Method for preparing biomass-based hard carbon negative electrode slurry by wet method and negative electrode slurry

Abstract

The invention belongs to the technical field of battery negative electrode materials, and particularly relates to a method for preparing biomass-based hard carbon negative electrode slurry by a wet method and the negative electrode slurry. By adjusting the production process, the first binder is divided into two parts, one part of the first binder is used for preparing the binder glue solution, and the rest of the first binder is added in the form of powder after the conductive agent and the negative electrode active material are uniformly dispersed in the slurry. Compared with an existing wet process, the viscosity of the biomass-based hard carbon negative electrode slurry can be effectively improved under the condition that the using amount of the binder is not increased, meanwhile, the conductive agent, the negative electrode active material and other components are evenly dispersed, particle agglomeration is effectively reduced, the stability of the slurry is remarkably improved, and the service life of the slurry is prolonged. Furthermore, the coating processing performance of a negative pole piece prepared from the biomass-based negative pole slurry and the electrochemical performance of a battery are improved.

Description

Technical Field

[0001] The present application belongs to the technical field of battery negative electrode materials, and more specifically, relates to a method for wet-process preparation of biomass-based hard carbon negative electrode slurry and negative electrode slurry. Background Art

[0002] As an alternative technology to lithium-ion batteries, sodium-ion batteries have experienced rapid development in recent years due to their abundant resources, low cost, and excellent low-temperature performance. The principles of sodium-ion batteries are similar to those of lithium-ion batteries, both based on the reversible insertion and extraction of metal ions in electrode materials. Therefore, the material systems of the two are relatively similar. The negative electrode materials of sodium-ion batteries are mainly hard carbon materials, and their precursors mainly include three categories: biomass-based, resin-based, and coal-based. Biomass-based hard carbon is the most widely used in the market due to its wide range of raw material sources and low cost.

[0003] Based on the order of mixing, negative electrode slurry processing techniques can be divided into three types: dry, semi-dry, and wet. In the traditional dry process, the main negative electrode material, conductive agent, and binder (such as CMC) powders are dry-mixed to produce a mixed powder. A solvent is then added for dispersion and stirring. Finally, the viscosity of the slurry is adjusted to produce the negative electrode slurry. In the traditional semi-dry process, the main negative electrode material and conductive agent are dry-mixed to produce a premixed powder. The binder solution and solvent are then added and stirred to produce the negative electrode slurry. Both dry and semi-dry processes require the dry-mixed powder and solvent to be stirred thoroughly. However, the material resistance between the dry-mixed powder and the solvent is high, requiring specialized equipment to achieve mixing and placing high torque requirements on the equipment. In actual production, operating the mixing equipment at high torque for extended periods of time can result in significant stress, unstable operation, and a high rate of equipment failure.

[0004] The traditional wet process is to dissolve the binder in water to obtain a binder glue, and then add a conductive agent, anode main material, etc. to the binder glue in turn for dispersion to obtain anode slurry. This process has a fast dispersion speed and low requirements for stirring and mixing equipment. It is widely used in battery slurry preparation, but the surface of biomass-based hard carbon anode main material often contains rich functional groups. These functional groups will interact with the binder sodium carboxymethyl cellulose CMC during the slurry processing, affecting the conformation of the binder molecules in the solvent and the intermolecular interaction, thereby affecting the viscosity and processing performance of the slurry, resulting in low viscosity and poor stability of the slurry.

[0005] Currently, the viscosity and stability of biomass-based hard carbon anode slurries produced by wet processing are mainly improved by increasing the amount of binder. However, this significantly increases the production cost of the battery, and the reduction in the proportion of the main anode material leads to a decrease in the battery's energy density. Therefore, improving the viscosity and stability of the slurry produced by the wet process without increasing the amount of binder is an urgent problem to be solved at this stage. Summary of the Invention

[0006] In response to the defects of the prior art, the purpose of this application is to provide a method for preparing biomass-based hard carbon negative electrode slurry by a wet process and a negative electrode slurry, aiming to solve the problems of low viscosity and poor stability of biomass-based hard carbon negative electrode slurry prepared by traditional wet process, high binder usage of biomass-based hard carbon negative electrode slurry prepared by existing wet process, high production cost of battery and reduced energy density.

[0007] To achieve the above objectives, in a first aspect, the present application provides a method for wet-processing a biomass-based hard carbon anode slurry, comprising the following steps: S1, mixing a portion of the first binder and a solvent to obtain a binder glue solution; S2, adding the conductive agent to the adhesive solution and mixing to obtain a first slurry; S3, adding the negative electrode active material to the first slurry and mixing them to obtain a second slurry; wherein the negative electrode active material is biomass-based hard carbon; S4, adding the remaining first binder to the second slurry and mixing to obtain a third slurry; S5. Add the second binder to the third slurry and mix well to obtain the biomass-based hard carbon negative electrode slurry.

[0008] Preferably, in step S1, the amount of the first binder is 70 wt% to 95 wt% of the total mass of the first binder.

[0009] Preferably, the mass ratio of the first binder, the conductive agent, the negative electrode active material and the second binder is (1-2):(1.5-3.5):(92-95):(2-3).

[0010] Preferably, the solid content of the biomass-based hard carbon negative electrode slurry is 50% to 55%.

[0011] Preferably, the first binder is one or more of sodium carboxymethyl cellulose, polyacrylic acid or derivatives thereof.

[0012] Preferably, the solvent is deionized water.

[0013] Preferably, the conductive agent is one or more of conductive carbon black, acetylene black, Ketjen black, conductive graphite, conductive carbon fiber, carbon nanotubes, and graphene.

[0014] Preferably, the second adhesive is styrene-butadiene rubber latex.

[0015] Preferably, in step S2, the mixing method is stirring and dispersing, and the stirring and dispersing conditions are: revolution speed 30 rpm~35 rpm, dispersion disk linear speed 14 m / s~16 m / s, time 1 h~1.5 h.

[0016] Preferably, in step S3, the mixing method is stirring and dispersing, and the stirring and dispersing conditions are: revolution speed 30 rpm ~ 35 rpm, dispersion disk linear speed 14 m / s ~ 16 m / s, time 2h ~ 3h; and / or, Preferably, in step S4, the mixing method is stirring and dispersing, and the stirring and dispersing conditions are: revolution speed 30 rpm~35 rpm, dispersion disk linear speed 14 m / s~16 m / s, time 0.5h~1.5h.

[0017] Preferably, in step S5, the mixing method is stirring and dispersing, and the stirring and dispersing conditions are: revolution speed 20 rpm~25 rpm, dispersion disk linear speed 0.5 m / s~1 m / s, time 0.5h~1h.

[0018] In a second aspect, the present application provides a biomass-based hard carbon negative electrode slurry prepared by the above method.

[0019] In a third aspect, the present application provides a negative electrode sheet comprising a negative electrode current collector and a negative electrode film layer disposed on at least one surface of the negative electrode current collector; The negative electrode film layer is prepared from the biomass-based hard carbon negative electrode slurry prepared by the above method or the above biomass-based hard carbon negative electrode slurry.

[0020] In a fourth aspect, the present application provides a secondary battery comprising the above-mentioned negative electrode plate.

[0021] In general, the above technical solutions conceived by this application have the following technical advantages compared with the existing technologies: (1) This application adjusts the production process to divide the first binder into two parts for separate use, wherein part of the first binder is used to prepare the binder glue, and the remaining first binder is added in the form of powder after the conductive agent and the negative electrode active material are evenly dispersed in the slurry. Compared with the existing wet process, this application can effectively increase the viscosity of the biomass-based hard carbon negative electrode slurry without increasing the amount of binder, while improving the dispersion effect of components such as the conductive agent and the negative electrode active material, significantly improving the stability of the slurry, and thus improving the coating processing performance of the biomass-based negative electrode slurry to prepare the negative electrode sheet, as well as the electrochemical performance of the battery.

[0022] (2) This application rationally regulates the proportion of each part of the first binder added, so that the binder paste prepared with most of the first binder can effectively disperse the conductive agent and the negative electrode active material, reduce particle agglomeration, improve the overall conductivity of the negative electrode slurry, ensure the rapid transfer of ions and charges, and enhance the rate performance of the battery. At the same time, the remaining small amount of first binder powder added later can effectively play a thickening effect, increase the viscosity of the biomass-based hard carbon negative electrode slurry, and prepare a negative electrode sheet with good appearance, which is beneficial to the improvement of the battery's electrochemical performance. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 This is a schematic flow chart of a method for preparing a biomass-based hard carbon negative electrode slurry by a wet process provided in an embodiment of the present application; Figure 2 This is a SEM image of the negative electrode sheet prepared in Example 1 of the present application; Figure 3 This is a SEM image of the negative electrode sheet prepared in Comparative Example 3 of the present application. DETAILED DESCRIPTION

[0024] In order to make the purpose, technical solutions and advantages of this application more clear, the following further describes this application in detail with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain this application and are not intended to limit this application.

[0025] In the description of this application, it should be understood that the term "and / or" describes an association relationship between associated objects, indicating that three relationships can exist. For example, A and / or B can represent: A exists alone, A and B exist simultaneously, and B exists alone. The symbol " / " herein indicates that the associated objects are in an "or" relationship, for example, A / B means either A or B.

[0026] In the specification and claims of this application, the terms "first", "second" and "third" are used to distinguish different objects rather than to describe the specific order of objects, and cannot be understood as indicating or implying relative importance or implicitly indicating the number of technical features indicated.

[0027] In the description of the embodiments of this application, words such as "exemplary" or "for example" are used to indicate examples, illustrations, or descriptions. Any embodiment or design described as "exemplary" or "for example" in the embodiments of this application should not be construed as being preferred or advantageous over other embodiments or designs. Rather, the use of words such as "exemplary" or "for example" is intended to present the relevant concepts in a concrete manner.

[0028] In the description of the embodiments of the present application, unless otherwise specified, “plurality” means two or more.

[0029] like Figure 1 As shown, the present application provides a method for preparing a biomass-based hard carbon negative electrode slurry by a wet process, comprising the following steps: S1, mixing a portion of the first binder and a solvent to obtain a binder glue solution; S2, adding the conductive agent to the adhesive solution and mixing to obtain a first slurry; S3, adding the negative electrode active material to the first slurry and mixing them to obtain a second slurry; wherein the negative electrode active material is biomass-based hard carbon; S4, adding the remaining first binder to the second slurry and mixing to obtain a third slurry; S5. Add the second binder to the third slurry and mix well to obtain a biomass-based hard carbon negative electrode slurry.

[0030] Based on the traditional wet method of preparing slurry, this application adjusts the production process and divides the first binder into two parts for separate use. Part of the first binder is used to prepare the binder glue, and the remaining first binder is added in the form of powder after the conductive agent and the negative electrode active material are evenly dispersed in the slurry. It can effectively disperse the conductive agent, negative electrode active material and other components, reduce the agglomeration of particles, and at the same time increase the viscosity of the slurry, improve the stability of the slurry, and improve the coating and processing performance of the slurry.

[0031] In some embodiments, in step S1, the amount of the above-mentioned part of the first binder is 70wt%~95wt% of the total mass of the first binder. The binder glue prepared using this amount of the first binder can effectively disperse the conductive agent and the negative electrode active material, reduce powder agglomeration, improve the stability of the slurry, and prevent the conductive agent and the negative electrode active material from being excessively wrapped, affecting the fluidity and dispersibility of the slurry.

[0032] In some embodiments, the mass ratio of the first binder, the conductive agent, the negative electrode active material, and the second binder is (1-2):(1.5-3.5):(92-95):(2-3).

[0033] In some embodiments, in the raw materials for preparing the biomass-based hard carbon negative electrode slurry, based on 100 parts by weight, the usage amounts of the above-mentioned first binder, conductive agent, negative electrode active material and second binder are: 1 to 2 parts of the first binder, 1.5 to 3.5 parts of the conductive agent, 92 to 95 parts of the negative electrode active material, and 2 to 3 parts of the second binder.

[0034] In some embodiments, the solid content of the biomass-based hard carbon negative electrode slurry is 50% to 55%, and a biomass-based hard carbon negative electrode slurry with high viscosity, good stability, and excellent coating and processing performance can be prepared.

[0035] In some embodiments, the first binder is one or more of sodium carboxymethyl cellulose (CMC), polyacrylic acid (PAA) or derivatives thereof.

[0036] In some embodiments, the first binder is one or more of sodium carboxymethyl cellulose (CMC), polyacrylic acid (PAA), sodium polyacrylate (PAAS), polyacrylamide (PAM), and polymethacrylic acid (PMAA).

[0037] In some embodiments, the solvent is deionized water.

[0038] In some embodiments, the conductive agent is one or more of conductive carbon black, acetylene black, Ketjen black, conductive graphite, conductive carbon fiber, carbon nanotubes, and graphene.

[0039] The present application does not limit the type and source of the above-mentioned biomass-based hard carbon. Any commercially available product well-known in the art or biomass-based hard carbon prepared by conventional preparation methods can be used.

[0040] In some embodiments, the second binder is styrene-butadiene rubber latex (SBR).

[0041] The present application does not limit the mixing method in step S1. As long as a uniformly mixed adhesive glue can be prepared, it is within the protection scope of the present application. In some embodiments, in step S1, the above-mentioned mixing method is stirring and dispersing. In some embodiments, the parameters of the above-mentioned stirring and dispersing are: revolution speed 30rpm~35rpm, dispersion disk linear speed 12m / s~14m / s, time 1h~1.5h, forming a uniform and stable glue system, which can effectively disperse components such as conductive agents and negative electrode active materials. Among them, the revolution speed refers to the speed of the dispersion disk around its rotation center in the stirring equipment, and the dispersion linear speed refers to the distance moved by the edge of the dispersion disk per unit time, that is, the movement speed of the edge of the dispersion disk.

[0042] The present application does not limit the mixing method in steps S2, S3, S4, and S5. As long as the various materials can be evenly dispersed, they are all within the scope of protection of the present application.

[0043] In some embodiments, the mixing method in step S2 is stirring dispersion, and the conditions for the stirring dispersion are: revolution speed 30rpm~35rpm, dispersion disk linear speed 14m / s~16m / s, time 1h~1.5h, so that the conductive agent is evenly dispersed, the agglomeration of the conductive agent is reduced, and the stability of the slurry is improved.

[0044] In some embodiments, the mixing method in step S3 is stirring dispersion, and the stirring and dispersing conditions are: revolution speed 30 rpm ~ 35 rpm, dispersion disk linear speed 14 m / s ~ 16 m / s, time 2h ~ 3h, so that the negative electrode active material is evenly dispersed. At the same time, the first binder interacts with the negative electrode active material, improves the adhesion between the first binder and the negative electrode active material, and improves the structural stability of the negative electrode active material.

[0045] In some embodiments, the mixing method in step S4 is stirring and dispersing, and the conditions for the stirring and dispersing are: revolution speed 30rpm~35rpm, dispersion disk linear speed 14m / s~16m / s, time 0.5h~1.5h, so that the remaining first binder is evenly dispersed in the above-mentioned second slurry, effectively exerting the thickening effect, thereby increasing the viscosity of the slurry and improving the coating processing performance of the slurry.

[0046] In some embodiments, the mixing method in step S5 is stirring and dispersing, and the conditions for the stirring and dispersing are: revolution speed 20rpm~25rpm, dispersion disk linear speed 0.5m / s~1m / s, time 0.5h~1h, so that the second binder styrene-butadiene rubber emulsion is evenly dispersed, the bonding force of the negative electrode plate is better, and the negative electrode plate coating is prevented from falling off.

[0047] On the other hand, the present application also provides a biomass-based hard carbon negative electrode slurry prepared by the above method.

[0048] On the other hand, the present application also provides a negative electrode sheet, which includes a negative electrode current collector and a negative electrode film layer provided on at least one surface of the negative electrode current collector; The negative electrode film layer is prepared from the biomass-based hard carbon negative electrode slurry prepared by the above method or the above biomass-based hard carbon negative electrode slurry.

[0049] In some embodiments, the negative electrode current collector may be a metal foil or a composite current collector. For example, aluminum foil or copper foil may be used as the metal foil. The composite current collector may include a polymer substrate and a metal layer formed on at least one surface of the polymer substrate. The composite current collector may be formed by forming a metal material (aluminum, aluminum alloy, copper, copper alloy, nickel, nickel alloy, titanium, titanium alloy, silver, and silver alloy) on a polymer substrate (such as polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0050] In some embodiments, the biomass-based hard carbon negative electrode slurry can be coated on the negative electrode current collector, and after drying, cold pressing and other processes, a negative electrode sheet can be obtained.

[0051] On the other hand, the present application also provides a secondary battery comprising the above-mentioned negative electrode plate.

[0052] In some embodiments, the secondary battery is any one of a sodium ion battery, a lithium ion battery, a magnesium ion battery, and a potassium ion battery.

[0053] In some embodiments, the secondary batteries described above may be assembled into a battery module. The battery module may contain one or more secondary batteries. Those skilled in the art may select an appropriate number based on the application scenario and capacity of the battery module.

[0054] It should be understood that materials of the same or similar type, model, quality, properties, or functions as the reagents and instruments used in the following examples can be used to implement this application. The experimental methods used in the following examples are all conventional methods unless otherwise specified. The materials, reagents, etc. used in the following examples, unless otherwise specified, can all be obtained from commercial sources.

[0055] The following are examples and comparative examples: Example 1 The solid content of the biomass-based hard carbon negative electrode slurry provided in this embodiment is 52%. The raw materials for its preparation, in parts by weight, include the following components: 1.7 parts of the first binder sodium carboxymethyl cellulose CMC, 2.0 parts of the conductive agent Super P, 93.7 parts of biomass-based hard carbon (product brand TN-1), 2.6 parts of the second binder styrene-butadiene rubber SBR, and the balance is deionized water.

[0056] The method for preparing a biomass-based hard carbon negative electrode slurry by a wet process provided in this embodiment includes the following steps: S1. Divide the first binder, sodium carboxymethyl cellulose (CMC), into two portions: the first portion comprising 80 wt% of the total CMC content and the second portion comprising 20 wt%. Disperse the first portion of CMC in deionized water using a high-speed blender at a speed of 35 rpm, a dispersion plate speed of 12 m / s, and a dispersion time of 1 hour to obtain a CMC adhesive.

[0057] S2. Add the conductive agent Super P to the above CMC glue solution and disperse it evenly. The revolution speed is 35 rpm, the linear speed of the dispersion disk is 14 m / s, and the dispersion time is 1 hour to form a first slurry.

[0058] S3. Add biomass-based hard carbon to the first slurry and disperse it evenly, with an orbital speed of 35 rpm, a dispersion disk linear speed of 14 m / s, and a dispersion time of 2.5 h to form a second slurry.

[0059] S4. Add the second portion of binder CMC powder to the second slurry and disperse it evenly. The revolution speed is 35 rpm, the linear speed of the dispersion disk is 14 m / s, and the dispersion time is 0.5 h to obtain a third slurry.

[0060] S5. Add the second binder styrene-butadiene rubber (SBR) to the third slurry and disperse it evenly. The revolution speed is 25 rpm, the dispersion disk linear speed is 0.5 m / s, and the dispersion time is 0.5 h to obtain a biomass-based hard carbon negative electrode slurry.

[0061] Example 2 The solid content of the biomass-based hard carbon negative electrode slurry provided in this embodiment is 52%. The raw materials for its preparation, in parts by weight, include the following components: 1.7 parts of the first binder sodium carboxymethyl cellulose CMC, 2.0 parts of the conductive agent Super P, 93.7 parts of biomass-based hard carbon (product brand TN-1), 2.6 parts of the second binder styrene-butadiene rubber SBR, and the balance is deionized water.

[0062] The method for preparing a biomass-based hard carbon negative electrode slurry by a wet process provided in this embodiment includes the following steps: S1. Divide the first binder, sodium carboxymethyl cellulose (CMC), into two portions: the first portion comprising 95 wt% of the total CMC content and the second portion comprising 5 wt%. Disperse the first portion of CMC in deionized water using a high-speed blender at a speed of 35 rpm, a dispersion plate speed of 12 m / s, and a dispersion time of 1 hour to obtain a CMC adhesive.

[0063] S2. Add the conductive agent Super P to the above CMC glue solution and disperse it evenly. The revolution speed is 35 rpm, the linear speed of the dispersion disk is 14 m / s, and the dispersion time is 1 hour to form a first slurry.

[0064] S3. Add biomass-based hard carbon to the first slurry and disperse it evenly, with an orbital speed of 35 rpm, a dispersion disk linear speed of 14 m / s, and a dispersion time of 2.5 h to form a second slurry.

[0065] S4. Add the second portion of binder CMC powder to the second slurry and disperse it evenly. The revolution speed is 35 rpm, the linear speed of the dispersion disk is 14 m / s, and the dispersion time is 0.5 h to obtain a third slurry.

[0066] S5. Add the second binder styrene-butadiene rubber (SBR) to the third slurry and disperse it evenly. The revolution speed is 25 rpm, the dispersion disk linear speed is 0.5 m / s, and the dispersion time is 0.5 h to obtain a biomass-based hard carbon negative electrode slurry.

[0067] Example 3 The solid content of the biomass-based hard carbon negative electrode slurry provided in this embodiment is 52%. The raw materials for its preparation, in parts by weight, include the following components: 1.7 parts of the first binder sodium carboxymethyl cellulose CMC, 2.0 parts of the conductive agent Super P, 93.7 parts of biomass-based hard carbon (product brand TN-1), 2.6 parts of the second binder styrene-butadiene rubber SBR, and the balance is deionized water.

[0068] The method for preparing a biomass-based hard carbon negative electrode slurry by a wet process provided in this embodiment includes the following steps: S1. Divide the first binder, sodium carboxymethyl cellulose (CMC), into two portions: the first portion comprising 70 wt% of the total CMC content and the second portion comprising 30 wt%. Disperse the first portion of CMC in deionized water using a high-speed blender at a speed of 35 rpm, a dispersion plate speed of 12 m / s, and a dispersion time of 1 hour to obtain a CMC adhesive.

[0069] S2. Add the conductive agent Super P to the above CMC glue solution and disperse it evenly. The revolution speed is 35 rpm, the linear speed of the dispersion disk is 14 m / s, and the dispersion time is 1 hour to form a first slurry.

[0070] S3. Add biomass-based hard carbon to the first slurry and disperse it evenly, with an orbital speed of 35 rpm, a dispersion disk linear speed of 14 m / s, and a dispersion time of 2.5 h to form a second slurry.

[0071] S4. Add the second portion of binder CMC powder to the second slurry and disperse it evenly. The revolution speed is 35 rpm, the linear speed of the dispersion disk is 14 m / s, and the dispersion time is 0.5 h to obtain a third slurry.

[0072] S5. Add the second binder styrene-butadiene rubber latex SBR to the third slurry and disperse it evenly. The revolution speed is 25 rpm, the dispersion disk linear speed is 0.5 m / s, and the dispersion time is 0.5 h to obtain a biomass-based hard carbon negative electrode slurry.

[0073] Example 4 The solid content of the biomass-based hard carbon negative electrode slurry provided in this embodiment is 52%. The raw materials for its preparation, in parts by weight, include the following components: 1.5 parts of the first binder sodium carboxymethyl cellulose CMC, 2.0 parts of the conductive agent Super P, 93.9 parts of biomass-based hard carbon (product brand TN-1), 2.6 parts of the second binder styrene-butadiene rubber SBR, and the balance is deionized water.

[0074] The wet method for preparing biomass-based hard carbon negative electrode slurry provided in this embodiment is the same as that in Example 1.

[0075] Comparative Example 1 The raw materials for preparing the biomass-based hard carbon negative electrode slurry provided in this comparative example are the same as those in Example 1.

[0076] This comparative example adopts the traditional wet process to prepare biomass-based hard carbon negative electrode slurry, including the following steps: S1. Disperse the first binder, sodium carboxymethyl cellulose (CMC), in deionized water using a high-speed stirrer at an orbital speed of 35 rpm, a dispersion disk linear speed of 12 m / s, and a dispersion time of 1 h to obtain a CMC glue solution.

[0077] S2. Add the conductive agent Super P to the above CMC glue solution and disperse it evenly. The revolution speed is 35 rpm, the linear speed of the dispersion disk is 14 m / s, and the dispersion time is 1 hour to form a first slurry.

[0078] S3. Add biomass-based hard carbon to the first slurry and disperse it evenly, with an orbital speed of 35 rpm, a dispersion disk linear speed of 14 m / s, and a dispersion time of 2.5 h to form a second slurry.

[0079] S4. Add the second binder styrene-butadiene rubber latex SBR to the third slurry and disperse it evenly. The revolution speed is 25 rpm, the dispersion disk linear speed is 0.5 m / s, and the dispersion time is 0.5 h to obtain a biomass-based hard carbon negative electrode slurry.

[0080] Comparative Example 2 The raw materials for preparing the biomass-based hard carbon negative electrode slurry provided in this comparative example are the same as those in Example 1.

[0081] This comparative example adopts a wet process to prepare a biomass-based hard carbon negative electrode slurry, including the following steps: S1. Divide the first binder, sodium carboxymethyl cellulose (CMC), into two portions: the first portion comprising 97 wt% of the total CMC content, and the second portion comprising 3 wt%. Disperse the first portion of CMC in deionized water using a high-speed blender at a speed of 35 rpm, a dispersion plate speed of 12 m / s, and a dispersion time of 1 hour to obtain a CMC adhesive.

[0082] S2. Add the conductive agent Super P to the above CMC glue solution and disperse it evenly. The revolution speed is 35 rpm, the linear speed of the dispersion disk is 14 m / s, and the dispersion time is 1 hour to form a first slurry.

[0083] S3. Add biomass-based hard carbon to the first slurry and disperse it evenly, with an orbital speed of 35 rpm, a dispersion disk linear speed of 14 m / s, and a dispersion time of 2.5 h to form a second slurry.

[0084] S4. Add the second portion of binder CMC powder to the second slurry and disperse it evenly. The revolution speed is 35 rpm, the linear speed of the dispersion disk is 14 m / s, and the dispersion time is 0.5 h to obtain a third slurry.

[0085] S5. Add the second binder styrene-butadiene rubber latex SBR to the third slurry and disperse it evenly. The revolution speed is 25 rpm, the dispersion disk linear speed is 0.5 m / s, and the dispersion time is 0.5 h to obtain a biomass-based hard carbon negative electrode slurry.

[0086] Comparative Example 3 The raw materials for preparing the biomass-based hard carbon negative electrode slurry provided in this comparative example are the same as those in Example 1.

[0087] This comparative example adopts a wet process to prepare a biomass-based hard carbon negative electrode slurry, including the following steps: S1. Divide the first binder, sodium carboxymethyl cellulose (CMC), into two portions: the first portion comprising 50 wt% of the total CMC content, and the second portion comprising 50 wt% of the total CMC content. Disperse the first portion of CMC in deionized water using a high-speed blender at a speed of 35 rpm, a dispersion plate speed of 12 m / s, and a dispersion time of 1 hour to obtain a CMC adhesive.

[0088] S2. Add the conductive agent Super P to the above CMC glue solution and disperse it evenly. The revolution speed is 35 rpm, the linear speed of the dispersion disk is 14 m / s, and the dispersion time is 1 hour to form a first slurry.

[0089] S3. Add biomass-based hard carbon to the first slurry and disperse it evenly, with an orbital speed of 35 rpm, a dispersion disk linear speed of 14 m / s, and a dispersion time of 2.5 h to form a second slurry.

[0090] S4. Add the second portion of binder CMC powder to the second slurry and disperse it evenly. The revolution speed is 35 rpm, the linear speed of the dispersion disk is 14 m / s, and the dispersion time is 0.5 h to obtain a third slurry.

[0091] S5. Add the second binder styrene-butadiene rubber latex SBR to the third slurry and disperse it evenly. The revolution speed is 25 rpm, the dispersion disk linear speed is 0.5 m / s, and the dispersion time is 0.5 h to obtain a biomass-based hard carbon negative electrode slurry.

[0092] Comparative Example 4 The raw materials for preparing the biomass-based hard carbon negative electrode slurry provided in this comparative example are the same as those in Example 1.

[0093] This comparative example adopts a wet process to prepare a biomass-based hard carbon negative electrode slurry, including the following steps: S1. Divide the first binder, sodium carboxymethyl cellulose (CMC), into two portions: the first portion comprising 80 wt% of the total CMC content and the second portion comprising 20 wt%. Disperse the first portion of CMC in deionized water using a high-speed blender at a speed of 35 rpm, a dispersion plate speed of 12 m / s, and a dispersion time of 1 hour to obtain a CMC adhesive.

[0094] S2. Add the conductive agent Super P to the above CMC glue solution and disperse it evenly. The revolution speed is 35 rpm, the linear speed of the dispersion disk is 14 m / s, and the dispersion time is 1 hour to form a first slurry.

[0095] S3. Add the second portion of binder CMC powder to the first slurry and disperse it evenly. The revolution speed is 35 rpm, the linear speed of the dispersion disk is 14 m / s, and the dispersion time is 0.5 h to obtain a second slurry.

[0096] S4. Add biomass-based hard carbon to the second slurry and disperse it evenly, with an orbital speed of 35 rpm, a dispersion disk linear speed of 14 m / s, and a dispersion time of 2.5 h to form a third slurry.

[0097] S5. Add the second binder styrene-butadiene rubber latex SBR to the third slurry and disperse it evenly. The revolution speed is 25 rpm, the dispersion disk linear speed is 0.5 m / s, and the dispersion time is 0.5 h to obtain a biomass-based hard carbon negative electrode slurry.

[0098] The biomass-based hard carbon negative electrode slurry prepared in the above examples and comparative examples is used to prepare a sodium ion battery, comprising the following steps: (1) Preparation of negative electrode sheets: The biomass-based hard carbon negative electrode slurry is evenly coated on the negative electrode current collector aluminum foil on an extrusion coating machine, dried at 85°C to 95°C, and then cold pressed, trimmed, cut, slit, and welded to the tabs to obtain the negative electrode sheets; (2) Preparation of positive electrode sheets: Dissolve the binder polyvinylidene fluoride (PVDF), conductive carbon black Super P, polyanion positive electrode material composite sodium iron phosphate (NFPP), and carbon nanotubes (CNT) in N-methylpyrrolidone at a mass ratio of 2.5:2.7:94.3:0.5 and disperse them evenly to obtain a positive electrode slurry. The positive electrode slurry is then evenly coated on the positive electrode current collector aluminum foil using an extrusion coater. After drying at 85°C to 95°C, the positive electrode sheet is cold pressed, trimmed, cut, slit, and the tabs are welded to obtain a positive electrode sheet.

[0099] (3) Preparation of sodium ion battery: The above-mentioned negative electrode sheet, positive electrode sheet and PP separator are wound and baked, and then injected with an electrolyte consisting of a mixed solution of 1 mol / L NaPF6 and ethylene carbonate (EC): ethyl methyl carbonate (EMC) = 1:1 vol.%. After packaging, formation, volume separation and other processes, a sodium ion battery is assembled.

[0100] The viscosity, resistivity and electrochemical performance of the sodium ion battery of the biomass-based hard carbon negative electrode slurry prepared in the examples and comparative examples were tested. The test method is as follows. The test results are shown in Table 1: (a) Slurry viscosity: The viscosity was measured using a viscometer with a No. 4 rotor.

[0101] (b) Slurry resistivity: tested using a slurry resistance meter.

[0102] (c) Electrochemical performance of sodium-ion batteries: The test was carried out using a charge and discharge test equipment. Specifically, the sodium-ion battery was charged at a constant current of 0.5C. When the battery voltage reached 3.65V, it was switched to constant voltage charging mode, maintaining the battery voltage at 3.65V while gradually reducing the charging current. When the charging current dropped to 0.05C, the charging was terminated. The battery was then discharged at different discharge rates (0.5C, 1C, 5C) until the battery voltage dropped to 1.5V. The battery capacity retention rate was tested.

[0103] Table 1 Viscosity, resistivity and electrochemical performance of biomass-based hard carbon anode slurry for sodium ion batteries

[0104] As can be seen from Table 1, the biomass-based hard carbon negative electrode slurry prepared by the wet method in this application has high viscosity, good resistivity consistency after standing for 24 hours, uniform distribution of the conductive agent in the slurry, good slurry stability, excellent coating processing performance, and good appearance of the negative electrode sheet ( Figure 2 ), and the sodium ion battery prepared in this way has excellent rate performance and can be applied to application scenarios with different rates, such as electric vehicles, hybrid vehicles, etc., and can meet the needs of fast charging and high power output while reducing battery loss and replacement costs.

[0105] Comparative Example 1 employed a conventional wet process, converting the first binder, sodium carboxymethyl cellulose, into a binder paste. After this, a conductive agent and biomass-based hard carbon material were sequentially added and stirred and dispersed. The resulting biomass-based hard carbon anode slurry exhibited low viscosity, making it difficult to ensure uniform dispersion of the conductive agent and anode active material within the slurry. Agglomeration and sedimentation were also likely to occur, impacting both the slurry's processing and battery performance. This was confirmed by resistivity test results and the appearance of the anode electrode sheet. After 24 hours of stabilization, the biomass-based hard carbon anode slurry prepared in Comparative Example 1 exhibited poor resistivity consistency, and the anode electrode sheet coating exhibited edge shrinkage and cracking. This resulted in poor slurry coating processability and even reduced battery performance.

[0106] The viscosity of the biomass-based hard carbon negative electrode slurry prepared in Comparative Example 2 is relatively low. The reason for this may be that, under the premise that the total amount of the first binder used remains unchanged, too little carboxymethyl cellulose sodium powder, the first binder, is added when preparing the third slurry, and it cannot effectively thicken the slurry, resulting in a low viscosity of the negative electrode slurry, which in turn leads to poor coating processing performance and battery performance. The viscosity of the biomass-based hard carbon negative electrode slurry prepared in Comparative Example 3 is high, but the appearance of the negative electrode sheet is poor. The reason for this may be that too little carboxymethyl cellulose sodium powder, the first binder, is used when preparing the binder solution, resulting in uneven dispersion of the conductive agent and the biomass-based hard carbon material, and agglomeration occurs ( Figure 3 ), thereby affecting the coating processability of the negative electrode slurry. The viscosity and stability performance of the biomass-based hard carbon negative electrode slurries prepared in Comparative Example 4 and Comparative Example 1 are relatively similar, indicating that the addition of a second portion of binder CMC powder after the addition of the conductive agent Super P in Comparative Example 4 has similar effects as the use of the binder CMC in Comparative Example 1 without splitting it into two portions, and cannot effectively improve the viscosity and stability of the biomass-based hard carbon negative electrode slurry.

[0107] It is easy for those skilled in the art to understand that the above is only a preferred embodiment of the present application and is not intended to limit the present application. Any modifications, equivalent substitutions and improvements made within the spirit and principles of the present application should be included in the scope of protection of the present application.

Claims

1. A method for preparing a biomass-based hard carbon negative electrode slurry by a wet process, characterized in that: The steps include: S1, mixing a portion of the first binder and a solvent to obtain a binder glue solution; S2, adding the conductive agent to the binder glue and mixing to obtain a first slurry; S3, adding a negative electrode active material to the first slurry and mixing to obtain a second slurry; wherein the negative electrode active material is biomass-based hard carbon; S4, adding the remaining first binder to the second slurry and mixing to obtain a third slurry; S5. Add the second binder to the third slurry and mix well to obtain the biomass-based hard carbon negative electrode slurry.

2. The method according to claim 1, characterized in that In step S1, the amount of the first binder is 70 wt% to 95 wt% of the total mass of the first binder.

3. The method according to claim 1 or 2, characterized in that The mass ratio of the first binder, the conductive agent, the negative electrode active material, and the second binder is (1-2):(1.5-3.5):(92-95):(2-3).

4. The method according to claim 3, characterized in that The solid content of the biomass-based hard carbon negative electrode slurry is 50% to 55%.

5. The method according to claim 1, wherein The first binder is one or more of sodium carboxymethyl cellulose, polyacrylic acid or derivatives thereof; and / or, The solvent is deionized water; and / or, The conductive agent is one or more of conductive carbon black, acetylene black, Ketjen black, conductive graphite, conductive carbon fiber, carbon nanotube, and graphene; and / or, The second binder is styrene-butadiene rubber latex.

6. The method according to claim 1, characterized in that In step S2, the mixing conditions are: revolution speed 30 rpm to 35 rpm, dispersion disk linear speed 14 m / s to 16 m / s, time 1 h to 1.5 h; and / or, In step S3, the mixing conditions are: revolution speed 30 rpm to 35 rpm, dispersion disk linear speed 14 m / s to 16 m / s, time 2 h to 3 h; and / or, In step S4, the mixing conditions are: revolution speed 30 rpm to 35 rpm, dispersion disk linear speed 14 m / s to 16 m / s, and time 0.5 h to 1.5 h.

7. The method according to claim 1, characterized in that In step S5, the mixing conditions are: revolution speed 20 rpm to 25 rpm, dispersion disk linear speed 0.5 m / s to 1 m / s, and time 0.5 h to 1 h.

8. A biomass-based hard carbon negative electrode slurry, characterized in that: The method is prepared according to any one of claims 1 to 7.

9. A negative electrode plate, characterized in that: The negative electrode plate includes a negative electrode current collector and a negative electrode film layer provided on at least one surface of the negative electrode current collector; The negative electrode film layer is prepared by the biomass-based hard carbon negative electrode slurry prepared by the method according to any one of claims 1 to 7 or the biomass-based hard carbon negative electrode slurry according to claim 8.

10. A secondary battery, characterized in that: The secondary battery includes the negative electrode sheet according to claim 9.

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