Lithium ion battery lithium precipitation nondestructive testing method based on ultrasonic signals

Abstract

The invention relates to a lithium ion battery lithium precipitation nondestructive testing method based on an ultrasonic signal. The method comprises the following steps: firstly, acquiring an ultrasonic flight time migration reference curve and a reference ultrasonic scanning graph of a battery under different working conditions; then, under a given working condition, carrying out a charge-discharge cycle test on the tested battery, collecting the ultrasonic flight time of the tested battery in real time in a charging stage, calculating ultrasonic flight time migration data at each moment, and obtaining an ultrasonic flight time migration test curve; after charging is finished each time, an ultrasonic scanning graph of the tested battery is collected to serve as a test ultrasonic scanning graph; finally, linear fitting is carried out on the ultrasonic flight time migration test data and the reference data of the tested battery in the charging later period under the given working condition, and an ultrasonic flight time migration test fitting straight line and a reference fitting straight line in the charging later period are obtained; and if the gradient difference between the ultrasonic flight time offset test fitting straight line and the reference fitting straight line in the later period of charging is greater than 0.5%, and a color block which is obviously different from the reference ultrasonic scanning image in chromatic aberration and is disordered appears in the test ultrasonic scanning image, it is indicated that lithium precipitation occurs. According to the method, a new lithium precipitation judgment standard based on ultrasonic signals is provided, whether lithium precipitation occurs or not can be judged according to historical operation conditions, and efficient detection of lithium precipitation is achieved.

Description

Technical Field

[0001] The invention belongs to the technical field of lithium deposition detection of lithium ion batteries, and in particular relates to a nondestructive detection method for lithium deposition of lithium ion batteries based on ultrasonic signals. Background Art

[0002] As users' requirements for charging efficiency continue to increase, fast charging technology has become a key means to improve the user experience of new energy vehicles, ensure battery life, and promote the widespread application of lithium-ion batteries. However, fast charging of lithium-ion batteries in low-temperature environments is prone to induce lithium precipitation side reactions, that is, lithium ions transmitted through the electrolyte gain electrons on the surface of the negative electrode and are reduced to lithium metal and deposited. The deposited lithium metal gradually evolves into lithium dendrites, and its continued growth will eventually penetrate the diaphragm, causing an internal short circuit in the battery, and then causing serious safety accidents such as thermal runaway or even explosion of the battery. Therefore, lithium precipitation detection is of vital importance to improving the safety and reliability of lithium-ion batteries during operation.

[0003] At present, the existing lithium plating detection can be divided into two categories, invasive and non-invasive, according to whether the battery needs to be disassembled. Although invasive detection can reveal the internal structure and status information of the battery in detail, it will destroy the structural integrity of the battery. Non-invasive detection includes coulomb efficiency method, electrochemical impedance method, mechanism model method, voltage curve method, ultrasonic detection and other methods. Among them, the coulomb efficiency method determines whether lithium plating occurs by the ratio of the total discharge charge of the battery to the total charge charge. It has high requirements for equipment detection accuracy and is only applicable to lithium plating detection in the early cycle stage of the battery. The electrochemical impedance method realizes real-time detection of battery lithium plating through impedance changes in the mid-frequency band. It requires a certain amount of lithium plating accumulation (about 1% of the capacity value), and its effectiveness and accuracy are affected by many factors. The voltage curve method uses the voltage curve after the lithium plating reaction to show a new observable voltage platform in the relaxation stage or the beginning of discharge to detect lithium plating. This method requires clear trough characteristics, the amount of lithium plating exceeds 1% of the capacity of the graphite negative electrode, and usually requires a long relaxation time. The existing ultrasonic detection method collects the ultrasonic flight time during the charging stage, and determines that lithium deposition has occurred when an inflection point appears in the ultrasonic flight time curve during the charging process. However, only a single mode of constant current charging is considered. In the constant current and constant voltage charging mode, an inflection point will appear in the ultrasonic flight time curve regardless of whether lithium deposition occurs. Therefore, the detection results of the existing ultrasonic detection method are one-sided. Summary of the invention

[0004] In view of the deficiencies in the prior art, the technical problem to be solved by the present invention is to propose a non-destructive detection method for lithium deposition in lithium-ion batteries based on ultrasonic signals.

[0005] The present invention solves the technical problem by adopting the following technical solution:

[0006] A nondestructive detection method for lithium deposition in lithium-ion batteries based on ultrasonic signals comprises the following steps:

[0007] Step 1: Obtaining ultrasonic flight time offset reference curves and reference ultrasonic scans of the battery under different operating conditions; the ultrasonic flight time offset reference curve refers to a curve formed by ultrasonic flight time offset data at each moment during the first charging process, and the reference ultrasonic scan refers to an ultrasonic scan collected after the first charging is completed;

[0008] Step 2: Perform a charge-discharge cycle test on the battery under test under given working conditions, collect the ultrasonic flight time of the battery under test in real time during the charging stage, calculate the ultrasonic flight time offset data at each moment, and obtain the ultrasonic flight time offset test curve; after each charging, collect the ultrasonic scan of the battery under test as a test ultrasonic scan;

[0009] Step 3: Perform straight line fitting on the ultrasonic flight time offset test data and the reference data of the tested battery at the late charging stage under given working conditions, respectively, to obtain a late charging ultrasonic flight time offset test fitting straight line and a reference fitting straight line; wherein the late charging stage refers to the period from the inflection point of the ultrasonic flight time offset curve to the end of charging;

[0010] If the difference in slope between the ultrasonic flight time offset test fitting line and the reference fitting line in the late charging period is greater than 0.5%, and the test ultrasonic scan image shows a color block with a significantly different color difference from the reference ultrasonic scan image and disordered color blocks, it indicates that lithium plating has occurred in the tested battery.

[0011] Furthermore, in the first step, the ultrasonic flight time of the battery during the first charging process under different working conditions is collected, and the ultrasonic flight time is subtracted from the reference time to obtain ultrasonic flight time offset data. The ultrasonic flight time offset data at all times form an ultrasonic flight time offset reference curve; wherein the reference time is the time corresponding to the maximum amplitude of the ultrasonic signal when the battery is 0% SOC in an open circuit state.

[0012] Compared with the prior art, the present invention has the following beneficial effects:

[0013] The present invention proposes a new lithium plating judgment standard based on ultrasonic signals, that is, the ultrasonic flight time offset test curve and the test ultrasonic scanning diagram of the tested battery under given working conditions are compared with the ultrasonic flight time offset reference curve and the reference ultrasonic scanning diagram respectively to judge whether lithium plating occurs. The lithium plating phenomenon under different working conditions and charging modes can be effectively detected in real time, and has the characteristics of high detection accuracy, short time, and no damage to the battery. In addition, the ultrasonic flight time offset reference curve and the reference ultrasonic scanning diagram can be obtained from the historical operating conditions of the battery. Therefore, the method of the present invention can also judge whether lithium plating occurs according to the historical operating conditions of the battery, and realizes efficient detection of lithium plating. Detecting lithium plating by ultrasonic signals avoids subjective detection errors caused by human observation. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] Figure 1 The following is the overall flow chart;

[0015] Figure 2 The ultrasonic flight time deviation test curve of Example 1 is compared with the reference curve;

[0016] Figure 3 is the reference ultrasound scan of Example 1;

[0017] Figure 4 This is the test ultrasound scan of Example 1;

[0018] Figure 5 is a negative electrode interface diagram of the tested battery of Example 1 after disassembly;

[0019] Figure 6 The ultrasonic flight time deviation test curve of Example 2 is compared with the reference curve;

[0020] Figure 7 is the reference ultrasound scan of Example 2;

[0021] Figure 8 This is a test ultrasound scan of Example 2;

[0022] Fig. 9 This is a diagram of the negative electrode interface of the tested battery of Example 2 after disassembly. DETAILED DESCRIPTION

[0023] Specific embodiments are given below in conjunction with the accompanying drawings. The specific embodiments are only used to further illustrate the technical solution of the present invention in detail and do not limit the protection scope of the present application.

[0024] The present invention provides a nondestructive detection method for lithium deposition in lithium-ion batteries based on ultrasonic signals (hereinafter referred to as the method, see Figures 1 to 9 ), comprising the following steps:

[0025] Step 1: Obtain ultrasonic flight time deviation reference curve and reference ultrasonic scanning diagram of lithium-ion battery under different working conditions;

[0026] An ultrasonic pulse transmitter and receiver is used to collect the ultrasonic flight time of the lithium-ion battery in the first charging process under different working conditions, that is, the time corresponding to the maximum amplitude of the ultrasonic signal; the ultrasonic flight time is subtracted from the reference time to obtain ultrasonic flight time offset data; the ultrasonic flight time offset data at each moment of the charging stage forms an ultrasonic flight time offset curve, and the curve is used as an ultrasonic flight time offset reference curve for lithium precipitation judgment; at the same time, after the first charging is completed, an ultrasonic scan of the lithium-ion battery is collected to obtain a reference ultrasonic scan of the lithium-ion battery under different working conditions;

[0027] The reference time is the time corresponding to the maximum amplitude of the ultrasonic signal when the lithium-ion battery is 0% SOC in the open circuit state, and different operating conditions are characterized by different temperatures and charging rates.

[0028] Step 2: Perform a charge-discharge cycle test on the lithium-ion battery under the given working conditions, collect the ultrasonic flight time of the lithium-ion battery in real time during the charging stage of each cycle, calculate the ultrasonic flight time offset data at each moment, and obtain the ultrasonic flight time offset test curve; at the same time, collect the ultrasonic scan of the lithium-ion battery as the test ultrasonic scan after each charging.

[0029] Step 3: Based on the ultrasonic flight time offset test curve and the reference curve of the tested lithium-ion battery under given working conditions, linear fitting is performed on the ultrasonic flight time offset test data and the reference data in the late charging period (the late charging period refers to the period from the inflection point of the ultrasonic flight time offset curve to the end of charging), respectively, to obtain a late charging ultrasonic flight time offset test fitting line and a reference fitting line;

[0030] The ultrasonic flight time offset test fitting line and the test ultrasonic scanning diagram of the tested lithium-ion battery in the late charging period under given working conditions are respectively compared with the ultrasonic flight time offset benchmark fitting line and the benchmark ultrasonic scanning diagram in the late charging period. If the difference in slope between the ultrasonic flight time offset test fitting line in the late charging period and the benchmark fitting line is greater than 0.5%, and the test ultrasonic scanning diagram has yellow, orange, red and other color blocks that are obviously different from the benchmark ultrasonic scanning diagram and are disordered, it indicates that lithium deposition has occurred in the tested lithium-ion battery.

[0031] Example 1

[0032] In this embodiment, a ternary lithium battery with a capacity of 5.8Ah is used as the battery to be tested, and a lithium ion battery lithium plating nondestructive testing method based on ultrasonic signals includes the following steps:

[0033] Step 1: Obtain the ultrasonic flight time deviation reference curve and reference ultrasonic scanning diagram of the ternary lithium battery at 0°C and 1C;

[0034] The ternary lithium battery under test was placed in a constant temperature box consistent with the working temperature. After standing for 3 hours, the ultrasonic pulse transmitter and receiver was used to collect the ultrasonic flight time of the ternary lithium battery under the working condition of 0℃ and 1C in the first charging process in real time. The ultrasonic flight time was subtracted from the reference time to obtain the ultrasonic flight time offset data. The ultrasonic flight time offset data at each moment of the charging stage formed an ultrasonic flight time offset curve and served as the ultrasonic flight time offset reference curve. Figure 2 At the same time, after charging is completed, the ultrasonic scan of the ternary lithium battery is collected as a reference ultrasonic scan, see Figure 3 Among them, the ultrasonic pulse transmitter and receiver has an ultrasonic transmission frequency of 5MHz and a sampling frequency of 625MHz.

[0035] Step 2: Perform a charge-discharge cycle test on the ternary lithium battery under 0°C and 1C conditions. In the charging stage of each cycle, the ultrasonic flight time of the ternary lithium battery under test is collected in real time, and the ultrasonic flight time offset data at each moment in the charging stage is calculated to obtain the ultrasonic flight time offset test curve. At the same time, after each charging, the ultrasonic scan of the ternary lithium battery under test is collected as the test ultrasonic scan. The ultrasonic flight time offset test curve and the test ultrasonic scan after the 10th charge-discharge cycle test are respectively shown in Figure 2 and 4 .

[0036] The third step: based on the ultrasonic flight time offset test curve and the benchmark curve of the tested ternary lithium battery under 0℃, 1C working conditions, the ultrasonic flight time offset test data and the benchmark data in the late charging stage are linearly fitted to obtain the ultrasonic flight time offset test fitting straight line and the benchmark fitting straight line in the late charging stage; the ultrasonic flight time offset test fitting straight line and the test ultrasonic scanning diagram of the tested ternary lithium battery under 0℃, 1C working conditions are respectively compared with the ultrasonic flight time offset benchmark fitting straight line and the benchmark ultrasonic scanning diagram in the late charging stage, and the difference in slope between the ultrasonic flight time offset test fitting straight line in the late charging stage and the benchmark fitting straight line is 0.82%. When yellow, orange, red and other color blocks with obviously different color difference from the benchmark ultrasonic scanning diagram and disorderly colors appear on the test ultrasonic scanning diagram, it indicates that lithium plating has occurred in the tested ternary lithium battery.

[0037] Figure 5 This is the negative electrode interface diagram of the tested ternary lithium battery after disassembly after the charge and discharge cycle test under 0℃ and 1C conditions. From the figure, it can be seen that there are a small amount of silver-white particles on the edge of the negative electrode surface of the battery. The silver-white particles are formed by the deposition of metallic lithium, proving that lithium plating has occurred in the tested ternary lithium battery.

[0038] Example 2

[0039] The present embodiment is different from the embodiment 1 only in the working conditions, which are -5°C and 1C. The rest of the detection process is the same as that of the embodiment 1 and will not be described in detail.

[0040] Figure 6 It is the comparison between the ultrasonic flight time deviation reference curve and the test curve of the tested ternary lithium battery under -5℃ and 1C conditions. Figure 7 , 8 They are the reference ultrasonic scan of the tested ternary lithium battery at 0℃ and 1C and the test ultrasonic scan at the end of the 6th charge and discharge cycle test. The ultrasonic flight time offset test fitting line and the test ultrasonic scan of the tested ternary lithium battery at -5℃ and 1C are compared with the ultrasonic flight time offset reference fitting curve and the reference ultrasonic scan in the late charging period. The difference in slope between the ultrasonic flight time offset test fitting curve and the reference fitting curve in the late charging period is 1.2%. When yellow, orange, and red color blocks with obviously different colors from the reference ultrasonic scan and disorderly colors appear on the test ultrasonic scan, it indicates that lithium deposition has occurred in the tested ternary lithium battery.

[0041] Fig. 9 This is the negative electrode interface diagram of the tested ternary lithium battery after disassembly after the charge and discharge cycle test at -5℃ and 1C conditions. From the figure, it can be seen that there are silvery-white particles on the edge of the negative electrode surface of the battery. The silver-white particles are formed by the deposition of metallic lithium, proving that lithium plating has occurred in the tested ternary lithium battery.

[0042] Any matters not described in the present invention are applicable to the prior art.

Claims

1. A nondestructive detection method for lithium deposition in lithium-ion batteries based on ultrasonic signals, characterized in that: The method comprises the following steps: Step 1: Obtaining ultrasonic flight time offset reference curves and reference ultrasonic scans of the battery under different operating conditions; the ultrasonic flight time offset reference curve refers to a curve formed by ultrasonic flight time offset data at each moment during the first charging process, and the reference ultrasonic scan refers to an ultrasonic scan collected after the first charging is completed; Step 2: Perform a charge-discharge cycle test on the battery under test under given working conditions, collect the ultrasonic flight time of the battery under test in real time during the charging stage, calculate the ultrasonic flight time offset data at each moment, and obtain the ultrasonic flight time offset test curve; after each charging, collect the ultrasonic scan of the battery under test as a test ultrasonic scan; Step 3: Perform straight line fitting on the ultrasonic flight time offset test data and the reference data of the tested battery at the late charging stage under given working conditions, respectively, to obtain a late charging ultrasonic flight time offset test fitting straight line and a reference fitting straight line; wherein the late charging stage refers to the period from the inflection point of the ultrasonic flight time offset curve to the end of charging; If the difference in slope between the ultrasonic flight time offset test fitting line and the reference fitting line in the late charging period is greater than 0.5%, and the test ultrasonic scan image shows a color block with a significantly different color difference from the reference ultrasonic scan image and disordered color blocks, it indicates that lithium plating has occurred in the tested battery.

2. The nondestructive testing method for lithium deposition of lithium ion batteries based on ultrasonic signals according to claim 1, characterized in that: In the first step, the ultrasonic flight time of the battery during the first charging process under different working conditions is collected, and the ultrasonic flight time is subtracted from the reference time to obtain the ultrasonic flight time offset data. The ultrasonic flight time offset data at all times form an ultrasonic flight time offset reference curve; wherein the reference time is the time corresponding to the maximum amplitude of the ultrasonic signal when the battery is 0% SOC in the open circuit state.

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