Nickel foil, preparation method thereof and secondary battery

Abstract

The invention relates to a nickel foil, a preparation method thereof and a secondary battery. The thickness of the nickel foil ranges from 5.5 micrometers to 6.5 micrometers, blind holes are distributed in one side of the nickel foil, the face of the side, where the blind holes are distributed, of the nickel foil in the thickness direction is a blind hole face, the face of the other side of the nickel foil is a smooth face, each blind hole is of a pit-shaped structure which does not penetrate through the nickel foil, the maximum height Rz of the contour of each blind hole face is larger than 3 micrometers, and the maximum height Rz of the contour of each blind hole face is larger than 5 micrometers. The maximum height Rz of the contour of the smooth surface is 2.5 [mu] m or less, and the nickel foil is not provided with a through hole.

Description

TECHNICAL FIELD

[0001] The present application relates to a nickel foil and a preparation method thereof, and a secondary battery, and belongs to the technical field of secondary battery electrode materials. BACKGROUND

[0002] Metal foils with pore structures as current collector core materials play a crucial role in modern lithium battery systems, and their performance directly determines the energy density, cycle life and rate characteristics of the battery. With the rapid growth of demand for high energy density batteries for new energy vehicles and portable electronic devices, developing electrode current collectors with high specific surface area and excellent mechanical integrity has become a key technical path for industrial progress. Among the many candidate materials, nickel foils with pore structures are considered as a potential replacement for copper foils due to their excellent electrical conductivity (resistivity of only 6.84 μΩ·cm), intrinsic oxidation resistance and high mechanical strength (tensile strength of more than 800 MPa).

[0003] However, for the next generation of batteries that pursue extreme energy density and safety, nickel foils with through-hole structures in the pore structure have the following inherent technical defects:

[0004] 1. Conflict between structural strength and porosity: Through holes seriously damage the continuity of the foil, resulting in a sharp decrease in tensile strength and bending fatigue life with increasing porosity. High-porosity (>50%) through-hole structures are prone to collapse and fracture during electrode rolling and battery cycling.

[0005] 2. Interface stability challenge: The combination of through-hole walls and active materials is mostly limited to physical adsorption. Under long-term charge and discharge stress, active materials are prone to fall off along the through direction of the through hole, leading to capacity decay.

[0006] 3. Safety risk: Through-hole channels provide a direct path for lithium dendrite growth to the opposite electrode, increasing the risk of battery short circuit. Especially under fast charging conditions, lithium metal is more likely to deposit unevenly in the channel, forming dendrites.

[0007] Currently, the demand for ultra-thin porous metal foils has shifted from simply "high porosity" to a deeper requirement for "precise control of pore structure". Therefore, developing an ultra-thin nickel foil preparation technology that can synergistically optimize mechanical strength, interface stability and safety has become an urgent need to break through the current bottleneck of high energy density lithium batteries. SUMMARY

[0008] Problem to be solved by the invention

[0009] When nickel foil is used as a current collector, thinning the foil and introducing a porous structure can increase the loading of active material, thereby improving the battery's energy density. However, ultra-thin nickel foil with a porous structure is prone to problems such as insufficient mechanical strength, poor interface stability, and high safety risks, especially ultra-thin nickel foil with through holes. Therefore, it is difficult to simultaneously improve battery energy density and enhance mechanical strength, interface stability, and safety performance.

[0010] To solve the above-mentioned technical problems, the inventors discovered that when the thickness of the nickel foil is reduced to 5.5-6.5μm, if the specific surface area can be increased by more than 50% by using a single-sided blind hole structure while maintaining the structural compactness, the loading of active material can be increased by more than 20% without significantly increasing the interfacial resistance, while completely eliminating the risk of dendrite penetration caused by the channel penetration.

[0011] Based on the above, one objective of the present invention is to provide a nickel foil with a thickness of 5.5-6.5 μm, which has a single-sided blind hole structure with high roughness and no through holes, thereby improving the loading of active material while also improving structural strength and interface stability, and significantly reducing the risk of dendrite penetration caused by through holes.

[0012] Another objective of this invention is to provide a secondary battery in which the nickel foil of this invention is used as the negative electrode current collector, thereby improving the battery's energy density while also improving mechanical strength, interface stability, and safety performance.

[0013] Another objective of this invention is to provide a method for preparing nickel foil that uses "electrodeposition-reverse electro-etching", which simplifies the preparation process, precisely controls the pore structure, and the resulting nickel foil has single-sided blind holes, which can increase the loading of active material, while also improving mechanical strength, interface stability, and safety performance.

[0014] Solution to the problem

[0015] [1] A nickel foil having a thickness of 5.5-6.5 μm,

[0016] The nickel foil has blind holes distributed on one side, wherein the side with the blind holes distributed in the thickness direction of the nickel foil is the blind hole side, and the other side is a smooth surface.

[0017] The blind hole refers to a pit-like structure that does not penetrate the nickel foil.

[0018] The maximum height Rz of the blind hole surface is 3 μm or more.

[0019] The maximum height Rz of the smooth surface profile is less than 2.5 μm.

[0020] The nickel foil does not have through holes.

[0021] [2] According to the nickel foil described in [1], wherein,

[0022] The maximum height Rz of the blind hole surface profile is less than 5 μm; and / or

[0023] The arithmetic mean deviation Ra of the blind hole surface profile is greater than 0.285 μm and less than 0.5 μm; and / or

[0024] The gloss level of the blind aperture surface is above 30 Gu and below 100 Gu; and / or

[0025] The elongation of the nickel foil is 2.5-3.5%; and / or

[0026] The tensile strength of the nickel foil is ≥1000MPa.

[0027] [3] According to the nickel foil described in [1] or [2], wherein,

[0028] The nickel foil has a nickel content of 90.0 wt% or more; and / or

[0029] The nickel foil has a single-layer structure.

[0030] [4] The nickel foil according to [1] or [2], wherein,

[0031] The maximum height Rz of the smooth surface profile is 1 μm or more; and / or

[0032] The arithmetic mean deviation Ra of the smooth surface profile is greater than 0.1 μm and less than 0.300 μm.

[0033] [5] A secondary battery comprising: a positive electrode, a negative electrode including a negative electrode current collector and a negative electrode active layer, a separator separating the positive electrode and the negative electrode, and an electrolyte.

[0034] The negative electrode current collector is any one of [1] to [4] nickel foil.

[0035] [6] A method for preparing nickel foil according to any one of [1] to [4], comprising the following steps:

[0036] Step 1: Place both the deposition anode and deposition cathode in the electrolyte for electrodeposition, thereby electrodepositing the initial nickel foil onto the deposition cathode.

[0037] The electrolyte contains: Ni at a concentration of 50-90 g / L. 2+ Boric acid with a concentration of 30-60 g / L, and Cl with a concentration of 100-400 mg / L -Buffers with a concentration of 4-10 g / L and pore regulators with a concentration of 40-100 mg / L,

[0038] The buffer is selected from one or more of the group consisting of sodium acetate and sodium tartrate;

[0039] Step 2: Using the deposition cathode with the initial nickel foil obtained in Step 1 as the etching anode, both the etching anode and the etching cathode are placed in the etching solution, and a current density of 1-5 A / dm is applied. 2 The charge per unit area is 10-120 C / dm² 2 Electro-etching creates blind holes on the side of the initial nickel foil that does not contact the etching anode in the thickness direction, thereby obtaining a nickel foil attached to the etching anode.

[0040] The etching solution contains an acid, which is any one of the following (i) to (iii):

[0041] (i) Sulfuric acid, with a concentration of 5-12 wt% based on the total weight of the etching solution.

[0042] (ii) Sulfamic acid, with a concentration of 5-15 wt% based on the total weight of the etching solution.

[0043] (iii) A combination of sulfuric acid and aminosulfonic acid, with the concentrations of sulfuric acid and aminosulfonic acid each independently ranging from 5 to 15 wt% based on the total weight of the etching solution;

[0044] Step 3: Remove the nickel foil obtained in Step 2 from the etching anode.

[0045] [7] According to the method for preparing nickel foil described in [6], wherein the pore control agent is selected from one or more of the group consisting of polyethylene glycol, sodium dihexyl succinate sulfonate, sodium dodecyl sulfate, sodium dodecylbenzene sulfonate and sodium dodecyl sulfonate.

[0046] [8] According to the method for preparing nickel foil as described in [6] or [7], wherein the electrolyte further comprises a grain refiner at a concentration of 30-100 mg / L.

[0047] The grain refiner is selected from one or more of the group consisting of thiourea, sodium polydithiopropane sulfonate, sodium saccharin, mercaptobenzothiazole, sodium polystyrene sulfonate, 3-mercaptopropionic acid, 2-mercaptopyridine, benzothione and hexamethylenetetramine.

[0048] [9] According to the method for preparing nickel foil as described in [6] or [7], wherein in step two, the current density of the electro-etching is 2-4 A / dm. 2 ; and / or etching time is 10-30s.

[0049]

[10] According to the method for preparing nickel foil as described in [6] or [7], wherein in step one, the current density of electrodeposition is 18-22 A / dm. 2 ; and / or the electrodeposition temperature is 35-60℃; and / or the pH value of the electrolyte is 2-5.

[0050] Effects of the invention

[0051] The nickel foil of the present invention can increase the loading of active materials while improving mechanical strength, interface stability and safety performance.

[0052] The secondary battery of the present invention uses the nickel foil of the present invention as the negative electrode current collector, which can improve the energy density of the battery while also improving mechanical strength, interface stability and safety performance.

[0053] The method for preparing nickel foil of the present invention, through "electrodeposition-reverse electro-etching", simplifies the preparation process, precisely controls the pore structure, and the resulting nickel foil can increase the loading of active material while improving mechanical strength, interface stability and safety performance. Attached Figure Description

[0054] Figure 1 This is a 1000x magnified SEM image of the side of the initial nickel foil obtained in step one of Example 1 that is not in contact with the cathode for deposition in the thickness direction.

[0055] Figure 2 The image is a 1000x magnified SEM image of the side of the nickel foil-pair I obtained in Comparative Example 1 that is not in contact with the etching anode in the thickness direction during the electro-etching process.

[0056] Figure 3 The image is a 5000x magnified SEM image of the side of the nickel foil-pair I obtained in Comparative Example 1 that is not in contact with the etching anode in the thickness direction during the electro-etching process.

[0057] Figure 4 This is a 1000x magnified SEM image of the side (blind hole side) of the nickel foil-I obtained in Example 1 that does not contact the etching anode in the thickness direction during the electro-etching process.

[0058] Figure 5 This is a 5000x magnified SEM image of the side (blind hole surface) of the nickel foil-I obtained in Example 1 that does not contact the etching anode in the thickness direction during the electro-etching process.

[0059] Figure 6This is a 10,000x magnified SEM image of the side (blind hole surface) of the nickel foil-I obtained in Example 1 that does not contact the etching anode in the thickness direction during the electro-etching process.

[0060] Figure 7 This is a 5000x magnified SEM image of the side (smooth surface) of the nickel foil-I obtained in Example 1 that is in contact with the etching anode in the thickness direction during the electro-etching process. Detailed Implementation

[0061] Various exemplary embodiments, features, and aspects of the present invention will be described in detail below. The term "exemplary" as used herein means "serving as an example, embodiment, or illustration." Any embodiment described herein as "exemplary" is not necessarily to be construed as superior to or better than other embodiments.

[0062] Furthermore, to better illustrate the present invention, numerous specific details are set forth in the following detailed embodiments. Those skilled in the art should understand that the present invention can be practiced without certain specific details. In other instances, methods, means, apparatus, and steps well known to those skilled in the art have not been described in detail in order to highlight the spirit of the present invention.

[0063] Unless otherwise stated, all units used in this specification are international standard units, and all numerical values ​​and ranges appearing in this invention should be understood to include systematic errors that are unavoidable in industrial production.

[0064] In this specification, the word "may" has two meanings: to perform a certain process and not to perform a certain process.

[0065] In this specification, references to "some specific / preferred embodiments," "other specific / preferred embodiments," "implementation," etc., refer to specific elements (e.g., features, structures, properties, and / or characteristics) related to that embodiment, which are included in at least one of the embodiments described herein and may or may not be present in other embodiments. Furthermore, it should be understood that these elements may be combined in any suitable manner in various embodiments.

[0066] In this specification, the range of values ​​referred to as “value A - value B” is the range that includes the endpoint values ​​A and B.

[0067] [Nickel foil]

[0068] One objective of this invention is to provide a nickel foil with a thickness of 5.5-6.5 μm. The nickel foil has blind holes distributed on one side, wherein the side with blind holes distributed in the thickness direction of the nickel foil is a blind hole surface, and the other side is a smooth surface. The blind hole refers to a pit-like structure that does not penetrate the nickel foil. The maximum outline height Rz of the blind hole surface is more than 3 μm, and the maximum outline height Rz of the smooth surface is less than 2.5 μm. The nickel foil does not have through holes.

[0069] The nickel foil of this invention is an ultra-thin nickel foil with a thickness of 5.5-6.5 μm. Its blind hole surface has a maximum profile height Rz of over 3 μm, exhibiting high roughness. Furthermore, a single-sided blind hole structure is formed by selectively etching away some surface material, achieving overall lightweighting of the foil. Compared to nickel foil of the same thickness without blind holes, this blind hole structure can effectively reduce the mass per unit area by 3% to 8%. This significantly reduces the mass proportion of the current collector in the battery, directly contributing to improving the battery's gravimetric energy density. It is noteworthy that this lightweighting is achieved through a single-sided blind hole structure on the blind hole surface, while the smooth surface maintains relative density with a maximum profile height Rz of less than 2.5 μm. This is entirely different from the lightweighting achieved by reducing the foil thickness or creating a high-porosity through-hole structure, the latter of which severely sacrifices the material's mechanical strength and conductive integrity. Therefore, the nickel foil of this invention achieves a balance between "lightweighting," "high strength," and "high interface stability."

[0070] The nickel foil of this invention features a blind-hole surface with high surface roughness (Rz≥3.0μm), synergistic optimization of lightweight (3%-8% reduction in mass per unit area) and high mechanical strength (tensile strength >1000MPa), and the mechanical interlocking effect of the blind holes significantly improves the electrode interface peel strength to over 25N / m. In summary, the nickel foil of this invention constructs a unique structure of "continuous dense substrate + single-sided micron-level blind holes," solving the technical problem of balancing high porosity and high strength in existing porous metal foils. This provides an ideal current collector solution for the development of next-generation high-energy-density, high-safety lithium batteries.

[0071] In one embodiment, the thickness of the nickel foil of the present invention can be 5.8-6.2 μm, preferably 6 μm. The maximum profile height Rz of the blind hole surface of the nickel foil can be 3 μm or more, 3.2 μm or more, 3.5 μm or more, or less than 5 μm or less than 4 μm. In the present invention, the maximum profile height Rz is measured according to ISO 4287 standard. When the maximum profile height Rz of the blind hole surface falls within the above range, the blind hole surface has a high roughness, thereby increasing the active material loading and giving it excellent active material anchoring ability.

[0072] In one embodiment, the arithmetic mean deviation Ra of the blind hole surface of the nickel foil of the present invention can be 0.285 μm or more, 0.300 μm or more, 0.320 μm or more, or less than 0.5 μm, less than 0.45 μm, or less than 0.4 μm. In the present invention, the arithmetic mean deviation Ra is measured according to ISO 4287 standard. The gloss of the blind hole surface of the nickel foil of the present invention can be 30 Gu or more, or less than 100 Gu, less than 90 Gu, or less than 85 Gu. In the present invention, the gloss is measured according to ASTM D523 standard. When the gloss and / or the arithmetic mean deviation Ra of the blind hole surface fall within the above ranges, the blind hole surface has a high roughness, which can further increase the specific surface area of ​​the nickel foil, increase the loading of active material, and give it a better active material anchoring ability.

[0073] In one embodiment, the elongation of the nickel foil of the present invention is preferably 2.5-3.5%, and can be 2.6-3.5%, or 2.7-3.5%. Preferably, both the transverse and longitudinal elongation are 2.5-3.5%. In one embodiment, the tensile strength of the nickel foil of the present invention is preferably 1000 MPa or more, more preferably 1100 MPa or more, and even more preferably 1200 MPa or more. The upper limit is not particularly limited; for example, it can be 2500 MPa or less, or 2000 MPa or less. Preferably, both the transverse and longitudinal tensile strength are 1000 MPa or more. The tensile strength and elongation of the nickel foil of the present invention refer to the average values ​​of the transverse and longitudinal tensile strength and elongation, respectively. When the tensile strength and / or elongation fall within the above ranges, the performance degradation is less compared to nickel foil without a porous structure, thus exhibiting excellent structural strength and safety performance.

[0074] In one embodiment, the nickel foil of the present invention may have a nickel content of 90.0 wt% or more, 95.0 wt% or more, or 98.0 wt% or more, and may also be a pure nickel foil with a nickel content of 99.0 wt% or more. In one embodiment, the nickel foil of the present invention may be doped with other elements, such as ≤2 wt% cobalt or ≤1 wt% molybdenum. The aforementioned doping elements replace the positions of nickel atoms in the face-centered cubic lattice to form a substitutional solid solution, thereby achieving crystal microstructure control at the atomic / lattice scale and improving conductivity.

[0075] In one embodiment, the nickel foil of the present invention can be a single-layer structure. A single-layer structure refers to a structure in which the internal structure and composition change continuously or remain unchanged, without interlayer interfaces.

[0076] In one embodiment, since the nickel foil of the present invention already possesses sufficient mechanical properties, it may not require a supporting substrate layer and / or a supporting composite layer. In this case, when used as a current collector in a secondary battery, it ensures the structural stability of the battery, reduces the mass ratio of the current collector thereby increasing the battery's energy density, and simplifies the battery manufacturing process. Here, "supportive" refers to the layer's function of supporting the physical structure and strength of the nickel foil. In one embodiment, the nickel foil of the present invention may not require a substrate layer and / or a composite layer. The substrate layer refers to a layered structure formed by bonding one or more other different materials to the nickel foil after its formation through physical lamination, coating, or subsequent composite processes. Specific examples of substrate layers include polymer substrate layers such as PET film and PI film; and metal foil substrate layers such as aluminum foil and copper foil. The composite layer refers to a layered structure with functional gradients in its microstructure, formed simultaneously in the same manufacturing process during the formation of the nickel foil. Specific examples of composite layers include diamond / copper composites, metal-ceramic gradient composites (such as Ti6Al4 / Al2O3), biomimetic gradient sinusoidal composites (BGS-CFRCs), and steel-glass fiber reinforced plastic (GFRP) gradient composite leaf spring systems.

[0077] In one embodiment, the sheet resistance of the nickel foil of the present invention can be ≤22mΩ / □ (four-point probe method, 20°C). When the sheet resistance of the nickel foil of the present invention is within the above range, its conductivity is strong, and when used as a current collector in a battery, it can reduce the internal resistance of the battery and improve the high-rate performance of the secondary battery.

[0078] In one embodiment, the maximum profile height Rz of the smooth surface of the nickel foil of the present invention can be 1 μm or more, 1.5 μm or more, 2.2 μm or less, or 2.1 μm or less. The arithmetic mean deviation Ra of the smooth surface profile can be 0.1 μm or more and 0.300 μm or less, 0.150 μm or more and 0.285 μm or less, or 0.200 μm or more and 0.280 μm or less. In the present invention, the arithmetic mean deviation Ra of the smooth surface profile can be smaller than that of the blind hole surface. By ensuring that the maximum profile height Rz and / or the arithmetic mean deviation Ra of the smooth surface profile fall within the above ranges, the smooth surface remains relatively dense, thereby imparting superior structural strength, interface stability, and safety performance. In one embodiment, the smooth surface of the nickel foil of the present invention does not have a blind hole structure.

[0079] [Rechargeable Battery]

[0080] One objective of this invention is to provide a secondary battery comprising: a positive electrode, a negative electrode including a negative electrode current collector and a negative electrode active layer, a separator separating the positive electrode and the negative electrode, and an electrolyte, wherein the negative electrode current collector is the nickel foil of this invention.

[0081] By using the nickel foil of the present invention as a current collector, when the active material is coated thereon, it can be fully filled into the blind holes to form a three-dimensional mechanical interlocking structure, with an interfacial peel strength ≥ 25 N / m, far exceeding that of traditional coated electrodes. Moreover, the blind hole structure guides the uniform deposition of lithium ions in the holes, resulting in a lithium nucleation overpotential ≤ 35 mV, effectively inhibiting dendrite growth. In particular, since the blind holes do not penetrate the current collector, the physical path for lithium dendrites to penetrate is blocked, improving the safety performance.

[0082] The secondary battery of the present invention is preferably, for example, a lithium secondary battery, a sodium secondary battery, or a sulfide all-solid-state battery, and further preferably a lithium secondary battery.

[0083] In the case where the secondary battery of the present invention is a lithium secondary battery, the details of each component of the battery are described as follows:

[0084] The aforementioned positive electrode includes a positive electrode current collector and a positive electrode active layer. The positive electrode current collector can be, for example, a metal foil formed of aluminum, stainless steel, titanium, etc. There is no particular limitation on the positive electrode active material included in the positive electrode active layer. For example, lithium composite oxides can be cited. As lithium composite oxides, for example, Li l CoO2, Li l NiO2, Li l MnO2, Li l Co m Ni 1-m O2, Li l Co m M 1-m O n 、Li l Ni 1-m M m O n 、Li l Mn2O4, Li l Mn 2-m M n O4 (in the above formulas, M represents at least one element selected from the group consisting of Na, Mg, Sc, Y, Mn, Fe, Co, Ni, Cu, Zn, Al, Cr, Pb, Sb, and B, 0 < l ≤ 1.2, 0 ≤ m ≤ 0.9, 2.0 ≤ n ≤ 2.3); specific examples of lithium composite oxides include LiNi 0.8 Co 0.1 Mn 0.1 O2.

[0085] The aforementioned negative electrode includes a negative electrode current collector and a negative electrode active layer. As the negative electrode active material included in the negative electrode active layer, for example, carbon materials such as natural graphite and artificial graphite can be cited, or silicon materials such as SiO a (0.05 < a < 1.95), etc.

[0086] Examples of the aforementioned electrolytes include: an electrolyte obtained using lithium hexafluorophosphate (LiPF6) as the lithium salt and carbonates such as ethylene carbonate (EC), ethyl methyl carbonate (EMC), and diethyl carbonate (DEC) as solvents; a specific example is LiPF6 / EC+EMC+DEC; the concentration of the lithium salt in the electrolyte is, for example, 0.5-2M, and can be 0.8-1.5M; the electrolyte may also optionally contain additives such as fluoroethylene carbonate and lithium difluorooxalate borate. In addition to the active material, the negative electrode active layer and the positive electrode active layer may also contain binders, conductive agents, solvents, additives, etc., as needed. Examples of the aforementioned separators include polyolefin separators such as polyethylene separators and polypropylene separators. The lithium secondary battery of the present invention is preferably a lithium-ion secondary battery.

[0087] In the case where the secondary battery of the present invention is a sodium secondary battery, the details of each battery component are as follows:

[0088] The aforementioned positive electrode includes a positive electrode current collector and a positive electrode active layer. Specific examples of the positive electrode current collector and separator are the same as in lithium-ion secondary batteries. Sodium composite oxides can be listed as positive electrode active materials included in the positive electrode active layer. For example, Na... x [Fe 1 / 2 Mn 1 / 2 O2, NaFePO4, Na3V2(PO4)3, etc.

[0089] Examples of negative electrode active materials included in the negative electrode active layer include hard carbon and soft carbon materials. Examples of electrolytes include those using sodium hexafluorophosphate (NaPF6) as the sodium salt and carbonates such as ethylene carbonate (EC), ethyl methyl carbonate (EMC), and diethyl carbonate (DEC) as solvents, wherein the concentration of the sodium salt in the electrolyte is, for example, 0.5-2M, and can be 0.8-1.5M. In addition to the active materials, the negative and positive electrode active layers may also contain binders, conductive agents, solvents, etc., as needed. The sodium secondary battery of the present invention is preferably a sodium-ion secondary battery.

[0090] In the case where the secondary battery of the present invention is a sulfide all-solid-state battery, the battery configuration is described in detail below:

[0091] The aforementioned diaphragm can be, for example, a dense solid electrolyte layer formed by the sulfide electrolyte itself, which simultaneously functions as both a diaphragm and an electrolyte. Examples of sulfide solid electrolytes include Li3PS4, Li6PS5X (X = Cl, Br, I), and Li... 10 GeP2S 12The negative electrode active material can be, for example, lithium metal, graphite, silicon-based materials, etc. The positive electrode current collector can be, for example, metal foil formed from aluminum, stainless steel, titanium, etc. The positive electrode active material layer can be, for example, a composite positive electrode active material layer formed by mixing NCM, LCO with solid electrolyte and conductive agent, etc.

[0092] In one specific embodiment, the secondary battery of the present invention comprises:

[0093] A positive electrode, a negative electrode, a ceramic-coated polyethylene porous membrane separating the positive and negative electrodes, and an electrolyte; the aforementioned positive electrode contains LiNi 0.83 Co 0.11 Mn 0.06 The positive electrode active layer of O2 and the aluminum foil serving as the positive electrode current collector; the aforementioned negative electrode contains a silicon-carbon composite material (SiO2). x The present invention comprises a negative electrode active layer (C) and a nickel foil as a negative electrode current collector; the electrolyte is in the form of EC+EMC+DEC (3:5:2 volume ratio) as solvent and contains 1.2M LiPF6 as lithium salt, and 5wt% fluoroethylene carbonate and 1wt% lithium difluorooxalate borate as additives.

[0094] [Methods for preparing nickel foil]

[0095] The method for preparing the nickel foil of the present invention includes the following steps:

[0096] Step 1: Place both the deposition anode and deposition cathode in the electrolyte for electrodeposition, thereby electrodepositing the initial nickel foil onto the deposition cathode.

[0097] The electrolyte contains: Ni at a concentration of 50-90 g / L. 2+ Boric acid with a concentration of 30-60 g / L, and Cl with a concentration of 100-400 mg / L - Buffers with a concentration of 4-10 g / L and pore regulators with a concentration of 40-100 mg / L,

[0098] The buffer is selected from one or more of the group consisting of sodium acetate and sodium tartrate;

[0099] Step 2: Using the deposition cathode with the initial nickel foil obtained in Step 1 as the etching anode, both the etching anode and the etching cathode are placed in the etching solution, and a current density of 1-5 A / dm is applied. 2 The charge per unit area is 10-120 C / dm² 2 Electro-etching creates blind holes on the side of the initial nickel foil that does not contact the etching anode in the thickness direction, thereby obtaining a nickel foil attached to the etching anode.

[0100] The etching solution contains an acid, which is any one of the following (i) to (iii):

[0101] (i) Sulfuric acid, with a concentration of 5-12 wt% based on the total weight of the etching solution.

[0102] (ii) Sulfamic acid, with a concentration of 5-15 wt% based on the total weight of the etching solution.

[0103] (iii) A combination of sulfuric acid and aminosulfonic acid, with the concentrations of sulfuric acid and aminosulfonic acid each independently ranging from 5 to 15 wt% based on the total weight of the etching solution;

[0104] Step 3: Remove the nickel foil obtained in Step 2 from the etching anode.

[0105] The nickel foil preparation method of this invention employs a composite process of "electrodeposition-reverse electro-etching," successfully constructing the unique structure of "continuous dense substrate + single-sided micron-level blind vias" described in the [nickel foil] section. This achieves high surface roughness, lightweight, high mechanical strength, high electrode interface peel strength, high interface stability, and high safety. The nickel foil preparation method of this invention offers strong controllability; by independently adjusting the electrodeposition and etching parameters, the density and depth of the blind via structure, as well as the surface roughness, can be precisely controlled to adapt to different application requirements.

[0106] The scope of protection of the nickel foil preparation method of the present invention covers any process improvement and structural optimization based on the core concept of "first depositing a dense layer, then etching to form a single-sided blind hole", including but not limited to the adjustment of the etching solution composition and the transformation of the electrodeposition waveform (such as pulse electroplating).

[0107] The following is a detailed description of each step in the preparation method of the nickel foil of the present invention.

[0108] (Step 1)

[0109] The deposition anode in this step can be, for example, coated titanium. Examples of coated titanium include ruthenium-iridium coated (RuO2-IrO2) titanium, iridium-tantalum coated (IrO2-Ta2O5-based) titanium, and iridium-tin coated (IrO2-SnO2) titanium. In one specific embodiment, an IrO2-SnO2 coated titanium mesh can be used. Preferably, the resulting deposition anode overpotential is ≤0.25V.

[0110] The cathode used for deposition in this step can be, for example, a titanium plate, such as a Gr1 grade industrial pure titanium plate. Preferably, the titanium plate is obtained through the pretreatment step described later.

[0111] The electrolyte used in this step can be water as a solvent. The following details the components and concentrations of the electrolyte.

[0112] Ni2+ Its concentration can be 50-90 g / L, preferably 60-80 g / L, more preferably 68-72 g / L, for example 70 g / L. In this invention, Ni... 2+ It can be provided by nickel sulfate.

[0113] Boric acid, with a concentration of 30-60 g / L, preferably 40-50 g / L, more preferably 42-48 g / L, for example 45 g / L.

[0114] Cl - Its concentration can be 100-400 mg / L, preferably 110-200 mg / L, more preferably 140-160 mg / L, for example 150 mg / L. In this invention, Cl is provided. - The substance can be one or more selected from the group consisting of NaCl, KCl and NiCl2.

[0115] The buffer has a concentration of 4-10 g / L, preferably 4.5-8 g / L, more preferably 5-7 g / L, and most preferably 6 g / L. The buffer can be one or more selected from the group consisting of sodium acetate and sodium tartrate, with sodium acetate being preferred. Furthermore, sodium citrate is preferably not used as the buffer. The buffer buffer buffers pH changes during electrodeposition; however, some buffers may be adsorbed in large quantities on the initial nickel foil surface, affecting the etching effect during electro-etching. By using the aforementioned types and concentrations of buffers, the buffering effect can be ensured while avoiding adverse effects on the etching effect. For example, citrate ions adsorb on the nickel surface, forming a "barrier film" that hinders etching, while acetate ions and others are hardly adsorbed, and tartrate ions are only adsorbed in small amounts, providing a clean active surface for subsequent electro-etching.

[0116] The pore control agent has a concentration of 40-100 mg / L, preferably 42-80 mg / L, more preferably 45-55 mg / L, for example 50 mg / L. The pore control agent can be one or more selected from the group consisting of polyethylene glycol, sodium dihexyl succinate sulfonate, sodium dodecyl sulfate, sodium dodecylbenzene sulfonate, and sodium dodecyl sulfonate, preferably sodium dodecylbenzene sulfonate. The molecular weight of the aforementioned polyethylene glycol can be 400-1000, for example 400, 600, or 1000, preferably 600. By adding a sufficient amount of pore control agent within the aforementioned concentration range, the hydrogen evolution process can be suppressed, ultimately resulting in a dense initial nickel foil or one containing only a small number of micropores. A concentration of the pore control agent lower than the aforementioned range will lead to the formation of through-pores. On the other hand, an excessively high concentration of the pore control agent may sometimes lead to a decrease in the elongation of the nickel foil.

[0117] Furthermore, the electrolyte of the present invention optionally contains a grain refiner at a concentration of 30-100 mg / L, preferably 40-80 mg / L, more preferably 55-65 mg / L, for example 60 mg / L. The grain refiner may be one or more selected from the group consisting of thiourea, sodium polydithiopropane sulfonate, sodium saccharin, mercaptobenzothiazole, sodium polystyrene sulfonate, 3-mercaptopropionic acid, 2-mercaptopyridine, benzothiophene, and hexamethylenetetramine. Furthermore, the electrolyte of the present invention preferably does not contain sodium citrate.

[0118] In this step, the pH value of the electrolyte can be 2-5, 3-4, or 3.5-4.1, which is the initial pH value of the electrolyte for electrodeposition. Methods for adjusting the pH value of the electrolyte include, for example, using dilute sulfuric acid, dilute hydrochloric acid, nickel hydroxide, sodium hydroxide, nickel carbonate, basic nickel carbonate, and sodium carbonate.

[0119] In this step, when both the deposition anode and the deposition cathode are placed in the electrolyte, the distance between the deposition anode and cathode can be 10-30 mm, for example, 20 mm. The parallelism deviation of the electrode surfaces can be ≤0.5 mm / m.

[0120] In this step, the electrodeposition current density can be 18-22 A / dm³. 2 For example, 20A / dm 2 The current can be a DC current with a ripple factor ≤ 3%.

[0121] In this step, the electrodeposition temperature can be 35-60℃, or 43-47℃, for example, 45℃.

[0122] In this step, the electrodeposition time is controlled to obtain an initial nickel foil with a final thickness of approximately 6 μm. It can be 80-100 s, 85-95 s, 88-90 s, or for example, 89 s.

[0123] During electrodeposition, the flow velocity of the electrolyte along the tangential flow of the cathode surface is, for example, 0.8-1.2 m / s.

[0124] This step can be performed by preparing the electrolyte and carrying out electrodeposition in any tank, such as an acid-resistant PP tank.

[0125] (Step Two)

[0126] In this step, the etching anode is anodicly polarized through electro-etching, primarily etching the side of the initial nickel foil that does not contact the etching anode in the thickness direction (i.e., the air surface in electrodeposition (step one)) to obtain a single-sided blind via structure. This side of the initial nickel foil that does not contact the etching anode in the thickness direction corresponds to the "blind via surface" of the [nickel foil] portion of this invention. This step selectively etches the grain boundaries and protrusions on the nickel foil surface to precisely form the desired blind via structure without etching through the entire foil.

[0127] In this step, the deposition cathode with the initial nickel foil from (Step 1) is used as the etching anode. After the aforementioned deposition cathode is removed from the electrolyte, the residual electrolyte on the surface can be appropriately rinsed off, and it can be dried with hot air before being used as the etching anode.

[0128] The etching cathode in this step can be, for example, a platinum electrode, a graphite electrode, a stainless steel plate, or a titanium plate, with a titanium plate being preferred, such as a Gr1 grade industrial pure titanium plate. The aforementioned titanium plate is preferably a titanium plate obtained through the pretreatment step described later.

[0129] The etching solution in this step contains an acid. When the acid is (i) sulfuric acid, the concentration of sulfuric acid is 5-12 wt%, preferably 8-10 wt%. When the acid is (ii) sulfamic acid, the concentration of sulfamic acid is 5-15 wt%, preferably 8-12 wt%, more preferably 10 wt%. When the acid is (iii) a combination of sulfuric acid and sulfamic acid, the concentrations of sulfuric acid and sulfamic acid are each independently 5-15 wt%, preferably 8-12 wt%, more preferably 10 wt%. The presence of sulfamic acid is beneficial for improving the mechanical properties of the resulting nickel foil, while the presence of sulfuric acid is beneficial for improving the etching effect. Furthermore, sulfamic acid is relatively weak in the low concentration range, and may sometimes reduce the conductivity of the solution, failing to destroy the passivation film spontaneously formed on the nickel foil surface. Therefore, using only sulfamic acid may sometimes affect the etching effect of the etching solution; while using only sulfuric acid results in poor etching uniformity, which may sometimes lead to a decrease in the mechanical properties of the nickel foil. Therefore, the preferred acid in this step is a combination of dilute sulfuric acid and aminosulfonic acid, which can simultaneously and significantly improve etching uniformity and etching efficiency, thereby obtaining nickel foil with significantly improved mechanical properties and active material loading. Furthermore, water can be used as the solvent in this step.

[0130] In this step, the current density for electro-etching can be 1-5 A / dm². 2 Preferably 2-4 A / dm 2 Preferably 3A / dm 2 The charge per unit area in electro-etching refers to the product of the current density and the etching time, and can be 10⁻¹²⁰ C / dm². 2It can be 20-100C / dm 2 It can be 30-70C / dm 2 By ensuring that the current density and / or charge per unit area during electro-etching are within the aforementioned range, the etching effect can be optimized to obtain nickel foil with suitable blind via structure and surface roughness. Maintaining the current density during electro-etching within the aforementioned range also makes the etching process easier to control, resulting in nickel foil with improved mechanical properties, interface stability, safety performance, and active material loading.

[0131] In this step, the etching time of the electro-etching can be set appropriately according to the current density and the charge per unit area, for example, 10-30s, 15-25s, or for example, 20s.

[0132] In this step, the etching temperature is kept consistent with the electrolyte temperature and the electrodeposition temperature, which can be 35-60℃, 43-47℃, or for example, 45℃.

[0133] This step can be performed by preparing the etching solution and conducting electro-etching in any tank, such as an acid-resistant PP tank.

[0134] (Step 3)

[0135] In this step, the nickel foil obtained in (Step 2) is stripped from the etching anode.

[0136] In this step, cleaning and / or drying are preferably performed before peeling. There are no particular limitations on the cleaning method; for example, it can be performed by one or more of static immersion, spray rinsing, and ultrasonic-assisted cleaning, preferably including all of them in a stepped water washing process. The conductivity of the residual liquid on the nickel foil surface after cleaning can, for example, be below 5 μS / cm.

[0137] In this step, there are no particular restrictions on the drying method. For example, it can be hot air drying, such as at a wind speed of 10 m / s and a temperature of 80°C for 30 seconds.

[0138] Furthermore, the method for preparing the nickel foil of the present invention optionally includes a pretreatment step, which pretreats the titanium plate and uses it as a cathode for deposition and / or etching. The pretreatment step may include one or more of alkaline degreasing, mixed acid activation, and deionized water rinsing, preferably all of them. The aforementioned alkaline degreasing is, for example, an alkaline degreasing treatment using 50 g / L NaOH at 60°C for 5 min. The aforementioned mixed acid activation is, for example, a mixed acid activation treatment using HF:HNO3:H2O=1:4:5 vol% at 25°C for 30 s. The pretreatment step can ensure that the hydrophilic contact angle of the titanium plate is ≤5°, and that the surface water film is continuous and unbroken, thereby improving the uniformity of electrodeposition.

[0139] Furthermore, one specific embodiment of the method for preparing the nickel foil of the present invention is as follows:

[0140] Prepare an electrolyte with the following components and concentrations: Nickel sulfate (providing 50-90 g / L Ni) 2+ Preferably 70±2 g / L), boric acid (30-60 g / L, preferably 45±3 g / L) and Cl - (100-400 mg / L, preferably 150±10 mg / L, introduced by sodium chloride), buffer (4-10 g / L), pore regulator (40-100 mg / L), grain refiner (30-100 mg / L); the pore regulator is selected from one or more of the group consisting of polyethylene glycol with a molecular weight of 600, sodium dihexyl succinate, sodium dodecyl sulfonate, and sodium dodecylbenzene sulfonate; the grain refiner is selected from one or more of the group consisting of thiourea, sodium polydithiopropane sulfonate, sodium saccharin, mercaptobenzothiazole, sodium polystyrene sulfonate, and 3-mercaptopropionic acid; the buffer is selected from one or more of the group consisting of sodium citrate, sodium acetate, and sodium tartrate. IrO2-SnO2 coated titanium mesh was used as the anode for deposition, and industrial pure titanium plate was used as the cathode. The pH of the electrolyte was stabilized at 3.8±0.3, the temperature was controlled at 45±2℃, and the electrolyte circulation flow rate was maintained at 0.8-1.2 m / s to ensure compositional uniformity, thereby achieving a current density of 18-22 A / dm³. 2 Electrodeposition is performed within a certain range, and an initial nickel foil is electrodeposited on the deposition cathode. Next, the deposition cathode with the aforementioned initial nickel foil is removed, rinsed, and dried before being used as the etching anode. A titanium plate is used as the etching cathode and inserted into another electrolytic cell containing an etching solution (the etching solution contains an acid, which is a combination of dilute sulfuric acid and aminosulfonic acid, with each of the dilute sulfuric acid and aminosulfonic acid having an independent concentration of 5-15 wt%), and the current density is (1-5 A / dm³). 2 Under short duration (10-30 seconds) and low charge per unit area (10-120 C / dm²) conditions. 2 The nickel foil is obtained by electro-etching the anode of the etching process to obtain a nickel foil attached to the anode of the etching process. Finally, the nickel foil is peeled off from the anode of the etching process to obtain the nickel foil of the present invention.

[0141] Example

[0142] The embodiments of the present invention will be described in detail below with reference to examples. However, those skilled in the art will understand that the following examples are for illustrative purposes only and should not be considered as limiting the scope of the invention. Unless otherwise specified in the examples, conventional conditions or conditions recommended by the manufacturer are followed. Reagents or instruments whose manufacturers are not specified are all commercially available conventional products.

[0143] [Nickel foil and its preparation method]

[0144] Example 1

[0145] IrO2-SnO2 coated titanium mesh was used as the deposition anode. Industrial pure titanium plates (Gr1 grade) were subjected to alkaline degreasing (using 50 g / L NaOH at 60℃ for 5 min), mixed acid activation (using HF:HNO3:H2O = 1:4:5 vol% at 25℃ for 30 s), and rinsing with deionized water, and then used as the deposition cathode. An electrolyte with the following component concentrations was prepared using water as the solvent: Ni 2+ 70g / L, boric acid 45g / L, Cl - The electrolyte solution contained 150 mg / L sodium acetate, 6 g / L sodium dodecylbenzenesulfonate, 50 mg / L sodium saccharin, and 60 mg / L sodium saccharin, with an initial pH of 3.8. Both the anode and cathode were immersed in the electrolyte solution for electrodeposition at a current density of 20 A / dm³. 2 The electrodeposition temperature was 45℃ and the electrodeposition time was 89s, thereby electrodepositing an initial nickel foil with a thickness of about 6μm on the cathode for deposition.

[0146] Next, the deposition cathode with the initial nickel foil deposited was removed, washed with water, and dried to serve as the etching anode, while the titanium plate was used as the etching cathode. An etching solution was prepared using water as a solvent with the following component concentrations: 10 wt% sulfuric acid and 10 wt% aminosulfonic acid. Both the etching anode and cathode were placed in the etching solution for electro-etching at a current density of 3 A / dm³. 2 The etching time is 20 seconds and the charge per unit area is 60 C / dm², so that the initial nickel foil is mainly etched on the side that is not in the thickness direction of the anode used for etching, thus obtaining the nickel foil.

[0147] After the etched nickel foil is washed with water using an anodic step wash and dried, the nickel foil is peeled off from the etched anodic anode, and the resulting nickel foil is designated as nickel foil-I.

[0148] Example 2

[0149] In electrodeposition, an electrolyte with the following component concentrations is prepared: Ni 2+ 70g / L, boric acid 45g / L, Cl - 150 mg / L sodium tartrate, 6 g / L sodium dodecylbenzenesulfonate, 50 mg / L sodium saccharin, 60 mg / L sodium saccharin. Except for these, the same steps as in Example 1 were used to obtain nickel foil, which is referred to as Nickel Foil-II.

[0150] Example 3

[0151] In electrodeposition, an electrolyte with the following components and concentrations is prepared: Ni2+ 70g / L, boric acid 45g / L, Cl - 150 mg / L sodium acetate, 6 g / L sodium dodecylbenzenesulfonate, 100 mg / L sodium saccharin, 60 mg / L sodium saccharin. Except for these, the same steps as in Example 1 were used to obtain nickel foil, which is designated as Nickel Foil-III.

[0152] Example 4

[0153] In electro-etching, the current density is 1 A / dm². 2 The etching time was 10 seconds and the charge per unit area was 10 C / dm². Apart from this, the same steps as in Example 1 were used to obtain the nickel foil, which is referred to as Nickel Foil-IV.

[0154] Example 5

[0155] In electro-etching, the current density is 1 A / dm². 2 The etching time was 20 seconds and the charge per unit area was 20 C / dm². Apart from this, the same steps as in Example 1 were used to obtain the nickel foil, which is denoted as Nickel Foil-V.

[0156] Example 6

[0157] In electro-etching, the current density is 1 A / dm². 2 The etching time was 30 seconds and the charge per unit area was 30 C / dm². Apart from this, the same steps as in Example 1 were used to obtain the nickel foil, which is denoted as Nickel Foil-VI.

[0158] Example 7

[0159] In electro-etching, the current density is 3 A / dm². 2 The etching time was 10 seconds and the charge per unit area was 30 C / dm². Apart from this, the same steps were used to obtain the nickel foil as in Example 1, which is denoted as Nickel Foil-VII.

[0160] Example 8

[0161] In electro-etching, the current density is 3 A / dm². 2 The etching time was 30 seconds and the charge per unit area was 90 C / dm². Apart from this, the same steps as in Example 1 were used to obtain the nickel foil, which is denoted as Nickel Foil-VIII.

[0162] Example 9

[0163] In electro-etching, the current density is 5 A / dm². 2The etching time was 10 seconds and the charge per unit area was 50 C / dm². Apart from this, the same steps were used to obtain the nickel foil as in Example 1, which is denoted as Nickel Foil-IX.

[0164] Example 10

[0165] In electro-etching, the current density is 5 A / dm². 2 The etching time was 20 seconds and the charge per unit area was 100 C / dm². Apart from this, the same steps as in Example 1 were used to obtain the nickel foil, which is denoted as nickel foil-X.

[0166] Example 11

[0167] In the electro-etching process, an etching solution with the following component concentrations was prepared: 5 wt% sulfuric acid. Otherwise, the same steps as in Example 1 were used to obtain the nickel foil, which is denoted as nickel foil-XI.

[0168] Example 12

[0169] In the electro-etching process, an etching solution with the following component concentrations was prepared: 10 wt% sulfuric acid. Otherwise, the same steps as in Example 1 were used to obtain the nickel foil, which is denoted as Nickel Foil-XII.

[0170] Example 13

[0171] In the electro-etching process, an etching solution with the following component concentrations was prepared: 5 wt% aminosulfonic acid. Otherwise, the same steps as in Example 1 were used to obtain the nickel foil, which was designated as nickel foil-XIII.

[0172] Example 14

[0173] In the electro-etching process, an etching solution with the following component concentrations was prepared: 10 wt% aminosulfonic acid. Otherwise, the same steps as in Example 1 were used to obtain the nickel foil, denoted as Nickel Foil-XIV.

[0174] Example 15

[0175] In the electro-etching process, an etching solution with the following component concentrations was prepared: 15 wt% aminosulfonic acid. Otherwise, the same steps as in Example 1 were used to obtain the nickel foil, denoted as nickel foil-XV.

[0176] Example 16

[0177] In the electro-etching process, an etching solution with the following component concentrations was prepared: 5 wt% sulfuric acid and 5 wt% aminosulfonic acid. Otherwise, the same steps as in Example 1 were used to obtain the nickel foil, which is denoted as nickel foil-XVI.

[0178] Example 17

[0179] In the electro-etching process, an etching solution with the following component concentrations was prepared: 15 wt% sulfuric acid and 15 wt% aminosulfonic acid. Otherwise, the same steps as in Example 1 were used to obtain the nickel foil, which is designated as nickel foil-XVII.

[0180] Comparative Example 1

[0181] In electrodeposition, an electrolyte with the following components and concentrations is prepared: Ni 2+ 70g / L, boric acid 45g / L, Cl - 150 mg / L, sodium citrate 6 g / L, sodium dodecylbenzenesulfonate 50 mg / L, sodium saccharin 60 mg / L, except that the same steps as in Example 1 were used to obtain nickel foil, denoted as Nickel Foil-Pair I.

[0182] Comparative Example 2

[0183] In electrodeposition, an electrolyte with the following components and concentrations is prepared: Ni 2+ 70g / L, boric acid 45g / L, Cl - 150 mg / L, sodium acetate 6 g / L, sodium dodecylbenzenesulfonate 30 mg / L, sodium saccharin 60 mg / L; except for these, the nickel foil was obtained using the same steps as in Example 1, and is referred to as Nickel Foil-II.

[0184] Comparative Example 3

[0185] In electro-etching, the current density is 5 A / dm². 2 The etching time was 30 seconds and the charge per unit area was 150 C / dm². Apart from this, the same steps were used to obtain the nickel foil as in Example 1, which is referred to as Nickel Foil-Pair III.

[0186] Comparative Example 4

[0187] In the electro-etching process, the etching solution with the following composition and concentration was prepared: 15 wt% sulfuric acid. Otherwise, the same steps as in Example 1 were used to obtain the nickel foil, which is referred to as nickel foil-to-IV.

[0188] The nickel foils of Examples 1-17 and Comparative Examples 1-4 were subjected to the following tests, and the test results are shown in [Table 1].

[0189] 1. Test methods for tensile strength and elongation:

[0190] The nickel foil to be tested was cut into 15*100mm pieces using a sample cutting machine. 2Sample strips of various sizes were used to test the tensile strength and elongation of the nickel foil in the transverse and longitudinal directions using a tensile testing instrument. Here, longitudinal direction refers to the length direction of the nickel foil, and transverse direction refers to the width direction of the nickel foil. The average value of the tensile strength in the transverse and longitudinal directions, and the average value of the elongation in the transverse and longitudinal directions, were taken to obtain the tensile strength and elongation.

[0191] The above measurements were repeated 10 times and the average value was taken to obtain the tensile strength and elongation of the nickel foil to be tested.

[0192] 2. Roughness Testing Method

[0193] A roughness profilometer was used to fix the nickel foil sample to be tested flat on the measuring platform, ensuring that the surface to be measured was facing upwards. Three different regions were randomly selected along the transverse and longitudinal directions of the sample, and measurements were performed according to ISO 4287 standard. The sampling length was 0.8 mm, and the evaluation length was 4.0 mm. The arithmetic mean deviation (Ra) and maximum profile height (Rz) of each region in the longitudinal and transverse directions were recorded. The average values ​​of Ra and Rz at the six measurement points in the longitudinal and transverse directions were calculated, and then the transverse and longitudinal roughnesses were averaged to obtain the roughness of the surface to be measured of the nickel foil.

[0194] 3. Gloss Test Method

[0195] A gloss meter with a 60° geometric angle was used. The nickel foil sample to be tested was placed flat on the test base, ensuring that the surface to be measured was facing upwards. Three different areas were randomly selected along the transverse and longitudinal directions of the sample for measurement, and the test was calibrated and performed according to ASTM D523 standard. The gloss units (GU) of each area were recorded. The average gloss of all six measurement points was calculated to obtain the gloss of the nickel foil to be tested.

[0196] 4. Bending fatigue life test method:

[0197] The nickel foil to be tested was cut into 15×150 mm pieces using the MIT flexural endurance tester (GB / T 2679.5). 2 The strip was tested until fracture under the following conditions:

[0198] Bending angle: 135°±1°

[0199] Bending radius: 1.0 ± 0.1 mm

[0200] Load: 0.50±0.01 kg

[0201] Frequency: 3 Hz

[0202] Record the number of folds when the sample breaks completely, and take the median of 10 samples (because the data is skewed).

[0203] [Table 1]

[0204]

[0205] The maximum height Rz of the smooth surface profile in Examples 1-17 and Comparative Examples 1-4 ranges from 1.686 to 2.500, and the arithmetic mean deviation Ra of the smooth surface profile ranges from 0.217 to 0.300.

[0206] It should be noted that in Table 1 of the Embodiments section and the aforementioned data, "blind hole surface" refers to the side of the nickel foil that does not contact the etching anode in the thickness direction during the electro-etching process of each embodiment and comparative example, and "smooth surface" refers to the side of the nickel foil that contacts the etching anode in the thickness direction. It does not necessarily refer to the blind hole surface or smooth surface that meets the requirements of the present invention.

[0207] As shown in Table 1, the nickel foils I to XVII obtained in Examples 1-17 have high tensile strength and elongation and excellent mechanical properties, and the high surface roughness of the blind holes can increase the active material loading of the aforementioned nickel foils.

[0208] In Comparative Example 1, sodium citrate was used as a buffer in the electrolyte for electrodeposition. Performance data and SEM images of the nickel foil-to-I electrode were obtained. Figure 2 , 3 It can be seen that there is almost no etching effect, no blind hole structure is generated, and the roughness of the nickel foil is significantly insufficient.

[0209] In Comparative Example 2, the concentration of pore conditioner was too low, which directly led to the difficulty in the overflow of hydrogen bubbles generated during the electrodeposition process, forming through holes on the initial nickel foil, resulting in a sharp decline in the mechanical properties of nickel foil-II.

[0210] Comparative Example 3 at 5A / dm 2 The etching time was too long at the current density, resulting in an excessive charge per unit area. After peeling, it was found that the nickel foil-III had individual through holes, which seriously affected the mechanical properties.

[0211] In Comparative Example 4, the sulfuric acid concentration was too high, resulting in excessive etching. After peeling, it was found that the nickel foil-IV produced individual through holes, which seriously affected the mechanical properties of the obtained nickel foil.

[0212] Furthermore, Examples 1-2 show that when the buffer is sodium acetate, the etching effect of the resulting nickel foil is better than that of sodium tartrate, and the roughness of the resulting nickel foil increases, which is beneficial to increasing the loading of active material.

[0213] Example 3 shows that increasing the concentration of the pore conditioner has no significant effect on the etching effect, but sometimes it can lead to a decrease in the elongation of the nickel foil.

[0214] Examples 4-6 show that when the current density is low, increasing the etching time to increase the charge per unit area sometimes fails to further improve the etching efficiency.

[0215] Examples 7-8 show that etching at this current density can effectively balance etching effect and mechanical properties by controlling the etching time and the amount of charge per unit area, and make etching easy to control. However, too low a charge per unit area may weaken the etching effect, while too high a charge per unit area may affect the surface morphology and mechanical properties.

[0216] Examples 9-10 show that the etching effect is good at this current density, but when the etching time is long and the charge per unit area is large, it may easily lead to a decrease in the mechanical properties of the nickel foil.

[0217] Examples 11-12 show that using a mixed solution of dilute sulfuric acid and aminosulfonic acid or an aminosulfonic acid solution as the etching solution improves the mechanical properties of nickel foil compared to a dilute sulfuric acid solution.

[0218] Examples 13-15 show that using a mixed solution of dilute sulfuric acid and aminosulfonic acid and a sulfuric acid solution improves the etching effect compared to an aminosulfonic acid solution.

[0219] Examples 16-17 show that when the etching solution is a mixture of dilute sulfuric acid and aminosulfonic acid, a lower concentration of the mixture can improve the mechanical properties of the nickel foil, while a higher concentration can improve the etching effect. However, too low or too high a concentration may affect the etching effect and the mechanical properties of the nickel foil, respectively.

[0220] [Rechargeable Battery]

[0221] The nickel foil obtained in Example 1 was used as the negative electrode current collector for a secondary battery, and a silicon-carbon composite material (SiO2) was coated on the blind hole surface. x A negative electrode active slurry (solid content 45wt%, mass ratio 94:2:2:2) consisting of -C (specific capacity 420mAh / g), conductive carbon black, polyacrylic acid binder, and sodium carboxymethyl cellulose was vacuum dried at 110℃ for 12 hours and then cold-pressed to obtain a negative electrode sheet with an active material surface density of 4.5mAh / cm². A 15μm thick aluminum foil was used as the positive electrode current collector for the secondary battery, and a high-nickel ternary material (LiNi) was coated onto it. 0.83 Co 0.11 Mn 0.06A positive electrode slurry (mass ratio 96:2:2) consisting of O2, conductive carbon black, and polyvinylidene fluoride was processed using the same process to obtain a positive electrode sheet with an active material areal density of 4.2 mAh / cm². An electrolyte was prepared using EC+EMC+DEC (3:5:2 volume ratio) as a solvent, with 1.2 M LiPF6 as the lithium salt, and 5 wt% fluoroethylene carbonate and 1 wt% lithium difluorooxalate borate as additives. This positive electrode, negative electrode, 16 μm thick ceramic-coated polyethylene porous membrane, and electrolyte were assembled into a 2.8 Ah 523450 type pouch battery in an argon glove box with a dew point < -40°C.

[0222] Tests show that the battery exhibits excellent electrochemical performance, with a surface temperature rise of ≤65℃ during the lithium battery nail penetration test and a thermal runaway trigger temperature >240℃; after 100 cycles, the electrode thickness expansion rate is ≤3.5%, and the capacity retention rate is ≥96%. It is evident that the nickel foil provided by this invention, when used as the negative electrode current collector in a secondary battery, can match high-capacity electrode materials and increase the loading rate to improve battery capacity, while simultaneously achieving excellent safety performance and cycle stability.

[0223] The various embodiments of the present invention have been described above. These descriptions are exemplary and not exhaustive, nor are they limited to the disclosed embodiments. Many modifications and variations will be apparent to those skilled in the art without departing from the scope and spirit of the described embodiments. The terminology used herein is chosen to best explain the principles, practical application, or technical improvements to the embodiments in the market, or to enable others skilled in the art to understand the embodiments disclosed herein.

Claims

1. A nickel foil, characterized in that, The thickness of the nickel foil is 5.5-6.5 μm. The nickel foil has blind holes distributed on one side, wherein the side with the blind holes distributed in the thickness direction of the nickel foil is the blind hole side, and the other side is a smooth surface. The blind hole refers to a pit-like structure that does not penetrate the nickel foil. The maximum height Rz of the blind hole surface is 3 μm or more. The maximum height Rz of the smooth surface profile is less than 2.5 μm. The nickel foil does not have through holes.

2. The nickel foil according to claim 1, characterized in that, The maximum height Rz of the blind hole surface profile is less than 5 μm; and / or The arithmetic mean deviation Ra of the blind hole surface profile is greater than 0.285 μm and less than 0.5 μm; and / or The gloss level of the blind aperture surface is above 30 Gu and below 100 Gu; and / or The elongation of the nickel foil is 2.5-3.5%; and / or The tensile strength of the nickel foil is ≥1000MPa.

3. The nickel foil according to claim 1 or 2, characterized in that, The nickel foil has a nickel content of 90.0 wt% or more; and / or The nickel foil has a single-layer structure.

4. The nickel foil according to claim 1 or 2, characterized in that, The maximum height Rz of the smooth surface profile is 1 μm or more; and / or The arithmetic mean deviation Ra of the smooth surface profile is greater than 0.1 μm and less than 0.300 μm.

5. A secondary battery, characterized in that, The secondary battery comprises: a positive electrode, a negative electrode including a negative electrode current collector and a negative electrode active layer, a separator separating the positive electrode and the negative electrode, and an electrolyte. The negative electrode current collector is the nickel foil according to any one of claims 1 to 4.

6. A method for preparing nickel foil according to any one of claims 1 to 4, characterized in that, Includes the following steps: Step 1: Place both the deposition anode and deposition cathode in the electrolyte for electrodeposition, thereby electrodepositing the initial nickel foil onto the deposition cathode. The electrolyte contains: Ni at a concentration of 50-90 g / L. 2+ Boric acid with a concentration of 30-60 g / L, and Cl with a concentration of 100-400 mg / L - Buffers with a concentration of 4-10 g / L and pore regulators with a concentration of 40-100 mg / L, The buffer is selected from one or more of the group consisting of sodium acetate and sodium tartrate; Step 2: Using the deposition cathode with the initial nickel foil obtained in Step 1 as the etching anode, both the etching anode and the etching cathode are placed in the etching solution, and a current density of 1-5 A / dm is applied. 2 The charge per unit area is 10-120 C / dm² 2 Electro-etching creates blind holes on the side of the initial nickel foil that does not contact the etching anode in the thickness direction, thereby obtaining a nickel foil attached to the etching anode. The etching solution contains an acid, which is any one of the following (i) to (iii): (i) Sulfuric acid, with a concentration of 5-12 wt% based on the total weight of the etching solution. (ii) Sulfamic acid, with a concentration of 5-15 wt% based on the total weight of the etching solution. (iii) A combination of sulfuric acid and aminosulfonic acid, with the concentrations of sulfuric acid and aminosulfonic acid each independently ranging from 5 to 15 wt% based on the total weight of the etching solution; Step 3: Remove the nickel foil obtained in Step 2 from the etching anode.

7. The method for preparing nickel foil according to claim 6, characterized in that, The pore control agent is selected from one or more of the group consisting of polyethylene glycol, sodium dihexyl succinate sulfonate, sodium dodecyl sulfate, sodium dodecylbenzene sulfonate, and sodium dodecyl sulfonate.

8. The method for preparing nickel foil according to claim 6 or 7, characterized in that, The electrolyte also contains a grain refiner at a concentration of 30-100 mg / L. The grain refiner is selected from one or more of the group consisting of thiourea, sodium polydithiopropane sulfonate, sodium saccharin, mercaptobenzothiazole, sodium polystyrene sulfonate, 3-mercaptopropionic acid, 2-mercaptopyridine, benzothione and hexamethylenetetramine.

9. The method for preparing nickel foil according to claim 6 or 7, characterized in that, In step two, the current density of the electro-etching is 2-4 A / dm². 2 ; and / or etching time is 10-30s.

10. The method for preparing nickel foil according to claim 6 or 7, characterized in that, In step one, the current density of the electrodeposition is 18-22 A / dm². 2 ; and / or the electrodeposition temperature is 35-60℃; and / or the pH value of the electrolyte is 2-5.

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