Amphiphilic polymer additive and preparation method thereof, carbon-coated slurry and carbon-coated foil

Abstract

The invention provides an amphiphilic polymer additive and a preparation method thereof, carbon-coated slurry and a carbon-coated foil, and belongs to the technical field of battery materials. The amphiphilic polymer auxiliary agent comprises an amphiphilic triblock skeleton and an acrylate end group connected to the tail end of the amphiphilic triblock skeleton; the amphiphilic triblock skeleton is formed by alternately connecting hydrophobic chain segments and hydrophilic chain segments through covalent bonds. In the amphiphilic three-block skeleton of the auxiliary agent, a hydrophobic chain segment can permeate a rolling oil film on the surface of an aluminum foil, and a hydrophilic chain segment is used for enhancing the compatibility with carbon coating slurry; acrylate end groups participate in crosslinking in the preparation process of the carbon layer and can be anchored to a conductive carbon network, so that the electrical conductivity is prevented from being damaged. Therefore, the additive is introduced into the carbon-coated slurry, so that the coating uniformity of a carbon layer and the adaptive selectivity of a foil can be improved, the processability of the carbon-coated foil is ensured, and the stripping force and the resistance of a pole piece are kept stable; the consistency and stability of the battery cell can be ensured, the electrochemical performance of the lithium ion battery can be optimized, and the service life of the lithium ion battery can be prolonged.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of battery materials, and particularly relates to an amphiphilic polymer additive, a preparation method thereof, a carbon coating slurry and a carbon coating foil. BACKGROUND

[0002] Aluminum foil has become the core substrate in the fields of battery current collectors, flexible electronic devices, etc. due to its excellent electrical conductivity, lightweight characteristics and processing formability. However, in the rolling process of the aluminum foil, rolling oil is usually used as a lubricating and cooling medium. The main components of the commercially available rolling oil are isomeric alkanes and fatty alcohol ester substances with C14-C18. Therefore, after rolling, these oily substances will firmly adhere to the surface of the aluminum foil in the form of a very thin (usually with a thickness of 50-200 nm) but dense residual oil film. The presence of the residual oil film seriously hinders the subsequent deep processing of the aluminum foil, especially when preparing a water-based conductive coating (such as a carbon coating slurry). Since the oil film has very low surface energy, and the surface tension of the water-based slurry is relatively high, the slurry will have serious wetting problems on the surface of the aluminum foil, such as shrinkage, wall climbing, etc., and cannot form a uniform and dense conductive coating.

[0003] To solve the above problems, the existing technology usually uses high-temperature annealing (temperature > 300℃) or acid-base cleaning process to remove the oil film. However, such methods will damage the work-hardened structure of the aluminum foil, resulting in a significant decrease in mechanical properties, such as a loss of tensile strength of H18 aluminum of 15-20%. Acid-base cleaning will also corrode the surface of the aluminum foil to form micro-defects, generate a large amount of industrial wastewater, and increase the environmental protection treatment cost. Whether high-temperature or chemical cleaning, it is accompanied by high energy consumption, environmental pressure and increased process complexity.

[0004] In view of the above technical defects, researchers have tried to use wetting agents to improve the wettability of the slurry, but commercially available products are difficult to meet the three major demands of oil film permeability, carbon black dispersion compatibility and conductive losslessness. For example, although polyether modified silicone oil type wetting agent has certain surface activity, it has limited improvement on the wettability of the oil film covered aluminum foil, and the contact angle of the oil film aluminum foil can only be reduced to 55°, which still cannot achieve uniform spreading of the slurry. Although phosphate ester type additives can enhance the permeability, they will have interface interaction with carbon black particles in the slurry, resulting in a 2-order increase in the resistivity of the slurry, which seriously affects the conductive performance of the product.

[0005] Therefore, it is a technical problem to be solved to develop a new type of additive which has excellent oil film permeability, good carbon black dispersion compatibility, and can guarantee the conductive performance without damage, so as to solve the wetting problem of the carbon coating slurry on the surface of the aluminum foil containing residual oil film, and avoid the damage to the performance of the aluminum foil by the traditional oil film removal process and the problems of high energy consumption and high pollution. SUMMARY

[0006] In view of the deficiencies of the prior art, the present application aims to provide an amphiphilic polymer additive, a preparation method thereof, a carbon coating slurry and a carbon coating foil. The present application designs an amphiphilic polymer additive, which comprises an amphiphilic triblock skeleton and an acrylate end group connected to the end of the amphiphilic triblock skeleton. The amphiphilic triblock skeleton is composed of hydrophobic segments and hydrophilic segments connected by covalent bonds in an alternating manner. The hydrophobic segments can efficiently dissolve, penetrate and spread on the rolling oil film on the surface of the foil, thereby destroying the dense structure of the oil film. At the same time, the hydrophilic segments can form good compatibility with the carbon coating slurry, thereby forming a stable interface layer at the oil-water interface and significantly reducing the interfacial tension between the slurry and the foil surface. The introduction of the acrylate end group can enable the additive to be firmly anchored in the conductive carbon network formed during the drying and solidification of the carbon coating slurry through cross-linking reaction, and become part of the conductive skeleton, thereby ensuring that the conductivity of the carbon layer is not affected. Therefore, the introduction of the amphiphilic polymer additive into the carbon coating slurry can greatly improve the uniformity of the carbon layer coating and the adaptability of the foil, and the good compatibility of the additive with the carbon coating slurry system can ensure the processability of the carbon coating foil, thereby maintaining the peel strength and resistance of the prepared electrode sheet stable. At the same time, the thickness uniformity of the carbon layer is effectively improved, thereby ensuring the consistency and stability of the battery cell, which is beneficial to optimize the electrochemical performance of the lithium ion battery and prolong its service life.

[0007] To achieve the above object, the present application adopts the following technical solutions:

[0008] In a first aspect, the present application provides an amphiphilic polymer additive, which comprises an amphiphilic triblock skeleton and an acrylate end group connected to the end of the amphiphilic triblock skeleton.

[0009] The amphiphilic triblock skeleton is composed of hydrophobic segments and hydrophilic segments connected by covalent bonds in an alternating manner.

[0010] The application designs an amphiphilic polymer additive, which comprises an amphiphilic triblock skeleton and an acrylate end group connected to the end of the amphiphilic triblock skeleton, wherein the amphiphilic triblock skeleton is composed of hydrophobic segments and hydrophilic segments connected by covalent bonds alternately, and the hydrophobic segments can be highly miscible, permeable and spread on the rolling oil film on the foil surface, thereby destroying the compact structure of the oil film, and the hydrophilic segments can form good compatibility with the carbon coating slurry, so as to form a stable interface layer at the oil-water interface, thereby significantly reducing the interfacial tension between the slurry and the foil surface; the introduction of the acrylate end group can make the additive firmly anchored in the conductive carbon network formed during the drying and curing of the carbon coating slurry through cross-linking reaction, and become part of the conductive skeleton, thereby ensuring that the conductivity of the carbon layer is not affected. Therefore, the introduction of the amphiphilic polymer additive into the carbon coating slurry can greatly improve the uniformity of the carbon coating and the adaptability of the foil, and the good compatibility of the additive with the carbon coating slurry system can ensure the processability of the carbon-coated foil, so that the peel strength and resistance of the prepared pole piece remain stable; at the same time, the thickness uniformity of the carbon layer is effectively improved, thereby ensuring the consistency and stability of the battery, which is beneficial to optimize the electrochemical performance of the lithium ion battery and prolong its service life.

[0011] Preferably, the amphiphilic triblock skeleton is a PO-EO-PO triblock skeleton.

[0012] In the PO-EO-PO triblock skeleton of the application, "PO" represents a polypropylene oxide, which is a hydrophobic segment, i.e., an oleophilic segment, formed by polymerization of propylene oxide monomers; "EO" represents a polyethylene oxide, which is a hydrophilic segment, formed by polymerization of ethylene oxide monomers; and "triblock" means that the entire polymer chain is connected at the head and tail by three different polymer segments. Therefore, the structure of the PO-EO-PO triblock skeleton can be represented as "hydrophobic segment (PO)-hydrophilic segment (EO)-hydrophobic segment (PO)", which is a typical B-A-B type triblock copolymer.

[0013] Preferably, in the PO-EO-PO triblock skeleton, the molar ratio of PO to EO is 1:(1-2.5), for example, it can be 1:1, 1:1.5, 1:2 or 1:2.5, etc.

[0014] It should be noted that the molar ratio of PO to EO can be tested by nuclear magnetic resonance hydrogen spectrum or by thermogravimetric analysis.

[0015] The application limits the molar ratio of PO to EO to 1:(1-2.5), which is beneficial to form a molecular structure with a suitable amphiphilic balance, so as to ensure that the hydrophobic segments can effectively penetrate the rolling oil film, and the hydrophilic segments can fully compatibilize with the aqueous slurry, thereby playing the best spreading and stabilizing role at the interface.

[0016] Preferably, the amphiphilic polymer additive has a molecular weight of 2000-5000 Da, for example, 2000 Da, 3000 Da, 4000 Da or 5000 Da, etc. A suitable molecular weight helps to achieve good dispersibility and interfacial migration rate in the slurry system, and a too low molecular weight can result in insufficient interfacial film strength, and a too high molecular weight can affect its diffusion and interfacial adsorption efficiency in the slurry.

[0017] Preferably, the amphiphilic polymer additive has an HLB value of 10.5-12.5, for example, 10.5, 11, 11.5, 12 or 12.5, etc.

[0018] It should be noted that the "HLB value" refers to the hydrophilic-lipophilic balance value, which is a numerical value for measuring the relative strength of the hydrophilic group and the lipophilic group in the amphiphilic molecule, and the test method is the Griffin method.

[0019] The amphiphilic polymer additive designed in the present application has an HLB value of 10.5-12.5, which is beneficial to establishing a stable interfacial bridge between the hydrophobic foil surface and the hydrophilic carbon-coated slurry, and significantly improving the wetting and spreading behavior of the slurry.

[0020] Preferably, the amphiphilic polymer additive has an esterification rate of >90%, for example, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98% or 99%, etc.

[0021] It should be noted that the esterification rate can be obtained by HPLC (high performance liquid chromatography).

[0022] In the present application, an esterification rate of >90% is beneficial to ensuring that a sufficient number of acrylate end groups are introduced, so that they can effectively participate in the crosslinking reaction in the subsequent carbon layer curing process, firmly anchor the conductive network, and avoid affecting the performance of the carbon layer due to the presence of unreacted hydroxyl groups.

[0023] In a second aspect, the present application provides a preparation method of the amphiphilic polymer additive according to the first aspect, and the preparation method comprises the following steps:

[0024] Preparation of the amphiphilic triblock copolymer.

[0025] Mixing the amphiphilic triblock copolymer, acrylic acid, catalyst, polymerization inhibitor and organic solvent to perform esterification reaction to obtain the amphiphilic polymer additive.

[0026] The preparation method can efficiently and controllably convert the hydroxyl groups at the ends of the amphiphilic triblock copolymer into acrylate groups, the esterification rate of the final product is more than 90%, the hydroxyl value is less than 2 mgKOH / g, and the high purity and reaction completeness of the auxiliary are effectively ensured; meanwhile, the reaction process is smooth and controllable, the product has light color (light yellow), and the post-treatment is simple, and the method is suitable for large-scale production.

[0027] Preferably, the preparation step of the amphiphilic triblock copolymer comprises:

[0028] (a) mixing a dihydric alcohol initiator, an organic base, propylene oxide and an alkaline catalyst to perform a first reaction to obtain a first product.

[0029] (b) mixing ethylene oxide and the first product to perform a second reaction to obtain the amphiphilic triblock copolymer.

[0030] In the preparation step of the amphiphilic triblock copolymer, the organic base (such as triethylamine) is introduced to neutralize the trace amount of acidic impurities that may exist in the reaction system, protect the activity of the alkaline catalyst, and ensure the smooth progress of the ring-opening polymerization reaction.

[0031] Preferably, the dihydric alcohol initiator comprises propylene glycol.

[0032] Preferably, the organic base comprises triethylamine.

[0033] Preferably, the alkaline catalyst comprises potassium hydroxide.

[0034] Preferably, the mass ratio of the dihydric alcohol initiator to the propylene oxide is 7.6:(1160-1740), for example, can be 7.6:1160, 7.6:1200, 7.6:1300, 7.6:1400, 7.6:1500, 7.6:1600, 7.6:1700 or 7.6:1740, etc.

[0035] Preferably, the amount of the alkaline catalyst is 0.4-1% of the total mass of the system, for example, can be 0.4%, 0.5%, 0.6%, 0.7%, 0.8%, 0.9% or 1%, etc. It should be noted that the system here refers to the mixed system of the dihydric alcohol initiator, the organic base, the propylene oxide and the alkaline catalyst.

[0036] Preferably, the amount of the organic base is 0.1-0.3% of the total mass of the system, for example, can be 0.1%, 0.2% or 0.3%, etc.

[0037] Preferably, the temperature of the first reaction is 110-130℃, for example, it can be 110℃, 120℃ or 130℃, etc. The suitable reaction temperature can keep the polymerization reaction of propylene oxide monomer at an appropriate rate, ensure the orderly growth of molecular chains, and avoid the occurrence of side reactions, effectively control the molecular weight distribution of the polymer.

[0038] Preferably, during the first reaction, the pressure is ≤0.4MPa, for example, it can be 0.4MPa, 0.3MPa, 0.2MPa or 0.1MPa, etc. The suitable pressure can ensure that propylene oxide is fully dissolved and mixed in the reaction system, and can maintain the stability and controllability of the reaction process.

[0039] Preferably, the mass ratio of propylene oxide to ethylene oxide is (1160-1740):(1320-1980), wherein the selected range of propylene oxide "1160-1740" can be 1160, 1200, 1300, 1400, 1500, 1600, 1700 or 1740, etc., and the selected range of ethylene oxide "1320-1980" can be 1320, 1400, 1500, 1600, 1700, 1800, 1900 or 1980, etc.

[0040] In the present application, the suitable mass ratio of propylene oxide to ethylene oxide is beneficial to accurately control the HLB value of the final product in the target range of 10.5-12.5, thereby optimizing the amphiphilic performance thereof.

[0041] Preferably, the temperature of the second reaction is 110-130℃, for example, it can be 110℃, 120℃ or 130℃, etc. The suitable reaction temperature can keep the polymerization reaction of ethylene oxide monomer at an appropriate rate, ensure the orderly growth of molecular chains, and avoid the occurrence of side reactions, effectively control the molecular weight distribution of the polymer.

[0042] Preferably, the time of the second reaction is 2.5-3h, for example, it can be 2.5h, 2.6h, 2.7h, 2.8h, 2.9h or 3h, etc.

[0043] Preferably, the hydroxyl value of the amphiphilic triblock copolymer is 80-100mgKOH / g, for example, it can be 80mgKOH / g, 90mgKOH / g or 100mgKOH / g, etc.

[0044] Preferably, the mass ratio of the amphiphilic triblock copolymer to acrylic acid is 1000:(85-105), for example, it can be 1000:85, 1000:90, 1000:95, 1000:100 or 1000:105, etc.

[0045] Preferably, the catalyst comprises concentrated sulfuric acid. It should be noted that concentrated sulfuric acid is a sulfuric acid aqueous solution with a mass fraction ≥70%, for example, concentrated sulfuric acid with a mass fraction of 98%.

[0046] Preferably, the polymerization inhibitor comprises hydroquinone.

[0047] Preferably, the amount of the catalyst is 0.6-1% of the total mass of the system, for example, it can be 0.6%, 0.7%, 0.8%, 0.9% or 1%, etc. It should be noted that the system here refers to the mixed system of the amphiphilic triblock copolymer, acrylic acid, catalyst and polymerization inhibitor.

[0048] Preferably, the amount of the polymerization inhibitor is 0.01-0.05% of the total mass of the system, for example, it can be 0.01%, 0.02%, 0.03%, 0.04% or 0.05%, etc.

[0049] Preferably, the temperature of the esterification reaction is 120-140℃, for example, it can be 120℃, 125℃, 130℃, 135℃ or 140℃, etc. The suitable reaction temperature can ensure that the esterification reaction proceeds efficiently, and the product has a high esterification rate.

[0050] Preferably, the time of the esterification reaction is 1.5-2h, for example, it can be 1.5h, 1.6h, 1.7h, 1.8h, 1.9h or 2h, etc.

[0051] Preferably, the hydroxyl value of the amphiphilic polymer additive is <2mgKOH / g, for example, it can be 1.8mgKOH / g, 1.6mgKOH / g, 1.4mgKOH / g or 1.2mgKOH / g, etc.

[0052] In the present application, the hydroxyl value of the amphiphilic polymer additive is <2mgKOH / g, and the surface modification additive avoids the potential corrosion of residual acid on the foil in subsequent applications, preventing the negative effects of acidic substances on the curing process of the carbon coating paste and long-term thermal stability.

[0053] Preferably, the preparation method comprises the following steps:

[0054] (1) Preparing an amphiphilic triblock copolymer, the specific steps comprising:

[0055] (a) In an inert atmosphere (for example, a nitrogen atmosphere, etc.), mix the dihydric alcohol initiator, potassium hydroxide and triethylamine, then inject propylene oxide, and carry out the first reaction at 110-130℃, controlling the pressure ≤0.4MPa, to obtain the first product.

[0056] The mass ratio of the dihydric alcohol initiator to the propylene oxide is 7.6:(1160-1740); the amount of the potassium hydroxide is 0.4-1% of the total mass of the system; and the amount of the triethylamine is 0.1-0.3% of the total mass of the system.

[0057] (b) adding ethylene oxide into the first product, performing a second reaction at 110-130℃ for 2.5-3h, and obtaining, after acid neutralization, an amphiphilic triblock copolymer with a hydroxyl value of 80-100mgKOH / g.

[0058] The mass ratio of the propylene oxide to the ethylene oxide is (1160-1740):(1320-1980).

[0059] (2) mixing the amphiphilic triblock copolymer, acrylic acid, concentrated sulfuric acid and hydroquinone in an organic solvent, performing an esterification reaction at 120-140℃ for 1.5-2h, with an esterification rate >90%, and removing the organic solvent by distillation under reduced pressure after the reaction to obtain an amphiphilic polymer additive with a hydroxyl value <2mgKOH / g.

[0060] The mass ratio of the amphiphilic triblock copolymer to the acrylic acid is 1000:(85-105); the amount of the concentrated sulfuric acid is 0.6-1% of the total mass of the system; the amount of the hydroquinone is 0.01-0.05% of the total mass of the system; and the organic solvent includes toluene.

[0061] In a third aspect, the present application provides a carbon coating slurry, which comprises a carbon material, a binder and the amphiphilic polymer additive as described in the first aspect.

[0062] In the carbon coating slurry, the mass percentage of the amphiphilic polymer additive is 0.5-2%, for example, 0.5%, 1%, 1.5% or 2%, etc.

[0063] The introduction of the amphiphilic polymer additive with the above mass percentage into the carbon coating slurry can fully optimize the spreading and adhesion behavior of the slurry on the surface of the rolling oil film foil, achieving uniform coating; at the same time, the additive has good compatibility with the carbon particles and the binder system, can effectively enhance the dispersion stability of the slurry, and can strengthen the interfacial bonding force between the carbon layer and the foil, improve the peel strength of the pole piece, and ensure the consistency of the internal resistance and the cycle life of the battery.

[0064] Preferably, the carbon material comprises conductive carbon black and / or graphite.

[0065] Preferably, the binder comprises any one or a combination of at least two of styrene butadiene rubber, acrylate emulsion or polyurethane dispersion.

[0066] Preferably, the mass ratio of the carbon material, the binder and the amphiphilic polymer additive is (2-6):(4-8):(0.03-0.07), wherein the selected range "2-6" of the carbon material may be 2, 3, 4, 5 or 6, etc., the selected range "4-8" of the binder may be 4, 5, 6, 7 or 8, etc., and the selected range "0.03-0.07" of the amphiphilic polymer additive may be 0.03, 0.04, 0.05, 0.06 or 0.07, etc.

[0067] In a fourth aspect, the present application provides a carbon-coated foil, which comprises a metal foil and a carbon layer provided on the surface of the metal foil, and the raw material for preparing the carbon layer comprises the carbon-coated slurry as described in the third aspect. For example, the carbon layer may be provided on one surface or opposite two surfaces of the metal foil. The metal foil may be an aluminum foil, etc.

[0068] The numerical ranges described herein also include any and all point values and sub-ranges contained therein. Due to the language of the patent statutes, only a limited number of the possible combinations of the constituting elements of the present application are expressly described. It is to be understood that all possible combinations and sub-combinations are within the scope of the present application.

[0069] Compared with the prior art, the present application has the following beneficial effects:

[0070] The present application designs an amphiphilic polymer additive, which comprises an amphiphilic triblock skeleton and an acrylate end group connected to the end of the amphiphilic triblock skeleton, wherein the amphiphilic triblock skeleton is composed of hydrophobic segments and hydrophilic segments connected by covalent bonds. The hydrophobic segments can efficiently dissolve, penetrate and spread on the rolling oil film on the surface of the foil, thereby destroying the dense structure of the oil film. At the same time, the hydrophilic segments can form good compatibility with the carbon-coated slurry, thereby forming a stable interface layer at the oil-water interface and significantly reducing the interfacial tension between the slurry and the surface of the foil. The introduction of the acrylate end group can enable the additive to be firmly anchored in the conductive carbon network formed during the drying and solidification of the carbon-coated slurry through cross-linking reaction, and become part of the conductive skeleton, thereby ensuring that the conductivity of the carbon layer is not affected. Therefore, the introduction of the amphiphilic polymer additive into the carbon-coated slurry can greatly improve the uniformity of the carbon layer and the adaptability of the foil, and the good compatibility of the additive with the carbon-coated slurry system can ensure the processability of the carbon-coated foil, thereby maintaining the peel strength and resistance of the prepared pole piece stable. At the same time, the thickness uniformity of the carbon layer is effectively improved, thereby ensuring the consistency and stability of the battery cell, which is beneficial to optimize the electrochemical performance of the lithium ion battery and prolong its service life. DETAILED DESCRIPTION

[0071] The technical solutions of the present application will be further described in the following specific embodiments. Those skilled in the art should understand that the embodiments are only used to help understand the present application and should not be regarded as specific limitations of the present application.

[0072] It should be noted that the specifications of the raw materials used in the following embodiments are as follows:

[0073] Propylene glycol (PG): industrial grade PG, moisture ≤0.1%, Yantai Wanhua. Potassium hydroxide (KOH): flaky KOH, purity ≥90%, Qinghai Salt Lake Industry. Triethylamine (TEA): industrial grade TEA, purity ≥99%, Zhejiang Xinhengcheng. Propylene oxide (PO): electronic grade, purity ≥99.9%, Sinopec. Ethylene oxide (EO): Sinopec. Acrylic acid (AA): satellite petrochemical. Concentrated sulfuric acid (H2SO4), industrial grade 98% concentrated sulfuric acid, Yunnan Yuntianhua. Hydroquinone (HQ), industrial grade HQ, purity ≥99.5%, Jiangsu Yangnong Chemical Industry. Toluene (TOL), industrial grade toluene, moisture ≤0.05%, Sinopec. T108 water-based adhesive: Guangdong Rongdong New Material Co., Ltd. XHL-D7001 water-based adhesive: Anhui Xinheli Technology Co., Ltd. K-702 water-based adhesive: Lubrizol.

[0074] Example 1

[0075] The present embodiment provides an amphiphilic polymer adjuvant, which comprises a PO-EO-PO triblock backbone and an acrylate end group connected to the end of the PO-EO-PO triblock backbone; wherein the PO-EO-PO triblock backbone is composed of hydrophobic segments (i.e. PO) and hydrophilic segments (i.e. EO) connected by covalent bonds.

[0076] In the PO-EO-PO triblock backbone, the molar ratio of PO to EO is 1:1.5; the molecular weight of the amphiphilic polymer adjuvant is 3200 Da; the HLB value of the amphiphilic polymer adjuvant is 11.2; and the esterification rate of the amphiphilic polymer adjuvant is 95%.

[0077] The present embodiment also provides a preparation method of the above-mentioned amphiphilic polymer adjuvant, which comprises the following steps:

[0078] (1) preparing an amphiphilic triblock copolymer, the specific steps comprising:

[0079] (a) mixing propylene glycol initiator (7.6 g), potassium hydroxide and triethylamine in a nitrogen atmosphere, then continuously injecting propylene oxide (1160 g) using a high-pressure jet mixer (Germany FLUXX, 8 bar), and performing a first reaction at 120°C, with the pressure controlled at 0.3 MPa, to obtain a first product.

[0080] The mass ratio of the propylene glycol initiator and the propylene oxide is 7.6:1160; the amount of potassium hydroxide is 0.6% of the total mass of the system; and the amount of triethylamine is 0.2% of the total mass of the system.

[0081] (b) adding ethylene oxide (1320 g) into the first product, performing a second reaction at 120℃ for 2.8 h, and obtaining, after acid neutralization, an amphiphilic triblock copolymer with a hydroxyl value of 88 mgKOH / g.

[0082] The mass ratio of the propylene oxide and the ethylene oxide is 1160:1320.

[0083] (2) mixing 1000 g of the amphiphilic triblock copolymer, acrylic acid (86.4 g), concentrated sulfuric acid and hydroquinone in toluene (500 mL), performing an esterification reaction at 130℃ for 1.8 h, with an esterification rate of 95%, and removing toluene by distillation under reduced pressure after the reaction to obtain an amphiphilic polymer additive (pale yellow viscous liquid) with a hydroxyl value of 1.5 mgKOH / g.

[0084] The mass ratio of the amphiphilic triblock copolymer and the acrylic acid is 1000:86.4; the amount of concentrated sulfuric acid is 0.8% of the total mass of the system; and the amount of hydroquinone is 0.03% of the total mass of the system.

[0085] The carbon coating slurry provided by the embodiment comprises conductive carbon black, artificial graphite, T108 water-based binder, the amphiphilic polymer additive and solvent water; the mass ratio of the conductive carbon black, artificial graphite, T108 water-based binder and amphiphilic polymer additive is 2:2:6:0.05.

[0086] The carbon coating slurry provided by the embodiment comprises conductive carbon black, artificial graphite, T108 water-based binder, the amphiphilic polymer additive and solvent water; the mass ratio of the conductive carbon black, artificial graphite, T108 water-based binder and amphiphilic polymer additive is 2:2:6:0.05.

[0087] Embodiment 2

[0088] The amphiphilic polymer additive provided by the embodiment comprises a PO-EO-PO triblock skeleton and acrylate end groups connected to the ends of the PO-EO-PO triblock skeleton; the PO-EO-PO triblock skeleton is composed of hydrophobic segments (i.e. PO) and hydrophilic segments (i.e. EO) connected by covalent bonds.

[0089] The molar ratio of PO and EO in the PO-EO-PO triblock skeleton is 1:2.5; the molecular weight of the amphiphilic polymer adjuvant is 4500 Da; the HLB value of the amphiphilic polymer adjuvant is 12.3; and the esterification rate of the amphiphilic polymer adjuvant is 94%.

[0090] The embodiment also provides a preparation method of the above amphiphilic polymer adjuvant, which comprises the following steps:

[0091] (1) preparing an amphiphilic triblock copolymer, the specific steps comprising:

[0092] (a) mixing propylene glycol initiator (7.6 g), potassium hydroxide and triethylamine in a nitrogen atmosphere, then continuously injecting propylene oxide (1160 g) by using a high-pressure jet mixer (Germany FLUXX, 8 bar), and performing a first reaction at 120°C, with the pressure being controlled at 0.35 MPa, to obtain a first product.

[0093] The mass ratio of the propylene glycol initiator to the propylene oxide is 7.6:1160; the amount of the potassium hydroxide is 0.6% of the total mass of the system; and the amount of the triethylamine is 0.2% of the total mass of the system.

[0094] (b) adding ethylene oxide (1980 g) into the first product, performing a second reaction at 120°C for 2.8 h, and obtaining an amphiphilic triblock copolymer with a hydroxyl value of 85 mgKOH / g after acid neutralization.

[0095] The mass ratio of the propylene oxide to the ethylene oxide is 1160:1980.

[0096] (2) mixing 1000 g of the amphiphilic triblock copolymer, acrylic acid (86.4 g), concentrated sulfuric acid and hydroquinone in toluene (500 mL), performing an esterification reaction at 130°C for 1.8 h, with the esterification rate being 94%, removing toluene by reduced pressure distillation after the reaction is completed, and obtaining an amphiphilic polymer adjuvant (pale yellow viscous liquid) with a hydroxyl value of 1.6 mgKOH / g.

[0097] The mass ratio of the amphiphilic triblock copolymer to the acrylic acid is 1000:86.4; the amount of the concentrated sulfuric acid is 0.8% of the total mass of the system; and the amount of the hydroquinone is 0.03% of the total mass of the system.

[0098] The embodiment also provides a carbon coating slurry, which comprises conductive carbon black, artificial graphite, T108 water-based binder, the amphiphilic polymer additive as described above and solvent water; the mass percentage of the amphiphilic polymer additive in the carbon coating slurry is 1%; the mass ratio of the conductive carbon black, artificial graphite, XHL-D7001 water-based binder and amphiphilic polymer additive is 2:2:6:0.05.

[0099] The embodiment also provides a carbon coating aluminum foil, which comprises an aluminum foil and a carbon layer arranged on one side surface of the aluminum foil, the carbon layer being obtained by coating and drying the carbon coating slurry.

[0100] Embodiment 3

[0101] The embodiment provides an amphiphilic polymer additive, which comprises a PO-EO-PO triblock skeleton and acrylate end groups connected to the ends of the PO-EO-PO triblock skeleton; wherein the PO-EO-PO triblock skeleton is composed of hydrophobic segments (i.e. PO) and hydrophilic segments (i.e. EO) connected by covalent bonds.

[0102] In the PO-EO-PO triblock skeleton, the molar ratio of PO to EO is 1:2; the molecular weight of the amphiphilic polymer additive is 3800 Da; the HLB value of the amphiphilic polymer additive is 11.8; and the esterification rate of the amphiphilic polymer additive is 96%.

[0103] The embodiment also provides a preparation method of the above amphiphilic polymer additive, which comprises the following steps:

[0104] (1) preparing an amphiphilic triblock copolymer, the specific steps comprising:

[0105] (a) mixing propylene glycol initiator (7.6 g), potassium hydroxide and triethylamine in a nitrogen atmosphere, then continuously injecting propylene oxide (1640 g) by using a high-pressure jet mixer (Germany FLUXX, 8 bar), and performing a first reaction at 120°C, with the control pressure being 0.32 MPa, to obtain a first product.

[0106] In the preparation method, the mass ratio of the propylene glycol initiator to the propylene oxide is 7.6:1160; the amount of the potassium hydroxide is 0.6% of the total mass of the system; and the amount of the triethylamine is 0.2% of the total mass of the system.

[0107] (b) adding ethylene oxide (1640 g) into the first product, performing a second reaction at 120°C for 2.8 h, and obtaining an amphiphilic triblock copolymer with a hydroxyl value of 86 mgKOH / g after acid neutralization.

[0108] The mass ratio of the propylene oxide to the ethylene oxide is 1640:1640.

[0109] (2) 1000 g of the amphiphilic triblock copolymer, acrylic acid (86.4 g), concentrated sulfuric acid and hydroquinone were mixed in toluene (500 mL) and subjected to an esterification reaction at 130°C for 1.8 h, the esterification rate was 96%, after the reaction, toluene was removed by distillation under reduced pressure to obtain an amphiphilic polymer additive (light yellow viscous liquid) with a hydroxyl value of 1.4 mgKOH / g.

[0110] The mass ratio of the amphiphilic triblock copolymer to the acrylic acid is 1000:86.4; the amount of the concentrated sulfuric acid is 0.8% of the total mass of the system; and the amount of the hydroquinone is 0.03% of the total mass of the system.

[0111] The carbon coating slurry comprises conductive carbon black, artificial graphite, K-702 water-based binder, the amphiphilic polymer additive and solvent water, the mass ratio of the conductive carbon black, the artificial graphite, the K-702 water-based binder and the amphiphilic polymer additive is 2:2:6:0.05, and the mass fraction of the amphiphilic polymer additive in the carbon coating slurry is 1%.

[0112] The carbon coating aluminum foil comprises an aluminum foil and a carbon layer arranged on one side surface of the aluminum foil, the carbon layer is obtained by coating and drying the carbon coating slurry.

[0113] Example 4

[0114] The difference between the present example and Example 3 is that the amount of the ethylene oxide is adjusted to 1980 g, so that the mass ratio of the propylene oxide to the ethylene oxide is 1640:1980. Accordingly, the molar ratio of PO to EO is changed to 1:2.4, the HLB value of the amphiphilic polymer additive is changed to 12.1, the esterification rate is 95%, and the hydroxyl value of the amphiphilic polymer additive is 1.5 mgKOH / g.

[0115] The rest of the preparation method and parameters are consistent with those of Example 3.

[0116] Example 5

[0117] The difference between the present example and Example 3 is that the amount of the ethylene oxide is adjusted to 2460 g, so that the molar ratio of PO to EO in the PO-EO-PO triblock skeleton is 1:3. Accordingly, the HLB value of the amphiphilic polymer additive is changed to 13.5, the esterification rate is 95%, and the hydroxyl value of the amphiphilic polymer additive is 1.5 mgKOH / g.

[0118] The rest of the preparation method and parameters are consistent with those of Example 3.

[0119] Example 6

[0120] The difference between this example and Example 3 is that the amount of ethylene oxide is adjusted to 820 g, so that the molar ratio of PO and EO in the PO-EO-PO triblock skeleton is 1:0.5. Accordingly, the HLB value of the amphiphilic polymer adjuvant is 9, the esterification rate is 93%, and the hydroxyl value of the amphiphilic polymer adjuvant is 1.7 mgKOH / g.

[0121] The rest of the preparation method and parameters remain the same as in Example 3.

[0122] Example 7

[0123] The difference between this example and Example 3 is that the HLB value of the amphiphilic polymer adjuvant is adjusted to 10 by adjusting the polymerization feed. Accordingly, the molar ratio of PO and EO is about 1:1.8, the esterification rate is 95%, and the hydroxyl value of the amphiphilic polymer adjuvant is 1.6 mgKOH / g.

[0124] The rest of the preparation method and parameters remain the same as in Example 3.

[0125] Example 8

[0126] The difference between this example and Example 3 is that the HLB value of the amphiphilic polymer adjuvant is adjusted to 13 by adjusting the polymerization feed. Accordingly, the molar ratio of PO and EO is about 1:2.7, the esterification rate is 94%, and the hydroxyl value of the amphiphilic polymer adjuvant is 1.6 mgKOH / g.

[0127] The rest of the preparation method and parameters remain the same as in Example 3.

[0128] Example 9

[0129] The difference between this example and Example 3 is that the amount of acrylic acid is reduced and the esterification reaction time is shortened, so that the esterification rate of the amphiphilic polymer adjuvant is 85%. Accordingly, the hydroxyl value of the amphiphilic polymer adjuvant is 3.5 mgKOH / g.

[0130] The rest of the preparation method and parameters remain the same as in Example 3.

[0131] Example 10

[0132] The difference between this example and Example 3 is that the hydroxyl value of the amphiphilic polymer adjuvant is controlled to be 3 mgKOH / g by controlling the esterification reaction process. Accordingly, the esterification rate of the amphiphilic polymer adjuvant is 90%.

[0133] The rest of the preparation method and parameters remain the same as in Example 3.

[0134] Example 11

[0135] The difference between this example and Example 3 is that the mass fraction of the amphiphilic polymer additive in the carbon coating slurry is 0.2%.

[0136] The rest of the preparation method and parameters are consistent with Example 3.

[0137] Example 12

[0138] The difference between this example and Example 3 is that the mass fraction of the amphiphilic polymer additive in the carbon coating slurry is 2.5%.

[0139] The rest of the preparation method and parameters are consistent with Example 3.

[0140] Comparative Example 1

[0141] The difference between this comparative example and Example 1 is that the preparation of the amphiphilic polymer additive is not performed, i.e., the carbon coating slurry does not contain the amphiphilic polymer additive, and the binder used is T108.

[0142] The rest of the preparation method and parameters are consistent with Example 1.

[0143] Comparative Example 2

[0144] The difference between this comparative example and Example 2 is that the preparation of the amphiphilic polymer additive is not performed, i.e., the carbon coating slurry does not contain the amphiphilic polymer additive, and the binder used is XHL-D7001.

[0145] The rest of the preparation method and parameters are consistent with Example 2.

[0146] Comparative Example 3

[0147] The difference between this comparative example and Example 3 is that the preparation of the amphiphilic polymer additive is not performed, i.e., the carbon coating slurry does not contain the amphiphilic polymer additive, and the binder used is K-702.

[0148] The rest of the preparation method and parameters are consistent with Example 3.

[0149] Comparative Example 4

[0150] The difference between this comparative example and Example 3 is that the esterification reaction in step (2) is not performed. That is, the amphiphilic triblock copolymer used in the carbon coating slurry is not terminated with acrylate, and the substance does not contain acrylate end groups (hydroxyl value is 86 mgKOH / g).

[0151] The rest of the preparation method and parameters are consistent with Example 3.

[0152] Performance Test

[0153] The positive electrode tab is prepared based on the carbon-coated aluminum foil provided in the above examples and comparative examples, and the specific steps include:

[0154] According to the mass ratio of lithium iron phosphate: conductive carbon black: PVDF (polyvinylidene fluoride) = 96:2:2, PVDF: NMP (N-methyl pyrrolidone) = 8:92, lithium iron phosphate, conductive carbon black and PVDF are mixed into NMP to prepare a positive electrode slurry; the positive electrode slurry is uniformly coated on the carbon-coated aluminum foil to obtain an unrolled positive electrode tab, and then rolled at a compaction density of 2.55 g / cc to obtain a rolled positive electrode tab.

[0155] The positive electrode tab is subjected to a peeling force test, and the test equipment is an electronic peeling tester.

[0156] The positive electrode tab is subjected to a resistance test, and the test equipment is a positive electrode tab resistance meter.

[0157] The test results are shown in Table 1.

[0158] Table 1

[0159]

[0160] Analysis:

[0161] The present application designs an amphiphilic polymer additive, which comprises an amphiphilic triblock skeleton and an acrylate end group connected to the end of the amphiphilic triblock skeleton, wherein the amphiphilic triblock skeleton is composed of hydrophobic segments and hydrophilic segments connected by covalent bonds, and the hydrophobic segments and the rolling oil film on the foil surface are highly miscible, permeable and spreadable, which can destroy the dense structure of the oil film, and the hydrophilic segments can form good compatibility with the carbon-coated slurry, thereby forming a stable interface layer at the oil-water interface and significantly reducing the interfacial tension between the slurry and the foil surface; the introduction of the acrylate end group can firmly anchor the additive in the conductive carbon network formed during the drying and curing of the carbon-coated slurry through cross-linking reaction, and become part of the conductive skeleton, ensuring that the carbon layer conductivity is not affected. Therefore, the introduction of the amphiphilic polymer additive into the carbon-coated slurry can greatly improve the uniformity of the carbon layer coating and the adaptability of the foil, and the good compatibility of the additive with the carbon-coated slurry system can ensure the processability of the carbon-coated foil, so that the peeling force and resistance of the prepared tab remain stable.

[0162] From the comparison of Example 1 and Examples 5-6, if the molar ratio of PO and EO in the PO-EO-PO triblock skeleton is too small, the hydrophilicity of the additive molecules is too strong, although it can ensure the compatibility with the slurry, but the hydrophobic segment is too short, it is difficult to effectively penetrate and destroy the rolling oil film on the foil surface, resulting in insufficient spreading of the slurry on the foil, the adhesion of the carbon layer is decreased and the conductivity is increased; if the molar ratio of PO and EO in the PO-EO-PO triblock skeleton is too large, the lipophilicity of the additive molecules is too strong, although it can better penetrate the oil film, but the compatibility with the aqueous slurry is poor, which can easily lead to uneven dispersion of the slurry, shrinkage during coating process and other defects (coating uniformity is "poor"), which also seriously damages the adhesion and conductivity of the carbon layer.

[0163] From the comparison of Example 1 and Examples 7-8, if the HLB value of the amphiphilic polymer additive is too small, it indicates that its lipophilicity dominates, which can weaken its dispersibility in the aqueous slurry and reduce its stability efficiency at the oil-water interface, resulting in insufficient bonding force between the carbon layer and the foil and increased resistance; if the HLB value of the amphiphilic polymer additive is too large, it indicates that its hydrophilicity is too strong, which can weaken its interaction with the rolling oil film on the foil surface, making it difficult to effectively bridge the slurry and the foil, also leading to poor peel strength and conductivity.

[0164] From the comparison of Example 1 and Example 9, if the esterification rate of the amphiphilic polymer additive is too low, it means that a large number of hydroxyl groups have not been converted to acrylate groups, these unreacted hydroxyl groups cannot participate in crosslinking reaction during carbon layer curing, making the additive molecules unable to be firmly "anchored" in the conductive carbon network, resulting in a significant decrease in the bonding strength between the carbon layer and the foil; at the same time, incomplete esterification reaction is usually accompanied by a higher hydroxyl value, which may pose a potential corrosion risk to the foil.

[0165] From the comparison of Example 1 and Example 10, if the hydroxyl value of the amphiphilic polymer additive is too large, there are more acrylic acids remaining after esterification, although its initial peel strength and resistance may be less affected, but these acidic substances may corrode the metal foil during subsequent processing or long-term use of the battery, affecting the reliability and service life of the battery.

[0166] From the comparison of Example 1 and Examples 11-12, if the mass ratio of the amphiphilic polymer additive in the carbon coating slurry is too small, it is not enough to form a complete and dense molecular layer at the slurry-foil interface, the interface modification effect is insufficient, which shows that the adhesion of the carbon layer is significantly insufficient; if the mass ratio of the amphiphilic polymer additive in the carbon coating slurry is too large, excessive additive molecules may form an insulating barrier between the conductive carbon particles, partially blocking the formation of conductive paths, thereby leading to increased resistance, although it may show higher peel strength due to more complete interface coverage.

[0167] As can be seen from the comparison between Example 1 and Comparative Examples 1-3, if the carbon coating slurry does not contain the amphiphilic polymer additive, the compatibility of the slurry with the foil surface with rolling oil film is very poor, the interfacial tension is high, which results in that the slurry cannot be effectively wetted and spread, the coating uniformity is "poor", the carbon layer has serious discontinuity, shrinkage and other problems, which causes that the carbon layer has very weak adhesion with the foil, and the conductivity is very poor, which cannot meet the application requirements.

[0168] As can be seen from the comparison between Example 1 and Comparative Example 4, if step (2) is not performed, that is, the PO-EO-PO triblock skeleton in the amphiphilic polymer additive does not contain acrylate end groups, the additive molecules only have the ability to improve the interfacial wetting, but completely lose the key function of being "anchored" to the conductive carbon network through cross-linking. This results in that the adhesion of the carbon layer with the foil after drying and curing is very poor, and due to the lack of effective anchoring, the carbon layer structure is loose, the conductive network is incomplete, and the resistance is significantly increased, which proves that the acrylate end group is an indispensable structural unit to achieve strong adhesion and high conductivity.

[0169] It should be noted that the process method of the present application is illustrated by the above examples, but the present application is not limited to the above process steps, that is, it does not mean that the present application must rely on the above process steps to be implemented. Those skilled in the art should understand that any improvement on the present application, equivalent replacement of the raw materials selected by the present application, addition of auxiliary ingredients, selection of specific methods, etc. fall within the protection scope and disclosure scope of the present application.

Claims

1. An amphiphilic polymer aid, characterized in that, The amphiphilic polymer aid comprises an amphiphilic triblock skeleton and acrylate end groups connected to the ends of the amphiphilic triblock skeleton. The amphiphilic triblock skeleton is composed of hydrophobic segments and hydrophilic segments connected by covalent bonds.

2. The amphiphilic polymer adjuvant according to claim 1, characterized in that, The amphiphilic triblock skeleton is a PO-EO-PO triblock skeleton. The molar ratio of PO segments to EO segments in the PO-EO-PO triblock skeleton is 1:(1-2.5). The molecular weight of the amphiphilic polymer aid is 2000-5000 Da. The HLB value of the amphiphilic polymer aid is 10.5-12.

5. The esterification rate of the amphiphilic polymer aid is >90%.

3. A process for the preparation of the amphiphilic polymer adjuvant according to claim 1 or 2, characterized in that, The preparation method comprises the following steps: Preparation of an amphiphilic triblock copolymer; Mixing the amphiphilic triblock copolymer, acrylic acid, catalyst, polymerization inhibitor, and organic solvent to perform esterification reaction to obtain the amphiphilic polymer aid.

4. The production method according to claim 3, characterized by, The preparation steps of the amphiphilic triblock copolymer comprise: (a) Mixing dihydric alcohol initiator, organic base, propylene oxide, and basic catalyst to perform first reaction to obtain first product; (b) Mixing ethylene oxide and the first product to perform second reaction to obtain the amphiphilic triblock copolymer.

5. The preparation method according to claim 4, characterized in that, The dihydric alcohol initiator comprises propylene glycol. The organic base comprises triethylamine. The basic catalyst comprises potassium hydroxide. The mass ratio of the dihydric alcohol initiator to the propylene oxide is 7.6:(1160-1740). The amount of the basic catalyst is 0.4-1% of the total mass of the reaction system. The amount of the organic base is 0.1-0.3% of the total mass of the reaction system. The temperature of the first reaction is 110-130°C. During the first reaction, the pressure is ≤0.4 MPa.

6. The preparation method according to claim 4, characterized in that, The mass ratio of the propylene oxide to the ethylene oxide is (1160-1740):(1320-1980). The temperature of the second reaction is 110-130°C. The time of the second reaction is 2.5-3h. The hydroxyl value of the amphiphilic triblock copolymer is 80-100 mgKOH / g.

7. The preparation method according to claim 5, characterized in that, The mass ratio of the amphiphilic triblock copolymer to acrylic acid is 1000:(85-105). The catalyst comprises concentrated sulfuric acid. The polymerization inhibitor comprises hydroquinone. The amount of the catalyst is 0.6-1% of the total mass of the reaction system. The amount of the polymerization inhibitor is 0.01-0.05% of the total mass of the reaction system. The temperature of the esterification reaction is 120-140°C. The time of the esterification reaction is 1.5-2h. The hydroxyl value of the amphiphilic polymer aid is <2 mgKOH / g.

8. The preparation method according to claim 4, characterized in that, The preparation method comprises the following steps: (1) Preparation of an amphiphilic triblock copolymer, the specific steps comprising: (a) mixing a dihydric alcohol initiator, potassium hydroxide and triethylamine in an inert atmosphere, then injecting propylene oxide to carry out a first reaction at 110-130 DEG C, controlling the pressure ≤0.4 MPa, to obtain a first product; The mass ratio of the dihydric alcohol initiator to the propylene oxide is 7.6:(1160-1740); the amount of the potassium hydroxide is 0.4-1% of the total mass of the system; and the amount of the triethylamine is 0.1-0.3% of the total mass of the system; (b) adding ethylene oxide to the first product to carry out a second reaction at 110-130 DEG C for 2.5-3 h, and then obtaining an amphiphilic triblock copolymer with a hydroxyl value of 80-100 mgKOH / g after acid neutralization; The mass ratio of the propylene oxide to the ethylene oxide is (1160-1740):(1320-1980). (2) mixing the amphiphilic triblock copolymer, acrylic acid, concentrated sulfuric acid and hydroquinone in an organic solvent to carry out an esterification reaction at 120-140 DEG C for 1.5-2 h, the esterification rate is >90%, and then removing the organic solvent by distillation under reduced pressure to obtain an amphiphilic polymer additive with a hydroxyl value <2 mgKOH / g; The mass ratio of the amphiphilic triblock copolymer to the acrylic acid is 1000:(85-105); the amount of the concentrated sulfuric acid is 0.6-1% of the total mass of the system; the amount of the hydroquinone is 0.01-0.05% of the total mass of the system; and the organic solvent includes toluene.

9. A carbon coating paste characterized by, The carbon coating slurry includes a carbon material, a binder and the amphiphilic polymer additive according to claim 1 or 2. In the carbon coating slurry, the mass ratio of the amphiphilic polymer additive is 0.5-2%.

10. A carbon-coated foil, characterized by, The carbon coating foil includes a metal foil and a carbon layer arranged on the surface of the metal foil, and the raw material for preparing the carbon layer includes the carbon coating slurry according to claim 9.

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