Secondary battery and preparation method thereof, energy storage device and electric equipment

Abstract

The invention provides a secondary battery and a preparation method thereof, an energy storage device and electric equipment, and relates to the technical field of energy storage. The preparation method comprises the following steps: carrying out first mixing on a negative electrode active material, first sodium carboxymethyl cellulose and a first conductive agent to obtain a first mixture, and then carrying out second mixing on the first mixture and a first solvent to obtain a second mixture; performing third mixing on the second mixture, second sodium carboxymethyl cellulose, a second conductive agent, first polyacrylic acid and a second solvent to obtain a third mixture, then performing fourth mixing on the third mixture and second polyacrylic acid to obtain a fourth mixture, adding butadiene styrene rubber, and performing fifth mixing to obtain negative electrode slurry; coating a current collector with the negative electrode slurry, and drying to obtain a negative electrode plate; and preparing the negative plate, the diaphragm and the positive plate into a naked battery cell, assembling the naked battery cell with a shell and a top cover, and injecting electrolyte to obtain the secondary battery. The secondary battery has relatively high rate capability, cycling stability and consistency.

Description

[0001] This invention is a divisional application of the invention patent application with the application date of April 14, 2025, application number 202510469475.3, and invention name: "Secondary battery and its preparation method, energy storage device and electrical equipment". Technical Field

[0002] The present invention relates to the field of energy storage technology, and in particular to a secondary battery and a preparation method thereof, an energy storage device and an electrical device. Background Art

[0003] The performance and lifespan of secondary batteries are closely linked to their materials, manufacturing processes, and process control. Anode slurry preparation is a crucial step in secondary battery production, directly impacting electrode and cell fabrication and performance. Creating a suitable and stable slurry is crucial for ensuring cell performance, uniformity, and stability, and the most critical step in slurry preparation is the homogenization method and process. Summary of the Invention

[0004] The main purpose of the present invention is to provide a secondary battery and its preparation method, energy storage device and electrical equipment, so as to solve the problems of poor rate performance, cycle stability and consistency of secondary batteries in the prior art.

[0005] To achieve the above-mentioned object, according to one aspect of the present invention, a method for preparing a secondary battery is provided, comprising: S1, first mixing raw materials including a negative electrode active material, a first sodium carboxymethyl cellulose, and a first conductive agent to obtain a first mixture; S2, second mixing raw materials including the first mixture and a first solvent to obtain a second mixture; S3, third mixing raw materials including the second mixture, a second sodium carboxymethyl cellulose, a second conductive agent, a first polyacrylic acid, and a second solvent to obtain a third mixture; S4, fourth mixing raw materials including the third mixture and the second polyacrylic acid to obtain a fourth mixture; S5, The raw materials including the fourth mixture and styrene-butadiene rubber are mixed for the fifth time to obtain a negative electrode slurry; S6, the negative electrode slurry is coated on a current collector and dried to obtain a negative electrode sheet; S7, the negative electrode sheet, the separator and the positive electrode sheet are made into a bare battery cell, the bare battery cell, the outer shell and the top cover are assembled, and the electrolyte is injected to obtain a secondary battery; wherein the mass ratio of the first sodium carboxymethyl cellulose to the second sodium carboxymethyl cellulose is 3:7 to 7:3, the mass ratio of the first conductive agent to the second conductive agent is 7:3 to 9:1, the mass ratio of the first polyacrylic acid to the second polyacrylic acid is 1:9 to 3:7, and the mass ratio of the first solvent to the second solvent is 2:8 to 4:6.

[0006] Furthermore, the ratio of the mass of the above-mentioned negative electrode active material, the total mass of the first sodium carboxymethyl cellulose and the second sodium carboxymethyl cellulose, the total mass of the first conductive agent and the second conductive agent, the total mass of the first polyacrylic acid and the second polyacrylic acid to the mass of styrene-butadiene rubber is (96-97):(0.2-0.4):(0.5-0.8):(0.2-0.4):(0.6-2.5); and / or, the total mass of the first solvent and the second solvent in the negative electrode slurry accounts for 52-62%.

[0007] Furthermore, the first mixing is carried out in a stirring state, and the stirring speed of the first mixing is 100-500 rpm; and / or, the time of the first mixing is 10-60 min; and / or, the second mixing is carried out in a stirring state, and the stirring speed of the second mixing is 100-300 rpm; and / or, the time of the second mixing is 30-60 min; and / or, the third mixing is carried out in a stirring state, and the stirring speed of the third mixing is 800-1500 rpm; and / or, the time of the third mixing is 60-120 min; and / or, the fourth mixing is carried out in a stirring state, and the stirring speed of the fourth mixing is 800-1500 rpm; and / or, the time of the fourth mixing is 30-90 min; and / or, the fifth mixing is carried out in a stirring state, and the stirring speed of the fifth mixing is 500-1200 rpm; and / or, the time of the fifth mixing is 60-120 min.

[0008] Furthermore, the raw materials in the above S5 also include alcohol auxiliary agents; and / or the mass ratio of the alcohol auxiliary agent to the negative electrode active material is (0.1~0.7):100; and / or the mass ratio of the alcohol auxiliary agent to the total mass of the first sodium carboxymethyl cellulose, the second sodium carboxymethyl cellulose, the first polyacrylic acid and the second polyacrylic acid is (10~30):100.

[0009] Furthermore, the above S5 includes: S51, performing a fifth A mixing of the fourth mixture and the alcohol auxiliary agent to obtain an intermediate mixture; S52, performing a fifth B mixing of the intermediate mixture and styrene-butadiene rubber to obtain a negative electrode slurry.

[0010] Furthermore, the above-mentioned alcohol auxiliary agent is selected from any one or more of propanol, methanol and methylbutynol; and / or the fifth A mixing is carried out under stirring, and the stirring speed of the fifth A mixing is 800-1200 rpm; and / or the fifth A mixing time is 30-60 min; and / or the fifth B mixing is carried out under stirring, and the stirring speed of the fifth B mixing is 500-800 rpm; and / or the fifth B mixing time is 30-45 min.

[0011] Furthermore, the negative electrode active material is graphite and / or silicon carbon; and / or the solvent is water; and / or the conductive agent is selected from any one or more of Super-P, acetylene black and Ketjen black.

[0012] Furthermore, the viscosity of the negative electrode slurry is 5000 to 20000 mPa·s; and / or the solid content of the negative electrode slurry is 52% to 62%.

[0013] According to another aspect of the present invention, a secondary battery is provided, comprising a positive electrode sheet, a separator, an electrolyte, and a negative electrode sheet. The secondary battery is prepared by the aforementioned secondary battery preparation method.

[0014] Furthermore, the above-mentioned negative electrode sheet includes a current collector and a negative electrode active layer, the negative electrode active layer contains a negative electrode active material, a conductive agent, sodium carboxymethyl cellulose, polyacrylic acid and styrene-butadiene rubber, and the particle gap size of the negative electrode active material is 0.1 to 1 μm; and / or the conductive agent, sodium carboxymethyl cellulose, polyacrylic acid and styrene-butadiene rubber are distributed on the surface of the negative electrode active material.

[0015] According to another aspect of the present invention, there is provided an energy storage device including a unit cell, wherein the unit cell is the aforementioned secondary battery.

[0016] According to another aspect of the present invention, there is provided an electrical device comprising the aforementioned energy storage device, wherein the energy storage device is used to provide power to the electrical device.

[0017] By applying the technical solution of the present invention, the beneficial effects of the present application are as follows: the present application helps to optimize the internal bonding structure of the slurry and increase the bonding force between the negative electrode active material and the sodium carboxymethyl cellulose, conductive agent, polyacrylic acid and styrene-butadiene rubber by mixing sodium carboxymethyl cellulose, conductive agent, polyacrylic acid and solvent in steps. In S1, the negative electrode active material, the first sodium carboxymethyl cellulose and the first conductive agent are first mixed, which helps to make the first sodium carboxymethyl cellulose and the first conductive agent evenly adhere to the surface of the negative electrode active material. In S2, the first solvent is added to help adjust the viscosity of the second mixture. In S3, the second mixture, the second sodium carboxymethyl cellulose, the second conductive agent, the first polyacrylic acid and the second solvent are third mixed, which helps to further enhance the bonding and stability of the negative electrode slurry. In S4, the third mixture and the second polyacrylic acid are fourth mixed, which helps to improve the uniformity of the dispersion of the second polyacrylic acid in the negative electrode active material. In S5, the fourth mixture and styrene-butadiene rubber are fifth mixed, which helps to further improve the viscosity stability of the negative electrode slurry. In particular, controlling the mass ratio of the first sodium carboxymethyl cellulose to the second sodium carboxymethyl cellulose to be between 3:7 and 7:3 helps improve the uniformity of the dispersion of sodium carboxymethyl cellulose on the surface of the negative electrode active material, thereby helping to improve the viscosity stability and consistency of the negative electrode slurry. Controlling the mass ratio of the first conductive agent to the second conductive agent and the mass ratio of the first polyacrylic acid to the second polyacrylic acid within the above ranges helps improve the uniformity of the dispersion of the conductive agent and polyacrylic acid on the surface of the negative electrode active material, thereby helping to improve the viscosity stability of the negative electrode slurry, and in turn, helping to improve the rate performance, cycle stability, and consistency of the secondary battery. Controlling the mass ratio of the first solvent to the second solvent within the above range helps promote the uniformity of the distribution of sodium carboxymethyl cellulose, the conductive agent, polyacrylic acid, and styrene-butadiene rubber on the surface of the negative electrode active material, thereby helping to improve the stability of the negative electrode slurry. Improving the viscosity stability and consistency of the negative electrode slurry helps to improve the consistency of the coating surface density, thereby helping to improve the rate performance, cycle stability, and consistency of the secondary battery. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] The accompanying drawings, which constitute part of this application, are intended to provide a further understanding of the present invention. The exemplary embodiments of the present invention and their descriptions are intended to explain the present invention and do not constitute an undue limitation of the present invention. In the accompanying drawings:

[0019] Figure 1 shows an SEM image of the negative electrode sheet in Example 1 of the present application;

[0020] Figure 2 A schematic diagram showing the distribution of particles in the negative electrode active layer of the present application is shown.

[0021] The above drawings include the following reference numerals:

[0022] 1. Negative electrode active material; 2. Auxiliary material particles. DETAILED DESCRIPTION

[0023] It should be noted that, in the absence of conflict, the embodiments and features of the embodiments in this application can be combined with each other. The present invention will be described in detail below with reference to the accompanying drawings and in combination with the embodiments.

[0024] As analyzed in the background technology of this application, secondary batteries in the prior art have problems with poor rate performance, cycle stability and consistency. In order to solve the above problems, this application provides a secondary battery and its preparation method, energy storage device and electrical equipment.

[0025] In a typical embodiment of the present application, a method for preparing a secondary battery is provided, comprising: S1, performing a first mixing of raw materials including a negative electrode active material, a first sodium carboxymethyl cellulose, and a first conductive agent to obtain a first mixture; S2, performing a second mixing of raw materials including the first mixture and a first solvent to obtain a second mixture; S3, performing a third mixing of raw materials including the second mixture, a second sodium carboxymethyl cellulose, a second conductive agent, a first polyacrylic acid, and a second solvent to obtain a third mixture; S4, performing a fourth mixing of raw materials including the third mixture and the second polyacrylic acid to obtain a fourth mixture; S5, performing a fourth mixing of raw materials including The fourth mixture and the raw material of styrene-butadiene rubber are mixed for the fifth time to obtain a negative electrode slurry; S6, the negative electrode slurry is coated on a current collector and dried to obtain a negative electrode sheet; S7, the negative electrode sheet, the separator and the positive electrode sheet are made into a bare battery cell, the bare battery cell, the outer shell and the top cover are assembled, and the electrolyte is injected to obtain a secondary battery; wherein the mass ratio of the first sodium carboxymethyl cellulose to the second sodium carboxymethyl cellulose is 3:7 to 7:3, the mass ratio of the first conductive agent to the second conductive agent is 7:3 to 9:1, the mass ratio of the first polyacrylic acid to the second polyacrylic acid is 1:9 to 3:7, and the mass ratio of the first solvent to the second solvent is 2:8 to 4:6.

[0026] The present application helps to optimize the internal bonding structure of the slurry and increase the bonding force between the negative electrode active material and the sodium carboxymethyl cellulose, conductive agent, polyacrylic acid and styrene-butadiene rubber by mixing sodium carboxymethyl cellulose, conductive agent, polyacrylic acid and solvent in steps. In S1, the negative electrode active material, the first sodium carboxymethyl cellulose and the first conductive agent are mixed for the first time, which helps to make the first sodium carboxymethyl cellulose and the first conductive agent evenly adhere to the surface of the negative electrode active material. In S2, the first solvent is added to help adjust the viscosity of the second mixture. S3, the second mixture, the second sodium carboxymethyl cellulose, the second conductive agent, the first polyacrylic acid and the second solvent are mixed for the third time, which helps to further enhance the bonding and stability of the negative electrode slurry. S4, the third mixture and the second polyacrylic acid are mixed for the fourth time, which helps to improve the dispersion uniformity of the second polyacrylic acid in the negative electrode active material. S5, the fourth mixture and styrene-butadiene rubber are mixed for the fifth time, which helps to further improve the viscosity stability of the negative electrode slurry. In particular, controlling the mass ratio of the first sodium carboxymethyl cellulose to the second sodium carboxymethyl cellulose to be between 3:7 and 7:3 helps improve the uniformity of the dispersion of sodium carboxymethyl cellulose on the surface of the negative electrode active material, thereby helping to improve the viscosity stability and consistency of the negative electrode slurry. Controlling the mass ratio of the first conductive agent to the second conductive agent and the mass ratio of the first polyacrylic acid to the second polyacrylic acid within the above ranges helps improve the uniformity of the dispersion of the conductive agent and polyacrylic acid on the surface of the negative electrode active material, thereby helping to improve the viscosity stability of the negative electrode slurry, and in turn, helping to improve the rate performance, cycle stability, and consistency of the secondary battery. Controlling the mass ratio of the first solvent to the second solvent within the above range helps promote the uniformity of the distribution of sodium carboxymethyl cellulose, the conductive agent, polyacrylic acid, and styrene-butadiene rubber on the surface of the negative electrode active material, thereby helping to improve the stability of the negative electrode slurry. Improving the viscosity stability and consistency of the negative electrode slurry helps to improve the consistency of the coating surface density, thereby helping to improve the rate performance, cycle stability, and consistency of the secondary battery.

[0027] It should be noted that the separator, positive electrode sheet and electrolyte of the present application are commonly used in the art and can be purchased or prepared using existing technologies.

[0028] In order to further improve the viscosity stability and consistency of the negative electrode slurry, in one embodiment of the present application, the mass ratio of the first sodium carboxymethyl cellulose to the second sodium carboxymethyl cellulose is preferably 5:5 to 7:3, the mass ratio of the first conductive agent to the second conductive agent is 8:2 to 9:1, the mass ratio of the first polyacrylic acid to the second polyacrylic acid is 2:8 to 3:7, and the mass ratio of the first solvent to the second solvent is 3:7 to 4:6.

[0029] In one embodiment of the present application, the ratio of the mass of the above-mentioned negative electrode active material, the total mass of the first sodium carboxymethyl cellulose and the second sodium carboxymethyl cellulose, the total mass of the first conductive agent and the second conductive agent, the total mass of the first polyacrylic acid and the second polyacrylic acid to the mass of styrene-butadiene rubber is (96-97):(0.2-0.4):(0.5-0.8):(0.2-0.4):(0.6-2.5); and / or, the total mass of the first solvent and the second solvent in the negative electrode slurry accounts for 52-62%.

[0030] Too many additives will increase costs and may reduce the activity of the negative electrode active material, while too few may not form a stable slurry structure, affecting the coating quality. Controlling the ratio of the mass of the negative electrode active material, the total mass of the first sodium carboxymethyl cellulose and the second sodium carboxymethyl cellulose, the total mass of the first conductive agent and the second conductive agent, the total mass of the first polyacrylic acid and the second polyacrylic acid to the mass of styrene-butadiene rubber within the above ranges helps maintain the activity of the negative electrode active material while improving the stability and uniformity of the negative electrode slurry. Controlling the total mass ratio of the first solvent and the second solvent in the negative electrode slurry within the above range helps control the viscosity of the negative electrode slurry, thereby helping to further improve the stability of the negative electrode slurry.

[0031] In one embodiment of the present application, the first mixing is carried out in a stirring state, and the stirring speed of the first mixing is 100-500 rpm; and / or, the time of the first mixing is 10-60 min; and / or, the second mixing is carried out in a stirring state, and the stirring speed of the second mixing is 100-300 rpm; and / or, the time of the second mixing is 30-60 min; and / or, the third mixing is carried out in a stirring state, and the stirring speed of the third mixing is 800-1500 rpm; and / or, the time of the third mixing is 60-120 min; and / or, the fourth mixing is carried out in a stirring state, and the stirring speed of the fourth mixing is 800-1500 rpm; and / or, the time of the fourth mixing is 30-90 min; and / or, the fifth mixing is carried out in a stirring state, and the stirring speed of the fifth mixing is 500-1200 rpm; and / or, the time of the fifth mixing is 60-120 min.

[0032] Controlling the stirring speed and time of the first mixing within the above ranges helps improve the uniformity of dispersion of the first sodium carboxymethyl cellulose and the first conductive agent on the surface of the negative electrode active material. Controlling the stirring speed and time of the second mixing within the above ranges helps improve the uniformity of dispersion of the first mixture in the first solvent. Controlling the stirring speed and time of the third mixing within the above ranges helps improve the uniformity and stability of the third mixture. Controlling the stirring speed and time of the fourth mixing within the above ranges helps improve the uniformity of dispersion of the second polyacrylic acid on the surface of the negative electrode active material. Controlling the stirring speed and time of the fifth mixing within the above ranges helps improve the uniformity of dispersion of styrene-butadiene rubber on the surface of the negative electrode active material.

[0033] In one embodiment of the present application, the raw materials in the above-mentioned S5 also include an alcohol auxiliary agent; and / or the mass ratio of the alcohol auxiliary agent to the negative electrode active material is (0.1~0.7):100; and / or the mass ratio of the alcohol auxiliary agent to the total mass of the first sodium carboxymethyl cellulose, the second sodium carboxymethyl cellulose, the first polyacrylic acid and the second polyacrylic acid is (10~30):100.

[0034] Alcohol additives contain hydroxyl groups, and their addition helps improve the dispersion stability of the negative electrode active material while reducing the viscosity of the negative electrode slurry, and has no significant effect on the solid content of the negative electrode slurry. Controlling the mass ratio of the alcohol additive to the negative electrode active material within the above range helps improve the dispersion uniformity of the negative electrode active material in the slurry without affecting the activity of the negative electrode active material. Controlling the mass ratio of the alcohol additive to the total mass of the first sodium carboxymethyl cellulose, the second sodium carboxymethyl cellulose, the first polyacrylic acid, and the second polyacrylic acid within the above range helps improve the uniformity of the dispersion of sodium carboxymethyl cellulose and polyacrylic acid on the surface of the negative electrode active material, thereby helping to improve the viscosity stability of the negative electrode slurry.

[0035] In one embodiment of the present application, the above S5 includes: S51, mixing the fourth mixture and the alcohol auxiliary agent in a fifth step A to obtain an intermediate mixture; S52, mixing the intermediate mixture and styrene-butadiene rubber in a fifth step B to obtain a negative electrode slurry.

[0036] By first mixing the fourth mixture with the alcohol additive in the fifth step (A), the rheology and dispersibility of the negative electrode slurry can be more accurately adjusted. Then, mixing the intermediate mixture with styrene-butadiene rubber can help improve the uniformity of the styrene-butadiene rubber distribution in the negative electrode slurry, thereby improving the stability of the negative electrode slurry.

[0037] In one embodiment of the present application, the above-mentioned alcohol auxiliary agent is selected from any one or more of propanol, methanol and methylbutynol; and / or the fifth A mixing is carried out in a stirring state, and the stirring speed of the fifth A mixing is 800-1200 rpm; and / or the fifth A mixing time is 30-60 min; and / or the fifth B mixing is carried out in a stirring state, and the stirring speed of the fifth B mixing is 500-800 rpm; and / or the fifth B mixing time is 30-45 min.

[0038] Propanol, methanol, and methylbutynol contain hydroxyl and methyl groups and have a relatively low boiling point. The hydroxyl and methyl groups simultaneously exert a dispersing effect, which helps to further improve the dispersion stability of the negative electrode active material and reduce the viscosity of the negative electrode slurry, and has no significant effect on the solid content of the negative electrode slurry. At the same time, due to the nature of the low boiling point, it can be fully volatilized during the electrode baking step of the coating process, leaving no residue in the electrode, and does not affect the performance of the electrode. Controlling the stirring speed and time of the fifth A mixing and the stirring speed and time of the fifth B mixing within the above range will help to further improve the stability of the negative electrode slurry.

[0039] In one embodiment of the present application, the above-mentioned alcohol auxiliary agent is a combination of propanol and methylbutynol, and the mass ratio of propanol to methylbutynol is (5:5) to (8:2), specifically 5:5, 6:4, 7:3, 8:2 and a range value between any two ratios.

[0040] Propanol contains a large number of hydroxyl groups, which can combine with hydrogen bonds to show strong hydrophilicity, and undergo esterification reaction with carboxyl groups to show good binding and adsorption stability to polyacrylic acid, styrene-butadiene rubber and sodium carboxymethyl cellulose; methylbutynol contains a large number of methyl groups, which shows hydrophobicity and can effectively combine with negative electrode active materials and conductive agents; using propanol and methylbutynol in combination, especially controlling the mass ratio of propanol and methylbutynol within the above range, helps to improve the mutual synergistic effect between the two, thereby helping to make the dispersion of each component more stable.

[0041] In order to further improve the stability of the negative electrode slurry, in one embodiment of the present application, it is preferred that the above-mentioned negative electrode active material is graphite and / or silicon carbon; and / or the solvent is water; and / or the conductive agent is selected from any one or more of Super-P, acetylene black and Ketjen black.

[0042] In one embodiment of the present application, the viscosity of the negative electrode slurry is 5000-20000 mPa·s; and / or the solid content of the negative electrode slurry is 52%-62%.

[0043] Controlling the viscosity and solid content of the negative electrode slurry within the above ranges helps to further improve the stability of the negative electrode slurry, thereby helping to further improve the consistency of the coating surface density, and further helping to further improve the rate performance, cycle stability and consistency of the secondary battery.

[0044] In another typical embodiment of the present application, a secondary battery is provided, comprising a positive electrode sheet, a separator, an electrolyte, and a negative electrode sheet. The secondary battery is prepared by the aforementioned secondary battery preparation method.

[0045] Since the secondary battery is prepared by the preparation method of the present application, the secondary battery has high rate performance, cycle stability and consistency.

[0046] In one embodiment of the present application, the negative electrode sheet comprises a current collector and a negative electrode active layer, wherein the negative electrode active layer contains a negative electrode active material, a conductive agent, sodium carboxymethyl cellulose, polyacrylic acid and styrene-butadiene rubber, and the particle gap size of the negative electrode active material is 0.1 to 1.4 μm, preferably 0.1 to 1 μm; and / or, the conductive agent, sodium carboxymethyl cellulose, polyacrylic acid and styrene-butadiene rubber are distributed on the surface of the negative electrode active material. Figure 2 As shown, the particles in the negative electrode active layer include a negative electrode active material 1 and auxiliary particles 2. The auxiliary particles 2 are distributed on the surface of the negative electrode active material 1. The auxiliary particles 2 include a conductive agent, sodium carboxymethyl cellulose, polyacrylic acid and styrene-butadiene rubber. Preferably, the surface of the negative electrode active material 1 includes a first coating layer and a second coating layer coated sequentially from the inside to the outside. The first coating layer includes polyacrylic acid and sodium carboxymethyl cellulose, and the second coating layer includes a conductive agent and styrene-butadiene rubber.

[0047] Controlling the interparticle size of the negative electrode active material within the above range helps form a suitable microstructure, ensuring sufficient contact area while providing a pathway for ion transmission between particles. Smaller interparticle sizes help shorten the ion diffusion path and accelerate the ion transmission rate, thereby helping to improve the charge and discharge rate and power density of the secondary battery. The components of the negative electrode active layer are evenly distributed, especially the conductive agent, sodium carboxymethyl cellulose, polyacrylic acid, and styrene-butadiene rubber distributed on the surface of the negative electrode active material, which helps to achieve uniform conduction of electrons and ions within the battery cell, reduce local resistance, and thus help the secondary battery have higher rate performance, cycle stability, and consistency.

[0048] It should be noted that the above-mentioned values ​​of the particle gap size of the negative electrode active material do not mean that all gaps are within this range, but that more than 70% of the gaps are within this range, and more than 95% of the negative electrode active material particles have gaps and will not fit together. The gaps are filled with other materials such as conductive agents.

[0049] In another typical embodiment of the present application, an energy storage device is provided, including a unit cell, which is the aforementioned secondary battery.

[0050] Since the unit cells in the above energy storage device are the secondary batteries of the present application, the energy storage device has a long service life and consistency.

[0051] In another typical embodiment of the present application, an electrical device is provided, comprising the aforementioned energy storage device, wherein the energy storage device is used to provide power to the electrical device.

[0052] Since the energy storage device in the above-mentioned electrical equipment contains the secondary battery of the present application, the electrical equipment has a long service life, consistency and safety.

[0053] The beneficial effects of the present application will be further illustrated below with reference to examples.

[0054] Example 1

[0055] S1, graphite, a first sodium carboxymethyl cellulose and a first Super-P are mixed for a first time to obtain a first mixture; S2, the first mixture and the first water are mixed for a second time to obtain a second mixture; S3, the second mixture, the second sodium carboxymethyl cellulose, the second Super-P, the first polyacrylic acid and the second water are mixed for a third time to obtain a third mixture; S4, the third mixture and the second polyacrylic acid are mixed for a fourth time to obtain a fourth mixture; S51, the fourth mixture and propanol are mixed for a fifth time A to obtain an intermediate mixture; S52, the intermediate mixture and styrene-butadiene rubber are mixed for a fifth time B to obtain a negative electrode slurry; S6, the negative electrode slurry is coated on a copper foil and dried to obtain a negative electrode sheet, wherein the particle gap size of the graphite in the negative electrode sheet is between 0.1 and 1 μm, such as Figure 2 As shown, the particles in the negative active layer of the negative electrode sheet include a negative electrode active material 1 (graphite) and auxiliary material particles 2 (Super-P, sodium carboxymethyl cellulose, polyacrylic acid and styrene-butadiene rubber), and the auxiliary material particles 2 are distributed on the surface of the negative electrode active material 1; S7, the negative electrode sheet, the polypropylene separator and the lithium iron phosphate positive electrode sheet are made into a bare battery cell, the bare battery cell is assembled with the outer shell and the top cover, and then a lithium hexafluorophosphate electrolyte is injected to obtain a secondary battery;

[0056] Among them, the mass ratio of the first sodium carboxymethyl cellulose to the second sodium carboxymethyl cellulose is 5:5, the mass ratio of the first Super-P to the second Super-P is 8:2, the mass ratio of the first polyacrylic acid to the second polyacrylic acid is 2:8, the mass ratio of the first water to the second water is 3:7, the mass ratio of graphite, the total mass of the first sodium carboxymethyl cellulose and the second sodium carboxymethyl cellulose, the total mass of the first Super-P and the second Super-P, the total mass of the first polyacrylic acid and the second polyacrylic acid to the mass of styrene-butadiene rubber is 96:0.4:0.8:0.4:0.6, the total mass of the first water and the second water in the negative electrode slurry accounts for 52%, the first mixing is carried out under stirring, the stirring speed of the first mixing is 100rpm, the first mixing time is 60min, the second mixing is carried out under stirring, and the second The stirring speed of the mixing is 100 rpm, the second mixing time is 60 min, the third mixing is carried out in a stirring state, the stirring speed of the third mixing is 800 rpm, and the third mixing time is 120 min, the fourth mixing is carried out in a stirring state, the stirring speed of the fourth mixing is 800 rpm, and the fourth mixing time is 90 min; the fifth A mixing is carried out in a stirring state, the stirring speed of the fifth A mixing is 800 rpm, and the fifth A mixing time is 60 min, the fifth B mixing is carried out in a stirring state, the stirring speed of the fifth B mixing is 500 rpm, and the fifth B mixing time is 45 min; the mass ratio of propanol to graphite is 0.1:100, and the ratio of the mass of propanol to the total mass of the first sodium carboxymethyl cellulose, the second sodium carboxymethyl cellulose, the first polyacrylic acid and the second polyacrylic acid is 12:100.

[0057] Example 2

[0058] The difference from Example 1 is that the mass ratio of the first sodium carboxymethyl cellulose to the second sodium carboxymethyl cellulose is 7:3, and a secondary battery is finally obtained, wherein the particle gap size of the graphite in the negative electrode sheet is between 0.1 and 1 μm.

[0059] Example 3

[0060] The difference from Example 1 is that the mass ratio of the first sodium carboxymethyl cellulose to the second sodium carboxymethyl cellulose is 3:7, and a secondary battery is finally obtained, wherein the particle gap size of the graphite in the negative electrode sheet is between 0.2 and 1.2 μm.

[0061] Example 4

[0062] The difference from Example 1 is that the mass ratio of the first Super-P to the second Super-P is 9:1, and a secondary battery is finally obtained, wherein the particle gap size of the graphite in the negative electrode sheet is between 0.2 and 1 μm.

[0063] Example 5

[0064] The difference from Example 1 is that the mass ratio of the first Super-P to the second Super-P is 7:3, and a secondary battery is finally obtained, wherein the particle gap size of the graphite in the negative electrode sheet is between 0.3 and 1.2 μm.

[0065] Example 6

[0066] The difference from Example 1 is that the mass ratio of the first polyacrylic acid to the second polyacrylic acid is 3:7, and a secondary battery is finally obtained, wherein the particle gap size of the graphite in the negative electrode sheet is between 0.3 and 1 μm.

[0067] Example 7

[0068] The difference from Example 1 is that the mass ratio of the first polyacrylic acid to the second polyacrylic acid is 1:9, and a secondary battery is finally obtained, wherein the particle gap size of the graphite in the negative electrode sheet is between 0.2 and 1.4 μm.

[0069] Example 8

[0070] The difference from Example 1 is that the mass ratio of the first water to the second water is 4:6, and a secondary battery is finally obtained, wherein the particle gap size of the graphite in the negative electrode sheet is between 0.1 and 1 μm.

[0071] Example 9

[0072] The difference from Example 1 is that the mass ratio of the first water to the second water is 2:8, and a secondary battery is finally obtained, wherein the particle gap size of the graphite in the negative electrode sheet is between 0.1 and 1.3 μm.

[0073] Example 10

[0074] The difference from Example 1 is that the ratio of the mass of graphite, the total mass of the first sodium carboxymethyl cellulose and the second sodium carboxymethyl cellulose, the total mass of the first Super-P and the second Super-P, the total mass of the first polyacrylic acid and the second polyacrylic acid to the mass of styrene-butadiene rubber is 97:0.2:0.8:0.2:2.5, the total mass of the first water and the second water in the negative electrode slurry accounts for 62%, the first mixing is carried out under stirring, the stirring speed of the first mixing is 500 rpm, and the time of the first mixing is 10 min, the second mixing is carried out under stirring, the stirring speed of the second mixing is 300 rpm, and the time of the second mixing is 30 min, The third mixing is carried out in a stirring state, the stirring speed of the third mixing is 1500 rpm, and the time of the third mixing is 60 minutes. The fourth mixing is carried out in a stirring state, the stirring speed of the fourth mixing is 1500 rpm, and the time of the fourth mixing is 30 minutes. The fifth A mixing is carried out in a stirring state, the stirring speed of the fifth A mixing is 1200 rpm, and the time of the fifth A mixing is 30 minutes. The fifth B mixing is carried out in a stirring state, the stirring speed of the fifth B mixing is 800 rpm, and the time of the fifth B mixing is 30 minutes. Finally, a secondary battery is obtained, wherein the particle gap size of the graphite in the negative electrode sheet is between 0.2 and 1.1 μm.

[0075] Example 11

[0076] The difference from Example 1 is that the fourth mixture, propanol, and styrene-butadiene rubber are mixed in a fifth step to obtain a negative electrode slurry, and ultimately a secondary battery. The fifth step is performed while stirring at a stirring speed of 800 rpm for 105 minutes. The interparticle size of the graphite in the negative electrode sheet is between 0.3 and 1.4 μm.

[0077] Example 12

[0078] The difference from Example 1 is that a combination of propanol and methylbutynol is used to replace propanol, and the mass ratio of propanol to methylbutynol in the combination of propanol and methylbutynol is 5:5. Finally, a secondary battery is obtained, wherein the particle gap size of the graphite in the negative electrode sheet is between 0.1 and 0.8 μm.

[0079] Example 13

[0080] The difference from Example 1 is that a combination of propanol and methylbutynol is used to replace propanol, and the mass ratio of propanol to methylbutynol in the combination of propanol and methylbutynol is 8:2. Finally, a secondary battery is obtained, wherein the particle gap size of the graphite in the negative electrode sheet is between 0.1 and 0.9 μm.

[0081] Example 14

[0082] The difference from Example 1 is that the mass ratio of propanol to graphite is 0.2:100, and the mass ratio of propanol to the total mass of the first sodium carboxymethyl cellulose, the second sodium carboxymethyl cellulose, the first polyacrylic acid and the second polyacrylic acid is 24:100. Finally, a secondary battery is obtained, wherein the particle gap size of the graphite in the negative electrode sheet is between 0.2 and 1 μm.

[0083] Example 15

[0084] The difference from Example 1 is that the addition of propanol is eliminated, and a secondary battery is finally obtained, wherein the particle gap size of graphite in the negative electrode sheet is between 0.2 and 1.2 μm.

[0085] Comparative Example 1

[0086] The difference from Example 1 is that the addition of the second sodium carboxymethyl cellulose in S3 is cancelled. In S1, graphite, the first sodium carboxymethyl cellulose, the second sodium carboxymethyl cellulose and the first Super-P are first mixed to finally obtain a secondary battery, wherein the particle gap size of the graphite in the negative electrode sheet is between 0.5 and 1.5 μm.

[0087] Comparative Example 2

[0088] The difference from Example 1 is that the addition of the second Super-P in S3 is cancelled. In S1, the graphite, the first sodium carboxymethyl cellulose, the first Super-P and the second Super-P are first mixed to finally obtain a secondary battery, wherein the particle gap size of the graphite in the negative electrode sheet is between 0.4 and 1.6 μm.

[0089] Comparative Example 3

[0090] The difference from Example 1 is that the addition of the second water in S3 is eliminated, and in S2, the first mixture, the first water and the second water are mixed for a second time to finally obtain a secondary battery, wherein the particle gap size of the graphite in the negative electrode sheet is between 0.4 and 1.7 μm.

[0091] Performance Testing

[0092] Three batches of negative electrode slurries were repeatedly prepared using the preparation methods of the embodiments and comparative examples for viscosity and solid content tests, and the viscosity difference and solid content difference were calculated. The viscosity difference = the maximum viscosity value among the three batches - the minimum viscosity value among the three batches, and the solid content difference = the maximum solid content value among the three batches - the minimum solid content value among the three batches. The viscosity test results and viscosity difference are shown in Table 1, and the solid content test results and solid content difference are shown in Table 2. Three batches of secondary batteries were tested for initial discharge specific capacity and capacity retention rate after 500 cycles. Specifically, the battery cells were charged and discharged using a current of 0.5P in a constant temperature chamber at 25°C. The initial discharge specific capacity = the capacity of the first discharge cycle / the design weight of the lithium iron phosphate material. The capacity retention rate of the 500th cycle = the capacity of the 500th discharge cycle / the capacity of the first discharge cycle. The initial discharge specific capacity difference and the capacity retention rate difference after 500 cycles were calculated. The initial discharge specific capacity difference = the maximum initial discharge specific capacity among the three batches - the minimum initial discharge specific capacity among the three batches. The capacity retention rate difference after 500 cycles = the maximum capacity retention rate after 500 cycles among the three batches - the minimum capacity retention rate after 500 cycles among the three batches. The initial discharge specific capacity test results and the initial discharge specific capacity difference are shown in Table 3. The capacity retention rate test results after 500 cycles and the capacity retention rate difference after 500 cycles are shown in Table 4.

[0093] Table 1

[0094]

[0095]

[0096] Table 2

[0097]

[0098]

[0099] Table 3

[0100]

[0101]

[0102] Table 4

[0103]

[0104]

[0105] Figure 1 This is the SEM image of the negative electrode sheet in Example 1 of the present application, Figure 1 It can be seen that the graphite particles are evenly distributed, the particle gap distribution is well concentrated, and the auxiliary material particles are distributed on the surface of the graphite particles.

[0106] From the above description, it can be seen that the above embodiments of the present invention achieve the following technical effects:

[0107] In Examples 1 to 3, adjusting the mass ratio of the first sodium carboxymethyl cellulose to the second sodium carboxymethyl cellulose helps to optimize the stability and consistency of the negative electrode slurry, especially controlling the mass ratio of the first sodium carboxymethyl cellulose to the second sodium carboxymethyl cellulose within the range of 5:5 to 7:3; in Examples 1, 4 and 5, by adjusting the mass ratio of the first Super-P to the second Super-P, it can be seen from the table that compared with the comparative example, the consistency of the negative electrode slurry is significantly improved, and the difference between batches is smaller; by comparing the test results of Examples 1, 6 and 7, it can be seen that the mass ratio of the first polyacrylic acid to the second polyacrylic acid has a certain influence on the consistency of the viscosity and solid content of the negative electrode slurry, especially when the mass ratio of the first polyacrylic acid to the second polyacrylic acid is controlled within the range of 2:8 to 3:7, the negative electrode slurry exhibits more excellent consistency and stability; from the viscosity and solid content data of the negative electrode slurry in Examples 1, 8 and 9, it can be seen that controlling the mass ratio of the first water to the second water within the range of 3:7 to 4:6 helps to further improve the stability and consistency of the negative electrode slurry, thereby helping to further improve the initial discharge capacity and cycle stability of the secondary battery. From the results of the data comparison of Examples 1 and 11 to 15, it can be seen that the alcohol additives and their addition order and addition amount help to further improve the viscosity and solid content stability and consistency of the negative electrode slurry. In particular, when the mass ratio of propanol to methylbutynol is controlled within the range of 5:5 to 8:2, the stability and consistency of the negative electrode slurry are even better. By comparing the data of the Examples and Comparative Examples, it can be seen that the batch addition of sodium carboxymethyl cellulose, Super-P and water has a significant effect on the stability and consistency of the negative electrode slurry. When sodium carboxymethyl cellulose, Super-P and water are added twice, the negative electrode slurry has higher stability and consistency, and the corresponding secondary battery has higher first discharge capacity and cycle stability.

[0108] The present application helps to optimize the internal bonding structure of the slurry and increase the bonding force between the negative electrode active material and the sodium carboxymethyl cellulose, conductive agent, polyacrylic acid and styrene-butadiene rubber by mixing sodium carboxymethyl cellulose, conductive agent, polyacrylic acid and solvent in steps. In S1, the negative electrode active material, the first sodium carboxymethyl cellulose and the first conductive agent are mixed for the first time, which helps to make the first sodium carboxymethyl cellulose and the first conductive agent evenly adhere to the surface of the negative electrode active material. In S2, the first solvent is added to help adjust the viscosity of the second mixture. S3, the second mixture, the second sodium carboxymethyl cellulose, the second conductive agent, the first polyacrylic acid and the second solvent are mixed for the third time, which helps to further enhance the bonding and stability of the negative electrode slurry. S4, the third mixture and the second polyacrylic acid are mixed for the fourth time, which helps to improve the dispersion uniformity of the second polyacrylic acid in the negative electrode active material. S5, the fourth mixture and styrene-butadiene rubber are mixed for the fifth time, which helps to further improve the viscosity stability of the negative electrode slurry. In particular, controlling the mass ratio of the first sodium carboxymethyl cellulose to the second sodium carboxymethyl cellulose to be between 3:7 and 7:3 helps improve the uniformity of the dispersion of sodium carboxymethyl cellulose on the surface of the negative electrode active material, thereby helping to improve the viscosity stability and consistency of the negative electrode slurry. Controlling the mass ratio of the first conductive agent to the second conductive agent and the mass ratio of the first polyacrylic acid to the second polyacrylic acid within the above ranges helps improve the uniformity of the dispersion of the conductive agent and polyacrylic acid on the surface of the negative electrode active material, thereby helping to improve the viscosity stability of the negative electrode slurry, and in turn, helping to improve the rate performance, cycle stability, and consistency of the secondary battery. Controlling the mass ratio of the first solvent to the second solvent within the above range helps promote the uniformity of the distribution of sodium carboxymethyl cellulose, the conductive agent, polyacrylic acid, and styrene-butadiene rubber on the surface of the negative electrode active material, thereby helping to improve the stability of the negative electrode slurry. Improving the viscosity stability and consistency of the negative electrode slurry helps to improve the consistency of the coating surface density, thereby helping to improve the rate performance, cycle stability, and consistency of the secondary battery.

[0109] The above are merely embodiments of the present invention and are not intended to limit the present invention. Those skilled in the art will readily appreciate that the present invention is susceptible to various modifications and variations. Any modifications, equivalent substitutions, or improvements made within the spirit and principles of the present invention shall be included within the scope of protection of the present invention.

Claims

1. A method for preparing a secondary battery, characterized in that: include: S1, mixing raw materials including a negative electrode active material, a first sodium carboxymethyl cellulose, and a first conductive agent to obtain a first mixture; S2, performing a second mixing of the raw materials including the first mixture and the first solvent to obtain a second mixture; S3, performing a third mixing of the raw materials including the second mixture, the second sodium carboxymethyl cellulose, the second conductive agent, the first polyacrylic acid, and the second solvent to obtain a third mixture; S4, performing a fourth mixing of the raw materials including the third mixture and the second polyacrylic acid to obtain a fourth mixture; S5, performing a fifth mixing of the raw materials including the fourth mixture and styrene-butadiene rubber to obtain a negative electrode slurry; S6, coating the negative electrode slurry on a current collector and drying it to obtain a negative electrode sheet; S7, forming a bare cell with the negative electrode sheet, separator, and positive electrode sheet, assembling the bare cell with a housing and a top cover, and injecting an electrolyte to obtain the secondary battery; The mass ratio of the first sodium carboxymethyl cellulose to the second sodium carboxymethyl cellulose is 3:7 to 7:3, the mass ratio of the first conductive agent to the second conductive agent is 7:3 to 9:1, the mass ratio of the first polyacrylic acid to the second polyacrylic acid is 1:9 to 3:7, and the mass ratio of the first solvent to the second solvent is 2:8 to 4:

6.

2. The method for preparing a secondary battery according to claim 1, wherein: The ratio of the mass of the negative electrode active material, the total mass of the first sodium carboxymethyl cellulose and the second sodium carboxymethyl cellulose, the total mass of the first conductive agent and the second conductive agent, the total mass of the first polyacrylic acid and the second polyacrylic acid to the mass of the styrene-butadiene rubber is (96-97):(0.2-0.4):(0.5-0.8):(0.2-0.4):(0.6-2.5); and / or, the total mass of the first solvent and the second solvent in the negative electrode slurry accounts for 52-62%.

3. The method for preparing a secondary battery according to claim 1, wherein: The first mixing is performed in a stirring state, and the stirring speed of the first mixing is 100 to 500 rpm; and / or the time of the first mixing is 10 to 60 minutes; and / or, the second mixing is performed in a stirring state, and the stirring speed of the second mixing is 100 to 300 rpm; and / or, the time of the second mixing is 30 to 60 minutes; and / or, the third mixing is performed in a stirring state, and the stirring speed of the third mixing is 800 to 1500 rpm; and / or, the time of the third mixing is 60 to 120 minutes; and / or, the fourth mixing is performed in a stirring state, and the stirring speed of the fourth mixing is 800 to 1500 rpm; and / or, the time of the fourth mixing is 30 to 90 minutes; And / or, the fifth mixing is performed in a stirring state, and the stirring speed of the fifth mixing is 500 to 1200 rpm; and / or, the time of the fifth mixing is 60 to 120 minutes.

4. The method for preparing a secondary battery according to any one of claims 1 to 3, characterized in that: The raw materials in S5 also include an alcohol auxiliary agent, and the mass ratio of the alcohol auxiliary agent to the negative electrode active material is (0.1-0.7):100; and / or, the mass ratio of the alcohol auxiliary agent to the total mass of the first sodium carboxymethyl cellulose, the second sodium carboxymethyl cellulose, the first polyacrylic acid and the second polyacrylic acid is (10-30):

100.

5. The method for preparing a secondary battery according to claim 4, wherein: The S5 includes: S51, performing a fifth A mixing of the fourth mixture and the alcohol auxiliary agent to obtain an intermediate mixture; S52, performing a fifth B mixing of the intermediate mixture and the styrene-butadiene rubber to obtain the negative electrode slurry.

6. The method for preparing a secondary battery according to claim 5, wherein: The alcohol auxiliary agent is selected from any one or more of propanol, methanol and methylbutynol; and / or, the fifth A mixing is carried out in a stirring state, and the stirring speed of the fifth A mixing is 800 to 1200 rpm; and / or, the time of the fifth A mixing is 30 to 60 minutes; And / or, the fifth B mixing is performed in a stirring state, and the stirring speed of the fifth B mixing is 500-800 rpm; and / or, the time of the fifth B mixing is 30-45 min.

7. The method for preparing a secondary battery according to any one of claims 1 to 3, characterized in that: The negative electrode active material is graphite and / or silicon carbon; and / or the first conductive agent and the second conductive agent are each independently selected from any one or more of Super-P, acetylene black and Ketjen black; and / or the first solvent and the second solvent are both water.

8. The method for preparing a secondary battery according to any one of claims 1 to 3, characterized in that: The viscosity of the negative electrode slurry is 5000 to 20000 mPa·s; and / or the solid content of the negative electrode slurry is 52% to 62%.

9. A secondary battery comprising a positive electrode, a separator, an electrolyte and a negative electrode, characterized in that: The secondary battery is prepared by the method for preparing a secondary battery according to any one of claims 1 to 8.

10. The secondary battery according to claim 9, wherein The negative electrode sheet includes a current collector and a negative electrode active layer, wherein the negative electrode active layer contains a negative electrode active material, a conductive agent, sodium carboxymethyl cellulose, polyacrylic acid and styrene-butadiene rubber, and the particle gap size of the negative electrode active material is 0.1 to 1 μm; and / or the conductive agent, sodium carboxymethyl cellulose, polyacrylic acid and styrene-butadiene rubber are distributed on the surface of the negative electrode active material.

11. An energy storage device comprising a unit cell, characterized in that: The unit cell is the secondary battery according to claim 9 or 10.

12. An electrical device, characterized in that: The energy storage device comprises the energy storage device according to claim 11, wherein the energy storage device is used to provide power for the electrical equipment.

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