Dry electrode current collector, method for preparing same, dry electrode sheet, and secondary battery

Abstract

The present invention provides a dry-process electrode current collector, a preparation method thereof, a dry-process electrode sheet and a secondary battery. The dry-process electrode current collector includes a foil; two bottom coatings are respectively disposed on the first surface and the second surface of the foil, and in a direction away from the foil, each of the bottom coatings includes a bottom coating A and a bottom coating B stacked in sequence; the bottom coating A includes a polymer A and a one-dimensional carbon material A, and the bottom coating B includes a polymer B and a one-dimensional carbon material B; the polymer A and the polymer B are the same or different, and are both thermoplastic polymers; the weight ratio of the one-dimensional carbon material A to the one-dimensional carbon material B is 1:(1.3-1.5). In the current collector structure obtained by the dry process of the present invention, a bottom coating containing a thermoplastic polymer and a carbon material is specially provided, and by controlling the content relationship of the carbon materials in each layer, good adhesion of the dry-process electrode sheet in the battery is achieved, problems such as easy collapse of its structure are solved, and the smoothness of the ion channels is improved.

Description

Technical Field

[0001] The present invention relates to the field of secondary batteries, and more particularly, to a dry-process electrode current collector, a method for preparing the same, a dry-process electrode sheet, and a secondary battery. Background Art

[0002] In the traditional wet-process electrode preparation process, due to the limited coating thickness, too thick coating will cause the electrode sheet to crack and peel off during the preparation and drying process, which is not conducive to its subsequent application.

[0003] Different from the wet-process electrode, the dry-process electrode technology is a new way of producing electrode sheets. During its preparation process, it does not need to use traditional liquid electrolytes for infiltration. Instead, it prepares the electrode by directly compacting the dry powder electrode material containing active substances, ensuring the intrinsic safety of the battery and being more in line with the future development trend of batteries. However, currently, the current collectors suitable for dry-process electrodes are not well-developed, it is difficult to achieve effective lamination of the dry-process film, and the two are prone to falling off, thus affecting the stability performance of the battery.

[0004] Based on this, how to provide a dry-process electrode current collector to balance the adhesiveness and conductivity between the current collector and the dry-process electrode film, thereby improving the cycle stability of the battery in which it is located, is one of the important problems to be solved in this field. Summary of the Invention

[0005] The main object of the present invention is to provide a dry-process electrode current collector, a method for preparing the same, a dry-process electrode sheet, and a secondary battery to solve the problem of poor stability of the secondary battery in the prior art due to the poor composite effect between the current collector and the electrode sheet.

[0006] To achieve the above object, in a first aspect of the present invention, there is provided a dry-process electrode current collector, which includes: a foil having a first surface and a second surface disposed opposite to each other; two bottom coatings respectively disposed on the first surface and the second surface, and along the direction away from the foil, each bottom coating includes a bottom coating A and a bottom coating B stacked in sequence; the bottom coating A includes a polymer A and a one-dimensional carbon material A, and the bottom coating B includes a polymer B and a one-dimensional carbon material B; the polymer A and the polymer B are the same or different, and are both thermoplastic polymers; the weight ratio of the one-dimensional carbon material A to the one-dimensional carbon material B is 1:(1.5 - 2.0).

[0007] Further, the thermoplastic polymer is selected from one or more of polyvinyl alcohol, polyamide, polyester, polyethylene, and polyurethane; preferably, the polymer A is polyester and polyethylene, and the weight ratio of polyester to polyethylene is (1.5 - 1.8):1; the polymer B is polyester and polyethylene, and the weight ratio of polyester to polyethylene is 1:(2.0 - 2.4); more preferably, the polyester is polyethylene terephthalate.

[0008] Further, based on the total weight of the bottom coating A being 100%, the weight fraction of polymer A is 20 - 50%, and the weight fraction of the one-dimensional carbon material A is 5 - 20%; and / or, based on the total weight of the bottom coating B being 100%, the weight fraction of polymer B is 20 - 60%, and the weight fraction of the one-dimensional carbon material B is 5 - 20%.

[0009] Further, the one-dimensional carbon material A and the one-dimensional carbon material B are each independently a carbon nanotube and / or a vapor-grown carbon fiber; preferably, the lengths of the one-dimensional carbon material A and the one-dimensional carbon material B are each independently 10 μm - 20 μm, and the diameters are each independently 100 nm - 200 nm.

[0010] Further, the bottom coating A and the bottom coating B each independently further include a conductive agent and a binder assistant; preferably, the conductive agent is an SP conductive agent, and the binder assistant is selected from one or more of polyvinylidene fluoride, polyacrylic acid, and carboxymethyl cellulose.

[0011] Further, the thickness of each bottom coating is 0.2 μm - 1.0 μm, and in each bottom coating, the thickness ratio of the bottom coating A to the bottom coating B is 1:(2 - 3).

[0012] The second aspect of the present invention provides a method for preparing the above dry-process electrode current collector, including: Step S1, preparing a bottom coating slurry A according to the composition of the bottom coating A; preparing a bottom coating slurry B according to the composition of the bottom coating B; Step S2, coating the bottom coating slurry A on the first surface and the second surface of the foil simultaneously through a double-sided coating device to form a bottom coating A on both the first surface and the second surface; Step S3, coating the bottom coating slurry B on the surface of the bottom coating A away from the foil, and drying to form a bottom coating B, thereby obtaining a dry-process electrode current collector.

[0013] Further, in Step S1, the preparation of the bottom coating slurry A and the bottom coating slurry B is carried out in an inert gas environment.

[0014] The third aspect of the present invention provides a dry-process electrode sheet, including a current collector and a dry-process electrode film provided on the current collector, and the current collector is the above dry-process electrode current collector.

[0015] The fourth aspect of the present invention provides a secondary battery, and the secondary battery includes the above dry-process electrode sheet.

[0016] Applying the technical solution of the present invention, for the current collector obtained by the dry process, a special bottom coating containing a thermoplastic polymer and a carbon material is provided in its structure, and by controlling the content relationship of the carbon materials in each layer, good adhesion of the dry-process electrode sheet in the battery is achieved, the problems such as the easy collapse of its structure are solved, and the smoothness of the ion channels is improved. Description of the Drawings

[0017] The accompanying drawings of the specification, which form a part of this application, are used to provide a further understanding of the present invention. The schematic embodiments of the present invention and their descriptions are used to explain the present invention and do not unduly limit the present invention. In the drawings:

[0018] Figure 1 It is a schematic diagram of one side structure of the dry electrode current collector in this application.

[0019] Among them, each reference numeral represents the following:

[0020] 10. One side of the foil; 20. The bottom coating on one side of the foil; 21. Bottom coating A; 22. Bottom coating B. Detailed implementation manners

[0021] It should be noted that, without conflict, the embodiments in this application and the features in the embodiments can be combined with each other. The present invention will be described in detail below with reference to the embodiments.

[0022] As described in the background art, the secondary battery in the prior art has the problem of poor stability due to the poor composite effect between the current collector and the electrode sheet. To solve the above technical problems, the first aspect of the present invention provides a dry electrode current collector, as Figure 1 shown, the dry electrode current collector includes: a foil 10 having a first surface and a second surface disposed opposite to each other; two bottom coatings 20 respectively disposed on the first surface and the second surface, and along the direction away from the foil 10, each bottom coating 20 includes a bottom coating A 21 and a bottom coating B 22 stacked in sequence; the bottom coating A 21 includes a polymer A and a one-dimensional carbon material A, and the bottom coating B 22 includes a polymer B and a one-dimensional carbon material B; the polymer A and the polymer B are the same or different, and both are thermoplastic polymers; the weight ratio of the one-dimensional carbon material A to the one-dimensional carbon material B is 1:(1.5 - 2.0).

[0023] The present invention is directed to the current collector obtained by the dry method. In its structure, a special bottom coating containing a thermoplastic polymer and a carbon material is provided, and by controlling the content relationship of the carbon materials in each layer, good adhesion of the dry electrode sheet in the battery is achieved, and problems such as easy collapse of its structure are solved. The above-mentioned double-layer structure current collector provided, because both layers of its double-layer structure are provided with thermoplastic polymers, can realize effective lamination of the dry film sheet and the dry current collector, and further improve the electrochemical stability of the electrode. More importantly, the one-dimensional carbon materials A and B in the double-layer bottom coating show a content gradient from low to high along the direction away from the current collector foil. On the one hand, it can make the internal microstructure of the bottom coating A, the bottom coating B, and their composite as a whole more stable, and can also provide a more smooth electron transport channel, thereby improving the comprehensive electrochemical performance of the obtained dry electrode current collector.

[0024] Further, the thermoplastic polymer is selected from one or more of polyvinyl alcohol, polyamide, polyester, polyethylene, and polyurethane. Theoretically, the thermoplastic polymer can be of the types commonly used in the art. However, the inventors, considering the provided dry-type current collector and the subsequent dry-type battery system, have preferably selected the above-mentioned polymer types with higher adaptability through a large number of experiments. In several more preferred embodiments, polymer A is preferably polyester and polyethylene, and the weight ratio of polyester to polyethylene is (1.5 - 1.8):1; polymer B is polyester and polyethylene, and the weight ratio of polyester to polyethylene is 1:(2.0 - 2.4). The resulting dry-type current collector not only exhibits higher compatibility, cooperativeness, and adhesiveness but also higher structural stability and longer service life. More preferably, the polyester is polyethylene terephthalate.

[0025] In several preferred embodiments, in order to further improve the adhesive force and conductivity of the obtained dry-type current collector, based on the total weight of the bottom coating A21 being 100%, the weight fraction of polymer A is 20 - 50%, and the weight fraction of the one-dimensional carbon material A is 5 - 20%; and / or, based on the total weight of the bottom coating B22 being 100%, the weight fraction of polymer B is 20 - 60%, and the weight fraction of the one-dimensional carbon material B is 5 - 20%.

[0026] Further, the one-dimensional carbon material A and the one-dimensional carbon material B are each independently a carbon nanotube and / or a vapor-grown carbon fiber. These two one-dimensional carbon materials can better interact with the thermoplastic polymer compared to other types of one-dimensional carbon materials commonly used in the art, thereby further optimizing the microstructure and enhancing the stability of the obtained dry-type electrode current collector. On this basis, the inventors have further preferably selected through a large number of experiments that the length of the one-dimensional carbon material A and the one-dimensional carbon material B is each independently 10 μm - 20 μm, and the diameter is each independently 100 nm - 200 nm, in order to obtain a dry-type electrode current collector with better structure, higher adhesiveness, and higher conductivity.

[0027] In several typical embodiments, to further improve the comprehensive performance of the dry-type electrode current collector, the bottom coating A21 and the bottom coating B22 each independently further include a conductive agent and a binder assistant. Preferably, the inventors have screened through a large number of experiments and selected the conductive agent as the SP conductive agent, and the binder assistant is selected from one or more of polyvinylidene fluoride, polyacrylic acid, and carboxymethyl cellulose. Because compared to other types of conductive agents and binder assistants in the art, these have higher compatibility with the above-mentioned dry-type electrode current collector system provided by the present invention. In particular, polyacrylic acid (PAA) can also play a certain synergistic cooperation role with polymers A and B in the bottom coatings A and B, thereby more significantly improving the comprehensive performance of the obtained dry-type electrode current collector.

[0028] For the optimization of the mechanical properties of the dry-process electrode current collector, further, the thickness of each bottom coating 20 is 0.2 μm to 1.0 μm, and in each bottom coating 20, the thickness ratio of the bottom coating A21 to the bottom coating B22 is 1:(2 - 3). The inventor optimized the thickness ratio of the bottom coating A21 to the bottom coating B22 through a large number of experiments and obtained the above range, and found that under the condition of this thickness relationship, the compatibility of each layer is better, and the corresponding dry-process electrode current collector also exhibits a more stable structure and a longer service life.

[0029] The second aspect of the present invention provides a method for preparing the above-mentioned dry-process electrode current collector, including: Step S1, preparing a bottom coating slurry A according to the composition of the bottom coating A21; preparing a bottom coating slurry B according to the composition of the bottom coating B22; Step S2, coating the bottom coating slurry A on the first surface and the second surface of the foil 10 simultaneously through a double-sided coating device, so as to form the bottom coating A21 on both the first surface and the second surface; Step S3, coating the bottom coating slurry B on the surface of the bottom coating A21 away from the foil 10, and drying to form the bottom coating B22, thereby obtaining the dry-process electrode current collector.

[0030] Regarding the above-mentioned dry-process electrode current collector, the present invention correspondingly provides a preparation method thereof, and relying on this simple and feasible preparation method, a dry-process electrode current collector with a stable structure, excellent compatibility and adhesiveness with the positive and negative electrode films prepared by the dry process is obtained.

[0031] In several typical embodiments, in order to improve the uniformity of the bottom coating slurry A and the bottom coating slurry B and the cooperation degree of each component therein, reduce various impurities that may exist in the two obtained bottom coatings, and finally improve the electrochemical performance of the obtained dry-process current collector, especially the cycle stability, it is preferably that in Step S1, the preparation of the bottom coating slurry A and the bottom coating slurry B is carried out in an inert gas environment.

[0032] The third aspect of the present invention provides a dry-process electrode sheet, including a current collector and a dry-process electrode film disposed on the current collector, and the current collector is the above-mentioned dry-process electrode current collector. The obtained dry-process electrode sheet exhibits a higher adhesive force, and it is more difficult for the current collector and the dry-process film to fall off; at the same time, the conductivity is also better.

[0033] The fourth aspect of the present invention provides a secondary battery, and the secondary battery includes the above-mentioned dry-process electrode sheet. The obtained corresponding secondary battery exhibits excellent electrical performance, especially long cycle stability, because both the positive electrode sheet and the negative electrode sheet have higher structural stability and conductivity.

[0034] The following further describes the present application in detail with specific embodiments, and these embodiments should not be construed as limiting the scope claimed by the present application.

[0035] Unless otherwise defined, all technical terms used hereinafter have the same meaning as commonly understood by those skilled in the art. The technical terms used herein are for the purpose of describing specific embodiments only and are not intended to limit the scope of protection of the present invention.

[0036] Example 1

[0037] 1. Preparation of a dry-process electrode current collector:

[0038] (1) Preparation of the primer slurry:

[0039] (1-1) Primer slurry A: Add PAA to the solvent NMP, evacuate and introduce an inert gas, and stir for 60 min; then add SP and VGCF (length 20 μm, diameter 100 nm), evacuate again and introduce an inert gas, and stir for 60 min; then mix PET, PE, and PVDF and add them thereto, evacuate again and introduce an inert gas, and stir for 120 min. After that, add the mixed slurry to a sand mill for sanding and circulate 3 times to obtain primer slurry A.

[0040] In primer slurry A, the addition ratio of the solvent NMP accounts for 70% of the total mass of the slurry; based on the weight of the solvent being 100%, the addition amount of PAA is 2%, SP is 1%, VGCF is 2%, PVDF is 12.5%, and the sum of PET and PE is 12.5% (where PET:PE = 1.5:1).

[0041] (1-1) Primer slurry B: Add PAA to the solvent NMP, evacuate and introduce an inert gas, and stir for 60 min; then add SP and VGCF (length 10 μm, diameter 200 nm), evacuate again and introduce an inert gas, and stir for 60 min; then mix PET, PE, and PVDF and add them thereto, evacuate again and introduce an inert gas, and stir for 120 min. After that, add the mixed slurry to a sand mill for sanding and circulate 3 times to obtain primer slurry B.

[0042] In primer slurry B, the addition ratio of the solvent NMP accounts for 70% of the total mass of the slurry; based on the weight of the solvent being 100%, the addition amount of PAA is 2%, SP is 1%, VGCF is 4%, PVDF is 12.5%, and the sum of PET and PE is 12.5% (where PET:PE = 1:2).

[0043] (2) Apply primer slurry A to the first and second surfaces of a 12-μm aluminum foil simultaneously at a speed of 100 m / s using a double-sided coating device, with a coating thickness of 0.3 μm. After drying at 100°C, a layer with a thickness of 0.3 μm and a surface density of 5 mg / cm 2Base coating A, in which the total weight fraction of PET and PE is 41%, and the weight fraction of VGCF is 10%;

[0044] (3) Apply the base coating slurry B through a double-sided coating device at a speed of 100 m / s and simultaneously coat it on the two sides of the base coating A. The coating thickness is 0.7 μm. After drying at 100 °C, two-sided base coatings B with a thickness of 0.7 μm and a surface density of 12 mg / cm 2 are formed. In the base coating B, the total weight fraction of PET and PE is 41%, and the weight fraction of VGCF is 13%. Finally, an aluminum foil dry electrode current collector for composite with the positive electrode film is formed.

[0045] (4) Replace the 12-μm aluminum foil in step (2) with 6-μm copper foil, and repeat steps (2) and (3). Finally, a copper foil dry electrode current collector for composite with the negative electrode film is formed. The schematic structural diagram of one side is as shown in Figure 1 .

[0046] 2. Preparation of the dry positive electrode sheet and the dry negative electrode sheet:

[0047] (1) Dry positive electrode sheet: 97% lithium iron phosphate + 1% PTFE + 2% SP are mixed and calendered to obtain a fibrous positive electrode film. The aluminum foil dry electrode current collector obtained above for composite with the positive electrode film and the positive electrode film are heated and laminated using a laminator, and then rolled by a rolling press to obtain a dry positive electrode sheet.

[0048] (2) Dry negative electrode sheet: 97% graphite + 1% PTFE + 2% SP are mixed and calendered to obtain a fibrous negative electrode film. The copper foil dry electrode current collector obtained above for composite with the negative electrode film and the negative electrode film are heated and laminated using a laminator, and then rolled by a rolling press to obtain a dry negative electrode sheet.

[0049] Example 2

[0050] 1. Preparation of a dry electrode current collector:

[0051] In this step, the difference between this example and Example 1 is only that: instead of adding PE, an equal weight of PET is used to replace PE, that is, in the base coating slurries A and B, PET is 12.5% in both.

[0052] 2. Preparation of the dry positive electrode sheet and the dry negative electrode sheet:

[0053] Using the dry electrode current collector obtained above, the dry positive and negative electrode sheets are prepared in the same manner as in Example 1.

[0054] Example 3

[0055] 1. Preparation of a dry-process electrode current collector:

[0056] In this step, the difference between this example and Example 1 is only that: instead of adding PET, an equal weight of PE is used to replace PET, that is, in the primer pastes A and B, the PE content is 12.5% in both.

[0057] 2. Preparation of the dry-process positive electrode sheet and the dry-process negative electrode sheet:

[0058] Using the obtained dry-process electrode current collector above, the dry-process positive and negative electrode sheets are prepared in the same manner as in Example 1.

[0059] Example 4

[0060] 1. Preparation of a dry-process electrode current collector:

[0061] In this step, the difference between this example and Example 1 is only that: in primer paste A, the sum of PET and PE is 12.5% (where PET:PE = 1:1); in primer paste B, the sum of PET and PE is 12.5% (where PET:PE = 1:1).

[0062] 2. Preparation of the dry-process positive electrode sheet and the dry-process negative electrode sheet:

[0063] Using the obtained dry-process electrode current collector above, the dry-process positive and negative electrode sheets are prepared in the same manner as in Example 1.

[0064] Example 5

[0065] 1. Preparation of a dry-process electrode current collector:

[0066] In this step, the difference between this example and Example 1 is only that: in primer paste A, the sum of PET and PE is 12.5% (where PET:PE = 2:1); in primer paste B, the sum of PET and PE is 12.5% (where PET:PE = 1:3).

[0067] 2. Preparation of the dry-process positive electrode sheet and the dry-process negative electrode sheet:

[0068] Using the obtained dry-process electrode current collector above, the dry-process positive and negative electrode sheets are prepared in the same manner as in Example 1.

[0069] Example 6

[0070] 1. Preparation of a dry-process electrode current collector:

[0071] In this step, the difference between this embodiment and Embodiment 1 is only that: in the obtained bottom coating A, the total weight fraction of PET and PE is 15%, and the weight fraction of VGCF is 25%; in the obtained bottom coating B, the total weight fraction of PET and PE is 15%, and the weight fraction of VGCF is 35%.

[0072] 2. Preparation of dry-process positive electrode sheet and dry-process negative electrode sheet:

[0073] Using the obtained dry-process electrode current collector, the dry-process positive and negative electrode sheets are prepared in the same manner as in Embodiment 1.

[0074] Embodiment 7

[0075] 1. Preparation of a dry-process electrode current collector:

[0076] In this step, the difference between this embodiment and Embodiment 1 is only that: in the obtained bottom coating A, the total weight fraction of PET and PE is 55%, and the weight fraction of VGCF is 2%; in the obtained bottom coating B, the total weight fraction of PET and PE is 65%, and the weight fraction of VGCF is 3%.

[0077] 2. Preparation of dry-process positive electrode sheet and dry-process negative electrode sheet:

[0078] Using the obtained dry-process electrode current collector, the dry-process positive and negative electrode sheets are prepared in the same manner as in Embodiment 1.

[0079] Embodiment 8

[0080] 1. Preparation of a dry-process electrode current collector:

[0081] In this step, the difference between this embodiment and Embodiment 1 is only that: the thickness of the obtained bottom coating A is 0.1 μm; the thickness of the obtained bottom coating B is 0.1 μm.

[0082] 2. Preparation of dry-process positive electrode sheet and dry-process negative electrode sheet:

[0083] Using the obtained dry-process electrode current collector, the dry-process positive and negative electrode sheets are prepared in the same manner as in Embodiment 1.

[0084] Embodiment 9

[0085] 1. Preparation of a dry-process electrode current collector:

[0086] In this step, the difference between this embodiment and Embodiment 1 is only that: the thickness of the obtained bottom coating A is 1.2 μm; the thickness of the obtained bottom coating B is 4.8 μm.

[0087] 2. Preparation of dry-process positive electrode sheet and dry-process negative electrode sheet:

[0088] Using the dry-process electrode current collector obtained above, the dry-process positive and negative electrode sheets are prepared in the same manner as in Example 1.

[0089] Example 10

[0090] 1. Preparation of a dry-process electrode current collector:

[0091] In this step, the difference between this example and Example 1 is only that: during the preparation of the undercoat slurries A and B, vacuum is not pumped and inert gas is not introduced, that is, the preparation of both undercoat slurries is carried out in an open air system.

[0092] 2. Preparation of the dry-process positive electrode sheet and the dry-process negative electrode sheet:

[0093] Using the dry-process electrode current collector obtained above, the dry-process positive and negative electrode sheets are prepared in the same manner as in Example 1.

[0094] Comparative Example 1

[0095] 1. Preparation of a dry-process electrode current collector:

[0096] In this step, the difference between this comparative example and Example 1 is only that: neither PET, PE, PAA nor PVDF is included in the undercoat slurries A and B, that is, only the surfaces of the 12-μm aluminum foil and the 6-μm copper foil are coated with carbon (SP), and they are respectively used as the positive electrode current collector and the negative electrode current collector.

[0097] 2. Preparation of the dry-process positive electrode sheet and the dry-process negative electrode sheet:

[0098] Using the dry-process electrode current collector obtained above, the dry-process positive and negative electrode sheets are prepared in the same manner as in Example 1.

[0099] Comparative Example 2

[0100] 1. Preparation of a dry-process electrode current collector:

[0101] In this step, the difference between this comparative example and Example 1 is only that: neither PET, PE nor PAA is included in the undercoat slurries A and B, that is, neither polymer A nor polymer B is included, and no additives are contained.

[0102] 2. Preparation of the dry-process positive electrode sheet and the dry-process negative electrode sheet:

[0103] Using the dry-process electrode current collector obtained above, the dry-process positive and negative electrode sheets are prepared in the same manner as in Example 1.

[0104] Comparative Example 3

[0105] 1. Preparation of a dry-process electrode current collector:

[0106] In this step, the difference between this comparative example and Example 1 is only that: neither of the primer slurries A and B contains the one-dimensional carbon material VGCF.

[0107] 2. Preparation of the dry-process positive electrode sheet and the dry-process negative electrode sheet:

[0108] Using the dry-process electrode current collector obtained above, the dry-process positive and negative electrode sheets are prepared in the same manner as in Example 1.

[0109] Comparative Example 4

[0110] 1. Preparation of a dry-process electrode current collector:

[0111] In this step, the difference between this comparative example and Example 1 is only that: the coating conditions are changed so that the weight fraction of VGCF in the obtained primer coating B is changed to 10%, and at this time, the weight ratio of the one-dimensional carbon materials in primer coatings A and B is changed to 1:1.

[0112] 2. Preparation of the dry-process positive electrode sheet and the dry-process negative electrode sheet:

[0113] Using the dry-process electrode current collector obtained above, the dry-process positive and negative electrode sheets are prepared in the same manner as in Example 1.

[0114] Comparative Example 5

[0115] 1. Preparation of a dry-process electrode current collector:

[0116] In this step, the difference between this comparative example and Example 1 is only that: the coating conditions are changed so that the weight fraction of VGCF in the obtained primer coating B is changed to 40%, and at this time, the weight ratio of the one-dimensional carbon materials in primer coatings A and B is changed to 1:4.

[0117] 2. Preparation of the dry-process positive electrode sheet and the dry-process negative electrode sheet:

[0118] Using the dry-process electrode current collector obtained above, the dry-process positive and negative electrode sheets are prepared in the same manner as in Example 1.

[0119] Preparation of battery samples: Take the dry-process positive electrode sheets and dry-process negative electrode sheets obtained in the above examples and comparative examples, and respectively combine them with diaphragms, aluminum-plastic films, tab ears, and electrolytes. After processes such as cutting, laminating, hot pressing, welding, encapsulating, forming, secondary sealing and cutting, and grading, 5 Ah soft-pack batteries corresponding to the above examples and comparative examples are prepared.

[0120] Testing method

[0121] Pole piece adhesion: Stick the pressure-sensitive tape on the stainless steel plate, then stick the pole piece on the pressure-sensitive tape, and use a tensile testing machine to clamp the pole piece for 180° peeling to obtain the pole piece adhesion; where the surface coated with the active material is defined as the front side, and the other side is the back side.

[0122] Pole piece resistivity: Test the pole piece using a four-probe tester.

[0123] Observation after disassembly after full charge: The number of black spots on the negative electrode color represents defects.

[0124] Battery capacity retention rate: Operate the battery on a charge-discharge device under the condition of normal temperature of 25 °C, and test its capacity retention rate after cycling 10 and 100 times at a charge-discharge rate of 0.1C.

[0125] The test results obtained are shown in Table 1-1 and Table 1-2.

[0126] Table 1-1

[0127]

[0128]

[0129] Table 1-2

[0130]

[0131]

[0132] It should be noted that, in order to avoid systematic errors and ensure the reproducibility of the data, for the performance tests in Table 1-1 and Table 1-2, three parallel samplings were performed on the same sample, and the average value of the performance tests was taken.

[0133] From the above description, it can be seen that the above embodiments of the present invention solve the problems of insufficient adhesion of the dry-process pole piece in the battery and easy collapse of the structure, and improve the smoothness of the ion channel.

[0134] It should be noted that the terms "first", "second", etc. in the specification and claims of this application are used to distinguish similar objects, and do not have to be used to describe a specific order or sequence. It should be understood that such terms can be interchanged under appropriate circumstances so that the embodiments of the present application described herein can be implemented in an order other than those described herein.

[0135] The above are only the preferred embodiments of the present invention and are not intended to limit the present invention. For those skilled in the art, the present invention may have various modifications and variations. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included within the protection scope of the present invention.

Claims

1. A dry electrode current collector, characterized in that: The dry electrode current collector comprises: The foil (10) has a first surface and a second surface arranged opposite to each other; Two primer layers (20), respectively disposed on the first surface and the second surface, and in a direction away from the foil (10), each primer layer (20) comprises a primer layer A (21) and a primer layer B (22) stacked in sequence; The thickness of each of the primer layers (20) is 0.2 μm to 1.0 μm, and in each of the primer layers (20), the ratio of the thickness of the primer layer A (21) to that of the primer layer B (22) is 1:(2-3); The undercoat layer A (21) includes a polymer A and a one-dimensional carbon material A, and the undercoat layer B (22) includes a polymer B and a one-dimensional carbon material B; The polymer A is polyester and polyethylene, and the weight ratio of the polyester to the polyethylene is (1.5-1.8):1; the polymer B is polyester and polyethylene, and the weight ratio of the polyester to the polyethylene is 1:(2.0-2.4); The polyester is polyethylene terephthalate; The weight ratio of the one-dimensional carbon material A to the one-dimensional carbon material B is 1:(1.3-1.5); Based on the total weight of the primer layer A (21) being 100%, the weight fraction of the polymer A is 20-50%, and the weight fraction of the one-dimensional carbon material A is 5-20%; and / or, Based on the total weight of the primer layer B (22) being 100%, the weight fraction of the polymer B is 20-60%, and the weight fraction of the one-dimensional carbon material B is 5-20%.

2. The dry electrode current collector according to claim 1, characterized in that: The one-dimensional carbon material A and the one-dimensional carbon material B are each independently a carbon nanotube and / or a vapor-grown carbon fiber.

3. The dry electrode current collector according to claim 1, characterized in that: The one-dimensional carbon material A and the one-dimensional carbon material B each independently have a length of 10 μm to 20 μm, and each independently have a diameter of 100 nm to 200 nm.

4. The dry electrode current collector according to any one of claims 1 to 3, characterized in that: The primer layer A (21) and the primer layer B (22) each independently further include a conductive agent and an adhesive aid.

5. The dry electrode current collector according to claim 4, characterized in that: The conductive agent is an SP conductive agent, and the bonding aid is selected from one or more of polyvinylidene fluoride, polyacrylic acid and carboxymethyl cellulose.

6. A method for preparing a dry electrode current collector according to any one of claims 1 to 5, characterized in that: include: Step S1, preparing a primer slurry A according to the composition of the primer layer A (21); Prepare a primer slurry B according to the composition of the primer B (22); Step S2, coating the primer slurry A on the first surface and the second surface of the foil (10) simultaneously by a double-sided coating device, so as to form the primer layer A (21) on both the first surface and the second surface; Step S3, coating the primer slurry B on the surface of the primer layer A (21) away from the foil (10), and drying to form the primer layer B (22), thereby obtaining the dry electrode current collector.

7. The method for preparing a dry electrode current collector according to claim 6, characterized in that: In step S1, the preparation of the primer slurry A and the primer slurry B is performed under an inert gas environment.

8. A dry electrode sheet, comprising a current collector and a dry electrode membrane arranged on the current collector, characterized in that: The current collector is the dry electrode current collector according to any one of claims 1 to 5.

9. A secondary battery, characterized in that: The secondary battery comprises the dry electrode sheet according to claim 8.

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