Sealing method for liquid injection port of lithium battery and liquid injection port structure

Abstract

The invention discloses a sealing method for a liquid injection port of a lithium battery and a liquid injection port structure. The sealing method comprises the following steps: placing a battery cell which is filled with liquid and has an upward liquid injection port in a closed cavity; the closed cavity is vacuumized to negative pressure, and an elastic sealing piece is assembled at the liquid injection opening to achieve preliminary sealing; and carrying out vacuum breaking treatment on the closed cavity to enable the interior of the closed cavity to reach normal pressure. The elastic sealing element clings to the liquid injection port by utilizing the internal and external pressure difference of the battery cell; and under the normal pressure state, a sealing piece covers the liquid injection opening to realize permanent sealing. The technical effect of the invention is reflected in the aspects of sealing quality and internal environment of the battery cell. In the aspect of sealing quality, the sealing nail is pressed in under vacuum negative pressure, normal pressure is recovered to form self-tightening sealing, then the sealing piece is welded through laser, and double reliable sealing is achieved. According to the process, electrolyte overflow pollution caused by clamp extrusion in traditional normal-pressure sealing is fundamentally avoided, and the one-time yield of sealing is remarkably improved.

Description

Technical Field

[0001] This invention relates to the field of lithium-ion battery design and manufacturing, and in particular to a lithium battery filling port structure and sealing method. Background Technology

[0002] In the manufacturing process of lithium-ion batteries, reliable sealing of the electrolyte filling port is crucial to ensuring the long-term safety and performance of the battery. Currently, the mainstream atmospheric pressure sealing process involves inserting the sealant into the filling port under atmospheric conditions and then performing laser welding. This method has a fundamental flaw: after sealing, a large amount of gas is sealed inside the battery cell.

[0003] These residual gases can cause serious problems during battery charging, discharging, and long-term use: On the one hand, the residual bubbles inside the core will worsen the interface contact between the electrode and the electrolyte, directly causing lithium metal to precipitate on the surface of the negative electrode during charging and discharging (lithium plating), which not only significantly reduces battery capacity and lifespan, but also poses serious safety hazards such as short circuits and thermal runaway; on the other hand, the free space inside the cell is occupied by atmospheric pressure gas, which leaves room for the battery to expand under harsh conditions such as high temperature, greatly increasing the risk of battery swelling, excessive thickness, or even premature opening of the explosion-proof valve.

[0004] Therefore, there is an urgent need in the existing technology for a sealing solution that can effectively eliminate gas inside the battery cell, so as to reduce the risk of lithium plating and gas expansion from the source and improve the safety and reliability of lithium-ion batteries. Summary of the Invention

[0005] The purpose of this invention is to provide a lithium battery filling port structure and sealing method, which fundamentally eliminates air bubbles and atmospheric pressure gas inside the battery cell, thereby significantly improving the sealing yield, safety performance and cycle life of lithium-ion batteries.

[0006] To achieve the above objectives, the present invention provides the following technical solution: In a first aspect, the present invention discloses a method for sealing the liquid filling port of a lithium battery, comprising the following steps: S1. Place the battery cell that has been filled with liquid and has the liquid inlet facing upwards into a sealed cavity. S2. Evacuate the sealed cavity to negative pressure and assemble an elastic sealing element at the injection port to achieve a preliminary seal. S3. Perform vacuum breaking treatment on the sealed cavity to bring its interior to normal pressure, and use the pressure difference between the inside and outside of the battery cell to make the elastic sealing element tightly adhere to the liquid injection port. S4. Under normal pressure, a sealing sheet is placed over the injection port to achieve a permanent seal.

[0007] A further approach: In step S2, the negative pressure is between -30 kPa and -95 kPa. Maintain the negative pressure for 5-30 seconds to ensure sufficient extraction and stabilization of the internal gas. Pressures below -30 kPa may result in incomplete degassing; pressures above -95 kPa may cause the electrolyte to boil or make it difficult to deform the seals. Preferably, the pressure is between -80 kPa and -95 kPa to achieve the best balance between degassing efficiency and process economy.

[0008] A further embodiment includes a step of cleaning the injection port before the elastic seal is assembled onto it. The inner wall and end face of the injection channel 1 are cleaned using at least one of a negative pressure suction nozzle, inert gas purging, or a wiping tool soaked in organic solvent.

[0009] A further solution: In step S4, the permanent sealing sheet is laser-welded to the injection port. Preferably, the laser power is 100-500W, the welding speed is 50-200mm / s, and the spot diameter is 0.1-0.5mm.

[0010] Secondly, the present invention discloses an injection port structure used in the above-mentioned sealing method, comprising: An injection channel formed on the top cover of the battery, the injection channel having a stepped structure; An elastic seal having a shaft that can be inserted into the injection channel and a cap connected to the shaft; A sealing sheet covers the cap body; In this embodiment, at least one of the cap body and the sealing sheet is in close contact with the stepped structure.

[0011] A further embodiment: the outer periphery of the column is provided with a first protrusion; and / or, the outer periphery of the cap is provided with a second protrusion.

[0012] A further solution: the first protrusion is a ring structure, and after assembly, the compressed height of the ring structure is not less than 50% of the original height.

[0013] A further embodiment: The stepped structure includes a first stepped portion and a second stepped portion, wherein the inner contour of the first stepped portion is tightly fitted with the cap body, and the inner contour of the second stepped portion is tightly fitted with the sealing sheet.

[0014] A further option: the elastic seal is made of fluororubber.

[0015] Thirdly, the present invention discloses a lithium-ion battery, wherein the lithium-ion battery includes an injection port structure as described in any one of claims 5-9. Compared with the prior art, the beneficial effects of the present invention are: The technical advantages of this invention are reflected in a comprehensive improvement in sealing quality, internal cell environment, overall performance, and production efficiency. Regarding sealing quality, a self-tightening seal is formed by pressing a sealing nail under vacuum negative pressure and then restoring it to normal pressure, followed by laser welding of the sealing sheet, achieving a double reliable seal. This process fundamentally avoids electrolyte overflow and contamination caused by clamping in traditional normal pressure sealing, and ensures that the laser welding process is free of defects such as blast points and porosity, significantly improving the first-pass yield of the sealing process and directly reducing cell scrap losses due to poor sealing.

[0016] Regarding the improvement of the internal environment of the battery cell, this invention effectively removes residual air bubbles inside the core and gas from the free space within the cell, allowing the electrolyte and electrode materials to be fully wetted, thus greatly improving the electrode-electrolyte interface characteristics. This not only significantly reduces the risk of lithium plating during charging and discharging, improving battery safety, but also creates a negative pressure environment inside the cell after sealing. This negative pressure environment provides space for gas generation during long-term cycling and high-temperature storage, effectively suppressing cell bulging (extra-thickness) and accidental opening of the explosion-proof valve, thereby improving the physical dimensional stability and structural reliability of the product.

[0017] Ultimately, the synergistic effect of these improvements leads to a significant enhancement in the overall performance of the battery. Specifically, this manifests as improved high-temperature storage life and high-temperature cycle performance, higher long-term capacity retention, and extended lifespan. In summary, this invention, through optimization of the sealing process and structure, achieves comprehensive optimization from production yield to end-product performance and safety, providing an effective guarantee for the production of highly reliable, long-life lithium-ion batteries, and demonstrating significant economic benefits and market competitiveness. Attached Figure Description

[0018] Figure 1 This is a schematic diagram of the injection port structure in this invention; Figure 2 This is an exploded view of the injection port structure in this invention; In the figure: 1-Injection channel, 11-First step, 12-Second step, 2-Elastic seal, 21-Column, 22-Cap, 23-First protrusion, 24-Second protrusion, 3-Sealing plate. Detailed Implementation

[0019] 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. 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.

[0020] In the description of this invention, it should be noted that the terms "upper," "lower," "left," "right," "inner," and "outer," etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings, or the orientation or positional relationship in which the product of this invention is usually placed during use. They are only used to facilitate the description of this invention and to simplify the description, and are not intended to indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on this invention.

[0021] Example Please see Figure 1-2 This embodiment discloses an injection port structure, including an injection channel 1, an elastic seal 2, and a sealing sheet 3. The injection channel 1 is formed on the battery top cover 4 and has a stepped structure. The elastic seal 2 has a column 21 that can be inserted into the injection channel 1, and a cap 22 connected to the column 21. The sealing sheet 3 covers the cap 22. At least one of the cap 22 and the sealing sheet 3 is tightly fitted to the stepped structure. The stepped structure provides precise installation positioning and support for the elastic seal 2 and the sealing sheet 3. The elastic seal 2, through the design of the column 21 and the cap 22, respectively achieves sealing of the depth and end face of the injection channel 1. This structure, in conjunction with the method, ensures a stable and reliable multi-stage sealing system during and after the vacuum-atmospheric pressure process.

[0022] Furthermore, the outer periphery of the column 21 is provided with a first protrusion 23; and / or, the outer periphery of the cap 22 is provided with a second protrusion 24. The arrangement of the first protrusion 23 and the second protrusion 24 constitutes multiple redundant sealing defenses. When the elastic seal 2 is pressed into the liquid injection channel 1, these protrusions will undergo elastic deformation, tightly filling the assembly gap, greatly enhancing the reliability of the seal, especially in dealing with vibration and pressure fluctuations during long-term battery use, effectively preventing electrolyte leakage.

[0023] Furthermore, the first protrusion 23 is an annular structure, and after assembly, the compression height of the annular structure is not less than 50% of the original height. Specifying the first protrusion 23 as an annular structure and limiting its compression height to not less than 50% ensures that the sealing boss can generate sufficiently large and uniform contact pressure and deformation recovery force after assembly, thereby providing a durable and stable high-compression seal. This is a key design parameter for achieving long-term effective sealing.

[0024] Furthermore, the stepped structure 11 includes a first stepped portion 11 and a second stepped portion 12, wherein the inner contour of the first stepped portion 11 is tightly fitted with the cap body 22, and the inner contour of the second stepped portion 12 is tightly fitted with the sealing sheet 3. By setting the first stepped portion 11 and the second stepped portion 12, and having them tightly fitted with the cap body 22 and the sealing sheet 3 respectively, a clear stepped sealing hierarchy is formed. This structure not only facilitates assembly and positioning, but more importantly, it spatially separates and optimizes the sealing functions of the elastic sealing element 2 and the sealing sheet 3, allowing each seal to perform effectively in its optimal position, collectively constructing a more robust sealing fortress.

[0025] Furthermore, the elastic seal 2 is made of fluororubber. Utilizing the excellent resistance to electrolyte corrosion, high temperature resistance, and low compression set of fluororubber, the elastic seal 2 ensures that it maintains its elasticity and sealing performance for a long time in the harsh chemical and thermal environment of the battery, thereby guaranteeing the long service life and safety of the battery.

[0026] This embodiment also discloses a sealing method for the above-mentioned injection port structure, including the following steps: S1. Place the battery cell that has been filled with liquid and has the liquid inlet facing upwards into a sealed cavity. S2. Evacuate the sealed cavity to negative pressure and assemble an elastic sealing element at the injection port to achieve a preliminary seal. S3. Perform vacuum breaking treatment on the sealed cavity to bring its interior to normal pressure, and use the pressure difference between the inside and outside of the battery cell to make the elastic sealing element tightly adhere to the liquid injection port. S4. Under normal pressure, a sealing sheet is placed over the injection port to achieve a permanent seal.

[0027] By employing a "vacuum first, then atmospheric pressure" process sequence, the technical performance is improved through the principle of pressure difference. First, preliminary sealing under negative pressure actively and effectively removes residual air bubbles from inside the cell (including deep within the winding core), fundamentally reducing the risk of lithium plating caused by air bubbles during subsequent use. Second, upon returning to atmospheric pressure, atmospheric pressure creates a strong and uniform force, tightly pressing the elastic seal 3 against the injection port, achieving a self-tightening and reliable pre-sealing. This provides a clean and stable foundation for subsequent permanent sealing. Ultimately, this method systematically improves sealing yield and battery safety.

[0028] Furthermore, in step S2, the negative pressure is between -30 kPa and -95 kPa. This pressure range ensures effective gas extraction while avoiding excessive pressure that could lead to excessive deformation of the seal or uneconomical process costs, thus ensuring optimal technical results while also considering the feasibility and stability of the process.

[0029] Furthermore, before the elastic seal is assembled onto the injection port, a step of cleaning the injection port is included. Adding a cleaning step thoroughly removes any residual electrolyte or contaminants from the injection port, ensuring that the weld joint is free of defects such as spalls and porosity during subsequent laser welding, directly improving the welding yield and sealing reliability of the final permanent seal.

[0030] Furthermore, in step S4, the permanent sealing sheet is laser-welded to the injection port. Laser welding is explicitly used for permanent sealing, leveraging its concentrated energy and high precision to achieve a deep fusion and excellent airtightness. This, together with the elastic seal, forms a robust physical barrier, ensuring absolute sealing of the battery throughout its entire lifespan. After restoring to normal pressure, the pressure differential acting on the surface of the cap 22 causes further compression deformation of the second protrusion 24, increasing the compression height to 55%-70% of its original height, thus forming a static seal with even better airtightness.

[0031] Comparative Example The only difference from Example 1 is the sealing method, which is as follows: S1. Under normal pressure, press the elastic seal tightly against the liquid injection port of the battery cell that has been filled with liquid and has the liquid injection port facing upwards; S2. Under normal pressure, a sealing sheet is placed over the injection port to achieve a permanent seal.

[0032] Test case To verify the actual effectiveness of the injection port structure and sealing process provided by this invention, a systematic comparative test was conducted. The tests strictly followed the evaluation standards and methods commonly used in the lithium battery industry, aiming to objectively and quantitatively assess its performance improvement. The tests selected cells using the process and structure of this invention (example) and cells using traditional atmospheric pressure sealing processes and ordinary injection port structures (comparative examples) as comparative samples. Except for the sealing process, both groups of cells maintained consistency in all other conditions, including material system, design specifications, and injection volume, to ensure the reliability and comparability of the test results. Specific test items and methods are as follows: Automated visual inspection and helium mass spectrometry leak detection were used to evaluate the sealing yield of the sealing process; a thickness measurement device was used to measure the thickness and distribution of the sealed cell; the number and distribution of lithium deposition points were statistically analyzed by disassembling the cell; finally, the cell was placed in a constant temperature chamber for high-temperature accelerated storage experiments, continuously monitored until the explosion-proof valve was opened, and its durability in days was recorded. All tests were conducted under controlled environmental conditions to ensure the accuracy and repeatability of the data.

[0033] Table 1

[0034] Analysis of the test results shows that the present invention achieves significant improvements in several key performance aspects compared to the traditional atmospheric pressure sealing process. Specifically, the defect rate of the liquid injection port sealing is significantly reduced from 0.55% in the control example to 0.01%; the cell thickness control is more stable, with its positive tolerance range narrowed from +0.3mm to +0.1mm; lithium plating is effectively suppressed, with the number of lithium plating points per 10 cells reduced from 15 to 1; and the battery durability under high-temperature storage is significantly enhanced, with the valve opening days extended from 270 days to 360 days. These data collectively demonstrate that the present invention, through vacuum negative pressure sealing technology and corresponding structural improvements, systematically improves the sealing quality, cell interface stability, and long-term storage reliability, fundamentally solving the problems of low yield and safety risks caused by gas residue in traditional processes.

[0035] Although this specification describes embodiments, not every embodiment contains only one independent technical solution. This narrative style is merely for clarity. Those skilled in the art should consider the specification as a whole. The technical solutions in each embodiment can also be appropriately combined to form other embodiments that can be understood by those skilled in the art.

[0036] Therefore, the above description is only a preferred embodiment of this application and is not intended to limit the scope of this application; that is, all equivalent modifications made in accordance with the scope of the claims of this application shall be within the protection scope of the claims of this application.

Claims

1. A method for sealing the electrolyte filling port of a lithium battery, characterized in that, Includes the following steps: S1. Place the battery cell that has been filled with liquid and has the liquid inlet facing upwards into a sealed cavity. S2. Evacuate the sealed cavity to negative pressure and assemble an elastic sealing element at the injection port to achieve a preliminary seal. S3. Perform vacuum breaking treatment on the sealed cavity to bring its interior to normal pressure, and use the pressure difference between the inside and outside of the battery cell to make the elastic sealing element tightly adhere to the liquid injection port. S4. Under normal pressure, a sealing sheet is placed over the injection port to achieve a permanent seal.

2. The sealing method according to claim 1, characterized in that, In step S2, the negative pressure is between -30 kPa and -95 kPa.

3. The sealing method according to claim 1, characterized in that, Before the elastic seal is assembled onto the injection port, a step of cleaning the injection port is also included.

4. The sealing method according to claim 1, characterized in that, In step S4, the permanent seal is achieved by laser welding the sealing plate to the injection port.

5. A liquid injection port structure used in the sealing method according to any one of claims 1-4, characterized in that, include: An injection channel formed on the top cover of the battery, the injection channel having a stepped structure; An elastic seal having a shaft that can be inserted into the injection channel and a cap connected to the shaft; A sealing sheet covers the cap body; In this embodiment, at least one of the cap body and the sealing sheet is in close contact with the stepped structure.

6. The injection port structure according to claim 5, characterized in that, The outer periphery of the column is provided with a first protrusion; and / or, the outer periphery of the cap is provided with a second protrusion.

7. The injection port structure according to claim 6, characterized in that, The first protrusion is a ring structure, and after assembly, the compressed height of the ring structure is not less than 50% of the original height.

8. The injection port structure according to claim 5, characterized in that, The stepped structure includes a first stepped portion and a second stepped portion, wherein the inner contour of the first stepped portion is tightly fitted with the cap body, and the inner contour of the second stepped portion is tightly fitted with the sealing sheet.

9. The injection port structure according to claim 5, characterized in that, The elastic seal is made of fluororubber.

10. A lithium-ion battery, characterized in that, The lithium-ion battery includes the injection port structure used in the sealing method as described in any one of claims 1-4.

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