Cylindrical battery center pin processing method and cylindrical battery center pin

Abstract

The invention discloses a cylindrical battery center pin machining method and a cylindrical battery center pin. The cylindrical battery center pin machining method comprises the steps that firstly, a PP material is selected and put into an extruder hopper, and secondly, the 190-210 DEG C hot melting PP material is adopted to extrude a pipe through an extruder; 3, the pipe is cooled and crystallized to 92%-96%; fourthly, the two ends of the pipe are cut to be flat; fifthly, the cut pipe is put into a vibration disc, and the vibration disc automatically feeds the pipe to double-end hot melting chamfering equipment; and 6, pretreatment is conducted through the double-end hot melting chamfering equipment, chamfers with preset angles are formed on the outer walls of the two ends of the pipe through an inner mold and an outer mold of the double-end hot melting chamfering equipment through a temperature pressure curve, and then the center needle is formed. A cylindrical battery center pin comprises a tube body formed by polypropylene through extrusion molding, the tube body is provided with an inner cavity, and the outer walls of the two ends of the hollow tube body are provided with chamfered hollow structure tube bodies through hot melting molding; and the chamfer is a hot melting chamfer surface with the gradient of 20-30 degrees.

Description

Technical Field

[0001] This invention relates to the field of cylindrical battery center pins, and particularly to a method for processing cylindrical battery center pins and a cylindrical battery center pin itself. Background Technology

[0002] The center pin is an important component of cylindrical batteries, mainly used to support the battery core and prevent it from collapsing and deforming inward.

[0003] There are two main types of existing center pins:

[0004] Option 1, for example, the existing design of a hollow metal tube with an internal cooling channel (currently, Panasonic has the best manufacturing precision in the industry). This design improves the thermal management efficiency of cylindrical batteries, but it has the following problems (refer to the "Power Battery Safety White Paper 2024"):

[0005] ① Heavy (It is made of titanium alloy with a density of 4.5g / cm³) 3 Therefore, the energy density loss is ≥5%;

[0006] ② High risk of short circuit; metallic materials can easily cause the positive and negative electrodes to conduct.

[0007] ③ The price and cost are high, and the processing steps include precision machining and plasma deposition of elemental materials to form an insulating structure;

[0008] Option 2, for example, CN116826189A uses an injection-molded carbon fiber reinforced polypropylene (PPS) center pin. While this structure achieves lightweighting and insulation, it faces the following problems:

[0009] ① Insufficient chemical resistance (swelling rate > 1.5% in high-temperature electrolyte after 240 hours);

[0010] ② High process energy consumption (injection molding requires 320℃, resulting in energy consumption > 5kW·h / kg and cavity structure yield < 85%);

[0011] ③ Bottlenecks such as high material costs (unit price of polypropylene PPS resin).

[0012] Therefore, the above two structures also have higher requirements for the accuracy of the center needle (coiling needle) in the newly added test items of the new national standard GB38031-2025.

[0013] For example:

[0014] ① Defects in the needle winding process (such as edge burrs) may lead to weak points in the casing welding, and high-precision needle winding is required to reduce the deformation stress of the battery cell;

[0015] ② Added "internal heating" trigger mode to simulate a more realistic internal short circuit scenario.

[0016] In the new tests, the insulation layer of the metal needle showed an increased breakage rate; and the electrolyte corrosion resistance of the carbon fiber reinforced polypropylene (PPS) center needle also decreased.

[0017] Meanwhile, the aforementioned costs are relatively high, making it difficult to achieve a price of less than $0.1 per piece, which restricts large-scale production. Summary of the Invention

[0018] The main objective of this invention is to propose a method for processing a cylindrical battery center pin and a cylindrical battery center pin, aiming to improve the existing center pin processing method, so as to achieve the required support and insulation, while having a lower processing cost and less wear between the center pin and the wound battery cell, thereby improving the processing accuracy.

[0019] To achieve the above objectives, this invention proposes a method for machining a center pin of a cylindrical battery, comprising:

[0020] Step 1: Select polypropylene (PP) material and place it into the extruder hopper;

[0021] Step 2: Extrude pipes using hot-melt polypropylene (PP) material at 190-210℃ through an extruder;

[0022] Step 3: Cool the pipe and allow it to crystallize to 92%-96%;

[0023] Step 4: Trim both ends of the pipe to make them flat;

[0024] Step 5: Feed the cut pipes into the vibratory feeder, which automatically feeds the pipes into the double-head hot melt chamfering equipment;

[0025] Step Six: Pre-treatment with a double-headed hot melt chamfering machine, and forming a chamfer at a predetermined angle on the outer walls of both ends of the pipe by using the inner and outer molds of the double-headed hot melt chamfering machine through temperature and pressure curves, i.e. forming the center pin.

[0026] A cylindrical battery center pin includes a polypropylene extruded tube with an inner cavity.

[0027] The outer walls at both ends of the hollow tube are hot-melted and formed with chamfered hollow structures.

[0028] The chamfer angle (based on the axis) is 20°-30° for the hot-melt chamfer surface.

[0029] The inner diameter of the cavity is a predetermined value of ±0.05 mm; the roughness Ra of the chamfer is ≤0.1 μm.

[0030] The beneficial effects of the technical solution of this invention:

[0031] 1. Regarding step two, PP low-temperature extrusion is used: processing temperature of 190-210℃ (to avoid degradation), swelling rate ≤0.5%, which means that the structural support of the center pin is improved through the material and extrusion molding method;

[0032] 2. Regarding step three, the preferred crystallization rate is 95%, wherein the highly crystalline and dense layer blocks electrolyte penetration (240h swelling experiment: 0.5% vs 1.5%);

[0033] 3. Regarding the strength and temperature of the molded center pin structure, the low-temperature toughness and impact strength at -30℃ are 22kJ / m. 2 ;

[0034] 4. The chamfering is formed by hot melt molding, which avoids the wear of burrs when inserting the center pin in the center of the wound battery. The chamfer is smooth and stable, which also reduces the processing difficulty and makes the processing stable. Attached Figure Description

[0035] Figure 1 This is a flowchart illustrating the processing of the present invention;

[0036] Figure 2 This is a schematic diagram of the center needle of this application;

[0037] Figure 3 This is a schematic diagram of the processing equipment;

[0038] Figure 4 This is a schematic diagram of a dual vibratory feeder.

[0039] Figure 5 This is a schematic diagram of a double-headed hot melt equipment.

[0040] In the diagram, the tube body is 100, the inner cavity is 101, and the chamfer is 102. Detailed Implementation

[0041] The technical solutions in 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 a part of the embodiments of the present invention, and not all of them. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0042] It should be noted that if the embodiments of the present invention involve directional indicators (such as up, down, left, right, front, back, top, bottom, inside, outside, vertical, horizontal, longitudinal, counterclockwise, clockwise, circumferential, radial, axial, etc.), the directional indicators are only used to explain the relative positional relationship and movement of the components in a certain specific posture (as shown in the figure). If the specific posture changes, the directional indicators will also change accordingly.

[0043] like Figures 1 to 5 As shown, a method for machining a center pin of a cylindrical battery includes the following steps:

[0044] Step 1: Select polypropylene (PP) material and place it into the extruder hopper;

[0045] Step 2: Extrude pipes using hot-melt polypropylene (PP) material at 190-210℃ through an extruder;

[0046] Step 3: Cool the pipe and allow it to crystallize to 92%-96%;

[0047] Step 4: Trim both ends of the pipe to make them flat;

[0048] Step 5: Feed the cut pipes into the vibratory feeder, which automatically feeds the pipes into the double-head hot melt chamfering equipment;

[0049] Step Six: Pre-treatment with a double-headed hot melt chamfering machine. The inner and outer molds of the double-headed hot melt chamfering machine are used to form chamfers of a predetermined angle on the outer walls of both ends of the pipe using a temperature and pressure curve; this forms the center pin.

[0050] The chamfering hot-melt process forms a dense skin layer (with a crystallinity greater than 98% at the chamfer position);

[0051] Step 7: Inspection - Discharge.

[0052] Beneficial effects of the design:

[0053] 1. Regarding step two, PP low-temperature extrusion is used: processing temperature 190-210℃ (to avoid degradation), swelling rate ≤0.5%;

[0054] 2. Regarding step three, the preferred crystallization rate is 95%, wherein the highly crystalline and dense layer blocks electrolyte penetration (240h swelling experiment: 0.5% vs 1.5%);

[0055] 3. Regarding the molded center pin, its low-temperature toughness and impact strength at -30℃ are 22 kJ / m. 2 ;

[0056] 4. The chamfer is formed by hot melt molding, which avoids the wear of burrs when inserting the center needle in the center of the wound battery. The chamfer is smooth and stable, and the processing is stable.

[0057] Specifically, the polypropylene (PP) material has a particle isotacticity > 95%, a melt flow index of 25 g / 10 min, and a maximum temperature of 230 °C; the polypropylene (PP) material has a plastic flow index (MI) > 20 g / 10 min.

[0058] The isotacticity of the particles is used to ensure stable plastic flow and uniform temperature distribution during extrusion molding, with a maximum temperature of 230℃ to prevent PP material degradation.

[0059] Specifically, the polypropylene (PP) material is homopolymer polypropylene (PP-H), including T30S, H30S and EPS30R.

[0060] The material possesses the following advantages: it is not limited to T30S, H30S, or EPS30R; this application utilizes PPT30S, which has a low native surface energy (29 mN / m) and an electrolyte contact angle >90°. The hot-melt process forms a dense skin layer (crystallinity increased to 98%), effectively preventing electrolyte penetration. By employing existing materials and combining them with automated processing methods and equipment, the high processing cost and numerous processing steps of existing center pins are improved, while simultaneously allowing for precise control of processing accuracy.

[0061] The extruder is a screw extruder, and the screw die size tolerance of the screw extruder is: predetermined value of screw outer diameter ±0.05mm; predetermined value of screw inner diameter ±0.05mm; the cooling adopts water cooling shaping sleeve conveying at 15℃ / S.

[0062] Raw materials, extrusion molding parameters, and beneficial effects: Material: Polypropylene (PP) granules, isotacticity > 98%, melt index 25 g / 10 min @ 230℃;

[0063]

[0064] Specifically, the hot melt temperature-pressure curve includes:

[0065] Heating stage: The polypropylene (PP) material rises from 25°C to 170°C within 0.5 seconds;

[0066] Pressure holding section: 0.5-0.7MPa compressed air maintained for 2.0s → Polypropylene (PP) molecular chains oriented and aligned.

[0067] Cooling section: Water cooling at 15℃ / 1.0s instantly locks the crystallinity of the chamfer to over 98%.

[0068] Specifically, the hot melt parameters and their beneficial effects:

[0069]

[0070] Precision control and quality assurance

[0071] 1. Constant Diameter Control: The hollow inner diameter of the chamfered area is ensured to remain unchanged during machining using a ceramic mandrel;

[0072] 2. Laser real-time monitoring of inner diameter; items with fluctuations > ±0.03mm are automatically rejected.

[0073] 3. Zero burr achievement: The mirror polishing precision of the inner and outer mold surfaces reaches Ra≤0.025μm + nano release coating; thus achieving demolding without adhesion;

[0074] 4. The chamfered edge with a radius of 0.1mm effectively avoids and eliminates microscopic burrs.

[0075] 5. No post-treatment required: PPT30S has low native surface energy (29mN / m) and an electrolyte contact angle >90°; the hot-melt process forms a dense skin layer (crystallinity reaches at least 98%), which blocks electrolyte penetration.

[0076] Specifically, the heating section uses a high-frequency generator to heat the chamfered portion of the polypropylene (PP) material.

[0077] Specifically, high-frequency heating is used, which can ensure precise heating and also provides faster heating efficiency;

[0078] Specifically, the inner mold is a ceramic mandrel.

[0079] The chamfer angle is 20°-30°.

[0080] The chamfer tolerance is ±0.5°;

[0081] The pretreatment is a self-lubricating process for the inner mold;

[0082] Laser monitoring of the inner diameter is used in real time during hot melt chamfering.

[0083] Automatic rejection for fluctuations > ±0.03mm

[0084] Nano-zirconia ceramic mandrel: self-lubricating and demolding, continuous operation > 500h;

[0085] High-frequency generator with high-frequency induction heating (2MHz) ensures a temperature gradient ≤ ±2℃; avoids local degradation of PP and guarantees Ra ≤ 0.1μm.

[0086] Processing parameters and beneficial effects of double-head hot melt chamfering equipment:

[0087]

[0088] It also includes a seventh step of detection, which uses a dual-CCD detection module.

[0089] The dual CCD detection module scans the chamfer.

[0090] The standard angle tolerance for the chamfer is ±0.5°;

[0091] The tolerance of the inner diameter of the center pin is ±0.03mm.

[0092] If the value does not meet the predetermined threshold, it will be rejected.

[0093] Dual cameras + servo scanning ensure 100% inspection accuracy with a precision of 0.01mm.

[0094] Ensure a constant diameter of ±0.05mm;

[0095] In addition, the dual-disc resonance interference elimination technology achieves a delivery yield of 99.5%;

[0096] Solve the industry problem of multi-channel synchronous feeding; vibration frequency 40-60Hz, directional conveying PP pipe.

[0097] The hot-melt chamfer can also be achieved by laser softening of the tube end followed by die-forming (wavelength 1064nm, power 50W); or by high-frequency induction heating (frequency 200kHz) followed by spinning.

[0098] Specifically, the entire processing steps differ from existing processing methods:

[0099]

[0100] Technical Comparison Regarding Chamfer Position (Part 1): Chamfer Geometric Optimization (Comparison with the Necked Structure of Scheme 2):

[0101]

[0102] Comparison with Option 1:

[0103] Limitations of Option 1: Injection molding of PPS requires a high temperature of 320℃, which leads to material degradation (240h electrolyte swelling rate >1.5%); the yield of complex cavity structures is <85%, and the cost is $0.18 / piece; the injection molding flow channel causes an inner diameter fluctuation of ±0.1mm and a 30% decrease in pressure relief flow.

[0104] Advantages of this solution:

[0105] 1. Low-temperature extrusion of PP: processing temperature of 190-210℃ (to avoid degradation), swelling rate ≤0.5%;

[0106] 2. Hot-melt chamfering instead of necking: no cavity structure, yield >99%, cost <$0.03 / piece;

[0107] 3. Constant diameter ensures pressure relief efficiency: inner diameter tolerance ±0.05mm, flow rate is 40% higher than Zhejiang University's solution.

[0108] 2. Chamfered mechanical protection performance (comparison with Scheme 1):

[0109]

[0110] Structural defects of the metal pressure relief valve (JP20201508677A) in Comparison Option 1:

[0111] 1. The hollow titanium alloy tube has a built-in cooling channel, and pressure relief requires the use of an independent explosion-proof membrane (response time > 5ms);

[0112] 2. Metal burrs cause the diaphragm perforation rate to be greater than 1.2% (actual measurement data from the 18650 production line);

[0113] 3. Weighing up to 4.2g / piece (18650 specification), reducing battery energy density by 5%+.

[0114] Advantages of this solution:

[0115] 1. Adopting a 20°-30° chamfer design: achieving "zero resistance insertion" (insertion force 0.5N vs. 18N in Scheme 1), with a chamfer curvature radius R0.2mm, eliminating the risk of snagging (diaphragm damage rate ↓ to 0.01%);

[0116] Constant inner diameter: pressure relief channel without necking, airflow velocity 450L / min (120L / min in scheme 1), response time <1.5ms;

[0117] 2. Burr-free: Hot melt chamfering is formed in one step, with a surface roughness Ra≤0.05μm (mirror grade).

[0118] II. Comparison of processing technology and Scheme 2

[0119] Process chain comparison (energy consumption per unit capacity and yield):

[0120]

[0121] (III) Production Comparison

[0122]

[0123] This application achieves hot-melt chamfering in one step:

[0124] 1. The outer diameter is radially compressed (reduction rate 25%~30%) using a 20°-30° tapered die at 160-180℃, while the inner diameter accuracy tolerance is maintained at ±0.05mm;

[0125] 2. It replaces the traditional two-step process of "narrowing + polishing", reducing equipment investment by 70%.

[0126] 3. No post-treatment required: PP has high crystallinity (>95%) and naturally low surface energy (29mN / m), with an electrolyte contact angle >90°, eliminating the need for fluorinated coating;

[0127] 4. Mass production performance advantages: p+ Single line monthly capacity: 6 million pieces (2 million pieces for Option 1)+ Equipment downtime: >5000 hours (MTBF certified)+ Changeover time: <3 minutes (quick mold change system).

[0128] (iv) Test Data

[0129]

[0130] This plan: pressure relief flow rate 450L / min → module temperature gradient <100℃ / s → no propagation in 180s.

[0131] A cylindrical battery center pin includes a polypropylene extruded tube with an inner cavity. The outer walls at both ends of the tube are hot-melt formed with chamfers. The inclination of the chamfer is a hot-melt chamfer surface of 20°-30°. The inner diameter of the inner cavity is a predetermined value ±0.05mm. The roughness Ra of the chamfer is ≤0.1μm.

[0132] Specifically, before or after the chamfering step, a spiral groove or a guide groove extending along its length can be formed on the outer wall of the center pin to achieve the predetermined technical requirements. The spiral groove or guide groove is formed by laser forming, which improves the crystallinity of the groove and further enhances the structural support. At the same time, the laser forming of micro-grooves is simpler in processing, and the processing method can be formed by clamping and rotating the jig.

[0133] The above description is merely a preferred embodiment of the present invention and does not limit the patent scope of the present invention. Any equivalent structural transformations made using the contents of the present invention's specification and drawings under the inventive concept of the present invention, or direct / indirect applications in other related technical fields, are included within the patent protection scope of the present invention.

Claims

1. A method for machining a center pin of a cylindrical battery, characterized in that, The processing steps include: Step 1: Select polypropylene (PP) material and place it into the extruder hopper; Step 2: Extrude pipes using hot-melt polypropylene (PP) material at 190-210℃ through an extruder; Step 3: Cool the pipe and allow it to crystallize to 92%-96%; Step 4: Trim both ends of the pipe to make them flat; Step 5: Feed the cut pipes into the vibratory feeder, which automatically feeds the pipes into the double-head hot melt chamfering equipment; Step Six: Pre-treatment with a double-headed hot melt chamfering machine, and forming a chamfer at a predetermined angle on the outer walls of both ends of the pipe by using the inner and outer molds of the double-headed hot melt chamfering machine through temperature and pressure curves, i.e. forming the center pin.

2. The method for machining the center pin of a cylindrical battery as described in claim 1, characterized in that: The polypropylene (PP) material has a particle isotacticity >95%, a melt index of 25 g / 10 min, and a maximum temperature of 230 °C. The plastic flowability of the polypropylene (PP) material is MI > 20 g / 10 min.

3. The method for machining the center pin of a cylindrical battery as described in claim 2, characterized in that: The polypropylene (PP) material is homopolymer polypropylene (PP-H), including T30S, H30S and EPS30R.

4. The method for machining the center pin of a cylindrical battery as described in claim 1, characterized in that: The extruder is a screw extruder, and the screw die dimensional tolerances of the screw extruder are: predetermined screw outer diameter ±0.05mm; predetermined screw inner diameter ±0.05mm. The cooling process employs a water-cooled shaping sleeve that is conveyed at a rate of 15°C / s.

5. The method for machining the center pin of a cylindrical battery as described in claim 1, characterized in that: The hot melt temperature-pressure curve includes: Heating stage: The polypropylene (PP) material rises from 25°C to 170°C within 0.5 seconds; Pressure holding section: 0.5-0.7MPa compressed air is maintained for 2.0s → Polypropylene (PP) molecular chain orientation and cooling section: Water cooling at 15℃ / 1.0s instantly locks the crystallinity of the chamfer to over 98%.

6. The method for machining the center pin of a cylindrical battery as described in claim 5, characterized in that: The heating section uses a high-frequency generator to heat the chamfered area of ​​the polypropylene (PP) material.

7. The method for machining the center pin of a cylindrical battery as described in claim 5, characterized in that: The inner mold is a ceramic mandrel, the chamfer angle is 20°-30°, the chamfer tolerance is ±0.5°, and the pretreatment is self-lubricating for the inner mold; During hot-melt chamfering, the inner diameter is monitored in real time using a laser, and any deviations greater than ±0.03mm are automatically rejected.

8. The method for machining the center pin of a cylindrical battery as described in claim 1, characterized in that: It also includes step seven: detection, which uses a dual CCD detection module. The dual CCD detection module scans the chamfer, and the standard angle tolerance of the chamfer is ±0.5°; The tolerance of the inner diameter of the center pin is ±0.03mm. If the value does not meet the predetermined threshold, it will be rejected.

9. The method for machining the center pin of a cylindrical battery as described in claim 5, characterized in that: The hot-melt chamfering can also be achieved by laser softening of the tube end followed by molding chamfering, using a laser wavelength of 1064nm and a power of 50W. Alternatively, it can be spun and formed after high-frequency induction heating, wherein the high-frequency induction heating frequency is 200kHz.

10. A cylindrical battery center pin, characterized in that, The tube comprises a polypropylene extruded tube having an inner cavity. The outer walls at both ends of the tube are hot-melted and chamfered. The chamfer is a hot-melt chamfer surface with an inclination of 20°-30°. The inner diameter of the cavity is a predetermined value ±0.05 mm; The roughness Ra of the chamfer is ≤0.1μm.

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