A lithium battery pole piece containing a cross-linked hydrogenated nitrile rubber binder and a preparation method thereof

Abstract

The present application relates to the field of lithium battery manufacturing technology, and in particular to a lithium battery pole piece containing a cross-linked hydrogenated nitrile rubber binder and a preparation method thereof. A preparation method for a lithium battery pole piece containing a cross-linked hydrogenated nitrile rubber binder comprises the following steps: S1, preparing a positive electrode slurry; S2, coating the pole piece to form a primary pole piece; S3, primary calendering; S4, gamma ray radiation cross-linking; S5, secondary calendering; S6, cutting: cutting the pole piece after the secondary calendering into the required size to obtain a lithium battery pole piece containing a cross-linked hydrogenated nitrile rubber binder. The present application significantly improves the strength, flexibility and electrochemical performance of the pole piece by using hydrogenated nitrile rubber as a binder and preparing the lithium battery pole piece through gamma ray radiation cross-linking technology. At the same time, the preparation method of the present application is environmentally friendly and efficient, and is suitable for large-scale production of high-performance lithium battery pole pieces.

Description

Technical Field

[0001] The present application relates to the technical field of lithium battery manufacturing, and in particular to a lithium battery pole piece containing a cross-linked hydrogenated nitrile rubber binder and a preparation method thereof. Background Art

[0002] Lithium-ion batteries are secondary batteries (rechargeable batteries) that primarily rely on the movement of lithium ions between the positive and negative electrodes to operate. The positive electrode material, a component of the lithium-ion battery's materials, directly impacts its performance and accounts for a significant proportion (the mass ratio of positive to negative electrode materials is 3:1-4:1). Typically, the positive electrode material is formulated into a mixture containing an active material (such as LiCoO2, LiFePO4, etc.), a dispersant, a binder, a conductive agent (such as carbon black), and a solvent. This mixture is stirred, kneaded, and dispersed in a specific ratio and sequence to form a slurry, which is then coated onto a current collector (such as aluminum foil) to form the positive electrode sheet. The performance of a lithium-ion battery's positive electrode sheet directly impacts the overall performance of the battery, and the binder is a key material in its fabrication. Traditional lithium-ion battery positive electrode binders typically use polyvinylidene fluoride (PVDF), but this material suffers from issues such as insufficient flexibility and environmental friendliness. Hydrogenated nitrile butadiene rubber (HNBR) offers excellent heat resistance, chemical resistance, and mechanical properties, but its uncrosslinked state as a binder results in poor strength and toughness. Chinese invention patent CN 110183691A discloses that the mechanical properties of HNBR rubber can be significantly improved by using peroxides, such as 1,3-bis(tert-butylperoxyisopropyl)benzene. However, the additional peroxide and other chemicals required may react with the cathode material, resulting in reduced battery performance. Therefore, physically crosslinking HNBR to improve electrode performance may be an effective method. This has significant implications for the application of HNBR in batteries. Summary of the Invention

[0003] In response to the shortcomings of the existing technology, the present application provides a lithium battery pole piece containing a cross-linked hydrogenated nitrile rubber binder and a preparation method thereof. The present application utilizes hydrogenated nitrile rubber as a binder and prepares the lithium battery pole piece through gamma ray radiation cross-linking technology, thereby significantly improving the strength, flexibility and electrochemical performance of the pole piece. At the same time, the preparation method of the present application is environmentally friendly and efficient, and is suitable for large-scale production of high-performance lithium battery pole pieces.

[0004] In a first aspect, the present application provides a method for preparing a lithium battery electrode containing a cross-linked hydrogenated nitrile rubber binder, using the following technical solution:

[0005] A method for preparing a lithium battery pole piece containing a cross-linked hydrogenated nitrile rubber binder comprises the following steps:

[0006] S1. Prepare positive electrode slurry: Mix the positive electrode active material, conductive agent and hydrogenated nitrile rubber binder in proportion, add solvent, and use a planetary mixer to stir at a certain speed for 1 to 5 hours to form a uniform positive electrode slurry;

[0007] S2. Coating the electrode sheet: evenly coat the positive electrode slurry on the aluminum foil current collector, control the coating thickness, and dry it at 80 to 120°C to remove the solvent to form a primary electrode sheet;

[0008] S3, first-stage calendering: the dried electrode is passed through a calendering machine for first-stage calendering to make the electrode thickness uniform and improve the density;

[0009] S4, gamma ray radiation cross-linking: placing the first-stage calendered electrode in a gamma ray radiation device for gamma ray radiation cross-linking treatment to cause a cross-linking reaction of the hydrogenated nitrile rubber binder;

[0010] S5, secondary calendering: the electrode after radiation cross-linking treatment is subjected to secondary calendering by a calendering machine;

[0011] S6. Cutting: Cut the electrode sheet after the secondary calendering into the required size to obtain a lithium battery electrode sheet containing a cross-linked hydrogenated nitrile rubber binder.

[0012] By adopting the above technical solution, S1: prepare the positive electrode slurry by mixing the positive electrode active material, conductive agent, hydrogenated nitrile rubber binder and solvent to form a uniform positive electrode slurry. This step ensures the uniform distribution of all components and provides a good foundation for subsequent coating and calendering. It ensures the uniformity and consistency of the materials in the subsequent coating process, which helps to improve the overall performance and consistency of the electrode. S2: Coat the electrode, evenly coat the positive electrode slurry on the aluminum foil current collector, and remove the solvent by drying. This step ensures the initial morphology and structure of the electrode. The uniformity of the coating directly affects the effect of subsequent calendering and cross-linking, and the drying process helps to reduce problems in subsequent processing. S3: Primary calendering, by calendering, the thickness of the electrode is made uniform and the density is increased. This helps to reduce defects in the electrode and improve its electrochemical performance. The uniform thickness and density provide a good physical basis for subsequent gamma ray radiation cross-linking. S4: Gamma ray radiation cross-linking, the electrode is subjected to gamma ray radiation cross-linking treatment to cause the hydrogenated nitrile rubber binder to undergo a cross-linking reaction. This step significantly improves the mechanical strength and flexibility of the electrode. The cross-linking reaction not only improves the physical properties of the electrode, but also enhances the electrochemical properties of the electrode, while providing a stable material basis for the subsequent secondary calendering. S5: Secondary calendering, further improving the density and thickness uniformity of the electrode through secondary calendering. This helps to further improve the overall performance of the electrode. Secondary calendering ensures that the final performance of the electrode meets the expected standards while reducing possible defects. S6: Cutting, cutting the calendered electrode into the required size. This step ensures the consistency of the final product and facilitates subsequent assembly. The cutting process ensures the dimensional accuracy and consistency of the electrode, which helps to improve the overall performance and reliability of the battery. Through the synergistic effect of the above steps, the preparation method of the present application not only improves the mechanical strength, flexibility and electrochemical properties of the lithium battery electrode, but also ensures the environmental protection and efficiency of the production process. These advantages make this method suitable for large-scale production of high-performance lithium battery electrodes.

[0013] Preferably, in step S1, the positive electrode active material is one of lithium iron phosphate (LiFePO4) and lithium cobalt oxide (LiCoO2).

[0014] Preferably, in step S1, the weight proportion of the hydrogenated nitrile rubber binder in the positive electrode slurry is 2% to 10%, preferably 5%; the acrylonitrile content of the hydrogenated nitrile rubber is 33-50%, the number average molecular weight is 20,000 to 2 million, and the degree of hydrogenation is greater than 95%, preferably greater than 99%.

[0015] By adopting the above technical solution, hydrogenated nitrile rubber, as a polymer material, exhibits excellent bonding properties, effectively bonding the positive electrode active material, conductive agent, and other components together to form a uniform positive electrode slurry. It also maintains structural stability during the electrode drying and calendering process, preventing delamination or shedding of the material. After gamma-ray cross-linking treatment, the hydrogenated nitrile rubber binder increases the crosslink density between its molecular chains, thereby improving the mechanical strength of the electrode. This enhanced mechanical strength helps reduce cracking and shedding during charge and discharge. The hydrogenated nitrile rubber binder exhibits excellent flexibility and ductility, allowing the electrode to adapt to volume changes during charge and discharge without fracturing. This is crucial for improving the overall performance and service life of the battery. The use of hydrogenated nitrile rubber binder meets the requirements of green manufacturing and sustainable development. Its optimal acrylonitrile content and degree of hydrogenation ensure the material's environmental friendliness and safety. During the preparation process, the weight proportion of the hydrogenated nitrile rubber binder is controlled between 2% and 10%, preferably 5%, to help balance the binder's impact on electrode performance with cost-effectiveness. At the same time, choosing a hydrogenated nitrile rubber binder with an acrylonitrile content of 33-50%, a number-average molecular weight of 20,000 to 2 million, and a degree of hydrogenation greater than 95% can ensure the optimal overall performance of the electrode. In summary, hydrogenated nitrile rubber binders play a key role in the preparation of lithium battery electrode sheets, not only improving the mechanical strength and flexibility of the electrode sheets, but also improving their electrochemical performance, while also meeting the requirements of environmental protection and sustainable development.

[0016] Preferably, in step S1, the solvent is N-methylpyrrolidone.

[0017] Preferably, in step S1, the conductive agent is at least one of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon nanotubes and graphene.

[0018] Preferably, in step S1, the thickness of the aluminum foil current collector is 10 to 50 microns, preferably 15 to 25 microns.

[0019] Preferably, in step S2, the coating thickness is 10 to 200 microns, preferably 80 to 120 microns.

[0020] Preferably, in step S4, the gamma ray radiation cross-linking treatment has a radiation dose of 10 to 20 kGy. A lower radiation dose cannot cross-link the hydrogenated nitrile rubber, while a higher dose may cause the positive electrode material to decompose, affecting battery performance.

[0021] By adopting the above technical solution, gamma-ray radiation can trigger a cross-linking reaction in the molecular chains of the hydrogenated nitrile rubber binder. This cross-linking reaction can significantly improve the material's mechanical strength and flexibility, while also improving its electrochemical performance. Through gamma-ray radiation cross-linking treatment, the electrode sheets exhibit better stability during the charge and discharge process, reducing cracking and shedding, thereby improving the overall performance and lifespan of the battery. The radiation dose is controlled between 10 and 20 kGy. This dose range ensures effective cross-linking of the hydrogenated nitrile rubber binder while avoiding excessive radiation decomposition of the positive electrode material, thereby ensuring that battery performance is not affected. The gamma-ray radiation cross-linking treatment is combined with other steps (such as primary and secondary calendering) in the electrode preparation process. This synergistic effect ensures that the electrode sheets achieve optimal uniformity, density, and electrochemical performance. The primary and secondary calendering processes can achieve a more uniform thickness of the electrode sheets, which helps to achieve uniformity after gamma-ray radiation cross-linking treatment. Calendering can increase the density of the electrode, which helps improve the stability and electrochemical performance of the electrode after gamma-ray cross-linking. Gamma-ray cross-linking combined with other steps can improve the electrochemical performance of the electrode, such as cycle life and energy density. In summary, gamma-ray cross-linking plays a key role in the preparation of lithium battery electrode sheets. Through synergistic effects with other steps, it improves the mechanical strength, flexibility, electrochemical performance of the electrode, and overall battery performance.

[0022] Preferably, in steps S3 and S5, the calendering pressures of the primary calendering and the secondary calendering are both 10 to 50 MPa, preferably 20 to 30 MPa.

[0023] In a second aspect, the present application provides a lithium battery electrode containing a cross-linked hydrogenated nitrile rubber binder, which adopts the following technical solution:

[0024] As a general technical concept, the present application also provides the above-mentioned lithium battery pole piece containing cross-linked hydrogenated nitrile rubber binder, which is prepared by the above-mentioned preparation method of lithium battery pole piece containing cross-linked hydrogenated nitrile rubber binder and has a structure containing radiation-crosslinked hydrogenated nitrile rubber binder.

[0025] In summary, the beneficial technical effects of this application are:

[0026] 1. Improved mechanical strength: By treating the hydrogenated nitrile rubber binder with gamma-ray cross-linking technology, the mechanical strength of the pole piece is significantly improved. This treatment method can effectively reduce the cracking and shedding of the pole piece during the charging and discharging process of the lithium battery, thereby improving the safety and reliability of the battery.

[0027] 2. Enhanced flexibility: The increased flexibility of the pole piece allows it to better adapt to the volume changes that occur during the lithium battery's charge and discharge process. This improvement not only increases the battery's service life but also reduces internal stress concentration caused by pole piece deformation.

[0028] 3. Improved electrochemical performance: Electrodes cross-linked with gamma rays also exhibit enhanced electrochemical performance. This is reflected in increased battery cycle life and energy density. This is crucial for improving overall battery performance and user experience.

[0029] 4. Environmentally friendly materials and technologies: The hydrogenated nitrile rubber binder and gamma-ray cross-linking technology used in this application both meet environmental and sustainable development requirements. This not only helps reduce environmental pollution during the production process but also reduces resource consumption, aligning with the trend of green development in modern manufacturing. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] In order to more clearly illustrate the technical solutions in the embodiments of the present application, the following briefly introduces the drawings used in the embodiments:

[0031] Figure 1 This is a flow chart for preparing a lithium battery electrode containing a cross-linked hydrogenated nitrile rubber binder according to the present application;

[0032] Figure 2 Schematic diagram of the structure of hydrogenated nitrile rubber before and after gamma-ray radiation cross-linking. DETAILED DESCRIPTION

[0033] The embodiments of the present application will be described in detail below with reference to the examples, but it will be understood by those skilled in the art that the following examples are merely illustrative of the present application and should not be considered as limiting the scope of the present application. In the examples, if specific conditions are not specified, the conditions are carried out according to conventional conditions or manufacturer recommendations. The reagents or instruments used are not specified by the manufacturer and are conventional products that can be purchased commercially.

[0034] In the following examples, the hydrogenated nitrile rubber has an acrylonitrile content of 42%, a number average molecular weight of 1.5 million, and a degree of hydrogenation of 99.5%.

[0035] Example 1

[0036] A method for preparing a lithium battery pole piece containing a cross-linked hydrogenated nitrile rubber binder comprises the following steps:

[0037] 920g of lithium iron phosphate (LiFePO4), 60g of carbon black and 20g of hydrogenated nitrile rubber (HNBR) were mixed, 1000mL of N-methylpyrrolidone (NMP) solvent was added, and the mixture was stirred at 2500rpm using a planetary mixer for 1 hour to form a uniform positive electrode slurry. The positive electrode slurry was evenly coated on an aluminum foil current collector with a thickness of 15 microns, and the coating thickness was controlled to be 80 microns. It was then dried at 80°C for 14 hours to form a primary electrode sheet. The dried electrode sheet was passed through a calender for primary calendering at a calendering pressure of 20MPa. The electrode sheet after primary calendering was placed in a gamma ray irradiation device and irradiated and cross-linked at a dose of 10kGy. The irradiated electrode sheet was passed through a calender for secondary calendering at a calendering pressure of 20MPa. The electrode sheet after secondary calendering was cut into the required size to obtain a lithium battery electrode sheet containing a cross-linked hydrogenated nitrile rubber binder.

[0038] Example 2

[0039] A method for preparing a lithium battery pole piece containing a cross-linked hydrogenated nitrile rubber binder comprises the following steps:

[0040] 920g of lithium iron phosphate (LiFePO4), 60g of carbon black and 80g of hydrogenated nitrile rubber (HNBR) were mixed, 1000mL of N-methylpyrrolidone (NMP) solvent was added, and the mixture was stirred at 2000rpm using a planetary mixer for 5 hours to form a uniform positive electrode slurry. The positive electrode slurry was evenly coated on a 25-micron thick aluminum foil current collector, controlling the coating thickness to 120 microns, and dried at 120°C for 8 hours to form a primary electrode sheet. The dried electrode sheet was passed through a calender for primary calendering at a calendering pressure of 30MPa. The electrode sheet after primary calendering was placed in a gamma ray irradiation device and irradiated and cross-linked at a dose of 20kGy. The irradiated electrode sheet was passed through a calender for secondary calendering at a calendering pressure of 30MPa. The electrode sheet after secondary calendering was cut into the required size to obtain a lithium battery electrode sheet containing a cross-linked hydrogenated nitrile rubber binder.

[0041] Example 3

[0042] A method for preparing a lithium battery pole piece containing a cross-linked hydrogenated nitrile rubber binder comprises the following steps:

[0043] 920g of lithium iron phosphate (LiFePO4), 50g of carbon black and 30g of hydrogenated nitrile rubber (HNBR) were mixed, 1000mL of N-methylpyrrolidone (NMP) solvent was added, and a planetary mixer was used to stir at a speed of 2000rpm for 2 hours to form a uniform positive electrode slurry. The positive electrode slurry was evenly coated on an aluminum foil current collector with a thickness of 20 microns, and the coating thickness was controlled to be 100 microns. It was dried at 100°C for 10 hours to form a primary electrode sheet. The dried electrode sheet was passed through a calender for primary calendering at a calendering pressure of 20MPa. The electrode sheet after primary calendering was placed in a gamma ray irradiation device and irradiated and cross-linked at a dose of 15kGy. The irradiated electrode sheet was passed through a calender for secondary calendering at a calendering pressure of 25MPa. The electrode sheet after secondary calendering was cut into the required size to obtain a lithium battery electrode sheet containing a cross-linked hydrogenated nitrile rubber binder.

[0044] Example 4

[0045] 900g of lithium cobalt oxide (LiCoO2), 50g of carbon black, and 50g of hydrogenated nitrile rubber (HNBR) were mixed, 1000mL of N-methylpyrrolidone (NMP) solvent was added, and the mixture was stirred at 2500rpm using a planetary mixer for 3 hours to form a uniform positive electrode slurry. The positive electrode slurry was evenly coated on a 15-micron thick aluminum foil current collector, controlling the coating thickness to 80 microns, and dried at 90°C for 12 hours to form a primary electrode sheet. The dried electrode sheet was passed through a calender for primary calendering at a calendering pressure of 15MPa. The electrode sheet after primary calendering was placed in a gamma ray irradiation device and irradiated and cross-linked at a dose of 10kGy. Secondary calendering: The irradiated electrode sheet was passed through a calender for secondary calendering at a calendering pressure of 20MPa. Cutting: The electrode sheet after secondary calendering was cut into the required size to obtain a lithium battery electrode sheet containing a cross-linked hydrogenated nitrile rubber binder.

[0046] Comparative Example 1

[0047] The same as Example 4, except that: the secondary calendering treatment is directly performed after the primary calendering, and no radiation cross-linking is performed.

[0048] Comparative Example 2

[0049] Same as Example 4, except that the radiation cross-linking dose is 40 kGy.

[0050] Comparative Example 3

[0051] The same as Example 4, except that an equal amount of PVDF type adhesive (adhesive 5130 produced by Solvay Corporation of the United States) is used instead of hydrogenated nitrile rubber.

[0052] Performance testing

[0053] Resistivity test method: Use a BER2500 resistance meter to test the electrode resistivity and battery internal resistance.

[0054] The assembly order of button cells is from bottom to top: negative electrode shell - spring - gasket - lithium sheet - electrolyte - diaphragm - electrolyte - electrode - positive electrode shell; PE porous polymer film is used as the diaphragm; 1 mol / L LiPF6 solution is used as the electrolyte;

[0055] The coin cells were charged and discharged 100 times at a constant current of 0.5 C in the voltage range of 2.8 V to 4.25 V at 25° C. Room temperature charge / discharge measurements were used to evaluate the capacity and charge / discharge efficiency.

[0056] Capacity retention [%]=[discharge capacity at the 100th cycle / discharge capacity at the 1st cycle]×100.

[0057] Tensile strength: A tensile testing machine is used to test the tensile strength of the electrode.

[0058] Bending times: Repeatedly bend the electrode 180° and record the number of times without cracking or falling off.

[0059] Table 1 Test results

[0060]

[0061] Analyzing the data in Table 1, we can see that:

[0062] 1) The lithium battery pole pieces containing cross-linked hydrogenated nitrile rubber binder prepared in Examples 1 to 4 are prepared by using hydrogenated nitrile rubber as a binder and by gamma ray radiation cross-linking technology, which significantly improves the strength, flexibility and electrochemical performance of the pole pieces.

[0063] 2) The performance comparison analysis of the lithium battery pole pieces containing cross-linked hydrogenated nitrile rubber binder prepared in combination with Example 4 and Comparative Examples 1-2 shows that gamma ray radiation can induce a cross-linking reaction of the molecular chains in the hydrogenated nitrile rubber binder. This cross-linking reaction can significantly improve the mechanical strength and flexibility of the material, while also improving its electrochemical properties. Through gamma ray radiation cross-linking treatment, the pole piece can show better stability during the charge and discharge process, reduce the cracking and falling off of the pole piece, thereby improving the overall performance and life of the battery. Lower radiation doses or the lack of gamma ray radiation treatment cannot cross-link the hydrogenated nitrile rubber, and higher doses may cause the positive electrode material to decompose, affecting battery performance.

[0064] 3) A comparative analysis of the performance of lithium battery pole pieces containing cross-linked hydrogenated nitrile rubber binder prepared in combination with Example 4 and Comparative Example 3 shows that the lithium battery pole pieces prepared by using hydrogenated nitrile rubber as a binder and through gamma ray radiation cross-linking technology are significantly superior to traditional PVDF binder pole pieces in terms of strength, flexibility and electrochemical properties, and have broad application prospects.

[0065] The above embodiments are only used to illustrate the technical solutions of the present application and are not intended to limit the present application. Although the above embodiments provide a detailed description of the present application, relevant technical personnel should understand that the specific implementation methods of the present application may still be modified or replaced by equivalents. Any modifications and equivalent replacements that do not depart from the spirit and scope of the present application should be included in the scope of protection of the present application.

Claims

1. A method for preparing a lithium battery pole piece containing a cross-linked hydrogenated nitrile rubber binder, characterized in that: The following steps are involved: S1. Prepare a positive electrode slurry: Mix the positive electrode active material, the conductive agent, and the hydrogenated nitrile rubber binder in proportion, add a solvent, and stir at 2500 rpm using a planetary mixer for 1-3 hours to form a uniform positive electrode slurry; wherein the weight proportion of the hydrogenated nitrile rubber binder in the positive electrode slurry is 5%; the hydrogenated nitrile rubber has an acrylonitrile content of 33-50%, a number average molecular weight of 20,000 to 2,000,000, and a degree of hydrogenation greater than 99%; S2. Coating the electrode sheet: evenly coat the positive electrode slurry on an aluminum foil current collector with a thickness of 15-25 μm, control the coating thickness to 80-120 μm, and dry it at 80-120°C to remove the solvent to form a primary electrode sheet; S3, first stage rolling: the dried electrode is passed through a rolling machine at a pressure of 20-30 MPa for first stage rolling; S4. Gamma ray radiation cross-linking: placing the first-stage calendered electrode in a gamma ray radiation device and performing radiation cross-linking treatment at a dose of 10-20 kGy to cause a cross-linking reaction of the hydrogenated nitrile rubber binder; S5, secondary calendering: the electrode after radiation cross-linking treatment is subjected to secondary calendering at a pressure of 20-30 MPa through a calender; S6. Cutting: Cutting the electrode sheet after the secondary rolling into a required size to obtain the lithium battery electrode sheet.

2. The method for preparing a lithium battery pole piece containing a cross-linked hydrogenated nitrile rubber binder according to claim 1, characterized in that: In step S1 , the positive electrode active material is one of lithium iron phosphate and lithium cobalt oxide.

3. The method for preparing a lithium battery pole piece containing a cross-linked hydrogenated nitrile rubber binder according to claim 1, characterized in that: In step S1, the solvent is N-methylpyrrolidone.

4. The method for preparing a lithium battery pole piece containing a cross-linked hydrogenated nitrile rubber binder according to claim 1, characterized in that: In step S1 , the conductive agent is at least one of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon nanotubes and graphene.

5. A lithium battery pole piece containing a cross-linked hydrogenated nitrile rubber binder, characterized in that: The lithium battery pole piece containing a cross-linked hydrogenated nitrile rubber binder is prepared by the preparation method of a lithium battery pole piece containing a cross-linked hydrogenated nitrile rubber binder according to any one of claims 1 to 4.

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