Fully automated laser welding and packaging process for lithium iron phosphate battery cells used in new energy vehicles

Abstract

This invention relates to the field of new energy vehicle power battery manufacturing technology, specifically a fully automated laser welding and packaging process for lithium iron phosphate battery cells used in new energy vehicles. The process includes: S1. The cell shell is made of 6061 aluminum alloy containing niobium, yttrium, and lanthanum, sandblasted, then ultrasonically cleaned with an ethanol solution containing a silane coupling agent, and dried at 85-95℃; S2. The cover plate is made of 304 stainless steel containing 0.15-0.25wt% zirconium and 0.06-0.08wt% cerium, and the sealing groove is pre-cured with modified polyimide adhesive and then butt-fitted to the shell; S3. The weld seam is pre-coated with a nano-coating containing 0.1-0.3wt% titanium hydride, pulsed welded using a 1064nm fiber laser, and protected with a mixture of argon, helium, and nitrogen gas; S4. Post-weld annealing, ultrasonic treatment by immersion in a titanate aqueous solution, and finally vacuum drying. This process optimizes the shell and cover plate materials, resulting in stable welding quality, high weld strength, good corrosion resistance, improved cell sealing performance and long-term reliability, fully automated operation, and excellent production efficiency and product consistency.

Description

Technical Field

[0001] This invention relates to the field of power battery manufacturing technology for new energy vehicles, specifically a fully automated laser welding and packaging process for lithium iron phosphate cells used in new energy vehicles. Background Technology

[0002] New energy vehicles place stringent requirements on the reliability, safety, and production efficiency of lithium iron phosphate battery cell packaging. Laser welding, due to its small heat-affected zone and high welding precision, has become the mainstream process for battery cell packaging. However, existing technologies still face several bottlenecks. First, there is insufficient compatibility between the battery cell casing and the cover plate materials. Traditional 6-series aluminum alloy casings lack trace element control, making it difficult to balance yield strength and corrosion resistance. 304 stainless steel cover plates, without composition optimization, are prone to forming brittle intermetallic compounds during welding with aluminum alloys, increasing the risk of weld cracking. Simultaneously, the surface pretreatment process for the casing is rough; simple sandblasting or pickling cannot effectively remove oxide layers and oil stains, leading to defects such as porosity and inclusions during subsequent welding.

[0003] Secondly, the precision of laser welding process control is insufficient. Existing processes mostly employ a single linear welding trajectory, resulting in poor molten pool stability. Furthermore, the shielding gas is often pure argon, making it difficult to balance molten pool protection and heat dissipation efficiency, leading to poor weld formation. While some processes attempt to add coatings, the coating composition is too simple to synergistically suppress porosity and refine grain size, resulting in a significant decrease in the mechanical properties of the weld after welding. In addition, the lack of real-time monitoring and feedback mechanisms means that key parameters such as molten pool width and temperature fluctuations cannot be dynamically adjusted, leading to poor product consistency in mass production.

[0004] Furthermore, the post-weld treatment process is inadequate. Traditional annealing process parameters are fixed and not optimized for the weld microstructure, easily leading to uneven weld hardness. Surface treatment often uses a single cleaning method, which cannot form an effective protective layer on the weld surface. During long-term use, the weld is susceptible to electrolyte corrosion, affecting the lifespan of the battery cell. At the same time, the environmental control and material handling throughout the process lack standardization. Insufficient cleanliness easily leads to dust adhesion, and the lack of electrostatic protection may damage the internal structure of the battery cell, further restricting the packaging quality.

[0005] Finally, the existing process suffers from low automation integration, with each step relying on manual intervention. This not only results in low production efficiency but also increases the risk of quality problems due to human error. In summary, the existing laser welding and packaging process for lithium iron phosphate cells has significant shortcomings in material optimization, process control, post-weld processing, and automation integration, making it difficult to meet the demands of new energy vehicles for high reliability, long lifespan, and large-scale production of battery cells. Breakthroughs in this technological bottleneck are urgently needed. Summary of the Invention

[0006] (a) Technical problems to be solved

[0007] To address the shortcomings of existing technologies, this invention provides a fully automated laser welding and packaging process for lithium iron phosphate battery cells used in new energy vehicles.

[0008] (II) Technical Solution

[0009] A fully automated laser welding and packaging process for lithium iron phosphate battery cells used in new energy vehicles includes the following steps:

[0010] S1. Cell Pretreatment: The cell casing is made of 6061 aluminum alloy, which contains 0.08-0.12 wt% niobium, 0.05-0.07 wt% yttrium, and 0.03-0.04 wt% lanthanum. It is prepared using a vacuum melting process to ensure a uniform distribution of the alloy composition. The casing surface is sandblasted using white corundum abrasive particles with a particle size controlled at 50-80 μm. The sandblasting pressure is set to 0.45-0.55 MPa, and the treatment time is 15-18 seconds, resulting in a uniformly rough surface. After sandblasting, the casing is placed in an ultrasonic cleaning tank. The cleaning solution is an ethanol solution containing 0.8-1.0 wt% silane coupling agent KH-560. The molecular structure of silane coupling agent KH-560 is... The ultrasonic frequency is 40kHz, and the cleaning time is 12-15 minutes. After cleaning, the shell is placed in a hot air drying oven at a temperature of 85-95℃ for 2-2.5 hours to ensure that the moisture content of the shell is ≤0.1%.

[0011] S2. Cover Plate Assembly: The cover plate is made of 304 stainless steel with 0.15-0.25wt% zirconium and 0.06-0.08wt% cerium added. It is smelted in an electric arc furnace and cold-rolled to a thickness of 2-2.5mm. Before the cover plate is connected to the battery cell housing, the connection surface is machined using a precision milling machine to control the connection gap to 0.03-0.04mm. A nano-level positioning fixture is used to fix the cover plate to the housing. The fixture body is made of silicon carbide, and the contact surface is coated with a high-temperature grease containing 0.5wt% graphene. The grease dropping point is ≥300℃, ensuring no scratches during positioning and smooth disassembly. After positioning, the connection gap is checked with a micrometer, one point every 10mm, ensuring that the gap at all test points meets the requirements.

[0012] S3. Laser Welding: A continuous fiber laser with a wavelength of 1064nm is used, with the laser power adjusted to 1400-1600W. The welding speed is set to 35-45mm / s, and the laser spot diameter is controlled at 0.25-0.35mm. A nano-coating is pre-applied to the welding area before welding. The coating's main components are 0.1-0.3wt% titanium hydride and 99.7-99.9wt% aluminum oxide. The titanium hydride undergoes a decomposition reaction at 300-500℃, and the reaction formula is as follows: The generated hydrogen gas can suppress the formation of weld porosity. During welding, a shielding gas is introduced, which is a mixture of 99.99% argon and 1-1.5% helium, with a gas flow rate of 18-22 L / min. The gas is delivered through a single nozzle, which is 6-7 mm away from the welding point and at a 30° angle to the welding surface.

[0013] S4. Post-weld treatment: Immediately after welding, the weld is subjected to laser annealing. The annealing laser power is 600-700W, the annealing time is 6-8 seconds, and the annealing area covers the weld and a 2mm radius on both sides of the weld. After annealing, the battery cell is immersed in an ultrasonic treatment tank. The treatment solution is an aqueous solution containing 0.5-0.6wt% titanate coupling agent. The molecular structure of the titanate coupling agent is... The ultrasonic treatment was performed at a frequency of 50 kHz, a temperature of 55℃ ± 2℃, and a time of 10-12 min. After ultrasonic treatment, the battery cells were transferred to a vacuum drying oven with a vacuum level of -0.096 to -0.098 MPa, a drying temperature of 70-75℃, and a drying time of 3-3.5 h. After drying, the overall moisture content of the battery cells was measured to be ≤0.05%.

[0014] Preferably, the present invention further includes a pre-treatment quality inspection step S1.1: using an eddy current flaw detector to inspect the surface of the sandblasted cell casing for defects. The flaw detection frequency is set to 100kHz, the probe moving speed is 5mm / s, and the inspection range covers the entire outer surface and mating surface of the casing. When a defect depth > 5μm or a defect area > 1mm² is detected, the casing needs to be sandblasted again. The inspection qualification standard is that the surface roughness Ra of the casing is between 3.2-6.3μm, and there are no obvious scratches, dents, or other defects. 5% of the casings in each batch are randomly selected for cross-sectional microscopic observation to verify the uniformity of the sandblasted layer thickness.

[0015] Preferably, the present invention further includes a step S2.1: processing the sealing groove of the cover plate. A modified polyimide adhesive is applied to the sealing groove of the cover plate, containing 5-8 wt% nano-alumina with a particle size of 20-30 nm. The nano-alumina is uniformly dispersed in the adhesive by high-speed stirring. A precision dispensing machine is used for the application, with a dispensing pressure of 0.2 MPa and a dispensing speed of 3 mm / s, ensuring the adhesive layer thickness is controlled at 0.05-0.1 mm without bubbles or gaps. After application, the cover plate is placed in a constant temperature oven and pre-cured at 120°C for 10-15 minutes. After pre-curing, the adhesive layer hardness is tested to be ≥ Shore D50, after which the cover plate and shell are assembled.

[0016] Preferably, in S3 of this invention, laser welding adopts a pulse mode, with the pulse frequency adjusted to 60-80Hz, the duty cycle set to 35-45%, and the pulse width 10-15μs. The welding path adopts a composite trajectory of alternating spiral and straight lines, wherein the spiral portion has a pitch of 0.1-0.2mm and a spiral radius of 0.5-0.8mm, and the straight portion has a length of 2-3mm, with the two trajectories seamlessly connected. During the welding process, an infrared thermometer is used to monitor the weld temperature in real time, controlling the temperature between 1800-2000℃. When the temperature exceeds the range, the pulse duty cycle is automatically adjusted by ±5% to maintain temperature stability.

[0017] Preferably, in step S3 of this invention, 0.1-0.3% nitrogen is added to the protective gas to form a ternary mixed protective gas of argon, helium, and nitrogen. The three gases are mixed in proportion by a gas mixer with a mixing accuracy of ±0.05%. The protective gas is delivered through a specially designed dual-channel nozzle. The main nozzle has a diameter of 8 mm and is located 5-8 mm from the welding point, delivering 90% of the protective gas. The auxiliary nozzle has a diameter of 4 mm and is arranged at a 45° angle to the main nozzle, delivering 10% of the protective gas. The auxiliary nozzle can effectively protect the edge area of ​​the molten pool and reduce oxidation.

[0018] Preferably, the present invention further includes an S3.1 online welding monitoring step: a high-speed camera is used to capture the molten pool morphology in real time during the welding process. The camera frame rate is set to 1000fps, the resolution to 1920×1080, and the lens focal length to 50mm to ensure clear capture of molten pool details. The molten pool width is analyzed through an image recognition algorithm. When the molten pool width fluctuates by >±0.05mm, the equipment control system automatically adjusts the laser power by ±50-100W and simultaneously fine-tunes the welding speed by ±2-3mm / s to restore the molten pool morphology to stability. After each cell is welded, the molten pool monitoring image is automatically saved for subsequent quality traceability.

[0019] Preferably, the ultrasonic treatment frequency in S4 of this invention is 45-55 kHz, the treatment time is 8-12 min, and the treatment solution is stirred every 3 min during the treatment to ensure uniform concentration. The pH value of the titanate coupling agent aqueous solution is adjusted to 6.5-7.5 by adding citric acid or sodium hydroxide, and the pH deviation is controlled within ±0.2. After ultrasonic treatment, the surface of the battery cell is rinsed with deionized water 2-3 times, each rinsing time is 1 min, to remove residual treatment solution.

[0020] Preferably, the present invention further includes S4.1 post-weld quality inspection step: using an X-ray flaw detector to inspect internal defects in the weld, with the flaw detection voltage set to 30kV, current 5mA, exposure time 10s, and the flaw detection range covering the entire weld area. When the diameter of pores inside the weld is detected to be >0.1mm, or the crack length is >0.3mm, or the inclusion area is >0.5mm², it is judged as a defective product; qualified welds need to undergo a water pressure test, with a test pressure of 1.5MPa and a pressure holding time of 30s, and no leakage is considered as qualified.

[0021] Preferably, the mechanical properties of the 6061 aluminum alloy used in the battery cell casing of this invention are: yield strength ≥ 200 MPa, tensile strength ≥ 260 MPa, and elongation ≥ 12%; the mechanical properties of the 304 stainless steel used in the cover plate are: tensile strength ≥ 650 MPa, yield strength ≥ 300 MPa, and elongation ≥ 40%. After welding, a tensile test is performed on the weld. The joint strength must be ≥ 85% of the base material strength, and the fracture location must be in the base material region, not the weld region.

[0022] Preferably, the entire process of this invention is carried out in a cleanroom with humidity controlled at ≤30%RH, temperature controlled at 23℃±2℃, and cleanliness level of Class 1000. A local cleanroom device is installed in the welding area, achieving a local cleanliness level of Class 100 through a high-efficiency air filter, with the number of airborne suspended particles ≥0.5μm ≤100 particles / ft³. Material transfer between steps utilizes anti-static vacuum suction cups made of nitrile rubber with a surface resistivity of [missing value]. This is to avoid static electricity damage to the battery cells during transportation.

[0023] (iii) Beneficial technical effects

[0024] Compared with existing technologies, the beneficial effects of this invention are:

[0025] This invention's process, through multi-dimensional technological innovation, effectively addresses the pain points of existing laser welding and packaging of lithium iron phosphate battery cells, possessing several core advantages. Regarding material compatibility, the 6061 aluminum alloy shell is enriched with niobium, yttrium, and lanthanum, while the 304 stainless steel cover plate is enriched with zirconium and cerium, significantly improving the material's mechanical properties and corrosion resistance, reducing the formation of brittle compounds during welding, and laying the foundation for weld reliability. The pretreatment stage combines sandblasting with silane coupling agent cleaning to thoroughly remove surface impurities, improving subsequent welding quality.

[0026] During welding, the combination of pulse mode and composite welding trajectory, along with a ternary mixed shielding gas and titanium hydride nano-coating, stabilizes the molten pool morphology, suppresses porosity, refines grains, and significantly improves weld formation and mechanical properties. The online monitoring system captures molten pool changes in real time and dynamically adjusts parameters to ensure consistency in batch production and avoid quality defects caused by parameter fluctuations.

[0027] Post-weld laser annealing precisely matches the weld microstructure requirements, eliminates internal stress, and improves weld hardness uniformity. Ultrasonic treatment with titanate coupling agent forms a protective layer on the weld surface, enhancing resistance to electrolyte corrosion and extending cell lifespan. Simultaneously, cleanroom environmental control and anti-static transport design prevent dust and static electricity from damaging the cells, ensuring cell safety after packaging.

[0028] The entire process is fully automated and integrated, with seamless connections between each step, reducing manual intervention and significantly improving production efficiency. Furthermore, multi-stage quality inspection steps, from pretreatment to post-soldering, ensure that the quality of each cell package meets standards. Ultimately, the lithium iron phosphate cells produced by this process have a robust package structure and reliable performance, making them suitable for the complex operating conditions of new energy vehicles and providing strong support for the large-scale, high-quality production of power batteries. Attached Figure Description

[0029] Figure 1 This is a flowchart of the fully automated laser welding and packaging process for lithium iron phosphate battery cells for new energy vehicles proposed in this invention;

[0030] Figure 2 This is a bar chart showing the ratio of weld strength to base metal strength in the embodiments and comparative examples of the present invention;

[0031] Figure 3 This is a line graph showing the fluctuation range of the molten pool width of different samples in the embodiments and comparative examples of the present invention;

[0032] Figure 4 This is a bar chart showing the cell capacity retention rate after 1000 charge-discharge cycles according to the present invention. Detailed Implementation

[0033] according to Figures 1 to 4 The specific embodiments of the present invention are as follows: Example

[0034] Raw material and equipment preparation

[0035] Battery cell casing material: 6061 aluminum alloy, with 0.10wt% niobium, 0.06wt% yttrium, and 0.035wt% lanthanum, purity 99.9%, and ingot hardness HB85 after smelting;

[0036] Cover plate material: 304 stainless steel, zirconium content 0.20wt%, cerium content 0.07wt%, cold-rolled thickness 2.2mm, tensile strength 660MPa;

[0037] Sandblasting material: white corundum abrasive particles, particle size 65μm, Mohs hardness 9.0, bulk density 1.6g / cm³;

[0038] Cleaning solution: ethanol solution, containing 0.9 wt% silane coupling agent KH-560 and 99.7% ethanol purity;

[0039] Sealant: Modified polyimide adhesive with 6.5wt% nano-alumina added, nano-alumina particle size 25nm, colloidal viscosity 2500mPa・s (25℃).

[0040] Welding coating: Nano coating, containing 0.2wt% titanium hydride, the remainder being aluminum oxide, with a coating thickness of 5μm;

[0041] Protective gases: argon (99.99% purity), helium (99.99% purity), and nitrogen (99.99% purity), mixed in a ratio of 97.6% argon, 1.2% helium, and 0.2% nitrogen.

[0042] Equipment: Vacuum melting furnace (ultimate vacuum -0.098MPa), sandblasting equipment (pressure adjustment range 0-1MPa), ultrasonic cleaner (frequency adjustment range 20-80kHz), precision milling machine (positioning accuracy ±0.001mm), nano-level positioning fixture (material silicon carbide, high temperature resistance 500℃), 1064nm fiber laser (power adjustment range 500-2000W), high-speed camera (frame rate 1000fps, resolution 1920×1080), laser annealing device (power adjustment range 300-1000W), vacuum drying oven (ultimate vacuum -0.1MPa), eddy current flaw detector (frequency 100kHz), X-ray flaw detector (voltage adjustment range 20-50kV), hydraulic pressure testing machine (pressure adjustment range 0-5MPa).

[0043] Preparation process

[0044] S1. Cell Pretreatment: 6061 aluminum alloy is placed in a vacuum melting furnace, with a melting temperature of 750℃ and a vacuum degree of -0.098MPa. After holding at this temperature for 2 hours, it is die-cast into a cell casing. The sandblasting equipment is started, white corundum abrasive particles are loaded, and the air pressure is adjusted to 0.5MPa. The casing surface is sandblasted for 16 seconds to ensure a uniformly rough surface. The sandblasted casing is then placed in an ultrasonic cleaner, and the prepared cleaning solution is poured in. The ultrasonic frequency is set to 40kHz, and the cleaning time is 13 minutes. After cleaning, the casing is transferred to a hot air drying oven, with a drying temperature of 85℃ and a drying time of 2.2 hours. After drying, the moisture content of the casing is measured using a moisture analyzer to ensure it is controlled below 0.08%.

[0045] S1.1 Pre-treatment Quality Inspection: The eddy current flaw detector was turned on, the frequency was adjusted to 100kHz, and the probe movement speed was 5mm / s. A comprehensive defect inspection was performed on the shell surface, with a focus on the mating surfaces and outer surfaces. The surface roughness of the shell was measured using a surface roughness meter, and the Ra value was found to be 4.8μm, with no defects deeper than 5μm or with an area greater than 1mm². 5% of the shells from each batch were randomly selected, and the cross-sections were observed using a metallographic microscope to confirm that the sandblasting layer thickness was uniform, with no areas that were too thick or too thin.

[0046] S2. Cover Plate Assembly: 304 stainless steel raw material is cold-rolled to a thickness of 2.2mm, and then the mating surface of the cover plate is machined using a precision milling machine, controlling the mating gap to be 0.035mm. A high-temperature grease containing 0.5wt% graphene is uniformly coated on the contact surface of the nano-level positioning fixture. This grease has a dropping point of 320℃, ensuring no scratches when the fixture contacts the cover plate and housing. The cover plate and cell housing are placed in the positioning fixture, and their positions are adjusted to ensure precise mating. The gap at each mating point is checked every 10mm using a micrometer; all checked gaps meet the 0.035mm requirement.

[0047] S2.1 Cover Plate Sealing Groove Treatment: Start the precision dispensing machine, draw in modified polyimide adhesive, adjust the dispensing pressure to 0.2MPa, and the dispensing speed to 3mm / s. Apply the adhesive layer to the cover plate sealing groove, controlling the adhesive layer thickness to 0.07mm. Ensure no air bubbles or adhesive breaks during the application process. Place the coated cover plate in a constant temperature oven, set the temperature to 120℃, and pre-curing for 12 minutes. After pre-curing, test the hardness of the adhesive layer with a Shore hardness tester. The measured hardness is Shore D52, which meets the requirements for subsequent assembly.

[0048] S3. Laser Welding: A nano-coating is pre-applied using a spraying method at the butt weld area between the cell casing and the cover plate, ensuring uniform coverage of the weld with a thickness of 5μm. The fiber laser is turned on, with a wavelength of 1064nm, laser power of 1500W, welding speed of 40mm / s, and laser spot diameter of 0.3mm. The shielding gas mixer is turned on, and argon, helium, and nitrogen are introduced in proportion, adjusting the total gas flow rate to 20L / min. The gas is delivered to the welding area through a dual-channel nozzle, with the main nozzle 6.5mm from the welding point and the auxiliary nozzle arranged at a 45° angle to the main nozzle. Laser welding is set to pulse mode with a pulse frequency of 70Hz, a duty cycle of 40%, and a pulse width of 12μs. The welding path uses a composite trajectory alternating between spiral and straight lines, with a spiral pitch of 0.15mm, a radius of 0.6mm, and a straight section length of 2.5mm. An infrared thermometer is turned on to monitor the weld temperature in real time, controlling it at 1900℃ to avoid excessively high or low temperatures affecting welding quality.

[0049] S3.1 Online Welding Monitoring: The high-speed camera is activated, and the lens focal length is adjusted to 50mm to ensure clear capture of the weld pool morphology. The image recognition system analyzes the weld pool width in real time. When the weld pool width fluctuates beyond ±0.05mm, the equipment control system automatically adjusts the laser power to ±75W and simultaneously fine-tunes the welding speed by ±2.5mm / s to stabilize the weld pool morphology. After each battery cell is welded, the system automatically saves the weld pool monitoring image for subsequent quality traceability and problem troubleshooting.

[0050] S4. Post-weld treatment: Immediately after welding, start the laser annealing device, set the annealing power to 650W, annealing time to 7s, and the annealing area to cover the weld and a 2mm radius on both sides of the weld to eliminate welding stress. Immerse the annealed battery cell in an ultrasonic treatment tank containing an aqueous solution of 0.55wt% titanate coupling agent, adjust the solution pH to 7.0, set the ultrasonic frequency to 50kHz, the treatment temperature to 55℃, and the treatment time to 11min. After ultrasonic treatment, rinse the battery cell surface twice with deionized water, 1min each time, to remove residual treatment solution. Transfer the rinsed battery cell to a vacuum drying oven, set the vacuum degree to -0.097MPa, the drying temperature to 72℃, and the drying time to 3.2h. After drying, check the overall moisture content of the battery cell, which should be controlled at 0.04%.

[0051] S4.1 Post-weld quality inspection: The X-ray flaw detector was turned on, with a voltage of 30kV, a current of 5mA, and an exposure time of 10s. Defect detection was performed on the internal weld seam. No pores larger than 0.1mm in diameter, cracks longer than 0.3mm, or inclusions larger than 0.5mm² in area were found. The flaw-detected cells were placed in a hydrostatic testing machine, with a test pressure of 1.5MPa and a holding time of 30s. No leakage was observed on the cell surface or at the weld seam. Tensile tests were performed on some cells. The weld joint strength was measured to be 88% of the base material strength, and the fracture locations were all within the base material region, meeting the quality requirements.

[0052] Environmental and Transfer Control: The entire process is conducted in a Class 1000 cleanroom, with the temperature controlled at 23℃ and humidity at 25%RH. The welding area achieves a local cleanliness level of Class 100 through HEPA filters, with the number of suspended particles ≥0.5μm ≤100 particles / ft³. Material transfer between steps utilizes anti-static vacuum suction cups made of nitrile rubber with a surface resistivity of [missing value]. This is to avoid static electricity damage to the battery cells during transportation.

[0053] Example 2

[0054] Raw material and equipment preparation

[0055] Battery cell casing material: 6061 aluminum alloy, niobium content 0.08wt%, yttrium content 0.05wt%, lanthanum content 0.03wt%, purity 99.9%, ingot hardness after melting HB82;

[0056] Cover plate material: 304 stainless steel, zirconium content 0.15wt%, cerium content 0.06wt%, cold-rolled thickness 2.0mm, tensile strength 655MPa;

[0057] Sandblasting material: white corundum abrasive particles, particle size 50μm, Mohs hardness 9.0, bulk density 1.6g / cm³;

[0058] Cleaning solution: ethanol solution, silane coupling agent KH-560 concentration 0.8wt%, ethanol purity 99.7%;

[0059] Sealant: Modified polyimide adhesive with 5wt% nano-alumina (20nm particle size), colloidal viscosity...

[0060] Welding coating: Nano coating, containing 0.1 wt% titanium hydride, the remainder being aluminum oxide, with a coating thickness of 4 μm;

[0061] Protective gases: 98.8% argon, 1% helium, and 0.2% nitrogen, all with a purity of 99.99%.

[0062] Equipment: Same as in Example 1, with parameters adjusted according to process requirements.

[0063] Preparation process

[0064] S1. Cell Pretreatment: 6061 aluminum alloy is placed in a vacuum melting furnace at 740℃ and a vacuum of -0.098MPa, held for 2 hours, and then die-cast. A sandblasting machine is used with 50μm white corundum abrasive particles at 0.45MPa for 15 seconds. The casing is then placed in an ultrasonic cleaner with a 0.8wt% KH-560 ethanol solution at 40kHz for 12 minutes. After cleaning, the casing is transferred to a hot air drying oven at 85℃ for 2 hours, and the moisture content is measured to be 0.09%.

[0065] S1.1 Pre-treatment quality inspection: Eddy current flaw detector at 100kHz, no defects exceeding the standard were detected; Ra value measured by surface roughness meter was 3.2μm; 5% sampling section observation showed that the sandblasting layer was uniform.

[0066] S2. Cover plate assembly: 304 stainless steel cold-rolled to 2.0mm thickness, with the mating surface machined by precision milling to a gap of 0.03mm. The positioning fixture is coated with high-temperature grease, and the cover plate and the housing are placed inside the fixture for mating. The gap at every 10mm point is measured with a micrometer and is 0.03mm.

[0067] S2.1 Cover Plate Sealing Groove Treatment: Modified polyimide adhesive is applied using a precision dispensing machine at a dispensing pressure of 0.2 MPa, a speed of 3 mm / s, and an adhesive layer thickness of 0.05 mm. After application, the adhesive is placed in a constant temperature oven and pre-cured at 120℃ for 10 minutes. The hardness of the adhesive layer is measured to be D50 using a Shore hardness tester.

[0068] S3. Laser Welding: A 4μm thick nano-coating containing 0.1wt% titanium hydride is pre-applied to the weld area. The fiber laser has a wavelength of 1064nm, a power of 1400W, a speed of 35mm / s, and a spot size of 0.25mm. The shielding gas flow rate is 18L / min, and the dual-channel nozzles have a main nozzle spacing of 5mm and an auxiliary nozzle angle of 45°. The pulse mode is 60Hz, with a duty cycle of 35%, a pulse width of 10μs, and a composite trajectory pitch of 0.1mm, a radius of 0.5mm, and a straight segment of 2mm. Infrared thermography is controlled at 1800℃.

[0069] S3.1 Online Welding Monitoring: A high-speed camera captures the molten pool. When the width fluctuates by more than ±0.05mm, the power is adjusted to ±50W and the speed to ±2mm / s, and the image is automatically saved.

[0070] S4. Post-weld treatment: Laser annealing power 600W, time 6s. Ultrasonic treatment tank contains 0.5wt% titanate coupling agent aqueous solution, pH 6.5, frequency 45kHz, temperature 53℃, treatment for 10min. After rinsing twice with deionized water, dry in a vacuum drying oven set to -0.096MPa, 70℃ for 3h, moisture content 0.05%.

[0071] S4.1 Post-weld quality inspection: X-ray inspection showed no defects exceeding the standard; water pressure test at 1.5MPa for 30s showed no leakage. Tensile test showed the joint strength to be 85% of the base material, and the fracture occurred at the base material.

[0072] Environmental and transport control: Cleanroom temperature 22℃, humidity 28%RH, welding area local Class 100. Antistatic chuck resistor. No static electricity is generated during the transfer process. Example

[0073] Raw material and equipment preparation

[0074] Battery cell casing material: 6061 aluminum alloy, niobium content 0.12wt%, yttrium content 0.07wt%, lanthanum content 0.04wt%, purity 99.9%, ingot hardness after melting HB88;

[0075] Cover plate material: 304 stainless steel, zirconium content 0.25wt%, cerium content 0.08wt%, cold-rolled thickness 2.5mm, tensile strength 670MPa;

[0076] Sandblasting material: white corundum abrasive particles, particle size 80μm, Mohs hardness 9.0, bulk density 1.6g / cm³;

[0077] Cleaning solution: ethanol solution, silane coupling agent KH-560 concentration 1.0wt%, ethanol purity 99.7%;

[0078] Sealant: Modified polyimide adhesive with 8wt% nano-alumina (30nm particle size), colloidal viscosity... ;

[0079] Welding coating: Nano coating, containing 0.3wt% titanium hydride, the remainder being aluminum oxide, with a coating thickness of 6μm;

[0080] Protective gases: 97.2% argon, 1.5% helium, and 0.3% nitrogen, all with a purity of 99.99%.

[0081] Equipment: Same as in Example 1, with parameters adapted to process requirements.

[0082] Preparation process

[0083] S1. Cell Pretreatment: 6061 aluminum alloy vacuum melting temperature 760℃, vacuum degree -0.098MPa, holding for 2.5h followed by die casting. Sandblasting equipment with air pressure 0.55MPa, 80μm sand particles treated for 18s. Ultrasonic cleaning with 1.0wt% KH-560 ethanol solution, frequency 40kHz, time 15min. Drying at 95℃ for 2.5h, moisture content 0.07%.

[0084] S1.1 Pre-treatment quality inspection: Eddy current testing showed no defects, Ra 6.3μm, and the sandblasting layer on the sampling section was uniform.

[0085] S2. Cover plate assembly: 304 stainless steel cold-rolled 2.5mm thick, butt joint gap 0.04mm, micrometer inspection qualified after positioning fixture is fixed.

[0086] S2.1 Cover plate sealing groove treatment: 0.1mm thick adhesive layer, pre-cured at 120℃ for 15min, hardness D53.

[0087] S3. Laser welding: 6μm coating containing The laser power is 1600W, the speed is 45mm / s, and the spot size is 0.35mm. The protective gas flow rate is 22L / min, the pulse frequency is 80Hz, the duty cycle is 45%, the trajectory pitch is 0.2mm, and the temperature measurement is 2000℃.

[0088] S3.1 Monitoring and Adjustment: Power ±100W, Speed ​​±3mm / s.

[0089] S4. Post-weld treatment: Annealing at 700W / 8s, 0.6wt% titanate solution pH7.5, sonication at 55kHz / 12min, drying at 95℃ for 3.5h, moisture content 0.03%.

[0090] S4.1 Quality Inspection: Flaw detection and water pressure testing are qualified, and the joint strength is 90% of the base material.

[0091] Environmental and transport control: Cleanroom temperature 24℃, humidity 26%RH, local Class 100, suction cup resistance. .

[0092] Comparative Example

[0093] Raw material and equipment preparation

[0094] Battery cell casing material: ordinary 6061 aluminum alloy, without niobium, yttrium, or lanthanum additives, purity 99.5%, ingot hardness HB75;

[0095] Cover plate material: ordinary 304 stainless steel, without zirconium or cerium additives, cold-rolled thickness 2.2mm, tensile strength 600MPa;

[0096] Cleaning solution: pure ethanol, without silane coupling agent;

[0097] Protective gas: Pure argon, 99.99% purity;

[0098] Equipment: Only basic laser welding machines and drying ovens are used; there is no online monitoring, eddy current testing, or other equipment.

[0099] Preparation process

[0100] S1. Cell Pretreatment: Ordinary 6061 aluminum alloy die-casting, only pickling to remove the surface oxide layer, no sandblasting. After pickling, clean with pure ethanol for 5 minutes, dry at 80℃ for 2 hours, moisture content 0.15%. No pretreatment quality inspection steps.

[0101] S2. Cover plate assembly: Ordinary 304 stainless steel cover plate, unprocessed mating surface, mating gap 0.1-0.15mm, fixed with ordinary clamps, no sealing groove glue application step.

[0102] S3. Laser Welding: No pre-applied nano-coating; uses a 1064nm fiber laser, 1500W power, 40mm / s speed, 0.3mm spot size. Pure argon gas is used for protection at a flow rate of 20L / min; the single nozzle is 8mm from the welding point. The welding trajectory is linear; there is no pulse mode or online monitoring; the weld pool is observed manually.

[0103] S4. Post-weld treatment: After welding, allow to cool naturally without laser annealing. Directly place in an 80℃ drying oven for 3 hours without ultrasonic treatment; moisture content is 0.12%.

[0104] S5. Post-weld quality inspection: Only visual inspection of the weld surface was performed, without X-ray flaw detection or hydrostatic testing, and no tensile test was conducted.

[0105] Environmental and transfer control: Conducted in a regular workshop with no cleanliness control; material transfer uses ordinary clamps with no electrostatic protection.

[0106] Performance test data charts

[0107] Table 1: Comparison of Material and Weld Mechanical Properties

[0108]

[0109] This table focuses on the core mechanical properties of the shell, cover plate materials, and welds, visually demonstrating the effects of material optimization and process improvement in this invention. The 6061 aluminum alloy shells in Examples 1-3, due to the addition of niobium, yttrium, and lanthanum, achieve a yield strength of 205-215 MPa, significantly higher than the 180 MPa of the ordinary aluminum alloy in the comparative examples. The 304 stainless steel cover plate, after the addition of zirconium and cerium, has a tensile strength increased to 655-670 MPa, superior to the 600 MPa of the comparative examples. Thanks to material optimization and precise welding processes, the weld strength to base material ratio in the examples reaches 85%-90%, while in the comparative examples it is only 65%, fully demonstrating that the technology of this invention can comprehensively improve the mechanical reliability of the packaging structure from materials to processes.

[0110] Table 2: Results of Welding Quality and Corrosion Resistance Tests

[0111]

[0112] This table quantitatively evaluates the welding and packaging quality from the dimensions of weld defects, surface quality, and corrosion resistance. Examples 1-3, through pretreatment purification, coating to suppress porosity, and precise welding control, achieved weld pore diameters of only 0.07-0.09 mm, a roughness Ra of 2.0-2.3 μm, and no significant corrosion in a 30-day salt spray test. In contrast, the comparative examples, lacking key processes, exhibited pore diameters as high as 0.35 mm, rough surfaces, and severe corrosion. This table clearly demonstrates that the pretreatment, welding control, and post-weld treatment processes of this invention effectively reduce weld defects, improve surface quality and corrosion resistance, and meet the long-term use requirements of battery cells.

[0113] Table 3: Comparison of Welding Process Stability and Energy Consumption

[0114]

[0115] This table compares the stability and economy of the production process. Examples 1-3, with the aid of online monitoring and dynamic parameter adjustment, show a weld pool width fluctuation of only ±0.02-0.04 mm, a welding interruption frequency of 0.1-0.3 times per thousand pieces, a weld formation qualification rate exceeding 99%, and a unit energy consumption as low as 0.82-0.90 kWh / piece. In contrast, the comparative examples, without monitoring and adjustment, exhibit drastic weld pool fluctuations, with an interruption frequency of 5.8 times per thousand pieces, a qualification rate of only 81.5%, and significantly higher energy consumption. This demonstrates that the process of this invention, while ensuring production stability and improving the qualification rate, also possesses excellent economic efficiency.

[0116] Table 4: Long-term reliability test of battery cells (after 1000 charge-discharge cycles)

[0117]

[0118] This table verifies the long-term performance of the battery cell packaging through 1000 charge-discharge cycle tests. Examples 1-3, due to their excellent sealing performance, strong weld corrosion resistance (weld corrosion area only 0.2-0.5 mm²), achieve a battery cell capacity retention rate of 90%-93%, demonstrating excellent sealing performance. The casing deformation was 0.04-0.06 mm; the comparative encapsulation showed significant failure, with a corrosion area of ​​8.6 mm², a capacity retention rate of only 75%, and insufficient sealing performance. This table strongly demonstrates that the process of this invention can significantly improve the long-term reliability and service life of the battery cell.

[0119] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A fully automated laser welding and packaging process for lithium iron phosphate battery cells used in new energy vehicles, characterized in that, Includes the following steps: S1. Cell Pretreatment: The cell casing is made of aluminum alloy with 0.08-0.12wt% niobium, 0.05-0.07wt% yttrium, and 0.03-0.04wt% lanthanum added. It is prepared by vacuum melting process. The surface of the casing is sandblasted with white corundum abrasive. After sandblasting, the casing is placed in an ultrasonic cleaning tank. The cleaning solution is an ethanol solution containing 0.8-1.0wt% silane coupling agent KH-560. After cleaning, the casing is placed in a hot air drying oven for 2-2.5 hours. S2. Cover plate assembly: The cover plate is made of stainless steel with 0.15-0.25wt% zirconium and 0.06-0.08wt% cerium added. It is smelted in an electric arc furnace and cold rolled. Before the cover plate is connected to the battery cell housing, the connection surface is machined with a precision milling machine to control the connection gap to 0.03-0.04mm. The cover plate and the housing are fixed with a nano-level positioning fixture. The main body of the fixture is made of silicon carbide and the contact surface is coated with high-temperature grease containing 0.5wt% graphene. After positioning, the connection gap is checked with a micrometer, and one point is checked every 10mm. S3. Laser Welding: A continuous fiber laser is used, with the laser power adjusted to 1400-1600W, the welding speed set to 35-45mm / s, and the laser spot diameter controlled at 0.25-0.35mm. Before welding, a nano-coating is pre-applied to the welding area. The coating mainly consists of 0.1-0.3wt% titanium hydride and 99.7-99.9wt% aluminum oxide. The titanium hydride undergoes a decomposition reaction at 300-500℃. During welding, a protective gas is introduced, which is a mixture of 99.99% argon and 1-1.5% helium, delivered through a single nozzle. S4. Post-weld treatment: The weld is laser annealed immediately after welding. After annealing, the battery cell is immersed in an ultrasonic treatment tank. The treatment solution is an aqueous solution containing 0.5-0.6wt% titanate coupling agent. After ultrasonic treatment, the battery cell is transferred to a vacuum drying oven and dried for 3-3.5 hours. After drying, the overall moisture content of the battery cell is tested.

2. The fully automated laser welding and packaging process for lithium iron phosphate battery cells for new energy vehicles according to claim 1, characterized in that, It also includes the S1.1 pretreatment quality inspection step: using an eddy current flaw detector to inspect the surface of the cell shell after sandblasting for defects. When the detected defect depth is >5μm or the defect area is >1mm², the shell is re-sandblasted. The inspection qualification standard is that the surface roughness Ra of the shell is between 3.2-6.3μm and there are no obvious scratches or dents. 5% of the shells in each batch are randomly selected for cross-sectional microscopic observation to verify the uniformity of the sandblasting layer thickness.

3. The fully automated laser welding and packaging process for lithium iron phosphate battery cells for new energy vehicles according to claim 1, characterized in that, It also includes the S2.1 cover plate sealing groove treatment step: a modified polyimide adhesive is applied to the sealing groove of the cover plate, which contains 5-8 wt% nano-alumina with a particle size of 20-30 nm. The nano-alumina is uniformly dispersed in the adhesive by stirring. The adhesive is applied using a precision dispensing machine with a dispensing pressure of 0.2 MPa and a dispensing speed of 3 mm / s. After the adhesive is applied, the cover plate is placed in a constant temperature oven and pre-cured at 120°C for 10-15 min. After pre-curing, the hardness of the adhesive layer is tested to be ≥ Shore D50. Then the cover plate and the shell are assembled.

4. The fully automated laser welding and packaging process for lithium iron phosphate battery cells for new energy vehicles according to claim 1, characterized in that, In S3, laser welding uses a pulse mode with a pulse frequency of 60-80Hz, a duty cycle of 35-45%, and a pulse width of 10-15μs. The welding path uses a composite trajectory of alternating spiral and straight lines. The spiral part has a pitch of 0.1-0.2mm and a spiral radius of 0.5-0.8mm, while the straight part is 2-3mm long. The two trajectories are seamlessly connected. During the welding process, an infrared thermometer is used to monitor the weld temperature in real time, and the temperature is controlled between 1800-2000℃. When the temperature exceeds the range, the pulse duty cycle is automatically adjusted by ±5% to maintain temperature stability.

5. The fully automated laser welding and packaging process for lithium iron phosphate battery cells for new energy vehicles according to claim 1, characterized in that, In S3, 0.1-0.3% nitrogen is added to the protective gas to form a ternary mixed protective gas of argon, helium and nitrogen. The three gases are mixed in proportion by a gas mixer. The protective gas is delivered through a specially designed dual-channel nozzle. The main nozzle has a diameter of 8mm and is 5-8mm away from the welding point, delivering 90% of the protective gas. The auxiliary nozzle has a diameter of 4mm and is arranged at a 45° angle with the main nozzle, delivering 10% of the protective gas.

6. The fully automated laser welding and packaging process for lithium iron phosphate battery cells for new energy vehicles according to claim 1, characterized in that, It also includes the S3.1 online welding monitoring step: a high-speed camera is used to capture the molten pool morphology in real time during the welding process, and the molten pool width is analyzed by image recognition algorithm. When the molten pool width fluctuates by more than ±0.05mm, the equipment control system automatically adjusts the laser power by ±50-100W and fine-tunes the welding speed by ±2-3mm / s. After each cell is welded, the molten pool monitoring image is automatically saved.

7. The fully automated laser welding and packaging process for lithium iron phosphate battery cells for new energy vehicles according to claim 1, characterized in that, The ultrasonic treatment frequency in S4 is 45-55kHz, the treatment time is 8-12min, and the treatment solution is stirred every 3min during the treatment. The pH value of the titanate coupling agent aqueous solution is adjusted to 6.5-7.5 by adding citric acid or sodium hydroxide, and the pH value deviation is controlled within ±0.

2. After ultrasonic treatment, the surface of the battery cell is rinsed with deionized water 2-3 times, each rinsing time is 1min, to remove residual treatment solution.

8. The fully automated laser welding and packaging process for lithium iron phosphate battery cells for new energy vehicles according to claim 1, characterized in that, It also includes the S4.1 post-weld quality inspection step: using an X-ray flaw detector to detect internal defects in the weld, with the flaw detection voltage set to 30kV, current 5mA, exposure time 10s, and the flaw detection range covering the entire weld area. When the diameter of the pores inside the weld is greater than 0.1mm, the crack length is greater than 0.3mm, or the inclusion area is greater than 0.5mm², it is judged as a non-conforming product; qualified welds need to undergo a water pressure test, with a test pressure of 1.5MPa and a pressure holding time of 30s.

9. The fully automated laser welding and packaging process for lithium iron phosphate battery cells for new energy vehicles according to claim 1, characterized in that, The mechanical properties of the 6061 aluminum alloy used for the battery cell casing are: yield strength ≥200MPa, tensile strength ≥260MPa, and elongation ≥12%; the mechanical properties of the 304 stainless steel used for the cover plate are: tensile strength ≥650MPa, yield strength ≥300MPa, and elongation ≥40%. After welding, a tensile test is performed on the weld. The joint strength must be ≥85% of the strength of the base material, and the fracture location must be in the base material area, not the weld area.

10. The fully automated laser welding and packaging process for lithium iron phosphate battery cells for new energy vehicles according to claim 1, characterized in that, The entire process is carried out in a cleanroom with humidity controlled at ≤30%RH and temperature at 23℃±2℃, achieving a cleanliness level of Class 1000. Local cleanroom devices are installed in the welding area, achieving a local cleanliness level of Class 100 through high-efficiency air filters, with the number of airborne suspended particles ≥0.5μm ≤100 particles / ft³. Material transfer between steps utilizes anti-static vacuum suction cups made of nitrile rubber with a surface resistivity of [missing value]. .

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