A lithium precipitation detection method and device based on a relaxation diffusion capacitor

Abstract

The application discloses a lithium precipitation detection method and device based on relaxation diffusion capacitance of energy storage battery, and belongs to the technical field of online safety detection of energy storage lithium ion battery. The method comprises the following steps: performing two electrochemical impedance spectrum tests at certain intervals in the relaxation time at the end of charging; exciting AC current by an energy storage converter; extracting voltage response and calculating AC impedance by a battery management system; comparing the change rate of diffusion capacitance of the two AC impedances based on a battery impedance model with a threshold value; and finally obtaining a lithium precipitation judgment result. The application captures the electrochemical impedance spectrum in the rest time at the end of battery charging, extracts the low-frequency diffusion capacitance and its change rate to diagnose lithium precipitation, improves the lithium precipitation detection sensitivity, realizes online, intelligent and accurate lithium precipitation state diagnosis of the energy storage lithium ion battery, and provides an effective basis for the safe operation of the power station.

Description

Technical Field

[0001] This invention belongs to the field of online safety testing technology for energy storage lithium-ion batteries, specifically relating to a method and apparatus for detecting lithium plating in energy storage batteries based on relaxation diffusion capacitance. Background Technology

[0002] The lithium-ion battery energy storage industry is experiencing continuous growth. However, while lithium-ion battery energy storage is developing rapidly, battery safety issues have gradually emerged. Fires and explosions at lithium-ion battery energy storage power stations caused by battery-related issues such as internal short circuits and thermal runaway are occurring frequently, seriously affecting public safety. Individual cells and modules of lithium-ion batteries used for power storage should meet certain requirements to prevent fires and explosions under conditions of overcharging, over-discharging, overload, short circuits, compression, and drops.

[0003] Initial safety testing of new batteries cannot guarantee the long-term safe and stable operation of lithium-ion battery energy storage power stations. Unknown internal defects and improper charging conditions can cause lithium plating on the negative electrode. Lithium plating reduces battery thermal stability and, in severe cases, induces lithium dendrites. Dendrite growth that pierces the separator can cause an internal short circuit, leading to thermal runaway. Lithium plating characteristics are insidious, and under current energy storage system architectures, the battery management system (BMS) lacks sufficient accuracy and speed to detect lithium plating online.

[0004] Currently, the main methods for online lithium plating detection in batteries are external characteristic methods, including relaxation voltage differential, discharge voltage differential, coulombic efficiency, and electrochemical impedance spectroscopy (EIS). Since lithium plating is a localized microscopic feature of the battery, the sensitivity issues of these external characteristic methods for detecting lithium plating in large-capacity energy storage batteries are amplified.

[0005] The relaxation voltage differential and discharge voltage differential methods for lithium plating detection diagnose lithium plating based on the voltage plateau during the lithium stripping process. However, these methods have low sensitivity, and when the amount of reversible lithium deposited during charging is limited, it is difficult to identify the voltage plateau from the relaxation curve. The coulombic efficiency method diagnoses lithium plating by assessing the battery's capacity loss after plating. However, since battery capacity is affected by factors such as temperature and current, the coulombic efficiency method requires strict control of environmental and current conditions during detection, making it unsuitable for online lithium plating detection in practical applications. Electrochemical impedance spectroscopy (EIS) extracts impedance at different reaction rates within a frequency band by sweeping the battery's frequency spectrum, offering high sensitivity. However, this method focuses on mid-frequency charge transfer impedance, lacks sufficient analysis of lithium plating characteristics, and suffers from inaccurate detection. Current lithium plating detection methods cannot provide online, intelligent, and accurate diagnosis of lithium plating status in energy storage batteries, and there is a lack of internal lithium plating detection and safety assessment during power plant operation. Summary of the Invention

[0006] To solve the above-mentioned technical problems, the present invention adopts the following technical solution:

[0007] A method for detecting lithium plating in energy storage batteries based on relaxation diffusion capacitance, comprising:

[0008] Step 1: Extract real-time data of individual lithium-ion battery cells collected by the battery management system and wait for the most recent charge completion marker.

[0009] Step 2: Set the energy storage converter to lithium plating detection mode;

[0010] Step 3, during the relaxation period after the charging completion marker appears. At any given time, run the electrochemical impedance spectroscopy test program once;

[0011] Step 4, during the charging relaxation period At that moment, run the second electrochemical impedance spectroscopy test program;

[0012] Step 5: Set the energy storage converter to standby mode;

[0013] Step 6: Using the battery impedance model, analyze the results of the two runs of the electrochemical impedance spectroscopy test program, and calculate the lithium plating parameters: diffusion capacitance of the first electrochemical impedance spectroscopy. and diffusion capacitance of the second electrochemical impedance spectroscopy ;

[0014] Step 7: Calculate the rate of change of diffusion capacitance in the two electrochemical impedance spectra. The rate of change of diffusion capacitance With threshold In comparison, if > For lithium plating, and vice versa. ≤ If no lithium has been deposited, output and display the lithium deposition detection result.

[0015] A lithium plating detection device for energy storage batteries based on relaxation diffusion capacitance, comprising:

[0016] The data extraction module extracts real-time data from individual lithium-ion battery cells collected by the battery management system and waits for the most recent end-of-charge marker.

[0017] The energy storage converter mode setting module sets the energy storage converter to lithium plating detection mode.

[0018] The first time the program runs, during the relaxation period after the charging end marker appears... At any given time, run the electrochemical impedance spectroscopy test program once;

[0019] The second program execution module, during the charging relaxation period At that moment, run the second electrochemical impedance spectroscopy test program;

[0020] The energy storage converter mode adjustment module sets the energy storage converter to standby mode.

[0021] The analysis module uses a battery impedance model to analyze the results of two runs of the electrochemical impedance spectroscopy test program, and calculates the lithium plating parameters: the diffusion capacitance of the first electrochemical impedance spectroscopy. and diffusion capacitance of the second electrochemical impedance spectroscopy ;

[0022] The calculation and results output module calculates the rate of change of diffusion capacitance in two electrochemical impedance spectroscopy analyses. The rate of change of diffusion capacitance With threshold In comparison, if > For lithium plating, and vice versa. ≤ If no lithium has been deposited, output and display the lithium deposition detection result.

[0023] An electronic device includes: one or more processors; and a memory for storing one or more programs, wherein when the one or more programs are executed by the one or more processors, the one or more processors cause the one or more processors to implement the lithium plating detection method for energy storage batteries based on relaxation diffusion capacitance.

[0024] A computer-readable storage medium having executable instructions stored thereon, which, when executed by a processor, cause the processor to implement the described lithium plating detection method for energy storage batteries based on relaxation diffusion capacitance.

[0025] A computer program product includes a computer program that, when executed by a processor, implements the aforementioned lithium plating detection method for energy storage batteries based on relaxation diffusion capacitance.

[0026] The present invention has the following beneficial effects:

[0027] (1) The lithium plating detection method for energy storage batteries based on relaxation diffusion capacitance of the present invention performs electrochemical impedance testing during the charging rest time, extracts low-frequency diffusion impedance characteristics for lithium plating detection, has low test power, low cost, and high sensitivity, and is suitable for online, intelligent and accurate identification of lithium plating status of large-capacity energy storage batteries.

[0028] (2) This invention utilizes the characteristic frequency range of lithium iron phosphate batteries to have more measurable low-frequency impedances, extracts the diffusion capacitance change rate and compares it with a threshold to diagnose whether the battery has lithium plating, thereby improving the accuracy of lithium plating diagnosis.

[0029] (3) This invention can be applied to online safety detection and optimized operation of lithium battery energy storage power stations, solving the problem of lack of detection and safety assessment of lithium plating inside batteries during power station operation. Attached Figure Description

[0030] Figure 1 This is a flowchart of the lithium plating detection method for energy storage batteries based on relaxation diffusion capacitance according to the present invention.

[0031] Figure 2 diffusion capacitor rate of change A schematic diagram of the curves showing the change with relaxation time. Detailed Implementation

[0032] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention. Furthermore, the technical features involved in the various embodiments of this invention described below can be combined with each other as long as they do not conflict with each other.

[0033] The test objects of this invention are various lithium-ion batteries.

[0034] like Figure 1 As shown, this invention provides a method for detecting lithium plating in energy storage batteries based on relaxation diffusion capacitance, comprising the following steps:

[0035] Step 1: Extract real-time data of individual lithium-ion battery cells collected by the battery management system (BMS) and wait for the most recent end-of-charge marker.

[0036] Step 2: Set the energy storage converter (PCS) to lithium plating detection mode;

[0037] Step 3, during the relaxation period after the charging completion marker appears. At any given time, run the electrochemical impedance spectroscopy test program once;

[0038] The specific steps of the electrochemical impedance spectroscopy test procedure are as follows: The battery management system (BMS) sends an electrochemical impedance spectroscopy test command to the energy storage converter (PCS). In response to the electrochemical impedance spectroscopy test command, the energy storage converter (PCS) sends a series of alternating currents of different frequencies. The battery management system (BMS) collects the alternating currents sent by the energy storage converter and simultaneously collects the voltage response of the energy storage battery cells to the alternating currents, and calculates the alternating impedance at each frequency point.

[0039] Step 4, during the charging relaxation period At that moment, run the second electrochemical impedance spectroscopy test program;

[0040] Step 5: Set the energy storage converter (PCS) to standby mode;

[0041] Step 6: Using the battery impedance model, analyze the results of the two runs of the electrochemical impedance spectroscopy test program, and calculate the lithium plating parameters: diffusion capacitance of the first electrochemical impedance spectroscopy. and diffusion capacitance of the second electrochemical impedance spectroscopy ;

[0042] Step 7: Calculate the rate of change of diffusion capacitance in the two electrochemical impedance spectra. The rate of change of diffusion capacitance With threshold In comparison, if > For lithium plating, and vice versa. ≤ If no lithium has been deposited, output and display the lithium deposition detection result.

[0043] In the above technical solution, the relaxation period is the rest period after charging is completed.

[0044] In the above technical solution, the charging end marker is the marker time given by the battery management system (BMS) when a complete charging cycle of the energy storage system ends. Not every moment when the charging current drops to 0A is considered a charging end marker. After the charging end marker, there is a relatively long rest period during which the current is 0A and the energy storage system is not operating. This invention utilizes this rest period to determine lithium plating.

[0045] In the above technical solution, the lithium plating detection mode, i.e., the energy storage converter (PCS), only completes a small power AC current output in this mode and is only used for electrochemical impedance spectroscopy testing.

[0046] In the above technical solution, the standby mode is that the energy storage converter (PCS) is waiting to start and can receive normal charging and discharging commands.

[0047] Specifically, in step 1, the real-time data of individual battery cells collected by the Battery Management System (BMS) mainly includes the voltage, current, and power of the individual battery cells. After charging is completed, a sufficiently long rest period (i.e., relaxation period) is necessary to meet the time requirements for determining lithium plating; this rest period is typically ≥3 hours. The specific method for determining the end-of-charge indicator is as follows: based on the battery energy storage system's charging and discharging strategy, the moment when the charging current drops to 0A is extracted, and the planned rest time after this moment is extracted. The length of the rest time is then determined. Preferably, if the rest time is ≥3 hours, the moment when the charging current drops to 0A can be used as the end-of-charge indicator. The specific end-of-charge indicator is based on the grid dispatch instructions and the power station's operating strategy, and is set according to actual needs. The simplest end-of-charge indicator occurs at the end of the energy storage system's charging instruction only.

[0048] Specifically, in step 3 The preferred time is 1 hour. The time is based on the depolarization characteristics of high-capacity energy storage lithium-ion batteries, and is the earliest time when the battery reaches a quasi-steady state after charging is completed.

[0049] Specifically, in steps 3 and 4, the selection of the amplitude of a series of AC currents of different frequencies emitted by the energy storage converter (PCS) is based on the formula: , This refers to the battery's ohmic or DC internal resistance. For a 280Ah high-capacity energy storage battery, the preferred AC current amplitude range is 10-20A. The selection principle for the AC current frequency range is based on the following two aspects: first, it needs to ensure that low-frequency diffusion impedance is still measurable at the energy storage battery's lowest operating temperature (generally 0℃); second, it needs to be able to measure the battery's ohmic internal resistance at high frequencies. For a 280Ah high-capacity lithium-ion energy storage battery, the preferred AC current frequency range is 1kHz-10mHz, with a total of 51 frequency points. Running an electrochemical impedance spectroscopy test program takes approximately 15 minutes.

[0050] Specifically, the method for calculating the AC impedance at each frequency point in steps 3 and 4 is as follows: extract the amplitude and phase angle corresponding to the voltage and current signals of the battery cells respectively, and calculate them using the piecewise variable window Fourier transform method.

[0051] Specifically, in step 4, The optimal timeframe is 3 hours. Based on experimental results, for high-capacity lithium-ion batteries, the diffusion capacitance change rate over 3 hours is the most effective way to distinguish between lithium-plated and non-lithium-plated batteries. For example... Figure 2 As shown, the 3-hour diffusion capacitance change rate of the undeposited lithium battery Below 0, the 3-hour diffusion capacitance change rate of lithium-ion batteries Then it is above 30%.

[0052] Specifically, in step 6, the total battery impedance From inductor Ohmic internal resistance Solid electrolyte (SEI) membrane resistance Amplitude of the interfacial admittance of the solid electrolyte (SEI) membrane and phase angle Charge transfer internal resistance Amplitude of charge transfer interface admittance and phase angle diffusion capacitance and phase angle constitute, Represents the imaginary unit. Let be the angular frequency. The battery impedance model follows the formula:

[0053] .

[0054] Furthermore, based on the nonlinear least squares method to identify the parameters of the impedance model, the key parameter for lithium plating detection, diffusion capacitance, is obtained. The diffusion capacitance of the first electrochemical impedance spectroscopy is... The diffusion capacitance of the second electrochemical impedance spectroscopy is .

[0055] Specifically, the rate of change of diffusion capacitance in the two electrochemical impedance spectroscopy tests in step 7. The calculation formula is . The value of was determined by previous lithium plating experiments on a large number of energy storage lithium-ion batteries, and can be set to . The average of the lower limit of the rate of change of diffusion capacitance in lithium-ion batteries and the upper limit of the rate of change of diffusion capacitance in non-lithium-ion batteries. Taking a lithium-ion battery lithium-ion battery lithium-ion plating experiment as an example, such as... Figure 2 As shown. Figure 2 diffusion capacitor rate of change A schematic diagram of the curves showing the change in capacitance with relaxation time, where each line represents the diffusion capacitance of the energy storage lithium-ion battery at a specific temperature (e.g., 25℃, 0℃) and a specific charging stage (e.g., 0-25% SOC, 0-50% SOC). rate of change The curve showing the change with relaxation time, where, =3 hours, the lower limit of the change rate of diffusion capacitance of lithium-plated battery and the upper limit of the change rate of diffusion capacitance of non-lithium-plated battery are indicated by arrows in the figure.

[0056] This invention relates to a method and apparatus for detecting lithium plating in energy storage batteries based on relaxation diffusion capacitance. It addresses the online diagnosis of lithium plating in energy storage lithium-ion batteries by capturing electrochemical impedance spectroscopy during the rest period after the battery charging is completed, extracting low-frequency diffusion capacitance and the rate of change of diffusion capacitance for lithium plating diagnosis. This improves the accuracy of online lithium plating detection and provides an effective basis for the safe operation and maintenance of power plants.

[0057] Those skilled in the art will understand that embodiments of the present invention can be provided as methods, systems, or computer program products. Therefore, the present invention can take the form of a completely hardware embodiment, a completely software embodiment, or an embodiment combining software and hardware aspects. Furthermore, the present invention can take the form of a computer program product implemented on one or more computer-usable storage media (including but not limited to disk storage, CD-ROM, optical storage, etc.) containing computer-usable program code. The solutions in the embodiments of the present invention can be implemented using various computer languages, such as the object-oriented programming language Java and the interpreted scripting language JavaScript.

[0058] This invention is described with reference to flowchart illustrations and / or block diagrams of methods, apparatus (systems), and computer program products according to embodiments of the invention. It will be understood that each block of the flowchart illustrations and / or block diagrams, and combinations of blocks in the flowchart illustrations and / or block diagrams, can be implemented by computer program instructions. These computer program instructions can be provided to a processor of a general-purpose computer, special-purpose computer, embedded processor, or other programmable data processing apparatus to produce a machine, such that the instructions, which execute via the processor of the computer or other programmable data processing apparatus, generate instructions for implementing the flowchart illustrations and / or block diagrams. Figure 1 One or more processes and / or boxes Figure 1 A device that provides the functions specified in one or more boxes.

[0059] These computer program instructions may also be stored in a computer-readable storage medium that can direct a computer or other programmable data processing device to function in a particular manner, such that the instructions stored in the computer-readable storage medium produce an article of manufacture including instruction means, which are implemented in a process Figure 1 One or more processes and / or boxes Figure 1 The function specified in one or more boxes.

[0060] These computer program instructions may also be loaded onto a computer or other programmable data processing equipment to cause a series of operational steps to be performed on the computer or other programmable equipment to produce a computer-implemented process, thereby providing instructions that execute on the computer or other programmable equipment for implementing the process. Figure 1 One or more processes and / or boxes Figure 1 The steps of the function specified in one or more boxes.

[0061] Although preferred embodiments of the invention have been described, those skilled in the art, upon learning the basic inventive concept, can make other changes and modifications to these embodiments. Therefore, the appended claims are intended to be interpreted as including the preferred embodiments as well as all changes and modifications falling within the scope of the invention.

[0062] Obviously, those skilled in the art can make various modifications and variations to this invention without departing from its spirit and scope. Therefore, if these modifications and variations fall within the scope of the claims of this invention and their equivalents, this invention also intends to include these modifications and variations.

Claims

1. A method for detecting lithium plating in energy storage batteries based on relaxation diffusion capacitance, characterized in that, include: Step 1: Extract real-time data of individual lithium-ion battery cells collected by the battery management system and wait for the most recent charge completion marker. Step 2: Set the energy storage converter to lithium plating detection mode; Step 3, during the relaxation period after the charging completion marker appears. At any given time, run the electrochemical impedance spectroscopy test program once; Step 4, during the charging relaxation period At that moment, run the second electrochemical impedance spectroscopy test program; Step 5: Set the energy storage converter to standby mode; Step 6: Using the battery impedance model, analyze the results of the two runs of the electrochemical impedance spectroscopy test program, and calculate the lithium plating parameters: diffusion capacitance of the first electrochemical impedance spectroscopy. and diffusion capacitance of the second electrochemical impedance spectroscopy ; The battery impedance model follows the formula: ； in, For battery inductance, For ohmic internal resistance, The internal resistance of the solid electrolyte membrane, and phase angle These represent the amplitude and phase angle of the solid electrolyte membrane interfacial admittance, respectively. For charge transfer internal resistance, and These represent the magnitude and phase angle of the charge transfer interface admittance, respectively. For diffusion capacitance, The phase angle, The imaginary unit, Angular frequency, This represents the total impedance of the battery. Step 7: Calculate the rate of change of diffusion capacitance in the two electrochemical impedance spectra. The rate of change of diffusion capacitance With threshold In comparison, if > For lithium plating, and vice versa. ≤ If no lithium has been deposited, output and display the lithium deposition detection result; Change rate of diffusion capacitance in two electrochemical impedance spectroscopy measurements The calculation formula is: .

2. The method for detecting lithium plating in energy storage batteries based on relaxation diffusion capacitance according to claim 1, characterized in that, In steps 3 and 4, the electrochemical impedance spectroscopy (EIS) test procedure is as follows: the battery management system sends an EIS test command to the energy storage converter. In response to the EIS test command, the energy storage converter sends a series of alternating currents of different frequencies. The battery management system collects the alternating currents sent by the energy storage converter and simultaneously collects the voltage response of the individual energy storage cells to the alternating currents, and calculates the alternating impedance at each frequency point.

3. The method for detecting lithium plating in energy storage batteries based on relaxation diffusion capacitance according to claim 1, characterized in that, In step 1, the real-time data of the energy storage lithium-ion battery cell includes the voltage, current, and power of the battery cell.

4. The method for detecting lithium plating in energy storage batteries based on relaxation diffusion capacitance according to claim 1, characterized in that, In step 3, Set to 1 hour.

5. The method for detecting lithium plating in energy storage batteries based on relaxation diffusion capacitance according to claim 2, characterized in that, In steps 3 and 4, the selection of the amplitude of a series of AC currents of different frequencies emitted by the energy storage converter is based on the formula: , This refers to the ohmic or DC internal resistance of the battery.

6. The method for detecting lithium plating in energy storage batteries based on relaxation diffusion capacitance according to claim 2, characterized in that, In steps 3 and 4, the specific method for calculating the AC impedance at each frequency point is as follows: extract the amplitude and phase angle corresponding to the voltage and current of the battery cell, and use the piecewise variable window Fourier transform method to calculate the AC impedance at each frequency point.

7. The method for detecting lithium plating in energy storage batteries based on relaxation diffusion capacitance according to claim 1, characterized in that, In step 4, Set to 3h.

8. The method for detecting lithium plating in energy storage batteries based on relaxation diffusion capacitance according to claim 1, characterized in that, In step 7, the threshold Set as The average of the lower limit of the rate of change of diffusion capacitance of lithium-ion batteries and the upper limit of the rate of change of diffusion capacitance of undeposited lithium-ion batteries.

9. A lithium plating detection device for energy storage batteries based on relaxation diffusion capacitance, characterized in that, include: The data extraction module extracts real-time data from individual lithium-ion battery cells collected by the battery management system and waits for the most recent end-of-charge marker. The energy storage converter mode setting module sets the energy storage converter to lithium plating detection mode. The first time the program runs, during the relaxation period after the charging end marker appears... At any given time, run the electrochemical impedance spectroscopy test program once; The second program execution module, during the charging relaxation period At that moment, run the second electrochemical impedance spectroscopy test program; The energy storage converter mode adjustment module sets the energy storage converter to standby mode. The analysis module uses a battery impedance model to analyze the results of two runs of the electrochemical impedance spectroscopy test program, and calculates the lithium plating parameters: the diffusion capacitance of the first electrochemical impedance spectroscopy. and diffusion capacitance of the second electrochemical impedance spectroscopy ; The battery impedance model follows the formula: ； in, For battery inductance, For ohmic internal resistance, The internal resistance of the solid electrolyte membrane, and phase angle These represent the amplitude and phase angle of the solid electrolyte membrane interfacial admittance, respectively. For charge transfer internal resistance, and These represent the magnitude and phase angle of the charge transfer interface admittance, respectively. For diffusion capacitance, The phase angle, The imaginary unit, Angular frequency, This represents the total impedance of the battery. The calculation and results output module calculates the rate of change of diffusion capacitance in two electrochemical impedance spectroscopy analyses. The rate of change of diffusion capacitance With threshold In comparison, if > For lithium plating, and vice versa. ≤ If no lithium has been deposited, output and display the lithium deposition detection result; Change rate of diffusion capacitance in two electrochemical impedance spectroscopy measurements The calculation formula is: .

10. An electronic device, characterized in that, include: One or more processors; A memory for storing one or more programs, wherein when the one or more programs are executed by the one or more processors, the one or more processors cause the one or more processors to implement the lithium plating detection method for energy storage batteries based on relaxation diffusion capacitance as described in any one of claims 1 to 8.

11. A computer-readable storage medium, characterized in that, It stores executable instructions that, when executed by a processor, cause the processor to implement the lithium plating detection method for energy storage batteries based on relaxation diffusion capacitance as described in any one of claims 1 to 8.

12. A computer program product, comprising a computer program, characterized in that, When executed by a processor, the computer program implements the lithium plating detection method for energy storage batteries based on relaxation diffusion capacitance as described in any one of claims 1 to 8.

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