Sodium ion battery sodium precipitation behavior working condition monitoring method based on battery impedance analysis

Abstract

The invention discloses a working condition monitoring method for a sodium ion battery sodium precipitation behavior based on battery impedance analysis. The core principle of the method is based on the following points: when sodium precipitation occurs, sodium metal is deposited on the surface of hard carbon, so that the physical and chemical properties of the surface of the hard carbon can be changed; the conductivity of sodium metal is obviously different from that of a hard carbon material, so that the charge transfer resistance of hard carbon is obviously changed. In addition, the appearance of the sodium metal also causes the change of the electric double layer capacitance on the hard carbon surface; therefore, whether sodium metal begins to be separated out or not can be accurately judged by detecting the change of the charge transfer resistance and the electric double-layer capacitance on the hard carbon surface; according to the scheme, in-situ monitoring of sodium metal precipitation can be achieved under the condition that the battery structure is not damaged, the sodium metal precipitation situation of the sodium ion battery in the half-battery discharging process can be sensitively captured, and sodium metal deposition of the half battery, the full battery and the soft package battery under the actual operation condition can be monitored in real time.

Description

Technical Field

[0001] The present invention relates to the field of battery technology, and in particular to a working condition monitoring method of sodium precipitation behavior of a sodium ion battery based on battery impedance analysis. Background Art

[0002] Sodium precipitation is an unfavorable side reaction that occurs in sodium-ion batteries during long-term cycling, and usually occurs on the hard carbon negative electrode side. This phenomenon will not only gradually intensify with the increase in the number of cycles, but will also lead to the formation of a large amount of sodium metal deposition on the hard carbon surface, thereby significantly causing irreversible decay of the battery capacity. This sodium deposition behavior has an extremely negative impact on the overall performance of sodium-ion batteries, especially safety and service life, and has become one of the key issues restricting the commercial application of sodium-ion batteries.

[0003] According to current research, the cause of the sodium precipitation phenomenon can be attributed to two main aspects. First, the surface polarization of the hard carbon negative electrode material is one of the important factors leading to sodium precipitation. Due to the difference in the transmission rate of sodium ions in the electrolyte and the hard carbon material, sodium ions are easily accumulated on the hard carbon surface, resulting in excessive surface sodium ion concentration. This local high concentration will trigger electrochemical polarization, which in turn induces the deposition of sodium metal on the hard carbon surface. Secondly, the mismatch between the positive and negative electrode capacities inside the battery may also lead to sodium precipitation. When the sodium ion storage capacity of the negative electrode material reaches saturation, the excess sodium ions cannot be embedded in the hard carbon structure and can only be precipitated in the form of metal and deposited on the negative electrode surface. Especially under extreme conditions such as high voltage, high rate or low temperature, the sodium precipitation phenomenon is more serious.

[0004] Therefore, how to effectively monitor and inhibit the deposition of sodium metal has become one of the key challenges to improving the performance of sodium-ion batteries. At present, the detection of sodium precipitation phenomenon usually relies on technical means such as X-ray diffraction (XRD), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). However, these methods are often destructive and require disassembly of the battery, making it difficult to achieve in-situ detection of the battery during actual cycling. To this end, it is urgent to develop an efficient and non-destructive sodium metal precipitation monitoring technology to achieve real-time condition monitoring of sodium precipitation behavior in actual battery operation, help early warning and optimize the battery working state, thereby extending the service life of sodium-ion batteries and improving their safety. Summary of the invention

[0005] In view of the problems existing in the above-mentioned prior art, the present invention provides a working condition monitoring method of sodium precipitation behavior of a sodium ion battery based on battery impedance analysis, which can effectively solve the problems existing in the above-mentioned prior art.

[0006] The technical solution of the present invention comprises the following steps:

[0007] S1, applying a sinusoidal current to the battery, performing impedance tests at different cycles or charge and discharge cycles, and obtaining the battery impedance values ​​at different charge states;

[0008] S2, record the electrochemical impedance spectroscopy data of the impedance test, use software to perform DRT analysis on the electrochemical impedance spectroscopy data, obtain the DRT values ​​of the battery at different states of charge, and fit the impedance values ​​using the equivalent circuit method based on the DRT results to obtain the electrolyte interface resistance, charge transfer resistance and double layer capacitance data;

[0009] S3, plotting the data obtained by fitting according to the equivalent circuit method;

[0010] S4, observing whether the data graphs of the charge transfer resistance and the double-layer capacitance in step S3 have significant inflection points, so as to determine whether there is sodium precipitation in the battery during different cycles or charge and discharge cycles;

[0011] S5. When a significant inflection point is observed in the data graphs of charge transfer resistance and double-layer capacitance, indicating that sodium precipitation occurs in the battery, the charge and discharge program is adjusted.

[0012] Furthermore, in step S1, the impedance test of different cycle periods is to perform impedance test within any cycle period of the battery according to different set cycle numbers, and record the impedance value under specific charge and discharge state; the cycle period ranges from 1 to 100 circles, and the impedance test includes the impedance values ​​under fully charged state C and fully discharged state D.

[0013] Furthermore, in step S1, the impedance test of the charge and discharge cycle is to test the battery impedance according to different set charge and discharge stages in any charging cycle of the battery to obtain impedance values ​​under different charge states.

[0014] Furthermore, the state of charge ranges from 0% to 150% SOC.

[0015] Further, in step S1, the battery includes one or more of a negative electrode button half-cell, a button full cell, a soft-pack cell and a cylindrical cell.

[0016] Further, in step S1, the sinusoidal current includes a sinusoidal current with a certain frequency range and a sinusoidal current with a specific frequency.

[0017] Furthermore, the frequency range of the sinusoidal current is 0.01-100000 Hz.

[0018] Furthermore, the test scenario of the impedance test method includes applying a sinusoidal current during the battery charging and discharging process or applying a sinusoidal current after the battery is allowed to rest.

[0019] Furthermore, the battery rest time ranges from 0.5 to 24 hours.

[0020] Furthermore, in step S2, DRT analysis is performed on the electrochemical impedance spectroscopy data using MATLAB.

[0021] By adopting the above technical solution, the present invention has the following beneficial effects compared with the prior art:

[0022] This scheme can realize in-situ monitoring of sodium metal precipitation without destroying the battery structure. This method can not only sensitively capture the sodium metal precipitation of sodium-ion batteries during half-cell discharge, but also monitor in real time the sodium metal deposition of half-cells, full cells and soft-pack batteries under actual operating conditions, thereby providing an early warning of sodium precipitation and achieving an accurate assessment of the battery health status. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0024] Figure 1 The impedance spectrum curve diagram of Example 1 in the present invention;

[0025] Figure 2 This is an impedance spectrum curve diagram of Example 2 in the present invention;

[0026] Figure 3 The state of charge curve of the electrolyte interface resistance obtained by impedance spectrum data fitting in Example 1 of the present invention;

[0027] Figure 4 The state of charge curve of the charge transfer resistance obtained by impedance spectrum data fitting in Example 1 of the present invention;

[0028] Figure 5 The charge state curve diagram of the double layer capacitor is obtained by fitting the impedance spectrum data in Example 1 of the present invention. DETAILED DESCRIPTION

[0029] The present invention will be further described in detail below in conjunction with the accompanying drawings and examples. It is particularly noted that the following examples are only used to illustrate the present invention, but are not intended to limit the scope of the present invention. Similarly, the following examples are only partial embodiments of the present invention rather than all embodiments, and all other embodiments obtained by those of ordinary skill in the art without creative work are within the scope of protection of the present invention.

[0030] like Figures 1 to 5 As shown, this scheme provides a working condition monitoring method for sodium precipitation behavior of sodium ion batteries based on battery impedance analysis.

[0031] The core principle of this method is based on the following points: When sodium precipitation occurs, sodium metal is deposited on the hard carbon surface, which will cause changes in the physical and chemical properties of the hard carbon surface. This is because the conductivity of sodium metal is significantly different from that of hard carbon materials, which in turn causes a significant change in the charge transfer resistance of hard carbon. In addition, the appearance of sodium metal will also cause changes in the double-layer capacitance of the hard carbon surface. Therefore, by detecting the changes in the charge transfer resistance and double-layer capacitance of the hard carbon surface, it is possible to accurately determine whether sodium metal has begun to precipitate.

[0032] Specifically, by applying a sinusoidal current to the battery, the impedance spectrum of the battery can be obtained, and then key parameters including electrolyte interface resistance, charge transfer resistance and double-layer capacitance can be obtained. Among them, the charge transfer resistance is directly related to the charge transfer characteristics of the hard carbon surface, and the double-layer capacitance reflects the change of the double-layer capacitance. By analyzing the impedance data of sodium-ion batteries under different states of charge, the changes of charge transfer resistance and double-layer capacitance during the charge and discharge process can be tracked. When a significant inflection point is observed in the charge transfer resistance and double-layer capacitance, it can be determined whether there is precipitation of sodium metal during the charge and discharge or cycle process.

[0033] This method comprises the following steps:

[0034] S1, applying a sinusoidal current to the battery, performing impedance tests at different cycles or charge-discharge cycles, and obtaining battery impedance values ​​at different charge states; the impedance tests at different cycle cycles are performed within any cycle of the battery according to different set cycle times, and the impedance values ​​at specific charge-discharge states are recorded; the cycle range is 1 to 100 cycles, and the impedance test includes impedance values ​​at fully charged state C and fully discharged state D. This is to analyze the performance changes of the battery during long-term cycling.

[0035] The impedance test of the charge and discharge cycle is to test the battery impedance according to the different set charge and discharge stages in any charging cycle of the battery, and obtain the impedance values ​​under different charge states. The range of the charge state is 0% to 150% SOC. To ensure that the battery impedance changes in normal and overcharged states are covered. The sinusoidal current includes sinusoidal currents with a certain range of frequencies and sinusoidal currents with specific frequencies. The frequency range of the sinusoidal current is 0.01 to 100000 Hz. The test scenarios of the impedance test method include applying a sinusoidal current during the battery charging and discharging process or applying a sinusoidal current after the battery is paused and left to stand. The battery standing time range is 0.5 to 24 hours.

[0036] S2, record the electrochemical impedance spectroscopy data of the impedance test, use software to perform DRT analysis on the electrochemical impedance spectroscopy data, obtain the DRT values ​​of the battery at different states of charge, and fit the impedance values ​​using the equivalent circuit method based on the DRT results to obtain the electrolyte interface resistance, charge transfer resistance and double layer capacitance data;

[0037] The equivalent circuit method is used to fit and analyze the impedance data. The electrochemical system is regarded as an equivalent circuit. This equivalent circuit is composed of basic components such as resistance (R), capacitance (C), and inductance (L) in different ways such as series or parallel connection. Through EIS, the composition of the equivalent circuit and the size of each component can be determined. The electrochemical meaning of these components can be used to analyze the structure of the electrochemical system and the properties of the electrode process. The following two different equivalent circuit models are used. Through this model fitting, we get parameters including electrolyte interface resistance (Rsei), charge transfer resistance (Rct), double layer capacitance (Cd), etc.

[0038] Model 1:

[0039]

[0040] Model 2:

[0041]

[0042] S3, plot the data obtained by fitting according to the equivalent circuit method; preferably, use MATLAB to perform DRT analysis on the electrochemical impedance spectroscopy data. When sodium precipitation occurs at the negative electrode of a sodium ion battery, a significant change in the charge transfer impedance and charge transfer resistance will be caused, and the degree of change is significantly related to the severity of sodium precipitation. In the electrochemical impedance spectrum, the change in charge transfer resistance is mainly reflected in the frequency range of 200Hz to 0.1Hz. The charge transfer resistance shows a three-stage change with the extension of discharge time. First, in the platform area, the charge transfer resistance shows a slow downward trend; below 0V, the charge transfer resistance accelerates to decrease; with the extension of discharge time, the charge transfer resistance shows a slow decrease.

[0043] S4, observing whether the data graphs of the charge transfer resistance and the double-layer capacitance in step S3 have significant inflection points, so as to determine whether there is sodium precipitation in the battery during different cycles or charge and discharge cycles;

[0044] S5. When a significant inflection point is observed in the data graphs of charge transfer resistance and double-layer capacitance, indicating that sodium precipitation occurs in the battery, the charge and discharge program is adjusted.

[0045] The following are the experimental steps and experimental results of using this method to detect the sodium precipitation behavior of batteries:

[0046] Embodiment 1:

[0047] The following steps are involved:

[0048] S1: Discharge the negative electrode button half-cell at temperature T, let it stand for a certain period of time, and then perform an AC impedance test.

[0049] S2: Extract the impedance spectrum data of the discharge stage in S1, use the equivalent circuit method to fit, take the value of Rct and the state of charge to plot, and according to the change of the curve in the figure, use the maximum difference method to screen out the value of sodium precipitation characteristic Rct;

[0050] S3: Charge and discharge the negative electrode button half-cell at different charge and discharge rates C at temperature T, and perform impedance tests on the battery at different cycle periods.

[0051] S4: Conduct impedance tests on the battery at different cycle periods / charge and discharge cycles according to S3, and compare the sodium precipitation of the hard carbon negative electrode at different rates.

[0052] Experimental group 1,

[0053] A button half-cell with a nominal specific capacity of 300 mAh / g is assembled with hard carbon. At temperature T, in any charging cycle of the above battery, the battery impedance is tested according to different SOC stages set while the battery is charged and discharged. The test range is 0.01-105 Hz, and the impedance values ​​at different SOCs are obtained. The SOC range is 0%-150% SOC. Figure 1 The impedance spectra at 0% SOC, 100% SOC and 150% SOC are shown. It can be observed that when the SOC exceeds 100%, Rct and Rsei change significantly.

[0054] Experimental group 2,

[0055] A button half-cell with hard carbon as the negative electrode is assembled. In any charging cycle of the above battery, after the battery is charged and discharged to different SOC stages, the battery is left to stand for 2 hours and the battery impedance is tested. The test frequency is fixed at 15 Hz to obtain the impedance values ​​at different SOCs.

[0056] Experimental group three,

[0057] A button half-cell with hard carbon as the negative electrode is assembled. In any charging cycle of the above battery, when the battery is charged and discharged to different SOC stages, a fixed-frequency sinusoidal current is applied to the battery. The test frequency is fixed at 15Hz to obtain the impedance values ​​at different SOCs.

[0058] Experimental group 4,

[0059] A button half-cell with a nominal specific capacity of 300 mAh / g is assembled with hard carbon. At temperature T, in any charging cycle of the above battery, the battery impedance is tested according to different set SOC stages while the battery is charged and discharged. The test range is 0.01-105 Hz, and the impedance values ​​at different SOCs are obtained.

[0060] The electrochemical impedance spectroscopy data obtained from experimental groups one to four were imported into MATLAB for DRT analysis.

[0061] Use any of the following models to fit the impedance data of experimental groups 1 to 4:

[0062] Model 1:

[0063]

[0064] Model 2:

[0065]

[0066] With the state of charge as the x-axis and the impedance value as the y-axis, a state of charge map of Rct, Rse i and Cd is constructed, and whether sodium precipitation occurs is identified based on the inflection point of the image.

[0067] Figure 3 The sodium precipitation inflection point in the charge state diagram of Rse i is shown. When sodium precipitation occurs, the change trend of Rse i changes significantly.

[0068] Figure 4 The sodium precipitation inflection point in the charge state curve of Rct is shown. When sodium precipitation occurs, the change trend of Rct changes significantly.

[0069] Figure 5 The sodium precipitation inflection point in the charge state curve of Cd is shown. When sodium precipitation occurs, the change trend of Cd changes significantly.

[0070] Embodiment 2:

[0071] The following steps are involved:

[0072] S1: Charge and discharge the sodium-ion soft-pack battery at temperature T, and collect AC impedance data at different voltages in the charging and discharging stages.

[0073] S2: Extract the impedance spectrum data of the charge and discharge stage in S1, fit it using the equivalent circuit method, plot the Rct value against the charge and discharge time, compare the Rct change trend in the charge and discharge stages, and screen out the Rct value of the sodium precipitation characteristic of the sodium ion soft-pack battery through the maximum difference method based on the curve changes.

[0074] S3: Charge and discharge the sodium ion soft-pack battery at different charge and discharge rates C at temperature T, and perform impedance tests on the battery at different cycle periods.

[0075] S4: Conduct impedance tests on the battery at different cycle periods / charge and discharge cycles in S3, and compare the sodium precipitation of the hard carbon negative electrode of the sodium ion soft-pack battery at different rates.

[0076] Experimental group 1,

[0077] Assemble a soft-pack battery with hard carbon as the negative electrode. At temperature T, in any charging cycle of the above battery, after the battery is charged and discharged to different SOC stages, the battery is left to stand for 2 hours, and the battery impedance is tested. The test range is 0.01~105Hz, and the impedance values ​​at different SOCs are obtained.

[0078] Experimental group 2,

[0079] Assemble a soft-pack battery with hard carbon as the negative electrode, and perform a long-cycle charge and discharge test on the battery at a rate of 1C, with 10 circles as a cycle. After each cycle, let it stand for 2 hours and test the battery impedance at temperature T. Repeat this step 100 times and record the impedance values ​​under different cycle periods. Figure 2 The impedance image changes under different SOC states are shown.

[0080] Figure 2 The impedance image changes under different SOC states are shown.

[0081] The remaining steps are the same as those in the first embodiment and will not be described in detail here.

[0082] The spectrum obtained in Example 2, when sodium precipitation occurs, is the same as the spectrum in Example 1, and the variation trends of Rsei, Rct and Cd all change significantly.

[0083] The above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit the same. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that the technical solutions described in the aforementioned embodiments may still be modified, or some of the technical features may be replaced by equivalents. However, these modifications or replacements do not deviate the essence of the corresponding technical solutions from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for monitoring the sodium precipitation behavior of a sodium ion battery based on battery impedance analysis, characterized in that: The steps include: S1, applying a sinusoidal current to the battery, performing impedance tests at different cycles or charge and discharge cycles, and obtaining the battery impedance values ​​at different charge states; S2, record the electrochemical impedance spectroscopy data of the impedance test, use software to perform DRT analysis on the electrochemical impedance spectroscopy data, obtain the DRT values ​​of the battery at different states of charge, and fit the impedance values ​​using the equivalent circuit method based on the DRT results to obtain the electrolyte interface resistance, charge transfer resistance and double layer capacitance data; S3, plotting the data obtained by fitting according to the equivalent circuit method; S4, observing whether the data graphs of the charge transfer resistance and the double-layer capacitance in step S3 have significant inflection points, so as to determine whether there is sodium precipitation in the battery during different cycles or charge and discharge cycles; S5. When a significant inflection point is observed in the data graphs of charge transfer resistance and double-layer capacitance, indicating that sodium precipitation occurs in the battery, the charge and discharge program is adjusted.

2. The method for monitoring the sodium precipitation behavior of a sodium ion battery based on battery impedance analysis according to claim 1, characterized in that: In step S1, the impedance test of different cycle periods is to perform impedance test in any cycle period of the battery according to different set cycle numbers, and record the impedance value under specific charge and discharge state; the cycle period ranges from 1 to 100 circles, and the impedance test includes the impedance values ​​under fully charged state C and fully discharged state D.

3. The method for monitoring the sodium precipitation behavior of a sodium ion battery based on battery impedance analysis according to claim 1, characterized in that: In step S1, the impedance test of the charge and discharge cycle is to test the battery impedance according to different set charge and discharge stages in any charge cycle of the battery to obtain impedance values ​​under different charge states.

4. A method for monitoring the sodium precipitation behavior of a sodium ion battery based on battery impedance analysis according to claim 3, characterized in that: The state of charge ranges from 0% to 150% SOC.

5. The method for monitoring the sodium precipitation behavior of a sodium ion battery based on battery impedance analysis according to claim 1, characterized in that: In step S1, the battery includes one or more of a negative electrode button half-cell, a button full cell, a soft-pack cell, and a cylindrical cell.

6. The method for monitoring the sodium precipitation behavior of a sodium ion battery based on battery impedance analysis according to claim 1, characterized in that: In step S1 , the sinusoidal current includes a sinusoidal current with a certain frequency range and a sinusoidal current with a specific frequency.

7. A method for monitoring the sodium precipitation behavior of a sodium ion battery based on battery impedance analysis according to claim 6, characterized in that: The frequency range of the sinusoidal current is 0.01-100000 Hz.

8. A method for monitoring the sodium precipitation behavior of a sodium ion battery based on battery impedance analysis according to claim 7, characterized in that: The test scenario of the impedance test method includes applying a sinusoidal current during the battery charging and discharging process or applying a sinusoidal current after the battery is paused and rested.

9. A method for monitoring the sodium precipitation behavior of a sodium ion battery based on battery impedance analysis according to claim 8, characterized in that: The battery standing time ranges from 0.5 to 24 hours.

10. The method for monitoring the sodium precipitation behavior of a sodium ion battery based on battery impedance analysis according to claim 1, characterized in that: In step S2, DRT analysis is performed on the electrochemical impedance spectroscopy data using MATLAB.

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