Preparation method of high-stability nickel-metal hydride battery electrode material

Abstract

The invention discloses a preparation method of a high-stability nickel-metal hydride battery electrode material, and relates to the technical field of electric vehicle batteries, more hydroxyls or active groups can be generated on the surface of foamed nickel through acid pickling to remove nickel oxide and low-temperature plasma etching, bonding with a protective layer is enhanced, and when a carbon-nitrogen protective layer is prepared, the stability of the nickel-metal hydride battery electrode material is improved. According to the method, a nanoscale transition layer is firstly manufactured, then a carbon-nitrogen protection layer is manufactured, foamed nickel and the carbon-nitrogen protection layer can be bridged through the nanoscale transition layer, the adhesive force is improved, active substance particles are ensured to be uniformly distributed by coating active substance slurry in a spray pyrolysis mode, and a small amount of components which are compatible with the carbon-nitrogen protection layer can be added into the active substance slurry; the active material layer and the carbon-nitrogen protection layer are bonded more firmly through the low-temperature heat treatment, more stable bonding can be formed between the active materials and between the active materials and the carbon-nitrogen protection layer through the low-temperature heat treatment, meanwhile, solvents or impurities in the active material slurry are removed, and the structural stability is further improved.

Description

Technical Field

[0001] This invention belongs to the field of electric vehicle battery technology, specifically relating to a method for preparing a high-stability nickel-metal hydride battery electrode material. Background Technology

[0002] Nickel-metal hydride (NiMH) batteries are one of the most commonly used batteries in electric vehicles. The electrode materials of NiMH batteries are mainly composed of positive electrode materials and negative electrode materials. Currently, the electrode materials are usually prepared by using hydrogen reduction or acid treatment to remove nickel oxide, and then by chemical vapor deposition and other processes, and finally filled into nickel foam.

[0003] For example, Chinese patent application number 201610668086.4 discloses a method for preparing an ultra-long-life nickel-metal hydride battery electrode material. This method includes the following steps: first, removing nickel oxide from the surface of the pore walls of nickel foam; then, growing a carbon- and / or nitrogen-containing protective layer on the surface of the pore walls of the nickel foam; then forming a uniform electrode active material layer on the surface of the carbon- and / or nitrogen-containing protective layer; and finally, filling the nickel foam with electrode active material. This invention, by removing nickel oxide from the surface of nickel foam and forming a carbon- and / or nitrogen-containing protective layer on its surface, effectively increases the bonding ability between the nickel foam and the electrode active material, reducing contact resistance; it effectively inhibits dendrite formation, preventing the separator from being punctured and causing a short circuit between the positive and negative electrodes; it effectively coats the nickel foam, preventing it from being corroded and consumed during battery cycling, maintaining the integrity of the electrode structure, and improving the utilization rate of the active material, thereby extending the cycle life of the nickel-metal hydride battery.

[0004] However, although the protective layer contains carbon or nitrogen to improve conductivity and bonding ability, if the interface between the protective layer and the nickel foam substrate is not strong, the protective layer may detach due to mechanical stress or chemical corrosion during long-term charge-discharge cycles. This can lead to uneven protective layer distribution and localized failure (such as damage to the electrode structure, resulting in electrode structure failure). The overall capacity decreases significantly with increasing cycle number, and residual nickel oxide or protective layer failure can increase contact resistance, exacerbate battery heating, and reduce efficiency, thus affecting the overall stability of battery material performance. Therefore, we need to propose a method for preparing highly stable nickel-metal hydride battery electrode materials to solve the above-mentioned problems, so as to effectively ensure the uniform distribution of active materials while improving the adhesion between the protective layer and the nickel foam, thereby improving the stability of electrode material performance. Summary of the Invention

[0005] The purpose of this invention is to provide a method for preparing a highly stable nickel-metal hydride battery electrode material, which can effectively ensure the uniform distribution of active materials while improving the adhesion between the protective layer and the nickel foam, thereby improving the stability of the electrode material performance and solving the problems mentioned in the background art.

[0006] To achieve the above objectives, the present invention adopts the following technical solution:

[0007] A method for preparing a highly stable nickel-metal hydride battery electrode material includes the following steps:

[0008] S1. Immerse the nickel foam in a 5%-8% dilute hydrochloric acid solution while simultaneously using ultrasonic vibration to remove the dense structure of nickel oxide on the surface of the nickel foam pores.

[0009] S2. Low-temperature plasma etching is performed on the deoxidized nickel foam to form active sites on the surface of the nickel foam.

[0010] S3. A nanoscale transition layer is coated on the etched nickel foam surface using the sol-gel method;

[0011] S4. A carbon-nitrogen protective layer is grown on the surface of a nanoscale transition layer using low-temperature chemical vapor deposition.

[0012] S5. Prepare an active substance slurry, coat the active substance slurry onto the surface of the carbon-nitrogen protective layer by spray pyrolysis, and dry it in a hot air environment.

[0013] S6. Place the surface-coated nickel foam into a vacuum chamber and use vacuum filtration and gradient pressurization to vacuum impregnate and fill the internal active material of the nickel foam to obtain the electrode material.

[0014] S7. Perform low-temperature heat treatment on the filled electrode material, and at the same time use inert gas to protect the electrode.

[0015] Preferably, when preparing a 5%-8% dilute hydrochloric acid solution, the amount of HCl and water is calculated based on a mass fraction of 5%-8%. In a fume hood, the concentrated hydrochloric acid is slowly poured into deionized water while stirring, and then cooled to 25-30°C.

[0016] Preferably, the nickel foam needs to be rinsed with deionized water before soaking in the dilute hydrochloric acid solution. Then, the cleaned nickel foam is completely immersed in the prepared dilute hydrochloric acid solution, avoiding the adhesion of air bubbles. At this time, the ultrasonic equipment is turned on for intermittent continuous oscillation. The ultrasonic equipment is set with a power of 150-200W, a frequency of 35-42kHz, an oscillation time of 10-15min, and an interval of 3-5 seconds. During the pickling process, the solution temperature is kept stable at 25-30℃. After the pickling time is completed, the nickel foam is immediately removed from the hydrochloric acid solution and the surface of the nickel foam is repeatedly rinsed with deionized water until the rinsing solution is neutral. Then, the rinsed nickel foam is placed in a vacuum drying oven and dried at 60-80℃ for 1-2 hours to remove surface moisture.

[0017] Preferably, during low-temperature plasma etching, argon and oxygen in a volume ratio of 9:1 are used as the gas source, the power is 80-100W, the processing time is 5-8min, and the surface roughness of the nickel foam after etching is reduced to 0.8-1.2μm. At the same time, a large number of active hydroxyl groups and unsaturated dangling bonds are generated on the surface of the hole wall.

[0018] The preferred etching process is as follows:

[0019] A1. Equipment Debugging: Use a 13.56MHz low-temperature radio frequency plasma etching instrument to check the airtightness of the equipment. Cut the nickel foam to the electrode size, lay it flat and fix it on the sample stage, and evacuate to 1×10⁻⁶. -3 -5×10 -3 Pa;

[0020] A2. Introduce the mixed gas at an Ar / O2 volume ratio of 9:1, with a total flow rate of 20-30 sccm, and control the chamber pressure at 10-20 Pa.

[0021] A3. Set the power to 80-100W and the time to 5-8min. Turn on the power and monitor that the plasma is a uniform light of pale blue. Ensure that the roughness reaches Ra = 0.8-1.2μm.

[0022] Preferably, the nanoscale transition layer is prepared by using cobalt nitrate and citric acid as raw materials to form a sol with a concentration of 0.2 mol / L. This sol is then used to uniformly cover the pore walls of the nickel foam through impregnation and lifting, with a lifting speed of 5-8 mm / s, followed by drying at 120-150°C. The Co in the nanoscale transition layer... 2+ It can react with the -OH on the surface of nickel foam to form Co-O-Ni chemical bonds. At the same time, the nanoscale transition layer itself is a porous structure with a pore size of 5-10 nm, which can form a mechanical bond with the subsequent carbon-nitrogen protective layer.

[0023] Preferably, during the growth of the carbon-nitrogen protective layer, the gas source is acetylene + ammonia with a volume ratio of 3:1, the reaction temperature is controlled at 500-550℃, and the holding time is 20-25min; the overall thickness of the generated carbon-nitrogen protective layer is 50-80nm, the distribution is relatively uniform, and it is embedded in the surface of the nickel foam through the porous structure of the nanoscale transition layer.

[0024] Preferably, when preparing the active material slurry, nickel hydroxide is used as the active material, 5%-8% carbon nanotubes are added as a conductive agent, 2%-3% sodium carboxymethyl cellulose is added as a dispersant, and 0.5%-1% melamine is added. The nitrogen-containing small molecules in melamine can react with the dangling bonds of the carbon-nitrogen protective layer. The slurry is stirred at high speed of 3000-4000 rpm for 30 minutes to ensure that the slurry is uniformly dispersed and the particle size distribution is ≤5μm.

[0025] Preferably, when coating the active material slurry by spray pyrolysis, the slurry is sprayed onto the surface of the carbon-nitrogen protective layer in the form of droplets through a high-pressure nozzle with a nozzle diameter of 0.1 mm, and dried in a hot air environment at 80-100℃. The coating thickness is controlled at 100-150 nm, and the flatness error is ≤5 nm.

[0026] The preferred low-temperature heat treatment process is as follows:

[0027] B1. If there is loose powder on the electrode surface, it needs to be wiped off; if a slurry coating is used, let it stand at room temperature for 10-15 minutes after coating to allow the solvent to evaporate, and check the airtightness of the tube furnace.

[0028] B2. Place the electrodes in a quartz boat in the constant temperature zone of the tube furnace, and introduce high-purity nitrogen gas at a rate of 100-150 mL / min for 15-20 min. Then purge the air to make the oxygen concentration ≤0.1%.

[0029] B3. Heat to 200-220℃ at a rate of 5-8℃ / min, hold for 30-40min to solidify the chemical bonds between the active material and the protective layer, and remove residual solvent;

[0030] B4. Reduce the temperature to below 80℃ at a rate of 3-5℃ / min, maintain with nitrogen, and remove the electrode after it reaches room temperature. After heat treatment, the surface of the obtained electrode has no powder falling off and has a uniform dark green appearance.

[0031] The method for preparing a high-stability nickel-metal hydride battery electrode material proposed in this invention has the following advantages compared with the prior art:

[0032] 1. This invention, through acid pickling to remove nickel oxide and low-temperature plasma etching, enables the generation of more hydroxyl or active groups on the surface of nickel foam, enhancing the bonding with the protective layer. During the preparation of the carbon-nitrogen protective layer, a nanoscale transition layer is first formed, followed by the carbon-nitrogen protective layer. The nanoscale transition layer bridges the nickel foam and the carbon-nitrogen protective layer, improving adhesion and ensuring a more uniform distribution of the carbon-nitrogen protective layer. The active material slurry is coated using a spray pyrolysis method to ensure uniform distribution of active material particles. A small amount of components with affinity for the carbon-nitrogen protective layer can be added to the active material slurry, making the bond between the active material layer and the carbon-nitrogen protective layer stronger, more uniform, and with higher utilization. Low-temperature heat treatment further enables the formation of more stable bonds between active materials and between active materials and the carbon-nitrogen protective layer, while removing solvents or impurities from the active material slurry, further improving structural stability and effectively reducing the shedding or failure of the carbon-nitrogen protective layer during cycling, thus improving the stability of the electrode material performance.

[0033] 2. The active hydroxyl groups and unsaturated dangling bonds generated during the etching process can chemically bond with the functional groups in the carbon-nitrogen protective layer, further strengthening the interfacial bonding. At the same time, these active sites can also serve as nucleation centers for subsequent electrode active materials, guiding the uniform deposition of active materials and avoiding capacity decay caused by local agglomeration. Attached Figure Description

[0034] Figure 1 A flowchart according to an embodiment of the present invention is shown;

[0035] Figure 2 A flowchart of the etching process according to an embodiment of the present invention is shown;

[0036] Figure 3 A flowchart of a low-temperature heat treatment process according to an embodiment of the present invention is shown. Detailed Implementation

[0037] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. The specific embodiments described herein are merely used to explain the present invention and are not intended to limit the present invention. 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.

[0038] This invention provides, for example Figure 1-3 The method for preparing a high-stability nickel-metal hydride battery electrode material, as shown, includes the following steps:

[0039] S1. Immerse the nickel foam in a 5%-8% dilute hydrochloric acid solution while simultaneously using ultrasonic vibration to remove the dense structure of nickel oxide on the surface of the nickel foam pores.

[0040] When preparing a 5%-8% dilute hydrochloric acid solution, calculate the amount of HCl and water based on a mass fraction of 5%-8%. For example, to prepare 1000g of solution, you need 50-80g of concentrated hydrochloric acid + 950-920g of deionized water. In a fume hood, slowly pour the concentrated hydrochloric acid into the deionized water (do not pour in the reverse direction to prevent bumping), stirring while pouring, and cool to 25-30℃.

[0041] Before immersing the nickel foam in dilute hydrochloric acid solution, it needs to be rinsed with deionized water to remove surface dust, oil, and other impurities. Then, the cleaned nickel foam is completely immersed in the prepared dilute hydrochloric acid solution, avoiding air bubbles. Air bubbles can prevent localized contact with the acid, resulting in residual nickel oxide. Therefore, it is crucial to ensure no air bubbles are present during immersion. At this point, an ultrasonic device is activated for intermittent continuous oscillation. The ultrasonic device is set to a power of 150-200W, a frequency of 35-42kHz, an oscillation time of 10-15 minutes, and an interval of 3-5 seconds. During the acid pickling process, the solution temperature is maintained at a stable 25-30℃. After the acid pickling time is completed, the nickel foam is immediately removed from the hydrochloric acid solution and repeatedly rinsed with deionized water until the rinsing solution is neutral (pH value reaches 7). The rinsed nickel foam is then placed in a vacuum drying oven and dried at 60-80℃ for 1-2 hours to remove surface moisture. Finally, X-ray photoelectron spectroscopy is used to detect the nickel oxide content on the surface of the nickel foam, ensuring that the residual amount is not higher than 0.1%.

[0042] Deep removal of nickel oxide can be achieved through acid pickling and ultrasonic assistance, laying the foundation for the subsequent growth of a carbon-nitrogen protective layer.

[0043] S2. Low-temperature plasma etching is performed on the deoxidized nickel foam to form active sites on the surface of the nickel foam.

[0044] During low-temperature plasma etching, argon and oxygen in a volume ratio of 9:1 are used as the gas source, with a power of 80-100W and a processing time of 5-8 minutes. After etching, the surface roughness of the nickel foam is reduced to 0.8-1.2μm, and a large number of active hydroxyl groups and unsaturated dangling bonds are generated on the surface of the hole walls. The specific etching process is as follows:

[0045] A1. Equipment Debugging: Use a 13.56MHz low-temperature radio frequency plasma etching instrument to check the airtightness of the equipment to avoid gas leakage that could lead to uneven etching. Cut the nickel foam to the electrode size, lay it flat and fix it on the sample stage, and evacuate to 1×10⁻⁶. -3 -5×10 -3 Pa, a high vacuum environment can reduce the interference of air impurities on etching;

[0046] A2. Introduce the mixed gas at a volume ratio of 9:1 for Ar / O2, with a total flow rate of 20-30 sccm. Control the chamber pressure at 10-20 Pa. Ar physically bombards to create a rough surface, while O2 helps generate functional groups.

[0047] Ar gas (inert gas): Its main function is to generate high-energy ions to physically bombard the surface of nickel foam, forming a rough structure;

[0048] O2 gas (reactive gas): It undergoes a slight oxidation-sputtering reaction with the metallic Ni on the surface of the nickel foam, and at the same time generates active hydroxyl groups (-OH) and unsaturated dangling bonds on the rough surface remaining after etching.

[0049] Control the total gas flow rate to 20-30 sccm (standard cubic centimeters per minute) and maintain the cavity pressure at 10-20 Pa (too high pressure will reduce ion kinetic energy, and too low pressure will result in insufficient ion density, both of which will affect the etching effect); set the RF power supply to 80-100W: if the power is too low, the ion bombardment energy will be insufficient and the roughness will not be effectively improved (it will be difficult to achieve Ra = 0.8-1.2μm); if the power is too high, it may lead to excessive etching of the foam nickel hole walls, which will damage the integrity of the substrate structure.

[0050] A3. Set the power to 80-100W and the time to 5-8min. Turn on the power and monitor that the plasma shows a uniform pale blue light. Ensure that the roughness reaches Ra = 0.8-1.2μm.

[0051] The roughness calculation formula is:

[0052]

[0053] Where Ra is the surface roughness, L is the sampling length, and y(x) is the perpendicular distance from a point on the surface profile to the baseline. dx is the integral of the absolute value of the profile deviation over the sampling length L, where dx is the differential sign in calculus and represents the length of the minimum segment over the sampling length L.

[0054] Turn on the RF power supply and begin etching: During the process, monitor the plasma color inside the chamber through the observation window of the device (normally a pale blue uniform glow; if uneven brightness occurs in some areas, the sample position or gas flow rate needs to be adjusted); after the set etching time is reached, first turn off the RF power supply, and then stop the introduction of Ar / O2 mixed gas; keep the vacuum pump running for 5-10 minutes to remove residual reactive gas from the chamber (to avoid residual O2 from continuously oxidizing the surface of the nickel foam); then introduce inert N2 gas into the chamber to atmospheric pressure and slowly open the chamber; after removing the nickel foam, immediately use an atomic force microscope (AFM) to check the surface roughness and confirm that the surface roughness Ra value reaches 0.8-1.2 μm.

[0055] A4. Verify surface-active groups using Fourier transform infrared spectroscopy (FTIR) or XPS: -OH groups must be detected (3200-3600 cm⁻¹). -1 Characteristic peaks) and unsaturated C=C / C=N bonds (1600-1700 cm⁻¹) -1 Characteristic peaks (generated by the breaking of surface chemical bonds induced by plasma bombardment);

[0056] After etching, the nickel foam needs to be transferred to the next carbon / nitrogen protective layer growth process within 30 minutes to avoid prolonged exposure to air, which could cause the active sites to be covered by moisture / CO2 in the air.

[0057] After etching, the surface of the nickel foam changes from a smooth state (Ra=0.2μm) to a micro-rough state with a roughness of 0.8-1.2μm, forming a micro-morphology similar to an anchoring structure. The subsequently grown carbon-nitrogen protective layer will be embedded in the depressions of the rough surface, significantly improving the interface adhesion through mechanical interlocking and preventing the protective layer from falling off due to mechanical stress during long-term charge-discharge cycles.

[0058] The active hydroxyl groups (-OH) and unsaturated dangling bonds generated during the etching process can chemically bond (such as hydrogen bonds and covalent bonds) with functional groups (such as amino-NH2, carboxyl-COOH, hydroxyl-OH) in the carbon-nitrogen protective layer, further strengthening the interfacial bonding force. At the same time, these active sites can also serve as nucleation centers for subsequent electrode active materials, guiding the uniform deposition of active materials and avoiding capacity decay caused by local agglomeration.

[0059] S3. A nanoscale transition layer is coated on the etched nickel foam surface using the sol-gel method;

[0060] During the coating process, a sol with a concentration of 0.2 mol / L was prepared using cobalt nitrate (Co(NO3)2) and citric acid as raw materials. This sol was then used to uniformly cover the pore walls of the nickel foam through impregnation and lifting, with a lifting speed of 5-8 mm / s. The layer was subsequently dried at 120-150℃ to avoid damaging the active sites at high temperatures. The Co in the nanoscale transition layer... 2+ It can react with the -OH on the surface of nickel foam to form Co-O-Ni chemical bonds. At the same time, the nanoscale transition layer itself is a porous structure with a pore size of 5-10 nm, which can form a mechanical bond with the subsequent carbon-nitrogen protective layer.

[0061] S4. A carbon-nitrogen protective layer is grown on the surface of a nanoscale transition layer using low-temperature chemical vapor deposition.

[0062] During the growth of the carbon-nitrogen protective layer, the gas source is acetylene (C2H2) + ammonia (NH3) with a volume ratio of 3:1. The reaction temperature is controlled at 500-550℃ and the holding time is 20-25min. The resulting carbon-nitrogen protective layer has an overall thickness of 50-80nm, is relatively uniformly distributed, and is embedded in the surface of nickel foam through a porous structure of nanoscale transition layer. The interfacial bonding force is improved to 15-20MPa (verified by scratch test), which solves the problem of protective layer peeling off during long-term cycling.

[0063] S5. Prepare an active substance slurry, coat the active substance slurry onto the surface of the carbon-nitrogen protective layer by spray pyrolysis, and dry it in a hot air environment.

[0064] When preparing the active material slurry, nickel hydroxide (Ni(OH)2) is used as the active material, 5%-8% carbon nanotubes are added as a conductive agent, 2%-3% sodium carboxymethyl cellulose (CMC) is added as a dispersant, and 0.5%-1% melamine is added. The nitrogen-containing small molecules in melamine can react with the dangling bonds of the carbon-nitrogen protective layer. The slurry is stirred at high speed of 3000-4000 rpm for 30 minutes to ensure uniform dispersion and a particle size distribution ≤5μm.

[0065] When coating active material slurry by spray pyrolysis, the slurry is sprayed onto the surface of carbon-nitrogen protective layer in the form of droplets through a high-pressure nozzle with a nozzle diameter of 0.1 mm. At the same time, it is dried in a hot air environment of 80-100℃. The coating thickness is controlled at 100-150 nm, and the flatness error is ≤5 nm.

[0066] S6. Place the surface-coated nickel foam into a vacuum chamber and use vacuum filtration and gradient pressurization to vacuum impregnate and fill the internal active material of the nickel foam to obtain the electrode material.

[0067] The process of vacuum impregnation and filling of internal active materials using vacuum filtration and gradient pressurization is as follows: The surface-coated nickel foam is placed in a vacuum tank with a vacuum level ≤ -0.095 MPa. An active material slurry is then injected, with its concentration 10%-15% higher than the surface-coated slurry. The mixture is allowed to stand for 5-8 minutes, and negative pressure is used to ensure the slurry completely penetrates the micropores inside the nickel foam. Gradual pressurization is then applied, gradually increasing the pressure from 0.5 MPa to 2 MPa, maintaining each pressure level for 3 minutes to ensure the active material is tightly packed within the micropores without voids, achieving an active material filling rate ≥ 98% and preventing localized capacity decay.

[0068] S7. Perform low-temperature heat treatment on the filled electrode material, and at the same time use inert gas to protect the electrode.

[0069] The process of low-temperature heat treatment is as follows:

[0070] B1. If there is loose powder on the electrode surface, it needs to be wiped off; if a slurry is used for coating, let it stand at room temperature for 10-15 minutes after coating to allow the solvent to evaporate, check the tube furnace sealing, and ensure that the temperature is controlled at 200-220℃, the nitrogen pipeline is leak-free and well-sealed.

[0071] Gently wipe the surface with a lint-free cloth to remove any loose active material powder adhering to it (to prevent powder from falling off during heat treatment and contaminating the equipment or causing localized loss of active material in the electrode); if a slurry (such as Ni(OH)2 slurry containing binders such as CMC and PVA) was used when filling the active material, it should be left to stand at room temperature for 10-15 minutes to allow excess solvent on the surface to evaporate naturally, in order to prevent the electrode from cracking due to rapid vaporization of the solvent during heat treatment.

[0072] A tubular furnace with atmosphere control function is used as the heat treatment equipment. The temperature control system, atmosphere inlet / outlet system and sealing performance of the equipment are checked. The temperature control system is ensured to be able to stably maintain 200-220℃ with an error of ±5℃. The atmosphere inlet / outlet system is ensured to be leak-free in the nitrogen pipeline and the flow meter is working properly. The quartz plugs at both ends of the tubular furnace must be tightened to seal and prevent air from seeping in.

[0073] B2. Place the electrodes in a quartz boat in the constant temperature zone of the tube furnace, and introduce high-purity nitrogen gas at a rate of 100-150 mL / min for 15-20 min. Then purge the air to make the oxygen concentration ≤0.1%.

[0074] Specifically, the pretreated electrodes are laid flat in a quartz boat to avoid chemical reactions with the electrodes, and then placed in the constant temperature zone of a tube furnace to ensure that the electrodes are in a uniform temperature zone and to avoid uneven treatment results caused by local temperature differences.

[0075] Close the exhaust valve of the tubular furnace and open the nitrogen inlet valve. Introduce high-purity nitrogen at a flow rate of 100-150 mL / min, with a nitrogen purity ≥99.999%, to avoid excessive oxygen content that could cause oxidation of the protective layer. After continuous ventilation for 15-20 minutes, slowly open the exhaust valve to maintain a slight positive pressure and prevent backflow of air. Expel the air (mainly oxygen and water vapor) from the tubular furnace through gas replacement, ensuring that the oxygen concentration inside the furnace is ≤0.1%. The oxygen concentration inside the furnace can be monitored in real time using an oxygen detector. Ensure that nitrogen equivalent to three times the furnace volume is replaced.

[0076] B3. Heat to 200-220℃ at a rate of 5-8℃ / min, hold for 30-40min to solidify the chemical bonds between the active material and the protective layer, and remove residual solvent;

[0077] Specifically, the tube furnace is set to heat up from room temperature to 200-220℃ at a rate of 5-8℃ / min. The purpose of slow heating is to avoid the residual solvent inside the electrode, such as water in CMC and ethanol in the slurry, caused by a sudden temperature rise. This allows the tube furnace to vaporize quickly, forming bubbles that would damage the integrity of the active material layer. At the same time, it prevents microcracks from appearing at the interface between the protective layer and the nickel foam due to a sudden increase in thermal stress.

[0078] After reaching 200-220℃, maintain this temperature for 30-40 minutes. The melamine and carbon-nitrogen bonds between the active material (such as Ni(OH)2) and the carbon-nitrogen protective layer (containing carbon-nitrogen groups) undergo a curing reaction, forming more stable chemical bonds.

[0079] The solvent remaining in the active substance slurry is completely evaporated. The solvent includes water and small molecule binder additives, and is discharged from the exhaust port with nitrogen. The discharge method can be observed by the drying tube connected to the exhaust port. Water condensation is observed until there is no obvious water mist in the drying tube, indicating that the solvent has been basically removed.

[0080] B4. Reduce the temperature to below 80℃ at a rate of 3-5℃ / min, maintain with nitrogen, and remove the electrode after it reaches room temperature. After heat treatment, the surface of the obtained electrode has no powder falling off and has a uniform dark green appearance.

[0081] Specifically, after the heat preservation is completed, the tubular furnace heating system is shut off, while nitrogen is continuously supplied. The nitrogen flow rate is reduced to 50-80 mL / min, and the programmed cooling rate is set to 3-5℃ / min. The furnace temperature is then reduced from 200-220℃ to below 80℃. Slow cooling can prevent structural deformation of the electrodes due to differences in thermal expansion and contraction. For example, uneven shrinkage of the foamed nickel channels can compress the active material layer. Simultaneously, it prevents the protective layer from oxidizing upon contact with air at high temperatures, such as the carbon protective layer being oxidized to CO2 and the nitrogen protective layer to NO. x .

[0082] After the furnace temperature drops to room temperature, close the nitrogen inlet valve, open the tube furnace, and remove the quartz boat and electrodes. At this time, there should be no obvious powder shedding on the electrode surface, and the active material layer should show a uniform dark green color (the characteristic color of Ni(OH)2), without any local blackening (oxidation) or whitening (solvent residue).

[0083] Low-temperature heat treatment (200-220℃) can promote the formation of coordination bonds between active groups (such as dangling bonds and hydroxyl groups) on the surface of the protective layer and metal atoms (Ni) on the surface of the nickel foam. At the same time, it can promote the dehydration condensation reaction between the hydroxyl groups on the surface of the active material (Ni(OH)2) and the carbon-nitrogen groups (such as amino and imino groups) of the protective layer, forming a stable chemical bonding system of nickel foam-protective layer-active material. The interfacial adhesion is improved by 30%-50%, avoiding local failure and attenuation of the protective layer during long-term cycling. The interfacial adhesion can be tested by cross-cut test: a 1mm×1mm grid is cut on the electrode surface with a blade, and there is no obvious peeling after the tape is applied.

[0084] The inert atmosphere (nitrogen) of low-temperature heat treatment can prevent the carbon-nitrogen protective layer from being oxidized during the process, and at the same time further remove the trace amount of nickel oxide that may remain on the surface of the nickel foam (i.e., at 200-220℃, nickel oxide can undergo a slight reduction reaction with carbon in the protective layer: NiO+C→Ni+CO↑, but this does not affect the nickel foam substrate), thereby reducing the contact resistance by 20%-30%. The contact resistance can be tested by the four-probe method, and the electrode body resistance is reduced from 8-10mΩ in the original method to 5-6mΩ.

[0085] By combining interface bonding reinforcement and active material structure stabilization, the capacity decay rate of the electrode is effectively reduced after 500 charge-discharge cycles, and the maximum battery temperature is also reduced by 8-12℃ during the cycle, resulting in improved efficiency and significantly enhanced overall performance stability.

[0086] By acid washing to remove nickel oxide and low-temperature plasma etching, more hydroxyl or active groups can be generated on the surface of the nickel foam, enhancing the bonding with the protective layer. In the preparation of the carbon-nitrogen protective layer, a nanoscale transition layer is first made, followed by the carbon-nitrogen protective layer. The nanoscale transition layer can bridge the nickel foam and the carbon-nitrogen protective layer, improving adhesion. At the same time, the carbon-nitrogen protective layer is more evenly distributed. The active material slurry is coated by spray pyrolysis to ensure the uniform distribution of active material particles. A small amount of components with affinity for the carbon-nitrogen protective layer can be added to the active material slurry to make the active material layer and the carbon-nitrogen protective layer bond more firmly, while being evenly distributed and highly utilized. Low-temperature heat treatment can form more stable bonds between active materials and between active materials and the carbon-nitrogen protective layer. At the same time, solvents or impurities in the active material slurry are removed, further improving structural stability and effectively reducing the shedding or failure of the carbon-nitrogen protective layer during cycling, thus improving the stability of electrode material performance.

[0087] Finally, it should be noted that the above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art can still modify the technical solutions described in the foregoing embodiments or make equivalent substitutions for some of the technical features. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for preparing a high-stability nickel-metal hydride battery electrode material, characterized in that: Includes the following steps: S1. Immerse the nickel foam in a 5%-8% dilute hydrochloric acid solution while simultaneously using ultrasonic vibration to remove the dense structure of nickel oxide on the surface of the nickel foam pores. S2. Low-temperature plasma etching is performed on the deoxidized nickel foam to form active sites on the surface of the nickel foam. S3. A nanoscale transition layer is coated on the etched nickel foam surface using the sol-gel method; S4. A carbon-nitrogen protective layer is grown on the surface of a nanoscale transition layer using low-temperature chemical vapor deposition. S5. Prepare an active substance slurry, coat the active substance slurry onto the surface of the carbon-nitrogen protective layer by spray pyrolysis, and dry it in a hot air environment. S6. Place the surface-coated nickel foam into a vacuum chamber and use vacuum filtration and gradient pressurization to vacuum impregnate and fill the internal active material of the nickel foam to obtain the electrode material. S7. Perform low-temperature heat treatment on the filled electrode material, and at the same time use inert gas to protect the electrode.

2. The method for preparing a high-stability nickel-metal hydride battery electrode material according to claim 1, characterized in that: When preparing a 5%-8% dilute hydrochloric acid solution, calculate the amount of HCl and water to be used based on a mass fraction of 5%-8%. In a fume hood, slowly pour the concentrated hydrochloric acid into deionized water while stirring, and cool to 25-30℃.

3. The method for preparing a high-stability nickel-metal hydride battery electrode material according to claim 2, characterized in that: Before immersing the nickel foam in dilute hydrochloric acid solution, it needs to be rinsed with deionized water. Then, the cleaned nickel foam is completely immersed in the prepared dilute hydrochloric acid solution, avoiding the adhesion of air bubbles. At this time, the ultrasonic equipment is turned on for intermittent continuous oscillation. The ultrasonic equipment is set with a power of 150-200W, a frequency of 35-42kHz, an oscillation time of 10-15min, and an interval of 3-5 seconds. During the pickling process, the solution temperature is kept stable at 25-30℃. After the pickling time is completed, the nickel foam is immediately removed from the hydrochloric acid solution and the surface of the nickel foam is repeatedly rinsed with deionized water until the rinsing solution is neutral. Then, the rinsed nickel foam is placed in a vacuum drying oven and dried at 60-80℃ for 1-2 hours to remove surface moisture.

4. The method for preparing a high-stability nickel-metal hydride battery electrode material according to claim 3, characterized in that: During low-temperature plasma etching, argon and oxygen in a volume ratio of 9:1 are used as the gas source, the power is 80-100W, and the processing time is 5-8min. After etching, the surface roughness of the nickel foam is reduced to 0.8-1.2μm, and a large number of active hydroxyl groups and unsaturated dangling bonds are generated on the surface of the hole wall.

5. The method for preparing a high-stability nickel-metal hydride battery electrode material according to claim 4, characterized in that: The etching process is as follows: A1. Equipment Debugging: Use a 13.56MHz low-temperature radio frequency plasma etching instrument to check the airtightness of the equipment. Cut the nickel foam to the electrode size, lay it flat and fix it on the sample stage, and evacuate to 1×10⁻⁶. -3 -5×10 -3 Pa; A2. Introduce the mixed gas at an Ar / O2 volume ratio of 9:1, with a total flow rate of 20-30 sccm, and control the chamber pressure at 10-20 Pa. A3. Set the power to 80-100W and the time to 5-8min. Turn on the power and monitor that the plasma is a uniform light of pale blue. Ensure that the roughness reaches Ra = 0.8-1.2μm.

6. The method for preparing a high-stability nickel-metal hydride battery electrode material according to claim 5, characterized in that: The nanoscale transition layer was prepared using cobalt nitrate and citric acid as raw materials to form a sol with a concentration of 0.2 mol / L. This sol was then used to uniformly cover the pore walls of the nickel foam through impregnation and lifting, with a lifting speed of 5-8 mm / s, followed by drying at 120-150℃. The Co in the nanoscale transition layer... 2+ It can react with the -OH on the surface of nickel foam to form Co-O-Ni chemical bonds. At the same time, the nanoscale transition layer itself is a porous structure with a pore size of 5-10 nm, which can form a mechanical bond with the subsequent carbon-nitrogen protective layer.

7. The method for preparing a high-stability nickel-metal hydride battery electrode material according to claim 6, characterized in that: During the growth of the carbon-nitrogen protective layer, the gas source is acetylene + ammonia with a volume ratio of 3:1, the reaction temperature is controlled at 500-550℃, and the holding time is 20-25min. The resulting carbon-nitrogen protective layer has an overall thickness of 50-80nm, is relatively uniformly distributed, and is embedded in the surface of nickel foam through the porous structure of the nanoscale transition layer.

8. The method for preparing a high-stability nickel-metal hydride battery electrode material according to claim 7, characterized in that: When preparing the active material slurry, nickel hydroxide is used as the active material, 5%-8% carbon nanotubes are added as a conductive agent, 2%-3% sodium carboxymethyl cellulose is added as a dispersant, and 0.5%-1% melamine is added. The nitrogen-containing small molecules in melamine can react with the dangling bonds of the carbon-nitrogen protective layer. The slurry is stirred at high speed of 3000-4000 rpm for 30 minutes to ensure uniform dispersion and a particle size distribution ≤5μm.

9. The method for preparing a high-stability nickel-metal hydride battery electrode material according to claim 8, characterized in that: When coating the active material slurry by spray pyrolysis, the slurry is sprayed onto the surface of the carbon-nitrogen protective layer in the form of droplets through a high-pressure nozzle with a nozzle diameter of 0.1 mm. At the same time, it is dried in a hot air environment of 80-100℃. The coating thickness is controlled at 100-150 nm, and the flatness error is ≤5 nm.

10. The method for preparing a high-stability nickel-metal hydride battery electrode material according to claim 9, characterized in that: The process of low-temperature heat treatment is as follows: B1. If there is loose powder on the electrode surface, it needs to be wiped off; if a slurry coating is used, let it stand at room temperature for 10-15 minutes after coating to allow the solvent to evaporate, and check the airtightness of the tube furnace. B2. Place the electrodes in a quartz boat in the constant temperature zone of the tube furnace, and introduce high-purity nitrogen gas at a rate of 100-150 mL / min for 15-20 min. Then purge the air to make the oxygen concentration ≤0.1%. B3. Heat to 200-220℃ at a rate of 5-8℃ / min, hold for 30-40min to solidify the chemical bonds between the active material and the protective layer, and remove residual solvent; B4. Reduce the temperature to below 80℃ at a rate of 3-5℃ / min, maintain with nitrogen, and remove the electrode after it reaches room temperature. After heat treatment, the surface of the obtained electrode has no powder falling off and has a uniform dark green appearance.

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