Low-moisture polymer lithium battery dispersing agent, preparation method and application

Abstract

The invention provides a low-moisture polymer lithium battery dispersing agent, a preparation method and application, N-vinyl pyrrolidone is dissolved in a special solvent for lithium ion battery slurry, a prepolymer containing the N-vinyl pyrrolidone is used as an initiation system, polymerization reaction is performed in a nitrogen atmosphere, and the low-moisture polymer lithium battery dispersing agent is obtained. Wherein the special solvent for the lithium ion battery slurry is at least one of N-methyl pyrrolidone, diethyl carbonate and diethyl carbonate. According to the low-moisture polymer lithium battery dispersing agent, the preparation method and the application, the technical problems that the requirement for the low moisture content is extremely high in the production process of lithium ion battery slurry in related technologies, and the low moisture content is difficult to realize by a conventional lithium battery dispersing agent are solved.

Description

Technical Field

[0001] The present invention relates to the technical field of lithium batteries, and in particular to a low-moisture polymer lithium battery dispersant, a preparation method and an application thereof. Background Art

[0002] In the production process of lithium-ion batteries, dispersants are one of the key additives, which have an important impact on the uniformity, stability and final battery performance of battery slurry. Traditional dispersants, such as polyvinylpyrrolidone (PVP), are widely used in the field of lithium batteries due to their excellent lipophilic and hydrophilic, dispersion, adhesion, film-forming and lubricating properties. However, the preparation methods of traditional lithium battery dispersants have many shortcomings.

[0003] First, the synthesis of traditional lithium battery dispersants mostly uses water or low-boiling alcohol as a solvent for solution polymerization, and then spray-drying to make a powdered product. For example, CN102863575B uses water as a solvent, synthesizes polyvinyl pyrrolidone with a composite initiator system, and then spray-dries it; CN115651108B uses water as a solvent, and synthesizes ultra-low molecular weight polyvinyl pyrrolidone with the cooperation of a composite initiator system and a molecular regulator; CN103254338B controls the synthesis of high molecular weight medicinal polyvinyl pyrrolidone in an aqueous solution under the action of a combined initiator; CN101585893B uses ethanol as a solvent, and synthesizes ultra-low molecular weight polyvinyl pyrrolidone through a composite initiator system at a solid content of 10-40%, but adds 5-10% water in the late stage of the polymerization reaction, and then spray-drying to obtain a polymer powder with a moisture content of less than 5%. This method easily introduces moisture during the preparation process, resulting in a high moisture content in the final product (usually around 5%, and the lowest can only reach 1.5%), which is difficult to meet the strict requirements of lithium-ion batteries for low moisture content.

[0004] Secondly, the solvents used in the traditional process are not commonly used in the preparation of lithium battery slurry. Therefore, in the preparation of lithium battery slurry, the lithium dispersant powder needs to be dissolved twice, which not only increases the production process, but also may cause dust pollution, long dissolution time, and re-absorption of water during the dissolution process.

[0005] In addition, inorganic metal ion impurities or insoluble co-catalysts may be introduced into the traditional polymerization system. CN111088299B uses a photoenzyme-catalyzed free radical synthesis method to synthesize ultra-high molecular weight polyvinyl pyrrolidone under photocatalytic anaerobic conditions with glucose oxidase as a catalyst in an aqueous solution; CN107880157B dissolves N-vinyl pyrrolidone in organic solvents such as ethanol, isopropanol, dimethylformamide or dioxane, uses transition metal salts and halogen-containing organic matter as catalysts, and combines cross-linked polyvinylpyrrolidone ligands to synthesize low molecular weight, low distribution polyvinyl pyrrolidone. These impurities may have an adverse effect on the performance of lithium batteries. At the same time, the production process of traditional processes is complicated, the production cycle is long, and the energy consumption is high, which is not conducive to large-scale production and cost control.

[0006] Therefore, the prior art needs to be further developed. Summary of the invention

[0007] The purpose of the present invention is to overcome the above-mentioned technical deficiencies and provide a low-moisture polymer lithium battery dispersant, a preparation method and an application, so as to solve the problem that the production process of lithium-ion battery slurry in the related technology has extremely high requirements for low moisture content, and conventional lithium battery dispersants are difficult to achieve low moisture content.

[0008] In order to achieve the above technical objectives, the present invention adopts the following technical scheme: a method for preparing a low-moisture polymer lithium battery dispersant is provided, N-vinyl pyrrolidone is dissolved in a special solvent for lithium-ion battery slurry, a prepolymer containing N-vinyl pyrrolidone is used as an initiator system, and a polymerization reaction is carried out in a nitrogen atmosphere to obtain a low-moisture polymer lithium battery dispersant; wherein the special solvent for lithium-ion battery slurry is at least one of N-methylpyrrolidone, diethyl carbonate and diethyl carbonate.

[0009] Furthermore, the prepolymer of organic peroxide and / or azo compound and N-vinyl pyrrolidone is used as the initiating system.

[0010] Furthermore, the ratio of the organic peroxide and / or azo compound to N-vinyl pyrrolidone is 1:(10-20). Furthermore, the organic peroxide is one or more of tert-butyl hydroperoxide, di-tert-butyl hydroperoxide, t-amyl hydroperoxide, t-amyl peroxypivalate, dibenzoyl peroxide, t-butyl peroxybenzoate, isopropyl peroxyneodecanoate, and t-butyl peroxyneodecanoate; the azo compound is one or more of azobisisobutyronitrile (AIBN), azobisisovaleronitrile, azobisisoheptanenitrile, dimethyl azobisisobutyrate, azobisisobutylamidine hydrochloride, and azoisobutylcyanoformamide.

[0011] Furthermore, the prepolymer of the organic peroxide and / or the azo compound and N-vinyl pyrrolidone is added at one time. Furthermore, the polymerization reaction is carried out under normal pressure and at a temperature of 30-120°C. Furthermore, the solid content of the polymerization system is controlled between 20% and 80%. A low-moisture polymer lithium battery dispersant is prepared by the above-mentioned preparation method. Furthermore, the low-moisture polymer lithium battery dispersant has a K value between 20 and 50, residual monomers <500 ppm, water <400 ppm, and a 5% aqueous solution pH ≤6.5.

[0012] The invention discloses an application of a low-moisture polymer lithium battery dispersant in lithium-ion battery slurry. The low-moisture polymer lithium battery dispersant is used as a dispersant for carbon nanotubes in the lithium battery slurry.

[0013] Beneficial effects: 1. The K value of the dispersant obtained by the preparation scheme of the present invention is between 20 and 50, the residual monomer is less than 500ppm, the water content is less than 400ppm, the pH value of 5% aqueous solution is ≤6.5, and the water content is ultra-low, which solves the technical problem that the low water content requirement in the production process of lithium-ion battery slurry is extremely high and it is difficult for conventional lithium battery dispersants to achieve low water content.

[0014] 2. The preparation method of the low-moisture polymer lithium battery dispersant of the present invention has a simple polymerization process, simple equipment, short process cycle, and direct use of solvents to avoid recycling, which is extremely easy to promote large-scale production.

[0015] 3. The application of the low-moisture polymer lithium dispersant of the present invention in lithium-ion battery slurry does not require secondary dissolution, has a short slurry preparation time, low energy consumption, is easy to increase slurry preparation capacity, and does not cause dust pollution in the workshop. DETAILED DESCRIPTION

[0016] In order to enable those skilled in the art to better understand the solution of the present application, the technical solution in the embodiment of the present application will be clearly and completely described below in combination with the embodiment of the present application. Obviously, the described embodiment is only a part of the embodiment of the present application, not all of the embodiments. Based on the embodiments in the present application, all other embodiments obtained by ordinary technicians in the field without creative work should fall within the scope of protection of the present application.

[0017] According to an embodiment of the present invention, a method for preparing a low-moisture polymer lithium dispersant is provided, wherein N-vinyl pyrrolidone (NVP) is dissolved in a special solvent for lithium-ion battery slurry (the special solvent for lithium-ion battery slurry is at least one of N-methylpyrrolidone (NMP), diethyl carbonate (DEC) and diethyl carbonate (DMC)), and a polymerization reaction is carried out in a nitrogen atmosphere to obtain a low-moisture polymer lithium dispersant. The lithium dispersant is a colorless to light yellow clear and transparent polyvinyl pyrrolidone viscous liquid. Compared with the traditional polymerization reaction, the preparation method of this embodiment does not use water or alcohol as a solvent for polymerization, and the moisture content of the obtained product is extremely low, avoiding the subsequent spray drying step, and realizing and meeting the extremely high requirements for low moisture content in the production process of lithium-ion battery slurry.

[0018] The initiation system in this embodiment is dissolved in a prepolymer of organic peroxide and / or azo compound and N-vinyl pyrrolidone at a mass ratio of 1: (10-20). If the ratio is too low, prepolymerization is difficult to occur, and the reaction progress is slow after addition; if the ratio is too high, there is a risk of excessive prepolymerization, which has a negative impact on subsequent reactions.

[0019] In this embodiment, the organic peroxide and / or the prepolymer of the azo compound and N-vinyl pyrrolidone are added at once before the polymerization reaction to ensure airtightness during the polymerization process. If added in batches, water vapor from outside will enter the system, resulting in an increase in moisture; and if there are substances to be polymerized in the reaction, if the waiting time is too long, the polymerization will fail, affecting the degree of polymerization.

[0020] In this embodiment, the polymerization reaction is carried out under normal pressure and at a temperature of 30-120° C., preferably 30-90° C.; the mass ratio of N-vinyl pyrrolidone in the special solvent for lithium-ion battery slurry is controlled between 20-80%, preferably 30-50%.

[0021] The K value of the low-moisture polymer lithium dispersant prepared by the above preparation method is between 20 and 50, the residual monomer is less than 500ppm, the water content is less than 400ppm, and the pH value of 5% aqueous solution is ≤6.5, while the water content of polyvinyl pyrrolidone prepared by the traditional method is usually 1.5% to 5%, the monomer residue is 0.1 to 0.2%, and the pH value is 3 to 11. It is obvious that the low-moisture polymer lithium dispersant has a small residual monomer content, extremely low water content, and the pH of the 5% aqueous solution can also be lower than 7 (the pH value is higher than 7 and metal ions are likely to exist). The K value of the dispersant is a viscosity characteristic value related to the molecular weight. The K value of PVP, which is traditionally prepared by solution polymerization using water or low-boiling alcohol as a solvent, is not a fixed numerical range, and is affected by processes such as polymerization conditions, product purification methods, and drying processes. For dispersants for lithium-ion battery slurries, the ideal K value of polyvinyl pyrrolidone is between 25 and 32. The K value of the low-moisture polymer lithium dispersant prepared by the preparation method of the present invention is between 20 and 50, which has covered the ideal value range.

[0022] The present invention is further described in detail below in conjunction with embodiments.

[0023] Example 1 Add 200g NMP solvent and 100g NVP to a 500ml three-necked glass flask, start stirring, set the speed, introduce a small amount of nitrogen to blow out the air in the system, raise the temperature to a preset temperature of 120°C, add the prepared mixed prepolymer initiator system (di-tert-butyl hydroperoxide and NVP, mass ratio of 1:20), protect with nitrogen throughout the process, and control the reaction at a constant temperature. After the reaction is completed, evaluate the appearance of the polymer solution, K value, moisture, residual monomer NVP, 5% aqueous solution pH, etc.

[0024] The reaction polymerization parameters are shown in Table 1, and the performance parameters of the polymer product are shown in Table 2.

[0025] About detection and analysis methods: (1) Solution appearance: Visual inspection of the original solution.

[0026] (2) K value detection: Use the polymerization solvent as the solvent, accurately dilute to a 1% solution, measure with the Ubbelohde viscometer method, and calculate with the K value formula specified in the Chinese Pharmacopoeia; (3) Residual monomers: high performance liquid chromatography; (4) Water content: Coulometric Karl Fischer; (5) pH of 5% aqueous solution: The polymer stock solution is diluted with distilled water to a 5% solid content solution and the pH is directly tested.

[0027] Embodiments 2 to 7 The operation process is the same as that of Example 1, except that the type of solvent, the amount of solvent and NVP, the prepolymer composition, the prepolymer mass ratio and the reaction temperature in Examples 2 to 7 are adjusted. See Table 1 for relevant details.

[0028] Control group Take a sample of PVP dispersant produced by Ningxia Weiyuan New Energy Co., Ltd. on the market, which uses water as solvent, ammonia water / hydrogen peroxide as initiator, aqueous solution polymerization, and spray drying. The performance parameters of the finished product are shown in Table 2.

[0029] Table 1 Polymerization parameters of each example and control group Table 2 Statistics of polymerization sample results of each embodiment and control group It can be seen from the examples and control groups in Table 2 above that the water content of the lithium dispersant polyvinyl pyrrolidone synthesized in the embodiment of the present invention can reach below 400ppm, the residual monomer is below 500ppm, the K value can reach 20.1~50.0, and the pH of the 5% aqueous solution is less than 7 (to be exact, between 2.7~6.5); while the K value of the control group is between the ideal K values, but its water content is extremely high. Therefore, the lithium dispersant polyvinyl pyrrolidone prepared by this scheme has extremely low water content, and the preparation process is simple, the process cycle is short, and the energy consumption is low. It can meet a variety of usage scenarios and is easy to promote and industrialize.

[0030] Performance Testing 12.5 g of the samples prepared in Example 4 and Example 7 were taken as dispersants, 20 g of entangled carbon nanotubes (CNT), 462.5 g of NMP, and 5 g of additives were added, and stirred for 8 hours by a planetary grinding mixer to prepare a positive electrode conductive slurry. After the preparation was completed, the slurry performance was tested, and the results are shown in Table 3. The slurry was a smooth, flowable black viscous conductive slurry.

[0031] Take 5.1g of powdered PVP and 20g of wrapped carbon nanotubes in the control group, add 469.9g of NMP and 5g of additives. Use the same configuration, test method and test environment, and the results are shown in Table 3.

[0032] Table 3 Performance test of conductive pastes configured in Example 4, Example 7 and the control group As can be seen from Table 2, the K values ​​obtained in Example 4, Example 7 and the control group are within the range of the ideal K value. The initial viscosity and the viscosity after standing for 24 hours of each dispersant were obtained by configuring the conductive slurry performance test. As can be seen from Table 3, the initial viscosity and the static viscosity of Examples 4 and 7 meet the industry standard requirements (both less than 4000 cP).

[0033] It should be noted that the specific examples in this embodiment can refer to the examples described in the above embodiments, and this embodiment will not be described in detail here.

[0034] The serial numbers of the above-mentioned embodiments of the present application are for description only and do not represent the advantages or disadvantages of the embodiments.

[0035] In the above embodiments of the present application, the description of each embodiment has its own emphasis. For parts that are not described in detail in a certain embodiment, please refer to the relevant description of other embodiments.

[0036] The above is only a preferred implementation of the present application. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principles of the present application. These improvements and modifications should also be regarded as the scope of protection of the present application.

Claims

1. A method for preparing a low-moisture polymer lithium battery dispersant, characterized in that: N-vinyl pyrrolidone is dissolved in a special solvent for lithium-ion battery slurry, a prepolymer containing N-vinyl pyrrolidone is used as an initiator system, and a polymerization reaction is carried out in a nitrogen atmosphere to obtain a low-moisture polymer lithium battery dispersant; wherein the special solvent for lithium-ion battery slurry is at least one of N-methylpyrrolidone, diethyl carbonate and ethylhexyl carbonate.

2. The method for preparing the low-moisture polymer lithium battery dispersant according to claim 1, characterized in that: The initiator system is a prepolymer of an organic peroxide and / or an azo compound and N-vinyl pyrrolidone.

3. The method for preparing the low-moisture polymer lithium battery dispersant according to claim 2, characterized in that: The mass ratio of the organic peroxide and / or azo compound to N-vinyl pyrrolidone is 1:(10-20).

4. The method for preparing the low-moisture polymer lithium battery dispersant according to claim 2 or 3, characterized in that: The organic peroxide is one or more of tert-butyl hydroperoxide, di-tert-butyl hydroperoxide, t-amyl hydroperoxide, t-amyl peroxypivalate, dibenzoyl peroxide, t-butyl peroxybenzoate, isopropyl peroxyneodecanoate, and t-butyl peroxyneodecanoate; the azo compound is one or more of azobisisobutyronitrile, azobisisovaleronitrile, azobisisoheptanenitrile, dimethyl azobisisobutyrate, azobisisobutyramidine hydrochloride, and azoisobutylcyanoformamide.

5. The method for preparing the low-moisture polymer lithium battery dispersant according to claim 2, characterized in that: Before the polymerization reaction, the prepolymer of the organic peroxide and / or the azo compound and N-vinyl pyrrolidone is added at one time to ensure airtightness during the polymerization process.

6. The method for preparing the low-moisture polymer lithium battery dispersant according to claim 1, characterized in that: The polymerization reaction is carried out under normal pressure and at a temperature of 30-120°C.

7. The method for preparing a low-moisture polymer lithium battery dispersant according to claim 1, characterized in that: The mass ratio of N-vinyl pyrrolidone in the special solvent for lithium-ion battery slurry is controlled between 20 and 80%.

8. A low-moisture polymer lithium battery dispersant, characterized in that: The low-moisture polymer lithium battery dispersant is prepared by the preparation method described in any one of claims 1-7.

9. The low-moisture polymer lithium battery dispersant according to claim 8, characterized in that: The low-moisture polymer lithium battery dispersant has a K value between 20 and 50, residual monomers less than 500 ppm, water content less than 400 ppm, and a 5% aqueous solution pH of ≤6.

5.

10. Application of a low-moisture polymer lithium dispersant in lithium-ion battery slurry, characterized in that: The low-moisture polymer lithium battery dispersant is used as a dispersant for carbon nanotubes in lithium battery slurry.

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