CN111123120B - Method for measuring self-discharge current of lithium ion battery - Google Patents
Method for measuring self-discharge current of lithium ion battery Download PDFInfo
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- CN111123120B CN111123120B CN201911205686.7A CN201911205686A CN111123120B CN 111123120 B CN111123120 B CN 111123120B CN 201911205686 A CN201911205686 A CN 201911205686A CN 111123120 B CN111123120 B CN 111123120B
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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
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B07—SEPARATING SOLIDS FROM SOLIDS; SORTING
- B07C—POSTAL SORTING; SORTING INDIVIDUAL ARTICLES, OR BULK MATERIAL FIT TO BE SORTED PIECE-MEAL, e.g. BY PICKING
- B07C5/00—Sorting according to a characteristic or feature of the articles or material being sorted, e.g. by control effected by devices which detect or measure such characteristic or feature; Sorting by manually actuated devices, e.g. switches
- B07C5/34—Sorting according to other particular properties
- B07C5/344—Sorting according to other particular properties according to electric or electromagnetic properties
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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
Abstract
The invention provides a method for measuring self-discharge current of a lithium ion battery, which comprises the following steps: charging the battery at constant current and constant voltage to a full state, and then discharging to a preset charge state; after the discharged battery is stood for the first time at normal temperature, pulse discharge is carried out on the battery, and then the relaxation voltage of the battery is detected; deriving a voltage-time curve after pulse discharge to obtain a slope, then calculating the slope of a capacity-voltage curve by combining an SOC-OCV curve, and calculating the self-discharge current of the battery by combining the slope of the voltage-time curve and the slope of the capacity-voltage curve; and evaluating the self-discharge degree of the battery according to the magnitude of the self-discharge current, wherein the larger the self-discharge current is, the larger the self-discharge degree is. The method for measuring the self-discharge current of the lithium ion battery provided by the invention prepares conditions for manufacturing the self-discharge test of the battery by the modes of battery charging and discharging, pulse discharging and the like, omits long-time open-circuit placement of the battery, and greatly reduces the time for the self-discharge test of the battery.
Description
Technical Field
The invention relates to the technical field of lithium ion batteries, in particular to a method for measuring self-discharge current of a lithium ion battery.
Background
Along with the invisibility of the global rise of electric vehicles and the continuous popularization of electric vehicles in the last two decades, the rechargeable battery industry as an energy storage power source of the electric vehicles is also rapidly developed. The performance of the power battery pack is a key factor influencing the normal operation of the electric automobile, and the performance of the power battery pack is inconsistent and has important influence on the performance and the service life of the battery pack. The length of the battery life depends on the consistency of the battery cells. For newly produced batteries, the batteries cannot be directly used for assembling a battery pack due to large performance difference, and need to be manually or automatically detected and sorted. The sorting basis widely used at present is the performance parameters of voltage, capacity, internal resistance and the like of the single batteries, the batteries with poor performance are removed according to the sorting basis, and the batteries with consistent performance are assembled into the battery pack. The battery pack constructed in this way has good consistency, but the difference of the performance becomes more and more obvious as the service time increases, so that the direction of the consistency research of the battery pack points to the self-discharge of the battery.
The self-discharge of the battery refers to a phenomenon that the voltage of the battery is reduced and the capacity is reduced in an open circuit state, and is one of main parameters for measuring the performance of the battery, and the self-discharge is not eliminated in the practical application of the battery due to the problems of the manufacturing process. The self-discharge of a single battery is too large, which often causes the voltage of the battery to drop rapidly, and further causes the charge retention capacity of the whole power battery pack to be weakened, so that the detection of the self-discharge of the battery is particularly important. The self-discharge process occurs in the battery, is related to battery materials and processes and changes along with the ambient temperature, the battery service life and the charge state, but the existing measurement method can not go deep into the battery to directly measure the battery, so that the detection of the self-discharge becomes difficult. The long-time open-circuit shelving method established according to the industry standard is to shelve the battery for 7 days or 28 days in an open circuit at a high temperature or normal temperature state, and judge the self-discharge performance of the battery by measuring the discharge capacity of the battery after the battery is discharged to a cut-off voltage. The method needs to carry out shelving detection on the battery for one month, has long time period, large influence factors and limited accuracy, occupies more equipment and fields for a long time, has poor test safety and wastes a large amount of manpower and financial resources. Therefore, how to exactly detect the self-discharge degree of the battery is a technical problem to be solved urgently in the industry.
Disclosure of Invention
Based on the technical problems in the background art, the invention provides a method for measuring the self-discharge current of a lithium ion battery.
The invention provides a method for measuring self-discharge current of a lithium ion battery, which comprises the following steps:
s1, charging the battery at constant current and then at constant voltage to a full state, and then discharging to a preset charge state;
s2, standing the discharged battery for a first time at normal temperature, carrying out pulse discharge on the battery, and then detecting the relaxation voltage of the battery;
s3, deriving a voltage-time curve after pulse discharge to obtain a slope, then combining an SOC-OCV curve to obtain the slope of a capacity-voltage curve, and then combining the slope of the voltage-time curve and the slope of the capacity-voltage curve to calculate to obtain the self-discharge current of the battery;
and S4, evaluating the self-discharge degree of the battery according to the magnitude of the self-discharge current, wherein the self-discharge degree is larger when the self-discharge current is larger.
Preferably, in step S1, the batteries are first constant-current charged to full-charge voltage with a preset charging current, and then the batteries are charged to full-charge state by constant-voltage charging.
Preferably, the charging current is 0.2 to 1C.
Preferably, the charging current is 0.33C.
Preferably, in step S1, the predetermined state of charge is 65% to 95%.
Preferably, the first time is greater than or equal to 20 hours.
Preferably, in step S2, during the pulse discharge of the battery, the pulse current I is 0.01C to 0.05C and the pulse time is 10S to 30S.
Preferably, the monitoring time of the relaxation voltage is 10 to 40 hours.
The method for measuring the self-discharge current of the lithium ion battery provided by the invention prepares conditions for manufacturing the self-discharge test of the battery by the modes of battery charging and discharging, pulse discharging and the like, omits long-time open-circuit placement of the battery, and greatly reduces the time for the self-discharge test of the battery.
In addition, in the invention, the self-discharge current of the battery is calculated through the slope of the voltage-time curve and the slope of the capacity-voltage curve, so that the accuracy and the efficiency of the self-discharge current test of the battery are improved, and the test time is further reduced.
Drawings
Fig. 1 is a flow chart of a method for measuring a self-discharge current of a lithium ion battery according to the present invention.
Detailed Description
Referring to fig. 1, the method for measuring the self-discharge current of the lithium ion battery provided by the invention comprises the following steps:
and S1, charging the battery with constant current and then with constant voltage to a full state, and then discharging to a preset charge state. Specifically, in this step, the batteries are first charged to full charge voltage at a constant current by a preset charging current, then charged to full charge by constant voltage charging, and then discharged to a preset charge state at a small current.
In the step, the charging current is 0.2-1C, specifically 0.33C, and the preset charge state is 65-95%.
And S2, standing the discharged battery for the first time at normal temperature, then carrying out pulse discharge on the battery, and then detecting the relaxation voltage of the battery. The first time is greater than or equal to 20 hours.
In the step, in the process of pulse discharge of the battery, the pulse current I is 0.01C-0.05C, and the pulse time is 10 s-30 s.
And S3, deriving the voltage-time curve after pulse discharge to obtain the slope, then combining the SOC-OCV curve to obtain the slope of the capacity-voltage curve, and then combining the slope of the voltage-time curve and the slope of the capacity-voltage curve to calculate the self-discharge current of the battery. Specifically, the monitoring time of the relaxation voltage is 10-40 hours.
And S4, evaluating the self-discharge degree of the battery according to the magnitude of the self-discharge current, wherein the self-discharge degree is larger when the self-discharge current is larger.
The invention will be further elucidated with reference to a specific embodiment.
In this embodiment, a 3.5Ah cylindrical lithium ion battery to be tested after formation is taken, and is subjected to constant current charging at 0.2C until the full-voltage is 4.2V, and then is subjected to constant voltage charging until the full-voltage state, specifically, the cutoff current of the constant voltage charging is 50mA, and then is subjected to constant current discharging at 0.2C until 90% SOC.
Standing the battery discharged to 90% SOC at room temperature for more than 20 hr until the voltage of the battery begins to drop, i.e. eliminating overpotential, applying a small current pulse of 0.03C to the battery, continuing for 30s, and discharging for about 2.7 × 10-14% SOC, then the voltage of the cell after the pulse was monitored for 40 hours.
When the slope of the voltage-voltage time change curve of the battery is negative, namely the voltage begins to fall, self-discharge becomes a main factor influencing the voltage of the battery, and the slope of the voltage-voltage time change curve is calculated by derivation:
then, according to the SOC-OCV curve, U is obtained1＝4.0865V，U2Capacity development between 4.085V is 2 × 10-3Ah, capacity-voltage curve at U1、U2Slope of (2) in between
Thereby calculating the self-discharge current of the discharge lamp,
in this embodiment, when the self-discharge degrees of the plurality of batteries are evaluated, the self-discharge current of the plurality of batteries may be sorted according to the self-discharge current, and the self-discharge degree is larger.
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 (8)
1. A method for measuring the self-discharge current of a lithium ion battery is characterized by comprising the following steps:
s1, charging the battery at constant current and then at constant voltage to a full state, and then discharging to a preset charge state;
s2, standing the discharged battery for a first time at normal temperature, carrying out pulse discharge on the battery, and then detecting the relaxation voltage of the battery;
s3, deriving a voltage-time curve after pulse discharge to obtain a slope, then combining an SOC-OCV curve to obtain the slope of a capacity-voltage curve, and then combining the slope of the voltage-time curve and the slope of the capacity-voltage curve to calculate the self-discharge current of the battery;
and S4, evaluating the self-discharge degree of the battery according to the magnitude of the self-discharge current, wherein the self-discharge degree is larger when the self-discharge current is larger.
2. The method according to claim 1, wherein in step S1, the batteries are first charged to full charge voltage by constant current with a predetermined charging current, and then charged to full charge by constant voltage charging.
3. The method for measuring the self-discharge current of the lithium ion battery according to claim 2, wherein the charging current is 0.2 to 1C.
4. The method of measuring the self-discharge current of a lithium ion battery according to claim 3, wherein the charge current is 0.33C.
5. The method for measuring the self-discharge current of the lithium ion battery according to claim 1, wherein in step S1, the predetermined state of charge is 65% to 95%.
6. The method of measuring the self-discharge current of a lithium ion battery according to claim 1, wherein the first time is 20 hours or more.
7. The method for measuring the self-discharge current of the lithium ion battery according to claim 1, wherein in the step S2, the pulse current I is 0.01C to 0.05C and the pulse time is 10S to 30S during the pulse discharge of the battery.
8. The method for measuring the self-discharge current of a lithium ion battery according to any one of claims 1 to 7, wherein the monitoring time of the relaxation voltage is 10 to 40 hours.
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| JP7146358B2 (en) * | 2020-08-07 | 2022-10-04 | プライムプラネットエナジー＆ソリューションズ株式会社 | Insulation inspection method for secondary batteries |
| CN112834941A (en) * | 2021-01-05 | 2021-05-25 | 上海捷新动力电池系统有限公司 | Rapid test method for battery incoming material self-discharge rate full-inspection |
| CN113466720B (en) * | 2021-07-06 | 2022-11-22 | 上汽大众动力电池有限公司 | Method for detecting leakage current of lithium battery of real vehicle |
| CN113359043B (en) * | 2021-08-09 | 2021-10-15 | 江苏时代新能源科技有限公司 | Method, device and equipment for detecting self-discharge current of battery cell and computer storage medium |
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