Electrodes and power storage devices

Abstract

The present invention provides an electrode having a current collector, an electrode composite material, and an electrode tab, wherein the current collector is a metal porous body, the metal porous body has a region A and a region B with a porosity smaller than that of the region A, the pores of the region A are filled with the electrode composite material, the electrode tab is fixed on the region B, the region A has a region A1 and a region A2 with a porosity smaller than that of the region A1, and the distance between the region A2 and the electrode tab is greater than that of the region A1. In addition, a storage device having the electrode is provided.

Description

Technical Field

[0001] The invention relates to an electrode and an electric storage device. Background Art

[0002] In the past, lithium-ion secondary batteries have been widely used as power storage devices with high energy density. Lithium-ion secondary batteries have the following structure, for example, a separator is present between the positive electrode and the negative electrode, and an electrolyte is filled. In addition, an all-solid-state battery is also known, which uses an inorganic solid electrolyte instead of an electrolyte.

[0003] Such lithium ion secondary batteries have various requirements depending on their use. For example, when used in automobiles, the volume energy density is required to be further improved. For this purpose, a method of increasing the packing density of the electrode active material is given.

[0004] As a method for increasing the packing density of the electrode active material, a method of using a foamed metal as a current collector constituting the positive electrode and the negative electrode is proposed (see Patent Documents 1 and 2). The foamed metal has a mesh structure with uniform pore diameters and a large surface area. Therefore, the electrode composite material containing the electrode active material is filled in the pores of the foamed metal, and the amount of the electrode active material per unit area of ​​the electrode can be increased.

[0005] [Prior Technical Literature]

[0006] (Patent Document)

[0007] Patent Document 1: Japanese Patent Application Laid-Open No. 7-099058

[0008] Patent Document 2: Japanese Patent Application Laid-Open No. 8-329954 Summary of the invention

[0009] [Problems to be solved by the invention]

[0010] However, the collector of the electrode composite material without the introduction of the foamed metal has the following problems, that is, the metal amount is very small relative to the collector foil, and the electronic resistance increases. In particular, when a large current is circulated, the electron supply from the collector is insufficient, and the electronic resistance increases significantly. Further, there is the following problem, the strength of the welding part and the collector is insufficient, and it is easy to break, etc., and the durability is reduced.

[0011] An object of the present invention is to provide an electrode capable of reducing electronic resistance and improving durability.

[0012] [Technical means to solve the problem]

[0013] One aspect of the present invention provides an electrode comprising a current collector, an electrode composite material, and an electrode tab, wherein the current collector is a metal porous body having a region A and a region B having a porosity smaller than that of the region A, the pores of the region A are filled with the electrode composite material, the electrode tab is fixed on the region B, the region A has a region A1 and a region A2 having a porosity smaller than that of the region A1, and the distance between the region A2 and the electrode tab is greater than that of the region A1.

[0014] Optionally, the aforementioned region B includes a region B1 to which the aforementioned electrode tab is fixed and a region B2 to which the aforementioned electrode tab is not fixed, and the porosity of the aforementioned region B1 is smaller than the porosity of the aforementioned region A.

[0015] Optionally, the aforementioned region A further has a region A3 connecting the aforementioned region A2 and the aforementioned region B, and the porosity of the aforementioned region A3 is smaller than the porosity of the aforementioned region A1.

[0016] Optionally, the aforementioned region A also has a region A3 connecting the aforementioned region A2 and the aforementioned region B. If the porosity of the aforementioned region A1, the porosity of the aforementioned region A2, the porosity of the aforementioned region A3, the porosity of the aforementioned region B1, and the porosity of the aforementioned region B2 are set to εA1, εA2, εA3, εB1 and εB2, respectively, then the formula εA1>εA3≥εA2>εB2≥εB1 is satisfied.

[0017] Optionally, the current collector is approximately in the shape of a rectangular parallelepiped.

[0018] Another aspect of the present invention provides an electric storage device having the above-mentioned electrode.

[0019] (Effects of the Invention)

[0020] According to the present invention, it is possible to provide an electrode capable of reducing electronic resistance and improving durability. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 This is a diagram showing an example of the electrode according to this embodiment.

[0022] Figure 2 It is depicted and Figure 1 Diagram of the electrode corresponding to the current collector.

[0023] Figure 3 It is depicted and Figure 1 FIG. 1 is a diagram of another example of an electrode corresponding to a current collector.

[0024] Figure 4 This is a graph showing the evaluation results of the initial cell resistance of the lithium ion secondary batteries of Example 1 and Comparative Example 1.

[0025] Figure 5 This is a graph showing the evaluation results of the C rate characteristics of the lithium ion secondary batteries of Example 1 and Comparative Example 1.

[0026] Figure 6 This is a graph showing the evaluation results of the capacity retention rates of the lithium ion secondary batteries of Example 1 and Comparative Example 1.

[0027] Figure 7 This is a graph showing the evaluation results of the resistance change rate of the electronic resistance (0.1S) of the lithium ion secondary batteries of Example 1 and Comparative Example 1.

[0028] Figure 8 This is a graph showing the evaluation results of the resistance change rate of the reaction resistance (1S) of the lithium ion secondary batteries of Example 1 and Comparative Example 1.

[0029] Fig. 9 This is a graph showing the evaluation results of the resistance change rate of the ion diffusion resistance (10S) of the lithium ion secondary batteries of Example 1 and Comparative Example 1. DETAILED DESCRIPTION

[0030] Hereinafter, embodiments of the present invention will be described with reference to the drawings.

[0031] <Electrode>

[0032] Figure 1 An example of the electrode of this embodiment is shown. Figure 2 Drawing and Figure 1 The electrode corresponds to the current collector.

[0033] The electrode 10 has a current collector 11, an electrode composite material 12, and an electrode tab 13. The current collector 11 is a metal porous body having a region A and a region B having a porosity smaller than that of the region A (see Figure 2 ). The electrode 10 is filled with an electrode composite material 12 in the pores of region A of the current collector 11, and an electrode tab 13 is fixed to region B of the current collector 11. Region A of the current collector 11 has region A1 and region A2 having a smaller porosity than region A1, and region A2 is farther away from the electrode tab than region A1.

[0034] In the electrode 10, since the porosity of the region B of the current collector 11 is smaller than the porosity of the region A of the current collector 11, the electronic conductivity between the electrode composite material 12 and the electrode tab 13 is improved, and as a result, the electronic resistance is reduced. Furthermore, the strength of the region B is improved, and the fracture and cracking of the electrode 10 are suppressed, so that the durability is improved.

[0035] In addition, in the electrode 10, since the porosity of the region A2 of the current collector 11 is smaller than the porosity of the region A1 of the current collector 11, the electron conductivity toward the end of the region A2 is improved, and as a result, the electron resistance is reduced. This is particularly advantageous when the electrode 10 is enlarged and lengthened.

[0036] The porosity of region A of current collector 11 is preferably 85% or more and 99% or less, and more preferably 90% or more and 98% or less.

[0037] The porosity of region B of current collector 11 is preferably 1% to 50%, and more preferably 1% to 10%.

[0038] The porosity of region A1 of current collector 11 is preferably 93% or more and 99% or less, and more preferably 95% or more and 98% or less.

[0039] The porosity of region A2 of current collector 11 is preferably 90% to 97%, and more preferably 90% to 93%.

[0040] Optionally, region B of current collector 11 includes region B1 to which electrode tab 13 is fixed and region B2 to which electrode tab 13 is not fixed, but the porosity of region B1 is smaller than that of region A. Thus, the electronic conductivity between electrode composite material 12 and electrode tab 13 is further improved.

[0041] In this specification and claims, the region B1 to which the electrode tab is fixed refers to the region where the electrode tab exists when the collector to which the electrode tab is fixed is viewed from the side to which the electrode tab is fixed, and also includes the region where the electrode tab is not actually formed. In addition, the region B2 to which the electrode tab is not fixed refers to the region where the electrode tab does not exist when viewed from above in the same manner as above.

[0042] The porosity of region B1 of current collector 11 is preferably 1% to 50%, and more preferably 1% to 10%.

[0043] The porosity of region B2 of current collector 11 is preferably 5% or more and 50% or less, and more preferably 5% or more and 20% or less.

[0044] Optionally, the region A of the current collector 11 further includes a region A3 connecting the region A2 of the current collector 11 and the region B of the current collector 11, and the porosity of the region A3 is less than the porosity of the region A1 (refer to Figure 3 ). As a result, the electron conductivity toward the end of the region A2 is further improved, and as a result, the electron resistance is further reduced.

[0045] Optionally, when region A of the current collector 11 further includes region A3, if the porosity of region A1, region A2, region A3, region B1, and region B2 of the current collector 11 are set to εA1, εA2, εA3, εB1, and εB2, respectively, the formula εA1>εA3≥εA2>εB2≤εB1 is satisfied. Thus, the electronic conductivity toward the end of region A2 is further improved, and as a result, the electronic resistance is further reduced.

[0046] The porosity of region A3 of current collector 11 is preferably 90% or more and 98% or less, and more preferably 93% or more and 95% or less.

[0047] The current collector 11 is obtained by, for example, appropriately pressing the metal porous body before or after filling the electrode composite material 12 to form the regions A ( A1 , A2 , A3 ) and the regions B ( B1 , B2 ).

[0048] The shape of the current collector 11 is not particularly limited, and a substantially rectangular parallelepiped shape or the like can be mentioned.

[0049] In the present specification and claims, a substantially rectangular parallelepiped includes a chamfered rectangular parallelepiped.

[0050] Herein, the chamfer may be a C chamfer and an R chamfer.

[0051] [Porous metal body]

[0052] The porous metal body is not particularly limited as long as the pores of the porous metal body can be filled with the electrode composite material, and examples thereof include foamed metals.

[0053] The foamed metal has a mesh structure and a large surface area. Using a current collector as a foamed metal, the electrode composite material can be filled in the pores of the foamed metal, which can increase the electrode active material mass per unit area of ​​the electrode, and can improve the volume energy density of the secondary battery. In addition, since the electrode composite material is easily fixed, even if the slurry used to apply the electrode composite material is not thickened, a thick electrode composite material film can be formed. In addition, the adhesive required for thickening the slurry can be reduced. Therefore, compared with using a metal foil as a current collector, a low-resistance thick electrode composite material film can be formed. Therefore, the capacity per unit area of ​​the electrode can be increased, and as a result, it can be beneficial to increase the capacity of the secondary battery.

[0054] Examples of the metal constituting the porous metal include nickel, aluminum, stainless steel, titanium, copper, silver, and nickel-chromium alloys. Among them, the porous metal constituting the positive electrode current collector is preferably foamed aluminum, and the porous metal constituting the negative electrode current collector is preferably foamed copper or foamed nickel.

[0055] [Electrode composite materials]

[0056] The electrode composite material contains an electrode active material and may also contain other components.

[0057] Examples of other components include a solid electrolyte, a conductive auxiliary agent, and a binder.

[0058] The positive electrode active material contained in the positive electrode composite material is not particularly limited as long as it can absorb and release lithium ions, for example, LiCoO2, Li(Ni 5 / 10 Co 2 / 10 Mn 3 / 10 )O2、Li(Ni 6 / 10 Co 2 / 10 Mn 2 / 10 )O2、Li(Ni 8 / 10 Co 1 / 10 Mn 1 / 10 )O2、Li(Ni 0.8 Co 0.15 Al 0.05 )O2、Li(Ni 1 / 6 Co 4 / 6 Mn 1 / 6 )O2、Li(Ni 1 / 3 Co 1 / 3 Mn 1 / 3 )O2, LiCoO4, LiMn2O4, LiNiO2, LiFePO4, lithium sulfide, sulfur, etc.

[0059] The negative electrode active material contained in the negative electrode composite material is not particularly limited as long as it can absorb and release lithium ions. Examples thereof include metallic lithium, lithium alloys, metal oxides, metal sulfides, metal nitrides, Si, SiO, and carbon materials.

[0060] Examples of the carbon material include artificial graphite, natural graphite, hard carbon, and soft carbon.

[0061] [Electrode tab]

[0062] The electrode tab is not particularly limited, and a known electrode tab can be used.

[0063] <Method for producing electrode>

[0064] The method for producing the electrode of the present embodiment is not particularly limited, and a common method in the technical field can be used.

[0065] The method for filling the pores of region A of the current collector with the electrode composite material is not particularly limited, and examples thereof include a method in which a plunger die coater is used to apply pressure to fill the pores of region A of the current collector with a slurry containing the electrode composite material.

[0066] As another method for filling the pores of the region A of the current collector with the electrode composite material, the following method is listed, in which a pressure difference is generated between the surface of one side of the electrode composite material introduced into the current collector and the surface on the opposite side thereof, and the pressure difference is utilized to make the electrode composite material penetrate and fill the pores of the region A of the current collector. At this time, the nature state of the introduced electrode composite material is not particularly limited, and it can be an electrode composite material powder or a liquid such as a slurry containing the electrode composite material.

[0067] After the pores of the current collector region A are filled with the electrode composite material, a common method in the art can be used. For example, after the current collector filled with the electrode composite material in region A is dried, it is pressed and the electrode tabs are welded to obtain an electrode. At this time, the porosity of the current collector and the density of the electrode composite material can be adjusted by pressing.

[0068] Furthermore, when the current collector filled with the electrode composite material in region A is pressed, the current collector is compressed to a fixed level by pressing, so that the magnitude relationship of the porosity in each region of the current collector does not change.

[0069] <Electrical Storage Devices>

[0070] The power storage device of this embodiment includes the electrode of this embodiment.

[0071] Examples of the power storage device include secondary batteries such as lithium ion secondary batteries and capacitors.

[0072] The lithium ion secondary battery may be a battery having a liquid electrolyte or a battery having a solid or gel electrolyte. In addition, the solid or gel electrolyte may be organic or inorganic.

[0073] The electrode of this embodiment may be used only for the positive electrode, only for the negative electrode, or for both the positive electrode and the negative electrode.

[0074] Furthermore, when the electrode of the present embodiment is used in a lithium ion secondary battery, since the electron conductivity of the negative electrode active material is high, it is particularly advantageous when the electrode of the present embodiment is used in a positive electrode.

[0075] [Lithium-ion secondary battery]

[0076] The lithium ion secondary battery of this embodiment includes a positive electrode, a negative electrode, and a separator or a solid electrolyte layer located between the positive electrode and the negative electrode. In the lithium ion secondary battery of this embodiment, at least one of the positive electrode and the negative electrode forms an electrode of this embodiment.

[0077] In the lithium ion secondary battery of the present embodiment, the positive electrode or negative electrode not using the electrode of the present embodiment is not particularly limited as long as it functions as the positive electrode or negative electrode of the lithium ion secondary battery.

[0078] In the lithium ion secondary battery of this embodiment, two materials are selected from materials that can constitute electrodes, the charge and discharge potentials of the two materials are compared, and the material showing a higher potential is used as the positive electrode and the material showing a lower potential is used as the negative electrode, thereby forming any battery.

[0079] When the lithium ion secondary battery of the present embodiment includes a separator, the separator is located between the positive electrode and the negative electrode.

[0080] The separator is not particularly limited, and a known separator that can be used for lithium ion secondary batteries can be used.

[0081] When the lithium ion secondary battery of the present embodiment includes a solid electrolyte layer, the solid electrolyte layer is located between the positive electrode and the negative electrode.

[0082] The solid electrolyte contained in the solid electrolyte layer is not particularly limited as long as it is a material that can conduct lithium ions between the positive electrode and the negative electrode.

[0083] Examples of the solid electrolyte include oxide-based electrolytes and sulfide-based electrolytes.

[0084] [Example]

[0085] Hereinafter, examples of the present invention will be described, but the present invention is not limited to the examples.

[0086] <Example 1>

[0087] [Production of positive electrode]

[0088] (Processing of porous metal bodies)

[0089] As a metal porous body, a 30 mm long, 40 mm wide, 1 mm high, 97% porosity, 46 monomers / inch, 0.5 mm pore diameter, and 5000 m2 specific surface area were prepared. 2 / m 3 A rectangular aluminum foam.

[0090] A sheet of foamed aluminum was laminated on the end portion of the side where the foamed aluminum electrode tab was fixed, and the porosity of region B was adjusted to 5%. In addition, the end portion of the side where the foamed aluminum electrode tab was not fixed was pressed, and the porosity of region A2 was adjusted to 95%, thereby obtaining a processed metal porous body.

[0091] The porosity of the processed metal porous body is calculated by the following method. First, the thickness of the sample punched into a Φ16mm circle in each area of ​​the processed metal porous body is measured to calculate the volume of the sample. Next, the mass of the sample is measured to calculate the density of the sample. Finally, the ratio of the density of the sample to the true density of the metal constituting the metal porous body is calculated and set as the porosity of the sample.

[0092] (Preparation of positive electrode composite material slurry)

[0093] As the positive electrode active material, prepare LiNi 0.5 Co 0.2 Mn 0.3 O2.

[0094] After mixing 94 mass % of positive electrode active material, 4 mass % of carbon black as a conductive aid, and 2 mass % of polyvinylidene fluoride (PVDF) as a binder, the obtained mixture is dispersed in an appropriate amount of N-methyl-2-pyrrolidone (NMP) to prepare a positive electrode composite material slurry.

[0095] (Filling of positive electrode composite material)

[0096] Use a plunger die coater with a coating amount of 90 mg / cm 2 , apply the positive electrode composite material slurry on the processed metal porous body, and then dry it at 120°C for 12 hours under vacuum conditions. Next, roll the processed metal porous body filled with the positive electrode composite material at a pressure of 15 tons to form a positive electrode collector filled with the positive electrode composite material. Next, weld area B of the positive electrode collector filled with the positive electrode composite material to the electrode ear to make a positive electrode. The weight per unit area of ​​the electrode composite material constituting the obtained positive electrode is 90 mg / cm 2 , density is 3.2g / cm 3 The positive electrode is punched into a size of 3 cm x 4 cm.

[0097] [Production of negative electrode]

[0098] (Preparation of negative electrode composite material slurry)

[0099] After mixing 96.5 mass% of natural graphite, 1 mass% of carbon black as a conductive aid, 1.5 mass% of styrene butadiene rubber (SBR) as a binder, and 1 mass% of sodium carboxymethyl cellulose (CMC) as a thickener, the obtained mixture is dispersed in an appropriate amount of distilled water to prepare a negative electrode composite material slurry.

[0100] (Formation of Negative Electrode Composite Material Layer)

[0101] As a negative electrode current collector, a copper foil having a thickness of 8 μm was prepared.

[0102] Use a die coater with a coating amount of 45 mg / cm 2 After coating the negative electrode composite material slurry on the current collector, it was dried at 120°C for 12 hours under vacuum conditions. Then, the current collector with the negative electrode composite material layer was rolled at a pressure of 10 tons to produce the negative electrode. The weight per unit area of ​​the electrode composite material layer constituting the obtained negative electrode was 45 mg / cm 2 , density is 1.5g / cm 3 The negative electrode was punched into a size of 3 cm x 4 cm for use.

[0103] [Manufacturing of lithium-ion secondary batteries]

[0104] As a separator, a microporous membrane formed of a three-layer laminate of polypropylene / polyethylene / polypropylene with a thickness of 25 μm was prepared and punched into a size of 3 cm×4 cm.

[0105] After the aluminum laminate for secondary batteries was heat-sealed and processed into a bag shape, a laminate having a separator disposed between a positive electrode and a negative electrode was inserted into the processed product to prepare a laminate battery.

[0106] As an electrolyte solution, a solution prepared by dissolving 1.2 mol of LiPF6 in a solvent in which ethylene carbonate, dimethyl carbonate, and ethyl methyl carbonate were mixed in a volume ratio of 3:4:3 was prepared.

[0107] An electrolyte solution was injected into the laminated battery to produce a lithium ion secondary battery.

[0108] <Comparative Example 1>

[0109] A lithium ion secondary battery was produced in the same manner as in Example 1, except that the metal porous body was used as it was without being processed when producing the positive electrode.

[0110] <Evaluation of Initial Characteristics of Lithium Ion Secondary Battery>

[0111] The lithium ion secondary batteries of Example 1 and Comparative Example 1 were evaluated for the following initial characteristics.

[0112] [Initial discharge capacity]

[0113] After the lithium ion secondary battery was placed at the measurement temperature (25°C) for 3 hours, it was charged to 4.2V at a constant current of 0.33C, and then charged to 4.2V at a constant voltage of 4.2V for 5 hours. Then, after the lithium ion secondary battery was placed for 30 minutes, it was discharged to 2.5V at a discharge rate of 0.33C, and the discharge capacity was measured. The obtained discharge capacity was set as the initial discharge capacity.

[0114] [Initial single cell resistance]

[0115] After measuring the initial discharge capacity, the lithium-ion secondary battery adjusts the charge level (State of Charge, SOC) to 50%. Then, discharge for 10 seconds with a current value of 0.2C, and measure the voltage 10 seconds after the discharge. Next, place the lithium-ion secondary battery for 10 minutes, and then perform supplementary charging to restore the SOC to 50%, and place the lithium-ion secondary battery for 10 minutes. Then, perform the above operations at C rates of 0.5C, 1C, 1.5C, 2C, and 2.5C, respectively, and plot with the horizontal axis as the current value and the vertical axis as the voltage. The slope of the approximate straight line obtained by the plot is set as the initial single cell resistance of the lithium-ion secondary battery.

[0116] Figure 4 1 and 2 show the evaluation results of the initial cell resistance of the lithium ion secondary batteries of Example 1 and Comparative Example 1.

[0117] Depend on Figure 4 It can be seen that the initial cell resistance (especially electronic resistance) of the lithium ion secondary battery of Example 1 is smaller than that of the lithium ion secondary battery of Comparative Example 1.

[0118] [C rate characteristics]

[0119] After the initial discharge capacity was measured, the lithium-ion secondary battery was placed at the measurement temperature (25°C) for 3 hours, and then charged to 4.2V at a constant current of 0.33C, and then charged to 4.2V at a constant voltage for 5 hours. Then, the lithium-ion secondary battery was placed for 30 minutes, and then discharged to 2.5V at a discharge rate (C rate) of 0.5C, and the initial discharge capacity was measured.

[0120] The above operation was performed at C rates of 0.33C, 1C, 1.5C, 2C, and 2.5C, and the initial discharge capacity at each C rate was converted into a capacity retention rate when the initial discharge capacity at 0.33C was set to 100%, which was defined as C rate characteristics.

[0121] Figure 5 2 and 3 show the evaluation results of the C rate characteristics of the lithium ion secondary batteries of Example 1 and Comparative Example 1.

[0122] Depend on Figure 5 It can be seen that the capacity retention rate of the lithium ion secondary battery of Example 1 is greater than that of the lithium ion secondary battery of Comparative Example 1.

[0123] <Characteristics Evaluation of Lithium Ion Secondary Batteries after Durability>

[0124] The lithium ion secondary batteries of Example 1 and Comparative Example 1 were subjected to the following evaluation of characteristics after endurance.

[0125] [Discharge capacity after endurance]

[0126] In a constant temperature bath at 45°C, the lithium-ion secondary battery is charged to 4.2V at a constant current of 0.6C, and then charged at a constant voltage of 4.2V for 5 hours or charged to a current value of 0.1C. Then, after the lithium-ion secondary battery is placed for 30 minutes, it is discharged to 2.5V at a constant current of 0.6C and placed for 30 minutes, and the above operation is repeated 100 cycles. Then, in a constant temperature bath at 25°C, the lithium-ion secondary battery is placed for 24 hours after being discharged to 2.5V, and then the discharge capacity after endurance is measured in the same manner as the initial discharge capacity. This operation is repeated every 100 cycles until 500 cycles, and the discharge capacity after endurance is measured.

[0127] [Single resistance after durability]

[0128] After 500 cycles of the post-endurance discharge capacity measurement, the charge level (State of Charge, SOC) was adjusted to 50%, and the post-endurance cell resistance was determined in the same manner as the initial cell resistance.

[0129] [Capacity retention rate]

[0130] The ratio of the discharge capacity after endurance to the initial discharge capacity for every 100 cycles was determined and defined as the capacity retention rate in each cycle.

[0131] Figure 6 The evaluation results of the capacity retention rate of the lithium ion secondary batteries of Example 1 and Comparative Example 1 are shown in

[0132] Depend on Figure 6 It is found that the capacity retention rate of the lithium ion secondary battery of Example 1 in 200 to 500 cycles is greater than that of the lithium ion secondary battery of Comparative Example 1.

[0133] [Resistance change rate]

[0134] The ratio of the cell resistance after endurance to the initial cell resistance was calculated and defined as the resistance change rate.

[0135] Figure 7 1 and 2 show the evaluation results of the resistance change rate of the electronic resistance (0.1S) of the lithium ion secondary batteries of Example 1 and Comparative Example 1.

[0136] Figure 8 1 and 2 show the evaluation results of the resistance change rate of the reaction resistance (1S) of the lithium ion secondary batteries of Example 1 and Comparative Example 1.

[0137] Fig. 9 1 and 2 show the evaluation results of the resistance change rate of the ion diffusion resistance (10S) of the lithium ion secondary batteries of Example 1 and Comparative Example 1.

[0138] Depend on Figures 7 to 9 It is found that the resistance change rates of the electronic resistance (0.1S) and the ion diffusion resistance (10S) of the lithium ion secondary battery of Example 1 in 500 cycles are smaller than those of the lithium ion secondary battery of Comparative Example 1.

[0139] From the above, it can be seen that the positive electrode of Example 1 has higher durability than the positive electrode of Comparative Example 1.

[0140] Reference numerals

[0141] 10 Electrodes

[0142] 11 Current Collector

[0143] 12 Electrode composite materials

[0144] 13 Electrode tabs

Claims

1. An electrode comprising a current collector, an electrode composite material, and an electrode tab, The current collector is a metal porous body having a region A and a region B having a porosity smaller than that of the region A. The pores in the region A are filled with the electrode composite material. The electrode tab is fixed to the region B. The region A comprises a region A1 and a region A2 having a smaller porosity than the region A1. The distance between the aforementioned region A2 and the aforementioned electrode tab is greater than that between the aforementioned region A1 and the aforementioned electrode tab. The region B includes a region B1 to which the electrode tab is fixed and a region B2 to which the electrode tab is not fixed. The porosity of the aforementioned region B1 is smaller than the porosity of the aforementioned region A. The aforementioned region A further includes a region A3 connecting the aforementioned region A2 and the aforementioned region B. The porosity of the aforementioned region A3 is smaller than the porosity of the aforementioned region A1.

2. The electrode according to claim 1, wherein If the porosity of the region A1, the porosity of the region A2, the porosity of the region A3, the porosity of the region B1, and the porosity of the region B2 are respectively and , then it satisfies the formula .

3. The electrode according to claim 1, wherein The current collector is approximately in the shape of a rectangular parallelepiped. 4 . An electricity storage device comprising the electrode according to claim 1 .

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