Negative electrode dispersing agent, preparation method thereof and lithium ion battery

Abstract

The invention relates to a negative electrode dispersant, a preparation method thereof and a lithium ion battery. The negative dispersing agent comprises a cellulose polymer, the cellulose polymer comprises an alkaline cellulose compound and a cross-linking agent, the cross-linking agent comprises a biphenyl compound, and 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. According to the scheme provided by the invention, by reducing the addition amount of the CMC, the cycle performance and the rate capability of the battery are not influenced while the energy density of the battery is improved.

Description

Technical Field

[0001] The present application relates to the field of battery technology, and in particular to a negative electrode dispersant and a preparation method thereof, and a lithium ion battery. Background Art

[0002] Lithium batteries have the advantages of high energy density, long cycle life and low self-discharge rate, and are widely used in electronic products and electric vehicles. The negative electrode material of lithium batteries plays an important role in battery performance. In the preparation process of negative electrode slurry, sodium carboxymethyl cellulose (CMC) is usually added as a dispersant, which can thicken and stabilize the slurry to prevent the sedimentation of negative electrode active materials.

[0003] In the related art, on the one hand, the energy density of lithium-ion batteries is improved by reducing the amount of CMC added, but 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 the inability to prepare the negative electrode sheet. On the other hand, due to the low viscosity of CMC, the amount of CMC added will be increased to ensure the suspension stability of the slurry, but this may result in a low mass proportion of the negative electrode active material, affecting the battery's cycle performance and rate performance. Summary of the invention

[0004] In order to solve or partially solve the problems existing in the related art, the present application provides a negative electrode dispersant and a preparation method thereof and a lithium ion battery, which can improve the energy density of the battery by reducing the amount of CMC added without affecting the cycle performance and rate performance of the battery.

[0005] In a first aspect, the present application provides a negative electrode dispersant, comprising a cellulose polymer, wherein the cellulose polymer comprises an alkaline cellulose compound and a cross-linking agent, wherein the cross-linking agent comprises a biphenyl compound, and the structural formula of the biphenyl compound is as follows:

[0006]

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

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

[0009] As an optional embodiment, the cross-linking 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 cross-linking 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 contains at least one of sodium hydroxide and lithium hydroxide.

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

[0015] dissolving cellulose in an alkaline solution to prepare a solution containing an alkaline cellulose compound;

[0016] Adding a crosslinking agent to a solution containing an alkaline cellulose compound to prepare a cellulose polymer, 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 the present application provides a lithium-ion battery, comprising a negative electrode sheet, wherein the negative electrode sheet comprises 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, wherein the negative electrode active material layer comprises the negative electrode dispersant described above or a negative electrode dispersant prepared by the method for preparing the negative electrode dispersant described above.

[0021] The technical solution provided by this application may have the following beneficial effects:

[0022] The alkaline cellulose compound in the present application can be obtained by alkalizing cellulose with an alkaline solvent, and has a strong nucleophilic group -O - X + , X + It can be sodium ion or lithium ion. Biphenyl compounds are used as crosslinking agents, and the -O - X +The group can undergo nucleophilic substitution reaction with the R1 and R2 groups contained in the biphenyl compounds to generate a cellulose polymer with a three-dimensional network structure. This network structure makes it difficult for the cellulose molecular chain to move, so that its glue still has a high viscosity at a low solid content, so a low amount of dispersant can still ensure the 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, graphite materials) through an efficient and rigid "sheet-to-point" bonding mode, giving the negative electrode excellent structural and interfacial stability to improve the battery's cycle performance and rate performance. In addition, the biphenyl group contained in the cross-linking agent provides sufficient rigidity to the cellulose polymer, increases the mechanical strength of the cellulose polymer, and can increase the cohesive force of the negative electrode sheet to a certain extent, thereby effectively alleviating the large volume expansion of the negative electrode active material during the cycle lithium insertion process, ensuring the contact between the negative electrode active material and the negative electrode current collector, and thereby improving the rate performance of the battery cell.

[0023] It should be understood that the foregoing general description and the following detailed description are exemplary and explanatory only and are not restrictive of the present application. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] The above and other objects, features and advantages of the present application will become more apparent by describing in more detail exemplary embodiments of the present application in conjunction with the accompanying drawings, wherein the same reference numerals generally represent the same components in the exemplary embodiments of the present application.

[0025] Figure 1 It is a schematic diagram of the structure of the negative electrode dispersant acting on the negative electrode active material shown in the embodiment of the present application.

[0026] In the figure: 1. Alkalized cellulose; 2. Cross-linking agent; 3. Negative electrode active material. DETAILED DESCRIPTION

[0027] The embodiments of the present application will be described in more detail below with reference to the accompanying drawings. Although the embodiments of the present application are shown in the accompanying drawings, it should be understood that the present application can be implemented in various forms and should not be limited by the embodiments described herein. On the contrary, these embodiments are provided to make the present application more thorough and complete, and to fully convey the scope of the present application to those skilled in the art.

[0028] The terms used in this application are for the purpose of describing specific embodiments only and are not intended to limit this application. The singular forms of "a", "said" and "the" used in this application and the appended claims are also intended to include plural forms unless the context clearly indicates other meanings. It should also be understood that the term "and / or" used herein refers to and includes any or all possible combinations of one or more 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 the same type of information from each other. For example, without departing from the scope of this application, the first information may also be referred to as the second information, and similarly, the second information may also be referred to as the first information. Thus, the features defined as "first" and "second" may explicitly or implicitly include one or more of the features. In the description of this application, the meaning of "multiple" is two or more, unless otherwise clearly and specifically defined.

[0030] During the preparation of negative electrode slurry, sodium carboxymethyl cellulose (CMC) is usually added as a dispersant, which can thicken and stabilize the slurry to prevent the negative electrode active material from settling.

[0031] In the related art, on the one hand, the energy density of lithium-ion batteries is improved by reducing the amount of CMC added, but 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 the inability to prepare the negative electrode sheet. On the other hand, due to the low viscosity of CMC, the amount of CMC added will be increased to ensure the suspension stability of the slurry, but this may result in a low mass proportion of the negative electrode active material, affecting the battery's cycle performance and rate performance.

[0032] In view of the above problems, an embodiment of the present application provides a negative electrode dispersant, which can improve the energy density of the battery without affecting the cycle performance and rate performance of the battery by reducing the amount of CMC added.

[0033] The technical solution of the embodiments of the present application is described in detail below with reference to the accompanying drawings.

[0034] Figure 1 It is a schematic diagram of the structure of the negative electrode dispersant acting on the negative electrode active material shown in the embodiment of the present application.

[0035] See also Figure 1 The present application provides a negative electrode dispersant, including a cellulose polymer, the cellulose polymer including an alkaline cellulose compound 1 and a cross-linking agent 2, the cross-linking agent 2 includes a biphenyl compound, and the structural formula of the biphenyl compound is as follows:

[0036]

[0037] Wherein, R1 and R2 are independently selected from one or more of aldehyde group, acyl group, ester group and carboxyl group, n is a positive integer, n represents the number of biphenyl groups, and the value of n can be 1-10.

[0038] In the embodiment of the present application, the alkaline 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 ion or lithium ion. Biphenyl compound is used as crosslinking agent 2, and -O of alkaline cellulose compound 1 - X + The group can undergo a nucleophilic substitution reaction with the R1 and R2 groups contained in the biphenyl compound to generate a cellulose polymer with a three-dimensional network structure. This network structure makes it difficult for the cellulose molecular chain to move, so that its glue still has a high viscosity at a low solid content, so a low amount of dispersant can still ensure the 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, graphite materials) through an efficient and rigid "sheet-to-point" bonding mode, giving the negative electrode excellent structural and interfacial stability to improve the battery's cycle performance and rate performance. In addition, the biphenyl group contained in the crosslinker 2 provides sufficient rigidity to the cellulose polymer, increases the mechanical strength of the cellulose polymer, and can increase the cohesive force of the negative electrode sheet to a certain extent, thereby effectively alleviating the large volume expansion of the negative electrode active material during the cycle lithium insertion process, ensuring the contact between the negative electrode active material and the negative electrode current collector, and thereby improving the rate performance of the battery cell.

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

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

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

[0042] As a preferred embodiment, the cross-linking agent comprises at least one of the following biphenyl compounds:

[0043]

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

[0045] In the embodiments of the present application, a cellulose polymer is configured into a colloid as a dispersant and applied to the negative electrode of a lithium-ion battery. By controlling the concentration of the cross-linking agent to adjust the cross-linking density of the alkaline cellulose compound, that is, the degree of polymerization of the cellulose polymer, the dispersant can have good adaptability to the volume change of the negative electrode active material during the lithiation / delithiation process, thereby ensuring the overall dynamic interface stability between the components of the negative electrode, providing continuous, stable and continuous electron and ion transport for the negative electrode reaction, and the three-dimensional network structure of the cellulose polymer improves 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 the present application, the mass ratio of the alkaline cellulose compound to the cross-linking agent may be 90:10, 92:8, 95:5 or any value within the above-defined range, which is not limited in the present application.

[0047] As an optional embodiment, taking the cross-linking agent selected from Compound 1 and Compound 2 as an example, the structural formula of the prepared cellulose polymer is as follows:

[0048]

[0049] wherein P is the degree of polymerization; R' is the same or different and is independently 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 embodiment of the present 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 optional embodiment, the alkali cellulose compound is obtained by alkalizing cellulose with an alkaline solvent.

[0053] The embodiment of the present application can prepare an alkaline cellulose compound by dissolving cellulose in an alkaline solution. The preparation method is simple to operate, low in cost, and convenient for large-scale industrial production. The prepared alkaline cellulose compound has a high viscosity and can maintain viscosity even in a high temperature and high pressure working environment.

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

[0055] In the present embodiment, cellulose is dissolved in sodium hydroxide or lithium hydroxide solution to obtain sodium carboxymethyl cellulose or lithium carboxymethyl cellulose. Among them, sodium carboxymethyl cellulose has a low raw material price and a simple preparation method, which can reduce production costs, and lithium carboxymethyl cellulose prepared as a negative electrode dispersant has better kinetic properties than sodium carboxymethyl cellulose.

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

[0057] The present invention also provides a method for preparing a negative electrode dispersant, comprising the following steps:

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

[0059] In the embodiment of the present application, cellulose and an alkaline solution are mixed 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 fiber and cotton particle fiber; the alkaline solvent includes at least one of sodium hydroxide and lithium hydroxide.

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

[0062] In the embodiments of the present application, a cellulose polymer is configured into a colloid as a dispersant and applied to the negative electrode of a lithium-ion battery. By controlling the concentration of the cross-linking agent to adjust the cross-linking density of the alkaline cellulose compound, that is, the degree of polymerization of the cellulose polymer, the dispersant can have good adaptability to the volume change of the negative electrode active material during the lithiation / delithiation process, thereby ensuring the overall dynamic interface stability between the components of the negative electrode, providing continuous, stable and continuous electron and ion transport for the negative electrode reaction, and the three-dimensional network structure of the cellulose polymer improves 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 the present application, the mass ratio of the alkaline cellulose compound to the cross-linking agent may be 90:10, 92:8, 95:5 or any value within the above-defined range, which is not limited in the present application.

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

[0065] In the embodiment of the present application, the cellulose polymer can be dissolved in deionized water, stirred at room temperature for a period of time, and configured into 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 embodiment of the present application, the negative electrode dispersant comprises a cellulose polymer and a solvent. Taking the mass percentage of the negative electrode dispersant as 100%, the solid content of the negative electrode dispersant refers to the mass percentage of the cellulose polymer in the negative electrode dispersant.

[0068] In the embodiments of the present application, the solid content of the negative electrode dispersant is low, but the viscosity is high, and the solid content of the negative electrode dispersant can be 1%, 1.5%, 2% or any value within the above-defined range, which is not limited in the present application.

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

[0070] In the embodiment of the present 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] Since conventional CMC contains abundant hydroxyl groups and a small amount of carboxyl groups, it has a certain solubility in water. The embodiment of the present application utilizes the reaction of hydroxyl groups on alkaline cellulose and functional groups on biphenyl compounds to transform linear alkaline 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, thereby increasing the proportion of negative electrode active materials and improving the energy density of lithium-ion batteries.

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

[0073] The negative electrode active material layer of the embodiment of the present application includes a negative electrode active material, a binder and a conductive agent, and the negative electrode active material includes natural graphite, artificial graphite, mesophase microcarbon beads, hard carbon, soft carbon, silicon, silicon-carbon composite, Li-Sn alloy, Li-Sn-O alloy, Sn, SnO, SnO2, spinel structured lithiated TiO2-Li4Ti5O 12 , Li-Al alloy.

[0074] The embodiments of the present application have no particular restrictions on the negative electrode current collector, as long as the purpose of the present application can be achieved, for example, it can be copper foil, copper alloy foil, nickel foil, stainless steel foil, titanium foil, foam nickel, foam copper or a composite current collector.

[0075] The present application also provides an electrical device, including the above-mentioned lithium-ion battery.

[0076] Exemplarily, the above-mentioned 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] In order to further understand the present invention, the present application is described below in conjunction with embodiments. These embodiments are only used to illustrate the present application and are not used to limit the scope of the present application.

[0078] Embodiment 1:

[0079] 1. Preparation of negative electrode sheet

[0080] 1. Weigh cellulose and a cross-linking agent in a mass ratio of cellulose to a cross-linking agent of 90:10, wherein the cross-linking agent is selected from compound 2;

[0081] 2. Completely dissolving cellulose in a sodium hydroxide solution and stirring at room temperature for 3 hours to obtain a solution containing an alkaline cellulose compound;

[0082] 3. Add compound 2 to the solution containing the alkaline cellulose compound, continue stirring for 3 hours to complete the reaction, centrifuge and vacuum dry to obtain a 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 = 13 μm to 15 μm) in a mass ratio of 1:1:98, and evenly disperse them in deionized water for 3 to 5 hours to prepare a negative electrode slurry;

[0085] 6. Apply the negative electrode slurry on the copper foil, and then dry, roll and cut to obtain the negative electrode sheet.

[0086] 2. Preparation of positive electrode slurry

[0087] Lithium cobalt oxide, a conductive agent and a 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 evenly coated on both sides of an aluminum foil, and a positive electrode sheet is obtained after drying, rolling and slitting.

[0088] 3. Battery Assembly

[0089] A separator is placed between the positive electrode sheet and the negative electrode sheet, and then a sandwich structure consisting of the positive electrode sheet, the negative electrode sheet and the separator is wound, and then the wound body is flattened and placed in an aluminum-plastic shell, and the aluminum-plastic shell is sealed after welding the pole ears to obtain a battery cell to be injected with liquid; a commercially available electrolyte is injected into the battery cell, and the battery cell is sealed, aged, and formed to prepare a lithium-ion battery.

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

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

[0092] Example 4: The basic contents are the same as those of Example 1, except that compound 1 is used as the cross-linking agent.

[0093] Example 5: The basic contents are the same as those of Example 1, except that compound 3 is used as the cross-linking agent.

[0094] Example 6: The basic contents are the same as those of Example 1, except that compound 4 is used as the cross-linking agent.

[0095] Example 7: The basic contents are the same as those of Example 1, except that compound 5 is used as the cross-linking agent.

[0096] Example 7: The basic content is the same as 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 contents are the same as those of Example 1, except that lithium hydroxide is used as the alkaline solvent.

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

[0100] Comparative Example 2: The basic contents are the same as those of Example 1, except that the mass ratio of cellulose to the cross-linking agent is 98:2.

[0101] Comparative Example 3: The basic contents are the same as those of Example 1, except that the mass ratio of cellulose to the cross-linking agent is 85:15.

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

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

[0104] Comparative Example 6: The basic contents are the same as those of Example 1, except that tri(ethylene glycol) bis(formate) is used as the cross-linking agent.

[0105] 4. Performance test:

[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°C), use a viscometer and a solid content meter to test the viscosity and solid content of the negative electrode dispersant and the negative electrode slurry.

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

[0109] 3) Battery cycle performance at 45°C:

[0110] At 45°C, charge the formed battery to the rated voltage with 1C constant current and constant voltage, and then discharge it to 3.0V with 1C constant current. Repeat the above charge / discharge cycle for 600 times to calculate the capacity retention rate of the 600th cycle, and use the PPG test to calculate the thickness expansion rate of the battery cell before and after the cycle. The calculation formula is as follows:

[0111] 600th cycle capacity retention rate (%) = (600th cycle discharge capacity / first cycle discharge capacity) × 100%.

[0112] The 600th cell thickness expansion rate (%) = (600th cell thickness / cell thickness before cycle loading) × 100%.

[0113] 4) Rate charging performance:

[0114] A. Test voltage, internal resistance, thickness and diameter at room temperature;

[0115] B. Charge the battery to the rated voltage at 0.2C, cut off at 0.05C, and leave it for 5 minutes;

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

[0117] D. Charge the battery to the rated voltage at 0.5C, cut off at 0.05C, and leave it for 5 minutes;

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

[0119] F. Charge the battery to the rated voltage at 1.0C, cut off at 0.05C, and leave it for 5 minutes;

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

[0121] H. Charge the battery to the rated voltage at 3.0C, cut off at 0.05C, and leave it for 5 minutes;

[0122] I. Discharge the battery to 3.0V at 0.2C and leave it 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 x width x length).

[0126] Table 1

[0127]

[0128]

[0129]

[0130] According to the data in Table 1, when the mass ratio of the crosslinking agent gradually increases, the crosslinking degree (polymerization degree) of the cellulose polymer increases. At the same solid content, the viscosity of the dispersant colloid will also increase, resulting in a decrease in the solid content of the negative electrode slurry and an increase in the viscosity of the discharge; and as the crosslinking degree (polymerization degree) of the cellulose polymer increases, the biphenyl groups contained in the crosslinking agent can increase the mechanical strength of the modified reticulated cellulose, and to a certain extent, can increase the cohesion of the negative electrode sheet, thereby effectively alleviating the large volume expansion of the negative electrode active material during the cyclic lithium insertion process, ensuring the contact between the negative electrode active material and the negative electrode current collector, and reducing the cycle expansion rate of the battery cell; at the same time, the nucleophilic reaction can introduce an ester functional group, enhance the wettability of the electrolyte, and thus improve the rate performance of the battery cell. Although the present application has been described with reference to the preferred embodiment, those skilled in the art will understand that various changes can be made and equivalents can replace its elements, as long as they do not deviate from the scope of the present application. In addition, many improvements can be made to adapt specific situations or materials to the teachings of the present application, as long as they do not deviate from the substantive scope of the present application. Therefore, it is intended that the application not be limited to the particular embodiment disclosed as the best mode contemplated for carrying out this application, but that the application will include all embodiments falling within the scope of the appended claims.

[0131] All ranges disclosed in this application are inclusive of the endpoints, and the endpoints are combinable with each other.

[0132] The embodiments of the present application have been described above, and the above description is exemplary, not exhaustive, and is not limited to the disclosed embodiments. Many modifications and changes will be apparent to those of ordinary skill in the art without departing from the scope and spirit of the described embodiments. The selection of terms used herein is intended to best explain the principles of the embodiments, practical applications, or improvements to the technology in the market, or to enable other persons of ordinary skill in the art to understand the embodiments disclosed herein.

Claims

1. A negative electrode dispersant, characterized in that The invention comprises a cellulose polymer, wherein the cellulose polymer comprises an alkaline cellulose compound and a cross-linking agent, wherein the cross-linking agent comprises a biphenyl compound, and the structural formula of the biphenyl compound is as follows: Wherein, R1 and R2 are each independently selected from one or more of aldehyde group, acyl group, ester group and carboxyl group, and n is a positive integer.

2. The negative electrode dispersant according to claim 1, characterized in that R1 and R2 are the same or different, and R1 and R2 are selected from one of -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-C20 alkane groups.

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

4. The negative electrode dispersant according to claim 1, characterized in that The mass ratio of the alkaline cellulose compound to the cross-linking agent is 90-95:5-10.

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

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

7. A method for preparing the negative electrode dispersant according to any one of claims 1 to 6, characterized in that: The following steps are involved: dissolving cellulose in an alkaline solution to prepare a solution containing an alkaline cellulose compound; Adding a crosslinking agent to a solution containing an alkaline cellulose compound to prepare a cellulose polymer, 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.

8. The method according to claim 7, characterized in that The solid content of the negative electrode dispersant is 1% to 2%.

9. The method according to claim 8, characterized in that The viscosity of the negative electrode dispersant is 3000 mPa﹒ s to 8000 mPa﹒ s.

10. A lithium ion battery, characterized in that: The invention comprises a negative electrode sheet, wherein the negative electrode sheet comprises a negative electrode current collector and a negative electrode active material layer located on at least one side of the negative electrode current collector, wherein the negative electrode active material layer comprises the negative electrode dispersant according to claims 1 to 6 or the negative electrode dispersant prepared by the preparation method of the negative electrode dispersant according to claims 7 to 9.

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