JP2017174804A - Aqueous binder for lithium ion battery negative electrode and preparation method of the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for preparing an aqueous binder for a lithium ion battery negative electrode having improved viscosity, low dispersion efficiency, and good cycle characteristics.SOLUTION: A method of preparing an aqueous binder for a lithium ion battery negative electrode is by the following procedure. A reactive emulsifier, a water-soluble acrylic monomer, an oil-soluble acrylic monomer, and an initiator solution are sequentially added and homogeneously mixed to obtain a base solution, the temperature is raised to initiate polymerization, and while maintaining stirring, a mixed solution of a water-soluble acrylic monomer and an oil-soluble acrylic monomer and an initiator solution are added and reacted.SELECTED DRAWING: Figure 4

Description

  The present invention belongs to the field of lithium ion battery technology, and specifically relates to an aqueous binder for a lithium ion battery negative electrode and a method for preparing the same.

  The new energy business, as an emerging industry, has greatly helped to adjust and transform the industrial structure in accordance with national policies and policies on energy conservation, emission reduction and sustainable development. Lithium ion secondary batteries are currently of particular importance in this industry as a very important component in the new energy industry.

  With the development of science and technology and the improvement of people's material and cultural life, people's demands for lithium-ion batteries are increasing. Lithium ion secondary batteries are widely used in 3C products such as mobile phones, electric vehicles, and automobiles, and their capacity and service life are critical for their large-scale spread and use.

  Lithium ion batteries are usually mixed with an active material, conductive additive and binder solution, and uniformly pulverized in a slurry, applied on a copper foil or aluminum foil as an electrode piece, dried, rolled and other processes Is processed. The capacity and life of the lithium ion secondary battery depend on the amount of the active material in the battery electrode piece and the performance of the binder for binding the active material and the electrode piece. This means that the larger the amount of the active material, the larger the capacity of the battery. However, the more active material during battery manufacture, the greater the influence on the binding strength. In addition, the currently widely used binder is a fluoropolymer binder, and the solvent that volatilizes during production not only pollutes the environment but also poses a health hazard to workers. Moreover, since the price of the solvent for the fluoropolymer is high, the manufacturing cost of the battery is increased. Therefore, it is very important to develop a safe, pollution-free and efficient aqueous binder for use in lithium ion batteries.

  Lithium ion battery binders are mainly divided into two types. One type is an oil-based binder, which uses an organic solvent as a dispersant. Another type is an aqueous binder, which uses water as a dispersant. Compared to oil-based binders, water-based binders use water as a dispersant, so they do not release solvents during production, have the advantages of being environmentally friendly, low in manufacturing costs, and high in safety. It is an important development direction of the binder industry. At present, in preparation of an aqueous binder for an electrode piece of a lithium ion battery negative electrode, as described in Patent CN201310322571.2, a means of blending sodium carboxycellulose (CMC) and styrene-butadiene latex (SBR) is generally used. Is used. The disadvantage of this measure is that the CMC needs to be sufficiently dissolved before it is mixed and dispersed with the negative electrode related material and SBR. However, the dissolution process of CMC in water is slow, inefficient, easy to produce transparent particles, poor dispersion performance, and affects the consistency of battery electrode pieces.

Patent CN01108511.8 discloses a method for preparing an aqueous binder of a lithium ion secondary battery electrode material and a current collector. The technical means are as follows. A hydrophilic monomer and a lipophilic monomer having the general formula CH ₂ = CR ₁ R ₂ are used as an initial polymerization unit. First, one, two or more hydrophilic monomers and one, two or more lipophilic monomers are mixed and an emulsifier and other additives are added. A water-soluble initiator such as ammonium persulfate and a redox system composed of NaSO ₃ and FeSO ₄ are used as an initiation system, and the reaction is performed at a temperature of 30 to 80 ° C. for 3 to 24 hours to obtain an aqueous binder. The resulting binder copolymer content is low, the viscosity is high, the dispersion efficiency is affected, the number of reagents used is large, the reaction time is long, and the production cost of the aqueous binder is high.

  Overcoming the deficiencies of the prior art.

This invention provides the preparation method of the aqueous binder for lithium ion battery negative electrodes, The specific procedure is as follows.
Reactive emulsifier, water-soluble acrylic monomer, oil-soluble acrylic monomer and initiator solution are added in order and mixed uniformly, then used as a base solution, heated to start polymerization and maintain rapid stirring while maintaining water A mixed liquid of an acrylic acrylic monomer and an oil-soluble acrylic monomer and an initiator solution are added and reacted at a high temperature to prepare an aqueous binder solution for a lithium ion battery negative electrode.

The ratio of the reactive emulsifier, the water-soluble acrylic monomer, the oil-soluble acrylic monomer and the initiator in the base liquid is 0.5 to 3:20 to 45:15 to 80: 0.1 to 10 by weight, Preferably it is 1.0-2.5: 25-40: 25-70: 1.0-8.0, More preferably, it is 1.5: 25: 60: 0.5.
The amount of the base solution used is 10 to 50% (% by weight, hereinafter the same) with respect to the total weight, and preferably 20 to 40%.
The base liquid uses water as a dispersion medium. The total weight includes the amount of the base solution used, the amount of the monomer mixture added to the reaction system in the dropping step, and the amount of initiator used, but does not include the amount of water used.

In the said preparation method, the ratio of the water-soluble acrylic monomer and oil-soluble acrylic monomer to be used is 5-40: 20-80, Preferably it is 20-40: 30-60, More preferably, it is 25:36 It is.
The amount of the initiator solution used accounts for 0.5 to 6% of the total amount of acrylic monomer used, and the acrylic monomer includes a water-soluble acrylic monomer and an oil-soluble acrylic monomer.
The lithium ion aqueous binder has a solid content of 30 to 60%, preferably 35 to 55%.
The dropping time of the monomer mixture is 1 to 3 hours, preferably 1.5 to 2.5 hours.
The monomer mixture is added dropwise for 2-10 minutes and then the initiator solution is added dropwise. Preferably it is 5 minutes.
The said reaction temperature is 60-90 degreeC, Preferably it is 70-85 degreeC.
The reaction time is 2 to 6 hours, preferably 3 to 5 hours. The reaction time is calculated after an initiator is added to the reaction system to initiate the polymerization reaction.

The reactive emulsifier is a compound that simultaneously contains a hydrophilic group, a lipophilic group and one or more reactive groups. The reactive group is a group involved in a polymerization reaction, for example, a carbon-carbon double bond, a carbon-carbon triple bond, an unsaturated bond such as carbonyl, —OH, —COOH, —NH ₂ or the like.
Preferably, the reactive emulsifier is one or more of sodium acrylamide isopropyl sulfonate, sodium vinyl sulfonate, sodium 2-allyl ether-3-hydroxypropane-1-sulfonate, sodium allyl ether hydroxypropane sulfonate, and the like. Selected from.

The water-soluble acrylic monomer has the general formula _{CH 2} = _CR 1 _R 2, _{wherein, R 1 = H, -CH 3} , -COOH, R 2 = -COOH, -CN, -CONH 2, - _{COONa, -CH 2 COOH, -OOCCH 3} , -COOCH 2 CH 2 OH, a -COOCH _{2 CH 2} CH ₂ OH.
Preferably, the water-soluble acrylic monomer is selected from one or more of acrylic acid, methacrylic acid, acrylonitrile, acrylamide, sodium acrylate, itaconic acid, N-hydroxymethyl acrylamide, hydroxyethyl acrylate and hydroxypropyl acrylate. The

The oil-soluble acrylic monomer has the general formula _CH 2 = _CR 3 _{R 4, wherein, R 3 = H, -CH 3} , -COOH, R 4 = -COOCH 3, -COOCH 2 CH 3, - _{COO (CH 2) 2 CH 3} , -COOCH 2 CH (CH 2 CH 3) CH 2 CH 2 CH 2 CH 3, -COO (CH 2) 11 CH 3,
It is.
Preferably, the oil-soluble acrylic monomer is one or more of methyl acrylate, methyl methacrylate, ethyl acrylate, propyl acrylate, butyl acrylate, octyl acrylate, lauryl acrylate, and isobornyl acrylate. Selected.

  The initiator is one of potassium persulfate, ammonium persulfate, sodium persulfate, sodium sulfite, sodium hydrogen sulfite, 2,2′-azobis (2,4-dimethylvaleronitrile) and azobisisobutyronitrile. Selected from the above.

The initiator solution is an aqueous solution of the initiator, and the mass percentage is 5 to 20%.
The aqueous binder for a lithium ion battery negative electrode is prepared by high-speed stirring at 200 to 800 rpm, and a protected state by nitrogen gas is maintained during the reaction.
In one embodiment of the present invention, the specific procedure for preparing the aqueous binder for a lithium ion battery negative electrode is as follows.
A reactive emulsifier, a water-soluble acrylic monomer, and an oil-soluble acrylic monomer are added in order, and the mixture is stirred uniformly at 200 to 800 rpm, and nitrogen gas is supplied. The temperature of the reaction system is 70-80 ° C. After adding an initiator and mixing uniformly, it is set as a base liquid. The ratio of reactive emulsifier, water-soluble acrylic monomer, oil-soluble acrylic monomer and initiator in the base solution is 1.5: 25: 60: 0.5 by weight, and the amount of base solution used is the total It accounts for 20-40% of the weight. After the reaction for 0.5 to 1.5 hours, a mixture of water-soluble and oil-soluble acrylic monomer is added dropwise with stirring, the monomer mixture is added dropwise for 2 to 10 minutes, and then the initiator solution is added dropwise. The dropping time is 1.5 to 2.5 hours. After completion of the dropwise addition, the temperature of the reaction system is raised to 70 to 85 ° C. and kept for 0.5 to 1.5 hours to obtain an aqueous binder for a lithium ion battery negative electrode. The ratio of water-soluble acrylic monomer to oil-soluble acrylic monomer used throughout the preparation process is 25:36, and the solid content of the lithium ion aqueous binder is 35-55%.

Another aspect of the present invention provides an aqueous binder for a lithium ion battery negative electrode. The aqueous binder for a lithium ion battery negative electrode is obtained by the above preparation method, and is a viscous liquid whose appearance is emulsion. The range of the solid content is 30 to 60%, preferably 35 to 55%. The viscosity range is 500 to 8000 mPa · s, preferably 500 to 5000 mPa · s.
Suitable electrode materials for the aqueous binder for lithium ion battery negative electrode of the present invention include coke, natural graphite, artificial graphite, LiCoO ₂ , LiNiO ₂ , LiMn ₂ O ₄ , LiFePO ₄ , Ni, Co, Mn ternary composite oxide, etc. is there.

Another aspect of the present invention provides an electrode piece for a lithium ion battery. The electrode piece is prepared by mixing the aqueous binder and the electrode active material to prepare a slurry, which is applied onto a current collector and dried. The content of the aqueous binder in the slurry is 1 to 8%, preferably 2 to 6%.
Another aspect of the present invention provides a lithium ion battery. The lithium ion battery includes a positive electrode, a negative electrode, an electrolytic solution, and a separation membrane, and the positive electrode and / or the negative electrode are electrode pieces of the above-described lithium ion battery.

  The method for preparing an aqueous binder for a lithium ion battery negative electrode according to the present invention has a simple operation process, a short reaction time, and a sufficient reaction. The prepared aqueous binder for lithium ion battery negative electrode is an emulsion viscous liquid, has a high solid content, excellent binding performance, and good mechanical stability. No other demulsification phenomenon occurs. The surface tension is low, the conductive agent and the electrode material are more easily dispersed, and the dispersion efficiency and film formability are greatly improved. At the same time, the binder prepared by this method has good flexibility and good fluidity, the formed film is soft, the produced battery electrode pieces are smooth and have good consistency. The battery manufactured using this electrode piece has good cycle performance, and the battery capacity retention rate after 450 cycles at 0.5c is 90% or more.

It is a TG-DSC curve of the aqueous binder for lithium ion battery negative electrodes by Example 4 of this invention. 6 is a charge / discharge curve of a test lithium ion battery according to Example 5. FIG. A negative electrode piece is produced using the aqueous binder prepared in Example 2, and the lithium ion battery is obtained in combination with the positive electrode piece. Here, the vertical axis represents battery voltage (V), and the horizontal axis represents capacity (mAh). 1 is a charge curve and 2 is a discharge curve. It is a cyclic voltammogram of the test lithium ion battery by Example 5, a negative electrode piece is manufactured using the aqueous binder prepared in Example 2, and it combines with the positive electrode piece of metallic lithium, and obtains the said lithium ion battery. Here, the vertical axis represents current (mA), and the horizontal axis represents potential (v). 6 is a charge / discharge cycle graph of a test lithium ion battery according to Example 5. FIG. A negative electrode piece is produced using the aqueous binder prepared in Example 2, and the lithium ion battery is obtained in combination with the positive electrode piece. Here, the vertical axis represents the capacity maintenance rate, and the horizontal axis represents the number of times of charging / discharging cycles (times).

DESCRIPTION OF EMBODIMENTS Hereinafter, technical solutions according to embodiments of the present invention will be described clearly and in detail with reference to the accompanying drawings according to embodiments of the present invention. Of course, the embodiments described herein are only a part rather than all of the embodiments of the present invention. All other embodiments obtained by a person of ordinary skill in the art based on the embodiments of the present invention without creative efforts shall fall within the protection scope of the present invention.
<Example 1>

  In this example, sodium vinyl sulfonate, acrylic acid and ethyl acrylate are used as reactive emulsifier, hydrophilic acrylic monomer and lipophilic acrylic monomer, respectively, and the ratio of the three in the whole preparation process is 0.5: It was 25:60.

  An emulsion of an aqueous binder for a lithium ion battery negative electrode was prepared according to the following procedure. In the reaction kettle, 1.5 parts of sodium vinyl sulfonate, 25 parts of acrylic acid, 60 parts of ethyl acrylate, and water were added in order and mixed and stirred. The rotation speed was 200 rpm. Nitrogen gas was supplied, the temperature was kept constant at 72 ° C., and 0.5 part of 10% aqueous ammonium persulfate solution was added to initiate the polymerization. The reaction time was 50 minutes. Then 50 parts of acrylic acid, 120 parts of ethyl acrylate aqueous solution and 10 parts of 10% (percent by mass) ammonium persulfate aqueous solution were slowly added dropwise. The dropping time was 3 hours, and the temperature of the reaction system at the time of dropping was 75 ° C. After completion of the dropping, the temperature was raised to 80 ° C. and kept for 60 minutes to obtain an emulsion of an aqueous binder for lithium ion batteries.

The prepared aqueous binder was a milky white viscous liquid having a solid content of 40% and a viscosity of 800 mPa · s.
<Example 2>

In this example, the components and proportions added sequentially to the reaction kettle were 1.5 parts sodium vinyl sulfonate, 12.5 parts acrylic acid, 30 parts ethyl acrylate, and water. The components dropped and their proportions were 62.5 parts acrylic acid and 150 parts ethyl acrylate. The other steps were the same as in Example 1.
The prepared aqueous binder was an emulsion viscous liquid, the solid content was 40%, and the viscosity was 1000-1500 mPa · s.
<Example 3>

  In this example, the water-soluble acrylic monomer and the oil-soluble acrylic monomer were hydroxyethyl acrylate and butyl acrylate, respectively, and the other steps were the same as in Example 1.

The prepared aqueous binder was an emulsion viscous liquid, the solid content was 50%, and the viscosity was 1500 mPa · s.
<Example 4>

  In this example, sodium allyl ether hydroxypropane sulfonate, acrylamide, lauryl acrylate, and azobisisobutyronitrile were used as a reactive emulsifier, a hydrophilic acrylic monomer, a lipophilic acrylic monomer, and an initiator, respectively. The ratio of reactive emulsifier, water-soluble acrylic monomer, oil-soluble acrylic monomer and initiator in the base solution is 0.6: 20: 80: 10, the base solution accounts for 30% of the total weight, and other steps Was the same as in Example 1.

  The prepared aqueous binder is an emulsion viscous liquid, the solid content is 40%, the viscosity is 1000 mPa · s, the mechanical stability is good, and the dispersion process is stable at 5000 rpm. Can exist.

The TG-DSC curve of the aqueous binder is shown in FIG. From the curve, it was found that the aqueous binder was excellent in thermal stability and the decomposition temperature was higher than 270 ° C.
<Example 5>

  A negative electrode slurry was prepared using the emulsion of the aqueous binder synthesized in Example 2 using BTR518 artificial graphite as a negative electrode material. The ratio of the material in the whole negative electrode slurry was 3.5% for the aqueous binder, 95.5% for the BTR518 artificial graphite, and 1% for the conductive agent SP.

  The prepared negative electrode slurry had a solid content of 58% and a viscosity of 3000 mPa · s. The negative electrode piece made of this slurry is smooth, has good consistency, and has a high surface density.

A lithium ion battery for test was manufactured by combining the above negative electrode piece with a lithium manganate (BN-M01) active material, and an application test was performed. The results are shown in FIGS. FIG. 2 is a charge / discharge curve of the test lithium ion battery. As shown in FIG. 2, the charge / discharge end voltage of the test battery was 3.10 to 4.20V. FIG. 3 is a cyclic voltammogram of the above-described test lithium ion battery. FIG. 4 is a charge / discharge cycle graph of the above-described test lithium ion battery. As shown in FIG. 4, the initial charge / discharge capacity of the test battery was larger than 96%, the capacity was excellent, and the flat region of the discharge curve was stable. Even after 200 cycles at 0.5c, the battery capacity retention rate was not clearly reduced and was basically maintained at 97.0% or more. After performing the cycle 450 times at 0.5c, the battery capacity retention rate was 90% or more, and the capacity decay was small.
<Example 6>

  A negative electrode slurry was prepared using the emulsion of the aqueous binder synthesized in Example 2 using graphite Q10 as the negative electrode material. The ratio of the material in the whole negative electrode slurry is 3.5% for the aqueous binder, 95.5% for the graphite Q10, and 1% for the conductive agent SP.

  The solid content of the prepared negative electrode slurry was 48%, and the viscosity of the slurry was 3400 centipoise. The negative electrode piece made of this slurry is smooth and has good consistency.

  Two lithium ion batteries for test were manufactured by combining the negative electrode piece with a lithium manganate (BN-M01) active material, and the numbers of the battery 1 and the battery 2 were given to the batteries. Battery cycle performance detection and drop test were performed. The results are shown in Tables 1-2.

Table 1 Results of cycle performance detection

  Battery 1 and Battery 2 have capacity of 99.6% and 99.7% (standard ≧ 96%) after 20 cycles at 0.5 C, respectively, and capacity after 20 cycles at 1 C. / The initial capacities are 99.2% and 99.2% (standard ≧ 95%), respectively, which meet the criteria.

Table 2 Drop test results

  The measurement results are as follows. The battery did not smoke, ignite, explode or leak. The battery 1 and the battery 2 each had a capacity retention rate of 95% or more after the charge / discharge cycle was performed three times at a current of 1 C at room temperature, that is, the capacity retention rates were both greater than 85%.

  The above is only a preferred embodiment of the present invention, and the present invention is not limited to this, and all modifications, equivalent replacements, etc. made within the spirit and principle of the present invention are all included. It should be included within the protection scope of the present invention.

Claims (10)

A method for preparing an aqueous binder for a lithium ion battery negative electrode, comprising:
Reactive emulsifier, water-soluble acrylic monomer, oil-soluble acrylic monomer and initiator solution are added in order and mixed uniformly, then used as a base solution, polymerization is started by raising the temperature, and while maintaining stirring, water-soluble acrylic A method for preparing an aqueous binder for a lithium ion battery negative electrode, wherein a mixed liquid of an acrylic monomer and an oil-soluble acrylic monomer and an initiator solution are added and reacted to prepare an aqueous binder for a lithium ion battery negative electrode.   The reactive emulsifier is selected from one or more of sodium acrylamide isopropyl sulfonate, sodium vinyl sulfonate, sodium 2-allyl ether-3-hydroxypropane-1-sulfonate, and sodium allyl ether hydroxypropane sulfonate. The preparation method of the aqueous binder for lithium ion battery negative electrodes of Claim 1. The water-soluble acrylic monomer has the general formula _{CH 2} = _CR 1 _R 2, _{wherein, R 1 = H, -CH 3} , -COOH, R 2 = -COOH, -CN, -CONH 2, - _{COONa, -CH 2 COOH, -OOCCH 3} , -COOCH 2 CH 2 OH, a -COOCH _{2 CH 2} CH ₂ OH, and / or,
The oil-soluble acrylic monomer has the general formula _CH 2 = _CR 3 _{R 4, wherein, R 3 = H, -CH 3} , -COOH, R 4 = -COOCH 3, -COOCH 2 CH 3, - _{COO (CH 2) 2 CH 3} , -COOCH 2 CH (CH 2 CH 3) CH 2 CH 2 CH 2 CH 3, -COO (CH 2) 11 CH 3,
The method for preparing an aqueous binder for a lithium ion battery negative electrode according to claim 1, wherein The water-soluble acrylic monomer is selected from one or more of acrylic acid, methacrylic acid, acrylonitrile, acrylamide, sodium acrylate, itaconic acid, N-hydroxymethyl acrylamide, hydroxyethyl acrylate and hydroxypropyl acrylate, and / or Or
The oil-soluble acrylic monomer is selected from one or more of methyl acrylate, methyl methacrylate, ethyl acrylate, propyl acrylate, butyl acrylate, octyl acrylate, lauryl acrylate, and isobornyl acrylate. The preparation method of the aqueous binder for lithium ion battery negative electrodes of Claim 3.   The initiator is one of potassium persulfate, ammonium persulfate, sodium persulfate, sodium sulfite, sodium hydrogen sulfite, 2,2′-azobis (2,4-dimethylvaleronitrile) and azobisisobutyronitrile. The preparation method of the aqueous binder for lithium ion battery negative electrodes of Claim 1 selected from the above.   The ratio of the reactive emulsifier, the water-soluble acrylic monomer, the oil-soluble acrylic monomer and the initiator in the base liquid is 0.5 to 3:20 to 45:15 to 80: 0.1 to 10 by weight, 2. The lithium ion battery negative electrode according to claim 1, wherein the amount of the base liquid used is 10 to 50% of the total weight, and the solid content of the lithium ion battery negative electrode aqueous binder is 30 to 60%. A method for preparing an aqueous binder.   In the preparation method, the ratio of the water-soluble acrylic monomer to the oil-soluble acrylic monomer used is 5 to 40:20 to 80, and / or after the monomer mixture is dropped for 2 to 10 minutes. The lithium ion battery negative electrode according to claim 1, wherein the addition of the initiator solution is started and / or the usage amount of the initiator solution occupies 0.5 to 6% of the total usage amount of the acrylic monomer. A method for preparing an aqueous binder.   2. The lithium according to claim 1, wherein a dropping time of the monomer mixture is 1 to 3 hours and / or a reaction temperature is 60 to 90 ° C. and / or a reaction time is 2 to 6 hours. A method for preparing an aqueous binder for an ion battery negative electrode.   The method for preparing an aqueous binder for a lithium ion battery negative electrode according to claim 1, wherein the aqueous binder for a lithium ion battery negative electrode is prepared by stirring at 200 to 800 rpm, and the protection state by nitrogen gas is maintained during the reaction.   An aqueous binder for a lithium ion battery negative electrode, wherein the aqueous binder for a lithium ion battery negative electrode is prepared by the method for preparing an aqueous binder for a lithium ion battery negative electrode according to any one of claims 1 to 9, and is solid. An aqueous binder for a lithium ion battery negative electrode having a content of 30 to 60% and a viscosity range of 500 to 8000 mPa · s.