Positive electrode sheet, battery, battery pack, power using device, and quality control method

Abstract

The application provides a positive plate, a battery, a battery pack, a power utilization device and a quality control method. K of the positive plate is 2-6; wherein K is calculated by formula 1. The positive plate of the application satisfies K, and K is 2-6. The positive plate can effectively improve the separation problem of the phosphate positive active material and the positive current collector in the battery cycle process, and further makes the battery have a high capacity retention rate and a low resistance growth rate.

Description

Technical Field

[0001] This application relates to the field of battery technology, and in particular to a positive electrode sheet, a battery, a battery pack, an electrical device, and a quality control method. Background Technology

[0002] With the rapid rise of the new energy industry, the demands of enterprises and consumers for lithium-ion batteries are constantly increasing, and battery lifespan has become a key research focus. Phosphate cathode active materials are widely used in lithium-ion batteries due to their excellent thermal stability; however, batteries experience capacity decay after charge-discharge cycles, leading to a reduction in battery range.

[0003] Currently, it is believed that the separation of phosphate cathode active material from the cathode current collector during battery cycling is the main cause of battery performance degradation, such as capacity decay. Therefore, to address this issue, improvements are often made to the cathode binder, such as increasing the amount of binder used to enhance the adhesion between the phosphate cathode active material and the cathode current collector. However, increasing the amount of binder undoubtedly leads to excessive battery impedance, affecting the battery's fast-charging performance. Summary of the Invention

[0004] This application provides a positive electrode sheet that effectively improves the problem of separation between the phosphate positive electrode active material and the positive electrode current collector during battery cycling by adjusting its compaction density, peel strength, full charge shrinkage rate and the particle size distribution of its phosphate positive electrode active material primary particles and matching them with each other. This can result in higher capacity retention and lower impedance growth of the battery after cycling.

[0005] This application also provides a battery including the above-mentioned positive electrode, which can maintain stable capacity output and excellent fast charging performance during long-term cycling.

[0006] This application also provides a battery pack including the aforementioned battery, which can maintain stable capacity output and high fast charging performance during long-term cycling.

[0007] This application also provides an electrical device that includes the aforementioned battery or battery pack, thus having the advantages of long standby time and fast charging capability.

[0008] This application also provides a quality control method for positive electrode sheets. This method can effectively control the quality of positive electrode sheets by detecting and judging their compaction density, peel strength, full charge shrinkage rate, and particle size distribution of phosphate positive electrode active materials.

[0009] This application provides a positive electrode sheet comprising a phosphate positive electrode active material, wherein K satisfies 2≤K≤6, and K is calculated by the following formula:

[0010] Formula 1;

[0011] In Equation 1, P D The compaction density of the positive electrode is given in g / cm³. 3 δ represents the peel strength of the positive electrode sheet, in N / 4cm; x represents the full-charge shrinkage rate of the positive electrode sheet, in %. 10 D 50 D 90 These are the particle size values, in μm, when the primary particle volume of the phosphate positive electrode active material reaches 10%, 50%, and 90%.

[0012] For the positive electrode as described above, δ satisfies 0.4 N / 4 cm ≤ δ ≤ 1.4 N / 4 cm; and / or, P D Meets 2.0g / cm 3 ≤P D ≤2.8g / cm 3 ; and / or, the x satisfies 1 < x < 8.

[0013] As described above, the positive electrode, the D 10 Satisfying 0.2μm≤D 10 ≤1μm; and / or, the D 50 Satisfying 0.5μm≤D 50 ≤3μm; and / or, the D 90 Satisfying 5μm≤D 90 ≤15μm.

[0014] As described above, the phosphate positive electrode active material includes Li x M y PO4 kernel and overlay on the Li x M y The PO4 core has a carbon coating layer on at least part of its surface, wherein 0.95≤x≤1.05, 0.95≤y≤1.05, and M includes at least one of Fe, Mn, Ni, and Co.

[0015] As described above, the thickness of the carbon coating layer is 5-20 nm; and / or, the mass percentage of the carbon coating layer in the phosphate positive electrode active material is 0.5-2.5%.

[0016] The positive electrode sheet described above further includes a conductive agent and a binder, and the mass ratio of the phosphate positive electrode active material, the conductive agent, and the binder is 92-98:1-4:1-4; and / or, the one-sided density of the positive electrode sheet is 150-275 g / m². 2 .

[0017] This application also provides a battery comprising the positive electrode sheet described in any of the above claims.

[0018] The battery as described above, wherein the electrolyte of the battery includes a lithium salt, a solvent and an additive, wherein the lithium salt includes at least one of LiPF6, LiPF2O2 and LiFSI, the solvent includes at least one of EC, EMC, DEC and DMC, and the additive includes VC.

[0019] This application also provides a battery pack comprising at least two batteries as described in any one of the above claims.

[0020] This application also provides an electrical device, including any of the batteries described above, or the battery packs described above.

[0021] This application also provides a quality control method for a positive electrode, comprising the following steps:

[0022] 1) Detect the actual K value of the positive electrode to be evaluated;

[0023] 2) Determine whether the actual K value meets the preset threshold;

[0024] The preset threshold is 2 to 6, and the actual K value is calculated according to Equation 1:

[0025] Formula 1;

[0026] In Equation 1, P D The compaction density of the positive electrode is given in g / cm³. 3 δ represents the peel strength of the positive electrode sheet, in N / 4cm; x represents the full-charge shrinkage rate of the positive electrode sheet, in %. 10 D 50 D 90 These are the particle size values, in μm, when the primary particle volume of the phosphate cathode active material reaches 10%, 50%, and 90%.

[0027] The positive electrode sheet provided in this application satisfies K as 2~6, where K is calculated from the compaction density, peel strength, full-charge shrinkage rate, and particle size values ​​of the primary particles of the phosphate positive electrode active material when their volume reaches 10%, 50%, and 90%. When the positive electrode sheet satisfies K, its compaction density, peel strength, full-charge shrinkage rate, and the particle size distribution of its primary particles of the phosphate positive electrode active material are more adaptable, which can effectively improve the problem of separation between the phosphate positive electrode active material and the positive electrode current collector during battery cycling, thereby enabling the battery to have high capacity retention and low resistance growth rate. Attached Figure Description

[0028] Figure 1This is an interface diagram of the positive electrode active layer and the positive electrode current collector aluminum foil after cycling in Embodiment 1 of this application;

[0029] Figure 2 This is an interface diagram of the positive electrode active layer and the positive electrode current collector aluminum foil after cycling in Comparative Example 3 of this application. Detailed Implementation

[0030] To make the objectives, technical solutions, and advantages of this application clearer, the technical solutions in the embodiments of this application will be clearly and completely described below in conjunction with the embodiments of this application. Obviously, the described embodiments are only some embodiments of this application, not all embodiments. Based on the embodiments of this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0031] During battery cycling, separation can occur between the phosphate cathode active material and the cathode current collector, leading to increased impedance and capacity decay. Increasing the amount of binder can improve the adhesion between the phosphate cathode active material and the cathode current collector, but even with increased use of non-conductive binder, the battery impedance can still become too high.

[0032] The inventors discovered that the peel strength, compaction density, full-charge shrinkage rate, and particle size distribution of the primary particles of the phosphate cathode active material of the positive electrode sheet are key factors affecting the stability of the positive electrode sheet during battery cycling. Among them, the peel strength of the positive electrode sheet reflects the tightness of the adhesion between the phosphate cathode active material and the cathode current collector. The higher the peel strength, the tighter the bond between the phosphate cathode active material and the cathode current collector, and the lower the degradation of the positive electrode sheet during battery cycling.

[0033] The compaction density of the positive electrode sheet is closely related to the stability of the positive electrode sheet structure and is associated with the peel strength of the positive electrode sheet. If the compaction density is too low, the adhesion between the phosphate positive electrode active material particles will decrease. Within a certain range, increasing the compaction density of the positive electrode sheet can increase the contact area between the phosphate positive electrode active material particles, thereby increasing the friction between the particles and helping to improve the peel strength. On the other hand, if the compaction density is too high, the mechanical properties of the positive electrode sheet will decrease, which will lead to a decrease in the peel strength of the positive electrode sheet.

[0034] Furthermore, when the positive electrode is completely delithilated, the cell volume of the phosphate positive electrode active material decreases, causing the fully charged positive electrode to shrink. This shrinkage induces stress changes within the positive electrode, thereby increasing the risk of the phosphate positive electrode active material peeling off from the positive electrode current collector. Therefore, controlling the full-charge shrinkage rate of the positive electrode is crucial for maintaining its structural stability.

[0035] The compaction density, peel strength, and full-charge shrinkage rate of the positive electrode sheet are related to the particle size distribution of the primary particles of the phosphate positive electrode active material. Specifically, the smaller the particle size of the primary particles of the phosphate positive electrode active material, the lower the adhesion between the particles, and the lower the compaction density and peel strength of the positive electrode sheet. However, when the particle size is large, the cell shrinkage stress of the phosphate positive electrode active material after charging will increase, resulting in an increase in the full-charge shrinkage rate of the positive electrode sheet.

[0036] Therefore, the compaction density, peel strength, and full-charge shrinkage of the positive electrode sheet are related to the D of the primary particles of the phosphate positive electrode active material. 10 D 50 and D 90 They influence each other.

[0037] Based on this, this application provides a positive electrode sheet, comprising a phosphate positive electrode active material, wherein K satisfies 2≤K≤6, and K is calculated by the following formula:

[0038] Formula 1;

[0039] In Equation 1, P D This is the compaction density of the positive electrode, expressed in g / cm³. 3 δ represents the peel strength of the positive electrode, in N / 4cm; x represents the full-charge shrinkage rate of the positive electrode, in %. 10 D 50 D 90 These are the particle size values, in μm, when the primary particle volume of the phosphate cathode active material reaches 10%, 50%, and 90%.

[0040] In detail, the positive electrode sheet of this application includes a positive current collector and a positive active layer disposed on at least one surface of the positive current collector. The positive active layer includes a phosphate positive active material, a conductive agent, and a binder. This application does not limit the selection of the conductive agent and binder; any conventional selections in the art can be used.

[0041] This application comprehensively analyzes the main parameters affecting the stability between the phosphate cathode active material and the cathode current collector, and obtains the relationship K=δ·P D +(P D / 5x)·((D 90 -D 10 ) / D 50 And make K values ​​2~6, the first term of the formula δ·P D This reflects the synergistic effect of positive electrode peel strength and compaction density. In the second item (D... 90 -D 10 ) / D 50 This represents the dispersion of the primary particle distribution of the phosphate cathode active material, while (P D / 5x)·((D 90 -D 10 ) / D 50 This reflects the dynamic balance between the volume change of the positive electrode and the primary particle distribution of the phosphate positive electrode active material. By adjusting the above parameters of the positive electrode to keep it within the K value range, the positive electrode not only meets the requirements of excellent initial performance, but also has high capacity retention and low impedance growth after cycling. This effectively improves the problem of increased impedance and capacity decay caused by changes in the positive electrode structure after cycling.

[0042] Specifically, the K value can be any value between 2 and 6. The unit of peel strength, N / 4cm, means the force required to peel off a 4cm wide positive electrode sheet, i.e., 1N / 4cm equals 25N / m. In this application, N / 4cm is used as the unit of peel strength for the positive electrode sheet.

[0043] When calculating the value of K, it is not necessary to substitute x as a percentage. For example, when x is 5%, simply substitute 5 into Equation 1 to calculate K.

[0044] It is not difficult to understand that through (D) 90 -D 10 ) / D 50 It is reasonable to calculate the primary particle size distribution range of phosphate cathode active materials because there may be a small number of particles with larger or smaller diameters. Such calculations can obtain the true particle size distribution to a greater extent.

[0045] This application does not limit δ, P D 、x、D 10 D 50 and D 90 The value range of K only needs to satisfy that the calculated K is in the range of 2 to 6.

[0046] The peel strength δ of the positive electrode sheet can be tested using a tensile testing machine. The peel strength of the positive electrode sheet in this application is determined as follows: One side of the positive electrode active layer is removed to obtain a single-sided sheet, which is then cut into 4cm × 10cm pieces. The side with the positive electrode active layer is attached to transparent tape, ensuring there are no air bubbles in the tape. Excess tape is removed according to the size of the electrode sheet. The tape and electrode sheet are torn 2cm apart from the bottom. The electrode sheet is fixed to the tensile testing machine. The torn current collector is adhered to the tensile end using double-sided tape. The peeling speed is set to 100mm / min, the peeling length to 50mm, and the sampling frequency to 10Hz. The tensile end is then raised at a uniform speed to peel at a 90° angle. The average peeling force is recorded as the peel strength of the positive electrode sheet.

[0047] The compaction density P of the positive electrode DThe compaction density of the positive electrode sheet can be calculated by measuring the mass and thickness of the positive electrode current collector. The compaction density of the positive electrode sheet in this application is determined as follows: a sample of the positive electrode sheet is taken using a φ1.5cm sampler and weighed to obtain the density in m³. 正极 Samples were taken from the positive electrode tab and weighed to obtain m. Al箔 The thickness h was obtained by measuring the positive electrode and the tab using a micrometer. 正极 and h Al箔 It is calculated according to the following formula:

[0048] .

[0049] The full-charge shrinkage rate x of the positive electrode sheet can be calculated by recording the thickness of the positive electrode sheet when the battery is fully charged and empty after assembling the positive electrode sheet into a battery. The full-charge shrinkage rate of the positive electrode sheet in this application is determined as follows: The positive electrode sheet is cut into two circular pieces with a diameter of 1.5 cm and assembled with lithium sheets to form two coin cell half-cells using conventional methods in the art. One coin cell is charged to 100% SOC at 0.1C, the coin cell is disassembled and the positive electrode sheet is removed, washed three times in DMC solution, and dried. The full-charge thickness h2 of the positive electrode sheet is measured. The other coin cell is charged to 100% SOC at 0.1C, left to stand for 10 minutes, and then discharged to 2.0V at 0.1C. The coin cell is disassembled and the positive electrode sheet is removed, washed three times in DMC solution, and dried. The empty-charge thickness h1 of the positive electrode sheet is measured and calculated according to the following formula:

[0050] .

[0051] D of primary particles of phosphate positive electrode active material 10 D 50 and D 90The test was conducted according to GB / T 19077-2016, "Particle Size Distribution by Laser Diffraction". When the test object is a positive electrode sheet, the phosphate positive electrode active material in the positive electrode sheet can be separated before testing using the following method. Specifically, the positive electrode sheet is immersed in water to deactivate the binder, thereby separating the positive electrode active layer from the positive electrode current collector. The positive electrode active layer is then dissolved in NMP by grinding and pulverizing, heated at 120°C and stirred at 1200 rpm for 2 hours to fully dissolve the binder. The mixture is then filtered to obtain a solid material, washed three times with NMP, and then filtered again to completely remove the residual binder. The remaining system is then added to water. Since the density of the phosphate positive electrode active material is greater than that of the conductive agent, the denser phosphate positive electrode active material sinks to the bottom, while the less dense conductive agent floats in the supernatant. By centrifuging the system at different speeds (5000-8000-10000-15000 rpm) and continuously removing the supernatant until no phosphate positive electrode active material is found in the SEM of the supernatant and no conductive agent is found in the lower layer, it can be determined that the conductive agent has been completely removed. The remaining solid material is then mixed, washed three times with deionized water, and dried to obtain pure phosphate positive electrode active material, which is then analyzed according to GB / T19077-2016 "Particle Size Distribution Laser Diffraction Method".

[0052] It should be noted that the K value in this application is limited to batteries whose actual capacity is above 90% of the rated capacity. As the battery cycles, as long as the actual capacity is above 90% of the rated capacity, the battery can be tested. During testing, the discharged battery is disassembled and the positive electrode is removed. Then, the relevant parameters of the positive electrode are tested according to the aforementioned testing method. As long as the K value is between 2 and 6, it is a battery of this application.

[0053] In one specific implementation, δ satisfies 0.4N / 4cm≤δ≤1.4 N / 4cm.

[0054] In detail, high peel strength means that the phosphate cathode active material and the cathode current collector have a higher adhesion. Peel strength is affected by compaction density. This limited range can better avoid the performance conflict that may be caused by compaction density and peel strength, and can also further improve the problem of phosphate cathode active material peeling off the cathode current collector.

[0055] In one specific implementation, P D Meets 2.0g / cm 3 ≤P D ≤2.8g / cm 3 .

[0056] In detail, compaction density affects the energy density and peel strength of the cathode sheet. Both excessively high and excessively low compaction density are detrimental to the cycle performance of the battery. This limited range can avoid the performance conflict that may be caused by compaction density and peel strength, and can also further improve the peeling problem between the phosphate cathode active material and the cathode current collector during the cycle of the cathode sheet.

[0057] In one specific implementation, x satisfies 1 < x < 8.

[0058] In detail, a higher full-charge shrinkage rate means a greater volume change of the positive electrode during battery cycling, and a greater risk of phosphate positive electrode active material stripping. This limit can further reduce the risk of phosphate positive electrode active material stripping from the positive electrode current collector during cycling while maintaining the high energy density of the positive electrode.

[0059] D of primary particles of phosphate positive electrode active material 10 The increase in battery impedance during cycling is affected by D. 10 Satisfying 0.2μm≤D 10 When the thickness is ≤1μm, the impedance growth rate of the battery is lower.

[0060] D of primary particles of phosphate positive electrode active material 50 The battery life is affected by side reactions that influence the charging and discharging process. When D 50 Satisfying 0.5μm≤D 50 With a thickness of ≤3μm, the battery has a longer lifespan.

[0061] D of primary particles of phosphate positive electrode active material 90 The energy density of the positive electrode is affected when D 90 Satisfying 5μm≤D 90 When the diameter is ≤15μm, the energy density of the positive electrode is higher.

[0062] In a specific embodiment of this application, the phosphate positive electrode active material in the positive electrode sheet includes Li x M y PO4 kernel and overlay on Li x M y The PO4 core has a carbon coating layer on at least part of its surface, wherein 0.95≤x≤1.05, 0.95≤y≤1.05, and M includes at least one of Fe, Mn, Ni, and Co.

[0063] In detail, the phosphate cathode active material includes one or more of LiFePO4, LiMnPO4, LiNiPO4, and LiCoPO4, which helps to improve the stability of the cathode during battery cycling.

[0064] Furthermore, when the thickness of the carbon coating is 5-20 nm, Li + The insertion and extraction transport is smoother, which can also stabilize the structure of phosphate active materials and reduce the occurrence of side reactions.

[0065] To further improve the conductivity and chemical stability of phosphate cathode active materials, the carbon coating layer accounts for 0.5-2.5% of the mass of the phosphate cathode active material.

[0066] In a specific embodiment, the positive electrode sheet also includes a conductive agent and a binder, and the mass ratio of the phosphate positive electrode active material, the conductive agent and the binder is 92-98:1-4:1-4. This limited range can further improve the stability of the positive electrode sheet during battery cycling.

[0067] The inventors discovered that when the density of one side of the positive electrode is 150-275 g / m², 2 At this time, the positive electrode can maintain high energy density and further reduce the risk of phosphate positive electrode active material falling off during cycling.

[0068] This application also provides a battery including the aforementioned positive electrode. The battery provided by this application has advantages corresponding to the aforementioned positive electrode, which will not be elaborated here.

[0069] This application does not limit the shape of the battery; for example, it can be a prismatic battery or a cylindrical battery.

[0070] It is conceivable that, in addition to the aforementioned positive electrode, the battery of this application also includes a negative electrode, an electrolyte, and a separator.

[0071] This application does not strictly limit the negative electrode active material in the negative electrode sheet. It can be at least one of the negative electrode active materials commonly used in lithium-ion batteries, such as graphite, hard carbon, soft carbon, mesophase carbon microspheres, silicon-based negative electrode materials (mainly including silicon suboxide and silicon-carbon negative electrode), and tin-based negative electrode materials (mainly including tin and tin alloy).

[0072] In a specific embodiment of this application, the electrolyte of the battery includes lithium salt, solvent and additives, wherein the lithium salt includes at least one of lithium hexafluorophosphate (LiPF6), lithium difluorophosphate (LiPF2O2) and lithium bis(fluorosulfonyl)imide (LiFSI), the solvent includes at least one of ethylene carbonate (EC), ethyl methyl carbonate (EMC), diethyl carbonate (DEC) and dimethyl carbonate (DMC), and the additive includes vinylene carbonate (VC).

[0073] When the lithium salt, solvent, and additives are selected as described above, the cycle performance of the battery is further enhanced.

[0074] This application does not strictly limit the choice of separator material. It can be one of the separator materials commonly used in lithium-ion batteries, such as polypropylene separator (PP), polyethylene separator (PE), polypropylene / polyethylene double-layer composite membrane (PP / PE), polyimide electrospun separator (PI), polypropylene / polyethylene / polypropylene triple-layer composite membrane (PP / PE / PP), cellulose nonwoven separator, and separator with ceramic coating.

[0075] In the preparation of lithium-ion batteries, the positive electrode, separator, and negative electrode are wound or stacked to obtain a bare cell, which is then packaged into a pre-stamped aluminum-plastic film bag. After the packaged battery is dried at 85°C, the electrolyte is injected into the dried battery. The battery undergoes resting, formation, and secondary sealing to complete the preparation of the lithium-ion battery.

[0076] This application also provides a battery pack comprising at least two of the aforementioned batteries, which has advantages corresponding to the aforementioned positive electrode, which will not be elaborated here.

[0077] Generally, a battery pack includes multiple batteries as individual cells, which are connected to form the battery pack. These batteries can be electrically connected using methods conventional in the art, such as series connection, parallel connection, or a combination of these connection methods, without any particular limitation.

[0078] This application also provides an electrical device, including the aforementioned battery or the aforementioned battery pack, which has advantages corresponding to the aforementioned positive electrode plate, which will not be elaborated here.

[0079] The electrical equipment used in this application can be conventional electrical equipment in the field, such as power equipment (e.g., electric vehicles, electric cars), electronic equipment (e.g., mobile phones, tablets, laptops, digital cameras, etc.), wearable devices (e.g., watches, bracelets, VR glasses, etc.), energy storage power stations, etc., without any particular limitation.

[0080] This application also provides a quality control method for a positive electrode, comprising the following steps:

[0081] 1) Detect the actual K value of the positive electrode to be evaluated;

[0082] 2) Determine whether the actual K value meets the preset threshold;

[0083] The preset threshold is 2~6, and the actual K value is calculated according to Equation 1:

[0084] Formula 1;

[0085] In Equation 1, P D This is the compaction density of the positive electrode, expressed in g / cm³. 3δ represents the peel strength of the positive electrode, in N / 4cm; x represents the full-charge shrinkage rate of the positive electrode, in %. 10 D 50 D 90 These are the particle size values, in μm, when the primary particle volume of the phosphate cathode active material reaches 10%, 50%, and 90%.

[0086] Specifically, the value of K can be any value between 2 and 6.

[0087] When calculating the value of K, it is not necessary to substitute x as a percentage. For example, when x is 5%, simply substitute 5 into Equation 1 to calculate K.

[0088] This application does not limit the order of measurement of the parameters in the K-value formula for the positive electrode. For example, the D-value of the primary particles of the phosphate positive electrode active material in the sample to be tested can be measured first. 10 D 50 and D 90 Then, the δ, x, and P values ​​of the sample to be tested are detected. D The K value is calculated using Equation 1, and this K value is the actual K value of the positive electrode. Where δ and P... D 、x、D 10 D 50 and D 90 The detection method is as described above and will not be repeated here.

[0089] Then, the K values ​​obtained from different test samples are compared. If the K value is any value between 2 and 6, then the test sample is a positive electrode that meets the high-quality requirements and is classified as a high-quality product; otherwise, it is classified as a general product.

[0090] This quality control method can be used to evaluate the quality of positive electrode sheets, screen out products that meet the K value of 2 to 6, and ensure that the capacity decrease trend and impedance increase trend of the screened products are effectively improved as the number of cycles increases.

[0091] The positive electrode sheet provided by the present invention will be described in detail below through specific embodiments.

[0092] Unless otherwise specified, the reagents, materials and instruments used in the following examples are all conventional reagents, materials and instruments in the art, and can be obtained commercially. The reagents involved can also be synthesized by conventional methods in the art.

[0093] Example 1

[0094] The preparation method of the positive electrode sheet in this embodiment includes the following steps:

[0095] 1) Slurry preparation: PVDF powder was dispersed in NMP by stirring at 1500 rpm for 2 hours, followed by the addition of carbon black powder and the stirring at 2000 rpm for 2 hours. Then, lithium iron phosphate material LiFePO4 (primary particle sizes D10 / D50 / D90 are 0.41 / 0.82 / 9.5 μm) was added and dispersed by stirring at 3000 rpm for 4 hours to obtain the positive electrode slurry.

[0096] The lithium iron phosphate material LiFePO4 includes a LiFePO4 matrix and a carbon coating layer. The thickness of the carbon coating layer is 10 nm, and the mass percentage of the carbon coating layer in the lithium iron phosphate material LiFePO4 is 1.3%.

[0097] The mass ratio of PVDF powder, carbon black powder, and lithium iron phosphate material is 1:1:50, and the solid content of the positive electrode slurry is 65.8%, with a viscosity of 2933 mPa·s.

[0098] 2) Coating: The positive electrode slurry was stored in a storage tank and degassed and stirred at 20 rpm. Then, it was coated on one side of the carbon-coated aluminum foil using a slit extrusion method. The die gap was adjusted to 130 μm, and the coating conveyor belt speed was 20 m / min. After coating one side, it was dried at 120℃. After drying, the other side was coated using the same method, resulting in a double-sided surface density of 400 g / m³. 2 Unrolled positive electrode sheet;

[0099] 3) Rolling: The unrolled positive electrode sheet is rolled twice. The first rolling pressure is 20 tons and the temperature is 80℃, and the second rolling pressure is 55 tons and the temperature is 25℃ to obtain the positive electrode sheet.

[0100] Example 2

[0101] The preparation method of the positive electrode sheet in this embodiment includes the following steps:

[0102] 1) Slurry preparation: PVDF powder was dispersed in NMP by stirring at 1500 rpm for 2 hours, followed by the addition of carbon black powder and the stirring at 2000 rpm for 2 hours. Then, lithium iron phosphate material LiFePO4 (primary particle sizes D10 / D50 / D90 are 0.62 / 0.95 / 10.1 μm) was added and dispersed by stirring at 3000 rpm for 4 hours to obtain the positive electrode slurry.

[0103] The lithium iron phosphate material LiFePO4 includes a LiFePO4 matrix and a carbon coating layer. The thickness of the carbon coating layer is 11 nm, and the mass percentage of the carbon coating layer in the lithium iron phosphate material LiFePO4 is 1.5%.

[0104] The mass ratio of PVDF powder, carbon black powder, and lithium iron phosphate material is 1:1:50, and the solid content of the positive electrode slurry is 65.8%, with a viscosity of 2716 mPa·s.

[0105] 2) Coating: The positive electrode slurry was stored in a storage tank and degassed and stirred at 20 rpm. Then, it was coated on one side of the carbon-coated aluminum foil using a slit extrusion method. The die gap was adjusted to 130 μm, and the coating conveyor belt speed was 20 m / min. After coating one side, it was dried at 120℃. After drying, the other side was coated using the same method, resulting in a double-sided surface density of 400 g / m³. 2 Unrolled positive electrode sheet;

[0106] 3) Rolling: The unrolled positive electrode sheet is rolled twice. The first rolling pressure is 20 tons and the temperature is 80℃, and the second rolling pressure is 55 tons and the temperature is 25℃ to obtain the positive electrode sheet.

[0107] Example 3

[0108] The preparation method of the positive electrode sheet in this embodiment includes the following steps:

[0109] 1) Slurry preparation: PVDF powder was dispersed in NMP by stirring at 1500 rpm for 2 hours, followed by the addition of carbon black powder and the stirring at 2000 rpm for 2 hours. Then, lithium iron phosphate material LiFePO4 (primary particle sizes D10 / D50 / D90 are 0.35 / 0.68 / 7 μm) was added and dispersed by stirring at 3000 rpm for 4 hours to obtain the positive electrode slurry.

[0110] The lithium iron phosphate material LiFePO4 includes a LiFePO4 matrix and a carbon coating layer. The thickness of the carbon coating layer is 10 nm, and the mass ratio of the carbon coating layer in the lithium iron phosphate material LiFePO4 is 1.2%.

[0111] The mass ratio of PVDF powder, carbon black powder, and lithium iron phosphate material is 1:1:50, and the solid content of the positive electrode slurry is 65.8%, with a viscosity of 3325 mPa·s.

[0112] 2) Coating: The positive electrode slurry was stored in a storage tank and degassed and stirred at 20 rpm. Then, it was coated on one side of the carbon-coated aluminum foil using a slit extrusion method. The die gap was adjusted to 130 μm, and the coating conveyor belt speed was 20 m / min. After coating one side, it was dried at 120℃. After drying, the other side was coated using the same method, resulting in a double-sided surface density of 400 g / m³. 2 Unrolled positive electrode sheet;

[0113] 3) Rolling: The unrolled positive electrode sheet is rolled twice. The first rolling pressure is 20 tons and the temperature is 80℃, and the second rolling pressure is 55 tons and the temperature is 25℃ to obtain the positive electrode sheet.

[0114] Example 4

[0115] The preparation method of the positive electrode sheet in this embodiment includes the following steps:

[0116] 1) Slurry preparation: PVDF powder was dispersed in NMP by stirring at 1500 rpm for 2 hours, followed by carbon black powder and dispersion by stirring at 2000 rpm for 2 hours. Then, lithium iron phosphate material LiFePO4 (primary particle sizes D10 / D50 / D90 are 1 / 2.2 / 5 μm) was added and dispersed by stirring at 3000 rpm for 4 hours to obtain the positive electrode slurry.

[0117] The lithium iron phosphate material LiFePO4 includes a LiFePO4 matrix and a carbon coating layer. The thickness of the carbon coating layer is 13 nm, and the mass percentage of the carbon coating layer in the lithium iron phosphate material LiFePO4 is 1.2%.

[0118] The mass ratio of PVDF powder, carbon black powder, and lithium iron phosphate material is 1:1:50, and the solid content of the positive electrode slurry is 65.8%, with a viscosity of 2576 mPa·s.

[0119] 2) Coating: The positive electrode slurry was stored in a storage tank and degassed and stirred at 20 rpm. Then, it was coated on one side of the carbon-coated aluminum foil using a slit extrusion method. The die gap was adjusted to 130 μm, and the coating conveyor belt speed was 20 m / min. After coating one side, it was dried at 120℃. After drying, the other side was coated using the same method, resulting in a double-sided surface density of 400 g / m³. 2 Unrolled positive electrode sheet;

[0120] 3) Rolling: The unrolled positive electrode sheet is rolled twice. The first rolling pressure is 20 tons and the temperature is 80℃, and the second rolling pressure is 65 tons and the temperature is 25℃ to obtain the positive electrode sheet.

[0121] Example 5

[0122] The preparation method of the positive electrode sheet in this embodiment includes the following steps:

[0123] 1) Slurry preparation: PVDF powder was dispersed in NMP by stirring at 1500 rpm for 2 hours, followed by the addition of carbon black powder and the stirring at 2000 rpm for 2 hours. Then, lithium iron phosphate material LiFePO4 (primary particle sizes D10 / D50 / D90 are 0.2 / 1.4 / 15 μm) was added and dispersed by stirring at 3000 rpm for 4 hours to obtain the positive electrode slurry.

[0124] The lithium iron phosphate material LiFePO4 includes a LiFePO4 matrix and a carbon coating layer. The thickness of the carbon coating layer is 12 nm, and the mass percentage of the carbon coating layer in the lithium iron phosphate material LiFePO4 is 1.5%.

[0125] The mass ratio of PVDF powder, carbon black powder, and lithium iron phosphate material is 1:1:50, and the solid content of the positive electrode slurry is 65.8%, with a viscosity of 1852 mPa·s.

[0126] 2) Coating: The positive electrode slurry was stored in a storage tank and degassed and stirred at 20 rpm. Then, it was coated on one side of the carbon-coated aluminum foil using a slit extrusion method. The die gap was adjusted to 185 μm, and the coating conveyor belt speed was 15 m / min. After coating one side, it was dried at 120℃. After drying, the other side was coated using the same method, resulting in a double-sided surface density of 400 g / m³. 2 Unrolled positive electrode sheet;

[0127] 3) Rolling: The unrolled positive electrode sheet is rolled twice. The first rolling pressure is 20 tons and the temperature is 80℃, and the second rolling pressure is 55 tons and the temperature is 25℃ to obtain the positive electrode sheet.

[0128] Example 6

[0129] The preparation method of the positive electrode sheet in this embodiment includes the following steps:

[0130] 1) Slurry preparation: PVDF powder was dispersed in NMP by stirring at 1500 rpm for 2 hours, followed by the addition of carbon black powder and the stirring at 2000 rpm for 2 hours. Then, lithium iron phosphate material LiFePO4 (primary particle sizes D10 / D50 / D90 are 0.41 / 0.82 / 9.5 μm) was added and dispersed by stirring at 3000 rpm for 4 hours to obtain the positive electrode slurry.

[0131] The lithium iron phosphate material LiFePO4 includes a LiFePO4 matrix and a carbon coating layer. The thickness of the carbon coating layer is 10 nm, and the mass percentage of the carbon coating layer in the lithium iron phosphate material LiFePO4 is 1.3%.

[0132] The mass ratio of PVDF powder, carbon black powder, and lithium iron phosphate material is 1:1:50, and the solid content of the positive electrode slurry is 65.8%, with a viscosity of 2933 mPa·s.

[0133] 2) Coating: The positive electrode slurry was stored in a storage tank and degassed and stirred at 20 rpm. Then, it was coated on one side of the carbon-coated aluminum foil using a slit extrusion method. The die gap was adjusted to 130 μm, and the coating conveyor belt speed was 20 m / min. After coating one side, it was dried at 120℃. After drying, the other side was coated using the same method, resulting in a double-sided surface density of 400 g / m³. 2 Unrolled positive electrode sheet;

[0134] 3) Rolling: The unrolled positive electrode sheet is rolled twice. The first rolling pressure is 20 tons and the temperature is 60℃, and the second rolling pressure is 40 tons and the temperature is 25℃ to obtain the positive electrode sheet.

[0135] Example 7

[0136] The preparation method of the positive electrode sheet in this embodiment is basically the same as that in Example 1, except that the pressure of the secondary rolling is 30 tons.

[0137] Example 8

[0138] The preparation method of the positive electrode sheet in this embodiment includes the following steps:

[0139] 1) Slurry preparation: PVDF powder was dispersed in NMP by stirring at 1500 rpm for 2 hours, followed by the addition of carbon black powder and the stirring at 2000 rpm for 2 hours. Then, lithium iron phosphate material LiFePO4 (primary particle sizes D10 / D50 / D90 are 0.41 / 0.82 / 9.5 μm) was added and dispersed by stirring at 3000 rpm for 4 hours to obtain the positive electrode slurry.

[0140] The lithium iron phosphate material LiFePO4 includes a LiFePO4 matrix and a carbon coating layer. The thickness of the carbon coating layer is 10 nm, and the mass percentage of the carbon coating layer in the lithium iron phosphate material LiFePO4 is 1.3%.

[0141] The mass ratio of PVDF powder, carbon black powder, and lithium iron phosphate material is 1:1:50, and the solid content of the positive electrode slurry is 65.8%, with a viscosity of 2933 mPa·s.

[0142] 2) Coating: The positive electrode slurry was stored in a storage tank and degassed and stirred at 20 rpm. Then, it was coated on one side of the carbon-coated aluminum foil using a slit extrusion method. The die gap was adjusted to 130 μm, and the coating conveyor belt speed was 20 m / min. After coating one side, it was dried at 120℃. After drying, the other side was coated using the same method, resulting in a double-sided surface density of 400 g / m³. 2 Unrolled positive electrode sheet;

[0143] 3) Rolling: The unrolled positive electrode sheet is rolled twice. The first rolling pressure is 30 tons and the temperature is 100℃, and the second rolling pressure is 55 tons and the temperature is 25℃ to obtain the positive electrode sheet.

[0144] Comparative Example 1

[0145] The preparation method of the positive electrode in this comparative example includes the following steps:

[0146] 1) Slurry preparation: PVDF powder was dispersed in NMP by stirring at 1500 rpm for 2 hours, followed by the addition of carbon black powder and the stirring at 2000 rpm for 2 hours. Then, lithium iron phosphate material LiFePO4 (primary particle sizes D10 / D50 / D90 are 0.1 / 0.5 / 2 μm) was added and dispersed by stirring at 3000 rpm for 4 hours to obtain the positive electrode slurry.

[0147] The lithium iron phosphate material LiFePO4 includes a LiFePO4 matrix and a carbon coating layer. The thickness of the carbon coating layer is 8 nm, and the mass percentage of the carbon coating layer in the lithium iron phosphate material LiFePO4 is 0.9%.

[0148] The mass ratio of PVDF powder, carbon black powder, and lithium iron phosphate material is 1:1:50, and the solid content of the positive electrode slurry is 49.5%, with a viscosity of 2233 mPa·s.

[0149] 2) Coating: The positive electrode slurry was stored in a storage tank and degassed and stirred at 20 rpm. Then, it was coated on one side of the carbon-coated aluminum foil using a slit extrusion method. The die gap was adjusted to 240 μm, and the coating conveyor belt speed was 12 m / min. After coating one side, it was dried at 120℃. After drying, the other side was coated using the same method, resulting in a double-sided areal density of 400 g / m³. 2 Unrolled positive electrode sheet;

[0150] 3) Rolling: The unrolled positive electrode sheet is rolled twice. The first rolling pressure is 30 tons and the temperature is 100℃, and the second rolling pressure is 70 tons and the temperature is 25℃ to obtain the positive electrode sheet.

[0151] Comparative Example 2

[0152] The preparation method of the positive electrode in this comparative example includes the following steps:

[0153] 1) Slurry preparation: PVDF powder was dispersed in NMP by stirring at 1500 rpm for 2 hours, followed by the addition of carbon black powder and the stirring at 2000 rpm for 2 hours. Then, lithium iron phosphate material LiFePO4 (primary particle sizes D10 / D50 / D90 are 1 / 2.5 / 18 μm) was added and dispersed by stirring at 3000 rpm for 4 hours to obtain the positive electrode slurry.

[0154] The lithium iron phosphate material LiFePO4 includes a LiFePO4 matrix and a carbon coating layer. The thickness of the carbon coating layer is 17 nm, and the mass percentage of the carbon coating layer in the lithium iron phosphate material LiFePO4 is 2.1%.

[0155] The mass ratio of PVDF powder, carbon black powder, and lithium iron phosphate material is 1:1:50, and the solid content of the positive electrode slurry is 65.8%, with a viscosity of 1422 mPa·s.

[0156] 2) Coating: The positive electrode slurry was stored in a storage tank and degassed and stirred at 20 rpm. Then, it was coated on one side of the carbon-coated aluminum foil using a slit extrusion method. The die gap was adjusted to 130 μm, and the coating conveyor belt speed was 20 m / min. After coating one side, it was dried at 120℃. After drying, the other side was coated using the same method, resulting in a double-sided surface density of 400 g / m³. 2 Unrolled positive electrode sheet;

[0157] 3) Rolling: The unrolled positive electrode sheet is rolled twice. The first rolling pressure is 30 tons and the temperature is 100℃, and the second rolling pressure is 70 tons and the temperature is 25℃ to obtain the positive electrode sheet.

[0158] Comparative Example 3

[0159] The preparation method of the positive electrode in this comparative example includes the following steps:

[0160] 1) Slurry preparation: PVDF powder was dispersed in NMP by stirring at 1500 rpm for 2 hours, followed by the addition of carbon black powder and the stirring at 2000 rpm for 2 hours. Then, lithium iron phosphate material LiFePO4 (primary particle sizes D10 / D50 / D90 are 0.41 / 0.82 / 9.5 μm) was added and dispersed by stirring at 3000 rpm for 4 hours to obtain the positive electrode slurry.

[0161] The lithium iron phosphate material LiFePO4 includes a LiFePO4 matrix and a carbon coating layer. The thickness of the carbon coating layer is 10 nm, and the mass percentage of the carbon coating layer in the lithium iron phosphate material LiFePO4 is 1.3%.

[0162] The mass ratio of PVDF powder, carbon black powder, and lithium iron phosphate material is 1:1:50, and the solid content of the positive electrode slurry is 65.8%, with a viscosity of 2933 mPa·s.

[0163] 2) Coating: The positive electrode slurry was stored in a storage tank and degassed and stirred at 20 rpm. Then, it was coated on one side of the carbon-coated aluminum foil using a slit extrusion method. The die gap was adjusted to 130 μm, and the coating conveyor belt speed was 20 m / min. After coating one side, it was dried at 120℃. After drying, the other side was coated using the same method, resulting in a double-sided surface density of 400 g / m³. 2 Unrolled positive electrode sheet;

[0164] 3) Rolling: The unrolled positive electrode sheet is rolled once at a pressure of 20 tons and a temperature of 25℃ to obtain the positive electrode sheet.

[0165] Experimental Example 1

[0166] The compaction density (P) of the positive electrode sheets in all embodiments and comparative examples D Peel strength (δ), full charge shrinkage (x), and D of primary particles of phosphate cathode active material 10 / D 50 / D 90 The K value was measured, and the results are shown in Table 1.

[0167] Compacted density (P) D ): The positive electrode is sampled and weighed using a φ1.5cm sampler to obtain m. 正极 Samples were taken from the positive electrode tab and weighed to obtain m. Al箔 The thickness h was obtained by measuring the positive electrode and the tab using a micrometer. 正极 and h Al箔 It is calculated according to the following formula:

[0168] .

[0169] Peel strength (δ): Remove the positive electrode active layer from one side of the positive electrode sheet to obtain a single-sided sheet. Cut the sheet to 4cm × 10cm. Attach the side with the positive electrode active layer to transparent tape, ensuring there are no air bubbles in the tape. Trim any excess tape according to the size of the electrode sheet. Tear the tape and electrode sheet 2cm apart from the bottom. Fix the electrode sheet to a tensile testing machine. Attach the torn current collector to the tensile end using double-sided tape. Set the peeling speed to 100mm / min, the peeling length to 50mm, and the sampling frequency to 10Hz. Then, raise the tensile end at a uniform speed to peel at 90°. Record the average peeling force; this is the peel strength of the positive electrode sheet.

[0170] Full-charge shrinkage rate (x): The positive electrode sheet was cut into two circular pieces with a diameter of 1.5 cm and assembled with lithium sheets to form two coin cell half-cells according to conventional methods in the art. One coin cell was charged to 100% SOC at 0.1C, the coin cell was disassembled and the positive electrode sheet was removed. After washing three times in DMC solution, it was dried, and the full-charge thickness h2 of the positive electrode sheet was measured. The other coin cell was charged to 100% SOC at 0.1C, left to stand for 10 min, and then discharged to 2.0V at 0.1C. The coin cell was disassembled and the positive electrode sheet was removed. After washing three times in DMC solution, it was dried, and the empty-charge thickness h1 of the positive electrode sheet was measured. The result was calculated according to the following formula:

[0171] .

[0172] D of primary particles of phosphate positive electrode active material 10 / D 50 / D 90 The positive electrode sheet is immersed in water to deactivate the binder, thereby separating the positive electrode active layer from the positive electrode current collector. The positive electrode active layer is then dissolved in NMP by grinding and pulverizing. The mixture is heated at 120°C and stirred at 1200 rpm for 2 hours to fully dissolve the binder. The mixture is then filtered to obtain a solid material. After washing three times with NMP and then filtering again, the residual binder is completely removed. The remaining system is then added to water. Because the density of the phosphate positive electrode active material is greater than that of the conductive agent, the denser phosphate positive electrode active material sinks to the bottom, while the less dense conductive agent floats in the supernatant. By centrifuging the system at different speeds (5000-8000-10000-15000 rpm) and continuously removing the supernatant, until no phosphate positive electrode active material is visible in the SEM of the supernatant and no conductive agent is present in the lower layer, it can be determined that the conductive agent has been completely removed. After mixing the remaining solid materials, wash them three times with deionized water and dry them to obtain pure phosphate positive electrode active material. Then, the material is tested according to GB / T 19077-2016 "Particle Size Distribution Laser Diffraction Method".

[0173] K value: The P obtained above D δ, x, D 10 / D 50 / D 90 Substituting into Equation 1, the K values ​​of the positive electrode sheets for all embodiments and comparative examples are calculated.

[0174] Table 1

[0175]

[0176] Experimental Example 2

[0177] All the positive electrode sheets from the examples and comparative examples were stacked with graphite negative electrodes and separators to obtain dry battery cells. After the cores were baked, electrolyte was injected and formation and capacity testing were performed. The specific formation process was as follows: after electrolyte injection, the battery was first aged at 45°C for 24 hours to ensure that the electrolyte was fully impregnated. The electrolyte consisted of 1 mol / L lithium salt LiPF6, solvent EC / EMC (3:7), and additive 3% VC. Then, it was charged at 0.05C to 15% SOC, then charged at a constant current of 0.2C to a cutoff voltage of 3.8V, and then charged at a constant voltage of 3.8V to a cutoff current of 0.05C. After that, it was placed in a 45°C oven for 24 hours of aging.

[0178] The DC impedance (DCIR) growth rate and capacity retention rate of the above batteries after 1000cls cycling were measured, and the results are shown in Table 2.

[0179] At 25°C, the battery is charged at a constant current and constant voltage of 0.33C to the upper limit voltage of 3.8V, then charged at a constant voltage of 3.8V to the cutoff current of 0.05C, and left to rest for 30 minutes; then discharged at a constant current of 0.33C to the lower limit voltage of 2V, and left to rest for 30 minutes; the above charging and discharging steps are repeated 3 times, and the capacity discharged in the third time is recorded as C0, in Ah; where C0 is the room temperature rated capacity of the battery, the following battery test uses the room temperature rated capacity C0 for current setting, that is, C=C0 as follows.

[0180] DCIR growth rate after 1000cls cycling: At 25℃, the battery was charged at a constant current and constant voltage of 0.33C to the upper limit voltage of 3.8V, then charged at a constant voltage of 3.8V to the cutoff current of 0.05C, and then discharged at a constant current of 0.33C to 50% SOC. After resting for 2 hours to reach thermal equilibrium, the open circuit voltage at 50% SOC was recorded as V0; then it was discharged at a constant current of 1.5C for 30s, and the discharge end voltage was recorded as V. 30 , (V0-V 30 The initial DC impedance (DCIR) of the battery is calculated as 1.5 / 1.5. The battery is subjected to a 1C charge-discharge cycle at 45°C for 1000 cls, and the DCIR after 1000 cls is measured using the method described above.

[0181] The DCIR growth rate after 1000cls of battery cycling = DCIR after 1000cls of cycling / initial DCIR - 1.

[0182] Capacity retention after 1000cls cycles: The battery was subjected to 1C charge-discharge cycles at 45℃ for 1000cls. The battery was then placed in a 45℃ oven for 6 hours to reach thermal equilibrium, charged at 1C to the upper limit voltage of 3.8V, and then charged at a constant voltage of 3.8V to the cutoff current of 0.05C, and rested for 30 minutes. Next, it was discharged at a constant current of 1C to the lower limit voltage of 2V, and rested for 30 minutes. This charge-discharge cycle was repeated 1000 times. The discharge capacity C1 of the first cycle and the capacity C1000 after 1000 cycles were recorded.

[0183] Capacity retention after 1000cls cycles = Capacity after 1000cls cycles C1000 / C1.

[0184] Table 2

[0185]

[0186] Combining Table 1 and Table 2, we can see that:

[0187] 1) When K is between 2 and 6, the battery capacity retention rate is significantly higher and the impedance growth rate is significantly lower.

[0188] 2) As can be seen from the examples and comparative examples, the P of the positive electrode... D δ, x and D of primary particles of phosphate positive electrode active material 10 D 50 and D 90 These parameters influence each other, therefore this application controls the K value that affects the battery capacity retention rate and DCIR growth rate by coordinating the above parameters.

[0189] Experimental Example 3

[0190] After assembling the positive electrode sheets from Example 1 and Comparative Example 3 into batteries, they were cycled at 45°C for 1000 cls. The interfacial separation between the phosphate positive electrode active material and the current collector in the cycled positive electrode sheet was measured. Measurement method: The cycled battery was discharged to 0% SOC and then disassembled to obtain the cycled positive electrode sheet. It was washed three times in anhydrous DMC solution and dried at 90°C. The positive electrode sheet was then cut using argon ion shearing (CP) to obtain a cross-section. The cross-section was examined using a scanning electron microscope (SEM) to observe the interfacial contact between the positive electrode active layer and the aluminum foil.

[0191] Figure 1 This is an interface diagram of the positive electrode active layer and the positive electrode current collector aluminum foil after cycling in Embodiment 1 of this application.

[0192] Figure 2 This is an interface diagram of the positive electrode active layer and the positive electrode current collector aluminum foil after cycling in Comparative Example 3 of this application.

[0193] Combination Figure 1 and Figure 2 It is known that the positive electrode sheet of this application has higher stability during battery cycling, and the phosphate positive electrode active material is less likely to detach from the positive electrode current collector.

[0194] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of this application, and are not intended to limit them. Although this application has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features therein. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of this application.

Claims

1. A positive electrode plate, characterized in that, This includes phosphate cathode active materials, where K satisfies 2≤K≤6, and K is calculated using the following formula: Formula 1; In Equation 1, P D The compaction density of the positive electrode is given in g / cm³. 3 δ represents the peel strength of the positive electrode sheet, in N / 4cm; x represents the full-charge shrinkage rate of the positive electrode sheet, in %. 10 D 50 D 90 These are the particle size values, in μm, when the primary particle volume of the phosphate positive electrode active material reaches 10%, 50%, and 90%.

2. The positive electrode sheet according to claim 1, characterized in that, The δ satisfies 0.4 N / 4 cm ≤ δ ≤ 1.4 N / 4 cm; and / or, The P D Meets 2.0g / cm 3 ≤P D ≤2.8g / cm 3 ; and / or, The x satisfies 1 < x < 8.

3. The positive electrode sheet according to claim 1 or 2, characterized in that, The D 10 Satisfying 0.2μm≤D 10 ≤1μm; and / or, The D 50 Satisfying 0.5μm≤D 50 ≤3μm; and / or, The D 90 Satisfying 5μm≤D 90 ≤15μm.

4. The positive electrode sheet according to any one of claims 1-3, characterized in that, The phosphate positive electrode active material includes Li x M y PO4 kernel and overlay on the Li x M y The PO4 core has a carbon coating layer on at least part of its surface, wherein 0.95≤x≤1.05, 0.95≤y≤1.05, and M includes at least one of Fe, Mn, Ni, and Co.

5. The positive electrode sheet according to claim 4, characterized in that, The thickness of the carbon coating layer is 5-20 nm; and / or, The carbon coating layer accounts for 0.5-2.5% of the mass of the phosphate cathode active material.

6. The positive electrode sheet according to any one of claims 1-5, characterized in that, It also includes conductive agents and binders, and the mass ratio of phosphate positive electrode active material, conductive agent, and binder is 92-98:1-4:1-4; and / or, The single-sided density of the positive electrode is 150-275 g / m³. 2 .

7. A battery, characterized in that, Includes the positive electrode sheet as described in any one of claims 1-6.

8. The battery according to claim 7, characterized in that, The electrolyte of the battery includes lithium salt, solvent and additives, wherein the lithium salt includes at least one of LiPF6, LiPF2O2 and LiFSI, the solvent includes at least one of EC, EMC, DEC and DMC, and the additive includes VC.

9. A battery pack, characterized in that, It includes at least two batteries as described in claim 7 or 8.

10. An electrical appliance, characterized in that, Includes the battery as described in claim 7 or 8, or the battery pack as described in claim 9.

11. A quality control method for a positive electrode, characterized in that, Includes the following steps: 1) Detect the actual K value of the positive electrode to be evaluated; 2) Determine whether the actual K value meets the preset threshold; The preset threshold is 2 to 6, and the actual K value is calculated according to Equation 1: Formula 1; In Equation 1, P D The compaction density of the positive electrode is given in g / cm³. 3 δ represents the peel strength of the positive electrode sheet, in N / 4cm; x represents the full-charge shrinkage rate of the positive electrode sheet, in %. 10 D 50 D 90 These are the particle size values, in μm, when the primary particle volume of the phosphate cathode active material reaches 10%, 50%, and 90%.

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