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. A binder for a battery, characterized in that: comprising 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.

2. The binder for a battery according to claim 1, characterized in that: the weight percentage of the hydrophilic unit and the hydrophobic unit in the polymer is 30-70% and 70-30%; preferably, the weight percentage of the hydrophilic unit to the hydrophobic unit is 40-60% to 60-40%.

3. The adhesive for batteries according to claim 1 or 2, characterized in that: the medium-low molecular weight polymer accounts for less than 2 wt% of the total polymer; preferably, the medium to low molecular weight polymer comprises less than 1 wt% of the total polymer.

4. The adhesive for a battery according to any one of claims 1 to 3, characterized in that: 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.

5. The adhesive for batteries according to any one of claims 1 to 4, characterized in that: the hydrophilic unit contains a carboxyl group or a sulfonic acid group.

6. The adhesive for batteries according to any one of claims 1 to 5, characterized in that: the hydrophobic units are introduced by lipophilic monomers and the hydrophilic units are introduced by hydrophilic monomers.

7. The adhesive for batteries according to claim 6, characterized in that:

the structural formula of the lipophilic monomer is: CH (CH)₂＝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, L i, Na, K, Ca, Zn or Mg;

R⁴selected from-H, -CH₃or-COOM²；M²Including H, L i, 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、-CH₂SO₃M orM³Including H, L i, Na, K, Ca, Zn or Mg.

8. The adhesive for a battery according to claim 7, characterized in that:

R²selected from-CN, -C₆H₅、─COOCH₃、─COOCH₂CH₃、─COOCH₂CH₂CH₂CH₃、-COOC(CH₃)₃、─COOCH₂CH(CH₂CH₃)CH₂CH₂CH₂CH₃、-COOC₁₂H₂₅、-COO(CH₂)₁₇CH₃ ─COOCH₂CH₂OH、─OCOCH₃Or

9. The adhesive for a battery according to claim 7, characterized in that: 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, N-vinyl pyrrolidone, itaconic acid, itaconate, maleic acid, and maleate.

10. The binder for a battery according to claim 9, 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 acryloyl and N-hydroxypropyl acryloyl.

11. The adhesive for batteries according to claim 8, 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 acryloyl;

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

12. The adhesive for a battery according to any one of claims 1 to 11, 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%.

13. The adhesive for a battery according to any one of claims 1 to 12, characterized in that: the adhesive for the battery also comprises a solvent, wherein the solvent is an organic solvent or water.

14. The binder for a battery according to claim 13, characterized in that: the solvent is water.

15. The adhesive for a battery according to claim 14, characterized in that: the pH value is 6-12, preferably 6.5-9.

16. The adhesive for a battery according to any one of claims 13 to 15, characterized in that: the adhesive 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.

17. The method for preparing the binder for battery according to claim 16, comprising the steps of: heating hydrophilic monomer, lipophilic monomer and water to reaction temperature in protective atmosphere, adding initiator to initiate reaction to obtain solid-liquid mixture, taking precipitate, and neutralizing to obtain the water-based adhesive.

18. Use of the binder for a battery according to any one of claims 1 to 17 in the preparation of a lithium ion battery pole piece.

19. The negative plate of the lithium ion battery comprises a negative active material and a binder, and is characterized in that: the adhesive is the adhesive for a battery according to any one of claims 1 to 17.

20. 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 19.

21. A battery pack comprising a plurality of cells, the cells being the lithium ion cells of claim 20.

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, and at present, the commonly used water-based adhesives are SBR (styrene butadiene rubber emulsion), L A132, L A133 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.

However, the adhesive has limited adhesive force, the adhesive force is slightly poor when the using amount is relatively small, the using amount of the adhesive is generally 3-4 percent (calculated by solid), and when the using amount is reduced, the electrode plate cannot meet the requirement of high yield.

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, L i, Na, K, Ca, Zn or Mg, R⁴Selected from-H, -CH₃or-COOM²；M²Including H, L i, 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、-CH₂SO₃M orM³Including H, L i, 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 acryloyl and N-hydroxypropyl acryloyl.

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 a specific embodiment, the lipophilic monomers are styrene, 2-ethylhexyl methacrylate and hydroxypropyl methacrylate and the hydrophilic monomers are maleic acid, N-vinylpyrrolidone and N-hydroxypropylacryloyl. In a particular embodiment, the lipophilic monomers are 2-ethylhexyl acrylate, ethyl acrylate and isobornyl methacrylate and the hydrophilic monomers are acrylic acid, methacrylic acid, N-hydroxyethyl acryloyl and propylene 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 of the invention are weight average molecular weights (Mw). The molecular weights of the invention are measured by gel chromatography, and the types of test equipment are Waters Alliance E2695. test conditions, three columns of chromatographic columns Waters StyRagel HR 3, 4 and 5 (water) are connected in series, NaCl solution with mobile phase Buffer pH of 7.2 and 3 mol/L, standard sodium polyacrylate PAA, CAS number 9003-04-7, molecular weight 2800, 11500, 193800, 392600, 585400, 750000, 804700, 1310000 and 2250000 (standard curves are made by using the above 9 standard samples with different molecular weights), which are purchased from American Polymer Standard corporation, the temperature is 0.6 ml/min. the molecular weights measured by different chromatographic columns and the standard products are different, and the error is not more than 20%.

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, L i, Na, K, Ca, Zn or Mg;

R⁴selected from-H, -CH₃or-COOM²；M²Including H, L i, 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、-CH₂SO₃M orM³Including H, L i, 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 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-hydroxyethylacryloyl, N-hydroxypropylacryloyl. 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 a specific embodiment, the lipophilic monomers are styrene, 2-ethylhexyl methacrylate and hydroxypropyl methacrylate and the hydrophilic monomers are maleic acid, N-vinylpyrrolidone and N-hydroxypropylacryloyl. In a particular embodiment, the lipophilic monomers are 2-ethylhexyl acrylate, ethyl acrylate and isobornyl methacrylate and the hydrophilic monomers are acrylic acid, methacrylic acid, N-hydroxyethyl acryloyl and propylene 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 a dispersant, it is possible to improve the coating paste when it is preparedDispersion properties.

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.