Composite silicon-based negative electrode sheet and preparation method and application thereof

Abstract

The application provides a composite silicon-based negative electrode sheet and a preparation method and application thereof. The composite silicon-based negative electrode sheet comprises a current collector and a carbon-based material coating and a silicon-based material coating which are sequentially stacked on the surface of the current collector. The silicon-based material coating comprises a silicon-based active material, a hard carbon tissue structure and a conductive network. The application designs a layered structure for the electrode sheet. The carbon-based active material and the silicon-based active material are respectively arranged in different electrode coatings. The silicon-based material coating and the carbon-based material coating ensure the stability of the overall structure of the electrode sheet through synergistic effect. On the other hand, the silicon-based material coating effectively inhibits the repeated generation of SEI film, prevents the rapid decay of the overall capacity and improves the cycle stability.

Description

Technical Field

[0001] This invention belongs to the field of lithium-ion battery technology, and relates to a composite silicon-based negative electrode sheet, its preparation method, and its application. Background Technology

[0002] Lithium-ion batteries are currently the most popular commercially available rechargeable batteries. The negative electrode active materials used in lithium-ion batteries include graphite and silicon-based materials. Graphite includes natural and artificial graphite. Its excellent structural stability and cycle performance make it the most widely used negative electrode active material for lithium batteries. However, graphite's theoretical specific capacity is only 372 mAh / g, which cannot meet the growing demand for high-energy-density lithium-ion batteries. Silicon-based negative electrode active materials include pure silicon, silicon-carbon, and silicon-oxygen, which are abundant in resources, inexpensive, and, more importantly, have a specific capacity as high as 4200 mAh / g, thus possessing enormous application potential in the field of lithium battery negative electrodes.

[0003] During the charging / discharging process, the volume expansion rate of silicon-based anode active materials is generally over 300%. Even silicon dioxide, which has a more balanced performance, has an expansion rate as high as 118% (the expansion rate of graphite is about 12%). This makes the silicon-based anode structure more susceptible to damage, and the surface solid electrolyte interphase (SEI) film is constantly destroyed / regenerated, resulting in rapid capacity decay and poor cycle stability.

[0004] CN112467063A discloses a method for preparing a silicon-based negative electrode sheet for lithium-ion batteries. The method involves: thoroughly mixing silicon-based negative electrode sheet material, a conductive agent, a binder, and a modifying additive with a certain mass ratio of reagents to form a slurry-like substance. The modifying additive is an organic small molecule containing at least one amino or carboxyl functional group, and its molar mass is less than 210 g / mol. This mixture is then uniformly coated onto the surface of a copper foil and dried at 50–80°C for 20–60 min and under vacuum at 100–140°C for 8–20 h, respectively, to obtain the silicon-based negative electrode sheet.

[0005] CN113140702A discloses a silicon-based negative electrode sheet with a sandwich structure, its preparation method and application, wherein the silicon-based negative electrode sheet includes a current collector, a buffer layer including a PEDOT / PSS composite material and an active material coating arranged sequentially; the silicon-based negative electrode sheet has a buffer layer including a PEDOT / PSS composite material between the current collector and the active material coating.

[0006] The silicon-based anode active material of the silicon-based anode sheet described in the above scheme has a high volume expansion rate during charging / discharging, the anode structure is destroyed, the surface SEI film is continuously destroyed / regenerated, the capacity decays rapidly, and the cycle performance is poor. Summary of the Invention

[0007] The purpose of this invention is to provide a composite silicon-based negative electrode sheet, its preparation method, and its application. This invention features a layered structure design for the electrode sheet, with carbon-based active materials and silicon-based active materials placed in different electrode coatings. The silicon-based material coating and the carbon-based material coating work synergistically to ensure the overall structural stability of the electrode sheet. On the other hand, the silicon-based material coating effectively inhibits the repeated formation of the SEI film, thus preventing rapid decay of the overall capacity and improving cycle stability.

[0008] To achieve this objective, the present invention adopts the following technical solution:

[0009] In a first aspect, the present invention provides a composite silicon-based negative electrode sheet, the composite silicon-based negative electrode sheet comprising a current collector and a carbon-based material coating and a silicon-based material coating sequentially stacked on the surface of the current collector, the silicon-based material coating comprising a silicon-based active material, a hard carbon microstructure and a conductive network.

[0010] In the composite silicon-based negative electrode sheet of this invention, the hard carbon material forms a highly elastic hard carbon microstructure under the action of a binder. When the volume of the silicon-based active material expands, the hard carbon microstructure is compressed and its volume decreases; when the volume of the silicon-based active material contracts, the hard carbon microstructure rebounds and its volume increases. The volume of the hard carbon microstructure decreases / increases with the expansion / contraction of the silicon-based active material. During the volume change of the silicon-based active material, the overall volume change of the silicon-based material coating is small, the structure is stable, and the damage to the electrode sheet as a whole is minimal. The SEI film is not repeatedly damaged, resulting in better cycle stability. The hard carbon microstructure is in direct contact with the electrolyte, forming a stable SEI film, and its internal pores are larger than those of graphite.

[0011] The conductive network composed of conductive additives is more uniformly distributed inside the silicon-based material coating, resulting in stronger conductivity and more complete reaction. This effectively reduces the polarization of the negative electrode and also reduces the formation of lithium dendrites, thus effectively enhancing the safety of lithium batteries.

[0012] The carbon-based material coating can improve the electrode capacity on the one hand, and when the silicon-based material coating extends laterally, it can both suppress its lateral stretching and act as a buffer layer to reduce the irreversible deformation of the current collector.

[0013] Preferably, in the silicon-based material coating, the hard carbon microstructure includes hard carbon material and a binder.

[0014] Preferably, the volume ratio of the hard carbon material to the silicon-based active material is (10-40):1, for example: 10:1, 15:1, 20:1, 30:1 or 40:1, etc., preferably 30:1.

[0015] Preferably, the mass ratio of the hard carbon material to the silicon-based active material is (5-25):1, for example: 5:1, 10:1, 15:1, 20:1 or 25:1, etc., and preferably 19:1.

[0016] Preferably, the hard carbon material includes carbon black.

[0017] Preferably, the carbon black is obtained by heat treatment and carbonization of a thermosetting precursor.

[0018] Preferably, the thermosetting precursor includes any one or a combination of at least two of sucrose, biomass materials, or phenolic resin.

[0019] Preferably, the carbon-based material coating and the silicon-based material coating are disposed on one or both sides of the current collector.

[0020] Preferably, the thickness of the carbon-based material coating on one side is 60-80 μm, for example: 60 μm, 65 μm, 70 μm, 75 μm or 80 μm.

[0021] Preferably, the thickness of the silicon-based material coating on one side is 70-90 μm, for example: 70 μm, 75 μm, 80 μm, 85 μm or 90 μm.

[0022] In a second aspect, the present invention provides a method for preparing a composite silicon-based negative electrode sheet as described in the first aspect, the method comprising the following steps:

[0023] (1) A carbon-based coating is obtained by mixing carbon-based materials, conductive agents, binders and solvents; a silicon-based coating is obtained by mixing silicon-based active materials, hard carbon materials, conductive additives, binders and solvents.

[0024] (2) The carbon-based coating is applied to both sides of the current collector, and after drying, the silicon-based coating is applied to the surface of the carbon-based coating. The composite silicon-based negative electrode sheet is obtained by cold pressing.

[0025] Preferably, the carbon-based material in step (1) includes graphite.

[0026] Preferably, the conductive agent includes any one or a combination of at least two of conductive carbon black, acetylene black, Ketjen black, or conductive graphite.

[0027] Preferably, the adhesive comprises any one or a combination of at least two of polyvinylidene fluoride, carboxymethyl cellulose, polyacrylonitrile, polyacrylate, polyacrylic acid, or styrene-butadiene rubber.

[0028] Preferably, the conductive additive includes any one or a combination of at least two of single-walled carbon nanotubes, multi-walled carbon nanotubes, or graphene.

[0029] Preferably, in the carbon-based coating described in step (1), the mass ratio of carbon-based material, conductive agent, and binder is (93-98):(0.5-2):(2-4), for example: 96:1:3, 94:2:4, 95:1:4, 96:1.5:2.5, or 97:1:2, etc.

[0030] Preferably, in the silicon-based coating described in step (1), the mass ratio of hard carbon material, silicon-based active material, conductive additive and binder is (90-95):(3-6):(0.5-2):(1-3), for example: 92:5:1:2, 91:6:2:1, 94:3:1:2, 93:5:1:1 or 94:3:1:2, etc.

[0031] Preferably, the coating temperature of the carbon-based coating in step (2) is 110 to 130°C, for example: 110°C, 115°C, 120°C, 125°C or 130°C.

[0032] Preferably, the coating speed of the carbon-based coating is 5 to 8 m / min, for example: 5 m / min, 5.5 m / min, 6 m / min, 7 m / min or 8 m / min, etc.

[0033] Preferably, the coating temperature of the silicon-based coating in step (2) is 80 to 100°C, for example: 80 m / min, 85 m / min, 90 m / min, 95 m / min or 100 m / min, etc.

[0034] Preferably, the coating speed of the silicon-based coating is 4 to 6 m / min, for example: 4 m / min, 4.5 m / min, 5 m / min, 5.5 m / min or 6 m / min, etc.

[0035] Thirdly, the present invention provides a lithium-ion battery comprising a composite silicon-based negative electrode as described in the first aspect.

[0036] Compared with the prior art, the present invention has the following beneficial effects:

[0037] (1) The present invention has a layered structure design for the electrode, with carbon-based active material and silicon-based active material placed in different electrode coatings. The silicon-based material coating and the carbon-based material coating work together to ensure the stability of the overall structure of the electrode. On the other hand, the silicon-based material coating effectively inhibits the repeated formation of the SEI film, which not only prevents the rapid decay of the overall capacity but also improves the cycle stability.

[0038] (2) The composite silicon-based negative electrode sheet described in this invention is applied to lithium-ion batteries, combining the advantages of single carbon-based or single silicon-based negative electrode sheets. On the one hand, it has a high capacity, and on the other hand, it still exhibits excellent capacity retention after 500 cycles. Attached Figure Description

[0039] Figure 1 This is a schematic diagram of the composite silicon-based negative electrode sheet described in Embodiment 1 of the present invention, wherein 1 is a silicon-based material coating, 2 is a carbon-based material coating, 3 is a current collector, 4 is a silicon-based active material, 5 is a hard carbon structure, and 6 is a single-walled carbon nanotube conductive network.

[0040] Figure 2 This is a comparison chart of the cycle performance of the negative electrode sheets prepared in Example 1 and Comparative Examples 1-2.

[0041] Figure 3 This is a comparison diagram of the capacity retention of the negative electrode sheets prepared in Example 1 and Comparative Examples 1-2. Detailed Implementation

[0042] The technical solution of the present invention will be further illustrated below through specific embodiments. Those skilled in the art should understand that the embodiments described are merely illustrative of the present invention and should not be construed as limiting the invention.

[0043] Example 1

[0044] This embodiment provides a composite silicon-based negative electrode sheet, and the preparation method of the composite silicon-based negative electrode sheet is as follows:

[0045] (1) Graphite, conductive carbon black SP, polyvinylidene fluoride and pure water are mixed and stirred in a mass ratio of 96:1:3:50 to obtain a carbon-based coating. Carbon black, silicon dioxide, single-walled carbon nanotubes, polyvinylidene fluoride and pure water are mixed and stirred in a mass ratio of 92:5:1:2:50 to obtain a silicon-based coating (the volume ratio of carbon black to silicon dioxide is 28:1, and the mass ratio of hard carbon material to silicon-based active material is 18.4:1).

[0046] (2) A carbon-based coating is uniformly coated onto the current collector copper foil at a coating temperature of 120°C and a coating speed of 6 m / min. After drying, a silicon-based coating is uniformly coated onto the carbon-based coating at a coating temperature of 90°C and a coating speed of 5 m / min. After drying, the composite silicon-based negative electrode sheet is obtained by cold pressing. The single-sided thickness of the carbon-based material coating in the composite silicon-based negative electrode sheet is 70 μm, and the single-sided thickness of the silicon-based material coating is 80 μm. The structural schematic diagram of the composite silicon-based negative electrode sheet is shown below. Figure 1 As shown, 1 is a silicon-based material coating, 2 is a carbon-based material coating, 3 is a current collector, 4 is a silicon-based active material, 5 is a hard carbon microstructure, and 6 is a single-walled carbon nanotube conductive network.

[0047] Example 2

[0048] This embodiment provides a composite silicon-based negative electrode sheet, and the preparation method of the composite silicon-based negative electrode sheet is as follows:

[0049] (1) Graphite, conductive carbon black SP, polyvinylidene fluoride and pure water are mixed and stirred in a mass ratio of 94:2:4:50 to obtain a carbon-based coating. Carbon black, silicon dioxide, single-walled carbon nanotubes, polyvinylidene fluoride and pure water are mixed and stirred in a mass ratio of 91.2:4.8:1.5:2.5:50 to obtain a silicon-based coating (the volume ratio of carbon black to silicon dioxide is 30:1, and the mass ratio of hard carbon material to silicon-based active material is 19:1).

[0050] (2) The carbon-based coating is uniformly coated on the current collector copper foil at a coating temperature of 115°C and a coating speed of 6.5 m / min. After drying, the silicon-based coating is uniformly coated on the carbon-based coating at a coating temperature of 95°C and a coating speed of 5.2 m / min. After drying, the composite silicon-based negative electrode sheet is obtained by cold pressing. The thickness of the carbon-based material coating on one side of the composite silicon-based negative electrode sheet is 72 μm, and the thickness of the silicon-based material coating on one side is 78 μm.

[0051] Example 3

[0052] The only difference between this embodiment and Embodiment 1 is that the thickness of the carbon-based material coating on one side is 55 μm. All other conditions and parameters are exactly the same as in Embodiment 1.

[0053] Example 4

[0054] The only difference between this embodiment and Embodiment 1 is that the thickness of the carbon-based material coating on one side is 85 μm; all other conditions and parameters are exactly the same as in Embodiment 1.

[0055] Example 5

[0056] The only difference between this embodiment and Embodiment 1 is that the thickness of the silicon-based material coating on one side is 65 μm. All other conditions and parameters are exactly the same as in Embodiment 1.

[0057] Example 6

[0058] The only difference between this embodiment and Embodiment 1 is that the thickness of the silicon-based material coating on one side is 95 μm. All other conditions and parameters are exactly the same as in Embodiment 1.

[0059] Comparative Example 1

[0060] This comparative example uses a conventional silicon-based anode sheet preparation process: graphite and silicon-based materials are mixed and mechanically stirred, then coated and cold-pressed to obtain the finished anode sheet.

[0061] Comparative Example 2

[0062] This comparative example uses a conventional carbon-based (graphite) negative electrode preparation process: graphite is stirred, coated, and cold-pressed to obtain the finished negative electrode.

[0063] Performance testing:

[0064] The cycle performance of the negative electrode sheets described in the examples and comparative examples was tested under ambient temperature and pressure, and 2A / 10A charge-discharge conditions. The capacity retention rate after 500 cycles was obtained, and the test results are shown in Table 1.

[0065] Table 1

[0066] Example 1 4.087 3.548 86.81 Example 2 4.079 3.538 86.74 Example 3 4.013 3.463 86.29 Example 4 3.998 3.456 86.44 Example 5 4.021 3.477 86.47 Example 6 4.026 3.460 85.94 Comparative Example 1 3.354 2.196 65.47 Comparative Example 2 2.509 2.161 86.13

[0067] As can be seen from Table 1, as obtained from Examples 1-2, the initial capacity of the negative electrode sheet of the present invention can reach more than 4.079 Ah, the capacity after 500 cycles can reach more than 3.538 Ah, and the capacity retention rate can reach more than 86.74%.

[0068] A comparison of Examples 1 and 3-4 shows that the thickness of the carbon-based material coating in the composite silicon-based negative electrode sheet of the present invention affects the performance of the composite silicon-based negative electrode sheet. Controlling the thickness of the carbon-based material coating to 60-80 μm results in a composite silicon-based negative electrode sheet with better performance. If the thickness of the carbon-based material coating is too small, the cycle performance will decrease. If the thickness of the carbon-based material coating is too large, the cycle performance will deteriorate.

[0069] A comparison of Examples 1 and 5-6 shows that the thickness of the silicon-based material coating in the composite silicon-based negative electrode sheet of the present invention affects the performance of the composite silicon-based negative electrode sheet. Controlling the thickness of the silicon-based material coating to 70-90 μm results in a composite silicon-based negative electrode sheet with better performance. If the thickness of the silicon-based material coating is too small, the cycle performance will decrease; if the thickness of the silicon-based material coating is too large, the cycle performance will deteriorate.

[0070] The cycle performance comparison diagram of the negative electrode sheets prepared in Example 1 and Comparative Examples 1-2 is shown in the figure below. Figure 2 As shown in the capacity retention comparison chart... Figure 3 As shown, by comparing Example 1 and Comparative Examples 1-2, it can be seen that Example 1 of the present invention has a higher capacity, better cycle stability and capacity retention than Comparative Examples 1-2.

[0071] The applicant declares that the above description is only a specific embodiment of the present invention, but the protection scope of the present invention is not limited thereto. Those skilled in the art should understand that any changes or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in the present invention fall within the protection and disclosure scope of the present invention.

Claims

1. A composite silicon-based negative electrode sheet, characterized in that, The composite silicon-based negative electrode includes a current collector and a carbon-based material coating and a silicon-based material coating sequentially stacked on the surface of the current collector. The silicon-based material coating includes a silicon-based active material, a hard carbon microstructure, and a conductive network. In the silicon-based material coating, the hard carbon microstructure includes hard carbon material and a binder; The thickness of the carbon-based material coating on one side is 60~80μm; the thickness of the silicon-based material coating on one side is 70~90μm. In the composite silicon-based negative electrode sheet, the hard carbon material forms a highly elastic hard carbon microstructure under the action of the binder.

2. The composite silicon-based negative electrode sheet as described in claim 1, characterized in that, The volume ratio of the hard carbon material to the silicon-based active material is (10~40):

1.

3. The composite silicon-based negative electrode sheet as described in claim 2, characterized in that, The volume ratio of the hard carbon material to the silicon-based active material is 30:

1.

4. The composite silicon-based negative electrode sheet as described in claim 1, characterized in that, The mass ratio of the hard carbon material to the silicon-based active material is (5~25):

1.

5. The composite silicon-based negative electrode sheet as described in claim 4, characterized in that, The mass ratio of the hard carbon material to the silicon-based active material is 19:

1.

6. The composite silicon-based negative electrode sheet as described in claim 1, characterized in that, The hard carbon material includes carbon black.

7. The composite silicon-based negative electrode sheet as described in claim 1, characterized in that, The hard carbon material is obtained by heat treatment and carbonization of a thermosetting precursor.

8. The composite silicon-based negative electrode sheet as described in claim 7, characterized in that, The thermosetting precursors include biomass materials and / or phenolic resins.

9. The composite silicon-based negative electrode sheet as described in claim 1, characterized in that, The carbon-based material coating and the silicon-based material coating are disposed on one or both sides of the current collector.

10. A method for preparing a composite silicon-based negative electrode sheet as described in any one of claims 1-9, characterized in that, The preparation method includes the following steps: (1) A carbon-based coating is obtained by mixing carbon-based materials, conductive agents, binders and solvents; a silicon-based coating is obtained by mixing silicon-based active materials, hard carbon materials, conductive additives, binders and solvents. (2) The carbon-based coating is applied to both sides of the current collector, and after drying, the silicon-based coating is applied to the surface of the carbon-based coating. The composite silicon-based negative electrode sheet is obtained by cold pressing.

11. The preparation method according to claim 10, characterized in that, The carbon-based material mentioned in step (1) includes graphite.

12. The preparation method according to claim 10, characterized in that, The conductive agent includes any one or a combination of at least two of conductive carbon black, acetylene black, Ketjen black, or conductive graphite.

13. The preparation method according to claim 10, characterized in that, The adhesive includes any one or a combination of at least two of polyvinylidene fluoride, carboxymethyl cellulose, polyacrylonitrile, polyacrylate, polyacrylic acid, or styrene-butadiene rubber.

14. The preparation method according to claim 10, characterized in that, The conductive additive includes any one or a combination of at least two of single-walled carbon nanotubes, multi-walled carbon nanotubes, or graphene.

15. The preparation method according to claim 10, characterized in that, In step (1), the mass ratio of carbon-based material, conductive agent and binder in the carbon-based coating is (93~98):(0.5~2):(2~4).

16. The preparation method according to claim 10, characterized in that, In step (1), the mass ratio of hard carbon material, silicon-based active material, conductive additive and binder in the silicon-based coating is (90~95):(3~6):(0.5~2):(1~3).

17. The preparation method according to claim 10, characterized in that, The coating temperature of the carbon-based coating in step (2) is 110~130℃.

18. The preparation method according to claim 10, characterized in that, The coating speed of the carbon-based coating is 5~8m / min.

19. The preparation method according to claim 10, characterized in that, The coating temperature of the silicon-based coating in step (2) is 80~100℃.

20. The preparation method according to claim 10, characterized in that, The coating speed of the silicon-based coating is 4~6m / min.

21. A lithium-ion battery, characterized in that, The lithium-ion battery comprises a composite silicon-based negative electrode as described in any one of claims 1-9.

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