JP5434326B2 - Current collector and secondary battery using the same - Google Patents

Description

  The present invention relates to a current collector and a secondary battery using the current collector. In particular, the present invention relates to a current collector that can relieve stress caused by expansion and contraction of an active material, and a secondary battery using the current collector.

  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 the 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. sell. In particular, alloy-based negative electrode materials can achieve a higher energy density than carbon / graphite-based negative electrode materials, and are expected as candidates for vehicle batteries.

  The alloy-based negative electrode material has particularly large expansion / contraction due to insertion / extraction of lithium ions. For example, the volume expansion when lithium ions are occluded is about 1.2 times that of graphite, but about 4 times that of silicon-based negative electrode materials. When the negative electrode active material expands greatly as described above, the contact between the active materials is weakened or the adhesion between the active material layer and the current collector is reduced while charging and discharging are repeated. As a result, the problem that the active material layer is cracked or pulverized, or peeled off from the current collector has been pointed out. In addition, the electrode which has such a problem may become the cause of reducing the cycling characteristics of a secondary battery.

  Therefore, Patent Document 1 proposes a negative electrode for a lithium ion secondary battery that includes a sheet-like current collector and an active material layer carried on the current collector. The current collector includes a base material part and a surface layer part that is more easily plastically deformed than the base material part, and the surface layer part has irregularities. The active material layer includes a plurality of columnar particles containing silicon, and the columnar particles have a structure supported on the surface layer portion. According to this technique, since the columnar active material particles containing silicon are intensively supported on the uneven projections of the surface layer portion of the current collector, a gap is formed between the columnar particles. As a result, the expansion stress of the columnar particles during charging is alleviated, and the columnar particles can be prevented from peeling off from the current collector, and deformation of the electrode plate is also suppressed.

JP 2008-098157 A

  In the above-mentioned Patent Document 1, a metal material such as copper is used as a material constituting the current collector. However, since these metal materials are hard, the above-mentioned means also causes expansion / contraction of the active material. There was a problem that relaxation of the generated stress was insufficient.

  Then, this invention aims at providing the electrical power collector which can relieve | moderate the stress produced by expansion | swelling / contraction of an active material effectively.

The current collector of the present invention is a current collector including a conductive resin layer, and the resin layer includes an electric field responsive polymer material that reversibly expands or contracts in response to application of an electric field. Thus, the dipole moment of the electric field responsive polymer material is 2.2 debye or more .

  According to the present invention, since the electric field responsive polymer material expands or contracts by extension or contraction by applying an electric field, the current collector can follow the expansion / contraction of the active material. Therefore, stress caused by expansion / contraction of the active material can be relaxed.

It is sectional drawing which represented the electrical power collector which concerns on one Embodiment of this invention typically. FIG. 1A is a cross-sectional view illustrating a state before an electric field is applied. FIG. 1B is a cross-sectional view illustrating a state in which an electric field is applied in the arrow direction (the surface direction of the current collector). It is sectional drawing which represented the electrical power collector which concerns on other embodiment of this invention typically, Comprising: An electric field responsive polymeric material is the surface direction of an electrical power collector, and an electric field non-responsive polymeric material is an electrical power collector. Are oriented in the thickness direction. FIG. 2A is a cross-sectional view illustrating a state before an electric field is applied. FIG. 2B is a cross-sectional view illustrating a state in which an electric field is applied in the arrow direction (the surface direction of the current collector). FIG. 6 is a cross-sectional view schematically showing a current collector according to another embodiment of the present invention, in which both the electric field responsive polymer material and the electric field non-responsive polymer material are oriented in the surface direction of the current collector. ing. FIG. 3A is a cross-sectional view illustrating a state before an electric field is applied. FIG. 3B is a cross-sectional view illustrating a state in which an electric field is applied in the arrow direction (the surface direction of the current collector). 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. It is sectional drawing which represented typically the whole structure of the bipolar | stacked laminated lithium ion secondary battery which concerns on this form. It is an external view of typical embodiment of the assembled battery which concerns on this form. 6A is a plan view of the assembled battery, FIG. 6B is a front view of the assembled battery, and FIG. 6C is a side view of the assembled battery. It is a conceptual diagram of the electric vehicle carrying the assembled battery which concerns on this form.

  Hereinafter, preferred embodiments of the present invention will be described. The present embodiment relates to a current collector having a conductive resin layer including an electric field responsive polymer material that reversibly expands or contracts in response to application of an electric field. Hereinafter, the resin layer having conductivity is also simply referred to as “resin layer”.

  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.

<Current collector>
FIG. 1 is a cross-sectional view schematically showing a current collector according to an embodiment of the present invention. FIG. 1A is a cross-sectional view illustrating a state before an electric field is applied. FIG. 1B is a cross-sectional view illustrating a state in which an electric field is applied in the arrow direction (the surface direction of the current collector). As shown in FIG. 1A, the current collector 1 of this embodiment is composed of a single resin layer having conductivity. The base material of the resin layer is a mixture of polypropylene 2 and liquid crystal elastomer 3 which is an electric field responsive polymer material. The base material is dispersed with ketjen black (not shown) as a conductive filler in order to impart conductivity. The liquid crystal elastomer 3 has a structure in which a liquid crystal molecule 5 containing a mesogen group is bonded to a main chain 4 which is a polymer via a spacer 6. According to FIG. 1A, the orientation of the liquid crystal molecules 5 in the liquid crystal elastomer 3 is random when no electric field is applied to the current collector. When an electric field is applied to the current collector 1 in the direction of the arrow as shown in FIG. 1B, the liquid crystal molecules 5 are aligned in one direction in response to the electric field. As the liquid crystal molecules 5 are aligned, the main chain 4 is also anisotropic, and macroscopic alignment occurs in the liquid crystal elastomer 3. As a result, the current collector 1 including the liquid crystal elastomer 3 extends in the alignment direction of the liquid crystal elastomer 3 while keeping the volume constant, and contracts in the direction perpendicular to the alignment direction. The elongation / contraction action of the current collector 1 can relieve stress generated by the expansion / contraction of the active material.

  Hereinafter, although the member which comprises the electrical power collector of this form is demonstrated, the technical scope of this invention is not restrict | limited only to the following form.

  The current collector has a function of mediating the movement of electrons from one surface on which the positive electrode active material layer is formed to the other surface on which the negative electrode active material layer is formed. The current collector of this embodiment includes a conductive resin layer containing an electric field responsive polymer material, and may further include other layers as necessary.

  The conductive resin layer is an essential component of the current collector of this embodiment, and of course has a function as an electron transfer medium, as well as the weight of the current collector and the expansion / contraction of the active material. It can contribute to the relaxation of the stress due to. The resin layer may include a base material including an electric field responsive polymer material and other members such as a conductive filler as necessary.

  Conventionally, metals have been mainly used as materials used for current collectors. However, in recent years, current collectors using polymer materials that are lighter than metals have been proposed from the viewpoint of improving the power density per unit mass of the battery. The present inventors have been studying to develop a higher performance current collector, and by using an electric field responsive polymer material as a polymer material, it has been possible to achieve stress relaxation, which has been a conventional problem. The title and the present invention have been completed.

  The electric field responsive polymer material used for the substrate is not particularly limited as long as it is a polymer material that deforms in response to application of an electric field, and examples thereof include liquid crystal elastomers and electrostrictive polymers.

  The liquid crystal elastomer is formed by bonding liquid crystal molecules containing a mesogenic group to a main chain which is a polymer via a spacer. The mesogenic group is a rod-like or plate-like rigid functional group that can form a liquid crystal, and has a dielectric anisotropy or permanent dipole that can respond to an electric field. When an electric field is applied to the liquid crystal elastomer, mesogenic groups are aligned in a certain direction in response to the electric field. Along with this, anisotropy is brought about in the main chain, and the liquid crystal elastomer undergoes macroscopic alignment. Due to this macroscopic orientation, the entire liquid crystal elastomer is deformed with expansion and contraction.

  The mesogenic group mainly contributes to electric field responsiveness, and generally has a structure in which 2 to 4 ring structures are connected via a bonding portion. In addition to this, a terminal substituent constituting the terminal part of the mesogenic group or a side substituent may be bonded to the ring structure. That is, the mesogenic group is composed of a ring structure and a bonding part, and, if necessary, structural units composed of a terminal substituent or a side substituent connected to each other. More specifically, mesogenic groups such as an azoxy group, a biphenyl group, a phenylcyclohexane group, a phenyl ester group, a cyclohexanecarboxylic acid phenyl ester group, a phenyl pyrimidine group, or a phenyl dioxane group can be given.

  Examples of the ring structure constituting the mesogen group include carbocycles such as benzene, cyclohexane, and cyclohexene; and heterocycles such as pyrimidine, dioxane, and pyridine.

  Examples of the bonding part that connects the ring structures include an ester bond, an acetylene bond (ethynylene group), an ethane bond (ethylene group), an ethylene bond (ethenylene group), and an azo bond.

  In addition, examples of the terminal substituent or the side substituent include a cyano group, a fluoro group, an alkyl group, an alkenyl group, and an alkoxy group. Among these, from the viewpoint of improving the electric field response, it is preferable to introduce a cyano group having a large polarity.

  The total number of structural units constituting the mesogenic group is not particularly limited, but is preferably 3 to 15. Further, it is preferable that the structural unit contains at least one selected from the group consisting of an alkyl group, an alkoxy group, and an oxoalkyl group.

  The main chain contributes to the properties of the liquid crystal elastomer as a polymer. The main chain is not particularly limited, and examples thereof include polysiloxanes, polymethacrylates, polychloroacrylates, and polystyrenes, and copolymers thereof. Of these, polysiloxanes are preferably used from the viewpoint of improving strength and resistance to electrolytic solution.

  The spacer mainly contributes to the properties as a liquid crystal. Although there is no restriction | limiting in particular as a spacer, For example, a C2-C10 alkyl chain is used. In general, as the spacer becomes longer, the liquid crystal molecules become easier to align.

  On the other hand, an electrostrictive polymer is a material that expands and contracts due to dielectric polarization by placing electrodes made of a conductive stretch material on both sides of a stretchable portion made of a sheet-like insulating stretchable material, and is applied with a voltage. And contracts in the direction between the electrodes and extends in a direction perpendicular to the direction between the electrodes. Examples of such electrostrictive polymers include urethane-based and ethylene-based thermoplastic elastomers, silicon elastomers, acrylic elastomers, and fluorine-based elastomers.

  Among such electric field responsive polymers, it is preferable to use a liquid crystal elastomer. This is because the liquid crystal elastomer has a large dipole moment, high geometric anisotropy, and is rigid, so that it can be driven (stretched / contracted) even at an extremely low voltage.

  In addition to the electric field responsive polymer material, the conductive resin layer can include an electric field non-responsive polymer material that is not deformed by the application of an electric field. As the electric field non-responsive polymer material, a conventionally known non-conductive polymer material or conductive polymer material can be used without limitation.

  Preferred non-conductive polymer materials include, for example, 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) , Polyvinyl chloride (PVC), polyvinylidene fluoride (PVdF), and polystyrene (PS). Such a non-conductive polymer material can have excellent potential resistance or solvent resistance (electrolytic solution resistance). Among these, from the viewpoint of solvent resistance, it is preferable to use polypropylene. This is because the solubility parameter (SP value) of polypropylene is separated from the solubility parameter of the solvent used in the electrolytic solution, so that the penetration of the electrolytic solution into the current collector can be suppressed. In addition, thermosetting resins such as phenol resins, epoxy resins, melamine resins, urea resins, and alkyd resins can also be used. Examples of preferable conductive polymer materials 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. These non-conductive polymer materials or conductive polymer materials may be used alone or in a combination of two or more.

  Although there is no restriction | limiting in particular in content of the electric field responsive polymeric material in a base material, It is preferable that it is 30-80 mass% with respect to the total mass of a base material, and it is more preferable that it is 40-70 mass%. preferable. When the content is 30% by mass or more, an excellent stress relaxation effect can be exhibited. On the other hand, a collector can be manufactured at low cost as content is 80 mass% or less.

  When the base material includes the above-described electric field responsive polymer material and electric field non-responsive polymer material, from the viewpoint of improving the electric field response of the resin layer, the dipole moment of the electric field responsive polymer material is It is preferable that it is larger than the dipole moment of the responsive polymer material. More preferably, the difference is 2 Debye or more, and more preferably, the difference is 2-8 Debye. In general, when a dipole moment is large, a molecule is easily oriented by an electric field. Therefore, if the dipole moment of the electric field responsive polymer material is larger than the dipole moment of the electric field non-responsive polymer material, the resin layer can exhibit a large expansion / contraction action even at a low voltage. It is. In addition, the value computed by molecular orbital method AM1 is employ | adopted for the dipole moment in this specification.

  The electric field responsive polymer material and the electric field non-responsive polymer material are preferably independently oriented in the surface direction or the surface thickness direction of the current collector. A more preferable form is a form in which both the electric field responsive polymer material and the electric field non-responsive polymer material are oriented in the plane direction of the current collector. Thus, by orienting the electric field responsive polymer material and the electric field non-responsive polymer material, the deformation rate of the current collector is further increased. The orientation of the electric field responsive polymer material here means the orientation of the whole polymer. That is, when the electric field responsive molecular material is a liquid crystal elastomer, it means a macroscopic orientation of the polymer, that is, the orientation of the main chain.

  FIG. 2 is a cross-sectional view schematically showing a current collector according to another embodiment of the present invention, in which the electric field responsive polymer material is in the electric field non-responsive polymer material in the plane direction of the current collector. Are oriented in the thickness direction of the current collector. FIG. 2A is a cross-sectional view illustrating a state before an electric field is applied. FIG. 2B is a cross-sectional view illustrating a state in which an electric field is applied in the arrow direction (the surface direction of the current collector). FIG. 3 is a cross-sectional view schematically showing a current collector according to another embodiment of the present invention. The electric field responsive polymer material and the electric field non-responsive polymer material are Oriented in the plane direction. FIG. 3A is a cross-sectional view illustrating a state before an electric field is applied. FIG. 3B is a cross-sectional view illustrating a state where an electric field is applied in the arrow direction (the surface direction of the current collector).

  According to FIG. 2A, the main chain 4 of the liquid crystal elastomer 3 which is an electric field responsive polymer material is oriented in the surface direction of the current collector, and the polypropylene 2 which is an electric field non-responsive polymer material is oriented in the surface direction of the current collector. ing. On the other hand, according to FIG. 3A, the main chain 4 of the liquid crystal elastomer 3 which is an electric field responsive polymer material and the polypropylene 2 which is an electric field non-responsive polymer material are oriented in the surface direction of the current collector. When an electric field is applied in the direction of the arrow (the surface direction of the current collector) as shown in FIG. 2B or 3B, the liquid crystal molecules 5 of the liquid crystal elastomer 3 are aligned. At this time, in FIG. 3B, the orientation of the liquid crystal molecules 5 is not easily disturbed by the main chain 4 and the polypropylene 2, so that the current collector is more prominently stretched and contracted. The orientation state of the electric field responsive polymer material and the electric field non-responsive polymer material can be evaluated by deflection Raman measurement.

  A conductive filler may be added to the substrate as necessary. In particular, when the resin as the base material does not contain a 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 form of the current collector is not particularly limited as long as it includes a resin layer having conductivity, and can take various forms. For example, in addition to the resin layer, a laminate including other layers as necessary may be used. Examples of other layers other than the resin layer include a metal layer and an adhesive layer, but are not limited thereto. However, in this embodiment, a conductive resin layer is preferably present on the surface of the current collector in order to relieve stress generated by expansion / contraction of the active material.

  The thickness of the current collector is preferably thinner in order to increase the output density of the battery by reducing the weight. Specifically, the thickness of the current collector is preferably 1 to 200 μm, more preferably 5 to 150 μm, and still more preferably 10 to 100 μm. By having such a thickness, it is possible to construct a battery having excellent output characteristics and excellent long-term reliability.

<Secondary battery>
FIG. 4 is a schematic cross-sectional view schematically showing the overall structure of a stacked lithium ion secondary battery (hereinafter, also simply referred to as “stacked secondary battery”) according to the present embodiment.

  As shown in FIG. 4, in the laminated secondary battery 10 of the present embodiment, 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. It has a structure. 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 stacked secondary 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 on the outer periphery of the unit cell layer 16 (not shown; see reference numeral 43 in FIG. 5) ) May be provided. 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. 4, the arrangement of the positive electrode and the negative electrode is reversed 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 respectively attached with a positive electrode terminal 18 and a negative electrode terminal 19 that are electrically connected to the respective electrodes (positive electrode and negative electrode), and are laminated films so as to be sandwiched between end portions of the laminate film 22. 22 has a structure led out to the outside. The positive electrode terminal 18 and the negative electrode terminal 19 are attached to the positive electrode current collector 11 and the negative electrode current collector 14 of each electrode by ultrasonic welding, resistance welding or the like via the positive electrode terminal lead 20 and the negative electrode terminal lead 21 as necessary. (This form is shown in FIG. 4). However, the positive electrode current collector 11 may be extended to form the positive electrode terminal 18 and may be led out from the laminate film 22. Similarly, the negative electrode current collector 14 may be extended to serve as the negative electrode terminal 19, and may be similarly derived from the battery exterior material 22.

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

  As shown in FIG. 5, in the power generation element 37 of the bipolar secondary battery 30 of the present embodiment, a positive electrode active material layer 32 that is electrically coupled to one surface of the current collector 31 is formed. And a plurality of bipolar electrodes 34 each having a negative electrode active material layer 33 electrically coupled thereto. Each bipolar electrode 34 is stacked via an electrolyte layer 35 to form a power generation element 37. The electrolyte layer 35 has a configuration in which an electrolyte is held at the center in the surface direction of a separator as a base material. At this time, the positive electrode active material layer 32 of one bipolar electrode 34 and the negative electrode active material layer 33 of another bipolar electrode 34 adjacent to the one bipolar electrode 34 face each other through the electrolyte layer 35. Each bipolar electrode 34 and electrolyte layer 35 are alternately laminated. That is, the electrolyte layer 35 is disposed between the positive electrode active material layer 32 of one bipolar electrode 34 and the negative electrode active material layer 33 of another bipolar electrode 34 adjacent to the one bipolar electrode 34. ing.

  The adjacent positive electrode active material layer 32, electrolyte layer 35, and negative electrode active material layer 33 constitute one unit cell layer 36. Therefore, it can be said that the bipolar secondary battery 34 has a configuration in which the single battery layers 36 are stacked. A positive electrode active material layer 32 is formed only on one side of the positive electrode side outermost layer current collector 31 a located in the outermost layer of the power generation element 37. Further, the negative electrode active material layer 33 is formed only on one side of the negative electrode side outermost layer current collector 31 b located in the outermost layer of the power generation element 37. However, the positive electrode active material layer 32 may be formed on both surfaces of the positive electrode side outermost layer current collector 31a. Similarly, the negative electrode active material layer 33 may be formed on both surfaces of the negative electrode side outermost layer current collector 31b.

  Further, in the bipolar secondary battery 30 shown in FIG. 5, the positive electrode current collector plate 44a is disposed so as to be adjacent to the positive electrode side outermost layer current collector 31a, and this is extended and led out from the laminate film 42 which is a battery exterior material. doing. On the other hand, the negative electrode current collector plate 44b is disposed so as to be adjacent to the outermost layer current collector 31b on the negative electrode side, and similarly, this is extended and led out from the laminate film 42 which is an exterior of the battery.

  In the bipolar secondary battery 30 shown in FIG. 5, a seal portion (insulating layer) 43 is usually provided around each single cell layer 36. The purpose of the seal portion 43 is to prevent the adjacent current collectors 31 in the battery from coming into contact with each other or a short circuit caused by a slight irregularity at the end of the unit cell layer 36 in the power generation element 37. Is provided. By installing such a seal portion 43, long-term reliability and safety can be ensured, and a high-quality bipolar lithium ion secondary battery 30 can be provided.

  Note that the number of stacks of the unit cell layers 36 is adjusted according to a desired voltage. As described above, the bipolar secondary battery 30 is advantageous in that a high voltage can be obtained by increasing the number of times the single battery layer 36 is stacked. In the bipolar secondary battery 30, the number of stacks of the single battery layers 36 may be reduced if a sufficient output can be ensured even if the thickness of the battery is reduced as much as possible. Even in the bipolar secondary battery 30, in order to prevent external impact and environmental degradation during use, the power generation element 37 is sealed under reduced pressure in a laminate film 42 that is a battery exterior material, and a positive current collector 44 a and a negative current collector 44 are used. It is preferable that the electric plate 44b be taken out of the laminate film 42.

  The constituent requirements and manufacturing method of the lithium ion secondary battery 10 and the bipolar secondary battery 30 are basically the same except that the electrical connection form (electrode structure) in both batteries is different. It is. 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.

[Positive electrode active material layer]
The positive electrode active material layer includes a positive electrode active material. The positive electrode active material has a composition that occludes ions during discharging and releases 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 sulfuric acid compounds; transition metal oxides such as V ₂ O ₅ , MnO ₂ , TiS ₂ , MoS ₂ , and MoO ₃ , and sulfides. Materials; 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 layer]
The negative electrode active material layer includes a negative electrode active material. The negative electrode active material has a composition capable of releasing ions during discharge and storing 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. Moreover, it is preferable that a negative electrode active material contains the element alloyed with lithium. By using an element that forms an alloy with lithium, it is 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 these, from the viewpoint of configuring a battery having excellent capacity and energy density, at least one selected from the group consisting of carbon materials and / or Si, Ge, Sn, Pb, Al, In, and Zn. It is preferable to include an element, and it is particularly preferable to include an element of a carbon material, Si, or Sn. These may be used alone or in combination of two or more.

  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.

  The active material layer may contain other materials if necessary. For example, a conductive aid, a binder, and the like can be included. When an ion conductive polymer is included, a polymerization initiator for polymerizing the polymer may be included.

  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.

  Examples of the binder include polyvinylidene fluoride (PVdF), polyimide, PTFE, SBR, and a synthetic rubber binder. However, it goes without saying that the binder is not limited to these. When the binder and the matrix polymer used as the gel electrolyte are the same, it is not necessary to use a binder.

  The compounding ratio of the components contained in the active material layer is not particularly limited. The blending ratio can be adjusted by appropriately referring to known knowledge about lithium ion secondary batteries. The thickness of the active material layer is not particularly limited, and conventionally known knowledge about the lithium ion secondary battery can be appropriately referred to. As an example, the thickness of the active material layer is preferably about 10 to 100 μm, and more preferably 20 to 50 μm. If the active material layer is about 10 μm or more, the battery capacity can be sufficiently secured. On the other hand, if the active material layer is about 100 μm or less, it is possible to suppress the occurrence of the problem of an increase in internal resistance due to the difficulty in diffusing lithium ions in the electrode deep part (current collector side).

  The method for forming the positive electrode active material layer (or the negative electrode active material layer) on the current collector surface is not particularly limited, and known methods can be used in the same manner. For example, as described above, a positive electrode active material (or a negative electrode active material) and, if necessary, an electrolyte salt for increasing ion conductivity, a conductive auxiliary agent for increasing electron conductivity, and a binder are appropriately used. A positive electrode active material slurry (or a negative electrode active material slurry) is prepared by dispersing and dissolving in a solvent. This is applied onto a current collector, dried to remove the solvent, and then pressed to form a positive electrode active material layer (or negative electrode active material layer) on the current collector. In this case, the solvent is not particularly limited, and N-methyl-2-pyrrolidone (NMP), dimethylformamide, dimethylacetamide, methylformamide, cyclohexane, hexane, water and the like can be used. When adopting polyvinylidene fluoride (PVdF) as a binder, NMP is preferably used as a solvent.

  In the above method, the positive electrode active material slurry (or the negative electrode active material slurry) is applied onto the current collector, dried, and then pressed. At this time, the porosity of the positive electrode active material layer (or the negative electrode active material layer) can be controlled by adjusting the pressing conditions.

  Specific means and press conditions for the press treatment are not particularly limited, and can be appropriately adjusted so that the porosity of the positive electrode active material layer (or the negative electrode active material layer) after the press treatment becomes a desired value. Specific examples of the press process include a hot press machine and a calendar roll press machine. Also, the pressing conditions (temperature, pressure, etc.) are not particularly limited, and conventionally known knowledge can be referred to as appropriate.

  When the current collector of this embodiment described above is used for a stacked electrode (positive electrode or negative electrode), for example, an electric field is applied in the surface direction of the current collector during charging, so that the current collector extends in the surface direction. sell. On the other hand, when the current collector of this embodiment is used for a bipolar electrode, an electric field is applied in the thickness direction of the current collector during charging, so that the current collector can extend in the thickness direction. Although the expansion / contraction of the active material occurs in the same direction, the conventional current collector cannot follow the expansion / contraction of the active material because it cannot be deformed in the surface direction or the thickness direction. . However, according to the current collector of this embodiment, the stress in the surface direction can be relieved when used in a stacked secondary battery, and the stress in the thickness direction is relieved when used in a bipolar secondary battery. can do. Thereby, it can prevent that an active material layer peels from a collector, and can improve the cycling characteristics of a secondary battery remarkably.

[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.

  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.

[Seal part]
The seal part is a member peculiar to the bipolar secondary battery, and is disposed at the peripheral part of the single battery layer for the purpose of preventing leakage of the electrolyte layer. In addition to this, it is possible to prevent the adjacent current collectors in the battery from contacting each other and the occurrence of a short circuit due to a slight irregularity at the end of the laminated electrode. In the form shown in FIG. 5, the seal portion 43 is disposed on the peripheral portion of the unit cell layer 36 so as to be sandwiched between the current collector 31 and the electrolyte layer 35. Examples of the constituent material of the seal portion include polyolefin resins such as PE and PP, epoxy resins, rubber, and polyimide. Of these, polyolefin resins are preferred from the viewpoints of corrosion resistance, chemical resistance, film-forming properties, economy, and the like.

[tab]
In a lithium ion secondary battery, tabs (a positive electrode tab and a negative electrode tab) that are electrically connected to a current collector are taken out of a laminate film that is an exterior material for the purpose of taking out current outside the battery.

  The material which comprises a tab in particular is not restrict | limited, The well-known highly electroconductive material conventionally used as a tab for lithium ion secondary batteries can be used. As a constituent material of a tab, metal materials, such as aluminum, copper, titanium, nickel, stainless steel (SUS), these alloys, are preferable, for example. 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 tab and the negative electrode tab, or different materials may be used. In the bipolar lithium ion battery 30, as shown in FIG. 5, the current collecting plates (44a, 44b) may be extended to form tabs, or separately prepared tabs may be used as the current collecting plates (44a, 44b). You may connect to.

[Positive terminal lead and negative terminal lead]
In the lithium ion battery 10 shown in FIG. 4, the current collector is electrically connected to the tab 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 elements (17, 37) may be packed using laminate films (22, 42) as shown in FIGS. 4 and 5 as exterior materials. The laminate film can be configured as a three-layer structure in which, for example, polypropylene, aluminum, and nylon are laminated in this order.

<Battery assembly>
An assembled battery can be obtained by electrically connecting a plurality of secondary batteries of this embodiment in series or in parallel. Thus, it becomes possible to adjust a capacity | capacitance and a voltage freely by parallelizing a some battery in series or in parallel.

  FIG. 6 is an external view of a typical embodiment of an assembled battery according to the present invention, FIG. 6A is a plan view of the assembled battery, FIG. 6B is a front view of the assembled battery, and FIG. 6C is an assembled battery. FIG.

  As shown in FIG. 6, the assembled battery 300 according to this embodiment forms a small assembled battery 250 that can be attached and detached by connecting a plurality of secondary batteries of this embodiment in series or in parallel. A large capacity and large output suitable for a vehicle driving power source and an auxiliary power source that require a high volume energy density and a high volume output density by connecting a plurality of these detachable small assembled batteries 250 in series or in parallel. It is also possible to form an assembled battery 300 having 6A is a plan view of the assembled battery, FIG. 6A is a front view, and FIG. 6C is a side view. The small assembled battery 250 that can be attached and detached is provided with an electrical connection means such as a bus bar. The assembled battery 250 is stacked in a plurality of stages using the connection jig 310. How many secondary batteries are connected to produce the assembled battery 250 and how many stages of the assembled battery 250 are stacked to produce the assembled battery 300 depend on the battery capacity of the vehicle (electric vehicle) to be mounted. Depending on the output.

<Vehicle>
The vehicle according to the present embodiment is characterized in that the secondary battery according to the present embodiment or an assembled battery formed by combining a plurality of these batteries is mounted. In this embodiment, since a battery having a long life and excellent long-term reliability and output characteristics can be configured, it is possible to configure a plug-in hybrid electric vehicle having a long EV travel distance and an electric vehicle having a long charge travel distance when such a battery is mounted. . In other words, the secondary battery of this embodiment or an assembled battery formed by combining a plurality of these batteries can be used as a power source for driving a vehicle. A secondary battery of this embodiment or an assembled battery formed by combining a plurality of these batteries is a vehicle, for example, if it is an automobile, a hybrid car, a fuel cell car, an electric car (all are four-wheeled vehicles (passenger cars, trucks, buses, etc. This is because it can be used for motorcycles (including motorcycles) and tricycles (in addition to mini vehicles, etc.)) to provide a long-life and highly reliable vehicle. However, the application is not limited to automobiles. For example, it can be applied to various power sources for moving vehicles such as other vehicles, for example, trains, and power sources for mounting such as uninterruptible power supplies. It is also possible to use as.

  FIG. 7 is a conceptual diagram of a vehicle equipped with the assembled battery of this embodiment. As shown in FIG. 7, in order to mount the assembled battery 300 on a vehicle such as the electric vehicle 400, the battery pack 300 is mounted under the seat at the center of the vehicle body of the electric vehicle 400. This is because if it is installed under the seat, the interior space and the trunk room can be widened. The place where the assembled battery 300 is mounted is not limited to the position under the seat, but may be a lower part of the rear trunk room or an engine room in front of the vehicle. The electric vehicle 400 using the assembled battery 300 as described above has high durability and can provide sufficient output even when used for a long period of time. Furthermore, it is possible to provide electric vehicles and hybrid vehicles that are excellent in fuel efficiency and running performance. A vehicle equipped with the assembled battery of this embodiment can be widely applied to a hybrid vehicle, a fuel cell vehicle and the like in addition to an electric vehicle as shown in FIG.

<Preparation of current collector>
[Example 1]
50% by mass of poly (methylhydrogensiloxane) serving as the main chain of the electric field-responsive polymer material, 30% by mass of (4-but-3-enyloxybenzoic acid-4-methoxyphenyl ester) serving as the side chain, and crosslinking 5% by mass of (1- (4-hydroxy-4′-biphenyl) -2- [4- (10-undecenyloxy) phenyl] butane) as a molecule and 15% by mass of ketjen black as a conductive filler were mixed. A current collector was prepared by radical polymerization.

[Example 2]
A current collector was prepared in the same manner as in Example 1 except that gold fine particles were used as the conductive filler.

[Example 3]
30% by mass of poly (methylhydrogensiloxane) serving as the main chain of the electric field responsive polymer material, 18% by mass of 4-but-3-enyloxybenzoic acid-4-methoxyphenyl ester serving as the side chain, and a crosslinking molecule 2% by mass of 1- (4-hydroxy-4′-biphenyl) -2- [4- (10-undecenyloxy) phenyl] butane, 35% by mass of polypropylene as an electric field non-responsive polymer material, conductive filler A current collector was prepared by mixing 15% by mass of ketjen black and performing radical polymerization.

[Example 4]
A current collector was produced in the same manner as in Example 3 except that gold fine particles were used as the conductive filler.

[Example 5]
A current collector was produced in the same manner as in Example 3 except that carbon nanotubes were used as the conductive filler.

[Example 6]
30% by mass of poly (methylhydrogensiloxane) serving as the main chain of the electric field responsive polymer material, 18% by mass of 4-but-3-enyloxybenzoic acid-4-methoxyphenyl ester serving as the side chain, and a crosslinking molecule 2% by mass of 1- (4-hydroxy-4′-biphenyl) -2- [4- (10-undecenyloxy) phenyl] butane, 35% by mass of polypropylene powder as an electric field non-responsive polymer material, conductive filler As a mixture, 15% by mass of ketjen black was mixed. The resulting mixture was sandwiched between two glass substrates. Then, a 1.2 T magnetic field is applied in parallel (in the plane direction) to the glass substrate by a superconducting magnet, and then a 2.4 T magnetic field is applied perpendicularly (in the perpendicular direction) to the glass substrate. While applying simultaneously, radical polymerization was performed to produce a current collector.

[Example 7]
30% by mass of poly (methylhydrogensiloxane) serving as the main chain of the electric field responsive polymer material, 18% by mass of 4-but-3-enyloxy-benzoic acid 4-methoxyphenyl ester serving as the side chain, and a crosslinking molecule 2% by mass of 1- (4-hydroxy-4′-biphenyl) -2- [4- (10-undecenyloxy) phenyl] butane, 35% by mass of polypropylene powder as an electric field non-responsive polymer material, conductive filler As a mixture, 15% by mass of ketjen black was mixed. The resulting mixture was sandwiched between two glass substrates. Then, radical polymerization was performed while applying a 2.4 T magnetic field in parallel (in the plane direction) to the glass substrate with a superconducting magnet to produce a current collector.

[Example 8]
Silicone elastomer dispersion (50% by mass as dry mass of silicon elastomer) as electric field responsive polymer material, 35% by mass of polypropylene powder as electric field non-responsive polymer material, and 15% by mass of ketjen black as conductive filler Were mixed. The obtained mixture was cast on a glass substrate and dried between two glass substrates to produce a current collector.

[Comparative Example 1]
A current collector was prepared by mixing 85% by mass of polypropylene (PP) and 15% by mass of ketjen black as a conductive filler, and injection-molding the resulting mixture.

<Production of bipolar electrode>
Using the current collectors produced in the above Examples and Comparative Examples, bipolar electrodes were produced by the following method.

(Positive electrode active material layer)
85% by mass of LiMn ₂ O ₄ as a positive electrode active material, 5% by mass of acetylene black as a conductive additive, 10% by mass of polyvinylidene fluoride (PVDF) as a binder, N-methyl-2-pyrrolidone (as a slurry viscosity adjusting solvent) NMP) was mixed in an appropriate amount to obtain a positive electrode active material slurry. Then, the slurry was applied to one surface of the current collector and dried. This was pressed to form a positive electrode active material layer having a thickness of 36 μm.

(Negative electrode active material layer)
A negative electrode active material slurry was obtained by mixing 90% by mass of silicon (Si) as a negative electrode active material, 10% by mass of polyimide as a binder, and an appropriate amount of NMP as a slurry viscosity adjusting solvent. Then, the slurry was applied to the other surface of the current collector (the surface on the side where the positive electrode active material layer was not formed) and dried. By pressing this, a negative electrode active material layer having a thickness of 30 μm was formed.

  The obtained positive electrode active material layer / current collector / negative electrode active material layer laminate was cut into a size of 140 × 90 (mm) and formed on the outer peripheral portion 10 mm from the outer edge and the negative electrode active material The bipolar electrode was completed by peeling off the layers. .

<Production of electrolyte>
LiPF ₆ as a lithium salt is dissolved at a concentration of 1.0 M in a PC-EC mixed solvent in which propylene carbonate (PC) and ethylene carbonate (EC) are mixed at 1: 1 (volume ratio) to prepare an electrolytic solution. did. 90% by mass of the obtained electrolytic solution, 10% by mass of a mixture of hexafluoropropylene (HFP) and polyvinylidene fluoride (PVDF) (HFP: PVDF = 90: 10 (mass ratio)) as a host polymer, and as a viscosity adjusting solvent An appropriate amount of dimethyl carbonate (DMC) was mixed to prepare a gel electrolyte.

<Production of bipolar battery>
The gel electrolyte was applied to the positive electrode active material layer and the negative electrode active material layer of the bipolar electrode, and the DMC was dried to obtain a bipolar electrode soaked with the gel electrolyte. Moreover, the gel polymer electrolyte layer was created by apply | coating the said gel electrolyte on both surfaces of a separator (thickness: 20 micrometers), and drying DMC.

  A gel polymer electrolyte layer was placed on the positive electrode active material layer of the bipolar electrode, and a seal portion having a width of 12 mm was disposed around the bipolar electrode. Six layers of bipolar electrodes were laminated in this order, and then fused by pressing (0.2 MPa, 160 ° C., 5 seconds) from above and below the seal portion to seal each single cell layer.

The obtained power generation element was sandwiched between aluminum tabs for current extraction (130 mm × 80 mm, thickness 100 μm), and vacuum sealed using an aluminum laminate film as an exterior material. This was hot-pressed using a hot press machine at a surface pressure of 1 kg / cm ² and a heating temperature of 100 ° C. for 1 hour to cure the uncured seal portion and complete a bipolar secondary battery.

<Cycle characteristics>
The cycle characteristics of each bipolar secondary battery produced above were evaluated. Under an atmosphere of 25 ° C., the battery was charged to 21.0 V by a constant current method (CC, current: 0.5 mA), then charged by a constant voltage method (CV, 21 V), and charged for 10 hours in total. Thereafter, the battery was discharged at a discharge capacity of 1C. With this as one cycle, the discharge capacity after one cycle and after 50 cycles was determined. And the relative value of the discharge capacity after 50 cycles when the discharge capacity after 1 cycle was set to 100 was calculated as a discharge capacity maintenance rate. The results are shown in Table 1.

  According to Table 1, in Examples 1-8, it was shown that cycling characteristics improve remarkably. This is because the stress caused by the expansion / contraction of the active material is relieved by the expansion / contraction action of the electric field responsive polymer material contained in the current collector, and the peeling of the active material layer from the current collector is suppressed. It was considered a thing.

  Further, as shown in Examples 3 to 8, by adding polypropylene to the electric field responsive polymer material, the solvent resistance of the current collector was further improved in cycle characteristics.

  In addition, as shown in Examples 6 and 7, when the electric field responsive polymer material and the electric field non-responsive polymer material are each independently oriented, the deformation rate of the current collector is further increased, and an excellent stress relaxation effect is obtained. Was demonstrated. In particular, when the electric field responsive polymer material and the electric field non-responsive polymer material were moved in the same direction as in Example 7, a more remarkable stress relaxation effect was obtained.

1, 31 current collector,
2 polypropylene,
3 Liquid crystal elastomer,
4 main chain,
5 liquid crystal molecules,
6 Spacer,
10 Lithium ion battery,
11 positive electrode current collector,
11a Outermost layer positive electrode current collector,
12, 32 positive electrode active material layer,
13, 35 electrolyte layer,
14 negative electrode current collector,
15, 33 negative electrode active material layer,
16, 36 cell layer,
17, 37 Power generation element,
18 positive electrode tab,
19 negative electrode tab,
20 positive terminal lead,
21 negative terminal lead,
22, 42 Laminated film,
30 Bipolar lithium-ion battery,
31a positive electrode side outermost layer current collector,
31b negative electrode side outermost layer current collector,
34 Bipolar electrode,
43 Sealing part (insulating layer),
44a positive electrode current collector plate,
44b negative electrode current collector plate,
250 small battery pack,
300 battery packs,
310 connection jig,
400 Electric car.

Claims (10)

A current collector including a resin layer having electrical conductivity;
The resin layer is viewed contains the electroactive polymer material which reversibly extended or retracted in response to application of an electric field,
The electric current responsive polymer material has a dipole moment of 2.2 debye or more . The resin layer further includes an electric field non-responsive polymer material,
The current collector according to claim 1, wherein a dipole moment of the electric field responsive polymer material is larger than a dipole moment of the electric field non-responsive polymer material.   The current collector according to claim 2, wherein a dipole moment of the electric field responsive polymer material is 2 Debye or more larger than a dipole moment of the electric field non-responsive polymer material.   The current collector according to claim 2 or 3, wherein the electric field responsive polymer material and the non-electric field responsive polymer material are independently oriented in a surface direction or a surface thickness direction of the current collector.   The current collector according to claim 4, wherein the electric field responsive polymer material and the electric field non-responsive polymer material are both oriented in a surface direction of the current collector.   The current collector according to any one of claims 2 to 5, wherein the electric field non-responsive polymer material includes polypropylene. The current collector according to any one of claims 1 to 6,
An electrode for a secondary battery comprising a positive electrode active material layer or a negative electrode active material layer formed on the surface of the current collector.   A lithium ion secondary battery comprising the secondary battery electrode according to claim 7 and an electrolyte layer.   The lithium ion secondary battery according to claim 8, which is a bipolar type.   An assembled battery formed by electrically connecting a plurality of the secondary batteries according to claim 8 or 9.