Long-circulation persistent adhesion type negative electrode composite electrode as well as preparation method and application of long-circulation persistent adhesion type negative electrode composite electrode

Abstract

The invention relates to the field of batteries, in particular to a long-circulation persistent adhesion type negative electrode composite electrode and a preparation method and application thereof. The long-circulation persistent adhesive type negative electrode composite electrode comprises a current collector, and a first adhesive layer, an active slurry coating and a second adhesive layer which are sequentially coated on two sides of the current collector, according to the invention, through the bonding effect between the second bonding layer and the diaphragm, the pole piece is uniformly stressed during cyclic expansion, the wrinkles of the pole piece are improved, the electrolyte infiltration is better in combination with the oil-absorbing conductive agent, the lithium ion transmission efficiency is improved, and the cycle life is prolonged; an interface structure formed by multi-layer coating can buffer lithium ion intercalation / deintercalation stress, so that the pole piece can still keep good binding power after circulation, and the cycle performance of the lithium ion battery can be effectively improved; the conductive agent contents of the first bonding layer, the active slurry coating and the second bonding layer are distributed in a concave gradient manner, so that the resistance is reduced, and the conductivity is enhanced.

Description

Technical Field

[0001] The present invention relates to the field of batteries, and in particular to a long-cycle adhesive negative composite electrode and a preparation method and application thereof. Background Art

[0002] Lithium-ion batteries, due to their high energy density, long cycle life, and lack of memory effect, are widely used in portable electronic devices, electric vehicles, and energy storage systems. Their performance is directly dependent on the stability of their electrode structure. As a crucial component of lithium-ion batteries, the performance of the negative electrode directly impacts the overall performance of the battery.

[0003] Traditional negative electrode sheets typically utilize a single-layer coating method, where a mixture of graphite, a conductive agent, and a binder is directly applied to the current collector surface. This technology suffers from several drawbacks: uneven binder distribution: The binder in a single-layer slurry must balance conductivity and bonding, making it difficult to form a high-concentration bonding network at the interface; weak interfacial bonding: The lack of a transition layer between the graphite particles and the copper foil relies solely on the physical adsorption of a small amount of binder. Expansion stress can easily lead to interfacial delamination during cycling, increasing the battery's internal resistance and accelerating capacity decay, severely impacting the battery's cycle life and performance; and a conductivity-bonding conflict: Increasing the conductive agent content reduces the binder content, and vice versa, resulting in performance compromises.

[0004] Currently, the main methods for improving the adhesion of negative electrode sheets include surface treatment of the current collector and optimization of the binder system. However, surface treatment of the current collector often increases production costs and process complexity; while optimizing the binder system can improve adhesion to a certain extent, the effect is limited and may have a negative impact on other battery properties. In addition, during the battery cycle, due to the expansion of the negative electrode sheet, the external stress at different locations is uneven, causing the negative electrode sheet to wrinkle and deform, which can easily cause uneven electrolyte infiltration, hinder lithium ion transmission, and affect the charge and discharge efficiency of the lithium-ion battery. In more serious cases, black spots and lithium precipitation may appear in the wrinkled area, posing a safety hazard.

[0005] Therefore, there is an urgent need to develop a composite electrode structure that can maintain high adhesion and high ion transport efficiency after long cycles. Summary of the Invention

[0006] The purpose of the present invention is to address the deficiencies in the prior art and to provide a long-cycle adhesive negative composite electrode and a preparation method and application thereof.

[0007] To achieve the above object, the technical solution adopted by the present invention is:

[0008] The first aspect of the present invention is to provide a long-cycle adhesive negative composite electrode, comprising: a current collector, a first adhesive layer, an active slurry coating, and a second adhesive layer sequentially coated on both sides of the current collector;

[0009] Wherein, the first bonding layer comprises: a first bonding agent, a first conductive agent and a first thickener;

[0010] The active slurry coating comprises: a negative electrode active material, a second binder, a second conductive agent and a second thickener;

[0011] The second adhesive layer includes a third adhesive, a third conductive agent, and a third thickener.

[0012] Preferably, the first binder, the second binder and the third binder are independently selected from at least one of polyvinylidene fluoride, styrene-butadiene rubber, polyacrylic acid and polytetrafluoroethylene.

[0013] Preferably, the first conductive agent, the second conductive agent and the third conductive agent are independently selected from at least one of carbon nanotubes, carbon black and carbon fibers.

[0014] Preferably, the first thickener, the second thickener and the third thickener are independently selected from sodium carboxymethyl cellulose and potassium carboxymethyl cellulose.

[0015] Preferably, in the first adhesive layer, the mass ratio of the first adhesive, the first conductive agent and the first thickener is (7-8): (1.5-2.5): 0.5;

[0016] In the active slurry coating, the mass ratio of the negative electrode active material, the second binder, the second conductive agent and the second thickener is (90-98): (1-3): (0.5-1): (0.5-2);

[0017] In the second adhesive layer, the mass ratio of the third adhesive, the third conductive agent, and the third thickener is (6-8):(1.5-2):0.5.

[0018] Preferably, the thickness of the first bonding layer is 2-5 μm; the thickness of the active slurry coating is 130-160 μm; and the thickness of the second bonding layer is 2-5 μm.

[0019] The second aspect of the present invention is to provide a method for preparing the above-mentioned long-cycle adhesive negative composite electrode, comprising the following steps:

[0020] S1. Weigh a first binder, a first conductive agent, and a first thickener according to a mass ratio, place them in deionized water and mix them evenly to obtain a first bonding layer slurry; apply the first bonding layer slurry to the surface of the current collector and dry it to obtain a first transition electrode;

[0021] S2. Weighing the negative electrode active material, the second binder, the second conductive agent, and the second thickener according to the mass ratio, and mixing them at high speed to obtain an active slurry; applying the active slurry to the surface of the first transition electrode sheet, and drying the mixture to obtain a second transition electrode sheet;

[0022] S3. Weigh the third binder, the third conductive agent, and the third thickener according to the mass ratio, place them in deionized water and mix them evenly to obtain a second bonding layer slurry; apply the second bonding layer slurry on the surface of the second transition electrode and dry it to obtain the long-cycle adhesive negative composite electrode.

[0023] Preferably, in step S1, the current collector is a copper foil with a thickness of 5-8 μm.

[0024] Preferably, in step S2, the solid content of the active slurry is 40-60%.

[0025] Preferably, in step S2, the high-speed mixing treatment comprises: stirring at a rotation speed of 1500-3000 rpm for 3-5 hours.

[0026] A third aspect of the present invention is to provide a lithium ion battery, the preparation steps of which include:

[0027] The long-cycle adhesive negative composite electrode, positive electrode sheet and separator are wound into a battery core, which is then preheated, hot pressed, ultrasonically welded to the adapter, laser welded to the adapter, and coated with a core. The core is then combined and placed into a battery casing, and the top cover is welded to the battery casing. The battery is then baked, injected with liquid once, formed, injected with liquid twice, and sealed with nails, to obtain a lithium-ion battery.

[0028] The present invention adopts the above technical solution, which has the following technical effects compared with the prior art:

[0029] (1) The present invention forms an anchoring network structure between the first adhesive layer and the current collector through the chemical anchoring effect of the first adhesive layer. The carboxyl groups at the end of the adhesive molecular chain react with the natural oxide layer on the surface of the current collector during the slurry coating and drying process to form a chemical bond at the interface. The bond energy is much higher than that of physical adsorption. In addition, the adhesive forms a continuous film during the drying process. The polymer chain penetrates into the micropores on the surface of the current collector and forms a mechanical interlocking structure after curing, which greatly improves the bonding strength and can effectively reduce the risk of the electrode peeling off during the charge and discharge process of the battery.

[0030] (2) The present invention uses the bonding effect between the second bonding layer and the diaphragm to keep the pole piece uniformly stressed during cyclic expansion, improve pole piece wrinkles, and combine with the oil-absorbing conductive agent to achieve better electrolyte infiltration, thereby improving lithium ion transmission efficiency and cycle life;

[0031] (3) The interface structure formed by multi-layer coating in the present invention can buffer the stress of lithium ion insertion / extraction, so that the electrode can still maintain good adhesion after cycling, which can effectively improve the cycling performance of lithium ion batteries;

[0032] (4) The conductive agent content of the first bonding layer, active slurry coating, and second bonding layer of the present invention is distributed in a concave gradient. The high-concentration conductive agent in the first bonding layer preferentially forms a transverse conductive network on the surface of the current collector. The conductive agent particles directly contact the current collector, filling the microscopic depressions on its surface, thereby reducing the interfacial contact resistance. During the coating and drying process, the solvent in the active slurry coating partially penetrates into the bonding layer, driving a small amount of conductive agent to migrate toward the bonding layer. The adhesive molecular chains in the bonding layer extend toward the active slurry coating, wrapping the conductive agent particles in the active slurry coating, forming a continuous conductive path, thereby achieving reduced resistance and enhanced conductivity.

[0033] (5) In conventional single-layer coating, the conductive network breaks due to graphite expansion, while the upper and lower adhesive layers of the multi-layer coating of the present invention enable the conductive agent in the middle active slurry coating to be elastically connected with the upper and lower adhesive layers, so that it can adapt to the volume change of the conductive agent expansion, enhance the conductive stability during use, and improve the charge and discharge efficiency;

[0034] (6) The second adhesive layer can also fill the micro-gap between the electrode and the diaphragm, increasing the effective contact area and reducing the internal resistance of the battery;

[0035] (7) The present invention does not require new equipment and does not require complex surface treatment of the current collector. Production can be achieved by simply optimizing the multi-layer coating sequence and slurry formula. The raw material cost is comparable to that of traditional methods, and it has good economic benefits and application prospects. BRIEF DESCRIPTION OF THE DRAWINGS

[0036] Figure 1 This is a schematic diagram of the basic structure of the long-cycle adhesive negative composite electrode in Example 1 of the present invention.

[0037] Reference numerals in the figures include:

[0038] Current collector 1; first bonding layer 2; active slurry coating 3; second bonding layer 4. DETAILED DESCRIPTION

[0039] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making any creative efforts shall fall within the scope of protection of the present invention.

[0040] It should be noted that, in the absence of conflict, the embodiments of the present invention and the features in the embodiments may be combined with each other.

[0041] The present invention will be further described below with reference to the accompanying drawings and specific embodiments, but they are not intended to limit the present invention.

[0042] Example 1

[0043] This embodiment provides a method for preparing a long-cycle adhesive negative composite electrode, comprising the following steps:

[0044] S1. Weigh a first binder (polyvinylidene fluoride:styrene-butadiene rubber = 1:1), a first conductive agent (carbon nanotubes), and a first thickener (sodium carboxymethyl cellulose) in a mass ratio of 8:1.5:0.5, place them in deionized water and mix them evenly to obtain a first bonding layer slurry; apply the first bonding layer slurry to the surface of a 6 μm copper foil and pre-dry at 70°C until the water content is less than 5%, thereby obtaining a first transition electrode having a first bonding layer; the thickness of the first bonding layer is 3 μm;

[0045] S2. Weigh the negative electrode active material (graphite), the second binder (styrene-butadiene latex), the second conductive agent (carbon black), and the second thickener (sodium carboxymethyl cellulose) in a mass ratio of 96:2:1:1, stir and mix them in a high-speed pulper at a speed of 2000 rpm, and adjust the solid content to 50% to obtain an active slurry; apply the active slurry to the surface of the first transition electrode piece, and dry it at 100°C to obtain a second transition electrode piece; the thickness of the active coating is 140 μm;

[0046] S3, weighing the third binder (polyacrylic acid: styrene-butadiene rubber = 3:1), the third conductive agent (carbon black: carbon nanotubes = 3:1) and the third thickener (sodium carboxymethyl cellulose) in a mass ratio of 6.5:2:0.5, placing them in deionized water and mixing them evenly to obtain a second bonding layer slurry; applying the second bonding layer slurry on the surface of the second transition electrode, and pre-drying it at 70°C to a water content of <5%, to obtain the long-cycle adhesive negative composite electrode ( Figure 1 ); the thickness of the second adhesive layer is 3 μm.

[0047] Example 2

[0048] This embodiment provides another method for preparing a long-cycle adhesive negative composite electrode, comprising the following steps:

[0049] S1. Weigh a first binder (polyvinylidene fluoride: polyacrylic acid = 1:1), a first conductive agent (carbon nanotubes: carbon fibers = 1:2), and a first thickener (potassium carboxymethyl cellulose) in a mass ratio of 7:2.5:0.5, place them in deionized water and mix them evenly to obtain a first bonding layer slurry; apply the first bonding layer slurry to the surface of a 6 μm copper foil and pre-dry at 70°C to a water content of <5%, thereby obtaining a first transition electrode having a first bonding layer; the thickness of the first bonding layer is 3 μm;

[0050] S2. Weigh the negative electrode active material (graphite), the second binder (styrene-butadiene rubber), the second conductive agent (carbon black), and the second thickener (sodium carboxymethyl cellulose) in a mass ratio of 96:2:1:1, stir and mix them in a high-speed pulper at a speed of 2000 rpm, and adjust the solid content to 50% to obtain an active slurry; apply the active slurry to the surface of the first transition electrode piece, and dry it at 100°C to obtain a second transition electrode piece; the thickness of the active coating is 145 μm;

[0051] S3. Weigh the third binder (polyacrylic acid: polytetrafluoroethylene = 2:1), the third conductive agent (carbon black: carbon nanotubes = 2:1) and the third thickener (sodium carboxymethyl cellulose) in a mass ratio of 7:1.5:0.5, place them in deionized water and mix them evenly to obtain a second bonding layer slurry; apply the second bonding layer slurry on the surface of the second transition electrode, and pre-dry it at 70°C to a water content of <5% to obtain the long-cycle persistent negative composite electrode; the thickness of the second bonding layer is 3 μm.

[0052] Comparative Example 1

[0053] This comparative example provides a method for preparing a negative electrode sheet, the steps comprising:

[0054] The active material graphite, conductive agent, and thickener were premixed in a ratio of 96%:1%:1%, followed by the addition of 2% binder and solvent water, resulting in a slurry with a solids content of 50%. The mixture was stirred in a high-speed pulper (2000 rpm) for 4 hours to ensure uniform mixing. The negative electrode active slurry was coated onto 6µm copper foil and dried at 100°C to produce a negative electrode sheet with a coating thickness of 160µm.

[0055] Comparative Example 2

[0056] This comparative example provides another method for preparing a negative electrode sheet, the steps comprising:

[0057] The mass ratio of S1, the first binder, the first conductive agent and the first thickener is adjusted to 9:0.5:0.5, and the rest is the same as in Example 2.

[0058] The mass ratio of S2, the negative electrode active material, the second binder, the second conductive agent, and the second thickener is adjusted to 85:2:10:3, and the rest is the same as in Example 2.

[0059] S3. Same as Example 2.

[0060] Detection Example

[0061] The 180° adhesion test was performed on the negative electrode sheets prepared in Examples 1-2 and Comparative Examples 1-2 according to the GB / T 2790-2021 standard. The test results are shown in Table 1.

[0062] Table 1

[0063]

[0064] The negative electrode sheets of Examples 1-2 and Comparative Examples 1-2 were respectively made into lithium-ion batteries and subjected to cycle performance and post-cycle electrode sheet adhesion tests. The preparation steps included:

[0065] The negative electrode sheet, positive electrode sheet and separator are wound into a battery core, and then the two cores are combined together through preheating, hot pressing, ultrasonic welding of adapter sheets, laser welding of adapter sheets, core wrapping and other processes, and then placed in the battery shell. The top cover and battery shell are welded together through the top cover welding process; the battery cell is then baked, injected with liquid once, formed and injected with liquid twice; and then the sealing pins are welded to make a lithium-ion battery; the electrolyte is made by dissolving LiPF6 as a lithium salt in a mixed solvent of EC, PC and DMC.

[0066] The test process is as follows:

[0067] (a) 0.3C constant current charging to 3.65V;

[0068] (b) Let stand for 10 min;

[0069] (c) 0.3C constant current discharge to 2.5V;

[0070] (d) let it stand for 10 min;

[0071] (e) Repeat steps ad.

[0072] After 200 cycles, the battery was disassembled to obtain the negative electrode plate after the cycle. The 180° adhesion strength was tested according to the GB / T 2790-2021 standard. The battery performance and plate adhesion test results after the cycle are shown in Table 2.

[0073] Table 2

[0074]

[0075] From the results in Table 1, it can be seen that the bonding strength of the negative electrode sheets prepared in Examples 1 and 2 is improved by 67.8% and 74.6% respectively compared with that in Comparative Example 1, and the diaphragm resistance is reduced by 27.3% and 33% respectively. In addition, the bonding strength and diaphragm resistance of the negative electrode sheets in Comparative Example 2 are not significantly improved compared with those in Comparative Example 1. From the results in Table 2, it can be seen that the batteries prepared from the electrodes of Examples 1 and 2 have a higher capacity retention rate after cycling, and during the cycling process, the attenuation of the bonding strength of the negative electrode sheets of the embodiments is also significantly less than that of Comparative Examples 1-2, which makes the lithium-ion battery have better cycling performance. In summary, the long-cycle adhesive negative composite electrode provided by the present invention has good bonding performance and can still maintain better bonding after cycling, thereby improving the cycling performance of the lithium-ion battery.

[0076] The above description is only a preferred embodiment of the present invention and does not limit the implementation mode and protection scope of the present invention. For those skilled in the art, it should be aware that all solutions obtained by equivalent substitutions and obvious changes made using the description and illustrations of the present invention should be included in the protection scope of the present invention.

Claims

1. A long-cycle adhesive negative composite electrode, characterized in that: include: A current collector (1), a first adhesive layer (2), an active slurry coating (3), and a second adhesive layer (4) sequentially coated on both sides of the current collector (1); Wherein, the first adhesive layer (2) comprises: a first adhesive, a first conductive agent and a first thickener; The active slurry coating (3) comprises: a negative electrode active material, a second binder, a second conductive agent and a second thickener; The second adhesive layer (4) comprises a third adhesive, a third conductive agent and a third thickener.

2. The long cycle adhesive negative composite electrode according to claim 1, characterized in that: The first binder, the second binder, and the third binder are independently selected from at least one of polyvinylidene fluoride, styrene-butadiene rubber, polyacrylic acid, and polytetrafluoroethylene.

3. The long cycle adhesive negative composite electrode according to claim 1, characterized in that: The first conductive agent, the second conductive agent, and the third conductive agent are independently selected from at least one of carbon nanotubes, carbon black, and carbon fibers.

4. The long cycle sustained adhesion type negative composite electrode according to claim 1, characterized in that: The first thickener, the second thickener and the third thickener are independently selected from sodium carboxymethyl cellulose and potassium carboxymethyl cellulose.

5. The long cycle sustained adhesion type negative composite electrode according to claim 1, characterized in that: In the first adhesive layer (2), the mass ratio of the first adhesive, the first conductive agent and the first thickener is (7-8): (1.5-2.5): 0.5; In the active slurry coating (3), the mass ratio of the negative electrode active material, the second binder, the second conductive agent and the second thickener is (90-98): (1-3): (0.5-1): (0.5-2); In the second adhesive layer (4), the mass ratio of the third adhesive, the third conductive agent and the third thickener is (6-8): (1.5-2): 0.

5.

6. The long cycle sustained adhesion type negative composite electrode according to claim 1, characterized in that: The thickness of the first bonding layer (2) is 2-5 μm; the thickness of the active slurry coating (3) is 130-160 μm; and the thickness of the second bonding layer (4) is 2-5 μm.

7. A method for preparing a long-cycle adhesive negative composite electrode according to any one of claims 1 to 6, characterized in that the steps include: S1. Weigh a first binder, a first conductive agent, and a first thickener according to a mass ratio, place them in deionized water and mix them evenly to obtain a first bonding layer slurry; apply the first bonding layer slurry on the surface of the current collector (1), and dry it to obtain a first transition electrode; S2. Weighing the negative electrode active material, the second binder, the second conductive agent, and the second thickener according to the mass ratio, and mixing them at high speed to obtain an active slurry; applying the active slurry to the surface of the first transition electrode sheet, and drying the mixture to obtain a second transition electrode sheet; S3. Weigh the third binder, the third conductive agent, and the third thickener according to the mass ratio, place them in deionized water and mix them evenly to obtain a second bonding layer slurry; apply the second bonding layer slurry on the surface of the second transition electrode and dry it to obtain the long-cycle adhesive negative composite electrode.

8. The preparation method according to claim 7, characterized in that In step S2, the solid content of the active slurry is 40-60%.

9. The preparation method according to claim 7, characterized in that In step S2, the high-speed mixing process includes stirring at a rotation speed of 1500-3000 rpm for 3-5 hours.

10. A use of the long-cycle-maintaining adhesive negative composite electrode according to any one of claims 1 to 6 or the long-cycle-maintaining adhesive negative composite electrode prepared by the preparation method according to any one of claims 7 to 9 in a lithium-ion battery, characterized in that: The preparation steps include: The long-cycle adhesive negative composite electrode, the positive electrode sheet and the separator are wound to form a battery core, which is then preheated, hot pressed, ultrasonically welded to the adapter, laser welded to the adapter, and coated with a core. The core is then combined and placed in a battery casing, and the top cover is welded to the battery casing. The battery is then baked, injected with a first liquid, formed, injected with a second liquid, and sealed with pins to obtain a lithium-ion battery.

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