NiO thin film, preparation method and application thereof

Abstract

The application discloses a preparation method of a NiO film, which comprises the following steps: dissolving a nickel source in an organic solvent, heating and stirring, adding an organic amine to obtain sol A; adding a solubilizing agent to the sol A, wherein the solubilizing agent is an oxygen-containing heterocyclic compound and a derivative thereof, and obtaining sol B after standing; immersing a substrate in the sol B for soaking, taking out the substrate after the soaking is completed, and drying the substrate; performing annealing treatment on the dried substrate, and forming a NiO film on the surface of the substrate after cooling. The application further provides the NiO film prepared by the above preparation method and application of the NiO film in the field of pre-plating nickel on a battery shell. The NiO film prepared by the method has low porosity and good corrosion resistance; and the application of the NiO film and the preparation method thereof in the pre-plating nickel on the battery shell enables the surface of the battery shell to form the NiO film with low porosity, and solves the problem of poor corrosion resistance caused by too many pinholes on the surface of a plating layer and further expansion of the pinholes after stamping treatment in the prior art.

Description

Technical Field

[0001] This invention belongs to the field of surface treatment technology, specifically relating to a NiO thin film, its preparation method, and its application. Background Technology

[0002] Currently, the commonly used casing materials for lithium batteries are mainly steel, aluminum, and aluminum-plastic film. Cylindrical lithium batteries generally use steel, which has strong physical stability, as the casing material. To prevent the positive electrode active material of the battery from oxidizing the steel casing, nickel plating is usually used to protect the iron matrix in the steel casing. The pre-plating nickel process refers to plating the base steel with nickel before the battery casing is stamped, and then subjecting it to high-temperature tempering treatment, thereby allowing the steel layer and nickel layer to diffuse and penetrate each other to form a nickel-iron alloy layer.

[0003] The battery casing is filled with an electrolyte solution, which is highly corrosive. Therefore, the battery casing material must have high corrosion resistance in battery design and manufacturing. However, during the nickel plating process, air bubbles on the cathode surface create insulation, preventing metal deposition. The plating layer thickens around the bubbles, and subsequent bubble escapes or ruptures, leaving pinhole marks. The pre-nickel plating process involves plating the battery casing with nickel before stamping. Since micro-pinholes inevitably form during pre-nickel plating, these pinholes enlarge further after subsequent stamping, severely affecting the corrosion resistance of the plating layer.

[0004] Existing technologies involve forming multiple layers (e.g., Ni-Co / Ni / Ni-Co coatings) on the substrate surface. By adjusting the thickness of each layer, the interlocking force between layers is increased, resulting in a denser coating structure, reduced porosity, and thus improved corrosion resistance of the battery casing. However, this method also increases the stress on the coating, which may affect the surface morphology and toughness of the coating after stamping. Furthermore, the process conditions for forming multiple layers are relatively stringent and cumbersome, hindering commercialization and large-scale production. Therefore, finding a simple and economical method to form a low-porosity, corrosion-resistant nickel coating on the surface of battery casings is one of the urgent problems to be solved in the field of metal surface treatment, especially in the pre-nickel plating of battery casings. Summary of the Invention

[0005] In view of all or part of the deficiencies of the prior art described above, the purpose of this invention is to provide a NiO thin film, its preparation method and application, with a simple process flow suitable for large-scale industrialization; the NiO thin film prepared by this method has low porosity and good corrosion resistance; applying the above-mentioned NiO thin film and its preparation method to pre-plating nickel on battery casings, so as to form a NiO thin film with low porosity on the surface of the battery casing, solving the problem of excessive pinholes on the plating surface in the prior art, which further enlarges after stamping and leads to poor corrosion resistance.

[0006] To achieve the above-mentioned objectives, the present invention provides the following technical solution:

[0007] This invention provides a method for preparing NiO thin films, comprising the following steps:

[0008] S1: Dissolve the nickel source in an organic solvent, heat and stir, add an organic amine to obtain sol A;

[0009] S2: Add a solubilizer to the sol A, wherein the solubilizer is an oxygen-containing heterocyclic compound and its derivatives, and after standing, sol B is obtained;

[0010] S3: Immerse the substrate in the sol B, and after immersion, remove and dry the substrate;

[0011] S4: Anneal the dried substrate and cool it to form a NiO film on the surface of the substrate.

[0012] The gel-sol method is a wet chemical process that involves dissolving, hydrolyzing, and concentrating a highly dispersed and uniform sol, then transforming it into a near-solid-state gel system through physicochemical means. Finally, the desired film is obtained by evaporating the solvent through heat treatment. Films obtained by this method have uniform composition, smooth surfaces, and excellent physicochemical properties. This invention utilizes organic amines to hydrolyze nickel ions in a nickel source to form colloidal particles, which dissolve in an organic solvent to form sol A. The oxygen heterocycles in the solubilizer are unstable and easily decompose after dissolution, subsequently coordinating with nickel ions in the sol. After subsequent heat treatment, the particle polymer network structure formed in the gel becomes denser and the porosity decreases, thereby improving the corrosion resistance of the film and making the film structure more stable, thus increasing the film's service life.

[0013] In step S1, the nickel source is 3-10 wt%, selected from at least one of nickel acetate, nickel nitrate, and nickel acetate; the organic solvent is at least one of ethylene glycol methyl ether, ethylene glycol, and diethyl ether; and the organic amine is 1-3 wt%, selected from at least one of ethanolamine, triethanolamine, and isopropanolamine.

[0014] In step S2, 0.1-0.5 wt% of a wetting agent is added to the sol A. The wetting agent is at least one selected from methyl butyl ether, propylene glycol butyl ether, and triethylene glycol monobutyl ether. The wetting agent can reduce the interfacial tension of the substrate, allowing the sol to spread more evenly on the substrate surface, reducing the generation of surface defects. Simultaneously, it is easily soluble in the solvent and does not affect the overall sol system.

[0015] In step S2, 10-20 ppm of a depore-reducing agent is added to the sol A. The depore-reducing agent is at least one of tributyl phosphate, trimethyl citrate, and trimethyl phosphate. The depore-reducing agent can diffuse to the gas-liquid interface, rendering the foam-stabilizing effect of the surfactant ineffective and thus eliminating bubbles. Simultaneously, the esters can promote liquid film drainage, increasing the bubble rupture rate. Since the main pores in the sol after subsequent heat treatment are caused by the delayed escape of bubbles generated during heating, the depore-reducing agent can effectively reduce the porosity of the film layer, improve its density, and thus enhance its corrosion resistance.

[0016] In S2, the solubilizer is 0.5-2 wt% and is selected from at least one of 3-carbonyloxetane, 3-bromooxetane, and oxetane.

[0017] In step S3, prior to immersion, the substrate is degreased and acid-washed to remove grease and oxide film from its surface. The immersion time is 1-3 minutes, the drying temperature is 80-120°C, and the drying time is 5-15 minutes. Too short an immersion time will affect the film's density, while too long an immersion time will result in an excessively thick film, affecting the conductivity of the substrate, such as a battery casing. Too low a drying temperature will increase drying time and cost, while too high a temperature will cause the sol to solidify too quickly, preventing internal gases from escaping in time and increasing the film's porosity.

[0018] In step S4, the annealing temperature is 400-600℃, and the holding time is 20-40 minutes. If the annealing temperature is too low, the process of forming a gel from the sol will be slow, increasing the cost; if the annealing temperature is too high, the orientation of the grains will be poor, and the surface film and the substrate will interdiffusion will occur, affecting the corrosion resistance of the film.

[0019] In step S1, the heating temperature is 50-60℃. Failure to heat or a lower heating temperature will affect the dissolution of the nickel source, which is detrimental to sol formation.

[0020] In step S2, the settling time is 12-24 hours. Too short a settling time will affect the stability of the sol and reduce its lifespan; too long a settling time is detrimental to saving production costs and improving production efficiency.

[0021] The present invention also provides a NiO thin film, which is prepared by the NiO thin film preparation method in the above technical solution and has good corrosion resistance.

[0022] This invention also provides an application of NiO thin film, applying the NiO thin film from the above-mentioned technical solution to the field of pre-plating nickel on battery casings, wherein the battery casing material is, for example, steel. This results in a coating with low porosity on the surface of the battery casing, solving the problem in the prior art where excessive pinholes on the coating surface lead to further enlargement of pinholes after stamping, resulting in poor corrosion resistance.

[0023] The NiO film formed on the surface of the battery case has a thickness of 3-5 μm. Within this thickness range, the corrosion resistance of the coating is guaranteed, while the conductivity of the battery case is not affected by the excessive thickness of the coating.

[0024] Compared with the prior art, the present invention has at least the following beneficial effects:

[0025] (1) The present invention reduces surface defects of substrate, eliminates bubbles, and forms a dense particle polymer network structure by adding a certain mass fraction of wetting agent, depore agent and solubilizer to the sol A system, thereby synergistically improving the corrosion resistance of NiO film;

[0026] (2) The present invention discloses preferred wetting agent, depore-reducing agent and solubilizing material and their mass fraction range, which, under the premise of controlling cost, ensure that the added wetting agent, depore-reducing agent and solubilizing agent can synergistically promote the further improvement of the corrosion resistance of NiO film in the system;

[0027] (3) The present invention discloses a preferred drying temperature (80-120℃) under this system. Under this temperature condition, the sol solidifies on the surface of the substrate. The solidification rate of the sol is more suitable within this temperature range, which avoids the internal gas from not being able to escape in time and thus generating too many pores, while also taking into account production efficiency.

[0028] (4) The present invention discloses a preferred annealing temperature (400-600℃) under this system. Under this temperature condition, the sol on the substrate surface forms a gel at a suitable rate, avoiding excessively high annealing temperature that would lead to poor grain orientation, while also taking into account production efficiency.

[0029] (5) The sol-gel method for preparing NiO thin films provided by the present invention has a simple process flow and is suitable for large-scale industrialization.

[0030] (6) The present invention applies the above-mentioned NiO thin film and its preparation method to the field of pre-plating nickel in battery shells, which solves the problem of excessive pinholes on the surface of the plating layer in the prior art, and the poor corrosion resistance caused by the further expansion of pinholes after stamping.

[0031] (7) This invention proposes a method for preparing NiO thin film on finished pre-plated nickel battery shells using the gel-sol method. NiO has good corrosion resistance. At the same time, since the standard electrode potential of the substrate Fe (-0.44V) is lower than that of Ni (-0.25V), the film will fill the cracks and pores, forming a uniform and flat film on the surface of the workpiece. This method is simple to operate, has a low heat treatment temperature, low cost, and the sol does not contain toxic substances, resulting in low environmental pollution. Attached Figure Description

[0032] To more clearly illustrate the technical solutions in the specific embodiments of the present invention, the drawings used in the description of the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0033] Figure 1 This is a schematic flowchart of the NiO thin film preparation method provided by the present invention. Detailed Implementation

[0034] The technical solutions in specific embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of them. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0035] This invention provides a NiO thin film, its preparation method, and its application. The preparation method of the NiO thin film is described in detail below. Figure 1 The above method will be described in detail below with reference to specific embodiments:

[0036] Example 1

[0037] This embodiment provides a method for preparing NiO thin films, including the following steps:

[0038] 3 wt% nickel acetate was dissolved in a certain amount of ethylene glycol methyl ether, heated to 50°C, stirred, and 1 wt% ethanolamine was slowly added to obtain sol A (forming a light green transparent uniform sol);

[0039] Add 0.1 wt% methyl butyl ether, 10 ppm tributyl phosphate and 1 wt% 3-carbonyloxetane to sol A, continue stirring until homogeneous, and let stand at room temperature for 12 h to obtain sol B;

[0040] The battery casing is degreased and acid-washed to remove surface grease and oxide film. The treated battery casing is then immersed in sol B for 1 minute, slowly and evenly removed, and rotated at high speed to remove excess sol so that the sol is evenly distributed on the inner and outer walls of the battery casing.

[0041] Place the coated battery casing in a drying oven and dry it at 80°C for 15 minutes to promote the volatilization of the liquid phase components.

[0042] The dried battery casing was placed in an annealing furnace and heated at 400°C for 40 minutes. After cooling in the furnace, a NiO film was formed on the surface of the battery casing with a thickness of 3.1 μm.

[0043] Example 2

[0044] This embodiment provides a method for preparing NiO thin films, including the following steps:

[0045] 4 wt% nickel nitrate was dissolved in a certain amount of ethylene glycol, heated to 55°C, stirred, and 1 wt% ethanolamine was slowly added to obtain sol A (forming a light green, transparent, and uniform sol).

[0046] Add 0.1 wt% methyl butyl ether, 10 ppm trimethyl citrate and 1.5 wt% oxacyclopentane to sol A, continue stirring until homogeneous, and let stand at room temperature for 14 h to obtain sol B;

[0047] The battery casing is degreased and acid-washed to remove surface grease and oxide film. The treated battery casing is then immersed in sol B for 1.5 minutes, slowly and evenly removed, and rotated at high speed to remove excess sol so that the sol is evenly distributed on the inner and outer walls of the battery casing.

[0048] Place the coated battery casing in a drying oven and dry it at 85°C for 13 minutes to promote the volatilization of the liquid phase components.

[0049] The dried battery casing was placed in an annealing furnace and heated at 450°C for 38 minutes. After cooling in the furnace, a NiO film was formed on the surface of the battery casing with a thickness of 3.3 μm.

[0050] Example 3

[0051] 6 wt% nickel acetate was dissolved in a certain amount of ethylene glycol methyl ether, heated to 60°C, stirred, and 3 wt% ethanolamine was slowly added to obtain sol A (forming a light green transparent uniform sol);

[0052] Add 0.3 wt% propylene glycol butyl ether, 20 ppm trimethyl phosphate and 0.5 wt% 3-carbonyloxetane to sol A, continue stirring until homogeneous, and let stand at room temperature for 16 h to obtain sol B;

[0053] The battery casing is degreased and acid-washed to remove surface grease and oxide film. The treated battery casing is then immersed in sol B for 3 minutes, slowly and evenly removed, and rotated at high speed to remove excess sol so that the sol is evenly distributed on the inner and outer walls of the battery casing.

[0054] Place the coated battery casing in a drying oven and dry it at 100°C for 10 minutes to promote the volatilization of the liquid phase components.

[0055] The dried battery casing was placed in an annealing furnace and heated at 500°C for 30 minutes. After cooling in the furnace, a NiO film was formed on the surface of the battery casing with a thickness of 4.2 μm.

[0056] Example 4

[0057] This embodiment provides a method for preparing NiO thin films, including the following steps:

[0058] 5 wt% nickel acetate was dissolved in a certain amount of diethyl ether, heated to 60°C, stirred, and 3 wt% triethanolamine was slowly added to obtain sol A (forming a light green transparent uniform sol).

[0059] Add 0.3 wt% triethylene glycol monobutyl ether, 20 ppm trimethyl citrate and 0.5 wt% 3-bromooxybutane to the sol A, continue stirring until homogeneous, and let stand at room temperature for 16 h to obtain sol B;

[0060] The battery casing is degreased and acid-washed to remove surface grease and oxide film. The treated battery casing is then immersed in sol B for 2 minutes, slowly and evenly removed, and rotated at high speed to remove excess sol so that the sol is evenly distributed on the inner and outer walls of the battery casing.

[0061] Place the coated battery casing in a drying oven and dry it at 100°C for 12 minutes to promote the volatilization of the liquid phase components.

[0062] The dried battery casing was placed in an annealing furnace and heated at 480°C for 25 minutes. After cooling in the furnace, a NiO film was formed on the surface of the battery casing with a thickness of 3.6 μm.

[0063] Example 5

[0064] 7.5 wt% nickel acetate was dissolved in a certain amount of ethylene glycol methyl ether, heated to 55°C, stirred, and 2.5 wt% ethanolamine was slowly added to obtain sol A (forming a light green transparent uniform sol);

[0065] Add 0.5 wt% triethylene glycol monobutyl ether, 10 ppm trimethyl phosphate and 2 wt% 3-carbonyloxetane to the sol A, continue stirring until homogeneous, and let stand at room temperature for 18 h to obtain sol B;

[0066] The battery casing is degreased and acid-washed to remove surface grease and oxide film. The treated battery casing is then immersed in sol B for 3 minutes, slowly and evenly removed, and rotated at high speed to remove excess sol so that the sol is evenly distributed on the inner and outer walls of the battery casing.

[0067] Place the coated battery casing in a drying oven and dry it at 110°C for 15 minutes to promote the volatilization of the liquid phase components.

[0068] The dried battery casing was placed in an annealing furnace and heated at 600°C for 20 minutes. After cooling in the furnace, a NiO film was formed on the surface of the battery casing with a thickness of 4.5 μm.

[0069] Example 6

[0070] This embodiment provides a method for preparing NiO thin films, including the following steps:

[0071] 5.5 wt% nickel acetate was dissolved in a certain amount of ethylene glycol, heated to 55°C, stirred, and 2.5 wt% isopropanolamine was slowly added to obtain sol A (forming a light green transparent uniform sol);

[0072] Add 0.5 wt% triethylene glycol monobutyl ether, 10 ppm trimethyl citrate and 2 wt% 3-carbonyloxetane to the sol A, continue stirring until homogeneous, and let stand at room temperature for 16 h to obtain sol B;

[0073] The battery casing is degreased and acid-washed to remove surface grease and oxide film. The treated battery casing is then immersed in sol B for 2.5 minutes, slowly and evenly removed, and rotated at high speed to remove excess sol so that the sol is evenly distributed on the inner and outer walls of the battery casing.

[0074] Place the coated battery casing in a drying oven and dry it at 120°C for 5 minutes to promote the volatilization of the liquid phase components.

[0075] The dried battery casing was placed in an annealing furnace and heated at 460°C for 22 minutes. After cooling in the furnace, a NiO film was formed on the surface of the battery casing with a thickness of 3.8 μm.

[0076] Example 7

[0077] 10 wt% nickel acetate was dissolved in a certain amount of ethylene glycol methyl ether, heated to 55°C, stirred, and 3 wt% ethanolamine was slowly added to obtain sol A (forming a light green transparent uniform sol).

[0078] Add 0.1 wt% triethylene glycol monobutyl ether, 15 ppm tributyl phosphate, trimethyl citrate, trimethyl phosphate and 1.5 wt% 3-carbonyloxetane, 3-bromooxetane and oxetane to sol A, continue stirring until homogeneous, and let stand at room temperature for 24 h to obtain sol B.

[0079] The battery casing is degreased and acid-washed to remove surface grease and oxide film. The treated battery casing is then immersed in sol B for 3 minutes, slowly and evenly removed, and rotated at high speed to remove excess sol so that the sol is evenly distributed on the inner and outer walls of the battery casing.

[0080] Place the coated battery casing in a drying oven and dry it at 120°C for 15 minutes to promote the volatilization of the liquid phase components.

[0081] The dried battery casing was placed in an annealing furnace and heated at 400°C for 40 minutes. After cooling in the furnace, a NiO film was formed on the surface of the battery casing with a thickness of 5 μm.

[0082] Example 8

[0083] 9 wt% nickel acetate was dissolved in a certain amount of ethylene glycol methyl ether, heated to 50°C, stirred, and 3 wt% ethanolamine was slowly added to obtain sol A (forming a light green transparent uniform sol);

[0084] Add 0.2 wt% propylene glycol butyl ether and triethylene glycol monobutyl ether, 12 ppm tributyl phosphate, trimethyl citrate and 1.5 wt% 3-bromooxetane and oxetane to sol A, continue stirring until homogeneous, and let stand at room temperature for 12 h to obtain sol B.

[0085] The battery casing is degreased and acid-washed to remove surface grease and oxide film. The treated battery casing is then immersed in sol B for 3 minutes, slowly and evenly removed, and rotated at high speed to remove excess sol so that the sol is evenly distributed on the inner and outer walls of the battery casing.

[0086] Place the coated battery casing in a drying oven and dry it at 115°C for 12 minutes to promote the volatilization of the liquid phase components.

[0087] The dried battery casing was placed in an annealing furnace and heated at 550°C for 28 minutes. After cooling in the furnace, a NiO film was formed on the surface of the battery casing with a thickness of 4.7 μm.

[0088] The battery casing described in the above embodiments of the present invention refers to the battery casing material before stamping, that is, applying the above-mentioned NiO thin film and its preparation method to the field of pre-nickel plating of battery casings. The NiO thin film formed by the present invention has low porosity, which solves the problem of excessive pinhole enlargement and poor corrosion resistance caused by the subsequent stamping process. The battery casing material used in the above embodiments is steel.

[0089] Comparative Example 1

[0090] The difference between Comparative Example 1 and Example 3 is that the standing time for sol B is 10 hours.

[0091] Comparative Example 2

[0092] The difference between Comparative Example 2 and Example 3 is that no trimethyl phosphate was added.

[0093] Comparative Example 3

[0094] The difference between Comparative Example 3 and Example 3 is that 3-carbonyloxetane is not added.

[0095] Comparative Example 4

[0096] The difference between Comparative Example 4 and Example 3 is that the amount of 3-carbonyloxetane added is 0.2 wt%.

[0097] Comparative Example 5

[0098] The difference between Comparative Example 5 and Example 3 is that the heating temperature was 45°C when preparing sol A.

[0099] Comparative Example 6

[0100] The difference between Comparative Example 6 and Example 3 is that the amount of trimethyl phosphate added is 8 ppm.

[0101] Comparative Example 7

[0102] The difference between Comparative Example 7 and Example 3 is that the coated battery casing was placed in a drying oven and dried at 200°C for 3 minutes.

[0103] Comparative Example 8

[0104] The difference between Comparative Example 8 and Example 3 is that the soaking time is 30 seconds.

[0105] Comparative Example 9

[0106] The difference between Comparative Example 9 and Example 3 is that propylene glycol butyl ether is not added.

[0107] Comparative Example 10

[0108] The difference between Comparative Example 10 and Example 3 is that the dried battery casing was placed in an annealing furnace and heated at 800°C for 10 minutes. After cooling in the furnace, a NiO film was formed on the surface of the battery casing.

[0109] Comparative Example 11

[0110] The difference between Comparative Example 11 and Example 3 is that the amount of propylene glycol butyl ether added is 0.05 wt%.

[0111] For the battery casings with NiO thin films prepared in Examples 1-8 and Comparative Examples 1-11 above, salt spray and blue spot tests were used to test their relevant performance. The salt spray test started timing after the sample was placed in the substrate and continued until discoloration appeared on the substrate surface; the time was recorded. For the blue spot test, the sample was covered with a potassium ferricyanide + sodium chloride solution after wetting it for 5 minutes, and then the number of discoloration points was observed. The test results are shown in Table 1 below:

[0112] Table 1. Summary of performance tests for Examples 1-8 and Comparative Examples 1-11

[0113]

[0114]

[0115] As shown in Table 1:

[0116] (1) Compared with the untreated battery case, the salt spray discoloration time of the battery case treated by the NiO film preparation method provided by the present invention is increased to more than 100h, and the corrosion resistance is significantly improved; and the blue spot test shows that the NiO film has a good sealing effect on the pores and cracks on the surface of the battery case. Among them, the effect of Example 3 is better, with its salt spray discoloration time reaching 110h.

[0117] (2) As can be seen from Examples 3 and Comparative Examples 9 and 11, the addition of wetting agent can effectively improve the corrosion resistance of NiO film and the sealing effect of NiO film on the pores and cracks on the battery case surface. When the amount of wetting agent added is less than 0.1 wt%, it has a certain adverse effect on the film performance. As can be seen from Examples 3 and Comparative Examples 2 and 6, the addition of anti-pore agent can effectively improve the corrosion resistance of NiO film and the sealing effect of NiO film on the pores and cracks on the battery case surface. When the amount of anti-pore agent added is less than 10 ppm, it has a certain adverse effect on the film performance. As can be seen from Examples 3 and Comparative Examples 3 and 4, the addition of solubilizer can effectively improve the corrosion resistance of NiO film and the sealing effect of NiO film on the pores and cracks on the battery case surface. When the amount of solubilizer added is less than 0.5 wt%, it has a certain adverse effect on the film performance.

[0118] (3) As can be seen from Example 3 and Comparative Examples 2, 3 and 9, the NiO film produced by adding wetting agent, depore-eliminating agent and solubilizer at the same time has significantly improved corrosion resistance and sealing effect compared with the NiO film produced by adding only two of them. This indicates that the simultaneous addition of wetting agent, depore-eliminating agent and solubilizer can reduce defect generation, eliminate bubbles and form a dense particle polymer network structure on the surface of the battery shell, thereby synergistically improving the performance of NiO film.

[0119] (4) As can be seen from Example 3 and Comparative Example 7, excessively high drying temperature will affect the performance of NiO film. The working principle may be that excessively high drying temperature will cause the sol to solidify too quickly, and the internal gas cannot escape in time, thus leading to an increase in the porosity of NiO film. The drying conditions (80-120℃ drying for 5-15 min) are the preferred preparation conditions in this system.

[0120] (5) As can be seen from Example 3 and Comparative Example 10, excessively high annealing temperature will affect the performance of NiO film. The mechanism may be that excessively high annealing temperature will lead to poor grain orientation, and at the same time, interdiffusion will occur between NiO film and the surface of battery casing steel, affecting the performance of NiO film. Annealing conditions (temperature 400-600℃, holding time 20-40min) are the preferred preparation conditions in this system.

[0121] (6) As shown in Example 3 and Comparative Example 1, a shorter settling time affects the performance of the NiO film, possibly due to poor sol stability caused by the shorter settling time. As shown in Example 3 and Comparative Example 5, a lower heating temperature during the preparation of sol A affects the performance of the NiO film. As shown in Example 3 and Comparative Example 8, a shorter soaking time affects the performance of the NiO film and the density of the film.

[0122] This invention proposes a method for preparing NiO thin films using a sol-gel method to improve the corrosion resistance of pre-plated nickel battery casings. The sol possesses excellent leveling ability and effectively fills cracks and pores in the plating layer after stamping, preventing discoloration of the battery casing due to uneven plating protection. The sol-gel method provided by this invention is simple, with low heating temperature and short heating time, and produces no environmental pollution, meeting environmental protection requirements. Furthermore, sol loss is only caused by carryover from the workpiece, avoiding the problem of film performance degradation due to internal ion content imbalance after repeated use. The NiO thin film provided by this invention has uniform thickness, a smooth surface, and a dense layer, exhibiting excellent corrosion resistance and high-temperature resistance. The NiO thin film and its preparation method provided by this invention are particularly suitable for salt spray treatment of finished pre-plated nickel battery casings.

[0123] The above description of the embodiments is only for the purpose of helping to understand the method and core idea of ​​the present invention. It should be noted that those skilled in the art can make several improvements and modifications to the present invention without departing from the principle of the present invention, and these improvements and modifications also fall within the scope of protection of the claims of the present invention.

Claims

1. A method for preparing a NiO thin film, characterized in that, Includes the following steps: S1: Dissolve the nickel source in an organic solvent, heat and stir at a temperature of 50-60℃, add an organic amine to obtain sol A; S2: Add 0.5-2 wt% of solubilizer, 0.1-0.5 wt% of wetting agent, and 10-20 ppm of depore-forming agent to sol A, and let it stand to obtain sol B. The standing time is 12-24 h. The solubilizer is selected from at least one of 3-carbonyloxetane, 3-bromooxetane, and oxetane. The wetting agent is at least one of methyl butyl ether, propylene glycol butyl ether, and triethylene glycol monobutyl ether. The depore-forming agent is at least one of tributyl phosphate, trimethyl citrate, and trimethyl phosphate. S3: Immerse the substrate in the sol B. Before immersion, the substrate is degreased and pickled. After immersion, the substrate is removed and dried. The immersion time is 1-3 minutes, the drying temperature is 80-120℃, and the drying time is 5-15 minutes. S4: Anneal the dried substrate at a temperature of 400-600℃ for 20-40 minutes. After cooling, a NiO film is formed on the surface of the substrate. The substrate is an iron part or a battery casing.

2. The preparation method according to claim 1, characterized in that, In step S1, the nickel source is 3-10 wt%, selected from at least one of nickel acetate, nickel nitrate, and nickel acetate; the organic solvent is at least one of ethylene glycol methyl ether, ethylene glycol, and diethyl ether; and the organic amine is 1-3 wt%, selected from at least one of ethanolamine, triethanolamine, and isopropanolamine.

3. A NiO thin film, characterized in that, The NiO thin film was prepared using the method described in claim 1 or 2.

4. An application of a NiO thin film, characterized in that, The NiO thin film described in claim 3 is applied to the field of pre-plating nickel in battery casings.

5. The application according to claim 4, characterized in that, The NiO film formed on the surface of the battery casing has a thickness of 3-5 μm.

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