Lithium ion battery and efficient formation method thereof

Abstract

The invention provides a lithium ion battery and a high-efficiency formation method thereof, which are characterized in that a lithium ion battery cell is subjected to low-rate constant-current charging after standing for one time; after secondary standing is carried out, high-rate constant-current charging is carried out; after standing for three times, carrying out constant-current charging; and finally standing for four times. Compared with the prior art, after high-rate formation and film formation, long-time standing is added, performance reduction caused by too fast film formation can be improved, the formation efficiency can be remarkably improved through the formation method, and the performance of the battery is not affected.

Description

Technical Field

[0001] The present invention belongs to the field of battery formation, and in particular relates to a lithium ion battery and a high-efficiency formation method thereof. Background Art

[0002] Formation is a critical process in the battery manufacturing process. The active materials of the battery cell are activated through the first charge and discharge, and a SEI film is formed on the negative electrode, which prevents the solvent molecules from further embedding into the negative electrode material. At the same time, it plays the role of passing ions and blocking electrons, ensuring the subsequent cycle and storage performance.

[0003] The quality of the SEI film has a great influence on the electrical performance of the battery. The traditional formation charging mode is usually a small current + large current step charging mode. The small current is generally 0.01C~0.1C (C is the abbreviation of battery capacity, which indicates the magnitude of the current when the battery is charging and discharging). The SEI film usually formed by small current is uniform, dense and stable, which helps to improve the performance of the battery; the large current is generally 0.1C~0.2C. The SEI film usually formed by large current is relatively loose, but it will increase the infiltration of the electrolyte, and the ionic conductivity of the formed SEI film is higher.

[0004] Due to these factors, traditional processes typically use a formation current that transitions from low to high, causing the SEI film to transition from dense to loose, ensuring that the formation is complete. While this traditional approach ensures battery performance, the current in the later stages of charging is overly conservative, resulting in a long charge time and impacting production efficiency. Furthermore, prolonged charging and discharging results in high energy consumption, increasing energy costs.

[0005] Based on the current trend of reducing costs and increasing efficiency in the lithium battery industry, it is particularly important to develop an efficient formation method. Summary of the Invention

[0006] The object of the present invention is to provide a lithium-ion battery and an efficient formation method thereof. By matching the parameters of each step and adding a long period of static standing after high-rate formation, it is helpful to improve the performance degradation caused by too fast film formation. The formation method of the present invention can significantly improve the formation efficiency without affecting the battery performance.

[0007] The specific technical solutions of the present invention are as follows:

[0008] A lithium-ion battery efficient formation method, specifically comprising:

[0009] After the lithium-ion battery cell is allowed to rest for the first time, it is charged at a low rate with a constant current; after the lithium-ion battery cell is allowed to rest for the second time, it is charged at a high rate with a constant current; after the lithium-ion battery cell is allowed to rest for the third time, it is charged at a third constant current; and finally, it is allowed to rest for the fourth time;

[0010] The first standing time is 5±0.5min;

[0011] The low rate constant current charging refers to 0.1C charging for 30±1min;

[0012] The second standing time is 3±0.5min;

[0013] The high rate constant current charging refers to 0.3C charging for 20±1min;

[0014] The third standing time is 20-30 minutes;

[0015] The constant current charging refers to charging at 0.2-0.5C for 24-60min;

[0016] The fourth standing time is 3±0.5min;

[0017] The lithium ion battery high-efficiency formation method has a battery current of 35% SOC after formation.

[0018] The high-efficiency lithium-ion battery formation method has a total formation time of ≤151 min, preferably ≤115 min.

[0019] The present invention provides a lithium ion battery prepared by adopting the above-mentioned high-efficiency formation method.

[0020] The present invention provides a high-efficiency lithium-ion battery formation method for lithium-ion battery formation, particularly for lithium-ion square aluminum-cased lithium iron phosphate batteries. After formation of a 105Ah cell, the method achieves a capacity of ≥111Ah, an initial efficiency of ≥91.70%, an internal resistance of ≤0.33mΩ, a K value of ≤0.054mv / h, a 25°C cycle (900 cycles) retention rate of ≥90.7%, a capacity retention of ≥98% after 7 days of storage at 55°C, and a good interface.

[0021] Formation is the process by which the SEI film forms in a battery. This process is accompanied by the generation of gases. Formation gas production is used to characterize and determine formation parameters and determine the SEI film formation time at different formation rates. High-rate formation increases the film formation rate, but the resulting film becomes loose, leading to decreased battery performance. Therefore, the present invention introduces a long rest period after high-rate formation to help mitigate performance degradation caused by overly rapid film formation. Adding a long period of rest after high-current charging has the following effects: 1) It can relieve the stress generated by high current in the electrode material and stabilize the material structure; 2) The uneven electrolyte concentration caused by uniform high current promotes the formation of a stable interface between the electrolyte and the electrode material, thereby improving electrochemical performance; 3) The high current has a faster film-forming rate, resulting in faster gas production. If the gas cannot be discharged in time, it will affect the battery interface. Increasing the rest period will help to discharge the gas; 4) The high current has a fast film-forming rate, and the SEI film is relatively loose. Increasing the rest period for aging will help to adjust the SEI film's own structure and stabilize the SEI film; 5) High current generates a lot of heat, which can easily cause local overheating. Increasing the rest period will make the internal temperature of the battery cell tend to be consistent, thereby improving overall performance. ③ After the formation gas production is completed, that is, the SEI film formation is completed, subsequent charging will only increase the formation SOC depth. A larger current can be used for charging, further improving the formation efficiency. The present invention further improves battery performance by combining subsequent constant current charging parameters after high-rate constant current charging and long-term rest.

[0022] Compared with the prior art, the present invention shortens the formation process time by rationally designing the formation process parameters (current rate and time), significantly improves the formation efficiency, improves production efficiency, reduces production energy consumption, and has no adverse effect on battery performance. DETAILED DESCRIPTION

[0023] To make the objectives, technical solutions, and advantages of the embodiments of the present invention more clear, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with 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. All other embodiments obtained by ordinary technicians in this field based on the embodiments of the present invention without making any creative efforts shall fall within the scope of protection of the present invention.

[0024] Example 1

[0025] A lithium-ion battery efficient formation method, specifically comprising:

[0026] 200 pieces of 105Ah battery cells after full infiltration after primary injection were taken as the implementation group, and the formation method was as follows: after the lithium-ion battery cells were allowed to stand for the first time, they were charged at a small rate with constant current; after the cells were allowed to stand for the second time, they were charged at a large rate with constant current; after the cells were allowed to stand for the third time, they were charged at a third constant current; and finally, they were allowed to stand for the fourth time; the formation process and parameters of Example 1 in Table 1 were used, and then aging, secondary injection, sealing, capacity division and self-discharge screening were carried out in sequence.

[0027] Example 2

[0028] A lithium-ion battery efficient formation method, specifically comprising:

[0029] 200 pieces of 105Ah battery cells after full infiltration after primary injection were taken as the implementation group. The same formation process as in Example 1 was followed, and the formation process and parameters of Example 2 in Table 1 were used. The specific process and parameters are shown in Table 1. Then, aging, secondary injection, sealing, capacity separation and self-discharge screening were carried out in sequence.

[0030] Example 3

[0031] A lithium-ion battery efficient formation method, specifically comprising:

[0032] 200 pcs of 105Ah cells fully infiltrated with the first injection were taken as the implementation group. The same formation process as in Example 1 was followed, using the formation process and parameters of Example 3 in Table 1. The specific process and parameters are shown in Table 1. After that, aging, secondary injection, sealing, capacity separation and self-discharge screening were carried out in sequence.

[0033] Example 4

[0034] A lithium-ion battery efficient formation method, specifically comprising:

[0035] 200 pieces of 105Ah battery cells after full infiltration after primary injection were taken as the implementation group. The same formation process as in Example 1 was followed, using the formation process and parameters of Example 4 in Table 1. The specific process and parameters are shown in Table 1. After that, aging, secondary injection, sealing, capacity separation and self-discharge screening were carried out in sequence.

[0036] Comparative Example 1

[0037] A lithium ion battery formation method, specifically:

[0038] 200 pcs of 105Ah batteries after full infiltration after primary injection were taken as the control group. The same formation process as in Example 1 was followed, and the formation process and parameters of Comparative Example 1 in Table 1 were used. The specific process and parameters are shown in Table 1. Then, aging, secondary injection, sealing, capacity separation and self-discharge screening were carried out in sequence.

[0039] Comparative Example 2

[0040] A lithium ion battery formation method, specifically:

[0041] 200 pcs of 105Ah batteries after full infiltration after primary injection were taken as the control group. The same formation process as in Example 1 was followed, and the formation process and parameters of Comparative Example 2 in Table 1 were used. The specific process and parameters are shown in Table 1. Then, aging, secondary injection, sealing, capacity separation and self-discharge screening were carried out in sequence.

[0042] Comparative Example 3

[0043] A lithium ion battery formation method, specifically:

[0044] 200 pcs of 105Ah batteries after full infiltration after primary injection were taken as the control group. The same formation process as in Example 1 was followed, and the formation process and parameters of Comparative Example 3 in Table 1 were used. The specific process and parameters are shown in Table 1. Then, aging, secondary injection, sealing, capacity separation and self-discharge screening were carried out in sequence.

[0045] Comparative Example 4

[0046] A lithium ion battery formation method, specifically:

[0047] 200 pcs of 105Ah batteries after full infiltration after primary injection were taken as the control group. The same formation process as in Example 1 was followed, and the formation process and parameters of Comparative Example 4 in Table 1 were used. The specific process and parameters are shown in Table 1. Then, aging, secondary injection, sealing, capacity separation and self-discharge screening were carried out in sequence.

[0048] Comparative Example 5

[0049] A lithium ion battery formation method, specifically:

[0050] 200 pcs of 105Ah batteries after full infiltration after primary injection were taken as the control group. The same formation process as in Example 1 was followed, and the formation process and parameters of Comparative Example 4 in Table 1 were used. The specific process and parameters are shown in Table 1. Then, aging, secondary injection, sealing, capacity separation and self-discharge screening were carried out in sequence.

[0051] Table 1 Formation process and parameters of each embodiment and comparative example

[0052]

[0053]

[0054] The test results of the batteries formed in each embodiment and comparative example are shown in Table 2. The test conditions are as follows:

[0055] Capacity: At 25°C, the formed cell is charged at a constant current rate of 0.5C to 3.65V, charged at a constant voltage rate of 0.05C, and discharged at 0.5C to 2.5V.

[0056] First effect: discharge capacity / (formation charge capacity + charge capacity before full discharge);

[0057] K value: After the battery capacity is reached, let it stand for 24 hours and measure the voltage ocv1. After standing for 2 days, measure the voltage ocv2. The K value is calculated as (ocv1-ocv2) / time;

[0058] Internal resistance: the resistance value tested synchronously when the battery cell is tested for ocv2;

[0059] 55℃ high-temperature storage: The battery cell is discharged for 1C at 25℃ to 2.5V, then fully charged for 1C, and discharged again for 1C to 2.5V. The discharged capacity is recorded as the capacity before storage c1. The battery cell is fully charged and stored at 55℃ for 7 days. The battery cell is taken out and cooled to 25℃, and discharged for 1C. The discharged capacity is c2, and the capacity retention rate is c2 / c1.

[0060] Table 2 shows the performance test results of various embodiments and comparative examples.

[0061]

[0062]

[0063] From the above-mentioned result demonstration, embodiment 1-embodiment 4 is produced according to processing parameter of the present invention, and the formation time is not only shorter, and battery performance is better.And Comparative Example 1 is a conventional method, and constant-current charging adopts 0.15C / 120min (not the large rate charging of employing 0.3C of the present invention) for the second time, but, comparative example 1 is long to form the time, and efficiency is low.The embodiment of the present invention 1-embodiment 4 performance is suitable or even more excellent with Comparative Example 1, but the time is shorter, and efficiency significantly increases, illustrates that constant-current charging of the present invention adopts large rate not to deteriorate battery performance for the second time, and can greatly improve formation efficiency.

[0064] In Comparative Example 2, although the second constant current charging adopts a high-rate constant current charging of 0.3C according to the present invention, the standing time is short, which affects the film formation and significantly reduces the battery performance.

[0065] Comparative Example 3 The first, second and third constant current charges adopt 0.1C constant current charging (the second and third charges do not meet the requirements of the present invention). The battery performance is comparable to that of the embodiment, but the charging time reaches 224min, which is too long and the formation efficiency is too low.

[0066] In Comparative Example 4, the second constant current charging adopts 0.2C constant current charging (the second charging does not meet the requirements of the present invention), and the electrical performance of the product is poor.

[0067] In comparative example 5, the third constant current charging adopts 0.8C constant current charging. Although the formation time is short, the charging current is too large, which leads to aggravated polarization of the battery cell and poor performance.

[0068] The inventors tested gassing during cell formation and found that the 105Ah cell completed gassing before ~13% SOC, indicating the completion of SEI film formation. Taking into account cell consistency and polarization factors, the second step, 0.3C film formation SOC, was extended to 15% to ensure complete film formation. Once film formation is complete, a higher rate of 0.5C can be used to charge to the formation cutoff SOC.

[0069] The underlined data do not meet the requirements of the present invention.

[0070] The above embodiments are described to facilitate understanding and use of the invention by those skilled in the art. It will be apparent that those skilled in the art can readily make various modifications to these embodiments and apply the general principles described herein to other embodiments without requiring inventive effort. Therefore, the present invention is not limited to the above embodiments. Improvements and modifications made by those skilled in the art based on the disclosure of the present invention without departing from the scope of the present invention should be within the scope of protection of the present invention.

Claims

1. A lithium ion battery high efficiency formation method, characterized in that: The lithium ion battery efficient formation method is specifically as follows: After the lithium-ion battery cell is allowed to rest for the first time, it is charged at a low rate with a constant current; after the lithium-ion battery cell is allowed to rest for the second time, it is charged at a high rate with a constant current; after the lithium-ion battery cell is allowed to rest for the third time, it is charged at a third constant current; and finally, it is allowed to rest for the fourth time; The low rate constant current charging refers to 0.1C charging for 30±1min; The high-rate constant-current charging refers to 0.3C charging for 20±1 min.

2. The lithium ion battery high-efficiency formation method according to claim 1, characterized in that: The first standing time is 5±0.5min.

3. The lithium ion battery high-efficiency formation method according to claim 1, characterized in that: The second standing time is 3±0.5min.

4. The lithium ion battery high-efficiency formation method according to claim 1, characterized in that: The three standing times are 20-30 minutes.

5. The lithium ion battery high-efficiency formation method according to claim 1, characterized in that: The third constant current charging refers to charging at 0.2-0.5C for 24-60 minutes.

6. The lithium ion battery high-efficiency formation method according to claim 1, characterized in that: The fourth standing time is 3±0.5 min.

7. The lithium ion battery high efficiency formation method according to claim 1, characterized in that: The lithium ion battery high-efficiency formation method has a battery current of 35% SOC after formation.

8. The lithium ion battery high-efficiency formation method according to claim 1, characterized in that: The lithium-ion battery high-efficiency formation method has a total formation time of ≤151 minutes.

9. A lithium-ion battery, characterized in that: The lithium ion battery is prepared by the high-efficiency formation method of any one of claims 1 to 8.

10. The lithium-ion battery according to claim 9, characterized in that After the 105Ah battery cell is formed, the capacity is ≥111Ah, the first efficiency is ≥91.70%, the internal resistance is ≤0.33mΩ, the K value is ≤0.054mv / h, the 25-degree cycle (900 weeks) retention rate is ≥90.7%, the capacity retention after storage at 55°C for 7 days is ≥98%, and the interface is good.

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