Formation process of soft package lithium ion battery

Abstract

The application relates to a formation process of a soft package lithium ion battery, and specifically comprises the following steps: S1, heating the battery and applying pressure to the surface of the battery; S2, sequentially performing three stages of constant current charging with gradually increased current on the battery; S3, reducing the charging current and performing the fourth stage of constant current charging; after the completion of the constant current charging of each stage in the step S2, 1-2 minutes of static standing is performed. The application innovatively adopts a multi-step constant current charging mode, the current density of each step is controlled, the formation current is improved under the condition of guaranteeing the properties of the SEI film, the time is shortened, and the production efficiency is effectively improved; the process requirement is low, the flow is simple, and no additional modification investment is needed for the equipment.

Description

Technical Field

[0001] This invention relates to the field of pouch batteries, and more particularly to a formation process for pouch lithium-ion batteries. Background Technology

[0002] In recent years, soft-pack lithium-ion batteries have been increasingly widely used in various fields such as consumer electronics and automotive industries. The formation process (i.e., the first charge of the battery) plays a crucial role in the production of lithium-ion batteries.

[0003] The formation of lithium-ion batteries has three main functions: first, to activate the active materials of the lithium-ion battery during the first charge, converting them into substances with normal electrochemical functions; second, to form a dense passivation film (SEI film (Surface Electrolyte Interface)) on the electrode surface, mainly the negative electrode surface. The performance of the SEI film can affect important performance characteristics of the battery, such as cycle life, rate capability, and high and low temperature discharge.

[0004] Existing soft-pack lithium-ion battery formation processes, such as the invention patent with application number CN201610750223.9 and authorization announcement number CN106340690A entitled "A Formation Process for Soft-Pack Lithium-ion Batteries," include two steps: charging and resting. The formation process includes the following steps: 1. Heating the battery cell to 50℃~80℃; 2. Applying pressure of 5~10 kg / cm² to the surface of the battery cell. 2 3. Perform the first stage of charging on the battery cell, with a charging current of 0.1C and a charging time of 10 to 30 minutes; 4. Perform the second stage of charging on the battery cell, with a charging current of 0.4C to 0.7C and a charging time of 60 to 120 minutes.

[0005] The existing chemical formation process takes a long time, about 70-150 minutes, and the utilization rate of equipment and personnel is low, resulting in low production efficiency. Summary of the Invention

[0006] (a) Technical problems to be solved

[0007] To address the aforementioned problems in the prior art, this invention provides a formation process for soft-pack lithium-ion batteries. Without reducing battery performance, the formation process is optimized, reducing the formation time to approximately 55-90 minutes. This shortened time effectively improves production efficiency. Furthermore, the process is simple and requires no additional investment in equipment modifications.

[0008] (II) Technical Solution

[0009] To achieve the above objectives, the main technical solutions adopted by the present invention include:

[0010] A formation process for a soft-pack lithium-ion battery, characterized by the following steps:

[0011] S1: Heat the battery cell and apply pressure to its surface;

[0012] S2: The battery cell is charged with a constant current that gradually increases in three stages.

[0013] S3: Reduce the charging current and perform the fourth stage of constant current charging;

[0014] Before each stage of constant current charging in steps S2 and S3, the device should be left to stand for 1-2 minutes.

[0015] Furthermore, in step S1, the heating temperature is 60-90℃, and the pressure applied to the surface of the battery cell is 6-12 kg / cm². 2 .

[0016] Furthermore, in step S2, the first stage charging current is 0.2-0.3C, the charging time is 6-15 minutes, and the battery voltage is greater than 3.2V at the end of charging.

[0017] Furthermore, in step S2, the second stage charging current is 0.3-0.5C, the charging time is 6-10 minutes, and the battery voltage is greater than 3.5V at the end of charging.

[0018] Furthermore, in step S2, the charging current in the third stage is 0.7-1C, the charging time is 35-40 minutes, and the battery voltage is greater than 3.8V at the end of charging.

[0019] Furthermore, in step S3, the charging current is 0.3-0.5C, and the charging time is 5-20 minutes.

[0020] Furthermore, the positive electrode active material of the battery cell used in this formation process is at least one of lithium cobalt oxide, lithium manganese oxide, and lithium nickel cobalt manganese oxide.

[0021] Furthermore, the negative electrode active material of the battery cell used in this formation process is graphite.

[0022] Furthermore, the separator used in the battery cell for this formation process is a commercially available PP separator.

[0023] Furthermore, the electrolyte used in the battery cell for this formation process is EC / EMC / DEC type electrolyte. After the battery cell is injected with electrolyte and allowed to stand and age to ensure that the electrode is fully wetted by the electrolyte, the formation process is then carried out.

[0024] (III) Beneficial Effects

[0025] The beneficial effects of this invention are: This invention innovatively adopts a multi-step constant current charging method, which controls the current density of each step, increases the formation current while ensuring the properties of the SEI film, thereby shortening the time and effectively improving production efficiency; moreover, the process requirements are low, the process is simple, and no additional investment is required in equipment modification. Attached Figure Description

[0026] To more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings used in the embodiments will be briefly introduced below. It should be understood that the following drawings only show some embodiments of the present invention and should not be regarded as a limitation of the scope. For those skilled in the art, other related drawings can be obtained from these drawings without creative effort.

[0027] Figure 1 This is a process flow diagram of the present invention;

[0028] Figure 2 This is a comparison chart of the cyclic performance of the embodiments and the comparative examples; Detailed Implementation

[0029] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of the present invention, not all of them. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention. Therefore, the following detailed description of the embodiments of the present invention provided in the accompanying drawings is not intended to limit the scope of the claimed invention, but merely to represent selected embodiments of the invention. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0030] Example 1:

[0031] A formation process for a pouch lithium-ion battery includes the following steps:

[0032] (1) The battery cell is pressurized and heated; the heating temperature is 70℃ and the pressurization pressure is 6kg / cm². 2Excessive pressure causes the electrolyte on the electrode surface to be squeezed out, reducing the ion concentration and hindering SEI film formation. Insufficient pressure prevents the electrodes from making sufficient contact. Too low a formation temperature results in a high formation current, preventing the ion activity rate from matching with the electron rate, thus affecting SEI film formation. Excessive formation temperature affects electrolyte performance, causing the formed SEI film to decompose. Appropriate temperature and pressure effectively improve the formation rate.

[0033] (2) After the battery in the state of step (1) is left to stand for 2 minutes, perform the first constant current charge with a charging current of 0.2C for 15 minutes; when the charging ends, the battery voltage is greater than 3.2V and the charging limit voltage is set to 3.25V; the use of a smaller current in this stage can make the organic components of the SEI film form quickly and form a dense SEI film near the anode surface to ensure battery performance.

[0034] (3) After the battery in step (1) and after step (2) is finished, let it stand for 1 minute, and then perform a second constant current charge. Charge for 10 minutes with a charging current of 0.3C. When the charging ends, the battery voltage is greater than 3.5V and the charging limit voltage is set to 3.65V. During this stage, the current can be increased appropriately, mainly to form the inorganic components of the SEI film and form a porous SEI film on the side close to the electrolyte.

[0035] (4) After the battery in step (1) and after the end of steps (2) and (3) is left to stand for 1 minute, it is charged for the third time with a constant current of 0.7C for 40 minutes. When the charging ends, the battery voltage is greater than 3.8V and the charging limit voltage is set to 3.95V. Since the SEI layer on the surface of the anode of the battery has been basically formed after the voltage is greater than 3.5V, a larger current can be used to accelerate the reaction.

[0036] (5) After the battery in step (1) and after the completion of steps (2), (3), and (4) is left to stand for 1 minute, it is then charged for the fourth time with a constant current of 0.3C for 20 minutes and a charging limit voltage of 4.15V. Because the high current charging in the previous step may cause electrochemical polarization due to the electrochemical reaction rate on the positive and negative electrodes being lower than the electron movement rate, especially for high-capacity batteries with large current, resulting in insufficient reaction, this step reduces the current to allow the reaction to occur fully and avoid battery swelling during subsequent charging and discharging. A standing time of 1-2 minutes is added between the above four charging steps. Because of the electrochemical polarization caused by high current charging, standing time is added between charging steps to eliminate some polarization. The charging limit voltage set in this step should be slightly higher than the reaction completion voltage to ensure sufficient reaction in this stage.

[0037] Example 2:

[0038] A formation process for a pouch lithium-ion battery includes the following steps:

[0039] (1) The battery cell is pressurized and heated; the heating temperature is 80℃ and the pressurization pressure is 8kg / cm². 2 ;

[0040] (2) After the battery in the state of step (1) is left to stand for 2 minutes, perform the first constant current charge with a charging current of 0.3C for 6 minutes;

[0041] (3) After the battery in step (1) and after step (2) is finished, let it stand for 1 minute, and then perform a second constant current charge with a charging current of 0.4C for 6 minutes.

[0042] (4) After the battery in step (1) and after step (2) and (3) are finished, let it stand for 1 minute, and then perform a third constant current charge with a charging current of 0.8C for 40 minutes.

[0043] (5) After the battery in step (1) and after the end of steps (2)(3)(4) is left to stand for 1 minute, it is charged for the fourth time with a constant current of 0.4C for 10 minutes.

[0044] Example 3:

[0045] A formation process for a pouch lithium-ion battery includes the following steps:

[0046] (1) The battery cell is pressurized and heated; the heating temperature is 90℃ and the pressurization pressure is 10kg / cm². 2 ;

[0047] (2) After the battery in the state of step (1) is left to stand for 2 minutes, perform the first constant current charge with a charging current of 0.3C for 6 minutes;

[0048] (3) After the battery in step (1) and after step (2) is finished, let it stand for 1 minute, and then perform a second constant current charge with a charging current of 0.5C for 6 minutes.

[0049] (4) After the battery in step (1) and after step (2) and (3) are finished, let it stand for 2 minutes, and then perform a third constant current charge at a charging current of 1C for 35 minutes.

[0050] (5) After the battery in step (1) and after the end of steps (2)(3)(4) is left to stand for 2 minutes, it is then charged for the fourth time with a constant current of 0.5C for 5 minutes.

[0051] The comparative example is a commonly used formation process in the prior art, which includes the following steps:

[0052] (1) Apply pressure and heat to the battery cell; the heating temperature is 90℃; (2) Apply pressure of 8kg / cm to the surface of the battery cell. 2 (3) Charge the battery cell in the first stage with a charging current of 0.1C and a charging time of 20min; (4) Charge the battery cell in the second stage with a charging current of 0.5C and a charging time of 90min.

[0053] Examples 1, 2, and 3 listed correspond to: low temperature and low current, medium temperature and medium current, and high temperature and high current, respectively. The process steps and times are compared with those of the comparative examples as follows: Table 1 shows the formation time and conditions of Example 1, Table 2 shows the formation time and conditions of Example 2, Table 3 shows the formation time and conditions of Example 3, and Table 4 shows the formation time and conditions of the comparative examples.

[0054] Table 1

[0055]

[0056]

[0057] Table 2

[0058]

[0059] Table 3

[0060]

[0061]

[0062] Table 4

[0063]

[0064] The formation time is longer when the current is small, and the formation time is reduced accordingly when the current is large. Compared with the comparative example, it can be concluded that the overall formation time is 90 minutes under slightly lower temperature and low current conditions, which is 20% shorter than the comparative example time. Under high temperature and high current conditions, the overall formation time is 57 minutes, which is 49% shorter than the comparative example time, and the efficiency is significantly improved.

[0065] After formation was completed, the cells from Examples 1, 2, and 3, as well as the comparative example, were disassembled and the interface black spots were statistically analyzed. After resealing, the cells from Examples 1, 2, and 3, as well as the comparative example, were subjected to 500 cycles. The statistical data is shown in Table 5, and the cycle details are as follows: Figure 2 .

[0066] Table 5

[0067] Group Interface breakdown statistics 500-week cycle retention rate / % Example 1 No black spots, no lithium plating 91.82 Example 2 No black spots, no lithium plating 94.50 Example 3 No black spots, no lithium plating 93.49 Comparative Example No black spots, no lithium plating 88.74

[0068] The above description is merely an embodiment of the present invention and does not limit the patent scope of the present invention. Any equivalent modifications made based on the content of the present invention specification and drawings, or direct or indirect applications in related technical fields, are similarly included within the patent protection scope of the present invention.

Claims

1. A formation process for a soft-pack lithium-ion battery, characterized in that: Specifically, it includes the following steps: S1: Heat the battery cell and apply pressure to its surface; S2: The battery cell is charged with a constant current that gradually increases in three stages. S3: Reduce the charging current and perform the fourth stage of constant current charging; Each stage of constant current charging in steps S2 and S3 is allowed to stand for 1-2 minutes before the process. In step S2, the charging current in the first stage is 0.2-0.3C; the charging current in the second stage is 0.3-0.5C; and the charging current in the third stage is 0.7-1C. The charging current in step S3 is 0.3-0.5C.

2. The formation process of a soft-pack lithium-ion battery according to claim 1, characterized in that: In step S1, the heating temperature is 60-90℃, and the pressure applied to the surface of the battery cell is 6-12 kg / cm².

3. The formation process of a soft-pack lithium-ion battery according to claim 1, characterized in that: In step S2, the first stage of charging takes 6-15 minutes; the battery voltage is greater than 3.2V at the end of charging.

4. The formation process of a soft-pack lithium-ion battery according to claim 1, characterized in that: The second stage of charging in step S2 takes 6-10 minutes; the battery voltage is greater than 3.5V at the end of charging.

5. The formation process of a soft-pack lithium-ion battery according to claim 1, characterized in that: The third stage of charging in step S2 takes 35-40 minutes; the battery voltage is greater than 3.8V at the end of charging.

6. The formation process of a soft-pack lithium-ion battery according to claim 1, characterized in that: The charging time in step S3 is 5-20 minutes.

7. The formation process of a soft-pack lithium-ion battery according to any one of claims 1-6, characterized in that: The positive electrode active material of the battery cell used in this formation process is at least one of lithium cobalt oxide, lithium manganese oxide, and lithium nickel cobalt manganese oxide.

8. The formation process of a soft-pack lithium-ion battery according to any one of claims 1-6, characterized in that: The negative electrode active material of the battery cell used in this formation process is graphite.

9. The formation process of a soft-pack lithium-ion battery according to any one of claims 1-6, characterized in that: The separator used in the battery cells for this formation process is a commercially available PP separator.

10. The formation process of a soft-pack lithium-ion battery according to any one of claims 1-6, characterized in that: The electrolyte used in this formation process is EC / EMC / DEC type electrolyte. After the battery cell is injected with electrolyte and allowed to stand for aging to ensure that the electrode is fully wetted by the electrolyte, the formation process is then carried out.

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