Lithium ion battery lithium precipitation quantification method based on pressure signal

Abstract

The invention relates to the technical field of lithium ion batteries, and discloses a lithium ion battery lithium precipitation quantification method based on a pressure signal, which comprises the following steps of: performing charging and discharging cycles of different rates on a to-be-detected battery cell and a comparison battery cell at a temperature T to a specified cycle index; obtaining a discharge capacity set Q, a voltage set V and an expansive force signal set P of the to-be-detected battery cell and the comparison battery cell in the discharge stage, and subtracting the initial discharge expansive force from the expansive force signals of the to-be-detected battery cell and the comparison battery cell in the discharge process; performing differential processing on the expansion force change curve to obtain a differential expansion force-discharge capacity curve; according to the method, nondestructive lithium precipitation detection can be achieved, reversible lithium quantitative analysis is carried out on a lithium precipitation battery, compared with a single relaxation voltage quantification method, the method introduces an expansive force signal, and it is judged that lithium precipitation happens to a battery cell when the starting point of a differential expansive force-discharge capacity curve in the discharge stage is smaller than first differential expansive force.

Description

Technical Field

[0001] The present invention relates to the technical field of lithium-ion batteries, and specifically to a method for quantifying lithium plating in lithium-ion batteries based on pressure signals. Background Art

[0002] Lithium-ion batteries have characteristics such as high energy density, long cycle life, and high power capacity, and are the mainstream power source for electric vehicles. During the charging process, obvious volume expansion caused by lithiation occurs in lithium-ion batteries, resulting in large stresses in battery modules or battery packs, which in turn affects the cycle life and even the safety performance of the batteries.

[0003] The existing methods for detecting lithium plating in lithium-ion batteries are mainly the relaxation voltage method and the disassembly method. The former requires the battery to be immediately static (relaxed) or discharged at a small current after a series of charge and discharge cycles, and by monitoring the change in voltage during the relaxation process, it is judged whether lithium plating occurs in the battery and the quantification of lithium plating. This has been proven by most researchers to be an effective method for detecting lithium plating; the latter is to disassemble a fully charged lithium battery and, by observing the surface of the negative electrode of the battery, if metallic lithium is present, it is determined that lithium plating has occurred in the lithium battery.

[0004] However, the voltage plateau in the relaxation stage is affected by the combined action of lithium stripping and lithium intercalation. When the temperature decreases, the lithium intercalation rate decreases. Therefore, the lithium stripping time reflected by the same amount of lithium plating is prolonged, which in turn affects the accuracy of lithium plating quantification; while the disassembly method belongs to destructive testing and the usage scenario is limited. Therefore, a method for quantifying lithium plating in lithium-ion batteries based on pressure signals is proposed to solve the above problems. Summary of the Invention

[0005] Aiming at the deficiencies of the prior art, the present invention provides a method for quantifying lithium plating in lithium-ion batteries based on pressure signals, which has the advantages of avoiding damaging the lithium battery while quantitatively detecting the reversible lithium capacity in the lithium-plated battery and improving the accuracy of lithium plating quantification, and solves the problems mentioned in the above background art.

[0006] To achieve the above object, the present invention provides the following technical solution: A method for quantifying lithium plating in lithium-ion batteries based on pressure signals, comprising the following steps: S1: At temperature T, perform charge and discharge cycles at different rates on the battery under test and the reference battery until the specified number of cycles is reached, to obtain the discharge capacity set Q, voltage set V, and expansion force signal set P during the discharge stage of the battery under test and the reference battery; S2: Subtract the initial expansion force during discharge from the expansion force signal during the discharge process of the battery under test and the reference battery to obtain the expansion force change curve, and perform differential processing on the expansion force change curve to obtain the differential expansion force-discharge capacity curve A; S3: Determine the lithium plating situation of the battery under test according to the differential expansion force-discharge capacity curve A of the battery under test and the reference battery; S4: Differentiate the differential expansion force-discharge capacity curve A of the battery under test and the reference battery again to obtain the second-order differential expansion force-discharge capacity curve A' of the battery under test and the reference battery; S5: Determine the lithium plating situation of the battery under test according to the second-order differential expansion force-discharge capacity curve A' of the battery under test and the reference battery; S6: Quantify the lithium plating situation of the battery under test.

[0007] Preferably, in step S1, the number of cycles is ten, and the charging rate is 0.2C - 1C.

[0008] Preferably, the specific steps in step S2 are: S2.1: Interpolate and extrapolate the correlation function of the pressure-voltage curve for the data points of the expansion force signal set P and the discharge capacity set Q, and perform difference calculation on the extrapolated curve. The expression is: ; ; where P i is an expansion force value in the expansion force signal set P, △P is the change value of the expansion force, Q i is a capacity value in the discharge capacity set Q, and △Q is the change value of the discharge capacity; S2.2: Plot the differential expansion force-discharge capacity curve A with the change value of the discharge capacity △Q after the difference calculation as the abscissa and the change value of the expansion force △P as the ordinate.

[0009] Preferably, the specific steps in step S3 are: S3.1: Determine that the starting point of the differential expansion force-discharge capacity curve A of the reference battery is the first differential discharge capacity Q r , and the starting point of the differential expansion force-discharge capacity curve A of the battery under test is the first differential discharge capacity Q r '; S3.2: Judge whether the first differential discharge capacity Q r ' < the first differential discharge capacity Q r . If so, lithium plating occurs in the battery under test; otherwise, no lithium plating occurs in the battery under test.

[0010] Preferably, the specific steps in step S5 are: S5.1: Determine that the target capacity at the maximum peak of the second-order differential expansion force-discharge capacity curve A' of the reference battery is Q r-plating , and the target capacity at the maximum peak of the second-order differential expansion force-discharge capacity curve A' of the battery under test is Qr-plating '; S5.2: Determine the target capacity Q of the maximum peak r-plating '> the target capacity Q of the maximum peak r-plating , if yes, then lithium plating occurs in the cell under test, and the target capacity Q of the maximum peak r-plating ' is the reversible lithium content C of the battery under test rev-plating , if no, then it is determined that no lithium plating occurs in the cell under test.

[0011] Preferably, the specific steps for determining the maximum peak of the second-order differential swelling force-discharge capacity curve A' in step S5 are as follows: Step 1: Remove the invalid values in the second-order differential swelling force-discharge capacity curve A' to ensure the validity and integrity of the data; Step 2: Traverse the second-order differential swelling force-discharge capacity curve A'. The experimental data is (x i, f i ). Directly find the point with the largest amplitude and record its index position. The expression is: ; where x i is the discharge capacity value, f i is the amplitude of the second-order differential swelling force-discharge capacity signal, N is the number of data points, is the index position of the largest amplitude, is the maximum amplitude of the second-order differential swelling force-discharge capacity signal, is the discharge capacity value corresponding to the maximum amplitude of the second-order differential swelling force-discharge capacity signal; Step 3: Obtain the corresponding discharge capacity value according to the index of the maximum amplitude point; Step 4: Output the maximum amplitude of the second-order differential swelling force-discharge capacity signal and the corresponding discharge capacity value rev-plating , which is the reversible lithium content C of the cell under test

[0012] Preferably, the specific steps of step S6 are as follows: ; ; ; ; where Q irrev.plating is the irreversible plating capacity, C ch is the charging capacity, C dc is the discharge capacity, C plating is the total capacity generated by lithium platingrev.plating is the reversible plating capacity, C irrev.plating is the irreversible plating capacity, n plating is the amount of lithium in the plating, F is the Faraday constant, m plating is the mass of lithium in the plating, M Li is the molar mass of lithium.

[0013] Compared with the prior art, the present invention provides a method for quantifying lithium plating in a lithium-ion battery based on a pressure signal, having the following beneficial effects: 1. The method for quantifying lithium plating in a lithium-ion battery based on a pressure signal can achieve non-destructive lithium plating detection, and at the same time, perform reversible lithium quantification analysis on the lithium-plated battery. Compared with the single relaxation voltage quantification method, this method introduces an expansion force signal. Experiments show that when the starting point of the differential expansion force-discharge capacity curve in the discharge stage is less than the first differential expansion force, it is determined that lithium plating occurs in the battery cell.

[0014] 2. The method for quantifying lithium plating in a lithium-ion battery based on a pressure signal, compared with the existing lithium plating detection technologies, this method does not require additional processing means. By comparing the first differential expansion force, the occurrence of lithium plating can be intuitively judged, reducing the detection time, reducing the limitation of the detection model's usage scenarios, and having high detection accuracy. On the other hand, in the second-order differential expansion force-discharge capacity curve, the capacity corresponding to the maximum peak intensity is the reversible lithium capacity of the lithium-plated battery. This discovery fills the gap in the current research on quantifying lithium plating by the expansion force signal. It can not only avoid damaging the lithium-ion battery, but also has higher accuracy compared with the commonly used relaxation voltage method in the prior art, improving the accuracy and adaptability of lithium plating quantification. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] Figure 1 is a schematic flow chart of a method for quantifying lithium plating in a lithium-ion battery based on a pressure signal proposed by the present invention; Figure 2 is a graph of the change in expansion force during small-current discharge at 0°C for a method for quantifying lithium plating in a lithium-ion battery based on a pressure signal proposed by the present invention; Figure 3 is a graph of the change in differential expansion force-discharge capacity during small-current discharge at 0°C for a method for quantifying lithium plating in a lithium-ion battery based on a pressure signal proposed by the present invention; Figure 4 is a graph of the change in second-order differential expansion force-discharge capacity during small-current discharge at 0°C for a method for quantifying lithium plating in a lithium-ion battery based on a pressure signal proposed by the present invention; Figure 5 is a graph of the differential voltage during small-current discharge at 0°C for a method for quantifying lithium plating in a lithium-ion battery based on a pressure signal proposed by the present invention; Figure 6 is Figure 5 a partial detailed view in Figure 7 This is the relaxation voltage diagram of small current discharge at 0°C in a lithium deposition quantification method for lithium-ion batteries based on pressure signals proposed by the present invention; Figure 8 is Figure 7 the local detailed drawing in Specific implementation manners

[0016] Next, the technical solutions in the embodiments of the present invention will be clearly and completely described in conjunction with the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without making creative efforts belong to the scope of protection of the present invention.

[0017] Please refer to Figures 1-8 , a lithium deposition quantification method for lithium-ion batteries based on pressure signals, comprising the following steps: S1: At temperature T, charge and discharge the battery under test and the reference battery at different rates until the specified number of cycles, and obtain the discharge capacity set Q, voltage set V, and expansion force signal set P during the discharge stage of the battery under test and the reference battery; The number of cycles is ten, and the charge rate is any value in 0.2C - 1C; In a constant temperature incubator at 0°C, charge and discharge 4 experimental soft-pack batteries of the same specification at different charge and discharge rates (0.2C, 0.5C, 0.75C, 1C). After 10 charge and discharge cycles, each experimental battery is charged at a constant current and constant voltage at the previous charge rate, and then immediately discharged at 1A to obtain the expansion force signal, voltage signal, and discharge capacity signal during the discharge process of the lithium-ion battery; It should be noted that in the currently widely used battery material systems, whether it is the positive electrode materials such as lithium iron phosphate, lithium manganese iron phosphate, ternary materials, or the negative electrode materials such as graphite and silicon-based materials, during the process of lithium ion extraction (insertion), the lattice spacing inside the positive and negative electrode materials will change, resulting in a change in the volume of the electrode. This volume change will ultimately be converted into the change in the expansion force detected by the sensor.

[0018] The positive electrode material of the lithium-ion battery used in this embodiment is lithium iron phosphate, and the negative electrode material is graphite. Its rated voltage is 2.0V - 3.65V, and the nominal capacity is 10Ah. The experimental equipment used includes: a three-plywood constant gap device, an Arbin charge and discharge tester (SN: 215671), a Galaxy high and low temperature incubator (SDJ405F), and the expansion force is collected through a SmowoLCS-C3 spoke-type sensor (accuracy: 0.03mV / V) connected to an Arbin pressure collector.

[0019] S2: Subtract the initial expansion force during discharge from the expansion force signals of the battery cell under test and the reference battery cell during the discharge process to obtain the expansion force change curve. Differentiate the expansion force change curve to obtain the differential expansion force - discharge capacity curve A; S3: Determine the lithium plating situation of the battery cell under test based on the differential expansion force - discharge capacity curve A of the battery cell under test and the reference battery cell; S4: Differentiate the differential expansion force - discharge capacity curve A of the battery cell under test and the reference battery cell again to obtain the second - order differential expansion force - discharge capacity curve A' of the battery cell under test and the reference battery cell; S5: Determine the lithium plating situation of the battery cell under test based on the second - order differential expansion force - discharge capacity curve A' of the battery cell under test and the reference battery cell; At the end of charging and transitioning to the small - current discharge stage, the negative electrode undergoes multiple behaviors such as lithium stripping and de - lithiation. Among them, the energy required for lithium stripping is relatively low. Therefore, at the initial stage of discharge, the battery mainly undergoes lithium stripping reactions. In a lithium - plated battery, since lithium is deposited on the surface of the negative electrode, which is different from the normal battery where lithium ions are embedded in the graphite lattice, the change in expansion force shows abnormality compared to a normal battery. Therefore, the reversible lithium quantification of a lithium - plated battery can be carried out by detecting the change in expansion force per unit capacity.

[0020] S6: Quantify the lithium plating situation of the battery cell under test.

[0021] Specific steps in step S2: S2.1: Interpolate and extrapolate the correlation function of the pressure - voltage curve for the data points of the expansion force signal set P and the discharge capacity set Q. Perform difference calculation on the extrapolated curve. The expression is: ; ; where P i is an expansion force value in the expansion force signal set P, △P is the change in expansion force, Q i is a capacity value in the discharge capacity set Q, and △Q is the change in discharge capacity; S2.2: Use the change in discharge capacity △Q after difference calculation as the abscissa and the change in expansion force △P as the ordinate to plot the differential expansion force - discharge capacity curve.

[0022] Specific steps in step S3 are: S3.1: Determine that the starting point of the differential expansion force - discharge capacity curve A of the reference battery cell is the first differential discharge capacity Q r , and the starting point of the differential expansion force - discharge capacity curve A of the battery cell under test is the first differential discharge capacity Q r '; S3.2: Judge the first differential discharge capacity Q r'<First differential discharge capacity Q r , if so, the battery under test has lithium plating phenomenon, otherwise the battery under test does not have lithium plating phenomenon.

[0023] The specific steps in step S5 are as follows: S5.1: Determine that the target capacity of the maximum peak of the second-order differential expansion force-discharge capacity curve A' of the comparison cell is Q r-plating , and the target capacity of the maximum peak of the second-order differential expansion force-discharge capacity curve A' of the cell under test is Q r-plating '; S5.2: Judge whether the target capacity Q r-plating ' of the maximum peak > the target capacity Q r-plating of the maximum peak. If so, the cell under test has lithium plating phenomenon, and the target capacity Q r-plating ' is the reversible lithium content C rev-plating of the battery under test. If not, it is determined that the cell under test does not have lithium plating.

[0024] The specific steps to determine the maximum peak of the second-order differential expansion force-discharge capacity curve A' in step S5 are as follows: Step 1: Remove the invalid values in the second-order differential expansion force-discharge capacity curve A' to ensure the validity and integrity of the data; Step 2: Traverse the second-order differential expansion force-discharge capacity curve A'. The experimental data is (x i, f i ). Directly find the point with the largest amplitude and record its index position. The expression is: ; Among them, x i is the discharge capacity value, f i is the amplitude of the second-order differential expansion force-discharge capacity signal, N is the number of data points, is the index position of the largest amplitude, is the maximum amplitude of the second-order differential expansion force-discharge capacity signal, is the discharge capacity value corresponding to the maximum amplitude of the second-order differential expansion force-discharge capacity signal; Step 3: Obtain the corresponding discharge capacity value according to the index of the maximum amplitude point; Step 4: Output the maximum amplitude of the second-order differential expansion force-discharge capacity signal and the corresponding discharge capacity value , which is the reversible lithium content C rev-plating of the cell under test, and mark the peak position in the signal in a visual way.

[0025] The specific steps of step S6 are as follows: ; ; ; ; Among them, Q irrev.plating is the irreversible plating capacity, C ch is the charging capacity, C dc is the discharging capacity, C plating is the total capacity generated by lithium plating, C rev.plating is the reversible plating capacity, C irrev.plating is the irreversible plating capacity, n plating is the amount of lithium in the plating, F is the Faraday constant, F = 96485.3399 C / mol -1 , m plating is the mass of lithium in the plating, M Li is the molar mass of lithium, M Li = 6.94 g / mol -1 .

[0026] In use, under the same charge-discharge conditions, the relaxation voltage method (VRP) and differential voltage method (DVA), which are currently recognized methods for quantifying lithium deposition, are used to verify the lithium deposition quantification method for lithium-ion batteries based on the expansion force signal described in this article.

[0027] Based on existing research, it is generally believed that the differential voltage method (DVA) has high accuracy in quantifying lithium deposition. Therefore, this study uses the DVA detection method as a benchmark; Table 1 ; Table 2 ; In summary, the lithium deposition quantification method for lithium-ion batteries based on the pressure signal can achieve non-destructive lithium deposition detection, and at the same time, reversible lithium quantification analysis is carried out for lithium-deposited batteries. Compared with the single relaxation voltage quantification method, this method introduces the expansion force signal. Experiments show that when the starting point of the differential expansion force-discharge capacity curve in the discharging stage is less than the first differential expansion force, it is determined that lithium deposition occurs in the battery cell; Moreover, compared with the existing lithium deposition detection technologies, this method does not require additional processing means. By comparing the first differential expansion force, the occurrence of lithium deposition can be intuitively judged, reducing the detection time, reducing the limitations of the detection model's usage scenarios, and having high detection accuracy. On the other hand, in the second-order differential expansion force-discharge capacity curve, the capacity corresponding to the maximum peak intensity is the reversible lithium capacity of the lithium-deposited battery. This discovery fills the gap in the current research on quantifying lithium deposition using the expansion force signal. It can not only avoid damaging the lithium-ion battery, but also has higher accuracy compared with the commonly used relaxation voltage method, improving the accuracy and adaptability of lithium deposition quantification.

[0028] It should be noted that the term "comprise", "include" or any other variant thereof is intended to cover non-exclusive inclusion, such that a process, method, article or apparatus comprising a series of elements not only includes those elements but also includes other elements not expressly listed, or further includes elements inherent to such process, method, article or apparatus. Without further limitation, an element defined by the phrase "comprising an..." does not exclude the presence of additional identical elements in the process, method, article or apparatus comprising said element.

[0029] Although the embodiments of the present invention have been shown and described, it will be understood by those of ordinary skill in the art that various changes, modifications, substitutions and variations can be made to these embodiments without departing from the principles and spirit of the present invention, and the scope of the present invention is defined by the appended claims and their equivalents.

Claims

1. A method for quantifying lithium plating in a lithium-ion battery based on pressure signals, characterized in that: Including the following steps: S1: At temperature T, perform charge and discharge cycles at different rates on the cell under test and the reference cell until a specified number of cycles is reached, obtaining the discharge capacity set Q, voltage set V, and swelling force signal set P during the discharge phase of the cell under test and the reference cell; S2: Subtract the initial swelling force during discharge from the swelling force signal during the discharge process of the cell under test and the reference cell to obtain the swelling force change curve, and perform differential processing on the swelling force change curve to obtain the differential swelling force-discharge capacity curve A; S3: Judge the lithium plating situation of the cell under test according to the differential swelling force-discharge capacity curve A of the cell under test and the reference cell; S4: Perform differential processing on the differential swelling force-discharge capacity curve A of the cell under test and the reference cell again to obtain the second-order differential swelling force-discharge capacity curve A' of the cell under test and the reference cell; S5: Judge the lithium plating situation of the cell under test according to the second-order differential swelling force-discharge capacity curve A' of the cell under test and the reference cell; S6: Quantify the lithium plating situation of the cell under test.

2. The method for quantitatively analyzing lithium deposition of a lithium-ion battery based on a pressure signal according to claim 1, wherein In step S1, the number of cycles is ten, and the charge rate is 0.2C-1C.

3. A method for quantifying lithium deposition in a lithium-ion battery based on pressure signals according to claim 1, characterized in that The specific steps in step S2 are: S2.1: Interpolate and extrapolate the correlation function of the pressure-voltage curve for the data points of the swelling force signal set P and the discharge capacity set Q, and perform difference calculation on the extrapolated curve. The expression is: ； ； Among them, P i is an expansion force value in the expansion force signal set P, △P is the expansion force change value, Q i is a capacity value in the discharge capacity set Q, and △Q is the discharge capacity change value; S2.2: Using the discharge capacity change value △Q after the difference calculation as the abscissa and the swelling force change value △P as the ordinate, plot to obtain the differential swelling force-discharge capacity curve A.

4. A method for quantifying lithium plating in a lithium-ion battery based on a pressure signal according to claim 1, characterized in that, The specific steps in step S3 are: S3.1: Determine that the starting point of the differential expansion force-discharge capacity curve A of the comparison cell is the first differential discharge capacity Q r , and the starting point of the differential expansion force-discharge capacity curve A of the cell under test is the first differential discharge capacity Q r '; S3.2: Determine the first differential discharge capacity Q r '< the first differential discharge capacity Q r , if yes, lithium plating occurs in the battery under test, otherwise lithium plating does not occur in the battery under test.

5. A method for quantifying lithium deposition in a lithium-ion battery based on pressure signals according to claim 1, characterized in that, The specific steps in step S5 are: S5.1: Determine that the target capacity of the maximum peak of the second-order differential expansion force-discharge capacity curve A' of the comparison cell is Q r-plating , and the target capacity of the maximum peak of the second-order differential expansion force-discharge capacity curve A' of the cell under test is Q r-plating '; S5.2: Determine the target capacity Q of the maximum peak r-plating '> the target capacity Q of the maximum peak r-plating , if yes, then lithium plating occurs in the cell under test, and the target capacity Q of the maximum peak r-plating ' is the reversible lithium content C of the battery under test rev-plating , if no, then it is determined that no lithium plating occurs in the cell under test.

6. The method for quantifying lithium deposition in a lithium-ion battery based on a pressure signal according to claim 5, characterized in that, The specific steps for determining the maximum peak value of the second-order differential swelling force-discharge capacity curve A' in step S5 are: Step 1: Remove the invalid values in the second-order differential swelling force-discharge capacity curve A' to ensure the validity and integrity of the data; Step 2: Traverse the second-order differential expansion force-discharge capacity curve A', and the experimental data is (x i, f i ). Directly find the point with the largest amplitude and record its index position. The expression is: ； where x i is the discharge capacity value, f i is the amplitude of the second-order differential expansion force-discharge capacity signal, N is the number of data points, is the index position with the maximum amplitude, is the maximum amplitude of the second-order differential expansion force-discharge capacity signal, is the discharge capacity value corresponding to the maximum amplitude of the second-order differential expansion force-discharge capacity signal; Step 3: According to the index of the maximum amplitude point, obtain the corresponding discharge capacity value; Step 4: Output the maximum second-order differential expansion force - the maximum amplitude of the discharge capacity signal and the corresponding discharge capacity value , which is the reversible lithium content C of the battery cell to be measured rev-plating , and mark the peak position in the signal in a visual way.

7. A method for quantifying lithium plating in a lithium-ion battery based on a pressure signal according to claim 1, characterized in that, The specific steps in step S6 are: ； ； ； ； Among them, Q irrev.plating is the irreversible plating capacity, C ch is the charging capacity, C dc is the discharging capacity, C plating is the total capacity generated by lithium plating, C rev.plating is the reversible plating capacity, C irrev.plating is the irreversible plating capacity, n plating is the amount of lithium in the plating, F is the Faraday constant, m plating is the mass of lithium in the plating, M Li is the molar mass of lithium.

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