A positive electrode sheet and a battery

Abstract

The application relates to the technical field of batteries, in particular to a positive plate and a battery, the positive plate comprising a positive current collector and a positive active layer located on at least one side surface of the positive current collector, the positive active layer comprising a first positive active layer and a second positive active layer, the first positive active layer being located on the surface of the second positive active layer, and the second positive active layer being located on the surface of the positive current collector. By adjusting the particle size distribution of the positive active material particles in the upper and lower coating layers, the positive plate can realize high compaction density while guaranteeing excellent ion and electron conductivity, thereby improving the energy density, charge and discharge performance and cycle storage performance of the battery containing the positive plate.

Description

Technical Field

[0001] This invention relates to the field of lithium-ion battery technology, and more particularly to a positive electrode and a battery. Background Technology

[0002] In recent years, with the rapid development of new energy vehicles and the demand for large-scale energy storage, the market's requirements for battery energy density have further increased. Currently, the highest initial charge capacity of lithium iron phosphate batteries has reached 162mAh / g-163mAh / g, approaching the theoretical capacity of lithium iron phosphate cathode active materials. Therefore, further improving battery energy density requires increasing the compaction density of the electrode sheets. However, as the compaction density increases, the porosity of the electrode sheets decreases further. This decrease in porosity leads to a decline in the kinetic performance of the electrode during lithium insertion / extraction, affecting the battery's rate charge / discharge performance. Consequently, it reduces the state of charge (SOC) corresponding to the lithium plating potential at high rates, increases charging time, further increases the discharge coefficient (DCR), and increases resistance to lithium-ion charge transfer and diffusion. It also has a certain impact on the battery's high-temperature storage performance. Therefore, it is crucial to invent a battery with high electrode compaction, good fast-charging kinetics, and excellent DCR, storage, and cycle performance. Summary of the Invention

[0003] To address the aforementioned problems, this invention provides a positive electrode sheet and a battery. By adjusting the particle size distribution of the positive electrode active material particles in the upper and lower coatings, this invention enables the positive electrode sheet to achieve high compaction density while ensuring excellent ionic and electronic conductivity, thereby improving the energy density, charge-discharge performance, and cycle storage performance of the battery containing this positive electrode sheet.

[0004] To achieve the above objectives, the technical solution adopted by the present invention is as follows: A first aspect of the present invention provides a positive electrode sheet, including a positive current collector and a positive active layer located on at least one side surface of the positive current collector, the positive active layer including a first positive active layer and a second positive active layer, the first positive active layer being located on the surface of the second positive active layer, and the second positive active layer being located on the surface of the positive current collector; The first positive electrode active layer includes first positive electrode active material particles, which include first lithium iron phosphate particles; the second positive electrode active layer includes second positive electrode active material particles, which include second lithium iron phosphate particles; the first positive electrode active material particles and the second positive electrode active material particles satisfy: 1 ​​< Span1 / Span2 ≤ 10, where Span is a particle size distribution width parameter, Span = (Dv90 - Dv10) / Dv50, Span1 is the Span value of the first positive electrode active material particle, and Span2 is the Span value of the second positive electrode active material particle.

[0005] A second aspect of the present invention provides a battery comprising the positive electrode sheet described in the first aspect of the present invention.

[0006] By employing the above technical solution, the present invention has at least the following advantages compared with the prior art: This invention adjusts the particle size distribution of the positive electrode active material particles in the upper and lower coatings, ensuring that the span value of the first positive electrode active material particles in the first positive electrode active layer is greater than the span value of the second positive electrode active material particles in the second positive electrode active layer, while satisfying the relationship: 1 < Span1 / Span2 ≤ 10. This allows the positive electrode to achieve high compaction density while effectively ensuring excellent ionic and electronic conductivity of the active layer, thereby improving the energy density, charge-discharge performance, and cycle storage performance of the battery containing this positive electrode. Firstly, by controlling the particle size distribution of the positive electrode active material particles in the upper and lower coatings to satisfy the above relationship, it is beneficial to form a rich porous structure in the first positive electrode active layer, which not only provides rapid diffusion for lithium ions but also... The channel also reduces the resistance to lithium ion migration from the second positive electrode active layer to the upper layer, significantly improving the electrode's lithium insertion / extraction kinetics and ensuring the electrode's fast-charging capability. Secondly, this design helps improve particle packing density, effectively increasing the electrode's compaction density and further ensuring the overall energy density of the electrode. The synergistic effect of the two-layer structure not only meets the high compaction requirements of the electrode but also avoids problems such as low porosity and hindered ion diffusion caused by a single structure. This allows the positive electrode to optimize lithium ion transport efficiency and electronic conduction performance while ensuring high energy density, thereby effectively improving the battery's DCR characteristics, enhancing the battery's rate charge / discharge performance, cycle stability, and high-temperature storage performance, meeting the requirements of new energy vehicles and large-scale energy storage scenarios for lithium iron phosphate batteries.

[0007] The endpoints and any values ​​of the ranges disclosed herein are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of the various ranges, the endpoint values ​​of the various ranges and individual point values, and individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed herein. Attached Figure Description

[0008] Figure 1 The diagram shown is a schematic diagram of the positive electrode sheet provided in an example of the present invention.

[0009] Figure 2 The image shown is a Raman spectrum of the first positive electrode active material particle provided in an example of the present invention.

[0010] Figure 3 The image shown is a Raman spectrum of the second positive electrode active material particles provided in an example of the present invention.

[0011] Figure 4 The image shown is a cross-sectional SEM image of the first positive electrode active layer at a 1K magnification according to an example of the present invention.

[0012] Figure 5 The image shown is a cross-sectional SEM image of the first positive electrode active layer at a magnification of 10K according to an example of the present invention.

[0013] Figure 6 The image shown is a cross-sectional SEM image of the second positive electrode active layer at a magnification of 10K according to an example of the present invention. Detailed Implementation

[0014] The following provides a detailed description of specific embodiments of the present invention. It should be understood that the specific embodiments described herein are for illustrative and explanatory purposes only and are not intended to limit the invention. Unless otherwise specified herein, data ranges include endpoints.

[0015] A first aspect of the present invention provides a positive electrode sheet, comprising a positive current collector and a positive active layer located on at least one surface of the positive current collector, the positive active layer comprising a first positive active layer and a second positive active layer, the first positive active layer being located on the surface of the second positive active layer, and the second positive active layer being located on the surface of the positive current collector, such as... Figure 1 As shown; The first positive electrode active layer includes first positive electrode active material particles, which include first lithium iron phosphate particles; the second positive electrode active layer includes second positive electrode active material particles, which include second lithium iron phosphate particles; the first positive electrode active material particles and the second positive electrode active material particles satisfy: 1 ​​< Span1 / Span2 ≤ 10 (e.g., 1.1, 1.2, 1.3, 1.4, 1.5, 1.6, 1.7, 1.8, 1.9, 2, 3, 4, 5, 6, 7, 8, 9 or 10), where Span is the particle size distribution width parameter, Span = (Dv90 - Dv10) / Dv50, Span1 is the Span value of the first positive electrode active material particle, and Span2 is the Span value of the second positive electrode active material particle.

[0016] In this invention, Dv50 is the particle size corresponding to 50% of the cumulative particle size distribution in the volumetric particle size distribution of the first positive electrode active material particles / second positive electrode active material particles; Dv10 is the particle size corresponding to 10% of the cumulative particle size distribution in the volumetric particle size distribution of the first positive electrode active material particles / second positive electrode active material particles; and Dv90 is the particle size corresponding to 90% of the cumulative particle size distribution in the volumetric particle size distribution of the first positive electrode active material particles / second positive electrode active material particles. The volumetric particle size distribution of the first positive electrode active material particles / second positive electrode active material particles can be obtained by laser particle size distribution testing using a Mastersizer instrument. In a specific implementation, the positive electrode sheet is cleaned with DMC and baked at a high temperature of 30 degrees Celsius. The active material particles of the first and second positive electrode active layers are scraped out, and then heated to 500°C-600°C while simultaneously starting the extraction process. This yields powdered particles of the first and second positive electrode active materials. The particle size distribution of the first and second positive electrode active materials can then be obtained by measuring the obtained powders using a laser particle size analyzer Mastersizer 3000.

[0017] This invention adjusts the particle size distribution of the positive electrode active material particles in the upper and lower coatings, ensuring that the span value of the first positive electrode active material particles in the first positive electrode active layer is greater than the span value of the second positive electrode active material particles in the second positive electrode active layer, while satisfying the relationship: 1 < Span1 / Span2 ≤ 10. This allows the positive electrode to achieve high compaction density while maintaining excellent ionic and electronic conductivity, thereby improving the energy density, charge-discharge performance, and cycle storage performance of the battery containing this positive electrode. First, by controlling the particle size distribution of the positive electrode active material particles in the upper and lower coatings to satisfy the above relationship, it is beneficial to form a richer porous structure in the first positive electrode active layer. This not only provides a fast diffusion channel for lithium ions but also reduces the resistance to lithium ion migration from the second active layer to the upper layer, significantly improving the electrode's lithium insertion / extraction kinetics and ensuring the fast-charging capability of the electrode. Second, this design helps to improve the particle packing density, effectively increasing the compaction density of the electrode and further ensuring the overall energy density of the electrode. The two-layer structure works synergistically to meet the high compaction requirements of the electrode while avoiding problems such as low porosity and hindered ion diffusion caused by a single structure. This allows the positive electrode to optimize lithium-ion transport efficiency and electronic conduction performance while ensuring high energy density, thereby improving the battery's DCR characteristics and effectively enhancing the battery's rate charge and discharge performance, cycle stability, and high-temperature storage performance, meeting the requirements of new energy vehicles and large-scale energy storage scenarios for lithium iron phosphate batteries.

[0018] In one specific embodiment, the first positive electrode active material particles and the second positive electrode active material particles satisfy the condition: 0.1 ≤ D1 / D2 < 1, where D1 is the average particle size of the first positive electrode active material particles and D2 is the average particle size of the second positive electrode active material particles. Furthermore, by adjusting the average particle size of the first positive electrode active material particles to be smaller than that of the second positive electrode active material particles, and satisfying the above relationship, the present invention can further enhance the structural synergy between the upper and lower active layers. This results in the first positive electrode active layer having an excellent porous structure, and the second positive electrode active layer having dense particle packing. This simultaneously meets the high-compaction requirements of the electrode sheet while avoiding problems such as excessively low porosity and hindered ion diffusion caused by a single structure. This allows the positive electrode sheet to optimize lithium-ion transport efficiency and electronic conduction performance while ensuring high energy density. Moreover, by further controlling the relationship between D1 and D2 while simultaneously satisfying 1 < Span1 / Span2 ≤ 10, the upper active layer with small particle size and wide particle size distribution can form a richer pore structure, thereby significantly improving lithium-ion diffusion efficiency and electronic conductivity; the lower active layer with large particle size and narrow particle size distribution forms a denser active layer, thus balancing electronic conductivity and energy density.

[0019] In one specific embodiment, D1 is 200nm-400nm, for example, 200nm, 210nm, 220nm, 230nm, 240nm, 250nm, 260nm, 270nm, 280nm, 300nm, 310nm, 320nm, 330nm, 340nm, 350nm, 360nm, 370nm, 380nm, 390nm or 400nm.

[0020] In one specific embodiment, D2 is 400nm-1500nm, for example, 400nm, 500nm, 600nm, 700nm, 800nm, 900nm, 1000nm, 1100nm, 1200nm, 1300nm, 1400nm or 1500nm.

[0021] In this invention, the average particle size of the first positive electrode active material particles and the average particle size of the second positive electrode active material particles can be determined by the statistical method of electron microscopy images: First, a high-resolution morphological image of the active material particles is obtained using a scanning electron microscope (SEM) or a transmission electron microscope (TEM); then, 100-200 clear and independent active material particles are randomly selected from the surface of the first positive electrode active layer (after scraping off the first positive electrode active layer, the surface image of the second positive electrode active layer is scanned), their particle size is measured, and the arithmetic mean is calculated to obtain the average particle size of the positive electrode active material particles.

[0022] In one specific implementation, 3 ≤ Span1 ≤ 10, for example, 3, 4, 5, 6, 7, 8, 9 or 10.

[0023] In one specific implementation, 1 ≤ Span2 < 3, for example, 1, 1.5, 2, 2.5, 2.6, 2.7, 2.8, 2.9 or 3.

[0024] In one specific embodiment, the Dv10 of the first positive electrode active material particle is 200nm-400nm, for example, 200nm, 220nm, 240nm, 260nm, 280nm, 300nm, 320nm, 340nm, 360nm, 380nm, or 400nm, and the Dv50 of the first positive electrode active material particle is 400nm-800nm, for example, 400nm, 420nm, 440nm, 460nm, 480nm, 500nm, 520nm, 540nm, or 560nm. The first positive electrode active material particle has a Dv90 of 4000nm-10000nm, for example, 4000nm, 4500nm, 5000nm, 5500nm, 6000nm, 6500nm, 7000nm, 7500nm, 8000nm, 8500nm, 9000nm, 9500nm, or 10000nm, with wavelengths of 580nm, 600nm, 620nm, 640nm, 660nm, 680nm, 700nm, 720nm, 740nm, 760nm, or 800nm.

[0025] In one specific embodiment, the Dv10 of the second positive electrode active material particle is 300nm-600nm, for example, 300nm, 320nm, 340nm, 360nm, 380nm, 400nm, 420nm, 440nm, 460nm, 480nm, 500nm, 520nm, 540nm, 560nm, 580nm, or 600nm, and the Dv50 of the second positive electrode active material particle is 600nm-1500nm, for example... The wavelengths of the second positive electrode active material particles are 600nm, 700nm, 800nm, 900nm, 1000nm, 1100nm, 1200nm, 1300nm, 1400nm, or 1500nm, and the Dv90 of the particles is 1500nm-6000nm, for example, 1500nm, 2000nm, 2500nm, 3000nm, 3500nm, 4000nm, 4500nm, 5000nm, 5500nm, or 6000nm.

[0026] It should be noted that because nanoscale materials have a particle effect and high surface energy, most of what is observed at Dv90 are aggregates of positive electrode active material particles, thus exhibiting a larger particle size, while the actual primary particle size of the material is smaller.

[0027] In one specific embodiment, the first positive electrode active material particle further includes a first carbon coating layer disposed on the surface of the first lithium iron phosphate particle, and the second positive electrode active material particle further includes a second carbon coating layer disposed on the surface of the second lithium iron phosphate particle; the Raman peak intensity of the first positive electrode active material particle is higher than that of I. d / I g The Raman peak intensity ratio of the particles smaller than that of the second positive electrode active material is I. d / I g .

[0028] In one specific embodiment, the Raman peak intensity of the first positive electrode active material particle is higher than that of I. d / I g The Raman peak intensity of the second positive electrode active material particle is 0.7-0.95 (e.g., 0.7, 0.75, 0.8, 0.85, 0.86, 0.87, 0.88, 0.89, 0.90, 0.91, 0.92, 0.93, 0.94, or 0.95), which is higher than that of I. d / I g It is 0.95-1.2 (e.g., 0.95, 0.96, 0.97, 0.98, 0.99, 1.00, 1.01, 1.02, 1.03, 1.04, 1.05, 1.06, 1.07, 1.08, 1.09, 1.1, 1.11, 1.12, 1.13, 1.14, 1.15, 1.16, 1.17, 1.18, 1.19, or 1.2).

[0029] In this invention, the Raman peak intensity ratio I between the first positive electrode active material particles and the second positive electrode active material particles can be measured by Raman spectroscopy. d / I g ,like Figure 2 and Figure 3 As shown, the Raman peak intensity ratio I of the first positive electrode active material particle in an example is... d / I g The Raman peak intensity ratio of the second positive electrode active material particles I d / I g Raman peak intensity is higher than I d / I g This can reflect the degree of graphitization of the carbon coating layer on the surface of the first and second positive electrode active material particles (because of the D peak in the Raman spectrum (approximately 1350 cm⁻¹)). -1 The D peak can reflect defects and disordered structures in materials. The higher the defect density, the greater the intensity of the D peak, while the G peak in the Raman spectrum (approximately 1580 cm⁻¹) reflects the defects and disordered structures in materials. -1 ) Corresponding SP 2 The higher the intensity of the G peak in the ordered vibrations of hybrid carbon, the better the crystallinity of the material.d / I g The ratio of I to I usually reflects the degree of graphitization of carbon materials. d / I g The smaller the ratio, the fewer defects in the material, the higher the degree of graphitization, and the better the conductivity of the carbon material. This invention controls the Raman peak intensity ratio of the first positive electrode active material particles to I... d / I g The Raman peak intensity ratio of the particles smaller than that of the second positive electrode active material is I d / I g This process significantly improves the conductivity of the upper active material particles, thereby facilitating the rapid diffusion of lithium ions from the surface layer and reducing the resistance when lower ions diffuse to the upper layer. This significantly enhances the lithium insertion / extraction dynamics of the electrode, ensuring the fast-charging capability of the electrode. The lower layer is closer to the current collector, resulting in shorter and more efficient electron transport distance. The selection of active material particles with higher peak intensity in the lower layer provides sufficient conductivity to meet the material's requirements and promotes particle growth during the material synthesis process. This allows the positive electrode to maintain high energy density while optimizing lithium ion transport efficiency and electron conduction performance, thereby improving the battery's DCR characteristics and effectively enhancing the battery's rate charge / discharge performance, cycle stability, and high-temperature storage performance.

[0030] In this invention, the specific test method for the Raman peak intensity ratio of the first positive electrode active material particle and the second positive electrode active material particle can be the layered scraping powder Raman test method: Preparation of the upper layer (first positive electrode active material layer) powder: Using a blade, along the parallel direction of the electrode surface, gently scrape off the powder from the electrode surface according to the measured upper layer thickness H1, ensuring that the scraped powder comes only from the first positive electrode active layer; transfer the scraped powder to an oven to dry; Upper layer Raman test: Take the dried upper layer powder and spread it evenly on a glass slide. Use a Raman spectrometer with the following test parameters: laser wavelength 532nm, laser power 5mW, scanning range 99cm. -1 -3200cm -1 Five test points were randomly selected for testing, and the Raman spectra of each test point were recorded. Data processing: The D peak (approximately 1350 cm⁻¹) in the spectrum of each test point was read using Raman spectroscopy analysis software. -1 ) and G peak (approximately 1580cm) -1 The peak intensity of ) is used to calculate I at each test point. d / I g The ratio and average value are taken as the I of the first positive electrode active material particles. d / I gRatio (In addition, after calculating the Id / Ig ratio of 5 test points, if the ratio of a certain test point deviates from the average value of the other 4 test points by more than ±10%, it is determined that the test point may have been mixed with conductive agent. After removing the outlier, the average value is calculated using the ratios of the remaining test points; if there are more than 2 outliers, the test points need to be reselected); Lower layer powder preparation: After scraping off the upper layer powder, continue along the parallel direction of the electrode surface, according to the measured lower layer thickness H2, scrape off the remaining active layer powder, ensuring that the scraped powder comes only from the second positive electrode active layer, and then perform the same drying process; Lower layer Raman test: Use the same Raman test parameters to test the lower dried powder, calculate and take the average value as the I of the second positive electrode active material particles. d / I g ratio.

[0031] In one specific embodiment, the first carbon coating layer comprises a polyethylene glycol (PEG) and CN composite material, wherein the CN composite material comprises at least one of graphene-nitrogen composite material, polypyrrole, lithium 3,4-dihydroxybenzonitrile (Li₂DHBN), and polydopamine (PDA). Referring to a specific test method for Raman peak intensity ratio, the active layer powder is scraped in layers, and nitrogen element detection is achieved using SEM-EDS (scanning electron microscopy coupled to energy dispersive spectroscopy), which can reflect the presence, content, and coating uniformity of the first carbon coating layer.

[0032] In one specific embodiment, the second carbon coating layer comprises glucose and polyethylene glycol.

[0033] In one specific embodiment, the electrode resistance of the first positive electrode active layer at 26 MPa is 4 Ω·cm to 8 Ω·cm, for example, 4 Ω·cm, 5 Ω·cm, 6 Ω·cm, 7 Ω·cm or 8 Ω·cm.

[0034] In one specific embodiment, the electrode resistance of the second positive electrode active layer at 26 MPa is 10 Ω·cm to 25 Ω·cm, for example, 10 Ω·cm, 11 Ω·cm, 12 Ω·cm, 13 Ω·cm, 14 Ω·cm, 15 Ω·cm, 16 Ω·cm, 17 Ω·cm, 18 Ω·cm, 19 Ω·cm, 20 Ω·cm, 21 Ω·cm, 22 Ω·cm, 23, 24 Ω·cm or 25 Ω·cm.

[0035] The first carbon coating layer of the upper layer of the first lithium iron phosphate particles in the positive electrode includes a PEG+CN composite material. This coating material has a higher degree of graphitization, a denser coating layer, and better electronic conductivity, significantly reducing the contact resistance between particles, accelerating surface electron transport, and synergizing with the rich porosity of the upper small-diameter particles to significantly improve lithium-ion diffusion efficiency and ensure battery rate performance. The resulting electrode resistance, measured with an electrode resistivity meter, is 4-8 Ω·cm at 26 MPa. The second carbon coating layer of the lower layer of the second lithium iron phosphate particles in the positive electrode includes glucose+PEG. This coating material has a slightly lower degree of graphitization in its carbon layer. The carbon layer formed by the pyrolysis of glucose and PEG are adapted to the stacking requirements of large-diameter primary particles, ensuring high compaction density of the electrode while providing basic conductivity. The resulting electrode resistance is 10-25 Ω·cm at 26 MPa. The upper layer's low resistance addresses the bottleneck in surface ion-electron transport, while the lower layer's high-compaction resistance design balances energy density and conductivity, avoiding the problems of excellent conductivity but insufficient compaction or high compaction but poor conductivity caused by single coating. Simultaneously, the dense coating reduces side reactions between active materials and the electrolyte, improving battery cycle life and high-temperature storage performance in conjunction with resistance stability. In practical implementation, the electrode resistance testing method is as follows: Take the electrode to be tested and cut it into 5 cm × 5 cm samples; perform thickness measurements at multiple locations on the electrode sample, and take the average value as the sample thickness; place the electrode sample at the test position on the testing equipment, gradually apply pressure, and collect the resistance value at a pressure of 26 MPa; repeat the above test process at multiple test points on the electrode sample, collecting a total of 9 sets of data, and taking the average value as the electrode resistance test result.

[0036] In one specific embodiment, the first lithium iron phosphate particle includes primary particles and secondary particles, wherein the mechanical strength Cs of the secondary particles is greater than 40 MPa. Using a mechanical strength tester, pressure is gradually applied to the secondary particles separated from the first lithium iron phosphate particles by centrifugation, and the pressure value at which the particles break is recorded; this pressure value is the mechanical strength Cs of the secondary particles. The secondary particles are filled with pores. By controlling the mechanical strength Cs of the secondary particles of the first lithium iron phosphate particles to be greater than 40 MPa, the breakage of the secondary particles during electrode compaction can be avoided, maintaining the integrity of the original pore structure between particles and ensuring unobstructed lithium-ion rapid diffusion channels. Simultaneously, it balances particle structure stability and porosity, neither affecting the high-pressure compaction requirements of the electrode nor hindering surface ion transport efficiency, thus contributing to optimized battery fast-charging performance.

[0037] In one specific embodiment, the second lithium iron phosphate particle includes primary particles. The primary particles have a dense structure and regular morphology, resulting in lower porosity during stacking. This significantly improves the particle packing density of the second positive electrode active layer, helping the electrode achieve high compaction density and ensuring battery energy density. Simultaneously, the inclusion of primary particles in the bottom layer reduces interfacial contact resistance between particles and, being close to the current collector, facilitates a more direct electron transport path. Combined with the underlying carbon coating and conductive agent design, this further optimizes electron conduction efficiency, reduces battery DCR, and improves cycle stability.

[0038] In one specific embodiment, the powder resistivity of the first positive electrode active layer is 1Ω·cm-5Ω·cm, for example, 1Ω·cm, 2Ω·cm, 3Ω·cm, 4Ω·cm or 5Ω·cm, and the powder resistivity of the second positive electrode active layer is 5Ω·cm-25Ω·cm, for example, 5Ω·cm, 6Ω·cm, 7Ω·cm, 8Ω·cm, 9Ω·cm, 10Ω·cm, 11Ω·cm, 12Ω·cm, 13Ω·cm, 14Ω·cm, 15Ω·cm, 16Ω·cm, 17Ω·cm, 18Ω·cm, 19Ω·cm, 20Ω·cm, 21Ω·cm, 22Ω·cm, 23Ω·cm, 24Ω·cm or 25Ω·cm.

[0039] The low resistivity of the first positive electrode active layer facilitates the diffusion of surface electrons to the bottom layer and enhances the surface charge transfer capability, further promoting the transport of ions and electrons in this layer. The second positive electrode active layer is closer to the current collector and inherently has an advantage in electron diffusion, so its resistivity can be slightly higher without affecting the overall electron transport to the current collector. The powder resistivity of the first and second positive electrode active layers of this invention can be measured using a four-probe powder resistivity meter. The specific testing method is as follows: Take the electrode sheet to be tested and cut it into 5 cm × 5 cm pieces. A sample of cm was prepared; thickness tests were performed at multiple locations on the electrode sample, and the average value was taken as the thickness of the sample; the electrode sample was placed at the test position of the testing equipment, and pressure was gradually applied until the pressure stabilized at 50.93 MPa, at which point the corresponding resistance value was collected; the above test process was repeated at multiple test points on the electrode sample, and a total of 9 sets of data were tested, and the average value was taken as the powder resistivity test result of the first positive electrode active layer; the first positive electrode active layer on the surface was gently scraped off with a blade along a direction parallel to the electrode surface, and after scraping, the sample surface was cleaned with a lint-free cloth dipped in dimethyl carbonate (DMC), dried, and the thickness of the second positive electrode active layer and the resistance values ​​of 9 evenly distributed test points at 50.93 MPa were tested in the same way as above, and the average value was taken as the powder resistivity test result of the second positive electrode active layer.

[0040] In one specific embodiment, the thickness ratio of the first positive electrode active layer to the second positive electrode active layer is (3:7)-(5:5), for example, 3:7, 4:6, or 5:5.

[0041] In a preferred embodiment, the thickness of the first positive electrode active layer is less than the thickness of the second positive electrode active layer. This thickness design is beneficial for the transport and diffusion of ions and electrons. Furthermore, the first positive electrode active layer should not be too thick, as this would affect the compaction density of the electrode and reduce the energy density of the battery.

[0042] In one specific embodiment, the mass content of the first positive electrode active material particles in the first positive electrode active layer is 95%-97%, for example, 95%, 95.5%, 96%, 96.5% or 97%; the mass content of the second positive electrode active material particles in the second positive electrode active layer is 97%-98.5%, for example, 97%, 97.5%, 98% or 98.5%.

[0043] In one specific embodiment, the first positive electrode active layer further includes a first binder, the first binder including polyvinylidene fluoride (PVDF), the first positive electrode active layer has a first weight loss range at 400℃-500℃, and the weight loss rate of the first weight loss range is 1.7%-2.1%, for example 1.7%, 1.8%, 1.9%, 2% or 2.1%.

[0044] In one specific embodiment, the second positive electrode active layer further includes a second binder, the second binder including polyimide (PI), and the second positive electrode active layer has a second weight loss range at 500℃-600℃, the weight loss rate of the second weight loss range being 1%-1.4%, for example 1%, 1.1%, 1.2%, 1.3% or 1.4%.

[0045] The first weight loss range (400℃-500℃, weight loss rate 1.7%-2.1%) corresponds to the amount of polyvinylidene fluoride added. By controlling it within this range, sufficient bonding force can be provided for the small-diameter particles (200nm-500nm) of the first positive electrode active layer, preventing surface cracking and detachment during electrode processing or charge-discharge cycles. At the same time, the amount of binder can be controlled to prevent clogging of the pores between particles, ensuring unobstructed lithium-ion rapid diffusion channels, and balancing structural stability and fast-charging kinetic performance. The second weight loss range (500℃-600℃, weight loss rate 1%-1.4%) matches the low addition ratio of polyimide, which can maximize the proportion of active material in the second positive electrode active layer (97%-98.5%), helping the electrode achieve high compaction density, thereby further improving the battery energy density. At the same time, an appropriate amount of polyimide, with its excellent thermal stability and bonding force, prevents particle agglomeration or detachment during high compaction, balancing structural strength and energy density. The upper layer meets the requirements of fast charging in terms of pore structure and structural stability, while the lower layer supports high compaction and high energy density. Furthermore, by controlling the clearly defined weight loss range and weight loss rate range, it can serve as a characterization basis for the two layers of binder components, which facilitates quality control.

[0046] In one specific embodiment, the first positive electrode active layer further includes a first conductive agent, a second conductive agent, and a third conductive agent. The first conductive agent includes conductive carbon black, the second conductive agent includes carbon nanotubes, and the third conductive agent includes graphene. In a cross-sectional SEM image of the first positive electrode active layer at 1K magnification, as shown... Figure 4 As shown, within any 50μm × 50μm area, the number of graphene atoms is greater than or equal to 5; in the cross-sectional SEM image of the first positive electrode active layer at 10K magnification, as shown... Figure 5 As shown, within any 10μm×10μm area, the number of carbon nanotubes is greater than 100.

[0047] In one specific embodiment, the second positive electrode active layer further includes a fourth conductive agent, which comprises conductive carbon black; within an arbitrary 10μm × 10μm area selected from the cross-sectional SEM image of the second positive electrode active layer at 10K magnification, such as Figure 6 As shown, the number of conductive carbon black particles is greater than 500.

[0048] The first positive electrode active layer comprises three conductive agents that together form a three-dimensional composite conductive system. By controlling the number of conductive agents (≥5 graphene cells in a 50μm×50μm region and >100 carbon nanotubes in a 10μm×10μm region), a continuous and efficient electron transport network can be constructed. The sheet-like structure of graphene can bridge across particles, and the one-dimensional structure of carbon nanotubes connects the pores. Combined with the filling effect of conductive carbon black, electrons transported from the upper active material can be rapidly conducted to the lower layer and discharged through the current collector, significantly reducing the surface electron diffusion resistance. Combined with the abundant pores of the small-diameter particles, this achieves rapid ion and electron transport, ensuring the fast-charging dynamic performance of the electrode. The conductive carbon black in the second positive electrode active layer and its quantity adjustment (>500 particles within a 10μm×10μm area) allow for highly dispersed conductive carbon black to uniformly fill the gaps between large-diameter primary particles. This ensures high compaction density while forming a dense electron conduction pathway. Furthermore, its proximity to the current collector shortens electron transport distance, rapidly guiding electrons to the current collector. This design, tailored to the high-activity material ratio of the lower layer, balances energy density and conductivity. This invention effectively solves the surface layer's ion-electron transport efficiency problem by designing different conductive agent configurations for the two active materials, while simultaneously ensuring conductivity and high compaction requirements of the lower layer. This avoids uneven conduction or pore blockage caused by a single conductive agent design, thereby improving the battery's rate charge / discharge performance, cycle stability, and DCR characteristics.

[0049] In one specific embodiment, the compacted density of the first positive electrode active material particles is 2.2 g / cm³. 3 -2.5g.cm 3 For example, 2.2g.cm 3 2.3g.cm 3 2.4g.cm 3 Or 2.5g.cm 3 The compacted density of the second positive electrode active material particles is 2.65 g / cm³. 3 -2.8g.cm 3 For example, 2.65g.cm 3 2.7g.cm 3 2.75g.cm 3 Or 2.8g.cm 3 The test method for powder compaction is based on the national standard GB / T44330-2024.

[0050] In one specific embodiment, the compaction density of the positive electrode sheet is 2.75 g·cm³. 3 -2.85g.cm 3 For example, 2.75g.cm 3 2.8g.cm 3Or 2.85g.cm 3 .

[0051] In one specific embodiment, the first positive electrode active layer further includes a first ion-conducting agent, which includes at least one of lithium lanthanum zirconium oxide (LLZO), lithium lanthanum titanium oxide (LLTO), and lithium titanium aluminum phosphate (LATP). The mass content of the first ion-conducting agent in the first positive electrode active layer is 0-0.5%, for example, 0, 0.1%, 0.2%, 0.3%, 0.4%, or 0.5%.

[0052] In one specific embodiment, the second positive electrode active layer further includes a second ion-conducting agent, which includes a lithium titanium aluminum lithium-carbon composite material. The mass content of the second ion-conducting agent in the second positive electrode active layer is 0-1%, for example, 0, 0.1%, 0.2%, 0.3%, 0.4%, 0.5%, 0.6%, 0.7%, 0.8%, 0.9% or 1%.

[0053] The addition of the first and second ion-conducting agents can utilize the excellent ion conduction capability of the fast ion conductor itself, and achieve electron-ion double-layer conduction in combination with the carbon coating layer, thereby compensating for the electronic insulation defects of the fast ion conductor. It can also further reduce lithium-ion diffusion resistance and charge transfer impedance, and enhance fast charging dynamic performance.

[0054] A second aspect of the present invention provides a battery comprising the positive electrode sheet described in the first aspect of the present invention.

[0055] In this invention, the battery further includes a negative electrode, a separator, and an electrolyte.

[0056] In this invention, the negative electrode sheet includes a negative electrode current collector and a negative electrode active layer located on at least one side of the surface of the negative electrode current collector. The negative electrode current collector can be copper foil or composite copper foil. The negative electrode active layer includes a negative electrode active material, a negative electrode conductive agent, and a negative electrode binder. The negative electrode conductive agent includes at least one of graphite, carbon black, graphene, carbon nanofibers, and carbon nanotubes, preferably carbon black. The negative electrode binder includes at least one of styrene-butadiene rubber, styrene-acrylic emulsion, polyacrylic acid, sodium carboxymethyl cellulose, and lithium carboxymethyl cellulose, preferably lithium carboxymethyl cellulose and lithium polyacrylate. The negative electrode active material includes at least one of graphite, silicon, silicon suboxide, hard carbon, soft carbon, and lithium titanate, preferably graphite.

[0057] In this invention, the separator can be any material suitable for secondary battery separators in the art, such as, but not limited to, at least one of polyethylene, polypropylene, polyvinylidene fluoride, aramid, polyethylene terephthalate, polytetrafluoroethylene, polyacrylonitrile, polyimide, polyamide, polyester, and natural fibers.

[0058] In this invention, the electrolyte comprises additives and an organic solvent. The organic solvent is a short-chain carbonate, which can reduce viscosity and solvation energy, increase conductivity and ion migration rate, and improve fast-charging performance. The additives contain Si-based, sulfate, and lithium salt types, resulting in inorganic SEM films with good stability, reduced side reactions, and high ionic conductivity.

[0059] In this invention, the battery is assembled from a positive electrode, a separator, a negative electrode, and an electrolyte. For example, the positive electrode, negative electrode, and separator are assembled into a cell using industry-standard winding or stacking methods, then encapsulated with an aluminum-plastic film, and subsequently undergo baking, electrolyte injection, formation, and secondary sealing processes to obtain a lithium-ion secondary battery.

[0060] The present invention will be further described in detail below with reference to specific embodiments. It should be understood that the following embodiments are merely illustrative and explanatory of the present invention and should not be construed as limiting the scope of protection of the present invention. All technologies implemented based on the above content of the present invention are covered within the scope of protection intended by the present invention.

[0061] Unless otherwise specified, the experimental methods used in the following examples are conventional methods; unless otherwise specified, the reagents and materials used in the following examples are commercially available.

[0062] Example 1 (1) Preparation of lithium iron phosphate cathode: The active material for the first positive electrode active layer is lithium iron phosphate (including primary and secondary particles, with the secondary particles having a mechanical strength Cs = 75 MPa). The surface coating material of the first lithium iron phosphate particles is a PEG+CN composite material, forming the first active material particles. The first positive electrode active layer slurry consists of the first active material particles, an upper conductive agent, an upper binder, and an upper ion-conducting agent. The mass content of the first active material particles in the first positive electrode active layer slurry is 95.5%. The upper conductive agent adopts a three-dimensional composite conductive agent body. The system comprises three layers: an upper conductive agent with a total mass content of 2%, which includes conductive carbon black (first conductive agent), carbon nanotubes (second conductive agent), and graphene (third conductive agent), with a mass ratio of 0.8%:0.6%:0.6% for conductive carbon black:carbon nanotubes:graphene; an upper binder consisting of polyvinylidene fluoride (first binder) with a mass content of 2.1%; and an upper slurry ion-conducting agent consisting of lithium titanium aluminum phosphate (first ion-conducting agent), with an average particle size of 150 nm and a mass content of 0.4%. The active material for the second positive electrode active layer is lithium iron phosphate (primary particles). The surface coating material of the second lithium iron phosphate particles is glucose + polyethylene glycol, forming the second active material particles. The second positive electrode active layer slurry consists of the second active material particles, a lower conductive agent, a lower binder, and a lower ion-conducting agent. The mass content of the second active material particles in the second positive electrode active layer slurry is 98%. The lower conductive agent is conductive carbon black (fourth conductive agent), with a mass content of 0.5%. The lower binder is polyimide (second binder), with a mass content of 1%. The lower ion-conducting additive is lithium titanium aluminum phosphate + carbon composite material, with an average particle size of 200 nm, and a mass content of 0.5%. The first positive electrode active layer slurry and the second positive electrode active layer slurry are prepared and mixed separately, filtered and impurity removed, and then fed into the inner mold cavity of the upper and lower layer die heads for double-layer coating. According to the thickness ratio of the upper and lower layers of 3:7 (upper layer is the first positive electrode active layer, lower layer is the second positive electrode active layer), a test piece is first made at the bottom. After passing the test piece, an upper layer slurry test piece is added on the bottom coating. After the test piece passes the test piece, a continuous coating operation is carried out to obtain the double-layer positive electrode sheet. (2) Preparation of negative electrode: The negative electrode uses artificial graphite as the negative electrode material, conductive carbon black as the conductive agent, and sodium carboxymethyl cellulose (CMC) and styrene-butadiene rubber (SBR) as binders. They are mixed in a mass ratio of 96:1:1.2:1.8, and deionized water is added as a solvent to form a slurry. After being mixed evenly, the slurry is coated in layers onto the surface of the copper foil current collector to obtain the negative electrode sheet.

[0063] (3) Preparation of electrolyte: The electrolyte is a mixed lithium salt system consisting of lithium hexafluorophosphate (LiPF6) and lithium bis(trifluoromethanesulfonyl)imide (LiTFSi). It uses ethylene carbonate (EC), dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), and additives. The corresponding materials are dissolved in a stirred reactor in the following proportions, stirred for 30 minutes, and then filtered and demagnetized to obtain the final electrolyte. The total mass of each component is 25% EC + 30% EMC + 25% DMC + 2.5% vinylene carbonate (VC) + 1% fluoroethylene carbonate (FEC) + 1.5% 1,3-propanesulfonyl lactone (DTD) + 5% LiFSI + 10% LiPF6.

[0064] (4) Preparation of lithium iron phosphate stacked lithium-ion batteries: The positive and negative electrode sheets were die-cut into the designed shapes. The positive electrode sheets, separator, and negative electrode sheets were stacked alternately in a Z-shaped stacking manner. The electrode cores and tabs were ultrasonically welded, with the positive electrode welded to the aluminum tabs and the negative electrode welded to the copper tabs. The stacked cores were then placed in a shell made of aluminum-plastic film by heat sealing. The stacked cores were sealed in the shell by heating, and electrolyte was added. The separator was a 11μm separator made of base film + ceramic + adhesive, thus obtaining a stacked lithium-ion battery. Formation was performed using a Blue Electric charging cabinet. After activation at 0.2C, the battery was charged at a constant current and constant voltage of 0.33C to 3.8V and discharged at 0.33C to 2.0V to obtain the lithium-ion battery of this embodiment. For specific settings, please refer to Table 1.

[0065] Example 2 group The battery was prepared according to the method of Example 1, except that the average particle size and particle size distribution width Span value of the first positive electrode active material particles and the second positive electrode active material particles were changed, so that the value of Span1 / Span2 was changed, as shown in Tables 1 and 2.

[0066] Comparative Example 1 The battery was prepared according to the method of Example 1, except that the average particle size and particle size distribution width Span value of the first positive electrode active material particles and the second positive electrode active material particles were changed, so that the value of Span1 / Span2 was changed, as shown in Tables 1 and 2.

[0067] Example 3 Group The battery was prepared according to the method of Example 1, except that the average particle size and particle size distribution width Span of the first positive electrode active material particles and the second positive electrode active material particles were changed, so that the value of D1 / D2 was changed, as shown in Tables 1 and 2.

[0068] Example 4 group The battery was prepared according to the method of Example 1, except that the average particle size and particle size distribution width Span value of the first positive electrode active material particles and the second positive electrode active material particles were changed, and the volume particle size parameters Dv10, Dv50 and Dv90 were changed at the same time. See Table 1 and Table 2 for details.

[0069] Comparative Example 2 The battery was prepared according to the method of Example 1, except that the average particle size and particle size distribution width Span value of the first positive electrode active material particles and the second positive electrode active material particles were changed, so that the values ​​of Span1 / Span2 and D1 / D2 were changed, as shown in Table 1 and Table 2.

[0070] Comparative Example 3 The battery was prepared according to the method of Example 1, except that only the second positive electrode active layer of the positive electrode sheet was coated with a single layer.

[0071] Example 5 group The battery was prepared according to the method of Example 1, except that the thicknesses of the first positive electrode active layer and the second positive electrode active layer were changed, thereby altering the thickness ratio of the upper and lower layers while keeping the total thickness of the two coatings unchanged. Specifically: Example 5-1: The thickness ratio of the upper and lower layers is 5:5, that is, the thickness of the first positive electrode active layer and the second positive electrode active layer are equal. Example 5-2: The thickness ratio of the upper and lower layers is 2:8. The first positive electrode active layer is thinner, and the second positive electrode active layer is thicker.

[0072] Example 6 group The battery was prepared according to the method of Example 1, except that the mass content ratio of the first ion-conducting agent in the first positive electrode active layer and / or the mass content ratio of the second ion-conducting agent in the second positive electrode active layer were changed. Specifically: In Example 6-1, the mass content of the first ion-conducting agent in the first positive electrode active layer is 0%, that is, no first ion-conducting agent is added to the first positive electrode active layer, and the mass content of the second ion-conducting agent in the second positive electrode active layer is 0.5%. In Example 6-2, the first ion-conducting agent has a mass content of 0.7% in the first positive electrode active layer, and the second ion-conducting agent has a mass content of 1% in the second positive electrode active layer. In Examples 6-3, the mass content of the first ion-conducting agent in the first positive electrode active layer is 0.5%, and the mass content of the second ion-conducting agent in the second positive electrode active layer is 0, that is, no second ion-conducting agent is added to the second positive electrode active layer. In Examples 6-4, the first ion-conducting agent has a mass content of 0.4% in the first positive electrode active layer, and the second ion-conducting agent has a mass content of 1.2% in the second positive electrode active layer.

[0073] Table 1 Table 2 Test case The batteries obtained in the above embodiments and comparative examples were subjected to the following tests, and the test results are recorded in Table 3.

[0074] (1) Cyclic performance test: At 25°C, the batteries obtained in the above embodiments and comparative examples were subjected to 3 cycles (3T) of constant current and constant voltage charge-discharge at 0.5C. After charging to 3.8V, the constant voltage was maintained until the current dropped to 0.05C and then the batteries were discharged at the corresponding rate at constant current to 2.0V. The capacity of the third discharge was defined as C0. Subsequently, a specific stepped charging regime was used to charge to 3.8V and discharge at 0.33C / 0.5C at constant current to 2.0V. After 1000 cycles, the discharge capacity was recorded. The cycle capacity retention rate (%) of the battery after 1000 cycles was calculated by (discharge capacity after 1000 cycles / C0) × 100%.

[0075] (2) Rate performance (charge and discharge performance) test: At 25°C, the batteries obtained in the above embodiments and comparative examples were activated using a Blue Electric charging and discharging cabinet. They were then charged at a constant current and constant voltage of 0.2C to 3.8V (with the constant voltage cutoff at 0.05C current). After standing for 5 minutes, they were discharged at a constant current of 0.33C to 2.0V. This process was repeated twice. After activation, a rate charge-discharge test was performed. The batteries were first discharged at a constant current of 0.33C to 2.0V, and then charged at a constant current and constant voltage of 5C to 3.8V (with the constant voltage cutoff at 0.05C current). The 5C rate charging constant current charge ratio (%) was calculated as (5C constant current stage charge capacity / total charge capacity) × 100%.

[0076] (3) Energy density test: At 25°C, the batteries obtained in the above embodiments and comparative examples were subjected to 3 cycles (3T) of constant current and constant voltage charge-discharge at 0.5C. After charging to 3.8V, the constant voltage was maintained until the current dropped to 0.05C, at which point the discharge was cut off. Subsequently, the batteries were discharged at a constant current of 0.5C to 2.0V. The effective discharge capacity of the 3rd cycle was taken as C. The battery energy E (unit: Wh) was calculated according to E=C×3.2V. Then, based on the battery length... Width The volume V (in L) of the battery is calculated from the high-dimensional data. Then, the volumetric energy density (Wh / L) of the battery can be obtained by dividing the battery energy E by the battery volume V.

[0077] Table 3 This invention adjusts the particle size distribution of the positive electrode active material particles in the upper and lower coatings, enabling the positive electrode to achieve high compaction density while ensuring excellent ionic and electronic conductivity, thereby improving the energy density, charge-discharge performance, and cycle storage performance of the battery containing the positive electrode.

[0078] The present invention will be described in detail below through embodiments. The embodiments described herein are only a part of the embodiments of the present invention, and not all of them. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without inventive effort are within the scope of protection of the present invention.

Claims

1. A positive electrode plate, characterized in that, It includes a positive current collector and a positive active layer located on at least one side surface of the positive current collector. The positive active layer includes a first positive active layer and a second positive active layer. The first positive active layer is located on the surface of the second positive active layer, and the second positive active layer is located on the surface of the positive current collector. The first positive electrode active layer includes first positive electrode active material particles, which include first lithium iron phosphate particles; the second positive electrode active layer includes second positive electrode active material particles, which include second lithium iron phosphate particles; the first positive electrode active material particles and the second positive electrode active material particles satisfy: 1 ​​< Span1 / Span2 ≤ 10, where Span = (Dv90 - Dv10) / Dv50, Span1 is the Span value of the first positive electrode active material particle, and Span2 is the Span value of the second positive electrode active material particle.

2. The positive electrode sheet according to claim 1, characterized in that, The first positive electrode active material particles and the second positive electrode active material particles satisfy: 0.1≤D1 / D2<1, where D1 is the average particle size of the first positive electrode active material particles and D2 is the average particle size of the second positive electrode active material particles. Preferably, D1 is 200nm-400nm; Preferably, the D2 is 400nm-1500nm.

3. The positive electrode sheet according to claim 1, characterized in that, 3 ≤ Span1 ≤ 10; and / or, 1 ≤ Span2 < 3; And / or, the Dv10 of the first positive electrode active material particle is 200nm-400nm, the Dv50 of the first positive electrode active material particle is 400nm-800nm, and the Dv90 of the first positive electrode active material particle is 4000nm-10000nm. And / or, the Dv10 of the second positive electrode active material particle is 300nm-600nm, the Dv50 of the second positive electrode active material particle is 600nm-1500nm, and the Dv90 of the second positive electrode active material particle is 1500nm-6000nm.

4. The positive electrode sheet according to any one of claims 1-3, characterized in that, The first lithium iron phosphate particle includes primary particles and secondary particles, and the mechanical strength Cs of the secondary particles is greater than 40 MPa; And / or, the second lithium iron phosphate particles comprise primary particles.

5. The positive electrode sheet according to any one of claims 1-3, characterized in that, The powder resistivity of the first positive electrode active layer is 1Ω·cm-5Ω·cm, and the powder resistivity of the second positive electrode active layer is 5Ω·cm-25Ω·cm. And / or, the thickness ratio of the first positive electrode active layer to the second positive electrode active layer is (3:7)-(5:5); And / or, the mass content of the first positive electrode active material particles in the first positive electrode active layer is 95%-97%, and the mass content of the second positive electrode active material particles in the second positive electrode active layer is 97%-98.5%.

6. The positive electrode sheet according to any one of claims 1-3, characterized in that, The first positive electrode active layer further includes a first binder, which includes polyvinylidene fluoride. The first positive electrode active layer exhibits a first weight loss range at 400℃-500℃, and the weight loss rate in the first weight loss range is 1.7%-2.1%. And / or, the second positive electrode active layer further includes a second binder, the second binder including polyimide, and the second positive electrode active layer has a second weight loss range at 500℃-600℃, the weight loss rate of the second weight loss range being 1%-1.4%.

7. The positive electrode sheet according to any one of claims 1-3, characterized in that, The first positive electrode active layer further includes a first conductive agent, a second conductive agent, and a third conductive agent. The first conductive agent includes conductive carbon black, the second conductive agent includes carbon nanotubes, and the third conductive agent includes graphene. In a cross-sectional SEM image of the first positive electrode active layer at 1K magnification, the number of graphene atoms in any 50μm × 50μm area is greater than or equal to 5. In a cross-sectional SEM image of the first positive electrode active layer at 10K magnification, the number of carbon nanotubes in any 10μm × 10μm area is greater than 100. And / or, the second positive electrode active layer further includes a fourth conductive agent, the fourth conductive agent including conductive carbon black; in the cross-sectional SEM image of the second positive electrode active layer at 10K magnification, the number of conductive carbon black particles in any 10μm×10μm area is greater than 500.

8. The positive electrode sheet according to any one of claims 1-3, characterized in that, The first positive electrode active material particle further includes a first carbon coating layer, which is disposed on the surface of the first lithium iron phosphate particle; the second positive electrode active material particle further includes a second carbon coating layer, which is disposed on the surface of the second lithium iron phosphate particle; the Raman peak intensity of the first positive electrode active material particle is greater than that of I. d / I g The Raman peak intensity ratio I is smaller than that of the second positive electrode active material particles d / I g ; Preferably, the Raman peak intensity of the first positive electrode active material particle is higher than that of I. d / I g The Raman peak intensity of the second positive electrode active material particles is 0.7-0.95, which is higher than that of I. d / I g The value is 0.95-1.2; Preferably, the first carbon coating layer comprises a polyethylene glycol and CN composite material, wherein the CN composite material comprises at least one of graphene-nitrogen composite material, polypyrrole, 3,4-dihydroxybenzonitrile dilithium salt, and polydopamine; Preferably, the second carbon coating layer comprises glucose and polyethylene glycol; Preferably, the electrode resistance of the first positive electrode active layer at 26 MPa is 4 Ω·cm-8 Ω·cm; Preferably, the electrode resistance of the second positive electrode active layer at 26 MPa is 10 Ω·cm to 25 Ω·cm.

9. The positive electrode sheet according to any one of claims 1-3, characterized in that, The compacted density of the first positive electrode active material particles is 2.2 g / cm³. 3 -2.5g.cm 3 The compacted density of the second positive electrode active material particles is 2.65 g / cm³. 3 -2.8g.cm 3 ; And / or, the compaction density of the positive electrode is 2.75 g·cm³. 3 -2.85g.cm 3 ; And / or, the first positive electrode active layer further includes a first ion-conducting agent, which includes at least one of lithium lanthanum zirconium oxide, lithium lanthanum titanium oxide, and lithium titanium aluminum phosphate, and the mass content of the first ion-conducting agent in the first positive electrode active layer is 0-0.5%; And / or, the second positive electrode active layer further includes a second ion-conducting agent, which includes a lithium titanium aluminum lithium-carbon composite material, and the mass content of the second ion-conducting agent in the second positive electrode active layer is 0-1%.

10. A battery, characterized in that, The battery includes the positive electrode sheet as described in any one of claims 1-9.

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