Methods for determining the lithium plating threshold voltage of a battery

Abstract

This invention discloses a method for determining the lithium plating threshold voltage of a battery, comprising the steps of: testing the lithium plating threshold voltage of the battery at different temperatures and charging rates; obtaining, based on the lithium plating threshold voltage and data of temperature and charging rate, voltage-rate fitting expressions for the lithium plating threshold voltage and charging rate, and voltage-temperature fitting expressions for the lithium plating threshold voltage and temperature; and calculating the lithium plating threshold voltage of the battery at different temperatures and charging rates based on the voltage-rate fitting expressions and voltage-temperature fitting expressions. The method of this invention can achieve rapid calculation by obtaining specific relationships through a small number of test points based on a known curve type, thus making battery standard design more accurate and faster.

Description

Technical Field

[0001] This invention relates to the field of battery testing technology, and in particular to a method for determining the lithium plating threshold voltage of a battery. Background Technology

[0002] The charging rate is the most direct parameter for how fast a battery charges. Due to the limitations of the internal electrochemical reaction mechanism of the battery, polarization and lithium plating often occur, which will reduce the battery's lifespan over time. The higher the charging rate, the more severe the polarization, resulting in a larger deviation in battery potential, making the battery unsuitable for the voltage limit of the current charging rate. At the same time, temperature differences also affect battery performance; for example, lithium plating is more likely to occur when charging and discharging at low temperatures.

[0003] Currently, high-current charge-discharge tests on batteries mostly employ a room-temperature stepped charging method. This method requires multiple tests to obtain the specific potential, resulting in a large amount of data. Furthermore, the lithium plating potential is unclear; exceeding the lithium plating potential corresponding to the charging rate can cause irreversible degradation of the battery, thus damaging its performance. Therefore, a precise method for obtaining the lithium plating voltage of batteries at different currents and temperatures is crucial. Summary of the Invention

[0004] The purpose of this invention is to address the problems in the prior art by providing a fast and simple method for determining the lithium plating threshold voltage of a battery.

[0005] Through extensive dQ / dV testing, the inventors discovered that the battery voltage, current, and temperature corresponding to each reaction peak in the dQ / dV-V curve exhibit a certain regularity. This invention is achieved through a method for determining the lithium plating threshold voltage of a battery, comprising the following steps:

[0006] The lithium plating threshold voltage of the battery was tested at different temperatures and charging rates.

[0007] Based on the lithium plating threshold voltage, temperature, and charging rate data, the voltage-rate fitting relationship between the lithium plating threshold voltage and the charging rate, and the voltage-temperature fitting relationship between the lithium plating threshold voltage and the temperature are obtained.

[0008] The lithium plating threshold voltage of the battery at different temperatures and charging rates is calculated based on the voltage-rate fitting formula and the voltage-temperature fitting formula.

[0009] The voltage-rate fitting formula between the lithium plating threshold voltage and the charging rate is obtained by plotting a scatter plot with the charging rate on the horizontal axis and the lithium plating voltage at a fixed temperature on the vertical axis, and then fitting the data.

[0010] The voltage-temperature fitting relationship between the lithium plating threshold voltage and temperature is obtained by plotting a scatter plot with temperature on the horizontal axis and lithium plating voltage at a fixed charging rate on the vertical axis, and then fitting the data.

[0011] The lithium plating threshold voltage of the battery is linearly related to the magnitude of the charging current and parabolicly related to the battery temperature.

[0012] Before charging the battery, it is first discharged with a small current to reduce the battery to a depleted state and then left to stand for a period of time before charging.

[0013] When charging the battery, it is first charged with constant current for a certain period of time, then put into sleep mode for a certain period of time. After multiple constant current charging and sleep mode cycles, the constant current charging is completed until the battery is charged to the preset voltage value. Then, it is discharged with a small current until the predetermined voltage value is reached, and then put into sleep mode again.

[0014] The battery is placed in a constant temperature chamber for charging and discharging to conduct tests. The constant temperature chamber can provide different test environment temperatures so that the battery reaches the required temperature before testing.

[0015] The battery was tested at temperatures of 0 degrees Celsius and above.

[0016] The battery is tested by charging and discharging it using a charge / discharge device.

[0017] Among them, the lithium plating threshold voltage of the battery at different temperatures and different charging rates was tested using a three-electrode test method.

[0018] This invention establishes a fitting relationship between lithium plating potential and current and temperature by testing the battery at arbitrary temperatures and rates. Specifically, it establishes the relationship between lithium plating potential and charging rate at a fixed temperature, and the relationship between lithium plating potential and temperature at a fixed charging rate. Based on the obtained fitting relationship, the lithium plating voltage of the battery at different temperatures and rates can be calculated. This allows for the rapid acquisition of the lithium plating boundary voltage of the battery at different currents and temperatures. The testing method is fast and simple, and has been proven to be highly accurate through experiments. Attached Figure Description

[0019] Figure 1 This is a flowchart illustrating the method for determining the lithium plating threshold voltage of a battery according to an embodiment of the present invention.

[0020] Figure 2 The graph shows the relationship between the lithium plating threshold voltage and the charging rate at different temperatures.

[0021] Figure 3 The graph shows the relationship between the lithium plating threshold voltage and temperature at different charging rates. Detailed Implementation

[0022] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below in conjunction with the embodiments of the present invention. Obviously, the described embodiments are some embodiments of the present invention, but not all embodiments.

[0023] In this embodiment of the invention, a battery charge / discharge instrument is used to perform charging tests on the battery at different temperatures and rates to determine the lithium plating threshold voltage. Then, the fitting formulas between the lithium plating threshold voltage and the charging rate and battery temperature are obtained. Based on the fitting formulas between the lithium plating threshold voltage and the charging rate and temperature, the lithium plating threshold voltage at different charging rates and temperatures can be calculated, thereby obtaining the boundary voltage of the battery used at different charging rates and temperatures.

[0024] Among them, the three-electrode test method can be used to test the lithium plating threshold voltage of the battery at different temperatures and charging rates. This is a well-known test technique and will not be elaborated further.

[0025] The specific implementation steps are as follows:

[0026] S1. Test the lithium plating threshold voltage of the battery at different temperatures and charging rates.

[0027] S2. Based on the data of lithium plating threshold voltage, temperature, and charging rate, obtain the voltage-rate fitting relationship between lithium plating threshold voltage and charging rate, and the voltage-temperature fitting relationship between lithium plating threshold voltage and temperature.

[0028] S3. Calculate the lithium plating threshold voltage of the battery at different temperatures and charging rates based on the voltage-rate fitting formula and the voltage-temperature fitting formula.

[0029] Based on the fitting relationship between the battery lithium plating voltage and the charging rate, and the fitting relationship between the battery lithium plating voltage and the temperature obtained in step S2, the lithium plating threshold voltage of the battery when charged at different charging rates or at different temperatures can be calculated, and the boundary voltage used by the battery at different charging rates and temperatures can be determined.

[0030] In step S1, testing the lithium plating threshold voltage of the battery at different temperatures and currents involves placing the battery in a constant temperature chamber for charging and discharging. The constant temperature chamber can provide different test environment temperatures so that the battery reaches the required temperature before testing.

[0031] The specific test includes the following steps:

[0032] S11. At a set battery temperature, the selected battery is first subjected to a small current discharge treatment to reduce it to an empty state, and then left to stand for a period of time;

[0033] S12. Perform non-destructive analysis tests on the lithium plating threshold voltage of the selected batteries at different charging rates, and record the charging rate and its corresponding lithium plating threshold voltage.

[0034] When performing non-destructive analysis tests on the lithium plating threshold voltage of the selected battery at different charging rates, the battery is charged at a constant current rate at the same charging rate. The battery is kept in a sleep state after each period of constant current charging until the constant current charging ends. Then, constant voltage charging is performed and ends. The battery is then discharged at a constant current rate until the set voltage is reached. After the constant current discharge ends, the battery is kept in a sleep state for a period of time before the test is performed at another charging rate.

[0035] S13. Following steps S11-S12 above, perform non-destructive analysis tests on the selected batteries at different temperatures to determine the lithium plating threshold, and record the battery temperature and its corresponding lithium plating threshold voltage.

[0036] In step S2, the data obtained in step S1 is analyzed. Based on the lithium plating threshold voltage, temperature, and charging rate data, voltage-rate fitting equations between the lithium plating threshold voltage and charging rate, and voltage-temperature fitting equations between the lithium plating threshold voltage and temperature are obtained. This includes the following steps:

[0037] S21. Plot a scatter plot with the charging rate on the x-axis and the lithium plating voltage at a fixed temperature on the y-axis. Then perform data fitting to obtain the fitting relationship between the battery lithium plating voltage and the charging rate.

[0038] S22. Plot a scatter plot with temperature on the x-axis and lithium plating voltage at a fixed charging rate on the y-axis. Then perform data fitting to obtain the fitting relationship between battery lithium plating voltage and temperature.

[0039] Among these methods, a charge / discharge tester is used to charge and discharge the battery as required for testing.

[0040] Example:

[0041] Take a 4.8Ah 21700 battery, place it in a 0℃ constant temperature chamber, discharge it to empty at 0.1C current, and let it stand for 30 minutes; then charge it at a constant current of 0.5C, with a 3s sleep time every 12s of charging, until it is charged to 4.2V, and then charge it at a constant voltage of 240mA; then discharge it at a constant current of 0.1C current to 2.5V, and let it sleep for 30 minutes.

[0042] The constant current charging rate was changed from 0.5C to 0.7C and 1C, and the above tests were performed respectively.

[0043] Through the above tests, the battery was tested in a 0℃ constant temperature chamber at different charging rates, and the test data were recorded.

[0044] Change the temperature to 10℃ and 25℃, and perform the above-mentioned 0.5C, 0.7C and 1C rate tests respectively according to the steps above. Finally, complete the battery test under different temperatures and different charging rates, and record the test data.

[0045] Plotting voltage U on the ordinate and charging rate on the abscissa, we obtain the relationship between battery lithium plating voltage and charging rate at different temperatures (0℃, 10℃, and 25℃), as shown in the figure. Figure 2 It can be seen that the battery charging rate and lithium plating voltage have a roughly linear relationship, which is y = -0.0787x + 4.2014 at 0℃. 2 =0.9944, and the relationship at 10℃ is y = -0.0911x + 4.2331, R 2 =0.9919, and the relationship at 25℃ is y = -0.0618x + 4.2237, R 2 =0.9995.

[0046] Plotting voltage U on the ordinate and temperature on the abscissa, a graph showing the relationship between battery lithium plating voltage and temperature at different charging rates is obtained, as shown below. Figure 3 It can be seen that the lithium plating voltage has a parabolic relationship with temperature. At a charging rate of 0.5C, the relationship between temperature and lithium plating voltage is y = -0.0001x. 2 +0.004x+4.165, R 2 =0.9913, at a charging rate of 0.7C, the relationship between temperature and lithium plating voltage is y = -0.00005x. 2 +0.0026x+4.158, R 2 =0.9962, at a charging rate of 1C, the relationship between temperature and lithium plating voltage is y = -0.0001x 2 +0.0047x+4.122, R 2 = 0.9869. Where, R 2 The closer the value is to 1, the better the fit and the more realistic the fitted function. R 2 R is a parameter that measures the goodness of fit of an equation. 2 The larger it is, the more realistic it becomes.

[0047] The battery was used for comparative verification by conducting tests at other rate levels.

[0048] Based on the voltage-current relationship, if the battery is charged at 0℃ and 0.8C, the fitted relationship is y=-0.0787x+4.2014, and the lithium plating voltage can be calculated as U=-0.0787*0.8+4.2014=4.138V; the actual test result is that the lithium plating voltage at 0℃ and 0.8C rate charging is 4.115V, with an error of 0.56%.

[0049] When the battery is charged at 0℃ and 0.2C, the fitted relationship is y=-0.0787x+4.2014, from which the lithium plating voltage can be calculated as U=-0.0787*0.2+4.2014=4.185V; the actual test result is that the lithium plating voltage at 0℃ and 0.2C rate charging is 4.194V, with an error of 0.21%. The test comparison is shown in Table 1.

[0050] Table 1

[0051]

[0052] Based on the voltage-temperature relationship, if the battery is charged at a rate of 0.5C, the fitted relationship is y = -0.00005x. 2 +0.0026x+4.158, at an oven temperature of 45℃, the lithium plating voltage can be calculated as U=-0.00005*45 2 +0.0026*45+4.158=4.174V, so the lithium plating voltage is 4.174V. The actual test result is that at 45℃, the lithium plating voltage at a 0.5C charging rate is 4.183V, with an error of 0.22%.

[0053] When the battery is charged at a rate of 0.5C, the fitted equation is y = -0.00005x² + 0.0026x + 4.158. At a chamber temperature of 5℃, the lithium plating voltage is obtained as U = -0.00005 * 5. 2 +0.0026*5+4.158=4.170V, indicating that the lithium plating voltage is 4.170V. The actual test result is that at 5℃, the lithium plating voltage at a 0.5C charging rate is 4.168V, with an error of -0.04%. The test comparison is shown in Table 2.

[0054] Table 2

[0055]

[0056] As can be seen, when the method of the present invention is applied to other battery testing processes, it can obtain specific relationships through a small number of test points based on known curve types, achieving the purpose of rapid calculation, thereby making the formulation of battery standards more accurate and faster.

[0057] As can be seen from the above description, the method of the present invention eliminates the need for extensive experiments to test the lithium plating potential, which not only saves testing resources and greatly shortens testing time, but also requires no special testing resources and is easy to promote and implement, thus providing a fast and efficient testing and calculation method for battery usage boundary optimization and management.

[0058] The above description is only a preferred embodiment of the present invention. It should be noted that, for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A method for determining the lithium plating threshold voltage of a battery, characterized in that, Including the following steps: The lithium plating threshold voltage of the battery was tested at different temperatures and charging rates. Based on the lithium plating threshold voltage, temperature, and charging rate data, the voltage-rate fitting relationship between the lithium plating threshold voltage and the charging rate, and the voltage-temperature fitting relationship between the lithium plating threshold voltage and the temperature are obtained. The lithium plating threshold voltage of the battery at different temperatures and charging rates is calculated based on the voltage-rate fitting formula and the voltage-temperature fitting formula.

2. The method for determining the lithium plating threshold voltage of a battery according to claim 1, characterized in that, The voltage-rate fitting formula between the lithium plating threshold voltage and the charging rate is obtained by plotting a scatter plot with the charging rate on the horizontal axis and the lithium plating voltage at a fixed temperature on the vertical axis, and then fitting the data.

3. The method for determining the lithium plating threshold voltage of a battery according to claim 1, characterized in that, The voltage-temperature fitting formula between the lithium plating threshold voltage and temperature is obtained by plotting a scatter plot with temperature as the abscissa and lithium plating voltage at a fixed charging rate as the ordinate, and then performing data fitting.

4. The method for determining the lithium plating threshold voltage of a battery according to claim 1, characterized in that, The lithium plating threshold voltage of the battery is linearly related to the magnitude of the charging current and parabolicly related to the battery temperature.

5. The method for determining the lithium plating threshold voltage of a battery according to claim 1, characterized in that, Before charging the battery, discharge it with a small current to reduce its charge to zero and let it rest for a period of time before charging.

6. The method for determining the lithium plating threshold voltage of a battery according to claim 2, characterized in that, When charging the battery, it is first charged with constant current for a certain period of time, then put into sleep mode for a certain period of time. After multiple constant current charging and sleep modes, the constant current charging is completed until the battery is charged to the preset voltage value. Then, it is discharged with a small current until the preset voltage value is reached, and then put into sleep mode again.

7. The method for determining the lithium plating threshold voltage of a battery according to claim 1, characterized in that, The battery is placed in a constant temperature chamber for charging and discharging to conduct tests. The constant temperature chamber can provide different test environment temperatures so that the battery reaches the required temperature before testing.

8. The method for determining the lithium plating threshold voltage of a battery according to claim 1, characterized in that, The battery was tested at temperatures of 0 degrees Celsius and above.

9. The method for determining the lithium plating threshold voltage of a battery according to claim 1, characterized in that, The battery is charged and discharged using a charge / discharge tester for testing.

10. The method for determining the lithium plating threshold voltage of a battery according to claim 1, characterized in that, The lithium plating threshold voltage of the battery at different temperatures and charging rates was tested using a three-electrode test method.

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