CN111282853A - A kind of screening method of lithium ion battery - Google Patents

Abstract

The invention discloses a method for screening lithium ion batteries, which comprises the following steps: firstly performing a charge and discharge test on the battery at normal temperature; The flow charge ratio screening coefficient m is used for screening; and then the self-discharge consistency test is carried out, and the screening is carried out by calculating the capacity retention rate η1 and the capacity recovery rate η2. The invention uses the discharge capacity Q, the capacity screening coefficient k, the median voltage screening coefficient l, the constant current charging ratio screening coefficient m, the capacity retention rate η1 and the capacity recovery rate by performing the charge-discharge test and the self-discharge consistency test on the battery. The comprehensive screening of the six parameters of η2 is conducive to maximizing the screening of single cells with consistent performance to form a battery pack, thereby improving the performance and service life of the battery pack.

Description

A kind of screening method of lithium ion battery

technical field

The invention relates to the technical field of lithium ion batteries, in particular to a screening method for lithium ion batteries.

Background technique

Energy and the environment have become the most concerned issues in the world, and electric vehicles have begun to be gradually promoted and applied around the world. Lithium-ion batteries have been widely used in special power supply systems such as mobile phones, notebooks, and electric vehicles because of their high energy density and poor cycle life. At the same time, people have higher and higher requirements for the safety performance and electrical performance of lithium batteries during use.

In the actual application process, it is necessary to combine multiple single cells in series and parallel to form a battery pack. The consistency of the single cell capacity, voltage, self-discharge rate, cycle life and internal resistance directly determines the performance of the battery pack. . Therefore, how to use a simple and reliable screening method to screen out the single cells with the same performance to form a battery pack to the greatest extent is beneficial to improve the performance and service life of the battery pack, and at the same time, it is helpful for the large-scale promotion and application of lithium-ion batteries. of great significance.

SUMMARY OF THE INVENTION

Based on the technical problems existing in the background art, the present invention proposes a screening method for lithium ion batteries.

The screening method of a lithium ion battery proposed by the present invention comprises the following steps:

平均放电中值电压

平均恒流充入比

S1. At room temperature, perform several charge-discharge cycles on multiple single cells with a rated capacity of C to obtain the discharge capacity Q, median voltage U and constant current charge ratio P of the single cells, and calculate all single cells. The average discharge capacity of

Average discharge median voltage

Average constant current charge ratio

S2. Calculate the capacity screening coefficient k of the single battery, the median voltage screening coefficient l, and the constant current charging ratio screening coefficient m, where

S3. Set the preset ranges of k, l, and m, and screen out the single cells whose values of k, l, and m are within the preset range, and whose discharge capacity Q is greater than the rated capacity, are recorded as primary screening batteries;

S4, carry out a self-discharge consistency test on the primary screening battery, and calculate its capacity retention rate η1 and capacity recovery rate η2;

S5. Set the preset ranges of η1 and η2, and screen out the single cells whose values of η1 and η2 are within the preset ranges.

The preset ranges of the capacity screening coefficient k, the median voltage screening coefficient l, and the constant current charging ratio screening coefficient m can be set by themselves according to the strictness of screening batteries; for example, the preset range of the capacity screening coefficient k is: : k<1, the preset range of the median voltage screening coefficient l is: l<0.06, and the preset range of the constant current charging ratio screening coefficient m is: m<0.25.

Preferably, the preset range of the capacity retention rate η1 is: η1>95%, and the preset range of the capacity recovery rate η2 is: η2>96%.

Preferably, in step S1, the number of charge-discharge cycles is 3-5 times.

Preferably, in the step S5, the specific method of the self-discharge consistency test includes the following steps:

a. The single battery is charged for the first time with constant current until it reaches 50% SOC, and the first charging capacity is recorded as Q ₁ ;

b. The battery after being charged for the first time in step a is first put on hold at high temperature, then cooled to normal temperature, and discharged with constant current for the first time to the lower limit cut-off voltage, and the first discharge capacity is recorded as Q ₂ ;

c. Charge the battery after the first discharge in step b for the second time until it is fully charged;

d. The battery after the second charge in step c is discharged to the lower limit cut-off voltage for the second time with constant current, the second discharge capacity is recorded as Q ₃ , and the capacity retention rate and the capacity recovery rate are calculated, wherein the capacity retention rate η1=Q ₂ /Q ₁ , the capacity recovery rate η2=Q ₃ /Q.

Preferably, in the step b, the temperature of the high temperature shelving is 45°C-60°C, and the time is 7 days.

Preferably, in the step b, the time for cooling to normal temperature is 5h-10h.

Preferably, in step c, the specific method of the second charging is: firstly charging with constant current to the upper limit cut-off voltage, and then charging with constant voltage to the cut-off current, that is, fully charged.

Preferably, the charge-discharge cycle in the step S1 and the self-discharge consistency test in the step S4 use the same charging current, which is 0.33C-1C; and the used discharge current is the same, which is 0.33C-1C.

The beneficial effects of the present invention are as follows:

The invention uses the discharge capacity Q, the capacity screening coefficient k, the median voltage screening coefficient l, the constant current charging ratio screening coefficient m, the capacity retention rate η1 and the capacity recovery by performing the charge-discharge test and the self-discharge consistency test on the battery. Comprehensive screening of the six parameters of rate η2 is conducive to screening out single cells with consistent performance to form a battery pack to the greatest extent, thereby improving the performance and service life of the battery pack. Among them, the test conditions for the self-discharge consistency test are: high-temperature shelving test for semi-electrical batteries, which can effectively amplify the difference in self-discharge rate, which is more conducive to screening, thereby better improving the performance of single cells. Performance consistency. The screening method of the present invention is easy to implement and is conducive to large-scale promotion.

Description of drawings

Fig. 1 is the charge-discharge cycle curve of No. 1# module and No. 2# module in Example 1 of the present invention, in the figure, 1# corresponds to the 1# module, and 2# corresponds to the No. 2# module.

Detailed ways

Hereinafter, the technical solutions of the present invention will be described in detail through specific embodiments.

Example 1

A method for screening lithium ion batteries, comprising the following steps:

平均放电中值电压

平均恒流充入比

S1. At room temperature, 30 square cells with model IFP20100140-27Ah and rated capacity of 27Ah were charged and discharged for 5 times with a current of 27A, and the discharge capacity Q, median voltage U and constant value of the single cell were obtained. Current charge-to-charge ratio P, calculate the average discharge capacity of all single cells

Average discharge median voltage

Average constant current charge ratio

S2. Calculate the capacity screening coefficient k of the single battery, the median voltage screening coefficient l, and the constant current charging ratio screening coefficient m, where

S3. Set the preset ranges of k, l, and m as follows: k < 1, l < 0.06, m < 0.25, screen out the ones satisfying k < 1, l < 0.06, m < 0.25, and the discharge capacity Q is greater than the rated capacity Single battery, recorded as primary screening battery;

S4. Carry out a self-discharge consistency test on the primary screening battery, and calculate its capacity retention rate η1 and capacity recovery rate η2;

S5. The preset ranges of η1 and η2 are set as follows: η1>95%, η2>96%, and the single cells with η1>95% and η2>96% are screened out as qualified batteries.

Wherein, in step S5, the specific method of self-discharge consistency test includes the following steps:

a. The single battery is charged with a constant current for the first time with a current of 27A until it reaches 50% SOC, and the first charging capacity is recorded as Q ₁ ;

b. The battery after the first charge in step a was first put on hold at a high temperature of 45°C for 7 days, and then cooled to room temperature for 5h, and the first discharge was carried out with a constant current of 27A to the lower limit cut-off voltage, and the first discharge The capacity is recorded as Q ₂ ;

c. Charge the battery after the first discharge in step b until it is fully charged. The specific method of the second charge is: first charge the battery with a constant current of 27A to the upper limit cut-off voltage, and then charge it with a constant voltage to The cut-off current is 0.05C, that is, it is fully charged;

d. The battery after the second charge in step c is discharged to the lower limit cut-off voltage for the second time at a constant current of 27A, and the second discharge capacity is recorded as Q ₃ , and the capacity retention rate and capacity recovery rate are calculated, wherein the capacity retention rate The rate η1=Q ₂ /Q ₁ , and the capacity recovery rate η2=Q ₃ /Q.

The test results of 30 single cells are shown in Table 1:

Table 1 Test results of single cells

According to the above screening method, it can be determined from the data in the table that the batteries numbered 1, 4, 6, 8, 15, 19, 23 and 29 are unqualified batteries.

Weld the qualified batteries numbered 2, 3, 5, 7, and 9 into a 5-parallel module, marked as 1# module; Qualified batteries are welded into a 5-parallel module, marked as 2# module. The 1# module and the 2# module were charged and discharged at a current of 135A under the conditions of 25±2°C, respectively, and the cycle curves corresponded to curve 1# and curve 2# in Figure 1 respectively; compare No. 1# The cycle curve of the module and No. 2# module is verified by the screening method provided by the present invention. It can be seen that the screening method of the present invention can effectively improve the consistency of the parallel modules, thereby prolonging the cycle life of the parallel modules.

The above description is only a preferred embodiment of the present invention, but the protection scope of the present invention is not limited to this. The equivalent replacement or change of the inventive concept thereof shall be included within the protection scope of the present invention.

Claims (8)

1. a screening method of lithium ion battery, is characterized in that, comprises the following steps: S1. At room temperature, perform several charge-discharge cycles on multiple single cells with a rated capacity of C to obtain the discharge capacity Q, median voltage U and constant current charge ratio P of the single cells, and calculate all single cells. The average discharge capacity of

Average discharge median voltage

Average constant current charge ratio

S2. Calculate the capacity screening coefficient k of the single battery, the median voltage screening coefficient l, and the constant current charging ratio screening coefficient m, where

S3. Set the preset ranges of k, l, and m, and screen out the single cells whose values of k, l, and m are within the preset range, and whose discharge capacity Q is greater than the rated capacity, are recorded as primary screening batteries; S4, carry out a self-discharge consistency test on the primary screening battery, and calculate its capacity retention rate η1 and capacity recovery rate η2; S5. Set the preset ranges of η1 and η2, and screen out the single cells whose values of η1 and η2 are within the preset ranges. 2. The method for screening lithium ion batteries according to claim 1, wherein the preset range of the capacity retention rate η1 is: η1>95%, and the preset range of the capacity recovery rate η2 is: η2>96 %. 3 . The method for screening lithium ion batteries according to claim 1 , wherein in step S1 , the number of charge-discharge cycles is 3-5 times. 4 . 4. The screening method for lithium-ion batteries according to any one of claims 1-3, wherein in the step S5, the specific method for the self-discharge consistency test comprises the following steps: a. The single battery is charged for the first time with constant current until it reaches 50% SOC, and the first charging capacity is recorded as Q ₁ ; b. The battery after being charged for the first time in step a is first put on hold at high temperature, then cooled to normal temperature, and discharged with constant current for the first time to the lower limit cut-off voltage, and the first discharge capacity is recorded as Q ₂ ; c. Charge the battery after the first discharge in step b for the second time until it is fully charged; d. The battery after the second charge in step c is discharged to the lower limit cut-off voltage for the second time with constant current, the second discharge capacity is recorded as Q ₃ , and the capacity retention rate and the capacity recovery rate are calculated, wherein the capacity retention rate η1=Q ₂ /Q ₁ , the capacity recovery rate η2=Q ₃ /Q. 5 . The method for screening lithium ion batteries according to claim 4 , wherein, in the step b, the temperature at which the high temperature is put on hold is 45° C.-60° C., and the time is 7 days. 6 . 6. The method for screening lithium ion batteries according to claim 4 or 5, characterized in that, in the step b, the time for cooling to normal temperature is 5h-10h. 7. The screening method of the lithium ion battery according to any one of claims 4-6, characterized in that, in step c, the specific method of charging for the second time is: first constant current charging to the upper limit cut-off voltage, then constant voltage It is fully charged when it is charged to the cut-off current. 8. The method for screening lithium ion batteries according to any one of claims 1-7, wherein the charge-discharge cycle in the step S1 and the self-discharge consistency test in the step S4 use the same charge current size , which is 0.33C-1C; the discharge current used is the same, which is 0.33C-1C.

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