Negative electrode binder, and preparation method therefor and use thereof

Abstract

The present invention provides a negative electrode binder, and a preparation method therefor and a use thereof. Raw materials for preparing the negative electrode binder comprise a soft monomer, a hard monomer, a urethane bond-containing acrylate monomer, an emulsifier, an initiator and water, and the urethane bond-containing acrylate monomer is prepared by making a small molecule diol monomethyl ether react with diisocyanate and endcapping by means of an acrylate containing terminal hydroxyl. The negative electrode binder has the characteristics of high bonding properties, good flexibility, electrolyte swelling resistance and high temperature stability.

Description

A negative electrode binder and its preparation method and application

[0001] This application claims priority to the Chinese patent application filed with the China Patent Office on July 31, 2023, with application number 202310947703.4 and application name “A negative electrode binder, its preparation method and application”, the entire contents of which are incorporated by reference into this application. Technical Field

[0002] The present invention belongs to the technical field of binders, and in particular relates to a negative electrode binder and a preparation method and application thereof. Background Art

[0003] As an essential additive in lithium-ion batteries, binders have two main functions in the battery: (1) to bind scattered active materials into a regular whole, increase the contact between active material particles, improve conductivity and thus improve energy storage performance; (2) to bind active materials to the current collector to prevent short circuits caused by the shedding of active materials and ensure the normal operation of the battery. Binders are crucial to lithium-ion batteries.

[0004] As an additive, the binder accounts for only about 1% of the entire electrode material. Although the added amount is low, the performance requirements are high. First, the binder needs to have good bonding ability. Second, during battery operation, the binder needs to be immersed in the electrolyte environment, ensuring that the binder will not be dissolved or swelled by the electrolyte, causing it to fail. Finally, during battery use, the battery needs to face temperature changes caused by heat generated by the environment and its own internal resistance, so the binder needs to have good temperature stability.

[0005] Polyvinylidene fluoride (PVDF) is one of the main binders used in the positive and negative electrodes of lithium batteries. It can meet the basic requirements of being an electrode binder and is widely used. CN112310399A discloses a lithium ion battery silicon negative electrode binder and its electrode preparation method and application. The lithium ion battery silicon negative electrode binder is composed of polyvinylidene fluoride and polyvinyl alcohol in a mass ratio of 10-1:1-10. The lithium ion battery silicon negative electrode binder can effectively suppress the irreversible lithium consumption of the electrode on the basis of improving the overall adhesion of the electrode. However, PVDF has a low elastic modulus, poor flexibility, and requires the use of toxic solvents during the processing process, which is inconsistent with the current concept of energy conservation and environmental protection. Therefore, PVDF is gradually being replaced by safe and environmentally friendly water-based binders.

[0006] CN113066982A discloses a modified water-based binder, a preparation method, and an application thereof. The modified water-based binder includes a main monomer, a soft monomer, and a homopolymer; wherein the main monomer includes polyacrylate, the soft monomer includes copolymerized 2-benzoyl-3-hydroxy-1-propylene and / or isooctyl acrylate, and the homopolymer includes polymethyl methacrylate. The modified water-based binder has high overall bonding strength, good dispersibility, and stable performance in electrolyte.

[0007] Water-based binders such as polyacrylic acid (PAA), polyacrylates (such as lithium polyacrylate, sodium polyacrylate or potassium polyacrylate), chitosan and its derivatives, carboxycellulose lithium (CMCLi), carboxycellulose sodium (CMCNa), styrene-butadiene rubber (SBR) or polytetrafluoroethylene (PTFE) are superior to PVDF in battery performance, and the cycle stability and electrochemical stability of the electrode have been improved to a certain extent. However, there are still some shortcomings. For example, CMCNa and PAA have problems such as insufficient bonding strength and high brittleness, and chitosan has poor cycle stability and does not meet the requirements for use.

[0008] Therefore, it is necessary to develop an adhesive with high bonding performance, good flexibility, resistance to electrolyte swelling and high temperature stability.

[0009] Summary of the Invention

[0010] In view of the deficiencies in the prior art, the present invention aims to provide a negative electrode binder and a preparation method and application thereof, wherein the negative electrode binder has the characteristics of high bonding performance, good flexibility, resistance to electrolyte swelling and high temperature stability.

[0011] To achieve this object, the present invention adopts the following technical solutions:

[0012] In a first aspect, the present invention provides a negative electrode binder, wherein the raw materials for preparing the negative electrode binder include a soft monomer, a hard monomer, an acrylate monomer containing a urethane bond, an emulsifier, an initiator, and water;

[0013] The acrylic acid ester monomer containing a urethane bond is prepared by reacting a small molecule diol monomethyl ether with a diisocyanate and then capping with an acrylic acid ester containing a terminal hydroxyl group.

[0014] In the present invention, the urethane bond can provide good bonding performance and flexibility. For example, waterborne polyurethane itself has abundant urethane bonds, which have good bonding performance and flexibility, and as a binder with excellent performance, is widely used in other industries such as furniture, clothing, etc. However, if polyurethane is used as a positive or negative electrode binder, it is not conductive in itself, which can seriously affect the performance of the battery; if polyurethane is blended with polyacrylate to form a binder, polyurethane can give the binder good bonding performance and flexibility, and acrylate can give the binder appropriate conductivity, which seems to solve the problems of binders in the prior art. However, most of the polyurethanes available on the market are applied to other fields, and their molecular weights are often relatively large (number average molecular weight>1000g / mol). Long-chain polyethers or polyesters are present in high-molecular-weight polyurethanes, which are easily dissolved under the action of electrolytes, causing the binder to lose effectiveness due to decomposition.

[0015] In the present invention, the negative electrode binder is compounded by soft monomers, hard monomers and acrylate monomers containing urethane bonds, and the urethane bonds are introduced into the negative electrode binder by using a free radical emulsion polymerization reaction, which significantly improves the bonding performance of the binder. The prepared negative electrode binder has the characteristics of high bonding performance, good flexibility, resistance to electrolyte swelling and high temperature stability.

[0016] In the present invention, the hard monomers in the raw materials used to prepare the negative electrode binder have a high glass transition temperature, which improves the structural strength of the binder while also increasing its thermal decomposition temperature. The soft monomers have a low glass transition temperature, giving the negative electrode binder excellent bonding properties and flexibility. The urethane-bonded acrylate monomer is a key component of the negative electrode binder and is prepared from a small molecule diol monomethyl ether, a diisocyanate, and an acrylate containing terminal hydroxyl groups. The presence of ethoxy groups in the small molecule diol monomethyl ether improves the electrochemical performance of the binder. The acrylate containing terminal hydroxyl groups primarily provides acrylic acid groups capable of participating in free radical polymerization. The diisocyanate acts as a bridge connecting the two, forming a urethane bond through reaction, which improves bonding properties.

[0017] Preferably, the soft monomer includes any one or a combination of at least two of alkyl acrylate, ethoxy acrylate, methoxy polyethylene glycol methacrylate, methoxy diethylene glycol methacrylate, alkyl methacrylate or methylethoxy acrylate, more preferably alkyl acrylate and / or ethoxy acrylate.

[0018] Preferably, the hard monomer includes any one of styrene, isobornyl acrylate, isobornyl methacrylate, methyl methacrylate or diisopropylbenzene, or a combination of at least two thereof.

[0019] Preferably, the small molecule glycol monomethyl ether includes any one of ethylene glycol monomethyl ether, propylene glycol monomethyl ether, diethylene glycol monomethyl ether or dipropylene glycol monomethyl ether, or a combination of at least two thereof.

[0020] Preferably, the diisocyanate includes any one of isophorone diisocyanate, dicyclohexylmethane diisocyanate, toluene diisocyanate or diphenylmethane diisocyanate, or a combination of at least two thereof, and more preferably isophorone diisocyanate.

[0021] In the present invention, an acrylate monomer containing a urethane bond is prepared by reacting a small molecule diol monomethyl ether with isophorone diisocyanate and capping with an acrylate containing a terminal hydroxyl group, and a ring structure is introduced to improve flexibility and further enhance the performance of the negative electrode binder.

[0022] Preferably, the acrylate containing terminal hydroxyl groups includes any one of hydroxyethyl methacrylate, hydroxyethyl acrylate, hydroxypropyl methacrylate or hydroxypropyl acrylate, or a combination of at least two thereof.

[0023] Preferably, the molar ratio of the small molecule diol monomethyl ether, diisocyanate and acrylate containing terminal hydroxyl groups is 1:1:1.

[0024] Preferably, the reaction is carried out by adding diisocyanate dropwise to small molecule diol monomethyl ether for reaction.

[0025] Preferably, the reaction temperature is below 10°C, for example, 0°C, 1°C, 2°C, 3°C, 4°C, 5°C, 6°C, 7°C, 8°C or 9°C.

[0026] Preferably, the reaction time is 1-2 h, for example, 1.1 h, 1.2 h, 1.3 h, 1.4 h, 1.5 h, 1.6 h, 1.7 h, 1.8 h or 1.9 h.

[0027] Preferably, the end-capping temperature is 70-80°C, such as 71°C, 72°C, 73°C, 74°C, 75°C, 76°C, 77°C, 78°C or 79°C.

[0028] Preferably, the blocking time is 2-3 h, for example, 2.1 h, 2.2 h, 2.3 h, 2.4 h, 2.5 h, 2.6 h, 2.7 h, 2.8 h or 2.9 h.

[0029] Preferably, the emulsifier includes an anionic emulsifier and a nonionic emulsifier.

[0030] Preferably, the mass ratio of the anionic emulsifier to the nonionic emulsifier is 1:1-2, for example, 1:1.1, 1:1.2, 1:1.3, 1:1.4, 1:1.5, 1:1.6, 1:1.7, 1:1.8 or 1:1.9, etc.

[0031] Preferably, the anionic emulsifier includes any one of sodium lauryl sulfonate (LAS), sodium lauryl sulfate (SDS) or sodium dodecylbenzene sulfonate (SDBS) or a combination of at least two thereof.

[0032] Preferably, the nonionic emulsifier includes any one of octylphenol polyoxyethylene ether (OP-10), sorbitan oleate or fatty alcohol polyoxyethylene ether, or a combination of at least two thereof.

[0033] Preferably, the sorbitan oleate comprises Span-20 and / or Span-80.

[0034] Preferably, the fatty alcohol polyoxyethylene ether includes AEO-9 and / or AEO-10.

[0035] Preferably, the initiator includes any one of ammonium persulfate (APS), potassium persulfate (KPS), azobisisobutyronitrile (AIBN) or dibenzoyl peroxide (BPO), or a combination of at least two thereof.

[0036] Preferably, the raw materials for preparing the negative electrode binder include the following components in parts by mass: 20-35 parts of soft monomer (for example, 21 parts, 23 parts, 25 parts, 27 parts, 29 parts, 30 parts, 32 parts or 34 parts, etc.), 15-30 parts of hard monomer (for example, 16 parts, 18 parts, 20 parts, 22 parts, 24 parts, 26 parts, 28 parts or 29 parts, etc.), 2-5 parts of acrylate monomer containing urethane bond (for example, 2.3 parts, 2.5 parts, 2.8 parts, 3 parts, 3.5 parts, 4 parts, 4.2 parts, 4.5 parts, etc.), or 4.8 parts, etc.), emulsifier 1.5-3.5 parts (for example, 1.7 parts, 1.9 parts, 2.0 parts, 2.3 parts, 2.5 parts, 2.8 parts, 3 parts, 3.2 parts or 3.4 parts, etc.), initiator 0.03-0.1 parts (for example, 0.04 parts, 0.05 parts, 0.06 parts, 0.07 parts, 0.08 parts or 0.09 parts, etc.) and water 35-65 parts (for example, 37 parts, 40 parts, 42 parts, 45 parts, 48 ​​parts, 50 parts, 52 parts, 55 parts, 58 parts, 60 parts or 63 parts, etc.).

[0037] In the present invention, if the mass fraction of the soft monomer is too small, the bonding performance and flexibility of the negative electrode binder will decrease; if the mass fraction of the soft monomer is too large, the glass transition temperature of the formed negative electrode binder will be too low, it will not be able to solidify, it will be difficult to maintain mechanical strength, and the resistance to electrolyte swelling will decrease; if the mass fraction of the acrylate monomer containing an urethane bond is too small, the acrylate monomer containing an urethane bond will not be able to play its due role, and the bonding performance of the obtained negative electrode binder will be poor; if the mass fraction of the acrylate monomer containing an urethane bond is too large, the amino groups in the formed negative electrode binder system will be too many, the emulsion will easily react and deteriorate, and the resistance to electrolyte swelling will decrease.

[0038] In a second aspect, the present invention provides a method for preparing a negative electrode binder as described in the first aspect, the preparation method comprising the following steps: mixing a soft monomer, a hard monomer, an acrylate monomer containing an urethane bond, an emulsifier, water and an initiator, and reacting them to obtain the negative electrode binder.

[0039] Preferably, the mixing comprises the following steps:

[0040] (1) A portion of the emulsifier and a portion of the water are mixed to obtain a base liquid; and a soft monomer, a hard monomer, an acrylate monomer containing a urethane bond, the remaining emulsifier and a portion of the water are mixed to obtain an emulsion.

[0041] (2) Mixing the base liquid of step (1), the emulsion of step (1) and the initiator.

[0042] Preferably, based on the total mass of the emulsifier as 100%, during the preparation of the base liquid in step (1), the mass percentage of the emulsifier in the portion is 30-35%, for example, 30.5%, 31%, 31.5%, 32%, 32.5%, 33%, 33.5%, 34% or 34.5%, etc.

[0043] Preferably, based on the total mass of water as 100%, during the preparation of the base liquid in step (1), the mass percentage of water in the portion is 65-70%, for example, 65.5%, 66%, 66.5%, 67%, 67.5%, 68%, 68.5%, 69% or 69.5%, etc.

[0044] Preferably, based on the total mass of the emulsifier as 100%, during the preparation of the emulsion in step (1), the mass percentage of the remaining emulsifier is 65-70%, for example, 65.5%, 66%, 66.5%, 67%, 67.5%, 68%, 68.5%, 69% or 69.5%, etc.

[0045] Preferably, based on the total mass of water as 100%, during the preparation of the emulsion in step (1), the mass percentage of water in the portion is 30-35%, for example, 30.5%, 31%, 31.5%, 32%, 32.5%, 33%, 33.5%, 34% or 34.5%, etc.

[0046] Preferably, the mixing in step (2) is performed by adding the emulsion and the initiator dropwise into the stirring base liquid for mixing.

[0047] Preferably, the reaction temperature is 83-85°C, such as 83.2°C, 83.5°C, 84°C, 84.5°C or 84.8°C.

[0048] Preferably, the reaction time is 1-2 h, for example, 1.1 h, 1.2 h, 1.3 h, 1.4 h, 1.5 h, 1.6 h, 1.7 h, 1.8 h or 1.9 h.

[0049] In a third aspect, the present invention provides a battery negative electrode slurry, wherein the battery negative electrode slurry includes the negative electrode binder as described in the first aspect.

[0050] In a fourth aspect, the present invention provides a negative electrode plate, which includes the negative electrode binder as described in the first aspect or the battery negative electrode slurry as described in the third aspect.

[0051] In a fifth aspect, the present invention provides an electrochemical energy storage device, comprising the negative electrode binder according to the first aspect or the battery negative electrode slurry according to the third aspect;

[0052] Preferably, the electrochemical energy storage device comprises a lithium-ion battery.

[0053] Compared with the prior art, the present invention has the following beneficial effects:

[0054] The present invention utilizes a free radical emulsion polymerization reaction to introduce urethane bonds into the negative electrode binder by compounding components such as soft monomers, hard monomers, and acrylate monomers containing urethane bonds, thereby significantly improving the adhesive properties of the binder. The resulting negative electrode binder has the characteristics of high adhesive properties, good flexibility, resistance to electrolyte swelling, and high temperature stability. The preparation method of the negative electrode binder is simple, and the product is safe and environmentally friendly. The bond strength of the negative electrode binder is 3.52-7.88 N / m, and the swelling rate is 45-150%. Preferably, the bond strength of the negative electrode binder is 5.45-7.88 N / m, and the swelling rate is 48-64%. DETAILED DESCRIPTION

[0055] The technical solution of the present invention is further described below by way of specific embodiments. It should be understood by those skilled in the art that the embodiments are merely to help understand the present invention and should not be regarded as specific limitations of the present invention.

[0056] All “parts” mentioned below are “parts by mass”.

[0057] Preparation Example 1

[0058] An acrylate monomer containing a urethane bond, specifically an acrylate monomer A containing a urethane bond, is prepared as follows:

[0059] A reaction apparatus was constructed and cooled with an ice water bath. Ethylene glycol monomethyl ether from which water had been removed was placed at the bottom of the reactor and stirring was started at 100 rpm. Isophorone diisocyanate was then added dropwise to the reactor through a constant pressure titration funnel (the reaction temperature was controlled at 9 ° C during the addition process) at a dropping rate of approximately 1 mL / min. After the addition was completed, the reaction was continued for 1 hour, and then the temperature was raised to 70 ° C. Hydroxyethyl methacrylate was added to the reactor, and the reaction was continued with stirring for 3 hours before cooling to terminate the reaction.

[0060] The molar ratio of the ethylene glycol monomethyl ether, isophorone diisocyanate and hydroxyethyl methacrylate is 1:1:1.

[0061] Preparation Example 2

[0062] An acrylate monomer containing a urethane bond, specifically an acrylate monomer B containing a urethane bond, is prepared as follows:

[0063] A reaction apparatus was built and cooled with an ice water bath. Propylene glycol monomethyl ether from which water had been removed was placed at the bottom of the reactor. Stirring was started at a speed of 100 rpm. Isophorone diisocyanate was then added dropwise to the reactor through a constant pressure titration funnel (the reaction temperature was controlled at 5 ° C during the addition process). The addition rate was approximately 1 mL / min. After the addition was completed, the reaction was continued for 1.5 hours. The temperature was then raised to 80 ° C. Hydroxypropyl methacrylate was added to the reactor. The reaction was continued with stirring for 2 hours and then cooled to terminate the reaction.

[0064] The molar ratio of the propylene glycol monomethyl ether, isophorone diisocyanate and hydroxypropyl methacrylate is 1:1:1.

[0065] Preparation Example 3

[0066] An acrylate monomer containing a urethane bond, specifically an acrylate monomer C containing a urethane bond, is prepared as follows:

[0067] A reaction apparatus was constructed and cooled with an ice water bath. Ethylene glycol monomethyl ether from which water had been removed was placed at the bottom of the reactor and stirring was started at 100 rpm. Isophorone diisocyanate was then added dropwise to the reactor through a constant pressure titration funnel (the reaction temperature was controlled at 1°C during the addition process) at a dropping rate of approximately 1 mL / min. After the addition was completed, the reaction was continued for 2 hours, and then the temperature was raised to 75°C. Hydroxyethyl acrylate was added to the reactor, and the reaction was continued with stirring for 2.5 hours before cooling to terminate the reaction.

[0068] The molar ratio of the ethylene glycol monomethyl ether, isophorone diisocyanate and hydroxyethyl acrylate is 1:1:1.

[0069] Preparation Example 4

[0070] An acrylate monomer containing a urethane bond, specifically acrylate monomer D containing a urethane bond, the preparation method of which is the same as that of Preparation Example 1 except that isophorone diisocyanate is replaced with an equal molar amount of hexamethylene diisocyanate, and other conditions are the same as those of Preparation Example 1.

[0071] Example 1

[0072] This embodiment provides a negative electrode binder and a preparation method thereof. The raw materials for preparing the negative electrode binder include 20 parts of a soft monomer, 30 parts of a hard monomer (styrene), 5 parts of an acrylate monomer A containing a urethane bond prepared in Preparation Example 1, 3.45 parts of an emulsifier, 0.09 parts of an initiator (KPS), and 42 parts of water.

[0073] The soft monomer is 5 parts of butyl acrylate and 15 parts of isooctyl acrylate;

[0074] The above-mentioned emulsifier is 1.15 parts of anionic emulsifier (SDS) and 2.3 parts of nonionic emulsifier (OP-10).

[0075] The preparation method of the above-mentioned negative electrode binder is as follows:

[0076] 14 parts of water, 1.5 parts of OP-10, and 0.75 parts of SDS were placed in a container and emulsified using a disperser at a speed of 700 rpm for 15 minutes. Then, 30 parts of styrene, 5 parts of butyl acrylate, 15 parts of isooctyl acrylate, and 5 parts of urethane-bonded acrylic acid ester monomer A prepared in Preparation Example 1 were added in sequence, and then stirred and emulsified for 30 minutes to obtain a stable emulsion.

[0077] 28 parts of water, 0.8 parts of OP-10, and 0.4 parts of SDS were placed in a reactor, stirred at 200 rpm, heated to 60°C, 1 / 5 of the emulsion was quickly added to the reactor, and then the temperature was continued to be raised to 70°C. 0.03 parts of KPS dispersed in an appropriate amount of water was added to the reactor, and the temperature was continued to be raised to 83°C and kept constant for 1 hour. The remaining emulsion and 0.06 parts of KPS (dispersed in an appropriate amount of water) were then added dropwise to the reactor using a peristaltic pump. The addition process lasted for 3.5 hours, and then the reaction was continued at a constant temperature for 1.5 hours. The reaction was then cooled to 50°C to terminate the reaction and discharge the material to obtain the negative electrode binder.

[0078] Example 2

[0079] This embodiment provides a negative electrode binder and a preparation method thereof. The raw materials for preparing the negative electrode binder include 35 parts of a soft monomer, 15 parts of a hard monomer (isobornyl methacrylate), 2 parts of an acrylate monomer B containing a urethane bond of Preparation Example 2, 1.5 parts of an emulsifier, 0.03 parts of an initiator (APS), and 54 parts of water.

[0080] The soft monomer includes 30 parts of butyl acrylate and 5 parts of methoxy polyethylene glycol 400 methacrylate;

[0081] The emulsifiers are 0.5 parts of anionic emulsifier (LAS) and 1 part of nonionic emulsifier (Span-20).

[0082] The preparation method of the above-mentioned negative electrode binder is as follows:

[0083] 18 parts of water, 0.65 parts of Span-20, and 0.35 parts of LAS were placed in a container and emulsified using a disperser at a speed of 700 rpm for 15 minutes. Then, 15 parts of isobornyl methacrylate, 30 parts of butyl acrylate, 5 parts of methoxypolyethylene glycol 400 methacrylate, and 2 parts of urethane bond-containing acrylate monomer B prepared in Preparation Example 2 were added in sequence. Stirring and emulsification were continued for 30 minutes to obtain a stable emulsion.

[0084] 36 parts of water, 0.35 parts of Span-20, and 0.15 parts of LAS were placed in a reactor, stirred at 200 rpm, heated to 60°C, 1 / 5 of the mass of the above emulsion was quickly added to the reactor, and then the temperature was continued to be raised to 70°C, 0.01 parts of APS dispersed in an appropriate amount of water was added to the reactor, and the temperature was continued to be raised to 85°C and kept constant for 1 hour. The remaining emulsion and 0.02 parts of APS (dispersed in an appropriate amount of water) were then added dropwise to the reactor using a peristaltic pump. The addition process lasted 3.5 hours, and then the reaction was continued at a constant temperature for 2 hours. The temperature was then lowered to 50°C to terminate the reaction and discharge the material to obtain the negative electrode binder.

[0085] Example 3

[0086] This embodiment provides a negative electrode binder and a preparation method thereof. The raw materials for preparing the negative electrode binder include 25 parts of a soft monomer, 25 parts of a hard monomer, 4 parts of an acrylate monomer C containing a urethane bond prepared in Preparation Example 3, 1.93 parts of an emulsifier, 0.06 parts of an initiator (BPO), and 39 parts of water.

[0087] The soft monomer includes 20 parts of isooctyl acrylate and 5 parts of methoxydiethylene glycol methacrylate;

[0088] The hard monomer includes 23 parts of styrene and 2 parts of diisopropylbenzene;

[0089] The emulsifiers are 0.88 parts of anionic emulsifier (SDBS) and 1.05 parts of nonionic emulsifier (OP-10).

[0090] The preparation method of the above-mentioned negative electrode binder is as follows:

[0091] 13 parts of water, 0.7 parts of OP-10, and 0.7 parts of SDBS were placed in a container and emulsified using a disperser at a speed of 700 rpm for 15 minutes. Then, 23 parts of styrene, 2 parts of diisopropylbenzene, 20 parts of isooctyl acrylate, 5 parts of methoxydiethylene glycol methacrylate, and 4 parts of urethane bond-containing acrylate monomer C prepared in Preparation Example 3 were added in sequence, and then stirred and emulsified for 30 minutes to obtain a stable emulsion.

[0092] 26 parts of water, 0.35 parts of OP-10, and 0.18 parts of SDBS were placed in a reactor, stirred at 200 rpm, heated to 60°C, and 1 / 5 of the mass of the above emulsion was quickly added to the reactor, and then the temperature was continued to be raised to 70°C. 0.02 parts of BPO dispersed in an appropriate amount of water were added to the reactor, and the temperature was continued to be raised to 84°C and kept constant for 1 hour. The remaining emulsion and 0.04 parts of BPO (dispersed in an appropriate amount of water) were then added dropwise to the reactor using a peristaltic pump. The addition process lasted for about 3.5 hours, and then the reaction was continued at a constant temperature for 1 hour. The reaction was then cooled to 50°C to terminate the reaction and discharge the material to obtain the negative electrode binder.

[0093] Example 4

[0094] This embodiment provides a negative electrode binder and a preparation method thereof. The raw materials for preparing the negative electrode binder include 25 parts of a soft monomer, 15 parts of a hard monomer (styrene), 3 parts of an acrylate monomer A containing a urethane bond prepared in Preparation Example 1, 2.4 parts of an emulsifier, 0.03 parts of an initiator (BPO), and 60 parts of water.

[0095] The soft monomer includes 10 parts of butyl acrylate and 10 parts of isooctyl acrylate;

[0096] The emulsifiers are 0.9 parts of anionic emulsifier (SDBS) and 1.5 parts of nonionic emulsifier (AEO-10).

[0097] The preparation method of the above-mentioned negative electrode binder is as follows:

[0098] 20 parts of water, 1 part of AEO-10, and 0.6 parts of SDBS were placed in a container and emulsified using a disperser at a speed of 700 rpm for 15 minutes. Then, 15 parts of styrene, 10 parts of butyl acrylate, 10 parts of isooctyl acrylate, and 3 parts of urethane-bonded acrylic acid ester monomer A prepared in Preparation Example 1 were added in sequence. Stirring and emulsification were continued for 30 minutes to obtain a stable emulsion.

[0099] 40 parts of water, 0.5 parts of AEO-10, and 0.3 parts of SDBS were placed in a reactor, stirred at 200 rpm, and heated to 60°C. 1 / 5 of the mass of the above emulsion was quickly added to the reactor, and then the temperature was continued to be raised to 70°C. 0.01 parts of AIBN dispersed in an appropriate amount of butyl acrylate was added to the reactor, and the temperature was continued to be raised to 83°C and kept constant for 1 hour. The remaining emulsion A and 0.02 parts of AIBN (dispersed in an appropriate amount of butyl acrylate) were then added dropwise to the reactor using a peristaltic pump. The addition process lasted for about 3.5 hours. After the reaction was continued at a constant temperature for 1.5 hours, the temperature was lowered to 50°C to terminate the reaction and discharge the material to obtain the negative electrode binder.

[0100] Example 5

[0101] This embodiment provides a negative electrode binder and a preparation method thereof. The raw materials for preparing the negative electrode binder include 25 parts of a soft monomer (isooctyl acrylate), 25 parts of a hard monomer, 3 parts of an acrylate monomer A containing a urethane bond prepared in Preparation Example 1, 1.8 parts of an emulsifier, 0.09 parts of an initiator (KPS), and 57 parts of water.

[0102] The hard monomer includes 15 parts of styrene and 10 parts of isobornyl methacrylate;

[0103] The emulsifiers are 0.6 parts of anionic emulsifier (SDBS) and 1.2 parts of nonionic emulsifier (OP-10).

[0104] The preparation method of the above-mentioned negative electrode binder is as follows:

[0105] 19 parts of water, 0.8 parts of OP-10, and 0.4 parts of SDBS were placed in a container and emulsified using a disperser at a speed of 700 rpm for 15 minutes. Then, 15 parts of styrene, 10 parts of isobornyl methacrylate, 20 parts of isooctyl acrylate, and 3 parts of urethane bond-containing acrylate monomer A prepared in Preparation Example 1 were added in sequence, and then stirred and emulsified for 30 minutes to obtain a stable emulsion;

[0106] 38 parts of water, 0.4 parts of OP-10, and 0.2 parts of SDBS were placed in a reactor, stirred at 200 rpm, and heated to 60°C. 1 / 5 of the mass of the above emulsion was quickly added to the reactor, and then the temperature was continued to be raised to 70°C. 0.03 parts of KPS dispersed in an appropriate amount of water was added to the reactor, and the temperature was continued to be raised to 83°C and kept constant for 1 hour. The remaining emulsion A and 0.06 parts of KPS (dispersed in an appropriate amount of water) were then added dropwise to the reactor using a peristaltic pump. The addition process lasted for about 3.5 hours, and then the reaction was continued at a constant temperature for 1.5 hours. The reaction was then cooled to 50°C to terminate the reaction and discharge the material to obtain the negative electrode binder.

[0107] Example 6

[0108] This embodiment provides a negative electrode binder and a preparation method thereof. The only difference between this embodiment and embodiment 1 is that the mass fraction of the acrylate monomer A containing a urethane bond is adjusted to 6 parts, and other conditions are the same as those in embodiment 1.

[0109] Example 7

[0110] This embodiment provides a negative electrode binder and a preparation method thereof. The only difference between this embodiment and embodiment 1 is that the mass fraction of the acrylate monomer A containing a urethane bond is adjusted to 1 part, and other conditions are the same as those in embodiment 1.

[0111] Example 8

[0112] This embodiment provides a negative electrode binder and a preparation method thereof. The only difference between this embodiment and embodiment 1 is that the mass fraction of the soft monomer is adjusted to 20 parts, and the soft monomer is 10 parts of butyl acrylate and 30 parts of isooctyl acrylate. Other conditions are the same as those in embodiment 1.

[0113] Example 9

[0114] This embodiment provides a negative electrode binder and a preparation method thereof. The only difference between this embodiment and embodiment 1 is that the mass fraction of the soft monomer is adjusted to 16 parts. The soft monomer is 4 parts of butyl acrylate and 12 parts of isooctyl acrylate. Other conditions are the same as those in embodiment 1.

[0115] Example 10

[0116] This embodiment provides a negative electrode binder and a preparation method thereof. The only difference between this embodiment and Example 1 is that the acrylate monomer A containing a urethane bond is replaced with the acrylate monomer D containing a urethane bond prepared in Preparation Example 4 of the same mass. Other conditions are the same as those in Example 1.

[0117] Comparative Example 1

[0118] This comparative example provides a negative electrode binder and a preparation method thereof, which differs from Example 1 only in that the acrylate monomer A containing a urethane bond is not added, and other conditions are the same as those in Example 1.

[0119] Performance Testing

[0120] The negative electrode binders provided in the examples and comparative examples were subjected to the following performance tests:

[0121] (1) Bonding strength: The electrode copper foil was cut into strips of a certain length and width. One side coated with slurry (the slurry was a mixture of graphite, sodium carboxymethyl cellulose, and the above-mentioned negative electrode binder in a mass ratio of 98:1:1, and the thickness of the coated slurry after drying was 85 μm) was affixed to 3M tape. The 3M tape was affixed to a stainless steel plate. After the sample was prepared, a universal tensile tester was used to fix the stainless steel plate and the electrode copper foil was peeled off from the stainless steel plate at 180°. To ensure the accuracy of the results, each sample was tested five times. The highest and lowest values ​​were removed, and the remaining values ​​were averaged to obtain the bonding strength.

[0122] (2) Resistance to electrolyte swelling: Place an appropriate amount of the above-mentioned negative electrode binder into a mold, bake it at 65°C for 72 hours to dry, and then select the middle part to take a 1.5×1.5 cm 2 For a sample of about 3 mm in size and thickness, accurately weigh the sample mass, record it as m1, soak the sample in electrolyte, place it at 65°C for 72 hours, take it out, use dust-free paper to absorb the residual liquid on the surface, weigh the sample mass again, record it as m2, and the swelling rate is calculated by the following formula.

[0123] (3) Flexibility test: Place an appropriate amount of the above-mentioned negative electrode binder into a mold, bake it at 65°C for 72 hours to dry, and then select the middle part to take a 1.5×1.5cm 2 Size, thickness of 3mm sample, manually folded 360° repeatedly 50 times;

[0124] After the test, if there is no crease on the sample and it can automatically return to its original shape, it means that the flexibility is good and is rated as "○";

[0125] After the test, there are slight creases on the sample, and it can slowly recover to its original shape, indicating that the flexibility is average, which is scored as "△";

[0126] After the test, the sample had serious cracks and could not be restored to its original shape, indicating that the flexibility was very poor, and was marked as "╳".

[0127] The test results are shown in Table 1.

[0128] Table 1

[0129] According to the test results in Table 1, the negative electrode binders provided in Examples 1-10 have a bonding strength of 3.52-7.88 N / m, a swelling ratio of 45-150%, and fair or good flexibility. The negative electrode binders provided in Example 1-5 have a bonding strength of 5.45-7.88 N / m, a swelling ratio of 48-64%, and fair or good flexibility.

[0130] Compared with Example 1, if the mass fraction of the acrylate monomer containing an urethane bond is too high (Example 6), the swelling rate increases and the resistance to electrolyte swelling decreases; if the mass fraction of the acrylate monomer containing an urethane bond is too low (Example 7), the bonding strength decreases and the flexibility is poor, which proves that the negative electrode binder prepared by using a specific mass fraction of the acrylate monomer containing an urethane bond has better performance.

[0131] Compared with Example 1, if the mass fraction of the soft monomer is too high (Example 8), the swelling rate increases and the resistance to electrolyte swelling decreases; if the mass fraction of the soft monomer is too low (Example 9), the bonding strength decreases and the flexibility is poor, which proves that the negative electrode binder prepared with a specific mass fraction of soft monomer has better performance.

[0132] Compared with Example 1, if the acrylate monomer A containing an urethane bond is replaced with the acrylate monomer D containing an urethane bond of the same mass (Example 10), the bonding strength decreases, the swelling rate increases, and the resistance to electrolyte swelling decreases, which proves that the negative electrode binder prepared by using the urethane bond-containing acrylate monomer prepared by isophorone diisocyanate has better performance.

[0133] Compared with Example 1, if the acrylic acid ester monomer containing a urethane bond is not added (Comparative Example 1), the bonding strength decreases, the swelling rate increases, the flexibility is poor, and the performance of the obtained negative electrode binder is poor.

[0134] The applicant declares that the present invention uses the above-mentioned embodiments to illustrate a negative electrode binder, its preparation method, and its application. However, the present invention is not limited to the above-mentioned embodiments, which does not necessarily mean that the present invention must rely on the above-mentioned embodiments in order to be implemented. Those skilled in the art should understand that any improvements to the present invention, equivalent replacements for various raw materials in the product of the present invention, addition of auxiliary components, and selection of specific methods, etc., fall within the scope of protection and disclosure of the present invention.

Claims

1. A negative electrode binder, characterized in that: The raw materials for preparing the negative electrode binder include soft monomers, hard monomers, acrylate monomers containing urethane bonds, emulsifiers, initiators and water; The acrylic acid ester monomer containing an urethane bond is prepared by reacting a small molecule diol monomethyl ether with a diisocyanate and capping with an acrylic acid ester containing a terminal hydroxyl group.

2. The negative electrode binder according to claim 1, characterized in that The soft monomer includes any one or a combination of at least two of alkyl acrylate, ethoxy acrylate, methoxy polyethylene glycol methacrylate, methoxy diethylene glycol methacrylate, alkyl methacrylate or methyl ethoxy acrylate, and more preferably alkyl acrylate and / or ethoxy acrylate; Preferably, the hard monomer includes any one of styrene, isobornyl acrylate, isobornyl methacrylate, methyl methacrylate or diisopropylbenzene, or a combination of at least two thereof.

3. The negative electrode binder according to claim 1 or 2, characterized in that: The small molecule diol monomethyl ether includes any one of ethylene glycol monomethyl ether, propylene glycol monomethyl ether, diethylene glycol monomethyl ether or dipropylene glycol monomethyl ether, or a combination of at least two thereof; Preferably, the diisocyanate includes any one or a combination of at least two of isophorone diisocyanate, dicyclohexylmethane diisocyanate, toluene diisocyanate or diphenylmethane diisocyanate, and is more preferably isophorone diisocyanate; Preferably, the acrylate containing terminal hydroxyl groups includes any one of hydroxyethyl methacrylate, hydroxyethyl acrylate, hydroxypropyl methacrylate or hydroxypropyl acrylate, or a combination of at least two thereof; Preferably, the molar ratio of the small molecule diol monomethyl ether, the diisocyanate and the acrylate containing terminal hydroxyl groups is 1:1:1; Preferably, the reaction is to dropwise add diisocyanate into small molecule diol monomethyl ether for reaction; Preferably, the reaction temperature is below 10°C; Preferably, the reaction time is 1-2h; Preferably, the end-capping temperature is 70-80°C; Preferably, the blocking time is 2-3 hours.

4. The negative electrode binder according to any one of claims 1 to 3, characterized in that: The emulsifier includes anionic emulsifier and nonionic emulsifier; Preferably, the mass ratio of the anionic emulsifier to the nonionic emulsifier is 1:1-2; Preferably, the anionic emulsifier includes any one or a combination of at least two of sodium dodecyl sulfonate, sodium dodecyl sulfate or sodium dodecylbenzene sulfonate; Preferably, the nonionic emulsifier includes octylphenol polyoxyethylene ether, sorbitan oleate Or any one or a combination of at least two of fatty alcohol polyoxyethylene ethers; Preferably, the initiator includes any one of ammonium persulfate, potassium persulfate, azobisisobutyronitrile or dibenzoyl peroxide, or a combination of at least two thereof.

5. The negative electrode binder according to any one of claims 1 to 4, characterized in that: The raw materials for preparing the negative electrode binder include the following components by weight: 20-35 parts of soft monomer, 15-30 parts of hard monomer, 2-5 parts of acrylate monomer containing urethane bond, 1.5-3.5 parts of emulsifier, 0.03-0.1 parts of initiator and 35-65 parts of water.

6. A method for preparing a negative electrode binder according to any one of claims 1 to 5, characterized in that: The preparation method comprises the following steps: mixing soft monomers, hard monomers, acrylic ester monomers containing urethane bonds, emulsifiers, water and initiators, and reacting them to obtain the negative electrode binder.

7. The preparation method according to claim 6, characterized in that: The mixing comprises the following steps: (1) mixing a part of the emulsifier and a part of the water to obtain a base liquid; mixing the soft monomer, the hard monomer, the acrylate monomer containing an urethane bond, the remaining emulsifier and a part of the water to obtain an emulsion; (2) mixing the base liquid of step (1), the emulsion of step (1) and an initiator; Preferably, based on the total mass of the emulsifier being 100%, during the preparation of the base liquid in step (1), the mass percentage of the emulsifier in the portion is 30-35%; Preferably, based on the total mass of water being 100%, during the preparation of the base solution in step (1), the mass percentage of the water in the portion is 65-70%; Preferably, based on the total mass of the emulsifier being 100%, during the preparation of the emulsion in step (1), the mass percentage of the remaining emulsifier is 65-70%; Preferably, based on the total mass of water as 100%, during the preparation of the emulsion in step (1), the mass percentage of water in the portion is 30-35%; Preferably, the mixing in step (2) is performed by dropping the emulsion and the initiator into the stirring base liquid for mixing; Preferably, the reaction temperature is 83-85°C; Preferably, the reaction time is 1-2 hours.

8. A battery negative electrode slurry, characterized in that: The battery negative electrode slurry comprises the negative electrode binder according to any one of claims 1 to 5.

9. A negative electrode plate, characterized in that: The negative electrode sheet comprises the negative electrode binder according to any one of claims 1 to 5 or the battery negative electrode slurry according to claim 8.

10. An electrochemical energy storage device, characterized in that: The electrochemical energy storage device comprises the negative electrode binder according to any one of claims 1 to 5 or the battery negative electrode slurry according to claim 8; Preferably, the electrochemical energy storage device comprises a lithium-ion battery.

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