JP2009080971A - Anode for lithium ion battery - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an anode for a lithium ion battery which can reduce an irreversible capacity when a battery is charged for the first time and improve a charge and discharge efficiency. <P>SOLUTION: The anode for a battery is provided with a current collector, an anode active substance layer which is formed on the surface of the current collector and includes an anode active substance and a binder, The binder is polyacrylate. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a negative electrode for a battery. In particular, the present invention relates to an improvement for improving the output density of a lithium ion secondary battery.

  In recent years, hybrid vehicles, electric vehicles, and fuel cell vehicles have been manufactured and sold from the viewpoints of environment and fuel efficiency, and new developments are continuing. In these so-called electric vehicles, it is indispensable to use a power supply device capable of discharging and charging. As the power supply device, a secondary battery such as a lithium ion battery or a nickel metal hydride battery, an electric double layer capacitor, or the like is used. In particular, lithium ion secondary batteries are considered suitable for electric vehicles because of their high energy density and high durability against repeated charging and discharging, and various developments have been intensively advanced. Generally, in a lithium ion secondary battery, a positive electrode active material layer including a positive electrode active material is formed on both surfaces of a positive electrode current collector, and a negative electrode active material layer including a negative electrode active material is formed on both surfaces of the negative electrode current collector. The negative electrode is connected via an electrolyte layer and is housed in a battery case.

  Here, for example, a lithium-transition metal composite oxide or the like is used as the positive electrode active material, and a carbon material such as graphite is used as the negative electrode active material. Moreover, the electrolyte solution used for an electrolyte layer contains solvents, such as ethylene carbonate (EC) and propylene carbonate (PC), for example. Since PC has comparatively low melting | fusing point, it can be used at low temperature.

However, the problems with graphite used as the negative electrode for lithium ion secondary batteries include the presence of irreversible capacity in the first cycle and the decomposition of PC by co-insertion of a solvent when propylene carbonate (PC) is used as the electrolyte. Reaction, and accompanying graphite decay. This is because if a battery using graphite as a negative electrode active material and PC is used as a solvent for the electrolyte, the PC is inserted between the graphite layers and the layer structure is broken. In order to solve this, for example, in Non-Patent Document 1 and Non-Patent Document 2, in order to use a graphite negative electrode in PC, an additive such as ethylene sulfite or vinylene carbonate is added to the electrolytic solution, A method of producing a coating that protects the graphite surface during charging is described. These additives are considered to decompose on the graphite surface, prevent insertion of PC into graphite, and allow only lithium ions to be inserted.
G. H. Wrodnig et al. , J .; Electrochem. Soc. , 146, 470 (1999) C. Jeholet et al. , Proc. Electrochem. Soc. , 97, 974 (1997)

  However, in the above method, since it is necessary to add an expensive additive to the electrolytic solution, a simpler method is required at a lower cost. Therefore, an object of the present invention is to solve the above-described problems and provide a means for manufacturing a high-capacity battery.

  The present inventors have conducted intensive research to solve the above problems. At that time, an attempt was made to coat the surface of the negative electrode active material with an ionic polymer such as polyacrylic acid or polyacrylate in the negative electrode active material layer of the battery negative electrode. As a result, it has been found that by adding polyacrylate as a binder in the negative electrode active material layer, charge / discharge characteristics in the first cycle can be improved without adding expensive additives, and the present invention is completed. It came to.

  That is, the present invention is a battery negative electrode comprising a current collector and a negative electrode active material layer including a negative electrode active material and a binder formed on a surface of the current collector, wherein the binder is A negative electrode for a battery, which is a polyacrylate.

  The negative electrode active material layer of the negative electrode for a battery of the present invention contains polyacrylate as a binder. Thereby, the irreversible capacity | capacitance in the first cycle of the produced lithium ion secondary battery can be suppressed, and it can contribute to the high capacity | capacitance of a battery.

  Hereinafter, embodiments of the present invention will be described. 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.

(First embodiment)
(Constitution)
The present invention is a negative electrode for a battery having a current collector and a negative electrode active material layer containing a negative electrode active material and a binder formed on the surface of the current collector, wherein the binder is a poly A negative electrode for a battery, which is an acrylate.

  Hereinafter, the structure of the negative electrode for a battery of the present invention will be described. The negative electrode for a battery of the present invention is an electrode in which a negative electrode active material layer is formed on one surface of a current collector. As will be described later, the composition of the negative electrode for a battery is mainly a negative electrode active material and a binder.

  The negative electrode for a battery of the present invention (hereinafter also simply referred to as “negative electrode”) is characterized in that the binder is a polyacrylate in the negative electrode active material layer.

  Polyacrylic acid is known as a water absorbent resin used in diapers and the like as a polymer absorber. When polyacrylic acid is used in the negative electrode active material layer as a binder, the polyacrylic acid absorbs the electrolyte and swells, and covers the surface of the negative electrode active material such as graphite, so that the PC is interposed between the graphite layers. It is thought to prevent entry. In particular, when a polyacrylate such as sodium polyacrylate or lithium polyacrylate is used as a binder, in addition to the above effects, the resin covering the surface of the negative electrode active material functions as a solid electrolyte. It is done.

  As a polyacrylate used as a binder, there is a polyacrylate that is neutralized with an alkali metal or an alkaline earth metal containing Mg and Be, preferably neutralized with Na or Li Sodium polyacrylate or lithium polyacrylate is used.

  A commercially available polyacrylic acid salt may be used, and commercially available polyacrylic acid or polyacrylic acid synthesized by a usual method may be neutralized with NaOH, LiOH, KOH or the like.

  The weight average molecular weight of the polyacrylate that can be used is preferably 10,000 to 10,000,000, more preferably 100,000 to 5,000,000. When the weight average molecular weight of the polyacrylate is in the above range, the electrolyte solution is absorbed and expanded, and the effect of covering the negative electrode active material is excellent. In addition, the value of the weight average molecular weight measured by liquid chromatography shall be employ | adopted for the said molecular weight.

  The content of the binder in the negative electrode active material layer is preferably 1 to 30% by mass, more preferably 1 to 20% by mass, and still more preferably 1 to 20% by mass with respect to the total mass of the negative electrode active material layer. 10% by mass. If content of the said binder is the said range, a negative electrode active material can be bound and the surface of a negative electrode active material can be coat | covered effectively.

  In the negative electrode of the present invention, the polyacrylate covers the surface of the negative electrode active material by including polyacrylate as a binder. Therefore, in particular, when graphite is used as the negative electrode active material, a favorable electrode reaction can be performed without collapsing the layer structure even when it is in contact with the electrolytic solution. The negative electrode of the present invention has a particularly remarkable effect when a battery is produced using PC as the electrolyte layer.

  Hereinafter, the configuration of the negative electrode for a battery of the present invention will be described by taking as an example a case where it is employed in a lithium ion secondary battery. The negative electrode for batteries of the present invention is characterized in that polyacrylate is used as a binder in the negative electrode active material layer. There is no particular limitation on the selection of the current collector, active material, supporting salt (lithium salt), ion-conducting polymer, and other compounds added as necessary. Depending on the intended use, it may be selected by appropriately referring to conventionally known knowledge.

[Current collector]
The current collector is made of foil, mesh, expanded grid (expanded metal), punched metal, or the like using a conductive material such as nickel, copper, or stainless steel (SUS). The mesh opening, wire diameter, number of meshes, etc. are not particularly limited, and conventionally known ones can be used. The general thickness of the current collector is 5 to 30 μm. However, a current collector having a thickness outside this range may be used.

  The size of the current collector is determined according to the intended use of the battery. If a large electrode used for a large battery is manufactured, a current collector having a large area is used. If a small electrode is produced, a current collector with a small area is used.

[Negative electrode active material layer]
A negative electrode active material layer is formed on the current collector. The negative electrode active material layer is a layer containing a negative electrode active material that plays a central role in charge / discharge reaction and a binder. Since the binder is as described above, the description is omitted here.

  A carbon material is preferable as the negative electrode active material. Examples of the carbon material include graphite-based carbon materials (graphite) such as natural graphite, artificial graphite, and expanded graphite, carbon black, activated carbon, carbon fiber, coke, soft carbon, and hard carbon. Preferably, graphite such as natural graphite, artificial graphite, and expanded graphite is used. As natural graphite, for example, scaly graphite, massive graphite and the like can be used. As the artificial graphite, massive graphite, vapor-grown graphite, flaky graphite, and fibrous graphite can be used. Among these, particularly preferable materials are flake graphite and massive graphite. The use of flaky graphite or massive graphite is particularly advantageous for reasons such as high packing density. In some cases, two or more negative electrode active materials may be used in combination.

  The average particle diameter of the negative electrode active material is not particularly limited, but is preferably 1 to 100 μm, more preferably 1 to 50 μm, and further preferably 1 to 20 μm. However, forms outside these ranges can also be employed. In the present application, the average particle diameter of the negative electrode active material is a value measured by laser diffraction particle size distribution measurement (laser diffraction scattering method).

  Further, the content of the negative electrode active material in the negative electrode active material layer is preferably 80 to 98% by mass, more preferably 90 to 98% by mass with respect to the total mass of the negative electrode active material layer. If the content of the negative electrode active material is within the above range, it is preferable because the energy density can be increased.

  In the electrode of the present invention, the thickness of the negative electrode active material layer (the thickness of one surface of the coating layer) is preferably 20 to 500 μm, more preferably 20 to 300 μm, and further preferably 20 to 150 μm. .

  The negative electrode active material layer may contain other substances if necessary. For example, a conductive aid, a supporting salt (lithium salt), an ion conductive polymer, and the like can be included. When an ion conductive polymer is included, a polymerization initiator for polymerizing the polymer may be included. The compounding ratio of these components is not particularly limited. The blending ratio can be adjusted by appropriately referring to known knowledge about lithium ion secondary batteries.

  A conductive assistant means the additive mix | blended in order to improve electroconductivity. Examples of the conductive assistant include carbon powder such as graphite, and various carbon fibers such as vapor grown carbon fiber (VGCF).

Examples of the supporting salt (lithium salt) include Li (C ₂ F ₅ SO ₂ ) ₂ N (LiBETI), LiPF ₆ , LiBF ₄ , LiClO ₄ , LiAsF ₆ , LiCF ₃ SO _{3 and the} like.

  Examples of the ion conductive polymer include polyethylene oxide (PEO) -based and polypropylene oxide (PPO) -based polymers. Here, the polymer may be the same as or different from the ion conductive polymer used in the electrolyte layer of the battery in which the electrode of the present invention is employed, but is preferably the same.

  The polymerization initiator is added to act on the crosslinkable group of the ion conductive polymer to advance the crosslinking reaction. Depending on the external factor for acting as an initiator, it is classified into a photopolymerization initiator, a thermal polymerization initiator and the like. Examples of the polymerization initiator include azobisisobutyronitrile (AIBN), which is a thermal polymerization initiator, and benzyl dimethyl ketal (BDK), which is a photopolymerization initiator.

(Production method)
The method for producing the negative electrode for a battery of the present invention is not particularly limited, and can be produced by appropriately referring to known knowledge. Hereafter, the manufacturing method of the negative electrode for batteries of this invention is demonstrated easily.

  The negative electrode for a battery is produced, for example, by preparing a negative electrode active material slurry containing a negative electrode active material, a binder, and a solvent, applying the negative electrode active material slurry onto a current collector, drying it, and pressing it. sell.

  First, a desired negative electrode active material, a binder, and, if necessary, other components (for example, a supporting salt (lithium salt), an ion conductive polymer, a polymerization initiator, etc.) are mixed in a solvent to obtain a negative electrode active material. A material slurry is prepared. Since the specific form of each component blended in the negative electrode active material slurry is as described in the column of the configuration of the electrode of the present invention, detailed description is omitted here.

  The kind of solvent and the mixing means are not particularly limited, and conventionally known knowledge can be referred to as appropriate. As an example of the solvent, N-methyl-2-pyrrolidone (NMP), dimethylformamide, dimethylacetamide, methylformamide and the like can be used. When an acrylate is employed as the binder, NMP and water may be used as a solvent.

  Subsequently, a current collector for forming the negative electrode active material layer is prepared. The specific form of the current collector prepared in this step is the same as that described in the column of the configuration of the electrode of the present invention, and a detailed description thereof will be omitted here.

  Subsequently, the negative electrode active material slurry prepared above is applied to the surface of the current collector prepared above to form a coating film.

  The application means for applying the negative electrode active material slurry is not particularly limited, but generally used means such as a self-propelled coater may be employed. However, when an ink jet method, a doctor blade method, or a combination thereof is used as the application unit, a thin layer can be formed.

  Thereafter, the coating film formed on the surface of the current collector is dried. Thereby, the solvent in a coating film is removed. The drying means for drying the coating film is not particularly limited, and conventionally known knowledge about electrode production can be appropriately referred to. For example, heat treatment is exemplified. Drying conditions (drying time, drying temperature, etc.) can be appropriately set according to the coating amount of the negative electrode active material slurry and the volatilization rate of the solvent of the slurry.

  Then, the coating film prepared above is pressed. The pressing means is not particularly limited, and conventionally known means can be appropriately employed. If an example of a press means is given, a calendar roll, a flat plate press, etc. will be mentioned.

(Second Embodiment)
In 2nd Embodiment, a battery is comprised using the negative electrode for batteries of said 1st Embodiment.

  That is, the second embodiment of the present invention is a battery having at least one unit cell layer in which a positive electrode, an electrolyte layer, and a negative electrode are laminated in this order, and the negative electrode is the electrode of the present invention. is there. A battery including the negative electrode of the present invention as at least one electrode belongs to the technical scope of the present invention. However, preferably, all of the electrodes constituting the battery are the electrodes of the present invention. By adopting such a configuration, the capacity and output of the battery can be effectively improved.

  The structure of the secondary battery of the present invention is not particularly limited, and when it is distinguished by the form and structure, any conventionally known form such as a stacked (flat) battery or a wound (cylindrical) battery is used.・ Applicable to structures. Further, when viewed in terms of electrical connection form (electrode structure) in a lithium ion secondary battery, it can be applied to both (internal parallel connection type) batteries and bipolar (internal series connection type) batteries. .

  In the present invention, long-term reliability can be ensured by a simple sealing technique such as thermocompression bonding by adopting a laminated (flat) battery structure, which is advantageous in terms of cost and workability.

  Therefore, in the following description, the (internal parallel connection type) lithium ion secondary battery and the bipolar type (internal series connection type) lithium ion secondary battery of the present invention will be described very simply with reference to the drawings. Should not be limited to.

  FIG. 1 shows a flat type (stacked type) lithium ion secondary battery (hereinafter simply referred to as a non-bipolar lithium ion secondary battery or a non-bipolar type secondary battery), which is a typical embodiment of the lithium ion battery of the present invention. 1 is a schematic cross-sectional view schematically showing the entire structure of a secondary battery.

  As shown in FIG. 1, in the non-bipolar lithium ion secondary battery 10 of this embodiment, a laminate film composed of a polymer and a metal is used for the battery exterior material 22, and the entire periphery is heat-sealed. The power generation element (battery element) 17 is housed and sealed by joining together. Here, the power generation element (battery element) 17 includes a positive electrode plate in which positive electrodes (positive electrode active material layers) 12 are formed on both surfaces of the positive electrode current collector 11, an electrolyte layer 13, and both surfaces of the negative electrode current collector 14 (power generation elements). The lowermost layer and the uppermost layer have a structure in which a negative electrode plate having a negative electrode (negative electrode active material layer) 15 formed thereon is laminated on one side. At this time, the positive electrode (positive electrode active material layer) 12 on one surface of one positive electrode plate and the negative electrode (negative electrode active material layer) 15 on one surface of one negative electrode plate adjacent to the one positive electrode plate face each other through the electrolyte layer 13. Thus, a plurality of layers of the positive electrode plate, the electrolyte layer 13, and the negative electrode plate are laminated in this order.

  As a result, the adjacent positive electrode (positive electrode active material layer) 12, electrolyte layer 13, and negative electrode (negative electrode active material layer) 15 constitute one unit cell layer 16. Therefore, it can be said that the lithium ion 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. Note that the positive electrode (positive electrode active material layer) 12 is formed only on one side of the outermost layer positive electrode current collector 11 a located in both outermost layers of the power generation element (battery element; laminate) 17. In addition, by changing the arrangement of the positive electrode plate and the negative electrode plate in FIG. 1, the outermost negative electrode current collector (not shown) is positioned in both outermost layers of the power generation element (battery element) 17, and the outermost layer negative electrode Also in the case of the current collector, the negative electrode (negative electrode active material layer) 15 may be formed only on one side.

  Further, the positive electrode tab 18 and the negative electrode tab 19 that are electrically connected to the respective electrode plates (positive electrode plate and negative electrode plate) are connected to the positive electrode current collector 11 and the negative electrode of each electrode plate via the positive electrode terminal lead 20 and the negative electrode terminal lead 21. It is attached to the current collector 14 by ultrasonic welding, resistance welding, or the like, and has a structure that is sandwiched between the heat fusion parts and exposed to the outside of the battery exterior material 22.

  FIG. 2 shows another typical embodiment of the lithium ion battery of the present invention, a bipolar flat type (stacked type) lithium ion secondary battery (hereinafter simply referred to as a bipolar lithium ion secondary battery, or bipolar). 1 is a schematic cross-sectional view schematically showing the entire structure of a secondary battery.

  As shown in FIG. 2, in the bipolar lithium ion secondary battery 30 of the present embodiment, a substantially rectangular power generation element (battery element) 37 in which a charge / discharge reaction actually proceeds is sealed inside the battery exterior material 42. Has a structured. As shown in FIG. 2, the power generation element (battery element) 37 of the bipolar secondary battery 30 of the present embodiment is adjacent to each other with the electrolyte layer 35 sandwiched between bipolar electrodes 34 composed of one or two or more sheets. A positive electrode (positive electrode active material layer) 32 and a negative electrode (negative electrode active material layer) 33 of the bipolar electrode 34 are opposed to each other. Here, the bipolar electrode 34 has a structure in which a positive electrode (positive electrode active material layer) 32 is provided on one surface of the current collector 31 and a negative electrode (negative electrode active material layer) 33 is provided on the other surface. That is, in the bipolar secondary battery 30, a bipolar electrode having a positive electrode (positive electrode active material layer) 32 on one surface of the current collector 31 and a negative electrode (negative electrode active material layer) 33 on the other surface. A power generation element (battery element) 37 having a structure in which a plurality of 34 are stacked via an electrolyte layer 35 is provided.

  The adjacent positive electrode (positive electrode active material layer) 32, electrolyte layer 35, and negative electrode (negative electrode active material layer) 33 constitute one single battery layer (= battery unit or single cell) 36. Therefore, it can be said that the bipolar secondary battery 30 has a configuration in which the single battery layers 36 are stacked. Further, a seal portion (insulating layer) 43 is disposed around the unit cell layer 36 in order to prevent liquid junction due to leakage of the electrolyte from the electrolyte layer 35. By providing the seal portion (insulating layer) 43, the adjacent current collectors 31 can be insulated and a short circuit due to contact between the adjacent electrodes (the positive electrode 32 and the negative electrode 33) can be prevented.

  The positive electrode 34a and the negative electrode 34b located in the outermost layer of the power generation element (battery element) 37 may not have a bipolar electrode structure, and are necessary for the current collectors 31a and 31b (or terminal plates). It is good also as a structure which has arrange | positioned the positive electrode (positive electrode active material layer) 32 or the negative electrode (negative electrode active material layer) 33 of only one side. A positive electrode (positive electrode active material layer) 32 may be formed on only one side of the positive electrode side outermost layer current collector 31 a located in the outermost layer of the power generation element (battery element) 37. Similarly, a negative electrode (negative electrode active material layer) 33 may be formed only on one side of the outermost current collector 31b on the negative electrode side located in the outermost layer of the power generation element (battery element) 37. In the bipolar lithium ion secondary battery 30, the positive electrode tab 38 and the negative electrode tab 39 are provided on the positive electrode side outermost layer current collector 31 a and the negative electrode side outermost layer current collector 31 b at both the upper and lower ends, respectively. 40 and the negative terminal lead 41 are joined. However, the positive electrode side outermost layer current collector 31 a may be extended to form a positive electrode tab 38, and may be derived from a laminate sheet that is the battery exterior material 42. Similarly, the negative electrode side outermost layer current collector 31b may be extended to form a negative electrode tab 39, which may be similarly derived from a laminate sheet that is the battery outer packaging material 42.

  In the bipolar lithium ion secondary battery 30, the power generation element (battery element; laminated body) 37 portion is used as a battery exterior material (exterior package) 42 in order to prevent external impact and environmental degradation during use. It is preferable to have a structure in which the positive electrode tab 38 and the negative electrode tab 39 are taken out of the battery exterior material 42 by being sealed under reduced pressure. The basic configuration of the bipolar lithium ion secondary battery 30 can be said to be a configuration in which a plurality of stacked single battery layers (single cells) 36 are connected in series.

  As described above, regarding each constituent requirement and manufacturing method of the non-bipolar lithium ion secondary battery and the bipolar lithium ion secondary battery, the electrical connection form (electrode structure) in the lithium ion secondary battery is different. Except for this, it is basically the same. Moreover, an assembled battery and a vehicle can also be comprised using the non-bipolar lithium ion secondary battery and / or bipolar lithium ion secondary battery of this invention.

[Appearance structure of lithium ion secondary battery]
FIG. 3 is a perspective view showing an appearance of a stacked flat non-bipolar or bipolar lithium ion secondary battery which is a typical embodiment of the lithium ion battery according to the present invention.

  As shown in FIG. 3, the stacked flat lithium ion secondary battery 50 has a rectangular flat shape, and a positive electrode tab 58 and a negative electrode tab 59 for taking out electric power from both sides thereof. Has been pulled out. The power generation element (battery element) 57 is wrapped by the battery outer packaging material 52 of the lithium ion secondary battery 50, and the periphery thereof is heat-sealed. The power generation element (battery element) 57 includes a positive electrode tab 58 and a negative electrode tab 59. It is sealed in a state where it is pulled out to the outside. Here, the power generation element (battery element) 57 corresponds to the power generation elements (battery elements) 17 and 37 of the non-bipolar or bipolar lithium ion secondary batteries 10 and 30 shown in FIG. 1 or FIG. A plurality of unit cell layers (single cells) 16 and 36 composed of positive electrodes (positive electrode active material layers) 12 and 32, electrolyte layers 13 and 35, and negative electrodes (negative electrode active material layers) 15 and 33 are laminated. It is a thing.

  The lithium ion battery of the present invention is not limited to the stacked flat shape shown in FIGS. 1 and 2, and the wound lithium ion battery has a cylindrical shape. It is not particularly limited, for example, such a cylindrical shape may be transformed into a rectangular flat shape. In the said cylindrical shape thing, a laminate film may be used for the exterior material, and the conventional cylindrical can (metal can) may be used, for example, It does not restrict | limit.

  3 is not particularly limited, and the positive electrode tab 58 and the negative electrode tab 59 may be pulled out from the same side, or the positive electrode tab 58 and the negative electrode tab 59 may be pulled out. However, the present invention is not limited to the one shown in FIG. 3, for example. Further, in a wound type lithium ion battery, instead of a tab, for example, a terminal may be formed using a cylindrical can (metal can).

  The lithium ion battery of the present invention is used as a power source for driving a vehicle or an auxiliary power source that requires a high volume energy density and a high volume output density as a large capacity power source for an electric vehicle, a hybrid electric vehicle, a fuel cell vehicle, a hybrid fuel cell vehicle, etc. It can be suitably used.

  Hereafter, the member which comprises the lithium ion secondary battery 10, 30, 50 of this embodiment is demonstrated easily. However, since the component which comprises a negative electrode is as having demonstrated above, description is abbreviate | omitted here. Further, the technical scope of the present invention is not limited to the following forms, and conventionally known forms can be similarly adopted.

[Positive electrode]
The positive electrodes 12 and 32 are electrodes in which a positive electrode active material layer is formed on one surface of a current collector. The positive electrode current collector is made of aluminum in a non-bipolar battery. Stainless steel is used for bipolar batteries.

As the positive electrode active material, a lithium-transition metal composite oxide is preferable, and examples thereof include a Li—Mn composite oxide such as LiMn ₂ O ₄ and a Li—Ni composite oxide such as LiNiO ₂ . In some cases, two or more positive electrode active materials may be used in combination.

  The average particle diameter of the positive electrode active material is not particularly limited, but is preferably 10 μm or less, more preferably 5 μm or less, and further preferably 1 μm or less. However, forms outside these ranges can also be employed. In addition, in this application, the particle diameter of a positive electrode active material shall employ | adopt the value measured by the laser diffraction scattering method.

  The positive electrode active material layer may contain other substances if necessary. For example, a binder, a conductive additive, a supporting salt (lithium salt), an ion conductive polymer, and the like can be included. Examples of the binder include polyvinylidene fluoride (PVdF) and a synthetic rubber-based binder. By using the binder, the active material is fixed to the conductive additive and can be stably held.

  Components such as a conductive additive, a supporting salt (lithium salt), and an ion conductive polymer are the same as in the case of the negative electrode active material layer. The compounding ratio of the components contained in the positive electrode active material layer is not particularly limited, and can be adjusted by appropriately referring to known knowledge about the lithium ion secondary battery.

[Electrolyte layer]
As the electrolyte constituting the electrolyte layers 13 and 35, a porous film separator containing a liquid electrolyte or a polymer electrolyte can be used. In particular, the effect of the electrode of the present invention is remarkable when the electrolyte layer contains an electrolytic solution.

  The electrolytic solution has a form in which a lithium salt that is a supporting salt is dissolved in an organic solvent that is a plasticizer. Examples of the organic solvent that can be used as the plasticizer include carbonates such as ethylene carbonate (EC), dimethyl carbonate (DMC), and propylene carbonate (PC).

  In the battery of the present invention, preferably, at least a part of the electrolytic solution is PC. Conventionally, when PC is used as the electrolytic solution, the material of the negative electrode active material is limited unless a treatment such as adding an additive to the electrolytic solution is performed, but according to the present invention, the above treatment is not performed. An electrolytic solution containing PC can be used. The lower limit of the content of PC in the organic solvent is not particularly limited, but is 5% by volume. If the PC content is in the above range, a battery that provides high performance at low temperatures can be produced.

  Further, as the supporting salt (lithium salt), a compound that can be added to the active material layer of the electrode, such as LiBETI, can be similarly employed.

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

  The gel electrolyte has a configuration in which the above liquid electrolyte is injected into a matrix polymer made of an ion conductive polymer. Examples of the ion conductive polymer used as the matrix polymer include polyethylene oxide (PEO), polypropylene oxide (PPO), polyethylene glycol (PEG), polyacrylonitrile (PAN), and polyvinylidene fluoride-hexafluoropropylene (PVdF-HEP). And poly (methyl methacrylate (PMMA) and copolymers thereof, etc. In such polyalkylene oxide polymers, electrolyte salts such as lithium salts can be well dissolved.

  In the case where the electrolyte layers 13 and 35 are composed of a liquid electrolyte or a gel electrolyte, a separator may be used for the electrolyte layer 17. Specific examples of the separator include a microporous film made of polyolefin such as polyethylene or polypropylene.

  The intrinsic polymer 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 layers 13 and 35 are made of an intrinsic polymer electrolyte, there is no fear of liquid leakage from the battery, and the reliability of the battery can be improved. In particular, when the battery of the present invention is produced using a polymer electrolyte such as polyethylene oxide (PEO), the effect of improving the output and capacity is remarkable.

  The matrix polymer of the gel electrolyte or the intrinsic polymer 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.

[Insulation layer]
The sealing portion (insulating layer) 43 has insulating properties, sealing properties against falling off of the solid electrolyte, sealing properties against moisture permeation from the outside (sealing properties), heat resistance at the battery operating temperature, and the like. For example, urethane resin, epoxy resin, polyethylene resin, polypropylene resin, polyimide resin, rubber or the like can be used. Of these, urethane resins and epoxy resins are preferred from the viewpoints of corrosion resistance, chemical resistance, ease of production (film forming properties), economy, and the like.

[tab]
As for the material of the tabs (positive electrode tabs 18 and 38 and negative electrode tabs 19 and 39), in the non-bipolar battery, aluminum can be used for the positive electrode tab, and copper, nickel, stainless steel, and alloys thereof can be used for the negative electrode tab. The bipolar battery is not particularly limited, and a known material conventionally used as a tab for a bipolar battery can be used. Examples thereof include aluminum, copper, titanium, nickel, stainless steel (SUS), and alloys thereof.

(Third embodiment)
In 3rd Embodiment, an assembled battery is comprised using the battery of said 2nd Embodiment.

  The assembled battery of the present invention is formed by connecting a plurality of lithium ion secondary batteries of the present invention. Specifically, at least two or more are used, and are configured by serialization, parallelization, or both. Capacitance and voltage can be freely adjusted by paralleling in series. In the assembled battery of the present invention, the non-bipolar lithium ion secondary battery and the bipolar lithium ion secondary battery of the present invention are used, and these are combined in series, in parallel, or in series and in parallel. Thus, an assembled battery can be configured.

  4 is an external view of a typical embodiment of the assembled battery according to the present invention, FIG. 4A is a plan view of the assembled battery, FIG. 4B is a front view of the assembled battery, and FIG. It is a side view of an assembled battery.

  As shown in FIG. 4, an assembled battery 300 according to the present invention forms a small assembled battery 250 in which a plurality of lithium ion secondary batteries of the present invention are connected in series or in parallel to be detachable. A plurality of detachable small assembled batteries 250 are connected in series or in parallel, and have a large capacity and a large output suitable for a vehicle drive power supply and an auxiliary power supply that require high volume energy density and high volume output density. The assembled battery 300 can also be formed. 4A is a plan view of the assembled battery, FIG. 4B is a front view, and FIG. 4C 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 non-bipolar or bipolar lithium ion secondary batteries are connected to produce the assembled battery 250, and how many assembled batteries 250 are stacked to produce the assembled battery 300 are mounted. What is necessary is just to determine according to the battery capacity and output of the vehicle (electric vehicle) to be.

(Fourth embodiment)
In 4th Embodiment, the battery 10 of said 2nd Embodiment or the assembled battery 300 of 3rd Embodiment is mounted, and a vehicle is comprised.

  The vehicle of the present invention is characterized in that the lithium ion battery of the present invention or an assembled battery formed by combining a plurality of these is mounted. When the high-capacity positive electrode of the present invention is used, a battery having a high energy density can be configured. Therefore, when such a battery is mounted, a plug-in hybrid electric vehicle having a long EV travel distance or an electric vehicle having a long charge travel distance can be configured. In other words, the lithium ion battery of the present invention or an assembled battery formed by combining a plurality of these can be used as a power source for driving a vehicle. The lithium ion battery of the present invention or an assembled battery formed by combining a plurality of these is a vehicle, for example, a car, a hybrid car, a fuel cell car, an electric car (all are four-wheeled vehicles (passenger cars, commercial vehicles such as trucks and buses, 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. 5 is a conceptual diagram of a vehicle equipped with the assembled battery of the present invention.

  As shown in FIG. 5, 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 the present invention 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.

  The effects of the present invention will be described using the following examples and comparative examples. However, the technical scope of the present invention is not limited to only the forms shown in the following examples.

<Example 1>
<Production of negative electrode>
For the solid content consisting of natural graphite (average particle size 3 μm) (90 mass%) as the negative electrode active material and lithium polyacrylate (PAALi) (weight average molecular weight 750,000) (10 mass%) as the binder, An appropriate amount of water as a slurry viscosity adjusting solvent was added to prepare a negative electrode active material slurry.

  On the other hand, a nickel mesh was prepared as a current collector for the negative electrode. The negative electrode active material slurry prepared above was applied to one surface of the prepared current collector by the doctor blade method to form a coating film. The coating film was then dried. The thickness of the negative electrode active material layer was 140 μm.

<Preparation of positive electrode and reference electrode>
A lithium metal foil having a thickness of 100 μm was prepared as a positive electrode and a reference electrode.

<Preparation of electrolyte>
Ethylene carbonate (EC) and dimethyl carbonate (DMC) were mixed at a volume ratio of 1: 1 to obtain a solvent for the electrolytic solution. Subsequently, LiClO ₄ which is a lithium salt was added to the electrolyte solution so as to have a concentration of 1M to prepare an electrolyte solution.

<Production of beaker type battery>
A beaker type battery 60 as shown in FIG. 6 was prepared using the test negative electrode 62, the positive electrode 61, the reference electrode 63, and the electrolytic solution 64 prepared above. The reference electrode 63 was used as a standard for determining the potential of the negative electrode 62.

<Evaluation of charge / discharge>
The beaker type battery produced above was evaluated for charge and discharge. It set so that it might become a 50 mA / g electric current with respect to a negative electrode active material, and the constant current charge was performed to 0V. After charging, the current was set to 50 mA / g with respect to the active material, and constant current discharge was performed up to 2V.

<Example 2>
A beaker type battery was produced in the same manner as in Example 1 except that sodium polyacrylate (PAANA) (weight average molecular weight 750,000) (10% by mass) was used as the binder.

<Comparative Example 1>
A beaker type battery was produced in the same manner as in Example 1 except that polyvinylidene fluoride (PVdF) (weight average molecular weight 100,000) (10% by mass) was used as the binder.

<Example 3>
A beaker type battery was produced in the same manner as in Example 1 except that propylene carbonate (PC) was used as the solvent for the electrolytic solution.

<Example 4>
A beaker type battery was produced in the same manner as in Example 3 except that sodium polyacrylate (PAANA) (weight average molecular weight 750,000) (10 mass%) was used as the binder.

<Comparative example 2>
A beaker type battery was produced in the same manner as in Example 3 except that polyvinylidene fluoride (PVdF) (weight average molecular weight 100,000) (10 mass%) was used as the binder.

  The initial charge capacity, initial discharge capacity, and initial charge / discharge efficiency of the beaker type battery produced above are shown in Table 1 below. Moreover, the charging / discharging curve of the battery produced in Example 1, 2 and the comparative example 1 is shown in FIG. 7, and the charging / discharging curve of the battery produced in Example 3, 4 and the comparative example 2 is shown in FIG.

  In FIG. 7, the results of Examples 1 and 2 using EC: DMC as the electrolyte and Comparative Example 1 were compared. As a result, PAALi or PAANA was used compared to Comparative Example 1 using PVdF as the binder. In Examples 1 and 2, it turns out that the irreversible capacity | capacitance of 0.8V vicinity has decreased. Moreover, it can be seen from Table 1 that in the comparative example using PVdF as the binder, the initial charge capacity is larger than those in Examples 1 and 2 using polyacrylate. There was no significant difference in discharge capacity. Therefore, in Examples 1 and 2, higher charge / discharge efficiency was obtained than in Comparative Example 1.

  From FIG. 8, comparing the results of Examples 3 and 4 using PC as the electrolytic solution and Comparative Example 2, in Comparative Example 2 using PVdF as the binder, a plateau that is considered to be the collapse of graphite at the first charge. From Table 1, it can be seen that the charging capacity is about three times the theoretical capacity. Moreover, the discharge capacity is about one third of the theoretical capacity, which suggests that the graphite structure has collapsed. On the other hand, in Examples 3 and 4 using PAALi or PAANA as a binder, the charge / discharge efficiency is higher than that of Comparative Example 2, and it can be seen that charge / discharge is performed well even when PC is used.

  (A) and (b) of FIG. 9 show the surfaces before and after the charge / discharge cycle when EC: DMC is used as the electrolytic solution, respectively. FIGS. 9C and 9D show the surfaces after 1 cycle and 10 cycles, respectively, when PC is used as the electrolytic solution. From FIG. 9, it was confirmed that the negative electrode of the present invention maintained the graphite structure even after the charge / discharge cycle.

  Thus, when the negative electrode of the present invention is used, a good charge / discharge curve can be obtained in an electrolytic solution containing PC without using an expensive additive, and a highly efficient battery can be produced.

1 is a schematic cross-sectional view schematically showing an outline of a laminated flat non-bipolar lithium ion secondary battery which is a typical embodiment of a lithium ion battery of the present invention. It is the cross-sectional schematic which represented typically the outline | summary of the laminated flat bipolar lithium ion secondary battery which is another typical embodiment of the lithium ion battery of this invention. BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a perspective view schematically showing an appearance of a stacked flat lithium ion secondary battery that is a typical embodiment of a lithium ion battery according to the present invention. 4A and 4B are external views schematically showing typical embodiments of the assembled battery according to the present invention, in which FIG. 4A is a plan view of the assembled battery, FIG. 4B is a front view of the assembled battery, and FIG. It is a side view of a battery. It is a conceptual diagram of the vehicle carrying the assembled battery of this invention. It is the schematic of the battery produced in the Example. It is a charging / discharging curve of the first cycle of the battery produced in Examples 1, 2 and Comparative Example 1. It is a charging / discharging curve of the first cycle of the battery produced in Examples 3 and 4 and Comparative Example 2. 2 is a SEM photograph of a cross section of a negative electrode before and after a charge / discharge cycle of batteries produced in Example 1 and Example 3. FIG.

Explanation of symbols

10 Non-bipolar lithium ion secondary battery,
11 positive electrode current collector,
11a Outermost layer positive electrode current collector,
12, 32 positive electrode (positive electrode active material layer),
13, 35 electrolyte layer,
14 negative electrode current collector,
15, 33 negative electrode (negative electrode active material layer),
16, 36 single battery layer (= battery unit or single cell),
17, 37, 57 Power generation element (battery element; laminate),
18, 38, 58 positive electrode tab,
19, 39, 59 negative electrode tab,
20, 40 Positive terminal lead,
21, 41 Negative terminal lead,
22, 42, 52 Battery exterior material (for example, laminate film),
30 Bipolar lithium ion secondary battery,
31 current collector,
31a The outermost layer current collector on the positive electrode side,
31b The outermost layer current collector on the negative electrode side,
34 Bipolar electrode,
34a, 34b The electrode located in the outermost layer,
43 Sealing part (insulating layer),
50 lithium ion secondary battery,
60 beaker type battery,
61 positive electrode,
62 negative electrode,
63 Reference electrode,
64 electrolyte,
250 small battery pack,
300 battery packs,
310 connection jig,
400 Electric car.

Claims (7)

A negative electrode for a battery, comprising: a current collector; and a negative electrode active material layer including a negative electrode active material and a binder formed on a surface of the current collector,
A negative electrode for a battery, wherein the binder is a polyacrylate.   The negative electrode for a battery according to claim 1, wherein the polyacrylate is a polyacrylate that is neutralized with Na or Li.   The negative electrode for a battery according to claim 1, wherein the negative electrode active material is graphite. A lithium ion secondary battery having at least one single cell layer in which a positive electrode, an electrolyte layer, and a negative electrode are laminated in this order,
The lithium ion secondary battery whose said negative electrode is a negative electrode for batteries of any one of Claims 1-3.   The lithium ion secondary battery according to claim 4, wherein the electrolyte layer includes an electrolytic solution, and at least a part of the electrolytic solution is propylene carbonate.   An assembled battery using the lithium ion secondary battery according to claim 4.   A vehicle equipped with the lithium ion secondary battery according to claim 4 or 5 or the assembled battery according to claim 6.