Positive pole piece, preparation method thereof and battery

Abstract

The invention provides a positive pole piece, a preparation method thereof and a battery. The positive pole piece comprises a current collector, a first active material layer and a second active material layer, wherein the first active material layer and the second active material layer are sequentially stacked on the surface of at least one side of the current collector; the first active material layer comprises a first active material and a first binder, and the second active material layer comprises a second active material and a second binder; the morphology of the first active material is spherical and / or sphere-like, and the morphology of the second active material is ellipsoidal and / or rod-like. According to the positive pole piece disclosed by the invention, the compaction density of the first active material layer is remarkably improved by regulating and controlling the morphology of the first active material, and the overall rate capability of the second active material layer and the battery is greatly improved by regulating and controlling the morphology of the second active material, so that the battery has high energy density and excellent rate capability.

Description

Technical Field

[0001] This invention belongs to the field of battery technology, and relates to a positive electrode sheet, its preparation method, and a battery. Background Technology

[0002] Lithium-ion batteries are widely used in digital products and electric vehicles due to their advantages such as high energy density, long cycle life, and environmental friendliness. With technological advancements, the demand for higher battery energy density is increasing. As a crucial component of lithium-ion batteries, one method to improve battery energy density in current technology is to increase the coating areal density of the positive electrode to reduce the proportion of inactive materials. However, with increased areal density, ohmic resistance and charge transfer resistance increase significantly, leading to a deterioration in the rate performance of lithium-ion batteries.

[0003] Based on the above research, there is a need to provide a positive electrode sheet that enables lithium-ion batteries to simultaneously possess high energy density and excellent rate performance. Summary of the Invention

[0004] The purpose of this invention is to provide a positive electrode sheet, its preparation method, and a battery. The positive electrode sheet significantly improves the compaction density of the first active material layer by controlling the morphology of the first active material, and greatly improves the rate performance of the second active material layer and the battery as a whole by controlling the morphology of the second active material, thereby enabling the battery to achieve both high energy density and excellent rate performance.

[0005] To achieve this objective, the present invention adopts the following technical solution:

[0006] In a first aspect, the present invention provides a positive electrode sheet, the positive electrode sheet comprising a current collector and an active layer on at least one side surface of the current collector, the active layer comprising a first active material layer and a second active material layer, the first active material layer being disposed on the surface of the current collector, and the second active material layer being disposed on the side surface of the first active material layer away from the current collector.

[0007] The first active material layer includes a first active material and a first binder, and the second active material layer includes a second active material and a second binder;

[0008] The first active material has a spherical and / or near-spherical morphology, and the second active material has an ellipsoidal and / or rod-shaped morphology.

[0009] Preferably, the sphericity Ds of the first active material is in the range of 0.8 ≤ Ds < 1.0.

[0010] Preferably, the aspect ratio Ra of the second active material is in the range of 1.5 ≤ Ra ≤ 3.0.

[0011] Preferably, the particle size D1v50 of the first active material is 1μm-2μm.

[0012] Preferably, the particle size D2v50 of the second active material is 0.5μm-1.5μm.

[0013] Preferably, the difference between the particle size D1v90 and the particle size D1v10 of the first active material is 1.5μm-2.5μm.

[0014] Preferably, the thickness d1 of the first active material layer is 60μm-120μm.

[0015] Preferably, the thickness d2 of the second active material layer is 60μm-120μm.

[0016] Preferably, the compaction density of the positive electrode sheet is 2.55 g / cm³. 3 above.

[0017] Preferably, the first active material and the second active material are each independently selected from any one or a combination of at least two of lithium iron phosphate, lithium manganese iron phosphate, or lithium nickel cobalt manganese oxide.

[0018] Preferably, the first active material includes a first doping element, wherein the first doping element includes any one or a combination of at least two of Ti, V or Ni, and the mass content of the first doping element in the first active material is 1000ppm-5000ppm.

[0019] Preferably, the second active material includes a second doping element, wherein the second doping element includes Mn, and the mass content of the second doping element in the second active material is 1000ppm-3000ppm.

[0020] Preferably, the difference between the weight-average molecular weight ω1 of the first adhesive and the weight-average molecular weight ω2 of the second adhesive is 30,000-100,000.

[0021] Preferably, the first adhesive and the second adhesive are each independently selected from any one or a combination of at least two of polyvinylidene fluoride, carboxylic acid-modified polyvinylidene fluoride, or acrylic acid-modified polyvinylidene fluoride.

[0022] Preferably, the first active material layer further includes a first conductive agent, and the mass ratio of the first active material, the first binder and the first conductive agent is (96.5~98.5):(1.5~2.5):(0~1).

[0023] Preferably, the second active material layer further includes a second conductive agent, and the mass ratio of the second active material, the second binder and the second conductive agent is (97~98.5):(1.0~1.5):(0.5~1.5).

[0024] In a second aspect, the present invention provides a method for preparing a positive electrode sheet as described in the first aspect, the method comprising the following steps:

[0025] The slurry of the first active material layer is coated on at least one side of the current collector. After drying, the slurry of the second active material layer is coated on the surface of the first active material layer. After drying and rolling, the positive electrode sheet is obtained.

[0026] Thirdly, the present invention provides a battery comprising a positive electrode as described in the first aspect.

[0027] Compared with the prior art, the present invention has the following beneficial effects:

[0028] This invention shortens the solid-phase transport distance of ions and improves rate performance by using a second active material with an ellipsoidal and / or rod-shaped morphology in the second active material layer. By using a first active material with a spherical and / or near-spherical morphology in the first active material layer, the positive electrode sheet can achieve a higher compaction density. Therefore, by combining the first and second active materials with two different morphologies, the positive electrode sheet can achieve both compaction density and rate performance, thereby enabling the battery to have both high energy density and rate performance. Detailed Implementation

[0029] While increasing the coating density of the positive electrode sheet can improve the energy density of the battery, it also significantly increases the ohmic resistance and charge transfer resistance, which leads to a deterioration in the battery's rate performance. Therefore, to address this problem, this invention sets two active material layers in the positive electrode sheet and sets two active materials with different morphologies, enabling the battery to have both high energy density and rate performance.

[0030] The technical solution of the present invention will be further illustrated below through specific embodiments.

[0031] In one specific embodiment, the present invention provides a positive electrode sheet, the positive electrode sheet including a current collector and an active layer on at least one side surface of the current collector, the active layer including a first active material layer and a second active material layer, the first active material layer being disposed on the surface of the current collector, and the second active material layer being disposed on the side surface of the first active material layer away from the current collector.

[0032] The first active material layer includes a first active material and a first binder, and the second active material layer includes a second active material and a second binder;

[0033] The first active material has a spherical and / or near-spherical morphology, and the second active material has an ellipsoidal and / or rod-shaped morphology.

[0034] This invention involves sequentially stacking a first active material layer and a second active material layer on the surface of a current collector. The second active material layer includes a second active material with an ellipsoidal and / or rod-shaped morphology, which can shorten the solid-phase transport distance of ions and improve rate performance. The first active material includes a first active material with a spherical and / or near-spherical morphology. The regularity of the spherical and / or near-spherical morphology allows the positive electrode sheet to achieve a higher compaction density. Therefore, by combining the first and second active materials with two different morphologies, the positive electrode sheet can achieve both compaction density and rate performance, thereby enabling the battery to simultaneously possess high energy density and rate performance.

[0035] Furthermore, the first and second active materials of the present invention need to be in specific positions. If the positions of the first and second active materials are interchanged, the rate performance of the battery will be deteriorated due to the lower kinetic performance of the first active material.

[0036] Preferably, the sphericity Ds of the first active material is in the range of 0.8 ≤ Ds < 1.0, for example, it can be 0.8, 0.85, 0.9, 0.95 or 0.99, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0037] The sphericity Ds of the first active material in this invention is preferably above 0.8. If the sphericity Ds of the first active material is too low, the pores between the particles of the first active material are large, and the particles will bridge during the rolling process, making it difficult to form the densest packing, which will reduce the compaction density of the positive electrode sheet and thus reduce the energy density of the battery.

[0038] Preferably, the aspect ratio Ra of the second active material is in the range of 1.5≤Ra≤3.0, for example, it can be 1.5, 2.0, 2.5 or 3.0, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0039] The aspect ratio Ra of the second active material of the present invention is preferably within a specific range. If the aspect ratio is too low, the improvement of the battery rate performance is not obvious; however, if the aspect ratio is too high, on the one hand, the manufacturing process is difficult, and on the other hand, the compaction density of the positive electrode sheet is reduced too much, resulting in excessive loss of battery energy density.

[0040] Preferably, the particle size D1v50 of the first active material is 1μm-2μm, for example, it can be 1μm, 1.2μm, 1.4μm, 1.6μm, 1.8μm or 2μm, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0041] Preferably, the particle size D2v50 of the second active material is 0.5μm-1.5μm, for example, it can be 0.5μm, 0.7μm, 0.9μm, 1.1μm, 1.3μm or 1.5μm, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0042] The particle size of the first active material and the particle size of the second active material in this invention are preferably within a specific range, which can achieve a balance between compaction density and capacity. When the particle size is too large, due to the long bulk output distance, the specific capacity of the positive electrode is not easily fully utilized in practical applications, resulting in capacity drift. This can easily lead to insufficient NP ratio (the ratio of the capacity of the negative electrode to the capacity of the positive electrode). When the NP ratio is insufficient, the capacity of the negative electrode cannot fully accommodate the lithium ions of the positive electrode, and the excess part is deposited on the surface, which can lead to lithium plating. When the particle size is too small, it will affect the compaction density of the electrode, resulting in a decrease in the energy density of the battery.

[0043] Furthermore, the particle size D2v50 of the second active material is smaller than that of the first active material D1v50, which is beneficial for matching the insertion and extraction sequence of lithium ions during charging and discharging, thereby improving rate performance.

[0044] Preferably, the difference between the particle size D1v90 and the particle size D1v10 of the first active material is 1.5μm-2.5μm, for example, it can be 1.5μm, 1.7μm, 1.9μm, 2.1μm, 2.3μm or 2.5μm, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0045] When the difference between the particle size D1v90 and the particle size D1v10 of the first active material of the present invention is too small, the particles are uniform and it is not easy to form a good particle size distribution, and the increase in electrode compaction density is limited. However, when the difference is too large, on the one hand, the small particles are too small, and the slurry is not easy to disperse during the processing, which may cause processing problems such as particle agglomeration and slurry gelation. On the other hand, the large particles are too large, which may cause capacity drift and lead to problems such as lithium plating.

[0046] Preferably, the thickness d1 of the first active material layer is 60μm-120μm, for example, it can be 60μm, 80μm, 100μm or 120μm, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0047] Preferably, the thickness d2 of the second active material layer is 60μm-120μm, for example, it can be 60μm, 80μm, 100μm or 120μm, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0048] The thickness d1 of the first active material layer and the thickness d2 of the second active material layer are preferably within a specific range. If the thickness of the active material layer is too low, the battery energy density will be insufficient and the manufacturing process will be difficult. However, if the thickness of the active material layer is too high, it will affect the rate performance of the battery.

[0049] Preferably, the compaction density of the positive electrode sheet is 2.55 g / cm³. 3 The above, for example, could be 2.55 g / cm³. 3 2.6g / cm 3 2.65g / cm 3 Or 2.7g / cm 3 However, this does not limit the listed values; other unlisted values ​​within the range are also applicable.

[0050] Preferably, the first active material and the second active material are each independently selected from any one or a combination of at least two of lithium iron phosphate, lithium manganese iron phosphate, or lithium nickel cobalt manganese oxide.

[0051] Preferably, the first active material includes a first dopant element, wherein the first dopant element includes any one or a combination of at least two of Ti, V or Ni, and the mass content of the first dopant element in the first active material is 1000ppm-5000ppm, for example, it can be 1000ppm, 2000ppm, 3000ppm, 4000ppm or 5000ppm, but is not limited to the listed values, and other unlisted values ​​within the range are also applicable.

[0052] The first doping element in this invention mainly plays the role of suppressing grain production. Preferably, the doping amount of the first doping element is within a specific range. If the doping amount is too low, the proportion of large particles will be high, affecting the rate performance of the battery; but if the doping amount is too high, the proportion of small particles will be high, affecting the compaction density of the positive electrode sheet.

[0053] Preferably, the second active material includes a second doping element, wherein the second doping element includes Mn, and the mass content of the second doping element in the second active material is 1000ppm-3000ppm, for example, it can be 1000ppm, 1500ppm, 2000ppm, 2500ppm or 3000ppm, but is not limited to the listed values, and other unlisted values ​​within the range are also applicable.

[0054] The second doping element in this invention mainly plays the role of regulating particle morphology. If the content of the second doping element is too low, it will affect the morphology of the second active material, thereby affecting the rate performance of the battery. However, if the content of the second doping element is too high, it will also affect the morphology of the second active material, causing the compaction of the positive electrode sheet to be reduced too much.

[0055] Preferably, the difference between the weight-average molecular weight ω1 of the first adhesive and the weight-average molecular weight ω2 of the second adhesive is 30,000-100,000, for example, it can be 30,000, 50,000, 70,000, 90,000 or 100,000, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0056] The second active material of this invention is more difficult to process than the first active material, requiring a binder with a smaller molecular weight to ensure the slurry effect. However, binders with smaller molecular weights also have the disadvantage of low peel strength. Therefore, the molecular weight difference between the first binder and the second binder is preferably within a specific range, thereby ensuring both the slurry effect and the peel strength of the positive electrode sheet. If the weight-average molecular weight of the second binder is too large, the second positive electrode slurry will gel and cannot be processed, and only a positive electrode sheet containing the first active material layer can be prepared.

[0057] Preferably, the weight-average molecular weight ω2 of the second adhesive is 350,000 to 420,000, for example, it can be 350,000, 370,000, 390,000, 410,000 or 420,000, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0058] Preferably, the first adhesive and the second adhesive are each independently selected from any one or a combination of at least two of polyvinylidene fluoride, carboxylic acid-modified polyvinylidene fluoride, or acrylic acid-modified polyvinylidene fluoride.

[0059] Preferably, the first active material layer further includes a first conductive agent, and the mass ratio of the first active material, the first binder and the first conductive agent is (96.5~98.5):(1.5~2.5):(0~1), for example, it can be 96.5:2.5:1, 97:2.5:0.5, 97.5:1.5:1, 98:2:0 or 98.5:1:0.5, but is not limited to the listed values, and other unlisted values ​​within the range are also applicable.

[0060] Preferably, the second active material layer further includes a second conductive agent, and the mass ratio of the second active material, the second binder and the second conductive agent is (97~98.5):(1.0~1.5):(0.5~1.5), for example, it can be 97:1.5:1.5, 97.5:1.0:1.5, 98.0:1.0:1.0 or 98.5:1.0:0.5, but is not limited to the listed values, and other unlisted values ​​within the range are also applicable.

[0061] Preferably, the first conductive agent and the second conductive agent each independently comprise any one or a combination of at least two of conductive carbon black, graphene, carbon nanotubes, or carbon nanofibers.

[0062] In one specific embodiment, the present invention provides a method for preparing the positive electrode sheet, the method comprising the following steps:

[0063] The slurry of the first active material layer is coated on at least one side of the current collector. After drying, the slurry of the second active material layer is coated on the surface of the first active material layer. After drying and rolling, the positive electrode sheet is obtained.

[0064] In one specific embodiment, the present invention provides a battery, the battery comprising the aforementioned positive electrode plate.

[0065] The technical solution of the present invention will be further illustrated below through specific embodiments. Those skilled in the art should understand that the embodiments are merely illustrative of the present invention and should not be construed as limiting the invention.

[0066] Example 1

[0067] This embodiment provides a positive electrode sheet, which includes a current collector and an active layer on one side surface of the current collector. The active layer includes a first active material layer and a second active material layer. The first active material layer is disposed on the surface of the current collector, and the second active material layer is disposed on the side surface of the first active material layer away from the current collector.

[0068] The thickness d1 of the first active material layer is 90 μm, comprising a first active material, a first binder, and a first conductive agent in a mass ratio of 97.5:1.5:1.5. The first active material has a spherical morphology with a sphericity Ds of 0.81, a particle size D1v50 of 1.02 μm, and a difference of 1.53 μm between particle sizes D1v90 and D1v10. The first active material is lithium iron phosphate doped with Ti (doping amount of 3000 ppm), the first binder is PVDF with a weight-average molecular weight ω1 of 470,000, and the first conductive agent is conductive carbon black.

[0069] The second active material layer has a thickness d2 of 90 μm and includes a second active material, a second binder, and a second conductive agent in a mass ratio of 97:1.5:1.5. The second active material has a rod-shaped morphology, an aspect ratio Ra of 2.97, and a particle size D2v50 of 0.53 μm. The second active material is lithium iron phosphate doped with Mn (doping amount of 2000 ppm). The second binder is PVDF with a weight average molecular weight ω2 of 407,000. The second conductive agent is conductive carbon black.

[0070] The method for preparing the positive electrode sheet includes the following steps:

[0071] According to the formula, the first active material, the first binder, the first conductive agent and N-methylpyrrolidone are stirred evenly to obtain the first positive electrode slurry. The second active material, the second binder, the second conductive agent and N-methylpyrrolidone are stirred evenly to obtain the second positive electrode slurry.

[0072] The first positive electrode slurry is coated onto one side of the current collector and dried to obtain the first active material layer. The second positive electrode slurry is coated onto the surface of the first active material layer, dried, and then rolled to obtain the positive electrode sheet.

[0073] Examples 2-14

[0074] Examples 2-14 provide a positive electrode sheet, which is the same as that in Example 1 except for the parameter adaptation changes in Table 1; wherein, in Example 2, the first binder is PVDF with a weight average molecular weight ω1 of 437,000, in Example 3 the second binder is PVDF with a weight average molecular weight ω2 of 370,000, and in Example 14 the second binder is PVDF with a weight average molecular weight ω2 of 365,000.

[0075] Comparative Example 1

[0076] This comparative example provides a positive electrode sheet, which is the same as in Example 1 except that the second active material is replaced by the first active material by the same mass, so that the positive electrode sheet only includes the first active material.

[0077] Comparative Example 2

[0078] This comparative example provides a positive electrode sheet, which is the same as in Example 1 except that the first active material is replaced by the second active material by the same mass, so that the positive electrode sheet only includes the second active material.

[0079] Comparative Example 3

[0080] This comparative example provides a positive electrode sheet, which is the same as in Example 1 except that the positions of the first active material and the second active material are interchanged, that is, the first active material is in the second active material layer and the second active material is in the first active material layer.

[0081] The positive electrode sheets obtained in Examples 1-14 and Comparative Examples 1-3 were used to prepare batteries. The preparation process is as follows: artificial graphite, carboxymethyl cellulose, styrene-butadiene rubber, and Super-P were mixed with deionized water in a stirring vessel at a ratio of 95.5:1.5:2:1 to form a homogeneous negative electrode slurry; the negative electrode slurry was coated onto a current collector and dried to obtain a negative electrode roll; the negative electrode roll was rolled to the target thickness on a roller press to obtain a rolled negative electrode sheet; the positive and negative electrode sheets were cut into the required sizes and stacked with a 12μm thick PP separator to obtain a dry cell; the dry cell was placed in an aluminum-plastic film and packaged to obtain a pouch cell; the pouch cell was dried in a vacuum drying oven and injected with an electrolyte. The electrolyte solvent was DMC, EMC, and EC in a volume ratio of 1:1:1 and contained 1.5 mol / L LiPF6; after formation and capacity testing, the pouch battery to be tested was obtained.

[0082] The method for testing rate performance is as follows:

[0083] 1C constant current charging to 3.65V, constant voltage charging to current ≤0.05C;

[0084] Discharge at a constant current of 1C to 2.5V, then mark the capacity C1;

[0085] 1C constant current charging to 3.65V, constant voltage charging to current ≤0.05C;

[0086] Discharge at a constant current of 5C to 2.5V, then mark the capacity C2;

[0087] The 5C discharge capacity of the battery is calculated using C2 / C1×100%.

[0088] The parameters, 5C rate performance, and compaction density of the positive electrode sheets described in the above embodiments and comparative examples are shown in Table 1. The sphericity test method is as follows: SEM testing is performed on the first active material, and the particles are statistically analyzed. The sphericity Ds is calculated using the formula: Ds = R_maximum inscribed circle radius of the particle / R_minimum circumscribed circle radius of the particle. The sphericity of each particle in the SEM is averaged to obtain the sphericity. The aspect ratio test method is as follows: SEM testing is performed on the second active material, and the particles are statistically analyzed. The aspect ratio is calculated using the formula: the ratio of the longest diameter passing through the interior of the particle to its longest perpendicular diameter. The particle size test method is as follows: a Malvern 3000 laser particle size analyzer is used. The compaction density test method for the positive electrode sheet is as follows: different roller pressing pressures are applied to different electrode sheet thicknesses using a roller press. The compaction density is calculated based on this. A coating film tester is used to test the flexibility of the compacted electrode sheet. The compaction density through the No. 4 needle of the coating film is taken as the electrode sheet compaction density.

[0089] Table 1

[0090]

[0091] As can be seen from Table 1 above:

[0092] As shown in Examples 1 and Comparative Examples 1-2, when the positive electrode sheet includes only the first active material or only the second active material, it is impossible to simultaneously achieve both compaction density and rate performance. As shown in Examples 1 and Comparative Example 3, even if the positive electrode sheet includes both the first and second active materials, but their positions are interchanged, it is still impossible to simultaneously achieve both compaction density and rate performance. As shown in Examples 1 and 14, as the molecular weight difference between the first binder and the second binder increases, the rate performance deteriorates. As shown in Examples 1, 4, and 9, as the sphericity of the first active material increases, the electrode compaction density increases, and the rate performance decreases slightly; however, when the sphericity is too small, the electrode compaction density will decrease. As shown in Examples 1 and 9-10, as the particle size D1v50 of the first active material increases, the electrode compaction increases. The rate performance deteriorates, but when the particle size D1v50 is too large, the rate performance deteriorates significantly due to the increased solid-phase diffusion distance; when the particle size D1v50 is too small, the electrode compaction density deteriorates due to the excessive number of small particles; as shown in Examples 1 and 10-11, as the difference in particle size between the large and small particles of the first active material increases, the electrode performance improves due to particle gradation, and the rate performance decreases due to the larger particles, but when the difference in particle size between the large and small particles is too large, the rate performance deteriorates significantly, and when the difference in particle size between the large and small particles is too small, the electrode compaction deteriorates significantly; as shown in Examples 1 and 12-13, as the aspect ratio of the second active material decreases, the rate performance deteriorates slightly, and the electrode compaction improves slightly, but when the aspect ratio is too small, the rate performance deteriorates significantly, and when the aspect ratio is too large, the electrode compaction deteriorates significantly. Preferably, the aspect ratio of the second active material is within a specific range.

[0093] The above description is only a specific embodiment of the present invention, but the protection scope of the present invention is not limited thereto. Those skilled in the art should understand that any changes or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in the present invention fall within the protection and disclosure scope of the present invention.

Claims

1. A positive electrode plate, characterized in that, The positive electrode includes a current collector and an active layer on at least one side surface of the current collector. The active layer includes a first active material layer and a second active material layer. The first active material layer is disposed on the surface of the current collector, and the second active material layer is disposed on the side surface of the first active material layer away from the current collector. The first active material layer includes a first active material and a first binder, and the second active material layer includes a second active material and a second binder; The first active material has a spherical and / or near-spherical morphology, and the second active material has an ellipsoidal and / or rod-shaped morphology.

2. The positive electrode sheet according to claim 1, characterized in that, The sphericity Ds of the first active material ranges from 0.8 to 1.

0. And / or, the aspect ratio Ra of the second active material is in the range of 1.5≤Ra≤3.

0.

3. The positive electrode sheet according to claim 1 or 2, characterized in that, The particle size D1v50 of the first active material is 1μm-2μm; And / or, the particle size D2v50 of the second active material is 0.5 μm-1.5 μm; And / or, the difference between the particle size D1v90 and the particle size D1v10 of the first active material is 1.5μm-2.5μm.

4. The positive electrode sheet according to claim 1 or 2, characterized in that, The thickness d1 of the first active material layer is 60μm-120μm; And / or, the thickness d2 of the second active material layer is 60μm-120μm.

5. The positive electrode sheet according to claim 1 or 2, characterized in that, The compaction density of the positive electrode sheet is 2.55 g / cm³. 3 above.

6. The positive electrode sheet according to claim 1 or 2, characterized in that, The first active material and the second active material are each independently selected from any one or a combination of at least two of lithium iron phosphate, lithium manganese iron phosphate, or lithium nickel cobalt manganese oxide. And / or, the first active material includes a first doping element, wherein the first doping element includes any one or a combination of at least two of Ti, V or Ni, and the mass content of the first doping element in the first active material is 1000ppm-5000ppm. And / or, the second active material includes a second doping element, wherein the second doping element includes Mn, and the mass content of the second doping element in the second active material is 1000ppm-3000ppm.

7. The positive electrode sheet according to claim 1 or 2, characterized in that, The difference between the weight-average molecular weight ω1 of the first adhesive and the weight-average molecular weight ω2 of the second adhesive is 30,000-100,000. And / or, the first adhesive and the second adhesive are each independently selected from any one or a combination of at least two of polyvinylidene fluoride, carboxylic acid-modified polyvinylidene fluoride, or acrylic acid-modified polyvinylidene fluoride.

8. The positive electrode sheet according to claim 1 or 2, characterized in that, The first active material layer further includes a first conductive agent, and the mass ratio of the first active material, the first binder and the first conductive agent is (96.5~98.5):(1.5~2.5):(0~1); And / or, the second active material layer further includes a second conductive agent, wherein the mass ratio of the second active material, the second binder and the second conductive agent is (97~98.5):(1.0~1.5):(0.5~1.5).

9. A method for preparing a positive electrode sheet as described in any one of claims 1-8, characterized in that, The preparation method includes the following steps: The slurry of the first active material layer is coated on at least one side of the current collector. After drying, the slurry of the second active material layer is coated on the surface of the first active material layer. After drying and rolling, the positive electrode sheet is obtained.

10. A battery, characterized in that, The battery includes a positive electrode as described in any one of claims 1-8.

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