A binder composition for secondary batteries, a negative electrode binder, and a secondary battery.

Abstract

This invention relates to a binder composition for secondary batteries and its application, as well as a negative electrode sheet for lithium-ion batteries. The polymer in the binder composition includes a thickener, an acrylic / acrylonitrile polymer, and an acrylate crosslinker polymer. The thickener accounts for 10%–15% of the total polymer weight; the acrylic / acrylonitrile polymer accounts for 10%–15% of the total polymer weight; and the acrylate crosslinker polymer accounts for 70%–80% of the total polymer weight. The binder composition consists of three components: a thickener, an acrylic / acrylonitrile polymer, and an acrylate crosslinker polymer. These three components work synergistically to improve the uniformity, coating performance, and conductivity of the material, thereby enhancing electrochemical stability; they also improve the toughness and adhesion of the material, thereby enhancing mechanical properties. Ultimately, this effectively improves adhesion, reduces electrode resistance and DCR, and increases capacity retention. A second objective of this invention is to provide a negative electrode binder containing this composition and a secondary battery. This invention belongs to the field of lithium battery material technology.

Description

Technical Field

[0001] This invention relates to the field of new energy materials, specifically to a binder composition for secondary batteries, a negative electrode binder, and a secondary battery. Background Technology

[0002] Lithium-ion batteries are one of the most widely used battery types. During their manufacturing process, electrode materials are primarily bonded together using adhesives. These adhesives uniformly fix the electrode materials to the current collector, preventing detachment or migration during battery operation and ensuring battery stability and safety. Furthermore, adhesives increase the contact area between the electrode and the current collector, enhancing adhesion and improving the utilization rate of the electrode materials. In addition, good contact performance between the electrode and the current collector helps reduce internal resistance and improve charge / discharge efficiency.

[0003] Traditional battery binder combinations typically employ a combination of sodium carboxymethyl cellulose (CMC) and styrene-butadiene rubber (SBR). Other researchers have proposed alternative solutions; for example, existing technology discloses a battery separator, its preparation method, and a lithium-ion battery, using binder particles selected from at least one of polyvinylidene fluoride (PVDF), PVDF-hexafluoropropylene, polymethyl methacrylate (PMMA), acrylate copolymers, styrene-acrylic resin, and SBR. However, these battery binders have limitations in terms of the rheological properties of the electrode slurry and battery performance. They may exhibit poor electrochemical stability, with some binder particles readily reacting chemically in the electrolyte, reducing battery cycle stability; or they may lack sufficient mechanical strength, with some binder particles exhibiting low mechanical strength, making them prone to breakage during battery charging and discharging, thus affecting battery lifespan.

[0004] Therefore, the electrochemical stability and mechanical strength of the binder material are key factors affecting the binder of the battery negative electrode.

[0005] Therefore, the technical problem to be solved in this case is: how to effectively improve the electrochemical stability and mechanical strength of the negative electrode binder in order to improve its electrochemical performance. Summary of the Invention

[0006] To address the aforementioned shortcomings, the present invention aims to provide a binder composition for secondary batteries, comprising three components: a thickener, an acrylic / acrylonitrile polymer, and an acrylate crosslinking polymer. The thickener primarily controls the suspension stability and slurry rheology of the material to improve processing, coating performance, and the dispersion uniformity of the acrylic / acrylonitrile polymer and the acrylate crosslinking polymer. The acrylic / acrylonitrile polymer primarily controls the material's adhesive strength. By using the acrylate crosslinking polymer, the toughness of the material and its dispersion and coating properties for graphite and conductive agents are regulated. Simultaneously, the acrylate crosslinking polymer achieves physical entanglement with the acrylic / acrylonitrile polymer through a crosslinking network, synergistically improving the material's adhesive performance and its dispersion and coating properties for graphite and conductive agents, thus constructing stable and uniform conductive channels. The synergistic effect of these three components improves the material's uniformity, coating performance, and conductivity, thereby enhancing electrochemical stability; it also improves the material's toughness and adhesive strength, thereby enhancing mechanical properties. Ultimately, this effectively improves adhesive strength and reduces electrode resistance, DCR, and capacity retention.

[0007] A second objective of this invention is to provide a negative electrode binder and a secondary battery containing the composition.

[0008] Therefore, the technical solution provided by the present invention is as follows:

[0009] A binder composition for secondary batteries, wherein the polymer in the binder composition includes a thickener, an acrylic / acrylonitrile polymer, and an acrylate crosslinking polymer;

[0010] The thickener accounts for 10% to 15% of the total weight of the polymer;

[0011] The acrylic acid / acrylonitrile polymer accounts for 10% to 15% of the total polymer weight;

[0012] The acrylate crosslinked polymer accounts for 70% to 80% of the total polymer weight;

[0013] The acrylate crosslinked polymer has a crosslinked network structure, and by controlling the monomer content of acrylate to be 50%–70%, it exhibits excellent flexibility. It can uniformly fix graphite and conductive carbon in the crosslinked network structure, constructing a stable conductive network channel during long-term cycling. The acrylate crosslinked polymer and the linear acrylic / acrylonitrile polymer interact through physical entanglement, which can further improve the stability of the crosslinked network and the electrochemical stability of the conductive network channel. At the same time, the excellent suspending ability provided by the thickener allows the acrylic / acrylonitrile polymer and the acrylate crosslinked polymer to be uniformly dispersed and form a relatively uniform physical entanglement structure. This physical entanglement structure can further improve the fixation stability of graphite and conductive carbon in the conductive network channel and the stability of the conductive network channel itself.

[0014] By combining the above three components, the stability of the conductive network structure can be significantly improved, maintaining the cycle stability inside the negative electrode binder during charging and discharging, and effectively reducing internal resistance and DCR.

[0015] The adhesion strength is primarily determined by the acrylic / acrylonitrile polymer, while the acrylate cross-linked polymer can further enhance it. The flexibility of the binder is mainly controlled by the acrylate cross-linked polymer. Through the interaction between the acrylic / acrylonitrile polymer and the acrylate cross-linked polymer, a negative electrode binder with strong adhesion and good flexibility can be obtained. Good flexibility can improve stability during charge and discharge processes, prevent binder cracking, and extend the binder's service life. Good adhesion not only achieves stable material bonding but also improves the contact between the binder and the current collector, which in turn reduces internal resistance and DCR. Similarly, since the mechanical strength is jointly determined by the acrylic / acrylonitrile polymer and the acrylate cross-linked polymer, it also relies on the excellent suspending ability provided by the thickener. Furthermore, there is an inherent correlation between the acrylic / acrylonitrile polymer and the thickener. The acrylic / acrylonitrile polymer has hydrophobic nitrile groups that can interact with the hydrophobic portion of the thickener, enhancing the stability and adhesion of the slurry. Simultaneously, it also increases the hydrophobic affinity between the acrylate cross-linked polymers, improving physical entanglement.

[0016] In summary, the reasonable combination of the thickener, acrylic / acrylonitrile polymer, and acrylate crosslinking polymer of this invention can effectively improve the stability and mechanical properties of the adhesive, enhance its adhesion and cycle performance, and reduce internal resistance and DCR.

[0017] In the above-mentioned binder composition for secondary batteries, the thickener A is at least one selected from carboxymethyl cellulose, carboxyethyl cellulose, polyoxyethylene ether, gelatin, carbomer, silk protein, starch, sodium alginate, guar gum, xanthan gum, chitosan, and polyacrylamide.

[0018] In the above-mentioned binder composition for secondary batteries, the synthetic monomers of the acrylic / acrylonitrile polymer are obtained by polymerizing a first acrylic monomer and a first acrylonitrile monomer;

[0019] The first acrylic monomer is equivalent to 40% to 60% of the total weight of the acrylic acid / acrylonitrile polymer;

[0020] The first acrylonitrile monomer is equivalent to 40% to 60% of the total weight of the acrylic acid / acrylonitrile polymer;

[0021] Preferably, the polyacrylic acid / acrylonitrile polymer is prepared by the following method:

[0022] 1) Feeding

[0023] Add emulsifier and deionized water to the reaction flask, heat to 60-80°C, reflux and condense, and introduce nitrogen to remove oxygen from the reaction flask.

[0024] 2) Polymerization

[0025] The initiator was added to the reaction flask, followed by the addition of the synthetic monomer over a period of 1.5 to 4 hours.

[0026] 3) Discharge

[0027] Adjust the pH to 6-8 and adjust the solid content to obtain an emulsion containing polyacrylic acid / acrylonitrile polymer.

[0028] In some preferred embodiments of the present invention, the weight ratio of acrylic monomers and acrylonitrile monomers is 40:60, 45:55, 50:50, 55:45 or 60:40.

[0029] In the above-mentioned binder composition for secondary batteries, the first acrylic monomer is acrylic acid and / or methacrylic acid; the first acrylonitrile monomer is one or more combinations of acrylonitrile, methacrylonitrile, 2-acetoxyacrylonitrile, 3-methoxyacrylonitrile, 2,3-dimethylacrylonitrile, and 3-(benzenesulfonyl)acrylonitrile.

[0030] The acrylate crosslinked polymer is formed by polymerization of reactive monomers and crosslinking monomers;

[0031] The reactive monomer is composed of acrylate monomers and functional monomers; the amount of acrylate monomers is equivalent to 50% to 70% of the weight of the reactive monomers; the functional monomers are one or more of the following: second acrylic monomers, acrylamide monomers, second acrylonitrile monomers, styrene monomers, and unsaturated monomers containing nitrogen heterocycles.

[0032] The amount of the crosslinking monomer used is equivalent to 0.15% to 0.3% of the weight of the reactant monomer.

[0033] Preferably, the acrylate crosslinked polymer is prepared by the following steps:

[0034] 1) Feeding

[0035] Add emulsifier, reaction monomer, crosslinking monomer and deionized water to the reaction flask, heat to 45-60℃, reflux and condense, and introduce nitrogen to remove oxygen in the reaction flask.

[0036] 2) Polymerization

[0037] Add the initiator dropwise over a period of 1.5–2 hours;

[0038] 3) Discharge

[0039] After filtration and pH adjustment to 6-8, an emulsion containing acrylate cross-linked polymers is obtained.

[0040] In the above-mentioned binder composition for secondary batteries, preferably, the acrylate monomer is one or a combination of C1-C10 alkyl acrylate, C1-C10 alkyl methacrylate, hydroxyalkyl acrylate, hydroxyalkyl methacrylate, methacrylate containing polyethylene glycol structural units, and methacrylate containing aromatic groups.

[0041] More preferably, the acrylate monomer is one or more combinations of C1-C8 alkyl acrylate, C1-C8 alkyl methacrylate, hydroxyalkyl acrylate, and hydroxyalkyl methacrylate.

[0042] In some embodiments of the present invention, the amount of the acrylate monomer is equivalent to 50%, 55%, 60%, 65%, or 70% of the weight of the reactant monomer.

[0043] In the above-described binder composition for secondary batteries, the second acrylic monomer is acrylic acid and / or methacrylic acid;

[0044] The acrylamide monomer is one or more combinations of acrylamide, methacrylamide, hydroxymethylacrylamide, and 2-acrylamido-2-methylpropanesulfonic acid;

[0045] The second acrylonitrile monomer is one or more combinations of acrylonitrile, methacrylonitrile, 2-acetoxyacrylonitrile, 3-methoxyacrylonitrile, 2,3-dimethylacrylonitrile, and 3-(benzenesulfonyl)acrylonitrile;

[0046] The styrene monomer is styrene and / or α-methylstyrene;

[0047] The unsaturated monomer containing a nitrogen heterocycle is one or more combinations of N-vinylpyrrolidone, vinylpyridine, and vinylimidazole;

[0048] The acrylate monomers are one or more combinations of methyl acrylate, ethyl acrylate, n-butyl acrylate, n-amyl acrylate, isoamyl acrylate, methyl methacrylate, ethyl methacrylate, n-butyl methacrylate, n-amyl methacrylate, isoamyl methacrylate, n-hexyl methacrylate, 2-ethylhexyl methacrylate, octyl methacrylate, isodecyl methacrylate, hydroxyethyl acrylate, hydroxyethyl methacrylate, hydroxypropyl acrylate, hydroxypropyl methacrylate, octadecyl polyethylene glycol acrylate, octadecyl polyethylene glycol methacrylate, methoxy polyethylene glycol methacrylate, and alkoxyphenol acrylate.

[0049] In the above-mentioned binder composition for secondary batteries, the reactive monomer is composed of acrylate, second acrylic monomer, acrylamide monomer, and second acrylonitrile monomer;

[0050] The second acrylic monomer is equivalent to 15% to 25% of the weight of the reactant monomer;

[0051] The acrylamide monomers are equivalent to 5% to 15% of the weight of the reactant monomers;

[0052] The second acrylonitrile monomer is equivalent to 5% to 15% of the weight of the reactant monomer.

[0053] In the above-mentioned binder composition for secondary batteries, the crosslinking monomer is one or more combinations of divinylbenzene, diallyl phthalate, trimethylolpropane triacrylate, trimethylolpropane tri(meth)acrylate, triethylene glycol di(meth)acrylate, dipentaerythritol hexa(meth)acrylate, divinyl glycol, diallyl itaconic acid, diallyl maleate, trimethylolpropane diallyl acrylate, divinyl glycol, pentaerythritol triacrylate, ditripropylene glycol diacrylate, dipropylene glycol diacrylate, and ethoxylated (30) bisphenol A diacrylate.

[0054] It should be noted that the adhesive composition of the present invention also includes a solvent, which is generally water. The solid content of the adhesive composition of the present invention is generally recommended to be sold in the form of 10 wt%, but the solid content can be adjusted according to customer needs, and can fluctuate within the range of 5 to 30 wt%. When using this adhesive composition, customers use it in conjunction with graphite, conductive carbon, etc., and add deionized water to prepare a slurry. Therefore, in the present invention, the solid content of the adhesive composition itself does not have a decisive impact on the formulation and performance of the final slurry.

[0055] In addition, the present invention also discloses a negative electrode binder, including graphite, conductive carbon, and binder compositions as described above.

[0056] Finally, a secondary battery is also disclosed, comprising a positive electrode, a negative electrode, an electrolyte, and a separator; the negative electrode comprises a current collector and a negative electrode binder as described above coated on the current collector.

[0057] In the aforementioned secondary battery, the secondary battery is a lithium-ion battery or a sodium-ion battery.

[0058] Compared with the prior art, the technical solution provided by the present invention has the following technical advantages:

[0059] The binder composition of this invention comprises three components: a thickener, an acrylic / acrylonitrile polymer, and an acrylate crosslinking polymer. The thickener primarily controls the suspension stability and slurry rheology of the material to improve its processing and coating properties, as well as the dispersion uniformity of the acrylic / acrylonitrile polymer and the acrylate crosslinking polymer. The acrylic / acrylonitrile polymer primarily controls the material's adhesion. By rationally controlling the glass transition temperature of the acrylate crosslinking polymer, the material's toughness and its dispersion and coating properties for graphite and conductive agents are regulated. Simultaneously, the acrylate crosslinking polymer achieves physical entanglement with the acrylic / acrylonitrile polymer through a crosslinking network, synergistically improving the material's adhesion and its dispersion and coating properties for graphite and conductive agents, thus constructing stable and uniform conductive channels. The synergistic effect of these three components improves the material's uniformity, coating properties, and conductivity, thereby enhancing electrochemical stability; it also improves the material's toughness and adhesion, thereby enhancing mechanical properties. Ultimately, this effectively improves adhesion, reduces electrode resistance and DCR, and increases capacity retention. Detailed Implementation

[0060] The technical solution of the present invention will be further described in detail below with reference to specific embodiments, but this does not constitute any limitation on the present invention.

[0061] Examples 1 to 18, Comparative Examples 1 to 6

[0062] This embodiment provides a binder composition for secondary batteries, which is prepared by the following method:

[0063] 1) Synthesis of acrylic acid / acrylonitrile polymer B emulsion

[0064] Add 0.5g of emulsifier sodium dodecyl sulfate and 300g of deionized water to a five-necked flask, heat to 60℃, reflux and condense, and purge with nitrogen to remove oxygen for 1 hour. Then add 0.15g of initiator sodium persulfate to the five-necked flask at once, followed by the addition of the synthetic monomer over 2 hours. After the addition is complete, filter the mixture through a 180-mesh filter, neutralize the pH to 7 with NaOH, and adjust the solid content to 10% with deionized water to obtain the acrylic acid / acrylonitrile polymer B emulsion.

[0065] 2) Synthesis of acrylate crosslinked polymer C emulsion

[0066] Add 1.5g of emulsifier sodium dodecyl sulfate, 400g of deionized water, acrylate monomers, functional monomers, and crosslinking monomers to a five-necked flask. Heat to 45°C, reflux and condense, purge with nitrogen to remove oxygen for 1 hour, then add 0.25g of initiator sodium persulfate dropwise over 1.5 hours. After the addition is complete, filter using a 180-mesh filter, neutralize the pH to 7 with NaOH, and adjust the solid content to 10% with deionized water to obtain acrylate crosslinking polymer C emulsion.

[0067] 3) Mixed adhesive

[0068] Thickener A, acrylic / acrylonitrile polymer B emulsion prepared in step 1), and acrylate crosslinked polymer C emulsion prepared in step 2) are mixed, and the solid content is adjusted to 10% with deionized water to obtain an adhesive composition.

[0069] The formulations of monomers and the proportions of each polymer in Examples 1 to 18 and Comparative Examples 1 to 6 of the present invention are referenced in Table 1.

[0070] Table 1. Monomer formulations and proportions for the examples and comparative examples.

[0071]

[0072]

[0073] It should be noted that the weight ratio of A, B, and C mentioned above refers to the weight ratio of thickener A, acrylic / acrylonitrile polymer in acrylic / acrylonitrile polymer B solution, and acrylate crosslinking polymer C in acrylate crosslinking polymer C solution.

[0074] Taking Example 1 as an example, the weight ratio of A, B, and C is 10:10:80; the amount of polymer A is 10g, the amount of acrylic acid / acrylonitrile polymer B solution is 100g, and the amount of acrylate crosslinking polymer C solution is 800g; when the secondary battery binder composition of the present invention is to be diluted to a final solid content of 10%, 90g of water is added to form a 1000g solution.

[0075] Examples 19 to 25

[0076] The preparation method of the secondary battery binder compositions in Examples 19 to 25 is the same as in Example 1; the thickener A and acrylic / acrylonitrile polymer B are the same as in Example 1, and the weight ratio of thickener A, acrylic / acrylonitrile polymer B and acrylate crosslinking polymer C is 10:10:80.

[0077] The selection and proportion of monomers used in the synthesis of acrylate crosslinking polymer C can be changed, as detailed in Table 2;

[0078] Table 2. Monomer formulations of acrylate crosslinking polymer C from Examples 19 to 25.

[0079]

[0080] Examples 26 to 29

[0081] The preparation methods of the secondary battery binder compositions in Examples 26 to 29 are the same as in Example 1; the thickener A and the acrylate crosslinking polymer C are the same as in Example 1, and the weight ratio of thickener A, acrylic acid / acrylonitrile polymer B and acrylate crosslinking polymer C is 10:10:80;

[0082] The monomer selection and ratio of acrylic acid / acrylonitrile polymer B can be changed, as detailed in Table 3;

[0083] Table 3. Monomer formulations of acrylic acid / acrylonitrile polymer B in Examples 26-29

[0084]

[0085] Example 30

[0086] The synthesis of a secondary battery binder composition includes the following steps:

[0087] 1) Synthesis of polyacrylic acid / acrylonitrile polymer B emulsion

[0088] Add 0.4g of sodium dodecyl sulfate emulsifier and 300g of deionized water to a five-necked flask, heat to 70℃, reflux and condense, and purge with nitrogen to remove oxygen for 1 hour. Then add 0.25g of sodium persulfate initiator to the five-necked flask at once, followed by the dropwise addition of 40g of acrylic acid and 60g of acrylonitrile over 3 hours. After the addition is complete, filter the mixture through a 180-mesh filter, neutralize the pH to 7 with NaOH, and adjust the solid content to 10% with deionized water to obtain polyacrylic acid / acrylonitrile polymer B emulsion.

[0089] 2) Synthesis of acrylate crosslinked polymer C emulsion

[0090] Add 1g of sodium dodecyl sulfate (emulsifier), 400g of deionized water, 60g of methyl acrylate, 20g of acrylic acid, 10g of acrylamide, 10g of acrylonitrile, and 0.25g of diallyl phthalate to a five-necked flask. Heat to 50°C, reflux and condense, purge with nitrogen to remove oxygen for 1 hour, then add 0.15g of sodium persulfate (initiator) dropwise over 2 hours. After the addition is complete, filter using a 180-mesh filter, neutralize the pH to 7 with NaOH, and adjust the solid content to 10% with deionized water to obtain the acrylate crosslinked polymer C emulsion.

[0091] 3) Mixed adhesive

[0092] Thickener A (carboxymethyl cellulose), polyacrylic acid / acrylonitrile polymer B emulsion prepared in step 1), and acrylate crosslinked polymer C emulsion prepared in step 2) were mixed in a mass ratio of 10:100:800, and the solid content was adjusted to 10% with deionized water to obtain the adhesive composition.

[0093] Example 31

[0094] The synthesis of a secondary battery binder composition includes the following steps:

[0095] 1) Synthesis of polyacrylic acid / acrylonitrile polymer B emulsion

[0096] Add 0.6g of sodium dodecyl sulfate emulsifier and 300g of deionized water to a five-necked flask, heat to 80℃, reflux and condense, and purge with nitrogen to remove oxygen for 1 hour. Then add 0.3g of sodium persulfate initiator to the five-necked flask at once, followed by the dropwise addition of 40g of acrylic acid and 60g of acrylonitrile over 4 hours. After the addition is complete, filter the mixture through a 180-mesh filter, neutralize the pH to 7 with NaOH, and adjust the solid content to 10% with deionized water to obtain polyacrylic acid / acrylonitrile polymer B emulsion.

[0097] 2) Synthesis of acrylate crosslinked polymer C emulsion

[0098] Add 3g of sodium dodecyl sulfate (emulsifier), 400g of deionized water, 60g of methyl acrylate, 20g of acrylic acid, 10g of acrylamide, 10g of acrylonitrile, and 0.25g of diallyl phthalate to a five-necked flask. Heat to 60°C, reflux and condense, purge with nitrogen to remove oxygen for 1 hour, then add 0.25g of sodium persulfate (initiator) dropwise over 2 hours. After the addition is complete, filter using a 180-mesh filter, neutralize the pH to 7 with NaOH, and adjust the solid content to 10% with deionized water to obtain the acrylate crosslinked polymer C emulsion.

[0099] 3) Mixed adhesive

[0100] Thickener A (carboxymethyl cellulose), polyacrylic acid / acrylonitrile polymer B emulsion prepared in step 1), and acrylate crosslinked polymer C emulsion prepared in step 2) were mixed in a mass ratio of 10:100:800, and the solid content was adjusted to 10% with deionized water to obtain the adhesive composition.

[0101] Comparative Example 7

[0102] A secondary battery binder composition is composed of carboxymethyl cellulose and styrene-butadiene rubber emulsion; the mass ratio of styrene-butadiene rubber in the carboxymethyl cellulose and styrene-butadiene rubber emulsion is 1.2:1.3, and the composition has a solid content of 50 wt%.

[0103] Comparative Example 8

[0104] The secondary battery binder composition contains commercially available LA136D, CMC (carboxymethyl cellulose), and SBR. The supplier of commercially available LA136D is Sichuan Yindile.

[0105] The commercially available LA136D, CMC:SBR weight ratio is 1.5:0.5:0.5;

[0106] SBR refers to styrene-butadiene rubber in styrene-butadiene emulsion.

[0107] Comparative Example 9

[0108] A secondary battery binder composition containing commercially available product 288C and CMC (carboxymethyl cellulose):SBR. The supplier of commercially available product 288C is Blue Ocean Blackstone.

[0109] The weight ratio of commercially available 288C and CMC:SBR products is 1.5:0.5:0.5.

[0110] SBR refers to styrene-butadiene rubber in styrene-butadiene emulsion.

[0111] Preparation and performance testing of secondary batteries

[0112] 1. Preparation of negative electrode sheet for lithium-ion batteries

[0113] The binder compositions of Examples 1 to 31 and Comparative Examples 1 to 9 were dispersed in deionized water, then conductive carbon was added and dispersed at high speed of 1000 rpm for 2 hours. Graphite was then added and dispersion at high speed continued for 2 hours, resulting in a slurry solid content of 50 wt%. After the fineness of the negative electrode slurry was tested and found to be qualified, it was stirred at low speed of 300 rpm for 30 minutes to defoam, then coated onto copper foil and dried to obtain a lithium-ion battery negative electrode sheet. The areal density of the lithium-ion battery negative electrode sheet was controlled to be 220 g / m². 2 The compacted surface density is 1.6 kg / m³. 3 .

[0114] The mass ratio of graphite, conductive carbon, and binder composition (based on the dry weight of the composition) is 96:1.5:2.5.

[0115] 2. Preparation of lithium-ion batteries

[0116] The active components of the positive electrode are: NCM nickel-cobalt-manganese 811: conductive carbon: PVDF5130 in a weight ratio of 96.75:2:1.25; the current collector of the positive electrode is aluminum foil.

[0117] The diaphragm is made of PP (polypropylene);

[0118] The above-mentioned negative and positive electrode sheets were assembled into a lithium-ion battery and subjected to constant current charge and discharge tests. The electrolyte used was Tinci Materials electrolyte, grade TC-E8630N3. The charging termination voltage was 2.7 to 4.2V, the charge and discharge rate was 1C, and the cut-off current was 100mA.

[0119] 3. Performance Testing

[0120] 3.1 Peel force test: The negative electrode sheet was made into test samples with a width of 2cm and a length of about 5cm. The peel force of each test sample was tested by a universal tensile tester at 180° with a pulling speed of 2mm / s. The unit of peel force is N / cm.

[0121] 3.2 Slurry viscosity test: The viscosity of the slurry was tested using a rotational viscometer with an RV04 or RV05 rotor at a speed of 20 rpm.

[0122] 3.3 Electrode Resistance Test: The resistance of the negative electrode was tested using a Yuaneng Technology BER2500 resistance meter at a pressure of 25MPa.

[0123] 3.4 Test method for capacity retention rate after 5 cycles of 3C / 1C charge and discharge: The uncharged lithium ions were placed in an environment of 25℃±2℃ and charged to 4.25V using a 3C rate constant current and constant voltage method. Then, they were discharged to 2.75V using a 1C rate constant current method. The capacity retention rate was obtained by comparing the battery capacity before and after the cycle.

[0124] 3.5 Battery DCR: The battery DCR was tested using a HIOKI BT4560 battery impedance meter. The measurement frequency range was set between 0.01Hz and 1.05kHz. The meter was connected to the positive and negative terminals of the battery and electrochemical impedance spectroscopy (EIS) was performed.

[0125] The test results are shown in Table 4;

[0126] Table 4 Test Results

[0127]

[0128]

[0129]

[0130] Results analysis:

[0131] 1. As can be seen from Examples 1 to 31 of the present invention, the slurry viscosity is between 3400 and 7100 cp, the peel strength is between 0.16 and 0.27 N / cm, the electrode resistance is less than 0.784 mΩ, the battery DCR is less than 47.22, and the discharge capacity retention rate is maintained above 86.3%. The compositions of the various embodiments of the present invention exhibit good electrochemical performance when applied to batteries and good mechanical properties when applied to electrodes.

[0132] 2. As can be seen from Examples 1 to 5, the slurry viscosity is closely related to carboxymethyl cellulose; the more carboxymethyl cellulose used, the higher the slurry viscosity. The peel strength is closely related to the amount of acrylic acid / acrylonitrile used; the more acrylic acid / acrylonitrile used, the higher the peel strength. The electrode resistance and DCR of Examples 1 to 5 are all kept at a low level, and the capacity retention rate is maintained above 86.3%, which shows good electrochemical performance.

[0133] 3. As can be seen from the comparison between Examples 1, 6, and 7, the increase or decrease of crosslinking agent can affect the viscosity and peel strength of the slurry. Although the crosslinking polymer of acrylate has the slightest impact on the mechanical properties of the slurry, the change in its degree of crosslinking will directly affect the mechanical properties of the slurry. At the same time, controlling the fluctuation of crosslinking agent within a reasonable range will affect the electrode resistance, DCR, and capacity retention, but all of them will be maintained in a state of good performance.

[0134] 4. As can be seen from Examples 8 and 9, increasing the amount of acrylic acid in the acrylic acid / acrylonitrile polymer improves the performance in terms of peel strength and slurry viscosity, but has no significant effect on electrochemical performance.

[0135] 5. As can be seen from Examples 1, 15, and 16, changing the thickener most significantly affects the viscosity of the microslurry. As can be seen from Examples 1, 17, and 18, further changing the acrylate content in the acrylate crosslinker resulted in a slight weakening of properties such as electrode resistance, DCR, and capacity retention. In particular, regarding capacity retention after 5 cycles of 3C / 1C charge-discharge, Examples 17 and 18 showed a consistent weakening compared to Examples 1, 10, to 14, indicating that controlling the acrylate content between 50% and 70% is an effective means of optimizing cycleability.

[0136] 6. As can be seen from Examples 1, 19 to 25, and 26 to 29, when the types of monomers in the acrylate crosslinking polymer and the types of monomers in the acrylic acid / acrylonitrile polymer are changed, the peel strength, slurry viscosity, and electrochemical performance remain at a relatively good level. As can be seen from Examples 30 and 31, the rational adjustment of the preparation process has no significant impact on the performance.

[0137] 7. As can be seen from Examples 1, 1, and 2, the absence of acrylic acid / acrylonitrile polymer or acrylonitrile will reduce the viscosity of the slurry and significantly reduce the peel strength. At the same time, the weakening of mechanical properties will lead to a deterioration of electrochemical performance. This is because acrylic acid / acrylonitrile polymer can improve the mechanical properties of the binder. At the same time, there is an interaction between acrylonitrile, thickener, and acrylate crosslinking polymer. The absence of any one of them will significantly reduce the mechanical properties of the slurry and its electrochemical performance after application in a battery.

[0138] 8. As can be seen from Comparative Examples 3 to 5, increasing the amount of acrylic acid / acrylonitrile directly leads to a significant increase in viscosity and peel strength, and thereby reduces the amount of acrylate crosslinking polymer, further weakening the electrochemical performance. Conversely, reducing the amount of thickener leads to a decrease in slurry viscosity, and the suspension uniformity and physical entanglement uniformity between the acrylic acid / acrylonitrile polymer and the acrylate crosslinking polymer deteriorate, thus weakening the electrochemical performance. As can be seen from Comparative Example 6, when the acrylate polymer is linear, its electrochemical performance deteriorates significantly, and the peel strength and slurry viscosity also weaken to some extent.

[0139] 9. The adhesive composition of the present invention and its performance when applied to a battery show significantly improved peel strength and electrochemical performance compared to commercially available products (Comparative Examples 7 to 9).

[0140] The above embodiments are preferred embodiments of the present invention, but the embodiments of the present invention are not limited to the above embodiments. Any changes, modifications, substitutions, combinations, or simplifications made without departing from the spirit and principle of the present invention shall be considered equivalent substitutions and shall be included within the protection scope of the present invention.

Claims

1. A binder composition for secondary batteries, characterized in that, The polymers in the adhesive composition include thickeners, acrylic / acrylonitrile polymers, and cross-linked acrylate polymers. The thickener accounts for 10% to 15% of the total weight of the polymer; The acrylic acid / acrylonitrile polymer accounts for 10% to 15% of the total polymer weight; The acrylate crosslinked polymer accounts for 70% to 80% of the total polymer weight.

2. The binder composition for secondary batteries according to claim 1, characterized in that, The thickener is at least one of carboxymethyl cellulose, carboxyethyl cellulose, polyoxyethylene ether, gelatin, carbomer, silk protein, starch, sodium alginate, guar gum, xanthan gum, chitosan, and polyacrylamide.

3. The binder composition for secondary batteries according to claim 1, characterized in that, The acrylic acid / acrylonitrile polymer is obtained by polymerizing a first acrylic acid monomer and a first acrylonitrile monomer; The first acrylic monomer is equivalent to 40% to 60% of the total weight of the acrylic acid / acrylonitrile polymer; The first acrylonitrile monomer accounts for 40% to 60% of the total weight of the acrylic acid / acrylonitrile polymer.

4. The binder composition for secondary batteries according to claim 3, characterized in that, The first acrylic monomer is acrylic acid and / or methacrylic acid; the first acrylonitrile monomer is one or more combinations of acrylonitrile, methacrylonitrile, 2-acetoxyacrylonitrile, 3-methoxyacrylonitrile, 2,3-dimethylacrylonitrile, and 3-(benzenesulfonyl)acrylonitrile.

5. The binder composition for secondary batteries according to claim 1, characterized in that, The acrylate crosslinked polymer is formed by the polymerization of reactive monomers and crosslinking monomers.

6. The binder composition for secondary batteries according to claim 5, characterized in that, The reactive monomer is composed of acrylate monomers and functional monomers; the amount of acrylate monomers is equivalent to 50% to 70% of the weight of the reactive monomers; the functional monomers are one or more of the following: second acrylic monomers, acrylamide monomers, second acrylonitrile monomers, styrene monomers, and unsaturated monomers containing nitrogen heterocycles. The acrylate monomer is one or a combination of C1-C10 alkyl acrylate, C1-C10 alkyl methacrylate, hydroxyalkyl acrylate, hydroxyalkyl methacrylate, methacrylate containing polyethylene glycol structural units, and methacrylate containing aromatic groups. The amount of the crosslinking monomer used is equivalent to 0.15% to 0.3% of the weight of the reactant monomer.

7. The binder composition for secondary batteries according to claim 6, characterized in that, The second acrylic monomer is acrylic acid and / or methacrylic acid; The acrylamide monomer is one or more combinations of acrylamide, methacrylamide, hydroxymethylacrylamide, and 2-acrylamido-2-methylpropanesulfonic acid; The second acrylonitrile monomer is one or more combinations of acrylonitrile, methacrylonitrile, 2-acetoxyacrylonitrile, 3-methoxyacrylonitrile, 2,3-dimethylacrylonitrile, and 3-(benzenesulfonyl)acrylonitrile; The styrene monomer is styrene and / or α-methylstyrene; The unsaturated monomer containing a nitrogen heterocycle is one or more combinations of N-vinylpyrrolidone, vinylpyridine, and vinylimidazole; The acrylate monomers are one or more of the following: methyl acrylate, ethyl acrylate, n-butyl acrylate, n-amyl acrylate, isoamyl acrylate, methyl methacrylate, ethyl methacrylate, n-butyl methacrylate, n-amyl methacrylate, isoamyl methacrylate, n-hexyl methacrylate, 2-ethylhexyl methacrylate, octyl methacrylate, isodecyl methacrylate, hydroxyethyl acrylate, hydroxyethyl methacrylate, hydroxypropyl acrylate, hydroxypropyl methacrylate, octadecyl polyethylene glycol acrylate, octadecyl polyethylene glycol methacrylate, methoxy polyethylene glycol methacrylate, and alkoxyphenol acrylate.

8. The binder composition for secondary batteries according to claim 6, characterized in that, The reactive monomers are composed of acrylate monomers, second acrylate monomers, acrylamide monomers, and second acrylonitrile monomers; The second acrylic monomer is equivalent to 15% to 25% of the weight of the reactant monomer; The acrylamide monomers are equivalent to 5% to 15% of the weight of the reactant monomers; The second acrylonitrile monomer is equivalent to 5% to 15% of the weight of the reactant monomer.

9. The binder composition for secondary batteries according to claim 5, characterized in that, The crosslinking monomer is one or more of the following: diallyl phthalate, trimethylolpropane triacrylate, trimethylolpropane tri(meth)acrylate, triethylene glycol di(meth)acrylate, pentaerythritol hexa(meth)acrylate, divinyl glycol, diallyl itaconic acid, diallyl maleate, trimethylolpropane diallyl acrylate, divinyl glycol, pentaerythritol triacrylate, tripropylene glycol diacrylate, dipropylene glycol diacrylate, and ethoxylated (30) bisphenol A diacrylate.

10. A negative electrode binder, characterized in that, It includes graphite, conductive carbon, and the binder composition as described in any one of claims 1 to 9.

11. A secondary battery, characterized in that, It includes a positive electrode, a negative electrode, an electrolyte, and a separator; the negative electrode includes a current collector and a negative electrode binder as described in claim 10 coated on the current collector.

12. The secondary battery according to claim 11, characterized in that, The secondary battery is a lithium-ion battery or a sodium-ion battery.

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