Accelerated evaluation method for cycle life attenuation of sodium ion battery

Abstract

An accelerated evaluation method for cycle life decay of a sodium ion battery relates to the field of sodium ion battery performance test and evaluation, and comprises the following steps: preparing a soft package / square shell / cylindrical battery from positive and negative pole pieces prepared in the same batch, performing formation and constant volume, adjusting the load to 100%, 50% and 0% SOC, disassembling the positive and negative pole pieces, soaking in a DMC solution, and assembling into a positive pole symmetrical battery and a negative pole symmetrical battery. Respectively carrying out cycle life testing, finally testing electrochemical alternating current impedance spectroscopy (EIS) of the positive and negative electrode symmetrical batteries before and after cycle aging, carrying out DRT conversion on an EIS curve, evaluating an impedance growth result, and comparing the EIS and DRT results with the EIS and DRT results of the positive or negative electrode symmetrical batteries in a BOL state; according to the method, on the premise that the failure mode of the sodium ion battery is known, the performance evaluation is carried out by utilizing the symmetric battery, the workload is reduced while the life evaluation is accelerated, the performance evaluation and the failure analysis work are promoted in a targeted manner, and the cycle capacity attenuation and the impedance increase of the sodium ion battery are promoted.

Description

Technical Field

[0001] The present invention relates to the field of sodium ion battery performance testing and evaluation, and in particular to a method for accelerating the evaluation of sodium ion battery cycle life attenuation. Background Art

[0002] It is well known that sodium-ion batteries (Na-ion batteries) have the advantages of low cost and abundant natural resource reserves compared to lithium-ion batteries. Their performance features, such as wide temperature range and long cycle life, make them a competitive next-generation power and energy storage battery system. The lifespan of Na-ion batteries is directly related to the service life of power and energy storage systems and is a crucial indicator for evaluating Na-ion battery performance. However, conventional lifespan evaluation methods require long equipment cycles, severely hindering research and development progress. To rapidly evaluate the lifespan of Na-ion batteries, there is an urgent need to develop more efficient accelerated lifespan evaluation methods.

[0003] The application number is 202010175496.1 and the application date is 2020.03.13. The name of the invention is a method for accelerating the prediction of lithium-ion battery life based on low-temperature cycles. This method determines the life of lithium-ion batteries at different temperatures and different rates through the numerical relationship between the number of low-temperature cycles and the number of cycles at room temperature attenuation to 80% SOH. This method is based on the numerical relationship of the number of cycles of the full battery at different temperatures. It does not consider the cycle aging mechanism, characteristics, and impact of the positive and negative electrodes on the cycle life, nor does it consider the evaluation of impedance growth after cycle aging; therefore, proposing an accelerated evaluation method for the cycle life attenuation of sodium-ion batteries to solve the problem of long cycle life evaluation period of sodium-ion batteries has become a basic demand of those skilled in the art. Summary of the Invention

[0004] In order to overcome the deficiencies in the background technology, the present invention discloses an accelerated evaluation method for the cycle life decay of a sodium ion battery.

[0005] In order to achieve the above-mentioned purpose, the present invention adopts the following technical solutions: An accelerated evaluation method for sodium ion battery cycle life attenuation, comprising the following steps: S1. Take the positive and negative electrodes prepared in the same batch to make soft-pack / square-shell / cylindrical batteries. After charging to a fixed capacity, adjust the charge to 100%, 50%, and 0% SOC respectively; S2. Disassemble the charged battery in a glove box protected by an inert atmosphere to obtain the positive and negative electrodes with SOC of 100%, 50%, and 0%, respectively. Then, soak the disassembled positive and negative electrodes in a DMC solution to remove the residual electrolyte. S3, respectively assembling two positive electrode sheets with 100% SOC and 0% SOC from which the electrolyte is removed into a positive electrode symmetrical battery, assembling two negative electrode sheets with 100% SOC and 0% SOC into a negative electrode symmetrical battery, assembling two positive electrode sheets with 50% SOC into a positive electrode symmetrical battery, and assembling two negative electrode sheets with 50% SOC into a negative electrode symmetrical battery; S4, performing cycle life tests on the positive electrode symmetrical battery and the negative electrode symmetrical battery respectively; S5. Test the electrochemical impedance spectroscopy (EIS) of the positive electrode symmetrical battery and the negative electrode symmetrical battery before and after cycle aging, perform DRT conversion on the EIS curve, evaluate the impedance growth results, and compare them with the EIS and DRT results of the positive or negative electrode symmetrical battery in the BOL state.

[0006] The accelerated evaluation method for sodium ion battery cycle life attenuation uses a current of 0.05C-0.33C when the charge is adjusted to 100% and 0% SOC, and a current of 0.05C-0.1C when the charge is adjusted to 50% SOC, to ensure that both the positive and negative electrodes are at the set SOC.

[0007] The accelerated evaluation method for the cycle life attenuation of sodium ion batteries is as follows: during the disassembly of the battery after charge adjustment in a glove box protected by an inert atmosphere, the oxygen content in the glove box is ≤0.1 ppm, the moisture content is ≤0.1 ppm, and the purity of the inert gas is ≥99.999%.

[0008] In the accelerated evaluation method for sodium ion battery cycle life attenuation, the immersion time in the DMC solution is 10-15 minutes.

[0009] In the accelerated evaluation method for sodium ion battery cycle life attenuation, the temperature and current of the cycle life test in step S4 are consistent with those of a normal battery, and the voltage range is -1V-1V; the specific cycle life test steps are: Place the positive or negative symmetrical battery at a test temperature of -40°C to 80°C for 4-8 hours, charge at constant current and then switch to constant voltage, place it at rest for 10 minutes, then discharge it, place it at rest again for 10 minutes, and stop the test when the SOH reaches 95%.

[0010] Due to the adoption of the above technical solution, the present invention has the following beneficial effects: 1. The present invention discloses a method for accelerating the evaluation of sodium-ion battery cycle life degradation. The method utilizes symmetrical cells, each with its positive and negative electrodes fabricated into symmetrical cells, and conducts cyclic charge-discharge tests. The method also assesses the structural changes in the active material and interfacial active ion consumption during repeated charge and discharge cycles for both the positive and negative electrodes. Because symmetrical cells employ a single electrode as both the positive and negative electrodes, a single charge and discharge cycle involves both sodium ion extraction and insertion. This accelerates the evaluation of active material capacity loss, interfacial active ion consumption, crystal structure changes (manifested as changes in solid-phase diffusion impedance) caused by multiple sodium ion extraction and insertion, and interfacial impedance growth due to interfacial side reactions. This accelerates the aging of the positive or negative electrode during cycling, including capacity degradation and impedance growth, relative to a full-cell system. The present invention utilizes symmetrical cells for targeted performance evaluation based on known sodium-ion battery failure modes. This accelerates lifespan evaluation while reducing workload and enabling targeted advancement of performance evaluation and failure analysis.

[0011] 2. The accelerated evaluation method for the cycle life attenuation of sodium-ion batteries described in the present invention adds symmetrical batteries assembled with 50% SOC electrodes, and can assemble symmetrical batteries with positive or negative electrodes obtained by disassembling a single battery. Compared with symmetrical batteries assembled at 100% SOC and 0% SOC states, the number of trial-produced soft-pack / cylindrical / prismatic batteries can be reduced, saving material usage and trial-production resources. Cycling capacity decay is usually related to an increase in side reactions at the electrode-electrolyte interface. The accumulation of interfacial side reaction products will cause the interfacial charge transfer impedance to increase. Conversely, the impedance growth will cause the constant voltage section at the end of charging to be too long. When the positive electrode material is under high voltage for a long time, the dissolution of transition metal elements will be aggravated, thereby promoting side reactions at the negative electrode interface. Therefore, cyclic capacity decay and impedance growth usually promote each other. The present invention has a promoting effect on both cyclic capacity decay and impedance growth of sodium ion batteries. BRIEF DESCRIPTION OF THE DRAWINGS

[0012] Figure 1 This is the cycle capacity decay curve of the positive electrode symmetrical battery in Example 1 (compared with the single-chip full battery); Figure 2 This is the cycle capacity decay curve of the negative electrode symmetrical battery in Example 2 (compared with the single-chip full battery); Figure 3 The EIS spectrum of the positive electrode symmetrical battery before and after cycle aging in Example 1; Figure 4 The EIS spectrum of the negative electrode symmetrical battery before and after cycle aging in Example 2; Figure 5 The EIS-DRT spectra of the positive electrode symmetrical battery before and after cycle aging in Example 1; Figure 6 The EIS-DRT spectrum of the negative electrode symmetrical battery before and after cycle aging in Example 2; DETAILED DESCRIPTION

[0013] The present invention can be explained in detail by the following examples, the purpose of which is to disclose the present invention and to protect all technical improvements within the scope of the present invention.

[0014] The accelerated evaluation method for sodium ion battery cycle life attenuation of the present invention specifically includes the following steps: S1. Take the positive and negative electrodes prepared in the same batch to make soft-pack / square-shell / cylindrical batteries. After being charged to a fixed capacity, adjust the charge to 100%, 50%, and 0% SOC respectively. The current used for adjusting the charge to 100% and 0% SOC is 0.05C-0.33C, and the current used for adjusting the charge to 50% SOC is 0.05C-0.1C to ensure that both the positive and negative electrodes are at the set SOC.

[0015] S2. Disassemble the charged battery in an inert atmosphere glove box to obtain the positive and negative electrodes with 100%, 50%, and 0% SOC, respectively. Soak the disassembled positive and negative electrodes in DMC solution for 10-15 minutes to remove residual electrolyte. The oxygen content in the glove box is ≤0.1 ppm, the moisture content is ≤0.1 ppm, and the purity of the inert gas is ≥99.999%. S3, respectively assembling two positive electrode sheets with 100% SOC and 0% SOC from which the electrolyte is removed into a positive electrode symmetrical battery, assembling two negative electrode sheets with 100% SOC and 0% SOC into a negative electrode symmetrical battery, assembling two positive electrode sheets with 50% SOC into a positive electrode symmetrical battery, and assembling two negative electrode sheets with 50% SOC into a negative electrode symmetrical battery; S4. Perform cycle life tests on the positive and negative symmetrical batteries respectively. The temperature and current of the cycle life tests are consistent with those of normal batteries, and the voltage range is -1V-1V. The specific cycle life test steps are as follows: Place the positive or negative symmetrical battery at a test temperature of -40°C to 80°C for 4-8 hours, charge at constant current and then switch to constant voltage, place it at rest for 10 minutes, then discharge it, place it at rest again for 10 minutes, and stop the test when the SOH reaches 95%. S5. The electrochemical impedance spectroscopy (EIS) of the positive and negative symmetrical batteries before and after cycle aging was tested respectively. The EIS curves were converted to DRT to evaluate the impedance growth results. The results were compared with the EIS and DRT results of the positive or negative symmetrical batteries in the BOL state. The DRT is a relaxation time distribution method. Example 1

[0016] The positive and negative electrodes of sodium ion batteries prepared in the same batch were made into soft-pack batteries. After being charged to a fixed capacity, they were charged to 100% SOC and 0% SOC respectively using a current of 0.1C. The battery after charge adjustment was disassembled in a glove box protected by an inert atmosphere to obtain the positive and negative electrodes with 100% SOC and 0% SOC, respectively. The positive and negative electrodes were immersed in DMC solution in a glove box for 10 min to remove residual electrolyte. Assemble the positive electrode sheets of 100% SOC and 0% SOC into positive electrode symmetrical batteries; The positive electrode symmetrical battery was left standing at 25°C for 6 hours and cycled at 0.5C and -1V-1V. The specific test steps were as follows: 0.5C constant current charging to 1V, switching to constant voltage, 0.05C cutoff, and standing for 10 minutes; 0.5C discharge to -1V, standing for 10 minutes, and cycle until 95% SOH and stop testing.

[0017] The cycled battery was subjected to EIS test, and the EIS curve was converted to DRT to evaluate the impedance growth results, which were compared with the EIS and DRT results of the positive electrode symmetrical battery in the BOL state. Example 2

[0018] The positive and negative electrodes of sodium ion batteries prepared in the same batch were made into soft-pack batteries. After being charged to a fixed capacity, they were charged to 100% SOC and 0% SOC respectively using a current of 0.33C. The battery after charge adjustment was disassembled in a glove box protected by an inert atmosphere to obtain the positive and negative electrodes with 100% SOC and 0% SOC, respectively. The positive and negative electrodes were immersed in DMC solution in a glove box for 15 min to remove residual electrolyte. Assemble the negative electrode sheets of 100% SOC and 0% SOC into negative electrode symmetrical batteries; The negative electrode symmetrical battery was left standing at 25°C for 6 hours and cycled at 0.5C and -1V-1V. The specific test steps were as follows: 0.5C constant current charging to 1V, switching to constant voltage, 0.05C cutoff, and standing for 10 minutes; 0.5C discharge to -1V, standing for 10 minutes, and cycle until 95% SOH and stop testing.

[0019] The cycled battery was subjected to EIS testing, and the EIS curve was converted to DRT to evaluate the impedance growth results, which were compared with the EIS and DRT results of the negative electrode symmetrical battery in the BOL state. Example 3

[0020] The positive and negative electrodes of sodium ion batteries prepared in the same batch were made into soft-pack batteries. After being charged to a fixed capacity, they were charged to 50% SOC using a current of 0.05C. The battery after charge adjustment was disassembled in a glove box protected by an inert atmosphere to obtain the positive and negative electrodes with a SOC of 50% respectively; The positive and negative electrodes were immersed in DMC solution in a glove box for 10 min to remove residual electrolyte. Assemble two 50% SOC positive electrode sheets into a positive electrode symmetrical battery; The positive electrode symmetrical battery was left at 45°C for 6 hours and cycled at 1C and -1V-1V. The specific test steps were as follows: 1C constant current charging to 1V, switching to constant voltage, 0.05C cutoff, and leaving it for 10 minutes; 1C discharge to -1V, leaving it for 10 minutes, and stopping the test when the SOH reached 95%.

[0021] The cycled battery was subjected to EIS testing, and the EIS curve was converted to DRT to evaluate the impedance growth results, which were then compared with the EIS and DRT results of the positive electrode symmetrical battery in the BOL state. Example 4

[0022] The positive and negative electrodes of sodium ion batteries prepared in the same batch were made into soft-pack batteries. After being charged to a fixed capacity, they were charged to 50% SOC using a current of 0.05C. The battery after charge adjustment was disassembled in a glove box protected by an inert atmosphere to obtain the positive and negative electrodes with a SOC of 50% respectively; The positive and negative electrodes were immersed in DMC solution in a glove box for 15 min to remove residual electrolyte. Assemble two 50% SOC negative electrode sheets into a negative electrode symmetrical battery; The positive electrode symmetrical battery was left at 35°C for 6 hours and cycled at 1C and -1V-1V. The specific test steps were as follows: 1C constant current charging to 1V, switching to constant voltage, 0.05C cutoff, and leaving it for 10 minutes; 1C discharge to -1V, leaving it for 10 minutes, and stopping the test when the SOH reached 95%.

[0023] The cycled battery was subjected to EIS testing, and the EIS curve was converted to DRT to evaluate the impedance growth results. The results were then compared with the EIS and DRT results of the negative electrode symmetrical battery in the BOL state.

[0024] Comparative Example 1 The positive and negative electrodes of sodium ion batteries prepared in the same batch were made into single-piece batteries (1 positive and 2 negative). After being charged to a fixed capacity, they were left standing at 25°C for 6 hours and cycled at 0.5C, 1.5V to 3.6V. The specific test steps were as follows: 0.5C constant current charging to 3.6V, switching to constant voltage, 0.05C cutoff, and standing for 10 minutes; 0.5C discharge to 1.5V, standing for 10 minutes, and the test was stopped when the SOH level was 95%.

[0025] The cycled battery was subjected to EIS testing, and the EIS curve was converted to DRT to evaluate the impedance growth results, which were compared with the EIS and DRT results of the single-chip battery in the BOL state.

[0026] Comparative Example 2 The positive and negative electrodes of sodium ion batteries prepared in the same batch were made into single-piece batteries (1 positive and 2 negative). After being charged to a fixed capacity, they were left standing at 45°C for 6 hours and cycled under 1C, 1.5V to 3.6V conditions. The specific test steps were: 1C constant current charging to 3.6V, switching to constant voltage, 0.05C cutoff, and standing for 10 minutes; 1C discharge to 1.5V, standing for 10 minutes, and cycling to 95% SOH to stop the test.

[0027] The cycled battery was subjected to EIS testing, and the EIS curve was converted to DRT to evaluate the impedance growth results, which were compared with the EIS and DRT results of the single-chip battery in the BOL state.

[0028] The EIS test method is as follows: the battery to be tested is charged to 50% SOC, allowed to stand at 25°C for 6 hours, and the EIS is tested using an electrochemical workstation with an excitation voltage of 5mV and a frequency range of 0.01Hz-100kHz. The EIS curve is obtained by scanning, and the EIS data is converted and processed using software based on the distribution relaxation time method (DRT) to obtain electrochemical process data of different relaxation times on the DRT curve. Different peaks of the DRT curve correspond to different types of electrochemical impedances. The peak intensity is integrated and calculated to obtain the peak area, which is the resistance value of the electrochemical impedance.

[0029] Some experimental parameters and test results in Examples 1-4 of the present invention and Comparative Examples 1-2 are shown in Table 1.

[0030] Table 1 Battery Type Test temperature / ℃ Charge and discharge rate / C Number of cycles corresponding to decay to 95% SOH Positive electrode interface impedance growth ratio Negative electrode interface impedance growth ratio Positive electrode solid phase diffusion impedance growth ratio Growth ratio of negative electrode solid phase diffusion impedance Example 1 Positive symmetry 25 0.5 428 37.9% ／ 10.4% ／ Example 2 Negative symmetry 25 0.5 91 ／ 185.9% ／ -35.0% Example 3 Positive symmetry 45 1 325 55.0% ／ 23.5% ／ Example 4 Negative symmetry 35 1 120 ／ 210.7% ／ -37.3% Comparative Example 1 Monolithic full battery 25 0.5 690 20.8% 66.7% 6.9% -30.6% Comparative Example 2 Monolithic full battery 45 1 560 36.1% 120.5% 14.5% -26.8%

[0031] Compared with Comparative Example 1, Examples 1-2 and 3-4, respectively, show that the rate of cycle capacity decay and the rate of interfacial impedance growth are both accelerated, which is beneficial for accelerating the evaluation of materials, formulations, electrolytes, etc., shortening the R&D cycle, and promoting the industrialization of sodium-ion materials and batteries.

[0032] The parts not described in detail in this invention are prior art.

[0033] The embodiments selected herein for the purpose of disclosing the invention are presently considered suitable, but it should be understood that the invention is intended to include all variations and modifications of the embodiments that fall within the scope of the concept and invention.

Claims

1. A method for accelerating the evaluation of sodium ion battery cycle life attenuation, characterized by: The specific steps include the following: S1. Take the positive and negative electrodes prepared in the same batch to make soft-pack / square-shell / cylindrical batteries. After charging to a fixed capacity, adjust the charge to 100%, 50%, and 0% SOC respectively; S2. Disassemble the charged battery in a glove box protected by an inert atmosphere to obtain the positive and negative electrodes with SOC of 100%, 50%, and 0%, respectively. Then, soak the disassembled positive and negative electrodes in a DMC solution to remove residual electrolyte. S3, respectively assembling two positive electrode sheets with 100% SOC and 0% SOC from which the electrolyte is removed into a positive electrode symmetrical battery, assembling two negative electrode sheets with 100% SOC and 0% SOC into a negative electrode symmetrical battery, assembling two positive electrode sheets with 50% SOC into a positive electrode symmetrical battery, and assembling two negative electrode sheets with 50% SOC into a negative electrode symmetrical battery; S4, performing cycle life tests on the positive electrode symmetrical battery and the negative electrode symmetrical battery respectively; S5. For the positive and negative symmetrical batteries before and after cycle aging, the electrochemical impedance spectroscopy (EIS) was tested respectively. The EIS curve was converted to DRT to evaluate the impedance growth results. The results were compared with the EIS and DRT results of the positive or negative symmetrical battery in the BOL state.

2. The accelerated evaluation method for sodium ion battery cycle life attenuation according to claim 1 is characterized in that: The current used to adjust the load to 100% and 0% SOC is 0.05C-0.33C, and the current used to adjust the load to 50% SOC is 0.05C-0.1C to ensure that both the positive and negative electrodes are at the set SOC.

3. The accelerated evaluation method for sodium ion battery cycle life attenuation according to claim 1 is characterized in that: During the disassembly of the charged battery in a glove box protected by an inert atmosphere, the oxygen content in the glove box is ≤0.1 ppm, the moisture content is ≤0.1 ppm, and the purity of the inert gas is ≥99.999%.

4. The accelerated evaluation method for sodium ion battery cycle life attenuation according to claim 1 is characterized in that: The soaking time in the DMC solution is 10-15 minutes.

5. The accelerated evaluation method for sodium ion battery cycle life attenuation according to claim 1 is characterized by: The temperature and current of the cycle life test in step S4 are consistent with those of a normal battery, and the voltage range is -1V-1V. The specific cycle life test steps are as follows: Place the positive or negative symmetrical battery at a test temperature of -40°C to 80°C for 4-8 hours, charge at constant current and then switch to constant voltage, place it at rest for 10 minutes, then discharge it, place it at rest again for 10 minutes, and stop the test when the SOH reaches 95%.

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