Formation and capacity determination method of lithium iron phosphate battery and application
By combining negative pressure and normal pressure static placement with low current aging and constant current and constant voltage charging, the problems of increased internal resistance and polarization in lithium iron phosphate batteries have been solved, thus improving battery performance and safety.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- 华能烟台新能源有限公司
- Filing Date
- 2026-04-03
- Publication Date
- 2026-06-23
AI Technical Summary
Existing lithium iron phosphate battery formation and capacity testing processes suffer from problems such as increased internal resistance, increased cell polarization, severe heat generation, and poor safety performance, which affect battery performance and safety.
A formation and capacity-building method combining negative and normal pressure static setting with low current aging and constant current and constant voltage charging is adopted. This method includes negative pressure static setting, normal pressure static setting, constant current charging, constant current discharging, and constant current and constant voltage charging. The formation and capacity-building process is optimized to reduce DC impedance and polarization.
It effectively reduces the DC resistance of lithium iron phosphate batteries, reduces cell polarization, improves cell performance, reduces temperature rise, and enhances battery safety.
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Abstract
Description
Technical Field
[0001] This invention belongs to the field of secondary battery technology, specifically relating to the formation and capacity testing methods and applications of lithium iron phosphate batteries. Background Technology
[0002] Existing formation and capacity testing processes directly influence the quality and polarization behavior of the solid electrolyte interphase (SEI) membrane by controlling parameters such as current, voltage, and settling time, thereby determining the DC internal resistance level of the secondary battery. Internal resistance is both a result of the process (reflecting the state of the SEI membrane and electrode structure) and a target for process control (optimizing consistency through capacity testing and screening).
[0003] The existing capacity-separating process has the following problems: (1) To improve production efficiency, the existing technology shortens the soaking time after liquid injection, and poor soaking will increase the internal resistance of the secondary battery; (2) Improper aging mechanism will aggravate the capacity loss of the secondary battery and increase the internal resistance of the secondary battery; (3) Improper capacity separation steps will also affect the capacity utilization of the cell. All of the above problems will cause the cell polarization to increase. Current passing through the internal resistance will generate heat. According to Joule's law, the power loss is I 2 Therefore, a high internal resistance in a secondary battery will lead to more severe heat generation under high current conditions, potentially causing temperature increases, affecting battery performance, and even posing safety risks. Besides increased power loss, a high internal resistance also reduces usable voltage, shortens driving range, and may cause performance degradation at low temperatures. Summary of the Invention
[0004] This invention aims to at least partially solve one of the technical problems in related technologies. To this end, embodiments of this invention propose a method for the formation and capacity testing of lithium iron phosphate batteries and their applications.
[0005] In a first aspect, embodiments of the present invention provide a method for the formation and capacity testing of lithium iron phosphate batteries, the method comprising the following steps:
[0006] (a) The lithium iron phosphate battery after liquid injection is first placed under negative pressure and then placed under normal pressure to obtain the lithium iron phosphate battery after standing. (b) The settled lithium iron phosphate battery is charged with constant current until the constant current charging ends and the lithium iron phosphate battery does not exceed 50% SOC, thus obtaining the formed lithium iron phosphate battery. (c) The formed lithium iron phosphate battery is charged and discharged at a constant current of less than 0.01C until the aging is completed, and the aged lithium iron phosphate battery is obtained. (d) The aged lithium iron phosphate battery is charged to 100% SOC by constant current and constant voltage, and the cutoff voltage is set to 4.0 to 4.2V. Then, it is discharged by constant current at different rates.
[0007] The advantages and technical effects of the formulation and compatibilization method of this invention are as follows: (1) The present invention provides a method for the formation and capacity testing of lithium iron phosphate batteries. This method optimizes the formation and capacity testing process by optimizing the post-filling static conditions, using low-current aging and constant current constant voltage charging (CCCV) stage with a high-voltage charging mechanism. This can effectively reduce the DC impedance of lithium iron phosphate batteries, reduce cell polarization, effectively improve cell performance, reduce cell temperature rise, and improve battery safety performance.
[0008] (2) The embodiments of the present invention provide the application of the above-mentioned lithium iron phosphate battery formation and capacity testing method. Given the advantages of the above-mentioned lithium iron phosphate battery formation and capacity testing method, it has good application prospects in the fields of lithium-ion battery preparation and performance testing.
[0009] According to the formation and capacity testing method of lithium iron phosphate battery according to an embodiment of the present invention, in step (a), the pressure of negative pressure settling is -60 to -80 kPa, the temperature of negative pressure settling is 25 to 40°C, and the time of negative pressure settling is 30 to 40 min.
[0010] According to the formation and capacity testing method of lithium iron phosphate battery according to an embodiment of the present invention, in step (a), the temperature of the atmospheric pressure standing is 40-45°C, and the time of atmospheric pressure standing is 24-36h.
[0011] According to the formation and capacity testing method of lithium iron phosphate battery according to an embodiment of the present invention, in step (b), constant current charging ends until the lithium iron phosphate battery reaches 34-36% SOC.
[0012] According to the formation and capacity testing method of lithium iron phosphate battery according to an embodiment of the present invention, step (b) of performing constant current charging on the lithium iron phosphate battery after standing in stages specifically includes: first charging the lithium iron phosphate battery after standing at a constant current of 0.08 to 0.12C to 1 to 1.4% SOC, standing for 5 to 10 minutes, and then charging it at a constant current of 0.15 to 0.2C to 34 to 36% SOC.
[0013] According to the formation and capacity testing method of lithium iron phosphate battery according to an embodiment of the present invention, in step (c), the formed lithium iron phosphate battery is first charged at a constant current of 0.008-0.01C for 20-30 minutes, and then discharged at a constant current of 0.008-0.01C for 20-30 minutes, and the cycle is repeated for 2 weeks to complete the aging process.
[0014] According to the formation and capacity testing method of lithium iron phosphate battery according to an embodiment of the present invention, in step (c), the change in SOC before and after aging is controlled to be <0.5% SOC; and / or, in step (c), the aging temperature is 40-50°C.
[0015] According to the formation and capacity testing method of lithium iron phosphate battery according to an embodiment of the present invention, in step (d), the battery is charged at a constant current and constant voltage of 0.5 to 1C until the cutoff voltage is 4.0 to 4.2V and the cutoff current is 0.01 to 0.05C, so that the lithium iron phosphate battery reaches 100% SOC.
[0016] According to the formation and capacity testing method of lithium iron phosphate battery according to an embodiment of the present invention, step (d) specifically includes constant current discharge at different rates: first, constant current discharge at 0.8 to 1.2C to 2.5V, then constant current discharge at 0.1 to 0.5C to 2.5V, and finally constant current discharge at 0.01 to 0.05C to 2.5V.
[0017] Secondly, embodiments of the present invention provide the application of the lithium iron phosphate battery formation and capacity testing method described in the first aspect in the field of lithium-ion battery preparation or testing. Detailed Implementation
[0018] To make the objectives, technical solutions, and advantages of this invention clearer, the technical solutions in the embodiments of this invention will be clearly and completely described below in conjunction with the embodiments of this invention. Those skilled in the art should understand that the embodiments described are merely illustrative of the invention and should not be considered as specific limitations thereof. All other embodiments obtained by those skilled in the art based on the embodiments of this invention without creative effort are within the scope of protection of this invention. Process parameters not specifically specified in the following embodiments are generally performed under conventional conditions.
[0019] The endpoints and any values of the ranges disclosed in this invention are not limited to the precise ranges or values, and these ranges or values should be understood to include values close to these ranges or values. For numerical ranges, the endpoint values of the various ranges, the endpoint values of the various ranges and individual point values, and individual point values can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed in this invention.
[0020] In a first aspect, embodiments of the present invention provide a method for the formation and capacity testing of lithium iron phosphate batteries, the method comprising the following steps: (a) Post-liquid injection and settling: After liquid injection, the lithium iron phosphate battery is first settling under negative pressure, and then settling under high temperature and normal pressure. (b) Formation: The lithium iron phosphate battery after step (a) is left to stand is charged with constant current until the constant current charging ends and the lithium iron phosphate battery does not exceed 50% SOC. (c) Aging: The lithium iron phosphate battery formed in step (b) is subjected to constant current charging and discharging at a small current below 0.01C until the aging is completed; (d) Capacity testing: The lithium iron phosphate battery aged in step (c) is charged to 100% SOC by constant current and constant voltage, and the cutoff voltage is set to 4.0~4.2V. Then, it is discharged by constant current at different rates.
[0021] Specifically, in step (a) of the electrolyte formation and capacity testing method in this embodiment of the invention, the lithium iron phosphate battery after electrolyte injection is first placed under vacuum conditions, mainly to promote electrolyte wetting, remove air bubbles and residual gas, and stabilize electrolyte distribution.
[0022] After formation, an aging process is performed. Current conventional aging processes typically involve directly placing the battery cells in a 45°C high-temperature environment for more than 12 hours without charging or discharging. This prolonged aging process inevitably leads to battery capacity degradation and increased internal resistance.
[0023] Unlike the conventional aging process described above, the aging stage of step (c) of the formation and capacity testing method in this embodiment of the invention uses constant current charging and discharging with a small current, which has the following advantages: ① shortens the aging time after formation and improves the production yield; ② the small current charging and discharging can perform secondary reconstruction of the SEI film, causing the electrolyte to selectively decompose at the initial SEI film defects, forming a denser LiF-rich interface layer; ③ eliminates the local polarization phenomenon after formation, reduces the lithium ion concentration gradient on the cell surface, and makes the charge distribution more balanced; ④ repairs the microcracks between the current collector and the active material.
[0024] In step (d) of the capacity testing method of this embodiment, the cutoff voltage of constant current constant voltage charging (CCCV) is 4.0 to 4.2V. The CCCV high-voltage charging mechanism is adopted. By appropriately increasing the cutoff voltage, the utilization rate of the battery active material can be stimulated (the capacity of lithium iron phosphate batteries is compensated by a high-voltage platform).
[0025] Therefore, the lithium iron phosphate battery formation and capacity testing method of the present invention optimizes the formation and capacity testing process by optimizing the post-filling static conditions, using low-current aging and constant current constant voltage charging (CCCV) stage with a high-voltage charging mechanism. This can effectively reduce the DC impedance of the lithium iron phosphate battery, reduce cell polarization, effectively improve cell performance, or reduce cell temperature rise and improve battery safety performance.
[0026] As an optional embodiment of the technical solution of the present invention, in step (a), the pressure of the negative pressure settling is -60 to -80 kPa (e.g., -60 kPa, -70 kPa or -80 kPa, etc.), the temperature of the negative pressure settling is 25 to 40°C (e.g., 25°C, 30°C, 35°C or 40°C, etc.), and the time of the negative pressure settling is 30 to 40 min (e.g., 30 min, 32 min, 35 min, 38 min or 40 min, etc.).
[0027] As an optional embodiment of the technical solution of the present invention, in step (a), the temperature for atmospheric pressure settling is 40-45°C (e.g., 40°C, 42°C, or 45°C), and the settling time is 24-36 hours (e.g., 24 hours, 28 hours, 30 hours, 32 hours, or 36 hours). The purpose of atmospheric pressure settling under the aforementioned temperature conditions is mainly to reduce the viscosity of the electrolyte and accelerate electrolyte wetting.
[0028] As an optional embodiment of the technical solution of the present invention, in step (a), the temperature of the atmospheric pressure settling is higher than that of the negative pressure settling. The low-temperature settling first allows the electrolyte to slowly and fully wet the cells; the high-temperature settling then enhances penetration and promotes the initial formation of the electrode-electrolyte interface, laying the foundation for subsequent stable film formation and improving battery consistency and safety.
[0029] As an optional embodiment of the technical solution of the present invention, step (b) of performing constant current charging on the lithium iron phosphate battery after it has been left to stand in stages specifically includes: first charging the lithium iron phosphate battery after it has been left to stand in step (a) at a constant current of 0.08 to 0.12C (e.g., 0.08C, 0.1C, or 0.12C, etc.) to 1 to 1.4% SOC (e.g., 1% SOC, 1.2% SOC, 1.4% SOC, etc.), letting it stand for 5 to 10 minutes (e.g., 5 minutes, 8 minutes, or 10 minutes, etc.), and then charging it at a constant current of 0.15 to 0.2C (e.g., 0.15C, 0.18C, or 0.2C, etc.) to 34 to 36% SOC (e.g., 34% SOC, 35% SOC, or 36% SOC, etc.).
[0030] In step (b), the formation stage, a staged constant current charging method is used to form a stable SEI film, focusing on SEI film construction and gas removal. The current is adjusted step by step. First, a small current (e.g., 0.08C to 0.12C) is used to control the growth rate of the SEI film, making it dense and uniform. Then, a large current (e.g., 0.15C to 0.2C) is gradually used to quickly complete the main reaction. The formation process is then controlled so that the lithium iron phosphate battery does not exceed 50% SOC (e.g., 34 to 36% SOC), which is less than the half-charge stage. This is mainly because at this SOC state, the additives in the electrolyte (e.g., VC (ethylene carbonate), FEC (fluoroethylene carbonate), DTD (ethylene sulfate), TMSP (tris(trimethylsilane) phosphate), MMDS (methylene disulfonate), LiPO2F2 (lithium difluorophosphate), LiDFOB (lithium difluorooxalate borate), etc.) basically complete the film formation reaction, and also achieve the purpose of energy saving and cost control.
[0031] As an optional embodiment of the technical solution of the present invention, in step (b), constant current charging is performed under the condition of 40-45℃ (e.g., 40℃, 41℃, 42℃, 43℃, 44℃ or 45℃, etc.).
[0032] As an optional embodiment of the technical solution of the present invention, in step (c), the lithium iron phosphate battery formed in step (b) is first charged at a constant current of 0.008-0.01C (e.g., 0.008C, 0.009C, or 0.01C) for 20-30 minutes (e.g., 20 minutes, 22 minutes, 25 minutes, 28 minutes, or 30 minutes), and then discharged at a constant current of 0.008-0.01C (e.g., 0.008C, 0.009C, or 0.01C) for 20-30 minutes (e.g., 20 minutes, 22 minutes, 25 minutes, 28 minutes, or 30 minutes), and cycled for 2 weeks to complete the aging process. If the constant current charge and discharge current is too large (e.g., exceeding 0.01C), it is not conducive to the stability of the SEI film formed after formation, specifically manifested as accelerated cell capacity decay and increased internal resistance.
[0033] The aging charge / discharge time (including the sum of constant current charging and constant current discharging times) is controlled at around 2 hours, mainly to reduce production energy consumption. The end of aging can be determined by the K value (voltage decay rate) stabilizing (e.g., <0.1mV / h) or the internal resistance (e.g., EIS) change rate being <5% and stabilizing.
[0034] In step (c), aging requires very gentle charging and discharging to stabilize the internal structure of the cell, so as to control the SOC change before and after aging to <0.5%. For example, the SOC change after aging is 0.05%, 0.1%, 0.2%, 0.3%, or 0.4% relative to the SOC before aging.
[0035] As an optional embodiment of the technical solution of the present invention, in step (c), the aging temperature is 40-50°C, for example 40°C, 42°C, 45°C, 48°C or 50°C.
[0036] As an optional embodiment of the technical solution of the present invention, in step (d), the lithium iron phosphate battery is charged at a constant current and constant voltage of 0.5 to 1C (e.g., 0.5C, 0.6C, 0.7C, 0.8C, 0.9C, or 1C, etc.) until the cutoff voltage is 4.0 to 4.2V (4.0V, 4.1V, or 4.2V, etc.) and the cutoff current is 0.01 to 0.05C (e.g., 0.01C, 0.02C, 0.03C, 0.04C, or 0.05C, etc.) so that the lithium iron phosphate battery reaches 100% SOC.
[0037] If the cutoff voltage of constant current constant voltage charging (CCCV) is a conventional 3.65V, compared with a cutoff voltage of 4.0 to 4.2V, the capacity utilization during the charging process is relatively less.
[0038] As an optional embodiment of the technical solution of the present invention, step (d) specifically includes constant current discharge at different rates: first, constant current discharge at 0.8 to 1.2C (e.g., 0.8C, 1C, or 1.2C, etc.) to 2.5V, then constant current discharge at 0.1 to 0.5C (e.g., 0.1C, 0.2C, 0.4C, or 0.5C, etc.) to 2.5V, and finally constant current discharge at 0.01 to 0.05C (e.g., 0.01C, 0.02C, 0.04C, or 0.05C, etc.) to 2.5V.
[0039] When discharging to 2.5V at a constant current of 0.8–1.2C, polarization occurs due to the large current of 0.8–1.2C (e.g., 1C), and some of the capacity cannot be utilized. Therefore, constant current discharge is performed again with small currents of 0.1–0.5C (e.g., 0.1C) and 0.01–0.05C (e.g., 0.01C). The polarization effect and internal resistance have minimal impact, and the tested capacity is close to the "true capacity".
[0040] As an optional embodiment of the technical solution of the present invention, in step (d), constant current and constant voltage charging is performed under the conditions of 23 to 27°C (e.g., 23°C, 24°C, 25°C, 26°C or 27°C).
[0041] The present invention will now be described in further detail with reference to specific embodiments.
[0042] It should be noted that in the following embodiments and comparative examples, the positive electrode of the lithium iron phosphate pouch battery cell system is the lithium iron phosphate positive electrode, and the negative electrode is the graphite negative electrode.
[0043] Example 1 This embodiment provides a method for the formation and capacity testing of lithium iron phosphate batteries, which includes the following steps: (a) Settling after liquid injection: The lithium iron phosphate battery after liquid injection is first settled under negative pressure, and then settled under normal pressure; wherein, the pressure of negative pressure settling is -80kPa, the temperature of negative pressure settling is 40℃, and the time of negative pressure settling is 40min; the temperature of normal pressure settling is 45℃, and the time of normal pressure settling is 24h.
[0044] (b) Formation: The lithium iron phosphate battery after being left to stand in step (a) is charged at 45°C in stages with constant current. Specifically, the lithium iron phosphate battery is charged at a constant current of 0.1C to 1.2% SOC, and then charged at a constant current of 0.16C to 35% SOC. The lithium iron phosphate battery reaches 35% SOC after the constant current charging is completed. (c) Aging: The lithium iron phosphate battery formed in step (b) is charged at a constant current of 0.01C for 30 minutes, and then discharged at a constant current of 0.01C for 30 minutes. The cycle is repeated for 2 weeks to complete the aging process. The aging temperature is 45℃, and the change in SOC before and after aging is controlled to be <0.5% SOC. (d) Capacity testing: At 25°C, the lithium iron phosphate battery aged in step (c) is charged at a constant current and constant voltage of 0.5C, with a cutoff voltage of 4.1V and a cutoff current of 0.01C, so that the lithium iron phosphate battery reaches 100% SOC. Then, it is discharged at a constant current rate through different rates, specifically, first discharged at a constant current of 1C to 2.5V, then discharged at a constant current of 0.1C to 2.5V, and finally discharged at a constant current of 0.01C to 2.5V.
[0045] Example 2 This embodiment provides a method for forming and capacity testing a lithium iron phosphate battery. Except for step (c) aging, which involves charging the lithium iron phosphate battery formed in step (b) at a constant current of 0.008C for 30 minutes and then discharging it at a constant current of 0.008C for 30 minutes, and cycling for 2 weeks, the remaining steps are the same as in Example 1.
[0046] Example 3 This embodiment provides a method for the formation and capacity testing of lithium iron phosphate batteries. Except for step (c) aging, in which the lithium iron phosphate batteries formed in step (b) are charged at a constant current of 0.01C for 20 minutes and then discharged at a constant current of 0.01C for 20 minutes, and cycled for 2 weeks, the remaining steps are the same as in Example 1.
[0047] Example 4 This embodiment provides a method for the formation and capacity testing of lithium iron phosphate batteries. Except for step (a), which adjusts the temperature of the negative pressure settling period to 30°C, the other steps are the same as in Embodiment 1.
[0048] Example 5 This embodiment provides a method for the formation and capacity testing of lithium iron phosphate batteries, which includes the following steps: (a) Settling after liquid injection: The lithium iron phosphate battery after liquid injection is first settled under negative pressure, and then settled under normal pressure; the pressure of negative pressure settling is -70 kPa, the temperature of negative pressure settling is 25°C, and the time of negative pressure settling is 30 min; the temperature of normal pressure settling is 40°C, and the time of normal pressure settling is 32 h.
[0049] (b) Formation: The lithium iron phosphate battery after being left to stand in step (a) is charged at 45°C in stages with constant current. Specifically, the lithium iron phosphate battery is charged at a constant current of 0.08C to 1.0% SOC, and then charged at a constant current of 0.18C to 36% SOC. The lithium iron phosphate battery reaches 36% SOC after the constant current charging is completed. (c) Aging: The lithium iron phosphate batteries formed in step (b) are charged at a constant current of 0.009C for 25 minutes, and then discharged at a constant current of 0.009C for 25 minutes. This cycle is repeated for 2 weeks to complete the aging process. The aging temperature is 50°C, and the SOC change before and after aging is controlled to be <0.5%. (d) Capacity testing: At 25°C, the lithium iron phosphate battery aged in step (c) is charged at a constant current and constant voltage of 1C, with a cutoff voltage of 4.1V and a cutoff current of 0.01C, so that the lithium iron phosphate battery reaches 100% SOC. Then, it is discharged at different rates: first at 1.2C constant current to 2.5V, then at 0.2C constant current to 2.5V, and finally at 0.02C constant current to 2.5V.
[0050] Comparative Example 1 This comparative example provides a method for the formation and capacity testing of a lithium iron phosphate battery. Except for step (c), which involves aging the lithium iron phosphate battery formed in step (b) at 45°C for 12 hours (without performing low-current constant-current charging and discharging during the aging process), the other steps are the same as in Example 1.
[0051] Comparative Example 2 This comparative example provides a method for the formation and capacity testing of lithium iron phosphate batteries. Except for deleting the negative pressure settling step in step (a), the lithium iron phosphate batteries after liquid injection are directly settling at normal pressure. The temperature of the normal pressure settling is 45°C, and the time of the normal pressure settling is about 24.67h (i.e. 24h + 40min). The remaining steps are the same as in Example 1.
[0052] Comparative Example 3 This comparative example provides a method for the formation and capacity testing of a lithium iron phosphate battery. Except for step (d), in which the lithium iron phosphate battery aged in step (c) is charged with constant current and constant voltage at 0.5C and the cutoff voltage is 3.65V, the other steps are the same as in Example 1.
[0053] Comparative Example 4 This comparative example provides a method for the formation and capacity testing of a lithium iron phosphate battery. Except for step (c) aging, which involves charging the lithium iron phosphate battery formed in step (b) at a constant current of 0.015C for 30 minutes and then discharging it at a constant current of 0.015C for 30 minutes, cycling for 2 weeks, the remaining steps are the same as in Example 1.
[0054] Performance testing The ampere capacity rate (ACR), direct current resistance (DCR), and cycle performance of the lithium iron phosphate batteries after capacity testing in each embodiment and comparative example were tested. The specific testing steps are as follows: AC impedance testing method: The AC internal resistance of the battery cell at 20% SOC was tested at 25℃. A small-amplitude AC signal was applied across the battery terminals, and the AC response was measured. The AC impedance was measured at a frequency of 1kHz. The 20% SOC cell refers to the cell obtained by charging an empty battery cell to 20% SOC using a constant current of 1C after capacity testing according to the above examples and comparative models. Specific test results are shown in Table 1.
[0055] DC internal resistance test method: A battery cell at 50% SOC (State of Charge) was used for DC internal resistance testing. A 50% SOC cell refers to a cell obtained by discharging a fully charged cell at a constant current of 1C to 50% SOC after capacity testing as described in the above examples and comparative examples. The battery sample was then discharged using a 2C current (I) for a limited time of 10 seconds. The battery voltage before charging / discharging was recorded as U1, and the battery voltage after charging / discharging was recorded as U2. The DC internal resistance R was calculated as R = (U2 - U1) / I. Specific test results are shown in Table 1.
[0056] Cyclic performance testing method: The batteries of the above embodiments and comparative embodiments were tested at 45°C after capacity testing. The specific method is as follows: (1) Charge at a constant current of 1C to 3.65V and then switch to constant voltage charging until the charging current drops to 0.05C and stop charging. Let it stand for 30 minutes. (2) Discharge at a constant current of 1C to 2.5V and stop discharging. Let it stand for 30 minutes and record the discharge capacity. (3) Repeat steps (1) to (2) for 1500 cycles. Use the ratio of the discharge capacity after 1500 cycles to the initial discharge capacity as the discharge capacity retention rate. The specific test results are shown in Table 1.
[0057] Table 1. Performance of batteries obtained by the formation and capacity testing methods of the above embodiments and comparative examples.
[0058] A comparison of the performance data of Example 1 and Comparative Example 1 in Table 1 shows that after aging with low current, the cell's initial efficiency increased from 89.23% to 90.34%, DCR decreased from 22.89 mΩ to 20.44 mΩ, ACR decreased from 4.40 mΩ to 4.11 mΩ, and the discharge capacity retention rate after 1500 cycles at 45℃ (1C / 1C) increased from 83.99% to 84.51%. Furthermore, a comparison of the performance data of Example 1 and Comparative Example 4 in Table 1 shows that after aging with low current, the cell's initial efficiency increased from 89.97% to 90.34%, DCR decreased from 22.13 mΩ to 20.44 mΩ, ACR decreased from 4.38 mΩ to 4.11 mΩ, and the discharge capacity retention rate after 1500 cycles at 45℃ (1C / 1C) increased from 84.08% to 84.51%.
[0059] Furthermore, a comparison of the performance data of Example 1 and Comparative Example 2 in Table 1 shows that optimizing the static conditions after electrolyte injection (improving cell immersion) also improves the overall performance of the cell, although the improvement effect is slightly worse than that of aging with a small current.
[0060] Furthermore, a comparison of the performance data of Example 1 and Comparative Example 3 in Table 1 shows that the use of a high-voltage charging mechanism in the constant current constant voltage charging (CCCV) stage of capacity grading also improves the overall performance of the battery cell, although the improvement effect is slightly worse than that of using a low-current aging method.
[0061] Therefore, it can be seen that optimizing the post-filling static conditions, low-current aging, and the constant current constant voltage charging (CCCV) high-voltage charging mechanism in the first step of capacity grading can jointly optimize the capacity grading process, effectively improve the first efficiency, reduce DC impedance, reduce cell polarization, significantly improve cell performance, reduce cell temperature rise, and improve battery safety performance.
[0062] In this invention, the terms "one embodiment," "some embodiments," "example," "specific example," or "some examples," etc., refer to a specific feature, structure, material, or characteristic described in connection with that embodiment or example, which is included in at least one embodiment or example of the invention. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples. Moreover, without contradiction, those skilled in the art can combine and integrate the different embodiments or examples described in this specification, as well as the features of different embodiments or examples.
[0063] Although embodiments of the present invention have been shown and described above, it is understood that the above embodiments are exemplary and should not be construed as limiting the present invention. Those skilled in the art can make changes, modifications, substitutions and variations to the above embodiments within the scope of the present invention.
Claims
1. A method for the formation and capacity testing of lithium iron phosphate batteries, characterized in that, The formulation and compatibilization method includes the following steps: (a) The lithium iron phosphate battery after liquid injection is first placed under negative pressure and then placed under normal pressure to obtain the lithium iron phosphate battery after standing. (b) The settled lithium iron phosphate battery is charged with constant current until the constant current charging ends and the lithium iron phosphate battery does not exceed 50% SOC, thus obtaining the formed lithium iron phosphate battery. (c) The formed lithium iron phosphate battery is charged and discharged at a constant current of less than 0.01C until the aging is completed, and the aged lithium iron phosphate battery is obtained. (d) The aged lithium iron phosphate battery is charged to 100% SOC by constant current and constant voltage, and the cutoff voltage is set to 4.0 to 4.2V. Then, it is discharged by constant current at different rates.
2. The method for forming and capacity testing a lithium iron phosphate battery according to claim 1, characterized in that, In step (a), the pressure of the negative pressure settling is -60 to -80 kPa, the temperature of the negative pressure settling is 25 to 40 °C, and the time of the negative pressure settling is 30 to 40 min.
3. The method for forming and capacity testing a lithium iron phosphate battery according to claim 1, characterized in that, In step (a), the temperature for standing at normal pressure is 40-45℃, and the standing time at normal pressure is 24-36h.
4. The formation and capacity testing method for lithium iron phosphate batteries according to claim 1, characterized in that, In step (b), constant current charging ends when the lithium iron phosphate battery reaches 34-36% SOC.
5. The method for forming and capacity testing a lithium iron phosphate battery according to claim 1, characterized in that, In step (b), the process of performing constant current charging on the lithium iron phosphate battery after it has been left to stand includes: first charging the lithium iron phosphate battery after it has been left to stand to 1-1.4% SOC at a constant current of 0.08-0.12C, letting it stand for 5-10 minutes, and then charging it to 34-36% SOC at a constant current of 0.15-0.2C.
6. The method for forming and capacity testing a lithium iron phosphate battery according to claim 1, characterized in that, In step (c), the formed lithium iron phosphate battery is first charged at a constant current of 0.008-0.01C for 20-30 minutes, and then discharged at a constant current of 0.008-0.01C for 20-30 minutes. This cycle is repeated for 2 weeks to complete the aging process.
7. The method for forming and capacity testing a lithium iron phosphate battery according to claim 6, characterized in that, In step (c), the change in SOC before and after aging is controlled to be <0.5% SOC; and / or, in step (c), the aging temperature is 40-50℃.
8. The method for forming and capacity testing a lithium iron phosphate battery according to claim 6, characterized in that, In step (d), the lithium iron phosphate battery is charged at a constant current and constant voltage of 0.5 to 1C until the cutoff voltage is 4.0 to 4.2V and the cutoff current is 0.01 to 0.05C, so that the lithium iron phosphate battery reaches 100% SOC.
9. The method for forming and capacity testing a lithium iron phosphate battery according to any one of claims 1 to 8, characterized in that, In step (d), the constant current discharge at different rates specifically includes: first, constant current discharge at 0.8 to 1.2C to 2.5V, then constant current discharge at 0.1 to 0.5C to 2.5V, and finally constant current discharge at 0.01 to 0.05C to 2.5V.
10. The application of the formation and capacity testing method for lithium iron phosphate batteries according to any one of claims 1 to 9 in the field of lithium-ion battery preparation or testing.