CN116559695A - Self-discharge testing method for lithium ion battery - Google Patents
Self-discharge testing method for lithium ion battery Download PDFInfo
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- CN116559695A CN116559695A CN202310756085.5A CN202310756085A CN116559695A CN 116559695 A CN116559695 A CN 116559695A CN 202310756085 A CN202310756085 A CN 202310756085A CN 116559695 A CN116559695 A CN 116559695A
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- HBBGRARXTFLTSG-UHFFFAOYSA-N Lithium ion Chemical compound [Li+] HBBGRARXTFLTSG-UHFFFAOYSA-N 0.000 title claims abstract description 123
- 229910001416 lithium ion Inorganic materials 0.000 title claims abstract description 123
- 238000012360 testing method Methods 0.000 title claims abstract description 34
- 238000000034 method Methods 0.000 claims abstract description 22
- 238000010998 test method Methods 0.000 claims abstract description 18
- 238000012544 monitoring process Methods 0.000 claims abstract description 12
- 230000008859 change Effects 0.000 claims description 20
- 238000007599 discharging Methods 0.000 claims description 17
- 238000007600 charging Methods 0.000 claims description 10
- 238000012216 screening Methods 0.000 claims description 8
- 238000010280 constant potential charging Methods 0.000 claims description 6
- 238000010277 constant-current charging Methods 0.000 claims description 6
- 230000008569 process Effects 0.000 abstract description 6
- 238000005259 measurement Methods 0.000 abstract description 5
- 238000004364 calculation method Methods 0.000 description 2
- 238000000691 measurement method Methods 0.000 description 2
- 238000012935 Averaging Methods 0.000 description 1
- WHXSMMKQMYFTQS-UHFFFAOYSA-N Lithium Chemical compound [Li] WHXSMMKQMYFTQS-UHFFFAOYSA-N 0.000 description 1
- 230000004075 alteration Effects 0.000 description 1
- 238000010281 constant-current constant-voltage charging Methods 0.000 description 1
- 238000012937 correction Methods 0.000 description 1
- 230000001351 cycling effect Effects 0.000 description 1
- 230000000694 effects Effects 0.000 description 1
- 238000005516 engineering process Methods 0.000 description 1
- 229910052744 lithium Inorganic materials 0.000 description 1
- GELKBWJHTRAYNV-UHFFFAOYSA-K lithium iron phosphate Chemical compound [Li+].[Fe+2].[O-]P([O-])([O-])=O GELKBWJHTRAYNV-UHFFFAOYSA-K 0.000 description 1
- 230000014759 maintenance of location Effects 0.000 description 1
- 238000004519 manufacturing process Methods 0.000 description 1
- 230000003446 memory effect Effects 0.000 description 1
- 238000012986 modification Methods 0.000 description 1
- 230000004048 modification Effects 0.000 description 1
- 230000000284 resting effect Effects 0.000 description 1
- 230000002269 spontaneous effect Effects 0.000 description 1
- 238000006467 substitution reaction Methods 0.000 description 1
Classifications
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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
-
- 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]
- G01R31/374—Arrangements for testing, measuring or monitoring the electrical condition of accumulators or electric batteries, e.g. capacity or state of charge [SoC] with means for correcting the measurement for temperature or ageing
-
- 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]
- G01R31/389—Measuring internal impedance, internal conductance or related variables
-
- 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]
- G01R31/396—Acquisition or processing of data for testing or for monitoring individual cells or groups of cells within a battery
-
- 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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- Physics & Mathematics (AREA)
- General Physics & Mathematics (AREA)
- Secondary Cells (AREA)
- Charge And Discharge Circuits For Batteries Or The Like (AREA)
Abstract
The invention provides a self-discharge test method of a lithium ion battery, which comprises the steps of carrying out self-discharge monitoring on the lithium ion battery to obtain open-circuit voltage and temperature of a plurality of continuous time nodes; correcting the corresponding open-circuit voltage according to the temperature according to a preset open-circuit voltage and temperature relation, and obtaining a corrected voltage value; and calculating the voltage drop of the lithium ion battery in unit time, namely a K value by utilizing the corrected voltage values of the plurality of time nodes. According to the embodiment of the disclosure, under the condition that the K value is influenced by temperature, the open-circuit voltage is corrected by incorporating the relation between the open-circuit voltage and the temperature in the self-discharge test process, the K value is tested in stages based on a plurality of time nodes, the influence of the temperature on the measurement result is weakened, and the test accuracy is improved.
Description
Technical Field
The invention relates to the technical field of lithium ion batteries, in particular to a self-discharge testing method of a lithium ion battery.
Background
The lithium ion battery has the advantages of high energy density, long sequential service life, no memory effect and the like, and is widely applied to the digital and power energy industries. The phenomenon of spontaneous loss of capacity when a lithium ion battery is in an open rest state is called self-discharge of the lithium ion battery, and may also be called charge retention capacity of the lithium ion battery.
How to realize accurate self-discharge test is a subject considered by the lithium ion battery industry.
Disclosure of Invention
Aiming at the problems in the prior art, the invention aims to provide a self-discharge testing method for a lithium ion battery, which aims to solve the problem of poor self-discharge testing accuracy of the lithium ion battery in the prior art.
The embodiment of the invention provides a self-discharge test method of a lithium ion battery, which comprises the following steps:
self-discharge monitoring is carried out on the lithium ion battery, and open-circuit voltage and temperature of a plurality of continuous time nodes are obtained;
correcting the corresponding open-circuit voltage according to the temperature according to a preset open-circuit voltage and temperature relation, and obtaining a corrected voltage value;
and calculating the voltage drop of the lithium ion battery in unit time by utilizing the corrected voltage values of the plurality of time nodes.
In some embodiments, the lithium ion battery self-discharge test method further comprises:
before self-discharge monitoring is carried out on the lithium ion battery, the charge state of the lithium ion battery is adjusted to a target charge state;
the open circuit voltage versus temperature relationship is for a corresponding target state of charge.
In some embodiments, adjusting the state of charge of the lithium ion battery to a target state of charge includes:
adjusting the lithium ion battery to a plurality of different target charge states;
at each target state of charge, self-discharge monitoring of the lithium ion battery is performed until a voltage drop per unit time is obtained.
In some embodiments, adjusting the state of charge of the lithium ion battery to a target state of charge includes:
fully discharging the lithium ion battery;
and carrying out constant-voltage and constant-current charging on the fully discharged lithium ion battery until the target state of charge is reached.
In some embodiments, the lithium ion battery self-discharge test method further comprises:
the lithium ion battery is left until a voltage steady state is reached, before the lithium ion battery is self-discharge monitored.
In some embodiments, calculating the voltage drop of the lithium ion battery per unit time using the corrected voltage values for the plurality of time nodes includes:
calculating voltage drop sub-values in unit time by using the corrected voltage values of every two adjacent time nodes to obtain a plurality of voltage drop sub-values;
and calculating an average value of the voltage drop sub-values to obtain the voltage drop of the lithium ion battery in unit time.
In some embodiments, the preset open circuit voltage versus temperature relationship is obtained by:
placing the lithium ion battery cell in a constant temperature box, and adjusting the temperature in the constant temperature box;
and under each constant temperature condition, standing the lithium ion battery cell for a target time period, collecting voltage change in the target time period, and fitting an open-circuit voltage and temperature relation according to the voltage change and the constant temperature.
In some embodiments, the lithium ion battery self-discharge test method further comprises:
before placing the lithium ion battery cell in the incubator, the lithium ion battery cell is left until a voltage steady state is reached.
In some embodiments, the lithium ion battery self-discharge test method further comprises:
fully discharging the lithium ion battery cell before the lithium ion battery cell is placed until reaching a voltage stable state;
constant-voltage and constant-current charging is carried out on the lithium ion battery core after full discharge until the target state of charge is reached;
the relation between the open-circuit voltage and the temperature is a relation when the lithium ion battery cell is in a target charge state.
In some embodiments, the target state of charge is obtained by:
fully charging the lithium ion battery core to be tested;
discharging the fully charged lithium ion battery cell to be tested to obtain a change curve of open-circuit voltage to battery cell capacity in different charge states;
and screening the corresponding state of charge according to the change curve of the open circuit voltage to the capacity of the battery core, and determining the state of charge as a target state of charge, wherein the screening rule is set to be that the change value of the open circuit voltage to the capacity of the battery core reaches a preset value and is kept in a target interval range.
The lithium ion battery self-discharge test method provided by the embodiment of the disclosure has the following advantages:
the method comprises the steps of obtaining open-circuit voltage and temperature of a plurality of continuous time nodes by carrying out self-discharge monitoring on a lithium ion battery; correcting the corresponding open-circuit voltage according to the temperature according to a preset open-circuit voltage and temperature relation, and obtaining a corrected voltage value; and calculating the voltage drop of the lithium ion battery in unit time, namely a K value by utilizing the corrected voltage values of the plurality of time nodes.
According to the embodiment of the disclosure, under the condition that the K value is influenced by temperature, the open-circuit voltage is corrected by incorporating the relation between the open-circuit voltage and the temperature in the self-discharge test process, the K value is tested in stages based on a plurality of time nodes, the influence of the temperature on the measurement result is weakened, and the test accuracy is improved.
Drawings
Other features, objects and advantages of the present invention will become more apparent upon reading of the detailed description of non-limiting embodiments, made with reference to the following drawings.
Fig. 1 shows one of flowcharts of a lithium ion battery self-discharge test method provided by an embodiment of the present disclosure;
FIG. 2 shows a second flowchart of a method for testing self-discharge of a lithium ion battery according to an embodiment of the disclosure;
FIG. 3 shows a third flowchart of a method for testing self-discharge of a lithium ion battery according to an embodiment of the disclosure;
FIG. 4 shows a fourth flowchart of a method for testing self-discharge of a lithium ion battery provided by an embodiment of the disclosure;
fig. 5 shows a correspondence curve between a state of charge and an open circuit voltage in a lithium ion battery self-discharge test method according to an embodiment of the present disclosure;
FIG. 6 shows dV/dQ curves at different SOCs in a lithium ion battery self-discharge test method according to an embodiment of the present disclosure;
fig. 7 shows an open circuit voltage-temperature relationship curve in a lithium ion battery self-discharge test method according to an embodiment of the present disclosure.
Detailed Description
Other advantages and effects of the present application will be readily apparent to those skilled in the art from the present disclosure, by describing embodiments of the present application with specific examples. The present application may be embodied or applied in other specific forms and details, and various modifications and alterations may be made to the details of the present application from different points of view and application without departing from the spirit of the present application. It should be noted that, in the case of no conflict, the embodiments and features in the embodiments may be combined with each other.
The embodiments of the present application will be described in detail below with reference to the drawings so that those skilled in the art to which the present application pertains can easily implement the same. This application may be embodied in many different forms and is not limited to the embodiments described herein.
The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the application. As used herein, the singular forms "a", "an" and "the" are intended to include the plural forms as well, unless the language clearly indicates the contrary. The meaning of "comprising" in the specification is to specify the presence of stated features, regions, integers, steps, operations, elements, and/or components, but does not preclude the presence or addition of other features, regions, integers, steps, operations, elements, and/or components.
Although not differently defined, including technical and scientific terms used herein, all terms have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs. The term addition defined in the commonly used dictionary is interpreted as having a meaning conforming to the contents of the related art document and the current hint, so long as no definition is made, it is not interpreted as an ideal or very formulaic meaning too much.
In the related art, a lithium ion battery self-test is performed using an open circuit voltage (Open Circuit Voltage, abbreviated as OCV) measurement method, wherein the open circuit voltage measurement method refers to a voltage drop of the battery in unit time, and is an index for measuring a self-discharge rate of the lithium battery, and is denoted as a K value. The calculation method is that the open-circuit voltage difference of the two tests is divided by the time interval of the two voltage tests, and the formula is OCV1-OCV 2/[ delta ] t, and the unit is: mV/h. The method is widely applied to actual production due to simple process.
When the related technology is researched, the open-circuit voltage and the K value are greatly influenced by temperature, and the measurement error is caused by the fluctuation of the ambient temperature in the standing process, so that the final K value is inaccurate in test, and the error screening or the screening leakage is caused.
Therefore, the embodiment of the disclosure provides an improved self-testing method for a lithium ion battery, so as to improve the self-testing accuracy.
Fig. 1 shows a method for testing self-discharge of a lithium ion battery according to an embodiment of the present disclosure, including, but not limited to, the following steps:
step 110: self-discharge monitoring is carried out on the lithium ion battery, and open-circuit voltage and temperature of a plurality of continuous time nodes are obtained;
step 120: correcting the corresponding open-circuit voltage according to the temperature according to a preset open-circuit voltage and temperature relation, and obtaining a corrected voltage value;
step 130: and calculating the voltage drop of the lithium ion battery in unit time, namely a K value by utilizing the corrected voltage values of the plurality of time nodes.
According to the embodiment of the disclosure, under the condition that the K value is influenced by temperature, the open-circuit voltage is corrected by incorporating the relation between the open-circuit voltage and the temperature in the self-discharge test process, the K value is tested in stages based on a plurality of time nodes, the influence of the temperature on the measurement result is weakened, and the test accuracy is improved.
In an embodiment of the present disclosure, calculating a voltage drop of a lithium ion battery in a unit time using corrected voltage values of a plurality of time nodes includes:
calculating voltage drop sub-values in unit time by using the corrected voltage values of every two adjacent time nodes to obtain a plurality of voltage drop sub-values;
and calculating an average value of the voltage drop sub-values to obtain the voltage drop of the lithium ion battery in unit time.
In this embodiment, the influence of the open circuit voltage at each stage on the temperature can be weakened by averaging, and the test accuracy can be improved.
In the disclosed embodiments, the median may also be employed as the final K value.
Fig. 2 shows a flow chart of a method for testing self-discharge of a lithium-ion battery according to one embodiment of the present disclosure, as shown in fig. 2, including, but not limited to, the following steps:
step 210: adjusting the charge state of the lithium ion battery to a target charge state;
step 220: self-discharge monitoring is carried out on the lithium ion battery, and open-circuit voltage and temperature of a plurality of continuous time nodes are obtained;
step 230: correcting the corresponding open-circuit voltage according to the temperature according to a preset open-circuit voltage and temperature relation, so as to obtain a corrected voltage value, wherein the open-circuit voltage and temperature relation is a relation corresponding to a target state of charge;
step 240: and calculating the voltage drop of the lithium ion battery in unit time by utilizing the corrected voltage values of the plurality of time nodes.
The battery state of charge SOC (state of charge) is a percentage of the current remaining capacity of the lithium ion battery to the rated capacity, and the self-discharge mode may be different at each SOC when the self-discharge test is performed, so that the relationship between the open circuit voltage and the temperature at each SOC may be determined in advance.
Therefore, the relational expression corresponding to the target state of charge means that the relational expression of the open circuit voltage and the temperature is a relational expression of the open circuit voltage and the temperature predetermined for the target state of charge.
In an embodiment of the present disclosure, adjusting a state of charge of a lithium ion battery to a target state of charge includes:
adjusting the lithium ion battery to a plurality of different target charge states;
at each target state of charge, self-discharge monitoring of the lithium ion battery is performed until a voltage drop per unit time is obtained.
In this embodiment, the steps 220-240 may be repeated to implement multiple sets of K-value tests by adjusting the lithium ion battery to different states of charge, taking the corresponding open circuit voltage and temperature for each target state of charge.
In the embodiment of the present disclosure, adjusting the state of charge of the lithium ion battery to the target state of charge may specifically include the following steps:
fully discharging the lithium ion battery;
and carrying out constant-voltage and constant-current charging on the fully discharged lithium ion battery until the target state of charge is reached.
And through full discharge, the electric quantity of the lithium ion battery is 0, and the lithium ion battery is further charged to a corresponding target state of charge at the moment, and the self-discharge test is performed on the lithium ion battery in the target state of charge at the moment. The target state of charge can be more accurately achieved by means of full discharge recharging.
In embodiments of the present disclosure, the lithium ion battery is left until a voltage steady state is reached, prior to self-discharge monitoring of the lithium ion battery. The voltage stable state is the normal state of the lithium ion battery, which can eliminate the problem of inaccurate test results caused by extremely unstable voltage.
As shown in fig. 3, the preset relationship between the open circuit voltage and the temperature is obtained by the following steps:
step 310: placing the lithium ion battery cell in a constant temperature box, and adjusting the temperature in the constant temperature box;
step 320: and under each constant temperature condition, standing the lithium ion battery cell for a target time period, collecting voltage change in the target time period, and fitting an open-circuit voltage and temperature relation according to the voltage change and the constant temperature.
The lithium ion battery cell is a finished product battery cell, and the constant temperature box can provide constant temperature, so that the voltage change of the lithium ion battery cell in a target time period can be monitored at each constant temperature, and the relation between the open-circuit voltage and the temperature can be fitted according to the voltage change and the constant temperature.
In an embodiment of the present disclosure, the self-discharge test method for a lithium ion battery further includes:
before placing the lithium ion battery cell in the incubator, the lithium ion battery cell is left until a voltage steady state is reached.
In an embodiment of the present disclosure, the self-discharge test method for a lithium ion battery further includes:
fully discharging the lithium ion battery cell before the lithium ion battery cell is placed until reaching a voltage stable state;
constant-voltage and constant-current charging is carried out on the lithium ion battery core after full discharge until the target state of charge is reached;
the relation between the open-circuit voltage and the temperature is a relation when the lithium ion battery cell is in a target charge state.
Using this method, an open circuit voltage versus temperature relationship can be determined for each target state of charge.
As shown in fig. 4, the target state of charge is obtained by:
step 410: fully charging the lithium ion battery core to be tested;
step 420: discharging the fully charged lithium ion battery cell to be tested to obtain a change curve of open-circuit voltage to battery cell capacity in different charge states;
step 430: and screening the corresponding state of charge according to the change curve of the open circuit voltage to the capacity of the battery core, and determining the state of charge as a target state of charge, wherein the screening rule is set to be that the change value of the open circuit voltage to the capacity of the battery core reaches a preset value and is kept in a target interval range.
In this embodiment, the change value of the open-circuit voltage to the capacity of the battery cell is larger and is stabilized within a certain target interval, and at this time, the open-circuit voltage has higher measurability, and the feasibility of the scheme is improved.
The principle of the lithium ion battery self-discharge test method provided by the embodiment of the present disclosure is described below with reference to specific examples.
Firstly, selecting a proper SOC by adopting the following steps:
s1, taking a 1pcs finished product battery cell, fully charging the battery cell, charging current I1, cut-off voltage OCV1, and then charging the battery cell at constant voltage, charging voltage OCV2 and cut-off current I2;
s2, recording detailed data of a discharging process, including open-circuit voltage V and battery capacity Q, of full charge core discharging, discharging current I3, cut-off voltage OCV3, and obtaining OCVs corresponding to different SOCs, namely (OCVs and SOCs), wherein as the SOCs are increased, the OCVs are continuously increased as shown in FIG. 5;
s3, deriving V from Q to obtain dV/dQ data, obtaining dV/dQ data under different OCVs, and obtaining dV/dQ curves under different SOCs according to the corresponding relation of (OCVs, SOCs) to be recorded as (SOCs, dV/dQ), wherein the self-discharge test SOCs are 15% SOCs as shown in FIG. 6;
s4, selecting a proper SOC according to a (SOC, dV/dQ) curve, ensuring that dV/dQ is large and relatively stable in a certain interval, and recording the corresponding OCV as V0.
Then, the open circuit voltage-temperature relation is obtained by the following steps:
s11, taking a 1pcs finished product battery cell, fully discharging the battery cell, discharging current I4, cut-off voltage OCV4, and then charging the battery cell at constant current and constant voltage, wherein the initial charging current I5, the cut-off voltage V0 and the cut-off current I6;
s12, setting the cell standing time t1 until the voltage of the cell is stable (dv/dt does not change obviously any more);
s13, placing the battery cell in an incubator, and obtaining an open-circuit voltage-temperature relation by adopting the following steps: 1) Setting the initial temperature of the incubator to 20 ℃; 2) Standing for 4-6 h; 3) Collecting the voltage of a current core;
4) Cycling 1) to 3) with the temperature set at 20 ℃, 23 ℃, 26 ℃ and 30 ℃; 5) Obtaining open-circuit voltages of the battery cells at different temperatures, and recording the open-circuit voltages as (T, OCV); 6) As shown in fig. 7, an open-circuit voltage-temperature relationship is obtained from (T, OCV) fitting: y= -0.12939x+3256.01254.
Finally, the self-discharge test of the lithium ion battery is carried out by adopting the following method:
s21, taking a group of self-discharging cells to be tested, adjusting the SOC in the reference step S11, fully discharging the cells, discharging the current I4, stopping the voltage OCV4, and then carrying out constant-current constant-voltage charging on the cells, wherein the initial charging current I5, the stopping voltage V0 and the stopping current I6;
s22, the cell resting time T1 is set, the voltage stability of the cell is ensured (dv/dt does not change obviously any more), and the open circuit voltage V1 and the temperature T1 are measured at the moment;
s23, the cell rest time t2 (assuming t2=5 days or other days), the cell voltage and temperature are tested every 24h during the rest period, for example, 24h: v2, T2;48h: v3, T3;72h: v4, T4;96h: v5, T5;120h: v6, T6;
s24, correcting the obtained voltages (V1, V2, V3, V4, V5 and V6) to voltages (V1 ', V2', V3', V4', V5', V6') at 25 ℃ according to an open-circuit voltage-temperature relation;
s25, K1 = (V2 '-V1')/24, k2 = (V3 '-V2')/24, k3 = (V4 '-V3')/24, k4 = (V5 '-V4')/24, k5 = (V6 '-V5'), then k1= (k1+k2+k3+k4+k5)/5.
Optionally, i1=0.3 to 0.5C, when the cell is a ternary cell, ocv1=4.2v, ocv3=2.75V; when the cell is a lithium iron phosphate cell, ocv1=3.65v, ocv3=2.5v. Ocv1=ocv2, i2=i3=0.02c. In the SOC adjustment flow, i4=i5=0.1 to 0.3c, i6=0.02C. Standing for 24-48 h at t 1.
Referring to the cell K value calculation table shown in table 1 below:
the self-discharge test was performed by taking 5 cells #1, #2, #3, #4 and #5 as above, respectively, to obtain 5K values.
The above parameters are examples, and in the corresponding embodiments, the corresponding parameters may be adjusted according to actual situations.
According to the method disclosed by the embodiment of the disclosure, a staged test method is adopted to measure the K value, the temperature of the voltage of each stage is corrected, the K value is calculated, and the average value of the K values of each stage is taken as the final K value. The voltage and the temperature of the battery cell are tested every 24 hours during the rest period, and voltage correction is carried out according to a voltage-temperature relation formula so as to weaken the influence of the temperature on a measurement result and improve the test accuracy.
The foregoing is a further detailed description of the invention in connection with the preferred embodiments, and it is not intended that the invention be limited to the specific embodiments described. It will be apparent to those skilled in the art that several simple deductions or substitutions may be made without departing from the spirit of the invention, and these should be considered to be within the scope of the invention.
Claims (10)
1. The self-discharge testing method of the lithium ion battery is characterized by comprising the following steps of:
self-discharge monitoring is carried out on the lithium ion battery, and open-circuit voltage and temperature of a plurality of continuous time nodes are obtained;
correcting the corresponding open-circuit voltage according to the temperature according to a preset open-circuit voltage and temperature relation, and obtaining a corrected voltage value;
and calculating the voltage drop of the lithium ion battery in unit time by utilizing the corrected voltage values of the plurality of time nodes.
2. The lithium ion battery self-discharge test method according to claim 1, further comprising:
before self-discharge monitoring is carried out on a lithium ion battery, the charge state of the lithium ion battery is adjusted to a target charge state;
the open circuit voltage and temperature relationship is a relationship corresponding to the target state of charge.
3. The method of claim 2, wherein said adjusting the state of charge of the lithium ion battery to a target state of charge comprises:
adjusting the lithium ion battery to a plurality of different target charge states;
and executing the self-discharge monitoring on the lithium ion battery under each target charge state until the voltage drop in the unit time is obtained.
4. The method of claim 2, wherein said adjusting the state of charge of the lithium ion battery to a target state of charge comprises:
fully discharging the lithium ion battery;
and carrying out constant-voltage and constant-current charging on the fully discharged lithium ion battery until the target state of charge is reached.
5. The lithium ion battery self-discharge test method according to claim 1, further comprising:
the lithium ion battery is left until a voltage steady state is reached, before the lithium ion battery is self-discharge monitored.
6. The method according to claim 1, wherein calculating the voltage drop of the lithium ion battery per unit time using the corrected voltage values of the plurality of time nodes comprises:
calculating voltage drop sub-values in unit time by using the corrected voltage values of every two adjacent time nodes to obtain a plurality of voltage drop sub-values;
and calculating an average value of the voltage drop sub-values to obtain the voltage drop of the lithium ion battery in unit time.
7. The method for testing the self-discharge of the lithium ion battery according to claim 1, wherein the preset relation between the open-circuit voltage and the temperature is obtained by the following steps:
placing a lithium ion battery cell in a constant temperature box, and adjusting the temperature in the constant temperature box;
and under each constant temperature condition, standing the lithium ion battery cell for a target time period, collecting voltage change in the target time period, and fitting the relation between the open-circuit voltage and the temperature according to the voltage change and the constant temperature.
8. The method of claim 7, further comprising:
before placing the lithium ion battery cell in the incubator, the lithium ion battery cell is left until a voltage steady state is reached.
9. The lithium ion battery self-discharge test method according to claim 8, further comprising:
fully discharging the lithium ion battery cell before the lithium ion battery cell is placed until a voltage stable state is reached;
performing constant-voltage and constant-current charging on the fully discharged lithium ion battery cell until reaching a target state of charge;
the relation between the open-circuit voltage and the temperature is the relation when the lithium ion battery cell is in the target charge state.
10. The method of claim 9, wherein the target state of charge is obtained by:
fully charging the lithium ion battery core to be tested;
discharging the fully charged lithium ion battery cell to be tested to obtain a change curve of open-circuit voltage to battery cell capacity in different charge states;
and screening the corresponding state of charge according to the change curve of the open circuit voltage to the battery core capacity, and determining the state of charge as the target state of charge, wherein the screening rule is set to be that the change value of the open circuit voltage to the battery core capacity reaches a preset value and is kept in a target interval range.
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| CN117406112B (en) * | 2023-12-13 | 2024-03-15 | 瑞浦兰钧能源股份有限公司 | Battery self-discharge screening method |
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