JPWO2013080379A1 - Lithium secondary battery and manufacturing method thereof - Google Patents

Abstract

A method for producing a lithium secondary battery, wherein the negative electrode mixture layer formed on the negative electrode of the battery has a pore diameter measured by pore distribution measurement based on a mercury intrusion method in a range of 0.3 μm to 4 μm (A ), And a pore diameter of 0 μm or more and less than 0.3 μm (B) has a maximum point, the maximum point pore capacity (VA) in the range A, and the maximum point in the range B. The ratio (VA / VB) to the pore volume (VB) is 2.1 or more and 3.4 or less.

Description

  The present invention relates to a lithium secondary battery. Specifically, the present invention relates to the battery excellent in capacity maintenance characteristics in a high temperature environment and a method for manufacturing the battery.

  Lithium ion batteries and other lithium secondary batteries are smaller, lighter and have a higher energy density than the existing batteries, and are excellent in output density. For this reason, in recent years, it is preferably used as a so-called portable power source for personal computers and portable terminals, and a power source for driving vehicles.

  This type of lithium secondary battery (typically a lithium ion battery) has a configuration in which an electrode body composed of a positive electrode and a negative electrode and an electrolyte (typically an electrolyte solution) are contained in a battery case. The electrodes (positive electrode and negative electrode) are electrode mixture layers (mainly composed of active materials capable of reversibly occluding and releasing charge carriers (typically lithium ions) on corresponding positive and negative current collectors) Specifically, a positive electrode mixture layer and a negative electrode mixture layer) are respectively formed.

  When a lithium secondary battery is used as a so-called portable power source, as described above, the battery is preferably small, light, and has a higher energy density (capacity). However, if the density in the electrode mixture layer is increased in order to obtain a high energy density, the diffusion resistance of charge carriers in the mixture layer increases, and the output density and durability (cycle characteristics) may deteriorate. . Patent documents 1-3 are mentioned as conventional technology with respect to this subject. For example, Patent Document 1 discloses a technique that can improve the power density by ensuring an appropriate pore distribution in the negative electrode mixture layer.

Japanese Patent Application Publication No. 09-129232 Japanese Patent Application Publication No. 2009-158396 Japanese Patent Application Publication No. 2006-059690

  By the way, in the lithium secondary battery, part of the electrolyte components (non-aqueous solvent, supporting salt, etc.) is reduced and decomposed during initial charging, and a film (SEI: Solid Electrolyte Interface) is formed on the surface of the negative electrode active material. Thereby, the interface between the negative electrode surface and the electrolyte is stabilized, and further reductive decomposition of the electrolyte component can be prevented during normal use. However, in such a battery, there is a risk that the SEI film grows in a high temperature environment to increase internal resistance or generate irreversible capacity. For this reason, in a lithium secondary battery (typically, a power source for driving a vehicle) whose use environment and / or storage environment can be high temperature (for example, 50 ° C. to 70 ° C.), characteristics (for example, power supply for vehicle driving) It is extremely important that the capacity retention rate in a high temperature environment (ie, high temperature storage characteristics) is excellent. However, the techniques described in Patent Documents 1 to 3 are not considered for such a problem.

  This invention is made | formed in view of this point, The place made into the objective is to provide the lithium secondary battery which has the outstanding high temperature storage characteristic. It is more preferable to provide a lithium secondary battery in which battery performance is improved (for example, resistance is reduced) in addition to the high-temperature storage characteristics.

To achieve the above object, according to the present invention, a slurry-like composition for forming a negative electrode mixture layer containing a negative electrode active material and a binder is prepared, and a slurry-like positive electrode mixture layer containing a positive electrode active material and a binder. Preparing a forming composition, forming the negative electrode composite layer on the current collector by applying the negative electrode mixture layer-forming composition on the negative electrode current collector, and forming the positive electrode Forming a positive electrode provided with a positive electrode composite material layer on the current collector by applying a composition for forming a composite material layer on the positive electrode current collector, a lithium secondary battery using the negative electrode and the positive electrode A method for manufacturing a lithium secondary battery is provided. In the manufacturing method disclosed herein, as a negative electrode used for constructing such a lithium secondary battery, a pore distribution based on a mercury intrusion method is measured, and a pore diameter by the measurement is in a range of 0.3 μm to 4 μm. (A) and a pore diameter of 0 μm or more and less than 0.3 μm (B), each having a local maximum point, a local maximum pore volume (V _A ) in the range _A and the range B The ratio (V _A / V _B ) to the pore volume (V _B ) of the local maximum point in is 2.1 or more and 3.4 or less.
According to the manufacturing method disclosed herein, the growth of the SEI film on the surface of the negative electrode active material particles can be suppressed even when the use environment and / or the storage environment is a high temperature (for example, 50 ° C. to 70 ° C.). Capacitance and contact resistance between the negative electrode active material particles can be reduced. Therefore, the lithium secondary battery provided with such a negative electrode mixture layer has excellent high-temperature storage characteristics. Moreover, according to the manufacturing method disclosed here, since appropriate pores are secured in the negative electrode composite material layer, a good conductive path (conductive path) can be maintained in the composite material layer. Furthermore, since the diffusion resistance of lithium ions can be preferably reduced, excellent battery performance (for example, reduction in battery resistance) can be exhibited.

In a preferred embodiment of the method for producing a lithium secondary battery disclosed herein, a negative electrode in which the density of the negative electrode mixture layer is 1.0 g / cm ³ or more and 1.6 g / cm ³ or less is exemplified.
The lithium secondary battery provided with the negative electrode mixture layer satisfying the above density range has a high energy density and can exhibit excellent battery performance even in a high temperature environment. Further, since appropriate pores are secured in the composite material layer, the diffusion resistance of lithium ions can be reduced, and more excellent battery performance (for example, reduction in battery resistance) can be exhibited.

In a preferred embodiment of the method for producing a lithium secondary battery disclosed herein, the negative electrode active material has a cumulative 50% particle size (D ₅₀ ) measured by particle size distribution measurement (laser diffraction / light scattering method) of 3 μm. The specific surface area is not less than 20 μm and the specific surface area measured by the nitrogen adsorption method is 2 m ² / g or more and 40 m ² / g or less.
Graphite as the negative electrode active material is highly safe and has a large theoretical capacity, so that a high energy density can be realized. Moreover, since the negative electrode composite material layer made of graphite satisfying the above particle size range can secure appropriate pores in the composite material layer, the diffusion resistance of lithium ions can be reduced. Furthermore, graphite satisfying the above specific surface area range has a higher energy density and can further reduce the contact resistance between the negative electrode active materials in a high temperature environment. Therefore, a battery provided with such graphite can exhibit better performance (for example, reduction in battery resistance).

In a preferred embodiment of the method for producing a lithium secondary battery disclosed herein, the composition for forming a negative electrode mixture layer includes at least styrene butadiene rubber and / or carboxymethyl cellulose.
The binder is excellent in adhesiveness, and can form a good conductive path (conductive path) between the negative electrode active material particles and between the active material particles and the negative electrode current collector. For this reason, the resistance in the negative electrode mixture layer can be reduced, and the battery performance can be improved.

In a preferred embodiment of the method for producing a lithium secondary battery disclosed herein, the solid content concentration of the composition for forming a negative electrode mixture layer is 40% or more and 60% or less.
When the solid content concentration of the negative electrode mixture slurry is in the above range, the dispersibility of the slurry is good, and the coating property is good because there are almost no coarse aggregates. Moreover, since the negative electrode mixture layer can be formed with high accuracy, an excellent conductive path (conductive path) can be formed in the negative electrode mixture layer. Therefore, in the lithium secondary battery provided with such a negative electrode mixture layer, the internal resistance can be reduced, and the battery performance can be further improved.

In order to achieve the above object, according to the present invention, a lithium secondary battery including an electrode body having a positive electrode and a negative electrode, wherein the negative electrode is formed on the negative electrode current collector and the negative electrode current collector. A lithium secondary battery including a negative electrode active material and a binder is provided. Here, in the pore distribution based on the mercury intrusion method, the negative electrode composite layer has a pore diameter range of 0.3 μm to 4 μm (A) and a pore diameter range of 0 μm to less than 0.3 μm (B). Each having a local maximum point, and the ratio (V _A / V) of the pore volume (V _A ) at the maximum point in the range A to the pore volume (V _B ) at the maximum point in the range B. _B ) is not less than 2.1 and not more than 3.4.
According to the battery having such a configuration, the irreversible capacity is reduced even in a high temperature environment for the reason described above, and an excellent capacity maintenance rate can be maintained. Moreover, the diffusion resistance of lithium ions can be reduced while maintaining a good conductive path in the negative electrode mixture layer. For this reason, the lithium secondary battery provided with such a negative electrode mixture layer can exhibit excellent battery performance (for example, reduction in battery resistance).

In a preferable embodiment of the lithium secondary battery disclosed herein, the density of the negative electrode mixture layer is 1.0 g / cm ³ or more and 1.6 g / cm ³ or less.
As described above, the lithium secondary battery including the negative electrode mixture layer that satisfies the above density range has a high energy density and can exhibit excellent battery performance even in a high temperature environment. Further, the diffusion resistance of lithium ions can be reduced, and the battery performance of the battery can be improved.

In a preferred embodiment of the lithium secondary battery disclosed herein, the negative electrode active material has a cumulative 50% particle size (D50) measured by particle size distribution measurement (laser diffraction / light scattering method) of 3 μm or more and 20 μm or less, In addition, the use of graphite having a specific surface area of 2 m ² / g or more and 40 m ² / g or less can be mentioned.
As described above, the negative electrode mixture layer made of graphite satisfying the above particle size range can reduce the diffusion resistance of lithium ions. Moreover, the graphite satisfying the above specific surface area range has a high energy density and can further reduce the contact resistance between the negative electrode active materials in a high temperature environment. For this reason, the battery performance of this battery can be improved more.

In a preferable embodiment of the lithium secondary battery disclosed herein, the composition for forming a negative electrode mixture layer includes at least styrene butadiene rubber and carboxymethyl cellulose.
The binder is excellent in adhesiveness and can form a good conductive path (conductive path) in the negative electrode mixture layer. For this reason, the battery performance of this battery can be improved more.

In a preferred embodiment of the lithium secondary battery disclosed herein, the product of the IV resistance (mΩ) at 25 ° C. and the capacity (Ah) of the battery is 18 (mΩ · Ah) or less, and at 25 ° C. The product of DC resistance (mΩ) based on AC impedance measurement and battery capacity (Ah) is 20 (mΩ · Ah) or less.
In such a battery, since the resistance is reduced as compared with the conventional battery, the battery performance can be improved.

  The lithium secondary battery disclosed herein is particularly suitable as a driving power source mounted on a vehicle such as an automobile because it has excellent high-temperature storage characteristics and can improve battery performance (for example, reduce internal resistance). is there. Therefore, according to the present invention, a vehicle (typically a plug-in hybrid) comprising any of the lithium secondary batteries disclosed herein (which may be in the form of an assembled battery to which a plurality of lithium secondary batteries are connected). Motor vehicles (PHV), hybrid vehicles (HV), electric vehicles such as electric vehicles (EV)) are provided.

FIG. 1 is a schematic diagram showing a configuration of a lithium secondary battery according to an embodiment of the present invention. FIG. 2 is a schematic diagram illustrating a configuration of a wound electrode body of a lithium secondary battery according to an embodiment of the present invention. FIG. 3 is a side view schematically showing a vehicle (automobile) provided with the lithium secondary battery according to the embodiment of the present invention as a power source for driving the vehicle. FIG. 4 is a chart showing the pore distribution of the negative electrode mixture layer measured by the mercury intrusion method according to one embodiment of the present invention. FIG. 5 is a graph showing the relationship between V _A / V _B and capacity retention rate (%) according to one embodiment of the present invention. FIG. 6 is a graph showing the relationship between V _A / V _B and the IV resistance value according to one embodiment of the present invention. FIG. 7 is a graph showing the relationship between V _A / V _B and the DC resistance value according to one embodiment of the present invention.

  In the present specification, the “lithium secondary battery” refers to a secondary battery that uses lithium ions as electrolyte ions and is charged / discharged by movement of charges accompanying the lithium ions between the positive and negative electrodes. Secondary batteries generally referred to as lithium ion batteries (or lithium ion secondary batteries), lithium polymer batteries, lithium-air batteries, lithium-sulfur batteries, and the like are typical examples included in the lithium secondary batteries in this specification. It is. Further, in this specification, the “active material” refers to a substance (compound) involved in power storage on the positive electrode side or the negative electrode side. That is, it refers to a substance that is involved in the insertion and extraction of electrons during battery charge / discharge.

  Hereinafter, preferred embodiments of the lithium secondary battery disclosed herein will be described. Note that matters other than matters specifically mentioned in the present specification and necessary for implementation can be grasped as design matters of those skilled in the art based on the prior art in this field. The lithium secondary battery having such a structure can be implemented based on the contents disclosed in the present specification and common technical knowledge in the field.

  As described above, the production method disclosed herein is a method characterized by the production of the negative electrode mixture layer, and preparing a slurry-like composition for forming a negative electrode mixture layer containing a negative electrode active material and a binder, Forming a negative electrode having a negative electrode mixture layer on the current collector by applying the negative electrode mixture layer forming composition onto the negative electrode current collector, and forming a slurry containing a positive electrode active material and a binder A positive electrode including a positive electrode mixture layer is formed on the current collector by preparing a positive electrode mixture layer forming composition and applying the positive electrode mixture layer forming composition onto the positive electrode current collector. And constructing a lithium secondary battery using the negative electrode and the positive electrode. Hereinafter, preferred embodiments of the production method will be described in detail.

  In the manufacturing method disclosed herein, the negative electrode of the lithium secondary battery includes a slurry-like (paste-like or ink-like) obtained by mixing a negative-electrode active material and a binder (binder) in an appropriate solvent. The negative electrode mixture layer forming composition (hereinafter referred to as “negative electrode mixture slurry”) is prepared, and the slurry is applied onto the negative electrode current collector to form the negative electrode mixture layer (also referred to as the negative electrode active material layer). In the form in which it is formed).

  As the negative electrode active material used here, one or more of materials conventionally used in lithium secondary batteries can be used without any particular limitation. For example, particulate graphite powder (carbon particles) including a graphite structure (layered structure) at least partially, oxides such as lithium titanate (LTO), alloys of tin (Sn), silicon (Si) and lithium, and the like Can be mentioned. As the graphite powder, graphite, non-graphitizable carbon (hard carbon), easily graphitized carbon (soft carbon), or a combination of these can be used. Can be preferably used. Examples of the graphite include natural graphite (also called graphite) extracted from natural minerals, artificial graphite manufactured from petroleum or coal-based materials, or the above-mentioned graphite subjected to processing such as pulverization or pressing It may be one or more selected from the above. More specifically, for example, scaly graphite, scaly (lumpy) graphite, earthy graphite, expanded graphite, pyrolytic graphite and the like can be mentioned. Such a shape may be scaly, spherical, fibrous, granular or the like. The proportion of the negative electrode active material in the entire negative electrode mixture layer is not particularly limited, but it is usually appropriately about 50% by mass or more, preferably about 90% by mass to 99% by mass (for example, about 95% by mass to 99% by mass).

The negative electrode active material used here has a cumulative 50% particle size (D ₅₀ ) of 2 μm or more (preferably 3 μm or more) according to the particle size distribution measured by particle size distribution measurement (laser diffraction / light scattering method). And 50 μm or less (typically 30 μm or less, preferably 20 μm or less). The negative electrode active material satisfying the above particle size range can form appropriate pores in the negative electrode mixture layer, and can reduce diffusion resistance associated with insertion and extraction of lithium ions. Moreover, since a favorable conductive path (conductive path) can be formed in the negative electrode mixture layer, battery performance can be improved (for example, resistance can be reduced and high-temperature storage characteristics can be improved).
The particle size distribution can be measured by particle size distribution measurement based on a laser diffraction / light scattering method. Specifically, first, a sample (powder) is dispersed in a measurement solvent. At this time, a dispersant such as a surfactant may be added within a range that does not affect the measurement result. Next, such a dispersion can be put into, for example, a particle size distribution measuring apparatus manufactured by Horiba, Ltd., model “LA-920”, and the measured value can be adopted. In this specification, “particle size” refers to a value that can be derived from the volume-based particle size distribution calculated from the measurement results, and the cumulative 50% particle size (D ₅₀ ) refers to the fine particle side in the volume-based particle size distribution. The particle diameter (median diameter) corresponding to the cumulative 50% from is shown.

Further, the specific surface area of the negative electrode active material used here is preferably 1 m ² / g or more (for example, 2 m ² / g or more, more preferably 4 m ² / g or more). Moreover, it is preferable that it exists in the range of 50 m < ² > / g or less (for example, 40 m < ² > / g or less, Furthermore, 30 m < ² > / g or less). If the specific surface area is too small, sufficient energy density may not be obtained, or the contact resistance between the active material particles may increase. On the other hand, if the specific surface area is too large, the irreversible capacity in a high-temperature environment increases as in one embodiment described later, which may reduce the battery capacity.
The specific surface area is measured by a gas adsorption method for measuring an adsorption isotherm of nitrogen gas, for example, using an automatic specific surface area / pore distribution measuring device “BELSORP (trademark) -18PLUS” manufactured by Nippon Bell Co., Ltd. A value (BET specific surface area) measured by a constant volume adsorption method can be adopted. Specifically, approximately 0.4 g of sample (powder) is filled in a cell, heated in a vacuum state, pretreated, cooled to liquid nitrogen temperature, and saturated adsorption of 30% nitrogen and 70% He gas. Let Thereafter, the amount of gas desorbed by heating to room temperature is measured, and the specific surface area is calculated from the obtained results by the BET method (for example, the BET one-point method).

As the binder used here, one kind or two or more kinds of substances conventionally used in lithium secondary batteries can be used without particular limitation. Typically, various polymer materials can be suitably used. For example, when the negative electrode mixture layer is formed using an aqueous liquid composition, a polymer material that is dissolved or dispersed in water can be preferably used. Examples of such polymer materials include cellulose polymers, fluorine resins, vinyl acetate copolymers, rubbers, and the like. More specifically, carboxymethylcellulose (CMC), hydroxypropylmethylcellulose (HPMC), polyvinyl alcohol (PVA), polytetrafluoroethylene (PTFE), tetrafluoroethylene-hexafluoropropylene copolymer (FEP), styrene butadiene rubber (SBR), acrylic acid-modified SBR resin (SBR latex), and the like. In particular, when SBR and CMC are used, they are preferably used because they have excellent adhesiveness and can form good conductive paths between the negative electrode active material particles and between the active material particles and the negative electrode current collector.
Alternatively, when the negative electrode mixture layer is formed using a solvent-based liquid composition (a solvent-based composition in which the main component of the dispersion medium is an organic solvent), a polymer material that is dispersed or dissolved in an organic solvent is preferably employed. Can do. Examples of the polymer material include polyvinylidene fluoride (PVdF), polyvinylidene chloride (PVdC), polyethylene oxide (PEO), and the like. Although it does not specifically limit, the usage-amount of the binder which occupies for the whole negative electrode compound-material layer layer can be 0.1 mass%-10 mass% (preferably 0.5 mass%-5 mass%), for example.

  As a solvent used here, 1 type, or 2 or more types can be used without specifically limiting among the solvents conventionally used for a lithium secondary battery. Such a solvent is roughly classified into an aqueous solvent and an organic solvent, and the aqueous solvent is preferably water or a mixed solvent mainly composed of water. As the solvent other than water constituting the mixed solvent, one or more organic solvents (lower alcohol, lower ketone, etc.) that can be uniformly mixed with water can be appropriately selected and used. For example, it is preferable to use an aqueous solvent in which about 80% by mass or more (more preferably about 90% by mass or more, more preferably about 95% by mass or more) of the aqueous solvent is water. A particularly preferable example is an aqueous solvent (for example, water) substantially consisting of water. Examples of the organic solvent include amides, alcohols, ketones, esters, amines, ethers, nitriles, cyclic ethers, aromatic hydrocarbons, and the like. More specifically, N-methyl-2-pyrrolidone (NMP), N, N-dimethylformamide (DMF), N, N-dimethylacetamide, 2-propanol, ethanol, methanol, acetone, methyl ethyl ketone, methyl propenoate, Cyclohexanone, methyl acetate, ethyl acetate, methyl acrylate, diethyl triamine, N, N-dimethylaminopropylamine, acetonitrile, ethylene oxide, tetrahydrofuran (THF), dioxane, benzene, toluene, ethylbenzene, xylene dimethyl sulfoxide (DMSO), dichloromethane, Examples include trichloromethane and dichloroethane.

  Moreover, you may add the material which can function as a dispersing agent, a electrically conductive material, etc. to the negative mix slurry prepared here as needed. Examples of the dispersant include polymer compounds having a hydrophobic chain and a hydrophilic group (for example, alkali salts, typically sodium salts), anionic compounds having sulfates, sulfonates, phosphates, and the like. And cationic compounds such as amines. More specifically, carboxymethyl cellulose (CMC), methyl cellulose, ethyl cellulose, hydroxypropyl cellulose, polyvinyl alcohol, modified polyvinyl alcohol, polyethylene oxide, polyvinyl pyrrolidone, polycarboxylic acid, oxidized starch, phosphate starch and the like are exemplified. A water-soluble polymer material such as carboxymethyl cellulose is preferably used.

  As a method for preparing a negative electrode mixture slurry, the negative electrode active material, a binder, and an additive such as a dispersing agent may be added to a solvent at a time and kneaded, or may be added in stages in several steps. You may knead. For example, first, CMC that can function as both a binder and a dispersant can be dispersed in a smaller amount of solvent than the target solvent, and then a negative electrode active material and SBR as a binder can be added in stages. That is, by first dispersing CMC having a high molecular weight and relatively poor dispersibility in a solvent, a negative electrode mixture slurry in which the negative electrode active material is uniformly dispersed can be obtained. Although not particularly limited, the solid content concentration (hereinafter referred to as “NV”) of the negative electrode mixture slurry is about 30% or more (preferably 40% or more, more preferably 45% or more), and 70% or less (preferably 60%, more preferably 55% or less). When the solid content concentration of the slurry is in the above range, the dispersibility is excellent and the coating property is good. For this reason, the negative electrode mixture layer can be formed with high accuracy.

As a method for forming the negative electrode mixture layer, a method in which an appropriate amount of the negative electrode mixture slurry is applied to one side or both sides of the negative electrode current collector and dried can be preferably employed.
The operation of applying the negative electrode mixture slurry can be performed in the same manner as in the case of producing a conventional general negative electrode for a lithium secondary battery. For example, by coating a predetermined amount of the negative electrode mixture slurry to a uniform thickness on the negative electrode current collector using a suitable coating device (slit coater, die coater, comma coater, gravure coater, etc.) Can be made.
Thereafter, the negative electrode mixture layer is dried by an appropriate drying means to remove the solvent contained in the negative electrode mixture slurry. In drying the negative electrode mixture layer, natural drying, hot air, low-humidity air, vacuum, infrared rays, far-infrared rays, electron beams, or the like can be used alone or in combination. In a preferred embodiment, the drying temperature is about 200 ° C. or lower (typically 80 ° C. or higher and lower than 200 ° C.). Thus, the negative electrode for lithium secondary batteries disclosed here can be obtained.

  Here, examples of the material for the negative electrode current collector include copper, nickel, titanium, and stainless steel. The form is not particularly limited, and a rod-like body, a plate-like body, a foil-like body, a net-like body, or the like can be used. A battery having a wound electrode body to be described later uses a foil shape. The thickness of the foil-shaped current collector is not particularly limited, but about 5 μm to 200 μm (more preferably 8 μm to 50 μm) can be preferably used in consideration of the capacity density of the battery and the strength of the current collector.

After drying the negative electrode mixture slurry, the thickness and density of the negative electrode mixture layer are appropriately subjected to press treatment (for example, various conventionally known press methods such as a roll press method and a flat plate press method can be employed). , The pore distribution can be adjusted. The density of the negative electrode mixture layer formed on the negative electrode current collector is, for example, 1.0 g / cm ³ or more (preferably 1.1 g / cm ³ or more, more preferably 1.2 g / cm ³ or more). 1.6 g / cm ³ or less (preferably 1.5 g / cm ³ or less). When the density of the negative electrode mixture layer is low (that is, the amount of active material in the negative electrode mixture layer is small), the capacity per unit volume of the battery decreases. On the other hand, if the density is too high, the diffusion resistance associated with the insertion / extraction of lithium ions tends to increase and the internal resistance tends to increase, as in an embodiment described later. However, a lithium secondary battery including a negative electrode mixture layer that satisfies the above density range has a high energy density and can reduce diffusion resistance of lithium ions, so that more excellent battery performance (for example, battery resistance) Reduction).

As the negative electrode used in the lithium secondary battery disclosed herein, in the pore distribution based on the mercury intrusion method, the pore diameter ranges from 0.3 μm to 4 μm (A), and the pore diameter ranges from 0 μm to 0.3 μm. Each having a maximum point in the range (B) of less than, the pore volume (V _A ) of the maximum point in the range _A and the pore volume (V _B ) of the maximum point in the range B The ratio (V _A / V _B ) is 2.1 or more and 3.4 or less. In general, storage of the battery in a high SOC region (eg, SOC 80% to 100%) and / or storage in a high temperature region (eg, 50 ° C. to 70 ° C.) significantly reduces the capacity of the battery. This is because an irreversible capacity is generated as the SEI film on the surface of the negative electrode active material particles grows. However, in the negative electrode satisfying the above range, since the growth of the SEI film on the surface of the active material particles can be suppressed even when the use environment and / or the storage environment become high temperature, the irreversible capacity and the contact resistance between the negative electrode active material particles Can be reduced. “SOC” means charge depth (State
of charge), and in a range of operating voltage that can be reversibly charged and discharged, the charging state (that is, the fully charged state) in which the upper limit voltage is obtained is 100%, and the lower limit voltage is obtained. The state of charge when the state (that is, the state of being not charged) is 0% is shown.

  In addition, in the negative electrode satisfying the above range, since appropriate pores are secured in the negative electrode mixture layer, diffusion resistance of lithium ions is maintained while maintaining a good conductive path (conductive path) in the mixture layer. Can be reduced. Therefore, the lithium secondary battery provided with such a negative electrode composite material layer has excellent high-temperature storage characteristics and can improve battery performance (for example, decrease in resistance), and can be used and / or particularly in a high-temperature environment. It is suitable for the battery that can be stored.

The pore distribution based on the mercury intrusion method in the negative electrode mixture layer can be measured using a mercury porosimeter. The mercury intrusion method is a method for measuring the pore distribution of a porous body, and includes voids between particles in the negative electrode mixture layer (that is, pores between negative electrode active materials) and fine particles present on the surface of the active material. The hole can be grasped. Such pores can be adjusted depending on the type and properties (for example, specific surface area) of the negative electrode active material to be used, the NV value at the time of coating the negative electrode mixture slurry, and rolling (press) conditions.
As a specific measurement method of the mercury intrusion method, first, the negative electrode mixture layer as a measurement target is peeled off from the negative electrode current collector to obtain a sample. Next, the sample is immersed in mercury in a vacuumed state, and the pressure is gradually increased. Then, mercury enters the pores of the sample, and the volume of the pores can be measured. That is, as the pressure applied to mercury increases, mercury gradually enters a smaller space. Since the pressure and the size of the pores are inversely proportional, the size of the pores and the volume distribution of the sample can be obtained based on this relationship. As such an apparatus, for example, Autopore III 9410 manufactured by Shimadzu Corporation can be used. In this case, for example, by measuring at 4 psi to 60000 psi, the volume distribution of the pores corresponding to the pore range of 50 μm to 0.003 μm can be grasped.

  The positive electrode of the lithium secondary battery disclosed here is a composition for forming a positive electrode mixture layer in a slurry state (including paste and ink) by mixing a positive electrode active material, a conductive material, a binder, and the like. (Hereinafter, referred to as “positive electrode mixture slurry”). A slurry in which the slurry is applied onto a positive electrode current collector to form a positive electrode mixture layer (also referred to as a positive electrode active material layer) is used.

As the positive electrode active material used here, one or more of materials conventionally used in lithium secondary batteries can be used without any particular limitation. For example, an oxide containing lithium and a transition metal element as constituent metal elements such as lithium nickel oxide (eg LiNiO ₂ ), lithium cobalt oxide (eg LiCoO ₂ ), lithium manganese oxide (eg LiMn ₂ O ₄ ) Examples thereof include lithium transition metal oxides), phosphates including lithium and transition metal elements such as lithium manganese phosphate (LiMnPO ₄ ) and lithium iron phosphate (LiFePO ₄ ) as constituent metal elements. Among them, a positive electrode active material (typically substantially lithium nickel cobalt manganese) having a layered structure lithium nickel cobalt manganese composite oxide (for example, LiNi _1/3 Co _1/3 Mn _1/3 O ₂ ) as a main component. A positive electrode active material made of a composite oxide is preferably used because of its excellent thermal stability and high energy density. Although not particularly limited, the ratio of the positive electrode active material to the entire positive electrode mixture layer is typically about 50% by mass or more (typically 70% to 99% by mass), and about 80%. It is preferable that it is mass%-99 mass%.

  Here, the lithium nickel cobalt manganese composite oxide is an oxide having Li, Ni, Co, and Mn as constituent metal elements, and at least one other metal element (Li, Ni, Co, and Mn) in addition to Li, Ni, Co, and Mn. The meaning also includes oxides containing transition metal elements and / or typical metal elements other than Ni, Co, and Mn. Such metal elements are, for example, one or more elements of Al, Cr, Fe, V, Mg, Ti, Zr, Nb, Mo, W, Cu, Zn, Ga, In, Sn, La, and Ce. It can be. The same applies to lithium nickel oxide, lithium cobalt oxide, and lithium manganese oxide. As such a lithium transition metal oxide (typically in particulate form), for example, a lithium transition metal oxide powder prepared by a conventionally known method can be used as it is.

As the conductive material used here, one kind or two or more kinds of substances conventionally used in lithium secondary batteries can be used without particular limitation. For example, various carbon blacks (for example, acetylene black (AB), furnace black, ketjen black (KB), channel black, lamp black, thermal black), graphite powder (natural products, artificial products), carbon fibers (PAN series) , Pitch system) or the like. Or metal fibers (e.g. Al, SUS or the like), conductive metal powder (e.g. Ag, Ni, Cu, etc.), metal oxides (e.g. ZnO, SnO _2, etc.), may be used the surface-coated synthetic fiber such as a metal . Among these, a preferable carbon powder is acetylene black (AB). The proportion of the conductive agent in the entire positive electrode mixture layer can be, for example, approximately 1% by mass to 15% by mass, and approximately 2% by mass to 8% by mass (more preferably 2% by mass to 6% by mass). It is preferable.

  As the binder used here, an appropriate material can be selected from the polymer materials exemplified as the binder for the negative electrode mixture layer. Examples thereof include polyvinylidene fluoride (PVdF), polytetrafluoroethylene (PTFE), styrene butadiene rubber (SBR), and the like. The ratio of the binder to the whole positive electrode composite material layer can be, for example, about 0.1% by mass to 10% by mass, and preferably about 1% by mass to 5% by mass.

As a method of forming the positive electrode mixture layer, a method of applying an appropriate amount of the positive electrode mixture slurry to one or both sides of the positive electrode current collector and drying it by the same operation as in the case of the negative electrode negative electrode mixture layer is preferably employed. be able to.
Thereafter, as in the case of the negative electrode negative electrode mixture layer, the solvent contained in the positive electrode mixture slurry is removed by drying the positive electrode mixture layer by an appropriate drying means. After drying the positive electrode mixture slurry, the thickness and density of the positive electrode mixture layer can be adjusted by appropriately performing a press treatment (for example, a roll press method, a flat plate press method, etc.).

  Here, examples of the material for the positive electrode current collector include aluminum, nickel, titanium, and stainless steel. The shape of the current collector is not particularly limited because it may vary depending on the shape of the battery constructed using the obtained electrode, and a rod-like body, a plate-like body, a foil-like body, a net-like body, or the like may be used. it can. In a battery provided with a wound electrode body to be described later, a foil-like body is mainly used. The thickness of the foil-shaped current collector is not particularly limited, but about 5 μm to 200 μm (more preferably 8 μm to 50 μm) can be preferably used in consideration of the capacity density of the battery and the strength of the current collector.

An electrode body in which the positive electrode and the negative electrode are laminated is prepared and accommodated in an appropriate battery case together with the electrolytic solution to construct a lithium secondary battery. In the typical configuration of the lithium secondary battery disclosed herein, a separator is interposed between the positive electrode and the negative electrode.
As a battery case, the material and shape which are used for the conventional lithium secondary battery can be used. Examples of the material include relatively light metal materials such as aluminum and steel, and resin materials such as PPS and polyimide resin. Further, the shape (outer shape of the container) is not particularly limited, and may be, for example, a cylindrical shape, a rectangular shape, a rectangular parallelepiped shape, a coin shape, a bag shape, or the like. The case may be provided with a safety mechanism such as a current interruption mechanism (a mechanism capable of interrupting current in response to an increase in internal pressure when the battery is overcharged).

As the electrolytic solution used here, one kind or two or more kinds similar to the nonaqueous electrolytic solution used in the conventional lithium secondary battery can be used without any particular limitation. Such a nonaqueous electrolytic solution typically has a composition in which an electrolyte (lithium salt) is contained in a suitable nonaqueous solvent.
As the non-aqueous solvent, aprotic solvents such as carbonates, esters, ethers, nitriles, sulfones, and lactones can be used. For example, ethylene carbonate (EC), propylene carbonate (PC), diethyl carbonate (DEC), dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), 1,2-dimethoxyethane, 1,2-diethoxyethane, tetrahydrofuran, Examples include 2-methyltetrahydrofuran, dioxane, 1,3-dioxolane, diethylene glycol dimethyl ether, ethylene glycol dimethyl ether, acetonitrile, propionitrile, nitromethane, N, N-dimethylformamide, dimethyl sulfoxide, sulfolane, and γ-butyrolactone. Of these, nonaqueous solvents mainly composed of carbonates are preferably used. For example, the nonaqueous solvent contains one or more carbonates, and the total volume of these carbonates is 60% by volume or more (more preferably 75% by volume or more, and further preferably 90% by volume) of the total volume of the nonaqueous solvent. The non-aqueous electrolyte solution occupying the above and substantially 100% by volume) is preferably used. Further, it may be a solid (gel) electrolytic solution in which a polymer is added to the liquid electrolytic solution.
Examples of the electrolyte include LiPF ₆ , LiBF ₄ , LiClO ₄ , LiN (SO ₂ CF ₃ ) ₂ , LiN (SO ₂ C ₂ F ₅ ) ₂ , LiCF ₃ SO ₃ , LiC ₄ F ₉ SO ₃ , LiC (SO ₂ CF ₃ ) ₃ , LiClO _{4 and the} like are exemplified. Of these, LiPF ₆ is preferably used. The concentration of the electrolyte is not particularly limited, but if the concentration of the electrolyte is too low, the amount of lithium ions contained in the electrolytic solution tends to be insufficient, and the ionic conductivity tends to decrease. On the other hand, if the concentration of the supporting electrolyte is too high, the viscosity of the non-aqueous electrolyte solution becomes too high, and the ionic conductivity tends to decrease. For this reason, a nonaqueous electrolytic solution containing an electrolyte at a concentration of about 0.1 mol / L to 5 mol / L (preferably about 0.8 mol / L to 1.5 mol / L) is preferably used.

  Moreover, in the electrolyte solution used here, for example, an additive (specifically, vinylene carbonate (VC), fluoroethylene carbonate (FEC), etc.) that improves battery performance, or an overcharge inhibitor. (A compound that decomposes in an overcharged state and generates a large amount of gas. Typically, various additives such as biphenyl (BP) and cyclohexylbenzene (CHB)) may be added as appropriate.

  As the separator used here, various porous sheets similar to those conventionally used for lithium secondary batteries can be used. For example, a porous resin sheet (film, nonwoven fabric, etc.) made of a resin such as polyethylene (PE), polypropylene (PP), polyester, cellulose, polyamide or the like can be mentioned. Such a porous resin sheet may have a single layer structure, or may have a two or more layers structure (for example, a three-layer structure in which a PP layer is laminated on both sides of a PE layer). Although it is not particularly limited, preferred porous sheets (typically porous resin sheets) used as the separator base material have an average pore diameter of about 0.001 μm to 30 μm and a thickness of 5 μm to 100 μm. Examples of the porous resin sheet are (more preferably 10 μm to 30 μm). The porosity (porosity) of the porous sheet may be, for example, about 20% to 90% by volume (preferably 30% to 80% by volume). Note that in a lithium secondary battery (lithium polymer battery) using a solid electrolyte, the electrolyte may also serve as a separator.

  Although not intended to be particularly limited, as a schematic configuration of the lithium secondary battery according to one embodiment of the present invention, a flatly wound electrode body (winding electrode body), a non-aqueous electrolyte solution, As an example, a lithium secondary battery (single cell) in a form in which the battery is housed in a flat box-shaped (cuboid) container is shown in FIGS. In the following drawings, members / parts having the same action are denoted by the same reference numerals, and redundant description may be omitted or simplified. The dimensional relationship (length, width, thickness, etc.) in each figure does not reflect the actual dimensional relationship.

As schematically shown in FIG. 1, a lithium secondary battery 100 according to this embodiment includes a wound electrode body 80 and a battery case 50, and includes a long positive electrode sheet 10 and a long negative electrode. An electrode body (winding electrode body) 80 in a form in which the sheet 20 is wound flatly through the long separators 40A and 40B is formed in a flat box shape (cuboid shape) together with a non-aqueous electrolyte (not shown). The battery case 50 is housed.
The battery case 50 includes a flat cuboid case main body 52 having an open upper end, and a lid 54 that closes the opening. On the upper surface (that is, the lid 54) of the battery case 50, there are a positive electrode terminal 70 that is electrically connected to the positive electrode 10 of the wound electrode body 80 and a negative electrode terminal 72 that is electrically connected to the negative electrode 20 of the electrode body 80. Is provided.

FIG. 2 is a diagram schematically showing a long sheet structure (electrode sheet) in a stage before assembling the wound electrode body 80. Of the positive electrode sheet 10 in which the positive electrode mixture layer 14 is formed along the longitudinal direction on one or both surfaces (typically both surfaces) of the long positive electrode current collector 12, and the long negative electrode current collector 22. The negative electrode sheet 20 on which the negative electrode mixture layer 24 is formed along the longitudinal direction on one side or both sides (typically both sides) is superposed together with the two long separators 40A and 40B in the longitudinal direction. Turn to produce a wound electrode body. A flat wound electrode body 80 is obtained by squashing and winding the wound electrode body from the side surface direction.
The positive electrode sheet 10 is formed such that the positive electrode mixture layer 14 is not provided (or removed) at one end along the longitudinal direction, and the positive electrode current collector 12 is exposed. Similarly, the wound negative electrode sheet 20 is not provided with (or removed from) the negative electrode mixture layer 24 at one end along the longitudinal direction, so that the negative electrode current collector 22 is exposed. Is formed. A positive electrode current collector plate is attached to the exposed end portion 74 of the positive electrode current collector 12, and a negative electrode current collector plate is attached to the exposed end portion 76 of the negative electrode current collector 22, respectively. Each is electrically connected to the negative terminal 72.

  The lithium secondary battery manufactured by the manufacturing method disclosed herein can be used for various applications, but is characterized by excellent high-temperature storage characteristics and reduced resistance of the battery. Therefore, for example, as shown in FIG. 3, the lithium secondary battery 100 disclosed herein can be suitably used as a power source (drive power source) for a motor mounted on a vehicle 1 such as an automobile. Although the kind of vehicle 1 is not specifically limited, Typically, a plug-in hybrid vehicle (PHV), a hybrid vehicle (HV), and an electric vehicle (EV) are mentioned. Moreover, the lithium secondary battery 100 may be used alone, or may be used in the form of an assembled battery that is connected in series and / or in parallel.

  EXAMPLES Hereinafter, the present invention will be specifically described with reference to examples. However, the present invention is not intended to be limited to those shown in the examples.

<Example 1>
First, artificial graphite (powder), styrene butadiene rubber (SBR), and carboxymethyl cellulose (CMC) as a negative electrode active material have a mass ratio of 98: 1: 1 and an NV value of 50% by mass. The mixture was mixed with ion-exchanged water so that an aqueous negative electrode mixture slurry was prepared. This slurry was applied to both sides of a long copper foil (negative electrode current collector) having a thickness of about 10 μm to form a negative electrode mixture layer, thereby obtaining a sheet-like negative electrode (negative electrode sheet (Example 1)). The negative electrode thus obtained was dried and then rolled (pressed) so that the negative electrode composite material layer had a density of about 1.4 g / cm ³ .

Next, LiNi _1/3 Co _1/3 Mn _1/3 O ₂ powder as the positive electrode active material powder, acetylene black as the conductive material, and polyvinylidene fluoride (PVdF) as the binder are added to the mass of these materials. A positive electrode mixture slurry was prepared by mixing with N-methylpyrrolidone (NMP) such that the ratio was 91: 6: 3 and the NV value was 55% by mass. This slurry was applied to both sides of a long aluminum foil (positive electrode current collector) having a thickness of about 15 μm to form a positive electrode mixture layer, thereby obtaining a sheet-like positive electrode (positive electrode sheet). The positive electrode thus obtained was dried and then rolled (pressed) so that the positive electrode mixture layer had a density of about 2.5 g / cm ³ .

The positive electrode sheet and the negative electrode sheet (Example 1) prepared above were overlapped and wound through two separators (here, a porous polyethylene sheet (PE) was used) to prepare each electrode body. . Such an electrode body is mixed with a nonaqueous electrolytic solution (here, a mixed solvent containing ethylene carbonate (EC), dimethyl carbonate (DMC), and dimethyl carbonate (EMC) at a volume ratio of 3: 4: 3, and LiPF ₆ as an electrolyte. And an electrolyte solution dissolved at a concentration of about 1 mol / L.) And was housed in a cylindrical battery case. A lid is attached to the opening of the battery case, and welded to form a 18650 type (diameter 18 mm, height 65 mm, battery capacity 0.5 Ah) lithium secondary battery (Example 1). .

<Examples 2 to 10>
Except for adjusting the particle size of the negative electrode active material to be used and the rolling (pressing) conditions of the negative electrode mixture layer in order to determine a preferable range of V _A / V _B in the production method disclosed herein, In the same manner as in Example 1, negative electrode sheets (Examples 2 to 10) were produced. Using this negative electrode sheet (Examples 2 to 10), a 18650 type (diameter 18 mm, height 65 mm) lithium secondary battery (Examples 2 to 10) was constructed in the same manner as Example 1.

  With respect to the negative electrode mixture layer formed on the prepared negative electrode sheets (Examples 1 to 10), the pore distribution was measured by the method described above. As a typical measurement example, the pore distribution (chart) of Example 1 is shown in FIG.

As shown in FIG. 4, in the pore distribution of the negative electrode composite layer of Example 1, two large peaks were observed, having maximum points at about 0.8 μm and about 0.25 μm. Further, the pore volume of the peak to the maximum point of the 0.8 [mu] m; and ^{_{(V A 0.58cm 3 / g)}} , pore volume of the peak and the maximum point of the 0.25μm _(V B; 0.34cm ³ / g) (V _A / V _B ) was approximately 1.7. V _A (larger pore) represents the pore volume between the negative electrode active material particles, and V _B (smaller pore) represents the pore volume on the surface of the negative electrode active material particles. it is conceivable that. When similarly measured for Examples 2 to 10, V _A / V _B of the negative electrode mixture layer was 1.8 (Example 2) to 4.6 (Example 10).

  In addition, for the lithium secondary batteries constructed as described above (Examples 1 to 10), at a temperature of 25 ° C., an appropriate conditioning process (an operation of charging with constant current up to 4.2 V at a charging rate of 0.3 C (CC charging)) Then, the following performance evaluation was performed after performing an initial charge / discharge treatment in which the operation of discharging at a constant current up to 3.0 V at a discharge rate of 0.3 C (CC discharge) was repeated four times.

[High temperature storage test]
Each battery after the conditioning treatment was charged at a constant current of 1 C up to 4.1 V under a temperature condition of 25 ° C., and then charged at a constant voltage until the total charging time was 2 hours. The battery after such CC-CV charge is held for 24 hours under a temperature condition of 25 ° C., then discharged at a constant current of 1 C from 4.1 V to 3.0 V, and then until the total discharge time is 2 hours. The battery was discharged at a constant voltage, and the discharge capacity (initial capacity (C _i )) at this time was measured. And the high temperature storage test was done with respect to each battery after the said initial capacity | capacitance measurement. Specifically, each battery was first charged to adjust the SOC to 80%. Then, after storing at 60 ° C. for 60 days, the charge / discharge operation was performed under the same conditions as the initial capacity measurement described above, and the discharge capacity (C _f ) was measured. From the initial capacity (C _i ) and the discharge capacity (C _f ) after the high-temperature storage test, the capacity retention rate ((C _f / C _i ) × 100 (%)) after high-temperature storage was calculated. The results are shown in FIG.

[IV resistance measurement]
Next, for each battery constructed as described above, each battery was adjusted to a state of charge of 60% SOC by constant current constant voltage (CC-CV) charging under a temperature condition of 25 ° C. Thereafter, discharging was performed at a current value of 10 C for 10 seconds, and IV resistance was calculated from a voltage drop amount 10 seconds after the start of discharge. The results are shown in FIG.

[DC resistance measurement]
The DC resistance was measured under the following conditions by an AC impedance measurement method. With respect to the obtained Cole-Cole plot (also referred to as Nyquist plot), an equivalent circuit was fitted to obtain a direct current resistance. The results are shown in FIG.
Equipment: “Solartron” model 1287 potentio / galvanostat and model 1255B frequency response analyzer (FRA)
Measurement frequency: 10 ⁻² to 10 ⁵ Hz
Measurement temperature: 25 ° C
Analysis software: ZPlot / Corware

As shown in FIG. 5, when V _A / V _B is small (that is, V _B is large), the high temperature storage characteristics are poor, and the excellent high temperature storage characteristics are exhibited as V _A / V _B increases. This is presumably because an irreversible capacity was generated with the growth of the SEI film on the surface of the negative electrode active material particles. That is, when V _B is large, the specific surface area of the negative electrode active material is increased, so that it is considered that the growth of the SEI film and the increase in the irreversible capacity become remarkable.
Therefore, it was confirmed that by setting V _A / V _B obtained from the negative electrode pore distribution to 2.1 or more, a lithium secondary battery having a high capacity retention rate of 88% or more in the high-temperature storage test can be obtained.

As shown in FIG. 6, when V _A / V _B is in the range of 2.1 or more and 3.4 or less, the IV resistance at 25 ° C. was reduced in the battery. On the other hand, when V _A / V _B is smaller than this range (that is, when V _A is small and / or V _B is large), the IV resistance is relatively high, and this is because the density of the negative electrode mixture layer is high Therefore, it was considered that the diffusion resistance of lithium ions in the mixture layer increased. Another reason is that the contact resistance between particles in the composite layer was increased by the growth of the SEI film having low conductivity as described above. Furthermore, when V _A / V _B is larger than this range (that is, when V _A is large), a relatively high IV resistance is exhibited. This is because the conductive path (conductive path) between the negative electrode mixture layers cannot be taken. (Or the conductive path is narrowed).
Therefore, by making V _A / V _B obtained from the negative electrode pore distribution in the range of 2.1 to 3.4, the IV resistance is 36 mΩ or less (that is, the IV resistance (mΩ) at 25 ° C. and the battery capacity ( It was confirmed that a lithium secondary battery whose product with Ah) was reduced to 18 (mΩ · Ah) or less) was obtained. In addition, since the diffusion resistance of lithium ions is suppressed in such a range, the battery having excellent output characteristics can be manufactured according to the manufacturing method disclosed herein.

As shown in FIG. 7, when V _A / V _B was 3.4 or less, the direct current resistance of the battery at 25 ° C. was reduced. On the other hand, when V _A / V _B is 3.4 or more (that is, V _A is large), the DC resistance shows a relatively high value. This is because, as described above, the conductive path between the negative electrode mixture layers ( It is conceivable that the conductive path) can no longer be taken.
Therefore, by setting V _A / V _B obtained from the negative electrode pore distribution to 3.4 or less, the DC resistance is 40 mΩ or less (that is, DC resistance (mΩ) based on AC impedance measurement at 25 ° C.) and battery capacity (Ah). It was confirmed that a lithium secondary battery in which the product of) was reduced to 20 (mΩ · Ah) or less) was obtained.

From the above results, when V _A / V _B is in the range of 2.1 or more and 3.4 or less, the lithium secondary battery has excellent high-temperature storage characteristics and improved battery performance (for example, reduced resistance). The method of manufacturing was shown.

  As mentioned above, although the specific example of this invention was demonstrated in detail, these are only illustrations and do not limit a claim. The technology described in the claims includes various modifications and changes of the specific examples illustrated above.

  The lithium secondary battery disclosed herein can be used for various applications, but is characterized by excellent high-temperature storage characteristics and improved battery performance (for example, reduced internal resistance). For this reason, for example, it can be suitably used as a power source (drive power source) for a motor mounted on a vehicle such as an automobile. Although the kind of vehicle is not specifically limited, Typically, a plug-in hybrid vehicle (PHV), a hybrid vehicle (HV), and an electric vehicle (EV) are mentioned.

1 Automobile (vehicle)
10 Positive electrode sheet (positive electrode)
12 Positive electrode current collector 14 Positive electrode mixture layer 20 Negative electrode sheet (negative electrode)
22 Negative electrode current collector 24 Negative electrode mixture layer 40A, 40B Separator sheet 50 Battery case 52 Case body 54 Cover body 70 Positive electrode terminal 72 Negative electrode terminal 80 Winding electrode body 100 Lithium secondary battery

Claims (12)

A method for manufacturing a lithium secondary battery, comprising:
Preparing a slurry-like composition for forming a negative electrode mixture layer containing a negative electrode active material and a binder;
Preparing a slurry-like composition for forming a positive electrode mixture layer containing a positive electrode active material and a binder;
Forming the negative electrode mixture layer on the current collector by applying the negative electrode mixture layer-forming composition onto the negative electrode current collector;
Applying the composition for forming a positive electrode mixture layer on a positive electrode current collector to form a positive electrode having a positive electrode mixture layer on the current collector; and using the negative electrode and the positive electrode Building a lithium secondary battery;
Including
Here, as a negative electrode used for constructing a lithium secondary battery, a pore distribution based on a mercury intrusion method was measured, and a pore diameter by the measurement was in a range of 0.3 μm to 4 μm (A), Each having a maximum point in the range (B) of 0 μm or more and less than 0.3 μm, and the maximum pore volume (V _A ) in the range A and the maximum point pore volume in the B range. _{(V B)} and the ratio of _(V a / V _B) is given to using from 2.1 to 3.4 or less, the manufacturing method of a lithium secondary battery. The method for producing a lithium secondary battery according to claim 1, wherein a negative electrode having a density of the negative electrode mixture layer of 1.0 g / cm ³ or more and 1.6 g / cm ³ or less is formed. As the negative electrode active material, the cumulative 50% particle size (D ₅₀ ) measured by particle size distribution measurement (laser diffraction / light scattering method) is 3 μm or more and 20 μm or less, and the specific surface area measured by the nitrogen adsorption method is 2 m. using the following graphite ² / g or more ^{40 m} 2 / g, a manufacturing method of a lithium secondary battery according to claim 1 or 2 wherein.   4. The method for producing a lithium secondary battery according to claim 1, wherein the composition for forming a negative electrode mixture layer includes at least styrene-butadiene rubber and / or carboxymethyl cellulose. 5.   The method for producing a lithium secondary battery according to claim 1, wherein a solid content concentration of the composition for forming a negative electrode mixture layer is 40% or more and 60% or less.   The lithium secondary battery obtained by the manufacturing method as described in any one of Claim 1 to 5. A lithium secondary battery including an electrode body having a positive electrode and a negative electrode,
The negative electrode includes a negative electrode current collector and a negative electrode mixture layer formed on the negative electrode current collector,
The negative electrode mixture layer includes a negative electrode active material and a binder,
Here, in the pore distribution based on the mercury intrusion method, the negative electrode mixture layer has a pore diameter range of 0.3 μm to 4 μm (A) and a pore diameter range of 0 μm to less than 0.3 μm (B). Each having a local maximum point, and the ratio (V _A / V) of the pore volume (V _A ) at the maximum point in the range of _{A to} the pore volume (V _B ) at the maximum point in the range of _{B B} ) is 2.1 or more and 3.4 or less, The lithium secondary battery characterized by the above-mentioned. The lithium secondary battery according to claim 7, wherein a density of the negative electrode mixture layer is 1.0 g / cm ³ or more and 1.6 g / cm ³ or less. The negative electrode active material has a cumulative 50% particle size (D ₅₀ ) measured by particle size distribution measurement (laser diffraction / light scattering method) of 3 μm or more and 20 μm or less, and a specific surface area measured by a nitrogen adsorption method. The lithium secondary battery according to claim 7 or 8, wherein the graphite is 2 m ² / g or more and 40 m ² / g or less.   The lithium secondary battery according to any one of claims 7 to 9, wherein the composition for forming a negative electrode mixture layer includes at least styrene-butadiene rubber and / or carboxymethylcellulose.   The product of IV resistance (mΩ) and battery capacity (Ah) at 25 ° C. is 18 (mΩ · Ah) or less, and DC resistance (mΩ) and battery capacity (Ah) based on AC impedance measurement at 25 ° C. 11. The lithium secondary battery according to claim 6, wherein the product of the lithium secondary battery is 20 (mΩ · Ah) or less.   A vehicle comprising the lithium secondary battery according to any one of claims 6 to 11 as a driving power source.

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