Additional low-frequency jitter formation process

Abstract

The invention provides an additional low-frequency jitter formation process. According to the process for additional low-frequency jitter formation, the processes of additional low-frequency jitter formation, stepped formation and the like are arranged, the lithium ion concentration gradient is broken through mild shearing force generated by low-frequency jitter, and precise parameter regulation and control of each stage of stepped formation are matched, so that the thickness deviation of an SEI film is greatly reduced, and the uniformity and consistency of the compactness of the film are guaranteed; sEM characterization shows that the surface of the film is flat and flawless, the uniform SEI film can effectively inhibit the growth of lithium dendrites, and by matching with the stage adaptability of stepped formation, the cycle life and capacity stability of the battery are improved, the internal short-circuit risk is reduced, the use safety is enhanced, and meanwhile, the dual effects of accelerating the mass transfer efficiency through shaking and optimizing the charging rhythm through stepped formation are achieved, so that the service life of the battery is prolonged. The formation time is greatly shortened, the production efficiency is improved, the unit manufacturing cost is reduced, the process compatibility is high, the low-frequency jitter module can be directly added to an existing production line, a battery cell does not need to be transformed or a power supply does not need to be replaced, and a mainstream battery cell system is adapted.

Description

Technical Field

[0001] This invention relates to the field of power battery manufacturing technology, and more specifically, to a process for adding low-frequency vibration formation. Background Technology

[0002] Lithium-ion batteries have become core energy storage devices for new energy vehicles and energy storage systems due to their advantages such as high energy density and long cycle life. The SEI film, as a protective interface film formed when the negative electrode surface comes into contact with the electrolyte, directly determines the cycle stability, safety and rate performance of the battery due to its uniformity and density. If the SEI film is too thick, it will increase the lithium-ion transmission impedance; if it is too thin, it will be easily eroded by the electrolyte. Local unevenness may also induce lithium dendrite growth, leading to the risk of battery short circuit.

[0003] However, the technical solution provided by this patent has the following problems: Currently, most mainstream formation processes employ static charging or conventional "constant current-constant voltage" control, optimizing the SEI film solely by adjusting the charging current and voltage gradient. This presents the following core problems: lithium ions easily form local concentration gradients when depositing on the negative electrode surface, leading to uneven SEI film thickness and significant differences in density; the mass transfer efficiency between the electrolyte and the negative electrode surface is low under static conditions, resulting in long formation times and low production efficiency; to improve uniformity, some processes add film-forming additives (such as VC and FEC), but these additives are expensive and cannot solve the problem of uneven deposition from a kinetic perspective; while there have been attempts at high-frequency vibration-assisted formation in existing technologies, high-frequency vibration easily leads to electrolyte splashing and electrode structure damage, and excessive shear force can actually disrupt the initial formation of the SEI film.

[0004] This invention significantly improves the uniformity and density of the SEI film by adding low-frequency vibration combined with a stepped formation process, effectively suppressing lithium dendrite growth, enhancing battery performance and safety, extending cycle life, while accelerating mass transfer efficiency, shortening formation time, and reducing costs and increasing efficiency. It has strong process compatibility, can be directly installed on existing production lines, and is easy to industrialize and promote. Summary of the Invention

[0005] The present invention aims to solve the technical problems mentioned in the background art and provide a process for additional low-frequency jitter formation.

[0006] To achieve the above objectives, the present invention provides the following technical solution: a process for additional low-frequency jitter formation, comprising the following steps: Step 1: Preparation of supporting equipment for the process: Set up the linkage device of the formation power supply, low frequency vibration module and cell fixing system; Step 2: Place the cell to be formed in a vacuum drying oven to dry and remove moisture from the electrodes, inject electrolyte, and let it stand to ensure that the electrolyte fully wets the electrodes; Step 3: Fix the pre-treated battery cell onto the vibration platform, connect the positive and negative terminals of the power supply, and set the vibration parameters; Step 4: Enable synchronization control and execute stepped charging; Step 5: After formation, let the cell stand for 1-2 hours to allow the SEI film to stabilize fully. Then, discharge it at a constant current of 0.1-0.2C to 2.5V or 2.0V to complete the SEI film activation and obtain a cell with a uniform SEI film surface.

[0007] Further preferred option: In step one, the linkage device includes a low-frequency vibration module and a cell fixing system.

[0008] Further preferred option: In step three, the jitter parameters are specifically a frequency of 2-3Hz, an amplitude of 1-1.5mm, and a jitter direction of reciprocating along the electrode plane.

[0009] Further preferred options: In step four, during the staged formation and charging process, the first stage is the initial formation stage of the SEI film; the second stage is the densification stage of the SEI film; and the third stage is the stabilization stage of the SEI film.

[0010] A further preferred solution: In the first stage, the lithium ions are charged to 2.0V at a constant current of 0.05-0.1C and continuously jittered to disperse them using shear force and avoid local deposition.

[0011] Further optimized scheme; in the second stage, the constant current is charged to 3.0V at 0.1-0.2C, keeping the jitter parameters unchanged, to promote uniform growth of SEI film.

[0012] A further preferred option: In the third stage, when the voltage reaches 3.0V, the low-frequency jitter is stopped, and the charging is switched to 0.2-0.3C constant current charging to 3.6V or 3.45V, and then switched to constant voltage charging until the current is ≤0.01C.

[0013] Further preferred options: In the third stage, when the battery cell is a ternary lithium battery cell, it is charged to 3.6V with constant current; when the battery cell is a lithium iron phosphate battery cell, it is charged to 3.45V with constant current.

[0014] Further preferred options: In step five, when the battery cell is a ternary lithium battery cell, it is discharged at a constant current of 0.1-0.2C to 2.5V; when the battery cell is a lithium iron phosphate battery cell, it is discharged at a constant current of 0.1-0.2C to 2.0V. Beneficial effects

[0015] 1. By setting an additional low-frequency dithering formation process, the local concentration gradient of lithium ions on the electrode surface is broken by the gentle shear force generated by the low-frequency dithering, which effectively solves the problems of uneven SEI film thickness and large differences in density in traditional processes. SEM characterization shows that the film surface is flat and smooth, without local protrusions or depressions, the thickness deviation is significantly reduced and the density is highly consistent. 2. By incorporating an additional low-frequency dithering formation process, battery performance and safety can be improved. A uniform SEI film can significantly reduce the probability of lithium dendrite germination and significantly improve battery cycle life. For example, the capacity retention rate of ternary cylindrical cells reaches 90.2% after 1000 1C charge-discharge cycles. 3. By incorporating an additional low-frequency vibration formation process, production efficiency is improved and costs are reduced. Vibration accelerates mass transfer efficiency, optimizes the mass transfer efficiency between the electrolyte and the negative electrode, shortens the formation time, and improves production efficiency. At the same time, the total formation time of ternary cylindrical cells is reduced by 32.8%, significantly improving production efficiency and reducing costs. In terms of safety, the short circuit rate of square lithium iron phosphate cells in the needle penetration test is 0, far exceeding the 15% level of traditional processes. Moreover, this process has strong compatibility and can be directly installed on existing production lines, adapting to mainstream cell systems. 4. In summary, this process with added low-frequency vibration formation achieves significant multi-dimensional optimizations by incorporating additional low-frequency vibration formation and stepped formation processes. It breaks down the lithium-ion concentration gradient through the gentle shear force generated by low-frequency vibration, and combined with precise parameter control at each stage of stepped formation, it significantly reduces SEI film thickness deviation, ensuring uniform and dense film. SEM characterization shows a smooth, defect-free film surface. The uniform SEI film effectively inhibits lithium dendrite growth. Combined with the adaptability of the stepped formation stages, it not only improves battery cycle life and capacity stability but also reduces the risk of internal short circuits, enhancing safety. Furthermore, the dual effects of vibration accelerating mass transfer efficiency and stepped formation optimizing charging rhythm significantly shorten formation time, improve production efficiency, and reduce unit manufacturing costs. This process is highly compatible; the low-frequency vibration module can be directly installed on existing production lines without modifying the battery cells or replacing the power supply, making it compatible with mainstream battery cell systems and easy to promote industrially. Detailed Implementation

[0016] The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the embodiments of the present invention.

[0017] In this embodiment of the invention, a process for adding low-frequency jitter formation includes the following steps: Step 1: Preparation of supporting equipment for the process: Set up the linkage device of the formation power supply, low-frequency vibration module and cell fixing system; Step 2: Place the cell to be formed in a vacuum drying oven to dry and remove moisture from the electrodes, inject electrolyte, and let it stand to ensure that the electrolyte fully wets the electrodes; Step 3: Fix the pre-treated battery cell onto the vibration platform, connect the positive and negative terminals of the power supply, and set the vibration parameters; Step 4: Enable synchronization control and execute stepped charging; Step 5: After formation, let the cell stand for 1-2 hours to allow the SEI film to stabilize fully. Then, discharge it at a constant current of 0.1-0.2C to 2.5V or 2.0V to complete the SEI film activation and obtain a cell with a uniform SEI film surface. In step one, the linkage device includes a low-frequency vibration module and a cell fixing system. In step three, the vibration parameters are specifically a frequency of 2-3Hz, an amplitude of 1-1.5mm, and a reciprocating vibration direction along the electrode plane. In step four, during the staged formation and charging process, the first stage is the initial formation stage of the SEI film; the second stage is the densification stage of the SEI film; and the third stage is the stabilization stage of the SEI film. In the first stage, the constant current charging is maintained at 0.05-0.1C to 2.0V, with continuous vibration to disperse lithium ions using shear force and avoid local deposition. In the second stage, the constant current charging is maintained at 0.1-0.2C to 3.0V. With the jitter parameters unchanged, the uniform growth of the SEI film is promoted. In the third stage, when the voltage reaches 3.0V, the low-frequency jitter is stopped, and the charging is switched to 0.2-0.3C constant current charging to 3.6V or 3.45V, and then switched to constant voltage charging until the current is ≤0.01C. In the third stage, when the cell is a ternary cell, the constant current charging is to 3.6V; when the cell is a lithium iron phosphate cell, the constant current charging is to 3.45V. In step five, when the cell is a ternary cell, the constant current discharge is to 0.1-0.2C constant current to 2.5V; when the cell is a lithium iron phosphate cell, the constant current discharge is to 0.1-0.2C constant current to 2.0V. Based on the above steps, when the battery cell is a ternary cylindrical cell, the additional low-frequency dithering formation steps are as follows: First, the device was set up and parameters were configured: the low-frequency jitter module was set to 2Hz, amplitude 1mm, jitter direction along the cell axis and electrode plane; the formation power supply was set with stepped current and voltage thresholds, and the synchronous controller was delayed by 5ms; the cell was fixed on the jitter platform, the power supply was connected, and jitter was started, entering the low-frequency jitter formation stage. In the first stage, the cell was charged to 2.0V with a constant current of 0.1C (0.2A) and jittered continuously for 10 hours, which is 5 hours less than the traditional process; in the second stage, the cell was charged to 3.0V with a constant current of 0.15C (0.3A) and jittered continuously for 6.7 hours; in the third stage, jitter was stopped. The battery was charged at a constant current of 0.2C (0.4A) to 3.6V, then switched to constant voltage charging until the current was ≤0.02A, taking 2.3 hours. After formation, it was left to stand for 1.5 hours, and then discharged at 0.15C (0.3A) to 2.5V to complete activation. The average thickness was 80nm with a deviation of 3.5% by SEM characterization. After 1000 charge-discharge cycles at 1C, the capacity retention rate was 90.2%. The total formation time was 21.5 hours, which is 10.5 hours less than the traditional static formation time of 32 hours, and the efficiency was improved by 32.8%. In this embodiment, the selected cell is a 18650 ternary cylindrical cell with a capacity of 2Ah. When the battery cell is a square lithium iron phosphate cell, the additional low-frequency dithering formation process is as follows: First, the device was set up and parameters were set: the low-frequency vibration module frequency was set to 3Hz, amplitude to 1.5mm, and vibration direction to be along the long side of the soft-pack lithium iron phosphate battery; the formation power supply was set to be compatible with the lithium iron phosphate voltage range, with a synchronization delay of 8ms; the soft-pack lithium iron phosphate battery cell was dried in an 80℃ vacuum drying oven for 10h. The positive electrode of the soft-pack lithium iron phosphate battery cell was made of LiFePO4 (lithium iron phosphate) material, and the negative electrode was made of graphite material; the electrolyte (1mol / L LiPF6-EC / DEC=1:1, containing 1% FEC) was injected into the glove box and left to stand for 3h; the low-frequency vibration formation stage began: in the first stage, the battery was charged to 2.0V at a constant current of 0.08C (0.4A) and vibrated continuously for 1 hour. 2.5h; the second stage is to charge to 3.0V with a constant current of 0.2C (1A) and maintain the jitter for 5h; the third stage stops the jitter, charges to 3.45V with a constant current of 0.3C (1.5A), and switches to constant voltage until the current is ≤0.01A, which takes 2h; after standing for 2h, discharge to 2.0V with 0.2C (1A); at this time, the average thickness of the SEI film is 75nm, with a deviation of 4.2%; in the safety performance test, the needle penetration test (φ3mm steel needle, speed 50mm / s) showed no fire or explosion, and the short circuit rate was 0%, while the short circuit rate of the traditional process was 15%; in this embodiment, the selected cell is a 314Ah square lithium iron phosphate cell with a size of 50.1×160×118.5mm.

[0018] In the aforementioned cell formation process, the gentle shear force generated by low-frequency vibration effectively breaks the local concentration gradient of lithium ions on the negative electrode surface, significantly solving the problems of uneven SEI film thickness and large differences in density. This method significantly reduces SEI film thickness deviation and maintains consistent density. SEM characterization shows no local protrusions or depressions on the film surface, thus providing more stable interface protection for the battery. Furthermore, vibration optimizes the mass transfer efficiency between the electrolyte and the negative electrode, shortening formation time while avoiding risks such as electrode damage and electrolyte splashing that can occur with high-frequency vibration. For example, in the formation process of ternary cylindrical cells, compared to traditional processes, the first stage time is reduced by 5 hours, the total formation time is reduced by 10.5 hours, efficiency is improved by 32.8%, and the safety of the production process is ensured. The low-frequency vibration formation process also reduces the probability of lithium dendrite germination in locally weak areas of the SEI film. A uniformly grown SEI film effectively inhibits lithium dendrite growth, thereby improving the battery's cycle life. After 1000 charge-discharge cycles at 1C, the capacity retention rate of ternary cylindrical cells can still reach 90.2%. The uniform SEI film not only inhibits lithium dendrite growth but also effectively improves the overall performance and safety of the battery. For square lithium iron phosphate cells, in the nail penetration test, cells using this process showed no fire or explosion, with a short circuit rate of 0%, while the short circuit rate of traditional processes was 15%, fully demonstrating the advantages of this process in improving battery safety. The vibration accelerates mass transfer efficiency, significantly shortening the formation time and greatly improving production efficiency, thereby reducing production costs. Furthermore, this process has strong compatibility; the low-frequency vibration module can be directly installed on existing formation production lines without modifying the cell structure or replacing the formation power supply. It is easy to promote industrially and can be well adapted to mainstream cell systems such as ternary and lithium iron phosphate, showing broad application prospects.

[0019] The preferred embodiments of the present invention have been described in detail above. However, the present invention is not limited to the specific details of the above embodiments. Within the scope of the technical concept of the present invention, various simple modifications can be made to the technical solutions of the present invention, and these simple modifications all fall within the protection scope of the present invention. In addition, it should be noted that the various specific technical features described in the above specific embodiments can be combined in any suitable manner without contradiction. In order to avoid unnecessary repetition, the present invention will not describe the various possible combinations separately. Furthermore, various different embodiments of the present invention can also be arbitrarily combined, as long as they do not violate the spirit of the present invention, they should also be regarded as the content disclosed by the present invention.

Claims

1. A process for adding low-frequency dithering, characterized in that: Includes the following steps: Step 1: Preparation of supporting equipment for the process: Set up the linkage device of the formation power supply, low frequency vibration module and cell fixing system; Step 2: Place the cell to be formed in a vacuum drying oven to dry and remove moisture from the electrodes, inject electrolyte, and let it stand to ensure that the electrolyte fully wets the electrodes; Step 3: Fix the pre-treated battery cell onto the vibration platform, connect the positive and negative terminals of the power supply, and set the vibration parameters; Step 4: Enable synchronization control and execute stepped charging; Step 5: After formation, let the cell stand for 1-2 hours to allow the SEI film to stabilize fully. Then, discharge it at a constant current of 0.1-0.2C to 2.5V or 2.0V to complete the SEI film activation and obtain a cell with a uniform SEI film surface.

2. The process for additional low-frequency jitter formation according to claim 1, characterized in that: In step one, the linkage device includes a low-frequency vibration module and a cell fixing system.

3. The process for additional low-frequency jitter formation according to claim 1, characterized in that: In step three, the jitter parameters are specifically a frequency of 2-3Hz, an amplitude of 1-1.5mm, and a jitter direction of reciprocating along the electrode plane.

4. The process for additional low-frequency dithering formation according to claim 1, characterized in that: In step four, during the phased formation and charging process, the first stage is the initial formation stage of the SEI film; the second stage is the densification stage of the SEI film; and the third stage is the stabilization stage of the SEI film.

5. The process for additional low-frequency jitter formation according to claim 4, characterized in that: The first stage involves constant current charging to 2.0V at 0.05-0.1C, followed by continuous vibration to disperse lithium ions using shear force and prevent localized deposition.

6. The process for additional low-frequency jitter formation according to claim 4, characterized in that; In the second stage, the film is charged at a constant current of 0.1-0.2C to 3.0V while keeping the jitter parameters constant to promote uniform growth of the SEI film.

7. The process for additional low-frequency jitter formation according to claim 4, characterized in that: The third stage involves stopping low-frequency jitter when the voltage reaches 3.0V, switching to 0.2-0.3C constant current charging to 3.6V or 3.45V, and then switching to constant voltage charging until the current is ≤0.01C.

8. The process for additional low-frequency jitter formation according to claim 7, characterized in that: In the third stage, when the battery cell is a ternary lithium battery cell, it is charged to 3.6V with constant current; when the battery cell is a lithium iron phosphate battery cell, it is charged to 3.45V with constant current.

9. The process for additional low-frequency jitter formation according to claim 1, characterized in that: In step five, when the battery cell is a ternary lithium battery cell, it is discharged at a constant current of 0.1-0.2C to 2.5V; when the battery cell is a lithium iron phosphate battery cell, it is discharged at a constant current of 0.1-0.2C to 2.0V.