Dispersant, preparation method and application thereof, negative electrode slurry and preparation method thereof, negative electrode sheet and electrochemical device

Abstract

This application discloses a dispersant and its preparation method and application, a negative electrode slurry and its preparation method, a negative electrode sheet, and an electrochemical device. On one hand, by reducing the chain length of sodium carboxymethyl cellulose (CMC) polymer, the crystallinity and rigidity of the CMC polymer are reduced, thereby improving the cracking problem during high-speed thick coating of the negative electrode slurry, thus increasing the energy density and efficiency of the battery. On the other hand, by polymerizing unsaturated carbon chain groups on some of the hydroxyl groups of the CMC polymer to obtain a copolymer, the copolymer has multiple branches. These branches provide flexible segments for the CMC polymer, reducing its rigidity, thereby improving the cracking problem during high-speed thick coating of the negative electrode slurry, thus increasing the energy density and efficiency of the battery.

Description

Technical Field

[0001] This application relates to the field of battery technology, specifically to dispersants and their preparation methods and applications, negative electrode slurries and their preparation methods, negative electrode sheets and electrochemical devices. Background Technology

[0002] With the increasing market demand for lithium-ion battery energy density, high-speed, thick coating during electrode fabrication is a necessary trend in subsequent cell design. High-speed, thick coating typically refers to a coating speed >25m / min, which can increase production capacity; thick coating refers to a coating weight >180mg / 1540.25mm. 2 High-speed thick coating can improve battery energy density. However, it also causes severe cracking during the drying process, leading to warping of the electrode sheets and further cracking during the rolling process. This reduces the battery's energy density and efficiency. Summary of the Invention

[0003] This application is made in view of the above-mentioned problems, and its purpose is to provide a dispersant that improves the cracking problem in the high-speed thick coating process of negative electrode slurry, thereby improving the energy density and efficiency of the battery.

[0004] To achieve the above objectives, embodiments of this application provide a dispersant and its preparation method and application, a negative electrode slurry and its preparation method, a negative electrode sheet and an electrochemical device.

[0005] In a first aspect, embodiments of this application provide a dispersant comprising a sodium carboxymethyl cellulose polymer, wherein the sodium carboxymethyl cellulose polymer has the following structural formula: [The dispersant is described in the original text, but the translation is incomplete.]

[0006]

[0007] Wherein, R includes groups containing carbon chains with unsaturated bonds, m is a positive integer from 1 to 10, and n is a positive integer from 1 to 100.

[0008] Therefore, in the technical solution of this application embodiment, on the one hand, by reducing the chain length of the sodium carboxymethyl cellulose polymer, the crystallinity and rigidity of the sodium carboxymethyl cellulose polymer are reduced, thereby improving the cracking problem during the high-speed thick coating of the negative electrode slurry, and thus increasing the energy density and efficiency of the battery. On the other hand, by polymerizing unsaturated carbon chain groups on some of the hydroxyl groups of the sodium carboxymethyl cellulose polymer to obtain a copolymer, the copolymer has multiple branches. These branches provide flexible segments for the sodium carboxymethyl cellulose polymer, reducing the rigidity of the sodium carboxymethyl cellulose polymer, thereby improving the cracking problem during the high-speed thick coating of the negative electrode slurry, and thus increasing the energy density and efficiency of the battery. At the same time, the unpolymerized hydroxyl groups on the sodium carboxymethyl cellulose polymer provide hydrogen bonding sites, possessing better bonding and dispersing properties, thereby reducing the use of plasticizers and increasing the proportion of active materials in the negative electrode slurry, further improving the energy density and efficiency of the battery. Where m takes a positive integer value from 1 to 10, it is beneficial to reduce the crystallinity of sodium carboxymethyl cellulose polymer. When m is greater than 10, the crystallinity of sodium carboxymethyl cellulose polymer is still too high, and the probability of cracking during coating is too high. n takes a positive integer value from 1 to 100, it is beneficial to reduce the crystallinity of sodium carboxymethyl cellulose polymer. When n is greater than 100, the crystallinity of sodium carboxymethyl cellulose polymer is still too high, and the probability of cracking during coating is too high.

[0009] In some embodiments of this application, the group containing the unsaturated carbon chain can be -C=C-. In some embodiments of this application, the group containing the unsaturated carbon chain can also be -C≡C-. In some embodiments of this application, the group containing the unsaturated carbon chain can simultaneously contain both -C=C- and -C≡C-.

[0010] In any embodiment, R comprises a group with an unsaturated carbon chain of 3 to 8 carbon atoms. This group can increase the flexibility of the sodium carboxymethyl cellulose polymer and reduce its crystallinity, thereby reducing the probability of cracking. When R is less than 3, the effect on increasing the flexibility of the sodium carboxymethyl cellulose polymer is limited. When R is greater than 8, the molecular chain of the unsaturated carbon chain group is relatively stiff, and its effect on increasing the flexibility of the sodium carboxymethyl cellulose polymer is also limited. Optionally, R comprises a group with an unsaturated carbon chain of 4 to 6 carbon atoms.

[0011] In any embodiment, R further includes oxygen-containing polar functional groups. These polar functional groups are beneficial for coating and dispersing graphite, thereby improving the dispersion performance of sodium carboxymethyl cellulose. In some embodiments of this application, the oxygen-containing polar functional groups can be carboxylic acids, esters, amides, or hydroxyl groups. In some embodiments of this application, the oxygen-containing polar functional groups can also be acrylic acid, acrylamide, or acrylates.

[0012] In any embodiment, R includes at least one of acrylic acid, acrylamide, and acrylate. Acrylic acid, acrylamide, and acrylate are commonly used substances in lithium battery formulations, have little impact on battery performance, and can improve the flexibility of sodium carboxymethyl cellulose polymer.

[0013] In any embodiment, m is a positive integer from 4 to 8. m less than 4 affects the dispersion performance of the negative electrode active material, while m greater than 8 affects the crystallinity of the sodium carboxymethyl cellulose polymer; and / or,

[0014] n is a positive integer from 30 to 60. When n is less than 30, the dispersion performance of sodium carboxymethyl cellulose polymer will be reduced. When n is greater than 60, the flexibility of sodium carboxymethyl cellulose polymer will be reduced and the cracking rate will be increased.

[0015] Secondly, embodiments of this application propose the application of the dispersant of the first aspect of this application in the negative electrode slurry.

[0016] Thirdly, embodiments of this application provide a method for preparing the dispersant of the first aspect of this application, comprising the following steps:

[0017] Sodium carboxymethyl cellulose monomer is activated with an activating agent to obtain activated sodium carboxymethyl cellulose monomer;

[0018] The activated sodium carboxymethyl cellulose monomer is polymerized with a compound containing an unsaturated carbon chain to obtain a sodium carboxymethyl cellulose polymer.

[0019] By activating sodium carboxymethyl cellulose monomer with an activator, some of the hydroxyl groups on the sodium carboxymethyl cellulose monomer can form oxygen free radicals, which facilitate polymerization with compounds containing unsaturated carbon chains to obtain sodium methyl cellulose polymers.

[0020] In any embodiment, the step of activating sodium carboxymethyl cellulose monomer with an activating agent yields activated sodium carboxymethyl cellulose monomer containing:

[0021] The activator includes inorganic peroxide compounds. Activating sodium carboxymethyl cellulose monomer with inorganic peroxide compounds can reduce side reactions between the activator and the sodium carboxymethyl cellulose monomer, while simultaneously allowing some of the hydroxyl groups on the monomer to form oxygen free radicals, thus improving the polymerization efficiency of sodium carboxymethyl cellulose monomer with compounds containing unsaturated carbon chains.

[0022] In any embodiment, the activator further includes a sulfur-containing compound. The sulfur-containing compound can further reduce side reactions between the activator and the sodium carboxymethyl cellulose monomer, while simultaneously enabling some of the hydroxyl groups on the sodium carboxymethyl cellulose monomer to form oxygen free radicals, thereby improving the polymerization efficiency of the sodium carboxymethyl cellulose monomer with the compound containing unsaturated carbon chains.

[0023] In any embodiment, the activator includes, but is not limited to, at least one of sodium bisulfite and ammonium persulfate, potassium persulfate, and sodium persulfate. By using at least one of the above activators, some hydroxyl groups on the sodium carboxymethyl cellulose monomer can form oxygen free radicals, while reducing side reactions between the activator and the sodium carboxymethyl cellulose monomer, thereby improving the polymerization efficiency of the sodium carboxymethyl cellulose monomer with compounds containing unsaturated carbon chains. In some embodiments of this application, the activator may include only one of sodium bisulfite and ammonium persulfate, or potassium persulfate and sodium persulfate. In other embodiments of this application, the activator may simultaneously include two or more of sodium bisulfite and ammonium persulfate, or potassium persulfate and sodium persulfate. For example, it may simultaneously contain sodium bisulfite and ammonium persulfate, or simultaneously contain potassium persulfate and sodium persulfate, or simultaneously contain sodium bisulfite, ammonium persulfate, and sodium persulfate.

[0024] In any embodiment, the step of activating sodium carboxymethyl cellulose monomer with an activator to obtain activated sodium carboxymethyl cellulose monomer, wherein the mass ratio of activator to sodium carboxymethyl cellulose monomer is (1-200):100. Optionally, the mass ratio of activator to sodium carboxymethyl cellulose monomer is (6-80):100. The mass ratio of activator to sodium carboxymethyl cellulose monomer affects the formation of oxygen free radicals by some hydroxyl groups on the sodium carboxymethyl cellulose monomer. When the mass ratio of activator to sodium carboxymethyl cellulose monomer is less than 1:100, insufficient oxygen free radicals are formed, reducing the degree of polymerization with compounds containing unsaturated carbon chains. When the mass ratio of activator to sodium carboxymethyl cellulose monomer is less than 200:100, excessive hydroxyl groups form oxygen free radicals, resulting in excessive polymerization with compounds containing unsaturated carbon chains, thereby reducing the number of hydroxyl groups, reducing the adhesion and dispersibility of sodium carboxymethyl cellulose, and reducing the energy density and efficiency of the battery; and / or,

[0025] The activation temperature is 50–100°C, optionally 60–80°C. The activation temperature affects the formation of oxygen free radicals from some hydroxyl groups on the sodium carboxymethyl cellulose monomer. When the activation temperature is below 50°C, the rate of oxygen free radical formation from hydroxyl groups is too slow. When the activation temperature is above 100°C, some of the activator itself will undergo side reactions with the sodium carboxymethyl cellulose monomer, thus affecting the formation of oxygen free radicals; and / or,

[0026] The activation time is 3 to 8 hours, optionally 4 to 6 hours. The activation time affects the formation of oxygen free radicals by some hydroxyl groups on sodium carboxymethyl cellulose monomers. When the activation time is less than 3 hours, there are not enough oxygen free radicals formed, which reduces the degree of polymerization with compounds containing unsaturated carbon chains. When the activation time is greater than 8 hours, too many hydroxyl groups form oxygen free radicals, resulting in excessive polymerization with compounds containing unsaturated carbon chains. This reduces the number of hydroxyl groups, decreases the adhesion and dispersibility of sodium carboxymethyl cellulose, and reduces the energy density and efficiency of the battery.

[0027] In any embodiment, the step of polymerizing activated sodium carboxymethyl cellulose monomer with a compound containing an unsaturated carbon chain yields a sodium carboxymethyl cellulose polymer.

[0028] The polymerization temperature is 50-80℃, optionally 60-70℃. The polymerization temperature affects the degree of polymerization of sodium carboxymethyl cellulose monomer and compounds containing unsaturated carbon chains. When the polymerization temperature is below 50℃, the degree of polymerization is lower, reducing the proportion of compounds containing unsaturated carbon chains in the sodium carboxymethyl cellulose polymer. When the polymerization temperature is above 80℃, the degree of polymerization is higher, resulting in excessive compounds containing unsaturated carbon chains in the sodium carboxymethyl cellulose polymer, thereby reducing the number of hydroxyl groups, decreasing the binding and dispersing properties of sodium carboxymethyl cellulose, and reducing the energy density and efficiency of the battery; and / or,

[0029] The mass ratio of activated sodium carboxymethyl cellulose monomer to the compound containing unsaturated carbon chains is 1:(1-100); optionally, the mass ratio is 1:(1-50). This mass ratio affects the degree of polymerization of the sodium carboxymethyl cellulose monomer and the compound containing unsaturated carbon chains. When the mass ratio is less than 1:100, the proportion of activated sodium carboxymethyl cellulose monomer is too small, and the proportion of the compound containing unsaturated carbon chains is too large. Excessive amounts of the compound containing unsaturated carbon chains in the sodium carboxymethyl cellulose polymer reduce the number of hydroxyl groups, thus decreasing the binding and dispersing properties of the sodium carboxymethyl cellulose, and consequently reducing the energy density and efficiency of the battery. When the mass ratio is greater than 1:1, the proportion of activated sodium carboxymethyl cellulose monomer is too large, and the proportion of the compound containing unsaturated carbon chains is too small, resulting in little improvement in the crystallinity of the sodium carboxymethyl cellulose polymer; and / or,

[0030] Compounds containing unsaturated carbon chains include, but are not limited to, at least one of acrylic acid, acrylamide, and acrylates. Compounds containing unsaturated carbon chains can increase the degree of polymerization of the compound with activated sodium carboxymethyl cellulose monomers and exhibit good electrochemical stability. In some embodiments of this application, the compound package containing unsaturated carbon chains may contain only one of acrylic acid, acrylamide, and acrylates; in other embodiments, the compound package containing unsaturated carbon chains may contain two or more of acrylic acid, acrylamide, and acrylates simultaneously.

[0031] Fourthly, embodiments of this application provide a negative electrode slurry, comprising a negative electrode active material, a conductive agent, a binder, and a dispersant according to the first aspect of this application.

[0032] By adding a dispersant to the negative electrode slurry, the risk of cracking of the negative electrode slurry during coating can be reduced while ensuring the dispersion performance of the negative electrode active material, thereby improving the energy density and stability of the battery.

[0033] In any embodiment, the dispersant accounts for 0.5% to 5% of the mass of the negative electrode slurry. The mass percentage of the dispersant in the negative electrode slurry affects the dispersion performance of the negative electrode slurry. When the mass percentage of the dispersant in the negative electrode slurry is less than 0.5%, the dispersion performance of the negative electrode slurry is poor, affecting the energy density and stability of the battery. When the mass percentage of the dispersant in the negative electrode slurry is greater than 5%, it affects the content of the negative electrode active material, thereby reducing the energy density and stability of the battery. Optionally, the mass percentage of the dispersant in the negative electrode slurry is 1% to 2%.

[0034] In any embodiment, the negative electrode active material includes, but is not limited to, at least one of graphite, non-graphitized carbon, carbon nanomaterials, carbon-based organometallic frameworks, and titanium oxides. Using the aforementioned negative electrode active materials can reduce costs while ensuring energy density; and / or,

[0035] The conductive agent includes, but is not limited to, at least one of carbon nanotubes and graphene. Using the aforementioned conductive agent can reduce costs while ensuring energy density and conductivity; and / or,

[0036] The adhesive includes, but is not limited to, at least one of styrene-acrylic emulsion, polyvinylidene fluoride, polytetrafluoroethylene, and polychlorotrifluoroethylene. Using the above adhesives can reduce costs while ensuring bonding performance.

[0037] Fifthly, embodiments of this application propose a method for preparing the negative electrode slurry according to the third aspect of this application, comprising the following steps:

[0038] The negative electrode active material, conductive agent and first part of dispersant are added to the solvent and mixed to obtain a premix;

[0039] The second part of the dispersant and binder is mixed with the premix to obtain the negative electrode slurry.

[0040] By mixing the negative electrode active material, conductive agent, and a first-part dispersant with a solvent to obtain a premix, the negative electrode active material can be better dispersed in the solvent. The second-part dispersant and binder are then mixed with the premix to obtain a negative electrode slurry. The steric hindrance of the sodium carboxymethyl cellulose polymer allows for better suspension and dispersion of the negative electrode active material in the solvent. In this application, the solvent includes, but is not limited to, water.

[0041] In any embodiment, the mass ratio of the first dispersant to the second dispersant is (1-10):7. The mass ratio of the first dispersant to the second dispersant affects the dispersion and suspension properties of the negative electrode active material. When the mass ratio of the first dispersant to the second dispersant is less than 1:7, the dispersion performance of the negative electrode active material is poor. When the mass ratio of the first dispersant to the second dispersant is greater than 10:7, the suspension performance of the negative electrode active material is poor. Optionally, the mass ratio of the first dispersant to the second dispersant is (2-5):7.

[0042] In any embodiment, the step of adding the negative electrode active material, the conductive agent, and the first portion of the dispersant to a solvent and mixing them to obtain a premix, wherein the mixing method includes kneading, wherein:

[0043] The kneading speed is 10-50 rpm. The kneading speed affects the dispersion performance of the negative electrode active material. When the kneading speed is less than 10 rpm, the dispersion performance is poor. When the kneading speed is greater than 50 rpm, it will shear the negative electrode active material, produce side reactions, and reduce the energy density and stability of the battery. Optionally, the kneading speed is 20-30 rpm.

[0044] The kneading time is 10 to 120 minutes. The kneading time affects the dispersion performance of the negative electrode active material. If the kneading time is less than 10 minutes, the dispersion performance is poor. If the kneading time is greater than 120 minutes, it will shear the negative electrode active material, produce side reactions, and reduce the energy density and stability of the battery. Optionally, the kneading time is 60 to 90 minutes.

[0045] Kneading, under conditions of high solid content, results in strong mechanical force and enhanced dispersion of the slurry. This strong mechanical force coats the negative electrode active material, allowing it to be better dispersed in the solvent.

[0046] Sixthly, embodiments of this application provide a negative electrode sheet, including the negative electrode slurry of the fifth aspect of this application.

[0047] In a seventh aspect, embodiments of this application provide an electrochemical device including the negative electrode sheet of the sixth aspect of this application.

[0048] In any embodiment, the electrochemical device includes a capacitor, a primary battery, or a secondary battery. Detailed Implementation

[0049] The following details the implementation of the electrolyte, the method for preparing the electrolyte, the solar power generation device, and the power consumption device of this application. However, unnecessary detailed descriptions may be omitted. For example, detailed descriptions of well-known matters and repetitive descriptions of actually identical structures may be omitted. This is to avoid making the following description unnecessarily lengthy and to facilitate understanding by those skilled in the art. Furthermore, the following description is provided to enable those skilled in the art to fully understand this application and is not intended to limit the subject matter of the claims.

[0050] 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.

[0051] Unless otherwise specified, all embodiments and optional embodiments of this application can be combined to form new technical solutions.

[0052] Unless otherwise specified, all technical features and optional technical features of this application may be combined to form new technical solutions.

[0053] 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 mention that the method may also include step (c) indicates 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.

[0054] With the increasing market demand for lithium-ion battery energy density, high-speed, thick coating during electrode fabrication is a necessary trend in subsequent cell design. High-speed, thick coating typically refers to a coating speed >25m / min, which can increase production capacity; thick coating refers to a coating weight >180mg / 1540.25mm. 2 High-speed thick coating can improve battery energy density. However, it also causes severe cracking during the drying process, leading to warping of the electrode sheets and further cracking during the rolling process. This reduces the battery's energy density and efficiency.

[0055] The high-speed thick coating exhibits severe cracking, primarily because sodium carboxymethyl cellulose generates drying stress during the drying process, causing the electrode sheets to warp and further crack during the rolling process.

[0056] Therefore, numerous technologies have emerged to address the problem of coating cracking. For example, a negative electrode slurry, a negative electrode sheet, and lithium batteries and energy storage devices are developed. The negative electrode slurry includes: a negative electrode active material, a conductive agent, a binder, a dispersant, and a plasticizer, wherein the plasticizer is propylene glycol and / or butylene glycol; based on the total mass of the negative electrode active material, the conductive agent, the binder, and the plasticizer, the amount of propylene glycol and butylene glycol added is 0.1–0.5 wt%. The plasticizer increases the toughness of the negative electrode sheet to solve the coating cracking problem and improve the energy density of the electrode sheet. By adding a new auxiliary plasticizer to the anode formulation, the crystallinity of sodium carboxymethyl cellulose is reduced by decreasing the hydrogen bonding between sodium carboxymethyl cellulose molecules, thereby improving molecular flexibility. However, due to the addition of new materials, the proportion of the active main material decreases, reducing the energy density. Furthermore, excessive plasticizer residue will cause interface problems. Plasticizers have poor compatibility with electrolytes, so excessive residue will worsen the interface, further affecting kinetics and safety issues.

[0057] Surprisingly, a sodium carboxymethyl cellulose (CCMC) polymer can be obtained by free radical polymerization of some of the hydroxyl groups of short-chain CCMC with unsaturated carbon chains. The unsaturated carbon chains provide flexible segments for the rigid CCMC, while the numerous hydroxyl groups on the CCMC provide hydrogen bonding sites, resulting in high adhesiveness. Using the synthesized flexible CCMC polymer as a dispersant eliminates the need for plasticizers, thereby solving interface problems and increasing the proportion of active materials. This also improves the energy density and stability of the battery.

[0058] Based on this, this application discloses a dispersant, its preparation method and application, a negative electrode slurry and its preparation method, a negative electrode sheet and an electrochemical device.

[0059] In a first aspect, embodiments of this application provide a dispersant comprising a sodium carboxymethyl cellulose polymer, wherein the sodium carboxymethyl cellulose polymer has the following structural formula: [The dispersant is described in the original text, but the translation is incomplete.]

[0060]

[0061] Wherein, R includes groups containing carbon chains with unsaturated bonds, m is a positive integer from 1 to 10, and n is a positive integer from 1 to 100.

[0062] Therefore, in the technical solution of this application embodiment, on the one hand, by reducing the chain length of the sodium carboxymethyl cellulose polymer, the crystallinity and rigidity of the sodium carboxymethyl cellulose polymer are reduced, thereby improving the cracking problem during the high-speed thick coating of the negative electrode slurry, and thus increasing the energy density and efficiency of the battery. On the other hand, by polymerizing unsaturated carbon chain groups on some of the hydroxyl groups of the sodium carboxymethyl cellulose polymer to obtain a copolymer, the copolymer has multiple branches. These branches provide flexible segments for the sodium carboxymethyl cellulose polymer, reducing the rigidity of the sodium carboxymethyl cellulose polymer, thereby improving the cracking problem during the high-speed thick coating of the negative electrode slurry, and thus increasing the energy density and efficiency of the battery. At the same time, the unpolymerized hydroxyl groups on the sodium carboxymethyl cellulose polymer provide hydrogen bonding sites, possessing better bonding and dispersing properties, thereby reducing the use of plasticizers and increasing the proportion of active materials in the negative electrode slurry, further improving the energy density and efficiency of the battery. Where m takes a positive integer value from 1 to 10, it is beneficial to reduce the crystallinity of sodium carboxymethyl cellulose polymer. When m is greater than 10, the crystallinity of sodium carboxymethyl cellulose polymer is still too high, and the probability of cracking during coating is too high. n takes a positive integer value from 1 to 100, it is beneficial to reduce the crystallinity of sodium carboxymethyl cellulose polymer. When n is greater than 100, the crystallinity of sodium carboxymethyl cellulose polymer is still too high, and the probability of cracking during coating is too high.

[0063] In some embodiments of this application, the group containing the unsaturated carbon chain can be -C=C-. In some embodiments of this application, the group containing the unsaturated carbon chain can also be -C≡C-. In some embodiments of this application, the group containing the unsaturated carbon chain can simultaneously contain both -C=C- and -C≡C-.

[0064] In any embodiment, R comprises a group with an unsaturated carbon chain of 3 to 8 carbon atoms. This group can increase the flexibility of the sodium carboxymethyl cellulose polymer and reduce its crystallinity, thereby reducing the probability of cracking. When R is less than 3, the effect on increasing the flexibility of the sodium carboxymethyl cellulose polymer is limited. When R is greater than 8, the molecular chain of the unsaturated carbon chain group is relatively stiff, and its effect on increasing the flexibility of the sodium carboxymethyl cellulose polymer is also limited. R can be a group comprising an unsaturated carbon chain of 3, 4, 5, 6, 7, or 8 carbon atoms. Optionally, R comprises a group comprising an unsaturated carbon chain of 4 to 6 carbon atoms.

[0065] In any embodiment, R further includes oxygen-containing polar functional groups. These polar functional groups are beneficial for coating and dispersing graphite, thereby improving the dispersion performance of sodium carboxymethyl cellulose. In some embodiments of this application, the oxygen-containing polar functional groups can be carboxylic acids, esters, amides, or hydroxyl groups. In some embodiments of this application, the oxygen-containing polar functional groups can also be acrylic acid, acrylamide, or acrylates.

[0066] In any embodiment, R includes at least one of acrylic acid, acrylamide, and acrylate. Acrylic acid, acrylamide, and acrylate are commonly used substances in lithium battery formulations, have little impact on battery performance, and can improve the flexibility of sodium carboxymethyl cellulose polymer.

[0067] In any embodiment, m is a positive integer from 4 to 8. m less than 4 affects the dispersion performance of the negative electrode active material, while m greater than 8 affects the crystallinity of the sodium carboxymethyl cellulose polymer. The value of m can be 4, 5, 6, 7, or 8; and / or...

[0068] n is a positive integer from 30 to 60. If n is less than 30, it will reduce the dispersion performance of sodium carboxymethyl cellulose polymer. If n is greater than 60, it will reduce the flexibility of sodium carboxymethyl cellulose polymer and increase the cracking rate. The value of n can be 30, 35, 40, 45, 50, 55 or 60, or any positive integer between 30 and 60.

[0069] Secondly, embodiments of this application propose the application of the dispersant of the first aspect of this application in the negative electrode slurry.

[0070] Thirdly, embodiments of this application provide a method for preparing the dispersant of the first aspect of this application, comprising the following steps:

[0071] Sodium carboxymethyl cellulose monomer is activated with an activating agent to obtain activated sodium carboxymethyl cellulose monomer;

[0072] The activated sodium carboxymethyl cellulose monomer is polymerized with a compound containing an unsaturated carbon chain to obtain a sodium carboxymethyl cellulose polymer.

[0073] By activating sodium carboxymethyl cellulose monomer with an activator, some of the hydroxyl groups on the sodium carboxymethyl cellulose monomer can form oxygen free radicals, which facilitate polymerization with compounds containing unsaturated carbon chains to obtain sodium methyl cellulose polymers.

[0074] In any embodiment, the step of activating sodium carboxymethyl cellulose monomer with an activating agent yields activated sodium carboxymethyl cellulose monomer containing:

[0075] The activator includes inorganic peroxide compounds. Activating sodium carboxymethyl cellulose monomer with inorganic peroxide compounds can reduce side reactions between the activator and the sodium carboxymethyl cellulose monomer, while simultaneously allowing some of the hydroxyl groups on the monomer to form oxygen free radicals, thus improving the polymerization efficiency of sodium carboxymethyl cellulose monomer with compounds containing unsaturated carbon chains.

[0076] In any embodiment, the activator further includes a sulfur-containing compound. The sulfur-containing compound can further reduce side reactions between the activator and the sodium carboxymethyl cellulose monomer, while simultaneously enabling some of the hydroxyl groups on the sodium carboxymethyl cellulose monomer to form oxygen free radicals, thereby improving the polymerization efficiency of the sodium carboxymethyl cellulose monomer with the compound containing unsaturated carbon chains.

[0077] In any embodiment, the activator includes, but is not limited to, at least one of sodium bisulfite and ammonium persulfate, potassium persulfate, and sodium persulfate. By using at least one of the above activators, some hydroxyl groups on the sodium carboxymethyl cellulose monomer can form oxygen free radicals, while reducing side reactions between the activator and the sodium carboxymethyl cellulose monomer, thereby improving the polymerization efficiency of the sodium carboxymethyl cellulose monomer with compounds containing unsaturated carbon chains. In some embodiments of this application, the activator may include only one of sodium bisulfite and ammonium persulfate, or potassium persulfate and sodium persulfate. In other embodiments of this application, the activator may simultaneously include two or more of sodium bisulfite and ammonium persulfate, or potassium persulfate and sodium persulfate. For example, it may simultaneously contain sodium bisulfite and ammonium persulfate, or simultaneously contain potassium persulfate and sodium persulfate, or simultaneously contain sodium bisulfite, ammonium persulfate, and sodium persulfate.

[0078] In any embodiment, the step of activating sodium carboxymethyl cellulose monomer with an activator to obtain activated sodium carboxymethyl cellulose monomer, wherein the mass ratio of activator to sodium carboxymethyl cellulose monomer is (1-200):100. Optionally, the mass ratio of activator to sodium carboxymethyl cellulose monomer is (6-80):100. The mass ratio of activator to sodium carboxymethyl cellulose monomer affects the formation of oxygen free radicals from some hydroxyl groups on the sodium carboxymethyl cellulose monomer. When the mass ratio of activator to sodium carboxymethyl cellulose monomer is less than 1:100, the number of oxygen free radicals formed is insufficient, reducing the polymerization efficiency with compounds containing unsaturated carbon chains. When the mass ratio of activator to sodium carboxymethyl cellulose monomer is less than 200:100, excessive hydroxyl groups form oxygen free radicals, leading to excessive polymerization with compounds containing unsaturated carbon chains. This reduces the number of hydroxyl groups, decreasing the adhesion and dispersibility of sodium carboxymethyl cellulose, and consequently reducing the energy density and efficiency of the battery. The mass ratio of activator to sodium carboxymethyl cellulose monomer can be 1:100, 1:80, 1:50, 1:10, 1:5, 1:4, 1:3, 1:2, 1:1, or 2:1, or any value between 1 and 200:100; and / or,

[0079] The activation temperature is 50–100°C. The activation temperature affects the formation of oxygen free radicals from some hydroxyl groups on the sodium carboxymethyl cellulose monomer. When the activation temperature is below 50°C, the rate of oxygen free radical formation from hydroxyl groups is too slow. When the activation temperature is above 100°C, some of the activator itself will undergo side reactions with the sodium carboxymethyl cellulose monomer, thus affecting the formation of oxygen free radicals. The activation temperature can be 50°C, 55°C, 60°C, 65°C, 70°C, 75°C, 80°C, 85°C, 90°C, 95°C, or 100°C. Optionally, the activation temperature is 60–80°C; and / or,

[0080] The activation time is 3–8 hours. The activation time affects the formation of oxygen free radicals from some of the hydroxyl groups on the sodium carboxymethyl cellulose monomer. When the activation time is less than 3 hours, insufficient oxygen free radicals are formed, reducing the degree of polymerization with compounds containing unsaturated carbon chains. When the activation time is greater than 8 hours, excessive hydroxyl groups form oxygen free radicals, resulting in excessive polymerization with compounds containing unsaturated carbon chains. This reduces the number of hydroxyl groups, decreases the binding and dispersing properties of sodium carboxymethyl cellulose, and reduces the energy density and efficiency of the battery. The activation time can be 3 hours, 3.5 hours, 4 hours, 4.5 hours, 5 hours, 5.5 hours, 6 hours, 6.5 hours, 7 hours, 7.5 hours, or 8 hours. Optionally, the activation time is 4–6 hours.

[0081] In any embodiment, the step of polymerizing activated sodium carboxymethyl cellulose monomer with a compound containing an unsaturated carbon chain yields a sodium carboxymethyl cellulose polymer.

[0082] The polymerization temperature is 50-80℃. The polymerization temperature affects the degree of polymerization of sodium carboxymethyl cellulose monomer and compounds containing unsaturated carbon chains. When the polymerization temperature is below 50℃, the degree of polymerization is relatively low, reducing the proportion of compounds containing unsaturated carbon chains in the sodium carboxymethyl cellulose polymer. When the polymerization temperature is above 80℃, the degree of polymerization is relatively high, resulting in an excessive number of compounds containing unsaturated carbon chains in the sodium carboxymethyl cellulose polymer, thereby reducing the number of hydroxyl groups, decreasing the binding and dispersing properties of sodium carboxymethyl cellulose, and reducing the energy density and efficiency of the battery. The polymerization temperature can be 50℃, 55℃, 60℃, 65℃, 70℃, 75℃, or 80℃; optionally, the polymerization temperature is 60-70℃; and / or...

[0083] The mass ratio of activated sodium carboxymethyl cellulose monomer to the compound containing unsaturated carbon chains is 1:(1~100). This mass ratio affects the degree of polymerization of both the activated sodium carboxymethyl cellulose monomer and the compound containing unsaturated carbon chains. When the mass ratio is less than 1:100, the proportion of activated sodium carboxymethyl cellulose monomer is too small, and the proportion of the compound containing unsaturated carbon chains is too large. Excessive amounts of the compound containing unsaturated carbon chains in the sodium carboxymethyl cellulose polymer reduce the number of hydroxyl groups, thereby reducing the adhesion and dispersibility of sodium carboxymethyl cellulose, and ultimately reducing the energy density and efficiency of the battery. When the mass ratio of activated sodium carboxymethyl cellulose monomer to the compound containing unsaturated carbon chains is greater than 1:1, the proportion of activated sodium carboxymethyl cellulose monomer is too large and the proportion of the compound containing unsaturated carbon chains is too small, resulting in insignificant improvement in the crystallinity of the sodium carboxymethyl cellulose polymer. The mass ratio of activated sodium carboxymethyl cellulose monomer to the compound containing unsaturated carbon chains can be 1:1, 1:5, 1:10, 1:15, 1:20, 1:25, 1:30, 1:35, 1:40, 1:45, 1:50, 1:60, 1:70, 1:80, 1:90, or 1:100, or any value between 1:(1-100); optionally, the mass ratio of activated sodium carboxymethyl cellulose monomer to the compound containing unsaturated carbon chains is 1:(1-50); and / or,

[0084] Compounds containing unsaturated carbon chains include, but are not limited to, at least one of acrylic acid, acrylamide, and acrylates. Compounds containing unsaturated carbon chains can increase the degree of polymerization of the compound with activated sodium carboxymethyl cellulose monomers and exhibit good electrochemical stability. In some embodiments of this application, the compound package containing unsaturated carbon chains may contain only one of acrylic acid, acrylamide, and acrylates; in other embodiments, the compound package containing unsaturated carbon chains may contain two or more of acrylic acid, acrylamide, and acrylates simultaneously.

[0085] Fourthly, embodiments of this application provide a negative electrode slurry, comprising a negative electrode active material, a conductive agent, a binder, and a dispersant according to the first aspect of this application.

[0086] By adding a dispersant to the negative electrode slurry, the risk of cracking of the negative electrode slurry during coating can be reduced while ensuring the dispersion performance of the negative electrode active material, thereby improving the energy density and stability of the battery.

[0087] In any embodiment, the dispersant accounts for 0.5% to 5% of the mass of the negative electrode slurry. The mass percentage of the dispersant in the negative electrode slurry affects the dispersion performance of the negative electrode slurry. When the mass percentage of the dispersant in the negative electrode slurry is less than 0.5%, the dispersion performance of the negative electrode slurry is poor, affecting the energy density and stability of the battery. When the mass percentage of the dispersant in the negative electrode slurry is greater than 5%, it affects the content of the negative electrode active material, thereby reducing the energy density and stability of the battery. The mass percentage of the dispersant in the negative electrode slurry can be 0.5%, 1%, 1.5%, 2%, 2.5%, 3%, 3.5%, 4%, 4.5%, or 5%, or any value between 0.5% and 5%. Optionally, the mass percentage of the dispersant in the negative electrode slurry is 1% to 2%.

[0088] In any embodiment, the negative electrode active material includes, but is not limited to, at least one of graphite, non-graphitized carbon, carbon nanomaterials, carbon-based organometallic frameworks, and titanium oxides. Using the aforementioned negative electrode active materials can reduce costs while ensuring energy density; and / or,

[0089] The conductive agent includes, but is not limited to, at least one of carbon nanotubes and graphene. Using the aforementioned conductive agent can reduce costs while ensuring energy density and conductivity; and / or,

[0090] The adhesive includes, but is not limited to, at least one of styrene-acrylic emulsion, polyvinylidene fluoride, polytetrafluoroethylene, and polychlorotrifluoroethylene. Using the above adhesives can reduce costs while ensuring bonding performance.

[0091] Fifthly, embodiments of this application propose a method for preparing the negative electrode slurry according to the third aspect of this application, comprising the following steps:

[0092] The negative electrode active material, conductive agent and first part of dispersant are added to the solvent and mixed to obtain a premix;

[0093] The second part of the dispersant and binder is mixed with the premix to obtain the negative electrode slurry.

[0094] By mixing the negative electrode active material, conductive agent, and a first-part dispersant with a solvent to obtain a premix, the negative electrode active material can be better dispersed in the solvent. The second-part dispersant and binder are then mixed with the premix to obtain a negative electrode slurry. The steric hindrance of the sodium carboxymethyl cellulose polymer allows for better suspension and dispersion of the negative electrode active material in the solvent. In this application, the solvent includes, but is not limited to, water.

[0095] In any embodiment, the mass ratio of the first dispersant to the second dispersant is (1-10):7. The mass ratio of the first dispersant to the second dispersant affects the dispersion and suspension properties of the negative electrode active material. When the mass ratio of the first dispersant to the second dispersant is less than 1:7, the dispersion performance of the negative electrode active material is poor. When the mass ratio of the first dispersant to the second dispersant is greater than 10:7, the suspension performance of the negative electrode active material is poor. The mass ratio of the first dispersant to the second dispersant can be 1:7, 2:7, 3:7, 4:7, 5:7, 6:7, 1:1, 8:7, 9:7, or 10:7, or any value between (1-10):7. Optionally, the mass ratio of the first dispersant to the second dispersant is (2-5):7.

[0096] In any embodiment, the step of adding the negative electrode active material, the conductive agent, and the first portion of the dispersant to a solvent and mixing them to obtain a premix, wherein the mixing method includes kneading, wherein:

[0097] The kneading speed is 10-50 rpm. The kneading speed affects the dispersion performance of the negative electrode active material. When the kneading speed is less than 10 rpm, the dispersion performance is poor. When the kneading speed is greater than 50 rpm, it will shear the negative electrode active material, produce side reactions, and reduce the energy density and stability of the battery. Optionally, the kneading speed is 20-30 rpm.

[0098] The kneading time is 10 to 120 minutes. The kneading time affects the dispersion performance of the negative electrode active material. If the kneading time is less than 10 minutes, the dispersion performance is poor. If the kneading time is greater than 120 minutes, it will shear the negative electrode active material, produce side reactions, and reduce the energy density and stability of the battery. Optionally, the kneading time is 60 to 90 minutes.

[0099] Kneading, under conditions of high solid content, results in strong mechanical force and enhanced dispersion of the slurry. This strong mechanical force coats the negative electrode active material, allowing it to be better dispersed in the solvent.

[0100] Sixthly, embodiments of this application provide a negative electrode sheet, including the negative electrode slurry of the fifth aspect of this application.

[0101] In a seventh aspect, embodiments of this application provide an electrochemical device including the negative electrode sheet of the sixth aspect of this application.

[0102] In any embodiment, the electrochemical device includes a capacitor, a primary battery, or a secondary battery.

[0103] The technical solution of the present invention will be further described in detail below with reference to specific embodiments. It should be understood that the following embodiments are only used to explain the present invention and are not intended to limit the present invention.

[0104] Example

[0105] The dispersants of Examples 1 to 17 of this application are as per the parameters in Table 1, and the negative electrode slurries of Examples 18 to 40 and Comparative Examples 1 to 8 are as per the parameters in Table 2.

[0106] Table 1 Parameters of the dispersants in Examples 1 to 17

[0107] dispersant Sodium carboxymethyl cellulose polymer Example 1 R = 2, m = 6, n = 50, containing oxygen-containing polar functional groups Example 2 R = 2, m = 1, n = 100, oxygen-containing polar functional groups Example 3 R = 3, m = 10, n = 1, oxygen-containing polar functional groups Example 4 R = 10, m = 6, n = 50, containing oxygen-containing polar functional groups Example 5 R = 3, m = 6, n = 50, oxygen-containing polar functional groups Example 6 R = 4, m = 6, n = 50, containing oxygen-containing polar functional groups Example 7 R=4, m=6, n=50, does not contain oxygen polar functional groups Example 8 R=6, m=6, n=50, oxygen-containing polar functional groups Example 9 R = 8, m = 6, n = 50, containing oxygen-containing polar functional groups Example 10 R = 5, m = 4, n = 30, oxygen-containing polar functional groups Example 11 R = 5, m = 8, n = 40, containing oxygen-containing polar functional groups Example 12 R=5, m=4, n=60, oxygen-containing polar functional groups Example 13 R is acrylic acid, m = 7, n = 55 Example 14 R is acrylamide, m = 7, n = 55 Example 15 R represents acrylate, m = 7, n = 55 Example 16 R represents acrylic acid and acrylamide, m = 7, n = 55 Example 17 R represents acrylic acid, acrylamide, or acrylate, m = 7, n = 55

[0108] Table 2. Parameters of the negative electrode slurries in Examples 18-40 and Comparative Examples 1-7.

[0109]

[0110]

[0111] Example 41

[0112] A method for preparing a dispersant includes the following steps:

[0113] Sodium carboxymethyl cellulose monomer is activated with an activating agent to obtain activated sodium carboxymethyl cellulose monomer;

[0114] The activated sodium carboxymethyl cellulose monomer is polymerized with a compound containing an unsaturated carbon chain to obtain a sodium carboxymethyl cellulose polymer.

[0115] Example 42

[0116] A method for preparing a dispersant, comprising the following steps:

[0117] Sodium carboxymethyl cellulose monomer was activated with an inorganic peroxide compound to obtain activated sodium carboxymethyl cellulose monomer;

[0118] The activated sodium carboxymethyl cellulose monomer is polymerized with a compound containing an unsaturated carbon chain to obtain a sodium carboxymethyl cellulose polymer.

[0119] Example 43

[0120] A method for preparing a dispersant, comprising the following steps:

[0121] Sodium carboxymethyl cellulose monomer was activated by simultaneously activating it with ammonium sulfate and potassium persulfate to obtain activated sodium carboxymethyl cellulose monomer. The mass ratio of activator to sodium carboxymethyl cellulose monomer was 50:100, the activation temperature was 65℃, and the activation time was 5h.

[0122] The activated sodium carboxymethyl cellulose monomer was polymerized with acrylic acid to obtain a sodium carboxymethyl cellulose polymer. The polymerization temperature was 65°C, and the mass ratio of the activated sodium carboxymethyl cellulose monomer to the compound containing unsaturated carbon chains was 1:2.

[0123] Example 44

[0124] A method for preparing a negative electrode slurry includes the following steps:

[0125] The negative electrode active material, conductive agent and first part of dispersant are added to the solvent and mixed to obtain a premix;

[0126] The second part of the dispersant and binder is mixed with the premix to obtain the negative electrode slurry.

[0127] Example 45

[0128] A method for preparing a negative electrode slurry includes the following steps:

[0129] Graphite, carbon nanotubes, and sodium carboxymethyl cellulose polymer (R=8, m=6, n=50, containing oxygen polar functional groups) were added to water and mixed to obtain a premix.

[0130] The second part, containing sodium carboxymethyl cellulose polymer with oxygen-containing polar functional groups (R=8, m=6, n=50) and polyvinylidene fluoride, is mixed with the premix to obtain a negative electrode slurry, wherein the mass ratio of the first part of the dispersant to the second part of the dispersant is 3:7.

[0131] Example 46

[0132] A method for preparing a negative electrode slurry includes the following steps:

[0133] Graphite, carbon nanotubes, and sodium carboxymethyl cellulose polymer with R=8, m=6, n=50 and oxygen-containing polar functional groups were added to water and kneaded at 25 rpm for 75 min to obtain a premix.

[0134] The second part, containing sodium carboxymethyl cellulose polymer with oxygen-containing polar functional groups (R=8, m=6, n=50) and polyvinylidene fluoride, is mixed with the premix to obtain a negative electrode slurry, wherein the mass ratio of the first part of the dispersant to the second part of the dispersant is 3:7.

[0135] Performance testing

[0136] 1. Slurry filterability test

[0137] The negative electrode slurries of Examples 14 to 32 and Comparative Examples 1 to 8 were filtered under a 150-mesh filter screen, folded into a triangle with a size of 25cm*25cm. 500mL of slurry was poured into the filter screen from the top, and the slurry flowed out from the tip of the filter screen. The filtration time of the slurry was recorded. The results are shown in Table 3.

[0138] 2. Observe the gelation and sedimentation state of the slurry.

[0139] The negative electrode slurries of Examples 14 to 32 and Comparative Examples 1 to 8 were placed for different times to observe whether the slurries would form a jelly-like gel state, and their slurry viscosity was tested. If the viscosity of the upper layer of slurry in the test beaker decreased and the lower layer of slurry became thicker, it indicated that slurry sedimentation had occurred. The results are shown in Table 3.

[0140] 3. Observe the slurry coating window

[0141] The negative electrode slurries of Examples 14 to 32 and Comparative Examples 1 to 8 were coated, and the cracking of the electrode sheets was observed. The maximum weight of the coating that did not crack was measured. The results are shown in Table 3.

[0142] 4. Battery DC resistance performance

[0143] At 25°C, the negative electrode slurries of Examples 14 to 32 and Comparative Examples 1 to 8 were respectively prepared into batteries. The batteries were charged at a constant current of 1 / 3C to 4.2V, then charged at a constant voltage of 4.2V to a current of 0.05C. After resting for 5 minutes, the voltage V1 was recorded. Then, the batteries were discharged at 1 / 3C for 30 seconds, and the voltage V2 was recorded. The internal resistance DCR of the battery was obtained by calculating (V2-V1) / 1 / 3C, and the results are shown in Table 3.

[0144] 5. Battery efficiency

[0145] The testing process is as follows: At 25°C, the battery corresponding to Example 1 was charged to 4.3V at a constant current of 1 / 3*C, then charged to a current of 0.05C at a constant voltage of 4.3V. After resting for 5 minutes, it was discharged to 2.8V at 1 / 3C. The resulting capacity was recorded as the initial capacity C0. The above steps were repeated for the same battery, but the charge / discharge rate was changed to 4C, and the cycle was repeated 10 times. Then, the same battery was cycled again at 0.33C for 1000 cycles, and the capacity C after 1000 cycles was recorded. 1000 Cyclic capacity retention rate C 1000 / C0, the larger this value, the better the cycle performance and battery efficiency.

[0146] Table 3 shows the performance of the negative electrode slurry in Examples 14 to 32 and Comparative Examples 1 to 8.

[0147]

[0148]

[0149] As demonstrated in Examples 18 to 40 and Comparative Examples 1 to 8, on the one hand, reducing the chain length of the sodium carboxymethyl cellulose polymer (CMC) reduces its crystallinity and rigidity, thereby improving the cracking problem during high-speed thick coating of the negative electrode slurry and thus increasing the battery's energy density and efficiency. On the other hand, by polymerizing unsaturated carbon chain groups on some of the hydroxyl groups of the CMC, a copolymer is obtained, resulting in a copolymer with multiple branches. These branches provide flexible segments for the CMC, reducing its rigidity and further improving the cracking problem during high-speed thick coating of the negative electrode slurry, thereby increasing the battery's energy density and efficiency. Simultaneously, the unpolymerized hydroxyl groups on the CMC provide hydrogen bonding sites, exhibiting good adhesion and dispersion properties. This reduces the need for plasticizers and increases the proportion of active materials in the negative electrode slurry, further improving the battery's energy density and efficiency. When m takes a positive integer value from 1 to 10, it is beneficial to reduce the crystallinity of sodium carboxymethyl cellulose polymer. When m is greater than 10, the crystallinity of sodium carboxymethyl cellulose polymer is still too high, and the probability of cracking during coating is too high. When n takes a positive integer value from 1 to 100, it is beneficial to reduce the crystallinity of sodium carboxymethyl cellulose polymer. When n is greater than 100, the crystallinity of sodium carboxymethyl cellulose polymer is still too high, and the probability of cracking during coating is too high.

[0150] As shown in Comparative Examples 1 to 8, when m is greater than 10, the crystallinity of the sodium carboxymethyl cellulose polymer is still too high, resulting in a high probability of cracking during coating. When m is 0, the softening effect is poor. When n is greater than 100, the crystallinity of the sodium carboxymethyl cellulose polymer is still too high, resulting in a high probability of cracking during coating. When n is 0, the dispersion effect is too poor.

[0151] As can be seen from Examples 35 to 40, the mass percentage of the dispersant in the negative electrode slurry affects the dispersion performance of the negative electrode slurry. When the mass percentage of the dispersant in the negative electrode slurry is less than 0.5%, the dispersion performance of the negative electrode slurry is poor, which affects the energy density and stability of the battery. When the mass percentage of the dispersant in the negative electrode slurry is greater than 5%, it affects the content of the negative electrode active material, thereby reducing the energy density and stability of the battery.

[0152] In summary, the dispersant proposed in this application, on the one hand, reduces the crystallinity and rigidity of the sodium carboxymethyl cellulose (CMC) polymer by decreasing its chain length, thereby mitigating the cracking problem during high-speed thick coating of the negative electrode slurry and improving battery efficiency. On the other hand, by polymerizing unsaturated carbon chain groups on some of the hydroxyl groups of the CMC polymer to obtain a copolymer with multiple branches, these branches provide flexible segments for the CMC polymer, reducing its rigidity and further mitigating the cracking problem during high-speed thick coating of the negative electrode slurry, thus increasing the battery's energy density and efficiency. Simultaneously, the unpolymerized hydroxyl groups on the CMC polymer provide hydrogen bonding sites, exhibiting good binding and dispersing properties, thereby reducing the use of plasticizers and increasing the proportion of active materials in the negative electrode slurry, further improving the battery's energy density and efficiency. When m is greater than 10, the crystallinity of sodium carboxymethyl cellulose polymer is still too high, and the probability of cracking during coating is too high. When n is greater than 100, the crystallinity of sodium carboxymethyl cellulose polymer is still too high, and the probability of cracking during coating is too high.

[0153] The above are merely preferred embodiments of the present invention and do not limit the patent scope of the present invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the patent protection scope of the present invention.

Claims

1. A dispersant for use in negative electrode slurry, characterized in that, This includes a sodium carboxymethyl cellulose polymer, the structural formula of which is: Where m is a positive integer from 4 to 8, n is a positive integer from 1 to 100, and R includes groups containing unsaturated carbon chains with 4 to 6 carbon atoms.

2. The dispersant as described in claim 1, characterized in that, R also includes oxygen-containing polar functional groups.

3. The dispersant as described in claim 1, characterized in that, n is a positive integer between 30 and 60.

4. The application of the dispersant as described in any one of claims 1 to 3 in the negative electrode slurry.

5. The method for preparing the dispersant according to any one of claims 1 to 3, characterized in that, Includes the following steps: Sodium carboxymethyl cellulose monomer is activated with an activating agent to obtain activated sodium carboxymethyl cellulose monomer; The activated sodium carboxymethyl cellulose monomer is polymerized with a compound containing an unsaturated carbon chain to obtain a sodium carboxymethyl cellulose polymer.

6. The method for preparing the dispersant as described in claim 5, characterized in that, The step involves activating sodium carboxymethyl cellulose monomer with an activating agent to obtain activated sodium carboxymethyl cellulose monomer. Activators include inorganic peroxide compounds.

7. The method for preparing the dispersant as described in claim 6, characterized in that, Activators also include sulfur-containing compounds.

8. The method for preparing the dispersant as described in claim 6, characterized in that, The activator includes at least one of sodium bisulfite and ammonium persulfate, potassium persulfate, and sodium persulfate.

9. The method for preparing the dispersant as described in claim 6, characterized in that, The step involves activating sodium carboxymethyl cellulose monomer with an activating agent to obtain activated sodium carboxymethyl cellulose monomer. The mass ratio of activator to sodium carboxymethyl cellulose monomer is (1~200):100; and / or, The activation temperature is 50–100°C; and / or, The activation time is 3-8 hours.

10. The method for preparing the dispersant as described in claim 6, characterized in that, The step involves activating sodium carboxymethyl cellulose monomer with an activating agent to obtain activated sodium carboxymethyl cellulose monomer. The mass ratio of activator to sodium carboxymethyl cellulose monomer is (6~80):100; and / or, The activation temperature is 60~80℃; and / or, The activation time is 4-6 hours.

11. The method for preparing the dispersant as described in claim 6, characterized in that, The step involves polymerizing activated sodium carboxymethyl cellulose monomer with a compound containing unsaturated carbon chains to obtain a sodium carboxymethyl cellulose polymer. The polymerization temperature is 50-80℃; and / or, The mass ratio of activated sodium carboxymethyl cellulose monomer to compounds containing unsaturated carbon chains is 1:(1~100).

12. The method for preparing the dispersant as described in claim 6, characterized in that, The step involves polymerizing activated sodium carboxymethyl cellulose monomer with a compound containing unsaturated carbon chains to obtain a sodium carboxymethyl cellulose polymer. The polymerization temperature is 60~70℃; and / or, The mass ratio of activated sodium carboxymethyl cellulose monomer to compounds containing unsaturated carbon chains is 1:(1~50).

13. A negative electrode slurry, characterized in that, It includes negative electrode active materials, conductive agents, binders, and dispersants as described in any one of claims 1 to 3.

14. The negative electrode slurry as described in claim 13, characterized in that, The dispersant accounts for 0.5% to 5% of the mass of the negative electrode slurry.

15. The negative electrode slurry as described in claim 13, characterized in that, The dispersant accounts for 1% to 2% of the mass of the negative electrode slurry.

16. The negative electrode slurry as described in claim 13, characterized in that, The negative electrode active material includes at least one of graphite, non-graphitized carbon, carbon-based organometallic framework, and titanium oxide; and / or, The conductive agent includes at least one of carbon nanotubes and graphene; and / or, The adhesive includes at least one of styrene-acrylic emulsion, polyvinylidene fluoride, polytetrafluoroethylene, and polychlorotrifluoroethylene.

17. The negative electrode slurry as described in claim 13, characterized in that, The negative electrode active material includes carbon nanomaterials.

18. A method for preparing a negative electrode slurry as described in any one of claims 13 to 17, characterized in that, Includes the following steps: The negative electrode active material, conductive agent and first part of dispersant are added to the solvent and mixed to obtain a premix; The second part of the dispersant and binder is mixed with the premix to obtain the negative electrode slurry.

19. The method for preparing the negative electrode slurry as described in claim 18, characterized in that, The mass ratio of the first part of the dispersant to the second part of the dispersant is (1~10):

7.

20. The method for preparing the negative electrode slurry as described in claim 18, characterized in that, The mass ratio of the first part of the dispersant to the second part of the dispersant is (2~5):

7.

21. The method for preparing the negative electrode slurry as described in claim 18, characterized in that, The steps involve adding the negative electrode active material, conductive agent, and first-part dispersant to a solvent and mixing them to obtain a premix. The mixing method includes kneading, wherein: The kneading speed is 10~50 rpm; The kneading time is 10~120 minutes.

22. The method for preparing the negative electrode slurry as described in claim 18, characterized in that, The steps involve adding the negative electrode active material, conductive agent, and first-part dispersant to a solvent and mixing them to obtain a premix. The mixing method includes kneading, wherein: The kneading speed is 20~30 rpm; The kneading time is 60-90 minutes.

23. A negative electrode sheet, characterized in that, It is prepared from a negative electrode slurry comprising the negative electrode slurry as described in any one of claims 13 to 17 or the negative electrode slurry preparation method as described in any one of claims 18 to 22.

24. An electrochemical device, characterized in that, Includes the negative electrode as described in claim 23.

25. The electrochemical device as claimed in claim 24, characterized in that, The electrochemical device includes a capacitor, a primary battery, or a secondary battery.

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