An ultrasonic-based non-destructive testing method and system for detecting internal micro-gas generation of a lithium battery

Abstract

The application discloses a kind of based on ultrasonic wave's lithium battery internal micro-gas nondestructive testing method and system, the method includes the following steps: based on ultrasonic echo-penetration method is carried out ultrasonic scanning detection to lithium battery, receives ultrasonic detection signal;The sound-electric conversion is carried out to the received ultrasonic detection signal, converts into digital signal;Ultrasonic detection signal is carried out wavelet decomposition, and the wavelet coefficient of different layers is extracted;Wavelet threshold function is constructed, and the wavelet coefficient less than threshold part is removed as interference noise, obtains the wavelet coefficient of ultrasonic signal after noise reduction;Wavelet reconstruction is carried out based on the wavelet coefficient of ultrasonic signal after noise reduction, obtains the reconstructed ultrasonic detection signal;Micro-gas thickness is calculated;Determine that there is internal micro-gas region, calculate the area of the region that exists micro-gas;The volume of internal micro-gas is calculated.The application carries out the organic fusion of the advantages of ultrasonic echo method and ultrasonic penetration method, realizes the accurate calculation of the volume of lithium battery internal micro-gas.

Description

Technical Field

[0001] This invention relates to the field of lithium battery testing technology, specifically to a non-destructive testing method and system for micro-gas generation inside lithium batteries based on ultrasound. Background Technology

[0002] During the manufacturing and use of lithium batteries, the internal state often deviates from the ideal state, leading to the generation of micro-gas inside the battery. This internal gas can displace the electrolyte in its localized areas, preventing active materials from participating in normal charging and discharging, resulting in battery capacity loss. Furthermore, its presence can cause uneven local temperatures within the battery, leading to inconsistent aging rates and ultimately shortening battery life, or even causing smoke, fire, or explosion. Due to the complexity and real-time nature of changes within lithium batteries, accurately characterizing the distribution of micro-gas inside the battery is often extremely difficult. Current mainstream detection methods focus on measuring various parameters of the battery and its surrounding environment at the time of an accident, which often fails to provide accurate and efficient results.

[0003] For example, a smart device for early warning of composite detection of lithium batteries, patent publication number CN218866061U, detects deformation of the lithium battery surface by attaching strain gauges to the surface, thereby providing early warning of shell deformation caused by internal gas production. On the other hand, it detects the concentration of gases released by battery aging through CO and H2 sensors and compares them with a database for early warning. However, the device can only cause structural deformation and release into the air when the internal gas production of the lithium battery is relatively large. Therefore, it cannot detect the presence of gas in the early stage of micro-gas production inside the lithium battery, nor can it accurately detect the distribution of defect states inside the lithium battery. In addition, monitoring the concentration of leaked gas cannot prevent the occurrence of danger in time, and it cannot detect and warn of abnormal conditions inside the lithium battery in a timely manner. Attaching strain gauges to the surface of the lithium battery will weaken the heat dissipation process during battery charging and discharging, which will increase the probability of risk factors.

[0004] For example, a non-destructive testing device for obtaining the internal state distribution of a lithium-ion battery, as disclosed in patent publication number CN208297685U, uses ultrasonic focusing detection to emit ultrasonic pulse signals and receive ultrasonic pulse signals passing through the lithium battery. It detects the internal state of the lithium battery by the attenuation of the ultrasonic pulse signals and displays the images. However, this device only uses ultrasonic penetration to detect internal defects in the lithium battery, which results in inaccurate localization of internal defects. It also does not perform noise reduction processing and error correction on the ultrasonic detection data, making the detection data susceptible to interference from the environment and the device itself, thus affecting the accuracy of the detection results. In addition, it does not have the function of early real-time safety warning based on the detection results of micro-gas generation inside the lithium battery. Summary of the Invention

[0005] To overcome the defects and shortcomings of existing technologies, this invention provides a non-destructive testing method and system for micro-gas generation inside lithium batteries based on ultrasound. This invention organically integrates the advantages of ultrasonic echo method and ultrasonic penetration method, calculates the thickness and area of ​​the micro-gas generation region inside the lithium battery, and further calculates the volume of the internal micro-gas generation, thereby achieving accurate calculation of the volume of micro-gas generation inside the lithium battery. It has the advantages of accurate defect location and high detection accuracy.

[0006] To achieve the above objectives, the present invention adopts the following technical solution:

[0007] This invention provides a non-destructive testing method for micro-gas generation inside lithium batteries based on ultrasound, comprising the following steps:

[0008] Lithium batteries are subjected to ultrasonic scanning detection based on the ultrasonic echo-penetration method, which receives ultrasonic detection signals, including ultrasonic echo signals and ultrasonic penetration signals.

[0009] The received ultrasonic detection signal is converted into a digital signal through acoustic-to-electric conversion.

[0010] Wavelet decomposition is performed on the ultrasonic detection signal to extract wavelet coefficients at different levels;

[0011] Construct a wavelet threshold function, remove the wavelet coefficients below the threshold as interference noise, and obtain the wavelet coefficients of the denoised ultrasonic signal.

[0012] Wavelet reconstruction is performed based on the wavelet coefficients of the denoised ultrasonic signal to obtain the reconstructed ultrasonic echo signal and ultrasonic penetration signal.

[0013] The thickness of the micro-generated gas is calculated based on the signal amplitudes of the reconstructed ultrasonic echo signal and the ultrasonic penetration signal.

[0014] The amplitude of the reconstructed ultrasonic echo signal is taken as the average value T1 of the ultrasonic echo signal amplitude, and the amplitude of the reconstructed ultrasonic penetration signal is taken as the average value T2 of the ultrasonic penetration signal amplitude. When the intensity of the ultrasonic echo signal exceeds the average value T1 and the intensity of the ultrasonic penetration signal is lower than the average value T2, it is determined that there is internal micro-gas production in the region, and the area of ​​the region with micro-gas production is calculated.

[0015] The volume of internal micro-gas is calculated based on the thickness of the micro-gas and the area of ​​the region where micro-gas exists.

[0016] As a preferred technical solution, wavelet decomposition is performed on the ultrasonic detection signal to extract wavelet coefficients at different levels, specifically as follows:

[0017]

[0018] Where ω(a,b) represents the wavelet coefficients of the ultrasonic detection signal x(n), and <> represents the inner product. The ultrasonic detection signal x(n) includes the ultrasonic echo signal and the ultrasonic transmission signal obtained by the ultrasonic echo-transmission method. Describe the wavelet basis functions. express The complex conjugate of , where a represents the scale factor, b represents the displacement factor, and n represents time;

[0019] After wavelet decomposition, the ultrasonic echo signal and ultrasonic penetration signal are respectively used to generate wavelet coefficients ω at point k at the j-level decomposition scale. 1,j,k With ω 2,j,k .

[0020] As a preferred technical solution, the wavelet threshold function is expressed as:

[0021]

[0022] in, ω represents the wavelet transform coefficient at point k in the j-level decomposition scale after denoising. j,k The wavelet transform coefficients at point k in the j-level decomposition scale of the noisy image are given. Let L be the threshold value and L be the length of the signal.

[0023] The wavelet coefficients ω at point k at the j-level decomposition scale generated by wavelet decomposition of the ultrasonic echo signal and ultrasonic penetration signal respectively 1,j,k With ω 2,j,k The wavelet coefficients obtained after noise reduction are and

[0024] As a preferred technical solution, the calculation formula for wavelet reconstruction is expressed as follows:

[0025]

[0026] Where X(n) represents the ultrasonic signal obtained by wavelet reconstruction, The wavelet coefficients represent the noise-reduced ultrasonic signal. Let represent the wavelet basis function, a represent the scaling factor, b represent the shift factor, and n represent time.

[0027] As a preferred technical solution, the thickness of the micro-generated gas is calculated based on the signal amplitudes of the reconstructed ultrasonic echo signal and the ultrasonic penetration signal. The calculation formula is as follows:

[0028]

[0029] Among them, I to I represents the intensity of the transmitted wave passing through a normal lithium battery. ttThe amplitude of the reconstructed ultrasonic transmission signal, i.e., the intensity of the transmitted wave, is represented by η, which represents the gas interface reflectivity. a and K are the ultrasonic attenuation ratio coefficients of the battery under test, and d represents the thickness of the micro-generated gas in each region.

[0030] As a preferred technical solution, the volume of the internal micro-gas is calculated based on the thickness of the micro-gas and the area of ​​the region where the micro-gas exists. The calculation formula is expressed as follows:

[0031] V=∫d dS

[0032] Where d represents the thickness of the micro-gas produced in each region, S represents the area of ​​the region where micro-gas produced exists, and V represents the volume of the internal micro-gas produced.

[0033] As a preferred technical solution, after obtaining the reconstructed ultrasound echo signal and ultrasound penetration signal, the method further includes a step of constructing full-matrix ultrasound data, specifically including:

[0034] Each array element sequentially excites an ultrasonic signal, and all array elements receive the echo signal to form full ultrasonic matrix data.

[0035] A Cartesian coordinate system is established within the area to be measured, with the direction of ultrasonic signal propagation as the z-axis. The area to be measured is then discretized into a grid to obtain the amplitude of the ultrasonic echo signal.

[0036] As a preferred technical solution, after calculating the volume of internal micro-gas production, an alarm threshold judgment step is also included, specifically including:

[0037] Set a safe threshold for internal gas production volume, and determine whether the volume of micro-gas production inside the lithium battery under test exceeds the safe threshold for internal gas production volume. If it is determined that the volume exceeds the safe threshold for internal gas production volume, an alarm signal is output.

[0038] As a preferred technical solution, after calculating the volume of internal micro-gas production, a state image characterization step is further included, specifically comprising:

[0039] The reconstructed ultrasonic penetration signal amplitude is mapped to the corresponding color using a color mapping algorithm, forming a micro-gas production imaging image inside the lithium battery.

[0040] The present invention also provides an ultrasonic-based non-destructive testing system for micro-gas generation inside lithium batteries, comprising: an ultrasonic scanning module, a probe motion control module, and a host computer;

[0041] The ultrasonic scanning module includes a multi-channel ultrasonic flaw detector and a communication module, wherein the multi-channel ultrasonic flaw detector is equipped with multiple ultrasonic probes;

[0042] The host computer is connected to the multi-channel ultrasonic flaw detector through a communication module. The ultrasonic probe emits two rounds of pulse signals to the lithium battery under test and sequentially receives the ultrasonic echo signal and ultrasonic penetration signal reflected back by the emitted signal, which are then transmitted to the host computer through the communication module.

[0043] The probe motion control module is sequentially connected to a programmable logic controller, a servo driver, a servo motor, and a cross module. The programmable logic controller is connected to a host computer.

[0044] The host computer is equipped with a parameter initialization module, an ultrasonic detection control signal generation module, a synchronous acquisition control signal generation module, an ultrasonic data conversion module, a wavelet decomposition module, a wavelet threshold noise reduction module, a wavelet reconstruction module, a micro-gas thickness calculation module, a micro-gas region judgment module, a micro-gas region area calculation module, and a micro-gas volume calculation module.

[0045] The parameter initialization module is used to initialize the control parameters;

[0046] The ultrasonic detection control signal generation module is used to generate ultrasonic detection control signals, which are then transmitted to the multi-channel ultrasonic flaw detector via the communication module.

[0047] The synchronous acquisition control signal generation module is used to generate synchronous acquisition control signals and transmit them to the programmable logic controller. The programmable logic controller transmits the control signals to the servo driver, which drives the rotation of the servo motor to drive the ultrasonic probe to perform mechanical movement through the cross module.

[0048] The ultrasonic data conversion module is used to convert the received ultrasonic detection signal into an electroacoustic signal and then into a digital signal.

[0049] The wavelet decomposition module is used to perform wavelet decomposition on the ultrasonic detection signal and extract wavelet coefficients at different levels.

[0050] The wavelet threshold denoising module is used to construct a wavelet threshold function, remove wavelet coefficients smaller than the threshold as interference noise, and obtain the wavelet coefficients of the denoised ultrasonic signal.

[0051] The wavelet reconstruction module is used to reconstruct the wavelet coefficients of the denoised ultrasonic signal to obtain the reconstructed ultrasonic echo signal and ultrasonic penetration signal.

[0052] The micro-generated gas thickness calculation module is used to calculate the micro-generated gas thickness based on the signal amplitude of the reconstructed ultrasonic echo signal and ultrasonic penetration signal.

[0053] The micro-gas-producing region determination module is used to determine the micro-gas-producing region. The signal amplitude of the reconstructed ultrasonic echo signal is used as the average value T1 of the ultrasonic echo signal amplitude, and the signal amplitude of the reconstructed ultrasonic penetration signal is used as the average value T2 of the ultrasonic penetration signal amplitude. When the intensity of the ultrasonic echo signal exceeds the average value T1 and the intensity of the ultrasonic penetration signal is lower than the average value T2, it is determined that there is internal micro-gas in the region.

[0054] The micro-gas-producing area calculation module is used to calculate the area of ​​the region where micro-gas production exists.

[0055] The micro-gas volume calculation module is used to calculate the internal volume of micro-gas based on the thickness of the micro-gas and the area of ​​the region where the micro-gas exists.

[0056] Compared with the prior art, the present invention has the following advantages and beneficial effects:

[0057] (1) Existing technologies often use ultrasonic echo or ultrasonic penetration methods alone to detect defects such as gas generation inside lithium batteries, which have problems such as incomplete defect detection and low detection accuracy. This invention organically integrates the advantages of ultrasonic echo and ultrasonic penetration methods, calculates the thickness and area of ​​the micro-gas generation area inside the lithium battery, and then further calculates the volume of the micro-gas generation inside the lithium battery, so as to realize the accurate calculation of the volume of micro-gas generation inside the lithium battery, which has the advantages of accurate defect location and high detection accuracy.

[0058] (2) The ultrasonic signal filtering algorithm based on the improved wavelet threshold function of this invention corrects the constant deviation problem caused by the conventional threshold function, thereby effectively maintaining the waveform characteristics of the signal while effectively reducing noise in the ultrasonic detection signal of lithium battery. Compared with the existing technology that uses the conventional threshold function for noise reduction, this filtering algorithm has the characteristics of good noise reduction effect and fast speed, thereby further improving the accuracy and anti-interference ability of the ultrasonic non-destructive testing system for lithium battery. Attached Figure Description

[0059] Figure 1 This is a flowchart illustrating the ultrasonic-based non-destructive testing method for micro-gas generation inside lithium batteries according to the present invention.

[0060] Figure 2 This is a flowchart illustrating the ultrasonic signal filtering algorithm based on the improved wavelet threshold function of this invention.

[0061] Figure 3 This is a schematic diagram of the wavelet decomposition process of the present invention;

[0062] Figure 4 This is a schematic diagram of the process for characterizing the micro-gas generation inside the lithium battery according to the present invention.

[0063] Figure 5 This is a schematic diagram of the architecture of the ultrasonic-based non-destructive testing system for micro-gas generation inside lithium batteries according to the present invention.

[0064] Figure 6 This is a schematic diagram of the motion control process of the dual-axis synchronous probe of the present invention;

[0065] Figure 7 This is a schematic diagram of the architecture of the ultrasonic-based non-destructive testing system for micro-gas generation inside a lithium battery, which includes an early warning module and a status image characterization module. Detailed Implementation

[0066] 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.

[0067] Example 1

[0068] like Figure 1 As shown, this invention provides a non-destructive testing method for micro-gas generation inside a lithium battery based on ultrasound, comprising the following steps:

[0069] S1: Initialize the control parameters via the host computer;

[0070] S2: Set the X-axis and Y-axis displacement distance, scanning step size and scanning speed of the ultrasound scan, set the ultrasonic signal frequency and excitation voltage, and control the ultrasonic probe to emit and receive ultrasonic signals.

[0071] In this embodiment, the lithium battery under test is immersed in a coupling agent silicone oil. The lithium battery is ultrasonically scanned using the ultrasonic reflection method combined with C-type scanning. The host computer sends a control signal to the multi-channel ultrasonic flaw detector via Ethernet. The ultrasonic probe emits two rounds of pulse signals to the lithium battery under test and sequentially receives the ultrasonic echo signal and ultrasonic penetration signal reflected back from the emitted signal.

[0072] S3: The servo motor drives the cross module to move the ultrasonic probe through the dual-axis synchronous probe motion control algorithm, so as to realize ultrasonic surface scanning detection of lithium battery;

[0073] S4: The ultrasonic probe converts acoustic signals into electrical signals, transforming the analog signals collected after scanning into digital signals;

[0074] In this embodiment, the multi-channel ultrasonic flaw detector collects the current generated by the ultrasonic probe due to the piezoelectric effect and converts it into an electrical signal to perform acoustic-to-electric conversion on the received ultrasonic detection signal. It then performs digital-to-analog conversion on the electrical signal through a built-in digital-to-analog converter, converting the collected analog signal into a digital signal. Finally, it uploads the processed signal to the industrial control computer via Ethernet.

[0075] S5: Signal Denoising: Digital signal denoising is performed using an improved ultrasonic signal filtering algorithm with a wavelet threshold function;

[0076] like Figure 2 As shown, an ultrasonic signal filtering algorithm based on an improved wavelet threshold function is used to effectively reduce noise in ultrasonic detection signals, specifically including:

[0077] like Figure 3 As shown, wavelet decomposition is performed on the ultrasonic detection signal. In the figure, x(n) is the ultrasonic detection signal, h0(n) represents the low-pass filter, and h l (n) represents a high-pass filter, A3 is the scaling coefficient, and D1, D2, and D3 are wavelet coefficients;

[0078] The wavelet decomposition process in this embodiment is specifically represented as follows:

[0079]

[0080] Where ω(a,b) represents the wavelet coefficients of the ultrasonic detection signal x(n), and <> represents the inner product. The ultrasonic detection signal x(n) includes the ultrasonic echo signal and the ultrasonic transmission signal obtained by the ultrasonic echo-transmission method. Describe the wavelet basis functions. express Let be the complex conjugate of , where a represents the scale factor, b represents the displacement factor, and n represents time. Let the received ultrasonic echo signal be x1(n) and the ultrasonic penetration signal be x2(n). After wavelet decomposition, the wavelet coefficients at point k at the j-level decomposition scale are ω. 1,j,k With ω 2,j,k .

[0081] In this embodiment, wavelet decomposition first decomposes the echo signal and ultrasonic penetration signal obtained by the ultrasonic echo-penetration method into several layers according to different frequency bands. The wavelet coefficients of different layers can be extracted to analyze the signal. The wavelet decomposition of a one-dimensional discrete signal divides the signal into low-frequency and high-frequency parts. If multiple decompositions are performed, the result of each layer of decomposition is that the low-frequency signal obtained in the previous decomposition is further decomposed into low-frequency and high-frequency parts until the required number of decompositions is reached. Since the increase in the number of decomposition levels will lead to the attenuation of the signal amplitude, only the detail coefficients generated in the first decomposition are used as wavelet coefficients. Because most of the noise in the signal is concentrated in the high-frequency components of the signal, wavelet coefficients with larger amplitudes are generally dominated by the signal, while coefficients with smaller amplitudes are largely noise. In this embodiment, the Daubechies wavelet is selected for wavelet decomposition.

[0082] Then, a thresholding method is used to reduce most noise coefficients to 0, that is, coefficients below the threshold are removed as interference noise. This embodiment removes interference noise based on an improved wavelet thresholding function, which is expressed as:

[0083]

[0084] in, ω represents the wavelet transform coefficient at point k in the j-level decomposition scale after denoising. j,k The wavelet transform coefficients at point k in the j-level decomposition scale of the noisy image are given. Let L be the threshold value and L be the length of the signal.

[0085] The wavelet coefficients ω at point k in the j-level decomposition scale generated after wavelet decomposition of the ultrasonic echo signal and ultrasonic penetration signal 1,j,k With ω 2,j,k The wavelet coefficients obtained after noise reduction are and

[0086] When ω=λ + hour, exist The place is continuous, and because It is an odd function, so obviously according to exist The continuity of the function can reduce the problems of spikes, peaks, and oscillations that occur during signal reconstruction caused by the hard threshold function. Therefore, the above formula proves that the threshold function in this embodiment is continuous, avoiding the discontinuity caused by the hard threshold function, thereby avoiding problems such as spikes during reconstruction.

[0087] Finally, wavelet reconstruction is performed to achieve noise reduction. The calculation formula for wavelet reconstruction is expressed as:

[0088]

[0089] Where X(n) represents the ultrasonic signal obtained by wavelet reconstruction, The wavelet coefficients represent the noise-reduced ultrasonic signal. Let represent the wavelet basis function, a represent the scaling factor, b represent the shift factor, and n represent time.

[0090] The wavelet coefficients ω at point k at the j-level decomposition scale generated after wavelet decomposition of the ultrasonic echo signal and ultrasonic penetration signal 1,j,k With ω 2,j,k Wavelet coefficients obtained after noise reduction and Substituting these values, we obtain X1(n) and X2(n), which are the reconstructed ultrasonic echo signal and ultrasonic penetration signal, respectively.

[0091] S6: Comprehensive detection of gas generation inside lithium battery: The volume of micro-gas generation is calculated based on the comprehensive detection algorithm of gas generation inside lithium battery using the ultrasonic echo-penetration method.

[0092] The comprehensive detection algorithm for micro-gas generation inside lithium batteries based on the ultrasonic echo-penetration method accurately calculates the distribution area and volume of gas generation inside lithium batteries. It organically integrates the advantages of the ultrasonic echo method and the ultrasonic penetration method to achieve accurate calculation of the volume of micro-gas generation inside lithium batteries. Specifically, it includes:

[0093] (1) Ultrasonic signal amplitude receiving and processing method:

[0094] The system receives and stores ultrasonic signal data and its amplitude for subsequent calculations based on the ultrasonic signal intensity. The full matrix data contains all acoustic information within the area to be measured. After the first element excites the ultrasonic signal, all elements receive the echo signal, denoted as S. 1n Then, the second array element excites an ultrasonic signal, which is received by all array elements. The received signal is denoted as S. 2n This process continues until the Nth array element excites an ultrasonic signal, which is then received by all array elements. Through these steps, a complete set of ultrasonic full-matrix data can be obtained, denoted as S. ij(t0) This represents the amplitude of the ultrasonic signal received at time t0 when the i-th array element excites and the j-th array element receives it. A Cartesian coordinate system is established within the test area, with the ultrasonic signal propagation direction as the z-axis, and the test area is discretized into a grid. For any discrete point P(x) within this area... p ,y p ), calculate the ultrasound signal from TX(x) tx ,z tx ) is sent and arrives at P(x) p ,z p Reflection at point RX(x) and then back to RX(x) rx ,z rx The amplitude of the ultrasonic signal received at point t0 is obtained after the noise reduction process described above. This amplitude is the intensity of the ultrasonic signal received at point t0, which is used to calculate the micro-gas production volume.

[0095] In this embodiment, the formula for calculating time t0 is expressed as follows:

[0096]

[0097] Where c is the sound velocity in the region to be measured, in m / s, and the region to be measured is assumed to be an isotropic medium.

[0098] (2) Comprehensive Calculation Method for Micro-Gas Production Volume

[0099] First, the ultrasonic transmission method is used. An ultrasonic probe emits ultrasonic waves from one side of the lithium-ion battery, and an ultrasonic probe on the other side receives the transmitted ultrasonic signal. After noise reduction, the amplitude of the received ultrasonic transmission signal at that point is obtained, which is the intensity of the received ultrasonic transmission signal at that point. The preset ultrasonic emission intensity is denoted as I0. The amplitude of the reconstructed ultrasonic transmission signal X2(n) is the transmitted wave intensity, denoted as I. tt The intensity of the transmitted wave passing through a normal lithium battery was measured in advance and denoted as I. to η is the gas interface reflectivity, and a and K are the ultrasonic attenuation coefficients of the battery, thus the gas thickness d in each region is obtained:

[0100]

[0101] Next, the area of ​​micro-gas production is detected and determined using the ultrasonic echo method and the penetration method, along with the area boundary correction method. Specifically, this involves: an ultrasonic probe emitting ultrasonic waves on one side of the lithium-ion battery, which are received by another ultrasonic probe on the same side. After noise reduction, the amplitude of the received ultrasonic echo signal at that point is obtained, representing the intensity of the received ultrasonic echo signal. An ultrasonic probe emitting ultrasonic waves on one side of the lithium-ion battery is received by another ultrasonic probe on the other side. After noise reduction, the amplitude of the received ultrasonic penetration signal at that point is obtained, representing the intensity of the received ultrasonic penetration signal. Based on the reconstructed ultrasonic echo signal and ultrasonic penetration signals X1(n) and X2(n), the average amplitudes T1 and T2 of the received ultrasonic echo signal and ultrasonic penetration signal are calculated, respectively. When the echo intensity exceeds T1 and the transmitted wave intensity is lower than T2 after the probe is moved, it can be determined that there is internal micro-gas production in that area. The area S occupied by the internal micro-gas production is obtained based on the area of ​​the area where micro-gas production is determined to exist. The volume V of the internal micro-gas production is then calculated as follows:

[0102] V=∫d dS

[0103] When the internal micro-gas production volume V exceeds the warning value, an alarm signal is issued to provide early warning.

[0104] In this embodiment, an alarm threshold determination step and a status image representation step are also provided;

[0105] The alarm threshold judgment steps specifically include: setting a safe threshold for internal gas production volume, judging whether the volume of micro-gas production inside the lithium battery under test exceeds the safe threshold for internal gas production volume, and outputting an alarm signal if it is determined to exceed the safe threshold for internal gas production volume, which can be sounded through a speaker; if it does not exceed the safe threshold for internal gas production volume, no sound alarm will be sounded.

[0106] The state image representation steps specifically include:

[0107] The reconstructed ultrasonic penetration signal amplitude is mapped to the corresponding color using a color mapping algorithm to form a micro-gas generation imaging image inside the lithium battery. The imaging image is then displayed on a screen, and the detected data is finally stored.

[0108] like Figure 4 As shown, the internal state image of the lithium battery is displayed on the user interface with high difference significance through the internal state image characterization algorithm. The color of each point in the image is distributed from blue to red according to the echo signal from weak to strong. At the same time, an imaging map of the lithium battery and its internal gas production with clear boundaries is also generated.

[0109] The transmitted sound pressure amplitude (f(x,y)) at various points in the lithium battery, obtained through the internal gas production volume algorithm, is mapped to corresponding colors, with different values ​​corresponding to different colors. According to colorimetry principles, any color can be synthesized from the three primary colors of red, green, and blue in different proportions. Therefore, the color mapping algorithm first sets three color-changing functions (TR function, TG function, TB function) for red, green, and blue. These three functions are sine functions with different phase values. Each f(x,y) value is processed by the TR function, TG function, and TB function, respectively, and the function results are exported. Then, the function results are processed through a general, predetermined RGB display function to obtain the final color. This color is then processed by the client's main program display interface and exported to the display screen, thus achieving a correspondence between a specific f(x,y) value and a specific color. The color-changing functions are represented as follows:

[0110] R(x,y)=TR{f(x,y)}

[0111] G(x,y)=TG{f(x,y)}

[0112] B(x,y)=TB{f(x,y)}

[0113] (R,G,B)={R(x,y),G(x,y),B(x,y)}.

[0114] Example 2

[0115] like Figure 5 , Figure 6 As shown, this embodiment provides a non-destructive testing system for micro-gas generation inside a lithium battery based on ultrasound, including: an ultrasonic scanning module, a probe motion control module, and a host computer;

[0116] The ultrasonic scanning module includes a multi-channel ultrasonic flaw detector and a communication module. The multi-channel ultrasonic flaw detector is equipped with multiple ultrasonic probes, preferably two in this embodiment. The communication module can be an Ethernet communication module or a local area network communication module.

[0117] The probe motion control module includes: a programmable logic controller, a servo driver, a servo motor, and a cross module;

[0118] The host computer is equipped with a parameter initialization module, an ultrasonic detection control signal generation module, a synchronous acquisition control signal generation module, an ultrasonic data conversion module, a wavelet decomposition module, a wavelet threshold noise reduction module, a wavelet reconstruction module, a micro-gas thickness calculation module, a micro-gas region judgment module, a micro-gas region area calculation module, and a micro-gas volume calculation module.

[0119] The host computer's parameter initialization module initializes the control parameters; the ultrasonic detection control signal generation module generates the ultrasonic detection control signal, which is transmitted to the multi-channel ultrasonic flaw detector through the communication module. The ultrasonic probe emits two rounds of pulse signals to the lithium battery under test and sequentially receives the ultrasonic echo signal and ultrasonic penetration signal reflected back by the emitted signal.

[0120] like Figure 6 As shown, the synchronous acquisition control signal generation module generates a synchronous acquisition control signal, which is transmitted to the programmable logic controller (PLC) via the CAN bus. The PLC then transmits the control signal to the servo driver, which in turn drives the servo motor to rotate, thereby enabling the cross module to drive the ultrasonic probe to perform mechanical movement.

[0121] Ultrasonic scanning of lithium batteries is performed by emitting ultrasonic pulse signals into the lithium battery under test using an ultrasonic probe and receiving the reflected ultrasonic echo signals to obtain the battery's internal state data. The data is then transmitted to a host computer via a communication module. After scanning one area, the probe is moved to the next area using a cross-shaped module for scanning. Based on the ultrasonic echo-penetration method, two probes placed on either side of the lithium battery are used for synchronous movement, with the two probes transmitting and receiving ultrasonic echo and ultrasonic penetration signals respectively, thus achieving the acquisition of ultrasonic signals using the ultrasonic echo-penetration method.

[0122] In this embodiment, the probes are mounted on probe holders on both sides of the battery. The probe holders are connected to the cross module, and under the drive of control signals, they move to complete the scanning of all areas of the battery. The host computer sends motion control parameters such as speed and scanning range to the programmable logic controller and outputs control signals to the servo motor driver to control the movement of a pair of servo motors. The pair of servo motors are connected to the cross module, which includes a horizontal axis and a vertical axis. The vertical axis is connected to the sliding table of the horizontal axis. The ultrasonic probe is connected to the sliding table of the vertical axis through a mounting component. The movement of the sliding table of each axis is controlled by the connected servo motor, realizing precise motion control of the ultrasonic probe in the vertical plane. Specifically, this includes:

[0123] (1) Parameter input

[0124] The host computer inputs the horizontal distance of the scanning range as a, the vertical distance as b, the moving speed as v, the single scan time as t, and the side length of the scanning area as c.

[0125] (2) Parameter passing

[0126] The horizontal distance a, vertical distance b, movement speed v, and single scan time t are transmitted to the corresponding variables of the programmable logic controller via the EtherCat protocol.

[0127] (3) Movement process

[0128] Turn on motion switch M0. The horizontal axis motor moves the first distance c. After the movement is completed, the delay switch M2 is triggered, and the motion control loop begins. During the loop, after the delay switch M2 is triggered, the motion enters a stationary state. After a single scan time t, the motion switch M3 within the loop is triggered to perform the next horizontal movement of distance c. After the movement is completed, the switch M4 is triggered to close switches M2 and M3 and turn on judgment switch M6: If the current horizontal distance is less than the horizontal distance a, then switch M2 is turned on to continue the horizontal movement loop; if the current horizontal distance is equal to or greater than the horizontal distance a, the loop stops, returns to the origin, and switch M7 is turned on to perform a vertical movement of distance c. After the vertical movement ends, the judgment switch M8 is turned on: If the current vertical distance is equal to or greater than the vertical distance b, the loop returns to the origin and the detection ends; if the current vertical distance is less than the vertical distance b, then switch M2 is turned on to enter the next loop.

[0129] In this embodiment, the ultrasonic data conversion module of the host computer is used to convert the received ultrasonic detection signal into an electroacoustic signal and then into a digital signal.

[0130] The wavelet decomposition module is used to perform wavelet decomposition on the ultrasonic detection signal and extract wavelet coefficients at different levels.

[0131] The wavelet threshold denoising module is used to construct a wavelet threshold function, remove wavelet coefficients smaller than the threshold as interference noise, and obtain the wavelet coefficients of the denoised ultrasonic signal.

[0132] The wavelet reconstruction module is used to reconstruct the wavelet coefficients of the denoised ultrasonic signal to obtain the reconstructed ultrasonic echo signal and ultrasonic penetration signal.

[0133] The micro-gas thickness calculation module is used to calculate the micro-gas thickness based on the signal amplitudes of the reconstructed ultrasonic echo signal and ultrasonic penetration signal.

[0134] The micro-gas-producing region judgment module is used to judge the micro-gas-producing region. The signal amplitude of the reconstructed ultrasonic echo signal is used as the average value T1 of the ultrasonic echo signal amplitude, and the signal amplitude of the reconstructed ultrasonic penetration signal is used as the average value T2 of the ultrasonic penetration signal amplitude. When the intensity of the ultrasonic echo signal exceeds the average value T1 and the intensity of the ultrasonic penetration signal is lower than the average value T2, it is determined that there is internal micro-gas in the region.

[0135] The micro-gas-producing area calculation module is used to calculate the area of ​​regions where micro-gas production exists.

[0136] The micro-gas production volume calculation module is used to calculate the internal micro-gas volume based on the thickness of the micro-gas and the area of ​​the region where the micro-gas exists.

[0137] The above implementation process is the same as that in Example 1, and will not be repeated here.

[0138] like Figure 7 As shown, this embodiment also includes an early warning module and a status image representation module;

[0139] The early warning module is used to set a safe threshold for the internal gas production volume and determine whether the volume of micro-gas production inside the lithium battery under test exceeds the safe threshold for the internal gas production volume. If it is determined that the volume exceeds the safe threshold for the internal gas production volume, an alarm signal is output.

[0140] The state image representation module is used to map the signal amplitude of the reconstructed ultrasonic penetration signal into the corresponding color according to the color mapping algorithm, forming a micro-gas generation imaging image inside the lithium battery.

[0141] The above implementation process is the same as that in Example 1, and will not be repeated here.

[0142] The above embodiments are preferred embodiments of the present invention, but the embodiments of the present invention are not limited to the above embodiments. Any changes, modifications, substitutions, combinations, or simplifications made without departing from the spirit and principle of the present invention shall be considered equivalent substitutions and shall be included within the protection scope of the present invention.

Claims

1. An ultrasonic-based non-destructive testing method for detecting internal micro-gas generation in a lithium battery, characterized in that, Includes the following steps: Lithium batteries are subjected to ultrasonic scanning detection based on the ultrasonic echo-penetration method, which receives ultrasonic detection signals, including ultrasonic echo signals and ultrasonic penetration signals. The received ultrasonic detection signal is converted into a digital signal through acoustic-to-electric conversion. Wavelet decomposition is performed on the ultrasonic detection signal to extract wavelet coefficients at different levels; Construct a wavelet threshold function, remove the wavelet coefficients below the threshold as interference noise, and obtain the wavelet coefficients of the denoised ultrasonic signal. Wavelet reconstruction is performed based on the wavelet coefficients of the denoised ultrasonic signal to obtain the reconstructed ultrasonic echo signal and ultrasonic penetration signal. After obtaining the reconstructed ultrasound echo signal and ultrasound penetration signal, the process also includes a step of constructing the full ultrasound matrix data, specifically including: Each array element sequentially excites an ultrasonic signal, and all array elements receive the echo signal to form full ultrasonic matrix data. A Cartesian coordinate system is established within the area to be measured, with the direction of ultrasonic signal propagation as the z-axis. The area to be measured is then discretized into a grid to obtain the amplitude of the ultrasonic echo signal. The formula for wavelet reconstruction is expressed as follows: ； in, This represents the ultrasonic signal obtained from wavelet reconstruction. The wavelet coefficients represent the noise-reduced ultrasonic signal. Let represent the wavelet basis functions, a represent the scaling factor, and b represent the shift factor. Indicates time; The thickness of the micro-generated gas is calculated based on the signal amplitudes of the reconstructed ultrasonic echo signal and ultrasonic penetration signal. The calculation formula is as follows: ； in, This indicates the intensity of the transmitted wave when it passes through a normal lithium battery. This represents the amplitude of the reconstructed ultrasonic transmission signal, i.e., the intensity of the transmitted wave. Indicates the reflectivity of the gas interface. K is the ultrasonic attenuation ratio coefficient of the battery under test, and d represents the thickness of the micro-generated gas in each region; The amplitude of the reconstructed ultrasonic echo signal is taken as the average value T1 of the ultrasonic echo signal amplitude, and the amplitude of the reconstructed ultrasonic penetration signal is taken as the average value T2 of the ultrasonic penetration signal amplitude. When the intensity of the ultrasonic echo signal exceeds the average value T1 and the intensity of the ultrasonic penetration signal is lower than the average value T2, it is determined that there is internal micro-gas production in the region, and the area of ​​the region with micro-gas production is calculated. The volume of the internal micro-gas is calculated based on the thickness of the micro-gas and the area of ​​the region where the micro-gas exists. The calculation formula is expressed as follows: ； Where d represents the thickness of the micro-gas produced in each region, S represents the area of ​​the region where micro-gas produced exists, and V represents the volume of the internal micro-gas produced.

2. The ultrasonic-based non-destructive testing method for micro-gas generation inside lithium batteries according to claim 1, characterized in that, Wavelet decomposition is performed on the ultrasonic detection signal to extract wavelet coefficients at different levels, as specifically expressed as follows: ； in, Indicates ultrasonic detection signal Wavelet coefficients, < > denote the inner product, ultrasonic detection signal This includes the ultrasonic echo signal and ultrasonic penetration signal obtained by the ultrasonic echo-penetration method. Describe the wavelet basis functions. express The complex conjugate of , where a represents the scale factor and b represents the displacement factor. Indicates time; After wavelet decomposition, the ultrasonic echo signal and ultrasonic penetration signal are respectively used to generate wavelet coefficients at point k at the j-level decomposition scale. and .

3. The ultrasonic-based non-destructive testing method for micro-gas generation inside lithium batteries according to claim 1, characterized in that, The wavelet threshold function is expressed as follows: ； in, This represents the wavelet transform coefficients at point k in the j-level decomposition scale after denoising. The wavelet transform coefficients at point k in the j-level decomposition scale of the noisy image are given. = Let L be the threshold value and L be the length of the signal. Wavelet coefficients at point k at the j-level decomposition scale generated from the ultrasonic echo signal and ultrasonic penetration signal, respectively. and The wavelet coefficients obtained after noise reduction are and .

4. The ultrasonic-based non-destructive testing method for micro-gas generation inside a lithium battery according to any one of claims 1-3, characterized in that, After calculating the volume of internal micro-gas production, an alarm threshold determination step is also included, specifically: Set a safe threshold for internal gas production volume, and determine whether the volume of micro-gas production inside the lithium battery under test exceeds the safe threshold for internal gas production volume. If it is determined that the volume exceeds the safe threshold for internal gas production volume, an alarm signal is output.

5. The ultrasonic-based non-destructive testing method for micro-gas generation inside a lithium battery according to any one of claims 1-3, characterized in that, After calculating the volume of internal micro-gas production, a state image characterization step is also included, specifically: The reconstructed ultrasonic penetration signal amplitude is mapped to the corresponding color using a color mapping algorithm, forming a micro-gas production imaging image inside the lithium battery.

6. A non-destructive testing system for micro-gas generation inside a lithium battery based on ultrasound, characterized in that, The method for implementing the ultrasonic-based non-destructive testing method for micro-gas generation inside a lithium battery according to any one of claims 1-5 includes: an ultrasonic scanning module, a probe motion control module, and a host computer. The ultrasonic scanning module includes a multi-channel ultrasonic flaw detector and a communication module, wherein the multi-channel ultrasonic flaw detector is equipped with multiple ultrasonic probes; The host computer is connected to the multi-channel ultrasonic flaw detector through a communication module. The ultrasonic probe emits two rounds of pulse signals to the lithium battery under test and sequentially receives the ultrasonic echo signal and ultrasonic penetration signal reflected back by the emitted signal, which are then transmitted to the host computer through the communication module. The probe motion control module is sequentially connected to a programmable logic controller, a servo driver, a servo motor, and a cross module. The programmable logic controller is connected to a host computer. The host computer is equipped with a parameter initialization module, an ultrasonic detection control signal generation module, a synchronous acquisition control signal generation module, an ultrasonic data conversion module, a wavelet decomposition module, a wavelet threshold noise reduction module, a wavelet reconstruction module, a micro-gas thickness calculation module, a micro-gas region judgment module, a micro-gas region area calculation module, and a micro-gas volume calculation module. The parameter initialization module is used to initialize the control parameters; The ultrasonic detection control signal generation module is used to generate ultrasonic detection control signals, which are then transmitted to the multi-channel ultrasonic flaw detector via the communication module. The synchronous acquisition control signal generation module is used to generate synchronous acquisition control signals and transmit them to the programmable logic controller. The programmable logic controller transmits the control signals to the servo driver, which drives the rotation of the servo motor to drive the ultrasonic probe to perform mechanical movement through the cross module. The ultrasonic data conversion module is used to convert the received ultrasonic detection signal into an electroacoustic signal and then into a digital signal. The wavelet decomposition module is used to perform wavelet decomposition on the ultrasonic detection signal and extract wavelet coefficients at different levels. The wavelet threshold denoising module is used to construct a wavelet threshold function, remove wavelet coefficients smaller than the threshold as interference noise, and obtain the wavelet coefficients of the denoised ultrasonic signal. The wavelet reconstruction module is used to reconstruct the wavelet coefficients of the denoised ultrasonic signal to obtain the reconstructed ultrasonic echo signal and ultrasonic penetration signal. The micro-generated gas thickness calculation module is used to calculate the micro-generated gas thickness based on the signal amplitude of the reconstructed ultrasonic echo signal and ultrasonic penetration signal. The micro-gas-producing region determination module is used to determine the micro-gas-producing region. The signal amplitude of the reconstructed ultrasonic echo signal is used as the average value T1 of the ultrasonic echo signal amplitude, and the signal amplitude of the reconstructed ultrasonic penetration signal is used as the average value T2 of the ultrasonic penetration signal amplitude. When the intensity of the ultrasonic echo signal exceeds the average value T1 and the intensity of the ultrasonic penetration signal is lower than the average value T2, it is determined that there is internal micro-gas in the region. The micro-gas-producing area calculation module is used to calculate the area of ​​the region where micro-gas production exists. The micro-gas volume calculation module is used to calculate the internal volume of micro-gas based on the thickness of the micro-gas and the area of ​​the region where the micro-gas exists.

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