JP2016126896A - Positive electrode for wound type lithium ion secondary battery, negative electrode for wound type lithium ion secondary battery, and wound type lithium ion secondary battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a secondary battery high in energy density and superior in high-rate discharge characteristic, which enables the coating by a coating method for an existing lithium ion secondary battery, and enables the further increase in electrode's thickness by adopting a current collector having adequate endurance against press working and adequate endurance against winding.SOLUTION: To solve the above problem, a wound type lithium ion secondary battery is provided according to an aspect of the present invention, which comprises: a positive electrode having a positive electrode current collector into which a piece of nonporous aluminum foil and a reticular aluminum porous body laminated on at least one face of the piece of nonporous aluminum foil are integrated; and a negative electrode having a negative electrode current collector into which a piece of nonporous copper foil and a reticular metal porous body laminated on at least one face of the piece of nonporous copper foil are integrated.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a positive electrode for a wound lithium ion secondary battery, a negative electrode for a wound lithium ion secondary battery, and a wound lithium ion secondary battery using the positive electrode and the negative electrode.

  In recent years, with the advent of smartphones and tablet terminals, there is a demand for further increase in capacity of lithium ion secondary batteries. As a method of increasing the capacity of the battery, in addition to improving the active material with a large capacity, improving the utilization efficiency of the active material, etc., there is an increase in the amount of active material used by increasing the thickness of the electrode (active material layer). can give. However, as the thickness of the electrode is increased, the current collecting property in the depth direction of the electrode is reduced and the movement distance of lithium ions is increased, resulting in a problem that the high-rate discharge characteristics are significantly lowered.

  As a technique for solving this problem, for example, Patent Documents 1 and 2 disclose that a porous body having a three-dimensional network structure is used as a current collector.

JP 2010-272425 A JP 2012-186139 A

  However, when a porous body having such a three-dimensional network structure is used as a current collector, coating by a coating method such as die-height coating, which uses an existing lithium ion battery, or coating using a doctor blade, etc. Therefore, it is necessary to newly introduce equipment of a coating method (for example, press-fitting method, dipping method, etc.) suitable for this.

  Further, when the porous body having the above three-dimensional network structure is used as a current collector, there has been a problem that the porous body is broken or collapsed during roll press processing, and the mixture containing the current collector is dropped. . Furthermore, the winding resistance of the electrode is insufficient, and problems such as dropping of the mixture containing the current collector and electrode breakage during winding have occurred.

  Therefore, the present invention has been made in view of the above problems, and the object of the present invention is that application by an existing lithium ion secondary battery coating method is possible, and sufficient press working resistance and An object of the present invention is to provide a secondary battery that can be made thicker by applying a current collector having winding resistance, has a high energy density, and is excellent in high rate discharge characteristics.

  In order to solve the above problems, according to one aspect of the present invention, the present invention is characterized by comprising a positive electrode current collector in which a net-like aluminum porous body is laminated and integrated on at least one surface of a non-porous aluminum foil. A positive electrode for a wound lithium ion secondary battery is provided.

  In the positive electrode for a wound lithium ion secondary battery according to this aspect, the positive electrode current collector has a structure in which a net-like aluminum porous body is laminated and integrated on at least one surface of a non-porous aluminum foil. Application by an application method of an existing lithium ion secondary battery is possible, and it has sufficient roll press processing resistance and winding resistance, and can suppress a decrease in current collecting performance in the depth direction of the electrode.

  Therefore, by applying the negative electrode current collector according to this aspect to a lithium ion secondary battery, the electrode can be made thicker, and a secondary battery having high energy density and excellent high rate discharge characteristics can be obtained. be able to.

  Here, the net-like aluminum porous body may be made of at least one of an aluminum nonwoven fabric and an aluminum expanded metal.

  According to this aspect, since the net-like aluminum porous body is made of at least one of an aluminum nonwoven fabric and an aluminum expanded metal, press working resistance and winding resistance are further improved.

  Moreover, it is preferable that the thickness of aluminum foil is 12 micrometers or less.

  According to this viewpoint, since the thickness of the aluminum foil is as thin as 12 μm or less, the energy density is further improved.

  Moreover, it is preferable that the thickness of a positive electrode electrical power collector is 0.2 mm or more and 0.5 mm or less.

  According to this viewpoint, since the thickness of the positive electrode current collector is 0.2 mm or more and 0.5 mm or less, the current collecting property in the depth direction of the electrode is further enhanced.

  The porosity of the positive electrode is preferably 60% or more and 87% or less.

  According to this aspect, since the porosity of the positive electrode is 60% or more and 87% or less, the retention of the positive electrode mixture with respect to the positive electrode current collector, the permeability of the electrolytic solution, and the energy density are further improved.

  According to another aspect of the present invention, a wound lithium ion secondary comprising a negative electrode current collector in which a net-like metal porous body is laminated and integrated on at least one surface of a nonporous metal foil. A negative electrode for a battery is provided.

  In the negative electrode for a wound lithium ion secondary battery according to this aspect, the negative electrode current collector has a structure in which a net-like metal porous body is laminated and integrated on at least one surface of a nonporous metal foil. Application by an application method of an existing lithium ion secondary battery is possible, and it has sufficient roll press processing resistance and winding resistance, and can suppress a decrease in current collecting performance in the depth direction of the electrode.

  Therefore, by applying the negative electrode current collector according to this aspect to a lithium ion secondary battery, the electrode can be made thicker, and a secondary battery having high energy density and excellent high rate discharge characteristics can be obtained. be able to.

  Here, the net-like metal porous body may be made of at least one of a copper nonwoven fabric, a nickel nonwoven fabric, a copper expanded metal, or a nickel expanded metal.

  According to this aspect, since the net-like metal porous body is made of at least one of a copper nonwoven fabric, a nickel nonwoven fabric, a copper expanded metal, or a nickel expanded metal, press working resistance and winding resistance are further improved.

  Moreover, it is preferable that the thickness of metal foil is 6 micrometers or less.

  According to this aspect, since the thickness of the metal foil is as thin as 6 μm or less, the energy density is further improved.

  Moreover, it is preferable that the thickness of a negative electrode collector is 0.2 mm or more and 0.5 mm or less.

  According to this viewpoint, since the thickness of the negative electrode current collector is 0.2 mm or more and 0.5 mm or less, the current collecting property in the depth direction of the electrode is further enhanced.

  The porosity of the negative electrode is preferably 60% or more and 87% or less.

  According to this aspect, since the porosity of the negative electrode is 60% or more and 87% or less, the retention of the negative electrode mixture with respect to the negative electrode current collector, the permeability of the electrolytic solution, and the energy density are further improved.

  According to another aspect of the present invention, a wound type lithium battery comprising: the above-described positive electrode for a wound lithium ion secondary battery; and the above-described negative electrode for a wound lithium ion secondary battery. An ion secondary battery is provided.

  The wound type lithium ion secondary battery according to this aspect can be applied by a coating method of an existing lithium ion secondary battery, has sufficient roll press working resistance and winding resistance, and has an electrode depth. Since the current collector capable of suppressing the decrease in the direction current collecting property is used, the electrode can be made thicker, and has high energy density and excellent high rate discharge characteristics.

  As described above, according to the present invention, as a positive electrode current collector, a current collector in which a net-like aluminum porous body is laminated and integrated on at least one surface of a non-porous aluminum foil, and as a negative electrode current collector, Since the current collector is made by laminating and integrating a net-like metal porous body on at least one side of a non-porous metal foil, it can be applied by the application method of existing lithium ion secondary batteries. The body has sufficient press working resistance and winding resistance, which makes it possible to make the electrode thicker. Therefore, the wound lithium ion secondary battery of the present invention is excellent in high energy density and high rate discharge characteristics.

It is a sectional side view which shows schematic structure of the lithium ion secondary battery which concerns on embodiment of this invention. It is explanatory drawing which shows the detailed structure of the positive electrode (negative electrode) collector and active material layer which concern on the embodiment.

  Exemplary embodiments of the present invention will be described below in detail with reference to the accompanying drawings. In addition, in this specification and drawing, about the component which has the substantially same function structure, duplication description is abbreviate | omitted by attaching | subjecting the same code | symbol.

<Configuration of lithium ion secondary battery>
First, based on FIG. 1 and FIG. 2, the structure of the lithium ion secondary battery 10 which concerns on this embodiment is demonstrated.

As shown in FIG. 1, the lithium ion secondary battery 10 includes a positive electrode 20, a negative electrode 30, and a separator layer 40. The charge voltage (redox potential) of the lithium ion secondary battery 10 is, for example, 4.3 V (vs. Li ^/ Li ⁺ ) or more and 5.0 V or less. In the present embodiment, the form of the lithium ion secondary battery 10 is not particularly limited as long as the electrode structure in which the separator layer 40 is sandwiched between the positive electrode 20 and the negative electrode 30 is a wound type. That is, the lithium ion secondary battery 10 may be cylindrical or rectangular as long as it can accommodate an electrode structure having a wound structure.

[Positive electrode 20]
The positive electrode 20 includes a positive electrode current collector 21 and a positive electrode active material layer 22.

(Positive electrode current collector 21)
As shown in FIG. 2, the positive electrode current collector 21 has a nonporous aluminum foil 211 as a support, a net-like aluminum porous body is laminated on at least one surface of the nonporous aluminum foil 211, and these are integrated. It is a thing. However, as shown in the figure, when the net-like aluminum porous bodies 213a and 213b are laminated and integrated on both surfaces of the non-porous aluminum foil 211, the press working resistance and the winding resistance of the current collector are further increased. .

  Here, examples of the net-like aluminum porous bodies 213a and 213b include at least one (any one or a combination) such as an aluminum nonwoven fabric or an aluminum expanded metal. As an example of the combination, there is a case where the aluminum porous body 213a on one side is made of an aluminum nonwoven fabric and the aluminum porous body 213b on the other side is made of an aluminum expanded metal. On the other hand, an aluminum porous sintered body as described in Patent Document 1 or an aluminum porous body obtained by applying aluminum plating to a resin porous body as described in Patent Document 2 and then removing the resin Although it has a high specific surface area and excellent current collecting properties, it is difficult to apply the coating method using an existing lithium ion secondary battery (for example, application using a die-height coating or a doctor blade). In addition, since the press working resistance and the winding resistance are low and there is a risk of breakage or collapse, it is not suitable as the reticulated aluminum porous body 213a, 213b according to this embodiment. As a reason for this, the present inventors have a low strength against compression and tension on the structure of an aluminum porous body obtained by applying aluminum plating to these aluminum porous sintered bodies and resin porous bodies and then removing the resin, This is thought to be due to the low ability to follow press and bending. On the other hand, the non-woven fabric and expanded betal used in the present embodiment are considered to be able to secure resistance because they exhibit sufficient followability to compression and tension during pressing and bending.

  The method for integrating the non-porous aluminum foil 211 and the net-like aluminum porous bodies 213a and 213b is not particularly limited as long as it can be integrated by adhesion, welding, or the like. Adhesion with a conductive resin, partial joining by spot welding, or the like can be used. Examples of the conductive resin include a combination of a general conductive material used as a battery material and a binder. For example, examples of the conductive material include graphite, carbon black, carbon nanotube, and graphene, and examples of the binder include H-NBR, PVdF, and CMC (carboxymethylcellulose).

  The thickness of the non-porous aluminum foil 211 is preferably thinner from the viewpoint of energy density as long as the strength can be ensured. Specifically, the thickness of the non-porous aluminum foil 211 is preferably 6 μm or more as a range in which the strength (high press working resistance and winding resistance) of the positive electrode current collector 21 can be secured. On the other hand, it is preferably 12 μm or less from the viewpoint of increasing the energy density of the positive electrode current collector 21.

  The total thickness of the positive electrode current collector 21 is preferably 0.2 mm or more and 0.5 mm or less in order to ensure the current collecting property in the depth direction of the electrode.

  Furthermore, the porosity of the positive electrode 20 is preferably 60% or more and 87% or less. By having the porosity in this range, the retention of the positive electrode mixture containing the positive electrode active material, the conductive agent, the binder, and the like with respect to the positive electrode current collector 21, the permeability of the electrolytic solution, and the energy density of the positive electrode 20 are improved. be able to. In addition, the porosity of the positive electrode 20 here means the ratio of the space | gap which exists in the positive electrode in the positive electrode volume, for example, can be measured by the mercury intrusion method.

  By using the positive electrode current collector 21 as described above, it is possible to apply a positive electrode mixture in a general coating method of an existing lithium ion secondary battery, and at the time of pressing and winding It is possible to prevent the current collector from being broken and the mixture containing the current collector from falling off. In addition, the construction of a three-dimensional current collection structure improves the current collection in the depth direction of the electrode when the electrode is thickened, and the high-rate discharge characteristics of the battery that occur when the electrode is thickened. Since the decrease is suppressed, it is possible to further increase the thickness of the electrode and thereby increase the energy density of the battery.

(Positive electrode active material layer 22)
The positive electrode active material layer 22 is held by the mesh portions of the net-like aluminum porous bodies 213a and 213b, includes at least a positive electrode active material, and may further include a conductive agent and a binder. The positive electrode active material is, for example, a transition metal oxide or a solid solution oxide containing lithium, but is not particularly limited as long as the material can electrochemically occlude and release lithium ions. Examples of the transition metal oxide containing lithium include Li / Co-based composite oxides such as LiCoO ₂ , Li / Ni / Co / Mn-based composite oxides such as LiNi _x Co _y Mn _z O ₂ , and LiNiO ₂ . Li / Ni-based composite oxides, Li / Mn-based composite oxides such as LiMn ₂ O ₄ and the like are conceivable. The solid solution oxide is, for example, Li _a Mn _x Co _y Ni _z O ₂ (1.150 ≦ a ≦ 1.430, 0.45 ≦ x ≦ 0.6, 0.10 ≦ y ≦ 0.15,. 20 ≦ z ≦ 0.28), LiMn _x Co _y Ni _z O ₂ (0.3 ≦ x ≦ 0.85, 0.10 ≦ y ≦ 0.3, 0.10 ≦ z ≦ 0.3), LiMn _1.5 Ni _0.5 O ₄ . The content ratio (content) of the positive electrode active material is not particularly limited as long as it is applicable to the positive electrode active material layer of the lithium ion secondary battery. Moreover, you may use these compounds individually or in mixture of multiple.

  Examples of the conductive agent include carbon black such as ketjen black and acetylene black, fibrous carbon such as natural graphite, artificial graphite, carbon nanotube, and carbon nanofiber, a composite of these fibrous carbon and carbon black, graphene, and the like. There is no particular limitation as long as it is for increasing the conductivity of the positive electrode. The content ratio of the conductive agent is not particularly limited as long as it is applicable to the positive electrode active material layer of the lithium ion secondary battery.

  The binder is, for example, polyvinylidene fluoride, a copolymer of vinylidene fluoride and hexafluoropropylene, a copolymer of vinylidene fluoride and tetrafluoroethylene, hydrogenated acrylonitrile butadiene rubber, fluoro rubber, polymethyl methacrylate, polyethylene, And a derivative thereof, in particular, as long as the positive electrode active material and the conductive agent can be bound on the current collector 20 and have oxidation resistance and electrolyte stability that can withstand the high potential of the positive electrode. Not limited. The content ratio of the binder is not particularly limited as long as the content ratio is applicable to the positive electrode active material layer of the lithium ion secondary battery. The thickness of the positive electrode active material layer 22 is not particularly limited as long as it is applicable to the positive electrode active material layer of the lithium ion secondary battery. In this embodiment, even if the positive electrode active material layer 22 is thickened, the lithium ion secondary battery 10 having a high energy density and excellent high rate discharge characteristics can be obtained.

  The positive electrode active material layer 22 is formed by, for example, dry-mixing a positive electrode active material, a conductive agent, and a binder to form a positive electrode mixture, and dispersing the positive electrode mixture in an appropriate organic solvent to form a positive electrode mixture slurry. The positive electrode mixture slurry is formed, coated on the positive electrode current collector 21, dried and pressed.

[Negative electrode 30]
The negative electrode 30 includes a negative electrode current collector 31 and a negative electrode active material layer 32.

(Negative electrode current collector 31)
As shown in FIG. 2, the negative electrode current collector 31 is obtained by laminating a net-like metal porous body on at least one surface of a non-porous metal foil 311 and integrating them. However, as shown in the figure, when the net-like metal porous bodies 313a and 313b are laminated and integrated on both surfaces of the nonporous metal foil 311, the press working resistance and the winding resistance of the current collector are further increased. . As the metal foil 311, for example, a copper foil, a nickel foil, a stainless steel foil, or the like can be used.

  Here, as the net-like metal porous bodies 313a and 313b, at least one of copper nonwoven fabric, nickel nonwoven fabric, stainless steel nonwoven fabric, copper expanded metal, nickel expanded metal, and stainless steel expanded metal (any one or Combination). As an example of the combination, there is a case where the metal porous body 313a on one side is made of a copper nonwoven fabric and the metal porous body 313b on the other side is made of stainless steel expanded metal. The metal porous bodies 313a and 313b are not limited to the examples described above, and examples thereof include metal nonwoven fabrics and expanded metals that are generally used for negative electrode current collectors of lithium ion secondary batteries. On the other hand, a porous metal sintered body as described in Patent Document 1 or a metal porous body obtained by applying metal plating to a resin porous body as described in Patent Document 2 and then removing the resin Although it has a high specific surface area and excellent current collecting properties, it is difficult to apply the coating method using an existing lithium ion secondary battery (for example, application using a die-height coating or a doctor blade). In addition, since the press working resistance and the winding resistance are low and there is a risk of breakage or collapse, it is not suitable as the mesh metal porous bodies 313a and 313b according to the present embodiment. The reason is the same as in the case of the positive electrode current collector 21.

  In addition, as a method of integrating the non-porous metal foil 311 and the net-like metal porous bodies 313a and 313b, for example, as with the positive electrode current collector 21, for example, bonding with a conductive resin, partial bonding by spot welding, etc. Can be used.

  The thickness of the non-porous metal foil 311 is preferably thinner from the viewpoint of energy density as long as the strength can be ensured. Specifically, for example, the thickness when the non-porous metal foil 311 is a copper foil is 4 μm or more as a range in which the strength (high press working resistance and winding resistance) of the negative electrode current collector 31 can be secured. preferable. On the other hand, it is preferably 6 μm or less from the viewpoint of increasing the energy density of the negative electrode current collector 31.

  Further, the thickness of the entire negative electrode current collector 31 is preferably 0.2 mm or more and 0.5 mm or less in order to ensure current collecting properties in the depth direction of the electrode.

  Furthermore, the porosity of the negative electrode 30 is preferably 60% or more and 87% or less. By having the porosity in this range, the retention of the negative electrode mixture containing the negative electrode active material, the conductive agent, the binder, and the like with respect to the negative electrode current collector 31, the permeability of the electrolytic solution, and the energy density of the negative electrode 30 are improved. be able to. The definition and measurement method of the porosity of the negative electrode 30 here are the same as those of the positive electrode 20.

  By using the negative electrode current collector 31 as described above, it is possible to apply a negative electrode mixture in a general coating method of an existing lithium ion secondary battery, and at the time of pressing and winding It is possible to prevent the current collector from being broken and the mixture containing the current collector from falling off. In addition, the construction of a three-dimensional current collection structure improves the current collection in the depth direction of the electrode when the electrode is thickened, and the high-rate discharge characteristics of the battery that occur when the electrode is thickened. Since the decrease is suppressed, it is possible to further increase the thickness of the electrode and thereby increase the energy density of the battery.

(Negative electrode active material layer 32)
The negative electrode active material layer 32 is held by the mesh portions of the mesh metal porous bodies 313a and 313b, and any material can be used as long as it is used as the negative electrode active material layer of the lithium ion secondary battery. Good. For example, the negative electrode active material layer 32 includes a negative electrode active material, and may further include a binder. Examples of the negative electrode active material include graphite active material (artificial graphite, natural graphite, a mixture of artificial graphite and natural graphite, natural graphite coated with artificial graphite, etc.), fine particles of silicon or tin or oxides thereof and graphite active material. , Silicon or tin fine particles, alloys based on silicon or tin, and titanium oxide compounds such as Li ₄ Ti ₅ O ₁₂ . The oxide of silicon is represented by SiO _x (0 ≦ x ≦ 2). Examples of the negative electrode active material include metallic lithium and the like in addition to these. The binder is the same as the binder constituting the positive electrode active material layer 22. The mass ratio between the positive electrode active material and the binder is not particularly limited, and the mass ratio employed in the conventional lithium ion secondary battery is also applicable in this embodiment.

  The negative electrode active material layer 32 forms a negative electrode mixture, for example, by dry mixing a negative electrode active material and a binder. Next, the negative electrode mixture is dispersed in a suitable solvent to form a negative electrode mixture slurry (slurry). The negative electrode mixture slurry is applied onto the negative electrode current collector 31, dried and pressed to produce a negative electrode active slurry. A material layer 32 is formed.

[Separator layer 40]
Separator layer 40 includes a separator and an electrolytic solution. The separator is not particularly limited, and any separator can be used as long as it is used as a separator for a lithium ion secondary battery. As the separator, it is preferable to use a porous film or a non-woven fabric exhibiting excellent high rate discharge performance alone or in combination. Examples of the material constituting the separator for a nonaqueous electrolyte battery include polyolefin resins typified by polyethylene and polypropylene, polyester resins typified by polyethylene terephthalate and polybutylene terephthalate, polyvinylidene fluoride, and vinylidene fluoride-hexa. Fluoropropylene copolymer, vinylidene fluoride-perfluorovinyl ether copolymer, vinylidene fluoride-tetrafluoroethylene copolymer, vinylidene fluoride-trifluoroethylene copolymer, vinylidene fluoride-fluoroethylene copolymer, fluorine Vinylidene fluoride-hexafluoroacetone copolymer, vinylidene fluoride-ethylene copolymer, vinylidene fluoride-propylene copolymer, vinylidene fluoride-trifluoropropylene copolymer, vinylidene fluoride - tetrafluoroethylene - hexafluoropropylene copolymer, vinylidene fluoride - ethylene - can be mentioned tetrafluoroethylene copolymer.

  As the electrolytic solution, the same non-aqueous electrolytic solution conventionally used for lithium secondary batteries can be used without any particular limitation. The electrolytic solution has a composition in which an electrolyte salt is contained in a nonaqueous solvent. Examples of the non-aqueous solvent include cyclic carbonates such as propylene carbonate, ethylene carbonate, butylene carbonate, chloroethylene carbonate, and vinylene carbonate; cyclic esters such as γ-butyrolactone and γ-valerolactone; dimethyl carbonate, diethyl carbonate, Chain carbonates such as ethyl methyl carbonate; chain esters such as methyl formate, methyl acetate and methyl butyrate; tetrahydrofuran or derivatives thereof; 1,3-dioxane, 1,4-dioxane, 1,2-dimethoxyethane, 1 Ethers such as 1,4-dibutoxyethane and methyldiglyme; nitriles such as acetonitrile and benzonitrile; dioxolane or derivatives thereof; ethylene sulfide, sulfolane, sultone or derivatives thereof Examples thereof include, but are not limited to, one or a mixture of two or more thereof.

Examples of the electrolyte salt include LiClO ₄ , LiBF ₄ , LiAsF ₆ , LiPF ₆ , LiSCN, LiBr, LiI, Li ₂ SO ₄ , Li ₂ B ₁₀ Cl ₁₀ , NaClO ₄ , NaI, NaSCN, NaBr, KClO _4. , KSCN and other inorganic ion salts containing one of lithium (Li), sodium (Na) or potassium (K), LiCF ₃ SO ₃ , LiN (CF ₃ SO ₂ ) ₂ , LiN (C ₂ F ₅ SO ₂ ) ₂ , LiN (CF ₃ SO ₂ ) (C ₄ F ₉ SO ₂ ), LiC (CF ₃ SO ₂ ) ₃ , LiC (C ₂ F ₅ SO ₂ ) ₃ , (CH ₃ ) ₄ NBF ₄ , (CH ₃ ) ₄ NBr, (C ₂ H ₅ ) ₄ NClO ₄ , (C ₂ H ₅ ) ₄ NI, (C ₃ H ₇ ) ₄ NBr, (n-C ₄ H ₉ ) ₄ NC _{lO 4, (n-C 4} H 9) 4 NI, (C2H 5) 4 N-maleate, (C 2 H 5) 4 N-benzoate, (C 2 H 5) 4 N-phtalate, lithium stearyl sulfonate, Examples include organic ionic salts such as lithium octyl sulfonate and lithium dodecylbenzene sulfonate, and these ionic compounds can be used alone or in admixture of two or more. The concentration of the electrolyte salt may be the same as that of the nonaqueous electrolytic solution used in the conventional lithium secondary battery, and is not particularly limited. In the present embodiment, an electrolytic solution containing an appropriate lithium compound (electrolyte salt) at a concentration of about 0.1 to 5 mol / L can be used.

<Method for producing lithium ion secondary battery>
Next, a method for manufacturing the lithium ion secondary battery 10 will be described. The manufacturing method in particular of the lithium ion secondary battery 10 is not restrict | limited, Arbitrary manufacturing methods are applicable.

[Production of Positive Electrode 20]
For example, the positive electrode 20 is manufactured as follows.

(Preparation of positive electrode current collector 21)
First, the net-like aluminum porous bodies 213a and 213b are laminated on at least one surface of the non-porous aluminum foil 211, respectively. Next, the non-porous aluminum foil 211 and the net-like aluminum porous bodies 213a and 213b are bonded with the above-described conductive resin or partially joined by spot welding, etc. The net-like aluminum porous bodies 213a and 213b are integrated. Thereby, the positive electrode current collector 21 is produced.

(Formation of positive electrode active material layer 22)
First, a positive electrode mixture slurry is formed by dispersing a positive electrode mixture in which a positive electrode active material, a conductive agent, and a binder are mixed in an organic solvent (for example, N-methyl-2-pyrrolidone). Next, the positive electrode mixture slurry is formed (for example, coated) on the current collector 21 and dried to form the positive electrode active material layer 22. The coating method is not particularly limited. As a coating method, an existing method can be used. For example, a coating method using a die-jet coating or a doctor blade can be used. The following coating steps are also performed by the same method. Next, the positive electrode active material layer 22 is pressed by a press machine, and then vacuum drying is performed. Thereby, the positive electrode 20 is produced.

[Manufacture of Negative Electrode 30]
The negative electrode 30 is also manufactured in the same manner as the positive electrode 20.

(Preparation of negative electrode current collector 31)
First, the net-like metal porous bodies 313a and 313b are laminated on at least one surface of the non-porous metal foil 311. Next, the nonporous metal foil 311 and the net-like metal porous bodies 313a and 313b are bonded with the above-described conductive resin, or are partially joined by spot welding, etc. The mesh metal porous bodies 313a and 313b are integrated. Thereby, the negative electrode collector 31 is produced.

(Formation of negative electrode active material layer 32)
First, a slurry is prepared by dispersing a mixture of a negative electrode active material and a binder in a solvent (eg, N-methyl-2-pyrrolidone, water). Next, the negative electrode active material layer 32 is produced by forming (for example, coating) the slurry on the negative electrode current collector 31 and drying the slurry. As the coating method, an existing method can be used as in the case of the positive electrode 20, and for example, a coating method using a die-height coating or a doctor blade can be used. Next, the negative electrode active material layer 32 is pressed by a press machine, and then vacuum drying is performed. Thereby, the negative electrode 30 is produced.

[Assembly of lithium ion secondary battery 10]
Next, the separator layer 40 is sandwiched between the positive electrode 20 and the negative electrode 30 to produce a flat electrode structure. Next, the flat electrode structure is wound, the electrode structure is processed into a desired shape (for example, a cylindrical shape, a rectangular shape, etc.), and inserted into the container of the shape. Next, by injecting the electrolytic solution having the above composition into the container, each pore in the separator is impregnated with the electrolytic solution and sealed. Thereby, the lithium ion secondary battery 10 is produced.

  Next, examples of the present embodiment will be described. Lithium ion secondary batteries according to Examples 1 and 2 and Comparative Examples 1 to 3 were produced by the following treatment.

<Production of lithium ion secondary battery>
[Example 1]
(Preparation of positive electrode current collector)
A 12-μm-thick non-porous aluminum foil (hereinafter “non-porous aluminum foil”) was used as a support, and a conductive resin was coated on the support. As the conductive resin, a conductive material paste dispersed in water with multi-walled carbon nanotubes (CNT): carboxymethyl cellulose (CMC) = 2: 1 (mass ratio) was used. Next, aluminum expanded metal with a processed thickness of 180 μm is laminated on both sides of the non-porous aluminum foil, the solvent in the conductive material paste is volatilized, and the non-porous aluminum foil and the aluminum expanded metal are integrated by bonding. Thus, a positive electrode current collector was produced.

(Preparation of positive electrode)
Li / Co composite oxide (LiCoO ₂ ) having an average particle diameter of 15 to 20 μm as a positive electrode active material, carbon black (CB) as a conductive material, and PVdF as a binder in a ratio of 98: 1: 1. By mixing, a positive electrode mixture was produced. Next, a positive electrode mixture slurry was obtained by adding an appropriate amount of N-methylpyrrolidone (NMP) as a solvent to the positive electrode mixture, mixing, and dispersing. Next, the prepared positive electrode mixture slurry was applied to both surfaces of the positive electrode current collector prepared above by a doctor blade method. At this time, it applied so that the area density (positive electrode area density) of mixture solid content in each surface might be 90 mg / cm < ² >. Then, NMP was volatilized by making it dry in the thermostat kept at 80 degreeC, exhausting NMP vapor | steam. Subsequently, the dried sheet was pressed using a roll press machine until the porosity became 80%, and further vacuum-dried at 100 ° C. to obtain a positive electrode. Further, when the presence or absence of the mixture was removed during the positive electrode pressing and the current collector was broken or damaged, the mixture was not dropped and the current collector was neither broken nor damaged.

(Preparation of negative electrode current collector)
A non-porous copper foil (hereinafter referred to as “non-porous copper foil”) having a thickness of 6 μm was used as a support, and a conductive resin was applied on the support. As the conductive resin, a conductive material paste dispersed in a solvent with multi-walled carbon nanotubes (CNT): hydrogenated nitrile butyl rubber (H-NBR) = 2: 1 (mass ratio) was used. Next, a nickel expanded metal having a thickness of 180 μm is laminated on both surfaces of the non-porous copper foil, the solvent in the conductive material paste is volatilized, and the non-porous copper foil and the nickel expanded metal are integrated with each other by adhesion. An electric body was produced.

(Preparation of negative electrode)
Artificial graphite, styrene butadiene rubber, and carboxymethyl cellulose (CMC) were mixed at 98: 1: 1 to prepare a negative electrode mixture. Next, an appropriate amount of water as a solvent was added to the negative electrode mixture and kneaded and dispersed to prepare a negative electrode mixture slurry. Next, this negative electrode mixture slurry was applied to both surfaces of the negative electrode current collector prepared above by a doctor blade method. Thereafter, the negative electrode current collector coated with the negative electrode mixture slurry was dried in a thermostatic bath maintained at 80 ° C. to volatilize water. The dried sheet was pressed using a roll press so that the volume density was 1.75 g / cm ³ , and further vacuum dried at 150 ° C. to obtain a negative electrode. The coating amount of the negative electrode mixture was designed and adjusted so that about 95% of the effective negative electrode active material layer facing the positive electrode was used reversibly.

(Preparation of electrolyte)
A LiPF ₆ solution was prepared by dissolving LiPF ₆ to 1.3 M in a solvent in which ethylene carbonate (EC) and dimethyl carbonate (DMC) were mixed at a volume ratio of 3: 7. Then, 10 parts by mass of fluoroethylene carbonate (FEC) was mixed with 90 parts by mass of the LiPF ₆ solution to obtain an electrolytic solution.

(Wound element and battery manufacturing method)
Using the positive electrode and the negative electrode prepared by the above method, a positive electrode, a separator, a negative electrode, and a separator were stacked in this order to prepare an electrode laminate. As the separator, a 14 μm thick separator made of ND314 (manufactured by Asahi Kasei E-Materials Co., Ltd.) was used. Subsequently, the wound element was produced by winding the electrode laminated body produced above. Next, a flat winding element was produced by crushing the winding element. Next, the flat wound element is inserted into the outer package (laminate film) together with the electrolytic solution prepared by the above method, and the outer package is sealed, so that the thickness 4.2 mm, the width 33 mm, and the height 32 mm are implemented The lithium ion secondary battery of Example 1 was obtained. When sealing the exterior body, the terminals that are connected to the current collectors are projected outside the exterior body.

[Example 2]
In producing the positive electrode current collector, a lithium ion secondary battery of Example 2 was obtained in the same manner as Example 1 except that an aluminum nonwoven fabric having a thickness of 180 μm was used instead of the aluminum expanded metal. In addition, when the presence or absence of the mixture was removed during the positive electrode pressing and the current collector was checked for breakage or damage, the mixture was not dropped or the current collector was not broken or damaged.

[Comparative Example 1]
Implemented except that a non-porous aluminum foil with a thickness of 12 μm was used as the positive electrode current collector, a positive electrode was prepared with a positive electrode area density of 45 mg / cm ² , and a negative electrode was prepared with a copper foil with a thickness of 6 μm as the negative electrode current collector In the same manner as in Example 1, a lithium ion secondary battery of Comparative Example 1 was obtained. In addition, when the presence or absence of the mixture was removed during the positive electrode pressing and the current collector was checked for breakage or damage, the mixture was not dropped or the current collector was not broken or damaged.

[Comparative Example 2]
A positive electrode was produced using a non-porous aluminum foil having a thickness of 12 μm as a positive electrode current collector. In addition, when the presence or absence of the mixture was removed during the positive electrode pressing and the current collector was checked for breakage or damage, the mixture was not dropped or the current collector was not broken or damaged. However, as will be described later, in Comparative Example 2, in the bending test of the flat electrode body, the electrode was broken or the mixture was dropped, so a lithium ion secondary battery was not manufactured (the battery performance was also evaluated). Not done).

[Comparative Example 3]
(Preparation of positive electrode)
According to the description in Patent Document 2, an aluminum porous body having a three-dimensional network structure obtained by performing aluminum plating on foamed urethane, which is a resin porous body, and then removing the resin was produced. The thickness of this aluminum porous body was 400 μm, and the porosity (corresponding to the porosity in the examples) was 95%. Next, the obtained aluminum porous body was immersed in a positive electrode mixture slurry prepared in the same manner as in Example 1, and the aluminum porous body was impregnated with the positive electrode mixture slurry in a vacuum state to fill the mixture. Then, NMP was volatilized by making it dry in the thermostat kept at 80 degreeC, exhausting NMP vapor | steam. The dried sheet was then pressed using a roll press until the porosity was 80%. In Comparative Example 3, it was confirmed that a problem that the mixture containing the current collector was dropped due to the fracture or collapse of the porous body (current collector) occurred during the press working of the positive electrode. As will be described later, in Comparative Example 3, in the bending test of the flat electrode body, the electrode was broken or the mixture was dropped, so a lithium ion secondary battery was not manufactured (the battery performance was also evaluated). Not done)

<Bending test>
About the flat electrode body produced in Examples 1, 2 and Comparative Examples 1-3, the presence or absence of the fracture | rupture of the electrode at the time of bending was investigated by the bending test. Specifically, it was evaluated by a load at which the electrode breaks when bent by an MIT folding resistance tester (manufactured by Yasuda Seiki). In the bending test, those that did not break at a load of 4N were evaluated as having no electrode breakage during bending, and those that were broken at a load of 4N or less were evaluated as having an electrode breakage during bending. As a result, Comparative Examples 2 and 3 were evaluated as having broken electrodes during bending. The electrode that breaks at 4N or less in the bending test was considered to break in the winding process at the time of battery production. Therefore, a lithium ion secondary battery was not produced, and evaluation of battery performance described below was not performed.

<Activation processing>
The lithium ion secondary batteries according to Examples 1 and 2 and Comparative Example 1 manufactured as described above were charged at a constant current and a constant voltage of 0.2 C until the battery voltage reached 4.40 V. Then, a charge / discharge cycle in which a constant current discharge of 0.2 C was performed until the battery voltage reached 2.75 V was performed once in a room temperature environment. Thereby, the lithium ion secondary battery was fully activated. Thereafter, the lithium ion secondary battery was subjected to the following evaluations.

<Evaluation of discharge capacity ratio>
In the evaluation of the discharge capacity ratio, constant current and constant voltage charging of 0.1 C was performed until the battery voltage reached 4.40V. That is, charging was performed at a constant current of 0.1 C until the battery voltage reached 4.40 V, and after the battery voltage reached 4.40 V, charging was performed while maintaining the battery voltage at 4.40 V. . Charging was terminated when the current value dropped to 0.05C. Thereafter, constant current discharge at 0.1 C was performed until the battery voltage reached 2.75V. With respect to the discharge capacities of the comparative examples and examples obtained by the above discharge, the relative ratio (%) of the discharge capacities of the examples when the discharge capacity of the comparative example 1 is 100 (%) is shown in Table 1.

<Evaluation of high rate discharge characteristics>
As an evaluation index for high rate discharge characteristics, the capacity retention rate measured as follows was used. In the first cycle, constant current / constant voltage charging at 0.1 C was performed until the battery voltage reached 4.40V. That is, charging was performed at a constant current of 0.1 C until the battery voltage reached 4.40 V, and after the battery voltage reached 4.40 V, charging was performed while maintaining the battery voltage at 4.40 V. . Charging was terminated when the current value dropped to 0.05C. Thereafter, constant current discharge at 0.1 C was performed until the battery voltage reached 2.75V. In the second cycle, constant current / constant voltage charging at 0.5 C was performed until the battery voltage reached 4.40V. That is, charging was performed at a constant current of 0.5 C until the battery voltage reached 4.40 V, and after the battery voltage reached 4.40 V, charging was performed while maintaining the battery voltage at 4.40 V. . Charging was terminated when the current value dropped to 0.05C. Thereafter, constant current discharge at 1.0 C was performed until the battery voltage reached 2.75V. A value obtained by dividing the discharge capacity at the second cycle by the discharge capacity at the first cycle was taken as the evaluation value of the high rate discharge characteristics. In Comparative Example 1, since the positive electrode area density is low (the thickness of the positive electrode active material layer is thin), the high rate discharge characteristics are not evaluated.

  The results are shown in Table 1.

  As shown in Table 1, the lithium ion secondary batteries of Examples 1 and 2 are superior in current collection in the electrode depth direction compared to the case of using the non-porous foil-only current collector of Comparative Example 2. It has been found that the high rate discharge characteristics are improved when the electrode is made thicker.

  In addition, when the porous body having the three-dimensional network structure of Comparative Example 3 is used for the positive electrode current collector, it is extremely difficult to apply a die-height coating that is a coating method of an existing lithium ion battery and a doctor blade, By using the current collectors of Examples 1 and 2 of the present invention, the center part in the thickness direction is partitioned by non-porous foil and the mixture slurry easily penetrates into the inside, so that the existing coating method is used. Coating is possible.

  Furthermore, when the porous body having the three-dimensional network structure of Comparative Example 3 was used as the positive electrode current collector, there was a problem that the mixture containing the current collector dropped due to the breakage or collapse of the porous body during roll press processing. On the other hand, in Examples 1 and 2, the current collector and the mixture could be pressed without breaking or falling off.

  In addition, the electrodes of Comparative Examples 2 and 3 have insufficient winding resistance, causing problems such as dropping of the mixture and breakage of the current collector, while Examples 1 and 2 of the present invention. Then, since the rigidity and winding resistance of the electrode are ensured, it is possible to produce a wound lithium ion secondary battery without causing the mixture to fall off or the non-porous foil as a support to break. all right.

  The preferred embodiments of the present invention have been described in detail above with reference to the accompanying drawings, but the present invention is not limited to such examples. It is obvious that a person having ordinary knowledge in the technical field to which the present invention pertains can come up with various changes or modifications within the scope of the technical idea described in the claims. Of course, it is understood that these also belong to the technical scope of the present invention.

  For example, the present invention can be applied to a circular, elliptical or polygonal secondary battery having a winding structure. Moreover, although the case where electrolyte solution was used as an electrolyte was demonstrated in the said embodiment and Example, you may make it use the gel electrolyte which hold | maintained electrolyte solution to holding bodies, such as a polymer compound. Furthermore, in the above embodiment, an electrode in which a net-like porous body is laminated and integrated on at least one surface of the foil is used for both the positive electrode and the negative electrode, but the present invention may be used only for either the positive electrode or the negative electrode. The effect of can be obtained.

DESCRIPTION OF SYMBOLS 10 Lithium ion secondary battery 20 Positive electrode 21 Positive electrode collector 22 Positive electrode active material layer 30 Negative electrode 31 Negative electrode collector 32 Negative electrode active material layer 40 Separator layer 211 Aluminum foil 213a, 213b Reticulated aluminum porous body 311 Copper foil 313a, 313b Reticulated Porous metal

Claims (11)

  A positive electrode for a wound lithium ion secondary battery, comprising a positive electrode current collector in which a net-like aluminum porous body is laminated and integrated on at least one surface of a nonporous aluminum foil.   The positive electrode for a wound lithium ion secondary battery according to claim 1, wherein the net-like aluminum porous body is made of at least one of an aluminum nonwoven fabric and an aluminum expanded metal.   The positive electrode for a wound lithium ion secondary battery according to claim 1, wherein the aluminum foil has a thickness of 12 μm or less.   The thickness of the said positive electrode electrical power collector is 0.2 mm or more and 0.5 mm or less, The positive electrode for wound lithium ion secondary batteries as described in any one of Claims 1-3 characterized by the above-mentioned.   5. The wound lithium ion secondary according to claim 1, wherein the positive electrode for the wound lithium ion secondary battery has a porosity of 60% to 87%. Battery positive electrode.   A negative electrode for a wound lithium ion secondary battery, comprising a negative electrode current collector in which a net-like porous metal is laminated and integrated on at least one surface of a nonporous metal foil.   The said mesh-like metal porous body consists of at least any one of a copper nonwoven fabric, a nickel nonwoven fabric, a stainless steel nonwoven fabric, a copper expanded metal, a nickel expanded metal, or a stainless steel expanded metal, The Claim 6 characterized by the above-mentioned. Negative electrode for wound type lithium ion secondary battery.   The negative electrode for a wound lithium ion secondary battery according to claim 6 or 7, wherein the thickness of the metal foil is 6 µm or less.   The negative electrode for a wound lithium ion secondary battery according to any one of claims 6 to 8, wherein the negative electrode current collector has a thickness of 0.2 mm or more and 0.5 mm or less.   The wound lithium ion secondary according to any one of claims 6 to 9, wherein a porosity of the negative electrode for the wound lithium ion secondary battery is 60% or more and 87% or less. Battery negative electrode. The positive electrode for a wound lithium ion secondary battery according to any one of claims 1 to 5,
A negative electrode for a wound lithium ion secondary battery according to any one of claims 6 to 10,
A wound-type lithium ion secondary battery comprising:

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