Anode slurry dispersing, compacting and anti-cracking auxiliary agent for lithium battery and preparation method thereof

Abstract

The invention relates to the technical field of lithium ion battery assistants, in particular to an anode slurry dispersing, compacting and anti-cracking assistant for a lithium battery and a preparation method of the anode slurry dispersing, compacting and anti-cracking assistant. The anti-cracking aid is prepared from the following raw materials in parts by mass: 20-80 parts of a special polymer, 10-30 parts of a wetting agent, 10-30 parts of a plasticizer and 10-100 parts of a solvent, wherein the preparation raw materials of the special polymer comprise a vinyl monomer, an acrylic monomer, a diene monomer and an initiator; the wetting agent comprises the following raw materials: an amine compound and a hydrazine compound; and the plasticizer is polyether phosphate. When the additive is used for preparing the lithium battery positive electrode slurry, the slurry is uniformly dispersed and low in viscosity, the use of solvents can be reduced, the production process is shortened, and the actual use effect is excellent.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of lithium ion battery additives, in particular to a positive electrode slurry dispersion pressure increasing and anti-cracking additive for lithium batteries and a preparation method thereof. BACKGROUND

[0002] Lithium ion batteries have been widely used in portable electronic devices, unmanned aerial vehicles, electric tools, electric vehicles and other fields due to their high voltage, high specific energy, long cycle life, high safety performance and low self-discharge rate. With the guidance opinion on promoting the high-quality development of light industry clearly listing high-energy lithium battery safety technology as a key research and development breakthrough direction, the industry has higher requirements for the capacity improvement and processing efficiency optimization of lithium batteries, which makes the increase of coating thickness and the improvement of coating speed of the electrode sheet become an important path for industrial upgrading.

[0003] In actual production process, the thick coating process of the electrode sheet needs to increase the solid content of the slurry at the same time. After the solid content is increased, it is necessary to ensure the uniform dispersion of solid particles, adhesives and other components, that is, the dispersion performance of the slurry needs to be strengthened. At the same time, the increase of coating speed will lead to the cracking of the electrode sheet in the drying stage, so the flexibility of the electrode sheet needs to be improved to avoid cracking. In addition, after the thick electrode sheet is dried and subjected to pressure densification treatment, the compaction density is further improved, which easily leads to the brittleness of the electrode sheet, and further increases the risk of light leakage of the electrode sheet in the process of winding, hot pressing and folding, affecting the stability and reliability of the battery product.

[0004] In view of the above technical problems, the existing technology generally adopts the solution of adding dispersants and flexibility enhancers to the slurry. For example, the technical solution disclosed in Chinese patent application CN119875131A can improve the fluidity of the slurry to a certain extent, but the effect of improving the flexibility of the electrode sheet, solving the cracking problem of thick and fast coating and improving the pressure densification performance still cannot meet the actual needs of the industry. At the same time, the addition ratio of the additive in the lithium battery positive electrode slurry is strictly limited, and generally should not exceed 0.5%. Excessive addition will lead to a significant decrease in the capacity of the lithium battery. In addition, the related additives on the market also have the problem of insufficient adaptability. In different slurry formula systems, the core performance of dispersion, flexibility enhancement and pressure increase is inconsistent, which is difficult to meet the diversified production needs. Therefore, the existing technology has not yet provided a multifunctional additive that can simultaneously solve the problems of insufficient dispersion of the slurry, low compaction density of the electrode sheet and cracking of thick and fast coating under the premise that the addition amount does not exceed 0.5%. The development of such a high-performance additive has become a technical problem to be solved in the field. SUMMARY

[0005] The present application is directed to the problem of poor dispersibility of slurry for lithium ion batteries after increasing solid content, and the problem of sheet cracking and poor flexibility in the process of thick coating and fast coating, and provides a dispersion pressure-increasing anti-cracking additive for lithium battery positive electrode slurry and a preparation method thereof.

[0006] The present application provides a lithium battery positive electrode slurry dispersion pressure-increasing anti-cracking additive, and the preparation raw materials thereof include, in terms of mass fraction, 20-80 parts of special polymer, 10-30 parts of wetting agent, 10-30 parts of plasticizer, and 10-100 parts of solvent.

[0007] As an implementable case, the preparation raw materials of the special polymer include vinyl monomer, acrylic monomer, diene monomer and initiator; and the structural formula of the special polymer is as follows: .

[0008] wherein 1≤n≤10, 5≤m≤20, and 1≤n≤10; R1 is phenyl, pyridyl or pyrrolidone group, and R2 is nitrile group, -COOH or -CH2H3PO4.

[0009] Further, the mass ratio of the vinyl monomer, the acrylic monomer and the diene monomer is (20-25):(30-35):(25-40).

[0010] Further, the vinyl monomer includes one of styrene, vinylpyridine or N-vinylpyrrolidone.

[0011] Further, the acrylic monomer includes one of acrylonitrile, acrylic acid, acrylamide and hydroxyethyl acrylate phosphate ester.

[0012] Further, the diene monomer includes 1,4-butadiene or isoprene.

[0013] Further, the initiator includes azo initiator or peroxide initiator.

[0014] Further, the azo initiator includes azobisisobutyronitrile or azobisisoheptyl nitrile.

[0015] Further, the peroxide initiator includes one of benzoyl peroxide, dodecanoyl peroxide, tert-butyl peroxybenzoate, tert-butyl peroxy-tert-amylate, cumene hydroperoxide, tert-butyl hydroperoxide, dicumyl peroxide, di-tert-butyl peroxide and di-tert-amyl peroxide.

[0016] As an implementable case, the preparation method of the special polymer includes: Mix the vinyl monomer, acrylic monomer and diene monomer, heat under N2 environment, add initiator and stir for 3-5 hours to obtain the special polymer.

[0017] The mass ratio of the vinyl monomer (such as styrene and N-vinyl pyrrolidone), the acrylic monomer (such as acrylonitrile and acrylic acid) and the diene monomer (such as 1,4-butadiene and isoprene) in the special polymer raw material is limited to (20-25):(30-35):(25-40), which can ensure the effective proportion of the dispersed core structure; the vinyl monomer can provide cyclic anchoring groups such as phenyl and pyrrolidone groups, and the acrylic monomer can provide polar anchoring groups such as nitrile groups and carboxyl groups, and the mass proportion of the two is up to 50%-60%, which can not only ensure that there are sufficient anchoring groups on the polymer chain to stably adsorb on the surface of lithium iron phosphate and conductive carbon black particles, but also avoid excessive rigidity of the chain segment due to too many anchoring groups, thereby reserving space for the flexible structure; secondly, the combination of the three components can regulate the elasticity and compatibility of the flexible core structure, and the mass proportion of the diene monomer is 25%-40%, the double-bond-containing alkene segment formed after polymerization is the key source of polymer elasticity, which can deform and absorb energy to prevent cracking when the pole piece is pressed / folded, and the proportion can balance the elasticity and slurry compatibility, a low proportion cannot improve the brittleness of the pole piece due to insufficient elasticity, and a high proportion can cause the slurry to separate due to the excessive alkene segment and the decreased compatibility with the PVDF (polyvinylidene fluoride) binder and NMP (N-methyl pyrrolidone) solvent; finally, the mass ratio can ensure the regularity and function of the comb-like chain structure, and the three types of monomers are copolymerized in the above proportion to avoid uneven distribution of the chain segment caused by excessive monomer, and finally form a comb structure with uniform distribution of anchoring groups and moderate insertion of elastic segments, which can not only realize the dispersion of the slurry through anchoring+steric hindrance, but also form an island structure with PVDF by means of the elastic segment, and assist the plasticizer to weaken the crystallization of PVDF, thereby improving the flexibility and compaction density of the pole piece.

[0018] As an implementable case, the raw material of the wetting agent includes an amine compound and a hydrazine compound.

[0019] Further, the mass ratio of the amine compound and the hydrazine compound is (5-20):(5-10).

[0020] Further, the amine compound includes one or more of isopropyl alcohol amine, ethanol amine, isobutyl alcohol amine or ethylene glycol amine.

[0021] Further, the hydrazine compound includes one or more of hydroxyethyl hydrazine, acetyl hydrazine or methyl hydrazine formate.

[0022] The application limits the mass ratio of the amine compound and the hydrazine compound to (5-20):(5-10) to be compounded as a wetting agent, which can efficiently solve the problem of positive electrode slurry dispersion and avoid the defects of single component. The amine compound can form hydrogen bonds with the hydroxyl groups on the particle surface through the amino group, reduce the surface tension of NMP solvent and the liquid-solid interfacial tension, and help the dispersion equipment to disperse the particle agglomerates; the hydrazine compound can generate electrostatic attraction with the anchoring groups of special polymers through the high-polarity hydrazine group, promote the stable adsorption of the hydrazine compound on the particle surface, and form a combination of “first breaking agglomeration and then stable dispersion”, which can avoid the problems of easy particle re-agglomeration caused by single use of amine and difficult to break the initial agglomeration caused by single use of hydrazine. In the application, the proportion of the amine compound is 5-20wt%, the lower limit can ensure the effective reduction of the interfacial tension to disperse the agglomeration, and the upper limit can avoid the neutralization of excessive alkaline amine and the carboxyl group of the polymer, and the gelation of the slurry caused by the crosslinking of PVDF. The proportion of the hydrazine compound is 5-10wt%, the lower limit can ensure the auxiliary anchoring effect to maintain stable dispersion, and the upper limit can prevent excessive hydrazine from reacting with water to generate bubbles and decomposing impurities during drying, and ensure the density of the electrode and the safety of the battery. At the same time, the compounding ratio can make the wetting agent account for a moderate proportion in the auxiliary system, which can neither squeeze the use amount of the core components such as special polymers and plasticizers, nor fully play the role of wetting.

[0023] As an implementable case, the plasticizer is polyether phosphate, and the preparation raw materials of the polyether phosphate include polyhydric alcohol and phosphate esterification reagent.

[0024] Further, the mass ratio of the polyhydric alcohol and the phosphate esterification reagent is (40-100):(10-20).

[0025] Further, the polyhydric alcohol includes PEG and / or PPG; the PEG includes PEG400 or PEG1000; and the PPG includes PPG800.

[0026] Further, the phosphate esterification reagent includes phosphorus pentoxide and / or polyphosphoric acid.

[0027] The application selects polyether phosphate as the plasticizer, and the polyether chain segment and the phosphate ester polar group contained in the polyether phosphate can precisely act on PVDF. The polyether chain segment can interact with the polar group of the PVDF molecular chain to replace the strong intermolecular force of PVDF to weaken the crystallinity of PVDF, so that the PVDF molecular chain is more active. The phosphate group can also combine with the hydroxyl groups on the surface of the positive electrode particles to enhance the compatibility of the plasticizer with the system, avoid the brittleness of the electrode caused by the rigid aggregation of PVDF, reduce the risk of cracking during thick coating and fast coating from the root, and efficiently improve the flexibility of the electrode.

[0028] The second aspect of the application provides a preparation method of a positive electrode slurry dispersion pressure-increasing anti-cracking auxiliary agent for lithium batteries, which comprises the following steps: The special polymer, wetting agent, plasticizer and solvent are mixed to obtain the positive electrode slurry dispersion pressure densification anti-cracking aid for lithium battery.

[0029] The positive electrode slurry prepared by the dispersion pressure densification anti-cracking agent has high solid content and small viscosity, uniform dispersion of the positive electrode slurry can be achieved by using relatively less solvent, the production process time is effectively saved, the production efficiency is improved, the cracking of the thick-coated pole piece is improved, the risk of belt breakage is reduced, and the compaction density of the pole piece is improved. Mainly because the cyclic group and the acidic group can be well adsorbed on the surface of lithium iron phosphate and conductive agent material as anchoring groups, the special comb structure plays a good steric hindrance effect, so it can play a good dispersion effect; the special polymer is used as a dispersed phase, PVDF is used as a continuous phase, and an island structure is formed. Under the action of external force, the elastomer deforms, a large number of silver lines and shear bands are generated and developed in the material, and a large amount of energy is absorbed. The elastomer can also terminate the silver lines generated in time without developing into destructive cracks. The elastomer particles and shear bands can also terminate the development of small cracks. The generation and development of silver lines consume a large amount of energy, thereby improving the damage energy of the material; silver lines are also the precursors of cracks and lead to material damage, and shear bands can consume energy and terminate silver lines. Therefore, the flexibility of the pole piece can be changed; the polar functional groups of the small molecule phosphate interact with the polar groups of the PVDF molecules, replacing the high polymer polar intermolecular interaction, thereby weakening the interaction force between the PVDF molecular chains, reducing the crystallinity of PVDF, and making the molecular chain movement easier. Therefore, the flexibility of the pole piece can also be changed. The amine compound and the hydrazine compound can reduce the surface tension and liquid-solid interfacial tension of NMP, can help the dispersion equipment to better break the agglomerated particles, and assist the special polymer to be anchored on the surface of the particles. And reducing the surface tension of NMP can significantly improve the cracking of the pole piece.

[0030] Advantages (1) The present application can make the positive electrode slurry maintain low viscosity under high solid content of 65-70wt%, realize uniform dispersion of lithium iron phosphate, conductive carbon black, PVDF and other components by using a small amount of NMP solvent, greatly shorten the mixing time of the slurry and the time consumption of the subsequent drying process, and significantly improve the production efficiency of the pole piece.

[0031] (2) The present application can effectively solve the cracking problem of the pole piece during the drying stage of thick coating and fast coating, reduce the risk of belt breakage during the coating process, and reduce the stress concentration of the pole piece caused by thick coating, thereby ensuring the forming quality of the thick pole piece.

[0032] (3) The pole piece processed by the aid provided by the present application can stably reach 2.65g / cm 3And the above, by optimizing the density of the pole piece, indirectly improve the capacity and cycle life of lithium battery, meet the performance requirements of high energy efficiency lithium battery.

[0033] (Four) The application significantly enhances the flexibility of the pole piece by means of the energy absorption of the molecular "island structure" deformation, the reduction of PVDF crystallinity, etc., which can reduce the breaking and light transmission phenomenon through the folding test, and reduce the risk of damage of the pole piece in subsequent processes such as winding and hot pressing.

[0034] (Five) The total additive amount is less than or equal to 0.5%, which can realize the above-mentioned multifunctional effect, and there is no problem of battery capacity decline caused by excessive addition; and each component has good compatibility with different positive electrode slurry formulations, stable performance, and avoids the defects of poor adaptability of the market additives. BRIEF DESCRIPTION OF DRAWINGS

[0035] Figure 1 The use effect schematic diagram of the final product 23 and the commercially available fine product. DETAILED DESCRIPTION

[0036] Example 1 The preparation method of the special polymer provided in this example is as follows: 100g NMP, 20g styrene, 30g acrylonitrile and 40g 1,4-butadiene are added to a reactor, stirred and heated to 70℃ under nitrogen protection, 0.9g azobisisobutyronitrile is added and reacted for 5h, and the reaction is completed.

[0037] The special polymer prepared in this example is recorded as special polymer 1#.

[0038] Example 2 The preparation method of the special polymer provided in this example is as follows: 100g NMP, 25g N-vinyl pyrrolidone, 35g acrylonitrile and 25g 1,4-butadiene are added to a reactor, stirred and heated to 70℃ under nitrogen protection, 0.9g azobisisobutyronitrile is added and reacted for 5h, and the reaction is completed.

[0039] The special polymer prepared in this example is recorded as special polymer 2#.

[0040] Example 3 The preparation method of the special polymer provided in this example is as follows: 100g NMP, 20g styrene, 30g acrylonitrile and 40g isoprene are added to a reactor, stirred and heated to 70℃ under nitrogen protection, 0.9g benzoyl peroxide is added and reacted for 5h, and the reaction is completed.

[0041] The special polymer prepared in this example is recorded as special polymer 3#.

[0042] Example 4 The example provides a wetting agent, and a preparation method thereof is as follows: isopropanolamine and acetylhydrazine are uniformly mixed in a mass ratio of 80:20, and the wetting agent is obtained.

[0043] The wetting agent prepared in the example is recorded as wetting agent 1#.

[0044] Example 5 The example provides a wetting agent, and a preparation method thereof is as follows: ethanolamine and hydroxyethylhydrazine are uniformly mixed in a mass ratio of 70:30, and the wetting agent is obtained.

[0045] The wetting agent prepared in the example is recorded as wetting agent 2#.

[0046] Example 6 The example provides a wetting agent, and a preparation method thereof is as follows: isobutanolamine and methylhydrazinecarboxylate are uniformly mixed in a mass ratio of 60:40, and the wetting agent is obtained.

[0047] The wetting agent prepared in the example is recorded as wetting agent 3#.

[0048] Example 7 The example provides a wetting agent, and a preparation method thereof is as follows: ethylene glycolamine and hydroxyethylhydrazine are uniformly mixed in a mass ratio of 50:50, and the wetting agent is obtained.

[0049] The wetting agent prepared in the example is recorded as wetting agent 4#.

[0050] Example 8 The example provides a polyether phosphate, and a preparation method thereof is as follows: 40g of PEG400 is added into a reaction bottle, then 14g of diphosphorus pentoxide is added in two batches, the temperature is increased to 60 DEG C, and reaction is carried out for 6h, and the polyether phosphate is obtained.

[0051] The polyether phosphate prepared in the example is recorded as polyether phosphate 1#.

[0052] Example 9 The example provides a polyether phosphate, and a preparation method thereof is as follows: 100g of PEG1000 is added into a reaction bottle, then 14g of diphosphorus pentoxide is added in two batches, the temperature is increased to 60 DEG C, and reaction is carried out for 6h, and the polyether phosphate is obtained.

[0053] The polyether phosphate prepared in the example is recorded as polyether phosphate 2#.

[0054] Example 10 The example provides a polyether phosphate, and a preparation method thereof is as follows: 40g of PEG400 is added into a reaction bottle, then 14g of polyphosphoric acid is added in two batches, the temperature is increased to 60 DEG C, and reaction is carried out for 6h, and the polyether phosphate is obtained.

[0055] The polyether phosphate prepared in the example is recorded as polyether phosphate 3#.

[0056] Application example The example provides 24 final products, the preparation raw materials and mass fraction are shown in Table 1.

[0057] Table 1

[0058] The preparation method of the final products 1-24 is as follows: the special polymer, wetting agent, plasticizer and solvent are mixed to obtain the final product, i.e. the positive electrode slurry dispersion pressure density anti-cracking aid for lithium battery. The use effect diagram of the final product 23 and the commercially available fine product is shown in Figure 1 .

[0059] Performance test The positive electrode slurry dispersion pressure density anti-cracking aid for lithium battery corresponding to the final products 1-24 is used to prepare the lithium ion battery positive electrode slurry, and then the positive electrode sheet is prepared by coating and rolling. The sheet thickness and sheet cracking are observed, and the viscosity and solid content of the lithium ion battery positive electrode slurry and the compaction density and flexibility of the sheet are tested.

[0060] 1. Preparation of lithium ion battery positive electrode slurry: The lithium ion battery positive electrode slurry has a solid content of 65-70wt%. The solid component contains 95.7wt% of lithium iron phosphate, 0.3wt% of dispersion pressure density anti-cracking agent (i.e. final product), 2wt% of conductive carbon black, and 2wt% of adhesive PVDF.

[0061] The preparation method of the lithium ion battery positive electrode slurry is as follows: First, 12g of adhesive PVDF is dissolved in 375g of N-methyl pyrrolidone solvent to prepare a solution, and then 576g of lithium iron phosphate, 12g of conductive carbon black and 1.725g of dispersion pressure density anti-cracking agent (i.e. final product) are added in sequence. The stirring speed is 1500r / min, and the stirring time is 60min, so that the powder materials are fully and uniformly mixed in the solvent to obtain the lithium iron phosphate positive electrode slurry.

[0062] 2. Preparation of sheet The coating surface density is 25.3 g / cm 3 . During the coating process, the sheet cracking is observed, and the compaction density is adjusted to 2.65 g / cm 3 , 2.69 g / cm 3 , 2.73 g / cm 3 .

[0063] 3. Viscosity test The sample is kept in a 25℃ constant temperature box for 2h, and the NDJ5S digital rotary viscometer is used to test the viscosity of the material. Then the sample is kept in a 25℃ constant temperature box for 24h, and the NDJ5S digital rotary viscometer is used to test the viscosity of the material again.

[0064] 4. Flexibility test The electrode sheet is cut into a 10 cm x 10 cm square electrode sheet, and then placed on a softness tester. By applying pressure to the electrode sheet, the electrode sheet exerts a counterforce on the softness tester. The pressure curve is displayed by the built-in sensor of the tester. The highest point of the curve is the softness of the electrode sheet. The greater the value, the harder the electrode sheet, and vice versa.

[0065] 5. Toughness test The electrode sheet is cut into a 25 cm long x 10 cm wide electrode sheet, and then folded in half along the middle by 180°. A cylindrical steel roller (with the same dimensions as specified in GB / T 2792-2014) is used to roll the electrode sheet. The electrode sheet is placed under LED light, and whether it breaks or transmits light is observed. If it transmits light, the number of folds and the number of light transmission points are recorded. If it does not transmit light, the electrode sheet is folded in the opposite direction along the previous fold, and rolled with the roller. Whether it transmits light is observed. If it transmits light, the number of folds and the number of light transmission points are recorded. If it does not transmit light, the folding continues until it transmits light or the electrode sheet breaks. The number of folds and the number of light transmission points are recorded.

[0066] The experimental results of the above tests are shown in Tables 2-3.

[0067] Table 2

[0068] Table 3

[0069] From the experimental results in Tables 2-3, it can be seen that the introduction of the anti-cracking aid can significantly reduce the viscosity of the positive electrode paste, improve the softness and toughness, and have excellent actual use effect.

Claims

1. A dispersion, compaction, and crack prevention additive for positive electrode slurry in lithium batteries, characterized in that, The raw materials for preparation, by mass parts, include 20-80 parts of special polymer, 10-30 parts of wetting agent, 10-30 parts of plasticizer, and 10-100 parts of solvent; The raw materials for preparing the special polymer include vinyl monomers, acrylic monomers, diene monomers, and initiators; The raw materials for the wetting agent include amine compounds and hydrazine compounds; The plasticizer is a polyether phosphate, and the raw materials for preparing the polyether phosphate include polyols and phosphorylation reagents.

2. The lithium battery positive electrode slurry dispersion, compaction, and crack prevention aid according to claim 1, characterized in that, The mass ratio of the vinyl monomer, acrylic monomer, and diene monomer is (20-25):(30-35):(25-40).

3. The lithium battery positive electrode slurry dispersion, compaction, and crack prevention aid according to claim 2, characterized in that, The acrylic monomers mentioned include one of acrylonitrile, acrylic acid, acrylamide, and hydroxyethyl phosphate acrylate.

4. The lithium battery positive electrode slurry dispersion, compaction, and crack prevention aid according to claim 2, characterized in that, The vinyl monomers include one of styrene, vinylpyridine, or N-vinylpyrrolidone.

5. The lithium battery positive electrode slurry dispersion, compaction, and crack prevention aid according to claim 2, characterized in that, The diene monomers include 1,4-butadiene or isoprene.

6. The lithium battery positive electrode slurry dispersion, compaction, and crack prevention aid according to claim 1, characterized in that, The amine compounds mentioned include one or more of isopropanolamine, ethanolamine, isobutanolamine, or ethylene glycolamine.

7. The lithium battery positive electrode slurry dispersion, compaction, and crack prevention aid according to claim 1, characterized in that, The hydrazine compounds mentioned include one or more of hydroxyethyl hydrazine, acetyl hydrazine, or methyl hydrazine carbamate.

8. The lithium battery positive electrode slurry dispersion, compaction, and crack prevention aid according to claim 1, characterized in that, The phosphoric acid esterification reagents include phosphorus pentoxide and / or polyphosphoric acid.

9. The lithium battery positive electrode slurry dispersion, compaction, and crack prevention aid according to claim 1, characterized in that, The polyols mentioned include PEG and / or PPG.

10. A method for preparing a lithium battery positive electrode slurry dispersion, compaction, and crack prevention additive according to any one of claims 1-9, characterized in that, Includes the following steps: By mixing a special polymer, wetting agent, plasticizer, and solvent, a dispersion, compression, and crack prevention aid for positive electrode slurry in lithium batteries is obtained.

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