JP2010160982A - Anode for lithium-ion secondary battery and lithium-ion secondary battery - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an anode for a lithium-ion secondary battery and a lithium-ion secondary battery for restraining exothermic reaction in preliminarily storing lithium. <P>SOLUTION: The anode for the lithium-ion secondary battery includes a collector, an anode active material layer containing an anode active material formed on a surface of the collector, and a protective layer formed on the anode active material layer containing an insulating material and lithium particles, with the surface of the lithium particles in contact with the anode active material layer. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a negative electrode for a lithium ion secondary battery and a lithium ion secondary battery, and more particularly to a negative electrode for a lithium ion secondary battery and a lithium ion secondary battery suitable for mounting on a vehicle.

  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 have extremely high output characteristics and high energy 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 a relatively high 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 both surfaces of a positive electrode current collector using a binder, and a negative electrode in which a negative electrode active material or the like is applied to both surfaces of a negative electrode current collector using a binder. However, it has the structure connected through an electrolyte layer and accommodated in a battery case.

Conventionally, carbon that is advantageous in terms of charge / discharge cycle life and cost, particularly graphite-based materials, has been used for the negative electrode of a lithium ion secondary battery. Recently, a material capable of alloying with lithium has been studied as a high-capacity negative electrode active material. For example, Si material occludes and releases 4.4 mol of lithium ions per mol during charge / discharge, and Li ₂₂ Si ₅ has a theoretical capacity of about 2000 mAh / g. Thus, since the material alloyed with lithium can increase the energy density of an electrode, it is anticipated as a negative electrode material in a vehicle use.

  However, lithium ion secondary batteries using many negative electrode active materials such as carbon materials having a large capacity or materials alloyed with lithium have a large irreversible capacity at the time of initial charge / discharge. There is a problem in that the capacity utilization rate decreases and the energy density of the battery decreases. Here, the irreversible capacity refers to the amount of lithium remaining in the negative electrode even after the discharge in the lithium ion secondary battery, in which all of the lithium occluded in the negative electrode during the initial charge cannot be released by the discharge. means. This problem of irreversible capacity has become a major development issue in the practical application to vehicle applications that require high capacity, and attempts to suppress the irreversible capacity have been actively made.

  As a technique for supplementing lithium corresponding to such irreversible capacity, a method has been proposed in which a carbon material in which a predetermined amount of lithium powder is previously deposited on an electrode is used as a negative electrode active material (see Patent Document 1). According to this disclosure, by preliminarily storing (pre-doping) lithium in an amount corresponding to the initial charge / discharge capacity difference in the negative electrode, the charge / discharge capacity difference can be eliminated at the first charge, and a high-capacity and safe battery can be obtained. Yes.

JP-A-5-234621

  However, in the negative electrode preliminarily occluded with lithium, an exothermic reaction occurs between lithium and the negative electrode active material when lithium is doped. In particular, when lithium is deposited on the negative electrode as in Patent Document 1, the amount of heat generated increases because the contact area between lithium and the negative electrode active material is large. As a result, there has been a problem that an electrode constituent material such as a binder contained in the electrode layer is dissolved to increase the resistance between the active materials, thereby increasing the internal resistance of the electrode.

  Therefore, an object of the present invention is to provide a means capable of compensating an irreversible capacity while preventing an excessive exothermic reaction between lithium and a negative electrode active material and suppressing an increase in internal resistance of the battery. And

  The inventors of the present invention diligently studied to achieve the above object, and on the current collector, a negative electrode active material layer including a negative electrode active material formed on the surface of the current collector, and the negative electrode active material layer. A negative electrode for a lithium ion secondary battery provided with a protective layer was completed. In particular, the protective layer includes an insulating material and lithium particles, and a part of the surface of the lithium particles is in contact with the negative electrode active material layer.

  In the negative electrode for a lithium ion secondary battery of the present invention, the protective layer contains an insulating material together with lithium particles. Therefore, the contact area between the lithium particles and the negative electrode active material layer can be reduced by the presence of the insulating material when doping lithium ions. Thereby, the exothermic reaction mentioned above can be suppressed. As a result, in the lithium ion secondary battery using the negative electrode of the present invention, the irreversible capacity can be compensated while suppressing an increase in internal resistance.

FIG. 1A is a schematic cross-sectional view showing a negative electrode for a lithium ion secondary battery, which is a typical embodiment of the present invention. FIG. 1B is an enlarged view schematically showing the structure of the interface between the negative electrode active material layer 2 and the protective layer 3 in FIG. 1 is a schematic cross-sectional view schematically showing the overall structure of a non-bipolar lithium ion secondary battery according to an embodiment of the present invention. 1 is a schematic cross-sectional view schematically showing the overall structure of a bipolar lithium ion secondary battery according to an embodiment of the present invention. FIG. 4A is an external view of an embodiment of the assembled battery of the present invention, FIG. 4A is a plan view, FIG. 4B is a front view, and FIG. 4C is a side view. It is a conceptual diagram of the vehicle carrying the assembled battery of this invention. It is a graph which shows the relationship between the porosity of the protective layer and output density in the Example of this invention.

  Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings. 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.

[Negative electrode]
One embodiment of the present invention relates to a negative electrode for a lithium ion secondary battery including a current collector and a negative electrode active material layer including a negative electrode active material formed on a surface of the current collector. And the negative electrode for lithium ion secondary batteries of this embodiment has a protective layer containing lithium particles and an insulating material on the surface of the negative electrode active material layer, and a part of the surface of the lithium particles in the protective layer is a negative electrode. It is in contact with the active material layer.

  FIG. 1A is a schematic cross-sectional view showing a negative electrode for a lithium ion secondary battery, which is a typical embodiment of the present invention. Hereinafter, the negative electrode for a lithium ion secondary battery shown in FIG. 1A will be described as an example, but the technical scope of the present embodiment is not limited to such a form.

  A negative electrode 10 of the present embodiment shown in FIG. 1A has a structure in which a current collector 1, a negative electrode active material layer 2, and a protective layer 3 are sequentially stacked. Here, the protective layer 3 includes lithium particles and an insulating material. As will be described in detail later, at least a part of the surface of the lithium particle is in contact with the negative electrode active material layer. The protective layer only needs to be present on the surface of the negative electrode active material layer, and is not limited to the form in which the illustrated layer is formed. For example, the protective layer may be attached to only a part of the surface of the negative electrode active material layer. The adhesion of the protective layer may be due to physical interaction or chemical interaction.

  FIG. 1B is an enlarged view schematically showing the structure of the interface between the negative electrode active material layer 2 and the protective layer 3 in FIG. The protective layer 3 includes lithium particles 4 and an insulating material 5 and is formed on the negative electrode active material layer 2. In a preferred embodiment, a part of the surface of each lithium particle 4 included in the protective layer 3 is in contact with the negative electrode active material layer 3, more specifically, the negative electrode active material 6. Further, in the protective layer 3, the lithium particles 4 are covered with an insulating material 5 and are not in direct contact with the adjacent lithium particles 4, and the insulating material 5 is interposed therebetween.

  Hereinafter, although the member which comprises the negative electrode for lithium ion secondary batteries of this embodiment is demonstrated, it does not restrict | limit only to the following form, A conventionally well-known form may be employ | adopted similarly.

[Current collector]
The current collector is made of a conductive material. The material constituting the current collector is not particularly limited as long as it has conductivity. For example, a metal or a conductive polymer can be adopted. Specifically, at least one current collector material selected from the group consisting of iron, chromium, nickel, manganese, titanium, molybdenum, vanadium, niobium, aluminum, copper, silver, gold, platinum, and carbon is preferable. Can be used. Although the thickness of a collector is not specifically limited, Usually, it is about 1-100 micrometers.

[Negative electrode active material layer]
The negative electrode active material layer contains a negative electrode active material, and a conductive agent, binder, electrolyte (polymer matrix, ion conductive polymer, electrolytic solution, etc.) for increasing electrical conductivity and an electrolyte for increasing ion conductivity as required. It further comprises a supporting salt (lithium salt) and the like.

  The compounding ratio of the components contained in the negative electrode active material layer is not particularly limited, and can be adjusted by appropriately referring to known knowledge about the lithium ion secondary battery.

(Negative electrode active material)
The negative electrode active material is not particularly limited, and any conventionally known negative electrode active material can be used. Among these, since the effect of forming the protective layer is remarkable, the negative electrode active material of the present embodiment is preferably an alloy-based active material containing a material alloyed with lithium. In addition, by using a material that is alloyed with lithium, it is possible to obtain a high-capacity battery having a higher energy density than conventional carbon-based materials.

The material to be alloyed 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 can be mentioned. Among these, it is preferable that at least one selected from the group consisting of Si, Ge, Sn, Pb, Al, In, and Zn is included from the viewpoint that a battery excellent in capacity and energy density can be configured. Further, it preferably contains Si or Sn, and particularly preferably contains Si. As the oxide, silicon monoxide (SiO), SiO _x (0 <x <2), tin dioxide (SnO ₂ ), SnO _x (0 <x <2), SnSiO ₃ or the like can be used. Moreover, silicon carbide (SiC) etc. can be used as a carbide | carbonized_material. These may be used alone or in combination of two or more.

In addition, carbon materials such as crystalline carbon materials such as natural graphite, artificial graphite, carbon black, acetylene black, graphite, activated carbon, carbon fiber, coke, soft carbon, hard carbon, and amorphous carbon materials, lithium metal, etc. Metal materials, lithium-transfer metal composite oxides such as lithium-titanium composite oxide (lithium titanate: Li ₄ Ti ₅ O ₁₂ ), and other conventionally known negative electrode active materials can be used. In some cases, two or more negative electrode active materials may be used in combination.

  However, in order to improve the capacity, it is preferable that the active material contains a large amount of the material alloyed with lithium. Specifically, the negative electrode active material contains 60% by mass or more, more preferably 80% by mass or more, still more preferably 90% by mass or more, and particularly preferably 100% by mass of a material to be alloyed with lithium.

  In the negative electrode of the present embodiment, the thickness of the negative electrode active material layer is about 2 to 100 μm, preferably 20 to 500 μm, more preferably 20 to 300 μm, and still more preferably 20 to 150 μm.

  The average particle size 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 size of the active material is a value measured by laser diffraction particle size distribution measurement (laser diffraction scattering method).

(Conductive agent)
The conductive agent refers to an additive blended to improve conductivity. Examples of the conductive agent include carbon black such as acetylene black, carbon powder such as graphite and graphite, and various carbon fibers such as vapor grown carbon fiber (VGCF). When the conductive agent is included, an electronic network inside the active material layer is effectively formed, which can contribute to improvement in reliability by improving output characteristics of the battery and improving liquid retention of the electrolyte. As the supporting salt, those contained in the electrolytic solution described later can be similarly used.

(binder)
The binder contained in the negative electrode active material layer includes polyamic acid, polyethylene (PE), polypropylene (PP), polyethylene terephthalate (PET), polyether nitrile (PEN), polyimide (PI), polyamide (PA), polytetrafluoro. Ethylene (PTFE), styrene butadiene rubber (SBR), polyacrylonitrile (PAN), polymethyl acrylate (PMA), polymethyl methacrylate (PMMA), polyvinyl chloride (PVC), polyvinylidene fluoride (PVdF), or a mixture thereof Is mentioned.

(Electrolyte / Supporting salt)
Examples of the electrolyte include, but are not limited to, ion conductive polymers (solid polymer electrolytes) including lithium salts such as polyethylene oxide (PEO), polypropylene oxide (PPO), and copolymers thereof. There is nothing.

The supporting salt (lithium salt), but are not limited _{to, LiPF 6, LiBF 4, LiClO} 4, LiAsF 6, LiTaF 6, LiAlCl 4, inorganic acid anion salts such as _{Li 2 B 10 Cl 10; LiCF} 3 SO ₃ , organic acid anion salts such as Li (CF ₃ SO ₂ ) ₂ N and Li (C ₂ F ₅ SO ₂ ) ₂ N. These supporting salts may be used alone or in combination of two or more.

[Protective layer]
The negative electrode for a lithium ion secondary battery of this embodiment is characterized in that a protective layer containing lithium particles and an insulating material is provided. As described in the column of problems to be solved by the present invention, when lithium is preliminarily occluded in the negative electrode, heat generated between lithium and the negative electrode at the time of initial charge is a problem. In this embodiment, since the lithium particles and the insulating material are mixed and placed on the negative electrode before the initial charge, the contact area between the lithium particles and the negative electrode is reduced by the presence of the insulating material. For this reason, excessive reaction between the negative electrode and the lithium particles during initial charging is suppressed, and rapid heat generation can be prevented. Moreover, even if it contains other components, such as a binder, a protective layer can be comprised only with an insulating substance except lithium particles. Therefore, the protective layer portion other than lithium does not affect the battery performance, and the protective layer can be easily produced.

  In the negative electrode for a lithium ion secondary battery of the present embodiment, the lithium particles in the protective layer are in contact with the negative electrode active material layer. This can be confirmed, for example, by cutting the negative electrode in the thickness direction and observing the cross section with a scanning electron microscope (SEM) at 500 to 10,000 times. In this embodiment, the lithium particles are in contact with the negative electrode active material layer means the following state. That is, when an arbitrary cross section of the negative electrode is observed as described above, among all lithium particles included in the observed image, at least a part of the surface is in contact with the negative electrode active material layer. State. The lithium particles in contact with the negative electrode active material layer are more preferably 90% or more, and most preferably 100%.

  In the protective layer, an insulating material is preferably interposed between the lithium particles. If the lithium particles are in contact with each other or agglomerated, the exothermic reaction during the pre-occlusion may be promoted. However, since the lithium particles are separated from each other by an insulating material, the exothermic reaction can be more reliably suppressed.

  In this embodiment, the presence of the insulating material between the lithium particles can be confirmed, for example, by cutting the negative electrode in the thickness direction and observing the cross section with a scanning electron microscope (SEM) at 500 to 10,000 times. . In this embodiment mode, the presence of an insulating material between lithium particles refers to the following state. That is, when an arbitrary cross section of the negative electrode is observed as described above, 80% or more of all lithium particles contained in the observed image are not in contact with other lithium particles. More preferably, the lithium particles that are not in contact with other lithium particles are 90% or more, and most preferably 100%.

  The insulating material contained in the protective layer is not particularly limited, but ceramics such as silicon oxide, aluminum oxide, titanium oxide, zirconium oxide, silicon carbide, and magnesium oxide are preferable. Among these, silicon oxide and aluminum oxide are more preferable because of low cost. The insulating material is preferably a powder having an average particle size of 0.05 to 40 μm, more preferably the average particle size is 0.1 to 20 μm, and still more preferably 0.1 to 10 μm. When the average particle diameter of the insulating material exceeds 40 μm, there is a possibility that a sufficient insulating effect cannot be obtained. On the other hand, when the average particle size is less than 0.05 μm, it is difficult to confirm a uniform insulating effect.

  The lithium particles preferably have an average particle size of 0.1 to 100 μm. When the average particle size is less than 0.1 μm, the particles are too fine, so that the proportion of the surface film is increased in the total volume of lithium particles, and lithium that can be effectively used is reduced. On the other hand, when the average particle diameter exceeds 100 μm, the lithium particles are too large, and it becomes difficult to uniformly disperse them on the electrode. The average particle size of the lithium particles is more preferably 1 to 80 μm, still more preferably 10 to 50 μm.

  The ratio of the insulating material to the lithium particles is such that the total volume of the lithium particles is preferably 50 to 105 vol%, more preferably 60 to 100 vol%, still more preferably 70 to 90 vol% of the total volume of the insulating material. If the lithium particles are less than 50 vol% with respect to the insulating material, the insulation resistance may be too high, and the battery output may decrease. On the other hand, if it exceeds 105 vol%, there is a possibility that heat will be easily generated during the initial charge.

  The protective layer may contain a binder in addition to the lithium particles and the insulating material. As binders, polyethylene (PE), polypropylene (PP), polyethylene terephthalate (PET), polyether nitrile (PEN), polyimide (PI), polyamide (PA), polytetrafluoroethylene (PTFE), styrene butadiene rubber (SBR) ), Polyacrylonitrile (PAN), polymethyl acrylate (PMA), polymethyl methacrylate (PMMA), polyvinyl chloride (PVC), polyvinylidene fluoride (PVdF), or mixtures thereof.

  The thickness of the protective layer is preferably 5 to 40 μm, more preferably 5 to 20 μm, and still more preferably 5 to 10 μm. If the thickness of the protective layer is less than 5 μm, there is a possibility that the charge / discharge capacity difference cannot be sufficiently eliminated at the first charge even if lithium is preliminarily occluded. On the other hand, when the thickness of the protective layer exceeds 40 μm, the thickness of the whole negative electrode becomes too thick, and as a result, the number of battery cells stacked when forming a lithium ion secondary battery is reduced. Therefore, the obtained battery tends to have a low energy density.

  The contact area between the negative electrode active material layer and the lithium particles is preferably such that the contact area between the lithium particles and the negative electrode active material layer is 0.01 to 0.1 times the total surface area of the lithium particles. If the contact area is less than this range, the charge / discharge capacity difference cannot be sufficiently eliminated at the time of initial charge. On the other hand, if it exceeds this range, excessive heat may be generated at the time of initial charge. The contact area is more preferably 0.02 to 0.08 times, and even more preferably 0.03 to 0.06 times.

  A contact area is calculated | required by cut | disconnecting the manufactured negative electrode and observing the cross section by 2000-10000 times using a scanning electron microscope (SEM). Measurement is performed by image analysis at an arbitrary measurement point. Since the lithium particles are usually spherical, the length of the portion where the lithium particles are in contact with the negative electrode active material layer is first measured from a two-dimensional image obtained by SEM observation. Next, the circumference of the lithium particles is obtained, the ratio of the length of the contact portion to the circumference is calculated, and the contact area can be roughly estimated based on this ratio.

  In the protective layer, lithium in the protective layer is ionized during the initial charge and moves to the negative electrode, the lithium particles existing before the initial charge disappear, and voids are generated in the lithium particle portion. Therefore, the protective layer becomes porous. Therefore, lithium ions can pass through the protective layer without being disturbed during charge and discharge after the initial charge, and the output characteristics of the battery are maintained in good condition.

  In order to obtain a high output density, the porosity of the protective layer after the initial charge is preferably 28 to 65%, more preferably 30 to 60%, and still more preferably 35 to 50%. There are the following methods for determining the porosity. After the first charge, the negative electrode is taken out from the battery, and the porosity of the whole negative electrode is measured with a mercury porosimeter. Next, the binder of the protective layer is dissolved with a solvent to remove the protective layer, and the porosity of the remaining part of the negative electrode is measured. The porosity of only the protective layer can be calculated from these two porosity.

  In addition, the structure of the negative electrode for lithium batteries of this Embodiment can also be applied to a positive electrode.

[Method for producing negative electrode for lithium secondary battery]
The method for producing the negative electrode for a lithium ion secondary battery of the present embodiment is not particularly limited, and can be produced by applying a conventionally known method.

  According to one embodiment of the present invention, first, a slurry containing a negative electrode active material is applied to one surface of a current collector and dried to form a negative electrode active material layer. Thereafter, a slurry containing lithium particles and an insulating material is applied onto the negative electrode active material layer and dried to form a protective layer, thereby manufacturing the negative electrode for a lithium ion secondary battery. By such a production method, it is possible to easily obtain a negative electrode for a lithium ion secondary battery that can suppress excessive reaction between lithium and the negative electrode active material, suppress reaction heat, and prevent an increase in resistance.

(Formation of negative electrode active material layer)
First, a negative electrode active material layer slurry is prepared by dispersing a mixture containing a negative electrode active material, a conductive agent and a negative electrode material such as a binder in a slurry viscosity adjusting solvent. When using a binder, you may mix with solid content, such as a negative electrode active material, in the slurry for negative electrode active material layers by the method of mixing by adding a solvent after mixing in a powder state. Or you may mix in the slurry for negative electrode active material layers by the method of dissolving in a small amount of solvent previously, and adding to the mixture containing an active material and a solvent.

  The slurry viscosity adjusting solvent for the negative electrode active material layer is not particularly limited, and for example, N-methyl-2-pyrrolidone (NMP), dimethylformamide, dimethylacetamide, methylformamide and the like can be used. The slurry for negative electrode active material layer is prepared from a solvent and solid content using a homogenizer or a kneading apparatus.

  Next, the negative electrode active material layer slurry is applied to the surface of the current collector. The application means for applying the negative electrode active material layer slurry to the current collector is not particularly limited. For example, commonly used means such as a self-propelled coater, a doctor blade method, and a spray method may be employed. In addition, when screen printing, an ink jet method, a doctor blade method, or a combination thereof is used as the application unit, a thin layer can be formed.

  Subsequently, the coating film formed on the surface of the current collector is dried. Thereby, the solvent in a coating film is removed. Thereby, the solvent in a coating film is removed. The drying conditions are not particularly limited, and may be set as appropriate according to the amount of slurry applied and the volatilization rate of the solvent in the slurry, and the organic solvent may be removed. The drying means is not particularly limited, and conventionally known knowledge about electrode production can be referred to as appropriate. Examples thereof include use of a vacuum dryer and heat treatment. The drying conditions can be, for example, 40 to 150 ° C. and 5 minutes to 20 hours. 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.

  Thereby, a negative electrode active material layer is formed on the surface of the current collector.

(Protective layer formation)
A protective layer is formed on the negative electrode active material layer produced as described above. First, the lithium particles constituting the protective layer and the insulating material are introduced into an organic solvent and mixed together with other components such as a binder as necessary to obtain a slurry for the protective layer. Each component is as described above.

  The organic solvent is not particularly limited, but benzene, toluene, xylene, acetone, diethyl ether, methyl ethyl ketone, tetrahydrofuran, dioxane, hexane, N-methyl-2-pyrrolidone (NMP), dimethylformamide, dimethylacetamide, and methylformamide can be used. preferable.

  The protective layer slurry is applied onto the negative electrode active material layer to form a protective layer coating. The application means for applying the slurry is not particularly limited, but a thin layer can be formed by using screen printing, an inkjet method, a doctor blade method, a spray coating method, a die coating method, a comma coating method, or a combination thereof.

  The lithium particles in the protective layer naturally come into contact with the negative electrode active material layer if the slurry mixed with the lithium particles is applied to an appropriate thickness by these methods. In order to make the lithium particles more easily contact the negative electrode active material layer, for example, a protective layer slurry can be formed by combining a small particle size insulating material powder and a relatively large particle size lithium particle. If it does in this way, when applying slurry, since lithium particles will sink relatively relatively, lithium particles are easy to be located in the anode active material layer side. The combination of the particle sizes of the lithium particles and the insulating material at this time varies depending on the coating method and the drying conditions of the solvent, and may be appropriately selected at the time of production.

  After the slurry application, the whole negative electrode is dried to complete the protective layer. The drying conditions are not particularly limited, and may be set as appropriate according to the amount of slurry applied and the volatilization rate of the solvent in the slurry, and the organic solvent may be removed. The drying means is not particularly limited, and conventionally known knowledge about electrode production can be referred to as appropriate. Examples thereof include use of a vacuum dryer and heat treatment. The drying conditions can be, for example, 40 to 150 ° C. and 5 minutes to 20 hours.

  In this embodiment, since lithium particles are used for forming the protective layer, it can be applied in a slurry form by a conventionally known means, and the lithium particles are easily and uniformly dispersed on the negative electrode active material layer. be able to. Furthermore, since the insulating material can also be prepared as a powder, excessive application of lithium can be uniformly suppressed on the negative electrode active material layer by coating with lithium particles.

[battery]
The negative electrode for a lithium ion secondary battery according to the above embodiment can be used for a lithium ion secondary battery. That is, one embodiment of the present invention is a lithium ion secondary battery configured by the lithium ion secondary battery negative electrode according to the above embodiment. The structure and form of the lithium ion secondary battery are not particularly limited, such as a stacked battery or a bipolar battery, and can be applied to any conventionally known structure. Hereinafter, the overall structure of the lithium ion secondary battery of the present embodiment will be described.

(Non-bipolar battery lithium-ion secondary battery)
FIG. 2 shows a typical embodiment of a lithium ion secondary battery of the present invention, which is a non-bipolar flat (stacked) lithium ion secondary battery (hereinafter simply referred to as a non-bipolar lithium ion secondary battery). FIG. 2 is a schematic cross-sectional view schematically showing the overall structure of a non-bipolar secondary battery).

  As shown in FIG. 2, the non-bipolar lithium ion secondary battery 10 of the present embodiment has a configuration in which the power generation element 17 is housed and sealed using a battery exterior material 22. Here, the power generation element 17 is a positive electrode plate in which the positive electrode active material layer 12 is formed on both surfaces of the positive electrode current collector 11, the electrolyte layer 13, and both surfaces of the negative electrode current collector 14 (for the lowermost layer and the uppermost layer of the power generation element). The negative electrode plate in which the negative electrode active material layer 15 and the protective layer 23 are formed is laminated on one side. The negative electrode for a lithium ion secondary battery of the present embodiment is included in the configuration of this negative electrode plate. At the time of lamination, the positive electrode active material layer 12 on one surface of one positive electrode plate and the negative electrode active material layer 15 including the protective layer 23 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.

  Thus, the negative electrode active material layer 15 including the adjacent positive electrode active material layer 12, electrolyte layer 13, and protective layer 23 constitutes a single 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 active material layer 12 is formed on only one side of the outermost positive electrode current collector 11 a located in both outermost layers of the power generation element 17. In addition, you may change arrangement | positioning of FIG. 2, a positive electrode plate, and a negative electrode plate. In that case, the outermost layer negative electrode current collector (not shown) is positioned on both outermost layers of the power generation element 17, and in the case of the outermost layer negative electrode current collector, the negative electrode active member provided with the protective layer 23 only on one side. The material layer 15 is formed.

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 or resistance welding. Thus, the positive electrode tab 18 and the negative electrode tab 19 that are electrically connected to the positive electrode current collector 11 and the negative electrode current collector 14 have a structure exposed to the outside of the battery exterior material 22. (Bipolar battery lithium ion secondary battery)
FIG. 3 shows another typical embodiment of the lithium battery of the present invention, which is a bipolar flat type (stacked type) lithium ion secondary battery (hereinafter simply referred to as a bipolar lithium ion secondary battery or a bipolar type). 1 is a schematic cross-sectional view schematically showing the entire structure of a secondary battery.

  As shown in FIG. 3, the bipolar lithium ion secondary battery 30 of the present embodiment has a structure in which a power generation element 37 in which a charge / discharge reaction actually proceeds is sealed inside a battery exterior member 42. As shown in FIG. 3, the power generation element 37 of the bipolar secondary battery 30 of the present embodiment has an electrolyte layer 35 sandwiched between two or more bipolar electrodes 34, and the positive electrode active of adjacent bipolar electrodes 34. The material layer 32 and the negative electrode active material layer 33 including the protective layer 44 are opposed to each other with the electrolyte layer 35 interposed therebetween. Here, the bipolar electrode 34 has a structure in which the positive electrode active material layer 32 is provided on one surface of the current collector 31 and the negative electrode active material layer 33 and the protective layer 44 are provided on the other surface. That is, the positive electrode active material layer is formed on one surface of the current collector of the negative electrode for the lithium ion secondary battery of the present embodiment. In the bipolar secondary battery 30, a bipolar electrode 34 having a positive electrode active material layer 32 on one surface of a current collector 31 and a negative electrode active material layer 33 having a protective layer 44 on the other surface, A power generation element 37 having a structure in which a plurality of layers are stacked via an electrolyte layer 35 is provided.

  The negative electrode active material layer 33 including the adjacent positive electrode active material layer 32, electrolyte layer 35, and protective layer 44 constitutes a single battery layer 36. Therefore, it can be said that the bipolar secondary battery 30 has a configuration in which the single battery layers 36 are stacked. In addition, an insulating layer 43 is disposed on the periphery of 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 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 active material layer 32 and the negative electrode active material layer 33) can be prevented.

  The positive electrode 34a and the negative electrode 34b located in the outermost layer of the power generation element 37 may not have a bipolar electrode structure. For example, a structure in which the negative electrode active material layer 33 including the positive electrode active material layer 32 or the protective layer 44 on only one side necessary for the current collectors 31a and 31b may be provided. Specifically, as shown in FIG. 3, a positive electrode active material layer 32 may be formed on only one side of the positive electrode side outermost layer current collector 31a located in the outermost layer of the power generation element 37. Good. Similarly, the negative electrode active material layer 33 including the protective layer 44 on only one side may be formed on the negative electrode side outermost layer current collector 31b located in the outermost layer of the power generation element 37. In the bipolar lithium ion secondary battery 30, current collector plates 38 a and 39 b are provided on the outer sides of the positive electrode side outermost layer current collector 31 a and the negative electrode side outermost layer current collector 31 b at the upper and lower ends, respectively. The current collecting plates 38 a and 39 b are extended to be a positive electrode tab 38 and a negative electrode tab 39, respectively. The current collecting plates 38a and 39b may be joined via a positive terminal lead and a negative terminal lead as necessary. Further, the positive electrode side outermost layer current collector 31 a may be extended to form a positive electrode tab 38, which 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.

Also, the bipolar lithium ion secondary battery 30 may have a structure in which the power generation element 37 is sealed in the battery outer packaging material 42 under reduced pressure, and the positive electrode tab 38 and the negative electrode tab 39 are taken out of the battery outer packaging material 42. This is because such a structure can prevent external impact and environmental degradation during use. The basic configuration of the bipolar lithium ion secondary battery 30 can be said to be a configuration in which a plurality of stacked unit cell layers 36 are connected in series. [Positive electrode]
[Positive electrode active material layer]
The positive electrode active material layer includes a positive electrode active material, and further includes a conductive agent, a binder, an electrolyte, an electrolyte supporting salt, and the like as necessary. Since the components other than the positive electrode active material among the components of the positive electrode active material layer are the same as those described above, the description thereof is omitted here. The compounding ratio of the components contained in the positive electrode active material layer and the thickness of the positive electrode active material layer are not particularly limited, and conventionally known knowledge about the lithium ion secondary battery can be appropriately referred to.

The positive electrode active material is not particularly limited as long as it is a material capable of occluding and releasing lithium, and a positive electrode active material usually used for a lithium ion secondary battery can be used. 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 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 this application, the average particle diameter of the active material is a value measured by laser diffraction particle size distribution measurement (laser diffraction scattering method).

  Moreover, the content of the active material in the positive electrode active material layer is preferably 70 to 98% by mass, more preferably 80 to 98% by mass with respect to the total mass of the active material layer. If the content of the active material is within the above range, it is preferable because the energy density can be increased.

  The thickness of the positive electrode active material layer is preferably 20 to 500 μm, more preferably 20 to 300 μm, and still more preferably 20 to 150 μm.

  Other materials may be included in the positive electrode active material layer. For example, a binder, a conductive agent, a supporting salt (lithium salt), and the like may be included. What was illustrated in the column of the said negative electrode active material layer can be used similarly for a binder, a electrically conductive agent, and support salt. In addition, the blending ratio of these components is not particularly limited, and can be adjusted by appropriately referring to known knowledge about the lithium ion secondary battery.

[Electrolyte layer]
The electrolyte layer is a layer containing a non-aqueous electrolyte. A nonaqueous electrolyte (specifically, a lithium salt) contained in the electrolyte layer has a function as a carrier of lithium ions that moves between the positive and negative electrodes during charge and discharge. The nonaqueous electrolyte is not particularly limited as long as it can exhibit such a function, but a liquid electrolyte or a polymer electrolyte may be used.

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 that can be used as the plasticizer include cyclic carbonates such as propylene carbonate (PC), ethylene carbonate (EC), dimethyl carbonate (DMC), and diethyl carbonate (DEC); dimethyl carbonate, methyl ethyl carbonate, diethyl Chain carbonates such as carbonate; ethers such as tetrahydrofuran, 2-methyltetrahydrofuran, 1,4-dioxane, 1,2-dimethoxyethane, 1,2-dibutoxyethane; lactones such as γ-butyrolactone; acetonitrile, etc. Nitriles; esters such as methyl propionate; amides such as dimethylformamide; plastics such as aprotic solvents in which at least one selected from methyl acetate and methyl formate is mixed Such as those used (organic solvent) can be used. These organic solvents may be used alone or in combination of two or more. As the supporting salt (lithium _{salt), Li (CF 3 SO 2} ) 2 N, Li (C 2 F 5 SO 2) 2 N, LiPF 6, LiBF 4, LiAsF 6, LiTaF 6, LiClO 4, LiCF 3 Compounds that can be added to the electrode mixture layer, such as SO _3, can be employed as well.

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

  The gel polymer electrolyte has a configuration in which the liquid electrolyte is injected into a matrix polymer (host polymer) made of an ion conductive polymer. Using a gel polymer electrolyte as the electrolyte is superior in that the fluidity of the electrolyte is lost and it is easy to block the ion conductivity between the layers. The ion conductive polymer used as the matrix polymer (host polymer) is not particularly limited. For example, polyethylene oxide (PEO), polypropylene oxide (PPO), polyvinylidene fluoride (PVDF), a copolymer of polyvinylidene fluoride and hexafluoropropylene (PVDF-HFP), polyethylene glycol (PEG), polyacrylonitrile (PAN), Examples thereof include polymethyl methacrylate (PMMA) and copolymers thereof. Here, the ion conductive polymer may be the same as or different from the ion conductive polymer used as the electrolyte in the positive electrode mixture layer and the negative electrode mixture layer, but is preferably the same. . The type of the electrolytic solution (electrolyte salt and plasticizer) is not particularly limited, and an electrolyte salt such as the lithium salt exemplified above and a plasticizer such as carbonates may be used.

  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, by using an intrinsic polymer electrolyte as the electrolyte, there is no fear of liquid leakage from the battery, and the battery reliability can be improved.

  The matrix polymer of gel polymer electrolyte or intrinsic polymer electrolyte can express 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.

  The non-aqueous electrolyte contained in these electrolyte layers may be one kind alone, or two or more kinds.

  In addition, when an electrolyte layer is comprised from a liquid electrolyte or a gel polymer electrolyte, a separator is used for the electrolyte layer. Specific examples of the separator include a microporous film made of polyolefin such as polyethylene or polypropylene.

  It can be said that the thinner the electrolyte layer, the better to reduce the internal resistance. The thickness of the electrolyte layer is 1 to 100 μm, preferably 5 to 50 μm.

[tab]
The material of the tab (positive electrode tab and negative electrode tab) can be aluminum, copper, nickel, stainless steel, alloys thereof, or the like. These are not particularly limited, and known materials conventionally used as tabs can be used.

[Battery exterior materials]
In a lithium ion secondary battery, it is desirable that the entire power generating element on which the electrolyte holding layer is formed is accommodated in a battery exterior material or a battery case in order to prevent external impact and environmental degradation during use. As a battery exterior material, a conventionally known metal can case can be used, and a bag-like case that can cover a power generation element using a laminate film containing aluminum can be used. Since the laminate sheet has a high degree of freedom in shape, it can be suitably applied to a battery using a negative electrode material having a large expansion and contraction in addition to being easily mounted in a narrow space.

  Since the metal can case type exterior body has strength, it can absorb even if the power generation element in the can expands and contracts somewhat, and the thickness of the cell does not change. Moreover, it is possible to obtain a can case having a desired strength and size by examining the material of the can, the design of the plate thickness, the clearance between the outer can and the power generation element, and the like.

  The polymer-metal composite laminate sheet is not particularly limited, and a conventionally known sheet formed by arranging a metal film between polymer films and laminating and integrating the whole can be used. Specifically, it is arranged as an outer protective layer (laminated outermost layer) made of a polymer film, a metal film layer, a heat-sealing layer (laminated innermost layer) made of a polymer film, and the whole is laminated and integrated. Is mentioned.

  Among these, it is particularly preferable to use an aluminum laminate film outer package having a high degree of freedom in shape. In this embodiment, “aluminum laminate” refers to a laminate containing aluminum. Specific examples of the aluminum laminate film include, but are not limited to, a laminate film having a three-layer structure in which polypropylene (PP), aluminum, and nylon (registered trademark) are laminated in this order. It is not a thing.

[Insulation layer]
Insulating layer (sealing part) prevents bipolar current collectors in a bipolar lithium-ion secondary battery from coming into contact with each other and short-circuiting due to slight unevenness at the end of the laminated electrode. In order to do so, it is arranged at the periphery of the cell layer. As the insulating layer, any insulating layer may be used as long as it has insulating properties, sealing properties against dropping 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 and 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.

[Battery manufacturing method]
The method for producing the lithium ion secondary battery of the present embodiment is not particularly limited, and can be produced by applying a conventionally known method.

  According to another aspect of the present invention, a lithium ion secondary comprising the steps of: producing a power generation element using the negative electrode for a lithium ion secondary battery produced by the above method; and aging the power generation element. A method for manufacturing a battery is provided.

(Production process of power generation element)
For example, in the case of a stacked battery, first, a positive electrode and a negative electrode are prepared. What is necessary is just to produce the negative electrode for lithium ion secondary batteries using the method mentioned above as a negative electrode. For the positive electrode, similarly to the negative electrode, a slurry for an electrode active material layer is prepared by dispersing a mixture of electrode slurries containing electrode materials such as an active material, a conductive agent and a binder in a slurry viscosity adjusting solvent. Next, the positive electrode active material layer slurry is applied to both sides of the current collector, and then dried and pressed.

  Next, the unit cell may be manufactured by stacking the positive electrode and the negative electrode so as to face each other with a separator interposed therebetween. Then, the stacking of separators and electrodes is repeated until the number of single cells reaches a desired number. According to such a manufacturing method, a separator can be formed by a simpler method, and a power generation element having high adhesion between the separator and the active material layer can be produced.

  Then, each positive electrode and negative electrode are bundled and leads are welded, and this laminate is placed in an aluminum laminate film bag with a structure in which the positive and negative electrode leads are taken out, and an electrolytic solution is injected with a liquid injector. The end is sealed under reduced pressure to obtain a battery.

  In the above description, the laminated battery in which the electrolyte is a liquid electrolyte has been described as an example. However, the production of a laminated battery in the case of using a gel electrolyte or an intrinsic polymer electrolyte can also be performed with reference to a known technique. And is omitted here.

(Aging process)
The battery thus obtained is aged for a predetermined time (still after the electrolyte is injected). Thereby, lithium particles present in the protective layer are ionized and diffused throughout the negative electrode active material layer, and are pre-occluded (pre-doped). By having an aging process, the lithium dope amount per unit area in the active material layer can be made uniform, and a battery with improved reliability can be obtained.

  The aging temperature is preferably 20 to 80 ° C., more preferably 40 to 60 ° C. from the viewpoint of increasing the dope rate. The aging time varies depending on the amount of active material and the amount of pre-doping. Therefore, the voltage of the battery after aging may be appropriately determined so as to be a desired level, but it is usually about 24 to 120 hours.

  The voltage of the battery after the aging process varies depending on the cell design, that is, the pre-doping amount. Preferably, it is preferably 1.0 V or more and 3.2 V or less, and more preferably 1.2 to 3.0 V. When the voltage is in such a range, lithium is sufficiently pre-doped in the active material layer.

  In the present embodiment, the aging process is not necessarily required, and the pre-occlusion (pre-doping) may be performed by performing the first charge / discharge after the assembly of the battery as in the conventional case. In this case, the battery manufacturing time can be shortened.

[Battery]
The present embodiment also provides an assembled battery using a battery incorporating the negative electrode of the present embodiment.

  The assembled battery of the present embodiment is configured by connecting a plurality of lithium ion secondary batteries having the above-described configuration. 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 this embodiment, a non-bipolar lithium ion secondary battery and a bipolar lithium ion secondary battery are used, and a plurality of these are combined in series, in parallel, or in series and parallel. An assembled battery can also be configured.

  FIG. 4 is an external view of a typical embodiment of the assembled battery according to the present embodiment. 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, the assembled battery 300 according to the present embodiment forms a small assembled battery 250 in which a plurality of lithium ion secondary batteries are connected in series or in parallel to be detachable. The battery pack 300 may further include a plurality of possible small battery packs 250 connected in series or in parallel. The small assembled batteries 250 that can be attached and detached are connected to each other using an electrical connection means such as a bus bar, and the assembled batteries 250 are stacked in multiple stages using a connection jig 310.

[vehicle]
The present embodiment also provides a vehicle equipped with the battery or the assembled battery.

  The vehicle according to the present embodiment is characterized by mounting the lithium ion secondary battery according to the present embodiment or an assembled battery formed by combining a plurality of these. When the high-capacity positive electrode according to the present embodiment 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 secondary battery of the present embodiment or the assembled battery formed by combining a plurality of these can be used as a power source for driving the vehicle. This is because the use of the lithium ion secondary battery of the present embodiment or the assembled battery formed by combining a plurality of these batteries in a vehicle provides a long-life and highly reliable automobile. For example, if the vehicle is a car, it is a hybrid car, a fuel cell car, an electric car (all include four-wheeled vehicles (passenger cars, trucks, buses and other commercial vehicles, light vehicles, etc.), two-wheeled vehicles (motorcycles) and tricycles). including. 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 embodiment. 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 this embodiment can be widely applied to a hybrid vehicle, a fuel cell vehicle, and the like in addition to the electric vehicle as shown in FIG.

  Hereinafter, the present invention will be described through examples.

Example 1
(Preparation of negative electrode)
As the negative electrode active material, 86 parts by mass of silicon monoxide having an average particle diameter of 8 μm, 8 parts by mass of acetylene black as a conductive agent, and 8 parts by mass of an NMP solution of polyamic acid as a binder were used. NMP was used as a solvent.

  First, high purity anhydrous NMP was charged into a dispersing mixer. Next, a negative electrode active material, a conductive agent, and a binder were added and mixed. Thereafter, a solvent was appropriately added to adjust the viscosity, and a negative electrode active material layer slurry was obtained.

The obtained negative electrode active material layer slurry was applied to 12 mg / cm ^{2 on} both surfaces of a 20 μm-thick copper foil as a negative electrode current collector using a coating apparatus. Then, it dried at 100 degreeC for 0.5 hour, and pressed with the roll press. Then, the imidation process of the binder was performed at 350 degreeC under pressure reduction of 10 Pa for 5 hours. In this way, a negative electrode having a thickness of 70 μm was obtained.

A protective layer was formed on the negative electrode active material layer as follows. First, alumina powder having an average particle diameter of 2 μm (true density 3.97 g / cm ³ ), lithium powder having an average particle diameter of 20 μm (true density 0.54 g / cm ³ ), styrene-butadiene rubber (SBR), and xylene are obtained in 88. The mixture was put into a dispersing mixer at a mass ratio of 8: 7.2: 4: 100. This was mixed to obtain a slurry for the protective layer. This protective layer slurry was applied onto the negative electrode active material layer formed as described above using a coating apparatus. Thereafter, the coating film was dried at 80 ° C. for 0.5 hour to complete a protective layer having a thickness of 5 μm.

  The volume ratio of the lithium particles in the protective layer to the insulating material was calculated from the true density of the lithium particles and the insulating material. The true density was measured by a pycnometer method using He gas.

Furthermore, a polyolefin microporous membrane (thickness 25 μm) was prepared as a separator. As a solvent for the electrolytic solution, ethylene carbonate (EC) and dimethyl carbonate (DMC) were mixed at a volume ratio of 1: 1. A solution obtained by dissolving LiPF ₆ as a supporting salt at a concentration of 1.0 mol / L was prepared in this mixed solution, and used as an electrolytic solution.

(Preparation of positive electrode)
86 parts by mass of lithium nickelate having an average particle size of 5 μm was used as the positive electrode active material, 8 parts by mass of polyvinylidene fluoride (PVdF) as the binder, and 8 parts by mass of acetylene black as the conductive agent. N-methyl-2-pyrrolidone (NMP) was used as the solvent.

  First, high purity anhydrous NMP was charged into a dispersing mixer. Next, PVdF was added and sufficiently dissolved in the NMP solvent. Thereafter, the positive electrode active material and the conductive agent were added little by little, and a viscosity was adjusted by adding a solvent as appropriate to obtain a slurry for the positive electrode active material layer.

The resulting positive electrode active material layer slurry, using a coating apparatus, and 60 mg / cm ² applied to both sides of an aluminum foil having a thickness of 20μm as a current collector. Then, it dried at 100 degreeC for 0.5 hour, and pressed with the roll press. In this way, a positive electrode having a thickness of 200 μm was obtained.

(Power generation element production)
The negative electrode, the separator, and the positive electrode obtained as described above were repeatedly stacked in this order using a jig so as not to cause positional displacement, and finally the negative electrode was stacked to produce a power generation element. Each member used was 5 positive electrodes, 6 negative electrodes and 12 separators.

  The electrode tab portion of the current collector was ultrasonically welded with an aluminum tab in the case of the positive electrode and a nickel tab in the case of the negative electrode, thereby making an electrical connection. Next, the power generation element was placed in an aluminum laminate film that had been previously formed into the size of the power generation element, leaving one piece into which the electrolyte was injected, and the remaining three sides were heat-sealed. A predetermined amount of electrolytic solution was injected from the opened port, and the separator was impregnated with the electrolytic solution. Then, the remaining one side was heat-sealed and sealed in a vacuum to complete a lithium ion secondary battery.

(Charge / discharge performance test)
Each evaluation cell produced by the above method was aged in a 50 ° C. atmosphere for 72 hours. The voltage of the battery after aging was 3.0V. Thereby, lithium in the lithium pre-doped layer is doped into the negative electrode active material layer.

  The charge / discharge performance of the produced lithium ion secondary battery was evaluated by the following energy density measurement and output measurement. The respective measurement results are shown in Table 1 below.

  1) For energy density measurement, the manufactured lithium ion secondary battery was charged with constant current and constant voltage (CCCV) at 0.5 C and 4.2 V for 3 hours and rested for 30 minutes. Thereafter, constant current discharging (CC) was performed at 0.5 C, and the operation was stopped when the voltage reached 2.5 V. The discharge capacity up to the stop was measured and integrated, and the battery divided by the mass of the lithium ion secondary battery was defined as the energy density (Wh / kg) of the battery. An energy density of 280 or more was considered good, and an energy density of 300 or more was considered best.

  Here, C indicates a time rate. Here, the time rate 1C refers to an amount of current sufficient to charge / discharge the entire capacity of the battery in one hour. For example, a current of 0.5 C refers to an amount of current that charges / discharges the entire capacity of the battery in 2 hours (= 1 / 0.5 hour).

  2) For the output measurement, the manufactured lithium ion secondary battery was charged with constant current and constant voltage (CCCV) at 0.5 C and 4.2 V for 3 hours and rested for 30 minutes. Thereafter, constant current discharge (CC) was performed at 0.5 C, and the battery was discharged to half of the discharge capacity obtained in 1), and the depth of charge was adjusted to 50%. Next, constant current discharge was performed at 0.5 C for 10 seconds. The output (W) was obtained from the voltage drop ΔV due to the discharge for 10 seconds and the current value, and divided by the mass of the lithium ion secondary battery was defined as the battery output density (W / kg). The power density was good if it was 3.0 or higher, and the best if 3.3 or higher.

(Presence or absence of contact between lithium particles and negative electrode active material layer)
The presence or absence of contact between the lithium particles in the protective layer and the negative electrode active material layer was evaluated as follows. First, the manufactured negative electrode was cut, and the cross section was observed at 500 times with a scanning electron microscope (SEM). If the lithium particles in contact with the negative electrode active material layer were 80% or more of all lithium particles in the observed image, it was determined that there was contact. The evaluation results are shown in Table 1 below.

(Presence or absence of contact between the lithium particles and the insulating material)
The presence / absence of contact between the lithium particles in the protective layer and the insulating material, that is, whether or not the lithium particles are separated by the insulating material was evaluated as follows. First, the manufactured negative electrode was cut, and the cross section was observed at 500 times with a scanning electron microscope (SEM). If all lithium particles in the observed image had 80% or more of lithium particles in contact with the insulating material, contact was made. The evaluation results are shown in Table 1 below.

(Porosity of protective layer after charge / discharge)
The porosity of the protective layer was determined by the following method after taking out the negative electrode after charge and discharge. First, the porosity of the whole negative electrode was measured with a mercury porosimeter. Next, the binder of the protective layer was dissolved with a solvent to remove the protective layer, and the porosity of the remaining part of the negative electrode was measured. The porosity of only the protective layer was calculated from these two porosity.

(Contact area)
The contact area between the lithium particles and the negative electrode active material layer in the protective layer was evaluated based on the contact area between the lithium particles and the negative electrode active material layer being several times the total surface area of the lithium particles. The evaluation result was obtained by image analysis from an observation image obtained by cutting the manufactured negative electrode and observing the cross section at 500 times with a scanning electron microscope (SEM). The measurement results are shown in Table 1 below.

(Example 2)
In Example 2, a lithium ion secondary battery was produced and evaluated in the same manner as in Example 1 except that the mixing ratio of alumina and lithium powder in the protective layer slurry was changed. The mixing ratio is shown as the ratio (vol%) of lithium particles to the insulating material in Table 1 below. The evaluation results are also shown in Table 1.

(Example 3)
In Example 3, a lithium ion secondary battery was produced and evaluated in the same manner as in Example 1 except that the mixing ratio of alumina and lithium powder in the protective layer slurry was changed. The mixing ratio is shown as the ratio (vol%) of lithium particles to the insulating material in Table 1 below. The evaluation results are also shown in Table 1.

Example 4
In Example 4, a lithium ion secondary battery was produced and evaluated in the same manner as in Example 1 except that the mixing ratio of alumina and lithium powder in the protective layer slurry was changed. The mixing ratio is shown as a ratio (vol%) of the lithium particles to the insulating material in Table 1 below. The evaluation results are also shown in Table 1.

(Example 5)
In Example 5, a lithium ion secondary battery was produced and evaluated in the same manner as in Example 1 except that the thickness of the protective layer was 15 μm. The mixing ratio is shown as the ratio (vol%) of lithium particles to the insulating material in Table 1 below. The evaluation results are also shown in Table 1.

(Example 6)
In Example 6, a lithium ion secondary battery was produced and evaluated in the same manner as in Example 1 except that the mixing ratio of alumina and lithium powder in the protective layer slurry was changed. The mixing ratio is shown as the ratio (vol%) of lithium particles to the insulating material in Table 1 below. The evaluation results are also shown in Table 1.

(Example 7)
In Example 7, a lithium ion secondary battery was prepared and evaluated in the same manner as in Example 1 except that the mixing ratio of alumina and lithium powder in the protective layer slurry was changed. The mixing ratio is shown as the ratio (vol%) of lithium particles to the insulating material in Table 1 below. The evaluation results are also shown in Table 1.

(Example 8)
In Example 8, a lithium ion secondary battery was prepared and evaluated in the same manner as in Example 1 except that the mixing ratio of alumina and lithium powder in the protective layer slurry was changed. The mixing ratio is shown as the ratio (vol%) of lithium particles to the insulating material in Table 1 below. The evaluation results are also shown in Table 1.

Example 9
In Example 9, a lithium ion secondary battery was prepared and evaluated in the same manner as in Example 1 except that the thickness of the protective layer was 30 μm. The evaluation results are shown in Table 1 below.

(Example 10)
In Example 10, a lithium ion secondary battery was produced and evaluated in the same manner as in Example 1 except that the thickness of the protective layer was 40 μm. The evaluation results are shown in Table 1 below.

(Example 11)
In Example 11, a lithium ion secondary battery was produced and evaluated in the same manner as in Example 1 except that the thickness of the protective layer was 45 μm. The evaluation results are shown in Table 1 below.

(Comparative Example 1)
In Comparative Example 1, a lithium ion secondary battery was produced and evaluated in the same manner as in Example 1 except that the protective layer was not provided. The evaluation results are shown in Table 1 below.

(Comparative Example 2)
In Comparative Example 2, the protective layer has a two-layer structure, and the protective layer is formed so that the lithium particles do not contact the insulating material. First, as the first layer, a layer containing lithium particles and alumina is formed on the negative electrode active material layer, and then, as the second layer, an alumina-only layer similar to that in Example 1 is used except that the lithium particles are not included. At this time, the volume ratio of lithium particles and alumina combined with the first layer and the second layer was the same as in Example 1. A lithium ion secondary battery was prepared and evaluated in the same manner as in Example 1 except that the protective layer was changed to two layers. The evaluation results are shown in Table 1 below.

(Comparative Example 3)
In Comparative Example 3, the protective layer has a two-layer structure, and the protective layer is formed so that the lithium particles and the negative electrode active material layer do not contact each other. First, as the first layer, an alumina-only layer similar to that of Example 1 except that lithium particles were not included was formed on the negative electrode active material layer, and then a layer containing lithium particles and alumina was formed as the second layer. . At this time, the volume ratio of the lithium particles combined with the first layer and the second layer to alumina was the same as in Example 1. A lithium ion secondary battery was prepared and evaluated in the same manner as in Example 1 except that the protective layer was changed to two layers. The evaluation results are shown in Table 1 below.

(Comparative Example 4)
In Comparative Example 4, a lithium ion secondary battery was produced and evaluated in the same manner as in Example 1 except that no insulating material was used. The evaluation results are shown in Table 1 below.

  As the results in Table 1 show, all of the lithium ion secondary batteries of the present invention showed very good charge / discharge performance. In contrast to the example, in Comparative Example 1, since there was no protective layer containing lithium particles, lithium was not preliminarily occluded and the energy density was low. In Comparative Example 2, the insulating material was not dispersed between the lithium particles in the protective layer, the insulation in the protective layer was insufficient, and the exothermic reaction could not be sufficiently suppressed. As a result, both energy density and power density decreased. In Comparative Example 3, since the lithium particles in the protective layer were not in contact with the negative electrode active material layer, lithium was not pre-occluded, and both the energy density and the output density were reduced. In Comparative Example 4, since the protective layer did not contain an insulating material, an exothermic reaction occurred during the initial charge, and both the energy density and the power density were reduced.

  Comparing Comparative Examples 1 and 3 with Examples, the battery having the negative electrode of the present invention has excellent charge / discharge performance due to the provision of the protective layer and the lithium particles being in contact with the negative electrode active material layer. It can be seen that

  Comparing Comparative Examples 2 and 4 with Examples, it can be seen that the exothermic reaction is effectively suppressed due to the presence of the insulating material between the lithium particles.

  Moreover, when Examples 1-10 are compared with Example 11, it turns out that it is more excellent in charging / discharging performance as the protective layer thickness is 5-40 micrometers.

  When Examples 6 and 8 are compared with Examples 1 to 5, 7, and 9 to 11, it can be seen that a higher output density can be obtained if the porosity of the protective layer is 30 to 60%.

  The graph which shows the relationship between the energy density of the lithium ion secondary battery in Examples 1-11 and the volume ratio with respect to the insulating material of the lithium particle of a protective layer is shown in FIG. The lithium ion secondary batteries of the examples all have a good energy density of 3.0 or more. However, it can be seen that if the volume ratio of the lithium particles to the insulating material is 60 to 100% centering on 80%, the energy density tends to be higher.

DESCRIPTION OF SYMBOLS 1 Current collector 2 Negative electrode active material layer 3 Protective layer 4 Lithium particle 5 Insulating material 6 Negative electrode active material 10a Non-bipolar lithium ion secondary 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,
14a outermost layer negative electrode current collector,
15, 33 negative electrode active material layer,
16, 36 cell layer,
17, 37 Power generation element,
18, 38 positive electrode tab,
19, 39 negative electrode tab,
20 positive terminal lead,
21 negative terminal lead,
22, 42 Battery exterior material,
23, 44 protective layer,
30 Bipolar lithium ion secondary battery,
31, 31a, 31b current collector,
34 Bipolar electrode 34a Positive electrode 34b Negative electrode 38a, 39b Current collector 43 Insulating layer,
50 lithium ion secondary battery,
250 small battery pack,
300 battery packs,
310 connection jig,
400 Electric car.

Claims (13)

A current collector,
A negative electrode active material layer including a negative electrode active material formed on a surface of the current collector;
A protective layer including an insulating material and lithium particles formed on the negative electrode active material layer, wherein a part of the surface of the lithium particles is in contact with the negative electrode active material layer. Negative electrode.   The negative electrode for a lithium ion secondary battery according to claim 1, wherein the insulating material is interposed between the lithium particles.   3. The negative electrode for a lithium ion secondary battery according to claim 1, wherein the total volume of the lithium particles is 60 to 100 vol% of the total volume of the insulating material.   The thickness of the said protective layer is 5-40 micrometers, The negative electrode for lithium ion secondary batteries as described in any one of Claims 1-3. It said insulating material is SiO ₂ and / or _Al 2 _{O 3} a negative electrode for a lithium ion secondary battery according to any one of claims 1 to 4,.   The negative electrode for a lithium ion secondary battery according to any one of claims 1 to 5, wherein the insulating material is a powder having an average particle size of 0.05 to 40 µm. Applying a slurry containing a negative electrode active material to one surface of the current collector and drying to form a negative electrode active material layer;
Applying a slurry containing lithium particles and an insulating material on the negative electrode active material layer and drying to form a protective layer;
The manufacturing method of the negative electrode for lithium ion secondary batteries containing.   The lithium ion secondary battery using the negative electrode for lithium ion secondary batteries as described in any one of Claims 1-6, or the negative electrode for lithium ion secondary batteries manufactured by the manufacturing method of Claim 7.   The lithium ion secondary battery according to claim 8, which is a bipolar lithium ion secondary battery. The process of manufacturing an electric power generation element using the negative electrode for lithium ion secondary batteries of any one of Claims 1-6, or the negative electrode for lithium ion secondary batteries manufactured by the manufacturing method of Claim 7. ,
Aging the power generation element;
A method for producing a lithium ion secondary battery, comprising:   The method of manufacturing a lithium ion secondary battery according to claim 10, wherein the voltage of the lithium ion secondary battery after the aging step is 1.0 V or more and 3.2 V or less.   An assembled battery using the lithium ion secondary battery according to claim 8 or 9, or the lithium ion secondary battery produced by the production method according to claim 10 or 11.   A vehicle equipped with the lithium ion secondary battery according to claim 8 or 9, the lithium ion secondary battery produced by the production method according to claim 10 or 11, or the assembled battery according to claim 12.