moreover, the average discharge capacity after 500 cycles was about 170 mAh, and the capacity retention rate was about 85%.

(Comparative Example 1)
A gel electrolyte paint was prepared and applied to the separator surface in the same manner as in Example 1 except that KF was not used. The gel electrolyte coating soaked into the separator, and the gel electrolyte was not uniformly formed on the separator surface.
A lithium ion secondary battery was produced in the same manner as in Example 1, and the rate characteristics and cycle characteristics were evaluated under the same conditions as in Example 1.

[Battery evaluation]
Rate characteristics and cycle characteristics were evaluated under the same conditions as in Example 1. The initial average discharge capacity was about 200 mAh. The 10C discharge capacity was about 126 mAh, and the discharge capacity retention rate was about 63%. The average discharge capacity after 500 cycles was about 130 mAh, and the capacity retention rate was about 65%.

  The conditions and results of Examples 1 to 8 and Comparative Example 1 are shown in Table 1 below.

  Lithium ion secondary batteries of Examples 1 to 7 using a separator on which a porous film added with PVDF and KF was formed, and lithium of Example 8 using a porous film added with PVDF and KF as a separator The ion secondary battery has significantly improved rate characteristics and cycle characteristics as compared with Comparative Example 1 in which KF was not added. In addition, Example 7 in which the content of KF in the second porous film is less than 0.01 parts by mass with respect to 100 parts by mass of PVDF is slightly lower in rate characteristics and cycle characteristics than Examples 1 to 6 and 8. As a result.

  DESCRIPTION OF SYMBOLS 10,20 ... Electrode, 12 ... Positive electrode collector, 14 ... Positive electrode active material layer, 15 ... First porous film, 18 ... Separator, 22 ... Negative electrode collector, 24 ... Negative electrode active material layer, 30 ... Laminate 19, 29 ... second porous membrane, 50 ... case, 52 ... metal foil, 54 ... polymer membrane, 60,62 ... lead, 100 ... lithium ion secondary battery.

Claims (12)

An electrically insulating first porous film, and a second porous film containing a fluororesin and a potassium salt and formed on at least one of the main surfaces of the first porous film,
Said 2nd porous film further contains an inorganic filler, The separator characterized by the above-mentioned. The separator which consists of a porous film characterized by including a fluororesin and potassium salt, and also including an inorganic filler. The separator according to claim 1 or 2, wherein the fluororesin is polyvinylidene fluoride. The separator according to any one of claims 1 to 3, wherein the potassium salt is potassium fluoride. The separator according to any one of claims 1 to 4, wherein a content of the potassium salt in the second porous membrane is 0.01 to 20 parts by mass with respect to 100 parts by mass of the fluororesin. The positive electrode, a negative electrode disposed so as to face the positive electrode, and the positive electrode and the negative electrode are interposed between the main surface of the positive electrode and the main surface of the negative electrode. An electrochemical device comprising: a separator; and an electrolyte contained in the separator. A step of applying a paint containing a fluororesin, a potassium salt, a solvent for ionizing the potassium salt, and a poor solvent for forming voids on the substrate, and removing the solvent in the paint applied on the substrate And obtaining a second porous membrane,
The said coating material is a manufacturing method of the separator which further contains an inorganic filler. The method for manufacturing a separator according to claim 7, wherein the base material is an electrically insulating first porous film. The method for manufacturing a separator according to claim 7, further comprising a step of removing the base material from the second porous membrane after the step of obtaining the second porous membrane. The manufacturing method of the separator as described in any one of Claims 7-9 whose said fluororesin is polyvinylidene fluoride. The manufacturing method of the separator of any one of Claims 7-10 whose said potassium salt is potassium fluoride. The said potassium salt is manufacture of the separator of any one of Claims 7-11 currently added to the said coating material so that it may become 0.01-20 mass parts with respect to 100 mass parts of said fluororesins. Method.

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