Positive pole piece containing lithium supplementing prime coat, preparation method of positive pole piece and electrochemical device

Abstract

The invention discloses a positive pole piece containing a lithium supplement prime coat, a preparation method of the positive pole piece and an electrochemical device, and belongs to the technical field of battery materials. The positive pole piece comprises a positive current collector, a composite lithium-supplementing priming coat and a positive active material layer, the composite lithium supplementing bottom coating comprises a first coating, a second coating, a third coating and a fourth coating which are sequentially arranged from the surface of the positive electrode current collector to the outside; wherein the first coating and the third coating are lithium supplementing layers, and the second coating and the fourth coating are packaging layers; the lithium supplementing layer contains a lithium supplementing material, conductive carbon black and an oil-based adhesive; the encapsulation layer contains a carbon tube and a water-based adhesive. According to the positive pole piece, through the compact composite structure design similar to plywood, the mechanical performance of the pole piece can be enhanced, and the cycle life of an electrochemical device is prolonged.

Description

Technical Field

[0001] The present invention relates to the technical field of battery materials, and in particular to a positive electrode sheet containing a lithium-supplementing primer, a preparation method thereof, and an electrochemical device. Background Art

[0002] With the surge in battery demand, the industry's need for lithium replenishment is becoming increasingly clear. In specific applications, lithium-rich inorganic materials used as positive electrode lithium replenishers, such as lithium nickelate and lithium ferrite, are susceptible to moisture absorption and difficulty in uniform slurry coating. Lithium-containing organic salts used as positive electrode lithium replenishers are expensive, hindering their practical application. Furthermore, negative electrode lithium replenishers are prone to reacting with air, causing combustion and explosion, posing a high risk. Furthermore, these replenishers have low compatibility with battery manufacturing processes. These compatibility issues primarily stem from their sensitivity to air, requiring significant investment in equipment and energy consumption during production, limiting production capacity and application. In other words, there is currently no product or material that allows lithium battery plants to replenish lithium using existing production line equipment in the most cost-effective and efficient manner, while maintaining existing production capacity and cycle times.

[0003] In view of this, the present invention is proposed. Summary of the Invention

[0004] The object of the present invention is to provide a positive electrode plate containing a lithium-supplementing primer, a preparation method thereof, and an electrochemical device, so as to solve or improve the above-mentioned technical problems.

[0005] The present invention can be achieved like this: In a first aspect, the present invention provides a positive electrode plate containing a lithium-supplementing primer, the positive electrode plate comprising a positive electrode current collector, a composite lithium-supplementing primer layer, and a positive electrode active material layer; the composite lithium-supplementing primer layer comprises a first coating layer, a second coating layer, a third coating layer, and a fourth coating layer sequentially arranged from the surface of the positive electrode current collector outward; Among them, the first coating layer and the third coating layer are both lithium replenishing layers, and the second coating layer and the fourth coating layer are both encapsulation layers; The lithium replenishing layer contains lithium replenishing materials, conductive carbon black and oil-based adhesive; the encapsulation layer contains carbon tubes and water-based adhesive.

[0006] In an optional embodiment, the first coating layer contains, by mass percentage, 25% to 45% of the first lithium replenishing material, 15% to 40% of the first conductive carbon black, and the remainder is the first oil-based adhesive; The first lithium supplement material includes at least two of lithium borate, lithium carbonate, lithium nitrate, lithium oxide, lithium silicate, lithium phosphate and lithium sulfate; and the first lithium supplement material is nano-scale; The first conductive carbon black includes at least one of Super P, Cabot Black BP2000, Ketjen Black EC-300J, and Ketjen Black ECP-600JD; The first oil-based adhesive includes at least one of hydrophobic PVDF and PTFE.

[0007] In an optional embodiment, the second coating layer contains 35% to 65% of the first carbon nanotubes, and the remainder is the first aqueous adhesive, calculated by mass percentage; The first carbon tubes are single-walled carbon tubes or multi-walled carbon tubes; and the first aqueous adhesive includes at least one of hydrophilic SBR, PAA, CMC and sodium alginate.

[0008] In an optional embodiment, the third coating layer contains, by mass percentage, 25% to 45% of the second lithium replenishing material, 15% to 40% of the second conductive carbon black, and the remainder is the second oil-based adhesive; The second lithium supplement material includes at least two of lithium oxalate, lithium squarate, lithium citrate and cobalt nitrate; and the second lithium supplement material is nano-scale; The second conductive carbon black includes at least one of Super P, Cabot Black BP2000, Ketjen Black EC-300J, and Ketjen Black ECP-600JD; The second oil-based adhesive includes at least one of hydrophobic PVDF and PTFE.

[0009] In an optional embodiment, the fourth coating layer contains 35% to 65% of the second carbon nanotubes in mass percentage, and the remainder is the second aqueous adhesive; The second carbon tubes are single-walled carbon tubes or multi-walled carbon tubes; and the second aqueous adhesive includes at least one of hydrophilic SBR, PAA, CMC and sodium alginate.

[0010] In an optional embodiment, the thickness of the composite lithium-supplementing primer layer provided on a single side surface of the positive electrode current collector is 1.5 μm to 3.5 μm, wherein the thickness of the first coating layer is 0.75 μm to 1.50 μm; the thickness of the second coating layer is 0.02 μm to 0.25 μm; the thickness of the third coating layer is 0.75 μm to 1.50 μm; and the thickness of the fourth coating layer is 0.02 μm to 0.25 μm.

[0011] In a second aspect, the present invention provides a method for preparing a positive electrode plate as in any of the aforementioned embodiments, comprising the following steps: preparing a first coating, a second coating, a third coating, a fourth coating and a positive electrode active material layer in sequence on the surface of at least one side of the positive electrode current collector according to a preset position.

[0012] In an optional embodiment, a first coating slurry containing a first lithium supplement material, a first conductive carbon black, and a first oil-based adhesive is applied to at least one surface of the positive electrode current collector according to a preset position and dried to obtain a first coating layer; applying a second coating slurry containing the first carbon tubes and the first aqueous adhesive on the surface of the first coating and drying the slurry to obtain the second coating; Applying a third coating slurry containing a second lithium supplementing material, a second conductive carbon black, and a second oil-based adhesive on the surface of the second coating, and drying to obtain a third coating; Applying a fourth coating slurry containing the second carbon tubes and the second aqueous adhesive on the surface of the third coating and drying to obtain the fourth coating; A positive electrode active material slurry containing a positive electrode active material is coated on the surface of the fourth coating layer and dried to obtain a positive electrode active material layer.

[0013] In an optional embodiment, the first coating slurry is obtained by mixing the first lithium supplement material, the first conductive carbon black, the first oil-based adhesive and the solvent and then ball milling or sand milling; The third coating slurry is obtained by mixing the second lithium supplement material, the second conductive carbon black, the second oil-based adhesive and the solvent and then ball milling or sand milling.

[0014] In a third aspect, the present invention provides an electrochemical device, comprising a positive electrode sheet containing a lithium-supplementing primer according to any one of the aforementioned embodiments.

[0015] The beneficial effects of the present invention include: The positive electrode plate in the present invention adopts a compact composite structure design similar to plywood, which can enhance the mechanical properties of the positive electrode plate and improve the cycle life of the electrochemical device. Among them, the first coating and the third coating serve as lithium replenishment functional coatings to provide a lithium source for lithium replenishment, and the second coating and the fourth coating serve as adhesive packaging layers to provide transitional interface adhesion and conductive paths. By adopting carbon tubes, the interface conductivity is maximized, which safeguards the high-rate charge and discharge of the positive electrode plate and improves the rate performance and overall safety performance. The alternating hydrophobic and hydrophilic structures of the above-mentioned first to fourth coatings ensure the stable bonding of the coating interface, improving the safety of the battery while improving the energy density; in addition, the alternating oil-based and water-based coatings are matched, and the plywood-like structure makes the interface microstructure within the system intertwined and stably composited, which is also conducive to increasing the overall performance and increasing the battery life. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the following briefly introduces the drawings required for use in the embodiments. It should be understood that the following drawings only illustrate certain embodiments of the present invention and therefore should not be regarded as limiting the scope. For ordinary technicians in this field, other relevant drawings can be obtained based on these drawings without paying any creative work.

[0017] Figure 1 This is a schematic structural diagram of the positive electrode plate containing a lithium-supplementing primer provided by the present invention.

[0018] Icon: 1-positive electrode active material layer; 2-fourth coating layer; 3-third coating layer; 4-second coating layer; 5-first coating layer; 6-positive electrode current collector. DETAILED DESCRIPTION

[0019] To make the purpose, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention are described clearly and completely below. Where specific conditions are not specified in the embodiments, conventional conditions or conditions recommended by the manufacturer are used. Where the manufacturer of the reagents or instruments is not specified, all are conventional products that can be purchased commercially.

[0020] The following is a detailed description of the positive electrode sheet containing a lithium-supplementing primer, its preparation method, and the electrochemical device provided by the present invention.

[0021] The present invention provides a positive electrode plate containing a lithium supplementing primer, such as Figure 1 As shown, the positive electrode plate includes a positive electrode current collector 6 and a composite lithium-supplementing primer layer and a positive electrode active material layer 1 provided on at least one side surface of the positive electrode current collector 6 .

[0022] In some optional embodiments, the composite lithium-replenishing primer layer may be disposed on only one surface of the positive electrode current collector 6. In other optional embodiments, the composite lithium-replenishing primer layer may be disposed on both surfaces of the positive electrode current collector 6.

[0023] The composite lithium-replenishing undercoat layer includes a first coating layer 5, a second coating layer 4, a third coating layer 3, and a fourth coating layer 2, which are sequentially arranged from the surface of the positive electrode current collector 6 outward. The first coating layer 5 and the third coating layer 3 are both lithium-replenishing layers, providing a lithium source for replenishment; the second coating layer 4 and the fourth coating layer 2 are both encapsulation layers, providing transitional interfacial adhesion and conducting the circuit.

[0024] The lithium replenishing layer contains lithium replenishing materials, conductive carbon black and oil-based adhesive; the encapsulation layer contains carbon tubes and water-based adhesive.

[0025] The alternating hydrophobic and hydrophilic composite structure ensures stable bonding at the coating interface, enhancing both energy density and battery safety. Furthermore, the alternating oil-based and water-based coatings, similar to the structure of plywood, create a staggered and stable composite microstructure within the system, which also helps enhance overall performance and extend battery life.

[0026] In some optional embodiments, the first coating layer 5 contains, by mass percentage, 25% to 45% of the first lithium replenishing material, 15% to 40% of the first conductive carbon black, and the remainder is the first oil-based adhesive.

[0027] The content of the first lithium-supplementing material in the first coating layer 5 can be 25%, 28%, 30%, 32%, 35%, 38%, 40%, 42%, or 45%, or other values within the range of 25% to 45%. If the content of the first lithium-supplementing material in the first coating layer 5 is less than 25%, its proportion as a lithium source is too small, which is not conducive to the full capacity of the lithium-supplementing layer. If the content of the first lithium-supplementing material in the first coating layer 5 is greater than 45%, the decomposition of the first lithium-supplementing material as a lithium source will produce too many pores and voids, which is not conducive to the stability of the overall structure of the electrode.

[0028] The content of the first conductive carbon black in the first coating layer 5 can be 15%, 28%, 30%, 32%, 35%, 38%, or 40%, or other values within the range of 15% to 40%. If the content of the first conductive carbon black in the first coating layer 5 is less than 15%, it cannot effectively reduce the internal resistance as a conductive agent, which is not conducive to reducing the lithium decomposition voltage. If the content of the first conductive carbon black in the first coating layer 5 is greater than 40%, it will occupy the space for the adhesive, which is not conducive to the bonding and lamination of the coating base layer and the current collector foil, resulting in a decrease in the electrode peeling force.

[0029] The first lithium-replenishing material may illustratively include at least two of lithium borate, lithium carbonate, lithium nitrate, lithium oxide, lithium silicate, lithium phosphate, and lithium sulfate; and the first lithium-replenishing material is nanoscale. These lithium salts are inexpensive, which helps reduce costs. Nanosizing them to nanoscale increases their reactivity. By combining at least two lithium salts, the lithium-replenishing layer can be used to stagger travel times during decomposition and gas production, reducing congestion and minimizing stress and impact on the electrode structure.

[0030] The first conductive carbon black illustratively may include at least one of Super P, Cabot Black BP2000, Ketjen Black EC-300J, and Ketjen Black ECP-600JD.

[0031] The first oil-based adhesive may illustratively include at least one of hydrophobic PVDF and PTFE.

[0032] In some optional embodiments, the second coating layer 4 contains 35% to 65% of the first carbon nanotubes by mass, and the remainder is the first aqueous adhesive.

[0033] The content of the first carbon tubes in the second coating layer 4 can be 35%, 38%, 40%, 42%, 45%, 48%, 50%, 52%, 55%, 58%, 60%, 62%, or 65%, or other values within the range of 35% to 65%. If the content of the first carbon tubes in the second coating layer 4 is less than 35%, they cannot effectively and fully crosslink and entangle with the two sides of the inner conductive agent, which is not conducive to reducing internal resistance and collecting current. If the content of the first carbon tubes in the second coating layer 4 is greater than 65%, they occupy space for the adhesive, which is not conducive to the bonding and compounding of the second coating layer 4 with the two sides, and will lead to a decrease in the machining performance of the electrode.

[0034] The first carbon nanotubes are single-walled carbon nanotubes or multi-walled carbon nanotubes; the first aqueous adhesive may illustratively include at least one of hydrophilic SBR, PAA, CMC, and sodium alginate. The use of carbon nanotubes maximizes interfacial conductivity, ensuring high-rate charge and discharge for the multi-layer composite electrode, and improving rate performance and overall safety.

[0035] In some optional embodiments, the third coating layer 3 contains, by mass percentage, 25% to 45% of the second lithium replenishing material, 15% to 40% of the second conductive carbon black, and the remainder is the second oil-based adhesive.

[0036] The content of the second lithium-supplementing material in the third coating layer 3 can be 25%, 28%, 30%, 32%, 35%, 38%, 40%, 42%, or 45%, or other values within the range of 25% to 45%. If the content of the second lithium-supplementing material in the third coating layer 3 is less than 25%, its proportion as a lithium source is too small, which is not conducive to the full capacity of the third coating layer 3. If the content of the second lithium-supplementing material in the third coating layer 3 is greater than 45%, the decomposition of the second lithium-supplementing material as a lithium source will produce too many pores and voids, which is not conducive to the stability of the overall structure of the electrode.

[0037] The content of the second conductive carbon black in the third coating layer 3 can be 15%, 22%, 25%, 28%, 30%, 32%, 35%, 38%, or 40%, or other values within the range of 15% to 40%. If the content of the second conductive carbon black in the third coating layer 3 is less than 15%, it cannot effectively reduce the internal resistance as a conductive agent, which is not conducive to reducing the lithium decomposition voltage. If the content of the second conductive carbon black in the third coating layer 3 is greater than 40%, it is not conducive to the adhesion and lamination of the third coating layer 3 with the two coating layers, and powder is easily lost, which is not conducive to subsequent coating.

[0038] The second lithium-supplementing material may illustratively include at least two of lithium oxalate, lithium squarate, lithium citrate, and cobalt nitrate; and the second lithium-supplementing material is nanoscale. Similarly, these raw materials are inexpensive, which helps reduce costs. Nanosizing them to nanoscale increases their reactivity. Preferably, the second lithium-supplementing material contains at least cobalt nitrate. While it does not contain lithium, it can serve as an auxiliary material in the second lithium-supplementing material to enhance dispersion.

[0039] In addition, in the present invention, the second lithium-supplementing material is different from the first lithium-supplementing material. The reason is that: through AI modeling of the electrode, high-throughput screening of the components and formulas of each lithium-supplementing material, and experimental verification, the mixed design is significantly better than a single component in decomposition efficiency and lithium salt residue.

[0040] The second conductive carbon black illustratively may include at least one of Super P, Cabot Black BP2000, Ketjen Black EC-300J, and Ketjen Black ECP-600JD.

[0041] The second oil-based adhesive may illustratively include at least one of hydrophobic PVDF and PTFE.

[0042] In some optional embodiments, the fourth coating layer 2 contains 35% to 65% of the second carbon nanotubes by mass, and the remainder is the second aqueous adhesive.

[0043] The content of the second carbon nanotubes in the fourth coating 2 can be 35%, 38%, 40%, 42%, 45%, 48%, 50%, 52%, 55%, 58%, 60%, 62%, or 65%, or other values within the range of 35% to 65%. If the content of the second carbon nanotubes in the fourth coating 2 is less than 35%, they cannot effectively cover the coating surface as a conductive agent, resulting in increased contact resistance and reduced electrode rate performance. If the content of the second carbon nanotubes in the fourth coating 2 is greater than 65%, it is not conducive to the bonding and compounding of the fourth coating 2 with both sides, resulting in a decrease in the machining performance of the electrode.

[0044] The second carbon nanotubes are single-walled carbon nanotubes or multi-walled carbon nanotubes; the second aqueous binder may illustratively include at least one of hydrophilic SBR, PAA, CMC, and sodium alginate. Similarly, the use of carbon nanotubes maximizes interfacial conductivity, ensuring high-rate charge and discharge of the positive electrode, and improving rate performance and overall safety.

[0045] Continuing from the above, the present invention utilizes a compact, plywood-like composite structure design to enhance the mechanical properties of the positive electrode and improve the cycle life of the electrochemical device. The first coating 5 and the third coating 3 serve as lithium-replenishing functional coatings, providing a lithium source. By using inexpensive lithium salts and subjecting them to nano-processing, their reactivity is increased. After curing with conductive carbon black, this helps reduce costs. The second coating 4 and the fourth coating 2 serve as adhesive encapsulation layers, providing transitional interfacial adhesion and conductive pathways. The use of carbon nanotubes maximizes interfacial conductivity, safeguarding the positive electrode's high-rate charge and discharge performance, improving rate performance and overall safety. The alternating hydrophilic-hydrophobic structures of the first coating 5 through the fourth coating 2 ensure stable bonding at the coating interface, enhancing both energy density and battery safety. Furthermore, the alternating oil-based and water-based coatings, creating a plywood-like structure, allow the positive electrode sheets to interlock and stabilize the microstructure at the interface, further enhancing overall performance and battery life.

[0046] In some optional embodiments, the thickness of the composite lithium-supplementing primer layer provided on one side of the positive electrode current collector 6 may be 1.5 μm to 3.5 μm, such as 1.5 μm, 2 μm, 2.5 μm, 3 μm or 3.5 μm, or other values within the range of 1.5 μm to 3.5 μm.

[0047] The thickness of the first coating 5 can be 0.70μm~1.50μm, such as 0.7μm, 0.8μm, 0.85μm, 0.9μm, 0.95μm, 1μm, 1.05μm, 1.1μm, 1.15μm, 1.2μm, 1.25μm, 1.3μm, 1.35μm, 1.4μm, 1.45μm or 1.5μm, etc., or it can be other values within the range of 0.70μm~1.50μm.

[0048] The thickness of the second coating 4 may be 0.02 μm to 0.25 μm, such as 0.02 μm, 0.05 μm, 0.08 μm, 0.1 μm, 0.12 μm, 0.15 μm, 0.18 μm, 0.2 μm, 0.22 μm or 0.25 μm, or other values within the range of 0.02 μm to 0.25 μm.

[0049] The thickness of the third coating layer 3 may be 0.70 μm to 1.50 μm, such as 0.7 μm, 0.8 μm, 0.9 μm, 1 μm, 1.1 μm, 1.2 μm, 1.3 μm, 1.4 μm or 1.5 μm, or other values within the range of 0.70 μm to 1.50 μm.

[0050] The thickness of the fourth coating layer 2 may be 0.02 μm to 0.25 μm, such as 0.02 μm, 0.05 μm, 0.08 μm, 0.1 μm, 0.15 μm, 0.2 μm or 0.25 μm, or other values within the range of 0.02 μm to 0.25 μm.

[0051] Accordingly, the present invention also provides a method for preparing the above-mentioned positive electrode plate, comprising the following steps: preparing a first coating 5, a second coating 4, a third coating 3, a fourth coating 2 and a positive electrode active material layer 1 in sequence on the surface of at least one side of the positive electrode current collector 6 according to a preset position.

[0052] In some optional embodiments, a first coating layer 5 slurry containing a first lithium-supplementing material, a first conductive carbon black, and a first oil-based adhesive can be applied to at least one surface of the positive electrode current collector 6 at a predetermined position and dried to form the first coating layer 5. The first coating layer 5 slurry is obtained by mixing the first lithium-supplementing material, the first conductive carbon black, the first oil-based adhesive, and a solvent (such as NMP) and then grinding them.

[0053] A second coating layer 4 slurry containing the first carbon tubes and the first aqueous adhesive is applied to the surface of the first coating layer 5 and dried to obtain the second coating layer 4 .

[0054] A third coating 3 slurry containing a second lithium-supplementing material, a second conductive carbon black, and a second oil-based adhesive is applied to the surface of the second coating 4 and dried to obtain the third coating 3. The third coating 3 slurry is obtained by mixing the second lithium-supplementing material, the second conductive carbon black, the second oil-based adhesive, and a solvent (such as NMP) and then grinding.

[0055] A fourth coating layer 2 slurry containing the second carbon tubes and the second aqueous adhesive is applied to the surface of the third coating layer 3 and dried to obtain the fourth coating layer 2 .

[0056] A positive electrode active material slurry containing a positive electrode active material is coated on the surface of the fourth coating layer 2 and dried to obtain a positive electrode active material layer 1 .

[0057] It should be noted that the present invention does not impose any special restrictions on the specific preparation method of the positive electrode sheet. The above method is only one of many preparation methods, as long as the function of the electrochemical device can be achieved. In addition, the present invention does not impose any restrictions on the type and thickness of the positive electrode collector 6, as long as the function of the electrochemical device can be achieved. For example, the positive electrode collector 6 may include aluminum foil, aluminum alloy foil or a composite current collector. The present invention does not impose any special restrictions on the positive electrode active material, as long as the function of the electrochemical device can be achieved. For example, the positive electrode active material may include but is not limited to at least one of NCM811, NCM523, lithium cobalt oxide, lithium nickel oxide, lithium manganese oxide, lithium iron phosphate and lithium manganese iron phosphate.

[0058] In addition, the present invention also provides an electrochemical device, which includes the above-mentioned positive electrode plate.

[0059] In some optional embodiments, the electrochemical device further includes a negative electrode sheet, a separator, an electrolyte, and a shell.

[0060] Among them, the negative electrode plate includes a negative electrode current collector and a negative electrode active material layer located on the surface of the negative electrode current collector. There is no special limitation on the negative electrode current collector, as long as it can realize the function of the electrochemical device. For example, it may include but is not limited to copper foil, copper alloy foil, composite current collector, etc. Similarly, the present invention does not limit the negative electrode active material, as long as it can realize the function of the electrochemical device. For example, it may include but is not limited to at least one of graphite, hard carbon, soft carbon, silicon and silicon-carbon composite. In addition, the present invention does not specifically limit the thickness of the negative electrode active material layer and the thickness of the negative electrode current collector, as long as it can realize the function of the electrochemical device. In some optional embodiments, the thickness of the negative electrode active material layer may be 60μm~120μm, and the thickness of the negative electrode current collector may be 3μm~18μm.

[0061] Similarly, the present invention does not impose any particular limitation on the isolation membrane, as long as it can realize the function of the electrochemical device.

[0062] The electrolyte includes a lithium salt and an organic solvent. There is no particular limitation on the electrolyte, as long as it can achieve the function of the electrochemical device.

[0063] The housing is used to accommodate the positive electrode sheet, separator, electrolyte and negative electrode sheet, as well as other known components contained in the assembled battery.

[0064] It should also be emphasized that the preparation process of the electrochemical device in the present invention is well known to those skilled in the art and is not particularly limited in the present invention.

[0065] The features and performance of the present invention are further described in detail below with reference to the embodiments.

[0066] Example 1 This embodiment provides a positive electrode plate, such as Figure 1 As shown, the positive electrode sheet includes a positive electrode current collector 6, with a composite lithium-replenishing primer layer and a positive electrode active material layer 1 provided on both sides of the positive electrode current collector 6. The composite lithium-replenishing primer layer includes a first coating layer 5, a second coating layer 4, a third coating layer 3, and a fourth coating layer 2, which are sequentially provided from the surface of the positive electrode current collector 6 outward.

[0067] The preparation method of the positive electrode plate includes: S1: Lithium silicate, lithium carbonate, Super P and PVDF were mixed in a mass ratio of 0.21:1.8:1:2, NMP was added as a solvent, and ball milling was carried out for 24 hours to obtain a first coating 5 slurry with a solid content of 20wt%; the first coating 5 slurry was coated on the front and back surfaces of the positive electrode current collector 6 with a thickness of 14μm, and baked at 120℃ for 3min to obtain a first coating 5 with a thickness of 1μm.

[0068] S2: Multi-walled carbon nanotubes and PAA were mixed in a mass ratio of 6:4, deionized water was added as a solvent, and the mixture was stirred evenly to obtain a second coating 4 slurry with a solid content of 3 wt%; the second coating 4 slurry was applied to the outer surface of the first coating 5, and the mixture was baked at 140°C for 3 minutes to obtain a second coating 4 with a thickness of 0.05 μm.

[0069] S3: Lithium oxalate, anhydrous cobalt nitrate, Super P and PVDF were mixed in a mass ratio of 2.02:0.19:1:2, NMP was added as a solvent, and ball milling was carried out for 24 hours to obtain a third coating 3 slurry with a solid content of 20wt%; the third coating 3 slurry was applied to the outer surface of the second coating 4, and baked at 160°C for 3 minutes to obtain a third coating 3 with a thickness of 1μm.

[0070] S4: Multi-walled carbon nanotubes and PAA were mixed in a mass ratio of 6:4, deionized water was added as a solvent, and the mixture was stirred evenly to obtain a fourth coating 2 slurry with a solid content of 3 wt%; the fourth coating 2 slurry was applied on the outer surface of the third coating 3, and baked at 180°C for 3 minutes to obtain a fourth coating 2 with a thickness of 0.05 μm.

[0071] S5: coating the lithium iron phosphate positive electrode material slurry on the surface of the fourth coating layer 2, drying to form a positive electrode active material layer 1, and obtaining a positive electrode sheet.

[0072] Example 2 The difference between this embodiment and embodiment 1 is that the mass ratio of lithium silicate, lithium carbonate, Super P and PVDF in the first coating 5 is 0.45:1.6:2:2.

[0073] Example 3 The difference between this embodiment and embodiment 1 is that the third coating layer 3 contains lithium oxalate, lithium citrate, anhydrous cobalt nitrate, conductive carbon black and PVDF in a mass ratio of 1:1:1:2:2.

[0074] Example 4 The difference between this embodiment and embodiment 1 is that the thickness of the first coating layer 5 is 1.5 μm.

[0075] Example 5 The difference between this embodiment and embodiment 1 is that the thickness of the third coating layer 3 is 1.5 μm.

[0076] Example 6 The difference between this embodiment and embodiment 1 is that the thickness of the second coating layer 4 is 0.10 μm, and the thickness of the fourth coating layer 2 is also 0.10 μm.

[0077] Example 7 The difference between this embodiment and embodiment 1 is that the thickness of the fourth coating layer 2 is 0.25 μm.

[0078] Example 8 The difference between this embodiment and embodiment 1 is that the thickness of the second coating layer 4 is 0.25 μm.

[0079] Example 9 The difference between this embodiment and embodiment 1 is that the thickness of the first coating layer 5 is 1.5 μm, and the thickness of the third coating layer 3 is 1.5 μm.

[0080] Example 10 The difference between this embodiment and embodiment 1 is that the baking temperature of each coating slurry is 105°C.

[0081] Example 11 The difference between this embodiment and embodiment 1 is that the baking temperature of each coating slurry is 135°C.

[0082] Example 12 The difference between this embodiment and embodiment 1 is that the baking temperature of each coating slurry is 155°C.

[0083] Example 13 The difference between this embodiment and embodiment 1 is that the preparation method of the first coating layer 5 slurry and the third coating layer 3 slurry is not ball milling, but sand milling, and the particle size of the sand-milled zirconium beads is 1 μm.

[0084] Example 14 The difference between this embodiment and embodiment 1 is that the preparation method of the first coating layer 5 slurry and the third coating layer 3 slurry is not ball milling, but sand milling, and the particle size of the sand-milled zirconium beads is 0.6 μm.

[0085] Example 15 The difference between this embodiment and embodiment 1 is that the mass ratio of the multi-walled carbon nanotubes to PAA in the second coating layer 4 and the fourth coating layer 2 is 1:1.

[0086] Example 16 The difference between this embodiment and embodiment 1 is that the mass ratio of multi-walled carbon nanotubes to PAA in the second coating layer 4 and the fourth coating layer 2 is 4:6.

[0087] Comparative Example 1 The difference between this comparative example and Example 1 is that the lithium iron phosphate positive electrode material is directly coated on a plain aluminum foil with a thickness of 14 μm.

[0088] That is, the positive electrode sheet of this comparative example does not contain the composite lithium-supplementing undercoat layer.

[0089] Comparative Example 2 The difference between this comparative example and Example 1 is that a conductive carbon black layer with a thickness of 1 μm is prepared on the front and back sides of a plain aluminum foil with a thickness of 14 μm, respectively, and then a lithium iron phosphate positive electrode material layer is prepared on the surface of the conductive carbon black layer.

[0090] That is, the positive electrode sheet of this comparative example adopts the commercially mainstream carbon black primer.

[0091] Comparative Example 3 The difference between this comparative example and Example 1 is that a conductive carbon black layer with a thickness of 2 μm is prepared on the front and back sides of a plain aluminum foil with a thickness of 14 μm, respectively, and then a lithium iron phosphate positive electrode material layer is prepared on the surface of the conductive carbon black layer.

[0092] That is, the positive electrode sheet of this comparative example adopts the commercially mainstream carbon black primer.

[0093] Test example The positive electrode sheets prepared in the above Examples 1 to 16 and Comparative Examples 1 to 3 were prepared into batteries according to the following method: the positive electrode sheets were rolled and then cut into pieces and dried to a moisture content of less than 200 ppm; the graphite negative electrode material, the negative electrode binder CMC and SBR were slurried and then rolled and cut into pieces and dried to a moisture content of less than 200 ppm; the above positive electrode sheets, separators and negative electrode sheets were wound to obtain dry battery cells, which were dried to a moisture content of less than 100 ppm, placed in an aluminum shell, and then liquid-filled, plastic-sealed and aged in an argon glove box to obtain a battery.

[0094] The cycle capacity of the above-mentioned battery cells was tested using an electrochemical test channel. The high-temperature cycle life test method is as follows: (1) The constant temperature is 45℃, first charge with 0.1C constant current to 4.2V, leave it for 30min, and then discharge with 0.1C to 2.5V; (2) Then charge and discharge at a constant current of 1C / 1C, 3.8V~2.5V, and cycle 750 times to obtain the battery capacity retention rate.

[0095] The test results are shown in Table 1.

[0096] Table 1 Test results

[0097] The results in Table 1 show that the positive electrode sheets prepared in Examples 1-16 of the present invention are more conducive to improving battery cycle performance than the positive electrode sheets prepared in Comparative Examples 1-3. This is because the positive electrode sheets prepared in Examples 1-16 of the present invention contain a compact, plywood-like, bonded lithium-replenishing primer layer. This compact bonded structure effectively maintains the mechanical stability of the lithium-replenishing layer, facilitating gas production and lithium replenishment. Furthermore, because the carbon tube layer (encapsulation layer) within the bonded core is effectively conductive, the electrical performance remains reliable even after long-term cycling.

[0098] In summary, the solution provided by the present invention has at least the following advantages: (1) It does not rely on stacking, and the carbon layer of the conventional primer can be replaced with a compact glued lithium-supplementing structure without increasing the thickness of the electrode; (2) It does not rely on semiconductor equipment or vacuum equipment, and the production line does not need to be upgraded, and no large investment in fixed equipment is required; (3) It does not rely on complex raw materials, has simple processing technology, high yield, and is economical, environmentally friendly and energy-saving.

[0099] The foregoing description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Those skilled in the art will readily appreciate that various modifications and variations of the present invention are possible. Any modifications, equivalent substitutions, or improvements made within the spirit and principles of the present invention are intended to be within the scope of protection of the present invention.

Claims

1. A positive electrode plate, characterized in that: The positive electrode plate comprises a positive electrode current collector, a composite lithium-supplementing bottom coating layer and a positive electrode active material layer; the composite lithium-supplementing bottom coating layer comprises a first coating layer, a second coating layer, a third coating layer and a fourth coating layer arranged in sequence from the surface of the positive electrode current collector outward; Wherein, the first coating layer and the third coating layer are both lithium replenishing layers, and the second coating layer and the fourth coating layer are both encapsulation layers; The lithium replenishing layer contains lithium replenishing material, conductive carbon black and oil-based adhesive; the encapsulation layer contains carbon tubes and water-based adhesive.

2. The positive electrode sheet according to claim 1, characterized in that: Calculated by mass percentage, the first coating contains 25% to 45% of a first lithium replenishing material, 15% to 40% of a first conductive carbon black, and the remainder is a first oil-based adhesive; Wherein, the first lithium supplement material comprises at least two of lithium borate, lithium carbonate, lithium nitrate, lithium oxide, lithium silicate, lithium phosphate and lithium sulfate; and the first lithium supplement material is nanoscale; The first conductive carbon black comprises at least one of Super P, Cabot Black BP2000, Ketjen Black EC-300J and Ketjen Black ECP-600JD; The first oil-based adhesive includes at least one of hydrophobic PVDF and PTFE.

3. The positive electrode sheet according to claim 1, characterized in that: The second coating layer contains 35% to 65% of the first carbon nanotubes in mass percentage, and the remainder is the first aqueous adhesive; The first carbon tubes are single-walled carbon tubes or multi-walled carbon tubes; and the first aqueous adhesive includes at least one of hydrophilic SBR, PAA, CMC and sodium alginate.

4. The positive electrode sheet according to claim 1, characterized in that: In terms of mass percentage, the third coating layer contains 25% to 45% of the second lithium replenishing material, 15% to 40% of the second conductive carbon black, and the remainder is the second oil-based adhesive; Wherein, the second lithium supplement material comprises at least two of lithium oxalate, lithium squarate, lithium citrate and cobalt nitrate; and the second lithium supplement material is nano-scale; The second conductive carbon black comprises at least one of Super P, Cabot Black BP2000, Ketjen Black EC-300J and Ketjen Black ECP-600JD; The second oil-based adhesive includes at least one of hydrophobic PVDF and PTFE.

5. The positive electrode sheet according to claim 4, characterized in that: The fourth coating layer contains 35% to 65% of the second carbon nanotubes in mass percentage, and the remainder is the second aqueous adhesive; The second carbon tubes are single-walled carbon tubes or multi-walled carbon tubes; and the second aqueous adhesive includes at least one of hydrophilic SBR, PAA, CMC and sodium alginate.

6. The positive electrode sheet according to any one of claims 1 to 5, characterized in that: The thickness of the composite lithium-supplementing primer layer provided on the single-side surface of the positive electrode current collector is 1.5 μm~3.5 μm; wherein, the thickness of the first coating layer is 0.70 μm~1.50 μm; the thickness of the second coating layer is 0.02 μm~0.25 μm; the thickness of the third coating layer is 0.70 μm~1.50 μm; and the thickness of the fourth coating layer is 0.02 μm~0.25 μm.

7. A method for preparing a positive electrode sheet according to any one of claims 1 to 6, characterized in that: The method comprises the following steps: sequentially preparing the first coating layer, the second coating layer, the third coating layer, the fourth coating layer and the positive electrode active material layer on the surface of at least one side of the positive electrode current collector according to preset positions.

8. The preparation method according to claim 7, characterized in that Applying a first coating slurry containing a first lithium supplement material, a first conductive carbon black, and a first oil-based adhesive to at least one side of the positive electrode current collector according to a preset position, and drying the coating to obtain a first coating; applying a second coating slurry containing first carbon tubes and a first aqueous adhesive on the surface of the first coating and drying the slurry to obtain a second coating; applying a third coating slurry containing a second lithium supplementing material, a second conductive carbon black, and a second oil-based adhesive on the surface of the second coating, and drying to obtain a third coating; applying a fourth coating slurry containing the second carbon tubes and the second aqueous adhesive on the surface of the third coating and drying to obtain the fourth coating; A positive electrode active material slurry containing a positive electrode active material is coated on the surface of the fourth coating layer and dried to obtain the positive electrode active material layer.

9. The preparation method according to claim 8, characterized in that The first coating slurry is obtained by mixing the first lithium supplement material, the first conductive carbon black, the first oil-based adhesive and a solvent and then grinding; The third coating slurry is obtained by mixing the second lithium supplementing material, the second conductive carbon black, the second oil-based adhesive and a solvent and then grinding them.

10. An electrochemical device, characterized in that The electrochemical device comprises the positive electrode sheet according to any one of claims 1 to 8.

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