CN116008840A - Method for judging optimal liquid injection amount of lithium ion battery - Google Patents
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Abstract
The invention provides a judging method of optimal liquid injection amount of a lithium ion battery, which comprises the following steps: providing a plurality of non-injected electric cores, and injecting electrolyte into the non-injected electric cores according to the injection coefficient to obtain a plurality of injected electric cores; and (3) at least one step of ageing, forming and degassing the injected electric cores, carrying out alternating current impedance test on the injected electric cores after each step is finished, judging the minimum injection coefficient according to the impedance value, and determining the optimal injection amount according to the minimum injection coefficient. The judging method provided by the invention is a nondestructive analysis method, does not need to disassemble and destroy the appearance of the battery cell, has visual and reliable data, simple related test equipment and low analysis cost, and is simple and practical.
Description
Technical Field
The invention belongs to the technical field of batteries, and relates to a method for judging the optimal liquid injection amount of a lithium ion battery.
Background
With the continuous development of society, the demand of lithium ion batteries with the advantages of high energy density, safety, reliability, no pollution and the like is increasing, and the demand of battery performance is increasing. The electrolyte provides a channel for lithium ion transmission in the battery, and is a bridge communicated with the anode and the cathode, wherein electrolyte lithium salt in the electrolyte is a source spring for providing lithium ions, so that the battery is ensured to have enough lithium ions to reciprocate back and forth in the anode and the cathode in the charge-discharge cycle process, and the reversible cycle is realized. It is necessary to ensure that a sufficient amount of electrolyte is present in the battery to maintain operation of the battery.
In industrial battery production of large-scale batteries, the electrolyte injection amount not only affects the wetting rate of the electrode and the diaphragm, but also can limit the capacity of the battery and affect the service life of the battery. The injection amount of the electrolyte is a difficult parameter to be qualitatively, and the influence of the injection amount of the electrolyte in an actual battery on the battery cycle performance is not linear. Excessive electrolyte usage can lead to a decrease in the overall energy density of the battery and an intangibly increased production cost of the battery, and too little space inside can lead to an increase in the internal pressure of the battery, with a certain risk of leakage. The influence of the electrolyte on the performance of the battery is fatal, so that the internal resistance of the battery is higher, the cycle life is quickly reduced to the later stage, lithium is separated out along with the cycle when serious, and the safety risk is caused.
CN110148793a discloses a method for discriminating the electrolyte infiltration state of a lithium ion battery, which comprises the following steps: (1) Preparing a colored impregnating compound, adding the colored impregnating compound into the electrolyte, and uniformly mixing to obtain the colored electrolyte; (2) And (3) injecting the colored electrolyte into the battery, respectively disassembling the battery when the battery completes the primary injection, formation and secondary injection processes, and judging the wetting state of the electrolyte by judging whether the color areas on the diaphragm and the pole piece are uniformly distributed so as to adjust the primary injection amount, the secondary injection amount and the formation process. According to the method, the battery is required to be disassembled, the test and analysis cost is high, and the wetting state of the electrolyte is judged through naked eye observation, so that the subjectivity of the obtained result is high.
CN109546070B discloses a method for determining the liquid injection amount of a lithium battery, wherein the liquid injection of the lithium battery is divided into primary liquid injection and secondary liquid injection, experiments of different primary liquid injection amounts are designed firstly, the formation gas production amount is determined, the residual electrolyte amount is determined by disassembling the battery, and the proper primary liquid injection amount is formulated; and then carrying out experiments on different secondary liquid injection amounts, and determining residual electrolyte amount and subsequent gas production amount by disassembling the battery to formulate proper secondary liquid injection amount. The method also needs to disassemble the battery, and has higher test analysis cost.
CN106159346a discloses a complete set of calculation method for the injection amount of lithium ion battery, which calculates theoretical porosity according to the true densities of various raw materials used by the lithium ion battery, and then obtains the actual injection amount of the electrolyte according to the electrolyte density and the calculated theoretical porosity. However, the theoretical liquid injection amount has a certain deviation from the actual cell design, the fluctuation of the coating amount of the positive and negative pole pieces and the porosities of different positive and negative pole main materials and diaphragms have great influence on the theoretical value calculation result, so the theoretical calculation value is only used as a reference.
Therefore, a method for determining the injection amount of a lithium ion battery with low test cost and high data reliability is needed.
Disclosure of Invention
Aiming at the defects existing in the prior art, the invention aims to provide a method for judging the optimal liquid injection amount of a lithium ion battery. The judging method provided by the invention is a nondestructive analysis method, does not need to disassemble and destroy the appearance of the battery cell, has visual and reliable data, simple related test equipment and low analysis cost, and is simple and practical.
To achieve the purpose, the invention adopts the following technical scheme:
the invention provides a judging method of optimal liquid injection amount of a lithium ion battery, which comprises the following steps:
(1) Providing a plurality of non-injected electric cores, and injecting electrolyte into the non-injected electric cores according to the injection coefficient to obtain a plurality of injected electric cores;
(2) And (3) at least one step of ageing, forming and degassing the injected electric cores, carrying out alternating current impedance test on the injected electric cores after each step is finished, judging the minimum injection coefficient according to the impedance value, and determining the optimal injection amount according to the minimum injection coefficient.
The invention provides a method for judging the optimal liquid injection amount of a lithium ion battery, which is used for carrying out alternating current impedance tests on injected battery cells at different stages and judging the optimal liquid injection amount of the battery cells through impedance values. The judgment method combines a plurality of working procedures to comprehensively judge the liquid injection quantity so as to solve the problem of error existing in single-procedure judgment. The judging method is a nondestructive analysis method, disassembly and damage to the appearance of the battery cell are not needed, the data are visual and reliable, related test equipment is simple, the analysis cost is low, and the method is simple and practical.
The term "several" in the "several battery cells without injection" in the present invention means at least 3, for example, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, or 20, etc.
The optimal injection amount is judged by a high-frequency impedance value obtained by an alternating current impedance test (EIS), and the high-frequency impedance value (HFR) is the intercept between a high-frequency region (> 1 kHz) of an EIS curve and a real axis.
As a preferable embodiment of the present invention, the injection amount of the electrolyte=injection coefficient is equal to the volume of the non-injected cell.
Preferably, the liquid injection coefficient is in gradient distribution.
Preferably, the injection coefficient is an arithmetic series.
Preferably, the variation of each gradient of the injection coefficient is 0.05-0.5 g/Ah, for example, 0.05g/Ah, 0.1g/Ah, 0.15g/Ah, 0.2g/Ah, 0.25g/Ah, 0.3g/Ah, 0.35g/Ah, 0.4g/Ah, 0.45g/Ah or 0.5g/Ah, etc.
Preferably, the injection coefficient is controlled within a range of 1-4 g/Ah, and may be, for example, 1g/Ah, 1.2g/Ah, 1.4g/Ah, 1.6g/Ah, 1.8g/Ah, 2g/Ah, 2.2g/Ah, 2.4g/Ah, 2.6g/Ah, 2.8g/Ah, 3g/Ah, 3.2g/Ah, 3.4g/Ah, 3.6g/Ah, 3.8g/Ah, or 4g/Ah, etc.
In the invention, the gradient of the liquid injection coefficient can be regulated according to the verification requirement, the gradient range and the precision can be freely designed, the designed gradient variation and range can be amplified for the cell of the rough verification liquid injection amount, and the designed gradient variation and range can be reduced for the cell of the requirement of the accurate determination of the optimal liquid injection amount.
In the step (2), the plurality of injected electric cells are sequentially aged, formed and degassed, and after the aging step is finished, the high-frequency impedance value of the injected electric cells is recorded as HFR w ；
After the formation step is finished, the high-frequency impedance value of the injected battery cell is recorded as HFR f ；
After the degassing step is finished, the high-frequency impedance value of the injected battery cell is recorded as HFR d ；
Calculating HFR w 、HFR f And HFR (high frequency R) d The high frequency impedance average value of (2) is recorded as HFR ave According to HFR ave And determining the minimum liquid injection coefficient.
In the invention, the impedance average value of multiple steps is calculated to reduce test errors and increase judgment accuracy.
As a preferred embodiment of the present invention, the method according to HFR ave The minimum liquid injection coefficient is determined as follows: acquiring the HFR of the injected battery cell corresponding to each injection coefficient ave And (3) taking the liquid injection coefficient as an abscissa, taking a high-frequency impedance average value as a ordinate drawing, determining an inflection point with a slope absolute value smaller than 0.05 in the drawing, wherein the abscissa of the inflection point is a minimum liquid injection coefficient, and the liquid injection amount corresponding to the inflection point is the minimum liquid injection amount.
The invention does not limit the drawn graph specifically, and the drawn graph can be a line graph or a fitting graph.
In the present invention, an inflection point before which the impedance drops sharply and after which the impedance drops gently may be determined from the plotted graph. After the inflection point is determined, the minimum liquid injection coefficient is obtained.
When the drawn graph is a line graph, the inflection point is one of the designed liquid injection coefficients.
As a preferable technical scheme of the invention, the determination of the optimal liquid injection amount according to the minimum liquid injection coefficient is performed in the following manner:
screening out a battery with a liquid injection coefficient greater than or equal to the minimum liquid injection coefficient for circulation, wherein after the circulation step is finished, the high-frequency impedance value of the injected battery cell is recorded as HFR c Calculating HFR of the battery corresponding to each liquid injection coefficient c With HFR ave The ratio of the two liquid injection coefficients is marked as K, the liquid injection coefficient corresponding to the minimum K value is the optimal liquid injection coefficient, and the liquid injection amount corresponding to the optimal liquid injection coefficient is the optimal liquid injection amount.
In the invention, when the inflection point abscissa is one of the designed liquid injection coefficients, the battery with the liquid injection coefficient larger than or equal to the inflection point abscissa is screened for circulation; and when the inflection point abscissa is not the designed liquid injection coefficient, the battery with the liquid injection coefficient larger than the inflection point abscissa is screened for circulation.
The invention only carries out the circulation test on the screened batteries, can improve the test efficiency and saves the test cost.
In the process of judging the liquid injection amount, a series of liquid injection coefficients with wider range and larger gradient variation can be designed by high-frequency impedance average HFR ave And screening out part of the liquid injection coefficients from the relation diagram of the liquid injection coefficients, and then based on the screened part of the liquid injection coefficients, designing a series of liquid injection coefficients with small gradient change amount for analysis and test. This is advantageous for rapid screening of the optimal liquid injection amount of the lithium ion battery.
In order to improve accuracy, each injection coefficient can test a plurality of battery cells, and average value is taken for judgment.
Preferably, the test parameters of the cycle are: the constant current charging may be performed at 0.1 to 1.2C, for example, 0.1C, 0.2C, 0.3C, 0.5C, 0.7C, 0.8C, 0.9C, 1C, 1.1C, or 1.2C, and the constant voltage charging may be performed at 0.01 to 0.08C, for example, 0.01C, 0.02C, 0.03C, 0.04C, 0.05C, 0.06C, 0.07C, or 0.08C, and the constant current discharging may be performed at 0.1 to 1.2C, for example, 0.1C, 0.2C, 0.3C, 0.5C, 0.7C, 0.8C, 0.9C, 1C, 1.1C, or 1.2C, after the charging is completed.
Preferably, the end conditions of the cycle are: the capacity retention rate of the injected cell is reduced to 75 to 85%, and may be 75%, 76%, 77%, 78%, 79%, 80%, 81%, 82%, 83%, 84%, 85%, or the like, for example.
As a preferable embodiment of the present invention, the aging temperature is 40 to 50℃and may be, for example, 40℃41℃ 42℃43℃44℃45℃46℃47℃48℃49℃50 ℃.
Preferably, the aging time is 22 to 26 hours, and may be 22 hours, 23 hours, 24 hours, 25 hours, 26 hours, or the like, for example.
As a preferable technical scheme of the invention, after the formation step is finished, the injected battery cell is discharged to 2-2.6V, for example, 2V, 2.1V, 2.2V, 2.3V, 2.4V, 2.5V or 2.6V, and then an alternating current impedance test is performed.
Preferably, an aging step is further provided between the formation and the degassing.
Preferably, the aging temperature is 40 to 50 ℃, and may be 40 ℃, 41 ℃, 42 ℃, 43 ℃, 44 ℃, 45 ℃, 46 ℃, 47 ℃, 48 ℃, 49 ℃, 50 ℃ or the like, for example.
Preferably, the aging time is 12 to 14 hours, and may be, for example, 12 hours, 12.5 hours, 13 hours, 13.5 hours, or 14 hours, etc.
As a preferred technical scheme of the invention, a capacity-dividing step is further arranged between the degassing and the circulation.
Preferably, the temperature of the cycle is 20 to 30 ℃, and may be, for example, 20 ℃, 21 ℃, 22 ℃, 23 ℃, 24 ℃, 25 ℃, 26 ℃, 27 ℃, 28 ℃, 29 ℃, 30 ℃, or the like.
Preferably, after the circulation step is finished, the injected electric core is discharged to 2-2.6V, for example, 2V, 2.1V, 2.2V, 2.3V, 2.4V, 2.5V or 2.6V, and then an alternating current impedance test is performed.
As a preferable technical scheme of the invention, the test frequency of the alternating current impedance test is 1-10 5 Hz。
Preferably, the ac signal amplitude of the ac impedance test is 8 to 12mV, for example, 8mV, 9mV, 10mV, 11mV, 12mV, or the like.
As a preferable technical scheme of the invention, the judging method specifically comprises the following steps:
providing a plurality of non-injected electric cores, and injecting electrolyte into the non-injected electric cores according to the gradient distribution injection coefficients to obtain a plurality of injected electric cores;
(II) ageing, forming and degassing the injected electric cores in sequence, and carrying out alternating current impedance test on the injected electric cores after each step is finished, wherein after the ageing step is finished, the high-frequency impedance value of the injected electric cores is recorded as HFR w The method comprises the steps of carrying out a first treatment on the surface of the After the formation step is finished, the liquid is injectedThe high frequency impedance of the cell is recorded as HFR f The method comprises the steps of carrying out a first treatment on the surface of the After the degassing step is finished, the high-frequency impedance value of the injected battery cell is recorded as HFR d According to HFR w 、HFR f And HFR (high frequency R) d Determining a minimum liquid injection coefficient;
(III) screening out a battery with a liquid injection coefficient greater than or equal to the minimum liquid injection coefficient for circulation, wherein after the circulation step is finished, the high-frequency impedance value of the injected battery cell is recorded as HFR c Calculating HFR of the battery corresponding to each liquid injection coefficient c With HFR ave The ratio of the two liquid injection coefficients is marked as K, the liquid injection coefficient corresponding to the minimum K value is the optimal liquid injection coefficient, and the liquid injection amount corresponding to the optimal liquid injection coefficient is the optimal liquid injection amount.
But are not limited to, the recited values, and other non-recited values within the range of values are equally applicable.
The numerical ranges recited herein include not only the recited point values, but also any point values between the recited numerical ranges that are not recited, and are limited to, and for the sake of brevity, the invention is not intended to be exhaustive of the specific point values that the recited range includes.
Compared with the prior art, the invention has the beneficial effects that:
the invention provides a method for judging the optimal liquid injection amount of a lithium ion battery, which is used for carrying out alternating current impedance tests on injected battery cells at different stages and judging the optimal liquid injection amount of the battery cells through impedance values. The judgment method combines a plurality of working procedures to comprehensively judge the liquid injection quantity so as to solve the problem of error existing in single-procedure judgment. The judging method is a nondestructive analysis method, disassembly and damage to the appearance of the battery cell are not needed, the data are visual and reliable, related test equipment is simple, the analysis cost is low, and the method is simple and practical.
Drawings
Fig. 1 is a graph of a relationship between a high-frequency impedance value and a liquid injection coefficient according to an embodiment of the present invention.
Fig. 2 is a graph of the relationship between the average value of the high-frequency impedance and the injection coefficient according to the embodiment of the present invention.
Detailed Description
The technical scheme of the invention is further described by the following specific embodiments.
Examples
The embodiment provides a method for judging the optimal liquid injection amount of a lithium ion battery, which specifically comprises the following steps:
s1: taking a non-injected cell with 3Ah three sides sealed and one side left with a liquid injection port and baked to be qualified, calculating theoretical liquid injection amount m, m=liquid injection coefficient and the capacity of the non-injected cell, and weighing the weight m of the cell before liquid injection by 6 groups of liquid injection coefficients as shown in table 1 1 The weight m of the battery cell is weighed after the liquid injection 2 Calculate the actual injection amount m' =m 2 -m 1 Sealing the liquid injection ports of the electric cores after the liquid injection is completed, wherein each group of liquid injection coefficients corresponds to 3 injected electric cores;
s2: placing the injected electric core into a high-temperature oven with the temperature of 45+/-5 ℃, aging for 24 hours, performing alternating current impedance test (EIS) on the aged injected electric core, recording high-frequency impedance values, and taking the average value of the high-frequency impedance values of 3 electric cores corresponding to each group of injection coefficients to obtain HFR corresponding to each group of injection coefficients w The subsequent steps are all performed with this treatment;
s3: performing a formation step on the injected battery cell, discharging the formed battery cell to 2.5V, and performing EIS test to obtain HFR corresponding to each group of injection coefficients f ；
S4: aging the injected battery cell at 45 ℃ for 12 hours, performing a degassing step, and performing EIS test on the degassed battery cell to obtain HFR corresponding to each group of injection coefficients d The high frequency impedance values of the injected cells are summarized in fig. 1;
s5: calculating high frequency impedance mean HFR ave ＝(HFR w +HFR f +HFR d ) Drawing a line graph by taking 6 groups of liquid injection coefficients as an abscissa and taking a high-frequency impedance average value as an ordinate, and determining an inflection point with a slope absolute value smaller than 0.05 in the graph as shown in figure 2, wherein the abscissa of the inflection point is a minimum liquid injection coefficient, the minimum liquid injection coefficient is 2.6g/Ah, and the liquid injection amount corresponding to the inflection point is the minimum liquid injection amount;
s6: screening out a battery with a liquid injection coefficient greater than or equal to the minimum liquid injection coefficient, wherein the screened liquid injection coefficient is 2.6gPerforming capacity division steps on the corresponding batteries of/Ah, 3.0g/Ah and 3.4g/Ah, performing cyclic test at 25 ℃ after capacity division off-line, wherein the test conditions are that 1C constant current charge is performed firstly, then C/20 constant voltage charge is performed, 1C constant current discharge is performed after charge is completed, the cyclic test is performed until 80% capacity retention rate is reached, the cabinet is discharged to 2.5V, and EIS test is performed, so that HFR corresponding to each group of liquid injection coefficients is obtained c ；
S7: HFR of corresponding batteries of 2.6g/Ah, 3g/Ah and 3.4g/Ah were calculated c With HFR ave The ratio of the liquid injection coefficient to the minimum K value is 3.0g/Ah, and the liquid injection amount corresponding to the optimal liquid injection coefficient is the optimal liquid injection amount.
The test conditions of EIS in this embodiment are: test frequency 1-10 5 Hz, ac signal amplitude 10mV.
TABLE 1
| Group of | Coefficient of liquid injection | Liquid injection amount |
| A | 1.4g/Ah | 4.2g |
| B | 1.8g/Ah | 5.4g |
| C | 2.2g/Ah | 6.6g |
| D | 2.6g/Ah | 7.8g |
| E | 3.0g/Ah | 9.0g |
| F | 3.4g/Ah | 10.2g |
TABLE 2
| Group of | HFR c | HFR ave | K |
| D | 14.8mΩ | 6.6mΩ | 2.242 |
| E | 13.9mΩ | 6.5mΩ | 2.138 |
| F | 14.6mΩ | 6.3mΩ | 2.317 |
The applicant declares that the above is only a specific embodiment of the present invention, but the scope of the present invention is not limited thereto, and it should be apparent to those skilled in the art that any changes or substitutions that are easily conceivable within the technical scope of the present invention disclosed by the present invention fall within the scope of the present invention and the disclosure.
Claims (10)
1. The method for judging the optimal liquid injection amount of the lithium ion battery is characterized by comprising the following steps of:
(1) Providing a plurality of non-injected electric cores, and injecting electrolyte into the non-injected electric cores according to the injection coefficient to obtain a plurality of injected electric cores;
(2) And (3) at least one step of ageing, forming and degassing the injected electric cores, carrying out alternating current impedance test on the injected electric cores after each step is finished, judging the minimum injection coefficient according to the impedance value, and determining the optimal injection amount according to the minimum injection coefficient.
2. The method according to claim 1, wherein the injection amount of the electrolyte=injection coefficient is not-injected cell capacity;
preferably, the liquid injection coefficients are distributed in a gradient manner;
preferably, the liquid injection coefficient is an arithmetic series;
preferably, the variation of each gradient of the liquid injection coefficient is 0.05-0.5 g/Ah;
preferably, the liquid injection coefficient is controlled within the range of 1-4 g/Ah.
3. The method according to claim 1 or 2, wherein in the step (2), the plurality of injected cells are sequentially subjected to aging, formation and degassing stepsAfter the aging step is finished, the high-frequency impedance value of the injected battery cell is recorded as HFR w ；
After the formation step is finished, the high-frequency impedance value of the injected battery cell is recorded as HFR f ；
After the degassing step is finished, the high-frequency impedance value of the injected battery cell is recorded as HFR d ；
Calculating HFR w 、HFR f And HFR (high frequency R) d The high frequency impedance average value of (2) is recorded as HFR ave According to HFR ave And determining the minimum liquid injection coefficient.
4. A judging method according to claim 3, wherein the HFR is ave The minimum liquid injection coefficient is determined as follows: acquiring the HFR of the injected battery cell corresponding to each injection coefficient ave And (3) taking the liquid injection coefficient as an abscissa, taking a high-frequency impedance average value as a ordinate drawing, determining an inflection point with a slope absolute value smaller than 0.05 in the drawing, wherein the abscissa of the inflection point is a minimum liquid injection coefficient, and the liquid injection amount corresponding to the inflection point is the minimum liquid injection amount.
5. The method according to any one of claims 1 to 4, wherein the determining the optimal liquid injection amount according to the minimum liquid injection coefficient is performed as follows:
screening out a battery with a liquid injection coefficient greater than or equal to the minimum liquid injection coefficient for circulation, wherein after the circulation step is finished, the high-frequency impedance value of the injected battery cell is recorded as HFR c Calculating HFR of the battery corresponding to each liquid injection coefficient c With HFR ave The ratio of the two liquid injection coefficients is recorded as K, the liquid injection coefficient corresponding to the minimum K value is the optimal liquid injection coefficient, and the liquid injection amount corresponding to the optimal liquid injection coefficient is the optimal liquid injection amount;
preferably, the test parameters of the cycle are: firstly, charging with 0.1-1.2C constant current, then charging with 0.01-0.08C constant voltage, and discharging with 0.1-1.2C constant current after charging is completed;
preferably, the end conditions of the cycle are: the capacity retention rate of the injected battery cell is reduced to 75-85%.
6. The method according to any one of claims 1 to 5, wherein the aging temperature is 40 to 50 ℃;
preferably, the aging time is 22 to 26 hours.
7. The method according to any one of claims 1 to 6, wherein after the formation step is completed, the injected cell is discharged to 2 to 2.6V, and then an ac impedance test is performed;
preferably, an aging step is further arranged between the formation and the degassing;
preferably, the temperature of the aging is 40-50 ℃;
preferably, the aging time is 12 to 14 hours.
8. The method according to any one of claims 1 to 7, wherein a step of partitioning is further provided between the deaeration and the circulation;
preferably, the temperature of the cycle is 20-30 ℃;
preferably, after the circulation step is finished, the injected electric core is discharged to 2-2.6V, and then the alternating current impedance test is carried out.
9. The method according to any one of claims 1 to 8, wherein the test frequency of the ac impedance test is 1 to 10 5 Hz；
Preferably, the alternating current signal amplitude of the alternating current impedance test is 8-12 mV.
10. The method according to any one of claims 1 to 9, characterized in that it comprises the following steps:
providing a plurality of non-injected electric cores, and injecting electrolyte into the non-injected electric cores according to the gradient distribution injection coefficients to obtain a plurality of injected electric cores;
(II) ageing a plurality of injected electric cores in sequenceThe method comprises the steps of formation, formation and degassing, and carrying out alternating current impedance test on the injected battery cell after each step is finished, wherein after the aging step is finished, the high-frequency impedance value of the injected battery cell is recorded as HFR w The method comprises the steps of carrying out a first treatment on the surface of the After the formation step is finished, the high-frequency impedance value of the injected battery cell is recorded as HFR f The method comprises the steps of carrying out a first treatment on the surface of the After the degassing step is finished, the high-frequency impedance value of the injected battery cell is recorded as HFR d According to HFR w 、HFR f And HFR (high frequency R) d Determining a minimum liquid injection coefficient;
(III) screening out a battery with a liquid injection coefficient greater than or equal to the minimum liquid injection coefficient for circulation, wherein after the circulation step is finished, the high-frequency impedance value of the injected battery cell is recorded as HFR c Calculating HFR of the battery corresponding to each liquid injection coefficient c With HFR ave The ratio of the two liquid injection coefficients is marked as K, the liquid injection coefficient corresponding to the minimum K value is the optimal liquid injection coefficient, and the liquid injection amount corresponding to the optimal liquid injection coefficient is the optimal liquid injection amount.
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