Method for prolonging service life of alkali metal ion battery

Abstract

The invention belongs to the technical field of chemical batteries, and particularly relates to a method for prolonging the service life of an alkali metal ion battery. A dynamic change model of the internal resistance, the charge-discharge current multiplying power and the SOC of the alkali metal ion battery is established through a mixed pulse power characteristic method, and the SOC interval with the minimum internal resistance change is determined as the optimal operation interval of the alkali metal ion battery. It is verified that the working temperature and surface pressure of the alkali metal ion battery in operation are reduced in the optimal working interval, and meanwhile the thermal safety performance of the alkali metal ion battery is improved. In addition, the optimal working interval not only improves the charge-discharge efficiency and safety of the alkali metal ion battery under high current rate, but also prolongs the service life of the alkali metal ion battery. Compared with a traditional method, the method is more accurate in result, more convenient to operate and not prone to being affected by the external working environment. The method is beneficial to improving the universality of the alkali metal ion battery and improving the economic benefit of the alkali metal ion battery as a large-scale long-time energy storage platform.

Description

Technical Field

[0001] The invention belongs to the technical field of chemical batteries, and in particular relates to a method for extending the service life of an alkali metal ion battery. Background Art

[0002] With the continuous development of large-scale, long-term energy storage, especially its role in peak shaving and valley filling and capacity supply in power systems, it is receiving widespread attention. Alkali metal ion batteries, as an energy system with wide temperature range and high rate performance, as well as abundant reserves and low cost, are considered to be the first choice for application in the field of large-scale, long-term energy storage. However, the cycle life of alkali metal ion batteries is still limited, mainly due to the formation of insoluble byproducts and irreversible alkali metal deposition, which can lead to unstable battery operation. This phenomenon is caused by the internal resistance generating heat and exacerbating side reactions at the electrodes when current flows through the battery, resulting in energy loss in the battery.

[0003] Traditional methods for extending the life of lithium-ion batteries primarily rely on optimizing charge and discharge protocols. Combining active controlled pulses with multi-step rapid pulses can effectively reduce lithium product on the graphite anode and minimize byproduct formation, thereby extending battery life. Constant potential protection can effectively promote anion decomposition, thereby enhancing the battery's calendar aging characteristics. The application of multi-step rapid charging methods can effectively mitigate lithium deposition and graphite cracking, significantly improving battery life. However, these methods are limited to lithium-ion batteries and are insufficient to meet the growing demand for alkali metal ion batteries. Furthermore, in current new energy microgrid systems, including user-side energy storage and power distribution systems, energy storage accounts for 20%-40% of the total construction cost. Currently, photovoltaic panels typically have a service life of over 20 years, but the service life of energy storage systems still falls far short of this. Crucially, these systems also face challenges such as high investment costs and safety risks. Therefore, to further improve the efficiency of new energy microgrid construction, it is urgent to develop methods to optimize the use of energy storage systems to ensure their safe and continuous operation, maximize their service life, and maximize economic benefits.

[0004] Considering the urgent need to develop a strategy to extend the life of alkali metal ion batteries and energy storage systems, the present invention proposes a method for determining the optimal operating range for extending the service life of alkali metal ion batteries, thereby filling the existing research gap in the field of alkali metal ion battery life extension. Summary of the Invention

[0005] The purpose of the present invention is to propose a method for determining the SOC working range for extending the service life of an alkali metal ion battery based on a hybrid pulse power characteristic method.

[0006] In order to achieve the above technical objectives, the technical solutions of the present invention are as follows:

[0007] In a first aspect, the present invention provides a method for determining an optimal operating range of an alkali metal ion battery, comprising the following steps:

[0008] 1) Place the alkali metal ion battery in a room temperature environment. After it has been left to stand for a sufficient period of time, fully charge the battery and record the charged capacity C1.

[0009] 2) Discharge at a constant current rate of 1C, and stop when the discharge capacity reaches a1 C1. It is considered that the battery SOC = 1-a1 at this time; a1 is a number in the range of 0.05 to 0.4; C is the battery charge and discharge capacity rate;

[0010] 3) Use a pulse current of XC rate to discharge the battery at a constant current for a duration of ts;

[0011] 4) Use a pulse current of XC rate to charge the battery with constant current for a duration of ts;

[0012] 5) gradually increase the value of the discharge capacity coefficient in step 2), and then repeat steps 2) to 4) several times so that the final discharge capacity battery SOC = a1;

[0013] ai is the coefficient of the discharge capacity of each step 2) to 4); the discharge capacity a of the first step 2) to 4) is recorded as a1, and the discharge capacity ai in subsequent repeated steps increases in sequence;

[0014] 6) Adjust the current magnification X to a multiple between 2 and 10, and repeat steps 1) to 5) to perform DC internal resistance tests at different pulse current magnifications;

[0015] Based on the voltage and current data obtained in the above steps, the ohmic internal resistance and polarization internal resistance of pulse discharge and charge are calculated according to equations (1) and (2) respectively;

[0016] R o =ΔU o / I=(UB-UA) / I (1)

[0017] R p = ΔU p / I=(UC-UB) / I (2)

[0018] Where: ΔU o and ΔU p are the voltage changes corresponding to the ohmic internal resistance and polarization internal resistance (V), respectively; during the pulse discharge process, UA is the termination voltage of step 2); UB is the voltage at any time point in step 3); UC is the termination voltage of step 3);

[0019] During the pulse charging process, UA is the termination voltage in step 3); UB is the voltage in step 4) at a time point corresponding to the same duration as UB in step 3); UC is the termination voltage in step 4);

[0020] According to the above calculation steps, taking SOC, charge and discharge rate and time as dimensions, we can get R o and R p Relationship model with SOC, charge and discharge rate and time;

[0021] According to formula (3), R o and R p Added together is the internal resistance R 内 ;

[0022] R o +R p =R 内 (3)

[0023] In the changing relationship model, find the internal resistance R 内 The smallest point R min ; Determine R min ~1.2R min The continuous SOC interval segments within the corresponding range are the optimal working ranges for alkali metal ion batteries.

[0024] Preferably, the optimal working range of the alkali metal ion battery is further determined by the following steps:

[0025] The alkali metal ion battery is tested using electrochemical impedance spectroscopy (EIS) at a test frequency of 10 MHz to 10 kHz and an amplitude of 2 to 10 mV with a gradient of Y% SOC, where Y ranges from 1 to 10. The internal resistance in the optimal operating range selected in step 6) is determined to be still less than the internal resistance in the comparison defective operating range. When the length of the optimal operating range exceeds 50% of the test range, all remaining test ranges are used as the comparison defective operating range.

[0026] The following three metrics are calculated:

[0027] Average internal resistance (R0):

[0028]

[0029] Sample standard deviation (σ):

[0030]

[0031] Actual internal resistance (R):

[0032] R=R0+σ (6)

[0033] Where Ri represents the measured internal resistance value, σ represents the sample standard deviation, and R represents the actual internal resistance value within the interval;

[0034] When the R value of the optimal working interval satisfies any one of the conditions of being always 1 mΩ or 15% smaller than the R value of the defective working interval, it is determined that the optimal working interval is successfully selected.

[0035] Preferably, after step 5) is completed, the battery is cyclically charged and discharged, and the process is repeated for 3 cycles.

[0036] Preferably, the value of X is 2, 3, 4, 5, or 10.

[0037] Preferably, in steps 3) and 4), the time interval for data collection is 0.1 s.

[0038] Preferably, after steps 2) to 4) are completed, the apparatus is left to stand for at least 1 hour to allow the voltage to return to a stable state, so as to prevent the subsequent calculation of the ohmic internal resistance and the polarization internal resistance from being affected.

[0039] In a second aspect, the present invention provides a method for extending the service life of an alkali metal ion battery, wherein the alkali metal ion battery is used in an optimal working range.

[0040] Preferably, when the optimal operating range is used, since the optimal operating range selects a portion of the entire SOC cycle of the alkali metal ion battery for cycling, the coulomb counting method is required to estimate the SOC when the battery is running:

[0041]

[0042] Where I represents the current, which is positive during charging and discharging, t represents the charging and discharging time, and Q represents the charging and discharging capacity of the alkali metal ion battery.

[0043] Furthermore, as alkali metal ion batteries age, their charge and discharge capacities gradually decrease. The cumulative error caused by the capacity drop will seriously affect the SOC estimation method. In order to reduce this error and determine the capacity loss trend, during use, a complete charge and discharge cycle (constant current and constant voltage charge-constant current discharge) is performed within a fixed voltage range of the battery, and the actual charge and discharge capacity value of the battery is determined after each fixed interval of cycles. Subsequently, the actual charge and discharge capacity value is updated to Equation (7) to achieve an accurate estimation of the SOC.

[0044] Furthermore, the charge and discharge capacity required to maintain a specified SOC range is calculated during the test, and the cycle test is performed based on the specified available capacity.

[0045] Compared with the prior art, the present invention has the following significant advantages:

[0046] By determining the internal resistance variation pattern of alkali metal ion batteries under actual operating conditions, the present invention selects an operating range that can maximize the service life of alkali metal ion batteries and improve the charge and discharge efficiency, optimizes the use of alkali metal ion batteries, and ensures that they remain in the optimal working state. At the same time, the battery's own heat generation is minimized, performance degradation is slowest, cycle life is longest, and safety is highest. This improves the adaptability of the alkali metal ion battery system to complex working conditions and extreme environments. It has good application prospects in the battery field and will also help promote the development of large-scale, long-term energy storage integrated platforms for alkali metal ion batteries. BRIEF DESCRIPTION OF THE DRAWINGS

[0047] Figure 1 This is the relationship model of the internal resistance of the sodium ion battery at 10C rate in test example 1 as a function of SOC, charge and discharge current rate and time.

[0048] In the figure: the Z-axis coordinate is the internal resistance value, the unit is mΩ; the horizontal axis is SOC, no unit; the vertical axis is time, the unit is s.

[0049] Figure 2 For the electrochemical impedance spectroscopy test in Test Example 1

[0050] In the figure: the ordinate is the imaginary part, the unit is Ω; the abscissa is the real part, the unit is Ω.

[0051] Figure 3 This is the relationship model of the internal resistance of the sodium ion battery at 2C rate in test example 2 with SOC, charge and discharge current rate and time

[0052] In the figure: the Z-axis coordinate is the internal resistance value, the unit is mΩ; the horizontal axis is SOC, no unit; the vertical axis is time, the unit is s.

[0053] Figure 4 The cycling difference between the optimal working range and defective working range of the sodium ion battery at 10C rate in test example 1

[0054] In the figure: the vertical axis is the number of cycles; the horizontal axis is SOH.

[0055] Figure 5 The cycling difference between the optimal working range and defective working range of the sodium ion battery at 2C rate in test example 2

[0056] In the figure: the vertical axis is the number of cycles; the horizontal axis is SOH. DETAILED DESCRIPTION

[0057] To facilitate understanding of the present invention, the following will be comprehensively and carefully explained in conjunction with the embodiments and drawings of the specification, but the protection scope of the present invention is not limited to the following specific embodiments.

[0058] Example 1

[0059] This embodiment adopts the following method: First, a complex relationship model of the internal resistance of the alkali metal ion battery with the SOC and the charge and discharge current rate is established through the mixed pulse power characteristic method, and the intervals with the minimum and maximum internal resistance of the alkali metal ion battery are determined based on this, and the intervals with the minimum internal resistance are respectively defined as the optimal working interval, and the interval with the maximum internal resistance is positioned as the defective working interval. Secondly, the AC impedance spectrum is used to test whether the internal resistance within the selected optimal working range is smaller than the internal resistance within the defective working range. If so, the standard denominator difference is calculated, and the internal resistance within the optimal working range and the internal resistance within the defective working range are normalized to the same value. When the internal resistance within the optimal working range is always less than the internal resistance within the defective working range by more than 1mΩ, it indicates that the optimal working range has been successfully selected. Secondly, by cycling the battery within the optimal working range, the cycle performance of the battery can be greatly improved. The specific steps are as follows:

[0060] Step 1: Determine the internal resistance change model using the hybrid pulse power characteristics method

[0061] 1) Place the alkali metal ion battery in a room temperature environment and let it sit for 48 hours until the voltage stabilizes. Fully charge the battery and record the charge capacity C1, which will be used to control the step-discharge capacity later.

[0062] 2) Perform constant current discharge at a rate of 1C, and stop when the discharge capacity reaches 0.1C1. It is considered that the battery SOC = 90% at this time. Let it stand for 1 hour to allow the voltage to return to a stable state to prevent it from affecting the subsequent calculation of the ohmic internal resistance and polarization internal resistance, and prepare for the next pulse charging;

[0063] 3) Use a pulse current of XC rate to discharge the battery at a constant current for 30 seconds, and let it stand for 1 hour to allow the voltage to return to a stable state, ready for the next pulse discharge;

[0064] 4) The battery is charged with a constant current pulse current of XC rate for 30 seconds and allowed to stand for 1 hour, so that the voltage returns to a stable state and the pulse steps in 3) and 4) have no effect on the actual capacity of the battery, that is, in the pulse step, the charging capacity and the discharging capacity offset each other.

[0065] 5) Repeat steps 2) to 4) until the battery SOC is 10%; obtain the relationship between the current and voltage changes of the battery between 10% and 90% SOC.

[0066] In steps 3) and 4), the data collection interval is 0.1s. Taking the discharge process as an example, at the moment the current is applied, a transient jump occurs at the battery terminal, followed by a relatively slow change in voltage. The transient voltage jump is caused by the ohmic internal resistance, while the subsequent slow change in voltage is caused by the polarization internal resistance. Based on the acquired voltage and current data, the ohmic internal resistance and polarization internal resistance can be calculated according to equations (1) and (2), respectively.

[0067] R o =ΔU o / I=(UB-UA) / I (1)

[0068] R p = ΔU p / I=(UC-UB) / I (2)

[0069] Where: R o 、R p are ohmic internal resistance and polarization internal resistance (mΩ), I is current (A), ΔU o and ΔU p are the voltage changes (V) corresponding to the ohmic internal resistance and polarization internal resistance respectively. Where: ΔU o and ΔU p are the voltage changes corresponding to the ohmic internal resistance and polarization internal resistance (V);

[0070] During the pulse discharge process, UA is the termination voltage of step 2); UB is the voltage at any time point in step 3); UC is the termination voltage of step 3);

[0071] During the pulse charging process, UA is the termination voltage in step 3); UB is the voltage in step 4) at a time point corresponding to the same duration as UB in step 3); and UC is the termination voltage in step 4).

[0072] According to the above calculation steps, the relationship model of Ro and Rp changing with SOC, charge and discharge rate and time can be calculated.

[0073] According to formula (3), R o and R p Added together is the internal resistance R i ;

[0074] R o +R p =R 内 (3)

[0075] In the changing relationship model, find the internal resistance R 内 The smallest point R min ; Determine R min ~1.2R minThe corresponding continuous SOC interval is the optimal working range for alkali metal ion batteries.

[0076] Step 2: Determine the optimal operating range using electrochemical impedance spectroscopy and standard denominator difference

[0077] The electrochemical impedance spectroscopy test uses a test frequency of 10mHZ-10kHZ and an amplitude of 5mV to test alkali metal ion batteries with a 5% SOC gradient, ranging from 10% to 90% SOC; an interval of equal length to the optimal working interval is selected outside the optimal working interval as a comparison defective working interval to determine whether the internal resistance in the selected optimal working interval is still smaller than the internal resistance in the defective working interval; when the length of the optimal working interval exceeds 50% of the test interval, all remaining test intervals are used as comparison defective working intervals.

[0078] The following three metrics are calculated:

[0079] Average internal resistance (R0):

[0080]

[0081] Sample standard deviation (σ):

[0082]

[0083] Actual internal resistance (R):

[0084] R=R0+σ (6)

[0085] Where Ri represents the measured internal resistance, n represents the sample standard deviation, which is used to eliminate measurement errors, and R represents the actual internal resistance within the interval. The optimal operating interval is successfully selected when the R value of the optimal operating interval is consistently 1 mΩ less than the R value of the defective operating interval.

[0086] Step 3: Apply the optimal operating range to extend the service life of alkali metal ion batteries

[0087] Since the optimal operating range selects a part of the entire SOC cycle of the alkali metal ion battery for cycling, the coulomb counting method needs to be used to estimate the SOC when the battery is running, as shown in equation (7):

[0088]

[0089] Where I represents the current, which is positive during both the charge and discharge processes, t represents the charge and discharge time, and Q represents the charge and discharge capacity of the alkali metal ion battery. As the alkali metal ion battery ages, the charge and discharge capacity gradually decreases. Therefore, the cumulative error caused by the capacity drop will seriously affect the SOC estimation method. In order to reduce this error and determine the capacity loss trend, a complete charge and discharge cycle (constant current and constant voltage charge-constant current discharge) was performed at a current rate of 0.2C within a fixed voltage range of the battery, and the actual charge and discharge capacity value of the battery was determined after each 200 cycles. Subsequently, the actual charge and discharge capacity value was updated to Equation (7) to achieve an accurate estimation of the SOC and calculate the charge and discharge capacity required to maintain the specified SOC range during the test. At the same time, the cycle test was performed based on the specified available capacity rather than following a fixed voltage limit.

[0090] Test Example 1

[0091] The cylindrical sodium ion battery was subjected to the pulse program in Example 1 at a rate of 10C, and the measurement range was 10%-90% SOC. After step 1), it was preliminarily determined that the internal resistance of the sodium ion battery in the range of 60%-90% SOC was in compliance, so it was defined as the optimal working range of the sodium ion battery. At the same time, the equal-length interval of 30%-60% SOC where the internal resistance was closest to the optimal working range was defined as the comparative defect working range of the sodium ion battery, as shown in FIG. Figure 1 As shown. The sodium ion battery was tested with an AC impedance spectrum in step 2) with a gradient of 5% SOC, and the test range was 30%-90% SOC. The test results are shown in Figure 2As shown, the internal resistance within the optimal operating range is 0.80mΩ, which is less than the internal resistance of 3.75mΩ within the defective operating range. The standard denominator difference calculation in step 2) was performed on the sodium-ion battery. The calculation results are shown in Table 1. The internal resistance of the sodium-ion battery within the optimal operating range is always more than 1mΩ less than the internal resistance within the defective operating range. The optimal operating range of the sodium-ion battery at a 10C rate is determined to be 60%-90% SOC. The sodium-ion battery was subjected to the cycle test in step 3), using a constant current and constant voltage charging program to charge to 100% SOC at a current of 0.2C. After reaching 100% SOC, it was discharged at a constant current of 0.2C until it reached the lower limit of its specified SOC range (30% SOC in 30%-60% and 60% SOC in 60%-90%), which was used to apply the optimal operating range and the comparative defective operating range. Secondly, the battery is cycled between the specified upper and lower limits of SOC (60%-90% SOC of the optimal working range and 30%-60% SOC of the defective working range), using 10C constant current and constant voltage charging and 10C constant current discharge for cycling. In order to minimize the impact of low current on battery performance during high-rate cycling, the SOC estimation in step 3) is performed every 200 cycles, and the capacity range corresponding to the optimal working range and the defective working range is updated. After 1600 cycles, the cycle life of the sodium-ion battery in the optimal working range is 120.08% higher than that in the defective working range. Figure 4 .

[0092] Table 1 Relationship between internal resistance, charge and discharge current rate, time and SOC range at 10C rate

[0093]

[0094] Test Example 2

[0095] The cylindrical sodium ion battery was subjected to the pulse program in step 1) at a 2C rate, and the measurement range was 30%-90% SOC. It was preliminarily determined that the internal resistance of the sodium ion battery was the smallest in the 60%-90% SOC range, so this was defined as the optimal operating range of the sodium ion battery. At the same time, the 30%-60% SOC range where the internal resistance was closest to the optimal operating range was defined as the comparative defect operating range of the sodium ion battery, as shown in the figure. Figure 3As shown. The standard denominator difference calculation in step 2) was performed on the sodium ion battery, and the calculation results are shown in Table 2. The internal resistance of the sodium ion battery in the optimal working range is always more than 1mΩ smaller than the internal resistance in the defective working range. It is determined that the optimal working range of the sodium ion battery at a 2C rate is 60%-90% SOC. The sodium ion battery was subjected to the cycle test in step 3). After 1600 cycles, although the capacity retention rates of the batteries in the optimal working range and the defective working range were both higher than 100%, during the cycle process, the capacity retention rate of the battery in the optimal working range was always higher than that of the battery in the defective working range, as shown in FIG. Figure 5 .

[0096] Table 2 Relationship between internal resistance, charge and discharge current rate, time and SOC range at 2C rate

[0097]

Claims

1. A method for determining the optimal operating range of an alkali metal ion battery, characterized in that: The steps include: 1) Place the alkali metal ion battery at room temperature and let it sit until the battery is completely exhausted. Then fully charge the battery and record the charged capacity C1. 2) Discharge at a constant current rate of 1C, and stop when the discharge capacity reaches a1 C1. At this time, the battery SOC = 1-a1; a1 is a number in the range of 0.05 to 0.4; 3) Use a pulse current of XC rate to discharge the battery at a constant current for a duration of ts; 4) Use a pulse current of XC rate to charge the battery with constant current for a duration of ts; 5) gradually increase the value of the discharge capacity coefficient in step 2), and then repeat steps 2) to 4) several times so that the final discharge capacity battery SOC = a1; ai is the coefficient of the discharge capacity of each step 2) to 4); the discharge capacity a of the first step 2) to 4) is recorded as a1, and the discharge capacity ai in subsequent repeated steps increases in sequence; 6) Adjust the current magnification X to a multiple between 2 and 10, and repeat steps 1) to 5) to perform DC internal resistance tests at different pulse current magnifications; Based on the voltage and current data obtained in the above steps, the ohmic internal resistance and polarization internal resistance of pulse discharge and charge are calculated according to equations (1) and (2) respectively; R o =ΔU o / I=(UB-UA) / I (1) R p =ΔU p / I=(UC-UB) / I (2) Where: ΔU o and ΔU p are the voltage changes corresponding to the ohmic internal resistance and polarization internal resistance (V); During the pulse discharge process, UA is the termination voltage of step 2); UB is the voltage at any time point in step 3); UC is the termination voltage of step 3); During the pulse charging process, UA is the termination voltage in step 3); UB is the voltage in step 4) at a time point corresponding to the same duration as UB in step 3); UC is the termination voltage in step 4); Taking SOC, charge and discharge rate and time as dimensions, we can get R o and R p Relationship model with SOC, charge and discharge rate and time; According to formula (3), R o and R p Added together is the internal resistance R 内 ; R o +R p =R 内 (3) In the model, find the internal resistance R 内 The smallest point R min ; Determine R min ~1.2R min The continuous SOC interval segments within the corresponding range are the optimal working ranges for alkali metal ion batteries.

2. The method for determining the optimal operating range of an alkali metal ion battery according to claim 1, wherein: The optimal working range of the alkali metal ion battery is further determined by the following steps: The alkali metal ion battery is tested using an electrochemical impedance spectroscopy test at a test frequency of 10 MHz to 10 kHz and an amplitude of 2 to 10 mV with a gradient of Y% SOC, where the value of Y ranges from 1 to 10. An interval equal in length to the optimal working interval is selected outside the optimal working interval as a comparison defective working interval, and it is determined whether the internal resistance in the optimal working interval selected in step 6) is still less than the internal resistance in the comparison defective working interval. When the length of the optimal working interval exceeds 50% of the test interval, all remaining test intervals are used as comparison defective working intervals. The following three metrics are calculated: Average internal resistance (R0): Sample standard deviation (σ): Actual internal resistance (R): R=R0+σ (6) Among them, R i Represents the measured internal resistance value, σ represents the sample standard deviation, and R represents the actual internal resistance value within the interval; When the R value of the optimal working interval satisfies any one of the conditions of being always 1 mΩ or 15% smaller than the R value of the comparative defective working interval, it is determined that the optimal working interval is successfully selected.

3. The method for determining the optimal operating range of an alkali metal ion battery according to claim 1, wherein: After step 5) is completed, the battery is cyclically charged and discharged, and the process is repeated for 3 cycles.

4. The method for determining the optimal operating range of an alkali metal ion battery according to claim 1, wherein: The value of X is 2, 3, 4, 5, or 10.

5. The method for determining the optimal operating range of an alkali metal ion battery according to claim 1, wherein: In steps 3) and 4), the time interval for data collection is 0.1 s.

6. The method for determining the optimal operating range of an alkali metal ion battery according to claim 1, wherein: After the completion of steps 2) to 4), the device is left to stand for at least 1 hour to allow the voltage to return to a stable state, so as to prevent the subsequent calculation of the ohmic internal resistance and the polarization internal resistance from being affected.

7. A method for extending the service life of an alkali metal ion battery, comprising using the alkali metal ion battery in an optimal operating range.

8. The method for extending the service life of an alkali metal ion battery according to claim 7, characterized in that: When used in the optimal operating range, the Coulomb counting method is used to estimate the SOC: Where I represents the current, which is positive during charging and discharging, t represents the charging and discharging time, and Q represents the charging and discharging capacity of the alkali metal ion battery.

9. The method for extending the service life of an alkali metal ion battery according to claim 8, characterized in that: A complete charge and discharge cycle is performed within a fixed voltage range of the battery, and the actual charge and discharge capacity value of the battery is determined after each fixed interval of cycles; then, the actual charge and discharge capacity value is updated to formula (7) to achieve an accurate estimation of the SOC.

10. The method for extending the service life of an alkali metal ion battery according to claim 9, characterized in that: The charge and discharge capacity required to maintain a specified SOC range is calculated during the test, and the cycling test is performed based on the specified available capacity.

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