JP2011060521A - Manufacturing method of electrode for secondary battery - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an electrode for a nonaqueous electrolyte secondary battery with excellent cycle characteristics, through effective restraint of problems of an active material pulverized due to expansion or contraction. <P>SOLUTION: The manufacturing method of the electrode for a secondary battery includes a process of forming an active material layer 3 by coating an active material slurry containing active materials 5a, 5b on at least one of the faces of a porous member 4 to be a carrier, and a process of jointing the active material layer 3 carried by the porous member 4 to a collector 2. An average pore size of the porous member 4 is to be smaller than d50 and larger than d10 in an accumulated particle size distribution of the active materials 5a, 5b. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a method for manufacturing a secondary battery electrode. In particular, the present invention relates to an improvement for suppressing the occurrence of problems due to expansion and contraction of an active material.

  In recent years, in order to cope with global warming, reduction of the amount of carbon dioxide is eagerly desired. In the automobile industry, there is a great expectation for reducing carbon dioxide emissions by introducing electric vehicles (EV) and hybrid electric vehicles (HEV), and the development of secondary batteries for motor drive that holds the key to commercialization of these is thriving. Has been done.

  As a secondary battery for driving a motor, it is required to exhibit extremely high output characteristics and high energy density as compared with a consumer lithium ion secondary battery used in a mobile phone, a notebook personal computer, or the like. Therefore, lithium ion secondary batteries having the highest theoretical energy among all the batteries are attracting attention, and are currently being developed rapidly.

  Generally, a lithium ion secondary battery includes a positive electrode in which a positive electrode active material or the like is applied to the surface of the current collector using a binder, and a negative electrode in which a negative electrode active material or the like is applied to the surface of the current collector using a binder. It is connected via an electrolyte layer containing an electrolyte and has a configuration of being housed in a battery case.

  As an active material used for such a lithium ion secondary battery, for example, in the negative electrode, a carbon / graphite negative electrode material or an alloy negative electrode material such as silicon (Si) or tin (Sn) that can be alloyed with lithium is used. Can be. In particular, alloy-based negative electrode materials are expected as candidates for vehicle batteries because they can achieve a higher energy density than carbon-graphite-based negative electrode materials.

  The above-mentioned alloy-based negative electrode material has particularly large expansion / contraction due to insertion / extraction of lithium ions. For example, volume expansion when lithium ions are stored is about 1.2 times that of graphite, whereas silicon-based negative electrode materials are silicon-based. The negative electrode material reaches about 4 times. When the active material expands greatly as described above, the active material may collapse and become finer when charge and discharge are repeated, and the active material may be detached from the electrode. Further, a large stress acts on the current collector as the volume of the thin film active material layer changes, and the electrode itself may be greatly swelled and deformed. These phenomena may cause deterioration of cycle characteristics when a battery is configured.

  As a technique for coping with this problem, Patent Document 1 discloses a negative electrode in which a metal foam containing silicon (silicon) is laminated on the surface of a metal current collector. According to the document, such a configuration suppresses the detachment of the active material in the charge / discharge cycle, and can improve the charge / discharge cycle characteristics of the battery.

JP 2004-259636 A

  However, even with the technique described in Patent Document 1, there is a problem that the occurrence of problems due to expansion / contraction of the active material may not be sufficiently suppressed.

  Then, an object of this invention is to provide the electrode for secondary batteries which can fully suppress generation | occurrence | production of the problem by expansion / contraction of an active material.

  The method for producing an electrode for a secondary battery of the present invention includes a step of applying an active material slurry containing an active material to one surface of a porous member to form an active material layer, and bonding the active material layer to a current collector And a step of performing.

  According to the present invention, among the active materials constituting the active material layer, those having a small particle diameter selectively enter into the pores of the porous member, and the active material layer positioned outside the pores of the porous member has a particle diameter of Consists of large active materials. Therefore, the space | gap between active materials outside the hole of a porous member becomes large, and the expansion allowance of an active material is securable. Thereby, generation | occurrence | production of the problem by expansion / contraction of an active material can fully be suppressed.

It is sectional drawing which represents typically the electrode for secondary batteries concerning one Embodiment of this invention. It is the figure which expanded a part of electrode for secondary batteries of FIG. It is sectional drawing which represents typically the electrode for secondary batteries concerning other one Embodiment of this invention. It is the figure which expanded a part of electrode for secondary batteries of FIG. It is sectional drawing which represented typically the whole structure of the laminated type lithium ion secondary battery which is not a bipolar type which concerns on this form.

  Hereinafter, preferred embodiments of the present invention will be described. Hereinafter, a lithium ion secondary battery will be described as an example, but the present invention is also applicable to a secondary battery other than a lithium ion secondary battery.

<Method for producing electrode>
In this embodiment, a first step of forming an active material layer by applying an active material slurry containing an active material to one surface of a porous member, and a second step of bonding the active material layer to a current collector, The present invention relates to a method for producing an electrode for a secondary battery.

  In the first step, first, an active material slurry containing an active material is prepared. The active material slurry can be prepared by dispersing the active material in a solvent or the like. In addition to the active material, additives such as a conductive additive and a binder may be added to the active material slurry as necessary.

[Active material]
An active material refers to a material having a function of generating electric energy by reversibly inserting and desorbing lithium ions. When manufacturing a positive electrode, an active material slurry is prepared using a positive electrode active material. On the other hand, when manufacturing a negative electrode, an active material slurry is prepared using a negative electrode active material.

(Positive electrode active material)
The positive electrode active material has a composition that occludes lithium ions during discharging and releases lithium ions during charging. A preferable example is a lithium-transition metal composite oxide that is a composite oxide of a transition metal and lithium. Specifically, Li · Co-based composite oxide such as LiCoO _2, Li · Ni-based composite oxide such as LiNiO _2, Li · Mn-based composite oxide such as spinel LiMn ₂ O _4, Li · such LiFeO ₂ Fe-based composite oxides and those obtained by replacing some of these transition metals with other elements can be used. These lithium-transition metal composite oxides are excellent in reactivity and cycle characteristics, and are low-cost materials. Therefore, it is possible to form a battery having excellent output characteristics by using these materials for electrodes. In addition, examples of the positive electrode active material include transition metal oxides such as LiFePO ₄ and lithium phosphate compounds and sulfate compounds; transition metal oxides such as V ₂ O ₅ , MnO ₂ , TiS ₂ , MoS ₂ , and MoO ₃ , and sulfides. PbO ₂ , AgO, NiOOH, etc. can also be used. The positive electrode active material may be used alone or in the form of a mixture of two or more.

  The average particle diameter of the positive electrode active material is not particularly limited, but is preferably 1 to 100 μm, more preferably 1 to 20 μm, from the viewpoint of increasing the capacity, reactivity, and cycle durability of the positive electrode active material. Within such a range, the secondary battery can suppress an increase in the internal resistance of the battery during charging and discharging under high output conditions, and can extract a sufficient current. When the positive electrode active material is secondary particles, it can be said that the average particle diameter of the primary particles constituting the secondary particles is preferably in the range of 10 nm to 1 μm. It is not limited to. However, it goes without saying that, depending on the manufacturing method, the positive electrode active material may not be a secondary particle formed by aggregation, agglomeration, or the like. As the particle diameter of the positive electrode active material and the particle diameter of the primary particles, a median diameter obtained by using a laser diffraction method can be used. The shape of the positive electrode active material varies depending on the type and manufacturing method, and examples thereof include a spherical shape (powdered shape), a plate shape, a needle shape, a column shape, and a square shape, but are not limited thereto. Any shape can be used without any problems. Preferably, an optimal shape that can improve battery characteristics such as charge / discharge characteristics is appropriately selected.

(Negative electrode active material)
The negative electrode active material has a composition capable of releasing lithium ions during discharging and occluding lithium ions during charging. The negative electrode active material is not particularly limited as long as it can reversibly occlude and release lithium. Examples of the negative electrode active material include metals such as Si and Sn, TiO, Ti ₂ O ₃ , TiO ₂ , or Metal oxides such as SiO ₂ , SiO, SnO ₂ , complex oxides of lithium and transition metals such as Li _4/3 Ti _5/3 O ₄ or Li ₇ MnN, Li—Pb alloys, Li—Al alloys , Li, or carbon materials such as natural graphite, artificial graphite, carbon black, activated carbon, carbon fiber, coke, soft carbon, or hard carbon. Among these, by using an element that forms an alloy with lithium, it becomes possible to obtain a battery having a high capacity and an excellent output characteristic having a higher energy density than that of a conventional carbon-based material. The negative electrode active material may be used alone or in the form of a mixture of two or more. The element alloying with lithium is not limited to the following, but specifically, Si, Ge, Sn, Pb, Al, In, Zn, H, Ca, Sr, Ba, Ru, Rh, Ir, Pd, Pt, Ag, Au, Cd, Hg, Ga, Tl, C, N, Sb, Bi, O, S, Se, Te, Cl, and the like.

  Among the active materials, it preferably contains a carbon material and / or at least one element selected from the group consisting of Si, Ge, Sn, Pb, Al, In, and Zn. Or it is more preferable that the element of Sn is included. Although these negative electrode active materials can constitute a battery having excellent capacity and energy density, the volume change due to expansion / contraction of the active material during charging / discharging is large, and the active material layer is deformed or the active material is detached from the electrode. It also had the problem of being easily separated. Therefore, by applying the present invention to an electrode containing such a negative electrode active material, the effect of the present invention that the above-mentioned problem due to expansion / contraction of the active material can be sufficiently suppressed becomes more remarkable. In addition, these negative electrode active materials may be used individually by 1 type, and may use 2 or more types together.

  Note that the particle diameter and shape of the negative electrode active material are not particularly limited, and can take the same form as the above-described positive electrode active material, and thus detailed description thereof is omitted here.

[solvent]
A solvent may be added to the active material slurry to adjust the viscosity of the slurry. Such a slurry viscosity adjusting solvent is not particularly limited, and examples thereof include N-methyl-2-pyrrolidone (NMP), dimethylformamide, dimethylacetamide, and methylformamide.

[Conductive aid]
A conductive support agent means the additive mix | blended in order to improve the electroconductivity of an active material layer. Examples of the conductive aid include carbon powders such as acetylene black, carbon black, ketjen black, and graphite, various carbon fibers such as vapor grown carbon fiber (VGCF; registered trademark), expanded graphite, and the like. However, it goes without saying that the conductive aid is not limited to these.

[Binder]
The binder is added for the purpose of maintaining the electrode structure by binding the constituent members in the active material layer or the active material layer and the current collector. The binder is not particularly limited, and synthetic rubber binders such as polyvinylidene fluoride (PVdF), polyimide, PTFE, and SBR can be used. However, it goes without saying that the binder is not limited to these.

  The active material slurry is converted into an ink from a solid content containing the active material and a solvent using a homogenizer or a kneader. There are no particular restrictions on the order in which the active material and the components such as the conductive additive and the binder that can be added as necessary are mixed and dispersed. All these components may be mixed and dispersed at the same time, or may be mixed and dispersed step by step for each component. In addition, the compounding ratio of each component can be adjusted with reference to the known knowledge about the electrode for secondary batteries suitably.

  After preparing the active material slurry, this is applied to one surface of the porous member to form an active material layer.

[Porous member]
The porous member is not particularly limited as long as the active material contained in the active material layer has a shape capable of holding a material having a small particle diameter, and a conventionally known shape such as a porous film shape or a mesh shape is appropriately adopted. can do. The material of the porous member is not particularly limited, and examples thereof include metals, metal oxides and alloys, polymer materials, and carbon materials.

  The metal contained in the metal, metal oxide, and alloy is not particularly limited, but Ni, Ti, Al, Cu, Pt, Fe, Cr, Sn, Zn, In, Sb, and K are preferably used. . Since such a metal, metal oxide, or alloy has excellent heat resistance, it can sufficiently withstand heating during electrode production. Among these, it is preferable that Al, Ni, or Cu is contained from a viewpoint of electric potential resistance.

  Polymer materials include polyethylene (PE; high density polyethylene (HDPE), low density polyethylene (LDPE)), polypropylene (PP), polyethylene terephthalate (PET), polyethernitrile (PEN), polyimide (PI), polyamideimide (PAI), polyamide (PA), polytetrafluoroethylene (PTFE), styrene-butadiene rubber (SBR), polyacrylonitrile (PAN), polymethyl acrylate (PMA), polymethyl methacrylate (PMMA), polyvinyl chloride (PVC) ), Polyvinylidene fluoride (PVdF), polystyrene (PS), polyetheretherketone (PEEK), polyethersulfone (PES), polysulfone (PSF), polyarylate (PAR) and the like Plastic resins: Thermosetting resins such as aramid, polyimide, phenolic resin, epoxy resin, melamine resin, urea resin, and alkyd resin; polyaniline, polypyrrole, polythiophene, polyacetylene, polyparaphenylene, polyphenylene vinylene, polyacrylonitrile, and polyoxa Examples thereof include conductive polymer materials such as diazole. Among these, it is preferable to use at least one selected from the group consisting of polyethylene, polypropylene, aramid, and polyimide.

  Examples of the carbon material include carbon fiber, but are not limited thereto.

  In addition, these metals, metal oxides, alloys, polymer materials, and carbon materials may be used alone or in combination of two or more.

  The average pore diameter of the porous member can be appropriately selected depending on the size and distribution of the active material particles used. Preferably, a porous member having an average pore size smaller than d50 in the cumulative particle size distribution of the active material and larger than d10 is used. By adopting a porous member having an average pore diameter in such a range, it is possible to fill the pores of the porous member with active material particles of an appropriate size and amount. The detachment of the active material from the electrode can be effectively suppressed. If the average pore diameter of the porous member is too small, the active material may not enter the pores of the porous member. Thereby, an active material with a small particle diameter may be arrange | positioned also outside the hole of a porous member. Moreover, even if the average pore diameter of the porous member is excessively large, it becomes difficult to selectively fill the pores of the porous member with an active material having a small particle diameter. Therefore, also in this case, an active material having a small particle diameter is disposed outside the pores of the porous member. Due to these causes, the gap between the active materials becomes small, and the expansion allowance cannot be secured, so the effect of suppressing the deformation of the active material and the detachment of the active material accompanied by the refinement of the active material is sufficient. There is a risk that it will not be demonstrated. In this specification, “cumulative particle size distribution” is measured by a particle size distribution measuring apparatus using a laser diffraction / scattering method. In the cumulative particle size distribution, d50 means a particle diameter having a cumulative value of 50%, and d10 means a particle diameter having a cumulative value of 10%. The “particle diameter” as used herein means the maximum distance among the distances between any two points on the particle outline. Such a cumulative particle size distribution can be measured using, for example, a microtrack particle size distribution measuring apparatus (model HRA9320-X100) manufactured by Nikkiso Co., Ltd.

  The porosity of the porous member is preferably larger from the viewpoint that more active materials can be filled, but the upper limit is about 98% due to the structural problem of the porous member.

  The method for applying the active material slurry to one surface of the porous member is not particularly limited, and conventionally known methods such as a die coater method, a screen printing method, and a doctor blade method can be appropriately employed. Then, the active material layer is formed by drying the solvent from the applied active material slurry.

  Thus, by applying the active material slurry to the surface of the porous member, among the active materials contained in the active material slurry, it can be selectively held in the pores of the porous member having a small particle diameter. . Therefore, the active material located outside the pores of the porous member has a large particle diameter and a large gap between adjacent active materials. Thereby, since the expansion allowance of the active material can be ensured, the deformation of the active material layer accompanying the expansion / contraction of the active material and the detachment of the active material from the electrode can be suppressed.

  After forming the active material layer on one surface of the porous member, the active material slurry is similarly applied to the other surface of the porous member and dried, so that the porous member is placed in the middle of the active material layer. You may arrange.

  In the second step in the manufacturing method of the present embodiment, the active material layer formed in the first step is joined to the current collector.

[Current collector]
The current collector is made of a conductive material, and an active material layer is disposed on one side or both sides thereof. There is no particular limitation on the material constituting the current collector, and for example, a conductive resin in which a conductive filler is added to a metal or a conductive polymer material or a non-conductive polymer material may be employed.

  Examples of the metal include aluminum, nickel, iron, stainless steel, titanium, and copper. In addition to these, a clad material of nickel and aluminum, a clad material of copper and aluminum, or a plating material of a combination of these metals can be preferably used. Moreover, the foil by which aluminum is coat | covered on the metal surface may be sufficient. Of these, aluminum, stainless steel, and copper are preferable from the viewpoints of electronic conductivity and battery operating potential.

  Examples of the conductive polymer material include polyaniline, polypyrrole, polythiophene, polyacetylene, polyparaphenylene, polyphenylene vinylene, polyacrylonitrile, and polyoxadiazole. Since such a conductive polymer material has sufficient conductivity without adding a conductive filler, it is advantageous in terms of facilitating the manufacturing process or reducing the weight of the current collector.

  Examples of non-conductive polymer materials include polyethylene (PE; high density polyethylene (HDPE), low density polyethylene (LDPE)), polypropylene (PP), polyethylene terephthalate (PET), polyether nitrile (PEN), polyimide ( PI), polyamideimide (PAI), polyamide (PA), polytetrafluoroethylene (PTFE), styrene-butadiene rubber (SBR), polyacrylonitrile (PAN), polymethyl acrylate (PMA), polymethyl methacrylate (PMMA), Examples include polyvinyl chloride (PVC), polyvinylidene fluoride (PVdF), and polystyrene (PS). Such a non-conductive polymer material may have excellent potential resistance or solvent resistance.

  A conductive filler may be added to the conductive polymer material or the non-conductive polymer material as necessary. In particular, when the resin used as the base material of the current collector is made of only a non-conductive polymer, a conductive filler is inevitably necessary to impart conductivity to the resin. The conductive filler can be used without particular limitation as long as it is a substance having conductivity. For example, metals, conductive carbon, etc. are mentioned as a material excellent in electroconductivity, electric potential resistance, or lithium ion barrier | blocking property. The metal is not particularly limited, but at least one metal selected from the group consisting of Ni, Ti, Al, Cu, Pt, Fe, Cr, Sn, Zn, In, Sb, and K, or these metals It is preferable to contain an alloy or metal oxide containing. The conductive carbon is not particularly limited, but is at least selected from the group consisting of acetylene black, vulcan, black pearl, carbon nanofiber, ketjen black, carbon nanotube, carbon nanohorn, carbon nanoballoon, and fullerene. It is preferable that 1 type is included. The amount of the conductive filler added is not particularly limited as long as it is an amount capable of imparting sufficient conductivity to the current collector, and is generally about 5 to 35% by mass.

  The current collector according to this embodiment preferably includes a conductive resin layer composed of a resin obtained by adding a conductive filler to the conductive polymer material or the non-conductive polymer material. The conductive resin layer has higher electrical resistance in the surface direction than the current collector made of metal, so even if a metal bar such as a nail is stuck in the battery, current concentration on the metal bar is suppressed. The battery can be prevented from being heated or ignited. In addition, since the conductive resin layer has a high contact resistance with the active material layer, when the active material layer is deformed or the active material is detached, it is compared with a current collector made of metal. There has been a problem that the electrical resistance of the electrode tends to increase rapidly. However, according to the present invention, since the active material can be prevented from being refined due to the expansion of the active material, even when the conductive resin layer is used as a current collector, the deformation of the active material layer or Further, desorption of the active material from the current collector is suppressed, and a rapid increase in the electrical resistance of the electrode can be prevented. In particular, in the bipolar secondary battery described later, it is important to reduce the electric resistance in the surface thickness direction. Therefore, the effect of the present invention can be remarkably exhibited by applying the present invention to a bipolar electrode having a conductive resin layer as a current collector.

  The size of the current collector is determined according to the intended use of the battery. For example, if it is used for a large battery that requires a high energy density, a current collector having a large area is used. Although there is no restriction | limiting in particular also about the thickness of a collector, Usually, it is about 1-100 micrometers.

  The method for joining the active material layer and the current collector is not particularly limited, and a conventionally known method can be appropriately employed. For example, the bonding may be performed by applying and bonding an adhesive between the active material layer and the current collector, or may be performed by heat-sealing by hot pressing.

  The electrode produced by the above method for producing an electrode for a secondary battery and the secondary battery using the electrode also belong to the technical scope of the present invention. Hereinafter, the present embodiment will be described with reference to the drawings. However, the technical scope of the present invention should be determined based on the description of the scope of claims, and is not limited to the following embodiments. In the description of the drawings, the same elements are denoted by the same reference numerals, and redundant description is omitted. In addition, the dimensional ratios in the drawings are exaggerated for convenience of explanation, and may be different from the actual ratios.

<Electrode>
In the secondary battery electrode of this embodiment, a current collector, an active material layer containing an active material, and a porous member are sequentially arranged. And at least a part of the active material is present in the pores of the porous member, and the average particle diameter of the active material existing outside the pores of the porous member is the average of the active material existing in the pores of the porous member. It is larger than the particle size.

  FIG. 1 is a cross-sectional view schematically showing an electrode for a secondary battery according to an embodiment of the present invention. According to FIG. 1, the electrode 1 </ b> A has a negative electrode active material layer 3 and a porous member 4 sequentially disposed on one surface of a current collector 2. The current collector 2 is made of a conductive resin layer in which ketjen black (not shown) as a conductive filler is dispersed in polypropylene. The negative electrode active material layer 3 contains silicon powder (not shown) as the negative electrode active material. The porous member 4 is made of a polyethylene porous film. As shown in FIG. 1, the anode active material layer 3 has a structure in which a part of the anode active material layer 3 enters the pores of the porous member 4.

  FIG. 2 is an enlarged view of a part of the electrode 1A of FIG. According to FIG. 2, the negative electrode active material layer 3 contains silicon powder (5a, 5b). Here, the silicon powder 5 a existing outside the pores of the porous member 4 has a larger average particle diameter than the silicon powder 5 a existing inside the pores of the porous member 4. That is, since the silicon powder 5b having a small particle diameter is selectively placed in the pores of the porous member 4, the silicon powder 5a having a large particle diameter outside the pores of the porous member 4 is disposed between the silicon powders 5a. The voids become large (the silicon powder 5b does not fill the voids between the silicon powders 5a). Since the voids serve as an expansion allowance for the silicon powder 5a, even when the silicon powder 5a expands due to charge / discharge, it is difficult to apply force to the adjacent silicon powder 5a. Therefore, deformation of the negative electrode active material layer 3 and detachment of the silicon powder 5a from the electrode are suppressed.

  1 and 2, the porous member 4 is located in the outermost layer on the side facing the current collector 2, and silicon is formed in the upper portion (upper side of the drawing) of the porous member 4. The powder 5b is not filled. By having such a structure, the porous member 4 also has a function as a separator that prevents a short circuit due to contact between adjacent electrodes. Thus, when the porous member functions as a separator, the thickness of the porous member is preferably about 100 to 150 μm.

  FIG. 3 is a cross-sectional view schematically showing a secondary battery electrode according to another embodiment of the present invention. According to FIG. 1, the electrode 1 </ b> B has a structure in which the negative electrode active material layer 3 and the porous member 4 are sequentially arranged on one surface of the current collector 2, and the porous member 4 is arranged in the middle of the negative electrode active material layer 3. Have

  FIG. 4 is an enlarged view of a part of the electrode 1B of FIG. According to FIG. 4, the negative electrode active material layer 3 contains silicon powder (5a, 5b). Here, the silicon powder 5 a existing outside the pores of the porous member 4 has a larger average particle diameter than the silicon powder 5 a existing inside the pores of the porous member 4. Also in the electrode 1B, the gap between the silicon powders 5a serves as an expansion allowance, as in the electrode 1A in FIG. Therefore, even when the silicon powder 5a expands, deformation of the negative electrode active material layer 3 and detachment of the silicon powder 5a from the electrode are suppressed.

  Further, by disposing the porous member in the middle of the negative electrode active material layer 3 as shown in FIGS. 3 and 4, as a result, the thickness of the negative electrode active material layer 3 in the portion located outside the hole of the porous member 4 is reduced. Get smaller. As a result, the anchor effect generated by filling the pores of the porous member 4 with the silicon powder 5b is further improved, and the deformation of the negative electrode active material layer 3 and the detachment of the active material from the electrode are effectively suppressed. Is done. Thus, when a porous member is located in the middle of an active material layer, it is preferable that the thickness of a porous member shall be about 10-50 micrometers.

  Note that in this specification, “the current collector, the active material layer containing the active material, and the porous member are sequentially disposed” means that the active material layer is more than the surface where the current collector is in contact with the active material layer. It means that there is a porous member on the side. Therefore, as shown in FIG. 1 described above, a form in which the porous member is present on the side of the active material layer that is not in contact with the current collector may be present, or as shown in FIG. The form which a quality member exists may be sufficient. 1 and 3, the active material layer is formed only on one surface of the current collector, but it is needless to say that the active material layer is formed on the other surface.

  Since each constituent member included in the electrode is as described in the method for manufacturing the secondary battery electrode, detailed description thereof is omitted here.

<Secondary battery>
FIG. 5 is a schematic cross-sectional view schematically showing the overall structure of a stacked lithium ion secondary battery (hereinafter also simply referred to as “lithium ion battery”) according to this embodiment.

  As shown in FIG. 5, the lithium ion battery 10 of the present embodiment has a structure in which a substantially rectangular power generation element 17 in which a charge / discharge reaction actually proceeds is sealed inside a laminate film 22 that is a battery exterior material. Have. Specifically, the power generation element 17 is housed and sealed by using a polymer-metal composite laminate film as a battery exterior material and joining all of its peripheral parts by thermal fusion.

  The power generation element 17 includes a positive electrode in which the positive electrode active material layer 12 is disposed on both surfaces of the positive electrode current collector 11 (only one side for the lowermost layer and the uppermost layer of the power generation element), an electrolyte layer 13, and a negative electrode current collector 14. The negative electrode in which the negative electrode active material layer 15 is disposed on both sides of the negative electrode is laminated. Specifically, the positive electrode, the electrolyte layer 13 and the negative electrode are laminated in this order so that one positive electrode active material layer 12 and the negative electrode active material layer 15 adjacent thereto face each other with the electrolyte layer 13 therebetween. Yes.

  As a result, the adjacent positive electrode, electrolyte layer 13 and negative electrode constitute one single cell layer 16. Therefore, it can be said that the lithium ion battery 10 of the present embodiment has a configuration in which a plurality of single battery layers 16 are stacked and electrically connected in parallel. Further, a seal portion (insulating layer) for insulating between the adjacent positive electrode current collector 11 and negative electrode current collector 14 may be provided on the outer periphery of the unit cell layer 16. The positive electrode active material layer 12 is disposed on only one side of the outermost positive electrode current collector 11 a located in both outermost layers of the power generation element 17. Note that the arrangement of the positive electrode and the negative electrode is reversed from that in FIG. 5 so that the outermost negative electrode current collector is positioned in both outermost layers of the power generation element 17, and the negative electrode is formed only on one side of the outermost layer negative electrode current collector. An active material layer may be arranged.

  The positive electrode current collector 11 and the negative electrode current collector 14 are attached with a positive electrode current collector plate 18 and a negative electrode current collector plate 19 that are electrically connected to the respective electrodes (positive electrode and negative electrode), and are sandwiched between end portions of the laminate film 22. Thus, it has a structure led out of the laminate film 22. The positive electrode current collector 18 and the negative electrode current collector 19 are connected to the positive electrode current collector 11 and the negative electrode current collector 14 of each electrode by ultrasonic welding or resistance via the positive electrode terminal lead 20 and the negative electrode terminal lead 21 as necessary. It may be attached by welding or the like. However, the positive electrode current collector 11 may be extended to form the positive electrode current collector plate 18 and may be led out from the laminate film 22. Similarly, the negative electrode current collector 14 may be extended to form a negative electrode current collector plate 19, which may be similarly derived from the battery exterior material 22.

  As another form of the secondary battery, a bipolar electrode in which a positive electrode active material layer is formed on one surface of a current collector and a negative electrode active material layer is formed on the other surface is interposed through an electrolyte layer. Bipolar secondary batteries stacked in this manner can be given. The lithium ion secondary battery 10 and the bipolar secondary battery are basically the same except that the electrical connection form (electrode structure) in both batteries is different.

  Hereinafter, although the member which comprises the lithium ion secondary battery of this form is demonstrated easily, it is not restrict | limited only to the following form, A conventionally well-known form may be employ | adopted similarly.

[Electrolyte layer]
The electrolyte layer functions as a spatial partition (spacer) between the positive electrode active material layer and the negative electrode active material layer. In addition, it also has a function of holding an electrolyte that is a lithium ion transfer medium between the positive and negative electrodes during charging and discharging.

  There is no restriction | limiting in particular in the electrolyte which comprises an electrolyte layer, Polymer electrolytes, such as a liquid electrolyte and a polymer gel electrolyte and a polymer solid electrolyte, can be used suitably.

The liquid electrolyte has a form in which a lithium salt as a supporting salt is dissolved in an organic solvent as a plasticizer. Examples of the organic solvent used as the plasticizer include carbonates such as ethylene carbonate (EC) and propylene carbonate (PC). As the supporting salt (lithium _{salt), LiN (SO 2 C 2} F 5) 2, LiN (SO 2 CF 3) 2, LiPF 6, LiBF 4, LiClO 4, electrodes such as LiAsF 6, LiSO ₃ CF ₃ A compound that can be added to the active material layer can be similarly used.

  On the other hand, the polymer electrolyte is classified into a gel electrolyte containing an electrolytic solution and a polymer solid electrolyte containing no electrolytic solution.

  The gel electrolyte has a configuration in which the above liquid electrolyte is injected into a matrix polymer having lithium ion conductivity. Examples of the matrix polymer having lithium ion conductivity include polyethylene oxide (PEO), polypropylene oxide (PPO), and copolymers thereof. In such a matrix polymer, an electrolyte salt such as a lithium salt can be well dissolved.

  In addition, when an electrolyte layer is comprised from a liquid electrolyte or a gel electrolyte, you may use a separator for an electrolyte layer. Specific examples of the separator include a microporous film made of a polyolefin such as polyethylene or polypropylene, a hydrocarbon such as polyvinylidene fluoride-hexafluoropropylene (PVdF-HFP), glass fiber, or the like. In the case where the electrode shown in FIG. 1 is used, since the porous member also functions as a separator, the secondary battery can be configured without separately providing a separator. However, when a separator is further used when such an electrode is used, an internal short circuit due to breakage of the separator can be more effectively prevented.

  The polymer solid electrolyte has a structure in which a supporting salt (lithium salt) is dissolved in the matrix polymer, and does not include an organic solvent that is a plasticizer. Therefore, when the electrolyte layer is composed of a polymer solid electrolyte, there is no fear of liquid leakage from the battery, and the battery reliability can be improved.

  A matrix polymer of a polymer gel electrolyte or a polymer solid electrolyte can exhibit excellent mechanical strength by forming a crosslinked structure. In order to form a crosslinked structure, thermal polymerization, ultraviolet polymerization, radiation polymerization, electron beam polymerization, etc. are performed on a polymerizable polymer (for example, PEO or PPO) for forming a polymer electrolyte, using an appropriate polymerization initiator. A polymerization treatment may be performed. In addition, the said electrolyte may be contained in the active material layer of an electrode.

[Current collector]
In a lithium ion secondary battery, for the purpose of extracting current outside the battery, a current collector plate (a positive current collector plate and a negative current collector plate) electrically connected to a current collector is external to the laminate film. Has been taken out.

  The material which comprises a current collector plate is not specifically limited, The well-known highly electroconductive material conventionally used as a current collector plate for lithium ion secondary batteries can be used. As a constituent material of the current collector plate, for example, metal materials such as aluminum, copper, titanium, nickel, stainless steel (SUS), and alloys thereof are preferable. From the viewpoint of light weight, corrosion resistance, and high conductivity, aluminum and copper are more preferable, and aluminum is particularly preferable. Note that the same material may be used for the positive electrode current collector plate and the negative electrode current collector plate, or different materials may be used.

[Positive terminal and negative terminal lead]
In the lithium ion battery 10 shown in FIG. 5, the current collector is electrically connected to the current collector plate via the positive terminal lead 20 and the negative terminal lead 21.

  As a material of the positive electrode and the negative electrode terminal lead, a lead used in a known lithium ion battery can be used. In addition, the parts removed from the battery exterior material should be heat-insulating so that they do not affect products (for example, automobile parts, especially electronic devices) by touching peripheral devices or wiring and causing leakage. It is preferable to coat with a heat shrinkable tube or the like.

[Exterior material]
A conventionally known metal can case can be used as the exterior material. In addition, the power generation element 17 may be packed using a laminate film 22 as shown in FIG. The laminate film can be configured as a three-layer structure in which, for example, polypropylene, aluminum, and nylon are laminated in this order.

  As described above, the secondary battery using the electrode of this embodiment can suppress the deformation of the active material layer and the detachment of the active material from the electrode, so that the cycle characteristics are significantly higher than those of the conventional secondary battery. Can be improved.

  Further, in the secondary battery configured using the electrode using the metal foam of Patent Document 1 described above, the metal foam is a current collector because the metal foam and the current collector are in direct contact with each other. There was a possibility that a hole might be generated. In particular, the bipolar electrode has a problem that when the current collector is perforated, the electrolyte flows into and out of the adjacent unit cell layers, causing a liquid junction. Further, even in a secondary battery having a structure in which electrodes are laminated via a separator, the metal foam and the separator are in direct contact with each other, so that there is a possibility that the separator is perforated. When the perforation of a separator generate | occur | produced, it also had the problem of causing a short circuit by a positive electrode active material layer and a negative electrode active material layer contacting directly.

  Furthermore, the electrode of Patent Document 1 has a structure in which a metal foam is inserted in the entire active material layer. Since the metal foam itself does not participate in the charge / discharge reaction, it has a problem that the battery capacity per volume is reduced.

  However, since the secondary battery using the electrode of the present embodiment can be configured without using the metal foam as in Patent Document 1, the above-described problems can be solved.

<Production of negative electrode>
[Example 1]
85 parts by mass of silicon powder (d50 in cumulative particle size distribution is 2 μm, d10 is 0.1 μm) as a negative electrode active material, 5 parts by mass of carbon powder as a conductive additive, 10 parts by mass of polyimide precursor resin as a binder, and slurry An appropriate amount of N-methyl-2-pyrrolidone (NMP) was mixed as a viscosity modifier to prepare a negative electrode active material slurry. The negative electrode active material slurry is applied to a porous film (size: 3 cm × 3 cm, thickness: 25 μm, average pore diameter: 0.5 μm) made of polyethylene as a porous member using a die coater, and then dried. -An active material layer laminate was obtained.

  On one surface of a copper current collector foil (size 3 cm × 3 cm, thickness 20 μm), carbon fiber “VGCF” (registered trademark (vapor phase carbon fiber), manufactured by Showa Denko KK) as a conductive filler and binder An adhesive solution prepared by mixing the polyvinylidene fluoride (PVDF) dispersion as VGCF: PVDF so as to be 1: 1 (mass ratio) was applied. And the negative electrode was completed by bonding together and bonding the active material layer side of the porous member-active material layer laminated body produced above to the surface which apply | coated this adhesive agent.

[Example 2]
As the current collector, a conductive resin layer in which 10% by mass of ketjen black as a conductive filler was dispersed in polypropylene was used. And the electrical power collector and the porous member-active material layer laminated body were joined using the hot press. Except for this, a negative electrode was produced in the same manner as in Example 1.

[Comparative Example 1]
A negative electrode was produced in the same manner as in Example 1 except that the negative electrode active material slurry was directly applied to the current collector and dried without using the porous member.

[Comparative Example 2]
A foam metal formed by impregnating and drying a negative electrode active material slurry with nickel foam metal (porosity 90%, size 3 cm × 3 cm, thickness 100 μm) and drying the active material in the pores of the foam metal— An active material complex was obtained. A negative electrode was produced in the same manner as in Example 1 except that the foam metal-active material composite was used instead of the porous member-active material layer laminate.

[Comparative Example 3]
A negative electrode was produced in the same manner as in Example 2 except that the negative electrode active material slurry was directly applied to the current collector and dried without using the porous member.

<Preparation of positive electrode>
90 parts by mass of lithium nickelate powder as a positive electrode active material, 5 parts by mass of carbon black as a conductive additive, 5% by mass of polyvinylidene fluoride (PVDF) as a binder, and N-methyl-2-pyrrolidone as a slurry viscosity modifier An appropriate amount of (NMP) was mixed to prepare a positive electrode active material slurry. The positive electrode active material slurry was applied to one surface of an aluminum current collector foil (size 3 cm × 3 cm, thickness 20 μm) using a die coater, dried, and rolled to produce a positive electrode.

<Production of battery>
As an electrolytic solution, a solution in which LiPF ₆ as a lithium salt was dissolved at a concentration of 1.0 mol / liter in a mixed solvent of ethylene carbonate (EC): diethylene carbonate (DEC) = 2: 3 (volume ratio) was prepared. .

  The above-prepared positive electrode and negative electrode are laminated via a separator (polyethylene porous membrane), the laminate is placed in a bag made of an aluminum laminate film, the electrolyte is injected, and the laminate is molded and sealed. The lithium ion secondary battery was completed.

<Charge / discharge characteristics test>
A charge / discharge characteristic test was performed on the lithium ion secondary battery produced above. Each battery is charged in a constant temperature bath at 25 ° C. with a constant current and constant voltage method (CCCV, current 0.5 C, cell voltage 4.2 V), and after 10 minutes of rest, a constant current method (CC, current 0.5 C) ) To a cell voltage of 2.5V. With this as one cycle, the discharge capacity retention rate (%) after 30 cycles with respect to the discharge capacity after 1 cycle was determined. C indicates a time rate. The time rate of 1 C refers to an amount of current sufficient to charge / discharge the entire capacity of the battery in one hour. For example, a current of 0.5 C refers to an amount of current that charges / discharges the entire capacity of the battery in 2 hours (= 1 / 0.5 hour).

  The results are shown in Table 1 below.

  From the results of Table 1, the secondary battery using the electrode including the porous member of Examples 1 and 2 had a remarkably high discharge capacity retention rate even after 30 cycles, and exhibited excellent cycle characteristics. This was thought to be due to the effective suppression of deformation of the active material layer and desorption of the active material from the electrode.

  On the other hand, Comparative Examples 1 to 3 had a low discharge capacity retention rate after 30 cycles. In particular, in Comparative Example 2, perforation occurred due to the metal foam breaking through the current collector.

1A, 1B electrode,
2, current collector,
3, 15 negative electrode active material layer,
4 porous members,
5a, 5b silicon powder,
10 Lithium ion battery,
11 positive electrode current collector,
11a Outermost layer positive electrode current collector,
12 positive electrode active material layer,
13 electrolyte layer,
14 negative electrode current collector,
16 cell layer,
17 Power generation elements,
18 positive current collector,
19 Negative current collector,
20 positive terminal lead,
21 negative terminal lead,
22 Laminated film.

Claims (10)

Applying an active material slurry containing the active material to one surface of the porous member to form an active material layer;
Joining the active material layer to a current collector, and a method for producing an electrode for a secondary battery.   The method for producing an electrode for a secondary battery according to claim 1, wherein an average pore diameter of the porous member is smaller than d50 and larger than d10 in the cumulative particle size distribution of the active material. A current collector,
An active material layer containing the active material;
Porous members are sequentially arranged,
At least a portion of the active material is present in the pores of the porous member;
An electrode for a secondary battery, wherein an average particle size of an active material existing outside the pores of the porous member is larger than an average particle size of an active material existing within the pores of the porous member.   An electrode for a secondary battery formed by applying an active material slurry containing an active material on one surface of a porous member to form an active material layer, and then bonding the active material layer to a current collector .   The electrode for a secondary battery according to claim 3 or 4, wherein the porous member is located in an outermost layer on a side facing the current collector.   The secondary battery electrode according to any one of claims 3 to 5, wherein an average pore diameter of the porous member is smaller than d50 and larger than d10 in the cumulative particle size distribution of the active material.   The electrode for secondary batteries of any one of Claims 3-6 in which the said electrical power collector contains the resin layer which has electroconductivity.   The secondary battery electrode according to claim 3, wherein the active material is a negative electrode active material capable of inserting and extracting lithium ions.   The secondary battery containing the electrode for secondary batteries of any one of said 3-8.   The secondary battery according to claim 9, wherein the secondary battery electrode and a separator are laminated.

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