JP2019160692A - Electrochemical device - Google Patents

Abstract

To provide a lithium battery having an excellent battery life.SOLUTION: The electrochemical device includes: an electrochemical element; an exterior body covering the electrochemical element; and a barrier layer covering at least an end face of the exterior body. The barrier layer includes at least one selected from a group consisting of parylene, diamond-like carbon, and a polymer compound including a heteroaromatic ring.SELECTED DRAWING: Figure 1

Description

  The present invention relates to an electrochemical device.

  A laminate outer package including a heat-resistant resin layer / metal layer / thermoadhesive layer is used to form an electrochemical element by covering an electrochemical element such as a battery or an electric double layer capacitor. Since the laminate outer package is lighter and thinner than the metal can outer package, it is relatively easy to improve the weight energy density and volume energy density of the electrochemical device. Moreover, since the laminate outer package is excellent in mechanical workability, electrochemical elements having various dimensions can be easily produced.

However, the electrochemical element using the laminate outer package has the end surface of the laminate package exposed to the atmosphere. Since the thermal adhesive layer transmits moisture to some extent, moisture penetrates into the exterior body over time. The invading moisture is electrolyzed inside the electrochemical element, generating hydrogen gas and oxygen gas, and the electrochemical element expands. In addition, when LiPF ₆ that easily reacts with water is used as the electrolyte salt, HF is generated, corroding the positive electrode active material and the aluminum foil / copper foil as the current collector, and the battery characteristics are deteriorated.

  For such a problem, Patent Document 1 discloses a film having a support layer and a polymer structure formed by vapor deposition. This polymer structure serves to prevent moisture from entering.

Special table 2011-523493 gazette

  However, even the method disclosed in Patent Document 1 cannot sufficiently suppress the intrusion of moisture, and it has been difficult to improve the battery life.

  The present invention has been made to solve the above problems, and an object of the present invention is to provide a lithium battery having an excellent battery life.

  As a result of intensive studies, the present inventors have found that by covering the exterior body with a barrier layer, it is possible to prevent moisture from entering the electrochemical element and to improve battery life. That is, in order to solve the above problems, the following means are provided.

(1) An electrochemical element according to a first aspect is an electrochemical element including an electrochemical element, an exterior body that covers the electrochemical element, and a barrier layer that covers at least an end surface of the exterior body. The barrier layer includes at least one selected from the group consisting of a polymer compound including parylene, diamond-like carbon, and a heteroaromatic ring.

(2) The barrier layer in the electrochemical device according to the above aspect may cover the entire surface of the outer package.

(3) The electrochemical element according to the above aspect further includes a lead having a first end connected to the electrochemical element body and a second end extending from the end face of the exterior body, , Covering at least a part of the lead, the thickness t of the barrier layer, the length a from the end surface of the outer package to the second end, and the lead from the end surface of the outer package to the barrier The length b to the end of the covering portion directly covered by the layer may satisfy the following general formula.
0.3 ≦ (b−t) / (at−t) <1

(4) The electrochemical element in the electrochemical device according to the above aspect includes a positive electrode, a negative electrode facing the positive electrode, and a nonaqueous electrolytic solution impregnated therein, and lithium metal is deposited on the negative electrode during charging. In addition, lithium metal may be dissolved from the negative electrode during discharge.

(5) The non-aqueous electrolyte in the electrochemical device according to the above aspect may include an ionic liquid.

(6) The ionic liquid in the electrochemical device according to the above aspect may include an amide anion.

(7) The amide anion in the electrochemical device according to the above aspect is (CF ₃ SO ₂ ) ₂ N ⁻ , (SO ₂ F) ₂ N ⁻ , (CF ₃ SO ₂ ) (CF ₃ CO) N ⁻ , and ( _{C 2 F 5 SO 2) 2} N - may be one or more selected from the group consisting of.

  The electrochemical device according to the above aspect has an effect of improving battery life by preventing moisture from entering.

It is a cross-sectional schematic diagram of the electrochemical element of this application.

  Hereinafter, the present embodiment will be described in detail with appropriate reference to the drawings. In the drawings used in the following description, in order to make the characteristics of the present invention easier to understand, there are cases where the characteristic parts are enlarged for the sake of convenience, and the dimensional ratios of the respective components are different from actual ones. is there. The materials, dimensions, and the like exemplified in the following description are merely examples, and the present invention is not limited to these, and can be appropriately changed and implemented within a range where the effects are exhibited.

[Electrochemical element]
FIG. 1 is a schematic cross-sectional view of an electrochemical device 100 according to the first embodiment. As shown in FIG. 1, the electrochemical element 100 includes an electrochemical element body 10, an exterior body 20, a barrier layer 30, and leads 40. The electrochemical element 10 is impregnated with an electrolytic solution. The exterior body 20 includes a heat resistant resin layer 21, a metal layer 22, and a heat bonding layer 23. The exterior body 20 prevents the electrolytic solution from leaking to the outside, and prevents external air and moisture from reaching the electrochemical element body 10. The barrier layer 30 prevents external air and moisture from reaching the electrochemical element 10. Although the electrochemical element 10 is described as a lithium secondary battery for convenience, the electrochemical element 10 may be an electric double layer capacitor.

(Electrochemical element)
The electrochemical element 10 includes a positive electrode, a negative electrode, and a separator. The electrochemical element body 10 shown in FIG. 1 has a pair of a positive electrode and a negative electrode arranged opposite to each other with a separator interposed therebetween.

  A nonaqueous electrolytic solution is provided between the positive electrode and the negative electrode. The non-aqueous electrolyte is impregnated in the separator and the positive electrode active material layer in FIG. The electrochemical device 100 performs charge / discharge by moving lithium ions between the positive electrode and the negative electrode through the non-aqueous electrolyte. That is, if there are a positive electrode, a negative electrode, and a non-aqueous electrolyte, the electrochemical device 100 operates.

<Positive electrode>
The positive electrode has a positive electrode current collector and a positive electrode active material layer provided on one surface thereof. The positive electrode current collector is only required to be composed of a conductive material, and for example, a thin metal plate of aluminum, copper, or nickel foil can be used.

The positive electrode active material used for the positive electrode active material layer is composed of lithium ion occlusion and release, lithium ion desorption and insertion (intercalation), or a counter anion (for example, PF ₆ ⁻ ) of lithium ions and lithium ions. An electrode active material capable of reversibly proceeding doping and dedoping can be used.

For example, lithium cobalt oxide (LiCoO _2), lithium nickelate (LiNiO _2), lithium manganate (LiMnO _2), lithium manganese spinel (LiMn ₂ O _4), and the 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 one type selected from Al, Mg, Nb, Ti, Cu, Zn, Cr Complex metal oxides represented by the above elements), lithium vanadium compounds (LiV ₂ O ₅ ), olivine-type LiMPO ₄ (where M is Co, Ni, Mn, Fe, Mg, Nb, Ti, Al, Zr) One or more elements or VO selected from the above, lithium titanate (Li ₄ Ti ₅ O ₁₂ ), LiNi _x Co _y Al _z O ₂ (0.9 <x + y + z < 1.1) and the like, and polyacetylene, polyaniline, polypyrrole, polythiophene, polyacene and the like.

  The positive electrode active material layer may have a conductive material. Examples of the conductive material include carbon powder such as carbon black, carbon nanotube, carbon material, fine metal powder such as copper, nickel, stainless steel and iron, a mixture of carbon material and fine metal powder, and conductive oxide such as ITO. It is done. In the case where sufficient conductivity can be ensured only by the positive electrode active material, the electrochemical element 10 may not contain a conductive material.

  The positive electrode active material layer includes a binder. A well-known thing can be used for a binder. For example, polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), tetrafluoroethylene-hexafluoropropylene copolymer (FEP), tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer (PFA), ethylene-tetrafluoro Fluorine resins such as ethylene copolymer (ETFE), polychlorotrifluoroethylene (PCTFE), ethylene-chlorotrifluoroethylene copolymer (ECTFE), and polyvinyl fluoride (PVF).

  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.

<Negative electrode>
The negative electrode has a negative electrode current collector and a negative electrode active material layer provided on one surface thereof. The same thing as a positive electrode can be used for a negative electrode collector, a electrically conductive material, and a binder. The binder used for the negative electrode may be, for example, cellulose, styrene / butadiene rubber, ethylene / propylene rubber, polyimide resin, polyamideimide resin, acrylic resin, etc. in addition to those listed for the positive electrode.

A known negative electrode active material can be used as the negative electrode active material used for the negative electrode active material layer. Examples of the negative electrode active material include carbon materials such as metallic lithium, graphite capable of occluding and releasing lithium ions (natural graphite, artificial graphite), carbon nanotubes, non-graphitizable carbon, graphitizable carbon, and low-temperature calcined carbon. Metals that can be combined with lithium such as aluminum, silicon and tin, amorphous compounds mainly composed of oxides such as SiO _x (0 <x <2) and tin dioxide, lithium titanate (Li ₄ Ti ₅ And particles containing O ₁₂ ) and the like.

  In the negative electrode, lithium ion occlusion / release reactions, precipitation / dissolution reactions, alloying / non-alloy reactions, and the like occur. In order to achieve a high theoretical capacity density, it is preferable that lithium metal precipitates on the negative electrode during charging and that the lithium metal dissolves from the negative electrode during discharging.

  When the deposition and dissolution reaction of metallic lithium is performed in the negative electrode, the negative electrode active material layer may not be in the initial state. This is because lithium ions in the electrolytic solution are deposited as metallic lithium on one surface of the negative electrode current collector. On the other hand, since the deposited metal lithium remains when charged one or more times, the layer containing this metal lithium can be regarded as the negative electrode active material layer. In preparation for the shortage of the amount of lithium contributing to charging / discharging, a lithium foil may be provided on one surface of the current collector from the initial state before charging / discharging.

<Separator>
The separator only needs to be formed of an electrically insulating porous structure, for example, a single layer of a film made of polyethylene, polypropylene or polyolefin, a stretched film of a laminate or a mixture of the above resins, or cellulose, polyester and polypropylene. A fiber nonwoven fabric made of at least one constituent material selected from the group consisting of:

<Non-aqueous electrolyte>
The nonaqueous electrolytic solution contains a nonaqueous solvent and a lithium salt. As the non-aqueous solvent, an ionic liquid, a cyclic carbonate, a chain carbonate, or the like can be used.

"Ionic liquid"
An ionic liquid is a salt which is liquid even below 100 ° C. obtained by a combination of a cation and an anion. Since the ionic liquid is a liquid composed only of ions, the ionic liquid has a strong electrostatic interaction and is characterized by non-volatility and nonflammability. In addition, since an electrolytic solution using an ionic liquid has low reactivity with water, it is difficult to generate hydrogen fluoride (HF) due to the reaction between water and a lithium salt. Therefore, the electrochemical device 100 using an ionic liquid as the electrolytic solution is excellent in safety.

  There are various types of ionic liquids depending on combinations of cations and anions. Examples thereof include nitrogen-based ionic liquids such as imidazolium salts, pyrrolidinium salts, piperidinium salts, pyridinium salts, and ammonium salts, phosphorus-based ionic liquids such as phosphonium salts, and sulfur-based ionic liquids such as sulfonium salts. Nitrogen-based ionic liquids can be divided into cyclic quaternary ammonium salts and chain quaternary ammonium salts.

  Nitrogen-based, phosphorus-based, sulfur-based and the like have been reported as cations of ionic liquids. The cation of the ionic liquid is preferably at least one selected from the group consisting of a quaternary ammonium cation, a sulfonium cation, and a phosphonium cation. These cations have a wide potential window on the reduction side. Therefore, these cations are hardly reduced and decomposed on the negative electrode surface.

  The quaternary ammonium cation is a nitrogen-based cation, and there are cyclic and chain ones. Examples of the cyclic cation include an imidazolium cation, a pyrrolidinium cation, a piperidinium cation, and a pyridinium cation, and the chain cation includes an ammonium cation.

  Specific examples of the imidazolium cation include 1 ethyl 3 methyl imidazolium, 1 butyl 3 methyl imidazolium, 1 octyl 3 methyl imidazolium, 1 butyl 3 dodecyl imidazolium and the like.

  Specific examples of the pyrrolidinium cation include 1 ethyl 1 propyl pyrrolidinium, 1 butyl 1 methyl pyrrolidinium, 1 methyl 1 pentyl pyrrolidinium, and the like.

  Specific examples of the piperidinium cation include propylmethylpiperidinium and butylmethylpiperidinium.

  Specific examples of the pyridinium cation include 1 hexa-4-methylpyridinium, 1 octyl 4-methylpyridinium, and the like.

  Examples of the chain ammonium cation include trimethylpropylammonium, trimethylbutylammonium, and trimethylhexylammonium.

  The sulfonium cation is a sulfur cation, and examples thereof include triethylsulfonium. The phosphonium cation is a phosphorus cation and includes triethylsulfonium.

  Nitrogen-based cations are excellent in terms of raw material availability, diversity, safety, operability and price. Among nitrogen-based cations, imidazolium-based, ammonium-based and pyridinium-based cations are relatively inexpensive and easily available.

As anions of the ionic liquid, AlCl ₄ ⁻ , NO ₂ ⁻ , NO ₃ ⁻ , I ⁻ , BF ₄ ⁻ , PF ₆ ⁻ , AsF ₆ ⁻ , SbF ₆ ⁻ , NbF ₆ ⁻ , TaF ₆ ⁻ , F (HF) _2.3 ⁻ , p-CH ₃ PhSO ₃ ⁻ , CH ₃ CO ₂ ⁻ , CF ₃ CO ₂ ⁻ , CH ₃ SO ₃ ⁻ , CF ₃ SO ₃ ⁻ , (CF ₃ SO ₂ ) ₃ C ⁻ , C ₃ F ₇ CO ₂ , C ₄ F ₉ SO ₃ ⁻ , (CF ₃ SO ₂ ) ₂ N ⁻ , (C ₂ F ₅ SO ₂ ) ₂ N ⁻ , (CF ₃ SO ₂ ) (CF ₃ CO) N ⁻ , (CN ) ₂ N ⁻ , (SO ₂ F) ₂ N ⁻ , and the like.

Preferably, the ionic liquid contains an amide anion. The amide anion has an “—N ⁻ —” bond in the molecule and includes an imide anion. In addition, the imide anion is a general name in which carbonyl groups are connected to both ends of “—N ⁻ —”, but also includes those in which carbon of the carbonyl group is substituted with sulfur, phosphorus or the like in this field. .

The anion of the ionic liquid can have a fluorine atom. Preferably, the amide anion is bis (trifluoromethanesulfonyl) imide (composition formula: (CF ₃ SO ₂ ) ₂ N ⁻ ), bis (fluorosulfonyl) imide (composition formula: (SO ₂ F) ₂ N ⁻ ), ( It is at least one selected from the group consisting of CF ₃ SO ₂ ) (CF ₃ CO) N ⁻ and (C ₂ F ₅ SO ₂ ) ₂ N ⁻ . When a fluorine-based anion is combined with the above-described cation, the fluorine atom attracts electrons, so that the cation is hardly reduced and decomposed.

"Lithium salt"
As the lithium salt, inorganic acid anion salts such as LiPF ₆ , LiBF ₄ , and LiBOB, organic acid anion salts such as LiCF ₃ SO ₃ , (CF ₃ SO ₂ ) ₂ NLi, and (FSO ₂ ) ₂ NLi are used. be able to. As the lithium salt, one that hardly generates hydrogen fluoride (HF) by reaction with water is preferable, and an organic acid anion salt containing no fluorine is more preferable.

"Cyclic carbonate and chain carbonate"
As cyclic carbonate, what can solvate electrolyte can be used. For example, ethylene carbonate, propylene carbonate, butylene carbonate, and the like can be used.

  The chain carbonate can reduce the viscosity of the cyclic carbonate. Examples thereof include diethyl carbonate, dimethyl carbonate, and ethyl methyl carbonate. In addition, methyl acetate, ethyl acetate, methyl propionate, ethyl propionate, γ-butyrolactone, 1,2-dimethoxyethane, 1,2-diethoxyethane, and the like may be mixed and used.

  The ratio of the cyclic carbonate and the chain carbonate in the non-aqueous solvent is preferably 1: 9 to 1: 1 by volume.

(Barrier layer)
The barrier layer 30 covers at least the end surface of the exterior body 20. When the barrier layer 30 is not present, the thermal bonding layer 23 is exposed to the atmosphere on the end face of the outer package 20. The barrier layer effectively prevents moisture from entering the electrochemical element 10 via the thermal bonding layer 23. Therefore, generation of hydrogen gas and oxygen gas accompanying water electrolysis inside the electrochemical element body 10 can be prevented, and expansion of the electrochemical element body 10 is prevented. Moreover, generation | occurrence | production of the product by reaction with electrolyte salt, such as lithium salt, and water is prevented. Thus, the battery life is improved by preventing the corrosion of the positive electrode active material and the aluminum foil / copper foil as the current collector.

  The barrier layer 30 may be formed using chemical vapor deposition (CVD). Chemical vapor deposition (CVD) can form a dense and uniform thin film. Since the dense and uniform barrier layer 30 can effectively prevent the penetration and permeation of water, the electrochemical device 100 covered with such a barrier layer 30 has an excellent waterproof property and hence an improved lifetime. Is provided.

  The material for the barrier layer 30 may be any material used by chemical vapor deposition (CVD). Specifically, the raw material of the barrier layer 30 may include at least one selected from the group consisting of parylene, which is a paraxylylene-based polymer compound, diamond-like carbon (DLC), and a polymer compound containing a heteroaromatic ring. . Preferably, parylene is used as a raw material for the barrier layer 30.

  Parylene has derivatives such as parylene C, parylene HT, parylene D, and parylene N depending on the substituent. Parylene is commercially available from, for example, Japan Parylene LLC.

  As the polymer compound containing a heteroaromatic ring, a polymer compound containing a heteroaromatic ring such as polyimide, polybenzoxazole, polybenzothiazole, polyphenyleneisophthalamide, or the like can be used.

  The barrier layer 30 may cover only the end surface of the exterior body 20. In this case, during the chemical vapor deposition (CVD), the deposition of the barrier layer 30 on a portion other than the end face of the outer package 20 is prevented using a mask or the like.

  The barrier layer 30 may cover the entire surface of the exterior body 20. In this case, the penetration of moisture into the electrochemical element 10 is effectively prevented, and the lifetime of the electrochemical element 100 is improved.

  The barrier layer 30 may further include a lead 40 having a first end connected to the electrochemical element body 10 and a second end extending from the end surface of the exterior body 20. The barrier layer 30 may cover at least a part of the lead 40. The thickness t of the barrier layer 30, the length a from the end surface of the outer package 20 to the second end, and the end surface of the outer package 20 to the end of the covering portion where the lead 40 is directly covered by the barrier layer 30. The length b can satisfy the general formula 0.3 ≦ (b−t) / (at−t) <1.

  Preferably, (bt) / (at) is 0.6 or more. More preferably, (bt) / (at) is 0.9 or more. When the barrier layer 30 covers at least a part of the lead 40, the intrusion of moisture into the electrochemical element 10 is suppressed, and the lifetime of the electrochemical element 100 is improved.

  The thickness t of the barrier layer 30 and the length b from the end face of the outer package 20 to the end of the covering portion where the lead 40 is directly covered by the barrier layer 30 are expressed by the general formula 0.5 mm ≦ (b− t) may be satisfied.

  The thickness t of the barrier layer 30 can be determined in consideration of waterproofness and mechanical properties. Specifically, the thickness of the barrier layer 30 may be not less than 0.5 μm and not more than 5 μm.

(Exterior body)
The exterior body 20 seals the electrochemical element body 10 and the electrolytic solution. The exterior body 20 can include a heat resistant resin layer 21, a metal layer 22, and a heat bonding layer 23. The exterior body 20 may have a heat resistant resin layer 21, a metal layer 22, and a heat bonding layer 23 in order from the outside.

<Heat resistant resin layer>
The heat-resistant resin layer 21 is preferably a material that does not require heat-fusibility and has a high melting point. Specifically, polyethylene terephthalate (PET), polyamide (PA) and the like are preferable.

<Metal layer>
The metal layer 22 may serve to protect the electrochemical device 100 by blocking moisture and air entering from the outside. The metal layer 22 is not particularly limited as long as it is a conductive metal. For example, Al, Cu, Ni, Pt, SUS, or the like can be used. Specifically, it is preferable to use Al.

<Thermal bonding layer>
The thermal adhesive layer 23 may include a resin. As the resin, a heat-fusible resin is preferably used, and for example, polyethylene (PE), polypropylene (PP), or the like can be used.

  As shown in FIG. 1, the thermal bonding layer 23 may be in direct contact with the barrier layer 30 at the end face of the outer package 20.

  When untreated polyethylene (PE) and polypropylene (PP) are used for the thermal adhesive layer 23, the adhesion with parylene or the like used for the barrier layer 30 may not be good. In order to improve the adhesion between the thermal adhesive layer 23 and the barrier layer 30, acid modification and / or plasma treatment of the thermal adhesive layer 23 may be performed. The improved adhesion between the thermal adhesive layer 23 and the barrier layer 30 can prevent moisture from entering the electrochemical element 10 via the thermal adhesive layer 23.

  The acid modification of the thermal adhesive layer 23 may be performed using an acid capable of modifying the thermal adhesive layer 23. Specifically, acid modification can be performed using carboxylic anhydride. Preferably, the acid modification can be performed using maleic anhydride.

  The plasma treatment of the thermal adhesive layer 23 can be performed by a method known to those skilled in the art that can modify the surface characteristics of the object.

  As a specific combination of the barrier layer 30 and the outer package 20 (barrier layer 30 / heat resistant resin layer 21 / metal layer 22 / thermal adhesive layer 23), parylene / polyamide (PA) / Al / polypropylene (PP), parylene / A combination of polyethylene terephthalate (PET) / Al / polypropylene (PP) or parylene / polyamide (PA) / Al / acid-modified polypropylene (PP) may be used.

(Lead)
The lead 40 is made of a conductive material such as aluminum. One end of the lead 40 is connected to the positive electrode and the negative electrode. The exterior body 20 is sealed with the lead 40 interposed therebetween, and the other end extends to the outside.

  The lead 40 can be roughened on at least part of its surface. Specifically, the lead 40 may be roughened at a portion that can directly contact the thermal bonding layer 23 and / or the barrier layer 30. The roughening of the surface of the lead 40 increases the surface area of the lead 40, so that the adhesion with the thermal bonding layer 23 and / or the barrier layer 30 can be improved. Further, the roughening of the surface of the lead 40 lengthens the moisture intrusion route, so that the waterproof effect of the electrochemical device 100 can be improved.

  The roughness of the surface of the lead 40 can be evaluated by the surface roughness. The surface roughness can be measured using methods known to those skilled in the art, such as a light wave interferometer. The measured surface roughness can be evaluated as centerline average roughness (hereinafter referred to as Ra). Ra of the lead 40 may be 0.20 μm or more and 50 μm or less.

  The surface of the lead 40 is roughened by chemical treatment, mechanical treatment, or the like. As chemical treatment, etching with acid or base may be used. As the mechanical treatment, sandblasting, file, or the like may be used. The chemical treatment and mechanical treatment conditions can be appropriately selected by those skilled in the art.

[Method for producing electrochemical element]
The electrochemical element body 10 of the electrochemical element 100 can be produced by a known method. Hereinafter, the manufacturing method of the electrochemical element 10 will be specifically described.

  First, a positive electrode and a negative electrode are prepared. The positive electrode and the negative electrode differ only in the material that becomes the active material, and can be produced by the same manufacturing method.

  A positive electrode active material, a binder, and a solvent are mixed to prepare a paint. A conductive material may be further added as necessary. As the solvent, for example, water, N-methyl-2-pyrrolidone, N, N-dimethylformamide or the like can be used. The constituent ratio of the positive electrode active material, the conductive material, and the binder is preferably 80 wt% to 98 wt%: 0.1 wt% to 10 wt%: 0.1 wt% to 10 wt% in mass ratio. These mass ratios are adjusted so as to be 100 wt% as a whole.

  The mixing method of these components constituting the paint is not particularly limited, and the mixing order is not particularly limited. The paint is applied to the positive electrode current collector. 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. Similarly, for the negative electrode, a paint is applied on the negative electrode current collector. When the negative electrode active material is metallic lithium, the negative electrode current collector may be used alone without applying the paint.

  Subsequently, the solvent in the paint applied on the positive electrode current collector and the negative electrode current collector is removed. The removal method is not particularly limited. For example, the positive electrode current collector and the negative electrode current collector to which the paint is applied may be dried in an atmosphere of 80 ° C. to 150 ° C. And a positive electrode and a negative electrode are completed.

  Subsequently, the produced positive electrode and negative electrode are laminated | stacked through a separator, and it encloses in the exterior body 20 with a non-aqueous electrolyte. For example, a positive electrode, a negative electrode, and a separator are laminated, and the electrochemical element body 10 is put into a bag-shaped exterior body 20 that is prepared in advance. The non-aqueous electrolyte may be injected into the outer package 20 or may be impregnated in the electrochemical element body 10.

  Next, the outer package 20 is produced. The exterior body 20 may be a laminate exterior body. The exterior body 20 can include a heat resistant resin layer 21, a metal layer 22, and a heat bonding layer 23. There are a method of directly forming the heat-resistant resin layer 21 and the thermal bonding layer 23 on the metal layer 22, a method of separately preparing and laminating them, and a method of using them together. The lamination may be performed by a hot press or an adhesive.

  Then, the produced electrochemical element 10 is enclosed in the outer package 20. The electrolytic solution may be injected into the outer package 20 or the electrochemical element 10 may be impregnated in the electrolytic solution. The outer package 20 can be folded at the center portion in the longitudinal direction with the heat-sealing resin layer inside, and can be heat-sealed at the left and right ends in the longitudinal direction. You may seal by putting the electrochemical element | base_body 10 and electrolyte solution in this bag-shaped exterior body 20, and heat-sealing the remaining opening part of the exterior body 20. FIG.

  Next, the barrier layer 30 is produced. The barrier layer 30 is formed on the exterior body 20 by chemical vapor deposition (CVD) using parylene or the like as a raw material so as to be a film having a predetermined thickness. The barrier layer 30 may cover the entire surface of the exterior body 20. The barrier layer 30 may cover only the end surface of the exterior body 20 from which the thermal adhesive layer 23 is exposed.

  Although the embodiments of the present invention have been described in detail with reference to the drawings, the configurations and combinations of the embodiments in the embodiments are examples, and the addition and omission of configurations are within the scope not departing from the gist of the present invention. , Substitutions, and other changes are possible.

First, a positive electrode was prepared. NCA (composition formula: Li _1.0 Ni _0.78 Co _0.19 Al _0.03 O ₂ ) was prepared as the positive electrode active material, carbon black as the conductive material, and PVDF as the binder. These were mixed in a solvent to prepare a paint, and applied onto a positive electrode current collector made of aluminum foil. The mass ratio of the positive electrode active material, the conductive material, and the binder was 95: 2: 3. After application, the solvent was removed.

  Copper foil was used for the negative electrode current collector. In the negative electrode, lithium metal was deposited during charging, and lithium metal was dissolved during discharging. The negative electrode active material layer was not formed at the stage of production.

The produced positive electrode and negative electrode were laminated via a separator to produce a power generation unit. The number of stacked positive and negative electrodes was one. For the separator, a laminate of polyethylene and polypropylene was used. The obtained power generation part was impregnated with a nonaqueous electrolytic solution and then enclosed in the exterior body. N-methyl-N-propylpyrrolidinium bis (fluorosulfonyl) imide (P ₁₃ -FSI) is used as the electrolyte, and lithium bis (trifluoromethanesulfonyl) imide (Li-TFSI) is used so as to have a concentration of 1 mol / L. ) Was used. And the barrier layer was each coated on the conditions shown in the following Table 1 (only Comparative Example 1 was not coated), and the capacity retention rate of the lithium secondary battery was measured.

  About the lithium ion secondary battery produced by the Example and the comparative example, the cycle characteristic was measured in 25 degreeC environment using the secondary battery charging / discharging test apparatus (made by Hokuto Denko Co., Ltd.). A charge / discharge cycle in which a constant current and a constant voltage were charged to 4.2 V at 0.5 C and a constant current was discharged to 2.8 V at 1 C was repeated 100 cycles, and the capacity retention rate after 100 cycles was measured. In addition, the sample measured by n = 5 about each level, respectively, and made the average value the evaluation value.

(Examples 1-6)
In Example 1, polypropylene (PP) was used as the resin for the thermal adhesive layer of the outer package 20. The barrier layer 30 was formed by chemical vapor deposition (CVD) using Parylene C as a raw material so as to be a film having a thickness of 0.5 μm. The barrier layer 30 was formed only on the end surface of the exterior body 20 from which the thermal bonding layer 23 was exposed by covering the portion other than the end surface of the exterior body 20 with a mask. In Examples 2 to 6, the thickness of the barrier layer 30 is changed to 1 μm (Example 2), 2 μm (Example 3), 3 μm (Example 4), 4 μm (Example 5), and 5 μm (Example 6). The conditions were the same as in Example 1 except for the above.

(Examples 7 to 9)
In Examples 7 to 9, the same conditions as in Example 4 were used except that the raw material of the barrier layer 30 was changed to Parylene HT (Example 7), Parylene D (Example 8), and Parylene N (Example 9). .

(Example 10)
In Example 10, the same conditions as in Example 4 were used except that the barrier layer 30 was formed on the entire surface of the outer package 20. By forming the barrier layer 30 on the entire surface of the outer package 20, the capacity retention rate of the electrochemical device 100 was improved as compared to the case where only the end surface was formed (Example 4).

(Examples 11 and 12)
In Example 11, it was set as the same conditions as Example 4 except having used polyethylene (PE) as resin for thermal adhesive layers. In Example 12, the same conditions as in Example 4 were used except that polyethylene (PE) was used as the resin for the thermal adhesive layer and the barrier layer 30 was formed on the entire surface of the outer package 20.

(Examples 13 to 15)
In Examples 13 to 15, the general formula (bt) / (at) described above was 0.3 (Example 13), 0.6 (Example 14), and 0.9 (Example 15). The conditions were the same as in Example 4 except that the barrier layer 30 directly covered a part of the lead 40 so as to satisfy the above condition. As the value of (bt) / (at) increases, that is, as the coverage of the barrier layer 30 on the leads 40 from the end face of the outer package 20 increases, the capacity retention rate of the electrochemical device 100 increases. Improved.

(Examples 16 and 17)
In Example 16, the same conditions as in Example 4 were used except that the surface plasma treatment of the thermal bonding layer 23 was performed. In Example 17, the same conditions as in Example 4 were used except that polyethylene (PE) was used as the thermal adhesive layer resin and the surface plasma treatment of the thermal adhesive layer 23 was performed. By performing the surface plasma treatment of the thermal bonding layer 23, the capacity retention rate of the electrochemical device 100 was improved as compared with the case where the surface plasma treatment was not performed (Examples 4 and 11).

(Examples 18 and 19)
In Example 18, the same conditions as in Example 4 were used except that DLC was used as a raw material for the barrier layer 30. In Example 19, the same conditions as in Example 4 were used except that a polymer compound containing a heteroaromatic ring, such as polyimide, polybenzoxazole, polybenzothiazole, polyphenyleneisophthalamide, was used as a raw material for the barrier layer 30. did.

(Examples 20 and 21)
In Example 20, the same conditions as in Example 4 were used except that acid-modified polypropylene (PP) was used as the resin for the thermal adhesive layer. In Example 21, the same conditions as in Example 4 were used except that acid-modified polypropylene (PP) was used as the resin for the thermal adhesive layer and the barrier layer 30 was formed on the entire surface of the outer package 20. By using acid-modified polypropylene (PP) instead of polypropylene (PP) as the resin for the thermal adhesive layer, the electrochemical device 100 is compared with the case of using untreated polypropylene (PP) (Example 4). Capacity maintenance rate improved.

(Examples 22 and 23)
In Example 22, the same conditions as in Example 4 were used except that acid-modified polyethylene (PE) was used as the resin for the thermal adhesive layer. In Example 23, the same conditions as in Example 4 were used except that acid-modified polyethylene (PE) was used as the resin for the thermal adhesive layer and the barrier layer 30 was formed on the entire surface of the exterior body 20. By using acid-modified polyethylene (PE) instead of polyethylene (PE) as the resin for the thermal adhesive layer, the electrochemical element 100 is compared with the case of using untreated polyethylene (PE) (Example 11). Capacity maintenance rate improved.

  In Examples 1 to 23 in which the end face or the entire surface of the outer package 20 was covered with the barrier layer 30, the electrochemical device 100 exhibited a capacity retention rate of 80% or more. It is considered that the barrier layer 30 covering the exterior body 20 effectively prevents moisture from entering the electrochemical element body 10. In particular, when the barrier layer 30 directly covers at least a part of the lead 40 from the end face of the outer package 20, the electrochemical device 100 exhibited a capacity retention rate of 95% or more. It is considered that the barrier layer 30 directly covering the lead 40 more effectively prevents moisture from entering the electrochemical element 10.

(Comparative Example 1)
In Comparative Example 1, polypropylene (PP) was used as the heat bonding layer resin of the outer package 20. The barrier layer 30 covering the exterior body 20 was not provided.

(Comparative Example 2)
In Comparative Example 2, the conditions were the same as in Example 16 except that the barrier layer 30 was formed only on the main surface of the outer package 20.

(Comparative Example 3)
In Comparative Example 3, the conditions were the same as in Example 17 except that the barrier layer 30 was formed only on the main surface of the exterior body 20.

(Comparative Example 4)
In Comparative Example 4, the conditions were the same as those in Example 20 or 22 except that the barrier layer 30 was formed only on the main surface of the outer package 20.

(Comparative Example 5)
In Comparative Example 5, the conditions were the same as those in Example 22 or 23 except that the barrier layer 30 was formed only on the main surface of the outer package 20.

  In Comparative Example 1 where there is no barrier layer 30 covering the outer package 20, the capacity retention rate of the electrochemical device 100 was 53%. In the absence of the barrier layer 30, the moisture can easily reach the electrochemical element 10, and thus the lifetime of the electrochemical element 100 is considered to be shortened. Moreover, in Comparative Examples 2 to 4 in which the barrier layer 30 covers only the main surface of the outer package 20, the capacity retention rate of the electrochemical device 100 was 63% to 66%. It is considered that moisture can easily reach the electrochemical element body 10 through the thermal adhesive layer 23 exposed at the end face of the outer package 20.

  The presence of the barrier layer 30 covering at least the end face of the outer package 20 effectively prevents moisture from entering the electrochemical element 10. Further, since the barrier layer 30 covers at least a part of the lead 40 from the end face of the outer package 20, the intrusion of moisture into the electrochemical element body 10 is further reduced. Thus, the lifetime of the electrochemical device 100 in which at least the end surface of the outer package 20 is covered with the barrier layer 30 of the present application is improved.

DESCRIPTION OF SYMBOLS 10 ... Electrochemical element body, 20 ... Exterior body, 21 ... Heat-resistant resin layer, 22 ... Metal layer, 23 ... Thermal adhesive layer, 30 ... Barrier layer, 40 ... Lead, 100 ... Electrochemical element

Claims (7)

An electrochemical element comprising: an electrochemical element; an outer covering that covers the electrochemical element; and a barrier layer that covers at least an end surface of the outer covering,
The said barrier layer is an electrochemical element containing at least 1 sort (s) selected from the group which consists of a high molecular compound containing parylene, diamond-like carbon, and a heteroaromatic ring.   The electrochemical device according to claim 1, wherein the barrier layer covers the entire surface of the exterior body. The first end is connected to the electrochemical element, and the second end further includes a lead extending from the end surface of the exterior body,
The barrier layer covers at least a portion of the lead;
A thickness t of the barrier layer;
A length a from the end surface of the exterior body to the second end;
The length b from the end face of the outer package to the end of the covering portion where the lead is directly covered by the barrier layer,
General formula 0.3 ≦ (b−t) / (at −) <1
The electrochemical element according to claim 1 or 2, satisfying The electrochemical element comprises a positive electrode, a negative electrode facing the positive electrode, and a non-aqueous electrolyte impregnated therein,
The electrochemical element according to any one of claims 1 to 3, wherein lithium metal is deposited on the negative electrode during charging, and lithium metal is dissolved from the negative electrode during discharging.   The electrochemical device according to claim 4, wherein the non-aqueous electrolyte contains an ionic liquid.   The electrochemical device according to claim 5, wherein the ionic liquid contains an amide anion. The amide anion is (CF ₃ SO ₂ ) ₂ N ⁻ , (SO ₂ F) ₂ N ⁻ , (CF ₃ SO ₂ ) (CF ₃ CO) N ⁻ , and (C ₂ F ₅ SO ₂ ) ₂ N ^−. The electrochemical element according to claim 6, which is at least one selected from the group consisting of:

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