A negative electrode sheet and a secondary battery
By designing differentiated active material layers in the negative electrode of lithium-ion batteries and adjusting the silicon content and binder ratio, the problems of volume expansion and insufficient power caused by silicon active materials were solved, resulting in batteries with high energy density and high power performance.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Patents(China)
- Current Assignee / Owner
- HUIZHOU LIWINON NEW ENERGY TECH CO LTD
- Filing Date
- 2022-08-30
- Publication Date
- 2026-06-05
Smart Images
Figure CN115360328B_ABST
Abstract
Description
Technical Field
[0001] This invention belongs to the field of secondary battery technology, and particularly relates to a negative electrode sheet and a secondary battery. Background Technology
[0002] Lithium-ion batteries, with their high energy density and fast charging capabilities, have been widely used in digital products and power supplies. However, with continuous technological upgrades, the energy density of lithium-ion batteries has reached its limit. Industrialized silicon anode materials are increasingly being used in commercial lithium-ion batteries. However, silicon active materials have a drawback: they are prone to volume expansion during charging and discharging, which affects battery performance. Furthermore, the use of silicon active materials requires the cooperation of binders; otherwise, insufficient power may occur. Therefore, a technical solution to address these issues is urgently needed. Summary of the Invention
[0003] The purpose of this invention is to address the shortcomings of existing technologies by providing a negative electrode sheet with a first active material layer and a second active material layer, wherein the materials in the first active material layer and the content of the materials in the second active material layer are different, thereby achieving a differentiated design to balance the insufficient battery dynamics under high silicon content and the problem of easy volume expansion during fast charging when the silicon content is high.
[0004] To achieve the above objectives, the present invention adopts the following technical solution:
[0005] A negative electrode sheet includes a negative current collector, a first active material layer disposed on at least one side of the negative current collector, and a second active material layer disposed on the side of the first active material layer away from the negative current collector. The first active material layer includes a binder and a first active material containing silicon, and the first active material layer satisfies the following relationship: 3≤M1 / 10000 / D1≤4, and 2≤A1 / B1≤2.5; the second active material layer includes a binder and a second active material containing silicon, and the second active material layer satisfies the following relationship: 3.5≤M2 / 10000 / D2≤5, and 1.5≤A2 / B2≤2.5; and A1≥A2; wherein,
[0006] D1 is the average particle size of the first active material layer, in μm;
[0007] M1 is the molecular weight of the binder in the first active material layer;
[0008] A1 represents the silicon content in the first active material layer;
[0009] B1 represents the content of the binder in the first active material layer;
[0010] D2 is the average particle size of the second active material layer, in μm;
[0011] M2 is the molecular weight of the binder in the second active material layer;
[0012] A2 represents the silicon content in the second active material layer;
[0013] B2 represents the content of the binder in the second active material layer.
[0014] Preferably, the first active material layer satisfies the following relationship: 3≤M1 / 10000 / D1≤4, 2≤A1 / B1≤2.5.
[0015] Preferably, the second active material layer satisfies the following relationship: 3.5≤M2 / 10000 / D2≤5, 1.5≤A2 / B2≤2.5.
[0016] Preferably, A1 > A2.
[0017] Preferably, the silicon content in the first active material layer satisfies: 5% ≤ Al ≤ 20%.
[0018] Preferably, the average particle size in the first active material layer satisfies: 15μm≤D1≤30μm.
[0019] Preferably, the molecular weight of the binder in the first active material layer is 700,000 to 1,000,000.
[0020] Preferably, the silicon content in the second active material layer satisfies: 1% ≤ A2 ≤ 10%.
[0021] Preferably, the average particle size in the second active material layer satisfies: 10μm≤D2≤20μm.
[0022] Preferably, the molecular weight of the binder in the second active material layer is 600,000 to 900,000.
[0023] The purpose of this invention is to provide a secondary battery that addresses the shortcomings of existing technologies, has high energy density, low volume expansion after multiple charge-discharge cycles, high rate capability, and can provide high power.
[0024] To achieve the above objectives, the present invention adopts the following technical solution:
[0025] A secondary battery includes a positive electrode, a separator, a negative electrode, an electrolyte, and a housing. The separator separates the positive electrode and the negative electrode, and the housing encapsulates the positive electrode, the separator, the negative electrode, and the electrolyte. The negative electrode is the aforementioned negative electrode.
[0026] positive electrode
[0027] The positive electrode includes a positive current collector and a positive active material layer disposed on at least one surface of the positive current collector. The positive active material layer includes a positive active material, which may be, but is not limited to, a chemical formula such as Li. a Ni x Co y M z O 2-b N b (where 0.95≤a≤1.2, x>0, y≥0, z≥0, and x+y+z=1, 0≤b≤1, M is selected from one or more combinations of Mn and Al, and N is selected from one or more combinations of F, P, and S) The positive electrode active material may also be, but is not limited to, LiCoO2, LiNiO2, LiVO2, LiCrO2, LiMn2O4, LiCoMnO4, Li2NiMn3O8, LiNi 0.5 Mn 1.5 The positive electrode active material can be one or more combinations thereof, including O4, LiCoPO4, LiMnPO4, LiFePO4, LiNiPO4, LiCoFSO4, CuS2, FeS2, MoS2, NiS, and TiS2. The positive electrode active material can also be modified. Methods for modifying the positive electrode active material are known to those skilled in the art. For example, coating, doping, and other methods can be used to modify the positive electrode active material. The materials used for modification can be one or more combinations thereof, including but not limited to Al, B, P, Zr, Si, Ti, Ge, Sn, Mg, Ce, and W. The positive electrode current collector is typically a structure or component that collects current. The positive electrode current collector can be any material suitable for use as a positive electrode current collector in lithium-ion batteries. For example, the positive electrode current collector can be, but is not limited to, metal foil, and more specifically, aluminum foil.
[0028] negative electrode
[0029] The negative electrode current collector is typically a structure or component that collects current. The negative electrode current collector can be any material suitable for use as a negative electrode current collector in lithium-ion batteries. For example, the negative electrode current collector can be, but is not limited to, metal foil, and more specifically, copper foil.
[0030] electrolyte
[0031] The lithium-ion battery also includes an electrolyte, which comprises an organic solvent, an electrolyte lithium salt, and additives. The electrolyte lithium salt can be LiPF6 and / or LiBOB used in high-temperature electrolytes; it can also be at least one of LiBF4, LiBOB, and LiPF6 used in low-temperature electrolytes; it can also be at least one of LiBF4, LiBOB, LiPF6, and LiTFSI used in overcharge-resistant electrolytes; or it can be at least one of LiClO4, LiAsF6, LiCF3SO3, and LiN(CF3SO2)2. The organic solvent can be a cyclic carbonate, including PC and EC; it can also be a chain carbonate, including DFC, DMC, or EMC; or it can be a carboxylic acid ester, including MF, MA, EA, MP, etc. The additives include, but are not limited to, at least one of film-forming additives, conductive additives, flame-retardant additives, overcharge-resistant additives, additives for controlling the H2O and HF content in the electrolyte, additives for improving low-temperature performance, and multifunctional additives.
[0032] The separator can be any material suitable for lithium-ion battery separators in the art, such as, but not limited to, one or more of polyethylene, polypropylene, polyvinylidene fluoride, aramid, polyethylene terephthalate, polytetrafluoroethylene, polyacrylonitrile, polyimide, polyamide, polyester, and natural fibers.
[0033] Preferably, the shell is made of stainless steel or aluminum-plastic film. More preferably, the shell is made of aluminum-plastic film.
[0034] Compared with the prior art, the beneficial effects of the present invention are as follows: the relationship between the molecular weight and silicon particles of the negative electrode sheet of the present invention can achieve precise composition design; on the one hand, it can match the particle size and content of the binder with that of silicon, so that the kinetics in the system are guaranteed and there will be no problem of excessive binder affecting the kinetics; at the same time, it can also ensure that the amount of binder is sufficient and ensure that the expansion of the system is within the required range of the product. Attached Figure Description
[0035] Figure 1 This is a schematic diagram of the structure of the present invention.
[0036] Among them, 1. First active material layer; 2. Second active material layer; 3. Negative electrode current collector. Detailed Implementation
[0037] The present invention will be further described in detail below with reference to specific embodiments and accompanying drawings, but the embodiments of the present invention are not limited thereto.
[0038] A negative electrode sheet of the present invention includes a negative current collector 3, a first active material layer 1 disposed on at least one side of the negative current collector 3, and a second active material layer 2 disposed on the side of the first active material layer 1 away from the negative current collector 3. The first active material layer 1 includes a binder and a first active material containing silicon, and the first active material layer 1 satisfies the following relationship: 3≤M1 / 10000 / D1≤4, and 2≤A1 / B1≤2.5; the second active material layer 2 includes a binder and a second active material containing silicon, and the second active material layer 2 satisfies the following relationship: 3.5≤M2 / 10000 / D2≤5, and 1.5≤A2 / B2≤2.5; and A1≥A2; wherein,
[0039] D1 is the average particle size of the first active material layer 1, in μm;
[0040] M1 is the molecular weight of the binder in the first active material layer 1;
[0041] A1 represents the content of silicon in the first active material layer 1;
[0042] B1 represents the content of the binder in the first active material layer 1;
[0043] D2 is the average particle size of the second active material layer 2, in μm;
[0044] M2 is the molecular weight of the binder in the second active material layer 2;
[0045] A2 represents the content of silicon in the second active material layer 2;
[0046] B2 represents the content of the binder in the second active material layer 2.
[0047] The first active material layer 1 contains a high silicon content, providing the battery with a high capacity. The second active material layer 2 uses silicon with a smaller particle size, giving the cell better kinetic performance. This invention designs the binder composition by matching the silicon compound content and particle size, achieving optimal binder values in the upper and lower electrode layers, thus obtaining superior performance. This invention uses a higher silicon content in the first active material layer 1 and a lower silicon content in the second active material layer 2, which is beneficial for adhesion and lithium-ion conduction. Simultaneously, setting M1 / 10000 / D1 within a certain range keeps the particles at a certain size, providing more bonding active sites, enabling the battery to have both good kinetic and cycle performance. By matching the silicon compound content and particle size to design the binder composition, optimal binder values in the upper and lower electrode layers are achieved, resulting in superior performance.
[0048] In some embodiments, the first active material layer 1 satisfies the following relationships: 3 ≤ M1 / 10000 / D1 ≤ 4, 2 ≤ A1 / B1 ≤ 2.5. In the formula M1 / 10000 / D1, if the value is too large, the particles are too small, resulting in fewer binding active sites and insufficient adhesion; if the value is too small, there are too many active sites, and the large particles cannot provide a binding effect, thus affecting kinetic performance. In the formula A1 / B1, if the value is too large, it indicates a high silicon content and insufficient binder, resulting in weak adhesion; if the value is too low, it indicates a low silicon content and excessive binder, reducing kinetics and causing unnecessary waste.
[0049] In some embodiments, the second active material layer 2 satisfies the following relationships: 3.5 ≤ M2 / 10000 / D2 ≤ 5, 1.5 ≤ A2 / B2 ≤ 2.5. In the formula M2 / 10000 / D2, if the value is too large, the particles are too small, resulting in fewer binding active sites and insufficient adhesion; if the value is too small, there are too many active sites, and the particles are too large to provide adequate binding, thus affecting kinetic performance. In the formula A2 / B2, if the value is too large, it indicates a high silicon content and insufficient binder, resulting in weak adhesion; if the value is too low, it indicates a low silicon content and excessive binder, reducing kinetics and causing unnecessary waste.
[0050] In some embodiments, A1>A2. Silicon affects the kinetics and expansion of the cell, so the silicon content in the first active material layer 1 needs to be greater than the silicon content in the second active material layer 2, which is beneficial for adhesion and lithium-ion conduction.
[0051] In some embodiments, the silicon content in the first active material layer 1 satisfies: 5% ≤ Al ≤ 20%. Preferably, the value of Al is 5%, 10%, 12%, 15%, 16%, 18%, or 20%.
[0052] In some embodiments, the average particle size in the first active material layer 1 satisfies: 15μm≤D1≤30μm. The average particle size of the first active material layer 1 is 15μm, 17μm, 18μm, 19μm, 20μm, 22μm, 23μm, 25μm, 27μm, 28μm, or 30μm.
[0053] In some embodiments, the molecular weight of the binder in the first active material layer 1 is 700,000 to 1,000,000. Preferably, the molecular weight of the binder in the first active material layer 1 is 700,000, 750,000, 800,000, 850,000, 900,000, 950,000, or 1,000,000.
[0054] In some embodiments, the silicon content in the second active material layer 2 satisfies: 1% ≤ A2 ≤ 10%. Preferably, the silicon content A2 in the second active material layer 2 is 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, or 10%. By setting a certain silicon content, the second active material layer can have both high energy and low volume expansion.
[0055] In some embodiments, the average particle size in the second active material layer 2 satisfies: 10 μm ≤ D2 ≤ 20 μm. Preferably, the average particle size D2 in the second active material layer 2 is 10 μm, 11 μm, 12 μm, 13 μm, 14 μm, 15 μm, 16 μm, 17 μm, 18 μm, 19 μm, or 17 μm.
[0056] In some embodiments, the molecular weight of the binder in the first active material layer 1 is 600,000 to 900,000. Preferably, the molecular weight of the binder is 600,000, 650,000, 700,000, 750,000, 800,000, 850,000, or 900,000.
[0057] A secondary battery with high energy density, low volume expansion after multiple charge-discharge cycles, high rate capability, and the ability to provide high power.
[0058] Example 1
[0059] Positive electrode sheet: The positive electrode active material LiCoO2, conductive agent acetylene black, conductive carbon nanotubes, and binder polyvinylidene fluoride (PVDF) are fully dispersed and uniformly coated onto an aluminum current collector in an N-methylpyrrolidone solvent system at a weight ratio of 97.8:0.6:0.4:1.2, and then cold-pressed into strips to obtain the positive electrode sheet.
[0060] Negative electrode sheet: A first negative electrode active material, conductive agent, and binder are mixed in a weight ratio of 97:0.5:2.5 to prepare a first negative electrode active material slurry; a second negative electrode active material, conductive agent, and binder are mixed in a weight ratio of 97.6:0.8:1.6 to prepare a second negative electrode active material slurry. The first active material slurry is coated onto a copper current collector to obtain a bottom first active material layer 1. Then, the second active material slurry is coated onto the first active material layer 1 to obtain an upper active material layer. The layers are then cold-pressed and slit to obtain the negative electrode sheet, as shown below. Figure 1 As shown.
[0061] Separator: A ceramic mixture is coated on the PE surface to serve as a separator.
[0062] Electrolyte: Ethyl carbonate (EC), propylene carbonate (PC), diethyl carbonate (DEC), and propyl propionate (PP) are mixed in a volume ratio of 1:1:4:4. Then, fully dried lithium salt LiPF6 is dissolved in the mixed organic solvent at a ratio of 1 mol / L to prepare the electrolyte.
[0063] Full cell fabrication: The positive electrode sheet, separator, and negative electrode sheet are wound or stacked to form a bare cell, which is then packaged and injected with electrolyte to produce a finished lithium-ion battery.
[0064] The secondary batteries of Examples 1-6 and Comparative Examples 1-3 were prepared in a similar manner to those of Example 1. The main difference was that the design of the negative electrode sheet adopted the design method and comparative method of the present invention.
[0065] Table 1 shows the negative electrode design parameters for all embodiments and comparative examples.
[0066]
[0067]
[0068] The secondary batteries prepared in Examples 1-6 and Comparative Examples 1-3 were subjected to adhesion force tests, capacity decay rate tests, and cyclic expansion tests. The test results are recorded in Table 2.
[0069] Adhesion strength: The electrode adhesion strength is tested on a high-speed rail tensile testing machine. The electrode is attached to the material surface with high-viscosity yellow adhesive, then one side is fixed and the other side is pulled with a clamp. The reading is taken when the equipment is stable.
[0070] Cycle decay rate: The cycle decay rate is the percentage of the cell's capacity remaining after 800 cycles of charging from 2.8C to 4.2V and then charging at a 1.8C rate to the cutoff voltage.
[0071] Cyclic expansion rate: At 25°C, the lithium-ion battery was charged at a constant current of 1C to 4.45V, then charged at a constant voltage to a current of 0.05C, and then discharged at a constant current of 1C to 3.0V. This constitutes the first cycle. The lithium-ion battery was subjected to 200 cycles under the above conditions. The electrode thickness before and after cycling was measured using a micrometer. The electrode thickness expansion rate was calculated using the following formula: Electrode thickness expansion rate = [(Thickness after cycling - Thickness before cycling) / Thickness before cycling] × 100%.
[0072] Table 2 shows the performance parameters for all embodiments and comparative examples.
[0073] Case Adhesion force / N Capacity decay rate / % Cyclic expansion / % Example 1 25.5 88 6.8 Example 2 23.3 82 8.8 Example 3 22.8 85 8.3 Example 4 22.6 83 9.6 Example 5 22 82 9.8 Example 6 22 81 9.8 Comparative Example 1 28 76 12.0 Comparative Example 2 16 73 15.6 Comparative Example 3 14 72 19.8
[0074] As shown in Tables 1 and 2, insufficient bonding force in the battery cell leads to abnormal expansion during cycling, thus affecting cycle performance. Conversely, excessive bonding force also affects the cell's kinetics; insufficient kinetics result in lithium plating, causing abnormal electrode thickness and impacting cell expansion. Therefore, this invention designs an electrode with optimized composition by combining the particle size of the active material and the molecular weight of the binder, thereby enabling the battery cell to possess excellent kinetic and cycling expansion performance.
[0075] Based on the disclosure and teachings of the foregoing specification, those skilled in the art can make changes and modifications to the above embodiments. Therefore, the present invention is not limited to the specific embodiments described above, and any obvious improvements, substitutions, or modifications made by those skilled in the art based on the present invention are within the scope of protection of the present invention. Furthermore, although some specific terms are used in this specification, these terms are only for convenience of explanation and do not constitute any limitation on the present invention.
Claims
1. A negative electrode sheet, characterized in that, The device includes a negative electrode current collector, a first active material layer disposed on at least one side of the negative electrode current collector, and a second active material layer disposed on the side of the first active material layer away from the negative electrode current collector. The first active material layer includes a binder and a first active material containing silicon, and the first active material layer satisfies the following relationship: 3≤M1 / 10000 / D1≤4, and 2≤A1 / B1≤2.5; the second active material layer includes a binder and a second active material containing silicon, and the second active material layer satisfies the following relationship: 3.5≤M2 / 10000 / D2≤5, and 1.5≤A2 / B2≤2.5; and A1>A2. The silicon content in the first active material layer satisfies: 5%≤A1≤20%, and the silicon content in the second active material layer satisfies: 1%≤A2≤10%. The molecular weight of the binder in the first active material layer is 700,000 to 1,000,000, 20≤D1≤30, and 10≤D2≤20. D1 is the average particle size of the first active material layer, in μm; M1 is the molecular weight of the binder in the first active material layer; A1 represents the silicon content in the first active material layer; B1 represents the content of the binder in the first active material layer; D2 is the average particle size of the second active material layer, in μm; M2 is the molecular weight of the binder in the second active material layer; A2 represents the silicon content in the second active material layer; B2 represents the content of the binder in the second active material layer.
2. The negative electrode sheet according to claim 1, characterized in that, The first active material layer satisfies the following relationship: 3≤M1 / 10000 / D1≤4, 2≤A1 / B1≤2.
5.
3. The negative electrode sheet according to claim 1, characterized in that, The second active material layer satisfies the following relationship: 3.5≤M2 / 10000 / D2≤5, 1.5≤A2 / B2≤2.
5.
4. The negative electrode sheet according to claim 1 or 3, characterized in that, The molecular weight of the binder in the second active material layer is 600,000 to 900,000.
5. A secondary battery, characterized in that, The device includes a positive electrode, a separator, a negative electrode, an electrolyte, and a housing. The separator is used to separate the positive electrode and the negative electrode, and the housing is used to encapsulate the positive electrode, the separator, the negative electrode, and the electrolyte. The negative electrode is the negative electrode as described in any one of claims 1-4.