JP5983822B2 - Negative electrode for lithium ion secondary battery and lithium ion secondary battery - Google Patents

Description

  The present invention relates to a negative electrode for a lithium ion secondary battery and a lithium ion secondary battery.

  Lithium ion secondary batteries have attracted attention as high-capacity secondary batteries, and various techniques for improving the performance of lithium ion secondary batteries have been developed (see Patent Documents 1 to 8, etc.).

Patent Document 1 discloses a negative electrode mixture layer formed on the surface of a current collector having a plurality of through holes, having a thickness of 10 to 60 μm and a density of 1.0 to 1.5 g / cm ^3. Yes. In the negative electrode mixture layer, a plurality of recesses are formed at positions corresponding to the plurality of through holes. Since the negative electrode mixture layer disclosed in Patent Document 1 can absorb the expansion of the negative electrode active material during charging by the concave portion, an increase in the thickness of the negative electrode mixture layer can be suppressed and stress on the separator can be relieved. .

  Patent Document 2 discloses a lithium ion secondary in which the active material coating thickness is 80 μm or less, the porosity of the active material layer on the current collector side is 30 to 50%, and the porosity on the separator side is 50 to 60%. A battery electrode is disclosed. When the electrode for a lithium ion secondary battery disclosed in Patent Document 2 is used for a lithium ion secondary battery, the amount of the electrolyte in the electrode increases, and the lithium ion transport force in the film thickness direction in the electrolyte in the electrode As a result, the output density can be further improved.

Patent Document 3 discloses an active material layer provided on the surface of a current collector, in which a large number of holes that do not penetrate the current collector are formed at intervals of 3 mm or less. As an example of such an active material layer, Patent Document 3 includes LiCoO ₂ as a positive electrode active material, has a weight of 50 mg / cm ² , a thickness of about 140 μm, and has holes formed at intervals of 2.25 mm. A positive electrode active material layer is disclosed. When the active material layer disclosed in Patent Document 3 is used in a lithium ion secondary battery, lithium ions can move smoothly into the active material layer through these holes, and load characteristics can be improved. Charge / discharge characteristics at a large current can be improved.

Patent Document 4 discloses a negative electrode mixture layer including a negative electrode active material and a charge storage material, having a density of 1.2 g / cm ^{3 to} 1.6 g / cm ³ and a thickness of 50 μm to 100 μm. ing. Since the negative electrode mixture layer disclosed in Patent Document 4 holds the charge carriers occluded by the charge storage material without releasing it, the potential of the negative electrode can be increased, and the operating voltage of the positive electrode is increased compared to the conventional case. Internal resistance can be reduced.

Patent Document 5 discloses a negative electrode mixture layer formed on a current collector and having a density of 1.2 g / cm ³ or more and 1.5 g / cm ³ or less. The negative electrode mixture layer has an oil absorption amount Fc per unit weight of the negative electrode active material in a region relatively close to the current collector when divided into two in the thickness direction, and a unit of the negative electrode active material in a region relatively close to the surface The oil absorption amount Fs per weight has a relationship of Fc> Fs. The amount of oil absorption means high affinity with the electrolyte. As an example of such a negative electrode mixture layer, Patent Literature 5 includes a natural graphite powder as a negative electrode active material, and an upper layer and a lower layer having different amounts of oil supply are each 18 mg / cm ² (per one side) of current collector. A negative electrode composite material layer having a density of 1.4 g / cm ³ formed on the surface of is disclosed. In the composite material layer disclosed in Patent Document 5, since the negative electrode composite material layer has a gradient of the oil absorption amount, the electrolytic solution spreads to the vicinity of the current collector, and the entire negative electrode composite material layer can be used effectively.

  Patent Document 6 discloses active material particles, a binder, a first solvent that dissolves the binder, a second solvent that is phase-separated from the first solvent, and an interface that disperses the second solvent. A slurry containing an activator is applied to the surface of the current collector, the first solvent is evaporated and the second solvent is phase-separated, and then the second solvent is evaporated to form a hole in the active material layer. A method of forming is disclosed. The active material layer produced by the method disclosed in Patent Document 6 allows the electrolytic solution to easily penetrate into the active material layer and has a large surface area, so that lithium ions can be smoothly diffused between the active material and the electrolytic solution. It can be carried out.

In Patent Document 7, lithium containing graphite-based carbon active material as an active material, the weight of the mixture after drying is about 10 mg / cm ² , and the pores have a maximum diameter of 100 μm at intervals of 7 mm in length and width. A battery electrode is disclosed. The lithium battery electrode disclosed in Patent Document 7 can improve the state of penetration of the electrolytic solution into the battery.

Patent Document 8, the true density by helium adsorption method at the 1.6~2.1g / cm ^3, the true density by butanol method a negative electrode active material 1.5 to 2.0 g / cm ³ 1.1 to A negative electrode including a negative electrode mixture having a density of 1.7 g / cm ³ and having a porosity smaller than the porosity of the positive electrode mixture is disclosed. The negative electrode disclosed in Patent Document 8 has a high output characteristic even at a low temperature, and can provide a lithium ion secondary battery excellent in high input / output load resistance.

JP 2012-9333 A (Claims 1, 4, paragraph 0012) JP 2002-151055 A (Claims 1 to 5, paragraphs 0022 to 0024) JP 2007-250510 A (Claim 1, paragraph 0020, paragraph 0023, paragraph 0024, paragraph 0025) JP 2013-235653 A (Claims 1, 3, 4, paragraph 0013) JP2011-149387A (Claim 1, Claim 6, Paragraph 0008, Paragraph 0053) JP2011-192615A (Claim 1, paragraph 0049) JP 2001-236945 A (Claim 1, paragraph 0005, paragraph 0011) JP 2007-207535 A (Claims 1, 10, 11, paragraph 0008)

The case where the negative electrode mixture layer disclosed in Patent Document 1 has the most negative electrode mixture layer is when the thickness is 60 μm and the density is 1.5 g / cm ³ . Even at this time, the amount of the negative electrode mixture of the negative electrode mixture layer is as small as 9 mg / cm ² . Since the negative electrode mixture contains a binder, a conductive material, and the like, the amount of the active material that the negative electrode mixture layer has is even smaller. Therefore, the lithium ion secondary battery using the negative electrode mixture layer disclosed in Patent Document 1 has a small capacity.

  The electrode for a lithium ion secondary battery disclosed in Patent Document 2 has an active material layer thickness of 20 to 80 μm and a separator-side porosity of 50% or more and 60% or less. The density is low. Therefore, the lithium ion secondary battery using the electrode has a problem that the energy density per unit volume (charge / discharge capacity) is low.

  Patent Document 3 discloses an example in which the active material layer is applied to the positive electrode, but does not disclose an example in which the active material layer is applied to the negative electrode. Therefore, when the active material layer is applied to the negative electrode, it is unclear whether the lithium ion secondary battery using the negative electrode has a high capacity.

In the negative electrode mixture layer disclosed in Patent Document 4, when the negative electrode active material is graphite and the density of the mixture is 1.6 g / cm ³ , the true density of graphite is approximately 2.2 g / cm ³ . The mixture is filled at a ratio of about 72% of the true density of graphite. Since the composite material is filled at a relatively high density as described above, the negative electrode composite material layer has few voids, is difficult to be impregnated with the electrolyte, and has many active materials that cannot be effectively used. Therefore, the lithium ion secondary battery using the negative electrode mixture layer disclosed in Patent Document 4 has a small battery capacity.

The negative electrode composite material layer disclosed in Patent Document 5 has a density of 1.4 g / cm ³ for both the upper layer and the lower layer. This is about 63.6% of the true density of graphite of the negative electrode active material, and the negative electrode mixture layer has a small amount of active material supported. If the density is increased to further support the active material, the negative electrode mixture layer has fewer voids, and the upper layer having low affinity with the electrolytic solution is particularly difficult to be impregnated with the electrolytic solution. As described above, the negative electrode mixture layer is difficult to reach the lower layer having high affinity with the electrolytic solution, and the active material cannot be used effectively because the electrolytic solution cannot be sufficiently distributed in the vicinity of the current collector. May increase, and it is difficult to increase the capacity of the battery.

  Since the active material layer disclosed in Patent Document 6 forms holes by evaporating the phase-separated second solvent, there is no active material in the portion occupied by the second solvent, Accordingly, the density of the active material is lowered, and the amount of the active material to be carried is small. Therefore, the lithium ion secondary battery using the negative electrode mixture layer disclosed in Patent Document 6 has a small battery capacity.

In the electrode for a lithium ion battery disclosed in Patent Document 7, the mass of the composite material is 10 mg / cm ² and the amount of the active material to be carried is small. Therefore, the lithium ion secondary battery using the electrode for lithium ion batteries disclosed in Patent Document 7 has a small capacity.

In the negative electrode disclosed in Patent Document 8, when the active material having the highest true density of 2.1 g / cm ³ is used, the upper limit of the density of the negative electrode mixture is 1.7 g / cm ^3. The active material is packed at a high density of about 80% of the true density of the material. Therefore, since there are few voids in the negative electrode, it is difficult for the electrolytic solution to impregnate and there are many active materials that cannot be used effectively. Further, when the density of the negative electrode mixture is reduced, the amount of the active material carried by the negative electrode is reduced. Therefore, the lithium ion secondary battery using the negative electrode disclosed in Patent Document 8 has a small battery capacity.

  Thus, conventionally, it has been difficult to produce a lithium ion secondary battery having a high capacity and a low internal resistance.

  In view of the above problems, an object of the present invention is to provide a negative electrode for a lithium ion secondary battery and a lithium ion secondary battery that can be charged and discharged quickly with a high capacity.

  A first aspect of the present invention includes a current collector and an active material layer formed on a surface of the current collector, and the active material layer has a plurality of holes formed on the surface, and the active material The density is 70 to 83% of the true density of the active material contained in the active material layer, and the thickness is 100 to 1000 μm.

A second aspect of the present invention is the invention based on the first aspect, wherein the active material layer includes graphite as the active material, and the active material density is 1.54 to 1.82 g / cm ³ . It is characterized by being.

A third aspect of the present invention is the invention based on the first aspect, wherein the active material layer includes non-graphitizable carbon as the active material, and the active material density is 1.26 to 1.49 g / It is characterized by being cm ³ .

A fourth aspect of the present invention is the invention based on the first aspect, wherein the active material layer includes graphitizable carbon as the active material, and the active material density is 1.26 to 1.49 g / It is characterized by being cm ³ .

A fifth aspect of the present invention is the invention based on the first aspect, wherein the active material layer includes Li ₄ Ti ₅ O ₁₂ as the active material, and the active material density is 2.30-2. It is 73 g / cm ³ .

A sixth aspect of the present invention is the invention based on the first aspect, wherein the active material layer includes SiO as the active material, and the active material density is 1.47 to 1.74 g / cm ³ . It is characterized by being.

A seventh aspect of the present invention is the invention based on the first aspect, wherein the active material layer contains Sn as the active material, and the active material density is 5.04 to 6.10 g / cm ³ . It is characterized by being.

An eighth aspect of the present invention is the invention based on the first aspect, wherein the active material layer contains Si as the active material, and the active material density is 1.61 to 1.90 g / cm ³ . It is characterized by being.

A ninth aspect of the present invention is the invention based on the first aspect, wherein the active material layer includes graphite, non-graphitizable carbon, graphitizable carbon, Li ₄ Ti ₅ O ₁₂ , SiO as the active material. , Sn, Si, and the active material density is more than 1.26 g / cm ^{3 and} less than 6.10 g / cm ³ .

  A tenth aspect of the present invention is an invention based on any one of the first to ninth aspects, wherein the active material layer comprises a conductive auxiliary agent in an amount of 0.0 to 10 wt%, a binder and a thickener. Is contained in an amount of 1.0 to 10 wt%.

  An eleventh aspect of the present invention is an invention based on any one of the first to tenth aspects, wherein a maximum diameter of the plurality of holes is 5 to 1500 μm.

  A twelfth aspect of the present invention is the invention based on any one of the first to eleventh aspects, characterized in that a center interval between the plurality of holes is 500 to 6000 μm.

  A thirteenth aspect of the present invention is the invention based on any one of the first to twelfth aspects, wherein the opening of the plurality of holes has a round shape, a triangular shape, a quadrangular shape, or a polygonal shape that is a pentagon or more. It is one or more selected from.

  A fourteenth aspect of the present invention is the invention based on any one of the first to thirteenth aspects, wherein the depth of the plurality of holes is 5% or more of the thickness of the active material layer. It is characterized by.

  A fifteenth aspect of the present invention is an invention based on any one of the first to fourteenth aspects, wherein the plurality of holes have a bottom portion.

  A sixteenth aspect of the present invention is the invention based on any one of the first to fourteenth aspects, wherein the active material layer is formed on both surfaces of the current collector, and the plurality of holes are formed. An opening is formed on the surface of one of the active material layers, the active material layer and the current collector are penetrated, and a bottom is formed by the other active material layer.

  A seventeenth aspect of the present invention is the invention based on the sixteenth aspect, wherein the plurality of holes have openings formed on the surface of the other active material layer, and the active material layer, the current collector, Including a hole having a bottom formed by the one active material layer, and an opening formed in the surface of the one active material layer and an opening formed in the surface of the other active material layer. The holes are alternately formed.

  An eighteenth aspect of the present invention includes a negative electrode for a lithium ion secondary battery based on any one of the first to seventeenth aspects.

  A negative electrode for a lithium ion secondary battery according to a first aspect of the present invention includes a current collector and an active material layer formed on a surface of the current collector, and the active material layer has a plurality of holes formed on the surface. The active material density is 70 to 83% of the true density of the active material contained in the active material layer, and the thickness is 100 to 1000 μm. When used in a secondary battery, in addition to the surface of the active material layer, even at positions deep in the thickness direction from the surface of the active material layer, electrons are transferred, lithium ions are inserted and desorbed, and the surface of the active material layer The active material at a deep position in the thickness direction can be used effectively, and the active material can be used more effectively because the movement distance of lithium ions in the negative electrode is not too long, and the lithium ion secondary battery with high capacity Can provide. In addition, when the negative electrode for a lithium ion secondary battery is used in a lithium ion secondary battery, the lithium ion released from the active material is located in the hole at a position deep in the thickness direction from the surface of the active material layer. Since the battery can be moved, the internal resistance of the battery is low, the battery can be charged and discharged quickly, and a high-power lithium ion secondary battery can be provided.

In the negative electrode for a lithium ion secondary battery according to the second aspect of the present invention, the active material layer contains graphite as an active material, and the active material density is 1.54 to 1.82 g / cm ^3. A negative electrode having a high density and a high-capacity lithium ion secondary battery can be provided.

In the negative electrode for a lithium ion secondary battery according to the third aspect of the present invention, the active material layer includes non-graphitizable carbon as the active material, and the active material density is 1.26 to 1.49 g / cm ³ . A negative electrode having a high density of active materials, and can provide a high-capacity lithium ion secondary battery.

In the negative electrode for a lithium ion secondary battery according to the fourth aspect of the present invention, the active material layer contains graphitizable carbon as an active material, and the active material density is 1.26 to 1.49 g / cm ³ . A negative electrode having a high density of active materials, and can provide a high-capacity lithium ion secondary battery.

In the negative electrode for a lithium ion secondary battery according to the fifth aspect of the present invention, the active material layer includes Li ₄ Ti ₅ O ₁₂ as an active material, and the active material density is 2.30 to 2.73 g / cm ³ . Therefore, it is a negative electrode which has an active material in high density, and can provide a high capacity | capacitance lithium ion secondary battery.

In the negative electrode for a lithium ion secondary battery according to the sixth aspect of the present invention, the active material layer contains SiO as the active material, and the active material density is 1.47 to 1.74 g / cm ^3. A negative electrode having a high density and a high-capacity lithium ion secondary battery can be provided.

In the negative electrode for a lithium ion secondary battery according to the seventh aspect of the present invention, the active material layer contains Sn as the active material, and the active material density is 5.04 to 6.10 g / cm ^3. A negative electrode having a high density and a high-capacity lithium ion secondary battery can be provided.

In the negative electrode for a lithium ion secondary battery according to the eighth aspect of the present invention, the active material layer contains Si as the active material, and the active material density is 1.61 to 1.90 g / cm ^3. A negative electrode having a high density and a high-capacity lithium ion secondary battery can be provided.

In the negative electrode for a lithium ion secondary battery according to the ninth aspect of the present invention, the active material layer is composed of graphite, non-graphitizable carbon, graphitizable carbon, Li ₄ Ti ₅ O ₁₂ , SiO, Sn, Si as the active material. Including two or more selected, the active material density is more than 1.26 g / cm ^{3 and} less than 6.10 g / cm ³ , so that it is a negative electrode having a high density of active material, and has a high capacity lithium ion A secondary battery can be provided.

  The negative electrode for a lithium ion secondary battery according to the tenth aspect of the present invention is supported because the active material layer contains 0.0 to 10 wt% of a conductive additive, 1.0 to 10 wt% of a binder and a thickener. Without reducing the amount of the active material, the active material can be sufficiently bound and have sufficient conductivity.

  Since the negative electrode for a lithium ion secondary battery according to the eleventh aspect of the present invention has a maximum diameter of a plurality of holes of 5 to 1500 μm, the lithium ion secondary battery using the negative electrode has a hole diameter of lithium ions. A lithium ion secondary battery that is suitable for movement and can be quickly charged and discharged with higher capacity can be provided.

  In the negative electrode for a lithium ion secondary battery according to the twelfth aspect of the present invention, since the center interval of the plurality of holes is 500 to 6000 μm, the number of holes and the interval between the holes are more suitable, and the capacity is increased quickly. A lithium ion secondary battery that can be charged and discharged can be provided.

  In the negative electrode for a lithium ion secondary battery according to the thirteenth aspect of the present invention, the shape of the opening of the hole is one or more selected from a round shape, a triangle shape, a quadrangular shape, or a polygonal shape of a pentagon or more. A lithium ion secondary battery that is suitable for battery reaction and can be charged and discharged quickly with a higher capacity can be provided.

  In the negative electrode for a lithium ion secondary battery according to the fourteenth aspect of the present invention, since the depth of the plurality of holes is 5% or more of the thickness of the active material layer, the depth of the holes is suitable for the battery reaction. Therefore, an active material deep in the thickness direction from the surface of the current collector can be used effectively, and a lithium ion secondary battery that can be charged and discharged quickly with a higher capacity can be provided.

  The negative electrode for a lithium ion secondary battery according to the fifteenth aspect of the present invention has a plurality of holes at the bottom, so that no holes are formed in the current collector, and the negative electrode for lithium ion secondary batteries and lithium In the manufacturing process of the ion secondary battery, the current collector is not easily broken, and the negative electrode for lithium ion secondary battery and the lithium ion secondary battery can be efficiently manufactured.

  In the negative electrode for a lithium ion secondary battery according to the sixteenth aspect of the present invention, the active material layer is formed on both surfaces of the current collector, and a plurality of holes are formed on the surface of the one active material layer. Since the bottom is formed by another active material layer through the active material layer and the current collector, the active material is as much as the surface of the bottom compared to the case where the bottom is formed by the current collector. Since the surface area of the layer increases, the number of active materials that easily contribute to the battery reaction increases, and charge and discharge can be performed more efficiently. In addition, the negative electrode for a lithium ion secondary battery has a plurality of holes at the bottom, the depth of the holes is deeper, and the liquid retention is higher, so the battery may be inclined and the electrolyte may be biased to one side. The lithium ion secondary battery in which the electrolytic solution is held in the hole and the performance is not easily lowered can be provided.

  In the negative electrode for a lithium ion secondary battery according to a seventeenth aspect of the present invention, a plurality of holes are formed in the surface of another active material layer, penetrates the active material layer and the current collector, A hole having a bottom formed by an active material layer is formed, and a hole having an opening formed on the surface of one active material layer and a hole having an opening formed on the surface of another active material layer are alternately formed. Therefore, when it is used for a lithium ion secondary battery in which a plurality of negative electrodes and positive electrodes are stacked, the opening of the hole always faces the separator, and charging and discharging can be performed more efficiently.

  Since the lithium ion secondary battery of the 18th viewpoint of this invention is equipped with the negative electrode for lithium ion secondary batteries based on any one of the 1st-17th viewpoint, it is high capacity | capacitance and can charge / discharge quickly.

1 is a schematic end view showing a longitudinal section of an electrode structure of a lithium ion secondary battery according to an embodiment of the present invention. It is a top view which shows arrangement | positioning of the opening of the hole of the active material layer surface which concerns on embodiment of this invention. FIG. 3A is a schematic end view showing a longitudinal section of a negative electrode for a lithium ion secondary battery according to a modification of the present invention, FIG. 3A is a negative electrode having a hole whose bottom is formed by a current collector, and FIG. 3B is an active material layer; A negative electrode having a through hole penetrating the current collector, FIG. 3C shows an opening formed on the surface of one active material layer, penetrating the active material layer and the current collector, and a bottom portion formed by another active material layer. FIG. 3D shows a hole having an opening formed on the surface of one active material layer, penetrating the active material layer and the current collector, and a bottom portion formed by another active material layer; An opening is formed on the surface of another active material layer, and shows a negative electrode in which holes that pass through the other active material layer and the current collector and whose bottoms are formed by one active material layer are alternately arranged. . FIG. 4A is a schematic end view showing a longitudinal section of an active material layer according to a modification of the present invention, FIG. 4A is an active material layer in which a hole with a triangular longitudinal section is formed, and FIG. 4B is a U-shaped longitudinal section. An active material layer in which holes are formed, FIG. 4C shows an active material layer in which holes having a pentagonal longitudinal cross-sectional shape are formed. It is a top view which shows roughly arrangement | positioning of the opening of the hole of the active material layer surface which concerns on the modification of this invention. FIG. 6A is a plan view schematically showing the arrangement of holes on the surface of an active material layer according to a modified example of the present invention. FIG. 6A shows a triangular opening, FIG. 6B shows a rectangular opening, and FIG. 6C shows an opening. An active material layer having a hexagonal hole is shown. FIG. 7A is a plan view showing the shape of an opening of a hole formed in an active material layer according to a modification of the present invention. FIG. 7A shows three vertices, FIG. 7B shows four vertices, and FIG. 7 is the number of vertices, FIG. 7E is the number of vertices, FIG. 7F is the number of vertices is 8, and FIG. 7G is a star-shaped opening with the number of vertices is 10 The shape of is shown. FIG. 8A is a schematic end view showing a longitudinal section of an electrode structure of a lithium ion secondary battery according to a modification of the present invention, FIG. 8A shows a negative electrode and a positive electrode having holes formed on both sides, and FIG. 1 shows an electrode structure of a lithium ion secondary battery in which a plurality of negative electrodes and positive electrodes in which holes and holes on the bottom surface are alternately arranged are stacked.

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

1. Configuration of Lithium Ion Secondary Battery According to Embodiment of the Present Invention As shown in FIG. 1, a lithium ion secondary battery 1 includes a negative electrode 2 for lithium ion secondary battery (hereinafter referred to as negative electrode 2) and a positive electrode according to the present invention. 3 and a separator 4 are provided. The negative electrode 2 and the positive electrode 3 are disposed to face each other with the separator 4 interposed therebetween. The negative electrode 2, the positive electrode 3, and the separator 4 are, for example, ethylene carbonate (hereinafter referred to as EC), diethyl carbonate (hereinafter referred to as DEC), dimethyl carbonate (hereinafter referred to as DMC), methyl ethyl carbonate (hereinafter referred to as MEC). .) And the like in a nonaqueous solvent containing a lithium salt such as LiPF ₆ , LiBF ₄ , LiClO ₄ or the like.

  In the negative electrode 2, a hole 7 having an opening 9 is formed on the surface of the negative electrode 2. The negative electrode 2 is arranged so that the opening 9 of the hole 7 faces the separator 4.

In the positive electrode 3, an active material layer 11 is formed on both surfaces of a current collector 10, and a hole 12 having an opening 13 on the surface is formed as in the negative electrode 2. The hole 12 formed in the positive electrode 3 is disposed so as to face the opening 9 of the hole 7 of the negative electrode 2 with the separator 4 interposed therebetween. The opening 9 of the hole 7 formed in the negative electrode 2 and the opening 13 of the hole 12 formed in the positive electrode 3 do not necessarily face each other, but the opening 9 of at least one hole 7 and the opening of the hole 12 are not necessarily required to face each other. It is desirable that 13 is facing. When the hole 7 and the hole 12 are facing, a lithium ion and a counter ion between the holes 12 of the hole 7 and the positive electrode 3 of the negative electrode 2 (e.g., PF ₆ ^- ions) can be moved smoothly, more battery reaction Get faster.

  In addition, the positive electrode 3 is not specifically limited, A well-known positive electrode for lithium ion secondary batteries can be used. The positive electrode 3 may be, for example, a conventional composite electrode having active material layers formed of a composite material containing an active material on both sides of the current collector.

2. Configuration of Negative Electrode for Lithium Ion Secondary Battery According to Embodiment of the Present Invention As shown in FIG. 1, the negative electrode 2 includes a current collector 5 and two active material layers 6. A material layer 6 is formed. The current collector 5 is a plate-like member, preferably a thin-film member having a thickness of 5 to 20 μm. The size, shape, and the like of the current collector 5 can be changed as appropriate according to the lithium ion secondary battery to be manufactured. The current collector 5 is not particularly limited as long as it is stable with respect to a chemical reaction that occurs during charging / discharging of the battery and is formed of a conductive member. For example, the current collector 5 can be a foil formed of copper, aluminum, silver, gold, platinum, nickel, titanium, iron, stainless steel, or the like. Further, as the current collector 5, a nonwoven fabric formed of metal fibers or carbon fibers can be used.

  The active material layer 6 is formed of a mixture containing an active material, a conductive aid, a binder, and a thickener. The active material layer 6 has an active material of 80.0 to 99.0 wt% and a conductive assistant of 0.0 to 10 when the total mass of the active material, the conductive assistant, the binder and the thickener is 100 wt%. 0.0 wt%, 1.0-10.0 wt% of binder and thickener. In addition, the conductive support agent does not necessarily need to be contained. It is desirable to contain the active material or the like at this ratio, but it may deviate from this ratio as long as the active material is contained at the active material density described below.

Examples of the active material include graphite such as natural graphite and artificial graphite, non-graphitizable carbon (hereinafter referred to as hard carbon), graphitizable carbon (hereinafter referred to as soft carbon), Li ₄ Ti ₅ O ₁₂ (hereinafter referred to as LTO). 1) or more selected from SiO (silicon monoxide), Sn (tin), Si (silicon), and the like. As the conductive assistant, acetylene black (hereinafter referred to as AB), ketjen black (hereinafter referred to as KB), carbon nanotube (hereinafter referred to as CNT), or the like can be used. As the binder, polyvinylidene fluoride (hereinafter referred to as PVDF), styrene butadiene rubber (hereinafter referred to as SBR), or the like can be used. As the thickener, carboxymethyl cellulose (hereinafter referred to as CMC) can be used.

  The active material layer 6 includes an active material density representing the amount of the active material contained in a unit volume of the active material layer 6 at 70 to 83% of the true density of the active material. Furthermore, the active material layer 6 preferably contains an active material at an active material density of 72 to 83% of the true density. When the ratio of the active material density to the true density is large, the negative electrode 2 carries a larger amount of active material, and the hole 7 is formed so that the electrolytic solution reaches a deep position in the depth direction of the active material layer 6. Lithium ions can reach more active materials than when no holes 7 are formed, and more active materials carried by the active material layer 6 can be used more effectively. Lithium ion secondary batteries can be provided. And since the negative electrode 2 can move the lithium ion in the electrolyte solution in the hole 7, it can provide the lithium ion secondary battery which can charge / discharge quickly with high capacity more reliably.

  If the ratio of the active material density to the true density of the active material layer 6 is smaller than 70%, the active material layer 6 can easily reach the inside even if the hole 7 is not formed in the active material layer 6. Even if the hole 7 is formed in the material layer 6, there are few active materials that can be effectively used for the first time by forming the hole 7, and it is difficult to increase the discharge capacity.

  In addition, when the ratio of the active material density to the true density of the active material layer 6 is greater than 83%, the active material density is extremely high, so that the voids in the active material layer 6 are small, and lithium ions are present in the active material layer 6. It is difficult to move. Therefore, even if the hole 7 is formed in the active material layer 6, only the active material in the portion exposed in the internal space of the hole 7 can be used, and the active material inside the active material layer cannot be effectively used. Even if the carrying amount increases, the discharge capacity is hardly increased.

For example, when graphite is used as the active material, since the true density of graphite is 2.2 g / cm ³ , the active material density of the active material layer 6 is 1.54 to 1.82 g / cm ³ .

Similarly, when hard carbon is used as the active material, since the true density of hard carbon is 1.8 g / cm ³ , the active material density of the active material layer 6 is 1.26 to 1.49 g / cm ³ .

When soft carbon is used as the active material, since the true density of soft carbon is 1.8 g / cm ³ , the active material density of the active material layer 6 is 1.26 to 1.49 g / cm ³ .

When LTO is used as the active material, since the true density of LTO is 3.3 g / cm ³ , the active material density of the active material layer 6 is 2.30 to 2.73 g / cm ³ .

When using a SiO as an active material, since the true density of the SiO is a 2.1 g / cm ^3, the active material density is 1.47~1.74g / cm ^3.

When Sn is used as the active material, the true density of Sn is 7.36 g / cm ³ , so the active material density is 5.04 to 6.10 g / cm ³ .

When Si is used as an active material, since the true density of Si is 2.3 g / cm ^3, the active material density is 1.61~1.90g / cm ^3.

When two or more kinds of active materials are used, the true density of the active material mixture is at least greater than the true density of 1.8 g / cm ³ when 100% of the hard carbon having the lowest true density is contained, and the true density is the highest. When the Sn content is 100%, the true density is less than 7.36 g / cm ³ . Therefore, the active material density in this case is in the range of more than 1.26 g / cm ^{3 and} less than 6.10 g / cm ³ .

  The active material layer 6 is formed in a film shape on the surface of the current collector 5. A plurality of holes 7 are formed in the active material layer 6. The hole 7 has an opening 9 on the surface of the active material layer 6 and is formed from the surface toward the current collector 5. In the case of this embodiment, the hole 7 has a bottom portion 8 formed on the surface of the active material layer 6 that contacts the current collector 5. That is, the hole 7 does not penetrate the current collector 5, and the bottom 8 is formed by the active material layer 6. The hole 7 is formed in a columnar shape, and the vertical cross-sectional shape is a quadrangle.

  The thickness of the active material layer 6 is 100 to 1000 μm. When the thickness of the active material layer 6 is 100 to 1000 μm, the negative electrode 2 can carry a sufficient active material and can provide a lithium ion secondary battery having a large battery capacity. And when the negative electrode 2 is used for a lithium ion secondary battery, the movement distance of lithium ions does not become too long, and the charge / discharge characteristics of the lithium ion secondary battery can be improved.

  Furthermore, the thickness of the active material layer 6 is more preferably 150 to 1000 μm. When the thickness of the active material layer 6 is 150 to 1000 μm, the negative electrode 2 can provide a lithium ion secondary battery that can be charged and discharged quickly with higher capacity and more reliably.

  As shown in FIG. 2, the hole 7 has a round opening 9. The holes 7 are arranged on the surface of the active material layer 6 so that the openings 9 are arranged at equal intervals in the vertical and horizontal directions at a predetermined interval.

  The maximum diameter of the hole 7 is not particularly limited, but is preferably 5 to 1500 μm. If the maximum diameter of the hole 7 is 5 to 1500 μm, the negative electrode 2 can smoothly move the lithium ions in the electrolytic solution impregnated in the hole 7, so that the battery reaction rate can be further improved. The negative electrode 2 has few voids in the active material layer 6 that are reduced by compression when forming the holes 7, and the active material that can be effectively used increases by forming the holes 7.

  Furthermore, it is particularly desirable that the maximum diameter of the hole 7 is 100 to 1000 μm. When the maximum diameter of the hole 7 is 100 to 1000 μm, the negative electrode 2 can move lithium ions more smoothly in the electrolytic solution accommodated in the hole 7 because the diameter of the hole 7 is increased. The speed of the battery reaction is further improved.

  The length between the centers of the adjacent holes 7 (hole center interval) is not particularly limited, but is preferably 500 to 6000 μm. When the center distance between the holes 7 is 500 to 6000 μm, the negative electrode 2 does not overlap the range in which the lithium ions in the electrolytic solution reach from one hole 7, and the lithium ions in the electrolytic solution are difficult to reach in the active material layer 6. Since the area decreases, the active material that can be effectively used increases by forming the holes 7.

  Furthermore, the center distance between the holes 7 is particularly preferably 500 to 2000 μm. When the center distance between the holes 7 is 500 to 2000 μm, the negative electrode 2 is more likely to cause lithium ions in the electrolytic solution to spread throughout the negative electrode 2, and the active material that can be effectively used increases.

  Further, the depth of the hole 7 is not particularly limited, but is preferably 5% or more of the thickness of the active material layer 6. When the depth of the hole 7 is 5% or more, lithium ions in the electrolytic solution easily reach a deep position in the depth direction of the active material layer 6, and the active material that can be effectively used increases.

  Further, it is particularly desirable that the depth of the hole 7 is 75% or more of the thickness of the active material layer 6. When the depth of the hole is 75% or more, lithium ions in the electrolytic solution are more likely to reach a deep position in the depth direction of the active material layer 6, and the active material that can be effectively used is further increased.

3. Manufacturing method of the negative electrode for lithium ion secondary batteries of this invention The manufacturing method of the negative electrode 2 for lithium ion secondary batteries is demonstrated. The active material, the binder, the thickener, and the conductive additive are weighed so as to have a predetermined mass ratio. After the measurement, the active material is charged into a solution obtained by dissolving the thickener in water and stirred. Subsequently, a conductive aid and a binder are added and stirred. Thereafter, the viscosity is adjusted by adding some water and further stirring to obtain a negative electrode slurry. The negative electrode slurry is a liquid used for forming the active material layer 6 on the surface of the current collector 5. Incidentally, the negative electrode slurry is generally called a composite slurry.

  Next, the negative electrode slurry prepared on both surfaces of the current collector 5 formed in a predetermined size is applied and dried at a predetermined temperature for a predetermined time. The coating method is not particularly limited, and for example, a doctor blade method or a die coating method can be used.

  The amount of the active material contained in the active material layer 6 can be adjusted by changing the viscosity of the negative electrode slurry and the coating thickness of the negative electrode slurry.

  Next, the current collector 5 on which the active material layer 6 is formed is passed through a roll press, and the active material layer 6 is formed to a predetermined thickness. The active material density of the active material layer 6 can be adjusted by changing the thickness of the active material layer 6 by adjusting the gap distance between the rolls of the roll press machine.

  Finally, a jig like a sword mountain with a large number of needles is pierced into the surface of the active material layer 6 to form a hole 7 to obtain the negative electrode 2 for a lithium ion secondary battery.

  The small hole 7 having a diameter of 500 μm or less can be formed by laser processing. In this method, the size of the hole 7 to be formed can be adjusted by changing the diameter of the laser beam to be irradiated, and for example, the frustum-shaped hole 7 can be formed by changing the incident angle.

4). Operation and Effect The operation of the lithium ion secondary battery 1 using the negative electrode 2 of the present invention will be described. In the lithium ion secondary battery 1, the negative electrode 2 and the positive electrode 3 are immersed in the electrolytic solution, and the electrolytic solution is also accommodated in the hole 7 formed in the active material layer 6 of the negative electrode 2. Since the hole 7 is formed in the active material layer 6, the electrolytic solution is impregnated in a deep position in the thickness direction from the surface of the active material layer 6.

  First, the operation during charging of the lithium ion secondary battery 1 will be described. A voltage is applied between the negative electrode 2 and the positive electrode 3 through an external circuit (not shown). Then, lithium in the active material of the positive electrode 3 is released into the electrolytic solution as lithium ions. Then, electrons are emitted from the active material and collected by the current collector 10.

  The electrons collected by the current collector 10 move to the negative electrode 2 through an external circuit (not shown). On the other hand, lithium ions move through the electrolytic solution to the negative electrode 2 and are inserted into the active material. Since the hole 7 is formed in the active material layer 6 of the negative electrode 2, lithium ions can be contained in the active material not only on the surface of the active material layer 6 but also at a position deep in the thickness direction from the surface of the active material layer 6. Inserted. Thus, in the negative electrode 2, lithium ions can move in the electrolyte contained in the hole 7, so that the lithium ions can easily move over a long distance from the positive electrode 3 to the negative electrode 2. The lithium ion secondary battery 1 is charged as described above.

  Next, the operation during discharging of the lithium ion secondary battery 1 will be described. The negative electrode 2 and the positive electrode 3 are connected to an external load (not shown). Then, lithium in the active material of the negative electrode 2 is released into the electrolytic solution as lithium ions. Electrons are emitted from the active material and collected by the current collector 5. As described above, since the hole 7 is formed in the active material layer 6, this reaction proceeds at a position deeper in the thickness direction from the surface of the active material layer 6 in addition to the surface of the active material layer 6.

  The electrons collected by the current collector 5 move from the negative electrode 2 to the positive electrode 3 through an external load. Lithium ions are desorbed from the active material and move to the positive electrode 3 through the electrolytic solution. Lithium ions are inserted into the active material at the positive electrode 3. In this way, the lithium ion secondary battery 1 is discharged.

  In the above configuration, the negative electrode 2 for a lithium ion secondary battery according to the embodiment of the present invention is configured to include the current collector 5 and the active material layer 6 formed on the surface of the current collector 5. did. The active material layer 6 has a plurality of holes 7 formed on the surface thereof, the active material density is 70 to 83% of the true density of the active material contained in the active material layer 6, and the thickness is 100 to 1000 μm. It was configured as follows.

  Therefore, since the negative electrode 2 has a plurality of holes 7 formed on the surface of the active material layer 6, when used in the lithium ion secondary battery 1, the surface of the active material layer 6 in addition to the surface of the active material layer 6 is used. Even at deep positions in the thickness direction, the movement of lithium ions is smooth, so that electrons can be exchanged, lithium ions can be inserted and desorbed.

  The negative electrode 2 can move in the electrolytic solution in which lithium ions released from the active material are accommodated in the holes 7 at positions deep in the thickness direction from the surface of the active material layer 6.

  Therefore, the lithium ion secondary battery 1 according to the embodiment of the present invention supports more active materials, can effectively use most of the supported active materials, has a high capacity, and has a battery reaction. The battery can be charged and discharged quickly and quickly, and the internal resistance of the battery is low and the output can be increased.

  Furthermore, since the positive electrode 2 for a lithium ion secondary battery according to an embodiment of the present invention can effectively use an active material without excessively moving the lithium ion within the negative electrode, a high capacity lithium ion secondary Battery can be provided.

Since lithium ions have a very small ion radius, it is considered that lithium ions are solvated with many solvents in the electrolytic solution. And the solvated lithium ion has a large movement resistance. Further, in the case of a conventional composite electrode formed by drying the composite slurry coated on the surface of the current collector and having no holes in the active material layer, electrolysis of LiPF ₆ as, for example, lithium salt PF ₆ ⁻ ions, which are counter ions when added to the solution, migrated through the electrolytic solution impregnated in the micropores formed between the active materials in the electrode.

Thus, in the lithium ion secondary battery using the conventional electrode is not formed holes, solvated lithium ions and PF ₆ ^- ions and because through the electrolytic solution impregnated in the micropores, lithium ions and PF ₆ ^- ions, easily caught by the constricted portion between the active materials were more further transfer resistance.

For contrast, in this embodiment, since the holes 7 in the active material layer 6 of the negative electrode 2 is formed, a lithium ion or PF ₆ the electrolytic solution existing in the hole 7 ^- ions as preferentially, holes 7 is a priority path through which ions can move quickly, and can move through the negative electrode 2 without being inhibited by lithium ions.

  Therefore, in the negative electrode 2 according to the embodiment of the present invention, since the holes 7 are formed, the battery reaction is fast even if the active material layer 6 carries the active material at a high density, and the active material layer 6 is further formed. Even when it is formed thick, the battery reaction is fast.

  Conventionally, it is considered that the long movement distance of lithium ions is the maximum rate-determining rate of the battery reaction, and there is almost no electrode having a thickness of 100 μm or more.

However, in practice, as described above, lithium ion or PF ₆ solvated ^- ions maximum rate-limiting movement resistance cell reaction when passing through the fine pores formed between the active material particles in the mixed material electrode It is thought that.

Therefore, by forming the hole 7 on the surface of the active material layer 6, lithium ions and PF ₆ ⁻ ions can move smoothly in the electrolyte solution impregnated in the hole 7. Ions can move smoothly, and the speed of the battery reaction can be increased. Therefore, the negative electrode 2 can provide a lithium ion secondary battery that can be charged and discharged quickly.

  Incidentally, in the case of a conventional composite electrode in which no hole is formed in the active material layer, lithium ions in the electrolyte solution are difficult to reach deeply in the thickness direction of the electrode, and the active material that can be used effectively is However, it was limited to those in the range of about 100 μm from the surface.

  When the active material density of the composite material is increased, the voids in the composite material are reduced, the electrolyte does not easily flow through the composite material, and the narrowed portion of the fine holes between the active materials is further reduced. The active material that can effectively use the lithium ion migration is limited to the active material at a shallower position.

  On the other hand, the negative electrode 2 has an active material layer 6 having an active material density of 70 to 83% of the true density of the active material and a thickness of 100 to 1000 μm, that is, the active material is supported at a high density. Even in the case of the thick electrode, when it is used in the lithium ion secondary battery 1, the lithium ion can move in the electrolytic solution existing in the hole 7, so that the lithium ion is also deep in the thickness direction of the active material layer 6. An active material that can move and is deep in the thickness direction of the active material layer 6 can also be used effectively.

  As mentioned above, the lithium ion secondary battery 1 using the negative electrode 2 for lithium ion secondary batteries which concerns on embodiment of this invention can charge / discharge quickly with high capacity | capacitance.

  Further, conventionally, in order to increase the capacity of the lithium ion secondary battery, it has been necessary to stack a plurality of positive electrodes and negative electrodes via a separator.

  However, the negative electrode 2 for a lithium ion secondary battery according to the embodiment of the present invention can increase the capacity of the battery by forming the active material layer 6 thick and the active material density high. A high capacity battery can be realized by the negative electrode 2 of the layer, and the number of separators 4 can be reduced.

  Moreover, the negative electrode 2 for lithium ion secondary batteries which concerns on embodiment of this invention improves the liquid retention property of the hole 7 by making the some hole 7 have the bottom part 8. FIG. Therefore, when the negative electrode 2 is used for the lithium ion secondary battery 1, even when the lithium ion secondary battery 1 is tilted and the electrolyte is biased to one side, the electrolyte is held in the hole 7, and the lithium ion secondary battery 1 A decrease in performance can be suppressed.

  Furthermore, since the negative electrode 2 does not have the hole 7 formed in the current collector 5, the current collector 5 is not easily broken in the manufacturing process of the negative electrode 2 and the lithium ion secondary battery 1, and the negative electrode 2 and the lithium ion secondary are efficiently separated. Battery 1 can be manufactured.

5). The present invention is not limited to the above-described embodiment, and can be appropriately changed within the scope of the gist of the present invention.

  For example, the materials of the active material, binder, thickener, conductive additive, electrolytic solution, separator, and current collector can be appropriately changed.

  In the above embodiment, the case where the negative electrode 2 has the hole 7 in which the opening 9 is formed on the surface of the active material layer 6 and the bottom 8 is formed by the active material layer 6 has been described. Is not limited to this. For example, as shown in FIG. 3A, the negative electrode 2A has a hole 7A in which an opening 9A is formed on the surface of the active material layer 6A, penetrates the active material layer 6A, and a bottom 8A is formed by the current collector 5A. You may do it.

  As shown in FIG. 3B, the negative electrode 2B has an opening 9B formed on the surface of one active material layer 6B and the other active material layer 6B, and the current collector 5B, the one active material layer 6B and the other active material layer 6B. You may have the hole 7B which penetrates the substance layer 6B. In this case, the negative electrode 2B can easily inject an electrolytic solution during the manufacturing process of the lithium ion secondary battery, and can easily discharge the gas generated during the initial charge.

  Furthermore, as shown in FIG. 3C, the negative electrode 2C has an opening 9C formed on the surface of one active material layer 6C, penetrates the active material layer 6C and the current collector 5C, and is bottomed by the other active material layer 26C. You may have the hole 7C in which 8C is formed. In this case, in the negative electrode 2C, the surface area of the active material layer is increased by the surface of the bottom 8C compared to the case where the bottom 8A of the hole 7A is formed by the current collector 5A. A lithium ion secondary battery capable of generating electricity more efficiently can be provided. Moreover, since the hole 7C has the bottom 8C and the depth of the hole is deeper than that of the hole 7, the liquid retaining property is further higher. Therefore, in the lithium ion secondary battery using the negative electrode 2C, even when the battery is tilted and the electrolyte is biased to one side, the electrolyte is sufficiently held in the hole 7C, and the performance is hardly deteriorated.

  As shown in FIG. 3D, the negative electrode 2D has an opening 9D formed on the surface of one active material layer 6D, penetrates the active material layer 6D and the current collector 5D, and is bottomed by the other active material layer 26D. A hole 7D in which 8D is formed, and an opening 29D is formed on the surface of the active material layer 26D, penetrates the active material layer 26D and the current collector 5D, and a bottom portion 28D is formed by the active material layer 6D. 27D, and the holes 7D and the holes 27D may be alternately arranged.

  Furthermore, in the above embodiment, the case where the vertical cross-sectional shape of the hole 7 is a square has been described, but the present invention is not limited to this, and the vertical cross-sectional shape of the hole 7 can be changed as appropriate. For example, as shown in FIG. 4A, the hole 7E may be formed in the active material layer 6E so that the longitudinal cross-sectional shape is a triangle and the apex of the triangle is the bottom 8E. Moreover, as shown in FIG. 4B, the hole 7F may be formed in the active material layer 6F so that the longitudinal cross-sectional shape of the tip portion is a semicircular shape, and the vertex of the semicircle becomes the bottom portion 8F. . In the case of this modification, the vertical cross-sectional shape of the hole 7F is U-shaped. Furthermore, as shown in FIG. 4C, the hole 7G may be formed in the active material layer 6G so that the longitudinal cross-sectional shape of the tip portion is triangular and the apex of the triangle is the bottom 8G. In the case of this modification, the vertical cross-sectional shape of the hole 7G is a pentagon.

  Further, the vertical cross-sectional shape of the holes 7A, 7B, 7C, 7D, and 27D shown in the above modification may be a triangle, a U shape, or a pentagon as described above. When the vertical cross-sectional shape of the hole 7A or the hole 7B is as described above, the current collectors 5A and 5B are exposed at the vertex at the deepest part of the hole or a hole is formed at the vertex so that the vertical cross-sectional shape is slightly Deform. For example, when the hole 7E is used as a through hole and applied to the negative electrode 2B, the vertical cross-sectional shape is a trapezoid whose bottom is shorter than the top.

  Furthermore, the holes 7 formed in the active material layer 6 do not have to have the same vertical cross-sectional shape of all the holes 7, and holes 7 having different vertical cross-sectional shapes may be mixed, And a hole having the bottom 8 may be mixed.

  In the above embodiment, the case where the holes 7 are arranged on the surface of the active material layer 6 so that the openings 9 are arranged at equal intervals in the vertical and horizontal directions with a predetermined interval has been described. However, the present invention is not limited to this. I can't. For example, as shown in FIG. 5, the holes 7H may have openings 9H arranged on the surface of the active material layer 6H so as to be arranged at equal intervals along an axis parallel to the diagonal line at a predetermined interval. The holes 7 may be arranged so that the openings 9 are arranged at a predetermined interval along a concentric circle centering on the center of the active material layer 6.

  Furthermore, in the above embodiment, the case where the shape of the opening 9 of the hole 7 is round has been described, but the present invention is not limited to this, and the shape of the opening 9 can be changed as appropriate. For example, the shape of the opening 9J may be a triangle like the hole 7J shown in FIG. 6A, the shape of the opening 9K may be a square like the hole 7K shown in FIG. 6B, and the hole 7L shown in FIG. As described above, the shape of the opening 9L may be a hexagon.

  In addition, the shape of the opening 9 may be a pentagon or a polygon that is a heptagon or more. For example, as shown in FIGS. 7A to 7G, the opening 9 of the hole 7 may be a star shape having about 3 to 10 vertices. And as for the shape of the opening 9 of the hole 7 formed in the active material layer 6, the opening 9 of all the holes 7 does not need to have the same shape, and the opening 9 of a different shape may be mixed. .

  Furthermore, the hole 7 may have a rectangular shape and a vertical cross-sectional shape of a triangle, for example, by appropriately combining the cross-sectional shape of the hole 7 and the surface shape of the hole 7 described in the above modification. In this case, the hole 7 is a quadrangular pyramid.

  In the above embodiment, the lithium ion secondary battery 1 having a single-layer structure in which the negative electrode 2 and the positive electrode 3 are stacked one by one with the separator 4 interposed therebetween has been described. However, the present invention is not limited to this, and the separator 4 Thus, a lithium ion secondary battery having a multilayer structure in which the negative electrode 2 and the positive electrode 3 are further laminated can be obtained. For example, as illustrated in FIG. 8A, the lithium ion secondary battery 1 </ b> A may have a multilayer structure in which four layers of the negative electrode 2 and the positive electrode 3 are alternately stacked via the separator 4. In this case, in the lithium ion secondary battery 1A, in all the separators 4, the opening 9 of the hole 7 of the negative electrode 2 and the opening 13 of the hole 12 of the positive electrode 3 can face each other with the separator 4 interposed therebetween. In addition, lithium ions easily move between the positive electrodes 3 and can be charged and discharged more efficiently.

  Further, as shown in FIG. 8B, the lithium ion secondary battery 1B has a multilayer structure in which the negative electrode 2D and the positive electrode 3D formed in the same shape as the negative electrode 2D are stacked in the same manner as the lithium ion secondary battery 1A. May be. Similarly, in all the separators 4 of the lithium ion secondary battery 1B, the opening 9D of the hole 7D of the negative electrode 2D, the opening 29D of the hole 27D of the negative electrode 2D, the opening 13D of the hole 12D of the positive electrode 3D, and the hole 32D of the positive electrode 3D. Since any of the openings 33D faces the separator 4, charging and discharging can be performed more efficiently.

  In the above-described embodiment and modification, the case where the active material layer 6 is formed on both surfaces of the current collector 5 has been described. However, the present invention is not limited to this, and the active material layer 6 includes the current collector 5. It may be formed only on one side.

Example I
(1) Production of electrochemical cell In Examples 1 to 6, a negative electrode for a lithium ion secondary battery using natural graphite as an active material was produced and applied to the negative electrode of the electrochemical cell. Although the electrochemical cell of Examples 1-6 differs in the depth of the hole formed in the active material layer, since the other structure is the same, the manufacturing method of an electrochemical cell is demonstrated to Example 1 as an example.

  First, natural graphite as an active material, SBR as a binder, and CMC as a thickener were weighed so that the mass ratio was 98: 1: 1. After weighing, CMC was dissolved in water to prepare an aqueous solution with a concentration of 1%, and the aqueous solution and natural graphite were put into a rotation and revolution hybrid mixer (manufactured by Shinky Co., Ltd., model: ARE-310) and stirred for 10 minutes. . Further, a solution in which SBR was dispersed was added and stirred for 10 minutes. Thereafter, water was appropriately added and further stirred to obtain a negative electrode slurry having a viscosity adjusted to 800 mPa · s.

  Next, a 10 μm thick copper foil cut to a size of 3 cm × 3 cm is prepared as a current collector, and a negative electrode slurry is applied to one surface of the copper foil with a comma roll coater and dried at 120 ° C. for 1 hour. Thus, an active material layer was formed. Thereafter, an active material layer was similarly formed on the other surface of the copper foil. The thickness of the formed active material layer is 300 μm.

Subsequently, the copper foil in which the active material layer was formed on both surfaces was subjected to a roll press machine (product name: 5 ton air hydro press) and compressed so that the thickness of the active material layer became 200 μm. A sword-shaped needle was pierced on one surface of the compressed active material layer to form holes having the parameters shown in Table 1. Thereafter, a plurality of holes were similarly formed on the other surface of the compressed active material layer. Through the above steps, an anode having an active material density of 1.70 g / cm ³ (77% of true density) and an active material layer containing 34 mg / cm ² of natural graphite on both sides was produced.

Subsequently, metallic lithium was punched out to the same size as the produced negative electrode to produce a counter electrode. A polyethylene separator having countless fine pores is sandwiched between the negative electrode and the counter electrode, and EC (ethylene carbonate), DMC (dimethyl carbonate), and MEC (methyl ethyl carbonate) are mixed at a volume ratio of 1: 1: 1. A laminate cell was prepared by inserting into an aluminum laminate pack together with an electrolyte obtained by adding 1M LiPF ₆ to the mixed solvent and vacuum packing. The laminate cell was used as the electrochemical cell of Example 1. Effective area of the electrode is 9cm ^2.

  The electrochemical cells of Examples 2 to 6 were also produced by the same method as in Example 1.

  For comparison, an electrochemical cell similar to Example 1 was produced as Comparative Example 1 except that no hole was formed in the negative electrode. Table 1 shows the data of the negative electrodes of Examples 1 to 6 and the negative electrode of Comparative Example 1.

  In Examples 7 to 11, a negative electrode for a lithium ion secondary battery using artificial graphite as an active material was prepared and applied to the negative electrode of an electrochemical cell. Although the electrochemical cells of Examples 7 to 11 differ in the center spacing of the holes formed in the active material layer, but the other configurations are the same, a method for manufacturing an electrochemical cell will be described using Example 7 as an example.

  First, artificial graphite as an active material, SBR as a binder, and CMC as a thickener were weighed so that the mass ratio was 98: 1: 1. After weighing, CMC was dissolved in water to prepare an aqueous solution having a concentration of 1%, and the aqueous solution and artificial graphite were put into a rotation / revolution hybrid mixer and stirred for 10 minutes. Further, a solution in which SBR was dispersed was added and stirred for 10 minutes. Thereafter, water was appropriately added and further stirred to obtain a negative electrode slurry having a viscosity adjusted to 1000 mPa · s.

  Next, a 10 μm thick copper foil cut to a size of 3 cm × 3 cm was prepared as a current collector, and an active material layer was formed on both sides of the copper foil by the same method as in Example 1. The thickness of the formed active material layer is 650 μm.

Subsequently, the copper foil in which the active material layer was formed on both surfaces was subjected to a roll press machine and compressed so that the thickness of the active material layer was 500 μm. In the same manner as in Example 1, holes having the parameters shown in Table 2 were formed, the active material density was 1.76 g / cm ³ (80% of the true density), and an active material containing 93 mg / cm ² of artificial graphite. A negative electrode having layers on both sides was prepared. An electrochemical cell was formed in the same manner as in Example 1 using the negative electrode. The electrochemical cells of Examples 8 to 11 were produced in the same manner as Example 7.

  For comparison, an electrochemical cell similar to that of Example 7 was produced as Comparative Example 2 except that no hole was formed. Table 2 shows the data of the negative electrodes of Examples 7 to 11 and the negative electrode of Comparative Example 2. In addition, Table 2 shows a value obtained by dividing the discharge capacity per mass by the theoretical discharge capacity per mass as the active material utilization rate (%). The theoretical discharge capacity per mass of artificial graphite is 360 mAh / g.

  In Examples 12 to 17, a negative electrode for a lithium ion secondary battery using natural graphite as an active material was produced and applied to the negative electrode of an electrochemical cell. The electrochemical cells of Examples 12 to 17 differ in the maximum diameter of the holes formed in the active material layer, and Examples 12 to 14 and Examples 15 to 17 have different hole formation methods and hole depths. Since other configurations are the same, a method for manufacturing an electrochemical cell will be described using Example 12 as an example.

  First, a negative electrode slurry having a viscosity adjusted to 1200 mPa · s was prepared by the same method as in Example 1 using natural graphite as an active material.

  Next, a 10 μm-thick copper foil cut to a size of 3 cm × 3 cm was prepared as a current collector, and an active material layer having a thickness of 900 μm was formed on both sides of the copper foil by the same method as in Example 1.

Subsequently, the copper foil in which the active material layer was formed on both sides was compressed by a roll press machine so that the thickness of the active material layer became 700 μm. Holes having the parameters shown in Table 3 were formed by irradiating a laser beam having a diameter of 5 μm using a laser processing machine (manufactured by Mitsubishi Electric Corporation: product name ML605GTF2). At this time, a similar hole was formed in the copper foil, and a through hole was formed in the negative electrode. In this manner, an anode having an active material density of 1.80 g / cm ³ (82% of the true density) and an active material layer containing 126 mg / cm ² of natural graphite on both sides was produced. An electrochemical cell was produced in the same manner as in Example 1 using the negative electrode. In Examples 15 to 17, holes were formed in the same manner as in Example 1 using a sword mountain needle. The electrochemical cells of Examples 13 to 17 were also produced in the same manner as Example 1.

  For comparison, an electrochemical cell similar to Example 12 was produced as Comparative Example 3 except that no hole was formed. Table 3 shows data of the negative electrodes of Examples 12 to 17 and the negative electrode of Comparative Example 3.

  In Examples 18 to 21, a negative electrode for a lithium ion secondary battery using artificial graphite as an active material was prepared and applied to the negative electrode of an electrochemical cell. The electrochemical cells of Examples 19 to 21 are different in the shape of the opening of the hole formed in the active material layer, but the other configurations are the same. Therefore, a method for manufacturing the electrochemical cell will be described using Example 18 as an example. .

  First, a negative electrode slurry having a viscosity adjusted to 900 mPa · s was prepared in the same manner as in Example 7 using artificial graphite as an active material.

  Next, a 10 μm thick copper foil cut to a size of 3 cm × 3 cm was prepared as a current collector, and an active material layer having a thickness of 400 μm was formed on both sides of the copper foil by the same method as in Example 1.

Subsequently, the copper foil in which the active material layer was formed on both sides was compressed by a roll press machine so that the thickness of the active material layer was 300 μm. Holes having the parameters shown in Table 4 were formed in the active material layer in the same manner as in Example 1. The active material density was 1.82 g / cm ³ (83% of the true density), and 55 mg / cm ² . A negative electrode having an active material layer containing artificial graphite on both sides was produced. An electrochemical cell was produced in the same manner as in Example 1 using the negative electrode. The electrochemical cells of Examples 19 to 21 were produced in the same manner as Example 18.

  For comparison, an electrochemical cell similar to that of Example 18 was produced as Comparative Example 4 except that no hole was formed. Table 4 shows data of the negative electrodes of Examples 18 to 21 and the negative electrode of Comparative Example 4.

  In Example 22, a negative electrode for a lithium ion secondary battery using a mixture of natural graphite and SiO as an active material was produced and applied to the negative electrode of an electrochemical cell.

  First, a mixture containing 90% natural graphite and 10% SiO by mass as an active material, carbon nanotubes as a conductive additive, SBR as a binder, and CMC as a thickener at a mass ratio of 97: 1: 1: 1 Weighed so that After weighing, CMC was dissolved in water to prepare an aqueous solution having a concentration of 1%, and the aqueous solution and a mixture of natural graphite and SiO were put into a rotation / revolution hybrid mixer and stirred for 10 minutes. Further, a solution in which carbon nanotubes and SBR were dispersed was added and stirred for 10 minutes. Thereafter, water was appropriately added and further stirred to obtain a negative electrode slurry having a viscosity adjusted to 800 mPa · s.

  Next, a 10 μm thick copper foil cut to a size of 3 cm × 3 cm was prepared as a current collector, and an active material layer having a thickness of 400 μm was formed on both sides of the copper foil by the same method as in Example 1.

Subsequently, the copper foil in which the active material layer was formed on both sides was compressed by a roll press machine so that the thickness of the active material layer was 300 μm. Holes having the parameters shown in Table 5 were formed in the active material layer in the same manner as in Example 1. The active material density was 1.76 g / cm ³ (80% of the true density), and 53 mg / cm ² . A negative electrode having an active material layer containing a mixture of natural graphite and SiO on both sides was produced. An electrochemical cell was produced in the same manner as in Example 1 using the negative electrode.

  For comparison, an electrochemical cell similar to that of Example 22 was prepared as Comparative Example 5 except that no hole was formed.

  In Example 23, a negative electrode for a lithium ion secondary battery using a mixture of artificial graphite and Sn as an active material was produced and applied to the negative electrode of an electrochemical cell.

  First, a mixture containing 65% artificial graphite and 35% Sn as an active material, carbon nanotubes as a conductive aid, SBR as a binder, and CMC as a thickener at a mass ratio of 97: 1: 1: 1 Weighed so that After weighing, CMC was dissolved in water to prepare an aqueous solution having a concentration of 1%, and the aqueous solution and a mixture of artificial graphite and Sn were put into a rotation / revolution hybrid mixer and stirred for 10 minutes. Further, a solution in which carbon nanotubes and SBR were dispersed was added and stirred for 10 minutes. Thereafter, water was appropriately added and further stirred to obtain a negative electrode slurry adjusted to a viscosity of 800 mPa · s.

  Next, a 10 μm thick copper foil cut to a size of 3 cm × 3 cm was prepared as a current collector, and an active material layer having a thickness of 280 μm was formed on both sides of the copper foil by the same method as in Example 1.

Subsequently, the copper foil in which the active material layer was formed on both sides was compressed by a roll press machine so that the thickness of the active material layer became 200 μm. Holes having the parameters shown in Table 5 were formed in the active material layer in the same manner as in Example 1, and the active material density was 3.0 g / cm ³ (75% of the true density), and 60 mg / cm ² A negative electrode having active material layers containing a mixture of artificial graphite and Sn on both sides was produced. An electrochemical cell was produced in the same manner as in Example 1 using the negative electrode.

  For comparison, an electrochemical cell similar to that of Example 21 was produced as Comparative Example 6 except that no hole was formed. The negative electrode data of Examples 20 and 21 and Comparative Examples 5 and 6 are shown in Table 5.

  In Examples 24-27, a negative electrode for a lithium ion secondary battery using natural graphite as an active material was prepared and applied to the negative electrode of an electrochemical cell.

  In Example 24, a negative electrode slurry containing natural graphite as an active material, SBR as a binder, CMC as a thickener, and AB as a conductive auxiliary agent in a mass ratio of 97: 1: 1: 1 was used. First, natural graphite, SBR, CMC, and AB were weighed so as to have the above mass ratio. After weighing, CMC was dissolved in water to prepare an aqueous solution having a concentration of 1%, and the aqueous solution and artificial graphite were put into a rotation / revolution hybrid mixer and stirred for 10 minutes. Further, a solution in which SBR and AB were dispersed was added and stirred for 10 minutes. Thereafter, water was appropriately added and further stirred, and the viscosity was adjusted to 800 mPa · s to prepare a negative electrode slurry.

  Using the prepared negative electrode slurry, an active material layer having a thickness of 118 μm is formed on both surfaces of a copper foil having a thickness of 10 μm, the active material layer is compressed to 100 μm, and shown in Table 6 in the same manner as in Example 1. A negative electrode with parameters was prepared.

  In Example 25, an active material layer having a thickness of 120 μm was formed on a copper foil having a thickness of 10 μm using the same negative electrode slurry as in Example 24 having a viscosity adjusted to 800 mPa · s, and the same method as in Example 24 was performed. A negative electrode having the parameters shown in Table 6 was prepared.

  In Example 26, an active material layer having a thickness of 125 μm was formed on a copper foil having a thickness of 10 μm using the same negative electrode slurry as in Example 24 having a viscosity adjusted to 800 mPa · s, and the same method as in Example 24 was used. A negative electrode having the parameters shown in Table 6 was prepared.

  In Example 27, an active material layer having a thickness of 130 μm was formed on a copper foil having a thickness of 10 μm using the same negative electrode slurry as in Example 24 having a viscosity adjusted to 800 mPa · s, and the active material layer was adjusted to 100 μm. The negative electrode having the parameters shown in Table 6 was prepared by compressing and irradiating the surface of the active material layer with a laser beam having a diameter of 100 μm using a laser processing machine.

  For comparison, as Comparative Example 7, a negative electrode slurry similar to Example 24 in which the viscosity was adjusted to 800 mPa · s was used, and a 110 μm thick active material layer was formed on both surfaces of a 10 μm thick copper foil, The active material layer was compressed to 100 μm, and negative electrodes having the parameters shown in Table 6 were produced in the same manner as in Example 1. As Comparative Example 8, an electrochemical cell having the same configuration as Comparative Example 7 was produced except that no hole was formed.

  As Comparative Example 9, a negative electrode slurry similar to that in Example 24 with the viscosity adjusted to 800 mPa · s was used to form a 115 μm thick active material layer on a 10 μm thick copper foil, and the same method as in Example 24 was used. Negative electrodes having the parameters shown in Table 6 were produced. As Comparative Example 10, an electrochemical cell having the same configuration as Comparative Example 7 was produced except that no hole was formed.

  Furthermore, Example 24 as Comparative Example 11, Example 25 as Comparative Example 12, Example 26 as Comparative Example 13, and Example 27 as Comparative Example 14 have the same structure except that they are not perforated. Each cell was fabricated. Table 6 shows the negative electrode data of Examples 24-27 and Comparative Examples 7-14.

  In this example, the maximum diameter of the holes formed in the active material layer, the center distance between the holes, and the depth of the holes were measured with a laser microscope (manufactured by Keyence Corporation, product name: VK-X100). These values were calculated by measuring each of 30 locations and obtaining the average value.

The active material density was calculated by the following method. First, the negative electrode was cut into a size of 1 cm ² and the weight and thickness thereof were measured. Then, the copper foil which is a collector was taken out from the cut negative electrode, and the weight and thickness of the taken-out copper foil were measured. Then, the thickness of the active material layer was calculated by subtracting the thickness of the copper foil from the thickness of the negative electrode (if the active material layer was formed on both sides of the copper foil, further dividing by 2). The volume of the active material layer was calculated by multiplying the calculated thickness value of the active material layer by the area of the cut current collector.

Subsequently, the value obtained by subtracting the weight of the copper foil from the weight of the negative electrode is multiplied by the weight fraction when the electrode slurry is produced (if the active material layer is formed on both sides of the copper foil, it is further divided by 2). ) The active material weight was calculated. In addition, the weight of the active material is cut to a size of 1 cm ² of the negative electrode of the actual battery, the current collector is peeled from a part of the cut negative electrode, the mixture layer containing the active material is dissolved in water, and centrifuged. After separating and drying only the active material, it can be measured by weighing.

  Finally, the active material density was calculated by dividing the active material weight determined above by the volume of the active material layer. In addition, the value which divided the value of the active material weight by the area of the cut negative electrode was made into the active material carrying amount per unit area.

(2) Electrochemical cell characteristic evaluation method The discharge capacity was measured to evaluate the electrochemical cell characteristics. The discharge capacity was measured at a temperature of 25 ± 1 ° C. using a charge / discharge test apparatus (manufactured by Asuka Electronics Co., Ltd., model: ACD-R1APS). In the electrochemical cells of all the examples and comparative examples, a constant current (CC: constant current) of 5 mA / cm ^2, a constant current of 0.005 V (CV: constant voltage), and a charging current value of 0.1 mA / cm After charging until the voltage drops to ² , the cut-off voltage is 1.0 Vvs. The electric capacity obtained when discharging at a constant current of 10 mA / cm ² as Li / Li ⁺ was taken as the discharge capacity.

(3) Evaluation results of electrochemical cell (3-1) Relationship between hole depth of active material layer and characteristics of electrochemical cell As shown in Table 1, the electrochemical cells of Examples 1 to 6 are active materials A hole having a ratio of the depth of the hole to the layer thickness of 5% or more is formed in the negative electrode, and the discharge capacity per unit mass is higher than that of the electrochemical cell of Comparative Example 1.

  Moreover, when the ratio of the depth of the hole to the thickness of the active material layer is in the range of 75% or more, the discharge capacity per mass is further higher as 339 to 353 mAh / g. From this, it can be seen that in the negative electrode for a lithium ion secondary battery of the present invention, the ratio of the hole depth to the thickness of the active material layer is more preferably 75% or more.

(3-2) About the relationship between the center distance of the hole of an active material layer, and the characteristic of an electrochemical cell As shown in Table 2, the electrochemical cell of Examples 7-11 is a space | interval whose hole center distance is 500-6000 micrometers. And a hole is formed in the negative electrode, and compared with the electrochemical cell of Comparative Example 2, the discharge capacity per mass is high.

  In particular, the discharge capacity per mass is as high as 334 to 353 mAh / g when the hole center distance is in the range of 500 to 2000 μm. From this, it can be seen that the negative electrode for the lithium ion secondary battery of the present invention preferably has a hole center distance of 500 to 2000 μm.

(3-3) Relationship between Maximum Diameter of Active Material Layer Hole and Characteristics of Electrochemical Cell As shown in Table 3, the electrochemical cells of Examples 12 to 17 have a maximum hole diameter of 5 to 1500 μm. Is formed on the negative electrode, and the discharge capacity per mass is higher than that of the electrochemical cell of Comparative Example 3.

  In particular, when the maximum hole diameter is in the range of 100 to 1000 μm, the discharge capacity per mass is 266 to 312 mAh / g, which is even higher. From this, it can be seen that the negative electrode for lithium ion secondary batteries of the present invention preferably has a maximum hole diameter of 100 to 1000 μm.

(3-4) Relationship between surface shape of hole in active material layer and characteristics of electrochemical cell As shown in Table 4, the electrochemical cells of Examples 18 to 21 were compared with the electrochemical cell of Comparative Example 4. The discharge capacity per mass is high. From the above, it can be seen that the negative electrode for a lithium ion secondary battery of the present invention can improve the discharge capacity per mass regardless of the surface shape of the hole formed in the active material layer.

(3-5) Relationship between Type of Active Material and Characteristics of Electrochemical Cell As shown in Table 5, the electrochemical cell of Example 22 has a higher discharge capacity than that of Comparative Example 5, and the electric power of Example 23 The chemical cell has a higher discharge capacity than Comparative Example 6. Thus, it can be seen that the negative electrode for a lithium ion secondary battery of the present invention can improve the discharge capacity even when a mixture of natural graphite and SiO and a mixture of artificial graphite and Sn are used as the active material.

(3-6) Relationship between Active Material Density of Active Material Layer and Electrochemical Cell Characteristics Table 6 shows the relationship between the active material density of the negative electrode active material layer and the discharge capacity of the electrochemical cell using the negative electrode. . As shown in Table 6, the electrochemical cells of Examples 24-27 are different from the electrochemical cells of Comparative Examples 11-14, which differ from the electrochemical cells of Examples only in that no holes are formed in the active material layer. Both the discharge capacity per mass and the discharge capacity per area are high. Thus, it can be seen that when the active material density is in the range of 70 to 82% of the true density, the discharge capacity is increased by forming the holes.

  Comparative Example 7 and Comparative Example 8, Comparative Example 9 and Comparative Example 10, Example 24 and Comparative Example 11, Example 25 and Comparative Example 12, Example 26 and Comparative Example 13, Example 27 and Comparative Example 14 are respectively compared. Then, by forming a hole, the discharge capacity per mass is about 1.04 times, about 1.06 times, about 1.08 times, about 1.11 times, about 1.22 times, about 1.6 times. As the active material density increases, the amount of increase in discharge capacity due to the formation of holes increases.

  When the ratio of the active material density to the true density is changed from 68% to 70%, the amount of increase in discharge capacity per mass due to the formation of holes is increased from about 1.06 times to about 1.08 times. On the other hand, when the ratio of the active material density to the true density is changed from 70% to 77%, the increase in discharge capacity per mass due to the formation of holes is increased from about 1.08 times to about 1.11 times. Yes.

  Thus, when the ratio of the active material density to the true density becomes 70% or more, the electrochemical cell starts to increase the discharge capacity per mass due to the formation of holes.

  Further, the electrochemical cell has a discharge capacity increase of more than 10% when the ratio of the active material density to the true density is in the range of 72 to 82%, and the increase in discharge capacity per mass due to the formation of holes is further increased. large.

  Thus, it can be seen that the active material density is desirably in the range of 72 to 82% of the true density.

Example II
Furthermore, in order to investigate the relationship between the active material density of the active material layer of the negative electrode and the discharge capacity of the electrochemical cell using the negative electrode, the active material density was in the range of 70 to 83% of the true density as Examples 28 to 38. The negative electrode of the present invention was produced by changing the above, and an electrochemical cell similar to the above was produced using the negative electrode.

In Examples 28 to 31, non-graphitizable carbon was used as the active material, the shape of the hole opening was round, and the holes having the parameters described in Table 7 were formed in the active material layer of the negative electrode. And for comparison, the active material density is 60 and 68% of the true density as Comparative Examples 15 and 17, and the negative electrode with holes having the same hole as the Examples, and Comparative Examples 15 and 17 as Comparative Examples 15 and 17 A negative electrode without holes having the same active material density as that of the negative electrode, and negative electrodes without holes having the same active material density as those of Examples 28 to 31 as Comparative Examples 19 to 22 were prepared to prepare electrochemical cells. The electrochemical cell was produced by the same method as in Example 1. The electrochemical cells of Examples 28 to 31 and Comparative Examples 15 to 22 were charged at a charging current of 1 mA / cm ² and a constant voltage of 0.005 V until the charging current value decreased to 0.1 mA / cm ² . The cut-off voltage is 1.0 Vvs. The discharge capacity was measured by discharging at a discharge current of 10 mA / cm ² as Li / Li ⁺ .

In Examples 32 to 35, graphitizable carbon was used as the active material, the shape of the hole opening was round, and the holes having the parameters described in Table 7 were formed in the active material layer of the negative electrode. For comparison, the active material density of Comparative Examples 23 and 25 is 62 and 68% of the true density, and the negative electrode with holes having the same holes as those of Examples, and Comparative Examples 24 and 26 of Comparative Examples 23 and 25 of Comparative Examples 23 and 25. A negative electrode without holes having the same active material density as that of the negative electrode, and negative electrodes having the same active material density as those of Examples 32 to 35 as Comparative Examples 27 to 30 were prepared to prepare electrochemical cells. The electrochemical cell was produced by the same method as in Example 1. The electrochemical cell of Examples 32-35 and Comparative Examples 23-30, after charging until the charging current of 1 mA / cm ^2, the charging current value in the constant voltage of 0.005V drops to 0.1 mA / cm ^2, The cut-off voltage is 1.0 Vvs. The discharge capacity was measured by discharging at a discharge current of 10 mA / cm ² as Li / Li ⁺ .

In Examples 36 to 38, LTO was used as the active material, the shape of the hole opening was round, and the holes having the parameters described in Table 7 were formed in the active material layer of the negative electrode. For comparison, as Comparative Examples 31 and 33, the active material density is 58 and 64% of the true density, and the holed negative electrode having the same hole as the Example, and Comparative Examples 32 and 34 are Comparative Examples 31 and 33. A negative electrode with no hole having the same active material density as that of the negative electrode and negative electrodes without holes having the same active material density as those of Examples 36 to 38 as Comparative Examples 35 to 37 were prepared. The electrochemical cell was produced by the same method as in Example 1. The electrochemical cells of Examples 36 to 38 and Comparative Examples 31 to 37 were charged at a charging current of 1 mA / cm ² and a constant voltage of 1.40 V until the charging current value decreased to 0.1 mA / cm ² . The cut-off voltage is set to 2.0 Vvs. The discharge capacity was measured by discharging at a discharge current of 10 mA / cm ² as Li / Li ⁺ .

  The measurement results of the negative electrode parameters and discharge capacity of the electrochemical cells of Examples 28 to 38 are shown in Table 7, and the negative electrode parameters and discharge capacity measurement results of the electrochemical cells of Comparative Examples 15 to 37 are shown in Table 8. The active material utilization rate (%) was calculated by dividing the discharge capacity per mass by the theoretical discharge capacity per mass. The theoretical discharge capacity per mass of non-graphitizable carbon is 170 mAh / g, the theoretical discharge capacity per mass of graphitizable carbon is 230 mAh / g, and the theoretical discharge capacity per mass of LTO is 160 mAh / g.

  When the active material is non-graphitizable carbon, the negative electrode electrochemical cell having an active material layer with holes having a ratio of the active material density to the true density of 60%, 68%, 70%, 72%, 77%, 83% is The increase in discharge capacity per mass due to the formation of the holes is about 1.02, about 1.06, about 1.12, about 1.17, about 1.33, about 1. 49 times.

  When the active material is graphitizable carbon, the negative electrode electrochemical cell having an active material layer with holes having a ratio of the active material density to the true density of 62%, 68%, 70%, 72%, 78%, 83% is The increase in discharge capacity per mass due to the formation of holes is 1.00 times, about 1.02 times, about 1.08 times, about 1.13 times, about 1.25 times, about 1.54 times. Is double.

  When the active material is LTO, the ratio of the active material density to the true density is 58%, 64%, 70%, 76%, 82%. The increase in discharge capacity per unit mass is 1.00 times, about 1.06 times, about 1.11 times, about 1.21 times, and about 1.31 times.

  When the active material is hard carbon as in the case of natural graphite, the amount of increase in discharge capacity per mass due to the formation of holes increases as the active material density increases.

  Further, it can be seen that when the ratio of the active material density to the true density is in the range of 70 to 83%, the amount of increase in discharge capacity per mass due to the formation of holes is particularly large.

  Note that when the active material density is higher than 83%, the negative electrode has an extremely high active material density, so that there are few voids in the active material layer and the size of the voids is small. Therefore, it is considered that the negative electrode has a very large resistance to movement of lithium ions because the amount of the electrolyte present in the negative electrode is small and the voids between the active materials are small. Therefore, even if a hole is formed in the active material layer, only the portion of the active material exposed in the internal space of the hole can be used, and it is considered that the active material inside the active material layer cannot be used effectively. As a result, even if the active material carried by the negative electrode is increased, the discharge capacity per mass is drastically reduced, and the capacity of the battery is greatly reduced.

  Thus, the negative electrode electrochemical cell in which holes are formed in the active material layer has a higher discharge capacity that is increased by forming holes as the active material density is higher, and a very high effect is obtained. This has not been clarified in the past techniques (references) disclosed so far. When the active material density is high, there are few gaps in the negative electrode that can be impregnated with the electrolyte, and the gaps between the active materials are narrow. Therefore, lithium ions that are solvated with the solvent, such as ethylene carbonate, do not pass through the gaps between the active materials, and in the negative electrode in which no holes are formed, Lithium ions will not reach. The higher the active material density, the narrower the gap between the active materials, and the more difficult it is for lithium ions to reach. Therefore, it is considered that the discharge capacity is extremely decreased as the active material density is higher.

  On the other hand, in the negative electrode in which the hole is formed, lithium ions can move in the electrolytic solution existing in the hole to the negative electrode at a portion far from the separator, and then permeate in the lateral direction of the hole. For this reason, lithium ions can reach the active material located deep in the thickness direction from the surface, and the number of active materials that can be used effectively has increased, so that a high discharge capacity can be obtained. The higher the active material density, the more the negative electrode carries more active materials, and the more active materials that can be used effectively, the higher the discharge capacity.

  Here, when Example 28 is compared with Comparative Example 19 that is different from Example 28 only in that no hole is formed, Example 28 has a discharge capacity per mass of Comparative Example 19 due to the formation of the hole. It is about 1.12 times. On the other hand, when Comparative Example 17 was compared with Comparative Example 18 that was different from Comparative Example 17 only in that no hole was formed, Comparative Example 17 had the same hole as Example 28 formed in the active material layer of the negative electrode. Nevertheless, the discharge capacity per mass is only about 1.06 times.

  In the case of the comparative example 18, the ratio of the true density to the active material density of the negative electrode is as low as 68%, and a lot of voids are formed accordingly. Therefore, the negative electrode contains a sufficient amount of electrolytic solution without forming a hole in the active material layer, and an active material located deep in the thickness direction from the surface can also be used effectively. Therefore, even if a hole is formed in the active material layer of the negative electrode as in Comparative Example 17, there is not much active material that can be effectively used for the first time because the hole is formed, and the increase in discharge capacity is small. It is thought. On the other hand, in the case of Comparative Example 19, since the active material density is as high as 70% of the true density, the amount of the electrolyte contained in the negative electrode is not sufficient, and the negative electrode is an active material located deep from the surface in the thickness direction. The substance could not be used effectively. Therefore, by forming a hole as in Example 28, the electrolyte also exists in the hole, so that lithium ions can reach deeper in the thickness direction from the surface, and the negative electrode becomes effective. The number of active materials that can be used is increased, and it is considered that the discharge capacity per mass of the electrochemical cell has increased. This is also supported by the fact that the higher the active material density, the larger the discharge capacity that is increased by forming the holes. Thus, it can be seen that when the active material density is 70% or more of the true density, the discharge capacity is greatly increased by forming the holes.

  Comparing Comparative Example 25, Comparative Example 26, Comparative Example 33, and Comparative Example 34, in which the ratio of the true density to the active material density is less than 70%, the amount of increase in discharge capacity per mass due to the formation of holes was about 1 0.02 times and about 1.06 times. On the other hand, in Examples 32 and 36 in which the ratio of the true density to the active material density is 70%, the increase in discharge capacity per mass due to the formation of the holes is about 1.08 times and about 1.11 times. Thus, the discharge capacity is greatly increased by forming the holes as compared with the comparative example in which the ratio of the active material density to the true density is less than 70%. Thus, the same tendency is shown even if the type of active material is soft carbon or LTO.

  Moreover, the negative electrode for lithium ion secondary batteries of this invention can reduce the quantity of the electrolyte solution which a negative electrode is impregnated. For example, the negative electrode of Example 30 has an active material density of 77%, and the other 23% contains voids, SBR, CMC, and AB. This negative electrode contains 97 wt% hard carbon, 1 wt% SBR, 1 wt% CMC, and 1 wt% AB. Considering these and the density of SBR, CMC, and AB, the volume occupied by SBR, CMC, and AB is about 6% in the negative electrode. Therefore, the porosity is about 17%.

  On the other hand, the negative electrode of Comparative Example 15 has an active material density of 60%. Therefore, when the same calculation is performed, the volume occupied by SBR, CMC, and AB is about 6%. Therefore, the porosity is about 34%.

  Since the electrolyte solution is impregnated in the gap of the negative electrode, the porosity in Example 30 is about ½ or less that in Comparative Example 15, and thus the electrolyte solution impregnated is also about ½ or less that in Comparative Example 15. . Thus, by having an active material at a high density, the amount of electrolyte impregnated in the negative electrode is reduced to about ½ or less. Therefore, the negative electrode for a lithium ion secondary battery of the present invention can reduce the amount of electrolyte used.

Example III
In order to investigate the relationship between the thickness of the active material layer and the discharge capacity of the electrochemical cell, the thickness of the active material layer was changed in the range of 100 to 1000 μm as Examples 39 to 42, and the negative electrode of the present invention was produced. An electrochemical cell was produced using the negative electrode. In Examples 39 to 42, the shape of the hole opening is round, and the holes having the parameters shown in Table 9 are provided. For comparison, the same negative electrodes as those in Examples were prepared except that the thicknesses of the active material layers were 50 and 85 μm as Comparative Examples 38 and 40, respectively, and holes were formed as Comparative Examples 39 and 41 to 45. Except for the above, negative electrodes similar to those in Examples 39 to 42 and Comparative Examples 38 and 40 were produced, and electrochemical cells were produced. The electrochemical cell was produced by the same method as in Example 1. The discharge capacity of these electrochemical cells is ² mA / cm ² charging current, 0.005 Vvs. After charging at a constant voltage of Li / Li ⁺ until the charging current value decreases to 0.1 mA / cm ² , the cut-off voltage is set to 1.0 Vvs. Li / Li ⁺ was measured by discharging at a discharge current of 10 mA / cm ² . Table 9 shows the parameters of the negative electrodes and measured discharge capacities of Examples and Comparative Examples.

  The electrochemical cells of Examples 39 to 42 were compared with the electrochemical cells of Comparative Examples 42 to 45 having negative holes with the same active material layer thickness as the respective examples, respectively, compared with the discharge capacity and area per mass. It can be seen that the discharge capacity per unit is high and the discharge capacity is increased by forming the holes.

  Each electrochemical cell having an active material layer in which holes are formed and each electrochemical cell having an active material layer in which holes are not formed are compared between electrochemical cells having the same active material layer thickness. . A negative electrode electrochemical cell having holes formed therein and having an active material layer with a thickness of 50 μm, 85 μm, 100 μm, 150 μm, 300 μm, and 1000 μm has a discharge capacity per mass of about 1. They are 08 times, about 1.21 times, about 1.24 times, about 1.36 times, about 1.97 times, and about 2.36 times.

  The electrochemical cell of Comparative Example 38 has a much higher discharge capacity per mass and discharge capacity per area than the electrochemical cell of Comparative Example 39 having the negative electrode without the same active material layer thickness. Absent. The increase in discharge capacity per mass due to the formation of the holes is also as small as about 1.08 times.

  When the thickness of the active material layer is relatively thin, such as 50 μm, the increase in discharge capacity due to the formation of holes in the active material layer is small. When the thickness of the active material layer is thin, lithium ions in the electrolyte solution can easily reach the active material inside the active material layer, and many active materials can be used effectively even if holes are not formed. It is done. Therefore, it is considered that the negative electrode having a thin active material layer has few active materials that can be newly used by forming holes in the active material layer, and the increase in discharge capacity is small.

  Further, when the active material layer is thick, there is a large increase in discharge capacity per mass due to the formation of holes. When the active material layer is thick, if no hole is formed, lithium ions move through the voids of the active material layer for a long distance, so the lithium ion has a high resistance to movement, and the active material layer is thick, so the thickness increases from the surface of the active material layer. It is considered that an active material that is deep in the vertical direction cannot be used, and there are few active materials that can be used effectively even if the amount of active material supported is large. Therefore, in the negative electrode electrochemical cell with a thick active material layer, the formation of holes in the active material layer facilitates the movement of lithium ions through the lithium ions preferentially through the electrolyte present in the holes. It is considered that the increase in the discharge capacity was large because the migration resistance of lithium ions was greatly reduced by this, and there were many active materials that were effectively used only after the formation of holes.

  Note that if the active material layer becomes thicker than 1000 μm, the movement distance of lithium ions becomes long even if lithium ions move in the electrolyte contained in the holes of the active material layer. Therefore, the electrochemical cell cannot efficiently perform a battery reaction, the discharge capacity per mass, the discharge capacity per area are reduced, and the increase in discharge capacity per mass due to the formation of holes is also reduced. It is thought to decline.

  When the thickness of the active material layer is 150 μm or more, the discharge capacity per mass is increased by about 1.36 times or more by forming holes, and the increase amount is particularly large. Thus, it can be seen that the thickness of the active material layer is particularly desirable to be 150 to 1000 μm.

DESCRIPTION OF SYMBOLS 1 Lithium ion secondary battery 2 Negative electrode for lithium ion secondary batteries 3 Positive electrode 4 Separator 5, 10 Current collector 6, 11 Active material layer 7, 12 Hole 8 Bottom part 9, 13 Opening

Claims (15)

A current collector, and an active material layer formed on the surface of the current collector,
The active material layer is
A plurality of holes are formed on the surface,
The active material density is 70 to 83% of the true density of the active material contained in the active material layer;
Thickness Ri 100~1000μm der,
The plurality of holes have a maximum diameter of 5 to 1500 μm, a center interval of 500 to 6000 μm, and a depth of 5% or more of the thickness of the active material layer. Negative electrode. 2. The negative electrode for a lithium ion secondary battery according to claim 1, wherein the active material layer includes graphite as the active material, and the active material density is 1.54 to 1.82 g / cm ³ . 2. The lithium ion secondary battery according to claim 1, wherein the active material layer includes non-graphitizable carbon as the active material, and the active material density is 1.26 to 1.49 g / cm ^3. Negative electrode. 2. The lithium ion secondary battery according to claim 1, wherein the active material layer includes graphitizable carbon as the active material, and the active material density is 1.26 to 1.49 g / cm ^3. Negative electrode. The active material layer, the comprises a _Li 4 _Ti 5 _{O 12} as the active material, the active material density is a lithium ion secondary of claim 1, characterized in that the 2.30~2.73g / cm ³ Negative electrode for secondary battery. 2. The negative electrode for a lithium ion secondary battery according to claim 1, wherein the active material layer contains SiO as the active material, and the active material density is 1.47 to 1.74 g / cm ³ . 2. The negative electrode for a lithium ion secondary battery according to claim 1, wherein the active material layer contains Sn as the active material, and the active material density is 5.04 to 6.10 g / cm ³ . 2. The negative electrode for a lithium ion secondary battery according to claim 1, wherein the active material layer contains Si as the active material, and the active material density is 1.61 to 1.90 g / cm ³ . The active material layer includes two or more kinds selected from graphite, non-graphitizable carbon, graphitizable carbon, Li ₄ Ti ₅ O ₁₂ , SiO, Sn, and Si as the active material, and the active material density is 1 The negative electrode for a lithium ion secondary battery according to claim 1, wherein the negative electrode is more than .26 g / cm ^{3 and} less than 6.10 g / cm ³ .   10. The lithium ion according to claim 1, wherein the active material layer includes 0.0 to 10 wt% of a conductive additive and 1.0 to 10 wt% of a binder and a thickener. Negative electrode for secondary battery. Shape of the opening of the plurality of holes, round, triangular, square or lithium ions according to any one of claims 1 to 10, characterized in that at least one of pentagonal selected from the above polygon Negative electrode for secondary battery. Wherein the plurality of holes, according to claim 1 to 11 negative electrode for a lithium ion secondary battery according to any one of which is characterized by having a bottom. The active material layer is formed on both surfaces of the current collector, the plurality of holes are formed with openings in the surface of the one active material layer, and pass through the active material layer and the current collector. other claim 1-11 or a negative electrode for a lithium ion secondary battery according to one of, wherein the bottom is formed by the active material layer. The plurality of holes include a hole in which an opening is formed on a surface of the other active material layer, penetrates the active material layer and the current collector, and a bottom is formed by the one active material layer. , according to claim 13, characterized in that the said opening to the surface of the one surface to the hole openings are formed in the active material layer and the other active material layer formed holes are formed alternately Negative electrode for lithium ion secondary battery. A lithium ion secondary battery comprising the negative electrode for a lithium ion secondary battery according to any one of claims 1 to 14 .

Images