A method, battery and device for testing gas production of lithium-ion batteries

Abstract

The present invention discloses a test method, battery and device for the gas production of lithium-ion batteries. The method comprises the following steps: performing an EIS test on the lithium-ion battery to obtain the EIS test results; analyzing the EIS test results using relaxation time analysis to determine the relaxation time center frequency of the contact impedance; performing a single frequency impedance scan during the battery cell charging process; the frequency adopts the relaxation time center frequency; comparing the contact impedance reduction rate of the first battery cell and the second battery cell to determine the gas production inside the first battery cell and the second battery cell; and the first battery cell and the second battery cell have the same internal reserved space. Completing the gas production test of the battery cell under non-destructive conditions helps to improve the performance and safety of the battery while reducing costs.

Description

Technical Field

[0001] The present invention relates to the technical field of lithium batteries, and in particular to a method, a battery and a device for testing the gas production of lithium ion batteries. Background Art

[0002] The contradiction between energy shortage and environmental pollution is becoming more and more serious, which has led to the large-scale development of energy storage technology. Among them, lithium-ion batteries are one of the most commonly used energy storage technologies and have been widely used in portable electronic products and electric vehicles. Based on the barrel effect, the battery capacity is determined by the electrode with the lowest specific capacity. At present, it is often limited by the positive electrode material. However, the aging and safety issues of high-specific-capacity positive electrode materials limit their use. Thermal runaway and gassing of batteries are two major research areas. Especially when operating under abuse conditions such as overcharging and discharging, operating outside the temperature limit, and crushing or puncturing to cause battery deformation, there are many sources of gas precipitation in lithium-ion batteries. In addition to causing safety problems, gas precipitation can also seriously affect battery performance and is related to electrode degradation, shortened shelf life, shortened cycle life, electrolyte displacement and increased battery impedance. The battery cell is a closed and complex electrochemical system. Although soft-packed pouch cells can be tested by the "drainage method", it is difficult to measure the gas production inside the cylindrical battery cell, square aluminum shell battery cell and other batteries with hard constraints on the outside.

[0003] The gas production of battery cells seriously affects the life of the battery cells. However, there is no convenient non-destructive measurement method for the gas production of cylindrical and square aluminum shell battery cells. Ultrasonic testing and neutron diffraction are better solutions, but the price of ultrasonic and neutron detection devices is often millions or tens of millions, which makes it difficult to apply them on a large scale. Summary of the invention

[0004] One of the purposes of the present invention is to provide a method, a battery and a device for testing the gas production of lithium-ion batteries, which can complete the gas production test of the battery cell under non-destructive conditions, help improve the performance and safety of the battery, and reduce costs.

[0005] To achieve the above object, the present invention provides the following technical solutions:

[0006] A method for testing the gas production of a lithium-ion battery, the method comprising the following steps:

[0007] Perform EIS test on lithium-ion batteries and obtain EIS test results;

[0008] The EIS test results are analyzed using relaxation time analysis to determine the relaxation time center frequency of the contact impedance;

[0009] During the battery cell charging process, a single frequency impedance scan is performed; the frequency is the relaxation time center point frequency;

[0010] The contact impedance reduction rates of the first battery cell and the second battery cell are compared to determine the gas generation amounts inside the first battery cell and the second battery cell; and the first battery cell and the second battery cell have the same internal reserved space.

[0011] In the above technical solution, the contact impedance reduction rate of the battery cell is compared to determine the gas production inside the battery cell, including:

[0012] The contact impedance of the first battery cell and the second battery cell during charging is calculated using a contact impedance calculation formula;

[0013] The contact impedance is derived to determine the contact impedance change rate between the first battery cell and the second battery cell, and the gas generation amount inside the first battery cell and the second battery cell is determined according to the contact impedance change rate between the first battery cell and the second battery cell.

[0014] In the above technical solution, the contact impedance calculation formula is:

[0015]

[0016] Where Z' is the real part of the cell's AC impedance, R Ω is the ohmic portion of the total impedance.

[0017] In the above technical solution, the gas production inside the first battery cell and the second battery cell is determined according to the change rate of the contact impedance between the first battery cell and the second battery cell, specifically:

[0018] When the contact impedance change rate of the first battery cell is greater than the contact impedance change rate of the second battery cell, the gas production of the first battery cell is greater than the gas production of the second battery cell;

[0019] When the contact impedance change rate of the second battery cell is greater than the contact impedance change rate of the first battery cell, the gas generation amount of the second battery cell is greater than the gas generation amount of the first battery cell.

[0020] In the above technical solution, the battery cell is a battery cell with rigid binding.

[0021] In the above technical solution, the EIS test is performed using a constant current method, the test frequency range is 10k-5mHz, and the amplitude is 50mA.

[0022] The present invention provides a lithium battery, characterized in that it includes: the lithium ion battery is tested using any of the above-mentioned testing methods for the gas production of lithium ion batteries.

[0023] The present invention provides a testing device for the gas production of a lithium-ion battery, the device comprising: a testing module, used to connect the lithium-ion battery, perform an EIS test on the battery, and obtain an EIS test result;

[0024] The analysis module uses relaxation time analysis to analyze the EIS test results and determine the relaxation time center frequency of the contact impedance;

[0025] A single-frequency impedance scanning module performs a single-frequency impedance scanning during the battery cell charging process; the frequency adopts the relaxation time center point frequency;

[0026] The gas production comparison module compares the contact impedance reduction rates of the first battery cell and the second battery cell to determine the gas production inside the first battery cell and the second battery cell; and the internal reserved spaces of the first battery cell and the second battery cell are the same.

[0027] Compared with the prior art, the present invention has the following beneficial effects:

[0028] The present invention provides a method, battery and device for testing the gas production of lithium-ion batteries. Without destroying the battery structure, the gas production of the battery cell can be quickly evaluated through electrochemical impedance spectroscopy testing and relaxation time analysis, thereby accelerating the optimization process of battery materials and electrolyte formulations. Compared with detection methods such as ultrasonic testing and neutron diffraction that require expensive equipment, this method is based on EIS and DRT, which are relatively economical and more suitable for large-scale applications. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1 It is a schematic diagram of the corresponding positions in the Nyquist curve in the EIS test provided by the present invention.

[0030] Figure 2 This is a schematic diagram of the characteristic relaxation time distribution of the interface process in the lithium-ion battery provided by the present invention.

[0031] Figure 3 The present invention is a schematic diagram of the process.

[0032] Figure 4 It is a schematic diagram of the EIS test results and DRT calculation results of the first battery cell and the second battery cell provided by the present invention.

[0033] Figure 5 This is a schematic diagram of the AC impedance equivalent circuit in the impedance test provided by the present invention.

[0034] Figure 6 It is a schematic diagram of the EIS test results and DRT calculation results of the battery cell 1 and the battery cell 2 provided by the present invention.

[0035] Figure 7 It is a schematic diagram of the test results of the battery cell 1 and the battery cell 2 in the first embodiment provided by the present invention.

[0036] Figure 8It is a schematic diagram of the gas type results of the battery cell 1 and the battery cell 2 in the first embodiment provided by the present invention.

[0037] Fig. 9 Schematic diagram of the EIS test results and DRT calculation results of the battery cell 3 and the battery cell 4 in the second embodiment of the present invention.

[0038] Fig.10 It is a schematic diagram of the test results of the battery cell 3 and the battery cell 4 in the second embodiment provided by the present invention.

[0039] Fig.11 It is a schematic diagram of the gas type results of the battery cell 3 and the battery cell 4 in the second embodiment provided by the present invention. DETAILED DESCRIPTION

[0040] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0041] The present invention provides a method and a battery and a device for testing the gas production of a lithium-ion battery, which complete the gas production test of a battery cell under non-destructive conditions, thereby helping to improve the performance and safety of the battery while reducing costs.

[0042] Electrochemical impedance spectroscopy (EIS) is a very effective electrochemical analysis method. Usually, an equivalent circuit model (ECM) is established based on the number and origin of all impedance-based processes. The impedance spectrum of the ECM is combined with the measured impedance spectrum to determine the parameters of each component in the ECM, thereby obtaining the internal impedance of the electrolysis. However, when the relaxation times of certain physical and chemical processes in the battery cell are similar, they have a serious coupling relationship, which makes it very difficult to use conventional equivalent circuits combined with Nyquist curves to determine the parameters of each component in the equivalent circuit. The method of relaxation time analysis (DRT) can solve this challenge well. The analysis of DRT is based on Figure 1 In the equivalent circuit shown, the inductive reactance part L0 in the ultra-high frequency band, the ohmic resistance R0 in the high frequency band, and the parallel element R / / C element of resistance R and capacitance C in the medium and high frequency bands are used to represent an interface polarization process, and multiple polarization processes are represented by the series connection of different R / / C elements.

[0043] In addition, the concentration polarization overpotential caused by lithium ion diffusion in the low frequency band lags behind the current, so the relationship between current and potential is similar to the capacitance response. The process can be represented by the series differential capacitance C0, and the total impedance Z total The relationship with the polarization process is given by equation (1):

[0044]

[0045] in, is the non-ideal inductor part of the total impedance, R0 is the ohmic part of the total impedance, It is caused by the SOC drift in the low frequency area. Then is the impedance of each RC element, which can be given by the following formula (2):

[0046]

[0047] Among them, R i With C i are the resistance and capacitance values ​​of a RC element, respectively. τi is the time constant of the RC element, which is the product of resistance and capacitance, that is:

[0048] τ i =R i C i (3)

[0049] When there are enough different interface processes in the battery cell, the discrete distribution will become a quasi-continuous relaxation resistance distribution peak. Therefore, the time impedance distribution function γ(τ) (i.e., DRT fitting analysis) that satisfies the following equation (4) is introduced. The corresponding position in the Nyquist curve of EIS is as follows: Figure 1 As shown:

[0050]

[0051] If the time impedance distribution function γ(τ) contains multiple relaxation time distribution peaks, by comparing equations (1) and (2), it can be seen that the area of ​​a single peak is the polarization resistance R in the i-th polarization process: i In lithium-ion batteries, the following Figure 2 As shown in the figure, the distribution of relaxation peaks represents the following four processes from small to large relaxation times:

[0052] 1. Contact impedance, the contact impedance between the electrode material and the current collector. Since there is a gap between the two, the impedance response between them is not a simple resistance response, but a relaxation process.

[0053] 2. Passivation film relaxation process;

[0054] 3. Charge transfer process;

[0055] 4. Solid-liquid phase diffusion process.

[0056] Different relaxation processes are used to analyze the changes in different interface processes. Therefore, in this application, the contact relaxation process between the electrode material and the current collector is used to analyze the changes in the interface. Since the contact gap and pressure have a huge impact on the contact impedance, the contact impedance of the battery cell will be reduced due to the expansion effect of the negative electrode during lithium ion charging. Further, if in a cylindrical or square aluminum shell lithium ion battery with a hard-bound battery cell, when gas is generated inside the battery cell, it will cause the internal pressure to increase, which will further reduce the contact impedance of the battery cell.

[0057] like Figure 3 As shown, the method comprises the following steps:

[0058] Step S1: Perform an EIS (electrochemical impedance spectroscopy) test on the lithium-ion battery to obtain the EIS test result. Figure 4 As shown, a schematic diagram of the EIS test results of the first battery cell and the second battery cell is used to obtain the impedance fitting result of the AC impedance, wherein the horizontal axis is the real part of the impedance and the vertical axis is the imaginary part.

[0059] In one embodiment, the EIS test is performed using a constant current method, with a test frequency range of 10k-5mHz and an amplitude of 50mA. The specific test frequency can be determined according to the specific conditions of the battery cell and is not limited here.

[0060] Step S2: Analyze the EIS test results using relaxation time analysis to determine the relaxation time center frequency of the contact impedance.

[0061] like Figure 4 As shown in the figure, the DRT calculation results for the first cell and the second cell are obtained. For the relaxation process, the time t0 is obtained, and the center frequency f0 of the contact impedance relaxation process is calculated, as well as L0, n and R in formula 4. Ω , that is, parameters such as R0.

[0062] Among them, the central frequency f0 of the contact impedance relaxation process is:

[0063]

[0064] Step S3: During the charging process of the battery cell, a single-frequency impedance scan is performed; the frequency adopts the relaxation time center point frequency f0; to capture the contact impedance changes during the charging and discharging process.

[0065] Step S4, comparing the contact impedance reduction rates of the first battery cell and the second battery cell to determine the gas generation amounts inside the first battery cell and the second battery cell; and the internal reserved spaces of the first battery cell and the second battery cell are the same.

[0066] Comparing the contact impedance reduction rates of the first battery cell and the second battery cell, and determining the gas generation amounts inside the first battery cell and the second battery cell, including:

[0067] The contact impedance of the first battery cell and the second battery cell during charging is calculated using a contact impedance calculation formula;

[0068] The contact impedance is derived to determine the contact impedance change rate between the first battery cell and the second battery cell, and the gas generation amount inside the first battery cell and the second battery cell is determined according to the contact impedance change rate between the first battery cell and the second battery cell.

[0069] Since the center frequency f0 of the contact process in the impedance test is a high-frequency response, it will not introduce other interface processes, such as Figure 5 As shown, this is the equivalent circuit diagram of the AC impedance at this time.

[0070] Its impedance expression is shown in the following formula (5), where w = 2Πf0:

[0071]

[0072] The real part of the impedance Z' is obtained by sorting:

[0073]

[0074] Furthermore, the contact impedance calculation formula is obtained as follows:

[0075]

[0076] Where Z' is the real part of the cell's AC impedance, R Ω is the ohmic portion of the total impedance.

[0077] R 接触 Derivative the SOC, the one with a larger change rate means the one with a larger gas production, that is, when the contact impedance change rate of the first battery cell is greater than the contact impedance change rate of the second battery cell, the gas production of the first battery cell is greater than the gas production of the second battery cell;

[0078] When the contact impedance change rate of the second battery cell is greater than the contact impedance change rate of the first battery cell, the gas generation amount of the second battery cell is greater than the gas generation amount of the first battery cell.

[0079] During the charging process of the battery cell, an impedance scan is performed on the characteristic frequency of the contact impedance. By comparing the contact impedance reduction rate of the battery cell, the pressure situation inside the battery cell can be known. If the reserved internal space during battery cell preparation is the same, the battery cell with a faster contact impedance reduction rate will produce more gas.

[0080] The above method is verified in combination with specific examples below, which provides a scientific basis for the evaluation of battery gas production and enhances the credibility of the test results.

[0081] Embodiment 1:

[0082] Two 18650 cylindrical cells with the same formula and the same internal reserved space during preparation were used. The capacity was 2500Ah. Both cells were charged and discharged for 1600 cycles. Battery 2 was the cell with serious self-discharge. First, an EIS test was performed using a constant current method. The test frequency range was 10k-5mHz and the amplitude was 50mA. The test results, fitting results and DRT analysis results are shown in Figure 2. Figure 6 The fitting parameters are shown in Table 1:

[0083] Table 1

[0084] Cell number Battery 1 Battery 2 n 1 1 L(H) 8.317019e-07 7.774003e-07 RΩ(Ω) 1.126189e-02 1.153336e-02 f0(Hz) 700 640 30-day self-discharge drop voltage (mV) 2.3 -1443.9

[0085] Discharge cell 1 and cell 2 to empty, let stand for a while, and then charge the cell with a current of 2A. During the charging process, perform a single-frequency dynamic AC impedance test on the cell at the center frequency f0 to obtain the change of Z' during the test. The results are as follows: Figure 7 As shown, it can be seen that the contact impedance of the battery cell 2 decreases faster and the gas production is greater.

[0086] GC-MS was used to quantitatively test the gas production of the battery cells to verify the test results of the battery cells 1 and 2.

[0087] After the core is rolled into the shell, the remaining space inside the battery is V0, the injection volume is V1, and a syringe is used to pierce the battery to extract gas and send it to GC-MS for testing. The total composition of the gas extracted is V2 for air and the gas production of the other gases is Vi, where i represents the i-th gas. Then the total gas production VT can be calculated using the following formula 8

[0088]

[0089] The results are shown in Table 2. The gas types are Figure 8 As shown, it can be seen that the GC-MS test shows that the gas production of battery cell 2 is greater than that of battery cell 1, which proves that the impedance test method of the present invention for identifying gas production is accurate and feasible.

[0090] Table 2

[0091] Cell number Gas production / mL Gas Type Battery 1 ～2.60 <![CDATA[CO,CH4,CO2,C2H4,C2H6]]> Battery 2 ～3.10 <![CDATA[CO,CH4,CO2,C2H4,C2H6]]>

[0092] Embodiment 2:

[0093] Two 18650 cylindrical cells with the same formula and the same internal reserved space during preparation were used. The capacity was 2500Ah. Both cells were charged and discharged for 1300 cycles. Cells 3 and 4 were self-discharged. First, an EIS test was performed using a constant current method. The test frequency range was 10k-5mHz and the amplitude was 50mA. The test results, fitting results and DRT analysis results are shown in Figure 2. Fig. 9 The fitting parameters are shown in Table 3:

[0094] Table 3

[0095] Cell number Battery 3 Battery 4 n 1 1 L(H) 8.317019e-07 7.774003e-07 RΩ(Ω) 1.126189e-02 1.153336e-02 f(Hz) 951 843 30-day self-discharge drop voltage (mV) -1.6 -498.5

[0096] As in Example 1, the battery cells 3 and 4 are discharged to empty, and after standing for a period of time, the battery cells 3 and 4 are charged with a current of 2A. During the charging process, the battery cells 3 and 4 are subjected to a single-frequency dynamic AC impedance test at the center frequency f0 to obtain the change of the real part Z' during the test. The results are as follows: Fig.10 shown.

[0097] It can be seen that the contact impedance of battery cell 3 and battery cell 4 decreases at a similar rate and has a similar gas production.

[0098] GC-MS was used to quantitatively test the gas production of the battery cell to verify the battery cell test results. The results are shown in Table 4. The types and details of the gas production are as follows: Fig.11 As shown, it can be seen that the GC-MS test shows that the gas production of battery cell 3 and battery cell 4 is equivalent, which proves that the impedance test method of the present invention for identifying gas production is accurate and feasible.

[0099] Table 4:

[0100] Cell number Gas production / mL Gas Type Battery 3 ～2.60 <![CDATA[CO,CH4,CO2,C2H4,C2H6]]> Battery 4 ～2.60 <![CDATA[CO,CH4,CO2,C2H4,C2H6]]>

[0101] Based on the same inventive concept, the present application provides a lithium battery, including: the lithium ion battery is tested using any of the above-described testing methods for gas production of lithium ion batteries.

[0102] Based on the same inventive concept, the present application also provides a testing device for the gas production of a lithium-ion battery, the device comprising: a testing module, used to connect the lithium-ion battery, perform an EIS test on the battery, and obtain an EIS test result;

[0103] The analysis module uses relaxation time analysis to analyze the EIS test results and determine the relaxation time center frequency of the contact impedance;

[0104] A single-frequency impedance scanning module performs a single-frequency impedance scanning during the battery cell charging process; the frequency adopts the relaxation time center point frequency;

[0105] The gas production comparison module compares the contact impedance reduction rates of the first battery cell and the second battery cell to determine the gas production inside the first battery cell and the second battery cell; and the internal reserved spaces of the first battery cell and the second battery cell are the same.

[0106] This application uses electrochemical impedance spectroscopy (EIS) and relaxation time analysis (DRT) without destroying the battery structure. This method can quickly evaluate the gas production of the battery cell, thereby accelerating the optimization process of battery materials and electrolyte formulations. Compared with detection methods such as ultrasonic testing and neutron diffraction that require expensive equipment, this method is based on EIS and DRT, which are relatively economical and more suitable for large-scale applications.

[0107] This application can optimize battery materials and electrolyte formulations in a targeted manner by accurately measuring and comparing the gas production of different battery cells to reduce gas production and improve battery performance. In addition, the ability to detect gas production problems in a timely manner helps to take preventive measures and improve the safety of battery use. By reducing gas production, battery performance degradation can be slowed down and the battery life can be extended, which is of great significance for reducing costs and improving the economy of battery technology. The present invention helps to identify and solve the gas production problem of the battery during the charging and discharging process, thereby improving the overall performance of the battery, such as the cycle life and energy density.

[0108] Although embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that various changes, modifications, substitutions and variations may be made to the embodiments without departing from the principles and spirit of the present invention, and that the scope of the present invention is defined by the appended claims and their equivalents.

Claims

1. A method for testing the gas production of a lithium-ion battery, characterized in that: The method comprises the following steps: Perform EIS test on lithium-ion batteries and obtain EIS test results; The EIS test results are analyzed using relaxation time analysis to determine the relaxation time center frequency of the contact impedance; During the battery cell charging process, a single frequency impedance scan is performed; the frequency is the relaxation time center point frequency; The contact impedance reduction rates of the first battery cell and the second battery cell are compared to determine the gas generation amounts inside the first battery cell and the second battery cell; and the internal reserved spaces of the first battery cell and the second battery cell are the same.

2. The method for testing gas production of lithium-ion batteries according to claim 1, characterized in that: Compare the contact impedance reduction rate of the battery cell to determine the gas production inside the battery cell, including: The contact impedance of the first battery cell and the second battery cell during charging is calculated using a contact impedance calculation formula; The contact impedance is derived to determine the contact impedance change rate between the first battery cell and the second battery cell, and the gas generation amount inside the first battery cell and the second battery cell is determined according to the contact impedance change rate between the first battery cell and the second battery cell.

3. The method for testing gas production of lithium-ion batteries according to claim 2, characterized in that: The contact impedance calculation formula is: Where Z' is the real part of the cell's AC impedance, R Ω is the ohmic portion of the total impedance.

4. The method for testing gas production of lithium-ion batteries according to claim 3, characterized in that: According to the change rate of the contact impedance between the first battery cell and the second battery cell, the gas generation amount inside the first battery cell and the second battery cell is determined, specifically: When the contact impedance change rate of the first battery cell is greater than the contact impedance change rate of the second battery cell, the gas production of the first battery cell is greater than the gas production of the second battery cell; When the contact impedance change rate of the second battery cell is greater than the contact impedance change rate of the first battery cell, the gas generation amount of the second battery cell is greater than the gas generation amount of the first battery cell.

5. The method for testing gas production of lithium-ion batteries according to claim 1, characterized in that: The battery cell is a battery cell with rigid binding.

6. The method for testing gas production of lithium-ion batteries according to claim 2, characterized in that: The EIS test was performed using a constant current method, with a test frequency range of 10k-5mHz and an amplitude of 50mA.

7. A lithium battery, characterized in that: include: The lithium-ion battery is tested using the test method for gas production of lithium-ion batteries as described in any one of claims 1 to 6.

8. A test device for the gas production of lithium-ion batteries, characterized in that: The device comprises: a test module, which is used to connect to a lithium-ion battery, perform an EIS test on the battery, and obtain an EIS test result; The analysis module uses relaxation time analysis to analyze the EIS test results and determine the relaxation time center frequency of the contact impedance; A single-frequency impedance scanning module performs a single-frequency impedance scanning during the battery cell charging process; the frequency adopts the relaxation time center point frequency; The gas production comparison module compares the contact impedance reduction rates of the first battery cell and the second battery cell to determine the gas production inside the first battery cell and the second battery cell; and the internal reserved spaces of the first battery cell and the second battery cell are the same.

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