Preparation method for negative electrode slurry, negative electrode sheet, and battery

Abstract

The present application provides a preparation method for a negative electrode slurry, a negative electrode sheet, a battery, and a negative electrode slurry prepared by the present application. The preparation method comprises the following steps: S1, preparing a first adhesive solution from a first binder and water, subjecting a negative electrode main material and a first conductive agent to dry-powder mixing, then adding the first adhesive solution thereto and continuing to mix same, so as to obtain a first mixed system; S2, adding part of a second binder to the first mixed system and mixing same, so as to obtain a second mixed system; S3, adding the remaining second binder to the second mixed system, so as to obtain a third mixed system; S4, adding a second conductive agent to the third mixed system and mixing same, so as to obtain a fourth mixed system; and S5, adding a third binder to the fourth mixed system, mixing same, and adjusting the solid content and viscosity thereof, so as to obtain a negative electrode slurry. The negative electrode slurry exhibits uniform dispersion and high stability, and has no obvious sedimentation and little viscosity change after long-term storage, and the electrode sheet prepared therefrom has a high peeling force, and the battery prepared therefrom has good cycle performance.

Description

Preparation method of negative electrode slurry, negative electrode sheet and battery

[0001] The present application claims priority to the Chinese patent application No. 202411245646.6 filed on September 5, 2024, entitled "Preparation method of negative electrode slurry, negative electrode sheet and battery", the whole content of which is incorporated herein by reference. TECHNICAL FIELD

[0002] The present application belongs to the technical field of lithium ion batteries, and specifically relates to a preparation method of negative electrode slurry, a negative electrode sheet and a battery. BACKGROUND

[0003] At present, in order to pursue high energy density of the battery, silicon negative electrode material is often used, but the silicon negative electrode material has poor conductivity and has huge volume expansion after charging and discharging, and thus the conductive network between materials is easily damaged, causing rapid cycle failure, so the single-walled carbon nanotube needs to be additionally added to ensure the conductivity of the negative electrode while the conventional carbon black conductive agent is added. However, the addition of multiple composite conductive agents greatly increases the difficulty of uniform slurry of the negative electrode slurry, and the conductive agent is prone to agglomeration and difficult to disperse, especially the single-walled carbon nanotube with high aspect ratio and high specific surface conductive agent, which is prone to agglomeration and difficult to disperse during the uniform slurry process, so a suitable silicon negative electrode uniform slurry process is very important. At present, most manufacturers in the industry generally add single-walled carbon nanotube conductive agent during the kneading stage of the uniform slurry process of the silicon negative electrode system, which easily causes agglomeration of the single-walled carbon nanotube, increases the difficulty of uniform slurry, and causes large slurry particles and poor stability. SUMMARY

[0004] To solve the problems and deficiencies in the related art, the present application provides a preparation method of negative electrode slurry, a negative electrode sheet and a battery. The negative electrode slurry prepared by the present application has high uniform dispersion and stability, no obvious sedimentation after long-term storage, and small viscosity change. The slurry has low fineness and low resistivity, so the negative electrode sheet prepared therefrom has high stability, high peel strength, and low resistance, thereby optimizing the cycle performance of the battery.

[0005] According to a first aspect of the present application, a preparation method of a negative electrode slurry is provided, comprising the following steps: S1. preparing a first glue solution by using a first binder and water; mixing a negative electrode main material and a first conductive agent, and then adding the first glue solution to continue mixing to obtain a first mixing system; the first binder comprises at least one of carboxymethyl cellulose, sodium carboxymethyl cellulose and lithium carboxymethyl cellulose; the negative electrode main material comprises a silicon-based material; the first conductive agent comprises at least one of conductive carbon black and conductive graphite; S2. adding part of a second binder to the first mixing system to obtain a second mixing system; the second binder comprises a polyacrylic glue solution; S3. continuously adding the remaining second binder to the second mixing system to obtain a third mixing system; S4. adding a second conductive agent to the third mixing system to obtain a fourth mixing system; the second conductive agent comprises single-walled carbon nanotubes; S5. adding a third binder to the fourth mixing system to adjust the solid content and the viscosity, and obtaining the negative electrode slurry; the third binder comprises at least one of a butadiene-styrene rubber emulsion and a styrene-acrylic rubber emulsion.

[0006] In the preparation method of the negative electrode slurry provided in the present application, the negative electrode main material and the first conductive agent are pre-mixed by dry powder mixing, which can fully break and disperse the conductive agent agglomerates, and the dry powder mixing can realize micro-mixing to form a fine and dispersed conductive agent deposition layer on the surface of large active material particles, thereby forming a good conductive network. The first conductive agent added in this step is carbon black or graphite conductive agent, which has good dispersibility whether in dry powder mixing or wet powder mixing. However, the single-walled carbon nanotube conductive agent with high aspect ratio and high specific surface area has poor dispersibility when directly mixed with the negative electrode main material by dry or wet mixing, which can easily cause agglomeration of the single-walled carbon nanotubes, increase the difficulty of uniform mixing, and cause large slurry particles and poor stability.

[0007] Subsequently, the first glue liquid is added to pre-knead with the negative main material. The first glue liquid is a carboxymethyl cellulose thickener, which has hydrophilic and lipophilic groups. The negative main material is lipophilic but not hydrophilic, and cannot be well infiltrated by the solvent. Therefore, the pre-kneading of such a thickener is mainly to coat the surface of the negative main material, so that the negative main material has hydrophilicity, improves the negative main material and solvent infiltration, and then the main material is well infiltrated and dispersed, and the main material is suspended. Then, the second binder is added in two parts in S2 and S3. The second binder is a polyacrylic glue liquid. Generally, such glue liquid is a water-soluble glue liquid, which is added in two steps to have different effects. The front S2 mainly continues to knead the negative main material, and the main effect is to coat the surface of the negative main material and the conductive agent, and to infiltrate the negative main material and the conductive agent, so that the negative main material and the conductive agent form good adhesion and coating. The remaining second binder is continuously added in S3. Because the first glue liquid and the second binder both contain a large amount of solvent such as water, the solid content and the viscosity of the whole system have been significantly reduced during the addition of the remaining second binder in S3. The dispersed phase is relatively easy, so the remaining second binder can be added in this process to suspend the whole system, and to ensure the stability of the system viscosity.

[0008] Therefore, after the addition of the remaining second binder, the second conductive agent such as single-walled carbon nanotubes with high aspect ratio and high specific surface area is added in S4, which can ensure that it can be effectively bonded by the second binder, and then ensure the firm adhesion of the single-walled carbon nanotubes and the negative main material.

[0009] Finally, the third binder is added. The third binder is a suspension emulsion, which is easy to break under high shear force. In order to improve the mixing effect during the early mixing of the slurry, the stirring speed or the dispersion linear speed is generally high. Therefore, the suspension emulsion is added when the slurry is well dispersed in the later stage, which is conducive to ensuring the stability of the suspension emulsion and fully playing the role of the third binder.

[0010] In summary, the present application designs a matching feeding sequence according to the properties of different raw materials, so that the binder and the conductive agent can be well coated on the surface of the negative main material, forming a good conductive network, and the negative plate and the battery prepared therefrom exhibit better performance. At the same time, such feeding sequence makes the negative main material, each conductive agent, and each binder have stronger dispersion stability in the system, and the attractive force and repulsive force of each material in the slurry reach a better balance, effectively improving the dispersion stability of the slurry, avoiding obvious sedimentation during long-term storage, having low solid content change, and having high stability. At the same time, the feeding sequence of the first conductive agent and the second conductive agent in the present application cannot be disturbed, and disturbance will affect the dispersion effect of the slurry and the coating effect of the conductive agent, resulting in problems such as large slurry particles, unstable viscosity, sedimentation, and conductive agent agglomeration; and the feeding sequence of the first binder, the second binder, and the third binder also cannot be disturbed, and disturbance will affect the dispersion effect of the slurry, resulting in problems such as large slurry particles, unstable viscosity, and sedimentation, and the change of the third binder sequence will cause demulsification.

[0011] In addition, the conductive agent used in the present application is a combination of carbon black or graphite and single-walled carbon nanotubes, which can take into account the dispersion difficulty, slurry stability, and conductivity during the dispersion process. This is because, the dispersion of conventional carbon black is better than that of graphite, and the dispersion difficulty is low, while the dispersion of single-walled carbon nanotubes is poor when the proportion exceeds a certain value, which greatly affects the material performance, therefore, the combination of the two is more conducive to obtaining better comprehensive performance of the slurry. Moreover, the binder used in the present application is also a combination of three types of binders, each of which has its own advantages and disadvantages, such as the carboxymethyl binder, which has general viscosity and brittleness, poor flexibility, and is easily cracked during charging and discharging, and is greatly affected by electrode ratio, pH value, and other conditions; the carboxyl group of the polyacrylic acid binder has strong hydrophilicity, which is easy to react with residual moisture in the battery, affecting the performance; the butadiene-styrene rubber and styrene-butadiene rubber suspension emulsion is unstable and easy to demulsify, affecting the performance. However, the combination of the three binders in the present application can effectively reduce the performance of these binders, optimize the binding, dispersion, and stability of the binder, and has a more obvious effect on optimizing the performance of the negative slurry.

[0012] It should be noted here that in the silicon-based negative slurry, if multi-walled carbon nanotubes are used, the adaptability is relatively low compared to single-walled carbon nanotubes, that is, it cannot well improve the conductivity and other properties of the silicon-based negative material, and affect the performance of the silicon-based negative plate or battery.

[0013] In some embodiments, in S2, the mass ratio of the first part of the second binder in the second binder is 40-70%, and the mass ratio of the remaining second binder in the second binder is 30-60%. Controlling the ratio of the two parts of the second binder in the range can make the slurry system more stable during the entire mixing process and easy to disperse, ensuring that the second binder and the first conductive agent and the first binder added before can better coat the surface of the negative main material, forming a more stable dispersion system and a more compact conductive network.

[0014] In some embodiments, in the negative slurry, the mass ratio of the negative main material, the first conductive agent, the second conductive agent, the first binder, and the second binder is 93-98:0.5-1.5:0.02-0.1:0.1-1:1-3:0.5-2. The ratio of each raw material can ensure that these materials are more stable in the slurry system, that is, the interaction between each material is in a good balance, and at the same time, the obtained negative slurry can exhibit high conductivity and dispersion stability, and the performance of the electrode sheet and the battery prepared therefrom can be optimized.

[0015] In some embodiments, in S1, the solid content of the first glue solution is 1.4-1.8%, and during the addition of the first glue solution, the mixing and stirring rate is 10-35 rpm, the mixing time is 30-60 min, and the solid content of the first mixing system is controlled to be 75-82%. Controlling the solid content of the first glue solution in the range can make the first binder be best dissolved and dispersed uniformly, and the viscosity of the glue solution is appropriate, avoiding being too high or too low, so as to affect the effect of slurry preparation. And the solid content of the first mixing system is 75-82%, which can ensure that the first binder and the negative main material can be well pre-kneaded, so that the first binder is effectively bonded and coated on the surface of the negative main material, improving the hydrophilicity of the negative main material.

[0016] In some embodiments, in S1, the solvent used for preparing the first glue solution includes water.

[0017] In some embodiments, in S1, during the preparation of the first glue solution, the mixing and stirring rate is 10-35 rpm, the dispersion linear velocity is 10-20 m / s, and the mixing time is 3-6 h. In the range of mixing and stirring speed, dispersion linear velocity and mixing time, it can ensure that the preparation of the glue solution has high time efficiency, and at the same time, the first binder can be best dissolved and dispersed uniformly. And the dispersion linear velocity in the range can make the first binder avoid being destroyed due to too high linear velocity of the material molecular chain structure, and at the same time, avoid affecting the dispersion effect and time due to too low linear velocity.

[0018] In some embodiments, in S1, the mixing and stirring rate of the dry powder mixing process of the negative electrode main material and the first conductive agent is 10-35 rpm, and the mixing time is 15-60 min. Under a certain mixing and stirring rate and mixing time, the macroscopic uniform mixing of the three powder materials can be ensured. And no dispersion speed is set in this mixing process, because the dispersion paddle cannot be started due to the high equipment load. In some embodiments, in S1, the negative electrode main material includes a first negative electrode main material and a second negative electrode main material; the first negative electrode main material includes at least one of artificial graphite, natural graphite, and mesocarbon microbeads; and the second negative electrode main material includes at least one of SiO x , SiC, and Si. The combination of the two negative electrode main materials is more conducive to balancing the energy density, fast charging and discharging, and silicon-based volume expansion of the silicon-based negative electrode, so that the comprehensive electrochemical performance of the silicon-based negative electrode is better.

[0019] In some embodiments, in S2, the solid content of the second binder is 20-40%, and in the process of adding part of the second binder, the mixing and stirring rate is 10-35 rpm, the mixing time is 60-120 min, and the solid content of the second mixing system is controlled to be 67-72%. The solid content of the second binder is 20-40%, which can ensure the dilution of the mixing system and ensure that it can be uniformly dispersed in the mixing system, better adhere to and coat the surface of the negative electrode main material together with other binders and conductive agents, and form a more stable and dispersed slurry system. At the same time, the solid content of the second mixing system is controlled to be 67-72%, which can ensure the optimal kneading state and ensure that the powder materials are fully infiltrated, avoid poor infiltration and poor dispersion due to too dry kneading state, and also avoid the failure to form a good kneading state and achieve the "dough kneading" effect due to too wet kneading state, resulting in small frictional shear force between materials and poor dispersion.

[0020] In some embodiments, in S3, in the process of adding the remaining second binder, the mixing and stirring rate is 10-35 rpm, the dispersion linear speed is 10-20 m / s, and the mixing time is 60-120 min.

[0021] In the process of adding the second binder in two steps in S3 and S4, the mixing and stirring rate and the dispersion linear speed are kept constant, which can ensure that the slurry is best dispersed and uniform without damaging the structure of the second binder material, and achieve the best dispersion effect.

[0022] In some embodiments, in S4, the mixing stirring rate is 10-35 rpm, the dispersion linear velocity is 10-20 m / s, and the mixing time is 60-120 min during the adding of the second conductive agent. Under the certain mixing stirring rate and dispersion linear velocity, the single-walled carbon nanotubes can be ensured not to be broken, and the single-walled carbon nanotubes and the slurry can achieve uniform dispersion.

[0023] In some embodiments, in S5, the solid content of the third binder is 30-50%, and the mixing stirring rate is 10-35 rpm, the dispersion linear velocity is not higher than 7 m / s, and the mixing time is 30-60 min during the adding of the third binder. Under the certain mixing stirring rate and dispersion linear velocity, the third binder can have a good dispersion effect. In particular, the dispersion linear velocity is not higher than 7 m / s, so that the third binder can be prevented from being broken due to high shear, and the stability of the third binder and the overall slurry can be ensured.

[0024] In some embodiments, in S5, the solid content is adjusted to 45-55%, and the viscosity is 2500-6000 mpa·s.

[0025] According to a second aspect of the present application, a negative electrode sheet is provided, which comprises a negative electrode active material layer prepared from a negative electrode slurry prepared by the method for preparing a negative electrode slurry. The negative electrode slurry prepared by the method provided in the present application has high dispersion stability, high slurry fineness, and high conductivity, so that the negative electrode sheet prepared therefrom has good conductivity and high peeling strength, and can maintain good structural stability after multiple charge and discharge cycles.

[0026] According to a third aspect of the present application, a battery is provided, which comprises the negative electrode sheet. The negative electrode sheet prepared by the present application has good conductivity, high peeling strength, and excellent structural stability, so that the battery prepared therefrom has better cycle performance. BRIEF DESCRIPTION OF DRAWINGS

[0027] FIG. 1 is an SEM picture of the negative electrode sheet in Example 1 and Comparative Example 1 in the present application.

[0028] FIG. 2 is a comparison chart of the cycle performance of the battery at 45°C in Example 1 and Comparative Example 1 in the present application. Embodiments of the present application

[0029] Example 1

[0030] 1. Preparation of the negative electrode slurry

[0031] The negative electrode slurry of the present example is prepared according to the following steps:

[0032] S1. A first adhesive carboxymethyl cellulose CMC, water is prepared to obtain a solid content of 1.6% of the first glue, the preparation process stirring rate is 20 rpm, the dispersion linear velocity is 15 m / s, the mixing time is 5 h; the first negative electrode main material graphite, the second negative electrode main material SiC, the first conductive agent conductive carbon black SP is mixed after dry powder, in the process of dry powder mixing, the mixing stirring rate is 15 rpm, the mixing time is 30 min; then add the first glue to continue mixing, get the first mixed system, and the stirring rate is 20 rpm in the mixing process, the mixing time is 30 min, and the solid content of the first mixed system is controlled to be 75~82%;

[0033] S2. After mixing part of the second adhesive polyacrylic acid glue PAA (solid content 30%) into the first mixed system, the second mixed system is obtained, and the stirring rate is 20 rpm in the mixing process, the mixing time is 90 min, and the solid content of the second mixed system is controlled to be 67~72%;

[0034] S3. Continue to add the remaining second adhesive polyacrylic acid glue PAA (solid content 30%) into the second mixed system, and the stirring rate is 20 rpm in the mixing process, the dispersion linear velocity is 15 m / s, the mixing time is 90 min, the third mixed system is obtained;

[0035] S4. The second conductive agent single-walled carbon nanotube SWCNT is added to the third mixed system and mixed, and the stirring rate is 20 rpm in the mixing process, the dispersion linear velocity is 15 m / s, the mixing time is 90 min, the fourth mixed system is obtained;

[0036] S5. The third adhesive styrene butadiene rubber emulsion SBR (solid content 40%) is added to the fourth mixed system and mixed, and the solid content and viscosity are adjusted to 50.08% and 4510 mpa·s respectively, and the stirring rate is 20 rpm in the mixing process, the dispersion linear velocity is 5.5 m / s, the mixing time is 30 min, and the vacuum degassing is carried out at-85 Kpa for 1 h, the negative electrode slurry is obtained;

[0037] In the prepared negative electrode slurry, the mass ratio of graphite: SiC: SP: SWCNT: CMC: SBR: PAA is 87.2: 8.96: 0.9: 0.04: 0.4: 1.7: 0.8, the feeding ratio of each raw material is calculated, and the mass ratio of each raw material is dry substance ratio, not including solvent;

[0038] And in S2 and S3, the mass ratio of part of the second adhesive PAA in the second adhesive PAA is 60%; the mass ratio of the remaining second adhesive PAA in the second adhesive PAA is 40%.

[0039] 2. Preparation of negative electrode sheet, positive electrode sheet and battery

[0040] (1) Preparation of the negative electrode sheet

[0041] The prepared negative electrode slurry was coated on the negative electrode current collector (copper foil), dried, and sliced to obtain the negative electrode sheet. In addition, the SEM image of the negative electrode sheet prepared in this example is shown in FIG. 1.

[0042] (2) Preparation of the positive electrode sheet

[0043] The positive electrode material NCM811, conductive carbon black SP, and binder PVDF were added to (N-methyl pyrrolidone) NMP in a mass ratio of 94:3:3, mixed uniformly, and a positive electrode slurry was obtained. The positive electrode sheet was prepared using the obtained positive electrode slurry.

[0044] (3) Preparation of the battery

[0045] The positive electrode sheet, the separator, and the negative electrode sheet were assembled, and the electrolyte (1 mol / L LiPF6 in ethylene carbonate EC + diethyl carbonate DEC + dimethyl carbonate DMC (volume ratio 1:1:1)) was injected. After formation and constant volume, the battery was prepared.

[0046] Example 2

[0047] 1. Preparation of the negative electrode slurry

[0048] In the preparation of the negative electrode slurry in this example, the difference from Example 1 is that in S2 and S3, the mass ratio of the second binder PAA in the second binder PAA is 30%; the mass ratio of the remaining second binder PAA in the second binder PAA is 70%. The solid content and viscosity of the final negative electrode slurry are 48.33% and 4902 mpa·s, respectively. The remaining operations are consistent with Example 1.

[0049] 2. Preparation of the negative electrode sheet, the positive electrode sheet, and the battery

[0050] The preparation of the negative electrode sheet, the positive electrode sheet, and the battery in this example is consistent with Example 1.

[0051] Example 3

[0052] 1. Preparation of the negative electrode slurry

[0053] In the preparation of the negative electrode slurry in this example, the difference from Example 1 is that in S2 and S3, the mass ratio of the second binder PAA in the second binder PAA is 80%; the mass ratio of the remaining second binder PAA in the second binder PAA is 20%; and the solid content and viscosity of the final negative electrode slurry are 50.51% and 4204 mpa·s, respectively. The remaining operations are consistent with Example 1.

[0054] 2. Preparation of negative electrode sheet, positive electrode sheet and battery

[0055] The preparation of the negative electrode sheet, the positive electrode sheet and the battery in this example is consistent with that in Example 1.

[0056] Example 4

[0057] 1. Preparation of negative electrode slurry

[0058] In the preparation of the negative electrode slurry in this example, the difference from Example 1 is that the feeding ratio of each raw material in the negative electrode slurry is calculated based on the mass ratio of graphite: SiC: SP: SWCNT: CMC: SBR: PAA being 87.6: 9.06: 0.4: 0.04: 0.4: 1.7: 0.8, where the mass ratio of each raw material is the dry substance ratio, excluding solvent; and the solid content and viscosity of the final negative electrode slurry are 50.75% and 4680 mpa·s, respectively. The rest of the operations are consistent with those in Example 1.

[0059] 2. Preparation of negative electrode sheet, positive electrode sheet and battery

[0060] The preparation of the negative electrode sheet, the positive electrode sheet and the battery in this example is consistent with that in Example 1.

[0061] Example 5

[0062] 1. Preparation of negative electrode slurry

[0063] In the preparation of the negative electrode slurry in this example, the difference from Example 1 is that the feeding ratio of each raw material in the negative electrode slurry is calculated based on the mass ratio of graphite: SiC: SP: SWCNT: CMC: SBR: PAA being 87.23: 8.96: 0.9: 0.01: 0.4: 1.7: 0.8, where the mass ratio of each raw material is the dry substance ratio, excluding solvent; and the solid content and viscosity of the final negative electrode slurry are 53.14% and 4927 mpa·s, respectively. The rest of the operations are consistent with those in Example 1.

[0064] 2. Preparation of negative electrode sheet, positive electrode sheet and battery

[0065] The preparation of the negative electrode sheet, the positive electrode sheet and the battery in this example is consistent with that in Example 1.

[0066] Example 6

[0067] 1. Preparation of negative electrode slurry

[0068] In the preparation of the negative electrode slurry in the present example, the difference from Example 1 is that in the negative electrode slurry, the feeding ratio of each raw material is calculated according to the mass ratio of graphite: SiC: SP: SWCNT: CMC: SBR: PAA being 87.09: 8.96: 0.9: 0.15: 0.4: 1.7: 0.8, where the mass ratio of each raw material is the dry substance ratio, excluding solvent; and the solid content and viscosity of the final negative electrode slurry are 44.23% and 4763 mpa·s, respectively. The rest of the operations are the same as in Example 1.

[0069] 2. Preparation of negative electrode sheet, positive electrode sheet and battery

[0070] The preparation of the negative electrode sheet, positive electrode sheet and battery in the present example is the same as in Example 1.

[0071] Example 7

[0072] 1. Preparation of negative electrode slurry

[0073] In the preparation of the negative electrode slurry in the present example, the difference from Example 1 is that in S1, the solid content of the first mixed system is controlled to be 85% during the addition of the first glue solution; and the solid content and viscosity of the final negative electrode slurry are 48.59% and 4805 mpa·s, respectively. The rest of the operations are the same as in Example 1.

[0074] 2. Preparation of negative electrode sheet, positive electrode sheet and battery

[0075] The preparation of the negative electrode sheet, positive electrode sheet and battery in the present example is the same as in Example 1.

[0076] Example 8

[0077] 1. Preparation of negative electrode slurry

[0078] In the preparation of the negative electrode slurry in the present example, the difference from Example 1 is that in S1, the solid content of the first mixed system is controlled to be 63% during the addition of the first glue solution; and the solid content and viscosity of the final negative electrode slurry are 50.78% and 5071 mpa·s, respectively. The rest of the operations are the same as in Example 1.

[0079] 2. Preparation of negative electrode sheet, positive electrode sheet and battery

[0080] The preparation of the negative electrode sheet, positive electrode sheet and battery in the present example is the same as in Example 1.

[0081] Example 9

[0082] 1. Preparation of negative electrode slurry

[0083] In the preparation of the negative electrode slurry in the present example, the difference from Example 1 is that in S5, the dispersing linear velocity is 9 m / s during the addition of the third binder; and the solid content and viscosity of the final negative electrode slurry are 48.65% and 5206 mpa·s, respectively. The remaining operations are consistent with those in Example 1.

[0084] 2. Preparation of negative electrode sheet, positive electrode sheet and battery

[0085] The preparation of the negative electrode sheet, the positive electrode sheet and the battery in the present example is consistent with that in Example 1.

[0086] Example 10

[0087] 1. Preparation of negative electrode slurry

[0088] In the preparation of the negative electrode slurry in the present example, the difference from Example 1 is that the first negative electrode main material is natural graphite, the first conductive agent is Ketjen black, and the third binder is phenylpropyl rubber emulsion; and the solid content and viscosity of the final negative electrode slurry are 49.71% and 4710 mpa·s, respectively. The remaining operations are consistent with those in Example 1.

[0089] 2. Preparation of negative electrode sheet, positive electrode sheet and battery

[0090] The preparation of the negative electrode sheet, the positive electrode sheet and the battery in the present example is consistent with that in Example 1.

[0091] Example 11

[0092] 1. Preparation of negative electrode slurry

[0093] In the preparation of the negative electrode slurry in the present example, the difference from Example 1 is that the first negative electrode main material is mesocarbon microbead, the first conductive agent is conductive graphite, and the first binder is sodium carboxymethyl cellulose; and the solid content and viscosity of the final negative electrode slurry are 49.15% and 4201 mpa·s, respectively. The remaining operations are consistent with those in Example 1.

[0094] 2. Preparation of negative electrode sheet, positive electrode sheet and battery

[0095] The preparation of the negative electrode sheet, the positive electrode sheet and the battery in the present example is consistent with that in Example 1.

[0096] Comparative Example 1

[0097] 1. Preparation of negative electrode slurry

[0098] The negative electrode slurry of the present comparative example is prepared according to the following steps:

[0099] S1. A first glue solution with a solid content of 1.6% is prepared using the first binder carboxymethyl cellulose CMC and water, the stirring rate is 20 rpm, the dispersing linear velocity is 15 m / s, and the mixing time is 5 h;

[0100] S2. The second binder polyacrylic acid glue PAA (solid content of 30%) is added (one-time addition) into the first glue to obtain a first mixed system, and the stirring rate is 20 rpm during the mixing process, and the mixing time is 90 min;

[0101] S3. The second conductive agent single-walled carbon nanotube SWCNT is added into the first mixed system to obtain a second mixed system, and the stirring rate is 20 rpm during the mixing process, the dispersion linear velocity is 15 m / s, and the mixing time is 90 min;

[0102] S4. The first negative electrode main material graphite, the second negative electrode main material SiC, and the first conductive agent conductive carbon black SP are dry-mixed, the mixing stirring rate is 15 rpm during the dry-mixing process, and the mixing time is 30 min; then 45% of the second mixed system by mass fraction is added and mixed, and the stirring rate is 20 rpm during the mixing process, and the mixing time is 90 min, to obtain a third mixed system;

[0103] S5. The remaining 55% of the second mixed system is added into the third mixed system for continuous mixing, and the stirring rate is 20 rpm during the mixing process, the dispersion linear velocity is 15 m / s, and the mixing time is 90 min, to obtain a fourth mixed system;

[0104] S6. The third binder styrene-butadiene rubber emulsion SBR (solid content of 40%) is added into the fourth mixed system for mixing, and the solid content and the viscosity are adjusted to 49.45% and 4980 mpa·s respectively, and the stirring rate is 20 rpm during the mixing process, the dispersion linear velocity is 5.5 m / s, the mixing time is 30 min, and the vacuum degassing is performed at -85 Kpa for 1 h, to obtain a negative electrode slurry;

[0105] In the prepared negative electrode slurry, the mass ratio of graphite: SiC: SP: SWCNT: CMC: SBR: PAA is 87.2: 8.96: 0.9: 0.04: 0.4: 1.7: 0.8, and the feeding ratio of each raw material is calculated, and the mass ratio of each raw material here is the dry substance ratio, not including the solvent.

[0106] 2. Preparation of the negative electrode sheet, the positive electrode sheet, and the battery

[0107] The preparation of the negative electrode sheet, the positive electrode sheet, and the battery in the present comparative example is consistent with that in Example 1. The SEM picture of the negative electrode sheet of the present comparative example is shown in FIG. 1.

[0108] Comparative Example 2

[0109] 1. Preparation of the negative electrode slurry

[0110] The comparative example is different from example 1 in that the second conductive agent single-walled carbon nanotube is replaced by multi-walled carbon nanotube in the preparation of the negative electrode slurry, and the solid content and viscosity of the final negative electrode slurry are 48.36% and 5032 mpa·s respectively. The rest of the operations are consistent with example 1.

[0111] 2. Preparation of negative electrode sheet, positive electrode sheet and battery

[0112] The preparation of the negative electrode sheet, the positive electrode sheet and the battery in the comparative example is consistent with example 1.

[0113] Comparative example 3

[0114] 1. Preparation of negative electrode slurry

[0115] The comparative example is different from example 1 in that the addition order of the first binder CMC (first glue solution) and the third binder (SBR emulsion) is exchanged in the preparation of the negative electrode slurry, and the solid content and viscosity of the final negative electrode slurry are 42.51% and 5508 mpa·s respectively. The rest of the operations are consistent with example 1.

[0116] 2. Preparation of negative electrode sheet, positive electrode sheet and battery

[0117] The preparation of the negative electrode sheet, the positive electrode sheet and the battery in the comparative example is consistent with example 1.

[0118] Comparative example 4

[0119] 1. Preparation of negative electrode slurry

[0120] The comparative example is different from example 1 in that the addition order of the first conductive agent conductive carbon black SP and the second conductive agent single-walled carbon nanotube SWCNT is exchanged in the preparation of the negative electrode slurry, and the solid content and viscosity of the final negative electrode slurry are 46.57% and 4304 mpa·s respectively. The rest of the operations are consistent with example 1.

[0121] 2. Preparation of negative electrode sheet, positive electrode sheet and battery

[0122] The preparation of the negative electrode sheet, the positive electrode sheet and the battery in the comparative example is consistent with example 1.

[0123] Test example

[0124] 1. Experimental construction method

[0125] The solid content, initial viscosity, slurry fineness, 24h sedimentation change, 24h viscosity, resistivity of the negative electrode slurry prepared in each example and comparative example were tested or calculated; at the same time, the coating peeling force, roll peeling force, electrode resistance, electrode roll 24h rebound change rate of the negative electrode sheet prepared in each example and comparative example were tested or calculated, and the coating of single-walled carbon nanotubes on the electrode sheet was observed under an electron microscope; and the capacity retention rate of the battery prepared in each example and comparative example was tested after 600 cycles. The specific test methods are as follows:

[0126] (1) The solid content of the negative electrode slurry was tested by a rapid moisture meter, the viscosity was tested by a rotary viscometer, the fineness was tested by a scraper fineness meter, and the test method of 24h sedimentation change was as follows: a, 200mL of slurry was taken and the sampling time was recorded, and the upper layer of the slurry was taken after 24h of standing in a stirring vehicle; b, three samples of the upper layer of the slurry were taken and tested for solid content; c, the slurry in the cup was poured out, and three samples of the slurry at the bottom of the cup were taken and tested for solid content; d, the sedimentation change was calculated by subtracting the solid content of the upper layer from the solid content of the lower layer.

[0127] (2) The test method of the coating / roll peeling force of the negative electrode sheet was as follows: the electrode sheet after coating / roll was taken, and a tensile testing machine was used to test the 90° peeling.

[0128] The test method of the electrode resistance was as follows: the electrode sheet after roll was taken, and an electrode resistance tester was used to test the electrode resistance.

[0129] The test method of the electrode roll 24h rebound change rate was as follows: the thickness of the electrode sheet was tested every 2h after roll until 24h, and the 24h rebound was calculated as (thickness at 24h-thickness at 0h) / 24.

[0130] (3) The test method of the capacity retention rate of the battery after 600 cycles was as follows: a, standing for 30min; b, 1C constant current and constant voltage charging to 4.2V, and the current was cut off at 0.05C; c, standing for 30min; d, 1C constant current discharging to 2.5V; e, cycle a-d for 600 times.

[0131] 2. Experimental results

[0132] (1) The related properties of the negative electrode slurry prepared in each example and comparative example were as shown in Table 1.

[0133] Table 1: Related performance results of the negative electrode slurry prepared in each example and comparative example

[0134]

[0135] (2) The related properties of the negative electrode sheet and battery prepared in each example and comparative example were as shown in Table 2.

[0136] Table 2: Performance results of the negative electrode sheet and battery prepared by each example and comparative example

[0137]

[0138] As can be seen from Table 1 and Table 2, the negative electrode slurry prepared by the method of the present application has high uniform dispersion stability, no obvious sedimentation after long-term storage, small viscosity change, low slurry fineness, and low resistivity. The negative electrode sheet prepared therefrom has high stability, high coating, rolling and peeling strength, and low resistance, thereby improving the cycle performance of the battery. For details, refer to the performance data of Examples 1-11 in Table 1 and Table 2.

[0139] In Comparative Example 1, the order of adding the materials is changed, specifically, the second binder PAA is added at one time, and the single-walled carbon nanotube is mixed with the PAA+CMC mixed glue first, and then mixed with the negative electrode main material and SP dry mixture to obtain a material which is mixed twice, resulting in poor mixing effect of the materials, causing the peeling force of the electrode sheet to decrease, the resistance to increase, the electrode sheet to have high rebound rate, and the battery cycle performance to decrease.

[0140] In addition, FIG. 1 and FIG. 2 are SEM pictures of the negative electrode sheet and cycle performance test diagrams of Example 1 and Comparative Example 1, respectively. As can be seen, in Example 1, the single-walled carbon nanotube is coated on the surface of the main material in a spider web form, and a good conductive network can be formed. In Comparative Example 1, the single-walled carbon nanotube is poorly coated, and only a few scattered ones are scattered on the surface of the main material, and cannot form a better conductive network as in Example 1. Therefore, by using the preparation method provided in the present application, the single-walled carbon nanotube has better dispersion in the slurry, and can form a better conductive network with other materials, which is more conducive to improving the dispersion stability of the slurry, and thereby optimizing the peeling force of the electrode sheet and the cycle performance of the battery.

[0141] In Comparative Example 2, the single-walled carbon nanotube is replaced by a multi-walled carbon nanotube. The multi-walled carbon nanotube has low adaptability to the negative electrode slurry system in the present application, and cannot well improve the conductivity and other properties of the silicon-based negative electrode material, thereby affecting the performance of the silicon-based negative electrode sheet or battery.

[0142] In Comparative Examples 3 and 4, the order of adding the materials is also changed. In Comparative Example 3, the order of adding the first binder CMC and the third binder SBR is exchanged, and in Comparative Example 4, the order of adding the first conductive agent SP and the second conductive agent SWCNT is exchanged. The exchange of the order of adding the binder or the conductive agent will result in poor dispersion stability of the negative electrode, causing the peeling force of the negative electrode sheet to decrease and the cycle performance of the battery to decrease.

[0143] By comparing example 1 and example 2, 3, the proportion of PAA in S2 in example 2 is low, and the proportion of PAA in S2 in example 3 is high, which causes the peel strength of the electrode sheet and the battery cycle performance to decrease, and the PAA is added in two parts in a certain proportion, which has a certain influence on the stability of the negative electrode slurry, and then affects the peel strength of the negative electrode sheet and the cycle performance of the battery.

[0144] Comparing example 1 and example 4, the proportion of the first conductive agent SP in example 4 is too small, which will cause poor slurry dispersion and affect the performance of the electrode sheet and the battery.

[0145] Comparing example 1 and example 5, 6, the proportion of the second conductive agent SWCNT in example 5 is too small, and the proportion of the second conductive agent SWCNT in example 6 is too large, and too little or too much SWCNT is not conducive to considering the conductivity and stability of the slurry, and then the peel strength of the negative electrode sheet and the cycle performance of the battery are affected.

[0146] Comparing example 1 and example 7, 8, in S1 of example 7, the solid content of the first mixed system is 85% during the addition of the first glue solution, which is too high; in S2 of example 8, the solid content of the second mixed system is 63% during the addition of part of the second binder, which is too low. Both cases will cause the dispersion of the binder in the slurry to decrease, which will affect the stability of the slurry, and will affect the performance of the negative electrode sheet and the battery.

[0147] Comparing example 1 and example 9, in S5 of example 9, the dispersion linear speed is 9m / s during the addition of part of the third binder, which is too large, which will cause the SBR to break, which will affect its stability, and then affect the stability of the slurry, and affect the performance of the negative electrode sheet and the battery.

[0148] Comparing example 1 and example 10, 11, it can be found that when some types of raw materials are replaced, the negative electrode slurry still has good performance, and thus the negative electrode sheet and the battery prepared finally also have good performance.

[0149] The above examples are only used to illustrate the technical solutions of the present application, and are not intended to limit the protection scope of the present application. Although the present application has been described in detail with reference to the examples, it should be understood by those skilled in the art that the technical solutions of the present application can be modified or replaced by equivalents, and these modifications or replacements are within the protection scope of the present application.

Claims

1. A method for preparing a negative electrode slurry, comprising the following steps: S1, preparing a first glue solution by using a first binder and water; mixing a negative electrode main material and a first conductive agent, and then adding the first glue solution to the mixture to obtain a first mixed system; the first binder comprises at least one of carboxymethyl cellulose, sodium carboxymethyl cellulose and lithium carboxymethyl cellulose; and the negative electrode main material comprises a silicon-based material; the first conductive agent comprises at least one of conductive carbon black and conductive graphite; S2, after mixing the part of the second binder into the first mixing system, a second mixing system is obtained; a second binder comprises a polyacrylic glue solution; S3, continuously adding the remaining second binder to the second mixed system to obtain a third mixed system; S4, adding a second conductive agent to the third mixed system to obtain a fourth mixed system; the second conductive agent comprises single-walled carbon nanotubes; S5, adding a third binder to the fourth mixed system to adjust the solid content and viscosity, thereby obtaining the negative electrode slurry; the third binder comprises at least one of a butadiene-styrene rubber emulsion and a styrene-acrylic rubber emulsion. 2.The method for preparing the negative electrode slurry according to claim 1, wherein in the S2, the mass ratio of the part of the second binder in the second binder is 40-70%, and the mass ratio of the remaining second binder in the second binder is 30-60%. 3.The method for preparing the negative electrode slurry according to claim 1 or 2, wherein in the negative electrode slurry, the mass ratio of the negative electrode main material, the first conductive agent, the second conductive agent, the first binder and the second binder is 93-98: 0.5-1.5: 0.02-0.1: 0.1-1: 1-3: 0.5-2. 4.The method for preparing the negative electrode slurry according to any one of claims 1-3, wherein in the S1, the solid content of the first glue solution is 1.4-1.8%; and during the addition of the first glue solution, the mixing and stirring rate is 10-35 rpm, the mixing time is 30-60 min, and the solid content of the first mixed system is controlled to be 75-82%. 5.The method for preparing the negative electrode slurry according to any one of claims 1-4, wherein in the S2, the solid content of the second binder is 20-40%; and during the addition of the part of the second binder, the mixing and stirring rate is 10-35 rpm, the mixing time is 60-120 min, and the solid content of the second mixed system is controlled to be 67-72%. 6.The method for preparing the negative electrode slurry according to any one of claims 1-5, wherein in the S3, during the addition of the remaining second binder, the mixing and stirring rate is 10-35 rpm, the dispersion linear velocity is 10-20 m / s, and the mixing time is 60-120 min. 7.The method for preparing the negative electrode slurry according to any one of claims 1-6, wherein in the S4, during the addition of the second conductive agent, the mixing and stirring rate is 10-35 rpm, the dispersion linear velocity is 10-20 m / s, and the mixing time is 60-120 min. ​ ​ 8. The method of claim 1 to 7, wherein in the S5, the third binder has a solid content of 30 to 50%. and the mixing and stirring rate is 10 to 35 rpm, the dispersion linear velocity is not higher than 7 m / s, and the mixing time is 30 to 60 min.

9. The method of claim 1 to 8, wherein in the S5, the solid content is adjusted to 45 to 55%, and the viscosity is 2500 to 6000 mpa-s.

10. A negative electrode sheet comprising a negative electrode active material layer, wherein the negative electrode active material layer is prepared from a negative electrode slurry, and the negative electrode slurry is prepared by the method of claim 1 to 9.

11. A battery comprising the negative electrode sheet of claim 10.

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