CN112924879A - Battery discharge depth detection method and system - Google Patents
Battery discharge depth detection method and system Download PDFInfo
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- 238000001514 detection method Methods 0.000 title claims abstract description 66
- 238000001453 impedance spectrum Methods 0.000 claims abstract description 53
- 238000000034 method Methods 0.000 claims abstract description 50
- 238000007599 discharging Methods 0.000 claims abstract description 48
- 238000012360 testing method Methods 0.000 claims description 31
- 230000008859 change Effects 0.000 claims description 20
- 230000008569 process Effects 0.000 claims description 15
- 230000005284 excitation Effects 0.000 claims description 8
- 210000003127 knee Anatomy 0.000 claims description 4
- 239000000523 sample Substances 0.000 claims 23
- 239000013068 control sample Substances 0.000 claims 1
- 238000002161 passivation Methods 0.000 abstract description 29
- 230000001276 controlling effect Effects 0.000 description 43
- WHXSMMKQMYFTQS-UHFFFAOYSA-N Lithium Chemical compound [Li] WHXSMMKQMYFTQS-UHFFFAOYSA-N 0.000 description 16
- 229910052744 lithium Inorganic materials 0.000 description 16
- FYSNRJHAOHDILO-UHFFFAOYSA-N thionyl chloride Chemical compound ClS(Cl)=O FYSNRJHAOHDILO-UHFFFAOYSA-N 0.000 description 14
- 230000004044 response Effects 0.000 description 13
- KWGKDLIKAYFUFQ-UHFFFAOYSA-M lithium chloride Chemical compound [Li+].[Cl-] KWGKDLIKAYFUFQ-UHFFFAOYSA-M 0.000 description 10
- 230000007613 environmental effect Effects 0.000 description 5
- 238000005259 measurement Methods 0.000 description 4
- 238000000627 alternating current impedance spectroscopy Methods 0.000 description 3
- 230000007423 decrease Effects 0.000 description 3
- 239000000126 substance Substances 0.000 description 3
- 239000006182 cathode active material Substances 0.000 description 2
- 238000010586 diagram Methods 0.000 description 2
- 238000011156 evaluation Methods 0.000 description 2
- 238000011160 research Methods 0.000 description 2
- 238000005070 sampling Methods 0.000 description 2
- -1 and meanwhile Chemical compound 0.000 description 1
- 230000007123 defense Effects 0.000 description 1
- 230000001066 destructive effect Effects 0.000 description 1
- 238000005553 drilling Methods 0.000 description 1
- 239000003792 electrolyte Substances 0.000 description 1
- 238000005516 engineering process Methods 0.000 description 1
- 238000000691 measurement method Methods 0.000 description 1
- 238000011056 performance test Methods 0.000 description 1
- 239000003208 petroleum Substances 0.000 description 1
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- 230000001105 regulatory effect Effects 0.000 description 1
- 239000002904 solvent Substances 0.000 description 1
- 238000006467 substitution reaction Methods 0.000 description 1
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
- G01R31/00—Arrangements for testing electric properties; Arrangements for locating electric faults; Arrangements for electrical testing characterised by what is being tested not provided for elsewhere
- G01R31/36—Arrangements for testing, measuring or monitoring the electrical condition of accumulators or electric batteries, e.g. capacity or state of charge [SoC]
- G01R31/385—Arrangements for measuring battery or accumulator variables
- G01R31/387—Determining ampere-hour charge capacity or SoC
- G01R31/388—Determining ampere-hour charge capacity or SoC involving voltage measurements
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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]
- G01R31/3644—Constructional arrangements
- G01R31/3648—Constructional arrangements comprising digital calculation means, e.g. for performing an algorithm
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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
- G01R31/38—Primary cells, i.e. not rechargeable
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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
Abstract
The embodiment of the invention discloses a method and a system for detecting the discharge depth of a battery. The battery depth of discharge detection method includes: discharging a battery to be tested according to a preset condition so as to control the battery to be tested to have a first state; detecting the open-circuit voltage of the battery to be detected; if the open-circuit voltage of the battery to be tested is smaller than the voltage threshold, acquiring a phase angle of the battery to be tested in a preset frequency band based on the alternating current impedance spectrum of the battery to be tested; and determining the residual capacity of the battery to be tested based on the phase angle of the preset frequency band and the corresponding relation between the preset phase angle and the residual capacity. According to the depth of discharge detection method provided by the embodiment of the invention, the influence of a passivation film is eliminated, the depth of discharge of the battery can be accurately estimated, and the problem that the accurate depth of discharge cannot be obtained when the open-circuit voltage of the battery is used for predicting the depth of discharge in the prior art is solved.
Description
Technical Field
The embodiment of the invention relates to a battery technology, in particular to a battery depth of discharge detection method and a system.
Background
Compared with other primary batteries, the lithium/thionyl chloride battery has higher specific energy and higher working voltage, and meanwhile, the working temperature range is extremely wide, and the annual self-discharge rate is extremely low, so that the lithium/thionyl chloride battery is increasingly applied to the fields of intelligent instruments, petroleum drilling, intelligent tracking, ETC, national defense and the like in more than ten years.
The most important issue for chemical power sources is the prediction of their availability, and it is of great interest to estimate the remaining capacity of the primary power source in a lossless manner. Currently, the remaining capacity of the battery is estimated mainly by detecting the open circuit voltage.
The lithium subcell is a typical liquid-cathode active material cell, the open circuit voltage of which is almost constant for a long period of time in the whole discharge period and is obviously changed only at the end of the discharge period, and once the discharge is suspended, the lithium anode gradually generates a passive film, which also has an influence on the value of the open circuit voltage. Therefore, it is difficult to obtain an accurate value using the open circuit voltage as a basis for predicting the depth of discharge of the lithium subcell.
Disclosure of Invention
The embodiment of the invention provides a battery discharge depth detection method and system, which are used for accurately detecting the residual capacity of an electric battery.
In a first aspect, an embodiment of the present invention provides a method for detecting a battery depth of discharge, including:
discharging a battery to be tested according to a preset condition so as to control the battery to be tested to have a first state;
detecting the open-circuit voltage of the battery to be detected;
if the open-circuit voltage of the battery to be tested is smaller than the voltage threshold, acquiring a phase angle of the battery to be tested in a preset frequency band based on the alternating current impedance spectrum of the battery to be tested;
and determining the residual capacity of the battery to be tested based on the phase angle of the preset frequency band and the corresponding relation between the preset phase angle and the residual capacity.
Optionally, the discharging the battery to be tested according to a preset condition to control the battery to be tested to have a first state, including:
and in a first temperature, controlling the battery to be tested to perform pulse discharge according to a preset current intensity so as to control the battery to be tested to have a first state, wherein the discharge capacity of the pulse discharge and the rated capacity of the battery to be tested have a preset relation.
Optionally, after the battery to be tested is discharged according to the preset condition to control the battery to be tested to have the first state, the method further includes:
controlling the battery to be tested to stand at a second temperature for a first time length so that the battery to be tested has a second state;
and controlling the battery to be tested to stand at the third temperature for a second time length so as to cool the battery to be tested.
Optionally, if the open-circuit voltage of the battery to be tested is smaller than the voltage threshold, obtaining the phase angle of the battery to be tested at the preset frequency band based on the alternating-current impedance spectrum of the battery to be tested includes:
if the open-circuit voltage of the battery to be tested is smaller than the voltage threshold, carrying out alternating current impedance test on the battery to be tested according to a preset excitation voltage to obtain an alternating current impedance spectrum of the battery to be tested;
and acquiring a phase angle of the battery to be tested in a preset frequency band based on the alternating-current impedance spectrum.
Optionally, the corresponding relationship between the preset phase angle and the remaining capacity is determined according to the following method:
controlling the sample battery to discharge at a first temperature;
in the discharging process, controlling the sample battery to perform an alternating current impedance test in a third state at intervals of preset discharging capacity so as to obtain alternating current impedance spectrum data of the sample battery at a corresponding discharging depth;
establishing a first variation relation of a negative value of a phase angle of the sample battery with a discharge depth of the sample battery based on the alternating-current impedance spectrum data;
and performing straight line fitting on each phase angle negative value of which the open-circuit voltage of the sample battery is smaller than the voltage threshold value based on the first variation relation to determine the corresponding relation between the phase angle and the residual capacity.
Optionally, the controlling the sample battery to perform an ac impedance test in a third state at every preset discharge capacity includes:
controlling the sample battery to stand for a first time at a second temperature every other preset discharge capacity so that the sample battery has a second state;
controlling the sample cell to stand at a third temperature for a second period of time so that the sample cell has a third state;
and carrying out an alternating current impedance test on the sample battery in the third state.
Optionally, the voltage threshold is determined according to the following method:
controlling the sample battery to discharge at a first temperature;
in the discharging process, controlling the sample battery to detect the open-circuit voltage once in a third state at intervals of preset discharging capacity so as to obtain the open-circuit voltage data of the sample battery at a corresponding discharging depth;
establishing a second variation relationship of the open-circuit voltage of the sample cell with the depth of discharge based on the open-circuit voltage data;
determining inflection point voltage with the change rate of the open-circuit voltage larger than a preset value based on the second change relation;
determining the knee voltage as the voltage threshold.
Optionally, the controlling the sample battery to detect an open-circuit voltage in a third state at every preset discharge capacity includes:
controlling the sample battery to stand for a first time at a second temperature every other preset discharge capacity so that the sample battery has a second state;
controlling the sample cell to stand at a third temperature for a second period of time so that the sample cell has a third state;
detecting an open circuit voltage of the sample cell at a time in the third state.
Optionally, before the controlling the sample battery to discharge at the first temperature, the method further includes:
and controlling the sample battery to stand at the first temperature for a third time period.
In a second aspect, an embodiment of the present invention further provides a battery depth of discharge detection system, which is applied to the battery depth of discharge detection method according to any embodiment of the present invention, where the detection system includes:
the discharging control equipment is used for discharging the battery to be tested according to preset conditions so as to control the battery to be tested to have a first state;
the voltage detection equipment is used for detecting the open-circuit voltage of the battery to be detected;
the detection equipment is used for acquiring a phase angle of the battery to be detected in a preset frequency band based on an alternating current impedance spectrum of the battery to be detected if the open-circuit voltage of the battery to be detected is smaller than a voltage threshold; and determining the residual capacity of the battery to be tested based on the phase angle of the preset frequency band and the corresponding relation between the preset phase angle and the residual capacity.
According to the battery discharge depth detection method provided by the embodiment of the invention, the battery to be detected is controlled to have the first state by pre-discharging the battery to be detected, so that the influence of an unknown passivation state on the open-circuit voltage of the battery is eliminated. And detecting whether the battery to be detected is deeply discharged or not by detecting the open-circuit voltage of the battery. When the open-circuit voltage of the battery to be tested is smaller than the voltage threshold, the battery to be tested is in a deep discharge state, at the moment, the phase angle of the battery to be tested in the preset frequency band is obtained by performing alternating current impedance test on the battery to be tested, and because the phase angle and the discharge depth of the battery have a determined linear relation, the residual capacity corresponding to the current phase angle is calculated according to the corresponding relation between the predetermined phase angle and the discharge depth, and therefore the residual capacity of the battery to be tested can be accurately estimated. Therefore, the method for detecting the depth of discharge provided by the embodiment of the invention eliminates the influence of the passivation film, can accurately estimate the depth of discharge of the battery, and solves the problem that the accurate depth of discharge cannot be obtained by using the open-circuit voltage of the battery to predict the depth of discharge in the prior art.
Drawings
Fig. 1 is a flowchart of a method for detecting a battery depth of discharge according to an embodiment of the present invention;
FIG. 2 is a flow chart of another method for detecting a depth of discharge of a battery according to an embodiment of the present invention;
FIG. 3 is an AC impedance spectrum in one embodiment;
FIG. 4 is a graph of open circuit voltage versus remaining capacity for an ER14250T sample cell in one embodiment;
FIG. 5 is a plot of negative phase angle versus depth of discharge for an ER14250T sample cell in an exemplary embodiment;
fig. 6 is a flowchart of another method for detecting a depth of discharge of a battery according to an embodiment of the present invention;
fig. 7 is a block diagram of a battery depth of discharge detection system according to an embodiment of the present invention.
Detailed Description
The present invention will be described in further detail with reference to the accompanying drawings and examples. It is to be understood that the specific embodiments described herein are merely illustrative of the invention and are not limiting of the invention. It should be further noted that, for the convenience of description, only some of the structures related to the present invention are shown in the drawings, not all of the structures.
Electrochemical ac impedance spectroscopy is a non-destructive parametric measurement and an efficient method of cell dynamic behavior measurement. A sine wave voltage signal with the frequency of w1 and small amplitude is applied to a battery system, the system generates a sine wave current response with the frequency of w2, and the change of the ratio of the excitation voltage to the response current is the impedance spectrum of the electrochemical system. From the ratio between the response signal and the disturbance signal of different frequencies, the modulus and the phase angle of the impedance at different frequencies can be obtained, and the real part and the imaginary part of the impedance can be further obtained through a formula. Useful information within the study is usually obtained by studying the real and imaginary components to form a complex impedance plane plot, a frequency vs. mode plot, and a frequency vs. phase angle plot (both collectively referred to as Bode plots).
In recent years, electrochemical ac impedance spectroscopy has been widely used in the research of various batteries, but has little application in the depth of discharge of lithium subcells. According to the embodiment of the invention, through researching the electrochemical impedance spectrum of the lithium sub-battery and researching the relation between each parameter in the electrochemical impedance spectrum and the battery discharge depth, the electrochemical parameter which can eliminate the influence of the passivation film and correctly reflect the battery discharge depth is obtained, and the battery discharge depth is predicted by detecting the electrochemical parameter. The above is the core idea of the present invention, and the method of the embodiment of the present invention is described in detail below with reference to the accompanying drawings.
Fig. 1 is a flowchart of a battery depth of discharge detection method according to an embodiment of the present invention, where the detection method according to this embodiment may be used for performing lossless depth of discharge estimation on a chemical power source to accurately estimate the remaining capacity of a chemical battery. Referring to fig. 1, the method specifically includes the following steps:
s110, discharging the battery to be tested according to a preset condition so as to control the battery to be tested to have a first state.
The purpose of controlling the battery to be tested to discharge according to the preset condition is to eliminate the influence of the passivation film on the discharge depth measurement. Taking a lithium subcell as an example, the cathode active material of the lithium subcell is thionyl chloride, and meanwhile, thionyl chloride is also a solvent of the battery electrolyte, and thionyl chloride gradually decreases in the discharging process, and when the thionyl chloride decreases to a certain extent, the phenomena of open-circuit voltage drop and electrochemical alternating-current impedance spectrum change occur.
The passivation film has two states, after thionyl chloride is contacted with lithium, a layer of compact lithium chloride passivation film can be generated on the surface of the lithium immediately, and then loose and porous lithium chloride passivation film can be gradually generated on the compact lithium chloride passivation film along with the prolonging of time.
The loose and porous lithium chloride passive film can be damaged and peeled off in the discharging process, the discharging is stopped, and the loose and porous lithium chloride passive film can start to grow.
Because the passivation state of the battery to be tested is unknown, the battery to be tested can be controlled to recover to the state that the passivation film completely falls off, namely the first state, by controlling the battery to be tested to discharge according to the preset conditions. The passivation films in different states can affect the open-circuit voltage and the electrochemical alternating-current impedance spectrum of the battery, so that the influence of the unknown passivation state can be eliminated by controlling the battery to be tested in the first state, and the influence of the unknown passivation state on the evaluation of the residual capacity of the battery can be avoided.
And S120, detecting the open-circuit voltage of the battery to be detected.
The purpose of detecting the open-circuit voltage of the battery to be detected is to judge whether the residual capacity of the battery to be detected is sufficient. In practical use, when the battery is fed (the residual capacity is insufficient), the battery affects the performance, parameter evaluation and the like of the applied instrument, so that the detection parameters of the instrument are inaccurate and the normal operation of the instrument is affected, and therefore, when the residual capacity of the battery is insufficient, the discharge depth of the battery needs to be accurately evaluated.
S130, if the open-circuit voltage of the battery to be tested is smaller than the voltage threshold, acquiring a phase angle of the battery to be tested in a preset frequency band based on the alternating-current impedance spectrum of the battery to be tested.
The voltage threshold is an empirical value and can be obtained by detecting a sample battery. When the open circuit voltage of the battery to be detected is higher than the voltage threshold value, the residual capacity of the battery is sufficient, and the discharge depth detection is not needed. And when the open-circuit voltage of the battery to be tested is smaller than the voltage threshold, the battery to be tested is indicated to be in a deep discharge state, and the residual capacity of the battery to be tested needs to be specifically evaluated under the working condition.
The AC impedance spectrum can be obtained by testing the AC impedance of the battery to be tested. The response characteristics of physical quantities such as impedance values, phase angles and the like of the battery to be tested can be obtained through the alternating-current impedance spectrum. In the embodiment, the phase angle of the battery to be measured in the preset frequency band is obtained through the alternating-current impedance spectrum, so that the depth of discharge of the battery to be measured is measured through the phase angle of the preset frequency band. The preset frequency band can be determined according to the alternating current impedance test result of the sample battery, and the phase angle of the preset frequency band and the discharge depth of the sample battery have a linear relation.
Taking a lithium subcell as an example, a semicircle of a high-frequency region of an electrochemical alternating-current impedance spectrum of the lithium subcell reflects properties of a passivation film, and experimental research on a relationship between physical quantities such as an impedance value, a real value, an imaginary value, a phase angle and the like and a discharge depth shows that a linear relationship between the phase angle and the discharge depth is the best, so that for the lithium subcell, the phase angle of a preset frequency band in this embodiment is the phase angle of the high-frequency band.
S140, determining the residual capacity of the battery to be tested based on the phase angle of the preset frequency band and the corresponding relation between the preset phase angle and the residual capacity.
The corresponding relation between the preset phase angle and the residual capacity is the corresponding relation in the preset frequency band, and the corresponding relation between the preset phase angle and the residual capacity can be obtained by testing alternating current impedance of sample batteries with different discharge depths. The specific determination method of the correspondence relationship between the phase angle and the remaining capacity can refer to the description of the following embodiments.
For example, taking a lithium secondary battery as an example, a certain linear relationship exists between a phase angle of a high frequency band of the lithium secondary battery and a discharge depth of the battery, and a corresponding relationship between the preset phase angle and a residual capacity is used for representing the linear relationship in the high frequency band.
After the phase angle of the battery to be measured in the preset frequency band is obtained, the detected phase angle is brought into the corresponding relation between the preset phase angle and the residual capacity, and the residual capacity of the battery to be measured in the current working condition can be obtained through function calculation.
According to the battery discharge depth detection method provided by the embodiment, the battery to be detected is controlled to have the first state by pre-discharging the battery to be detected, so that the influence of an unknown passivation state on the open-circuit voltage and the electrochemical alternating-current impedance spectrum of the battery is eliminated. And detecting whether the battery to be detected is deeply discharged or not by detecting the open-circuit voltage of the battery. When the open-circuit voltage of the battery to be tested is smaller than the voltage threshold, the battery to be tested is in a deep discharge state, at the moment, the phase angle of the battery to be tested in the preset frequency band is obtained by performing alternating current impedance test on the battery to be tested, and because the phase angle and the discharge depth of the battery have a determined linear relation, the residual capacity corresponding to the current phase angle is calculated according to the corresponding relation between the predetermined phase angle and the discharge depth, and therefore the residual capacity of the battery to be tested can be accurately estimated. Therefore, the method for detecting the depth of discharge provided by the embodiment of the invention eliminates the influence of the passivation film, can accurately estimate the depth of discharge of the battery, and solves the problem that the accurate depth of discharge cannot be obtained by using the open-circuit voltage of the battery to predict the depth of discharge in the prior art.
Optionally, fig. 2 is a flowchart of another method for detecting a depth of discharge of a battery according to an embodiment of the present invention, and the embodiment is optimized based on the foregoing embodiment. Referring to fig. 2, the method specifically includes the following steps:
s210, controlling the battery to be tested to perform pulse discharge according to preset current intensity at a first temperature so as to control the battery to be tested to have a first state, wherein the discharge capacity of the pulse discharge and the rated capacity of the battery to be tested have a preset relation.
As analyzed in the foregoing embodiment, the passivation state of the battery to be tested is unknown, and in order to control the battery to be tested to have the first state, the present embodiment eliminates the passivation film with unknown thickness by controlling the battery to be tested to perform pulse discharge according to the preset current intensity, simulates the state where the discharge is just finished, and restores the battery to be tested to the state where the passivation film completely falls off.
In general, a pulse discharge with a large current for a short time can be used to restore the battery to a state in which the passivation film is completely peeled off with a very small capacity loss. The current intensity for pulse discharge and the specific discharge time are adjusted according to the type of the battery. The discharge capacity of the pulse discharge is not more than 0.5% of the total capacity of the battery.
For example, for an ER14250T battery, the battery to be tested can be placed in a 23 ± 2 environment and subjected to pulse discharge with 50mA current, wherein the discharge time is 0.5s, and the discharge time is 100s and 300 cycles. The passivation film with unknown thickness is eliminated, and the state of the discharge just finished is simulated.
S220, the battery to be tested is controlled to stand at the second temperature for the first time length, so that the battery to be tested has the second state.
And the battery to be tested in the second state has the required thickness of the passivation film. In the step, the battery to be tested is controlled to stand at the second temperature for the first time period, namely, the passive film of the battery to be tested is controlled to grow again from a completely falling state, and the growth environment of the passive film of the battery to be tested which grows again after discharging is controlled to be consistent with the growth environment of the passive film of the sample battery in the process of determining the corresponding relation between the preset phase angle and the residual capacity, so that the thickness of the passive film of the battery to be tested is equal to that of the sample battery.
Illustratively, after the pulse discharge of the ER14250T battery is completed in the above steps, the battery to be tested is placed in an environment of 70 ± 2 ℃ for standing for a certain period of time, and the specific period of standing may be a certain period of time H between 48 and 72 hours, so that the battery to be tested has the second state.
And S230, controlling the battery to be tested to stand at the third temperature for a second time period so as to cool the battery to be tested.
The third temperature may be, for example, room temperature, and the objective of this step is to cool the high-temperature battery to be tested so as to detect the open-circuit voltage of the battery to be tested when the state of the battery to be tested is completely stable. For example, after standing for a certain period of time in the high-temperature environment, the battery to be tested is taken out and left at room temperature for 4 hours, so that the battery to be tested is completely cooled.
S240, if the open-circuit voltage of the battery to be tested is smaller than the voltage threshold, carrying out alternating current impedance test on the battery to be tested according to the preset excitation voltage to obtain an alternating current impedance spectrum of the battery to be tested.
The preset excitation voltage has amplitude-frequency characteristics meeting requirements. The alternating current impedance spectroscopy is a nondestructive parameter measurement and an effective battery dynamic behavior measurement method. And applying a small-amplitude sine wave voltage signal to the battery to be tested, detecting the response current, and determining that the change of the ratio of the excitation voltage to the response current is the alternating current impedance spectrum of the battery to be tested.
For example, an alternating current impedance test can be performed on a battery to be tested of an ER14250T model by using an excitation voltage with an alternating current amplitude of 10mV and a frequency of 0.4-100000 Hz, so as to obtain an alternating current impedance spectrum shown in FIG. 3.
In some embodiments, the voltage threshold is obtained by detecting the sample cell specifically as follows:
controlling the sample battery to discharge at a first temperature;
in the discharging process, controlling the sample battery to detect the open-circuit voltage once in a third state every other preset discharging capacity so as to obtain the open-circuit voltage data of the sample battery at the corresponding discharging depth;
establishing a second variation relation of the open-circuit voltage of the sample battery along with the discharge depth based on the open-circuit voltage data;
determining inflection point voltage with the change rate of the open-circuit voltage larger than a preset value based on the second change relation;
the knee voltage is determined as the voltage threshold.
In particular, the third state is achieved in particular by regulating the ambient temperature of the sample cell. The ambient temperature in the third state is different from the first temperature, that is, the ambient temperature for detecting the open circuit voltage is different from the ambient temperature for discharging. In one embodiment, the open-circuit voltage data of different discharge depths is obtained by increasing the sample amount of the sample battery, controlling a certain number of sample batteries for each discharge capacity in advance, and sequentially detecting the open-circuit voltages of the sample batteries with different discharge capacities from the sample battery with the rated capacity in the detection process.
The second variation reflects the variation of the open circuit voltage of the sample cell with the depth of discharge. The change rate of the open-circuit voltage refers to the change amplitude of the open-circuit voltage of the latter depth of discharge relative to the open-circuit voltage of the former depth of discharge, and the open-circuit voltage with sudden change can be detected by comparing the change rate of the open-circuit voltage with a preset value, namely the inflection point voltage.
For example, after the open-circuit voltage data of the sample battery is obtained, the remaining capacity is plotted on the abscissa and the open-circuit voltage is plotted on the ordinate, and a curve of the open-circuit voltage with the remaining capacity is plotted. Fig. 4 is a graph of the open circuit voltage of the ER14250T type sample cell as a function of the remaining capacity in one embodiment, and from fig. 4, it can be observed that the open circuit voltage is almost constant before 550mAh for the remaining capacity, and the open circuit voltage starts to drop significantly after 550mAh for the remaining capacity, and the voltage threshold of the ER14250T type cell is determined to be 3.67V according to the graph.
Optionally, in some embodiments, the step of controlling the sample battery to detect the open-circuit voltage in the third state at every preset discharge capacity is specifically implemented by the following method:
controlling the sample battery to stand for a first time at a second temperature every preset discharge capacity so that the sample battery has a second state;
controlling the sample battery to stand at a third temperature for a second time period so that the sample battery has a third state;
the open circuit voltage of the primary sample cell is detected in the third state.
Specifically, the sample battery is a new battery, and the new battery does not have a passivation film in an unknown state, so that the sample battery can be directly kept stand at the second temperature for a first time, the passivation film with a certain thickness is grown on the sample battery, and after the growth of the passivation film is completed, the sample battery is cooled at the third temperature for a certain time, so that various parameters of the sample battery are stable, and further, the open-circuit voltage detection is performed on the sample battery in a stable state. The environmental factors of the open-circuit voltage of the sample battery detected in this step are applied to the environmental factor control in the open-circuit voltage detection process of the battery to be detected, that is, the environmental conditions before and during the open-circuit voltage detection of the battery to be detected are consistent with the environmental conditions in this step.
Taking new batteries of ER14250T model as an example, discharging in an environment of 23 +/-2 ℃ respectively, wherein the discharge depth is from the rated capacity to zero, and taking one point every 50mAh and taking three batteries to discharge each point. Immediately after the discharge, the cell was left to stand at 70. + -. 2 ℃ for 60 hours. And after the placement is finished, taking out the battery, placing the battery at room temperature for 4h, and detecting the open-circuit voltage of the sample battery after the battery is completely cooled.
And S250, acquiring a phase angle of the battery to be tested in a preset frequency band based on the alternating current impedance spectrum.
For example, for the ER14250T battery under test, as can be seen from the above embodiments, the phase angle at the highest point of the semicircle in the high frequency region of the ac impedance spectrum is an easily observable characteristic value, and the linear relationship with the depth of discharge is the best, so the phase angle at the highest point of the semicircle in the high frequency region is read according to the ac impedance spectrum, and the depth of discharge of the battery under test is determined by taking the phase angle as a variable.
And S260, determining the residual capacity of the battery to be tested based on the phase angle of the preset frequency band and the corresponding relation between the preset phase angle and the residual capacity.
In the step, a corresponding relation between a phase angle and a residual capacity is determined by detecting a sample battery with a certain sample amount.
In one embodiment, the correspondence between the phase angle and the remaining capacity is determined specifically by the following method:
controlling the sample battery to discharge at a first temperature;
in the discharging process, controlling the sample battery to perform an alternating current impedance test in a third state every other preset discharging capacity so as to obtain alternating current impedance spectrum data of the sample battery at a corresponding discharging depth;
establishing a first change relation of a phase angle negative value of the sample battery along with the discharge depth of the sample battery based on the alternating-current impedance spectrum data;
and performing straight line fitting on negative values of the phase angles of which the open-circuit voltages of the sample batteries are smaller than the voltage threshold value based on the first variation relation to determine the corresponding relation between the phase angles and the residual capacity.
The method comprises the following steps of firstly, sampling the batteries to be tested, and then, sampling the batteries to be tested, wherein the sample batteries are new batteries with the same type as the batteries to be tested, the discharge depth is from the rated capacity to zero, in the process, alternating current impedance tests are carried out on a certain number of sample batteries at intervals of certain discharge capacity, and the alternating current impedance spectrum data of the sample batteries at different discharge depths are obtained.
It should be noted that the discharge conditions of the sample cell in this step are not the same as those of the ac impedance test. Specifically, the environmental temperature of the sample battery is adjusted, so that the sample battery has a discharge condition and an alternating current impedance spectrum detection condition which meet requirements. For example, the sample amount of the sample battery can be increased, a certain number of sample batteries are arranged at each discharge capacity stage, and then the sample batteries at different discharge capacity stages are subjected to alternating current impedance tests in sequence from the sample battery with the rated capacity to acquire alternating current impedance spectrum data at different discharge depths.
In one embodiment, the ac impedance test performed on the sample battery in the third state every predetermined discharge capacity is specifically implemented by the following method:
controlling the sample battery to stand for a first time at a second temperature every preset discharge capacity so that the sample battery has a second state;
controlling the sample battery to stand at a third temperature for a second time period so that the sample battery has a third state;
and carrying out an alternating current impedance test on the sample battery in the third state.
Specifically, the sample battery is a new battery, and the new battery does not have a passive film in an unknown state, so that the sample battery can be directly kept stand at the second temperature for a first time, the passive film with a certain thickness is grown on the sample battery, after the growth of the passive film is completed, the sample battery is cooled at the third temperature for a certain time, various parameters of the sample battery are stable, and then the cooled sample battery is subjected to alternating current impedance testing.
Taking new batteries of ER14250T model as an example, discharging in an environment of 23 +/-2 ℃ respectively, wherein the discharge depth is from the rated capacity to zero, taking one point every 50mAh, and taking three batteries for discharging each point. Immediately after the discharge, the cell was left to stand at 70. + -. 2 ℃ for 60 hours. And after the placement is finished, taking out the battery, placing the battery at room temperature for 4h, and measuring the alternating current impedance spectrum of the battery after the battery is completely cooled.
After the AC impedance spectrum data of all the discharge depths are obtained, a curve of the negative number-theta of the phase angle changing along with the discharge depths is drawn by taking the residual capacity as the abscissa and taking the negative number of the phase angle of the preset frequency band of the AC impedance spectrum as the ordinate. Fig. 5 is a graph of negative phase angle values of a battery of ER14250T type according to discharge depth in a specific embodiment, and it can be observed from fig. 5 that when the remaining capacity is greater than 600mAh, theta fluctuates in a larger range, and when the remaining capacity is less than or equal to 600mAh, theta starts to decrease and is almost linear. And fitting a linear fitting method to obtain a linear relation between-theta and the depth of discharge when the residual capacity is less than or equal to the voltage threshold value of 600 mAh:
and-theta is 0.0507W +2.7539, namely, the first variation of the negative value of the phase angle of the sample battery with the discharge depth of the sample battery.
Therefore, after the first change relationship is established, the actually detected phase angle (specifically, the negative number of the phase angle) of the preset frequency band of the battery to be tested is substituted into the first change relationship, so that the current residual capacity of the battery to be tested can be calculated, namely the discharge depth of the battery to be tested.
Optionally, in some embodiments, in order to eliminate the influence of the unstable factor of the sample battery on the relationship between the discharge depth and the phase angle, before discharging the sample battery, the method further includes the following steps:
and controlling the sample battery to stand at the first temperature for a third time period.
Illustratively, new batteries of ER14250T model are taken, and before being respectively discharged in the environment of 23 +/-2 ℃, the new batteries of ER14250T model are respectively discharged after being placed in the environment of 23 +/-2 ℃ for one day so as to control the comprehensive state stability of the sample batteries.
In the method for detecting the discharge depth of the battery provided in this embodiment, the discharge control under a certain condition is performed on the sample battery, the open-circuit voltage of the sample battery is detected once at intervals of a certain discharge capacity according to a preset condition, and a variation relationship between the open-circuit voltage and the discharge depth is established, so that an open-circuit voltage point at which the open-circuit voltage is significantly reduced is obtained, that is, the voltage threshold of the battery. Meanwhile, in the discharging process, the sample battery is controlled to carry out an alternating current impedance test on the sample battery at regular intervals of discharging capacity according to a set condition, so that the change relation of the discharging depth of the battery along with the phase angle of a preset frequency band is established, and when the open-circuit voltage of the battery is lower than a voltage threshold value, the linear corresponding relation exists between the residual capacity of the battery and the phase angle of the battery in the preset frequency band, so that the corresponding relation between the phase angle and the residual capacity is established; and then the actual residual capacity of the battery to be detected is calculated by bringing the phase angle of the battery to be detected into the corresponding relation, so that the discharge depth of the battery is accurately detected.
Optionally, fig. 6 is a flowchart of another method for detecting battery depth of discharge provided in an embodiment of the present invention, where the embodiment is optimized on the basis of the above embodiment, and the method includes a stage of fitting a linear curve and a stage of testing, where the fitting linear curve is a corresponding curve fit after detecting a selected new sample battery, the stage of testing is to detect a battery to be detected, and finally, the remaining capacity of the battery to be detected is calculated according to the fitted curve and a phase angle of the battery to be detected. Referring to fig. 6, the method specifically includes the following steps:
and S610, discharging the new battery to different degrees.
Wherein, the new battery is the sample battery.
S620, storing for a period of time at 70 ℃.
Referring to the above embodiment, the storage time period of this step corresponds to the first time period in the above embodiment, so that a passivation film with a certain thickness is grown on a new battery.
And S630, measuring the open-circuit voltage of the batteries with different residual capacities.
The remaining capacity W1 at the point where the voltage drops significantly is shown by the voltage V1, wherein the voltage V1 corresponds to the voltage threshold in the above embodiment.
And S640, measuring electrochemical alternating current impedance spectrums of batteries with different residual capacities.
Drawing to obtain a linear relation of the phase angle with the residual capacity when the residual capacity is less than W1, and fitting a linear equation based on the linear relation: - θ ═ aW + b.
Steps S610 to S640 are a stage of curve fitting the sample new battery, and finally, based on the detection result of the sample new battery, the above linear equation is obtained.
And S650, eliminating the passivation film by using the large-current pulse.
The purpose of this step is to eliminate the passivation film of unknown thickness, simulating the state of the discharge just over
S660, storing for a period of time at 70 ℃.
The storage period here coincides with the storage period for the new battery in step S620.
And S670, measuring the open-circuit voltage.
And S680, detecting the open-circuit voltage.
If the open-circuit voltage is greater than V1, the remaining capacity is greater than W1, and the capacity is sufficient.
If the open circuit voltage is less than or equal to V1, step S690 is performed.
And S690, measuring the electrochemical alternating-current impedance spectrum to obtain a phase angle theta at the highest point of the high-frequency semicircle.
And S700, calculating the residual capacity.
And substituting the phase angle theta at the highest point of the high-frequency semicircle obtained in the step S680 into the linear equation fitted in the step S640 to obtain the residual capacity of the battery.
Optionally, on the basis of the foregoing embodiment, an embodiment of the present invention further provides a battery depth of discharge detection system, and fig. 7 is a block diagram of a structure of the battery depth of discharge detection system according to the embodiment of the present invention, where the depth of discharge detection system is configured to implement the depth of discharge detection method described in any of the foregoing embodiments, and with reference to fig. 7, the depth of discharge detection system includes:
the discharging control equipment is used for discharging the battery to be tested according to preset conditions so as to control the battery to be tested to have a first state;
the voltage detection equipment is used for detecting the open-circuit voltage of the battery to be detected;
the detection equipment is used for acquiring a phase angle of the battery to be detected in a preset frequency band based on an alternating current impedance spectrum of the battery to be detected if the open-circuit voltage of the battery to be detected is smaller than a voltage threshold; and determining the residual capacity of the battery to be tested based on the phase angle of the preset frequency band and the corresponding relation between the preset phase angle and the residual capacity.
The discharge control device can be, for example, a battery performance test cabinet, and is connected with the detection device to respond to a discharge control instruction of the detection device and perform discharge control on the battery to be tested and the sample battery.
The voltage detection device can be, for example, an alternating current internal resistance tester, which is connected with the detection device and is used for performing open-circuit voltage detection on the battery to be detected and the sample battery in response to a voltage detection instruction of the detection device.
The detection device is used as a control component of the detection system and is used for sending corresponding control instructions to other connected devices. The detection device can be, for example, an upper computer, and the detection function is realized by operating a built-in detection program.
In addition, the depth of discharge detection system also comprises an alternating current impedance detection device and a temperature control device which are respectively connected with the detection device, wherein,
the AC impedance detection device, which may be an electrochemical workstation, for example, is used for measuring AC impedance spectrums of the battery to be tested and the sample battery and outputting the detected AC impedance spectrums to the control device.
The temperature control device, which may be, for example, a blast oven, is used to provide a constant temperature environment for the battery under test and the sample battery. Specifically, the present embodiment may be configured with a plurality of air blast thermostats, each of which is connected to the control device to provide a desired constant temperature environment in response to a temperature adjustment command from the control device.
Optionally, on the basis of the above technical solution, the discharge control device is specifically configured to:
and in the first temperature, controlling the battery to be tested to perform pulse discharge according to preset current intensity so as to control the battery to be tested to have a first state, wherein the discharge capacity of the pulse discharge and the rated capacity of the battery to be tested have a preset relation.
The temperature control equipment is specifically used for providing a constant temperature environment with the environment temperature being a first temperature for the battery to be tested.
Optionally, on the basis of the above technical solution, the control device is further specifically configured to:
controlling the battery to be tested to stand at the second temperature for the first time length so that the battery to be tested has a second state;
and controlling the battery to be tested to stand at the third temperature for a second time period so as to cool the battery to be tested.
The temperature control equipment is also specifically used for providing a constant temperature environment with a second temperature for the battery to be tested.
Optionally, on the basis of the above technical solution, the control device is further specifically configured to:
if the open-circuit voltage of the battery to be detected is smaller than the voltage threshold, acquiring an alternating current impedance spectrum of the battery to be detected, which is output by the alternating current impedance detection equipment;
and acquiring a phase angle of the battery to be tested in a preset frequency band based on the alternating-current impedance spectrum.
The alternating current impedance detection device is specifically configured to: and responding to a detection instruction of the control equipment to perform alternating current impedance test on the battery to be tested according to a preset excitation voltage to obtain an alternating current impedance spectrum of the battery to be tested, and outputting detection data to the control equipment.
Optionally, on the basis of the above technical solution, the control device is further specifically configured to:
controlling the sample battery to discharge at a first temperature;
in the discharging process, acquiring alternating current impedance spectrum data output by alternating current impedance detection equipment;
establishing a first change relation of a phase angle negative value of the sample battery along with the discharge depth of the sample battery based on the alternating-current impedance spectrum data;
and performing straight line fitting on negative values of the phase angles of which the open-circuit voltages of the sample batteries are smaller than the voltage threshold value based on the first variation relation to determine the corresponding relation between the phase angles and the residual capacity.
The alternating current impedance detection device is further specifically configured to: and responding to a detection instruction of the control equipment to control the sample battery to perform an alternating current impedance test at a third state at intervals of a preset discharge capacity so as to obtain alternating current impedance spectrum data of the sample battery at a corresponding discharge depth, and outputting the alternating current impedance spectrum data to the detection equipment.
The temperature control device is further specifically configured to: and providing a discharge environment of a first temperature for the sample battery in response to a temperature adjustment command of the control device.
Optionally, on the basis of the above technical solution, the control device is further specifically configured to:
controlling the sample battery to stand for a first time at a second temperature every preset discharge capacity so that the sample battery has a second state;
and controlling the sample battery to stand at the third temperature for a second time period so that the sample battery has a third state.
The alternating current impedance detection device is further specifically configured to: and carrying out an alternating current impedance test on the sample battery in the third state.
The temperature control device is further specifically configured to: and providing the sample battery with a constant temperature environment at a second temperature and a constant temperature environment at a third temperature in response to the temperature adjustment instruction of the control device.
Optionally, on the basis of the above technical solution, the control device is further specifically configured to:
controlling the sample battery to discharge at a first temperature;
in the discharging process, acquiring open-circuit voltage data output by voltage detection equipment;
establishing a second variation relation of the open-circuit voltage of the sample battery along with the discharge depth based on the open-circuit voltage data;
determining inflection point voltage with the change rate of the open-circuit voltage larger than a preset value based on the second change relation;
the knee voltage is determined as the voltage threshold.
The voltage detection device is further specifically configured to: and controlling the sample battery to detect the open-circuit voltage once in the third state every other preset discharge capacity so as to obtain the open-circuit voltage data of the sample battery at the corresponding discharge depth, and outputting the open-circuit voltage data to the control equipment.
The temperature control device is further specifically configured to: providing a constant temperature discharge environment of a first temperature for the sample cell in response to a temperature adjustment command from the control device.
Optionally, on the basis of the above technical solution, the control device is further specifically configured to:
controlling the sample battery to stand for a first time at a second temperature every preset discharge capacity so that the sample battery has a second state;
and controlling the sample battery to stand at the third temperature for a second time period so that the sample battery has a third state.
The voltage detection device is further specifically configured to: the open circuit voltage of the primary sample cell is detected in the third state.
The temperature control device is further specifically configured to: and providing the sample battery with a constant temperature environment at a second temperature and a constant temperature environment at a third temperature in response to the temperature adjustment instruction of the control device.
Optionally, on the basis of the above technical solution, the control device is further specifically configured to:
and controlling the sample battery to stand at the first temperature for a third time period.
The temperature control device is further specifically configured to provide a constant temperature environment of a first temperature to the sample cell in response to a temperature adjustment command of the control device.
It is to be noted that the foregoing is only illustrative of the preferred embodiments of the present invention and the technical principles employed. It will be understood by those skilled in the art that the present invention is not limited to the particular embodiments described herein, but is capable of various obvious changes, rearrangements and substitutions as will now become apparent to those skilled in the art without departing from the scope of the invention. Therefore, although the present invention has been described in greater detail by the above embodiments, the present invention is not limited to the above embodiments, and may include other equivalent embodiments without departing from the spirit of the present invention, and the scope of the present invention is determined by the scope of the appended claims.
Claims (10)
1. A battery depth of discharge detection method, comprising:
discharging a battery to be tested according to a preset condition so as to control the battery to be tested to have a first state;
detecting the open-circuit voltage of the battery to be detected;
if the open-circuit voltage of the battery to be tested is smaller than the voltage threshold, acquiring a phase angle of the battery to be tested in a preset frequency band based on the alternating current impedance spectrum of the battery to be tested;
and determining the residual capacity of the battery to be tested based on the phase angle of the preset frequency band and the corresponding relation between the preset phase angle and the residual capacity.
2. The method for detecting the battery depth of discharge according to claim 1, wherein the discharging the battery to be tested according to the preset condition to control the battery to be tested to have the first state comprises:
and in a first temperature, controlling the battery to be tested to perform pulse discharge according to a preset current intensity so as to control the battery to be tested to have a first state, wherein the discharge capacity of the pulse discharge and the rated capacity of the battery to be tested have a preset relation.
3. The method for detecting the battery depth of discharge according to claim 1, wherein after the battery to be tested is discharged according to a preset condition to control the battery to be tested to have the first state, the method further comprises:
controlling the battery to be tested to stand at a second temperature for a first time length so that the battery to be tested has a second state;
and controlling the battery to be tested to stand at the third temperature for a second time length so as to cool the battery to be tested.
4. The method for detecting the depth of discharge of the battery according to claim 1, wherein if the open-circuit voltage of the battery to be tested is smaller than the voltage threshold, acquiring the phase angle of the battery to be tested in a preset frequency band based on the ac impedance spectrum of the battery to be tested comprises:
if the open-circuit voltage of the battery to be tested is smaller than the voltage threshold, carrying out alternating current impedance test on the battery to be tested according to a preset excitation voltage to obtain an alternating current impedance spectrum of the battery to be tested;
and acquiring a phase angle of the battery to be tested in a preset frequency band based on the alternating-current impedance spectrum.
5. The battery depth of discharge detection method of claim 1, wherein the correspondence between the preset phase angle and the remaining capacity is determined as follows:
controlling the sample battery to discharge at a first temperature;
in the discharging process, controlling the sample battery to perform an alternating current impedance test in a third state at intervals of preset discharging capacity so as to obtain alternating current impedance spectrum data of the sample battery at a corresponding discharging depth;
establishing a first variation relation of a negative value of a phase angle of the sample battery with a discharge depth of the sample battery based on the alternating-current impedance spectrum data;
and performing straight line fitting on each phase angle negative value of which the open-circuit voltage of the sample battery is smaller than the voltage threshold value based on the first variation relation to determine the corresponding relation between the phase angle and the residual capacity.
6. The method of claim 5, wherein the step of controlling the sample battery to perform an AC impedance test in a third state every a predetermined discharge capacity comprises:
controlling the sample battery to stand for a first time at a second temperature every other preset discharge capacity so that the sample battery has a second state;
controlling the sample cell to stand at a third temperature for a second period of time so that the sample cell has a third state;
and carrying out an alternating current impedance test on the sample battery in the third state.
7. The battery depth of discharge detection method of claim 1, wherein the voltage threshold is determined as follows:
controlling the sample battery to discharge at a first temperature;
in the discharging process, controlling the sample battery to detect the open-circuit voltage once in a third state at intervals of preset discharging capacity so as to obtain the open-circuit voltage data of the sample battery at a corresponding discharging depth;
establishing a second variation relationship of the open-circuit voltage of the sample cell with the depth of discharge based on the open-circuit voltage data;
determining inflection point voltage with the change rate of the open-circuit voltage larger than a preset value based on the second change relation;
determining the knee voltage as the voltage threshold.
8. The method of claim 7, wherein the step of controlling the sample cell to detect the open-circuit voltage once in the third state at every predetermined discharge capacity comprises:
controlling the sample battery to stand for a first time at a second temperature every other preset discharge capacity so that the sample battery has a second state;
controlling the sample cell to stand at a third temperature for a second period of time so that the sample cell has a third state;
detecting an open circuit voltage of the sample cell at a time in the third state.
9. The method of any of claims 5-8, wherein prior to discharging the control sample cell at the first temperature, the method further comprises:
and controlling the sample battery to stand at the first temperature for a third time period.
10. A battery depth-of-discharge detection system applied to the battery depth-of-discharge detection method according to any one of claims 1 to 9, the detection system comprising:
the discharging control equipment is used for discharging the battery to be tested according to preset conditions so as to control the battery to be tested to have a first state;
the voltage detection equipment is used for detecting the open-circuit voltage of the battery to be detected;
the detection equipment is used for acquiring a phase angle of the battery to be detected in a preset frequency band based on an alternating current impedance spectrum of the battery to be detected if the open-circuit voltage of the battery to be detected is smaller than a voltage threshold; and determining the residual capacity of the battery to be tested based on the phase angle of the preset frequency band and the corresponding relation between the preset phase angle and the residual capacity.
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