Adhesive for battery, lithium ion battery negative electrode sheet and lithium ion battery

文档序号:712127 发布日期:2021-04-16 浏览:20次 中文

阅读说明:本技术 电池用粘合剂、锂离子电池负极片以及锂离子电池 (Adhesive for battery, lithium ion battery negative electrode sheet and lithium ion battery ) 是由 潘中来 张晓正 陶伟 于 2020-06-15 设计创作,主要内容包括:本发明涉及电池用粘合剂、锂离子电池负极片以及锂离子电池,属于锂离子电池技术领域。本发明解决的技术问题是提供一种电池用粘合剂。该粘合剂,包含同时带有亲水单元和疏水单元的聚合物;且该聚合物中,中低分子量聚合物占聚合物总量的5wt%以下,所述中低分子量聚合物的分子量≤10万。本发明的粘合剂,其粘合力强,制备方法简单成本低,与现有的负极片粘合剂用量2.5~5%相比,本发明的粘合剂用量1.5~2%时,不仅能体现出更高的粘接力,还能提升活性材料的比例,从而增加电池的能量密度。(The invention relates to a battery adhesive, a lithium ion battery negative plate and a lithium ion battery, belonging to the technical field of lithium ion batteries. The invention aims to provide a binder for a battery. The adhesive comprises a polymer having both hydrophilic and hydrophobic units; in the polymer, the medium and low molecular weight polymer accounts for less than 5 wt% of the total amount of the polymer, and the molecular weight of the medium and low molecular weight polymer is less than or equal to 10 ten thousand. The adhesive disclosed by the invention is strong in adhesive force, simple in preparation method and low in cost, and compared with the existing negative plate adhesive amount of 2.5-5%, when the amount of the adhesive is 1.5-2%, the adhesive not only can show higher adhesive force, but also can improve the proportion of active materials, so that the energy density of a battery is increased.)

1. The adhesive for the battery is characterized by being prepared by the following method: heating a hydrophilic monomer, a lipophilic monomer and water to a reaction temperature under a protective atmosphere, adding an initiator to initiate a reaction to obtain a solid-liquid mixture, and taking a precipitate to obtain the solid-liquid mixture;

the lipophilic monomer comprises at least one of acrylonitrile, methacrylonitrile, styrene, methyl acrylate, ethyl acrylate, n-butyl acrylate, tert-butyl acrylate, 2-ethylhexyl acrylate, cyclohexyl acrylate, isobornyl acrylate, hydroxyethyl acrylate, hydroxypropyl acrylate, vinyl acetate, methyl methacrylate, ethyl methacrylate, n-butyl methacrylate, 2-ethylhexyl methacrylate, cyclohexyl methacrylate, isobornyl methacrylate, hydroxyethyl methacrylate, hydroxypropyl methacrylate and glycidyl methacrylate;

the hydrophilic monomer comprises at least one of acrylic acid, acrylate, methacrylic acid, methacrylate, allyloxy hydroxypropyl sulfonic acid, allyloxy hydroxypropyl sulfonate, vinyl sulfonic acid, vinyl sulfonate, 2-acrylamide-2-methylpropane sulfonic acid, propylene sulfonate, methyl propylene sulfonic acid, methyl propylene sulfonate, itaconic acid, itaconate, maleic acid and maleate.

2. The binder for a battery according to claim 1, characterized in that: the hydrophilic monomer also includes N-vinyl pyrrolidone.

3. The adhesive for batteries according to claim 1 or 2, characterized in that: the hydrophilic monomer also comprises at least one of acrylamide, N-methacrylamide, N-ethyl acrylamide, N-dimethyl acrylamide, N-diethyl acrylamide, 2-methyl acrylamide, N-hydroxymethyl acrylamide, N-hydroxyethyl acrylamide and N-hydroxypropyl acrylamide.

4. The adhesive for a battery according to any one of claims 1 to 3, characterized in that: the weight percentage of the hydrophilic monomer and the lipophilic monomer is 30-70% and 70-30%; preferably, the weight percentage of the hydrophilic monomer and the lipophilic monomer is 40-60% and 60-40%.

5. The binder for a battery according to claim 1, characterized in that: the lipophilic monomer is acrylonitrile and butyl acrylate, and the hydrophilic monomer is acrylic acid, N-vinyl pyrrolidone and acrylamide;

or the lipophilic monomer is methacrylonitrile, methyl acrylate and hydroxypropyl acrylate, and the hydrophilic monomer is methacrylic acid and N-methacrylamide;

or the lipophilic monomer is 2-ethylhexyl acrylate, cyclohexyl methacrylate and ethyl methacrylate, and the hydrophilic monomer is 2-acrylamide-2-methylpropanesulfonic acid, N-diethylacrylamide and itaconate;

or the lipophilic monomer is ethyl acrylate, vinyl acetate and hydroxyethyl methacrylate, and the hydrophilic monomer is acrylate, 2-methacrylamide and vinyl sulfonate;

or the lipophilic monomer is styrene, 2-ethylhexyl methacrylate and hydroxypropyl methacrylate, and the hydrophilic monomer is maleic acid, N-vinyl pyrrolidone and N-hydroxypropyl acrylamide;

or the lipophilic monomer is 2-ethylhexyl acrylate, ethyl acrylate and isobornyl methacrylate, and the hydrophilic monomer is acrylic acid, methacrylic acid, N-hydroxyethyl acrylamide and acrylic sulfonic acid.

6. An aqueous binder for a battery, characterized in that: the binder for a battery is obtained by adjusting the pH value of the binder for a battery of any one of claims 1 to 5 to 6 to 12 in water.

7. The aqueous binder for batteries according to claim 6, wherein: the pH value is 6.5-9.

8. The aqueous binder for batteries according to claim 6, wherein: the aqueous binder for the battery also comprises additives, wherein the additives comprise at least one of a dispersing agent, a leveling wetting agent, a defoaming agent and a flexibility enhancing agent.

9. Use of the adhesive for a battery according to any one of claims 1 to 5 or the aqueous adhesive for a battery according to any one of claims 6 to 8 for producing a lithium ion battery electrode sheet.

10. The negative plate of the lithium ion battery comprises a negative active material and a binder, and is characterized in that: the binder is the binder for a battery according to any one of claims 1 to 5 or the aqueous binder for a battery according to any one of claims 6 to 8.

11. A lithium ion battery, comprising a positive electrode, a negative electrode and an electrolyte, wherein the negative electrode is the negative electrode sheet of the lithium ion battery of claim 10.

12. A battery pack comprising a plurality of cells, the cells being the lithium ion cells of claim 11.

Technical Field

The invention relates to a battery adhesive, a lithium ion battery negative plate and a lithium ion battery, belonging to the technical field of lithium ion batteries.

Background

As an ideal mobile power supply, the lithium ion battery has the advantages of high energy density, small volume, long service life, no pollution and the like which are incomparable with other batteries, and is widely applied to electric vehicles, aerospace, communication and various portable electrical appliances.

The lithium ion battery mainly comprises electrode plates (including a positive plate and a negative plate), a diaphragm, electrolyte and the like; and the electrode plates are all composed of electrode active material powder, adhesive, conductive agent and current collector. When preparing the electrode plate of the lithium ion battery, the electrode active material, the conductive agent and the adhesive solution are mixed and ground uniformly to form slurry, and then the slurry is coated on copper foil and aluminum foil serving as a current collector, and the slurry is obtained through the processes of drying, rolling and the like. It can be seen that the binder plays a key role in the preparation of the electrode sheet.

The water-based adhesive has the advantages of safety, no pollution, no need of solvent recovery, simple operation and the like, and becomes the first choice of the lithium ion battery electrode adhesive. Currently, water-based binders commonly used are SBR (styrene butadiene rubber latex), LA132, LA133, and the like.

The SBR water-based adhesive takes water as a dispersion medium of the negative active material powder, is environment-friendly and pollution-free, and is harmful to production operators. However, due to the limitation of chemical properties of the material components, the SBR is used as a binder of the negative active material powder of the lithium ion battery, and the comprehensive performance of the battery cannot meet the application requirements of increasing battery quality.

Chinese patent applications ZL01108511.8 and zl01108524.x, both of which were earlier studies by the present inventors, disclose binders as powders of negative active materials for lithium ion batteries, and lithium ion batteries fabricated using these binders have excellent performance. However, since the adhesive has a limited adhesive strength, the adhesive strength is slightly poor when the amount of the adhesive used is relatively small, and the amount of the adhesive used is generally 3 to 4% (in terms of solids), and when the amount of the adhesive used is reduced, the electrode sheet cannot meet the high yield requirement.

Disclosure of Invention

In view of the above drawbacks, the present invention provides a battery adhesive having high adhesive strength.

The binder for a battery of the present invention comprises a water-soluble polymer having both a hydrophilic unit and a hydrophobic unit; in the polymer, the medium and low molecular weight polymer accounts for less than 5 wt% of the total amount of the polymer, and the molecular weight of the medium and low molecular weight polymer is less than or equal to 10 ten thousand.

In one embodiment, the weight percentage of the hydrophilic unit and the hydrophobic unit in the polymer is 30-70% and 70-30%. As a specific embodiment, the weight percentage of the hydrophilic unit and the hydrophobic unit is 40-60% and 60-40%.

In one embodiment, the medium to low molecular weight polymer comprises less than 2% of the total polymer. In a specific embodiment, the medium to low molecular weight polymer comprises less than 1% of the total polymer.

Preferably, the low molecular weight polymer accounts for less than 0.5 wt% of the total polymer, and the molecular weight of the low molecular weight polymer is less than or equal to 5 ten thousand.

In one embodiment, the hydrophilic unit contains a carboxyl group or a sulfonic acid group.

As an embodiment, the hydrophobic unit is introduced by a lipophilic monomer and the hydrophilic unit is introduced by a hydrophilic monomer.

In one embodiment, the lipophilic monomer has the formula CH2=CR1R2Wherein R is1Selected from-H or-CH3;R2Selected from-CN, -C6H5、─COOCH3、─COOCH2CH3、─COOCH2CH2CH2CH3、-COOC(CH3)3、─COOCH2CH(CH2CH3)CH2CH2CH2CH3、-COOC12H25、-COO(CH2)17CH3 ─COOCH2CH2OH、─COOCH3CHCH2OH、─COOCH2CHOHCH3、─OCOCH3Or

The structural formula of the hydrophilic monomer is as follows: CHR3=CR4R5Wherein R is3Selected from-H, -CH3or-COOM1;M1Including H, Li, Na, K, Ca, Zn or Mg; r4Selected from-H, -CH3or-COOM2;M2Including H, Li, Na, K, Ca, Zn or Mg; r5Selected from-COOM3、─CH2COOM3、─COO(CH2)6SO3M3、─CONH2、─CONHCH3─CONHCH2CH3、─CON(CH3)2、─CON(CH2CH3)2、─CH2CHCONHCH2OH、─CH2CHCONHCH2CH2OH、─CONHC(CH3)2CH2SO3H、-CH2SO3M3OrM3Including H, Li, Na, K, Ca, Zn or Mg.

As an embodiment, R2Selected from-CN, -C6H5、─COOCH3、─COOCH2CH3、─COOCH2CH2CH2CH3、-COOC(CH3)3、─COOCH2CH(CH2CH3)CH2CH2CH2CH3、-COOC12H25、-COO(CH2)17CH3 ─COOCH2CH2OH、─OCOCH3Or

In a specific embodiment, the lipophilic monomer is at least one selected from acrylonitrile, methacrylonitrile, styrene, methyl acrylate, ethyl acrylate, n-butyl acrylate, t-butyl acrylate, 2-ethylhexyl acrylate, cyclohexyl acrylate, isobornyl acrylate, hydroxyethyl acrylate, hydroxypropyl acrylate, vinyl acetate, methacrylonitrile, methyl methacrylate, ethyl methacrylate, n-butyl methacrylate, 2-ethylhexyl methacrylate, cyclohexyl methacrylate, isobornyl methacrylate, hydroxyethyl methacrylate, hydroxypropyl methacrylate, and glycidyl methacrylate; the hydrophilic monomer comprises at least one of acrylic acid, acrylate, methacrylic acid, methacrylate, allyloxy hydroxypropyl sulfonic acid, allyloxy hydroxypropyl sulfonate, vinyl sulfonic acid, vinyl sulfonate, 2-acrylamide-2-methylpropane sulfonic acid, propylene sulfonate, methyl propylene sulfonic acid, methyl propylene sulfonate, N-vinyl pyrrolidone, itaconic acid, itaconate, maleic acid, and maleate.

Further, the hydrophilic monomer also comprises at least one of acrylamide, N-methacrylamide, N-ethyl acrylamide, N-dimethyl acrylamide, N-diethyl acrylamide, 2-methyl acrylamide, N-hydroxymethyl acrylamide, N-hydroxyethyl acrylamide and N-hydroxypropyl acrylamide.

In one embodiment, the lipophilic monomers are acrylonitrile and butyl acrylate and the hydrophilic monomers are acrylic acid, N-vinyl pyrrolidone and acrylamide. In one embodiment, the lipophilic monomers are methacrylonitrile, methyl acrylate and hydroxypropyl acrylate and the hydrophilic monomers are methacrylic acid and N-methacrylamide. In a specific embodiment, the lipophilic monomers are 2-ethylhexyl acrylate, cyclohexyl methacrylate and ethyl methacrylate and the hydrophilic monomers are 2-acrylamido-2-methylpropanesulfonic acid, N-diethylacrylamide and itaconate. In one embodiment, the lipophilic monomers are ethyl acrylate, vinyl acetate and hydroxyethyl methacrylate and the hydrophilic monomers are acrylate, 2-methacrylamide and vinyl sulfonate. In one embodiment, the lipophilic monomers are styrene, 2-ethylhexyl methacrylate and hydroxypropyl methacrylate and the hydrophilic monomers are maleic acid, N-vinylpyrrolidone and N-hydroxypropylacrylamide. In a specific embodiment, the lipophilic monomers are 2-ethylhexyl acrylate, ethyl acrylate and isobornyl methacrylate and the hydrophilic monomers are acrylic acid, methacrylic acid, N-hydroxyethyl acrylamide and acrylic sulfonic acid.

Further, the weight percentage of the hydrophilic monomer and the lipophilic monomer is 30-70% and 70-30%. In some embodiments, the weight percentage of the hydrophilic monomer and the lipophilic monomer is 40-60% to 60-40%.

In one embodiment, the binder for a battery further includes a solvent, and the solvent is an organic solvent or water.

As a specific embodiment, the solvent is water.

Further, the pH value of the adhesive with water as a solvent is 6-12; in some embodiments, the pH of the binder is 6.5 to 9.

In one embodiment, the binder for a battery further comprises an additive, wherein the additive comprises at least one of a dispersing agent, a leveling wetting agent, a defoaming agent and a flexibility increasing agent.

The invention also provides a preparation method of the adhesive for the battery, wherein the solvent is water.

The preparation method of the adhesive for the battery comprises the following steps: heating hydrophilic monomer, lipophilic monomer and water to reaction temperature in protective atmosphere, adding initiator to initiate reaction to obtain solid-liquid mixture, taking out precipitate, and neutralizing to obtain the adhesive for battery.

The invention also provides application of the adhesive for the battery in preparation of a lithium ion battery negative plate.

The invention also provides application of the adhesive for the battery in preparation of a lithium ion battery pole piece.

The adhesive for the battery has high adhesive force, can be applied to the preparation of a lithium ion battery pole piece, and improves the performance of the battery.

The invention also provides a lithium ion battery negative plate.

The lithium ion battery negative plate comprises a negative active material and an adhesive, wherein the adhesive is the adhesive for the battery.

The invention also provides a lithium ion battery.

The lithium ion battery comprises a positive electrode, a negative electrode and electrolyte, wherein the negative electrode is the lithium ion battery negative plate.

The invention also provides a battery pack comprising a plurality of batteries.

Compared with the prior art, the invention has the following beneficial effects:

the adhesive disclosed by the invention is strong in adhesive force, simple in preparation method and low in cost, and compared with the existing negative plate adhesive amount of 2.5-5%, when the adhesive amount is 1.5-2%, the adhesive not only can show higher adhesive force, but also can improve the proportion of an active material (negative electrode material), so that the energy density of a battery is increased.

Drawings

FIG. 1 shows the results of the molecular weight test of the adhesives of example 1 of the present invention and comparative example 1.

Fig. 2 is a graph showing the cycle performance of batteries manufactured using the binders of example 1 of the present invention and comparative examples 1 and 2.

Fig. 3 is a low-temperature discharge result of batteries manufactured using the binders of example 1 of the present invention and comparative examples 1 and 2.

Detailed Description

The prior aqueous binder for batteries is also an amphiphilic copolymer containing hydrophilic units and hydrophobic units, and is mostly produced by a direct polymerization method, and a binder product is directly obtained after polymerization reaction, wherein the product is an aqueous emulsion or a solution. It is well known in the art that the presence of residual monomer after polymerization can cause environmental pollution and occupational health problems for practitioners in the subsequent battery production. Therefore, the conventional polymerization reactions are all extremely complete polymerization of monomers. And as the polymerization reaction is carried out, the concentration of the monomer after polymerization consumption is reduced, and as the length of the polymer molecular chain is in direct proportion to the concentration of the monomer, certain middle and low molecular weight chain segments are inevitably generated at the later stage of the polymerization reaction. After the reaction is completed, the low-molecular weight chain segments cannot be separated in industrial production, and can be remained in the polymer, thereby influencing the performance of the adhesive, and influencing the bonding performance of the adhesive and the performance of a battery prepared by the adhesive.

However, the inventor of the present invention found that the hydrophilic monomer exists in the form of acid or salt in water according to the pH, and the hydrophilic monomer has low hydrophilic ability when existing in the form of acid. If the monomers of the polymerization are copolymerized in the aqueous phase with a composition having a low hydrophilic power, the reaction product will precipitate due to insufficient hydrophilic power, forming a mixture of water, residual monomers and precipitate. At this time, the polymerization reaction is terminated, the formation of the medium and low molecular weight polymer is greatly reduced, the precipitate is further separated by a physical method, unreacted monomers and a small amount of the medium and low molecular weight polymer are left in the reaction system (aqueous phase), the precipitate is a high molecular weight polymer, the content of the medium and low molecular weight polymer in the precipitate is low, the polymer can be directly dissolved in an organic solvent such as NMP and used as a binder, alkali can be added for neutralization or hydrolysis, and after the hydrophilic capacity of the copolymer is improved, the copolymer is uniformly dispersed in the aqueous phase to obtain the aqueous binder.

The obtained adhesive has obviously improved mechanical properties such as cohesive force, adhesive force and the like due to the reduction of the content of the medium-low molecular weight polymer, so that the adhesive prepared by adopting the precipitate has better bonding property, the dosage of the adhesive is further reduced, and the battery performance is improved.

Based on this, the binder for a battery of the present invention comprises a polymer having both a hydrophilic unit and a hydrophobic unit; in the polymer, the medium and low molecular weight polymer accounts for less than 5 wt% of the total amount of the polymer, and the molecular weight of the medium and low molecular weight polymer is less than or equal to 10 ten thousand. When the content of the medium-low molecular weight polymer is low, the adhesive property of the adhesive and the performance of the battery prepared by using the adhesive are better.

The binder for a battery of the present invention comprises a polymer having both a hydrophilic unit and a hydrophobic unit; in the polymer, the medium and low molecular weight polymer accounts for less than 5 wt% of the total amount of the polymer, and the molecular weight of the medium and low molecular weight polymer is less than or equal to 10 ten thousand.

As some embodiments, the medium and low molecular weight polymer is controlled to constitute 0.5 wt%, 0.8 wt%, 1 wt%, 1.5 wt%, 2 wt%, 2.5 wt%, 3 wt%, 3.5 wt%, 4 wt%, 4.5 wt%, 5 wt%, etc. of the total amount of the polymer.

In one embodiment, the weight percentage of the hydrophilic unit and the hydrophobic unit in the polymer is 30-70% and 70-30%.

As specific examples, the weight percentages of hydrophilic units and hydrophobic units in the polymer are 30% to 70%, 35% to 65%, 40% to 60%, 42% to 58%, 45% to 55%, 47% to 53%, 50% to 50%, 51% to 49%, 55% to 45%, 58% to 42%, 60% to 40%, etc.

In one embodiment, the weight percentage of the hydrophilic unit to the hydrophobic unit is 40-60% to 60-40%.

In one embodiment, the medium to low molecular weight polymer comprises less than 2% of the total polymer. In a specific embodiment, the medium to low molecular weight polymer comprises less than 1% of the total polymer.

Preferably, the content of the low-molecular polymer having a molecular weight of 5 ten thousand or less is controlled together with the control of the low-molecular polymer. In one embodiment, the low molecular weight polymer is present in an amount of 0.5 wt% or less of the total polymer, and has a molecular weight of 5 ten thousand or less.

As some specific embodiments, the low molecular weight polymer is controlled to be 0.1 wt%, 0.2 wt%, 0.3 wt%, 0.4 wt%, 0.5 wt%, etc. of the total amount of the polymer.

The molecular weights stated in the present invention are all weight average molecular weights (Mw). The molecular weight of the invention is determined by gel chromatography, and the types of the testing equipment are as follows: waters Alliance E2695. And (3) testing conditions are as follows: three chromatographic columns, namely Waters StyRagel HR 3, 4 and 5 (water), are connected in series; mobile phase Buffer pH 7.2, 3mol/L NaCl solution; standard sodium polyacrylate, PAA, CAS number 9003-04-7, molecular weight 2800; 11500; 193800, respectively; 392600, respectively; 585400, respectively; 750000; 804700, respectively; 1310000, respectively; 2250000 (Standard curves using the above 9 different molecular weight Standards) were purchased from American Polymer Standards Corporation at a temperature of 0.6 ml/min. The molecular weights determined using different columns and standards will vary with an error of no more than 20% at most.

The medium and low molecular weight polymer is a polymer with the molecular weight less than or equal to 10 ten thousand.

The low molecular polymer of the invention is a polymer with a molecular weight less than or equal to 5 ten thousand.

The polymer is an amphiphilic copolymer due to the fact that the polymer has a hydrophobic unit and a hydrophilic unit, and the hydrophilic unit contains a carboxyl group or a sulfonic group. Preferably, the hydrophobic units of the polymer are introduced by a lipophilic monomer and the hydrophilic units are introduced by a hydrophilic monomer containing a carboxyl group or a sulfonic acid group. The amphiphilic polymers of the present invention may be obtained by copolymerization of a lipophilic monomer and a hydrophilic monomer.

In some embodiments, the lipophilic monomer has the formula CH2=CR1R2Wherein, in the step (A),

R1selected from-H or-CH3

R2Selected from-CN, -C6H5、─COOCH3、─COOCH2CH3、─COOCH2CH2CH2CH3、-COOC(CH3)3、─COOCH2CH(CH2CH3)CH2CH2CH2CH3、-COOC12H25、-COO(CH2)17CH3 ─COOCH2CH2OH、─COOCH3CHCH2OH、─COOCH2CHOHCH3、─OCOCH3Or

The structural formula of the hydrophilic monomer is as follows: CHR3=CR4R5Wherein, in the step (A),

R3selected from-H, -CH3or-COOM1;M1Including H, Li, Na, K, Ca, Zn or Mg;

R4selected from-H, -CH3or-COOM2;M2Including H, Li, Na, K, Ca, Zn or Mg;

R5selected from-COOM3、─CH2COOM3、─COO(CH2)6SO3M3、─CONH2、─CONHCH3─CONHCH2CH3、─CON(CH3)2、─CON(CH2CH3)2、─CH2CHCONHCH2OH、─CH2CHCONHCH2CH2OH、─CONHC(CH3)2CH2SO3H、-CH2SO3M3OrM3Including H, Li, Na, K, Ca, Zn or Mg.

In some embodiments, R2Selected from-CN, -C6H5、─COOCH3、─COOCH2CH3、─COOCH2CH2CH2CH3、-COOC(CH3)3、─COOCH2CH(CH2CH3)CH2CH2CH2CH3、-COOC12H25、-COO(CH2)17CH3 ─COOCH2CH2OH、─OCOCH3Or

In a specific embodiment, the lipophilic monomer comprises at least one of acrylonitrile, methacrylonitrile, styrene, methyl acrylate, ethyl acrylate, n-butyl acrylate, t-butyl acrylate, 2-ethylhexyl acrylate, cyclohexyl acrylate, isobornyl acrylate, hydroxyethyl acrylate, hydroxypropyl acrylate, vinyl acetate, methacrylonitrile, methyl methacrylate, ethyl methacrylate, n-butyl methacrylate, 2-ethylhexyl methacrylate, cyclohexyl methacrylate, isobornyl methacrylate, hydroxyethyl methacrylate, hydroxypropyl methacrylate, glycidyl methacrylate.

The hydrophilic monomer comprises at least one of acrylic acid, acrylate, methacrylic acid, methacrylate, allyloxy hydroxypropyl sulfonic acid, allyloxy hydroxypropyl sulfonate, vinyl sulfonic acid, vinyl sulfonate, 2-acrylamide-2-methylpropane sulfonic acid, propylene sulfonate, methyl propylene sulfonic acid, methyl propylene sulfonate, N-vinyl pyrrolidone, itaconic acid, itaconate, maleic acid, and maleate.

Since the hydrophilic unit contains a carboxyl group or a sulfonic acid group, it is necessary to ensure that at least one hydrophilic monomer contains a carboxyl group or a sulfonic acid group. The monomer containing carboxyl or sulfonic group can be adjusted in hydrophilic ability to ensure that the polymer is precipitated in water and changed into a salt form after being added with alkali liquor, thereby improving the hydrophilic ability and dissolving the polymer in water.

In a specific embodiment of the present invention, the hydrophilic monomer further comprises at least one of acrylamide, N-methacrylamide, N-ethylacrylamide, N-dimethylacrylamide, N-diethylacrylamide, 2-methacrylamide, N-methylolacrylamide, N-hydroxyethylacrylamide, and N-hydroxypropylacrylamide. The introduction of these amide hydrophilic monomers can provide other functions.

The polymer in the adhesive of the present invention is copolymerized from at least one hydrophilic monomer and at least one lipophilic monomer. In one embodiment, the polymer is copolymerized from a lipophilic monomer and a hydrophilic monomer. In one embodiment of the invention, the lipophilic monomer is acrylonitrile and the hydrophilic monomer is acrylic acid. In one embodiment, the lipophilic monomer is methacrylonitrile and the hydrophilic monomer is methacrylic acid. In one embodiment, the lipophilic monomer is hydroxyethyl acrylate and the hydrophilic monomer is vinyl sulfonate. In one embodiment, the lipophilic monomer is cyclohexyl methacrylate and the hydrophilic monomer is methacrylate. In one embodiment, the lipophilic monomer is vinyl acetate and the hydrophilic monomer is methacrylic acid. In one embodiment, the lipophilic monomer is glycidyl methacrylate and the hydrophilic monomer is itaconic acid. In one embodiment, the lipophilic monomer is 2-ethylhexyl acrylate and the hydrophilic monomer is maleic acid. In one embodiment, the lipophilic monomer is hydroxyethyl methacrylate and the hydrophilic monomer is vinylsulfonic acid. In one embodiment, the lipophilic monomer is methacrylonitrile and the hydrophilic monomer is 2-acrylamido-2-methylpropanesulfonic acid. In one embodiment, the lipophilic monomer is styrene and the hydrophilic monomer is propylene sulfonic acid. In one embodiment, the lipophilic monomer is methyl acrylate and the hydrophilic monomer is allyloxy hydroxypropyl sulfonic acid. In one embodiment, the lipophilic monomer is t-butyl acrylate and the hydrophilic monomer is methacrylate.

As another embodiment, the polymer in the adhesive of the present invention is copolymerized from a lipophilic monomer and hydrophilic monomers. In one embodiment, the lipophilic monomer is acrylonitrile and the hydrophilic monomers are acrylic acid and methacrylic acid. In one embodiment, the lipophilic monomer is acrylonitrile and the hydrophilic monomer is acrylic acid and acrylamide. In one embodiment, the lipophilic monomer is methacrylonitrile and the hydrophilic monomer is acrylate, methacrylic acid, and N-methacrylamide. In one embodiment, the lipophilic monomer is styrene and the hydrophilic monomer is acrylic acid, acrylate, methacrylic acid, methacrylate, and acrylamide. In one embodiment, the lipophilic monomer is methyl acrylate and the hydrophilic monomers are vinylsulfonic acid, 2-acrylamido-2-methylpropanesulfonic acid, and itaconic acid. In one embodiment, the lipophilic monomer is, and the hydrophilic monomer is. In one embodiment, the lipophilic monomer is n-butyl methacrylate and the hydrophilic monomer is acrylic acid, an acrylate, and acrylamide. In one embodiment, the lipophilic monomer is t-butyl acrylate and the hydrophilic monomer is N, N-dimethylacrylamide, 2-methacrylamide, and maleic acid. In one embodiment, the lipophilic monomer is acrylonitrile and the hydrophilic monomer is acrylate, methacrylic acid, methacrylate, acrylamide, N-methylacrylamide and N-ethylacrylamide.

As another embodiment, the polymer in the adhesive of the present invention is copolymerized from a plurality of lipophilic monomers and a hydrophilic monomer. In one embodiment, the lipophilic monomer is acrylonitrile, methacrylonitrile, styrene, and methyl acrylate, and the hydrophilic monomer is acrylic acid. In one embodiment, the lipophilic monomer is styrene, methyl acrylate, ethyl acrylate, and t-butyl acrylate and the hydrophilic monomer is methacrylic acid. In one embodiment, the lipophilic monomer is vinyl acetate, methacrylonitrile, methyl methacrylate, and ethyl methacrylate and the hydrophilic monomer is allyloxy hydroxypropyl sulfonic acid. In one embodiment, the lipophilic monomer is cyclohexyl methacrylate, isobornyl methacrylate, and glycidyl methacrylate and the hydrophilic monomer is maleic acid. In one embodiment, the lipophilic monomers are styrene, methyl acrylate and hydroxypropyl acrylate and the hydrophilic monomer is itaconic acid. In one embodiment, the lipophilic monomer is allyloxy hydroxypropyl sulfonic acid. In one embodiment, the lipophilic monomer is hydroxypropyl acrylate, vinyl acetate, methacrylonitrile, and methyl methacrylate and the hydrophilic monomer is vinylsulfonic acid. In one embodiment, the lipophilic monomer is styrene, methacrylonitrile, methyl methacrylate, and isobornyl methacrylate and the hydrophilic monomer is propylene sulfonic acid.

As another embodiment, the polymer in the adhesive of the present invention is copolymerized from a plurality of lipophilic monomers and a plurality of hydrophilic monomers. In one embodiment, the lipophilic monomers are acrylonitrile and butyl acrylate and the hydrophilic monomers are acrylic acid, N-vinyl pyrrolidone and acrylamide. In one embodiment, the lipophilic monomers are methacrylonitrile, methyl acrylate and hydroxypropyl acrylate and the hydrophilic monomers are methacrylic acid and N-methacrylamide. In a specific embodiment, the lipophilic monomers are 2-ethylhexyl acrylate, cyclohexyl methacrylate and ethyl methacrylate and the hydrophilic monomers are 2-acrylamido-2-methylpropanesulfonic acid, N-diethylacrylamide and itaconate. In one embodiment, the lipophilic monomers are ethyl acrylate, vinyl acetate and hydroxyethyl methacrylate and the hydrophilic monomers are acrylate, 2-methacrylamide and vinyl sulfonate. In one embodiment, the lipophilic monomers are styrene, 2-ethylhexyl methacrylate and hydroxypropyl methacrylate and the hydrophilic monomers are maleic acid, N-vinylpyrrolidone and N-hydroxypropylacrylamide. In a specific embodiment, the lipophilic monomers are 2-ethylhexyl acrylate, ethyl acrylate and isobornyl methacrylate and the hydrophilic monomers are acrylic acid, methacrylic acid, N-hydroxyethyl acrylamide and acrylic sulfonic acid.

In one embodiment, the weight percentage of the hydrophilic monomer and the lipophilic monomer is 30-70% to 70-30%. In one embodiment, the weight percentage of the hydrophilic monomer and the lipophilic monomer is 40-60% to 60-40%.

As a specific embodiment, the weight percentage of the hydrophilic monomer and the lipophilic monomer is 40% to 60%; as another specific embodiment, the weight percentage of the hydrophilic monomer and the lipophilic monomer is 45% to 55%; as another specific embodiment, the weight percentage of the hydrophilic monomer and the lipophilic monomer is 50% to 50%; as another specific embodiment, the weight percentage of the hydrophilic monomer and the lipophilic monomer is 55% to 45%; as another specific embodiment, the weight percentage of the hydrophilic monomer and the lipophilic monomer is 60% to 40%, and the like.

The adhesive for the battery can be solid as a product, can be used after being added with a solvent to form glue when in use, and can also be a liquid product for direct use.

In one embodiment, the binder for a battery further includes a solvent, and the solvent is an organic solvent or water.

Organic solvents commonly used in the art are suitable for use in the present invention, such as NMP and the like.

As a preferred embodiment, the solvent is water. The adhesive using water as solvent has the advantages of safety, no pollution, no need of solvent recovery, simple operation and the like.

In one embodiment, the pH value of the adhesive is 6-12. When the pH value is 6-12, the polymer exists in the form of ionic polymer, so that the hydrophilic capacity of the polymer can be improved, and the polymer can be well dissolved in water. The pH value can be adjusted by a conventional method, and as a specific embodiment, the pH value is adjusted by adding an alkali solution, wherein the alkali solution is an alkali metal hydroxide, such as a sodium hydroxide solution, a potassium hydroxide solution, or the like, and can also be an alkali solution such as sodium carbonate, ammonia water, or organic amine, or the like. In a specific embodiment, the pH is adjusted with sodium hydroxide solution. In a specific embodiment, the pH value of the adhesive is 6.5-9.

As one embodiment, the binder for a battery according to the present invention consists only of a polymer and water, and the binder does not contain other additives.

In another embodiment, the binder for a battery further comprises an additive, wherein the additive comprises at least one of a dispersant, a leveling wetting agent, a defoaming agent and a softening agent.

The amount of these additives is conventional in the art, for example, the additive is present in an amount of less than 5% by weight based on the total weight of the water-based adhesive. In some embodiments, the additive is present in an amount of less than 3%, less than 1%, less than 0.5%, less than 0.1%, 0%, etc., based on the total weight of the adhesive.

Wherein the dispersant can be anionic dispersant such as oleate, sulfonate, carboxylate, etc., or cationic dispersant such as ammonium salt, quaternary ammonium salt, pyridineSalts, etc., and also nonionic dispersants such as polyethers, acetylene glycols, CMC, etc., and also supramolecular dispersants such as high-molecular polymers of the phosphate type. By adding the dispersant, the dispersing property can be improved when the coating slurry is prepared.

The leveling and wetting agent is a high boiling point solvent such as alcohols, ketones, esters or a high boiling point solvent mixture with multiple functional groups, can be long-chain resin type such as acrylic acid, fluorocarbon resin and the like, and can also be organic silicon type such as diphenyl polysiloxane, methyl phenyl polysiloxane and the like. By these leveling wetting agents, the smoothness of the slurry can be improved, and the use is facilitated.

The defoaming agent can be organic small molecular alcohol or ether such as ethanol, isopropanol, butanol, etc., and also can be organic silicon, polyether, such as polydimethylsiloxane, pentaerythritol ether, etc.

The softening agent is water-soluble organic solvent with freezing point less than 100 deg.C, such as ethanol, propylene glycol, butanediol, glycerol, dimethyl sulfoxide, etc., or water-based polymer or emulsion with glass transition temperature (Tg) less than 100 deg.C. The flexibilizing agent can increase the flexibility of the adhesive film layer.

The adhesive for the battery can be prepared by adopting a conventional method. As one embodiment, the hydrophilic monomer may be present in water in the form of an acid or a salt depending on the pH, and when present in the form of an acid, it has a low hydrophilic ability. Therefore, the adhesive for the battery can be prepared by the following method: the monomer of the polymerization reaction is copolymerized in the water phase in a low hydrophilic capacity composition and form, the reaction product forms water dispersion slurry in a precipitation form due to insufficient hydrophilic capacity of the copolymer, the precipitate can be separated in a physical mode, the copolymer precipitate is neutralized or hydrolyzed by adding alkali, and after the hydrophilic capacity of the copolymer is improved, the copolymer is uniformly dispersed in the water phase to obtain the adhesive for the battery.

For example, during polymerization, carboxylic acid or sulfonic acid groups are retained in monomers of polymerization reaction, after polymerization, the precipitate is taken out, alkali is added, the carboxylic acid or sulfonic acid in the polymer can be neutralized into corresponding carboxylate or sulfonate, the hydrophilic ability of the carboxylate or sulfonic acid is improved, and then the carboxylate or sulfonic acid is dispersed in a water phase.

The method can greatly reduce the content of residual monomers and low molecular weight polymers, so that the adhesive meets the requirement that the content of the low molecular weight polymers is less than 5 percent, thereby improving the mechanical properties of the copolymer, such as cohesive force, adhesive force and the like.

As a specific embodiment of the present invention, a binder for a battery is prepared by the following method: adding a hydrophilic monomer, a lipophilic monomer and water into a reaction container, heating to a reaction temperature under a protective atmosphere, adding an initiator to initiate a reaction, obtaining a solid-liquid mixture after the reaction is finished, taking a precipitate, adding an alkali liquor to neutralize to a pH value of 6-12, and obtaining the adhesive for the battery, wherein the adhesive is a transparent viscous liquid. Drying to remove water from the adhesive and obtain the adhesive solid product.

The reaction temperature is selected differently according to the type of the monomer to be polymerized, and can be determined by the skilled person according to the type of the monomer, the type of the initiator, the process conditions, and the like.

If it is desired to add additives to the binder, the additives may be added during the synthesis, during or after neutralization by addition of lye.

The protective atmosphere in the invention is an atmosphere which does not participate in the reaction, such as nitrogen, helium, neon, argon, krypton or xenon.

The adhesive for the battery can be used in battery preparation and plays a role in adhesion, such as the preparation of a negative plate, the preparation of a positive plate or the preparation of a diaphragm. As one technical scheme, the adhesive for the battery is used for preparing the lithium ion battery pole piece, has high adhesive force and can improve the performance of the battery.

The invention also provides a lithium ion battery negative plate.

The lithium ion battery negative plate comprises a negative active material and an adhesive, wherein the adhesive is the adhesive for the battery.

The negative plate of the invention can be obtained by coating negative coating slurry on a current collector and drying, wherein the negative coating slurry comprises a negative active material, a conductive agent, a binder, a solvent and the like.

When the dosage of the adhesive in the negative electrode is less than or equal to 2 percent, the 90-degree stripping force of the negative electrode coating is more than or equal to 160N/m; preferably, the 90-degree peeling force of the negative coating is 160-220N/m; more preferably, the 90 DEG peel force of the negative electrode coating is 180 to 200N/m. The dosage of the binder is the ratio of the solid component content of the binder to the weight of the negative electrode material and the conductive agent material in the negative electrode, and the negative electrode material is other components except the solvent in the negative electrode coating slurry and comprises a negative electrode active material, a conductive agent, a binder and the like.

The 90 peel force test method of the present invention is described in reference to the American society for testing and materials Standard ASTM D3330.

The invention also provides a lithium ion battery.

The lithium ion battery comprises a positive electrode, a negative electrode and electrolyte, wherein the negative electrode is the lithium ion battery negative plate.

The invention also provides a battery pack comprising a plurality of batteries. The battery pack may include a battery module composed of a plurality of batteries. The cells may be connected in series or in parallel. In particular, they are connected in series.

The following examples are provided to further illustrate the embodiments of the present invention and are not intended to limit the scope of the present invention.

Example 1

In the embodiment, hydrophilic monomers of Acrylic Acid (AA), N-vinyl pyrrolidone (NVP), Acrylamide (AM) and lipophilic monomers of Acrylonitrile (AN) and Butyl Acrylate (BA) are copolymerized in AN aqueous phase to prepare the water-based adhesive for the lithium ion battery.

The preparation method comprises the following steps: adding 5 parts of acrylamide, 8 parts of N-vinyl pyrrolidone and 566 parts of distilled water into a reaction container, stirring and dissolving at the rotating speed of 300 r/min; introducing nitrogen to drive oxygen for 30 min; heating to 70 ℃, and then adding 38 parts of acrylic acid, 45 parts of acrylonitrile and 4 parts of butyl acrylate until the temperature is constant at 70 ℃; and then 0.05 part of ammonium persulfate is added to initiate reaction, the precipitate is taken out after the reaction is carried out for 9 hours, and alkali liquor is added to neutralize the pH value to 6.5-9, so as to prepare the transparent water-based adhesive for the lithium ion battery.

The molecular weight and the molecular weight distribution of the water-based adhesive for the lithium ion battery are measured by adopting a gel chromatography (GPC method), and the types of the testing equipment are as follows: waters Alliance E2695. And (3) testing conditions are as follows: three chromatographic columns, namely Waters StyRagel HR 3, 4 and 5 (water), are connected in series; the mobile phase Buffer pH is 7.23M NaCl standard PAA temperature 0.6 ml/min. As shown in FIG. 1, the test results showed that small molecules having a molecular weight of 5 ten thousand or less accounted for 0.2 wt%, low molecules having a molecular weight of 10 ten thousand or less accounted for 0.8 wt%, and high molecules having a molecular weight of 50 ten thousand or more accounted for 73 wt%.

Example 2

In the embodiment, hydrophilic monomers of methacrylic acid and N-methacrylamide, and lipophilic monomers of methacrylonitrile, methyl acrylate and hydroxypropyl acrylate are copolymerized in a water phase to prepare the water-based adhesive for the lithium ion battery.

The preparation method comprises the following steps: adding 7 parts of N-methacrylamide and 400 parts of distilled water into a reaction vessel, and stirring for dissolving; introducing nitrogen to drive oxygen for 30 min; heating to 65 ℃, and then adding 23 parts of methacrylic acid, 18 parts of methyl acrylate, 31 parts of hydroxypropyl acrylate and 21 parts of methacrylonitrile until the temperature rises to 65 ℃; and then adding an ammonium persulfate initiator to initiate reaction, taking out the precipitate after reacting for 22 hours, adding alkali liquor to neutralize the pH value to 6.5-9, and preparing the aqueous binder for the lithium ion battery.

The molecular weight and molecular weight distribution were measured by the method of example 1, and the small molecules having a molecular weight of 5 ten thousand or less accounted for 0.4 wt%, the low molecules having a molecular weight of 10 ten thousand or less accounted for 5 wt%, and the high molecules having a molecular weight of 50 ten thousand or more accounted for 60 wt%.

Example 3

In the embodiment, hydrophilic monomers such as 2-acrylamide-2-methylpropanesulfonic acid, N-diethylacrylamide and itaconate, and lipophilic monomers such as 2-ethylhexyl acrylate, cyclohexyl methacrylate and ethyl methacrylate are copolymerized in a water phase to prepare the water-based adhesive for the lithium ion battery.

The preparation method comprises the following steps: adding 18 parts of 2-acrylamide-2-methylpropanesulfonic acid, 22 parts of N, N-diethylacrylamide, 5 parts of itaconate and 400 parts of distilled water into a reaction vessel, and stirring for dissolving; then 20 parts of 2-ethylhexyl acrylate, 12 parts of cyclohexyl methacrylate and 22 parts of ethyl methacrylate are added, and nitrogen is introduced to expel oxygen for 30 min; heating to 75 ℃, adding a potassium persulfate initiator to initiate reaction, taking out the precipitate after reacting for 18h, adding alkali liquor to neutralize the pH value to 6.5-9, and preparing the aqueous binder for the lithium ion battery.

The molecular weight and molecular weight distribution were measured by the method of example 1, and the small molecules having a molecular weight of 5 ten thousand or less accounted for 0.2 wt%, the low molecules having a molecular weight of 10 ten thousand or less accounted for 2 wt%, and the high molecules having a molecular weight of 50 ten thousand or more accounted for 61 wt%.

Example 4

In the embodiment, hydrophilic monomer acrylate, 2-methacrylamide, vinyl sulfonate and lipophilic monomer ethyl acrylate, vinyl acetate and methacrylic acid-hydroxyethyl are copolymerized in a water phase to prepare the water-based adhesive for the lithium ion battery.

The preparation method comprises the following steps: adding 31 parts of acrylate, 12 parts of 2-methacrylamide, 12 parts of vinyl sulfonate and 400 parts of distilled water into a reaction vessel, and stirring for dissolving; then adding 31 parts of ethyl acrylate, 9 parts of vinyl acetate and 5 parts of methacrylic acid-hydroxyethyl ester, and introducing nitrogen to drive oxygen for 30 min; heating to 60 ℃, adding an ammonium persulfate initiator to initiate reaction, taking out a precipitate after reacting for 20 hours, adding alkali liquor to neutralize the pH value to 6.5-9, and preparing the aqueous binder for the lithium ion battery.

The molecular weight and molecular weight distribution were measured by the method of example 1, and the small molecules having a molecular weight of 5 ten thousand or less accounted for 0.5 wt%, the low molecules having a molecular weight of 10 ten thousand or less accounted for 1 wt%, and the high molecules having a molecular weight of 50 ten thousand or more accounted for 70 wt%.

Example 5

In the embodiment, hydrophilic monomers of maleic acid, N-vinyl pyrrolidone and N-hydroxypropyl acrylamide, and lipophilic monomers of styrene, 2-ethylhexyl methacrylate and hydroxypropyl methacrylate are copolymerized in an aqueous phase to prepare the aqueous binder for the lithium ion battery.

The preparation method comprises the following steps: adding 3 parts of N-hydroxypropyl acrylamide and 400 parts of distilled water into a reaction container, and stirring for dissolving; then adding 31 parts of maleic acid, 10 parts of propylene sulfonic acid, 18 parts of N-vinyl pyrrolidone, 13 parts of styrene, 12 parts of 2-ethylhexyl methacrylate and 13 parts of hydroxypropyl methacrylate, and introducing nitrogen to drive oxygen for 30 min; heating to 55 ℃, adding a potassium persulfate initiator to initiate reaction, taking out the precipitate after reacting for 25h, adding alkali liquor to neutralize the pH value to 6.5-9, and preparing the aqueous binder for the lithium ion battery.

The molecular weight and molecular weight distribution were measured by the method of example 1, and the small molecules having a molecular weight of 5 ten thousand or less accounted for 0.6 wt%, the low molecules having a molecular weight of 10 ten thousand or less accounted for 1.4 wt%, and the high molecules having a molecular weight of 50 ten thousand or more accounted for 65 wt%.

Example 6

In the embodiment, hydrophilic monomers of acrylic acid, methacrylic acid, N-hydroxyethyl acrylamide, acrylic sulfonic acid and lipophilic monomers of 2-ethylhexyl acrylate, ethyl acrylate and isobornyl methacrylate are copolymerized in a water phase to prepare the water-based adhesive for the lithium ion battery.

The preparation method comprises the following steps: adding 8 parts of N-hydroxyethyl acrylamide, 9 parts of propylene sulfonic acid and 400 parts of distilled water into a reaction vessel, and stirring for dissolving; then adding 13 parts of acrylic acid, 15 parts of methacrylic acid, 30 parts of 2-ethylhexyl acrylate, 15 parts of ethyl acrylate and 10 parts of isobornyl methacrylate, and introducing nitrogen to expel oxygen for 30 min; heating to 67 ℃, adding an ammonium persulfate initiator to initiate reaction, taking out a precipitate after reacting for 23 hours, adding alkali liquor to neutralize the pH value to 6.5-9, and preparing the aqueous binder for the lithium ion battery.

The molecular weight and molecular weight distribution were measured by the method of example 1, and the small molecules having a molecular weight of 5 ten thousand or less accounted for 0.2 wt%, the low molecules having a molecular weight of 10 ten thousand or less accounted for 4.5 wt%, and the high molecules having a molecular weight of 50 ten thousand or more accounted for 63 wt%.

Example 7

In this example, 28 parts of hydrophilic monomer, 2-acrylamido-2-methylpropanesulfonic acid, 32 parts of N, N-diethylacrylamide, 10 parts of itaconate, and 10 parts of lipophilic monomer, 2-ethylhexyl acrylate, 12 parts of cyclohexyl methacrylate, and 8 parts of ethyl methacrylate were copolymerized in an aqueous phase to prepare an aqueous binder for a lithium ion battery.

The preparation method comprises the following steps: adding 28 parts of 2-acrylamide-2-methylpropanesulfonic acid, 32 parts of N, N-diethylacrylamide, 10 parts of itaconate and 400 parts of distilled water into a reaction vessel, and stirring for dissolving; then adding 10 parts of 2-ethylhexyl acrylate, 12 parts of cyclohexyl methacrylate and 8 parts of ethyl methacrylate, and introducing nitrogen to drive oxygen for 30 min; heating to 73 ℃, adding an ammonium persulfate initiator to initiate reaction, taking out a precipitate after reacting for 19h, adding alkali liquor to neutralize the pH value to 6.5-9, and preparing the aqueous binder for the lithium ion battery.

The molecular weight and molecular weight distribution were measured by the method of example 1, and the small molecules having a molecular weight of 5 ten thousand or less accounted for 0.3 wt%, the low molecules having a molecular weight of 10 ten thousand or less accounted for 3.3 wt%, and the high molecules having a molecular weight of 50 ten thousand or more accounted for 66 wt%.

Example 8

In the embodiment, hydrophilic monomers of acrylic acid, N-vinyl pyrrolidone and N-hydroxyethyl acryloyl, and lipophilic monomers of acrylonitrile and hydroxypropyl acrylate are copolymerized in a water phase to prepare the water-based adhesive for the lithium ion battery.

The preparation method comprises the following steps: adding 22 parts of N-hydroxyethyl acryloyl and 300 parts of distilled water into a reaction vessel, and stirring for dissolving; adding 30 parts of acrylic acid and 15 parts of N-vinyl pyrrolidone, and then introducing nitrogen to drive oxygen for a certain time; after heating to 66 ℃, 25 parts of acrylonitrile and 8 parts of hydroxypropyl acrylate are added; and then adding a certain amount of potassium persulfate to initiate reaction, taking out the precipitate after the reaction is carried out for 13 hours, adding alkali liquor to neutralize the pH value to 6.5-9, and preparing the aqueous binder for the lithium ion battery with the components.

The molecular weight and molecular weight distribution were measured by the method of example 1, and 3.1 wt% was accounted for by small molecules having a molecular weight of 5 ten thousand or less, 8.4 wt% was accounted for by low molecules having a molecular weight of 10 ten thousand or less, and 48 wt% was accounted for by high molecules having a molecular weight of 50 ten thousand or more.

Comparative example 1

In the comparative example, hydrophilic monomers of Acrylic Acid (AA), N-vinyl pyrrolidone (NVP), Acrylamide (AM) and lipophilic monomers of Acrylonitrile (AN) and Butyl Acrylate (BA) are copolymerized in a water phase to prepare the water-based adhesive for the lithium ion battery.

The preparation method comprises the following steps: adding 5 parts of acrylamide, 8 parts of N-vinyl pyrrolidone and 566 parts of distilled water into a reaction container, stirring and dissolving at the rotating speed of 300 r/min; adding 38 parts of acrylic acid, adding alkali liquor to adjust the pH value, and introducing nitrogen to drive oxygen for 30 min; heating to 70 ℃, adding 45 parts of acrylonitrile and 4 parts of butyl acrylate, and keeping the temperature at 70 ℃; and then 0.21 part of ammonium persulfate is added to initiate reaction, 0.21 part of ammonium persulfate is supplemented every 3 hours to promote conversion, and after 24 hours of reaction, alkali liquor is added to neutralize the pH value to 6.5-9, so that the aqueous binder for the lithium ion battery with the components is prepared.

The molecular weight and molecular weight distribution were measured by the method of example 1, and the results are shown in FIG. 1, in which small molecules having a molecular weight of 5 ten thousand or less account for 5 wt%, low molecules having a molecular weight of 10 ten thousand or less account for 10 wt%, and high molecules having a molecular weight of 50w or more account for 39 wt%.

Comparative example 2

The binder of comparative example 2 was composed of CMC (sodium carboxymethylcellulose) and SBR (styrene butadiene rubber), CMC: SBR (proportion by weight of solid) 1:2

Comparative example 3

The adhesive of comparative example 3 was the product prepared in patent ZL01108511.8, example four.

Comparative example 4

In the comparative example, hydrophilic monomer 2-acrylamide-2-methylpropanesulfonic acid, acrylic acid, lipophilic monomer 2-ethylhexyl acrylate and cyclohexyl methacrylate are copolymerized in a water phase to prepare the water-based adhesive for the lithium ion battery.

The preparation method comprises the following steps: adding 150 parts of distilled water, 15 parts of 2-acrylamide-2-methylpropanesulfonic acid and 5 parts of acrylic acid into a reaction container, and adding alkali liquor to adjust the pH value; then adding 50 parts of 2-ethylhexyl acrylate and 30 parts of cyclohexyl methacrylate, and introducing nitrogen to drive oxygen for a certain time; after heating to 75 ℃, adding a certain amount of ammonium persulfate to initiate reaction, and reacting for 17h to obtain the aqueous binder for the lithium ion battery.

The adhesive is emulsion, needs to be matched with CMC for use, and has the performance similar to SBR.

Test example 190 ℃ peel force measurement

The adhesives of the above examples and comparative examples were used to prepare negative electrode sheets, and the 90 ° peel force was measured, using the following specific methods and results:

artificial graphite (product of type 8C from jiangxi violet essence encoder) used as a negative electrode active material, a binder (binders of examples 1 to 8 and comparative examples 1 to 4, respectively), and conductive carbon black (super-p) were added to deionized water in the proportions shown in table 1 to prepare a negative electrode mixture slurry. The negative electrode mixture slurry was coated on a copper (Cu) foil current collector having a thickness of 12 μm, and then dried and rolled. The surface density of the formed product is 20mg/cm2Compacted density 1.65g/cm3And (5) a negative pole piece.

Table 1.

item/Material Negative electrode active Material (%) Conductive carbon Black (%) Adhesive (%)
Examples 1 to 8 96 2 2
Comparative example 1 96 2 2
Comparative examples 2 and 4 95 2 3
Comparative example 3 96 2 2

Note: the above proportions are the weight proportions of the solids of the various components.

Testing the pole piece bonding force: the specific method refers to ASTM-D3330 test method, equipment and tools: YISIDA mechanical tester (DS 2-50N); 3M adhesive tape: (Scotch 600/25mm wide). The specific results are shown in Table 2.

TABLE 2

Test example 2 Battery Performance test

Using the binders of examples 1, 2, 4 and comparative examples 1, 2, 3 described above, batteries were prepared and their properties were measured:

1. preparation of negative pole piece

The preparation method of the negative electrode plate is the same as that of test example 1.

2. Preparation of positive pole piece

94% by weight of lithium cobalt oxide as a positive electrode active material, 2% by weight of carbon black (super-p) as a conductive material, and 4% by weight of polyvinylidene 1, 1-difluoroethylene (PVdF) as a binder were addedWas added to an N-methyl-2-pyrrolidone (NMP) solvent, thereby preparing a positive electrode mixture slurry. Coating the slurry on an aluminum foil current collector with a thickness of 18 microns, drying, and rolling to form a positive electrode mixture slurry with an areal density of 39mg/cm2Compacted density 4.1g/cm3The positive electrode plate of (2).

3. Battery winding and electrolyte injection

A cell of specification 406379 was prepared using the electrode prepared above and the separator as above. The battery is manufactured by winding the anode, the diaphragm and the cathode, and the battery is packaged by aluminum-plastic composite. The assembled battery was charged with an electrolyte (ethylene carbonate (EC)/Ethyl Methyl Carbonate (EMC) 1/2 (volume ratio) containing 1 mol/l of lithium hexafluorophosphate (LiPF6), and was sealed by vacuum-pumping to obtain a battery ready to be activated.

4. Formation of battery

And (3) placing the obtained battery cell in an environment of 45 ℃ for standing for 20h, and then shaping the battery cell by hot pressing at 95 ℃ for 1 min. The cell is directly placed on formation equipment without being clamped and pressed by a clamp, the cell is formed in an environment of 30 +/-2 ℃, the formation current is 1C (C is the theoretical capacity of the cell), the formation time is 100min, and the formation cut-off potential is 4.35V. And then placing the battery in a charge-discharge tester to sequentially perform charge/discharge/charge, wherein the cut-off potential is 3.8V, and then performing degassing and air bag cutting operations on the battery cell to obtain the battery. In the process, only 8 minutes of hot and cold pressing is needed, other clamps are not needed for clamping each battery for formation, and the whole formation grading time is 270 minutes.

5. And (3) testing the battery performance:

5.1, cycle Performance

The current with the multiplying power of 1C is charged to 4.35V, and the voltage is constant at 4.35V; and then discharging the battery by adopting current with 1C multiplying power, wherein the cut-off voltage is 3.0V, and completing one cycle. The results are shown in FIG. 2.

As can be seen from FIG. 1, the product of example 1 of the present invention has good cycle performance.

5.2, Low temperature discharge test

Under the condition of normal temperature, charging the battery cell to 4.35V according to the current of 0.2C multiplying power, and keeping the voltage constant at 4.35V; and then placing the battery cell at different temperatures, standing for 16 hours, and discharging at a corresponding temperature by using current with a multiplying power of 1.0C, wherein the cut-off voltage is 3.0V. See figure 3 and table 3 for details.

TABLE 3

From the battery performance test results, it is obvious that the battery prepared by the binder has better performance.

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