Preparation method of negative pole piece, prepared negative pole piece and lithium ion battery

Abstract

The invention discloses a preparation method of a negative pole piece, the prepared negative pole piece and a lithium ion battery. The preparation method comprises the following steps: mixing an active substance, a high-conductivity ion characteristic additive, a binder, a conductive agent and water, and stirring to obtain negative active slurry; coating the surface of a negative current collector with the negative active slurry, drying to obtain an active coating, and rolling to obtain a negative pole piece; wherein the high-conductivity ion characteristic additive is selected from one or more of a hard carbon material, a porous carbon material and a metal oxide solid electrolyte, and the mass fraction of the high-conductivity ion characteristic additive in the active coating is 0.1%-5%. The defect that diffusion channels of lithium ions in the pole piece are blocked is overcome, and the dynamic performance of the negative pole piece is improved.

Description

Technical Field

[0001] This application relates to the technical field of lithium-ion batteries, and particularly relates to a method for preparing a negative electrode sheet, the obtained negative electrode sheet, and a lithium-ion battery. Background Art

[0002] Currently, the structure of commercial lithium-ion batteries mainly consists of a positive electrode sheet, a negative electrode sheet, a separator, an electrolyte, and a casing. In the process of manufacturing the negative electrode sheet of a lithium-ion battery, a foil (copper foil or aluminum foil) is used as the current collector, and an active material is coated on one or both sides of the current collector for lithium-ion insertion or extraction. In the prior art, after coating an active material such as graphite on the surface of the current collector and then rolling, the contact between the active material particles becomes closer. However, after the active material particles are in close contact, some of the diffusion channels of lithium ions in the electrode sheet will be blocked, which is instead not conducive to the improvement of the electrode sheet kinetics. Summary of the Invention

[0003] In view of this, the main purpose of this application is to provide a method for preparing a negative electrode sheet, the obtained negative electrode sheet, and a lithium-ion battery. This method solves the defect that the diffusion channels of lithium ions in the electrode sheet are blocked and improves the kinetic performance of the electrode sheet.

[0004] To achieve the above-mentioned invention purpose, the first aspect of this application provides a method for preparing a negative electrode sheet, including:

[0005] Mix an active material, a high-conductivity ion characteristic additive, a binder, a conductive agent, and water, and stir to obtain a negative electrode active slurry;

[0006] Coat the negative electrode active slurry on the surface of a negative electrode current collector, dry it to obtain an active coating, and then roll it to obtain a negative electrode sheet;

[0007] Wherein, the high-conductivity ion characteristic additive is selected from one or more of hard carbon materials, porous carbon materials, and metal oxide solid electrolytes; the mass fraction of the high-conductivity ion characteristic additive in the active coating is 0.1%-5%.

[0008] In this application, the high-conductivity ion characteristic additive has the effect of conducting lithium ions in the solid phase. It can conduct lithium ions by itself. By introducing this high-conductivity ion characteristic additive between the particles of the active material, the gap between the active material particles can be widened, and the lithium-ion diffusion channels can be extended. The mass fraction of the high-conductivity ion characteristic additive in the active coating is 0.1%-5%, such as 0.1%, 0.3%, 0.5%, 0.8%, 1%, 1.5%, 2%, 2.5%, 3.0%, 3.5%, 4%, 4.5%, 5%, etc. Setting within the above mass fraction range can effectively solve the defect that the contact between the active material particles of the electrode sheet is too close after rolling, resulting in blocked lithium-ion diffusion.

[0009] Further, the metal oxide solid electrolyte is selected from one or more of lithium lanthanum titanium oxide (LLTO), lithium lanthanum zirconium oxide (LLZO), lithium aluminum titanium phosphate (LATP), and fast ion conductors (LISICON, NASICON). The hard carbon material is selected from one or more of resin-based hard carbon, organic polymer carbon, carbon black, and biomass carbon. The porous carbon material is selected from one or more of biomass-based porous carbon and resin-based porous carbon, and the pore diameter is 1-2 nm. Selecting the porous carbon material within the above pore diameter range, on the one hand, the micropores therein can further serve as lithium ion diffusion channels, and on the other hand, it can avoid side reactions such as electrolyte infiltration caused by too large pore diameter.

[0010] Further, the high ionic conductivity additive includes a hard carbon material and a metal oxide solid electrolyte, and the mass ratio of the hard carbon material to the metal oxide solid electrolyte is 0.8-1.5:1, such as 0.8:1, 1:1, 1.2:1, 1.5:1, etc.

[0011] Further, the high ionic conductivity additive includes a porous carbon material and a metal oxide solid electrolyte, and the mass ratio of the porous carbon material to the metal oxide solid electrolyte is 0.8-1.5:1, such as 0.8:1, 1:1, 1.2:1, 1.5:1, etc.

[0012] Further, the active material is selected from one or more of graphite materials and silicon materials.

[0013] Further, the graphite material is selected from one or more of artificial graphite primary particles, artificial graphite secondary particles, natural graphite, and microcrystalline graphite.

[0014] Further, the silicon material is selected from one or more of silicon monoxide, prelithiated silicon monoxide, premagnesiated silicon monoxide, and silicon-carbon materials.

[0015] Further, the mass fraction of the high ionic conductivity additive in the active coating is 0.5%-5%.

[0016] Further, the mass fraction of the active material in the active coating is 80% to 98%, the mass fraction of the conductive agent in the active coating is 0.5% to 10%, and the mass fraction of the binder in the active coating is 1% to 5%. Setting within the above mass fraction ranges can ensure good contact between the electrode particles.

[0017] Further, the particle size D50 of the high-conductivity ionic property additive is 0.01 μm - 5 μm, such as 0.01 μm, 0.03 μm, 0.05 μm, 0.08 μm, 0.1 μm, 0.2 μm, 0.3 μm, 0.4 μm, 0.5 μm, 0.6 μm, 0.7 μm, 0.8 μm, 0.9 μm, 1 μm, 1.5 μm, 2 μm, 2.5 μm, 3 μm, 3.5 μm, 4 μm, 4.5 μm, 5 μm, etc. Selecting the high-conductivity ionic property additive within the above particle size range can match with the active material particles to achieve better electrode kinetics effects.

[0018] Further, the binder is selected from one or more of sodium carboxymethyl cellulose or lithium (CMC), styrene-butadiene rubber (SBR), and polyacrylic acid (PAA).

[0019] Further, the conductive agent is selected from one or more of carbon nanotubes (CNT) and carbon black (SP).

[0020] Further, the conditions for the stirring include: first performing primary stirring and then secondary stirring. The rotation speed of the primary stirring is 1000 - 1500 rpm / min, the time of the primary stirring is 1 - 3 h, the rotation speed of the secondary stirring is 400 - 600 rpm / min, and the time of the secondary stirring is 1 - 2 h. Stirring under the above conditions can make the materials evenly mixed and have good stability.

[0021] It can be understood that the specific parameters of the drying and rolling are referred to the conventional manufacturing process of the electrode in the art, and this application does not make special restrictions.

[0022] The second aspect of the present invention provides a negative electrode sheet prepared by the above preparation method, including a current collector and an active coating provided on the surface of the current collector. The active coating includes an active material, a high-conductivity ionic property additive, a binder, and a conductive agent.

[0023] The third aspect of the present invention provides a lithium-ion battery, and the lithium-ion battery includes the negative electrode sheet as described above.

[0024] Compared with the prior art, the present application has the following advantages:

[0025] The preparation method of the negative electrode plate provided by the present invention includes: mixing an active material, a high-conductivity ion characteristic additive, a binder, a conductive agent and water, and stirring to obtain a negative electrode active slurry; coating the negative electrode active slurry on the surface of a negative electrode current collector, drying to obtain an active coating, and then rolling to obtain a negative electrode plate; the high-conductivity ion characteristic additive is selected from one or more of a hard carbon material, a porous carbon material and a metal oxide solid electrolyte, and the mass fraction of the high-conductivity ion characteristic additive in the active coating is 0.1%-5%. After the high-conductivity ion characteristic additive is introduced into the active coating, it can be filled into the active material particles to solve the problem that the contact of the active material particles in the electrode plate is too tight after rolling, resulting in hindered lithium ion diffusion, so that the lithium ion diffusion channel becomes wider and the resistance becomes smaller, and the gap between the active material particles can be filled with the electrolyte to improve the liquid retention situation at the interface between the active material particles (such as graphite particles), achieving the best electrochemical performance and solving the problem of poor kinetics of the silicon-containing negative electrode plate.

[0026] Other features and advantages of the present application will be described in detail in the following specific embodiments. Description of the Drawings

[0027] Figure 1 Schematic diagram of the lithium ion diffusion channel of the negative electrode plate in Comparative Example 1.

[0028] Figure 2 Schematic diagram of the lithium ion diffusion channel of the negative electrode plate in Example 1. Specific Embodiments

[0029] The following will clearly and completely describe the concept and technical effects generated by the present application in combination with the embodiments to fully understand the purpose, features and effects of the present application. Obviously, the described embodiments are only part of the embodiments of the present application, not all of them. Other embodiments obtained by those skilled in the art based on the embodiments of the present application without creative efforts shall fall within the scope of protection of the present application.

[0030] The following embodiments are all used to illustrate the negative electrode plate, its preparation method and lithium ion battery of the present application.

[0031] Example 1

[0032] Mix graphite (QCG-X), a high-conductivity ion characteristic additive (resin-based hard carbon), styrene-butadiene rubber (SBR), sodium carboxymethyl cellulose (CMC), a conductive agent carbon black (SP) and water, stir at a speed of 1200 rpm for 2 h, and then switch to a speed of 500 rpm and stir for 1 h to obtain a negative electrode active slurry. Then, the negative electrode active slurry is applied at 200 g / m 2The areal density is double-sided coated on a copper foil (negative current collector) with a thickness of 6 μm. During the coating process, a drying process is accompanied, and the drying temperature is 60 °C. Then, rolling is carried out according to a rolling density of 1.65 g / cm 3 to obtain the negative electrode sheet.

[0033] Among them, graphite: CMC: SBR: SP: hard carbon are mixed in a ratio of 96%: 1.2%: 1.8%: 0.5%: 0.5%. The mass ratio of water to the solid phase material (including graphite, CMC, SBR, SP, hard carbon) is 1:1. The particle size D50 of the hard carbon is 3 μm, and the areal density of the electrode sheet is 200 g / m 2 , and the electrode sheet is compacted to 1.65 g / cm 3 .

[0034] Example 2

[0035] The preparation process refers to Example 1.

[0036] Among them, graphite (QCG-X): CMC: SBR: SP: hard carbon are mixed in a ratio of 91.5%: 1.2%: 1.8%: 0.5%: 5%. The particle size D50 of the hard carbon is 3 μm, and the areal density of the electrode sheet is 200 g / m 2 , and the electrode sheet is compacted to 1.65 g / cm 3 .

[0037] Example 3

[0038] The preparation process refers to Example 1.

[0039] Among them, graphite (QCG-X): silicon material (HC1600): CMC: SBR: SP: hard carbon are mixed in a ratio of 91%: 5%: 1.2%: 1.8%: 0.5%: 0.5%. The particle size D50 of the hard carbon is 3 μm, and the areal density of the electrode sheet is 200 g / m 2 , and the electrode sheet is compacted to 1.65 g / cm 3 .

[0040] Example 4

[0041] The preparation process refers to Example 1.

[0042] Among them, graphite (QCG-X): CMC: SBR: SP: lithium aluminum titanium phosphate LATP are mixed in a ratio of 96%: 1.2%: 1.8%: 0.5%: 0.5%. The particle size D50 of the hard carbon is 2 μm, and the areal density of the electrode sheet is 200 g / m 2 , and the electrode sheet is compacted to 1.65 g / cm 3 .

[0043] Example 5

[0044] The preparation process refers to Example 1.

[0045] Among them, graphite (QCG-X): CMC: SBR: SP: biomass-based porous carbon are mixed in a ratio of 93.5%: 1.2%: 1.8%: 0.5%: 3%. The pore size of the porous carbon is 2 nm, the particle size D50 is 3 μm, and the electrode surface density is 200 g / m 2 , and the electrode is compacted at 1.65 g / cm 3 .

[0046] Example 6

[0047] The preparation process refers to Example 1.

[0048] Among them, graphite (QCG-X): CMC: SBR: SP: hard carbon: lithium titanium aluminum phosphate LATP are mixed in a ratio of 96%: 1.2%: 1.8%: 0.5%: 0.25%: 0.25%. The particle size D50 of the hard carbon is 2 μm, and the electrode surface density is 200 g / m 2 , and the electrode is compacted at 1.65 g / cm 3 .

[0049] Example 7

[0050] The preparation process refers to Example 1.

[0051] Among them, graphite (QCG-X): CMC: SBR: SP: biomass-based porous carbon: lithium titanium aluminum phosphate LATP are mixed in a ratio of 96%: 1.2%: 1.8%: 0.5%: 0.3%: 0.2%. The pore size of the porous carbon is 2 nm, the particle size D50 is 2 μm, and the electrode surface density is 200 g / m 2 , and the electrode is compacted at 1.65 g / cm 3 .

[0052] Example 8

[0053] The preparation process refers to Example 1.

[0054] Among them, graphite (QCG-X): CMC: SBR: SP: hard carbon are mixed in a ratio of 96.45%: 1.2%: 1.8%: 0.5%: 0.05%. The particle size D50 of the hard carbon is 3 μm, and the electrode surface density is 200 g / m 2 , and the electrode is compacted at 1.65 g / cm 3 .

[0055] Example 9

[0056] The preparation process refers to Example 1.

[0057] Among them, graphite (QCG-X): CMC: SBR: SP: hard carbon are mixed in a ratio of 96%: 1.2%: 1.8%: 0.5%: 0.5%, and the areal density of the electrode is 200 g / m 2 , and the electrode is compacted to 1.65 g / cm 3 . The D50 of the hard carbon particle size is 0.005 μm.

[0058] Comparative Example 1

[0059] Among them, graphite: CMC: SBR: SP: hard carbon are mixed in a ratio of 96.5%: 1.2%: 1.8%: 0.5%: 0%, and the areal density of the electrode is 200 g / m 2 , and the electrode is compacted to 1.65 g / cm 3 .

[0060] The negative electrodes prepared in the examples and comparative examples were made into symmetric cells for evaluation:

[0061] The symmetric cell includes two layers of negative electrodes, an electrolyte, and a layer of separator. The electrolyte system (EC: DMC: DEC: FEC: VC = 0.3: 0.3: 0.3: 0.07: 0.03, and the component ratios of the electrolyte are all mass ratios). The negative electrode, a layer of separator, and a layer of negative electrode were assembled in sequence, 10 g of electrolyte was injected, and left standing for 24 h;

[0062] Among them, ethylene carbonate (EC), dimethyl carbonate (DMC), diethyl carbonate (DEC), fluoroethylene carbonate (FEC), vinylene carbonate (VC).

[0063] EIS tests were carried out using an electrochemical workstation. The ease of lithium ion diffusion was represented by Rd, and the test results are shown in Table 1 below.

[0064] Table 1

[0065] Comparison item Rd Example 1 20.1 Example 2 19.4 Example 3 19.8 Example 4 19.0 Example 5 19.1 Example 6 18.8 Example 7 18.6 Example 8 22.5 Example 9 24.2 Comparative example 1 25.1

[0066] It can be seen from the data in Table 1 that compared with Comparative Example 1, in Examples 1-9 of the present application, high-conductivity ion characteristic additives were introduced, and the Rd value decreased to varying degrees, which can significantly improve the lithium ion diffusion kinetics. In Example 8, the dosage of the high-conductivity ion characteristic additive (hard carbon) was not within the preferred parameter range of the present invention, and in Example 9, the particle size of the high-conductivity ion characteristic additive (hard carbon) was not within the preferred parameter range of the present invention. The Rd value reduction effect in Examples 8-9 was not obvious, and the improvement degree of lithium ion diffusion kinetics was worse than that in Examples 1-7.

[0067] Figure 1 Schematic diagram showing the lithium ion diffusion channel situation of the negative electrode in Comparative Example 1, where lithium ion diffusion is blocked. Figure 2Schematically shows the situation of the lithium-ion diffusion channels in the negative electrode plate of Example 1. The lithium-ion diffusion channels are opened, and the gaps between the particles are significantly increased.

[0068] Obviously, the above-mentioned embodiments of the present application are merely examples for clearly illustrating the present application, rather than limitations on the implementation manners of the present application. For those of ordinary skill in the art, other different forms of changes or modifications can be made based on the above description. It is impossible to list all the implementation manners here. All obvious changes or modifications derived from the technical solutions of the present application are within the spirit scope covered by the present application.

Claims

1. A method for preparing a negative electrode plate, characterized in that, Comprising: Mixing an active material, a high-ion-conductivity additive, a binder, a conductive agent, and water, and stirring to obtain a negative electrode active paste; Coating the negative electrode active paste on the surface of a negative electrode current collector, drying to obtain an active coating, and then roll-pressing to obtain a negative electrode plate; Wherein, the high-ion-conductivity additive is selected from one or more of hard carbon materials, porous carbon materials, and metal oxide solid electrolytes; the mass fraction of the high-ion-conductivity additive in the active coating is 0.1%-5%.

2. The preparation method according to claim 1, wherein, The metal oxide solid electrolyte is selected from one or more of lithium lanthanum titanium oxide, lithium lanthanum zirconium oxide, lithium titanium aluminum phosphate, and fast ion conductors; the hard carbon material is selected from one or more of resin-based hard carbon, organic polymer carbon, carbon black, and biomass carbon; the porous carbon material is selected from one or more of biomass-based porous carbon and resin-based porous carbon, and the pore diameter of the porous carbon is 1-2 nm.

3. The preparation method according to claim 1 or 2, characterized in that, The high-ion-conductivity additive comprises a hard carbon material and a metal oxide solid electrolyte, and the mass ratio of the hard carbon material to the metal oxide solid electrolyte is 0.8-1.5:1; alternatively, the high-ion-conductivity additive comprises a porous carbon material and a metal oxide solid electrolyte, and the mass ratio of the porous carbon material to the metal oxide solid electrolyte is 0.8-1.5:

1.

4. The preparation method according to claim 1, characterized in that, The active material is selected from one or more of graphite materials and silicon materials; the graphite material is selected from one or more of artificial graphite primary particles, artificial graphite secondary particles, natural graphite, and microcrystalline graphite; the silicon material is selected from one or more of silicon monoxide, pre-lithiated silicon monoxide, pre-magnesium silicon monoxide, and silicon-carbon materials.

5. The preparation method according to claim 1 or 2, characterized in that, The mass fraction of the high-ion-conductivity additive in the active coating is 0.5%-5%, and / or the particle size D50 of the high-ion-conductivity additive is 0.01 μm-5 μm.

6. The preparation method according to claim 1, wherein, The binder is selected from one or more of sodium carboxymethyl cellulose or lithium, styrene-butadiene rubber, and polyacrylic acid; and / or the conductive agent is selected from one or more of carbon nanotubes and carbon black.

7. The preparation method according to claim 1, characterized in that, The mass fraction of the active material in the active coating is 80%-98%, the mass fraction of the conductive agent in the active coating is 0.5%-10%, and the mass fraction of the binder in the active coating is 1%-5%.

8. The preparation method according to claim 1, characterized in that, The conditions of the stirring include: first performing primary stirring, and then performing secondary stirring. The rotation speed of the primary stirring is 1000-1500 rpm / min, the time of the primary stirring is 1-3 h, the rotation speed of the secondary stirring is 400-600 rpm / min, and the time of the secondary stirring is 1-2 h.

9. A negative electrode plate, characterized in that, Prepared by the preparation method according to any one of claims 1-8, the negative electrode plate comprises a current collector and an active coating provided on the surface of the current collector, and the active coating comprises an active material, a high-ion-conductivity additive, a binder, and a conductive agent.

10. A lithium-ion battery, the lithium-ion battery comprises the negative electrode plate according to claim 9 or the negative electrode plate prepared by the method according to any one of claims 1-8.

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