Negative plate preparation method, negative plate and battery

Abstract

The invention discloses a negative plate preparation method, a negative plate and a battery, and relates to the technical field of battery manufacturing. The preparation method of the negative electrode plate specifically comprises the following steps: preparing negative electrode slurry; coating the surface of a negative current collector with the prepared negative electrode slurry, and drying; carrying out rolling treatment on the dried pole piece, and carrying out punching molding treatment on the pole piece before the last time of rolling; carrying out the last rolling on the pole piece subjected to the punching and shaping treatment; and carrying out die cutting and slitting on the pole piece which is rolled for the last time. According to the negative plate preparation method provided by the invention, under the condition that the thickness of the negative plate is not changed basically, the energy density of the battery is improved, and the fast charging capability of the battery is enhanced.

Description

Technical Field

[0001] The present invention relates to the field of battery manufacturing, and in particular to a method for preparing a negative electrode sheet, a negative electrode sheet, and a battery. Background Art

[0002] Currently, the development of the new energy industry requires further improvements in the energy density, fast charging capability, and safety performance of batteries. To achieve these goals, researchers are exploring various approaches. Among them, a common improvement direction is to increase the energy density by increasing the coating thickness of the negative electrode sheet, thereby increasing the compaction density and reducing the weight of the negative current collector. In theory, increasing the coating thickness of the negative electrode sheet can directly increase the active material content per unit volume of the battery, thereby improving the overall energy storage capacity of the battery. However, this method usually results in a larger internal resistance, affecting the power performance and cycle life of the battery.

[0003] On the other hand, to increase battery charging speed, some researchers have proposed strategies to reduce the coating thickness and compaction density of the negative electrode sheet. Thinner electrode coatings and lower tortuosity can shorten the migration path of lithium ions within the electrode, thereby speeding up the charging process. However, this approach often leads to a decrease in the battery's energy density due to the reduction in the amount of active material per unit volume. Therefore, how to balance these two contradictions has become a major challenge in the current development of battery technology.

[0004] Recently, an inventor has proposed a method for creating pores in the negative electrode sheet, aiming to increase the fast-charging capability of thick electrodes by creating additional ion transport channels. This innovative approach not only maintains a high energy density but also significantly improves the battery's charging performance. However, despite the many theoretical advantages of this technology, it still faces many challenges in practical application. For example, when creating pores in the negative electrode sheet, whether using mechanical or laser pore creation, it is inevitable that mechanical damage will occur, resulting in increased thickness, which in turn affects the overall performance of the battery. Summary of the Invention

[0005] In order to solve the above problems, the present invention provides a method for preparing a negative electrode sheet, a negative electrode sheet, and a battery, which can improve the energy density of the battery and enhance the fast charging capability of the battery without substantially changing the thickness of the negative electrode sheet.

[0006] The present invention provides a method for preparing a negative electrode sheet, comprising the following steps: preparing anode slurry; Apply the prepared negative electrode slurry on the surface of the negative current collector and dry it; The dried electrode is rolled and punched before the last rolling. Perform the final rolling on the electrode after the punching and shaping process; The pole piece that has completed the last rolling is die-cut and striped.

[0007] In one embodiment of the present invention, the negative electrode slurry includes a negative electrode active material, a first conductive agent, a first binder, and a first dispersant. The negative electrode active material, the first conductive agent, the first binder, and the first dispersant are added to water in a mass percentage of (90-98)%: (0-1.5)%: (0.5-2)%: (1-2)% and stirred to form a negative electrode slurry.

[0008] In a preferred embodiment of the present invention, the mass percentages of the negative electrode active material, the first conductive agent, the first binder, and the first dispersant are (96-98)%: (0.6-1.2)%: (1-1.8)%: (1-1.5)%, for example, 96%: 1.2%: 1.8%: 1%.

[0009] In one embodiment of the present invention, the negative electrode active material includes one or more of graphite, Si material, and hard carbon; the first conductive agent includes one or more of acetylene black, carbon black, carbon nanotubes, and graphene; the first binder includes one or more of polyvinylidene fluoride, polyacrylic acid, and styrene-butadiene rubber; and the first dispersant includes one or more of sodium carboxymethyl cellulose and lithium carboxymethyl cellulose.

[0010] In one embodiment of the present invention, the punching shaping processing methods include but are not limited to laser punching, mechanical punching, and a combination of laser punching and mechanical punching.

[0011] In one embodiment of the present invention, a plurality of shaping holes are formed in the electrode after the punching shaping process, and the aperture of the shaping holes is 10μm-60μm, for example, 10μm, 20μm, 45μm, 50μm, 60μm, preferably 30μm-45μm; the hole depth of the shaping holes is 0%-100% of the thickness of the electrode, for example, 10%, 40%, 50%, 70%, 100%, preferably 40%-60%; the hole spacing of the shaping holes is 30μm-500μm, for example, 40μm, 80μm, 100μm, 150μm, 300μm, 500μm, preferably 100μm-300μm.

[0012] In one embodiment of the present invention, the shape of the shaping hole includes but is not limited to a cone, a truncated cone, a cylinder, and a spherical cap.

[0013] In one embodiment of the present invention, the number of rolling times in the rolling process is ≥1.

[0014] The present invention also provides a negative electrode sheet, which is prepared by the negative electrode sheet preparation method described above.

[0015] The present invention also provides an electrode, comprising a positive electrode sheet, a separator, and the negative electrode sheet as described above.

[0016] Compared with the existing technology, the present invention has the following beneficial technical effects: The present invention provides a method for preparing a negative electrode sheet, a negative electrode sheet, and a battery. The method completes the punching process by calculation before the last rolling process, and then completes the electrode sheet shaping by the final rolling process to obtain a shaped electrode sheet that is not affected by thickness. Since the electrode sheet is punched, additional ion transmission channels can be added, the ion transmission speed can be improved, and the fast charging capability of the battery can be improved. Due to the presence of the shaped holes, the surface area of the electrode sheet is increased, so that the electrolyte is fully infiltrated, the active material can be increased, the temperature rise of the battery cell is reduced, the cycle lithium deposition is improved, and the energy density of the battery can be improved. Therefore, the present invention can improve the energy density of the battery and enhance the fast charging capability of the battery without basically changing the thickness of the negative electrode sheet. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 This is a schematic diagram of the structure of the electrode after punching and shaping before the final rolling.

[0018] Figure 2 Schematic diagram of the structure of the pole piece after the last rolling process.

[0019] Figure 3 Schematic diagram of the change in discharge capacity retention rate of the batteries in Example 1, Comparative Example 1, and Comparative Example 2 at different cycle numbers.

[0020] Wherein: 10-negative electrode slurry; 20-negative current collector; 30-molding hole. DETAILED DESCRIPTION

[0021] The following embodiments of the present invention are described in further detail with reference to the accompanying drawings and examples. The following examples are used to illustrate the present invention but are not intended to limit the scope of the present invention.

[0022] In the description of the present invention, it should be noted that the orientations or positional relationships indicated in this description are based on the orientations or positional relationships shown in the accompanying drawings, and are only for the convenience of describing the present invention and simplifying the description, and do not indicate or imply that the referred parts or elements must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as a limitation on the present invention.

[0023] See also Figure 1 and Figure 2The present invention provides a method for preparing a negative electrode sheet, comprising the following steps: a first step of preparing a negative electrode slurry 10; a second step of applying the prepared negative electrode slurry 10 on the surface of a negative current collector 20 and drying it; a third step of rolling the dried electrode sheet and performing a punching and shaping process on the electrode sheet before the last rolling process; a fourth step of rolling the electrode sheet after the punching and shaping process for the last time; and a fifth step of die-cutting and striping the electrode sheet after the last rolling process.

[0024] Since the electrode is punched to form a shaped hole 30, it is possible to add an additional ion transmission channel, improve the ion transmission speed, and thus improve the fast charging capability of the battery. The presence of the shaped hole 30 increases the surface area of the electrode, allowing the electrolyte to be fully infiltrated, which can increase the active material, reduce the temperature rise of the battery cell, improve the cycle lithium deposition, and thus improve the energy density of the battery. In the prior art, the shaped hole 30 is generally obtained by mechanical punching or laser punching. However, both methods will inevitably cause certain mechanical damage to the electrode, resulting in an increase in thickness. For example, the negative electrode is mechanically punched using a shaping roller to squeeze the electrode, which will cause the negative collector to deform. The electrode surface material is squeezed by the shaping boss to cause the surface to bulge, resulting in an increase in the electrode thickness. When a laser hole is used, after high-energy laser shooting, the electrode surface material around the hole moves to form a "crater" pattern, resulting in an increase in the thickness of the electrode on a thickness scale. However, the increase in thickness usually brings a larger internal resistance, affecting the power performance and cycle life of the battery, and thus affecting the overall performance of the battery. The present invention chooses to complete the punching shape through calculation before the last rolling process. Even if the thickness increases at this time, the electrode sheet can be shaped after the last rolling, and a shaped electrode sheet without thickness influence can be obtained. Therefore, the present invention can improve the energy density of the battery and enhance the fast charging capability of the battery without basically changing the thickness of the negative electrode sheet.

[0025] Specifically, the negative electrode slurry 10 includes a negative electrode active material, a first conductive agent, a first binder, and a first dispersant. The negative electrode active material, the first conductive agent, the first binder, and the first dispersant are added to water in a mass ratio of (90-98)%: (0-1.5)%: (0.5-2)%: (1-2)% and stirred to form the negative electrode slurry. Preferably, the mass ratios of the negative electrode active material, the first conductive agent, the first binder, and the first dispersant are (96-98)%: (0.6-1.2)%: (1-1.8)%: (1-1.5)%. The negative electrode active material includes one or more of graphite, Si material, and hard carbon; the first conductive agent includes one or more of acetylene black, carbon black, carbon nanotubes, and graphene; the first binder includes one or more of polyvinylidene fluoride, polyacrylic acid, and styrene-butadiene rubber; and the first dispersant includes one or more of sodium carboxymethyl cellulose and lithium carboxymethyl cellulose. After the negative electrode slurry 10 is prepared, it is coated on the negative current collector 20 and dried. After drying, a roll pressing process can be performed, and the number of roll pressing times in the roll pressing process is ≥1.

[0026] In order to improve the energy density and fast charging capability of the battery, it is necessary to perform a punching and shaping process on the electrode. The punching and shaping process includes but is not limited to laser punching, mechanical punching, and a combination of laser punching and mechanical punching. In the combination of laser punching and mechanical punching, laser scratching and mechanical punching can be used. Since laser punching, mechanical punching, and a combination of laser punching and mechanical punching will cause mechanical damage to the electrode, resulting in an increase in the thickness of the electrode, the present invention completes the punching and shaping process by calculation before the last rolling process. Even if the thickness increases at this time, the electrode shaping can be completed after the last rolling process, and a shaped electrode without thickness influence can be obtained. After the electrode is punched and shaped, a plurality of shaped holes 30 are formed. The shaped holes 30 in the present invention are blind holes. The diameter of the shaped holes 30 is 10μm-60μm, the depth of the shaped holes 30 is 0%-100% of the thickness of the electrode, and the hole spacing of the shaped holes 30 is 30μm-500μm. The shape of the shaping hole 30 includes but is not limited to a cone, a truncated cone, a cylinder, and a spherical cap.

[0027] The negative electrode sheet prepared by the above-mentioned preparation method can be assembled with the separator and the positive electrode sheet into a bare battery cell, and then undergoes packaging, baking, liquid injection, formation, degassing, folding, capacity separation and other processes to make a finished battery; packaging and subsequent processes are processes commonly used in the prior art, and can be referred to the prior art and will not be repeated here.

[0028] In order to further describe the present invention, the present invention provides two comparative examples and embodiments for comparative analysis, as follows: Comparative Example 1 Graphite, acetylene black, polyvinylidene fluoride, and sodium carboxymethyl cellulose are added to water in a mass percentage of 96%:1.2%:1.8%:1% and stirred evenly to prepare a negative electrode slurry; the prepared negative electrode slurry 10 is coated on the surface of the negative current collector and dried; after drying, the prepared electrode sheet is subjected to a roller pressing process, and after rolling is completed, it is die-cut and stripped to obtain a negative electrode sheet with a length of 120 mm, a width of 65 mm, a thickness of 106.7 μm, and a tab width of 12 mm; the prepared negative electrode sheet, separator, and positive electrode sheet are assembled into a bare battery cell, and then the finished battery is made through processes such as packaging, baking, liquid injection, formation, degassing, folding, and capacity division.

[0029] Comparative Example 2 Graphite, acetylene black, polyvinylidene fluoride, and sodium carboxymethyl cellulose are added to water in a mass percentage of 96%:1.2%:1.8%:1% and stirred evenly to prepare a negative electrode slurry; the prepared negative electrode slurry 10 is coated on the surface of the negative current collector and dried; after drying, the prepared electrode is subjected to a roller pressing process, and after rolling is completed, the electrode is punched and shaped. The punching method adopts mechanical punching to obtain a plurality of shaped holes. The shaped holes are conical, the aperture of the shaped holes is 45μm, the hole depth of the shaped holes is 50% of the thickness of the electrode, and the hole spacing of the shaped holes is 150mm; subsequently, die-cutting and striping are performed to obtain a negative electrode sheet with a length of 120mm, a width of 65mm, a thickness of 115.6μm, and a tab width of 12mm. The prepared negative electrode sheet, separator, and positive electrode sheet are assembled into a bare battery cell, and then the finished battery is made through packaging, baking, liquid injection, formation, degassing, folding, and capacity separation.

[0030] Example 1 Graphite, acetylene black, polyvinylidene fluoride, and sodium carboxymethyl cellulose are added to water in a mass percentage of 96%: 1.2%: 1.8%: 1% and stirred evenly to prepare a negative electrode slurry; the prepared negative electrode slurry is coated on the surface of the negative current collector and dried; after drying, the prepared electrode is subjected to a roller pressing process, and the electrode is punched and shaped before the last word of rolling. The punching method adopts mechanical punching to obtain multiple shaped holes, the shaped holes are conical, and the shaped holes are The aperture is 45μm, the depth of the shaping hole is 50% of the thickness of the electrode piece, and the hole spacing of the shaping hole is 150mm; the final rolling is carried out, followed by die-cutting and striping to obtain the negative electrode piece, which is 120mm long, 65mm wide, 106.9μm thick, and 12mm wide. The prepared negative electrode piece, separator, and positive electrode piece are assembled into a bare battery cell, and then the finished battery is made through packaging, baking, liquid injection, formation, degassing, folding, capacity separation and other processes.

[0031] Example 2 Graphite, acetylene black, polyvinylidene fluoride, and sodium carboxymethyl cellulose are added to water in a mass percentage of 90%:5%:3.8%:1.2% and stirred evenly to prepare a negative electrode slurry; the prepared negative electrode slurry is coated on the surface of the negative current collector and dried; after drying, the prepared electrode is subjected to a roller pressing process, and the electrode is punched and shaped before the final rolling. The punching method adopts mechanical punching to obtain a plurality of shaped holes. The shaped holes are conical, the pore diameter of the shaped holes is 10μm, the pore depth of the shaped holes is 40% of the thickness of the electrode, and the pore spacing of the shaped holes is 500mm; then the final rolling is carried out, followed by die cutting and striping to obtain a negative electrode sheet with a length of 120mm, a width of 65mm, a thickness of 110μm, and a tab width of 12mm. The prepared negative electrode sheet, separator, and positive electrode sheet are assembled into a bare battery cell, and then the finished battery is made through packaging, baking, liquid injection, formation, degassing, folding, and capacity separation.

[0032] Example 3 Graphite, acetylene black, polyvinylidene fluoride, and sodium carboxymethyl cellulose are added to water in a mass percentage of 98%: 0.5%: 1.1%: 0.4% and stirred evenly to prepare a negative electrode slurry; the prepared negative electrode slurry is coated on the surface of the negative current collector and dried; after drying, the prepared electrode is subjected to a roller pressing process, and the electrode is punched and shaped before the last word of rolling. The punching method adopts mechanical punching to obtain multiple shaped holes, and the shaped holes are conical. The diameter of the molded hole is 55μm, the depth of the molded hole is 60% of the thickness of the electrode, and the hole spacing of the molded hole is 350mm; then the final rolling is carried out, followed by die cutting and striping to obtain the negative electrode sheet, which is 120mm long, 65mm wide, 103μm thick, and 12mm wide. The prepared negative electrode sheet, diaphragm, and positive electrode sheet are assembled into a bare battery cell, and then the finished battery is made through packaging, baking, liquid injection, formation, degassing, folding, and capacity separation.

[0033] Example 4 Graphite, acetylene black, polyvinylidene fluoride, and sodium carboxymethyl cellulose are added to water in a mass percentage of 98%: 0.5%: 1.1%: 0.4% and stirred evenly to prepare a negative electrode slurry; the prepared negative electrode slurry is coated on the surface of the negative current collector and dried; after drying, the prepared electrode is subjected to a roller pressing process, and the electrode is punched and shaped before the last word of rolling. The punching method adopts mechanical punching to obtain multiple shaped holes, and the shaped holes are conical. The diameter of the molded hole is 60μm, the depth of the molded hole is 80% of the thickness of the electrode piece, and the hole spacing of the molded hole is 200mm; then the final rolling is carried out, followed by die cutting and striping to obtain the negative electrode piece, which is 120mm long, 65mm wide, 103μm thick, and 12mm wide. The prepared negative electrode piece, separator, and positive electrode piece are assembled into a bare battery cell, and then the finished battery is made through packaging, baking, liquid injection, formation, degassing, folding, capacity separation and other processes.

[0034] The batteries prepared in Comparative Example 1, Comparative Example 2 and Examples 1-4 were subjected to a fast lithium charging and discharging test for 50 cycles (one cycle is counted as one cycle after one charge), and a cycle life test within 12 minutes (the number of cycles required for the capacity retention rate to decrease to 80% within 12 minutes to be able to cycle). The test results are shown in Tables 1 and Figure 1 , the specific test method can refer to the existing technology.

[0035] Table 1 Results of fast lithium charging and cycle life tests of Comparative Examples 1-2 and Examples 1-4

[0036] From Table 1 and Figure 3 It can be seen that by comparing Examples 1-4 with Comparative Examples 1-2, it can be seen that the difference between punching the electrode and not punching is that the punching treatment can avoid the phenomenon of lithium ions being reduced to metallic lithium on the surface of the negative electrode during the fast charging process of the battery, that is, the lithium plating phenomenon. Lithium plating consumes active lithium, reduces the battery capacity and cycle life, therefore, the punching treatment can also improve the cycle life of the battery; as can be seen from Table 1, by comparing Examples 1-4 with Comparative Example 2, it can be seen that the punching treatment after rolling increases the thickness of the electrode, and the increase in thickness usually brings about a larger internal resistance, which affects the power performance and cycle life of the battery, while the present invention performs a punching treatment before the last rolling and basically does not change the thickness of the electrode. Therefore, it can not only avoid lithium plating, ensure the amount of active material, and improve the energy density of the battery, but also improve the cycle life of the battery, that is, it can improve the fast charging capability of the battery.

[0037] From the above description, it can be known that the present invention provides a method for preparing a negative electrode sheet, a negative electrode sheet, and a battery. The punching process is completed by calculation before the last rolling process, and the electrode sheet is shaped by the final rolling to obtain a shaped electrode sheet that is not affected by thickness. Since the electrode sheet is punched, additional ion transmission channels can be added, the ion transmission speed can be improved, and the fast charging capability of the battery can be improved. Due to the presence of the shaped holes, the surface of the electrode sheet is increased, so that the electrolyte is fully infiltrated, the active material can be increased, the temperature rise of the battery cell is reduced, and the cycle lithium precipitation is improved, thereby improving the energy density of the battery. Therefore, the present invention can improve the energy density of the battery and enhance the fast charging capability of the battery without basically changing the thickness of the negative electrode sheet.

[0038] The above are merely preferred embodiments of the present invention and are not intended to limit the present invention in any form. Although the present invention has been disclosed as a preferred embodiment, it is not intended to limit the present invention. Any technician familiar with this profession can make some changes or modifications to equivalent embodiments of equivalent changes using the technical content disclosed above without departing from the scope of the technical solution of the present invention. However, any simple modifications, equivalent changes and modifications made to the above embodiments based on the technical essence of the present invention without departing from the content of the technical solution of the present invention are still within the scope of the technical solution of the present invention.

Claims

1. A method for preparing a negative electrode sheet, characterized in that: The following steps are involved: preparing a negative electrode slurry (10); Applying the prepared negative electrode slurry (10) on the surface of the negative current collector (20) and drying it; The dried electrode is rolled and punched before the last rolling. Perform the final rolling on the electrode after the punching and shaping process; The pole piece that has completed the last rolling is die-cut and striped.

2. The method for preparing a negative electrode sheet according to claim 1, wherein: The negative electrode slurry (10) comprises a negative electrode active material, a first conductive agent, a first binder, and a first dispersant, wherein the mass percentages of the negative electrode active material, the first conductive agent, the first binder, and the first dispersant are (90-98)%: (0-1.5)%: (0.5-2)%: (1-2)%.

3. The method for preparing a negative electrode sheet according to claim 2, wherein: Preferably, the mass percentages of the negative electrode active material, the first conductive agent, the first binder, and the first dispersant are (96-98)%: (0.6-1.2)%: (1-1.8)%: (1-1.5)%.

4. The method for preparing a negative electrode sheet according to claim 2, wherein: The negative electrode active material includes one or more of graphite, Si material, and hard carbon; The first conductive agent includes one or more of acetylene black, carbon black, carbon nanotubes, and graphene; The first binder includes one or more of polyvinylidene fluoride, polyacrylic acid, and styrene-butadiene rubber; The first dispersant includes one or more of sodium carboxymethyl cellulose and lithium carboxymethyl cellulose.

5. The method for preparing a negative electrode sheet according to claim 1, wherein: The punching and shaping processing methods include but are not limited to laser punching, mechanical punching, and a combination of laser punching and mechanical punching.

6. The method for preparing a negative electrode sheet according to claim 1, wherein: After the electrode is subjected to the punching and shaping process, a plurality of shaping holes (30) are formed. The diameter of the shaping holes (30) is 10 μm-60 μm, preferably 30 μm-45 μm; the hole depth of the shaping holes (30) is 0%-100% of the thickness of the electrode, preferably 40%-60%; the hole spacing of the shaping holes (30) is 30 μm-500 μm, preferably 100 μm-300 μm.

7. The method for preparing a negative electrode sheet according to claim 6, wherein: The shape of the molding hole (30) includes but is not limited to a cone, a truncated cone, a cylinder, and a spherical cap.

8. The method for preparing a negative electrode sheet according to claim 1, wherein: The number of rolling times in the rolling process is ≥1.

9. A negative electrode sheet, characterized in that: The negative electrode sheet is prepared by the negative electrode sheet preparation method according to any one of claims 1 to 8.

10. An electrode comprising a positive electrode sheet, a separator, and a negative electrode sheet, characterized in that: The negative electrode sheet is prepared by the negative electrode sheet preparation method according to any one of claims 1 to 8.

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