Primary pressurization liquid injection optimization method for improving wettability of lithium battery electrolyte

Abstract

The invention discloses a one-time pressurized liquid injection optimization method for improving wettability of an electrolyte of a lithium battery. The method comprises the following steps: step S1, executing contact angle testing operation: testing the sizes of contact angles of the electrolyte of the lithium battery on a positive plate, a negative plate and a diaphragm in advance; step S2, executing liquid injection treatment operation: inserting a liquid injection cap into the open end of the lithium battery, then injecting electrolyte into the lithium battery at one time, then transferring the lithium battery with the liquid injection cap into a vacuum box, executing preset liquid discharging operation on the vacuum box, pulling out the liquid injection cap after the liquid discharging operation is completed, and then sealing the lithium battery; the method can solve the problems of poor electrolyte infiltration and long electrolyte injection time caused by a conventional single electrolyte injection process, ensures that the electrolyte achieves a better infiltration effect more efficiently, reduces the occurrence frequency of the problems that the internal resistance value of the battery is large, the electrical performance cannot be effectively exerted and the like due to the fact that the battery pole piece is not completely infiltrated by the electrolyte, and improves the service life of the battery. And the capacity and the electrical performance of the finished battery are obviously improved.

Description

Technical Field

[0001] The invention relates to the technical field of batteries, and in particular to a one-time pressurized liquid injection optimization method for improving the wettability of lithium battery electrolyte. Background Art

[0002] At present, lithium-ion batteries have been widely used in digital products, electric vehicles and energy storage fields due to their advantages such as high energy density, good cycle performance, and green and pollution-free.

[0003] As a medium for ion transmission in lithium batteries, electrolyte is crucial to the performance of batteries. However, in the actual production process of batteries, the electrolyte often cannot fully infiltrate the electrode, leaving a dry area in the middle of the electrode (such as Figure 1a to Figure 1c The middle area A, B, and C in the horizontal distribution of the electrolyte are not smooth in this area, which will affect the performance of the battery. It may also cause local overheating due to large resistance, causing safety problems and reducing battery life. Therefore, improving the wettability of the electrolyte is of great significance to improving battery performance.

[0004] The wettability of the electrolyte is affected by many factors, such as active materials, electrode and diaphragm pores, electrolyte characteristics, injection process, etc. Among them, improving the injection process is one of the most convenient and effective methods, which can improve the wetting of the electrolyte on the electrode without changing the electrode design and without adding additional costs. The simplest injection process is: injecting under vacuum conditions, so that the gas in the battery cell is discharged under negative pressure conditions, so that the electrolyte can directly contact the electrode. However, the ideal wetting effect cannot be achieved by only vacuum injection, and a long wetting time is required, resulting in low overall battery production efficiency.

[0005] The existing injection optimization process adopts the method of vacuuming combined with pressurizing cycle, which is currently an effective injection method to improve the wettability of cylindrical battery electrolyte. Vacuuming can accelerate the electrolyte to enter the shell, and the pressurizing process can increase the driving force of liquid flow, thereby better pressing the electrolyte into the battery cell and improving the performance and safety of the battery. However, due to the insufficient capacity of some vacuum box equipment, the inner cavity of the vacuum box cannot be equipped with two sets of working equipment that meet the vacuuming and pressurizing requirements at the same time. Therefore, during the vacuuming and pressurizing cycle, the two sets of working equipment need to be frequently replaced, which will increase the time of the injection process.

[0006] It should be noted that the main purpose of the vacuum and pressurization cycle is to form multiple pressure differences to accelerate infiltration. After vacuuming, nitrogen is filled until the vacuum pressure value is 0, and then pressurized to restore to normal pressure, and the generated gas is extracted. This process itself can also achieve multiple pressure differences, that is, it is feasible to shorten the injection time and improve the electrolyte infiltration by one pressurization.

[0007] However, experiments have confirmed that for a single pressurized liquid injection process, the state of the electrode group before pressurization often affects the actual wetting effect: when there is more floating liquid above the electrode group, pressurization will accelerate the penetration of the electrolyte into the pores of the electrode and diaphragm cross-section. After pressurization, the electrolyte will flow normally, but due to less capillary diffusion in the width direction of the electrode, the actual wetting area of ​​the electrolyte is small. In addition, extending the vacuum time has limited effect on improving the penetration of the electrolyte and is not conducive to efficient production.

[0008] Based on the above reasons, the current conventional single injection process has poor electrolyte infiltration after only vacuum injection, and the required vacuum injection time is long, which leads to a long overall injection time. The vacuum injection combined with the pressurized cycle has high requirements for the pressure equipment.

[0009] Therefore, there is an urgent need to develop a technology that can solve the problems of poor electrolyte infiltration and long injection time caused by the existing conventional single injection process. Summary of the invention

[0010] The purpose of the present invention is to provide a one-time pressurized liquid injection optimization method for improving the wettability of lithium battery electrolyte in view of the technical defects existing in the prior art.

[0011] To this end, the present invention provides a one-time pressurized liquid injection optimization method for improving the wettability of lithium battery electrolyte, which comprises the following steps:

[0012] Step S1, performing a contact angle test operation: pre-testing the contact angle of the electrolyte of the lithium battery on the positive electrode sheet, the negative electrode sheet and the separator;

[0013] Step S2, performing a liquid injection process: inserting a liquid injection cap into the open end of the lithium battery, and then injecting electrolyte into the lithium battery at one time, and then transferring the lithium battery with the liquid injection cap into a vacuum box, performing a preset liquid injection process on the vacuum box, and after the liquid injection process is completed, removing the liquid injection cap, and then sealing the lithium battery;

[0014] The preset liquid discharging operation includes the following steps:

[0015] The first step is to perform a first vacuuming operation on the vacuum box for a preset first time period to accelerate the electrolyte to enter the lithium battery housing;

[0016] The second step is to release the pressure of the vacuum box;

[0017] The third step is to pressurize the inside of the vacuum box to accelerate the electrolyte to flow into the lithium battery housing, thereby promoting the infiltration process of the electrolyte in the lithium battery placed in the vacuum box on the battery pole piece;

[0018] The fourth step is to continue to perform a second vacuuming operation on the vacuum box for a preset second time period, and to discharge bubbles generated by the electrolyte inside the lithium battery shell during the pressurization process through negative pressure to ensure the infiltration effect of the electrolyte.

[0019] It can be seen from the technical solution provided by the present invention above that, compared with the prior art, the present invention provides a one-time pressurized injection optimization method for improving the wettability of lithium battery electrolyte. The method is scientifically designed and is a simple and convenient method for confirming the injection process. It can solve the problems of poor electrolyte wetting and long injection time caused by the conventional single injection process. By testing the electrolyte contact angle in advance, the wetting effect of the electrolyte on the battery pole piece can be judged in advance, and then the injection process and parameters can be confirmed to ensure that the actual injection process of the electrolyte can achieve better wetting effect more efficiently, reduce the frequency of problems such as large internal resistance of the battery and inability to effectively exert electrical performance due to failure of the electrolyte to completely wet the battery pole piece, significantly improve the capacity and electrical performance of the finished battery, and extend the service life of the battery, which has great practical significance.

[0020] By applying the present invention, after confirming the vacuum evacuation time required for the electrolyte, the pressurization treatment is performed, which is of great significance for improving the electrolyte infiltration, enhancing the battery performance and improving the production efficiency. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1a This is a picture showing that in the actual production process of the battery, the electrolyte cannot fully infiltrate the first type of battery electrode sheet, thereby leaving an uninfiltrated dry area A in the middle of the first type of battery electrode sheet;

[0022] Figure 1b The figure is a picture of an unwetted dry area B in the middle of the second battery electrode sheet due to the inability of the electrolyte to fully wet the second battery electrode sheet during the actual battery production process;

[0023] Figure 1c This is a picture showing that in the actual production process of the battery, the electrolyte cannot fully infiltrate the third type of battery electrode, thereby leaving an uninfiltrated dry area C in the middle of the third type of battery electrode;

[0024] Figure 2 A basic flow chart of a one-time pressurized liquid injection optimization method for improving the wettability of lithium battery electrolyte provided by the present invention;

[0025] Figure 3a Schematic diagram of the contact angle between the electrolyte and the positive electrode sheet obtained in advance in Example 1;

[0026] Figure 3b Schematic diagram of the contact angle between the electrolyte and the negative electrode sheet obtained in advance in Example 1;

[0027] Figure 3c Schematic diagram of the contact angle between the electrolyte and the bright surface of the diaphragm obtained in the pre-test in Example 1;

[0028] Figure 3d Schematic diagram of the contact angle between the electrolyte and the ceramic surface of the diaphragm obtained in advance in Example 1;

[0029] Figure 4a Schematic diagram of the contact angle between the electrolyte and the positive electrode sheet obtained in advance in Example 2;

[0030] Figure 4b Schematic diagram of the contact angle between the electrolyte and the negative electrode sheet obtained in advance in Example 2;

[0031] Figure 4c Schematic diagram of the contact angle between the electrolyte and the bright surface of the diaphragm obtained in advance in Example 2;

[0032] Figure 4d Schematic diagram of the contact angle between the electrolyte and the ceramic surface of the diaphragm obtained in advance in Example 2;

[0033] Figure 5 It is a schematic diagram of the normal temperature cycle capacity retention rate of a battery cell that has completed the liquid injection process in Example 2 of the present invention;

[0034] Figure 6 It is a schematic diagram of the normal temperature cycle capacity retention rate of the battery cell that has completed the liquid injection treatment operation in Comparative Example 5;

[0035] Figure 7 Schematic diagram of the room temperature cycle capacity retention rate of the battery cell that has completed the liquid injection treatment operation in Comparative Example 6. DETAILED DESCRIPTION

[0036] 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.

[0037] In the description of the present invention, it should be understood that the terms "center", "longitudinal", "lateral", "length", "width", "thickness", "up", "down", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inside", "outside", "clockwise", "counterclockwise" and the like indicate orientations or positional relationships based on the orientations or positional relationships shown in the accompanying drawings, and are only for the convenience of describing the present invention and simplifying the description, and do not indicate or imply that the referred device or element must have a specific orientation, be constructed and operated in a specific orientation, and therefore should not be understood as a limitation on the present invention.

[0038] In the description of this patent, it should be noted that, unless otherwise clearly specified and limited, the terms "installed", "connected", "connected", and "set" should be understood in a broad sense, for example, it can be fixedly connected or set, or it can be detachably connected or set, or connected or set in one piece. For ordinary technicians in this field, the specific meanings of the above terms in this patent can be understood according to specific circumstances.

[0039] In addition, the terms "first" and "second" are used for descriptive purposes only and should not be understood as indicating or implying relative importance or implicitly indicating the number of the indicated technical features. Therefore, the features defined as "first" and "second" may explicitly or implicitly include one or more of the features. In the description of the present invention, the meaning of "plurality" is two or more, unless otherwise clearly and specifically defined.

[0040] In order to enable those skilled in the art to better understand the scheme of the present invention, the present invention is further described in detail below in conjunction with the accompanying drawings and implementation modes.

[0041] See also Figure 2 The present invention provides a one-time pressurized liquid injection optimization method for improving the wettability of lithium battery electrolyte, comprising the following steps:

[0042] Step S1, performing a contact angle test operation: pre-testing the contact angle of the electrolyte of the lithium battery on the positive electrode sheet, the negative electrode sheet and the separator;

[0043] It should be noted that the wetting angle refers to the angle between the solid-liquid interface through the liquid to the gas-liquid interface at the junction of solid, liquid and gas phases. It is called the contact angle, also known as the wetting angle. As a liquid, the contact angle of the electrolyte on the surface of the solid material is an important parameter to measure the wetting performance of the liquid on the material surface.

[0044] In the present invention, in the specific implementation, the contact angle test process, taking the fully automatic surface tension tester as an example, quickly captures the contour image formed by the droplet on the solid surface through the optical system and CCD camera, displays it on the computer screen and stores it, and then calculates the contact angle according to the shape of the droplet. The specific operation can be: during the test, sample the electrolyte used in the experiment and the corresponding positive and negative electrodes and diaphragms, take an appropriate amount of electrolyte in the sample tube, clamp it just above the sample table, and fix the electrode or diaphragm flatly on the sample table, open the existing contact angle test software, enter the contact angle test page, adjust the focal length, determine the plane, ensure that the sample tube and the sample table can be clearly displayed in the center of the computer screen, click the automatic analysis mode, gently spin out a certain volume of electrolyte (such as 2μL), move the sample table, and quickly move it down after it touches the liquid surface, click the test button on the contact angle test software interface, and the contact angle test software can automatically analyze and calculate the contact angle.

[0045] The above contact angle test principle and method are well-known technical principles in the prior art, and will not be described in detail here. The test method is not limited to the above method, and of course, other well-known contact angle test principles and methods in the prior art can also be used.

[0046] In the present invention, in a specific implementation, based on the above existing contact angle testing principles and methods, the contact angles of the electrolyte with the positive electrode sheet, the negative electrode sheet and the diaphragm are tested respectively, the total time can be controlled within 3 minutes, the amount of electrolyte can be less than 0.1 ml, and the amount of the positive electrode sheet, the negative electrode sheet and the diaphragm can be less than 30 mm*30 mm.

[0047] It should be noted that the differences in the composition of different types of electrolytes and the compatibility of electrolytes and pole pieces will lead to different contact angles during injection, which plays a decisive role in the injection and infiltration process. For example, when the proportion of alkyl carbonates in the electrolyte solvent is large, the viscosity of the electrolyte is large, and the intermolecular force is large, which will affect the infiltration effect and battery performance. In terms of adaptability, the contact angles of the electrolyte on different positive and negative pole pieces vary greatly. Usually, the contact angle on the iron-lithium material is smaller, which is more conducive to the absorption and retention of the electrolyte, and the ternary type will be relatively poor. When the diaphragm is a base film, the contact angle can reach more than 30°, while for ceramic diaphragms or rubber-coated diaphragms, the contact angle will be greatly reduced. In short, the smaller the surface tension of the electrolyte, the smaller the contact angle, and the lower the viscosity, the more conducive it is to the spreading of the electrolyte on the surface of the pole piece, that is, the faster the infiltration rate of the electrolyte.

[0048] In view of this, the present invention proposes a one-time pressurized injection method for improving electrolyte infiltration. By first testing the contact angle of the electrolyte on the positive and negative electrode sheets and the diaphragm, and then confirming the vacuum time, the trial and error process of verifying the injection conditions during injection can be reduced, and the actual electrolyte infiltration area is small and the effect is poor due to premature pressurization. This method of confirming the injection conditions in advance based on the differentiated characteristics of each system can predict the electrolyte infiltration effect in advance without increasing additional costs, greatly saving injection time, improving injection efficiency, and improving electrolyte infiltration, thereby improving battery performance.

[0049] Step S2, performing a liquid injection process: inserting a liquid injection cap into the open end of the lithium battery, and then injecting electrolyte into the lithium battery at one time, and then transferring the lithium battery with the liquid injection cap into a vacuum box, performing a preset liquid injection process on the vacuum box, and after the liquid injection process is completed, removing the liquid injection cap, and then sealing the lithium battery (for example, welding a battery cover plate for sealing);

[0050] The preset liquid discharging operation includes the following steps:

[0051] The first step is to perform a first vacuuming operation on the vacuum box for a preset first time period to accelerate the electrolyte to enter the lithium battery housing;

[0052] The second step is to release the pressure of the vacuum box (relieve the pressure to normal pressure, which is 1 standard atmospheric pressure);

[0053] The third step is to pressurize the inside of the vacuum box to accelerate the electrolyte to flow into the lithium battery housing, thereby promoting the infiltration process of the electrolyte in the lithium battery placed in the vacuum box on the battery electrode (i.e., promoting the electrolyte to flow);

[0054] The fourth step is to continue to perform a second vacuuming operation on the vacuum box for a preset second time period (for example, 1 minute), and to discharge the bubbles generated by the electrolyte inside the lithium battery shell during the pressurization process through negative pressure to ensure the infiltration effect of the electrolyte.

[0055] In the present invention, in specific implementation, the vacuuming operation can be realized by the function of the vacuum box itself. The pressurizing operation can be realized by existing pressurizing equipment, such as a pressure tank or a booster pump, by connecting the pressure output end of the pressure tank or the booster pump to the vacuum box.

[0056] It should be noted that, in the present invention, the electrolyte is injected into the battery only once, and the injection is completed before the battery is placed in the vacuum box, which is easy to operate. The subsequent vacuuming and pressurizing operations are all to promote liquid infiltration and infiltration.

[0057] It should be noted that, for the present invention, the overall process is: injecting electrolyte → vacuum liquid → pressurizing liquid → vacuum exhaust → sealing. After the electrolyte is injected in the liquid injection machine, vacuum and pressurization are completed in the vacuum box.

[0058] In the present invention, in a specific implementation, electrolyte can be injected into the lithium battery through a battery injection machine (i.e., an existing injection device), specifically: the injection needle of the battery injection machine extends into the main cap on the top of the battery to inject electrolyte into the interior of the lithium battery shell.

[0059] It should be noted that, for the present invention, the liquid lowering process is: vacuuming for the first time until there is less floating liquid in the electrolyte, and then pressurizing until the liquid is completely lowered. The key point is to confirm the time required for the first vacuuming, scientifically plan this time, and perform pressurization operation to ensure the effectiveness of liquid lowering, so as to improve efficiency and the effect of liquid lowering.

[0060] In the present invention, in step S2, in specific implementation, when performing the first and second vacuum pumping operations on the vacuum box, the vacuum degree of the first and second vacuum pumping operations is preferably -80kPa to -95kPa (that is, the vacuum degree in the vacuum box is pumped to this vacuum degree); specifically, the vacuum pumping operation can be performed by a vacuum pump provided on the vacuum box.

[0061] In the present invention, in step S2, in specific implementation, when the vacuum box is pressurized, the pressurization pressure is 0.3 MPa to 0.5 MPa. Specifically, the pressurization operation can be performed by a pressure tank or a booster pump.

[0062] In the present invention, in the specific implementation of step S2, it should be noted that the duration of the first vacuum operation of the injection is determined according to the contact angle measured in step S1. The wetting of the diaphragm has little effect on the wetting of the electrode sheet, so the wetting of the positive electrode sheet and the negative electrode sheet is mainly referred to. Among them, when the average value of the contact angle of the electrolyte to the positive electrode sheet and the negative electrode sheet is less than 15°, the preset first duration of the first vacuum operation is determined to be 3-5 minutes;

[0063] When the average contact angle of the electrolyte to the positive electrode sheet and the negative electrode sheet is greater than 25°, the preset first duration of the first vacuum operation reaches 20-30 minutes;

[0064] When the average contact angle of the electrolyte to the positive electrode sheet and the negative electrode sheet is within the range of 15-25°, the preset first duration of the first vacuum operation is 10-15 minutes;

[0065] Among them, optimization can be made according to the contact angle of the diaphragm. For example, when the average contact angle of the electrolyte to the positive and negative electrodes is 15-25°, the diaphragms used in each batch of batteries may be different. When ordinary diaphragms are used, the contact angle is large and the time is 10-15min, so 15min can be optimized. When ceramic diaphragms are used, the contact angle is small and the optimization time can be shorter, such as 10min.

[0066] It should be noted that when the contact angle of the electrolyte to the diaphragm is small, the electrolyte spreads quickly on the diaphragm and may "absorb liquid and retain liquid" in the part prone to dry areas, which will be beneficial to the infiltration of the electrolyte on the positive and negative electrode sheets, and the vacuum time can be appropriately shortened.

[0067] In a specific implementation, the average contact angle of the electrolyte to the positive electrode sheet and the negative electrode sheet is the average of the contact angle of the electrolyte to the positive electrode sheet and the contact angle of the negative electrode sheet.

[0068] In a specific implementation, the second duration is preset, preferably 1 minute.

[0069] In the present invention, it is necessary to ensure that there is about 1-4mm of floating liquid above the electrode group before pressurization. At this time, pressurization can achieve the best wetting effect. It should be noted that the correspondence between the average contact angle of the electrolyte to the positive electrode sheet and the negative electrode sheet and the preset first time of vacuuming is obtained from the experience of multiple batches of liquid injection experiments, which can achieve the expected liquid lowering effect.

[0070] It should be noted that the electrolyte infiltration process can be regarded as the capillary movement of the electrolyte, and the electrode pores can be regarded as the capillaries for the electrolyte penetration. Therefore, the preset first duration of vacuuming can be verified based on the Washburn penetration model according to the electrolyte characteristic parameters and the measured contact angle.

[0071] Among them, for several common positive and negative electrode systems of lithium batteries, the form radius value related to the capillary characteristics in the permeation model has been verified to be approximately 1. For this reason, the present invention forms the following calculation formula for the preset first duration of the first vacuum operation:

[0072]

[0073] In the above formula, H is the liquid absorption height, which is equal to the average value of the width of the positive electrode sheet and the width of the negative electrode sheet of the lithium battery, in mm;

[0074] t is the preset first duration of the first vacuuming operation, in seconds;

[0075] σ is the surface tension of the electrolyte;

[0076] θ is the average value of the contact angles of the electrolyte to the positive electrode and the negative electrode; η is the viscosity of the electrolyte.

[0077] In the present invention, in a specific implementation, the pressure and time of the vacuum box are set in advance. In this process, after the lithium battery is filled with liquid, the battery with the filling cap is transferred to the vacuum box, and the first vacuuming operation is performed in the vacuum box. After the first vacuuming operation is completed, the vacuum box is depressurized and then pressurized to accelerate the electrolyte to flow into the lithium battery shell. After that, a second vacuuming operation (for example, a vacuuming operation of 1 minute) is performed to achieve negative pressure to discharge the gas that may be generated inside the battery shell during the pressurization process, so as to facilitate subsequent infiltration.

[0078] In summary, for the present invention, by determining the corresponding vacuuming time through such contact angle test, it can be ensured that there is not too much floating liquid above the battery electrode group in the battery housing before pressurization, which can shorten the injection time to a greater extent. At the same time, it is beneficial to the lateral infiltration of the electrolyte, increasing the infiltration area, thereby improving the battery performance.

[0079] In order to more clearly understand the technical solution of the present invention, the technical solution of the present invention is described below through specific embodiments.

[0080] Example 1.

[0081] The first step is to test the contact angle between the electrolyte and the positive electrode sheet, negative electrode sheet and separator used in the battery cell;

[0082] In this embodiment, the contact angles of the electrolyte with the positive electrode sheet, the negative electrode sheet, the bright surface of one side of the diaphragm (i.e., the base film surface) and the ceramic surface of the other side of the diaphragm are 10.86°, 26.6°, 43.36° and 10.22°, respectively. Figures 3a to 3d As shown;

[0083] Among them, the diaphragm is a ceramic diaphragm, and the contact angle of the ceramic surface is smaller than that of the base film surface. The average contact angle of the positive and negative electrodes is large, and the wettability is poor, ranging from 15-25°. Combined with the contact angle of the diaphragm, in this embodiment, it is required that when performing the preset liquid lowering operation in the second step, the vacuum pressure of the first vacuum operation and the second vacuum operation is preset to -85kPa, the preset first duration of the first vacuum operation is 15min, the pressurization pressure in the vacuum box is 0.4MPa, the pressurization time is 3min, and then the second vacuum exhaust is supplemented for 1min.

[0084] In the second step, the cylindrical battery electrode group (i.e., battery cell) is injected with liquid after shelling, grooving, dust removal and other processes. The accuracy of the injection amount is controlled within ±0.05g. Then, the battery cell with the injection cap is placed in a vacuum box, and then the preset liquid injection operation is performed;

[0085] The preset liquid-dropping operation in the second step is specifically as follows: a lithium battery with a liquid-filled (electrolyte has just been injected) liquid-filled cap is placed in the vacuum box, and then the vacuum box is subjected to a first vacuuming operation for a preset first time duration (specifically 15 minutes). After the first vacuuming operation is completed, the vacuum box is continuously depressurized (depressurized to normal pressure), and then pressurized (pressurized pressure 0.4 MPa, pressurized time 3 minutes) to pressurize the electrolyte into the lithium battery housing, and then the vacuum box is subjected to a second vacuuming operation (e.g., a vacuuming operation for 1 minute, a vacuuming pressure of -85 kPa, i.e., a negative pressure exhaust operation) to discharge the gas that may be generated inside the lithium battery housing during the pressurization process through negative pressure (to eliminate bubbles), and then the lithium battery is sealed to complete the liquid-filling operation.

[0086] It should be noted that after the liquid injection was completed, the appearance of the electrode group was normal, with no floating liquid on the top, and then it was assembled into a 2170 cylindrical lithium battery.

[0087] Comparative example 1.

[0088] Due to the large contact angle, the electrolyte cannot quickly infiltrate the electrode if only vacuum is drawn after liquid injection. For the battery cell that has been injected with electrolyte, it is placed in a vacuum box and the vacuum box is vacuumed for 35 minutes until the electrolyte is completely drained. For the battery cell of the comparative example 1, at least 5 battery cells are tested, and the internal resistance is averaged.

[0089] Comparative example 2.

[0090] Due to the large contact angle, the electrolyte cannot quickly infiltrate the electrode if only vacuum is drawn after injection. The battery cell that has been injected with electrolyte is placed in a vacuum box, and the vacuum box is vacuumed for 5 minutes, pressurized for 3 minutes, and the pressurized pressure is 0.4MPa. For the battery cell of the comparative example 2, at least 5 battery cells are tested, and the internal resistance is averaged.

[0091] Comparative example 3.

[0092] Due to the large contact angle, the electrolyte cannot quickly infiltrate the electrode if only vacuum is drawn after injection. For the battery cell that has been injected with electrolyte, it is placed in a vacuum box, and the vacuum box is vacuumed for 10 minutes, pressurized for 3 minutes, and the pressurized pressure is 0.4MPa. For the battery cell of the comparative example 3, at least 5 battery cells are tested, and the internal resistance is averaged.

[0093] Comparative example 4.

[0094] Due to the large contact angle, the electrolyte cannot quickly infiltrate the electrode if only vacuum is drawn after liquid injection. For the battery cell that has been injected with electrolyte, it is placed in a vacuum box, and the vacuum box is vacuumed for 15 minutes, pressurized for 3 minutes, and the pressurized pressure is 0.3MPa. For the battery cell of the comparative example 4, at least 5 battery cells are tested, and the internal resistance is taken as the average value.

[0095] For the battery cells of the above-mentioned Example 1 and Comparative Examples 1 to 4, after the liquid injection treatment operation is completed, the battery cells are disassembled respectively, the electrode dry area width after the battery cells are injected and pre-treated and left to stand is observed, and the battery internal resistance is tested to compare and confirm the electrolyte infiltration effect. The specific electrolyte infiltration effect is shown in the following Table 1.

[0096] Table 1: Experimental injection conditions and results

[0097]

[0098] As can be seen from Table 1 above, the electrode dry area width and the internal resistance of the battery cell of Example 1 of the present invention are smaller than those of Comparative Examples 1 to 4, indicating that the electrolyte infiltration effect is better in the battery cell of Example 1 of the present invention.

[0099] In the battery cell provided in Comparative Example 2, which was vacuumed for 5 minutes and pressurized for 3 minutes, there was no floating liquid after the injection, and the width of the dry area of ​​the pole piece after the injection was not much different from that of the battery cell that was only vacuumed. However, after pre-calcination and standing, it was found that the electrolyte was not completely infiltrated, and the resistance value was also larger. The reason is that: if the pressure is applied too early, the electrolyte will penetrate more of the pores in the cross section of the pole piece and the diaphragm, and the actual infiltration area in the width direction is small, which cannot better exert the performance.

[0100] The wetting effect of the battery cell provided in Comparative Example 3, which was evacuated for 10 minutes, is slightly better than that of the battery cell provided in Comparative Example 2, which was evacuated for 5 minutes.

[0101] From the results of the battery cell injection in Comparative Example 4, it can be seen that when pressurized at a pressure of 0.3 MPa, the pressure difference is insufficient and the wetting effect is poor. It is verified that when the battery is injected with liquid and pressurized, it should be pressurized when there is less floating liquid above the electrode group, which is beneficial to the wetting. This is also the technical solution specially designed and required by the present invention.

[0102] Example 2.

[0103] The first step is to test the contact angle between the electrolyte and the positive electrode sheet, negative electrode sheet and separator used in the battery cell;

[0104] In this embodiment, the contact angles of the electrolyte with the positive electrode sheet, the negative electrode sheet, the bright surface of one side of the diaphragm (i.e., the base film surface) and the ceramic surface of the other side of the diaphragm are 4.38°, 15.01°, 43.78° and 11.04°, respectively. Figures 4a to 4dAs shown; that is, the liquid is spread well on the electrode, the liquid is easy to be poured, and the first vacuuming time can be shortened. In this embodiment, it is required that when performing the second step of the liquid injection operation, the vacuuming pressure of the first vacuuming operation and the second vacuuming operation is set to -85kPa, the preset first time of the first vacuuming is 5min, the pressurization pressure in the vacuum box is 0.4MPa, the pressurization time is 3min, and then the second vacuuming exhaust is supplemented for 1min.

[0105] In the second step, the cylindrical battery electrode group (i.e., battery cell) is injected with liquid after shelling, grooving, dust removal and other processes. The accuracy of the injection amount is controlled within ±0.05g. Then, the battery cell with the injection cap is placed in a vacuum box, and then the preset liquid injection operation is performed;

[0106] The preset liquid-dropping operation in the second step is specifically as follows: a lithium battery with a liquid-filled (electrolyte has just been injected) liquid-filled cap is placed in the vacuum box, and then the vacuum box is subjected to a first vacuuming operation for a preset first time duration (specifically 5 minutes). After the first vacuuming operation is completed, the vacuum box is depressurized (depressurized to normal pressure), and then pressurized (pressurized pressure 0.4 MPa, pressurized time 3 minutes) to pressurize the electrolyte into the lithium battery housing. After that, the vacuum box is subjected to a second vacuuming operation (e.g., a vacuuming operation for 1 minute, a vacuuming pressure of -85 kPa, i.e., a negative pressure exhaust operation), so as to discharge the gas that may be generated inside the lithium battery housing during the pressurization process through negative pressure (to eliminate bubbles), and then the lithium battery is sealed to complete the liquid-filling operation.

[0107] It should be noted that after the liquid injection was completed, the appearance of the electrode group was normal, with no floating liquid on the top, and then it was assembled into a 2170 cylindrical lithium battery.

[0108] Comparative Example 5.

[0109] Comparative Example 5 is substantially the same as Example 2, and the only difference between Comparative Example 5 and Example 2 is that the preset first duration of the first vacuuming in Comparative Example 6 is extended from 5 minutes in Example 2 to 10 minutes.

[0110] Comparative Example 6.

[0111] Comparative Example 6 is basically the same as Example 2. The only difference between Comparative Example 6 and Example 2 is that: Comparative Example 6 does not perform pressurized liquid injection, and only completes the liquid injection through a 20-minute vacuum process to ensure that there is no floating liquid above the electrode group.

[0112] For the battery cells of the above-mentioned Example 2 and Comparative Examples 5 to 6, after the liquid injection treatment operation is completed, the battery cells are disassembled respectively, the electrode dry area width after the battery cells are injected and pre-treated and left to stand is observed, and the battery internal resistance is tested to compare and confirm the electrolyte infiltration effect. The specific electrolyte infiltration effect is shown in the following Table 2.

[0113] Table 2: Experimental injection conditions and results

[0114]

[0115] As can be seen from Table 2 above, the battery cell of Example 2 of the present invention has better electrolyte infiltration, smaller resistance value, and slightly higher capacity retention rate in room temperature cycles.

[0116] However, for the battery cell provided in Comparative Example 5, extending the vacuum pumping time has no obvious effect on improving electrolyte wetting;

[0117] For the battery cell provided in Comparative Example 6, since only vacuuming is performed (without electrolyte pressurization operation), it takes a longer time to drain the electrolyte.

[0118] See also Figures 5 to 7 From the schematic diagram of room temperature cycle capacity retention rate of battery cells after liquid injection treatment operation of Example 2, Comparative Example 5 and Comparative Example 6 shown in the figure, it can be seen that the number of room temperature cycle diving circles (i.e., the number of cycle diving times) of the one-time pressurization scheme adopted by the present invention is more than 50 circles different from the vacuum only scheme of Comparative Example 6, indicating that the vacuuming-pressurization liquid injection process determined by the present invention based on the contact angle test can achieve better infiltration effect in a shorter liquid injection time and will not affect the battery life.

[0119] Compared with the prior art, the one-time pressurized liquid injection optimization method for improving the wettability of lithium battery electrolyte provided by the present invention has the following beneficial effects:

[0120] The present invention provides a simple method for confirming the injection process, which predicts the electrolyte wetting effect by testing the electrolyte contact angle in advance, and then confirms the injection process, optimizes the injection conditions, and evacuates the electrode group to keep it in a state with less floating liquid after injection, and then completes efficient injection through the pressure difference generated by one pressurization. It can achieve better electrolyte wetting effect in a shorter injection time, which is conducive to more full play of the electrical performance of the lithium battery, and can reduce the problems of incomplete electrolyte wetting, too long injection time, low production efficiency, etc. caused by the undifferentiated injection process.

[0121] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principle of the present invention. These improvements and modifications should also be regarded as the scope of protection of the present invention.

Claims

1. A one-time pressurized injection optimization method for improving the wettability of lithium battery electrolyte, characterized in that: The following steps are involved: Step S1, performing a contact angle test operation: pre-testing the contact angle of the electrolyte of the lithium battery on the positive electrode sheet, the negative electrode sheet and the separator; Step S2, performing a liquid injection process: inserting a liquid injection cap into the open end of the lithium battery, and then injecting electrolyte into the lithium battery at one time, and then transferring the lithium battery with the liquid injection cap into a vacuum box, performing a preset liquid injection process on the vacuum box, and after the liquid injection process is completed, removing the liquid injection cap, and then sealing the lithium battery; The preset liquid discharging operation includes the following steps: The first step is to perform a first vacuuming operation on the vacuum box for a preset first time period to accelerate the electrolyte to enter the lithium battery housing; The second step is to release the pressure of the vacuum box; The third step is to pressurize the inside of the vacuum box to accelerate the electrolyte to flow into the lithium battery housing, thereby promoting the infiltration process of the electrolyte in the lithium battery placed in the vacuum box on the battery electrode; The fourth step is to continue to perform a second vacuuming operation on the vacuum box for a preset second time period, and to discharge bubbles generated by the electrolyte inside the lithium battery shell during the pressurization process through negative pressure to ensure the infiltration effect of the electrolyte.

2. The one-time pressurized liquid injection optimization method for improving the wettability of lithium battery electrolyte according to claim 1, characterized in that: In step S2, when the first and second vacuuming operations are performed on the vacuum box, the vacuum degrees of the first and second vacuuming operations are -80 kPa to -95 kPa.

3. The one-time pressurized liquid injection optimization method for improving the wettability of lithium battery electrolyte according to claim 1, characterized in that: In step S2, when the electrolyte is pressurized, the pressurization pressure is 0.3 MPa to 0.5 MPa.

4. The one-time pressurized liquid injection optimization method for improving the wettability of lithium battery electrolyte according to claim 1, characterized in that: In step S2, when the average value of the contact angle of the electrolyte to the positive electrode sheet and the negative electrode sheet is less than 15°, the preset first duration of the first vacuuming operation is determined to be 3-5 minutes.

5. The one-time pressurized injection optimization method for improving the wettability of lithium battery electrolyte according to claim 1, characterized in that: In step S2, when the average contact angle of the electrolyte to the positive electrode sheet and the negative electrode sheet is greater than 25°, the preset first duration of the first vacuuming operation reaches 20-30 minutes.

6. The one-time pressurized liquid injection optimization method for improving the wettability of lithium battery electrolyte according to claim 1, characterized in that: In step S2, when the average value of the contact angle of the electrolyte to the positive electrode sheet and the negative electrode sheet is within the value range of 15-25°, the preset first duration of the first vacuuming operation is 10-15 minutes.

7. The one-time pressurized injection optimization method for improving the wettability of lithium battery electrolyte according to claim 1, characterized in that: In step S2, the second time length is preset to 1 minute.

8. The one-time pressurized liquid injection optimization method for improving the wettability of lithium battery electrolyte according to claim 1, characterized in that: The calculation formula for the preset first duration of the first vacuuming operation is as follows: In the above formula, H is the liquid absorption height, which is equal to the average value of the width of the positive electrode sheet and the width of the negative electrode sheet of the lithium battery, in mm; t is the preset first duration of the first vacuuming operation, in seconds; σ is the surface tension of the electrolyte; θ is the average measured contact angle of the electrolyte to the positive electrode and the negative electrode; η is the viscosity of the electrolyte.

9. The one-time pressurized liquid injection optimization method for improving the wettability of lithium battery electrolyte according to any one of claims 1 to 7, characterized in that: The vacuum operation is realized through the function of the vacuum box itself; The pressurization operation is achieved through a pressurizing device, which is a pressure tank or a pressurizing pump; The pressure output end of the pressure tank or the booster pump is connected to the vacuum box.

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