Secondary battery, method for preparing same, energy storage device, and electrical equipment

Abstract

The present invention provides a secondary battery, a preparation method thereof, an energy storage device and an electrical equipment, relating to the technical field of energy storage. The preparation method includes: performing a first mixing on a negative electrode active material, a first sodium carboxymethylcellulose and a first conductive agent to obtain a first mixture, and then performing a second mixing with a first solvent to obtain a second mixture; performing a third mixing on the second mixture, a second sodium carboxymethylcellulose, a second conductive agent, a first polyacrylic acid and a second solvent to obtain a third mixture, and then performing a fourth mixing with a second polyacrylic acid to obtain a fourth mixture, adding styrene-butadiene rubber for a fifth mixing to obtain a negative electrode paste; coating the negative electrode paste on a current collector and drying to obtain a negative electrode sheet; fabricating the negative electrode sheet, a separator and a positive electrode sheet into a bare battery cell, assembling the bare battery cell with a housing and a top cover, and injecting an electrolyte to obtain the secondary battery. The secondary battery has high rate performance, cycle stability and consistency.

Description

Technical Field

[0001] The present invention relates to the technical field of energy storage, and in particular, to a secondary battery, a preparation method thereof, an energy storage device, and an electrical device. Background Art

[0002] The performance and lifespan of secondary batteries are closely related to materials, manufacturing processes, and manufacturing process control. Negative electrode homogenization is a very crucial step in the production of secondary batteries, and its quality directly affects the production of electrodes and battery cells as well as the performance of battery cells. Manufacturing suitable and stable slurries is the key to ensuring the performance, uniformity, and stability of battery cells, and the most crucial step in preparing slurries is the homogenization method and process. Summary of the Invention

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

[0004] To achieve the above object, according to one aspect of the present invention, a preparation method of a secondary battery is provided, including: S1, performing a first mixing on raw materials including a negative electrode active material, a first sodium carboxymethylcellulose, and a first conductive agent to obtain a first mixture; S2, performing a second mixing on raw materials including the first mixture and a first solvent to obtain a second mixture; S3, performing a third mixing on raw materials including the second mixture, a second sodium carboxymethylcellulose, a second conductive agent, a first polyacrylic acid, and a second solvent to obtain a third mixture; S4, performing a fourth mixing on raw materials including the third mixture and a second polyacrylic acid to obtain a fourth mixture; S5, performing a fifth mixing on 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 to obtain a negative electrode sheet; S7, manufacturing a bare battery cell from the negative electrode sheet, a separator, and a positive electrode sheet, assembling the bare battery cell with a housing and a top cover, and then injecting an electrolyte to obtain a secondary battery; wherein, the mass ratio of the first sodium carboxymethylcellulose to the second sodium carboxymethylcellulose 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.

[0005] Further, 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 ratio of the first solvent and the second solvent in the negative electrode slurry is 52 - 62%.

[0006] Further, the above-mentioned first mixing is carried out under 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 under 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 under 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 under 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 under 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.

[0007] Further, the raw materials in the above-mentioned 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.

[0008] Further, the above-mentioned S5 includes: S51, performing a fifth A mixing on the fourth mixture and the alcohol auxiliary agent to obtain an intermediate mixture; S52, performing a fifth B mixing on the intermediate mixture and styrene-butadiene rubber to obtain a negative electrode slurry.

[0009] Further, the above-mentioned alcohol auxiliary agent is selected from any one or more of propanol, methanol and methyl butynol; and / or, the fifth A mixing is carried out under a stirring state, and the stirring speed of the fifth A mixing is 800 - 1200 rpm; and / or, the time of the fifth A mixing is 30 - 60 min; and / or, the fifth B mixing is carried out under 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.

[0010] Further, the negative electrode active material is graphite and / or silicon carbide; 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] Further, the viscosity of the negative electrode paste is 5000~20000 mPa·s; and / or, the solid content of the negative electrode paste is 52%~62%.

[0012] According to another aspect of the present invention, there is provided a secondary battery, comprising a positive electrode sheet, a separator, an electrolyte, and a negative electrode sheet, and the secondary battery is prepared by the preparation method of the aforementioned secondary battery.

[0013] Further, the 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. The particle gap size of the negative electrode active material is 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.

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

[0015] According to still another aspect of the present invention, there is provided an electrical equipment, comprising the aforementioned energy storage device, and the energy storage device is used to provide power for the electrical equipment.

[0016] Applying the technical solution of the present invention, the beneficial effects of this application are as follows: By mixing sodium carboxymethylcellulose, conductive agent, polyacrylic acid and solvent step by step, this application helps to optimize the bonding structure inside the slurry and increase the binding force between the negative electrode active material and sodium carboxymethylcellulose, conductive agent, polyacrylic acid and styrene-butadiene rubber. In S1, the first mixing of the negative electrode active material, the first sodium carboxymethylcellulose and the first conductive agent helps to make the first sodium carboxymethylcellulose and the first conductive agent evenly adhere to the surface of the negative electrode active material. Adding the first solvent in S2 helps to adjust the viscosity of the second mixture. In S3, the third mixing of the second mixture, the second sodium carboxymethylcellulose, the second conductive agent, the first polyacrylic acid and the second solvent helps to further enhance the adhesiveness and stability of the negative electrode slurry. In S4, the fourth mixing of the third mixture and the second polyacrylic acid helps to improve the dispersion uniformity of the second polyacrylic acid on the negative electrode active material. In S5, the fifth mixing of the fourth mixture and styrene-butadiene rubber helps to further improve the viscosity stability of the negative electrode slurry. Especially by controlling the mass ratio of the first sodium carboxymethylcellulose to the second sodium carboxymethylcellulose to be 3:7 to 7:3, it helps to improve the dispersion uniformity of sodium carboxymethylcellulose 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 to improve the dispersion uniformity 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 further 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 ranges helps to promote the distribution uniformity of sodium carboxymethylcellulose, 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 coating surface density, thereby helping to improve the rate performance, cycle stability and consistency of the secondary battery. BRIEF DESCRIPTION OF THE DRAWINGS

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

[0018] Figure 1 The SEM diagram of the negative electrode sheet in Embodiment 1 of this application is shown;

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

[0020] Among them, the above-mentioned accompanying drawings include the following reference numerals:

[0021] 1. Negative active material; 2. Auxiliary material particles. Detailed implementation manners

[0022] It should be noted that, without conflict, the embodiments in the present application and the features in the embodiments can be combined with each other. The present invention will be described in detail below with reference to the drawings and in combination with the embodiments.

[0023] As analyzed in the background art of the present application, there are problems of poor rate performance, cycle stability and consistency in secondary batteries in the prior art. To solve the above problems, the present application provides a secondary battery, a preparation method thereof, an energy storage device and an electrical equipment.

[0024] In a typical implementation manner of the present application, a preparation method of a secondary battery is provided, including: S1, performing a first mixing on raw materials including a negative active material, a first sodium carboxymethyl cellulose and a first conductive agent to obtain a first mixture; S2, performing a second mixing on raw materials including the first mixture and a first solvent to obtain a second mixture; S3, performing a third mixing on 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 on raw materials including the third mixture and a second polyacrylic acid to obtain a fourth mixture; S5, performing a fifth mixing on raw materials including the fourth mixture and styrene-butadiene rubber to obtain a negative electrode paste; S6, coating the negative electrode paste on a current collector and drying to obtain a negative electrode sheet; S7, manufacturing a bare battery cell from the negative electrode sheet, a separator and a positive electrode sheet, assembling the bare battery cell with a casing and a top cover, and then injecting an electrolyte 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.

[0025] In this application, by mixing sodium carboxymethylcellulose, conductive agent, polyacrylic acid and solvent step by step, it helps to optimize the bonding structure inside the slurry, and increase the binding force between the negative active material and sodium carboxymethylcellulose, conductive agent, polyacrylic acid and styrene-butadiene rubber. In S1, the first mixing of the negative active material, the first sodium carboxymethylcellulose and the first conductive agent helps to make the first sodium carboxymethylcellulose and the first conductive agent uniformly adhere to the surface of the negative active material. Adding the first solvent in S2 helps to adjust the viscosity of the second mixture. In S3, the third mixing of the second mixture, the second sodium carboxymethylcellulose, the second conductive agent, the first polyacrylic acid and the second solvent helps to further enhance the adhesiveness and stability of the negative electrode slurry. In S4, the fourth mixing of the third mixture and the second polyacrylic acid helps to improve the dispersion uniformity of the second polyacrylic acid on the negative active material. In S5, the fifth mixing of the fourth mixture and styrene-butadiene rubber helps to further improve the viscosity stability of the negative electrode slurry. Especially by controlling the mass ratio of the first sodium carboxymethylcellulose to the second sodium carboxymethylcellulose to be 3:7 to 7:3, it helps to improve the dispersion uniformity of sodium carboxymethylcellulose on the surface of the negative active material, thus 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 to improve the dispersion uniformity of the conductive agent and polyacrylic acid on the surface of the negative active material, thus helping to improve the viscosity stability of the negative electrode slurry, and further 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 ranges helps to promote the dispersion uniformity of sodium carboxymethylcellulose, conductive agent, polyacrylic acid and styrene-butadiene rubber on the surface of the negative active material, thus 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 coating surface density, thus 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 this application are all commonly used in the art and can be obtained by purchase or prepared by existing technologies.

[0027] In order to further improve the viscosity stability and consistency of the negative electrode slurry, in an embodiment of this application, it is preferably that the mass ratio of the first sodium carboxymethylcellulose to the second sodium carboxymethylcellulose is 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.

[0028] In an embodiment of the present application, 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 is (96~97):(0.2~0.4):(0.5~0.8):(0.2~0.4):(0.6~2.5); and / or, the total mass ratio of the first solvent and the second solvent in the negative electrode slurry is 52~62%.

[0029] Excessive additives will lead to increased costs and may reduce the activity of the negative electrode active material, while too little 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 range helps to improve the stability and uniformity of the negative electrode slurry while maintaining the activity of the negative electrode active material. Controlling the total mass ratio of the first solvent and the second solvent in the negative electrode slurry within the above range helps to control the viscosity of the negative electrode slurry, thereby helping to further improve the stability of the negative electrode slurry.

[0030] In an embodiment of the present application, the above-mentioned 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 ranges helps to improve the dispersion uniformity of the first sodium carboxymethylcellulose 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 to improve the dispersion uniformity of the first mixture in the first solvent. Controlling the stirring speed and time of the third mixing within the above ranges helps to improve the uniformity and stability of the third mixture. Controlling the stirring speed and time of the fourth mixing within the above ranges helps to improve the dispersion uniformity 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 to improve the dispersion uniformity of styrene-butadiene rubber on the surface of the negative electrode active material.

[0032] In an embodiment of the present application, the raw materials in S5 further include an alcohol auxiliary; and / or, the mass ratio of the alcohol auxiliary to the negative electrode active material is (0.1~0.7):100; and / or, the mass ratio of the alcohol auxiliary to the total mass of the first sodium carboxymethylcellulose, the second sodium carboxymethylcellulose, the first polyacrylic acid and the second polyacrylic acid is (10~30):100.

[0033] The alcohol auxiliary contains hydroxyl groups. Its addition helps to improve the dispersion stability of the negative electrode active material, while reducing the viscosity of the negative electrode slurry, and has no obvious effect on the solid content of the negative electrode slurry. Controlling the mass ratio of the alcohol auxiliary to the negative electrode active material within the above ranges helps to 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 auxiliary to the total mass of the first sodium carboxymethylcellulose, the second sodium carboxymethylcellulose, the first polyacrylic acid and the second polyacrylic acid within the above ranges helps to improve the dispersion uniformity of sodium carboxymethylcellulose and polyacrylic acid on the surface of the negative electrode active material, thereby helping to improve the viscosity stability of the negative electrode slurry.

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

[0035] By first performing a fifth A mixing on the fourth mixture and the alcohol auxiliary, it helps to more precisely adjust the rheology and dispersibility of the negative electrode slurry. Then mixing the intermediate mixture with styrene-butadiene rubber helps to improve the distribution uniformity 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 additives are selected from any one or more of propanol, methanol, and methyl butynol; 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 time of the fifth A mixing 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 time of the fifth B mixing is 30 - 45 min.

[0037] Propanol, methanol, and methyl butynol contain hydroxyl and methyl groups and have relatively low boiling points. The hydroxyl and methyl groups play a dispersing role simultaneously, 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 property, it can volatilize sufficiently during the baking step of the electrode sheet in the coating process and leave no residue in the electrode sheet, without affecting the performance of the electrode sheet. 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 ranges helps to further improve the stability of the negative electrode slurry.

[0038] In one embodiment of the present application, the above-mentioned alcohol additives are a combination of propanol and methyl butynol, and the mass ratio of propanol to methyl butynol is (5:5) - (8:2), specifically, it can be 5:5, 6:4, 7:3, 8:2, and the range values between any two ratios.

[0039] Propanol contains a large number of hydroxyl groups, can show strong hydrophilicity by binding with hydrogen bonds, and can show good binding and adsorption stability to polyacrylic acid, styrene-butadiene rubber, and sodium carboxymethyl cellulose by undergoing esterification reactions with carboxyl groups; methyl butynol contains a large number of methyl groups and shows hydrophobicity, and can effectively bind with the negative electrode active material and the conductive agent; using propanol and methyl butynol in combination, especially controlling the mass ratio of propanol to methyl butynol 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 above-mentioned 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 contributing to further improving the consistency of the coating surface density, and further contributing to improving 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, which includes a positive electrode sheet, a separator, an electrolyte and a negative electrode sheet, and the secondary battery is prepared by the preparation method of the aforementioned secondary battery.

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

[0045] In an embodiment of the present application, the above 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. 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. As Figure 2 shown, the particles in the negative electrode active layer include 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 sequentially coated 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 particle gap size of the negative electrode active material within the above ranges helps to form a suitable microstructure, which not only ensures sufficient contact area but also provides a path for ion transport between particles. A smaller particle gap size is beneficial to shortening the ion diffusion path and accelerating the ion transport rate, thereby contributing to improving the charge and discharge rate and power density of the secondary battery. The components in the negative electrode active layer are evenly distributed. In particular, 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 achieve uniform conduction of electrons and ions inside the battery cell, reduce local resistance, and thus contribute to the secondary battery having high rate performance, cycle stability and consistency.

[0047] It should be noted that the above numerical value regarding the particle gap size of the negative electrode active material does 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 do not fit together, and other materials such as conductive agents are filled between the gaps.

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

[0049] Since the unit cell in the above energy storage device is the secondary battery of the present application, the energy storage device has a relatively long service life and high consistency.

[0050] In yet another typical embodiment of the present application, an electrical equipment is provided, including the above energy storage device, and the energy storage device is used to provide power for the electrical equipment.

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

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

[0053] Embodiment 1

[0054] S1. First mix graphite, first sodium carboxymethyl cellulose and first Super-P to obtain a first mixture; S2. Second mix the first mixture and first water to obtain a second mixture; S3. Third mix the second mixture, second sodium carboxymethyl cellulose, second Super-P, first polyacrylic acid and second water to obtain a third mixture; S4. Fourth mix the third mixture and second polyacrylic acid to obtain a fourth mixture; S51. Fifth A mix the fourth mixture and propanol to obtain an intermediate mixture; S52. Fifth B mix the intermediate mixture and styrene-butadiene rubber to obtain a negative electrode paste; S6. Coat the negative electrode paste on a copper foil and dry it to obtain a negative electrode sheet. The particle gap size of graphite in the negative electrode sheet is between 0.1 and 1 μm. As Figure 2 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. Make a bare battery cell from the negative electrode sheet, polypropylene separator and lithium iron phosphate positive electrode sheet, assemble the bare battery cell with a shell and a top cover, and then inject a lithium hexafluorophosphate electrolyte 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, and the mass ratio of the 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 percentage of the first water and the second water in the negative electrode slurry is 52%. The first mixing is carried out under stirring, the stirring speed of the first mixing is 100 rpm, and the time of the first mixing is 60 min. The second mixing is carried out under stirring, the stirring speed of the second mixing is 100 rpm, and the time of the second mixing is 60 min. The third mixing is carried out under stirring, 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 under stirring, 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 under stirring, 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 under stirring, 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. Finally, a secondary battery is obtained, in which 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. Finally, a secondary battery is obtained, in which 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. Finally, a secondary battery is obtained, in which the particle gap size of the 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 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 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 mass ratio of graphite, the total mass of the first sodium carboxymethylcellulose and the second sodium carboxymethylcellulose, 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 ratio of the first water and the second water in the negative electrode slurry is 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 1500 rpm, and the time of the third mixing is 60 min. The fourth mixing is carried out under stirring, the stirring speed of the fourth mixing is 1500 rpm, and the time of the fourth mixing is 30 min. The fifth A mixing is carried out under stirring, the stirring speed of the fifth A mixing is 1200 rpm, and the time of the fifth A mixing is 30 min. The fifth B mixing is carried out under stirring, the stirring speed of the fifth B mixing is 800 rpm, and the time of the fifth B mixing is 30 min. Finally, a secondary battery is obtained, wherein the particle gap size of graphite in the negative electrode sheet is between 0.2 and 1.1 μm.

[0074] Example 11

[0075] The difference from Example 1 is that the fourth mixture, propanol and styrene-butadiene rubber are subjected to the fifth mixing to obtain a negative electrode slurry, and finally a secondary battery is obtained. Among them, the fifth mixing is carried out under stirring, the stirring speed of the fifth mixing is 800 rpm, and the time of the fifth mixing is 105 min. Among them, the particle gap size of 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 the 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 graphite in the negative electrode sheet is between 0.1 and 0.8 μm.

[0078] Example 13

[0079] The difference from Example 1 is that the 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 graphite in the negative electrode sheet is between 0.1 and 0.9 μm.

[0080] Example 14

[0081] 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, in which the particle gap size of graphite in the negative electrode sheet is between 0.2 and 1 μm.

[0082] Example 15

[0083] The difference from Example 1 is that the addition of propanol is cancelled, and finally a secondary battery is obtained, in which 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 subjected to a first mixing, and finally a secondary battery is obtained, in which the particle gap size of 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 subjected to a first mixing, and finally a secondary battery is obtained, in which the particle gap size of 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. In S2, the first mixture, the first water, and the second water are subjected to a second mixing, and finally a secondary battery is obtained, in which the particle gap size of graphite in the negative electrode sheet is between 0.4 and 1.7 μm.

[0090] Performance Test

[0091] The preparation methods of the examples and comparative examples were repeated to prepare three batches of anode slurries for viscosity and solid content tests, and the viscosity difference and solid content difference were calculated. Viscosity difference = the maximum viscosity value among the three batches - the minimum viscosity value among the three batches, and 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. The three batches of secondary batteries were tested for initial discharge specific capacity and capacity retention rate after 500 cycles. Specifically, in a 25°C constant temperature oven, the charge and discharge tests of the battery cells were carried out with a current of 0.5C. Initial discharge specific capacity = the capacity of the first cycle discharge / the designed weight of the lithium iron phosphate material, and the capacity retention rate of the 500th cycle = the capacity of the 500th cycle discharge / the capacity of the first cycle discharge. And the initial discharge specific capacity difference and capacity retention rate difference after 500 cycles were calculated. 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, and 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 initial discharge specific capacity difference are shown in Table 3, and the capacity retention rate test results and 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 anode sheet in Example 1 of this application. From Figure 1 it can be seen that the graphite particles are evenly distributed, the concentration degree of the particle gaps 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 carboxymethylcellulose to the second sodium carboxymethylcellulose, it is helpful to optimize the stability and consistency of the negative electrode slurry, especially when controlling the mass ratio of the first sodium carboxymethylcellulose to the second sodium carboxymethylcellulose 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; through the comparison of the test results of Examples 1, 6, and 7, it can be known 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 controlling the mass ratio of the first polyacrylic acid to the second polyacrylic acid within 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 known 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 first discharge specific capacity and cycle stability of the secondary battery. From the comparison results of the data in Examples 1, 11 to 15, it can be known that the alcohol additives, their addition sequence and addition amount help to further improve the stability and consistency of the viscosity and solid content of the negative electrode slurry. Especially when controlling the mass ratio of propanol to methylbutynol 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 the comparative examples, it can be known that the batchwise addition of sodium carboxymethylcellulose, Super-P, and water has a significant impact on the stability and consistency of the negative electrode slurry. Adding sodium carboxymethylcellulose, Super-P, and water in two batches, the negative electrode slurry has high stability and consistency, and the corresponding secondary battery has a high first discharge capacity and cycle stability.

[0103] In this application, by mixing sodium carboxymethylcellulose, conductive agent, polyacrylic acid and solvent step by step, it helps to optimize the bonding structure inside the slurry and increase the binding force between the negative active material and sodium carboxymethylcellulose, conductive agent, polyacrylic acid and styrene-butadiene rubber. In S1, the first mixing of the negative active material, the first sodium carboxymethylcellulose and the first conductive agent helps to make the first sodium carboxymethylcellulose and the first conductive agent evenly adhere to the surface of the negative active material. Adding the first solvent in S2 helps to adjust the viscosity of the second mixture. In S3, the third mixing of the second mixture, the second sodium carboxymethylcellulose, the second conductive agent, the first polyacrylic acid and the second solvent helps to further enhance the adhesiveness and stability of the negative electrode slurry. In S4, the fourth mixing of the third mixture and the second polyacrylic acid helps to improve the dispersion uniformity of the second polyacrylic acid on the negative active material. In S5, the fifth mixing of the fourth mixture and styrene-butadiene rubber helps to further improve the viscosity stability of the negative electrode slurry. Especially by controlling the mass ratio of the first sodium carboxymethylcellulose to the second sodium carboxymethylcellulose to be 3:7 to 7:3, it helps to improve the dispersion uniformity of sodium carboxymethylcellulose on the surface of the negative 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 to improve the dispersion uniformity of the conductive agent and polyacrylic acid on the surface of the negative active material, thereby helping to improve the viscosity stability of the negative electrode slurry, and further 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 ranges helps to promote the distribution uniformity of sodium carboxymethylcellulose, conductive agent, polyacrylic acid and styrene-butadiene rubber on the surface of the negative 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 coating surface density, thereby helping to improve the rate performance, cycle stability and consistency of the secondary battery.

[0104] The above are only the embodiments of the present invention and are not intended to limit the present invention. For those skilled in the art, the present invention can have various changes and modifications. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principle of the present invention shall be included within the protection scope of the present invention.

Claims

1. A method for preparing a secondary battery, characterized in that, Including: S1, performing a first mixing on 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 on raw materials including the first mixture and a first solvent to obtain a second mixture; S3, performing a third mixing on 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 on raw materials including the third mixture and a second polyacrylic acid to obtain a fourth mixture; S5, performing a fifth mixing on raw materials including the fourth mixture and styrene-butadiene rubber to obtain a negative electrode paste; S6, coating the negative electrode paste on a current collector and drying to obtain a negative electrode sheet; S7, fabricating a bare battery cell from the negative electrode sheet, a separator, and a positive electrode sheet, assembling the bare battery cell with a casing and a top cover, and then injecting an electrolyte to obtain the secondary battery; The mass ratio of the first sodium carboxymethyl cellulose to the second sodium carboxymethyl cellulose is 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; 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; Both the first solvent and the second solvent are water; The raw materials in S5 further include an alcohol auxiliary agent.

2. The manufacturing method of the secondary battery according to claim 1, characterized in that, The mass 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 to 97):(0.2 to 0.4):(0.5 to 0.8):(0.2 to 0.4):(0.6 to 2.5); and / or, the total mass ratio of the first solvent and the second solvent in the negative electrode paste is 52 to 62%; 3. The method for preparing a secondary battery according to claim 1, characterized in that, The first mixing is carried out under 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 min; and / or, the second mixing is carried out under 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 min; and / or, the third mixing is carried out under 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 min; and / or, the fourth mixing is carried out under 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 min; And / or, the fifth mixing is carried out under 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.

4. The method for preparing a secondary battery according to any one of claims 1 to 3, characterized in that, The mass ratio of the alcohol auxiliary agent to the negative 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 manufacturing method of the secondary battery according to claim 4, characterized in that, The S5 includes: S51, performing a fifth A mixing on the fourth mixture and the alcohol auxiliary agent to obtain an intermediate mixture; S52, performing a fifth B mixing on the intermediate mixture and the styrene-butadiene rubber to obtain the negative electrode paste.

6. The manufacturing method of the 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 carried out under a stirring state, and the stirring speed of the fifth A mixing is 800-1200 rpm; and / or, the time of the fifth A mixing is 30-60 min; And / or, the fifth B mixing is carried out under 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 active material is graphite and / or silicon carbon.

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

9. A secondary battery, comprising a positive electrode sheet, a separator, an electrolytic solution, and a negative electrode sheet, characterized in that, The secondary battery is prepared by the preparation method of the 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 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. 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. A energy storage device, comprising unit cells, characterized in that, The unit cell is the secondary battery according to claim 9 or 10.

12. An electrical device, characterized in that, Including the energy storage device according to claim 11, and the energy storage device is used to provide power for the electrical equipment.

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