High-porosity thick pole piece as well as preparation method and application thereof

Abstract

The invention relates to the field of lithium ion batteries, in particular to a high-porosity thick pole piece and a preparation method and application thereof. The thick pole piece comprises a negative current collector, a first active material coating and a second active material coating; the first active material coating and the second active material coating are sequentially coated on two sides of the negative electrode current collector, and the second active material coating is provided with a plurality of pores; the additive is added into the first active material slurry, so that the surface tension of the first active material coating after film formation is reduced, and the surface tension difference is generated between the second active material coating and the surface of the first active material coating in the coating stage; further, the second active material slurry cannot be randomly spread on the surface of the first active material coating, so that a second active material coating with pores is prepared; the pores in the second active material coating can accelerate the infiltration of electrolyte into the inner layer of the pole piece, and can provide more lithium ion transmission channels, so that the electrical performance of the lithium ion battery is improved.

Description

Technical Field

[0001] The present invention relates to the field of lithium ion batteries, and in particular to a high-porosity thick electrode sheet and a preparation method and application thereof. Background Art

[0002] With the continuous advancement of science and technology, lithium-ion batteries have become an indispensable energy storage and conversion tool in modern society. They have significant advantages such as high energy density, long life and environmental protection, and are widely used in mobile devices, electric vehicles and renewable energy storage. However, the development of lithium-ion battery technology also faces many challenges. First of all, key technical issues such as high energy density, high charging rate, long cycle life and battery safety still need to be broken through.

[0003] Lithium-ion batteries are mainly composed of positive pole pieces, negative pole pieces, separators, electrolytes, mechanical parts, etc., wherein the positive and negative pole pieces are made of slurries containing positive and negative active substances coated on the surface of the negative current collector. During the charge and discharge process of lithium-ion batteries, lithium ions are embedded and removed back and forth between the positive and negative electrodes. From a theoretical design point of view, in order to make lithium-ion batteries have higher capacity and energy density, the amount of active substances is often increased and the compaction density of the pole pieces is increased. However, simply increasing the content of active substances, that is, increasing the coating thickness of the pole pieces, will seriously affect the transmission efficiency of lithium ions between the positive and negative electrodes, and thus affect the battery charge and discharge efficiency and cycle performance. Therefore, it is very necessary to invent a pole piece and a manufacturing method that can increase the capacity of the pole piece without affecting the lithium ion transmission efficiency, thereby enabling the battery to have good electrochemical properties. Summary of the invention

[0004] The purpose of the present invention is to provide a high-porosity thick electrode sheet and a preparation method and application thereof in view of the deficiencies in the prior art.

[0005] To achieve the above object, the technical solution adopted by the present invention is:

[0006] The first aspect of the present invention is to provide a high-porosity thick electrode sheet, comprising: a negative electrode current collector, a first active material coating and a second active material coating;

[0007] The first active material coating and the second active material coating are sequentially coated on both sides of the negative electrode current collector, and the second active material coating is provided with a plurality of pores.

[0008] The second aspect of the present invention is to provide a method for preparing the thick electrode sheet, the steps comprising:

[0009] S1, weighing a first active material, a first conductive agent, a first binder, a first thickener and an additive and performing a first stirring and mixing treatment to obtain a first active material slurry, coating the first active material slurry on both sides of a negative electrode current collector and performing a first drying treatment to obtain a negative electrode current collector coated with a first active material coating;

[0010] S2. Weigh the second active material, the second conductive agent, the second binder and the second thickener and perform a second stirring and mixing process to obtain a second active material slurry, apply the second active material slurry to both sides of the negative electrode current collector coated with the first active material coating obtained in step S1, and perform a second drying process, a rolling process and a die-cutting process in sequence to obtain the thick electrode sheet.

[0011] Preferably, in step S1, the mass ratio of the first active material, the first conductive agent, the first binder, the first thickener and the additive is 95.5-97.5: 0.5-1: 1-1.5: 0.5-1.5: 0.2-0.5.

[0012] Preferably, in step S2, the mass ratio of the second active material, the second conductive agent, the second binder and the second thickener is 95.5-97.5:0.5-1:1-2:0.5-1.5.

[0013] Preferably, the first active material and the second active material are independently selected from at least one of graphite, hard carbon, soft carbon, and silicon-based materials.

[0014] Preferably, the first conductive agent and the second conductive agent are independently selected from at least one of conductive carbon black, carbon nanotubes, acetylene black and superconducting carbon.

[0015] Preferably, the first binder and the second binder are independently selected from at least one of polyvinylidene fluoride, styrene-butadiene rubber, polyacrylic acid and polytetrafluoroethylene.

[0016] Preferably, the first thickener and the second thickener are independently selected from at least one of sodium carboxymethyl cellulose and lithium carboxymethyl cellulose.

[0017] Preferably, the additive is selected from at least one of silicate, polyacrylate, acrylic / ester modified silicone and polysiloxane.

[0018] The third aspect of the present invention is to provide an application of the thick electrode sheet or the thick electrode sheet prepared by the above preparation method in a lithium ion battery, wherein the preparation method of the lithium ion battery comprises:

[0019] A1. A positive electrode active material, a conductive agent, a binder, a dispersant and a solvent are stirred and mixed to prepare a positive electrode active material slurry, the positive electrode active material is coated on a positive electrode collector and then dried, rolled and die-cut in sequence to obtain a positive electrode sheet;

[0020] A2. The thick electrode sheet, the positive electrode sheet and the separator are wound into a battery roll core, which is assembled and placed in a battery shell. After baking, primary liquid injection, formation and secondary liquid injection are performed in sequence, the lithium-ion battery is sealed.

[0021] The present invention adopts the above technical solution, and has the following technical effects compared with the prior art:

[0022] The present invention reduces the surface tension of the first active material coating after film formation by adding an additive to the first active material slurry, so that the second active material coating has a surface tension difference with the surface of the first active material coating during the coating stage, thereby preventing the second active material slurry from spreading freely on the surface of the first active material coating, thereby obtaining a second active material coating with pores; the pores on the second active material coating can not only accelerate the infiltration of the electrolyte into the inner layer of the electrode sheet, but also provide more lithium ion transmission channels, thereby improving the battery capacity, charge and discharge efficiency and other electrical properties of the lithium ion battery. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 A schematic diagram of the cross-sectional structure of a thick electrode in one embodiment of the present invention;

[0024] Figure 2 Schematic diagram of the surface structure of a thick electrode in one embodiment of the present invention.

[0025] Reference numerals in the figures include:

[0026] Negative electrode current collector 1; first active material coating 2; second active material coating 3; pores 4. DETAILED DESCRIPTION

[0027] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0028] It should be noted that, in the absence of conflict, the embodiments of the present invention and the features in the embodiments may be combined with each other.

[0029] The present invention will be further described below in conjunction with the accompanying drawings and specific embodiments, but they are not intended to limit the present invention.

[0030] Example 1

[0031] This embodiment provides a method for preparing a thick electrode sheet and a lithium-ion battery prepared using the thick electrode sheet.

[0032] The preparation steps of thick electrode include:

[0033] S1. Weigh the first active material (graphite), the first conductive agent (carbon black SP), the first binder (SBR, PAA), the first thickener (sodium carboxymethyl cellulose) and the additive (acrylic acid modified silicone) in a mass ratio of 96.8:1:1.5:0.5:0.2, place them in a high-speed mixer and stir and mix them for the first time at a speed of 1000±100 rpm to obtain the first active material slurry, apply the first active material slurry to both sides of the negative electrode current collector 1 with a thickness of 6 μm, and perform the first drying treatment at 70° C. to obtain the negative electrode current collector 1 coated with the first active material coating 2;

[0034] S2. Weigh the second active material (graphite), the second conductive agent (carbon black SP), the second binder (SBR, PAA) and the second thickener (sodium carboxymethyl cellulose) in a ratio of 96:1:2:1, place them in a high-speed mixer and stir and mix them for the second time at a speed of 1000±100 rpm to obtain the second active material slurry, and then apply the second active material slurry to both sides of the negative electrode current collector 1 coated with the first active material coating 2 obtained in step S1, and perform a second drying treatment at 70°C, a rolling treatment and a die-cutting treatment in sequence to obtain a thick electrode sheet with a thickness of 150 μm.

[0035] The steps for preparing lithium-ion batteries include:

[0036] A1. The positive electrode active material, conductive agent, binder, dispersant and solvent are stirred and mixed in a high-speed stirrer to prepare a positive electrode active material slurry, and the positive electrode active material is coated on a 14 μm thick positive electrode current collector and dried at 110° C., rolled and die-cut in sequence to obtain a positive electrode sheet with a thickness of 190 μm;

[0037] A2. The thick electrode sheet, the positive electrode sheet and the separator are wound into a battery core, which is assembled and placed in a battery casing. After baking, primary liquid injection, formation and secondary liquid injection are performed in sequence, the lithium-ion battery is sealed. The electrolyte is LiPF6 as a lithium salt dissolved in a mixed solvent of EC, PC and DMC.

[0038] Example 2

[0039] This embodiment provides another method for preparing a thick electrode sheet and a lithium-ion battery prepared using the thick electrode sheet.

[0040] The preparation steps of thick electrode include:

[0041] S1. Weigh the first active material (graphite), the first conductive agent (carbon black SP), the first binder (SBR, PAA), the first thickener (carboxymethyl cellulose lithium) and the additive (silicate) in a mass ratio of 97.5:0.5:1:0.5:0.5, place them in a high-speed stirrer at a speed of 1000±100 rpm for a first stirring and mixing treatment to obtain a first active material slurry, apply the first active material slurry to both sides of a 6 μm negative electrode current collector 1, and perform a first drying treatment at 70° C. to obtain a negative electrode current collector 1 coated with a first active material coating 2;

[0042] S2. Weigh the second active material (graphite), the second conductive agent (carbon black SP), the second binder (SBR, PAA) and the second thickener (lithium carboxymethyl cellulose) in a ratio of 96:1:2:1, place them in a high-speed mixer and stir and mix them for the second time at a speed of 1000±100 rpm to obtain the second active material slurry, and then apply the second active material slurry to both sides of the negative electrode current collector 1 coated with the first active material coating 2 obtained in step S1, and perform a second drying treatment at 70°C, a rolling treatment and a die-cutting treatment in sequence to obtain a thick electrode sheet with a thickness of 150 μm.

[0043] The steps for preparing lithium-ion batteries include:

[0044] A1. The positive electrode active material, conductive agent, binder, dispersant and solvent are stirred and mixed in a high-speed stirrer to prepare a positive electrode active material slurry, and the positive electrode active material is coated on a 14 μm thick positive electrode current collector and dried at 110° C., rolled and die-cut in sequence to obtain a positive electrode sheet with a thickness of 190 μm;

[0045] A2. The thick electrode sheet, the positive electrode sheet and the separator are wound into a battery core, which is assembled and placed in a battery casing. After baking, primary liquid injection, formation and secondary liquid injection are performed in sequence, the lithium-ion battery is sealed. The electrolyte is LiPF6 as a lithium salt dissolved in a mixed solvent of EC, PC and DMC.

[0046] Comparative Example 1

[0047] This comparative example provides another method for preparing a thick electrode sheet and a lithium-ion battery prepared using the thick electrode sheet.

[0048] The preparation steps of the thick electrode sheet include: uniformly mixing the active material (graphite), conductive agent (carbon black SP), binder (SBR, PAA), and thickener (sodium carboxymethyl cellulose) in a ratio of 96:1:2:1 in a high-speed mixer at a speed of 1000±100rpm to obtain a negative electrode active material slurry; coating the negative electrode active material slurry on a 6μm negative electrode collector, drying at 70°C, and rolling and die-cutting to obtain a thick electrode sheet with a thickness of 150μm.

[0049] The preparation process of the lithium ion battery is the same as that of Example 1.

[0050] Comparative Example 2

[0051] This comparative example provides another method for preparing a thick electrode sheet and a lithium-ion battery prepared using the thick electrode sheet.

[0052] The preparation steps of the thick electrode sheet include: uniformly mixing the active material (graphite), conductive agent (carbon black SP), binder (SBR, PAA), and thickener (lithium carboxymethyl cellulose) in a ratio of 97:1:1.5:0.5 in a high-speed mixer at a speed of 1000±100rpm to obtain a negative electrode active material slurry; coating the negative electrode active material slurry on a 6μm negative electrode collector, drying at 70°C, and rolling and die-cutting to obtain a thick electrode sheet with a thickness of 150μm.

[0053] The preparation process of the lithium ion battery is the same as that of Example 1.

[0054] Detection Example

[0055] The thick pole pieces obtained in Example 1-2 and Comparative Example 1-2 were tested for pole piece porosity on a fully automatic mercury intrusion porosimetry instrument. The test was performed at 25±3°C.

[0056] The lithium-ion batteries prepared in Example 1-2 and Comparative Example 1-2 were subjected to initial charge and discharge tests and their capacity retention and lithium precipitation after 300 cycles. The test was conducted at 25±3°C, with a charge and discharge current of 0.5C. The test results are shown in Table 1.

[0057] Table 1

[0058] Porosity First charge and discharge efficiency 300 cycles capacity retention rate Lithium precipitation Example 1 49.5％ 93.08％ 98.74％ No lithium precipitate Example 2 50.2％ 92.96％ 99.02％ No lithium precipitate Comparative Example 1 21.6％ 90.87％ 97.18％ Slight lithium deposition Comparative Example 2 22.3％ 91.05％ 97.36％ Slight lithium deposition

[0059] From the results in Table 1, it can be seen that the lithium-ion batteries prepared in Examples 1-2 have higher initial charge and discharge efficiency, and the capacity retention rate and charge and discharge efficiency after 300 cycles are much higher than those of the lithium-ion batteries in Comparative Examples 1-2. At the same time, the thick electrode sheets prepared in Examples 1-2 can effectively improve the phenomenon of lithium plating at the negative electrode of lithium batteries.

[0060] The above description is only a preferred embodiment of the present invention, and does not limit the implementation mode and protection scope of the present invention. For those skilled in the art, it should be aware that all solutions obtained by equivalent substitutions and obvious changes made using the description and illustrations of the present invention should be included in the protection scope of the present invention.

Claims

1. A high porosity thick electrode sheet, characterized in that: include: A negative electrode current collector (1), a first active material coating (2) and a second active material coating (3); The first active material coating (2) and the second active material coating (3) are sequentially coated on both sides of the negative electrode current collector (1), and the second active material coating (3) is provided with a plurality of pores (4).

2. A method for preparing a thick electrode as claimed in claim 1, characterized in that the steps include: S1, weighing a first active material, a first conductive agent, a first binder, a first thickener and an additive and performing a first stirring and mixing process to obtain a first active material slurry, coating the first active material slurry on both sides of a negative electrode current collector (1) and performing a first drying process to obtain a negative electrode current collector (1) coated with a first active material coating (2); S2. Weigh the second active material, the second conductive agent, the second binder and the second thickener and perform a second stirring and mixing process to obtain a second active material slurry. Then, apply the second active material slurry to both sides of the negative electrode current collector (1) coated with the first active material coating (2) obtained in step S1 and perform a second drying process, a rolling process and a die-cutting process in sequence to obtain the thick electrode sheet.

3. The preparation method according to claim 2, characterized in that: In step S1, the mass ratio of the first active material, the first conductive agent, the first binder, the first thickener and the additive is 95.5-97.5: 0.5-1: 1-1.5: 0.5-1.5: 0.2-0.

5.

4. The preparation method according to claim 2, characterized in that: In step S2, the mass ratio of the second active material, the second conductive agent, the second binder and the second thickener is 95.5-97.5:0.5-1:1-2:0.5-1.

5.

5. The preparation method according to claim 2, characterized in that: The first active material and the second active material are independently selected from at least one of graphite, hard carbon, soft carbon, and silicon-based materials.

6. The preparation method according to claim 2, characterized in that: The first conductive agent and the second conductive agent are independently selected from at least one of conductive carbon black, carbon nanotubes, acetylene black, and superconducting carbon.

7. The preparation method according to claim 2, characterized in that: The first binder and the second binder are independently selected from at least one of polyvinylidene fluoride, styrene-butadiene rubber, polyacrylic acid, and polytetrafluoroethylene.

8. The preparation method according to claim 2, characterized in that: The first thickener and the second thickener are independently selected from at least one of sodium carboxymethyl cellulose and lithium carboxymethyl cellulose.

9. The preparation method according to claim 2, characterized in that: The additive is selected from at least one of silicate, polyacrylate, acrylic acid / ester modified silicone and polysiloxane.

10. An application of the thick electrode sheet according to claim 1 or the thick electrode sheet prepared by the preparation method according to any one of claims 2 to 9 in a lithium ion battery, characterized in that: The preparation method of the lithium ion battery comprises: A1. A positive electrode active material, a conductive agent, a binder, a dispersant and a solvent are stirred and mixed to prepare a positive electrode active material slurry, the positive electrode active material is coated on a positive electrode collector and then dried, rolled and die-cut in sequence to obtain a positive electrode sheet; A2. The thick electrode sheet, the positive electrode sheet and the separator are wound into a battery roll core, which is assembled and placed in a battery shell. After baking, primary liquid injection, formation and secondary liquid injection are performed in sequence, the lithium-ion battery is sealed.

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