Negative electrode dispersing agent, method for preparing the same, and lithium ion battery

Abstract

The application relates to a negative electrode dispersant, a preparation method thereof and a lithium ion battery. The negative electrode dispersant comprises a cellulose polymer, the cellulose polymer comprises an alkaline cellulose compound and a crosslinking agent, the crosslinking agent comprises a biphenyl compound, the biphenyl compound comprises at least one biphenyl group, and further comprises one or more of an aldehyde group, an acyl group, an ester group and a carboxyl group. The scheme provided by the application can reduce the addition amount of CMC, improve the energy density of the battery, and does not affect the cycle performance and rate performance of the battery.

Description

Technical Field

[0001] This application relates to the field of battery technology, and in particular to negative electrode dispersants, their preparation methods, and lithium-ion batteries. Background Technology

[0002] Lithium-ion batteries possess advantages such as high energy density, long cycle life, and low self-discharge rate, leading to their widespread application in electronics and electric vehicles. The negative electrode material plays a crucial role in battery performance. Sodium carboxymethyl cellulose (CMC) is typically added as a dispersant during the formulation of the negative electrode slurry, serving to thicken and stabilize the slurry and prevent the sedimentation of the active material.

[0003] In related technologies, on the one hand, the energy density of lithium-ion batteries can be improved by reducing the amount of CMC added. However, this may cause the viscosity of the negative electrode slurry to be too low, resulting in the sedimentation of the negative electrode active material and making it impossible to prepare a negative electrode sheet. On the other hand, since the viscosity of CMC is low, the amount of CMC added is increased to ensure the suspension stability of the slurry. However, this may result in a low mass ratio of negative electrode active material, affecting the cycle performance and rate performance of the battery. Summary of the Invention

[0004] To address or partially address the problems existing in related technologies, this application provides a negative electrode dispersant, its preparation method, and a lithium-ion battery, which can improve the energy density of the battery without affecting its cycle performance and rate performance by reducing the amount of CMC added.

[0005] A first aspect of this application provides a negative electrode dispersant comprising a cellulose polymer, said cellulose polymer comprising a basic cellulose compound and a crosslinking agent, said crosslinking agent comprising a biphenyl compound, the structural formula of which is as follows:

[0006]

[0007] R1 and R2 are each independently selected from one or more of aldehyde, acyl, ester, and carboxyl groups, and n is a positive integer.

[0008] As an optional embodiment, R1 and R2 may be the same or different, and R1 and R2 are selected from -COX1 and -COOX2, wherein X1 is selected from one or more of H, Cl, Br, and I, and X2 is selected from one or more of H and C1 to C20 alkane groups.

[0009] As an optional embodiment, the crosslinking agent comprises at least one of the following biphenyl compounds:

[0010]

[0011] As an optional embodiment, the mass ratio of the alkaline cellulose compound to the crosslinking agent is 90-95:5-10.

[0012] As an optional embodiment, the alkaline cellulose compound is obtained by alkalizing cellulose with an alkaline solvent.

[0013] As an optional embodiment, the alkaline solvent comprises at least one of sodium hydroxide and lithium hydroxide.

[0014] A second aspect of this application provides a method for preparing the aforementioned negative electrode dispersant, comprising the following steps:

[0015] A solution containing an alkaline cellulose compound is prepared by dissolving cellulose in an alkaline solution.

[0016] A cellulose polymer is prepared by adding a crosslinking agent to a solution containing an alkaline cellulose compound, wherein the mass ratio of the alkaline cellulose compound to the crosslinking agent is 90-95:5-10.

[0017] The cellulose polymer is dissolved in a solvent to prepare a negative electrode dispersant.

[0018] As an optional embodiment, the solid content of the negative electrode dispersant is 1% to 2%.

[0019] As an optional embodiment, the viscosity of the negative electrode dispersant is 3000 mPa·s to 8000 mPa·s.

[0020] A third aspect of this application provides a lithium-ion battery, including a negative electrode sheet, the negative electrode sheet including a negative electrode current collector and a negative electrode active material layer located on at least one side surface of the negative electrode current collector, the negative electrode active material layer including the aforementioned negative electrode dispersant or a negative electrode dispersant prepared by the aforementioned method of preparing negative electrode dispersant.

[0021] The technical solution provided in this application may include the following beneficial effects:

[0022] The basic cellulose compound in this application can be obtained by alkalizing cellulose with an alkaline solvent and has a strongly nucleophilic group -O. - X + X + It can be sodium ions or lithium ions. Biphenyl compounds act as cross-linking agents, and the -O group of basic cellulose compounds... - X +The crosslinking agent can undergo nucleophilic substitution reactions with the R1 and R2 groups contained in biphenyl compounds to generate cellulose polymers with a three-dimensional network structure. This network structure makes it difficult for cellulose molecular chains to move, resulting in a high viscosity of the slurry even at a low solid content. Therefore, a lower amount of dispersant can still ensure uniform dispersion and suspension stability of the slurry, thereby improving the energy density of the battery. Moreover, this network structure can separate and fix the negative electrode active material (such as silicon-based materials and graphite materials) through an efficient and rigid "sheet-to-point" bonding mode, giving the negative electrode excellent structural and interfacial stability, thereby improving the cycle performance and rate performance of the battery. In addition, the biphenyl groups contained in the crosslinking agent provide sufficient rigidity to the cellulose polymer, increasing the mechanical strength of the cellulose polymer. To a certain extent, this can increase the cohesive force of the negative electrode sheet, thereby effectively mitigating the large volume expansion of the negative electrode active material during cyclic lithium intercalation, ensuring the contact between the negative electrode active material and the negative electrode current collector, and thus improving the rate performance of the cell.

[0023] It should be understood that the above general description and the following detailed description are exemplary and explanatory only, and do not limit this application. Attached Figure Description

[0024] The above and other objects, features and advantages of this application will become more apparent from the more detailed description of exemplary embodiments thereof in conjunction with the accompanying drawings, wherein the same reference numerals generally represent the same components in the exemplary embodiments thereof.

[0025] Figure 1 This is a schematic diagram illustrating the structure of the negative electrode dispersant acting on the negative electrode active material, as shown in the embodiments of this application.

[0026] In the diagram: 1. Alkalized cellulose; 2. Crosslinking agent; 3. Negative electrode active material. Detailed Implementation

[0027] Embodiments of this application will now be described in more detail with reference to the accompanying drawings. While embodiments of this application are shown in the drawings, it should be understood that this application may be implemented in various forms and should not be limited to the embodiments set forth herein. Rather, these embodiments are provided to make this application more thorough and complete, and to fully convey the scope of this application to those skilled in the art.

[0028] The terminology used in this application is for the purpose of describing particular embodiments only and is not intended to be limiting of the application. The singular forms “a,” “the,” and “the” used in this application and the appended claims are also intended to include the plural forms unless the context clearly indicates otherwise. It should also be understood that the term “and / or” as used herein refers to and includes any or all possible combinations of one or more of the associated listed items.

[0029] It should be understood that although the terms "first," "second," "third," etc., may be used in this application to describe various information, this information should not be limited to these terms. These terms are only used to distinguish information of the same type from one another. For example, without departing from the scope of this application, first information may also be referred to as second information, and similarly, second information may also be referred to as first information. Thus, a feature defined as "first" or "second" may explicitly or implicitly include one or more of that feature. In the description of this application, "multiple" means two or more, unless otherwise explicitly specified.

[0030] Sodium carboxymethyl cellulose (CMC) is usually added as a dispersant during the preparation of negative electrode slurry. It can thicken and stabilize the slurry and prevent the sedimentation of negative electrode active materials.

[0031] In related technologies, on the one hand, the energy density of lithium-ion batteries can be improved by reducing the amount of CMC added. However, this may cause the viscosity of the negative electrode slurry to be too low, resulting in the sedimentation of the negative electrode active material and making it impossible to prepare a negative electrode sheet. On the other hand, since the viscosity of CMC is low, the amount of CMC added is increased to ensure the suspension stability of the slurry. However, this may result in a low mass ratio of negative electrode active material, affecting the cycle performance and rate performance of the battery.

[0032] To address the aforementioned issues, this application provides a negative electrode dispersant that can improve the battery's energy density without affecting its cycle performance and rate performance by reducing the amount of CMC added.

[0033] The technical solutions of the embodiments of this application are described in detail below with reference to the accompanying drawings.

[0034] Figure 1 This is a schematic diagram illustrating the structure of the negative electrode dispersant acting on the negative electrode active material, as shown in the embodiments of this application.

[0035] See Figure 1 This application provides a negative electrode dispersant comprising a cellulose polymer, the cellulose polymer comprising a basic cellulose compound 1 and a crosslinking agent 2, the crosslinking agent 2 comprising a biphenyl compound, the structural formula of which is as follows:

[0036]

[0037] R1 and R2 are each independently selected from one or more of aldehyde, acyl, ester, and carboxyl groups, and n is a positive integer representing the number of biphenyl groups, which can range from 1 to 10.

[0038] In this embodiment, basic cellulose compound 1 can be obtained by alkalizing cellulose with an alkaline solvent and has a strong nucleophilic group -O. - X + X + It can be sodium ions or lithium ions. Biphenyl compounds act as crosslinking agent 2, and basic cellulose compound 1 has a -O group. - X + The crosslinking agent 2 can undergo nucleophilic substitution reactions with the R1 and R2 groups contained in biphenyl compounds to generate cellulose polymers with a three-dimensional network structure. This network structure makes it difficult for cellulose molecular chains to move, resulting in a high viscosity of the slurry even at a low solid content. Therefore, a low amount of dispersant can still ensure uniform dispersion and suspension stability of the slurry, thereby improving the energy density of the battery. Moreover, this network structure can separate and fix the negative electrode active material 3 (such as silicon-based materials and graphite materials) through an efficient and rigid "sheet-to-point" bonding mode, giving the negative electrode excellent structural and interfacial stability, thereby improving the cycle performance and rate performance of the battery. In addition, the biphenyl groups contained in the crosslinking agent 2 provide sufficient rigidity to the cellulose polymer, increasing the mechanical strength of the cellulose polymer. To a certain extent, this can increase the cohesive force of the negative electrode sheet, thereby effectively mitigating the large volume expansion of the negative electrode active material during cyclic lithium intercalation, ensuring the contact between the negative electrode active material and the negative electrode current collector, and thus improving the rate performance of the cell.

[0039] As an optional embodiment, R1 and R2 may be the same or different, and R1 and R2 are selected from -COX1 and -COOX2, wherein X1 is selected from one or more of H, Cl, Br, and I, and X2 is selected from one or more of H and C1 to C20 alkane groups.

[0040] In the embodiments of this application, R1 and R2 can be selected from the same group or different groups. For example, both R1 and R2 can be selected from aldehyde groups, or R1 can be selected from aldehyde groups and R2 can be selected from acyl groups. This application does not limit this.

[0041] In the embodiments of this application, X1 and X2 are substituents of aldehyde, acyl, and ester groups, respectively, and different substituents can be selected according to different application requirements.

[0042] In a preferred embodiment, the crosslinking agent comprises at least one of the following biphenyl compounds:

[0043]

[0044] As an optional embodiment, the mass ratio of the basic cellulose compound to the crosslinking agent is 90-95:5-10.

[0045] In this embodiment, cellulose polymer is formulated into a gel and used as a dispersant in the negative electrode of a lithium-ion battery. By controlling the concentration of the crosslinking agent to adjust the crosslinking density of the alkaline cellulose compound, i.e. the degree of polymerization of the cellulose polymer, the dispersant can adapt well to the volume changes of the negative electrode active material during the lithiation / delithiation process, ensuring the overall dynamic interface stability between the components of the negative electrode. This provides continuous, stable, and uninterrupted electron and ion transport for the negative electrode reaction. Furthermore, the three-dimensional network structure of the cellulose polymer enhances the mechanical properties of the dispersant and ensures the stability of the negative electrode structure. Therefore, under the synergistic effect of multiple functions of the dispersant, the cycle stability and rate performance of the battery can be effectively improved.

[0046] In the embodiments of this application, the mass ratio of alkaline cellulose compound to crosslinking agent can be 90:10, 92:8, 95:5 or any value within the above-defined range, and this application does not limit it in this regard.

[0047] As an optional embodiment, taking compounds 1 and 2 as crosslinking agents, the structural formula of the prepared cellulose polymer is as follows:

[0048]

[0049] Where P is the degree of polymerization; R' is the same or different, and their independence is selected from H, CH2COONa or CH2COOLi.

[0050] Preferably, the molecular weight of the cellulose polymer is 300,000 to 2,000,000.

[0051] In the embodiments of this application, the molecular weight of the cellulose polymer is controlled within the range of 300,000 to 2,000,000, and the cellulose polymer has moderate viscosity and good solubility.

[0052] As an alternative embodiment, the alkaline cellulose compound is obtained by alkalizing cellulose with an alkaline solvent.

[0053] This application embodiment describes the preparation of basic cellulose compounds by dissolving cellulose in an alkaline solution. The preparation method is simple, inexpensive, and suitable for large-scale industrial production. Furthermore, the resulting basic cellulose compounds exhibit high viscosity and maintain this viscosity even under high-temperature and high-pressure operating conditions.

[0054] As a preferred embodiment, the alkaline solvent comprises at least one of sodium hydroxide and lithium hydroxide.

[0055] In this embodiment, cellulose is dissolved in sodium hydroxide or lithium hydroxide solution to obtain sodium carboxymethyl cellulose or lithium carboxymethyl cellulose. Sodium carboxymethyl cellulose has a low raw material price and a simple preparation method, which can reduce production costs. Lithium carboxymethyl cellulose, when prepared as a negative electrode dispersant, exhibits better kinetic performance than sodium carboxymethyl cellulose.

[0056] Corresponding to the aforementioned application function implementation method embodiments, this application also provides a method for preparing a negative electrode dispersant, a lithium-ion battery, and corresponding embodiments.

[0057] This application also provides a method for preparing a negative electrode dispersant, comprising the following steps:

[0058] S1. Dissolve cellulose in an alkaline solution to prepare a solution containing an alkaline cellulose compound.

[0059] In this embodiment, cellulose is mixed with an alkaline solution and stirred at room temperature for a period of time until the cellulose is completely dissolved, thereby obtaining a solution containing an alkaline cellulose compound.

[0060] The cellulose can be selected from one or more of refined cotton fibers and cotton pellet fibers; the alkaline solvent includes at least one of sodium hydroxide and lithium hydroxide.

[0061] S2. A cellulose polymer is prepared by adding a crosslinking agent to a solution containing an alkaline cellulose compound, wherein the mass ratio of the alkaline cellulose compound to the crosslinking agent is 90-95:5-10.

[0062] In this embodiment, cellulose polymer is formulated into a gel and used as a dispersant in the negative electrode of a lithium-ion battery. By controlling the concentration of the crosslinking agent to adjust the crosslinking density of the alkaline cellulose compound, i.e. the degree of polymerization of the cellulose polymer, the dispersant can adapt well to the volume changes of the negative electrode active material during the lithiation / delithiation process, ensuring the overall dynamic interface stability between the components of the negative electrode. This provides continuous, stable, and uninterrupted electron and ion transport for the negative electrode reaction. Furthermore, the three-dimensional network structure of the cellulose polymer enhances the mechanical properties of the dispersant and ensures the stability of the negative electrode structure. Therefore, under the synergistic effect of multiple functions of the dispersant, the cycle stability and rate performance of the battery can be effectively improved.

[0063] In the embodiments of this application, the mass ratio of alkaline cellulose compound to crosslinking agent can be 90:10, 92:8, 95:5 or any value within the above-defined range, and this application does not limit it in this regard.

[0064] S3. Dissolve the cellulose polymer in a solvent to prepare a negative electrode dispersant.

[0065] In this embodiment, cellulose polymer can be dissolved in deionized water and stirred at room temperature for a period of time to prepare a colloidal negative electrode dispersant.

[0066] As an optional embodiment, the solid content of the negative electrode dispersant is 1% to 2%.

[0067] In the embodiments of this application, the negative electrode dispersant comprises a cellulose polymer and a solvent. The solid content of the negative electrode dispersant refers to the percentage of the cellulose polymer in the negative electrode dispersant, with the mass percentage of the negative electrode dispersant being 100%.

[0068] In the embodiments of this application, the solid content of the negative electrode dispersant is low, but the viscosity is high. The solid content of the negative electrode dispersant can be 1%, 1.5%, 2%, or any value within the above-mentioned range. This application does not limit this.

[0069] In a preferred embodiment, the viscosity of the negative electrode dispersant is 3000 mPa·s to 8000 mPa·s.

[0070] In the embodiments of this application, when the solid content of the negative electrode dispersant is only 1% to 2%, the viscosity of the negative electrode dispersant can also be relatively high, and the viscosity can reach 8000 mPa·s.

[0071] Because conventional CMC contains abundant hydroxyl groups and a small amount of carboxyl groups, it has a certain degree of solubility in water. In this application, the hydroxyl groups on basic cellulose react with the functional groups on biphenyl compounds to transform linear basic cellulose into a cellulose polymer with a three-dimensional network structure, thereby increasing its viscosity in water. This high-viscosity negative electrode dispersant obtained by dissolving in water can maintain dispersion performance when used in lithium-ion batteries while reducing the amount used, thus increasing the proportion of negative electrode active material and improving the energy density of lithium-ion batteries.

[0072] This application also provides a lithium-ion battery, including a negative electrode sheet. The negative electrode sheet includes a negative current collector and a negative active material layer located on at least one side of the surface of the negative current collector. The negative active material layer includes the aforementioned negative dispersant or a negative dispersant prepared by the aforementioned method for preparing negative dispersants.

[0073] The negative electrode active material layer in this application embodiment includes a negative electrode active material, a binder, and a conductive agent. The negative electrode active material includes natural graphite, artificial graphite, mesophase micro carbon spheres, hard carbon, soft carbon, silicon, silicon-carbon composite, Li-Sn alloy, Li-Sn-O alloy, Sn, SnO, SnO2, and spinel-structured lithiated TiO2-Li4Ti5O. 12 At least one of Li-Al alloys.

[0074] The embodiments of this application do not have any particular limitations on the negative electrode current collector, as long as it can achieve the purpose of this application. For example, it can be copper foil, copper alloy foil, nickel foil, stainless steel foil, titanium foil, nickel foam, copper foam, or composite current collector, etc.

[0075] This application also provides an electrical device including the aforementioned lithium-ion battery.

[0076] For example, the aforementioned electrical devices may include mobile devices (such as mobile phones, laptops, etc.), electric vehicles (such as pure electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, electric bicycles, electric scooters, electric golf carts, electric trucks, etc.), electric trains, ships and satellites, energy storage systems, etc., but are not limited thereto.

[0077] To further understand the present invention, the following embodiments are provided to illustrate the present application. These embodiments are for illustrative purposes only and are not intended to limit the scope of the present application.

[0078] Example 1:

[0079] I. Preparation of the negative electrode sheet

[0080] 1. Weigh out cellulose and crosslinking agent according to a mass ratio of 90:10, wherein the crosslinking agent is selected from compound 2;

[0081] 2. Prepare a solution containing an alkaline cellulose compound by completely dissolving cellulose in a sodium hydroxide solution and stirring at room temperature for 3 hours.

[0082] 3. Add compound 2 to a solution containing an alkaline cellulose compound, continue stirring for 3 hours to allow the reaction to complete, centrifuge, and vacuum dry to obtain the cellulose polymer;

[0083] 4. Dissolve the cellulose polymer in deionized water and stir at room temperature for 2 hours to prepare a negative electrode dispersant with a solid content of 1.0 wt%.

[0084] 5. Mix the negative electrode dispersant, styrene-butadiene rubber (SBR) solution and graphite particles (D50 = 13μm ~ 15μm) at a mass ratio of 1:1:98, and disperse them evenly in deionized water for 3 to 5 hours to prepare the negative electrode slurry.

[0085] 6. The negative electrode slurry is coated onto copper foil, and after drying, rolling and cutting, the negative electrode sheet is obtained.

[0086] II. Preparation of positive electrode slurry

[0087] Lithium cobalt oxide, conductive agent, and binder polyvinylidene fluoride are mixed in a mass ratio of 98.5:0.5:1 and dispersed in N-methyl-2-pyrrolidone to obtain a positive electrode slurry. The positive electrode slurry is then uniformly coated on both sides of an aluminum foil, and after drying, rolling, and slitting, a positive electrode sheet is obtained.

[0088] III. Battery Assembly

[0089] A separator is placed between the positive and negative electrode plates. Then, the sandwich structure composed of the positive electrode plate, negative electrode plate and separator is wound up. The wound body is flattened and placed in an aluminum-plastic shell. After welding the tabs, the aluminum-plastic shell is sealed to obtain the cell to be injected with electrolyte. Commercially available electrolyte is injected into the cell, and the cell is sealed, aged and formed to obtain a lithium-ion battery.

[0090] Example 2: The basic content is the same as Example 1, except that the mass ratio of cellulose to crosslinking agent is 92:8.

[0091] Example 3: The basic content is the same as Example 1, except that the mass ratio of cellulose to crosslinking agent is 95:5.

[0092] Example 4: The basic content is the same as in Example 1, except that the crosslinking agent used is compound 1.

[0093] Example 5: The basic content is the same as in Example 1, except that compound 3 is used as the crosslinking agent.

[0094] Example 6: The basic content is the same as in Example 1, except that compound 4 is used as the crosslinking agent.

[0095] Example 7: The basic content is the same as in Example 1, except that compound 5 is used as the crosslinking agent.

[0096] Example 7: The basic content is the same as in Example 1, except that the solid content of the negative electrode dispersant is 1.5%.

[0097] Example 8: The basic content is the same as Example 1, except that the solid content of the negative electrode dispersant is 2%.

[0098] Example 9: The basic content is the same as Example 1, except that lithium hydroxide is used as the alkaline solvent.

[0099] Comparative Example 1: The basic content is the same as Example 1, except that conventional CMC is used as the negative electrode dispersant.

[0100] Comparative Example 2: The basic content is the same as Example 1, except that the mass ratio of cellulose to crosslinking agent is 98:2.

[0101] Comparative Example 3: The basic content is the same as Example 1, except that the mass ratio of cellulose to crosslinking agent is 85:15.

[0102] Comparative Example 4: The basic content is the same as in Example 1, except that the solid content of the negative electrode dispersant is 0.5%.

[0103] Comparative Example 5: The basic content is the same as Example 1, except that the solid content of the negative electrode dispersant is 2.5%.

[0104] Comparative Example 6: The basic content is the same as in Example 1, except that the crosslinking agent used is tri(ethylene glycol) bis(formate).

[0105] IV. Performance Testing:

[0106] The above embodiments and comparative examples were subjected to the following tests, and the test results are shown in Table 1.

[0107] 1) At room temperature (25℃), the viscosity and solid content of the negative electrode dispersant and negative electrode slurry were tested using a viscometer and a solids meter.

[0108] 2) Store the negative electrode slurry at room temperature (25℃) for 48 hours and observe whether the slurry settles.

[0109] 3) Battery cycle performance at 45℃:

[0110] At 45°C, the formed battery was charged to its rated voltage using a 1C constant current and constant voltage method, and then discharged to 3.0V using a 1C constant current method. After repeating the above charge / discharge cycle 600 times, the capacity retention rate after the 600th cycle was calculated, and the cell thickness expansion rate was calculated using PPG testing of the cell thickness before and after the cycle. The calculation formula is as follows:

[0111] Capacity retention rate after 600 cycles (%) = (Discharge capacity after 600 cycles / Discharge capacity after the first cycle) × 100%.

[0112] Cell thickness expansion rate (%) after 600 cycles = (Cell thickness after 600 cycles / Cell thickness before cycle loading) × 100%.

[0113] 4) Rate charging performance:

[0114] A. Test voltage, internal resistance, thickness, and diameter; the test environment is room temperature.

[0115] B. Charge the battery cell at 0.2C to the rated voltage, stop at 0.05C, and let it rest for 5 minutes;

[0116] C. Discharge the battery cell at 0.2C to 3.0V and let it rest for 5 minutes;

[0117] D. Charge the battery cell at 0.5C to the rated voltage, stop at 0.05C, and let it rest for 5 minutes;

[0118] E. Discharge the battery cell to 3.0V at 0.2C and let it rest for 5 minutes;

[0119] F. Charge the battery cell at 1.0C to the rated voltage, stop at 0.05C, and let it rest for 5 minutes;

[0120] G. Discharge the battery cell to 3.0V at 0.2C and let it rest for 5 minutes;

[0121] H. Charge the battery cell to the rated voltage at 3.0C, stop at 0.05C, and let it rest for 5 minutes;

[0122] 1. Discharge the battery cell to 3.0V at 0.2C and let it rest for 5 minutes.

[0123] Rate charging performance (0.2C / 3C) = (3C constant current charging capacity / 0.2C constant current charging capacity) × 100%.

[0124] 5) Energy density:

[0125] Energy density ED = 0.2C discharge capacity / (cell thickness × width × length).

[0126] Table 1

[0127]

[0128]

[0129]

[0130] As shown in Table 1, as the mass ratio of the crosslinking agent gradually increases, the degree of crosslinking (degree of polymerization) of the cellulose polymer increases. Under the same solid content, the viscosity of the dispersant solution also increases, leading to a decrease in the solid content and an increase in the viscosity of the negative electrode slurry. Furthermore, with the increase in the degree of crosslinking (degree of polymerization) of the cellulose polymer, the biphenyl groups contained in the crosslinking agent can improve the mechanical strength of the modified network cellulose, which can increase the cohesive force of the negative electrode sheet to a certain extent. This effectively alleviates the large volume expansion of the negative electrode active material during cyclic lithium intercalation, ensuring contact between the negative electrode active material and the negative electrode current collector, and reducing the cycle expansion rate of the battery cell. Simultaneously, the nucleophilic reaction can introduce ester functional groups, enhancing the wettability to the electrolyte, thereby improving the rate performance of the battery cell. Although this application has been described with reference to preferred embodiments, those skilled in the art will understand that various changes can be made and equivalents can be substituted for its elements, as long as they do not depart from the scope of this application. In addition, many modifications can be made to adapt specific situations or materials to the teachings of this application, as long as they do not depart from the essential scope of this application. Therefore, this application is not intended to be limited to the specific embodiments disclosed as the best mode of carrying out this application as conceived, but rather this application will include all embodiments falling within the scope of the appended claims.

[0131] All scopes disclosed in this application include endpoints, and endpoints can be combined with each other.

[0132] The various embodiments of this application have been described above. These descriptions are exemplary and not exhaustive, nor are they limited to the disclosed embodiments. Many modifications and variations will be apparent to those skilled in the art without departing from the scope and spirit of the described embodiments. The terminology used herein is chosen to best explain the principles, practical application, or improvement of the technology in the market, or to enable others skilled in the art to understand the embodiments disclosed herein.

Claims

1. A negative electrode dispersant, characterized in that, The product includes a cellulose polymer, which comprises a basic cellulose compound and a crosslinking agent, wherein the crosslinking agent comprises a biphenyl compound, the structural formula of which is as follows: R1 and R2 are each independently selected from one or more of -COX1 and -CHO, where X1 is selected from one or more of Cl and Br, and n is a positive integer; the mass ratio of the alkaline cellulose compound to the crosslinking agent is 90~95:5~10; the solid content of the negative electrode dispersant is 1%~2%, and the viscosity of the negative electrode dispersant is 3000 mpa·s~8000 mpa·s.

2. The negative electrode dispersant according to claim 1, characterized in that, R1 and R2 may be the same or different.

3. The negative electrode dispersant according to claim 2, characterized in that, The crosslinking agent comprises at least one of the following biphenyl compounds: Compound 1 Compound 2.

4. The negative electrode dispersant according to claim 1, characterized in that, The basic cellulose compound is obtained by alkalizing cellulose with an alkaline solvent.

5. The negative electrode dispersant according to claim 4, characterized in that, The alkaline solvent comprises at least one of sodium hydroxide and lithium hydroxide.

6. A method for preparing the negative electrode dispersant according to any one of claims 1 to 5, characterized in that, Includes the following steps: A solution containing an alkaline cellulose compound is prepared by dissolving cellulose in an alkaline solution. A cellulose polymer is prepared by adding a crosslinking agent to a solution containing an alkaline cellulose compound, wherein the mass ratio of the alkaline cellulose compound to the crosslinking agent is 90~95:5~10. The cellulose polymer is dissolved in a solvent to prepare a negative electrode dispersant.

7. A lithium-ion battery, characterized in that, The negative electrode includes a negative electrode current collector and a negative electrode active material layer located on at least one side of the surface of the negative electrode current collector. The negative electrode active material layer includes a negative electrode dispersant as described in any one of claims 1 to 5 or a negative electrode dispersant prepared by the method for preparing a negative electrode dispersant as described in claim 6.

Images