Binder, secondary battery and electric device

Abstract

The present application provides a binder, a secondary battery and an electric device. The secondary battery comprises a negative electrode sheet. The negative electrode sheet comprises a negative electrode current collector and a negative electrode film layer. The negative electrode film layer comprises a negative electrode active material and a modified polyacrylic acid (PAA) binder, wherein the modified polyacrylic acid binder comprises an -SO3H group. Special functional group modification is performed on a PAA system, such that the binder comprises a -SO3H group. The -SO3H group can promote the desolvation of active ions. Specifically, by participating in the solvated coordination structure of active ions, the -SO3H group can reduce the activation energy barrier required for the desolvation of the active ions, and reduce the strong interaction force between the solvent molecules and the active ions, which helps active ions to be released, and thus can improve the kinetic performance of a secondary battery.

Description

Adhesives, secondary batteries and electrical devices Cross-references to related applications

[0001] This application claims priority to Chinese patent application 202410968575.6, filed on July 18, 2024, entitled "Adhesive, Secondary Battery and Electrical Device", the entire contents of which are incorporated herein by reference. Technical Field

[0002] This application relates to the field of battery technology, and in particular to an adhesive, a secondary battery, and an electrical device. Background Technology

[0003] The kinetic performance of lithium batteries depends on the transport and diffusion capabilities of lithium ions in the cathode and anode. The higher the ionic conductivity of lithium ions, the better their kinetic performance. A common method to improve kinetics is to use styrene-butadiene rubber (SBR) binders with high glass transition temperatures. These binders form high-hardness electrodes, creating pores within the electrode particles that facilitate ion transport. However, electrodes made with these high-hardness SBR binders are brittle, resulting in poor rate performance and low-temperature performance.

[0004] In addition, introducing pore-forming agents (such as inorganic Na2CO3 and SiO2) into solution-type binders can create good ion transport channels. However, the addition of inorganic materials reduces the cohesion of the electrode and destroys the conductive network on the electrode surface, affecting the long-term cycle stability of the battery. Summary of the Invention

[0005] This application provides an adhesive, a secondary battery, and an electrical device to address the problem of insufficient battery kinetics when using a polyacrylic acid system as an adhesive.

[0006] The first aspect of this application provides a secondary battery including a negative electrode sheet, the negative electrode sheet including a negative current collector and a negative electrode film layer, the negative electrode film layer including a negative electrode active material and a modified polyacrylic acid binder, the modified polyacrylic acid binder including -SO3H groups.

[0007] This application modifies the PAA system with specific functional groups to include -SO3H groups in the binder. These -SO3H groups can promote the desolvation of active ions. Specifically, the -SO3H groups can participate in the solvation coordination structure of active ions to lower the activation energy barrier required for desolvation and reduce the strong interaction force between solvent molecules and active ions, thus facilitating the release of active ions and improving the kinetic performance of the secondary battery.

[0008] In any embodiment of the first aspect, the modified polyacrylic acid adhesive further includes -SO3M groups, where M includes Li + Na+ or K + One or more of them

[0009] In any embodiment of the first aspect, the modified polyacrylic acid adhesive further includes a -COC- group.

[0010] In any embodiment of the first aspect, the mass content of sulfur in the modified polyacrylic acid adhesive is 2%-20%.

[0011] In any embodiment of the first aspect, the modified polyacrylic acid adhesive comprises The modified polyacrylic acid adhesive also includes structural units containing -SO3H groups and / or structural units containing -COC- groups. The structural units containing -SO3H groups include... Structural units containing -COC- groups include One or two of them, where n is an integer from 1 to 100.

[0012] In any embodiment of the first aspect, when the secondary battery is in a 50% SOC state, the charge transfer resistance Rct of the negative electrode at 25°C is 5-12Ω.

[0013] In any embodiment of the first aspect, when the secondary battery is in a 0% SOC state, the cohesive force of the negative electrode sheet is 250 N / m-480 N / m, which can be selected as 250 N / m-300 N / m or 420 N / m-460 N / m.

[0014] In any embodiment of the first aspect, the polyacrylic acid adhesive has a weight-average molecular weight of 80W-320W.

[0015] In any embodiment of the first aspect, the negative electrode film layer comprises, by weight percentage, 93%-99% of negative electrode active material, 0.5%-5% of modified polyacrylic acid binder and 0%-2% of conductive agent.

[0016] A second aspect of this application provides a modified polyacrylic acid adhesive comprising -SO3H groups.

[0017] In any embodiment of the second aspect, the modified polyacrylic acid adhesive further includes -SO3M groups and / or -COC- groups, where M includes Li + Na + or K + One or more of them.

[0018] In any embodiment of the second aspect, the molar content of sulfur in the modified polyacrylic acid adhesive is 5%-20%.

[0019] In any embodiment of the second aspect, the modified polyacrylic acid adhesive has a molar content of -SO3H of 3%-30% and / or a molar content of -COC- groups of 5%-30%.

[0020] In any embodiment of the second aspect, the modified polyacrylic acid adhesive includes The modified polyacrylic acid adhesive also includes structural units containing -SO3H groups and / or structural units containing -COC- groups. The structural units containing -SO3H groups include... Structural units containing -COC- groups include One or two of them, where n is an integer from 1 to 100.

[0021] In any embodiment of the second aspect, the weight-average molecular weight of the polyacrylic acid adhesive is 80W-320W.

[0022] In any embodiment of the second aspect, the viscosity of an aqueous solution of a modified polyacrylic acid adhesive with a solid content of 2% is 900 mPa·s-1500 mPa·s, measured at 25°C and 12 rpm.

[0023] A third aspect of this application provides a method for preparing a modified polyacrylic acid adhesive, the method comprising: copolymerizing acrylic acid and propylene sulfonate under the action of a free radical initiator to obtain polyacrylic acid modified with -SO3H groups, wherein the propylene sulfonate includes any one or more of sodium propylene sulfonate, lithium propylene sulfonate, and potassium propylene sulfonate.

[0024] In any embodiment of the third aspect, the copolymerization reaction is carried out at 60°C-90°C, and the free radical initiator includes any one or more of hydrogen peroxide, benzoyl peroxide, cyclohexanone peroxide, and tert-butyl hydroperoxide.

[0025] In any embodiment of the third aspect, the molar amount of propylene sulfonate is 5%-30% of the total molar amount of acrylic acid and propylene sulfonate.

[0026] In any embodiment of the third aspect, the above preparation method further includes: grafting -SO3H group-modified polyacrylic acid with polyethylene oxide to obtain a polyacrylic acid adhesive modified with -SO3H group and -COC- group.

[0027] In any embodiment of the third aspect, the process of grafting -SO3H group-modified polyacrylic acid with polyethylene oxide includes: continuously adding polyethylene oxide to -SO3H group-modified polyacrylic acid under conditions of 60°C-90°C, pH 3.6-4, and stirring, so that polyethylene oxide is grafted onto the chain structure of polyacrylic acid.

[0028] In any embodiment of the third aspect, the molar amount of the polyethylene oxide, calculated in terms of -O-CH2-CH2- units, is 5%-30% of the total molar amount of the acrylic acid and the propylene sulfonate.

[0029] The fourth aspect of this application provides an electrical device including a secondary battery, which includes any of the secondary batteries provided in the first aspect above. Attached Figure Description

[0030] To more clearly illustrate the technical solutions of the embodiments of this application, the drawings used in the embodiments of this application will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on the drawings without creative effort.

[0031] Figure 1 is the infrared diffraction pattern of the adhesive 1 prepared in this application.

[0032] Figure 2 shows the activation energy comparison curves of the negative electrode 6 of this application and the control negative electrode 1.

[0033] Figure 3 is a schematic diagram of a secondary battery according to an embodiment of this application.

[0034] Figure 4 is an exploded view of the secondary battery according to one embodiment of this application, as shown in Figure 3.

[0035] Figure 5 is a schematic diagram of a battery module according to one embodiment of this application.

[0036] Figure 6 is a schematic diagram of a battery pack according to one embodiment of this application.

[0037] Figure 7 is an exploded view of the battery pack of one embodiment of this application shown in Figure 6.

[0038] Figure 8 is a schematic diagram of an electrical device using a secondary battery as a power source according to an embodiment of this application.

[0039] The accompanying drawings are not drawn to scale.

[0040] Explanation of reference numerals in the attached figures:

[0041] 1 Battery pack; 2 Upper housing; 3 Lower housing; 4 Battery module; 5 Secondary battery cell; 51 Housing; 52 Electrode assembly; 53 Top cover assembly. Detailed Implementation

[0042] The embodiments of this application will be described in further detail below with reference to the accompanying drawings and examples. The detailed description of the following embodiments and the accompanying drawings are used to illustrate the principles of this application by way of example, but should not be used to limit the scope of this application, that is, this application is not limited to the described embodiments.

[0043] The following detailed description, with appropriate reference to the accompanying drawings, specifically discloses embodiments of the adhesive, secondary battery, and power supply device of this application. However, unnecessary details may be omitted. For example, detailed descriptions of well-known matters and repetitive descriptions of practically identical structures may be omitted. This is to avoid unnecessarily lengthy descriptions and to facilitate understanding by those skilled in the art. Furthermore, the accompanying drawings and the following description are provided for the purpose of enabling those skilled in the art to fully understand this application and are not intended to limit the subject matter of the claims.

[0044] The "range" disclosed in this application is defined by a lower limit and an upper limit. A given range is defined by selecting a lower limit and an upper limit, which define the boundaries of a particular range. Ranges defined in this way can include or exclude endpoints and can be arbitrarily combined; that is, any lower limit can be combined with any upper limit to form a range. For example, if ranges of 60-120 and 80-110 are listed for a specific parameter, it is expected that ranges of 60-110 and 80-120 are also included. Furthermore, if minimum range values ​​of 1 and 2 are listed, and if maximum range values ​​of 3, 4, and 5 are listed, then the following ranges are all expected: 1-3, 1-4, 1-5, 2-3, 2-4, and 2-5. In this application, unless otherwise stated, the numerical range "ab" represents a shortened representation of any combination of real numbers between a and b, where a and b are real numbers. For example, the numerical range "0-5" indicates that all real numbers between "0-5" have been listed in this article; "0-5" is simply a shortened representation of these numerical combinations. Furthermore, when a parameter is stated as an integer ≥2, it is equivalent to disclosing that the parameter is, for example, an integer such as 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

[0045] Unless otherwise specified, all embodiments and optional embodiments of this application can be combined to form new technical solutions.

[0046] Unless otherwise specified, all technical features and optional technical features of this application may be combined to form new technical solutions.

[0047] Unless otherwise specified, all steps in this application may be performed sequentially or randomly, preferably sequentially. For example, the method includes steps (a) and (b), indicating that the method may include steps (a) and (b) performed sequentially, or it may include steps (b) and (a) performed sequentially. For example, the method may also include step (c), indicating that step (c) may be added to the method in any order. For example, the method may include steps (a), (b), and (c), or it may include steps (a), (c), and (b), or it may include steps (c), (a), and (b), etc.

[0048] Unless otherwise specified, the terms "comprising" and "including" as used in this application are open-ended. For example, "comprising" and "including" may mean that other components not listed may also be included or contained.

[0049] Unless otherwise specified, the term "or" is inclusive in this application. For example, any of the following conditions satisfies the condition "A or B": A is true (or exists) and B is false (or does not exist); A is false (or does not exist) and B is true (or exists); or both A and B are true (or exist).

[0050] Modified polyacrylic acid adhesive

[0051] Polyacrylic acid (PAA) binders are linear binders, and their effect on graphite coating is better than that of dot-shaped styrene-butadiene rubber (SBR), thus improving the cohesion of the negative electrode sheet. However, the formation of a non-conductive layer on the surface of the negative electrode active material by polyacrylic acid coating severely affects the surface conductive network of the negative electrode active material, hindering lithium-ion transport and resulting in insufficient battery kinetics.

[0052] To address this issue, the applicant investigated the desolvation process of active ions at the negative electrode interface within a secondary battery. The study revealed that during desolvation, active ions need to remove solvent molecules adsorbed on the surface, then pass through the SEI film to recombine with electrons and embed themselves in graphite. Excessive difficulty in desolvation of active ions leads to battery polarization, resulting in insufficient battery kinetics and accelerated cycle performance degradation. Therefore, improving the desolvation of active ions can effectively improve battery kinetic performance. Based on this, the first embodiment of this application provides a modified polyacrylic acid binder, which includes -SO3H groups.

[0053] The polyacrylic acid in the above-mentioned modified polyacrylic acid adhesive can be characterized by measuring the -CH2- and -COO- groups in the adhesive.

[0054] This application modifies the PAA system with specific functional groups to include -SO3H groups in the binder. These -SO3H groups can promote the desolvation of active ions. Specifically, the -SO3H groups can participate in the solvation coordination structure of active ions to lower the activation energy barrier required for desolvation and reduce the strong interaction force between solvent molecules and active ions, thus facilitating the release of active ions and improving the kinetic performance of the secondary battery.

[0055] Molecular dynamics (MD) simulations show that, taking lithium-ion solvation as an example, the -SO3H group forms hydrogen bonds with the =O atoms on neighboring solvent molecules, making it easier for them to participate in the solvation structure of lithium ions. Therefore, introducing a -SO3H group into the binder can reduce the resistance to lithium-ion extraction by replacing a solvent molecule into the solvation structure during solvation, thus aiding in lithium-ion desolvation. Analysis through molecular dynamics simulations and DFT calculations of different groups reveals that the -SO3H group has good compatibility with polyacrylic acid and a low desolvation energy barrier, which helps active ions extract from the solvation structure. Furthermore, the -SO3H group can be freely bent and rotated, reducing rigidity and enhancing the flexibility of the polymer backbone. The -SO3H group also makes the polymer particle surface more negatively charged, easily forming numerous hydrogen bonds with the negative electrode active material and current collector surface, further enhancing the compatibility between the binder and the negative electrode active material. This, in turn, can improve the cohesive force and elastic modulus of the negative electrode sheet, better suppressing its expansion. Meanwhile, the -SO3H group is a group with strong electron-withdrawing properties, making it easier for active ions to dissociate.

[0056] Furthermore, during battery formation, the -SO3H group, as a polar group, adsorbs lithium salts, promoting the preferential formation of inorganic component LiF, thereby increasing the proportion of elements such as F in the SEI film and improving the longitudinal uniformity of LiF in the SEI. Moreover, based on the linear coating characteristics of the polyacrylic acid system, it can promote the uniform dispersion of the aforementioned -SO3H groups, which is more conducive to the participation of functional groups at the interface in the solvation structure of lithium coordination. This reduces the adsorption of active ions and solvent molecules, which is beneficial to better reduce the desolvation energy barrier of active ions, thereby improving the transport capacity of active ions at the interface.

[0057] The functional groups in the above-mentioned binder can be obtained by conventional infrared diffraction. When the above-mentioned modified polyacrylic acid binder is used in the preparation of secondary batteries with negative electrode sheets, the -SO3H groups can be tested by the following method:

[0058] After separating the negative electrode sheet of the secondary battery at 0% SOC, it was thoroughly cleaned with DMC (dimethyl carbonate) and dried. The negative electrode active layer material was then collected by the scraping method. 50 mg of the negative electrode active layer material was taken and ground into powder of tens of micrometers using a ball mill. The powder was mixed with potassium bromide powder and spread evenly on a sample dish. The infrared spectrum of the sample was tested according to the national standard method GB / T 6040-2019.

[0059] In some embodiments, the modified polyacrylic acid adhesive further includes -SO3M groups, where M includes Li + Na + or K + One or more of the following. The use of -SO3M reduces the increased acidity of the modified polyacrylic acid binder caused by the introduction of -SO3H groups, making the binder more neutral and controlling its corrosion of the negative electrode current collector.

[0060] In some embodiments, the modified polyacrylic acid binder further includes -COC- groups. The ether oxygen bonds in the -COC- groups promote the affinity of the electrolyte for active ions, thereby synergistically enhancing the transport capacity of active ions at the interface and promoting the formation of a composite binder with high kinetic capabilities. Simultaneously, numerous interchain hydrogen bonds are formed between the -SO3H and -COC- groups. The long side chains provided by the -COC- groups provide steric hindrance, ensuring uniform dispersion of the molecular chains. Furthermore, the overall interchain interaction is enhanced through dynamic intermolecular hydrogen bonding, improving the binder's flexibility and thus improving the contact effect between the negative electrode active material, binder, and current collector, thereby further increasing the cohesion of the negative electrode sheet.

[0061] The -COC- groups mentioned above can be detected using the same detection method as -SO3H.

[0062] According to the description of the above embodiments, the modified polyacrylic acid adhesive contains C, S, and O elements, wherein the S element mainly comes from -SO3H, therefore the S element content to a certain extent indicates the -SO3H content. In some embodiments, the mass content of S element in the modified polyacrylic acid adhesive is 2%-20%, optionally 2%-15%, 5%-15%, or 10%-15%.

[0063] When the above-mentioned modified polyacrylic acid binder is used in the preparation of secondary batteries with negative electrode sheets, the sulfur content in the modified polyacrylic acid binder of the negative electrode sheet can be tested by the following inductively coupled plasma atomic emission spectrometry (ICP method):

[0064] 1) After separating the negative electrode sheet of the secondary battery at 0% SOC, thoroughly clean it with DMC (dimethyl carbonate), dry it, and collect the negative electrode active layer material by scraping powder. Then, according to the national standard GB-T 13464-2008, the collected negative electrode active layer material and the reference blank crucible are heated under nitrogen atmosphere at a heating rate of 10℃ / min. The temperature and mass changes during the heating process are tested, and the corresponding TG curves are obtained. By analyzing the characteristic decomposition temperature of the modified polyacrylic acid binder in the TG curve, the content of modified polyacrylic acid binder in the negative electrode active layer material is calculated.

[0065] 2) Inductively Coupled Plasma Atomic Emission Spectrometry (US EPA 6010D-2018): The negative electrode active layer material was microwave-digested using concentrated nitric acid as a digesting agent at 200°C and 150 bar. The digested solution was then vaporized and ionized in a plasma torch. The intensity of the excited characteristic spectral lines was measured. Combined with the content of the modified polyacrylic acid binder in the negative electrode active layer material, the sulfur (S) content in the modified polyacrylic acid binder was calculated.

[0066] The content of each group in the modified polyacrylic acid binder can be controlled by adjusting the amount of monomers added during preparation. In some embodiments, the molar content of -SO3H in the modified polyacrylic acid binder is 3%-30% (e.g., 3%, 5%, 8%, 10%, 12%, 15%, 20%, 25%, or 30%), and more preferably 3%-20% or 20%-30%. This avoids the problem of insufficient grafting or polymerization on the polyacrylic acid backbone due to a high -SO3H content, leading to a high content of small molecule monomers in the binder, which in turn affects the coating of the active material slurry and causes sticking to the rollers during calendering, resulting in electrode material shortages and electrode cracking and edge bursting during cold pressing. Therefore, the above range allows for the full utilization of sulfonic acid groups to improve lithium-ion transport performance while maintaining the basic polypropylene framework structure of the polyacrylic acid binder. The content of -SO3H in the modified polyacrylic acid binder can be adjusted by adjusting the amount of the corresponding monomers during binder preparation. The above molar content is calculated based on the total molar amount of propylene groups.

[0067] The -SO3H content was tested using thermogravimetric mass spectrometry (TGA). Taking the test of the -SO3H content in the modified polyacrylic acid binder in a secondary battery as an example, the method is as follows: The negative electrode sheet was disassembled from the secondary battery, thoroughly cleaned with DMC (dimethyl carbonate), and dried. According to the national standard GB-T 13464-2008, the specified negative electrode sheet and the reference blank crucible were heated under a nitrogen atmosphere at a heating rate of 10℃ / min. The temperature and mass during the heating process were tested, and the corresponding TG curves were obtained. By analyzing the characteristic decomposition temperature of the modified polyacrylic acid binder in the TG curve, the content of the modified polyacrylic acid binder in the negative electrode sheet was calculated. Then, the gas generated by pyrolysis was introduced into the mass spectrometer, and the content was measured according to the national standard GB-T... According to 6041-2020, the gas produced by the pyrolysis of the negative electrode sheet is first ionized using a mass spectrometer and then separated according to the mass-to-charge ratio of the ions. The abundance (i.e., peak intensity) of the produced SO2 is detected. By utilizing the superposition property of mass spectrometry, the molar ratio of the total amount of produced gas to the total substance is combined with the content of the modified polyacrylic acid binder in the negative electrode sheet to reversely determine the proportion of -SO3H groups in the polymer.

[0068] In some embodiments, the molar content of -COC- groups in the modified polyacrylic acid binder is 5%-30% (e.g., 5%, 8%, 10%, 12%, 15%, 20%, 25%, or 30%), and more preferably 5%-20% or 20%-30%. This avoids the problem of insufficient grafting or polymerization on the polyacrylic acid backbone due to a high content of -COC- groups, leading to a higher content of small molecule monomers in the binder. This, in turn, affects the coating of the active material slurry and causes sticking to the rollers during calendering, resulting in electrode material shortages and electrode cracking and edge bursting during cold pressing. Therefore, the above range allows for the full utilization of -COC- to improve lithium-ion transport performance while maintaining the basic polypropylene framework structure of the polyacrylic acid binder system. The -COC- content in the modified polyacrylic acid binder can be adjusted by adjusting the amount of the corresponding monomers during binder preparation. The above molar content is calculated based on the total molar amount of propylene groups.

[0069] When both -SO3H and -COC- groups are present, in some embodiments, the molar content of -SO3H in the modified polyacrylic acid adhesive is 3%-30% (e.g., 3%, 5%, 8%, 10%, 12%, 15%, 20%, 25%, or 30%), and the molar content of -COC- groups is 5%-30% (e.g., 5%, 8%, 10%, 12%, 15%, 20%, 25%, or 30%).

[0070] In some embodiments, the molar content of carbon element in the modified polyacrylic acid adhesive is 60%-80%.

[0071] In some embodiments, the molar content of oxygen in the modified polyacrylic acid adhesive is 10%-30%.

[0072] In some embodiments, the modified polyacrylic acid adhesive also includes nitrogen (N) element, which is introduced from the raw materials used to prepare acrylic acid and is typically present as -CN.

[0073] The content of the above elements can be determined using the same testing method as that for element S.

[0074] In some embodiments, the modified polyacrylic acid adhesive includes The structural unit further includes structural units containing -SO3H groups and / or structural units containing -COC- groups, wherein the structural units containing -SO3H groups include Structural units containing -COC- groups include One or two of the following, where n is an integer from 1 to 100. The above structural unit has a main chain structure formed by the polymerization of acrylic acid monomers, and the -SO3H groups and -COC- groups are grafted onto the main chain structure and dispersed as uniformly as possible. The formed molecular chains have excellent molecular mobility, which gives the binder better toughness and provides a controllable space for the deformation of the active material.

[0075] To improve the workability of the adhesive, in some embodiments, the weight-average molecular weight of the modified polyacrylic acid adhesive is 80W-320W, optionally 100W-300W. The molecular weight of the adhesive can be determined using gel permeation chromatography (GPC), specifically as follows: the modified polyacrylic acid adhesive is diluted with ultrapure water to a solid content of 2%, and then injected at a flow rate of 2 mL / min and a pressure of 1250 psi to test the molecular weight distribution. A porous gel is used as the stationary phase, and separation is achieved based on the different flow rates of solute molecules of different molecular weights through the gel. Testing instrument: Waters e2695.

[0076] To improve the workability of the adhesive, in some embodiments, the viscosity of an aqueous solution of modified polyacrylic acid adhesive with a solid content of 2% is measured at 25°C and 12 rpm to be 900 mPa·s-1500 mPa·s, optionally 900 mPa·s-1100 mPa·s. The viscosity test method is as follows: according to the national standard GB / T 33061.10-2016, the adhesive is diluted with ultrapure water to a solid content of 2%, and the viscosity of the adhesive is tested on a viscometer using a standard solution of 5000 MPa·s at 12 rpm.

[0077] The second embodiment of this application provides a method for preparing the above-mentioned modified polyacrylic acid adhesive. This method includes: copolymerizing acrylic acid and propylene sulfonate under the action of a free radical initiator to obtain polyacrylic acid modified with -SO3H groups. The propylene sulfonate includes any one or more of sodium propylene sulfonate, lithium propylene sulfonate, and potassium propylene sulfonate.

[0078] The above preparation method involves adding a small amount of a substance containing sulfonic acid groups to an acrylic acid monomer solution and then copolymerizing it to graft sulfonic acid groups onto the side chains (the oxygen atoms on the sulfonic acid groups copolymerize with the carboxyl groups on the polyacrylic acid monomers). The basic mechanism of the copolymerization method described above is for reference.

[0079] In some embodiments, the copolymerization reaction is carried out at 60°C-90°C, and the free radical initiator includes any one or more of hydrogen peroxide, benzoyl peroxide, cyclohexanone peroxide, and tert-butyl hydroperoxide. Using the above method can increase the proportion of -SO3H groups in the polymer.

[0080] In some embodiments, the molar amount of propylene sulfonate is 5%-30% of the total molar amount of acrylic acid and propylene sulfonate. This is to control the content of -SO3H groups in the formed adhesive chain structure.

[0081] In some embodiments, polyacrylic acid modified with -SO3H groups is grafted onto polyethylene oxide to obtain a polyacrylic acid adhesive modified with both -SO3H and -COC- groups. Further modification with the -COC- groups enhances the cohesive strength of the resulting adhesive and synergistically improves the ability of active ions to transport at the interface, in conjunction with the -SO3H groups.

[0082] In some embodiments, the grafting reaction of -SO3H-modified polyacrylic acid with polyethylene oxide includes: continuously adding polyethylene oxide to the -SO3H-modified polyacrylic acid at 60°C-90°C, a pH of 3.6-4, and under stirring conditions, so that the polyethylene oxide is grafted onto the chain structure of the polyacrylic acid. This continuous addition can be done dropwise, by flowing addition, etc., which helps to improve the grafting rate of polyethylene oxide. The pH value can be adjusted by adding aqueous solutions of conventional organic / inorganic acids or organic / inorganic bases, such as aqueous solutions of sodium hydroxide, potassium hydroxide, hydrochloric acid, nitric acid, etc.

[0083] In some embodiments, the molar amount of polyethylene oxide, calculated as -O-CH2-CH2- units, is 5%-30% of the total molar amount of acrylic acid and propylene sulfonate. This is to control the content of -COC- groups in the formed adhesive chain structure.

[0084] [Negative electrode plate]

[0085] A negative electrode typically includes a negative current collector and a negative electrode film layer disposed on at least one surface of the negative current collector, the negative electrode film layer comprising a negative electrode active material.

[0086] As an example, the negative electrode current collector has two surfaces opposite each other in its own thickness direction, and the negative electrode film layer is disposed on either or both of the two opposite surfaces of the negative electrode current collector. The negative electrode film layer includes a negative electrode active material and any of the modified polyacrylic acid binders provided in the first embodiment.

[0087] The negative electrode sheet with the modified polyacrylic acid binder provided in the first embodiment of this application has better active ion transport capability, which can improve the dynamic performance of the secondary battery with the negative electrode sheet; the modified polyacrylic acid binder has strong cohesion and high elasticity, which is beneficial to controlling the expansion of the negative electrode sheet during charging and improving the cycle life and cycle stability of the secondary battery.

[0088] Since the modified polyacrylic acid binder of this application improves the lithium-ion transport effect, its charge transfer resistance is also reduced. In some embodiments, when the secondary battery is in a 50% SOC state, the charge transfer resistance Rct of the negative electrode sheet measured at 25°C is 5Ω-12Ω.

[0089] The test method for the charge transfer resistance Rct is as follows: The secondary battery is charged at a rate of 0.1C to a voltage of 3.65V, then charged at a constant voltage rate of 0.05C to 100% SOC, and then discharged at a rate of 0.1C to 50% SOC. The electrodes disassembled from the secondary battery are used to assemble a symmetrical battery. The interfacial charge transfer resistance Rct is tested at different temperatures (-20℃, -10℃, 0℃, 10℃, 25℃). Furthermore, the activation energy EIS can be fitted using the Arrhenius equation, and the fitting formula is as follows:

[0090] Log(T / Rct)=-(Ea / 2.303R)×(1000 / T)

[0091] T is the absolute temperature; Rct is the interfacial charge transfer resistance; Ea represents the activation energy EIS; R is the gas constant 8.314.

[0092] Taking Figure 2 as an example, the secondary battery L at 50% SOC n Figure 2 shows the relationship between Rct and 100 / T. As can be seen from Figure 2, the slopes of the curves for the 50% lithium intercalation state of negative electrode 6 and the control negative electrode 1 are 7.39 and 7.614, respectively, with calculated activation energies of 61.4 KJ / mol and 63.3 KJ / mol. It is evident that the activation energy of negative electrode 6 is lower than that of the control negative electrode 1, indicating that the interfacial reaction process is more readily carried out.

[0093] After modification with -SO3H groups, or a combination of -SO3H and -COC- groups, the cohesive force of the binder is improved. This allows for better confinement of the negative electrode active material, controlling its volume expansion during charging and improving battery cycle life and stability. In some embodiments, the cohesive force of the negative electrode sheet is 250 N / m to 480 N / m.

[0094] The test method for the above cohesion is as follows:

[0095] After thoroughly cleaning and drying the negative electrode sheet of the secondary battery with DMC (dimethyl carbonate) at 0% SOC, at room temperature and humidity of 55±5%, tape is applied to the coated side of the negative electrode sheet to be tested, leaving one end of the tape unattached to the negative electrode sheet to be tested. The negative electrode sheet to be tested is fixed, and the unattached end of the tape is peeled off from the coating surface at a uniform speed using a tensile testing machine (the tensile testing machine is set to a tensile speed of 50 mm / min). The force value of the tape peeling off from the coating surface is measured, which represents the cohesive force of the negative electrode sheet.

[0096] In some embodiments, the cohesive force of the negative electrode sheet can optionally be 250 N / m-300 N / m (e.g., the cohesive force of the negative electrode sheet when the modified polyacrylic acid binder has -SO3H groups) or 420 N / m-460 N / m (e.g., the cohesive force of the negative electrode sheet when the modified polyacrylic acid binder has -SO3H groups and -COC- groups).

[0097] The negative electrode film layer in the negative electrode sheet of this application may contain the modified polyacrylic acid binder described above. Other components may refer to the composition of conventional negative electrode film layers. In some embodiments, the negative electrode film layer includes 93%-99% negative electrode active material, 0.5%-5% (optionally 1%-5%, such as 1.5%, 2.5%, 3.5%, 4.5% or 5%) modified polyacrylic acid binder and 0%-2% conductive agent by weight percentage.

[0098] In some embodiments, the compaction density of the negative electrode film is 1.5 g / cm³. 3 -2.5g / cm 3 .

[0099] In some embodiments, the negative electrode current collector may be a metal foil or a composite current collector. For example, copper foil may be used as the metal foil. The composite current collector may include a polymer material substrate and a metal layer formed on at least one surface of the polymer material substrate. The composite current collector may be formed by forming a metal material (copper, copper alloy, nickel, nickel alloy, titanium, titanium alloy, silver and silver alloy, etc.) on a polymer material substrate (such as a substrate of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0100] In some embodiments, the negative electrode active material may be a negative electrode active material known in the art for use in batteries. As an example, the negative electrode active material may include at least one of the following materials: artificial graphite, natural graphite, soft carbon, hard carbon, silicon-based materials, tin-based materials, and lithium titanate, etc. Silicon-based materials may be selected from at least one of elemental silicon, silicon oxide compounds, silicon-carbon composites, silicon-nitrogen composites, and silicon alloys. Tin-based materials may be selected from at least one of elemental tin, tin oxide compounds, and tin alloys. However, this application is not limited to these materials, and other conventional materials that can be used as negative electrode active materials for batteries may also be used. These negative electrode active materials may be used alone or in combination of two or more.

[0101] In some embodiments, as an example, the conductive agent may be selected from at least one of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0102] In some embodiments, the negative electrode film may optionally include other additives, such as thickeners (e.g., sodium carboxymethyl cellulose (CMC-Na)).

[0103] In some embodiments, the negative electrode sheet can be prepared by dispersing the components used to prepare the negative electrode sheet, such as the negative electrode active material, conductive agent, binder and any other components, in a solvent (e.g., deionized water) to form a negative electrode slurry; coating the negative electrode slurry onto the negative electrode current collector, and then obtaining the negative electrode sheet after drying, cold pressing and other processes.

[0104] [Rechargeable Battery]

[0105] Secondary batteries, also known as rechargeable batteries or storage batteries, are batteries that can be recharged after being discharged to activate the active materials and continue to be used.

[0106] Typically, a secondary battery consists of a positive electrode, a negative electrode, a separator, and an electrolyte. During charging and discharging, active ions (such as lithium ions) repeatedly insert and extract between the positive and negative electrodes. The separator, positioned between the positive and negative electrodes, primarily prevents short circuits while allowing active ions to pass through. The electrolyte, also positioned between the positive and negative electrodes, mainly serves to conduct active ions.

[0107] The fourth embodiment of this application provides a secondary battery, which includes any of the negative electrode sheets provided in the third embodiment. The negative electrode sheet includes a negative current collector and a negative electrode film layer. The negative electrode film layer includes a negative electrode active material and a modified polyacrylic acid binder from the first aspect.

[0108] Both groups in the aforementioned modified polyacrylic acid binder can lower the activation energy barrier required for the desolvation of active ions by participating in the solvation coordination structure of ions, and reduce the strong interaction force between solvent molecules and active ions, thus facilitating the extraction of active ions and improving the kinetic performance of the secondary battery. Furthermore, the modified polyacrylic acid binder exhibits strong cohesion and high elasticity, which helps control the expansion of the negative electrode during charging, thereby improving the cycle life and cycle stability of the secondary battery.

[0109] [Positive electrode plate]

[0110] A positive electrode typically includes a positive current collector and a positive electrode film layer disposed on at least one surface of the positive current collector, the positive electrode film layer including a positive electrode active material.

[0111] As an example, the positive current collector has two surfaces opposite each other in its own thickness direction, and the positive electrode film layer is disposed on either or both of the two opposite surfaces of the positive current collector.

[0112] In some embodiments, the positive current collector may be a metal foil or a composite current collector. For example, aluminum foil may be used as the metal foil. The composite current collector may include a polymer substrate and a metal layer formed on at least one surface of the polymer substrate. The composite current collector may be formed by forming a metal material (aluminum, aluminum alloy, nickel, nickel alloy, titanium, titanium alloy, silver and silver alloy, etc.) on a polymer substrate (such as a substrate of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0113] In some embodiments, the positive electrode active material may be a known battery positive electrode active material. As an example, when the secondary battery is a lithium-ion secondary battery, the positive electrode active material may include at least one of the following materials: lithium phosphates with an olivine structure, lithium transition metal oxides, and their respective modified compounds. However, this application is not limited to these materials, and other conventional materials that can be used as battery positive electrode active materials may also be used. These positive electrode active materials may be used alone or in combination of two or more. Examples of lithium transition metal oxides include, but are not limited to, lithium cobalt oxides (such as LiCoO2), lithium nickel oxides (such as LiNiO2), lithium manganese oxides (such as LiMnO2, LiMn2O4), lithium nickel cobalt oxides, lithium manganese cobalt oxides, lithium nickel manganese oxides, and lithium nickel cobalt manganese oxides (such as LiNi). 1 / 3 Co 1 / 3 Mn 1 / 3 O2 (also known as NCM) 333 LiNi 0.5 Co 0.2 Mn 0.3 O2 (also known as NCM) 523 LiNi 0.5 Co 0.25 Mn 0.25 O2 (also known as NCM) 211 LiNi 0.6 Co 0.2 Mn 0.2 O2 (also known as NCM) 622 LiNi 0.8 Co 0.1 Mn 0.1 O2 (also known as NCM) 811 ), lithium nickel cobalt aluminum oxide (such as LiNi) 0.85 Co 0.15 Al 0.05 At least one of O2 and its modified compounds. Examples of lithium phosphates with an olivine structure include, but are not limited to, lithium iron phosphate (such as LiFePO4 (also referred to as LFP)), lithium iron phosphate and carbon composites, lithium manganese phosphate (such as LiMnPO4), lithium manganese phosphate and carbon composites, lithium manganese iron phosphate, and lithium manganese iron phosphate and carbon composites.

[0114] When the secondary battery is a sodium-ion secondary battery, as an example, the positive electrode active material of the sodium-ion secondary battery may include at least one of the following materials: sodium transition metal oxides, polyanionic compounds, and Prussian blue compounds. However, this application is not limited to these materials, and other conventionally known materials that can be used as positive electrode active materials for sodium-ion batteries may also be used.

[0115] As an optional technical solution in this application, the transition metal in the sodium transition metal oxide can be at least one selected from Mn, Fe, Ni, Co, Cr, Cu, Ti, Zn, V, Zr, and Ce. For example, the sodium transition metal oxide is Na. x MO2, where M is one or more of Ti, V, Mn, Co, Ni, Fe, Cr and Cu, and 0 < x ≤ 1.

[0116] As an optional technical solution in this application, the polyanionic compound can be a compound containing sodium ions, transition metal ions, or a tetrahedral (YO4) structure. n- A class of compounds with anionic units. The transition metal can be at least one of Mn, Fe, Ni, Co, Cr, Cu, Ti, Zn, V, Zr, and Ce; Y can be at least one of P, S, and Si; n represents (YO4). n- The price state.

[0117] Polyanionic compounds can also contain sodium ions, transition metal ions, or tetrahedral (YO4) ions. n- A class of compounds containing anionic units and halide anions. The transition metal can be at least one of Mn, Fe, Ni, Co, Cr, Cu, Ti, Zn, V, Zr, and Ce; Y can be at least one of P, S, and Si, and n represents (YO4). n- The valence state; the halogen can be at least one of F, Cl and Br.

[0118] Polyanionic compounds can also be sodium-containing tetrahedral (YO4) compounds. n- Anionic unit, polyhedral unit (ZO) y ) m+ And a class of compounds with optional halide anions. Y can be at least one of P, S, and Si, and n represents (YO4). n- The valence state; Z represents a transition metal, which can be at least one of Mn, Fe, Ni, Co, Cr, Cu, Ti, Zn, V, Zr, and Ce; m represents (ZO) y ) m+ The valence state; the halogen can be at least one of F, Cl and Br.

[0119] Polyanionic compounds include, for example, NaFePO4, Na3V2(PO4)3 (sodium vanadium phosphate, abbreviated as NVP), Na4Fe3(PO4)2 (P2O7), NaM'PO4F (M' is one or more of V, Fe, Mn and Ni), and Na3(VO4) y )2(PO4)2F 3-2y At least one of (0≤y≤1).

[0120] Prussian blue compounds can be a class of compounds containing sodium ions, transition metal ions, and cyanide ions (CN-). The transition metal can be at least one of Mn, Fe, Ni, Co, Cr, Cu, Ti, Zn, V, Zr, and Ce. Examples of Prussian blue compounds include Na. a Me b Me' c (CN)6, wherein Me and Me' are each independently at least one of Ni, Cu, Fe, Mn, Co and Zn, 0 < a ≤ 2, 0 < b < 1, 0 < c < 1.

[0121] In some embodiments, the positive electrode film layer may optionally include a binder. As an example, the binder may include at least one of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), PVDF-tetrafluoroethylene-propylene terpolymer, PVDF-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, and fluorinated acrylate resin.

[0122] In some embodiments, the positive electrode film may optionally include a conductive agent. As an example, the conductive agent may include at least one selected from superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0123] In some embodiments, the positive electrode sheet can be prepared by dispersing the above-mentioned components for preparing the positive electrode sheet, such as positive active material, conductive agent, binder and any other components, in a solvent (e.g., N-methylpyrrolidone) to form a positive electrode slurry; coating the positive electrode slurry onto the positive electrode current collector, and then obtaining the positive electrode sheet after drying, cold pressing and other processes.

[0124] [Electrolytes]

[0125] The electrolyte acts as a conductor of ions between the positive and negative electrodes. This application does not impose specific restrictions on the type of electrolyte; it can be selected according to requirements. For example, the electrolyte can be liquid, gel, or entirely solid.

[0126] In some embodiments, the electrolyte is liquid and includes an electrolyte salt and a solvent.

[0127] In some embodiments, the electrolyte salt may be selected from at least one of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium perchlorate, lithium hexafluoroarsenate, lithium bis(fluorosulfonyl)imide, lithium bis(trifluoromethanesulfonyl)imide, lithium trifluoromethanesulfonate, lithium difluorophosphate, lithium difluorooxalate borate, lithium dioxalate borate, lithium difluorodioxalate phosphate, and lithium tetrafluorooxalate phosphate.

[0128] In some embodiments, the solvent may be selected from at least one of ethylene carbonate, propylene carbonate, methyl ethyl carbonate, diethyl carbonate, dimethyl carbonate, dipropyl carbonate, methyl propyl carbonate, ethyl propyl carbonate, butyl carbonate, fluoroethylene carbonate, methyl formate, methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, propyl propionate, methyl butyrate, ethyl butyrate, 1,4-butyrolactone, sulfolane, dimethyl sulfone, methyl ethyl sulfone, and diethyl sulfone.

[0129] In some embodiments, the electrolyte may optionally include additives. As examples, additives may include negative electrode film-forming additives, positive electrode film-forming additives, and may also include additives that can improve certain battery performance, such as additives that improve battery overcharge performance, additives that improve battery high-temperature or low-temperature performance, etc.

[0130] [Isolation membrane]

[0131] In some embodiments, the secondary battery also includes a separator. This application does not impose any particular limitation on the type of separator; any known porous separator with good chemical and mechanical stability can be selected.

[0132] In some embodiments, the material of the separator can be selected from at least one of glass fiber, nonwoven fabric, polyethylene, polypropylene, and polyvinylidene fluoride. The separator can be a single-layer film or a multi-layer composite film, without particular limitation. When the separator is a multi-layer composite film, the materials of each layer can be the same or different, without particular limitation.

[0133] In some implementations, the positive electrode, negative electrode, and separator can be fabricated into an electrode assembly using a winding or stacking process.

[0134] In some implementations, the secondary battery includes a single secondary battery cell, or a battery module and a battery pack.

[0135] In some embodiments, the secondary battery may include an outer packaging. This outer packaging may be used to encapsulate the electrode assembly and electrolyte described above.

[0136] In some embodiments, the outer packaging of the secondary battery can be a hard shell, such as a hard plastic shell, an aluminum shell, or a steel shell. The outer packaging of the secondary battery can also be a soft pack, such as a pouch. The material of the soft pack can be plastic; examples of plastics include polypropylene, polybutylene terephthalate, and polybutylene succinate.

[0137] This application does not impose any particular limitation on the shape of the secondary battery cell; it can be cylindrical, square, or any other arbitrary shape. For example, Figure 3 shows a square-structured secondary battery cell 5 as an example.

[0138] In some embodiments, referring to FIG4, the outer packaging may include a housing 51 and a top cover assembly 53. The housing 51 may include a base plate and side plates connected to the base plate, the base plate and side plates forming a receiving cavity. The housing 51 has an opening communicating with the receiving cavity, and the top cover assembly 53 can cover the opening to close the receiving cavity. A positive electrode sheet, a negative electrode sheet, and a separator can be formed into an electrode assembly 52 by a winding process or a stacking process. The electrode assembly 52 is encapsulated within the receiving cavity. Electrolyte is immersed in the electrode assembly 52. ​​The number of electrode assemblies 52 contained in the secondary battery cell 5 can be one or more, which can be selected by those skilled in the art according to specific practical needs.

[0139] In some implementations, the secondary battery cells can be assembled into a battery module. The number of secondary battery cells contained in the battery module can be one or more, and the specific number can be selected by those skilled in the art according to the application and capacity of the battery module.

[0140] Figure 5 shows a battery module 4 as an example. Referring to Figure 5, in the battery module 4, multiple secondary battery cells 5 can be arranged sequentially along the length of the battery module 4. Of course, they can also be arranged in any other manner. Furthermore, the multiple secondary battery cells 5 can be fixed in place using fasteners.

[0141] Optionally, the battery module 4 may also include a housing with a receiving space in which multiple secondary battery cells 5 are received.

[0142] In some embodiments, the battery modules described above can also be assembled into a battery pack, and the number of battery modules contained in the battery pack can be one or more, the specific number of which can be selected by those skilled in the art according to the application and capacity of the battery pack.

[0143] Figures 6 and 7 illustrate a battery pack 1 as an example. Referring to Figures 6 and 7, the battery pack 1 may include a battery box and multiple battery modules 4 disposed within the battery box. The battery box includes an upper body 2 and a lower body 3, with the upper body 2 covering the lower body 3 to form a closed space for accommodating the battery modules 4. The multiple battery modules 4 can be arranged in any manner within the battery box.

[0144] In addition, this application also provides an electrical device, which includes the secondary battery provided in this application. The secondary battery can be used as a power source for the electrical device, or as an energy storage unit for the electrical device. The electrical device may include, but is not limited to, mobile devices (e.g., mobile phones, laptops, etc.), electric vehicles (e.g., pure electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, electric bicycles, electric scooters, electric golf carts, electric trucks, etc.), electric trains, ships and satellites, energy storage systems, etc.

[0145] As the electrical device, a single secondary battery cell, a battery module, or a battery pack can be selected according to its usage requirements.

[0146] Figure 8 shows an example of an electrical device. This device is a pure electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle, etc. To meet the high power and high energy density requirements of the secondary battery for this device, a battery pack or battery module can be used.

[0147] [Example]

[0148] The following describes embodiments of this application. The embodiments described below are exemplary and are only used to explain this application, and should not be construed as limiting this application. Where specific techniques or conditions are not specified in the embodiments, they are performed according to the techniques or conditions described in the literature in this field or according to the product instructions. Reagents or instruments used, unless otherwise specified, are all conventional products that can be obtained commercially.

[0149] Preparation example:

[0150] PAA adhesive preparation:

[0151] First, acrylic acid is placed in distilled water, and then a certain amount of sodium hydroxide is added to make the pH of the system 6-7. Then, crosslinking agent N,N-methyleneacrylamide and initiator potassium persulfate are added. The weight ratio of acrylic acid, crosslinking agent and initiator is 90:7:3. The mixture is stirred and dissolved at 60-90℃. The solution is then cooled at 65℃ and allowed to stand for 1 hour to obtain PAA adhesive, which is used as control adhesive 1.

[0152] Preparation of COC- group modified polyacrylic acid adhesive:

[0153] At a heating temperature of 60-90℃, the pH value of the aqueous solution of the control group adhesive 1 was controlled between 3.6 and 4. Small molecule PEO (molecular weight between 1000-50W) was slowly added to the aqueous solution of the control adhesive 1 (the molar amount of polyethylene oxide based on -O-CH2-CH2- units was 20% of the molar amount of acrylic acid) and stirred evenly for 2 hours. Small molecule PEO was grafted onto the side of the control adhesive 1 to generate a polyacrylic acid adhesive modified with -COC- groups, which was used as the control adhesive 2.

[0154] Preparation of PAA-SO3H composite binder by copolymerization:

[0155] A 1M mixed solution (deionized water + acrylic acid + sodium propylene sulfonate, molar ratio 5-30%) was slowly added dropwise to a flask at 60-90℃ over 1 hour. Then, an appropriate amount of a mixed solution of deionized water and H₂O₂ (H₂O₂ volume ratio approximately 30%) was added dropwise. After the addition was complete, the mixture was stirred uniformly at 90℃ for 30 minutes until the experiment was finished, yielding a PAA-SO₃H composite binder, a copolymer of sulfonic acid and acrylic acid.

[0156] The molar ratio of sodium propylene sulfonate was adjusted according to the molar content of -SO3H recorded in Table 1 (corresponding to the molar content of propylene sulfonate in acrylic acid and propylene sulfonate) to obtain PAA-SO3H composite adhesives with different molar contents of -SO3H.

[0157] Preparation of modified polyacrylic acid adhesive:

[0158] At a heating temperature of 60-90℃, small molecule polyethylene oxide (PEO) (molecular weight between 1000-50W) was slowly added to the aqueous solution of some of the PAA-SO3H composite adhesives listed in Table 1 (the molar amount of polyethylene oxide, calculated as -O-CH2-CH2- units, is 5%-30% of the total molar amount of acrylic acid and propylene sulfonate) and stirred uniformly for 2 hours. Throughout the process, the pH value of the system was controlled between 3.6 and 4. Small molecule PEO was branched onto the side of the PAA-SO3H composite adhesive to generate polyacrylic acid adhesive modified with -SO3H and -COC- groups.

[0159] By adjusting the addition ratio of PEO according to the molar content of -COC- groups recorded in Table 1, modified polyacrylic acid adhesives with different -COC- group contents were obtained, thus preparing adhesives 1 to 8.

[0160] test:

[0161] The functional group composition of the dry-state modified polyacrylic acid adhesive was determined using infrared diffraction spectroscopy. 50 mg of the dry-state modified polyacrylic acid adhesive was ground into a powder of tens of micrometers using a ball mill. This powder was mixed with potassium bromide powder and spread evenly on a sample dish. The infrared spectra of the sample were tested according to the national standard method GB / T 6040-2019. The infrared diffraction pattern of adhesive 1 in Table 1 is recorded in Figure 1. Figure 1 shows the diffraction pattern at 1043 cm⁻¹. -1 Sulfonate R-SO2-OM appeared at the site + The strong absorption peak of SO3 is at 1178 cm⁻¹. -1 A stretching vibration peak of the sulfonic acid group R-SO2-OH appears at 2940 cm⁻¹. -1 An absorption peak of -CH2- appears at 1416 cm⁻¹. -1 An absorption peak of symmetric stretching of carboxylate COO- appears at 1122 cm⁻¹.-1 The appearance of a weak absorption peak for the stretching of saturated fatty ether COC at the location confirms the presence of COC in the binder. The presence of -SO3H and -COC-.

[0162] Test of molar content of sulfur element:

[0163] Inductively coupled plasma atomic emission spectrometry (Inductively Coupled Plasma Atomic Emission Spectrometry, US EPA 6010D-2018) was used. The negative electrode of the secondary battery at 0% SOC was disassembled, thoroughly cleaned with DMC (dimethyl carbonate), dried, and the negative electrode active layer material was collected by a scraping method. The negative electrode active layer material was then microwave-digested using concentrated nitric acid at 200°C and 150 bar. The digested solution was then vaporized and ionized in a plasma torch. The intensity of the excited characteristic spectral lines was measured, and the mass percentage of sulfur was analyzed. The test results are recorded in Table 1.

[0164] The weight-average molecular weight of the modified polyacrylic acid binder was determined by gel permeation chromatography (GPC). In GPC, the binder was diluted with ultrapure water to a solid content of 2%, and the molecular weight distribution was determined by injection at a flow rate of 2 mL / min and a pressure of 1250 psi. A porous gel was used as the stationary phase, and separation was achieved based on the different flow rates of solute molecules of different molecular weights through the gel. The testing instrument was a Waters E2695. The test results are recorded in Table 1.

[0165] The viscosity of the modified polyacrylic acid adhesive was tested at 25℃ and 12 rpm. The adhesive viscosity test method was as follows: according to the national standard GB / T 33061.10-2016, the adhesive was diluted with ultrapure water to a solid content of 2%, and the viscosity was tested on a viscometer using a standard solution at 5000 MPa.s and 12 rpm. The test results are recorded in Table 1.

[0166] Table 1

[0167] Negative electrode preparation:

[0168] Graphite, binder, and SP conductive carbon were mixed according to the proportions in Table 2, and then mixed with water to form a slurry with a solid content of 70%. This slurry was coated onto a copper foil substrate and rolled to form a negative electrode sheet. The forming temperature was 80-90℃, and the forming time was 30 minutes. The double-layer coating amount of the negative electrode sheet was 400 mg / 1540.2 cm². 2 The coating thickness is approximately 150 μm, the copper foil thickness is 10 μm, and the compaction of the negative electrode film is 1.6 g / cm³. 3 .

[0169] The binders used for each negative electrode are recorded in Table 2.

[0170] Negative electrode adhesion test:

[0171] After thoroughly cleaning and drying the negative electrode sheet of the secondary battery at 0% SOC with DMC (dimethyl carbonate), apply adhesive tape to the coated side of the negative electrode sheet to be tested, leaving one end of the tape unattached to the negative electrode sheet to be tested. Fix the negative electrode sheet to be tested, and use a tensile testing machine to peel the unattached end of the tape from the coating surface at a uniform speed (set the tensile testing machine to a tensile speed of 50 mm / min). Measure the force at which the tape is peeled from the coating surface, which represents the cohesive force between the active materials.

[0172] Secondary battery fabrication:

[0173] Positive electrode preparation: The positive electrode formulation is 94.7wt% LiFePO4 + 5wt% PVDF + 0.3wt% SP. The positive electrode is prepared by wet slurry preparation and coated on an aluminum foil substrate. The forming time is 30 min.

[0174] Separator: 7μm thick PP+PE membrane (the thickness ratio of the two is 6:4).

[0175] Electrolyte: Composed of 90% EC + 5% DMC + 3% DEC + 1% PC + 1% additives (VC:FEC mass ratio is 1 / 1, and all percentages are mass percentages), and also contains LiPF6 at a concentration of 0.1 mol / L.

[0176] The positive electrode, separator, and negative electrode are stacked in sequence, with the separator positioned between the anode and cathode to provide isolation, resulting in a bare cell. The bare cell is then placed in outer packaging, injected with prepared electrolyte, and subjected to processes such as encapsulation, electrolyte filling, formation, and venting to obtain a lithium-ion battery.

[0177] The secondary battery was charged at a rate of 0.1C to a voltage of 3.65V, then charged at a constant voltage rate of 0.05C to 100% SOC, and then discharged at a rate of 0.1C to 50% SOC. Fresh electrode fragments from the disassembled secondary battery were used to assemble a symmetrical cell. The interfacial charge transfer resistance Rct was tested at different temperatures (-20℃, -10℃, 0℃, 10℃, 25℃). Furthermore, the activation energy EIS can be fitted using the Arrhenius equation, with the following fitting formula:

[0178] Log(T / Rct)=-(Ea / 2.303R)×(1000 / T)

[0179] T represents absolute temperature; Rct represents interfacial charge transfer resistance; Ea represents activation energy EIS; R is the gas constant 8.314. The results of Rct and activation energy are recorded in Table 2. The comparison data of activation energy between negative electrode 6 and control negative electrode 1 are recorded in Figure 2.

[0180] The DCR value of a secondary battery at 50% SOC is tested according to the test method specified in the Japan Electric Vehicles Association standard JEVSD713-2003, "Test Method for Output Density and Input Density of Sealed Nickel-Metal Hybrid Electric Vehicles". The test equipment forces a constant DC current I through the battery for a short 10 seconds, measures the voltage ΔU across the battery terminals, and calculates the current battery internal resistance using the formula R = ΔU / I. Specifically, the battery is charged and discharged at 50% SOC using a 4C rate (discharge first, then charge): 4C charging for 30 seconds, 4C discharging for 30 seconds; the lower limit voltage of the process protection is 2.0V, and the upper limit voltage is 3.8V. The resulting DC internal resistance is DCR.

[0181]

[0182] Based on the comparison between negative electrode 1 and control negative electrode 1 to 2, it can be seen that when modified with -SO3H group, the Rct and SEI film activation energy of the negative electrode are reduced, and the DCR value of the secondary battery is reduced, indicating that -SO3H improves the kinetic performance of the secondary battery.

[0183] The data comparison of negative electrode sheets 2 to 7 above shows that as the content of SO3H groups or -COC- groups in the binder increases, the cohesive force of the electrode sheet increases. This indicates that the binder modified by SO3H groups and -COC- groups strengthens the binding of the negative electrode active material, thereby reducing its expansion during charging and discharging. Moreover, the decrease in Rct, SEI film activation energy, and DCR value indicates that the synergistic effect of SO3H groups and -COC- groups more significantly modifies the binder, improves the transport capacity of active ions, and lowers the energy barrier for active ions to desolvate, which is beneficial to improving the dynamic performance of the battery.

[0184] Although this application has been described with reference to preferred embodiments, various modifications can be made thereto and components can be replaced with equivalents without departing from the scope of this application. In particular, the technical features mentioned in the various embodiments can be combined in any manner, provided there is no structural conflict. This application is not limited to the specific embodiments disclosed herein, but includes all technical solutions falling within the scope of the claims.

Claims

1. A secondary battery comprising a negative electrode sheet, wherein, The negative electrode sheet comprises a negative electrode current collector and a negative electrode film layer, and the negative electrode film layer comprises a negative electrode active material and a modified polyacrylic acid binder. The modified polyacrylic acid binder comprises -SO3H groups.

2. The secondary battery according to claim 1, wherein The modified polyacrylic adhesive further comprises -SO3M groups, M comprising one or more of Li + , Na + , or K + .

3. The secondary battery according to claim 1 or 2, wherein The modified polyacrylic acid binder further comprises -C-O-C- groups.

4. The secondary battery according to any one of claims 1 to 3, wherein The mass percentage of S in the modified polyacrylic acid binder is 2%-20%.

5. The secondary battery according to any one of claims 1 to 4, wherein The modified polyacrylic binder comprises a structural unit comprising a -SO3H group, and / or a structural unit comprising a -C-O-C- group, the structural unit comprising a -SO3H group comprising the structural unit comprising a -C-O-C- group comprising one or both of -CH2-CH(OH)-CH2- and -CH2-C(O)-CH2-, n being an integer from 1 to 100.

6. The secondary battery according to any one of claims 1 to 5, wherein The weight average molecular weight of the modified polyacrylic acid binder is 80W-320W.

7. The secondary battery according to any one of claims 1 to 6, wherein When the secondary battery is in a 50% SOC state, the charge transfer resistance Rct of the negative electrode sheet at 25°C is 5-12Ω.

8. The secondary battery according to any one of claims 1 to 7, wherein When the secondary battery is in a 0% SOC state, the cohesion of the negative electrode sheet is 250N / m-480N / m.

9. The secondary battery according to any one of claims 1 to 8, wherein The negative electrode film layer comprises, in terms of weight percentage, 93%-99% of a negative electrode active material, 0.5%-5% of a modified polyacrylic acid binder, and 0%-2% of a conductive agent.

10. A modified polyacrylic binder, wherein, The modified polyacrylic acid binder comprises -SO3H groups.

11. The modified polyacrylic binder of claim 10, wherein, The modified polyacrylic adhesive further comprises -SO3M groups and / or -C-O-C- groups, M comprising one or more of Li + , Na + , or K + .

12. The modified polyacrylic binder according to claim 10 or 11, wherein, The modified polyacrylic binder comprises Structural units, the modified polyacrylic binder further comprises structural units comprising -SO3H groups and / or structural units comprising -C-O-C- groups, the structural units comprising -SO3H groups comprising the structural units comprising -C-O-C- groups comprising one or both of -CH2-CH(OH)-CH2- and -CH2-C(O)-O-CH2-, n being an integer from 1 to 100.

13. The modified polyacrylic binder according to any one of claims 10 to 12, wherein, The weight average molecular weight of the polyacrylic acid binder is 80W-320W.

14. The modified polyacrylic binder according to any one of claims 10 to 13, wherein, The viscosity of a 2% solid content aqueous solution of the modified polyacrylic acid binder is 900mPa·s-1500mPa·s at 25°C and 12rpm.

15. A method of preparing a modified polyacrylic binder, wherein, The preparation method comprises: The acrylic acid and the propylene sulfonate are subjected to a copolymerization reaction under the action of a free radical initiator to obtain a -SO3H group modified polyacrylic acid, and the propylene sulfonate comprises any one or more of sodium propylene sulfonate, lithium propylene sulfonate, and potassium propylene sulfonate.

16. The method of making according to claim 15, wherein, The copolymerization reaction is performed at 60°C-90°C, and the free radical initiator comprises any one or more of hydrogen peroxide, benzoyl peroxide, cyclohexanone peroxide, and tert-butyl hydroperoxide.

17. The method of manufacturing according to claim 15 or 16, wherein, The molar amount of the propylene sulfonate is 5%-30% of the total molar amount of the acrylic acid and the propylene sulfonate.

18. The production method according to any one of claims 15 to 17, wherein, The preparation method further comprises: The -SO3H group modified polyacrylic acid is subjected to a grafting reaction with polyethylene oxide to obtain a -SO3H group and -C-O-C- group modified polyacrylic acid binder.

19. The method of making according to claim 18, wherein, The process of grafting the -SO3H group modified polyacrylic acid with polyethylene oxide comprises: The polyethylene oxide is continuously added to the -SO3H group modified polyacrylic acid under the conditions of 60°C-90°C, a pH value of 3.6-4, and stirring, so that the polyethylene oxide is grafted on the chain structure of the polyacrylic acid.

20. The method of making according to claim 19, wherein, In terms of -O-CH2-CH2- units, the molar amount of the polyethylene oxide is 5%-30% of the total molar amount of the acrylic acid and the propylene sulfonate.

21. An electrically powered device comprising a secondary battery, wherein The secondary battery comprises the secondary battery of any one of claims 1-9.

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