Preparation method of modified carboxymethyl cellulose, modified carboxymethyl cellulose and pole piece

Abstract

The invention provides a preparation method of modified carboxymethyl cellulose, the modified carboxymethyl cellulose and a pole piece. The preparation method comprises the following steps: S100, alkalization reaction: treating a cellulose raw material by adopting an alkalizer to obtain an alkalized material; s200, etherification reaction: treating the alkalized material with an etherifying agent to obtain modified carboxymethyl cellulose; wherein the chemical general formula of the etherifying agent is X-R-M, X is halogen, R is an organic group, and M is sulfonic acid group or sulfonate. The modified carboxymethyl cellulose obtained by the invention is used as a dispersing agent or a thickening agent used in the preparation of a pole piece, so that the direct-current internal resistance of a battery cell can be reduced.

Description

Technical Field

[0001] The present invention relates to the technical field of batteries, and in particular to a method for preparing modified carboxymethyl cellulose, the modified carboxymethyl cellulose and an electrode. Background Art

[0002] Batteries, as efficient and environmentally friendly energy storage devices, have been widely used in various fields in recent years. Batteries are a core component of electric vehicles, and with the rapid development of the global new energy vehicle market, demand for power batteries continues to grow. Batteries also have enormous potential for application in energy storage applications such as grid peak regulation, renewable energy integration, home energy storage, and backup power for communication base stations. Furthermore, batteries are widely used in consumer electronics such as smartphones, laptops, Bluetooth headsets, and wearable devices.

[0003] The rate performance of a battery refers to the performance of the battery at different charge and discharge rates, and is an important indicator for measuring battery performance. Specifically, it reflects the battery's ability to accept or release a large amount of electrical energy in a short period of time. Rate performance is usually expressed as a percentage of the capacity that the battery can provide at different rates. The higher the rate, the shorter the charge and discharge time, and the higher the capacity. The rate performance of a battery is affected by many factors, including the conductivity and electrochemical reaction kinetics of the active material, the conductivity and ion transfer rate of the electrolyte, and the battery structure design. Batteries with high rate performance are crucial for applications that require high power output, such as electric vehicles and mobile devices. How to improve the rate performance of a battery is one of the technical problems that those skilled in the art need to solve. Summary of the Invention

[0004] One of the problems solved by the present invention is how to improve the rate performance of the battery.

[0005] To solve the above problems, the present invention provides a method for preparing modified carboxymethyl cellulose, which comprises: S100, alkalization reaction: treating the cellulose raw material with an alkalizing agent to obtain an alkalized material; S200, etherification reaction: treating the alkalized material with an etherifying agent to obtain modified carboxymethyl cellulose; The general chemical formula of the etherifying agent is: XRM, where X includes a halogen, R includes an organic group, and M is a sulfonic acid group or a sulfonate.

[0006] In the above technical solution, In S100, the mass ratio of the cellulose raw material to the alkalizing agent is (15-20): (20-30); and / or; In S200, the mass ratio of the alkalizing material to the etherifying agent is (15-20): (20-30).

[0007] In any of the above technical solutions, the etherifying agent includes at least one of an alkane compound, an aromatic compound and a heterocyclic compound.

[0008] In any of the above technical solutions, the etherifying agent includes at least one of p-chlorobenzenesulfonic acid, p-chlorobenzenesulfonate, o-chlorobenzenesulfonate, o-chlorobenzenesulfonic acid, m-chlorobenzenesulfonic acid, m-chlorobenzenesulfonate, bromobenzenesulfonic acid, bromobenzenesulfonate, fluorobenzenesulfonic acid, fluorobenzenesulfonate, chloroethanesulfonic acid, chloroethanesulfonate, bromoethanesulfonic acid, bromoethanesulfonate, bromopyridinesulfonic acid, bromopyridinesulfonate, trichlorobenzenesulfonic acid and trichlorobenzenesulfonate, or a combination thereof.

[0009] In any of the above technical solutions, the etherifying agent is at least one of p-chlorobenzenesulfonic acid, p-chlorobenzenesulfonate, chloroethanesulfonic acid and chloroethanesulfonate, or a combination thereof.

[0010] It is understood that the p-chlorobenzenesulfonate includes at least one of potassium p-chlorobenzenesulfonate, lithium p-chlorobenzenesulfonate and sodium p-chlorobenzenesulfonate; The o-chlorobenzenesulfonate includes at least one of potassium o-chlorobenzenesulfonate, lithium o-chlorobenzenesulfonate and sodium o-chlorobenzenesulfonate; The m-chlorobenzenesulfonate includes at least one of potassium m-chlorobenzenesulfonate, lithium m-chlorobenzenesulfonate and sodium m-chlorobenzenesulfonate; The bromobenzenesulfonate includes at least one of potassium bromobenzenesulfonate, lithium bromobenzenesulfonate and sodium bromobenzenesulfonate; The fluorobenzenesulfonate includes at least one of potassium fluorobenzenesulfonate, lithium fluorobenzenesulfonate and sodium fluorobenzenesulfonate; The chloroethanesulfonate includes at least one of potassium chloroethanesulfonate, lithium chloroethanesulfonate and sodium chloroethanesulfonate; The bromoethanesulfonate salt includes at least one of potassium bromoethanesulfonate, lithium bromoethanesulfonate and sodium bromoethanesulfonate; The bromopyridine sulfonate includes at least one of potassium bromopyridine sulfonate, lithium bromopyridine sulfonate and sodium bromopyridine sulfonate; The trichlorobenzenesulfonate includes at least one of potassium trichlorobenzenesulfonate, lithium trichlorobenzenesulfonate and sodium trichlorobenzenesulfonate.

[0011] In any of the above technical solutions, the cellulose raw material includes at least one of cotton fiber, wood fiber, stalk fiber and bast fiber, or a combination thereof.

[0012] In any of the above technical solutions, the alkalizing agent includes at least one of sodium hydroxide, lithium hydroxide and potassium hydroxide, or a combination thereof; and / or the alkalization reaction is carried out under the protection of an inert gas; and / or the alkalization reaction is carried out in an ethanol system; and / or the alkalization reaction is carried out while stirring; and / or the alkalization reaction time is 20 min to 100 min; and / or the alkalization reaction temperature is 20° C. to 60° C.

[0013] In any of the above technical solutions, the etherification reaction is carried out under the protection of an inert gas; and / or the etherification reaction is carried out in an ethanol system; and / or the etherification reaction time is 40 min to 120 min; and / or the etherification reaction temperature is 50° C. to 90° C.

[0014] The present invention also provides a modified carboxymethyl cellulose, which is obtained by using the preparation method of any of the above technical solutions.

[0015] The present invention also provides a pole piece, which comprises the modified carboxymethyl cellulose as described above.

[0016] Beneficial effects The present invention provides a preparation method of modified carboxymethyl cellulose, which comprises at least two steps of alkalization reaction and etherification reaction. In the alkalization reaction, an alkalizing agent is used to treat the cellulose raw material to obtain an alkalized material. The general chemical formula of the etherifying agent is: XR-SO3H, X includes a halogen, R includes an organic group, and SO3H is a sulfonic acid group. In the etherification reaction, an etherifying agent is used to treat the alkalized material to obtain modified carboxymethyl cellulose. Compared with the existing technology using chloroacetic acid as an etherifying agent, the present invention uses an organic compound with a halogen group and a sulfonic group as an etherifying agent. It utilizes the Williamson ether synthesis method to react a halide containing a sulfonic group with the sodium alcohol of the material obtained by the alkalization reaction, and obtains the modified carboxymethyl cellulose through a bimolecular nucleophilic substitution reaction (SN2). The modified carboxymethyl cellulose of the present invention contains a polar functional group -SO3H, which is resistant to Li + It has a high affinity, which enables Li+ to migrate spatially through flexible chain coupling / decoupling and segment motion, thus providing Li + The transport of Li + The modified carboxymethyl cellulose of the present invention increases the lithium ion conductivity and reduces the lithium ion concentration gradient during the electrochemical reaction. + The conduction effect reduces the DCR (Direct Current Resistance) of the battery cell and improves the dynamic performance of the battery. DETAILED DESCRIPTION

[0017] In order to make the above-mentioned objects, features and advantages of the present invention more obvious and easy to understand, the following is a detailed description of the specific embodiments of the present invention.

[0018] Unless otherwise specified, the materials used in the present invention can be purchased from commercial sources. Experimental methods in the following examples where specific conditions are not specified were performed according to conventional methods and conditions, or selected according to the product specifications.

[0019] This invention provides a method for preparing modified carboxymethyl cellulose (CMC). CMC is a water-soluble cellulose derivative obtained by chemically modifying (carboxymethylating) natural cellulose. It exhibits excellent thickening, film-forming, adhesive, and stability properties and is widely used in food, medicine, daily chemicals, textiles, oil extraction, and new energy applications.

[0020] Carboxymethyl cellulose is an anionic polymer formed by replacing the hydroxyl groups (-OH) on the cellulose backbone with carboxymethyl groups (-CH2COO⁻). It is readily soluble in water, forming a clear or slightly turbid colloidal solution. The viscosity of a carboxymethyl cellulose aqueous solution increases with concentration and molecular weight, and its viscosity can be controlled by adjusting the degree of substitution.

[0021] Carboxymethyl cellulose plays a crucial role in battery fabrication. First, it stabilizes active materials (such as graphite and silicon-based materials) through hydrogen bonding and van der Waals forces, preventing electrode shedding. Furthermore, carboxymethyl cellulose acts as a dispersant, improving the uniformity of mixing between the conductive agent and the active material and reducing interfacial impedance. Carboxymethyl cellulose also buffers the volume expansion of the negative electrode, extending cycle life.

[0022] The disadvantage of batteries in the prior art is that their rate performance still has room for improvement. The present invention is dedicated to providing a modified carboxymethyl cellulose that improves the rate performance of the battery when used in battery manufacturing.

[0023] The preparation method of the modified carboxymethyl cellulose of the present invention comprises: S100, alkalization reaction: treating the cellulose raw material with an alkalizing agent to obtain an alkalized material; S200, etherification reaction: treating the alkalized material with an etherifying agent to obtain modified carboxymethyl cellulose, wherein the etherifying agent has a general chemical formula of XR-SO3H, where X includes a halogen, R includes an organic group, and SO3H is a sulfonic acid group.

[0024] In the above steps, the cellulose raw materials can include cotton fibers, wood fibers, stalk fibers, and bast fibers. Wood fibers exist in tree trunks, such as fibers in pine, fir, poplar, and willow. Pulp made from wood is an important raw material for producing regenerated cellulose fibers. Stalk fibers include wheat straw, rice straw, corn stalks, sorghum stalks, reeds, etc., which have the advantages of being cheap and readily available, and easy to pulp. Bast fibers exist in the stalks of some dicotyledonous plants, such as mulberry, paper mulberry, and celery. In addition, hemp plants such as ramie, flax, jute, and hemp also have particularly developed bast fiber bundles. Among them, industrial cotton is preferably used as the cellulose raw material.

[0025] The alkalizing agent includes at least one of sodium hydroxide, lithium hydroxide and potassium hydroxide or a combination thereof.

[0026] The purpose of the alkalization reaction is to activate the hydroxyl groups (-OH) of cellulose to produce alkali cellulose with stronger reaction activity. Taking sodium hydroxide as an alkalizing agent, the reaction mechanism of the alkalization reaction is: the hydroxyl groups in cellulose react with sodium hydroxide (NaOH) to produce cellulose sodium salt, which enhances nucleophilicity: Cellulose-OH+NaOH→Cellulose-O−Na + +H2O; Here, Cellulose represents the glucose structural unit.

[0027] The alkalization reaction generally involves soaking and stirring, extruding, and aging. The soaking and stirring step involves soaking the cellulose raw material in a treatment solution containing an alkalizer and stirring to ensure full contact and reaction with the treatment solution. Preferably, the alkalization reaction is conducted in an ethanol system with stirring. In other words, the treatment solution can be prepared by mixing the alkalizer with ethanol. The mass ratio of cellulose to alkalizer is (15-20):(20-30), and the mass ratio of alkalizer to ethanol is (20-30):(25-40). Excess alkalizer and ethanol ensure complete cellulose reaction. The ethanol concentration can range from 92% v / v to 95% v / v. In addition to ethanol, an appropriate amount of water can be added to the treatment solution, preferably at a volume ratio of alkalizer to water of 1:(0.5-1.5). The alkalization reaction is preferably conducted under inert gas protection. The alkalization reaction duration is preferably 20 to 100 minutes. The alkalization reaction temperature is preferably 20°C to 60°C. After the impregnation is completed, the excess alkali solution is removed by squeezing to obtain alkali cellulose (containing sodium cellulose and a small amount of free alkali). It is then aged for 24 to 48 hours to allow the alkali to penetrate evenly and further improve the reaction activity.

[0028] The purpose of the prior art etherification reaction is to introduce carboxymethyl groups (-CH2COO) into the cellulose backbone to produce carboxymethyl cellulose. The etherifying agent is usually chloroacetic acid or chloroacetate. The reaction mechanism is a nucleophilic substitution reaction (SN2) between alkali cellulose and chloroacetic acid or chloroacetate. Taking sodium chloroacetate (ClCH2COONa) as an example, the reaction formula is: Cellulose-O−Na + +ClCH2COONa→Cellulose-O-CH2COO−Na + +NaCl.

[0029] The general chemical formula of the etherifying agent used in the present invention is: XRM, where X includes a halogen, R includes an organic group, and M is a sulfonic acid group or a sulfonate.

[0030] The etherifying agent of the present invention may include at least one of an alkane compound, an aromatic compound and a heterocyclic compound, or a combination thereof.

[0031] The etherifying agent used in the present invention can be a halogenated benzenesulfonic acid. A halogenated benzenesulfonic acid is a widely used compound having both a halogen group and a sulfonate group, formed by introducing a halogen and a sulfonate group into a benzene ring. The etherifying agent used in the present invention can be chlorobenzenesulfonic acid (such as p-chlorobenzenesulfonic acid, p-chlorobenzenesulfonate, o-chlorobenzenesulfonic acid, o-chlorobenzenesulfonate, m-chlorobenzenesulfonic acid, m-chlorobenzenesulfonate), bromobenzenesulfonic acid (such as p-bromobenzenesulfonic acid, bromobenzenesulfonate), fluorobenzenesulfonic acid, fluorobenzenesulfonate, etc.

[0032] The etherifying agent used in the present invention may also be a halogenated sulfonic acid alkane. A halogenated sulfonic acid alkane is formed by attaching a halogen and a sulfonic group to the same or different alkane backbones. For example, the etherifying agent used in the present invention may be chloroethanesulfonic acid (ClCH2CH2SO3H), chloroethanesulfonate, bromoethanesulfonic acid (BrCH2CH2SO3H), or bromoethanesulfonate.

[0033] The etherifying agent used in the present invention can also be a heterocyclic compound containing a halogen group and a sulfonate group. In some heterocyclic aromatic compounds, both a halogen and a sulfonate group can be introduced simultaneously. Examples include bromopyridinesulfonic acid (e.g., 5-bromopyridine-3-sulfonic acid, 2-bromopyridine-3-sulfonic acid) or bromopyridinesulfonate.

[0034] The etherifying agent used in the present invention may also be a halosulfonyl compound, which is a compound in which a halogen is directly attached to a sulfonyl group (-SO2-), such as chlorosulfonic acid (ClSO3H), chlorosulfonates, bromosulfonic acid (BrSO3H), or bromosulfonates.

[0035] In addition, polyhalogenated sulfonic acid compounds with multiple halogens and sulfonic groups introduced into one compound can also be used as the etherifying agent of the present invention, such as trichlorobenzenesulfonic acid (C6H2Cl3SO3H) or trichlorobenzenesulfonic acid salts.

[0036] Preferably, the etherifying agent of the present invention may be at least one of p-chlorobenzenesulfonic acid, p-chlorobenzenesulfonate, chloroethanesulfonic acid and chloroethanesulfonate, or a combination thereof.

[0037] The etherification reaction mechanism of the present invention converts the -COOH groups of the carboxymethyl cellulose in the prior art into -SO3H groups, which are then grafted onto the cellulose. For example, using sodium hydroxide as the alkalizing agent and 2-chloroethanesulfonic acid as the etherifying agent in S100, the reaction formula is: Cellulose-O−Na + +ClCH2CH2SO3H→Cellulose-O-CH2CH2SO3−Na + +NaCl.

[0038] It will be appreciated that the above reaction is carried out in an alkaline system. For example, the etherification reaction can be carried out by first mixing the alkalized material (i.e., alkali cellulose) with the etherifying agent used in the present invention, then adding a small amount of water or ethanol to form a paste, which is then heated and stirred to react. Preferably, the mass ratio of the alkalized material to the etherifying agent is (15-20):(20-30), with an excess of etherifying agent ensuring complete reaction of the cellulose. Preferably, the etherification reaction is carried out in an ethanol system under inert gas protection. Preferably, the etherification reaction lasts for 40 to 120 minutes. Preferably, the etherification reaction temperature is 50°C to 90°C.

[0039] Compared with the existing technology that uses chloroacetic acid as an etherifying agent, the present invention uses an organic compound with a halogen group and a sulfonic group as an etherifying agent. It uses the Williamson ether synthesis method to react the halide containing sulfonic group with the sodium alcohol obtained by the alkalization reaction, and obtains the modified carboxymethyl cellulose through a bimolecular nucleophilic substitution reaction (SN2). The modified carboxymethyl cellulose has both a hydrophobic part (the main chain without carboxyl modification) and a hydrophilic part (the sulfonic modified part). Therefore, on the one hand, it is adsorbed on the surface of the electrode material such as graphite particles through the hydrophobic main chain, and on the other hand, the hydrophilic sulfonic group can make the electrode material suspended in a solvent system such as water or ethanol, ensuring that the slurry system is uniform and stable. On this basis, the modified carboxymethyl cellulose of the present invention contains a polar functional group sulfonic acid group, which is sensitive to Li + Has a higher affinity, making Li + Able to spatially migrate through flexible chain coupling / decoupling and segmental motion, thus providing Li +The transport of Li+ builds a continuous path, promotes the conduction of Li+, and reduces the lithium ion concentration gradient during the electrochemical reaction. + The conduction effect reduces the DCR (Direct Current Resistance) of the battery cell and improves the rate performance of the lithium battery.

[0040] After obtaining the modified carboxymethyl cellulose, it can be further subjected to neutralization, bleaching, washing, drying, and pulverization. Specifically, the post-treatment steps of neutralization, bleaching, washing, drying, and pulverization can purify and refine the modified carboxymethyl cellulose.

[0041] Neutralization neutralizes residual alkali in the reaction solution and adjusts the pH to neutral to prevent product instability or corrosiveness. Dilute hydrochloric acid (HCl, 5-10%) can be used as the pH adjuster for the neutralization reaction. Stirring can be performed during the neutralization process to maintain a final pH of 7 to 8. Bleaching removes colored impurities (such as residual lignin) from the product and improves the whiteness and purity of the modified carboxymethyl cellulose. Bleaching agents include hydrogen peroxide (H2O2, 3-5%) or sodium hypochlorite (NaClO, 5-10% available chlorine). Sodium thiosulfate (Na2S2O3) can be added after bleaching to terminate the reaction. Washing removes byproducts, unreacted etherifying agent, and bleaching agent residue. Washing solvents are typically ethanol, methanol, or acetone. Hot air drying is preferred for drying, but vacuum drying or freeze drying are also options. Finally, bulky materials are broken down using equipment such as a jaw crusher or hammer mill, followed by airflow milling or ball milling. Screening is then performed to obtain the finished product.

[0042] The modified carboxymethyl cellulose obtained in this invention can be used in both positive and negative electrode materials. Common positive electrode materials include lithium iron phosphate (LFP), ternary materials (NCM / NCA), and lithium cobalt oxide (LCO). Common negative electrode materials include graphite, silicon-carbon composites, and silicon-oxygen composites. The preparation processes for both positive and negative electrode materials primarily involve slurry preparation, coating, drying, and roller pressing. Slurry preparation involves mixing the electrode active material, additives, and solvent (such as NMP / water) in appropriate proportions to form a uniform slurry. The coating process involves evenly coating the slurry onto an aluminum foil current collector to form an electrode sheet. The electrode sheet is then dried in a high-temperature oven to remove the solvent. A roller press is then used to compact the electrode sheet to increase energy density and mechanical strength, resulting in the electrode material. After preparing the positive and negative electrode sheets, the coated electrode sheets are cut into strips according to the battery size requirements. These strips are then further cut into the desired shape (such as round or square). In the above slurry preparation process, the additives mainly include conductive agents (such as carbon black), binders (such as PVDF / CMC / SBR), dispersants, and thickeners. Among them, the modified carboxymethyl cellulose obtained by the present invention can be used as a dispersant or thickener in the preparation of lithium electrode materials.

[0043] Since the modified carboxymethyl cellulose of the present invention contains polar functional groups -SO3H, these functional groups are very sensitive to Li + Has high affinity, making Li + Able to spatially migrate through flexible chain coupling / decoupling and segmental motion, thus providing Li + The transport of Li + The modified carboxymethyl cellulose of the present invention helps to improve the rate performance of lithium batteries.

[0044] The following is further described through specific examples.

[0045] Example 1: The preparation method of the modified carboxymethyl cellulose of this embodiment is as follows: S100, alkalization reaction: Sodium hydroxide, 95% v / v ethanol solution and water were mixed to form a treatment solution, wherein the volume ratio of the ethanol solution to water was 1:1, and the mass ratio of the sodium hydroxide to the ethanol solution was 20:25.

[0046] At 40° C. and under a nitrogen atmosphere, the cotton fiber was immersed in the treatment solution and stirred for 60 minutes, and the mass ratio of the cotton fiber to the sodium hydroxide was controlled to be 17:25.

[0047] After stirring is completed, excess alkali solution is removed by squeezing to obtain alkali cellulose.

[0048] Finally, the alkalized material was obtained by aging for 36 hours.

[0049] S200, etherification reaction: Under a nitrogen atmosphere, chloroethanesulfonic acid and the above-mentioned alkalized material are mixed, and then a 95% v / v ethanol solution is added to form a paste. The mixture is then heated to 70° C. and stirred for 80 minutes to obtain a modified carboxymethyl cellulose intermediate, wherein the mass ratio of the alkalized material to chloroethanesulfonic acid is 17:25.

[0050] S300, adding 7% by mass concentration of dilute hydrochloric acid to the modified carboxymethyl cellulose intermediate obtained in S200 to adjust the pH to 7; Then, hydrogen peroxide with a mass concentration of 3% was added for bleaching, and sodium thiosulfate (Na2S2O3) was added after bleaching to terminate the reaction; wherein the mass ratio of the modified carboxymethyl cellulose intermediate to hydrogen peroxide was 100:2; After bleaching, the final modified carboxymethyl cellulose is obtained by washing, drying and crushing in sequence.

[0051] Example 2: The preparation method of the modified carboxymethyl cellulose of this embodiment is as follows: S100, alkalization reaction: Sodium hydroxide, 95% v / v ethanol solution and water were mixed to form a treatment solution, wherein the volume ratio of the ethanol solution to water was 1:1, and the mass ratio of the sodium hydroxide to the ethanol solution was 20:25.

[0052] At 20° C. and under a nitrogen protective atmosphere, the wood fiber was immersed in the treatment liquid and stirred for 100 minutes, and the mass ratio of the wood fiber to the sodium hydroxide was controlled to be 15:20.

[0053] After stirring is completed, excess alkali solution is removed by squeezing to obtain alkali cellulose.

[0054] Finally, the alkalized material was obtained by aging for 36 hours.

[0055] S200, etherification reaction: Under a nitrogen atmosphere, p-chlorobenzenesulfonic acid and the above-mentioned alkalized material are mixed, and then a 95% v / v ethanol solution is added to form a paste. The mixture is then heated to 50° C. and stirred for 120 minutes to obtain a modified carboxymethyl cellulose intermediate, wherein the mass ratio of the alkalized material to p-chlorobenzenesulfonic acid is 15:20.

[0056] S300, adding 7% by mass concentration of dilute hydrochloric acid to the modified carboxymethyl cellulose intermediate obtained in S200 to adjust the pH to 7; Then, hydrogen peroxide with a mass concentration of 3% was added for bleaching, and sodium thiosulfate (Na2S2O3) was added after bleaching to terminate the reaction; wherein the mass ratio of the modified carboxymethyl cellulose intermediate to hydrogen peroxide was 100:2; After bleaching, the final modified carboxymethyl cellulose is obtained by washing, drying and crushing in sequence.

[0057] Example 3: The preparation method of the modified carboxymethyl cellulose of this embodiment is as follows: S100, alkalization reaction: Sodium hydroxide, 95% v / v ethanol solution and water were mixed to form a treatment solution, wherein the volume ratio of the ethanol solution to water was 1:1, and the mass ratio of the sodium hydroxide to the ethanol solution was 20:25.

[0058] At 60° C. and in a protective atmosphere of nitrogen, the stem fiber was immersed in the treatment liquid and stirred for 20 minutes, and the mass ratio of the stem fiber to sodium hydroxide was controlled to be 20:30.

[0059] After stirring is completed, excess alkali solution is removed by squeezing to obtain alkali cellulose.

[0060] Finally, the alkalized material was obtained by aging for 36 hours.

[0061] S200, etherification reaction: Under a nitrogen atmosphere, chloroethanesulfonic acid and the above-mentioned alkalized material are mixed, and then a 95% v / v ethanol solution is added to form a paste. The mixture is then heated to 90° C. and stirred for 40 minutes to obtain a modified carboxymethyl cellulose intermediate, wherein the mass ratio of the alkalized material to chloroethanesulfonic acid is 20:30.

[0062] S300, adding 7% by mass concentration of dilute hydrochloric acid to the modified carboxymethyl cellulose intermediate obtained in S200 to adjust the pH to 7; Then, hydrogen peroxide with a mass concentration of 3% was added for bleaching, and sodium thiosulfate (Na2S2O3) was added after bleaching to terminate the reaction; wherein the mass ratio of the modified carboxymethyl cellulose intermediate to hydrogen peroxide was 100:2; After bleaching, the final modified carboxymethyl cellulose is obtained by washing, drying and crushing in sequence.

[0063] Example 4: The only difference between this embodiment and embodiment 1 is that the etherifying agent is bromoethanesulfonic acid.

[0064] Comparative Example 1: In this comparative example, commercial CMC-Na and chloroethanesulfonic acid were directly mixed, and then a 95% v / v ethanol solution was added to form a paste. The mixture was then heated to 70°C and stirred for 80 minutes to obtain a modified carboxymethyl cellulose intermediate, wherein the mass ratio of CMC-Na to chloroethanesulfonic acid was 17:25.

[0065] Adding 7% dilute hydrochloric acid to the obtained modified carboxymethyl cellulose intermediate to adjust the pH to 7; Then, hydrogen peroxide with a mass concentration of 3% was added for bleaching, and sodium thiosulfate (Na2S2O3) was added after bleaching to terminate the reaction; wherein the mass ratio of the modified carboxymethyl cellulose intermediate to hydrogen peroxide was 100:2; After bleaching, the final modified carboxymethyl cellulose is obtained by washing, drying and crushing in sequence.

[0066] Comparative Example 2 This comparative example is commercial CMC-Na.

[0067] Test Case The modified carboxymethyl cellulose obtained in the above examples and comparative examples was applied to batteries to obtain batteries obtained in each example and comparative example, wherein the application of the modified carboxymethyl cellulose in the battery is as follows: Lithium-ion battery preparation Step 1: Glue preparation: N-methylpyrrolidone (NMP) is used as a solvent for the positive electrode to prepare a polyvinylidene fluoride (PVDF) glue solution with a solid content of 6%. Water is used as a solvent for the negative electrode to prepare a dispersant glue solution with a solid content of 1.5%, wherein the dispersant is the modified carboxymethyl cellulose in each embodiment and comparative example.

[0068] Step 2: Slurry preparation; the mass ratio of the positive electrode slurry is: 94.5% LFP + 3.5% Super-P + 2% PVDF, and the solid content of the positive electrode slurry is 58%; the mass ratio of the negative electrode slurry is: 96.2% graphite + 0.8% Super-P + 1.2% modified carboxymethyl cellulose + 1.8% SBR, and the solid content of the negative electrode slurry is 52%.

[0069] Step 3: Coating and roller pressing; apply the slurry on the metal foil and evenly apply the prepared positive and negative electrode slurry on the current collector to make the electrode sheet. Aluminum foil is used as the positive electrode current collector and copper foil is used as the negative electrode. After the electrode sheet is dried, it is roller pressed to obtain the positive and negative electrode sheets.

[0070] Step 4: Stacking: Stack in the order of negative electrode, separator, positive electrode, separator...positive electrode, separator, negative electrode.

[0071] Step 5: Packaging: The stacked battery cells need to undergo tab welding. The welded battery cells are placed in the punched aluminum-plastic film and undergo top and side sealing processes.

[0072] Step 6: Injection. Inject electrolyte into the packaged battery cell; Electrolyte mass ratio: 26%EC+25%DMC+34%EMC+12.5%LiPF6+2.5%VC.

[0073] Step 7: Formation: After the battery is filled, it needs to be charged at a low current, which is equivalent to the activation process of the lithium-ion battery. During the first charging process, a SEI film will form on the surface of the negative electrode. In order to ensure the consistency of battery performance, the lithium-ion battery needs to be divided into different capacities. in: The chemical process steps are as follows: 0.02C constant current charging to 3.0V; 0.1C constant current charging to 3.3V; 0.2C constant current charging to 3.5V; The steps of capacity separation are as follows: 0.33C constant current charging to 3.65V, constant voltage charging to 0.05C; 0.33C constant current discharge to 2.0V; 0.1C constant current discharge to 2.0V; 0.05C constant current discharge to 2V.

[0074] Performance testing: Battery rate performance test: The batteries obtained from each embodiment and comparative example after capacity separation were subjected to rate performance test. The test results are shown in Table 1. The test steps are as follows: (1) Let it stand for 30 minutes; (2) 0.33C constant current discharge to 2.5V (3) Let stand for 1 hour; (4) 0.33C constant current charging to 3.65V, constant voltage charging to 0.05C; (5) Let it stand for 1 hour (6) 1C constant current discharge to 2.5V; (7) Let stand for 1 hour; (8) Repeat steps (4) to (7) five times; the average discharge capacity of the last three cycles is recorded as C0; (9) Let stand for 1 hour; (10) 0.33C constant current charging to 3.65V, constant voltage charging to 0.05C; (11) Let stand for 1 hour; (12) 3C constant current discharge to 2.5V, record the capacity as C1; 3C discharge capacity retention rate = C1 / C0.

[0075] DC internal resistance test: The batteries prepared in each embodiment and comparative example were then subjected to a battery rate performance test. The test results are shown in Table 1. The test steps are as follows: (1) Let it stand for 30 minutes; (2) 0.33C constant current discharge to 2.5V; (3) Let it stand for 30 minutes; (4) 0.33C constant current charging to 3.65V, constant voltage charging to 0.05C; (5) Let it stand for 30 minutes; (6) 0.33C constant current discharge to 2.5V; (7) Let it stand for 30 minutes; (8) Repeat steps (4) to (7) three times; (9) 0.33C constant current charging to 3.65V, constant voltage charging to 0.05C; (10) Let it stand for 30 minutes; (11) 0.33C constant current discharge to 50% SOC; (12) Let it stand for 2 hours and record the voltage at the last second as U0; (13) 2C constant current discharge for 10s, record the voltage at 10s as U1; 50% SOC 2C@10s DC internal resistance = (U0-U1) / 2C current.

[0076] Table 1 As shown in Table 1, the modified carboxymethyl cellulose obtained in this application can improve the rate performance of batteries. Although the present invention is disclosed above, it is not limited thereto. Any person skilled in the art may make various changes and modifications without departing from the spirit and scope of the present invention. Therefore, the scope of protection of the present invention shall be based on the scope defined by the claims.

Claims

1. A method for preparing modified carboxymethyl cellulose, characterized in that: The preparation method comprises: S100, alkalization reaction: treating the cellulose raw material with an alkalizing agent to obtain an alkalized material; S200, etherification reaction: treating the alkalized material with an etherifying agent to obtain the modified carboxymethyl cellulose; The general chemical formula of the etherifying agent is: XRM, where X includes a halogen, R includes an organic group, and M is a sulfonic acid group or a sulfonate.

2. The preparation method according to claim 1, characterized in that In S100, the mass ratio of the cellulose raw material to the alkalizing agent is (15-20): (20-30); and / or; In S200, the mass ratio of the alkalizing material to the etherifying agent is (15-20): (20-30).

3. The preparation method according to claim 1, characterized in that The etherifying agent includes at least one of an alkane compound, an aromatic compound and a heterocyclic compound, or a combination thereof.

4. The preparation method according to claim 3, characterized in that The etherifying agent includes at least one of p-chlorobenzenesulfonic acid, p-chlorobenzenesulfonate, o-chlorobenzenesulfonic acid, o-chlorobenzenesulfonate, m-chlorobenzenesulfonic acid, m-chlorobenzenesulfonate, bromobenzenesulfonic acid, bromobenzenesulfonate, fluorobenzenesulfonic acid, fluorobenzenesulfonate, chloroethanesulfonic acid, chloroethanesulfonate, bromoethanesulfonic acid, bromoethanesulfonate, bromopyridinesulfonic acid, bromopyridinesulfonate, trichlorobenzenesulfonic acid and trichlorobenzenesulfonate, or a combination thereof.

5. The preparation method according to claim 4, characterized in that The etherifying agent is at least one of p-chlorobenzenesulfonic acid, p-chlorobenzenesulfonate, chloroethanesulfonic acid and chloroethanesulfonate, or a combination thereof.

6. The preparation method according to claim 1, characterized in that The cellulose raw material includes at least one of cotton fiber, wood fiber, stalk fiber and bast fiber, or a combination thereof.

7. The preparation method according to any one of claims 1 to 6, characterized in that The alkalizing agent comprises at least one of sodium hydroxide, lithium hydroxide and potassium hydroxide or a combination thereof; and / or The alkalization reaction is carried out under the protection of an inert gas; and / or The alkalization reaction is carried out in an ethanol system; and / or The alkalization reaction is carried out under stirring; and / or The alkalization reaction time is 20 min to 100 min; and / or The temperature of the alkalization reaction is 20°C to 60°C.

8. The preparation method according to any one of claims 1 to 6, characterized in that The etherification reaction is carried out under the protection of an inert gas; and / or The etherification reaction is carried out in an ethanol system; and / or The etherification reaction time is 40 min to 120 min; and / or The temperature of the etherification reaction is 50°C to 90°C.

9. A modified carboxymethyl cellulose, characterized in that The modified carboxymethyl cellulose is obtained by the preparation method according to any one of claims 1 to 8.

10. A pole piece, characterized in that: The pole piece comprises the modified carboxymethyl cellulose as claimed in claim 9.

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