Lithium ion battery formation and grading method capable of shortening k value test period and application

Abstract

The application provides a lithium ion battery formation and grading method and application capable of shortening a K value test period, and relates to the technical field of batteries. The lithium ion battery formation and grading method only utilizes negative pressure grading during grading, and adjusts the front and back sequences of the negative pressure grading in a process flow, that is, adjusts the negative pressure grading between negative pressure formation and high temperature aging, thereby greatly shortening the first normal temperature standing time of the battery cell, reducing the first normal temperature standing time from the traditional 48-72h to 4-6h, and significantly shortening the K value test period. The application also provides the application of the above-mentioned lithium ion battery formation and grading method. In view of the advantages of the above-mentioned lithium ion battery formation and grading method, the application has good application in the production process of lithium ion batteries, can shorten the battery process period, and effectively improves the production capacity.

Description

Technical Field

[0001] This invention belongs to the field of battery technology and relates to a lithium-ion battery formation and capacity testing method and its application that can shorten the K-value testing cycle. Background Technology

[0002] The typical mid-to-late stage manufacturing process for battery cells is as follows: negative pressure formation → aging → secondary injection → helium filling and nailing → sealing nail welding → capacity grading → first 48-hour rest at room temperature → OCV1 test → second 72-hour rest at room temperature → OCV2 test. The OCV (Open Circuit Voltage) test measures the battery voltage in an open-circuit (no current flowing) state. By testing the open-circuit voltage for different times using OCV1 and OCV2, the voltage drop per unit time, i.e., the K value, can be calculated, reflecting the consistency of cell voltage drop and used to measure the battery's self-discharge.

[0003] In the aforementioned production process, the first room temperature resting, OCV1 test, second room temperature resting, and OCV2 test are typically considered as K-value testing steps. Because the cells become polarized after capacity grading, the first room temperature resting usually requires a relatively long time, such as 48–72 hours, to eliminate the adverse effects of this polarization on the K-value test and to maintain a constant cell temperature. This results in a long K-value testing cycle, accounting for approximately one-quarter of the total cell manufacturing cycle, which not only increases the production cost but also affects the cell yield.

[0004] In view of this, the present invention is hereby proposed. Summary of the Invention

[0005] In view of the shortcomings and defects of the existing technology, the present invention aims to provide a lithium-ion battery formation and capacity testing method and application that can shorten the K-value testing cycle.

[0006] To achieve the above objectives, the following technical solution is adopted:

[0007] The first objective of this invention is to provide a lithium-ion battery formation and capacity testing method that can shorten the K-value testing cycle, comprising the following steps:

[0008] S1. The lithium-ion battery cell that has completed one liquid injection and settling is then subjected to negative pressure formation;

[0009] S2. Perform negative voltage capacity testing on the cells after negative voltage formation;

[0010] S3. After the negative voltage capacity test, the battery cells are subjected to high-temperature aging, followed by secondary electrolyte injection and sealing;

[0011] S4. After sealing, the battery cell is subjected to OCV1 test after the first resting at room temperature, and then to OCV2 test after the second resting at room temperature. The K value of the battery cell is calculated. The first resting time at room temperature is 4-6 hours, and the second resting time at room temperature is 72-96 hours.

[0012] Furthermore, based on the above technical solution of the present invention, in step S1, the amount of liquid injected in one injection is 88-93 wt% of the total amount of liquid injected into the lithium-ion battery.

[0013] And / or, in step S1, the settling temperature is 40-50℃ and the settling time is 22-26h.

[0014] Furthermore, based on the above-described technical solution of this invention, in step S1, the negative pressure formation is carried out at a temperature of 45±5℃, specifically as follows:

[0015] Let it sit for 2-5 minutes;

[0016] Charge at a constant current of 0.1-0.2C for 30-50 minutes, with the negative pressure controlled at 45±5 kPa during the process;

[0017] Let it sit for 2-5 minutes;

[0018] Charge at a constant current of 0.2-0.3C for 50-90 minutes, with the negative pressure controlled at 85±5 kPa during the process;

[0019] Let it sit for 2-5 minutes, then it's done.

[0020] Furthermore, based on the above-mentioned technical solution of the present invention, in step S2, the cell after negative pressure formation is first replenished with liquid, and then negative pressure capacity testing is performed. The amount of liquid replenished is 7-12 wt% of the total liquid volume of the lithium-ion battery.

[0021] Furthermore, based on the above-mentioned technical solution of the present invention, in step S2, the negative pressure volume division is carried out at a temperature of 25±3℃ and a negative pressure of 45±5Kpa, as follows:

[0022] Let it sit for 2-5 minutes;

[0023] Constant current and constant voltage charging: charging current 0.5-1C, charging time 120-180min, cut-off current 0.05-0.1C, cut-off voltage 3.65-4.40V;

[0024] Let it sit for 2-5 minutes;

[0025] Constant current discharge: discharge current 0.5-1.0C, discharge time 120-180min, cutoff voltage 2.0-3.0V;

[0026] Let it sit for 2-5 minutes;

[0027] Constant current discharge: discharge current 0.2-0.5C, discharge time 120-180min, cutoff voltage 2.0-3.0V;

[0028] Let it sit for 2-5 minutes;

[0029] Constant current charging: charging current 0.2-0.5C, charging time 20-35min, cutoff voltage 3.0-4.0V;

[0030] Let it sit for 2-5 minutes, then it's done.

[0031] Furthermore, based on the above technical solution of the present invention, in step S3, the high-temperature aging temperature is 40-50℃ and the time is 22-26h.

[0032] Furthermore, based on the above technical solution of the present invention, in step S3, the amount of liquid injected in the secondary injection is 1-5 wt% of the total amount of liquid injected into the lithium-ion battery.

[0033] And / or, in step S3, the sealing includes the steps of helium filling and nailing, and welding of the sealing nails.

[0034] Furthermore, based on the above technical solution of the present invention, in step S4, the first time to stand at room temperature is 4-5 hours;

[0035] And / or, in step S4, the second standing time at room temperature is 72-90 hours.

[0036] Furthermore, based on the above-described technical solution of the present invention, in step S4, the K value is calculated using the following formula (1):

[0037] K=(OCV1- OCV2) / (t2- t1) (1)

[0038] Where OCV1 is the cell voltage of the first test; t1 is the time of the first test; OCV2 is the cell voltage of the second test; and t2 is the time of the second test.

[0039] The second objective of this invention is to provide the application of the above-mentioned lithium-ion battery formation and capacity testing method in the production of lithium-ion batteries.

[0040] Compared with the prior art, the technical solution of the present invention has at least the following technical effects:

[0041] (1) This invention provides a lithium-ion battery formation and capacity testing method. During capacity testing, only negative pressure capacity testing is used. By adjusting the sequence of negative pressure capacity testing in the process flow—specifically, adjusting it between negative pressure formation and high-temperature aging—the time for the cell to first rest at room temperature is significantly shortened from the traditional 48-72 hours to 4-6 hours. This method optimizes the cell manufacturing process, shortens the entire cell manufacturing cycle, and effectively improves cell production capacity.

[0042] (2) The present invention provides the application of the above-mentioned lithium-ion battery formation and capacity testing method. Given the advantages of the above-mentioned lithium-ion battery formation and capacity testing method, it has good application in the lithium-ion battery production process, which can shorten the battery process cycle and effectively improve production capacity. Detailed Implementation

[0043] 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.

[0044] 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.

[0045] According to a first aspect of the present invention, a lithium-ion battery formation and capacity testing method that can shorten the K-value testing cycle is provided, comprising the following steps:

[0046] S1. The lithium-ion battery cell that has completed one liquid injection and settling is then subjected to negative pressure formation;

[0047] S2. Perform negative voltage capacity testing on the cells after negative voltage formation;

[0048] S3. After the negative voltage capacity test, the battery cells are subjected to high-temperature aging, followed by secondary electrolyte injection and sealing;

[0049] S4. After sealing, the battery cell undergoes an OCV1 test after the first settling at room temperature, and then an OCV2 test after the second settling at room temperature. The K value of the battery cell is then calculated. The first settling time at room temperature is 4-6 hours (e.g., 4h, 4.5h, 5h, 5.5h, or 6h), and the second settling time at room temperature is 72-96 hours (e.g., 72h, 75h, 78h, 82h, 86h, 88h, 90h, 92h, 94h, or 96h).

[0050] Unlike conventional processes, this invention performs negative pressure capacity grading directly after negative pressure formation. During the initial full charge (formation + capacity grading to 100% SOC), the battery cell continuously generates gas, which can affect its cycle performance. Using negative pressure during formation and capacity grading helps to extract the waste gas from the battery cell, reducing the impact on cell performance.

[0051] After negative voltage capacity testing, the battery cell will develop polarization, which will affect the open circuit voltage and cause the K-value test result to be too high, thus leading to mismeasurement of the K-value. In order to eliminate the polarization of the battery cell after capacity testing, conventional processes usually require a relatively long first room temperature resting time after capacity testing, such as 48-72 hours. Unlike conventional processes, this invention directly performs high-temperature aging after negative voltage capacity testing. After capacity testing, the battery cell will experience concentration polarization due to the inability to replenish the electrode surface in time due to the consumption of reactants. The high-temperature environment of the subsequent high-temperature aging process can accelerate the thermal movement of the reactants and quickly eliminate the polarization phenomenon. Therefore, after the high-temperature aging process, the battery cell does not need to undergo a long resting time after secondary electrolyte injection and sealing. Only 4-6 hours of resting is required during the first room temperature resting time. This can greatly shorten the room temperature resting time and the K-value test cycle, thereby reducing the overall battery cell manufacturing cycle.

[0052] The lithium-ion battery formation and capacity testing method provided by this invention utilizes only negative pressure capacity testing during the process. By adjusting the sequence of negative pressure capacity testing in the process flow—specifically, placing it between negative pressure formation and high-temperature aging—the initial room-temperature resting time of the battery cell is significantly shortened from the traditional 48-72 hours to 4-6 hours. This method optimizes the battery cell manufacturing process, shortens the entire process cycle, and effectively improves battery cell production capacity.

[0053] Before the negative pressure formation of lithium-ion cells, a liquid injection is performed. The relevant process parameters for the liquid injection include: static negative pressure -20 to -150 kPa and negative pressure time 10 to 100 seconds (s); static positive pressure 200 to 900 kPa and positive pressure time 100 to 400 seconds (s); the above alternation of negative and positive pressure constitutes one cycle, and a total of 1 to 20 cycles are performed.

[0054] During a single injection, typical but non-restrictive static negative pressures are -20 kPa, -40 kPa, -50 kPa, -60 kPa, -80 kPa, -100 kPa, -120 kPa, -140 kPa, or -150 kPa, etc., and typical but non-restrictive negative pressure durations are 10 s, 20 s, 40 s, 50 s, 60 s, 80 s, or 100 s, etc.; typical but non-restrictive static positive pressures are 200 kPa, 30 kPa, etc. 0 kPa, 400 kPa, 500 kPa, 600 kPa, 700 kPa, 800 kPa or 900 kPa, etc., with typical but non-restrictive positive pressure times of 100 s, 150 s, 200 s, 250 s, 300 s, 350 s or 400 s, etc.; and typical but non-restrictive number of cycles of 1, 2, 3, 5, 6, 8, 10, 14, 15, 16, 18 or 20, etc.

[0055] The amount of electrolyte injected in a single injection varies slightly for different battery systems, but the difference is not significant. As an optional embodiment of the present invention, in step S1, the amount of electrolyte injected in a single injection is 88-93 wt% of the total electrolyte volume of the lithium-ion battery, for example, 88 wt%, 89 wt%, 90 wt%, 91 wt%, 92 wt%, or 93 wt%, or any value range between any two points.

[0056] After one injection, the solution is allowed to stand. In an optional embodiment of the invention, in step S1, the standing temperature is 40-50°C, and the standing time is 22-26 hours. Typical but non-limiting standing temperatures include 40°C, 42°C, 44°C, 45°C, 48°C, or 50°C, and any range between any two points; typical but non-limiting standing times include 22 hours, 23 hours, 24 hours, 26 hours, and any range between any two points.

[0057] The process conditions for negative pressure formation of lithium-ion cells have also been optimized to some extent. As an optional embodiment of the present invention, in step S1, negative pressure formation includes the following process performed at a temperature of 45±5℃:

[0058] Let it rest for 2-5 minutes (e.g., 2 minutes, 3 minutes, 4 minutes, or 5 minutes, etc.);

[0059] Charge at a constant current of 0.1-0.2C (e.g., 0.1C, 0.15C, 0.2C, etc.) for 30-50 minutes (e.g., 30 minutes, 40 minutes, or 50 minutes, etc.), with the negative pressure controlled at 45±5 kPa (e.g., 40 kPa, 42 kPa, 45 kPa, 48 kPa, or 50 kPa, etc.) during this process;

[0060] Let it rest for 2-5 minutes (e.g., 2 minutes, 3 minutes, 4 minutes, or 5 minutes, etc.);

[0061] Charge at a constant current of 0.2-0.3C (e.g., 0.2C, 0.25C, 0.3C, etc.) for 50-90 minutes (e.g., 50 minutes, 60 minutes, 70 minutes, 80 minutes, or 90 minutes, etc.), with the negative pressure controlled at 85±5 kPa (e.g., 80 kPa, 82 kPa, 85 kPa, 88 kPa, or 90 kPa, etc.) during this process;

[0062] Let it sit for 2-5 minutes (e.g., 2 minutes, 3 minutes, 4 minutes, or 5 minutes), then it's done.

[0063] Considering that electrolyte loss may occur during the negative pressure capacity testing process, which may result in insufficient free electrolyte in the cell and lithium plating may occur in some areas of the cell, as an optional embodiment of the present invention, in step S2, the cell after negative pressure formation is first replenished with electrolyte and then negative pressure capacity testing is performed. The amount of electrolyte replenished is 7-12 wt% of the total electrolyte volume of the lithium-ion battery, for example, 7 wt%, 8 wt%, 9 wt%, 10 wt%, 11 wt%, or 12 wt%, etc., and any numerical range between any two points.

[0064] As an optional embodiment of the present invention, in step S2, the negative pressure volume division is carried out at a temperature of 25±3℃ (e.g., 22℃, 25℃, or 28℃) and a negative pressure of 45±5Kpa (e.g., 40Kpa, 42Kpa, 45Kpa, 48Kpa, or 50Kpa), as detailed below:

[0065] Let it rest for 2-5 minutes (e.g., 2 minutes, 3 minutes, 4 minutes, or 5 minutes, etc.);

[0066] Constant current and constant voltage charging (CV): charging current 0.5-1C (e.g., 0.5C, 0.6C, 0.8C, or 1C), charging time 120-180min (e.g., 120min, 130min, 150min, 160min, or 180min), cutoff current 0.05-0.1C (e.g., 0.05C, 0.06C, 0.08C, or 0.1C), cutoff voltage 3.65-4.40V (e.g., 3.65V, 3.80V, 4.00V, 4.10V, 4.20V, 4.30V, or 4.40V);

[0067] Let it rest for 2-5 minutes (e.g., 2 minutes, 3 minutes, 4 minutes, or 5 minutes, etc.);

[0068] Constant current discharge (DV): Discharge current 0.5-1.0C (e.g., 0.5C, 0.6C, 0.8C, or 1C), discharge time 120-180min (e.g., 120min, 130min, 150min, 160min, or 180min), cutoff voltage 2.0-3.0V (e.g., 2.0V, 2.2V, 2.4V, 2.5V, 2.6V, 2.8V, or 3.0V);

[0069] Let it rest for 2-5 minutes (e.g., 2 minutes, 3 minutes, 4 minutes, or 5 minutes, etc.);

[0070] Constant current discharge (DC): Discharge current 0.2-0.5C (e.g., 0.2C, 0.3C, 0.4C, or 0.5C), discharge time 120-180min (e.g., 120min, 130min, 150min, 160min, or 180min), cutoff voltage 2.0-3.0V (e.g., 2.0V, 2.2V, 2.4V, 2.5V, 2.6V, 2.8V, or 3.0V);

[0071] Let it rest for 2-5 minutes (e.g., 2 minutes, 3 minutes, 4 minutes, or 5 minutes, etc.);

[0072] Constant current charging (CC): charging current 0.2-0.5C (e.g., 0.2C, 0.3C, 0.4C, or 0.5C), charging time 20-35min (e.g., 20min, 25min, 30min, or 35min), cutoff voltage 3.0-4.0V (e.g., 3.0V, 3.2V, 3.4V, 3.5V, 3.6V, 3.8V, or 4.0V);

[0073] Let it sit for 2-5 minutes (e.g., 2 minutes, 3 minutes, 4 minutes, or 5 minutes), then it's done.

[0074] After negative voltage capacity testing, the battery cells undergo high-temperature aging, and the process conditions for high-temperature aging are optimized to some extent. As an optional embodiment of the present invention, in step S3, the high-temperature aging temperature is 40-50℃, and the time is 22-26 hours. Typical but non-limiting high-temperature aging temperatures are 40℃, 42℃, 44℃, 45℃, 48℃, or 50℃, and any range between any two points; typical but non-limiting high-temperature aging times are 22 hours, 23 hours, 24 hours, or 26 hours, and any range between any two points.

[0075] The amount of liquid injected for secondary injection is usually calculated based on the amount injected during primary injection and the amount replenished before negative pressure capacity testing. As an optional embodiment of the present invention, in step S3, the amount of liquid injected for secondary injection is 1-5 wt% of the total amount of liquid injected into the lithium-ion battery, for example, 1 wt%, 2 wt%, 3 wt%, 4 wt%, or 5 wt%, or any value range between any two points.

[0076] After the second injection is completed, the opening can be sealed. In an optional embodiment of the present invention, step S3 includes helium filling and nailing, as well as welding the sealing nails.

[0077] After the battery cell is sealed, it enters the battery cell K-value testing process. As an optional embodiment of the present invention, in step S4, the first standing time at room temperature is 4-5 hours, preferably 4 hours.

[0078] As an optional embodiment of the present invention, in step S4, the second standing time at room temperature is 72-90 hours.

[0079] As an optional embodiment of the present invention, in step S4, the value of K is calculated using the following formula (1):

[0080] K=(OCV1- OCV2) / (t2- t1) (1)

[0081] Where OCV1 is the cell voltage of the first test; t1 is the time of the first test; OCV2 is the cell voltage of the second test; and t2 is the time of the second test.

[0082] According to a second aspect of the present invention, the application of the lithium-ion battery formation and capacity testing method provided in the first aspect of the present invention in the production of lithium-ion batteries is also provided.

[0083] Given the advantages of the lithium-ion battery formation and capacity testing method provided by this invention, it has good application in the lithium-ion battery production process, which can shorten the battery process cycle and effectively improve production capacity.

[0084] The present invention will now be described in further detail with reference to specific embodiments and comparative examples.

[0085] Example 1

[0086] This embodiment provides a method for the formation and capacity testing of lithium-ion batteries (lithium iron phosphate), including the following steps:

[0087] S1. Perform one injection of lithium-ion battery cell: first, place under negative pressure of -70Kpa for 30s, then place under positive pressure of 450Kpa for 120s. The alternation of negative and positive pressure constitutes one cycle, and the cycle is repeated 10 times. The amount of liquid injected in one cycle is 345-355g.

[0088] After one injection, the lithium-ion battery cell is left to stand: the standing temperature is 45±5℃ and the standing time is 22-26h.

[0089] The lithium-ion cells, after being left to stand, are placed in a formation cabinet (temperature 45±5℃) for negative pressure formation, as follows:

[0090] Let it sit for 2 minutes first;

[0091] The device was charged at a constant current of 10A (CC) for 40 minutes, with the negative pressure controlled at 45±5Kpa during the process.

[0092] Let it sit for another 2 minutes;

[0093] Then it is charged with a constant current of 30A (CC) for 90 minutes, during which the negative pressure is controlled at 85±5Kpa;

[0094] Let it sit for 2 minutes, then it's done.

[0095] S2. Replenish the electrolyte in the cell after negative pressure formation: First, place it under negative pressure of -70Kpa for 30s, then place it under positive pressure of 450Kpa for 120s. The alternation of negative and positive pressure constitutes one cycle, and the cycle is repeated twice. The amount of electrolyte replenished is 45-55g.

[0096] Then, after replenishing the electrolyte, the battery cells were subjected to negative pressure capacity testing at a temperature of 25±3℃ and a negative pressure of 45±5Kpa, as detailed below:

[0097] Let it sit for 5 minutes first;

[0098] Constant current and constant voltage charging (CV): charging current 50A, charging time 180min, cut-off current 5A, cut-off voltage 3.65V;

[0099] Let it sit for 5 minutes;

[0100] Constant current discharge (DC): discharge current 50A, discharge time 180min, cutoff voltage 2.5V;

[0101] Let it sit for 5 minutes;

[0102] Constant current discharge (DC): discharge current 50A, discharge time 180min, cutoff voltage 2.5V;

[0103] Let it sit for 5 minutes;

[0104] Constant current charging (CC): charging current 50A, charging time 25min, cutoff voltage 3.5V;

[0105] Let it sit for 5 minutes, then it's done.

[0106] S3. Perform high-temperature aging on the cells after negative voltage capacity testing: temperature 45±5℃, time 22-26h;

[0107] For the battery cells that have been aged at high temperature, perform a second electrolyte injection: first, place them under negative pressure of -70 kPa for 30 seconds, then place them under positive pressure of 450 kPa for 120 seconds. The alternation of negative and positive pressure constitutes one cycle, and the cycle is repeated twice. The amount of electrolyte added is 15-35 g.

[0108] After the second electrolyte injection, the battery cell is sealed: helium filling and nailing, and sealing nail welding;

[0109] S4. After sealing, the battery cell is left to stand at room temperature for the first time: the standing temperature is 25±3℃ and the standing time is 4h.

[0110] After the first resting at room temperature, the battery cells were tested for OCV1: OCV1 was 3.2532~3.2599V, DC internal resistance (IMP) was 0.2687~0.2781mΩ, and side voltage was -0.02~0.043mV;

[0111] Then, a second settling process was carried out at room temperature: the settling temperature was 25±3℃, and the settling time was 72 hours.

[0112] After the cells were left to stand at room temperature for the second time, an OCV2 test was conducted: OCV2 was 3.2503~3.2575V, DC internal resistance (IMP) was 0.2669~0.2843mΩ, and side voltage was -0.017~0.0432mV.

[0113] It should be noted that when performing the above-mentioned cell testing and capacity testing, multiple cells from the same batch are tested simultaneously. Therefore, the OCV, DC internal resistance, and side voltage obtained during OCV1 and OCV2 tests are expressed as numerical ranges.

[0114] Example 2

[0115] This embodiment provides a method for the formation and capacity testing of lithium-ion batteries (lithium iron phosphate). Except for adjusting the first room temperature standing time from 4 hours to 5 hours, the other steps and process parameters are the same as in Embodiment 1.

[0116] Example 3

[0117] This embodiment provides a method for the formation and capacity testing of lithium-ion batteries (lithium iron phosphate). Except for adjusting the first room temperature standing time from 4 hours to 6 hours, the other steps and process parameters are the same as in Embodiment 1.

[0118] Example 4

[0119] This embodiment provides a method for the formation and capacity testing of a lithium-ion battery (ternary material 811), including the following steps:

[0120] S1. Perform one injection of lithium-ion battery cell: first, stand under negative pressure of -80Kpa for 50s, then stand under positive pressure of 500Kpa for 150s. The alternation of negative and positive pressure constitutes one cycle, and the cycle is repeated 14 times. The injection volume is 505-515g.

[0121] After one injection, the lithium-ion battery cell is left to stand: the standing temperature is 45±5℃ and the standing time is 22-26h.

[0122] The lithium-ion cells, after being left to stand, are placed in a formation cabinet (temperature 45±5℃) for negative pressure formation, as follows:

[0123] Let it sit for 2 minutes first;

[0124] The device was charged at a constant current of 14.4A (CC) for 40 minutes, with the negative pressure controlled at 45±5 kPa during the process.

[0125] Let it sit for another 2 minutes;

[0126] The device was charged at a constant current of 43.2A (CC) for 50 minutes, with the negative pressure controlled at 85±5Kpa during the process.

[0127] Let it sit for 2 minutes;

[0128] The device was charged at a constant current of 72A (CC) for 32 minutes, with the negative pressure controlled at 85±5Kpa during the process.

[0129] Let it sit for 2 minutes, then it's done.

[0130] S2. Replenish the electrolyte in the cell after negative pressure formation: First, place it under negative pressure of -80Kpa for 50s, then place it under positive pressure of 500Kpa for 150s. The alternation of negative and positive pressure constitutes one cycle. Repeat the cycle twice. The amount of electrolyte replenished is 60-70g.

[0131] Then, after replenishing the electrolyte, the battery cells were subjected to negative pressure capacity testing at a temperature of 25±3℃ and a negative pressure of 45±5Kpa, as detailed below:

[0132] Let it sit for 5 minutes first;

[0133] Constant current and constant voltage charging (CV): charging current 72A, charging time 180min, cut-off current 7.2A, cut-off voltage 4.25V;

[0134] Let it sit for 5 minutes;

[0135] Constant current discharge (DC): discharge current 72A, discharge time 180min, cutoff voltage 3.0V;

[0136] Let it sit for 5 minutes;

[0137] Constant current discharge (DC): discharge current 72A, discharge time 180min, cutoff voltage 3.0V;

[0138] Let it sit for 5 minutes;

[0139] Constant current charging (CC): charging current 72A, charging time 25min, cutoff voltage 4.0V;

[0140] Let it sit for 5 minutes, then it's done.

[0141] S3. Perform high-temperature aging on the cells after negative voltage capacity testing: temperature 45±5℃, time 22-26h;

[0142] For the battery cells that have been aged at high temperature, perform a second electrolyte injection: first, place them under negative pressure of -80 kPa for 50 seconds, then place them under positive pressure of 500 kPa for 150 seconds. The alternation of negative and positive pressure constitutes one cycle, and the cycle is repeated twice. The amount of electrolyte added is 15-35 g.

[0143] After the second electrolyte injection, the battery cell is sealed: helium filling and nailing, and sealing nail welding;

[0144] S4. After sealing, the battery cell is left to stand at room temperature for the first time: the standing temperature is 25±3℃ and the standing time is 4 hours.

[0145] After the first resting at room temperature, the battery cells were tested for OCV1: OCV1 was 3.5771~3.5843V, DC internal resistance (IMP) was 0.2445~0.2643mΩ, and side voltage was -0.0115~0.0512mV.

[0146] Then, a second settling process was carried out at room temperature: 25±3℃, for 72 hours.

[0147] After the cells were left to stand at room temperature for the second time, an OCV2 test was conducted: OCV2 was 3.5736~3.5811V, DC internal resistance (IMP) was 0.2448~0.2642mΩ, and side voltage was -0.0132~0.0528mV.

[0148] Comparative Example 1

[0149] This comparative example provides a method for the formation and capacity testing of a lithium-ion battery (lithium iron phosphate). Except for adjusting the first room temperature standing time from 4 hours to 1 hour, the other steps and process parameters are the same as in Example 1.

[0150] Comparative Example 2

[0151] This comparative example provides a method for the formation and capacity testing of a lithium-ion battery (lithium iron phosphate). Except for adjusting the first room temperature standing time from 4 hours to 2 hours, the other steps and process parameters are the same as in Example 1.

[0152] Comparative Example 3

[0153] This comparative example provides a method for the formation and capacity testing of a lithium-ion battery (lithium iron phosphate). Except for adjusting the first room temperature standing time from 4 hours to 3 hours, the other steps and process parameters are the same as in Example 1.

[0154] Comparative Example 4

[0155] This comparative example provides a method for the formation and capacity testing of a lithium-ion battery (lithium iron phosphate). Except for adjusting the first room temperature standing time from 4 hours to 7 hours, the other steps and process parameters are the same as in Example 1.

[0156] Comparative Example 5

[0157] This comparative example provides a method for the formation and capacity testing of a lithium-ion battery (lithium iron phosphate). Except for adjusting the first room temperature standing time from 4 hours to 8 hours, the other steps and process parameters are the same as in Example 1.

[0158] Comparative Example 6

[0159] This comparative example provides a method for the formation and capacity testing of a lithium-ion battery (lithium iron phosphate), including the following steps:

[0160] S1. Perform one injection of lithium-ion cells: first, place under negative pressure of -70Kpa for 30s, then place under positive pressure of 450Kpa for 120s, repeat 10 times, and inject 345-355g of electrolyte each time.

[0161] After one injection, the lithium-ion battery cell is left to stand: standing temperature 45±5℃, time 22-26h;

[0162] The lithium-ion cells, after being left to stand, are placed in a formation cabinet (temperature 45±5℃) for negative pressure formation, as follows:

[0163] Let it sit for 2 minutes first;

[0164] The device was charged at a constant current of 10A (CC) for 40 minutes, with the negative pressure controlled at 45±5Kpa during the process.

[0165] Let it sit for another 2 minutes;

[0166] Then it is charged with a constant current of 30A (CC) for 90 minutes, during which the negative pressure is controlled at 85±5Kpa;

[0167] Let it sit for 2 minutes, then it's done.

[0168] S2. High-temperature aging of the cells after negative voltage formation: temperature 45±5℃, time 22-26h;

[0169] After high-temperature aging, the battery cells are injected with electrolyte a second time: first, they are placed under negative pressure of -70Kpa for 30s, then under positive pressure of 450Kpa for 120s. This process is repeated twice, with a total electrolyte replenishment volume of 45-55g.

[0170] After the second electrolyte injection, the battery cell is sealed: helium filling and nailing, and sealing nail welding;

[0171] S3. After sealing, the battery cells are subjected to atmospheric pressure capacity testing at 25±3℃, as detailed below:

[0172] Let it sit for 5 minutes;

[0173] Constant current and constant voltage charging (CV): charging current 50A, charging time 180min, cut-off current 5A, cut-off voltage 3.65V;

[0174] Let it sit for 5 minutes;

[0175] Constant current discharge (DC): discharge current 50A, discharge time 180min, cutoff voltage 2.5V;

[0176] Let it sit for 5 minutes;

[0177] Constant current discharge (DC): discharge current 50A, discharge time 180min, cutoff voltage 2.5V;

[0178] Let it sit for 5 minutes;

[0179] Constant current charging (CC): charging current 50A, charging time 25min, cutoff voltage 3.5V;

[0180] Let it sit for 5 minutes, then it's done.

[0181] S4. Allow the cells after capacity testing to stand at room temperature for the first time: temperature 25±3℃, time 48h;

[0182] After the first resting at room temperature, the battery cells underwent an OCV1 test: OCV1 was 3.2592~3.2641V, DC internal resistance (IMP) was 0.2738~0.2868mΩ, and the side voltage was -0.02~0.043mV.

[0183] Then, a second settling process was carried out at room temperature: the settling temperature was 25±3℃ and the settling time was 72 hours.

[0184] After the second period of resting at room temperature, the cells were subjected to OCV2 testing: OCV2 was 3.2566~3.2616V, DC internal resistance (IMP) was 0.2645~0.2874mΩ, and side voltage was -0.0189~0.0452mV.

[0185] Comparative Example 7

[0186] This comparative example provides a method for the formation and capacity testing of a lithium-ion battery (ternary material 811), including the following steps:

[0187] S1. Perform one injection of lithium-ion battery cell: first, stand under negative pressure of -80Kpa for 50s, then stand under positive pressure of 500Kpa for 150s. The alternation of negative and positive pressure constitutes one cycle, and the cycle is repeated 14 times. The injection volume is 505-515g.

[0188] After one injection, the lithium-ion battery cell is left to stand: standing temperature 45±5℃, time 22-26h;

[0189] The lithium-ion cells, after being left to stand, are placed in a formation cabinet (temperature 45±5℃) for negative pressure formation, as follows:

[0190] Let it sit for 2 minutes first;

[0191] The device was charged at a constant current of 14.4A (CC) for 40 minutes, with the negative pressure controlled at 45±5 kPa during the process.

[0192] Let it sit for another 2 minutes;

[0193] The device was charged at a constant current of 43.2A (CC) for 50 minutes, with the negative pressure controlled at 85±5Kpa during the process.

[0194] Let it sit for 2 minutes;

[0195] The device was charged at a constant current of 72A (CC) for 32 minutes, with the negative pressure controlled at 85±5Kpa during the process.

[0196] Let it sit for 2 minutes, then it's done.

[0197] S2. High-temperature aging of the cells after negative voltage formation: temperature 45±5℃, time 22-26h;

[0198] After high-temperature aging, the battery cells are injected with electrolyte a second time: first, they are placed under negative pressure of -80Kpa for 50s, then under positive pressure of 500Kpa for 150s. The alternation of negative and positive pressure constitutes one cycle, and the cycle is repeated twice. The amount of electrolyte added is 60-70g.

[0199] After the second electrolyte injection, the battery cell is sealed: helium filling and nailing, and sealing nail welding;

[0200] S3. After sealing, the battery cells are subjected to atmospheric pressure capacity testing at 25±3℃, as detailed below:

[0201] Let it sit for 5 minutes first;

[0202] Constant current and constant voltage charging (CV): charging current 72A, charging time 180min, cut-off current 7.2A, cut-off voltage 4.25V;

[0203] Let it sit for 5 minutes;

[0204] Constant current discharge (DC): discharge current 72A, discharge time 180min, cutoff voltage 3.0V;

[0205] Let it sit for 5 minutes;

[0206] Constant current discharge (DC): discharge current 72A, discharge time 180min, cutoff voltage 3.0V;

[0207] Let it sit for 5 minutes;

[0208] Constant current charging (CC): charging current 72A, charging time 25min, cutoff voltage 4.0V;

[0209] Let it sit for 5 minutes, then it's done.

[0210] S4. After capacity testing, the cells are left to stand at room temperature for the first time: standing temperature 25±3℃, standing time 48h;

[0211] After the first resting at room temperature, the battery cells were tested for OCV1: OCV1 was 3.5782~3.5841V, DC internal resistance (IMP) was 0.2382~0.2581mΩ, and side voltage was -0.011~0.0523mV;

[0212] Then, a second settling process was carried out at room temperature: 25±3℃, for 72 hours.

[0213] After the cells were left to stand at room temperature for the second time, an OCV2 test was conducted: OCV2 was 3.5747~3.5804V, DC internal resistance (IMP) was 0.2390~0.2583mΩ, and side voltage was -0.0121~0.0552mV.

[0214] Examples 1-3 and Comparative Examples 1-5 above mainly examine the effect of the first room temperature resting time on the K-value time under the same battery system. The specific results are shown in Table 1. The K-value is calculated using the following formula (1):

[0215] K=(OCV1- OCV2) / (t2- t1) (1)

[0216] Where OCV1 is the cell voltage of the first test; t1 is the time of the first test; OCV2 is the cell voltage of the second test; and t2 is the time of the second test.

[0217] Table 1

[0218]

[0219]

[0220] As can be seen from the data in Table 1, the cells did not reach a stable state during the first 3 hours of resting at room temperature, resulting in inaccurate K-value tests. After 4 hours of resting at room temperature, the cells reached a stable state, and the K-value of the cells showed no significant correlation with the resting time.

[0221] Meanwhile, Example 1 and Comparative Example 6 are comparative experiments, and Example 4 and Comparative Example 7 are comparative experiments. Taking Example 1, Comparative Example 6, Example 4 and Comparative Example 7 as examples, comparisons are made from the perspectives of charge and discharge capacity, internal resistance and other aspects. The charge and discharge capacity is tested during the negative voltage capacity test, and the internal resistance is tested during the OCV test. The specific results are shown in Table 2.

[0222] Table 2

[0223]

[0224] As can be seen from the data in Table 2, the lithium-ion battery formation and capacity testing method provided by this invention does not adversely affect the cell performance for different battery systems, and also significantly shortens the K-system testing time.

[0225] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention shall be within the scope of protection of the pending claims of the present invention.

Claims

1. A method for forming and capacity testing lithium-ion batteries that can shorten the K-value testing cycle, characterized in that, Includes the following steps: S1. The lithium-ion battery cell that has completed one liquid injection and settling is then subjected to negative pressure formation; S2. Perform negative voltage capacity testing on the cells after negative voltage formation. The negative voltage capacity testing is carried out at a temperature of 25±3℃ and a negative voltage of 45±5Kpa, as follows: Let it sit for 2-5 minutes; Constant current and constant voltage charging: charging current 0.5-1C, charging time 120-180min, cut-off current 0.05-0.1C, cut-off voltage 3.65-4.40V; Let it sit for 2-5 minutes; Constant current discharge: discharge current 0.5-1.0C, discharge time 120-180min, cutoff voltage 2.0-3.0V; Let it sit for 2-5 minutes; Constant current discharge: discharge current 0.2-0.5C, discharge time 120-180min, cutoff voltage 2.0-3.0V; Let it sit for 2-5 minutes; Constant current charging: charging current 0.2-0.5C, charging time 20-35min, cutoff voltage 3.0-4.0V; Let it sit for 2-5 minutes, then it's done. S3. After negative voltage capacity testing, the cells are subjected to high-temperature aging, followed by secondary electrolyte injection and sealing; the high-temperature aging temperature is 40-50℃ and the time is 22-26h. S4. After sealing, the battery cell is subjected to OCV1 test after the first resting at room temperature, and then to OCV2 test after the second resting at room temperature. The K value of the battery cell is calculated. The first resting time at room temperature is 4-6 hours, and the second resting time at room temperature is 72-96 hours.

2. The lithium-ion battery formation and capacity testing method according to claim 1, characterized in that, In step S1, the amount of liquid injected in one injection is 88-93 wt% of the total amount of liquid injected into the lithium-ion battery. And / or, in step S1, the settling temperature is 40-50℃ and the settling time is 22-26h.

3. The lithium-ion battery formation and capacity testing method according to claim 1, characterized in that, In step S1, the negative pressure formation is carried out at a temperature of 45±5℃, as detailed below: Let it sit for 2-5 minutes; Charge at a constant current of 0.1-0.2C for 30-50 minutes, with the negative pressure controlled at 45±5Kpa during the process; Let it sit for 2-5 minutes; Charge at a constant current of 0.2-0.3C for 50-90 minutes, with the negative pressure controlled at 85±5Kpa during the process; Let it sit for 2-5 minutes, then it's done.

4. The lithium-ion battery formation and capacity testing method according to claim 1, characterized in that, In step S2, the cells after negative pressure formation are first replenished with electrolyte, and then negative pressure capacity testing is performed. The amount of electrolyte replenished is 7-12 wt% of the total electrolyte volume of the lithium-ion battery.

5. The lithium-ion battery formation and capacity testing method according to claim 1, characterized in that, In step S3, the amount of liquid injected in the secondary injection is 1-5 wt% of the total amount of liquid injected into the lithium-ion battery; And / or, in step S3, the sealing includes the steps of helium filling and nailing, and welding of the sealing nails.

6. The lithium-ion battery formation and capacity testing method according to claim 1, characterized in that, In step S4, the first standing time at room temperature is 4-5 hours; And / or, in step S4, the second standing time at room temperature is 72-90 hours.

7. The lithium-ion battery formation and capacity testing method according to claim 1, characterized in that, In step S4, the value of K is calculated using the following formula (1): K=(OCV1-OCV2) / (t2- t1) (1) Where OCV1 is the cell voltage of the first test; t1 is the time of the first test; OCV2 is the cell voltage of the second test; and t2 is the time of the second test.

8. The application of the lithium-ion battery formation and capacity testing method according to any one of claims 1-7 in the production of lithium-ion batteries.

Images