Electrochemical window testing method for battery electrolyte

Abstract

The invention relates to the technical field of secondary battery electrolyte, in particular to a battery electrolyte electrochemical window testing method. The assembly sequence of the two-electrode testing device is the negative electrode shell, the reference electrode, the counter electrode, the electrolyte, the diaphragm, the electrolyte, the working electrode, the gasket, the elastic sheet and the positive electrode shell, a lithium sheet or a sodium sheet is used as the reference electrode and the counter electrode, the pretreated foam metal is used as the working electrode, the two-electrode testing device is assembled into a button cell, the electrolyte is added to the two sides of the diaphragm, and the diaphragm and the working electrode are assembled into the button cell. A gasket and an elastic piece need to be assembled on one side of the working electrode, a two-electrode testing device is obtained through assembling and used for testing after being placed, and an electrolyte electrochemical window is tested through LSV; wherein the foam metal comprises foam copper or foam nickel. The testing and assembling means are simple and convenient, the lithium / sodium ion battery electrolyte reduction window can be effectively and stably represented, the film-forming potential of the electrolyte additive can be obviously distinguished, and the film-forming behavior can be analyzed.

Description

Technical Field

[0001] This invention relates to the field of secondary battery electrolyte technology, and in particular to a method for testing the electrochemical window of battery electrolyte. Background Technology

[0002] Electrolytes are a crucial component of lithium / sodium-ion batteries, significantly impacting battery safety, kinetics, and thermodynamic performance. Current research on electrolytes primarily focuses on their electrochemical window and polarization properties.

[0003] Among the various electrolytes studied, the electrochemical oxidation window is relatively well-researched and highly reproducible. However, the electrochemical reduction window is less well-documented due to the high technical requirements and difficulty in detection. Currently, because electrolyte additives are complex and difficult to analyze directly using gas chromatography or ion chromatography, characterizing the electrochemical reduction window is crucial not only for analyzing the thermodynamic characteristics of electrolytes but also for corroborating the results of gas chromatography and ion chromatography. Therefore, accurate characterization of the electrochemical reduction window plays a vital role in the development of electrolyte research. Summary of the Invention

[0004] The purpose of this invention is to overcome the shortcomings of the prior art and provide a method for testing the electrochemical window of battery electrolytes. Our research found that using metal foam as the working electrode can effectively induce the deposition of additives involved in SEI film formation in the electrolyte, thereby obtaining the film-forming reaction potentials of each component of the electrolyte, which plays an important auxiliary role in observing the film-forming behavior of each component of the electrolyte.

[0005] The objective of this invention is achieved through the following technical solution: A method for testing the electrochemical window of a battery electrolyte includes the following steps: The assembly sequence of the two-electrode testing device is as follows: negative electrode shell, reference electrode and counter electrode, electrolyte, diaphragm, working electrode, gasket, spring, and positive electrode shell. Using lithium or sodium sheets as reference and counter electrodes, and pretreated foam metal as the working electrode, the devices are assembled into a coin cell. Electrolyte is added to both sides of the separator. A gasket and spring are assembled on the working electrode side to obtain a two-electrode test device. After being placed in the test, the electrochemical window of the electrolyte is tested using LSV. The foam metal includes copper foam or nickel foam.

[0006] Furthermore, the electrochemical window is a reduction window.

[0007] Furthermore, the gaskets, springs, positive electrode shells, and negative electrode shells all need to be cleaned. The cleaning process involves ultrasonic cleaning in anhydrous ethanol for 1-3 hours and drying at a constant temperature of 70-90℃.

[0008] Preferably, the electrolyte is added in the form of 20-80 μL on each side of the diaphragm; the diaphragm includes PP diaphragm and composite diaphragm; the composite diaphragm includes at least two of PP diaphragm, ceramic and hot-press adhesive; the thickness of the diaphragm is 9 mm-60 mm; the resting includes resting at room temperature for 6-48 hours.

[0009] It should be noted that after the two-electrode testing device is assembled, it needs to be left at room temperature for 6-48 hours before it can be tested and used; otherwise, the test results will be deviated due to polarization issues.

[0010] Furthermore, the diaphragm used in the two-electrode testing device needs to be able to fully wet the electrolyte to meet experimental requirements. The method for detecting whether the diaphragm can fully wet the electrolyte includes the following steps: The diaphragm needs to be fully wetted with the electrolyte, and the wetted mass after 24 hours should be no less than 0.006g. The specific test method for wetted mass is as follows: weigh 3-5mL of electrolyte into a wide-mouth screw-top culture bottle, weigh the diaphragm before wetting, and weigh it again under the same conditions after 24 hours of wetting. The difference between the two weighings is the wetted mass.

[0011] Preferably, the working electrode has a thickness of 0.5-1.5mm and a length and width of (10±3mm)×(10±3mm). The four corners of the working electrode sheet need to be chamfered with a chamfer size of (1±0.3mm)×(1±0.3mm).

[0012] It should be noted that the purpose of the chamfer is to prevent short circuits.

[0013] Preferably, the gasket is a stainless steel gasket with a thickness of 0.3-0.7 mm and a diameter of 15.5-16.2 mm; the spring is a stainless steel funnel spring with a thickness of 1.0-1.2 mm and a diameter of 15.5-16.2 mm; the stainless steel is one of 304 stainless steel, 316 stainless steel, and 316L stainless steel.

[0014] Preferably, the LSV test electrolyte electrochemical window is used, and the steps include a scan rate of 1-5mV and a scan range from open circuit voltage to -0.1~-1V.

[0015] Preferably, after using LSV to test the electrochemical window of the electrolyte, it is determined whether IR compensation is needed for the test results based on the test conditions. The basis for compensation is internal resistance and current. If compensation is needed, manual compensation is performed based on internal resistance and LSV test current, with a compensation ratio of 50%-90%.

[0016] Furthermore, the compensation needs to be based on the internal resistance and current, where the internal resistance is greater than 2Ω and the current is greater than 0.001A.

[0017] Preferably, the method for preparing pretreated foamed metal includes the following steps: The foamed metal is cleaned and then calcined. Under a reducing atmosphere, the temperature is raised to 150-250℃ and held for 0.5-2 hours. Then, the temperature is raised to 450-600℃ and held for 1-3 hours. The temperature is then allowed to cool naturally to obtain pretreated foamed metal. The reducing atmosphere includes one of the following: high-purity hydrogen, 5%~10% hydrogen-argon mixture, or ammonia.

[0018] Furthermore, the preparation method of pretreated foamed metal includes the following steps: The foamed metal is cleaned and then immersed in a plating solution at 45-60℃. A dual-electrode system is used, with the foamed metal as the working electrode and a high-purity nickel plate as the counter electrode, at a voltage of 1-5 mA / cm². 2 At a current density of 5-30 min, deposition is carried out, with the target film thickness controlled at 30-80 nm. After deposition, the film is removed, rinsed, and dried to obtain the deposited foam metal. The deposited foam metal is then immersed in PEI solution for 15-30 min for soaking and adsorption. After immersion, the film is removed, cleaned, and dried to obtain the pretreated foam metal. The plating solution includes 200 g / L nickel sulfate hexahydrate, 20-40 g / L sodium hypophosphite, 30-60 g / L sodium acetate, and 0.1-1 g / L surfactant. The pH of the plating solution is adjusted to 4.5-5.5.

[0019] Furthermore, the cleaning process includes the following steps: In deionized water, ultrasonically clean for 0.5-2 hours, then ultrasonically clean with ethanol for 0.5-1 hour; finally, ultrasonically clean with acetone for 0.5-1 hour, and then dry at 45-60℃ for 6-12 hours.

[0020] Compared with the prior art, the beneficial effects of the present invention are: This invention provides a method for testing the electrochemical window of a battery electrolyte, and also discloses a characterization method for testing the reduction window of lithium / sodium-ion battery electrolytes. This method describes a scheme for characterizing the reduction window of lithium / sodium-ion battery electrolytes, mainly addressing the problem of unstable test results when testing the electrochemical reduction window using a three-electrode or Li|| steel sheet. In the Li|| steel sheet: Li serves as both the counter electrode and the reference electrode; the steel sheet is the working electrode.

[0021] Our research found that using metal foam as the working electrode can effectively induce the deposition of additives involved in SEI film formation in the electrolyte, thereby obtaining the film formation reaction potential of each component of the electrolyte, which plays an important auxiliary role in observing the film formation behavior of each component of the electrolyte.

[0022] In other words, the advantages of this invention are that the testing and assembly methods are simple and convenient, and can effectively and stably characterize the reduction window of lithium / sodium ion battery electrolytes. In addition, it can clearly distinguish the film-forming potential of electrolyte additives and analyze film-forming behavior.

[0023] This invention also provides two methods for pretreating foamed metal. One method involves calcining the foamed metal to 500℃ in a reducing atmosphere to remove oxides from the Ni surface, ultimately obtaining a foamed nickel framework with a clean metal surface. This provides a certain degree of electronic conductivity and specific surface area; however, it lacks the ability to actively regulate SEI formation.

[0024] Another approach involves constructing a three-layer structure. From the inside out, nickel foam serves as the framework, a Ni-P amorphous layer is deposited, and a polyelectrolyte (PEI) layer is formed by immersion in the electrolyte. Specifically, by controlling the current density and plating solution ratio, an amorphous metal film is grown in situ on the surface of the framework (nickel foam) using electrochemical deposition. This amorphous metal film is a Ni-P layer (nickel-phosphorus alloy plating), which exhibits a grain boundary-free continuous phase structure, possessing a higher specific surface area and a larger density of electronic states (DOS), providing uniform charge distribution and the ability to control reaction perturbations. Then, positively charged PEI is selected and self-assembled onto the surface of the nickel foam in an electrolyte environment. Due to the weakly negative charge of the Ni-P surface, PEI can form a stable monolayer functional film through electrostatic adsorption, hydrogen bonding, and surface polarity interactions.

[0025] In subsequent use, the primary and secondary amine groups on the PEI layer can adsorb and complex negatively charged SEI precursors (such as BOB) in the electrolyte. - ODFB - And adjust its migration rate and reaction timing at the interface.

[0026] Comparing the two, it was found that the adsorption capacity of the Ni-P and PEI modified nickel foam (Example 2) for SEI precursor anions exceeded that of the pretreated nickel foam in Example 1, and the adsorption rate could be increased from 9% to 91%.

[0027] This invention also provides a method for detecting whether the diaphragm can adequately wet the electrolyte. Because the diaphragm used in the two-electrode testing device needs to be able to adequately wet the electrolyte to meet experimental requirements. This invention examined various types of diaphragms (60mm thick PP diaphragm, 30mm thick PP diaphragm, 13mm thick composite diaphragm, and 9mm thick composite diaphragm), and the results showed that all types of diaphragms met the experimental requirements. The 60mm thick PP diaphragm had the lowest wetting quality.

[0028] Subsequently, this invention selected a working electrode with low adsorption capacity and a PP diaphragm with the lowest wetting mass to assemble a two-electrode testing device. It was found that even under these conditions, a relatively wide electrochemical window was still maintained, and significant current response perturbations were observed in the LSV test. This indicates that even under the most unfavorable conditions, the structure and process of this invention can still induce the formation of a stable and controllable interfacial film, demonstrating excellent interfacial control capability and electrolyte response adaptability under extreme conditions. Attached Figure Description

[0029] The accompanying drawings are provided to further illustrate the invention and form part of the specification. They are used together with the embodiments of the invention to explain the invention and do not constitute a limitation thereof.

[0030] In the attached diagram: Figure 1 This is the electrochemical reduction window of Example 6.

[0031] Figure 2 This is the electrochemical reduction window of Example 7.

[0032] Figure 3 This is the electrochemical reduction window of Example 8. Detailed Implementation

[0033] To better illustrate the purpose, technical solution, and advantages of this invention, the invention will be further described below with reference to specific embodiments. Furthermore, unless otherwise specified, all reagents used in the following embodiments are commercially available or can be synthesized by referring to existing literature or known methods. For reactions or test conditions not listed, they are all conventional techniques readily available to those skilled in the art. The terminology used in this invention is generally accepted in the art, and its meaning will be clearly understood by those skilled in the art; therefore, it will not be elaborated upon individually.

[0034] Example 1 Preparation of pretreated nickel foam: The nickel foam was ultrasonically cleaned in deionized water for 0.5 hours to rinse off any residual soluble salt solution on the surface. Then it was ultrasonically cleaned with ethanol for 1 hour to remove the deionized water. Finally, it was ultrasonically cleaned with acetone for 1 hour to remove organic matter from the surface. After cleaning, it was dried at 60°C for 6 hours to remove the acetone.

[0035] The cleaned and dried nickel foam is calcined to remove oxide impurities.

[0036] The calcination process is as follows: under a 5% hydrogen-argon mixed atmosphere, the temperature is raised to 200℃ at a heating rate of 10℃ / min, held for 1 hour, then raised to 500℃ at a heating rate of 5℃ / min, held for 2 hours, and then cooled naturally to obtain pretreated nickel foam.

[0037] Example 2 Preparation of pretreated nickel foam: raw material: PEI: Polyethyleneimine, molecular weight 70,000, 50% aqueous solution; The above raw materials were used for preparation: 1 mm thick nickel foam was ultrasonically cleaned in deionized water for 0.5 h to rinse off residual soluble salt solution on the surface, then ultrasonically cleaned with ethanol for 1 h to remove deionized water, and finally ultrasonically cleaned with acetone for 1 h to remove organic matter on the surface. After cleaning, it was dried at 60°C for 6 h to remove acetone and obtain pretreated nickel foam.

[0038] Prepare the plating solution, which consists of: 200 g / L nickel sulfate hexahydrate, 20-40 g / L sodium hypophosphite, 30-60 g / L sodium acetate, and 0.1-1 g / L surfactant. Adjust the pH of the plating solution to 4.5-5.5 using dilute acetic acid or sodium hydroxide solution.

[0039] Electrochemical deposition was used, in which pretreated nickel foam was immersed in a plating bath at 45-60℃. A dual-electrode system was employed, with the nickel foam as the working electrode and a high-purity nickel plate as the counter electrode. The electrode pressure was 1-5 mA / cm². 2 At a current density of [value missing], deposition was carried out for 5-30 minutes, with the target film thickness controlled at 50 nm. After deposition, the film was removed, thoroughly rinsed with deionized water and anhydrous ethanol, and dried under an argon atmosphere to obtain deposited nickel foam.

[0040] Weigh 0.584 g of NaCl, dissolve it in ultrapure water, and dilute to 1 L to obtain an electrolyte solution.

[0041] Weigh 50.0 mg of PEI and dissolve it in 50 mL of electrolyte solution to obtain a PEI solution.

[0042] The charge type of the deposited nickel foam surface was tested using the Zeta potential method, and it was found to be a weakly negatively charged surface.

[0043] Therefore, the deposited nickel foam is immersed in PEI solution for 15-30 minutes to absorb and adsorb, and then the adsorbed nickel foam is removed, gently washed to remove unadsorbed residual molecules, and dried to obtain pretreated nickel foam.

[0044] To investigate the effects of pretreated nickel foam electrodes from Examples 1 and 2 on BOB (Borosilicate glass) - ODFB - The adsorption behavior of the additive in the standard electrolyte was investigated, and the adsorption of SEI precursor anions was quantitatively tested.

[0045] Prepare the borate electrolyte: the solute is LiPF6:LiBOB:LiODFB = 0.8 M: 0.1 M: 0.1 M, and the solvent is EC:EMC:DMC = 1:1:1.

[0046] Take the pretreated nickel foam samples from Examples 1 and 2 respectively; cut them into the same size, 10mm×10mm×1mm; clean them with anhydrous ethanol and dry them under vacuum at 60°C for 2 hours for later use.

[0047] Take 50 mL of borate electrolyte and place it in a stoppered glass bottle for later use; before using the electrolyte, first use UV-Vis to detect the initial concentration.

[0048] Two sets of nickel foam samples (Example 1 and Example 2) were placed in bottles containing 50 mL of test electrolyte. After sealing, they were placed in a constant temperature shaking water bath for adsorption. The adsorption temperature was 25 °C and the adsorption time was 24 h. After adsorption, the samples were taken out, the electrolyte was filtered through a filter membrane, and the supernatant was used for analysis.

[0049] Electrolyte determination in BOB using UV-Vis - Absorbance at characteristic absorption wavelengths; Calculate the adsorption rate: Adsorption rate = (Initial concentration - Post-adsorption solution concentration) ÷ Initial concentration × 100% Table 1 Adsorption Results

[0050] Experimental results show that the adsorption capacity of Ni-P and PEI modified nickel foam (Example 2) for SEI precursor anions exceeds that of the pretreated nickel foam in Example 1, and the adsorption rate can be increased from 9% to 91%.

[0051] In Example 1, the Ni surface oxides were removed by stepwise heating to 500°C under a reducing atmosphere, ultimately yielding a foamed nickel framework with a clean metal surface. This provides a certain degree of electronic conductivity and specific surface area; however, it lacks the ability to actively regulate SEI formation.

[0052] In Example 2, a three-layer structure was constructed. From the inside out, nickel foam served as the framework, a Ni-P amorphous layer was deposited, and a polyelectrolyte was impregnated to form a PEI layer.

[0053] Specifically, by controlling the current density and plating solution ratio, an amorphous metal film is grown in situ on the surface of the skeleton (nickel foam) using electrochemical deposition. This amorphous metal film is a Ni-P layer (nickel-phosphorus alloy plating), which has a grain boundary-free continuous phase structure, a higher specific surface area and a larger density of electronic states (DOS), and provides uniform charge distribution and the ability to control reaction perturbations.

[0054] Then, positively charged PEI is selected and self-assembled onto the surface of nickel foam in an electrolyte environment. Since the Ni-P surface is weakly negatively charged, PEI can form a stable monolayer functional film through electrostatic adsorption, hydrogen bonding and surface polarity.

[0055] In subsequent use, the primary and secondary amine groups on the PEI layer can adsorb and complex negatively charged SEI precursors (such as BOB) in the electrolyte. - ODFB - And adjust its migration rate and reaction timing at the interface.

[0056] Subsequently, the nickel foam from Example 1 with low adsorption capacity was selected and used to assemble a two-electrode testing device to observe the results.

[0057] Example 3 Preparation of working electrode: Using the pretreated nickel foam from Example 1 as the working electrode, the working electrode was cut to the following dimensions: 1 mm thickness and 10 mm x 10 mm length and width.

[0058] After the working electrode sheet is cut, the four corners need to be chamfered to prevent short circuits. The chamfer size is 1mm×1mm.

[0059] It should be noted that the chamfer dimension refers to trimming the right-angled edge of the working electrode plate, removing the original 90° sharp angle to form an isosceles right triangle with a side length of 1mm. The meanings of other chamfer dimensions can be found here.

[0060] Example 4 Preparation of working electrode: Using the pretreated nickel foam from Example 2 as the working electrode, the working electrode was cut to the following dimensions: 1 mm thickness and 10 mm x 10 mm length and width.

[0061] After the working electrode sheet is cut, the four corners need to be chamfered to prevent short circuits. The chamfer size is 1mm×1mm.

[0062] The diaphragm used in the two-electrode testing device needs to be fully wetted with the electrolyte to meet experimental requirements. The following method is given to test whether the diaphragm can be fully wetted with the electrolyte, including the following steps: The diaphragm needs to be fully wetted with the electrolyte, and the wetted mass after 24 hours should be no less than 0.006g. The specific test method for wetted mass is as follows: weigh 3-5mL of electrolyte into a wide-mouth screw-top culture bottle, weigh the diaphragm before wetting, and weigh it again under the same conditions after 24 hours of wetting. The difference between the two weighings is the wetted mass.

[0063] Example 5 Diaphragm wetting test A 16mm diameter diaphragm was punched out using a Φ=16mm punching machine and dried using a gradient drying method, increasing the temperature from 30℃ to 75℃ at a rate of 1℃ / min to remove moisture and prevent diaphragm curling. The dried diaphragms were then immersed in a standard electrolyte solution (1 M LiPF6 concentration, solvent EC:EMC:DMC=1:1:1) for 24 hours. The wetted mass of the diaphragm was then observed to be greater than 0.006g. Various types of diaphragms were investigated, and the results are shown in Table 2. The results indicate that all types of diaphragms met the experimental requirements.

[0064] Specifically, diaphragm types are divided into: 60mm thick PP diaphragm 30mm thick PP diaphragm 13mm Thick Composite Separator: 9mm thick PP separator + 3mm thick ceramic + 1mm thick hot-press adhesive. Specifically, the ceramic slurry is evenly coated onto one side of the 9mm thick PP base film using a coating machine. After drying in an oven and solvent evaporation, a 3mm thick ceramic coating is formed. A 1mm thick hot-press adhesive layer is then laminated onto the ceramic-coated PP separator using a hot press.

[0065] 9mm thick composite diaphragm: 6mm thick PP diaphragm + 3mm thick ceramic. Specifically, the ceramic slurry is evenly coated onto one side of the 6mm thick PP base film using a coating machine. After drying in an oven and evaporation of the solvent, a 3mm thick ceramic coating is formed.

[0066] Table 2

[0067] Next, we selected a 60mm thick PP diaphragm with the lowest wetting quality to assemble a two-electrode testing device and observed the results.

[0068] Example 6 Electrochemical window testing of standard electrolyte (LiPF6 concentration of 1 M, solvent EC:EMC:DMC=1:1:1).

[0069] (1) Assemble the two-electrode testing device The test device is assembled as follows: a lithium sheet is used as the reference electrode and counter electrode, and the working electrode of Example 3 is used as the working electrode. It is assembled into a 2032 coin cell. The electrolyte is added at a rate of 40 μL on each side of the separator. The separator is a PP separator with a diameter of 16 mm and a thickness of 60 mm. The stainless steel gasket has a size of 15.5 mm × 0.5 mm (diameter × thickness), and the spring has a size of 15.5 mm × 1 mm (diameter × thickness). Both are made of 316L stainless steel.

[0070] It should be noted that the assembly order, from bottom to top, is: negative electrode shell, lithium sheet, electrolyte (one side), separator, electrolyte (the other side), working electrode, stainless steel gasket, funnel spring, and positive electrode shell.

[0071] (2) Shelving After the two-electrode testing device is assembled, it should be left at room temperature for 24 hours before use. It should be noted that this is to avoid deviations in test results due to polarization issues.

[0072] (3) Test characterization The electrochemical window of the electrolyte was tested using linear sweep voltammetry (LSV). The steps were set as follows: sweep rate 2mV, and sweep range from open circuit voltage to -0.2V.

[0073] Results reference Figure 1 .

[0074] Example 7 Electrochemical window testing of borate electrolyte (solute: LiPF6: LiBOB: LiODFB = 0.8 M: 0.1 M: 0.1 M, solvent: EC:EMC:DMC = 1:1:1).

[0075] (1) Assemble the two-electrode testing device The test device is assembled as follows: a lithium sheet is used as the reference electrode and counter electrode, and the working electrode of Example 3 is used as the working electrode. It is assembled into a 2032 coin cell. The electrolyte is added at a rate of 40 μL on each side of the separator. The separator is a PP separator with a diameter of 16 mm and a thickness of 60 mm. The stainless steel gasket has a size of 15.5 mm × 0.5 mm (diameter × thickness), and the spring has a size of 15.5 mm × 1 mm (diameter × thickness). Both are made of 316L stainless steel.

[0076] It should be noted that the assembly order, from bottom to top, is: negative electrode shell, lithium sheet (counter electrode), electrolyte (one side), separator, electrolyte (the other side), working electrode, stainless steel gasket, funnel spring, and positive electrode shell.

[0077] (2) Shelving After the two-electrode testing device is assembled, it should be left at room temperature for 24 hours before use. It should be noted that this is to avoid deviations in test results due to polarization issues.

[0078] (3) Test characterization The electrochemical window of the electrolyte was tested using linear sweep voltammetry (LSV). The steps were set as follows: sweep rate 2mV, and sweep range from open circuit voltage to -0.2V.

[0079] Results reference Figure 2 .

[0080] Example 8 Electrochemical window testing was conducted on a borate electrolyte (solute: LiPF6: LiBOB: LiODFB = 0.8 M: 0.1 M: 0.1 M, solvent: EC:EMC:DMC = 1:1:1). The test materials and procedures were completely consistent with those in Example 7, the only difference being that Example 7 used the nickel foam described in Example 3 as the working electrode, while Example 8 did not use the nickel foam as the working electrode, but instead used the stainless steel gaskets of the specifications described in Examples 6 and 7 directly as the working electrode.

[0081] It should be noted that the assembly order, from bottom to top, is: negative electrode shell, lithium sheet (counter electrode), electrolyte (one side), separator, electrolyte (the other side), stainless steel gasket, funnel spring, and positive electrode shell.

[0082] Results reference Figure 3 .

[0083] Figure 1 and Figure 2 and Figure 3 Comparative analysis: Figure 1 (Example 6, Standard Electrolyte): The horizontal axis represents the potential range from -1.0V to 2.5V, and the vertical axis represents the current range from -0.0006A to 0.0000A. Within the tested potential range, the electrolyte remained relatively stable, with no significant decomposition reaction.

[0084] The current begins to decrease slowly around 1.5 V, but there are no drastic fluctuations throughout the process, until it is completely reduced below 0 V, indicating that the standard electrolyte has a wide electrochemical reduction window.

[0085] Figure 2 (Example 7, borate electrolyte): The horizontal axis represents the potential range from -1.0V to 2.5V, and the vertical axis represents the current range from -0.0006A to 0.0000A. The curve shows significant current fluctuations (peak value approximately -0.0001A) in the range of 0V to 1.5V, followed by sharp fluctuations near 0V, indicating that the electrolyte has been completely reduced.

[0086] The current fluctuations may originate from the process of the borate additive (LiBOB / LiODFB) forming an SEI film at the electrode interface. However, no drastic decomposition occurred throughout the fluctuations, indicating that the electrolyte remains stable above 0V and has a wide electrochemical reduction window.

[0087] Figure 3 (Example 8, borate electrolyte) Comparing Example 8 with Example 7, it can be seen that when high-specific-surface-area nickel foam is not used as the working electrode, the formation potential of the SEI film lags by ~0.5 V, resulting in a significant underestimation of the theoretical film formation potential in the experimental results. Therefore, using metal foam as the working electrode can effectively induce the deposition of additives involved in SEI film formation in the electrolyte, thereby obtaining the film formation reaction potentials of each component of the electrolyte, which plays an important auxiliary role in observing the film formation behavior of each component of the electrolyte.

[0088] It should be noted that this invention selects a working electrode with low adsorption capacity and a PP membrane with minimal wetting mass for assembling a two-electrode testing device. Under these conditions, a relatively wide electrochemical window was still observed, with significant current response perturbations observed in LSV testing. This indicates that even under the most unfavorable conditions, the structure and process of this invention can still induce the formation of a stable and controllable interfacial film, demonstrating superior interfacial control capability and electrolyte response adaptability even under extreme conditions.

[0089] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit the scope of protection of the present invention. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the essence and scope of the technical solutions of the present invention.

Claims

1. A method for testing the electrochemical window of a battery electrolyte, characterized in that, Includes the following steps: The assembly sequence of the two-electrode testing device is as follows: negative electrode shell, reference electrode and counter electrode, electrolyte, diaphragm, working electrode, gasket, spring, and positive electrode shell. Using lithium or sodium sheets as reference and counter electrodes, and pretreated foam metal as the working electrode, the devices are assembled into a coin cell. Electrolyte is added to both sides of the separator. A gasket and spring are assembled on the working electrode side to obtain a two-electrode test device. After being placed in the test, the electrochemical window of the electrolyte is tested using LSV. The foam metal includes copper foam or nickel foam.

2. The method for testing the electrochemical window of a battery electrolyte according to claim 1, characterized in that, The electrolyte is added in the form of 20-80 μL on each side of the diaphragm; the diaphragm includes PP diaphragm and composite diaphragm; the composite diaphragm includes at least two of the following: PP diaphragm, ceramic, and hot-press adhesive; the thickness of the diaphragm is 9 mm-60 mm; the resting time includes resting at room temperature for 6-48 hours.

3. The method for testing the electrochemical window of a battery electrolyte according to claim 1, characterized in that, The working electrode has a thickness of 0.5-1.5mm and a length and width of (10±3mm)×(10±3mm). The four corners of the working electrode sheet need to be chamfered, with a chamfer size of (1±0.3mm)×(1±0.3mm).

4. The method for testing the electrochemical window of a battery electrolyte according to claim 1, characterized in that, The gaskets include stainless steel gaskets with a thickness of 0.3-0.7 mm and a diameter of 15.5-16.2 mm; the springs include stainless steel funnel springs with a thickness of 1.0-1.2 mm and a diameter of 15.5-16.2 mm; the stainless steel includes one of 304 stainless steel, 316 stainless steel, and 316L stainless steel.

5. The method for testing the electrochemical window of a battery electrolyte according to claim 1, characterized in that, The LSV test was used to measure the electrochemical window of the electrolyte. The steps included a scan rate of 1-5mV and a scan range from open circuit voltage to -0.1 to -1V.

6. The method for testing the electrochemical window of a battery electrolyte according to claim 1, characterized in that, After using LSV to test the electrochemical window of the electrolyte, determine whether IR compensation is needed based on the test conditions. The basis for compensation is internal resistance and current. If compensation is needed, perform manual compensation based on internal resistance and LSV test current, with a compensation ratio of 50%-90%.

7. The method for testing the electrochemical window of a battery electrolyte according to claim 6, characterized in that, The compensation is based on the internal resistance and current, where the internal resistance is greater than 2Ω and the current is greater than 0.001A.

8. The method for testing the electrochemical window of a battery electrolyte according to claim 1, characterized in that, The preparation method of pretreated foamed metal includes the following steps: The foamed metal is cleaned and then calcined. Under a reducing atmosphere, the temperature is raised to 150-250℃ and held for 0.5-2 hours. Then, the temperature is raised to 450-600℃ and held for 1-3 hours. The temperature is then allowed to cool naturally to obtain pretreated foamed metal. The reducing atmosphere includes one of the following: high-purity hydrogen, 5%~10% hydrogen-argon mixture, or ammonia.

9. The method for testing the electrochemical window of a battery electrolyte according to claim 1, characterized in that, The preparation method of pretreated foamed metal includes the following steps: The foamed metal is cleaned and then immersed in a plating solution at 45-60℃. A dual-electrode system is used, with the foamed metal as the working electrode and a high-purity nickel plate as the counter electrode, at a voltage of 1-5 mA / cm². 2 At a current density of 5-30 min, deposition is carried out, with the target film thickness controlled at 30-80 nm. After deposition, the film is removed, rinsed, and dried to obtain the deposited foam metal. The deposited foam metal is then immersed in PEI solution for 15-30 min for soaking and adsorption. After immersion, the film is removed, cleaned, and dried to obtain the pretreated foam metal. The plating solution includes 200 g / L nickel sulfate hexahydrate, 20-40 g / L sodium hypophosphite, 30-60 g / L sodium acetate, and 0.1-1 g / L surfactant. The pH of the plating solution is adjusted to 4.5-5.

5.

10. A method for testing the electrochemical window of a battery electrolyte according to claim 8 or 9, characterized in that, Cleaning includes the following steps: In deionized water, ultrasonically clean for 0.5-2 hours, then ultrasonically clean with ethanol for 0.5-1 hour; finally, ultrasonically clean with acetone for 0.5-1 hour, and then dry at 45-60℃ for 6-12 hours.

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