JP2009009858A - Electrode for lithium ion secondary battery - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a means preventing electrocrystallization of lithium on the surface of an electrode and micro short circuit in the electrode for a lithium ion secondary battery. <P>SOLUTION: The electrode for the lithium ion secondary battery has a current collector, and a negative electrode active material layer formed on the current collector and containing a negative electrode active material. Absorption of lithium in the negative electrode active material layer in charging starts in earlier stages in a nearer place to the current collector. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to an electrode for a lithium ion secondary battery. In particular, the present invention relates to an improvement for improving the output characteristics 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, a lithium ion secondary battery has a positive electrode in which a positive electrode active material layer containing a positive electrode active material is applied on both sides of a positive electrode current collector and a negative electrode active material layer containing a negative electrode active material applied on both sides of the negative electrode current collector. The negative electrode is connected via an electrolyte layer and is housed in a battery case (see, for example, Patent Document 1).
JP 2003-7345 A

  In recent years, high-capacity batteries for EVs have a tendency to thicken the active material layer in order to improve capacity. In the case of a battery using such a thick film electrode, there has been a problem that in the negative electrode, lithium is electrodeposited at the first charge and a micro short circuit occurs. That is, when the lithium ion secondary battery is charged for the first time, lithium ions contained in the electrolyte layer are introduced into the negative electrode active material to cause a negative electrode reaction in which lithium ions are reduced. When used in the negative electrode active material layer, the diffusion of lithium ions in the active material layer is difficult to proceed, so the negative electrode reaction during the initial charge is concentrated in the region near the surface of the active material layer that contacts the electrolyte layer. To do. For this reason, lithium deposits on the electrode surface, causing a micro short circuit.

  Then, an object of this invention is to provide the means which suppresses the electrodeposition of lithium and a micro short circuit on the electrode surface in the electrode for lithium ion secondary batteries.

  The present inventors have conducted intensive research to solve the above problems. In that case, the negative electrode active material layer has a structure in which the negative electrode reaction at the time of charging occurs earlier in the region near the current collector than in the region near the surface in contact with the electrolyte layer. It was found that the lithium ion diffusion rate limiting of the negative electrode reaction in the above region can be solved. As a result, it was found that lithium ion electrodeposition on the negative electrode surface during the initial charge was suppressed, and a battery having excellent battery capacity could be constructed, and the present invention was completed.

  That is, the present invention is an electrode for a lithium ion secondary battery having a current collector and a negative electrode active material layer containing a negative electrode active material formed on the surface of the current collector, wherein the negative electrode active material layer The lithium ion secondary battery electrode is characterized in that the occlusion of lithium at the time of charging occurs earlier as it approaches the current collector.

  Further, the present invention is an electrode for a lithium ion secondary battery comprising a current collector and a positive electrode active material layer including a positive electrode active material formed on a surface of the current collector, wherein the positive electrode active material The lithium ion secondary battery electrode is characterized in that the lithium uptake at the time of discharge in the layer occurs earlier as it approaches the current collector.

  In the negative electrode active material layer of the electrode for a lithium ion secondary battery of the present invention, the occlusion of lithium at the time of charging occurs earlier as it approaches the current collector. Thereby, the electrodeposition which arises on the electrode surface by the diffusion control of the lithium ion in a negative electrode active material can be suppressed. Therefore, when the electrode of the present invention is used as a negative electrode of a lithium ion secondary battery, it can contribute to an increase in battery capacity.

  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 an electrode for a lithium ion secondary battery having a current collector and a negative electrode active material layer including a negative electrode active material formed on a surface of the current collector, wherein the negative electrode active material layer includes: The lithium ion secondary battery electrode is characterized in that occlusion of lithium during charging occurs earlier as the current collector approaches the current collector.

  Preferably, in the electrode for a lithium ion secondary battery of the present invention, the negative electrode active material layer is formed of two or more layers, and the reaction potential of the negative electrode active material contained in each layer with respect to lithium metal is negative electrode active material. It becomes higher toward the layer on the side of the current collector in the thickness direction of the layer.

  Hereinafter, the structure of the electrode for a lithium ion secondary battery of the present invention will be described with reference to the drawings. In the present invention, the drawings are exaggerated for convenience of explanation, and the technical scope of the present invention is not limited to the forms shown in the drawings. Also, embodiments other than the drawings may be employed.

  FIG. 1 is a schematic cross-sectional view showing an embodiment of an electrode for a lithium ion secondary battery of the present invention. The lithium ion secondary battery electrode 1 in the form shown in FIG. 1 is an electrode in which a negative electrode active material layer 3 is formed on one surface of a current collector 2. The lithium ion secondary battery electrode 1 comes into contact with the electrolyte layer 5 on the surface of the negative electrode active material layer 3 when incorporated in the battery.

  As shown in FIG. 1, a battery electrode (hereinafter, also simply referred to as “electrode”) 1 of the present invention has a negative electrode active material layer 3 containing a negative electrode active material 4a having a low reaction potential for lithium metal. (Layer 1) 3a and a current collector side layer (Layer 2) 3b including a negative electrode active material 4b having a high reaction potential with respect to lithium metal.

  In the embodiment shown in FIG. 1, the reaction potential of the negative electrode active material contained in the negative electrode active material layer 3 with lithium metal is low in the surface side layer (layer 1) 3a, and the current collector side layer (layer 2). By making it high at 3b, at the time of charging, lithium ions are easily occluded on the collector side, and as a result, lithium electrodeposition on the electrode surface can be suppressed.

  The charging characteristics of the electrode using the negative electrode active material 4a and the negative electrode active material 4b as described above are, for example, as shown in FIG. During charging, the negative electrode active material 4b reacts with lithium ions at a relatively high potential, and the negative electrode active material 4a reacts with lithium ions at a relatively low potential. In the electrode using the negative electrode active material 4b, the negative electrode reaction is started earlier, and the reaction proceeds as the charging progresses. On the other hand, an electrode using the negative electrode active material 4a can react at a potential close to that of lithium metal to obtain a high battery voltage. Therefore, in the negative electrode active material layer, when the negative electrode active material 4a is used for the surface side layer in contact with the electrolyte layer and the negative electrode active material 4b is used for the current collector side layer, the negative electrode reaction with lithium ions occurs near the electrode surface. You can avoid concentrating.

  In the electrode of the present invention, the negative electrode active material layer may be formed of two layers containing different negative electrode active materials, as shown in FIG. You may form from the single layer that the reaction potential with respect to a metal becomes high toward the said collector side in the thickness direction of a negative electrode active material layer. The thickness of the negative electrode active material layer is preferably 1 to 300 μm, more preferably 10 to 100 μm. When layers containing different negative electrode active materials are laminated, preferably, layers having a thickness of 1 to 200 μm, more preferably 10 to 100 μm, are laminated.

When the negative electrode active material layer is formed of the surface side layer 1 and the current collector side layer 2 containing different negative electrode active materials, the reaction potential of the negative electrode active material contained in the layer 1 with respect to lithium metal is preferably Is 0 to 2.0 V (vs. Li ⁺ / Li), more preferably 0.1 to 1.6 V (vs. Li ⁺ / Li), still more preferably 0.1 to 1.0 V (vs. Li ⁺ / Li). The reaction potential of the negative electrode active material contained in the layer 2 with respect to lithium metal is preferably 0.2 to 3.0 V (vs. Li ⁺ / Li), more preferably 0.6 to 2.0 V (vs. Li). ⁺ / Li), and more preferably 0.8 to 1.6 V (vs. Li ⁺ / Li). If the reaction potential with respect to the lithium metal of the negative electrode active material contained in each layer is within the above range, a battery having excellent battery capacity can be obtained, and electrodeposition on the electrode surface can be effectively suppressed. Moreover, the difference of the reaction potential with respect to the lithium metal of the negative electrode active material contained in the layer 1 and the layer 2 is preferably 0.1 to 1.0 V, and more preferably 0.2 to 0.5 V.

  In the present invention, the reaction potential of the negative electrode active material with lithium metal is the reaction initiation potential of the active material and lithium ions measured by a cyclic voltammetry method using the active material as a working electrode, lithium metal as a reference electrode, and a counter electrode, etc. Means. As the reaction potential of the negative electrode active material with lithium metal, the value measured by the method of the reaction starting potential between the active material and lithium ions measured by a cyclic voltammetry method or the like is used.

  The ratio of the thickness of the layer 1 to the thickness of the layer 2 is preferably 0.1 to 10 (layer 1 / layer 2), more preferably 0.2 to 5, and further preferably 0. .5 to 2. If the film thickness ratio is in the above range, a battery having excellent battery capacity is produced.

In the case where the negative electrode active material layer is formed of three layers, that is, a surface side layer 1, a current collector side layer 3, and a layer 2 that is an intermediate layer between the layer 1 and the layer 3, the layer 1 The reaction potential of the negative electrode active material contained in the lithium metal is preferably 0 to 1.5 V (vs. Li ⁺ / Li), more preferably 0.1 to 1.0 V (vs. Li ⁺ / Li). More preferably, it is 0.1 to 0.6 V (vs. Li ⁺ / Li). The reaction potential of the negative electrode active material contained in the layer 2 with respect to lithium metal is preferably 0 to 2.0 V (vs. Li ⁺ / Li), more preferably 0.1 to 1.6 V (vs. Li ⁺ / Li). More preferably, it is 0.2 to 1.0 V (vs. Li ⁺ / Li). The reaction potential of the negative electrode active material contained in the layer 3 with respect to lithium metal is preferably 0.2 to 3.0 V (vs. Li ⁺ / Li), more preferably 0.5 to 1.6 V (vs. Li ⁺ / Li), more preferably 0.6 to 1.0 V (vs. Li ⁺ / Li). Further, the difference in reaction potential with respect to lithium metal of the negative electrode active material contained in the adjacent layer is preferably 0.1 to 1.0 V, more preferably 0.1 to 0.5 V, and The difference of the reaction potential with respect to the lithium metal of the negative electrode active material contained in the layer 3 is preferably 0.1 to 1.0 V, and more preferably 0.1 to 0.5 V. The ratio of the thickness of the layer 1 to the thickness of the layer 2 is preferably 0.1 to 10 (layer 1 / layer 2), more preferably 0.2 to 5, and further preferably 0. .5 to 2. The ratio of the thickness of the layer 2 to the thickness of the layer 3 is preferably 0.1 to 10 (layer 2 / layer 3), more preferably 0.2 to 5, and still more preferably 0. .5 to 2.

Further, the negative electrode active material layer is formed of n layers of layers 1 to n (n is an integer of 3 or more) from the surface side toward the current collector side, and the negative electrode active material contained in the layer 1 The reaction potential for lithium metal is preferably 0 to 1.5 V (vs. Li ⁺ / Li), more preferably 0.1 to 1.0 V (vs. Li ⁺ / Li), still more preferably 0.2. ~ 0.6V (vs. Li ⁺ / Li). The reaction potential with respect to the lithium metal of the negative electrode active material contained in the layers 2 to (n-1) is preferably 0 to 2.0 V (vs. Li ⁺ / Li), more preferably 0.1 to 1. 6 V (vs. Li ⁺ / Li), more preferably 0.2 to 1.0 V (vs. Li ⁺ / Li). The reaction potential of the negative electrode active material contained in the layer 3 with respect to lithium metal is preferably 0.2 to 3.0 V (vs. Li ⁺ / Li), more preferably 0.5 to 2.0 V ( Vs Li ⁺ / Li), more preferably 0.6 to 1.6 V (vs Li ⁺ / Li). The stacking number n is preferably 3 to 10 layers, and more preferably 3 to 5 layers. By laminating a large number of layers, it is possible to more effectively reduce the concentration of current on the electrode surface during the initial charge, and it is possible to produce an electrode with less electrodeposition. The difference in reaction potential with respect to lithium metal of the negative electrode active material contained in the adjacent layer is preferably 0.1 to 1.0 V, more preferably 0.1 to 0.6 V, and layer 1 and layer n The difference of the reaction potential with respect to the lithium metal of the negative electrode active material contained in is preferably 0.1 to 1.5V, and more preferably 0.2 to 1.0V.

  Further, the present invention is an electrode for a lithium ion secondary battery comprising a current collector and a positive electrode active material layer including a positive electrode active material formed on a surface of the current collector, wherein the positive electrode active material The lithium ion secondary battery electrode is characterized in that the lithium uptake at the time of discharge in the layer occurs earlier as it approaches the current collector.

  In the positive electrode of a lithium ion secondary battery, lithium ions are introduced into the active material layer during discharge, and a positive electrode reaction occurs. Therefore, in the positive electrode active material layer, the region closer to the current collector has a structure in which the positive electrode reaction at the time of discharge occurs earlier, so that lithium ions are efficiently diffused into the region near the current collector, and the first discharge Precipitation of lithium on the electrode surface can be suppressed.

  The positive electrode active material layer is preferably formed of two or more layers, and the reaction potential of the positive electrode active material contained in each layer with respect to lithium metal is directed from the surface side layer toward the current collector side layer. It has a laminated structure so as to be lowered.

  Alternatively, the positive electrode active material layer may include two or more positive electrode active materials, and a reaction potential of the positive electrode active material with respect to lithium metal may decrease from the surface side toward the current collector side. Good.

When the positive electrode active material layer is formed of the surface side layer 1 and the current collector side layer 2 containing different positive electrode active materials, the reaction potential of the positive electrode active material contained in the layer 1 with respect to lithium metal is preferably Is 1.5 to 4.5 V (vs. Li ⁺ / Li), more preferably 1.6 to 4.2 V (vs. Li ⁺ / Li), and further preferably 3 to 3.9 V (vs. Li ⁺ / Li). The reaction potential of the positive electrode active material contained in the layer 2 with respect to lithium metal is preferably 1.5 to 4.2 (vs. Li ⁺ / Li), more preferably 1.6 to 4.0 V (vs. Li). ⁺ / Li), and more preferably 2.0 to 3.9 V (vs. Li ⁺ / Li). If the reaction potential with respect to the lithium metal of the positive electrode active material contained in each layer is within the above range, a battery having excellent battery capacity can be obtained, and electrodeposition on the electrode surface during the first discharge can be effectively suppressed. Moreover, the difference in the reaction potential with respect to the lithium metal of the positive electrode active material contained in the layer 1 and the layer 2 is preferably 0.1 to 3.0V, and more preferably 0.1 to 2.0V.

  Hereinafter, the configuration of the electrode of the present invention will be described. There is no particular limitation on the selection of the current collector, active material, binder, 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. The electrode of the present invention can be applied to both the positive electrode and the negative electrode, but when applied to the negative electrode, a more remarkable effect can be obtained. When applied to the positive electrode, a compound known to act as a current collector and positive electrode active material for the positive electrode may be employed as the current collector and active material.

[Current collector]
The current collector 2 is made of a conductive material such as an aluminum foil, a nickel foil, a copper foil, or a stainless steel (SUS) foil. The general thickness of the current collector is 1 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.

[Active material layer]
An active material layer 3 is formed on the current collector 2. The active material layer 3 is a layer containing an active material that plays a central role in the charge / discharge reaction. When the electrode of the present invention is used as a positive electrode, the active material layer contains a positive electrode active material. On the other hand, when the electrode of the present invention is used as a negative electrode, the active material layer contains a negative electrode active material.

The positive electrode active material is preferably a lithium-transition metal composite oxide, a lithium-transition metal phosphate compound, or a lithium-transition metal sulfate compound. For example, LiCoO ₂ (reaction potential with respect to lithium metal: 3.8 to 4.0 V ( Li—Co based composite oxide such as Li ⁺ / Li), LiMn ₂ O ₄ (reaction potential against lithium metal: 3.0 to 4.0 V (relative to Li ⁺ / Li)) And LiNiO ₂ (reaction potential for lithium metal: 3.8 to 4.0 V (vs. Li ⁺ / Li), Li—Ni-based composite oxides, LiFePO ₄ (reaction potential for lithium metal: 3.4 V (vs. Li ⁺ / Li) etc. In some cases, two or more positive electrode active materials may be used in combination.

  As the negative electrode active material, a carbon material, the above-described lithium transition metal-composite oxide, metal material, or lithium-metal alloy material is preferable. Examples of the carbon material include graphite-based carbon materials such as natural graphite, artificial graphite, and expanded graphite, carbon black, activated carbon, carbon fiber, coke, soft carbon, and hard carbon. Examples of the metal material include lithium metal and the like, and examples of the lithium-metal alloy material include Li-Al alloy and Sn-based alloy. In some cases, two or more positive electrode active materials may be used in combination.

The negative electrode characteristics of the carbon material vary depending on the crystallinity, orientation, shape, etc. of the carbon. For example, in the case of a graphite material having an interlayer distance d002 of 0.34 nm or less, the reaction potential for lithium metal is 0.3 V or less (vs. Li ⁺ / Li), but in the case of an amorphous carbon material, lithium metal at a higher potential. React with. For example, in the electrode as shown in FIG. 1, it is preferable to use a graphite material for the layer 1 and an amorphous carbon material for the layer 2. Examples of the amorphous carbon material include hard carbon (reaction potential with respect to lithium metal: 1.0 V (vs. Li ⁺ / Li) and soft carbon (reaction potential with respect to lithium metal: 1.5 V (vs. Li ⁺ / Li)). In addition, hard carbon, soft carbon, or a precursor thereof can be fired at various temperatures to produce materials having different negative electrode characteristics, for example, hard carbon or a precursor thereof can be fired at 2000 ° C. The reaction potential of the carbon material obtained with respect to lithium metal is 1.0 V (vs. Li ⁺ / Li), but the reaction potential of the carbon material obtained by firing at 1500 ° C. with respect to lithium metal is 1.2 V (vs. Li ⁺ / Li), and the reaction potential of the carbon material obtained by firing at 1200 ° C. with respect to lithium metal is 1.5 V (vs. Li ⁺ / Li). It is.

  In particular, when the negative electrode active material layer is formed from two layers of layer 1 and layer 2 from the surface side to the current collector side, graphite material is used for layer 1 on the surface side, and hard carbon or a precursor thereof is used for layer 2. When an amorphous carbon material obtained by firing the body, preferably at 1000 to 3000 ° C., is used, the battery characteristics are particularly excellent.

  In addition, when the negative electrode active material layer is formed from three layers of layer 1, layer 2, and layer 3 from the surface side toward the current collector side, graphite material is used for surface layer 1 and hard carbon is used for layer 2. Alternatively, the precursor is preferably an amorphous carbon material fired at 1200 to 3000 ° C., and the layer 3 is hard carbon or its precursor, preferably an amorphous carbon material fired at 1000 to 2000 ° C. .

  In the case where the negative electrode active material layer is formed of four layers of layer 1, layer 2, layer 3, and layer 4 from the surface side toward the current collector side, a graphite material is applied to layer 1 on the surface side, and layer 2 Amorphous carbon material obtained by firing hard carbon or a precursor thereof, preferably at 1500 to 3000 ° C., an amorphous carbon material obtained by firing hard carbon or a precursor thereof for layer 3, preferably at 1200 to 2000 ° C., The layer 4 may be an amorphous carbon material obtained by firing hard carbon or a precursor thereof, preferably at 1000 to 1500 ° C.

  The average particle diameter of the positive electrode active material or the negative electrode active material that can be used for the electrode of the present invention is not particularly limited, but is preferably 0.1 to 50 μm, more preferably 1 to 20 μm, and particularly preferably. It is 5-10 micrometers or less. However, forms outside these ranges can also be employed. In the present application, the average particle diameter of the active material is a value measured by a laser diffraction scattering method.

  Examples of the binder include polyvinylidene fluoride (PVdF) and a synthetic rubber binder. By using the binder, the active material carried in the conductive structure can be fixed and stably held.

  The conductive auxiliary agent refers to an additive blended to improve the conductivity of the active material layer particularly in the positive electrode. Examples of the conductive aid 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.

  In the electrode of the present invention, the compounding ratio of the components contained in the positive electrode active material layer or the negative electrode active material layer is not particularly limited. The blending ratio can be adjusted by appropriately referring to known knowledge about lithium ion secondary batteries.

  When using the electrode of this invention as a negative electrode, content of the negative electrode active material contained in a negative electrode active material layer becomes like this. Preferably it is 50-99 mass%, More preferably, it is 80-98 mass%, More preferably It is 85-95 mass%.

  Moreover, when using the electrode of this invention as a positive electrode, content of the positive electrode active material contained in a positive electrode active material layer becomes like this. Preferably it is 50-99 mass%, More preferably, it is 80-95 mass%, Preferably it is 80-90 mass%.

(Production method)
The method for producing the battery electrode of the present invention is not particularly limited, and the electrode of the present invention can be produced by appropriately referring to conventionally known knowledge in the field of battery electrode production. Hereinafter, as shown in FIG. 1, an electrode 1 having an active material layer formed of a plurality of layers, in which the reaction potential of the active material contained in each layer with lithium metal increases toward the current collector side. The method will be briefly described.

  The electrode 1 can be produced, for example, by individually preparing active material slurries containing each active material, and sequentially applying and pressing the active material slurries on the surface of the current collector. Hereinafter, such a manufacturing method will be described in detail in the order of steps.

  First, a desired active material and other components (for example, a binder, a supporting salt (lithium salt), an ion conductive polymer, a polymerization initiator, and the like) are mixed in a solvent to obtain an active material slurry. Prepare. The specific form of each component blended in the active material slurry is as described in the column of the configuration of the electrode of the present invention, and thus detailed description thereof is omitted here. In order to produce the negative electrode as shown in FIG. 1, the negative electrode active material is added to the slurry. However, it is natural that the positive electrode active material should be added to the slurry to produce the positive electrode.

  The kind of solvent and the mixing means are not particularly limited, and conventionally known knowledge about electrode production can be appropriately referred to. As an example of the solvent, N-methyl-2-pyrrolidone (NMP), dimethylformamide, dimethylacetamide, methylformamide and the like can be used. When adopting polyvinylidene fluoride (PVdF) as a binder, NMP is preferably used as a solvent.

  Subsequently, a current collector 2 for forming the active material layer 3 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 active material slurry prepared above is applied to the surface of the current collector 2 prepared above to form a coating film. Thereafter, a drying process is performed. Thereby, the solvent in a coating film is removed and the coating film which should become an active material layer is formed.

  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.

  The electrode of the present invention can be preferably produced by repeating the combination step of the step of forming the above-mentioned coating film and the step of pressing the coating film twice or more.

  Note that an active material layer having a structure in which the active material layer includes two or more active materials and a reaction potential of the active material with respect to lithium metal increases toward the active material layer on the current collector side is manufactured. For example, a method of impregnating a porous metal current collector with an active material slurry can be used.

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

  That is, the second embodiment of the present invention is a 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, and at least one of the positive electrode and the negative electrode is the present invention. It is a battery which is an electrode. The electrode of the present invention can be applied to any of a positive electrode, a negative electrode, and a bipolar electrode. A battery including the 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 durability 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. 3 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. 3, in the non-bipolar lithium ion secondary battery 10 of the present embodiment, a laminate film composed of a polymer and a metal is used for the battery exterior material 22, and the entire peripheral part 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. 3, the outermost layer negative electrode current collector (not shown) is positioned on both outermost layers of the power generation element (battery element) 17 by changing the arrangement of the positive electrode plate and the negative electrode plate. 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. 4 shows another typical embodiment of the lithium ion battery of the present invention, which is a bipolar flat (stacked) 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. 4, the bipolar lithium ion secondary battery 30 according to the present embodiment has a substantially rectangular power generation element (battery element) 37 in which a charge / discharge reaction actually proceeds is sealed inside the battery exterior member 42. Has a structured. As shown in FIG. 4, 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 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. 5 is a perspective view showing the 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. 5, the laminated 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. 3 or FIG. 4 described above. 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 as shown in FIGS. 3 and 4, 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.

  5 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. 5, 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).

  Hereinafter, members constituting the batteries 10, 30, and 50 of the present embodiment will be briefly described. However, since the components constituting the electrode are as described above, the description thereof is 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.

[Electrolyte layer]
As the electrolyte constituting the electrolyte layers 13 and 35, a liquid electrolyte or a polymer electrolyte can 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 carbonates such as ethylene carbonate (EC) and propylene carbonate (PC). 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), and copolymers thereof. In such polyalkylene oxide polymers, electrolyte salts such as lithium salts can be well dissolved.

  In addition, when the electrolyte layers 13 and 35 are comprised from a liquid electrolyte or a gel electrolyte, you may use a separator for the electrolyte layers 13 and 35. FIG. 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.

  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.

[Seal (insulating layer)]
In the bipolar battery 30, a seal portion (insulating layer) 43 is usually provided around each single battery layer 36. The seal portion (insulating layer) 43 prevents the adjacent current collectors 31 in the battery from contacting each other and short-circuiting due to slight unevenness of the end of the unit cell layer 36 in the battery element 37. It is provided for the purpose. By installing such a seal portion (insulating layer) 43, long-term reliability and safety are ensured, and a high-quality bipolar battery 30 can be provided.

  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]
The material of the tabs (positive electrode tabs 18, 38, 58 and negative electrode tabs 19, 39, 59) is not particularly limited, and a known material conventionally used as a tab for a battery can be used. Examples thereof include aluminum, copper, titanium, nickel, stainless steel (SUS), and alloys thereof. The positive electrode tabs 18, 38, 58 and the negative electrode tabs 19, 39, 59 may be made of the same material or different materials.

  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.

(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.

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

  As shown in FIG. 6, an assembled battery 300 according to the present invention forms a small assembled battery 250 in which a plurality of lithium ion secondary batteries according to 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 vehicle power supplies and auxiliary power supplies that require high volume energy density and high volume output density. The assembled battery 300 can also be formed. 6A is a plan view of the assembled battery, FIG. 6A is a front view, and FIG. 6C is a side view. The small assembled battery 250 that can be attached and detached is provided with an electrical connection means such as a bus bar. The assembled battery 250 is stacked in a plurality of stages using the connection jig 310. How many 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, a vehicle is comprised using the battery of said 2nd Embodiment or the assembled battery of 3rd Embodiment.

  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. 7 is a conceptual diagram of a vehicle equipped with the assembled battery of the present invention.

  As shown in FIG. 7, in order to mount the assembled battery 300 on a vehicle such as the electric vehicle 400, the battery pack 300 is mounted under the seat at the center of the vehicle body of the electric vehicle 400. This is because if it is installed under the seat, the interior space and the trunk room can be widened. The place where the assembled battery 300 is mounted is not limited to the position under the seat, but may be a lower part of the rear trunk room or an engine room in front of the vehicle. The electric vehicle 400 using the assembled battery 300 as described above has high durability and can provide sufficient output even when used for a long period of time. Furthermore, it is possible to provide electric vehicles and hybrid vehicles that are excellent in fuel efficiency and running performance. A vehicle equipped with the assembled battery of 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>
<Creation of negative electrode>
As a negative electrode active material, a hard carbon precursor calcined at 2000 ° C. (amorphous carbon material 1, average particle size: 10 μm, reaction potential with lithium metal: 1.0 V (vs. Li / Li ⁺ )) (90 N-methyl-2-pyrrolidone (NMP), which is a slurry viscosity adjusting solvent, is added to a solid content of polyvinylidene fluoride (PVdF) (10 parts by mass), which is a binder, and a binder. Material slurry 2 was prepared.

  On the other hand, a copper foil (thickness: 10 μm) was prepared as a current collector for the negative electrode. The negative electrode active material slurry 2 prepared above was applied to one surface of the prepared current collector with a desktop coater and pressed to a coating thickness of 10 μm to form layer 2.

Next, an appropriate amount of NMP is added to the solid content of graphite (average particle size: 10 μm, reaction potential with lithium metal: 0.2 V (vs. Li / Li ⁺ )) (90 parts by mass) and PVdF (10 parts by mass). The negative electrode active material slurry 1 was prepared by addition.

  Next, the negative electrode active material slurry 1 was applied onto the layer 2 with a desktop coater and pressed to a coating thickness of 80 μm to form the layer 1.

<Preparation of positive electrode>
A lithium metal foil (thickness: 100 μm) was prepared as a positive electrode.

<Production of test cell>
In order to use as a positive electrode and a negative electrode of a test cell, the positive electrode and the negative electrode prepared above were punched to 20 mmφ and 18 mmφ, respectively, using a punch.

Furthermore, a polyethylene microporous film (thickness: 30 μm) was prepared as a separator. Further, as an electrolytic solution was prepared that the LiPF ₆ is equal volume mixture of lithium salt of ethylene carbonate (EC) and diethyl carbonate (DEC) was dissolved in a concentration of 1M.

  The negative electrode, separator, and positive electrode obtained above were laminated in this order, and the electrolyte was injected into the separator. Next, a current extraction terminal (aluminum terminal for the positive electrode and a nickel terminal for the negative electrode) is connected to the negative electrode and the positive electrode, respectively, and the battery element is placed in an aluminum laminate film so that the current extraction terminal is exposed to the outside. The opening of the laminate film was sealed under reduced pressure to produce a test cell.

<Example 2>
A test cell was prepared in the same manner as in Example 1 except that a negative electrode having a coating thickness of layer 2 of 20 μm and a coating thickness of layer 1 of 70 μm was used.

<Example 3>
A test cell was prepared in the same manner as in Example 1 except that a negative electrode having a coating thickness of the layer 2 of 29 μm and a coating thickness of the layer 1 of 61 μm was used.

<Example 4>
A test cell was prepared in the same manner as in Example 1 except that a negative electrode was used in which the coating thickness of the layer 2 was 39 μm and the coating thickness of the layer 1 was 51 μm.

<Example 5>
A test cell was prepared in the same manner as in Example 1 except that a negative electrode was used in which the coating thickness of the layer 2 was 48 μm and the coating thickness of the layer 1 was 42 μm.

<Example 6>
A test cell was prepared in the same manner as in Example 1 except that a negative electrode was used in which the coating thickness of the layer 2 was 57 μm and the coating thickness of the layer 1 was 33 μm.

<Example 7>
A test cell was prepared in the same manner as in Example 1 except that a negative electrode was used in which the coating thickness of the layer 2 was 65 μm and the coating thickness of the layer 1 was 25 μm.

<Example 8>
A test cell was prepared in the same manner as in Example 1 except that a negative electrode having a coating thickness of layer 2 of 74 μm and a coating thickness of layer 1 of 16 μm was used.

<Example 9>
A test cell was prepared in the same manner as in Example 1 except that a negative electrode having a coating thickness of layer 2 of 82 μm and a coating thickness of layer 1 of 8 μm was used.

<Example 10>
As a negative electrode active material, a hard carbon precursor calcined at 1500 ° C. (amorphous carbon material 2, average particle diameter: 10 μm, reaction potential with lithium metal: 1.2 V (vs. Li / Li ⁺ )) (90 N-methyl-2-pyrrolidone (NMP), which is a slurry viscosity adjusting solvent, is added to a solid content of polyvinylidene fluoride (PVdF) (10 parts by mass), which is a binder, and a binder. Material slurry 3 was prepared.

  A copper foil (thickness: 10 μm) was prepared as a current collector for the negative electrode. The negative electrode active material slurry 3 prepared above was applied to one surface of the prepared current collector with a desktop coater and pressed to a coating thickness of 58 μm to form layer 3.

Thereafter, the hard carbon precursor was fired at 2000 ° C. (amorphous carbon material 1, average particle size: 10 μm, reaction potential with lithium metal: 1.5 V (vs. Li / Li ⁺ )) (90 parts by mass) An appropriate amount of NMP was added to the solid content of PVdF (10 parts by mass) to prepare a negative electrode active material slurry 2.

  Next, on the layer 3, the negative electrode active material slurry 2 was apply | coated with the desktop coater, and it pressed so that it might become a coating film thickness of 16 micrometers, and the layer 2 was formed.

Next, an appropriate amount of NMP is added to the solid content of graphite (average particle size: 10 μm, reaction potential with lithium metal: 0.2 V (vs. Li / Li ⁺ )) (90 parts by mass) and PVdF (10 parts by mass). The negative electrode active material slurry 1 was prepared by addition.

  Next, the negative electrode active material slurry 1 was applied onto the layer 2 with a desktop coater and pressed to a coating thickness of 16 μm to form the layer 1.

  A test cell was prepared in the same manner as in Example 1 except that the negative electrode was prepared as described above.

<Example 11>
As a negative electrode active material, a hard carbon precursor fired at 1200 ° C. (amorphous carbon material 3, average particle size: 10 μm, reaction potential with lithium metal: 1.5 V (vs. Li / Li ⁺ )) (90 N-methyl-2-pyrrolidone (NMP), which is a slurry viscosity adjusting solvent, is added to a solid content of polyvinylidene fluoride (PVdF) (10 parts by mass), which is a binder, and a binder. Material slurry 4 was prepared.

  A copper foil (thickness: 10 μm) was prepared as a current collector for the negative electrode. The negative electrode active material slurry 4 prepared above was applied to one surface of the prepared current collector with a desktop coater and pressed to a coating thickness of 42 μm to form a layer 4.

Next, a hard carbon precursor fired at 1500 ° C. (amorphous carbon material 2, average particle size: 10 μm, reaction potential with lithium metal: 1.2 V (vs. Li / Li ⁺ )) (90 parts by mass) An appropriate amount of NMP was added to the solid content of PVdF (10 parts by mass) to prepare a negative electrode active material slurry 3.

  Next, on the layer 4, the negative electrode active material slurry 3 was apply | coated with the desktop coater, and it pressed so that it might become a coating film thickness of 16 micrometers, and the layer 3 was formed.

Thereafter, the hard carbon precursor was fired at 2000 ° C. (amorphous carbon material 1, average particle size: 10 μm, reaction potential with lithium metal: 1.0 V (vs. Li / Li ⁺ )) (90 parts by mass) An appropriate amount of NMP was added to the solid content of PVdF (10 parts by mass) to prepare a negative electrode active material slurry 2.

  Next, on the layer 3, the negative electrode active material slurry 2 was apply | coated with the desktop coater, and it pressed so that it might become a coating film thickness of 16 micrometers, and the layer 2 was formed.

Next, an appropriate amount of NMP is added to the solid content of graphite (average particle size: 10 μm, reaction potential with lithium metal: 0.2 V (vs. Li / Li ⁺ )) (90 parts by mass) and PVdF (10 parts by mass). The negative electrode active material slurry 1 was prepared by addition.

  Next, the negative electrode active material slurry 1 was applied onto the layer 2 with a desktop coater and pressed to a coating thickness of 16 μm to form the layer 1.

  A test cell was prepared in the same manner as in Example 1 except that the negative electrode was prepared as described above.

<Comparative Example 1>
As a negative electrode active material, a solid content composed of graphite (average particle size: 10 μm, reaction potential with lithium metal: 0.2 V (vs. Li / Li ⁺ )) (90 parts by mass) and PVdF (10 parts by mass), An appropriate amount of NMP was added to prepare a negative electrode active material slurry 1.

  A copper foil (thickness: 10 μm) was prepared as a current collector for the negative electrode. The negative electrode active material slurry 1 was applied to one surface of the prepared current collector with a desktop coater and pressed to a coating thickness of 90 μm to form layer 1.

  A test cell was prepared in the same manner as in Example 1 except that the negative electrode was prepared as described above.

<Comparative Example 2>
As a negative electrode active material, a solid content composed of graphite (average particle size: 10 μm, reaction potential with lithium metal: 0.2 V (vs. Li / Li ⁺ )) (90 parts by mass) and PVdF (10 parts by mass), An appropriate amount of NMP was added to prepare a negative electrode active material slurry 2.

  A copper foil (thickness: 10 μm) was prepared as a current collector for the negative electrode. The negative electrode active material slurry 1 described above was applied to one surface of the prepared current collector with a desktop coater and pressed to a coating film thickness of 39 μm to form a layer 2.

Next, the solid content of amorphous carbon material 1 (average particle size: 10 μm, reaction potential with lithium metal: 1.0 V (vs. Li / Li ⁺ )) (90 parts by mass) and PVdF (10 parts by mass) On the other hand, an appropriate amount of NMP was added to prepare a negative electrode active material slurry 1.

  Next, the negative electrode active material slurry 1 was applied onto the layer 2 with a desktop coater and pressed to a coating thickness of 51 μm to form the layer 1.

  A test cell was prepared in the same manner as in Example 1 except that the negative electrode was prepared as described above.

<Evaluation of battery characteristics of test cell>
Test cells were prepared for each of the above Examples and Comparative Examples, and initial charging and degassing were performed. Each test cell was charged with a constant current and constant voltage (CCCV) at 0.5 C for 8 hours (upper limit voltage 4.2 V). After charging, aging was performed for 1 week, and degassing was performed, and discharge capacity was measured at 0.5 C (cutoff voltage 2.5 V. Degassing was performed by placing the battery on a flat plate in a container and placing the weight on the top surface. It was carried out by putting the pressure inside the container under reduced pressure.

  Thereafter, the produced test cell was discharged for 5 seconds from full charge with a 50 CA current value calculated from the active material theoretical capacity, and a resistance value was calculated from the potential and current value after 5 seconds, and used as an output index. . Table 1 below shows the specific output of the test cell produced in each example when the comparative example is 1.

  From the comparison between each example and the comparative example, the negative electrode active material layer of the electrode is formed from two or more layers, and the reaction potential with the lithium metal of the negative electrode active material is higher in the layer on the current collector side. Thus, it can be seen that the diffusion of lithium ions in the active material layer is improved, and the capacity of the battery can be improved.

  As described above, the electrode of the present invention can suppress the precipitation of lithium on the surface of the electrode layer, and as a result, can effectively contribute to the improvement of the battery capacity.

It is a schematic sectional drawing which shows one Embodiment (1st Embodiment) of the battery electrode of this invention. It is a schematic sectional drawing which shows the charge characteristic of the active material which can be used for the electrode of this invention 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. FIG. 6A is an external view schematically showing a typical embodiment of an assembled battery according to the present invention, FIG. 6A is a plan view of the assembled battery, FIG. 6B is a front view of the assembled battery, and FIG. It is a side view of a battery. It is a conceptual diagram of the vehicle carrying the assembled battery of this invention.

Explanation of symbols

1 electrode,
2 current collector,
3, 3a, 3b active material layer,
4, 4a, 4b active material,
5 electrolyte layer,
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,
250 small battery pack,
300 battery packs,
310 connection jig,
400 Electric car.

Claims (17)

An electrode for a lithium ion secondary battery, comprising: a current collector; and a negative electrode active material layer including a negative electrode active material formed on a surface of the current collector,
An electrode for a lithium ion secondary battery, wherein the occlusion of lithium at the time of charging in the negative electrode active material layer occurs earlier as it approaches the current collector.   The negative electrode active material layer is formed of two or more layers, and the reaction potential of the negative electrode active material contained in each layer with respect to lithium metal is directed toward the current collector side layer in the thickness direction of the negative electrode active material layer. The electrode for a lithium ion secondary battery according to claim 1, wherein the electrode is high.   The negative electrode active material layer includes two or more negative electrode active materials, and the reaction potential of the negative electrode active material with respect to lithium metal increases toward the current collector in the thickness direction of the negative electrode active material layer. The electrode for a lithium ion secondary battery according to claim 1 or 2.   4. The negative electrode active material according to claim 1, wherein the negative electrode active material includes one or more materials selected from the group consisting of a carbon material, a lithium-transition metal compound, a metal material, and a lithium-metal alloy material. Of lithium ion secondary battery. The negative electrode active material layer is formed of a surface side layer 1 and a current collector side layer 2, and the reaction potential of the negative electrode active material contained in the layer 1 with respect to lithium metal is 0 to 2.0 V (vs. Li ⁺ / Li), and the reaction potential of the negative electrode active material contained in the layer 2 with respect to lithium metal is 0.2 to 3.0 V (vs. Li ⁺ / Li). Of lithium ion secondary battery.   6. The electrode for a lithium ion secondary battery according to claim 5, wherein a ratio of the film thickness of the layer 1 to the film thickness of the layer 2 is 0.1-10.   The electrode for a lithium ion secondary battery according to claim 5 or 6, wherein the layer 1 includes graphite and the layer 2 includes an amorphous carbon material. The negative electrode active material layer is formed of a surface side layer 1, a current collector side layer 3, and a layer 2 that is an intermediate layer between the layer 1 and the layer 3. The reaction potential with respect to lithium metal is 0 to 1.5 V (vs. Li ⁺ / Li), and the reaction potential with respect to lithium metal of the negative electrode active material contained in the layer 2 is 0 to 2.0 V (vs. Li ⁺ / Li). 5. The reaction potential of the negative electrode active material contained in the layer 3 with respect to lithium metal is 0.2 to 3.0 V (vs. Li ⁺ / Li), 5. The electrode for lithium ion secondary batteries as described in the item. The negative electrode active material layer is formed of n layers of layers 1 to n (n is an integer of 3 or more) from the surface side toward the current collector side, and lithium metal of the negative electrode active material contained in the layer 1 The reaction potential with respect to lithium is 0 to 1.5 V (vs. Li ⁺ / Li), and the reaction potential with respect to lithium metal of the negative electrode active material contained in the layers 2 to (n−1) is 0 to 2.0 V (vs. Li ⁺ / Li), and the reaction potential of the negative electrode active material contained in the layer 3 with respect to lithium metal is 0.2 to 3.0 V (vs. Li ⁺ / Li). 5. The electrode for a lithium ion secondary battery according to any one of 4 above. An electrode for a lithium ion secondary battery, comprising: a current collector; and a positive electrode active material layer including a positive electrode active material formed on a surface of the current collector,
An electrode for a lithium ion secondary battery, wherein lithium uptake at the time of discharging in the positive electrode active material layer occurs earlier as it approaches the current collector.   The positive electrode active material layer is formed of two or more layers, and the reaction potential of the positive electrode active material included in each layer with respect to lithium metal is directed toward the current collector side layer in the thickness direction of the positive electrode active material layer. The electrode for a lithium ion secondary battery according to claim 10, wherein the electrode is lowered.   The positive electrode active material layer includes two or more positive electrode active materials, and the reaction potential of the positive electrode active material with respect to lithium metal decreases toward the current collector in the thickness direction of the positive electrode active material. The electrode for a lithium ion secondary battery according to claim 10 or 11.   The said positive electrode active material contains one or more materials selected from the group which consists of a lithium transition metal oxide, a lithium transition metal phosphate compound, a lithium transition metal sulfate compound, The any one of Claims 10-12 The electrode for lithium ion secondary batteries as described in the item. 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 according to any one of claims 10 to 13, wherein the negative electrode is an electrode for a lithium ion secondary battery according to any one of claims 1 to 9, and / or the positive electrode is a lithium ion secondary battery according to any one of claims 10 to 13. Lithium ion secondary battery, which is an electrode for use.   The lithium ion secondary battery according to claim 14, wherein the electrolyte layer includes a liquid electrolyte, a gel electrolyte, or a polymer electrolyte.   An assembled battery using the lithium ion secondary battery according to claim 14.   A vehicle equipped with the lithium ion secondary battery according to claim 14 or 15 or the assembled battery according to claim 16.

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