Rapid formation process of high energy density soft-pack lithium ion battery

Abstract

The present application relates to the technical field of lithium battery, and particularly relates to a high-energy-density soft-pack lithium ion battery rapid formation process. The present application is formed through three stages of "first constant current charging, second constant current charging and third constant current discharging". The first constant current charging stage can effectively control the growth rate of SEI film in a manner of small current, medium current and large current step charging combination, and improve the stability of SEI film. The second constant current charging stage adopts medium current constant current charging to improve the liquid retention of the battery and reduce the thickness expansion in the cycle process. The third constant current discharging to the specified state of charge can enhance the interface stability of the battery and reduce the capacity loss of the battery in the hot pressing process. The formation process can improve the comprehensive performance of the high-energy-density soft-pack lithium ion battery, and can also shorten the formation time and improve the production efficiency.

Description

Technical Field

[0001] This invention relates to the field of lithium battery technology, specifically to a rapid formation process for a high-energy-density soft-pack lithium-ion battery. Background Technology

[0002] As digital terminal products develop towards larger screens and more diverse functions, the requirements for the energy density of lithium-ion batteries are constantly increasing. To improve the volumetric energy density of lithium-ion batteries, high-energy, high-pressure active materials are typically used, while also improving the effective space utilization rate.

[0003] When using high-energy, high-compaction active materials, several new problems often arise. These mainly include: 1. Reduced electrode porosity leads to slower electrolyte wetting and decreased battery electrolyte retention; 2. The solid electrolyte interphase (SEI) film formed on the surface of the high-compaction negative electrode is incomplete and unstable; 3. Higher compaction results in greater electrode rebound and increased battery cycle thickness expansion. Furthermore, high-energy-density pouch lithium-ion batteries maximize space utilization in their structural design, making them prone to deformation during cycling within the limited casing space.

[0004] Formation, a crucial step in the current production of pouch lithium-ion batteries, directly impacts the density and stability of the SEI film, self-discharge, consistency, thickness expansion, cycle life, and rate capability. Chinese patent application CN110854458A discloses a formation method for high-voltage pouch lithium-ion batteries, primarily employing shallow charging and deep discharging with low currents. While this method improves cycle performance, the resulting SEI film is thicker due to the low current, affecting the rate capability of high-energy-density systems, hindering thickness expansion control during cycling, and resulting in a longer formation time. Therefore, it is necessary to provide a more efficient formation method suitable for high-energy-density pouch lithium-ion batteries to further improve the overall battery performance. Summary of the Invention

[0005] The purpose of this invention is to address the technical deficiencies of existing technologies by providing a rapid formation process for high-energy-density soft-pack lithium-ion batteries. This process can effectively control the growth rate of the SEI film, increase the battery's liquid retention capacity, and reduce thickness expansion during cycling, thereby further improving the overall performance of the battery.

[0006] Therefore, this invention provides a rapid formation process for high-energy-density pouch lithium-ion batteries. The formation process includes three stages: a first constant-current charging stage, a second constant-current charging stage, and a third constant-current discharging stage. Specifically, it includes the following steps:

[0007] The first step is to place the fully wetted battery into the clamping formation equipment, clamp the battery and let it stand until the battery temperature and pressure reach the preset temperature and pressure of the formation equipment, and then carry out the formation.

[0008] The second step involves using a constant current charging method with a current ranging from 0.05C to 2C to charge the battery in stages until it reaches 60%-75% of its charge level, after which it is placed in a dormant state.

[0009] The third step is to charge the battery with a constant current of 0.5C-1C until it reaches the full charge cutoff voltage, and then let it rest in a dormant state.

[0010] The fourth step involves a third constant current discharge, where the battery is discharged at a current of 0.3C-1C to a state of charge of 55%-65%. After the process is completed, the battery is cold-pressed.

[0011] In the first step, the fixture formation temperature is 40-85℃, and the surface pressure of a single battery is controlled at 0.3-1.4Mpa; the settling time is 1-10min; the settling time in the second and third steps is also 1-10min.

[0012] In the second step, the three constant current charging methods are low-current charging, medium-current charging, and high-current charging. The low-current charging method uses a charging current of 0.05C-0.3C, charging to a state of charge (SOC) of ≤3%; the medium-current charging method uses a charging current of 0.5C-1C, charging to a SOC of 5%-10%; and the high-current charging method uses a charging current of 1C-2C, charging to a SOC of 60%-75%.

[0013] Preferably, in the second step, the three constant current charging modes are low-current charging mode, medium-current charging mode, and high-current charging mode. The low-current charging mode has a charging current of 0.05C-0.3C and a state of charge of ≤3%; the medium-current charging mode has a charging current of 0.5C-1C and charges to a state of charge of 5%-10%; the high-current charging mode has a charging current of 1C-2C and charges to a state of charge of 60%-75%.

[0014] Preferably, the charging current during the second constant current charging process in the third step is 0.7C-1.0C.

[0015] Preferably, the third constant current discharge current in the fourth step is 0.7C-1.0C.

[0016] In the fourth step, the cold pressing temperature is 25℃, the cold pressing pressure is the same as the formation pressure, the surface pressure of a single battery is controlled at 0.3-1.4 MPa, and the time is 5-10 minutes. The total formation time is 1-2.5 hours.

[0017] As can be seen from the technical solution provided by the present invention above, compared with the prior art, the present invention provides a rapid formation process for high-energy-density soft-pack lithium-ion batteries, employing a three-stage formation method of "first constant current charging, second constant current charging, and third constant current discharging". The first constant current charging stage, using a combination of small current, medium current, and large current step-by-step charging, can effectively control the growth rate of the SEI film and improve its stability. The second constant current charging stage, using medium current, can improve the uniformity of electrolyte wetting in the high-energy-density system, increasing the battery's electrolyte retention capacity; it also avoids the lithium plating problem caused by insufficient negative electrode kinetics due to high current and the low production efficiency caused by small current. Simultaneously, full charging with medium current allows the battery to achieve a pre-expansion effect, releasing stress before hot pressing and preventing battery deformation due to large negative electrode expansion during cycling, thus reducing thickness expansion during battery cycling. The third constant current discharging stage, discharging to a specified state of charge, enhances battery interface stability and reduces capacity loss during hot pressing. Therefore, this formation process can improve the overall performance of energy density soft-pack lithium-ion batteries, while also shortening the formation time and improving production efficiency. Attached Figure Description

[0018] Figure 1 A flowchart of a rapid formation process for a high-energy-density soft-pack lithium-ion battery provided by the present invention;

[0019] Figure 2 This is a comparison chart of the cycle performance of high energy density soft-pack lithium-ion batteries obtained by the formation processes of Example 1 and the comparative example of the present invention. Detailed Implementation

[0020] The embodiments of the present invention will be further described below with reference to specific examples.

[0021] Unless otherwise specified, the technical means used in this invention are conventional in the field.

[0022] The following are specific embodiments: Both the embodiments and comparative examples are high-energy-density soft-pack lithium-ion batteries. The positive electrode active material is high-voltage lithium cobalt oxide, and the negative electrode active material is high-pressure graphite. The battery 0.2C discharge capacity test conditions are: one charge-discharge cycle at 25±3℃ with a 0.2C current between 3-4.48V; the cycle test conditions are: charging at 25±3℃ with a 0.8C current, discharging at a 0.5C current, and performing charge-discharge cycles between 3-4.48V. The high-temperature storage test conditions are: first, the battery is tested for its 0.2C discharge capacity before storage and then charged to a full voltage of 4.48V with a cutoff current of 0.05C. Then, the fully charged battery is placed in a 60℃ constant temperature chamber for 28 days, and the battery thickness, 0.2C discharge capacity, and voltage drop are recorded before and after storage.

[0023] Example 1

[0024] The rapid formation process of the high-energy-density pouch lithium-ion battery in this embodiment is as follows:

[0025] 1) Place the fully wetted battery into the clamping formation equipment. The clamping temperature and pressure are 60℃ and 0.8Mpa / pcs, respectively. Clamp the battery and let it stand for 2 minutes to carry out the formation.

[0026] 2) Charge to 1% state of charge with a constant current of 0.2C, then charge to 5% state of charge with a constant current of 0.5C, then charge to 65% state of charge with a constant current of 1.2C, and then let stand for 1 minute.

[0027] 3) Charge the battery at a constant current of 0.7C to its full charge voltage of 4.48V, then let it rest for 5 minutes.

[0028] 4) Discharge the battery to 60% state of charge using a constant current of 0.7C. Then, perform cold pressing on the battery at a temperature of 25°C and a pressure of 0.8 MPa / pcs for 5 minutes to complete the formation process.

[0029] After formation, the battery undergoes hot pressing, capacity testing, and aging processes to finally obtain battery A1. Basic performance, high-temperature storage, and cycle performance tests were performed on the battery of this embodiment. The results of the basic performance tests are shown in Table 1, the results of the high-temperature storage tests are shown in Table 2, and the results of the cycle performance tests are shown in Table 3. Figure 2 .

[0030] Example 2

[0031] The rapid formation process of the high-energy-density pouch lithium-ion battery in this embodiment is as follows:

[0032] 1) Place the fully wetted battery into the clamping formation equipment. The clamping temperature and pressure are 60℃ and 0.8Mpa / pcs, respectively. Clamp the battery and let it stand for 2 minutes to carry out the formation.

[0033] 2) Charge to 1% state of charge with a constant current of 0.1C, then charge to 5% state of charge with a constant current of 0.5C, then charge to 65% state of charge with a constant current of 1.2C, and then let stand for 1 minute.

[0034] 3) Charge the battery at a constant current of 0.7C to its full charge voltage of 4.48V, then let it rest for 5 minutes.

[0035] 4) Discharge the battery to 60% state of charge using a constant current of 0.7C. Then, perform cold pressing on the battery at a temperature of 25°C and a pressure of 0.8 MPa / pcs for 5 minutes to complete the formation process.

[0036] After the formation process is completed, the battery undergoes hot pressing, capacity testing, and aging to finally obtain battery A2. Basic performance tests were performed on the battery of this embodiment, and the test results are shown in Table 1.

[0037] Example 3

[0038] The rapid formation process of the high-energy-density pouch lithium-ion battery in this embodiment is as follows:

[0039] 1) Place the fully wetted battery into the clamping formation equipment. The clamping temperature and pressure are 60℃ and 0.8Mpa / pcs, respectively. Clamp the battery and let it stand for 2 minutes to carry out the formation.

[0040] 2) Charge to 1% state of charge with a constant current of 0.2C, then charge to 5% state of charge with a constant current of 0.7C, then charge to 65% state of charge with a constant current of 1.2C, and then let stand for 1 minute.

[0041] 3) Charge the battery at a constant current of 0.7C to its full charge voltage of 4.48V, then let it rest for 5 minutes.

[0042] 4) Discharge the battery to 60% state of charge using a constant current of 0.7C. Then, perform cold pressing on the battery at a temperature of 25°C and a pressure of 0.8 MPa / pcs for 5 minutes to complete the formation process.

[0043] After the formation process is completed, the battery undergoes hot pressing, capacity testing, and aging to finally obtain battery A3. Basic performance tests were performed on the battery of this embodiment, and the test results are shown in Table 1.

[0044] Example 4

[0045] The rapid formation process of the high-energy-density pouch lithium-ion battery in this embodiment is as follows:

[0046] 1) Place the fully wetted battery into the clamping formation equipment. The clamping temperature and pressure are 60℃ and 0.8Mpa / pcs, respectively. Clamp the battery and let it stand for 2 minutes to carry out the formation.

[0047] 2) Charge to 1% state of charge with a constant current of 0.2C, then charge to 5% state of charge with a constant current of 0.5C, then charge to 65% state of charge with a constant current of 1.5C, and then let stand for 1 minute.

[0048] 3) Charge the battery at a constant current of 0.7C to its full charge voltage of 4.48V, then let it rest for 5 minutes.

[0049] 4) Discharge the battery to 60% state of charge using a constant current of 0.7C. Then, perform cold pressing on the battery at a temperature of 25°C and a pressure of 0.8 MPa / pcs for 5 minutes to complete the formation process.

[0050] After the formation process is completed, the battery undergoes hot pressing, capacity testing, and aging to finally obtain battery A4. Basic performance tests were performed on the battery of this embodiment, and the test results are shown in Table 1.

[0051] Example 5

[0052] The rapid formation process of the high-energy-density pouch lithium-ion battery in this embodiment is as follows:

[0053] 1) Place the fully wetted battery into the clamping formation equipment. The clamping temperature and pressure are 60℃ and 0.8Mpa / pcs, respectively. Clamp the battery and let it stand for 2 minutes to carry out the formation.

[0054] 2) Charge to 1% state of charge with a constant current of 0.2C, then charge to 5% state of charge with a constant current of 0.5C, and then charge to 65% state of charge with a constant current of 1.2C, and then let stand for 1 minute.

[0055] 3) Charge the battery at a constant current of 1.0C to its full charge voltage of 4.48V, then let it rest for 5 minutes.

[0056] 4) Discharge the battery to 60% state of charge using a constant current of 0.7C. Then, perform cold pressing on the battery at a temperature of 25°C and a pressure of 0.8 MPa / pcs for 5 minutes to complete the formation process.

[0057] After the formation process is completed, the battery undergoes hot pressing, capacity testing, and aging to finally obtain battery A5. Basic performance tests were performed on the battery of this embodiment, and the test results are shown in Table 1.

[0058] Example 6

[0059] The rapid formation process of the high-energy-density pouch lithium-ion battery in this embodiment is as follows:

[0060] 1) Place the fully wetted battery into the clamping formation equipment. The clamping temperature and pressure are 60℃ and 0.8Mpa / pcs, respectively. Clamp the battery and let it stand for 2 minutes to carry out the formation.

[0061] 2) Charge to 1% state of charge with a constant current of 0.2C, then charge to 5% state of charge with a constant current of 0.5C, then charge to 65% state of charge with a constant current of 1.2C, and then let stand for 1 minute.

[0062] 4) Charge the battery at a constant current of 0.7C to its full charge voltage of 4.48V, then let it rest for 5 minutes.

[0063] 5) Discharge the battery to 60% state of charge using a constant current of 1.0C. Then, perform cold pressing on the battery at a temperature of 25°C and a pressure of 0.8 MPa / pcs for 5 minutes to complete the formation process.

[0064] After the formation process is completed, the battery undergoes hot pressing, capacity testing, and aging to finally obtain battery A6. Basic performance tests were performed on the battery of this embodiment, and the test results are shown in Table 1.

[0065] Comparative Example

[0066] The comparative example differs from the embodiment in that it employs a conventional formation process, specifically including the following steps:

[0067] 1) Place the fully wetted battery into the clamping formation equipment. The clamping temperature and pressure are 60℃ and 0.8Mpa / pcs, respectively. Clamp the battery and let it stand for 2 minutes to carry out the formation.

[0068] 2) Charge to 1% state of charge using a constant current of 0.1C;

[0069] 3) Charge to 5% state of charge using a constant current of 0.2C;

[0070] 3) Charge the battery to 65% state of charge with a constant current of 0.5C, then perform cold pressing at a temperature of 25℃ and a pressure of 0.8 MPa / pcs for 5 minutes to complete the formation.

[0071] After formation, the battery underwent hot pressing, capacity testing, and aging processes to obtain battery B1. Basic performance, high-temperature storage, and cycle performance tests were conducted on this comparative battery. The results of the basic performance tests are shown in Table 1, the results of the high-temperature storage tests are shown in Table 2, and the results of the cycle performance tests are shown in Table 3. Figure 2 .

[0072] Basic performance testing

[0073] The net electrolyte volume, K value, and standard deviation of the K value were obtained by testing the lithium-ion batteries of Examples 1-6 and the comparative examples, as shown in Table 1 below. The net electrolyte volume was calculated as: mass of battery electrolyte / battery capacity; the K value was calculated as: open-circuit voltage difference before and after aging / time interval between voltage tests before and after aging.

[0074] Table 1

[0075]

[0076] As shown in Table 1, the lithium-ion batteries produced using the formation process provided by this invention have improved net electrolyte volume, self-discharge performance, and battery consistency compared to those produced using conventional formation processes.

[0077] Storage performance test

[0078] The lithium-ion batteries of Example 1 and the comparative example were subjected to a 60°C 28-day full-charge storage performance test. The test results are shown in Table 2 below.

[0079] Table 2

[0080]

[0081] As shown in Table 2, after a 28-day full-charge storage test at 60 degrees Celsius, the thickness expansion rate of the lithium-ion battery using the formation process of Example 1 of the present invention is lower than that of the comparative example, the residual capacity retention rate is higher than that of the comparative example, and the voltage drop is significantly lower than that of the comparative example. This indicates that the formation process of the present invention can significantly improve the storage performance of high-energy-density soft-pack lithium-ion batteries.

[0082] Depend on Figure 2 It can be seen that the lithium-ion battery using the formation process of Example 1 of the present invention has an average capacity retention rate of 95.7% and an average thickness expansion rate of 6.1% after 400 cycles at room temperature; while the comparative example has an average capacity retention rate of 93.2% and an average thickness expansion rate of 7.64%. In terms of both cycle trend and thickness expansion, Example 1 is better than the comparative example and has better cycle stability.

[0083] The above-described embodiments are merely several implementations of the present invention. It should be noted that those skilled in the art can make various improvements and modifications without departing from the principles of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A rapid formation process for a high-energy-density soft-pack lithium-ion battery, characterized in that, Includes the following steps: The first step is to place the fully wetted battery into the clamping formation equipment, clamp the battery and let it stand until the battery temperature and pressure reach the preset temperature and pressure of the formation equipment, and then carry out the formation. The second step involves the first constant current charging, which uses three constant current charging modes—small current, medium current, and large current—within the 0.05-2C range to charge the battery in stages until it reaches 60%-75% of its charge level, after which it is placed into a dormant state. The three constant current charging modes are low current charging mode, medium current charging mode, and high current charging mode; the low current charging mode has a charging current of 0.05C-0.3C and a state of charge of ≤3%; the medium current charging mode has a charging current of 0.5C-1C and charges to a state of charge of 5%-10%; the high current charging mode has a charging current of 1.2C-2C and charges to a state of charge of 60%-75%. The third step is to charge the battery with a constant current of 0.5C-1C until it reaches the full charge cutoff voltage, and then let it rest in a dormant state. The fourth step involves a third constant current discharge, where the battery is discharged at a current of 0.3C-1C to a state of charge of 55%-65%. After the process is completed, the battery is cold-pressed.

2. The formation process as described in claim 1, characterized in that: In the first step, the fixture formation temperature is 40-85℃, and the surface pressure of a single battery is controlled at 0.3-1.4 MPa; the settling time is 1-10 minutes; the settling time in the second and third steps is 1-10 minutes.

3. The formation process as described in claim 1, characterized in that: The low-current charging mode uses a charging current of 0.1C-0.2C to charge to 1% state of charge; the medium-current charging mode uses a charging current of 0.5C-0.7C to charge to 5% state of charge; and the high-current charging mode uses a charging current of 1.2C-1.5C to charge to 65% state of charge.

4. The formation process as described in claim 1, characterized in that: In the third step, the charging current during the second constant current charging process is 0.7C-1.0C.

5. The formation process as described in claim 1, characterized in that: In the fourth step, the third constant current discharge current is 0.7C-1.0C.

6. The formation process as described in claim 1, characterized in that: In the fourth step, the cold pressing temperature is 25℃, the cold pressing pressure is the same as the formation pressure, the surface pressure of a single battery is controlled at 0.3-1.4Mpa, and the time is 5-10min.

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