JP2004362859A - Lithium ion secondary battery - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an electrode for a lithium-ion secondary battery capable of lowering Li-ion diffusion resistance inside the electrode when high-current-rate charge and discharge are carried out. <P>SOLUTION: The electrode for a lithium-ion secondary battery has an electrolyte-retaining material arranged in gaps between electrode active materials. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a lithium ion secondary battery, and more particularly to a lithium ion secondary battery using an electrode for an electrolyte holding material.
[0002]
[Prior art]
In recent years, reduction of carbon dioxide emission has been urgently required for environmental protection. In the automotive industry, expectations are growing for the reduction of carbon dioxide emissions through the introduction of electric vehicles (EV) and hybrid electric vehicles (HEV), and the development of motor-driven secondary batteries, which are key to their practical use, is keenly pursued. Is being done. As a secondary battery, attention has been focused on a lithium ion secondary battery capable of achieving high energy density and high output density. However, in order to apply it to an automobile, it is necessary to use a plurality of secondary batteries connected in series in order to secure a large output.
[0003]
However, when a battery is connected via the connection, the output decreases due to the electrical resistance of the connection. Also, batteries with connections have spatial disadvantages. That is, the connection portion lowers the output density and energy density of the battery.
[0004]
As a solution to this problem, a bipolar battery in which a positive electrode active material and a negative electrode active material are arranged on both sides of a current collector has been developed.
[0005]
Among them, a bipolar battery using a polymer electrolyte as an electrolyte has been proposed (for example, see Patent Documents 1 and 2). Among them, the bipolar polymer battery using a solid polymer electrolyte has high reliability because there is no solution (electrolyte solution) in the battery, so there is no risk of liquid leakage or gas generation, and the structure is sealed. This has the advantage that a bipolar battery that does not require a seal can be provided. In addition, a bipolar battery using a polymer gel electrolyte as a polymer electrolyte has excellent ionic conductivity and can sufficiently obtain the output density and energy density of the battery, so it is expected to be the closest bipolar battery to the stage of practical use. I have.
[0006]
In a bipolar battery electrode, particularly when a lithium ion secondary battery electrode is used, by increasing the particle size of the active material, the surface area of the active material is increased, and the distance over which Li ions diffuse in the active material particles is reduced. The reaction resistance has been reduced (for example, see Patent Document 3).
[0007]
[Patent Document 1]
JP 2000-100471 A
[Patent Document 2]
JP-A-11-204136
[Patent Document 3]
JP-A-2000-260423
[0008]
[Problems to be solved by the invention]
However, when an attempt is made to discharge at a high current rate in such an electrode, the Li ions in the electrolyte contained in the electrode are rapidly incorporated into the active material, and the Li ion concentration in the electrode decreases, and the separator The resistance of the diffusion of Li ions supplied from the electrolyte in the electrode in the electrode determines the overall reaction.
[0009]
The Li ion diffusion resistance in the electrode can be reduced by reducing the thickness of the entire electrode, but there is a problem that the capacity density of the battery decreases when the electrode is thinned.
[0010]
An object of the present invention is to provide an electrode for a lithium ion secondary battery that can prevent a decrease in Li ion concentration inside the electrode, which occurs during charge and discharge at a high current rate.
[0011]
[Means for Solving the Problems]
The present invention is an electrode for a lithium ion secondary battery, comprising an electrolyte holding material disposed in a gap between electrode active materials.
[0012]
【The invention's effect】
Since the electrode for a lithium ion secondary battery of the present invention has an electrolyte holding material between electrode active materials, it may be possible to increase the amount of electrolyte held in the electrode. As a result, the Li ion diffusion resistance can be reduced, and it is possible to prevent a decrease in the Li ion concentration inside the electrode, which occurs during charge and discharge at a high current rate. Therefore, a lithium ion secondary battery using the electrode of the present invention can have excellent output characteristics.
[0013]
Further, by converting the battery of the present invention into a bipolar type and a battery pack, a high-capacity, high-output battery can be obtained, which is useful as a drive power source for vehicles such as EVs and HEVs.
[0014]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, embodiments of the present invention will be described.
[0015]
The present invention relates to an electrode for a lithium ion secondary battery, comprising an electrolyte holding material disposed in a gap between electrode active materials.
[0016]
For reference, FIG. 1 shows a schematic view of a general lithium ion secondary battery electrode and an electrolyte layer. FIG. 1 shows a structure in which an electrolyte layer (electrolyte film) 3 is further formed on an electrode in which an electrode layer 2 is formed on one current collector 1. In the electrode layer 2, the electrolyte 5 is filled in the electrode active material 4 and the space between the electrode active materials 4. When charging and discharging are performed at a high current rate in such a battery, Li ions 6 existing inside the electrode layer 2 are rapidly absorbed into the electrode active material 4. As a result, when the Li ion concentration in the electrode layer 2 decreases, Li ions 6 are diffused and supplied from the electrolyte layer 3. As described above, at the same time as the Li ions 6 move in and out of the electrolyte layer 3, the electrons move through the conductive material (not shown).
[0017]
The present inventors have paid attention to the fact that the diffusion resistance of Li ions 6 supplied from the electrolyte layer 3 in the electrode layer 2 determines the rate of the entire reaction, and as a result of intensive studies, as a result, the electrode active material It has been found that the electrode characteristics can be improved by disposing the electrolyte holding material in the voids. Hereinafter, the electrode of the present invention will be described in more detail.
[0018]
FIG. 2 schematically shows the electrode for a lithium ion secondary battery of the present invention. In the present invention, the drawings are exaggerated for the sake of explanation, but the technical scope of the present invention is not limited to the illustrated drawings.
[0019]
FIG. 2 shows a structure in which an electrode layer 2 is formed on a current collector 1 and an electrolyte layer (electrolyte film) 3 is formed on the electrode layer 2. The electrode layer 2 has an electrode active material 4, an electrolyte 5, and an electrolyte holding material 7 arranged in a gap between the electrode active materials 4. 2A shows an example in which a ceramic porous body (activated carbon) is used as the electrolyte holding material 7, and FIG. 2B shows an example in which a resin hollow fiber is used as the electrolyte holding material 7, and FIG. In this example, a nonwoven fabric is used as the electrolyte holding material 7.
[0020]
The electrolyte holding material is a member that holds an electrolyte. Thereby, the amount of the electrolyte held inside the electrode can be increased, and further, the electrolyte can be held deep inside the electrode by the electrolyte holding material.
[0021]
For example, as an electrolyte, when an electrolytic solution is used by impregnating the separator with the electrolytic solution or the like, there is a movement of the electrolytic solution from the separator side to the electrode side, and the electrolytic solution is absorbed by the voids and the electrolyte holding material in the electrode. Will be. The polymer electrolyte as the electrolyte includes a polymer gel electrolyte and an all solid polymer electrolyte. When using an all-solid polymer electrolyte as the electrolyte, there is no movement of the electrolyte from the electrolyte layer to the electrode side, so the polymer electrolyte is also put in the electrode side in advance and absorbed in the gaps in the electrode and the electrolyte holding material. There is a need. When a polymer gel electrolyte is used as the electrolyte, the electrolyte in the gel may move to the electrode side, and thus the electrolyte may move to the electrode side. However, since the movement of the electrolytic solution in the gel is not desirable, it is preferable to put a polymer gel electrolyte on the electrode side in advance and absorb it in the gaps in the electrode or the electrolyte holding material.
[0022]
Since such an electrolyte holding material is present inside the electrode, Li ions are also supplied from the electrolyte holding material during high-rate charge / discharge, so that Li ion conduction becomes smooth. Therefore, the diffusion resistance of Li ions can be reduced, and it is possible to prevent a decrease in Li ion concentration inside the electrode. Therefore, the electrode having the electrolyte holding material of the present invention can reduce the diffusion resistance of Li ions without reducing the thickness of the entire electrode, and furthermore, reduces the capacity density of the battery due to the thinner electrode. Can also be prevented. The electrode layer may contain a binder, a conductive additive, and the like so that the electrode of the present invention has the desired electrode characteristics. However, in the drawings, the description is omitted for convenience of explanation.
[0023]
Examples of the electrolyte retaining material used in the present invention include a resin hollow fiber, a nonwoven fabric, a porous alumina, a ceramic porous body, and activated carbon.
[0024]
Examples of the resin hollow fiber include a polyethylene hollow fiber and a polypropylene hollow fiber, and it is preferable to use a porous hollow fiber in order to increase the amount of retained electrolyte. Further, it is preferable to use a resin hollow fiber having a hollow diameter of 0.1 to 90 μm. In addition, in this invention, "hollow diameter" means the diameter of the hollow part which the straw-shaped resin hollow fiber has.
[0025]
Examples of the nonwoven fabric include a polyethylene nonwoven fabric and a polypropylene nonwoven fabric. It is preferable to use a nonwoven fabric having a porosity of 30 to 95%.
[0026]
Examples of the porous ceramics include porous ceramics such as porous alumina and porous zirconia. Activated carbon includes coconut shell activated carbon. The ceramic porous body and activated carbon preferably have a pore diameter of 0.1 to 90 μm.
[0027]
These may be used alone or in combination of two or more. The electrolyte holding material is not particularly limited as long as the material holds the electrolyte.
[0028]
The content of the electrolyte retaining material in the electrode of the present invention may be appropriately determined so as to obtain desired electrode characteristics such as the electrode thickness and the reaction resistance.
[0029]
Since the size of the electrolyte holding material varies depending on the type and cannot be uniformly defined, it may be appropriately determined so as to obtain desired electrode characteristics such as electrode thickness and reaction resistance, but preferably from 1.0 to 1.0. It is 100 μm, more preferably in the range of 5.0 to 50 μm. Here, the “size of the electrolyte holding material” refers to the absolute maximum length of the electrolyte holding material (meaning the maximum size that the substance can take). When the nonwoven fabric is reduced, it is desirable that the size of the expanded nonwoven fabric is included in the above range.
[0030]
The electrolyte holding material in the electrode can be analyzed by observing the cross section of the electrode with an electron microscope or the like. In addition, even when the battery of the present invention is included in a battery, the battery can be disassembled, the electrode can be taken out, and the electrolyte-holding material can be analyzed in the same manner as described above.
[0031]
The electrode layer of the positive electrode (also simply referred to as “positive electrode layer”) contains an electrolyte holding material and a positive electrode active material, and further includes a conductive auxiliary material for enhancing electron conductivity, a binder, and an ion conductive material. , A lithium salt for increasing the concentration, an electrolyte, and the like.
[0032]
As the positive electrode active material, a lithium-transition metal composite oxide which is a composite oxide of a transition metal and lithium can be suitably used. As the positive electrode active material, specifically, LiCoO ₂ Li-Co based composite oxides such as LiNiO ₂ Li-Ni based composite oxide such as spinel LiMn ₂ O ₄ Li-Mn based composite oxides such as LiFeO ₂ Li-Fe-based composite oxides such as those described above, and those obtained by partially replacing these transition metals with other elements can be used. These lithium-transition metal composite oxides are excellent in reactivity and cycle durability, and are low-cost materials. Therefore, using these materials for the electrode is advantageous in that a battery having excellent output characteristics can be formed. In addition, LiFePO ₄ Phosphoric acid compounds and sulfuric acid compounds of transition metals and lithium; ₂ O ₅ , MnO ₂ , TiS ₂ , MoS ₂ , MoO ₃ Transition metal oxides and sulfides such as PbO ₂ , AgO, NiOOH and the like.
[0033]
The particle size of the positive electrode active material is not particularly limited, and a particle having a conventionally known particle size range may be used. Specifically, in order to reduce the electrode resistance, the average particle size of the fine particles of the positive electrode active material is reduced. The diameter is preferably 0.1 to 5 μm.
[0034]
Examples of the conductive additive include acetylene black, carbon black, and graphite. However, it is not limited to these.
[0035]
As the binder, polyvinylidene fluoride (PVDF), SBR, polyimide or the like can be used. However, it is not limited to these.
[0036]
Examples of lithium salts include LiBETI (lithium bis (perfluoroethylenesulfonylimide); Li (C ₂ F ₅ SO ₂ ) ₂ N), LiBF ₄ , LiPF ₆ , LiN (SO ₂ CF ₃ ) ₂ , LiN (SO ₂ C ₂ F ₅ ) ₂ , LiBOB (lithium bis oxide borate) or a mixture thereof can be used. However, it is not limited to these.
[0037]
When a polymer electrolyte is used for the electrolyte layer, it is desirable that the positive electrode layer also contains the polymer electrolyte. By filling the gap between the positive electrode active materials in the positive electrode layer with the polymer electrolyte, the ion conduction in the positive electrode layer becomes smooth, and the output of the lithium ion secondary battery as a whole can be improved.
[0038]
Examples of the polymer electrolyte include, in the present invention, a polymer gel electrolyte in which a polymer holds an electrolytic solution, and an all-solid polymer electrolyte composed only of a polymer electrolyte and a supporting salt such as a lithium salt. Can be
[0039]
The all solid polymer electrolyte is not particularly limited, and examples thereof include polyethylene oxide (PEO), polypropylene oxide (PPO), and a copolymer thereof. Such a polyalkylene oxide-based polymer is LiBF ₄ , LiPF ₆ , LiN (SO ₂ CF ₃ ) ₂ , LiN (SO ₂ C ₂ F ₅ ) ₂ And other lithium salts. Further, by forming a crosslinked structure, excellent mechanical strength is exhibited. In the present invention, the all solid polymer electrolyte is preferably contained in both the positive electrode layer and the negative electrode layer in order to further improve the electrode characteristics.
[0040]
As the polymer gel electrolyte, an all-solid polymer electrolyte having ion conductivity and an electrolyte solution is included, but a skeleton of a polymer (host polymer) having no lithium ion conductivity is further provided. Among them, those holding similar electrolytes are also included.
[0041]
Here, the electrolyte solution (electrolyte salt and plasticizer) contained in the polymer gel electrolyte may be any one that is usually used in a lithium ion battery. For example, LiBOB (lithium bisoxide borate), LiPF ₆ , LiBF ₄ , LiClO ₄ , LiAsF ₆ , LiTaF ₆ , LiAlCl ₄ , Li ₂ B ₁₀ Cl ₁₀ Acid anion salts such as LiCF ₃ SO ₃ , Li (CF ₃ SO ₂ ) ₂ N, Li (C ₂ F ₅ SO ₂ ) ₂ N (LiBETI) and other organic acid anion salts, at least one lithium salt (electrolyte salt), and cyclic carbonates such as propylene carbonate (PC) and ethylene carbonate (EC); dimethyl carbonate; Chain carbonates such as methyl ethyl carbonate and diethyl carbonate; ethers such as tetrahydrofuran, 2-methyltetrahydrofuran, 1,4-dioxane, 1,2-dimethoxyethane and 1,2-dibutoxyethane; and γ-butyrolactone Lactones; nitriles such as acetonitrile; esters such as methyl propionate; amides such as dimethylformamide; an aprotic solvent in which at least one or two or more selected from methyl acetate and methyl formate are mixed Organic solvents such as plastic ), And the like can be used as that used. However, it is not limited to these.
[0042]
Examples of the polymer having no lithium ion conductivity used for the polymer gel electrolyte include polyvinylidene fluoride (PVDF), polyvinyl chloride (PVC), polyacrylonitrile (PAN), and polymethyl methacrylate (PMMA). it can. However, it is not limited to these. Since PAN, PMMA, and the like fall into the category of having little ionic conductivity, they can be the above-mentioned polymers having ionic conductivity, but are used here as polymer gel electrolytes. It is exemplified as a polymer having no lithium ion conductivity.
[0043]
The ratio (mass ratio) between the host polymer and the electrolytic solution in the polymer gel electrolyte may be determined according to the purpose of use, etc., and is in the range of 2:98 to 90:10. That is, leakage of the electrolyte from the outer peripheral portion of the electrode layer can be effectively sealed by providing the insulating layer and the insulating portion. Therefore, the battery characteristics can be given a relatively high priority also with respect to the ratio (mass ratio) between the host polymer and the electrolytic solution in the polymer gel electrolyte.
[0044]
In the positive electrode layer, the amount of components such as a positive electrode active material, a conductive auxiliary material, a binder, a polymer electrolyte (a host polymer, an electrolytic solution, etc.), a lithium salt, etc. depends on the purpose of use of the battery (e.g. The decision should be made in consideration of gender. For example, if the blending amount of the polymer electrolyte in the electrode layer is too small, the ionic conduction resistance and the ionic diffusion resistance in the electrode layer will increase, and the battery performance will decrease. On the other hand, if the blending amount of the polymer electrolyte in the positive electrode layer is too large, the energy density of the battery decreases. Therefore, a polymer (gel) electrolytic mass that meets the purpose is determined in consideration of these factors.
[0045]
The thickness of the positive electrode layer is not particularly limited, and should be determined in consideration of the intended use of the battery (e.g., emphasis on output, energy, etc.) and ionic conductivity, as described for the blending amount. The thickness of a general positive electrode layer is about 10 to 500 μm. That is, by having the electrolyte holding material, the Li ion diffusion resistance can be reduced without reducing the thickness of the positive electrode, and a sufficient battery capacity density can be obtained.
[0046]
Next, in the electrode layer of the negative electrode (also simply referred to as “negative electrode layer”), a negative electrode active material and an electrolyte holding material are included, and in addition to these, a conductive auxiliary material for improving electron conductivity, a binder, and the like. , A lithium salt for enhancing ionic conductivity, a polymer electrolyte, and the like.
[0047]
When an all solid polymer electrolyte is used for the electrolyte layer, it is desirable that the negative electrode layer also contains the all solid polymer electrolyte. By filling the voids between the negative electrode active materials in the negative electrode layer with the all-solid polymer electrolyte, the ion conduction in the negative electrode layer becomes smooth, and the output of the lithium ion secondary battery as a whole can be improved.
[0048]
Except for the type of the negative electrode active material, the content is basically the same as that described in the section of “Positive electrode layer”, and thus the description is omitted here.
[0049]
Examples of the negative electrode active material include various natural graphites and artificial graphites, for example, graphites such as fibrous graphite, flaky graphite, spherical graphite, and various lithium alloys. Specifically, carbon, graphite, metal oxide, lithium-metal composite oxide and the like can be used, and carbon or lithium-transition metal composite oxide is preferable. These carbon or lithium-transition metal composite oxides are excellent in reactivity and cycle durability, and are low-cost materials. Therefore, by using these materials for the electrodes, a battery having excellent output characteristics can be formed. In addition, as the lithium-transition metal composite oxide, for example, Li ₄ Ti ₅ O ₁₂ And the like can be used. As the carbon, for example, graphite (graphite), hard carbon, soft carbon, or the like can be used.
[0050]
The thickness of the negative electrode layer is not particularly limited, and should be determined in consideration of the intended use of the battery (e.g., emphasis on output and energy) and ionic conductivity, similarly to the positive electrode layer. The thickness of a general negative electrode layer is about 10 to 500 μm. That is, even if the negative electrode is not made thin, the Li ion diffusion resistance can be reduced, and a sufficient capacity density of the battery can be obtained.
[0051]
Further, the current collector used for the electrode (negative electrode and positive electrode) of the present invention is not particularly limited, and a conventionally known current collector can be used. For example, aluminum foil, stainless steel foil, nickel and aluminum , A clad material of copper and aluminum, or a plated material of a combination of these metals is preferably used. Alternatively, a current collector in which aluminum is coated on a metal surface may be used. In some cases, a current collector in which two or more metal foils are bonded may be used. It is preferable to use an aluminum foil as a current collector from the viewpoints of corrosion resistance, ease of production, economy, and the like.
[0052]
The thickness of the current collector is not particularly limited, but is usually about 1 to 100 μm. Further, the length or shape of the current collector may be appropriately determined so that a desired electrode is obtained.
[0053]
The method for producing an electrode according to the present invention includes a step of preparing a slurry containing an electrode active material and an electrolyte retaining material, and a step of applying the slurry on a current collector. According to such a manufacturing method of the present invention, it is possible to manufacture an electrode including an electrolyte holding material by a simple method.
[0054]
First, in the step of adjusting the slurry containing the electrode active material and the electrolyte holding material, as necessary, in addition to the electrode active material and the electrolyte holding material, a binder, a conductive auxiliary agent, and the like are mixed in a solvent to form a slurry. adjust. Since the electrode active material, the electrolyte holding material, and other components in the positive electrode and the negative electrode are as described above, the description thereof is omitted here.
[0055]
The solvent of the slurry and the mixing means may use various known techniques, and are not particularly limited. Examples of the solvent for the slurry include dimethylformamide, dimethylacetamide, methylformamide, N-methyl-2-pyrrolidone (NMP) and the like. When polyvinylidene fluoride (PVDF) is used as the binder, it is preferable to use N-methyl-2-pyrrolidone (NMP).
[0056]
After the slurry containing the electrolyte holding material is applied and dried on the current collector, the slurry containing no electrolyte holding material is applied and dried, so that the electrolyte holding material is also provided at the back of the electrode as shown in FIG. Material can be retained. Thereby, Li ion conduction at the time of high-rate charge / discharge becomes smooth, the diffusion resistance of Li ions can be reduced, and a decrease in Li ion concentration inside the electrode can be prevented.
[0057]
Next, the step of applying the slurry on the current collector is not particularly limited, and the slurry may be applied by a known method such as a coater or a screen printing method so as to obtain a desired thickness of the electrode. The first manufacturing method is suitable for a case where a separator in which an electrolyte of a battery is impregnated with an electrolytic solution is used.
[0058]
In addition, the method for manufacturing the electrode of the present invention is not limited to the above-described method, and the second method includes the steps of: drying the applied slurry; and impregnating the dried slurry with an electrolyte solution. And the step of polymerizing the electrolyte solution. Such a second manufacturing method is suitable for a case where a polymer electrolyte is used as the electrolyte of the battery.
[0059]
At the stage of drying the applied slurry, the drying method is not particularly limited, and may be performed using a vacuum dryer or the like. At this stage, a void is formed between the electrode active materials, and the electrolyte holding material is provided in the void. Further, the drying time and the drying temperature may be appropriately determined according to the supply amount of the slurry and the volatilization rate of the solvent of the slurry.
[0060]
As a step of impregnating the dried slurry with the electrolyte solution, the impregnation method is not particularly limited, and may be performed using a conventionally known method. In addition, a small amount can be supplied by using an applicator or a coater. The electrolyte solution to be impregnated is preferably the same as the electrolyte solution used for forming the electrolyte layer, and may further contain a polymerization initiator, a solvent in the case of a polymer electrolyte, and the like.
[0061]
The polymerization initiator needs to be appropriately selected according to the polymerization method (thermal polymerization method, ultraviolet polymerization method, radiation polymerization method, electron beam polymerization method, etc.) and the compound to be polymerized. For example, benzyl dimethyl ketal as an ultraviolet polymerization initiator and azobisisobutyronitrile as a thermal polymerization initiator are exemplified, but not limited thereto.
[0062]
At the stage of polymerizing the electrolyte solution, the polymerization method is not particularly limited, and examples thereof include a polymerization method using thermal polymerization, ultraviolet polymerization, radiation polymerization, and electron beam polymerization. The polymerization method may be appropriately selected according to the compound contained in the impregnated electrolyte solution, but it is preferable to perform thermal polymerization because the polymerization can be performed easily and reliably. The polymerization conditions and the like are determined according to the supply amount of the solvent, the evaporation rate of the solvent, the crosslinking rate, and the like. Further, a drying step may be added if necessary.
[0063]
As a third manufacturing method of the electrode of the present invention, an electrolyte solution may be included in the step of adjusting the slurry in the first manufacturing method. That is, the method for producing an electrode of the present invention may include a step of applying a slurry containing an electrode active material, an electrolyte holding material, and an electrolyte solution onto a current collector, and a step of polymerizing the electrolyte solution. Such a third manufacturing method is suitable for a case where a polymer electrolyte is used as the electrolyte of the battery.
[0064]
As a fourth manufacturing method of the electrode of the present invention, first, a positive electrode slurry containing an electrode active material and an electrolyte holding material is applied on a current collector and dried, and in the same manner, a negative electrode slurry is coated on another current collector. And dried. Next, these may be laminated in the order of a negative electrode, a separator, a positive electrode, and a separator via a separator such as a porous polypropylene film, and then impregnated with an electrolyte solution and polymerized to produce an electrode. Such a fourth manufacturing method is suitable for a case where a polymer electrolyte is used as the electrolyte of the battery.
[0065]
As described above, the electrode of the present invention can prevent a decrease in the concentration of Li ions inside the electrode that occurs at the time of high-rate charging and discharging, and can smoothly perform the electrode reaction. Therefore, a lithium ion secondary battery using the electrode of the present invention for the positive electrode and / or the negative electrode can be a battery having excellent output characteristics. A secondary battery including the electrode of the present invention as at least one electrode belongs to the technical scope of the present invention.
[0066]
In such a battery, it is preferable to use a lithium-transition metal composite oxide as a positive electrode active material and use carbon or a lithium-transition metal composite oxide as a negative electrode active material. By using such a compound, an electrode having excellent reactivity and cycle durability can be obtained with a low-cost material.
[0067]
The lithium-transition metal composite oxide in the positive electrode active material is as described above. ₂ O ₄ , LiCoO ₂ , LiNiO ₂ And those obtained by partially substituting these transition metals with other elements.
[0068]
As for the negative electrode active material, as described above, carbon such as hard carbon and graphite, and lithium-transition metal composite oxide such as Li ₄ Ti ₅ O ₁₂ And the like.
[0069]
As the electrolyte, as described above, a polymer electrolyte is preferably used. This is because there is no problem of liquid leakage, and a highly reliable battery can be obtained.
[0070]
Since the electrode active material, the electrolyte holding material, and other components in the positive electrode and the negative electrode are as described above, detailed description thereof is omitted here.
[0071]
The lithium ion secondary battery using the electrode of the present invention is not particularly limited. For example, when distinguished by the form and structure, a stacked (flat) battery and a wound (cylindrical) battery The present invention can be applied to any conventionally known forms and structures such as batteries. In addition, when viewed in terms of the electrical connection form (electrode structure) in a lithium ion secondary battery, it applies to both non-bipolar (internal parallel connection type) batteries and bipolar (internal series connection type) batteries. What you get. In a bipolar battery, a cell having a higher voltage than a normal battery and having excellent capacity and output characteristics can be constructed. Further, since the polymer battery does not cause liquid leakage, it is advantageous in that a non-aqueous battery having high reliability without a liquid junction problem, and having excellent output characteristics can be formed with a simple configuration. Furthermore, a lithium ion secondary battery using a lithium-transition metal composite oxide as a positive electrode active material is a material having excellent reactivity, cycle durability, and low cost. This is advantageous in that a battery having better output characteristics can be formed. In addition, by adopting a stacked (flat) battery structure, long-term reliability can be ensured by a simple sealing technique such as thermocompression bonding, which is advantageous in terms of cost and workability. However, the lithium ion secondary battery of the present invention is preferably used as a bipolar type lithium ion secondary battery in order to obtain an excellent battery. However, the present invention is not particularly limited thereto. For example, a stacked lithium ion secondary battery, a rechargeable lithium ion secondary battery, and the like can be exemplified. Preferably, a bipolar lithium ion secondary battery (hereinafter simply referred to as a “bipolar battery”) is used. ).
[0072]
The following briefly describes a bipolar battery using a polymer electrolyte (more specifically, an all-solid polymer electrolyte or a polymer gel electrolyte) as one of the preferred embodiments of the lithium ion secondary battery of the present invention. Will be described. However, these are only examples of the present invention, and the present invention is not limited to these.
[0073]
The basic configuration of the bipolar battery of the present invention will be briefly described with reference to FIGS. 3 is a schematic cross-sectional view schematically showing the structure of a bipolar electrode constituting a bipolar battery, and FIG. 4 is a cross-sectional view schematically showing the structure of a unit cell layer constituting a bipolar battery. FIG. 5 is a schematic cross-sectional view schematically showing the entire structure of the bipolar battery, and FIG. 6 is a diagram in which a plurality of unit cell layers stacked in the bipolar battery are connected in series. FIG. 2 is a schematic diagram conceptually showing (symbolizing) this.
[0074]
As shown in FIGS. 3 to 6, the bipolar electrode 15 (see FIG. 3) in which the positive electrode layer 12 is provided on one surface of one current collector 11 and the negative electrode layer 13 is provided on the other surface, is The electrode layers 12 and 13 of the bipolar electrode 15 adjacent to each other with the molecular electrolyte layer 14 interposed therebetween face each other. That is, in the bipolar battery 21, a plurality of bipolar electrodes (electrode layers) 15 having the positive electrode layer 12 on one surface of the current collector 11 and the negative electrode layer 13 on the other surface are provided via the electrolyte layer 14. It comprises an electrode laminate (bipolar battery body) 17 having a laminated structure. The electrodes 15a and 15b of the uppermost layer and the lowermost layer are not of a bipolar electrode structure but are formed on only one side of the electrode layer (the negative electrode layer 13 or the positive electrode layer 12) required for the current collector 11 (or the negative electrode terminal plate 19 or the positive electrode terminal plate 18) (See FIG. 5).
[0075]
The number of laminations of the bipolar electrode is adjusted according to a desired voltage. If a sufficient output can be ensured even if the thickness of the sheet-shaped battery is made as thin as possible, the number of times of laminating the bipolar electrodes may be reduced.
[0076]
Further, in the bipolar battery 21 of the present invention, in order to prevent external impact and environmental degradation at the time of use, it is preferable that the electrode laminate 17 is sealed under reduced pressure in a battery exterior material (exterior package) 20 (FIG. 5, 6).
[0077]
From the viewpoint of weight reduction, a polymer-metal composite laminate such as an aluminum laminate pack in which a metal (including an alloy) such as aluminum, stainless steel, nickel, or copper is coated with an insulator such as a polypropylene film is used as the battery exterior material 20. It is preferable that the electrode laminate 17 is housed and sealed under reduced pressure (sealing) by using a conventionally known film or the like and partially or entirely joining the periphery thereof by heat fusion.
[0078]
The basic configuration of the bipolar battery 21 can be said to be a configuration in which a plurality of stacked unit cell layers (single cells) 16 are connected in series, as shown in FIG. The bipolar battery of the present invention is used for a bipolar lithium ion secondary battery in which charging and discharging are mediated by movement of lithium ions. However, this does not prevent application to other types of batteries as long as effects such as improvement in battery characteristics can be obtained.
[0079]
The other components of the bipolar battery of the present invention are not particularly limited, and can be widely applied to conventionally known bipolar batteries.
[0080]
In addition, as a method for manufacturing a bipolar battery, the above-described electrode for a lithium ion secondary battery of the present invention is used as a bipolar electrode, and after thoroughly drying this and an electrolyte layer (membrane) under high vacuum, Cut out the right size. This is a method for producing a bipolar battery laminate (electrode laminate) by laminating a predetermined number of cut-out bipolar electrodes and electrolyte layers.
[0081]
Further, in the case of a bipolar electrode having an electrolyte layer (membrane) formed on one or both surfaces, the electrode is sufficiently heated and dried under a high vacuum, and then a plurality of electrodes having the electrolyte layer (membrane) are formed to an appropriate size. The cut-out and cut-out electrodes may be directly bonded to each other to produce a bipolar battery body (electrode laminate).
[0082]
The number of layers of the electrode stack is determined in consideration of battery characteristics required for a bipolar battery. In the outermost layer on the positive electrode side, an electrode in which only the positive electrode layer is formed on the current collector is arranged. In the outermost layer on the negative electrode side, an electrode in which only the negative electrode layer is formed on the current collector is arranged. The step of obtaining a bipolar battery by laminating a bipolar electrode and an electrolyte layer (membrane) or laminating an electrode on which an electrolyte layer (membrane) is formed is difficult from the viewpoint of preventing moisture and the like from being mixed into the battery. It is preferable to carry out under an active atmosphere. For example, a bipolar battery is preferably manufactured in an argon atmosphere or a nitrogen atmosphere.
[0083]
When the all solid polymer electrolyte layer is used, the electrolyte layer is as described above. For example, the electrolyte layer was prepared by dissolving the raw material polymer of the all solid polymer electrolyte, a lithium salt, and the like in a solvent such as NMP. Manufactured by curing the solution. In the case of using the polymer gel electrolyte layer, the electrolyte layer is, for example, heated and dried in an inert atmosphere by heating a pregel solution comprising a host polymer, an electrolyte solution, a lithium salt, a polymerization initiator, and the like as raw materials for the polymer gel electrolyte. At the same time, it is produced by polymerization (promoting a crosslinking reaction).
[0084]
For example, the prepared solution or pregel solution is applied on the electrode (positive electrode and / or negative electrode), and an electrolyte layer having a predetermined thickness or a part thereof (an electrolyte membrane having a thickness of about half the electrolyte layer thickness) is formed. Form. Thereafter, by curing or heating and drying the electrode on which the electrolyte layer (membrane) is laminated and polymerizing (promoting a crosslinking reaction), the mechanical strength of the electrolyte is increased, and the electrolyte layer (membrane) is formed into a film (completed). Let it do).
[0085]
Alternatively, an electrolyte layer laminated between the electrodes or a part thereof (an electrolyte membrane having a thickness of about half the electrolyte layer thickness) is separately prepared. The electrolyte layer (membrane) is produced by applying the above solution or pregel solution on a suitable film such as a PET film, and curing (or accelerating the crosslinking reaction) at the same time as heating and drying.
[0086]
For curing or heat drying, a vacuum dryer (vacuum oven) or the like can be used. The conditions of the heat drying are determined according to the solution or the pregel solution and cannot be uniquely defined, but are usually at 30 to 110 ° C. for 0.5 to 12 hours.
[0087]
The thickness of the electrolyte layer (membrane) can be controlled using a spacer or the like. When a photopolymerization initiator is used, it is poured into a light-transmitting gap and irradiated with ultraviolet rays using an ultraviolet irradiation device capable of drying and photopolymerization, thereby photopolymerizing the polymer in the electrolyte layer and performing a crosslinking reaction. It is advisable to proceed the film formation. However, it is a matter of course that the present invention is not limited to this method. Depending on the type of the polymerization initiator, radiation polymerization, electron beam polymerization, thermal polymerization, and the like are properly used.
[0088]
Further, since the film used above may be heated to about 80 ° C. during the manufacturing process, the film has sufficient heat resistance at the temperature, and has no reactivity with the solution or the pregel solution. It is desirable to use a material excellent in releasability from the necessity of peeling and removing with, for example, polyethylene terephthalate (PET), a polypropylene film and the like can be used, but it is not limited thereto.
[0089]
The width of the electrolyte layer is often slightly smaller than the size of the electrode forming portion of the current collector of the bipolar electrode.
[0090]
The composition of the above solution or pregel solution and the amount thereof should be appropriately determined according to the purpose of use.
[0091]
The separator impregnated with the electrolytic solution has the same configuration as the electrolyte layer used for the conventional non-bipolar type solution-based bipolar battery, and conventionally known various manufacturing methods, for example, a separator impregnated with the electrolytic solution is used. Since it can be manufactured by a method of sandwiching and stacking between bipolar electrodes or a vacuum injection method, a detailed description thereof will be omitted below.
[0092]
The insulating layer is formed around each electrode for the purpose of preventing current collectors from contacting each other, leaking out of the electrolytic solution, and short-circuiting due to slight irregularities at the ends of the stacked electrodes. (Not shown). An insulating layer may be provided on the current collector extension side. This is because, when used as a vehicle drive power source, considering that a longer battery life is desired, during the use period, the current collector extension and the insulating separator are separated from the electrolyte layer. This is because it is very slow, but there is no danger of seeping out.
[0093]
As the insulating layer, any material having an insulating property, a sealing property (sealing property) against leakage of electrolyte and moisture permeation from the outside, heat resistance at a battery operating temperature, and the like may be used. Rubber, polyethylene, polypropylene, polyimide and the like can be used, but from the viewpoints of corrosion resistance, chemical resistance, ease of production (film-forming properties), economy, etc., epoxy resins are preferred.
[0094]
The positive and negative electrode terminal plates may be used as needed. When used, it is better to have as thin as possible from the viewpoint of thinning in addition to having the function as a terminal, but since the laminated electrodes, electrolyte and current collector all have low mechanical strength, It is desirable to have enough strength to sandwich and support from above. Further, from the viewpoint of suppressing the internal resistance at the terminal portion, it can be said that the thickness of the positive electrode and negative electrode terminal plates is usually preferably about 0.1 to 2 mm.
[0095]
As the material of the positive electrode terminal and the negative electrode terminal plate, a material usually used in a lithium ion battery can be used. For example, aluminum, copper, titanium, nickel, stainless steel (SUS), alloys thereof, and the like can be used. It is preferable to use aluminum from the viewpoints of corrosion resistance, ease of production, economy, and the like.
[0096]
The materials of the positive electrode terminal plate and the negative electrode terminal plate may be the same or different. Further, these positive and negative electrode terminal plates may be formed by laminating different materials from each other in multiple layers.
[0097]
In the bipolar battery, the entire battery stack, which is the bipolar battery main body, may be housed in a battery exterior material or a battery case (not shown) in order to prevent external impact and environmental degradation during use. From the viewpoint of weight reduction, a conventionally known battery package such as a polymer-metal composite laminate film or an aluminum laminate pack in which a metal (including an alloy) such as aluminum, stainless steel, nickel, or copper is coated with an insulator such as a polypropylene film. It is preferable that the battery laminate is housed and sealed by using a material and joining a part or all of its peripheral portion by heat fusion. In this case, the positive electrode and the negative electrode lead may have a structure sandwiched between the heat-sealed portions and exposed to the outside of the battery exterior material. In addition, the use of a polymer-metal composite laminate film or aluminum laminate pack with excellent thermal conductivity allows the heat to be efficiently transmitted from the heat source of the vehicle and quickly heats the inside of the battery to the battery operating temperature. preferable.
[0098]
Further, in the present invention, a battery pack formed by connecting a plurality of the above-mentioned lithium ion secondary batteries can be provided. That is, a battery module having a high capacity and a high output is formed by using at least two or more lithium ion secondary batteries of the present invention to be connected and connected in series and / or parallel to form a battery pack. Can be done. Therefore, it is possible to respond to the demand for the battery capacity and output for each purpose of use relatively inexpensively.
[0099]
Specifically, for example, N pieces of the above-described lithium ion secondary batteries are connected in parallel, and N pieces of the lithium ion secondary batteries in parallel are further connected in series to be housed in a metal or resin assembled battery case. And a battery pack. At this time, the number of series / parallel connected lithium ion secondary batteries is determined according to the purpose of use. For example, as a large-capacity power supply such as an electric vehicle (EV) or a hybrid electric vehicle (HEV), the power supply may be combined so as to be applicable to a power supply for driving a vehicle requiring a high energy density and a high output density. In addition, the positive electrode terminal and the negative electrode terminal for the assembled battery and the electrode lead of each lithium ion secondary battery may be electrically connected using a lead wire or the like. Further, when connecting lithium ion secondary batteries in series / parallel, the lithium ion secondary batteries may be electrically connected using an appropriate connecting member such as a spacer or a bus bar. However, the battery pack of the present invention should not be limited to the battery described here, and a conventionally known battery can be appropriately used. In addition, the assembled battery may be provided with various measuring devices and control devices according to the intended use, for example, a voltage measuring connector or the like may be provided to monitor the battery voltage. There is no particular limitation.
[0100]
According to the present invention, a vehicle equipped with the above-described lithium ion secondary battery and / or assembled battery as a driving power supply or the like can be provided. The lithium ion secondary battery and / or battery pack of the present invention have various characteristics as described above, and are particularly excellent in output characteristics. For this reason, the present invention provides an electric vehicle and a hybrid vehicle which are suitable as a drive power source for a vehicle, for example, an electric vehicle or a hybrid electric vehicle, which has particularly strict requirements regarding energy density and output density, and which are excellent in fuel efficiency and running performance. it can. For example, it is convenient to mount an assembled battery as a driving power source under a seat in the center of the body of an electric vehicle or a hybrid electric vehicle, because it is possible to widen the office space and the trunk room, which is convenient. However, the present invention is not limited to these, and the battery can be installed under the floor of the vehicle, in a trunk room, in an engine room, on a roof, in a hood, or the like. In the present invention, not only the assembled battery but also a bipolar battery may be mounted depending on the intended use, or these assembled batteries and a lithium ion secondary battery may be mounted in combination. Further, as the vehicle on which the lithium ion secondary battery and / or battery pack of the present invention can be mounted as a driving power source, the above-described electric vehicle or hybrid electric vehicle is preferable, but is not limited thereto. Further, the lithium ion secondary battery and / or the battery pack of the present invention may be used as an auxiliary power source of a fuel cell vehicle or a hybrid fuel cell vehicle in addition to a driving power source.
[0101]
【Example】
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 the following examples.
[0102]
Example 1
<Preparation of electrode for lithium ion secondary battery>
(1) Preparation of positive electrode
First, a positive electrode slurry containing a positive electrode active material and an electrolyte holding material was applied on a current collector. LiMn as positive electrode active material ₂ O ₄ (75% by mass), acetylene black (5% by mass) as a conductive aid, PVDF (10% by mass) as a binder, porous alumina (10% by mass) having an average particle size of 10 μm and a pore size of 1 μm as an electrolyte retaining material, and The positive electrode slurry was adjusted using NMP (suitable amount) as a slurry viscosity adjusting solvent. The slurry was applied to one side of a SUS foil (thickness: 20 μm) as a current collector. Next, the applied slurry was dried at about 120 ° C. to form a positive electrode layer having a thickness of 20 μm.
[0103]
(2) Preparation of negative electrode
First, a negative electrode slurry containing a negative electrode active material and an electrolyte holding material was applied on a current collector. Hard carbon (80% by mass) as a negative electrode active material, PVDF (10% by mass) as a binder, porous alumina having an average particle size of 10 μm and a pore size of 1 μm (10% by mass) as an electrolyte holding material, and a slurry viscosity adjusting solvent The negative electrode slurry was adjusted using NMP (suitable amount). The negative electrode slurry was applied to the opposite side of the SUS foil on which the positive electrode was applied. Next, the applied negative electrode slurry was dried at about 120 ° C. to prepare a negative electrode layer having a thickness of 20 μm.
[0104]
<Preparation of polymer gel electrolyte layer (membrane)>
A polymer (copolymer of polyethylene oxide and polypropylene oxide, weight average molecular weight 8,000, 10% by mass) and a solvent (plasticizer) of EC: PC = 1: 1 (mass ratio) as a lithium salt in 1.0M LiBETI Was dissolved (90% by mass) and t-hexylperoxypiparate (1% by mass based on the polymer) as a polymerization initiator to prepare a pregel solution. This pregel solution was impregnated into a PP nonwoven fabric (thickness: 100 μm) as a separator, and was subjected to thermal polymerization at 90 ° C. in an inert atmosphere.
[0105]
<Preparation of bipolar battery>
Impregnating the same pregel solution as used for the polymer electrolyte into the lithium ion secondary battery electrode (bipolar electrode composed of a positive electrode and a negative electrode) prepared as described above, and thermally polymerizing at 90 ° C. in an inert atmosphere. As a result, the polymer gel electrolyte was held in the electrode.
[0106]
The unit cell layer was formed by laminating the positive electrode and the negative electrode of the bipolar electrode so as to face each other with a separator (polymer gel electrolyte) holding the electrolyte therebetween. Further, the electrodes were laminated so that five unit cell layers (for five unit cell layers) were formed to obtain a laminate.
[0107]
The laminate was sealed with an aluminum laminate film as a battery exterior material to produce a bipolar battery.
[0108]
Comparative Example 1
In the same manner as in Example 1 except that bipolar electrodes (a negative electrode and a positive electrode) having no electrolyte holding material were used, the electrodes were stacked so that five unit cell layers (for five unit cells) were formed. A bipolar battery sealed with an aluminum laminate film was produced.
[0109]
<Evaluation>
The bipolar battery of the present invention of Example 1 and the polymer bipolar battery having no electrolyte retaining material of Comparative Example 1 were placed in a constant temperature bath, the battery temperature was adjusted to 25 ° C., and the discharge performance was measured using a charge / discharge device. The test was performed.
[0110]
In the discharge performance test, the battery was charged to a full charge (21.0 V) by charging at a constant current and a constant voltage, and was discharged at a constant current of 15.0 V at a current rate of 5 CA. The reaction was performed by determining the reaction rate (discharge capacity at 5 CA / theoretical capacity of battery × 100). FIG. 7 shows the result.
[0111]
Note that the theoretical capacity of the battery is obtained from the theoretical capacity of the positive electrode active material and the coating amount of the positive electrode active material.
[0112]
FIG. 7 shows that the discharge reaction rate of the bipolar battery of Comparative Example 1 was 55%, while that of the bipolar battery of the present invention was 96%.
[Brief description of the drawings]
FIG. 1 is a schematic diagram of a general lithium ion secondary battery electrode and an electrolyte layer.
FIG. 2 is a schematic view of an electrode for a lithium ion secondary battery of the present invention. 2A shows an example in which a ceramic porous body (activated carbon) is used as the electrolyte holding material 7, and FIG. 2B shows an example in which a resin hollow fiber is used as the electrolyte holding material 7, and FIG. In this example, a nonwoven fabric is used as the electrolyte holding material 7.
FIG. 3 is a schematic sectional view schematically showing a basic structure of a bipolar electrode constituting the bipolar battery of the present invention.
FIG. 4 is a schematic sectional view schematically showing a basic structure of a unit cell layer (single cell) constituting the bipolar battery of the present invention.
FIG. 5 is a schematic sectional view schematically showing the basic structure of the bipolar battery of the present invention.
FIG. 6 is a schematic diagram schematically showing a basic configuration of a bipolar battery of the present invention.
FIG. 7 is a view showing a result of a discharge performance test of the bipolar battery of the present invention.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1, 11 ... current collector, 2 ... electrode layer, 3 ... electrolyte layer, 4 ... electrode active material, 5 ... electrolyte, 6 ... lithium ion, 7 ... electrolyte retention material, 12 ... positive electrode layer, 13 ... negative electrode layer, 14 ... Polymer electrolyte, 15 ... Bipolar electrode, 15a ... Electrode with negative electrode layer only on one side of current collector required, 15b ... Electrode with positive electrode layer only on one side required of current collector, 16 ... Single cell Layer: 17: Electrode laminate, 18: Positive terminal plate, 19: Negative terminal plate, 20: Battery exterior material, 21: Bipolar battery.

Claims (11)

An electrode for a lithium ion secondary battery, comprising an electrolyte holding material disposed in a gap between electrode active materials. 2. The electrode for a lithium ion secondary battery according to claim 1, wherein the electrolyte retaining material has at least one selected from a resin hollow fiber, a nonwoven fabric, a ceramic porous body, and activated carbon. 3. Adjusting the slurry containing the electrode active material and the electrolyte retaining material,
Applying the slurry on a current collector;
A method for producing an electrode for a lithium ion secondary battery comprising: Electrode active material, electrolyte holding material, a step of applying a slurry containing an electrolyte solution on the current collector,
Polymerizing the electrolyte solution,
A method for producing an electrode for a lithium ion secondary battery comprising: A lithium ion secondary battery comprising the electrode for a lithium ion secondary battery according to claim 1 or 2, or the electrode for a lithium ion secondary battery manufactured by the method according to claim 3 or 4. . The lithium ion secondary battery according to claim 5, wherein the positive electrode active material is a lithium-transition metal composite oxide. 7. The lithium ion secondary battery according to claim 5, wherein the negative electrode active material is carbon or a lithium-transition metal composite oxide. The lithium ion secondary battery according to any one of claims 5 to 7, wherein the electrolyte is a polymer electrolyte. The lithium ion secondary battery according to any one of claims 5 to 8, which is a bipolar battery. An assembled battery comprising a plurality of the lithium ion secondary batteries according to claim 5 connected to each other. A vehicle equipped with the lithium ion secondary battery according to any one of claims 5 to 9 or the assembled battery according to claim 10.

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