Liquid injection process for improving cycle performance

Abstract

The invention relates to the technical field of cylindrical batteries, in particular to a liquid injection process for improving cycle performance, which comprises the steps of normal pressure standing, vacuumizing, exhausting, vacuum standing, vacuumizing, exhausting, vacuum standing, vacuumizing, exhausting, vacuum standing, pressurizing and the like which are respectively carried out after next liquid injection under the cooperation of an automatic battery liquid injection machine. In the liquid injection process, the processes of vacuumizing, exhausting and vacuum standing are all carried out in a negative pressure environment, and the vacuum standing time is adaptively changed along with the increase of the vacuumizing times, so that air in the battery pole piece is fully exhausted, and the electrolyte can fully and averagely infiltrate the battery pole piece after final pressurization; therefore, the cycle performance of the finished battery can be effectively improved finally.

Description

Technical Field

[0001] The invention relates to the technical field of cylindrical batteries, and in particular to a liquid injection process for improving cycle performance. Background Art

[0002] Battery injection is to evenly infiltrate the electrolyte into the battery pole piece so that the electrochemical capacity of the pole piece can be brought into play to the best. The performance consistency of the battery with incomplete infiltration effect will also be affected. The existing injection processes include normal pressure injection, negative pressure injection, isobaric injection, and high pressure injection, and the processes are relatively mature. From the development history, they are all aimed at increasing the infiltration speed of the pole piece electrolyte, thereby improving production efficiency. The most important parameters for assessing battery injection include injection volume, infiltration effect (sufficient and uniform) and injection accuracy. These three points are achieved through the injection machine. Therefore, the injection equipment is also very important in the lithium battery production process and directly affects the battery performance. To achieve the best infiltration effect in the shortest time is the most important manifestation of the process capability of the injection machine.

[0003] Negative pressure injection is the mainstream injection method. Even the popular isobaric injection uses differential pressure to first inject the electrolyte into the battery cell, and then uses the high-pressure isobaric principle to do static circulation to increase the electrolyte infiltration speed. During the injection process, vacuuming the battery can effectively reduce the resistance generated by the air, thereby reducing the obstacles to electrolyte diffusion. At the same time, pressurized injection of the electrolyte can significantly enhance the driving force of liquid flow and further promote the rapid diffusion of the electrolyte. Therefore, this process combination of vacuuming and pressurized injection greatly accelerates the electrolyte infiltration process and ensures the uniform distribution and efficient utilization of the electrolyte in the electrode pores, but there will also be poor infiltration effect and uneven distribution leading to poor cycle performance. The uneven distribution of the electrolyte causes inconsistency in battery capacity and cycle performance, posing a serious threat to battery performance and reliability. Summary of the invention

[0004] The technical problem to be solved by the present invention is to provide a new battery injection process, so that the electrolyte can fully and evenly infiltrate the battery pole piece, thereby improving the cycle performance of the battery.

[0005] In order to solve the above technical problems, the technical solution adopted by the present invention is: a liquid injection process for improving circulation performance, comprising the following steps: Step 1: Place the battery in the liquid injection chamber and place it at normal pressure for at least 100 seconds after filling the battery. Step 2: Vacuum the liquid injection cavity to a vacuum degree of -0.085Mpa--0.09Mpa, and maintain it for at least 50s; Step 3: Exhaust the air in the electrolyte and control the vacuum degree in the injection cavity to -0.06Mpa--0.07Mpa; Step 4: Vacuum standing, the battery is placed in the liquid injection chamber with a vacuum degree of -0.06Mpa--0.07Mpa for at least 120s; Step 5: Vacuum the liquid injection cavity again to make the vacuum degree in the liquid injection cavity -0.085MPa--0.09Mp, and maintain it for at least 50s; Step 6: Exhaust the air in the electrolyte again and control the vacuum degree in the injection cavity to -0.06Mpa--0.07Mpa; Step 7: Vacuum standing, the battery is placed in the liquid injection cavity with a vacuum degree of -0.06Mpa--0.07Mpa for at least 180s; Step 8: Vacuum the liquid injection cavity again to make the vacuum degree in the liquid injection cavity -0.085MPa--0.09Mp, and maintain it for at least 50s; Step 9: Exhaust the air in the electrolyte again and control the vacuum degree in the injection cavity to -0.06Mpa--0.07Mpa; Step 10: Vacuum standing, the battery is placed in the liquid injection cavity with a vacuum degree of -0.06Mpa--0.07Mpa for at least 240s; Step 11: Pressurize the liquid injection cavity by filling nitrogen to make the pressure in the liquid injection cavity 0.4Mpa-0.5Mpa, and maintain it for at least 100s; Step 12: After the filling is completed, remove the battery from the filling cavity.

[0006] As a preferred solution, the dew point temperature in steps 1 to 12 is 18-28°C.

[0007] As a preferred solution, in step 1, step 5 and step 8, the time for evacuating the liquid injection cavity does not exceed 8 seconds.

[0008] As a preferred solution, in step three, step six and step nine, the exhaust time is 1 second.

[0009] As a preferred solution, in step 11, the nitrogen flushing time does not exceed 13 seconds.

[0010] Compared with the prior art, the present invention has the following beneficial effects: by optimizing the liquid injection process, the present invention enables the electrolyte to fully and evenly infiltrate the battery pole piece, thereby improving the battery's infiltration effect, improving the consistency of the battery's cycle performance, improving the battery's cycle retention rate, and avoiding the phenomenon of a drop in the capacity retention rate in the later stage of the battery cycle, thereby effectively improving the battery's cycle performance. BRIEF DESCRIPTION OF THE DRAWINGS

[0011] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0012] Figure 1 This is a graph showing the capacity retention rate changes of two groups of 18650 batteries in a long cycle test of full charge at 1C constant current and constant voltage and discharge at 1C constant current; Figure 2 The capacity retention rate change diagram of two groups of 18650 batteries in a long cycle test of full charge at 0.5C constant current and constant voltage and discharge at 1C constant current; Figure 3 The capacity retention rate change diagram of two groups of 21700 batteries in a long cycle test of full charge at 1C constant current and constant voltage and discharge at 1C constant current; Figure 4 The capacity retention rate change chart of two groups of 21700 batteries in a long cycle test of full charge at 0.5C constant current and constant voltage and discharge at 1C constant current. DETAILED DESCRIPTION

[0013] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention. Example

[0014] A liquid injection process for improving cycle performance comprises the following steps: Step 1: Place the battery to be injected into the injection chamber, inject the battery, and place it at normal pressure for at least 100 seconds. In this step, the electrolyte penetrates freely without any external pressure interference, and the electrolyte penetration speed is relatively slow.

[0015] Step 2: Vacuum the liquid injection cavity for no more than 8 seconds, so that the vacuum degree in the liquid injection cavity is -0.085Mpa--0.09Mpa, and it is maintained for at least 50 seconds. The purpose of vacuuming is to increase the infiltration rate of the electrolyte. Under the high vacuum degree of -0.085Mpa--0.09Mpa, the air between the electrode particles can be quickly discharged, which is conducive to the full infiltration of the electrolyte.

[0016] Step 3: Exhaust, exhaust the air in the electrolyte, the exhaust time is 1s, and the vacuum degree in the injection cavity is controlled to -0.06Mpa--0.07Mpa. Exhaust is to reduce the vacuum degree in the injection cavity and slow down the infiltration rate of the electrolyte, but the injection cavity is still in a negative pressure state as a whole. Vacuuming and exhausting are performed alternately to increase the infiltration efficiency of the electrolyte and allow the electrolyte to be fully immersed.

[0017] Step 4: Vacuum standing, the battery is placed in a liquid injection cavity with a vacuum degree of -0.06Mpa--0.07Mpa for at least 120s. In this step, the battery is placed in a low vacuum degree, and the infiltration driving effect of the electrolyte under this vacuum degree is relatively small compared to that under high vacuum degree. At this time, the pressure effect on the battery is more conducive to the electrolyte infiltration into the small gaps in the battery pole piece, so that both the large gaps and small gaps of the battery electrode are fully infiltrated.

[0018] Step 5: Vacuum the liquid injection cavity again. The vacuum time should not exceed 8s, so that the vacuum degree in the liquid injection cavity is -0.085MPa--0.09Mp, and it should be maintained for at least 50s.

[0019] Step 6: Exhaust the air in the electrolyte again. The exhaust time is 1s. At the same time, control the vacuum degree in the injection cavity to -0.06Mpa--0.07Mpa.

[0020] Step 7: Vacuum standing, the battery is placed in the liquid injection chamber with a vacuum degree of -0.06Mpa--0.07Mpa for at least 180s.

[0021] Step 8: Evacuate the liquid injection cavity again to make the vacuum degree in the liquid injection cavity -0.085MPa--0.09Mp, and maintain it for at least 50s.

[0022] Step 9: Exhaust the air in the electrolyte again and control the vacuum degree in the injection cavity to -0.06Mpa--0.07Mpa.

[0023] Step 10: Vacuum standing, the battery is placed in the liquid injection cavity with a vacuum degree of -0.06Mpa--0.07Mpa for at least 240s; Step 11: Pressurize and fill the liquid injection cavity with nitrogen for no more than 13 seconds, so that the pressure in the liquid injection cavity is 0.4Mpa-0.5Mpa and maintained for at least 100 seconds.

[0024] Step 12: After the filling is completed, remove the battery from the filling cavity.

[0025] During the battery filling process from step 1 to step 12 above, the dew point temperature should be maintained at 18-28°C.

[0026] The liquid injection process of the present invention is realized in cooperation with the automatic battery liquid injection machine of the prior art. The pressure state in the liquid injection cavity can be accurately controlled by the automatic battery liquid injection machine, thereby meeting the requirements of each step.

[0027] After the electrolyte is injected into the battery electrode, it first quickly covers the edge area of ​​the battery electrode, and then gradually penetrates into the center area until the entire electrode is fully soaked. This results in a lot of air in the battery electrode that cannot be discharged when the electrolyte diffuses and penetrates in the battery electrode.

[0028] The liquid injection process of the present invention, the process of vacuuming-exhausting-standing is all under negative pressure environment, and is cycled 3 times or even more times. As the number of vacuuming times increases, the low vacuum standing time is gradually increased. The purpose is to discharge the air from the battery pole piece, and then pressurize the air after it is discharged, so that the electrolyte can fully infiltrate the battery pole piece, thereby effectively improving the cycle performance of the finished battery.

[0029] Most of the existing injection processes using automated battery injection machines involve repeated steps such as negative pressure, nitrogen (inert gas) pressurization, and standing, without considering the effects of negative pressure vacuum and standing time on battery performance. Although excessive vacuum is conducive to rapid infiltration of the electrolyte, it is insufficient, and the electrolyte is unevenly distributed in the positive and negative electrode diaphragms of the battery. Excessive pressurization is not conducive to the discharge of air bubbles in the electrolyte. The air accumulated in the electrode particles hinders the electrochemical reaction, and the gas dissolves in the electrolyte, which will seriously affect the performance of the battery in the later stage; the standing time is too short, resulting in the electrolyte being unable to fully penetrate into the battery electrode, and the standing time is too long, which will also cause the electrolyte to volatilize, and the long standing time will increase the cost of the production line. Therefore, the negative pressure state, operation time, and pressurization process steps in the injection process have higher and more stringent requirements to ensure that the produced battery has the best cycle performance. The present invention utilizes existing liquid injection equipment and adopts a new liquid injection process without changing the battery production system to achieve the effects of improving battery liquid injection efficiency and liquid injection effect, and improving battery cycle performance and battery consistency.

[0030] The liquid injection process of the present invention can be used for batteries of models such as 18650 and 21700.

[0031] As a specific implementation method for injecting 18650 or 21700 batteries: first, place the battery in the injection chamber of an automated battery injection machine, inject electrolyte into the battery, let it stand at normal pressure for 100 seconds, evacuate the injection chamber for 8 seconds, and maintain it at a vacuum degree of -0.085Mpa for 50 seconds, then exhaust for 1 second and control the vacuum degree at -0.066Mpa, and let the battery stand at a vacuum degree of -0.066Mpa for 120 seconds; Then, the liquid injection cavity is evacuated again for 8 seconds to make the vacuum degree in the liquid injection cavity -0.085Mpa, and after maintaining for 50 seconds, the vacuum is exhausted for 1 second. After exhausting, the vacuum degree in the liquid injection cavity is controlled at -0.066Mpa, and the battery is left to stand for 180 seconds at the vacuum degree of -0.066Mpa; Then evacuate the liquid injection cavity again for 8 seconds and make the vacuum degree in the liquid injection cavity -0.085Mpa, maintain it for 50 seconds, then exhaust for 1 second, control the vacuum degree in the liquid injection cavity to -0.066Mpa, and then let the battery stand at a vacuum degree of -0.066Mpa for 240 seconds, and then fill the liquid injection cavity with nitrogen and pressurize it for 13 seconds. After the pressure in the liquid injection cavity is increased to 0.47Mpa, maintain it for 100 seconds, and then take out the battery after liquid injection or send it to the next process through automated equipment.

[0032] In order to demonstrate the improvement effect of the liquid injection process of the present invention on the battery cycle performance, the applicant selected 30-50pcs of 18650 batteries as the experimental group, and also selected 30-50pcs of 18650 batteries as the control group. The two groups of batteries use the same winding core, and the processes such as spot welding, grooving, sealing, heat shrinkage and formation are the same. The difference is that the experimental group uses the liquid injection process of the present invention when injecting liquid, while the control group uses the existing conventional liquid injection process when injecting liquid. After completing all processing operations, 3 batteries were taken from each of the experimental group and the control group, and tested at 0.5C constant current and constant voltage. After full charge, 1C constant current discharge, and long cycle, the final capacity retention rate of the two groups of batteries is as follows Figure 2 Take 3 more batteries from each of the experimental group and the control group, test 1C constant current constant voltage after full charge, 1C constant current discharge, and perform long cycle. Finally, the structure of the capacity retention rate of the two groups of batteries is as follows Figure 1 Both tests were conducted at 25°C. Figure 1 and Figure 2 Feedback results show that the battery produced by the liquid injection process of the present invention has a higher capacity retention rate and better cycle performance.

[0033] The applicant also selected 30-50pcs of 21700 batteries as the experimental group, and 30-50pcs of 21700 batteries as the control group. Similarly, the two groups of batteries use the same winding core, and the processes such as spot welding, grooving, sealing, heat shrinking and formation are the same. The difference is that the experimental group uses the injection process of the present invention when injecting liquid, while the control group uses the existing conventional injection process when injecting liquid. After completing all processing operations, 3 batteries were taken from each of the experimental group and the control group, and tested at 0.5C constant current and constant voltage. After full charge, 1C constant current discharge, and long cycle, the final capacity retention rate of the two groups of batteries is as follows Figure 4Take 3 more batteries from each of the experimental group and the control group, test 1C constant current constant voltage after full charge, 1C constant current discharge, and perform intestinal circulation. Finally, the structure of the capacity retention rate of the two groups of batteries is as follows Figure 3 Both tests were conducted at 25°C. Figure 3 and Figure 4 The feedback result shows that the battery produced by the liquid injection process of the present invention has a higher capacity retention rate and better cycle performance.

[0034] In the description of this specification, the description with reference to the terms "one embodiment", "example", "specific example", etc. means that the specific features, structures, materials or characteristics described in conjunction with the embodiment or example are included in at least one embodiment or example of the present invention. In this specification, the schematic representation of the above terms does not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials or characteristics described can be combined in any one or more embodiments or examples in a suitable manner.

[0035] The above description is only a preferred specific implementation manner of the present invention, but the protection scope of the present invention is not limited thereto. Any technician familiar with the technical field can make equivalent replacements or changes according to the technical scheme and inventive concept of the present invention within the technical scope disclosed by the present invention, which should be covered by the protection scope of the present invention.

Claims

1. A liquid injection process for improving cycle performance, characterized in that: The following steps are involved: Step 1: Place the battery in the liquid injection chamber and place it at normal pressure for at least 100 seconds after filling the battery. Step 2: Vacuum the liquid injection cavity to a vacuum degree of -0.085Mpa--0.09Mpa, and maintain it for at least 50s; Step 3: Exhaust the air in the electrolyte and control the vacuum degree in the injection cavity to -0.06Mpa--0.07Mpa; Step 4: Vacuum standing, the battery is placed in the liquid injection chamber with a vacuum degree of -0.06Mpa--0.07Mpa for at least 120s; Step 5: Vacuum the liquid injection cavity again to make the vacuum degree in the liquid injection cavity -0.085MPa--0.09Mp, and maintain it for at least 50s; Step 6: Exhaust the air in the electrolyte again and control the vacuum degree in the injection cavity to -0.06Mpa--0.07Mpa; Step 7: Vacuum standing, the battery is placed in the liquid injection cavity with a vacuum degree of -0.06Mpa--0.07Mpa for at least 180s; Step 8: Vacuum the liquid injection cavity again to make the vacuum degree in the liquid injection cavity -0.085MPa--0.09Mp, and maintain it for at least 50s; Step 9: Exhaust the air in the electrolyte again and control the vacuum degree in the injection cavity to -0.06Mpa--0.07Mpa; Step 10: Vacuum standing, the battery is placed in the liquid injection cavity with a vacuum degree of -0.06Mpa--0.07Mpa for at least 240s; Step 11: Pressurize the liquid injection cavity by filling nitrogen to make the pressure in the liquid injection cavity 0.4Mpa-0.5Mpa, and maintain it for at least 100s; Step 12: After the filling is completed, remove the battery from the filling cavity.

2. A liquid injection process for improving cycle performance according to claim 1, characterized in that: The dew point temperature in step 1 to step 12 is 18-28°C.

3. A liquid injection process for improving cycle performance according to claim 2, characterized in that: In step 1, step 5 and step 8, the time for evacuating the liquid injection cavity is no more than 8 seconds.

4. A liquid injection process for improving cycle performance according to claim 2, characterized in that: In step 3, step 6 and step 9, the exhaust time is 1 second.

5. A liquid injection process for improving cycle performance according to claim 2, characterized in that: In step 11, the nitrogen flushing time does not exceed 13 seconds.

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