Pre-nickel plated steel for battery shell and preparation method thereof

Abstract

The present invention relates to the technical field of metal materials, and discloses a pre-nickel-plated steel for battery shells and a preparation method thereof. The method includes hot rolling, coiling, pickling, cold rolling, nickel electroplating and continuous annealing; the nickel electroplating process includes: preparing nickel sulfate, nickel chloride, cobalt sulfate, boric acid, sodium lauryl sulfate, citric acid, pre-treated filler, nano-titanium dioxide particles and cerium salt into an electroplating solution, and then placing the steel substrate obtained after cold rolling in the electroplating solution for electroplating, wherein the concentration of the pre-treated filler is 1.2-1.5 g / L, the concentration of the nano-titanium dioxide particles is 0.5-1.0 g / L, and the concentration of the cerium salt is 0.1-0.2 g / L. The pre-nickel-plated steel for battery shells prepared by this method has excellent corrosion resistance, high hardness, good stamping performance, strong bonding between the nickel plating layer and the steel substrate, and low surface iron exposure rate.

Description

Technical Field

[0001] The present invention relates to the technical field of metal materials, and in particular to a pre-nickel-plated steel for battery shells and a preparation method thereof. Background Art

[0002] With the vigorous development of the new energy vehicle industry, the demand for power lithium batteries has increased dramatically. As a key component to protect the internal components of the battery, the performance of the battery shell directly affects the safety and service life of the battery. Pre-nickel-plated steel for battery shells is widely used in the manufacture of battery shells, but there are many problems with the products currently on the market. On the one hand, the bonding strength between the nickel plating layer and the steel substrate is insufficient. During the production and use of the battery, the nickel plating layer is easy to fall off, resulting in a decrease in the corrosion resistance of the battery shell and even causing safety hazards such as battery short circuits. On the other hand, the hardness of existing pre-nickel-plated steel for battery shells needs to be improved. When the internal pressure of the low-hardness battery shell increases when it is exposed to the risk of short circuit, it is very easy to crack, which increases the risk of failure during service.

[0003] Chinese patent application CN116516429A discloses a pre-nickel-plated steel strip for power lithium batteries and its preparation method. This patent application uses a specific electroplating solution formula, which contains multiple components such as nickel sulfate, nickel chloride, cobalt sulfate, etc., and combines it with a subsequent heat treatment process to improve the hardness, wear resistance and corrosion resistance of the steel strip. However, while improving the overall performance of the steel strip, the patent does not fully consider the high-speed stamping requirements in the battery shell production process. Its preparation process mainly revolves around electroplating and heat treatment parameters, and lacks targeted measures to improve the stamping performance of the steel-based strip itself. When faced with high-speed stamping, problems such as stamping cracking of the steel shell and decreased bonding strength between the nickel plating layer and the substrate will occur, affecting the production efficiency and quality of the battery shell.

[0004] Chinese patent application CN118099554A discloses a nickel-plated steel, a method for manufacturing the same, and a battery case. This patent application focuses on the welding performance and corrosion resistance of nickel-plated steel, and achieves performance improvement by controlling the relevant parameters of the Fe-Ni diffusion alloy layer, such as the distance between the position containing 80% of the Fe element and the position containing 80% of the Ni element. However, this patent has shortcomings in high-speed stamping. Its processing technology for the steel substrate is mainly cold rolling, continuous nickel electroplating, and continuous furnace annealing heat treatment. When optimizing welding and corrosion resistance, these processes do not fully consider the special requirements of high-speed stamping for the strength, plasticity and surface quality of the steel strip. During the high-speed stamping process, due to the poor coordination of the strength and plasticity of the steel strip, defects such as stamping cracking occur. At the same time, the surface quality cannot meet the stringent requirements of high-speed stamping due to different process emphases.

[0005] Chinese patent application CN117448673A discloses an ultra-low-carbon pre-nickel-plated steel strip and its preparation method. This patent application improves the overall mechanical properties of the steel strip by designing the chemical composition of the ultra-low-carbon steel matrix, such as strictly controlling the contents of elements such as C, Si, and Mn, and combining it with specific rolling and annealing processes. However, due to the use of ultra-low-carbon components, the product hardness is relatively low and cannot meet the pressure resistance requirements of battery steel casings.

[0006] Chinese patent application CN115787004A discloses a high-speed pre-nickel-plated steel strip for new energy vehicle battery shells and its manufacturing method. This patent application takes into account the needs of high-speed stamping to a certain extent, and improves the deep drawability of the steel strip by optimizing the process route, controlling raw material inclusions and other measures. However, there are still shortcomings when facing higher-demand high-speed stamping scenarios. Although its nickel plating process adopts a three-layer plating structure, during the high-speed stamping process, the bonding strength between the coatings and the bonding strength between the coatings and the steel strip substrate cannot meet the requirements under complex stress conditions, and the coating is prone to delamination and shedding. In addition, this patent also uses ultra-low carbon components, and the product's pressure resistance is relatively low. Summary of the Invention

[0007] The purpose of the present invention is to overcome the problems of poor bonding strength, low hardness, and poor corrosion resistance of the nickel-plated layer of pre-nickel-plated steel for battery shells in the prior art, and to provide a pre-nickel-plated steel for battery shells and a preparation method thereof. The pre-nickel-plated steel for battery shells prepared by the method described in the present invention has a nickel-plated layer that is firmly bonded to the steel substrate and is not easy to fall off during subsequent processing and use; it has high hardness and can meet the pressure resistance requirements when the battery is short-circuited; it has excellent corrosion resistance in various environments, especially in media such as electrolytes that the battery comes into contact with during use, effectively extending the service life of the battery shell and improving the safety and stability of the battery; it also has a low iron exposure rate and excellent corrosion resistance in natural environments, effectively improving the surface quality of the product.

[0008] In order to achieve the above-mentioned object, the first aspect of the present invention provides a method for preparing pre-nickel plated steel for battery shell, which comprises hot rolling, coiling, pickling, cold rolling, nickel electroplating and continuous annealing;

[0009] The nickel electroplating process comprises: preparing an electroplating solution with nickel sulfate, nickel chloride, cobalt sulfate, boric acid, sodium lauryl sulfate, citric acid, pretreated filler, nano titanium dioxide particles and cerium salt, and then placing the cold-rolled steel substrate in the electroplating solution for electroplating;

[0010] The concentration of the pretreated filler is 1.2-1.5 g / L, the concentration of the nano-titanium dioxide particles is 0.5-1.0 g / L, and the concentration of the cerium salt is 0.1-0.2 g / L;

[0011] The pre-nickel-plated battery shell steel has a hardness HV0.3 of 140-160, a yield strength of 240MPa-270MPa, a tensile strength of 360MPa-390MPa, and an elongation of ≥35%.

[0012] Preferably, the preparation process of the pretreated filler comprises the following steps:

[0013] (1) subjecting a hydrogen-containing double-capped, epoxy-terminated allyl polyether, concentrated sulfuric acid, and a catalyst to a first reaction under a first heating condition to obtain an epoxy monomer;

[0014] (2) performing a second reaction on the epoxy monomer and KH-550 under a second heating condition, cooling, and purifying to obtain coupling agent A;

[0015] (3) mixing hydrogen peroxide and concentrated sulfuric acid to obtain a pretreatment solution, and then placing a filler in the pretreatment solution, stirring, and centrifuging, wherein the filler includes graphene oxide and diamond;

[0016] (4) The centrifuged product is placed in toluene for ultrasonic dispersion, and then a complex coupling agent is added and stirred under an inert atmosphere, centrifuged, washed, and dried to obtain a pretreated filler, wherein the complex coupling agent includes a coupling agent A and an aminosilane coupling agent.

[0017] Preferably, the preparation process of the pretreated filler includes:

[0018] Mixing a hydrogen-containing double-end cap, an epoxy-terminated allyl polyether, and concentrated sulfuric acid, heating to 65° C.-75° C., adding a catalyst, and keeping the temperature for reaction for 4-5 hours to obtain an epoxy monomer, wherein the catalyst is chloroplatinic acid, and the amount of the catalyst is 0.2-0.4wt% of the total amount of the hydrogen-containing double-end cap and the epoxy-terminated allyl polyether, and the molar ratio of the hydrogen-containing double-end cap to the epoxy-terminated allyl polyether is 1:2-2.2;

[0019] Mix the epoxy monomer and KH-550, heat to 65-75°C, stir and react for 2-3 hours, cool after the reaction, and purify to obtain coupling agent A, wherein the mass ratio of the epoxy monomer to KH-550 is 8-10:1;

[0020] Mixing hydrogen peroxide and concentrated sulfuric acid to obtain a pretreatment solution, then placing a filler in the pretreatment solution, stirring at 60°C-65°C for 3h-4h, collecting the product by centrifugation, washing and drying, wherein the filler includes graphene oxide and diamond, and the mass ratio of graphene oxide to diamond is 1:2, and the amount ratio of hydrogen peroxide to concentrated sulfuric acid is 1:2;

[0021] The centrifuged product is placed in anhydrous toluene and ultrasonically dispersed for 1 h-2 h, and then a complex coupling agent is added, stirred for 20 h-24 h under a nitrogen environment, centrifuged, washed, and vacuum dried to obtain a pretreated filler, wherein the complex coupling agent includes coupling agent A and aminosilane coupling agent, the amount of coupling agent A is 15-18 wt% of the complex coupling agent, and the amount of the complex coupling agent is 0.2-0.5 wt% of the filler.

[0022] Preferably, the electroplating adopts pulse electroplating, with a forward pulse current density of 6-8A / dm², a pulse width of 2-4ms; a reverse pulse current density of 1-2A / dm², a pulse width of 0.5-1ms, and a duty cycle of 30-50%; the plating solution temperature of the electroplating is 55-60°C, and the electroplating time is 40-50min.

[0023] Preferably, the continuous annealing is performed in a full hydrogen protective atmosphere continuous annealing furnace, the annealing temperature is 720-740°C, the annealing time is 120-180s, the hydrogen flow rate is controlled at 20-30m³ / h, and the pressure is maintained at 50-80kPa.

[0024] Preferably, the heating temperature of the hot rolling is 1200-1240°C, and the final rolling temperature is 860-920°C.

[0025] Preferably, the coiling temperature is 560-600°C.

[0026] Preferably, the cold rolling adopts five-stand continuous rolling with a total reduction rate of 82-87%, and smooth roller rolling is adopted in the last stand, with the roughness controlled at ≤0.4μm and RPc≥230.

[0027] Preferably, in the electroplating solution, the concentration of nickel sulfate is 220-250 g / L, the concentration of nickel chloride is 40-45 g / L, the concentration of cobalt sulfate is 2-3 g / L, the concentration of boric acid is 30-40 g / L, the concentration of sodium lauryl sulfate is 0.25-0.35 g / L, and the concentration of citric acid is 5-7 g / L.

[0028] Preferably, during the electroplating process, the electroplating solution is ultrasonically stirred, wherein the ultrasonic frequency is 20-40 kHz and the ultrasonic power is 100-200 W.

[0029] Preferably, the preparation process further includes leveling.

[0030] The leveling conditions include: the roughness Ra of the leveling roller is 1.4-1.6 μm, and the leveling elongation is 0.7-1.2%.

[0031] The second aspect of the present invention provides a pre-nickel-plated steel for a battery shell prepared by the method described above, wherein the pre-nickel-plated steel for a battery shell comprises a steel substrate and a nickel layer covering the surface of the steel substrate;

[0032] The steel matrix contains the following chemical components in weight percentage:

[0033] C: 0.03%-0.06%, Si: 0.01%-0.03%, Mn: 0.15%-0.30%, P: 0.008%-0.015%, S: ≤0.010%, Ti: 0.035%-0.055%, Cr: 0.04%-0.08%, Ni: 0.02%-0.05%, and the balance is Fe and unavoidable impurities.

[0034] Preferably, the thickness of the nickel layer covering the surface of the steel substrate is 1-10 μm.

[0035] Compared with the prior art, the present invention has at least the following beneficial effects:

[0036] The method disclosed in the present invention electroplates a steel substrate in an electroplating solution containing specific components, and controls the concentrations of pretreated fillers, nano-titanium dioxide particles and cerium salts in the electroplating solution within a specific range, thereby producing pre-nickel-plated steel for battery shells having strong nickel plating adhesion, excellent corrosion resistance, low surface iron exposure rate, high hardness and good stamping performance.

[0037] Specifically, the pre-nickel-plated steel for battery shells prepared according to the preparation method of the present invention has the following excellent properties after testing: the nickel-plated layer has strong bonding with the substrate, and the nickel layer does not fall off in the cross-hatch test and the tape sticking test; in the accelerated corrosion test simulating the battery electrolyte environment, after 72 hours of testing, there is no obvious corrosion sign on the surface of the steel strip, showing excellent corrosion resistance; the hardness reaches HV0.3: 140-160, the surface has high hardness and strong compressive resistance; it has good stamping performance, with a yield strength of 240MPa-270MPa, a tensile strength of 360MPa-390MPa, and an elongation of ≥35%, which can meet the stamping requirements of complex-shaped battery shells, effectively reduce the scrap rate in the production process, and improve the quality and production efficiency of the battery shell. In particular, the surface exposed iron rate is low, and the surface exposed iron rate is ≤3% after testing. Compared with products that do not use the continuous annealing process of this patent, the surface exposed iron rate can be reduced by 2-4 percentage points, greatly improving the surface quality and corrosion resistance of the product. DETAILED DESCRIPTION

[0038] The following is a detailed description of the specific embodiments of the present invention. It should be understood that the specific embodiments described herein are only used to illustrate and explain the present invention and are not intended to limit the present invention.

[0039] The endpoints of the ranges and any values ​​disclosed herein are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoints of each range, the endpoints of each range and individual point values, and the individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered to be specifically disclosed herein.

[0040] The method for preparing pre-nickel-plated steel for battery shells provided by the present invention comprises hot rolling, coiling, pickling, cold rolling, nickel electroplating and continuous annealing.

[0041] In a more specific embodiment, the method includes molten iron pretreatment, converter smelting, refining outside the furnace, continuous casting, hot rolling, coiling, pickling, cold rolling, preparation of pretreated filler, nickel electroplating and continuous annealing.

[0042] In a preferred embodiment, the steel matrix obtained after cold rolling contains the following chemical components in weight percentage:

[0043] C: 0.03%-0.06%, Si: 0.01%-0.03%, Mn: 0.15%-0.30%, P: 0.008%-0.015%, S: ≤0.010%, Ti: 0.035%-0.055%, Cr: 0.04%-0.08%, Ni: 0.02%-0.05%, and the balance is Fe and unavoidable impurities.

[0044] The following describes in detail the effect of containing the above chemical components in the steel matrix and limiting each component to the above range.

[0045] Carbon (C): Controlling the carbon content to 0.03%-0.06% improves the strength of the steel to a certain extent. At the same time, in conjunction with the production process of the present invention, it reduces the adverse effects of interstitial solid solution carbon on the plasticity and deep drawing properties of the steel, improves the purity of the steel, and ensures good bonding between the nickel plating layer and the steel substrate.

[0046] Silicon (Si): Limit the silicon content and control it within 0.01%-0.03% to prevent it from forming a difficult-to-remove oxide film on the steel surface, avoid affecting the quality and surface properties of the nickel plating layer, and ensure surface stability during stamping and use.

[0047] Manganese (Mn): An appropriate amount of manganese can improve the strength and toughness of steel, compensate for the strength loss caused by low carbon, optimize the processing performance of steel, and help improve the deformation ability of steel strip during the stamping process. Therefore, the manganese content is controlled at 0.15%-0.30%.

[0048] Phosphorus (P): Within a certain range, phosphorus can improve the corrosion resistance of steel, but its upper limit needs to be strictly controlled to prevent phosphorus segregation from having a negative impact on the stamping performance and forming quality of the steel strip. Therefore, the phosphorus content is controlled at 0.008%-0.015%.

[0049] Sulfur (S): Minimize the sulfur content to reduce hot brittleness, improve the ductility and toughness of the steel, avoid cracks during rolling and stamping, and improve the corrosion resistance of the steel. Therefore, the sulfur content is controlled to ≤0.010%.

[0050] Titanium (Ti): Titanium is a strong carbide-forming element. Controlling its content within 0.035%-0.055% can hinder the growth of austenite grains, refine the grains, improve the deep drawing performance and strength of steel, and improve the bonding strength between the nickel plating layer and the substrate.

[0051] Chromium (Cr) and Nickel (Ni): Chromium and nickel have a synergistic effect. Controlling the chromium content to 0.04%-0.08% and the nickel content to 0.02%-0.05% can significantly improve the corrosion resistance of steel, forming a dense oxide film on the steel surface, enhancing resistance to corrosive media such as electrolytes. Chromium also helps improve the adhesion of the nickel layer, strengthening the bond between the nickel plating and the steel substrate. Traditional battery case steel typically does not contain Cr or Ni. However, the present invention uses the synergistic effect of trace amounts of Cr and Ni to improve the corrosion resistance of the substrate (Cr forms a passivation film) and the bonding strength between the substrate and the nickel plating (Ni reduces the interfacial potential difference).

[0052] In the present invention, operations such as molten iron pretreatment, converter smelting, refining outside the furnace, and continuous casting can be performed according to common processes in the art, as long as the purpose of the present invention can be achieved.

[0053] In one embodiment, molten iron pretreatment uses processes such as slag skimming and blowing to deeply remove harmful impurities such as sulfur and phosphorus in the molten iron, reduce the sulfur content to a lower level, reduce the impact of impurities on steel properties during subsequent smelting, and improve the purity of the molten steel.

[0054] In one embodiment, the converter smelting precisely controls the oxygen blowing intensity, slag making system and final carbon content to ensure uniform composition of the molten steel, effectively remove harmful gases and inclusions in the molten steel, and create good conditions for subsequent refining.

[0055] In one embodiment, the off-furnace refining adopts LF refining + RH refining. In the LF refining stage, white slag refining is used to further desulfurize and deoxidize, and the composition of the molten steel is accurately adjusted; during RH refining, vacuum degassing treatment is used to remove gases such as hydrogen and nitrogen in the molten steel, reduce the content of harmful elements in the steel, and improve the purity and quality stability of the molten steel.

[0056] In one embodiment, continuous casting adopts protective casting technology to prevent secondary oxidation of molten steel, optimize the crystallizer cooling system and billet drawing speed, ensure good surface quality of the billet, dense and uniform internal structure, reduce internal defects, and provide high-quality billets for subsequent rolling.

[0057] In the present invention, the hot rolling heating temperature is controlled to 1200-1240°C to fully dissolve the alloying elements, thereby improving the plasticity and deformability of the steel. In the present invention, the hot rolling finishing temperature is controlled to 860-920°C to ensure that the rolling is carried out in the unrecrystallized austenite region, thereby refining the grains and improving the strength and toughness of the steel strip.

[0058] In the present invention, the coiling temperature may be 560-600° C. Low-temperature coiling can improve the surface quality of the steel strip, refine the grains, and improve the overall performance of the steel strip.

[0059] In one embodiment, the pickling adopts a continuous pickling process to completely remove the iron oxide scale on the surface of the hot-rolled steel strip through pickling to ensure that the surface of the steel strip is clean.

[0060] In some embodiments, the cold rolling process utilizes a five-stand continuous rolling process, with a total reduction ratio of 82%-87%. This high reduction ratio can increase grain distortion energy in the steel, lower the recrystallization temperature, refine grains, and significantly enhance the deep-drawing performance of the steel strip. Furthermore, smooth roller rolling is employed in the final stand, with a roughness controlled to ≤0.4μm and RPc ≥230, effectively improving the surface quality of the finished sheet and enhancing the adhesion of the nickel plating.

[0061] In the present invention, the purpose of preparing the pretreated filler is to use it as a chemical component of the electroplating solution for preparing the electroplating solution.

[0062] In one embodiment, the process of preparing the pretreated filler comprises the following steps:

[0063] (1) subjecting a hydrogen-containing double-capped, epoxy-terminated allyl polyether, concentrated sulfuric acid, and a catalyst to a first reaction under a first heating condition to obtain an epoxy monomer;

[0064] (2) performing a second reaction on the epoxy monomer and KH-550 under a second heating condition, cooling, and purifying to obtain coupling agent A;

[0065] (3) mixing hydrogen peroxide and concentrated sulfuric acid to obtain a pretreatment solution, and then placing a filler in the pretreatment solution, stirring, and centrifuging, wherein the filler includes graphene oxide and diamond;

[0066] (4) The centrifuged product is placed in toluene for ultrasonic dispersion, and then a complex coupling agent is added and stirred under an inert atmosphere, centrifuged, washed, and dried to obtain a pretreated filler, wherein the complex coupling agent includes a coupling agent A and an aminosilane coupling agent.

[0067] In a more specific embodiment, the process for preparing the pretreated filler comprises the following steps:

[0068] Mixing a hydrogen-containing double-end cap, an epoxy-terminated allyl polyether, and concentrated sulfuric acid, heating to 65° C.-75° C., adding a catalyst, and keeping the temperature for reaction for 4-5 hours to obtain an epoxy monomer, wherein the catalyst can be chloroplatinic acid, and the amount of the catalyst is 0.2-0.4wt% of the total amount of the hydrogen-containing double-end cap and the epoxy-terminated allyl polyether, and the molar ratio of the hydrogen-containing double-end cap to the epoxy-terminated allyl polyether is 1:2-2.2;

[0069] Mix the epoxy monomer and KH-550, heat to 65-75°C, stir and react for 2-3 hours, cool after the reaction, and purify to obtain coupling agent A, wherein the mass ratio of the epoxy monomer to KH-550 is 8-10:1;

[0070] Mixing hydrogen peroxide and concentrated sulfuric acid to obtain a pretreatment solution, then placing a filler in the pretreatment solution, stirring at 60°C-65°C for 3h-4h, collecting the product by centrifugation, washing and drying, wherein the filler includes graphene oxide and diamond, and the mass ratio of graphene oxide to diamond is 1:2, and the amount ratio of hydrogen peroxide to concentrated sulfuric acid is 1:2;

[0071] The centrifuged product is placed in anhydrous toluene and ultrasonically dispersed for 1 h-2 h, and then a complex coupling agent is added, stirred under a nitrogen environment for 20 h-24 h, centrifuged, washed, and vacuum dried to obtain a pretreated filler, wherein the complex coupling agent includes coupling agent A and aminosilane coupling agent, the amount of coupling agent A is 15-18 wt% of the complex coupling agent, and the amount of the complex coupling agent is 0.2%-0.5 wt% of the filler.

[0072] In the present invention, the concentration of concentrated sulfuric acid used in the preparation of the pretreated filler is 98 wt %.

[0073] In a preferred embodiment, the nickel electroplating process includes preparing an electroplating solution containing nickel sulfate, nickel chloride, cobalt sulfate, boric acid, sodium lauryl sulfate, citric acid, a pretreated filler, nano-titanium dioxide particles, and a cerium salt, and then placing the cold-rolled steel substrate in the electroplating solution for electroplating. During the electroplating process described herein, only nickel covers the surface of the steel substrate. The inventors have discovered that the presence of the pretreated filler increases the hardness and wear resistance of the resulting coating, thereby preventing scratches during stamping. Furthermore, trace amounts of nano-titanium dioxide particles and cerium salt effectively refine the grain size of the nickel-plated layer.

[0074] In a more preferred embodiment, the concentration of nickel sulfate in the electroplating solution is 220-250 g / L, the concentration of nickel chloride is 40-45 g / L, the concentration of cobalt sulfate is 2-3 g / L, the concentration of boric acid is 30-40 g / L, the concentration of sodium lauryl sulfate is 0.25-0.35 g / L, the concentration of citric acid is 5-7 g / L, the concentration of pretreated filler is 1.2-1.5 g / L, the concentration of nano-titanium dioxide particles is 0.5-1.0 g / L, and the concentration of cerium salt is 0.1-0.2 g / L. By limiting the components and contents in the electroplating solution to this range, especially controlling the concentrations of pretreated fillers, nano-titanium dioxide particles and cerium salts within an appropriate range, the concentrations of various components in the electroplating solution can be precisely controlled so that nickel sulfate and nickel chloride can work together to ensure a stable supply of nickel ions and promote anode activation, cobalt sulfate and boric acid can refine the grains and maintain a stable pH value in the plating solution, and citric acid can complex impurities to improve the purity of the coating. Combined with the wetting and dispersing effect of sodium dodecyl sulfate and the strengthening effect of fillers such as graphene oxide and nano-titanium dioxide, the ultimate goal is to achieve significantly enhanced bonding between the nickel plating layer and the steel substrate, excellent corrosion resistance, qualified hardness and high-quality performance suitable for high-speed stamping, effectively solving the problems of coating shedding, corrosion failure and processing defects in existing pre-nickel-plated steel for battery shells.

[0075] In the present invention, the electroplating method utilizes pulse electroplating, wherein the forward pulse current density is 6-8A / dm², the pulse width is 2-4ms, the reverse pulse current density is 1-2A / dm², the pulse width is 0.5-1ms, and the duty cycle is 30-50%. This electroplating method achieves grain refinement, surface flattening, enhanced bonding, and improved uniformity of the nickel plating layer through the cyclical action of "deposition-dissolution-activation." This solves the common problems of rough coating, poor bonding, and insufficient corrosion resistance in traditional DC electroplating, and is particularly suitable for the high-speed stamping and harsh corrosion resistance requirements of power lithium battery shells.

[0076] In some embodiments, the electroplating conditions include: a plating solution temperature of 55-60° C. and an electroplating time of 40-50 min. In more specific embodiments, the electroplating process can be performed under ultrasonic stirring, wherein the ultrasonic frequency can be 20-40 kHz and the ultrasonic power can be 100-200 W.

[0077] In the present invention, continuous annealing is performed in a continuous annealing furnace in a full hydrogen protective atmosphere. The annealing temperature is 720-740°C, the annealing time is 120-180 seconds, the hydrogen flow rate is controlled at 20-30 m³ / h, and the pressure is maintained at 50-80 kPa. During the annealing process, by controlling the annealing temperature, the bonding strength between the nickel plating layer and the steel substrate can be improved. By precisely controlling the flow rate and pressure of hydrogen in the furnace within the aforementioned range, the hydrogen can be uniformly contacted with the surface of the steel strip. Furthermore, the running speed of the steel strip is strictly controlled to maintain a stable running state in the furnace, wherein the running speed can be 180-220 m / min. In summary, under the aforementioned continuous annealing conditions, atomic diffusion between the nickel plating layer and the steel substrate can be effectively promoted, forming a tighter bonding interface between the nickel plating layer and the steel substrate, and reducing defects and pores at the interface; moreover, hydrogen has a reducing effect at high temperatures, which can reduce the very small amount of iron oxide that may exist on the surface of the steel strip into iron, further reducing the possibility of surface iron exposure, thereby effectively reducing the surface iron exposure rate.

[0078] In the present invention, the preparation process further includes leveling the steel strip after continuous annealing. This leveling can be performed using a laser texturing roller. In some embodiments, the leveling conditions include: a leveling elongation of 0.7-1.2%, a leveling roller roughness Ra of 1.4-1.6 μm, ensuring the steel plate surface roughness is 0.5 μm ≤ Ra ≤ 0.9 μm, and RPc ≥ 130.

[0079] The pre-nickel-plated steel for battery shells prepared by the method described in the present invention has excellent corrosion resistance, high hardness, good stamping performance, and significantly reduced surface iron exposure rate. At the same time, the nickel plating layer has strong bonding with the steel substrate, the nickel layer does not fall off, and the overall performance is excellent.

[0080] The present invention also provides a pre-nickel plated steel for battery shells prepared by the method described above.

[0081] The pre-nickel plated steel for battery case includes a steel substrate and a nickel layer covering the surface of the steel substrate.

[0082] In some preferred embodiments, the steel matrix contains the following chemical compositions in weight percentage:

[0083] C: 0.03%-0.06%, Si: 0.01%-0.03%, Mn: 0.15%-0.30%, P: 0.008%-0.015%, S: ≤0.010%, Ti: 0.035%-0.055%, Cr: 0.04%-0.08%, Ni: 0.02%-0.05%, and the balance is Fe and unavoidable impurities.

[0084] In some more preferred embodiments, the steel matrix contains the following chemical components in weight percentage:

[0085] C: 0.03%-0.05%, Si: 0.015%-0.025%, Mn: 0.15%-0.25%, P: 0.008%-0.015%, S: ≤0.010%, Ti: 0.035%-0.045%, Cr: 0.05%-0.075%, Ni: 0.025%-0.04%, with the balance being Fe and unavoidable impurities. Limiting the chemical composition of the steel matrix to this range can further improve the overall performance of steel used in pre-nickel-plated battery cases.

[0086] In one embodiment, the thickness of the nickel layer covering the surface of the steel substrate can be 1-10 μm. Limiting the thickness of the nickel layer to this range can ensure that the pre-nickel plated battery shell steel has excellent comprehensive properties.

[0087] The pre-nickel-plated steel for battery shells containing the structure and chemical composition of the present invention prepared by the method described in the present invention has excellent corrosion resistance, high hardness, good stamping performance, and significantly reduced surface iron exposure rate. At the same time, the nickel-plated layer has strong bonding with the steel substrate, and the nickel layer does not fall off.

[0088] The present invention will be described in detail below by way of examples, but the scope of protection of the present invention is not limited thereto. In the following examples, unless otherwise specified, the raw materials used are all commonly available commercial products.

[0089] In the following examples, the hydrogen-containing double head was purchased from Shandong Huachen New Materials Co., Ltd.; the epoxy-terminated allyl polyether was purchased from Hangzhou Danwei Technology Co., Ltd.; the aminosilane coupling agent has the structural formula NH2(CH2)3Si(OC2H5)3 and was purchased from Hangzhou Danwei Technology Co., Ltd. Example 1

[0090] The steel matrix of the pre-nickel-plated battery shell steel provided in this embodiment contains the following chemical components in weight percentage:

[0091] C: 0.03%, Si: 0.02%, Mn: 0.20%, P: 0.010%, S: 0.008%, Ti: 0.040%, Cr: 0.06%, Ni: 0.03%, and the balance is Fe and inevitable impurities.

[0092] The preparation process of the pre-nickel-plated battery shell steel includes: molten iron pretreatment, converter smelting, refining outside the furnace, continuous casting, hot rolling, coiling, pickling, cold rolling, pretreatment filler preparation, nickel electroplating, continuous annealing and leveling;

[0093] The heating temperature of the hot rolling is 1230°C, and the final rolling temperature is 880°C;

[0094] The coiling temperature is 580°C;

[0095] The cold rolling adopts five-stand continuous rolling with a total reduction rate of 85%;

[0096] The steel matrix obtained after cold rolling has the following chemical compositions in weight percentages:

[0097] C: 0.03%, Si: 0.02%, Mn: 0.20%, P: 0.010%, S: 0.008%, Ti: 0.040%, Cr: 0.06%, Ni: 0.03%, and the balance is Fe and inevitable impurities.

[0098] The process of preparing the pretreated filler comprises the following steps:

[0099] A hydrogen-containing double-end cap, an epoxy-terminated allyl polyether, and concentrated sulfuric acid (98 wt%) were mixed, heated to 70°C (pretreatment temperature), a catalyst was added, and the mixture was kept warm for 4.5 hours to obtain an epoxy monomer, wherein the catalyst was chloroplatinic acid, the amount of the catalyst was 0.3 wt% of the total amount of the hydrogen-containing double-end cap and the epoxy-terminated allyl polyether, the molar ratio of the hydrogen-containing double-end cap to the epoxy-terminated allyl polyether was 1:2, and the mass ratio of the concentrated sulfuric acid to the hydrogen-containing double-end cap was 2:1;

[0100] The epoxy monomer and KH-550 were mixed, heated to 70°C, stirred and reacted for 2.5 hours, cooled after the reaction, and purified to obtain coupling agent A, wherein the mass ratio of the epoxy monomer to KH-550 was 9:1;

[0101] Mixing hydrogen peroxide and concentrated sulfuric acid (98 wt%) to obtain a pretreatment solution, then placing a filler in the pretreatment solution, stirring at 60° C. for 3.5 hours, collecting the product by centrifugation, washing, and drying, wherein the filler comprises graphene oxide and diamond, and the mass ratio of graphene oxide to diamond is 1:2, and the amount ratio of hydrogen peroxide to concentrated sulfuric acid is 1:2;

[0102] The centrifuged product was ultrasonically dispersed in anhydrous toluene for 1.5 hours, and then a complex coupling agent was added. The mixture was stirred for 22 hours under a nitrogen environment, centrifuged, washed, and vacuum-dried to obtain a pretreated filler, wherein the complex coupling agent included coupling agent A and aminosilane coupling agent. The amount of coupling agent A was 16wt% of the complex coupling agent, and the amount of the complex coupling agent was 0.3wt% of the filler.

[0103] The nickel electroplating process includes: a cold-rolled steel substrate is placed in an electroplating solution composed of 230 g / L nickel sulfate, 40 g / L nickel chloride, 2 g / L cobalt sulfate, 35 g / L boric acid, 0.3 g / L sodium lauryl sulfate, 6 g / L citric acid, 1.5 g / L pretreated filler, 0.8 g / L nano-titanium dioxide particles, and 0.1 g / L cerium salt (cerium nitrate) for electroplating. The electroplating utilizes pulse plating technology, with a forward pulse current density of 6 A / dm², a pulse width of 3 ms, a reverse pulse current density of 1.5 A / dm², a pulse width of 0.8 ms, and a duty cycle of 40%. The electroplating solution is maintained at a temperature of 55°C for 45 minutes. During the electroplating process, the electroplating solution is ultrasonically agitated at a frequency of 30 kHz and a power of 150 W. The nickel layer covering the surface of the steel substrate has a thickness of 3 μm.

[0104] Continuous annealing is carried out in a full hydrogen protective atmosphere continuous annealing furnace. The annealing temperature is 730°C, the annealing time is 150s, the hydrogen flow rate is controlled at 25m³ / h, and the pressure is maintained at 60kPa. Furthermore, the running speed of the steel strip is strictly controlled to maintain a stable running state in the furnace at a running speed of 200m / min.

[0105] The surface is smoothed by a laser texturing roller, the roughness Ra of the smoothing roller is 1.5 μm, and the smoothing elongation is 0.9%.

[0106] Examples 2-5 and Comparative Examples 1-7 were implemented according to the method of Example 1, except that the chemical composition and process conditions were different. The thickness specification of the final products obtained was 0.30 mm. For details, see Table 1, Table 2 and Table 3.

[0107] Table 1 Chemical composition of steel matrix, wt%

[0108] serial number C Si Mn P S Ti Cr Ni Nb Example 1 0.03% 0.02% 0.20% 0.010% 0.008% 0.040% 0.06% 0.032% - Example 2 0.05% 0.025% 0.25% 0.012% 0.007% 0.045% 0.07% 0.040% - Example 3 0.035% 0.015% 0.18% 0.009% 0.006% 0.038% 0.05% 0.025% - Example 4 0.045% 0.022% 0.22% 0.011% 0.007% 0.042% 0.065% 0.035% - Example 5 0.048% 0.023% 0.23% 0.013% 0.008% 0.044% 0.075% 0.040% - Comparative Example 1 0.021% 0.02% 0.15% 0.012% 0.008% 0.035% 0.05% 0.03% - Comparative Example 2 0.03% 0.02% 0.20% 0.010% 0.008% 0.040% 0.06% 0.032% - Comparative Example 3 0.03% 0.02% 0.20% 0.010% 0.008% 0.040% 0.06% 0.032% - Comparative Example 4 0.03% 0.02% 0.20% 0.010% 0.008% 0.040% 0.06% 0.032% - Comparative Example 5 0.004% 0.03% 0.14% 0.018% 0.012% 0.055% - - 0.015% Comparative Example 6 0.006% 0.020% 0.32% 0.012% 0.007% 0.045% - - 0.015% Comparative Example 7 0.03% 0.02% 0.20% 0.010% 0.008% 0.040% 0.06% 0.032% -

[0109] Table 2 Hot rolling and electroplating process

[0110] serial number Heating temperature / ℃ Finish rolling temperature / ℃ Coiling temperature / ℃ Pickling cold rolling total reduction rate / % Pretreatment temperature / ℃ Plating time / min Pretreatment filler concentration g / L, nano titanium dioxide concentration g / L, cerium salt concentration g / L Example 1 1230 880 580 85 70 45 1.5、0.8、0.1 Example 2 1225 875 575 84 68 42 1.2、1、0.2 Example 3 1235 885 585 86 72 48 1.3、0.5、0.2 Example 4 1228 878 578 84.5 71 44 1.4、0.6、0.15 Example 5 1232 882 582 85.5 69 46 1.4、0.9.1.2 Comparative Example 1 1230 880 580 85 70 45 1.5、0.8、0.1 Comparative Example 2 1230 880 580 85 70 45 1.5、0.3、0.1 Comparative Example 3 1230 880 580 85 70 45 1.5、1.5、0.1 Comparative Example 4 1230 880 580 85 70 45 1.0、0.8、0.1 Comparative Example 5 1230 880 580 85 70 45 1.8、0.8、0.1 Comparative Example 6 1230 880 580 85 70 45 1.5、0.8、0.05 Comparative Example 7 1230 880 580 85 70 45 1.5、0.8、0.3

[0111] Table 3 Annealing process

[0112]

[0113] Test Case

[0114] The final products obtained in the examples and comparative examples were subjected to comprehensive performance testing, and the test items and results are shown in Table 4. The nickel plating adhesion test used a cross-hatch test and a tape sticking test to evaluate the degree of adhesion between the nickel layer and the substrate. The corrosion resistance was tested by an accelerated corrosion test using 5% NaCl salt spray, and the corrosion of the steel strip surface was recorded after 48 hours. The hardness test used a Vickers hardness tester to measure the surface HV0.3 hardness value. The stamping performance was evaluated by performing a stamping test on a 150-piece / min steel shell stamping equipment to evaluate the yield strength, tensile strength, elongation, and quality after stamping, and to observe whether there were defects such as cracks and lugs. The surface exposed iron rate was measured by observing the nickel-plated surface using a scanning electron microscope (SEM). Within the unit detection area, the area containing iron elements was identified and counted using energy spectrum analysis (EDS) technology. The proportion of this area is the surface exposed iron rate.

[0115] Table 4

[0116] serial number Nickel plating adhesion Surface exposed iron rate Accelerated corrosion test results Hardness HV0.3 Yield strength Rp0.2 / MPa Tensile strength Rm / MPa Elongation A50 / % Stamping and forming evaluation Nickel layer thickness (μm) Example 1 No shedding 2.32% No obvious signs of corrosion on the surface 146 245 370 36 No obvious defects, good molding 3.1 Example 2 No shedding 2.15% No obvious signs of corrosion on the surface 151 262 380 35 No obvious defects, good molding 3.6 Example 3 No shedding 1.46% No obvious signs of corrosion on the surface 148 257 375 37 No obvious defects, good molding 4.5 Example 4 No shedding 2.23% No obvious signs of corrosion on the surface 152 255 385 36 No obvious defects, good molding 3.8 Example 5 No shedding 2.69% No obvious signs of corrosion on the surface 155 263 390 35 No obvious defects, good molding 3.7 Comparative Example 1 No shedding 2.38% No obvious signs of corrosion on the surface 123 224 340 36 Low strength and hardness 3.4 Comparative Example 2 No shedding 5.73% Obvious corrosion 135 240 366 36 Low hardness and high iron exposure rate 2.8 Comparative Example 3 Slight shedding 5.94% A few corrosion spots appear 162 263 390 35 Stamping plating falls off and the exposed iron rate is high 2.5 Comparative Example 4 Slight shedding 3.12% A small amount of corrosion occurs 138 243 376 38 The stamping plating is peeling off 3.2 Comparative Example 5 No shedding 5.69% A few corrosion spots appear 132 240 360 34 Mixed crystals appear locally, elongation is low, and stamping lugs are severe. 4.2 Comparative Example 6 No shedding 5.36% A few corrosion spots appear 125 225 365 37 Low hardness and strength 3.2 Comparative Example 7 No shedding, but uneven coating thickness 5.42% A few corrosion spots appear 143 248 372 36 Plating peeling off during stamping 3.2

[0117] As can be seen from Table 4, the various properties of Examples 1-5 can meet the expected requirements of the present invention. The nickel plating layer has strong bonding strength, excellent corrosion resistance, low surface iron exposure rate, high hardness and good stamping performance, which can meet the high-quality production requirements of power lithium battery shells.

[0118] The C content in Comparative Example 1 is relatively low, resulting in insufficient hardness and strength of the material.

[0119] In Comparative Example 2, the concentration of nano-titanium dioxide is relatively low, the coating grains are coarse, the surface hardness is relatively low, the exposed iron rate is increased, and the corrosion resistance is weak.

[0120] In Comparative Example 3, the nano-titanium dioxide exceeds the upper limit requirement, resulting in a rough coating surface, high surface hardness, a significantly increased exposed iron rate, and weak corrosion resistance.

[0121] In Comparative Example 4, the concentration of the pre-treated filler was lower than the lower limit requirement, resulting in weak bonding between the coating and the steel substrate, peeling of the coating, and weak corrosion resistance.

[0122] Comparative Example 5 employed an ultra-low carbon composition, resulting in low hardness and a high risk of mixed crystals, resulting in low elongation and defects such as stamping lugs. The pretreatment filler concentration exceeded the upper limit requirement, causing filler aggregation during the electroplating process, forming coarse grains on the coating surface, poor adhesion, and cracks in the coating after stamping.

[0123] Comparative Example 6 also employed an ultra-low carbon composition design without the addition of Cr or Ni, resulting in low hardness and yield strength, and insufficient pressure resistance. The low cerium salt concentration resulted in coarse grains on the coating surface, increased porosity, and a higher iron exposure rate, resulting in poor corrosion resistance.

[0124] In Comparative Example 7, due to the high concentration of cerium salt in the electroplating solution, the surface of the coating is rough, the exposed iron rate is high, and the thickness of the coating surface is uneven.

[0125] It should be understood that parts not elaborated in detail in this specification belong to the prior art.

[0126] The preferred embodiments of the present invention have been described in detail above, but the present invention is not limited thereto. Within the technical concept of the present invention, various simple variations of the technical solution of the present invention may be made, including combining the various technical features in any other appropriate manner. These simple variations and combinations should also be regarded as disclosed in the present invention and fall within the scope of protection of the present invention.

Claims

1. A method for preparing pre-nickel plated steel for battery shells, characterized in that: The method includes hot rolling, coiling, pickling, cold rolling, nickel electroplating and continuous annealing; The nickel electroplating process comprises: preparing an electroplating solution with nickel sulfate, nickel chloride, cobalt sulfate, boric acid, sodium lauryl sulfate, citric acid, pretreated filler, nano titanium dioxide particles and cerium salt, and then placing the cold-rolled steel substrate in the electroplating solution for electroplating; The concentration of the pretreated filler is 1.2-1.5 g / L, the concentration of the nano-titanium dioxide particles is 0.5-1.0 g / L, and the concentration of the cerium salt is 0.1-0.2 g / L; The pre-nickel-plated battery shell steel has a hardness HV0.3 of 140-160, a yield strength of 240MPa-270MPa, a tensile strength of 360MPa-390MPa, and an elongation of ≥35%; The preparation process of the pretreated filler comprises the following steps: (1) subjecting a hydrogen-containing double-capped, epoxy-terminated allyl polyether, concentrated sulfuric acid, and a catalyst to a first reaction under a first heating condition to obtain an epoxy monomer; (2) performing a second reaction on the epoxy monomer and KH-550 under a second heating condition, cooling, and purifying to obtain coupling agent A; (3) mixing hydrogen peroxide and concentrated sulfuric acid to obtain a pretreatment solution, and then placing a filler in the pretreatment solution, stirring, and centrifuging, wherein the filler includes graphene oxide and diamond; (4) The centrifuged product is placed in toluene for ultrasonic dispersion, and then a complex coupling agent is added and stirred under an inert atmosphere, centrifuged, washed, and dried to obtain a pretreated filler, wherein the complex coupling agent includes a coupling agent A and an aminosilane coupling agent.

2. The method according to claim 1, characterized in that The preparation process of the pretreated filler comprises: Mixing a hydrogen-containing double-end cap, an epoxy-terminated allyl polyether, and concentrated sulfuric acid, heating to 65° C.-75° C., adding a catalyst, and keeping the temperature for reaction for 4-5 hours to obtain an epoxy monomer, wherein the catalyst is chloroplatinic acid, and the amount of the catalyst is 0.2-0.4wt% of the total amount of the hydrogen-containing double-end cap and the epoxy-terminated allyl polyether, and the molar ratio of the hydrogen-containing double-end cap to the epoxy-terminated allyl polyether is 1:2-2.2; Mix the epoxy monomer and KH-550, heat to 65-75°C, stir and react for 2-3 hours, cool after the reaction, and purify to obtain coupling agent A, wherein the mass ratio of the epoxy monomer to KH-550 is 8-10:1; Mixing hydrogen peroxide and concentrated sulfuric acid to obtain a pretreatment solution, then placing a filler in the pretreatment solution, stirring at 60° C.-65° C. for 3 h-4 h, collecting the product by centrifugation, washing, and drying, wherein the filler comprises graphene oxide and diamond, and the mass ratio of graphene oxide to diamond is 1:2, and the amount ratio of hydrogen peroxide to concentrated sulfuric acid is 1:2; The centrifuged product is placed in anhydrous toluene and ultrasonically dispersed for 1 h-2 h, and then a complex coupling agent is added, stirred for 20 h-24 h under a nitrogen environment, centrifuged, washed, and vacuum dried to obtain a pretreated filler, wherein the complex coupling agent includes coupling agent A and aminosilane coupling agent, the amount of coupling agent A is 15-18 wt% of the complex coupling agent, and the amount of the complex coupling agent is 0.2-0.5 wt% of the filler.

3. The method according to claim 1, characterized in that The electroplating adopts pulse electroplating, with a forward pulse current density of 6-8A / dm², a pulse width of 2-4ms; a reverse pulse current density of 1-2A / dm², a pulse width of 0.5-1ms, and a duty cycle of 30-50%; the plating solution temperature of the electroplating is 55-60°C, and the electroplating time is 40-50min.

4. The method according to claim 1, wherein The continuous annealing is carried out in a continuous annealing furnace in a full hydrogen protective atmosphere, the annealing temperature is 720-740°C, the annealing time is 120-180s, the hydrogen flow rate is controlled at 20-30m³ / h, and the pressure is maintained at 50-80kPa.

5. The method according to claim 1, wherein The heating temperature of the hot rolling is 1200-1240°C, and the final rolling temperature is 860-920°C; and / or, the coiling temperature is 560-600° C.; And / or, the cold rolling adopts five-stand continuous rolling with a total reduction rate of 82-87%, and smooth roller rolling is adopted in the last stand, with the roughness controlled at ≤0.4μm and RPc≥230.

6. The method according to claim 1, characterized in that In the electroplating solution, the concentration of nickel sulfate is 220-250 g / L, the concentration of nickel chloride is 40-45 g / L, the concentration of cobalt sulfate is 2-3 g / L, the concentration of boric acid is 30-40 g / L, the concentration of sodium lauryl sulfate is 0.25-0.35 g / L, and the concentration of citric acid is 5-7 g / L; And / or, during the electroplating process, the electroplating solution is ultrasonically stirred, wherein the ultrasonic frequency is 20-40 kHz and the ultrasonic power is 100-200 W.

7. The method according to claim 1, characterized in that The method also includes leveling; The smoothing conditions include: the roughness Ra of the smoothing roller is 1.4-1.6 μm, and the smoothing elongation is 0.7-1.2%.

8. The pre-nickel plated steel for battery shell prepared by the method according to any one of claims 1 to 7, characterized in that: The pre-nickel-plated steel for battery shells comprises a steel substrate and a nickel layer covering the surface of the steel substrate; The steel matrix contains the following chemical components in weight percentage: C: 0.03%-0.06%, Si: 0.01%-0.03%, Mn: 0.15%-0.30%, P: 0.008%-0.015%, S: ≤0.010%, Ti: 0.035%-0.055%, Cr: 0.04%-0.08%, Ni: 0.02%-0.05%, and the balance is Fe and unavoidable impurities.

9. The pre-nickel plated steel for battery case according to claim 8, characterized in that: The thickness of the nickel layer covering the surface of the steel substrate is 1-10 μm.

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