Pre-charging process for improving performance of high-voltage soft-package lithium ion battery cell

Abstract

The invention belongs to the technical field of lithium batteries, and particularly relates to a pre-charging process for improving the performance of a high-voltage soft-package lithium ion battery cell. Comprising the following steps: putting a pre-sealed battery cell after liquid injection into a cabinet, raising the temperature and applying pressure, and starting segmented charging of the battery cell; carrying out ladder type pre-charging in five sections; and constant-current discharging is carried out, the constant-current discharging current is 0.8 C, the voltage reaches the preset delivery voltage, and standing is carried out. According to the pre-charging process, easy-to-oxidize components in the electrolyte can be consumed in the pre-charging process, oxidation and gas production under high voltage during later capacity grading are prevented, an excellent SEI film can be formed to improve the cell performance, especially the cycle performance, and the performance at low temperature is obviously improved; according to the present invention, the pre-charging process is adopted, such that the high capacity and the high stability can be maintained under the extreme temperature condition, the total time of the pre-charging process is about 2.4 h, and the production efficiency can be substantially improved.

Description

Technical Field

[0001] The present invention belongs to the technical field of lithium batteries, and in particular relates to a pre-charging process for improving the performance of high-voltage soft-pack lithium-ion batteries. Background Art

[0002] Lithium-ion batteries have the advantages of small size, high voltage, high capacity, and good cycle performance, and are widely used in daily life. As the pace of society accelerates, people have higher and higher requirements for the performance of lithium-ion batteries, especially the cycle performance. One of the key factors affecting these battery performance is the solid electrolyte film (SEI film) formed by the decomposition of electrolytes on the negative electrode surface in lithium-ion batteries. This passivation film covers the surface of the electrode material and is Li + It is an excellent conductor and also has the function of blocking electrons. The formation components of the SEI film and the density and uniformity of the film have an extremely important influence on the performance of the battery. In addition, the SEI film can exist stably in the organic electrolyte solution, and the solvent molecules cannot pass through this passivation film, which can effectively prevent the co-embedding of the solvent molecules from damaging the electrode material, greatly improving the cycle performance of the battery. In the process of SEI film formation, the pre-charging process is crucial. At present, the voltage after pre-charging in the formation process is low. For high-voltage systems, the electrolyte is easily oxidized and gasified again during the later capacity division, resulting in abnormal swelling of the battery cell. In addition, since the SEI film forms uneven inorganic and organic layers, the inorganic layer expands and shrinks by 10%-20% during the charge and discharge process. As the number of charge and discharge times increases, the SEI film will continue to thicken, resulting in the formation of faults in the SEI film, which ultimately shortens the cycle life of the battery.

[0003] In the prior art, the patent application document with patent publication number CN109841914A discloses a pre-charging method for a ternary soft-pack lithium-ion power battery, which mainly includes the following steps: a) placing the battery cell that has been filled with liquid and left to stand on the pre-charging equipment for three-stage step-by-step pre-charging; b) subjecting the battery cell pre-charged in step a) to high-temperature aging; c) subjecting the battery cell after high-temperature aging in step b) to vacuum shaping to obtain a finished ternary soft-pack battery. The above technical solution improves the stability of the SEI film properties to a certain extent, but its pre-charging process time is still relatively long, and the production efficiency still needs to be further improved. Summary of the invention

[0004] In view of the above problems, the present invention proposes a pre-charging process for improving the performance of high-voltage soft-pack lithium-ion batteries, which effectively solves the problem that the voltage after pre-charging in the formation process in the prior art is low. For high-voltage systems, the electrolyte is easily oxidized and gasified again during the subsequent capacity division, resulting in abnormal swelling of the battery cell and shortening the cycle life of the battery.

[0005] In order to achieve the above-mentioned purpose, the technical solution adopted by the present invention is as follows: a pre-charging process for improving the performance of high-voltage soft-pack lithium-ion batteries.

[0006] The steps include:

[0007] S1. After the cells are filled and pre-sealed, they are placed on the cabinet, the temperature rises to 50℃-90℃, and the pressure applied to the surface of the cells is 4-12kg / cm 2 , the battery cell starts charging in segments;

[0008] S2, first stage constant current charging, wherein the first stage charging current is 0.2C, the voltage reaches the first predetermined voltage of 4.1V, and the pre-charging cut-off time is 25min;

[0009] S3, the second stage constant current charging, wherein the second stage charging current is 0.5C, the voltage reaches the predetermined voltage of 4.48V, the pre-charge cut-off time is 18min, and it is left to stand for 1min;

[0010] S4, the third stage constant current charging, wherein the third stage charging current is 0.75C, the voltage reaches the predetermined voltage of 4.48V, the pre-charge cut-off time is 40min, and it is left to stand for 15min;

[0011] S5, the fourth stage constant current charging, wherein the fourth stage charging current is 0.8C, the voltage reaches the predetermined voltage of 4.48V, and the pre-charging cut-off time is 35min;

[0012] S6, the fifth stage of constant current charging, wherein the fifth stage of charging current is 0.5C, the voltage reaches the predetermined voltage of 4.48V, the pre-charge cut-off time is 10min, and it is left to stand for 1min;

[0013] S7, constant current discharge, where the constant current discharge current is 0.8C, the voltage reaches the predetermined delivery voltage, and it is left to stand for 15 minutes.

[0014] Further, in S1, the temperature is increased to 60°C-80°C.

[0015] Furthermore, in S1, the pressure applied to the surface of the battery cell is 6-10 kg / cm 2 .

[0016] Compared with the prior art, the present invention has the following beneficial effects:

[0017] The pre-charging process of the present invention consumes easily oxidizable components in the electrolyte during the pre-charging process, prevents oxidation and gas production at high voltage during the later capacity division, and can form an excellent SEI film to improve the performance of the battery cell. In addition, the performance at low temperatures is significantly improved, so that it can still maintain a high capacity and stability under extreme temperature conditions. It effectively extends the cycle life of the battery cell, reduces capacity attenuation, improves the long-term performance of the battery cell, and improves the reliability and scope of application of the battery cell. In addition, the total time of this pre-charging process is about 2.4 hours, which can greatly improve production efficiency compared to the prior art.

[0018] In the present invention, in step S2, after the first stage of charging, it is not necessary to stand still, and the operation of step S3 can be directly performed, which can not only form a dense SEI film, but also save time. In addition, step S3, step S4 and step S5 use different magnifications for step-by-step pre-charging. Due to the different electrolyte additives, additive addition amounts, reaction potentials and times of the additives, the charging rates required for the reactions are different. The use of a large step-by-step magnification can not only save pre-charging time, but also allow the SEI film formed in S1 to reconstruct a suitable pore structure and composition, thereby improving the performance of the battery cell. The step-by-step process first uses a small current of 0.5C, and then continues to increase 0.75C and 0.8C. This is because when the formation voltage suddenly increases, the reaction is too violent, resulting in a faster gas production rate inside the battery, and the gas cannot be discharged in time. The gas that is not discharged in time accumulates inside the battery cell, affecting the formation of the SEI film. Furthermore, the S6 uses a 0.5C low current charge, which mainly improves the SOC of the battery cell. Under high SOC, the electrolyte can fully react to prevent the secondary gas production caused by excessive voltage during the later capacity division, which affects the performance. Secondly, the membrane formed by the low current formation is relatively dense and has better high-temperature performance. Among them, all charging processes are carried out under uniform temperature and pressure conditions, and there is no need to change the temperature and pressure in the middle, which is more convenient for production. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 This is a disassembled physical picture of the battery cell of Example 1 of the present invention;

[0020] Figure 2 This is a disassembled picture of the battery cell of Comparative Example 1 of the present invention;

[0021] Figure 3 This is a disassembled physical picture of the battery cell of Comparative Example 2 of the present invention;

[0022] Figure 4 A bar chart showing the high and low temperature performance test results of the lithium ion batteries of Example 1 of the present invention and Comparative Example 1 and Comparative Example 2;

[0023] Figure 5 The graph is a result of the cycle performance test of the lithium ion batteries of Example 1 and Comparative Examples 1 and 2 of the present invention. DETAILED DESCRIPTION

[0024] 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.

[0025] Example 1

[0026] The pre-charging process for improving the performance of a high-voltage soft-pack lithium-ion battery cell provided in this embodiment includes the following steps:

[0027] S1. After the cells are filled and pre-sealed, they are placed on the cabinet, the temperature rises to 80±5℃, and the pressure applied to the surface of the cells is 6-10kg / cm 2 , the battery cell starts charging in segments;

[0028] S2, first stage constant current charging, wherein the first stage charging current is 0.2C, the voltage reaches the first predetermined voltage of 4.1V, and the pre-charging cut-off time is 25min;

[0029] S3, the second stage constant current charging, wherein the second stage charging current is 0.5C, the voltage reaches the predetermined voltage of 4.48V, the pre-charge cut-off time is 18min, and it is left to stand for 1min;

[0030] S4, the third stage constant current charging, wherein the third stage charging current is 0.75C, the voltage reaches the predetermined voltage of 4.48V, the pre-charge cut-off time is 40min, and it is left to stand for 15min;

[0031] S5, the fourth stage constant current charging, wherein the fourth stage charging current is 0.8C, the voltage reaches the predetermined voltage of 4.48V, and the pre-charging cut-off time is 35min;

[0032] S6, the fifth stage of constant current charging, wherein the fifth stage of charging current is 0.5C, the voltage reaches the predetermined voltage of 4.48V, the pre-charge cut-off time is 10min, and it is left to stand for 1min;

[0033] S7, constant current discharge, where the constant current discharge current is 0.8C, the voltage reaches the predetermined delivery voltage, and it is left to stand for 15 minutes.

[0034] Example 2

[0035] The pre-charging process for improving the performance of a high-voltage soft-pack lithium-ion battery cell provided in this embodiment includes the following steps:

[0036] S1. After the cells are filled and pre-sealed, they are placed on the cabinet. The temperature rises to 65±5℃ and the pressure applied to the cell surface is 4-8kg / cm 2, the battery cell starts charging in segments;

[0037] S2, first stage constant current charging, wherein the first stage charging current is 0.2C, the voltage reaches the first predetermined voltage of 4.1V, and the pre-charging cut-off time is 25min;

[0038] S3, the second stage constant current charging, wherein the second stage charging current is 0.5C, the voltage reaches the predetermined voltage of 4.48V, the pre-charge cut-off time is 18min, and it is left to stand for 1min;

[0039] S4, the third stage constant current charging, wherein the third stage charging current is 0.75C, the voltage reaches the predetermined voltage of 4.48V, the pre-charge cut-off time is 40min, and it is left to stand for 15min;

[0040] S5, the fourth stage constant current charging, wherein the fourth stage charging current is 0.8C, the voltage reaches the predetermined voltage of 4.48V, and the pre-charging cut-off time is 35min;

[0041] S6, the fifth stage of constant current charging, wherein the fifth stage of charging current is 0.5C, the voltage reaches the predetermined voltage of 4.48V, the pre-charge cut-off time is 10min, and it is left to stand for 1min;

[0042] S7, constant current discharge, where the constant current discharge current is 0.8C, the voltage reaches the predetermined delivery voltage, and it is left to stand for 15 minutes.

[0043] Example 3

[0044] The pre-charging process for improving the performance of a high-voltage soft-pack lithium-ion battery cell provided in this embodiment includes the following steps:

[0045] S1. After the cells are filled and pre-sealed, they are placed on the cabinet. The temperature rises to 70±5℃ and the pressure applied to the cell surface is 9-12kg / cm 2 , the battery cell starts charging in segments;

[0046] S2, first stage constant current charging, wherein the first stage charging current is 0.2C, the voltage reaches the first predetermined voltage of 4.1V, and the pre-charging cut-off time is 25min;

[0047] S3, the second stage constant current charging, wherein the second stage charging current is 0.5C, the voltage reaches the predetermined voltage of 4.48V, the pre-charge cut-off time is 18min, and it is left to stand for 1min;

[0048] S4, the third stage constant current charging, wherein the third stage charging current is 0.75C, the voltage reaches the predetermined voltage of 4.48V, the pre-charge cut-off time is 40min, and it is left to stand for 15min;

[0049] S5, the fourth stage constant current charging, wherein the fourth stage charging current is 0.8C, the voltage reaches the predetermined voltage of 4.48V, and the pre-charging cut-off time is 35min;

[0050] S6, the fifth stage of constant current charging, wherein the fifth stage of charging current is 0.5C, the voltage reaches the predetermined voltage of 4.48V, the pre-charge cut-off time is 10min, and it is left to stand for 1min;

[0051] S7, constant current discharge, where the constant current discharge current is 0.8C, the voltage reaches the predetermined delivery voltage, and it is left to stand for 15 minutes.

[0052] Comparative Example 1

[0053] The pre-charging process of the high-voltage soft-pack lithium-ion battery cell provided in this comparative example specifically includes the following steps:

[0054] Step 1: After the liquid is injected and the pre-sealed battery cell is placed on the cabinet, the temperature rises to 80±5℃, and the pressure applied to the surface of the battery cell is 6-10kg / cm 2 , the battery cell starts charging in segments;

[0055] Step 2: The first stage of constant current charging, wherein the first stage of charging current is 0.2C, the voltage reaches the first predetermined voltage of 4.1V, and the cut-off time is 18min;

[0056] Step 3: The second stage of constant current charging, wherein the second stage of charging current is 0.5C, the voltage reaches a predetermined voltage of 4.48V, and the cut-off time is 86min.

[0057] Comparative Example 2

[0058] The pre-charging process of the high-voltage soft-pack lithium-ion battery cell provided in this comparative example specifically includes the following steps:

[0059] Step 1: After the liquid is injected and the pre-sealed battery cell is placed on the cabinet, the temperature rises to 80±5℃, and the pressure applied to the surface of the battery cell is 6-10kg / cm 2 , the battery cell starts charging in segments;

[0060] Step 2: constant current charging, wherein the first charging current is 0.2C, the voltage reaches the first predetermined voltage of 4.1V, and the pre-charging cut-off time is 25min;

[0061] Step 3: constant current charging, where the second stage charging current is 0.5C, the voltage reaches the predetermined voltage of 4.48V, the pre-charge cut-off time is 20min, and it is left to stand for 1min;

[0062] Step 4: constant current charging, where the third charging current is 0.75C, the voltage reaches the predetermined voltage of 4.48V, the pre-charge cut-off time is 50min, and it is left to stand for 15min.

[0063] It should be noted that the high-voltage soft-pack lithium-ion battery cells used in the above embodiments and comparative examples have lithium cobalt oxide as the positive electrode, artificial graphite as the negative electrode material, and a high-temperature fast-charging electrolyte as the electrolyte, and the operations are all carried out on the same formation cabinet.

[0064] Test Example 1

[0065] The cells of Example 1, Comparative Example 1 and Comparative Example 2 were subjected to a capacity division process, in which the capacity division process adopted a 0.5C charge to 4.48V, a cut-off current of 0.02C, and a 0.5C discharge to 3.0V.

[0066] The battery cells are disassembled, and the fully charged battery cells after capacity division are disassembled in a dehumidified environment. The disassembly of Example 1 and Comparative Example 1 and Comparative Example 2 are respectively as follows: Figure 1 , 2 , as shown in Figure 3. Figure 1 The disassembly interface is good. By comparison, it can be seen that the gas production and swelling of the battery cell obtained by the pre-charging process in Example 1 basically disappear. Reducing gas production and swelling can extend the service life of the battery cell and improve the safety and stability of the battery cell.

[0067] The pre-charging process of Example 1 adopts multi-stage constant current charging, and sets an appropriate rest time after each stage of charging. This segmented charging method can effectively control the chemical reaction rate inside the battery cell, reduce the occurrence of side reactions, and thus reduce gas production and swelling. By optimizing the charging current and rest time, the pre-charging process of Example 1 can reduce the stress accumulation inside the battery cell while ensuring the charging efficiency, thereby improving the overall performance of the battery cell. In addition, the total time of this pre-charging process is about 2.4 hours, which can greatly improve production efficiency compared to the prior art.

[0068] Test Example 2

[0069] The corresponding lithium ion batteries of Example 1 and Comparative Examples 1 and 2 were tested for high and low temperature performance.

[0070] The test conditions are as follows:

[0071] High temperature: After the battery cell is fully charged, place it at 55℃±2℃ for 2h, then discharge it according to the 0.2C discharge method and record the battery cell capacity;

[0072] Low temperature: After the battery cell is fully charged, place it at 0℃ / -10℃ / -20℃±2℃ for 4h, then discharge it according to the 0.2C discharge method and record the battery cell capacity.

[0073] After 4 hours of storage, discharge the battery according to the 0.2C discharge method and record the battery capacity. Figure 4 In particular, the cell capacity is significantly improved at low temperatures.

[0074] The improvement in performance at low temperatures means that the battery cell is more suitable for use in extreme environments and can better cope with the usage requirements in high and low temperature environments, thereby improving the reliability and applicability of the battery cell.

[0075] Test Example 3

[0076] The corresponding lithium ion batteries of Example 1 and Comparative Example 1 and Comparative Example 2 were tested for cycle performance. The specific test conditions were as follows: at room temperature 25±1°C, the charging current was 1.4C and charged to 4.1V, the cut-off current was 1C, and the charge was charged to 4.2V at 1C, the cut-off current was 0.5C, and the charge was charged to 4.48V at 0.5C, and the cut-off current was 0.02C, and the discharge was discharged at 0.5C to 3.0V. The voltage range was 3.0-4.48V. The number of cycle charge and discharge and the cell capacity were recorded. Figure 5 As shown in the test results, it can be seen that the pre-charging method of Example 1 significantly prolongs the cycle life of the battery cell.

[0077] The extended cycle life means that the battery cell has a longer service life, which reduces the frequency of battery replacement, reduces the cost of use, and also reduces the impact on the environment.

[0078] Although the present invention has been described in detail with reference to the aforementioned embodiments, it is still possible for those skilled in the art to modify the technical solutions described in the aforementioned embodiments, or to make equivalent substitutions for some of the technical features therein. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the protection scope of the present invention.

Claims

1. A pre-charging process for improving the performance of high-voltage soft-pack lithium-ion batteries, characterized in that: The steps include: S1. After the cells are filled and pre-sealed, they are placed on the cabinet, the temperature rises to 50℃-90℃, and the pressure applied to the surface of the cells is 4-12kg / cm 2 , the battery cell starts charging in segments; S2, first stage constant current charging, wherein the first stage charging current is 0.2C, the voltage reaches the first predetermined voltage of 4.1V, and the pre-charging cut-off time is 25min; S3, the second stage constant current charging, wherein the second stage charging current is 0.5C, the voltage reaches the predetermined voltage of 4.48V, the pre-charge cut-off time is 18min, and it is left to stand for 1min; S4, the third stage constant current charging, wherein the third stage charging current is 0.75C, the voltage reaches the predetermined voltage of 4.48V, the pre-charge cut-off time is 40min, and it is left to stand for 15min; S5, the fourth stage constant current charging, wherein the fourth stage charging current is 0.8C, the voltage reaches the predetermined voltage of 4.48V, and the pre-charging cut-off time is 35min; S6, the fifth stage of constant current charging, wherein the fifth stage of charging current is 0.5C, the voltage reaches the predetermined voltage of 4.48V, the pre-charge cut-off time is 10min, and it is left to stand for 1min; S7, constant current discharge, where the constant current discharge current is 0.8C, the voltage reaches the predetermined delivery voltage, and it is left to stand for 15 minutes.

2. The pre-charging process for improving the performance of high-voltage soft-pack lithium-ion batteries according to claim 1, characterized in that: In S1, the temperature is raised to 60°C-80°C.

3. The pre-charging process for improving the performance of high-voltage soft-pack lithium-ion batteries according to claim 1, characterized in that: In S1, the pressure applied to the cell surface is 6-10kg / cm 2 .

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