Polymer and preparation method thereof, binder, electrode and lithium ion battery

Abstract

The invention provides a polymer and a preparation method thereof, a binder, an electrode and a lithium ion battery. The preparation method of the polymer comprises the following steps: mixing monomers, and polymerizing at the temperature of 65-85 DEG C to prepare the polymer; wherein the monomer comprises acrylic acid and a raw material in a mass ratio of (2-4): 1, and the raw material has the following structural formula; r1, R2, R3 and R4 are respectively and independently selected from one of-H, C1-C10 of substituted or unsubstituted alkyl and substituted or unsubstituted C2-C5 alkenyl; the substituent groups in R1, R2, R3 and R4 are independently selected from one of D, a hydroxyl group, a C1-C5 alkyl group and a C2-C5 alkenyl group when appearing each time. According to the present invention, the binder comprising the polymer with the structure is used, and the polymer has rich carboxyl groups, such that the binding performance is effectively improved, the good mechanical property is provided, and the electrode expansion can be effectively inhibited.

Description

Technical Field

[0001] This application relates to the field of adhesive materials technology, and in particular to a polymer and its preparation method, an adhesive, an electrode, and a lithium-ion battery. Background Technology

[0002] With the rapid development of new energy vehicles and portable electronic devices, higher demands are being placed on the charging speed and energy density of lithium batteries. However, during high-rate charging and discharging, electrode materials (especially silicon-based anodes) undergo significant volume expansion, leading to active material shedding, increased interfacial impedance, and reduced cycle life.

[0003] The traditional negative electrode binder is a sodium carboxymethyl cellulose / styrene-butadiene rubber latex (CMC / SBR) system. SBR performs poorly under fast charging conditions, and the effect of this binder in alleviating the problem of electrode volume expansion needs to be improved. Summary of the Invention

[0004] Therefore, it is necessary to provide a polymer that can effectively alleviate electrode volume expansion, as well as its preparation method, binder, electrode, and lithium-ion battery.

[0005] This application provides a method for preparing a polymer, comprising the following steps:

[0006] The polymer is prepared by polymerizing mixed monomers at a temperature of 65°C to 85°C.

[0007] The monomer comprises acrylic acid in a mass ratio of (2~4):1 and a raw material, wherein the raw material has the following structural formula. ;

[0008] R1, R2, R3 and R4 are each independently selected from one of -H, substituted or unsubstituted alkyl C1 to C10 and substituted or unsubstituted C2 to C5 alkenyl groups;

[0009] The substituents described in R1, R2, R3 and R4, each time appearing, are independently selected from one of D, hydroxyl, C1~C5 alkyl and C2~C5 alkenyl.

[0010] In one embodiment, R1, R2, R3 and R4 are each independently selected from substituted or unsubstituted C1 to C5 alkyl groups.

[0011] In one embodiment, an initiator is also included, the initiator having a mass of 1% to 3% of the monomer mass.

[0012] In one embodiment, the initiator includes one or more of persulfate, hydrogen peroxide, benzoyl peroxide, azobisisobutyronitrile, azobisisoheptanenitrile, cumene hydroperoxide, and tert-butyl hydroperoxide.

[0013] In one embodiment, the polymerization time is 2 to 4 hours.

[0014] This application also provides a polymer prepared according to the above-described preparation method.

[0015] This application also provides an adhesive comprising an emulsion in a mass ratio of 1:(1~3) and a polymer as described above or a polymer prepared by the method described above.

[0016] In one embodiment, the emulsion includes one or both of styrene-acrylic emulsion and styrene-butadiene rubber emulsion.

[0017] Furthermore, this application provides an electrode comprising a current collector and an active material and a conductive agent attached to the surface of the current collector, wherein the active material and the conductive agent are attached to the surface of the current collector by an adhesive as described above.

[0018] In one embodiment, the mass ratio of the binder, the active material, and the conductive agent is 2:(80~96):(2~18).

[0019] Furthermore, this application provides a lithium-ion battery, including a positive electrode, a negative electrode, a separator, and an electrolyte. The separator is disposed between the positive electrode and the negative electrode. The positive electrode, the negative electrode, and the separator are immersed in the electrolyte. The positive electrode and the negative electrode each independently include the electrodes as described above.

[0020] This application uses a binder comprising the above-described polymer structure. This polymer, due to its abundant carboxyl groups, effectively improves the bonding performance while also possessing good mechanical properties, and can effectively suppress electrode expansion. Attached Figure Description

[0021] To more clearly illustrate the technical solutions in the specific embodiments of this application or the prior art, the drawings used in the description of the specific embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of this application. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0022] Figure 1 The graphs show the capacity retention rate curves of lithium-ion batteries using the binder of Example 1 and Comparative Example 1, with the horizontal axis representing capacity retention rate and the vertical axis representing the number of cycles.

[0023] Figure 2 The image shows the infrared spectrum of the polymer prepared in Example 1, with wavenumber on the horizontal axis and transmittance on the vertical axis. Detailed Implementation

[0024] To facilitate understanding of this application, it may be implemented in many different forms and is not limited to the embodiments described herein. Rather, these embodiments are provided to provide a more thorough and complete understanding of the disclosure of this application.

[0025] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs. The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the application.

[0026] As used herein, the term "and / or" encompasses any one of two or more of the related listed items, as well as any and all combinations of the related listed items. These arbitrary and all combinations include any two related listed items, any more related listed items, or a combination of all related listed items. For example, "A and / or B" includes three parallel options: A, B, and "a combination of A and B".

[0027] In this document, unless otherwise stated, "one or more" means any one of the listed items or any combination of the listed items. Similarly, "one or more" and other instances of "one or more" are to be understood in the same way unless otherwise stated.

[0028] In this document, terms such as "further," "even further," "especially," "for example," "like," "example," and "exemplary" are used for descriptive purposes to indicate a connection in the coverage of different technical solutions presented earlier and later. However, they should not be construed as limitations on the preceding technical solution or on the scope of protection of this document. Unless otherwise specified, in this document, A (e.g., B) indicates that B is a non-limiting example of A, and it can be understood that A is not limited to B.

[0029] In this document, "optionally," "optionally," and "optional" mean that something is optional, that is, it is selected from either "present" or "absent." If multiple "options" appear in a technical solution, unless otherwise specified and there are no contradictions or mutual constraints, each "option" is independent. In this application, descriptions such as "optionally contains" and "optionally includes" indicate "contains or does not contain." "Optional component X" indicates whether component X exists or does not exist, or whether component X is contained or not.

[0030] In this document, the terms "first aspect," "second aspect," "third aspect," and "fourth aspect," etc., are used for descriptive purposes only and should not be construed as indicating or implying relative importance or quantity, nor should they be construed as implicitly indicating the importance or quantity of the indicated technical features. Moreover, "first," "second," "third," and "fourth" serve only as a non-exhaustive enumeration and should be understood as not constituting a closed limitation on quantity.

[0031] In this article, the technical features described in an open-ended manner include both closed technical solutions composed of the listed features and open technical solutions that include the listed features.

[0032] In this document, when referring to numerical intervals (i.e., numerical ranges), unless otherwise specified, the distribution of selectable values ​​within a numerical interval is considered continuous, and includes the two endpoints (i.e., the minimum and maximum values) of the numerical interval, as well as every value between these two endpoints. Unless otherwise specified, when a numerical interval refers only to integers within that interval, it includes the two endpoint integers of the numerical range, as well as every integer between the two endpoints, which is equivalent to directly listing every integer. When multiple numerical ranges are provided to describe features or characteristics, these numerical ranges can be merged. In other words, unless otherwise specified, the numerical ranges disclosed herein should be understood to include any and all subranges included therein. The "numerical value" in this numerical interval can be any quantitative value, such as a number, percentage, ratio, etc. The term "numerical interval" can be broadly included to include percentage intervals, ratio intervals, proportion intervals, and other numerical interval types.

[0033] In this document, the terms "room temperature" or "normal temperature" generally refer to 4°C to 35°C, for example, 20°C ± 5°C. In some embodiments of this document, "room temperature" or "normal temperature" refers to 10°C to 30°C. In some embodiments of this document, "room temperature" or "normal temperature" refers to 20°C to 30°C.

[0034] In this document, for methods involving multiple steps, unless otherwise explicitly stated herein, there is no strict order constraint on the execution of these steps; they may be executed in any order other than those described. Moreover, any step may include multiple sub-steps or multiple stages, which are not necessarily completed at the same time, but may be executed at different times, and their execution order is not necessarily sequential, but may be executed in turn, alternately, or simultaneously with other steps or parts of the sub-steps or stages of other steps.

[0035] This application provides a method for preparing a polymer, comprising the following steps:

[0036] Mix monomers, polymerize them, and prepare polymers.

[0037] The monomers include acrylic acid in a mass ratio of (2~4):1 and raw materials, the raw materials having the following structural formula. R1, R2, R3 and R4 are each independently selected from one of -H, substituted or unsubstituted alkyl groups of C1 to C10 and substituted or unsubstituted alkenyl groups of C2 to C5;

[0038] The substituents described in R1, R2, R3 and R4, each time appearing, are independently selected from one of D, hydroxyl, C1~C5 alkyl and C2~C5 alkenyl.

[0039] In a specific example, R1, R2, R3, and R4 are each independently selected from substituted or unsubstituted C1-C5 alkyl groups.

[0040] Furthermore, the molecular weight of the polymer is 30,000 to 80,000. The molecular weight of the polymer can be, but is not limited to, 30,000, 35,000, 40,000, 45,000, 50,000, 55,000, 60,000, 65,000, 70,000, 75,000 or 80,000.

[0041] Furthermore, the structural formula of the raw material is as follows: .

[0042] In a specific example, in addition to the monomer, an initiator is also included, with the initiator having a mass of 1% to 3% of the monomer mass. Specifically, the mass of the initiator may be, but is not limited to, 1%, 1.5%, 2%, 2.5%, or 3% of the monomer mass.

[0043] Furthermore, the above polymerization is a solution polymerization, in which the monomer is placed in a solvent, the temperature is raised to the polymerization temperature, and an initiator is added to carry out the polymerization. Specifically, the solvent may be, but is not limited to, water, and the mass percentage of the monomer is 5% to 15%, which may be, but is not limited to, 5%, 6%, 7%, 8%, 9%, 10%, 11%, 12%, 13%, 14%, or 15%.

[0044] In a specific example, the polymerization temperature is 65°C to 85°C. Specifically, the polymerization temperature may be, but is not limited to, 65°C, 66°C, 67°C, 68°C, 69°C, 70°C, 71°C, 72°C, 73°C, 74°C, 75°C, 76°C, 77°C, 78°C, 79°C, 80°C, 81°C, 82°C, 83°C, 84°C, or 85°C.

[0045] In a specific example, the aggregation time is 2 to 4 hours. Specifically, the aggregation time can be, but is not limited to, 2 hours, 2.5 hours, 3 hours, 3.5 hours, or 4 hours.

[0046] In one specific example, the initiator includes one or more of persulfate, hydrogen peroxide (H2O2), benzoyl peroxide (BPO), azobisisobutyronitrile (AIBN), azobisisoheptanenitrile (ABVN), cumene hydroperoxide (CHP), and tert-butyl hydroperoxide (TBHP).

[0047] Furthermore, persulfates include one or both of potassium persulfate and ammonium persulfate.

[0048] This application also provides a polymer obtained according to the above preparation method.

[0049] This application uses a binder containing the polymer. Because the polymer has abundant carboxyl groups, it effectively improves the bonding performance while also having good mechanical properties, which can effectively suppress electrode expansion.

[0050] The binder includes an emulsion and the aforementioned polymer, and further, the mass ratio of the emulsion to the polymer is 1:(1~3). Specifically, the mass ratio of the emulsion to the polymer may be, but is not limited to, 1:1, 1:1.5, 1:2, 1:2.5, or 1:3.

[0051] The emulsion includes one or both of styrene-acrylic emulsion and styrene-butadiene rubber emulsion (SBR emulsion).

[0052] Understandably, styrene-acrylic emulsion (styrene-acrylate emulsion) is a water-based polymer material made by emulsion copolymerization of styrene and acrylate monomers. The solid content of styrene-acrylic emulsion is 20% to 70%.

[0053] Specifically, the solid content of the styrene-acrylic emulsion may be, but is not limited to, 20%, 25%, 30%, 35%, 40%, 45%, 50%, 55%, 60%, 65%, or 70%. Furthermore, the viscosity of the styrene-acrylic emulsion is 10 mPa·s to 2000 mPa·s. The viscosity of the styrene-acrylic emulsion may be, but is not limited to, 10 mPa·s, 100 mPa·s, 200 mPa·s, 300 mPa·s, 400 mPa·s, 500 mPa·s, 600 mPa·s, 700 mPa·s, 800 mPa·s, 900 mPa·s, 1000 mPa·s, 1100 mPa·s, 1200 mPa·s, 1300 mPa·s, 1400 mPa·s, 1500 mPa·s, 1600 mPa·s, 1700 mPa·s, 1800 mPa·s, 1900 mPa·s, or 2000 mPa·s. The monomer residue in the styrene-acrylic emulsion is <0.5%. The pH value of styrene-acrylic emulsion is 6 to 9. The pH value of styrene-acrylic emulsion can be, but is not limited to, 6, 6.5, 7, 7.5, 8, 8.5 or 9.

[0054] The addition of a highly elastic styrene-acrylic emulsion to the binder allows it to interact with the polymer's highly ion-conducting elastic network, effectively improving ion conduction efficiency. This binder boasts a Young's modulus of 5.8 MPa and an elongation at break of 150%-250%, effectively suppressing electrode expansion, particularly negative electrode expansion, thus extending the cycle life of batteries using the aforementioned negative electrode.

[0055] This application further provides an electrode, including a current collector and an active material and a conductive agent attached to the surface of the current collector, wherein the active material and the conductive agent are attached to the surface of the current collector by an adhesive as described above.

[0056] In one specific example, the mass ratio of binder, active material and conductive agent is 2: (80~96): (2~18).

[0057] Furthermore, the active material includes one or more of graphite, silicon, lithium iron phosphate, lithium nickel cobalt manganese oxide, and lithium nickel cobalt aluminum oxide.

[0058] Furthermore, the conductive agent includes one or more of graphene, carbon black, carbon nanotubes, and polyaniline.

[0059] This application provides a lithium-ion battery, including a positive electrode, a negative electrode, a separator, and an electrolyte. The separator is disposed between the positive electrode and the negative electrode. The positive electrode, the negative electrode, and the separator are immersed in the electrolyte. The positive electrode and the negative electrode each independently include the electrodes as described above.

[0060] The present application will be further described in detail below with reference to specific embodiments. It should be understood that these embodiments are for illustrative purposes only and are not intended to limit the scope of the present application. For experimental methods in the following embodiments where specific conditions are not specified, please refer to the guidelines given in this application, or follow experimental manuals or conventional conditions in the art, or follow the conditions recommended by the manufacturer, or refer to experimental methods known in the art.

[0061] In the specific embodiments described below, the measurement parameters of the raw material components may have slight deviations within the weighing accuracy range unless otherwise specified. Temperature and time parameters are subject to acceptable deviations due to instrument testing accuracy or operational precision. "Ambient temperature" refers to 25°C; "atmospheric pressure" refers to 100 kPa or 101 kPa.

[0062] Example 1

[0063] This embodiment provides an adhesive comprising a polymer and a styrene-acrylic emulsion in a mass ratio of 2:1.

[0064] The preparation method of the above polymer includes the following steps: dissolving acrylic acid monomer and sulfobetaine methacrylate monomer in deionized water at a mass ratio of 2:1 to prepare a 10% mass solution, adding it to a reaction vessel, heating it to 75°C and maintaining it for 15 minutes, adding 1 wt% of ammonium persulfate (APS) as an initiator to initiate polymerization, and reacting for 2.5 hours to prepare a polymer with a molecular weight of 80,000.

[0065] Example 2

[0066] This embodiment provides an adhesive comprising a polymer in a mass ratio of 2:1 and a styrene-acrylic emulsion (purchased from Yanyi New Materials, brand name B ONE S2).

[0067] The preparation method of the above polymer includes the following steps: dissolving acrylic acid monomer and sulfobetaine methacrylate monomer in deionized water at a mass ratio of 2:1 to prepare a 10% mass solution, adding it to a reaction vessel, heating it to 75°C and maintaining it for 15 minutes, adding 3 wt% of ammonium persulfate (APS) as an initiator to initiate polymerization, and reacting for 1.5 hours to prepare a polymer with a molecular weight of 30,000.

[0068] Example 3

[0069] This embodiment provides an adhesive comprising a polymer in a mass ratio of 2:1 and an SBR emulsion (GD1332L purchased from Shanghai Daoying).

[0070] The preparation method of the above polymer includes the following steps: dissolving acrylic acid monomer and sulfobetaine methacrylate monomer in deionized water at a mass ratio of 2:1 to prepare a 10% mass solution, adding it to a reaction vessel, heating it to 75°C and maintaining it for 15 minutes, adding 1 wt% of ammonium persulfate (APS) as an initiator to initiate polymerization, and reacting for 2.5 hours to prepare a polymer with a molecular weight of 80,000.

[0071] Comparative Example 1

[0072] The binder in this comparative example is a composite system of styrene-butadiene rubber latex and carboxymethyl cellulose (SBR / CMC), in which the mass ratio of SBR to CMC is 3:2.

[0073] Comparative Example 2

[0074] This comparative example provides an adhesive comprising a polymer in a mass ratio of 2:1 and a styrene-acrylic emulsion (purchased from Yanyi New Materials, brand name B ONE S2).

[0075] The preparation method of the above polymer includes the following steps: dissolving acrylic acid monomer in deionized water to prepare a 10% mass solution, adding it to a reaction vessel, heating it to 75°C and maintaining it for 15 minutes, adding 1 wt% of ammonium persulfate (APS) as an initiator to initiate polymerization, and reacting for 2.5 hours to prepare a polymer with a molecular weight of 80,000.

[0076] Performance testing and results analysis

[0077] The binder, active material graphite, and conductive agent carbon black of the above embodiments and comparative examples were mixed at a mass ratio of 2:96.5:1.5, and deionized water was added to adjust the mixture into a slurry. This slurry was then coated onto a copper foil current collector, dried, and rolled into shape. Lithium iron phosphate was used as the negative electrode, and PE was used as the separator. The mixture was placed in an electrolyte EC, DMC (1 mol / L LiPF6 lithium salt in an EC, DMC electrolyte with a mass ratio of 3:7) to prepare a lithium-ion battery for electrical testing. The test results are shown in Table 1 below.

[0078] Table 1

[0079] 6C charging capacity at 25℃ Capacity retention rate after 2000 cycles Example 1 1900mAh 87% Example 2 1900mAh 82% Example 3 1900mAh 80% Comparative Example 1 1900mAh 75% Comparative Example 2 1900mAh 80%

[0080] Stress-strain tests were conducted on the adhesives of the above embodiments and comparative examples. The test method was to cut the adhesive film into dumbbell-shaped strips with a length of 20 cm and a tensile speed of 100 mm / min. The test results are shown in Table 2 below.

[0081] Table 2

[0082] Young's modulus (MPa) Elongation at break (%) Example 1 4.9 221 Example 2 3.7 165 Example 3 4.1 172 Comparative Example 1 1.5 181 Comparative Example 2 2.6 163

[0083] like Figure 1 The figures shown are the capacity retention curves of lithium-ion batteries using binders from Example 1 and Comparative Example 1, respectively. Figure 2 The image shown is the infrared spectrum of the polymer in this embodiment.

[0084] The test data above show that Examples 1 to 3 all contain polymers. The negative electrode formed using the polymer binder exhibits a capacity retention rate of 80% to 87% after 2000 cycles in lithium-ion batteries. The Young's modulus of the binder reaches 3.7 MPa to 4.9 MPa, and the elongation at break is 165% to 221%. In Comparative Example 1, a common styrene-butadiene rubber latex and carboxymethyl cellulose composite negative electrode is used as the negative electrode binder. The resulting lithium-ion battery exhibits a capacity retention rate of 75% after 2000 cycles, which is not significantly reduced. However, the Young's modulus of this binder is only 1.5 MPa, and the elongation at break is 181%. Comparative Example 2 uses a negative electrode binder without adding sulfonate betaine methacrylate to the monomer. The resulting lithium-ion battery exhibits a capacity retention rate of 80% after 2000 cycles, but the Young's modulus of this binder is only 2.6 MPa, and the elongation at break is 163%, indicating a significant decrease in the mechanical properties of the binder. It is evident that the negative electrode binders prepared in Comparative Example 1 and Comparative Example 2 cannot simultaneously satisfy both good mechanical properties and mechanical properties as used in lithium-ion batteries.

[0085] It is evident that this application uses a binder comprising the polymer. Since the polymer has abundant carboxyl groups, it effectively improves the bonding performance while also possessing good mechanical properties, which can effectively suppress electrode expansion.

[0086] The technical features of the above embodiments can be combined in any way. For the sake of brevity, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0087] The embodiments described above are merely illustrative of several implementation methods of this application, and while the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the invention patent. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of this application, and these all fall within the protection scope of this application. Therefore, the protection scope of this patent application should be determined by the appended claims, and the specification can be used to interpret the scope of the claims.

Claims

1. A method for preparing a polymer, characterized in that, Includes the following steps: The polymer is prepared by polymerizing mixed monomers at a temperature of 65°C to 85°C. The monomer comprises acrylic acid in a mass ratio of (2~4):1 and a raw material, wherein the raw material has the following structural formula. ; R1, R2, R3 and R4 are each independently selected from one of -H, substituted or unsubstituted alkyl C1 to C10 and substituted or unsubstituted C2 to C5 alkenyl groups; The substituents described in R1, R2, R3 and R4, each time appearing, are independently selected from one of D, hydroxyl, C1~C5 alkyl and C2~C5 alkenyl.

2. The method for preparing the polymer according to claim 1, characterized in that, R1, R2, R3, and R4 are each independently selected from substituted or unsubstituted C1-C5 alkyl groups.

3. The preparation method according to claim 1 or 2, characterized in that, It also includes an initiator, the mass of which is 1% to 3% of the mass of the monomer.

4. The preparation method according to claim 3, characterized in that, The initiator includes one or more of persulfate, hydrogen peroxide, benzoyl peroxide, azobisisobutyronitrile, azobisisoheptanenitrile, cumene hydroperoxide, and tert-butyl hydroperoxide.

5. The preparation method according to claim 1 or 2, characterized in that, The aggregation time is 2 to 4 hours.

6. A polymer, characterized in that, Prepared according to the preparation method according to any one of claims 1 to 5.

7. An adhesive, characterized in that, It includes an emulsion in a mass ratio of 1:(1~3) and the polymer as described in claim 6.

8. The adhesive as claimed in claim 7, characterized in that, The emulsion includes one or both of styrene-acrylic emulsion and styrene-butadiene rubber emulsion.

9. An electrode, characterized in that, It includes a current collector and an active material and a conductive agent attached to the surface of the current collector, wherein the active material and the conductive agent are attached to the surface of the current collector by an adhesive as described in claim 7 or 8.

10. A lithium-ion battery, characterized in that, It includes a positive electrode, a negative electrode, a separator, and an electrolyte, wherein the separator is disposed between the positive electrode and the negative electrode, and the positive electrode, the negative electrode, and the separator are immersed in the electrolyte, and the positive electrode and the negative electrode each independently include the electrode as described in claim 9.

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