In-situ detection method and system for liquid metal battery

Abstract

The present invention discloses an in-situ detection method and system for a liquid metal battery, which belongs to the field of battery detection technology, and includes: during the normal operation of the liquid metal battery, an ultrasonic signal is transmitted to the liquid metal battery through an ultrasonic module; the ultrasonic module is coupled to the bottom of the liquid metal battery, and is used to transmit ultrasonic waves and receive reflected echo signals; the echo signal reflected by the liquid metal battery is received through the ultrasonic module, and the echo signal reflected by the interface between the positive electrode and the electrolyte is extracted from it, and its amplitude change is calculated; the alloying degree of the positive electrode is determined according to the correspondence between the pre-calibrated amplitude change and the alloying degree of the positive electrode; the current discharge capacity C1 of the battery is determined according to the correspondence between the pre-calibrated amplitude change and the discharge capacity; the state of charge SoC is estimated according to #imgabs0#. The present invention can realize accurate detection of the alloying / de-alloying process of the positive electrode in the liquid metal battery without disassembling the battery.

Description

Technical Field

[0001] The present invention belongs to the technical field of battery detection, and more specifically, relates to an in-situ detection method and system for a liquid metal battery. Background Art

[0002] Liquid metal batteries are a new type of electrochemical energy storage technology. They usually use liquid metals with low electronegativity such as Li, Na, Ca, and Mg as negative electrodes, liquid metals / alloys with higher electronegativity as positive electrodes, and inorganic molten salts as electrolytes. Due to density differences and incompatibility, they spontaneously form a three-layer all-liquid structure. This all-liquid structure can effectively avoid the problems of electrode structure deformation and dendrite growth in traditional solid electrodes during the cycle process, thus giving liquid metal batteries an ultra-long service life. At the same time, the rapid mass transfer kinetics at the liquid / liquid interface also give such batteries excellent rate performance.

[0003] Different from the embedding / de-embedding reaction of traditional lithium-ion batteries, the electrochemical reaction of liquid metal batteries during the cycle process is the alloying / de-alloying process of the positive electrode. During discharge, the alloy solid grows at the positive electrode / electrolyte interface, and during charging, the positive electrode side is dealloyed and transformed into a liquid electrode. The construction of the battery's full liquid phase structure requires a high operating temperature. The electrode material's sensitivity to water and oxygen requires a sealed battery structure. The entire battery is made of stainless steel with a thickness of about 3mm, which makes the in-situ analysis and monitoring of the liquid metal battery alloying process very limited. In-situ detection technologies used in other electrochemical energy storage systems, such as in-situ XRD, in-situ SEM, neutron imaging, etc., have problems such as high cost, complex equipment, low penetration, and the need for additional battery structure design. They are not suitable for liquid metal batteries that operate at high temperatures and have sealed structures.

[0004] In the patent application document with application publication number CN 112903950 A, a device for high-temperature in-situ nondestructive testing of liquid metal batteries is disclosed. When the battery is working, radiation, ultrasound, and electromagnetic waves enter from the incident window and incident hole of the device, pass through the detection sample, and then pass through the transmission hole and transmission window. The external detector collects the signal and performs subsequent analysis on it. The incident window and incident hole of the device are parallel to the battery sealing component. The device can realize the nondestructive testing of the microstructure and morphology of some components during the operation of the battery, and analyze the corrosion process of liquid metal electrodes and molten salt electrolytes on key battery components. However, since radiation and electromagnetic waves cannot penetrate the stainless steel shell of the battery; if the ultrasound enters from the incident hole of the device, it cannot propagate to the positive electrode / electrolyte interface of the battery, so the device cannot realize the in-situ observation of the electrochemical reaction process on the positive electrode surface inside the liquid metal battery. And due to the limitation of the design structure, the same device cannot detect and analyze liquid metal batteries of different volumes, and accordingly, it cannot detect and analyze batteries of different capacities, and has certain limitations in application.

[0005] Accurately predicting the state of charge (SoC) of batteries is the theoretical basis and technical support for achieving long-term and safe operation of batteries. However, SoC, as a battery internal state variable, cannot be directly measured. In the current research on liquid metal batteries, the estimation of the SoC of single cells mainly adopts the ampere-hour integration method calculated according to the SoC definition by the electrochemical test program. This method will be affected by the cumulative error and the change of battery state, and it is inevitable to deviate from the true value in a long-term test of a cycle. The method of estimating SoC based on the equivalent circuit model requires the establishment of an accurate and effective battery equivalent model and the identification of unknown parameters in the model. In 2017, Wang Dalei et al. proposed a method for estimating the state of charge of liquid metal batteries based on the second-order Thevenin model and the extended Kalman filter algorithm. The estimation error was less than 4% in the actual working condition test (DOI: 10.13334 / j.0258-8013.pcsee.160520). In 2019, Liu et al. proposed a liquid metal battery state of charge estimation method using an adaptive unscented Kalman filter method. The root mean square error of the battery SoC estimation using this method is only 0.2145 (DOI: 10.1016 / j.apenergy.2019.05.032). The above methods for estimating the SoC of liquid metal batteries based on equivalent circuits have their own advantages and disadvantages and have not been widely used.

[0006] In the patent application document with application publication number CN 106772063 A, a method and device for monitoring battery SoC and SoH (State of Health) by using sound waves are disclosed. The invention uses ultrasonic waves to penetrate the battery, collects acoustic parameters after the sound waves penetrate the battery, and establishes the relationship between the acoustic parameters and the battery state to achieve real-time analysis of the battery state. However, since the attenuation of ultrasonic waves in gas is relatively large, for liquid metal batteries containing gas, the signal collected after ultrasonic waves are transmitted is relatively weak. Therefore, the method of ultrasonic wave transmission is not suitable for liquid metal batteries containing gas; in addition, since ultrasonic waves will pass through each interface in the battery in turn during the transmission process, the method of acoustic wave transmission cannot analyze the changes of a specific interface in a battery containing multiple interfaces. Moreover, neither the device in the invention nor the device disclosed in the Chinese invention patent CN107238804 A can be applied to liquid metal batteries with asymmetric upper and lower configurations and a sealing structure assembled at the top, and cannot achieve state monitoring of liquid metal batteries.

[0007] In general, there is currently no in-situ detection method suitable for the alloying process of liquid metal batteries and liquid metal battery SoC. Summary of the invention

[0008] In view of the defects of the prior art and the need for improvement, the present invention provides an in-situ detection method and system for a liquid metal battery, the purpose of which is to accurately detect the alloying / de-alloying process of the positive electrode in the liquid metal battery without disassembling the liquid metal battery.

[0009] To achieve the above object, according to one aspect of the present invention, there is provided an in-situ detection method for a liquid metal battery, comprising the following steps:

[0010] (S1) During the normal operation of the liquid metal battery, an ultrasonic signal is transmitted to the liquid metal battery through an ultrasonic module; the ultrasonic module is coupled to the bottom of the liquid metal battery to transmit the ultrasonic wave and receive the reflected echo signal;

[0011] (S2) receiving an echo signal reflected by the liquid metal battery through an ultrasonic module, and extracting an echo signal reflected by the interface between the positive electrode and the electrolyte as a target echo signal;

[0012] (S3) Calculating the amplitude variation of the target echo signal, and determining the alloying degree of the positive electrode according to the correspondence between the pre-calibrated amplitude variation and the alloying degree of the positive electrode.

[0013] The present invention transmits ultrasonic waves from the bottom of the liquid metal battery to the inside of the liquid metal battery through an ultrasonic module coupled to the bottom of the liquid metal battery. Since ultrasonic waves have strong penetrating power, and the coupled contact mode isolates the ultrasonic module from the air and tightly combines with the battery, it is ensured that the emitted ultrasonic waves can enter the battery. Unlike traditional ultrasonic transmission detection, the present invention receives the echo signal reflected from the inside of the battery at the bottom of the battery for analysis, and identifies the echo signal reflected from the positive electrode / electrolyte interface. Experiments have found that the echo signal reflected at the positive electrode / electrolyte interface can accurately reflect the interface changes, and the amplitude change of the echo signal has a specific corresponding relationship with the degree of alloying of the positive electrode. The present invention determines the degree of alloying based on the echo signal and the pre-calibrated corresponding relationship, and can achieve accurate detection of the degree of alloying of the positive electrode. The present invention does not need to disassemble the battery during the detection process, and is a non-destructive in-situ detection method. In general, the present invention can realize accurate detection of the alloying / de-alloying process of the positive electrode in the liquid metal battery without disassembling the liquid metal battery, which is of great significance for studying the change process of the positive electrode during the charging and discharging process of the liquid metal battery and analyzing the mechanism of the electrochemical reaction of the liquid metal battery.

[0014] Furthermore, the amplitude change calculation method includes:

[0015] Convert the target echo signal into a voltage signal;

[0016] Calculate the peak value max[y ch (t1≤t f ≤t2,t3≤t d ≤t4)] and valley value min[y ch (t1≤t≤t2, t3≤t d ≤t4)], and the peak value of the voltage signal of the liquid metal battery in the undischarged state max[y ch (t1≤t f ≤t2,t d =0)] and valley value min[y ch (t1≤t f ≤t2,t d =0)];

[0017] according to Calculate the amplitude change.

[0018] The amplitude change calculated by the present invention in the above manner can accurately reflect the difference between the echo signals reflected by the ultrasonic wave at the specific interface inside the battery when the battery is in a discharged state and in a non-discharged state, thereby accurately reflecting the changes in the positive electrode / electrolyte interface in the battery, and further improving the accuracy of subsequent analysis results on the degree of alloying of the positive electrode.

[0019] Furthermore, step (S3) further comprises:

[0020] According to the correspondence between the pre-calibrated amplitude change and the discharge capacity, the current discharge capacity C1 of the liquid metal battery is determined;

[0021] according to Estimate the state of charge (SoC) of liquid metal batteries;

[0022] Wherein, C0 represents the rated discharge capacity of the liquid metal battery.

[0023] Experiments have found that there is a specific corresponding relationship between the amplitude change of the echo signal reflected at the positive electrode / electrolyte interface and the discharge capacity of the battery. The present invention determines the discharge capacity of the battery based on the echo signal and the pre-calibrated corresponding relationship, and estimates the charge state of the battery based on the discharge capacity. It can accurately detect the degree of alloying of the positive electrode and accurately estimate the charge state of the liquid metal battery.

[0024] Furthermore, before step (S2), the method further includes: adjusting the signal parameters of the ultrasonic signal so that the difference between the flight time of the echo signal reflected by the interface between the positive electrode and the electrolyte and the flight time of the echo signal and the clutter signal reflected by other interfaces is greater than a preset threshold;

[0025] The signal parameters include at least one of the following:

[0026] Gain, transmit voltage, pulse width, repetition frequency.

[0027] Before detecting the target echo signal, the present invention adjusts the parameters of the ultrasonic signal so that the difference between the flight time of the echo signal reflected at the interface between the positive electrode and the electrolyte and the flight time of the echo signals and clutter signals reflected at other interfaces is larger (greater than a preset threshold), thereby making the target echo signal clearly distinguishable from other echo signals and clutter signals, facilitating the subsequent accurate extraction of the target echo signal.

[0028] According to another aspect of the present invention, there is provided an in-situ detection system for a liquid metal battery, comprising: a battery tester, an ultrasonic module, and a control module;

[0029] A battery tester, connected to the positive and negative electrodes of the liquid metal battery to be tested, respectively, and used to apply current to the liquid metal battery to enable the liquid metal battery to operate normally;

[0030] An ultrasonic module, coupled to the bottom of the liquid metal battery, for transmitting ultrasonic waves and receiving reflected echo signals;

[0031] A control module, connected to the ultrasonic module, is used to extract an echo signal reflected by the interface between the positive electrode and the electrolyte from the echo signal reflected by the liquid metal battery as a target echo signal;

[0032] The control module is also used to calculate the amplitude change of the target echo signal, and determine the alloying degree of the positive electrode according to the corresponding relationship between the pre-calibrated amplitude change and the alloying degree of the positive electrode.

[0033] Furthermore, the amplitude change calculation method includes:

[0034] Convert the target echo signal into a voltage signal;

[0035] Calculate the peak value max[y ch (t1≤t f ≤t2,t3≤t d ≤t4)] and valley value min[y ch (t1≤t≤t2, t3≤t d ≤t4)], and the peak value of the voltage signal of the liquid metal battery in the undischarged state max[y ch (t1≤t f ≤t2,t d =0)] and valley value min[y ch (t1≤t f ≤t2,t d =0)];

[0036] according to Calculate the amplitude change.

[0037] Furthermore, the control module is also used to determine the current discharge capacity C1 of the liquid metal battery according to the corresponding relationship between the pre-calibrated amplitude change and the discharge capacity; and Estimate the state of charge (SoC) of liquid metal batteries;

[0038] Wherein, C0 represents the rated discharge capacity of the liquid metal battery.

[0039] Furthermore, the ultrasound module includes an ultrasound probe and a wedge matching the ultrasound probe.

[0040] In the present invention, the ultrasonic module includes not only the ultrasonic probe but also a wedge block matched with the ultrasonic probe. The use of the wedge block can eliminate the detection blind area caused by the irregular shape of the sound field on the probe surface, thereby further improving the detection accuracy.

[0041] Furthermore, the ultrasonic module also includes a cooling structure fixed to the bottom of the liquid metal battery.

[0042] The operating temperature of the liquid metal battery of some systems is high and may exceed the Curie temperature of the piezoelectric crystal inside the ultrasonic probe. In the detection system provided by the present invention, the ultrasonic module also includes a cooling structure fixed to the bottom of the liquid metal battery, which can avoid affecting the detection accuracy due to the temperature of the contact between the battery and the ultrasonic probe exceeding the operating temperature range of the ultrasonic probe.

[0043] Furthermore, the ultrasonic probe is a single crystal probe, a phased array linear array probe or a phased array area array probe.

[0044] In general, through the above technical scheme conceived by the present invention, a contact-type ultrasonic reflection detection method is adopted. Without disassembling the battery and without affecting the battery operation, the interfacial reaction changes of the positive electrode / electrolyte interface inside the liquid metal battery are detected in real time by analyzing the echo signal occurring at a specific interface, thereby realizing the in-situ detection of the alloying / de-alloying degree of the liquid metal battery positive electrode, and further realizing the in-situ detection of the state of charge (SoC) of the liquid metal battery.

[0045] The present invention does not require the design of a special detection device, effectively overcoming the problem of the complex structure of the liquid metal battery affecting battery detection. It can detect the interface reaction changes of the positive electrode / electrolyte interface inside the battery in real time without affecting the battery operation. It is of great significance for studying the positive electrode change process in the charge and discharge cycle of the liquid metal battery and analyzing the mechanism of the electrochemical reaction of the liquid metal battery. At the same time, compared with other non-destructive in-situ detection methods, the contact ultrasonic reflection detection method is simple and convenient, and does not require the additional design of a complex detection structure. It can detect liquid metal batteries of different capacities, providing a new idea for the field of battery detection. BRIEF DESCRIPTION OF THE DRAWINGS

[0046] Figure 1 A flow chart of an in-situ detection method for a liquid metal battery provided by an embodiment of the present invention;

[0047] Figure 2 A schematic diagram of an in-situ detection method for a Li||Ga room temperature liquid metal battery provided by an embodiment of the present invention;

[0048] Figure 3 A schematic diagram of a theoretical propagation path of ultrasound in a liquid metal battery provided by an embodiment of the present invention;

[0049] Figure 4 A schematic diagram showing the relationship between the amplitude of the positive electrode / electrolyte interface echo signal and the discharge capacity of a Li||Ga room temperature liquid metal battery provided in an embodiment of the present invention;

[0050] Figure 5 Two-dimensional ultrasonic imaging of a Li||Ga room temperature liquid metal battery provided by an embodiment of the present invention;

[0051] Figure 6 Three-dimensional ultrasonic imaging of continuous changes in the positive electrode / electrolyte interface of a Li||Ga room temperature liquid metal battery during discharge provided by an embodiment of the present invention;

[0052] Figure 7 Schematic diagram of Li||Bi high-temperature liquid metal battery detection provided by an embodiment of the present invention. DETAILED DESCRIPTION

[0053] In order to make the purpose, technical solutions and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not intended to limit the present invention. In addition, the technical features involved in the various embodiments of the present invention described below can be combined with each other as long as they do not conflict with each other.

[0054] In the present invention, the terms "first", "second", etc. (if any) in the present invention and the accompanying drawings are used to distinguish similar objects but not necessarily to describe a specific order or sequence.

[0055] In order to solve the technical problem that the existing liquid metal battery detection method cannot effectively realize the in-situ detection of the positive electrode alloying / de-alloying process during the battery cycle, the present invention provides an in-situ detection method and system for liquid metal batteries, the overall idea of ​​which is: utilizing the strong penetrating power and rapid propagation characteristics of ultrasound, adopting a contact ultrasonic detection method, emitting ultrasound from the bottom of the battery to the inside of the battery, and acquiring in real time the echo signal reflected from the positive electrode / electrolyte interface of the battery during the detection process, so as to realize continuous observation of the positive electrode / electrolyte interface, and by determining the detection parameters, calibrating the reflected echo signal of the positive electrode at different alloying degrees, so as to realize the detection of the alloying degree of the positive electrode of the battery by using the detected echo signal; on this basis, by determining the detection parameters, calibrating the reflected echo signal of the battery at each different SoC, so as to realize the estimation of the current SoC of the battery by using the amplitude of the echo signal.

[0056] The following are examples.

[0057] Embodiment 1:

[0058] An in-situ detection method for a liquid metal battery. In this embodiment, the liquid metal battery detected is a Li||Ga room temperature liquid metal battery;

[0059] See also Figure 1 and Figure 2 , this embodiment includes the following steps:

[0060] (S1) During the normal operation of the liquid metal battery, an ultrasonic signal is transmitted to the liquid metal battery through an ultrasonic module; the ultrasonic module is coupled to the bottom of the liquid metal battery to transmit the ultrasonic wave and receive the reflected echo signal;

[0061] See also Figure 2 In this embodiment, a battery tester connected to both the positive and negative electrodes of the battery applies a test current to the battery to enable the battery to operate normally; optionally, in this embodiment, the discharge current is set to 7 mA to start discharging the Li||Ga liquid metal battery; through the battery tester, the battery voltage can also be collected in real time during the detection process in this embodiment;

[0062] See also Figure 2In this embodiment, the ultrasonic module includes an ultrasonic probe and a wedge matched with the ultrasonic probe. The lower bottom surface of the wedge of the probe / wedge as a whole is connected to the bottom of the Li||Ga liquid metal battery, and silicone oil or other ultrasonic coupling agents are used to fully couple the probe and the battery. Optionally, in this embodiment, the ultrasonic probe in the ultrasonic module is specifically a 5MHz ultrasonic longitudinal wave single crystal probe;

[0063] The wedge in the ultrasonic module is used to eliminate the detection blind area where irregular noise exists near the surface of the probe, ensuring the accuracy of the detection; by coupling the ultrasonic module as a whole with the bottom of the battery, the ultrasonic probe and the battery can be isolated from the air and tightly combined to ensure that the ultrasonic waves emitted by the probe can enter the battery;

[0064] When ultrasonic waves are incident from the bottom of the liquid metal battery, theoretically, they will pass through the positive electrode current collector / positive electrode interface, positive electrode / electrolyte interface, and electrolyte / negative electrode interface from bottom to top (taking the fully charged state as an example). At each interface, due to the different acoustic impedances of the media on both sides of the interface, transmission and reflection will occur, such as Figure 3 As shown; the above three interfaces are Figure 3 Interface 1, Interface 2 and Interface 3 in it;

[0065] (S2) receiving an echo signal reflected by the liquid metal battery through an ultrasonic module, and extracting an echo signal reflected by the interface between the positive electrode and the electrolyte as a target echo signal;

[0066] In order to realize continuous observation of the positive electrode / electrolyte interface of the battery and detect the alloying degree of the positive electrode, this embodiment only analyzes the echo signal reflected from the positive electrode / electrolyte interface; in practical applications, after receiving the echo signal reflected from the battery, the echo signals reflected from different interfaces can be distinguished according to the flight time of the ultrasonic signal;

[0067] In order to accurately extract the echo signal reflected by the positive electrode / electrolyte interface, as a preferred embodiment, before step (S2), one or more signal parameters of the ultrasonic signal such as gain, transmission voltage, pulse width, repetition frequency, etc. are adjusted so that the difference between the flight time of the echo signal reflected by the interface between the positive electrode and the electrolyte and the flight time of the echo signal and the clutter signal reflected by other interfaces is greater than a preset threshold, thereby making the echo signal reflected by the positive electrode / electrolyte interface clearly distinguishable from other echo signals or clutter signals;

[0068] (S3) Calculating the amplitude variation of the target echo signal, and determining the alloying degree of the positive electrode according to the correspondence between the pre-calibrated amplitude variation and the alloying degree of the positive electrode.

[0069] In this embodiment, the positive electrode of the (semi-) liquid metal battery is gallium metal Ga, which can maintain liquid state at room temperature, the battery operating temperature is within the operating temperature range of the ultrasonic probe, and the ultrasonic probe can directly contact the bottom of the battery; optionally, this embodiment uses a simple ultrasonic longitudinal wave single crystal probe to analyze the receiving voltage of the echo signal. During the battery discharge process, the amplitude of the echo signal belonging to the positive electrode / electrolyte interface changes, and experiments have found that the amplitude change of the echo signal can accurately reflect the interface change, and the amplitude change of the echo signal has a specific corresponding relationship with the degree of positive electrode alloying. Qualitatively speaking, if the amplitude of the echo signal is enhanced, it means that the degree of positive electrode alloying has increased, and conversely, if the amplitude of the echo signal is weakened, it means that the degree of positive electrode alloying has weakened; it is easy to understand that since the positive electrode dealloying process is the reverse process of the alloying process, the detection of the positive electrode alloying degree also reflects the degree of positive electrode dealloying to a certain extent.

[0070] Based on the above theoretical analysis, this embodiment preliminarily detects the positive electrode / electrolyte interface echo signal of a Li||Ga liquid metal battery with a known positive electrode alloying degree through the above steps (S1) and (S2), and calculates the amplitude change, thereby determining the amplitude change corresponding to different positive electrodes with different alloying degrees, and completing the calibration; based on the calibration result, the corresponding positive electrode alloying degree can be determined according to the amplitude change of the positive electrode / electrolyte interface echo signal of the battery to be detected.

[0071] Considering that the alloying degree of the positive electrode is related to the discharge state of the battery, as a preferred implementation, this embodiment calculates the amplitude change of the target echo signal in the following manner:

[0072] Convert the target echo signal into a voltage signal;

[0073] Calculate the peak value max[y ch (t1≤t f ≤t2,t3≤t d ≤t4)] and valley value min[y ch (t1≤t≤t2, t3≤t d ≤t4)], and the peak value of the voltage signal of the liquid metal battery in the undischarged state max[y ch (t1≤t f ≤t2,t d =0)] and valley value min[y ch (t1≤t f ≤t2,t d =0)];

[0074] according to Calculate the amplitude change.

[0075] In the above formula, y ch is the echo signal receiving voltage (V), which is positively correlated with the echo amplitude; t f is the flight time, t1≤t f ≤t2 means that the echo signal area belonging to the cathode / electrolyte interface is selected; t3=0 means the discharge start time, t4 means the discharge end time; t d Indicates a certain moment in the discharge process, t d =0 indicates the start of discharge; the amplitude change calculated in the above manner in this embodiment can accurately reflect the difference between the echo signals of the battery in the discharged state and the non-discharged state for ultrasonic reflection, thereby accurately reflecting the changes in the positive electrode / electrolyte interface in the battery, and further improving the accuracy of the subsequent analysis results on the degree of positive electrode alloying.

[0076] Further research found that the amplitude change δ calculated by the above method in this embodiment has a specific corresponding relationship with the battery discharge capacity. For example, in this embodiment, in the Li||Ga liquid metal battery, the amplitude change of the echo signal reflected by the positive electrode / electrolyte interface has a relatively obvious linear relationship with the battery discharge capacity, such as Figure 4 As shown, the current discharge capacity of the battery can be inferred by calculating the δ value at a certain moment in the discharge process, thereby estimating the SoC of the battery; as a preferred implementation, step (S3) of this embodiment further includes:

[0077] According to the correspondence between the pre-calibrated amplitude change and the discharge capacity, the current discharge capacity C1 of the liquid metal battery is determined;

[0078] according to Estimate the state of charge (SoC) of liquid metal batteries;

[0079] Wherein, C0 represents the rated discharge capacity of the liquid metal battery.

[0080] The calibration method for the corresponding relationship between the amplitude change of the target echo signal and the discharge capacity is similar to the calibration method for the corresponding relationship between the amplitude change and the degree of alloying of the positive electrode. That is, for a Li||Ga liquid metal battery with a known state of charge, the amplitude change of its target echo signal is detected by the above method, so as to determine the amplitude change corresponding to different discharge capacities and complete the calibration.

[0081] It should be noted that in practical applications, when the liquid metal battery is other types of batteries, it is necessary to recalibrate the corresponding relationship between the amplitude change and the degree of alloying of the positive electrode and the corresponding relationship between the amplitude change and the discharge capacity.

[0082] In general, this embodiment transmits ultrasonic waves from the bottom of the liquid metal battery to the inside of the liquid metal battery through an ultrasonic module coupled to the bottom of the liquid metal battery. Since ultrasonic waves have strong penetrating power and the coupled contact method isolates the ultrasonic module from the air and tightly combines with the battery, it is ensured that the emitted ultrasonic waves can enter the battery. Different from traditional ultrasonic transmission detection, this embodiment receives the echo signal reflected from the inside of the battery at the bottom of the battery for analysis, and identifies the echo signal reflected from the positive electrode / electrolyte interface. Based on the echo signal and the pre-calibrated corresponding relationship, this embodiment determines the alloying degree and estimates the charge state of the battery, which can realize accurate detection of the alloying degree and charge state of the positive electrode.

[0083] Different ultrasonic probes can emit ultrasonic waves of different specific frequencies. The higher the ultrasonic frequency, the higher the detection resolution, but the penetration is weakened. It needs to be selected and adjusted according to the actual battery detection effect. Considering that the operating temperature of liquid metal batteries in most systems is high, exceeding the Curie temperature of the piezoelectric crystal inside the ultrasonic probe, when the probe cannot directly contact the bottom of the battery, a simple cooling structure can be added between the probe / wedge block structure and the battery to reduce the temperature of the contact part between the battery and the ultrasonic probe to within the operating temperature range of the ultrasonic probe; at this time, in order to avoid the introduction of the cooling structure and affect the intensity of the ultrasonic wave entering the battery, a low-frequency ultrasonic probe can be used to enhance the ultrasonic penetration.

[0084] Embodiment 2:

[0085] An in-situ detection method for a liquid metal battery. In this embodiment, the liquid metal battery detected is a Li||Ga room temperature liquid metal battery;

[0086] This embodiment is similar to the above-mentioned embodiment 1, except that in this embodiment, the ultrasonic probe in the ultrasonic module is specifically a 5MHz phased array linear array probe, and this embodiment performs two-dimensional imaging of the longitudinal cross-section direction of the battery while completing the in-situ detection of the positive electrode alloying degree and the battery state of charge in the battery, so as to locate the positive electrode / electrolyte interface of the battery, such as Figure 5 shown.

[0087] Embodiment 3:

[0088] An in-situ detection method for a liquid metal battery. In this embodiment, the liquid metal battery detected is a Li||Ga room temperature liquid metal battery;

[0089] This embodiment is similar to the above-mentioned embodiment 1, except that in this embodiment, the ultrasonic probe in the ultrasonic module is specifically a 5MHz phased array ultrasonic probe, and this embodiment performs three-dimensional acoustic imaging of the inside of the battery while completing the in-situ detection of the positive electrode alloying degree and the battery charge state in the battery, intercepts the positive electrode / electrolyte interface, directly observes the changes of the interface during the discharge process, and analyzes the alloying process, such as Figure 6 shown.

[0090] Embodiment 4:

[0091] An in-situ detection system for a liquid metal battery. In this embodiment, the liquid metal battery detected is a Li||Ga room temperature liquid metal battery;

[0092] See also Figure 2 , this embodiment includes: a battery tester, an ultrasonic module and a control module;

[0093] A battery tester, connected to the positive and negative electrodes of the liquid metal battery to be tested, respectively, and used to apply current to the liquid metal battery to enable the liquid metal battery to operate normally;

[0094] An ultrasonic module, coupled to the bottom of the liquid metal battery, for transmitting ultrasonic waves and receiving reflected echo signals;

[0095] A control module, connected to the ultrasonic module, for extracting an echo signal reflected by the interface between the positive electrode and the electrolyte from the echo signal reflected by the liquid metal battery as a target echo signal;

[0096] The control module is also used to calculate the amplitude change of the target echo signal, and determine the alloying degree of the positive electrode according to the correspondence between the pre-calibrated amplitude change and the alloying degree of the positive electrode; in this embodiment, the control module is composed of Figure 2 Computer implementation in

[0097] See also Figure 2 In this embodiment, the ultrasound module includes an ultrasound probe and a wedge block matched with the ultrasound probe, and Figure 2 The ultrasonic signal transmitter / receiver shown in the figure; the function of the wedge is to eliminate the detection blind area where irregular noise exists near the surface of the probe to ensure the accuracy of the detection; in actual measurement, the probe / wedge as a whole is coupled to the bottom of the liquid metal battery through ultrasonic coupling agents such as silicone oil. Through coupling, the ultrasonic probe and the battery are isolated from the air and tightly combined to ensure that the ultrasonic wave emitted by the probe can enter the battery.

[0098] Similar to the above method embodiment, in this embodiment, the amplitude change amount calculation method includes:

[0099] Convert the target echo signal into a voltage signal;

[0100] Calculate the peak value max[y ch (t1≤t f ≤t2,t3≤t d ≤t4)] and valley value min[y ch (t1≤t≤t2, t3≤t d ≤t4)], and the peak value of the voltage signal of the liquid metal battery in the undischarged state max[y ch (t1≤t f ≤t2,t d =0)] and valley value min[y ch (t1≤t f ≤t2,t d =0)];

[0101] according to Calculate the amplitude change;

[0102] In this embodiment, the control module is also used to determine the current discharge capacity C1 of the liquid metal battery according to the corresponding relationship between the pre-calibrated amplitude change and the discharge capacity; and Estimate the state of charge (SoC) of liquid metal batteries;

[0103] Wherein, C0 represents the rated discharge capacity of the liquid metal battery.

[0104] In this embodiment, the specific implementation method of the control module completing the above signal analysis can refer to the description in the above embodiment 1, which will not be repeated here.

[0105] Embodiment 5:

[0106] An in-situ detection system for a liquid metal battery. In this embodiment, the liquid metal battery detected is a Li||Bi liquid metal battery;

[0107] This embodiment is similar to the above-mentioned embodiment 4, except that, considering that the operating temperature of the Li||Bi liquid metal battery is higher than the Curie temperature of the piezoelectric crystal inside the ultrasonic probe, in order to ensure the normal operation of the ultrasonic probe, refer to Figure 7 In this embodiment, in addition to the ultrasonic probe and the matching wedge block, a cooling structure is also provided between the probe / wedge block as a whole and the bottom of the battery; in this embodiment, the cooling structure can be cooled by air cooling or water cooling;

[0108] In order to avoid the introduction of a cooling structure that affects the intensity of the ultrasonic waves entering the battery, in this embodiment, the ultrasonic frequency emitted by the ultrasonic probe is 2 MHz. The ultrasonic probe may be a single crystal probe, a phased array linear array probe, or a phased array surface array probe.

[0109] It will be easily understood by those skilled in the art that the above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions and improvements made within the spirit and principles of the present invention should be included in the protection scope of the present invention.

Claims

1. An in-situ detection method for a liquid metal battery, characterized in that: The steps include: (S1) During the normal operation of the liquid metal battery, an ultrasonic signal is transmitted to the liquid metal battery through an ultrasonic module; the ultrasonic module is coupled to the bottom of the liquid metal battery and is used to transmit ultrasonic waves and receive reflected echo signals; (S2) receiving the echo signal reflected by the liquid metal battery through the ultrasonic module, and extracting the echo signal reflected by the interface between the positive electrode and the electrolyte as the target echo signal; (S3) calculating the amplitude change of the target echo signal, and determining the alloying degree of the positive electrode according to the correspondence between the pre-calibrated amplitude change and the alloying degree of the positive electrode; The amplitude change calculation method includes: Converting the target echo signal into a voltage signal; Calculate the peak value max[y ch (t1≤t f ≤t2,t3≤t d ≤t4)] and valley value min[y ch (t1≤t≤t2, t3≤t d ≤t4)], and the peak value max[y ch (t1≤t f ≤t2,t d =0)] and valley value min[y ch (t1≤t f ≤t2,t d =0)]; according to Calculating the amplitude change; The step (S3) further comprises: Determine the current discharge capacity C1 of the liquid metal battery according to the correspondence between the pre-calibrated amplitude change and the discharge capacity; according to estimating the state of charge (SoC) of the liquid metal battery; Wherein, C0 represents the rated discharge capacity of the liquid metal battery.

2. The in-situ detection method of a liquid metal battery according to claim 1, characterized in that: Before the step (S2), the method further includes: adjusting the signal parameters of the ultrasonic signal so that the difference between the flight time of the echo signal reflected by the interface between the positive electrode and the electrolyte and the flight time of the echo signal and the clutter signal reflected by other interfaces is greater than a preset threshold; The signal parameters include at least one of the following: Gain, transmit voltage, pulse width, repetition frequency.

3. An in-situ detection system for a liquid metal battery, characterized in that: include: Battery tester, ultrasonic module, and control module; The battery tester is connected to the positive and negative electrodes of the liquid metal battery to be tested, respectively, and is used to apply current to the liquid metal battery to enable the liquid metal battery to operate normally; The ultrasonic module is coupled to the bottom of the liquid metal battery and is used to transmit ultrasonic waves and receive reflected echo signals; The control module is connected to the ultrasonic module and is used to extract the echo signal reflected by the interface between the positive electrode and the electrolyte from the echo signal reflected by the liquid metal battery as the target echo signal; The control module is further used to calculate the amplitude change of the target echo signal, and determine the alloying degree of the positive electrode according to the correspondence between the pre-calibrated amplitude change and the alloying degree of the positive electrode; The amplitude change calculation method includes: Converting the target echo signal into a voltage signal; Calculate the peak value max[y ch (t1≤t f ≤t2,t3≤t d ≤t4)] and valley value min[y ch (t1≤t≤t2, t3≤t d ≤t4)], and the peak value max[y ch (t1≤t f ≤t2,t d =0)] and valley value min[y ch (t1≤t f ≤t2,t d =0)]; according to Calculating the amplitude change; The control module is further used to determine the current discharge capacity C1 of the liquid metal battery according to the correspondence between the pre-calibrated amplitude change and the discharge capacity; and estimating the state of charge (SoC) of the liquid metal battery; Wherein, C0 represents the rated discharge capacity of the liquid metal battery.

4. The in-situ detection system for liquid metal batteries according to claim 3, characterized in that: The ultrasonic module includes an ultrasonic probe and a wedge matched with the ultrasonic probe, as well as an ultrasonic signal transmitter and an ultrasonic signal receiver.

5. The in-situ detection system for liquid metal batteries according to claim 4, characterized in that: The ultrasonic module also includes a cooling structure fixed to the bottom of the liquid metal battery.

6. The in-situ detection system for liquid metal batteries according to claim 4, characterized in that: The ultrasonic probe is a single crystal probe, a phased array linear array probe or a phased array area array probe.

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