Testing method for electrochemical energy storage device

Abstract

The invention relates to the technical field of electrochemical energy storage devices, in particular to a lithium / sodium ion battery and supercapacitor testing method, which comprises the following steps of: in the manufacturing process of an electrochemical energy storage device, introducing a copper wire as a reference electrode, connecting the reference electrode with a negative electrode of charging and discharging equipment, and connecting a positive electrode end of the energy storage device with a positive electrode of the charging and discharging equipment; running a constant-current charging program, testing the electrochemical energy storage device through a constant-current intermittent titration (GITT) technology, selecting an energy storage device monomer which is subjected to a working condition test or continuously runs for a relatively long time, carrying out three-electrode test and GITT test again, and drawing a corresponding voltage curve graph and a GITT curve graph. Through comparison of GITT curves before and after circulation, accurate tracing of an attenuation mechanism is realized, and the potential change of a working electrode and a counter electrode is accurately separated in combination with a three-electrode system, so that accurate analysis of aging and failure reasons is realized.

Description

Technical Field

[0001] This invention relates to the field of electrochemical energy storage device technology, and in particular to testing methods for lithium / sodium ion batteries and supercapacitors. Background Technology

[0002] Due to their excellent electrochemical performance and long cycle life, supercapacitors and other electrochemical energy storage devices have been widely used in energy storage systems and vehicle starting power supplies. However, as the usage time continues to increase and the number of charge and discharge cycles accumulates, the performance of the battery will inevitably gradually decline. This performance degradation phenomenon is usually manifested as capacity loss, increased internal resistance, and reduced charge and discharge efficiency.

[0003] Accurate assessment of the aging status of electrochemical energy storage devices is crucial for predicting remaining lifespan, optimizing actual operating conditions, and ensuring the safe and stable operation of related equipment. In large-scale energy storage systems, rational scheduling based on battery aging status can improve overall system efficiency and reliability. In automotive electrochemical energy storage devices, accurate assessment of aging status can prevent safety hazards caused by sudden failure. The aging / failure process of electrochemical energy storage devices is extremely complex, involving multiple chemical reactions and physical processes. Simply monitoring battery voltage, capacity, and internal resistance cannot comprehensively, deeply, and accurately analyze the complex mechanisms involved in the aging process of energy storage devices, and it is difficult to accurately reflect the actual aging status of the positive and negative electrode materials under the combined effects of various complex factors, thus leading to inaccurate assessments.

[0004] Current technologies quantify the degree of aging by comparing basic parameters such as capacity, internal resistance, and voltage of electrochemical energy storage devices before and after aging. A simple method is the GITT test. 1. Take a fresh energy storage device and measure its basic parameters such as capacity, internal resistance, and average voltage; 2. After a series of cycles or tests, remeasure the basic parameters of this energy storage device, such as capacity, internal resistance, and average voltage. 3. By comparing the differences between the data before and after, the degree of aging and the cause of failure can be easily determined.

[0005] Existing technologies only provide simple assessments of aging and failure causes, which are insufficient to accurately reflect the actual aging status of positive and negative electrode materials under the combined influence of multiple complex factors, resulting in inaccurate evaluations. Therefore, developing a new technical method capable of more accurately assessing the aging state of energy storage devices is the key issue of this invention. Summary of the Invention

[0006] The technical problem this invention aims to solve is to overcome the shortcomings of existing technologies and provide a new testing method for electrochemical energy storage devices. This invention employs a combination of three-electrode and GITT technology to analyze the aging and failure phenomena of energy storage devices, which is simple and efficient. The combination of these two technologies allows for in-depth analysis of the evolution of electrode material structure, interface characteristics, and kinetic parameters during battery aging, thereby pinpointing the root cause of degradation. Through "precise potential measurement" and "kinetic parameter separation," the "macroscopic capacity decay" of battery aging is transformed into a quantitative analysis of "microscopic electrode / interface changes." By comparing parameters such as equilibrium potential, polarization voltage, and ion diffusion coefficient before and after aging, the causes of aging can be clearly identified. This provides support for the improvement of electrochemical energy storage devices and the optimization of usage strategies.

[0007] To achieve the above objectives, the technical solution adopted by the present invention is as follows: This application first provides a testing method for electrochemical energy storage devices, characterized in that: Step 1: In the process of manufacturing electrochemical energy storage devices, a copper wire is introduced as a reference electrode; Step 2: Connect the reference electrode to the negative terminal of the charging and discharging device, connect the positive terminal of the energy storage device to the positive terminal of the charging and discharging device, and run the constant current charging program to deposit lithium onto the reference electrode with a small current. Step 3: The electrochemical energy storage device was tested using GITT (Geochemical Intermittent Titration) with constant current. The ion diffusion calculation formula is as follows: Where V is the volume of the electrode material after coating; ε is the porosity; Sb is the contact area between the electrode material and the electrolyte; mb is the mass of the electrode material; ΔEs is the voltage change during relaxation; ΔEt is the voltage change during charging / discharging. Step 4: Select individual energy storage devices that have undergone operating condition testing or have been running continuously for a long time, and re-perform the three-electrode test and GITT test, and plot the corresponding voltage curve and GITT curve.

[0008] To further optimize the above plan, the following measures were also taken: As one of the preferred methods, the electrochemical energy storage device is a cylindrical hybrid supercapacitor. Its positive electrode uses traditional battery positive electrode materials and stores and releases energy through electrochemical reactions, while the negative electrode uses double-layer capacitor materials.

[0009] As a preferred method, step 1 further includes cutting the prepared enameled copper wire to a suitable length, controlling the length to be 0.5-1.5 times the battery height, quickly burning both ends of the copper wire with a flame to remove the surface enamel film without breaking the copper wire, immersing the treated portion of the copper wire in a dilute sulfuric acid / hydrochloric acid solution to remove the burning marks until the treated portion shows a smooth and bright copper color, and immersing the treated copper wire in an ethanol solution for later use to prevent oxidation.

[0010] As one of the preferred methods, step 1 further includes drilling a small hole with a diameter of 1 mm on the surface of the shell, removing burrs around the hole for later use, unfolding the outer layer after the inner core is wound, placing the treated copper wire between the positive and negative electrode plates, and adding an additional diaphragm to prevent short circuits, with the treated part of the copper wire completely covering the space between the diaphragms; after the inner core is inserted into the shell, the copper wire is led out from the hole, the nickel electrode tab is welded to the other end of the copper wire and fixed to the shell, ensuring that it does not affect the subsequent production process and that the copper wire is not damaged.

[0011] As one of the preferred methods, step 2 further includes controlling the charging current to 10-200µA and the charging time to 4-10h; when the process is completed, connect the charging and discharging equipment to the negative terminal of the energy storage device, and charge again using the same procedure to ensure that the copper wire is fully lithium plated. Connect the energy storage device to the charging and discharging equipment normally, connect the data acquisition device to the energy storage device, monitor the positive-reference voltage and the negative-reference voltage respectively, and run the test program to test the energy storage device.

[0012] As a preferred method, step 3 further includes placing the energy storage device in a constant temperature chamber at 25°C for 5 hours and then starting to run the GITT test program. The test program is as follows: Test program 1: charge / discharge with a current of 10C, each pulse time is set to 9s, and the pulse cycle is set to 40 times; Test program 2: charge / discharge with a current of 20C, each pulse time is set to 9s, and the pulse cycle is set to 20 times. The initial GITT curve is plotted based on the test results.

[0013] As one of the preferred methods, the entire charge / discharge range is 0%≤SOC≤100%.

[0014] As one of the preferred methods, the electrochemical energy storage device is a single soft-pack hybrid supercapacitor.

[0015] As a preferred method, step 1 further includes unfolding the outermost negative electrode sheet after the inner core of the soft-pack battery is stacked, placing the treated copper wire end between the positive and negative electrodes, and adding an additional separator to prevent short circuit. The treated part of the copper wire is completely covered between the separators, and the copper wire is placed parallel to the positive and negative electrode tabs. A stamping machine is used to punch out a cavity in the aluminum-plastic film, and the inner core is placed into the cavity, ensuring that the electrode tabs and copper wires are exposed from the opening end of the aluminum-plastic film.

[0016] As a preferred method, step 1 further includes cutting two pieces of polyethylene sealing film before pre-sealing, clamping the copper wire in the center, aligning it with the heat-sealing position, to prevent the copper wire from being damaged during the pre-sealing process; after pre-sealing, welding the nickel tab to the other end of the copper wire and fixing it to the outer aluminum-plastic film to ensure that it does not affect subsequent manufacturing processes and that the copper wire is not damaged.

[0017] Because of the above-mentioned approach, one or more technical solutions provided in this application embodiment have at least the following technical effects or advantages: By using "precise potential measurement" and "kinetic parameter separation," the "macroscopic capacity decay" of battery aging is transformed into a quantitative analysis of "microscopic electrode / interface changes." By comparing parameters such as equilibrium potential, polarization voltage, and ion diffusion coefficient before and after aging, the cause of aging can be clearly identified. This provides support for the improvement of electrochemical energy storage devices and the optimization of usage strategies. Attached Figure Description

[0018] To more clearly illustrate the technical solutions of the embodiments of this application, the accompanying drawings of the embodiments will be briefly described below. Obviously, the drawings described below only involve some embodiments of this application and should not be construed as limiting this application.

[0019] Figure 1 A comparison chart of data measured by the three electrodes and voltage data during the charging and discharging process. Detailed Implementation To enable those skilled in the art to better understand the technical solutions of this invention, the technical solutions of the embodiments of this invention will be clearly and completely described below with reference to the accompanying drawings, so as to more clearly understand the purpose, features and advantages of this invention. It should be understood that the embodiments shown in the drawings are not intended to limit the scope of this invention, but are only for illustrating the essential spirit of the technical solutions of this invention. Obviously, the described embodiments are only a part of the embodiments of this invention, and not all of them. Based on the embodiments of this invention, all other embodiments obtained by those skilled in the art without creative effort should fall within the scope of protection of this invention.

[0020] Unless the context requires otherwise, throughout the specification and claims, the word “comprising” and its variations, such as “including” and “having”, shall be understood to have an open, inclusive meaning, that is, to be interpreted as “including, but not limited to”.

[0021] Throughout this specification, references to "an embodiment" or "an embodiment" indicate that a particular feature, structure, or characteristic described in connection with the embodiment is included in at least one embodiment. Therefore, the appearance of "in an embodiment" or "an embodiment" in various places throughout the specification does not necessarily refer to the same embodiment. Furthermore, a particular feature, structure, or characteristic may be combined in any manner in one or more embodiments.

[0022] The singular forms “a” and “the” used in this specification and the appended claims include plural references unless otherwise expressly stated herein. It should be noted that the term “or” is generally used to mean “and / or” unless otherwise expressly stated herein.

[0023] In the following description, in order to clearly demonstrate the structure and working method of the present invention, a number of directional terms will be used. However, terms such as "front", "back", "left", "right", "outside", "inside", "outward", "inward", "up", and "down" should be understood as convenient terms and not as limiting terms.

[0024] The implementation details of the embodiments of the present invention will be described in detail below with reference to the accompanying drawings. The following content is only for the convenience of understanding the implementation details and is not necessary for implementing this solution.

[0025] Referring to the accompanying drawings, in this embodiment, an in-situ testing method for aging / failure analysis of electrochemical energy storage devices is provided. The electrochemical energy storage device can be a cylindrical hybrid supercapacitor, characterized by using traditional battery cathode materials for the positive electrode to store and release energy through electrochemical reactions, and using double-layer capacitor materials for the other electrode, so that it has both the high energy density of ion batteries and the high power density of capacitors.

[0026] The testing method includes the following steps: Step 1: In the fabrication of electrochemical energy storage devices, copper wire is introduced as a reference electrode. The prepared enameled copper wire is cut to a suitable length, controlling the length to be 0.5-1.5 times the battery height. Both ends of the copper wire are quickly scorched with a flame to remove the surface enamel film without breaking the wire. The treated portion is then immersed in a dilute sulfuric acid / hydrochloric acid solution to remove scorching marks until the treated portion exhibits a smooth, bright copper color. The treated copper wire is then immersed in an ethanol solution for later use to prevent oxidation.

[0027] Drill a small hole with a diameter of about 1 mm on the surface of the shell, and remove the burrs around the hole for later use.

[0028] After the inner core is wound, the outer layer is unfolded, and the treated copper wire is placed between the positive and negative electrode plates. An additional separator is added to prevent short circuits, and the treated part of the copper wire is completely covered between the separators.

[0029] After the inner core is inserted into the shell, the copper wire is led out from the hole, and the nickel electrode tab is welded to the other end of the copper wire and fixed to the shell to ensure that it does not affect the subsequent production process and that the copper wire is not damaged.

[0030] Step 2: Connect the reference electrode to the negative terminal of the charging / discharging device, and connect the positive terminal of the energy storage device to the positive terminal of the charging / discharging device. Run the constant current charging program to deposit lithium onto the reference electrode with a small current, controlling the charging current between 10-200µA and the charging time between 4-10 hours. After this process is completed, connect the charging / discharging device to the negative terminal of the energy storage device and repeat the charging process to ensure complete lithium plating on the copper wire.

[0031] Connect the energy storage device normally to the charging and discharging equipment, and connect the data acquisition unit to the energy storage device to monitor the positive-reference voltage and negative-reference voltage respectively. Run the test program to test the energy storage device, and plot the initial state voltage curve by combining the test results from the charging and discharging equipment and the data acquisition unit results, as shown in the attached figure. Figure 1 .

[0032] Step 3: The electrochemical energy storage device was tested using GITT (Geochemical Intermittent Titration) with constant current. The ion diffusion calculation formula is as follows: Where V is the volume of the electrode material after coating; ε is the porosity; Sb is the contact area between the electrode material and the electrolyte; mb is the mass of the electrode material; ΔEs is the voltage change during relaxation; and ΔEt is the voltage change during charging / discharging.

[0033] After placing the energy storage device in a constant temperature chamber at 25°C for 5 hours, the GITT test program was started.

[0034] Test Procedure 1: Charge / discharge at 10C current, with each pulse duration set to 9s and the pulse cycle set to 40 times.

[0035] Test Procedure 2: Charge / discharge at 20C current, with each pulse duration set to 9s and the pulse cycle set to 20 times.

[0036] Plot the initial GITT curve based on the test results.

[0037] Step 4: Select individual energy storage devices that have undergone operating condition testing or have been running continuously for a long time, and re-perform the three-electrode test and GITT test, and plot the corresponding voltage curve and GITT curve.

[0038] Hybrid supercapacitor energy storage devices focus more on charge and discharge capabilities at high rates, and in actual operation, they typically operate under high current conditions. High-current GITT can simulate high-rate operating conditions and accurately capture key information such as polarization, diffusion, and interface reactions of the battery under high current. The high-current GITT can perform pulse-rest cycles point by point throughout the entire charge and discharge range (e.g., from SOC 0% to 100%) to record the polarization changes at different SOCs. Taking test program 2 as an example, each pulse is 5% SOC.

[0039] At high SOC (e.g., >80%) or low SOC (e.g., <20%), polarization tends to increase rapidly under high current. High-current GITT can accurately locate the "polarization-sensitive SOC range" and provide data support for battery charging and discharging strategies.

[0040] By comparing the GITT curves before and after cycling, the attenuation mechanism can be accurately traced. Combined with the three-electrode system, the potential changes of the working electrode and the counter electrode can be accurately separated, enabling accurate analysis of the causes of aging and failure.

[0041] As a preferred embodiment, the electrochemical energy storage device of this invention is a cylindrical hybrid supercapacitor. The energy storage devices involved in this patent include supercapacitors and lithium / sodium-ion batteries in various forms such as cylindrical, square, and pouch cells. The supercapacitors also include hybrid supercapacitors. If the form of the energy storage device changes, step 1 in the above testing method should change accordingly. If the energy storage device is a pouch hybrid supercapacitor cell, the corresponding step 1 is as follows: After the inner core of the soft-pack battery is stacked, the outermost negative electrode sheet is unfolded, the treated copper wire end is placed between the positive and negative electrodes, and an additional separator is added to prevent short circuits. The treated part of the copper wire is completely covered between the separators, and the copper wire is placed parallel to the positive and negative electrode tabs.

[0042] Use a stamping machine to punch out a cavity in the aluminum-plastic film, then place the inner core into the cavity, ensuring that the tabs and copper wires protrude from the open end of the aluminum-plastic film.

[0043] Before pre-sealing, cut two pieces of polyethylene sealing film, sandwich the copper wire in the center, align it with the heat sealing position, and prevent the copper wire from being damaged during the pre-sealing process.

[0044] After pre-sealing, the nickel tab is welded to the other end of the copper wire and fixed to the outer aluminum-plastic film to ensure that it does not affect subsequent production and that the copper wire is not damaged.

Claims

1. A testing method for electrochemical energy storage devices, characterized in that: Step 1: In the process of fabricating electrochemical energy storage devices, copper wire is introduced as a reference electrode; Step 2: Connect the reference electrode to the negative terminal of the charging and discharging device, connect the positive terminal of the energy storage device to the positive terminal of the charging and discharging device, and run the constant current charging program to deposit lithium onto the reference electrode with a small current. Step 3: The electrochemical energy storage device was tested using GITT (Geochemical Intermittent Titration) with constant current. The ion diffusion calculation formula is as follows: ； Where V is the volume of the electrode material after coating; ε is the porosity; Sb is the contact area between the electrode material and the electrolyte; mb is the mass of the electrode material; ΔEs is the voltage change during relaxation; ΔEt is the voltage change during charging / discharging. Step 4: Select individual energy storage devices that have undergone operating condition testing or have been running continuously for a long time, and re-perform the three-electrode test and GITT test, and plot the corresponding voltage curve and GITT curve.

2. The test method according to claim 1, characterized in that: The electrochemical energy storage device is a cylindrical hybrid supercapacitor. Its positive electrode uses traditional battery positive electrode materials and stores and releases energy through electrochemical reactions, while the negative electrode uses double-layer capacitor materials.

3. The test method according to claim 1, characterized in that: Step 1 further includes cutting the prepared enameled copper wire to a suitable length, controlling the length to be 0.5-1.5 times the height of the battery, quickly burning both ends of the copper wire with a flame to remove the surface enamel film without breaking the copper wire, immersing the treated part of the copper wire in a dilute sulfuric acid / hydrochloric acid solution to remove the burning marks until the treated part shows a smooth and bright copper color, and immersing the treated copper wire in an ethanol solution for later use to prevent oxidation.

4. The test method according to claim 3, characterized in that: Step 1 also includes drilling a small hole with a diameter of 1 mm on the surface of the shell, removing burrs around the hole for later use, unfolding the outer layer after the inner core is wound, placing the treated copper wire between the positive and negative electrode plates, and adding an additional diaphragm to prevent short circuits, with the treated part of the copper wire completely covering the space between the diaphragms; after the inner core is inserted into the shell, the copper wire is led out from the hole, the nickel electrode tab is welded to the other end of the copper wire and fixed to the shell to ensure that it does not affect the subsequent production process and that the copper wire is not damaged.

5. The test method according to claim 1, characterized in that: Step 2 further includes controlling the charging current to 10-200µA and the charging time to 4-10h. After the process is completed, the charging and discharging equipment is connected to the negative terminal of the energy storage device, and the charging procedure is repeated to ensure that the copper wire is fully lithium plated. The energy storage device is then connected to the charging and discharging equipment, and the data acquisition device is connected to the energy storage device to monitor the positive-reference voltage and the negative-reference voltage respectively. The test program is then run to test the energy storage device.

6. The test method according to claim 1, characterized in that: Step 3 further includes placing the energy storage device in a constant temperature chamber at 25°C for 5 hours and then starting the GITT test program. The test program is as follows: Test program 1: charge / discharge with a current of 10C, each pulse time is set to 9s, and the pulse cycle is set to 40 times; Test program 2: charge / discharge with a current of 20C, each pulse time is set to 9s, and the pulse cycle is set to 20 times. The initial GITT curve is plotted based on the test results.

7. The test method according to claim 6, characterized in that: The entire charge / discharge range is 0% ≤ SOC ≥ 100%.

8. The test method according to claim 1, characterized in that: The electrochemical energy storage device is a single soft-pack hybrid supercapacitor.

9. The test method according to claim 8, characterized in that: Step 1 further includes unfolding the outermost negative electrode sheet after the inner core of the soft-pack battery is stacked, placing the treated copper wire end between the positive and negative electrodes, and adding an additional separator to prevent short circuits. The treated part of the copper wire is completely covered between the separators, and the copper wire is placed parallel to the positive and negative electrode tabs. A stamping machine is used to punch out a cavity in the aluminum-plastic film, and the inner core is placed into the cavity, ensuring that the electrode tabs and copper wires are exposed from the opening end of the aluminum-plastic film.

10. The test method according to claim 9, characterized in that: Step 1 further includes cutting two pieces of polyethylene sealing film before pre-sealing, clamping the copper wire in the center, aligning it with the heat-sealing position, to prevent the copper wire from being damaged during the pre-sealing process; after pre-sealing, welding the nickel tab to the other end of the copper wire and fixing it to the outer aluminum-plastic film to ensure that it does not affect subsequent production and that the copper wire is not damaged.

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