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

Technical Field

[0001] 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 equipment. Background Art

[0002] The performance and life of secondary batteries are closely related to materials, manufacturing processes and manufacturing process control, and negative electrode homogenization is a very critical step in the production of secondary batteries. Its quality directly affects the production of electrodes and cells and the performance of cells. Making appropriate and stable slurry is the key to ensuring the performance, uniformity and stability of the cell, and the most critical step in preparing slurry is the homogenization method and process. Summary of the invention

[0003] The main purpose of the present invention is to provide a secondary battery and a preparation method thereof, an energy storage device and an electrical equipment to solve the problems of poor rate performance, cycle stability and consistency of secondary batteries in the prior art.

[0004] In order 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 3:7~7:3, the mass ratio of the first conductive agent to the second conductive agent is 7:3~9:1, the mass ratio of the first polyacrylic acid to the second polyacrylic acid is 1:9~3:7, and the mass ratio of the first solvent to the second solvent is 2:8~4:6.

[0005] 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%.

[0006] Further, the first mixing is carried out under stirring, and the stirring speed of the first mixing is 100-500rpm; and / or, the time of the first mixing is 10-60min; and / or, the second mixing is carried out under stirring, and the stirring speed of the second mixing is 100-300rpm; and / or, the time of the second mixing is 30-60min; and / or, the third mixing is carried out under stirring, and the stirring speed of the third mixing is 800-1500rpm; and / or, the time of the third mixing is 60-120min; and / or, the fourth mixing is carried out under stirring, and the stirring speed of the fourth mixing is 800-1500rpm; and / or, the time of the fourth mixing is 30-90min; and / or, the fifth mixing is carried out under stirring, and the stirring speed of the fifth mixing is 500-1200rpm; and / or, the time of the fifth mixing is 60-120min.

[0007] 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.

[0008] Furthermore, 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.

[0009] Furthermore, 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 under stirring, and the stirring speed of the fifth A mixing is 800~1200rpm; and / or, the fifth A mixing time is 30~60min; and / or, the fifth B mixing is carried out under stirring, and the stirring speed of the fifth B mixing is 500~800rpm; and / or, the fifth B mixing time is 30~45min.

[0010] 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.

[0011] Furthermore, 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%.

[0012] 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, and the secondary battery is prepared by the aforementioned secondary battery preparation method.

[0013] 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 0.1~1μm; 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.

[0014] According to another aspect of the present invention, there is provided an energy storage device, comprising a unit cell, wherein the unit cell is the aforementioned secondary battery.

[0015] 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 for the electrical device.

[0016] 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 bonding structure inside the slurry and increase the bonding force between the negative electrode active material and the sodium carboxymethyl cellulose, the conductive agent, the polyacrylic acid and the styrene-butadiene rubber by mixing the sodium carboxymethyl cellulose, the conductive agent, the polyacrylic acid and the 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 uniformly attached 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 the styrene-butadiene rubber are fifth mixed, which helps to further improve the viscosity stability of the negative electrode slurry. In particular, by controlling the mass ratio of the first sodium carboxymethyl cellulose to the second sodium carboxymethyl cellulose to be 3:7 to 7:3, it is helpful to 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 range helps to 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 then 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 to promote the uniformity of the distribution of sodium carboxymethyl cellulose, 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. The improvement of the viscosity stability and consistency of the negative electrode slurry helps to improve the consistency of the coated surface density, thereby helping to improve the rate performance, cycle stability and consistency of the secondary battery. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] The drawings constituting a part of the present application are used to provide a further understanding of the present invention. The exemplary embodiments of the present invention and their descriptions are used to explain the present invention and do not constitute an improper limitation of the present invention. In the drawings:

[0018] Figure 1 The SEM image of the negative electrode sheet in Example 1 of the present application is shown;

[0019] Figure 2 A schematic diagram showing the distribution of particles in the negative electrode active layer of the present application is shown.

[0020] The above drawings include the following reference numerals:

[0021] 1. Negative electrode active material; 2. Auxiliary material particles. DETAILED DESCRIPTION

[0022] It should be noted that, in the absence of conflict, the embodiments and features in the embodiments of the present 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.

[0023] 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 a preparation method thereof, an energy storage device and an electrical equipment.

[0024] In a typical embodiment of the present application, 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, mixing 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 3:7~7:3, the mass ratio of the first conductive agent to the second conductive agent is 7:3~9:1, the mass ratio of the first polyacrylic acid to the second polyacrylic acid is 1:9~3:7, and the mass ratio of the first solvent to the second solvent is 2:8~4:6.

[0025] The present application helps to optimize the bonding structure inside the slurry and increase the bonding force between the negative electrode active material and the sodium carboxymethyl cellulose, the conductive agent, the polyacrylic acid and the styrene-butadiene rubber by mixing the sodium carboxymethyl cellulose, the conductive agent, the polyacrylic acid and the 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 attached 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 third mixed, which helps to further enhance the bonding and stability of the negative electrode slurry. 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. S5, the fourth mixture and the styrene-butadiene rubber are fifth mixed, which helps to further improve the viscosity stability of the negative electrode slurry. In particular, by controlling the mass ratio of the first sodium carboxymethyl cellulose to the second sodium carboxymethyl cellulose to be 3:7 to 7:3, it is helpful to 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 range helps to 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 then 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 to promote the uniformity of the distribution of sodium carboxymethyl cellulose, 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. The improvement of the viscosity stability and consistency of the negative electrode slurry helps to improve the consistency of the coated surface density, thereby helping to improve the rate performance, cycle stability and consistency of the secondary battery.

[0026] 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.

[0027] In order to further improve the viscosity stability and consistency of the negative electrode slurry, in one embodiment of the present application, it is preferred that the mass ratio of the first sodium carboxymethyl cellulose to the second sodium carboxymethyl cellulose is 5:5~7:3, the mass ratio of the first conductive agent to the second conductive agent is 8:2~9:1, the mass ratio of the first polyacrylic acid to the second polyacrylic acid is 2:8~3:7, and the mass ratio of the first solvent to the second solvent is 3:7~4:6.

[0028] 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%.

[0029] 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 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 ratio of styrene-butadiene rubber within the above range will help improve the stability and uniformity of the negative electrode slurry while maintaining the activity of the negative electrode active material. Controlling the total mass proportion of the first solvent and the second solvent in the negative electrode slurry within the above range will help control the viscosity of the negative electrode slurry, thereby helping to further improve the stability of the negative electrode slurry.

[0030] In one embodiment of the present application, the first mixing is carried out under stirring, 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 under stirring, 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 under stirring, 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 under stirring, 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 under stirring, and the stirring speed of the fifth mixing is 500-1200 rpm; and / or, the time of the fifth mixing is 60-120 min.

[0031] Controlling the stirring speed and time of the first mixing within the above range helps to 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 range helps to 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 range helps to improve the uniformity and stability of the third mixture. Controlling the stirring speed and time of the fourth mixing within the above range helps to 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 range helps to improve the uniformity of dispersion of styrene-butadiene rubber on the surface of the negative electrode active material.

[0032] In one embodiment of the present application, the raw materials in the above 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.

[0033] Alcohol additives contain hydroxyl groups, and their addition helps to improve the dispersion stability of negative electrode active materials and reduce the viscosity of negative electrode slurry, and has no significant effect on the solid content of negative electrode slurry. Controlling the mass ratio of alcohol additives to negative electrode active materials within the above range helps to improve the uniformity of dispersion of negative electrode active materials in the slurry without affecting the activity of negative electrode active materials. Controlling the mass ratio of alcohol additives 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 to improve the uniformity of dispersion of sodium carboxymethyl cellulose and polyacrylic acid on the surface of negative electrode active materials, thereby helping to improve the viscosity stability of negative electrode slurry.

[0034] In one embodiment of the present application, the above S5 includes: S51, mixing the fourth mixture and the alcohol auxiliary agent for a fifth time A to obtain an intermediate mixture; S52, mixing the intermediate mixture and styrene-butadiene rubber for a fifth time B to obtain a negative electrode slurry.

[0035] 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 adjusted more accurately. Then, mixing the intermediate mixture with styrene-butadiene rubber can help improve the uniformity of the distribution of styrene-butadiene rubber in the negative electrode slurry, thereby helping to improve the stability of the negative electrode slurry.

[0036] 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 under stirring, and the stirring speed of the fifth A mixing is 800~1200rpm; and / or, the fifth A mixing time is 30~60min; and / or, the fifth B mixing is carried out under stirring, and the stirring speed of the fifth B mixing is 500~800rpm; and / or, the fifth B mixing time is 30~45min.

[0037] Propanol, methanol and methylbutynol contain hydroxyl and methyl groups and have a low boiling point. The hydroxyl and methyl groups play a dispersing role at the same time, 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 obvious effect on the solid content of the negative electrode slurry. At the same time, due to the low boiling point, it can be fully volatilized in 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.

[0038] 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.

[0039] Propyl alcohol 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; the combination of propanol and methylbutynol, 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.

[0040] 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.

[0041] 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%.

[0042] 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.

[0043] 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, and the secondary battery is prepared by the aforementioned secondary battery preparation method.

[0044] Since the secondary battery is prepared by the preparation method of the present application, the secondary battery has higher rate performance, cycle stability and consistency.

[0045] In one embodiment of the present application, the negative electrode sheet comprises 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, the particle gap size of the negative electrode active material is 0.1-1.4 μm, preferably 0.1-1 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.

[0046] Controlling the interparticle size of the negative electrode active material within the above range helps to form a suitable microstructure, which not only ensures sufficient contact area, but also provides a path for ion transmission between particles. Smaller interparticle size is conducive to shortening the ion diffusion path and accelerating the ion transmission rate, thereby helping to improve the charge and discharge rate and power density of the secondary battery. The components in the negative electrode active layer are evenly distributed, especially the conductive agent, sodium carboxymethyl cellulose, polyacrylic acid and styrene-butadiene rubber are distributed on the surface of the negative electrode active material, which helps to make the electrons and ions in the battery cell uniformly conducted and reduce local resistance, thereby helping to make the secondary battery have higher rate performance, cycle stability and consistency.

[0047] It should be noted that the above-mentioned numerical value of the particle gap size of the negative electrode active material does not mean that all the 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.

[0048] In another typical embodiment of the present application, an energy storage device is provided, including a unit cell, wherein the unit cell is the aforementioned secondary battery.

[0049] Since the unit cells in the above energy storage device are the secondary batteries of the present application, the energy storage device has a higher service life and consistency.

[0050] 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 for the electrical device.

[0051] Since the energy storage device in the above-mentioned electrical equipment contains the secondary battery of the present application, the electrical equipment has a higher service life, consistency and safety.

[0052] The beneficial effects of the present application will be further illustrated below in conjunction with embodiments.

[0053] Example 1

[0054] S1, mixing graphite, a first sodium carboxymethyl cellulose and a first Super-P to obtain a first mixture; S2, mixing the first mixture and the first water to obtain a second mixture; S3, mixing the second mixture, the second sodium carboxymethyl cellulose, the second Super-P, the first polyacrylic acid and the second water to obtain a third mixture; S4, mixing the third mixture and the second polyacrylic acid to obtain a fourth mixture; S51, mixing the fourth mixture and propanol to obtain an intermediate mixture; S52, mixing the intermediate mixture and styrene-butadiene rubber to obtain a negative electrode slurry; S6, coating the negative electrode slurry on a copper foil and drying it 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 electrode active layer of the negative electrode sheet include 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 and the shell and the top cover are assembled, and then the lithium hexafluorophosphate salt electrolyte is injected to obtain a secondary battery;

[0055] 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, and the mass ratio 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 time of the second mixing 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 time of the third mixing 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 time of the fourth mixing 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 time of the fifth A mixing 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 time of the fifth B mixing is 45 min; the mass ratio of propanol to graphite is 0.1:100, 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 12:100.

[0056] Example 2

[0057] 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.

[0058] Example 3

[0059] 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.

[0060] Example 4

[0061] 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 graphite in the negative electrode sheet is between 0.2 and 1 μm.

[0062] Example 5

[0063] 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 graphite in the negative electrode sheet is between 0.3 and 1.2 μm.

[0064] Example 6

[0065] 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 graphite in the negative electrode sheet is between 0.3 and 1 μm.

[0066] Example 7

[0067] 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 graphite in the negative electrode sheet is between 0.2 and 1.4 μm.

[0068] Example 8

[0069] 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.

[0070] Example 9

[0071] 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.

[0072] Example 10

[0073] 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 under stirring, the stirring speed of the third mixing is 1500rpm, and the time of the third mixing is 60min; the fourth mixing is carried out under stirring, the stirring speed of the fourth mixing is 1500rpm, and the time of the fourth mixing is 30min; the fifth A mixing is carried out under stirring, the stirring speed of the fifth A mixing is 1200rpm, and the time of the fifth A mixing is 30min; the fifth B mixing is carried out under stirring, the stirring speed of the fifth B mixing is 800rpm, and the time of the fifth B mixing is 30min, and finally a secondary battery is obtained, wherein the particle gap size of the graphite in the negative electrode sheet is between 0.2~1.1μm.

[0074] Embodiment 11

[0075] The difference from Example 1 is that the fourth mixture, propanol and styrene-butadiene rubber are mixed for the fifth time to obtain a negative electrode slurry, and finally a secondary battery is obtained. The fifth mixing is performed under stirring, the stirring speed of the fifth mixing is 800 rpm, the time of the fifth mixing is 105 min, and the particle gap size of the graphite in the negative electrode sheet is between 0.3 and 1.4 μm.

[0076] Example 12

[0077] 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, and finally a secondary battery is obtained, wherein the particle gap size of graphite in the negative electrode sheet is between 0.1 and 0.8 μm.

[0078] Embodiment 13

[0079] 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, and finally a secondary battery is obtained, wherein the particle gap size of graphite in the negative electrode sheet is between 0.1 and 0.9 μm.

[0080] Embodiment 14

[0081] The difference from Example 1 is that the mass ratio of propanol to graphite is 0.2:100, 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, 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.

[0082] Embodiment 15

[0083] 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.

[0084] Comparative Example 1

[0085] 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.

[0086] Comparative Example 2

[0087] The difference from Example 1 is that the addition of the second Super-P in S3 is cancelled. In S1, 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.

[0088] Comparative Example 3

[0089] The difference from Example 1 is that the addition of the second water in S3 is cancelled, 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.

[0090] Performance Testing

[0091] Three batches of negative electrode slurries were repeatedly prepared by the preparation method of the embodiment and the comparative example 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 the viscosity difference are shown in Table 1, and the solid content test results and the solid content difference are shown in Table 2. The three batches of secondary batteries were tested for initial discharge specific capacity and capacity retention rate after 500 cycles. Specifically, in a constant temperature box at 25°C, the battery cells were charged and discharged using a current of 0.5P. 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.

[0092] Table 1

[0093]

[0094] Table 2

[0095]

[0096] Table 3

[0097]

[0098] Table 4

[0099]

[0100] Figure 1 This is the SEM image of the negative electrode sheet in Example 1 of the present application, from Figure 1 It can be seen that the graphite particles are evenly distributed, the particle gap distribution concentration is good, and the auxiliary material particles are distributed on the surface of the graphite particles.

[0101] From the above description, it can be seen that the above embodiments of the present invention achieve the following technical effects:

[0102] In Examples 1 to 3, by adjusting the mass ratio of the first sodium carboxymethyl cellulose to the second sodium carboxymethyl cellulose, it is helpful 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 in 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 in the range of 2:8 to 3:7, the negative electrode slurry shows 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 in 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 specific capacity and cycle stability of the secondary battery. From the results of the data comparison of Examples 1, 11 to 15, it can be seen that the alcohol additives and their addition order and addition amount are helpful to further improve the stability and consistency of the viscosity and solid content of the negative electrode slurry, especially 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 more excellent. 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. The sodium carboxymethyl cellulose, Super-P and water are added twice, and the negative electrode slurry has higher stability and consistency, and the corresponding secondary battery has higher first discharge capacity and cycle stability.

[0103] The present application helps to optimize the bonding structure inside the slurry and increase the bonding force between the negative electrode active material and the sodium carboxymethyl cellulose, the conductive agent, the polyacrylic acid and the styrene-butadiene rubber by mixing the sodium carboxymethyl cellulose, the conductive agent, the polyacrylic acid and the 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 attached 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 third mixed, which helps to further enhance the bonding and stability of the negative electrode slurry. 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. S5, the fourth mixture and the styrene-butadiene rubber are fifth mixed, which helps to further improve the viscosity stability of the negative electrode slurry. In particular, by controlling the mass ratio of the first sodium carboxymethyl cellulose to the second sodium carboxymethyl cellulose to be 3:7 to 7:3, it is helpful to 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 range helps to 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 then 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 to promote the uniformity of the distribution of sodium carboxymethyl cellulose, 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. The improvement of the viscosity stability and consistency of the negative electrode slurry helps to improve the consistency of the coated surface density, thereby helping to improve the rate performance, cycle stability and consistency of the secondary battery.

[0104] The above are only embodiments of the present invention and are not intended to limit the present invention. For those skilled in the art, the present invention may have various modifications and variations. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included in the protection scope 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 the negative electrode slurry to obtain a negative electrode sheet; S7, preparing a bare cell from the negative electrode sheet, the separator and the 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 3:7-7:3, the mass ratio of the first conductive agent to the second conductive agent is 7:3-9:1, the mass ratio of the first polyacrylic acid to the second polyacrylic acid is 1:9-3:7, and the mass ratio of the first solvent to the second solvent is 2:8-4:

6.

2. The method for preparing a secondary battery according to claim 1, characterized in that: 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, characterized in that: The first mixing is performed under stirring, 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 performed under stirring, 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 performed under stirring, 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 performed under stirring, and the stirring speed of the fourth mixing is 800-1500 rpm; and / or, the fourth mixing time is 30-90 min; And / or, the fifth mixing is performed under stirring, and the stirring speed of the fifth mixing is 500-1200 rpm; and / or, the time of the fifth mixing is 60-120 min.

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 further 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.

5. The method for preparing a secondary battery according to claim 4, characterized in that: The S5 includes: S51, performing a fifth mixing A on 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, characterized in that: The alcohol auxiliary agent is selected from any one or more of propanol, methanol and methyl butynol; and / or, the fifth A mixing is performed 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 performed under stirring, 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 solvent is water; and / or the conductive agent is selected from any one or more of Super-P, acetylene black and Ketjen black.

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 5000-20000 mPa·s; and / or the solid content of the negative electrode slurry is 52%-62%.

9. A secondary battery comprising a positive electrode sheet, a separator, an electrolyte and a negative electrode sheet, 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, characterized in that: 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 0.1-1 μm; and / or the conductive agent, the sodium carboxymethyl cellulose, the polyacrylic acid and the styrene-butadiene rubber are distributed on the surface of the negative electrode active material.

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

12. An electrical equipment, characterized in that: It includes the energy storage device as described in claim 11, and the energy storage device is used to provide power for the electrical equipment.

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