A negative electrode sheet, a secondary battery, and an electric device

Abstract

The application provides a negative electrode sheet, a secondary battery and a power utilization device. The negative electrode sheet of the application 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 0.70≤(M1*H1) / (M2*H2)≤1.5, wherein M1 represents the molar ratio of O element and C element in the surface element of the first active layer; M2 represents the molar ratio of O element and C element in the surface element of the second active layer; H1 represents the thickness of the first active layer in μm; H2 represents the thickness of the second active layer in μm; and M1 is not equal to M2. By regulating the parameters between the composite negative electrode sheet coatings, the entire active material layer of the composite electrode can maintain similar interface stability in a wider temperature range.

Description

Technical Field

[0001] This application relates to the field of battery technology, and in particular to a negative electrode sheet, a secondary battery, and an electrical device. Background Technology

[0002] To further improve battery energy density and achieve significant cost reduction, more and more battery designers are focusing on the design and application of composite electrodes. However, in actual manufacturing processes, many appearance defects often occur. Especially when there are significant differences in the active material layer slurry system, the appearance defect rate increases significantly, seriously affecting the battery yield and performance.

[0003] Therefore, there is a need to provide a negative electrode sheet with good appearance and performance. Summary of the Invention

[0004] The purpose of this application is to overcome the defects of poor appearance performance of existing composite electrodes and provide a negative electrode with good appearance performance.

[0005] To achieve the above objectives, a first aspect of this application provides a negative electrode sheet, the 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, the negative electrode sheet satisfying the following relationship:

[0006] 0.70≤(M1*H1) / (M2*H2)≤1.5;

[0007] Where M1 represents the molar ratio of O to C elements in the surface elements of the first active layer;

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

[0009] H1μm represents the thickness of the first active layer;

[0010] H2μm represents the thickness of the second active layer;

[0011] M1 is not equal to M2.

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

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

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

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

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

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

[0018] As an embodiment of this application, the active material includes at least one of silicon-carbon composite materials, carbon-coated silicon suboxide, and carbon materials.

[0019] As an embodiment of this application, 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.

[0020] As an embodiment of this application, the adhesive includes 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 fluororubber.

[0021] As an embodiment of this application, the surfactant includes at least one selected from sodium carboxymethyl cellulose, lithium carboxymethyl cellulose, sodium dodecylbenzene sulfonate, sodium dodecyl sulfate, alkyl glucoside, quaternary ammonium compounds, 1,3-butanediol, and n-octanol.

[0022] As an embodiment of this application, the particle size D of the active material is... V50 The diameter is 3–20 μm, D V50 The particle size is the size corresponding to when the cumulative volume of the active material reaches 50%.

[0023] A second aspect of this application provides a secondary battery, including the negative electrode sheet described in the first aspect of this application.

[0024] A third aspect of this application provides an electrical device comprising the secondary battery described in the second aspect of this application.

[0025] Compared with the prior art, the beneficial effects of this application are:

[0026] This application achieves similar interfacial stability of the entire active material layer (including the first and second active layers) of the composite electrode over a wide temperature range by controlling the surface functional groups and thickness between the coatings of the composite negative electrode sheet. This ensures the uniformity of the coating of the composite electrode and avoids poor appearance from the perspective of electrode design. Attached Figure Description

[0027] Figure 1 This is a schematic diagram of the negative electrode sheet of this application. In the figure, 1 is the first active layer, 2 is the second active layer, and 3 is the current collector.

[0028] Figure 2 The image shows a physical picture of the negative electrode sheet prepared for the example. As can be seen from the picture, the surface is smooth and uniform.

[0029] Figure 3 This is a photograph of the negative electrode sheet after it has been wound up, as shown in Example 1. Detailed Implementation

[0030] To better illustrate the purpose, technical solution, and advantages of this application, specific embodiments will be used to further describe this application below. However, these embodiments do not limit this application in any way. Unless otherwise specified, the reagents, methods, and equipment used in this application are conventional reagents, methods, and equipment in this technical field. Unless otherwise specified, all reagents and materials used in this application are commercially available.

[0031] An embodiment of this application provides a negative electrode sheet, the 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, the negative electrode sheet satisfying the following relationship:

[0032] 0.70≤(M1*H1) / (M2*H2)≤1.5;

[0033] Where M1 represents the molar ratio of O to C elements in the surface elements of the first active layer;

[0034] M2 represents the molar ratio of O to C elements in the surface elements of the second active layer;

[0035] H1μm represents the thickness of the first active layer;

[0036] H2μm represents the thickness of the second active layer;

[0037] M1 is not equal to M2.

[0038] After the negative electrode sheet is coated with an active material coating, it needs to be baked to remove the solvent in the coating slurry and form a film. However, baking is a process from room temperature to high temperature. The surface tension of different coating slurries will change differently due to the temperature. Currently, conventional composite negative electrode sheets are prone to large differences in surface tension between different coatings during high temperature baking, which in turn leads to different degrees of bulging and other phenomena in the prepared negative electrode sheet, affecting the use of the electrode sheet.

[0039] Therefore, this application achieves similar interfacial stability of the entire active material layer (including the first and second active layers) of the composite electrode over a wide temperature range by controlling the surface functional groups and thickness between the coatings of the composite negative electrode, thereby ensuring the uniformity of the coating of the composite electrode and avoiding poor appearance from the perspective of electrode design.

[0040] In some embodiments, the value of M1 is 0.01 ≤ M1 ≤ 0.5.

[0041] In some embodiments, the value of M2 is 0.01 ≤ M2 ≤ 0.5.

[0042] M1 and M2 are the molar ratios of O and C elements on the surfaces of the first and second active layers, respectively. In this application, the molar contents of O and C elements on the surface of the active layer are obtained by XPS (photoelectron spectroscopy) analysis.

[0043] Within the aforementioned suitable range, the difference in interlayer surface tension between M1 and M2 can be further reduced, resulting in a composite negative electrode sheet with a smooth surface and good appearance.

[0044] In some embodiments, the value of H1 is 10μm≤H1≤200μm.

[0045] In some embodiments, the value of H2 is 10μm≤H2≤200μm.

[0046] In the negative electrode sheet, if the coating thickness is within the above-mentioned suitable range, the mechanical strength, energy density and discharge capacity of the electrode sheet can be balanced, so that the prepared secondary battery has excellent electrochemical cycle performance.

[0047] In some embodiments, the negative electrode sheet satisfies: 1.0 ≤ (M1*H1) / (M2*H2) ≤ 1.2. When the parameter relationship of the negative electrode sheet is within this range, the resulting negative electrode sheet exhibits better appearance and performance.

[0048] In some embodiments, the negative electrode sheet comprises, independently, the first active material layer and the second active material layer as follows: 65-99.85 wt% active material, 0.05-15 wt% conductive agent, 0.05-15 wt% binder, and 0.05-5 wt% surfactant.

[0049] In some embodiments, the active material includes a negative electrode active material, and commonly used negative electrode active materials in the art can be used in this application.

[0050] The negative electrode active material includes, but is not limited to, at least one of silicon-carbon composite materials, carbon-coated silicon suboxide, and carbon materials. The carbon materials include, but are not limited to, graphite and hard carbon.

[0051] Commonly used conductive agents in this field can be used in this application. These conductive agents include, but are not limited to, at least one of conductive carbon black, acetylene black, Ketjen black, conductive graphite, conductive carbon fiber, carbon nanotubes, metal powder, and carbon fiber.

[0052] Commonly used adhesives in this field can be used in this application. These adhesives include, but are 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 fluororubber.

[0053] In some embodiments, the surfactant includes at least one of sodium carboxymethyl cellulose, lithium carboxymethyl cellulose, sodium dodecylbenzene sulfonate, sodium dodecyl sulfate, alkyl glucoside, quaternary ammonium compounds, 1,3-butanediol, and n-octanol.

[0054] In some embodiments, the particle size D of the active material V50 The diameter is 3–20 μm, D V50 This refers to the particle size corresponding to when the cumulative volume of the active material reaches 50%. Within this particle size range, the electrode can achieve higher density while maintaining good appearance.

[0055] In some embodiments, the current collector may be at least one of the following commonly used in the art: copper foil, aluminum foil, copper mesh, aluminum mesh, aluminum foil coated with a conductive carbon layer, copper foil coated with a conductive carbon layer, polymer film coated with aluminum, polymer film coated with copper, and conductive polymer film.

[0056] An embodiment of this application also provides a secondary battery, including positive / negative electrodes prepared from the above-described negative electrode sheet, a separator, and an electrolyte.

[0057] Embodiments of this application also provide an electrical device including the secondary battery.

[0058] The following are specific embodiments of this application, and the technical solutions of this application are further described in conjunction with the embodiments. However, this application is not limited to these embodiments. Unless otherwise specified, the reagents, methods, and equipment used in this application are all conventional reagents, methods, and equipment in this technical field.

[0059] Example 1

[0060] This embodiment provides a negative electrode sheet, the preparation method of which includes the following steps:

[0061] A double-layer coating machine was used to coat the first and second active layer slurries onto one side of the current collector copper foil. After drying, the same coating operation was performed on the other side of the copper foil. After coating, the foil was dried at 90-110℃ and then rolled to obtain a compaction density of 1.6 g / cm³. 3 The composite negative electrode sheet, structural schematic diagram is as follows: Figure 1 As shown, Figure 2 This is a photograph of the negative electrode sheet prepared in this embodiment. Figure 3 This is the negative electrode sheet after winding.

[0062] The upper die head of the double-layer coating machine is coated with the second active layer slurry, and the lower die head is coated with the first active layer slurry. The upper and lower dies are coated simultaneously.

[0063] The first active layer slurry is composed of 94% carbon-coated silica (D... V50 =5μm, specific capacity 450mAh / g), 3% Super P (conductive carbon black), 1.5% CMC activator (sodium carboxymethyl cellulose), 1.5% binder (styrene-butadiene rubber), mixed with water to obtain a first active layer slurry with a solid content of 40wt%. After being uniformly coated onto the surface of the current collector, the O / C molar ratio M1 on the surface of the active layer was measured to be 0.50.

[0064] The composition of the second active layer slurry is: 94% graphite (D V50 =5μm, specific capacity 350mAh / g), 3% Super P (conductive carbon black), 1.5% CMC activator (sodium carboxymethyl cellulose), 1.5% binder (styrene-butadiene rubber), mixed with water to obtain a second active layer slurry with a solid content of 50wt%. After being uniformly coated onto the surface of the current collector, the O / C molar ratio M2 of the active layer surface was measured to be 0.435.

[0065] Other parameters are detailed in Table 1.

[0066] Examples 2-11, Comparative Examples 1-2

[0067] A series of negative electrode sheets are provided and prepared according to the steps of Example 1. The difference from Example 1 is that the parameters of the active material in the active layer (such as changing the O / C molar ratio on the surface of the active material by changing the proportion of raw materials in the active slurry layer) or the coating parameters are changed to prepare negative electrode sheets with parameters as shown in Table 1.

[0068] Table 1 Parameters of the negative electrode sheet

[0069]

[0070] The performance of the negative electrode sheets obtained in the above embodiments and comparative examples was tested. The specific test items, test methods, and results are as follows:

[0071] 1. Bulging test after winding: The negative electrode sheet is wound up (thickness radius exceeds 10cm). 17 points are taken longitudinally (along the coating direction) at the bulging position. The maximum and minimum values ​​are removed from these 17 points, and the average value of the remaining 15 points is taken. The difference d (μm) between this thickness and the thickness of the normal area is recorded.

[0072] 2. Impact on battery performance: The electrodes (identified as negative electrodes based on the active material) and medium-nickel LiNi electrodes prepared in the above examples and comparative examples were compared. 0.6 Co 0.1 Mn 0.3 The O2 positive electrode sheet (maintaining an N / P ratio of 1.13) and PP separator are assembled into a square shell (MEB square shell, T*W*H is 33*220*110mm). After winding the same number of layers, the lithium-ion battery is obtained through processes such as electrolyte injection (electrolyte: 1mol / L lithium hexafluorophosphate solution, solvent is ethylene carbonate (EC): methyl ethyl carbonate (EMC) = 3:7 (V / V) mixture), formation, aging, and sealing. The obtained lithium-ion battery is then tested using the Xinwei Power Battery Testing System. A 0.5A charge-discharge test was performed. The battery was charged and discharged at a 1C current. When the battery terminal voltage reached the charging limit voltage of 4.2V, the charging was switched to constant voltage charging until the charging current was less than or equal to 1 / 20C. Charging was then stopped and the battery was left to stand for 0.5h to 1h. Then, the battery was discharged at a 1C current to the termination voltage of 2.75V. After the discharge was completed, the battery was left to stand for 0.5h to 1h before the next charge-discharge cycle was performed. The number of cycles at room temperature (25℃) to 80% capacity retention (80% SOH) was recorded. The test results are shown in Table 2.

[0073] Table 2 Performance Test Results

[0074]

[0075] The results above show that:

[0076] In a double-coated negative electrode sheet, when the parameters of the two coating layers satisfy the relationship of this application, the appearance performance of the electrode sheet can be significantly improved, thereby enabling the prepared battery to have good cycle performance.

[0077] The negative electrode sheet that meets the above conditions of this application has good appearance and cycle performance, with bulge thickness of 2.5 μm or less; the number of cycles to 80% SOH is more than 1200 cycles, and can be as high as 2653 cycles.

[0078] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of this application and are not intended to limit the scope of protection of this application. Although this application has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of this application without departing from the substance and scope of the technical solutions of this 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, characterized in that, The negative electrode sheet satisfies the following relationship: 0.70≤(M1*H1) / (M2*H2)≤1.5; Where M1 represents the molar ratio of O to C elements in the surface elements of the first active layer; M2 represents the molar ratio of O to C elements in the surface elements of the second active layer; H1μm represents the thickness of the first active layer; H2μm represents the thickness of the second active layer; M1 is not equal to M2; 0.01≤M1≤0.5; 0.01≤M2≤0.

5.

2. The negative electrode sheet according to claim 1, characterized in that, The value of H1 is 10μm≤H1≤200μm.

3. The negative electrode sheet according to claim 1, characterized in that, The value of H2 is 10μm≤H2≤200μm.

4. The negative electrode sheet according to claim 1, characterized in that, The negative electrode sheet satisfies: 1.0≤(M1*H1) / (M2*H2)≤1.

2.

5. The negative electrode sheet according to claim 1, characterized in that, In the negative electrode sheet, the first active layer and the second active layer each independently include 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.

6. The negative electrode sheet according to claim 5, characterized in that, At least one of the following conditions must be met: 1) The active material includes at least one of silicon-carbon composite materials and carbon materials; 2) The conductive agent includes at least one of conductive carbon black, conductive graphite, carbon nanotubes, metal powder, and carbon fiber; 3) The adhesive includes 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 fluororubber; 4) The surfactant includes at least one of sodium carboxymethyl cellulose, lithium carboxymethyl cellulose, sodium dodecylbenzene sulfonate, sodium dodecyl sulfate, alkyl glucoside, quaternary ammonium compounds, 1,3-butanediol, and n-octanol; 5) The particle size D of the active material V50 The diameter is 3~20μm, D V50 This refers to the particle size corresponding to when the cumulative volume of the active material reaches 50%.

7. The negative electrode sheet according to claim 6, characterized in that, The silicon-carbon composite material includes carbon-coated silicon suboxide.

8. The negative electrode sheet according to claim 6, characterized in that, The conductive carbon black includes at least one of acetylene black and Ketjen black.

9. A secondary battery, characterized in that, Includes the negative electrode sheet as described in any one of claims 1 to 8.

10. An electrical appliance, characterized in that, Includes the secondary battery as described in claim 9.

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