Method for improving demulsification property of SBR (Styrene Butadiene Rubber) through polymerization reaction

Abstract

The invention discloses a method for improving demulsification of SBR (styrene butadiene rubber) through polymerization reaction, and relates to the technical field of lithium batteries. Butyl lithium is used as an initiator to enable styrene and styrene-butadiene rubber to be subjected to polymerization reaction, and long-chain alkyl is introduced to improve the demulsification performance of the styrene-butadiene rubber; wherein the mass ratio of the styrene butadiene rubber to the styrene to the butyl lithium initiator is 100: (5-30): (1-5); preparing an emulsion from the modified butadiene styrene rubber and deionized water, mixing the emulsion with a semi-finished product slurry obtained by mixing and stirring carboxymethyl cellulose, graphite and conductive carbon black, coating the surface of a copper foil with the mixed slurry, and drying to obtain a negative pole piece; the negative pole piece has a good bonding effect in a stripping force test.

Description

Technical Field

[0001] The invention relates to the technical field of lithium batteries, in particular to a method for improving the demulsibility of SBR through polymerization reaction. Background Art

[0002] In the preparation and application of lithium battery negative electrode materials, styrene-butadiene rubber (SBR) is an important binder, and its demulsification performance has a significant impact on the quality of the electrode and battery performance. Specifically, in the preparation process of lithium battery negative electrode slurry, stirring and other operations are required to achieve uniform mixing of the various components. However, if the mechanical force is too strong, such as the stirring speed is too fast, the raw material purity, environmental factors, etc., the acidity and alkalinity of the slurry are difficult to maintain stable, thereby increasing the risk of SBR demulsification. This can easily lead to SBR demulsification, causing the slurry to settle, clog holes during filtration, and other problems, affecting subsequent processing. During the drying process after the electrode is coated, if the drying temperature, humidity and other conditions are not properly controlled, SBR may also demulsify. For example, if the drying temperature is too high or the drying speed is too fast, the water in the SBR will evaporate quickly, causing the emulsion structure to be destroyed, affecting its bonding performance and the quality of the electrode.

[0003] During the long-term use of lithium batteries, SBR is affected by the complex chemical environment inside the battery, temperature changes and other factors, and its demulsification stability may gradually decrease. As the number of cycles increases, SBR may gradually demulsify, reducing the bonding effect and affecting the long-term performance and safety of the battery.

[0004] The demulsibility of SBR limits the performance improvement and production efficiency of lithium battery anode materials. Existing lithium battery anode slurries typically use deionized water as the solvent. SBR is not easily soluble in water and must be prepared as an emulsion before being added to the anode slurry. Furthermore, various additives are often added to improve other lithium battery properties. SBR is easily affected by various factors and can demulsify.

[0005] Therefore, the present invention proposes a method for improving the demulsification performance of SBR, thereby reducing the occurrence of demulsification, making the lithium battery negative electrode slurry more stable, and improving production efficiency and battery performance. Summary of the Invention

[0006] The object of the present invention is to provide a method for improving the demulsibility of SBR by polymerization reaction, so as to solve the problems raised in the prior art.

[0007] To achieve the above object, the present invention provides the following technical solutions: A method for improving the demulsification property of SBR by polymerization reaction comprises the following steps: placing styrene-butadiene rubber in cyclohexane under an inert atmosphere and stirring and dissolving the mixture; adding styrene and butyl lithium initiator; reacting the mixture under constant temperature and stirring; and purifying and drying the mixture to obtain modified styrene-butadiene rubber.

[0008] The mass ratio of styrene-butadiene rubber, styrene and butyl lithium initiator is 100: (3-40): (0.3-6); Preferably, the mass ratio of styrene-butadiene rubber, styrene and butyl lithium initiator is 100: (5-30): (1-5); Preferably, the temperature of the constant temperature stirring is 30-70°C, the speed of the constant temperature stirring is 200-400 r / min, and the constant temperature stirring reaction is 3-8 hours; The above-mentioned method of improving the demulsibility of SBR through polymerization reaction can be used in the preparation process of lithium battery negative electrode slurry.

[0009] Preferably, the preparation process of the negative electrode slurry for lithium batteries comprises the following steps: Step 1: After obtaining the modified styrene-butadiene rubber through polymerization, mix it with deionized water and stir and disperse it to obtain a uniform emulsion; Step 2: Weigh carboxymethyl cellulose, graphite and conductive carbon black according to the mass ratio, add deionized water and stir to obtain a semi-finished product slurry; Step 3: adding the emulsion prepared in step 1 to the semi-finished product slurry prepared in step 2, stirring and mixing to obtain a lithium battery negative electrode slurry; Step 4: Apply the lithium battery negative electrode slurry prepared in step 3 on the surface of the copper foil and dry it to obtain the negative electrode sheet.

[0010] Preferably, in step 1, the mass ratio of modified styrene-butadiene rubber to deionized water is (1-3): (7-9); Preferably, the stirring and dispersing speed in step 1 is 1000-1200 r / min, and the stirring and dispersing time is 2-3 h; Preferably, in step 2, the mass ratio of carboxymethyl cellulose, graphite and conductive carbon black is 1:95:2; The solid content of the semi-finished slurry is 50-70%; Preferably, the solid content of the semi-finished product slurry is 50-60%; Preferably, in step 2, the stirring speed is 400-600 r / min and the stirring time is 1-3 h; In step 3, the mass ratio of the emulsion to the semi-finished product slurry is (1-4):20; the stirring speed is 200-700 r / min, and the stirring time is 0.5-2h; Preferably, in step 3, the mass ratio of the emulsion to the semi-finished product slurry is (1-3):20; the stirring speed is 200-500 r / min, and the stirring time is 0.5-2h; Preferably, the thickness of the negative electrode slurry after coating and drying in step 4 is 100-300 μm; Preferably, the drying temperature in step 4 is 100-150° C. and the drying time is 20-60 min.

[0011] Compared with the prior art, the present invention has the following beneficial effects: In lithium battery negative electrode slurry, the method of using butyl lithium as an initiator to cause polymerization of styrene and SBR (styrene-butadiene rubber) to improve the demulsification of SBR has the following advantages: 1. High reaction activity: Butyl lithium has high initiation activity and can quickly initiate the polymerization reaction of styrene and SBR, shorten the reaction time, improve production efficiency, and achieve efficient polymerization under relatively mild reaction conditions; 2. Good initiation efficiency: The reaction can be precisely controlled to allow the styrene monomer to be incorporated into the SBR molecular chain as expected, achieving effective modification of the SBR molecular structure. The product structure and performance are highly reproducible and of stable quality. 3. Low-temperature reaction: Butyl lithium still has good activity at low temperatures and can initiate polymerization under low-temperature conditions, which is beneficial to reduce side reactions and reduce the impact on other components in the reaction system. It is especially suitable for temperature-sensitive systems; The following technical effects can be achieved through the above polymerization reaction: 1. Improved demulsification performance: The addition of long-chain alkyl groups increases the hydrophobicity and steric hindrance of SBR molecules, making SBR more stable in aqueous systems and less prone to demulsification. This improves the stability of lithium battery negative electrode slurry and facilitates subsequent processing and storage. 2. Enhanced bonding performance: The introduction of long-chain alkyl groups adjusts the molecular structure and properties of SBR, thereby enhancing the bonding between SBR and electrode materials, helping to improve the overall performance and cycle stability of the electrode, and reducing the shedding and pulverization of the electrode during charge and discharge. DETAILED DESCRIPTION

[0012] The following is a clear and complete description of the technical solutions in the embodiments of the present invention. Obviously, the embodiments described are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making any creative efforts are within the scope of protection of the present invention.

[0013] In the experiment, styrene-butadiene rubber (SBR) model S08 was purchased from Rongdong Materials; cyclohexane was purchased from Jiaxi Chemical; butyl lithium was purchased from Fuxinyuan; styrene was industrial grade and purchased from Xinchuang Chemical; carboxymethyl cellulose was purchased from Hongquan Chemical; graphite particle size D50 was 18±1μm and purchased from Dongheng New Energy; conductive carbon black N539 was purchased from Hexing Chemical; Example 1: This example provides a method for preparing a negative electrode sheet for a lithium battery, which specifically includes the following steps: Step 1: After the glove box is filled with nitrogen, 100 g of styrene-butadiene rubber is placed in 500 mL of cyclohexane and stirred to dissolve to form a uniform solution. 20 g of styrene and 3 g of butyl lithium initiator are added. The temperature is controlled at 50°C and the reaction is carried out at a constant temperature and stirring speed of 200 r / min for 3 hours. The solution is allowed to stand and cooled to room temperature for precipitation. After filtering, the precipitate is removed and rinsed with n-hexane, transferred to an oven, and dried at 80°C for 1 hour to obtain modified styrene-butadiene rubber; Step 2: 20 g of the modified styrene-butadiene rubber prepared in step 1 was mixed with 80 g of deionized water, and the mixture was stirred and dispersed at a speed of 1200 r / min for 2 h to obtain a uniform emulsion; Step 3: Carboxymethyl cellulose, graphite, and conductive carbon black were weighed in a mass ratio of 1:95:2, mixed, added with deionized water, and stirred at a speed of 500 r / min for 2 h to obtain 2 kg of a semi-finished slurry with a solid content of 50%; Step 4: Add 100 g of the emulsion prepared in step 2 to 2 kg of the semi-finished product slurry prepared in step 3, and stir and mix at a speed of 200 r / min for 1 hour to obtain a lithium battery negative electrode slurry; Step 5: The lithium battery negative electrode slurry prepared in step 4 is coated on a copper foil with a thickness of 8 μm, and dried at 100° C. for 1 h to obtain a coating thickness of 200 μm, thereby obtaining a lithium battery negative electrode sheet.

[0014] Example 2: The preparation method is similar to that of Example 1, except that the amount of styrene added is changed to 3 g. The method specifically comprises the following steps: Step 1: After the glove box is filled with nitrogen, 100 g of styrene-butadiene rubber is placed in 500 mL of cyclohexane and stirred to dissolve to form a uniform solution. 3 g of styrene and 3 g of butyl lithium initiator are added. The temperature is controlled at 50°C and the reaction is carried out at a constant temperature of 200 r / min for 3 hours. The solution is allowed to stand and cooled to room temperature for precipitation. After filtering, the precipitate is washed with n-hexane, transferred to an oven, and dried at 80°C for 1 hour to obtain modified styrene-butadiene rubber; Step 2: 20 g of the modified styrene-butadiene rubber prepared in step 1 was mixed with 80 g of deionized water, and the mixture was stirred and dispersed at a speed of 1200 r / min for 2 h to obtain a uniform emulsion; Step 3: Carboxymethyl cellulose, graphite, and conductive carbon black were weighed in a mass ratio of 1:95:2, mixed, added with deionized water, and stirred at a speed of 500 r / min for 2 h to obtain 2 kg of a semi-finished slurry with a solid content of 50%; Step 4: Add 100 g of the emulsion prepared in step 2 to 2 kg of the semi-finished product slurry prepared in step 3, and stir and mix at a speed of 200 r / min for 1 hour to obtain a lithium battery negative electrode slurry; Step 5: The lithium battery negative electrode slurry prepared in step 4 is coated on a copper foil with a thickness of 8 μm, and dried at 100° C. for 1 h to obtain a coating thickness of 200 μm, thereby obtaining a lithium battery negative electrode sheet.

[0015] Example 3: The preparation method is similar to that of Example 1, except that the amount of styrene added is changed to 5 g; the method specifically comprises the following steps: Step 1: After the glove box is filled with nitrogen, 100 g of styrene-butadiene rubber is placed in 500 mL of cyclohexane and stirred to dissolve to form a uniform solution. 5 g of styrene and 3 g of butyl lithium initiator are added. The temperature is controlled at 50°C and the reaction is carried out at a constant temperature of 200 r / min for 3 hours. The solution is allowed to stand and cooled to room temperature for precipitation. After filtering, the precipitate is washed with n-hexane, transferred to an oven, and dried at 80°C for 1 hour to obtain modified styrene-butadiene rubber; Step 2: 20 g of the modified styrene-butadiene rubber prepared in step 1 was mixed with 80 g of deionized water, and the mixture was stirred and dispersed at a speed of 1200 r / min for 2 h to obtain a uniform emulsion; Step 3: Carboxymethyl cellulose, graphite, and conductive carbon black were weighed in a mass ratio of 1:95:2, mixed, added with deionized water, and stirred at a speed of 500 r / min for 2 h to obtain 2 kg of a semi-finished slurry with a solid content of 50%; Step 4: Add 100 g of the emulsion prepared in step 2 to 2 kg of the semi-finished product slurry prepared in step 3, and stir and mix at a speed of 200 r / min for 1 hour to obtain a lithium battery negative electrode slurry; Step 5: The lithium battery negative electrode slurry prepared in step 4 is coated on a copper foil with a thickness of 8 μm, and dried at 100° C. for 1 h to obtain a coating thickness of 200 μm, thereby obtaining a lithium battery negative electrode sheet.

[0016] Example 4: Referring to the preparation method of Example 1, the difference is that the amount of styrene added is changed to 15g; specifically comprising the following steps: Step 1: After the glove box is filled with nitrogen, 100 g of styrene-butadiene rubber is placed in 500 mL of cyclohexane and stirred to dissolve to form a uniform solution. 15 g of styrene and 3 g of butyl lithium initiator are added. The temperature is controlled at 50°C and the reaction is carried out at a constant temperature and stirring speed of 200 r / min for 3 hours. The solution is allowed to stand and cooled to room temperature for precipitation. After filtering, the precipitate is removed and rinsed with n-hexane, transferred to an oven, and dried at 80°C for 1 hour to obtain modified styrene-butadiene rubber; Step 2: 20 g of the modified styrene-butadiene rubber prepared in step 1 was mixed with 80 g of deionized water, and the mixture was stirred and dispersed at a speed of 1200 r / min for 2 h to obtain a uniform emulsion; Step 3: Carboxymethyl cellulose, graphite, and conductive carbon black were weighed in a mass ratio of 1:95:2, mixed, added with deionized water, and stirred at a speed of 500 r / min for 2 h to obtain 2 kg of a semi-finished slurry with a solid content of 50%; Step 4: Add 100 g of the emulsion prepared in step 2 to 2 kg of the semi-finished product slurry prepared in step 3, and stir and mix at a speed of 200 r / min for 1 hour to obtain a lithium battery negative electrode slurry; Step 5: The lithium battery negative electrode slurry prepared in step 4 is coated on a copper foil with a thickness of 8 μm, and dried at 100° C. for 1 h to obtain a coating thickness of 200 μm, thereby obtaining a lithium battery negative electrode sheet.

[0017] Example 5: The preparation method is similar to that of Example 1, except that the amount of styrene added is changed to 30 g. The method specifically comprises the following steps: Step 1: After the glove box is filled with nitrogen, 100 g of styrene-butadiene rubber is placed in 500 mL of cyclohexane and stirred to dissolve to form a uniform solution. 30 g of styrene and 3 g of butyl lithium initiator are added. The temperature is controlled at 50°C and the reaction is carried out at a constant temperature and stirring speed of 200 r / min for 3 hours. The solution is allowed to stand and cooled to room temperature for precipitation. After filtering, the precipitate is washed with n-hexane, transferred to an oven, and dried at 80°C for 1 hour to obtain modified styrene-butadiene rubber; Step 2: 20 g of the modified styrene-butadiene rubber prepared in step 1 was mixed with 80 g of deionized water, and the mixture was stirred and dispersed at a speed of 1200 r / min for 2 h to obtain a uniform emulsion; Step 3: Carboxymethyl cellulose, graphite, and conductive carbon black were weighed in a mass ratio of 1:95:2, mixed, added with deionized water, and stirred at a speed of 500 r / min for 2 h to obtain 2 kg of a semi-finished slurry with a solid content of 50%; Step 4: Add 100 g of the emulsion prepared in step 2 to 2 kg of the semi-finished product slurry prepared in step 3, and stir and mix at a speed of 200 r / min for 1 hour to obtain a lithium battery negative electrode slurry; Step 5: The lithium battery negative electrode slurry prepared in step 4 is coated on a copper foil with a thickness of 8 μm, and dried at 100° C. for 1 h to obtain a coating thickness of 200 μm, thereby obtaining a lithium battery negative electrode sheet.

[0018] Example 6: The preparation method is similar to that of Example 1, except that the amount of styrene added is changed to 40 g. The method specifically comprises the following steps: Step 1: After the glove box is filled with nitrogen, 100 g of styrene-butadiene rubber is placed in 500 mL of cyclohexane and stirred to dissolve to form a uniform solution. 40 g of styrene and 3 g of butyl lithium initiator are added. The temperature is controlled at 50°C and the reaction is carried out at a constant temperature of 200 r / min for 3 hours. The solution is allowed to stand and cooled to room temperature for precipitation. After filtering, the precipitate is washed with n-hexane, transferred to an oven, and dried at 80°C for 1 hour to obtain modified styrene-butadiene rubber; Step 2: 20 g of the modified styrene-butadiene rubber prepared in step 1 was mixed with 80 g of deionized water, and the mixture was stirred and dispersed at a speed of 1200 r / min for 2 h to obtain a uniform emulsion; Step 3: Carboxymethyl cellulose, graphite, and conductive carbon black were weighed in a mass ratio of 1:95:2, mixed, added with deionized water, and stirred at a speed of 500 r / min for 2 h to obtain 2 kg of a semi-finished slurry with a solid content of 50%; Step 4: Add 100 g of the emulsion prepared in step 2 to 2 kg of the semi-finished product slurry prepared in step 3, and stir and mix at a speed of 200 r / min for 1 hour to obtain a lithium battery negative electrode slurry; Step 5: The lithium battery negative electrode slurry prepared in step 4 is coated on a copper foil with a thickness of 8 μm, and dried at 100° C. for 1 h to obtain a coating thickness of 200 μm, thereby obtaining a lithium battery negative electrode sheet.

[0019] Example 7: The preparation method is similar to that of Example 1, except that the amount of butyl lithium initiator added is changed to 0.3 g. The method comprises the following steps: Step 1: After the glove box is filled with nitrogen, 100 g of styrene-butadiene rubber is placed in 500 mL of cyclohexane and stirred to dissolve to form a uniform solution. 20 g of styrene and 0.3 g of butyl lithium initiator are added. The temperature is controlled at 50°C and the reaction is carried out at a constant temperature of 200 r / min for 3 hours. The solution is allowed to stand and cooled to room temperature for precipitation. After filtering, the precipitate is washed with n-hexane, transferred to an oven, and dried at 80°C for 1 hour to obtain modified styrene-butadiene rubber; Step 2: 20 g of the modified styrene-butadiene rubber prepared in step 1 was mixed with 80 g of deionized water, and the mixture was stirred and dispersed at a speed of 1200 r / min for 2 h to obtain a uniform emulsion; Step 3: Carboxymethyl cellulose, graphite, and conductive carbon black were weighed in a mass ratio of 1:95:2, mixed, added with deionized water, and stirred at a speed of 500 r / min for 2 h to obtain 2 kg of a semi-finished slurry with a solid content of 50%; Step 4: Add 100 g of the emulsion prepared in step 2 to 2 kg of the semi-finished product slurry prepared in step 3, and stir and mix at a speed of 200 r / min for 1 hour to obtain a lithium battery negative electrode slurry; Step 5: The lithium battery negative electrode slurry prepared in step 4 is coated on a copper foil with a thickness of 8 μm, and dried at 100° C. for 1 h to obtain a coating thickness of 200 μm, thereby obtaining a lithium battery negative electrode sheet.

[0020] Example 8: The preparation method is similar to that of Example 1, except that the amount of butyl lithium initiator added is changed to 1 g. The method comprises the following steps: Step 1: After the glove box is filled with nitrogen, 100 g of styrene-butadiene rubber is placed in 500 mL of cyclohexane and stirred to dissolve to form a uniform solution. 20 g of styrene and 1 g of butyl lithium initiator are added. The temperature is controlled at 50°C and the reaction is carried out at a constant temperature and stirring speed of 200 r / min for 3 hours. The solution is allowed to stand and cooled to room temperature for precipitation. After filtering, the precipitate is washed with n-hexane, transferred to an oven, and dried at 80°C for 1 hour to obtain modified styrene-butadiene rubber; Step 2: 20 g of the modified styrene-butadiene rubber prepared in step 1 was mixed with 80 g of deionized water, and the mixture was stirred and dispersed at a speed of 1200 r / min for 2 h to obtain a uniform emulsion; Step 3: Carboxymethyl cellulose, graphite, and conductive carbon black were weighed in a mass ratio of 1:95:2, mixed, added with deionized water, and stirred at a speed of 500 r / min for 2 h to obtain 2 kg of a semi-finished slurry with a solid content of 50%; Step 4: Add 100 g of the emulsion prepared in step 2 to 2 kg of the semi-finished product slurry prepared in step 3, and stir and mix at a speed of 200 r / min for 1 hour to obtain a lithium battery negative electrode slurry; Step 5: The lithium battery negative electrode slurry prepared in step 4 is coated on a copper foil with a thickness of 8 μm, and dried at 100° C. for 1 h to obtain a coating thickness of 200 μm, thereby obtaining a lithium battery negative electrode sheet.

[0021] Example 9: The preparation method is similar to that of Example 1, except that the amount of butyl lithium initiator added is changed to 5 g. The method specifically comprises the following steps: Step 1: After the glove box is filled with nitrogen, 100 g of styrene-butadiene rubber is placed in 500 mL of cyclohexane and stirred to dissolve to form a uniform solution. 20 g of styrene and 5 g of butyl lithium initiator are added. The temperature is controlled at 50°C and the reaction is carried out at a constant temperature of 200 r / min for 3 hours. The solution is allowed to stand and cooled to room temperature for precipitation. After filtering, the precipitate is washed with n-hexane, transferred to an oven, and dried at 80°C for 1 hour to obtain modified styrene-butadiene rubber; Step 2: 20 g of the modified styrene-butadiene rubber prepared in step 1 was mixed with 80 g of deionized water, and the mixture was stirred and dispersed at a speed of 1200 r / min for 2 h to obtain a uniform emulsion; Step 3: Carboxymethyl cellulose, graphite, and conductive carbon black were weighed in a mass ratio of 1:95:2, mixed, added with deionized water, and stirred at a speed of 500 r / min for 2 h to obtain 2 kg of a semi-finished slurry with a solid content of 50%; Step 4: Add 100 g of the emulsion prepared in step 2 to 2 kg of the semi-finished product slurry prepared in step 3, and stir and mix at a speed of 200 r / min for 1 hour to obtain a lithium battery negative electrode slurry; Step 5: The lithium battery negative electrode slurry prepared in step 4 is coated on a copper foil with a thickness of 8 μm, and dried at 100° C. for 1 h to obtain a coating thickness of 200 μm, thereby obtaining a lithium battery negative electrode sheet.

[0022] Example 10: The preparation method is similar to that of Example 1, except that the amount of butyl lithium initiator added is changed to 6 g; the method specifically comprises the following steps: Step 1: After the glove box is filled with nitrogen, 100 g of styrene-butadiene rubber is placed in 500 mL of cyclohexane and stirred to dissolve to form a uniform solution. 20 g of styrene and 6 g of butyl lithium initiator are added. The temperature is controlled at 50°C and the reaction is carried out at a constant temperature and stirring speed of 200 r / min for 3 hours. The solution is allowed to stand and cooled to room temperature for precipitation. After filtering, the precipitate is washed with n-hexane, transferred to an oven, and dried at 80°C for 1 hour to obtain modified styrene-butadiene rubber; Step 2: 20 g of the modified styrene-butadiene rubber prepared in step 1 was mixed with 80 g of deionized water, and the mixture was stirred and dispersed at a speed of 1200 r / min for 2 h to obtain a uniform emulsion; Step 3: Carboxymethyl cellulose, graphite, and conductive carbon black were weighed in a mass ratio of 1:95:2, mixed, added with deionized water, and stirred at a speed of 500 r / min for 2 h to obtain 2 kg of a semi-finished slurry with a solid content of 50%; Step 4: Add 100 g of the emulsion prepared in step 2 to 2 kg of the semi-finished product slurry prepared in step 3, and stir and mix at a speed of 200 r / min for 1 hour to obtain a lithium battery negative electrode slurry; Step 5: The lithium battery negative electrode slurry prepared in step 4 is coated on a copper foil with a thickness of 8 μm, and dried at 100° C. for 1 h to obtain a coating thickness of 200 μm, thereby obtaining a lithium battery negative electrode sheet.

[0023] Example 11: The preparation method of Example 1 is the same as that of Example 1, except that the rotation speed in step 4 is adjusted to 500 r / min and the mixture is stirred for 30 min. The method specifically comprises the following steps: Step 1: After the glove box is filled with nitrogen, 100 g of styrene-butadiene rubber is placed in 500 mL of cyclohexane and stirred to dissolve to form a uniform solution. 20 g of styrene and 3 g of butyl lithium initiator are added. The temperature is controlled at 50°C and the reaction is carried out at a constant temperature and stirring speed of 200 r / min for 3 hours. The solution is allowed to stand and cooled to room temperature for precipitation. After filtering, the precipitate is removed and rinsed with n-hexane, transferred to an oven, and dried at 80°C for 1 hour to obtain modified styrene-butadiene rubber; Step 2: 20 g of the modified styrene-butadiene rubber prepared in step 1 was mixed with 80 g of deionized water, and the mixture was stirred and dispersed at a speed of 1200 r / min for 2 h to obtain a uniform emulsion; Step 3: Carboxymethyl cellulose, graphite, and conductive carbon black were weighed in a mass ratio of 1:95:2, mixed, added with deionized water, and stirred at a speed of 500 r / min for 2 h to obtain 2 kg of a semi-finished slurry with a solid content of 50%; Step 4: Add 100 g of the emulsion prepared in step 2 to 2 kg of the semi-finished product slurry prepared in step 3, and stir and mix at a speed of 500 r / min for 30 min to obtain a lithium battery negative electrode slurry; Step 5: The lithium battery negative electrode slurry prepared in step 4 is coated on a copper foil with a thickness of 8 μm, and dried at 100° C. for 1 h to obtain a coating thickness of 200 μm, thereby obtaining a lithium battery negative electrode sheet.

[0024] Example 12: Referring to the preparation method of Example 1, the difference is that the mass ratio of the emulsion to the semi-finished product slurry is 1:5; specifically comprising the following steps: Step 1: After the glove box is filled with nitrogen, 100 g of styrene-butadiene rubber is placed in 500 mL of cyclohexane and stirred to dissolve to form a uniform solution. 20 g of styrene and 3 g of butyl lithium initiator are added. The temperature is controlled at 50°C and the reaction is carried out at a constant temperature and stirring speed of 200 r / min for 3 hours. The solution is allowed to stand and cooled to room temperature for precipitation. After filtering, the precipitate is removed and rinsed with n-hexane, transferred to an oven, and dried at 80°C for 1 hour to obtain modified styrene-butadiene rubber; Step 2: 80 g of the modified styrene-butadiene rubber prepared in step 1 was mixed with 320 g of deionized water, and the mixture was stirred and dispersed at a speed of 1200 r / min for 2 h to obtain a uniform emulsion; Step 3: Carboxymethyl cellulose, graphite, and conductive carbon black were weighed in a mass ratio of 1:95:2, mixed, added with deionized water, and stirred at a speed of 500 r / min for 2 h to obtain 2 kg of a semi-finished slurry with a solid content of 50%; Step 4: Add 400 g of the emulsion prepared in step 2 to 2 kg of the semi-finished product slurry prepared in step 3, and stir and mix at a speed of 200 r / min for 1 hour to obtain a lithium battery negative electrode slurry; Step 5: The lithium battery negative electrode slurry prepared in step 4 is coated on a copper foil with a thickness of 8 μm, and dried at 100° C. for 1 h to obtain a coating thickness of 200 μm, thereby obtaining a lithium battery negative electrode sheet.

[0025] Example 13: The preparation method is similar to that of Example 1, except that the rotation speed in step 4 is adjusted to 700 r / min and the mixture is stirred for 30 min. The method further comprises the following steps: Step 1: After the glove box is filled with nitrogen, 100 g of styrene-butadiene rubber is placed in 500 mL of cyclohexane and stirred to dissolve to form a uniform solution. 20 g of styrene and 3 g of butyl lithium initiator are added. The temperature is controlled at 50°C and the reaction is carried out at a constant temperature and stirring speed of 200 r / min for 3 hours. The solution is allowed to stand and cooled to room temperature for precipitation. After filtering, the precipitate is removed and rinsed with n-hexane, transferred to an oven, and dried at 80°C for 1 hour to obtain modified styrene-butadiene rubber; Step 2: 20 g of the modified styrene-butadiene rubber prepared in step 1 was mixed with 80 g of deionized water, and the mixture was stirred and dispersed at a speed of 1200 r / min for 2 h to obtain a uniform emulsion; Step 3: Carboxymethyl cellulose, graphite, and conductive carbon black were weighed in a mass ratio of 1:95:2, mixed, added with deionized water, and stirred at a speed of 500 r / min for 2 h to obtain 2 kg of a semi-finished slurry with a solid content of 50%; Step 4: Add 100 g of the emulsion prepared in step 2 to 2 kg of the semi-finished product slurry prepared in step 3, and stir and mix at a speed of 700 r / min for 30 min to obtain a lithium battery negative electrode slurry; Step 5: The lithium battery negative electrode slurry prepared in step 4 is coated on a copper foil with a thickness of 8 μm, and dried at 100° C. for 1 h to obtain a coating thickness of 200 μm, thereby obtaining a lithium battery negative electrode sheet.

[0026] Example 14: Referring to the preparation method of Example 1, the difference is that the solid content of the semi-finished product slurry is 70%; specifically comprising the following steps: Step 1: After the glove box is filled with nitrogen, 100 g of styrene-butadiene rubber is placed in 500 mL of cyclohexane and stirred to dissolve to form a uniform solution. 20 g of styrene and 3 g of butyl lithium initiator are added. The temperature is controlled at 50°C and the reaction is carried out at a constant temperature and stirring speed of 200 r / min for 3 hours. The solution is allowed to stand and cooled to room temperature for precipitation. After filtering, the precipitate is removed and rinsed with n-hexane, transferred to an oven, and dried at 80°C for 1 hour to obtain modified styrene-butadiene rubber; Step 2: 20 g of the modified styrene-butadiene rubber prepared in step 1 was mixed with 80 g of deionized water, and the mixture was stirred and dispersed at a speed of 1200 r / min for 2 h to obtain a uniform emulsion; Step 3: Carboxymethyl cellulose, graphite, and conductive carbon black were weighed in a mass ratio of 1:95:2, mixed, added with deionized water, and stirred at a speed of 500 r / min for 2 h to obtain 2 kg of a semi-finished slurry with a solid content of 70%; Step 4: Add 100 g of the emulsion prepared in step 2 to 2 kg of the semi-finished product slurry prepared in step 3, and stir and mix at a speed of 200 r / min for 1 hour to obtain a lithium battery negative electrode slurry; Step 5: The lithium battery negative electrode slurry prepared in step 4 is coated on a copper foil with a thickness of 8 μm, and dried at 100° C. for 1 h to obtain a coating thickness of 200 μm, thereby obtaining a lithium battery negative electrode sheet.

[0027] Comparative Example 1: As a control experiment of Example 1, the difference is that no modification treatment is performed on the styrene-butadiene rubber.

[0028] Comparative Example 2: As a control experiment of Example 13, the difference is that the styrene-butadiene rubber is not modified.

[0029] Comparative Example 3: As a control experiment of Example 12, the difference is that the styrene-butadiene rubber is not modified.

[0030] Detection test Peel strength test: Ten 120 mm * 50 mm samples were randomly cut from each of the negative electrode sheets prepared in Examples 1-14 and Comparative Examples 1-3. The cut samples were attached to a steel plate using 3M double-sided tape and rolled back and forth twice with a 2 kg roller. A 3M transparent tape with a side length of 220 mm * 12.7 mm was attached to the negative electrode slurry layer and rolled back and forth twice with a 2 kg roller. The slurry layer peel strength test was then performed using a horizontal peel tester. The results are shown in Table 1: Table 1

[0031] Conclusion: It can be seen from the above peeling force test data that the ratio and process parameters set in Example 1 achieve better bonding effect and improved demulsification performance than those in the other examples; Comparative Example 1 is used as a reference experiment for Example 1, and unmodified styrene-butadiene rubber is used in the negative electrode slurry. The peeling force decreases significantly, which shows that the use of modified styrene-butadiene rubber has a high improvement on the bonding performance; Comparing the data of Example 13 with that of Comparative Example 2, it can be seen that after the demulsification performance is improved, the preparation time of the slurry is effectively reduced; Comparing the data of Comparative Example 12 with that of Comparative Example 3, it can be seen that after the demulsification performance is improved, the amount of styrene-butadiene rubber used is effectively reduced, the cost is reduced, and the production efficiency is improved.

[0032] It will be apparent to those skilled in the art that the present invention is not limited to the details of the exemplary embodiments described above and that the invention can be embodied in other specific forms without departing from the spirit or essential characteristics of the invention. Therefore, the embodiments should be considered in all respects as illustrative and non-restrictive, and the scope of the invention is defined by the appended claims rather than the foregoing description, and it is intended that all variations that come within the meaning and range of equivalents of the claims be embraced therein.

Claims

1. A method for improving the demulsibility of SBR by polymerization reaction, characterized in that: The method comprises the following steps: placing styrene-butadiene rubber in cyclohexane under an inert atmosphere, stirring and dissolving the mixture, adding styrene and butyl lithium initiator, stirring and reacting at a constant temperature, and purifying and drying the mixture to obtain the modified styrene-butadiene rubber.

2. A method for improving the demulsibility of SBR by polymerization according to claim 1, characterized in that, The mass ratio of styrene-butadiene rubber, styrene and butyl lithium initiator is 100: (5-30): (1-5).

3. A method for improving the demulsibility of SBR by polymerization according to claim 1, characterized in that, The temperature of the constant temperature stirring is 30-70° C., the speed of the constant temperature stirring is 200-400 r / min, and the constant temperature stirring reaction is carried out for 3-8 hours.

4. An application of the method for improving the demulsibility of SBR by polymerization reaction according to any one of claims 1 to 3, characterized in that: The invention relates to a preparation process for negative electrode sheets of lithium batteries.

5. The application of the method for improving the demulsibility of SBR by polymerization according to claim 4, characterized in that: The preparation process of the negative electrode of lithium battery includes the following steps: Step 1: After obtaining the modified styrene-butadiene rubber through polymerization, mix it with deionized water and stir and disperse it to obtain a uniform emulsion; Step 2: Weigh carboxymethyl cellulose, graphite and conductive carbon black according to the mass ratio, add deionized water and stir to obtain a semi-finished product slurry; Step 3: adding the emulsion prepared in step 1 to the semi-finished product slurry prepared in step 2, stirring and mixing to obtain a lithium battery negative electrode slurry; Step 4: Apply the lithium battery negative electrode slurry prepared in step 3 on the surface of the copper foil and dry it to obtain the negative electrode sheet.

6. The application of the method for improving the demulsibility of SBR by polymerization reaction according to claim 5, characterized in that: The mass ratio of the modified styrene-butadiene rubber to deionized water in step 1 is (1-3): (7-9); the stirring and dispersing speed in step 1 is 1000-1200 r / min, and the stirring and dispersing time is 2-3 h.

7. The application of the method for improving the demulsibility of SBR by polymerization reaction according to claim 5, characterized in that: In step 2, the mass ratio of carboxymethyl cellulose, graphite and conductive carbon black is 1:95:2; and the solid content of the semi-finished product slurry is 50-60%.

8. The application of the method for improving the demulsibility of SBR by polymerization reaction according to claim 5, characterized in that: In step 2, the stirring speed is 400-600 r / min, and the stirring time is 1-3 h.

9. The application of the method for improving the demulsibility of SBR by polymerization reaction according to claim 5, characterized in that: In step 3, the mass ratio of the emulsion to the semi-finished product slurry is (1-3):20; the stirring speed is 200-500 r / min, and the stirring time is 0.5-2 h.

10. The use of the method for improving the demulsibility of SBR by polymerization reaction according to claim 5, characterized in that: The thickness of the negative electrode slurry after coating and drying in step 4 is 100-300 μm; the drying temperature is 100-150° C., and the drying time is 20-60 min.

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