Negative electrode sheet, secondary battery and electronic device

Abstract

The present application provides a negative electrode sheet, a secondary battery and an electronic device. The negative electrode sheet of the present application comprises a current collector, and a first active layer and a second active layer which are sequentially arranged on at least one surface of the current collector; and the negative electrode sheet meets: 0.70≤(M1*H1) / (M2*H2)≤1.5, wherein M1 represents the molar ratio of an element O to an element C among surface elements of the first active layer; M2 represents the molar ratio of an element O to an element C among the surface elements of the second active layer; H1 represents the thickness of the first active layer; H2 represents the thickness of the second active layer; and M1 is not equal to M2. By regulating and controlling parameters of coatings of a composite negative electrode sheet, the whole active material layer of a composite electrode keeps similar interface stability in a wide temperature interval.

Description

Negative electrode sheet, secondary battery, and electric device

[0001] The present application claims priority to the Chinese patent application No. 202410421320.8, filed on April 9, 2024, and entitled "A negative electrode sheet, a secondary battery, and an electric device", the whole content of which is incorporated herein by reference. TECHNICAL FIELD

[0002] The present application relates to the technical field of batteries, in particular to a negative electrode sheet, a secondary battery, and an electric device. BACKGROUND

[0003] In order to further improve the energy density of the battery and pursue significant cost reduction benefits, more and more batteries in the design will focus on the design and use of composite electrodes. However, in the actual production process, many appearance defects often occur. Especially in the case of large difference in active material layer slurry system, the appearance defect rate increases significantly, which seriously affects the yield and performance of the battery.

[0004] Therefore, it is necessary to provide a negative electrode sheet with good appearance performance. SUMMARY

[0005] The purpose of the present application is to overcome the defects of the appearance performance of the existing composite electrode sheet, and to provide a negative electrode sheet with good appearance performance.

[0006] To achieve the above-mentioned purpose, the first aspect of the present application provides a negative electrode sheet, the negative electrode sheet comprising a current collector, a first active layer and a second active layer arranged in sequence on at least one surface of the current collector, the negative electrode sheet satisfying the following relationship: 0.70≤(M1*H1) / (M2*H2)≤1.5;

[0007] wherein M1 represents the molar ratio of O element and C element in the surface element of the first active layer;

[0008] M2 represents the molar ratio of O element and C element in the surface element of the second active layer;

[0009] H1 represents the thickness of the first active layer;

[0010] H2 represents the thickness of the second active layer;

[0011] M1 is not equal to M2.

[0012] As an embodiment of the present application, the value of M1 is 0.01≤M1≤0.5.

[0013] As an embodiment of the present application, the value of M2 is 0.01≤M2≤0.5.

[0014] As an embodiment of the present application, the value of H1 is 10 μm≤H1≤200 μm.

[0015] As an embodiment of the present application, the value of H2 is 10 μm≤H2≤200 μm.

[0016] As an embodiment of the present application, the negative electrode sheet satisfies: 1.0≤(M1*H1) / (M2*H2)≤1.2.

[0017] As an embodiment of the present application, in the negative electrode sheet, the first active material layer and the second active material layer independently comprise the following components: 65-99.85wt% of active material, 0.05-15wt% of conductive agent, 0.05-15wt% of binder, and 0.05-5wt% of surfactant.

[0018] As an embodiment of the present application, the active material comprises at least one of silicon-carbon composite material, carbon-coated silicon monoxide, and carbon material.

[0019] As an embodiment of the present application, the conductive agent comprises at least one of conductive carbon black, acetylene black, ketjen black, conductive graphite, conductive carbon fiber, carbon nanotube, metal powder, and carbon fiber.

[0020] As an embodiment of the present application, the binder comprises at least one of polyvinylidene fluoride, polyvinyl alcohol, starch, hydroxypropyl cellulose, regenerated cellulose, polyvinylpyrrolidone, tetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene terpolymer, sulfonated EPDM, styrene butadiene rubber, and fluorine rubber.

[0021] As an embodiment of the present application, the surfactant comprises at least one of sodium carboxymethyl cellulose, lithium carboxymethyl cellulose, sodium dodecylbenzenesulfonate, sodium dodecyl sulfate, alkyl glucoside, quaternary ammonium, 1,3 butanediol, and n-octanol.

[0022] As an embodiment of the present application, the particle size D V50 of the active material is 3-20 μm, and D V50 is the particle size corresponding to the cumulative volume of 50% of the active material.

[0023] In a second aspect of the present application, a secondary battery is provided, comprising the negative electrode sheet of the first aspect of the present application.

[0024] In a third aspect of the present application, an electric device is provided, comprising the secondary battery of the second aspect of the present application.

[0025] Compared with the prior art, the present application has the following beneficial effects:

[0026] The application regulates the surface functional groups and thickness between the coating layers of the composite negative electrode sheet, so that the entire active material layer (including the first active layer and the second active layer) of the composite electrode maintains similar interface stability in a wider temperature range, thereby ensuring the uniformity of the coating of the composite electrode, and avoiding appearance defects from the perspective of sheet design. BRIEF DESCRIPTION OF DRAWINGS

[0027] FIG. 1 is a structural schematic diagram of the negative electrode sheet of the application, in which 1 is the first active layer, 2 is the second active layer, and 3 is the current collector;

[0028] FIG. 2 is a physical diagram of the negative electrode sheet prepared in the example, from which it can be seen that the surface is smooth and uniform;

[0029] FIG. 3 is a physical diagram of the negative electrode sheet after winding in Example 1. DETAILED DESCRIPTION

[0030] In order to better illustrate the purpose, technical scheme and advantages of the application, specific examples will be further described below, but the examples do not limit the application in any form. Unless otherwise specified, the reagents, methods and equipment used in the application are conventional reagents, methods and equipment in the technical field. Unless otherwise specified, the reagents and materials used in the application are commercially available.

[0031] The example of the application provides a negative electrode sheet, which comprises a current collector, a first active layer and a second active layer arranged in sequence on at least one surface of the current collector, and satisfies the following relationship: 0.70≤(M1*H1) / (M2*H2)≤1.5.

[0032] wherein M1 represents the molar ratio of O element and C element in the surface elements of the first active layer;

[0033] M2 represents the molar ratio of O element and C element in the surface elements of the second active layer;

[0034] H1 represents the thickness of the first active layer;

[0035] H2 represents the thickness of the second active layer;

[0036] M1 is not equal to M2.

[0037] After the negative pole piece is coated with an active material coating, it needs to be baked to remove the solvent film in the coating slurry, but baking is a process from room temperature to high temperature, and the surface tension of different coating slurries will be affected by temperature and become different. Currently, the conventional composite negative pole piece is prone to cause a large difference in surface tension between different coatings during high-temperature baking, thereby causing the prepared negative pole piece to have different degrees of bulging and other phenomena, affecting the use of the pole piece.

[0038] Therefore, by adjusting the surface functional groups and thickness between the coatings of the composite negative pole piece, the entire active material layer (including the first active layer and the second active layer) of the composite electrode can maintain similar interface stability within a wide temperature range, thereby ensuring the uniformity of the coating of the composite electrode, and avoiding appearance defects from the perspective of pole piece design.

[0039] In some embodiments, the value of M1 is 0.01≤M1≤0.5.

[0040] In some embodiments, the value of M2 is 0.01≤M2≤0.5.

[0041] M1 and M2 are the molar ratios of O elements and C elements on the surfaces of the first active layer and the second active layer, respectively. In this application, the molar contents of O elements and C elements on the surface of the active layer are obtained by XPS (X-ray photoelectron spectroscopy) analysis test.

[0042] M1 and M2 within the above suitable range can further reduce the difference in interlayer surface tension, and obtain a composite negative pole piece with a flat surface and good appearance performance.

[0043] In some embodiments, the value of H1 is 10μm≤H1≤200μm.

[0044] In some embodiments, the value of H2 is 10μm≤H2≤200μm.

[0045] In the negative pole piece, the thickness of the coating is within the above suitable range, which can take into account the mechanical strength, energy density and discharge capacity of the pole piece, so that the prepared secondary battery has excellent electrochemical cycle performance.

[0046] In some embodiments, the negative pole piece satisfies: 1.0≤(M1*H1) / (M2*H2)≤1.2. The parameter relationship of the negative pole piece is within the range, and the appearance performance of the obtained negative pole piece is better.

[0047] In some embodiments, the first active material layer and the second active material layer each independently comprise the following components: 65-99.85 wt% of an active material, 0.05-15 wt% of a conductive agent, 0.05-15 wt% of a binder, and 0.05-5 wt% of a surfactant.

[0048] In some embodiments, the active material comprises a negative active material, and any negative active material commonly used in the art can be used in the present application.

[0049] The negative active material comprises, but is not limited to, at least one of a silicon-carbon composite material, a carbon-coated silicon monoxide, and a carbon material. The carbon material comprises, but is not limited to, graphite, hard carbon, and the like.

[0050] Any conductive agent commonly used in the art can be used in the present application. The conductive agent comprises, but is not limited to, at least one of conductive carbon black, acetylene black, ketjen black, conductive graphite, conductive carbon fiber, carbon nanotube, metal powder, and carbon fiber.

[0051] Any binder commonly used in the art can be used in the present application. The binder comprises, but is not limited to, at least one of polyvinylidene fluoride, polyvinyl alcohol, starch, hydroxypropyl cellulose, regenerated cellulose, polyvinylpyrrolidone, tetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene terpolymer, sulfonated EPDM, styrene butadiene rubber, and fluoro rubber.

[0052] In some embodiments, the surfactant comprises at least one of sodium carboxymethyl cellulose, lithium carboxymethyl cellulose, sodium dodecylbenzenesulfonate, sodium dodecyl sulfate, alkyl glucoside, quaternary ammonium, 1,3-butanediol, and n-octanol.

[0053] In some embodiments, the particle size D V50 of the active material is 3-20 μm, and D V50 is the particle size corresponding to 50% of the cumulative volume of the active material. The particle size of the active material in this range can allow the electrode sheet to have a higher density while ensuring that the electrode sheet has good appearance performance.

[0054] In some embodiments, the current collector can be at least one of a copper foil, an aluminum foil, a copper mesh, an aluminum mesh, an aluminum foil coated with a conductive carbon layer, a copper foil coated with a conductive carbon layer, a polymer film coated with aluminum, a polymer film coated with copper, and a conductive polymer film.

[0055] Embodiments of the present application also provide a secondary battery comprising the positive / negative electrode prepared from the negative electrode sheet, a separator, and an electrolyte.

[0056] Embodiments of the present application also provide an electrical device comprising the secondary battery.

[0057] The following are specific embodiments of the present application, and the technical solutions of the present application are further described in conjunction with the embodiments, but the present application is not limited to these embodiments. The reagents, methods and equipment used in the present application are conventional reagents, methods and equipment in the technical field, unless otherwise specified.

[0058] Example 1

[0059] The present embodiment provides a negative electrode sheet, and the preparation method comprises the following steps:

[0060] The first active layer slurry and the second active layer slurry are coated onto one side surface of the current collector copper foil using a double-layer coating machine, and after drying, the same coating operation is performed on the other side of the copper foil; after coating is completed, drying is performed at 90-110°C, and after rolling, a composite negative electrode sheet with a compaction density of 1.6 g / cm 3 The structure schematic diagram is shown in FIG. 1, FIG. 2 is a physical diagram of the negative electrode sheet prepared in the present embodiment, and FIG. 3 is the negative electrode sheet after winding.

[0061] The upper die head of the double-layer coating machine coats the second active layer slurry, and the lower die head coats the first active layer slurry, and the upper and lower die heads coat simultaneously.

[0062] The composition of the first active layer slurry is: 94% carbon-coated silicon monoxide (D V50 = 5 μm, specific capacity 450 mAh / g), 3% SuperP (conductive carbon black), 1.5% CMC active agent (sodium carboxymethyl cellulose), and 1.5% binder (styrene-butadiene rubber), and water is added and mixed uniformly to obtain a first active layer slurry with a solid content of 40 wt%, which is uniformly coated onto the surface layer of the current collector, and after testing, the O / C molar ratio M1 of the surface of the active layer is 0.50;

[0063] The composition of the second active layer slurry is: 94% graphite (D V50 = 5 μm, specific capacity 350 mAh / g), 3% SuperP (conductive carbon black), 1.5% CMC active agent (sodium carboxymethyl cellulose), and 1.5% binder (styrene-butadiene rubber), and water is added and mixed uniformly to obtain a second active layer slurry with a solid content of 50 wt%, which is uniformly coated onto the surface layer of the current collector, and after testing, the O / C molar ratio M2 of the surface of the active layer is 0.435.

[0064] Other parameters are shown in Table 1.

[0065] Examples 2-11, Comparative Examples 1-2

[0066] A series of negative electrode sheets were prepared according to the steps of Example 1, except that the parameters of the active material in the active layer (such as the O / C molar ratio of the surface of the active material by changing the proportion of raw materials in the active slurry layer) or the coating parameters were changed to prepare negative electrode sheets with parameters as shown in Table 1.

[0067] Table 1 Parameters of negative electrode sheets

[0068] The performance of the negative electrode sheets obtained in the above examples and comparative examples was tested, and the specific test items, test methods and results are as follows:

[0069] 1. Bulge test after winding: The negative electrode sheet was wound (the thickness radius exceeded 10 cm), and 17 points were taken in the longitudinal direction (along the coating direction) at the bulge position. The average value of the remaining 15 points was taken by removing the maximum and minimum values from the 17 points, and the thickness difference d (μm) from the normal area thickness was recorded;

[0070] 2. Effect on battery performance: The sheets prepared in the above examples and comparative examples (judged from the active material as negative electrode sheets), LiNi 0.6 Co 0.1 Mn 0.3 O2 positive electrode sheets (maintaining N / P ratio = 1.13), and PP separators were assembled into a square shell (MEB square shell, T*W*H was 33*220*110 mm). After winding the same number of layers, the lithium ion battery was obtained after the processes of liquid injection (electrolyte: lithium hexafluorophosphate solution with a concentration of 1 mol / L, solvent: ethylene carbonate (EC): methyl ethyl carbonate (EMC) = 3:7 (V / V) mixture), formation, aging, sealing, etc. The new power battery test system was used to test the lithium ion battery at a current of 0.5 A. When the battery terminal voltage reached the charging limit voltage 4.2 V, it was changed to constant voltage charging until the charging current was less than or equal to 1 / 20 C, the charging was stopped, and the battery was left for 0.5 h-1 h. Then, the battery was discharged at a current of 1 C to the terminal voltage of 2.75 V. After the discharge was completed, the battery was left for 0.5 h-1 h, and the next charge-discharge cycle was carried out. The cycle number when the capacity retention rate was 80% (80% SOH) at room temperature (25°C) was recorded, and the test results are shown in Table 2.

[0071] Table 2 Performance test results

[0072] From the above results, it can be seen that:

[0073] In the double-layer coated negative electrode sheet, when the parameters in the two coating layers satisfy the relationship of the present application, the appearance performance of the sheet can be significantly improved, and the battery prepared therefrom has good cycle performance.

[0074] The negative electrode tab satisfying the above conditions of the present application has good appearance and cycle performance, and the thickness of the bulge is all below 2.5 μm; the cycle number when cycled to 80% SOH is all above 1200 cycles, and can be as high as 2653 cycles.

[0075] Finally, it should be noted that the above examples are only used to illustrate the technical solutions of the present application and not to limit the scope of protection of the present application. Although the present application has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that the technical solutions of the present application can be modified or equivalently replaced without departing from the essence and scope of the technical solutions of the present application.

Claims

1. A negative electrode sheet comprising a current collector, a first active layer and a second active layer sequentially disposed on at least one surface of the current collector, wherein: The negative electrode plate satisfies the following relationship: 0.70≤(M1*H1) / (M2*H2)≤1.5; Wherein, M1 represents the molar ratio of O element to C element in the surface elements of the first active layer; M2 represents the molar ratio of O and C in the surface elements of the second active layer; H1 represents the thickness of the first active layer; H2 represents the thickness of the second active layer; M1 is not equal to M2.

2. The negative electrode sheet according to claim 1, wherein: The value of M1 is 0.01≤M1≤0.

5.

3. The negative electrode sheet according to claim 1, wherein: The value of M2 is 0.01≤M2≤0.

5.

4. The negative electrode sheet according to claim 1, wherein: The value of H1 is 10 μm≤H1≤200 μm.

5. The negative electrode sheet according to claim 1, wherein: The value of H2 is 10 μm≤H2≤200 μm.

6. The negative electrode sheet according to claim 1, wherein: The negative electrode plate satisfies: 1.0≤(M1*H1) / (M2*H2)≤1.

2.

7. The negative electrode sheet according to claim 1, wherein: In the negative electrode sheet, the first active layer and the second active layer independently include the following components: 65-99.85 wt% of active material, 0.05-15 wt% of conductive agent, 0.05-15 wt% of binder, and 0.05-5 wt% of surfactant.

8. The negative electrode sheet according to claim 7, wherein: The active material includes at least one of a silicon-carbon composite material, carbon-coated silicon oxide, and a carbon material.

9. The negative electrode sheet according to claim 8, wherein: The carbon material includes graphite or hard carbon.

10. The negative electrode sheet according to claim 7, wherein: The conductive agent includes at least one of conductive carbon black, acetylene black, Ketjen black, conductive graphite, conductive carbon fiber, carbon nanotubes, metal powder, and carbon fiber.

11. The negative electrode sheet according to claim 7, wherein: The binder includes at least one of polyvinylidene fluoride, polyvinyl alcohol, starch, hydroxypropyl cellulose, regenerated cellulose, polyvinyl pyrrolidone, tetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene terpolymer, sulfonated EPDM, styrene-butadiene rubber, and fluororubber.

12. The negative electrode sheet according to claim 7, wherein: The surfactant includes at least one of sodium carboxymethyl cellulose, lithium carboxymethyl cellulose, sodium dodecylbenzene sulfonate, sodium lauryl sulfate, alkyl glucoside, quaternary ammonium compound, 1,3-butanediol, and n-octanol.

13. The negative electrode sheet according to claim 7, wherein: The particle size D of the active material V50 3~20μm, D V50 It is the particle size corresponding to when the cumulative volume of the active material reaches 50%.

14. The negative electrode sheet according to claim 1, wherein: The current collector is at least one of copper foil, aluminum foil, copper mesh, aluminum mesh, aluminum foil coated with a conductive carbon layer, copper foil coated with a conductive carbon layer, a polymer film coated with aluminum, a polymer film coated with copper, and a conductive polymer film.

15. A secondary battery, wherein: The negative electrode sheet comprises the negative electrode sheet according to any one of claims 1 to 14.

16. An electrical device, wherein: The secondary battery according to claim 15 is included.

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