A surface-porous current collector and a method for manufacturing the same

Abstract

This invention relates to the field of non-aqueous secondary battery technology, specifically to a surface porous current collector and its preparation method. The surface porous current collector includes a current collector base layer and a porous coating located on at least one surface of the current collector base layer. The surface porous current collector has a surface pore count > 5 pores / m². By adding a certain proportion of a low-boiling-point solvent and water to the conductive material and adhesive, especially when isopropanol and water are added, the isopropanol and water can form an azeotrope. During oven baking, the mixed solvent of isopropanol and water can evaporate quickly, resulting in fine pores on the surface of the porous coating. This increases the surface area of ​​the porous coating, improves the bonding area between the active material and the porous coating, and effectively reduces the interfacial resistance when the active material contacts the dense surface fluid, thereby greatly improving the rate performance and charge / discharge performance when applied to secondary batteries.

Description

Technical Field

[0001] This invention relates to the field of non-aqueous secondary battery technology, specifically to a surface porous current collector and its preparation method. Background Technology

[0002] In modern society, non-aqueous secondary batteries are widely used in various electronic products and transportation tools. They mainly include lead-acid batteries, nickel-cadmium batteries, nickel-hydrogen batteries, and lithium-ion batteries. The difference between secondary batteries and primary batteries is that secondary batteries can be used repeatedly. Therefore, secondary batteries are also called rechargeable batteries or storage batteries.

[0003] In non-aqueous secondary batteries, active materials need to be added to the positive and negative electrodes to participate in the flow-forming reaction. Simultaneously, to improve the battery's rate performance and the adhesion of the active materials to the electrode sheets, a conductive layer is usually formed by coating the surface of the current collector with a conductive material. Currently, the manufacturing process of the conductive layer typically uses inexpensive water as a solvent. For example, patent application "An Inert Lithium Powder Composite Slurry and Preparation Method, Lithium-Added Negative Electrode and Preparation Method, Lithium-ion Battery" (application number: CN202211296316.0) discloses a method of coating a mixture of negative electrode active material, conductive agent, electrode binder, and electrode solvent onto a negative electrode current collector. The negative electrode active material is selected from at least one of artificial graphite, natural graphite, hard carbon, silicon carbide, silicon oxide, and lithium titanate; the conductive agent is selected from at least one of conductive carbon black, carbon fiber, acetylene black, graphene, and carbon nanotubes; the electrode binder is selected from at least one of fluorinated resin, fiber-type binder, rubber-type binder, and polyimide-type binder; and the electrode solvent is water.

[0004] In existing technologies, conductive agents and binders are dispersed using water. Due to the high boiling point of water, the evaporation rate is low after it is coated on the surface of the current collector, resulting in a dense conductive layer. Consequently, when the active material is coated onto the conductive layer, the contact area between the two is small, leading to a larger interfacial resistance between the active material and the current collector, and thus a poorer battery performance. Summary of the Invention

[0005] The purpose of this invention is to provide a surface porous current collector and its preparation method to solve the technical problems mentioned in the background art.

[0006] To achieve the above objectives, the present invention discloses a surface porous current collector, comprising: a current collector base layer and a porous coating located on at least one surface of the current collector base layer, wherein the surface porous current collector has a surface pore number of >5 pores / m².

[0007] Furthermore, the thickness of the porous coating is 0.05-5 micrometers, the thickness of the current collector substrate is 2-18 micrometers, and the total thickness of the porous current collector on the surface is 3-20 micrometers.

[0008] Another objective of this invention is to provide a method for preparing the above-mentioned porous surface current collector, the method comprising: 1) preparing a porous coating slurry: firstly, adding a conductive material to water and stirring, then adding a low-boiling-point solvent and stirring, and finally adding a binder and stirring; 2) coating the porous coating slurry: firstly, coating the porous coating slurry obtained in step 1) onto at least one surface of the current collector substrate using a coating system, and then drying and winding it to obtain the porous surface current collector.

[0009] Optionally, the low-boiling solvent has a boiling point of 75-90°C, including isopropanol.

[0010] Optionally, the mass ratio of conductive material to binder is 1:0.5-1.

[0011] Optionally, the mass ratio of water to low-boiling-point solvent is 1:0.007-0.3.

[0012] Optionally, the conductive material includes one or more of carbon nanofibers, carbon nanotubes, carbon black, graphene, graphite powder, and conductive carbon black.

[0013] Optionally, the adhesive includes one or more of the following: acrylic water-based adhesive, polyvinyl alcohol water-based adhesive, ethylene acetate water-based adhesive, polyvinylidene fluoride water-based adhesive, epoxy water-based adhesive, phenolic water-based adhesive, silicone water-based adhesive, rubber water-based adhesive, and polyurethane water-based adhesive.

[0014] Optionally, the current collector substrate includes: copper foil, aluminum foil, copper-aluminum alloy foil, composite copper-based current collector, or composite aluminum-based current collector.

[0015] Optionally, the drying method is multi-stage, with the first stage having the highest drying temperature.

[0016] Optionally, the solids content of the porous coating slurry is 5-25%.

[0017] Compared with the prior art, the surface porous current collector of the present invention has the following advantages:

[0018] This porous surface current collector includes a current collector base layer and a porous coating located on at least one surface of the current collector base layer. The number of pores on the surface of the porous surface current collector is >5 pores / m². By adding a certain proportion of a low-boiling-point solvent and water to the conductive material and adhesive, especially when isopropanol and water are added, the isopropanol and water can form an azeotrope. When baked in an oven, the mixed solvent of isopropanol and water can evaporate quickly, which at the same time makes the surface of the porous coating finer. This increases the surface area of ​​the porous coating, improves the bonding area between the active material and the porous coating, and effectively reduces the interfacial resistance when the active material comes into contact with the dense surface fluid. This greatly improves the rate performance and charge / discharge performance when applied to secondary batteries. Attached Figure Description

[0019] Figure 1 This is a schematic diagram of a surface porous current collector structure according to an embodiment of the present invention. Detailed Implementation

[0020] The technical solution of the present invention will be described in detail below through specific embodiments.

[0021] The porous surface current collector comprises: a current collector base layer and a porous coating located on at least one surface of the current collector base layer, wherein the number of surface pores of the porous surface current collector is >5 pores / m². Furthermore, the obtained porous surface current collector exhibits a puncture strength ≥55gf, a transverse tensile strength ≥154MPa, a longitudinal tensile strength ≥162MPa, a transverse elongation ≥2%, a longitudinal elongation TD ≥1%, and a peel force of the porous coating >10N / m.

[0022] The preparation method of the above-mentioned porous surface current collector includes: 1) preparing a porous coating slurry: first, adding a conductive material to water and stirring, then adding a low-boiling-point solvent and stirring, and finally adding a binder material and stirring; 2) coating the porous coating slurry: first, applying the porous coating slurry obtained in step 1) to at least one surface of the current collector substrate using a coating system, and then drying and winding it up to obtain the porous surface current collector. Simultaneously, the drying method can be a multi-stage drying oven, first using high temperature to promote pore formation, and then using low temperature to complete the drying.

[0023] By controlling the type and proportion of raw materials in the preparation method, a porous surface current collector can be prepared. The preparation process is described in Examples 1-4 below.

[0024] Example 1

[0025] Measure out 40 kg of water, 5 kg of carbon black as conductive material, 16 kg of 1,1,1-trichloroethane (boiling point 74.0℃) as low-boiling point solvent, 2 kg of acrylic water-based adhesive as adhesive, and 13 micrometer thick composite copper current collector as current collector base layer. The mass ratio of water to low-boiling point solvent is 1:0.4, and the mass ratio of conductive material to adhesive is 1:0.4.

[0026] Preparation of surface porous current collectors:

[0027] 1) To prepare the porous coating slurry, first add 10 kg of carbon black to 40 kg of water and stir for 90 minutes, then add 16 kg of 1,1,1-trichloroethane and stir for 100 minutes, and finally add 4 kg of acrylic water-based adhesive and stir for 50 minutes.

[0028] 2) Coating with porous coating slurry: First, the porous coating slurry obtained in step 1) is coated on the two surfaces of the 13-micron thick composite copper current collector through a coating system at a speed of 100 m / min and an unwinding tension of 50 N / m. Then, it is dried and wound up in a three-stage oven at 70℃, 55℃ and 40℃ respectively to obtain the surface porous current collector.

[0029] In this embodiment 1, the number of surface pores of the porous current collector is 6 per square meter, the solid content of the prepared porous coating slurry is about 11.1%, the total thickness of the obtained porous current collector is 15 micrometers, and the thickness of a single layer of the porous coating is 1 micrometer.

[0030] Example 2

[0031] 40 kg of water, 8 kg of graphite powder as conductive material, 6 kg of isopropanol (boiling point 82.45℃) as low-boiling point solvent, 6 kg of polyvinyl alcohol water-based adhesive as adhesive, and 13 micrometer thick composite copper current collector as current collector base layer were measured. The mass ratio of water to low-boiling point solvent was 1:0.15, and the mass ratio of conductive material to adhesive was 1:0.75. The main difference from Example 1 is the proportion of each component in the porous coating slurry and the use of isopropanol as the low-boiling point solvent.

[0032] Preparation of surface porous current collectors:

[0033] 1) To prepare the porous coating slurry, first add 8 kg of graphite powder to 40 kg of water and stir for 80 minutes, then add 6 kg of isopropanol and stir for 50 minutes, and finally add 6 kg of polyvinyl alcohol water-based adhesive and stir for 60 minutes.

[0034] 2) Coating with porous coating slurry: First, the porous coating slurry obtained in step 1) is coated on the two surfaces of the 13-micron thick composite copper current collector at a speed of 100 m / min and an unwinding tension of 50 N / m using a coating system. Then, it is dried and wound up in a three-stage oven at 80℃, 65℃ and 50℃ respectively to obtain a surface porous current collector.

[0035] In this embodiment 2, the number of surface pores of the porous current collector is 12 per square meter, the solid content of the prepared porous coating slurry is about 23.3%, the total thickness of the obtained porous current collector is 18.05 micrometers, and the thickness of a single layer of the porous coating is 2.525 micrometers.

[0036] Example 3

[0037] 40 kg of water, 8 kg of graphite powder as conductive material, 0.28 kg of isopropanol (boiling point 82.45℃) as low-boiling point solvent, 4 kg of ethylene acetate water-based adhesive as adhesive, and 8 micrometer thick aluminum foil as current collector substrate were measured. The mass ratio of water to low-boiling point solvent was 1:0.007, and the mass ratio of conductive material to adhesive was 1:0.5. The main difference from Example 2 is the proportion of each component in the porous coating slurry, the use of graphite powder as conductive material, and the use of aluminum foil as current collector substrate.

[0038] Preparation of surface porous current collectors:

[0039] 1) To prepare the porous coating slurry, first add 8 kg of graphite powder to 40 kg of water and stir for 80 minutes, then add 0.28 kg of isopropanol and stir for 20 minutes, and finally add 4 kg of ethylene acetate water-based adhesive and stir for 50 minutes.

[0040] 2) Coating with porous coating slurry: First, the porous coating slurry obtained in step 1) is coated on the two surfaces of an 8-micron thick aluminum foil at a speed of 80 m / min and an unwinding tension of 50 N / m through a coating system. Then, it is dried and wound up in a three-stage oven at 70℃, 55℃ and 40℃ respectively to obtain a surface porous current collector.

[0041] In this embodiment 3, the number of surface pores of the porous current collector is 10 pores / m², the solid content of the prepared porous coating slurry is about 23.0%, the total thickness of the obtained porous current collector is 8.1 micrometers, and the single layer thickness of the porous coating is 0.05 micrometers.

[0042] Example 4

[0043] 40 kg of water, 5 kg of carbon nanofibers as conductive material, 12 kg of isopropanol (boiling point 82.45℃) as low-boiling point solvent, 5 kg of polyvinylidene fluoride water-based adhesive as adhesive, and 8 micrometer thick aluminum foil as current collector base layer were measured. The mass ratio of water to low-boiling point solvent was 1:0.3, and the mass ratio of conductive material to adhesive was 1:1. The main difference from Example 3 is the proportion of each component in the porous coating slurry and the fact that the conductive material is carbon nanotubes.

[0044] Preparation of surface porous current collectors:

[0045] 1) To prepare the porous coating slurry, first add 5 kg of carbon nanotubes to 40 kg of water and stir for 60 minutes, then add 12 kg of isopropanol and stir for 90 minutes, and finally add 5 kg of polyvinylidene fluoride water-based adhesive and stir for 60 minutes.

[0046] 2) Coating with porous coating slurry: First, the porous coating slurry obtained in step 1) is coated on the two surfaces of an 8-micron thick aluminum foil at a speed of 80 m / min and an unwinding tension of 50 N / m through a coating system. Then, it is dried and wound up in a three-stage oven at 80℃, 65℃ and 50℃ respectively to obtain a surface porous current collector.

[0047] In this embodiment 4, the number of surface pores of the porous current collector is 9 per square meter, the solid content of the prepared porous coating slurry is about 16.1%, the total thickness of the obtained porous current collector is 18 micrometers, and the thickness of a single layer of the porous coating is 5 micrometers.

[0048] Comparative Example 1

[0049] Preparation of surface-dense fluids:

[0050] First, add 10 kg of carbon black to 40 kg of water and stir for 90 minutes. Then, apply the slurry obtained in step 1) to the two surfaces of a 13-micron thick composite copper current collector through a coating system at a speed of 100 m / min and an unwinding tension of 50 N / m, and then dry it at 50°C.

[0051] Comparative Example 2

[0052] Preparation of surface-dense fluids:

[0053] First, add 8 kg of graphite powder to 40 kg of water and stir for 80 minutes. Then, add 6 kg of polyvinyl alcohol water-based adhesive and stir for 60 minutes. Finally, coat the resulting slurry onto the two surfaces of a 13-micron thick composite copper current collector at a speed of 100 m / min and an unwinding tension of 50 N / m using a coating system. Then, dry the slurry in a two-stage oven at 50℃ and 60℃ respectively.

[0054] Comparative Example 3

[0055] Preparation of surface-dense fluids:

[0056] First, 5 kg of carbon nanotubes were added to 40 kg of water and stirred for 60 minutes. Then, 12 kg of isopropanol was added and stirred for 90 minutes. Next, 5 kg of polyvinylidene fluoride water-based adhesive was added and stirred for 60 minutes to obtain a slurry. Finally, the slurry was coated on the two surfaces of a 13-micron thick composite copper current collector at a speed of 100 m / min and an unwinding tension of 50 N / m. The slurry was then dried in a three-stage oven at 50℃, 70℃, and 90℃ in sequence.

[0057] Performance testing

[0058] The surface porous current collectors obtained in Examples 1-4 and the surface dense current collectors obtained in Comparative Examples 1-3 were tested for capacity retention when applied in a 20Ah lithium iron phosphate battery. The test results are shown in Table 1.

[0059] Table 1. Test results of embodiments and comparative examples of the present invention.

[0060]

[0061] As can be seen from the above test results, the surface porous current collector prepared in this embodiment of the invention has a better overall capacity retention rate and interface resistance than the comparative example. In this embodiment of the invention, a certain proportion of low-boiling-point solvent and water are added as a mixed solvent. In particular, when isopropanol and water are added, since isopropanol and water can form an azeotrope, the mixed solvent of isopropanol and water can evaporate quickly during oven baking. At the same time, the surface of the porous coating is made finer, which can increase the surface area of ​​the porous coating and improve the adhesion area between the active material and the porous coating. Compared with the surface dense fluid prepared in the comparative example, the surface porous current collector effectively reduces the interface resistance between the active material and the surface dense fluid, thereby greatly improving the rate performance and charge-discharge performance when applied to secondary batteries.

[0062] The above description is only a preferred embodiment of the present invention and is not intended to limit the invention. Any modifications, equivalent substitutions, improvements, etc., made within the design concept of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for preparing a surface-porous current collector, characterized by, The surface porous current collector includes a current collector base layer and a porous coating located on at least one surface of the current collector base layer, wherein the surface porous current collector has a surface pore number > 5 per square meter; The method includes the following steps: Preparation of porous coating slurry: First, add conductive material to water and stir, then add low-boiling-point solvent and stir, and finally add binder and stir; the mass ratio of conductive material to binder is 1:0.5-1; the mass ratio of water to low-boiling-point solvent is 1:0.007-0.3; wherein, the low-boiling-point solvent includes isopropanol; Applying a porous coating slurry: The porous coating slurry obtained in step 1) is applied to at least one surface of the current collector substrate through a coating system, and then dried and wound to obtain a surface porous current collector; wherein the drying method is multi-stage, and the first stage of drying has the highest temperature, first using high temperature to promote the formation of pores, and then using low temperature to complete the drying.

2. The method of making a surface porous current collector of claim 1, wherein, The thickness of the porous coating is 0.05-5 micrometers, the thickness of the current collector substrate is 2-18 micrometers, and the total thickness of the surface porous current collector is 3-20 micrometers.

3. The method of making a surface porous current collector of claim 1, wherein, The conductive material includes one or more of carbon nanofibers, carbon nanotubes, carbon black, graphene, graphite powder, and conductive carbon black.

4. The method of making a surface porous current collector of claim 1, wherein, The adhesive includes one or more of the following: acrylic water-based adhesive, polyvinyl alcohol water-based adhesive, ethylene acetate water-based adhesive, polyvinylidene fluoride water-based adhesive, epoxy water-based adhesive, phenolic water-based adhesive, silicone water-based adhesive, rubber water-based adhesive, and polyurethane water-based adhesive.

5. The method of making a surface porous current collector of claim 1, wherein, The current collector substrate includes: copper foil, aluminum foil, copper-aluminum alloy foil, composite copper-based current collector, or composite aluminum-based current collector.

6. The method of making a surface porous current collector of claim 1, wherein, The solid content of the porous coating slurry is 5-25%.

7. The method of making a surface porous current collector of claim 1, wherein, Step 2) The coating speed is 80-100 m / min and the unwinding tension is 50 N / m.

8. The method of making a surface porous current collector of claim 1, wherein, The multi-stage drying process consists of three stages, with the temperature decreasing sequentially.

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