CN112114260A - Method for testing and evaluating overcharge stability of lithium ion battery monomer - Google Patents
Method for testing and evaluating overcharge stability of lithium ion battery monomer Download PDFInfo
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- HBBGRARXTFLTSG-UHFFFAOYSA-N Lithium ion Chemical compound [Li+] HBBGRARXTFLTSG-UHFFFAOYSA-N 0.000 title claims abstract description 84
- 229910001416 lithium ion Inorganic materials 0.000 title claims abstract description 84
- 238000012360 testing method Methods 0.000 title claims abstract description 75
- 238000000034 method Methods 0.000 title claims abstract description 55
- 239000000178 monomer Substances 0.000 title claims abstract description 21
- 238000007600 charging Methods 0.000 claims abstract description 35
- 230000008569 process Effects 0.000 claims abstract description 19
- 238000010998 test method Methods 0.000 claims abstract description 4
- 238000010280 constant potential charging Methods 0.000 claims description 16
- 238000007599 discharging Methods 0.000 claims description 11
- 238000004880 explosion Methods 0.000 claims description 6
- 239000007788 liquid Substances 0.000 claims description 6
- 238000011156 evaluation Methods 0.000 abstract description 20
- 230000006872 improvement Effects 0.000 abstract description 5
- 238000002474 experimental method Methods 0.000 description 6
- 208000032953 Device battery issue Diseases 0.000 description 4
- 238000013112 stability test Methods 0.000 description 4
- 238000005516 engineering process Methods 0.000 description 3
- 230000002035 prolonged effect Effects 0.000 description 3
- 238000011161 development Methods 0.000 description 2
- 238000004146 energy storage Methods 0.000 description 2
- WHXSMMKQMYFTQS-UHFFFAOYSA-N Lithium Chemical compound [Li] WHXSMMKQMYFTQS-UHFFFAOYSA-N 0.000 description 1
- 230000009286 beneficial effect Effects 0.000 description 1
- 230000036541 health Effects 0.000 description 1
- 230000020169 heat generation Effects 0.000 description 1
- 229910052744 lithium Inorganic materials 0.000 description 1
- 238000005259 measurement Methods 0.000 description 1
- 238000012986 modification Methods 0.000 description 1
- 230000004048 modification Effects 0.000 description 1
- 238000009783 overcharge test Methods 0.000 description 1
- 230000010287 polarization Effects 0.000 description 1
- 230000009467 reduction 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
- G01R31/3865—Arrangements for measuring battery or accumulator variables related to manufacture, e.g. testing after manufacture
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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]
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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]
- G01R31/392—Determining battery ageing or deterioration, e.g. state of health
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Abstract
The invention provides a method for testing the overcharge stability of a lithium ion battery monomer, which comprises the steps of measuring the discharge capacity of the lithium ion battery; the method comprises two steps of calibrating the capacity of the lithium ion battery after multiple small-amplitude charging cycles, and also comprises a test method. Through testing and evaluating the overcharge stability of lithium ions, whether the lithium ion battery can endure multiple small-amplitude overcharge conditions in the actual use process is analyzed, so that the performance stability is maintained, the improvement of the battery process level is promoted, the stability and the safety of the lithium ion battery for the electric automobile are improved, and a new evaluation method is provided for evaluating the performance and the safety of the lithium ion battery.
Description
Technical Field
The invention belongs to the technical field of new energy, and particularly relates to a method for testing and evaluating the overcharge stability of a lithium ion battery monomer.
Background
In recent years, the wide application of lithium ion batteries in the field of electric automobiles promotes the rapid development of the technology thereof. In order to meet the requirements of high-speed running, long endurance and long service life of the electric automobile, the lithium ion battery needs to be improved in the technical aspects of energy density, cycle life, safety and the like. Charging of an electric vehicle is a key problem affecting the safety of a battery, and one of the important problems is the overcharge of the battery. On the one hand, due to the differences in consistency between the cells, there are differences in basic parameters such as capacity, internal resistance, heat generation, etc. between the cells over a long period of use, and these differences result in some of the cells reaching the cut-off voltage earlier during the rapid charging process and causing a slight overcharge due to polarization problems. On the other hand, as the battery ages, if the battery management system has errors in the estimation accuracy of the state of charge (SOC) and state of health (SOH) of the battery cells, a problem of overcharging may also be caused during charging. In principle, overcharging can lead to capacity fade due to loss of the lithium source inside the cell and increase the safety risk of internal short circuits.
With the rapid development of the power battery technology, the power battery testing technology as an evaluation means is also greatly improved. In the overcharge test method of the power battery, the national standard GB/T31485-2015 of China proposes a test method for a power battery monomer in the form of 1I1(A) And the current is charged in a constant current mode until the voltage reaches 1.5 times of the charging termination voltage specified in the enterprise technical conditions or the charging time reaches 1 hour, and then the charging is stopped. In the practical use of a power cell however,due to the existence of the battery management system, the battery is not likely to be overcharged for a long time, but a multiple overcharge phenomenon of a small amplitude may occur more easily due to the above-described reasons. However, due to the presence of batteries in series and parallel in the battery system, some overcharged batteries cannot be found necessarily, so that the electric automobile has a safety hazard. How to test and evaluate the stability of the power battery against such small-amplitude multiple overcharging is a problem to be solved.
Disclosure of Invention
In view of the above, the present invention provides a method for testing and evaluating the overcharge stability of a lithium ion battery cell, so as to analyze whether the lithium ion battery can endure multiple small-amplitude overcharge conditions in the actual use process and maintain stable performance, promote improvement of battery process level, increase the stability and safety of the lithium ion battery for an electric vehicle, and provide a new evaluation method for evaluating the performance and safety of the lithium ion battery.
In order to achieve the purpose, the technical scheme of the invention is realized as follows:
a test method for the overcharge stability of a lithium ion battery monomer comprises the steps of measuring the discharge capacity of the lithium ion battery; calibrating the capacity of the lithium ion battery after multiple small-amplitude charging cycles;
the method for measuring the discharge capacity of the lithium ion battery specifically comprises the following steps:
(1) with 1I1Discharging the battery to a cut-off voltage at a constant current, wherein I1The rated capacity of the single body corresponds to the current value;
(2) standing to restore the temperature of the battery to room temperature;
(3) with 1I1Charging the battery to cut-off voltage by constant current, and charging to constant voltage until the current is reduced to 0.05I1-0.1I1；
If the parameter is more than 0.1I1This will result in too short a constant voltage charging process time for D0The accuracy of the acquisition of the parameters causes an impact; if the parameter is less than 0.05I1Then, thenThe constant voltage charging process can be too long, and the overall implementation time of the method is greatly prolonged.
(4) Standing to restore the temperature of the battery to room temperature;
(5) with 1I1Constant current discharged the cell to cutoff voltage and discharge capacity D was recorded0；
The method for calibrating the capacity of the lithium ion battery after multiple small-amplitude charging cycles specifically comprises the following steps:
(A) with 1I1Charging the battery by constant current until the charging capacity reaches D01.05 times of;
the 1.05 times of parameters can correspond to a lithium ion battery overcharge stability evaluation table, and the method for efficiently and accurately evaluating the overcharge stability of the battery sample is provided. If the parameter is higher, the parameter is inconsistent with the actual application condition of the test sample, the battery is seriously heated, potential safety hazards such as internal short circuit and the like are caused, the sample is damaged in a shorter experiment period, and a real test result cannot be obtained; if the parameter is lower, the testing time is greatly prolonged, and the evaluation results are all higher than the B level, so that the grading evaluation function cannot be realized.
(B) Standing to restore the temperature of the battery to room temperature, and repeating the steps (1) to (4);
(C) with 1I1Constant current discharged the cell to cutoff voltage and discharge capacity D was recordedn；
(D) After allowing to stand to return the battery temperature to room temperature, D was calculatedn/D0Value if Dn/D0If > 0.7, repeating the steps (A) - (C); if D isn/D0If the test time is less than or equal to 0.7, stopping the test and recording the cycle number n.
If the parameter 0.7 set in the method is set to be too high, the test result is low; if the setting is too low, the test result will be higher.
A method for evaluating the overcharge stability of a lithium ion battery cell, which comprises the following steps of testing the lithium ion battery cell by the testing method of any one of claims 1 to 2, and evaluating the test result: when the cycle number n is more than or equal to 50, the overcharge stability of the lithium ion battery monomer is excellent; when the cycle number is more than or equal to 40 and less than 50, the overcharge stability of the lithium ion battery monomer is good; when the cycle number is more than or equal to 30 and less than 40, the overcharge stability of the lithium ion battery monomer is qualified; when the cycle number n is less than 30, the overcharge stability of the lithium ion battery monomer is unqualified; and (3) when the safety problems of fire, explosion, liquid leakage, open circuit and short circuit of the battery occur in the processes of the steps (A) to (C), the battery cannot be continuously tested, the overcharge stability of the lithium ion battery is unqualified, and the battery fails.
According to the lithium ion battery overcharge stability evaluation table provided by the invention, the lithium ion battery overcharge stability is graded. A represents that the battery overcharge stability is excellent; b represents that the overcharge stability of the battery is good; c represents that the overcharge stability of the battery is qualified; d represents that the battery overcharge stability is unqualified; e represents that the cell overcharge stability was not good and the cell failed, much worse than grade D.
TABLE 1 evaluation table for overcharge stability of lithium ion battery
| Test results | Rank of |
| n≥50 | A |
| 40≤n＜50 | B |
| 30≤n＜40 | C |
| n＜30 | D |
| Failure of battery | E |
Compared with the prior art, the method for testing and evaluating the overcharge stability of the lithium ion battery monomer has the following advantages:
through testing and evaluating the overcharge stability of lithium ions, whether the lithium ion battery can endure multiple small-amplitude overcharge conditions in the actual use process is analyzed, so that the performance stability is maintained, the improvement of the battery process level is promoted, the stability and the safety of the lithium ion battery for the electric automobile are improved, and a new evaluation method is provided for evaluating the performance and the safety of the lithium ion battery.
Based on the safety problems of poor consistency, low power quality, unmatched charging strategies and the like of the single batteries of the lithium ion battery in the charging process, a testing method is designed to verify the stability of the lithium ion battery to the condition of repeated small-amplitude overcharge. The lithium ion battery overcharge stability evaluation table can clearly and hierarchically evaluate the overcharge stability of the lithium ion battery, help electric vehicles and energy storage enterprises to select the battery type according to the requirements of the electric vehicles and the energy storage enterprises, and promote the improvement of the battery process level. The method provided by the invention is beneficial to increasing the safety of the lithium ion battery for the electric automobile in the actual use process, and provides a new method for testing and evaluating the lithium ion battery.
Drawings
The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate embodiments of the invention and, together with the description, serve to explain the invention without limitation. In the drawings:
fig. 1 is a flow chart of the overcharge stability test and evaluation of lithium ion battery cells according to the inventive example.
Detailed Description
It should be noted that the embodiments and features of the embodiments of the present invention may be combined with each other without conflict.
The invention will be described in detail with reference to the following embodiments with reference to the attached drawings.
Example 1
18650 type lithium ion monomers with rated capacity of 2.35Ah are selected as test objects, and overcharge stability test and evaluation are carried out. The specific process is as follows:
1. the discharge capacity of the lithium ion battery is measured by the specific method:
(1) discharging the battery to a cut-off voltage at a constant current of 2.35A;
(2) standing to restore the temperature of the battery to room temperature;
(3) charging the battery to a cut-off voltage with a constant current of 2.35A, converting the constant voltage charging to a constant voltage charging until the current is reduced to 0.1175A;
(4) standing to restore the temperature of the battery to room temperature;
(5) the cell was discharged to cutoff voltage at 2.35A constant current and the discharge capacity D was recorded0＝2.34Ah；
2. The lithium ion battery is subjected to a plurality of small-amplitude overcharge cycles, and the capacity is calibrated after each overcharge cycle.
The specific method comprises the following steps:
(A) charging the battery with 2.35A constant current until the charging capacity reaches 2.457 Ah;
(B) standing to restore the temperature of the battery to room temperature, and repeating the steps (1) to (4);
(C) the cell was discharged to cutoff voltage at 2.35A constant current and the discharge capacity D was recordedn；
(D) After allowing to stand to return the battery temperature to room temperature, D was calculatedn/D0Value if Dn/D0If > 0.7, repeating the steps (A) - (C); if D isn/D0If the test time is less than or equal to 0.7, stopping the test, and recording the test result as the cycle number n.
If the battery has the phenomena that the safety problems such as ignition, explosion, liquid leakage, open circuit, short circuit and the like cannot be continuously tested in the processes of the steps (A) to (C), recording the test result as 'battery failure'
Cycle number and discharge capacity D in this stepnAnd Dn/D0The changes are shown in Table 2 below, over 32 cycles of steps (A) - (C), Dn/D0< 0.7, record the test result as "cycle number n ═ 32".
Table 2 experimental data tabulation in example 1
3. Evaluation of results
According to the lithium ion battery overcharge stability evaluation table provided by the invention, n is 32 and belongs to an interval of 30-40 n. The lithium ion battery was rated as class C in terms of overcharge stability.
Example 2
18650 type lithium ion monomers with rated capacity of 2.6Ah are selected as test objects.
For step (3) "with 1I1The parameters of the cut-off current after the constant current charges the battery to the cut-off voltage and the constant voltage charges to the current reduction are respectively 0.2I1(0.52A)，0.1I1(0.26A)，0.05I1(0.13A)，0.01I1(0.026A) the procedure for measuring the discharge capacity of the lithium ion battery was as follows:
1. at an off current of 0.2I1The method is used for measuring the discharge capacity of the lithium ion battery as a cut-off condition, and comprises the following specific steps:
(1) discharging the battery to a cut-off voltage at a constant current of 2.6A; (ii) a
(2) Standing to restore the temperature of the battery to room temperature;
(3) charging the battery to cut-off voltage with 2.6A constant current, converting to constant voltage charging until the current is reduced to 0.52A;
(4) standing to restore the temperature of the battery to room temperature;
(5) the cell was discharged to cutoff voltage at 2.6A constant current and the discharge capacity D was recorded0＝2.12Ah。
Experiments prove that the test time of the step (3) is 61 minutes, and the obtained discharge capacity D0The rated capacity was 82% at 2.12Ah, and the measurement result was greatly deviated from the actual rated capacity of 2.6 Ah.
2. At an off current of 0.1I1The method is used for measuring the discharge capacity of the lithium ion battery as a cut-off condition, and comprises the following specific steps:
(1) discharging the battery to a cut-off voltage at a constant current of 2.6A;
(2) standing to restore the temperature of the battery to room temperature;
(3) charging the battery to cut-off voltage by constant current of 2.6A, and converting the constant voltage charging to constant voltage charging until the current is reduced to 0.26A;
(4) standing to restore the temperature of the battery to room temperature;
(5) the cell was discharged to cutoff voltage at 2.6A constant current and the discharge capacity D was recorded0＝2.52Ah；
Experiments prove that the testing time of the step (3) is 80 minutes, and the obtained discharge capacity D0The discharge capacity was 97% of the rated discharge capacity, which was 2.52Ah, and the data was close to the actual rated capacity of 2.6 Ah.
3. At an off current of 0.05I1The method is used for measuring the discharge capacity of the lithium ion battery as a cut-off condition, and comprises the following specific steps:
(1) discharging the battery to a cut-off voltage at a constant current of 2.6A;
(2) standing to restore the temperature of the battery to room temperature;
(3) charging the battery to cut-off voltage by constant current of 2.6A, and converting the constant voltage charging to constant voltage charging until the current is reduced to 0.13A;
(4) standing for 30min to restore the temperature of the battery to room temperature;
(5) the cell was discharged to cutoff voltage at 2.6A constant current and the discharge capacity D was recorded0＝2.54Ah。
Experiments prove that the discharge capacity D obtained after the testing time of 102 minutes in the step (3)02.54Ah, 98% of rated discharge capacity, and actual rated capacity 26Ah data are close.
4. The cutoff current parameter range is 0.01I1The method is used for measuring the discharge capacity of the lithium ion battery as a cut-off condition, and comprises the following specific steps:
(1) discharging the battery to a cut-off voltage at a constant current of 2.6A;
(2) and standing to restore the temperature of the battery to room temperature.
(3) Charging the battery to cut-off voltage by constant current of 2.6A, and charging to constant voltage until the current is reduced to 0.026A;
(4) standing to restore the temperature of the battery to room temperature;
(5) the cell was discharged to cutoff voltage at 2.6A constant current and the discharge capacity D was recorded0＝2.56Ah。
Experiments prove that the discharge capacity D obtained after the testing time of 221 minutes in the step (3)0The rated discharge capacity is 98% at 2.56Ah, which is close to the actual rated capacity of 2.6 Ah. But the test time is increased by 119 minutes compared with the 'off current of 0.05I 1', which seriously increases the test time and increases the test cost.
Example 3
Three soft package lithium ion battery monomers with the rated capacity of 10Ah in the same batch are respectively selected as test objects to carry out overcharge stability test and evaluation.
The specific test flow of the first battery is as follows:
1. the discharge capacity of the lithium ion battery is measured by the specific method:
(1) discharging the battery to a cut-off voltage at a constant current of 10A;
(2) standing for 1h to restore the temperature of the battery to the room temperature;
(3) charging the battery to cut-off voltage with constant current of 10A, converting the constant voltage charging to constant voltage charging until the current is reduced to 0.5A;
(4) standing for 1h to restore the temperature of the battery to the room temperature;
(5) the cell was discharged to the cut-off voltage at a constant current of 10A, and the discharge capacity D was recorded0＝9.82Ah；
2. The lithium ion battery is subjected to a plurality of small-amplitude overcharge cycles, and the capacity is calibrated after each overcharge cycle. The specific method comprises the following steps:
(A) the battery was charged at a constant current of 10A to a charge capacity of 11Ah (1.1I)1)；
(B) Standing to restore the temperature of the battery to room temperature, and repeating the steps (1) to (4);
(C) the cell was discharged to the cut-off voltage at a constant current of 10A, and the discharge capacity D was recordedn；
(D) Standing to restore the temperature of the battery to room temperature, and calculating Dn/D0Value if Dn/D0If > 0.7, repeating the steps (A) - (C); if D isn/D0If the test time is less than or equal to 0.7, stopping the test, and recording the test result as the cycle number n.
If the battery has the phenomena that the safety problems such as ignition, explosion, liquid leakage, open circuit, short circuit and the like cannot be continuously tested in the processes of the steps (A) to (C), recording the test result as 'battery failure'
In this test, the cut-off voltage was set to 1.1I due to overcharge1When the value is too high, the battery sample begins to bulge and become serious gradually in the 4 th cycle and has an open circuit condition in the 9 th cycle, and the test result is recorded as 'battery failure'
The specific test flow of the second battery is as follows:
1. the discharge capacity of the lithium ion battery is measured by the specific method:
(1) discharging the battery to a cut-off voltage at a constant current of 10A;
(2) standing for 1h to restore the temperature of the battery to the room temperature;
(3) charging the battery to cut-off voltage with constant current of 10A, converting the constant voltage charging to constant voltage charging until the current is reduced to 0.5A;
(4) standing for 1h to restore the temperature of the battery to the room temperature;
(5) the cell was discharged to the cut-off voltage at a constant current of 10A, and the discharge capacity D was recorded0＝9.82Ah；
2. The lithium ion battery is subjected to a plurality of small-amplitude overcharge cycles, and the capacity is calibrated after each overcharge cycle. The specific method comprises the following steps:
(A) the battery was charged at a constant current of 10A to a charge capacity of 10.1Ah (1.01I)1)；
(B) Standing to restore the temperature of the battery to room temperature, and repeating the steps (1) to (4);
(C) the cell was discharged to the cut-off voltage at a constant current of 10A, and the discharge capacity D was recordedn；
(D) Standing to restore the temperature of the battery to room temperature, and calculating Dn/D0Value if Dn/D0If > 0.7, repeating the steps (A) - (C); if D isn/D0If the test time is less than or equal to 0.7, stopping the test, and recording the test result as the cycle number n.
If the battery has the phenomena that the safety problems such as fire, explosion, liquid leakage, open circuit, short circuit and the like cannot be continuously tested in the processes of the steps (A) to (C), recording the test result as the cycle number and the discharge capacity D in the experiment that the battery failsnAnd Dn/D0The changes in values are shown in table 3 below.
Table 3 test data list for the second cell in example 3
Through 200 cycles of steps (A) - (C), Dn/D00.97 > 0.7, the test stop condition is still far from being reached. This is because the overcharge-cut-off voltage was set to 1.01I1And if the temperature is too low, the test cycle number and the test time are greatly prolonged, and the test result is seriously deviated from the parameter range in the lithium ion battery overcharge stability evaluation table.
The specific test flow of the third battery is as follows:
1. the discharge capacity of the lithium ion battery is measured by the specific method:
(1) discharging the battery to a cut-off voltage at a constant current of 10A;
(2) standing to restore the temperature of the battery to room temperature;
(3) charging the battery to cut-off voltage with constant current of 10A, converting the constant voltage charging to constant voltage charging until the current is reduced to 0.5A;
(4) standing to restore the temperature of the battery to room temperature;
(5) the cell was discharged to the cut-off voltage at a constant current of 10A, and the discharge capacity D was recorded0＝9.83Ah；
2. The lithium ion battery is subjected to a plurality of small-amplitude overcharge cycles, and the capacity is calibrated after each overcharge cycle. The specific method comprises the following steps:
(A) the battery was charged at a constant current of 10A to a charge capacity of 10.5Ah (1.05I)1)；
(B) Standing to restore the temperature of the battery to room temperature, and repeating the steps (1) to (4);
(C) the cell was discharged to the cut-off voltage at a constant current of 10A, and the discharge capacity D was recordedn；
(D) After allowing to stand to return the battery temperature to room temperature, D was calculatedn/D0Value if Dn/D0If > 0.7, repeating the steps (A) - (C); if D isn/D0If the test time is less than or equal to 0.7, stopping the test, and recording the test result as the cycle number n.
If the battery has the phenomena that the safety problems such as ignition, explosion, liquid leakage, open circuit, short circuit and the like cannot be continuously tested in the processes of the steps (A) to (C), recording the test result as 'battery failure'
Cycle number and discharge capacity D in this stepnAnd Dn/D0The changes in values are shown in table 4 below. Through 44 cycles of steps (A) - (C), Dn/D0< 0.7, record the test result as "cycle number n ═ 44".
Table 4 test data list for the second cell in example 3
According to the lithium ion battery overcharge stability evaluation table provided by the invention, n is 44, and belongs to the interval of n being more than or equal to 40 and less than 50. The lithium ion battery was classified as class B in overcharge stability.
Example 4
And selecting a square hard-shell lithium ion battery monomer with the rated capacity of 20Ah as a test object, and carrying out overcharge stability test and evaluation. The specific test flow is as follows:
1. the discharge capacity of the lithium ion battery is measured by the specific method:
(1) discharging the battery to a cut-off voltage at a constant current of 20A;
(2) standing to restore the temperature of the battery to room temperature;
(3) charging the battery to cut-off voltage at a constant current of 20A, converting the constant voltage into constant voltage and charging until the current is reduced to 2A;
(4) standing for 30min to restore the temperature of the battery to room temperature;
(5) the cell was discharged to cutoff voltage at a constant current of 20A and the discharge capacity D was recorded0＝19.40Ah；
2. The lithium ion battery is subjected to a plurality of small-amplitude overcharge cycles, and the capacity is calibrated after each overcharge cycle. The specific method comprises the following steps:
(A) the battery was charged at a constant current of 20A to a charge capacity of 21Ah (1.05I)1)；
(B) Standing to restore the temperature of the battery to room temperature, and repeating the steps (1) to (4);
(C) the cell was discharged to cutoff voltage at a constant current of 20A and the discharge capacity D was recordedn；
(D) Standing to restore the temperature of the battery to room temperature, and calculating Dn/D0The value is obtained. Respectively select Dn/D0≤0.6，Dn/D0Less than or equal to 0.7 and Dn/D0And taking the condition of stopping the test as the condition of stopping the test, wherein the test is less than or equal to 0.8.
Cycle number and discharge capacity D in this stepnAnd Dn/D0The changes in values are shown in table 5 below.
Table 5 experimental data tabulation in example 4
When in accordance with Dn/D0Not more than 0.6, and D is determined as a test stop condition because the battery is dead when n is 53n/D0The condition less than or equal to 0.6 cannot be achieved. Thus if Dn/D0If the value is set too low, the determination index may be invalid.
When in accordance with Dn/D0And (5) less than or equal to 0.8, and when the test is stopped, n is equal to 40. In this case, according to the lithium ion battery overcharge stability evaluation chart provided by the present invention, the rating of the battery is between the C-level and the B-level, so that the rating of the battery is unclear.
When in accordance with Dn/D0Not more than 0.7, and when the test was stopped, n is 49, and the overcharge stability of the lithium ion battery was classified into class B according to the lithium ion battery overcharge stability evaluation table proposed in the present invention, and the determination was made efficiently.
The above description is only for the purpose of illustrating the preferred embodiments of the present invention and should not be taken as limiting the invention, so that any modifications, equivalents, improvements and the like, which are within the spirit and principle of the present invention, should be included in the scope of the present invention.
Claims (3)
1. A method for testing the overcharge stability of a lithium ion battery monomer is characterized in that: measuring the discharge capacity of the lithium ion battery, and calibrating the capacity of the lithium ion battery after multiple small-amplitude charging cycles;
the method for measuring the discharge capacity of the lithium ion battery specifically comprises the following steps:
(1) with 1I1Discharging the battery to a cut-off voltage at a constant current, wherein I1The rated capacity of the single body corresponds to the current value;
(2) standing to restore the temperature of the battery to room temperature;
(3) with 1I1Charging the battery to cut-off voltage by constant current, and charging to constant voltage until the current is reduced to 0.05I1-0.1I1；
(4) Standing to restore the temperature of the battery to room temperature;
(5) with 1I1Constant current discharged the cell to cutoff voltage and discharge capacity D was recorded0；
The method for calibrating the capacity of the lithium ion battery after multiple small-amplitude charging cycles specifically comprises the following steps:
(A) with 1I1Charging the battery by constant current until the charging capacity reaches D01.05 times of;
(B) standing to restore the temperature of the battery to room temperature, and repeating the steps (1) to (4);
(C) with 1I1Constant current discharged the cell to cutoff voltage and discharge capacity D was recordedn；
(D) After allowing to stand to return the battery temperature to room temperature, D was calculatedn/D0Value if Dn/D0If > 0.7, repeating the steps (A) - (C); if D isn/D0If the test time is less than or equal to 0.7, stopping the test and recording the cycle number n.
2. The method for testing the overcharge stability of a lithium ion battery cell according to claim 1, wherein: the step (3) is carried out by 1I1The constant current is used for charging the battery to cut-off voltage, and the cut-off current is changed into constant voltage charging until the current is reduced and is preferably 0.05I1。
3. A method for evaluating the overcharge stability of a lithium ion battery monomer is characterized by comprising the following steps: after the lithium ion battery cell is tested by the test method of any one of claims 1 to 2, the test result is evaluated: when the cycle number n is more than or equal to 50, the overcharge stability of the lithium ion battery monomer is excellent; when the cycle number is more than or equal to 40 and less than 50, the overcharge stability of the lithium ion battery monomer is good; when the cycle number is more than or equal to 30 and less than 40, the overcharge stability of the lithium ion battery monomer is qualified; when the cycle number n is less than 30, the overcharge stability of the lithium ion battery monomer is unqualified; and (3) when the safety problems of fire, explosion, liquid leakage, open circuit and short circuit of the battery occur in the processes of the steps (A) to (C), the battery cannot be continuously tested, the overcharge stability of the lithium ion battery is unqualified, and the battery fails.
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