Softening agent for positive pole piece of lithium ion battery as well as preparation method and application of softening agent

Abstract

The invention relates to the technical field of lithium ion battery auxiliaries, in particular to a lithium ion battery positive pole piece softening agent and a preparation method and application thereof. The preparation method of the softening agent comprises the following steps: performing catalytic reaction on a first polymer and a second polymer in a first solvent through a catalyst to obtain a first product; adding a third polymer into the first product to continuously react to obtain a second product; and adding a plasticizer into the second product, and mixing and stirring. According to the prepared softening agent, under the low addition amount of 0.5% or below, the compaction density of the lithium iron phosphate positive pole piece can be increased by 0.05-0.3 g / cm < 3 >, the flexibility of the pole piece can be remarkably enhanced, the problems of breakage and powder falling of the high-compaction pole piece in the winding, lamination and other manufacturing procedures are effectively avoided, the high energy density and the manufacturing procedure stability of the battery are considered, and the service life of the battery is prolonged. And the method has strong suitability with the existing slurry preparation process, and is easy for industrial application.

Description

Technical Field

[0001] This invention relates to the field of lithium-ion battery additives technology, and in particular to a lithium-ion battery positive electrode flexible agent, its preparation method and application. Background Technology

[0002] Lithium-ion batteries, as a new generation of high-efficiency energy storage devices, have become the core power source for electric vehicles, portable electronic devices, and large-scale energy storage systems due to their advantages such as high energy density, long cycle life, and environmental friendliness. With the rapid development of the new energy industry, market demands for the performance of lithium-ion batteries continue to rise, especially in terms of high energy density, long cycle life, and safety, where more stringent standards are being set. The positive electrode, as the core component for energy storage and conversion in lithium-ion batteries, directly determines the overall performance of the battery through its structural stability and mechanical properties. The development of flexible agents is a key technological direction for addressing the performance bottlenecks of positive electrode sheets.

[0003] The preparation of positive electrode sheets typically uses aluminum foil as the current collector. A slurry composed of positive electrode active material, binder, and conductive agent is loaded onto the surface of the current collector through a coating process. After drying and rolling, an electrode structure with a certain thickness and compaction density is formed. Among them, the positive electrode active material accounts for more than 90% of the electrode mass, and its own physicochemical properties play a dominant role in the electrode performance. However, most mainstream positive electrode active materials have a rigid crystalline structure with high particle hardness and poor ductility, resulting in significant overall brittleness of the electrode. In addition, in the rolling process, in order to improve energy density, the electrode sheet needs to be compacted to a high density through high pressure. Stress concentration between the rigid active material particles and the current collector can easily lead to electrode cracking and powder shedding, reducing production yield. During battery manufacturing and service, the brittleness of the positive electrode sheet can also easily cause a series of performance degradations.

[0004] Against this backdrop, flexible agents have been proposed as a novel type of functional additive. The core function of flexible agents is to achieve a balance between "flexibility enhancement and performance compatibility" through molecular design. They must possess good elasticity and interfacial adhesion, dispersing and absorbing internal stress within the electrode while simultaneously improving electrode flexibility. Therefore, developing flexible agents that combine high flexibility with good compatibility has become a key technology for overcoming the performance bottlenecks of lithium-ion batteries and promoting their application in high-end energy storage. Summary of the Invention

[0005] To address the aforementioned technical problems, this invention provides a method for preparing a flexible agent for the positive electrode of a lithium-ion battery, comprising the following steps: S1. Dissolve the first polymer and the second polymer in the first solvent, then add the catalyst, and heat to 20-150℃ to react for 1-10 hours to obtain the first product; S2. Cool the first product to 20~30℃, add the third polymer, and then heat to 50~150℃ to react for 1~10h to obtain the second product; S3. Cool the second product to 20~30℃, add plasticizer, mix and stir for 0.5~5h to obtain the lithium-ion battery flexibility agent.

[0006] As an implementable example, the first solvent includes NMP (N-methylpyrrolidone).

[0007] As an implementable example, the first polymer includes one or more of polypropylene glycol, polyethoxyethylene ether, polytetrahydrofuran glycol, or polycaprolactone glycol.

[0008] In this invention, when the first polymer is two or more of the specific choices mentioned above, there are no special limitations on the ratio of the specific substances mentioned above, and they can be mixed in any ratio.

[0009] As an implementable example, the second polymer includes one or more of TDI (toluene diisocyanate), MDI (diphenylmethane diisocyanate), or HDI (hexamethylene diisocyanate).

[0010] In this invention, when the second polymer is two or more of the specific choices mentioned above, there are no special limitations on the ratio of the specific substances mentioned above, and they can be mixed in any ratio.

[0011] As an example of an implementable catalyst, the catalyst includes one of triethylamine, dibutyltin dilaurate, or an organobismuth catalyst.

[0012] Furthermore, the organic bismuth catalyst is a DY-20 organic bismuth catalyst.

[0013] As an implementable example, the plasticizer is one or more of the following: triethyl phosphate, tributyl phosphate, dioctyl sebacate, tri(2-ethylhexyl) phosphate, N-ethyl-p-toluenesulfonamide, trioctyl trimellitate, polypropylene adipate, dioctyl adipate, 1-butyl-3-methylimidazolium hexafluorophosphate, and polymethyl methacrylate.

[0014] In this invention, when the plasticizer is two or more of the specific choices mentioned above, there are no special limitations on the ratio of the specific substances mentioned above, and they can be mixed in any ratio.

[0015] As an implementable example, the third polymer includes one or more of 2,2-bis(hydroxymethyl)propionic acid, 1,4-butanediol, 1,6-hexanediol, or ethylenediamine.

[0016] As an implementable example, the mass ratio of the first polymer to the first solvent is 5:(5-100), the mass ratio of the second polymer to the first solvent is (5-15):(5-100), the mass ratio of the catalyst to the first solvent is (0.1-2):100, and the mass ratio of the plasticizer to the first solvent is (0.05-10):(10-100).

[0017] Furthermore, the mass ratio of the second polymer to the first solvent is (5-10):(5-50).

[0018] Furthermore, the mass ratio of the catalyst to the first solvent is (0.1 to 1): 100.

[0019] Furthermore, the mass ratio of the third polymer to the first solvent is (0.1-20):100.

[0020] Furthermore, the mass ratio of the plasticizer to the first solvent is (0.05-10):(10-50).

[0021] As an feasible example, both steps S1 and S2 are carried out by heating under a nitrogen atmosphere.

[0022] Furthermore, the reaction temperature in step S1 is 50~120℃.

[0023] Furthermore, the reaction temperature in step S2 is 50~100℃.

[0024] Furthermore, the reaction time for step S1 is 2 to 8 hours.

[0025] Furthermore, the reaction time for step S2 is 2-5 hours.

[0026] In this invention, the first polymer has a low glass transition temperature, good flexibility, and deformability, and can absorb stress in the positive electrode sheet when the volume of the positive electrode sheet changes. However, the absorption of stress by the soft segment alone is insufficient to significantly improve the flexibility of the positive electrode sheet. Furthermore, the absorbed stress cannot be released in time, which can easily lead to an increase in the porosity of the active material in the positive electrode slurry, resulting in a decrease in the energy density and cycle life of the battery.

[0027] To improve the stress-relieving properties of the first polymer, the first polymer is modified with a second polymer to obtain a structure that simultaneously absorbs and releases stress. The modification reaction mechanism is as follows: ; In the above formula, n = 10~40.

[0028] In this product, hard segment microregions exist as a dispersed phase, while soft segment microregions exist as a continuous phase. The separation of these microphases between the hard and soft segments when the material is subjected to external forces gives the product unique properties. The hard segment microregions act as physical cross-linking points in the soft segment matrix, preventing relative slippage between molecular chains. Simultaneously, the soft segments generally have lower glass transition temperatures, giving the material good low-temperature elasticity.

[0029] From a microscopic morphological perspective, highly polar and rigid urethane groups, due to their large cohesive energy, can form hydrogen bonds between molecules, aggregating to form hard segment microphase regions. At room temperature, these microphase regions exhibit glassy subcrystalline or microcrystalline states. The less polar first polymer segments aggregate to form soft segment phase regions. Although the soft and hard segments have some miscibility, the hard and soft segment phase regions are thermodynamically incompatible, leading to microphase separation. Furthermore, the soft and hard segment microphase regions exhibit their own glass transition temperatures.

[0030] From a macroscopic perspective, polyurethane, with its "hard-soft" two-phase structure, exhibits an isotropic, bicontinuous phase. When a cracked sample is subjected to external force, the "hard-soft" phase structure in polyurethane causes fatigue cracks to encounter and require the breakdown of a harder phase material that is stronger than a single polymer chain. The hard phase material can enhance the mechanical strength of the material, inhibit the crack propagation rate during fracture, and maintain the integrity of the material. Once the molecular chains in the hard phase break, the malleable soft phase bears most of the load, forming a spherical polymer chain that unfolds, thus improving the flexibility of the positive electrode sheet.

[0031] The introduction of plasticizers in this invention not only provides excellent wetting properties for lithium iron phosphate, carbon conductive agents, etc., but also weakens intermolecular interactions by intercalating between polymer molecular chains, improving the crystallinity of the binder and thus making the material more flexible. Furthermore, plasticizers can lower the glass transition temperature of the polymer, allowing the material to maintain flexibility at low temperatures, increasing the elongation of the polymer, reducing tensile strength, and improving the plasticity of the material.

[0032] The second aspect of the present invention provides a lithium-ion battery positive electrode flexible agent prepared by the above-mentioned lithium-ion battery positive electrode flexible agent preparation method. The flexible agent can make the battery electrode more flexible and achieve higher flexibility under the same compaction density when the amount of the flexible agent is added is relatively low, which can meet the requirements of high energy density lithium-ion batteries.

[0033] A third aspect of this invention provides an application of a lithium-ion battery positive electrode flexible agent, which is used in the preparation of lithium-ion battery positive electrode slurry. Adding less than 0.5% of the lithium-ion battery positive electrode flexible agent can increase the compaction density of the lithium iron phosphate positive electrode by 0.05-0.3 g / cm³. 3It can meet the needs of high energy density lithium-ion batteries.

[0034] Beneficial effects (i) The positive electrode sheet made by the lithium-ion battery positive electrode sheet flexibility agent of the present invention has a higher compaction density under the same electrode sheet flexibility and softness, and has better flexibility and softness under the same compaction density. This allows the positive electrode sheet to achieve better process in cell manufacturing processes such as winding and stacking, effectively avoiding the occurrence of electrode sheet breakage caused by high compaction electrode sheet in winding and other processes, and can improve the energy density of the battery under the same electrode sheet flexibility.

[0035] (II) In the preparation of the softening agent, the product molecules contain highly polar and rigid urethane groups and other groups with high cohesive energy, which can form hydrogen bonds between molecules and aggregate to form hard segment microphase regions. The weaker polar first polymer segments aggregate to form soft segment phase regions. The combination of the two can play a role in microphase separation. When the material is subjected to external force, the existence of microphase separation between the soft and hard segments gives the product unique properties. The hard segment microregions act as physical crosslinking points in the soft segment matrix, which can prevent relative slippage between molecular chains. At the same time, the soft segment has a lower glass transition temperature, which can give the material good low-temperature elasticity.

[0036] (III) The flexible agent obtained by this invention is a polyurethane with a "hard-soft" two-phase structure, which exhibits isotropic bicontinuous phases. When a sample with cracks is subjected to external force, the "hard-soft" phase structure in the polyurethane causes fatigue cracks to encounter and require the destruction of a hard phase material that is stronger than a single polymer chain during propagation. The hard phase material can enhance the mechanical strength of the material, inhibit the crack propagation rate during fracture, and maintain the integrity of the material. Once the molecular chains in the hard phase break, the ductile soft phase bears most of the load, forming a spherical polymer chain that unfolds, thereby improving the flexibility of the positive electrode sheet. Attached Figure Description

[0037] Figure 1 This is a schematic diagram showing the compaction density and softness data of the positive electrode slurry for Application Example 1 and Comparative Application Example 1.

[0038] Figure 2 This is a schematic diagram showing the compaction density and softness data of the positive electrode slurry for Application Example 4 and Comparative Application Example 2.

[0039] Figure 3 The thermogravimetric analysis diagram is shown for the softener prepared in Example 1.

[0040] Figure 4 The resistivity test graphs are for Application Example 1 and Comparative Application Example 1.

[0041] Figure 5 Photographs of the front coating of Application Examples 1 and 4 and Comparative Application Examples 1 and 2.

[0042] Figure 6 Photographs of the reverse coating of Application Examples 1 and 4 and Comparative Application Examples 1 and 2.

[0043] Figure 7 Photographs showing the flexibility of application examples 1 and 4 and comparison application examples 1 and 2. Detailed Implementation

[0044] Example 1 The first aspect of this example provides a method for preparing a flexible agent for the positive electrode sheet of a lithium-ion battery, including the following steps: Under S1 and N2 conditions, 5 parts of polycaprolactone diol and 8 parts of MDI were dissolved in 100 parts of NMP, and reacted at 80°C for 8 hours under the catalysis of 1 part of dibutyltin dilaurate to obtain the first product. S2. Cool the first product to 25°C, add 15 parts of 1,4-butanediol under N2 environment, heat to 80°C and react for 5 hours to obtain the second product; S3. Cool the second product to 25°C, add 5 parts of tributyl phosphate under N2 environment, mix and stir at 300 rpm for 1 hour at room temperature (25°C). The polymer solution obtained after uniform mixing is the lithium battery positive electrode flexible agent.

[0045] The second aspect of this example provides a lithium-ion battery positive electrode flexible agent prepared by the above-described method for preparing a lithium-ion battery positive electrode flexible agent; after the flexible agent polymer solution is dried, thermogravimetric analysis is performed (crucible type: alumina, atmosphere: nitrogen). Figure 3 As shown, the initial decomposition temperature is 221℃.

[0046] Example 2 This example provides a method for preparing a flexible agent for the positive electrode sheet of a lithium-ion battery, including the following steps: Under S1 and N2 conditions, 5 parts of polycaprolactone diol and 10 parts of MDI were dissolved in 100 parts of NMP, and the mixture was reacted at 80°C for 8 hours under the catalysis of 1 part of dibutyltin dilaurate to obtain the first product. S2. Cool the first product to 25°C, add 15 parts of 2,2-bis(hydroxymethyl)propionic acid under N2 environment, and heat to 80°C for 5 hours to obtain the second product. S3. Cool the second product to 25°C, add 10 parts of dioctyl adipate under N2 environment, mix and stir at 300 rpm for 1 hour at room temperature (25°C). The polymer solution obtained after uniform mixing is the lithium battery positive electrode flexible agent.

[0047] Example 3 This example provides a method for preparing a flexible agent for the positive electrode sheet of a lithium-ion battery, including the following steps: Under S1 and N2 conditions, 5 parts of polycaprolactone diol and 10 parts of MDI were dissolved in 100 parts of NMP, and the mixture was reacted at 80°C for 8 hours under the catalysis of 1 part of dibutyltin dilaurate to obtain the first product. S2. Cool the first product to 25°C, add 15 parts of 2,2-bis(hydroxymethyl)propionic acid under N2 environment, and heat to 80°C for 5 hours to obtain the second product. S3. Cool the second product to 25°C, add 15 parts of dioctyl adipate under N2 environment, mix and stir at 300 rpm for 1 hour at room temperature (25°C). The polymer solution obtained after uniform mixing is the lithium battery positive electrode flexible agent.

[0048] Example 4 The first aspect of this example provides a method for preparing a flexible agent for the positive electrode sheet of a lithium-ion battery, including the following steps: Under S1 and N2 conditions, 5 parts of polycaprolactone diol and 10 parts of MDI were dissolved in 100 parts of NMP, and the mixture was reacted at 80°C for 8 hours under the catalysis of 1 part of dibutyltin dilaurate to obtain the first product. S2. Cool the first product to 25°C, add 15 parts of 1,6-hexanediol under N2 environment, heat to 80°C and react for 5 hours to obtain the second product; S3. Cool the second product to 25°C, add 5 parts of 1-butyl-3-methylimidazolium hexafluorophosphate under N2 environment, mix and stir at 300 rpm for 1 hour at room temperature (25°C). The polymer solution obtained after uniform mixing is the lithium battery positive electrode flexible agent.

[0049] Example 5 The first aspect of this example provides a method for preparing a flexible agent for the positive electrode sheet of a lithium-ion battery, including the following steps: Under S1 and N2 conditions, 5 parts of polycaprolactone diol and 10 parts of MDI were dissolved in 100 parts of NMP, and the mixture was reacted at 80°C for 8 hours under the catalysis of 1 part of dibutyltin dilaurate to obtain the first product. S2. Cool the first product to 25°C, add 15 parts of 1,6-hexanediol under N2 environment, heat to 80°C and react for 5 hours to obtain the second product; S3. Cool the second product to 25°C, add 10 parts of trioctyl trimellitate under N2 environment, mix and stir at 300 rpm for 1 hour at room temperature (25°C). The polymer solution obtained after uniform mixing is the lithium battery positive electrode flexible agent.

[0050] Application Example 1 This example provides the application of a flexible agent for lithium-ion battery positive electrode sheets, which is used in the preparation of positive electrode slurry. Specifically, the flexible agent polymer solution obtained in Example 1 is used to prepare a positive electrode slurry according to the weight ratio of lithium iron phosphate: carbon black: binder PVDF (polyvinylidene fluoride): flexible agent polymer solution = 96.3:1.5:2:0.2. The solid content, discharge viscosity, and fineness of the positive electrode slurry are tested, and the appearance, areal density, and compaction density of the electrode sheet are also tested.

[0051] The lithium iron phosphate powder, model YN-7, was purchased from Hunan Yuneng New Energy Battery Materials Co., Ltd.; the carbon black was purchased from Temicor, model SP; and the PVDF binder, model HSV900, was available from Arkema, France.

[0052] Application Example 2 The specific implementation method in this example is the same as in application example 1, except that: Lithium iron phosphate: carbon black: binder PVDF: softener polymer solution = 96.4:1.5:2:0.1.

[0053] Application Example 3 The specific implementation method in this example is the same as in application example 1, except that: Lithium iron phosphate: carbon black: binder PVDF: softener polymer solution = 96.2:1.5:2:0.3.

[0054] Application Example 4 The specific implementation method in this example is the same as in application example 1, except that: The lithium iron phosphate powder, model DY-3, was purchased from Shenzhen Defang Nanotechnology Co., Ltd.

[0055] Application Example 5 The specific implementation method in this example is the same as in application example 4, except that: Lithium iron phosphate: carbon black: binder PVDF: softener polymer solution = 96.4:1.5:2:0.1.

[0056] Application Example 6 The specific implementation method in this example is the same as in application example 4, except that: Lithium iron phosphate: carbon black: binder PVDF: softener polymer solution = 96.2:1.5:2:0.3.

[0057] Comparative Application Example 1 The specific implementation method in this example is the same as in application example 1, except that: 1. The raw materials used in the preparation do not include the polymer solution for softening agents; 2. Lithium iron phosphate: carbon black: PVDF binder = 96.5: 1.5: 2.

[0058] The electrode resistivity test graphs for Application Example 1 and Comparative Application Example 1 are shown below. Figure 3 As shown.

[0059] Comparative Application Example 2 The specific implementation method in this example is the same as in application example 4, except that: 1. The raw materials used in the preparation do not include the polymer solution for softening agents; 2. Lithium iron phosphate: carbon black: PVDF binder = 96.5: 1.5: 2.

[0060] The photographs of application examples 1 and 4 and comparison application examples 1 and 2, showing the front coating, are shown below. Figure 5 As shown.

[0061] Photographs of application examples 1 and 4 and comparison examples 1 and 2 (reverse coating) are shown. Figure 6 As shown.

[0062] Application examples 1 and 4, and comparison photos of flexibility in application examples 1 and 2 are shown. Figure 7 As shown.

[0063] The solid content, viscosity (25℃), and fineness of the positive electrode slurry in test applications 1-6 and comparative applications 1-2 are shown in Table 1.

[0064] Table 1

[0065] The additive content, double-sided coating density, coating method, and compaction density of the positive electrode slurry in test application examples 1-6 and comparative application examples 1-2 are shown in Table 2.

[0066] Table 2

[0067] The compaction density and softness data of the positive electrode slurry corresponding to Application Examples 1 and 4, and Comparative Application Examples 1 and 2 are as follows: Figures 1-2 As shown.

[0068] Compared to comparative examples 1-2, the softness of application examples 1 and 4, under conditions of similar or identical discharge viscosity, solid content, fineness, and coating surface density, shows that the softness of application examples 1 and 4 with added positive electrode flexibleizer is superior to that of comparative examples 1-2 without added agent. When comparing at the same softness level, application examples 1 and 4 with added positive electrode flexibleizer show a 0.2 g / cm³ increase compared to comparative examples 1-2 without added agent. 3 The above compaction density.

[0069] Therefore, the softening polymer solution obtained in Example 1 can significantly improve the softness of the positive electrode sheet, and increase the compaction density by 0.2 g / cm³ while maintaining the same level of softness. 3 The above demonstrates a broader application prospect in the field of high energy storage and high energy density batteries.

Claims

1. A method for preparing a flexible agent for a lithium-ion battery positive electrode sheet, characterized in that, Includes the following steps: S1. Dissolve the first polymer and the second polymer in the first solvent, then add the catalyst, and heat to 20-150℃ to react for 1-10 hours to obtain the first product; S2. Cool the first product to 20~30℃, add the third polymer, and then heat to 50~150℃ to react for 1~10h to obtain the second product; S3. Cool the second product to 20~30℃, add plasticizer, mix and stir for 0.5~5h to obtain the lithium-ion battery flexibility agent; The first polymer includes one or more of polypropylene glycol, polyethoxyethylene ether, polytetrahydrofuran glycol, or polycaprolactone glycol; The second polymer includes one or more of TDI, MDI, or HDI; The third polymer includes one or more of 2,2-bis(hydroxymethyl)propionic acid, 1,4-butanediol, 1,6-hexanediol, and ethylenediamine.

2. The method for preparing the lithium-ion battery positive electrode flexible agent according to claim 1, characterized in that, The catalyst includes one of triethylamine, dibutyltin dilaurate, and an organobismuth catalyst.

3. The method for preparing the lithium-ion battery positive electrode flexible agent according to claim 2, characterized in that, The organic bismuth catalyst mentioned is DY-20 organic bismuth catalyst.

4. The method for preparing the lithium-ion battery positive electrode flexible agent according to claim 1, characterized in that, The mass ratio of the first polymer to the first solvent is 5:(5~100).

5. The method for preparing the lithium-ion battery positive electrode flexible agent according to claim 1, characterized in that, The mass ratio of the second polymer to the first solvent is (5-15):(5-100).

6. The method for preparing the lithium-ion battery positive electrode flexible agent according to claim 1, characterized in that, The mass ratio of the catalyst to the first solvent is (0.1-2):

100.

7. The method for preparing the lithium-ion battery positive electrode flexible agent according to claim 1, characterized in that, The mass ratio of the plasticizer to the first solvent is (0.05-10):(10-100).

8. The method for preparing the lithium-ion battery positive electrode flexible agent according to claim 7, characterized in that, The plasticizer includes one or more of the following: triethyl phosphate, tributyl phosphate, dioctyl sebacate, tri(2-ethylhexyl) phosphate, N-ethyl-p-toluenesulfonamide, trioctyl trimellitate, polypropylene adipate, dioctyl adipate, 1-butyl-3-methylimidazolium hexafluorophosphate, or polymethyl methacrylate.

9. A lithium-ion battery positive electrode flexible agent prepared by the method of preparing the lithium-ion battery positive electrode flexible agent according to any one of claims 1-8.

10. The application of the lithium-ion battery positive electrode flexible agent according to claim 9, characterized in that, It is used in the preparation of positive electrode slurry for lithium-ion batteries.

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