Positive electrode active material, positive electrode sheet, and lithium ion battery comprising the same

Abstract

The application provides a positive electrode active material, a positive electrode sheet and a lithium ion battery comprising the same, and relates to the technical field of lithium ion batteries. The positive electrode active material is a high-nickel ternary positive electrode material, and the high-nickel ternary positive electrode material is composed of single-crystal particles and polycrystal particles. The mass percentage of the polycrystal particles in the high-nickel ternary positive electrode material is 55wt%-85wt%, and the following relationship is satisfied: The application quantifies the internal relationship between the gas generation behavior of the positive electrode material in the process of thermal abuse and cycling, the primary particle morphology of the polycrystal particles and the secondary spherical structure, establishes the above quantitative relationship between the intrinsic parameters of the polycrystal particles and the macroscopic performance of the battery, and then realizes the comprehensive optimization of the thermal safety, rate performance and cycle life of the battery by synergistically controlling the gas generation capacity and particle morphology of the polycrystal particles.

Description

Technical Field

[0001] This invention relates to the field of lithium-ion battery technology, and in particular to a positive electrode active material, a positive electrode sheet, and a lithium-ion battery including the same. Background Technology

[0002] The cathode material of a lithium-ion battery is crucial in determining key performance characteristics such as energy density, safety, and lifespan. Currently, the most common cathode material is the high-nickel ternary material, which has high energy density but poor thermal stability, and there is room for improvement in cycle life and rate performance.

[0003] Existing technologies typically improve a single performance characteristic through elemental doping or surface coating. For example, doping with elements such as Mg, Al, and Ti enhances structural stability, while oxide coating suppresses interfacial side reactions. However, these methods struggle to achieve a balanced improvement in performance. More importantly, current research lacks quantitative models that systematically correlate multiple intrinsic parameters of materials (such as gas generation characteristics and morphology) with multiple macroscopic performance characteristics of batteries (thermal safety, rate capability, and lifespan). This results in long material development cycles, high trial-and-error costs, and limitations in performance optimization.

[0004] In view of this, the present invention is hereby proposed. Summary of the Invention

[0005] The first objective of this invention is to provide a positive electrode active material. This application establishes a quantitative relationship between the intrinsic parameters of polycrystalline particles in the positive electrode active material and the macroscopic performance of the battery. Furthermore, by synergistically regulating the gas generation capacity and particle morphology of the polycrystalline particles, it achieves comprehensive optimization of battery thermal safety, rate performance, and cycle life.

[0006] The second objective of this invention is to provide a positive electrode sheet.

[0007] A third objective of this invention is to provide a lithium-ion battery.

[0008] In order to achieve the above-mentioned objectives of the present invention, the following technical solution is adopted: The present invention provides a positive electrode active material, wherein the positive electrode active material is a high-nickel ternary positive electrode material, and the high-nickel ternary positive electrode material is composed of single crystal particles and polycrystalline particles; The high-nickel ternary cathode material contains polycrystalline particles with a mass ratio of 55wt% to 85wt%, and satisfies the following relationship: The SCF value satisfies: 10 ≤ SCF ≤ 30; In the formula: SCF: Represents the synergistic regulation factor that polycrystalline particles in high-nickel ternary cathode materials need to satisfy, that is, the relationship that the intrinsic parameters of polycrystalline particles need to satisfy; W: Represents the mass percentage of polycrystalline particles in the high-nickel ternary cathode material, in wt% H: represents the absolute value of the enthalpy change of the main exothermic peak in the DSC test after the polycrystalline particle is charged to 4.4V. It represents the energy released per unit mass during the thermal decomposition of the polycrystalline particle, in J / g. ρ: Represents the tap density of polycrystalline particles, in g / cm³. 3 ; D 50多 : Indicates the median secondary particle size of polycrystalline particles, in μm; X: represents the average aspect ratio (major diameter / minor diameter) of the primary polycrystalline particles.

[0009] Furthermore, the SCF value satisfies: 15 ≤ SCF ≤ 25.

[0010] Furthermore, the general formula of the high-nickel ternary cathode material is: LiNi a Co b M c N （1-a-b-c） O2, wherein 0.8≤a<0.95, 0<b≤0.1, 0<c≤0.1, M is at least one of Mn and Al, and N is one or more of Zr, Mg, Ti, Ta, La, Sr, Sb, Cr, Ce, Y, and Ga; Preferably, the surface of the high-nickel ternary cathode material is coated with a metal compound layer; More preferably, the metal compound in the metal compound layer is one or more of Al2O3, ZrO2, TiO2, AlPO4, LiFePO4, Li2ZrO3, LiNbO3, LiBO2, LATP, LLZO, AlF3, and MgF2.

[0011] Furthermore, the median particle size D of the polycrystalline particles in the high-nickel ternary cathode material... 50多 Satisfies: 8.0μm≤D 50多 ≤14.5μm; The median particle size D of the single crystal particles in the high-nickel ternary cathode material 50单 Satisfies: 2.0μm≤D 50单 ≤4.5μm.

[0012] The present invention provides a positive electrode sheet, the positive electrode sheet comprising a current collector and a positive electrode coating on both sides of the current collector; The positive electrode coating includes the aforementioned positive electrode active material, conductive agent, and binder.

[0013] Furthermore, the conductive agent includes at least one of carbon nanotubes (CNTs), vapor-grown carbon fibers (VGCF), and conductive carbon black (SP).

[0014] Furthermore, the adhesive includes at least one of thermoplastic polyimide (TPI), polyvinylidene fluoride (PVDF), and polyvinylidene fluoride-trifluorochloroethylene copolymer (P(VDF-CTFE)).

[0015] Furthermore, the mass ratio of the positive electrode active material, positive electrode binder and conductive agent in the positive electrode coating is (95~98):(1~2):(1~2).

[0016] Furthermore, the areal density of the positive electrode sheet is 18~30 mg / cm³. 2 The compacted density is 3.3~3.8 g / cm³. 3 .

[0017] The present invention provides a lithium-ion battery, wherein the lithium-ion battery includes the above-mentioned positive electrode sheet.

[0018] Compared with the prior art, the beneficial effects of the present invention are as follows: This invention provides a positive electrode active material, which is a high-nickel ternary positive electrode material composed of single-crystal particles and polycrystalline particles; wherein the mass percentage of polycrystalline particles in the high-nickel ternary positive electrode material is 55wt%~85wt%, and satisfies the following relationship: This invention quantifies the gas generation behavior of cathode materials during thermal abuse and cycling, as well as the intrinsic relationship between the primary particle morphology and secondary spherical structure of polycrystalline particles. It establishes the aforementioned quantitative relationship between the intrinsic parameters of polycrystalline particles and the macroscopic performance of the battery. Furthermore, by synergistically controlling the gas generation capacity and particle morphology of polycrystalline particles, it achieves comprehensive optimization of battery thermal safety, rate performance, and cycle life.

[0019] The positive electrode sheet provided by this invention includes a current collector and positive electrode coatings on both sides of the current collector; wherein the positive electrode coating includes the aforementioned positive electrode active material, a conductive agent, and a binder. Due to the performance of the aforementioned positive electrode active material, this positive electrode sheet exhibits excellent electrochemical performance. Similarly, lithium-ion batteries and electrical devices incorporating this positive electrode sheet also possess the aforementioned excellent performance. Detailed Implementation

[0020] The technical solution of the present invention will be clearly and completely described below with reference to the embodiments. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0021] According to one aspect of the present invention, a positive electrode active material is a high-nickel ternary positive electrode material, wherein the high-nickel ternary positive electrode material is composed of single-crystal particles and polycrystalline particles; The high-nickel ternary cathode material contains polycrystalline particles with a mass ratio of 55wt% to 85wt%, and satisfies the following relationship: The SCF value satisfies: 10 ≤ SCF ≤ 30; In the formula: SCF: represents the synergistic regulation factor that polycrystalline particles in high-nickel ternary cathode materials need to satisfy, that is, the relationship that the intrinsic parameters of polycrystalline particles need to satisfy; W: Represents the mass percentage of polycrystalline particles in the high-nickel ternary cathode material, in wt% H: represents the absolute value of the enthalpy change of the main exothermic peak in the DSC test after the polycrystalline particle is charged to 4.4V. It represents the energy released per unit mass during the thermal decomposition of the polycrystalline particle, in J / g. ρ: Represents the tap density of polycrystalline particles, in g / cm³. 3 ; D 50多 : Indicates the median secondary particle size of polycrystalline particles, in μm; X: represents the average aspect ratio (major diameter / minor diameter) of the primary polycrystalline particles.

[0022] This invention provides a positive electrode active material, which is a high-nickel ternary positive electrode material composed of single-crystal particles and polycrystalline particles; wherein the mass percentage of polycrystalline particles in the high-nickel ternary positive electrode material is 55wt%~85wt%, and satisfies the following relationship: This invention quantifies the gas generation behavior of cathode materials during thermal abuse and cycling, as well as the intrinsic relationship between the primary particle morphology and secondary spherical structure of the materials. It establishes the aforementioned quantitative relationship between the intrinsic parameters of polycrystalline particles and the macroscopic performance of the battery. Furthermore, by synergistically controlling the gas generation capacity and particle morphology of the materials, it achieves comprehensive optimization of battery thermal safety, rate performance, and cycle life.

[0023] Specifically as follows: 1. This application achieves precise control of polycrystalline interface reactions by satisfying the SCF formula: This application utilizes the polycrystalline ratio (W) and thermal stability parameter in the SCF formula. H) Collaborative control quantifies the interfacial side reactions of polycrystalline materials during high-voltage charging (4.4V), which can predict the oxygen release of materials in a deep delamination state, thereby reducing the thermal safety risks caused by gas production.

[0024] 2. This application optimizes the ion transport pathway by satisfying the SCF formula: The particle size (D50+) and aspect ratio (X) of polycrystalline particles have a certain influence on the lithium-ion conduction path. The tap density (ρ) can reflect the packing situation of the material. Establishing the quantitative relationship between the parameters in this application is beneficial to reducing the interface impedance and improving the rate performance. 3. This application extends battery cycle life and reduces the risk of failure by satisfying the SCF formula: This application adjusts the polycrystalline ratio and works in conjunction with... H reduces side reactions between grain boundaries and electrolyte during cycling, inhibits transition metal dissolution, and avoids battery impedance increase and capacity decay.

[0025] As an optional implementation, the SCF value satisfies: 15≤SCF≤25, for example, it can be 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, or any value between 15 and 25; In a preferred embodiment of the present invention, the SCF value satisfies: 15≤SCF≤25.

[0026] In a preferred embodiment of the present invention, the general formula of the high-nickel ternary cathode material is: LiNi a Co b M c N （1-a-b-c） O2, wherein 0.8≤a<0.95, 0<b≤0.1, 0<c≤0.1, M is at least one of Mn and Al, and N is one or more of Zr, Mg, Ti, Ta, La, Sr, Sb, Cr, Ce, Y, and Ga; Preferably, the surface of the high-nickel ternary cathode material is coated with a metal compound layer; More preferably, the metal compound in the metal compound layer is one or more of Al2O3, ZrO2, TiO2, AlPO4, LiFePO4, Li2ZrO3, LiNbO3, LiBO2, LATP, LLZO, AlF3, and MgF2.

[0027] In a preferred embodiment of the present invention, the median particle size D of the polycrystalline particles in the high-nickel ternary cathode material is... 50多 Satisfies: 8.0μm≤D 50多 ≤14.5μm; As an optional implementation, D 50多 Satisfies: 8.0μm≤D 50多 ≤14.5μm, for example, it can be 8.0μm, 9μm, 10μm, 11μm, 12μm, 13μm, 14μm, 14.5μm, or any value between 8.0μm and 14.5μm; In a preferred embodiment of the present invention, the median particle size D of the single crystal particles in the high-nickel ternary cathode material is... 50单 Satisfies: 2.0μm≤D 50单 ≤4.5μm.

[0028] As an optional implementation, D 50单 Satisfies: 2.0μm≤D 50单 ≤4.5μm, for example, it can be 2.0μm, 2.5μm, 3.0μm, 3.5μm, 4.0μm, 4.5μm, or any value between 2.0μm and 4.5μm; According to one aspect of the present invention, a positive electrode sheet includes a current collector and a positive electrode coating on both sides of the current collector; The positive electrode coating includes the aforementioned positive electrode active material, conductive agent, and binder.

[0029] The positive electrode sheet provided by this invention includes a current collector and positive electrode coatings on both sides of the current collector; wherein the positive electrode coating includes the aforementioned positive electrode active material, a conductive agent, and a binder. Due to the performance of the aforementioned positive electrode active material, this positive electrode sheet exhibits excellent electrochemical performance.

[0030] In a preferred embodiment of the present invention, the conductive agent includes at least one of carbon nanotubes (CNTs), vapor-grown carbon fibers (VGCF), and conductive carbon black (SP).

[0031] In a preferred embodiment of the present invention, the adhesive includes at least one of thermoplastic polyimide (TPI), polyvinylidene fluoride (PVDF), and polyvinylidene fluoride-trifluorochloroethylene copolymer (P(VDF-CTFE)).

[0032] In a preferred embodiment of the present invention, the mass ratio of the positive electrode active material, the positive electrode binder and the conductive agent in the positive electrode coating is (95~98):(1~2):(1~2).

[0033] In a preferred embodiment of the present invention, the areal density of the positive electrode sheet is 18~30 mg / cm³. 2 The compacted density is 3.3~3.8 g / cm³. 3 .

[0034] As an optional implementation, the areal density of the positive electrode sheet is 18~30 mg / cm³. 2 For example, it could be 18 mg / cm³ 2 20 mg / cm 2 22 mg / cm 2 24 mg / cm 2 26 mg / cm 2 28 mg / cm 2 30mg / cm 2 It can also be 18~30 mg / cm³ 2 Any value between; According to one aspect of the present invention, a lithium-ion battery includes the above-described positive electrode.

[0035] The technical solution of the present invention will be further described below with reference to the embodiments.

[0036] The following embodiments of this application The testing methods for H and X are as follows: (one) The test method for H is as follows: 1. Half-cell preparation: The ternary positive electrode polycrystalline material, conductive agent Super P, and binder polyvinylidene fluoride (PVDF) of each embodiment were uniformly mixed in N-methylpyrrolidone (NMP) solvent at a mass ratio of 96:2:2 to form a slurry. This slurry was coated onto an aluminum foil current collector, and after drying, cold pressing, and slicing, a positive electrode sheet was formed. Using lithium metal sheet as the counter electrode and reference electrode, Celgard 2320 as the separator, and a 1M LiPF6 EC / DEC / EMC (volume ratio 1:1:1) solution as the electrolyte, a CR2032 type coin cell was assembled in an argon-protected glove box.

[0037] 2. Charging Process: The battery testing system charges the above half-cell to 4.3V (relative to Li) at a constant current of 0.1C at 25℃. + / Li), and then charge at a constant voltage until the current drops to 0.05C, so that the cathode material is in a delithiation state.

[0038] 3. Sample Preparation: Disassemble the charged half-cell in a glove box, remove the positive electrode, and thoroughly soak it in sufficient dimethyl carbonate (DMC) solvent, shaking and rinsing it three times to completely remove residual electrolyte. Then, place the electrode in the transition chamber of the glove box and vacuum dry for 1 hour. Finally, scrape the charged positive electrode material powder from the electrode, seal it, and store it for testing.

[0039] 4. DSC Test: A Mettler Toledo DSC3+ or PerkinElmer DSC8500 differential scanning calorimeter, equipped with a high-pressure sealed crucible, was used. 3.0 ± 0.5 mg of the sample prepared in step c) was accurately weighed, placed in the high-pressure sealed crucible, and sealed with a pressure cap. An empty crucible was used as a reference. Under a high-purity nitrogen gas flow of 50 mL / min, the temperature was increased from 30 °C to 400 °C at a rate of 10 °C / min, and the DSC curve was recorded.

[0040] 5. ΔH Calculation: Integrate the main exothermic peaks on the DSC curve (usually located between 180℃ and 300℃), with the integration baseline being the straight line between the peak's start and end points. The integrated area of ​​the exothermic peak is the absolute value of the exothermic enthalpy change ΔH of the material under a 4.25V charging state, expressed in J / g.

[0041] (ii) X: The aspect ratio of primary particles is obtained by scanning electron microscopy (SEM) image analysis. Specifically, the sample is dispersed and fixed on the sample stage, and multiple random field-of-view images are taken at magnification of 20,000 to 50,000. The major and minor axis dimensions of at least 50 independent primary particles are identified and measured using image analysis software (such as ImageJ). The aspect ratio is calculated as X = major axis / minor axis. The final result is the arithmetic mean of all measurements.

[0042] Example 1 A positive electrode sheet, the method for preparing the positive electrode sheet comprising: (1) Positive electrode active material: The positive electrode active material is a high-nickel ternary positive electrode material, which includes single crystal particles and polycrystalline particles. The single crystal particles and polycrystalline particles are mixed to obtain the positive electrode active material. The chemical structural formulas of both the polycrystalline and single-crystal particles are: LiNi 0.85 Co 0.03 Mn 0.11 Ti 0.01 O2@Al2O3; (That is, LiNi coated with the metal compound Al2O3) 0.85 Co 0.03 Mn 0.11 Ti 0.01 O2); The intrinsic parameters and SCF values ​​of the polycrystalline particles in the high-nickel ternary cathode material are shown in the table below.

[0043] Table 1:

[0044] Note: In this embodiment, the mass percentage (W) of polycrystalline particles in the high-nickel ternary cathode material is 80 wt%, with the remainder being single-crystal particles.

[0045] (2) Preparation of positive electrode: The above positive electrode active material was mixed with Super-P conductive carbon black (conductive agent) and polyvinylidene fluoride PVDF (binder) in a ratio of 96:2:2; Subsequently, the above-mentioned positive electrode active material, Super-P conductive carbon black (conductive agent) and polyvinylidene fluoride PVDF (binder) were added to N-methylpyrrolidone and stirred to form a positive electrode slurry with a solid content of 68%.

[0046] The above-mentioned positive electrode slurry was coated onto the positive electrode current collector, dried, and rolled to obtain a positive electrode sheet with an areal density of 23.6 mg / cm³. 2 The compacted density is 3.5 g / cm³. 3 The positive electrode sheet.

[0047] Examples 2-7 Except for the selection of high-nickel ternary cathode material in step (1), the intrinsic parameters of polycrystalline particles, and the SCF value, the embodiments of this application 2-7 are the same as those of embodiment 1; as shown in Tables 2 and 3.

[0048] Table 2:

[0049] Table 3:

[0050] Example 8 Except for step (2), in which “the positive electrode active material is mixed with Super-P conductive carbon black (conductive agent) and polyvinylidene fluoride PVDF (binder) in a ratio of 98:1:1”, the rest of this embodiment is the same as in embodiment 1.

[0051] Example 9 In this embodiment, the areal density of the positive electrode sheet after rolling in step (2) is 26.45 mg / cm³. 2 The compacted density is 3.3 g / cm³. 3 Except for the above, the rest is the same as in Example 1.

[0052] Example 10 In this embodiment, the areal density of the positive electrode sheet after rolling in step (2) is 19.22 mg / cm³. 2 The compacted density is 3.8 g / cm³. 3 Except for the above, the rest is the same as in Example 1.

[0053] Example 11 A positive electrode sheet, the method for preparing the positive electrode sheet comprising: (1) Positive electrode active material: The positive electrode active material is a high-nickel ternary positive electrode material, which includes single crystal particles and polycrystalline particles. The single crystal particles and polycrystalline particles are mixed to obtain the positive electrode active material. The chemical structural formulas of both the polycrystalline and single-crystal particles are: LiNi 0.85 Co 0.03 Mn 0.11 Ti 0.01 O2 (This embodiment does not have metal compound coating); The intrinsic parameters and SCF values ​​of the polycrystalline particles in the high-nickel ternary cathode material are shown in the table below. Table 4:

[0054] Note: In this embodiment, the mass percentage (W) of polycrystalline particles in the high-nickel ternary cathode material is 80 wt%, with the remainder being single-crystal particles.

[0055] All other parameters are the same as in Example 1.

[0056] Comparative Examples 1-4 The Comparative Examples 1-4 of this application are the same as Example 1 except for the selection of high-nickel ternary cathode material in step (1), the intrinsic parameters of polycrystalline particles, and the SCF value; as shown in Tables 5 and 6.

[0057] Table 5:

[0058] Table 6:

[0059] Experimental Example In this experimental example, the positive electrode sheets prepared in Examples 1-11 and Comparative Examples 1-4 were assembled into experimental cells and their performance was tested. (I) Assembling the experimental battery: 1. The positive electrode of the experimental battery is the positive electrode prepared in Examples 1-11 and Comparative Examples 1-4.

[0060] 2. Method for preparing negative electrode sheet: The negative electrode sheet includes a copper foil as a negative electrode current collector and a layer of negative electrode active material coated on both sides of the current collector. The negative electrode coating comprises 96% artificial graphite and silicon carbon (silicon carbon accounting for 10 wt%), 1.0% conductive agent, 1.0% thickener and 2% binder by mass percentage. The above materials are added to deionized water as a solvent and stirred to obtain a negative electrode slurry with a solid content of 40%. The slurry is then coated on both sides of the copper foil to obtain the negative electrode sheet.

[0061] 3. Electrolyte preparation method: Lithium salt LiPF6 is dissolved in an organic solvent, which is prepared by mixing ethylene carbonate (EC), diethyl carbonate (DEC) and methyl ethyl carbonate in a volume ratio of 1:1:1, wherein the additive content is 0.2%-5%, and finally an electrolyte with a concentration of 1 mol / L is prepared.

[0062] 4. Assembly method: After the positive electrode and negative electrode are cut and die-cut, they are wound together with the separator to obtain the battery core. The core is then installed into the battery casing. After completing the liquid injection, sealing and formation processes, the experimental battery is obtained.

[0063] (II) Battery performance testing, the specific testing methods are as follows: I. Capacity retention test, 25℃, 1C / 1C; Take a fresh battery, place it in a 25°C constant temperature chamber for more than 4 hours, and test it according to the following steps: (1) Discharge the battery at a constant current of 0.1C until it reaches 2.5V cutoff, and let it stand for 5 minutes; (2) Charge the battery at a constant current of 0.2C until it reaches 4.2V, then charge it at a constant voltage until it reaches 0.05C, and let it stand for 5 minutes. (3) Discharge the battery at a constant current of 0.2C until it is cut off at 2.5V, and let it stand for 5 minutes. Then read the capacity value C0 at this time. (4) Charge the battery at a constant current of 1.0C to 4.2V, and then charge it at a constant voltage of 0.05C until it stops, and let it stand for 5 minutes; (5) Discharge the battery at a constant current of 1.0C until it reaches 2.5V cutoff, and let it stand for 5 minutes; (6) Repeat steps (4) and (5) 500 times; (7) The discharge capacity of the 500th cycle and the capacity retention rate of the 1st cycle.

[0064] II. Ratio Performance Test: The batteries prepared in the above-described embodiments and comparative examples were placed in a constant temperature chamber at 25°C for more than 4 hours, with a voltage window of 2.5V-4V, and tested according to the following steps: (1) Discharge the battery at a constant current of 0.1C until it reaches 2.5V cutoff, and let it stand for 10 minutes; (2) Charge the battery at a constant current of 0.1C until it reaches 4.2V, then charge it at a constant voltage until it reaches 0.01C, and let it stand for 10 minutes. (3) Discharge the battery at a constant current of 0.1C until it is cut off at 2.5V, and let it stand for 10 minutes. Then read the capacity value C0 at this time. (4) Charge the battery at a constant current of 0.1C to 4.2V and at a constant voltage of 0.01C until it stops, and let it stand for 10 minutes; (5) Discharge the battery at a constant current of 0.5C until it reaches 2.5V cutoff, and let it stand for 10 minutes; (6) Charge the battery at a constant current of 0.1C to 4.2V and at a constant voltage of 0.01C until it stops, and let it stand for 10 minutes; (7) Discharge the battery at a constant current of 1C until it is cut off at 2.5V, and let it stand for 10 minutes; (8) Charge the battery at a constant current of 0.1C to 4.2V and at a constant voltage of 0.01C until it stops, and let it stand for 10 minutes; (9) Discharge the battery under constant current at 2C until it is cut off at 2.5V, and let it stand for 10 minutes; (10) Charge the battery at a constant current of 0.1C to 4.2V and at a constant voltage of 0.01C until it stops, and let it stand for 10 minutes; (11) Discharge the battery under constant current at 3C until it is cut off at 2.5V, and let it stand for 10 minutes; (12) Charge the battery at a constant current of 0.1C to 4.2V and at a constant voltage of 0.01C until it stops, and let it stand for 10 minutes; (13) Discharge the battery under constant current at 4C until it is cut off at 2.5V, and let it stand for 10 minutes; (14) Charge the battery at a constant current of 0.1C to 4.2V and at a constant voltage of 0.01C until it stops, and let it stand for 10 minutes; (15) Discharge the battery at a constant current of 5C until it is cut off at 2.5V, and let it stand for 10 minutes; (16) The ratio of the 5C rate discharge to the first discharge capacity is used to obtain the rate performance of the battery, i.e., the capacity retention rate.

[0065] III. Overcharge Test: Take a cylindrical lithium battery prepared according to any of the above embodiments, place it in a constant temperature chamber at 25°C for more than 4 hours, and test it according to the following steps: (1) Discharge the battery at a constant current of 0.1C until it reaches 2.5V cutoff, and let it stand for 5 minutes; (2) Charge the battery at a constant current of 0.2C until it reaches 4.2V, then charge it at a constant voltage until it reaches 0.05C, and let it stand for 5 minutes. (3) Discharge the battery at a constant current of 0.2C until it is cut off at 2.5V, and let it stand for 5 minutes; (4) Temperature sensing wires are attached to the head, middle, and bottom of the battery cell to collect temperature signals; (5) Charge to 6.0V using 3C constant current, then switch to constant voltage charging for 1 hour, with a sampling interval of 1 second; (6) Let stand for 30 minutes; (7) A cell that does not catch fire or explode and whose maximum temperature does not exceed 150°C is considered to have passed. The pass rate is calculated after parallel testing of 5 cells.

[0066] (III) The specific test results are shown in Table 7; Table 7:

[0067] As can be seen from the above, the positive electrode sheets prepared in Examples 1 to 11 of this application all have SCF values ​​that satisfy 10 ≤ SCF ≤ 30. Experimental verification shows that the positive electrode sheets prepared in Examples 1 to 11 all have excellent electrochemical performance, with a 500-cycle capacity retention rate ≥ 85%, a 5C discharge capacity retention rate ≥ 82%, and an overcharge pass rate of 5 / 5. Specifically: Examples 1-7, consisting of high-nickel ternary cathode materials coated with metal compounds, all exhibited excellent electrochemical performance. This demonstrates that even with variations in chemical composition (e.g., nickel content ranging from 0.8 to 0.92, and coating layers changing from Al2O3 to LiBO2), as long as the SCF value falls within the range of 10-30, the prepared batteries all demonstrate excellent and balanced overall performance. In particular, their capacity retention after 500 cycles is all above 85%, their 5C rate discharge capacity retention is all above 82%, and all passed the overcharge test (5 / 5 passed).

[0068] Although the ratio of positive electrode active material to conductive agent and binder is different in Example 8 compared to Example 1 (98:1:1 in Example 8), its SCF value still satisfies 10≤SCF≤30.

[0069] As shown in Table 7, Example 8 reduced the proportion of the positive electrode active material, but it still exhibited excellent electrochemical performance. This indicates that when the mass ratio of the positive electrode active material, positive electrode binder, and conductive agent in the positive electrode coating of the present invention is 96~98:1~2:1~2, the prepared battery exhibits excellent electrochemical performance. Therefore, to obtain better battery performance, it is recommended to maintain the mass ratio within the preferred range of 96~98:1~2:1~2.

[0070] Compared to Example 1, Examples 9 and 10, although differing in areal density and compaction density of the positive electrode from Example 1, all satisfy the SCF value of 10 ≤ SCF ≤ 30. As shown in Table 7, Examples 9 and 10 also exhibit excellent electrochemical performance. This demonstrates that, under the condition of an SCF value within the range of 10–30, this application can utilize an areal density of 18–30 mg / cm³. 2 The compacted density is 3.3~3.8 g / cm³.3 The electrode fabrication process provides flexibility for battery design.

[0071] Compared to Example 1, Example 11, due to the use of a high-nickel ternary cathode material without metal compound coating, although meeting the requirement of SCF value of 10≤SCF≤30, showed an observable decline in the overall performance of the battery: the cycle life (82.2%) and rate performance (80.3%) were the lowest among the examples, and one case failed the thermal safety test (out of 4 / 5 passing). This also demonstrates that coating modification with a metal compound layer is an effective means to improve the electrochemical performance of the cathode active material of this application. Without coating modification, although it is possible to meet the SCF value by adjusting other parameters, the long-term cycle stability and safety of the battery performance will be significantly reduced.

[0072] In contrast, the positive electrode plates of Comparative Examples 1 to 4 all do not satisfy the SCF value of 10≤SCF≤30, and their electrochemical performance is worse than that of Examples 1 to 11 of this application.

[0073] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention 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; and these 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 the present invention.

Claims

1. A positive electrode active material, characterized in that, The positive electrode active material is a high-nickel ternary positive electrode material, which is composed of single crystal particles and polycrystalline particles. The high-nickel ternary cathode material contains polycrystalline particles with a mass ratio of 55wt% to 85wt%, and satisfies the following relationship: The SCF value satisfies: 10 ≤ SCF ≤ 30; In the formula: SCF: Represents the synergistic regulation factor that polycrystalline particles in high-nickel ternary cathode materials need to satisfy, that is, the relationship that the intrinsic parameters of polycrystalline particles need to satisfy; W: Represents the mass percentage of polycrystalline particles in the high-nickel ternary cathode material, in wt% H: represents the absolute value of the enthalpy change of the main exothermic peak in the DSC test after the polycrystalline particle is charged to 4.4V. It represents the energy released per unit mass during the thermal decomposition of the polycrystalline particle, in J / g. ρ: Represents the tap density of polycrystalline particles, in g / cm³. 3 ; D 50多 : Indicates the median secondary particle size of polycrystalline particles, in μm; X: represents the average aspect ratio of the primary particles of the polycrystalline grain.

2. The positive electrode active material according to claim 1, characterized in that, The SCF value satisfies: 15≤SCF≤25.

3. The positive electrode active material according to claim 1, characterized in that, The general formula of the high-nickel ternary cathode material is: LiNi a Co b M c N （1-a-b-c） O2, wherein 0.8≤a<0.95, 0<b≤0.1, 0<c≤0.1, M is at least one of Mn and Al, and N is one or more of Zr, Mg, Ti, Ta, La, Sr, Sb, Cr, Ce, Y, and Ga; Preferably, the surface of the high-nickel ternary cathode material is coated with a metal compound layer; More preferably, the metal compound in the metal compound layer is one or more of Al2O3, ZrO2, TiO2, AlPO4, LiFePO4, Li2ZrO3, LiNbO3, LiBO2, LATP, LLZO, AlF3, and MgF2.

4. The positive electrode active material according to claim 1, characterized in that, The median particle size D of the polycrystalline particles in the high-nickel ternary cathode material 50多 Satisfies: 8.0μm≤D 50多 ≤14.5μm; The median particle size D of the single crystal particles in the high-nickel ternary cathode material 50单 Satisfies: 2.0μm≤D 50单 ≤4.5μm.

5. A positive electrode sheet, characterized in that, The positive electrode includes a current collector and a positive electrode coating on both sides of the current collector; The positive electrode coating comprises the positive electrode active material, conductive agent, and binder as described in any one of claims 1 to 4.

6. The positive electrode sheet according to claim 5, characterized in that, The conductive agent includes at least one of carbon nanotubes, vapor-grown carbon fibers, and conductive carbon black.

7. The positive electrode sheet according to claim 5, characterized in that, The adhesive includes at least one of thermoplastic polyimide, polyvinylidene fluoride, and polyvinylidene fluoride-chlorotrifluoroethylene copolymer.

8. The positive electrode sheet according to claim 5, characterized in that, The mass ratio of the positive electrode active material, positive electrode binder, and conductive agent in the positive electrode coating is 96~98:1~2:1~2.

9. The positive electrode sheet according to claim 5, characterized in that, The areal density of the positive electrode sheet is 18~30 mg / cm³. 2 The compacted density is 3.3~3.8 g / cm³. 3 .

10. A lithium-ion battery, characterized in that, The lithium-ion battery includes the positive electrode sheet as described in any one of claims 5 to 9.

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