CN118409211B - Battery cell quality detection device and detection method - Google Patents
Battery cell quality detection device and detection method Download PDFInfo
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- CN118409211B CN118409211B CN202410576390.0A CN202410576390A CN118409211B CN 118409211 B CN118409211 B CN 118409211B CN 202410576390 A CN202410576390 A CN 202410576390A CN 118409211 B CN118409211 B CN 118409211B
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- WHXSMMKQMYFTQS-UHFFFAOYSA-N Lithium Chemical compound [Li] WHXSMMKQMYFTQS-UHFFFAOYSA-N 0.000 description 8
- 229910052744 lithium Inorganic materials 0.000 description 8
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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
- G01R19/00—Arrangements for measuring currents or voltages or for indicating presence or sign thereof
- G01R19/165—Indicating that current or voltage is either above or below a predetermined value or within or outside a predetermined range of values
- G01R19/16533—Indicating that current or voltage is either above or below a predetermined value or within or outside a predetermined range of values characterised by the application
- G01R19/16538—Indicating that current or voltage is either above or below a predetermined value or within or outside a predetermined range of values characterised by the application in AC or DC supplies
- G01R19/16542—Indicating that current or voltage is either above or below a predetermined value or within or outside a predetermined range of values characterised by the application in AC or DC supplies for batteries
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
- G01R19/00—Arrangements for measuring currents or voltages or for indicating presence or sign thereof
- G01R19/25—Arrangements for measuring currents or voltages or for indicating presence or sign thereof using digital measurement techniques
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
- G01R27/00—Arrangements for measuring resistance, reactance, impedance, or electric characteristics derived therefrom
- G01R27/02—Measuring real or complex resistance, reactance, impedance, or other two-pole characteristics derived therefrom, e.g. time constant
- G01R27/26—Measuring inductance or capacitance; Measuring quality factor, e.g. by using the resonance method; Measuring loss factor; Measuring dielectric constants ; Measuring impedance or related variables
- G01R27/2605—Measuring capacitance
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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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- 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]
- G01R31/389—Measuring internal impedance, internal conductance or related variables
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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
- G01R31/50—Testing of electric apparatus, lines, cables or components for short-circuits, continuity, leakage current or incorrect line connections
- G01R31/52—Testing for short-circuits, leakage current or ground faults
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
- H01M10/00—Secondary cells; Manufacture thereof
- H01M10/42—Methods or arrangements for servicing or maintenance of secondary cells or secondary half-cells
- H01M10/4285—Testing apparatus
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- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
- Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
- Y02E60/00—Enabling technologies; Technologies with a potential or indirect contribution to GHG emissions mitigation
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Abstract
本发明公开了一种电池电芯质量检测装置及检测方法，属于电变量测量技术领域，包括在未注液的电池电芯的两端施加直流高压；在所述直流高压上叠加低压交流电源，控制电池电芯反复充放电，进入交直流叠加测试阶段：检测电池电芯两端的电压和流过电池电芯的电流，并分离出其中的交流分量，计算电池电芯的交流阻抗和等效电容值；在等效电容值大于设定容值时，判定电芯内部的隔膜厚度过薄；在交流阻抗大于设定阻值时，判定电芯正负极片之间存在因浆液分散不均而导致的团聚现象。本发明采用交直流叠加技术对未注液的电池电芯进行检测，不仅可以准确地筛选出有问题的电池，而且可以识别出电池所存在的缺陷类型。
The present invention discloses a battery cell quality detection device and detection method, which belongs to the field of electrical variable measurement technology, including applying a DC high voltage to both ends of a battery cell that is not injected with liquid; superimposing a low-voltage AC power supply on the DC high voltage, controlling the battery cell to charge and discharge repeatedly, and entering the AC/DC superposition test stage: detecting the voltage at both ends of the battery cell and the current flowing through the battery cell, and separating the AC component therein, calculating the AC impedance and equivalent capacitance value of the battery cell; when the equivalent capacitance value is greater than the set capacitance value, determining that the thickness of the diaphragm inside the battery cell is too thin; when the AC impedance is greater than the set resistance value, determining that there is agglomeration between the positive and negative plates of the battery cell due to uneven dispersion of slurry. The present invention uses AC/DC superposition technology to detect battery cells that are not injected with liquid, which can not only accurately screen out problematic batteries, but also identify the types of defects existing in the batteries.
Description
Technical Field
The invention belongs to the technical field of electric variable measurement, and particularly relates to a device and a method for detecting the quality of a battery core.
Background
Along with popularization of new energy sources, the application of the lithium battery is more and more extensive, and whether the quality of the lithium battery is qualified directly relates to the electricity safety problem of electrical equipment, so that the lithium battery needs to be subjected to quality test in the production and manufacturing process of the lithium battery.
The production process of the lithium battery comprises the production of the pole piece and the process aspect, and the process with great influence on the microstructure mainly comprises the steps of mixing, coating, drying and rolling. The rolling process comprises rolling a diaphragm between positive and negative plates of the battery; after the diaphragm rolling is completed, laminating and rolling the positive and negative plates and the diaphragm; and (5) winding after the lamination rolling is completed. In the whole rolling process, if the electrode slurry is unevenly dispersed, serious agglomeration phenomenon can be generated, and the electrochemical performance of the battery is affected. In the diaphragm rolling process, the diaphragm thickness should meet certain requirements; during lamination and rolling, impurities cannot be introduced between the positive and negative plates and the diaphragm, and impurities cannot be introduced in the winding process. However, in the production process, due to the reasons of mechanical equipment, personnel, production process and the like, problems of thinner diaphragm thickness, introduction of metal impurities and the like are easy to occur, and the service life of the lithium battery is shortened. If the metal impurity particles are larger, internal short circuit of the battery can be caused, and spontaneous combustion accidents of the lithium battery can be caused.
In order to detect a battery with a problem in quality in the manufacturing process, the battery cell detection methods widely used in the industry at present mainly comprise three types:
The first is the insulation test method. Namely, the direct-current high-voltage source is utilized to charge the battery cell which is not injected with liquid, the battery cell is kept for a period of time after reaching the set voltage, the direct-current resistance of the battery cell is tested, and the quality of the battery cell is judged according to the resistance. The problems with this test method are: the data of the battery cell in the charging stage may be the same as that of the normal battery cell, but the discharge speed may be suddenly increased in the discharging stage, which indicates that the battery cell has a micro-short circuit problem which cannot be detected by the insulation test method.
The second is the pulse test method. Namely, the battery cell which is not injected with liquid is charged by using a direct-current high-voltage source and then stops after reaching a set voltage, whether the battery voltage is rapidly reduced is tested, and if the battery voltage is rapidly reduced, the problem that the battery cell is in micro short circuit or has low insulation resistance is indicated; and after the test time is reached, discharging the battery cell, and ending the test process. The problems with this test method are: if the metal impurities introduced into the battery core are smaller and the short circuit is not obvious, the testing method cannot detect the battery with the problem.
The third is a low-voltage alternating current test method which is only applicable to battery cells after liquid injection. Namely, electrolyte is injected into a battery cell, then a low-voltage alternating current source is applied to two ends of the cell, alternating current impedance of the cell is measured, and whether the cell is good or not is judged according to the impedance. The problems with this test method are: if the diaphragm between the positive electrode plate and the negative electrode plate of the battery core is too thin, the lithium ion crystal generated by the positive electrode of the battery core is easier to puncture the diaphragm after the battery core is charged and discharged for many times, and spontaneous combustion of the lithium battery is further caused. Moreover, the battery cell detects a problem after the liquid is injected, and the battery cell cannot be used any more, so that the electrolyte is wasted greatly.
In addition, the three existing testing methods are also ubiquitous: the method can not detect whether the thickness of the diaphragm between the positive pole piece and the negative pole piece of the battery core meets the requirement, and can not test the agglomeration phenomenon caused by uneven slurry dispersion between the pole pieces.
Disclosure of Invention
The invention aims to provide a device and a method for detecting the quality of a battery cell, which are used for solving the problem that the existing test method is single in identifying the defect type of a battery.
In order to solve the technical problems, the invention is realized by adopting the following technical scheme:
In one aspect, the present invention provides a device for detecting quality of a battery cell, for detecting quality of a battery cell without filling, including:
the adjustable direct current high voltage source is used for applying direct current high voltage to two ends of the battery cell without liquid injection;
The adjustable alternating current voltage source is used for superposing a low-voltage alternating current power supply on the direct current high voltage output by the adjustable direct current high voltage source so as to control the battery cell to be repeatedly charged and discharged and enter an alternating current-direct current superposition test stage;
the voltage measuring loop is used for detecting the voltage at two ends of the battery cell;
a current measurement loop for detecting a current flowing through the battery cell;
An ac/dc separation circuit for ac/dc separating the voltage detection signal output from the voltage measurement circuit or the current detection signal output from the current measurement circuit, and outputting an ac voltage component or an ac current component;
an alternating current reference unit for generating two paths of alternating current reference signals which are different in phase by 90 degrees and have the same frequency with the low-voltage alternating current power supply;
A multiplier unit for multiplying the ac voltage component and the ac current component by the two ac reference signals, respectively, and outputting two voltage signals and two current signals;
The control unit is used for receiving the two paths of voltage signals and the two paths of current signals output by the multiplier unit in the alternating current-direct current superposition test stage and calculating the alternating current impedance and the equivalent capacitance value of the battery cell; when the equivalent capacitance value is larger than the set capacitance value, generating a test result that the thickness of the isolation film inside the battery cell is too thin; when the alternating current impedance is larger than the set resistance value, a test result of agglomeration phenomenon caused by uneven slurry dispersion between the positive and negative electrode plates of the battery core is generated.
In some embodiments of the present application, the control unit may be configured to calculate the ac impedance and equivalent capacitance of the battery cells in the following manner:
Generating two voltage components U 1、U2 and two current components I 1、I2 according to the two voltage signals and the two current signals output by the multiplier unit respectively; then, the cell voltage maximum U z and the phase angle β are calculated using the following formulas:
U1=Uzsin(ωt+β)sinωt
U2=Uzsin(ωt+β)cosωt；
The maximum value of the current I z and the phase angle γ flowing through the cell are calculated using the following formulas:
I1=Izsin(ωt+γ)sinωt
I2=Izsin(ωt+γ)cosωt；
calculating the equivalent impedance Z and the corresponding phase angle theta of the battery cell:
Z=Uz/Iz
θ=β-γ;
calculating the alternating current impedance R and the equivalent capacitance value C of the battery cell:
R=Zcosθ
C=Zsinθ。
In some embodiments of the present application, whether a metal impurity exists in the battery cell may be detected in the ac/dc superposition test stage, that is, the control unit may be configured to receive the voltage detection signal output by the voltage measurement circuit in the ac/dc superposition test stage, and if the voltage detection signal drops rapidly and reaches the lower limit value, a test result may be generated in which a micro short circuit problem caused by the metal impurity exists in the cell.
In some embodiments of the application, it may be provided in the control unit that:
the control chip outputs a high-voltage set value to the adjustable direct-current high-voltage source, and controls the adjustable direct-current high-voltage source to gradually rise the output direct-current voltage to the high-voltage set value and keep the high-voltage set value in a set time;
The control chip controls the first switch to be conducted in an alternating current-direct current superposition test stage and controls the adjustable direct current high-voltage source to transmit direct current bus voltage to the adjustable alternating current voltage source;
The second change-over switch receives a control signal output by the control chip in an alternating current-direct current superposition test stage so as to superimpose a low-voltage alternating current power supply output by the adjustable alternating current voltage source on a direct current high voltage output by the adjustable direct current high voltage source;
A divider which receives the voltage detection signal output by the voltage measurement loop and the current detection signal output by the current measurement loop and performs division operation to generate an analog quantity signal reflecting the resistance value of the battery cell;
the ADC chip is communicated with the control chip, receives different analog quantity signals in different testing stages, converts the analog quantity signals into digital quantity signals and sends the digital quantity signals to the control chip; wherein,
When the direct-current voltage output by the adjustable direct-current high-voltage source is in a rising stage, the control chip controls the ADC chip to carry out analog-to-digital conversion on voltage detection signals and current detection signals output by the voltage measurement loop and the current measurement loop so as to generate voltage data and current data, the voltage data are sent to the control chip to calculate current variation and voltage variation, and when the current variation or the voltage variation exceeds a set threshold value, a test result of micro short circuit problem caused by metal impurities in the battery core is generated;
When the direct-current voltage output by the adjustable direct-current high-voltage source is in a high-voltage maintaining stage, the control chip controls the ADC chip to carry out analog-to-digital conversion on an analog quantity signal output by the divider, generates resistance data and sends the resistance data to the control chip to calculate the resistance variation of the battery cell, and when the resistance variation exceeds a normal threshold value, generates a test result that the battery cell has a micro-short circuit problem or a membrane in the battery cell is broken by an insulating substance due to thinner thickness to cause a lower insulating resistance problem;
And the control chip controls the ADC chip to carry out analog-to-digital conversion on the voltage signal and the current signal output by the multiplier unit in an alternating current-direct current superposition test stage, and judges the defect type of the battery according to the received voltage data and the received current data.
In some embodiments of the present application, in order to implement comprehensive detection on the battery core, the control chip may be configured to enter a self-discharge test stage after the end of the ac/dc superposition test stage, i.e., to control the adjustable dc high voltage source to stop running, so as to enable the core to self-discharge; in the self-discharge stage, the control chip is configured to control the ADC chip to perform analog-to-digital conversion on the voltage detection signal output by the voltage measurement loop, and if the descending amplitude of the received voltage data in the set time exceeds a set threshold value, a test result of the micro-short circuit problem caused by metal impurities in the battery core or the problem of lower insulation resistance caused by thinner thickness or puncture of a diaphragm in the battery core can be generated.
In another aspect, the invention further provides a method for detecting the quality of a battery cell, which is applied to a battery cell without liquid injection, and comprises the following steps:
Applying direct-current high voltage to two ends of a battery cell without liquid injection;
and superposing a low-voltage alternating current power supply on the direct current high voltage, controlling the repeated charge and discharge of the battery core, and entering an alternating current-direct current superposition test stage:
Detecting voltages at two ends of a battery cell and currents flowing through the battery cell, separating alternating current components in the voltages, multiplying the voltages with two paths of alternating current reference signals with 90 degrees of phase difference, and calculating alternating current impedance and equivalent capacitance of the battery cell by using the generated four paths of signals; wherein, the two paths of alternating current reference signals and the low-voltage alternating current power supply have the same frequency;
When the equivalent capacitance value is larger than the set capacitance value, judging that the thickness of the diaphragm in the battery cell is too thin;
when the alternating current impedance is larger than the set resistance, the agglomeration phenomenon caused by uneven slurry dispersion between the positive and negative electrode plates of the battery cell is judged.
In some embodiments of the present application, the ac impedance and equivalent capacitance values of the battery cells may be calculated using the following methods:
generating two paths of alternating current reference signals with the same frequency and 90 degrees of phase difference according to the frequency of the low-voltage alternating current power supply:
A=sinωt
B=cosωt;
Collecting voltages at two ends of a battery cell, performing AC/DC separation, extracting AC voltage components, and multiplying the AC voltage components with two paths of AC reference signals respectively to obtain a voltage component U 1、U2:
U1=Uzsin(ωt+β)sinωt
U2=Uzsin(ωt+β)cosωt；
Collecting current flowing through a battery cell, performing AC/DC separation, extracting AC current components, and multiplying the AC current components with two paths of AC reference signals respectively to obtain current components I 1、I2:
I1=Izsin(ωt+γ)sinωt
I2=Izsin(ωt+γ)cosωt；
Calculating a cell voltage maximum value U z and a phase angle beta by using the voltage component U 1、U2;
Calculating a current maximum value I z and a phase angle gamma of the current flowing through the battery cell by using the current component I 1、I2;
calculating the equivalent impedance Z and the corresponding phase angle theta of the battery cell:
Z=Uz/Iz
θ=β-γ;
calculating the alternating current impedance R and the equivalent capacitance value C of the battery cell:
R=Zcosθ
C=Zsinθ。
In some embodiments of the present application, in order to identify whether metal impurities are introduced into the battery cell, voltages at two ends of the battery cell may be detected in the ac/dc superposition test stage, and if the voltages at two ends of the battery cell rapidly drop and fall to a lower limit value, it may be considered that a micro-short circuit problem caused by the metal impurities exists in the battery cell.
In some embodiments of the present application, in order to improve the timeliness and accuracy of the battery defect detection, two test phases may be configured before the ac/dc superposition test phase, namely:
voltage rising stage: applying direct current voltage at two ends of a battery cell, and controlling the direct current voltage to gradually rise to a high-voltage set value in set time; detecting the current flowing through the battery cell and the voltage at two ends of the battery cell in the voltage rising process, and if the current variation or the voltage variation exceeds a set threshold value, considering that the problem of micro short circuit caused by metal impurities exists in the battery cell;
High pressure holding stage: and keeping the direct-current voltage at a high-voltage set value, collecting the current flowing through the battery core and the voltages at two ends of the battery core in real time, and calculating the resistance change quantity of the battery core, wherein if the resistance change quantity exceeds a normal threshold value, the problem of micro short circuit of the battery core or the problem of low insulation resistance caused by the fact that a diaphragm in the battery core is thinner or is punctured by an insulation substance can be considered.
In some embodiments of the present application, after the ac-dc superposition test phase is finished, a self-discharge test phase may be further configured, that is: stopping applying voltage to the battery core to enable the battery core to enter a self-discharging process; in this period, the voltage across the cell is detected, and if the magnitude of the decrease in the voltage across the cell in the set time exceeds the set threshold, it is considered that there is a problem of micro-shorting due to metal impurities inside the cell or a problem of low insulation resistance due to a thin thickness or a puncture of the separator inside the cell by an insulating substance.
Compared with the prior art, the invention has the advantages and positive effects that:
1. According to the method for designing and measuring the battery cell without liquid injection, because the battery cell is subjected to direct-current high voltage at two ends of the battery cell before liquid injection, whether the thickness of a diaphragm between positive and negative pole pieces of the battery cell meets the requirement or not can not be detected, and the problem of agglomeration phenomenon caused by uneven slurry dispersion between the pole pieces can not be tested; the battery core can not apply direct current high voltage at two ends of the battery core after liquid injection, and the direct current high voltage can lead the battery core after liquid injection to be broken down by the high voltage to cause battery explosion, so that certain types of battery defects can not be identified only by applying low-voltage alternating current power supplies at two ends of the battery core after liquid injection. Therefore, the invention adopts a mode of superposing a low-voltage alternating current power supply on a direct-current high voltage to form alternating current voltage with high-voltage bias, and the alternating current voltage is applied to two ends of a battery cell without liquid injection, so that the power supply requirement of the battery cell can be met, the safety of the battery cell test is ensured, the parameter characteristics of the battery cell in an alternating current power supply state can be detected, and certain defects possibly appearing in the battery cell under the alternating current power supply can be identified.
2. In order to realize comprehensive detection of possible quality problems of the battery cells, the invention designs four test stages of voltage rise, high-voltage maintenance, AC/DC superposition and self-discharge, and designs different strategies in each test stage to carry out multi-azimuth detection and identification on possible defects of the battery cells, thereby finding out the problem battery in time, ending the test process as early as possible and avoiding further damage to the problem battery.
3. The invention can detect the battery with quality problems and identify the defect type of the battery with quality problems, thereby guiding personnel to carry out targeted repair work and improving the production efficiency of the battery.
4. The invention aims at the battery cell design detection method without liquid injection, solves the problem of serious waste of electrolyte caused by the fact that the battery cannot be used after the traditional low-voltage alternating current test method tests the liquid injection battery, can greatly reduce the manufacturing cost of the battery and saves resources.
5. The battery cell quality detection device is designed to carry out full-automatic detection on the battery cells without liquid injection, automatically generate a test result, do not need personnel to intervene, and are convenient and quick.
Other features and advantages of the present invention will become apparent upon review of the detailed description of the invention in conjunction with the drawings.
Drawings
In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings that are needed in the embodiments will be briefly described below, and it is obvious that the drawings in the following description are some embodiments of the present invention, and other drawings may be obtained according to these drawings without inventive effort for a person skilled in the art.
FIG. 1 is a schematic block diagram of a battery cell quality detection apparatus according to one embodiment of the present invention;
FIG. 2 is a general flow chart of one embodiment of a battery cell quality detection method according to the present invention;
Fig. 3 is a voltage waveform diagram for each test stage.
Detailed Description
The following description of the technical solutions according to the embodiments of the present invention will be made clearly and completely with reference to the accompanying drawings in the embodiments of the present invention, and it is apparent that the described embodiments are only some embodiments of the present invention, but not all embodiments. All other embodiments, which can be made by a person skilled in the art without any inventive effort, are intended to be within the scope of the present invention based on the embodiments of the present invention.
The battery cell which is not filled with the liquid cannot apply alternating current power supply with alternating current and alternating current, and the battery cell after being filled with the liquid cannot apply direct current high voltage, otherwise spontaneous combustion or explosion of the battery cell is easy to cause. Therefore, the existing battery cell detection methods apply a type of power supply to both ends of the battery cell, which causes certain defects of the battery to be difficult to be obviously represented in a power supply mode, so that the omission ratio of the problem battery is high, and the defect type is difficult to identify.
In order to realize comprehensive detection of the quality problem of the battery cells, four test stages are designed in the embodiment: the voltage rising stage, the high-voltage holding stage, the alternating current-direct current superposition stage and the self-discharge stage adopt different power supply modes in different testing stages and cooperate with different parameter detection means, so that the potential problems in the battery can be captured in multiple directions, and the omission ratio of the battery in question is reduced.
In order to realize automatic detection of a problem battery, the embodiment designs a battery cell quality detection device, as shown in fig. 1, which mainly comprises an adjustable direct-current high-voltage source, an adjustable alternating-current voltage source, a voltage measurement loop, a current measurement loop, an alternating-current and direct-current separation circuit, an alternating-current reference unit, a multiplier unit, a control unit and the like.
The adjustable direct current high voltage source is used for converting external alternating current commercial power into direct current power, and applying direct current high voltage to the battery cell to be tested. In this embodiment, the dc voltage output by the adjustable dc high voltage source may be freely adjusted between 25V and 2000V, and the configuration control unit is connected to the adjustable dc high voltage source to provide a high voltage set value for the adjustable dc high voltage source, for example, the high voltage set value may be set to be above 500V, so that the measured battery cell works in a high voltage power supply state. Meanwhile, the adjustable dc high voltage source of the present embodiment also has a function of adjusting the rising time of the output voltage according to the setting time of the user, so that the control unit can be configured to output the setting time to the adjustable dc high voltage source to control the adjustable dc high voltage source to gradually rise the output voltage to the high voltage setting value within the setting time, such as section a in fig. 3, so as to be applied to the test of the voltage rising stage.
The adjustable alternating current voltage source is used for outputting an alternating current power supply with adjustable frequency and voltage, and the alternating current power supply is overlapped on the direct current voltage output by the adjustable direct current high voltage source to form a sine variable positive voltage. In this embodiment, in order to meet the test requirement, an ac voltage source with a high voltage bias, such as section c in fig. 3, may be formed after the ac voltage source with an adjustable ac voltage source outputs a low voltage ac power source (for example, an ac power source with a voltage of 100V or less) is superimposed with a dc high voltage output by an adjustable dc high voltage source, so as to be applied to an ac-dc superimposed test stage.
In some embodiments, the adjustable DC high voltage source can be used for providing DC bus voltage for the adjustable AC voltage source, so as to simplify the system circuit design and achieve the purpose of adjusting the output voltage of the adjustable AC voltage source.
In order to obtain the dc high-voltage and low-voltage ac power supplies required for the battery cell test and realize the superposition of the dc high-voltage and low-voltage ac power supplies in the ac-dc superposition test stage, the control unit of the embodiment is provided with a control chip MCU, a first switch and a second switch, as shown in fig. 1. The control chip MCU generates a high-voltage set value and a direct-current bus voltage value, and transmits the set value and the direct-current bus voltage value to the adjustable direct-current high-voltage source so as to adjust the direct-current high voltage applied to two ends of the battery cell by the adjustable direct-current high-voltage source and the direct-current bus voltage output to the adjustable alternating-current voltage source. Meanwhile, the control chip MCU generates a switch control signal to control on-off of the first change-over switch and the second change-over switch.
In this embodiment, the first switch is connected between the adjustable dc high voltage source and the adjustable ac voltage source, and the second switch is connected between the adjustable ac voltage source and the power supply line of the battery cell. In an AC/DC superposition test stage, the control chip MCU controls the first switch and the second switch to be conducted, the DC bus voltage output by the adjustable DC high-voltage source is transmitted to the adjustable AC voltage source, the adjustable AC voltage source is electrified to operate, the inversion output low-voltage AC power supply is transmitted to a power supply loop of the battery cell through the second switch, and AC/DC superposition is realized.
The alternating reference unit is used for generating an alternating reference voltage signal and transmitting the alternating reference voltage signal to the adjustable alternating voltage source so as to adjust the frequency of the low-voltage alternating current power supply output by the adjustable alternating voltage source. Meanwhile, two paths of alternating current reference signals A, B which are different in phase by 90 degrees and have the same frequency as the low-voltage alternating current power supply are generated through an alternating current reference unit so as to be used for quadrature phase discrimination.
In some embodiments, the ac reference unit may be constructed using an oscillating circuit, a phase shifting circuit, a shaping circuit, etc. Specifically, the square wave signal with the set frequency can be generated by the oscillating circuit, and the square wave signal is processed by the shaping circuit to form an alternating current reference voltage signal, and the alternating current reference voltage signal is transmitted to the adjustable alternating current voltage source. Then, the phase shift circuit is utilized to shift the phase of the square wave signal output by the oscillating circuit so as to generate two paths of square wave signals with 90 DEG phase difference, and the square wave signals are processed by the shaping circuit so as to form two paths of same-frequency alternating current reference signals A, B with 90 DEG phase difference. The method can be concretely expressed as follows:
A=sinωt
B=cosωt;
Wherein ω is angular frequency, related to the frequency of the low voltage ac power supply; t is the sampling time.
The voltage measuring loop can be connected to two ends of the battery cell and is used for collecting voltages at two ends of the battery cell and reducing the voltages according to a certain proportion. In this embodiment, an operational amplifier, such as an AD8510 chip with a bandwidth of 8MHz, may be disposed in the voltage measurement loop to accurately measure the rapid change of the voltage across the battery cell.
The current measuring loop is used for detecting the current flowing through the battery cell and amplifying the current according to a certain proportion. In some embodiments, a sampling resistor R1 may be connected in series in a power supply loop of the battery cell, a current measurement loop is connected to two ends of the sampling resistor R1, and by detecting a voltage difference across the sampling resistor R1, a current flowing through the battery cell is calculated in cooperation with a resistance value of the sampling resistor R1, that is, a voltage signal is used to reflect a current change.
The AC/DC separation circuit is used for carrying out AC/DC separation on the voltage detection signal output by the voltage measurement loop and the current detection signal output by the current measurement loop so as to output an AC voltage component and an AC current component, and the AC voltage component and the AC current component are transmitted to the multiplier unit.
In some embodiments, the ac/dc separation circuit may be provided with two paths, where one path is connected to the voltage measurement circuit, and is configured to perform ac/dc separation on the voltage detection signal output by the voltage measurement circuit, and transmit the separated ac voltage component to the multiplier unit. The other path of alternating current-direct current separation circuit is connected with the current measurement loop and is used for performing alternating current-direct current separation on the current detection signal output by the current measurement loop and transmitting the separated alternating current component to the multiplier unit.
The multiplier unit receives two paths of alternating current reference signals A, B output by the alternating current reference unit at the same time, multiplies the two paths of alternating current reference signals A, B by alternating current voltage components and alternating current components respectively, and outputs four paths of signals for calculating alternating current impedance and equivalent capacitance of the battery cell. For clarity of description, the four signals may be defined as two voltage signals and two current signals, respectively, and transmitted to the filter unit to remove high frequency components therein, and then transmitted to the control unit.
In some embodiments, four independent multipliers may be provided in the multiplier unit, for multiplying the ac reference signal a and the ac voltage component, for multiplying the ac reference signal B and the ac voltage component, for multiplying the ac reference signal a and the ac current component, and for multiplying the ac reference signal B and the ac current component.
Four independent filters can be arranged in the filter unit, and four paths of signals output by the four multipliers are respectively subjected to filtering processing so as to eliminate high-frequency components in the four paths of signals and improve the accuracy of the test.
In the embodiment, an ADC chip is further provided in the control unit, and the voltage detection signal collected by the voltage measurement loop, the current detection signal collected by the current measurement loop, and the four-way signal output by the filter unit may be directly transmitted to the ADC chip for analog-to-digital conversion, so as to generate a digital signal and send the digital signal to the control chip MCU.
In this embodiment, a divider may be further disposed in the control unit, as shown in fig. 1, so as to receive the voltage detection signal output by the voltage measurement loop and the current detection signal output by the current measurement loop in the high voltage holding stage, and after dividing, a voltage signal reflecting the resistance may be obtained, and the voltage signal may be transmitted to the ADC chip for analog-to-digital conversion, and then transmitted to the control chip MCU, so as to reduce the data processing capacity of the control chip MCU.
The following describes a method for detecting the quality of a battery cell with reference to the apparatus for detecting the quality of a battery cell shown in fig. 1, and the method is divided into four test stages as shown in fig. 2.
(1) Stage of voltage rise
The method comprises the steps of applying gradually rising direct current voltage to two ends of a battery cell to be tested, collecting current flowing through the battery cell and voltage at the two ends of the cell, and judging whether micro short circuit caused by metal impurities exists in the cell according to current variation and voltage variation.
Specifically, the battery cell without liquid injection is connected to the detection device, the control chip MCU outputs a high voltage set point, and the adjustable dc high voltage source is controlled to gradually increase the dc voltage output by the adjustable dc high voltage source to the high voltage set point within a set time, as in the section a in fig. 3.
In the voltage rising process, voltages at two ends of the battery cell are collected in real time through the voltage measuring loop, current flowing through the battery cell is collected in real time through the current measuring loop, the control chip MCU informs the ADC chip to receive voltage detection signals and current detection signals output by the voltage measuring loop and the current measuring loop, and after analog-to-digital conversion is carried out, voltage data and current data are generated and sent to the control chip MCU.
The control chip MCU calculates current variation and voltage variation according to the received voltage data and current data, and if the current variation or the voltage variation exceeds a set threshold value, the micro-short circuit problem is indicated to exist in the battery cell, and the micro-short circuit problem is caused by metal impurities introduced into the battery cell. Otherwise, the subsequent testing phase is continued.
The embodiment can configure the control chip MCU to directly generate the test result and output the test result through the display device, so that the test result is convenient for operators to check.
(2) High pressure holding stage
Namely, direct-current high voltage is continuously applied to two ends of a battery cell to be tested, meanwhile, current flowing through the battery cell and voltage at two ends of the cell are collected, the resistance change of the cell is calculated, and whether the micro-short circuit problem exists in the cell or whether the insulation resistance of a diaphragm in the cell is lower due to the fact that the thickness of the diaphragm is thinner or the diaphragm is punctured by an insulation substance is judged according to the resistance change.
Specifically, the control chip MCU controls the adjustable dc high voltage source to be maintained when the dc voltage output by the adjustable dc high voltage source reaches a high voltage set point, as in section b of fig. 3, so as to continuously apply a dc high voltage across the battery cells.
And in the high-voltage holding stage, the voltages at two ends of the battery cell are collected in real time through a voltage measuring loop, the current flowing through the battery cell is collected in real time through a current measuring loop, and a divider is started to divide the received voltage detection signal and the current detection signal so as to generate a voltage signal reflecting the resistance of the cell and send the voltage signal to an ADC chip.
The control chip MCU informs the ADC chip of receiving the voltage signal output by the divider, converts the voltage signal into a digital signal (resistance value) and sends the digital signal to the control chip MCU.
The control chip MCU detects the resistance value change of the battery cell, if the resistance change exceeds a set normal threshold value, the battery cell is indicated to have a micro-short circuit problem, or the thickness of a diaphragm in the battery cell is not satisfied, for example, the thickness of the diaphragm is thinner, or the diaphragm is pierced by an insulating substance. Thinner membranes or puncture by insulating substances can lead to problems with lower insulation resistance values of the cells.
Some battery cells have relatively thin internal diaphragms, but do not cause micro-shorting within the cell, so that testing only the voltage across the cell and the current through the cell cannot detect such defects, i.e., such defects are undetectable during the voltage rise phase. Therefore, the method of calculating the insulation resistance value of the battery cell in the high-voltage holding stage is adopted in the embodiment, so that the battery cell with the defects can be found conveniently, and the aim of improving the accuracy of the test result is fulfilled.
If the resistance change calculated in the high voltage holding stage is normal, the subsequent test process can be continued to further screen the battery defect.
Likewise, the MCU can be configured to directly generate a test result and output the test result through the display device, so that the test result is convenient for operators to check.
(3) Ac/dc superposition stage
That is, a low-voltage alternating current power supply is superimposed on the direct current high voltage applied to both ends of the battery cell, and the battery cell is controlled to be repeatedly charged and discharged. Meanwhile, collecting the current flowing through the battery core and the voltages at two ends of the battery core, and judging whether metal impurities exist in the battery core according to voltage changes; calculating alternating current impedance and equivalent capacitance value of the battery cell by using the collected voltage and current, and judging whether the thickness of a diaphragm inside the battery cell meets the requirement or not according to the equivalent capacitance value; judging whether agglomeration phenomenon caused by uneven slurry dispersion exists between the positive and negative plates of the power core according to alternating current impedance.
Specifically, the control chip MCU controls the adjustable direct current high voltage source to continuously output direct current high voltage and output a direct current bus voltage value, and controls the adjustable direct current high voltage source to generate the direct current bus voltage required by the adjustable alternating current voltage source. During this time, the control chip MCU activates the AC reference unit to provide a reference frequency to the adjustable AC voltage source and outputs a two-way AC reference signal A, B. Meanwhile, the control chip MCU controls the first change-over switch and the second change-over switch to be conducted, the direct current bus voltage output by the adjustable direct current high-voltage source is transmitted to the adjustable alternating current voltage source through the first change-over switch, the adjustable alternating current voltage source is controlled to output a low-voltage alternating current power supply in an inversion mode, and the low-voltage alternating current power supply is overlapped to two ends of the battery cell through the second change-over switch. That is, alternating high voltage, with positive voltage at all times, is applied across the battery cells, as in section c of fig. 3.
In the ac/dc superposition stage, the embodiment adopts the ac voltage with high voltage bias to supply power to the battery cells, so that the battery cells can be controlled to work in the state of repeated charge and discharge, and therefore, the defect cells which have the same data as the normal cells in the charging stage of some battery cells, but have the problems of suddenly accelerating discharge speed and the like in the discharging stage can be detected.
The main reason that such defective cells exhibit such abnormal phenomena is that metal impurities exist inside the cells, which have not penetrated through the separator in the voltage rising stage and the high voltage holding stage, causing the micro-short circuit problem of the cells, so that each item of data in the charging stage is the same as that of the normal cells, which results in failure to detect such defects in the voltage rising stage and the high voltage holding stage. After entering the AC/DC superposition stage, the battery cell without liquid injection pierces the diaphragm under the action of the repeatedly changed electric field force because of repeated charge and discharge of the battery cell, so that micro short circuit occurs in the battery cell, and the voltage at two ends of the battery cell is rapidly reduced in the discharge stage and even lower than the set lower limit value. Therefore, in the alternating current-direct current superposition stage, whether metal impurities exist in the battery cell can be judged according to the voltage changes at the two ends of the battery cell. Specifically, if the voltage across the cell drops rapidly to the lower limit, it is considered that the cell has a problem of micro-short circuit due to metal impurities.
Aiming at battery cells without liquid injection, the existing insulation test method and pulse test method cannot realize accurate detection on the battery cells with a small amount of metal impurities and unobvious short circuit, and by adopting the alternating current-direct current superposition test method of the embodiment, even if the metal impurities introduced into the battery cells are small and few, the micro short circuit problem hidden by the battery cells is obvious in the repeated charge-discharge process of the battery cells, so that the problems are convenient to find and identify.
Therefore, on the detection and identification problems of micro short circuit defects of the battery cell caused by the introduction of metal impurities into the battery cell, compared with the traditional battery cell detection method, the AC/DC superposition test method of the embodiment is obviously more accurate and comprehensive.
And according to the detection result, if the battery cell does not have the micro-short circuit problem, further detecting and identifying whether the battery cell has the problem that the thickness of the diaphragm does not meet the requirement or whether slurry between the positive and negative plates has agglomeration caused by uneven dispersion.
Specifically, the control chip MCU may be configured to start an ac/dc separation circuit to perform ac/dc separation on the voltage detection signal and the current detection signal, so as to extract an ac voltage component and an ac current component therein, and transmit the ac voltage component and the ac current component to the multiplier unit to be multiplied by two paths of ac reference signals A, B having a phase difference of 90 ° respectively, so as to generate two paths of voltage signals and two paths of current signals, output the two paths of voltage signals and the two paths of current signals to the filter unit, remove a high frequency component therein, and transmit the two paths of voltage data and the two paths of current data to the ADC chip to perform analog-to-digital conversion, and further generate two paths of voltage data and two paths of current data to the control chip MCU.
The control chip MCU generates two voltage components U 1、U2 and two current components I 1、I2 according to the received two voltage data and two current data, and calculates the alternating current impedance and the equivalent capacitance value of the battery cell according to the voltage components U 1、U2 and the current components I 1、I2. The specific process is as follows:
the cell voltage maximum U z and the phase angle β are calculated using the following formulas:
U1=Uzsin(ωt+β)sinωt
U2=Uzsin(ωt+β)cosωt；
The maximum value of the current I z and the phase angle γ flowing through the cell are calculated using the following formulas:
I1=Izsin(ωt+γ)sinωt
I2=Izsin(ωt+γ)cosωt；
calculating the equivalent impedance Z and the corresponding phase angle theta of the battery cell:
Z=Uz/Iz
θ=β-γ;
calculating the alternating current impedance R and the equivalent capacitance value C of the battery cell:
R=Zcosθ
C=Zsinθ。
the equivalent model of the battery cell without liquid injection is a capacitor, and high voltage can be applied to the two ends of the equivalent model; the positive and negative plates of the battery cell without liquid injection are equivalent to the positive and negative electrodes of the capacitor; the diaphragm between the positive and negative plates is equivalent to an insulating medium between the positive and negative electrodes of the capacitor, and the thickness of the diaphragm reflects the distance between the positive and negative electrodes of the capacitor.
According to a factor formula affecting the capacitance:
C’=εs/(4πkd)；
Where ε is the dielectric constant of the dielectric and represents the conductivity of a substance; s is the facing area of two parallel metal plates; k is an electrostatic force constant; d is the spacing of two parallel metal plates. The larger the distance between the positive electrode and the negative electrode of the capacitor is, the smaller the capacitance value is, so that the larger the thickness of a diaphragm between the positive electrode plate and the negative electrode plate of the equivalent battery cell without filling liquid is, the smaller the equivalent capacitance value of the battery cell is. Therefore, whether the thickness of the diaphragm meets the requirement can be judged by detecting whether the equivalent capacitance value of the battery cell which is not filled with the liquid meets the threshold value, and the battery cell with the diaphragm thickness which does not meet the requirement is a defective product with quality problems.
Based on the above, in this embodiment, the set volume value is determined according to the equivalent capacitance value corresponding to the cell of the non-injected battery, where the thickness of the diaphragm meets the requirement, and written into the control chip MCU. After calculating the equivalent capacitance value C of the battery cell, the control chip MCU can be directly compared with the set capacitance value, if the equivalent capacitance value C is larger than the set capacitance value, the thickness of the diaphragm inside the cell can be considered as not meeting the requirement, namely, the thickness of the diaphragm is too thin, the problem of low insulation resistance of the cell is easily caused, and the cell can be considered as a defective product.
The equivalent models of the battery cell before liquid injection and the battery cell after liquid injection are very different. The equivalent capacitance of the battery cell after liquid injection is very small and is difficult to detect, and high voltage cannot be applied to the two ends of the battery cell after liquid injection, if the high voltage is applied, the battery cell can be broken down to cause spontaneous combustion or explosion. Therefore, a low-voltage alternating current power supply can be applied to two ends of the battery cell after liquid injection, and the quality of the battery cell can be judged by measuring the alternating current resistance of the battery cell. The equivalent model of the battery cell before liquid injection is a capacitor and can bear high voltage, so that the alternating current power supply with high voltage bias can be applied, and whether the diaphragm between the positive pole piece and the negative pole piece of the cell meets the thickness requirement can be judged by measuring the equivalent capacitance value of the cell. Whether the thickness of the diaphragm meets the requirement or not is the detection and identification of the battery defect, which is a function not possessed by the existing battery cell detection method.
In addition, in the stage of AC/DC superposition test, whether the battery cell has the problem of uneven slurry dispersion can be detected and identified.
Specifically, if the slurry between the positive and negative electrode plates of the battery cell is unevenly dispersed, a serious agglomeration phenomenon can be generated, so that the electrochemical performance of the battery is affected. Under the condition that the same voltage is applied to the two ends of the battery cell without liquid injection, the alternating current in the battery cell without liquid injection with even slurry dispersion is larger than that in the battery cell without liquid injection with uneven slurry dispersion, that is, the equivalent resistance of the battery cell with uneven slurry dispersion is larger. Therefore, whether the battery core has agglomeration phenomenon caused by uneven slurry dispersion can be judged by detecting the alternating current impedance of the battery core without filling liquid.
Based on the above, in this embodiment, an ac-dc superposition test is performed on the un-injected battery cells with uniformly dispersed slurry between the pole pieces, to determine a reasonable set resistance value, and write the resistance value into the control chip MCU. In the actual detection stage, after the configuration control chip MCU calculates the alternating current impedance R of the battery cell to be detected, the alternating current impedance R can be directly compared with a set resistance value, and if the alternating current impedance R is larger than the set resistance value, the phenomenon of agglomeration caused by uneven slurry dispersion between the positive and negative electrode plates of the battery cell can be considered, and the battery cell is a disqualified battery cell. Otherwise, the slurry between the pole pieces of the battery cell to be tested can be uniformly dispersed, and the agglomeration phenomenon is avoided.
The existing method for measuring the alternating current internal resistance of the battery cell is to measure the alternating current internal resistance of the battery cell after liquid injection, and only whether the battery cell after liquid injection is good or bad can be judged according to the alternating current internal resistance of the battery cell after liquid injection, and whether the battery cell is caused by uneven slurry dispersion between pole pieces cannot be tested, and the accuracy of measuring the internal resistance of the battery cell is affected because the internal resistance of the battery cell is too small due to electrolyte in the battery cell. In addition, high-voltage power can not be applied to the two ends of the battery cell after liquid injection, otherwise, the cell can be burnt out, and the internal resistance of the liquid injection cell is not easy to measure. The alternating current power supply with high-voltage bias is applied to the two ends of the battery core without liquid injection, and then alternating current components are separated out for calculating the internal resistance of the battery core, so that the influence of electrolyte on the measurement of the internal resistance of the battery core can be eliminated, and the problem of large alternating current resistance caused by uneven slurry dispersion between pole pieces can be accurately detected.
The battery cell quality problem caused by factors can be detected more accurately by using the AC/DC superposition power supply to test the battery cell without injection, so that the improvement of the production technology is facilitated, the accuracy of the battery cell measurement result before injection is improved, and the problem of electrolyte waste caused by the problem battery after injection can be effectively prevented. The accuracy of cell measurement before liquid injection is improved, the probability of defective products flowing to the market can be reduced, and the occurrence of spontaneous combustion accidents of the battery is reduced.
Likewise, the MCU can be configured to directly generate a test result and output the test result through the display device, so that the test result is convenient for operators to check.
(4) Self-discharge stage
That is, the application of voltage to the battery cell to be measured is stopped, the battery cell is made to enter a self-discharge process, and whether the micro-short circuit problem or the insulation resistance problem is low inside the battery cell is judged by detecting the voltage drop condition at the two ends of the battery cell.
Specifically, after the alternating current-direct current superposition test phase is finished, the configuration control chip MCU controls the adjustable direct current high-voltage source to stop outputting and enter the battery self-discharging phase. Since the battery cell under test has completed charging, the voltage across it will drop slowly after the power is turned off, as shown by the d-segment waveform in fig. 3.
In the self-discharge stage, the control chip MCU can be configured to inform the ADC chip of receiving the voltage detection signal acquired and output by the voltage measurement loop, and the voltage detection signal is sent to the control chip MCU after analog-to-digital conversion.
The control chip MCU detects voltage changes at two ends of the battery cell according to the received voltage data, and if the detected voltage at two ends of the battery cell falls within a set time to exceed a set threshold, namely, the self-discharge speed is too high, the problem of micro short circuit caused by metal impurities can be considered to exist in the battery cell, or the self-discharge speed of the battery cell is too high because the thickness of a diaphragm in the battery cell is relatively thin or the insulation resistance of the diaphragm is relatively low because the diaphragm is pierced by an insulation substance.
Specifically, which type of defect can be obtained by comprehensively analyzing the test results of the four stages. For example, in the AC/DC superposition stage, whether metal impurities exist in the battery core, whether the thickness of the diaphragm meets the requirement and whether slurry between the pole pieces is uniformly dispersed can be tested; if the defects do not exist, namely, the battery cell is normal in the AC/DC superposition stage, the battery cell enters the self-discharge stage, and if the self-discharge speed of the battery cell is detected to be too high, the battery cell can be considered to have insulating substances inside, so that the battery cell defect type identification function is realized.
Likewise, the MCU can be configured to directly generate a test result and output the test result through the display device, so that the test result is convenient for operators to check.
According to the embodiment, the battery cell with the problem can be accurately detected by detecting the voltage and current change of the battery cell of the non-injected battery in the boosting stage, the internal resistance change of the battery cell in the pressure maintaining stage, the alternating current impedance and equivalent capacitance change of the alternating current and direct current superposition stage and the voltage change of the battery cell in the self-discharging stage, and the defect type of the battery cell with the problem can be identified, wherein the defect type comprises the introduction of metal impurities and insulating impurities into the battery cell, the unsatisfied requirement of the thickness of a diaphragm in the battery cell, the uneven dispersion of slurry between the positive and negative electrode plates and the like.
Of course, the above embodiments are only for illustrating the technical solution of the present invention, and are not limited thereto. Although the invention has been described in detail with reference to the foregoing embodiments, it will be apparent to one skilled in the art that modifications may be made to the embodiments described, or equivalents may be substituted for elements thereof; such modifications and substitutions do not depart from the spirit and scope of the corresponding technical solutions.
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