CN110888078A - Charge-discharge testing method for accurately monitoring cycle life of lithium ion battery - Google Patents
Charge-discharge testing method for accurately monitoring cycle life of lithium ion battery Download PDFInfo
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- CN110888078A CN110888078A CN201911113753.2A CN201911113753A CN110888078A CN 110888078 A CN110888078 A CN 110888078A CN 201911113753 A CN201911113753 A CN 201911113753A CN 110888078 A CN110888078 A CN 110888078A
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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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- 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]
- G01R31/378—Arrangements for testing, measuring or monitoring the electrical condition of accumulators or electric batteries, e.g. capacity or state of charge [SoC] specially adapted for the type of battery or accumulator
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Abstract
The invention provides a charge-discharge test method for accurately monitoring the cycle life of a lithium ion battery, which comprises the following steps: s1, obtaining initial capacity C of battery cell0And DC internal resistance DCR0(ii) a S2, carrying out periodic charging and discharging on the battery, wherein each charging and discharging period comprises a times of cyclic charging and discharging, and the cyclic charging and discharging is carried out at 1C/1C during the first a-1 times of charging and discharging; in the a-th charging and discharging, after 1C charging, discharging to cut-off voltage by 1C, standing for the first time, and then discharging to cut-off voltage by 0.1C; standing for the first time, and discharging to cut-off voltage at 0.01 ℃; s3, detecting the current capacity C of the battery cell after k charge and discharge cyclesnAnd DC internal resistance DCRn(ii) a a ≧ 10 k; s4, according to the current capacity CnAnd DC internal resistance DCRnJudging whether the cycle life of the battery cell is terminated; if yes, recording the cycle life of the battery; otherwise, the process returns to step S2. The invention can eliminate circulation uniformlyAccumulated polarization enables the negative electrode to separate more effective lithium to ensure circulation, and the cycle life test result of the lithium ion battery is improved by more than 30%.
Description
Technical Field
The invention relates to the technical field of lithium battery production, in particular to a charge and discharge testing method for accurately monitoring the cycle life of a lithium ion battery.
Background
The lithium ion battery has the advantages of high reversibility, long cycle life, high energy density, no memory effect, environmental friendliness and the like, is widely applied to various digital electronic devices, and has wide application prospects in the fields of electric automobiles, energy storage power stations and the like. As an important component of a new energy automobile, the performance of a battery determines the comprehensive performance of the automobile to a great extent. Meanwhile, the long cycle life of the lithium ion battery is an important ring for evaluating the comprehensive performance of the lithium ion battery, and is related to the matching and the cost of the battery core and other important problems. Meanwhile, there are many factors affecting the service life of the lithium ion battery, such as material types, moisture, electrolyte, pole piece design parameters and the like; in addition to the influence of the cells, the test environment and conditions are also important factors affecting the life, such as test rate, cut-off voltage, current, overcharge and overdischarge during the test, and the like. Wherein different test methods also have an impact on battery life. Researches show that along with the progress of the circulation process, the polarization of the battery core is continuously increased, the voltage of the negative electrode is lower and lower, the voltage of the positive electrode is higher and higher, and the available capacity of circulation is lower and lower; the polarization increase of the battery core leads to that partial Li + can not be separated, and effective lithium is slowly reduced, so that the test result of the cycle life of the battery is greatly reduced, and the accuracy of the performance test of the battery is influenced.
Disclosure of Invention
Based on the technical problems in the background art, the invention provides a charge and discharge testing method for accurately monitoring the cycle life of a lithium ion battery.
The invention provides a charge-discharge test method for accurately monitoring the cycle life of a lithium ion battery, which comprises the following steps:
s1, obtaining initial capacity C of battery cell0And DC internal resistance DCR0；
S2, carrying out periodic charging and discharging on the battery, wherein each charging and discharging period comprises a times of cyclic charging and discharging, and the cyclic charging and discharging is carried out at 1C/1C during the first a-1 times of charging and discharging; in the a-th charging and discharging, after 1C charging, discharging to cut-off voltage by 1C, standing for the first time, and then discharging to cut-off voltage by 0.1C; standing for the first time, and discharging to cut-off voltage at 0.01 ℃;
s3, detecting the current capacity C of the battery cell after k charge and discharge cyclesnAnd DC internal resistance DCRn；a≧10k；
S4, according to the current capacity CnAnd DC internal resistance DCRnDetermining the cycle life of the battery cellWhether to terminate; if yes, recording the cycle life of the battery; otherwise, the process returns to step S2.
Preferably, a is 50.
Preferably, k is 4.
Preferably, the first time is 1 h.
Preferably, in step S1, the initial capacity C of the battery cell is acquired0The specific mode is as follows: the average value of 3 weeks of constant volume of the battery cell is tested under the condition of 0.33C and is taken as the initial capacity C0。
Preferably, in step S3, the current battery cell capacity CnComprises the following steps: and testing the obtained cell constant capacity value under the condition of 0.33C in a normal-temperature static environment.
Preferably, in step S1, the dc internal resistance DCR0DCR value at 50% DOD; in step S3, the dc internal resistance DCRnDCR value at 50% DOD.
Preferably, according to the current capacity CnAnd DC internal resistance DCRnThe specific method for judging whether the battery cell cycle life is terminated is as follows: judging the capacity retention rate Cn/C0Whether it is less than a preset capacity threshold or a DC resistance increase rate DCRn/DCR0Whether the internal resistance is larger than a preset internal resistance threshold value or not; if yes, judging the end of the cycle life of the battery cell; otherwise, the process returns to step S2.
Preferably, the capacity threshold is 80% and the internal resistance threshold is 150%.
The charge-discharge testing method for accurately monitoring the cycle life of the lithium ion battery can uniformly eliminate the polarization of cycle accumulation, enables more effective lithium to be separated from a negative electrode to ensure the cycle, enables the cycle life testing result of the lithium ion battery to be improved by more than 30%, and ensures the accuracy of the testing result.
The invention is realized by the RPT (Reference Performance Test), can monitor the health state of the battery more intuitively and effectively, and can judge the service life and the failure state of the lithium ion battery timely and accurately
According to the invention, the coulomb efficiency value of each circle of circulation can be automatically monitored through software, and the qualitative probability that the acceleration attenuation possibly occurs in the later period of the battery can be judged by performing relevant operation.
Drawings
FIG. 1 is a flow chart of a charge-discharge testing method for accurately monitoring the cycle life of a lithium ion battery according to the present invention;
FIG. 2 is a comparison and coulombic efficiency life prediction curve before and after the normal temperature 25-1C/1C cycle performance of a lithium iron phosphate battery is improved;
FIG. 3 is a comparison and coulombic efficiency predicted life curve before and after improvement of high temperature 45-1C/1C cycle performance of a ternary NCM622 battery;
FIG. 4 is a comparison and coulombic efficiency predicted life curve before and after the normal temperature 25-1C/1C cycle performance of ternary Ni85 battery is improved.
Detailed Description
Referring to fig. 1, the charge and discharge testing method for accurately monitoring the cycle life of the lithium ion battery provided by the invention comprises the following steps:
s1, obtaining initial capacity C of battery cell0And DC internal resistance DCR0. Specifically, in the present embodiment, the initial capacity C is obtained by measuring the average value of 3 constant volumes of the battery cell at 0.33C0. In the present embodiment, the dc internal resistance DCR0Is the DCR value at 50% DOD (depth of discharge, percentage of battery discharge to battery rated capacity).
S2, carrying out periodic charging and discharging on the battery, wherein each charging and discharging period comprises a times of cyclic charging and discharging, and the cyclic charging and discharging is carried out at 1C/1C during the first a-1 times of charging and discharging; in the a-th charging and discharging, after 1C charging, discharging to cut-off voltage by 1C, standing for the first time, and then discharging to cut-off voltage by 0.1C; then, the mixture was left standing for the first time and discharged to the cut-off voltage at 0.01C.
Therefore, in the embodiment, the polarization of cycle accumulation is uniformly eliminated in the test process by inserting the low-current discharge process in the multiple cycle charge-discharge process, so that more effective lithium is separated from the negative electrode, and the cycle life of the lithium ion battery is ensured.
Specifically, in the present embodiment, a is 50, and the first period is 1 h.
S3, detecting the current capacity C of the battery cell after k charge and discharge cyclesnAnd DC internal resistance DCRn. a ≧ 10 k. In the present embodiment, k is 4. And, the current capacity C of the battery cellnComprises the following steps: testing the obtained cell constant capacity value under the condition of 0.33C in a normal-temperature static environment; direct current internal resistance DCRnDCR value at 50% DOD. Thus, the current capacity C of the battery cell is ensurednAnd initial capacity C of battery cell0Is consistent with the test condition of the current direct current internal resistance DCRnAnd DC internal resistance DCR0The consistency of the voltage and the current is beneficial to ensuring the accurate judgment of the subsequent cycle life of the battery cell.
S4, according to the current capacity CnAnd DC internal resistance DCRnJudging whether the cycle life of the battery cell is terminated; if yes, recording the cycle life of the battery; otherwise, the process returns to step S2.
Specifically, in the present embodiment, the current capacity C is set according tonAnd DC internal resistance DCRnThe specific method for judging whether the battery cell cycle life is terminated is as follows: judging the capacity retention rate Cn/C0Whether it is less than a preset capacity threshold or a DC resistance increase rate DCRn/DCR0Whether the internal resistance is larger than a preset internal resistance threshold value or not; if yes, judging the end of the cycle life of the battery cell; otherwise, the process returns to step S2. Specifically, the capacity threshold is 80%, and the internal resistance threshold is 150%.
Example 1
Selecting two square lithium iron phosphate batteries with better consistency, wherein 1 is subjected to 1C/1C circulation according to a conventional charge-discharge method, and the other is subjected to circulation according to the charge-discharge method provided by the invention; other conditions such as current, cut-off voltage, rest time, test cabinet and external environment were kept consistent. The cycle results are shown in fig. 2, the data related to elimination of polarization in the process in fig. 2 is omitted, and only the normal cycle data is selected for comparison. It can be seen that the predicted life is about 1000 weeks according to the product of the coulombic efficiency values of each cycle, the actually measured life is 2000 weeks, and the predicted life only accounts for 50% of the actually measured life, which indicates that the cycle polarization causes more lithium deposition on the negative electrode, less cycle effective lithium is generated, and more lithium is additionally removed from the positive electrode as compensation, which is not favorable for the stability of the positive electrode material structure. Meanwhile, the service life measured by using the charge-discharge method provided by the invention is more than 2600 weeks, is improved by about 30% compared with the conventional actual service life, and the cycle performance improvement effect is obvious.
Example 2
Selecting two VDA ternary 622 batteries with better consistency, wherein 1 is subjected to 1C/1C circulation according to a conventional charge-discharge method, and the other is subjected to circulation according to the charge-discharge method provided by the invention; other conditions such as current, cut-off voltage, rest time, test cabinet and external environment were kept consistent. The cycle results are shown in fig. 3, the data related to elimination of polarization in the process in fig. 3 is omitted, and only the normal cycle data is selected for comparison. It can be seen that the predicted service life is about 500 weeks according to the product of the coulombic efficiency values of each cycle, the actually measured service life is 930 weeks, and the predicted service life is only about 54% of the actually measured service life, which indicates that the cyclic polarization still causes more lithium deposition of the negative electrode, so that the cyclic effective lithium is reduced, and more lithium needs to be additionally removed from the ternary positive electrode as compensation, which is not favorable for the stability of the ternary material structure, and can cause the increase of lithium-nickel mixed emission, the breakage of material particles and the like, thereby shortening the service life of the battery. But at the same time, the service life measured by using the charge-discharge method provided by the invention is about 1200 weeks, which is improved by about 30% compared with the conventional actual service life, and the cycle performance improvement effect is obvious.
Example 3
Selecting two soft package ternary Ni85 batteries with better consistency, wherein 1 is subjected to 1C/1C circulation according to a conventional charge-discharge method, and the other is subjected to circulation according to the charge-discharge method provided by the invention; other conditions such as current, cut-off voltage, rest time, test cabinet and external environment were kept consistent. The cycle results are shown in fig. 4, the data related to elimination of polarization in the process is omitted, and only the normal cycle data is selected for comparison. It can be seen that the predicted service life is about 450 weeks according to the product of the coulombic efficiency values of each cycle, the actually measured service life is 900 weeks, and the predicted service life only accounts for about 50% of the actually measured service life, which indicates that the cyclic polarization still causes more lithium deposition of the negative electrode, so that the cyclic effective lithium is reduced, and more lithium needs to be additionally removed from the ternary positive electrode as compensation, which is not favorable for the stability of the ternary material structure, and can cause the increase of lithium-nickel mixed emission, the breakage of material particles and the like, thereby shortening the service life of the battery. But at the same time, the service life measured by using the charge-discharge method provided by the invention is about 1350 weeks, which is 50% longer than the conventional measured service life, and the cycle performance improvement effect is obvious, because the cycle polarization phenomenon is more serious for the high-nickel anode material with high energy density.
By combining the above 3 embodiments, it can be known that the testing method provided by the present invention can uniformly eliminate polarization of cycle accumulation, so that more effective lithium is extracted from the negative electrode, thereby improving the cycle life of the battery by more than 30%.
The above description is only for the preferred embodiment of the present invention, but the scope of the present invention is not limited thereto, and any person skilled in the art should be considered to be within the technical scope of the present invention, and the technical solutions and the inventive concepts thereof according to the present invention are equivalent to or changed within the technical scope of the present invention.
Claims (9)
1. A charge-discharge test method for accurately monitoring the cycle life of a lithium ion battery is characterized by comprising the following steps:
s1, obtaining initial capacity C of battery cell0And DC internal resistance DCR0；
S2, carrying out periodic charging and discharging on the battery, wherein each charging and discharging period comprises a times of cyclic charging and discharging, and the cyclic charging and discharging is carried out at 1C/1C during the first a-1 times of charging and discharging; in the a-th charging and discharging, after 1C charging, discharging to cut-off voltage by 1C, standing for the first time, and then discharging to cut-off voltage by 0.1C; standing for the first time, and discharging to cut-off voltage at 0.01 ℃;
s3, detecting the current capacity C of the battery cell after k charge and discharge cyclesnAnd DC internal resistance DCRn；a≧10k；
S4, according to the current capacity CnAnd DC internal resistance DCRnJudging whether the cycle life of the battery cell is terminated; if yes, recording the cycle life of the battery; otherwise, the process returns to step S2.
2. The charge-discharge test method for accurately monitoring the cycle life of a lithium ion battery according to claim 1, wherein a is 50.
3. The charge-discharge test method for accurately monitoring the cycle life of a lithium ion battery according to claim 1, wherein k is 4.
4. The charge-discharge test method for accurately monitoring the cycle life of a lithium ion battery according to claim 1, wherein the first time is 1 hour.
5. The charge-discharge test method for accurately monitoring the cycle life of the lithium ion battery as claimed in claim 1, wherein in step S1, the initial capacity C of the battery cell is obtained0The specific mode is as follows: the average value of 3 weeks of constant volume of the battery cell is tested under the condition of 0.33C and is taken as the initial capacity C0。
6. The charge-discharge test method for accurately monitoring cycle life of lithium ion battery as claimed in claim 5, wherein in step S3, the current capacity C of battery cellnComprises the following steps: and testing the obtained cell constant capacity value under the condition of 0.33C in a normal-temperature static environment.
7. The charge-discharge test method for accurately monitoring the cycle life of the lithium ion battery as claimed in claim 1, wherein in step S1, the dc internal resistance DCR0DCR value at 50% DOD; in step S3, the dc internal resistance DCRnDCR value at 50% DOD.
8. The charge-discharge test method for accurately monitoring the cycle life of a lithium ion battery according to any one of claims 1 to 7, wherein the current capacity C is determined according to the current capacitynAnd DC internal resistance DCRnThe specific method for judging whether the battery cell cycle life is terminated is as follows: judging the capacity retention rate Cn/C0Whether it is less than a preset capacity threshold or a DC resistance increase rate DCRn/DCR0Whether or not toGreater than a preset internal resistance threshold value; if yes, judging the end of the cycle life of the battery cell; otherwise, the process returns to step S2.
9. The method according to claim 8, wherein the capacity threshold is 80% and the internal resistance threshold is 150%.
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Cited By (3)
| Publication number | Priority date | Publication date | Assignee | Title |
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| CN112684356A (en) * | 2020-10-31 | 2021-04-20 | 浙江锋锂新能源科技有限公司 | Cycle test method of lithium ion battery |
| CN113109728A (en) * | 2021-04-16 | 2021-07-13 | 惠州亿纬锂能股份有限公司 | Method and device for testing shallow DOD (disk on disk) cycle life |
| CN112684356B (en) * | 2020-10-31 | 2024-06-04 | 浙江锋锂新能源科技有限公司 | Circulation test method of lithium ion battery |
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Application publication date: 20200317 |