CN107641170B - Polymer emulsion, preparation method, prepared water-based adhesive, method and application - Google Patents
Polymer emulsion, preparation method, prepared water-based adhesive, method and application Download PDFInfo
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Abstract
The preparation method of the polymer emulsion comprises the steps of mixing water, a sulfonic acid type reactive emulsifier and an acrylic monomer, adding a cross-linking agent and an initiator for polymerization reaction, adding the sulfonic acid type reactive emulsifier, the acrylic monomer and the initiator for polymerization reaction, and continuing the polymerization reaction. The water-based adhesive is formed by compounding a water-soluble high molecular compound, the polymer emulsion and water; or is polymerized by water-soluble high molecular compound, raw material for preparing polymer emulsion and water through random copolymerization polymerization; the invention also discloses a preparation method of the water-based adhesive. The aqueous adhesive is applied to the preparation of the positive plate of the lithium-sulfur battery. The polymer emulsion has easily controlled molecular weight and uniform particle size distribution; the aqueous adhesive has wide solid content and viscosity range, and the electrochemical performance is excellent when the aqueous adhesive is used for preparing the anode; the method is simple, low in cost and environment-friendly.
Description
Technical Field
The invention relates to a polymer emulsion, a preparation method, a prepared water-based adhesive, a preparation method and application, in particular to a polymer emulsion for a lithium-sulfur battery, a preparation method, a prepared water-based adhesive, a preparation method and application.
Background
Polymer emulsions are generally composed of water, monomers, emulsifiers and initiators, where the emulsifiers do not participate in the chemical reaction and are not easily removed, are mainly carried into the product in the form of physical adsorption on the polymer surface, affect the applicability of the emulsion, and are prone to gel formation under high shear. The polymer emulsion is used as a binder for manufacturing an electrode plate of a lithium secondary battery, emulsifier molecules can migrate in the film forming process of an electrode membrane to form a layer of emulsifier film on the surface of the electrode membrane, and fine channels can be formed in the migration process of the emulsifier molecules to influence the lithium ion conductivity, the mechanical property, the electrical property, the optical property, the water resistance and the like of the electrode membrane. The polymer emulsion prepared by soap-free emulsion polymerization usually consists of water, monomers and an initiator, so that the problems are avoided, the prepared emulsion particles have monodispersity, the particle size is larger than that of the conventional emulsion polymerization, and the emulsion particles can be prepared into functional particles with surface chemical energy, for example, a charge layer can be formed on the surface of the emulsion particles to endow the emulsion particles with new functions.
In the world, new energy technology is rapidly developed, and new expectations and requirements for the energy density of rechargeable batteries are continuously provided along with the development of the fields of clean energy, intelligent communication and electric automobiles, so that the energy density of rechargeable batteries far exceeds the level actually achieved by the current batteries. The lithium-sulfur battery is a practical secondary battery system which most possibly realizes the great increase of the energy storage density on the basis of the existing lithium ion battery. The lithium-sulfur battery is a lithium secondary battery in which sulfur is used as a positive electrode material and metal lithium is used as a negative electrode. Theoretically, the reaction of lithium and elemental sulfur is completely a two-electron reaction, the theoretical specific capacity of a sulfur electrode is 1675mAh/g, the theoretical capacity of a metal lithium cathode is 3860mAh/g, the theoretical energy density of a lithium-sulfur secondary battery system constructed by the two can reach 2600Wh/kg, and the lithium-sulfur secondary battery system has a very wide application prospect.
However, studies have found that there are still four very critical problems to be solved: (1) elemental sulfur and a discharge product lithium sulfide have poor conductivity; (2) the dissolution and migration of polysulfide ions in the discharge intermediate product cause a severe shuttling effect; (3) after elemental sulfur is discharged to generate lithium sulfide, the volume expansion of the elemental sulfur generates lithium sulfide, so that the structure of the battery is damaged; (4) the lithium metal powdering seriously causes the sudden deterioration of the battery and the problem of safety. These problems are caused by the fact that during the charging and discharging of the lithium-sulfur battery, sulfur and metallic lithium undergo two-electron reaction to generate a series of reaction intermediate polysulfide ions, including polysulfide ions with high solubility and Li with low solubility2S2And Li2S, the high-solubility long-chain polysulfide ions can generate a serious shuttle effect when the battery is charged, insoluble products can be deposited on the outer surfaces of a positive electrode and a negative electrode, active sulfur is continuously lost, and the charging and discharging efficiency is not high.
In order to solve the problems of the lithium-sulfur battery, a method that various carbon materials and conductive polymers are introduced into a positive electrode material is generally adopted at present, the problem of poor elemental sulfur conductivity is solved to relieve volume expansion, and the dissolution and migration of polysulfide ions are also inhibited to a certain extent, so that the cycle life of the lithium-sulfur battery is prolonged, but the migration of the polysulfide ions cannot be completely inhibited, and the specific energy of the battery is reduced. In addition, there are also methods for solving the problems of lithium dendrite and lithium pulverization by adding additives to the electrolyte or pretreating the surface of the lithium metal, but the effect is still not ideal.
The lithium-sulfur battery mainly comprises a positive electrode, a negative electrode, a diaphragm, a non-aqueous electrolyte and the like. The positive electrode and the negative electrode are prepared by mixing and dispersing an electroactive material, a conductive additive and a binder to prepare uniform slurry, coating the uniform slurry on a current collector, and performing processes such as drying, rolling and the like. The main function of the binder is therefore to bind and retain the active substance, and also to: (1) the contact between the electrode active material and the conductive agent is enhanced, and the active material is bonded on the current collector, so that the structure of the pole piece is better stabilized, and the pole piece has great influence on the internal resistance, capacity, cycle life, specific energy and the like of a sulfur electrode and even the whole lithium-sulfur battery; (2) for the battery material which expands and contracts in volume in the charging and discharging process, the proper adhesive can also play a certain buffering role to the battery material, and the stability of the electrode structure is maintained; (3) the adhesive with excellent performance can also inhibit the shuttle effect of polysulfide ions and better improve the electrochemical performance of the pole piece. The study of suitable binders to improve the electrochemical performance of lithium-sulfur batteries is becoming a mainstream for improving lithium-sulfur batteries today.
Currently, binders commonly used for lithium secondary batteries mainly include two major types, one is an oily binder represented by a fluoropolymer PVDF, and the other is an aqueous binder represented by LA series (CN 1328102A, CN 1328104A) and CMC-SBR hybrid system. The fluoroolefin polymer binder represented by PVDF has ionic and electronic insulation properties, volume expansion at high temperature, and the dispersant N-methylpyrrolidone (NMP) thereof is not environment-friendly, expensive, and dissolves polysulfides, which may affect the electrochemical performance of the lithium-sulfur battery and increase the battery manufacturing cost. The main structure of the LA series adhesive is high-polarity polyacrylic acid soap-free copolymerized water emulsion, the glass transition temperature is high, the flexibility of the electrode plate is reduced along with the volatilization of water in the drying process when the electrode plate is prepared, and the electrode plate is easy to curl, crack or break. CN103367754A discloses a flexible-package aqueous lithium iron phosphate power battery and a preparation method thereof, wherein an aqueous binder is prepared by a compounding scheme of sodium carboxymethylcellulose (CMC) and Styrene Butadiene Rubber (SBR), but the battery has the technical defects that the CMC is required to be fully dissolved first and then is mixed and dispersed with an electrode material and the SBR, and the CMC is slowly dissolved in water, easily generates transparent particles and has poor dispersibility, so that the consistency of the electrode is influenced; meanwhile, the oxidation resistance of the system adhesive is poor, and the system adhesive is only suitable for a negative electrode.
CN 105576284A discloses a lithium ion battery cathode aqueous binder and a preparation method thereof, which is represented by the general formula CH2=CR1R2The acrylic hydrophilic monomer and the hydrophilic oil monomer are polymerized monomers, and a reactive emulsifier and an initiator are added,preparing a base solution, heating for polymerization, adding a water-based monomer mixed solution and an oil-based monomer mixed solution and an initiator, and reacting for 3-5 hours at 70-85 ℃ to prepare the water-based adhesive. However, the technical scheme requires preparation of a base solution, the process is complicated, and the binder is generally used for a negative electrode due to low oxidation resistance, and has technical obstacles when being used for a positive electrode of a lithium-sulfur battery. CN104538634A discloses an electrode binder and a preparation method thereof, the electrode binder has technical obstacles when being directly used in a positive electrode of a lithium-sulfur battery, and meanwhile, the used raw materials are more in variety, the preparation process is complex, and the cost of the aqueous binder is increased. CN104882612A discloses a binder for lithium ion batteries, but there are technical obstacles to the direct use of the binder in lithium sulfur batteries.
Disclosure of Invention
The invention aims to solve the technical problem of overcoming the defects in the prior art and provide a polymer emulsion which has no migration of an emulsifier, easily controlled molecular weight and uniform particle size distribution.
The invention further aims to solve the technical problem of overcoming the defects in the prior art and provide a preparation method of the polymer emulsion, which has the advantages of simple process, low cost and environmental protection.
The present invention further aims to solve the technical problem of overcoming the above-mentioned defects of the prior art, and to provide an aqueous adhesive which can effectively adsorb polysulfide to inhibit the shuttle effect, has strong adhesive property, and can greatly improve the structural stability and cycle life of the electrode.
The invention further aims to solve the technical problem of overcoming the defects in the prior art and provide a preparation method of the water-based adhesive, which has the advantages of simple process, low cost, environmental friendliness and environmental protection.
The present invention further solves the technical problem of providing an application of the aqueous binder for lithium-sulfur batteries, which overcomes the above-mentioned defects of the prior art.
The technical scheme adopted by the invention for solving the technical problems is as follows: a polymer emulsion having a molecular structure of the general formula:
n is more than 0 and less than or equal to 100; wherein R is1is-C2H3CO3、—COO(CH2)nCH3(n is 0 to 8) and-CH3C6H5、—CN、—OCOCH3、—OCOH、—CONH2、—NHCOO(CH2)nCH3(n is 0 to 8) and-COOCH2CH2CH2OH or-COOCH2CH2OH、—COOCH2CH2CH2O；R2is-H or-CH3；M=Na+，K+Or Li+；
Or the following steps:
n is more than 0 and less than or equal to 100; wherein R is1is-CH2、—CH2OCH2CHOHCH—、—CONH2C(CH3)2CH2-or-COOCH2CH2CH2—；R2is-C2H3CO3、—COO(CH2)nCH3(n is 0 to 8) and-CH3C6H5、—CN、—OCOCH3、—OCOH、—CONH2、—NHCOO(CH2)nCH3(n is 0 to 8) and-COOCH2CH2CH2OH、—COOCH2CH2OH or-COOCH2CH2CH2O；R3is-H or-CH3；M=Na+，K+Or Li+；
Or the following steps:
n is more than 0 and less than or equal to 100; wherein R is1is-CH2、—CH2OCH2CHOHCH—、—CONH2C(CH3)2CH2-or-COOCH2CH2CH2—；R2is-H, -CH3、—C2H3CO3、—COO(CH2)nCH3(n is 0 to 8) and-CH3C6H5、—CN、—OCOCH3、—OCOH、—CONH2、—NHCOO、—COOCH2CH2CH2OH or-COOCH2CH2OH；R3is-C2H3CO3、—COO(CH2)nCH3(n is 0 to 8) and-CH3C6H5、—CN、—OCOCH3、—OCOH、—CONH2、—NHCOO(CH2)nCH3(n is 0 to 8) and-COOCH2CH2CH2OH、—COOCH2CH2OH or-COOCH2CH2CH2O；R4is-H or-CH3；R5is-H or-CH3；M=Na+，K+Or Li+。
The polymer emulsion takes a reactive emulsifier as an emulsifier and a reactive monomer, the prepared emulsion does not contain free micromolecular emulsifier, the harmful reaction caused by the migration of emulsifier molecules in the using process is avoided, and meanwhile, the polymer emulsion prepared by using the polymerization technology has the advantages of easily controlled molecular weight, good particle size monodispersity and uniform distribution.
Preferably, the polymer emulsion is prepared by mixing 10 to 100 parts (more preferably 20 to 80 parts) by weight of a sulfonic acid type reactive emulsifier, 60 to 200 parts (more preferably 80 to 180 parts) by weight of an acrylic monomer, 2 to 10 parts (more preferably 4 to 9 parts) by weight of a crosslinking agent, 1 to 8 parts (more preferably 1.5 to 6.0 parts) by weight of a water-soluble initiator, and 200 to 800 parts (more preferably 250 to 600 parts) by weight of water. The sulfonic acid type reactive emulsifier is a reactive monomer and an emulsifier, the acrylic acid monomer is a reactive monomer of the polymer emulsion and is a main component of the polymer emulsion, the cross-linking agent mainly bonds and cross-links linear molecules into a net structure in the reaction process, and the initiator is heated and decomposed into free radicals to initiate the polymerization of the acrylic acid monomer. Too much or too little of the reactive emulsifier, monomer, crosslinker, and initiator may cause the polymer emulsion to break.
Preferably, the structural formula of the sulfonic acid type reactive emulsifier is CH2=CR1R2SO3M, wherein R1is-H or-CH3，R2is-CH2、—H、—CONHC(CH3)2CH2、—CH2OCH2CHOHCH2or-COOCH2CH2，M=Na+，K+Or Li+。
Preferably, the acrylic monomer has a structural formula CR1R2=CR3R4Wherein R is1is-H or-CH3，R2is-C2H3CO3or-COO (CH)2)nCH3(n is 0 to 8), R3is-H or-CH3，R4is-CH3C6H5、—CN、—OCOCH3、—OCOH、—CONH2、—NHCOO—、—COOCH2CH2CH2OH or-COOCH2CH2OH。
Preferably, the crosslinking agent is a polymerizable monomer containing one or more double bonds.
Preferably, the water-soluble initiator is one or more of ammonium persulfate, potassium persulfate, hydrogen peroxide, azodiisobutyronitrile or azodiisobutyamidine.
Preferably, the sulfonic acid type reactive emulsifier is one or more of 3-allyloxy-2-hydroxy-1-propane sulfonate, hydroxypropyl methacrylate sulfonate, vinyl sulfonate, allyl sulfonate, methacrylic sulfonate, 2-acrylamido-2-methyl-1-propane sulfonate or styrene sulfonate, and the sulfonate is lithium sulfonate, sodium sulfonate, potassium sulfonate or the like.
Preferably, the acrylate monomer is one or more of methyl acrylate, ethyl acrylate, n-propyl acrylate, lauryl acrylate, stearic acid ester, isopropyl acrylate, tert-butyl acrylate, isodecyl acrylate, butyl acrylate, hydroxyethyl acrylate, hydroxypropyl acrylate, hydroxybutyl acrylate, isooctyl acrylate, hydroxypropyl acrylate, hydroxybutyl acrylate, acrylonitrile, methyl methacrylate, ethyl methacrylate, n-propyl methacrylate, n-butyl methacrylate, lauryl methacrylate, stearic acid ester methacrylate, hydroxypropyl methacrylate, hydroxyethyl methacrylate, isobutyl methacrylate, allyl glycidyl ester, glycidyl methacrylate, tert-butyl methacrylate or isooctyl methacrylate.
Preferably, the crosslinking agent is one or more of N-methylol acrylamide, allyl methacrylate, divinylbenzene, trimethylolpropane triacrylate, diallyl adipate, methylene bisacrylamide, allyl glycidyl ether and the like.
The technical scheme adopted for further solving the technical problems is as follows: a process for preparing the polymer emulsion includes such steps as mixing water, part of sulfonic acid type reactive emulsifier and part of acrylic acid monomer, adding cross-linking agent and part of water-soluble trigger, polymerizing reaction, adding the rest of sulfonic acid type reactive emulsifier, the rest of acrylic acid monomer and the rest of water-soluble trigger, and polymerizing reaction. The addition of the emulsion is carried out in batches, so that the molecular weight of the polymer and the particle size distribution of latex particles are easy to control.
Preferably, the temperature of the previous polymerization reaction is 50-80 ℃ and the time is 1-6 h.
Preferably, the temperature of the post-polymerization reaction is 50-85 ℃ and the time is 1-6 h.
If the polymerization temperature is too high, the polymerization reaction rate is increased, and the coagulation rate is easily increased; if the polymerization temperature is too low, the emulsifying ability of the emulsifier is reduced and the monomer cannot be completely converted, the yield is low, and the reaction time is too long to achieve a relative conversion.
Preferably, the mass ratio of the sulfonic acid type reactive emulsifier added in sequence is 1: 0.3-1.0.
Preferably, the mass ratio of the sequentially added acrylic monomers is 1: 0.4-0.7.
If the mass ratio of the sulfonic acid type reactive emulsifier to the acrylic acid monomer is too large or too small, the reaction colloidal particles are easy to separate out and form gel.
Preferably, the mass ratio of the water-soluble initiators added successively is 1: 0.3-0.8. If the mass ratio of the initiators added successively is too large, the reaction is too violent in the early stage of the reaction, so that the implosion is easy to occur, and the test fails; if the mass ratio is too small, the conversion of the monomer is not facilitated, and the yield is impaired.
The invention further solves the technical problem by adopting the technical scheme that: the water-based adhesive is mainly compounded by a water-soluble high molecular compound, the polymer emulsion and water according to a mass ratio of 1: 6-18: 8-20.
Or the emulsion is mainly prepared by polymerizing a water-soluble high molecular compound, a raw material for preparing polymer emulsion and water in a mass ratio of 1: 6-18: 8-20 by a random copolymerization method. The water-soluble high molecular compound is firstly dissolved in water, the sulfonic acid type reactive emulsifier and the acrylic acid monomer are sequentially added to prepare the polymer emulsion by adopting a random copolymerization method, the water-soluble high molecular compound has double functions in the process, can be used as a dispersing agent to prevent emulsion breaking and can also be used as an adhesive, and ether groups, hydroxyl groups, carboxyl groups, amino groups and other functional groups on the surface of the water-soluble high molecular compound can form a physical barrier to effectively adsorb polysulfide ions and inhibit the dissolution and shuttle effect of the polysulfide ions in electrolyte; the random copolymerization method is characterized in that water-soluble macromolecules are used as a dispersing agent, a sulfonic acid type reactive emulsifier and an acrylic monomer are copolymerized to form polymer particles with sulfonate or carboxylate on the surfaces, and the polymer particles are subjected to intramolecular or intermolecular crosslinking in the presence of a crosslinking agent. The content of the water-soluble high molecular compound is lower than the range, so that the demulsification phenomenon is easily caused. The water content below or above the range tends to result in a solid content of the aqueous binder that is too high or too low.
Preferably, the water-soluble polymer compound is one or more of polyethylene glycol, polyvinyl alcohol, polyvinylpyrrolidone, polyethylene oxide, water-soluble polyurethane, polyacrylic acid or polyacrylamide.
In the electrode plate prepared by the adhesive prepared by the conventional emulsifier, emulsifier molecules can migrate in the film forming process to form an emulsifier film on the surface of the electrode plate, and meanwhile, fine channels can be formed in the emulsifier molecule migration process to influence the ion conductivity and the electrochemical performance of the electrode plate. The method utilizes the characteristic that polymer colloidal particles and water-soluble high molecular polymer belong to two phases which are completely incompatible in thermodynamics and are easy to generate phase separation, and obtains the network structure water-based adhesive which is jointly constructed by functional polymer colloidal particles and high molecular dispersing agents by introducing functional groups such as sulfonate, carboxylate and the like. The aqueous adhesive prepared by the invention is a compound consisting of a water-soluble high molecular compound and an acrylic soap-free copolymerized water emulsion with sulfonate or carboxylate on the surface, each component of the compound adhesive plays its own role, and the functions of both adhesive force and polysulfide shuttle effect inhibition can be realized.
The technical scheme adopted by the invention for further solving the technical problems is as follows: a process for preparing water-base adhesive includes such steps as adding water-soluble high-molecular compound to water, stirring until it is dissolved, adding said polymer emulsion, and mixing.
Or adding the water-soluble high molecular compound into water, stirring until the water-soluble high molecular compound is dissolved, mixing the water, a part of the sulfonic acid type reactive emulsifier and a part of the acrylic acid monomer, adding the cross-linking agent and a part of the water-soluble initiator for polymerization reaction, adding the rest of the sulfonic acid type reactive emulsifier, the rest of the acrylic acid monomer and the rest of the water-soluble initiator for polymerization reaction, and continuing the polymerization reaction. The addition of the emulsion is carried out in batches, so that the molecular weight of the polymer and the particle size distribution of latex particles are easy to control.
Or adding the water-soluble high molecular compound into water, stirring until the water-soluble high molecular compound is dissolved, mixing a part of the sulfonic acid type reactive emulsifier and a part of the acrylic acid monomer, adding the cross-linking agent and a part of the water-soluble initiator for polymerization, adding the rest of the sulfonic acid type reactive emulsifier, the rest of the acrylic acid monomer and the rest of the water-soluble initiator for polymerization, and continuing the polymerization. The difference between this method and the former method is that water is added successively and added together when dissolving the water-soluble high molecular compound.
Preferably, the temperature for stirring until the water-soluble high molecular compound is dissolved is between normal temperature and 90 ℃, and the system temperature needs to be reduced to be less than or equal to 75 ℃ after the water-soluble high molecular compound is dissolved. The heating temperature is not higher than the softening point of the water-soluble polymer compound, and decomposition is caused at a temperature higher than the softening point.
Preferably, the temperature of the previous polymerization reaction is 50-80 ℃ and the time is 1-6 h.
Preferably, the temperature of the post-polymerization reaction is 50-85 ℃ and the time is 1-6 h.
If the polymerization temperature is too high, the polymerization reaction rate is increased, and the coagulation rate is easily increased; if the polymerization temperature is too low, the emulsifying ability of the emulsifier is reduced and the monomer cannot be completely converted, the yield is low, and the reaction time is too long to achieve a relative conversion.
Preferably, the mass ratio of the sulfonic acid type reactive emulsifier added in sequence is 1: 0.3-1.0.
Preferably, the mass ratio of the sequentially added acrylic monomers is 1: 0.4-0.7.
If the mass ratio of the sulfonic acid type reactive emulsifier to the acrylic acid monomer is too large or too small, the reaction colloidal particles are easy to separate out and form gel.
Preferably, the mass ratio of the water-soluble initiators added successively is 1: 0.3-0.8. If the mass ratio of the initiator added successively is too large, the reaction is too violent in the early stage of the reaction, so that the implosion is easy, the experiment fails, and if the mass ratio is too small, the monomer is not easy to convert, so that the yield is influenced.
The technical scheme adopted by the invention for further solving the technical problems is as follows: the application of the aqueous adhesive in the preparation of the positive plate of the lithium-sulfur battery.
Preferably, the base material of the positive plate is one or more of elemental sulfur, organic sulfide, porous carbon/sulfur composite material, polymer/sulfur composite material or lithium sulfide. The porous carbon/sulfur composite material is preferably a mesoporous carbon/sulfur composite material.
Preferably, the amount of the aqueous binder is 0.5-15% (more preferably 1-10%) of the mass of the positive plate of the lithium-sulfur battery.
Preferably, the preparation method of the lithium-sulfur battery positive plate is a button cell production process commonly used in the industry. The button cell is manufactured by the following specific steps:
(1) diluting 5-15 parts by weight of water-based adhesive for lithium-sulfur batteries based on solid content with 20-40 parts by weight of deionized water, magnetically stirring for 3-5 hours, adding 70-90 parts by weight of lithium-sulfur battery positive plate base material and 8-12 parts by weight of conductive additive, stirring for 1.5-2.5 hours at a rotating speed of 1500-2500 rmp, mixing and dispersing into uniform slurry, uniformly coating the uniform slurry on a clean aluminum foil, baking for 1.5-2.5 hours under an infrared lamp, cutting into a pole piece with the diameter of 10-20 mm, vacuum drying for 10-15 hours at 90-110 ℃ in a vacuum drying oven to obtain a sulfur positive electrode piece, and transferring into a glove box filled with argon for later use;
(2) taking a PP (polypropylene) and PE (polyethylene) microporous membrane or a coating membrane as a battery diaphragm and metal lithium as a counter electrode for the sulfur positive electrode plate obtained in the step (1), manufacturing a winding type lithium-sulfur battery, packaging the battery by using an aluminum-plastic membrane, carrying out vacuum drying for 10-24 hours at 80 +/-10 ℃, transferring the battery into an anhydrous oxygen-free glove box or a drying room with the humidity of less than or equal to 1%, and injecting electrolyte special for the lithium-sulfur battery to obtain the sulfur positive electrode plate; the electrolyte contains 1.0mol/L LiTFSI, DME: DO (v: v =1: 1) and additive LiNO3，1 wt %。
The conductive additive is carbon black, carbon nano tubes, conductive graphite, Sup-P or acetylene black.
Compared with the prior art, the water-based binder can effectively adsorb polysulfide to inhibit shuttle effect, and the network structure can fix the anode material powder in the point, line and body directions to improve the binding force. Compared with the anode supported by the traditional binder, the internal resistance of the battery is reduced to a certain extent, and the internal energy consumption of the battery is reduced. Because the active material and the conductive agent can be fixed in three directions by the adhesive, the using amount of the adhesive is very small, and when the mass of the general adhesive accounts for about 5% of the mass of the whole anode material, the adhesive effect on each component of the anode can be completely realized, the specific gravity of the sulfur active material is improved, and the specific capacity of the battery is improved. The network structure can well bear the mechanical stress caused by the volume change of the lithium-sulfur battery in the charging and discharging processes, and the stability of the pole piece can be well maintained; introduced functional groups such as ether group, hydroxyl group, carboxyl group, amino group and the like can effectively adsorb polysulfide ions and inhibit the dissolution and shuttle effect of the polysulfide ions in electrolyte; meanwhile, a sulfonic acid group and a carboxylic acid group on the surface of the polymer emulsion can form an electrostatic field force, the electrostatic field force can facilitate lithium ion transmission, and can realize an electrostatic shielding effect on polysulfide, so that polysulfide is limited on one side of a positive electrode.
The invention has the following beneficial effects:
(1) the polymer emulsion does not contain a small molecular emulsifier, so that the problem of migration of the emulsifier is avoided, and meanwhile, the molecular weight of the polymer emulsion is easy to control and the particle size distribution is uniform;
(2) the aqueous adhesive for the lithium-sulfur battery is milky white, has the solid content of 5-30 wt%, has the viscosity of 2000-10000 cp at 25 ℃, and is not beneficial to bonding of powder materials if the viscosity is too low; the binder has wide application range and can be used for various types of sulfur anode materials;
(3) the aqueous binder for the lithium-sulfur battery is used for preparing the positive electrode, and the positive electrode and the metallic lithium negative electrode form a secondary lithium-sulfur battery, wherein the positive electrode polysulfide material has a stable structure, and the utilization rate and the rate characteristic of active substances are improved, so that the cyclicity, the specific energy and the specific power of the battery are improved, through detection, the first discharge specific capacity can reach 1185.7mAh/g by charging and discharging at the voltage of 1.7-2.8V and under the C/10 rate within 25 ℃, the capacity can still be kept at 871.9mAh/g after 100 cycles, and the capacity retention rate is 73.5%;
(3) the method has the advantages of simple production process, low manufacturing cost, environmental friendliness and environmental protection.
Drawings
FIG. 1 is a graph showing a distribution of particle sizes of aqueous adhesives obtained in examples 1 to 2 of the present invention;
FIG. 2 is an infrared spectrum of an aqueous adhesive 1-2 obtained in example 1-2 of the present invention;
FIG. 3 is a scanning electron micrograph of an aqueous adhesive 1-2 obtained in example 1-2 of the present invention;
FIG. 4 is a charge-discharge curve of a 2032 button-type lithium-sulfur battery prepared from the aqueous binder 1-2 obtained in example 1-2 of the present invention; wherein, a and b are charging and discharging curves of the 1 st week, c and d are charging and discharging curves of the 2 nd week, e and f are charging and discharging curves of the 50 th week, and g and h are charging and discharging curves of the 100 th week;
FIG. 5 is a graph showing cycle characteristics of lithium sulfur batteries prepared by using the aqueous binders 1 to 2 obtained in examples 1 to 2 of the present invention;
FIG. 6 is a charge-discharge curve of a 2032 button lithium-sulfur battery prepared according to comparative example 1 of the present invention using a commercial LA133 aqueous binder; wherein, a and b are charging and discharging curves of the 1 st week, c and d are charging and discharging curves of the 2 nd week, e and f are charging and discharging curves of the 50 th week, and g and h are charging and discharging curves of the 100 th week;
fig. 7 is a graph of cycle performance of a lithium sulfur battery prepared from the commercial LA133 aqueous binder of comparative example 1 of the present invention.
Detailed Description
The invention is further illustrated by the following examples and figures.
The starting materials or chemicals used in the examples of the present invention are, unless otherwise specified, commercially available in a conventional manner.
Examples 1 to 9 of Polymer emulsions
Polymer emulsion example 1 molecular structure general formula:
polymer emulsion example 2 molecular structure general formula:
polymer emulsion example 3 molecular structure general formula:
polymer emulsion example 4 molecular structure general formula:
polymer emulsion example 5 molecular structure general formula:
polymer emulsion example 6 molecular structure general formula:
polymer emulsion example 7 molecular structure general formula:
polymer emulsion example 8 molecular structure general formula:
polymer emulsion example 9 molecular structure general formula:
the weight parts of the raw materials of the polymer emulsion examples 1-9 are shown in Table 1:
TABLE 1 weight parts of the raw materials for Polymer emulsion examples 1 to 9
Note: in the table, "-" indicates no addition; "/" is used to distinguish the amounts added in sequence in the preparation process.
Method for preparing Polymer emulsion examples 1 to 3
According to the weight parts of the raw materials in the embodiments 1 to 3 shown in the table 1, deionized water, a sulfonic acid type reactive emulsifier and an acrylic monomer (methyl acrylate in the embodiment 3) are mixed, then a cross-linking agent and a water-soluble initiator are added, after polymerization reaction is carried out for 6 hours at 65 ℃, the sulfonic acid type reactive emulsifier, the acrylic monomer (acrylonitrile in the embodiment 3) and the water-soluble initiator are added, and polymerization reaction is carried out for 8 hours at 65 ℃ continuously. (note: parts by weight of the sulfonic acid type reactive emulsifier, the acrylic monomer or the water-soluble initiator added one after another correspond to the two values before and after the separation by "/" in each item of Table 1, the same applies hereinafter).
Preparation of Polymer emulsion example 4
According to the weight parts of the raw materials in the embodiment 4 shown in the table 1, the deionized water, the sulfonic acid type reactive emulsifier and the acrylic acid monomer are mixed, then the cross-linking agent and the water-soluble initiator are added, after the polymerization reaction is carried out for 3 hours at the temperature of 80 ℃, the sulfonic acid type reactive emulsifier, the acrylic acid monomer and the water-soluble initiator are supplemented, and the polymerization reaction is carried out for 4 hours at the temperature of 80 ℃ continuously, so that the acrylic acid/acrylic acid composite material is obtained.
Preparation method of Polymer emulsion examples 5 to 6
According to the weight parts of the raw materials in the embodiments 5-6 shown in the table 1, the deionized water, the sulfonic acid type reactive emulsifier and the acrylic acid monomer are mixed, then the cross-linking agent and the water-soluble initiator are added, after the polymerization reaction is carried out for 4 hours at 75 ℃, the sulfonic acid type reactive emulsifier, the acrylic acid monomer and the water-soluble initiator are added, and the polymerization reaction is carried out for 6 hours at 75 ℃ continuously, so that the acrylic acid/acrylic acid copolymer is obtained.
Preparation of Polymer emulsion example 7
According to the weight parts of the raw materials in the embodiment 7 shown in the table 1, the deionized water, the sulfonic acid type reactive emulsifier and the acrylic acid monomer are mixed, then the cross-linking agent and the water-soluble initiator are added, the mixture is polymerized for 5 hours at the temperature of 60 ℃, then the sulfonic acid type reactive emulsifier, the acrylic acid monomer and the water-soluble initiator are supplemented, and the polymerization reaction is continued for 6 hours at the temperature of 60 ℃ to obtain the acrylic acid modified acrylic acid.
Preparation of Polymer emulsion example 8
According to the weight parts of the raw materials in the example 8 shown in the table 1, deionized water, a sulfonic acid type reactive emulsifier and allyl glycidyl ester are mixed, a cross-linking agent and a water-soluble initiator are added, the mixture is polymerized for 6 hours at 65 ℃, then, the sulfonic acid type reactive emulsifier, isooctyl acrylate and the water-soluble initiator are supplemented, and the polymerization reaction is continued for 5 hours at 80 ℃ to obtain the compound.
Preparation of Polymer emulsion example 9
According to the weight parts of the raw materials in the example 9 shown in the table 1, the deionized water, the sulfonic acid type reactive emulsifier and the acrylic acid monomer are mixed, then the cross-linking agent and the water-soluble initiator are added, after the polymerization reaction is carried out for 4 hours at 65 ℃, the sulfonic acid type reactive emulsifier, the acrylic acid monomer and the water-soluble initiator are supplemented, and the polymerization reaction is carried out for 8 hours at 65 ℃ continuously, so that the acrylic acid/acrylic acid copolymer is prepared.
Examples 1 to 9 of aqueous adhesive
The weight parts of the raw materials of the water-based adhesive examples 1-9 are shown in Table 2:
TABLE 2 weight parts of raw materials for examples 1 to 9 of aqueous binders
Note: in the table, "-" indicates no addition.
Wherein, according to the weight parts of the raw materials in the table 2, the water-based adhesive formed by compounding the water-soluble high-polymer compound, the polymer emulsion examples 1-9 and deionized water is marked as water-based adhesive 1-9-1;
according to the weight parts of the raw materials in Table 2, the water-based adhesives obtained by polymerizing the raw materials for preparing polymer emulsions in examples 1 to 9 and deionized water by a random copolymerization polymerization method using a water-soluble polymer compound as a colloid protective agent are denoted as water-based adhesives 1-2 to 9-2.
Preparation method of aqueous adhesive examples 1-1 to 3-1
According to the weight parts of the raw materials in the examples 1-3 shown in the table 2, the water-soluble high molecular compound is added into deionized water respectively, the mixture is heated to 90 ℃, stirred until the water-soluble high molecular compound is dissolved, cooled to 65 ℃, added into the polymer emulsion in the examples 1-3 and mixed to obtain the water-based adhesive 1-3-1.
Preparation of aqueous Binder example 4-1
According to the weight parts of the raw materials of the example 4 shown in the table 2, the water-soluble high molecular compound is added into deionized water, heated to 90 ℃, stirred until the water-soluble high molecular compound is dissolved, cooled to 70 ℃, added into the polymer emulsion example 4 and mixed to obtain the water-based adhesive 4-1.
Preparation method of aqueous adhesive examples 5-1 to 6-1
According to the weight parts of the raw materials in the examples 5 to 6 shown in the table 2, the water-soluble high molecular compound is added into deionized water respectively, the mixture is stirred at normal temperature until the water-soluble high molecular compound is dissolved, and the polymer emulsion in the examples 5 to 6 is added and mixed to obtain the water-based adhesive 5-1 to 6-1.
Preparation of aqueous Binder example 7-1
According to the weight parts of the raw materials in the example 7 shown in the table 2, the water-soluble high molecular compound is added into deionized water, stirred at normal temperature until the water-soluble high molecular compound is dissolved, and then the polymer emulsion in the example 7 is added and mixed to obtain the water-based adhesive 7-1.
Preparation of aqueous Binder example 8-1
According to the weight parts of the raw materials of the example 8 shown in the table 2, the water-soluble high molecular compound is added into deionized water, stirred at normal temperature until the water-soluble high molecular compound is dissolved, and then the polymer emulsion example 8 is added for mixing, so as to obtain the water-based adhesive 8-1.
Preparation of aqueous Binder example 9-1
According to the weight parts of the raw materials in the example 9 shown in the table 2, the water-soluble high molecular compound is added into deionized water, stirred at normal temperature until the water-soluble high molecular compound is dissolved, and then the polymer emulsion in the example 9 is added and mixed to obtain the water-based adhesive 9-1.
Preparation method of aqueous adhesive examples 1-2 to 3-2
According to the weight parts of the raw materials of the examples 1 to 3 shown in the table 2, respectively adding a water-soluble high molecular compound into deionized water, heating to 90 ℃, stirring until the water-soluble high molecular compound is dissolved, cooling to 65 ℃, then according to the weight parts of the raw materials of the examples 1 to 3 shown in the table 1, mixing the deionized water, a sulfonic acid type reactive emulsifier and an acrylic acid monomer (methyl acrylate in the example 3), adding a cross-linking agent and a water-soluble initiator, performing polymerization reaction for 6 hours at 65 ℃, then supplementing the sulfonic acid type reactive emulsifier, the acrylic acid monomer (acrylonitrile in the example 3) and the water-soluble initiator, and continuing to perform polymerization reaction for 8 hours at 65 ℃ to obtain the water-based adhesive 1-2-3-2.
Preparation of aqueous Binder example 4-2
According to the weight parts of the raw materials in the example 4 shown in the table 2, adding a water-soluble high molecular compound into deionized water (the sum of the deionized water in the table 1 and the deionized water in the table 2), heating to 90 ℃, stirring until the water-soluble high molecular compound is dissolved, cooling to 70 ℃, then according to the weight parts of the raw materials in the example 4 shown in the table 1, mixing a sulfonic acid type reaction type emulsifier and an acrylic acid type monomer, adding a cross-linking agent and a water-soluble initiator, carrying out a polymerization reaction for 3 hours at 80 ℃, then supplementing the sulfonic acid type reaction type emulsifier, the acrylic acid type monomer and the water-soluble initiator, and continuing the polymerization reaction for 4 hours at 80 ℃ to obtain the water-based adhesive 4-2.
Preparation of aqueous Binders examples 5-2, 6-2
According to the weight parts of the raw materials of the examples 5 and 6 shown in the table 2, respectively adding a water-soluble high molecular compound into deionized water (the total of the deionized water in the table 1 and the deionized water in the table 2), stirring at normal temperature until the water-soluble high molecular compound is dissolved, according to the weight parts of the raw materials of the examples 5 and 6 shown in the table 1, mixing a sulfonic acid type reactive emulsifier and an acrylic acid monomer, adding a cross-linking agent and a water-soluble initiator, carrying out polymerization reaction for 4 hours at 75 ℃, then supplementing the sulfonic acid type reactive emulsifier, the acrylic acid monomer and the water-soluble initiator, and carrying out polymerization reaction for 6 hours at 75 ℃ continuously to obtain the water-based adhesive 5-2-6-2.
Preparation of aqueous Binder example 7-2
According to the weight parts of the raw materials of the example 7 shown in the table 2, adding a water-soluble high molecular compound into deionized water, stirring at normal temperature until the water-soluble high molecular compound is dissolved, according to the weight parts of the raw materials of the example 7 shown in the table 1, mixing the deionized water, a sulfonic acid type reactive emulsifier and an acrylic acid monomer, adding a cross-linking agent and a water-soluble initiator, carrying out polymerization reaction for 5 hours at 60 ℃, then supplementing the sulfonic acid type reactive emulsifier, the acrylic acid monomer and the water-soluble initiator, and continuing to carry out polymerization reaction for 6 hours at 60 ℃ to obtain the water-based adhesive 7-2.
Preparation of aqueous Binder example 8-2
According to the weight parts of the raw materials of the example 8 shown in the table 2, adding a water-soluble high molecular compound into deionized water, stirring at normal temperature until the water-soluble high molecular compound is dissolved, mixing the deionized water, a sulfonic acid type reactive emulsifier and allyl glycidyl ester according to the weight parts of the raw materials of the example 8 shown in the table 1, adding a cross-linking agent and a water-soluble initiator, performing polymerization reaction for 6 hours at 65 ℃, then supplementing the sulfonic acid type reactive emulsifier, an isooctyl acrylate monomer and the water-soluble initiator, and continuing the polymerization reaction for 5 hours at 80 ℃ to obtain the water-based adhesive 8-2.
Preparation of aqueous Binder example 9-2
According to the weight parts of the raw materials of the example 9 shown in the table 2, adding a water-soluble high molecular compound into deionized water, stirring at normal temperature until the water-soluble high molecular compound is dissolved, according to the weight parts of the raw materials of the example 9 shown in the table 1, mixing the deionized water, a sulfonic acid type reactive emulsifier and an acrylic acid monomer, adding a cross-linking agent and a water-soluble initiator, carrying out polymerization reaction for 4 hours at 65 ℃, then supplementing the sulfonic acid type reactive emulsifier, the acrylic acid monomer and the water-soluble initiator, and continuing to carry out polymerization reaction for 8 hours at 65 ℃ to obtain the water-based adhesive 9-2.
The gel fraction of the water-based adhesive in the embodiment 1-2-9-2 is lower than 2%, the emulsion breaking phenomenon is not easy to occur in the random copolymerization process, and the success rate of the finished product is more than 98%, because the water-soluble high molecular compound has the function of protecting colloid particles in the polymerization process, and the emulsion breaking phenomenon caused by too large or too small hydrophilic-hydrophobic proportion along with the increase of molecular chains is prevented.
Comparative example 1
A commercial LA133 aqueous binder was used as a binder for lithium sulfur batteries.
The performance of the aqueous adhesive examples 1 to 9 and comparative example 1 was examined, and the results are shown in table 3.
TABLE 3 Performance test results for Water-based adhesive examples 1 to 9 and comparative example 1
As can be seen from Table 3, in examples 1 to 9, the appearance is milky, the solid content is 11.8 to 27.4wt%, the viscosity at 25 ℃ is 3400 to 8200 cp, the range is wide, and the adhesive has good adhesive capacity to sulfur powder of elemental sulfur, organic sulfide, porous carbon/sulfur composite material, polymer/sulfur composite material or lithium sulfide and the like.
The particle size analysis of the aqueous adhesive 1-2 of the present invention was carried out:
as can be seen from fig. 1, the particle size distribution of the resultant aqueous adhesive, from which it can be seen that the aqueous adhesive 1-2 has a better particle size distribution, exhibiting the noted normal distribution, where D50 is 0.34 μm, D10=0.14 μm, and D90=0.67 μm.
The aqueous binder 1-2 of the invention was subjected to infrared detection:
as can be seen from FIG. 2, the length is 3350cm-1The left and right have a larger dispersion peak, which is corresponding to the dispersion peak of polyvinyl alcohol hydroxyl (O-H); 1452cm-1And 1680cm-1The absorption peak corresponds to-CH in the polyvinyl alcohol high molecular polymer2Stretching vibration and O-H bending vibration peaks; c = C at 1638 cm-1，964 cm-1，920cm-1Nearby characteristic absorption peaks do not appear; CH of M monomer3The asymmetric telescopic vibration is positioned at 2954cm-1；–SO3 2-The stretching vibration of the base is positioned at 980cm-1And 1050cm-1At 1735cm-1A strong absorption peak corresponding to the vibration absorption peak of ester carbonyl (C = O) is present, indicating that the reaction of MA, AN and SAS is via double bond cleavage to form a copolymer; at 2900 cm in SAS-1Corresponding to the absorption peak is CH2The stretching vibration of (2) in the ionic polymer membrane changes to 3100cm in peak shift due to the change of the surrounding environment after the copolymerization-1(ii) a At the same time, the polymer emulsion is at 2243cm-1A new absorption peak appears, corresponding to the stretching vibration absorption of C [ identical to ] N triple bond.
Scanning the aqueous adhesive 1-2 of the present invention by an electron microscope:
as is clear from FIG. 3, the aqueous adhesive 1-2 of the present invention is mainly composed of polymer emulsion particles which are colloidal particles having a uniform size and a particle diameter of 200 to 400nm, and a water-soluble polymer compound attached to the surfaces of the polymer emulsion particles, and the stacked structure of the polymer emulsion particles contributes to the aqueous adhesive bonding of powder materials in a multi-dimensional direction, thereby improving the bonding strength.
The aqueous binders of the present invention 1-1, 1-2 and comparative example 1 were applied to lithium sulfur batteries, respectively, and performance tests were performed:
the aqueous adhesives 1-1 and 1-2 and the aqueous adhesive of the comparative example 1 are respectively applied to the preparation of the positive plate of the lithium-sulfur battery and are prepared into the button cell, and the specific preparation process is as follows:
(1) according to the weight parts, 10 parts of the water-based adhesive 1-1 and 1-2 in terms of solid content or the water-based adhesive in comparative example 1 are respectively diluted by 30 parts of deionized water, magnetically stirred for 4 hours, then added with 80 parts of mesoporous carbon/sulfur composite material and 10 parts of Sup-P, stirred for 2 hours at the rotating speed of 2000rmp, mixed and dispersed into uniform slurry, uniformly coated on a clean aluminum foil, baked for 2 hours under an infrared lamp, cut into pole pieces with the diameter of 14mm, vacuum-dried for 12 hours at the temperature of 100 ℃ in a vacuum drying oven, and transferred into a glove box filled with argon for standby;
(2) taking a PP/PE/PP microporous membrane with the diameter of 19.2mm as the sulfur positive electrode slice obtained in the step (1)Preparing a winding type lithium-sulfur battery by using a battery diaphragm and metal lithium as a counter electrode, packaging the winding type lithium-sulfur battery by using an aluminum plastic film, vacuum-drying the battery at 80 ℃ for 12h, transferring the battery into an anhydrous oxygen-free glove box, and injecting electrolyte special for the lithium-sulfur battery (LiTFSI 1.0mol/L, DME: DOL =1:1 (v/v), LiNO)3Adding 1wt percent of the additive, and obtaining the product.
And carrying out constant-current charge and discharge test on the obtained lithium-sulfur battery by using a charge and discharge instrument, wherein the discharge cut-off voltage is 1V, the charge cut-off voltage is 3V, and the test is carried out under the C/10 multiplying power.
Through detection, the first-week reversible capacity of the lithium-sulfur battery prepared by the water-based adhesive 1-1 can reach 980mAh/g, the first-week reversible capacity is 550mAh/g after circulation for 100 weeks, and the capacity retention rate is 56.1%.
As can be seen from FIGS. 4 and 5, the first cycle reversible capacity of the lithium-sulfur battery prepared by the aqueous binder 1-2 of the present invention can reach 1185.7mAh/g, the cycle reversible capacity is 871.9mAh/g after 100 cycles, and the capacity retention rate is 73.5%.
As can be seen from fig. 6 and 7, the reversible capacity of the lithium-sulfur battery prepared from the commercialized LA133 aqueous binder is 1150mAh/g, the cycle reversible capacity after the cycle reversible capacity is severely attenuated, the attenuation after 100 weeks of the cycle is 505.6mAh/g, and the capacity retention rate is only 44.0%.
The conventional adhesive does not have the function of inhibiting the shuttle effect of polysulfide, polysulfide ions have the function of crossing a membrane in the process of carrying out electrochemical reaction, and shuttle is carried out on the two sides of a positive electrode and a negative electrode. In the aqueous adhesive of the present invention, the water-soluble polymer compound and the polymer emulsion act synergistically to form a physical barrier and an electrostatic barrier to prevent shuttling of polysulfides. The water-soluble high molecular compound can adsorb polysulfide and provide a physical barrier; the polymer emulsion and the water-soluble macromolecular compound contain carboxyl, hydroxyl, ester, ether, sulfonate and the like, the carboxyl can form hydrogen bonds with polysulphide anions, and functional groups such as the hydroxyl, the ester, the ether, halogen atoms and the like have the property of Lewis alkali due to the existence of lone pair electrons and can be mixed with Lewis acid Li in lithium polysulfide and lithium sulfide+Formation of coordinate hydrogen bondsThe stronger bond energy can enable active substances and conductive carbon black in the slurry to be more uniformly dispersed, reduce agglomeration, provide larger specific surface area and sulfur carrying capacity, and relieve the problem of sulfur shuttling, thereby improving the performance of the battery. In addition, the carboxylate and sulfonate allow lithium ions to pass through, but prevent polysulfide negative ions from passing through, thereby improving the utilization rate of the positive active material, and further improving the electrochemical performance of the battery.
In conclusion, the lithium-sulfur battery prepared by the aqueous binder of the invention has good reversible capacity cycling performance after cycling, while the lithium-sulfur battery prepared by the aqueous binder of comparative example 1 has serious reversible capacity fading after cycling, which shows that the utilization rate of active substances is reduced along with the shuttle effect of polysulfide ions in the cycling process, so as to cause capacity fading.
Claims (6)
1. The aqueous adhesive for the lithium-sulfur battery is characterized by being mainly formed by compounding a water-soluble high molecular compound, a polymer emulsion and water in a mass ratio of 1: 6-18: 8-20; or the emulsion is mainly prepared by polymerizing a water-soluble high molecular compound, a raw material for preparing polymer emulsion and water in a mass ratio of 1: 6-18: 8-20 by a random copolymerization method; the water-soluble high molecular compound is one or more of polyvinyl alcohol, polyvinylpyrrolidone, polyethylene oxide, water-soluble polyurethane and polyacrylic acid; the polymer emulsion is prepared by mixing 10-100 parts by weight of sulfonic acid type reactive emulsifier, 60-200 parts by weight of acrylic monomer, 2-10 parts by weight of cross-linking agent, 1-8 parts by weight of water-soluble initiator and 200-800 parts by weight of water, and the molecular structure general formula of the polymer emulsion is
Wherein n is more than or equal to 1 and less than or equal to 100.
2. The aqueous binder for lithium sulfur batteries according to claim 1, characterized in that: the preparation method of the polymer emulsion comprises the following steps: mixing water, a part of the sulfonic acid type reactive emulsifier and a part of the acrylic acid monomer, adding the cross-linking agent and a part of the water-soluble initiator for polymerization, adding the rest of the sulfonic acid type reactive emulsifier, the rest of the acrylic acid monomer and the rest of the water-soluble initiator, and continuing polymerization.
3. The aqueous binder for lithium sulfur batteries according to claim 2, characterized in that: the temperature of the previous polymerization reaction is 50-80 ℃, and the time is 1-6 h; the temperature of the post-polymerization reaction is 50-85 ℃, and the time is 1-6 h; the mass ratio of the sequentially added sulfonic acid type reactive emulsifying agents is 1: 0.3-1.0; the mass ratio of the sequentially added acrylic monomers is 1: 0.4-0.7; the mass ratio of the water-soluble initiators added successively is 1: 0.3-0.8.
4. A method for preparing the aqueous binder for lithium-sulfur batteries according to any one of claims 1 to 3, characterized in that: adding water-soluble high molecular compound into water, stirring until the water-soluble high molecular compound is dissolved, adding polymer emulsion, and mixing; or adding the water-soluble high molecular compound into water, stirring until the water-soluble high molecular compound is dissolved, mixing the water, a part of the sulfonic acid type reactive emulsifier and a part of the acrylic acid monomer, adding the cross-linking agent and a part of the water-soluble initiator for polymerization, supplementing the rest of the sulfonic acid type reactive emulsifier, the rest of the acrylic acid monomer and the rest of the water-soluble initiator, and continuing the polymerization reaction; or adding the water-soluble high molecular compound into water, stirring until the water-soluble high molecular compound is dissolved, mixing a part of the sulfonic acid type reactive emulsifier and a part of the acrylic acid monomer, adding the cross-linking agent and a part of the water-soluble initiator for polymerization, adding the rest of the sulfonic acid type reactive emulsifier, the rest of the acrylic acid monomer and the rest of the water-soluble initiator for polymerization, and continuing the polymerization.
5. The method for preparing the aqueous binder for lithium sulfur batteries according to claim 4, wherein: the temperature of stirring until the water-soluble high molecular compound is dissolved is normal temperature to 90 ℃, and the system temperature is firstly reduced to be less than or equal to 75 ℃ after the water-soluble high molecular compound is dissolved; the temperature of the previous polymerization reaction is 50-80 ℃, and the time is 1-6 h; the temperature of the post-polymerization reaction is 50-85 ℃, and the time is 1-6 h; the mass ratio of the sequentially added sulfonic acid type reactive emulsifying agents is 1: 0.3-1.0; the mass ratio of the sequentially added acrylic monomers is 1: 0.4-0.7; the mass ratio of the water-soluble initiators added successively is 1: 0.3-0.8.
6. Use of an aqueous binder for lithium-sulphur batteries according to any one of claims 1 to 3, wherein: applying the aqueous binder according to any one of claims 1 to 3 to the preparation of a positive plate of a lithium-sulfur battery; the base material of the positive plate is one or more of elemental sulfur, organic sulfide, porous carbon/sulfur composite material, polymer/sulfur composite material or lithium sulfide; the amount of the water-based adhesive accounts for 0.5-15% of the mass of the lithium-sulfur battery positive plate.
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