CN113125977A - Lithium ion battery and self-discharge screening method thereof - Google Patents
Lithium ion battery and self-discharge screening method thereof Download PDFInfo
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- CN113125977A CN113125977A CN202110202054.6A CN202110202054A CN113125977A CN 113125977 A CN113125977 A CN 113125977A CN 202110202054 A CN202110202054 A CN 202110202054A CN 113125977 A CN113125977 A CN 113125977A
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- HBBGRARXTFLTSG-UHFFFAOYSA-N Lithium ion Chemical compound [Li+] HBBGRARXTFLTSG-UHFFFAOYSA-N 0.000 title claims abstract description 224
- 229910001416 lithium ion Inorganic materials 0.000 title claims abstract description 224
- 238000012216 screening Methods 0.000 title claims abstract description 165
- 238000000034 method Methods 0.000 title claims abstract description 73
- WHXSMMKQMYFTQS-UHFFFAOYSA-N Lithium Chemical compound [Li] WHXSMMKQMYFTQS-UHFFFAOYSA-N 0.000 claims abstract description 224
- 229910052744 lithium Inorganic materials 0.000 claims abstract description 224
- 238000007599 discharging Methods 0.000 claims abstract description 27
- 230000015572 biosynthetic process Effects 0.000 claims abstract description 25
- 238000005259 measurement Methods 0.000 claims description 135
- 238000001514 detection method Methods 0.000 claims description 27
- 238000005507 spraying Methods 0.000 claims description 8
- 238000009826 distribution Methods 0.000 abstract description 3
- 238000004519 manufacturing process Methods 0.000 description 23
- 238000006243 chemical reaction Methods 0.000 description 7
- 230000002829 reductive effect Effects 0.000 description 7
- 230000008569 process Effects 0.000 description 5
- 230000008859 change Effects 0.000 description 4
- 230000002427 irreversible effect Effects 0.000 description 4
- 239000003792 electrolyte Substances 0.000 description 3
- 230000000670 limiting effect Effects 0.000 description 3
- 239000012535 impurity Substances 0.000 description 2
- 230000002035 prolonged effect Effects 0.000 description 2
- 230000002441 reversible effect Effects 0.000 description 2
- 238000004904 shortening Methods 0.000 description 2
- 235000013547 stew Nutrition 0.000 description 2
- 238000012937 correction Methods 0.000 description 1
- 230000007547 defect Effects 0.000 description 1
- 239000006185 dispersion Substances 0.000 description 1
- 230000000694 effects Effects 0.000 description 1
- 230000006872 improvement Effects 0.000 description 1
- 230000014759 maintenance of location Effects 0.000 description 1
- 238000012986 modification Methods 0.000 description 1
- 230000004048 modification Effects 0.000 description 1
- 230000036961 partial effect Effects 0.000 description 1
- 230000009467 reduction Effects 0.000 description 1
- 230000003068 static effect Effects 0.000 description 1
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
- G01R31/00—Arrangements for testing electric properties; Arrangements for locating electric faults; Arrangements for electrical testing characterised by what is being tested not provided for elsewhere
- G01R31/36—Arrangements for testing, measuring or monitoring the electrical condition of accumulators or electric batteries, e.g. capacity or state of charge [SoC]
- G01R31/385—Arrangements for measuring battery or accumulator variables
- G01R31/387—Determining ampere-hour charge capacity or SoC
- G01R31/388—Determining ampere-hour charge capacity or SoC involving voltage measurements
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
- H01M10/00—Secondary cells; Manufacture thereof
- H01M10/05—Accumulators with non-aqueous electrolyte
- H01M10/052—Li-accumulators
- H01M10/0525—Rocking-chair batteries, i.e. batteries with lithium insertion or intercalation in both electrodes; Lithium-ion batteries
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
- H01M10/00—Secondary cells; Manufacture thereof
- H01M10/42—Methods or arrangements for servicing or maintenance of secondary cells or secondary half-cells
- H01M10/44—Methods for charging or discharging
- H01M10/446—Initial charging measures
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- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
- Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
- Y02E60/00—Enabling technologies; Technologies with a potential or indirect contribution to GHG emissions mitigation
- Y02E60/10—Energy storage using batteries
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Abstract
The application provides a lithium ion battery and a self-discharge screening method thereof. The self-discharge screening method of the lithium ion battery comprises the following steps: firstly, capacity screening is carried out through the capacity percentage difference during formation and capacity grading of the lithium ion battery, so as to carry out preliminary screening on the self-discharge lithium ion battery and obtain a pre-screened lithium battery. And then, the pre-screened lithium battery is switched to voltage screening. The battery is placed for a period of time in a high-temperature state when the battery is charged to 100% SOC and placed for a period of time in a high-temperature state when the battery is charged to 0% SOC, K1 tested and K2 tested and placed for a period of time in a high-temperature state when the battery is charged to 0% SOC, grading screening is carried out according to the average value distribution of K value absolute values in different SOC states, and the K3 mean value +/-Sigma is used as a basis for judging whether the lithium battery is a self-discharging lithium battery. The self-discharge screening method of the lithium ion battery can effectively shorten the standing time of the lithium battery and improve the self-discharge screening accuracy.
Description
Technical Field
The invention relates to the technical field of lithium ion batteries, in particular to a lithium ion battery and a self-discharge screening method thereof.
Background
The self-discharge phenomenon of a battery refers to a phenomenon in which the capacity of the battery is spontaneously lost when the battery is left open, and is also called charge retention capability. Self-discharge can be generally classified into two types: reversible self-discharge and irreversible self-discharge. The lost capacity can be compensated reversibly by reversible self-discharge, the principle of which is similar to the normal discharge reaction of a battery. The main reason for the irreversible self-discharge is that irreversible reactions occur inside the battery, including reactions between the positive electrode and the electrolyte, reactions between the negative electrode and the electrolyte, reactions caused by impurities carried in the electrolyte, and irreversible reactions caused by micro-short circuits caused by impurities carried in the manufacturing process. Self-discharge consistency is an important factor affecting the consistency of the battery pack, and batteries with inconsistent self-discharge have large differences in SOC after being stored for a period of time, which greatly affects capacity and safety. The self-discharge battery is discharged in advance, the whole level of the battery pack is improved, the service life is prolonged, and the reject ratio of products is reduced.
At present, lithium battery manufacturing enterprises screen self-discharge batteries in a normal-temperature standing mode, so that the overall voltage consistency is improved. In order to reduce the proportion of the self-discharge sieve leakage as much as possible, the standing time is generally ensured to be longer. The screening effect of the self-discharge battery can be improved by long standing time, but the production period of the battery can be prolonged, the production cost is increased, and the method does not accord with the great trend of cost reduction and efficiency improvement of the whole market. When the number of batteries is small, it is difficult to determine the self-discharge battery by the voltage dispersion degree, and the conditions of erroneous determination and missed determination may occur.
Disclosure of Invention
The invention aims to overcome the defects in the prior art and provide the lithium ion battery and the self-discharge screening method thereof, which can shorten the standing time of the lithium battery and improve the self-discharge screening accuracy.
The purpose of the invention is realized by the following technical scheme:
a self-discharge screening method of a lithium ion battery comprises the following steps:
carrying out first-time capacity detection operation on the battery core body during formation to obtain a first capacity value;
carrying out secondary capacity detection operation on the battery core body during capacity grading to obtain a second capacity value;
carrying out capacity difference value screening operation on the first capacity value and the second capacity value to obtain a pre-screened lithium battery;
charging the pre-screened lithium battery to a 100% SOC state;
standing the charged pre-screened lithium battery at a first preset temperature for a first preset time;
performing a first voltage measurement operation on the pre-screened lithium battery after the first standing operation to obtain a first voltage value;
standing the pre-screened lithium battery subjected to the first voltage measurement operation at a second preset temperature for a second preset time;
performing a second voltage measurement operation on the pre-screened lithium battery subjected to the second standing operation to obtain a second voltage value;
discharging the pre-screened lithium battery subjected to the second voltage measurement operation to a 0% SOC state;
standing the discharged pre-screened lithium battery for a third preset time at a constant temperature of a third preset temperature;
performing a third voltage measurement operation on the pre-screened lithium battery after the third standing operation to obtain a third voltage value;
standing the pre-screened lithium battery subjected to the third voltage measurement operation for a fourth preset time at a constant temperature of a fourth preset temperature;
performing fourth voltage measurement operation on the pre-screened lithium battery after the fourth standing operation to obtain a fourth voltage value;
calculating a K3 value of the lithium ion battery to be tested, wherein a K1 value is (first voltage value/second voltage value)/(first preset time + second preset time), a K2 value is (third voltage value-fourth voltage value)/(third preset time + fourth preset time), and a K3 value is | K2/K1 |;
judging whether the lithium ion battery to be tested is a self-discharge lithium ion battery or not according to a comparison result of the K3 value and the lithium ion battery self-discharge screening standard; the screening criteria were K3 means ± Σ for grading.
In one embodiment, before the step of performing a first capacity detection operation on the battery core during formation to obtain a first capacity value, the self-discharge screening method for the lithium ion battery further includes the following steps:
and spraying the two-dimensional code on the battery core body.
In one embodiment, after the pre-screened lithium battery is charged to a 100% SOC state, the pre-screened lithium battery is placed in a constant temperature state at a first preset temperature, and after the pre-screened lithium battery is placed for a first preset time, a first voltage measurement operation is performed on the pre-screened lithium battery to obtain a first voltage value, where the method for screening lithium ion battery by self-discharge further includes the following operations:
and applying a first pressure to the pre-screened lithium battery charged to the 100% SOC state at the constant temperature state of the first preset temperature, and maintaining the pressure and standing for a first preset time.
In one embodiment, in the step of standing the pre-screened lithium battery after the first voltage measurement operation at a constant temperature at a second preset temperature for a second preset time, performing a second voltage measurement operation on the pre-screened lithium battery to obtain a second voltage value, the self-discharge screening method for lithium ion batteries further includes the following operations:
and applying a second pressure to the pre-screened lithium battery which completes the first voltage measurement operation in the constant temperature state of the second preset temperature, and maintaining the pressure and standing for a second preset time.
In one embodiment, after the pre-screened lithium battery that has completed the second voltage measurement operation is discharged to a 0% SOC state, the pre-screened lithium battery that has been discharged to the 0% SOC state is left to stand at a constant temperature of a third preset temperature for a third preset time, and then the third voltage measurement operation is performed on the pre-screened lithium battery to obtain a third voltage value, where the method for screening lithium ion batteries by self-discharge further includes the following operations:
and applying a third pressure to the pre-screened lithium battery discharged to the 0% SOC state at the constant temperature state of the third preset temperature, and maintaining the pressure and standing for a third preset time.
In one embodiment, in the step of standing the pre-screened lithium battery after the third voltage measurement operation at a constant temperature at a fourth preset temperature for a fourth preset time, performing a fourth voltage measurement operation on the pre-screened lithium battery to obtain a fourth voltage value, the self-discharge screening method for the lithium ion battery further includes the following operations:
and applying fourth pressure to the pre-screened lithium battery which is subjected to the third voltage measurement operation in a constant temperature state at the fourth preset temperature, and maintaining the pressure and standing for a fourth preset time.
In one embodiment, the first preset temperature is the same as the third preset temperature.
In one embodiment, the second preset temperature is the same as the fourth preset temperature.
In one embodiment, the first preset time is the same as the third preset time.
A lithium ion battery adopts the self-discharge screening method of the lithium ion battery as described in any of the above embodiments to perform self-discharge screening.
Compared with the prior art, the invention has at least the following advantages:
1. the self-discharge screening method of the lithium ion battery comprises the steps of firstly grading and screening the capacity percentage difference value of a battery core body during formation and capacity grading, then charging the lithium ion battery to a 100% SOC state, then discharging to a 0% SOC state, applying certain pressure to the lithium ion battery during the process, carrying out voltage measurement operation on the lithium ion battery in different charge states at different temperature states to obtain corresponding voltage values, grading and screening through the voltage drop change proportion value of the voltage values of the lithium ion battery, and taking the K3 mean value +/-sigma as a basis for judging whether the lithium battery is the self-discharge lithium battery. Therefore, compared with the prior art, the self-discharge screening method of the lithium ion battery can obviously improve the screening accuracy of the self-discharge lithium ion battery.
2. In the lithium ion battery self-discharge screening method, the lithium ion battery is subjected to two standing operations, namely, the lithium ion battery is charged to a 100% SOC state, the first standing operation is carried out after the first voltage measurement operation is carried out on the lithium ion battery, the lithium ion battery is discharged to a 0% SOC state, the second standing operation is carried out after the third voltage measurement operation is carried out on the lithium ion battery discharged to the 0% SOC state, and the lithium ion battery self-discharge screening method not only can improve the accuracy of lithium ion battery self-discharge screening, but also can remarkably shorten the lithium ion battery standing time compared with the standing time of a normal-temperature standing mode by carrying out the two standing operations on the lithium ion battery under two different SOC states, thereby shortening the production cycle of the lithium ion battery and reducing the production cost of the lithium ion battery.
Drawings
In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings needed to be used in the embodiments will be briefly described below, it should be understood that the following drawings only illustrate some embodiments of the present invention and therefore should not be considered as limiting the scope, and for those skilled in the art, other related drawings can be obtained according to the drawings without inventive efforts.
Fig. 1 is a flowchart of a self-discharge screening method for a lithium ion battery in an embodiment.
Detailed Description
To facilitate an understanding of the invention, the invention will now be described more fully with reference to the accompanying drawings. Preferred embodiments of the present invention are shown in the drawings. This invention may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete.
It will be understood that when an element is referred to as being "secured to" another element, it can be directly on the other element or intervening elements may also be present. When an element is referred to as being "connected" to another element, it can be directly connected to the other element or intervening elements may also be present. The terms "vertical," "horizontal," "left," "right," and the like as used herein are for illustrative purposes only and do not represent the only embodiments.
Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. The terminology used herein in the description of the invention is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention. As used herein, the term "and/or" includes any and all combinations of one or more of the associated listed items.
The application provides a self-discharge screening method of a lithium ion battery. The self-discharge screening method of the lithium ion battery comprises the following steps: carrying out first-time capacity detection operation on the battery core body during formation to obtain a first capacity value; carrying out secondary capacity detection operation on the battery core body during capacity grading to obtain a second capacity value; carrying out capacity difference value screening operation on the first capacity value and the second capacity value to obtain a pre-screened lithium battery; charging the pre-screened lithium battery to a 100% SOC state; standing the charged pre-screened lithium battery at a first preset temperature for a first preset time; performing a first voltage measurement operation on the pre-screened lithium battery after the first standing operation to obtain a first voltage value; standing the pre-screened lithium battery subjected to the first voltage measurement operation at a second preset temperature for a second preset time; performing a second voltage measurement operation on the pre-screened lithium battery subjected to the second standing operation to obtain a second voltage value; discharging the pre-screened lithium battery subjected to the second voltage measurement operation to a 0% SOC state; standing the discharged pre-screened lithium battery for a third preset time at a constant temperature of a third preset temperature; performing a third voltage measurement operation on the pre-screened lithium battery after the third standing operation to obtain a third voltage value; standing the pre-screened lithium battery subjected to the third voltage measurement operation for a fourth preset time at a constant temperature of a fourth preset temperature; performing fourth voltage measurement operation on the pre-screened lithium battery after the fourth standing operation to obtain a fourth voltage value; calculating a K3 value of the lithium ion battery to be tested, wherein a K1 value is (first voltage value/second voltage value)/(first preset time + second preset time), a K2 value is (third voltage value-fourth voltage value)/(third preset time + fourth preset time), and a K3 value is | K2/K1 |; judging whether the lithium ion battery to be tested is a self-discharge lithium ion battery or not according to a comparison result of the K3 value and the lithium ion battery self-discharge screening standard; the screening criteria were K3 means ± Σ for grading.
The self-discharge screening method of the lithium ion battery comprises the steps of firstly grading and screening the capacity percentage difference value of a battery core body during formation and capacity grading, then charging the lithium ion battery to a 100% SOC state, then discharging to a 0% SOC state, applying certain pressure to the lithium ion battery during the process, carrying out voltage measurement operation on the lithium ion battery in different charge states at different temperature states to obtain corresponding voltage values, grading and screening through the voltage drop change proportion value of the voltage values of the lithium ion battery, and judging whether the lithium battery is the self-discharge lithium battery according to K3 mean value +/-sigma. Therefore, compared with the prior art, the self-discharge screening method of the lithium ion battery can obviously improve the screening accuracy of the self-discharge lithium ion battery. Further, in the self-discharge screening method of the lithium ion battery, the lithium ion battery is subjected to two standing operations, namely, the lithium ion battery is charged to a 100% SOC state, and the first standing operation is carried out after the first voltage measurement operation is carried out on the lithium ion battery, and discharging the lithium ion battery to 0% SOC state, performing a second standing operation after performing a third voltage measurement operation on the lithium ion battery discharged to 0% SOC state, through the standing operation of the lithium ion battery under two different SOC states, the accuracy of the self-discharge screening of the lithium ion battery can be improved, compared with the standing time of a normal-temperature standing mode, the standing time of the lithium ion battery can be remarkably shortened, the production period of the lithium ion battery is further shortened, and the production cost of the lithium ion battery is reduced.
In order to better understand the self-discharge screening method of the lithium ion battery of the present invention, the following further explains the self-discharge screening method of the lithium ion battery of the present invention, and the self-discharge screening method of the lithium ion battery of an embodiment includes part or all of the following steps:
and S10, carrying out first capacity detection operation on the battery core body during formation to obtain a first capacity value.
It can be understood that formation generally refers to that a series of process measures are performed on the lithium ion battery which is charged for the first time to make the performance of the lithium ion battery tend to be stable, that is, the battery capacity tends to be stable after the lithium ion battery is formed. In this embodiment, the first capacity value is obtained by performing the first capacity detection operation on the battery core body during formation, so as to conveniently form a difference value with the capacity of the lithium battery during capacity grading, and the screening is performed by grading and screening the capacity percentage difference value of the battery core body during formation and capacity grading, so that the screening accuracy of the self-discharge lithium battery is improved.
And S20, carrying out the second time of capacity detection operation on the battery core body during capacity grading to obtain a second capacity value.
It can be understood that the data of each detection point is obtained through computer management during the capacity grading of the battery, so that the data of the capacity, the internal resistance and the like of the battery are analyzed, and the quality grade of the battery is determined. The other purpose of capacity grading is to classify and organize the batteries, namely screening out the single batteries with the same internal resistance and capacity for combination. In this embodiment, the second capacity value is obtained by performing the second capacity detection operation on the battery core body during capacity grading, so that the percentage difference between the second capacity value and the first capacity value is graded and screened, and the screening accuracy of the self-discharge lithium battery is further improved.
And S30, carrying out capacity difference value screening operation on the first capacity value and the second capacity value to obtain the pre-screened lithium battery.
In this embodiment, the capacity percentage difference of the battery core during formation and capacity grading is graded and screened, so that the self-discharge condition of the lithium ions can be preliminarily screened, and the screening accuracy of the self-discharge lithium battery is improved. In addition, through the self-discharge screening condition of the battery core body during formation and capacity grading, reference basis can be provided for subsequent voltage screening, and therefore the screening accuracy of the self-discharge lithium battery is further improved. Furthermore, the screening is carried out according to the volume percentage of less than or equal to 3 percent.
And S40, charging the pre-screening lithium battery to a 100% SOC state.
It is understood that SOC, i.e., state of charge, is used to reflect the remaining capacity of the battery, which is numerically defined as the ratio of the remaining capacity to the battery capacity. In this embodiment, the pre-screened lithium battery is charged to a 100% SOC state, i.e., the pre-screened lithium battery is charged to a fully charged state.
And S50, standing the charged pre-screened lithium battery at a first preset temperature for a first standing operation for a first preset time.
In this embodiment, after the pre-screening lithium battery is charged to the 100% SOC state, before the first voltage measurement operation is performed on the pre-screening lithium battery, the pre-screening lithium battery is allowed to stand at a constant temperature of a first preset temperature for a first preset time to be processed, so that the measurement accuracy is improved. Furthermore, the first preset temperature is higher than the normal temperature, so that the first preset time in the standing operation can be obviously shorter, and the production period of the lithium ion battery can be shortened and the production cost of the lithium ion battery can be reduced.
And S60, performing first voltage measurement operation on the pre-screened lithium battery after the first standing operation to obtain a first voltage value.
In this embodiment, a first voltage measurement operation is performed on the pre-screened lithium battery after the first standing operation, and the first voltage measurement operation is performed in a state that the pre-screened lithium battery is fully charged, so as to obtain a first voltage value, where the first voltage value is an important index for calculating the self-discharge degree of the lithium ion battery.
And S70, standing the pre-screened lithium battery which is subjected to the first voltage measurement operation at a second preset temperature for a second preset time.
In this embodiment, the pre-screened lithium battery that has completed the first voltage measurement operation is subjected to a second standing operation at a second preset temperature for a second preset time. After the pre-screened lithium battery is kept still for the second preset time, partial capacity loss occurs, namely the pre-screened lithium battery has a discharge phenomenon. The second voltage value is measured conveniently, and the second voltage value and the first voltage value are used as an important index for calculating the self-discharge degree of the lithium ion battery.
And S80, performing a second voltage measurement operation on the pre-screened lithium battery after the second standing operation to obtain a second voltage value.
And after the pre-screened lithium battery is stood for the second preset time, performing a second voltage measurement operation to obtain a second voltage value, comparing the second voltage value with the first voltage value, wherein the second voltage value is an important index for calculating the self-discharge degree of the lithium ion battery, and the second voltage value and the first voltage value are used for calculating the self-discharge screening of the lithium ion battery, so that whether the lithium ion battery to be tested is the self-discharge lithium ion battery is judged, and the screening accuracy of the self-discharge lithium ion battery can be remarkably improved. Furthermore, the second preset temperature is higher than the normal temperature, so that the second preset time in the standing operation can be obviously shorter, and the production period of the lithium ion battery can be shortened and the production cost of the lithium ion battery can be reduced.
And S90, discharging the pre-screened lithium battery which completes the second voltage measurement operation to 0% SOC state.
It is understood that SOC, i.e., state of charge, is used to reflect the remaining capacity of the battery, which is numerically defined as the ratio of the remaining capacity to the battery capacity. In this embodiment, the pre-screening lithium battery that completes the second voltage measurement operation is discharged to the 0% SOC state, that is, the pre-screening lithium battery discharges the energy that can be discharged by the constant current discharge, so that the second voltage value measurement of the pre-screening lithium battery is facilitated, and is compared with the voltage value of the pre-screening lithium battery that is charged to the 100% SOC state.
And S100, standing the discharged pre-screened lithium battery for a third preset time at a constant temperature of a third preset temperature.
In this embodiment, the discharged pre-screened lithium battery is subjected to a third standing operation for a third preset time in a constant temperature state at a third preset temperature, and it can be understood that the pre-screened lithium battery discharged to the 0% SOC state is allowed to stand in the constant temperature state at the third preset temperature, so that the accuracy of self-discharge screening of the lithium ion battery can be effectively improved.
And S110, performing third voltage measurement operation on the pre-screened lithium battery after the third standing operation to obtain a third voltage value.
In this embodiment, a third voltage measurement operation is performed on the pre-screened lithium battery after the third standing operation, and after the third standing operation is performed for a third preset time, the third voltage measurement operation is performed on the pre-screened lithium battery to obtain a third voltage value, where the third voltage value is an important index for calculating the self-discharge degree of the lithium ion battery. Furthermore, the third preset temperature is higher than the normal temperature, so that the third preset time in the standing operation can be obviously shorter, and the production period of the lithium ion battery can be shortened and the production cost of the lithium ion battery can be reduced.
And S120, standing the pre-screened lithium battery subjected to the third voltage measurement operation for a fourth preset time at a constant temperature of a fourth preset temperature.
It can be understood that the pre-screened lithium battery has discharged the full capacity that can be discharged by the constant current discharge after the third voltage measurement operation in the state of discharging to 0% SOC, but at this time, if the pre-screened lithium battery is discharged with a smaller current, the pre-screened lithium battery can continue to discharge. In this embodiment, the pre-screened lithium battery that has completed the third voltage measurement operation is subjected to a fourth standing operation at a constant temperature of a fourth preset temperature for a fourth preset time, so as to perform voltage measurement on the pre-screened lithium battery again.
And S130, performing fourth voltage measurement operation on the pre-screened lithium battery after the fourth standing operation to obtain a fourth voltage value.
In this embodiment, the fourth voltage measurement operation is performed on the pre-screened lithium battery after the fourth standing operation, and after the fourth standing operation is performed for a fourth preset time, the fourth voltage measurement operation is performed on the pre-screened lithium battery to obtain a fourth voltage value, where the fourth voltage value is an important index for calculating the self-discharge degree of the lithium ion battery. The K2 value can be calculated through the fourth voltage value and the third voltage value, and the K3 mean value is calculated with the K1 value, so that whether the lithium ion battery to be tested is the self-discharge lithium ion battery or not is judged, and the screening accuracy of the self-discharge lithium ion battery can be remarkably improved.
S140, calculating a K3 value of the lithium ion battery to be tested, where the K1 value is (first voltage value/second voltage value)/(first preset time + second preset time), the K2 value is (third voltage value-fourth voltage value)/(third preset time + fourth preset time), and the K3 value is | K2/K1 |.
In this embodiment, K1 is set to be (first voltage value/second voltage value)/(first preset time + second preset time), K2 is set to be (third voltage value-fourth voltage value)/(third preset time + fourth preset time), and | K2/K1| is set to be K3, and K3 mean ± Σ is classified as a screening criterion for self-discharge of the lithium ion battery. It can be understood that, the present application firstly classifies and screens the capacity percentage difference between the formation and the capacity of the battery core, and then measures the K1 value after the lithium ion battery is left standing for a period of time in a high temperature state when the lithium ion battery is charged to 100% SOC state, and measures the K2 value after the lithium ion battery is left standing for a period of time in a high temperature state when the lithium ion battery is discharged to 0% SOC state. And then, calculating K value absolute values under different SOC states according to the K1 value and the K2 value, namely average value distribution of K2 mean values, performing grading screening, and judging whether the lithium battery is the self-discharge lithium ion battery according to the K3 mean value +/-sigma, thereby remarkably improving the screening accuracy of the self-discharge lithium ion battery compared with the prior art.
S150, judging whether the lithium ion battery to be detected is the self-discharge lithium ion battery or not according to a comparison result of the K3 value and the lithium ion battery self-discharge screening standard; the screening criteria were K3 means. + -. Sigma for grading.
In this embodiment, whether the lithium ion battery to be tested is a self-discharge lithium ion battery is judged according to a comparison result of the K3 value and the lithium ion battery self-discharge screening standard; the screening criteria were ranked as K3 mean + -Sigma, Sigma representing the sign of the summation. Specifically, the value of K3 is compared with the screening standard, and if the value of K3 is greater than the screening standard, that is, the value of K3 is greater than the mean value of K3 ± Σ, it is determined that the lithium ion battery to be tested is a self-discharge lithium ion battery, that is, the lithium ion battery to be tested is not qualified. And if the K3 value is smaller than or equal to the screening standard, namely the K3 value is smaller than or equal to the K3 mean value +/-Sigma, determining that the lithium ion battery to be tested is a non-self-discharge lithium ion battery, namely the lithium ion battery to be tested is qualified. By comparing the K3 value obtained by calculation with the screening standard, the difference value between the K3 value and the screening standard can be accurately seen, so that the screening accuracy of the self-discharge lithium ion battery is remarkably improved.
In one embodiment, before the step of performing the first capacity detection operation on the battery core body during formation to obtain the first capacity value, the self-discharge screening method for the lithium ion battery further includes the following steps: and (4) spraying the two-dimensional code on the battery core body. In this embodiment, when formation, the battery core is subjected to first capacity detection operation, and before the step of obtaining a first capacity value, the two-dimensional code spraying operation is performed on the surface of the battery core, so that the battery core can be identified and distinguished, that is, the lithium ion battery can be identified and distinguished, and therefore batch detection operation of the lithium ion battery is facilitated, and a disordered situation in the detection process is avoided. In addition, the computer system can be connected with the two-dimensional code by spraying the two-dimensional code on the surface of the lithium ion battery, so that the information of the lithium ion battery is recorded in the two-dimensional code, and the information of the lithium ion battery, such as a detection result, can be recorded and calculated by the computer system, so that the self-discharge screening efficiency of the lithium ion battery can be remarkably improved. In addition, the two-dimensional code has the advantages of high-density coding, large information capacity, wide coding range, strong fault tolerance, error correction function and high decoding reliability.
In one embodiment, after the step of performing the first capacity detection operation on the battery core body during formation to obtain the first capacity value, and before the step of performing the second capacity detection operation on the battery core body during capacity grading to obtain the second capacity value, the self-discharge screening method for the lithium ion battery further includes the following steps: and carrying out first code scanning operation on the battery core body which completes the first capacity detection operation. The code scanning operation is performed for the first time on the battery core body which completes the first time of capacity detection operation, and the measurement result of the battery core body in the first time of capacity detection operation is uploaded to a computer system, so that the first capacity value is conveniently recorded, the formula is conveniently put into the first capacity value and the subsequent measurement result for calculation, and further the self-discharge screening efficiency of the lithium ion battery is effectively improved, and data are better stored.
Further, after the step of performing the second capacity detection operation on the battery core body during capacity grading to obtain the second capacity value, and before the step of performing the capacity difference value screening operation on the first capacity value and the second capacity value to obtain the pre-screened lithium battery, the self-discharge screening method for the lithium ion battery further includes the following steps: and carrying out second code scanning operation on the battery core body which completes the second capacity detection operation. The code scanning operation is carried out for the second time on the battery core body which finishes the second time of capacity detection operation, and the measuring result of the lithium ion battery in the second time of capacity detection operation is uploaded to a computer system, so that the second capacity value is conveniently recorded, the formula is conveniently put into the second capacity value and the first capacity value for calculation, and further the self-discharge screening efficiency of the lithium ion battery is effectively improved, and data are better stored.
In one embodiment, after the pre-screened lithium battery is charged to the 100% SOC state, the pre-screened lithium battery is placed in a constant temperature state at a first preset temperature, and after the pre-screened lithium battery is placed for a first preset time, a first voltage measurement operation is performed on the pre-screened lithium battery, before the step of obtaining a first voltage value, before the step of placing the pre-screened lithium battery, which has completed the first voltage measurement operation, in a constant temperature state at a second preset temperature, and after the pre-screened lithium battery is placed for a second preset time, a second voltage measurement operation is performed on the pre-screened lithium battery, and before the step of obtaining a second voltage value, the self-discharge screening method for the lithium ion battery further includes the following steps: and carrying out code scanning operation for the third time on the pre-screened lithium battery which completes the first voltage measurement operation. In this embodiment, the code scanning operation is performed for the third time on the pre-screened lithium battery which completes the first voltage measurement operation, and the measurement result of the pre-screened lithium battery in the first voltage measurement operation is uploaded to a computer system, so that the first voltage value is conveniently recorded, the first voltage value and the subsequent measurement result are conveniently put into a formula for calculation, and further, the self-discharge screening efficiency of the lithium ion battery is effectively improved, and data are better stored.
In one embodiment, after the step of standing the pre-screened lithium battery after the first voltage measurement operation at a constant temperature of a second preset temperature for a second preset time, performing a second voltage measurement operation on the pre-screened lithium battery to obtain a second voltage value, after discharging the pre-screened lithium battery after the second voltage measurement operation to a 0% SOC state, standing the pre-screened lithium battery discharged to the 0% SOC state at a constant temperature of a third preset temperature for a third preset time, performing a third voltage measurement operation on the pre-screened lithium battery, and before the step of obtaining a third voltage value, the self-discharge screening method for lithium ion batteries further includes the following steps: and carrying out fourth code scanning operation on the pre-screened lithium battery which is subjected to the second voltage measurement operation. In this embodiment, the code scanning operation is performed for the fourth time on the pre-screened lithium battery which completes the second voltage measurement operation, and the measurement result of the pre-screened lithium battery in the second voltage measurement operation is uploaded to a computer system, so that the second voltage value is conveniently recorded, the second voltage value and the subsequent measurement result are conveniently put into a formula for calculation, and further, the self-discharge screening efficiency of the lithium ion battery is effectively improved, and data are better stored.
In one embodiment, after discharging the pre-screened lithium battery with the second voltage measurement operation to the 0% SOC state, standing the pre-screened lithium battery with the second voltage measurement operation to the 0% SOC state at a constant temperature of a third preset temperature for a third preset time, performing a third voltage measurement operation on the pre-screened lithium battery to obtain a third voltage value, standing the pre-screened lithium battery with the third voltage measurement operation at a constant temperature of a fourth preset temperature for a fourth preset time, performing a fourth voltage measurement operation on the pre-screened lithium battery, and before the step of obtaining the fourth voltage value, the self-discharge screening method for the lithium ion battery further includes the following steps: and carrying out a fifth code scanning operation on the pre-screened lithium battery which is subjected to the third voltage measurement operation. In this embodiment, the code scanning operation is performed for the fifth time on the pre-screened lithium battery which completes the third voltage measurement operation, and the measurement result of the pre-screened lithium battery in the third voltage measurement operation is uploaded to the computer system, so that the third voltage value is conveniently recorded, the third voltage value and the subsequent measurement result are conveniently put into a formula for calculation, and further, the self-discharge screening efficiency of the lithium ion battery is effectively improved, and data are better stored.
In one embodiment, after the step of standing the pre-screened lithium battery after the third voltage measurement operation at a constant temperature at a fourth preset temperature for a fourth preset time, performing a fourth voltage measurement operation on the pre-screened lithium battery to obtain a fourth voltage value, the self-discharge screening method for the lithium ion battery further includes the following steps: and carrying out sixth code scanning operation on the pre-screened lithium battery which is subjected to the fourth voltage measurement operation. In this embodiment, the code scanning operation is performed for the sixth time through the pre-screening lithium battery which completes the fourth voltage measurement operation, and the measurement result of the pre-screening lithium battery in the fourth voltage measurement operation is uploaded to a computer system, so that the fourth voltage value is conveniently recorded, the fourth voltage value and the subsequent measurement result are conveniently put into a formula for calculation, and further, the self-discharge screening efficiency of the lithium ion battery is effectively improved, and data are better stored.
In one embodiment, after the pre-screened lithium battery is charged to the 100% SOC state, the pre-screened lithium battery is placed in a constant temperature state at a first preset temperature, and after the pre-screened lithium battery is placed for a first preset time, a first voltage measurement operation is performed on the pre-screened lithium battery to obtain a first voltage value, where the method for screening lithium ion battery by self-discharge further includes the following operations: and applying a first pressure to the pre-screened lithium battery charged to the 100% SOC state at a constant temperature state of a first preset temperature, and maintaining the pressure and standing for a first preset time. It can be understood that, the pre-screening lithium battery is charged to a state of 100% SOC, that is, the pre-screening lithium battery is charged to a fully charged state, and a first voltage value is obtained by performing a first voltage measurement operation in the fully charged state of the pre-screening lithium battery, where the first voltage value is an important index for calculating the self-discharge degree of the lithium ion battery. In order to further improve the screening accuracy of the self-discharging lithium battery, under the constant temperature state of a first preset temperature, applying a first pressure to the pre-screened lithium battery charged to the 100% SOC state, maintaining the pressure and standing for a first preset time to obtain a voltage value of the pre-screened lithium battery charged to the 100% SOC state under the first preset temperature state after applying the first pressure, so that the voltage values obtained after applying certain pressure to the pre-screened lithium battery under different charge states and different temperature states are calculated and screened, and the screening accuracy of the self-discharging lithium battery is further improved.
In one embodiment, in the step of standing the pre-screened lithium battery after the first voltage measurement operation at a constant temperature of a second preset temperature for a second preset time, performing a second voltage measurement operation on the pre-screened lithium battery to obtain a second voltage value, the self-discharge screening method for the lithium ion battery further includes the following operations: and applying a second pressure to the pre-screened lithium battery which finishes the first voltage measurement operation in a constant temperature state of a second preset temperature, and maintaining the pressure and standing for a second preset time. It can be understood that after the pre-screened lithium battery is left standing for the second preset time, the capacity is partially lost, that is, the pre-screened lithium battery is discharged. And after the pre-screened lithium battery is stood for the second preset time, performing a second voltage measurement operation to obtain a second voltage value, comparing the second voltage value with the first voltage value, wherein the second voltage value is an important index for calculating the self-discharge degree of the lithium ion battery, and the second voltage value and the first voltage value are used for calculating the self-discharge screening of the lithium ion battery, so that whether the lithium ion battery to be tested is the self-discharge lithium ion battery is judged, and the screening accuracy of the self-discharge lithium ion battery can be remarkably improved. In order to further improve the screening accuracy of the self-discharge lithium ion battery, in this embodiment, in a constant temperature state at a second preset temperature, a second pressure is applied to the pre-screened lithium ion battery that has completed the first voltage measurement operation, and the pre-screened lithium ion battery that has completed the first voltage measurement operation is kept static for a second preset time to obtain a voltage value of the pre-screened lithium ion battery that has completed the first voltage measurement operation after the second pressure is applied in the first preset temperature state, so that the voltage values obtained after the pre-screened lithium ion battery is applied with a certain pressure in different charge states and different temperature states are calculated and screened, thereby further improving the screening accuracy of the self-discharge lithium ion battery.
In one embodiment, after the pre-screened lithium battery that has completed the second voltage measurement operation is discharged to a 0% SOC state, the pre-screened lithium battery that has been discharged to the 0% SOC state is left to stand at a constant temperature of a third preset temperature for a third preset time, and then the third voltage measurement operation is performed on the pre-screened lithium battery to obtain a third voltage value, the self-discharge screening method for lithium ion batteries further includes the following operations: and applying a third pressure to the pre-screened lithium battery discharged to the 0% SOC state at a constant temperature state of a third preset temperature, and maintaining the pressure and standing for a third preset time. It can be understood that after the lithium ion battery is kept still for the third preset time, the third voltage measurement operation is performed on the pre-screened lithium ion battery to obtain a third voltage value, and the third voltage value is an important index for calculating the self-discharge degree of the lithium ion battery. In order to further improve the screening accuracy of the self-discharge lithium battery, in this embodiment, in a constant temperature state at a third preset temperature, a third pressure is applied to the pre-screened lithium battery discharged to the 0% SOC state, the pre-screened lithium battery is kept standing for a third preset time, and then a third voltage measurement operation is performed on the pre-screened lithium battery to obtain a third voltage value of the pre-screened lithium battery discharged to the 0% SOC state after the third pressure is applied in the third preset temperature state, so that the voltage values obtained after the pre-screened lithium battery is applied with a certain pressure in different charge states and different temperature states are calculated and screened, thereby further improving the screening accuracy of the self-discharge lithium battery.
In one embodiment, in the step of standing the pre-screened lithium battery after the third voltage measurement operation at a constant temperature at a fourth preset temperature for a fourth preset time, performing a fourth voltage measurement operation on the pre-screened lithium battery to obtain a fourth voltage value, the self-discharge screening method for the lithium ion battery further includes the following operations: and applying fourth pressure to the pre-screened lithium battery which finishes the third voltage measurement operation in a constant temperature state of a fourth preset temperature, and maintaining the pressure and standing for a fourth preset time. It can be understood that after the lithium ion battery is kept still for the fourth preset time, the fourth voltage measurement operation is performed on the pre-screened lithium ion battery to obtain a fourth voltage value, and the fourth voltage value is an important index for calculating the self-discharge degree of the lithium ion battery. In order to further improve the screening accuracy of the self-discharging lithium battery, in this embodiment, in a constant temperature state at a fourth preset temperature, a fourth pressure is applied to the pre-screened lithium battery that has completed the third voltage measurement operation, the pre-screened lithium battery is kept standing for a fourth preset time, and then the fourth voltage measurement operation is performed on the pre-screened lithium battery to obtain a fourth voltage value of the pre-screened lithium battery that has completed the third voltage measurement operation after the fourth pressure is applied in the fourth preset temperature state, so that the difference value calculation can be performed on the voltage values of the pre-screened lithium battery that has completed the third voltage measurement operation after a certain pressure is applied in different charge states and different temperature states, and the grading screening is performed through the voltage drop change proportion value of the battery voltage value, thereby further improving the screening accuracy of the self-discharging lithium battery.
For the accuracy of the lithium ion battery self-discharge screening, in one embodiment, the first preset temperature is the same as the third preset temperature. That is to say, the temperature of standing after the pre-screening lithium battery is charged to the 100% SOC state is the same as the temperature of standing after the pre-screening lithium battery which is to finish the second voltage measurement operation is discharged to the 0% SOC state, so that the influence on the discharging condition of the lithium ion battery due to different temperatures and the influence on the screening of the self-discharging of the lithium ion battery are avoided. Further, the first preset temperature and the third preset temperature are both 20-30 ℃, so that the reaction rate of the electrode and the output power of the battery are improved, and the charge and discharge performance of the lithium ion battery is further improved.
In one embodiment, the second predetermined temperature is the same as the fourth predetermined temperature. That is to say, the temperature that the pre-screening lithium battery that will accomplish the voltage measurement operation of the first time stews is the same with the temperature that the pre-screening lithium battery that will accomplish the voltage measurement operation of the third time stews to avoid influencing the voltage measurement of lithium ion battery after charging and after discharging because the temperature is different, and then guarantee the accuracy of lithium ion battery self discharge screening. Furthermore, the second preset temperature and the fourth preset temperature are both 40-50 ℃, so that the standing time of the lithium ion battery can be obviously shortened, the production period of the lithium ion battery is further shortened, and the production cost of the lithium ion battery is reduced.
In one embodiment, the first preset time is the same as the third preset time. That is to say, the time for standing the pre-screened lithium battery after being charged to the 100% SOC state is the same as the time for standing the pre-screened lithium battery after being discharged to the 0% SOC state, so as to avoid the influence on the discharge condition of the lithium ion battery due to different time, and further influence on the screening of the self-discharge of the lithium ion battery. Further, the first preset time and the third preset time are both 24 hours to 48 hours.
In one embodiment, the second preset time is the same as the fourth preset time. That is to say, the time for the pre-screened lithium battery to complete the first voltage measurement operation to stand is the same as the time for the pre-screened lithium battery to complete the third voltage measurement operation to stand, so that the voltage measurement of the lithium ion battery after charging and discharging is prevented from being influenced by different time, and the accuracy of the lithium ion battery self-discharge screening is ensured. Furthermore, the second preset time and the fourth preset time are both 15-30 hours, and compared with the standing time in the normal-temperature standing mode, the standing time of the lithium ion battery is obviously shortened, so that the production period of the lithium ion battery is shortened, and the production cost of the lithium ion battery is reduced.
Example 1
Spraying two-dimension code distinguishing identification on a lithium ion battery core body to be tested, scanning a code uploading system for capacity in formation, scanning a code uploading system for capacity in capacity grading, firstly, carrying out capacity screening through a capacity percentage difference between formation and capacity grading, and screening the capacity percentage which is less than or equal to 3% to obtain a pre-screened lithium battery. The method comprises the steps of charging a pre-screened lithium battery to a 100% SOC state, maintaining the pressure at a constant temperature of 20 ℃ for a first preset time t1 at a first pressure, measuring the voltage V1 of the battery after the voltage is measured, scanning a two-dimensional code, and uploading the two-dimensional code to a computer system. And after the voltage V1 is measured, maintaining the pressure of the pre-screened lithium battery at the constant temperature of 40 ℃ for a period of time t2 at a second pressure, and scanning the two-dimensional code to upload the voltage V2 to a computer system when the voltage of the pre-screened lithium battery is finished. And discharging the pre-screened lithium battery to a 0% SOC state, maintaining the pressure at a constant temperature of 20 ℃ for a period of time t3 at a third pressure, measuring the battery voltage V3 after the pressure is maintained, scanning the two-dimensional code, and uploading the two-dimensional code to a computer system. And after the voltage V3 is measured, maintaining the pressure of the pre-screened lithium battery at the constant temperature of 40 ℃ for a period of time t4 at a fourth pressure, and scanning the two-dimensional code to upload the voltage V4 of the pre-screened lithium battery to a computer system when the voltage is finished. The method comprises the steps of (V1/V2)/(t1+ t2) for K1, and (V3-V4)/(t3+ t4) for K2, grading | K2/K1| -K3, K3 mean value +/-Sigma, and automatically judging the lithium ion battery exceeding the standard as a self-discharge lithium battery and sorting the lithium ion battery according to the production product requirement (K3 mean value +/-Sigma) as a screening standard.
Example 2
Spraying two-dimension code distinguishing identification on a lithium ion battery core body to be tested, scanning a code uploading system for capacity in formation, scanning a code uploading system for capacity in capacity grading, firstly, carrying out capacity screening through a capacity percentage difference between formation and capacity grading, and screening the capacity percentage which is less than or equal to 3% to obtain a pre-screened lithium battery. The method comprises the steps of charging a pre-screened lithium battery to a 100% SOC state, maintaining the pressure at a constant temperature of 30 ℃ for a first preset time t1 at a first pressure, measuring the voltage V1 of the battery after the voltage is measured, scanning a two-dimensional code, and uploading the two-dimensional code to a computer system. And after the voltage V1 is measured, maintaining the pressure of the pre-screened lithium battery at the constant temperature of 50 ℃ for a period of time t2 at a second pressure, and scanning the two-dimensional code to upload the voltage V2 to a computer system when the voltage of the pre-screened lithium battery is finished. And discharging the pre-screened lithium battery to a 0% SOC state, maintaining the pressure at a constant temperature of 30 ℃ for a period of time t3 under a third pressure, measuring the battery voltage V3 after the pressure is maintained, scanning the two-dimensional code, and uploading the two-dimensional code to a computer system. And after the voltage V3 is measured, maintaining the pressure of the pre-screened lithium battery at the constant temperature of 50 ℃ for a period of time t4 at a fourth pressure, and scanning the two-dimensional code to upload the voltage V4 of the pre-screened lithium battery to a computer system when the voltage is finished. The method comprises the steps of (V1/V2)/(t1+ t2) for K1, and (V3-V4)/(t3+ t4) for K2, grading | K2/K1| -K3, K3 mean value +/-Sigma, and automatically judging the lithium ion battery exceeding the standard as a self-discharge lithium battery and sorting the lithium ion battery according to the production product requirement (K3 mean value +/-Sigma) as a screening standard.
Example 3
Spraying two-dimension code distinguishing identification on a lithium ion battery core body to be tested, scanning a code uploading system for capacity in formation, scanning a code uploading system for capacity in capacity grading, firstly, carrying out capacity screening through a capacity percentage difference between formation and capacity grading, and screening the capacity percentage which is less than or equal to 3% to obtain a pre-screened lithium battery. The method comprises the steps of charging a pre-screened lithium battery to a 100% SOC state, maintaining the pressure at a constant temperature of 25 ℃ for a first preset time t1 at a first pressure, measuring the voltage V1 of the battery after the voltage is measured, scanning a two-dimensional code, and uploading the two-dimensional code to a computer system. And after the voltage V1 is measured, maintaining the pressure of the pre-screened lithium battery at the constant temperature of 45 ℃ for a period of time t2 at a second pressure, and scanning the two-dimensional code to upload the voltage V2 to a computer system when the voltage of the pre-screened lithium battery is finished. And discharging the pre-screened lithium battery to a 0% SOC state, maintaining the pressure at a constant temperature of 25 ℃ for a period of time t3 at a third pressure, measuring the battery voltage V3 after the pressure is maintained, scanning the two-dimensional code, and uploading the two-dimensional code to a computer system. And after the voltage V3 is measured, maintaining the pressure of the pre-screened lithium battery at the constant temperature of 45 ℃ for a period of time t4 at a fourth pressure, and scanning the two-dimensional code to upload the voltage V4 to a computer system when the voltage of the pre-screened lithium battery is finished. The method comprises the steps of (V1/V2)/(t1+ t2) for K1, and (V3-V4)/(t3+ t4) for K2, grading | K2/K1| -K3, K3 mean value +/-Sigma, and automatically judging the lithium ion battery exceeding the standard as a self-discharge lithium battery and sorting the lithium ion battery according to the production product requirement (K3 mean value +/-Sigma) as a screening standard.
The K1 value, the K2 value and the K3 value of the lithium ion battery to be measured in the above embodiment are measured and recorded respectively, and the specific measurement results are shown in table 1:
TABLE 1
As can be seen from the data results in table 1, according to the method for screening a self-discharging lithium ion battery in embodiments 1 to 3 of the present invention, the lithium ion battery is screened by classifying according to the average value distribution of the absolute values of K values in different SOC states by K1 tested by leaving the battery in a high temperature state for a certain period of time when the battery is charged to 100% SOC and K2 tested by leaving the battery in a high temperature state for a certain period of time when the battery is charged to 0% SOC, and whether the lithium ion battery is a self-discharging lithium ion battery is determined according to the K3 mean ± Σ. Therefore, compared with the prior art, the method can accurately obtain the K3 value and the screening standard K3 mean value +/-Sigma, namely, the screening accuracy of the self-discharging lithium battery can be obviously improved, and even if the number of batteries is small, the method for judging whether the batteries are the self-discharging lithium battery still has high accuracy.
The application also provides a lithium ion battery, and the lithium ion battery adopts the self-discharge screening method of the lithium ion battery described in any of the above embodiments to perform self-discharge screening.
Compared with the prior art, the invention has at least the following advantages:
1. the self-discharge screening method of the lithium ion battery comprises the steps of firstly grading and screening the capacity percentage difference value of a battery core body during formation and capacity grading, then charging the lithium ion battery to a 100% SOC state, then discharging to a 0% SOC state, applying certain pressure to the lithium ion battery during the process, carrying out voltage measurement operation on the lithium ion battery in different charge states at different temperature states to obtain corresponding voltage values, grading and screening through the voltage drop change proportion value of the voltage values of the lithium ion battery, and taking the K3 mean value +/-sigma as a basis for judging whether the lithium battery is the self-discharge lithium battery. Therefore, compared with the prior art, the self-discharge screening method of the lithium ion battery can obviously improve the screening accuracy of the self-discharge lithium ion battery.
2. In the lithium ion battery self-discharge screening method, the lithium ion battery is subjected to two standing operations, namely, the lithium ion battery is charged to a 100% SOC state, the first standing operation is carried out after the first voltage measurement operation is carried out on the lithium ion battery, the lithium ion battery is discharged to a 0% SOC state, the second standing operation is carried out after the third voltage measurement operation is carried out on the lithium ion battery discharged to the 0% SOC state, and the lithium ion battery self-discharge screening method not only can improve the accuracy of lithium ion battery self-discharge screening, but also can remarkably shorten the lithium ion battery standing time compared with the standing time of a normal-temperature standing mode by carrying out the two standing operations on the lithium ion battery under two different SOC states, thereby shortening the production cycle of the lithium ion battery and reducing the production cost of the lithium ion battery.
The above examples only show some embodiments of the present invention, and the description thereof is more specific and detailed, but not construed as limiting the scope of the invention. It should be noted that, for a person skilled in the art, several variations and modifications can be made without departing from the inventive concept, which falls within the scope of the present invention. Therefore, the protection scope of the present patent shall be subject to the appended claims.
Claims (10)
1. A self-discharge screening method of a lithium ion battery is characterized by comprising the following steps:
carrying out first-time capacity detection operation on the battery core body during formation to obtain a first capacity value;
carrying out secondary capacity detection operation on the battery core body during capacity grading to obtain a second capacity value;
carrying out capacity difference value screening operation on the first capacity value and the second capacity value to obtain a pre-screened lithium battery;
charging the pre-screened lithium battery to a 100% SOC state;
standing the charged pre-screened lithium battery at a first preset temperature for a first preset time;
performing a first voltage measurement operation on the pre-screened lithium battery after the first standing operation to obtain a first voltage value;
standing the pre-screened lithium battery subjected to the first voltage measurement operation at a second preset temperature for a second preset time;
performing a second voltage measurement operation on the pre-screened lithium battery subjected to the second standing operation to obtain a second voltage value;
discharging the pre-screened lithium battery subjected to the second voltage measurement operation to a 0% SOC state;
standing the discharged pre-screened lithium battery for a third preset time at a constant temperature of a third preset temperature;
performing a third voltage measurement operation on the pre-screened lithium battery after the third standing operation to obtain a third voltage value;
standing the pre-screened lithium battery subjected to the third voltage measurement operation for a fourth preset time at a constant temperature of a fourth preset temperature;
performing fourth voltage measurement operation on the pre-screened lithium battery after the fourth standing operation to obtain a fourth voltage value;
calculating a K3 value of the lithium ion battery to be tested, wherein a K1 value is (first voltage value/second voltage value)/(first preset time + second preset time), a K2 value is (third voltage value-fourth voltage value)/(third preset time + fourth preset time), and a K3 value is | K2/K1 |;
judging whether the lithium ion battery to be tested is a self-discharge lithium ion battery or not according to a comparison result of the K3 value and the lithium ion battery self-discharge screening standard; the screening criteria were K3 means ± Σ for grading.
2. The method for screening lithium ion battery self-discharge according to claim 1, wherein before the step of performing the first capacity detection operation on the battery core body during formation to obtain the first capacity value, the method for screening lithium ion battery self-discharge further comprises the following steps:
and spraying the two-dimensional code on the battery core body.
3. The method for screening lithium ion batteries by self-discharge according to claim 1, wherein after the pre-screened lithium battery is charged to a 100% SOC state, the pre-screened lithium battery is left at a constant temperature of a first preset temperature for a first preset time, and then a first voltage value is obtained by performing a first voltage measurement operation on the pre-screened lithium battery, the method further comprising the following operations:
and applying a first pressure to the pre-screened lithium battery charged to the 100% SOC state at the constant temperature state of the first preset temperature, and maintaining the pressure and standing for a first preset time.
4. The method for screening lithium ion batteries by self-discharge according to claim 1, wherein in the step of standing the pre-screened lithium battery after the first voltage measurement operation at a constant temperature at a second preset temperature for a second preset time, performing a second voltage measurement operation on the pre-screened lithium battery to obtain a second voltage value, the method for screening lithium ion batteries by self-discharge further comprises the following operations:
and applying a second pressure to the pre-screened lithium battery which completes the first voltage measurement operation in the constant temperature state of the second preset temperature, and maintaining the pressure and standing for a second preset time.
5. The method for screening lithium ion batteries by self-discharge according to claim 1, wherein after the pre-screened lithium battery that has completed the second voltage measurement operation is discharged to a 0% SOC state, the pre-screened lithium battery that has been discharged to the 0% SOC state is left to stand at a constant temperature of a third preset temperature for a third preset time, and then the pre-screened lithium battery is subjected to a third voltage measurement operation to obtain a third voltage value, the method for screening lithium ion batteries by self-discharge further comprises the following operations:
and applying a third pressure to the pre-screened lithium battery discharged to the 0% SOC state at the constant temperature state of the third preset temperature, and maintaining the pressure and standing for a third preset time.
6. The method for screening lithium ion batteries by self-discharge according to claim 1, wherein in the step of standing the pre-screened lithium battery after the third voltage measurement operation at a constant temperature at a fourth preset temperature for a fourth preset time, performing a fourth voltage measurement operation on the pre-screened lithium battery to obtain a fourth voltage value, the method for screening lithium ion batteries by self-discharge further comprises the following operations:
and applying fourth pressure to the pre-screened lithium battery which is subjected to the third voltage measurement operation in a constant temperature state at the fourth preset temperature, and maintaining the pressure and standing for a fourth preset time.
7. The method according to claim 1, wherein the first predetermined temperature is the same as the third predetermined temperature.
8. The method according to claim 1, wherein the second predetermined temperature is the same as the fourth predetermined temperature.
9. The method according to claim 1, wherein the first predetermined time is the same as the third predetermined time.
10. A lithium ion battery, characterized in that the lithium ion battery is self-discharge screened by the method for screening lithium ion battery self-discharge according to any one of claims 1 to 9.
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