Secondary battery integrated positive electrode sheet and preparation method and application thereof

Abstract

This invention discloses an integrated positive electrode sheet for secondary batteries, its preparation method, and its application. The preparation method includes the following steps: mixing positive electrode active material, conductive agent, binder, alkali metal hydroxide powder, and organic solvent; coating the resulting positive electrode slurry onto the surface of an aluminum foil current collector; and drying it at 100-170 °C, causing the alkali metal hydroxide powder to corrode the surface of the aluminum foil current collector in situ, forming pits. The depth of the pits is 1%-10% of the thickness of the aluminum foil current collector, thus obtaining the integrated positive electrode sheet. This invention eliminates the need for additional primer coating or special current collector processes. By introducing alkali metal hydroxide powder into conventional positive electrode slurry, the in-situ micro-corrosion effect of the powder on the aluminum foil current collector during drying forms an anchoring structure to improve adhesion. Simultaneously, it balances the mechanical strength of the electrode sheet with battery cycle and high-temperature storage performance, making it easy to achieve large-scale industrial production.

Description

Technical Field

[0001] This invention relates to the field of secondary battery electrode technology, specifically to an integrated positive electrode sheet for secondary batteries, its preparation method, and its application. Background Technology

[0002] Secondary batteries (such as lithium-ion and sodium-ion batteries) have broad application prospects in large-scale energy storage and low-speed electric vehicles. The positive electrode is the core component of a secondary battery. The conventional manufacturing process involves mixing positive electrode active materials, conductive agents, binders, and organic solvents to form a slurry, coating it onto the surface of an aluminum foil current collector, and then drying and rolling it to produce the finished electrode. In actual production and use, the adhesion between the positive electrode coating and the aluminum foil current collector directly affects battery performance and lifespan. If the adhesion is insufficient, the coating is prone to peeling and powdering during rolling, slitting, and assembly. During battery charge-discharge cycles, the repeated expansion and contraction of the active material also exacerbates coating peeling, leading to increased internal resistance, accelerated capacity decay, and decreased cycle stability.

[0003] To address the issue of insufficient adhesion of the positive electrode coating, existing technologies primarily employ two approaches: First, pre-coating the aluminum foil surface with a conductive carbon primer enhances the adhesion between the coating and the current collector. However, this approach requires specialized primer coating equipment and processes, increasing production complexity, and the high cost of carbon materials and coating makes it unsuitable for low-cost industrial production. Second, using aluminum foil with a microporous surface as the current collector leverages the physical interlocking effect of the micropores to improve adhesion. However, microporous aluminum foil requires a special perforation process, which is complex, has a low yield, and results in significantly higher material costs than ordinary aluminum foil, also leading to high production costs.

[0004] Furthermore, secondary battery systems are extremely sensitive to moisture. Trace amounts of moisture remaining during electrode fabrication can react with sodium / lithium salts in the electrolyte to form hydrofluoric acid (HF), which corrodes the electrode materials and current collectors, disrupts battery interface stability, and reduces battery cycle life and high-temperature storage performance. Current technologies that improve adhesion cannot simultaneously address the issue of residual moisture on the electrodes, making it difficult to balance adhesion, production costs, and electrochemical performance.

[0005] In summary, existing technologies for improving the adhesion of positive electrode sheets in secondary batteries suffer from drawbacks such as cumbersome processes, high costs, and inability to simultaneously improve electrochemical performance. There is an urgent need to develop a positive electrode sheet and its preparation method that is simple to process, low in cost, and can significantly improve coating adhesion while optimizing battery electrochemical performance. Summary of the Invention

[0006] The purpose of this invention is to solve the above-mentioned technical problems and provide an integrated positive electrode sheet for secondary batteries, its preparation method and application.

[0007] The above-mentioned objective of the present invention is achieved through the following technical solution:

[0008] The first aspect of this invention provides a method for preparing an integrated positive electrode sheet, comprising the following steps:

[0009] (1) A positive electrode material is obtained by mixing positive electrode active material, conductive agent, binder and alkali metal hydroxide powder, wherein the amount of alkali metal hydroxide powder added is 0.1%-5% of the mass of the positive electrode material; the positive electrode material is mixed with organic solvent to obtain positive electrode slurry;

[0010] (2) The positive electrode slurry is coated on the surface of the aluminum foil current collector, and the coated aluminum foil current collector is dried at 100-170°C to allow the alkali metal hydroxide powder to corrode the surface of the aluminum foil current collector in situ to form pits. The integrated positive electrode sheet is obtained by roll pressing. The depth of the pits is 1%-10% of the thickness of the aluminum foil current collector.

[0011] This invention provides a method for preparing an integrated electrode. By introducing alkali metal hydroxide powder into a conventional positive electrode slurry, and utilizing its in-situ chemical reaction during the drying process, the microstructuring of the aluminum foil current collector surface and the anchoring of the positive electrode coating are simultaneously achieved. The specific mechanism is as follows:

[0012] During the drying stage of the positive electrode, the alkali metal hydroxide powder in the slurry absorbs trace amounts of residual moisture from the system and environment, forming a locally strongly alkaline microenvironment on the surface of the aluminum foil current collector. First, the alkali metal hydroxide powder reacts with the dense alumina passivation film on the surface of the aluminum foil current collector: Al₂O₃ + 2 MOH → 2 MAlO₂ + H₂O (where M represents an alkali metal). After the localized alumina passivation film is damaged, the high temperature environment during drying prevents the timely formation and repair of a new oxide film. The exposed aluminum metal continues to react with water and hydroxides in the alkaline microenvironment: 2Al + 2MOH + 2H₂O → 2MAlO₂ + 3H₂↑. This reaction occurs only in the localized area where the alkali metal hydroxide powder contacts the aluminum foil current collector, forming uniformly distributed micron-sized pits on the surface of the aluminum foil current collector, increasing the actual surface area of ​​the aluminum foil current collector. By adjusting the particle size, dosage, and drying process parameters of the alkali metal hydroxide powder, the pitting depth can be precisely controlled within the range of 1%-10% of the aluminum foil current collector thickness. During the drying process, the positive electrode slurry gradually solidifies, and the positive electrode coating, composed of the positive electrode active material, conductive agent, and binder, embeds itself into the pits, forming an "anchoring" effect, thereby significantly improving the peel strength between the positive electrode coating and the aluminum foil current collector. Simultaneously, the alkali metal hydroxide powder continuously consumes trace amounts of moisture in the system throughout the process, and the resulting aluminate is uniformly distributed at the interface between the positive electrode coating and the current collector, effectively improving interface stability and thus enhancing the material's cycle stability.

[0013] Further, in step (1), the mass ratio of the positive electrode active material, conductive agent, binder and alkali metal hydroxide powder is (90-95):(2-3):(2-4):(0.1-5).

[0014] Further, in step (1), the positive electrode active material is selected from sodium-ion battery positive electrode active materials or lithium-ion battery positive electrode active materials; the sodium-ion battery positive electrode active material is selected from one or more of sodium iron phosphate, sodium iron pyrophosphate, and layered oxides; the lithium-ion battery positive electrode active material is selected from one or more of lithium iron phosphate, nickel-cobalt-manganese ternary materials, nickel-cobalt-aluminum ternary materials, lithium cobalt oxide, lithium manganese oxide, and lithium manganese iron phosphate.

[0015] Further, in step (1), the conductive agent is carbon black; the binder is polyvinylidene fluoride (PVDF).

[0016] Further, in step (1), the alkali metal hydroxide powder is selected from one or more of sodium hydroxide (NaOH) powder, lithium hydroxide (LiOH) powder and potassium hydroxide (KOH) powder.

[0017] On the one hand, the alkali metal hydroxide powder acts as an in-situ desiccant, effectively reducing the residual moisture content of the electrode and inhibiting the generation of HF in the subsequent battery, thus reducing the corrosion of electrode materials and aluminum foil current collectors by HF. On the other hand, the aluminate generated by the reaction forms a uniform coating layer at the positive electrode interface, which acts as a solid electrolyte interface film, stabilizing the electrode / electrolyte interface and further improving the cycle life and high-temperature storage performance of the battery.

[0018] Further, in step (1), the particle size of the alkali metal hydroxide powder is 0.3-30 μm, preferably 1-15 μm.

[0019] Furthermore, in step (1), the moisture content of the alkali metal hydroxide powder is less than 500 ppm to prevent the powder from absorbing moisture and reacting prematurely during the slurry preparation stage.

[0020] Further, in step (1), the organic solvent is N-methylpyrrolidone (NMP).

[0021] Furthermore, in step (1), the solid content of the positive electrode slurry is 50%-70%.

[0022] Further, in step (2), the positive electrode slurry is coated onto the surface of the aluminum foil current collector using an extrusion coating machine. The coating speed is 1.5-15 m / min, and the coating surface density is 150-250 g / m³. 2 .

[0023] Furthermore, in step (2), the drying process is carried out at a constant temperature, and the drying time is 0.5-2 hours.

[0024] The second aspect of the present invention provides an integrated positive electrode sheet prepared by the preparation method described in the first aspect.

[0025] The third aspect of this invention provides an application of the integrated positive electrode sheet described in the second aspect in the assembly of a secondary battery.

[0026] Furthermore, the secondary battery is a sodium-ion battery or a lithium-ion battery.

[0027] A fourth aspect of the present invention provides a secondary battery comprising the integrated positive electrode, negative electrode, separator, and electrolyte described in the second aspect.

[0028] The above-described technical solution of the present invention has the following beneficial effects:

[0029] 1. This invention provides a method for preparing an integrated positive electrode sheet. By introducing alkali metal hydroxide powder into a conventional positive electrode slurry, the powder is used to form an anchoring structure to enhance adhesion by utilizing the in-situ micro-corrosion effect of the powder on the aluminum foil current collector during the drying process.

[0030] 2. The corrosion reaction in the preparation of the integrated positive electrode sheet in this invention is completed simultaneously with the oven drying process of conventional positive electrode sheets, without adding any extra production steps. It is fully compatible with existing lithium-ion battery and sodium-ion battery coating production lines, making it easy to achieve large-scale industrial production. Compared with existing carbon-coated aluminum foil and microporous aluminum foil technologies, it eliminates the complex processes of primer coating or current collector perforation, significantly reducing production costs. Attached Figure Description

[0031] Figure 1 An optical microscope image (scale bar 20 μm) of the aluminum foil current collector surface after removing the positive electrode coating from the integrated positive electrode sheet prepared in Example 1.

[0032] Figure 2 An optical microscope image (scale bar 20 μm) of the aluminum foil current collector surface of the integrated positive electrode sheet prepared in Comparative Example 1 after the positive electrode coating is removed. Detailed Implementation

[0033] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains. The terminology used herein in the specification of this invention is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention. The term "and / or" as used herein includes any and all combinations of one or more of the associated listed items.

[0034] The present invention will be further described below with reference to the accompanying drawings and specific embodiments, so that those skilled in the art can better understand and implement the present invention. However, the embodiments described are not intended to limit the present invention.

[0035] Unless otherwise specified, the experimental methods used in the following examples are conventional methods, and the materials and reagents used are commercially available.

[0036] Example 1

[0037] A method for preparing an integrated positive electrode sheet includes the following steps:

[0038] (1) Sodium iron pyrophosphate, carbon black, PVDF and NaOH powder (D50=1 μm, moisture 300 ppm) were weighed in a mass ratio of 94:2.5:3:0.5 and mixed to obtain the positive electrode material. The amount of NaOH powder added was 0.5% of the mass of the positive electrode material. It was mixed with NMP to prepare the positive electrode slurry and the solid content of the slurry was controlled to be 55%.

[0039] (2) The positive electrode slurry was coated onto the surface of a 12 μm thick aluminum foil current collector using an extrusion coating machine. The coating speed was 15 m / min, and the coating surface density was 180 g / m². 2 After being dried in an oven at 120 ℃ for 1 h, a positive electrode coating is formed, which is then rolled to obtain an integrated positive electrode sheet.

[0040] Example 2

[0041] A method for preparing an integrated positive electrode sheet is basically the same as that in Example 1, except that in step (1), sodium iron pyrophosphate, carbon black, PVDF and LiOH powder (D50=10 μm, moisture 300 ppm) are weighed in a mass ratio of 94:2:3:1 to a total of 1000 g, and the amount of LiOH powder added is 1.0% of the mass of the positive electrode material.

[0042] Example 3

[0043] A method for preparing an integrated positive electrode sheet is basically the same as that in Example 1, except that: in step (1), sodium iron pyrophosphate, carbon black, PVDF and NaOH powder (D50=0.3 μm, moisture 300 ppm) are weighed in a mass ratio of 94:2.9:3:0.1, and the amount of NaOH powder added is 0.1% of the mass of the positive electrode material; in step (2), the drying temperature is 100℃.

[0044] Example 4

[0045] A method for preparing an integrated positive electrode sheet is basically the same as that in Example 1, except that: in step (1), sodium iron pyrophosphate, carbon black, PVDF and NaOH powder (D50=30 μm, moisture 300 ppm) are weighed in a mass ratio of 90:2:3:5 to a total of 1000 g, and the amount of NaOH powder added is 5% of the mass of the positive electrode material; in step (2), the drying temperature is 170 ℃.

[0046] Example 5

[0047] A method for preparing an integrated positive electrode sheet is basically the same as that in Example 1, except that: in step (1), sodium iron pyrophosphate, carbon black, PVDF and NaOH powder (D50=5 μm, moisture 300 ppm) are weighed in a mass ratio of 93:2:3:2 to a total of 1000 g, and the amount of NaOH powder added is 2.0% of the mass of the positive electrode material; in step (2), the drying temperature is 140 ℃.

[0048] Example 6

[0049] A method for preparing an integrated positive electrode sheet is basically the same as that in Example 1, except that: in step (1), sodium iron pyrophosphate, carbon black, PVDF and NaOH powder (D50=15 μm, moisture 300 ppm) are weighed in a mass ratio of 92:2:3:3 to a total of 1000 g, and the amount of NaOH powder added is 3% of the mass of the positive electrode material; in step (2), the drying temperature is 150 ℃.

[0050] Example 7

[0051] A method for preparing an integrated positive electrode sheet is basically the same as that in Example 1, except that: in step (1), sodium iron pyrophosphate, carbon black, PVDF and NaOH powder (D50=20 μm, moisture 300 ppm) are weighed in a mass ratio of 91:2:3:4 to a total of 1000 g, and the amount of NaOH powder added is 4% of the mass of the positive electrode material; in step (2), the drying temperature is 160 ℃.

[0052] Example 8

[0053] A method for preparing an integrated positive electrode sheet is basically the same as that in Example 1, except that: in step (1), sodium iron pyrophosphate, carbon black, PVDF and NaOH powder (D50=5 μm, moisture 300 ppm) are weighed in a mass ratio of 90:2:3:5 to a total of 1000 g, and the amount of NaOH powder added is 5% of the mass of the positive electrode material; in step (2), the drying temperature is 140 ℃.

[0054] Comparative Example 1

[0055] A method for preparing an integrated positive electrode sheet includes the following steps:

[0056] (1) Weigh out 1000 g of sodium iron pyrophosphate, carbon black and PVDF in a mass ratio of 94:3:3 and mix them with NMP to prepare a positive electrode slurry, controlling the solid content of the slurry to be 55%.

[0057] (2) The positive electrode slurry was coated onto the surface of a 12 μm thick aluminum foil current collector using an extrusion coating machine. The coating speed was 15 m / min, and the coating surface density was 180 g / m². 2 After being dried in an oven at 120 ℃ for 1 h, a positive electrode coating is formed, which is then rolled to obtain an integrated positive electrode sheet.

[0058] Comparative Example 2

[0059] A method for preparing an integrated positive electrode sheet is basically the same as that in Example 1, except that: in step (1), sodium iron pyrophosphate, carbon black, PVDF and NaOH powder (D50=5 μm, moisture 300 ppm) are weighed in a mass ratio of 88:2:3:7 to a total of 1000 g, and the amount of NaOH powder added is 7% of the mass of the positive electrode material; in step (2), the drying temperature is 140 ℃.

[0060] Comparative Example 3

[0061] A method for preparing an integrated positive electrode sheet is basically the same as that in Example 1, except that: in step (1), sodium iron pyrophosphate, carbon black, PVDF and NaOH powder (D50=5 μm, moisture 300 ppm) are weighed in a mass ratio of 93:2:3:2 to a total of 1000 g, and the amount of NaOH powder added is 2.0% of the mass of the positive electrode material; in step (2), the drying temperature is 90 ℃.

[0062] Comparative Example 4

[0063] A method for preparing an integrated positive electrode sheet is basically the same as that in Example 1, except that: in step (1), sodium iron pyrophosphate, carbon black, PVDF and NaOH powder (D50=5 μm, moisture 300 ppm) are weighed in a mass ratio of 93:2:3:2 to a total of 1000 g, and the amount of NaOH powder added is 2.0% of the mass of the positive electrode material; in step (2), the drying temperature is 200 ℃.

[0064] Test Example 1

[0065] The integrated positive electrode sheets prepared in Example 1 and Comparative Example 1 were respectively immersed in N-methylpyrrolidone (NMP) by heating to remove the positive electrode coating adhering to the surface. The surface of the aluminum foil current collector was then observed using an optical microscope. The test results are as follows: Figure 1 and Figure 2 As shown. Figure 1 The results show that after in-situ corrosion by alkali metal hydroxide powder, uniformly distributed micron-sized pits were formed on the surface of the aluminum foil current collector. Figure 2 The comparison aluminum foil current collector without added alkali metal hydroxide powder showed a smooth and flat surface with no obvious corrosion defects.

[0066] Test Example 2

[0067] The integrated positive electrode sheets prepared in Examples 1-8 and Comparative Examples 1-4 were subjected to peel strength and tensile strength tests, and the test methods are as follows:

[0068] (1) Peel strength test: Cut the positive electrode sheet into strips 25 mm wide and 300 mm long, ensuring that the edges are neat and burr-free; flatly paste 3M 610 test tape on the surface of the positive electrode sheet, and roll the tape back and forth 3 times with a 2 kg standard pressure roller at a speed of 300 mm / min to ensure that the tape and the positive electrode sheet are tightly bonded without air bubbles; fix one end of the positive electrode sheet with tape to the lower clamp of the tensile testing machine, fold the free end of the tape 180° in the opposite direction and clamp it to the upper clamp; stretch at a constant speed of 200 mm / min, and the equipment automatically records the force curve of the peeling process; ignore the 25 mm unsteady area at the beginning and end of the curve, take the data of the middle 50 mm stable section to calculate the average peel force, peel strength (N / mm) = average peel force (N) / sample width (mm).

[0069] (2) Tensile strength test: Cut the electrode sheet into strips 25 mm wide and 100 mm long, ensuring that the edges of the sample are flat and free of burrs and wrinkles; use a rubber-surface flat-push clamp, and in a standard laboratory environment of 23 ± 2 ℃ and 50 ± 5% RH, set an appropriate preload, a tensile speed of 10 mm / min, and a corresponding data acquisition frequency; start the equipment to record the force-displacement curve and stress-strain curve of the entire tensile process. Tensile strength (MPa) = maximum tensile force (N) / original cross-sectional area of ​​the sample (mm²) 2 Tensile strength testing can determine whether the pitting on the surface of the aluminum foil current collector is too deep, or even penetrates the aluminum foil, significantly reducing the mechanical properties and conductivity of the positive electrode.

[0070] The integrated positive electrode sheets prepared in Examples 1-8 and Comparative Examples 1-4 were used to assemble CR2032 coin cells. A sodium metal sheet was used as the counter electrode, and a 9 μm thick polyethylene film was used as the separator. Sodium hexafluorophosphate was dissolved in a mixed solvent of ethylene carbonate (EC) and propylene carbonate (PC) at a volume ratio of 1:1 to prepare an electrolyte with a sodium hexafluorophosphate concentration of 1 mol / L. The electrochemical performance of the assembled CR2032 coin cells was tested, including the initial coulombic efficiency and the capacity retention after 100 charge-discharge cycles. The test methods are as follows:

[0071] (1) Initial coulombic efficiency test: The sodium-ion battery was left to stand at 60 °C for 40 min, then charged at a rate of 0.1 C to the upper limit of activation voltage (3.8 V), and then discharged to the lower limit of activation voltage (1.6 V). The initial coulombic efficiency was measured. Initial coulombic efficiency = initial discharge capacity / initial charge capacity.

[0072] (2) Capacity retention rate: First, capacity calibration was performed at a 1C rate, and the initial discharge capacity was recorded as C0. Then, charge-discharge cycles were performed at a constant 1C rate (charged to 3.8 V, discharged to 1.6 V), and the discharge capacity C of the 100th cycle was recorded. 100 Capacity retention ratio R=C 100 / C0 × 100%.

[0073] The test results are shown in Table 1:

[0074] Table 1

[0075]

[0076] This invention can precisely control the depth of pitting on the surface of aluminum foil by adjusting the type, particle size, amount added, and drying temperature of alkali metal hydroxide powder, thereby achieving a flexible balance between the adhesion, mechanical strength, and electrochemical performance of the positive electrode sheet.

[0077] Comparative Example 1, with its positive electrode sheet without alkali metal hydroxide powder, maintained a smooth surface, and the adhesion between the coating and the aluminum foil current collector was moderate. Its various battery electrochemical performance parameters served as a benchmark for this invention. Under the parameter combination of Example 1, uniform pitting of suitable depth could be formed on the surface of the aluminum foil current collector, increasing the electrode sheet peel strength by approximately 80% compared to Comparative Example 1, while only slightly decreasing the tensile strength. Simultaneously, the in-situ dehydration by NaOH powder and the resulting sodium aluminate interface layer effectively improved the battery electrochemical performance. Example 2, using relatively weakly alkaline LiOH powder, still achieved effective pitting formation, demonstrating a significant performance improvement.

[0078] To ensure a similar particle count, the amount of NaOH powder added increased with increasing particle size. In Example 3, using smaller particle size, lower NaOH powder, and a lower drying temperature, only slight corrosion occurred on the aluminum foil current collector surface, and the mechanical strength of the electrode remained largely unaffected, but the adhesion improvement was limited. As the alkaline powder particle size increased, the amount added increased, and the drying temperature rose, the pitting depth on the aluminum foil current collector surface gradually increased. In Example 4, the pitting depth approached 10% of the aluminum foil thickness, significantly improving the coating peel strength, but correspondingly decreasing the electrode's tensile strength. Alkaline residue may have some impact on the battery's cycle stability. Example 5 had moderate parameters, suitable pitting depth, and a good balance between electrode peel strength and tensile strength, resulting in optimal battery electrochemical performance. Example 6 used a higher amount of NaOH powder and a higher drying temperature, significantly improving the electrode peel strength while maintaining a reasonable tensile strength, demonstrating excellent overall performance. Example 7 used a high amount of large-particle-size NaOH powder, resulting in deeper pitting and peel strength approaching the peak value, but a significant decrease in tensile strength.

[0079] Compared to Example 5, when the amount of NaOH powder added was increased from 2.0% to 5.0% (Example 8) and 7.0% (Comparative Example 2), respectively, the number of alkaline particles in the system increased, and the number and density of pitting corrosion on the surface of the aluminum foil current collector increased accordingly, further improving the peel strength to 0.043 N / mm and 0.044 N / mm. However, excessive addition caused excessive corrosion of the aluminum foil current collector, resulting in a significant decrease in its mechanical strength, with tensile strength dropping to 165 MPa and 150 MPa, respectively. Comparative Example 2 was already below the conventional minimum requirement for the tensile strength of aluminum foil in battery electrode processing (≥ 160 MPa); at the same time, the residual alkali content increased, side reactions intensified, and electrochemical performance showed a significant decline.

[0080] The results of Examples 5 and Comparative Examples 3 and 4 show that when the drying temperature drops to 90 °C, the reaction kinetics of alkali metal hydroxide and alumina are low, with only a few active sites experiencing weak corrosion. The resulting electrode peel strength is only 0.022 N / mm, comparable to Comparative Example 1. When the drying temperature rises to 200 °C, the corrosion reaction becomes too vigorous, with pitting depths on the aluminum foil surface exceeding 10% of the foil thickness, posing a risk of perforation in localized areas. The electrode tensile strength drops sharply to 160 MPa. Simultaneously, the excessively high temperature causes the NMP solvent to evaporate too quickly, leading to cracking of the positive electrode coating surface and ultimately deteriorating the battery's electrochemical performance.

[0081] The above results demonstrate that, under appropriate parameter combinations, uniform pitting of suitable depth can be formed on the surface of the aluminum foil current collector, which can not only significantly improve adhesion but also control the decrease in electrode mechanical strength within an acceptable range. At the same time, thanks to the in-situ dehydration effect of alkaline powder and the coating effect of the aluminate interface generated by the reaction, the initial coulombic efficiency and cycle stability of the battery can be significantly improved.

[0082] Obviously, the above embodiments of the present invention are merely examples for clearly illustrating the present invention, and are not intended to limit the implementation of the present invention. Those skilled in the art should understand that other variations or modifications can be made based on the above description. It is neither necessary nor possible to exhaustively describe all embodiments here. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the scope of protection of the claims of the present invention.

Claims

1. A method for preparing an integrated positive electrode sheet, characterized in that, Includes the following steps: (1) A positive electrode material is obtained by mixing positive electrode active material, conductive agent, binder and alkali metal hydroxide powder, wherein the amount of alkali metal hydroxide powder added is 0.1%-5% of the mass of the positive electrode material; the positive electrode material is mixed with organic solvent to obtain positive electrode slurry; (2) The positive electrode slurry is coated on the surface of the aluminum foil current collector, and the coated aluminum foil current collector is dried at 100-170 °C to allow the alkali metal hydroxide powder to corrode the surface of the aluminum foil current collector in situ to form pits. The integrated positive electrode sheet is obtained by roll pressing. The depth of the pits is 1%-10% of the thickness of the aluminum foil current collector.

2. The preparation method according to claim 1, characterized in that, In step (1), the mass ratio of the positive electrode active material, conductive agent, binder and alkali metal hydroxide powder is (90-95):(2-3):(2-4):(0.1-5).

3. The preparation method according to claim 1, characterized in that, In step (1), the positive electrode active material is selected from sodium-ion battery positive electrode active materials or lithium-ion battery positive electrode active materials; the sodium-ion battery positive electrode active material is selected from one or more of sodium iron phosphate, sodium iron pyrophosphate, and layered oxides; the lithium-ion battery positive electrode active material is selected from one or more of lithium iron phosphate, nickel-cobalt-manganese ternary materials, nickel-cobalt-aluminum ternary materials, lithium cobalt oxide, lithium manganese oxide, and lithium iron manganese phosphate; the conductive agent is carbon black; the binder is polyvinylidene fluoride; and the organic solvent is N-methylpyrrolidone.

4. The preparation method according to claim 1, characterized in that, In step (1), the alkali metal hydroxide powder is selected from one or more of sodium hydroxide powder, lithium hydroxide powder and potassium hydroxide powder.

5. The preparation method according to claim 1, characterized in that, In step (1), the particle size of the alkali metal hydroxide powder is 0.3-30 μm; the moisture content of the alkali metal hydroxide powder is less than 500 ppm.

6. The preparation method according to claim 1, characterized in that, In step (1), the solid content of the positive electrode slurry is 50%-70%.

7. The preparation method according to claim 1, characterized in that, In step (2), the positive electrode slurry is coated on the surface of the aluminum foil current collector by using an extrusion coater, the coating speed is 1.5-15 m / min, and the coating area density is 150-250 g / m 2 .

8. An integrated positive electrode sheet prepared by the preparation method according to any one of claims 1-7.

9. The application of the integrated positive electrode sheet as described in claim 8 in the assembly of a secondary battery.

10. A secondary battery, characterized in that, It includes the integrated positive electrode, negative electrode, separator, and electrolyte as described in claim 8.

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