A method for accelerating the infiltration of electrolyte in a lithium-ion battery

Abstract

The present invention relates to the field of lithium batteries. In order to address the problem of long electrolyte infiltration time in batteries, a method for accelerating electrolyte infiltration in lithium-ion batteries is provided, comprising the following steps: (1) restraining the battery after injection in a restraint disk, and then fixing the restraint disk on a vibration platform; (2) placing the vibration platform in a static environment at 42-48°C, setting the parameters of the vibration platform, vibrating with a sine wave, using a logarithmic frequency sweep method, and vibrating in a direction perpendicular to the positive and negative poles of the battery; (3) after the battery has been static for a total of 6-10 hours, turning off the vibration platform to release the restraining force of the battery. The present invention restrains the battery after injection by applying pressure to the battery and vibrates the battery at a certain frequency. Compared with achieving electrolyte infiltration through capillary phenomena alone, the electrolyte infiltration time can be significantly shortened.

Description

Technical Field

[0001] The present invention relates to the field of lithium batteries, and in particular to a method for accelerating electrolyte infiltration of lithium ion batteries. Background Art

[0002] With the development of lithium battery new energy technology, the technical differences among major lithium battery manufacturers in electrochemistry, materials, etc. are getting smaller and smaller. What makes major battery manufacturers compete is engineering and technical capabilities, and they aim to reduce manufacturing costs by shortening process time and saving process steps.

[0003] After the battery is filled, it needs to be left standing at high temperature for a long time to allow the electrolyte to fully soak into the positive and negative electrodes and the separator. The industry typically achieves this by leaving the battery at 45±5°C for 24 to 60 hours. With the demand for higher energy density and higher compaction pressure, the electrolyte soaking time is getting longer and longer, and production costs are also increasing. If the soaking requirements cannot be met, the electrolyte composition is modified to reduce the viscosity and improve the battery's wettability. For example, patent CN113488696B discloses a highly wettable electrolyte for cylindrical lithium-ion batteries. The electrolyte contains a non-electrochemically active wettability additive, perhalogenated amide polyoxyethylene ester. This additive significantly reduces the surface energy of the electrolyte, increases the rate of electrolyte absorption by the electrode sheets and separator, and allows the electrolyte to quickly form a uniform distribution inside and outside the cylindrical battery cell. However, the use of this additive requires strict control of dosage to avoid affecting the battery cell's dynamic performance, and also increases costs. Therefore, an ideal solution is needed. Summary of the Invention

[0004] In order to overcome the problem of long battery electrolyte infiltration time, the present invention provides a method for accelerating the electrolyte infiltration of lithium-ion batteries. By applying pressure to the battery after injection to restrain the battery and vibrating the battery at a certain frequency, the electrolyte infiltration time can be significantly shortened compared to achieving electrolyte infiltration through capillary phenomenon alone.

[0005] In order to achieve the above object, the present invention adopts the following technical solutions:

[0006] A method for accelerating the infiltration of lithium-ion battery electrolyte comprises the following steps:

[0007] (1) The battery after injection is restrained in the restraint plate, and then the restraint plate is fixed on the vibration platform;

[0008] (2) Place the vibration platform in a static environment at 42-48°C, set the parameters of the vibration platform, vibrate with a sine wave, use a logarithmic frequency sweep method, and the vibration direction is perpendicular to the positive and negative poles of the battery;

[0009] (3) After the battery has been left to rest for a total of 6-10 hours, turn off the vibration platform to release the restraining force of the battery.

[0010] Ordinary batteries require 24-60 hours of infiltration after injection. Poor electrolyte infiltration will lead to problems such as reduced initial efficiency and poor gram capacity of the battery. The present invention restrains and vibrates the battery in sequence to shorten the electrolyte infiltration time to 6-10 hours. Restraining the battery can prevent it from being dislocated up and down, detaching from the restraint plate, etc. during vibration. When the battery is left stationary after injection, the vibration platform vibrates at a certain frequency, freeing the electrolyte inside the entire battery shell and accelerating the infiltration of the electrode pores or diaphragm pores.

[0011] Preferably, the injection amount of the injection in step (1) is: the injection coefficient of the battery of the nickel-manganese-cobalt ternary system is 2.0-3.0 g / Ah, and the injection coefficient of the battery of the lithium iron phosphate system is 3.5-4.5 g / Ah.

[0012] As a further preference, in step (1), the battery cell with qualified moisture content is injected with liquid, and the moisture standard is: the positive and negative electrode mixed sample is continuously baked at a temperature of 200° C. for 10 minutes, and the sample moisture content is required to be ≤300ppm.

[0013] Preferably, in step (1), several batteries after injection are sequentially inserted into the restraint plate, with adjacent batteries separated by acrylic plates with a width of 5-11 mm, and a silicone layer with a width of 1-2 mm provided between the acrylic plates and the batteries. The silicone acts as a buffer.

[0014] Preferably, the restraint disc is fixed to the vibration platform by fixing the restraint disc at four corners of the vibration platform with bolts to prevent the restraint disc from shifting during vibration.

[0015] Preferably, the restraint pressure in step (1) is 0.05 to 0.15 MPa.

[0016] Preferably, the static environment in step (2) is provided by a tunnel furnace or a constant temperature box. The temperature of the static environment is further preferably 45°C.

[0017] Preferably, the logarithmic frequency sweep in step (2) is performed from 20 Hz to 100 Hz and back to 20 Hz within 25-35 minutes. Further preferably, the logarithmic frequency sweep in step (2) is performed at an acceleration of 5-9 m / s2 from 20 Hz to 100 Hz, and the amplitude is controlled at 0.2-0.4 mm. After each vibration cycle, the sample is left for 25-35 minutes. The electrolyte is absorbed from the end face of the cell through the diaphragm into the cell. The electrolyte infiltration step inside the cell can be divided into three steps: ① The electrolyte is transported in the gap between the electrode and the diaphragm under the action of capillary force; ② The electrolyte preferentially seeps into the pores of the diaphragm (because the surface tension and porosity of the diaphragm are much greater than those of the porous coating of the electrode, the electrolyte infiltration rate in the diaphragm is much greater than that in the porous coating of the electrode); ③ The electrolyte diffuses through the diaphragm to the surfaces of the positive and negative electrodes on both sides and seeps into the pores of the porous electrode. Therefore, the present invention uses a logarithmic frequency sweep method to perform sinusoidal vibration on the battery, which is better than a linear frequency sweep method. The frequency change of the linear frequency sweep is linear, while the frequency of the logarithmic frequency sweep changes logarithmically, with the characteristics of slow low frequency and fast high frequency. In the electrolyte infiltration process, the first step is relatively the easiest, and the infiltration can be completed quickly only by the capillary force of the battery itself. The third step is the slowest and is the "short board" step that restricts the electrolyte penetration efficiency. By increasing the vibration frequency, the electrolyte free at the bottom floats to the top, shortening the electrolyte climbing distance. In order to avoid damage to the internal structure of the battery cell in a long-term high-frequency state, such as internal short circuit caused by burrs falling off the pole piece or bumping the surface of the battery cell, a linear frequency sweep mode is not adopted, but a logarithmic frequency sweep with high and low frequency switching is adopted. The present invention obtains a logarithmic frequency sweep mode that matches the electrolyte penetration step by regulating important parameters such as the starting vibration frequency, vibration frequency change acceleration, and amplitude of the logarithmic frequency sweep, which can significantly improve the electrolyte penetration efficiency.

[0018] Preferably, after releasing the restraining force of the battery in step (2), the battery is transferred to the formation process for formation and capacity separation until the battery cell is offline.

[0019] Therefore, the beneficial effects of the present invention are as follows: (1) Battery restraint and static: The battery is placed in a restraint tray and fixed on the tray with a restraint force of 0.05 to 0.15 MPa to prevent the battery from being misplaced up and down during vibration; (2) Vibration during static: When the battery is static after injection, the vibration platform vibrates at a certain frequency, so that the electrolyte is freed inside the entire battery shell, accelerating the infiltration of the electrode pores or the diaphragm pores. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 It is a schematic diagram of the implementation of the present invention;

[0021] In the picture, 1. Vibration platform, 2. Telescopic rod, 3. Acrylic plate, 4. Silicone layer, 5. Battery, 6. Bolt. DETAILED DESCRIPTION

[0022] The technical solution of the present invention is further described below through specific embodiments.

[0023] In the present invention, unless otherwise specified, the raw materials and equipment used can be purchased from the market or are commonly used in the field. The methods in the embodiments, unless otherwise specified, are all conventional methods in the field. The vibration platform is a vibration platform in the prior art, and the specific structure is not described here.

[0024] Example 1

[0025] A method for accelerating the infiltration of lithium-ion battery electrolyte comprises the following steps:

[0026] The battery's positive and negative electrodes are made of lithium iron phosphate and graphite, respectively. The compacted density of the lithium iron phosphate is 2.6g / cc, and the compacted density of the negative electrode is 1.7g / cc. A 30Ah prismatic aluminum-cased battery is fabricated. After the cells are baked, they are tested for moisture. The moisture standard is: a mixed sample of positive and negative electrodes is baked at 200°C for 10 minutes, with a moisture content of ≤300ppm.

[0027] (1) After the moisture test meets the standard, inject 4.0g / Ah electrolyte, such as Figure 1 As shown, batteries 5 are sequentially inserted into the tray. Adjacent batteries 5 are separated by 8mm-wide acrylic panels 3. A 1mm-wide silicone layer 4 acts as a buffer between the acrylic panels 3 and the batteries 5. The tray is then secured with 0.1MPa pressure using telescopic rods 2 and transferred to a vibration platform 1. Bolts 6 are used at the four corners of the platform to prevent it from shifting during vibration.

[0028] (2) The tunnel furnace is heated to 45°C, and the vibration platform is pushed into the tunnel furnace and allowed to stand. The parameters of the vibration platform are set to vibrate with a sine wave, and the frequency is swept from 20 Hz to 100 Hz and back to 20 Hz in 30 minutes in a logarithmic sweep mode. The vibration direction of the vibration platform is perpendicular to the positive and negative pole directions of the battery; the logarithmic sweep mode is to scan at an acceleration of 5 m / s2 from 20 Hz to 100 Hz, and control the amplitude to 0.3 mm, that is, the displacement is 0.6 mm. After each vibration cycle, it is left for 30 minutes, and the total standing time is 6 hours. After the standing is completed, the vibration platform is turned off to release the restraint force of the battery.

[0029] (3) The battery is transferred to the formation process for formation and capacity separation until the battery cell is off the production line.

[0030] Example 2

[0031] Compared with Example 1, the total standing time in step (2) was changed to 8 h, and the other conditions were the same as those in Example 1.

[0032] Example 3

[0033] Compared with Example 1, the total standing time in step (2) was changed to 10 h, and the other conditions were the same as those in Example 1.

[0034] Example 4

[0035] Compared with Example 1, the locking pressure of the tray in step (1) is changed to 0.05 MPa, and the other conditions are the same as those in Example 1.

[0036] Example 5

[0037] Compared with Example 1, the locking pressure of the tray in step (1) is changed to 0.15 MPa, and the other conditions are the same as those in Example 1.

[0038] Example 6

[0039] Compared with Example 1, the acceleration of the vibration platform in step (2) is changed to 9 m / s2, and the other conditions are the same as those in Example 1.

[0040] Comparative Example 1

[0041] Compared with Example 1, the battery cell does not vibrate in a high temperature environment

[0042] The positive and negative electrodes are made of lithium iron phosphate and graphite materials respectively. The compaction density of lithium iron phosphate is 2.6g / cc, and the compaction density of the negative electrode is 1.7g / cc. A 30Ah square aluminum shell battery is prepared. After the battery cell is baked and the moisture test is passed, 4.0g / Ah electrolyte is injected and the total standing time in a high temperature environment of 45°C is 6 hours. After the standing time is completed, the battery cell is divided into different capacities until it is offline.

[0043] Comparative Example 2

[0044] Compared with Example 1, the battery cell does not vibrate in a high temperature environment, and the static time is extended to 48 hours.

[0045] The positive and negative electrodes are made of lithium iron phosphate and graphite materials respectively. The compaction density of lithium iron phosphate is 2.6g / cc, and the compaction density of the negative electrode is 1.7g / cc. A 30Ah square aluminum shell battery is prepared. After the battery cell is baked and the moisture test is passed, 4.0g / Ah electrolyte is injected and the total standing time in a high temperature environment of 45°C is 48 hours. After the standing time is completed, the battery cell is divided into different capacities until it is offline.

[0046] Comparative Example 3

[0047] Compared with Example 1, the standing time of the battery cell in step (2) is changed to 5 hours, and the rest is the same as Example 1.

[0048] Comparative Example 4

[0049] Compared with Example 1, the standing time of the battery cell in step (2) is changed to 11 hours, and the rest is the same as Example 1.

[0050] Comparative Example 5

[0051] Compared with Example 1, the tray in step (1) has no locking pressure, and the rest is the same as Example 1.

[0052] Comparative Example 6

[0053] Compared with Example 1, the locking pressure of the tray in step (1) is changed to 0.2 MPa, and the rest is the same as Example 1.

[0054] Comparative Example 7

[0055] Compared with Example 1, the acceleration of the vibration platform is changed to 4m / s2, and the rest is the same as Example 1.

[0056] Comparative Example 8

[0057] Compared with Example 1, the acceleration of the vibration platform is changed to 10m / s2, and the rest is the same as Example 1.

[0058] Comparative Example 9

[0059] Compared with Example 1, in step (2), the vibration platform vibrates with a sine wave and adopts a linear frequency sweep mode, and the rest is the same as Example 1. The parameter of the linear frequency sweep is: 60 Hz.

[0060] Comparative Example 10

[0061] Compared with Example 1, in step (2), the vibration platform vibrates with a sine wave and adopts a linear frequency sweep mode, and the rest is the same as Example 1. The parameter of the linear frequency sweep is: 100 Hz.

[0062] Performance Testing

[0063] The battery performance of each embodiment and comparative example was tested using the following test methods:

[0064] Evaluation Method 1: After standing at high temperature, charge the cell at a constant current and constant voltage of 0.2C to 3.65V. Then discharge it at a constant current of 0.2C to 2.5V. Calculate the 0.2C charge capacity, 0.2C discharge capacity, and initial efficiency (initial efficiency = 0.2C discharge capacity / 0.2C charge capacity).

[0065] Evaluation method 2: Perform DCR test on the battery cells after capacity separation, including the following steps:

[0066] ① The battery is charged and discharged for 2cls at a current of 0.5C, and the second capacity is recorded as C0;

[0067] ② Adjust the battery capacity to 50% C0;

[0068] ③Discharge with a current of 3C0 for 10s;

[0069] ④ Calculate the internal resistance of the battery at 50% C0, that is, internal resistance = (U before discharge - U after discharge) / 3C0.

[0070] The test results are shown in the following table.

[0071] Group First efficiency / % Discharge capacity / Ah Internal resistance (mΩ) Remark Example 1 88.6 30.4 1.34 Example 2 88.5 30.4 1.35 Example 3 88.6 30.3 1.35 Example 4 88.8 30.4 1.33 Example 5 88.5 30.3 1.34 Example 6 88.6 30.2 1.35 Comparative Example 1 82.3 27.6 3.65 Comparative Example 2 88.3 30.2 1.45 Comparative Example 3 86.6 29.5 1.89 Comparative Example 4 88.5 30.4 1.34 Comparative Example 5 - - - The tray falls apart during vibration and the battery cells are damaged. Comparative Example 6 86.4 29.3 1.78 Comparative Example 7 87.6 29.6 1.45 Comparative Example 8 - - - The tray falls apart during vibration and the battery cells are damaged. Comparative Example 9 87.2 29.1 1.57 Comparative Example 10 - - - The battery cell is damaged during vibration

[0072] It can be seen from the battery performance of each embodiment that the expected effect can be achieved within the parameter range of the present invention.

[0073] Compared with Example 1:

[0074] ① Comparative Example 1 was not vibrated in a high-temperature environment, and the initial efficiency and capacity of the battery cell were poor under the same standing time, because the battery was not fully wetted after liquid injection, resulting in a high internal resistance of the battery; Comparative Example 2 was not vibrated in a high-temperature environment but the standing time was extended to 48h, and the initial efficiency and capacity were comparable to those of Example 1, but the internal resistance was relatively large, indicating that although only extending the aging time can ensure the wetting effect of the battery cell, long-term wetting leads to low production capacity and high energy consumption.

[0075] ② Comparative Example 3 employed the vibration soaking method of the present invention, but the high-temperature rest time was insufficient, resulting in a relatively high internal resistance of the battery. Comparative Example 4 employed the vibration soaking method of the present invention, but the high-temperature rest time was too long, resulting in no change in the initial efficiency and internal resistance of the battery cell. This indicates that after the battery is fully soaked, extending the rest time is unnecessary and, in fact, increases energy consumption. This suggests that rest time must be within a reasonable range to achieve optimal results.

[0076] ③ In comparative example 5, the battery cells are placed in the tray without any restraint, resulting in a large displacement of the battery after vibration, breaking away from the fixture and damaging the corners of the battery, making it impossible to achieve mass production; in comparative example 6, the excessive restraint pressure squeezes out all the pores of the electrode and diaphragm, which in turn leads to poor electrolyte infiltration, resulting in a large internal resistance of the battery.

[0077] ④ In Comparative Example 7, the vibration platform's acceleration was too low, preventing the electrolyte from fully penetrating the electrode, resulting in slightly higher internal resistance and reduced battery capacity and initial efficiency. In Comparative Example 8, the vibration platform's acceleration was too high, causing the battery to significantly shift after vibration, disengage from the fixture, and damage the battery corners. Comparative Examples 9 and 10 used linear frequency sweeps. Although vibration also accelerated electrolyte penetration, the battery performance was inferior to that of Example 1 at the same vibration time, indicating that linear frequency sweeps are less efficient than logarithmic frequency sweeps.

[0078] In summary, the technical solution of the present invention can effectively shorten the battery infiltration time and improve the battery production efficiency within the preferred parameter range.

[0079] The above description is merely a preferred embodiment of the present invention and does not constitute any form of limitation to the present invention. Although the present invention has been disclosed as a preferred embodiment, it is not intended to limit the present invention. Any technician familiar with the present profession can make some changes or modifications to equivalent embodiments of equivalent changes using the technical contents disclosed above without departing from the scope of the technical solution of the present invention. However, any simple modifications, equivalent changes and modifications made to the above embodiments based on the technical essence of the present invention without departing from the content of the technical solution of the present invention are still within the scope of the technical solution of the present invention.

Claims

1. A method for accelerating the infiltration of lithium ion battery electrolyte, characterized in that: The following steps are involved: (1) Constrain the battery after injection into the restraint plate, and then fix the restraint plate on the vibration platform; (2) Place the vibration platform in a static environment at 42-48°C, set the parameters of the vibration platform, vibrate with a sine wave, use a logarithmic sweep method, and the vibration direction is perpendicular to the positive and negative poles of the battery. The logarithmic sweep method is to sweep from 20 Hz to 100 Hz and return to 20 Hz within 25-35 minutes, and sweep from 20 Hz to 100 Hz with an acceleration of 5-9 m / s², and control the amplitude to 0.2-0.4 mm. After each vibration cycle, put it aside for 25-35 minutes; (3) After the battery has been at rest for a total of 6-10 hours, turn off the vibration platform to release the restraining force of the battery.

2. The method according to claim 1, wherein The injection amount of the injection in step (1) is: the injection coefficient of the battery of the nickel-manganese-cobalt ternary system is 2.0~3.0 g / Ah, and the injection coefficient of the battery of the lithium iron phosphate system is 3.5~4.5 g / Ah.

3. The method according to claim 1 or 2, characterized in that Step (1) injecting liquid into the battery cell with qualified moisture content, the moisture standard is: the mixed positive and negative electrode samples are continuously baked at a temperature of 200°C for 10 minutes, and the sample moisture content is required to be ≤300ppm.

4. The method according to claim 1, wherein Step (1) inserts several liquid-filled batteries into the restraint plate in sequence, with adjacent batteries separated by acrylic plates with a width of 5-11 mm, and a silicone layer with a width of 1-2 mm is provided between the acrylic plates and the batteries.

5. The method according to claim 1 or 4, characterized in that The restraint pressure in step (1) is 0.05~0.15MPa.

6. The method according to claim 1, characterized in that The static environment in step (2) is provided by a tunnel furnace or a constant temperature box.

7. The method according to claim 1, characterized in that After releasing the restraint of the battery in step (2), the battery is transferred to the formation process for formation and capacity separation until the battery cell is offline.

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