Positive plate, lithium ion battery and preparation method
By setting a ceramic layer of boehmite and modified PVDF on the positive electrode, the problems of burrs and hard edges on the positive electrode of lithium-ion batteries are solved, the flexibility and production efficiency of the electrode are improved, the risk of breakage is reduced, and the manufacturing efficiency and performance of lithium-ion batteries are enhanced.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2025-11-26
- Publication Date
- 2026-03-13
AI Technical Summary
During the slitting or die-cutting process of lithium-ion battery positive electrode sheets, metal burrs may be generated at the edges, leading to internal short circuits. Furthermore, uneven stress release at the contact surface between the ceramic edge and the positive electrode coating can cause cracking and hard edge problems, affecting production efficiency.
A ceramic layer containing borosilicate, binder, and pore-forming agent is disposed along the length of the positive electrode sheet. Modified PVDF is preferred. The flexibility of the contact surface between the ceramic layer and the positive electrode active material layer is synergistically improved through the porous structure and the improved flexibility of the modified PVDF, thereby reducing the risk of wavy edges and strip breakage.
It effectively prevents wavy edges on the positive electrode, improves stress release during the electrode drying process, reduces the risk of breakage due to rolling, and enhances production efficiency and battery performance.
Smart Images
Figure CN121662726A_ABST
Abstract
Description
Technical Field
[0001] This invention relates to the field of battery technology, and in particular to a positive electrode, a lithium-ion battery, and a method for preparing them. Background Technology
[0002] During the manufacturing process of lithium-ion batteries, metal burrs (Al foil or electrode material debris) may be generated at the edges of the positive electrode sheets (such as LFP and NCM) during slitting or die-cutting. If the burrs are too long, they may pierce the separator, causing direct contact between the positive and negative electrode sheets and triggering an internal short circuit. Coating the edges of the positive electrode sheets with ceramic edges can effectively solve the problem of burrs at the edges. However, generally speaking, there will be uneven stress release at the contact surface between the ceramic edge and the positive electrode coating, resulting in cracking and hard edges. Furthermore, as the market demand for energy density of lithium-ion batteries continues to increase, the problem of hard edges between the slurry and the ceramic layer is becoming increasingly serious. This can lead to serious problems such as strip breakage during the electrode rolling process, greatly affecting the production schedule and resulting in low battery manufacturing efficiency. Summary of the Invention
[0003] The purpose of this invention is to overcome the shortcomings and defects of the prior art and to provide a positive electrode, a lithium-ion battery, and a preparation method thereof.
[0004] To achieve the above objectives, this application adopts the following solution:
[0005] A positive electrode sheet includes a positive current collector and a coating disposed on the positive current collector; the coating includes a central positive active coating and ceramic layers disposed on both sides of the positive active coating along the length direction of the positive electrode sheet; the ceramic layers include borosilicate and a binder.
[0006] As one form, the ceramic layer includes burlite, a binder, and a pore-forming agent; preferably, the binder is PVDF.
[0007] Preferably, the mass ratio of the borosilicate, binder, and pore-forming agent is (70-90):(5-15):(5-15); more preferably, it is 80:10:10.
[0008] Preferably, the pore-forming agent is one or a mixture of ammonium carbonate, ammonium bicarbonate, and azobisisobutyronitrile.
[0009] In another form, the adhesive is modified PVDF; the modified PVDF is prepared in the following manner:
[0010] 1) Dissolve a certain amount of PVDF in DMF, stir evenly, and then add hexamethylenediamine. Preferably, the mass ratio of PVDF to hexamethylenediamine is (30-50):1; more preferably, it is 40:1.
[0011] 2) Stir thoroughly at 60-80℃ for 1-2 hours; allow to return to room temperature, pour the reacted solution into deionized water to precipitate, filter, wash, and dry to obtain the intermediate product;
[0012] 4) Grind the intermediate product and polyethylene oxide in a mortar and mix them in a mixer at 180-200°C for 5-15 minutes; then pelletize and grind to obtain modified PDVF; preferably, the mass ratio of intermediate product to polyethylene oxide is (20-30):(70-80); preferably 25:75;
[0013] Preferably, the mass ratio of boehmite to binder is (70-90):(10-30); more preferably, it is 80:20.
[0014] The width of the ceramic layer on one side is 5-10 mm, and the width of the positive electrode active coating is 150-300 mm.
[0015] As a preferred embodiment, the ceramic layer consists of two layers arranged vertically, including a first ceramic layer close to the positive current collector and a second ceramic layer away from the positive current collector.
[0016] Preferably, the first ceramic layer comprises a pore-forming agent, boehmite, and PVDF adhesive;
[0017] Preferably, the mass ratio of pore-forming agent, boehmite, and PVDF adhesive is (10-15):(75-80):(5-15); more preferably, it is 10:80:10.
[0018] Preferably, the pore-forming agent is one or a mixture of ammonium carbonate, ammonium bicarbonate, and azobisisobutyronitrile.
[0019] Preferably, the second ceramic layer comprises borosilicate and adhesive; preferably, the mass ratio of borosilicate to modified PVDF adhesive is (74-80):(20-26).
[0020] The adhesive is PVDF or modified PVDF;
[0021] Preferably, the coating amount of the first ceramic layer and the second ceramic layer is independently 3.5-4.5 g / cm³. 3 The positive electrode active coating includes a positive electrode active material, a positive electrode conductive agent, and a positive electrode binder;
[0022] Preferably, the mass ratio of the positive electrode active material, the positive electrode conductive agent, and the positive electrode binder is (90-98):(1-5):(1-5);
[0023] Preferably, the positive electrode active material is lithium iron phosphate or a ternary positive electrode;
[0024] Preferably, the positive electrode conductive agent is one or a mixture of carbon black, conductive graphite, Ketjen black, acetylene black, carbon nanotubes, or carbon fiber.
[0025] Preferably, the positive electrode binder is one or a mixture of polyvinylidene fluoride, tetrafluoroethylene-hexafluoropropylene copolymer, tetrafluoroethylene-ethylene copolymer, vinylidene fluoride-hexafluoropropylene copolymer, vinylidene fluoride-trifluorochloroethylene, or vinylidene fluoride-tetrafluoroethylene copolymer.
[0026] The present invention also includes a method for preparing the positive electrode sheet, comprising the following steps: S1: preparing a positive electrode active slurry and a ceramic slurry; S2: applying the positive electrode active slurry to the middle position of the positive electrode current collector along its length direction, and applying the ceramic slurry to the edge portion of the positive electrode current collector along its length direction.
[0027] The positive electrode active slurry is prepared by mixing a positive electrode binder and a positive electrode conductive agent; adding the positive electrode active material to the mixture in two batches and stirring thoroughly; adding a solvent and performing a viscosity test; preferably, the solvent is N-methylpyrrolidone, and the viscosity of the positive electrode active slurry is less than 13000.
[0028] Preferably, the ceramic slurry is prepared by the following method: mixing the binder and solvent; slowly adding boehmite powder, optionally including a pore-forming agent, to the mixture; first, pre-dispersing by slow stirring at a certain speed, then fast stirring; subsequently, adding the remaining solvent; and then entering a low-speed stirring mode for dilution and final viscosity adjustment; preferably, the slow stirring speed is 10-30 rpm; more preferably 20 rpm; and the fast stirring speed is 1000-3000 rpm; more preferably 2000 rpm.
[0029] Preferably, the solvent is N-methylpyrrolidone;
[0030] Preferably, the viscosity of the ceramic slurry is between 5000 and 7000.
[0031] The present invention also includes a lithium-ion battery comprising the aforementioned positive electrode.
[0032] The present invention also includes a method for preparing the lithium-ion battery, comprising the following steps: assembling the corresponding positive electrode and negative electrode into a battery by means of winding, assembling, liquid injection, formation and aging.
[0033] Compared with the prior art, the beneficial effects of this application are as follows:
[0034] This invention provides a means to effectively prevent wavy edges from forming on the positive electrode. A certain proportion of pore-forming agent is added to the ceramic layer. The porous structure helps release stress during the electrode drying process and increases the flexibility of the contact area between the ceramic layer and the positive electrode active material layer. The addition of modified PVDF improves the wavy edges caused by excessive hardness in the junction area between the ceramic layer and the positive electrode active material layer by reducing the crystallinity of the PVDF adhesive and increasing flexibility, thereby reducing the risk of electrode breakage due to crushing. As a preferred embodiment, the pore-forming agent and modified PVDF are added as the first ceramic layer and the second ceramic layer, respectively, which can synergistically improve the performance of the positive electrode. Attached Figure Description
[0035] Figure 1 This is an overall schematic diagram of the positive electrode sheet of the present invention;
[0036] Figure 2 These are grating images of the positive electrode sheet during laser cutting in different embodiments of the present invention. Detailed Implementation
[0037] The present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention.
[0038] See appendix Figure 1 As shown, a positive electrode sheet includes a positive current collector 1 and a coating disposed on the positive current collector; the coating includes a central positive active coating 3 and ceramic layers 2 disposed on both sides of the positive active coating along the length direction of the positive electrode sheet.
[0039] Comparative Example 1: Preparation of positive electrode slurry and positive electrode sheet. The weight fraction ratio of positive electrode active material, positive electrode conductive agent and positive electrode binder is 94.9wt%: 2.5wt%: 2.6wt%. The positive electrode active material is lithium iron phosphate, the conductive additives are carbon black and carbon nanotubes, the ratio of carbon black and carbon nanotubes is 1wt%: 1.5wt%, and the binder is polyvinylidene fluoride.
[0040] The preparation method of the positive electrode slurry is as follows:
[0041] 1) First, prepare a polyvinylidene fluoride adhesive solution with a solid content of 6% using NMP for later use;
[0042] 2) Mix the polyvinylidene fluoride adhesive in (1) with carbon nanotubes according to the above weight ratio and stir thoroughly;
[0043] 3) Add conductive carbon black to the mixture described in (2) and stir thoroughly;
[0044] 4) Add a certain proportion of positive electrode active material (60% of the total amount of positive electrode active material) to the mixture described in (3), stir at low speed of 20 rpm for 30 min, scrape the material, stir at low speed of 200 rpm for 15 min, and then stir at high speed of 2000 rpm for 30 min.
[0045] 5) Add the remaining positive electrode active material to the mixture described in (4), stir at a low speed of 20 rpm for 30 min, scrape the material, stir at a low speed of 200 rpm for 15 min, and then stir at a high speed of 2000 rpm for 30 min.
[0046] 6) Add a certain proportion of NMP to the slurry in (5) and stir at 1000 rpm for 60 min;
[0047] 7) Test the viscosity of the slurry. If the viscosity of the slurry is below 13000, it can be discharged. If the viscosity is too high, continue to add NMP to adjust the viscosity of the slurry to the design value of less than 13000, and then discharge the slurry under vacuum.
[0048] The method for preparing ceramic slurry is as follows:
[0049] 8) Prepare a polyvinylidene fluoride adhesive solution with a solid content of 6% using NMP for later use;
[0050] 9) Slowly add the borosilicate powder to (8), first stir slowly at 20 rpm for pre-dispersion, then stir quickly at 2000 rpm (while adding a cooling water pipe throughout the process), then add the remaining solvent NMP, enter the low-speed stirring mode at 15 rpm, adjust the viscosity of the ceramic slurry to the design value between 5000-7000, and then vacuum discharge the material.
[0051] The mass ratio of boehmite to the binder polyvinylidene fluoride is 80:20;
[0052] The positive electrode active slurry is applied to the middle position of the positive electrode current collector aluminum foil along its length, and the ceramic slurry is applied to the edge part of the positive electrode current collector aluminum foil along its length to form the positive electrode sheet. The single-sided width of the ceramic layer is 5.5mm; the width of the positive electrode active coating is 260mm.
[0053] Example 1: The difference from Comparative Example 1 is that, in step (9), in addition to adding a certain proportion of boehmite powder, Example 1 adds 10% of pore-forming agents ammonium carbonate, ammonium bicarbonate and azobisisobutyronitrile, in the ratio of the three to 3:5:2, and the ratio of boehmite:pore-forming agent and binder PVDF is 80:10:10.
[0054] Example 2: The difference from Comparative Example 1 is that the adhesive is modified PVDF, i.e., in step 8), a modified PVDF adhesive solution with a solid content of 6% is prepared using NMP for later use; wherein, the modified PVDF is prepared by the following steps:
[0055] 1) Dissolve a certain amount of PVDF in DMF, stir well, and then add hexamethylenediamine; the mass ratio of PVDF to hexamethylenediamine is 40:1.
[0056] 2) Stir thoroughly at 75℃ for 1-2 hours; allow to return to room temperature, pour the reacted solution into deionized water to precipitate, filter, wash, and dry to obtain the intermediate product;
[0057] 3) Place the intermediate product and polyethylene oxide into a mortar and grind them. Stir and mix them in a mixer at 180-200℃ for 5-15 minutes. Then pelletize and grind to obtain modified PDVF. Preferably, the mass ratio of intermediate product to polyethylene oxide is 25:75.
[0058] Example 3: The difference from Comparative Example 1 is that two ceramic slurries were prepared, namely the first ceramic slurry and the second ceramic slurry.
[0059] The first ceramic slurry was prepared using the method described in Example 1 above;
[0060] The second ceramic slurry was prepared using the method described in Example 2 above.
[0061] A first ceramic slurry is coated onto a surface near the positive electrode current collector to form a first ceramic layer. A second ceramic slurry is then coated onto the first ceramic layer to form a second ceramic layer. The coating weights of both the first and second ceramic layers are independently 4.0 g / cm³. 3 .
[0062] The effects are illustrated using Comparative Example 1 and Examples 1-3 as examples. See Table 1, which shows the porosity of the ceramic coatings prepared in Examples 1-3 and Comparative Example 1, the rolling breakage rate of the positive electrode sheet, and the wavy edge condition. Figure 2 These are grating images of the positive electrode sheets prepared by laser cutting in Examples 1-3 and Comparative Example 1.
[0063] Table 1
[0064] Porosity of ceramic coating Electrode breakage frequency per 1000m Wavy edge situation Comparative Example 1 28.76％ 6 2.0 / 1.8 / 1.9 / 2.0 Example 1 35.87％ 2 1.5 / 1.5 / 1.4 / 1.5 Example 2 29.45％ 3 1.6 / 1.7 / 1.7 / 1.6 Example 3 31.41％ 1 (Caused by ear injury) 1.4 / 1.3 / 1.4 / 1.2
[0065] In the electrode laser cutting process, the equipment's grating shines onto the electrode. If the electrode surface is uneven, the equipment may misinterpret the presence of air bubbles when the electrode vibrates, creating a false impression for the R&D personnel's assessment of electrode quality. From the above process problem records and laser-cut electrode grating photographs, it is clearly evident that the wavy edge problem in Comparative Example 1 is extremely severe, causing the electrode to break six times during the 1000m rolling process, significantly reducing production efficiency. In Example 1, due to the addition of 10% pore-forming agent, the stress during coating drying is greatly released, and the area where the ceramic layer meets the positive electrode active coating does not exhibit a slight wavy edge phenomenon, although it is not obvious. Example 2 only added modified PVDF to the ceramic layer, which did not significantly improve the wavy edge of the ceramic, and the wavy edge phenomenon still existed. The electrode sheet produced in Example 3 combined modified PVDF with a pore-forming agent. The area where the ceramic layer and the positive electrode active coating were in good condition, the surface was flat and there were no abnormalities. There was only one breakage during rolling, which was caused by a scratch on the electrode tab. When the electrode sheet was placed flat on the glass plate, the unevenness was reduced from 2.0 mm in Comparative Example 1 to 1.4 mm, which is within the normal standard.
[0066] The foregoing has shown and described the basic principles, main features, and advantages of the present invention. It will be apparent to those skilled in the art that the present invention is not limited to the details of the above exemplary embodiments, and that the present invention can be implemented in other specific forms without departing from the spirit or basic features of the present invention.
[0067] Therefore, the embodiments should be regarded as exemplary and non-limiting in all respects, and the scope of the invention is defined by the appended claims rather than the foregoing description. Thus, it is intended that all variations falling within the meaning and scope of the equivalents of the claims be included within the invention.
[0068] Furthermore, it should be understood that although this specification describes embodiments, not every embodiment contains only one independent technical solution. This narrative style is merely for clarity. Those skilled in the art should consider the specification as a whole, and the technical solutions in each embodiment can also be appropriately combined to form other embodiments that can be understood by those skilled in the art.
Claims
1. A positive electrode plate, characterized in that, It includes a positive current collector and a coating disposed on the positive current collector; the coating includes a central positive active coating and ceramic layers disposed on both sides of the positive active coating along the length direction of the positive electrode sheet; the ceramic layers include borosilicate and a binder.
2. The positive electrode sheet according to claim 1, characterized in that, The ceramic layer comprises burlite, a binder, and a pore-forming agent; preferably, the binder is PVDF. Preferably, the mass ratio of the borosilicate, binder, and pore-forming agent is (70-90):(5-15):(5-15); more preferably, it is 80:10:
10. Preferably, the pore-forming agent is one or a mixture of ammonium carbonate, ammonium bicarbonate, and azobisisobutyronitrile.
3. The positive electrode sheet according to claim 1, characterized in that, The adhesive is modified PVDF; the modified PVDF is prepared in the following manner: 1) Dissolve a certain amount of PVDF in DMF, stir evenly, and then add hexamethylenediamine. Preferably, the mass ratio of PVDF to hexamethylenediamine is (30-50):1; more preferably, it is 40:
1. 2) Stir thoroughly at 60-80℃ for 1-2 hours; allow to return to room temperature, pour the reacted solution into deionized water to precipitate, filter, wash, and dry to obtain the intermediate product; 3) Place the intermediate product and polyethylene oxide into a mortar and grind them. Stir and mix them in a mixer at 180-200℃ for 5-15 minutes. Then, granulate and grind them to obtain modified PDVF. Preferably, the mass ratio of intermediate product to polyethylene oxide is (20-30):(70-80); more preferably, it is 25:
75. Preferably, the mass ratio of borosilicate to binder is (70-90):(10-30); more preferably, it is 80:
20.
4. The positive electrode sheet according to claim 1, characterized in that, The width of the ceramic layer on one side is 5-10 mm, and the width of the positive electrode active coating is 150-300 mm.
5. The positive electrode sheet according to claim 1, characterized in that, The ceramic layer consists of two layers arranged vertically, including a first ceramic layer close to the positive electrode current collector and a second ceramic layer away from the positive electrode current collector. Preferably, the first ceramic layer comprises a pore-forming agent, boehmite, and PVDF adhesive; Preferably, the mass ratio of pore-forming agent, boehmite, and PVDF adhesive is (10-15):(75-80):(5-15); more preferably, it is 10:80:
10. Preferably, the pore-forming agent is one or a mixture of ammonium carbonate, ammonium bicarbonate, and azobisisobutyronitrile. Preferably, the second ceramic layer comprises borosilicate and adhesive; preferably, the mass ratio of borosilicate to modified PVDF adhesive is (74-80):(20-26). The adhesive is PVDF or modified PVDF; Preferably, the coating amount of the first ceramic layer and the second ceramic layer is independently 3.5-4.5 g / cm³. 3 .
6. The positive electrode sheet according to claim 1, characterized in that, The positive electrode active coating includes a positive electrode active material, a positive electrode conductive agent, and a positive electrode binder; Preferably, the mass ratio of the positive electrode active material, the positive electrode conductive agent, and the positive electrode binder is (90-98):(1-5):(1-5); Preferably, the positive electrode active material is lithium iron phosphate or a ternary positive electrode; Preferably, the positive electrode conductive agent is one or a mixture of carbon black, conductive graphite, Ketjen black, acetylene black, carbon nanotubes, or carbon fiber. Preferably, the positive electrode binder is one or a mixture of polyvinylidene fluoride, tetrafluoroethylene-hexafluoropropylene copolymer, tetrafluoroethylene-ethylene copolymer, vinylidene fluoride-hexafluoropropylene copolymer, vinylidene fluoride-trifluorochloroethylene, or vinylidene fluoride-tetrafluoroethylene copolymer.
7. A method for preparing a positive electrode sheet according to any one of claims 1-6, characterized in that, The process includes the following steps: S1: preparing a positive electrode active slurry and a ceramic slurry; S2: applying the positive electrode active slurry to the middle position of the positive electrode current collector along its length and applying the ceramic slurry to the edge portion of the positive electrode current collector along its length.
8. The preparation method according to claim 7, characterized in that, The positive electrode active slurry is prepared by mixing a positive electrode binder and a positive electrode conductive agent; adding the positive electrode active material to the mixture in two batches and stirring thoroughly; adding a solvent and performing a viscosity test; preferably, the solvent is N-methylpyrrolidone, and the viscosity of the positive electrode active slurry is less than 13000. Preferably, the ceramic slurry is prepared by the following method: mixing the binder and solvent; slowly adding boehmite powder, optionally including a pore-forming agent, to the mixture; first, pre-dispersing by slow stirring at a certain speed, then fast stirring; subsequently, adding the remaining solvent; and then entering a low-speed stirring mode for dilution and final viscosity adjustment; preferably, the slow stirring speed is 10-30 rpm; more preferably 20 rpm; and the fast stirring speed is 1000-3000 rpm; more preferably 2000 rpm. Preferably, the solvent is N-methylpyrrolidone; Preferably, the viscosity of the ceramic slurry is between 5000 and 7000.
9. A lithium-ion battery, characterized in that, Includes the positive electrode sheet as described in any one of claims 1-6.
10. A method for preparing a lithium-ion battery according to claim 9, characterized in that, The process includes the following steps: assembling the corresponding positive and negative electrode sheets into a battery by winding, assembling, liquid injection, formation, and aging.