Electrode plate multilayer coating preparation method, positive plate, negative plate and lithium battery

Abstract

The invention discloses an electrode plate multilayer coating preparation method, a positive plate, a negative plate and a lithium battery, and relates to the technical field of lithium battery electrode plates. The multi-layer coating preparation method comprises the following steps: preparing electrode slurry containing active substances with different particle sizes; an electrode plate is coated with electrode slurry containing small-particle-size active substances and then coated with electrode slurry containing large-particle-size active substances, and the electrode plate is prepared. According to the invention, the electrode plate is coated with the electrode slurry with different particle sizes, the electrode slurry with small particle sizes is firstly coated, and then the electrode slurry with large particle sizes is coated, so that the electrode plate with active layers with different particle sizes is formed. The active layers with different particle sizes have different Mars particles and different compaction densities, gap gradients are generated, and particle transmission channels with different gradients are formed, so that the lithium ion transmission rate and the electron transmission rate in the electrode plate are improved, the internal resistance value of the electrode plate is reduced, and the energy density of the battery is improved.

Description

Technical Field

[0001] The present application relates to the technical field, in particular to a method for preparing a multi-layer coated electrode sheet, a positive electrode sheet, a negative electrode sheet and a lithium battery. Background Art

[0002] The electrode sheet is an important component of a lithium-ion battery, and the electrical properties of the electrode sheet directly affect the electrical properties of the lithium battery. High energy density is a development direction of lithium batteries, and generally it is necessary to increase the areal density of the active material in the electrode sheet.

[0003] In the thick electrode sheet with a high areal density, the electron transport distance increases and the electron resistance increases, but the increase degree is limited. In the thick electrode sheet, the increase in the migration impedance of lithium ions in the electrolyte is the main reason affecting the rate performance. Considering the porosity and the tortuosity of the pores, the migration distance of ions in the pores is many times more than the thickness of the electrode sheet.

[0004] Therefore, how to increase the areal density of the active material in the electrode sheet while reducing the increase amplitude of the internal resistance caused by the thickness increase is a problem that needs to be solved at present. Summary of the Invention

[0005] In order to solve at least one of the above technical problems and develop an electrode sheet with a low internal resistance, the present application provides a method for preparing a multi-layer coated electrode sheet, a positive electrode sheet, a negative electrode sheet and a lithium battery.

[0006] On the one hand, a method for preparing a multi-layer coated electrode sheet provided by the present application includes the following steps:

[0007] S1. Prepare electrode slurries

[0008] Prepare a positive electrode slurry and a negative electrode slurry respectively. The positive electrode slurry includes a large-particle-size positive electrode slurry and a small-particle-size positive electrode slurry. The large-particle-size positive electrode slurry includes large-particle-size positive electrode active materials, and the small-particle-size positive electrode slurry includes small-particle-size positive electrode active materials; the particle size of the large-particle-size positive electrode active materials is larger than that of the small-particle-size positive electrode active materials;

[0009] The negative electrode slurry includes a large-particle-size negative electrode slurry and a small-particle-size negative electrode slurry. The large-particle-size negative electrode slurry includes large-particle-size negative electrode active materials, and the small-particle-size negative electrode slurry includes small-particle-size negative electrode active materials; the particle size of the large-particle-size negative electrode active materials is larger than that of the small-particle-size negative electrode active materials;

[0010] S2. Prepare the electrode sheet

[0011] First coat the small-particle-size positive electrode slurry on the bottom of the electrode sheet, and then coat the large-particle-size positive electrode slurry, and obtain the positive electrode sheet through drying and calendaring processes;

[0012] First, apply the negative electrode slurry with small particle size at the bottom of the electrode sheet, and then apply the negative electrode slurry with large particle size. After drying and calendering processes, a negative electrode sheet is obtained.

[0013] Optionally, in the step S1, the weight ratio of the large particle size positive electrode active material to the small particle size positive electrode active material is 7:3;

[0014] and / or, the weight ratio of the large particle size negative electrode active material to the small particle size negative electrode active material is 7:3.

[0015] Optionally, in the step S1, the particle size distribution of the large particle size positive electrode active material is: D10≥0.5μm, 1.8μm≥D50≥1.2μm, D90≤8.0μm;

[0016] and / or, the particle size distribution of the small particle size positive electrode active material is: D10≥0.2μm, 0.8μm≥D50≥0.6μm, D90≤2.0μm;

[0017] and / or, the particle size distribution of the large particle size negative electrode active material is: D10≥5.0μm, 17.0μm≥D50≥13.0μm, D90≤35.0μm;

[0018] and / or, the particle size distribution of the small particle size negative electrode active material is: D10≥2.0μm, 10.0μm≥D50≥6.0μm, D90≤15.0μm.

[0019] Optionally, in the step S1, the large particle size positive electrode active material is lithium iron phosphate;

[0020] and / or, the small particle size positive electrode active material is lithium iron phosphate;

[0021] and / or, the large particle size negative electrode active material is graphite;

[0022] and / or, the small particle size negative electrode active material is graphite.

[0023] Optionally, in the step S1, in the large particle size positive electrode slurry, the weight ratio of lithium iron phosphate, PVDF, SP, and CNT is (95±2):(2±1):(2±1):(1±1);

[0024] and / or, in the small particle size positive electrode slurry, the weight ratio of lithium iron phosphate, PVDF, SP, and CNT is (95±2):(2±1):(2±1):(1±1);

[0025] and / or, in the large particle size negative electrode slurry, the weight ratio of graphite, SP, sodium carboxymethyl cellulose, and polyacrylate aqueous binder is (90±5):(1±1):(1.5±1):(2±1);

[0026] And / or, in the negative electrode slurry with small particle size, the weight ratio of graphite, SP, sodium carboxymethyl cellulose, and water-based binder of polyacrylate is (90±5):(1±1):(1.5±1):(2±1).

[0027] Optionally, in the step S1, the solid content of the large particle size positive electrode slurry is 45.5-54.5%, and the discharge viscosity is 3000±500CP;

[0028] And / or, the solid content of the small particle size positive electrode slurry is 45.5-54.5%, and the discharge viscosity is 3000±500CP;

[0029] And / or, the solid content of the large particle size negative electrode slurry is 45.5-54.5%, and the discharge viscosity is 3000±500CP;

[0030] And / or, the solid content of the small particle size negative electrode slurry is 45.5-54.5%, and the discharge viscosity is 3000±500CP.

[0031] In a second aspect, the present application provides a positive electrode sheet prepared by the above preparation method.

[0032] In a third aspect, the present application provides a negative electrode sheet prepared by the above preparation method.

[0033] In a fourth aspect, the present application provides a lithium battery including the above positive electrode sheet and / or the above negative electrode sheet.

[0034] In summary, the present application coats electrode slurries with different particle sizes on the electrode sheet, and first coats the electrode slurry with small particle size, and then coats the electrode slurry with large particle size to form an electrode sheet with active layers of different particle sizes. The active particles of the active layers with different particle sizes are different, the compaction density is different, void gradients are generated, and particle transport channels with different gradients are formed, which improves the rate of lithium ion transport and the rate of electron transport in the electrode sheet, reduces the internal resistance value of the electrode sheet, and improves the battery energy density. Detailed Embodiments

[0035] The following further elaborates the present application in conjunction with embodiments.

[0036] In the following embodiments of the present application, unless otherwise specified, the main components involved are all purchased from commercially available products.

[0037] In the following embodiments of the present application, the positive electrode active material is exemplarily lithium iron phosphate, wherein:

[0038] The large particle size lithium iron phosphate is exemplarily with the following particle sizes: D10≥0.5μm, 1.8μm≥D50≥1.2μm, D90≤8.0μm;

[0039] For small particle size lithium iron phosphate, the following particle sizes are exemplary: D10≥0.2μm, 0.8μm≥D50≥0.6μm, D90≤2.0μm.

[0040] In the following examples of this application, the negative electrode active material is exemplary graphite, where:

[0041] For large particle size graphite, the following particle sizes are exemplary: D10≥5.0μm, 17.0μm≥D50≥13.0μm, D90≤35.0μm;

[0042] For small particle size graphite, the following particle sizes are exemplary: D10≥2.0μm, 10.0μm≥D50≥6.0μm, D90≤15.0μm. Specific examples

[0044] Preparation Examples 1-2 are used to prepare a positive electrode slurry, as follows.

[0045] Preparation Example 1

[0046] This preparation example is used to prepare a large particle size positive electrode slurry, and the following formula is exemplary. The weight ratio of lithium iron phosphate, PVDF, SP, and CNT is 95:2:2:1, where the particle size distribution of lithium iron phosphate is: D10≥0.5μm, 1.8μm≥D50≥1.2μm, D90≤8.0μm. According to the above formula, a large particle size positive electrode slurry is prepared.

[0047] Preparation Example 2

[0048] This preparation example is used to prepare a small particle size positive electrode slurry, and the following formula is exemplary. The weight ratio of lithium iron phosphate, PVDF, SP, and CNT is 95:2:2:1, where the particle size distribution of lithium iron phosphate is: D10≥0.2μm, 0.8μm≥D50≥0.6μm, D90≤2.0μm. According to the above formula, a small particle size positive electrode slurry is prepared.

[0049] Preparation Examples 3-4 are used to prepare a negative electrode slurry, as follows.

[0050] Preparation Example 3

[0051] This preparation example is used to prepare a large particle size negative electrode slurry, and the following formula is exemplary. The weight ratio of graphite, SP, sodium carboxymethylcellulose, and polyacrylate aqueous binder is 90:1:1.5:2, where the particle size distribution of graphite is: D10≥5.0μm, 17.0μm≥D50≥13.0μm, D90≤35.0μm. According to the above formula, a large particle size negative electrode slurry is prepared.

[0052] Preparation Example 4

[0053] This preparation example is used to prepare a small-particle-size negative electrode slurry, and the following formula is exemplarily adopted. The weight ratio of graphite, SP, sodium carboxymethyl cellulose, and water-based polyacrylate binder is 90:1:1.5:2, where the particle size distribution of graphite is: D10≥2.0μm, 10.0μm≥D50≥6.0μm, D90≤15.0μm. According to the above formula, a small-particle-size negative electrode slurry is prepared.

[0054] Examples 1 to 4 are used to prepare an electrode sheet, which is specifically as follows.

[0055] Example 1

[0056] This example is used to prepare a positive electrode sheet. First, the small-particle-size positive electrode slurry prepared in Preparation Example 2 is used for primary coating, and then the large-particle-size positive electrode slurry prepared in Preparation Example 1 is used for secondary coating.

[0057] Among them, the coating density of the small-particle-size positive electrode slurry is 120 g / cm 2 ; the coating density of the large-particle-size positive electrode slurry is 280 g / cm 2 . That is, the weight ratio of the large-particle-size positive electrode slurry to the small-particle-size positive electrode slurry is 7:3, and a positive electrode sheet is obtained through the drying and calendering processes.

[0058] Example 2

[0059] This example is used to prepare a positive electrode sheet. First, the small-particle-size positive electrode slurry prepared in Preparation Example 2 is used for primary coating, and then the large-particle-size positive electrode slurry prepared in Preparation Example 1 is used for secondary coating.

[0060] Among them, the coating density of the small-particle-size positive electrode slurry is 80 g / cm 2 ; the coating density of the large-particle-size positive electrode slurry is 320 g / cm 2 . That is, the weight ratio of the large-particle-size positive electrode slurry to the small-particle-size positive electrode slurry is 4:1, and a positive electrode sheet is obtained through the drying and calendering processes.

[0061] Example 3

[0062] This example is used to prepare a positive electrode sheet. First, the small-particle-size positive electrode slurry prepared in Preparation Example 2 is used for primary coating, and then the large-particle-size positive electrode slurry prepared in Preparation Example 1 is used for secondary coating.

[0063] Among them, the coating density of the small-particle-size positive electrode slurry is 150 g / cm 2 ; the coating density of the large-particle-size positive electrode slurry is 250 g / cm 2 . That is, the weight ratio of the large-particle-size positive electrode slurry to the small-particle-size positive electrode slurry is 5:3, and a positive electrode sheet is obtained through the drying and calendering processes.

[0064] Example 4

[0065] This example is used to prepare a negative electrode sheet. First, the small-particle-size negative electrode slurry prepared in Preparation Example 4 is used for primary coating, and then the large-particle-size negative electrode slurry prepared in Preparation Example 3 is used for secondary coating.

[0066] Among them, the coating density of the small-particle-size negative electrode slurry is 80 g / cm 2 ; the coating density of the large-particle-size negative electrode slurry is 140 g / cm 2 . That is, the weight ratio of the large-particle-size negative electrode slurry to the small-particle-size negative electrode slurry is 7:4. After drying and calendaring processes, a negative electrode sheet is obtained.

[0067] Example 5

[0068] This example is used to prepare a negative electrode sheet. First, the small-particle-size negative electrode slurry prepared in Preparation Example 4 is used for primary coating, and then the large-particle-size negative electrode slurry prepared in Preparation Example 3 is used for secondary coating.

[0069] Among them, the coating density of the small-particle-size negative electrode slurry is 60 g / cm 2 ; the coating density of the large-particle-size negative electrode slurry is 160 g / cm 2 . That is, the weight ratio of the large-particle-size negative electrode slurry to the small-particle-size negative electrode slurry is 8:3. After drying and calendaring processes, a negative electrode sheet is obtained.

[0070] Example 6

[0071] This example is used to prepare a negative electrode sheet. First, the small-particle-size negative electrode slurry prepared in Preparation Example 4 is used for primary coating, and then the large-particle-size negative electrode slurry prepared in Preparation Example 3 is used for secondary coating.

[0072] Among them, the coating density of the small-particle-size negative electrode slurry is 40 g / cm 2 ; the coating density of the large-particle-size negative electrode slurry is 180 g / cm 2 . That is, the weight ratio of the large-particle-size negative electrode slurry to the small-particle-size negative electrode slurry is 9:2. After drying and calendaring processes, a negative electrode sheet is obtained.

[0073] Comparative Example 1

[0074] This comparative example is used to prepare a positive electrode sheet. The large-particle-size positive electrode slurry prepared in Preparation Example 1 is used for coating, and the coating density of the large-particle-size positive electrode slurry is 400 g / cm 2 . After drying and calendaring processes, a positive electrode sheet is obtained.

[0075] Comparative Example 2

[0076] This comparative example is used to prepare a negative electrode sheet. The large-particle-size negative electrode slurry prepared in Preparation Example 3 is used for coating, and the coating density of the large-particle-size negative electrode slurry is 220 g / cm 2 . After drying and calendaring processes, a negative electrode sheet is obtained.

[0077] Application Example 1

[0078] In this application example, the positive electrode sheet prepared in Example 1 and the negative electrode sheet prepared in Example 4 were assembled into a 5 Ah soft-pack battery.

[0079] Application Example 2

[0080] In this application example, the positive electrode sheet prepared in Example 2 and the negative electrode sheet prepared in Example 5 were assembled into a 5 Ah soft-pack battery.

[0081] Application Example 3

[0082] In this application example, the positive electrode sheet prepared in Example 3 and the negative electrode sheet prepared in Example 4 were assembled into a 5 Ah soft-pack battery.

[0083] Application Example 4

[0084] In this application example, the positive electrode sheet prepared in Example 3 and the negative electrode sheet prepared in Example 6 were assembled into a 5 Ah soft-pack battery.

[0085] Application Example 5

[0086] In this application example, the positive electrode sheet prepared in Comparative Example 1 and the negative electrode sheet prepared in Comparative Example 2 were assembled into a 5 Ah soft-pack battery.

[0087] The electrode sheets prepared in Examples 1 to 6, Comparative Examples 1 to 2, and the batteries assembled in Application Examples 1 to 5 were tested, and the results are shown in Table 1.

[0088] Table 1

[0089]

[0090]

[0091] As can be seen from Table 1, the internal resistance values of the positive and negative electrode sheets prepared in Examples 1 to 6 of the present application decreased by more than 50% compared with those of the positive and negative electrode sheets prepared in Comparative Examples 1 to 2. This shows that under the condition of the same coating thickness of the electrode sheets, the technical solution of the present application is beneficial to electron transmission and lithium ion migration, and significantly reduces the internal resistance value of the electrode sheets.

[0092] Through the detection of the batteries in Application Examples 1 to 5, it can be known that the initial efficiency of the batteries assembled with the electrode sheets prepared by the technical solution of the present application can reach more than 91.2%, which is significantly higher than 89% of Application Example 5; the 1000-week cycle retention rate reaches more than 93.5%, which is significantly higher than 91.5% of Application Example 5. This shows that after the electrode sheets prepared by the technical solution of the present application are assembled into batteries, the performance of the batteries is better, the energy density is higher, and the cycle life is longer than those of the batteries assembled with the electrode sheets prepared in Comparative Examples 1 to 2.

[0093] Furthermore, by further analyzing Table 1, it can be seen that the internal resistance value of the positive electrode sheet prepared in Example 1 is much lower than that of the positive electrode sheets prepared in other examples. Therefore, it can be known that when the weight ratio of the large-particle-size positive electrode active material to the small-particle-size positive electrode active material in the positive electrode sheet prepared by the technical solution of the present application is 7:3, the internal resistance value of the positive electrode sheet can be further reduced.

[0094] The internal resistance value of the negative electrode sheet prepared in Example 4 is much lower than that of the negative electrode sheets prepared in other examples. Therefore, it can be known that when the weight ratio of the large-particle-size negative electrode active material to the small-particle-size negative electrode active material in the negative electrode sheet prepared by the technical solution of the present application is 7:4, the internal resistance value of the negative electrode sheet can be further reduced.

[0095] Moreover, when using the positive electrode sheet prepared in Example 1 (the weight ratio of the large-particle-size positive electrode active material to the small-particle-size positive electrode active material is 7:3) and the negative electrode sheet prepared in Example 4 (the weight ratio of the large-particle-size negative electrode active material to the small-particle-size negative electrode active material is 7:4) simultaneously, the initial efficiency of the assembled battery is relatively higher than that of other technical solutions of the present application, and the retention rate after 1000 cycles is also higher.

[0096] The above are all the preferred embodiments of the present application. The protection scope of the present application is not limited thereby. Therefore, all equivalent changes made according to the structure, shape, and principle of the present application should be covered within the protection scope of the present application.

Claims

1. A method for preparing an electrode sheet by multilayer coating, characterized in that: The following steps are involved: S1. Preparation of electrode slurry Prepare positive electrode slurry and negative electrode slurry respectively, wherein the positive electrode slurry comprises a large-particle-size positive electrode slurry and a small-particle-size positive electrode slurry, wherein the large-particle-size positive electrode slurry comprises a large-particle-size positive electrode active material, and the small-particle-size positive electrode slurry comprises a small-particle-size positive electrode active material; and the particle size of the large-particle-size positive electrode active material is larger than that of the small-particle-size positive electrode active material; The negative electrode slurry includes a large-particle-size negative electrode slurry and a small-particle-size negative electrode slurry, wherein the large-particle-size negative electrode slurry includes a large-particle-size negative electrode active material, and the small-particle-size negative electrode slurry includes a small-particle-size negative electrode active material; the particle size of the large-particle-size negative electrode active material is larger than the particle size of the small-particle-size negative electrode active material; S2. Electrode sheet preparation Firstly, a small-particle positive electrode slurry is coated on the bottom of the electrode sheet, and then a large-particle positive electrode slurry is coated, and a positive electrode sheet is obtained through drying and calendering processes; The bottom of the electrode sheet is first coated with a small-particle negative electrode slurry, and then coated with a large-particle negative electrode slurry, and a negative electrode sheet is obtained through drying and calendering processes.

2. The preparation method according to claim 1, characterized in that In S1, the weight ratio of the large-particle positive electrode active material to the small-particle positive electrode active material is 7:3; And / or, the weight ratio of the large-particle negative electrode active material to the small-particle negative electrode active material is 7:

4.

3. The preparation method according to claim 1, characterized in that: In S1, the particle size distribution of the large-particle positive electrode active material is: D10 ≥ 0.5 μm, 1.8 μm ≥ D50 ≥ 1.2 μm, D90 ≤ 8.0 μm; And / or, the particle size distribution of the small-particle positive electrode active material is: D10 ≥ 0.2 μm, 0.8 μm ≥ D50 ≥ 0.6 μm, D90 ≤ 2.0 μm; And / or, the particle size distribution of the large-particle negative electrode active material is: D10 ≥ 5.0 μm, 17.0 μm ≥ D50 ≥ 13.0 μm, D90 ≤ 35.0 μm; And / or, the particle size distribution of the small-particle negative electrode active material is: D10≥2.0 μm, 10.0 μm≥D50≥6.0 μm, D90≤15.0 μm.

4. The preparation method according to claim 1, characterized in that: In S1, the large-particle positive electrode active material is lithium iron phosphate; and / or, the small-particle positive electrode active material is lithium iron phosphate; And / or, the large-particle negative electrode active material is graphite; And / or, the small-particle negative electrode active material is graphite.

5. The preparation method according to claim 4, characterized in that: In S1, in the large-particle cathode slurry, the weight ratio of lithium iron phosphate, PVDF, SP, and CNT is (95±2):(2±1):(2±1):(1±1); And / or, in the small-particle cathode slurry, the weight ratio of lithium iron phosphate, PVDF, SP, and CNT is (95±2):(2±1):(2±1):(1±1); and / or, in the large-particle negative electrode slurry, the weight ratio of graphite, SP, sodium carboxymethyl cellulose, and polyacrylate aqueous binder is (90±5): (1±1): (1.5±1): (2±1); And / or, in the small-particle negative electrode slurry, the weight ratio of graphite, SP, sodium carboxymethyl cellulose, and polyacrylate aqueous binder is (90±5): (1±1): (1.5±1): (2±1).

6. The preparation method according to claim 1, characterized in that: In S1, the solid content of the large-particle positive electrode slurry is 45.5-54.5%, and the discharge viscosity is 3000±500CP; And / or, the solid content of the small-particle positive electrode slurry is 45.5-54.5%, and the discharge viscosity is 3000±500CP; And / or, the solid content of the large-particle negative electrode slurry is 45.5-54.5%, and the discharge viscosity is 3000±500CP; And / or, the solid content of the small-particle negative electrode slurry is 45.5-54.5%, and the discharge viscosity is 3000±500CP.

7. A positive electrode sheet, characterized in that: The product is prepared by the preparation method described in claim 1.

8. A negative electrode sheet, characterized in that: The product is prepared by the preparation method described in claim 1.

9. A lithium battery, characterized in that: It includes the positive electrode sheet described in claim 7 and / or the negative electrode sheet described in claim 8.

Images