A positive electrode sheet, a method for manufacturing the same, and use thereof

Abstract

The application provides a positive electrode sheet and a preparation method and application thereof, the positive electrode sheet comprises a positive electrode current collector and a first active material layer and a second active material layer which are sequentially stacked on the surface of the positive electrode current collector, the first active material layer comprises a first particle size positive electrode material and a second particle size positive electrode material; and the second active material layer comprises a third particle size positive electrode material and polytriphenylamine, the application changes the active material morphology and particle size distribution of the upper and lower active layers to optimize the pore structure of the electrode sheet along the thickness direction; and polytriphenylamine is added in the slurry of the upper active layer, the polytriphenylamine is compounded with the positive electrode material, and the excellent ion and electron conduction capacity and other characteristics of the polytriphenylamine are utilized to further provide a fast electron / ion transmission channel. Through the simple compounding of the upper and lower layers, the power performance of the battery is improved, and the high-rate performance is improved in particular.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of lithium ion batteries, and relates to a positive electrode sheet and a preparation method and application thereof. BACKGROUND

[0002] Electric vehicles driven by lithium ion batteries are one of the promising zero-emission transportation tools for solving air pollution and energy crisis problems. In recent years, with the rapid development of the global electric vehicle market, higher requirements and standards have been put forward for the performance of lithium ion batteries, especially the demand for lithium ion batteries with high energy density and high power has been increasing.

[0003] However, the energy density of the existing power lithium ion battery is insufficient, which limits the cruising range of the electric vehicle. In terms of electrode structure, by preparing a high-load thick electrode and implementing rolling, the proportion of active substances is increased, which is a promising solution to improve the energy density. However, increasing the thickness of the electrode will significantly increase the migration distance of electric charge and resistance, limit the transmission dynamics of electrons and lithium ions, and unevenly distribute the current and lithium ion concentration along the thickness direction, thereby increasing polarization and reducing the utilization rate of active materials, which ultimately leads to the deterioration of the rate power performance and hinders the improvement of the energy density.

[0004] CN113675369A discloses a positive electrode sheet and a lithium ion battery, the positive electrode sheet comprising: a current collector; a first coating layer; a second coating layer; the first coating layer and the second coating layer comprising lithium cobaltate doped with a metal element. The D50 of the lithium cobaltate in the first coating layer is smaller than the D50 of the lithium cobaltate in the second coating layer, and in the first coating layer and the second coating layer, the smaller the particle size of the lithium cobaltate, the lower the doping amount of the metal element.

[0005] CN109546080A discloses a positive electrode sheet, the positive electrode sheet comprising a current collector and a first electrode material layer and a second electrode material layer arranged in sequence on one side of the current collector; the conductive agent in the first electrode material layer is a first conductive agent, and the conductive agent in the second electrode material layer is a second conductive agent, and the conductivity of the first conductive agent is greater than the conductivity of the second conductive agent.

[0006] The positive electrode sheet described in the above scheme has the problems of low energy density and poor rate performance, which limits its application in practice. SUMMARY

[0007] The application aims to provide a positive electrode sheet, a preparation method and application thereof.

[0008] To achieve the above object, the application adopts the following technical scheme:

[0009] In a first aspect, the application provides a positive electrode sheet, which comprises a positive electrode current collector and a first active material layer and a second active material layer sequentially stacked on the surface of the positive electrode current collector, wherein the first active material layer comprises a first particle size positive electrode material and a second particle size positive electrode material; and the second active material layer comprises a third particle size positive electrode material and polytriphenylamine.

[0010] The application adopts active materials with different particle sizes to prepare an active lower layer (first active material layer) with high compactness, which can form more conductive paths and improve the electronic conductivity near the current collector end; and adopts large particle size active materials to prepare an active upper layer with higher porosity and larger pore size, which can improve the ionic conductivity. The gradient porosity structure electrode can improve the electronic conductivity and ionic conductivity, improve the energy density, and improve the battery performance. Polytriphenylamine has a high electronic conductivity skeleton, excellent ionic conductivity and long cycle performance, and is a prominent high-power electrode material. When it is applied to the electrode, it can meet different battery requirements. The addition of polytriphenylamine in the active upper layer can promote the rapid desorption and adsorption of lithium ions in the electrolyte, further improve the Li - ion transfer in the electrode, solve the problem of decreased electronic conductivity caused by the increased porosity of the upper layer, reduce the polarization degree, and improve the battery power performance. +

[0011] Preferably, the active materials of the first active material layer and the second active material layer comprise any one or a combination of at least two of lithium nickel cobalt manganese oxide, lithium iron phosphate or lithium cobaltate.

[0012] Preferably, the first particle size positive electrode material comprises a polycrystalline material with a particle size of 10-20 μm (for example, 10 μm, 12 μm, 15 μm, 18 μm or 20 μm, etc.).

[0013] Preferably, the second particle size positive electrode material comprises a single crystal and / or polycrystalline material with a particle size of 3-5 μm (for example, 3 μm, 3.5 μm, 4 μm, 4.5 μm or 5 μm, etc.). ​

[0014] Preferably, the third particle size positive electrode material comprises a polycrystalline material with a particle size of 10-20 μm, for example 10 μm, 12 μm, 15 μm, 18 μm or 20 μm, etc.

[0015] Preferably, the thickness of the first active material layer is 100-200 μm, for example 100 μm, 120 μm, 150 μm, 180 μm or 200 μm, etc.

[0016] Preferably, the thickness of the second active material layer is 40-160 μm, for example 40 μm, 50 μm, 80 μm, 100 μm or 160 μm, etc.

[0017] Preferably, the mass fraction of the polytriphenylamine is 1-6% based on 100% of the mass of the second active material layer, for example 1%, 2%, 3%, 4%, 5% or 6%, etc.

[0018] Preferably, the first active material layer further comprises a conductive agent and a binder.

[0019] Preferably, the total mass fraction of the first particle size positive electrode material and the second particle size positive electrode material is 80-98% based on 100% of the mass of the first active material layer, for example 80%, 85%, 90%, 96% or 98%, etc.

[0020] Preferably, the mass fraction of the conductive agent is 1-10%, for example 1%, 2%, 5%, 8% or 10%, etc.

[0021] Preferably, the mass fraction of the binder is 1-10%, for example 1%, 2%, 5%, 8% or 10%, etc.

[0022] Preferably, the second active material layer further comprises a conductive agent and a binder.

[0023] Preferably, the mass fraction of the third particle size positive electrode material is 80-98% based on 100% of the mass of the second active material layer, for example 80%, 85%, 90%, 96% or 98%, etc.

[0024] Preferably, the mass fraction of the conductive agent is 1-10%, for example 1%, 2%, 5%, 8% or 10%, etc.

[0025] Preferably, the mass fraction of the binder is 1-10%, for example 1%, 2%, 5%, 8% or 10%, etc.

[0026] In a second aspect, the present application provides a preparation method of the positive electrode sheet as described in the first aspect, and the preparation method comprises the following steps:

[0027] (1) mixing the first particle size positive electrode material, the second particle size positive electrode material, the conductive agent and the binder with a solvent to obtain a first slurry, and mixing the third particle size positive electrode material, polytriphenylamine, the conductive agent and the binder with a solvent to obtain a second slurry;

[0028] (2) coating the first slurry on the surface of the positive electrode current collector, coating the second slurry on the surface of the first slurry, and drying to obtain the positive electrode sheet.

[0029] Preferably, the solid content of the first slurry and the second slurry in step (1) is 30-70%, for example, 30%, 40%, 50%, 60% or 70%, etc.

[0030] Preferably, the temperature of the drying in step (2) is 110-130℃, for example, 110℃, 115℃, 120℃, 125℃ or 130℃, etc.

[0031] Preferably, the time of the drying is 0.5-2h, for example, 0.5h, 0.8h, 1h, 1.5h or 2h, etc.

[0032] In a third aspect, the present application provides a lithium ion battery, which comprises the positive electrode sheet as described in the first aspect.

[0033] Compared with the prior art, the present application has the following beneficial effects:

[0034] (1) The positive electrode sheet of the present application adopts a simple active upper and lower layer composite structure, forms a gradient, the upper layer adopts a single particle size active material, and the lower layer adopts different particle size positive electrode materials for doping, which improves the conductivity of the positive electrode sheet, improves the porosity and energy density of the sheet, and improves the Li + mass transfer, and at the same time solves the problem of decreased electronic conductivity caused by increased porosity in the upper layer, reduces the degree of polarization, and improves the battery power performance.

[0035] (2) The porosity of the first active material layer of the positive electrode sheet of the present application can reach more than 8%, the porosity of the second active material layer can reach more than 30%, the 1C energy density can reach more than 307Wh / kg, and the capacity retention rate at 4C can reach more than 97%. DETAILED DESCRIPTION

[0036] The technical solutions of the present application will be further described through specific embodiments. Those skilled in the art should understand that the embodiments are only used to help understand the present application and should not be regarded as specific limitations on the present application.

[0037] Example 1

[0038] This embodiment provides a positive electrode sheet, and the preparation method of the positive electrode sheet is as follows:

[0039] 15 μm of polycrystalline NCM811, 4 μm of single-crystal NCM811, conductive carbon black and polyvinylidene fluoride were mixed with N-methylpyrrolidone according to a mass ratio of 50:46:2:2 to obtain a first slurry with a solid content of 40%, and 15 μm of polycrystalline NCM811, polytriphenylamine, conductive carbon black and polyvinylidene fluoride were mixed with N-methylpyrrolidone according to a mass ratio of 94:2:2:2 to obtain a second slurry with a solid content of 40%;

[0040] (2) The first slurry was coated on the surface of the positive current collector, and the second slurry was coated on the surface of the first slurry, and the positive electrode sheet was obtained by drying at 120 ℃ for 1 h.

[0041] The thickness of the first active material layer of the positive electrode sheet was 150 μm, and the thickness of the second active material layer was 80 μm.

[0042] Example 2

[0043] The positive electrode sheet was prepared according to the following method.

[0044] 12 μm of polycrystalline NCM811, 4.5 μm of single-crystal NCM811, conductive carbon black and polyvinylidene fluoride were mixed with N-methylpyrrolidone according to a mass ratio of 48:49:1:2 to obtain a first slurry with a solid content of 45%, and 14 μm of polycrystalline NCM811, polytriphenylamine, conductive carbon black and polyvinylidene fluoride were mixed with N-methylpyrrolidone according to a mass ratio of 93:2:3:2 to obtain a second slurry with a solid content of 45%.

[0045] (2) The first slurry was coated on the surface of the positive current collector, and the second slurry was coated on the surface of the first slurry, and the positive electrode sheet was obtained by drying at 120 ℃ for 1 h.

[0046] The thickness of the first active material layer of the positive electrode sheet was 160 μm, and the thickness of the second active material layer was 100 μm.

[0047] Example 3

[0048] The difference between this example and Example 1 is that the mass fraction of polytriphenylamine in the second active material layer is 0.5%, and other conditions and parameters are exactly the same as those in Example 1.

[0049] Example 4

[0050] The difference between this example and Example 1 is that the mass fraction of polytriphenylamine in the second active material layer is 7%, and other conditions and parameters are exactly the same as those in Example 1.

[0051] Comparative Example 1

[0052] The comparative example differs from example 1 only in that the second active material layer uses the same size particle mixed positive electrode main material as the first active material layer, and other conditions and parameters are exactly the same as example 1.

[0053] Comparative example 2

[0054] The comparative example differs from example 1 only in that the second active material layer does not add polytriphenylamine, and other conditions and parameters are exactly the same as example 1.

[0055] Performance test:

[0056] The negative electrode active material (graphite and silicon-based material), conductive agent (SP), binder (SBR), thickening agent (CMC) are mixed and dispersed with deionized water according to the mass ratio of 96.5:1:1.2:1.3 to obtain a negative electrode slurry. Then the slurry is coated on both sides of the negative electrode current collector, and through cold pressing and die cutting, a negative electrode sheet is obtained. The positive electrode sheet and the negative electrode sheet obtained in examples 1-4 and comparative examples 1-2 are rolled, punched, laminated, dried, injected, sealed, formed, and placed according to the process of rolling, punching, laminating, drying, injecting, sealing, forming, and placing to make a soft package battery;

[0057] Porosity characterization: porosity is tested by mercury porosimeter;

[0058] Energy density test: after weighing the prepared soft package battery, it is charged to 4.2V at 1C constant current and constant voltage, and then discharged to 2.75V at 1C constant current. Record the discharge energy and calculate the 1C energy density;

[0059] Rate test: the battery is charged to 4.2V at 1C constant current and constant voltage, and then discharged to 2.75V at 1C, 2C and 4C, respectively. Record the discharge capacity and calculate the capacity retention rate. The test results are shown in Table 1:

[0060] Table 1

[0061]

[0062] As can be seen from Table 1, from examples 1-2, the porosity of the first active material layer of the positive electrode sheet can reach more than 8%, the porosity of the second active material layer can reach more than 30%, the 1C energy density can reach more than 307Wh / kg, and the capacity retention rate at 4C can reach more than 97%.

[0063] From the comparison of Example 1 and Examples 3-4, it can be seen that the mass ratio of polytriphenylamine in the second active material layer of the positive electrode plate according to the present application affects its performance. When the mass fraction of polytriphenylamine in the second active material layer is controlled to be 1-6%, the performance of the prepared positive electrode plate is better. If the mass ratio of polytriphenylamine is too low, the addition amount of polytriphenylamine is too low, which has a certain effect on improving the mass transfer of lithium ions and the electronic conductivity in the electrode plate, and the rate performance of the battery is improved. With the increase of the addition amount, the rate performance is further improved. If the addition amount is too high, it will affect the distribution of each component in the electrode plate, the effective utilization rate of the active material and polytriphenylamine is reduced, resulting in a decrease in energy density, a decrease in capacity retention rate at high rate, and a decrease in rate performance.

[0064] From the comparison of Example 1 and Comparative Example 1, it can be seen that the active material mixed with different particle sizes is used to prepare an active lower layer with high compaction density, which can form more conductive paths and improve the electronic conductivity near the current collector end. The use of large-particle-size active material to prepare an active upper layer with higher porosity and larger pore size can improve the ionic conductivity. The gradient porosity structure electrode can improve the electronic conductivity and ionic conductivity, improve the energy density, and improve the battery performance.

[0065] From the comparison of Example 1 and Comparative Example 2, it can be seen that polytriphenylamine has a high electronic conductivity skeleton, excellent ionic conductivity and long cycle performance, and is a prominent high-power electrode material. Its application in the electrode can meet the needs of different batteries. The addition of polytriphenylamine in the active upper layer can promote the rapid desorption and adsorption of lithium salts (PF6) - in the electrolyte, further improve the Li + mass transfer in the electrode plate, and at the same time solve the problem of decreased electronic conductivity caused by the increase of porosity in the upper layer, reduce the polarization degree, and improve the power performance of the battery.

[0066] The applicant declares that the above description is only a specific embodiment of the present application, but the protection scope of the present application is not limited thereto. It should be understood by those skilled in the art that any changes or replacements within the technical scope disclosed by the present application can be easily thought of by those skilled in the art, and all fall within the protection scope and disclosure scope of the present application.

Claims

1. A positive electrode sheet, characterized by, The positive electrode sheet comprises a positive electrode current collector and a first active material layer and a second active material layer which are sequentially stacked on the surface of the positive electrode current collector, the first active material layer comprises a first particle size positive electrode material and a second particle size positive electrode material; the second active material layer comprises a third particle size positive electrode material and polytriphenylamine; The first particle size positive electrode material comprises a polycrystalline material with a particle size of 10-20 μm. The second particle size positive electrode material comprises a single crystal and / or polycrystalline material with a particle size of 3-5 μm.

2. The cathode sheet of claim 1, wherein, The active material of the first active material layer and the second active material layer comprises any one or a combination of at least two of nickel cobalt lithium manganate, lithium iron phosphate or lithium cobaltate.

3. The cathode sheet of claim 1, wherein The third particle size positive electrode material comprises a polycrystalline material with a particle size of 10-20 μm.

4. The cathode sheet of claim 1, wherein, The thickness of the first active material layer is 100-200 μm.

5. The cathode sheet of claim 1, wherein The thickness of the second active material layer is 40-160 μm.

6. The cathode sheet of claim 1, wherein, The mass fraction of the polytriphenylamine is 1-6% based on 100% of the mass of the second active material layer.

7. The cathode sheet of claim 1, wherein The first active material layer further comprises a conductive agent and a binder.

8. The cathode sheet of claim 1, wherein, The total mass fraction of the first particle size positive electrode material and the second particle size positive electrode material is 80-98% based on 100% of the mass of the first active material layer.

9. The cathode sheet of claim 7, wherein, The mass fraction of the conductive agent is 1-10%.

10. The cathode sheet of claim 7, wherein, The mass fraction of the binder is 1-10%.

11. The cathode sheet of claim 1, wherein, The second active material layer further comprises a conductive agent and a binder.

12. The cathode sheet of claim 1, wherein, The mass fraction of the third particle size positive electrode material is 80-98% based on 100% of the mass of the second active material layer.

13. The cathode sheet of claim 11, wherein, The mass fraction of the conductive agent is 1-10%.

14. The cathode sheet of claim 11, wherein, The mass fraction of the binder is 1-10%.

15. A method of making the positive electrode sheet according to any one of claims 1 to 14, characterized by, The preparation method comprises the following steps: (1) mixing a first particle size positive electrode material, a second particle size positive electrode material, a conductive agent and a binder with a solvent to obtain a first slurry, and mixing a third particle size positive electrode material, polytriphenylamine, a conductive agent and a binder with a solvent to obtain a second slurry; (2) coating the first slurry on the surface of a positive electrode current collector, coating the second slurry on the surface of the first slurry, and drying to obtain the positive electrode sheet.

16. The production method according to claim 15, wherein The solid content of the first slurry and the second slurry in step (1) is 30-70%.

17. The production method according to claim 15, wherein The temperature of the drying in step (2) is 110-130 °C.

18. The production method according to claim 15, wherein The time of the drying is 0.5-2 h.

19. A lithium-ion battery, characterized by, The lithium ion battery comprises the positive electrode sheet according to any one of claims 1-14.

Images