High-power lithium ion battery screening method

Abstract

The invention discloses a high-power lithium ion battery screening method, which can complete screening work of battery self-discharge, consistency, capacity retention ratio and high-power discharge and capacity grading work of batteries only through twice screening. The rate capability and the charge retention capability of the battery are comprehensively screened, the internal characteristics of the battery are accurately reflected, the consistency of the high-power discharge performance of the battery is improved, and the speed, the reliability and the safety of battery screening are ensured.

Description

Technical Field

[0001] The invention relates to the technical field of battery screening, and in particular to a high-power lithium-ion battery screening method. Background Art

[0002] In recent years, with the rapid development of drones and power tools in the civilian field and the increasing demand for various start-stop power supplies and high-power weapons and equipment in the military field, the power performance requirements of lithium-ion batteries are becoming higher and higher. They need to have 15-75C continuous discharge capability and 30-100C ultra-high power pulse discharge capability, as well as good consistency and cycle performance.

[0003] At present, the common lithium ion screening method is generally to first roughly screen the voltage and internal resistance of the battery, and then screen the self-discharge and capacity of the battery. However, for high-power batteries, this screening method cannot completely screen out defective batteries. Because high-power batteries will be polarized and produce polarized low-head voltage when used under ultra-high power conditions. However, in actual use, it is found that there are still defective batteries with lower low-head voltage after screening only by conventional screening methods. Such defective batteries may produce greater polarization during ultra-high power discharge due to tiny short-circuit points inside the battery, and the low-head voltage and cut-off voltage are lower than qualified batteries. In actual use, the internal resistance of such defective batteries becomes larger, the heat generation is higher, and the side reactions increase, thereby affecting the battery capacity and cycle performance. If only conventional screening methods are used to use such defective batteries in groups, the capacity of the defective batteries will decay greatly during actual use, which will directly affect the capacity and service life of the battery pack, and there are certain hidden dangers to the safety of the battery pack. Therefore, it is very important to develop a high-power lithium-ion battery screening method. Summary of the invention

[0004] The present invention provides a high-power lithium-ion battery screening method, which can be applicable to various forms of batteries, including soft-pack batteries, square batteries, etc., and can screen high-power lithium-ion batteries more comprehensively and accurately.

[0005] The present invention is achieved by a high-power lithium-ion battery screening method, comprising the following steps:

[0006] S1. Charge and discharge test: After formation, perform a 1C charge and discharge test on the battery to obtain the first 1C discharge capacity C 1 and discharge energy Q 1 After standing for 10 minutes, charge the battery to full power at 1C constant current and constant voltage. 1 Then conduct the first screening;

[0007] S2. Voltage and AC internal resistance measurement: After step S1, the battery is left to stand for 24 hours, and a 1kHz AC internal resistance meter is used to measure the battery voltage U 1With AC internal resistance r 1 , calculate the average internal resistance

[0008] S3, charge maintenance: the battery is left at room temperature for 1 After that, the battery is inspected for appearance, voltage and AC internal resistance in turn to obtain the voltage U after aging. 2 With AC internal resistance r 2 , calculate the internal resistance screening coefficient m, battery self-discharge rate K, Where, m is the internal resistance screening coefficient; r 1 is the AC internal resistance before aging, mΩ; is the average internal resistance before aging, mΩ; K is the battery self-discharge rate, mV / D; U 1 is the voltage before aging, V; U 2 is the voltage after aging, V; t 1 is the aging days, d;

[0009] S4. Battery self-discharge rate test: The battery is discharged at a constant current of 1C to the cut-off voltage, and the discharge capacity C is recorded. 2 and discharge energy Q 2 , calculate the average discharge voltage U C2 , battery capacity retention rate η, average capacity retention rate and capacity retention coefficient a, Where, η is the battery capacity retention rate, %; C 1 is the first 1C discharge capacity, Ah; C 2 is the discharge capacity after aging, Ah; is the average capacity retention rate of the battery, %;

[0010] S5. Primary screening of batteries: Screening is performed by screening appearance, capacity, internal resistance screening coefficient m, battery self-discharge rate K and battery capacity retention rate η to select qualified batteries for primary screening; the screening range is set according to actual conditions;

[0011] S6. Battery capacity classification: Perform 2 1C charge and discharge cycles on qualified batteries, charge at 1C constant current to the cut-off voltage, then charge at constant voltage to 0.05C cut-off current, let stand for 10 minutes, then discharge at 1C constant current to the cut-off voltage, cycle 2 times, and record the two discharge capacities C 3 , C 4 After standing for 10 minutes, charge to 50% state of charge at 1C current and calculate the average discharge capacity The volumetric coefficient b, In the formula, C 4 is the second discharge capacity, Ah; is the second average discharge capacity, Ah; it is divided into grades according to the capacity division coefficient b, and the grade range is determined according to the actual situation;

[0012] S7. Secondary battery screening: After the battery capacity is divided, let it stand for 24 hours, and conduct a high current test on each battery level. The battery is discharged at the maximum rate specified by the battery itself for the same time t 2 , record the battery starting discharge voltage U 3 , termination voltage U 4 , low head voltage U 5 Or the discharge time is Voltage U 6 , discharge capacity C 5 , discharge energy Q 5 , calculate the voltage difference ΔU, the voltage difference median ΔU Med , Average low head voltage and discharge screening coefficient b 1 、b 2 , ΔU=U 4 -U 3 、b 1 =|ΔU Med -ΔU|, Where ΔU is the secondary screening discharge voltage difference, V; b 1 、b 2 is the secondary discharge screening coefficient; ΔU Med is the median value of the secondary screening discharge voltage difference, V; U 5 is the low head voltage during the secondary screening discharge process, V; is the average low head voltage, V; the discharge screening coefficient b is determined according to the actual situation 1 、b 2 Filter range.

[0013] The 2 It is the time required to discharge 10%-50% of the battery capacity at the maximum rate specified by the battery itself.

[0014] The advantages and beneficial effects of the present invention compared with the prior art are as follows:

[0015] The present invention combines the actual use of high-power batteries to develop a high-power lithium-ion battery screening method, which completes the screening of battery self-discharge, consistency, capacity retention rate, high-power discharge and battery capacity division through only two screenings. The battery's rate performance and charge retention capacity are fully screened, accurately reflecting the internal characteristics of the battery, improving the consistency of the battery's high-power discharge performance, and ensuring the speed, reliability and safety of battery screening. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 The figure is a secondary screening discharge curve diagram of a lithium-ion battery screened by the present invention. DETAILED DESCRIPTION

[0017] The high-power lithium-ion battery screening method proposed by the present invention is further described in detail below in conjunction with the accompanying drawings and specific embodiments.

[0018] The high-power lithium-ion battery screening method of the present invention comprises the following steps:

[0019] S1. Charge and discharge test: After formation, perform a 1C charge and discharge test on the battery to obtain the first 1C discharge capacity C 1 and discharge energy Q 1 After standing for 10 minutes, charge the battery to full power at 1C constant current and constant voltage. 1 Then conduct the first screening;

[0020] S2. Voltage and AC internal resistance measurement: After step S1, the battery is left to stand for 24 hours, and a 1kHz AC internal resistance meter is used to measure the battery voltage U 1 With AC internal resistance r 1 , calculate the average internal resistance

[0021] S3, charge maintenance: the battery is left at room temperature for 1 After that, the battery is inspected for appearance, voltage and AC internal resistance in turn to obtain the voltage U after aging. 2 With AC internal resistance r 2 , calculate the internal resistance screening coefficient m, battery self-discharge rate K, Where, m is the internal resistance screening coefficient; r 1 is the AC internal resistance before aging, mΩ; is the average internal resistance before aging, mΩ; K is the battery self-discharge rate, mV / D; U 1 is the voltage before aging, V; U 2 is the voltage after aging, V; t 1 is the aging days, d;

[0022] S4. Battery self-discharge rate test: The battery is discharged at a constant current of 1C to the cut-off voltage, and the discharge capacity C is recorded. 2 and discharge energy Q 2 , calculate the average discharge voltage U C2 , battery capacity retention rate η, average capacity retention rate and capacity retention coefficient a, Where, η is the battery capacity retention rate, %; C 1 is the first 1C discharge capacity, Ah; C 2 is the discharge capacity after aging, Ah; is the average capacity retention rate of the battery, %;

[0023] S5. Primary screening of batteries: Screening is performed by screening appearance, capacity, internal resistance screening coefficient m, battery self-discharge rate K and battery capacity retention rate η to select qualified batteries for primary screening; the screening range is set according to actual conditions;

[0024] S6. Battery capacity classification: Perform 2 1C charge and discharge cycles on qualified batteries, charge at 1C constant current to the cut-off voltage, then charge at constant voltage to 0.05C cut-off current, let stand for 10 minutes, then discharge at 1C constant current to the cut-off voltage, cycle 2 times, and record the two discharge capacities C 3 , C 4 After standing for 10 minutes, charge to 50% state of charge at 1C current and calculate the average discharge capacity The volumetric coefficient b, In the formula, C 4 is the second discharge capacity, Ah; is the second average discharge capacity, Ah; it is divided into grades according to the capacity division coefficient b, and the grade range is determined according to the actual situation;

[0025] S7. Secondary battery screening: After the battery capacity is divided, let it stand for 24 hours, and conduct a high current test on each battery level. The battery is discharged at the maximum rate specified by the battery itself for the same time t 2 , record the battery starting discharge voltage U 3 , termination voltage U 4 , low head voltage U 5 Or the discharge time is Voltage U 6 , discharge capacity C 5 , discharge energy Q 5 , calculate the voltage difference ΔU, the voltage difference median ΔU Med , Average low head voltage and discharge screening coefficient b 1 、b 2 , ΔU=U 4 -U 3 、b 1 =|ΔU Med -ΔU|, Where ΔU is the secondary screening discharge voltage difference, V; b 1 、b 2 is the secondary discharge screening coefficient; ΔU Med is the median value of the secondary screening discharge voltage difference, V; U 5 is the low head voltage during the secondary screening discharge process, V; is the average low head voltage, V; the discharge screening coefficient b is determined according to the actual situation 1 、b 2 Filter range.

[0026] The 2It is the time required to discharge 10%-50% of the battery capacity at the maximum rate specified by the battery itself.

[0027] Example 1

[0028] This embodiment takes a soft-pack battery as an example and specifically includes the following steps:

[0029] S1. Charge and discharge test: After formation, perform a 1C charge and discharge test on the battery to obtain the first 1C discharge capacity C 1 After standing for 10 minutes, charge the battery to full power at 1C constant current and constant voltage. 1 Then conduct the first screening;

[0030] S2. Voltage and AC internal resistance measurement: After step S1, the battery is left to stand for 24 hours, and a 1kHz AC internal resistance meter is used to measure the battery voltage U 1 With AC internal resistance r 1 , calculate the average internal resistance

[0031] S3, charge maintenance: the battery is left at room temperature for 1 After that, the battery is inspected for appearance, voltage and AC internal resistance in turn to obtain the voltage U after aging. 2 With AC internal resistance r 2 , calculate the internal resistance screening coefficient m and the battery self-discharge rate K;

[0032] S4. Battery self-discharge rate test: The battery is discharged at a constant current of 1C to the cut-off voltage, and the discharge capacity C is recorded. 2 , calculate the battery capacity retention rate η and average capacity retention rate and capacity retention coefficient a;

[0033] S5. Battery primary screening: The qualified batteries are screened out through the following screening methods:

[0034] a. If the battery has dents, damage, leakage or other appearance defects, it is a defective battery;

[0035] b. If C 2 <1.02C 额 It is a defective battery;

[0036] c. If m>5%, it is a defective battery;

[0037] d. Calculate the battery self-discharge rate K. If K>1mV / day, it is a defective battery;

[0038] e. Calculate battery capacity retention rate η and average capacity retention rate and capacity retention coefficient a. If η<94% and a>0.5%, it is a defective battery.

[0039] S6. Battery capacity: Perform 2 1C charge and discharge cycles on the battery. Charge to the cut-off voltage with 1C constant current, then charge to 0.05C cut-off current with constant voltage, let stand for 10 minutes, then discharge to the cut-off voltage with 1C constant current, repeat 2 cycles, and record the discharge capacity C twice. 3 , C 4 , after standing for 10 minutes, charge to 50% state of charge at 1C current; calculate the average discharge capacity Capacity division coefficient b: divided into grades according to capacity division coefficient b, with each 1% being one grade of capacity division;

[0040] S7. Secondary battery screening: After the battery capacity is divided, let it stand for 24 hours, conduct a high current test on each battery, discharge the battery at 30C for 2s, and record the battery initial discharge voltage U 3 , termination voltage U 4 , calculate the voltage difference ΔU, the voltage difference median ΔU Med and discharge screening coefficient b 1 , ΔU=U 4 -U 3 、b 1 =|ΔU Med -ΔU|, if b 1 >50mv is a defective battery;

[0041] Table 1 shows the secondary screening test data of the battery screened by the present invention, where ΔU Med =447.4mV.

[0042] Table 1 Battery secondary screening test data

[0043]

[0044]

[0045] According to Table 1 and Figure 1 It can be seen that this method can quickly and successfully screen out defective batteries, ensuring the consistency and reliability of the power performance of qualified batteries.

[0046] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions and improvements made within the spirit and principles of the present invention should be included in the protection scope of the present invention.

Claims

1. A high-power lithium-ion battery screening method, characterized in that: The following steps are involved: S1. Charge and discharge test: After formation, perform a 1C charge and discharge on the battery to obtain the first 1C discharge capacity C1 and discharge energy Q1; after standing for 10 minutes, charge the battery to full power at 1C constant current and constant voltage, and perform the first screening after standing for t1; S2. Voltage and AC internal resistance measurement: After step S1, the battery is left to stand for 24 hours, and a 1kHz AC internal resistance meter is used to measure the battery voltage U1 and AC internal resistance r1, and the average internal resistance is calculated. S3, charge retention: After the battery is left at room temperature for t1, the appearance inspection, voltage and AC internal resistance test are carried out on the battery in turn to obtain the voltage U2 and AC internal resistance r2 after aging, and the internal resistance screening coefficient m and battery self-discharge rate K are calculated. Where, m is the internal resistance screening coefficient; r1 is the AC internal resistance before aging, mΩ; is the average internal resistance before aging, mΩ; K is the battery self-discharge rate, mV / D; U1 is the voltage before aging, V; U2 is the voltage after aging, V; t1 is the aging days, d; S4. Battery self-discharge rate test: The battery is discharged at a constant current of 1C to the cut-off voltage, the discharge capacity C2 and discharge energy Q2 are recorded, and the average discharge voltage U is calculated. C2 , battery capacity retention rate η, average capacity retention rate and capacity retention coefficient a, Wherein, η is the battery capacity retention rate, %; C1 is the first 1C discharge capacity, Ah; C2 is the discharge capacity after aging, Ah; is the average capacity retention rate of the battery, %; S5. Primary screening of batteries: Screening is performed by screening appearance, capacity, internal resistance screening coefficient m, battery self-discharge rate K and battery capacity retention rate η to select qualified batteries for primary screening; the screening range is set according to actual conditions; S6. Battery capacity classification: Perform 2 1C charge and discharge cycles on qualified batteries. Charge to the cut-off voltage with 1C constant current, then charge to 0.05C cut-off current with constant voltage, let stand for 10 minutes, then discharge to the cut-off voltage with 1C constant current, repeat 2 cycles, record the two discharge capacities C3 and C4, let stand for 10 minutes, charge to 50% state of charge with 1C current, and calculate the average discharge capacity The volumetric coefficient b, Where, C4 is the second discharge capacity, Ah; is the second average discharge capacity, Ah; Divide into grades according to the capacity coefficient b, and the grade range is determined according to the actual situation; S7. Secondary battery screening: After the battery capacity is divided, let it stand for 24 hours, and conduct a high current test on each battery. Discharge the battery at the maximum rate specified by the battery for the same time t2, and record the battery's initial discharge voltage U3, termination voltage U4, low head voltage U5 or discharge time. When the voltage is U6, the discharge capacity is C5, and the discharge energy is Q5, the voltage difference ΔU and the median voltage difference ΔU are calculated. Med , Average low head voltage With discharge screening coefficients b1, b2, ΔU = U4-U3, b1 = |ΔU Med -ΔU|, Where, ΔU is the secondary screening discharge voltage difference, V; b1, b2 are the secondary discharge screening coefficients; ΔU Med is the median value of the secondary screening discharge voltage difference, V; U5 is the low head voltage during the secondary screening discharge process, V; is the average low head voltage, V; the screening range of discharge screening coefficients b1 and b2 is determined according to actual conditions.

2. The high-power lithium-ion battery screening method according to claim 1, characterized in that: The t2 is the time required to discharge 10%-50% of the battery capacity at the maximum rate specified by the battery itself.

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