In-situ non-destructive diagnosis method for sodium ion battery low-temperature charging sodium precipitation

Abstract

This invention provides an in-situ non-destructive diagnostic method for sodium deposition during low-temperature charging of sodium-ion batteries, belonging to the field of battery diagnostic technology. In this invention, ultrasonic emission, reflection, and transmission receiving modules are arranged along the thickness direction of the battery under test, connected to an electrochemical workstation, constructing a dual-mode ultrasonic detection architecture of transmission and reflection to achieve in-situ non-destructive testing. The battery is adjusted to a fully discharged state, placed in a high-low temperature test chamber, and a room-temperature control group is set up. It is charged with a preset constant current, and AC disturbances are simultaneously applied to drive ultrasonic pulses. Cyclic testing is performed at set time intervals to achieve in-situ, continuous, and synchronous acquisition of electrochemical and ultrasonic data. Charge transfer impedance is extracted based on impedance spectroscopy, interface main echo and layered slice imaging are obtained based on ultrasonic reflection data, and a two-dimensional sound velocity distribution image is established based on ultrasonic transmission data. A multi-signal joint criterion is used to determine sodium deposition and distinguish between early and late stages, effectively improving the accuracy and flexibility of low-temperature sodium deposition diagnosis.

Description

Technical Field

[0001] This invention belongs to the field of battery diagnostic technology, specifically relating to an in-situ non-destructive diagnostic method for sodium deposition during low-temperature charging of sodium-ion batteries. Background Technology

[0002] Sodium-ion batteries are prone to sodium precipitation and dendrite growth at the negative electrode under low temperature and high-rate charging conditions, which leads to battery capacity decay, shortened cycle life, and in severe cases, internal short circuits and safety hazards. Therefore, there is an urgent need for accurate and in-situ sodium precipitation diagnosis methods.

[0003] Existing methods for detecting sodium deposition in sodium-ion batteries mostly employ external monitoring, such as the technical solution described in Chinese invention patent application number "202510078455.3". This method involves using a flexible encapsulated cell and applying a fixed external pressure. A pressure sensor is used to monitor the cell's expansion and volume changes, and sodium deposition is determined based on the irreversible pressure increase, thus achieving indirect detection of sodium deposition.

[0004] However, existing technologies rely solely on external pressure / volume changes to determine sodium deposition, which is susceptible to interference from battery expansion, stress relaxation, and temperature fluctuations. They cannot distinguish between normal lithium intercalation / deintercalation volume changes and abnormal expansion caused by sodium deposition, resulting in poor sensitivity and accuracy. Furthermore, they can easily damage the battery, which is detrimental to its subsequent use. Summary of the Invention

[0005] The technical problem to be solved by this invention is how to achieve non-destructive testing of sodium-ion batteries with sodium deposition while ensuring the sensitivity and accuracy of sodium deposition detection. In view of the shortcomings of the prior art, this invention provides an in-situ non-destructive diagnostic method for sodium deposition during low-temperature charging of sodium-ion batteries.

[0006] To solve the above-mentioned technical problems, the technical solution adopted by the present invention is as follows: This invention provides an in-situ non-destructive diagnostic method for sodium deposition during low-temperature charging of sodium-ion batteries, comprising: S1. Along the thickness direction of the battery under test, an ultrasonic transmitting module and a reflection receiving module are coupled and installed on one side of the battery under test, and a transmission receiving module is coupled and installed on the opposite side of the battery under test, connecting the electrochemical workstation to the battery under test. S2. Adjust the battery under test to a fully discharged state, and at the same time adjust the temperature of the high and low temperature test chamber to the preset target temperature. Place the battery under test into the high and low temperature test chamber and let it stand for a preset standing time. Simultaneously set the room temperature control group. S3. The battery under test is charged with a constant current using a preset current. At the same time, an AC disturbance of a preset amplitude is applied through the electrochemical workstation within a preset frequency range to synchronously drive the ultrasonic emission module to output ultrasonic pulses. The above process is repeated at preset time intervals during the charging process of the battery under test. S4. Measure and record the impedance spectrum of the battery under test based on the electrochemical workstation, and record the ultrasonic reflection data and ultrasonic transmission data through the reflection receiving module and the transmission receiving module respectively. S5. Obtain the charge transfer impedance based on the impedance spectrum, and simultaneously obtain the interface main echo and layered slice imaging results based on the ultrasonic reflection data, and establish a two-dimensional sound velocity distribution image based on the ultrasonic transmission data. S6. When the charge transfer impedance, the interface main echo, and the local sound velocity of the two-dimensional sound velocity distribution image are all abnormal, it is determined that the battery under test has undergone sodium deposition. S7. When it is determined that sodium deposition has occurred in the battery under test, the sodium deposition area is located based on the abnormal sound velocity area in the two-dimensional sound velocity distribution image, and the sodium deposition distribution in the depth direction is obtained based on the layered slice imaging results.

[0007] Compared to existing technologies, the beneficial effects of this invention include: First, along the thickness direction of the battery under test, an ultrasonic transmitting module and a reflection receiving module are coupled and installed on one side, and a transmission receiving module is coupled and installed on the other side. The electrochemical workstation is connected to the electrode of the battery under test. This setup can construct a dual-mode ultrasonic detection architecture of transmission and reflection, simultaneously realizing electrochemical excitation and signal acquisition. This solves the problems that a single ultrasonic mode cannot simultaneously acquire interface reflection and overall transmission information, and that a single electrochemical method cannot locate physical defects, providing a hardware foundation for multi-signal fusion diagnosis. Based on this, the battery is adjusted to a fully discharged state, the high and low temperature test chamber is adjusted to the target temperature, and the battery is placed inside and left to stand. A room temperature control group is simultaneously set up, thereby eliminating systematic errors caused by the initial state and temperature gradient, ensuring the stability of the test baseline under low-temperature conditions, and solving the problem of diagnostic distortion caused by inconsistent initial states at low temperatures. Next, the battery is charged with a preset constant current. An AC disturbance of preset frequency and amplitude is applied through the electrochemical workstation, synchronously driving the ultrasonic transmitting module to output pulses, and then... Repeated time-interval tests enable in-situ, synchronous, and continuous acquisition of electrochemical and ultrasonic data during charging, addressing the issues of offline detection lag and inability to capture dynamic sodium deposition processes. Then, an electrochemical workstation records impedance spectra, while a reflection / transmission receiving module records ultrasonic reflection and transmission data respectively, achieving synchronous acquisition and alignment of the two types of signals to provide a data source for subsequent joint analysis. Subsequently, charge transfer impedance is extracted from the impedance spectrum, interface main echo and layered slice imaging results are extracted from the ultrasonic reflection data, and a two-dimensional sound velocity distribution image is established from the transmission data, completing the synchronous quantification of electrochemical and physical structural features and addressing the problem of single signals being susceptible to temperature and polarization interference. Next, when charge transfer impedance, interface main echo, and local sound velocity are all abnormal, sodium deposition is determined. A three-signal joint criterion is used to eliminate false positives from a single signal, improving confidence. Finally, the planar sodium deposition location is determined based on the sound velocity anomaly area, and the depth distribution is obtained based on the layered slices, achieving three-dimensional localization of the sodium deposition plane and depth, solving the problem that traditional methods cannot accurately locate the sodium deposition area and distribution.

[0008] Optionally, the preset target temperature includes any value from -20 to 45°C, the preset resting time includes any value from 8 to 24 hours, the preset current includes any value from 0.2 to 1C, the preset frequency range is 20kHz to 0.1Hz, the preset time interval is any value from 30s to 10min, and the preset amplitude is any value from 5 to 10mV.

[0009] Optionally, obtaining the charge transfer impedance based on the impedance spectrum in step S5 specifically includes: S51, a parallel resistance fitting element and a constant phase element are connected in series with the Weber diffusion impedance to construct an RQ equivalent circuit, and the mid-low frequency region of the impedance spectrum is truncated. S52. Fit the RQ equivalent circuit using the nonlinear least squares method, and extract the charge transfer impedance from the fitting result after the fitting converges.

[0010] Optionally, the step of simultaneously acquiring the interface main echo and layered slice imaging results based on the ultrasound reflection data in S5 specifically includes: S53. Perform time-domain noise reduction and envelope extraction on the ultrasonic reflection echo signal of the ultrasonic reflection data to obtain the reflection peak sequence of each interface of the battery under test. S54. Based on the battery under test and the sound wave propagation path, locate the reflection peak corresponding to the hard carbon negative electrode / separator interface, record it as the main echo of the interface, and extract the arrival time and amplitude. S55. Based on the ultrasonic reflection data, divide the electrode area of ​​the battery under test into continuous thin layers with a preset thickness value according to the thickness direction of the battery under test. S56. Calculate the depth position of each layer of the continuous thin layer based on the flight time of the ultrasonic reflected echo signal, and form the layered slice imaging result.

[0011] Optionally, the step of establishing a two-dimensional sound velocity distribution image based on the ultrasonic transmission data in S5 specifically includes: S57. Collect the transmission flight time of each transmission channel in the ultrasonic transmission data, and calculate the average sound velocity of each transmission channel according to the thickness of the battery under test. S58. Using the position of each of the transmission channels as coordinates, map the average sound velocity to the corresponding pixel point, and perform interpolation reconstruction on the discrete sound velocity data to establish the two-dimensional sound velocity distribution image.

[0012] Optionally, S6 specifically includes: S61. When the increase in charge transfer impedance is greater than a preset increase threshold, it is determined that the charge transfer impedance meets the first abnormal condition for sodium precipitation. S62. When the amplitude of the echo of the main echo of the interface is greater than the preset enhancement threshold, it is determined that the main echo of the interface meets the second abnormal condition for sodium precipitation. S63. When the decrease in the local sound velocity is greater than the preset decrease threshold, it is determined that the local sound velocity meets the third abnormal condition for sodium precipitation. S64. When the first abnormal condition for sodium deposition is met, the enhancement amplitude is less than and close to the preset enhancement threshold, and the decrease amplitude is less than and close to the preset decrease threshold, it is determined that the battery under test has undergone early sodium deposition. S65. When the first abnormal condition for sodium precipitation, the second abnormal condition for sodium precipitation, and the third abnormal condition for sodium precipitation are all met, it is determined that the battery under test has undergone mid-to-late stage sodium precipitation.

[0013] Optionally, the preset rise threshold is any value between 20% and 50%, the preset enhancement threshold is any value between 15% and 30%, and the preset fall threshold is any value between 8% and 15%.

[0014] Optionally, S6 further includes: when a new signal peak appears before the main echo of the interface, and the new signal peak is greater than or equal to a first preset multiple of the signal peak of the main echo of the interface, and greater than or equal to a second preset multiple of the system noise amplitude, determining that the battery under test has undergone sodium deposition, wherein the first preset multiple is greater than or equal to 0.2, and the second preset multiple is equal to 3.

[0015] Optionally, the step of locating the sodium precipitation region based on the sound velocity anomaly region in the two-dimensional sound velocity distribution image in step S7 specifically includes: S71. Using the sound velocity of the transmission channel of the room temperature control group as a benchmark, calculate the rate of change of the sound velocity at each point in the two-dimensional sound velocity distribution image, and mark the pixels with the rate of change less than the preset sound velocity anomaly threshold as anomaly points, wherein the preset sound velocity anomaly threshold is any value between -8% and -15%. S72. Perform connected component analysis on the abnormal points to form the boundary coordinates of the abnormal region. Based on the ratio between the physical size of the linear array and the pixel coordinates of the two-dimensional sound velocity distribution image, convert the boundary coordinates of the abnormal region into the actual physical location of the battery under test, and determine the sodium deposition region.

[0016] Optionally, the step of simultaneously obtaining the sodium deposition distribution in the depth direction based on the layered slice imaging results in S7 specifically includes: S73. Normalize the echo amplitude of each slice layer in the layered slice imaging result to obtain the reflection intensity of the slice layer; S74. Mark the slice layer with a reflection intensity greater than a preset intensity threshold as a sodium precipitation generation layer, and obtain the sodium precipitation distribution curve and sodium precipitation thickness, wherein the preset intensity threshold is any value between 15% and 30%. Attached Figure Description

[0017] The present invention will now be described in further detail with reference to the accompanying drawings.

[0018] Figure 1 : A schematic flowchart of the in-situ non-destructive diagnostic method for sodium deposition during low-temperature charging of sodium-ion batteries in this embodiment of the invention.

[0019] Figure 2 The following is a comparison of ultrasonic transmission imaging of the test batteries in the diagnostic group and the room temperature control group before charging, at 25% SOC and 50% SOC, respectively, in the embodiments of the present invention.

[0020] Figure 3 The following is a comparison of ultrasonic transmission imaging of the test batteries in the diagnostic group and the room temperature control group at 75% SOC, 100% SOC, and after discharge in the embodiments of the present invention.

[0021] Figure 4 Comparison of ultrasonic reflection tomography of slices 1 and 2 of the test batteries in the diagnostic group and the room temperature control group in this embodiment of the invention.

[0022] Figure 5 : Comparison of ultrasonic reflection tomography of slices 4 and 5 of the test batteries in the diagnostic group and the room temperature control group in this embodiment of the invention.

[0023] Figure 6 : Comparison of ultrasonic intensity of the test batteries in the diagnostic group and the room temperature control group in this embodiment of the invention.

[0024] Figure 7 : Schematic diagram of the impedance spectrum of the room temperature control group in this embodiment of the invention.

[0025] Figure 8 : Schematic diagram of the impedance spectrum of the diagnostic group in this embodiment of the invention. Detailed Implementation

[0026] To better understand the present invention, the following embodiments further illustrate the content of the invention, but the scope of protection of the present invention is not limited to the following embodiments. Numerous specific details are set forth in the following description to provide a more thorough understanding of the invention. However, it will be apparent to those skilled in the art that the present invention can be practiced without one or more of these details.

[0027] The term "comprising" and its variations as used herein are open-ended, meaning "including but not limited to"; the term "based on" means "at least partially based on"; the term "one embodiment" means "at least one embodiment"; the term "another embodiment" means "at least one additional embodiment"; the term "some embodiments" means "at least some embodiments"; and the term "optionally" means "optional embodiments". Definitions of other terms will be given in the following description. It should be noted that the concepts of "first," "second," etc., mentioned in this invention are used only to distinguish different devices, modules, or units, and are not intended to limit the order of functions performed by these devices, modules, or units or their interdependencies.

[0028] It should be noted that the terms "a" and "a plurality of" used in this invention are illustrative rather than restrictive. Those skilled in the art should understand that, unless otherwise expressly indicated in the context, they should be understood as "one or more".

[0029] An embodiment of the present invention provides an in-situ non-destructive diagnostic method for sodium deposition during low-temperature charging of sodium-ion batteries, comprising: S1, coupling and installing an ultrasonic emission module and a reflection receiving module on one side of the battery under test along the thickness direction of the battery under test, and coupling and installing a transmission receiving module on the opposite side of the battery under test, connecting an electrochemical workstation to the battery under test; S2, adjusting the battery under test to a fully discharged state, simultaneously adjusting the temperature of the high and low temperature test chamber to a preset target temperature, placing the battery under test in the high and low temperature test chamber and allowing it to stand for a preset standing time, and simultaneously setting a room temperature control group; S3, charging the battery under test with a preset current using a constant current, and simultaneously applying a preset amplitude AC disturbance within a preset frequency range through the electrochemical workstation, synchronously driving the ultrasonic emission module to output ultrasonic pulses, and during the charging process of the battery under test... The above process is repeated at preset time intervals during the process; S4, the impedance spectrum of the battery under test is measured and recorded based on the electrochemical workstation, and ultrasonic reflection data and ultrasonic transmission data are recorded through the reflection receiving module and the transmission receiving module, respectively; S5, the charge transfer impedance is obtained based on the impedance spectrum, and the interface main echo and layered slice imaging results are obtained based on the ultrasonic reflection data, and a two-dimensional sound velocity distribution image is established based on the ultrasonic transmission data; S6, when the charge transfer impedance, the interface main echo and the local sound velocity of the two-dimensional sound velocity distribution image are all abnormal, it is determined that sodium deposition has occurred in the battery under test; S7, when it is determined that sodium deposition has occurred in the battery under test, the sodium deposition area is located based on the abnormal sound velocity area in the two-dimensional sound velocity distribution image, and the sodium deposition distribution in the depth direction is obtained based on the layered slice imaging results.

[0030] Specifically, the ultrasonic transmitting module, the transmission receiving module, and the reflection receiving module can be composed of a piezoelectric ultrasonic transducer and a focused ultrasonic probe; the electrochemical workstation can be a Princeton PARSTAT 4000 electrochemical workstation.

[0031] In this embodiment, firstly, as... Figure 1 As shown in S1, along the thickness direction of the battery under test, an ultrasonic transmitting module and a reflection receiving module are coupled and installed on one side, and a transmission receiving module is coupled and installed on the other side. The electrochemical workstation is connected to the electrode of the battery under test. This setup can construct a dual-mode ultrasonic detection architecture of transmission and reflection, simultaneously realizing electrochemical excitation and signal acquisition. This solves the problems that a single ultrasonic mode cannot simultaneously acquire interface reflection and overall transmission information, and that a single electrochemical method cannot locate physical defects, providing a hardware foundation for multi-signal fusion diagnosis; based on this, as Figure 1As shown in S2, the battery is adjusted to a fully discharged state, the high and low temperature test chamber is adjusted to the target temperature and the battery is placed inside and left to stand. A room temperature control group is simultaneously set up to eliminate systematic errors caused by the initial state and temperature gradient, ensuring the stability of the test baseline under low temperature conditions and solving the problem of diagnostic distortion caused by inconsistent initial states at low temperatures. Then, as... Figure 1 As shown in S3, constant current charging with a preset current is used. An AC disturbance of preset frequency and amplitude is applied through an electrochemical workstation to synchronously drive the ultrasonic emission module to output pulses. The test is repeated at fixed time intervals, achieving in-situ, synchronous, and continuous acquisition of electrochemical and ultrasonic data during charging, solving the problems of offline detection lag and inability to capture the dynamic sodium precipitation process; then, as... Figure 1 As shown in S4, the impedance spectrum is recorded by the electrochemical workstation, and the reflection / transmission receiving module records the ultrasonic reflection and transmission data respectively, realizing the synchronous acquisition and alignment of the two types of signals, providing a data source for subsequent joint analysis; subsequently, as... Figure 1 As shown in S5, charge transfer impedance is extracted from impedance spectrum, interface main echo and layered slice imaging results are extracted from ultrasonic reflection data, and a two-dimensional sound velocity distribution image is established from transmission data. This achieves simultaneous quantization of electrochemical and physical structural characteristics, solving the problem of single signals being susceptible to temperature and polarization interference. Then, as... Figure 1 As shown in S6, sodium deposition is determined when the charge transfer impedance, interface main echo, and local sound velocity are all abnormal. The three-signal joint criterion eliminates false positives from a single signal, thus increasing the confidence level. Finally, as... Figure 1 As shown in S7, the sodium precipitation location is located in the plane based on the sound velocity anomaly region, and the depth distribution is obtained based on the layered slices, realizing three-dimensional positioning of the sodium precipitation plane and depth, solving the problem that traditional methods cannot accurately locate the sodium precipitation region and distribution.

[0032] Optionally, the preset target temperature includes any value from -20 to 45°C, the preset resting time includes any value from 8 to 24 hours, the preset current includes any value from 0.2 to 1C, the preset frequency range is 20kHz to 0.1Hz, the preset time interval is any value from 30s to 10min, and the preset amplitude is any value from 5 to 10mV.

[0033] Specifically, the preset target temperature can be -20℃, 0℃, or 25℃; the preset resting time can be 8h, 12h, or 24h; the preset current can be 0.2C, 0.5C, or 1C; the preset time interval can be 30s, 5min, or 10min; and the preset amplitude can be 5mV or 10mV.

[0034] In this optional embodiment, firstly, the target temperature is set to -20~45℃, covering low temperature, room temperature, and conventional high temperature operating conditions, adapting to the full temperature range of sodium-ion battery usage scenarios, and solving the problem that a single temperature cannot evaluate the low-temperature sodium precipitation characteristics. Based on this, a resting time of 8~24h is set to ensure uniform internal battery temperature or stable electrochemical state, eliminating test deviations caused by temperature hysteresis and stress relaxation. Next, a constant current charging of 0.2~1C is used, accommodating both conventional charging and fast charging scenarios, matching actual operating conditions, and avoiding low testing efficiency due to excessively low current or abnormal sodium precipitation due to excessively high current. Then, a wide frequency range of 20kHz~0.1Hz is selected, covering the entire frequency band of solution impedance, SEI impedance, charge transfer impedance, and solid-phase diffusion, ensuring complete acquisition of interface dynamics information. Subsequently, sampling is performed at intervals of 30s~10min to balance time resolution and data volume, achieving continuous monitoring without interfering with the charging process. Finally, a small amplitude AC signal of 5~10mV is used to ensure the system is in the linear response region, avoiding polarization distortion caused by large signals and insufficient signal-to-noise ratio of small signals, thus improving impedance test accuracy.

[0035] Optionally, the step of obtaining the charge transfer impedance based on the impedance spectrum in S5 specifically includes: S51, connecting a parallel resistance fitting element and a constant phase element, and connecting them in series with the Weber diffusion impedance to construct an RQ equivalent circuit, while simultaneously extracting a semi-circular interval in the mid-to-low frequency region of the impedance spectrum; S52, fitting the RQ equivalent circuit using the nonlinear least squares method, and extracting the charge transfer impedance from the obtained fitting result after the fitting converges.

[0036] Specifically, the resistance fitting element can be an ideal resistor R or a charge transfer impedance Rct; the constant phase element can be CPE-1 or CPE-2; and the Weber diffusion impedance can be an ideal Warburg impedance or a finite-layer Warburg impedance.

[0037] In this optional embodiment, in the specific process of obtaining charge transfer impedance based on the impedance spectrum, firstly, the resistance fitting element and the constant phase element are connected in parallel, and the Weber diffusion impedance is connected in series to construct the RQ equivalent circuit. At the same time, a semi-circular interval in the low-frequency region of the impedance spectrum is extracted. This interval uniquely corresponds to the charge transfer process, eliminating interference from high-frequency Rs, Rf and low-frequency W, and solving the problem of Rct distortion caused by temperature and diffusion effects in full-spectrum fitting. On this basis, the real part curve and imaginary part curve of the measured impedance in this interval are extracted. The nonlinear least squares method is used to iteratively fit the Rct-CPE loop with the goal of minimizing the sum of squared residuals between the measured value and the model calculated value, continuously optimizing the Rct and CPE parameters until convergence. Finally, the charge transfer impedance Rct is extracted from the fitting result to achieve accurate and interference-resistant acquisition of the interface charge transfer resistance, providing a core electrochemical indicator for early sodium precipitation determination, and solving the problem of misjudgment caused by increased polarization and impedance drift at low temperatures.

[0038] Optionally, the step of simultaneously acquiring the interface main echo and layered slice imaging results based on the ultrasonic reflection data in S5 specifically includes: S53, performing time-domain noise reduction and envelope extraction on the ultrasonic reflection echo signal of the ultrasonic reflection data to obtain the reflection peak sequence of each interface of the battery under test; S54, locating the reflection peak corresponding to the hard carbon negative electrode / separator interface according to the battery under test and the sound wave propagation path, recording it as the interface main echo, and extracting the arrival time and amplitude; S55, dividing the electrode area of ​​the battery under test into continuous thin layers with a preset thickness value based on the ultrasonic reflection data according to the thickness direction of the battery under test; S56, calculating the depth position of each layer of the continuous thin layer based on the flight time of the ultrasonic reflection echo signal, and forming the layered slice imaging result.

[0039] Specifically, time-domain denoising can be achieved through wavelet denoising or mean filtering; envelope extraction can be achieved through Hilbert transform or sliding window envelope detection.

[0040] In this optional embodiment, in the specific process of obtaining the interface main echo and layered slice imaging results based on the ultrasonic reflection data, firstly, temporal domain noise reduction and envelope extraction are performed on the ultrasonic reflection echo to suppress electromagnetic and system noise, highlight the interface reflection peak, and solve the problem of inaccurate peak position identification under weak signals; on this basis, the hard carbon negative electrode / separator reflection peak is located according to the battery structure and acoustic path, and recorded as the interface main echo. The arrival time and amplitude are extracted. The time reflects the interface distance, while the amplitude reflects the degree of interface roughness, providing physical characteristics for sodium deposition; next, the electrode is divided into continuous thin layers of a preset thickness along the thickness direction to establish a depth coordinate system; finally, the depth of each layer is calculated, the echo amplitude is mapped to grayscale, and layered slice imaging is generated to realize the visualization of the structure in the depth direction and solve the problem of not being able to obtain the distribution of sodium deposition along the thickness.

[0041] Optionally, the step of establishing a two-dimensional sound velocity distribution image based on the ultrasonic transmission data in S5 specifically includes: S57, acquiring the transmission flight time of each transmission channel in the ultrasonic transmission data, and calculating the average sound velocity of each transmission channel according to the thickness of the battery under test; S58, mapping the average sound velocity to the corresponding pixel point using the position of each transmission channel as coordinates, and interpolating and reconstructing the discrete sound velocity data to establish the two-dimensional sound velocity distribution image.

[0042] Specifically, the transmission channels include 16-channel or 32-channel linear array probes; the interpolation reconstruction can be bilinear interpolation reconstruction or kriging interpolation reconstruction.

[0043] In this optional embodiment, during the process of establishing a two-dimensional sound velocity distribution image based on the ultrasonic transmission data, firstly, the flight time of each transmission channel is collected, and the average sound velocity is calculated to achieve single-point sound velocity quantization. Based on this, the sound velocity is mapped to the corresponding pixel using the channel position as coordinates, forming a discrete sound velocity field. Subsequently, the discrete data is interpolated and reconstructed to obtain a two-dimensional sound velocity distribution image, with the sound velocity reduction region corresponding to the sodium precipitation region, achieving planar visualization. This setup transforms transmission data into an intuitive image, solving the problem that a single flight time cannot intuitively determine the sodium precipitation region and range, and providing a basis for planar positioning.

[0044] Optionally, S6 specifically includes: S61, when the increase in charge transfer impedance is greater than a preset increase threshold, determining that the charge transfer impedance meets the first abnormal condition for sodium deposition; S62, when the increase in the echo amplitude of the main interface echo is greater than a preset increase threshold, determining that the main interface echo meets the second abnormal condition for sodium deposition; S63, when the decrease in local sound velocity is greater than a preset decrease threshold, determining that the local sound velocity meets the third abnormal condition for sodium deposition; S64, when the first abnormal condition for sodium deposition is met, the increase is less than and close to the preset increase threshold, and the decrease is less than and close to the preset decrease threshold, determining that the battery under test has undergone early sodium deposition; S65, when the first abnormal condition for sodium deposition, the second abnormal condition for sodium deposition, and the third abnormal condition for sodium deposition are all met, determining that the battery under test has undergone mid-to-late stage sodium deposition.

[0045] In this optional embodiment, during the specific process of S6, firstly, when the increase in Rct exceeds a preset threshold, the first abnormal condition is determined to be met, reflecting obstructed interface charge transfer. Based on this, when the amplitude of the main echo increases beyond a threshold, the second abnormal condition is determined to be met, reflecting interface roughening and dendrite formation. Next, when the local sound velocity decreases beyond a threshold, the third abnormal condition is determined to be met, reflecting sodium metal precipitation leading to a decrease in sound velocity. Based on this, if only Rct meets the condition of exceeding the preset threshold in terms of increase, while the main echo amplitude and local sound velocity are close to their respective thresholds, it is determined to be early sodium precipitation, achieving a trace sodium precipitation early warning. Finally, when the first, second, and third abnormal conditions for sodium precipitation are all met, it is determined to be mid-to-late stage sodium precipitation, achieving graded diagnosis. This setup, through graded and multi-condition joint determination, can eliminate interference from temperature and polarization, solving the problems of misjudgment based on a single signal and the inability to distinguish the sodium precipitation stage.

[0046] Optionally, the preset rise threshold is any value between 20% and 50%, the preset enhancement threshold is any value between 15% and 30%, and the preset fall threshold is any value between 8% and 15%.

[0047] Specifically, the preset increase threshold can be 20%, 30%, or 50%; the preset enhancement threshold can be 15%, 20%, or 30%; and the preset decrease threshold can be 8%, 10%, or 15%.

[0048] In this optional embodiment, firstly, the Rct rise threshold is set to 20%~50% to ensure sensitive identification of interface degradation while avoiding noise interference. Based on this, the main echo amplitude enhancement threshold is set to 15%~30% to match the interface reflection enhancement pattern induced by sodium precipitation. Next, the local sound velocity decrease threshold is set to 8%~15% to adapt to the sound velocity reduction characteristics of sodium metal relative to the electrode material. This setting, experimentally verified, balances sensitivity and specificity, solving the problems of missed detection due to excessively high thresholds and false detection due to excessively low thresholds, ensuring stable and reliable graded diagnosis.

[0049] Optionally, S6 further includes: when a new signal peak appears before the main echo of the interface, and the new signal peak is greater than or equal to a first preset multiple of the signal peak of the main echo of the interface, and greater than or equal to a second preset multiple of the system noise amplitude, determining that the battery under test has undergone sodium deposition, wherein the first preset multiple is greater than or equal to 0.2, and the second preset multiple is equal to 3.

[0050] Specifically, the first preset multiple can be 0.2, 0.3, or 0.5.

[0051] In this optional embodiment, based on S6, a method for determining sodium deposition in the battery is also provided. During the determination process, the time domain interval in front of the main echo of the monitoring interface is monitored. When a new signal peak appears and is ≥0.2 times the main echo peak and ≥3 times the system noise, it indicates that a new peak has been formed. The new peak is generated by the formation of a new interface by dendrites, which is a unique physical characteristic of sodium deposition. Temperature and polarization do not generate new peaks, so sodium deposition can be determined. With this setting, the above determination method can be used as a direct supplementary criterion, which can be mutually verified with the aforementioned three signals to further eliminate interference, significantly improve confidence, and solve the problem that traditional methods cannot directly confirm dendrite formation.

[0052] Optionally, the step of locating the sodium deposition region based on the abnormal sound velocity region in the two-dimensional sound velocity distribution image in step S7 specifically includes: S71, using the sound velocity of the transmission channel of the room temperature control group as a reference, calculating the rate of change of sound velocity at each point in the two-dimensional sound velocity distribution image, and marking pixels with a rate of change less than a preset sound velocity anomaly threshold as anomaly points, wherein the preset sound velocity anomaly threshold is any value between -8% and -15%; S72, performing connected component analysis on the anomaly points to form the boundary coordinates of the anomaly region, and converting the boundary coordinates of the anomaly region to the actual physical location of the battery under test according to the ratio between the linear array physical size and the pixel coordinates of the two-dimensional sound velocity distribution image, thereby determining the sodium deposition region.

[0053] In this optional embodiment, during the process of locating the sodium precipitation region based on the abnormal sound velocity region in the two-dimensional sound velocity distribution image, firstly, using the sound velocity of the room temperature control group as a benchmark, the rate of change of sound velocity at each point is calculated. Pixels with a rate of change of sound velocity lower than -8% to -15% are marked as abnormal points, highlighting the area of ​​reduced sound velocity caused by sodium precipitation. Based on this, connected component analysis is performed on the abnormal points to obtain boundary coordinates. Subsequently, according to the pixel-to-physical size ratio, the image coordinates are converted into actual positions, and the connections are formed to form the sodium precipitation region, achieving precise planar positioning. This setup solves the problem that traditional methods cannot determine the specific location and size of sodium precipitation, providing a basis for failure analysis and optimization.

[0054] Optionally, the step of simultaneously obtaining the sodium precipitation distribution in the depth direction based on the layered slice imaging results in S7 specifically includes: S73, normalizing the echo amplitude of each slice layer in the layered slice imaging results to obtain the reflection intensity of the slice layer; S74, marking the slice layer with the reflection intensity greater than a preset intensity threshold as the sodium precipitation generation layer, and obtaining the sodium precipitation distribution curve and sodium precipitation thickness, wherein the preset intensity threshold is any value between 15% and 30%.

[0055] Specifically, the preset intensity threshold can be 15%, 20%, or 30%.

[0056] In this optional embodiment, during the process of obtaining the sodium deposition distribution in the depth direction based on the layered slice imaging results, firstly, the amplitude of each slice layer is normalized to obtain the reflection intensity, eliminating the influence of system gain; based on this, layers with a reflection intensity greater than the preset intensity threshold are marked as sodium deposition occurrence layers, and sodium deposition distribution curves are obtained by sorting them by depth; subsequently, the thicknesses of the corresponding layers are accumulated to obtain the total sodium deposition thickness, achieving depth-direction quantification. This setup can solve the problem of not being able to determine the distribution and thickness of sodium deposition inside the negative electrode, providing direct data for assessing the severity of sodium deposition and the risk of diaphragm puncture.

[0057] For example, such as Figure 2 and Figure 3 As shown, ultrasound transmission imaging was compared at different SOCs. In the control group at room temperature, the sound velocity distribution was uniform. In the diagnostic group (the embodiment of this invention), a significant localized area of ​​decreased sound velocity appeared as the SOC increased, and this area continued to expand. This demonstrates that two-dimensional sound velocity imaging can identify the initiation and spread of sodium precipitation in situ and visually, achieving early warning and planar localization, solving the problem that traditional methods cannot intuitively observe the dynamic sodium precipitation process. Figure 4 and Figure 5 As shown, ultrasound reflectance tomography was performed on different slices for comparison. In the room temperature group, the reflectance intensity of all slices was stable. In the diagnostic group, the reflectance intensity significantly increased in the slices corresponding to the negative electrode / diaphragm, demonstrating that layered slice imaging can accurately obtain the sodium deposition distribution in the depth direction, clearly identify the sodium deposition concentration layers, and provide a basis for judging the dendrite growth depth and diaphragm contact risk. Figure 6 As shown, ultrasound intensity was compared. The reflection intensity of the diagnostic group was significantly higher than that of the room temperature group, and it continued to increase with charging. This verifies that the enhanced amplitude of the main echo at the interface can stably characterize the interface roughening and dendrite formation caused by sodium precipitation, exhibiting strong signal specificity and being unaffected by temperature and polarization. Figure 7 and Figure 8 As shown, impedance spectrum comparison was performed. In the room temperature group, the low-frequency semicircle was small, while in the diagnostic group, the semicircle was significantly enlarged, proving that Rct increased significantly under low-temperature charging, which can sensitively reflect the obstruction of interface charge transfer. At the same time, combined with ultrasound signal judgment, the impedance increase caused by temperature and polarization alone was ruled out, achieving anti-interference and high-confidence diagnosis.

[0058] In summary, the embodiments of the present invention achieve early identification, grading and determination of sodium precipitation at low temperatures, and three-dimensional localization with planar depth by in-situ synchronous acquisition and mutual corroboration of three signals: electrochemical impedance, ultrasonic reflection and ultrasonic transmission. This effectively eliminates interference from temperature fluctuations and increased polarization, significantly improves diagnostic sensitivity, accuracy and confidence, and realizes in-situ non-destructive, dynamic continuous and visualized diagnosis of sodium precipitation at low temperatures in sodium-ion batteries.

[0059] The above are merely preferred embodiments of the present invention and are not intended to limit the present invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. An in-situ non-destructive diagnosis method for sodium-ion battery low-temperature charging sodium extraction, characterized in that, include: S1. Along the thickness direction of the battery under test, an ultrasonic transmitting module and a reflection receiving module are coupled and installed on one side of the battery under test, and a transmission receiving module is coupled and installed on the opposite side of the battery under test, connecting the electrochemical workstation to the battery under test. S2. Adjust the battery under test to a fully discharged state, and at the same time adjust the temperature of the high and low temperature test chamber to the preset target temperature. Place the battery under test into the high and low temperature test chamber and let it stand for a preset standing time. Simultaneously set the room temperature control group. S3. The battery under test is charged with a constant current using a preset current. At the same time, an AC disturbance of a preset amplitude is applied through the electrochemical workstation within a preset frequency range to synchronously drive the ultrasonic emission module to output ultrasonic pulses. The above process is repeated at preset time intervals during the charging process of the battery under test. S4. Measure and record the impedance spectrum of the battery under test based on the electrochemical workstation, and record the ultrasonic reflection data and ultrasonic transmission data through the reflection receiving module and the transmission receiving module respectively. S5. Obtain the charge transfer impedance based on the impedance spectrum, and simultaneously obtain the interface main echo and layered slice imaging results based on the ultrasonic reflection data, and establish a two-dimensional sound velocity distribution image based on the ultrasonic transmission data. S6. When the charge transfer impedance, the interface main echo, and the local sound velocity of the two-dimensional sound velocity distribution image are all abnormal, it is determined that the battery under test has undergone sodium deposition. S7. When it is determined that sodium deposition has occurred in the battery under test, the sodium deposition area is located based on the abnormal sound velocity area in the two-dimensional sound velocity distribution image, and the sodium deposition distribution in the depth direction is obtained based on the layered slice imaging results.

2. The in-situ non-destructive diagnosis method of sodium stripping during low-temperature charging of sodium-ion batteries according to claim 1, characterized in that, The preset target temperature includes any value from -20 to 45℃, the preset resting time includes any value from 8 to 24h, the preset current includes any value from 0.2 to 1C, the preset frequency range is 20kHz to 0.1Hz, the preset time interval is any value from 30s to 10min, and the preset amplitude is any value from 5 to 10mV.

3. The in-situ non-destructive diagnostic method for sodium deposition during low-temperature charging of sodium-ion batteries as described in claim 1, characterized in that, The specific steps in S5, namely obtaining the charge transfer impedance based on the impedance spectrum, include: S51, a parallel resistance fitting element and a constant phase element are connected in series with the Weber diffusion impedance to construct an RQ equivalent circuit, and the mid-low frequency region of the impedance spectrum is truncated. S52. Fit the RQ equivalent circuit using the nonlinear least squares method, and extract the charge transfer impedance from the fitting result after the fitting converges.

4. The in-situ non-destructive diagnostic method for sodium deposition during low-temperature charging of sodium-ion batteries as described in claim 1, characterized in that, The simultaneous acquisition of interface main echo and layered slice imaging results based on the ultrasound reflection data in S5 specifically includes: S53. Perform time-domain noise reduction and envelope extraction on the ultrasonic reflection echo signal of the ultrasonic reflection data to obtain the reflection peak sequence of each interface of the battery under test. S54. Based on the battery under test and the sound wave propagation path, locate the reflection peak corresponding to the hard carbon negative electrode / separator interface, record it as the main echo of the interface, and extract the arrival time and amplitude. S55. Based on the ultrasonic reflection data, divide the electrode area of ​​the battery under test into continuous thin layers with a preset thickness value according to the thickness direction of the battery under test. S56. Calculate the depth position of each layer of the continuous thin layer based on the flight time of the ultrasonic reflected echo signal, and form the layered slice imaging result.

5. The in-situ non-destructive diagnostic method for sodium deposition during low-temperature charging of sodium-ion batteries as described in claim 1, characterized in that, The specific steps in S5, including establishing a two-dimensional sound velocity distribution image based on the ultrasonic transmission data, include: S57. Collect the transmission flight time of each transmission channel in the ultrasonic transmission data, and calculate the average sound velocity of each transmission channel according to the thickness of the battery under test. S58. Using the position of each of the transmission channels as coordinates, map the average sound velocity to the corresponding pixel point, and perform interpolation reconstruction on the discrete sound velocity data to establish the two-dimensional sound velocity distribution image.

6. The in-situ non-destructive diagnostic method for sodium deposition during low-temperature charging of sodium-ion batteries as described in any one of claims 1 to 5, characterized in that, S6 specifically includes: S61. When the increase in charge transfer impedance is greater than a preset increase threshold, it is determined that the charge transfer impedance meets the first abnormal condition for sodium precipitation. S62. When the amplitude of the echo of the main echo of the interface is greater than the preset enhancement threshold, it is determined that the main echo of the interface meets the second abnormal condition for sodium precipitation. S63. When the decrease in the local sound velocity is greater than the preset decrease threshold, it is determined that the local sound velocity meets the third abnormal condition for sodium precipitation. S64. When the first abnormal condition for sodium deposition is met, the enhancement amplitude is less than and close to the preset enhancement threshold, and the decrease amplitude is less than and close to the preset decrease threshold, it is determined that the battery under test has undergone early sodium deposition. S65. When the first abnormal condition for sodium precipitation, the second abnormal condition for sodium precipitation, and the third abnormal condition for sodium precipitation are all met, it is determined that the battery under test has undergone mid-to-late stage sodium precipitation.

7. The in-situ non-destructive diagnostic method for sodium deposition during low-temperature charging of sodium-ion batteries as described in claim 6, characterized in that, The preset increase threshold is any value between 20% and 50%, the preset enhancement threshold is any value between 15% and 30%, and the preset decrease threshold is any value between 8% and 15%.

8. The in-situ non-destructive diagnostic method for sodium deposition during low-temperature charging of sodium-ion batteries as described in any one of claims 1 to 5, characterized in that, S6 further includes: when a new signal peak appears before the main echo of the interface, and the new signal peak is greater than or equal to a first preset multiple of the signal peak of the main echo of the interface, and greater than or equal to a second preset multiple of the system noise amplitude, it is determined that the battery under test has undergone sodium deposition, wherein the first preset multiple is greater than or equal to 0.2, and the second preset multiple is equal to 3.

9. The in-situ non-destructive diagnostic method for sodium deposition during low-temperature charging of sodium-ion batteries as described in any one of claims 1 to 5, characterized in that, The specific steps in S7 of locating the sodium precipitation region based on the sound velocity anomaly region in the two-dimensional sound velocity distribution image include: S71. Using the sound velocity of the transmission channel of the room temperature control group as a benchmark, calculate the rate of change of the sound velocity at each point in the two-dimensional sound velocity distribution image, and mark the pixels with the rate of change less than the preset sound velocity anomaly threshold as anomaly points, wherein the preset sound velocity anomaly threshold is any value between -8% and -15%. S72. Perform connected component analysis on the abnormal points to form the boundary coordinates of the abnormal region. Based on the ratio between the physical size of the linear array and the pixel coordinates of the two-dimensional sound velocity distribution image, convert the boundary coordinates of the abnormal region into the actual physical location of the battery under test, and determine the sodium deposition region.

10. The in-situ non-destructive diagnostic method for sodium deposition during low-temperature charging of sodium-ion batteries as described in any one of claims 1 to 5, characterized in that, The step of simultaneously obtaining the sodium deposition distribution in the depth direction based on the layered slice imaging results in S7 specifically includes: S73. Normalize the echo amplitude of each slice layer in the layered slice imaging result to obtain the reflection intensity of the slice layer; S74. Mark the slice layer with a reflection intensity greater than a preset intensity threshold as a sodium precipitation generation layer, and obtain the sodium precipitation distribution curve and sodium precipitation thickness, wherein the preset intensity threshold is any value between 15% and 30%.

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